USE OF AN AQUEOUS DISPERSION OF BIODEGRADABLE POLYESTERS

Abstract

The present invention relates to the use of an aqueous dispersion of at least one biodegradable polyester in the form of a coating for improving the barrier properties of packaging materials made of paper or paperboard, in particular of packaging materials made of recycled paper or paperboard, with respect to mineral oils. The present invention also relates to a process for producing barrier coatings on paper or paperboard, in particular on recycled paper or paperboard.

Description

The present invention relates to the use of an aqueous dispersion of at least one biodegradable polyester in the form of a coating for improving the barrier properties of packaging materials made of paper or paperboard, in particular of packaging materials made of recycled paper or paperboard, with respect to mineral oils. The present invention also relates to a process for producing barrier coatings on paper or paperboard, in particular on recycled paper or paperboard.

Paper packaging and paperboard packaging are often produced from recycled paper. When printed paper is used, in particular newspaper, the recycled paper can comprise mineral oil residues, e.g. from the printing inks usually used for the printing of newspapers. Even at room temperature, volatile content vaporizes from said residues and in the case of packaging for food or drink this is deposited on the food or drink packaged in the box, for example pasta, semolina, rice, or cornflakes. Most of the inner bags used nowadays and made of polymer foils also provide no adequate protection from this effect. Studies by the Cantonal Laboratory of Zurich demonstrated the presence of considerable amounts of mineral oil residues in food or drink packaged in packaging made of recycled paper. The volatile constituents of mineral oil mainly involve aromatic hydrocarbons, in particular those having from 15 to 25 carbon atoms, and paraffinic and naphthenic hydrocarbons, these being hazardous to health.

There is therefore a need to reduce the risk of contamination of food or drink with mineral oil residues. One possibility would be to avoid recycling of newspaper in the production of cartons for the packaging of food or drink. This is undesirable for environmental reasons and impractical because the available amounts of fresh pulp are inadequate. Another solution would be to avoid mineral oils in the printing inks used for printing newspapers. However, there are technological obstacles to that solution, especially in relation to the resistance of the print to wiping from the surface of the paper.

Packaging materials made of paper or paperboard are often equipped with a barrier coating in order to reduce penetration of the vegetable or animal fats or oils comprised within foods.

By way of example, WO 2006/053849 describes coatings based on water-based (meth)acrylate polymer dispersions, e.g. styrene-acrylate polymer dispersions, for paper and paperboard. The polymers exhibit good barrier properties with respect to liquid oils and fats. However, it has been found that good barrier action with respect to liquid oils and fats is not necessarily also attended by good barrier action with respect to volatile mineral oils, in particular with respect to mineral oils which penetrate in the form of gas, e.g. paraffinic and naphthenic hydrocarbons which are hazardous to health, and aromatic hydrocarbons, in particular those having from 15 to 25 carbon atoms, since the transport mechanisms involved for the penetrating substances differ. In the case of liquid fats and oils, the transport takes place by way of the fibers, relevant factors being capillary forces and surface wetting. When problems arise with substances penetrating in the form of gas, capillary action and wetting play no part, but instead sorption, diffusion, and porosity are relevant. Fats and oils moreover differ from hydrocarbons, i.e. from mineral oil constituents, in their polarity, and hence in their behavior in diffusion through barrier layers.

The patent application PCT/EP2011/054471, with priority date before that of the present application, discloses aqueous polyester dispersions of biodegradable polyesters. The polyester dispersions are used inter alia for the coating of paper. Coatings thus produced exhibit good barrier action with respect to vegetable oils and fatty acids. No mention is made of any barrier action with respect to mineral oils, in particular volatile substances.

Surprisingly, it has now been found that good barrier action with respect to mineral oils, in particular to mineral oils penetrating in the form of gas, can be achieved via coating of paper or paperboard with aqueous polyester dispersions. In particular, barrier action can be improved at the same weight per unit area of coating by applying the polyester dispersion in at least two layers to the paper or the paperboard. Since the polyesters comprised in the dispersions are biodegradable, better compostability of the coated packaging materials is moreover achieved.

Accordingly, the present invention provides the use of aqueous dispersions of at least one biodegradable polyester, as defined here and hereinafter, in the form of a coating for improving the barrier properties of packaging material made of paper or paperboard with respect to mineral oils, in particular with respect to volatile mineral oils, in particular with respect to mineral oils that penetrate in the form of gas, specifically those having from 15 to 25 carbon atoms, e.g. paraffinic and naphthenic hydrocarbons which are hazardous to health, and aromatic hydrocarbons.

Because the aqueous dispersions of the at least one biodegradable polyester have a high level of barrier action with respect to the abovementioned mineral oils, they are particularly suitable for producing barrier coatings on paper or paperboard which have been produced from recycled paper and which therefore comprise mineral oil residues, in particular volatile mineral oil residues, specifically those having from 15 to 25 carbon atoms, e.g. paraffinic and naphthenic hydrocarbons which are hazardous to health, and aromatic hydrocarbons.

Accordingly, one preferred embodiment of the invention provides the use of aqueous dispersions of at least one biodegradable polyester, as defined here and hereinafter, in the form of a coating for improving the barrier properties of packaging material made of paper or paperboard with respect to mineral oils, where the packaging material has been produced at least to some extent, generally to an extent of at least 30% by weight (% by weight, based on total fiber mass), in particular to an extent of at least 50% by weight, or completely, from mineral-oil-contaminated recycling paper.

Accordingly, one preferred embodiment of the invention provides the use of aqueous dispersions of at least one biodegradable polyester, as defined here and hereinafter, in the form of a coating for improving the barrier properties of paper or paperboard, or of packaging material made of paper or paperboard, with respect to mineral oils, where the paper or the paperboard, or the packaging material, has been produced at least to some extent, generally to an extent of at least 30% by weight (% by weight, based on total fiber mass), in particular to an extent of at least 50% by weight, or completely, from mineral-oil-contaminated recycling paper, in particular a packaging material of this type which is intended for the packaging of food or drink. Among these materials are sales packaging, such as cartons or paper products, and also consumer packaging, for example disposable tableware, e.g. plates, cups, or beakers made of paperboard.

The coating of the invention is found on at least one of the paper surfaces or paperboard surfaces, or on at least one surface of the packaging material. It can also form at least one, e.g. at least one or in particular two, of a plurality of layers of a multilayer coating of the paper, or of the paperboard, or of the packaging material. The coating of the invention can have been arranged directly on a surface of the sheet-like backing material (paper or paperboard). Between the backing material and the coating of the invention there can also, however, be other layers, e.g. primer layers, further barrier layers, or colored or black-and-white layers of printing inks. It is preferable that the coating of the invention is found on the inner side of the packaging material: the side facing toward the contents of the package.

Adequate barrier action is generally achieved when the weight per unit area of the coating is at least 1 g/m², often at least 2 g/m², in particular at least 3 g/m², and specifically at least 5 g/m², calculated as solids per m² of the coated surface. The weight per unit area of the coating is preferably in the range from 2 to 50 g/m², in particular from 3 to 40 g/m², specifically from 5 to 30 g/m², calculated as solids per m² of the coated surface. The thickness of the coating is accordingly on average at least 1 μm, often at least 2 μm, in particular at least 3 μm, and specifically at least 5 μm, e.g. in the range from 2 to 50 μm, in particular from 3 to 40 μm, specifically from 5 to 30 μm.

One specific embodiment of the invention relates to the use for the coating of paperboard, in particular paperboard which has been produced at least to some extent, generally to an extent of at least 30% by weight (% by weight, based on total fiber mass), in particular to an extent of at least 50% by weight, or completely, from mineral-oil-contaminated recycling paper. The weight per unit area of the coating here is generally at least 2 g/m², often at least 3 g/m², in particular at least 4 g/m², and specifically at least 5 g/m², calculated as solids per m² of the coated paperboard surface. It is preferable that the weight per unit area of the coating is in the range from 3 to 50 g/m², in particular from 4 to 40 g/m², specifically from 5 to 30 g/m², calculated as solids per m² of the coated paperboard surface. The thickness of the coating is accordingly on average at least 2 μm, often at least 3 μm, in particular at least 4 μm, and specifically at least 5 μm, e.g. in the range from 2 to 50 μm, in particular from 3 to 40 μm, specifically from 5 to 30 μm.

Another embodiment of the invention relates to the use for the coating of paper, in particular paper which has been produced at least to some extent, generally to an extent of at least 30% by weight (% by weight, based on total fiber mass), in particular to an extent of at least 50% by weight, or completely, from mineral-oil-contaminated recycling paper. The weight per unit area of the coating here is generally at least 1 g/m², often at least 2 g/m², in particular at least 3 g/m², calculated as solids per m² of the coated paper surface. It is preferable that the weight per unit area of the coating is in the range from 1 to 30 μ/m², in particular from 2 to 25 g/m², specifically from 3 to 20 g/m², calculated as solids per m² of the coated paper surface. The thickness of the coating is accordingly on average at least 1 μm, often at least 2 μm, in particular at least 3 μm, e.g. in the range from 12 to 30 μm, in particular from 2 to 25 μm, specifically from 3 to 20 μm.

The coating of the invention can have one layer, or preferably more than one layer, e.g. two, three, four, or five layers arranged on one another, where these have been produced with use of the aqueous polyester dispersion. The weight per unit area of the individual layers of the coating will generally amount to at least 0.5 g/m², often at least 1 g/m², in particular at least 2 g/m², specifically at least 3 g/m², and is typically in the range from 1 to 30 g/m², in particular from 1 to 25 g/m², specifically from 2 to 20 g/m², or from 2 to 12 g/m², calculated as solids per m² of the coated surface. It is preferable that the coating of the invention has at least two, in particular two, three, four, or five, and specifically two or three, layers arranged on one another, where these have been produced with use of the aqueous polyester dispersion. As far as the weight per unit area of the entire coating is concerned, the statements made above are applicable.

Aqueous dispersions of biodegradable polyesters are known from patent application PCT/EP2011/054471, the priority date of which is before that of the present application, and from the prior art cited therein, or can be produced by analogy with the method described therein, the entire content of which is hereby incorporated herein by way of reference.

Biodegradability generally means that the polyesters decompose within an appropriate and demonstrable period of time. The degradation generally takes place hydrolytically, and is predominantly brought about via exposure to microorganisms, such as bacteria, yeasts, fungi, and algae, or via the hydrolases comprised therein. In one example of a method for determining biodegradability, polyester is mixed with compost and stored for a defined time. In ASTM D5338, ASTM D6400 and DIN V 54900, CO₂-free air is by way of example passed through ripened compost during the composting process, and the compost is subjected to a defined temperature profile. Biodegradability is defined here as a percentage degree of biodegradation by taking the ratio of the net amount of CO₂ released from the specimen (after subtraction of the amount of CO₂ released by the compost without specimen) to the maximum amount of CO₂ that can be released from the specimen (calculated from the carbon content of the specimen). Biodegradable polyesters generally exhibit marked signs of degradation after just a few days of composting, examples being fungal growth, cracking, and perforation. Polyesters of this type are known to the person skilled in the art and are available commercially.

The polyesters comprised in the aqueous dispersions are typically insoluble in water and are therefore present in the form of particles in the dispersion used in the invention. The weight-average diameter of the polymer particles (weight average determined via light scattering) in said dispersions will not generally exceed a value of 10 μm, often 5 μm, in particular 2000 nm, specifically 1500 nm, and is typically in the range from 50 nm to 10 μm, often in the range from 100 nm to 5 μm, in particular in the range from 150 to 2000 nm, specifically in the range from 200 to 1500 nm. It is preferable that less than 90% by weight of the polymer particles do not exceed a diameter of 10 μm, in particular 5 μm, and specifically 2 μm. Particle size is determined in a manner known per se via light scattering on dilute dispersions (from 0.01 to 1% by weight).

Biodegradable polyesters are by way of example the polyesters from the groups of the aliphatic polyesters, aliphatic copolyesters, and aliphatic-aromatic copolyesters. Other suitable materials are blends of the abovementioned biodegradable polyesters with one another, or blends with other biodegradable polymers which are preferably insoluble in water, e.g. starch or polyalkylene carbonates. Examples of these blends are blends made of at least one aliphatic copolyester with at least one polymer from the group of starch, polyalkylene carbonates, and aliphatic polyesters, e.g. polylactic acid or polyhydroxyalkanoates, and also blends made of at least one aliphatic-aromatic copolyester with at least one polymer from the group of starch, polyalkylene carbonates, and aliphatic polyesters, e.g. polylactic acid or polyhydroxyalkanoates. The proportion of the biodegradable polyester will generally amount to at least 30% by weight, in particular at least 40% by weight, based on total solids content of the dispersion.

