Method to treat animal skins prior to tanning

Details Method to treat animal skins prior to tanning Method to treat animal skins prior to tanning

1993-05-21

1994-12-27

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, 252 857, C14C 108, C14C 1100

Patent

active

053761421

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/GB92/01769 filed Sep. 25, 1992.
The present invention relates to the use of hydroxyalkyl phosphine compounds in the production of leather.
Animal skins, being predominantly protein, are subject to decomposition by microorganism and autolysis. The increased mechanical, chemical and biological stability which leather possesses in comparison to fresh skins or hides results primarily from the tanning operation, in combination with various finishing processes which make the leather acceptable to the purchaser. Tannery processes are usually divided into distinct pretanning, tanning and finishing operations. Because of the complexity of the chemistry involved, the substrates which are the objects of treatment in these respective circumstances differ widely in chemical constitution, and mechanical stability. For example, the water in the fresh hide may be as high as 80% in the cured hide it is reduced to about 40%, and in finished leather it remains to the extent of about 10-15%. Hence the choice of reagents for the individual stages is difficult, e.g., much work has been devoted to the development of synthetic tanning agents to replace conventional chrome or vegetable tans, but necessarily on a largely empirical basis, since their mechanisms of action are poorly understood.
Attempts to explain the relevant interactions have invoked such different phenomena as electrovalency or salt-forming and physical adsorption. Generally it is desired to effect chemical cross-linkage and therefore polymerisation within the substrate in question, thus imparting thereto hydrothermal stability with respect to shrinkage, which is necessary for example in the finished product and to prevent damage to the substrate during those steps of the tanning process which require treatment with water, and improved fixation of media superimposed thereon as required for example in post-tanning finishing operations.
Fresh skins and hides are normally salted or soaked in brine to preserve them during the period of storage prior to tanning, although some tanneries operate directly on the fresh skins.
The skins are typically cleaned and scraped to remove extraneous matter and then degreased using either solvent such as paraffin, or preferably, from ,the point of view of safety and the environment, by heating in an aqueous degreasing solution. The latter typically contains brine, but heating the skins in brine is liable to cause shrinkage. To avoid this problem, shrinkage agents, such as glutaraldehyde, are normally added to the degreasing solution.
The main operations, which are comprised by the tanning step itself, involve contacting the skins with various tannages e.g., vegetable tannages, based essentially on tanning, mineral tannages such as chrome salts or molybdenum salts, various synthetic organic tannages and combinations of the aforesaid tannages.
After tanning it is common to apply a finish to the tanned leather. This is normally a curable polymer e.g., a natural polymer such as casein or a synthetic polymer such as polyurethane. The finish is finally cured by the application of a cross linking agent. Casein finishes have hitherto been cured by the application of products such as formaldehyde.
Formaldehyde presents considerable problems on toxicological and environmental grounds, which may foreseeably lead to restrictions in its use. Substitutes for formaldehyde hitherto proposed have been substantially more expensive and generally less effective. An important object of the invention, therefore, is to provide an effective and environmentally acceptable replacement for formaldehyde in post tanning operations such as curing of finishes and especially in curing casein finishes.
A further object of the invention is to replace glutaraldehyde as an inhibitor of shrinkage during pretanning operations such as degreasing.
A third object of the invention is to offer alternatives to cross linking agents such as aziridine which have hitherto been used to cure synthetic polymer finishes on leather.
It has been proposed

REFERENCES:
patent: 3104151 (1963-09-01), Windus et al.
patent: 3734684 (1973-05-01), Donaldson et al.

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