RECYCLABLE BARRIER PAPER

A barrier paper having a paper substrate having a front side and a back side opposite the front side, and a barrier layer disposed to the front side of the paper substrate. The barrier layer has of a polymeric binder and a wax based on a vegetable oil, the use of a barrier paper as wrapping paper, lining paper, paper for inner-bag packaging, interleaving paper and/or release paper for foods, and also to a method for producing a barrier paper.

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Description
CROSS REFERENCE TO RELATED APPLICATIONS

This is a U.S. national stage of Application No. PCT/EP2018/085566 filed Dec. 18, 2018. Priority is claimed on German Application No. DE 10 2017 131 277.3 filed Dec. 22, 2017 the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a barrier paper, to the use of a barrier paper of the invention as wrapping paper, lining paper, paper for inner-bag packaging, interleaving paper and/or release paper for foods, and a method for producing a barrier paper.

2. Description of Related Art

Customers of foods that are sold loose, such as sausage, cheese, or bakery products, typically receive their products, for reasons of hygiene or freshness retention, in packaging. Stringent requirements with regard to packaging are imposed in particular in the case of fatty foods. Where conventional, paper-based packaging is used, the packaging material in the case of fatty foods may be penetrated by the fat from the food. This may result in the packaging material softening and tearing, or in the fat contaminating other articles if they come into contact with the packaging.

WO 2007/050964 A1 describes a fat-resistant and water-resistant article that comprises a coating of a paraffin wax and polyvinyl alcohol.

US 2003/0152707 A1 describes a carrier coated with a wax made from a vegetable oil, and which is highly resistant to water.

DE 10 2014 119 572 A1 describes a packaging paper for foods that has an areal density of between 20 g/m2 and 40 g/m2 and that has a mass fraction of filler of less than 20%, based on the mass of the uncoated paper. The packaging paper at least on one side has a coating that comprises a polymer-encapsulated vegetable oil, talc, and a binder.

Fatty foods are frequently packaged using a wood-free, fatproof “greaseproof” paper, which by virtue of wet beating of the fibrous materials, has a certain fat resistance. Frequently, however, the fat resistance of these greaseproof papers is inadequate.

Wet beating is achieved by wide bars set widely apart or by basalt rock barring in conjunction with a long beating time. The fibers, rather than being shredded, are squeezed. This produces a high swelling fiber mucilage, a slimy and greasy pulp, which undergoes only slow dewatering on the paper machine. The paper acquires a high density, but loses opacity. It becomes glassily translucent. Where the extent of fiber shortening is low, the term “long wet” is used. Fibers shortened to a greater extent are referred to as “short wet”. Where the substrate is made predominantly short wet fibers, its tear initiation resistance and tearing resistance are only low.

Frequently used as a more fat-resistant alternative to greaseproof paper is composite packaging. Composite packaging may consist, for example, of a composite formed from a paper and from a polymeric and/or aluminum foil. If no polyethylene coating (PE) takes place, fluorocarbons can be used as water-repellent chemicals. Paper here is coated for example on one side with polyethylene, frequently in an extrusion process, or with an aluminum foil. Composite packaging of this kind is notable for high fat resistance. This composite packaging, however, cannot easily be passed for paper recycling, since first it is necessary for the foil layer to be removed. Nor is it possible to compost these composites, because the polymeric or aluminum foils used do not biodegrade.

Moreover, the growing concern about the scarcity of fossil, nonrenewable resources, such as petroleum or natural gas, has resulted in a steadily growing interest in the production of materials from renewable raw materials. Reference may be made in this context to, for example, polyethylene furanoate, a plastic based on 2,5-furandicarboxylic acid, the starting substances of which may be produced from sugars. It has emerged, however, that the existing polymers produced from renewable raw materials either are nonbiodegradable or do not have the properties needed for use in packaging materials.

The requirements imposed on the barrier paper, namely a high and/or defined resistance to penetration by fats, oils, water, and water vapor, and high reusability or biodegradability, are requirements that typically contradict one another. Within industry, therefore, there is a great demand to provide packaging paper for food that can be produced wholly or predominantly from renewable raw materials and at the same time can be effectively reused or biodegraded.

SUMMARY OF THE INVENTION

It is an object of one aspect of the present invention to provide a barrier paper for food contact that exhibits high resistance to fats, and/or oils, and/or moisture, and/or water or water vapor, and at the same time can be produced wholly or predominantly from renewable raw materials. Additionally it is desirable if the barrier paper can be readily reused or biodegraded, i.e., composted.

One aspect of the invention is a barrier paper 10 comprising:

    • a) a paper substrate 11 having a front side and a back side opposite the front side,

and

    • b) a barrier layer 12 disposed to the front side and/or the back side of the paper substrate,

wherein the barrier layer 12 comprises or consists of a polymeric binder and a wax based on a vegetable oil.

Surprisingly it has emerged that barrier papers according to one aspect of the invention exhibit high resistance to fats and/or oils and/or moisture and at the same time can be produced wholly or predominantly from renewable raw materials. As a result of the use of a polymeric binder, surprisingly, the barrier layer is designed such that it does not part from the paper substrate or that the wax transfers to other articles or the foods.