In one preferred embodiment, dispersions are used in which the polyester is sole polymer constituent insoluble in water, i.e. sole dispersed polymer constituent, or the proportion of the biodegradable polyester is at least 80% by weight, in particular at least 90% by weight, based on total solids content of the dispersion. In another embodiment, dispersions are used which comprise, alongside the biodegradable polyester, at least one other polymer constituent insoluble in water, i.e. dispersed polymer constituent, where this is preferably likewise biodegradable. The content of the biodegradable polyester will then generally be from 30 to 90% by weight, in particular from 40 to 80% by weight, based on total solids content of the dispersion. The content of the dispersed polymer constituent that is not the polyester is then generally from 10 to 70% by weight, in particular from 20 to 60% by weight, based on the total amount of the polymers dispersed in the dispersion. Suitable other dispersed polymer constituents which can be comprised, together with the polyester, in the dispersion are preferably likewise biodegradable and by way of example selected from starch and polyalkylene carbonates.

The number-average molecular weight MN of the polyesters comprised in the dispersions used in the invention is typically in the range from 5000 to 1 000 000 daltons, in particular in the range from 8000 to 800 000 daltons, and specifically in the range from 10 000 to 500 000 daltons. The weight-average molecular weight Mw of the polymer is generally in the range from 20 000 to 5 000 000 daltons, often in the range from 30 000 daltons to 4 000 000 daltons, and in particular in the range from 40 000 to 2 500 000 daltons. The polydispersity index Mw/MN is generally at least 2, and is often in the range from 3 to 20, in particular in the range from 5 to 15. Molecular weight and polydispersity index can be determined by way of example via gel permeation chromatography (GPC) to DIN 55672-1.

The intrinsic viscosity of the polyesters is an indirect measure of molecular weight and is typically in the range from 50 to 500 ml/g, often in the range from 80 to 300 ml/g, and in particular in the range from 100 to 250 ml/g (determined to EN ISO 1628-1 at 25° C. on a 0.5% by weight solution of the polymer in o-dichlorobenzene/phenol (1:1 w/w)).

The polyesters comprised in the dispersions used in the invention can be amorphous or semicrystalline.

In one preferred embodiment of the invention, the polyester comprised in the dispersion is in essence unbranched, i.e. the value of the degree of branching is generally <0.005 mol/kg, in particular <0.001 mol/kg, and specifically <0.0005 mol/kg. In another embodiment of the invention, the polyester is branched, where the value of the degree of branching preferably does not exceed 1 mol/kg, in particular 0.5 mol/kg, and specifically 0.3 mol/kg. The degree of branching is the number of monomer units condensed into the molecule and having more than two, e.g. three, four, five, or six, functional groups which are suitable for the condensation process and which react to form bonds with carboxylic acid groups or with hydroxy groups, an example being carboxylate, OH, isocyanate (NCO), or NH₂ groups (or ester- or amide-forming derivatives thereof). The degree of branching of this embodiment of the polyester is generally from 0.0005 to 1 mol/kg, preferably from 0.001 to 0.5 mol/kg, and in particular from 0.005 to 0.3 mol/kg.

The biodegradable polyester is in particular one selected from the group of the aliphatic polyesters, aliphatic copolyesters, aliphatic-aromatic copolyesters, and mixtures of these.

An aliphatic polyester is a polyester composed exclusively of aliphatic monomers. An aliphatic copolyester is a polyester composed exclusively of at least two, in particular at least three, aliphatic monomers, where the acid component and/or the alcohol component preferably comprises at least two different monomers. An aliphatic-aromatic copolyester is a polyester composed not only of aliphatic monomers but also of aromatic monomers, where the acid component preferably comprises at least one aliphatic acid and at least one aromatic acid.

The aliphatic polyesters and copolyesters are in particular polylactides (polylactic acid), polycaprolactone, block copolymers of polylactide with poly-C₂-C₄-alkylene glycol, block copolymers of polycaprolactone with poly-C₂-C₄-alkylene glycol, or else the copolyesters defined hereinafter which are composed of at least one aliphatic or cycloaliphatic dicarboxylic acid or one ester-forming derivative thereof and of at least one aliphatic or cycloaliphatic diol component, and also optionally other components.

The term “polylactides” denotes polycondensates of lactic acid. Suitable polylactides are described in WO 97/41836, WO 96/18591, WO 94/05484, U.S. Pat. No. 5,310,865, U.S. Pat. No. 5,428,126, U.S. Pat. No. 5,440,008, U.S. Pat. No. 5,142,023, U.S. Pat. No. 5,247,058, U.S. Pat. No. 5,247,059, U.S. Pat. No. 5,484,881, WO 98/09613, U.S. Pat. No. 4,045,418, U.S. Pat. No. 4,057,537, and also in Adv. Mater. 2000, 12, 1841-1846. These products are polymers based on lactide acid lactone (A), which is converted via ring-opening polymerization to polylactide acid polymers (B):

The degree of polymerization n in formula (B) is in the range from 1000 to 4000, preferably from 1500 to 3500, and particularly preferably from 1500 to 2000 (number average). The average molar masses (number average) of these products are, in accordance with the degree of polymerization, in the range from 71000 to 284000 g/mol. Suitable polylactides are obtainable by way of example from Cargill Dow LLC (e.g. PLA Polymer 404ID, PLA Polymer 4040D, PLA Polymer 4031D, PLA Polymer 2000D, or PLA Polymer 1100) or from Mitsui Chemicals (Lactea). Other suitable materials are diblock and triblock copolymers of polylactides with poly-C₂-C₄-alkylene glycol, in particular with polyethylene glycol). These block copolymers are marketed by way of example by Aldrich (e.g. product number 659649). These are polymers that have polylactide blocks and poly-C₂-C₄-alkylene oxide blocks. These block copolymers are obtainable by way of example via condensation of lactic acid or via ring-opening polymerization of lactide acid lactone(A) in the presence of poly-C₂-C₄-alkylene glycols.

Other biodegradable polyesters suitable in the invention are polycaprolactones. The person skilled in the art understands these to be polymers described by the formula D indicated below, where n is the number of repeat units in the polymer, i.e. the degree of polymerization.

The degree of polymerization n in formula (D) is in the range from 100 to 1000, preferably from 500 to 1000 (number average). The number-average molar masses of these products are, in accordance with the degree of polymerization, in the range from 10 000 g/mol to 100 000 g/mol. Particularly preferred polymers of the formula (D) have average molar masses (number average) of 50 000 g/mol (CAPA 6500), 80 000 g/mol (CAPA 6800), and 100 000 g/mol (CAPA FB 100). Polycaprolactones are generally produced via ring-opening polymerization of ε-caprolactone (compound C) in the presence of a catalyst. Polycaprolactones are obtainable commercially from Solvay as CAPA polymers, e.g. CAPA 6100, 6250, 6500 or CAPA FB 100. Other suitable polymers are diblock and triblock copolymers of polycaprolactone with poly-C₂-C₄-alkylene glycols, in particular with polyethylene glycols (=polyethylene oxides), i.e. polymers which have at least one polycaprolactone block of the formula D and at least one polyalkylene glycol block. These polymers can by way of example be produced via polymerization of caprolactone in the presence of polyalkylene glycols, for example by analogy with the processes described in Macromolecules 2003, 36, pp 8825-8829.

Particular biodegradable polyesters suitable in the invention are copolyesters composed of at least one aliphatic or cycloaliphatic dicarboxylic acid or of one ester-forming derivative thereof and of at least one aliphatic or cycloaliphatic diol component, and also optionally of other components.

The polymer to be dispersed in the invention in particular involves an aliphatic or aliphatic-aromatic copolyester consisting essentially of:

• • a) at least one dicarboxylic acid component A, which is composed of
    • a1) at least one aliphatic or cycloaliphatic dicarboxylic acid or ester-forming derivatives of these, or a mixture thereof (component a1), and
    • a2) optionally one or more aromatic dicarboxylic acids which have no sulfonic acid group, or ester-forming derivatives of these, or a mixture thereof (component a2),
    • a3) optionally one or more aromatic dicarboxylic acids which have at least one sulfonic acid group, or ester-forming derivatives of these, or a mixture thereof (component a3);
  • b) at least one diol component B selected from aliphatic and cycloaliphatic diols and mixtures of these;
  • c) optionally one or more other bifunctional compounds C which react to form bonds with carboxylic acid groups or with hydroxy groups; and
  • d) optionally one or more compounds D which have at least three, e.g. three, four, or five, functionalities which react to form bonds with carboxylic acid groups or with hydroxy groups;
    where the molar ratio of component A to component B is generally in the range from 0.4:1 to 1:1, in particular in the range from 0.6:1 to 0.99:1, and components A and B generally account for at least 80% by weight, in particular at least 90% by weight, and specifically at least 96% by weight, of all of the ester-forming constituents of the polyester, or of the total weight of the polyester.

The term “aliphatic copolyesters” here and hereinafter means copolyesters which comprise, as component A, exclusively component al). The term “aliphatic-aromatic copolyesters” here and hereinafter means copolyesters which comprise, as component A, condensed into the molecule not only component a1) but also component a) and optionally a3).

The data in % by weight based on the ester-forming constituents are based here and hereinafter on the constituents of components A, B, C, and D in the form condensed into the molecule, and therefore on the total mass of the polyester, and not on the amounts used to produce the polyester, unless otherwise stated.

Acid component A in said copolyesters preferably comprises

• • a1) from 30 to 100 mol %, in particular from 35 to 90 mol %, or from 40 to 90 mol %, of at least one aliphatic or at least one cycloaliphatic dicarboxylic acid or ester-forming derivatives of these, or a mixture thereof,
  • a2) from 0 to 70 mol %, in particular from 10 to 65 mol %, or from 10 to 60 mol %, of at least one aromatic dicarboxylic acid or ester-forming derivative of these, or a mixture thereof,
  • a3) from 0 to 5 mol %, in particular from 0 to 3 mol %, or from 0 to 2 mol %, of one or more aromatic dicarboxylic acids which have at least one sulfonic acid group, or ester-forming derivatives of these, or a mixture thereof,
    where the molar percentages of components a1), a2), and a3) give a total of 100%.

In preferred embodiments of the invention, aqueous dispersions of copolyesters are used where acid component A of these comprises the following constituents:

• • a1) from 35 to 90 mol %, or from 40 to 90 mol %, and specifically from 60 to 90 mol %, of at least one aliphatic or at least one cycloaliphatic dicarboxylic acid or ester-forming derivatives of these, or a mixture thereof,
  • a2) from 10 to 65 mol %, or from 10 to 60 mol %, and specifically from 10 to 40 mol %, of at least one aromatic dicarboxylic acid or ester-forming derivative of these, or a mixture thereof,
  • a3) from 0 to 5 mol %, in particular from 0 to 3 mol %, or from 0 to 2 mol %, of one or more aromatic dicarboxylic acids which have at least one sulfonic acid group, or ester-forming derivatives of these, or a mixture thereof,
    where the molar percentages of components a1), a2), and a3) give a total of 100%.

Acid component A can comprise, condensed into the molecule, small amounts of a sulfonated aromatic dicarboxylic acid, e.g. sulfoisophthalic acid, or a salt thereof, where the content of the sulfonated carboxylic acid generally amounts to no more than 5 mol %, often no more than 3 mol %, in particular no more than 2 mol %, being by way of example in the range from 0.1 to 5 mol %, or from 0.1 to 3 mol %, or from 0.2 to 2 mol %, based on the total amount of compounds of component A. In one embodiment of the invention, the amount of sulfonated carboxylic acids is less than 1 mol %, in particular less than 0.5 mol %, based on component A. In another embodiment of the invention, these copolyesters comprise from 0.01 to 0.2 mmol/g, in particular from 0.05 to 0.15 mmol/g, of sulfonic acid groups. In another embodiment of the invention, these copolyesters comprise less than 0.05 mmol/g, in particular less than 0.01 mmol/g, of sulfonic acid groups.

