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

• the present invention relates to a new process for removing the keratin-containing parts of animal hides and pelts and the keratin-containing parts adhering to such hides and pelts, for example hairs or scales.
• chlorine is formed as a by-product.
• the chlorine fulfills two functions which are of importance in the production of leather, namely, on the one hand, chlorination of the natural fat and, on the other hand, chlorination of the collagen.
• the fixation of the chlorine onto the collagen considerably strengthens the structure of the leather and thereby suppresses the formation of loose grain in the upper layer of the leather, which occurs often when unhairing is effected according to the usual methods with lime and sulfide.
• the hair and keratin-containing parts of hides and pelts loosen and separate from the hides and pelts after a sufiiciently long time of action of the chlorine dioxide.
• the unhairing process is usually carried out in the presence of water and can be effected by introducing into an aqueous bath either chlorine dioxide gas or substances which, in an aqueous, preferably acid, medium, give off chlorine dioxide.
• alkali metal chlorites preferably sodium or potassium chlorite, are especially suitable.
• the alkali metal chlorites are preferably used in an aqueous acid solution at temperatures of up to about 45 C. and at. pH-values up to 7, preferably up to 6.
• the present invention is based on the discovery that it is not necessary to convert the total keratin sulfur into the sulfonic acid form, but that even the conversion of a considerably smaller portion, about half, of the sulfur of the keratin to sulfonic acid is suflicient for dissolving the hair or other keratin-containing parts in water if the afore said treatment is followed by a treatment with an inorganic or organic base at pH-values above 7.5, preferably above 8.5.
• This new method permits the removal of the keratin-containing parts such as epidermis, hairs or scales from the hides in substantially shorter periods of time, in general after about 28 hours and in most cases within 3-5 hours.
• this new method also permits a considerable reduction in the necessary amount of chlorine dioxide so that only 0.3-1 kg. of chlorine dioxide per kg. of keratin-containing substance are required.
• the present invention particularly relates to a process for removing keratin-containing parts of animal hides and pelts and keratin-containing parts adhering to such hides and pelts by first exposing the hides and pelts to the oxidizing action of chlorine dioxide in the presence of Water, the time of chlorine dioxide exposure and the quantity of chlorine dioxide used being considerably smaller than in the prior art process described in US. Patent 3,294,479, and then exposing the hides and pelts so treated to inorganic or organic bases.
• the chemical and physical structure of the keratin-containing parts of the hides and pelts are modified so that the keratin-containing parts, especially the hair, become gelatinous and soft.
• the fraction of keratin which at this stage has passed into solution is still very small and the lead acetate reaction is clearly positive because of the sulfhydryl groups still contained in the undissolved keratin parts.
• the keratin-containing parts such as epidermis and hair loosen and separate from the hides and pelts only during a subsequent treatment with inorganic or organic bases, and then dissolve in the alkaline bath employed.
• chlorine dioxide in gaseous form suitably with exclusion of oxygen in order to reduce the risk of an explosion and preferably in admixture with an inert gas such as carbon dioxide or nitrogen, can be allowed to act on the wet hides and pelts.
• an inert gas such as carbon dioxide or nitrogen
• chlorine dioxide is applied to the hides and pelts from an aqueous bath.
• chlorine dioxide gas may be introduced into an aqueous medium which contains the hides and pelts to be treated.
• the chlorine dioxide gas can be produced in a suitable apparatus in an easy and simple manner, for example by unsrmtvun BIU'UIIE acidification of an alkali metal chlorite solution, or by reduction of chlorous acid or of the salts thereof with suitable reducing agents such as nitrous acid or oxalic acid, or by the action of concentrated sulfuric acid on alkali metal chlorates.
• suitable reducing agents such as nitrous acid or oxalic acid
• suitable reducing agents such as nitrous acid or oxalic acid
• concentrated sulfuric acid on alkali metal chlorates for example by unsrmtvun BIU'UIIE acidification of an alkali metal chlorite solution, or by reduction of chlorous acid or of the salts thereof with suitable reducing agents such as nitrous acid or oxalic acid, or by the action of concentrated sulfuric acid on alkali metal chlorates.
