PROCESS FOR THE COATING OF TEXTILES

Abstract

The present invention relates to a process for the production of coated textiles in which a textile substrate is firstly brought into contact with an aqueous dispersion comprising at least one inorganic salt and at least one modified cellulose.

Description

The present invention relates to a process for the production of coated textiles in which a textile substrate is firstly brought into contact with an aqueous dispersion comprising at least one inorganic salt and at least one modified cellulose.

The production of synthetic leather by coating textiles with plastics has been known for some time. Synthetic leathers are employed, inter alia, as shoe upper materials, for articles of clothing, as bag-making material or in the upholstery sector, for example. Besides other plastics, such as PVC, the main coating material used here is polyurethane, The generally known principles of coating textiles with polyurethane are described in W. Schröer, Textilveredlung [Textile Finishing] 1987, 22 (12), 459-467, A description of the coagulation process is additionally found in “New Materials Permeable to Water Vapor”, Harro Träubel, Springer Verlag, Berlin, Heidelberg, New York, 1999, ISBN 3-540-64946-8, pages 42 to 63.

The main processes used in the production of synthetic leather are the direct coating process, the transfer coating process (indirect coating) and the coagulation (wet) process. In contrast to the direct process, the coating in the transfer process is applied to a temporary support with a subsequent lamination step, in which the film is combined with the textile substrate and detached from the temporary support (release paper). The transfer process is preferably employed with textile substrates, which do not permit high tensile stresses during coating, or with open fabrics which are not particularly dense.

In the coagulation process, a textile substrate is usually coated with a solution comprising polyurethane in DMF. In a second step, the coated substrate is passed through DMF/water baths, where the proportion of water is increased stepwise. Precipitation of the polyurethane and formation of a microporous film occur here. Use is made here of the fact that DMF and water have excellent miscibility and DMF and water serve as a solvent/non-solvent pair for polyurethane. Coagulated polyurethane coatings are employed, in particular, for high-quality synthetic leather, since they have comparatively good breathing activity and a leather feel. The basic principle of the coagulation process is based on the use of a suitable solvent/non-solvent pair for polyurethane. The great advantage of the coagulation process is that microporous, breathing-active synthetic leather having an excellent leather feel can be obtained. Examples are, for example, the synthetic leather brands Clarino® and Alcantara®. A disadvantage of the coagulation process is the necessity to use large amounts of DMF as an organic solvent. In order to minimize the exposure of employees to DMF emissions during production, additional design measures have to be taken, which represent a not inconsiderable increased outlay compared with simpler processes. Furthermore, it is necessary to dispose of or work up large amounts of DMF/water mixtures. This is problematical since water and DMF form an azeotrope and can therefore only be separated by distillation with increased effort.

One object of the present invention was therefore to develop a process for the coating of textile substrates which still enables coated textiles having good properties, such as, for example, good feel, to be obtained without the need to employ toxicologically unacceptable solvents, such as, for example, DMF.

The object has been achieved by a process for the production of coated textiles, comprising at least the steps of

a) bringing a textile substrate into contact with an aqueous dispersion A comprising at least one inorganic salt and at least one modified cellulose,

b) bringing a textile substrate into contact with an aqueous dispersion B comprising at least one polymer selected from the group consisting of polyacrylate and polybutadiene and

c) precipitation of the at least one polymer selected from the group consisting of polyacrylate and polybutadiene in or on the textile substrate.

In step a), a textile substrate is brought into contact with an aqueous solution comprising at least one inorganic salt and at least one modified cellulose.

The inorganic salt is preferably a salt selected from the group comprising alkali metal salts and alkaline-earth metal salts. The inorganic salt is particularly preferably a salt selected from the group consisting of alkali metal halides, alkali metal phosphates, alkali metal nitrates, alkali metal sulfates, alkali metal carbonates, alkali metal hydrogen carbonates, alkaline-earth metal halides, alkaline-earth metal nitrates, alkaline-earth metal phosphates, alkaline-earth metal sulfates, alkaline-earth metal carbonates and alkaline-earth metal hydrogen carbonates. The inorganic salt is very particularly preferably sodium chloride, potassium chloride, sodium sulfate, sodium carbonate, potassium sulfate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, magnesium chloride, magnesium sulfate, magnesium nitrate, calcium chloride, calcium nitrate or calcium sulfate. The inorganic salt is even more preferably calcium nitrate, magnesium nitrate, calcium chloride or magnesium chloride.

