Bayer Aktiengesellschaft

Peter Schultz

Edzard Tholema

Dieter Maertens

Hans Gossmann

Heinz-Gerd Nonnenbruch

Andreas Huppertz

If the edge of a filter cloth is coated with one or more layers of a polychloroprene latex mixture which contains zinc oxide and a silicate filler in addition to a polychloroprene with carboxyl groups, sticking is so greatly reduced that the durability of the filter cloths is substantially increased.

Edge sealing for filter cloths

The invention relates to a process for the preparation of 1,5-dihydroxyanthraquinone and 1,8-dihydroxy-anthraquinone and of their mixtures. Alkali metal salts or alkaline earth metal salts of the corresponding anthraquinonedisulphonic acid are treated, in an aqueous medium under pressure and at elevated temperatures, with lime, buffer substances and, if appropriate, oxidizing agents, a surface-active agent is added to the resulting reaction mixture and the mixture is then acidified in a continuous process with mineral acid at temperatures of 50.degree. C to 150.degree. C and a pressure of 1-3 bars, and the dihydroxyanthraquinone which has precipitated is isolated. Compared to the known procedure, the process according to the invention is distinguished by a substantially improved space-time yield with at least equal purity of the reaction products.

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Leverkusen, Germany

Peter Schultz