US2885300A - Method for producing resin treated leather - Google Patents

Description

METHOD FOR PRODUCING RESIN TREATED LEATHER John W. Cunningham, San Antonio, and Robert S. Singleton, Blanco, Tex., and George W. Singleton, Greenville, S.C., assignors to Lucille V. Singleton, doing business as Russell A. Singleton & Sons, Blanco, Tex.

No Drawing. Application October 22, 1952 Serial No. 316,314

8 Claims. (Cl. 117-7) This invention relates to new and useful improvements in resin treated leather and methods for producing such leather. p

The invention is concerned with the production of treated leather having increased abrasion resistance While retaining the various natural attributes of leather virtually unchanged. Manifestly, such leather has many and varied uses. For the purpose of simplicity, however, the invention will be described in conjunction with the use of the treated leather in the textile industry.

In the branches of the textile industry concerned with the handling of various textile yarns, and in particular, with the spinning of such yarns, there are various instances in which the yarn is passed in contact with leather belts or leather rollers. While leather serves very well in such instances and provides beneficial results, it has certain shortcomings, such as a lack of resistance to abrasion, and some efforts have been made to replace the leather with other materials such as reinforced rubber or various synthetics.

A particular point at which trouble has been experienced has been in spinning frames which employ long draft spinning aprons as well as covered rollers known as spinning cots. During the spinning operation, the spinning aprons are driven by relatively small rollers which may be knurled, fluted, etched or otherwise provided with an uneven or roughened surface, and also pass over and around stationary metal bars at a relatively sharp angle. The driving roller and the metal bar come in contact with the inner side of the apron, which is in the form of a small endless belt, this inner side being the flesh side in the case of a leather apron. Obviously, the wear and abrasion on the inner side of the apron is severe. The outer surfaces of the aprons, which in the case of leather aprons is the grain side, engage the yarn being processed and further receive considerable abrasion and wear from such yarn.

Leather is the most desirable material presently known for use in spinning aprons and, by and large, produces better yarn. The leather belts are more uniform in thickness, produce yarn of better quality because of the cushioning effect of the leather and because of the gripping power of the leather grain surface. Further, leather is oil absorbent so as to prevent the accumulation of any oil upon the surface of the apron, and leather belts may be spliced in place upon the spinning frame so as not to require disassembly of the frames for replacement of the aprons.

None of the foregoing is true of the various synthetic or rubber long draft spinning aprons which have been developed and which are in use, but the latter have the advantage of greater abrasion resistance upon both their inner and outer surfaces. Synthetic aprons often break due to an accumulation of lint or yarn upon the roller over which the apron or belt passes, but in general, have a longer useful life than ordinary leather aprons because of their greater toughness and abrasion resistance. They have replaced ordinary leather aprons to some extent United States Patent because of their lower cost and because they cause less trouble due to stretching.

Thus, both of the presently available types of spinningaprons have certain advantages and disadvantages, but no apron or belt is available which combines the desirable features of both the synthetic and leather aprons and at the same time avoids their undesirable points.

The foregoing disadvantages of ordinary leather have.

an adverse effect upon its use in other fields than the textile industry and either shorten the useful life of the leather, or discourage its use. The natural pliability, resilience and elasticity of leather, along with its feel or appearance, and other well-known attributes, have not been completely duplicated in other materials, such as the synthetics, and yet the shortcomings of leather as to;

insufiicient abrasion resistance, surface cracking and the like, remain as objectionable characteristics of conventional leather.

It is, therefore, one object of this invention to provide an improved treated leather which has all of the desirable features of conventional leather, and in addition, has increased toughness and abrasion resistance which greatly enhance the useful life of the leather.

A particular object of the invention is to provide an improved long draft spinning apron formed of leather properly treated with a resin to increase the toughness and abrasion resistance of the leather throughout its thickness.

Yet another object of the invention is to provide an improved apron of the character described in which the inherent characteristics of the natural leather are retained, and in particular, wherein the oil absorbency of the leather is retained to a large degree.

