US3672943A

US3672943A - Process for the production of an artificial leather and the resultant product

Info

Publication number: US3672943A
Application number: US54787A
Authority: US
Inventors: Gerhard Seibert; Klaus Gerlach
Original assignee: Glanzstoff AG
Current assignee: Glanzstoff AG
Priority date: 1969-07-16
Filing date: 1970-07-14
Publication date: 1972-06-27
Anticipated expiration: 1989-06-27
Also published as: ES380405A1; LU61332A1; NL7008046A; AU449513B2; DK136222C; NO129304B; IL34476A; JPS4948482B1; CS151560B2; FR2051784A1; DE1936073A1; IE34115L; FI53326C; DK136222B; CH533201A; AT309088B; FR2051784B1; SU460633A3; GB1307294A; BE750989A

Abstract

PRODUCTION OF AN IMITATION OR ARTIFICIAL LEATHER BY IMPREGNATION OF A NON-WOVEN FIBROUS WEB IN SUCCESSIVE OR SEPARATE STEPS WITH A SOLVENT SOLUTION OF AN ELASTOMER SUCH THAT INCREASING CONCENTRATIONS OF THE ELASTOMER ARE SUPPLIED OVER THE THICKNESS OF THE WEB, IMMEDIATELY COAGULATING THE WEB IN A CONVENTIONAL BATH AFTER THE LAST SOLUTION OF THE ELASTOMER HAS BEEN APPLIED AND THEN WASHING AND DRYING THE WEB TO PROVIDE A FIBER-REINFORCED MICROPOROUS ELASTOMERIC STRUCTURE CLOSELY RESEMBLING NATURAL LEATHER.

Description

June 27, 1972 G. SEIBERT 3,672,943

PROCESS FOR THE PRODUCTION OF AN ARTIFICIAL LEATHER AND THE RESULTANT PRODUCT Filed July 14, 1970 4 AQUEOUS PRECIPITATING BATH/ FIG, 2

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GERHARD SEIBERT KLAUS GERLACH BYQ W W M W Y ATTYS United States Patent 3,672,943 PROCESS FOR THE PRODUCTION OF AN ARTI- FICIAL LEATHER AND THE RESULTANT PRODUCT Gerhard Seibert, Erlenbach, and Klaus Gerlach, Obernau, Germany, assignors to Glanzstoif AG, Wuppertal, Germany Filed July 14, 1970, Ser. No. 54,787

Claims priority, application Germany, July 16, 1969,

Int. Cl. D06m 3/00; B44d 1/16 17 Claims US. Cl. 117-63 ABSTRACT OF THE DISCLOSURE As is well known, an imitation leather can be produced from fibrous mats, webs or fleeces which are impregnated with an elastomeric binder to form a flexible, porous sheet which may then be coated with a top layer. The base material or substrate used for this purpose is preferably a fibrous fleece or non-woven web which has been produced by carding or by manufacture on a paper machine and which has been strengthened by mechanical means, for exampleby stitching or by some other treatment such as heating. Impregnation is carried out using a solution or gel of a synthetic elastomeric polymer, polyurethanes being particularly suitable, with which the web is treated so that the solution or gel completely penetrates the fibrous substrate. After coagulation of the elastomeric polymer in a conventional precipitation bath, the solvent is washed out and the product dried, a substrate or base layer thus being produced in which approximately 20 to 75 parts by weight of the elastomeric binder are uniformly distributed in 80 to 25 parts by weight of fibers. To. produce imitation leather with a smooth surface, fibrous webs which have been treated with the binder and hardened into the porous substrate are then ground on at least one surface and then provided with a top layer, e.g. a thin surface layer of the same elastomer or another suitable polymer.

Although imitation leathers which can be manufactured by known processes have certain very advantageous properties, such as fine pores, flexibility, abrasion resistance and the like, they still differ considerably from natural leather in their structure. As is well known, natural leather comprises a very compact upper surface (grain side) and a less dense, more fibrous underside (flesh side), a structure which has not previously been achieved in an imitation leather. The top layer or surface coating of an imitation leather cannot simply be compared with the grain side of natural leather because some of the most important properties such as stretching or elongation, density and compressibility are very different from those of natural leather. Other particularly valuable properties of natural leather, such as bending characteristics, the soft handle of its underside and the absence of the so-called orange peel effect are due to the distinctive structure of natural leather. Many attempts have been made to produce an imitation leather'which resembles natural leather as closely as possible. However, previous attempts to obtain a top 3,672,943 Patented June 27, 1972 surface similar to the grain side of natural leather have not been satisfactory, even when combining the impregnated fibrous substrate with a coated fabric.

