US2933418A - Impregnation of the grain side of leather with polysulfides - Google Patents

Description

April 19, 1960 E. c. DOGLIOTTI ET AL 2,933,418

IMPREGNATION OF THE GRAIN SIDE OF LEATHER WITH POLYSULFIDES Filed Feb. 4, 1959 Hes/L Side Legend:

Mat

Elasiomerz'c dep sizf' of organic polqsulfa'de polymer plus zefrqhydrafur/urql alcohol and or morpholine.

INVENTORS Eugene C-DOQZLOdi.

Joseph ClBcurg.

Charles 14/. Mam

ATTORNEY United States Patent IMPREGNATION (BF THE GRAIN SIDE OF LEATHER WITH PQLYSULFIDES Eugene C. Dogliotti, Sherborn, Mass, Joseph C. Barry, Woonsociret, RE, and Charies W. Mann, Framing ham, Masn, assignors to the United States of America as represented by the Secretary of the Army Application February 4, 1959, Serial No. 791,238

17 Claims. (Cl. 117-135.5) (Granted under Title 35, US. Code (1952), see. 266) The invention described herein, if patented, may be manufactured and used by or for the Government for governmental purposes, without the payment to us of any royalty thereon.

This invention relates to the impregnation of the grain side of leather with polysulfides, and more particularly with the impregnation of leather from the grain side with a. composition containing a liquid polysulfide polymer and tetrahydrofurfuryl alcohol and/or morpholine. The leather thus impregnated possesses outstanding coldweather-resistance and is resistant against the penetration of water and petroleum and against attack by corrosive liquids; thus, footwear, handwear and other articles of clothing and equipment made from such leather are highly useful for a variety of military and civilian purposes, such as work in an open air motor pool or field maintenance shop where the operator encounters varieties of climate, rain, spilled gasoline and oil, battery acid and other corrosive liquids.

Thus, a principal object of our invention is to provide a novel leather treatment which is useful in impregnating the grain surface of leather for the purpose of resisting, from the grain side, the penetration of liquids such as water, petroleum products, and corrosive type liquids,

such as battery acid.

Another object is the impregnation of leather with a material which when introduced into the interfiber space of the leather will permit the treated leather to be serviceable at low temperature and will not adversely influence the durability and other desirable physical characteristics expected of leather.

A further object of our invention is a preformed liquid composition treating agent containing as its principal ingredient a liquid alkylene polysulfide polymer capable of being cured to form an elastomer, and tetrahydrofurfuryl alcohol and/ or morpholine as its other component(s), so as to make it possible to introduce the compositions into the leather from the grain side and to effect a quick cure in the interfiber space of the leather.

A further advantage of our invention is a leather treating procedure which is simple, requires little time to perform, and can be carried outwith conventional equipment customarily on hand in commercial tanneries.

Other objects and advantages will be apparent from the following description of our invention.

A leather impregnating composition for the purposes of our invention comprises a liquid mixture of from about 50 to about 80 parts by weight of a liquid alkylene polysulfide polymer capable of being cured to form an elastomer, and from about 20 parts to 50 parts by weight of tetrahydrofurfuryl alcohol or morpholine or a mixture of tetrahydrofurfuryl alcohol and morpholine. Depending on the formula used, it may be desirable to add an effective amount of oleic acid, i.e., about A to about 2 parts by Weight per 100 parts by weight of the composition, to prevent an excessively fast and possibly uneven cure of the composition in the interfiber space of the leather. Representative proportions of the principal components ice of our compositions in accordance with our invention are: About, 50-75 parts by weight of polysulfide to about 25-50 parts of tetrahydrofurfuryl alcohol; or about parts by Weight of polysulfide to about 20-25 parts of morpholine; or about 7580 parts by weight of polysulfide to about 20-50 parts of a mixture of tetrahydrofurfuryl alcohol and morpholine.