Among the preferred copolyesters, particular preference is given to those in which the content of diol component B is from 98 to 102 mol %, in particular from 99 to 101 mol %, based on the total amount of components a1), a2), and optionally a3).

Among the particularly preferred copolyesters, particular preference is given to those in which the polyester-forming constituents comprise no more than 2% by weight, in particular no more than 1% by weight, based on the total weight of the polyester, of one or more other bifunctional compounds C which react to form bonds with carboxylic acid groups or with hydroxy groups.

Among the particularly preferred copolyesters, particular preference is given to those in which the polyester-forming constituents comprise no more than 2% by weight, in particular no more than 1% by weight, based on the total weight of the polyester, of one or more compounds D which have at least three, e.g. three, four, or five, functionalities which react to form bonds with carboxylic acid groups or with hydroxy groups.

In the preferred copolyesters, components a1), a2), a3), and b) in particular account for from 96 to 100% by weight, in particular from 98 to 100% by weight, of these copolyesters.

One specific embodiment of the invention involves aqueous dispersions of semiaromatic or aliphatic-aromatic copolyesters characterized via the following constitution:

• • a1) from 60 to 80 mol %, often from 65 to 80 mol %, in particular from 66 to 75 mol %, based on the total amount of components al) and a2), of at least one aliphatic dicarboxylic acid, or ester-forming derivative of this, or a mixture thereof, and
  • a2) from 20 to 40 mol %, often from 20 to 35 mol %, in particular from 25 to 34 mol %, based on the total amount of components a1) and a2), of terephthalic acid or ester-forming derivatives of this, or a mixture thereof;
  • b) from 98 to 102 mol % of at least one diol component b) selected from 1,3-propanediol and 1,4-butanediol and mixtures of these;
  • d) from 0.1 to 2% by weight, often from 0.2 to 2% by weight, in particular from 0.3 to 1.8% by weight, and specifically from 0.4 to 1.5% by weight, based on the total amount of components a1) and a2), respectively calculated as dicarboxylic acids, and b), of one or more compounds D which have at least three functionalities which react to form bonds with carboxylic acid groups or with hydroxy groups;
    where components a1), a2), and b) account for from 80 to 99.8% by weight, in particular from 90 to 99.7% by weight, and specifically from 95 to 99.6% by weight, of the polyester.

Aliphatic dicarboxylic acids al) which are suitable in the invention generally have from 2 to 10 carbon atoms, preferably from 4 to 8 carbon atoms, and in particular 6 carbon atoms. They can be either linear or branched acids. The cycloaliphatic dicarboxylic acids that can be used for the purposes of the present invention are generally those having from 7 to 10 carbon atoms and in particular those having 8 carbon atoms. However, it is also possible in principle to use dicarboxylic acids having a greater number of carbon atoms, for example up to 30 carbon atoms. Examples that may be mentioned are: malonic acid, succinic acid, glutaric acid, 2-methylglutaric acid, 3-methylglutaric acid, adipic acid, pimelic acid, azelaic acid, sebacic acid, fumaric acid, 2,2-dimethylglutaric acid, suberic acid, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, diglycolic acid, itaconic acid, maleic acid, and 2,5-norbornanedicarboxylic acid. Ester-forming derivatives of the abovementioned aliphatic or cycloaliphatic dicarboxylic acids which can equally be used and which may be mentioned are in particular the di-C₁-C₆-alkyl esters, e.g. dimethyl, diethyl, di-n-propyl, diisopropyl, di-n-butyl, diisobutyl, di-t-butyl, di-n-pentyl, diisopentyl, or di-n-hexyl ester. It is equally possible to use anhydrides of the dicarboxylic acids. Preferred dicarboxylic acids are succinic acid, adipic acid, sebacic acid, azelaic acid, and brassylic acid, and also the respective ester-forming derivatives of these, and mixtures thereof. Particular preference is given to adipic acid, sebacic acid, or succinic acid, and also to the respective ester-forming derivatives of these, and mixtures thereof.

Aromatic dicarboxylic acids a2 that may be mentioned are generally those having from 8 to 12 carbon atoms and preferably those having 8 carbon atoms. Examples that may be mentioned are terephthalic acid, isophthalic acid, 2,6-naphthoic acid, and 1,5-naphthoic acid, and also ester-forming derivatives thereof. Particular mention may be made here of the di-C₁-C₆-alkyl esters, e.g. dimethyl, diethyl, diethyl, di-n-propyl, diisopropyl, di-n-butyl, diisobutyl, di-t-butyl, di-n-pentyl, diisopentyl, or di-n-hexyl ester. The anhydrides of the dicarboxylic acids a2 are equally suitable ester-forming derivatives. However, it is also in principle possible to use aromatic dicarboxylic acids a2 having a greater number of carbon atoms, for example up to 20 carbon atoms. The aromatic dicarboxylic acids or ester-forming derivatives thereof a2 can be used individually or in the form of mixture made of two or more thereof. It is particularly preferable to use terephthalic acid or ester-forming derivatives of this acid, e.g. dimethyl terephthalate.

The sulfonated aromatic dicarboxylic acids and ester-forming derivatives of these are typically those derived from the abovementioned nonsulfonated aromatic dicarboxylic acids, and bear one or two sulfonic acid groups. An example that may be mentioned is sulfoisophthalic acid or a salt thereof, e.g. the sodium salt (Nasip).

The diols B are generally selected from branched or linear alkanediols having from 2 to 12 carbon atoms, preferably from 4 to 8 carbon atoms, or in particular 6 carbon atoms, or from cycloalkanediols having from 5 to 10 carbon atoms.

Examples of suitable alkanediols are ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,4-butanediol, 1,5-pentanediol, 2,4-dimethyl-2-ethylhexane-1,3-diol, 2,2-dimethyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 2,2,4-trimethyl-1,6-hexanediol, in particular ethylene glycol, 1,3-propanediol, 1,4-butanediol or 2,2-dimethyl-1,3-propanediol (neopentyl glycol); cyclopentanediol, 1,4-cyclohexanediol, 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, or 2,2,4,4-tetramethyl-1,3-cyclobutanediol. It is also possible to use mixtures of various alkanediols. Diol component B in said copolyesters is preferably selected from C₂-C₁₂ alkanediols and mixtures thereof. Preference is given to 1,3-propanediol and in particular to 1,4-butanediol.

If an excess of OH end groups is desired, an excess of component B can be used. In one preferred embodiment, the molar ratio of components used A:B can be in the range from 0.4:1 to 1.1:1, preferably in the range from 0.6:1 to 1.05:1, and in particular in the range from 0.7:1 to 1.02:1. The molar ratio of component A incorporated into the polymer to component B incorporated into the polymer is preferably in the range from 0.8:1 to 1.01:1, with preference from 0.9:1 to 1:1, and in particular in the range from 0.99:1 to 1:1.

The polyesters can comprise, condensed into the molecule, not only components A and B but also further bifunctional components C. Said bifunctional compounds have two functional groups which react to form bonds with carboxylic acid groups or preferably hydroxy groups. Examples of functional groups which react with OH groups are in particular isocyanate groups, epoxy groups, oxazoline groups, carboxy groups in free or esterified form, and amide groups. Particular functional groups which react with carboxy groups are hydroxy groups and primary amino groups. These materials are particularly those known as bifunctional chain extenders, in particular the compounds of groups c3) to c7). Among components C are:

• • c1) dihydroxy compounds of the formula I

HO-[(A)-O]_m—H   (I)

• •  in which A is a C₂-C₄-alkylene unit, such as 1,2-ethanediyl, 1,2-propanediyl, 1,3-propanediyl, or 1,4-butanediyl, and m is an integer from 2 to 250;
  • c2) hydroxycarboxylic acids of the formula IIa or IIb

• •  in which p is an integer from 1 to 1500 and r is an integer from 1 to 4, and G is a radical selected from the group consisting of phenylene, —(CH₂)_q—, where q is an integer from 1 to 5, —C(R)H—, and —C(R)HCH₂, where R is methyl or ethyl;
  • c3) amino-C₂-C₁₂ alkanols, amino-C₅-C₁₀ cycloalkanols, and mixtures thereof;
  • c4) diamino-C₁-C₈ alkanes;
  • c5) 2,2′-bisoxazolines of the general formula Ill

• •  where R₁ is a single bond, a (CH₂)_z,-alkylene group, where z=2, 3, or 4, or a phenylene group;
  • c6) aminocarboxylic acids which by way of example are selected from naturally occurring amino acids, polyamides with a molar mass of at most 18000 g/mol, obtainable via polycondensation of a dicarboxylic acid having from 4 to 6 carbon atoms and of a diamine having from 4 to 10 carbon atoms, compounds of the formulae IVa and IVb

• •  in which s is an integer from 1 to 1500 and t is an integer from 1 to 4, and T is a radical selected from the group consisting of phenylene, —(CH₂)_u—, where u is an integer from 1 to 12, —C(R²)H—, and —C(R²)HCH₂, where R² is methyl or ethyl,
  •  and polyoxazolines having the repeat unit V

• •  in which R³ is hydrogen, C₁-C₆-alkyl, C₅-C₈-cycloalkyl, unsubstituted phenyl or phenyl substituted up to three times with C₁-C₄-alkyl groups, or is tetrahydrofuryl; and
  • c7) diisocyanates.

Examples of component c1 are diethylene glycol, triethylene glycol, polyethylene glycol, polypropylene glycol, and polytetrahydrofuran (polyTHF), particularly preferably diethylene glycol, triethylene glycol, and polyethylene glycol, and it is also possible here to use mixtures thereof, or compounds which have different alkylene units A (see formula I), e.g. polyethylene glycol which comprises propylene units (A=1,2- or 1,3-propanediyl). The latter are obtainable by way of example via polymerization of first ethylene oxide and then propylene oxide, by methods known per se. Particular preference is given to copolymers based on polyalkylene glycols having various variables A, where units formed from ethylene oxide (A=1,2-ethanediyl) predominate. The molar mass (number average M_n) of the polyethylene glycol is generally selected to be in the range from 250 to 8000 g/mol, preferably from 600 to 3000 g/mol.

In one of the embodiments it is possible by way of example to use, for the production of the copolyesters, from 80 to 99.8 mol %, preferably from 90 to 99.5 mol %, of the diols B, and from 0.2 to 20 mol %, preferably from 0.5 to 10 mol %, of the dihydroxy compounds c1, based on the molar amount of B and c1.

Examples of preferred components c2 are glycolic acid, D-, L-, or D,L-lactic acid, 6-hydroxyhexanoic acid, cyclic derivatives thereof, e.g. glycolide (1,4-dioxane-2,5-dione), D- or L-dilactide (3,6-dimethyl-1,4-dioxane-2,5-dione), p-hydroxybenzoic acid, and also oligomers thereof, and polymers, such as 3-polyhydroxybutyric acid, polyhydroxyvaleric acid, polylactide (obtainable by way of example in the form of EcoPLA® (Cargill)), or else a mixture of 3-polyhydroxybutyric acid and polyhydroxyvaleric acid (the latter being obtainable as Biopol® from Zeneca). The low-molecular-weight and cyclic derivatives thereof are particularly preferred for producing copolyesters. Examples of amounts that can be used of the hydroxycarboxylic acids or their oligomers and/or polymers are from 0.01 to 20% by weight, preferably from 0.1 to 10% by weight, based on the amount of A and B.

Preferred components c3 are amino-C₂-C₆ alkanols, such as 2-aminoethanol, 3-aminopropanol, 4-aminobutanol, 5-aminopentanol, 6-aminohexanol, and also amino-C₅-C₆ cycloalkanols, such as aminocyclopentanol and aminocyclohexanol, or a mixture thereof.

Preferred components c4) are diamino-C₄-C₆ alkanes, such as 1,4-diaminobutane, 1,5-diaminopentane, and 1,6-diaminohexane.

In one preferred embodiment, the amounts used for producing the copolyesters are from 0.5 to 20 mol %, preferably from 0.5 to 10 mol %, of c3, based on the molar amount of B, and from 0 to 15 mol %, preferably from 0 to 10 mol %, of c4, based on the molar amount of B.

