Bleaching and dyeing; fluid treatment and chemical modification – Treatment of hides – skins – feathers and animal tissues – Treatment of untanned skins or hides
Patent
1992-04-30
1994-07-05
Willis, Jr., Prince
Bleaching and dyeing; fluid treatment and chemical modification
Treatment of hides, skins, feathers and animal tissues
Treatment of untanned skins or hides
8 9415, 8 9425, 8 9426, 8 9427, 8 9428, 8 9429, 8 9433, C14C 108, C14C 304
Patent
active
053263774
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of pretreating and mineral-tanning hides which have been delimed and steeped in bate, i.e. have been bated. This method is intended to obviate the pickling and basifying steps (German: "Abstumpfen") which respectively precede and follow the conventional mineral tanning process.
Because of a greater awareness of present day environmental problems, the method is intended to reduce effluent emissions which contain contaminating mineral salts, acids and mineral tanning substances irreversibly bound to the hides.
By pickling is meant the treatment of organic products with salts, often in weak acid solutions. In the production of leather, the object of the pickling process is to bring the prepared hides and skins to a slightly acid state, suitable for mineral-tanning purposes.
The hide-substance can be brought to the desired degree of acidity, by treating the hide material with a strong acid in salt solution. Subsequent to being bated, the pelts, i.e. the hides stripped from hair, softened and delimed or decalcinated, will contain varying quantities of alkali.
Another object of the pickling process is to stabilize reaction of the pelts on the acid side, so as to create favorable conditions in the initial stages of the mineral-tanning process.
Hides or pelts to which acids are chemically bound have a lower affinity to tanning mineral salts than hides which are chemically neutral. Tanning is rendered more gentle by proceeding in the aforesaid manner and "drawing of the grain" and other leather defects are eliminated. The salt contained in the pickled pelts also has the same effect.
Strong mineral acid solutions result in pronounced swelling of the hides. This swelling can be reduced by adding a neutral salt, e.g. sodium chloride, which functions to dehydrate the functional hide-groups ionized by the acid.
It is necessary to adapt the amount of acid used in the pickling process to the nature of the pretreatment to which the hide or pelt has been subjected, and also to the type of leather to be produced and to the subsequent tanning process. Mineral acid, for instance sulfuric acid, is used in quantities which range from 0.5-2 percent, based on the weight of the pelt. The amount of salt required is normally about 10 percent calculated on the weight of the pelt. The salt-concentration should not be less than 5 percent, since a weaker salt solution than 5 percent is unable to prevent acid-swelling totally.
By basifying ("Abstumpfung") is meant increasing the acid pH-value, necessary in the initial stage of a mineral-tanning process, to a weaker acid range.
Furthermore, it is desired to convert to tanning-active carboxyl anions those carboxylic groups which are responsible for binding the mineral-tanning substances to the fibers of the hide. At the same time, the anions present in the mineral-tanning substance complex shall be exchanged for hydroxyl ions ("masking"), thereby resulting in a condensation reaction between the complex mineral-tanning substance bound to the fibers of the hide ("Verolung").
This condensation reaction results in cross-linking within the hide and therewith in stabilization of the hide fibre-network (tanning).
Basification is achieved either by adding more or less strongly basic reacting salts (e.g. NaHCO.sub.3, HCOONa, MgO) or not-readily dissolved but acid-soluble salts (e.g. MgO, MgCO.sub.3) already present in the mineral tanning substance.
An object of the present invention is to provide a method in which hides can be tanned with mineral tanning substances in the absence of pickling and basifying ("Abstumpfen") processes.
Another object of the invention is to reduce the quantities of salt, acid and non-bound mineral tanning substances contained in the waste water discharged from tanneries to the recipient.
Another object is to provide a method of treating hides with which tanning can be effected satisfactorily with smaller quantities of mineral tanning substances, by more efficient use of said substances.
These objects are achieved in accordance wit
REFERENCES:
patent: 875382 (1907-12-01), Rohm
patent: 2004473 (1935-06-01), Pensel
patent: 4614520 (1986-09-01), Ibello et al.
"The Use of Carbon Dioxide for Deliming", by Edwin E. Ochs, JALCA, vol. 48, pp. 105-110, (1953).
Tuohimaa Timo
Ukkonen Aila
AGA Aktiebolag
Diamond Alan D.
Willis Jr. Prince
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