These compositions may be prepared by simple mixing the ingredients in suitable proportions, depending on the type of leather being treated and on the degree of protection needed. The mixing may be'acco-mplished with the undiluted materials or by employing a common solvent. Suitable solvents include hydrocarbon solvents such as toluene or halogenated solvents such as perchloroethylene and thelike.

Representative suitable low molecular weight liquid polysulfide polymers were found to have a molecular weight of about 1,000 to 5,000, and a viscosity of approximately 7 to 45 poises at 25 C. Such polysulfides are commercially available from Thiokol Corp, Trenton, New Jersey, under designations such as Thiokol LP-32, Thiokol LP-2, Thiokol LP-33, and Thiokol LP3. These polysulfides have polymer segments compose-d of a number of formal groups linked by sulfur bonds and are terminated by mercaptan groups; some SH side groups may also be present in the chain or repeating formal units and some chain segments may also be cross-linked at various points. Thus, the average structure of Thiokol LP-32 may be represented as a characteristic feature of the repeating units of these thiokols is the presence of alkylene groups, such as -C H However, it will be understood that the practice of our invention is not limited to the Thiokols enumerated above, but that other alkylene polysulfides may successfully be used instead.

Without limiting ourselves to any particular theory we ascribe the efficacy of tetrahydrofurfuryl alcohol and/or rno-rpholine in the practice of our invention to their favorable solvent characteristics, absence of toxic eifects, and low flammability. In addition to their solvent action on and compatibility with the alkylene polysulfide, tetrahydrofurfuryl alcohol acts as a copolymer, and morpholine as a curing agent. The optional addition of a small amount of oleic acid serves to control the speed of the reaction and to prevent a runaway reaction; this, however, can also be accomplished by careful control of the reaction conditions even without the use of oleic acid.

We generally carry out the impregnation of leather in accordance with our invention by applying the liquid polysulfide polymer impregnating composition to the grain surface of the leather. The treating composition may be applied to the leather by any suitable manner such as rolling, swabbing, spraying or brushing. Shortly after application, during the mild to moderate heat curing operation preferably at about -160" F., say for 15 minutes to two days, a permanent polymeric barrier forms within the upper strata of the protein lattice of the leather. Polymer penetration into the leather is completely accomplished with the result that the appearance and feel of the leather remains substantially the same as for untreated leather. Strength characteristics of the leather are not decreased by the treating process and indications are that an improvement in some strength properties, e.g., abrasion resistance, are achieved. Leather comfort characteristics, e.g., water vapor permeability in the treated leather are adequate for use in handwear or footwear.

'These results are in sharp contrast to leather dipped into the treating composition so that polymer penetration into the leather occurs from the flesh side as well as the grain side. In the latter case the leather, to possess good liquid resistance, will be too stiff for use, especially at low temperatures and the flesh side will not possess good feel and will. have lost most, if not all, of its ability to absorb perspiration.

Satisfactory results are attained when the impregnated leather contains from 12 to 20 grams of polysulfide polymer per square foot of leather for light leathers such as glove or garment type. Shoe upper leather requires more of the polymer in order to achieve good results, approximately 20-30 grams of polymer per square foot of leather. In general, l-18 grams of polymer are preferred for glove or garment leather while 24-30 grams are best for shoe upper leather. Ordinarily, one application sufiices for glove or garment type leathers; while two applications may be found necessary in some cases for shoe upper leather.

Leather impregnation in accordance with our invention improves the liquid penetration resistance of many types of tanned leather, as, for example, leathers tanned by mineral tannages such as chrome, zirconium, etc.; leathers tanned by vegetable tannages, such as chestnut, and by mixtures of vegetable tanning extracts comnionly used in the leather industry; leathers tanned by a mineral or vegetable material followed by a vegetable or mineral retannage; leathers tanned by synthetic type tannages, such as glyoxal or succinaldehyde; and the treatment is applicable to leather prepared from any type of animal hide or skin, such as cowhide, horsehide, sheepskin, deerslcin and the like.

