_ Patented Jan. 7, 1947 I 2,413,806 UNITED STATES PATENT OFFICE 2,413,806 METHOD OF MAKING WEAR-RESISTANT LEATHER _ \ George Virtue, Boston, Mass. No Drawing. Application March 18, 1943, Serial No. 479,591 1 This invention pertains . to 3 Claims. wear-resistant tanned leather, more'particularly to shoe soles and to shoes having soles made of such leather, and to a novel method of preparing such leather, soles and shoes. Previous attempts have been made to make tanned leather, intended for shoe soles, more re sistant to wear, but so far as is known to‘ me, no such prior attempts have been attended with any I (Cl. 12-146) 2 substance of the previously tanned leather a me dium which itself is inherently resistant to wear and which increases the tensile strength, resist ance to abrasion, resistance to wear and. pref erably, resistance to penetration by moisture as compared with ordinary soles. A further object is to provide tanned leather having‘ within its substance a permeating medium which tena Y ciously binds together the normal ?bers of the real degree of success. Obviously, no treatment 10 leather, thereby increasing the resistance to wear of leather intended for a shoe sole should lower of the leather itself. . the resistance of the leather to penetration by A further object is to provide a tanned leather moisture, since the free entrance of moisture re whose individual ?bers retain their normal sults in leaching out the tannin or other water strength and other usual characteristics but hav soluble constituents of the leather with resultant 15 ing within its substance a tough continuum, net~ deterioration. Neither must the treatment of the work, or skeleton of abrasion-resistant, water-in- sole substantially detract from those characteris tics of conventionally tanned leather which are soluble synthetic resin, increasing the weight of ’ the leather by approximately 8% to 12%, but recognized as essential to its use in the manufac whose presence does not unduly lessen the nor ture of shoes, such, for instance, as durability, 20 mal porosity of the leather. ?exibility, strength and color; amenability to the A further object isto provide a novel method usual operations involved in shoe making, for ex of treating ordinary fully tanned leather, for in ample retention of cements customarily em stance- shoe soles, and a novel method of making ployed; capability of receiving and retaining sew shoes thereby to impart to the leather, to the sole, ing stitches; workability in response to leveling 25 and to the shoe increased wear resistance. Other pressure; edge trimming, edge setting; bottom and further objects and advantages of the inven ?nishing, etc., and such porosity as is requisite to foot comfort when worn. Manifestly, to be of any real value, the characteristics imparted by tion will be pointed out' in the following more de tailed description. In accordance with a preferred procedure, and the wear-increasing treatment must be substan 30 assuming that the ultimate purpose is to provide tially permanent. shoes having wear-resistant soles, the leather Prior proposed impregnation of the leather (fully tanned and ?nished in accordance with with oils, waxes, etc., or its treatment with vari usual and customary practice) is ?rst cut into ous chemicals which alter the characteristics of soles either by the cut-sole manufacturer or by the leather ?ber have not met all of the above 35 the shoe manufacturer. The treatment of the requirements, nor has the previously proposed cut-soles in accordance with the present inven impregnation of the leather with synthetic res tion, and which it is contemplated will usually be ins which become polymerized in situ by the ap carried out by the shoe manufacturer, involves plication of heat adequately solved the problem, the immersion of the soles in a ?uid-treating since any heat treatment necessary for such pol 40 medium under such conditions and for so long a ymerization adversely affects the strength of the period of time as to insure their impregnation conventionally tanned leatherl?ber with the ul with the ?uid. timate result of decreasing rather than prolong The treating ?uid. in accordance with the pres ing the useful life of the material. As a matter ent invention, comprises a synthetic resin which of fact, most of the prior attempts at wear in is water-insoluble but soluble in certain organic crease have been directed primarily to the exclu— 45 solvents, together with an appropriate plasticizer, sion of moisture from the leather, and with that dispersed in a suitable volatile solvent. It should object in view have resorted to the use of mate be noted particularly that the resin has been rials which reduced the natural porosity of the polymerized to the extent that it