In the context of one aspect of the invention, a wax based on a vegetable oil is understood to mean a wax obtained by chemical modification of a vegetable oil. The chemical modification may, for example, be a partial or complete hydrogenation with a metallic catalyst, for example nickel, and hydrogen, wherein all or some of the double bonds in the oil are hydrogenated to single bonds. Unlike vegetable oils, waxes are not in liquid form but in solid form at 20° C. The effect of the chemical modification of the vegetable oil is thus an increase in the melting point.

A vegetable oil is understood to mean a fatty acid triglyceride that is obtained from plants or plant parts. The oil is typically obtained by pressing, extraction or refining of the oils from the plants or plant parts. The obtaining of the oils is known to the person skilled in the art. If plant seeds are used for obtaining oil, these are referred to as oilseeds. The oil in the seeds is in the form of lipids that constitute the cell membranes and energy reserves thereof. Depending on the proportion of unsaturated fatty acids in the oil, a distinction is made between nondrying oils (for example olive oil), semidrying oils (for example soybean oil or rapeseed oil) and drying oils (for example linseed oil or poppyseed oil). The term “drying” here does not mean evaporation, but rather the solidification of the oil caused by oxidation and polymerization of the unsaturated fatty acids. Preference is given to the use of semidrying and drying oils as starting material for production of the waxes used in accordance with one aspect of the invention.

Possible sources for vegetable oil are açaí oil, algae oil, argan oil (from the fruit of the argan tree), avocado oil (from the fruit flesh of the avocado from the avocado tree), babaçu oil, cottonseed oil (from the seeds of the cotton plant), borage oil or borageseed oil (from the seeds of the borage plant), cupuaçu butter, cashewshell oil, safflower oil (also called “saflor oil”, from the seeds of the safflower or carthamus), peanut oil (from the fruit of the peanut plant), hazelnut oil (from hazelnuts from the hazelnut bush), hemp oil (from the seeds of edible hemp), Jatropha oil (from the seeds of Jatropha curcas), jojoba oil (actually a liquid wax; from the seeds of the jojoba bush), Camellia oil (from the seeds of Camellia oleifera, Camellia sinensis or Camellia japonica), cocoa butter, coconut oil (from the seed flesh of the coconut, the tree fruit of the coconut palm), pumpkinseed oil (also referred to as seed oil; from the seed kernels of the Styrian oil pumpkin), linseed oil (from ripe linseeds from flax), false flax oil (from the seeds of the false flax, Brassicaceae family), macadamia oil (from the nuts of the macadamia tree), maize kernel oil (from the kernels of maize), almond oil (from almonds from the almond tree), mango butter (from Mangifera indica), apricot kernel oil (from the apricot kernel—i.e., the almond of the apricot stone—the apricot), poppyseed oil (from the seed grains of the poppy), evening primrose oil, olive oil (from the fruit flesh and core of the olive, the fruit of the olive tree), palm oil (from the fruit flesh of the palm fruit, the fruit of the oil palm), palm kernel oil (from the kernels of the palm fruit, the fruit of the oil palm), papaya oil, pistachio oil, pecan nut oil, perilla oil from the seeds of the perilla plant (shiso, sesame leaf), rapeseed oil (from the seeds of rape, Brassicaceae family), rice oil, castor oil (from the seeds of the castor oil plant), sea buckthorn oil (from the fruit flesh of the sea buckthorn berry, the fruit of the sea buckthorn bush), sea buckthorn kernel oil (from the kernels of the sea buckthorn berry, the fruit of the sea buckthorn bush), mustard oil (from the seed kernels of black mustard), black cumin oil (from the seeds of the fruit capsule of the black cumin plant), sesame oil (from the seeds of the sesame plant), shea butter (from the seeds of the shea nut tree), soya oil (from the beans of the soybean), sunflower oil (from the kernels of the sunflower), tung oil, walnut oil (from the kernels of the nuts from the walnut tree), watermelonseed oil, grapeseed oil (from the kernels of the fruits (grapes) of the grape plant or grapevine), wheat germ oil (from the germ of wheat) and/or cedar oil (from the wood of the Lebanon cedar), and the like. This list should not be regarded as conclusive; it shows ways of obtaining vegetable oils that can be converted to a wax used in accordance with the invention.

Preference is given in accordance with one aspect of the invention to a barrier paper wherein the wax based on a vegetable oil is a wax based on an oil selected from the list encompassing palm oil, coconut oil, poppyseed oil, olive oil, linseed oil, soybean oil, sunflower oil, safflower oil, and rapeseed oil, the wax based on a vegetable oil preferably being a wax based on a soybean oil, i.e., soybean oil wax or soy wax.

Our own investigations have shown that waxes made from the oils specified as preferred above have particularly good properties. The waxes produced from these oils are notable for high durability and can be produced with high melting points. The waxes used in accordance with one aspect of the invention, namely palm oil wax, coconut oil wax, poppyseed oil wax, olive oil wax, linseed oil wax, soybean oil wax, sunflower oil wax, safflower oil wax, and rapeseed oil wax, show a significant increase in resistance to fats and/or oils and/or moisture when used in barrier papers of the invention. In particular, the use of soybean oil wax is preferred in accordance with the invention. Our own investigations have shown that, when soybean oil wax is used, not only the resistance to fat, oil, and moisture but also very low water vapor permeability can be obtained. Soybean oil wax additionally has the advantage that it can be produced in taste- and odor-neutral form.

