GB1436798A - Self-colouring pressure sensitive recording sheets - Google Patents

Abstract

1436798 Microcapsules FUJI PHOTO FILM CO Ltd 14 Aug 1973 [14 Aug 1972] 39509/73 Addition to 1416224 Heading B8C [Also in Division D2] Microcapsules for use in pressure sensitive recording sheets are prepared by emulsifying in a polar liquid capable of forming a continuous phase an oily liquid containing (A) a colour former, and (B) and (C) first and second coreacting wall film-forming materials, adding a third wall film-forming material capable of reacting with the first wall film-forming material to form a high M.W. compound to the polar liquid either before or after emulsification, and forming capsule walls around the oil droplets of the emulsified oily liquid, the capsule walls being formed from inside the oil droplets by a reaction between the first and second wall film-forming materials, and simultaneously, by the reaction at the surface of the oil droplets between the first and third wall film-forming materials. The first wall film-forming material may be selected from polyisocyanates, polythioisocyanates, and their addition products containing residual isocyanate or isothiocyanate groups; the second wall film-forming material may be selected from polyhydroxy compounds, epoxy compounds, polycarboxylic acids, polythiols; and the third wall film-forming material may be selected from polyamines, modified polyamines, polyhydroxy compounds, polycarboxylic acids, polythiols. Other combinations are also described. The polar liquid may be water, an alcohol, or a ketone. Protective colloids and surfactants may be used for emulsification. Catalysts may be used to speed up microencapsulation. In a typical example, an adduct of hexamethylene diisocyanate and trimethylol propane containing residual isocyanate groups and polyoxypropylene glycol were added to a solution of crystal violet lactone and benzoyl lencomethylene blue in diisopropyl naphthalene together with a catalyst, dibutyltin laurate. The resulting oily solution was added to water containing carboxymethyl cellulose and polyvinyl alcohol to form oil droplets. After addition of water and an adduct of a polyamine and an epoxy compound, followed by heating, microcapsules were formed.