1461355 Polyamide composition; thixotropic agent COATES BROS & CO Ltd 28 April 1975 [29 May 1974] 23700/74 Headings C3R and C3P A rheological control agent comprises a particulate blend of hydrogenated castor oil and an oligomeric polyamide obtained by reacting (a) hydroxystearic acid, (b) one or more saturated aliphatic alpha-omega diamines having 2, 4, 6, 8 or 10 C atoms, and (c) one or more saturated aliphatic alpha-omega C 2-10 dicarboxylic acids and/or hydrogenated dimer acids in proportions providing 0À05 to 0À5 moles (c) per mole of (a) and 0À8 to 1À15 amine groups per carboxyl group. The hydrogenated castor oil and polyamide may be melt blended in proportion from 9 : 1 to 1 : 9 and then cooled and finely ground to an average particle size below 25 microns. Thixotropic compositions may be obtained by incorporating the agents in various surface coating compositions, e.g. paints, varnishes, printing inks, adhesives and laminates based on various resin systems, e.g. acrylic, alkyd, oleo, epoxy and unsaturated polyester resins and chlorinated rubbers with or without conventional solvents. The powdered blend may first be formulated into a 15% w./w. dispersion with an organic medium compatible with the coating composition, e.g. white spirit by means of high speed stirring generating a temperature of about 35‹ C. After cooling the dispersion is added to the paint mill-base prior to grinding in proportions depending on the flow control desired but typically providing about 0À5 wt. per cent of the solid additive. Specific examples illustrate the use of various blends of the invention in coating compositions based on alkyd/melamine, hydroxy acrylic/melamine, chlorinated rubber, and unsaturated polyester/styrene resins with various conventional paint solvents and additives.
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