Preferred bisoxazolines III of component c5) are those in which R¹ is a single bond, a (CH2)_z-alkylene group, where z 32 2, 3, or 4, e.g. methylene, ethane-1,2-diyl, propane-1,3-diyl, propane-1,2-diyl, or a phenylene group. Particularly preferred bisoxazolines that may be mentioned are 2,2′-bis(2-oxazoline), bis(2-oxazolinyl)methane, 1,2-bis(2-oxazolinyl)ethane, 1,3-bis(2-oxazolinyl)propane, or 1,4-bis(2-oxazolinyl)butane, 1,4-bis(2-oxazolinyl)benzene, 1,2-bis(2-oxazolinyl)benzene, or 1,3-bis(2-oxazolinyl)benzene. Bisoxazolines of the general formula III are generally obtainable via the process of Angew. Chem. Int. Edit., Vol. 11 (1972), pp. 287-288.

Examples of amounts that can be used for producing the polyesters are from 80 to 98 mol % of B, up to 20 mol % of c3, e.g. from 0.5 to 20 mol % of c3, up to 20 mol % of c4, e.g. from 0.5 to 20 mol %, and up to 20 mol % of c5, e.g. from 0.5 to 20 mol %, based in each case on the total of the molar amounts of components B, c3, c4, and c5. In another preferred embodiment it is possible to use from 0.1 to 5% by weight of c5, preferably from 0.2 to 4% by weight, based on the total weight of A and B.

Component c6 used can comprise naturally occurring aminocarboxylic acids. Among these are valine, leucine, isoleucine, threonine, methionine, phenylalanine, tryptophan, lysine, alanine, arginine, aspartamic acid, cysteine, glutamic acid, glycine, histidine, proline, serine, tryosine, asparagine, and glutamine.

Preferred aminocarboxylic acids of the general formulae IVa and IVb are those in which s is an integer from 1 to 1000 and t is an integer from 1 to 4, preferably 1 or 2, and T is selected from the group of phenylene and —(CH₂)_u—, where u is 1, 5, or 12.

c6 can also moreover be a polyoxazoline of the general formula V. However, component c6 can also be a mixture of various aminocarboxylic acids and/or polyoxazolines.

Amounts of c6 that can be used in one preferred embodiment are from 0.01 to 20% by weight, preferably from 0.1 to 10% by weight, based on the total amount of components A and B.

Component c7 used can comprise aromatic or aliphatic diisocyanates. However, it is also possible to use isocyanates of higher functionality. Examples of aromatic diisocyanates are tolylene 2,4-diisocyanate, tolylene 2,6-diisocyanate, diphenylmethane 2,2′-diisocyanate, diphenylmethane 2,4′-diisocyanate, diphenylmethane 4,4′-diisocyanate, naphthylene 1,5-diisocyanate, and xylylene diisocyanate. Examples of aliphatic diisocyanates are especially linear or branched alkylene diisocyanates or cycloalkylene diisocyanates having from 2 to 20 carbon atoms, preferably having from 3 to 12 carbon atoms, e.g. hexamethylene 1,6-diisocyanate, isophorone diisocyanate, or methylenebis(4-isocyanatocyclohexane). Other components c7 that can be used are tri(4-isocyanatophenyl)methane, and also the cyanurates, uretdiones, and biurets of the abovementioned diisocyanates.

Amounts generally used of component c7, if desired, are from 0.01 to 5 mol %, preferably from 0.05 to 4 mol %, particularly preferably from 0.1 to 4 mol %, based on the total of the molar amounts of A and B.

Among other components which can optionally be used for producing the polyesters are compounds D which comprise at least three groups/functionalities which react with carboxylic acid groups or with hydroxy groups, to form bonds. Particular examples of functional groups which react with OH groups are isocyanate groups, epoxy groups, oxazoline groups, carboxy groups in free or esterified form, and amide groups. Particular functional groups which react with carboxy groups are hydroxy groups and primary amino groups. Compounds of this type are also termed crosslinking agents. By using the compound D, it is possible to construct biodegradable copolyesters which are pseudoplastic. The rheology of the melts improves; the biodegradable copolyesters are easier to process, for example easier to draw by melt-solidification processes to give foils. The compounds D have a shear-thinning effect, i.e. viscosity decreases under load. The compounds D preferably comprise from 3 to 10, e.g. 3, 4, 5, or 6, functional groups capable of forming ester bonds. Particularly preferred compounds D have from three to six functional groups of this type in the molecule, in particular from three to six hydroxy groups and/or carboxy groups. Examples that may be mentioned are: polycarboxylic acids and hydroxycarboxylic acids, e.g. tartaric acid, citric acid, malic acid; trimesic acid; trimellitic acid, trimellitic anhydride; pyromellitic acid, pyromellitic dianhydride, and hydroxyisophthalic acid, and also polyols, such as trimethylolpropane and trimethylolethane; pentaerythritol, polyethertriols, and glycerol. Preferred compounds D are polyols, preferably trimethylolpropane, pentaerythritol, and in particular glycerol. The amounts used of the compounds D, insofar as these are desired, are generally from 0.0005 to 1 mol/kg, preferably from 0.001 to 0.5 mol/kg, and in particular from 0.005 to 0.3 mol/kg, based on total amount of components A, B, C, and D, or on the total weight of the polyester. The amounts used of the compounds D, insofar as these are desired, are preferably from 0.01 to 5% by weight, in particular from 0.05 to 3% by weight, and in particular from 0.1 to 2% by weight, and specifically from 0.2 to 2% by weight, based on the total amount of components A, B, C, and D, or on the total weight of the polyester.

It is generally advisable to add the crosslinking (at least trifunctional) compounds D at a relatively early juncture in the polycondensation process.

Production of the copolyesters preferred in the invention can also use, alongside the abovementioned components A, B, and optionally C, and optionally D, bi- or polyfunctional epoxides (component E). Particularly suitable bi- or polyfunctional epoxides are copolymers which contain epoxy groups and which are based on styrene, acrylate, and/or methacrylate. The units bearing epoxy groups are preferably glycidyl (meth)acrylates. Copolymers which have proven successful are those having a proportion of greater than 20% by weight, particularly preferably greater than 30% by weight, and with particular preference greater than 50% by weight, of glycidyl methacrylate, based on the copolymer. The epoxy equivalent weight (EEW) in said polymers is preferably from 150 to 3000 g/equivalent and with particular preference from 200 to 500 g/equivalent. The average molecular weight (weight average) M_W of the polymers is preferably from 2000 to 25 000, in particular from 3000 to 8000. The average molecular weight (number average) M_n of the polymers is preferably from 400 to 6000, in particular from 1000 to 4000. Polydispersity (Q) is generally from 1.5 to 5. Copolymers of the abovementioned type, containing epoxy groups, are marketed by way of example by BASF Resins B.V. with trademark Joncryl® ADR. Joncryl® ADR 4368 is particularly suitable as component E. Component E is usually used as chain extender. In relation to the amount, the information given above for component E, and in particular for components c2), c3), c4), c5), and c6), is applicable.

Some of the copolyesters are known, e.g. from EP-A 488 617, WO96/15173, and WO 04/67632, or can be produced by methods known per se. It is particularly preferable to produce the copolyesters by the continuous process described in EP application No. 08154541.0.

In one first embodiment, the copolyesters described are synthesized in a two-stage reaction cascade. The general method begins by reacting the dicarboxylic acids or their derivatives A together with component B and optionally D in the presence of an esterification catalyst (or if the carboxylic acids A are used in the form of their esters, in the presence of a transesterification catalyst) to give a prepolyester. The intrinsic viscosity (IV) of said prepolyester is generally from 50 to 100 mL/g, preferably from 60 to 90 mL/g. The catalysts used generally comprise zinc catalysts, aluminum catalysts, and in particular titanium catalysts. An advantage of titanium catalysts, such as tetra(isopropyl) orthotitanate and in particular tetrabutyl orthotitanate (TBOT), over the tin catalysts, antimony catalysts, cobalt catalysts, and lead catalysts often used in the literature, an example being tin dioctanoate, is that if any residual amounts of the catalyst or of downstream products of the catalyst remain within the product, they are less toxic. This is a particularly important factor for the biodegradable polyesters, since they pass directly into the environment, by way of example in the form of composting bags or mulch films. The polyesters of the invention are then optionally chain-extended by the processes described in WO 96/15173 and EP-A 488 617. The prepolyester is, by way of example, reacted with chain extenders C), e.g. with diisocyanates, or with epoxy-containing polymethacrylates, in a chain-extension reaction to give a polyester with IV of from 60 to 450 mL/g, preferably from 80 to 250 mL/g.

In another method, component A is first condensed in the presence of an excess of component B and optionally D, together with the catalyst. The melt of the resultant prepolyester is then condensed, usually at an internal temperature of from 200 to 250° C., while diol liberated is removed by distillation, until the desired viscosity has been reached, the intrinsic viscosity (IV) being from 60 to 450 mL/g, and preferably from 80 to 250 mL/g. Said condensation reaction generally takes place within a period of from 3 to 6 hours at reduced pressure. A reaction with the chain extender of component D then optionally follows.

It is particularly preferable to produce the copolyesters by the continuous process described in EP application No. 08154541.0. Here, by way of example, a mixture made of components A and B and optionally of further comonomers is mixed to give a paste, without addition of any catalyst, or as an alternative the liquid esters of component A and component B and optionally further comonomers are fed to the reactor, without addition of any catalyst, and

• • 1. in a first stage, said mixture is continuously esterified or, respectively, transesterified together with the entire amount or a portion of the catalyst;
  • 2. in a second stage, optionally with the remaining amount of catalyst, the transesterification or esterification product obtained in 1.) is continuously precondensed—preferably in a tower reactor, where the product stream is conducted cocurrently by way of a falling-film cascade, and the reaction vapors are removed in situ from the reaction mixture—until an intrinsic viscosity of from 20 to 60 mL/g to DIN 53728 is reached;
  • 3. in a third stage, the product obtainable from 2.) is continuously polycondensed—preferably in a cage reactor—until an intrinsic viscosity of from 70 to 130 mL/g to DIN 53728 is reached and optionally
  • 4. in a fourth stage, the product obtainable from 3.) is continuously reacted in a polyaddition reaction with a chain extender in an extruder, List reactor, or static mixer, until an intrinsic viscosity of from 80 to 250 mL/g to DIN 53728 is reached.

The abovementioned intrinsic viscosity ranges serve merely as guides to preferred process variants, and are not intended to have any restricting effect on the subject matter of the present application.

The copolyesters of the invention can be produced not only by the continuous process described above but also in a batch process. For this, components A, B, and optionally D are mixed in any desired feed sequence and condensed to give a prepolyester. A polyester with the desired intrinsic viscosity can be obtained with the optional aid of component D.

The number-average molecular weight M_N of the preferred copolyesters is generally in the range from 5000 to 1 000 000 daltons, in particular in the range from 8000 to 800 000 daltons, and specifically in the range from 10 000 to 500 000 daltons. The weight-average molecular weight Mw of the copolyesters preferred in the invention is generally in the range from 20 000 to 5 000 000 daltons, often in the range from 30 000 daltons to 4 000 000 daltons, and in particular in the range from 40 000 to 2 500 000 daltons. The polydispersity index M_W/M_N is generally at least 2, and is often in the range from 3 to 25, in particular in the range from 5 to 20. The copolyesters are preferably semicrystalline and preferably have a melting point or melting range in the range from 80 to 170° C., in particular in the range from 90 to 150° C. The intrinsic viscosity of the copolyesters is typically in the range from 50 to 500 ml/g, often in the range from 80 to 300 ml/g, and in particular in the range from 100 to 250 ml/g (determined to EN ISO 1628-1 at 25° C. on a 0.5% strength by weight solution of the polymer in o-dichlorobenzene/phenol (1:1 w/w)). The preferred copolyesters are characterized firstly via high melt viscosity η₀, which at 180° C. is generally at least 60 Pa·s, often at least 80 Pa·s, in particular at least 100 Pa·s, e.g. from 60 to 20 000 Pa·s, in particular from 80 to 15 000 Pa·s, and specifically from 100 to 10 000 Pa·s, and via a low acid number, which is less than 5 mg KOH/g of polymer, in particular at most 3 mg KOH/g of polymer, and specifically at most 1 mg KOH/g of polymer.

