Tioxide Group, Plc

Gerald K Chip

Alfred Rudin

Hrire Gharapetian

A process for the manufacture of core/shell polymer particles comprises forming a core particle containing acid functionality, a first shell around said core of a copolymer of a nonionic monoethylenically unsaturated aromatic monomer and a copolymerisable polar monomer in an amount of at least 15% by weight of the copolymer and having a solubility in water at 20.degree. C. of at least 1% by weight and a second shell around said first shell of a polymer or copolymer of a nonionic monomer having a solubility in water at 20.degree. C. of less than 1% by weight and swelling the particle with a non-volatile alkali to generate one or more vesicles. Preferably each shell contains a polymer or copolymer of styrene.

Preparation of vesiculated core/shell polymeric particles

Polymer particles or beads for use as opacifiers in paints are described in which a core is provided with a hard sheath and the particle has one or more voids produced by reaction with a non-volatile permanent or fixed base. The sheath is a coploymer of an ethylenically unsaturated aliphatic monomer free of acid groups and at least 2 percent by weight of a soft ester-containing monomer and optionally styrene in an amount of up to 25 mole percent. The core is formed from an ethylenically unsaturated monomer with acid functionality. The sheath polymer has a glass transition temperature of at least 40.degree. C. The particles have a size of up to 40000 nanometers before swelling the core by some 150 to 2000 percent.

Polymeric particles and their preparation

Polymer particles or beads for use as opacifiers in paints are described in which a core is provided with a hard sheath and the particle has one or more voids produced by reaction with a nonvolatile permanent or fixed base. The sheath is a copolymer of an ethylenically unsaturated aliphatic monomer free of acid groups and at least 2 percent by weight of a soft ester-containing monomer and optionally styrene in an amount of up to 25 mole percent. The core is formed from an ethylenically unsaturated monomer with acid functionality. The sheath polymer has a glass transition temperature of at least 40.degree. C. The particles have a size of up to 40000 nanometers before swelling the core by some 150 to 2000 percent.

Swollen core/sheath polymeric particles are disclosed having one or more voids in the core formed by reaction with a base such as sodium hydroxide. The sheath contains styrene or similar monomer polymerized in an amount greater than 25 mole percent and the polymer is free of acid groups. The core contains acid groups. Swelling is effected at an elevated temperature and in the absence of an organic solvent. The swollen particles on drying in a paint or other composition have air in the voids and act then as opacifying agents.

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Scarborough, Canada

Gerald K Chip