US3419344A - Fatliquoring with tetrakis (hydroxy-alkylene) phosphonium halide and an organic phosphate ester and leather flameproofed thereby - Google Patents

Description

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atent FATLIQUORING WITH TETRAKHS (HYDROXV- ALKYLENE) PHGSPHGNIURI HALIDE AND AN ORGANIC PHOSPHATE ESTER AND LEATHER FLAMEPROOFED THEREBY Richard N. Jones, Reading, Mass, assignor to Swift &

Company, Chicago, 111., a corporation of Illinois N Drawing. Filed Apr. 20, 1966, Ser. No. 543,783

11 Claims. (Cl. 8-?423) This invention relates tothe flame-proofing and reduction of afterglow in leathers. The invention is directed to the treatment of hides and skins with the express purpose of incorporating self-extinguishing properties into the leather. More specifically, the invention concerns treatment of mineral tanned leather with certain phosphorus containing compounds and to a unique fat-liquoring process wherein the leather has pronounced resistance to flaming and afterglow.

The military has a definite requirement for pilots gloves which when subject to flash fires will not ignite and, more important, will not continue to have a glowing ash after the actual flame has been extinguished. Most leathers have a certain resistance to flammability, but mineral tanned leathers do exhibit the afterglow characteristic. Further, glove leather tends to shrink while it is burning resulting in the fact that the glove must be cut off the pilots hand. The result is that serious burns to the hands of pilots caught in flash fires has frequently occurred. While various workers skilled in the leather art have been working on the problem over the past -12 years, all efforts to produce glove leather having dimensional stability and being resistant to afterglow have failed.

The bulk of commercial leathers are tanned with either mineral ions, such as: salts of chromium, zirconium, and aluminum, etc., or organic products such as: vegetable tannins, aldehydes, syntans, etc. Organic tanning agents do not generally impart the afterglow characteristic to leather, but by the same token, they are often not capable of producing certain other chemical and physical properties required for many leather applications. For example, the requirements for good gloving leather are more readily satisfied by a mineral tannage since such tannage produces the soft and stretchy character required for finger dexterity and comfort, as well as resistance to the harmful effects of perspiration. Yet, on the other hand, mineral tanning agents, especially those of chromium, often produce in leather a property known as afterglow; that is, when leather so tanned is subjected to a flame, a slow but steady combustion of the leather occurs even after the actual flames have been extinguished. In fact, this steady combustion of the leather resulting in a greenish colored ash is one means of determining Whether a piece of leather has been chrome tanned.

It is generally necessary to fat-liquor most leathers with fatty substances of animal, mineral, or vegetable origin to impart the desired flexibility characteristics as well as other properties to the leather. It is frequently necessary to use these fatty substances to the extent of about /6 to about /3 the dry weight of the leather in order to impart the desired properties. These fatty substances are combustible materials, and it follows that leathers containing moderately high amounts of these fatty substances will be more subject to burning than if they were absent. Accordingly, it has not been possible to manufacture a mineral-tanned, heavily fat liquored leather that exhibited good fire resistance; i.e., resistance to both after-flaming and afterglow.

It is, therefore, an object of this invention to provide leather segments which exhibit self-extinguishin g propertie and which possess pronounced resistance to afterglow.

It is also an object of the invention to provide a process for treating mineral-tanned leather which suppresses the tendency of the mineral ion to afterglow as well as imparting the necessary flexibility characteristics to the treated leather.

Additional objects, if not specifically set forth herein, will be readily apparent to those skilled in the art from the detailed description of the invention which follows.

In general, this invention consists of a 2-part treatment that can be applied to conventionally mineral-tanned leather, retaining all the desired features which mineraltanning imparts. The first part consists of retannage with a phosphonium halide to restrict the ability of the chromium ion to afterglow. The second part employs a unique fat-liquorine composition containing a phosphate ester which aids in rendering the leather resistant to corn bustion. Both steps are important. Treatment with only the phosphonium halide will not prevent afterglow nor is treatment with only the phosphate ester satisfactory. It is believed that one of the functions of the phosphate ester in the fat-liquoring composition is to curb the combustion of the more conventional fat-liquoring ingredient. This, in turn, prevents the temperature of the leather from building u to the point where the phosphonium halide will no longer be effective. The invention is not restricted to the above theory, however, since this explanation is merely set forth so that one may better understand the importance of using both the phosphonium halide and the phosphate ester. The net result is a chrome-tanned leather with pronounced resistance to flaming and afterglow. In addition, the leather segments treated in accordance with the teachings of this invention exhibit improved dimensional stability when subjected to flame.