The copolyesters moreover preferably have in essence no functional groups which make the polymers soluble in water. Accordingly, the number of sulfonic acid groups in the copolyester is generally less than 0.1 mmol/g of polymer, in particular less than 0.05 mmol/g of polymer, or less than 0.01 mmol/g of polymer.

The solids content of the aqueous dispersions of the copolyester is generally in the range from 10 to 60% by weight, in particular in the range from 20 to 55% by weight, and specifically in the range from 30 to 50% by weight.

The viscosity of the dispersions used in the invention, determined by the Brookfield method at 20° C., is preferably at most 5 Pa·s, often at most 2 Pa·s, e.g. in the range from 10 to 5000 mPa·s, in particular in the range from 50 to 2000 mPa·s (measured by a Brookfield viscosimeter at 20° C. and 20 rpm with spindle 4).

The aqueous dispersion generally comprises, alongside the dispersed polymers, at least one surfactant substance to stabilize the polymer particles dispersed in the dispersion. The content of surfactant substances will generally not exceed 20% by weight, based on total solids content, being typically in the range from 0.1 to 20% by weight and often in the range from 0.2 to 10% by weight, based on total solids content. Among the suitable surfactant substances are polymeric surfactant substances with molecular weights above 2000 daltons (number average), e.g. from 2200 to 10⁶ daltons, these generally being termed protective colloids, and also low-molecular-weight surfactant substances with molecular weights up to 2000 daltons, often up to 1500 daltons (number average), these generally being termed emulsifiers. The surfactant substances can be cationic, anionic, or neutral.

In one preferred embodiment of the invention, the aqueous dispersion medium comprises at least one protective colloid, for example one neutral, anionic, or cationic protective colloid, optionally in combination with one or more emulsifiers.

Examples of protective colloids are water-soluble polymers, e.g.

• • neutral protective colloids: e.g. polysaccharides, for example water-soluble starches, starch derivatives, and cellulose derivatives, such as methylcellulose, hydroxypropylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, and also polyvinyl alcohols, inclusive of partially hydrolyzed polyvinyl acetate with a degree of hydrolysis which is preferably at least 40%, in particular at least 60%, polyacrylamide, polyvinylpyrrolidone, polyethylene glycols, graft polymers of vinyl acetate and/or vinyl propionate onto polyethylene glycols, and polyethylene glycols mono- or bilaterally end-group-capped with alkyl, carboxy, or amino groups;
  • anionic water-soluble polymers, the main polymer chain of which has a plurality of carboxy groups, sulfonic acid groups or, sulfonate groups, and/or phosphonic acid groups or phosphonate groups, e.g. carboxymethylcellulose, homo- and copolymers of ethylenically unsaturated monomers which comprise at least 20% by weight, based on the total amount of the monomers, of at least one ethylenically unsaturated monomer which comprises at least one carboxy group, sulfonic acid group, and/or phosphonic acid group incorporated within the polymer, and salts of these, in particular the alkali metal salts and ammonium salts. When the abovementioned anionic water-soluble polymers are in an aqueous medium, the sulfonic acid groups bonded to the main polymer chain are generally in the salt form, i.e. in the form of sulfonate groups, the phosphonic acid groups correspondingly being in the form of phosphonate groups. The counterions are then typically alkali metal ions and alkaline earth metal ions, examples being sodium ions, and calcium ions, and ammonium ions (NH₄⁺);
  • cationic polymers, e.g. polydiallyldimethylammonium salts, e.g. the chlorides;
  • anionically or cationically modified starches. Examples of anionically modified starches are carboxymethylated starches and n-octenylsuccinyl-modified starch, examples of these being obtainable in the form of products from Cargill (CEmCap/CEmTex/CDeliTex n-octenylsuccinylated starches). Examples of cationically modified starches are starches modified with 2-hydroxy-3-(trimethylammonium)propyl groups, examples being starches which are obtainable by reacting conventional starches with N-(3-chloro-2-hydroxypropyl)trimethylammonium chloride (CHPTAC), and which preferably have a degree of substitution of from 0.02 to 0.1. The products Hi-Cat 21370 from Roquette and Perlcore 134P from Lyckeby are examples of these.

Examples of the anionic water-soluble polymers of which the main chain has a plurality of carboxy groups, sulfonic acid groups or sulfonate groups, and/or phosphonic acid groups or phosphonate groups, are:

• • homo- and copolymers of monoethylenically unsaturated monocarboxylic acids having from 3 to 6 carbon atoms (hereinafter monoethylenically unsaturated C₃-C₆ monocarboxylic acids), examples being acrylic acid and methacrylic acid, and salts thereof, in particular the alkali metal salts and ammonium salts;
  • copolymers of monoethylenically unsaturated C₃-C₆ monocarboxylic acids with neutral monomers, e.g. vinylaromatics, such as styrene, C₁-C₁₀-alkyl esters of monoethylenically unsaturated C₃-C₆ monocarboxylic acids, and/or C₄-C₆ dicarboxylic acids, examples being methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, n-hexyl acrylate, n-hexyl methacrylate, hydroxyethyl esters, and in particular hydroxyethyl and hydroxypropyl esters of the abovementioned monoethylenically unsaturated C₃-C₆ monocarboxylic acids and/or C₄-C₆ dicarboxylic acids, examples being hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate and hydroxypropyl methacrylate, and also vinyl esters of aliphatic carboxylic acids, examples being vinyl acetate and vinyl propionate;
  • homo- and copolymers of monoethylenically unsaturated sulfonic acids, e.g. vinylsulfonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-acryloxyethanesulfonic acid, 2-acryloxypropanesulfonic acid, etc., and also copolymers thereof with the abovementioned neutral monomers, and also the salts of the abovementioned homo- and copolymers, in particular the alkali metal salts and ammonium salts;
  • homo- and copolymers of monoethylenically unsaturated phosphonic acids, e.g. vinylphosphonic acid, 2-acrylamido-2-methylpropanephosphonic acid, 2-acryloxyethanephosphonic acid, 2-acryloxypropanephosphonic acid, etc., and also copolymers thereof with the abovementioned neutral monomers, and also the salts of the abovementioned homo- and copolymers, in particular the alkali metal salts and ammonium salts;
    where the proportion of the neutral comonomers in the abovementioned copolymers generally does not exceed a proportion of 80% by weight, in particular 70% by weight, based on the total amount of the monomers constituting the copolymer.

Particular anionic water-soluble polymers, the main chain of which has a plurality of sulfonate groups, are also

• • water-soluble copolyesters which have an amount of from 0.3 to 1.5 mmol/g of polyester, in particular from 0.5 to 1.0 mmol/g of polyester, of aromatically bonded sulfonic acid groups and, respectively, sulfonate groups, and salts of these, in particular the alkali metal salts and ammonium salts thereof, where the water-soluble copolyesters are preferably composed of:
    • i) from 6 to 30 mol %, based on the total amount of components i), ii), and iii), of at least one aromatic dicarboxylic acid which has at least one sulfonate group and which is preferably selected from 5-sulfoisophthalic acid or from salts thereof, in particular the sodium salt of sulfoisophthalic acid, or ester-forming derivatives thereof;
    • ii) optionally one or more aromatic dicarboxylic acids which have no sulfonyl groups and which are preferably selected from terephthalic acid and isophthalic acid and mixtures thereof, or ester-forming derivatives thereof;
    • iii) optionally one or more aliphatic or cycloaliphatic dicarboxylic acids, or ester-forming derivatives thereof;
    • iv) from 95 to 105 mol %, based on the total amount of components i), ii), and iii), of one or more aliphatic diols, e.g. ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,4-butanediol, 1,5-pentanediol, 2,4-dimethyl-2-ethylhexane-1,3-diol, 2,2-dimethyl-1,3-propanediol, 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 2,2,4-trimethyl-1,6-hexanediol, in particular ethylene glycol, 1,3-propanediol, 1,4-butanediol or 2,2-dimethyl-1,3-propanediol (neopentyl glycol),
    • where the total amount of components ii) and iii) makes up from 70 to 94 mol %, based on the total amount of components i), ii) and iii), where components i), ii), iii), and iv) generally make up at least 99% by weight of all of the ester-forming constituents of the polyester (based on the components comprised within the polyester). Water-soluble copolyesters of this type are known by way of example from U.S. Pat. No. 6,521,679, the disclosure of which is hereby in its entirety incorporated herein by way of reference.

Examples of familiar nonionic emulsifiers are C₂-C₃-alkoxylated, in particular ethoxylated, mono-, di-, and trialkylphenols (degree of ethoxylation from 3 to 50, alkyl radical: C₄ to C₁₂), and also C₂-C₃-alkoxylated, in particular ethoxylated, fatty alcohols (degree of ethoxylation from 3 to 80; alkyl radical: C₈ to C₃₆). Examples of these are the Lutensol® A grades (C₁₂ to C₁₄ fatty alcohol ethoxylates, degree of ethoxylation from 3 to 8), Lutensol® AO grades (C₁₃ to C₁₅ oxo alcohol ethoxylates, degree of ethoxylation from 3 to 30), Lutensol® AT grades (C₁₆ to C₁₈ fatty alcohol ethoxylates, degree of ethoxylation from 11 to 80), Lutensol® ON grades (C10 oxo alcohol ethoxylates, degree of ethoxylation from 3 to 11), and the Lutensol® TO grades (C13 oxo alcohol ethoxylates, degree of ethoxylation from 3 to 20), from BASF SE.

Conventional anionic emulsifiers are the salts of amphiphilic substances which have an anionic functional group, such as a sulfonate, phosphonate, sulfate, or phosphate group. Examples of these are the salts, in particular the alkali metal salts and ammonium salts, of alkyl sulfates (alkyl radical: C₈ to C₁₂), the salts, in particular the alkali metal salts and ammonium salts, of amphiphilic compounds which have a sulfated or phosphated oligo-C₂-C₃-alkylene oxide group, in particular a sulfated or phosphated oligoethylene oxide group, examples being the salts, in particular the alkali metal salts and ammonium salts, of sulfuric acid hemiesters of ethoxylated alkanols (degree of ethoxylation from 2 to 50, in particular from 4 to 30, alkyl radical: C₁₀ to C₃₀, in particular C₁₂ to C₁₈), the salts, in particular the alkali metal salts and ammonium salts, of sulfuric acid hemiesters of ethoxylated alkylphenols (degree of ethoxylation from 2 to 50, alkyl radical: C₄ to C₁₂), the salts, in particular the alkali metal salts and ammonium salts, of phosphoric acid hemiesters of ethoxylated alkanols (degree of ethoxylation from 2 to 50, in particular from 4 to 30, alkyl radical: C₁₀ to C₃₀, in particular C₁₂ to C₁₈), the salts, in particular the alkali metal salts and ammonium salts, of phosphoric acid hemiesters of ethoxylated alkylphenols (degree of ethoxylation from 2 to 50, alkyl radical: C₄ to C₁₂), the salts, in particular the alkali metal salts and ammonium salts, of alkylsulfonic acids (alkyl radical: C₁₂ to C₁₈), the salts, in particular the alkali metal salts and ammonium salts, of alkylarylsulfonic acids (alkyl radical: C₉ to C₁₈), and also the salts, in particular the alkali metal salts and ammonium salts, of alkylbiphenyl ether sulfonic acids (alkyl radical: C₆ to C₁₈), an example being the product marketed as Dowfax® 2A1.

Suitable cationic emulsifiers are generally cationic salts having a C₆-C₁₈-alkyl, C₁-C₁₀-alkylaryl, or heterocyclic radical, examples being primary, secondary, tertiary, and quaternary ammonium salts, alkanolammonium salts, pyridinium salts, imidazolinium salts, oxazolinium salts, morpholinium salts, thiazolinium salts, and also salts of amine oxides, quinolinium salts, isoquinolinium salts, tropylium salts, sulfonium salts, and phosphonium salts, in particular the appropriate sulfates, methosulfates, acetates, chlorides, bromides, phosphates, and hexafluorophosphates, and the like. Examples that may be mentioned are dodecylammonium acetate or the corresponding sulfate, the sulfates or acetates of the various paraffinic esters which involve the 2-(N,N,N-trimethylammonium)ethyl radical, N-cetylpyridinium sulfate, N-laurylpyridinium sulfate, and also N-cetyl-N,N,N-trimethylammonium sulfate, N-dodecyl-N,N,N-trimethylammonium sulfate, N-octyl-N,N,N-trimethylammonium sulfate, N,N-distearyl-trimethylammonium N,N-dimethylammonium sulfate, and also the Gemini surfactant N,N′-(lauryldimethyl)ethylenediamine disulfate, ethoxylated tallow fatty alkyl-N-methylammonium sulfate, and ethoxylated oleylamine (for example Uniperol® AC from BASF SE, about 12 ethylene oxide units).