The inorganic salt is preferably present in dispersion A in an amount of 0.01 to 25% by weight, particularly preferably in an amount of 0.5 to 15% by weight, and very particularly preferably in an amount of 0.5 to 10% by weight, based on the total amount of dispersion A.

The chemically modified cellulose is preferably a compound selected from the group consisting of alkylated celluloses, hydroxyalkylated celluloses and carboxyalkylated celluloses.

The chemically modified cellulose is particularly preferably a compound selected from the group consisting of methylcellulose, ethylcellulose, propylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxymethylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, carboxyethylcellulose and carboxypropylcellulose.

The chemically modified cellulose is very particularly preferably methylcellulose or ethylcellulose.

The modified cellulose is preferably present in dispersion A in an amount of 10 ppm to 5% by weight, particularly preferably in an amount of 100 ppm to 3% by weight, very particularly preferably in an amount of 400 ppm to 1.5% by weight, based on the total amount of dispersion A.

The textile substrate is preferably brought into contact with an aqueous dispersion A at room temperature for a period of 2 to 4 minutes, particularly preferably 1 to 2 minutes, very particularly preferably 0.2. to 1 minute. For the purposes of the present invention, bringing into contact means partial or complete immersion, preferably complete immersion, in a dispersion or application of the dispersion by means of a hand coater, printing or spraying.

After being brought into contact with a dispersion A, the textile substrate is preferably passed through a wringer device consisting of two rollers in order to remove the excess dispersion A. The wringer device here should preferably be set in such a way that dispersion A remains in the textile substrate in an amount of 60 to 180% by weight, particularly preferably 70 to 140%, very particularly preferably 80 to 120%, based on the weight per unit area of the substrate (liquor uptake), before the substrate is brought into contact with a dispersion B containing at least one polymer selected from the group consisting of polyacrylate and polybutadiene. The textile substrate is preferably partially dried for a period of 2 to 10 minutes, particularly preferably 1 to 5 minutes, using air, infrared or hot cylinders before it can be brought into contact with a dispersion B containing at least one polymer selected from the group consisting of polyacrylate and polybutadiene.

The polyacrylate and polybutadiene present in dispersion B is not particularly restricted so long as they are soluble in water.

Polyacrylate polymers are prepared from monomers containing hydroxyl groups, “acidic” monomers, or monomers that contain neither acidic nor OH groups.

Suitable hydroxyl group-containing monomers include hydroxyalkyl esters of acrylic acid or methacrylic acid, preferably with 2 to 4 carbon atoms in the alkyl radical, such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-or 3-hydroxypropyl acrylate and methacrylate, the isomeric hydroxybutyl acrylates and methacrylates and mixtures of these monomers.

Suitable “acidic” comonomers include olefinically unsaturated, polymerizable compounds that contain at least one carboxyl group and/or sulfonic acid group, such as olefinically unsaturated monocarboxylic or dicarboxylic acids having a molecular weight of 72 to 207. Examples include acrylic acid, methacrylic acid, maleic acid, itaconic acid and olefinically unsaturated compounds containing sulfonic acid groups, for example, 2-acrylamido-2-methylpropanesulfonic acid and mixtures of these olefinically unsaturated acids.

A third group of olefinically unsaturated monomers that may be jointly used in the production of polyacrylate polymers include olefinically unsaturated compounds that do not contain either acidic groups or hydroxyl groups. Examples include esters of acrylic acid or methacrylic acid with 1 to 18, preferably 1 to 8 carbon atoms in the alcohol radical, such as methyl acrylate, ethyl acrylate, isopropyl acrylate, n-propyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, isobornyl acrylate, n-stearyl acrylate, the methacrylates corresponding to these acrylates, styrene, alkyl-substituted styrenes, butadiene, isoprene, acrylonitrile, methacrylonitrile, vinyl acetate, vinyl stearate, and mixtures of these monomers. Comonomers containing epoxy groups, such as glycidyl acrylate or methacrylate, or monomers, such as N-methoxymeth-acrylamide or N-methacrylamide, may also be used in minor amounts.