Preference is given in accordance with the invention to barrier papers wherein the wax has a melting point above 40° C., preferably above 50° C., more preferably above 60° C.

Our own investigations have shown that it is already possible to achieve very good results when waxes having a melting point above 20° C. are used. However, it has been found that, surprisingly, when waxes having a melting point above 40° C. are used, the resistance of the barrier papers to mechanical stress can be enhanced. This resistance is enhanced even further at even higher melting points of the waxes. Our own investigations have additionally shown that the optimal melting point of the waxes is in the range from 60 to 80° C. if the barrier papers are to be used at temperatures between 6° C. and 30° C. If the barrier papers are also to be employed at higher temperatures, it may be advisable to use a wax having a higher melting point.

Preference is given in accordance with one aspect of the invention to barrier papers wherein the mass fraction of the wax based on a vegetable oil in the barrier layer is 6 to 98%, preferably 20 to 90%, more preferably 50 to 89%, very preferably 50 to 78%, based on the total mass of the barrier layer.

Our own investigations have shown that, surprisingly, there is a disproportionately significant decrease in fat, oil, and moisture barrier properties in the case of a mass fraction of the wax based on a vegetable oil below 6%, whereas excellent barrier properties can be obtained in the case of a mass fraction of the wax based on a vegetable oil above 98%, but there is a disproportionately significant decrease in the mechanical stability of the barrier layer. Our own investigations have shown that particularly good barrier papers with optimal barrier and mechanical properties can be obtained when the mass fraction of the wax based on a vegetable oil is 50 to 89%, preferably 50 to 78%.

Suitable polymeric binders are all binders that are customary in papermaking. Our own investigations, however, have shown that a suitable selection of the binder may significantly improve the mechanical properties of the barrier layer and/or the biodegradability of the barrier paper. Our own investigations have shown that it is advantageous and therefore preferred in accordance with the invention if the polymeric binder is a crosslinked or noncrosslinked binder selected from the group consisting of starch, polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, ethylene-vinyl alcohol copolymer, a combination of polyvinyl alcohol and ethylene-vinyl alcohol copolymer, ethylene-vinyl acetate copolymer, silanol group-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, modified polyethylene glycol, unmodified polyethylene glycol, α-isodecyl-ω-hydroxy-poly(oxy-1,2-ethanediyl), styrene-butadiene latex, styrene-acrylate polymers, acrylic copolymers, and mixtures thereof.

Our own investigations have revealed that barrier papers of one aspect of the invention have particularly high resistance to fat, oil, and moisture if the polymeric binder is one or more styrene-acrylate polymers or the binder comprises the latter.

Of the binders stated above, ethylene-vinyl alcohol copolymer and polyvinyl alcohol are the least preferred. Particular preference is therefore given to barrier papers of one aspect of the invention, which do not comprise ethylene-vinyl alcohol copolymer and/or polyvinyl alcohol in the barrier layer.

It is preferred in accordance with one aspect of the invention if the barrier layer comprises no ethylene.

It is preferred here in accordance with one aspect of the invention here if the mass fraction of the polymeric binder in the barrier layer is 94 to 2%, preferably 80 to 10%, more preferably 50 to 11%, based on the total mass of the barrier layer.

Our own investigations have shown that an amount of polymeric binders below a mass fraction of 2% leads to barrier papers wherein there is a disproportionately significant decrease in the mechanical resistance of the barrier layer. Where an amount of polymeric binders is above a mass fraction of 94%, the mechanical resistance of the barrier layer is indeed sufficiently high, although it has emerged that there is a disproportionately significant decrease in the barrier properties with respect to fat, oil, and moisture. Our own investigations here have revealed that particularly good barrier papers having optimum barrier properties and mechanical properties can be obtained if the amount of polymeric binders amounts to a mass fraction 50 to 11%.

It is particularly preferred here in accordance with one aspect of the invention if the mass fraction of the polymeric binder in the barrier layer is 94 to 2% and the mass fraction of the wax in the barrier layer is 6 to 98%, and it is further preferred if the mass fraction of the polymeric binder in the barrier layer is 80 to 10% and the mass fraction of the wax in the barrier layer is 80 to 90%, and it is preferred still further if the mass fraction of the polymeric binder in the barrier layer is 50 to 11% and the mass fraction of the wax in the barrier layer is 50 to 89%.

Preferred in accordance with one aspect of the invention are barrier papers wherein the mass per unit area of the barrier layer is in the range from 1.5 to 8 g/m2, preferably in the range from 2.0 to 5.5 g/m2, more preferably in the range from 3.0 to 5.0 g/m2. It has surprisingly emerged that barrier papers with the low masses per unit area as specified here have very good resistances with respect to fat, oil, and moisture. While the resistance can be slightly improved by increasing the mass per unit area, the improvement is only minimal, and so the slight improvement is not justified by increased consumption of material. At a mass per unit area of below 1.5 g/m2, the resistance of the pure carrier substrate is indeed likewise improved, but the resistance is not always sufficient for certain areas of application (e.g., very fatty and moist foods). Our own investigations have shown that an optimum resistance can be obtained if the mass per unit area of the barrier layer is in the range from 3.0 to 5.0 g/m2.

