CA1075545A - Method of coating fabric with polyurethane - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A fabric is coated by spreading a one-package liquid mixture of a polyamine carbamate and a free isocyanate group - containing reaction product of a polyisocyanate with a polyhydroxy material onto a release surface, heating the coating at the decomposition temperature of the carbamate to cause gelling and partial foaming, placing a woven or nonwoven fabric over the gelled coating, heating the resulting laminate to complete the foaming and the cure, and finally stripping the release surface from the coated fabric. Alternatively, the coat-ing may be fully foamed and cured before applying the fabric and a conventional adhesive is employed to secure said coating to the fabric. An unfoamed conven-tional skin coating may also be applied to the release surface before the foam-ing material is spread onto it. Direct coating of suitable fabric substrates can also be carried out.

Description

10755~S
Although solvent-free polyurethane coating systems have been devised to permit the placement of thicker coats upon fabrics and avoid solvent removal operations, the use of such systems by the textile industry has been seriously limited by the application problems that they pose. As pointed out by various authors, the difficulties experienced with these so-called 100% solids systems arise from the complications inherent in attempting to deposit films of chemi-cally reactive mixtures in thicknesses that must be closely controlled. Thus, ;
a typical 100% solids system involves two components which must be mixed just before application to the substrate and therefore has a very short pot life.
Obviously, such a system requires close technical supervision as well as pro-portionating, mixing and distributing equipment designed to extremely close -tolerances. Although it is sometimes possible to operate without proportionat-ing equipment, as is the case with some systems which, after mixing, have a re-latively long pot life, e.g. about four hours, thè fact remains generally that, as a result of these demanding chemical limitations and requirements, the appli-cation of foamable two-component polyurethane mixtures to fabrics suffers from lack of reproducibility and high operational cost. As to non-~oaming one-pack-age solventless polyurethane fabric coating, it should be noted that the art does provide some quick-curing preparations having a long pot life, but these 20 rather specialized materials, as disclosed in U.S. Patent No. 3,539,424, cannot yield a laminate that breathes.
Processes are also known that employ precast foam layers which are subsequently adhered to a fabric by various chemical or physical means such as, for instance, flame bonding. A recent illustration of this approach is dis-closed in U.S. Patent No. 3,855,o48.
It is therefore an object of the present invention to provide a pro-cess for coating fabrics with a foamed polyurethane layer by means of a one-package storage-stable quick-curing liquid prepolymer preparation. A further object of this invention is to provide a process for coating knit, woven or :

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~075545 unwoven fabrics of any weight and obtain, without special preparation of the fabric, a full, soft, flexible, scuff resistance polyurethane coated fabric possessing the pleasant characteristic "break" of fine leather. S~ill another object of this invention is to provide a process which can be carried out by means of conventional artificial leather manufacturing equip-ment and techniques, without the need of specialized machinery or instruments not generally found in the polyvinyl chloride plastisol fabric coating plants.
These and other objects which will become evident upon disclosure of the invention have been accomplished by providing a fabric coating process comprising the application to the fabric, by direct or transfer technique, of a liquid polyurethane prepolymer-polyamine carbamate mixture, followed by heating the applied mixture for a few minutes at the decomposition temperature of the carbamate to release carbon dioxide and a polyamine which, respectively, cause the coating to foam and cure.
According to the present invention, there is provided a method for preparing a polyurethane coated fabric, comprising; la) providing a storage stable one-package foamable composition comprising (1) a liquid prepolymer consisting of a free isocyanate g~oup-containing reaction product of a poly-isocyanate with a polyhydroxy compound mixture consisting of at least one diol and one triol, said triol constituting up to about 10% of said mixture by weight and (2) a finely dispersed polyamide carbonate ~b) applying said composition to a fabric as a thin coating, and (c) heating at a temperature within the range of about 150 to 300F for a period of up to five minutes to liberate the carbon dioxide and the polyamine and cause the coating to fo~m and cure.
The prepolymer-carbamate mixtures employed in the process are con-ventional mixtures of liquid, free isocyanate group-containing reaction products of polyisocyanates with polyhydroxy compounds and finely dispersed carbon dioxide-blocked polyamine curing agent. The mixtures may also contain conventional additives such as fillers, plasticizers, pigments, protective agents and the like.

