FORFARANDE FOR FRAMSTELLNING AV MONOCELLULERA GASFYLLDA PARTIKLAR OCH MEDEL FOR DESS GENOMFORANDE

1389122 Expandable microcapsules DOW CHEMICAL CO 4 Aug 1972 [5 Aug 1971] 36603/72 Heading B8C Microcapsules which are expandable on heating to a temperature below 100‹ C. and are composed of a thermoplastic polymer mantle enclosing a volatile liquid raising agent are, before being heated, contacted with an aqueous solution containing 0À15 to 2 hydrogen gram equivalents per 100 grams of water of a watersoluble metal salt. To form the expanded microcapsules, unexpanded microcapsules which have been so treated are heated in contact with water to a temperature sufficient to drive off the volatile core material and expand the mantles. Suitable salts include: CaCl 2 , MgCl 2 , BaCl 2 , ZnCl 2 , NaCl and FeCl 3 . Preferred polymers are vinylidene chloride copolymers, e.g. with acrylonitrile.