Classifications

• • C—CHEMISTRY; METALLURGY
  • C14—SKINS; HIDES; PELTS; LEATHER
  • C14C—CHEMICAL TREATMENT OF HIDES, SKINS OR LEATHER, e.g. TANNING, IMPREGNATING, FINISHING; APPARATUS THEREFOR; COMPOSITIONS FOR TANNING
  • C14C1/00—Chemical treatment prior to tanning
  • C14C1/06—Facilitating unhairing, e.g. by painting, by liming

Definitions

• This invention relates to improvements in the processing of animal hides into leather and more particularly relates to improved compositions and methods for the unhairing of the hides during such processing.
• the cured hides undergo a soaking operation wherein the hides are contacted with water over an extended period of time, generally of 24 hours or more.
• the purpose of this operation is to remove any salt, dirt and soluble protein matter from the hides as well as to allow the skin fibers of the hides to absorb water and swell.
• the hides are removed from the water and are fleshed, i.e., the flesh is removed from the hide, thus allowing the skins to hydrate better so as to expedite the soaking and subsequent operations.
• the fleshing operation the soaking process is completed and the hides are in condition for the unhairing process.
• the hides are subjected to the action of some material which will loosen the hair on the hides so that it may be easily removed.
• the materials used for unhairing should not have any deleterious effect on either the hide itself or on the hair which is removed.
• the reason for avoiding destruction of the latter is that the hair is a valuable by-product which is desirably recovered and sold. The reason for avoiding destruction of the former is, of course, obvious.
• Another object of the present invention is to provide,
• compositions for use in the unhairing of animal hides which composition, in conjunction with lime, effects a rapid unhairing, without appreciable damage to the hair.
• a further object of the present invention is to provide an improved process for the unhairing of animal hides which process may be carried out rapidly without damaging either the hide or the hair which is removed.
• the lime solution used is generally a slurry of lime
• this acidity effects a further dissolving of more calcium hydroxide.
• the resulting increased calcium concentration in the solution then results in a lowering of the pH of the solution, due to a common ion effect in the solubility product equation of the calcium hydroxide.
• this lowering of the pH value in the unhairing solution has a beneficial effect in decreasing the swelling of the hides or skins, it has been found that too large a reduction in pH value is to be avoided in that this results in a slowing of the unhairing action. Accordingly, in some instances, it may be desirable to provide additional alkalinity in the unhairing solution so as to prevent an excessive drop in the pH.
• phosphorusand sulphur-containing compounds having the preferred sulphur to phosphorus ratio, which will be effective in the unhairing of hides and skins.
• suitable inorganic phospho-sulphur compounds containing at least one P-S bond which may be used are the phosphorus sulfides, such as phosphorus pentasulfide, (P 8 or P 5 phosphorus polysulfides such as P 8 the various alkali metal thiophosphates, such as the sodium thiophosphates, to mention only a few.
• compounds such as the phosphorus sulfides may be used in conjunction with an alkali metal hydroxide so as to form in situ, the corresponding alkali metal thiophosphates, in the unhairing solution.
• an alkaline mateiral such as sodium hydroxide or potassium hydroxide
• the reduction in pH of the hairing solution also can be compensated for by combining the phosphorus and sulphur compound, such as phosphorus sulfides, with a small amount of an alkali metal sulfide, such as sodium sulfide.
• the amount of alkali metal sulfide used will, of course, be small, as compared to the amount of phosphorus sulfide used.
• an alkali metal sulfhydrate such as sodium sulfhydrate
• This material acts as a sharpening agent in the unhairing solution, as well as contributing to the pH.
• the amount of these materials present will be less than that which would cause any damage to the hair which is removed.
• the phosphorus and sulphur containing compound used is a phosphorus sulfide, such as phosphorus pentasulfide
• the alkali metal or alkaline earth metal thiophosphate is first formed and that this in turn hydro lyzes to the sulfhydrate ions and phosphate ions. Thereafter, the sulfhydrate ions are further hydrolyzed to form hydrogen sulfide, which material, it is believed, efiects the actual unhairing.
• the inorganic phospho-sulphur compounds containing at least one P-S bond which may be used in the present invention may be thought of as those phosphorus and sulphur compounds, preferably having a sulphur to phosphorus ratio not less than about 5:2, which in a lime slurry or solution will ultimately hydrolyze to form hydrogen sulfide.