• the production of chlorine dioxide from chlorous acid and oxalic acid is of particular advantage, because carbon dioxide is formed as an oxid
• the stream of chlorine dioxide gas is then intro quizzed, if desired together with an inert gas as a diluent, into the unhairing bath through a distributing line.
• the unhairing bath should not be alkaline and should have a pH-value below 7.0, generally a value up to 6.0.
• aqueous solutions of substances which give off chlorine dioxide instead of gaseous chlorine dioxide.
• substances which give off chlorine dioxide the water-soluble salts of chlorous acid, particularly the alkali metal chlorites, are especially suitable.
• sodium chlorite or potassium chlorite are usually used.
• aqueous solutions of these substances generate more chlorine dioxide the lower their pH-value is.
• an acid bath having a pH-value of up to about 6.5, preferably in. the range of pH 1.5 to 3.5, is generally used in order to secure con tinuous and not too violent generation of gas.
• any desired inorganic or organic acids which are intert toward chlorine dioxide may be used.
• inorganic acids such as sulfuric acid, hydrochloric acid, or phosphoric acid are preferably used.
• Organic acids such as formic acid, acetic acid, lactic acid, glycollic acid, ben'zene-sulfonic acid, or naphthalene-sulfonic acid may also be used.
• mixtures of different acids can be employed. If strong inorganic acids are used, the generation of chlorine dioxide can be slowed down by the addition of butter salts.
• acid salts such as primary sodium phosphate or primary sodium sulfate, or acid buffer mixtures, for example a mixture of a mineral acid and a salt such as sodium acetate, may be employed,
• the optimum quantity of liquor depends on the manner of carrying out the treatment.
• unhairing is carried out in a pit, relatively large quantities of water must usually be used since the material must be completely covered by the unhairing solution. In this case, the quantity of water depends considerably on the size and shape of the pit.
• oxidation is effected in a closed drum, which is the preferred method in practice, only a relatively small quantity of bath is required, viz about l00%, preferably 3070%, by the weight of the soaked hides and pelts.
• chlorine dioxide is allowed to act on hides and pelts for several hours, preferably at room temperature or even at lower temperatures or at slightly elevated temperatures, with or without movement of the hides and pelts.
• the temperature used influences the treatment time in the oxidation process. If very low temperatures, for example below 8 C., are used, the oxidation proceeds too slowly and economical operation is no longer possible.
• the use of too high temperatures, for example temperatures exceeding 50 C. involves the risk that the collagen of the hides will be damaged. For this reason, the use of temperatures above about 45 C. is to be excluded. In practice, temperatures in the range of from about 10 to 40 C. are generally used. In principle, however, unhairing with chlorine dioxide may also be effected at temperatures exceeding 50 C., provided that the collagen has been previously treated with tanning agents according to known methods and has thereby been made insensitive to heat.
• the time of exposure to chlorine dioxide required for effecting partial oxidation according to the unhairing process of the present invention depends in the first instance on the type of the hides and pelts to be treated, and, furthermore, on the concentration in which the chlorine dioxide is used in the aqueous bath. If the chlorine dioxide is used in a high concentration, oxidation proceeds faster than if the chlorine dioxide is used in diluted state.
• the oxidation treatment When the treatment is carried out under conditions which are preferably used in practice, for example at temperatures of about 2538 C., with a quantity of liquor of about 3070% (referred to the weight of the soaked hides and pelts), a chlorine dioxide amount of 0.33% (referred to the weight of the soaked hides and pelts), and an average rotation of the drum of about 5-12 revolutions per minute, the oxidation treatment will generally be concluded after about 2-8 hours, depending on the type of the hides and pelts to be unhaired.
• the oxidation conditions i.e., the temperature, quantity of water, quantity of chlorine dioxide, and number of revolutions of the drum will be so adjusted that the treatment is com plete within about 4 hours.
• the oxidation treatment can be terminated when the hairs and other keratin-containing substances to be removed can be easily and smoothly separated from the hides and pelts after a following relatively short treatment with mild alkaline agents.
• the oxidation treatment with chlorine dioxide should be discontinued before observing that the black coloration of the sulfhydryl reaction with lead acetate no longer appears.
• the oxidation treatment requires 2-8 hours. In most cases, a treatment for a period of about 35 hours is sutficient.