is an abrasion leather or its ?exibility to a degree such as greatly resistant solid, capable of forming a tough ten 50 to lessen its desirability for use in making shoe uous ?lm on deposit from solution, and stable soles. I against spontaneous further polymerization, and The principal object of the present invention is that further polymerization of- the resin in situ to provide tanned leather, for example shoe soles, by theuse of ‘heat is neither requisite nor desir possessing substantially all of the usual charac able. ' teristics of conventionally tanned leather with Merely by way of speci?c examples of suitable respect to suitability for use in the manufacture treating media, but without intent to limit the and wear of shoe soles, by including within the ' invention to such speci?c examples, the following 2,413,808 4 formulae have been found to give the sought-for results: brittle and highly resistant to abrasion when de posited from solution by evaporation of the sol (1) Lewisol-ZL (maleic resin) '______pounds__ 120 Abalyn . properly plasticized it must be tough rather than I ___ do _ 40 Xylol ______ __'__'_ __________ "gallons" 16 Stoddard solvent (or 32 gal. aromatic pe troleum solvent) _________ _.-_/;ga.1lons_.. (2) Lewisol No. 125 l6 vent, and it must be stable against further spon taneous polymerization or oxidation. In herein referring to "polymerization," it is thereby intended to designate any chemical re action, for example esteri?cation, which results in an increase in the size of the, resin molecule (modi?ed phenolic resin) ___________________ __pounds__ 100 10 Blown castor oil ______________ __do_..___ 60 Stoddard solvent ___________ "gallons", 32 In the above formulae, the substance Lewisol 2L is a modi?ed alkyd resin, to wit, a maleic acid, with attendant changes in the physical proper ties of the resin such as change in melting point, solubility, tensile strength or resistance to abra sion. Having prepared the selected lmpregnant ?uid, it is conveniently applied by placing the ?uid in glycerol, rosin combination, this alkyd resin was 15 an elongate open-topped tank or trough, the at one time sold by J. D. Lewis, Inc., 68 Traverse depth of the fluid being sufiicient completely to Street, Providence, Rhode Island, but is now mar immerse the leather which is to be placed in the keted by the Hercules Powder Co., of Wilmington, trough or tank for treatment. If cut-soles are to Delaware. be treated, they are preferably packed in an open Abalyn (methyl abietate) is a viscous pale yellow 20 work basket and lowered into the ?uid near one liquid containing approximately 95% of a mix end of the tank. The basket is then moved to ture of methyl esters of several isomeric forms of ward the opposite end of the tank to make room abietic acid; has the approximate chemical for for a second basket and so on until the ?rstbas. mula C19H29COO.CH3; completely dissolves most ket arrives at the further end of the tank when 25 synthetic resins now in use, and is miscible at it is lifted out. A treating period 01' the order room temperature with solutions of resins in prac of 20 minutes, more or less, has been found suf tically all solvents, including alcohol and ben ?cient to provide the desired result. After re zene; and is a product of the Hercules Powder moval from the tank, the soles are allowed to l ‘ drain and then removed from the basket and so Stoddard Solvent is the name used to designate 30 stacked or otherwise arranged as to prevent free a well-known type of petroleum base solvent; it access of dry air and allowed to mull in moist may be purchased, from Cities Service Corp., condition for a period of two or three days, among others; it is sometimes called “White Spir more or less, during which the treating medi its” or “Naphtha Safety” solvent; it is insoluble um becomes substantially uniformly distributed in water; has a sp. gr. of 0.78-0.79; a boiling point. 35 throughout the entire ?brous substance of the of 155-190° C.; and a ?ash point of 39° C. leather. " Xylol is commercial xylene and is of the ap The soles (now containing within their ?brous Co., of Wilmington, Delaware. proximate formula CsH4(CH3) 2. , ‘ interstices the substantially uniformly distrib Any single petroleum solvent which may be sub uted plasticized and polymerized resin together stituted for Stoddard solvent-xylol combina 40 with some solvent) are now ready for use in mak tion-should be high in aromatics; and should ing shoes. However, they may, if preferred, be have approximately the same boiling range and subjected to a drying operation at this point, as solvent power as the Stoddard solvent-xylol for example by passing them through a drying chamber or by blowing air over them, but care Lewisol No. 125 is a phenolic