• These phosphorus and sulphur containing compounds may be used by themselves or in conjunction with a material which will be hydrolyzed to provide a source of alkalinity in the lime solution or slurry. It is believed that in addition to the specific phosphorus and sulphur containing compounds which have been set forth hereinabove, other similar compounds will become apparent to those skilled in the art.
• the inorganic phospho-sulphur compounds containing at least one P-S bond used in the present invention may be a phosphorus sulfide such as phosphorus pentasulfide, phosphorus polysulfide, a sodium thiophosphate or a combination which will yield sodium thiophosphate in situ, such as a mixture of phosphorus pentasulfide and caustic soda.
• a sodium thiophosphate which may be used in the present method is one prepared by the reaction of phosphorus pentasulfide (P 5 and sodium hydroxide in a water solution.
• This reaction may be carried out by adding the phosphorus pentasulfide to a concentrated aqueous solution of caustic soda at such a rate that the temperature of the reaction is maintained at about degrees centigrade, the reaction being moderately rapid and exothermic in nature.
• the sodium thiophosphate product may be crystallized from the reaction mixture by cooling it to a temperature of about 30 degrees centigrade provided the NaOH cencentration has been sufficiently high. The mother liquor which remains after the removal of the crystals may then be reused in additional runs.
• the white to cream-colored crystals obtained can be purified by recrystallization from Water to give the final sodium thiophosphate product which melts in its water of crystallization at about 65 degrees cen tigrade and which decomposes with the evolution of hydrogen sulfide at about to decrees centiurnde.
• a solution or slurry of lime is used.
• a lime slurry be used so that solid lime is always available to go into solution and replenish the lime which has been used. While, obviously, this result could be obtained :by continuously adding lime to the unhairing solution at a rate to correspond to the rate at which the lime is being used, a simpler and hence preferable, method is to use a lime slurry.
• the slurry used will contain about 6 percent of lime, based on the total weight of the hides being unhaired.
• This amount of lime includes both the lime which is in solution and that which remains in the solid state suspended in the solution. Although a slurry containing about 6 percent by weight of lime is preferred, it should be appreciated that lime slurries containing either greater or lesser amounts of lime may be used with satisfactory results.
• an inorganic phosphosulphur compound containing at least one P-S bond is added to the above lime slurry.
• the amount of this compound added whether phosphorus sulfides or sodium thiophosphates or other similar compounds will generally be within the range of about 0.1 to about 10 percent by weight of the hides or skins being treated. Excellent results have been obtained in the practice of the present invention when the amount of phosphorus and sulphur containing compound used is within the range of about 1 to 2 percent by weight of the hides being treated. Accordingly, this amount of phosphorus and sulphur containing compound is preferred.
• an alkaline material such as caustic soda
• an alkaline forming material such as sodium sulfhydrate
• these materials will generally be present in an amount by weight not substantially in excess of the phosphorus and sulphur containing compound.
• the weight amounts will be substantially less than the amount of phosphorus and sulphur containing compound.
• alkali such as caustic soda
• phosphorus and sulphur containing compound such as phosphorus pentasulfide
• the hides or skins are preferably subjected to an aqueous soaking operation prior to the time when they are contacted with the unhairing slurry or solution.
• an aqueous soaking operation prior to the time when they are contacted with the unhairing slurry or solution.
• one of the pre-tanning treatments which animal hides and skins customarily undergo is that of curing. This treatment customarily involves treating the hides with rock salt so as to prevent decay prior to processing into leather.
• the salt be removed. This removal of the salt as well as dirt and other soluble matter from the hide is one function of the soaking operation.
• a second and equally important function is that of restoring water to the hides so as to return them to a condition which is, as nearly as possible, equivalent to their condition at the time they were on the live animals.
• the soaking operation prior to unhairing may be carried out using water as the soaking media.
• water as the soaking media.
• an alkali metal sulfhydrate and/or an alkali metal tetrasulfide are added to the soaking water. Where these materials are added to the soaking solution, it is found that a preliminary loosening of the hair is achieved during the soaking operation.