It is a primary object of the invention to produce an imitation leather which more closely resembles natural leather in its entire structure.

Another object of the invention is to provide a process for the production of an imitation leather employing conventional non-woven webs and elastomeric binders to achieve a microporous, flexible, fiber-reinforced elastomer layer having a variation in its cross-sectional properties quite similar to natural leather. Other objects and advantages of the invention will become more apparent hereinafter.

According to the present invention, it has now been found that a substantial improvement can be achieved in a process for the production of an imitation leather by the steps comprising successively applying a plurality of said solutions of elastomer onto one surface of a moving nonwoven fibrous web at intervals along said surface spaced sufficiently to permit a substantially complete penetration of one solution into the Web before application of the next succeeding solution, the individual solutions having an increased concentration of the elastomer in each succeeding application, conducting the impregnated web through a precipitation bath to coagulate the elastomer after the last solution of the elastomer has been applied, washing solvent from the web containing the coagulated elastomer, and drying the washed web.

Alternatively, it is also possible to apply a first solutionof elastomer to the lower surface of the moving nonwoven fibrous Web while then applying only one additional solution having a substantially greater concentration of elastomer to the upper surface of the moving web at a point of time which is not substantially prior .to the application of the first solution to the lower surface, i.e. so that impregnation of the upper surface occurs at-approximately the same time or shortly after impregnation of the lower surface. The applications of the elastomer soltuions of different concentrations from below and above the fibrous web must be regulated in place and amount such that a partial overlapping of impregnated layers of separate solutions is provided from top to bottom over the thickness of the web. With these partially overlapping impregnations, the web is then coagulated, washed and dried to provide a microporous layer of increasing density from the bottom to the top thereof.

The process of the invention is especially advantageously carried out by combining both of these techniques in the following manner. A solution of an elastomer polymer is applied to the underside or lower surface of the fibrous web, preferably by means of a roller applicator, and at the same time or thereafter a plurality of at least two elastomer solutions are successively applied to the upper surface of the moving web. The solution applied to the lower surface of the mat has a lower concentration of the elastomer than any of the solutions applied to the upper surface of the mat and, with several solutions being applied to the upper surface, the elastomer concentration of that solution which is applied at a later stage is higher than that of the solutions previously applied. The distances or intervals between the different positions where the solutions are applied to the upper surface of the web are so chosen that before a new solution is applied, the one previously applied has already penetrated into the surface of the web.

Thus, it is desirable to regulate the application of all of the elastomeric solutions as to point of application and amount so as to provide a partial overlapping of each adjacent layer of impregnated separate solutions from the top to the bottom of the thickness of the web.

The initial material used for the fibrous fleece or web to be impregnated advantageously consists at least partly of synthetic fibres and exhibits a density of 0.08 to 0.30 g./cm. and preferably 0.12 to 0.20 g./cm. These webs or fleeces may be produced in a conventional manner by carding or by a process of deposition from water on a paper-making machine, and then consolidated or strengthened in known manner by stitching and/or by a heat treatment.

The concentration of the elastomer solutions should preferably extend over a range from about 8 to 35% by weight, preferably between 12 and 30% by weight. The concentrations of the individual solutions, which are applied separately to the non-woven web, are preferably adjusted to the density of the inital web so that the finished product will have as large as possible a difference in density between the upper surface and the lower or bottom surface.

Although it is feasible to employ an initial web of somewhat increasing density from bottom to top in order to enhance the desired effect, it is an advantage of the invention that the initial web itself may be of substantially uniform density. As a general rule, it has been found that in using a fibrous web of comparatively low uniform density, a difference in concentration between the different elastomer solutions has a more pronounced effect in producing a variations in the density over the thickness or width of the finished product than in webs of higher uniform density. On the other hand, comparatively more highly concentrated solutions should be used for initial fibrous webs of lower density.

In order to produce imitation leather which has a very high density on its upper surface and thus resembles natural leather very closely in its structure, additional compacting or compression of the fibrous web is advantageously carried out, preferably during coagulation of the elastomer in the precipitation bath. This may be achieved by compressing the completely impregnated fibrous web between rotating rollers in an aqueous precipitating bath after coagulation of the impregnated elasmeric binder has started. This may be carried out in several stages, for example by passing the impregnated Web successively between several pairs of nip or pinch rollers with decreasing distances between the two rollers of each pair. In this way, for example, the density at the upper surface of the finished imitation leather can be increased by to 60%, as compared to that of the product which has not been compressed.

impregnating materials which are especially suitable for this process are solutions of polyurethanes is dimethylformamide or in similar organic solvents known for this purpose. The handle and suppleness of the imitation leather can be improved by adding 5 to 30% by weight of paraffin oil or silicone oil (based on the weight of elastomer) to the elastomer solution applied to the bottom surface of the web. The elastomer solution or solutions applied to the upper surface may contain up to by weight, based on the total polymer content of a vinyl chloride polymer such as polyvinyl chloride or vinyl chloride copolymers. This improves the capacity of the material to be fixed by heat, which is especially important if the imitation leather is to undergo subsequent processing commonly employed in the shoe industry.

