US2512389A

US2512389A - Waterproofing leather

Info

Publication number: US2512389A
Application number: US669430A
Authority: US
Inventors: Charles G Shaw
Original assignee: Individual
Current assignee: Individual
Priority date: 1946-05-13
Filing date: 1946-05-13
Publication date: 1950-06-20
Anticipated expiration: 1967-06-20

Description

JUL: 2%, 19% c. s. SHAW WATERPROOFING LEATHER Filed May 13, 1946 WNMWWNW W ENVENTOR Patented June 20, 1950 UNITED STATES PATENT OFFICE 4 Claims. E

This invention relates to improvements in the art of waterproofing leather by impregnating it with fats and greases.

The term waterproofing as used herein refers to the art of incorporating waterproofing substances in leather but is not intended to imply that the leather is rendered absolutely impervious to water. The term "impregnating as used herein means the substantially complete filling of the voids or the air spaces in the leather by the waterproofing compound.

The principal object of the invention is the provision of waterproofed leather which, while impregnated with fats or greases, has the normal appearance, feel and springiness of non-waterproofed leather; is capable of being channelled, buifed, finished and cemented in accordance with conventional shoe-factory methods; and has a non-greasy surface which, in contact with '-.wet pavements, has a relatively high coeillcient of friction which compares favourably with that of non-waterproofed leather and substantially reduces the hazard of slipping as compared with sole leather in which fatty and greasy waterproofing substances have been incorporated in accordance with prior art procedures.

The foregoing object is achieved by impregnating leather, particularly sole leather, with waterproofing substances selected from the class comprising hard high melting point fats and waxes; then, without damaging the leather, effecting substantial removal of the fats or greases from the grain and fiesh sides to a depth sufllcient to enable the leather to be buffed, channelled, finished, or cemented in accordance with conventional shoe-factory methods; and then cooling the leather so that the waterproofing substance left in the interior portion of the leather is solidified to a hard brittle condition in which it is fixed against migration or absorption into the outer portions and is resistant to the displacing or squeezing-out effect of the high internal pressure created in the leather when the latter is wet and the fibres thereof are swollen by absorption of warm water.

The fats and greases employed in accordance with my invention are those which have a relatively sharp softening range and with melting point not substantially below 120 F. and which, at normal temperature, are hard and brittle. Because of their high melting temperatures such fats and greases will not migrate or exude into the fat and grease free outer portions of the leather when subjected to the heat of the foot or to the heat of summer temperatures or of warm, sand such as might be met with in the 'wear conditions. A fat approaching full hydrogenation such as hydrogenated tallow may be mentioned as a specific example of a hard, high melting point waterproofing substance which maybe used in accordance with my invention. This substance has been found satisfactory for waterproofing sole leather for service in Europe and America. In waterproofing sole leather for service in extremely hot climates it has been found beneficial to raise the melting point by addition of a suitable substance such as fully hydrogenated castor oil. In general, however, carnauba wax or any waterproofing fat or grease substance-or compound having a sharp melting point not substantially below 120 F. may be advantageously employed in accordance with my invention.

In the practice of my invention the leather is dried, immediately prior to impregnation, at a temperature of, preferably, 100 F. to 140 F., until the moisture content is brought to a very low percentage throughout the leather. The dried leather is then impregnated, with a hard fat, until the leather has absorbed the desired amount of fat, the impregnation being usually continued until all the air spaces and voids in the leather are substantially completely filled by the fat. The impregnation is preferably accomplished by dipping the leather in a tank containing the melted fat and permitting the leather to remain there until the absence of air bubbles indicates complete filling of the leather by the fat. Alternately, the fat may be incorporated in vegetable tanned leather by a stufling procedure in a hot air drum similar to that employed in stufllng harness leather. Other suitable methods of impregnation may also be employed.

Following impregnation thereof, the leather is brieily drained off or hung in an atmosphere well above the melting temperature of the incorporated waterproofing substance until the surface is quite drained off and dry looking. Appreciable cooling of the leather during this stage of the process is undesirable.