The accompanying drawing shows an enlarged edge view of a piece of leather impregnated from the grain side in accordance with our invention, the penetration of the interfiber space of the leather by the polysulfide being diagrammatically indicated by dots.

TESTS In the following examples, the water and gasoline resistances of the leather were evaluated as follows:

Water resistance was measured by the Quartermaster tap tester illustrated and described on pages 637 and 638 of the December 1956 issue of Journal of the American Leather Chemists Association. It consists essentially of a rotating anvil which provides a uniform wet surface, an arm and hammer which provides a definite force per unit area on the leather specimen and a cam mechanism for lifting and releasing the hammer, thus allowing it to fall on the anvil. During each stroke the fall of the hammer causes the mounted leather specimen to strike the wet anvil and thus exert a force or' strain on the fibers. in addition, the grain side of the specimen rubs against the rotating wet anvil under pressure until the cam lifts the arm. A tapping and rubbing action is thus repeated with each cycle (75 cycles per minute). Penetration of the water completes an electrical circuit through the arm and rotating anvil to sound a buzzer, thus providing a well defined end point of the test. A one-half pound load is generally employed for glove or garment leathers while a two pound load is generally used for upper leather. A hammer drop distance of /z-inch is used for all leathers.

The Maeser water penetration machine is illustrated and described on pages 401 and 402 of the August 1947 issue of Journal of the American Leather Chemists A..- sociation. The tester employs the principles of testing for water penetration rate as specified in Method 8021 (dated January 19, 1953) of the Federal Specification, Leather: Methods of Sampling and Testing, KK-L- 311a, dated June 26, 1956.

The apparatus consists of two V-shaped clamps with wedges that hold the specimen in the position of a V- shaped trough so that it can be immersed in water without leakage between the clamps and the leather. One clamp is fixed while the other is attached to an eccentric that is powered by a motor. On rotating the eccentric the leather is flexed in a manner simulating service conditions. The apparatus is equipped with an adjustable water tank so that the lowest point of eachclamp is approximately one inch below the surface of the water. A counter records the number of cycles through which the specimen is flexed. Specimen is-flexed approximately cycles per minute. Following clamping of the leather specimen with the grain side exposed to the water, the specimen is flexed until the first appearance of water inside the leather trough is observed. The number of cycles is then read and used to represent the degree of water resistance possessed by the leather.

Gasoline resistance was measured by determining the time required for penetration of gasoline through a leather specimen rubbed with a rubber covered finger. The specimen is placed grain side up on a paper towel resting on a fiat surface. Approximately 1 ml. of gasoline is poured onto the grain surface and rubbed vigorously with the rough surface of the rubber finger. The specimen is lifted after 30 seconds, 1 minute and 2 minutes to see if penetration and staining of the absorbent paper has occurred. The penetration time and corresponding ratings are as follows:

Penetration time, minutes Rating Below 0.5 Poor. 0.5 to 1.0 Fair. 1.0 to 2.0 Good. Above 2.0 Excellent.

Pertinent evaluation of other leather properties were generally performed in general accordance with methods specified in Federal Specification KK-L-Zilla.

We now proceed to describe the practice of our invention by means of several specific examples, without, limiting ourselves to any details of operating conditions or specific proportions set forth therein.

Example I There was employed a leather treating composition containing 57 parts by weight of Thiokol LP-32 and 43 parts by weight of tetrahydrofurfuryl alcohol.

Thirty sides of degreased chrome tanned cowhide garment leather were treated in a tannery with the above composition using a 7" mohair paint roller to manually spread the material over the grain surface of the leather. Approximately one fluid ounce of the material was applied per square foot of leather. Within 15 minutes after treatment, each treated side was conveyed through a drying tunnel at Mil-160 F. for 15 minutes. After all sides had been passed through the tunnel once, and in a few cases twice, depending on the amount of impregnating material remaining on the grain surface, they were placed in a drying loft overnight at approximately 90- F. The dried leathers were then washed, fatliquored to 4% oil, dried and staked.