• the alkali metal sulfhydrate such as sodium sulfhydrate and the alkali metal tetrasulfide such as sodium tetrasulfide may be added to the soaking water in amounts up to about 2 percent by weight of the hides being soaked.
• the time required for soaking of the hides prior to unhairing will be upwards to about 24 hours, whether or not additives such as sodium sulfhydrate and/ or sodium tetrasulfide are used. While, obviously, the minimum amount of soaking solution used is that which will provide for a thorough wetting of the hides, there has not been found to be any critical maximum amount. In general, a weight ratio of soaking solution to hides of about 4:1 have been found to give very good results and for this reason is preferred.
• the temperatures utilized in the soaking operation again, have not been found to be critical, although, it will be appreciated that at higher temperatures the soaking will proceed more rapidly.
• the soaking operation is generally carried out at about room temperature, i.e., about 70 degrees Fahrenheit. Higher or lower temperatures can be used, however, in this operation without detrimental effects.
• the hides or skins may be agitated or paddled. The frequency and amount of such agitation or paddling will be determined by whatever practice is normally followed in ordinary soaking procedures.
• the hides or skins are placed in the unhairing solution.
• the unhairing is carried out in paddles although, if desired, vats or still pits may be used.
• the lime slurry which forms the basis for the unhairing solution is made up in the concentration as set forth hereinabove.
• To the lime slurry is added the desired inorganic phospho-sulphur compound containing at least one P-S bond in amount heretofore indicated.
• the unhairing solution is generally at about room temperature, i.e., about 70 degrees to degrees Fahrenheit.
• the amount of solution used -in the unhairing is generally about the same as that used for the soaking operation, i.e., a weight ratio of solution to hides of about 4: 1.
• the hides or skins to be unhaired are then combined with the unhairing solution in the paddle where they remain until the hair has been sufiiciently loosened.
• the time required may be variable, depending on the hides, solution strength, and so forth. Generally, however, periods of about '1-8 to 24 hours should be sufiicient to effect substantially complete unhairing of the hides.
• the hides are in contact with the unhairing solution, they are agitated or paddled so as to elfect a more intimate contact between the hides and the solution.
• the time and the nature of paddling will be those which are suitable.
• the hides or skins are removed from the unhairing solution, they are passed through conventional unhairing equipment wherein substantially all the hair on the hide is removed.
• Example 1 Grams of Hair Sample Phosphorus Final pH Unhalring Conditions
• Example 2 The 'procedure of Example -1 is repeated with the exception that varying quantities of sodium sulfhydrate and/or phosphorus pentasul-fide are added to the lime solution. The unhairing of the hide pieces is again evaluated after 24 hours. Using this procedure, the following results are obtained:
• phosphorus pentasulfide is effective in increasing the unhairing efficiency of a lime slurry. It is further seen that unhairing with phosphorus pentasulfide is effected when using either a water soak prior to the unhairing process or an aqueous solution containing sodium sulfhydrate and sodium tetrasultide, although the use of the latter soak solutions does result in a somewhat increased effectiveness for the phosphorus pentasuliide.
• Example 4 The following illustrates the preparation of a sodium thiophosphate for use in the unhairing process of the present invention.
• Phosphorus pentasulfide P 8 is reacted with a 10 percent excess of a strong caustic solution containing percent by weight NaOH.
• the reaction is moderately rapid and exothermic, and the temperature during the reaction is held at about 70 degrees centigrade by controlling the rate of addition of the P 8 to the caustic solution.
• a concentration of sodium thiophosphate between 80-85 grams per 100 cubic centimeters of water is obtained. Cooling this solution to degrees centigrade, effects crystallization of a heavy crop of crystals. These crystals are separated from the mother liquor and solid caustic soda and P 8 are again added to the mother liquor to prepare a second batch.