In general, the process of the invention is applicable to any solvent-soluble synthetic elastomeric binder capable of being coagulated into a vapor-permeable and preferably microporous film or substrate. These elastomeric polymer binders are referred to more simply as elastomers. Suitable elastomers and their solvents as well as non-solvents employed to gel or coagulate the dissolved polymer are disclosed in great detail in the prior art, for example as set forth in U.S. Pats. No.

2,871,218, No. 3,190,766 and No. 3,208,875. The polyurethanes exhibit especially desirable leather-like qualities whether used along or in combination with other wellknown elastomeric polymers or even small amounts of non-leastornen'c polymers. For this reason, the use of a polyurethane elastomer is especially preferred without excluding minor proportions of other'suitable elastomers. Moreover, it is desirable to select an elastomer which can be dissolved over the broadest possible range of concentration consistent with subsequent coagulation and formation of a vapor-permeable structure, and the polyurethane elastomers are especially suitable for this purpose. Of course, other known additives may also be included in the initially prepared elastomer solutions, usually in very minor amounts although the solution forming the top layer in the process of the invention may contain relatively larger amounts of other elastomers and/or compatible additives.

The process according to the invention is relatively simple and can be carried out continuously with conventional and rather inexpensive apparatus. The process is further illustrated by means of the accompanying drawings in which:

FIG. 1 is a schematic flow sheet or side elevational view of suitable apparatus for continuously carrying out the process of the invention; and

FIG. 2 is a diagrammatic longitudinal cross-sectional view on an enlarged scale of the non-woven fibrous web undergoing impregnation with different elastomer solutions.

In FIG. 1, a substantially dry non-woven fibrous web is continuously supplied by means of a pair of feed rollers 2 and passed over a roller applicator 3 which rotates in a vat 4 containing a first polyurethane solution of relatively low concentration. A stripping knife 5 is directed toward the surface of the roller just before its point of contact with the fibrous web. The distance of this knife 5 from the surface of the roller may be, for example, about or A the thickness of the fibrous web, the thickness of layer of polyurethane remaining on the surface of the roller and transferred to the fibrous web being substantially equal to a predetermined set interval between the knife and the surface of the roller. The polyurethane solution penetrates the fibrous web from the bottom side and is absorbed relatively quickly by the web. 7

A doctor knife 6 is arranged above the roller 3 to sup ply an elastomer solution onto the top surface of the web, this second solution having a substantially higher concentration of elastomer than the first solution A. In order to obtain an initially formed layer of elastomer solution B having the required thickness, the width of the gap between the doctor knife 6 and the surface of the web 1 is adjusted to about A or of the thickness of the fibrous web. Since the rate at which the elastomer solution penetrates the web depends partly on the viscosity of the solution, i.e. the quantity of binder used for impregnation is not determined entirely by the width of the gap between the doctor knife and the surface of the web, it is advisable to determine the most suitable width of the gap by a few trial adjustments. After the point or short transverse zone of application of the solution'B, the fibrous web is carried along freely until the applied coating or layer applied has penetrated into the fleece. This point of penetration is easily recognized since the surface of the web then appears to be fibrous and almost dry.

Another elastomer solution C of still higher concentration than either of the solutions A and B is then applied 1 onto the top surface of the web 1 by means of a doctor knife 7, in this case arranged above a roller 8. Here again the width of the gap between the doctor knife 7 and the surface of the web 1 is adjusted'according to the thickness of the layer of elastomeric impregnating agent which is to be applied to the fibrous web, as explained above. As soon as this layer C has penetrated into the web, thecontinuously moving web passes between a pair of nip rollers 9 which exert a very slight pressure on the fleece in order to relatively even out the impregnation but without squeezing off any elastomer solution or changing the relative positions of the separately applied layers.