At this point, it is mentioned that the words retanned or retannage used throughout the specification to classify the treatment of the leather with the phosphonium halide should not be given a restrictive meaning. The word retan is used, because, from a sequence of operations standpoint, the treatment is applied at the normal point of retanning leather. However, the phosphonium halide treatment does not produce any noticeable leather effects (added weight, greater roundness, more or less stretch) which are commonly associated with and are generally the sole purpose of conventional retans. Also, it is still possible to include conventional retanning steps, if such retannages are deemed necessary to regulate the aforementioned leathering effects.

In the etaiied description which follows, glove leather will be used in the specific embodiments. However, it should be realized that the principles elucidated herein apply to other leathers; that is to say that while the specific examples in discussion relate to glove leather the invention also encompasses the production of fire resistant leathers in general, regardless of their intended use. Further, the term skins as used herein shall include the skins and hides of all animals commercially tanned, including cattle hide, horsehide, sheepskin, goatskin, pigskin, furs and the like. In addition, the process of the invention is not restricted to use on mineral-tanned leather. The process may be applied to skins which have been initially tanned by any of the known methods in commercial practice, although, for reasons mentioned above, it is most significant in the case of chrome-tanned skins.

In the order of the sequence of events, this invention relates to the treatment of leather after the normal tanning step. More specifically, after the normal tanning step and the customary mechanical operations which follow immediately thereafter (flashing, splitting, shaving, etc.) have been conducted, the skins are ready for treatment with the phosphonium halide and the phosphate ester. The skins are then deposited into tanning drums and washed. The temperature of the Wash water and that of the retanning bath may vary widely, up to the shrinkage temperature of the hide being treated. Generally the skins are washed at a temperature of about 80 F. to 130 F. for to 30 minutes. If the original tannage was completed at a pH below about 4.5, no adjustment in pH is required at this point. On the other hand, if the pH was above 4.5, it should be lowered to about 4.0 with a weak acid such as formic or acetic acid. Further, adequate running time for equilibrium conditions to be reached should be contemplated.

After the initial tanning of the skins and adjustment of the pH to below about 4.5, preferably in the range of about 3.5 to 4.5, the skins are subjected to treatment with the phosphonium halide. The desirable halides utilized in this invention may be best characterized as those containing four hydroxyalkylene radicals directly attached to the phosphorus atoms. Structurally, the phosphonium halide may be represented by the formula:

wherein x is an integer from 1 to 4 and X is chlorine, bromine, fluorine or iodine. As a practical matter X is usually chlorine or bromine, preferably chlorine as the phosphonium bromide is more expensive than the chloride. The amount of phosphonium halide utilized may range from about 1l2%, based on the wet, drained weight of the skins. It has been found that the best results have been obtained using tetrakis (hydroxymethyl) phosphoriium chloride in an amount between about 0.5% to about 10.0%, preferably 1.5% to 5%, by weight, based on the weight of the drained, tanned skins. Generally, the percentage of the tetrakis (hydroxyalkylene) phosphonium halide employed will depend on the type of initial tannage.

Treatment of the skins with tetrakis (hydroxyalkylene) phosphonium halide is conducted for a period of time to insure adequate penetration of the halide: into the skins. This time will vary between minutes and 2 hours but will generally be reached in a period of about 30-60 minutes.

To insure reaction of the phosphonium halide with the skin substance, as well as adequate exhaustion of the halide from the liquor, the leather is gradually neutralized to a pH of about 6.5 to about 7.5 with a mild alkaline substance such as sodium bicarbonate. This gradual neutralization should take place relatively slowly, i.e., the neutralizing agent should be added in three or four feeds encompassing a period of from about 60-90 minutes.

At the completion of this retanning operation, the skins are thoroughly washed, and the temperature, float, and pH are adjusted as required for the next step in the operation. This will normally be the drum dyeing process, but as previously mentioned, conventional retannages can be included at this point if so desired. Said conventional retannages and/ or the drum dyeing may be carried out in the usual manner and form no part of the instant invention.

