US2015441A - Finishing of artificial leather - Google Patents

Description

P 1935, M. o. SCHUR ET AL I FINISHING OF ARTIFICIAL LEATHER Filed Jan.. 27, 1955 75 dizakw er/gaze (7&dd

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Patented Sept. 24, 1935 UNITED STATES FINISHING 0F ARTIFICIAL LEATHER Milton 0. Schur and Benjamin G. Hoos, Berlin, N. 11., assignors to Brown Company, Berlin, N. H., a corporation of Maine Application January 27, 1933, Serial no. 653,854

14 Claims.

This invention relates to the manufacture of artificial leathers more particularly of the kind comprising a base of interfelted cellulose fibers bonded together with rubber as an impregnating Artificial leather of this general class is customarily made by forming a bibulous, waterlaid web or felt on machinery of the papermaking type, impregnating the dry web with a suitable latex composition, and drying the impregnated web so as to coagulate the rubber bonding agent, which imparts to the dried product, toughness, tear-resistance, water-repellency, body, and other leatherlike qualities. In some instances, the rubber may be coagulated in the freshly-impregnated web through the use of suitable coagulating media, such as acetic acid, alum, or the like, as this does away with the tendency for the dispersed'rubber particles to migrate to the surface of the web during the drying operation.- It is usually preferable to put the rubber impregnant introduced into the web in a vulcanized condition, as by using a vulcanized latex composition to begin with and/or by adding vulcanizing ingredients to .the latexcomposition and then drying the lateximpregnated web under vulcanizing temperature conditions;

Before artificial leather fabricated as just describedis useful in many arts, it must be finished to simulate very closely calf-skin, kidskin, or other similar soft or pliant natural leathers treated with a, so-called water finish. While this desideratum applies to artificial leathers to serve, for instance, in note book covers, cigarette cases, belts, automobile tops, or the like, it also obtains in connection with artificial leathers which are used for upholstering furniture, automobile seats, or the like, and as shoe upper material. In these latter connections, moreover, the artificial leather must be finished in such a way as to undergo satisfactory tacking, stitching, or similar anchorage and, above all, to resist effectively abrasion and flexing incident to such service.

So far as we are aware, no one has hitherto prepared an artificial leather intended to simulate calf-skin, kid-skin, or other similar genuine smooth leathers and which has successfully been used on a commercial scale as upper stock in the manufacture of shoes. The difiiculties have been many, not the least of which is the difficulty of finishing smooth surface artificial leather to answer the requirements of the trade, because blemishes, minute and otherwise, present in the artificial leather base would show up. disconcertingly plainly in a smooth surface resembling the finished skin side of such natural leathers as calf-skin, kid-skin, or the like. Indeed, water-finished artificial leathers, as heretofore made, either had the coarse, hungry 8 look of split leather, or, if coated sufficiently heavily to fill the surface pores, were apt to resemble oil cloth more nearly than natural leather, because of the absence therefrom of pores and other surface markings such as occur in natural leather and lend a characteristic appearance thereto. The fact is that when artificial v leather is so finished as to cover up the surface blemishes inhering in an artificial leather comprising even the best-textured and smoothest faced felted base, several serious difllculties immediately crop up. Thus, the finished surface rather than being leatherlike in appearance and in properties is, as already indicated, reminiscent of oil cloth, develops a coarse break and 20 becomes permanently and unsightly wrinkled upon flexing, and is apt to be practically impervious to the passage of perspiration therethrough, i. e., to lack breathing qualities, with consequent "burning of the feet when used as 35 a shoe upper material. This holds true when the finishing composition contains any one or V a mixture of such materials as rubber, lacquer, wax, resin, casein, or oxidizable oil. When it is attempted to lend grain to the artificial leather 30 by embossing, it is found exceedingly diificult, if not practically impossible, to realize a grain sufficiently characteristic of natural leather.

In accordance with the present invention, we produce an artificial leather which is so fin-35 ished that not only is it highly satisfactory for the various purposes hereinbefore enumerated, but is eminently suited for the exacting role of a shoe upper material. It is in this latter role, v therefore, that we shall now describe our fin- 4o ished artificial leather. In producing our finished artificial leather, we recognize that a skin is necessary not only to disguise or to cover the relatively coarse grain of the base sheet,

a but also to protect the sheet against abrasion 45 suffered during shoe-making as well as against scufiing encountered during service. We therefore provide our base sheet with a skin sufficiently tough to withstand to a reasonable degree abrasion and scufiing,-yet not so thick 50 that unsightly breaking and creasing occurs as a result of flexing. In addition, the skin is sufliciently elastic to remain intact throughout molding or lasting and sufliciently tough and abrasion-resistant to withstand the severe wip- 56 Q '10 were afragment scuffed up and an attempt,

made to pick it up, an entireor large area of skin would be removed from the base sheet. It is capable of undergoing continued flexing as at the vamp portion of a shoe without crack- 15 ing or serious wrinkling. All of the foregoing properties are exceedingly important, as failure to realize any one of them means the failure of a shoe upper stock from a. commercial point of view.