An additional object of the invention is to provide an improved method for treating leather with resins to increase the abrasion resistance of the leather, the method being applicable to both vegetable-tanned leather and chrome-tanned leather.

One objection to ordinary leather draft aprons is the tendency of the leather to wear unevenly because of hard and soft spots in the leather. The invention by suitably impregnating the leather with a resin overcomes this difficulty and causes the apron to wear evenly and uniformly.

Another objection of ordinary leather draft aprons has been their tendency to develop surface cracks which nip or pinch the yarn as the apron is flexed. This action results in uneven yarns and, hence, is undesirable. The apron produced by this invention is resistant to cracking on the outer or skin side as well as abrasive wear on the inner or flesh side.

A further object of the invention is to provide an improved method for impregnating leather with resin wherein excessive shrinking and/or plumping of the leather is avoided or minimized.

Still another object of the invention is to provide an improved method for the impregnation of leather with resin wherein controlled drying of the leather after impregnation permits control of the shrinking or plumping of the leather.

A particular object of the invention is to provide a resin-treated leather long draft spinning apron which will wear much longer than an ordinary leather apron, and which retains all of the advantageous characteristics of ordinary leather aprons while avoiding the disadvantages thereof and while achieving substantially all of the beneficial characteristics of rubber or synthetic aprons.

' Methods of carrying out the invention will be herein.- after described as well as the nature and structure of the improved leather produced thereby.

Various other objectives and features of the invention will appear more fully from a reading of the following Patented May 5, 1959.

specification wherein examples of the invention and the methods therein involved are described.

In carrying out the invention, the leather, which may be vegetable-tanned or chrome-tanned, is impregnated with a stu'table water dispersion of a resin selected from the group of resins which are inherently flexible, oil resistant, abrasion resistant, and subject to dispersion in an aqueous medium. The resin should be thermo-plastic and should be capable of being made flexible without the use of mobile plasticizers which are subject to selective absorption by leather.

Saturation of the leather can be obtained by brushing, spraying, or roller coating the flesh side of the leather or by total immersion of the leather in the water dispersion of the resin. It has been found that total immersion is preferable, but any of the methods of resin saturation should be followed by removal of the excess resin by passing the leather through squeeze rollers or by subjecting the leather to centrifugal action.

Following saturation of the leather with the resin, the leather is dried slowly, desirably in an atmosphere of controlled humidity in order to minimize shrinkage and/ or plumping of the leather. Vegetable-tanned leather tends to plump following the resin treatment, while chrome-tanned leather tends to shrink both in length and width. Since long draft spinning aprons of the best quality must conform to relatively small tolerances of the magnitude of a few thousandths of an inch, the thickness of the leather, when it is to be used for spinning aprons, must be carefully controlled and maintained throughout this treating process.

When the treated leather has been properly dried, it is desirably submitted to a resin fusing step in which the leather is subjected to an elevated temperature for a short period of time, desirably under pressure, to fuse or weld the deposited resin. Because of the nature of the resin impregnation steps employed, the pores and interstitial spaces of the leather are not completely filled with resin, but instead, the resin apparently is deposited at the intersections and points of continuity of the leather fibers so that the fusing or curing process results in the bonding of the leather fibers to one another at a multitude of spaced points.

Hence, the leather is reinforced, not by a continuous resin film or body, but rather, by a multiplicity of closely spaced but separated resin bodies of minute size. The resulting resin reinforced leather is believed to be novel in that the oil absorbency and other normal characteristics of the leather are not materially reduced, and extreme flexing of the treated leather does not result in destruction of the bond between the resin and the leather or mechanical destruction of the minute bodies of resin.

While the desired long draft spinning aprons reasonably could be formed from the leather following treatment, it is preferable to cut the leather to the desired width and thickness prior to the treating process so that, following the treatment, the leather requires no additional processing other than cutting into proper lengths and preparation for the joining of the ends of each length to form an endless long draft spinning apron.