Our own investigations have shown that it is particularly advantageous if the polymeric binder consists of two or more binders and at least one binder is an anionic binder. An anionic binder here is understood to mean a binder that comprises a plurality of negative charges, which are stabilized by cations (e.g., metal cations or ammonium).

In the context of the present invention, a polymeric binder is understood to mean a binder which has been synthesized by polycondensation from a multitude of molecules, and in which one or more kinds of atoms or atomic moieties (called repeat units) are strung together repeatedly, with the number of repeat units per molecule being more than 25.

It is preferred here in accordance with one aspect of the invention if the glass transition temperature of the anionic binder as determined by differential scanning calorimetry (DSC) is less than or equal to 120° C. Our own investigations have shown that at a glass transition temperature of above 120° C., it is very difficult to produce the barrier layer, and the barrier papers that are produced do not have such good properties as barrier papers of the invention that have been produced using an anionic binder having a glass transition temperature of less than or equal to 120° C.

It is preferred in accordance with one aspect of the invention here if the anionic binder is a copolymer.

Suitable anionic binders are, for example, partly or fully deprotonated polyacrylic acid (or copolymers thereof, with acrylic esters, for example), partly or fully deprotonated polymethacrylic acid (or copolymers thereof, with methacrylic esters, for example), copolymers of polyacrylic esters (preferably methyl or ethyl esters), copolymers of polymethacrylic esters (preferably methyl or ethyl esters), or polyacrylamides, or copolymers thereof.

It is preferred in accordance with one aspect of the invention if an aqueous solution or dispersion of the anionic binder has a basic pH, where present in dispersion or solution in water with a mass fraction of 10%, and preferably in the range from 8 to 10.

To determine the pH of the anionic binder, an aqueous solution or dispersion of the anionic binder can be prepared that has a mass fraction of 10%, and the pH can be determine by customary means.

In a likewise preferred aspect of the present invention, the barrier layer (12) additionally comprises a wax based on saturated hydrocarbons.

Our own investigations have surprisingly shown that the combination of a wax based on a vegetable oil and a wax based on saturated hydrocarbons leads to particularly good resistance toward fats and/or oils and/or moisture and/or water or water vapor. The combination of saturated hydrocarbons and fatty acid triglyceride waxes appears to lead to layers having particularly high molecular densities. Without wishing to be tied to any particular theory, the high molecular density may be explained by the saturated hydrocarbons filling up the lipophilic parts of the fatty acid triglyceride waxes. As a result, a resistance is achieved which cannot be achieved only with the fatty acid triglyceride waxes or with waxes based on saturated hydrocarbons. The combination of a wax based on a vegetable oil and a wax based on saturated hydrocarbons therefore exhibits a synergistic effect, resulting in particularly good resistance with respect to fats and/or oils and/or moisture and/or water or water vapor.

This synergistic effect is particularly pronounced if the wax based on saturated hydrocarbons is octacosane and/or the wax based on a vegetable oil is a wax based on soybean oil.

Preference is given in accordance with the invention to barrier papers wherein the wax based on saturated hydrocarbons has a melting point above 40° C., preferably above 50° C., more preferably above 60° C.

Preference is given in accordance with the invention to barrier papers wherein the wax based on saturated hydrocarbons comprises or consists of one, two, three or more than three alkanes selected from the group consisting of heneicosane, docosane, tricosane, tetracosane, pentacosane, hexacosane, heptacosane, octacosane, nonacosane, triacontane, hentriacontane, dotriacontane, tritriacontane, tetratriacontane, pentatriacontane, hexatriacontane, heptatriacontane, octatriacontane, and nonatriacontane, preferably selected from the group consisting of hexacosane, heptacosane, octacosane, nonacosane, and triacontane. Particular preference is given in accordance with the invention to barrier papers wherein the wax based on saturated hydrocarbons is a wax based on octacosane.

More preferably in accordance with the invention, the acrylate copolymer in the barrier layer is a copolymer having an average molar mass in the range from 50000 to 150000 g/mol, preferably in the range from 80000 to 130000 g/mol, more preferably in the range from 90000 to 100000 g/mol. The average molar mass is determined here with the aid of gel permeation chromatography (GPC) with tetrahydrofuran (THF; tetramethylene oxide; 1,4-epoxybutane; oxacyclopentane) as solvent, polystyrene as standard, and detection by RI detector (refractive index detector).

More preferably in accordance with the invention, the acrylate copolymer in the barrier layer is a copolymer prepared using two, three, four, five, six or all monomers selected from the group consisting of methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, and styrene.

Through a selection of the monomers used for preparation of the acrylate copolymer, it is possible to optimize the properties of the resulting acrylate copolymer. Our own investigations have surprisingly shown here that an acrylate copolymer that has been prepared from methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate and/or styrene has particularly good barrier properties.

As well as methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, and styrene, further monomers may have been used here for preparation of the acrylate copolymer, or the copolymer has been prepared from two, three, four, five, six or all monomers selected from the group consisting of methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, and styrene.

More preferably in accordance with one aspect of the invention, the acrylate copolymer is a random copolymer.

