Bayer Aktiengesellschaft

Heinrich Spahrkas

Wolfhard Luck

Helga Heinze

Ernst Komarek

Josef Muller

Klaus Backer

Herbert Knopf

A pulverulent spray dried chrome tanning agent having about 1.8 to 2.6 mols of formate/mol Cr.sub.2 O.sub.3, a basicity of at least about 42% and a sulphate content of at least about 1.8 mols SO.sub.3 /mol Cr.sub.2 O.sub.3, maintaining its solubility in water over a prolonged period of time compared with a similar composition having a lower sulphate content, i.e. the latter becomes increasingly water-insoluble with the passage of time.

Age resistant chrome tanning agents

In the chrome-tanning of animal skins and hides by pretanning the pickled pelts with chromium (III) salts, followed by full tanning with chromium (III) salts and acid-binding agents, the improvement which comprises effecting full tanning with the reaction of product at least one of formic acid and a formate with a basic chromium (III) sulphate, at least 2 moles of formate plus formic acid being used per mole of Cr.sub.2 O.sub.3 in the chrome-tanning agent used for full tanning, the total input of chromium oxide being from about 1.0 to 1.8%, based on the weight of the pelts, and tanning being carried out with a liquor volume of at most 100%, based on the weight of the pelts, up to a final pH-value of at least 4.0.

Chrome-tanning

In the chrome-tanning of hides to produce leather wherein a hide is pickled, pretanned with a chromium (III) salt, and full tanned with a tanning mixture containing a chromium (III) salt, an acid-binding agent and a polycarboxylic acid or salt thereof, the improvement which comprises employing as said polycarboxylic acid or salt thereof at least 1.6 moles per mole of Cr.sub.2 O.sub.3 in the chromium (III) salt employed for full tanning of an aliphatic dicarboxylic acid of 4 to 6 carbon atoms or an aromatic dicarboxylic or tricarboxylic acid containing 8 to 13 carbon atoms or a salt thereof, the total quantity of Cr.sub.2 O.sub.3 employed in pretanning and full tanning ranging from 1.2 to 2% by weight of the hide, full tanning being carried out with up to 100% of the tanning liquor based on the weight of the hide to a final pH of the liquor of at least 3.6. Advantageously, a powder composition comprising additional chromium (III) salt, polycarboxylic acid or salt and acid-binding agent, preferably dolomite, is added after pretanning.

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Leverkusen, Germany

Heinrich Spahrkas