The treated leather displays qualities comparable to those of untreated leather, and in addition, overcomes some of the undesirable characteristics of untreated leather. The oil absorbency of the treated leather is retained along with the natural cushioning effect of the leather and the inherent gripping power of the grained surface. On the other hand, the tendency of leather to develop surface cracks is eliminated, and stretching of the leather is reduced. At the same time, the treated leather has much greater toughness and abrasion resistance than the untreated leather and is fully equivalent if not superior to rubber or synthetic material in this respect.

Both chrome-tanned and vegetable-tanned leather, treated and untreated, have been tested for abrasion resistance with a standard Taber abraser, providing the following results, each figure representing the average of five individual tests. Treated and untreated samples were cut from adjacent portions of the same hides to insure comparability:

Comparative abrasion resistance Number of Wear-Cycles Loss in Thickness Chrome-Tanned Vegetable-Tanned Treated Un- Treated Untreated treated The above results show a significant increase in flat abrasion resistance as a result of the resin treatment. A much greater increase in wear life was observed, however, when flexure was included in the test by placing treated and untreated leather aprons in actual use in a spinning mill. While all of the tests in actual commercial use have not yet been completed due to inability to produce failure of treated aprons in order to define the useful life of the same, the results of one test may be given.

In a spinning frame handling number ten rayon, which is very damaging to ordinary leather aprons, a number of ordinary leather bottom aprons were installed and an equal number of treated leather bottom aprons. In a four month period, two of the untreated leather aprons had to be replaced, and measurement of the thickness of the aprons disclosed that the treated aprons showed no'wear while the untreated aprons had already lost about onehalf of their useful life.

In addition, both the abraser and the spinning frame tests disclosed that the untreated leather wore unevenly because of the hard and soft spots inherently present in the leather. The treated leather wore evenly in both cases, this being attributed to a greater concentration of resin in the soft areas of the leather due to such areas taking up more resin during the treating process.

The uneven wear of aprons is very undesirable in that it adversely affects the quality and uniformity of the yarn being spun, and this elimination of uneven wear is thought to be quite novel as well as beneficial.

The treated aprons displayed marked abrasion resistance on their flesh side, and showed no tendency to develop surface cracks upon their skin sides. The extent of the useful life of the treated apron has not yet been determined because of inability to date to wear out or destroy the treated aprons in commercial use.

The tests upon the Taber abraser were quite beneficial in determining the qualities of the treated and untreated leather. A sample of untreated leather subjected to 3000 wear cycles was worn down of an inch, the leather fibers were torn and distorted, and the wear was very uneven. As much as $1000 of an inch variance in wear was observed.

A treated sample of leather subjected to 3000 wear cycles was worn X of an inch, the wear was even, and the leather fibers were not torn or distorted.

The most desirable resin yet found for treating the leather is a water dispersion of polyvinyl chloride, preferably plasticized with a butadiene-acrylonitrile copolymer. Increasing the butadiene-acrylonitrile content reduces the abrasion resistance of the apron but increases the flexibility thereof. Specifically, optimum properties for improved long draft spinning aprons are exhibited by a treated leather containing from 2% to 6% resin de- Total solids percent 45-50 pH i 8-9 Surface tension (dynes/cm.) 35-42 Viscosity (centipoises) 10-20 Particle size (microns) 0.25 Specific gravity (latex) 1.08

The compositions and methods of preparation of suit able resin dispersions, as described hereinabove, are set forth in the patent to Wheelock, No. 2,614,094, issued October 14, 1952.

Various other resins have proved usable including the acrylic, butadiene-styrene, vinyl butyral, and styrene polymers. In addition to the polyvinyl chloride, the polystyrenes and the polyvinyl butyrals have proven particularly useful.

It is manifest that many resins may be employed and that it is not feasible to recite herein all possible resins and combinations of resins which are useful for the purposes outlined. As stated hereinbefore, the usable group of resins includes those which display abrasion resistance, resistance to oils and greases, good aging characteristics and availability in aqueous dispersions with relatively small resin particle size. The resin or resins should also be inherently flexible or subject to being made flexible by means of a chemically combined or otherwise immobile plasticizer. In addition, the resin should be thermo-plastic, or be subject to fusing or curing at temperatures of 300 F. or below.