Particularly preferred in accordance with one aspect of the invention is a barrier paper (10) comprising

    • a) a paper substrate 11 comprising a front side and a back side opposite the front side,

and

    • b) a barrier layer 12 disposed to the front side and/or back side of the paper substrate and consisting of or comprising
      • i) an acrylate copolymer having an average molar mass in the range from 50000 to 150000 g/mol, the acrylate copolymer having been prepared from two, three, four, five, six or seven monomers selected from the group consisting of methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, and styrene,
      • and
      • ii) a wax based on saturated hydrocarbons, the wax based on saturated hydrocarbons preferably being octacosane or the wax based on saturated hydrocarbons preferably comprising octacosane,
      • and
      • iii) a wax based on a vegetable oil.

Preference is given in accordance with the invention to a barrier paper wherein the mass ratio between the polymeric binder and the wax based on saturated hydrocarbons is 999:1 to 70:30, preferably 99:1 to 80:20, more preferably 95:5 to 85:15.

Preference is given in accordance with one aspect of the invention to a barrier paper wherein the barrier paper additionally comprises an interlayer 13 and the interlayer 13 is disposed between the paper substrate and the barrier layer. In our own investigations it has emerged that the properties of the resultant barrier paper are particularly good if the barrier layer is not applied directly to the base paper as paper substrate, but instead first an interlayer is applied to the paper substrate.

It is preferred in accordance with one aspect of the invention here if the interlayer 13 comprises a pigment.

Preference is given in accordance with the invention to a barrier paper if the pigment is an organic pigment, inorganic pigment, or a mixture of organic pigments and inorganic pigments.

Preference is given in accordance with one aspect of the invention to a barrier paper if the pigment is an inorganic pigment selected from the list consisting of calcined kaolin, kaolin, kaolinite, hydrated magnesium silicate, silicon oxide, bentonite, calcium carbonate, aluminum hydroxide, aluminum oxide, and boehmite.

Our own investigations have shown that particularly good properties can be obtained if the pigment is lamellar in formation, preferably with an aspect ratio of 5 to 100, more preferably of 15 to 100, very preferably of 20 to 80. The aspect ratio is the quotient formed between the diameter and the thickness of the lamellar pigment platelet prior to mixing with the further components. An aspect ratio of 20 means that the diameter of the platelet is 20 times greater than the thickness of the platelet. Kaolin, kaolinite, and talc, for example, are lamellar and therefore particularly preferred as pigment.

Preference is given in accordance with one aspect of the invention to a barrier paper if the mass fraction of the pigment in the interlayer is 5 to 60%, preferably 15 to 40%, more preferably 20 to 40%, based on the total mass of the interlayer.

Preference is given in accordance with one aspect of the invention to a barrier paper if the interlayer comprises a binder and the binder is preferably a crosslinked or noncrosslinked binder selected from the group consisting of starch, polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, ethylene-vinyl alcohol copolymer, a combination of polyvinyl alcohol and ethylene-vinyl alcohol copolymer, ethylene-vinyl acetate copolymer, silanol group-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, acrylate copolymer, modified polyethylene glycol, unmodified polyethylene glycol, α-isodecyl-ω-hydroxy-poly(oxy-1,2-ethanediyl), styrene-butadiene latex, styrene-acrylate polymers, film-forming acrylic copolymers, and mixtures thereof.

Preference is given in accordance with one aspect of the invention to a barrier paper if the binder comprises or consists of one or more acrylate copolymers and/or styrene-acrylate polymers.

Preference is given in accordance with one aspect of the invention to a barrier paper if the mass fraction of the binder in the interlayer is 95 to 40%, preferably 85 to 60%, more preferably 80 to 60%, based on the total mass of the interlayer.

Preferred in accordance with one aspect of the invention are barrier papers wherein the mass per unit area of the interlayer is in the range from 1.5 to 6 g/m2, preferably in the range from 2.0 to 5.5 g/m2, more preferably in the range from 2.0 to 4.8 g/m2.

Preferred in accordance with one aspect of the invention are barrier papers wherein the paper substrate features a short-fiber pulp having a Schopper-Riegler freeness of at least 30° SR and a long-fiber pulp having a Schopper-Riegler freeness of at least 25° SR and wherein the paper substrate comprises at least a mass fraction of 50% of short-fiber pulp, based on the total mass of short-fiber pulp and long-fiber pulp.

It is further preferred if the short-fiber pulp has a Schopper-Riegler freeness of at least 35° SR, preferably of at least 39° SR, and/or the long-fiber pulp has a Schopper-Riegler freeness of at least 30° SR, preferably of at least 33° SR.

It is preferred in accordance with one aspect of the invention if the paper substrate comprises a mass fraction of at least 70% of short-fiber pulp, preferably between 70 and 75% of short-fiber pulp, based on the total mass of short-fiber pulp and long-fiber pulp.

It is preferred in accordance with one aspect of the invention if the barrier paper on one side or on both sides has a Bekk smoothness, determined to ISO 5627, in the range from 100 to 1200 s. It is preferred here if the barrier layer has a Bekk smoothness in the range from 100 to 1200 s insofar as the barrier layer is an outer layer. In deviation from ISO 5627, the Bekk smoothness in this case is determined not on both sides of the barrier paper, but only on the barrier layer of the barrier paper.

Preference is given in accordance with one aspect of the invention to a barrier paper if the barrier paper has a water vapor permeability to DIN 53122-1 of less than or equal to 300 g/(m2d), preferably less than or equal to 250 g/(m2d), more preferably of less than or equal to 150 g/(m2d).