The leather is then washed with an aqueous solution of a, suitable detergent until the surface film of fat has been removed and the appearance of .the leather indicates that it is uniformly wet by the aqueous solution. The temperature and/or time factors of this washing treatment, which is necessarily carried out at a temperature above the relatively high melting temperature of the waterproofing substance, must be controlled or regulated to prevent damage to the leather. Agitation or scrubbing may be employed during this washing treatment but the removal of the dim of fat is due mainly to the fact that ailinity of the detergent solution for wetting the fibres of the leather is greater than that of the waterproofing substance. As an example of detergents which may be employed in this washing procedure I may mention sulphated fatty alcohols which are suitable in solutions maintained at an effective acidity of approximately pH 3. The concentration of the detergent solution is a variable factor, being adjusted to suit various conditions. In many cases, using a solution of sulphated fatty alcohol, a solution of 1% to 2% has been found efllcient.

In connection with the washing of the leather with the detergent solution at a temperature above the relatively high melting temperature of the waterproofing substances, it is important to note that ordinary vegetable tannages differ considerably in their ability to resist heat in the presence of water or aqueous solution and that therefore time factor of the washing operation is important.

when dealing with the washing of vegetable tanned leather with a solution of sulphated fatty alcohol the washing may be carried out in two stages in which temperature and time factors are controlled to avoid damage to the leather. The initial washing of the fat film from the leather is preferably done at a temperature of about 150 F. which, in some cases, may be too high for the period of time required to wet the leather with the aqueous solution to the depth of the grain layer or such other depth as it may be desired to clean the waterproofing substance from the interior of the grain and/or flesh layers. In those cases where prolonged washing at 150 F. is apt to damage the leather, the leather is initially washed at this temperature for a relatively short period, say two or three minutes, and is then given a second washing or soaking with the detergent solutionat a temperature of approximately 130 F. for a period of from about 20 minutes to three quarters of an hour or longer, depending on the depth to which the waterproofing substance is to be removed from the grain and/or flesh of the leather. The concentration of the detergent solution used in the second stage washing may be reduced as com-,

pared with that used in the first stage, since the capillarity of the fibres as modified by the first stage washing enables the detergent solution used in the second stage to readily penetrate the leather and swell the fibres by absorption of aqueous solution so that a large portion of the waterproofing substance, which is softened and exuded at the temperature used in the second washing, is squeezed out.

when the washing of the impregnated leather with the detergent solution is carried out in an immersion tank, the surface of the solution, at least where the leather is removed from the tank,

should be skimmed free of the softened or melted fat which rises and fioats on the surface in considerable quantity.

The second washing or soaking of the leather with the detergent solution removes large amounts of the waterproofing substances from the grain and leaves it in a condition in which it may be lightly buffed with a new sharp bufilng paper. However, in order to condition the leather for satisfactory buiilng and channelling it is necessary to resort to a further carefully controlled slicking or scudding operation to squeeze or slick out the greater portion of the remaining fat or greasy waterproofing substance from the grain and flesh sides of the leather. This final treatment of the leather may be accomplished by subjecting it to a scudding or s1ick-. ing operation on a suitable scudding machine such as the Whitney Model P scudding machine which is equipped with setting-out" cylinders which have been found very advantageous for the purpose. The Whitney machine includes a spraying device which sprays the surface of the leather with detergent solution while contacted by the cylinders. For the purpose of the present invention the Whitney machine may be equipped with additional spraying devices, one of which is arranged to spray the flesh side of the leather prior to the entry of the leather into the feed rolls to thereby enable a considerable amount of waterproofing substance to be squeezed out of the flesh side by the feed rolls. The solution fed to the sprays preferably contains some detergent and is heated to a temperature of F. to F. This solution is preferably fed to the sprays by a recirculating pumping system.

Following the final cleaning of the waterproofing substance from the interior of the grain and flesh layers by the slicking or scudding treatment, the leather is hung up in a cool place or dipped in cold water so that the waterproofing substance left in the interior portion of the leather will quickly chill and have little or no tendency thereafter to migrate into or be absorbed by the leather in the grain or the flesh. In this connection it will be understood that if the temperature of the leather were maintained at, say, 120 F. after the slicking or scudding operation, then the waterproofing substance which is softened or melted at this temperature would be absorbed among the fibres in the grain as the water evaporates and would thus spoil the whole effect.

Similarly, if portions of the impregnating compound cr substance remain liquid long after other portions have crystallized or hardened, as might be the case in a mixture of fats covering a wide melting range, the fat or fats having the lower melting temperature may either migrate into the grain of the leather as the water evaporates therefrom or be subsequently squeezed or forced by capillary action from the interior of the leather into the grain by absorption into the leather fibres of the interior portion of some of the water from the grain layer.

