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_ 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.
.
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