• any desired inorganic bases may be used, for example the alkali metal and alkaline earth metal hydroxides and soluble carbonates and bicarbonates such as calcium hydroxide, sodium hydroxide, or potassium hydroxide or, preferably, sodium carbonate or potassium carbonate, or the corresponding bicarbonates, ammonia, or organic bases such, for example as methylamine, ethylamine, mono-, dior triethanolamine, and similar primary, secondary, and tertiary alkylamine and hydroxyalkylamine bases can be employed.
• alkali metal and alkaline earth metal hydroxides and soluble carbonates and bicarbonates such as calcium hydroxide, sodium hydroxide, or potassium hydroxide or, preferably, sodium carbonate or potassium carbonate, or the corresponding bicarbonates, ammonia, or organic bases such, for example as methylamine, ethylamine, mono-, dior triethanolamine, and similar primary, secondary, and tertiary alkylamine and hydroxyalkylamine bases can be employed
• alkaline agents for the alkaline after-treatment, for example alkali metal sulfides or alkali metal hypochlorites.
• alkali metal sulfides or alkali metal hypochlorites for example alkali metal sulfides or alkali metal hypochlorites.
• the pH of the bath for the alkaline after-treatment is adjusted, after termination of the oxidation, to pH-values of at least 7.5, advantageously to values above 8.0, by the use of. inorganic or organic bases. If it is not intended to prevent the swelling of the hides which occurs in stronger alkaline media, there is no upper limit on the pH-value.
• the treatment with inorganic or organic bases is carried out in the alkaline range up to about pH 11. It is preferred to adjust the pH of the bath to pH- values in the range of between 8.5 and 9.5.
• a solution of inorganic or organic bases can be applied to the hides or pelts.
• the hides or pelts may also be treated with gaseous ammonia, or they may be introduced into a bath containing inorganic or organic bases.
• the period of time during which the hides and pelts are treated with organic or inorganic bases may be relatively short. Care must be taken, however, that the keratin-containing parts of the hides and pelts are completely soaked with the alkaline solution.
• the keratin-containing parts loosen and separate from the hides and pelts, or the keratin-containing parts such as hairs, scales and similar substances dissolve in the aqueous alkaline solution after only a short. period of time, about -20 minutes.
• waste water conditions are already substantially more favorable than are those in conventional unhairing process using lime-sulfide.
• the waste waters obtained after unhairing with chlorine dioxide are non-toxic and are innocuous to fish.
• the quantities of waste water in such a process are considerably smaller than are those in the unhairing process with lime and sulfide.
• This is best achieved in a very eflicient manner by combination of the acid waste waters from pickling, tanning, dyeing, and greasing with the alkaline unhairing solution obtained in the proo ess of the present invention.
• the dissolved keratin sulfate, in its precipitated acid form has a distinct cationic character and a spongy structure with anion-exchanging properties. Thus, it can absorb all anionic chemicals and thereby remove them from the waste water.
• the bleaching effect produced by chlorine dioxide on the phenolic melanine color pigments of hairs and roots of hairs is greater with full oxidation of keratin-sulfur than with partial oxidation as in the method of the present invention.
• the phenolic melanines turn dark in an alkaline solution.
• it is suitable to add a small amount of chlorine dioxide, or of a salt which yields chlorine dioxide, to the pickling bath which is usually used prior to chrome tanning, and to drum the hides further for about one hour in the tanning drum.
• Such baths in general comprise an acid in an amount of about 0.52%, common salt (NaCl) in an amount of about 5-15 and water in an amount of about 30-200% (by weight of the soaked hides or pelts).
• common salt NaCl
• water in an amount of about 30-200% (by weight of the soaked hides or pelts).
• an amount of about 0.10.4% (by weight of the soaked hides and pelts), or the corresponding quantity of a salt yielding chlorine dioxide is generally sufi'icient.
• This small amount of chlorine dioxide is very rapidly consumed and restores the light color of the hides.
• this after-treatment with small amounts of chlorine dioxide or of substances which yield chlorine dioxide may also be carried out in an operation separate from pickling.
• chrome tanning can be carried out as usual, for example by adding a basic chromium sulfate in an amount of about 2-6% by weight, calculated as Cr O to the pickling bath. The tanning operation can then be completed as usual.
• the process of the present invention permits, for the first time, the production by a simple method of a completely tanned leather from a salted green hide in only about 10-15 hours.