Surprisingly it has emerged that the barrier paper of one aspect of the invention has not only a very high resistance toward fat but also a low water vapor permeability. A low water vapor permeability in the case of packaging is desirable in the case of foods because the packaged foods do not dry out prematurely and remain fresh for longer.

Preference is given in accordance with one aspect of the invention to a barrier paper if the barrier paper has a KIT rating of at least 5, preferably of at least 8, more preferably of at least 12, measured according to the Tappi 559 method.

Our own investigations have shown that barrier papers of one aspect of the invention can have a KIT rating of more than 12 and hence exhibit excellent bed resistance, situated within the same range as the fat resistance of barrier papers coated with polymeric or aluminum foil.

Preference is given in accordance with one aspect of the invention to a barrier paper if the barrier paper has a fat permeability with turpentine oil to Tappi 454 of at least 1300 s, preferably of at least 1500 s, more preferably of at least 1800 s.

Preference is given in accordance with one aspect of the invention to a barrier paper wherein the barrier paper has a fat permeability of at least level 5, preferably of at least level 3, more preferably of at least level 1, measured by the DIN 53116 method.

Preference is given in accordance with one aspect of the invention to a barrier paper if the mass per unit area of the barrier paper is in the range from 30 to 120 g/m2, preferably in the range from 35 to 80 g/m2, more preferably in the range from 40 to 50 g/m2.

In certain embodiments of the paper of one aspect of the invention it is advantageous if the carrier paper used is paper, paperboard or cardboard. Especially where paperboard or cardboard is used as carrier paper, the mass per unit area of the resultant barrier paper is higher than 120 g/m2. Preferably the mass per unit area is in the range from 120 g/m2 to 600 g/m2 in the case of cardboard and more than 600 g/m2 in the case of cardboard.

Preference is given in accordance with one aspect of the invention to a barrier paper if the wax based on a vegetable oil and the polymeric binder are distributed homogeneously in the barrier layer. In this case it is not absolutely necessary for the wax and the polymeric binder to be thoroughly mixed; instead, there may be local differences in concentration, resulting from the specific production using small wax particles. In accordance with the invention, however, the wax is not encapsulated—in other words, it does not have a core-shell structure.

Preferred in accordance with one aspect of the invention is a barrier paper for use as wrapping paper, lining paper, interleaving paper and/or release paper for foods, preferably for the packaging of bakery products, sandwiches, bread, burgers, meat products, fish, sausage products and/or cheese.

In one embodiment of the barrier paper of one aspect of the invention, the paper substrate is coated both to the front side and to the back side with the barrier layer, and preferably there is an interlayer disposed in each case between the barrier layers and the paper substrate. Regarding the embodiment of the interlayers, reference is made to the observations above concerning the interlayer.

Especially in the embodiment with two barrier layers, but also in the embodiment with only one barrier layer, it has emerged, surprisingly, that the barrier papers of the invention not only have excellent resistance toward fats and/or oils and/or moisture, but also, moreover, possess a barrier effect or blocking effect with respect to mineral oils. Mineral oils occur frequently in recycled papers or paperboards that are not intended for the direct packaging of foods. Where, however, they do come into contact with foods, as for example if foods are dispatched in a cardboard box, it is impossible to rule out mineral oils transferring onto the food, even if the foods are packed in a separate packaging. In the past, for example, mineral oil residues have been found in chocolate from Advent calenders, having been absorbed from the chocolate by the contact of the chocolate with the cardboard packaging. Barrier papers of the invention are notable, surprisingly, for not only preventing the emergence of fats, oils, and moisture from the food to the outside, but also, additionally, protecting the food packaged therewith from contamination by mineral oils.

It is also possible, for example, to produce packaging cartons from barrier papers of the invention, these cartons having the barrier layer in the interior of the packaging carton. Alternatively it is also possible to produce inner-bag packaging from barrier papers of one aspect of the invention.

A further aspect of the present invention relates to the use of a barrier paper of the invention as wrapping paper, lining paper, paper for inner-bag packaging, interleaving paper and/or release paper for foods, preferably for the wrapping, lining, interleaving and/or separation of bakery products, fried and/or deep-fried products, snack products, sandwiches, bread, burgers, meat products, fish products, sausage products, and/or cheese.

A further aspect of the present invention relates to the use of a barrier paper of the invention for packaging foods, preferably for packaging fatty foods, with the barrier paper repelling the fat from the food.

A further aspect of the present invention relates to a method for producing a barrier paper, preferably a barrier paper of the invention, comprising the following steps:

    • (i) producing or providing a paper substrate,
    • (ii) producing or providing a barrier coat comprising a wax emulsion, the wax being a wax based on a vegetable oil,
    • (iii) applying the produced or provided barrier coat to one sides of the paper substrate and subsequently drying the barrier coat, to give a barrier layer.

In this case it is preferred in accordance with one aspect of the invention if the wax emulsion is a wax-in-oil emulsion and the wax emulsion additionally comprises an anionic polymeric binder which is preferably suitable for stabilizing the wax emulsion.

It is preferred in accordance with one aspect of the invention in this case if the produced or provided barrier coat comprises a (further) polymeric binder besides the wax emulsion.

It is preferred in accordance with one aspect of the invention if the average particle size of the wax particles is in the range from 600 to 1100 nm, preferably in the range from 700 to 1000 nm. The particle size of the wax particles can be determined using laser diffraction particle size analysis. Our own investigations have shown that particles of this order of size lead to barrier layers having very good barrier and mechanical properties, since there is effective mixing between polymeric binder and wax particles.

