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

摘要

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.