After long-continued investigation and research, we have found that a skin-forming com-' position wherein glue, glycerine, and latex, are' combined in definite proportions can be applied to a base sheet of artificial leather in controlled 25. amount to yield a primary skin or membrane posessing many of the foregoing desiderata. Each of the components of the skin-forming composition contributes most significantly to the properties desired in the skin deposited on the 30.--base sheet. Thus, the rubber afiorded by the [latex imparts elasticity to the skin. The glue furnishes the desired resistance to abrading or scufilng action. The glycerine functions not only as a plasticizing or flexibilizing agent for the 35 glue, but increases the capacity of the skin-for permitting moisture and perspiration to diffuse therethrough and thus to minimize the danger of the leather burning the feet. If excessive glue is used, the skin becomes brittle 40 and cracks during flexing an'd/or stretching. If

excessive glycerine is used to compensate for such defect, the skin becomes sticky and cannot be finished to look like leather. If excessive rubber is used, the skin falls to adhere properly to 45 the base, so that, when the skin is scuffed up in use and a protruding fragment is picked at, the skin will peel over a substantial area. When the skin-forming composition is properly compounded, however, a fragment of skin will, when so, picked at, break oif in much the same way' that "the skin on natural leather does.

.We shall now give a typical primary skinforming composition falling within the purview of the present invention. Here is the formula 55 such a compo'fltionr- Per cent Latex solids added as in the form of normal latex containing about 30% to 40% latex solids 60 to 80 00 --Anti-oxidant as in the form of {Age- Rite White", about 0.36

Dye or. pigment such as "Con. Pheno 8G about 1.33 Animal glue solids 10 to 25 Glycerine as in the form of anhydrous commercial gLvcerine 7 to 15 'The foregoingskin-f'orming composition may be applied to the surface of the artificial leather 7o Qas a dilute aqueous mixture having a water content of say, about 82%, when application is made by the usual atomizer or spray gun. While the composition may be applied by the use of the usual coating or spreading machines as one or is -more layers, it is preferable to spray the composition onto the surface of the artificial leather as four successive coats with partial drying of one coat before a succeeding coat is superimposed. In any case, however, the thickness of the deposited skin is closely regulated so that in dry condition it weighs from about 6 to 18 grams per square foot of artificial leather surface. When the composition is applied by a spreading machine, it may be of a creamy 'or thicker consistency so as to facilitate spreading. If desired, suitable thickening agents, such as the alginates, may be added in small amount to the composition to promote easy-spreading thereof.

While there are various sequences of preparing the primary skin-forming composition, we prefer to dissolve the dye and the glue as a mixture in a sniall amount of warm water and to add the dissolved anixture slowly and with constant gentle stirring to a previously prepared 20 aqueous mixture containing the .latex, anti-oxidant, and glycerine in appropriate amount and diluted with sufllcient water to yield a composition amenable to successful spraying. In order that the sprayed composition may dry into the smoothest kind of skin, it is preferable that drying of the sprayed composition be accomplished slowly at about room temperature.

'After a primary skin has been deposited and dried as hereinbefore described on the base sheet of artificial leather, it is surfaced with a film of a glue-glycerine mixture. The mixture may consist of about 30% to 60% of commercial anhydrous glycerine and 70% to 40% of animal glue.

a typically good mixture consisting of 55% glycer- 35 to the solution so as to impart the desired color thereto. The dried film, by virtue of the flexibilizing action of the glycerine on the glue, resembles closely the protein skin of natural leather and becomes integrated with the underlying primary skin. For the best results, the film when 1 dried should add from 0.05 to 0.50 grams to each square foot of the artificial leather. It is thus seen that the surfacing film is very much thinner than the underlying skin. The surfacing film may be dressed with a mixture of shellac, ox-

blood, glue and glycerine, or any other suitable water finish which may be conveniently applied with a swab. The water finish may serve to add depth, gloss, feel, and other artistic qualities to the artificial leather and may in some instances w I include dyes and/or p miehts.