After this the skins are washed and pH of the system raised to between about 4.0 to 4.5 if the pH at the conclusion of the preceding step was below about 3.5. Washing time and the amount of float will vary, but it has been found that washing for about 10 minutes at around 120 F. to 130 F. is normally adequate.

In the fat-liquoring step, about 4-18% of the fat-liquor composition, based on the weight of the drained, tanned skins is dispersed in about 3 to 5 times its weight of water. The liquoring operation is carried out for a time sulficient to render softness and flexibility characteristics to the leather. In this connection, the fat-liquor must have a specific exhaust and penetration rate in order to produce the desired results. While time required for liquoring will vary somewhat, it has been found that about 30-60 minutes is usually adequate. The skins are then washed for a short period, say about 5 or 10 minutes at F., and then removed and handled in the usual manner.

The fat-liquors employed may be defined as those conventional sulfated mono-, diand triglycerides, sulfated fatty acids or any combination thereof wherein the glyceride or fatty acids contain 8-30 carbons per chain. The glyceride and/or fatty acid can be derived from animal, vegetable or marine sources. The degree of sulfation is important and it has been found that the degree of sulfation must range between about 1.5% to 12% in order to permit a controlled exhaustion rate, and impart to the leather the required temper and surface characteris tics necessary for a wide variety of end-use products.

Generally speaking, conventional fat-liquors may be used as long as they are capable of emulsifying the required amount of phosphate ester. Since the skins are treated with about r18%, by Weight, of fat-liquor, and since the fat-liquor must contain at least 30% phosphate ester, it therefore follows that at least 1.2% phosphate ester is required for contacting the skins.

The phosphate esters which are present in at least about 30%, by weight, of the fatty-liquor composition may be defined as alkyl phosphate esters, aryl phosphate esters, alkylaryl phosphate esters and phosphate esters of polyoxyethylenated alkylaryl alcohols or polyoxyethylenated aliphatic alcohols.

Representatives of the alkyl phosphate esters are the C -C alkyl esters of phosphoric acid. Specific members include trimethyl phosphate, triethyl phosphate, tripropyl phosphate, tributyl phosphate, tripentyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate, including all isomers as well as mixed esters, i.e., diethyl monobutyl phosphate.

Representatives of aryl phosphate esters include all aromatic esters of phosphoric acid wherein the aromatic portion is unsubstituted or substituted with non-interfering groups. Examples are triphenyl phosphate and trinaphthyl phosphate. Included within the term alkylaryl phosphate esters are the C -C alkyl substituted phenol and naphthol esters of phosphoric acid. Generally the aromatic portion will contain 1-3 alkyl groups in ortho, meta, or para positions. A preferred member of the group is tricresyl phosphate.

The polyoxyethylenated esters may be represented by the formulas:

and

wherein R is selected from the group consisting of (D -C alkyl radicals and C -C alkyl phenyl radicals, M is a cation and usually an alkali metal or /2 alkaline earth metal hydrogen or ammonium ion, and n is an integer of about 1 /2 to about 30. The esters will normally contain about 20-75 percent, by weight, of ethylene oxide. Specific examples include phosphate esters of polyoxyethylenated nonyl phenol containing about 63% ethylene oxide and phosphate esters of polyoxyethylenated tridecyl alcohol containing about 52% ethylene oxide.

As a specific, non-limiting embodiment of the invention, one may use a fat-liquor composition containing about 5-35 parts of highly sulfated sperm oil, about 5-35 parts of low sulfated cod plu mineral oil, and about 30-90 parts of tricresyl phosphate for a combined total of 100 parts. The amount in proportion of the 2 sulfated oils is adjusted to produce the desired exhaustion rate and penetration of the fat-liquor, and will vary depending upon the initial tannage.

At this point, it should be mentioned that tricresyl phosphate, being water insoluble, must be emulsified to work in the water system employed in the fat-liquoring step. Several systems were examined, and it was discovered that a proper balance of the materials selected resulted in more proper stability. This balance required a sulfated oil of combined S of between about 8% to 12% in conjunction with a sulfated oil of combined 80;, of between about 1.5 to 3% in order to produce good glove leather. The specific combination of oils and emulsifiers to be used is more related to the properties desired in the leather than it is to the fire retardant properties. That is to say, when glove leather is desired, the particular fatliquor composition is relatively important if the desired finished characteristics are to be obtained.