The production of aqueous dispersions containing polyacrylate and/or polybutadiene is carried out according to known free-radical polymerization methods, for example, solution polymerization, emulsion polymerization and suspension polymerization. The process of free-radical emulsion polymerization in an aqueous medium is preferred.

Continuous or discontinuous polymerization processes may be used. Examples of discontinuous processes are the batch process and feed process, the latter being preferred. In the feed process water is added alone or with part of the anionic emulsifier and optionally a non-ionic emulsifier, as well as with part of the monomer mixture, and is heated to the polymerization temperature. In the case of a monomer addition the polymerization is started by free radicals and the remaining monomer mixture is metered in together with an initiator mixture and the emulsifier over a period of 1 to 10 hours, preferably 3 to 6 hours. If necessary, the reaction mixture is then post-activated in order to carry out the polymerization to a conversion of at least 99%.

The emulsifiers used are may be anionic and/or non-ionic. Anionic emulsifiers are those containing carboxylate, sulfate, sulfonate, phosphate or phosphonate groups. Emulsifiers are preferred that contain sulfate, sulfonate, phosphate or phosphonate groups. The emulsifiers may have a low molecular weight or high molecular weight. The latter are described, for example, in DE-A 3 806 066 and DE-A 1 953 349.

Preferred anionic emulsifiers are those that are built up from long-chain alcohols or substituted phenols and a polyether chain bonded to the hydroxyl group containing 2 to 100 ethylene oxide units as well as a sulfuric acid or phosphoric acid group bonded in the form of an ester unit. Ammonia or amines are preferred neutralizing agents for the unesterified acid groups. The emulsifiers may be added to the emulsion batch individually or as mixtures.

Suitable as non-ionic emulsifiers, which may be used in combination with the anionic emulsifiers, are reaction products of aliphatic, araliphatic, cycloaliphatic or aromatic carboxylic acids, alcohols, phenol derivatives and/or amines with epoxides, such as ethylene oxide. Examples include reaction products of ethylene oxide with castor oil carboxylic acids and abietic acid; with long-chain alcohols such as oleyl alcohol, lauryl alcohol, stearyl alcohol; with phenol derivatives such as substituted benzyl phenols, phenyl phenols and nonyl phenols; and with long-chain amines such as dodecylamine and stearylamine. The reaction products with ethylene oxide include oligoethers and/or polyethers with degrees of polymerization of 2 to 100, preferably 5 to 50.

These emulsifiers are added in amounts of 0.1 to 10 wt. %, based on the mixture of the monomers. Suitable co-solvents include water-soluble as well as water-insoluble solvents. Suitable co-solvents include aromatic compounds such as benzene, toluene, xylene and chlorobenzene; esters such as ethyl acetate, butyl acetate, methyl glycol acetate, ethyl glycol acetate and methoxypropyl acetate; ethers such as butyl glycol, tetrahydrofuran, dioxane, ethyl glycol ether and ethers of diglycol; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone; trichloromonofluoroethane; and cyclic amides such as N-Methyl-pyrrolidone and N-methylcaprolactam.

The free radical-initiated polymerization may be started by water-soluble and water-insoluble initiators or initiator systems whose radical decomposition half-lives at temperatures from 10° C. to 100° C. are 0.5 sec. to 7 hours.

In general the polymerization is carried out in aqueous emulsion in the aforementioned temperature range, preferably between 30° C. and 90° C., under a pressure of 10³ to 2×10⁴ mbar. The exact polymerization temperature is determined according to the type of initiator. The initiators are used in amounts of 0.05 to 6 wt. %, based on the total amount of monomers.

Suitable initiators include water-soluble and water-insoluble azo compounds such as azoisobutyrodinitrile or 4,4′-azo-bis-(4-cyanopentanoic acid); inorganic and organic peroxides such as dibenzoyl peroxide, t-butyl perpivalate, t-butyl-per-2-ethylhexanoate, t-butyl perbenzoate, t-butyl hydroperoxide, di-t-butyl peroxide, cumene hydroperoxide, dicyclohexyl dicarbonate, dibenzyl peroxydicarbonate, the sodium, potassium and ammonium salts of peroxodisulfuric acid, and hydrogen peroxide. The peroxodisulfates and hydrogen peroxides may be used in combination with reducing agents, such as the sodium salt of formamidinesulfinic acid, ascorbic acid or polyalkylene polyamines. A significant reduction of the polymerization temperature is generally thereby achieved.

