EP0022633B1 — Process for making multistage polymer particles, …

Claim 1

Independent Claim 259 words

A process for making an aqueous dispersion of water-insoluble multi-stage polymer comprising (i) sequentially emulsion polymerising at a temperature of 10 to 100°C in an aqueous medium containing free radical initiator (a) at least one monomer charge containing carboxylic acid monomer to thereby form dispersed core particles having an average diameter of 0.05 to 1 micrometer, and encapsulating the resulting core stage(s) by (ii) polymerising thereon (b) at least one subsequent sheath monomer system comprising monoethylenically unsaturated monomer having no ionizable group, to form sheath polymer on the core particles, any monoethylenically unsaturated carboxylic acid in the sheath monomer being present in an amount of no more than 10% by weight of the sheath monomer the proportion of carboxylic acid in the sheath monomer mixture(s) being less than one third of the proportion thereof in the core monomer mixture(s) the resultant core-sheath particles having an average diameter before neutralization and swelling of from 0.07 to 4.5 micrometers the relative amounts of core monomer (a) and sheath monomer (b) being such that the weight ratio of the core stage(s) to the total polymer in the resulting dispersed particles is from 1:4 to 1 :100, said acid stage(s) being swellable upon at least partial neutralisation with volatile base and said encapsulating stage(s) being permeable to volatile base selected from ammonia and amines, the exterior sheath having a T, of greater than 50°C, and (iii) neutralising with ammonia or amine so as to swell the core and form particles which when dried contain a single void; the particles being non-film-forming at 20°C.

Claim 2

Dependent Claim 259 words

A process for making an aqueous dispersion of water-insoluble multi-stage polymer comprising (i) sequentially emulsion polymerising at a temperature of 10 to 100°C in an aqueous medium containing free radical initiator (a) at least one monomer charge containing carboxylic acid monomer to thereby form dispersed core particles having an average diameter of 0.05 to 1 micrometer, and encapsulating the resulting core stage(s) by (ii) polymerising thereon (b) at least one subsequent sheath monomer system comprising monoethylenically unsaturated monomer having no ionizable group, to form sheath polymer on the core particles, any monoethylenically unsaturated carboxylic acid in the sheath monomer being present in an amount of no more than 10% by weight of the sheath monomer the proportion of carboxylic acid in the sheath monomer mixture(s) being less than one third of the proportion thereof in the core monomer mixture(s) the resultant core-sheath particles having an average diameter before neutralization and swelling of from 0.07 to 4.5 micrometers the relative amounts of core monomer (a) and sheath monomer (b) being such that the weight ratio of the core stage(s) to the total polymer in the resulting dispersed particles is from 1:4 to 1 :100, said acid stage(s) being swellable upon at least partial neutralisation with volatile base and said encapsulating stage(s) being permeable to volatile base selected from ammonia and amines, the exterior sheath having a T, of greater than 50°C, and (iii) neutralising with ammonia or amine so as to swell the core and form particles which when dried contain a single void; the particles being non-film-forming at 20°C.

Claim 3

Dependent Claim 31 words

A process according to claim 1 wherein the sheath monomer mixture(s) form a sheath which is impermeable at 20°C to fixed or permanent bases including sodium, potassium, calcium and magnesium hydroxides.

Claim 4

Dependent Claim 27 words

A process according to claim 1 or 2 wherein at least about 85% of the core particles are encapsulated as evidenced by titration with aqueous potassium hydroxide.

Claim 5

Dependent Claim 132 words

A process according to any preceding claim in which the formation of dispersed core particles in (a) is a multistage process involving first the preparation of seed polymer from monoethylenically unsaturated monomer which may or may not comprise monomer containing an acid group, and a second stage polymerization, on the seed particles, of ethylenically unsaturated monomer comprising (1) 5 to 100 weight % of carboxylic acid, (2) 0 to 95 weight % of monoethylenically unsaturated monomer lacking an ionizable group, and (3) 0 to 20 weight % of polyethylenically unsaturated monomer, using conditions to obtain core polymer particles having an average diameter of from 0.1 to 0.5 micrometer in unswollen condition, and the subsequently polymerised sheath provides core/sheath particles having an average diameter of up to about 2.0 micrometers in unswollen condition.