When the conventional transfer technique is employed, the prepolymer-r- ~ ~ 2 ~

carbamate mixture is cast on a release surface which may or may not have been precoated with a polymeric skin coat, heated at the decomposition temperature -~
of the carbamate to cause the polymer to gel and the resulting gelled coating is then applied to a fabric and further heated to foam and fully cure, an operation requiring only a few minutes. The release surface is then stripped off.
Alternatively, in the course of the transfer coating process, the ~ -prepolymer-carbamate mixture may be completely foamed and cured before application to the fabric. In that case, a convention fabric adhesive is -applied be-_ 2a -.; ~,, tween the foam and the fabric, or the foamed polyurethane may be flame bonded to the fabric.
The process of this invention consists essentially in applying to a fabric a one-package liquid quick-curing storage-stable foamable mixture of a polyurethane prepolymer and a carbon dioxide-blocked polyamine, and in causing said mixture to foam and cure by decomposing the blocked polyamine to release carbon dioxide, which acts as a blowing agent, and the polyamine which reacts with the prepolymer to cure it.
The exact sequence of these physical and chemical operations depends to some extent on the coating process selected and on the nature and propor-tions of the coating ingredients, considerations which also affect inter alia the desirability of employing or not employing an adhesive to secure the foam layer to the fabric.
The foamable coating mixture may be applied directly to the fabric, and spread evenly, for instance by means of a doctor knife, and the coated fab-ric passed through a heating unit to cause the mixture to foam and cure. How-ever, the transfer coating method is preferred since it is not only less depend- -ent on the condition of the fabric substrate but also permits the practice of various operating variations which affect favorably both the coating process and the coated product.
Thus, for instance, the foamable coating mixture may be applied in a conventional manner to a release surface, e.g. a silicone treated paper, heated for a few moments so that the mixture gels to a still tacky coating, applied to the fabric, heated to a few minutes more at the decomposition temperature of the carbamate to complete the foaming and the cure. The release paper is then stripped, leaving the foam coated fabric. If desired, an unformed skin coating is first placed on the release surface and fully or partially dried before the foamable mixture is applied. Several commercial polyurethane preparations of this type are available which yield abrasion resistant surfaces and give the finished fabric a soft hand. In some circumstances, depending again on the nature and quality of the substrate fabric, the particular formulation of the foamable polyurethane prepolymer mixture, and the effect desired in the finish-ed fabric in view of the ultimate use intended, the foamable coating, after application to the release surface or to a skin coated release surface, is heated until it is fully foamed and cured before application to the fabric.
In such cases, a coat of conventional adhesive may be employed to secure the fabric to the foamed coating. Such adhesive materials are well known and in-clude polyurethane preparations of various type. Alternatively, the cured foam may be flame bonded to the fabric.
The compositions responsible for the process and product advantages derived from the practice of this invention comprise esentially a polyamine carbamate dispersed into a liquid polyurethane prepolymer consisting of a free isocyanate group-containing reaction product of a polyisocyanate with a poly-hydroxy material. Fillers, pigments, plasticizers, antioxidants, and other con-ventional additives may be incorporated provided they do not contain active hydrogen.
The usable prepolymers are low molecular weight reaction products of polyisocyanates with polyhydroxy compounds. Excellent results have been obtain-ed with mixtures of triols and diols in which the triol compounds constitute upto about 10% of the total polyhydroxy compound mix weight.
It is possible however to employ much larger proportions of triol material, indeed to exclude diols entirely, and still obtain coated textiles with useful properties. In such instances, adjustments in the nature and contents of other crosslinking materials later used, e.g. triamines and tetramines, may be indicated in order to retain or achieve some desirable properties such as good flexibility and the like.