Water and gasoline resistance was determined on leather specimens removed from four areas of the side: the backbone-tail, the backbone-center, belly-center, and shoulder. Ten of the thirty sides were used in the evaluation studies to give 40 leather test specimens. Duplicate water resistance measurements were made on all specimens While gasoline resistance was performed only once per specimen.

The results of the water resistance measurements showed that 32 of the 80 measurements did not produce a leak in 600 cycles, thus indicating a relatively high degree of water resistance. Five values fell below the 100 cycle level, the lowest value being 71 cycles. Similar results were obtained on eight of the sides whereas the other two showed a significant difference in water resistance. The side with the lowest resistance had four forwater and gasoline resistance.

to several different liquid chemicals.

polysulfide-treated leather was tested against corrosive 'trol samples.

assent-s of its values below 100 cycles while the best side did not leak in any test.

In contrast to the above results, untreated leather permits water penetration in approximately 20 cycles.

A wet brick test was conducted on mittens fabricated from the polysulfide-treated leather. In this severe test, the test subject handles wet bricks, lifting, turning and stacking them from a resting position in'approximately one inch of water. The test subject detected initial water penetration in approximately 22 minutes on the average for three mittens while untreated leather mittens took only an average of 30 seconds. In less than minutes the untreated leather palm was saturated with water. In contrast the polysuliide-treated leather mittens retained a dry, comfortable feel after 30 minutes, except for slight water penetration in isolated areas of the palm where the leather had been tightly squeezed against the wet bricks. The polysulfide-treated leather mittens were also found to be comparable to or better than untreated leather in other water resistance properties, such as drying time and flexibility or softness after soaking.

Since the Water resistance characteristics of leather could be adversely affected by leaching or migration of the treating material during use, especially by repeated wetting and drying cycles, a severe test was made on specimens from five of the ten sides of treated leather to determine the permanency of the the treatment. The

leather specimens were subjected to a series of ten cycles of laundering and drying. In each cycle the leather speci- -mens were washed with laundry soap for 15 minutes at 140 F., rinsed and dried at 140 F. for 30 minutes. After the cycles the leather specimens were tested All specimens resisted water penetration for more than 600 cycles and theyall received a rating of excellent in gasoline resistance. This shows the permanent characteristics of the treatment.

type liquids, such as battery acid (34 percent sulphuric acid),.2 N sodium hydroxide, and liquids such as ethylene glycol. In each determination, the liquid chemical was simply poured liberally onto the grain surface of the'leather and permitted to stand for one hour. Comparison of the bursting strength property showed no loss in strength for the exposed and adjacent areas except in the exposure to the sodium hydroxide solution.

'At room temperature and at -4i) F., the effect of the polysulfide treatment on the stiifness characteristic of leather was measured with the Tinius Olsen stillness tester and found to be not inferior to the untreated con- Substantially the same results were obtained by substituting Thiokol LP-2 for Thiokol LP-32. ThiOkOl LP-2 has a structure and molecular Weight (about 4000) generally corresponding to Thiokol LP-32, but is more crosslinked than Thiokol LP-32.

Example 11.

Cowhide glove leather was impregnated on the grain side with a solution composed of Parts by weight Polysulfide polymer (Thiokol LP-32) M 64.3 Tetrahydrofurfuryl alcohol 29 Morpholine 6.4 Oleic acid .3

For example, the

for one hour instead of 15 minutes. Most treated leather test specimens resisted water penetration for 600 cycles /2 pound load), or better, on the Quartermaster tap tester.

The grain surfaces of sheepskin, deerskin and horsehide glove leathers were also treated in accordance with the foregoing examples so as to receive a concentration of about 15-18 grams of polymer per square foot of leather. Water resistance values of 600 cycles or higher with a Quartermaster tap tester were observed.

