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
  • C14C3/00—Tanning; Compositions for tanning
  • C14C3/02—Chemical tanning
  • C14C3/04—Mineral tanning
  • C14C3/06—Mineral tanning using chromium compounds
• • 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
  • C14C3/00—Tanning; Compositions for tanning
  • C14C3/02—Chemical tanning
  • C14C3/08—Chemical tanning by organic agents
  • C14C3/10—Vegetable tanning
• • 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
  • C14C3/00—Tanning; Compositions for tanning
  • C14C3/02—Chemical tanning
  • C14C3/30—Chemical tanning using physical means combined with chemical means

Definitions

• the present invention relates to a method of tanning animal skins.
• animal skin includes hides and skins of animal origin, for example of cattle, goats, sheep, buffaloes etc.
• the conventional production of ready-made leathers or skins is divided into processing steps that take place in the so-called water workshop, and in the subsequent finishing of the leather or fur.
• the water workshop in turn is divided into the areas of soft, hair removal (liming), skin digestion, first wash, descale, pickling, second wash, pimples and finally the tanning.
• the raw material is freed from dirt and preserving salt and gets back to its original water content.
• the switch is performed at a pH between 7 and 9.
• water-soluble proteins are dissolved out.
• the existing proteins are hydrolyzed, d. H. made water soluble, and washed out.
• the polypeptide chains of the dermis are attacked and broken up by the strongly reducing lime and sulfur compounds, which are also known as liming. This leads to a greater mobility of the fibers, which gives the leather increased elasticity and softness.
• This process is also referred to as skin digestion. During the entire liming process, the skin swells due to strong anionic charge and the associated repulsion of the same charged groups.
• the skin is split. Fleshing and splitting is done in a combination of manual labor and machine work for each piece of skin individually.
• the rawhide is called nakedness.
• the pelt has a water content of about 60 to about 80%.
• the dry matter is about 98% collagen.
• the last remnants of superficial skin protein are removed.
• the swelling caused by the strong alkalinity in the liming season must be removed before tanning, so that the tannins can penetrate into the fibrillar interstices of the skin fiber structure.
• weak organic acids eg. As aliphatic or aromatic dicarboxylic acids such as sulfophthalic acid, or by adding weakly acidic inorganic salts, eg. For example, ammonium sulfate, ammonium chloride or polyphosphates.
• Descaling removes the calcium hydroxide in the skin.
• the skin can be further digested by fermentation.
• Descaling and pickling are carried out in a slightly heated liquor, i. H. at about 30 to 35 ° C, performed.
• the duration of the pickling and pickling process is about 8 to 24 hours at a pH of 2.5.
• the skin obtained after pickling and pimpling, which is soaked with aqueous solution, is called Pickelblösse.
• the ratio between the mass of tanning solution and the mass of the pimpling skin to be tanned is between 8: 1 and 1: 1, with an excess of tanning solution typically being used.
• the tanning process is often done in rolling barrels and then called tanning.
• As salt formic acid, sulfuric acid, sodium bicarbonate and other additives used.
• the bondable groups of the collagens crosslink with the tannins.
• the pH is raised to values between 3.6 and 4 by addition of alkali.
• the excess, ie not absorbed by the leather or fur to be tanned soot solution represents wastewater, which must be disposed of.
• Tanning alone accounts for 160 to 200 million tonnes of wastewater worldwide. If this wastewater is not purified by suitable processes, it causes great environmental pollution.
• the purification of the waste water produced during the tanning usually takes place in several stages, wherein first of all a solids separation, for example by means of decanters and then a biological clarification can take place. In any case, wastewater treatment is time-consuming and expensive and is often not carried out, especially in third world and emerging market countries. Instead, the wastewater is unpurified initiated into rivers or lakes and leads there to severe environmental damage.
• the tanning liquid adhered to and in the hides is removed from the hides by mechanical methods (so-called wilting).
• the hides present after the wilting are called "wet-blue" in the chrome tanning, in the tanning by vegetable tanning agents as “wet-brown” and in the aluminum tanning as “wet-white”.
• the acid originating from the tanning is neutralized and then the leather is put together to form dyeing parties. It follows, depending on the leather type, a filling and coloring with z. B. water-soluble dyes. By a subsequent addition of fats finally required for the finished leather softness is achieved. Finally, the leather is dried, for example by vacuum drying or hanging drying.