Claim 6

Dependent Claim 42 words

A process according to any preceding claim in which the core/sheath particles have an average diameter of from 0.2 to 2.0 micrometers in unswollen condition and in which 0.1% to 3% of polyunsaturated crosslinking monomer is included in the core monomer mixture.

Claim 7

Dependent Claim 55 words

A process according to any preceding claim in which, after the formation of the exterior sheath in (b), a outer layer of relatively softer polymer, of monomer selected to provide a polymer having a T ; of less than 50°C and at least 10°C lower than that of the hard exterior sheath polymer, is applied.

Claim 8

Dependent Claim 94 words

A process according to any preceding claim in which, the formation of the sheath is a multi- stage formation in at least one stage of which crosslinked polymer is formed from a mixture of monoethylenically unsaturated monomer and polyethylenically unsaturated monomer, the amount of the latter being 1 % to 50% by weight of the mixture, the core/sheath polymer being swollen by at least partial neutralization by application of volatile base prior to the completion of the crosslinking stage when the amount of polyethylenically unsaturated monomer exceeds 5% by weight of the monomer mixture.

Claim 9

Dependent Claim 128 words

A multi-stage polymer such as obtained by a process according to claim 1 having at least one core stage polymerized from monomer comprising carboxylic acid monomer and at least one subsequent stage substantially encapsulating said acid-containing stage(s) in a weight ratio in unswollen condition of core stage(s) to total polymer of 1:4 to 1 :100, said acid stage(s) being swellable upon neutralisation with volatile base and said encapsulating stage(s) being permeable to said base, the exterior sheath having a T ; of greater than 50°C and the particles being non-film-forming at 20°C and either being capable, on neutralisation with ammonia or amine so as to swell the core and subsequent drying of formation of a single void or, having been so neutralised and dried, containing a single void.

Claim 10

Dependent Claim 114 words

A composition comprising an aqueous dispersion of particles of water-insoluble core/sheath polymer according to claim 8 having an average diameter of 0.07 to 4.5 micrometers, having a core polymerised from one or more monoethylenically unsaturated monomers having a group of the formula -HC=C<, at least one of said unsaturated monomers having a carboxylic acid group, and at least one encapsulating stage (a) having a T ; greater than 50°C (b) being non-film-forming at 20°C (c) being permeable to ammonia and amines, (d) being substantially impermeable at 20°C to fixed or permanent bases including sodium, potassium, calcium and magnesium hydroxides, said core being swollen by neutralisation with ammonia or amine in the presence of water.

Claim 11

Dependent Claim 58 words

The use of an aqueous dispersion of polymer particles of claim 8 or an aqueous dispersion of claim 9 or the product of a process of any of claims 1 to 7 in a mixture with an aqueous dispersion of a particulate material selected from pigments, extenders, vinyl addition emulsion polymers, and mixtures thereof as a coating composition.

Claim 12

Dependent Claim 50 words

The use according to claim 10 in which a film of the coating composition is deposited on a solid substrate to be coated and/or impregnated, and the composition is subsequently dried, so forming single cavities in the cores of particles therein so as to contribute to opacity of said film.

Claim 13

Dependent Claim 59 words

The use of an aqueous dispersion of water-insoluble core/sheath polymer particles of claim 8 or an aqueous dispersion of claim 9 or a product of a process of any of claims 1 to 7 in a composition for coating and/or impregnating a substrate which composition also comprises film-forming vinyl addition polymer either dissolved or dispersed in an aqueous medium.

Claim 14

Dependent Claim 58 words

The use of core/sheath product produced by the process of claim 6 in a composition for coating and/or impregnating, admixed, at a pigment volume concentration of 5 to 50%, or higher, with an aqueous dispersion of water-insoluble emulsion vinyl addition polymer having an apparent second order transition temperature (T,) of 17 to 20°C, inorganic pigment and optionally extender.

Claim 15

Dependent Claim 24 words

An opaque composition comprising swollen and subsequently dried particles of polymer of claim 8 or 9 having a single cavity in the core thereof.

Process for making multistage polymer particles, product thus obtained, process for making aqueous dispersions of these particles, product thus obtained, process for making films, compositions for coating and/or impregnating, multistage polymers and their use

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