However, the invention is not restricted to specific fatliquoring compositions inasmuch as self-extinguishing properties may be rendered to the leather as long as both the phosphonium halide and the phosphate ester are utilized. In order to impart the self-extinguishing properties as well as the elimination of the afterglow effect to the leather, both phosphorus containing compounds are required. For example, chrome-tanned collagen that has been after treated with tetrakis (hydroxymethyl) phosphonium chloride will exhibit fire retardancy but it will possess afterglow and is useless for military gloving purposes unless it is thereafter heavily fat-liquored with the composition containing the phosphate ester. On the other hand, a chrome-tanned leather, fat-liquored with the phosphate ester only exhibits some fire resistance but also possesses afterglow.

The following examples are presented to illustrate the invention. It will be understood that the specific embodiments and illustrations should not be taken in any manner as limiting the invention which is defined in the appended claims.

EXAMPLE I All percentages are based on the pickle weight of the skins.

A quantity of conventionally chrome-tanned sheepskins were placed in a tanning drum and washed at 100 F. for about minutes. The pH of the system was adjusted to about 4. In a float of 150%, about 1.5% of the tetrakis (hydroxymethyl) phosphonium chloride was added and the system drummed for about 30 minutes. The leather was then gradually neutralized to a pH of about 6.5 to 7.0 with 3% sodium bicarbonate, using 3 feeds during a period of about 60 minutes to accomplish the neutralization. The leather was then washed for about 5 minutes in a 250% float at a temperature of about 130 F. The skins were then dyed in the usual manner and after dyeing were washed for about minutes at 120 F. to 130 F. A quantity of fat-liquor was dispersed in four times its weight of 130 F. water and added to the drum and run for 45 minutes. The quantity of fat-liquor utilized was by weight, of the drained tanned skins and consisted of about 5 4% sulfated sperm oil (8.58.8% S0 content), 5 /4% sulfated cod and mineral oil (2.3-2.5 S0 content) and 4 /2 tricresyl phosphate based on the Weight of the skins. The skins were then Washed for 5 minutes at 100 -F., dumped and allowed to dry. The exhaust of the fat-liquor composition was very good. The temper of the dried leather was soft and with run, and the grain surface feel was rich without being greasyall of these attributes being necessary requirements of good gloving leather.

EXAMPLES II-XI Listed below are other examples of the invention which are typical of the skin types and process variations possible. Each of these is like Example I, with the following exceptions:

ALL PERCENTAGES BASED ON THE PICKLE WEIGHT OF SKIN Fat-liquor, percent Example Skin Percent THPC 1 Oil A Oil B Phosphate ester 2 1. 50 3.0 1. 5 a 2.00 4.0 7. 5 b 4. 25 2. 0 7. 5 c 3. 00 3. 0 3. 0 d 3. 00 1. 5 1. 5 e

Oil C Oil D VII Calfskin. 1. 5 2. 50 2. 50 5 0 f VIII. Cowhide 3.0 4.00 1. 50 3. 0 g 5.0 5. 25 5. 25 4. 5 h

7. 5 1.00 3. 00 3.0 i Oowhide 10.0 3.00 0.50 1 5 THPO tetrakis (hydroxymethyl) phosphonium chloride.

Oil A=Sulfated 45 sperm oil (8.5-8.8% S03 content).

Oil B=Sulfated cod and mineral oil (2.3-2.57 S03 content).

Oil C=Sulfated tall oil fatty acid (5.05.2% S03 content).

Oil D=Soap-type containing Oil 0, sheep oil, and soap (32-36% SOr content).

2 Phosphate ester: a=triethy1 phosphate, b=tricresyl phosphate, c=tricrosyl phosphate, d=triethyl phosphate, e=triphenyl phosphate, f=tricrosyl phosphate, g=tricresyl phosphate, h=triethyl phosphate, i=tricresyl phosphate, j=triphenyl phosphate.