In the case of a hard fat and a cool temperature, the continued absorption of water into the interior portion of the leather from the grain layer will not force the fat from the interior into the grain layer of the leather as would be the case if any portion of the fat were soft at normal temperatures. This is an important point to bear in mind in connection with the present invention since, in order that the fat may stay where it is desired, 1. e. in the interior portion of the vsdeather, it must have sufficient hardness to resist the pressure within the structure of the impregnated leather due to the capillarity or absorption of water by the leather fibre itself. As an example, a properly impregnated vegetable tanned sole leather as produced by my invention would, when immersed in water during a tempering operation in a shoe factory, be wet to the full depth of the grain layer in a relatively short time and the grain would be soft and easily channelled as in ordinary leather. Prolonged soaking, however, will produce absorption of water by the fibres in the interior at a very greatly reduced rate and, at the same time due to the swelling of the leather fibres in the interior portionof the leather, create a heavy internal pressure on the waterproofing compounds which lie between fibrils and fibre bundles of the hide structure in the interior portion of the leather as the waterproofing compound is not soluble in the leather fibre substance itself as is water. This pressure may be readily recognized by the fact that a sole treated by my method being immersed for, say, 24 hours will be peculiarly firm and perhaps even firmer than before wetting and will sometimes be curled by the pressures created in the outer strata of the interior portion of the leather. In some instances this pressure created is so great when the leather is impregnated with really hard fats that the water appears to no longer enter the leather. From this it will be apparent that, compared with the softer lower melting temperature fats and those of a plastic nature at normal temperatures which have previously been employed for impregnating leather in accordance with prior art practice, the hard high melting point fats or compounds employed in accordance with my invention may be more advantageously used both to ensure a higher degree of waterproofness and to maintain the position of the waterproofing substance where it is most desired and in a condition such that it will not migrate or be squeezed out during tempering of the leather and thus interfere with the subsequent shoe making operations such as bufiing and channelling operations.

The condition in which the leather is left following the slicking or scudding treatment is illustrated by the accompanying drawing, in which the single figure is a cross sectional view of a piece of sole leather. In this figure the showing to the left of the vertical line AA illustrates the condition of leather which has been subjected to waterproofing and subsequent cleaning operations in accordance with my invention, while the showing to the right of said line illustrates the comparative condition of leather which has been waterproofed with relatively low temperature waterproofing substances and then surface cleaned in accordance with prior art procedures.

Referring more particularly to the drawing,

the dotted line BB represents the approximate line of demarcation between the grain layer C and the interior portion D of the leather; the dotted line E-E' represents the approximate line of demarcation between the interior portion D and the flesh layer F; and the dotted line G-G indicates the depth to which the hair holes H and the grain C are ordinarily cleaned of waterproofing substances when the leather is impregnated and cleaned in accordance with prior art practice.

With reference to the condition of the leather appearing to the right of line AA it will be noted that the grain layer C and the hair holes H are filled up to the line G-G with finely dispersed particles J of waterproofing compound which interfere with satisfactory bufilng of theleather to the required depth and also with the wetting of the grain layer C to the depth necessary to permit of easy and satisfactory channelling of the leather. It will also be noted that the flesh layer of the leather appearing to the right of the line AA contains a substantial amount of relatively large particles K of waterproofing compound which interfere with the cementing of the leather and give rise to other disadvantages.

In connection with the foregoing description of the condition of the impregnated and cleaned leather appearing to the right of line AA, it may be explained what prior proposals for impregnating leather with fats and greases have been based on the use of parafiine wax and relatively low melting point materials such as Vaseline and other waterproofing fats and greases which are comparatively soft at normal temperatures. In cleaning the grain and/or flesh layers of leather impregnated with these waterproofing substances, the cleaning temperatures employed, while above the melting temperatures of the waterproofing substance, have been too low to give more than a superficial cleaning of the grain layer C to the shallow depth represented. by the line GG. The use of hard fats and greases apparently was avoided because of the fact that their melting temperatures lie above or close to the temperatures at which damage to leather, particularly vegetable tanned leather, would ordinarily be expected. The damage would result from using prior art method of prolonged cleaning of the grain and flesh layers of the impregnated leather with an aqueous solution at a temperature above the relatively high melting temperature of the hard fats and greases such as are employed in accordance with my invention.