resin modi?ed by 45 must be taken not to heat the soles, at any stage the addition of rosin and originally made and of the procedure, to a temperature substantially sold by J. D. Lewis, Inc., 68 Traverse Street, Prov exceeding 120° F., for example, such as might sub idence, Rhode Island, but now marketed by the stantially dehydrate or change the structure, Hercules Powder (30., of Wilmington, Delaware. strength or other characteristic of the leather or Other resins suggested, merely by way of fur 50 leather ?ber. 7 ther example, are Hercules Polypale ester No. 1 Following usual practice, the soles are coated (polymerized rosin and ethylene glycol) or Her on the ?esh side, preparatory to laying, with a ‘cules Resin No. 2190—26' (alkyd terpene), both suitable cement, the soles treated as above de products of Hercules Powder C0., of Wilmington, scribed being substantially as retentive of usual combination. Delaware. ' It may further be noted that if a resin 55 cements as are untreated soles. After sole lay be employed which has incorporated within its ing, the shoe proceeds from one usual operation molecule a plasticizing element (as is common to another, and during this time the solvent, in the modi?ed alkyd resin), no additional plas whic originally represents from 50 to 60% by ticizer may be necessary. weig t of the treating ?uid, gradually evaporates It is to be emphasized that whatever resin be 60 until at the time the shoe is finished, substantial selected, it should not require the application of ly all‘~of the volatile solvent has disappeared, heat for polymerizing it after its incorporation in the plqsticized resin remaining apparently as a the leather, since subjection of tanned leather to sort of continuum or network extending through a temperature high enough to e?ect polymeriza out the isubstance of‘ the leather, embracing or tion of synthetic resin would be injurious to the encasing'the individual ?bers and bonding them leather ?ber. Moreover, it must be at a stage of together. 'This resinous material apparently polymerization, when applied, such that it will forms an integral though open and tenuous readily dissolve, in proportions substantially as skeleton, coextensive with the sole, which is it above suggested, in the solvent selected so as to self tough and abrasion-resistant, thus adding yield a solution of low viscosity which will readily 70 its own strength and ability to resist wear to penetrate the leather, preferably without recourse that of the original leather. Apparently the to the use of vacuum or pressure. A solution vis cosity of 60.5 seconds, at 100° F., Saybolt is sug water-absorbent, non-?brous, organic constitu ents of the tanned leather become permeated with the plasticized resin which acts as a size, mak 75 be su?iciently polymerized to be a solid; when gested as desirable. . On the other hand, it must 2,413,800 5 " ing such organic constituents .highly water-re-. . 6 pregnated with the ?uid, removing them from the bath, allowing them to mull until the treat ing ?uid is substantially uniformly distributed sistant and binding them together so as to in crease their resistance to wear and abrasion. By following the above procedure, the weight I throughout the ?brous structure of the soles, and permitting the solvent to evaporate, and drying of the treated leather, after evaporation of the solvent, is from 8 to 12% greater than before treatment. While the exact disposition of the added material within the structure of the tanned leather is not de?nitely‘known, it is believed, as the soles by exposure to moving air the soles being kept at a temperature, not substantially‘ exceeding 120° F., sumclently low throughout the treatment to avoid ,any further polymerization above suggested, that it may be visualized as a 10 of the resin or any injury to the leather fibers. sort of skeleton of resin, which coats the walls 2. Method of making leather shoe soles which of the original pores, voids or interstices of. the. are wear-resistant and in which the individual tannedv leather, permeates the softer constitu fibers of the leather retain their normal strength cuts of the leather and reduces the aggregate and, substantially normal‘?exibility and other volume of such voids by not \more than approxi 15 usual characteristics but wherein the leather has mately one-half, and which is stable in com- , within its substances. tough continuous network of abrasion-resistant water-insoluble synthetic position and not subject to oxidation, further spontaneous polymerization, or other change dur ing the wear of the sole. Since this skeleton of resin does not form an appreciable coating upon the outer surface of the leather (principally be cause during mulling they are not/freely exposed resin whose