Thereafter, a fourth elastomer solution D of highest concentration is applied by means of a doctor knife 11 arranged over a roller 10. Lastly, the web, which is now completely impregnated with elastomer solutions is introduced into a vat 12 containing water as a non-solvent precipitating bath in which coagulation of the elastomeric binder takes place. Subsequent treatment can-also be carried out continuously in known manner inconventional apparatus (not shown) arranged after the vat, the solvent first being washed out and the resulting porous product then dried. The impregnated fibrous web after being dried can be wound and stored. Also, it may then be ground to smooth the top surface and provided with a top layer of an elastomer such as the preferred polyurethane. Alternatively, the material may be directly subjectedto the usualleather finishing treatments immediately after drying, especially if the last applied layer of polyurethane has not been permitted to completely penetrate into the top surface before coagulation. I I

The process explained with reference to FIG. 1 may, of course, be modified within the scope of the invention. For example, fewer or more than threeelastomer solutions may be applied successively to the top surface fibrous web, provided the concentration of the solutions increases with each successive application.

In general, however, it is usually desirable to employ a minimum of three separate elastomer solutions, one of which can be impregnated from the bottom surface, up to a maximum of about five or six separate elastomer solutions depending upon the total thickness of the initial nonwoven fibrous web and excluding any final top surface coating which does not fully impregnate the web.

v The process illustrated in FIG. 1 may also be modified in that all the solutions may be applied to the upper surface of the web or, instead of applying solution B in approximately the same location as solution A, it may be applied at some distance displaced from the location of application of solution A in the direction of continuous movement of the fibrous web. In this case, another combined assembly of doctorknife and guide roller is arranged after the guide roller.3.

Furthermore, it is not absolutely necessary to provide a pair of rollers 9 between the points of application of solutions '0 and D. On the other hand, such pairs of nip rollers, which even out the application of the impregnation as described more fully below, may be arranged advantageously between every two points or zones of application of the different solutions. Also, afterentering the aqueous bath 12, where the web is transported on suitable guide rollers 12a (usually over a greater length thanthat shown in the drawing), one or more pairs of compression rollers 12b can be employed during coagulation to further increase the elastomer density.

. As a general rule, the individual elastomer solutions are most conveniently applied by means of a knife or doctor blade except for those instances in which the first solution A is applied to the bottom surface where a roller applicator is preferred. In all cases, it is helpful to apply approximately equal thicknesses of the solution layers which are intended to fully impregnate the fibrous web and in such an amount that the last of such layers of elastomer solution will substantially completely impregnate into the web so that the void spaces between fibers is filled or almost filled. Thus, with three separate elastomeric solutions, disregarding a final top layer which remains at least partially above the web surface, the individual impregnated layers can each be about onethird of the thickness of the initial dry web. This procedure is of course subject to a relatively broad variation, but it will generally be found preferable to employ variations in such a manner that those solutions with the lowest concentration of elastomer are applied in wider or thicker layers while the more concentrated solutions are correspondingly reduced in thickness.

The primary object of a carefully regulated application of individual elastomer solutions of different concentra tion is to achieve an impregnated web with a moreor less gradually increasing content of the elastomer from the bottom surface to the top surface. The nip rollers 9 located between the last fully impregnated solution C and the top coating D and/or between preceding impregnated solutions B and C have the effect of achieving not only a more uniform evening out of individual layers of solution but also a bringing together of the applied layers internally of the web and ensuring a partial overlapping of the layers in terms of a variation in the concentration content of elastomer over the thickness of the web. The liquid solvent in each layer is somewhat more fluid or exchangeable between adjacent layers, and by using a very slight pressure on the completely or partially impregnated web, there occurs a blending of the fluid solutions at their interfaces and a corresponding transfer of one layer of more concentrated elastomer into the next adjacent layer of less concentrated elastomer. It will be understood, of course, that such evening out or blending of the solution layers must not cause any substantial removal of solvent, and a complete blending of one layer with another must be avoided. Therefore, depending upon the viscosity of the layers, it is often preferred to avoid using the nip rollers 9 or else employ them only under an extremely slight pressure since there is a natural tendency for the layers to blend by themselves.

In this respect, it is also generally preferred to apply successive layers of the elastomer solutions as closely together as possible, e.g. by adding a succeeding layer almost immediately upon disappearance of the preceding layer'into the surface of the web. Also, once the web is fully impregnated, with or without a top covering or coating layer, it is generally desirable to conduct the impregnated web immediately into the coagulating bath, i.e. without undue delay so as to prevent excessive blending one solution layer into the next adjacent layer. The allowable time of delay will of course also depend upon the relative viscosity of the individual elastomer solutions and the extent to which blending has been promoted by slightly compressing the web prior to its entry into 7 the precipitating bath. Once the impregnated elastomeric binder begins to coagulate, it is believed that this blending between adjacent layers is stopped or at least substantially retarded since the viscosity of the layers increases rapidly with gelling or coagulation.