The relatively soft waterproofing substances employed in accordance with the prior art practices referred to do not have either a high melting point or a short plastic range. On the contrary, they have either or both a low melting point or a long plastic range. When leather impregnated with these low-melting point or long plastic range materials is bent it has a leady" feel and loses its springiness and does not readily lend itself to the production of comfortable well made foot wear.

When the internal pressure of leather impregnated with soft, low melting point waterproofing substance is increased by swelling of the leather fibres due to absorption of water, an appreciable amount of the relatively soft waterproofing substance is squeezed out of the leather so that, as the leather is repeatedly wet and dried, its resistance to water absorption is greatly lowered. Such impregnated leather may therefore have three times the water absorption of one incorporating a higher melting point hydrogenated tallow or similar hard, high melting point waterproofing substance which, at normal temperature, is sufiiciently hard and brittle to stay placed in the interior portion of the leatherv despite repeated wetting and drying of the leather under service conditions or during tempering, channeling, or processing of the leather subsequent to its impregnation with the waterproofing substance.

Reverting again to the drawing, it will be noted that the grain C and hair holes H of the leather appearing at the left of line AA are free of waterproofing compound to the full depth of the grain and that the fiesh side or layer F is also free of the waterproofing substance. This is the preferred condition in which the leather is left by the impr nating, detergent-cleaning, and clicking or scudding operations comprising my invention. Such leather can be worked in a similar manner as non-waterproofed leather and ha essentially.the same appearance, feel and springiness. During the bumng operations the depth to which the grain layer has been cleaned of the waterproofing substance and the nature of the waterproofing substance itself prevents any possibility of melting and migration of said waterproofing substance into the grain layer which would result in unsightly and unsaleable "oil spotted appearance of the sole.

The ability of the hard, high melting temperature waterproofing substance to stay placed within the interior portion D of the leather is also 01' importance in that this characteristic of the waterproofing substance enables it to increase the wear resistance of poorly fibred portions of impregnated leather out of proportion to similar poorly fibred portions of non-impregnated leather. In this connection it will be understood that the loose fibres are held in their matrix of water soluble substance and hard waterproofing substances until they wear off in smaller particles rather than tear loose as is ordinarily the case.

Soles cut irom th shoulder and impregnated with waterproofing substances in accordance with my invention have been known to wear longer than soles cut from the better portions of nonimpregnated bend leather.

With reference to the use oi my improved leather in insoles the following advantages may be noted. Since the grain layer which is next to the foot is substantially free of waterproofing substance and is not greas the moisture of the foot is not shut off entirely from entering into the leather. This is important since total exclusion of the moisture vapors from entering the insole, as occurs with ordinary waterproofed leather in which the grain layer is substantially impregrated with the waterproofing substance results in the discomfort known as burning feet.

Chrome retanned and chrome tanned leathers are much more resistant to heat than vegetable tanned leathers. Consequently, in applying my invention to the waterproofing of chrome retanned and chrome tanned leathers it is sometimes feasible to dispense with the previously described two-stage washing of the leather with a detergent solution prior to the slicking or sendding operation and to employ a single stage washing procedure in which the leather is washed with or soaked in the detergent solution for a period of half an hour at a temperature of approximately 150 F. Such a procedure can be resorted to in the case of chrome retanned and chrome tanned leathers when the waterproofing substance used is not extraordinarily hard and does not have too high a melting temperature. In

cases where the waterproofing compounds are extraordinarily hard and have a correspondingly high melting temperature recourse should be had to the two-stage detergent washing procedure described in connection with the waterproofing oi vegetable tanned leather.

when impregnating upper leather in accordance with my invention a very shallow cleaning may sufilce for the light.bufilng to which upper leather is usually subjected. In this case the upper leather produced in accordanc with my invention has the decided advantage of being much more thoroughly waterprooied than that ordinarily in use and will take a very satisfactory polish.

Having thus described the nature of my invention and several practical applications thereof it will be understood that various modifications may be resorted to within the scope and spirit of the invention as defined by the appended claims.

I claim:

1. In the art of waterproofing leather, the steps comprising impregnating the leather with a waterproofing substance selected from the class consisting of fats and greases which are hard and brittle at normal temperature and have a sharp melting temperature not substantially below F. and then washing the leather with an aqueous solution of sulfated fatty alcohol maintained at an efiective acidity of approximately pH 3.