In one preferred embodiment of the invention, the aqueous dispersion comprises at least one neutral protective colloid, in particular one neutral, protective colloid bearing OH groups, optionally in combination with one or more emulsifiers, preferably anionic or nonionic emulsifiers, in particular anionic emulsifiers which bear a sulfate or sulfonate group. Examples of neutral protective colloids bearing OH groups are polysaccharides, e.g. water-soluble starches, starch derivatives, and cellulose derivatives, such as methylcellulose, hydroxypropylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, and also polyvinyl alcohols, inclusive of partially hydrolyzed polyvinyl acetate having a degree of hydrolysis which is preferably at least 40%, in particular at least 60%. In particular, the neutral protective colloid bearing OH groups has been selected from polyvinyl alcohols, inclusive of partially hydrolyzed polyvinyl acetates having a degree of hydrolysis which is preferably at least 40%, in particular at least 60%.

The dispersions of biodegradable polyesters can be produced by analogy with the method in the patent application PCT/EP2011/054471, the priority date of which is previous to that of the present application. Here, a composition which comprises the polyester and which is generally composed of at least 99% by weight of the polyester, or of a blend of the polyester with a different polymer, and optionally of one or more surfactant substances, is introduced, at a temperature above the melting point or softening point of the polyester or of the blend, into an aqueous dispersion medium which generally comprises at least one surfactant substance, and the resultant aqueous emulsion is quenched. The introduction of the composition of the polymer into the aqueous dispersion medium generally takes place in a mixing apparatus which has at least one rotor-stator mixer.

In this process, the temperature at which the thermoplastic polyester is introduced into the aqueous dispersion medium is, in the case of an amorphous polyester, a temperature above the softening point of the polyester, and in the case of a crystalline or semicrystalline polyester it is above the melting point of the polyester. The term “softening point” of amorphous polyesters means the temperature corresponding to the glass transition temperature as can be determined by way of example by means of dynamic differential calorimetry (DSC) to ASTM D3418 or preferably to DIN 53765, or via dynamic mechanical analysis (DMA). The term “melting point” is the temperature which leads to melting or softening of the polyester and which can be determined in a manner known per se by means of dynamic differential calorimetry (DSC) to DIN 53765 or differential thermoanalysis (DTA).

The term “amorphous polyester” means a polyester which comprises less than 1% by weight of crystalline regions. The term “crystalline” or “semicrystalline” polyester means a polyester which comprises more than 1% by weight, in particular at least 5% by weight, of crystalline regions. The degree of crystallinity of a polyester can be determined in a manner known per se via X-ray diffractometry or via thermochemical methods, such as DTA or DSC, in a manner known per se.

The rotor-stator mixers used to produce the aqueous dispersion of the biodegradable polyester are familiar to the person skilled in the art and in principle comprise all of the types of dynamic mixer in which a high-speed, preferably rotationally symmetrical, rotor interacts with a stator to form one or more operating regions which in essence have the shape of an annular gap. Within said operating regions, the material to be mixed is subjected to severe shear stresses, and high levels of turbulence often prevail in these annular gaps, and likewise promote the mixing process. The rotor-stator apparatus is operated at a relatively high rotation rate, generally from 1000 to 20000 rpm. This gives high peripheral velocities and a high shear rate, thus subjecting the emulsion to severe shear stresses, which lead to effective communition of the melt and thus to very effective emulsification. Among the rotor-stator mixers are by way of example toothed-ring dispersers, annular-gap mills, and colloidal mills.

Preference is given to those rotor-stator mixers which have means of generating cavitation forces. Means of this type can be elevations arranged on the rotor side and/or on the stator side, where these protrude into the mixing chamber and which have at least one area where the normal has a tangential fraction, examples being pins, teeth, or knives or coaxial rings with radially arranged slots. The rotor-stator mixer preferably has, on the side of the rotor, at least one toothed ring arranged so as to be rotationally symmetrical, and/or at least one ring which has radial slots (tooth gaps) arranged so as to be rotationally symmetrical. Apparatuses of this type are also termed toothed-ring dispersers or toothed-ring dispersing machines. In particular, the rotor-stator mixer has, on the side of the rotor and also on the side of the stator, at least one toothed ring arranged so as to be rotationally symmetrical, and/or at least one ring with radial slots (tooth gaps), where the (toothed) rings on the side of the rotor and on the side of the stator are arranged coaxially and undergo mutual intermeshing to form an annular gap.

In one particularly preferred embodiment, the rotor-stator mixer is a toothed-ring dispersing machine which has a conical stator with a concentric frustoconical recess, and which has a likewise concentric conical rotor, where the rotor protrudes into the frustoconical operating chamber of the stator in such a way as to form an annular operating chamber, into which teeth protrude on the side of the rotor and of the stator, and these are respectively arranged on the rotor and the stator in such a way as to take the form of one or more, e.g. two, three, or four coaxial toothed rings on the side of the rotor and of one or more, e.g. one, two, three, or four coaxial toothed rings on the side of the stator, and in such a way that the toothed rings undergo mutual offset intermeshing. Apparatuses of this type are known to the person skilled in the art by way of example from DE 10024813 A1 and US 2002/076639, and are supplied by way of example by Cavitron Verfahrenstechnik v. Hagen & Funke GmbH, Sprockhövel, Germany.

The composition of the polyester is generally mixed with the aqueous dispersion medium at a temperature above the softening point of the polymer. To this end, the composition of the polyester is usually heated to a temperature above the softening point and introduced, preferably continuously, into the mixing apparatus. The required amount of aqueous dispersion medium is similarly, preferably continuously, introduced into the mixing apparatus. The amount of dispersion medium here is generally selected in such a way as to give the desired solids content of the dispersion. However, it is also possible to use a larger amount of the dispersion medium and then to concentrate the resultant dispersion. It is equally possible to begin by producing a relatively concentrated dispersion and to dilute this with further dispersion medium and/or water. The mass ratio of polymer introduced to the total amount of aqueous dispersion medium is typically in the range from 1:20 to 1.2:1, often in the range from 1:10 to 1:1.1, and in particular in the range from 1:3 to 1:1. In the case of continuous addition of polymer and of aqueous dispersion medium, the mass ratio of the streams of materials introduced is within the abovementioned ranges. In the case of multistage addition of dispersion medium, the mass ratio of polymer introduced to the total amount of aqueous dispersion medium introduced in the first to the penultimate stage can also be up to 4:1 or up to 2.3:1. It is preferable that polymer and aqueous dispersion medium are introduced at a constant addition rate, i.e. that the mass ratio of thermoplastic polymer to dispersion medium is constant during the process, or does not deviate by more than 10% from the preselected mass ratio.

The temperature at which the composition of the polyester is introduced into the aqueous dispersion medium is typically a temperature which is at least 5 K, often at least 10 K, and in particular at least 20 K, e.g. from 5 to 150 K, often from 10 to 100 K, and in particular from 20 to 80 K, above the melting point or softening point of the composition. This temperature is also termed mixing temperature hereinafter. The temperature at which the composition is introduced into the aqueous dispersion medium is generally a temperature of at most 300° C., e.g. from 50 to 300° C., often from 60 to 250° C., and in particular from 100 to 200° C.

Because the mixing temperature is comparatively high, the pressure at which the composition is introduced into the aqueous dispersion medium is usually above atmospheric pressure, generally being a pressure in the range from 1 to 50 bar, often from 1.1 to 40 bar, in particular in the range from 1.5 to 20 bar.

The mixing procedure can be carried out in one or more, e.g. two, three, four, or five, stages, where at least one stage is carried out in a rotor-stator mixer. In the case of a multistage process, it is preferable to carry out all of the stages in rotor-stator mixers.

In one first embodiment of the invention, the mixing takes place in one stage, i.e. the mixing apparatus comprises a rotor-stator mixer. In this process, the amounts of composition and dispersion medium required to produce the dispersion are generally introduced into the rotor-stator mixer. A method that has proven successful for this heats the dispersion medium, prior to introduction, to the desired mixing temperature or a temperature of at least 20 K below the mixing temperature, and preferably to a temperature in the range mixing temperature +/−20 K.

In a second, preferred embodiment of the invention, the mixing takes place in a plurality of stages, i.e. in a mixing apparatus which has a plurality of, e.g. two, three, four, or five, in particular three or four, rotor-stator mixers connected to one another in series. In a method which has proven successful here, the composition of the polyester and a portion of the dispersion medium are added to the first stage, i.e. to the first rotor-stator mixer, where they are mixed at a temperature above the melting or softening point of the composition, using the portion of the aqueous dispersion medium. The portion of the dispersion medium added to the first stage here is usually from 10 to 60% by weight, in particular from 15 to 40% by weight, based on the total amount of the dispersion medium introduced into the mixing apparatus. The introduction of the composition into the portion of the aqueous dispersion medium typically takes place here at a temperature which is at least 5 K, often at least 10 K, and in particular at least 20 K, e.g. in the range from 5 to 150 K, often in the range from 10 to 100 K, and in particular in the range from 20 to 80 K, above the melting or softening point of the composition. The mixing temperature in the first rotor-stator mixer is generally at most 300° C., being by way of example in the range from 50 to 300° C., often from 80 to 250° C., and in particular from 100 to 200° C. In a method which has proven successful for this, the portion of dispersion medium introduced into the first rotor-stator mixer is heated, prior to introduction, to the desired mixing temperature or to a temperature which is at least 20 K below the mixing temperature, preferably to a temperature in the range mixing temperature +/31 20 K. The aqueous dispersion produced in the first rotor-stator mixer is then transferred to a further rotor-stator mixer, where it is mixed with a further portion, or with the remaining portion, of the dispersion medium. There can be, for example, 1 or 2 further rotor-stator mixers following the second rotor-stator mixer, and the dispersion produced in the second rotor-stator mixer is mixed in the optional further rotor-stator mixer(s), e.g. in the third rotor-stator mixer, with the remaining amount, or with a further portion, of the aqueous dispersion medium. The temperature at which the dispersion produced in the first rotor-stator mixer is mixed with further dispersion medium in the second rotor-stator mixer can be the same as the temperature in the first rotor-stator mixer, or higher or lower. It is preferably below the temperature in the first rotor-stator mixer. In a method which has proven particularly successful, the mixing temperature in the first of the rotor-stator mixers connected to one another in series is at least 20 K, preferably at least 30 K, e.g. from 20 to 200 K, in particular from 30 to 120 K, above the temperature in the last of the rotor-stator mixers connected to one another in series. In particular, the temperature in the last of the rotor-stator mixers connected to one another in series is at least 5 K, in particular at least 10 K, e.g. from 5 to 200 K, in particular from 10 to 150 K, below the melting or softening point of the composition.

In one preferred embodiment of the invention, the composition of the polyester and the aqueous dispersion medium are simultaneously introduced, preferably continuously, and in particular at a constant rate by volume, into the rotor-stator mixer(s), and the dispersion is removed in similar fashion.

However, it is also possible, in a preceding step, to mix the composition of the polyester with the aqueous dispersion medium, thus obtaining a primary emulsion, at a temperature above the melting or softening point of the composition of the polyester, and to introduce this mixture to the rotor-stator mixer. Said preceding step is preferably carried out in a kneader or extruder. The resultant pre-emulsion is then introduced into the rotor-stator mixer(s). It is preferable that the pre-emulsion is kept at a temperature above the melting or softening point of the composition of the polyester.

The aqueous emulsion which is initially obtained and which is produced in the mixing apparatus, and which comprises the polymer in the aqueous dispersion medium, is then, i.e. after discharge from the mixing apparatus, quenched, i.e. rapidly cooled to a temperature below the softening point of the composition of the polyester, in order to avoid agglomeration of the polymer particles in the emulsion. The quenching process can be undertaken in a manner which is conventional per se, for example by using suitable cooling apparatuses and/or via dilution with cooled dispersion medium. The residence time of the emulsion at temperatures above the melting or softening point of the polymer, after discharge from the mixing apparatus, should preferably be no longer than 20 s, in particular no longer than 10 s. In the case of a mixing apparatus which has a plurality of rotor-stator mixers connected to one another in series, the quenching process can also take place in the second and the optional further rotor-stator mixers.