Once the impregnated web is being coagulated or hardened in the precipitating bath, a considerably greater pressure can be applied thereto by one or a plurality of nip rollers. Surprisingly, this leads to a much greater increase in the density of the uppermost layer and a pro portionately smaller increase in density of the next lower layers, the smallest increase in density appearing in the bottom layer of originally the least concentration. This effect not only enhances the desired variation in density but also tends to provide a more compact and stronger product with excellent surface characteristics as between the so-called grain side and flesh side of the imitation leather.

The overlapping or blending processes which occur when impregnation is carried out in several stages are illustrated diagrammatically in FIG. 2. The initially dry fibrous web 13 is shown on a scale which is greatly enlarged compared to the linear indication of the web 1 shown in FIG. 1. This web 13 corresponds to a longitudinal cross-section of a short length of the moving web, the arrow indicating the continuous direction of open space bounded by the top surface 13a and the bottom surface 13b.

, The elastomer solution A is applied to the bottom side. 1311 of the web by means of the roller 14. This first layer A of the impregnating agent on roller 14 is stripped oif by means of a knife (not shown) to a thickness equal to about /3 of the thickness of the fibrous web 13. Owing to therelatively low viscosity of solution A, it penetrates fairly rapidly into the fleece which is being moved forward, andit becomes distributed over the shaded area or thickness of the web roughly indicated by the reference numeral 15. The solution B, which is more highly concentrated, is applied at a position transverse to the moving web and approximately directlyabove the axis of the roller 14'by means of a doctor blade 18. Owing to its higher viscosity, thissolution B penetrates the fleece slightly 'more slowly and becomes distributed as the shaded layer 16 in the fibrous web. SolutionC, the distribution of which is indicated by the referencenumeral l 7 ,'"i s applied with doctor blade 19 to the top surface 13a of the web at the transverse location 17 when no.

more-ofthe impregnating agent or solution B can beseenonthe surface of the web, i.e. when the surface appears almostdry. Owing to the still higher viscosity of this solution C and the solutions already present in the web solution C, penetrates evenmore slowly. Theboundaries of the layers of impregnating agent. 15, 16 and 17 are not sharpQbut-blurred or blended together. Viewed as a whole, it is precisely due to these gradual transitions from one layer of an elastomer solution to the next in the fibrous web that the density of the elastomer material increases more or less continuously from the bottom surface 13b to the upper surface 13a in the finished imitation or synthetic leather product.

The accumulation of elastomer solution on the lower edge of the doctor blades 18and 19 has also been greatly exaggerated in FIG. 2, since it is generally desirable to maintain the level of such accumulating binder or impregnating agent at about the height of the short gap between the

blade

18 or 19 and the top surface 134; of the web. This can be accomplished very easily by regulating the flow of elastomer solution down the inclined edge of each doctor blade as indicated in FIG. 1 or by employing a suitable metering feed trough or other conventional feed means for continuouslysupplying elastomer solution directly to the tip of the doctor blade at a predetermined rate.

The application of the top coating or layer of elastomer D as shown in FIG. 1 is optional, for example to ensure a final complete impregnation of the web or an excess surface coated layer to completely hide the fibrous material of the web, e.g. to prevent any loose ends or loops from projecting from the top surface. When used. for this latter purpose, a special elastomer composition may be.

employed to provide a relatively thin but dense and abrasion-resistant surface coating. On the other hand, the

elastomer concentration of D may be approximately the same as that ofsolution C, simply to provide a finish-' ing touch or final filling of the web to provide avery uniform top layer just before coagulation. These and other variations can obviously be carried out, e.g. such as grinding and/or bufling the surfaces of the finishedtions and the stepwise application of these solutions successive operations according to the invention ensure the formation of a structure which resembles that of natural leather to a much greater extent than'has been achieved prior to this invention. With a very' thin non woven fibrous web, it is feasible to employ only one top layer and onebottom layer of elastomer solution applied onto the'opposite side or surfaces of the web. Even. though the variation in density is somewhat less in this case, it can be improved by preferably preblending the layers with slight compression before entering the pre- 8 cipitation bath and further compressing the web during coagulation in the bath.

The final products produced in accordance with. the.in-. vention exhibit a finely porous, dense grain side 7 (upper surface) and a softer, fibrous flesh side (bottom,surface). This structure can be clearly observed when the synthetic leather is split. The split layers, moreover distinctly exhibit a firmness which'decreases and a pore size which increases from the upper surface to the bottomsurface of the synthetic leather.