• Example 5 The procedure of Example 1 is repeated with the exception that varying quantities of sodium thiophosphate,
• Example 6 The procedure of Example 5 is repeated with the exception that varying quantities of sodium sulfhydrate and/ or sodium thiophosphate are added to the lime solution. The unhairing of the hides is then evaluated after 24 hours. Using this procedure, the following results are obtained:
• Example 3 The procedure of Example 3 is repeated, using a soak of sodium sulfhydrate and sodium tetrasulfide, with the exception that varying quantities of sodium thiophospbate, prepared in the manner set forth in Example 4, are added to the lime solution. Evaluation of unhairing is made after 24 hours. Using this procedure, the following results are obtained:
• sodium thiophosphate like phosphorus pentasulfide, is effective in increasing the unhairing efficiency of a lime slurry or solution. It is further seen that the sodium thiophosphate may be used by itself, or in conjunction with an alkaline material such as sodium sulfhydrate in effecting the unhairing. In this regard, it is to be noted in Example 6 that where the amount of sodium sulfhydrate used in conjunction with the sodium thiophosphate is too great, some hair damage does result. The above examples further illustrate that the sodium thiophosphate may be used for unhairing after either a conventional water soak or the preferred soak of an aqueous solution containing sodium sulfhydrate and sodium tetrasulfide.
• Ammonium hydroxide 10 g. N a thiophosphate.
• Example 9 Hides to be unhaired are soaked in water overnight at 70 degrees Fahrenheit and then divided into samples of 500 grams each. Unhairing slurries are made containing 6 percent by weight of lime, based upon the weight of the hides to be unhaired, plus additional substituents in the amounts as indicated hereinbelow. The additional substituents may be added individually but it is often preferred to premix them, either with or without the lime, and add them as a dry mix or sometimes, even as a solution or slurry. The percentages given are based on the weight high concentration of caustic soda in the solution, resulting in the absorption of caustic soda by the hide. This indicates desirability of allowing some time to elapse after mixing the phosphorus pentasulfide and caustic soda with the lime slurry and before the hides are put into this slurry. This is further illustrated by the following example.
• Example 10 In this experiment, the hides are soaked in water according to the procedure used in the preceding example. To the unhairing slurry, containing 6 percent by weight of lime, based on the weight of the hides to be unhaired and 2 percent by weight of phosphorus pentasulfide, based on the weight of the hides, are added varying amounts of caustic soda, as indicated hereinbelow. A series of runs was made wherein different times elapsed between the addition of the phosphorus pentasulfide and caustic soda to the slurry and the addition of the hides to the slurry. After 24 hours, the amount of unhairing on the hides was noted and, additionally, the amount of swelling of the hide was evaluated.
• the amount of swelling which takes place is rated on a scale of from 0 to 2, using the amount of swelling occurring when sodium sulfhydrate is used in the unhairing solution as a standard.
• 0 is comparable to sodium sulfhydrate;
• (l) is slightly more swollen than sodium sulfhydrate;
• (2) is considerably more swollen than sodium sulfhydrate.
• Example 11 Materials Mole ratio Sample NaO HI Unhairing P185, NaOH, NsSH, P155 percent g. percent Good.
• Example 12 the hides are soaked overnight in a soak solution containing 2 percent by weight of sodium sulfhydrate and 0.25 percent by weight sodium tetrasulfide, the weights being based on the weight of stock soaked.
• the weight ratio of the soaking solution to the hides being soaked is 4:1 and the temperature of the soaking solution during the soaking period is room temperature, 70 degrees Fahrenheit.
• T the hides are placed in a lime slurry containing 6 percent by weight of lime, based on the Weight of the stock, as well as varying amounts of phosphorus pentasulfide and caustic soda, as indicated hereinbelow, proportions given being based on the weights of the hides.
• sodium pentasulfide-caustic soda containing system shows better unhairing at the end of 24 hours than does the sulfhydrate control. In no instances in these runs was there any evidence of hair damage nor was there any excessive swelling of the hide.
• the phosphorus sulfide compound used in the unhairing solution is a phosphorus polysulfide approximating the formula P 8
• 4000 grams of cattle hides were soaked in a soaking solution containing 2% by weight of sodium sulfhydrate and 0 .25
• Example 14 This example is carried out in order to evaluate the present invention on a commercial scale. In this run, 20 sides of green salted cattle hides, weighing 500 pounds, were placed in a paddle with water at degrees Fahrenheit. The sides were floated for onehalf hour, paddled for 5 minutes and then allowed to rest for an additional hour. At the end of this period, the stock was pulled and fleshed.
• the paddle was then drained, refilled with water at degrees Fahrenheit and to this water was added 2 percent sodium sulfhydrate (based on the stock weight) and 0.25 percent sodium tetrasulfide (based on the stock weight). These percentages are of the commercial products containing 74 percent sodium sulfhydrate and 70 percent sodiunitetrasulfide, respectively.