Leather prepared in accordance with the above Examples was subjected to fire resistant tests. In these tests, rectangular specimen-s of the leather were cut so that they measured 3 inches by 14 inches. Two metal bars of about inch stock measuring 1 by 3 inches were placed on both sides of the leather specimen along one of its 3 inch edges. The resulting sandwich was securely tightened in a buret clamp which was attached to a ring stand so that the grain side of the specimen faced down. A second ring stand was placed nearby and has fastened to it a horizontal metal rod. The free end of the leather specimen was draped over the rod so that the leather was inclined at an angle of 45 with the inclined portion measuring 3 inches by 7 inches. A third metal bar was taped to the free end to serve as a counterweight. The apparatus was further adjusted so that center of a gas burner was about 2 inches below the grain surface and exactly centered underneath the exposed specimen. The gas burner, with air ports closed, was adjusted to produce a flame of about 3 inches in height. The burner was placed in position so that the flame played against the specimen for 12 seconds. It was then quickly removed and the following times noted: (1) afterfiame: time between burner removal and cessation of flames on the specimen, i.e., self-extinguishing properties, and (2) afterglow: period between end of afterflame and cessation of the reddish afterglow. After the specimen cooled, it was removed and the percentage of the original area (21 square inches) that was retained was calculated. All leathers tested exhibited less than 5 seconds of afterflame, and less than 10 seconds of afterglow and hence were deemed to be fire resistant. All leathers exhibited an area retention greater than 50% and hence Were considered to have good dimension-a1 stability when exposed to flame. All leathers treated in accordance with the above examples consistently showed excellent fire resistance and dimensional stability when tested in accordance with the above method. To the contrary, all other presently known commercial types of gloving leather as well as many other types of leather, notably those which are chrome-tanned, fail to pass the test.

Obviously many modifications and variations of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

1. A process for fireproofing skins comprising treating skins with tetrakis (hydroxyalkylene) phosphonium halide and a fat-liquor composition containing a phosphate ester whereby the skins become resistant to flaming and afterglow.

2. The process of claim 1 wherein the halide is tetrakis (hydroxymethyl) phosphonium chloride.

3. The process of claim 1 wherein the phosphate ester is a member selected from the group consisting of phosphate esters of polyoxyethylenated alkyl aromatic alcohols, phosphate esters of polyoxyethylenated aliphatic alcohols, and alkyl, aryl and alkylaryl phosphate esters.

4. The process of claim 1 wherein the phosphate ester is tricresyl phosphate.

5. The process of claim 1 wherein the halide is tetrakis (hydroxymethyl) phosphonium chloride and is present in an amount of about .5% to 10.0%, based on the drained weight of the skins.

6. The process of claim 1 wherein the halide is tetrakis (hydroxymethyl) phosphonium chloride, the phosphate ester is tricresyl phosphate and the phosphate ester is present in an amount of about 1.2% to 6%, by weight, based on the drained weight of the skins.

7. The process of claim 1 wherein the skins are treated with an aqueous solution of tetrakis (hydroxymethyl) phosphonium chloride at a pH of less than about 4.5.

8. The process of claim 1 wherein the phosphonium ester is emulsified in a sulfated glyceride oil having an S0 content of between about 1.5% and 12%.

9. The process of claim 8 wherein the sulfated glyceride comprises about 5-35 parts of sulfated sperm oil, 5-35 parts of sulfated cod oil and the phosphate ester is tricresyl phosphate.

10. As an article of manufacture, a leather having pronounced resistance to flaming and afterglow, said leather produced by treating, under acidic conditions, a mineral tanned skin with a tetrakis (hydroxyalkylene) phosphonium halide and a phosphate ester.

11. The article of claim 10' wherein the halide is tetrakis (hydroxymethyl) phosphoniurn chloride and the ester is tricresyl phosphate.

References Cited UNITED STATES PATENTS 2,732,278 l/1956 Filachione 8 94.33 3,104,151 9/1963 Windus 8-94.32 XR NORMAN G. TORCHIN, Primary Examiner.

D. LEVY, Assistant Examiner.

U.S. Cl. X.R.

Claims (1)

1. A PROCESS FOR FIREPROOFING SKINS COMPRISING TREATING SKINS WITH TETRAKIS (HYDROXYALKYLENE) PHOSPHONIUM HALIDE AND A FAT-LIQUOR COMPOSITION CONTAINING A PHOSPHATE ESTER WHEREBY THE SKINS BECOME RESISTANT TO FLAMING AND "AFTERGLOW."