The dispersions suitable for use in the invention can be composed solely of water, optionally of surfactant substance, and of the polymers dispersed in water. However, the dispersion can also comprise further additives, e.g. fillers, antiblocking agents, dyes, leveling agents, thickeners for adjusting rheology, or wetting aids. These additions will generally account for no more than 50% by weight, based on total solids content of the dispersion. Said additions are generally added after the dispersion of the polymer(s) of the dispersion. In one embodiment of the invention, the aqueous dispersion of the polyester comprises up to 50% by weight, based on total solids content of the dispersion, of one or more lamellar pigments. Examples of lamellar pigments are talc powder, clay, and mica. Talc powder is preferred. Preferred shape factors (length to thickness ratio) are greater than 10.

The present invention also provides a process for producing a barrier coating on paper or paperboard, comprising application of at least one aqueous dispersion of at least one biodegradable polyester, as defined here, to at least one surface of the paper or paperboard.

The aqueous dispersion(s) of the at least one biodegradable polyester (hereinafter polymer dispersion) can be applied in a manner known per se. By way of example, the polymer dispersion can be applied by using suitable coating machinery to apply the polymer dispersion to the backing material, i.e. paper or paperboard. To the extent that materials in the form of webs are used, the polymer dispersion is usually applied from a trough by way of an applicator roll and leveled with the aid of an airbrush. Other successful methods of applying the polymer dispersion use, for example, the reverse gravure process, spray processes, or a doctor roller, or other coating methods known to the person skilled in the art. At least one side of the backing substrate here is provided with a coating, i.e. single- or double-sided coating of the substrate is possible. Preferred application processes for paper and paperboard are curtain coating, airbrush coating, bar coating, and doctor coating. Once the aqueous polymer dispersion has been applied to the backing substrates, volatile constituents, especially water, are vaporized. An example of a method for this, in continuous operation, passes the material through a drying tunnel, which can have been equipped with an infrared irradiation apparatus. The coated and dried packaging material is then usually passed over a cooling roll, and finally reeled.

The amount of the polymer dispersion generally applied to the backing substrate is at least 1 g/m², often at least 2 g/m², in particular at least 3 g/m², and specifically at least 5 g/m², calculated as solid per m² of the coated surface. The amount of the polymer dispersion applied to the backing substrate is preferably from 2 to 50 g/m², in particular from 3 to 40 g/m², specifically from 5 to 30 g/m², calculated as solid per m² of the coated surface. The resultant thickness of the coating is accordingly on average at least 1 μm, often at least 2 μm, in particular at least 3 μm, and specifically at least 5 μm, e.g. in the range from 2 to 50 μm, in particular from 3 to 40 μm, specifically from 5 to 30 μm.

One specific embodiment of the invention provides a process for the coating of paperboard, in particular paperboard which has been produced at least to some extent, generally to an extent of at least 30% by weight (% by weight, based on total fiber mass), in particular to an extent of at least 50% by weight, or completely, from mineral-oil-contaminated recycling paper. The total amount of the polymer dispersion (based on the total amount of the layers) applied here to the surface of the paperboard to be coated is generally at least 2 g/m², often at least 3 g/m², in particular at least 4 g/m², and specifically at least 5 g/m², calculated as solid per m². It is preferable that the total amount of the dispersion applied to the paperboard surface to be coated is in the range from 3 to 50 g/m², in particular from 4 to 40 g/m², specifically from 5 to 30 g/m², calculated as solid per m². The thickness of the coating is accordingly on average at least 2 μm, often at least 3 μm, in particular at least 4 μm, and specifically at least 5 μm, e.g. in the range from 2 to 50 μm, in particular from 3 to 40 μm, specifically from 5 to 30 μm.

Another embodiment of the invention provides a process for the coating of paper, in particular paper which has been produced at least to some extent, generally to an extent of at least 30% by weight (% by weight, based on total fiber mass), in particular to an extent of at least 50% by weight, or completely, from mineral-oil-contaminated recycling paper. The total amount of the polymer dispersion (based on the total amount of the layers) applied here to the surface of the paper to be coated is generally at least 1 g/m², often at least 2 g/m², in particular at least 3 g/m², calculated as solid per m². It is preferable that the total amount of the dispersion applied to the paper surface to be coated is in the range from 1 to 30 g/m², in particular from 2 to 25 g/m², specifically from 3 to 20 g/m², calculated as solid per m². The thickness of the coating is accordingly on average at least 1 μm, often at least 2 μm, in particular at least 3 μm, e.g. in the range from 12 to 30 μm, in particular from 2 to 25 pm, specifically from 3 to 20 μm.

In a method that has proven advantageous here, a first layer is produced in a first step via application of the aqueous dispersion to a surface of the paper or paperboard, and preferably then in at least one further step, e.g. in one, two, three, or four further steps, in particular in one or two further steps, at least one further layer arranged on the first layer is produced via application of the aqueous dispersion to the first layer obtained in the first step. Drying steps can be implemented between the individual steps. However, the individual coatings can also be applied wet-on-wet, i.e. no separate drying steps are carried out.

In a general procedure for this, in a first step, the polymer dispersion is applied in the manner described above to the substrate, i.e. to at least one surface of the paper or of the paperboard, the material is optionally dried, and then the polymer dispersion is again applied in the manner described above to the resultant coated surface of the substrate. This procedure can be repeated one or more times, until the desired weight per unit area of coating has been achieved. The statements made above are applicable here. The amount applied of the polymer dispersion is generally selected here in such a way that the amount applied in the individual steps is at least 0.5 g/m², often at least 1 g/m², in particular at least 2 g/m², specifically at least 3 g/m², typically being in the range from 1 to 30 g/m², in particular from 2 to 25 g/m², specifically from 2 to 20 g/m², or from 3 to 20 g/m², very specifically from 2 to 12 g/m², or from 3 to 12 g/m², calculated as solid per m² of the coated surface. This method gives a coating composed of a number of layers arranged on one another, where the resultant weight per unit area of coating per layer corresponds to the amount of solid applied. The number of layers, and the amount applied per layer, is naturally selected in such a way that the total amount of solid applied, and therefore the resultant weight per unit area of the coating, is preferably in the range from 2 to 50 g/m², in particular from 3 to 40 g/m², specifically from 5 to 30 g/m². In the case of paperboard, the number of layers, and the amount applied per layer, is often selected in such a way that the total amount of solid applied, and therefore the resultant weight per unit area of the coating, is preferably in the range from 3 to 50 g/m², in particular from 4 to 40 g/m², specifically from 5 to 30 g/m², calculated as solid per m². In the case of paper, the number of layers, and the amount applied per layer, is often selected in such a way that the total amount of solid applied, and therefore the resultant weight per unit area of the coating, is preferably in the range from 1 to 30 g/m², in particular from 2 to 25 g/m², specifically from 3 to 20 g/m², calculated as solid per m².

In relation to the composition of the aqueous dispersion of the at least one polyester, and also in relation to preferred polyesters, and to the substrates, the statements made above are applicable.

Another preferred embodiment of the present invention provides a process for producing a barrier coating on paper or paperboard in the manner described above, where the paper or the paperboard has been produced at least to some extent, generally to an extent of at least 30% by weight (% by weight, based on total fiber mass), in particular to an extent of at least 50% by weight, or completely, from mineral-oil-contaminated recycling paper. In particular, the invention provides a process of this type in which the paper or the paperboard is intended for the packaging of food or drink. Among these materials are sales packaging, such as cartons or paper products, and also consumer packaging, for example disposable tableware, e.g. plates, cups, or beakers made of paperboard.

The present invention equally provides coated paper or paperboard which is obtainable via the process of the invention. It features not only good barrier action both with respect to nonvolatile vegetable oils, vegetable fats, and animal fats or oils, but also good barrier action with respect to mineral oils, in particular with respect to volatile mineral oils, i.e. with respect to mineral oils which permeate in the form of gas, specifically those having from 15 to 25 carbon atoms, e.g. paraffinic and naphthenic hydrocarbons hazardous to health, and aromatic hydrocarbons. Good blocking resistance values are moreover achieved, and papers coated in the invention can be reeled without sticking.

The invention is illustrated by examples hereinafter.

I. Analysis

To determine zero-shear viscosity η₀, dynamic viscosity measurement was used on the polymer melts at 180° C., using oscillatory low-amplitude shear, at shear rates in the range from 0.01 to 500 s⁻¹ with a shear amplitude of 100 Pa, to determine viscosity curves, and zero-shear viscosity η₀ was determined from these via extrapolation to shear rate 0 s⁻¹. The viscosity curves were determined by using a “Dynamic Stress Rheometer (DSR)” from Rheometrics with plate-on-plate geometry (diameter 25 mm, gap 1 mm).

Shear viscosity of the polymer melt under the dispersing conditions was determined by means of dynamic viscosity measurement on the polymer melts with a rotary rheometer (SR5) from Rheometrics at the temperature stated in the examples.

The viscosity of the dispersion medium under dispersing conditions was determined by the Brookfield method, using an MCR301 rotary rheometer from Anton Paar GmbH at the temperature stated in the examples, where the measurement was carried out up to a shear rate of 1000/s, and viscosity under dispersing conditions was determined via extrapolation to the shear rate corresponding to the example.

Intrinsic viscosity was determined to EN ISO 1628-1 at 25° C. on a 0.5% by weight solution of the polymer in o-dichlorobenzene/phenol (1:1 w/w).

Molecular weights were determined via gel permeation chromatography (GPC) to DIN 55672-1.

Particle size distribution was determined on a 1% by weight dilution of the dispersion, via light scattering at 25° C.

Brookfield viscosity of the dispersions was determined at 20° C. to DIN EN ISO 2555 by using a Physika MCR rotary viscometer with CC 27 Couette geometry.

II. Polyesters Used

Polyester 1: Aliphatic-Aromatic Copolyester

Polybutylene terephthalate adipate produced as follows: 1095.2 g of terephthalate (47 mol %), 700 g of 1,4-butanediol (65 mol %), and 1 ml of glycerol (0.05% by weight, based on the polymer) were first mixed together with 1.1 ml of tetrabutyl orthotitanate (TBOT), and the mixture was heated to 160° C. The resultant methanol was removed by distillation within 1 h. The tank was then cooled to about 140° C. 929.5 g of adipic acid (53 mol %), 700 g of 1,4-butanediol (65 mol %) and 1 ml of glycerol (0.05% by weight, based on the polymer), together with 1.04 ml of tetrabutyl orthotitanate (TBOT), were then added to the mixture. The reaction mixture was heated to a temperature of 190° C., and the resultant water was removed by distillation at this temperature over a period of 1 h. The temperature was then increased to 240° C., and the system was evacuated stepwise. Excess 1,4-butanediol was removed by distillation in vacuo (<1 mbar) over a period of 1 h.

The number-average molar mass of the resultant copolyester was 21000 g/mol, and the weight-average molar mass was 59000 g/mol. Intrinsic viscosity IV was 106. Zero-shear viscosity η₀ at 180° C. was 136 Pa·s. Acid number was less than 1 mg KOH/g.

Polyester 2: Aliphatic-Aromatic Copolyester

Polybutylene terephthalate adipate produced as follows: 1388.5 g of terephthalate (55 mol %), 1000 g of 1,4-butanediol (85 mol %), and 1 ml of glycerol (0.05% by weight, based on the polymer) were first mixed together with 1.1 ml of tetrabutyl orthotitanate (TBOT), and the mixture was heated to 160° C. The resultant methanol was removed by distillation within 1 h. The tank was then cooled to about 140° C. 854.9 g of adipic acid (45 mol %), 523 g of 1,4-butanediol (45 mol %), and 1 ml of glycerol (0.05% by weight, based on the polymer) were then added to the mixture, together with 1.04 ml of tetrabutyl orthotitanate (TBOT). The reaction mixture was heated to a temperature of 190° C., and the resultant water was removed by distillation at this temperature over a period of 1 h. The temperature was then increased to 240° C. and the system was evacuated stepwise. Excess 1,4-butanediol was removed by distillation in vacuo (<1 mbar) over a period of 1 h.