It is distinctly desirable to insolubilize or to tan the glue component of the skin as a whole, including that of the surface film. While various insolubilizing or tanning agents may be used for 55 this purpose, it is preferable to expose, the finished sheet to the action of formaldehyde under the appropriate time, concentration and temperature conditions. One satisfactory procedure is to expose the flnished sheet to an'atmosphere of formaldehyde vapor atv room temperature for about 16 hours and then to heat the sheet to a temperature of about 220 to 230? F. in the air and to the sheet at this temperature for about IOminutes or so. The final heating'operar V tannic acid, the usual tanning extracts and, un-.

der carefully controlled conditions, through the use of chromates and ultra-violet light.

Our practice of finishing artificial leather is comparatively inexpensive and surprisingly effective. The primary skin has remarkably high scuff resistance and tenacity of bond with the base sheet of artificial leather. The primary skin cannot, however, be successfully glazed because of its high rubber content. As is wellknown, leather is glazed or burnished by frictioning it with smooth, hard objects, usually by bringing a curved glass surface to bear against its surface and reciprocating the curved glass surface thereagainst until the desired gloss is reached. The rubber component of the primary skin prevents smooth sliding action of the glass surface thereupon and tends to become so heated as to stick to the glass surface and thus to inhibit smooth burnishing' action. It is for this reason and also because the primary skin is comparatively easily scratched and defaced by the digging-in action of the wipers of a bed-lasting machine, that we surface and dress the primary skin with films which are highly resistant to scratching and which makes possible satisfactory glazing and staking of the artificial leather. The films amalgamate intimately with the primary skin so as to constitute in effect a single skin which possesses the desired combined properties of both the primary skin and surface film. In order to demonstrate the scufi resistance of artificial leathers finished in accordance with our invention, samples were rubbed on the finished surface against a coarse canvas pad as shown in Figures 1, 2, and 2a, wherein,---

Figure 1 is a side view of the testing machine.

Figure 2 is a section on the line 2-4 of Figure 1.

Figure 2a. is an enlarged view of a member of the machine.

As shown in Figures 1 and 2, a can i provided with shot 2 is mounted on the carriage] supported by the curved member 4 to which is clamped the specimen of leather 5, finished. side down, resting on the canvas 6 fastened to the hardwood base bymeans of thumb-tacks. The dimension p is 1 inch; the radius of curvature r is inches.

' The total weight carried by the specimen is 600 Wet canvas Dry canvas Natural kid-skin 5 to 12 minutes 5 to 12 minutes. Natural calf-skin 5 to 20 minutes... to 20 minutes. Our artificial leather 5+ minutes 5 to 20 minutes.

I The natural leathers used for purposes of comparison were of the usual commercial variety weighted 3 and were finished in the conventional manner. The values tabulated above represent the time required to rub up fibers on the specimens listed. It is to be observed that the scufi. resistance of our finished artificial leather approaches that of 5 the usual commercial natural upper leathers. The remarkable thing about our-finished artificial leather is that this scuif resistance is realized in combination with the equally important surface qualities hereinbefore mentioned, including elasticity, flexibility, hardness, scratch resistance, and an appearance simulating that of natural leather.

It is important that theglycerine remain in the skin. We have found that while a tough, 15 flexible film may initially be laid down on the artificial leather, nevertheless the glycerine tends to migrate into the base sheet, thereby rendering the film, so to speak, unstable, for, as the percentage of glycerine in the film is reduced, the film becomes less elastic and is apt to crack easily under'the stresses of continued flexing. We have found that if the base sheet contains the proper quantity of glycerine, the skin is rendered comparatively stable, because the tendency for migration of glycerine is greatly reduced, and the elasticity of the film is greatly enhanced.

