US1955892A - Artificial leather - Google Patents

Description

Patented Apr. 24, 1934 PATENT OFFICE ARTIFICIAL LEATHER Milton 0. Schur, Berlin, Company, Berlin, N. H.

N. H., assignor to Brown a corporation of Maine No Drawing. Application January 11 1932, Serial No. 586,091

4 Claims.

This invention relates to the manufacture of an artificial leather, and more especially one which can be'produced at low cost and yet be serviceable as a shoe innersole stock, or for other purposes.

In making artificial leathers, one of the most inexpensive raw materials available for making the fibrous foundation is preliberated cellulose pulp, and more specifically wood pulp which 'can be converted into a waterlaid web on machinery of the papermaking type. impregnated with rubber solutions of water-dispersed rubber, e. g., rubber latex, and then dried, it takes on leather-like properties to such an extent that it can serve for such purposes as'shoe innersoles. Thus, the rubber-impregnated web is possessed of sufiicient residual porosity to permit breathing of the foot and its constituent fibers are sufiiciently bonded together to resist disintegration through the action of moisture and perspiration.

I have found that in making such artificial leathers, it is highly advantageous to use as the fibrous base a waterlaid web composed of a blend of both cellulose fibers like preliberated wood pulp and wool fibers. Aside from the fact that wool fibers lend themselves to web formation, especially when blended with cellulose fibers, and can take" on rubberfrom rubber solutions or aqueous dispersions, wool fibers can be had on the market at a much lowercost than even wood pulps of the cheapest grade. For example, it is possible now to purchase wool cuttings or shoddies at as low as $10 a ton, which is much'lower than the current cost of even the cheapest grades of wood pulp. .These wool cuttings or shoddies are sometimes made up of wool fibers of different colors, in which case they impart a pleasing variegation of the web, both in its raw and rubber-impregnated state. The wool fibers alone, however, do not conduce to waterlaid Webs having a uniform texture, which result may, however, be had when ,cellulos'e fibers or the like are blendedwith the wool fibers in aqueous suspension'and the mixed fibrous suspension is run off into a web on a suitable papermaking machine, e. g., a machine of the Fourdrinier or cylinder type.

The cellulose fibers used as raw material may be any one or a mixture of the well-known chemical wood pulps, e. g., sulphite or kraft pulp, either in bleached or unbleached condition. Preferably, however, a refinedwood'pulp of an alpha cellulose content of about 93% to 96% is employed, as such pulp leads to webs of greater absorptivity on a given papermaking machine.

When such a web is' Preliberated cellulose pulps other than wood pulp may be used when available, in lieu of part or all of the wood pulp, for instance the longer-fibered pulps derived from manila, sisal, ramie, or the like. The blend may contain various proportions of preliberated cellulose pulp and wool fiber, for instance a prepondera'nt proportion of either. on the other hand, the use of more cellulose pulp than wool fiber is ordinarily to bepreferred because of the uniform web texture attainable in such case without much trouble. For example, a blend of about to 50% refined wood pulp and about 25% to 50% Wool fiber has been found to yield an excellent web for use as an artificial leather base.

I shall now give a specific example of procedur which has been found to give an artificial leather eminently satisfactory for use as shoe innersole stock. I first prepare an aqueous fiber suspension in a beater engine made up of about 75% 75 refined wood pulp of an alpha cellulose content of about 93% to 96% and about 25% wool shoddy,. which may contain fibers of mixed colors. The beater should be operated in such a way as to eifect a mixing of the fibers without much hydration or gelatinization of the Wood pulp fraction, if a comparatively flexible artificial leather is de- 1 sired; if a stifier leather is in view, the Wood fibers may be correspondingly hydrated.

The mixed aqueous fiber suspension is diluted with sufiicient water to form a comparatively dilute and uniform fiber suspension,'which is run off on a paper'making machine operated under conditions to deliver a dry web havinga compactnessof, say, about 40 and a basis weight of about 300. The compactness value is obtained by dividing the basis weight in pounds by the thickness in inches, and multiplying by the factor 10*. v The expression basic weight as known in papermaking circles represents the weight in pounds of 480 sheets whose dimensions are 24 x 36 inches, this being equivalent to 2880 square feet of sheet material. In other words, the compactness value really represents the weight of fiber per unit volume of sheet material.

The dried, raw web is then impregnated with a suitable latex composition, as by immersion in the composition, and then dried. No difliculty whatever-is encountered in securing complete impregnation of the sheet, because it is comparative-- 1y porous. Preferably, the latex composition contains casein as a stiflening agent, and also lime, which latter compound serves to prevent migration of the rubber particles to the surface of the impregnated sheet during the drying operation, 110

It is desirable to add a slight amount of viscose a result of impregnation with a latex composito the latex composition, as the regenerated celtion and drying presents a moreperfect surface. lulose produced in the sheet during drying im- This is evidently attributable to the resiliency of proves its characteristics. Wheh viscose is presthe wool fibers and the tendency of a web con 5 ent in the composition, boric acid is also prefertaining such fibers to recover from any localized ably added along with the'viscose to promote the denting or marring action which it undergoes regeneration of the cellulose from the viscose. during manufacturing operations. The fluffy The boric acid or its equivalent is added to the kind of webs of low compactness which I fabriviscose without causing a gelling, and serves pricate as the foundations for artificial leather prodmarily to neutralize part of the alkali associated nets are susceptible to becoming surface-blem with the viscose. A suitable anti-oxidant, such ished, especially when of high basis weight.