Example" III The grain surface of cowhide upper leather was treated with a composition composed of liquid polysulfide poly mer 62.5 parts by weight, tetrahydrofurfuryl alcohol 31.25 parts by weight, morpholine 6.25 parts by weight. A concentration of approximately 24-30 grams polymer per square foot of leather grain surface was imparted Example IV The grain surfaces of ten sides of cowhide glove leather were treated in a tannery with a composition of polysulfide polymer 77 parts by weight, and morpholine 23 parts by weight so as to receive a concentration of 15-18 grams polymer per square foot of leather. The leathers were treated by a swab technique ascommonly employed in the tannery. After application, the leather was heatcured at 140-160 F. for 16 hours and then at -100 F. for 16-24 hours. The leathers were found by laboratory evaluation to possess good resistance to penetration i water and petroleum products. A field wear test with mittens fabricated from this treated leather and similar butuntreated leather showed the untreated mittens to absorb petroleum products at a rate nearly three times that of the treated ones. After a 22-day test, the treated mittens were found to be in a relatively dry condition as compared to the poor feel and appearance of the untreated ones. The test conclusions were that the treated leather mittens would be considered satisfactory for resisting petroleum products and that both types were adeto the grain side only resulted generally in leather either of poor liquid resistance or poor leather comfort characteristics. In contradistinction, our invention permits adequate impregnation of the leather from the grain side for the purpose of achieving the intended objects of our invention.

Having thus described several practical examples of leather impregnation in accordance with our invention, ityvill be understood, of course, that changes and variations in procedural conditions may be made without departing from the spirit and scope of our invention. Thus, for instance, liquid alkylene polysulfide partial polymers (i.e., liquid polymers capable of further polymerization to form an elastomer) other than Thiokol LP-32 (which Was the Thiokol employed in Examples I to IV unless otherwise noted) may be used; or the curing at an elevated temperature non-injurious to the leather may be interrupted prior to elfecting a complete cure of the polysulfide partial polymer in the inter-fiber space of the leather, e.g., after about 15 minutes, so as to permit the cure to be completed at room temperature. We desire to encompass these and other variations and modifications within the scope of our invention which we intend to claim broadly and. to this end have appended the following claims. a s

We claim:

1. Method of treating leather, which comprises impregnating said leather from the grain surface inwardly with a liquid composition comprising from about 50 to about 80 parts by weight of a liquid alkylene polysulfide polymer capable of being cured to form an elastomer, and from about 20 to about 50 parts by Weight of a member of the group consisting of tetrahydrofurfuryl alcohol, morpholine, and a mixture of tetrahydrofurfuryl alcohol and morpholine, and at least partially curing said composition in the interfiber space of said leather at a temperature above room temperature but non-injurious to said leather; whereby a flexible, liquid-resistant and cold-weather-resistant impregnated leather is obtained.

2. The method according to claim 1, wherein said composition also contains from about A part to about 2 parts by weight of oleic acid.

3. Method of treating leather, which comprises impregnating said leather from the grain surface inwardly with a liquid composition comprising from about 50 to about 75 parts by weight of a liquid alkylene polysulfide polymer capable of being cured to form an elastomer, and from about 25 to about 50 parts by weight of tetrahydrofurfuryl alcohol, and at least partially curing said composition in the interfiber space of said leather at a temperature above room temperature but non-injurious to said leather, whereby a flexible liquid-resistant and cold-weather-resistant impregnated leather is obtained.

4. Method of treating leather, which comprises impregnating said leather from the grain surface inwardly with a liquid composition comprising from about 75 to 80 parts by weight of a liquid alkylene polysulfide polymer capable of being cured to form an elastomer, and from about 20 to 25 parts by weight of morpholine, and at least partially curing said composition in the interfiber space of said leather at a temperature above room temperature but non-injurious to said leather; whereby a flexible liquid-resistant and cold-we'ather-resistant impregnated leather is obtained.