In order to regulate the molecular weight of the polymers conventional regulators may be used, such as n-dodecylmercaptan, t-dodecylmercaptan, diisopropyl xanthogene disulfide, di(methylene-trimethylolpropane)xanthogene disulfide and thioglycol. The regulators are added in amounts of at most 3 wt. %, based on the monomer mixture.

If necessary after the end of the polymerization reaction, neutralizing agents are added to the polymers present in aqueous dispersion to obtain a degree of neutralization of 30 to 100%, preferably 50 to 100%. inorganic bases, ammonia or amines are added as neutralizing agents. Examples include inorganic bases, such as sodium hydroxide and potassium hydroxide; and amines such as ammonia, trimethylamine, triethylamine, dimethylethanolamine, methyldiethanolamine and triethanolamine. The neutralizing agents may be used in substoichiometric or excess stoichiometric amounts, which results in the aforementioned contents of sulfonate and/or carboxylate groups, in particular carboxylate groups and the aforementioned acid numbers.

When there is complete neutralization of the acidic groups that may optionally be present, the result is an acid number of zero, such that the content of sulfonate and/or carboxylate groups corresponds to the original content of sulfonic acid groups and/or carboxyl groups. With partial neutralization the content of sulfonate and/or carboxylate groups corresponds to the amount of neutralizing agent that is employed. The resulting aqueous dispersions have the aforementioned concentrations and viscosities. The optional co-solvents may remain in the aforementioned amounts in the aqueous dispersion or may be removed by distillation after the polymerization reaction.

Preferred aqueous dispersions B comprising polyacrylates are dispersions sold under the brand name Primal® which are available from Rohm and Hass, Philadelphia, Pa., USA. Preferred aqueous dispersions B comprising polybutadiene include Euderm®-Resin40B and Euderm®-Resin50B.

In a further preferred embodiment, dispersion B comprises at least one coagulant besides at least one polymer selected from the group consisting of polyacrylate and polybutadiene. A coagulant is a salt or acid, for example ammonium salts of organic acids, which causes coagulation of the at least one polymer selected from the group consisting of polyacrylate and polybutadiene under certain conditions, such as, for example, a particular temperature. These substances include an acid-generating chemical agent, i.e. a substance which is not an acid at room temperature, but becomes an acid after warming. Certain examples of such compounds include ethylene glycol diacetate, ethylene glycol formate, diethylene glycol formate, triethyl citrate, monostearyl citrate and an organic acid ester.

The coagulant is preferably present in the composition in an amount of 1 to 10% by weight, based on the solids content of dispersion B.

In order to achieve good sedimentation stability, the number average particle size of the specific polyacrylate dispersions and polybutadiene dispersions is preferably less than 750 nm, particularly preferably less than 500 nm and very particularly preferably less than 400 nm, determined by means of laser correlation spectroscopy.

The manner in which the precipitation in or on the textile substrate is accomplished depends to a large extent on the chemical composition of the dispersion B used in accordance with the invention and in particular on the type of coagulant, if present. For example, the precipitation can be carried out by evaporation coagulation or by salt, acid or electrolyte coagulation.

In general, the precipitation is achieved by an increase in temperature. For example, the textile substrate can be subjected to brief heat treatment with steam, for example at 100 to 110° C., for 1 to 10 s. This is particularly preferred if ammonium salts or organic acids are used as coagulant. If, on the other hand, the above-mentioned acid-generating chemicals are used as coagulant, the precipitation is preferably carried out as described in U.S. Pat. No. 5,916,636, U.S. Pat. No. 5,968,597, U.S. Pat. No. 5,952,413 and U.S. Pat. No. 6,040,393.

