Preparation of Disperse Azo Dyestuffs in the Presence of Acetylenic Diol/Dispersant Combinations
Publication Date: 2005-Sep-15
The IP.com Prior Art Database
Presence of Acetylenic Diol/Dispersant Combinations
1. Objective. Disperse azo dyestuffs are a class of dyes in which a sparingly water-soluble azo compound is produced by the reaction of a diazonium salt of an aromatic or hetero-aromatic amine with a coupling component, typically in water. The resulting product is obtained as an aqueous slurry of precipitated dye that is sometimes subjected to a heat treatment step to convert the material into a thermally stable form and/or to improve the ease of performing subsequent steps such as filtration. The slurry is filtered and washed in preparation for subsequent processing. During the coupling reaction, it is desirable to limit the amount of reaction foaming and product tarring, and to maximize product yield and purity. For dyes that require a heat treatment step, minimization of time and temperature requirements to achieve the required properties is desirable so as to minimize energy costs.
Reaction product isolation is an important step in disperse dye processing. Short filtration time and ease of washing of product are desired so as to afford a high space/time yield and to minimize the generation of waste effluent. In addition, it is desirable to obtain as high of a level of solids in the filter cake as possible. If the solids level of the filter cake is too low for the dye paste to be used directly in subsequent processing, then a drying step must be added to the manufacturing process. If the filter cake solids level is sufficiently high, then the expensive drying step can be avoided.
Heat treatment of disperse azo dye slurries upon completion of the coupling reaction, sometimes necessary to convert the dye to its required crystal form, often results in improved filtration properties when compared to dyestuff that has not been heat treated.
2. Prior Art. Incorporation of certain additives during the coupling reaction is known to enhance the filtration properties of disperse azo dyestuff without heat treatment, the process being dependent on the dyestuff and on the process employed. In addition, the use of certain additives has been reported in the context of heat treatment for the purpose of effecting change in crystal form of disperse azo dyes.
US 5,532,344 discloses the use of polyoxyethylene higher fatty acid ester nonionic surfactants in the preparation of monoazo dye by coupling a p-nitroaniline derivative with an N,N-disubstituted aniline derivative.
US 4,785,082 and 4,828,622 disclose the use of surfactants with cloud points between 5-90 oC, including EO/PO block copolymers and oxyalkylates of aliphatic, aromatic, cycloaliphatic, or heterocyclic hydroxy or amino compounds, in the preparation of concentrated press cakes of disperse dyes and water-insoluble or sparingly water-soluble solids.