Bleaching and dyeing; fluid treatment and chemical modification – Treatment of hides – skins – feathers and animal tissues – Tanning
Patent
1997-11-19
1999-05-04
Diamond, Alan
Bleaching and dyeing; fluid treatment and chemical modification
Treatment of hides, skins, feathers and animal tissues
Tanning
8 9415, 8 9418, 8 9433, 8 942, 8 9421, 8 9424, 8 9425, 8 9427, 8 9432, C14C 104, C14C 300, C14C 902
Patent
active
059000279
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for finishing animal hides or pelts. Animal hides and pelts are required in many areas of daily life and also for industrial applications. Examples are the clothing industry, medical articles, furniture industry, automotive accessories and cleaning materials. The processing of pelts and hides is a significant economic factor in industrialized countries and in agrarian countries.
The hides or pelts have to be finished in accordance with the various end uses. The principal aims of finishing are to establish durability and to generate the desired morphological (e.g. handle, tear strength, suppleness, water resistance) and color properties.
The text below describes by way of example the customary processing and finishing of pelts or skins, which corresponds in large areas with the processing and finishing of leathers and hides. The main function of the various pelt or hide treatment steps is to reach a state of swelling of the skin pores and of the hairs, in which state penetration of tanning chemicals and thus the crosslinking and strengthening of the collagen chains is possible. Unlike the preparation of leather, where an unhairing step is required, pelt processing requires unconditionally that the coat of hair is maintained. To aid comprehension, the individual steps of conventional pelt or skin finishing, which are detailed below, are reproduced in FIGS. 1 and 2 the form of a flow diagram.
The pelts removed are usually not processed fresh but are preserved by drying, salting or deep-freezing. The first processing step in the finishing of skins, therefore, is a soak, by means of which the pelts are prepared for subsequent treatment. The soak is usually conducted with cold water to which a certain amount of surfactants have been added. The soaking period is from 8 to 24 hours. The mass ratio between the solution, in this case the soak solution, and the pelts, which is referred to below as the liquor ratio, is between 6-12:1. After the end of the soak, the liquid discharged from the soak tub together with the pelts is removed by centrifuging and obtained together with the remaining soak solution as waste water. The pelts are sorted and subjected to various mechanical processing steps (turning, cutting, drawing). In the next process step the pelts are washed. This usually takes place with a warmed (25-35.degree. C.) water/surfactant solution to which small amounts of salt have been added. The added salt and the elevated temperature produce slight swelling of the pores and of the keratin structure of the hair. The soaking period and the liquor ratio are identical to those for the soak. After the end of the wash, the pelts are again centrifuged and mechanically processed. The wash solution is obtained as waste water.
In a further bath, the pelts are "opened up". For this purpose, the pelts are treated in an aqueous solution the pH of which has been set to 3.8 to 4. For this purpose, in most cases organic acids are employed. To avoid hairslip, the so-called "pickling solution" used for opening up must have relatively large amounts of salt added to it in order to attenuate the effect of the acid. The aim of opening up is to widen the pores and the hair structure for subsequent tanning in order to enable the tanning solution to penetrate. Here too, the liquor ratios are from 6 to 12:1. The soaking periods are usually substantially longer than in the case of the preceding baths and are in the range from 12 to 48 hours. In the case of the preparation of leather, the hides are unhaired at this point, which is achieved by altering the pH and the salt concentration in contrast to the dressing of skins. The opening-up solution or, respectively, the unhairing solution is obtained as waste water and must if appropriate be filtered and neutralized before being introduced into the waste-water system.
In the next processing step, tanning, the pelts are treated with a buffered solution of tanning chemicals in water. As a result of tanning, the peptide chains of the collagen are crosslinked, s
REFERENCES:
patent: 5326377 (1994-07-01), Tuohimaa et al.
patent: 5512058 (1996-04-01), Gavend et al.
Sharphouse, The Leatherworker's Handbook, pp. 37-42 (month unknown), 1963.
Geihsler Helmut
Weidner Eckhard
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