Intrinsic viscosity IV was 91. Acid number was less than 1 mg KOH/g.

Polyester 3: Aliphatic Copolyester

Polybutylene succinate sebacate produced as follows: 6.8 kg of sebacic acid (5 mol %), 75.7 kg of succinic acid (95 mol %), 79.1 kg of 1,4-butanediol (130 mol %), and 298 g of glycerol (0.25% by weight, based on the polymer) were mixed and heated to 120° C. 11 g of tetrabutyl orthotitanate (TBOT) were then mixed with the mixture, which was heated to 200° C. The resultant water was removed by distillation within 1 h. The tank was then cooled to about 140° C. 22 g of tetrabutyl orthotitanate (TBOT) were then added to the mixture. The temperature was then increased to 250° C., and the system was evacuated stepwise. Excess 1,4-butanediol was removed by distillation in vacuo (<5 mbar) over a period of 1 h.

Intrinsic viscosity IV was 153. Zero-shear viscosity η₀ at 180° C. was 271 Pa·s. Acid number was less than 1 mg KOH/g.

III. Production of Polyester Dispersion

Dispersion Example 1:

A 12-stage inline disperser equipped with shear elements of toothed-ring type served as rotor-stator mixer.

An amount of 1.2 kg/h of polyester 1 was drawn continuously by way of the feed hopper into the single-screw extruder (Tech-line E 16 T from Dr. Collin GmbH), where it was melted at 155° C. The polymer melt was fed into the first stage disperser (4000 rpm). Shear rate was 12566 s⁻¹. The viscosity of the polymer at this shear rate was 35 Pa s. At the same time, a 7% by weight aqueous solution of a partially hydrolyzed polyvinyl alcohol (Kuraray Poval 224E) which comprised 1% by weight of an anionic surfactant (Emulphor FAS 30 from BASF SE) with solution viscosity 0.038 Pa s was fed into the inline disperser in such a way as to give solids contents of 55% by weight and, respectively, 45% by weight in the first and the fourth stage. Solids content in the tenth stage was adjusted to 43% by weight. The temperature in the first ten stages was 155° C.; the temperature in the eleventh and twelfth stages was 130° C. Total residence time was 1.2 min. Once the dispersion had left the final stage, a cooling bath was used for quenching to 20° C. The solids content of the dispersion was 43% by weight and its average particle diameter d₃₂ was 1.6 μm.

Dispersion Example 2:

A 12-stage inline disperser equipped with shear elements of toothed-ring type served as rotor-stator mixer.

An amount of 1.2 kg/h of the copolyester from polymer production example 1 (η₀=136 Pa·s) was drawn continuously by way of the feed hopper into the single-screw extruder (Tech-line E 16 T from Dr. Collin GmbH), where it was melted at 155° C. The polymer melt was fed into the first stage disperser (4000 rpm). Shear rate was 12 566 s⁻¹. The viscosity of the polymer at this shear rate was 36 Pa s, measured by a Göttfert-Rheograph 2003 capillary rheometer. At the same time, a 7% by weight aqueous solution of a partially hydrolyzed polyvinyl alcohol (Kuraray Poval 224E) which comprised 1% by weight of an anionic surfactant (Emulphor FAS30 from BASF SE) with solution viscosity 0.038 Pa s was fed into the inline disperser in such a way as to give solids contents of 60% by weight and, respectively, 50% by weight in the first and the fourth stage. Solids content in the tenth stage was adjusted to 46% by weight. The temperature in the first ten stages was 155° C.; the temperature in the eleventh and twelfth stages was 130° C. Total residence time was 1.8 min. Once the dispersion had left the final stage, a cooling bath was used for quenching to 30° C. The solids content of the dispersion was 46% by weight and its average particle diameter d₃₂ was 1.6 μm.

IV. Production of Coated Paper:

The following experiments were carried out on a miniplant spreading machine from Bachofen & Meier. The specification of the machine was as follows: operating width: 330 mm; machine speed: from 10 to 150 m/min; unwound: max. 600 mm diameter; core diameter: 70, 76, and 150 mm; application system: roll; drying: 6 dryer hoods: air heater, 47 kW, radiant heater, 14 kW; with metering system: doctor roller or doctor bar.

Example 1

Single Coating on Untreated Paperboard

The miniplant spreading machine was used to apply the dispersion of dispersion example 1 to the untreated paperboard (300 g/m² Smurfit Kappa Gernsbach) in a single pass, using a doctor roller. Machine speed was 50 m/min, amount applied: 10 g/m² (solid).

Example 2

Double Coating on Untreated Paperboard

The miniplant spreading machine was used to apply the dispersion of dispersion example 1 to the untreated paperboard (300 g/m² Smurfit Kappa Gernsbach) in two passes, using a doctor roller. Machine speed was 50 m/min, amount applied per pass: 5 g/m² (solid).

Example 3

Single Coating on Untreated Stora-Enso Paper

The miniplant spreading machine was used to apply the dispersion of dispersion example 1 to untreated paper (Stora-Enso Kabel 37 g/m² LWC) in a single pass using a doctor bar. Machine speed was 50 m/min, amount applied: 10 g/m² (solid).

Example 4

Single Coating on Untreated Magnostar Paper

The miniplant spreading machine was used to apply the dispersion of dispersion example 1 to untreated paper (untreated Magnostar paper, 58 g/m²) in a single pass using a doctor bar. Machine speed was 50 m/min, amount applied: 10 g/m² (solid).

Example 5

Double Coating on Untreated Magnostar Paper

The miniplant spreading machine was used to apply the dispersion of dispersion example 1 to untreated paper (untreated Magnostar paper, 58 g/m²) in two passes using a doctor bar. Machine speed was 50 m/min, amount applied in the pass 5 g/m² (solid), and in the second pass 4 g/m² (solid).

V Testing of Barrier Properties

• • (1) Barrier test with respect to gaseous mineral oil constituents (test method 1) 9 ml of hexane are placed in a vessel with a sponge, and the system is sealed with a lid which has an aperture and a sealing ring (internal diameter 63 mm). The aperture has been securely sealed with the barrier material to be tested, and this barrier material does not come into contact with the hexane-saturated sponge. The weight loss from the vessel is measured at various junctures. The weight loss is a measure of the amount of hexane escaping by way of the gas phase through the barrier material and is therefore a measure of the quality of the barrier action with respect to gaseous mineral oil constituents. The weight loss in grams is recalculated to represent 1 m² of paper area and is then stated as g/m² d (per day). Table 1 below collates the results.

	Untreated paperboard	Hexane migration
	300 g/m2 Smurfit	[g/m2 d]
	Kappa Gernsbach	1 h	4 h
	Without coating	7768	7063
	Example 1	4576	4760
	Example 2	96	81

Barrier test with respect to edible oil/oleic acid (test example 2)

The “Oil Penetration Test” was used to study the barrier properties of the uncoated papers/paperboards and of the papers/paperboards coated with the polyester dispersions. To this end, 2 ml of oleic acid was used to wet the coated paper side. The paper was then stored for a defined time at 60° C. The reverse side of the coated paper was then assessed visually at various junctures to determine the extent of staining. 100% means complete penetration, and 0% means no penetration.

Test paper or	Extent of staining
test paperboard	After 30 min	After 1 h	After 4 h	After 7 h
Untreated paperboard	100%	100%	100%	100%
00 g/m2 Smurfit
Kappa Gernsbach
without coating
Stora-Enso Kabel	100%	100%	100%	100%
37 g/m2 LWC
without coating
Magnostar 58 g/m2	100%	100%	100%	100%
without coating
Example 1	5%	6%	8%	10%
Example 2	0%	0%	0%	0%
Example 3	15%	40%	100%	100%
Example 4	15%	40%	100%	100%
Example 5	0%	0%	1%	n.d.
n.d. = not determined

Claims

1.-20. (canceled)

21. The use of an aqueous dispersion of at least one biodegradable polyester in the form of a coating for improving the barrier properties of packaging material made of paper or paperboard with respect to mineral oils.

22. The use according to claim 21, where the packaging material has been produced at least to some extent from mineral-oil-contaminated recycling paper.

23. The use according to claim 21, where the packaging material is intended for the packaging of food or drink.

24. The use according to claim 21, where the weight per unit area of the coating is from 2 to 50 g/m2.

25. The use according to claim 21, where the coating has at least two layers arranged on top of one another.

26. The use according to claim 25, where the coating weight per unit area of each of the layers is from 1 to 30 g/m2.

27. The use according to claim 21, where the content of biodegradable polyester, based on the total solids content of the polyester dispersion, accounts for at least 30% by weight.

28. The use according to claim 21, where the biodegradable polyester is selected from the group of the aliphatic polyesters, aliphatic copolyesters, aliphatic-aromatic copolyesters, and mixtures of these.

29. The use according to claim 21, where the polyester consists essentially of: where the molar ratio of component A to component B is in the range from 0.4:1 to 1:1, and components A and B account for at least 80% by weight of the polyester.

a) at least one dicarboxylic acid component A, which is composed of a1) at least one aliphatic or cycloaliphatic dicarboxylic acid or ester-forming derivatives of these, or a mixture thereof, and a2) optionally one or more aromatic dicarboxylic acids which have no sulfonic acid group, or ester-forming derivatives of these, or a mixture thereof, a3) optionally one or more aromatic dicarboxylic acids which have at least one sulfonic acid group, or ester-forming derivatives of these, or a mixture thereof;

b) at least one diol component B selected from aliphatic and cycloaliphatic diols and mixtures of these;

c) optionally one or more other bifunctional compounds C which react to form bonds with carboxylic acid groups or with hydroxy groups; and

d) optionally one or more compounds D which have at least three functionalities which react to form bonds with carboxylic acid groups or with hydroxy groups;

30. The use according to claim 29, where the polyester consists essentially of:

a) at least one dicarboxylic acid component A which is composed of a1) from 35 to 90 mol % of at least one aliphatic or cycloaliphatic dicarboxylic acid, or ester-forming derivatives of these, or a mixture thereof, and a2) from 10 to 65 mol % of one or more aromatic dicarboxylic acids or ester-forming derivatives of these, or a mixture thereof; a3) from 0 to 5 mol % of one or more aromatic dicarboxylic acids which have at least one sulfonic acid group, or ester-forming derivatives of these, or a mixture thereof, where the mol % data for components a1), a2), and a3) give a total of 100 mol %;

b) from 98 to 102 mol %, based on the total amount of components a1) and a2), of at least one diol component B selected from aliphatic and cycloaliphatic diols and mixtures of these;

c) from 0 to 2% by weight, based on the total weight of the polyester, of one or more other bifunctional compounds C which react to form bonds with carboxylic acid groups or with hydroxy groups; and

d) from 0 to 2% by weight, based on the total weight of the polyester, of one or more compounds D which have at least 3 functionalities which react to form bonds with carboxylic acid groups or with hydroxy groups.

31. The use according to claim 21, where the number-average molecular weight of the polymer is in the range from 5000 to 1 000 000 daltons.

32. The use according to claim 21, where the weight-average molecular weight of the polymer is in the range from 10 000 to 5 000 000 daltons.

33. A process for producing a barrier coating on paper or paperboard via application of at least one aqueous dispersion of at least one biodegradable polyester as defined in claim 21, to at least one surface of the paper or paperboard, where a first layer is produced in a first step via application of the aqueous dispersion to a surface of the paper or paperboard, and then at least one further layer, arranged on the first layer, is produced in at least one further step via application of the aqueous dispersion to the first layer obtained in the first step.

34. The process according to claim 33, where the amount of the polyester dispersion applied in each step is such that the resultant weight per unit area of the coating is in the range from 1 to 30 g/m2 per layer.

35. The process according to claim 33, where the amount of the polyester dispersions applied in the steps is such that the resultant total weight per unit area of the coating is in the range from 2 to 50 g/m2.

36. The process according to claim 33, where the content of biodegradable polyester, based on the total solids content of the polyester dispersion, accounts for at least 30% by weight.

37. The process according to claim 33, where the biodegradable polyester is a polyester according to claim 28.

38. The process according to claim 33, where the paper or the paperboard has been produced at least to some extent from mineral-oil-contaminated recycling paper.

39. The process according to claim 33, where the coated paper or the coated paperboard is intended to be packaging material for the packaging of food or drink.

40. A coated paper or paperboard, obtainable according to claim 33.