• the DE 30 27 637 A1 describes a tanning process in which tanning is carried out with a greatly reduced amount of liquid.
• the wet skins are contacted with dry chromium powder for tanning.
• the resulting chrome tanning results in the result of the conventionally performed chrome tanning.
• the tanning time is 6 hours, whereby the tanned hides must rest for at least 48 hours before the subsequent dressing.
• the inventors of the present application have leather according to the in DE 30 27 637 A1 treated doctrine.
• the leather obtained was of poor and by no means marketable quality.
• the resulting leather apparently due to the small amount of highly concentrated tanning solution, was tanned only superficially, a process of tanning in the tanning industry. referred to as.
• the skin layer of the leather detached which is known under the term "Losnarbmaschine".
• the DE 10 2006 008 190 A1 describes a process for the fatliquoring of leather, in which an oil, fat or polymer is first applied to the animal skin to be treated, for example by spraying, and then the skin is treated in a compressed gas in order to apply the applied oil, fat, etc. well distribute and remove excess oil, grease etc.
• the U.S. Patent 5,512,058 describes a similar process.
• a tanning of pickled and pickled animal skins with aqueous chromate solution in the presence of a compressed gas (preferably carbon dioxide) in a reactor under certain pressure and temperature conditions is known.
• the stained and pickled animal skins are fed directly to the tanning without an intermediate step.
• the present invention provides the novel tanning process specified in claim 1, which is characterized in that the animal skin to be treated is first pickled and pickled in aqueous solution, then the liquid content of the animal skin is reduced, whereupon at least one Part of the previously removed from the animal skin amount of liquid is replaced by a Gerbweed containing the absorbed by the animal skin tanning agent in an amount corresponding to a maximum of 80%, and finally containing the gerbösung animal skin in a pressure vessel with compressed gas for a period of at least 15 minutes.
• the liquor ratio which is defined as the mass of the tanning solution divided by the mass of the animal skins to be tanned and soaked with the aqueous solution, has a value of less than 1.
• treating generally refers to contacting the animal skin containing the tanning solution meant the compressed gas.
• the amount of tanning agent to be absorbed by the animal skin is determined by the desired percentage of tanning agent which the tanned ready-to-use animal skin is to contain in order to obtain the desired leather quality, verifiable by the shrinkage temperature of the finished treated leather.
• the method according to the invention preferably as much liquid is added in the tanning step as that which has previously been removed from the animal skin to be treated in the liquid content reduction step. In this way it is ensured that the total amount of liquid added from the animal skin to be treated can be included. There is therefore no excess of (tanning) solution in the pressure vessel.
• the method according to the invention surprisingly results in leathers and skins meeting the highest requirements, ie the resulting leathers or skins are excellently deep-tanned despite minimal or no wastewater attack.
• Another advantage is with the Process according to the invention a significantly reduced compared to conventional methods treatment time.
• the hides obtained after the pickling and pickling steps usually contain about 70 to 75% by weight of liquid, based on their total weight (dry skin plus liquid).
• the liquid content of the animal skin is reduced by 5% to 90%, preferably by 20% to 70% and particularly preferably by 30% to 50%.
• the soaked animal skin is deprived of about half of the liquid contained in it.
• the reduction of the liquid content of the animal skin can be done in any suitable manner. Thermal, adsorptive or mechanical methods as well as any combination of these methods may be used.
• a mechanical crimping method is used, by means of which the desired amount of liquid is pressed out of the animal skin.
• the liquor ratio should not be greater than 2, more preferably it has a value less than 1, d. H. a mass of tanning solution is added which corresponds at most to the amount of liquid removed and which is always smaller than the mass of the skin of the animal soaked with aqueous solution from the pickling and pickling step.
• the liquor ratio in such a case assumes values of 0.05 to 0.9, more preferably the value of the liquor ratio is in the range of 0.1 to 0.7, and more preferably in the range of 0.3 to 0.6.
• the tanning solution can be added, for example by spraying, but also by immersing the animal skin in an appropriate amount of Gerb diseases.
• the added tanning solution may contain vegetable and / or synthetic tanning agents.
• the tanning solution contains tannins containing metal cations, for example chromium or aluminum salts.
