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AssigneeRohm and Haas Company
InventorsAlexander Kowalski, Martin Vogel, Robert M. Blankenship
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The present invention is concerned with the production and use of water-insoluble particulate heteropolymers made by sequential emulsion polymerization in dispersed particles of which a "core" of a polymeric acid is at least partially encased in a "sheath" polymer that is permeable to a volatile base, such as ammonia or an organic amine, adapted to cause swelling of the core by neutralization. The aqueous dispersion of the acid-containing core/sheath particles is useful in making water-base coating compositions wherein it may serve as an opacifying agent when a volatile base is used to at least partially (to a pH of at least 6) neutralize the heteropolymer, microvoids being formed in cores of the swollen particles in the film during the drying thereof. Thus, the heteropolymer dispersion can serve as an opacifying agent in coating compositions, such as water-base paints, as a supplement or replacement of part or all of the pigmentary material or extenders that would otherwise be used in such coating compositions. For convenience of description herein, the terms "core", "sheath", and "core/sheath polymr" are frequently used to refer to the distinct functional components of the individual polymer particles of the essential "mode" of the heteropolymers of the present invention even though in actuality, the components of the polymer particles thereof may not have the precise arrangement implied by this terminology.
A process for making an aqueous dispersion of water-insoluble core/sheath polymer particles comprising
A composition comprising an aqueous dispersion of water-insoluble core/sheath polymer particles having an average diameter of 0.07 to 4.5 microns, having a core polymerized from a monomer system comprising one or more monoethylenically unsaturated monomers having a group of the formula --HC.dbd.C<, at least one of said unsaturated monomers having a carboxylic acid group, and having at least one sheath polymerized from at least one different monomer system, at least one of said different monomer systems being hard and producing a polymer (a) having a T.sub.i greater than 50.degree. C., (b) being non film-forming at 20.degree. C., (c) being permeable to ammonia and amines, said core being swollen by neutralization with ammonia or amine in the presence of water, said particles having a property such that when subsequently dried a single cavity forms in said core and said particles cause opacity in compositions in which they are contained.
An opaque composition comprising dried core/sheath particles having a single cavity in said core and an average particle size of about 0.07 to 4.5 micron and having a core polymerized from a monomer system comprising one or more monoethylenically unsaturated monomers having a group of the formula --HC.dbd.C<, at least one of said unsaturated monomers having a carboxylic acid group, and having at least one sheath polymerized from at least one different monomer system, at least one of said different monomer systems being hard and producing a polymer (a) having a T.sub.i greater than 50.degree. C., (b) being non film-forming at 20.degree. C., (c) being permeable to ammonia and amines, said core having been swollen by neutralization with ammonia or amine in the presence of water, and subsequently dried.
Dependencies are inferred from the claim text.