• all these operations can be performed during this time in the same drum, without it being necessary to transfer the hides to another container.
• it is only necessary to change the bath twice. All chemicals and additives can be added in liquid form during the rotation of the drum.
• the aqueous baths which are to be removed between the individual operations can be drained through a slide valve which can be controlled electronically. This permits automation of the total process with the aid of a program control.
• EXAMPLE 1 4 black and white bovine hides of North American origin, having a weight. of 102 kg. in salted state, were soaked, dehaired and tanned in a drum within 14 hours in the following 3 process steps:
• EXAMPLE 2 3 air-dried snake hides having a dry weight of 752 g. were soaked in a standing drum for 24 hours with 7.5 liters of water with addition of g. of soda as soaking accelerator until the hides were soaked uniformly and showed a supple touch.
• the hides were then drummed in a revolving drum with 3 l. of water while introducing 21 g. of chlorine dioxide gas through the hollow axle into the free space of the drum.
• the gaseous chlorine dioxide may be produced either from an aqueous 5% chlorine dioxide solution, obtained as an intermediate product in chlorite produc tion, by slow heating to 50 C. while simultaneously passing through a stream of carbon dioxide, or it may be proucked according to known methods by acidification of an alkali metal chlorite solution or reduction of an alkali metal chlorate solution with oxalic acid.
• Drumming of the hides was continued for 24 hours at 25 C.
• the design of the snake, which design consists of melanines, was thereby bleached to a large extent, so that it appeared below the undissolved keratin scales as a light brown residual pigmentation.
• the snake hides can be tanned according to known methods with chromium or alum tanning agents, dyed and dressed.
• EXAMPLE 3 3 sheep hide swere dehaired by means of a wet-shearing machine to a shearing depth of 3 mm.
• the wool so obtained can be sold as particularly fine sheared wool.
• the residual wool, which is fixed to the corium, and the keratin-containing epidermis were removed from the hides as follows.
• the hides were drummed for 5 hours with 5 l. of water, 50 g. of sulfuric acid, 500 g. of common salt (NaCl), and 230 g. of sodium chlorite.
• the temperature of the bath thereby rose from 20 to 37 C., and the pH-avlue was 2.5.
• the solution was free of chlorine di oxide and the residual hairs were gelatinized to a high degree.
• the sheep hides were well degreased and their otherwise normally spongy structure was considerably solidified.
• the greasy first unhairing bath from which the hairs can be flocked out by acidification, was drained.
• the hides were then subjected in the same drum to a 2-hour after-treatment with 30 g. of sodium chlorite in S l. of water, 25 g. of sulfuric acid, and 250 g. of common salt.
• the hides thus dehaired were pure white, completely de haired, and also showed an excellent hard grain.
• the fat content of the hides was reduced from originally 28-30% to 8.5-- 11%. This may be due to better emulsifiability of chlorinated fats.
• the hides can be tanned, oiled and dressed according to known methods.
• the good polishability of the grain side and flesh side of the hides in the wet state, which sheep hides which have been 'unhaired by the lime sulfide method do not show, is of particular advantage.
• EXAMPLE 4 A. bovine hide having a weight of about 20 kg. was introduced into a pit filled with 500% by the weight of the hide of water at 30 C. The bath was adjusted to a pH-value of 3.54.0, and gaseous chlorine dioxide was introduced through a distributing tube during a period of 4 to 6 hours. Taking into account the consumption of 50-60% of the chlorine dioxide by the keratin of the hair, the amount of chlorine dioxide introduced should not be more than 11 liters per hour in order not to exceed the solubility of chlorine dioxide in water which is about 5 g./l.
• the bleaching effect of the chlorine dioxide became apparent after a period of exposure of 3 hours. After 4-6 hours, the hairs were strongly damaged. At this stage, a small cutting of the treated hide was introduced into a solution of an alkali, preferably sodium carbonate, having a strength of 1%. The oxidized hairs must dissolve within 15 minutes, otherwise the treatment with chlorine dioxide is continued for 12 hours and the test is then repeated. When the test was positive, introduction of chlorine dioxide was discontinued and the bath. was adjusted to a pI-Lvalue of 7.5-8.5 by means of an alkali, preferably sodium carbonate. The hairs dissolved completely within 15-30 minutes. It is advantageous to move the hides slightly during this time.
