| abstract |
Aqueous polymeric microemulsions such as acrylic ester copolymers contain very fine particles having a number average particle size of generally 600 Angstroms or less. The glass transition temperature of the particles is low and with respect to acrylic polymers is generally 20°C or lower. The aqueous polymeric microemulsion can can be based on polymers such as an acrylic polymer or copolymers thereof, vinylidene chloride polymers or copolymers, acrylonitrile-butadiene (nitrile) polymers or copolymers thereof, polyvinyl chloride polymers or copolymers, vinyl acetate polymers or copolymers, ethylene copolymers, and the like, as well as blends of the above. The polymeric microemulsions are made by utilizing at least one water soluble initiator or a redox initiator system and a low but effective amount of one or more emulsifying agents and adding the monomers thereto on an incremental basis. Acrylic polymeric microemulsions are desired due to their high heat stability. The fine-size polymeric microemulsions have good film formation, high pigment loading ability, unexpectedly high shear holding time, and the like. They are thus suitable for imparting improved strength to paper and when used with various fillers improve the opacity of the paper. |