It is preferred in accordance with one aspect of the invention if the wax emulsion is basic and preferably has a pH in the range from 8 to 10.

It is preferred in accordance with one aspect of the invention if the wax based on a vegetable oil is a soy wax.

It is preferred in accordance with one aspect of the invention if the drying of the barrier coat takes place at a temperature above the melting point of the wax (e.g., at 40, 60, 80 or 100° C.) and/or in a separate step the paper substrate comprising the (optionally dried) barrier coat is heated above the melting point of the wax (e.g., at 40, 60, 80 or 100° C.).

In an embodiment of the method that is in accordance with one aspect of the invention, a coated paper substrate is used as paper substrate or a coat is applied to one sides of the paper substrate and the coat is then dried, to give an interlayer, before the barrier coat is applied. Preferably, therefore, the method of one aspect of the invention additionally comprises the following steps:

a) producing or providing a coat comprising pigments and binders,

b) applying the produced or provided coat to one side of the paper substrate and subsequently drying the coat, to give an interlayer, where the steps a) and b) are carried out preferably between the steps i) and ii).

A further aspect of one aspect of the present invention relates to a barrier paper produced by a method of the invention.

A further aspect of the present invention relates to a the use of a wax based on a vegetable oil for producing a paper coating, preferably for producing a barrier layer of a barrier paper.

In the context of one aspect of the present invention, preferably two or more of the aspects identified above as being preferred are realized at the same time; especially preferred are those combinations of such aspects, and of the corresponding features, that arise from the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further embodiments are apparent from the examples and working examples that are elucidated in more detail by means of the figures. In these figures:

FIG. 1 is a layer construction of barrier paper;

FIG. 2 is a layer construction of barrier paper;

FIG. 3 is a layer construction of barrier paper; and

FIG. 4 is a layer construction of barrier paper.

 DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 1 shows a barrier paper 10 that consists of a paper substrate 11 and a barrier layer 12. The paper substrate has a front side and a back side opposite the front side, and disposed on the front side of the paper substrate 11 is a barrier layer 12, which consists of a polymeric binder and a wax based on a vegetable oil.

FIG. 2 shows a barrier paper 10 that consists of a paper substrate 11, an interlayer 13, and a barrier layer 12. The paper substrate has a front side and a back side opposite the front side, and disposed on the front side of the paper substrate 11 is the interlayer 13. Disposed on the interlayer 13 in turn is the barrier layer 12, which consists of a polymeric binder and a wax based on a vegetable oil. The interlayer 13 preferably comprises a pigment and a binder.

FIG. 3 shows a barrier paper 10 that consists of a paper substrate 11 and two barrier layers 12. The paper substrate has a front side and a back side opposite the front side, and disposed on each of the front side and the back side of the paper substrate 11 is a respective barrier layer 12, which consists of a polymeric binder and a wax based on a vegetable oil.

FIG. 4 shows a barrier paper 10 that consists of a paper substrate 11, two interlayers 13, and two barrier layers 12. The paper substrate has a front side and a back side opposite the front side, and, disposed on each of the front side and the back side of the paper substrate 11, there is a respective interlayer 13. Disposed on each of the interlayers 13 in turn is a respective barrier layer 12, which consists of a polymeric binder and a wax based on a vegetable oil. The interlayers preferably comprise a pigment and a binder.

Example 1: Production of a Barrier Paper of the Invention

As paper substrate, a paper web provided with resin sizing in the stock and having a mass per unit area of 33.3 g/m2 was produced on a paper machine from short-fiber stocks (100% short-fiber pulp) having a freeness of 50° SR and with addition of talc as filler with a mass fraction of 1%, based on the total mass of the paper substrate. The paper substrate produced was calendered under a linear load of 100 kN/m and a temperature of 100° C.

A curtain coater was used to apply, to the front side, a priming coat comprising water, an aqueous dispersion of an acrylic-acetate copolymer (solids content 33%, mass fraction in the priming coat 0.03% (oven-dry); Sterocoll BL), an aqueous dispersion of an acrylic copolymer (solids content 40%, mass fraction in the priming coat 1.27% (oven-dry); trade name: Sterocoll FS), an aqueous dispersion of a styrene-acrylate copolymer (solids content 50%, mass fraction in the priming coat 70.5% (oven-dry); trade name: Sterocoll FS), and kaolin (solids content 70%, mass fraction in the priming coat 28.2% (oven-dry); trade name: Capim NP), with a coat weight of 3.5 g/m2, and the priming coat was subsequently dried by IR and air drying, to give an interlayer.

A curtain coater was used to apply, to the interlayer, a barrier coat comprising water, a wax based on a vegetable oil (solids content 30%, mass fraction in the priming coat 82% (oven-dry); trade name: SWX 155), a polyacrylate dispersion (solids content 48%, mass fraction in the priming coat 16.4% (oven-dry); trade name: Tecryl PB 16/3), and a mixture of nonionic surfactants (solids content 100%, mass fraction in the priming coat 1.6% (oven-dry); trade name: Metolat 700), with a coat weight of 4 g/m2, and the barrier coat was subsequently dried by means of IR and air drying, to give a barrier layer.