• the tanning solution may contain additives which impart certain desired properties to the animal skin to be treated.
• additives may include dyes, adhesives, moisture control formulations, flame retardants, microparticles, nanoparticles, emulsifiers, emulsions, water repellents, lipophilicating agents, Brightening agents, fats, tears or oils and a suitable combination of such substances.
• the tannin content in the added tanning solution is preferably such that it corresponds approximately to the tannin content which the animal skin to be treated is to absorb in order to achieve a good leather quality.
• a tannery content of 4% by weight based on the ready-to-use leather, is aimed at in this respect.
• Leathers with such a tannin content have shrinkage temperatures of about 95 degrees Celsius. If one takes certain reductions in the shrinkage temperature into account, i. If one is satisfied with lower shrinkage temperatures, tannin contents of 3% by weight can also lead to passable leather qualities. Sometimes a certain excess of tannin may be beneficial. Thus, the excess tannin content may be up to about 80%, but more preferably at most 20%.
• the excess of tannin is considerably lower than that used in the classical procedure. Accordingly, in the process according to the invention, the tanning agent contained in the tanning solution (liquor) passes almost completely into the treated animal skin. This ensures, on the one hand, that the animal skin to be treated receives the amount of tanning agent required for complete tanning and, on the other hand, it avoids having to treat significant amounts of unused tanning agent.
• the period during which the animal skin containing the tanning solution is treated with compressed gas under pressure in a pressure vessel is preferably 30 minutes to 30 hours and more preferably 1 to 3 hours.
• the pressure in the pressure treatment step may be in the range of 10 bar to 200 bar, but is preferably in the range of 15 bar to 100 bar and more preferably in the range of 20 bar to 60 bar.
• the temperature in the pressure treatment step may be in the range of 0 ° C to 80 ° C, but is preferably in the range of 10 ° C to 60 ° C, and more preferably in the range of 25 ° C to 40 ° C.
• Particularly suitable compressed gas are carbon dioxide and nitrogen and mixtures thereof.
• the animal skins are preferably moved to achieve uniform tanning.
• the treated animal skins may be removed from the pressure vessel and dressed in a conventional manner.
• the liquid contained in the pressure-treated animal hides can be separated mechanically or thermally. If the separated liquid is recovered, which is easily possible, for example, during the thermal separation and drying, it can be returned to the process, so that the tanning step is completely free of wastewater.
• the pickling and pickling step is carried out in a pressure vessel in the presence of a compressed gas
• the gas is preferably carbon dioxide, but z. B. can also be nitrogen or a mixture of CO 2 and N 2 .
• dissolved carbon dioxide in the liquid phase causes an increase in the pH to about 3.3, so that the otherwise usual buffering of the pH by added alkalis is unnecessary. In this way, the inventive method can achieve a further saving of chemicals.
• the degree of dissolving in the liquid phase carbon dioxide can be adjusted by the pressure in the pressure vessel, which dissolves more carbon dioxide at higher pressure.
• tanning chemicals into the animal skin which is required for tanning the quality.
• the tanning process is shortened to a few hours and a deep tanning is achieved at liquor ratios that are far below the values technically previously considered feasible.
• commonly used chemicals to adjust the pH may be partially or completely be replaced by carbon dioxide and / or nitrogen, whereby the environmental impact is significantly reduced.
• a rawhide (bovine pimples) weighing 1,000 g has been mechanically decoked.
• the skin weight after this procedure was 600 g.
• the skin was brought into contact with 400 g of tanning solution.
• the skin has taken up the 400 g solution after about one hour.
• the skin was treated in an autoclave at 30 bar and 40 ° C with carbon dioxide for 2 hours.
• the tanning solution consisted of 310g of water, 65g of chromium sulphate and 25g of salt.
• the calculation of the minimum chromium sulfate to be used is listed as an example.
• the pH has been adjusted to 3.6 by means of sodium carbonate.
• the following example shows the calculation of the necessary amount of tanning chemicals with an overdose of 80%.
• the skin content in wet blue is on average 35 wt .-%.
