Microcapsules contg. hydrophobic substances - in hydrophilic coatings with improved moisture resistance, for use on copying paper

摘要

In the known process of forming microcapsule dispersions by depositing at least two hydrophilic colloidal substances around fine particles of a hydrophobic substance and gelling the coacervate, =1 ammonium salt of hydrolysed polymers contg. styrene and maleic anhydride is present in the dispersion contg. gelled coacervate, in combination with =1 aldehyde. The polymer is pref. a copolymer of styrene and maleic anhydride in equimolar ratio, and may contain =50 mol% of a third monomer e.g. (meth)acrylic acid or ester, vinyl monomers, maleic acid, etc. =5 (pref. 10-200) parts ammonium salt per 100 pts. hydrophilic colloid is used. The microcapsules are suitable for making pressure-sensitive copying papers, an electron-donating colourless chromogenic material being dissolved in the hydrophobic substance. Addition of the ammonium salt improves moisture resistance of the microcapsules and reduces smearing of the copying paper during storage or handling.