While the artificial leather base, which is finished in accordance with our invention, may be made in many ways from various kinds of fibrous foundations, including woven as well as felted webs of fiber, and various rubber-impregnating compositions, including rubber solutions as well as rubber dispersions, such as latex, we prefer to start with a web or felt of unbleached purified 85 wood pulp and to impregnate the web with a vulcanized latex composition compounded withglycerine, additional vulcanizing agents, and a. suitable anti-oxidant, such as Age-Rite White, as disclosed in application Serial No. 575,164, 40 filed November 14, 1931 by Milton 0. Schur. As described in that application, a soft, fiuify web composed of substantially unbeaten, interfelted wood pulp fibers having an alpha cellulose con tent of at least about 93% may be passed progressively as a sheet of indefinite length through a bath of the prevulcanized and compounded latex composition, thence through squeeze rolls, and finally through a hot-air drier maintained at about 170 at its inlet end and at about 220 F. at its exit end. Drying of the impregnated web is thus performed under temperature conditions leading to a secondary vulcanization of the rubber impregnant. The dried, vulcanized sheet is pliant and mellow by reason of the plasticizing 56 effect of the glycerine on the non-rubber solids, including resins and proteins, associated with the latex and by reason of the softening action of the glycerine on the cellulose fibers. Of the impregnating materials added to theweb, which 00 may amount to about 60%, about one-fourth may be glycerine. In this connection, it is to be emphasized that the presence of glycerine in substantial amount in the base sheet of artificial leather is of decided advantage in that this means I that the migration of glycerine from the primary skin and surfacing films subsequently deposited on the sheet is minimized and accordingly that the stability of the finished product is enhanced. Before finishing the dried sheet of artificial [0 leather, the sheet is preferably moistened and gently stretched while passing over heated, polished steel drums. The side of the sheet pressed against the smooth drum faces may then be finished as hereinbefore described. In some in- ;roils or by pressing between hot smooth plates in a hydraulic press, and to coat and finish the smoothed sheet as above disclosed, the vulcaniis pulled apart as in a tensile strength tester, the skin and base sheet break practically together.

nation of the rubber in the base sheet being completed during the pressing and/or tanning steps.

*The sheet may then again be pressed under a fine skiver plate whereby the grain of natural leather is very closely simulated. It is characteristic of a sheet of interfelted, substantially unhydrated fiber to be of comparatively lumpy formation, so that proper smoothing is essential if minute surface blemishes are to be properly covered up with a relatively thin skin.

As a measure of the flexing resistance of our product we clamped specimens in the testing machine shown in Figures 3 and 4 which creases them in much the way they are flexed across the vamp of the shoe in use. The testing machine is shown in Figures 3 and 4, wherein,-

Figure 3 is a front view of the machine.

Figure 4 is a section on the line 4-4 of Figure 3. The specimen I is clamped to the forms 2 and 3 and are held in place by the spring-steel tapes 4. The forms are roimded at the corners, the radius of curvature being 8' inch. The form 2 is :fixed on the base 5; the form 3 is mounted in he guides O and is reciprocated by the eccentric I, the throw of which is inch and which makes 350 R. P. M. The specimen is mounted with the form 3 at its position furthest to the i right at which time the distance between the nearest faces of the forms is inch. The tests were conducted at 45% humidity and 70 F. It was found that specimens of upper stock, the skin of whichwould remain intact for 200 hours in the tester, would last about six weeks in actual use in the vamp of a woman's shoe; samples which held up 100 hours in the tester lasted only about 4 weeks in service.

It is characteristic of our product that it will fiex on the testing machine without failure of the surface or of the base material for at least 150 hours. In spite of the fact that it will undergo this severe fiexing test, it will not peel off inlarge pieces if scuffed up and picked at. It is also significant that when our artificial leather We wish to have it understood that we are using the term fglue" in the foregoing description and in the appended claims in its comprehensive sense to include animal glue or equivalent water-dispersible, film-forming substance, no matter what the parent material for the glue may be, for, it

is well known, that various proteinous or animal substances, such as fish, bones, blood albumen,

casein, or the like, may go into the preparation of water-soluble or water-dispersibleglues. The

allies which we employ in the skin coat may, as

hereinbefore indicated, undergo a tanning treatment, although in the case of soluble glues, like ammonium caseinate, a simple heating of the skin coat, forinstance, heating as hereinbefore described to a temperature of about 220 to 230 1". for about minutes or so, may sufilce to convert such glues to a relatively inert or waterinsoluble condition. I

We claim:

1. An artificial leather comprising a felted fibrous base impregnated with a rubber composl- 5 tion and provided with an elastic surfacing of a weight ranging from about 6 to 18 grams per square foot, possessed of breathing qualities, capable of withstanding without impairment a flexing test of at least 150 hours, and having a 10 wet Or dry scuff resistance of at least about 4 minutes, said surfacing comprising tanned glue and being finished to simulate the finished skin side of natural leather.

' 2. An artificial leather comprising a coated and impregnated felted fibrous base, the coating and the base containing the same plasticizer so as to prevent migration of the plasticizer into the base with attendant embrittlement of the coating, said coating comprising tanned glue, being of a weight ranging from about 6 to 18 grams per square foot, and being finished to simulate the finished skin side of natural leather.

3. An artificial leather comprising a rubberbonded base of interfelted fibers coated with a tanned glue composition, the coating and the base containing the same plasticizer to inhibit migration of the plasticizer into the base sheet, said coating being of a weight ranging from about 6 to 18 grams per square foot and being finished to simulate the finished skin side of natural leather.

