PU Synthetic Leather 3

الوصف

In the production of mineral tanned and/or re-tanned leather it is desired to keep the yield and efficiency of the mineral tanning agent as high as possible, be it in order to achieve a high-yield mineral(re)tanning or in order to decrease as far as possible the residual mineral tanning agent content of the back-water. In the after-treatment of leather with fatting agents*-particularly such with hydrophobizing properties*-that are fixed with polyvalentmetal cations, it is also desired to improve the yield and efficiency of the treatment.

It has now been found that using defined anionic polymeric compounds these aims can be attained in a surprisingly high degree.

The invention thus provides a process for the production of mineral tanned or/and retanned or/and after-treated leather or pelt, wherein before a mineral tanning, directly after a mineral tanning, directly before a mineral re-tanning, after amineral re-tanning or/and with the after-treatment of a fatliquoring with a polyvalent metal cation, the substrate is treated with

(A) a polymeric carboxylic acid containing .alpha.-hydroxyacrylic acid units, optionally in salt form, as constituent units of the polymer.

As polymeric carboxylic acids (A) or their salts come principally into consideration (co)poly-.alpha.-hydroxyacrylic acids, optionally further containing non-ionic and/or other anionic co-monomeric units as constituents of the polymer or theirsalts. The other anionic co-monomeric units*-indicated in the free acid form*-are advantageously derivatives of ethylenically unsaturated monomeric carboxylic acids (principally of aliphatic C.sub.**5 -carboxylic acids), in particular (meth)acrylicacid, crotonic acid, maleic acid, itaconic acid, aconitic acid and citraconic acid, among which maleic acid and (meth)acrylic acid are preferred, especially acrylic acid. As non-ionic monomeric units come principally into consideration the derivativesof (meth)acrylamide, (meth)acrylonitrile and/or vinylmethylether. Copolymers comprising .alpha.-hydroxyacrylic acid units and acrylic acid units and/or their salts or, in particular, consisting thereof are preferred. As "derivatives" of the monomersare meant here monomer units deriving from the copolymerisation of the mentioned monomers.

The numerical average molecular weight M.sub.n of the polymers (A) is advantageously in the range of **0 to **0,**0, preferably **0 to *0,**0. Of the polymers to be employed are furthermore preferred those whose weight average molecular weightM.sub.w is in the range of ***0 to **0,**0, preferably ***0 to **0,**0. The indicated molecular weights are intended in the form of the sodium salts of the polymeric acids.