The process of the invention is further illustrated in detail by reference to the following examples, it being understood that the invention .is not restricted to such examples.

EXAMPLE 1 A non-woven fleece or web is prepared from an aqueous dispersion of nylon fibers and regeneratedcellulose fibers (in a weight ratio of polyamidezviscose fibers of :20) by 'deposition'ona paper-making machine, and the waterlaid web is consolidated, i-.e., rendered more strongly coherent, by a brief heat treatment. The dry fibrous web has a weight of 310 g./m a density of 0.13 'gl/cmfiand a thickness of 2.4 mm. e

'Thefollowing elastomer pregnating'the web: Solution A:

solutions are used for im- Percent by Polyurethane 14.0 Dimethylformamide 78.0 SiIicone oil 2.0 Water 6,0- Solution B: I j j Polyurethane 16.5 :Dimethylformamide 77.5 Water i 6.0 Solution C: p j p i f Polyurethane 20.0

V Copolymer of vinyl chloride and maleic acid anhydride .1; 7.0 Dimethylformamide j i Water j"3.0

The polyurethane used inall solutions is the reaction product of polybutylene adipate'having an average 'molecular weight of approximately 1000, diphenylmethanetfl' diisocyanate and butanediolin a molar ratio *or1;'3.1 :211.

The silicone oil is a phenylmethyl"polysiloxane with a with solution A. A knife is arranged just beforethepoint ofcontact 'between'the roller and the bottomsuiface or; the web-at a short distance from the roller surface in order to strip the solution-A to a layer thickness of'0.'5

mm. The elastomersolution transferred to the bottonr surface of the webisthereby applied in a thickness correspondingtoabout 0.5 kilogram per square meter: of the web. Solution B-is applied at the'same time by means of a doctor blade situated above the webin line wim'meaxis of the roller-situated below-the web. The gap be tween the doctor blade: and the upper surface of'the' web is 0.6 mm. Solution B is thereby applied at the rate of 0.77 kg.-/m-.3-of.the web. e s

After the roller applicator and the first doctor-blade, the web or fieeceruns freely for alength 0150.6 meter (60 cm.) and is then passed between a pair of hip rollers providing a slight pressure. Before the web enters this pair of ;niprollers, the solution-B has completely 'pene- I trated into the fibrous web, i.e.'so .that the surface of the I distance of 0.5'meter (50 cm.) beyond the pair of'nip rollers, the web is conveyed over a guide roller arranged to cooperate with a second doctor blade, which is arranged at a gap distance of 0.7 mm. from the top surface of the web and applies solution C at the rate of 0.8 kg. of solution per square meter of fibrous web.

At a distance of 2 meters (200 cm.) beyond the guide roller and second doctor blade, the web enters a bath of water maintained at a temperature of 40 C. in which the elastomers are coagulated and the solvent is washed out to form a porous elastomeric structure. The web is then dried carefully under conventional conditions to maintain the desired porous structure. The finished synthetic leather weighs 715 g./m.

To determine its density, the finished product is split into three layers of equal thickness, each layer amounting to 0.64 mm. The densities of these layers taken in order from the bottom surface to the upper surface, are found to be 0.29, 0.34 and 0.48 g./cm. respectively.

In a second experiment under otherwise the same conditions but wherein about 80 seconds after immersion in the precipitation bath, by which time coagulation of the impregnated elastomer has already begun, the completely impregnated fibrous web is passed successively between 6 pairs of nip rollers which are arranged about 40 cm. apart in the bath, each pair of rollers exerting a force of 9 kg./ cm. on the web. An imitation or synthetic leather which has a'wei'ght of 705 g./m. is then obtained after drying. The three layers, each 0.41 mm. in thickness, obtained by splitting as in the preceding experiment are found to have densities of 0.45, 0.52 and 0.73 g./cm. respectively.

EXAMPLE 2 The process described in Example 1 is repeated, using a dry fibrous web of the aforesaid composition which has a thickness of 2.53 mm. and a density of 0.13 g./cm. The polymer solutions used in succession have the following compositions:

Solution A:

Polyurethane Percent by wt. 16.0

- The polyurethane used in this instance was prepared by reacting polybutylene adipate (molecular weight of approximately 1000), diphenyhnethane-4,4'-diisocyanate and butanediol in proportions of 1:2: 1.