• Example 1 The procedure and setting of all the parameters of Example 1 have also been used for Example 2 (withering from 1,000 g to 600 g with subsequent tanning dipping and taking in 400 g). Only the adjustment of the pH of the tanning solution by means of alkalis was dispensed with. After a one-hour dipping of the skin at pH 2.5 and subsequent treatment of the drained skin with compressed carbon dioxide at 30 bar, 40 ° C for 2 hours, a chromium content of> 4% Cr 2 O 3 was achieved. The shrinkage temperature was T s > 95 ° C with very good tensile strength of 40 N / mm 2 .
• a cowhide weighing 1.5 kg has been prepared according to the tanning method described in Example 1. Weakened and then added to tanning solution 600 g. The process was carried out similarly to that in Example 1, with the difference that in the autoclave, a pressure of 20 bar has been set. Both the shrinkage temperature (T s ⁇ 90 ° C) and the tensile strength (14 N / mm 2 ) have shown that the leather has not been tanned.
• a bovine skin with a wet weight of 1.2 kg was wilted (480 g) and dipped by the method described in Example 1. The skin was then moved pressure-free for 2.5 h and rested for more than 24 h after the experiment. This skin was not tanned. Optically and haptically, a horn-like drying of the untreated skin collagen could be determined after finishing.
• Example 2 The procedure, parameters and mass ratios chosen in Example 2 have been used.
• the wet weight of the skin was 3.5 kg. Wounded and absorbed were 1,400 g.
• the leather also has a shrinkage temperature of T s > 90 ° C and the optical and haptic analysis of the dressed leather has shown high leather quality.
• Example 1 The parameters used in Example 1 were used (pimpling size of 1,000 g, after withering to 600 g, followed by absorption of 400 g of tanning solution, 30 bar and 40 ° C for 2 hours). Instead of taking carbon dioxide, it has been tanned under a nitrogen atmosphere. Haptic and optical control gave good leather quality. The shrinkage test confirmed this (TS> 90 ° C).
• a tanning with vegetable tannin has been done for beef and goat skin. Each 1 kg of skin was used. It has not withered away but has been tanned with liquor. Based on the weight of the skin, 2.5% by weight of Picaltal dandruff (as a salt substitute), 15% of vegetable tanning agent (Tara) and 500% of water have been added. The pH has been raised to 4.0. The process parameters have been set to 200 bar, 40 ° C and 10 revolutions per minute. After a process time of 4 h, a high leather quality was achieved. The leathers have been tested by shrinkage temperature (T Svegetabil > 70 ° C), optical and haptic analysis.
• a rawhide (bovine pimples) with a weight of 1000g has been mechanically wilted off. The weight after this process was 600g. Then it is the skin has been contacted with 400g of tanning solution. In this tanning solution so much chromium sulfate was dissolved that a quantity of 10.06 g chromium III ions was present. This corresponds to 1.05 times the target value of 4% chromium oxide in the leather, which was chosen as a guideline for achieving a good leather quality. After the skin had taken up the tanning solution, it was treated with carbon dioxide in an autoclave for 3 hours at 60 bar and 40 ° C.
• the insert basket in which the piece of skin was located, rotated at a speed of 10 revolutions per minute. Immediately after releasing the pressure and opening the autoclave, a shrinkage temperature of 99 ° C was measured. The contact of the tanned cowhide with boiling water left the latter completely clear, which is an indication that neither chromium nor proteins are boiled out of the skin.
• Example 1 The remaining piece of skin was then trimmed.
• the shrinkage temperature of the dressed piece increased to 100 ° C. Also in this test, no discoloration of the boiling water was observed.
• the other quality parameters were comparable to Example 1 and showed a very high quality of tanned leather.

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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)
• Coloring (AREA)

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• 2009
  • 2009-04-21 DE DE102009018232A patent/DE102009018232B8/de not_active Expired - Fee Related
• 2010
  • 2010-04-21 US US13/380,803 patent/US9206486B2/en active Active
  • 2010-04-21 CN CN201080017504.4A patent/CN102405297B/zh active Active
  • 2010-04-21 DK DK10715707.5T patent/DK2421995T3/da active
  • 2010-04-21 WO PCT/EP2010/002452 patent/WO2010121804A1/de not_active Ceased
  • 2010-04-21 ES ES10715707T patent/ES2400075T3/es active Active
  • 2010-04-21 EP EP10715707A patent/EP2421995B1/de active Active

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