. A detailed description of one specific form of the process of treating leather is recited hereinbelow, it being pointed out that the process is subject to conventional variation at several points.

The leather, cut to strips of the desired Width and thickness is saturated with the water dispersion of resin, desirably by total immersion in the body of treating liquids. The leather should be agitated only long enough to Wet both sides and then allowed to soak in the resin dispersion. Vegetable-tanned leather requires only about three to five minutes soaking, while chrome- Specific gravity (resin) tanned leather may desirably be left immersed for some r weight.

Concentration of Dry Resin Con- Resin Bath tent of Treated (Percent Resin Leather (Percent, Solids) based on original Drying of the resin saturated leather can be accomplished at any air temperature up to around 180 F. without damaging the leather. It has been found desirable, however, to dry the leather not only under con- 6. trolled temperature conditions, but also under controlled conditions of humidity.

Following removal of the excess resin from the leather strips, the latter are desirably mounted upon suitable supports to minimize shrinkage, and are placed in a drying compartment which may be of the forced draft type having humidity control. The leather is dried for a period of time, for instance 4 hours, at a temperature of approximately 100 to 125 F., with a relative humidity of to At the end of this initial drying period, the humidity is allowed to gradually decrease to 50 to 60% relative, and the drying is continued for a second suitable period, desirably of 4 hours. Following the second drying period, the humidity is allowed to drop to 30 to 40 percent relative, which often is the approximate humidity range of the outside air, and the drying at the temperature of to F. is continued for a third period of several hours, for instance a period of four hours length.

Following the drying step, it is desirable that the leather be subjected to a resin fusing or curing step as Well as a pressure rolling step. While the latter two steps may be carried out in any desired order, it has been found preferable to fuse the resin first and then to carry out the rolling operation.

The fusing or curing step may be completed at a low temperature, for instance 120 F., applied approximately for a period of one hour, at intermediate temperatures for shorter periods, for instance, F. for five minutes, or by higher temperatures, for instance 225 to 300 F., applied for 50 to 60 seconds, depending upon the temperature employed. The application of pressure during the curing step is advantageous, and good results have been obtained by pressing the leather in an automatic electric iron at a temperature of 225 F., the leather being subjected to the heat and pressure of the iron for 15 seconds on each side.

' Following the curing, the leather strip, while still hot from the curing step is passed between two metallic squeeze rolls to reduce the leather to uniform thickness throughout and to compress any strips that may have plumped during the soaking and drying steps. By spacing the squeeze rolls the proper distance apart, the treated leather strips may be made more uniform in thickness than they were before commencing the treating operation.

It has been determined that vegetable-tanned leather tends to plump during the process while chrome-tanned leather tends to shrink. Both types of leather may exhibit both phenomena, but each tends to the particular shortcoming recited. Fast drying of the leather after resin saturation exaggerates the shrinking and/ or plumping of the leather, and for this reason, the controlled drying of the saturated leather is thought to be important. Further, the rolling of the leather after the drying step is most desirable in producing a uniform and consistent product of controlled dimensions.

The use of the treated leather in long draft spinning aprons provides a very important and beneficial result in that the size and quality of the yarn may be closely controlled over long periods of time. The uniformity in thickness as Well as the uniformity in apparent hardness or consistency of the aprons is conducive to a uniform spinning operation and the production of yarn of uniform size and quality. In addition, the even wear of the aprons in use, coupled with their greatly extended useful life, extends the time of this accurate quality control and assures retention of the control over long periods of time. So far as is presently known, the useful life of the aprons and the length of time over which they will afford good control of the yarn quality, will be substantially equal to the actual physical life of the aprons. In other words, good control of the yarn size may be retained until the apron fails physically. In other types of aprons, this period of acceptable yarn quality control extends onlyuntil such time as the apron, through deterioration, causes production of a yarn of unacceptable quality. From a physical viewpoint, such aprons might be capable of long-continued operation, but they would fail to produce yarn of the necessary quality. Hence, an important benefit of the invention is the long-continued and excellent control over the quality of the yarn produced.