After application of the solutions in the same manner as described in Example 1, the impregnated web is passed through the water bath without any appreciable application of pressure during coagulation. The resulting imitation leather after being dried has a weight of 775 g./m. and a thickness of 1.29 mm. The densities of the three split layers, each 0.43 mm. in thickness, are 0.52, 0.60 and 0.68 g. cm. respectively, measured in the order of the layers from bottom to top.

EXAMPLE 3 Solution A: Percent by wt. I Polyurethane 14.0 Paraflin oil 2.0

10 Solution A: Percent by wt. Water 6.0 Dimethylformamide 78.0 Solution B:

Polyurethane 16.5 Water 6.0 Dimethylformamide 77.5 Solution C:

Polyurethane 20.0 Vinyl chloride copolymer of Example 1 5.0 Water 4.0 Dimethylformamide 71.0

The polyurethane in this instance was prepared by reacting polybutylene adipate (molecular weight of approximately 1000), diphenylmethane-4,4-diisocyanate and butanediol in the ratio of 1:2.5: 1.5.

The coagulation treatment in the aqueous bath is carried out without application of pressure. The resulting imitation leather has a.weight of 778 g./m. and a thickness of 1.75 mm. The three split layers, each of 0.58 mm. in thickness, have densities of 0.33, 0.46 and 0.56 g./cm. respectively.

EXAMPLE 4 A fibrous web having a density of 0.145 g./cm. and a thickness of 2.81 mm. is again impregnated as in Example 1 with three distinct solutions of the following compositions:

The polyurethane was prepared by reacting polybutylene adipate (molecular weight of approximately 1000), diphenylmethane-4,4-diisocyanate and butanediol in the ratio of 1:2.25:1.25.

After treating the impregnated fibrous web for coagulation of the elastomers without application of pressure followed by washing and drying, the finished imitation leather product had a weght of 885 g./m. and a thickness of 2.40 mm. The three split layers, each of 0.80 mm. in thickness, have densities of 0.29, 0.36 and 0.45 g./cm. respectively.

When coagulation is carried out under pressure as in the second experiment of Example 1, an imitation leather product having a weight of 874 g./m. and a thickness of 1.62 mm. is obtained. The split layers of 0.54 mm. in thickness have densities of 0.41, 0.50 and 0.63 g./cm. respectively.

EXAMPLE 5 A fibrous web of 1.85 mm. in thickness and having a density of 0.22 g./cm. is used as the initial material and is impregnated successively as in Example 1 with solutions having the same composition as indicated in Example 4.

The imitation leather, which is slightly compacted during coagulation, exhibits a weight of 687 g./m. and a thickness of 1.31 mm. The split layers, which are 0.41 mm. in thickness, have a density of 0.47, 0.52 and 0.67 g./cm. respectively.

EXAMPLE 6 Starting with the same non-woven fibrous web as in Example 5, impregnation is carried out in three stages 1 1 under the same conditions as indicated in Example 1. The solutions applied in succession have the composition set forth in Example 2. Coagulation of the polymer is then carried out without application of pressure and conventionally washed and dried. The imitation leather product has a weight of 705 g./m. and a thickness of 1.31 mm. The split layers have a thickness of 0.4 mm. each and densities of 0.48, 0.52 and 0.62 g./cm. respectively.

Similar results are achieved when all three of the clastomer solutions are applied and impregnated into the top surface of the fibrous web. However, the results are somewhat more uniform when applying the solution of lowest concentration by means of a roller applicator to the bottom surface of the web. Likewise, it is possible to achieve very satisfactory results, when using three, four or even more successively added solutions of increasing elastomer concentration in addition to the solution impregnated into the bottom surface. Moreover, when the finished synthetic leather product is split into increasingly smaller layers, for example by halving the first three split layers, a very desirable gradual increase in density from bottom to top can be more completely identified.

It is not essential to further treat the initially coagulated, washed and dried product of the invention since it can be immediately used as a non-finished leather-like product, although it is usually desirable in this case to apply the top layer or a final surface coated layer just prior to coagulation. In order to fully develop the grain side of the product of the invention, it can be buffed or polished and then further coated with a thin film-forming polymer or still another microporous elastomeric layer as is often required for synthetic shoe leathers, especially so as to provide -a water-impervious but vapor-permeable outer surface. Otherwise, the smoothed or developed grain side of the product according to the invention can be merely dyed or finished in the same manner as normally observed for the conventional treatment of both natural and synthetic leathers.

Both the visual appearance and the physical properties of the synthetic leather materials of the present invention are so closely related to natural leather as to provide an excellent substitute for a very wide variety of leather applications.

