US 6,184,300 B2 · Bowl-shaped polymer particles, aqueous dispersion of polymer particles, processes for producing these, and thermal recording material

Abstract

Bowl-shaped polymer particles characterised by having a bowl-like shape as is formed by partly cutting along a plane each spherical hollow polymer particle having a void in the inside, and in which the cross-section perpendicular to the cut plane and passing through the center of the particle has a shape as is formed by partly cutting a double circle along a straight line, and the lengths H of the perpendiculars from the outer arc of the double circle in the cross-section to the straight line have a maximum value Hmax equal to or larger than the radius of the outer circle of the double circle. The bowl-shaped polymer particles have a multi-layer structure, and are produced by multi-stage polymerization in which monomer mixtures are successively polymerized in a manner such that the proportion of a monomer having an acidic group gradationally decreases and by treating the resultant polymer with a base. The bowl-shaped polymer particles are useful as a heat-insulating material, organic pigment, or opacifying agent, and especially as a heat-insulating interlayer to be formed in a thermal recording material.

Claims22

Dependent claims

Bowl-shaped polymer particles characterized by having a bowl-like shape as is formed by partly outting along a plane each spherical hollow polymer particle having a void in the inside, and in which the cross-section perpendicular to the cut plane and passing through the center of the particle has a shape as is formed by partly cutting a double circle along a straight line, and the lengths H of the perpendiculars from the outer arc of the double circle in the cross-section to the straight line have a maximum value Hmax equal to or larger than the radius of the outer circle of the double circle.

A process for producing bowl-shaped polymer particles, characterized by comprising the steps of:

(1) copolymerizing a monomer mixture comprising 30 to 65% by weight of an acidic group-containing monomer and 70 to 35% by weight of a monomer copolymerizable therewith to prepare a nucleus polymer particle;
(2) copolymerizing a monomer mixture comprising 10 to 35% by weight of an acidic group-containing monomer and 90 to 65% by weight of a monomer copolymerizable therewith in the presence of the nuclear polymer particle to prepare a core polymer particle substantially surrounding the nucleus polymer particle, wherein the content of the acidic group-containing monomer units in the core polymer particle is equal to or smaller than the content of the acid group-containing monomer units in the nucleus polymer particle;
(3) copolymerizing a monomer mixture comprising 1 to 12% by weight of an acidic group-containing monomer and 99 to 88% by weight of a monomer copolymerizable therewith in the presence of the nucleus/core polymer particle to form at least one intermediate polymer layer which substantially surrounds the nucleus/core polymer particle;
(4) polymerizing an aromatic vinyl monomer alone or copolymerizing a monomer mixture comprising up to 0.5% by weight of an acidic group-containing monomer and at least 99.5% by weight of an aromatic vinyl monomer copolymerizable therewith in the presence of the polymer particle which is prepared in step (3) and comprising the intermediate polymer layer substantially surrounding the nucleus/core polymer particle, to prepare an outer polymer layer which substantially surrounds the polymer particle prepared in step (3);
(5) adding a base to an aqueous dispersion of the polymer particle which is prepared in step (4) and has a multi-layer structure comprising at least four layers, to adjust the pH value of the aqueous polymer dispersion to at least 7;
(6) adding an aromatic vinyl monomer or a monomer mixture comprising at least 90% by weight of an aromatic vinyl monomer and not larger than 10% by weight of a monomer copolymerizable copolymerize the monomer mixture in the presence of the polymer particle with the multi-layer structure, prepared in step (5), to form an outermost polymer layer surrounding the outer polymer layer prepared in step (4);
and then,
(7) drying the thus-prepared aqueous polymer dispersion.

5 more elements

Dependencies are inferred from the claim text.

Bowl-shaped polymer particles, aqueous dispersion of polymer particles, processes for producing these, and thermal recording material

Life of this patent

Bowl-shaped polymer particles, aqueous dispersion of polymer particles, processes for producing these, and thermal recording material

Life of this patent

Abstract

Claims22