The carbamates employed with the prepolymers are, as already mentioned, the reaction products of polyamines and carbon dioxide under anhydrous condi-tions. The compounds so prepared are generally stable solid materials pulver-ized for ultimate dispersion into the polyurethane prepolymer. The preferred particle size of the carbamate for mechanical stability of the prepolymer mix and the uniformity of the cured polyurethane mass is such that the powder should pass through a 200 mesh or finer U.S. Bureau of Standards screen. Typical ex-amples of usable carbamates are provided in U.S. Patent 3,029,227, 3,344,175 and 3,635,903. It should be kept in mind that there can be used with the prepolymer liquid one or more carbamates, either prepared separately and com-bined thereafter or prepared from a desired mixture of polyamines. In combina-tion with various prepolymers, such polyamine mixtures or blends will affectthe degree of cross-linking of the cured polymer and thus alter such coated fabric properties as elasticity, dry cleaning resistance and the like in a desired direction. Furthermore, the mixing of carbamates with different decom-position temperatures may serve to refine the control of two-stage cures, when such are desired as in the case where an adhesive tie coat is omitted.
Subject to the preferences already expressed in terms of prepolymers, i.e. partial reaction products of cyclic diisocyanates with mixtures of diols and triols, such as polyalkylene glycols and polyhydroxy polyethers, there may be used other polyisocyanates and polyhydroxy compounds to achieve useful, if not optimum properties in the finished coated fabric.
Among the polylsocyanates that may be employed in this manner are:
the various unsubstituted phenylene diisocyanates, as well as those having one or more substituents such as methyl and other lower alkyl groups having up to about 4 carbon atoms, halogen atoms, nitro groups, alkoxy and aryloxy groups, various substituted and unsubstituted biphenylene diisocyanates; substituted and unsubstituted diphenyl diisocyanates such as the diphenylmethanes-, diphenylisopropylidenes- and the diphenylsulfone diisocyanates; the naphthalene diisocyanates; alkylene diisocyanates containing up to about ten alkylene carbon atoms; cycloalkyl diisocyanates containing one or more cycloalkane rings such as 1,3-cyclopentane- and 4,4' - dicyclohexyemethane diisocyanate; and other diisocyanates such as l-ethyleneisocyanato-4-phenylisocyanate. Examples of tri- and tetra- isocyanates that may be used include the benzene and toluene triisocyanates, 2-methyl-2-(4-isocyanatophenyl)- trimethylene diisocyanate, tetrakis-(4-isocyanatophenyl) methane and bis-(4-methyl-2,5-isocyanatophenyl) methane. Polymeric materials such as polymethylene polyphenylisocyanate may also be employed.
In selecting the isocyanate to be used for a given preparation, factors such as ultimate use, color of finished fabric, and the like should be considered in order to take advantage of the teachings of the art. Thus, the need for lightproofness, important in white or pastel colored finished fabrics generally calls for the use of an acyclic or cyclic aliphatic polyisocyanate while a requirement of greater strength favors the aromatic variety. It should be noted however, that surprising resistance to discoloration has been experi-enced in this type of application with aromatic polyisocyanates.
Suitable compounds that will react with the above isocyanates to yield the necessary prepolymers include polyols such as ethylene glycol, glycerol, pentaerythrytol, sorbitol, triethanolamine, as well as polymeric compounds such as polyglycols, polyhydroxy polyesters, polyhydroxy polyesteramides and poly-hydroxy polyether oils.
Typical polyglycols include polyalkylene glycols, such as polyethyleneglycol, polypropylene glycol, and polybutylene glycol.
Representative polyesters are reaction products of dihydric alcohols, such as ethylene glycol, diethylene glycol, tetraethylene glycol, 1,3-propylene glycol, dipropylene glycol, or higher polyhydric alcohols such as glycerol, trimethylol propane, pentaerythritol, mannitol, or mixtures of two or more of the alcohols with a polycarboxylic acid or anhydride such as succinic, adipic, glutaric, malonic, sebacic, azelaic, phthalic, terephthalic, isophthalic, trimellitic and pyromellitic acids and their anhydrides. Mixtures of the acids and anhydrides can be employed.