4. An artificial leather comprising a felted fibrous base impregnated with a rubber composition and provided with a surfacing of a weight ranging from about 6 to 18 grams per square foot, possessed of breathing qualities, capable of withstanding without impairment a flexing test of at least 150 hours, and which when scufled up and picked at will break off in small pieces 40 rather than peel off in large portions, said surfacing comprising tanned glue, being of a weight ranging from about 6 to 18 grams per square foot, and being finished to simulate the finished skin side of natural leather.

5. An artificial leather comprising a rubberimpregnated felted fibrous base carrying on a face thereof a skin including a primary coating of rubber, glue, and glycerine, and a surface coating of tanned glue and glycerine, said skin being possessed of "breathing qualities, having a weight ranging from about 6 to 18 grams per square foot, and being finished to simulate the [finished skin side of natural leather.

- dried-out latex composition and carrying on a face thereof a skin including a primary coating ofrubber, glue, and glycerine, and a secondary coating of tanned glue and glycerine, said skin being possessed of "breathing qualities, having a weight ranging from about 6 to 18 grams per square foot, and being finished to simulate the finished skin side of natural leather.

7. An artificial leather comprising a felted fibrous base impregnated with a glycerinated, dried-out and vulcanized latex composition and carrying on a face thereof a skin including a primary coating of rubber, glue, and glycerine, and a secondary coating of tanned glue and glycerine, said skin being possessed of breathing" qualities, having a weight ranging from about 6 to 18 grams per square foot, and being finished to simulate the finished skin side of natural leather.

8. An artificial leather comprising a rubbering comprising tanned glue and vulcanized rub--.

her and finished to simulate the finished skin side of natural leather, said coating being of a weight ranging from about 6 to 18 grams per square foot, possessed-of breathing qualities, capable of withstanding without impairment a flexing test of at least hours, and having a wet or dry scuff resistance of at least about 4 minutes.

9. A method of finishing artificial leather comprising a rubber-impregnated felted fibrous base, which comprises applying to the surface of such leather a skin comprising a primary coat containing latex, glue, and glycerine and a secondary coat containing glue and glycerine while restricting said skin to a thickness ranging from about 6 to 18 grams per square foot, and tanning the glue content of said coats carried by said artificial leather.

10. A method of finishing artificial leather comprising a rubber-impregnated. felted fibrous base, which comprises applying to the surface of such leather a skin comprising a primary coat containing latex, glue, 'and glycerine and a secondary coat containing glue and glycerine while restricting said skin to a thickness ranging from about 6 to 18 grams persquare foot, and exposing said artificial leather carrying said coats of'restricted thickness to the action of a gaseous atmosphere of tanning agent.

11. A method of finishing artificial leather comprising a rubber-impregnated fibrous felted base, which comprises applying to the surface of such leather a skin comprising a primary coat containing latex, glue, and glycerine and a secondary coat containing glue and glycerine while restricting said skin to a thickness ranging from about 6 to 18 grams per square foot, exposing said artificial leather carrying said coats of restricted thickness to the action of a gaseous atmosphere of tanning agent, and frictioning the surface coat until it acquires the desired polish. 12. A method of finishing artificial leather comprising a rubber-impregnated felted fibrous base, which comprises applying to the surface of 5 such leather a skin comprising a primary coat containing latex, glue and glycerine and a secondary coat containing glue and glycerine while restricting said skin to a thickness ranging from about 6 to 18 grams per square foot, and exposing said coated artificial leather to the action of formaldehyde vapor, thereby tanning the glue content of said coats.

13. A method of finishing artificial leather comprising a rubber-impregnated felted fibrous 15 base, which comprises applying to the surface of such leather a skin comprising a primary coat containing latex, glue, and glycerine and a secondary coat containing glue and glycerine while restricting said skin to a thickness ranging from 20 about 6 to 18 grams per square foot, and exposing said coated artificial leather to the action of formaldehyde vapor, thereby tanning the glue content of said coats, at least part of said tanning reaction being promoted by elevated temperature. 25

14. A method of finishing artificial leather comprising a rubber-impregnated felted fibrous base, which comprises applying to the surface of such lea her a skin comprising a primary coat containing latex, glue, and glycerine and a sec- 30 ondary coat containing glue and glycerine while restricting said skin to a thickness ranging from about 6 to 18 grams per square foot, exposing said coated artificial leather to the action of formaldehyde vapor at room temperature for a considerable period of time, thereby tanning the glue content of said coats, and then heating the artificial leather to complete the tanning reaction.

MILTON 0. serum. BENJAMIN G. HOOS;

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