Various changes and modifications in the methods and products outlined and disclosed herein may be made within the scope of the claims appended hereto without departing from the spirit of the invention.

What we claim and desire to secure by Letters Patent is:

1. The method of treating leather including the steps of, impregnating the leather with an aqueous dispersion of a synthetic resin, anchoring the leather to prevent shrinkage thereof, drying the impregnated leather while so anchored, and subjecting the leather to heat to fuse the resin in the leather.

2. The method of treating leather including the steps of, impregnating the leather with an aqueous dispersion of a synthetic resin, drying the impregnated leather, and subjecting the leather to heat to fuse the resin in the leather, and passing the leather through a pressure rolling step.

3. The method of treating leather including the steps of, impregnating the leather with an aqueous dispersion of a synthetic resin, drying the impregnated leather, and subjecting the leather to heat to fuse the resin in the leather, and passing the leather through a pressure rolling step while the leather is still warm from the heating step. v -4. The method of treating leather including the steps of, incorporating from 1% to by weight of a synthetic resin into the leather by impregnating the leather with an aqueous dispersion of the synthetic resin, immobilizing the leather to prevent shrinkage thereof, drying the impregnated leather slowly in an atmosphere of decreasing humidity, and subjecting the dried leather to heat to fuse the resin in the leather.

5. The method of treating leather including the steps of, incorporating from 1% to 10% by weight of a synthetic resin into the leather by impregnating the leather with an aqueous dispersion of the synthetic resin, removing excess resin from the leather so as to leave the latter impregnated with the aforesaid 1% to 10% resin concentrated at the junctures and intersections of'the fibers of the leather, drying the impregnated leather, and subjecting the leather to heat to fuse the resin in the leather in a multiplicity of small spaced bodies.

6. The method of treating leather including the steps of, incorporating from 1% to 10% by weight of a synthetic resin into the leather by impregnating the leather with an aqueous dispersion of the synthetic resin, removing excess resin from the leather by applying pressure thereto so as to leave the latter impregnated with the aforesaid 1% to 10% resin concentrated at the junctures and intersections of the fibers of the leather, drying the impregnated leather, and subjecting the leather to heat to fuse the resin in the leather in a multiplicity of small spaced bodies.

7. The method of treating leather including the steps of, impregnating the leather with an aqueous dispersion of a synthetic resin, expressing from the leather excess resin while the resin is still in aqueous dispersion, the

expressing being carried to a degree sufficient to leave the leather with a resin content of 1% to 10% by dry weight, drying the impregnated leather, and subjecting the leather to heat to fuse the resin.

8. The method of treating leather including the steps of, impregnating the leather with an aqueous dispersion of a synthetic resin, expressing from the leather excess resin while the resin is still in aqueous dispersion, the expressing being carried to a degree sufficient to leave the leather with a resin content of 1% to 10% by dry weight, drying the impregnated leather, subjecting the leather to heat to fuse the resin, and passing the leather through a pressure application step while the resin is still plastic from the heating step.

References Cited inthe file of this patent I UNITED STATES PATENTS 1,740,680 Burnham et al Dec. 24, 1929 2,272,057 Cheetham Feb. 3, 1942 2,356,879 Pense et al Aug. 29, 1944 2,452,536 Kirk Nov. 2, 1948 2,614,094 Wheelock Oct. 14, 1952 2,635,060 Cheronis et al. Apr. 14, 1953 FOREIGN PATENTS 439,884 Great Britain Dec. 9, 1935

Claims (1)

1. THE METHOD OF TREATING LEATHER INCLUDING THE STEPS OF, IMPREGNATING THE LEATHER WITH AN AQUEOUS DISPERSION. OF A SYNTHETIC RESIN, ANCHORING THE LEATHER TO PREVENT SHRINKAGE THEREOF, DRYING THE IMPREGNATED LEATHER WHILE SO ANCHORED, AND SUBJECTING THE LEATHER TO HEAT TO FUSE THE RESIN IN THE LEATHER.