Examples of polyhydroxy polyethers include linear hydroxyl-containing polymers and copolymers of cyclic ethers such as ethylene oxide, epichlorohydrin, 1,2-propylene oxide, oxacyclobutane, and tetrahydrofuran, or branched polyethers obtained from the condensation of the aforementioned ethers with branched poly-hydroxy compounds such as glycerol, l,l-trimethylolpropane, pentaerythritol, sorbitol and sucrose. Hydrophobic polyethers are preferred. Mixtures of linear and branched polyethers or mixtures of polyesters and polyethers can also be employed.
Illustrative polyhydroxy polyesteramides are the reaction products of a polyhydric alcohol with a dicarboxylic acid, examples of both of which nave been mentioned above, and as necessary, diamines or amino-alcohols such as ethylene diamine, hexamethylene dia~ine, phenylene diamine, benzidine and monoethanolamine.
Other polyhydroxy materials, for example, esters of hydroxycarboxylic acids, such as castor oil and glyceryl monoricinoleate, can also be used.
As is the case with the polyisocyanates and the carbamates earlier discussed, the selection of polyhydroxy compounds which will form the prepolymer depends on such factors as extent of crosslinking, resistance to hydrolysis, presence or absence of an adhesive layer, etc., as well as the attendant effects of such capabilities on the physical and chemical properties of the finished coated fabric. Thus~ a prepolymer based substantially on a polyhydroxy poly-ether will be favored where a good hand is desired in the fabric and where po-tential hydrolysis of the cured material is possible under conditions of use.
On the other hand, polyesters and polyamides can be selected where hydrolytic conditions are unlikely to exist and where strength of the finished product is considered more important than the best of hands. The qualities desired can also be reinforced by using mixtures of polyhydroxy compounds, especially in terms of linear and branched compounds. In this respect, mixtures of diols and triols may be employed, for instance, in which the triol content may con-stitute up to about 10% by weight of the polyhydroxy compound mix, and prefer-ably, between about 2 to 5~, in order to obtain a coated fabric which is most widely useful due to balanced flexibility and strength.
As described so far, the liquid foamable fabric coating preparations that can be used in the process of this invention are essentially mixture of free isocycanate group-terminated prepolymer with polyamine carbamates. Upon liberation of the polyamine by heat, satisfactory crosslinking of the prepoly-mer is generally achieved with a terminal isocyanate group to amino group chemi-10 cal equivalent ratio of about 1:1 to 1:2.5. These proportions may vary more broadly depending, inter alia, on the nature of the components used and the degree of crosslinking desired. Thus, in the instances when an intermediate tacky stage is desired, ratios of about 1:0.5 to 1:1 are preferred in order to obtain optimum adhesion. Preferred ratios also depend to some extent on the nature of the polyhydroxy compounds from which the prepolymers are made. Thus, it has been found that a range of about 1.1 : 1.3 is acceptable for polyethers while 1:1.7 is preferred for polyesters.
In addition to the essential ingredients just discussed, the foamablecoating preparations may contain various other known addltives which include -20 surface active agents, fillers, plasticizers, pigments, preservatives, and the like. Examples of specific materials that can be incorporated in conventional ;amounts for such purposes are calcium carbonate, calcium silicate, silica, chrysotile asbestos, carbon black, titanium dioxide, calcined clays, talcum powder, antimony oxide, dioctyl phthalate, di(2-ethylhexyl) adipate, silicone emulsifiers, epoxydized oils, organic polymeric fillers such as polyvinyl ace-tate and polybutadiene, and the like. If desired there can also be incorporated in the coating preparations used in this invention, small quantities of conven-tional blowing agents in order to obtain foams of various densities. Examples of suitable substances are the relatively high boiling halogenated hydrocarbons,.

