CS238523B1 - The method of chrominating leather and fur - Google Patents

Abstract

The essence of the solution is that the bark after deliming, pickling and pickling is tanned with chromium compounds at a temperature higher than the glass transition temperature, but 3 to 5 °C lower than the shrinkage temperature of skin collagen in a given environment. The specified temperature can be achieved by heating the liquid used in the preparation of the pickling and/or tanning bath or during tanning using supplied steam, or by pumping the tanning bath through a heat exchanger.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to methods of chrominating hides and skins at a suitable controlled temperature tanning bath.

Chromium tanning is the most important method in the production of leather and fur. At present, it is carried out at lower temperatures, usually in the range of 20 to 30 ° C. This conversion is irreversible and the modified gelatin state is not suitable for leather and fur production. The transformation temperature, or the temperature at which the first observable change occurs, the so-called shrinkage temperature Ts, lies in the native non-swollen collagen of most skins around 60 ®C. In the acidic environment in which it is made, the shrinkage temperature is reduced to about 40 to 30 ° C, depending on the ratio of acidity and prior treatment methods. In addition, it is known that long-term heating transforms collagen into gelatin even at temperatures below the shrinkage temperature. It is known in the tanneries to use higher temperatures in chromium tanning, but this is only done in the final stage of the process by the addition of hot water and is intended to hydrolyze chromium complexes instead of using alkaline agents in the so-called blunting. Such procedures have been described by Rickly, Lee, Whiton in J. Soc. Leather Trade Chem. 51, 385, (1967), 53, 20, (1969) and Heideman, Bresler in Das Leder, 12, 69 (1961). As a result of a study on the effect of temperature on the kinetics of cross-linking of collagen by chromium complexes, it has now been found that the temperature increase is very beneficial for the cross-linking process.

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Accordingly, the present invention provides a method of chrominating leather and shin leather, characterized in that the descaling, pickling and piclining of the clearing is made by chromium compounds at a temperature higher than

238 523 is the glass transition temperature, but 3 to 5 C lower than the shrinkage temperature of the skin collagen in the environment ·

The most important is the influence on the content of usable reactive groups of skin collagen. This phenomenon can be explained by an increase in the motivities of the molecular lengths of the carboxyl group side chains of the polypeptide chains. It has been shown that a characteristic second order structural transformation occurs in the collagen around 38-40 ° C. In this conversion, the crystalline tri-helical collagen structure remains, but the freer vibrational and rotational movement of the molecular segments avvv Φ vv is possible _{due to} particularly side chains. This transformation has the character of the so-called glass transition temperature. The greater freedom of the segment allows for a greater number of configurations. Such crosslinking, leading to the stabilization trojhelikální collagen structure, the main purpose of tanning method * ^x emperature Tg collagen is also dependent on the degree of covalent crosslinking and therefore rise during tanning * Determination of the temperature is possible by turning on the dependence of some deformation properties of collagen to temperature * in

In Figure 1 _; illustrating the effect of temperature on the rate of cross-link formation, a significant effect of temperature on the rate of cross-link formation in collagen during chromium tanning is shown. o _r

Increase in the number of usable reactive groups that can

Μ φ V - W to participate in the formation of the crosslink through the chromium complex is proportional to the increase in the temperature of the chromium tanning * is shown in Figure 2, which shows the number of total crosslinks per mole of tropo-collagen when tanning at temperatures higher than the glass transition temperature, particularly in the presence of caustic magnesite as a blunting agent and in the presence of catalysis agents for exchanging ligand tremor (e.g. magnesium, aluminum, zinc, etc./, the shrinkage temperature increases very quickly *

Thus, the adverse effect of long-term heating on the shrinkage temperature reduction is ruled out. This allows for a safe and fast chromium-plating process characterized by. very good hydrothermal sta3

238 523 by the tannin collagen and improved use of chromium compounds. The tanning liquid can be heated to a relatively high temperature of 60 to 80 ° 0 soon after tanning commences. This can be done both by preheating the liquids used in the preparation of the pickling and tanning solution, and by gradually raising the temperature during tanning with pump circuit heat exchangers located inside or outside the tanning vessel, or by heating with hot steam preferably in the pit floor in the tanning vessel. However, the heating must be adapted to the changes in Ts vvv especially at the beginning of tanning. The bath temperature should not approach more than 3 ° 0, preferably 5 ° 0, to the shrinkage temperature of the collagen in the environment. It is suitable to use a programmed control circuit controlling the heating rate. The final temperature at which the heating is terminated will depend on economic considerations and may be e.g.

(& 85 0. If so-called caustic magnesite self-hulling and catalysis are carried out, the temperature may rise to this maximum value as early as 15-40 minutes from the start of tanning.

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The process according to the invention makes it possible to achieve a higher content

Μ In cross-links in tanned collagen / and thus higher temperature resistance of the produced leather.

Example 1

Descaling and with clearcut vymořená pikluje in the heated solution, ^one which somewhat temperature depends on the composition plots and lies in the interval 53 ^E C. 30ář pickling time is shortened to about one half the time used in cold scheming. In the heated picnic bath, tanning with chromium compounds is carried out in an amount corresponding to 2-2.4% θ ^Γ 2θ3 ^{per in} weight weight. The tanning time is 2-6 hours, depending on the type of ground and blunting methods.

Example 2 v v v ®

The descaled, purged and commonly plated wort is made with chromium salts / in an amount corresponding to 4.6-2.4% Cr ₂ O ₃ per holin weight. At the same time, aluminum dust is added in an amount of 1 g / l and caustic magnesite in an amount of 0.3-0.7% per haline φ φ weight.

238 523 by heating it by pumping through a heat exchanger · The heating rate is 1 ° C per minute, so that the bath has a temperature of about 75 ° C for 5θ minutes of tanning. the leather is well tanned and can be further processed without further care ·

Example 3

Decalcified, decorticated and normally plated wort is made chromite with salts equivalent to 1.6-2.2% θ ^Γ 2θ3 per shale weight in the presence of 0.4-0.6% caustic magnesite, for 30 minutes · After this time with the introduction of sharp steam or by pumping the bath through the heat exchanger, the tanning solution heats the tanning solution to 65 ° C · tanning is then continued for 2-3 hours · After this time, leather and thicker cowhide are well prepared and can be further processed

Claims (3)

1. A process for stunting goats and fur, characterized in that the descaling, pickling and pickling process is performed with chromium compounds at a temperature higher than the glass transition temperature but 3-5% below the shrinkage temperature of the skin collagen in the environment. O M A method according to claim 1, characterized in that said temperature can be achieved by heating the liquid used in the preparation of the dipping and / or tanning bath. Φ χ O 3. A method according to claim 1 or 2 _, characterized in that said temperature can be reached during tanning by means of supplied steam or by pumping the tanning bath through a heat exchanger.