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
  • C14C1/08—Deliming; Bating; Pickling; Degreasing

Definitions

• the invention relates to a process for deliming skins, in which cyclic carbonates of polyhydric aliphatic alcohols are used as "safety deliming agents". This avoids the disadvantages associated with overdosing of the known decalcifying agents.
• Ashes of the skins for the purpose of depilation and skin disruption in the context of leather production are carried out in an alkaline medium, usually with the help of inorganic or organic sulfides.
• Lime is usually used as the alkaline agent, usually alone, but occasionally also in a mixture with caustic soda or soda. Then the material must be freed from the liming chemicals, especially the lime, in preparation for further processing, that is, "descaled". This is usually done with acids or acidic salts, for example phthalic acid, sulfophthalic acid, formic acid, acetic acid, boric acid, aliphatic dicarboxylic acid mixtures, hydrochloric acid, sulfuric acid and their ammonium salts.
• acids or acidic salts for example phthalic acid, sulfophthalic acid, formic acid, acetic acid, boric acid, aliphatic dicarboxylic acid mixtures, hydrochloric acid, sulfuric acid and their ammonium salts.
• the amount of chemicals required for descaling depends heavily on the skins' content of lime and other basic compounds, e.g. Sodium sulfide and sodium hydroxide. Since this always fluctuates, exact dosing of the decalcifying chemicals is hardly possible in practice. It is therefore easy to overdose. As a result, the pH value drops to or even below the isoelectric point of the protein (pH approx. 5) at the start of decalcification. In the process of liming, protein substances that have gone into solution are precipitated, possibly together with other dissolved "dirt". They deposit on the surface of the skin material in a form that is difficult to remove, make it unsightly and interfere with later processing steps, especially when dyeing. The grip is also adversely affected.
• ammonium salts as so-called "safety decalcifying agents".
• these agents since the pH of aqueous ammonium salt solutions can be below 5, these agents also do not offer the desired safety.
• the use of ammonium salts is also problematic from an ecological point of view. Ammonium salts are only partially broken down in sewage treatment plants and thus increase the COD value of the waste water.
• butyrolactone as a deliming agent is known from DE-PS 804 827.
• this internal ester hydrolyzes very slowly under the usual descaling conditions. The necessary descaling times are therefore very long. This is probably the reason why butyrolactone has not found its way into practice.
• hydrolyzing esters are used under the descaling conditions. They overcome the above-mentioned disadvantages of conventional decalcifying agents by not dropping the pH below 5 and also being free of ammonium salts. However, they too cannot prevent hydrogen sulfide from being released when they are overdosed. Due to the high toxicity of hydrogen sulfide, this possibility represents a permanent latent danger to life for the personnel, apart from the unpleasant smell.
• the invention was therefore based on the object of developing a deliming process which not only avoids the disadvantages of the usual deliming agents mentioned above, but also the development of hydrogen sulfide with certainty.
• cyclic carbonates of polyhydric aliphatic alcohols preference is given to those whose equivalent weight (with respect to the carbonic acid component, not the alcohol component) is below 150, preferably below 100 and in particular below 60.
• Suitable carbonates are Correspondingly, the carbonic diesters of polyhydric, that is to say more than one, preferably 2 to 3, in particular 2 hydroxyl groups, aliphatic alcohols having 2 to 6, preferably 2 to 3, carbon atoms, which optionally contain free hydroxyl groups, at least 2 hydroxyl groups to one another in 1, 3- or preferably the 1,2-position are arranged, for example the cyclic carbonates of 1,2-butanediol, 2,3-butanediol, neopentyl glycol, glycerol, the dicarbonate of pentaerythritol (spiro compound), preferably the cyclic carbonate of ethylene glycol and 1,2-propylene glycol.
• the carbonic diesters of polyhydric that is to say more than one, preferably 2 to 3, in particular 2 hydroxyl groups, aliphatic alcohols having 2 to 6, preferably 2 to 3, carbon atoms, which optionally contain free hydroxyl groups, at least 2 hydroxyl groups
• the carbonates are prepared in a known manner, e.g. by reacting the alcohols with phosgene or preferably epoxides with carbon dioxide.
• the carbonate is hydrolyzed by the limestone contained in the liming so far until a pH value in the range of - depending on the carbonate excess - 7.8 to 7.5 is reached.
• the lime is dissolved as calcium bicarbonate. Then the hydrolysis stops.
• the pH did not fall below 7.5 in any experiment. This range is optimal, because on the one hand this ensures that no hydrogen sulfide escapes from the solution, on the other hand the pH is not higher than is absolutely necessary to avoid the formation of hydrogen sulfide. Too high pH values are also undesirable with regard to the grain smoothness and the feel of the leather as well as the safety of limescale removal.
• the amounts used for the carbonate depend on the content of lime and other basic compounds (e.g. sodium sulfide and sodium hydroxide) in the skin material. They are of the order of 0.8 to 4%, preferably 1 to 2%, based on the weight of the wet hides.
• the carbonates are preferably dissolved in water.
• the emulsification or dispersion of insufficiently water-soluble carbonates can be carried out in a conventional manner with cationic, anionic or nonionic emulsifiers. It is in no way problematic.
• Example 1 was repeated in exactly the same way, except that a commercially available product based on the ammonium salt of sulfophthalic acid was used as the deliming agent. After 5 minutes of walking, the pH of the decalcifying liquor was measured at 3.2, 15 minutes later it had risen to 7, and then after 40 minutes of walking adjust to the final pH of 8.6.
• Example 2 100 parts of bare bark were always decalcified. The test results are summarized in the table.

Landscapes

• 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)
• Detergent Compositions (AREA)
• Compounds Of Alkaline-Earth Elements, Aluminum Or Rare-Earth Metals (AREA)
• Peptides Or Proteins (AREA)
• Separation Using Semi-Permeable Membranes (AREA)
• Diaphragms For Electromechanical Transducers (AREA)

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Citations (2)

• 1981
  • 1981-03-06 DE DE19813108428 patent/DE3108428A1/de not_active Withdrawn
• 1982
  • 1982-02-12 US US06/348,277 patent/US4377387A/en not_active Expired - Lifetime
  • 1982-02-27 EP EP82101530A patent/EP0059909B1/fr not_active Expired
  • 1982-02-27 DE DE8282101530T patent/DE3260040D1/de not_active Expired
  • 1982-02-27 AT AT82101530T patent/ATE6164T1/de not_active IP Right Cessation

Patent Citations (2)

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