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AssigneeHoechst Aktiengesellschaft
InventorsJoachim Weide, Erwin Dietz, Reinhold Deubel
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According to the invention, addition of one or more surfactants having a cloud point in aqueous solution to an aqueous suspension of an azo disperse dye gives after the isolation of the dye at a temperature above the cloud point aqueous press cakes containing a large amount of this dye. The direct processing of press cakes as obtained for example after the synthesis and isolation of azo disperse dyes to practical dispersions for use requires a minimum dye content in the press cakes. The minimum content is frequently not obtained when conventional methods of isolation are used, so that it is necessary to proceed via the indirect route of drying to obtain powders and redispersing the powders. By using the process according to the invention it is possible to cut out the costly indirect route or, if desired, to reduce the expense of drying to obtain powders by an appreciable margin.
A process for preparing a highly concentrated aqueous press cake of an azo disperse dye, which comprises adding one or more surfactants which have a cloud point in aqueous solution in the course of the preparation of the respective dye in an aqueous medium, at the latest before the dye is isolated, and isolating the azo disperse dye at a temperature above the cloud point of the surfactant or surfactants used.
A process for the preparing a highly concentrated aqueous press cake of an azo disperse dye by isolation from a relatively dilute aqueous medium, which comprises
Dependencies are inferred from the claim text.