presence increases the weight of the _ 20 leather by approximately 8 to 12% but which does not unduly lessen the normal porosity of the leather, which comprises as'steps providing a sole cut from leather previously fully tanned and ?nished, immersing the sole in a bath comprising to the air), nor apparently ever‘illls more than approximately one-half of the original voids in ’ ~synthetic resin of the modi?ed alkyd class, polythe leather, the treated leather is still porous to 25 merized to the solid state and which is tough ya degree such that it is cool, dry and comfort _ and resistant to abrasion and stable against spon able to the wearer, while thevtexture of the taneous further polymerization but which is solu I leather is not detrimentally a?’ected with respect ble in volatile organic solvents, methyl abietate to its working characteristics in shoe making. as a plasticizer, and a volatile solvent; said media The complete sole is thus ?exible and its color 30 being in substantially the following proportions: is substantially the same as before treatment. Resin _______________________ -'_-..pounds__ 120 Plasticizerdo 40 0n the other hand, the sole is resistant to. pene tration or saturation by moisture and greatly im proved with respect to its resistance to wear. Solvent gallons-.. 32 Thus, for example, in careful tests, wherein the 35 keeping the sole in the bath until it is impreg treated soles have been compared with untreated nated, removing the sole from the bath, and per soles by incorporating them in shoes and subject mitting the solvent to evaporate, all of the afore ing the shoes to actual wear, it has been found said steps being carried out at a temperature, not that the treated soles outwear theuntreated soles substantially exceeding 120° F., so low as to avoid by approximately 50%. ' ' 40 further polymerization of the resin. While a preferred mode of treating leather has ' 3. Method of making leather shoe soles which hereinabove been speci?cally described by way of example, it .is to be understood that the in vention is not necessarily limited to this particu lar mode of treatment, but that any and all treat , usual characteristics but wherein the leather has the invention. of abrasion-resistant water-insoluble synthetic resin whose presence increases the weight of the leather ‘by approximately 8 to 12% but which ments for improving wear and moisture-resist ance which fall within the terms of the appended claims are to be regarded as within the scope of within its substance a tough continuous network I claim: does not unduly lessen the normal porosity of 1. Method of making leather shoe soles which are wear-resistant and in which the individual ?bers of the leather retain their normal strength and substantially normal ?exibility and other usual characteristics but wherein the leather has : within its substance a tough continuous net work of abrasion-resistant water-insoluble syn thetic resin whose presence increases the weight of the leather by approximately 8 to ‘12% but which does not unduly lessen the normal porosity of the leather, which comprises ‘as steps provid ' ing soles cut from leather previously tanned and are wear-resistant and in which the individual ?bers of the leather retain their normal strength and substantially normal ?exibility and other the leather, which comprises as steps providing a ' sole cut from leather previously fully tanned and ?nished, immersing the sole in a bath contain ing synthetic resin polymerized to the solid state and stable against spontaneous further polymer ization but soluble in organic solvents, a plas ticizer and avolatile solvent, said media being in substantially the following proportions: ' Resin _____ -.___-_, _____________ _-pounds.._ 120 60 Plasticizer Solvent do 40 "lions" 32 ?nished, immersing the soles in a ?uid bath hav ing a solution viscosity of 60.5 seconds at 100° F., Saybolt, said bath comprising a soluble syn minutes, removing it from the bath, allowing it thetic ‘resin which has been polymerized to the to mull while protected from free contact with immersing the leather in said bath and keeping it immersed for a period of approximately 20 solid state--a plasticizer and a volatile solvent; the air for a period of the order of 2 or 3 days said media being in substantially the following proportions: and permitting the solvent to evaporate, the en tire treatment being carried out at a tempera Resin _____________________ __I.._-.Ypounds_- 12o 70 ture,lnot substantially exceeding 120° F., so low Plasticizer . ‘ ‘ do _ .40 Solvent .................... _.._’.-gallons._ 32 keeping the soles in the bath until they are im that the resin'is not further polymerized and the leather is not dehydrated nor its ?bers injured. onoaom vm'run. .