Alternatively, the coagulation is caused by dipping into a salt solution. The coagulation is preferably carried out using an inorganic salt selected from the group consisting of alkali metal salts and alkaline-earth metal salts. The inorganic salt is particularly preferably a salt selected from the group consisting of alkali metal halides, alkali metal nitrates, alkali metal phosphates, alkali metal sulfates, alkali metal carbonates, alkali metal hydrogen carbonates, alkaline-earth metal halides, alkaline-earth metal phosphates, alkaline-earth metal nitrates, alkaline-earth metal sulfates, alkaline-earth metal carbonates and alkaline-earth metal hydrogen carbonates. The inorganic salt is very particularly preferably sodium chloride, potassium chloride, sodium sulfate, sodium carbonate, potassium sulfate, potassium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, magnesium chloride, magnesium sulfate, calcium chloride or calcium sulfate. The inorganic salt is still more preferably calcium chloride or magnesium chloride.

The inorganic salt is preferably present in the salt solution in an amount of 1 to 25% by weight, particularly preferably in an amount of 1 to 15% by weight, very particularly preferably in an amount of 1 to 10% by weight, based on the total amount of salt solution.

After the precipitation in step c), further steps, such as drying or condensation, are carried out if necessary.

The textile substrate employed is preferably a woven fabric, knitted fabric or nonwoven based on natural and/or synthetic fibers. The textile substrate is particularly preferably a nonwoven (staple fiber nonwoven, microfiber nonwoven or the like).

The textile substrate can preferably be built up from fibers of polyester, nylon (6 or 6,6), cotton, polyester/cotton blends, wool, ramie, spandex, glass, thermoplastic polyurethane (TPU), thermoplastic olefins (TPO) or the like. The textile substrate can have a linked/mesh-like (knitted), woven or nonwoven construction.

The textile substrate can be treated with dyes, colorants, pigments, UV absorbers, plasticizers, soil redeposition agents, lubricants, antioxidants, flame inhibitors, rheology agents and the like, either before coating or thereafter, but there is a preference for such additions before coating.

If a defined nonwoven fabric is impregnated with an elastomer polymer and coagulated, and a normal coloring process is subsequently carried out, a suede-like synthetic leather having good color development properties is obtained.

The present invention therefore furthermore relates to a coated textile, preferably synthetic leather, obtained by the process according to the invention.

Claims

1.-11. (canceled)

12. A process for the production of a coated textile, comprising at least the steps of

a) bringing a textile substrate into contact with an aqueous dispersion A comprising at least one inorganic salt and at least one modified cellulose,

b) bringing a textile substrate into contact with an aqueous dispersion B comprising at least one polymer selected from the group consisting of polyacrylate and polybutadiene and

c) precipitating the at least one polymer selected from the group consisting of polyacrylate and polybutadiene in or on the textile substrate.

13. The process according to claim 12, wherein the inorganic salt is a salt selected from the group consisting of alkali metal salts and alkaline-earth metal salts.

14. The process according to claim 13, wherein the alkali metal salt is a salt selected from the group consisting of alkali metal halides, alkali metal nitrates, alkali metal phosphates, alkali metal sulfates, alkali metal carbonates and alkali metal hydrogen carbonates.

15. The process according to claim 13, wherein the alkaline-earth metal salt is a salt selected from the group consisting of alkaline-earth metal halides, alkaline-earth metal nitrates, alkaline-earth metal phosphates, alkaline-earth metal sulfates, alkaline-earth metal carbonates and alkaline-earth metal hydrogen carbonates.

16. The process according to claim 12, wherein the inorganic salt is present in dispersion A in an amount of 0.01 to 25% by weight, based on the total amount of dispersion A.

17. The process according to claim 12, wherein the modified cellulose is a compound selected from the group consisting of methylcellulose, ethylcellulose, propylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, carboxymethylcellulose, carboxyethylcellulose and carboxypropylcellulose.

18. The process according to claim 12, wherein the modified cellulose is present in dispersion A in an amount of 10 ppm to 5% by weight, based on the total amount of dispersion A.

19. The process according to claim 12, wherein the textile substrate employed is a woven fabric, knitted fabric or nonwoven based on natural and/or synthetic fibers.

20. The process according to claim 12, wherein the at least one polymer selected from the group consisting of polyacrylate and polybutadiene is precipitated in step c) in a bath containing water or on use of a temperature in the range from 80 to 120° C.)

21. A coated textile obtained by a process according to claim 12.

22. The coated textile according to claim 21, wherein the coated textile is synthetic leather.