``- 107554~

i.e. those boiling at above about 40 C, such as 1,1,2-trichloro-1,2,2-triflu-orethane and the like. These liquids can provide further expansion during heat curing of the coatings.
For ease of handling by standard fabric coating machinery, the liquid prepolymer-carbamate mixture described should have a viscosity preferably within the range of about 12,000 to 15,000 cps although viscosities ranging from about

2,500 to 50,000 cps can be accommodated if their use is otherwise indicated.
One of the most interesting advantages of using the foamable mixtures described above for coating fabrics lies in that since the foam that they pro-duce provides by itself sufficient cushioning, the textile coater is liberatedfrom the necessity of using napped sheered fabrics or any of the other specially constructed or prepared fabrics which often must be used to prevent overpenetra-tion by the coating or to cover sufficiently well so that the woven pattern of the fabric does not show in the finished product. The use of cheaper fabrics such as light knits and other thin fabrics thus becomes feasible.
Another advantage of the foamable coatings used in the process if this invention lies in the rapidity of the cure. As intimated earlier, carbamates decompose quickly on heating, at temperatures within the range of about 150 to 300 F, to release carbon dioxide and very reactive polyamines, so once the coat is heated to the particular decomposition temperature of the specific carbamate~ curing of the prepolymer takes place in a matter of minutes, generally five or less~ When gelling is desired, to be followed by full curing in contact with the fabric as explained earlier, this can be effected generally in not more than two minutes at temperatures under 200 F
or in shorter times yet at higher temperatures.
As pointed out earlier it is often desirable to provide the foam coated fabric with either or both a skin coat and an adhesive tie coat. The skin coat may consist of any of several commercially available materials de-signed to yield abrasion resistant film which may impart such desirable prop-_ g _ perties as a soft hand to the fabric. Examples of such vapor permeable adhe-sive and finish layer materials are disclosed in U.S. Patent 3,633,351; these consist essentially of polyurethane-water-tetrahydrofuran polyurethane mixtures.
Latexes, as well as one-package solutions of polymeri~ed polyester polyurethanes in volatile organic solvents, constitute further examples of conventional mate-rials that can be employed for these purposes.
The following detailed examples are provided to illustrate preferred embodiments of the invention.
Example 1 A stable prepolymer-carbamate composition was prepared from the following ingredients:
Components Parts by Weight Poly(oxypropylene~ glycol, mol. wt. 2000 (POPG) 51.24 Poly(oxypropylene) triol, mol. wt. 2500 (POPT) 3.70 Diethylene glycol (DEG) 1.86 Titanium dioxide (anastase type) 2-45 Hydrated magnesium silicate 7.29 Isophorone diisocyanate 18.92 Dibutyltin dilaurate 0.03 Diethylenetriamine carbamate (DETAC), 35% Solids 14-51 100.00 The hydroxy compounds - POPG, POPT, DEG, and the inorganic ingredients were first mixed in a steam-jacketed glass-lined reactor. The mix was heated to 100 C and the reactor evacuated to remove water. After complete removal of water, the batch was cooled to 50 F or less and the diisocyanate was introduced.
The temperature was adjusted at 86F and the reaction was carried out at that temperature until the isocyanate content of the prepolymer mixture reached about 4.4%. The reaction product was then cooled to 30 C and the DETAC disper-sion mixed in to complete the one-package coating preparation.

The DETAC dispersion consisted essentially of a finely divided form of DETAC, having an average particle size of 2 microns and a distribution ranging from less than 1 micron to 8 microns, suspended in an organic liquid and stabilized by means of conventional surfactants. The specific composition employed in this embodiment was the following one:
Components Parts by Weight Diethylenetriamine carbamate 5-14 Diisodecyl phthalate 5.95 Organo-silicone copolymer 2.54 10 Sodium bis [tridecyl~ sulfosuccinate0.72 Hydrogenated castor oil 0.16 14.51 The prepolymer~carbamate mixture thus prepared had an isocyanate-hydroxy group ratio of 1.88, a viscosity of about 15000 cps and a density of about 34 lbs per cubic foot.
The mixture was applied to a fabric by means of conventional textile coating equipment comprising one coating head and two oven drying units.
A silicone-treated release paper was first passed through the coating head and a 10 mil "fixed gap" coating of the mixture was applied to the paper by means of a knife-over-roller coating unit. The coated paper was then passed through the first oven unit where it was heated for a few moments, namely approx-imately 15 seconds at 240 F to cause the mixture to gel to a still tacky state.
A nylon velour fabric was pressed onto this tacky coating by means of a roller system. The assembly was then passed into the second oven unit where it was heated at 240 F for 3 minutes in order to complete the foaming and curing processes. The release paper was stripped, leaving the foam coated fabric.
Example 2 A three-yard cotton knit was coated with a 10 mil layer of the composition of Example 1 by means of apparatus comprising two coating heads " .