as Agerite White is preferably added to the Thus, at a basis weight of about 150 pounds and latex composition in order to improve the ageing higher, such webs tend to acquire surface cracks qualities of the dried, rubber-impregnated sheet. and other blemishes, probably on account of their I do not herein claim as the invention the advancontact with the instrumentalities of the papertageous latex composition, as this subject matter making and impregnating machines, for instance is disclosed and claimed in my patent application the rolls and/or drying drums of these machines, Serial No. 541,959, filed June 3, 1931. The parand/or probably because of the tendency of the ticular latex composition used as the impregnant inner lay rs of a mp iv ly hi k sh t may have a total solids content (1. e., rubber and pipe or to crack when bent into a small arc. non-rubber solids) of about 9% in the bath A web made from only a refined wood pulp and whereinto the raw web is dipped. When the imhaving a basis weight of 200 pounds and a compregnated sheet is i d, it t i b t 20% pactness of 40 showed surface defects even though to added solids, and compares favorably the smallest roll on the papermaking machine 25 with an artificial leather made entirely of a reat the dry end d d t exce 4 inches in fined wood pulp base and impregnated ith a, ameter. When the furnish contained 25% wool similar latex composition to a much higher solids fibers, there was no evidence whatever of surface content. I present herewith a table showing the defects in a web of the same high bas s Weight characteristics of the artificial leather of the and low co p Heretofore, in the manupresent invention, alongside of one whose fibrous facture of a 3-iron artificial leather (i. e., leather base consisted entirely of refined wood pulp of Of a thickness of 3/48 inches) intended as fo a compactness of about 30 d hi h i bib d innersoles, it was found necessary to use at least about twice as much solids from a common latex w pli f w b stock of a pa tn ss of about composition used as the impregnant: 40, in order to realize a product of satisfactory appearance. The plies were superposed and bonded together after each had undergone impregnation with rubber independently to acquire the desired leather-like characteristics. If it is attempted to produce a similar artificial leather product from only a single ply of 300 pounds basis weight containing only cellulose fiber, it is found that the finished product is badly cracked on its surface and presents a distinctly inferior appearance. When, on the other hand, the furnish from which the web is prepared contains about 25% wool, it is found that a single-ply web can be properly fabricated at a basis weight of 300 pounds or even higher, and that such a web can serve as the complete base for an artificial leather innersolepractically free from unsightly surface markings. Besides, it is more economical to work with a single ply of heavy weight, because it is sufficiently strong asit comes 01f the dry end of the paper machine, even at low compactnesses, say at a compactness of about 40, to resist rupture or breakage when processed as a continuous sheet and because the cost of laminating is eliminated.

It is noteworthy of mention that webs containing refined wood pulp of an alpha cellulose content of, say, about 93% to 96% are generally more absorptive and lead to artificial leathers of greater flexibility and suppleness than do unre-' fined pulps. If it is attempted to cheapen the furnish by substituting unrefined pulp for part or all of the refined wood pulp, the quality of the web is correspondingly impaired. It was only after considerable experimentation that wool fiber was established as being a component which would reduce the cost of the furnish and yet in Artificial (lgaagier 1 re fined wood pulp base) New artiflcial leather Solids added based on fiber) Thickness Stifiness, wide bend:

With direction of sheet Across direction of. sheet 45 Stiffness, sharp bend:

With direction of sheet Across direction of sheet Tack holding Internal ply adhesion 50 It is thus seen that in so far as concerns those properties such as stiffness, tack-holding ability, and internal ply adhesion, desired in innersoles, the new artificial leather compares quite favorably with a much more expensive artificial leather 55 containing only refined wood pulp as the fibrous base, and far more added solids. The new artificial leather has lower tear resistance than the single ply artificial leather used as a basis of com-. parison, but this feature is not of great moment 0 in such articles as inner soles, which do not undergo tearing stresses in use. Were a two-ply artificial leather, but otherwise similar to the standard of comparison appearing in the table, used as a basis of comparison, however, the new 5 artificial leather would measure up with such a two-ply artificial leather, even in such respects as tear resistance.

One of the important advantages attending the use of wool fiber along with cellulose fiber in the ""'70. -furnish-is that the web producible therefrom is muctffreei ir m wrinkes, cracks, or other surcertain important respects enhance the quality face blemishes than we repared from an allof the web and the ultimate artificial leather, cellulose fiber furnish, and acc gwrlixigLparticularly when the wool is used in proportion ber-imp t artificial leather produc up to, say, about 40% to 50% of the dry weight 75 which the wool-containing web is converted as oftfieentirefller furnish. 150

,inches and multiplying by a a basis weight of fibers made up partly of substantially unhytially unbeaten wood pulp h drated wood pulp and partly of wool shoddy, said 'web having a compactness not exceeding about 40, as determined by dividing its basis weight in pounds by its thickness in inches and multiply-' ing by the factor 10-, and a basis weight'of at least about 150, but at the same time being substantially free from surface defects.

3. A dried, latex-impregnated, waterlaid web of interfelted fibers made up largely of substanaving an alpha celweight of at least time being substantially free from surface delulose content of at least about 93% and a sub-1 ordinate proportion of wool shoddy, said'web having a compactness notexceeding'about 40, as determined by dividing its basis weight in pounds by its thickness in the factor 10-, and a about 150, but at the same tially free from surface defects.

:4. A dried, latex-impregn ted, of interfelted fibers 50% of substantially unhydrated wood pulp of an alpha cellulose content of about 93% to 96% in admixture with about 25% .to 50% of wool shoddy, said web having a ceeding about 40, as determined by dividing its basis weight in pounds by its thickness in inches and multiplying by. the factor 10-, and a basis about 150, but at the same basis weight of at least waterlaid web fects. v

MILTON 0L SCHUR.

inches and multiplying by 7 made up of about 15% to time being substancompactness not ex- 7