• the hide After this treatment with the weak alkali solution, the hide had a light yellow to brown color which is due to the phenolic groups of the pigments of the air.
• the hide For preparing dark or covered leather, the hide can be further treated in the usual manner.
• the bath For pre paring a pure white hide, for example as those required in the manufacture of light aniline leather, the bath is acidified again to pH 3.5-4 and the hide is exposed for 1 hour to the action of chlorine dioxide. A pure white and well degreased hide is then obtained, the fat wrinkles of which are suppressed to a large extent.
• EXAMPLE 5 A calf hide soaked in an acid soak and having a weight in soaked state of about 8 kg. was hung up in wet state in a chamber which can be closed in air-tight manner and which is provided with a gas inlet and outlet tube. After closing the chamber, the air contained in it was displaced by nitrogen. A uniform stream of a gas mixture, consisting of 1 part by volume of chlorine dioxide and 1 part by volume of nitrogen, was passed through for 4 hours at 20 C. The quantity of chlorine dioxide should not exceed 6 liters per hour. The chlorine dioxide was produced from an acidified sodium chlorite solution and was passed over with the aid of nitrogen serving as inert gas. After 4 hours, the hair was very strongly bleached and strongly damaged.
• a small cutting of the hide was introduced into a sodium bicarbonate solution having a strength of 2%.
• the hair must dissolve completely within minutes, otherwise the treatment with chlorine dioxide is continued for another hour.
• the gas mixture in the chamber was replaced by nitrogen; the hide was then treated at C. in a drum with 100% by the weight of the hide in soaked state of a bath which had been adjusted to pH 7.5-8.5 by means of sodium bicarbonate.
• the hairs dissolved completely within 10-20 minutes.
• the hide thus treated with alkali had a slightly yellow color which was due to the hair pigments.
• the hide can then be further treated by the usual methods, for example, pickling, tanning, etc. either in the unhairing bath or in a fresh bath.
• the hide For preparing a pure white hide, for example, as that required in the manufacture of aniline leather, the hide can subsequently be treated with a pickling bath with the addition of 0.5-1% of sodium chlorite. It is also possible to introduce the hide into the chamber described above and to bleach it therein for about /2 to 1 hour, after displacement of the air by nitrogen, by the action of about 6 liters of gaseous chlorine dioxide. A pure white hide is then obtained which can be used for the manufacture of very light colored aniline leather.
• a method for removing the keratin-containing parts of animal hides and pelts and the keratin-containing parts adhering to such hides and pelts comprises contacting said hides and pelts with chlorine dioxide in an aqueous bath at a pH of up to 6 for 2 to 8 hours until said keratin-containing parts have jellified and softened, and then treating said hides and pelts with an alkaline bath having a pH-value of at least 7.5 until said keratincontaining parts are loosened and removed.
• a method for removing the keratin-containing parts of animal hides and pelts and the keratin-containing parts adhering to such hides and pelts which method comprises contacting water-soaked hides and pelts in the absence of a bath with gaseous chlorine dioxide for 2 to 8 hours until said keratin-containing parts have jellified and softened and then treating said hides and pelts with an alkaline bath having a pH-value of at least 7.0 until said keratin-containing parts are loosened and removed.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Treatment And Processing Of Natural Fur Or Leather (AREA)
• Cosmetics (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

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Family Applications (1)

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Cited By (1)

Citations (2)

• 1966
  • 1966-10-05 FI FI2619/66A patent/FI41188B/fi active
  • 1966-10-20 NL NL6614786A patent/NL6614786A/xx unknown
  • 1966-10-26 NO NO165348A patent/NO116210B/no unknown
  • 1966-12-22 DK DK664766AA patent/DK121314B/da unknown
• 1967
  • 1967-02-17 US US616798A patent/US3508857A/en not_active Expired - Lifetime
  • 1967-02-23 ES ES337190A patent/ES337190A2/es not_active Expired
  • 1967-02-24 SE SE2546/67A patent/SE306985B/xx unknown
  • 1967-02-27 BE BE694686D patent/BE694686A/xx unknown
  • 1967-02-27 GB GB9194/67A patent/GB1170801A/en not_active Expired

Patent Citations (2)

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