5. Method of treating leather, which comprises impregnating said leather from the grain surface inwardly with a liquid composition comprising from about 50 to 80 parts by weight of a liquid alkylene polysulfide polymer capable of being cured to form an elastomer, and from about 20 to 50 parts by weight of a mixture of tetra- ,hydrofurfuryl alcohol and morpholine, and at least parleather is obtained.

6. The method according to claim 1, wherein said liquid polymer has a molecular weight of about 1000 5000.

7. The method according to claim 1, wherein said liquid polymer has a'viscosity of about 7 to about poises at 25 C.

8. The method according to claim 1, wherein said alkylene is C H 9. The method according to claim 1, wherein said curing temperature is about 90-160 F.

10. Method of treating leather, which comprises impregnating said leather from the grain surface inwardly with a liquid composition comprising from about to about 80 parts by Weight of a liquid alkylene polysulfide polymer having a molecular weight of about 1000-5000 and capable of being cured to form an elastomer, and

from about 20 to about 50 parts by weight of a member of the group consisting of tetrahydrofurfuryl alcohol, morpholine and a mixture of tetrahydrofurfuryl alcohol and morpholine, and at least partially curing said composition in the interfiber space of said leather at about 90-160 F.; whereby a flexible, liquid-resistant and coldweather-resistant impregnated leather is obtained.

11. The method according to claim 10, wherein said composition also contains from about A part to about 2 parts by weight of oleic acid.

12. A flexible, liquid-resistant and cold-weather-resistant impregnated leather produced by the method of claim 1.

13. A liquid composition for impregnating leather, comprising from about 50 to about 80 parts by weight of a liquid alkylene polysulfide polymer capable of being cured to form an elastomer, and from about 20 to about 50 parts by weight of a member of the group consisting of tetrahydrofurfuryl alcohol, morpholine, and a mixture of tetrahydrofurfuryl alcohol and morpholine.

14. A composition according to claim 13, said composition also containing from about A part to about 2 parts by Weight of oleic acid.

'15. A liquid composition for impregnating leather, comprising from about 50 to about 75 parts by weight of a liquid alkylene polysulfide polymer capable of being cured to form an elastomer, and from about 25 to about cured to form an elastomer', and from about 20 to about 25 parts by weight of morpholine.

17. A liquid composition for impregnating leather,

comprising from about 50 to about parts by weightof a liquid alkylene polysulfide polymer capable of being cured to form an elastomer, and from about 20 to about 50 parts by weight of a mixture of tetrahydrofurfuryl F alcohol and morpholine.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. METHOD OF TREATING LEATHER, WHICH COMPRISES IMPREGNATING SAID LEATHER FROM THE GRAIN SURFACE INWARDLY WITH A LIQUID COMPOSISTION COMPRISING FROM ABOUT 50 TO ABOUT 80 PARTS BY WEIGHT OF A LIQUID ALKYLENE POLYSULFIDE POLYMER CAPABLE OF BEING CURED TO FORM AN ELASTOMER, AND FROM ABOUT 20 TO ABOUT 50 PARTS BY WEIGHT OF A MEMBER OF THE GROUP CONSISTING OF TETRAHYDROFURFURYL ALCHOL, MORPHOLINE, AND A MIXTURE OF TETRAHYDROFURFURYL ALCOHOL AND MORPHOLINE, AND AT LEAST PARTIALLY CURING SAID COMPOSITION IN THE INTERFIBER SPACE OF SAID LEATHER AT A TEMPERATURE ABOVE ROOM TEMPERATURE BUT NON-INJURIOUS TO SAID LEATHER, WHEREBY A FLEXIBLE, LIQUID-RESISTANT AND COLD-WEATHER-RESISTANT IMPREGNATED LEATHER IS OBTAINED.

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