Samples were taken from the completed barrier paper, and typical parameters were determined from these samples and are collated in the table below.

KIT rating (Tappi 559) >12 Water vapor permeability 23° C./85% rh 115 g/(m2d) Water vapor permeability 38° C./90% rh 249 g/(m2d) Fat resistance palm kernel fat method I 8 breakthroughs (<1 mm) setting I > 24 h with weight 0 breakthroughs (>1 mm) Fat resistance palm kernel fat method II 0 breakthroughs (<1 mm) setting I > 24 h with weight 4 breakthroughs (>1 mm)

The results show that the barrier paper of the invention exhibits fat resistance outstandingly and a low water vapor permeability.

Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

Claims

1.-16. (canceled)

17. A barrier paper comprising: and

a paper substrate having a front side and a back side opposite the front side;
a barrier layer disposed on the front side and/or back side of the paper substrate,
wherein the barrier layer comprises at least a polymeric binder and a wax based on a vegetable oil.

18. The barrier paper as claimed in claim 17, wherein the wax based on a vegetable oil is a wax based on an oil selected from one or more of palm oil, coconut oil, poppyseed oil, olive oil, linseed oil, soybean oil, sunflower oil, safflower oil, and rapeseed oil.

19. The barrier paper as claimed in claim 17, wherein the wax based on a vegetable oil is a wax based on a soybean oil.

20. The barrier paper as claimed in claim 17, wherein a mass fraction of the wax in the barrier layer is at least one of:

6 to 98% based on a total mass of the barrier layer,
20 to 90% based on the total mass of the barrier layer, and
50 to 89%, based on the total mass of the barrier layer.

21. The barrier paper as claimed in claim 17, wherein a mass fraction of the wax in the barrier layer is 20 to 78%.

22. The barrier paper as claimed in claim 17, wherein the wax has a melting point of above at least one of 40° C., 50° C., and 60° C.

23. The barrier paper as claimed in claim 17, wherein the polymeric binder is a crosslinked or noncrosslinked binder selected from the group consisting of starch, polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, ethylene-vinyl alcohol copolymer, a combination of polyvinyl alcohol and ethylene-vinyl alcohol copolymer, ethylene-vinyl acetate copolymer, silanol group-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, acrylate copolymer, modified polyethylene glycol, unmodified polyethylene glycol, α-isodecyl-ω-hydroxy-poly(oxy-1,2-ethanediyl), styrene-butadiene latex, styrene-acrylate polymers, and mixtures thereof.

24. The barrier paper as claimed in claim 17, wherein the polymeric binder comprises one or more styrene-acrylate polymers.

25. The barrier paper as claimed in claim 24, wherein the acrylate copolymer is a copolymer prepared using two or more monomers selected from the group consisting of methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, and styrene.

26. The barrier paper as claimed in claim 17, wherein a mass fraction of the polymeric binder in the barrier layer is at least one of:

94 to 2% based on a total mass of the barrier layer,
80 to 10% based on the total mass of the barrier layer, and
50 to 11% based on the total mass of the barrier layer.

27. The barrier paper as claimed in claim 17, wherein the barrier layer further comprises a wax based on saturated hydrocarbons.

28. The barrier paper as claimed in claim 27, wherein the wax based on saturated hydrocarbons has a melting point of above at least one of 40° C., 50° C., and 60° C.

29. The barrier paper as claimed in claim 27, wherein the wax based on saturated hydrocarbons comprises at least one alkane selected from the group consisting of heneicosane, docosane, tricosane, tetracosane, pentacosane, hexacosane, heptacosane, octacosane, nonacosane, triacontane, hentriacontane, dotriacontane, tritriacontane, tetratriacontane, pentatriacontane, hexatriacontane, heptatriacontane, octatriacontane, and nonatriacontane.

30. The barrier paper as claimed in claim 17, further comprising:

an interlayer disposed between the paper substrate and the barrier layer.

31. The barrier paper as claimed in claim 17, wherein the barrier paper is configured as one or more of wrapping paper, lining paper, interleaving paper and/or release paper for foods, for wrapping, lining, interleaving and/or separating of bakery products, fried and/or deep-fried products, snack products, sandwiches, bread, burgers, meat products, fish products, sausage products, and/or cheese.

32. A method for producing a barrier paper, comprising:

(i) one of producing and providing a paper substrate;
(ii) one of producing and providing a barrier coat comprising a wax emulsion, wherein the wax is based on a vegetable oil; and
(iii) applying the barrier coat to one side of the paper substrate and subsequently drying the barrier coat, to provide a barrier layer.

33. The method for producing a barrier paper of claim 32, further comprising:

(iv) disposing an interlayer between the paper substrate and the barrier layer.
Patent History
Publication number: 20200370244
Type: Application
Filed: Dec 18, 2018
Publication Date: Nov 26, 2020
Inventors: Dieter BECKER (Georgsmarienhütte), Nadia EL-KARZAZI (Bielefeld), Konstantinos KALESSIOS (Frankfurt), Jochen SCHLEGEL (Heroldsberg)
Application Number: 16/956,049
Classifications
International Classification: D21H 19/18 (20060101); D21H 17/34 (20060101); D21H 17/60 (20060101); D21H 19/20 (20060101); D21H 19/82 (20060101); D21H 27/10 (20060101);