2. In the art of waterproofing leather, the steps comprising impregnating the leather with a waterproofing substance selected from the class consisting of fats and greases which are hard and brittle at normal temperatures and have a sharp melting temperature not substantially below 120 F. and then removing the waterproofing substance from the grain and flesh layers of the leather to a depth sufiicient to permit the leather to be bufi'ed, channelled, finished and cemented in a similar manner to ordinary non-waterproofed leather, said removal of the waterproofing substance from the grain and flesh layers of the leather being carried out at a temperature above the melting point of the waterproofing substance by wetting the grain and flesh layers to the required depth with an aqueous solution of sulfated fatty alcohol detergent which causes the leather fibre in the wetted area to swell and force the waterproofing substance from said area by a squeezing or expressing action and controlling the time and temperature factors of the wetting procedure to avoid damage to the leather by excessive heating thereof and then promptly cooling the leather to solidify and harden the waterproofing substance remaining in the interior portions of the leather.

3. In the art of waterproofing leather, the steps comprising impregnating the leather with a hard high melting temperature waterproofing substance selected from the class consisting of fats and greases which have a sharp melting temperature not substantially below 120 F. and which, at temperatures substantially below said melting temperature, are sufliciently hard to resist being squeezed out of the leather by internal pressure created in the leather due to swelling of the leather fibres by absorption of water, then draining the impregnated leather in an atmosphere well above the melting temperature of the waterproofing substance until the surface of the leather is well drained off and is dry looking, then without appreciable intermediate cooling of the leather, washing it at a temperature of 150 F. for a relatively short period of time insufiicient to result in excessive heating and damaging of the leather with an aqueous solution of a sulfated fatty alcohol effective to remove the waterproofing substance from the grain and flesh layers of the leather to a substantial depth by swelling the leather fibre and causing it to express the waterproofing substance from the portion of the leather wetted by said detergent, repeating the washing operation with the solution of sulfated fatty alcohol at a lower temperature of approximately F. and for a longer period of time to wash out a further quantity of the waterproofing substance irom the grain and flesh layers, then subiecting the leather to a slicking or scudding treat- 75 ment at a temperature above the melting temperature of the waterproofing substance to remove the residual waterproofing substance from the grain and flesh layers previously wetted by the washing solution and then promptly cooling the leather to solidify the waterproofing substance remaining in the interior portion of the leather to a hard condition in which said substance has no tendency to migrate into the previously cleaned grain and flesh layers of the leather and is resistant to being squeezed out of the interior portion of the leather by the internal pressure created in the leather when fibres thereof are swollen by absorption of water.

4. In the art of waterproofing leather, the steps comprising impregnating the leather with a hard high melting temperature waterproofing substance selected from the class consisting of fats and greases which have a sharp melting temperature not substantially below 120 F. and

which, at temperatures below said melting tem- 20 perature. are sufilciently hard to resist being squeezed out of the leather by the pressure created in the leather when the fibres thereof are swollen by absorption of water, then removing the waterproofing substance from the grain and flesh layers of theleather to a depth sufilcient for bufiing, channelling, finishing and cementing purposes by washing the leather, at a temperature of approximately 150 F. and for a period of time alcohol.

' CHARLES G. SHAW.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Date Number Name 408,360 Sommers Aug. 6, 1889 649,155 Bohm May 8, 1900 776,453 Case Nov. 29, 1904 1,036,267 Kornacher Aug. 20, 1912 1,865,783 Orthmann July 5, 1932 1,885,179 Binger Nov. 1, 1932 2,089,925 Neiley Aug. 10, 1937 2,328,431

Doser et a1. Aug. 31, 1943

Claims

1. IN THE ART OF WATERPROOFING LEATHER, THE STEPS COMPRISING IMPREGNATING THE LEATHER WITH A WATERPROOFING SUBSTANCE SELECTED FROM THE CLASS CONSISTING OF FATS AND GREASES WHICH ARE HARD AND BRITTLE AT NORMAL TEMPERATURE AND HAVE A SHARP MELTING TEMPERATURE NOT SUBSTANTIALLY BELOW 120* F. AND THEN WASHING THE LEATHER WITH AN AQUEOUS SOLUTION OF SULFATED FATTY ALCOHOL MAINTAINED AT AN EFFECTIVE ACIDITY OF APPROXIMATELY PH 3.