and two oven drying units.
The composition again was applied onto a silicone release paper and passed through the first oven, this time residing at 240 F for 3 minutes in order to complete the foaming and the curing of the prepolymer. The foam-coated paper was then passed through the second coating head where there was applied a 5 mil layer of a commercial polyester crystallizing urethane adhesive in the form of a 20,000 cps, 25% solids solution in l:l methylethyl ketone -dimethyl formamide. The adhesive solution contained 3 parts per lO0 parts by weight of a 50% ethyl acetate solution of a commercial ketoxime-capped TDI-triol adduct as a crosslinking agent. The fabric was then pressed onto the wet adhe-sive surface on the foam and the assembly passed through the second oven for a stay of 3 minutes at 220 to 325 F to cause the adhesive layer to dry and cure.
The fabric was then removed from the release paper.
The resulting foam-coated fabric had moderately good dry cleaning properties and showed no discoloration after lO0 hours of testing with a fadometer.
Example 3 In another embodiment of the invention, a three-yard cotton knit fab-ric was again coated with foam in the manner of Example 2, with the difference that an extra coating head and oven drying unit were employed to place a layer of ~1top skin" coating onto the release paper prior to placement of the foaming material. The skin coating material employed was a conventional commercial lightfast linear aliphatic polyester urethane elastomer dissolved in a isopropyl alcohol-toluene mixture at a solids content of about 25% by weight. About 5 mils of this ~7500 cps solutions was applied by the knife-over-roll technique and dried for 2 minutes at 200F. The foamable material then followed, as in Example 2.
In this manner7 there was obtained an elastic moisture resistant foam-coated fabric which had a very soft hand and possessed excellent abrasion .

~C~7S545 resistance.
Finally, although the examples just described are fairly specific in conditions, materials, and techniques and provide inter alia an illustration of the best mode of practicing the present invention, it must be kept in mind that it is possible for the man skilled in the art to vary the number, the nature and the thickness of the various layers in order to affect the processing char-acteristics and the final properties of the coated fabrics in any desired direc-tion. It should be kept in mind also, as these variations are carried out, that certain properties of the finished fabrics are more dependent on the nature or the absence of a given layer than on other factors. Thus, the hand of the fab-ric is related to a large extent on the foam and skin layers while abrasion re-sistance is essentially a function of the skin. The adhesive layer, on the other hand, strongly influences peel strength and the dry cleaning capacity. In any event, it is evident that many variations can be effected without departing from the limits of the invention as defined in the appended claims.

Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for preparing a polyurethane coated fabric, comprising;
(a) providing a storage stable one-package foamable compositon comprising (1) a liquid prepolymer consisting of a free isocyanate group-containing reaction product of a polyisocyanate with a polyhydroxy compound mixture consisting of at least one diol and one triol, said triol constituting up to about 10% of said mixture by weight and (2) a finely dispersed polyamine carbonate.
(b) applying said composition to a fabric as a thin coating, and (c) heating at a temperature within the range of about 150 to 300°F for a period of up to five minutes to liberate the carbon dioxide and the polyamine and cause the coating to foam and cure.

2. The process of claim 1 wherein the diol component of the mixture comprises at least one polyether.

3. The process of claim 1 wherein the polyisocyanate is an alicyclic or an aromatic diisocyanate and the polyamine is selected from the group consisting of aliphatic diamines, triamines, tetramines, and mixtures thereof.

4. The process of claim 1 wherein the ratio of free isocyanate groups to polyamine amino groups is within the range of 1:0.5 to 1:2.5.

5. The process of claim 1 wherein the foamable composition is applied directly to the fabric and then heated to cause foaming and to cure.

6. The process of claim 1 wherein the foamable composition is first applied to a release surface.

7. The process of claim 6 wherein the composition is heated to a gelled tacky state before being pressed onto the fabric where it is heated further to complete the cure.

8. The process of claim 6 wherein the composition is fully cured on the release surface and is then coated with an adhesive layer before being pressed onto the fabric.

9. The process of claim 6 wherein the release surface has been previously coated with an unfoamed polymeric skin layer.