• the pH of this soak solution was 8.6 and the temperature was 72 degrees Fahrenheit.
• the fleshed sides were then placed in the solution, paddled for 10 minutes, rested for one-half hour and then paddled for an additional 10 minutes. The stock remained in this solution for 24 hours. At the end of this time, the paddle was drained and the stock was refloated with water at degrees Fahrenheit, paddled for 5 minutes, drained, and then floated again with water at 80 degrees Fahrenheit.
• the hides were then unhaired on a standard unhairing machine without any adjustment of the machine from the regular production stock runs.
• the unhairing was substantially complete and was equivalent to that obtained from the regular process in the tannery wherein a normal 2 day process in the lime was used.
• the stock was lime split and was placed in a regular production pack for bate, pickle and tan operation. All of the sides were made into a vegetable ret-an shoe upper leather of a relatively soft type. The leather was evaluated and found comparable to regular production leather in all respects. The sides were smooth, mellow, free of draw and well let-out in the neck, flanks and belly.
• a method for unhairing animal hides and/or skins which comprises contacting the hides and/or skins to be unhaired with an aqueous solution containing an unhairing amount of inorganic phospho-sulphur compound containing at least one P-S bond which compound is hydrolyzable in the solution to form sulfhydrate ions and maintaining the hides and/or skins in this solution for a sufi'icient period of time to effect substantially complete loosening of the hair thereon.
• a method for unhairing animal hides and/or skins which comprises contacting the hides and/or skins to be unhaired with an aqueous suspension of lime containing an unhairing amount of an inorganic phospho-sulp-hur compound containing at least one P-S bond, which com pound is hydrolyzable in the solution to form sulfhydrate ions and maintaining the hides and/ or skins in this solution for a sufiicient period of time to effect substantially complete loosening of the hair thereon.
• the inorganic phospho-sulphur compound containing at least one P-S bond is a compound selected from the group consisting of phosphorus pentasulfide, polymeric phosphorus sulfides and alkali metal thiophosphates.
• a method for unhairing animal hides and/or skins which comprises contacting the hides and/or skins to be unhaired with an aqueous suspension of lime containing an unhairing amount of an inorganic phospho-sulphur compound containing at least one P-S bond which compound is hydrolyzable in the solution to form sulfhydrate ions and a material which is hydrolyzed in the solution to provide a source of alkalinity, the amount of said latter material being suflicient to maintain the pH of the solution substantially constant, and maintaining the hides and/ or skins in the solution for a sufficient period of time to efiect substantially complete loosening of the hair thereon.
• the inorganic phospho-sulphur compound containing at least one P-S bond is a compound selected from the group consisting of phosphorus pentasulfide, polymeric phosphorus sulfides, and alkali metal thiophosphates and the alkalinity supplying material is an alkali metal hydroxide.
• a method for unhairing animal hides and/or skins which comprises soaking the hides and/or skins to be unhaired in an aqueous solution containing an alkali metal sult'hydrate in an amount within the range of about 0 to about 2 percent by Weight of the hides and/ or skins, and an alkali metal tetrasulfide in an amount within the range of about 0 to about 2 percent by weight of the hides and/or skins, contacting the hides and/or skins after soaking with an aqueous suspension of lime containing an unhairing amount of an inorganic phosphosulphur compound containing at least one P-S bond which is hydrolyzable in the solution to form sulfhydrate ions and maintaining the hides and/or skins in this solution for a suflicient period of time to eifect substantially com-plete loosening of the hair thereon.
• the inorganic phospho-sulphur compound containing at least one P-S bond is a compound selected from the group consisting of phosphorus pentasulfide, polymeric phosphorus sulfides, and alkali metal thiophosphates, and the material providing a source of alkalinity is an alkali metal hydroxide.

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Citations (8)

• 1962
  • 1962-11-30 US US241132A patent/US3365265A/en not_active Expired - Lifetime
• 1963
  • 1963-10-31 GB GB43059/63A patent/GB1065726A/en not_active Expired
  • 1963-11-14 FR FR953705A patent/FR1410983A/fr not_active Expired
  • 1963-11-29 NL NL301172A patent/NL301172A/nl unknown

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