The invention is hereby claimed as follows:

. 1.In a process for the production of an imitation leather" wherein a non-woven fibrous web is impregnated with a solvent solution of an elastomer capable of being coagulated and hardened into a microporous elastomeric structure, the impregnated elastomer is coagulated by immersion in a precipitation bath, solvent is washed from the web containing the impregnated and coagulated elastomer and the resulting washed web is dried, the improvement which comprises:

successively applying a plurality of said impregnating solutions of elastomer onto one surface of a moving non-woven fibrous web at intervals along said surface spaced sufliciently to permit a substantially complete penetration of one solution into the web before application of the next succeeding solution, theindividual solutions having an increased concentration of the elastomer in each succeeding application and the total amount of said individual solutions being sulficient to provide at least two partially overlapping impregnations within said web; and conducting. the impregnated web through a precipitation bath to coagulate the elastomer only after the last solution ofthe elastomer has been applied. 2'. A process as claimed in claim 1 wherein one solvent solution of the elastomer is applied to the lower surface of the moving web from a roller applicator while successively applying said plurality of other solvent solutions of elastomer to the upper surface of the moving web such that the first of the applications to the upper surface occurs at a point of time which is not substantially prior to the application of said one solution to said lower surface, the

12 solution applied to said lower surface having a lower con: centration of elastomer than anyv of thesolutions applied to the upper surface. v

3. A process as claimed in claim 2 wherein the solvent solution applied to the lower surface of the web contains. about 5 to 30% by weight, with reference. to the weight of elastomer, of parafiin oil or silicone oil.

4. A process as claimed in claim 1 wherein the increasing concentration of the elastomer in succeeding applications from a solvent solution ranges between about 8 and 35% by weight.

5. A process as claimed in claim 1 wherein the increasing concentration of the elastomer in succeeding applica-: tions from a solvent solution ranges between about 12 a nd 30% by weight. 1 a w 6. A process as claimed in claim 1 wherein the initial non-woven fibrous web to be impregnated has a density of from about 0.08 to 0.30 gram/cm. v

7. A process as claimed in claim 1 wherein said elastomer consists essentially of polyurethane.

8. A process as claimed in claim 7 wherein the last applied solution contains up to about 35 by weight,- with reference to the polyurethane elastomer, :of aavinyl chloride polymer.

9. A process. as claimed in claim 1 whereinthe im-' pregnated web is compressed in the precipitation bath: during coagulation of the elastomer. I 1

10. A process as claimed in claim 1 wherein there are at least three succeeding applications of said solvent solu-# tion of elastomer.

11. The imitation leather product obtained by the process of claim 1 exhibiting a graduallyincreasing density over the thickness of the impregnated non-woven-fibrous web. I

if 12. In a process for the production of an imitation leather wherein a non-woven fibrous web is-impregna'ted with a solvent solution of an elastomer capable of being coagulated and hardened into a microporous elastomeric structure, the impregnated elastomer is coagulated by immersion in a precipitation bath, solvent is washed from the web containing the impregnated and coagulated elastomer and the resultingwashed'web is dried,,the' improvement which comprises: 7

applying a first solution of elastomer to the lower surface of the moving non-woven Web; I I E applying at least one additional solution of the elastomer to the upper surface of the moving web at a point of time which is not substantially prior to the application of the first solution to'said lower surface, the concentration of elastomer in said at least one additional solution applied to' the upper surface being substantially greater than the concentration of elastomer in said first solution and said concentration of elastomer being increased in any successive applica-. tions of more than oneto said upper surface, all of the' applications of elastomer solutions being regulated as to place and amount as to provide a partial over-.- lapping of impregnated layers of, separate solutions from top to bottom over the thickness of the web;" conducting the impregnated web through a precipitation; bath to coagulate the elastomer after the last solution of the elastomer has been applied. 13. A process as claimed in claim 12 wherein, the initial non-woven fibrous to be impregnated has a density of about 0.08 to 0.30 gram/emf. 4

14. A process as claimed in claim 12 wherein the initial non-woven fibrous to be impregnated has a density, of about 0.12 to 0.20 gram/emi v 15. A process as claimed in claim .12 wherein the iin-j pregnated web is compressed in the precipitation bath web.

References Cited UNITED STATES PATENTS Fukushima et al 117-63 Dunderdale 117-76 T Hochberg 11768 X 10 Hodge et a1 117-76 T 14 Knibbe et a1 117-76 TX Saligny et a1 ll763 Russell ll783 Holden 117-135.5

WILLIAM D. MARTIN, Primary Examiner R. HUSACK, Assistant Examiner US. Cl. X.R.

ll765.2, 68, 76 T, 111R, 135.5