Preparation of sequential polymers and use thereof in coating compositions and as thickening agents

Claim 2

A process for making an aqueous dispersion of water-insoluble multi-stage polymer comprising sequentially polymerising (a) at least one monomer charge containing carboxylic acid monomer and encapsulating the resulting stage(s) by polymerising (b) at least one subsequent stage thereon, the encapsulation being such as to give a titer of said polymerised acid with aqueous alkali metal hydroxide for less than 50% thereof thereby indicating more than 50% encapsulation, said acid stage(s) being swellable upon at least partial neutralisation with volatile base and said encapsulating stage(s) being permeable to volatile base, the exterior sheath having a T i of below 50°C and the particles being film-forming,

Claim 3

A process according to claim 1 of making an aqueous dispersion of water insoluble core/sheath polymer particles in which the core contains sufficient acid groups to render the core swellable by neutralisation with a volatile base to at least twice its volume and the sheath is permeable to said base, comprising (a) sequentially emulsion polymerizing, at a temperature of from 10° to 100 0 C. in an aqueous medium containing a free radical initiator: monoethylenically unsaturated monomer having a group of the formula -HC= C <, at least one of which has a carboxylic acid group, emulsified in the medium, the monomer comprising as hydrophilic monomer, (i) non-acid monomer copolymerised with at least 5% of carboxylic acid monomer, or (ii) 15-100% of acid monomer when no other hydrophilic monomer is present, based on the weight of the monomer utilized to prepare the core polymer particles, to thereby form dispersed core polymer particles, said core particles having an average diameter of 0.05 to 1 micron, the core monomer having no more than 40% of butyl acrylate or no more than an amount of an equivalent monomer which would give a comparable T i when using the same comonomer combination, and (b) then adding to the polymer dispersion resulting from a) monoethylenically unsaturated sheath 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 total sheath monomer, the proportion of carboxylic acid in the sheath monomer being less than 1/3 the proportion thereof in the core monomer, the core/sheath particles having an average diameter, before neutralisation and swelling, of 0.07 to 4.5 microns, the relative amounts of core-forming monomer and sheath forming monomer being such that the ratio of the weight of the core to the weight of the total polymer in the resulting dispersed particles is 1:4 to 1:100, said sheath being permeable at 20 0 C to aqueous volatile base selected from ammonia and amines, and substantially impermeable at 20°C. to fixed or permanent bases including sodium, potassium, calcium or magnesium hydroxide, the exterior sheath having a T i of below 50°C., the particles being film-forming; (c) neutralising with ammonia or amine so as to swell said core.

Claim 4

A process according to claim 2 wherein the acid in a) comprises acrylic acid, methacrylic acid, acryloxypropionic acid,methacryloxypropionic acid, acryloxyacetic acid, methacryloxyacetic acid, monomethyl acid maleate, monomethyl acid itaconate and/or crotonic acid.

Claim 5

A process according to claim 2 or 3 wherein the acid in a) is acrylic acid and/or methacrylic acid, and the core monomer comprises at least 15% of said acid monomer, the core monomer containing no more than 40% of butyl acrylate or no more than an amount of an equivalent monomer which would give a comparable T i when using the same comonomer combination.

Claim 6

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

Claim 7

A process according to any of claims 2 to 5 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 polymerisation 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, thereby obtaining said core particles a) and in which the core particle average diameter is 0.1 to 0.5 microns in unswollen condition, and the subsequently polymerised sheath particles have an overall size of up to 2.0 microns in unswollen condition.

Claim 8

A process according to claim 6 in which the acid is acrylic acid, methacrylic acid, acryloxypropionic acid, methacryloxypropionic acid, acryloxyacetic acid, methacryloxyacetic acid, monomethyl acid maleate, monomethyl acid itaconate and/or crotonic acid, and the core monomer comprises at least 15% of said acid.

Claim 9

A process according to claim 7 in which the acid is selected from the group consisting of acrylic acid, methacrylic acid, and mixtures thereof, said exterior sheath being film-forming under conditions of use, and the core/sheath particles have an average diameter of from about 0.2 to about 2.0 microns in an unswollen condition, in which 0.1% to 3% of a polyunsaturated crosslinking monomer is included in the core monomer mixture.

Claim 10

A process according to any of claims 2 to 8 in which the formation of the sheath in b) is a multistage process.

Claim 11

A process according to any preceding claim in which the exterior sheath monomers consist of those which are monoethylenically unsaturated whereby said exterior sheath is not crosslinked.

Claim 12

A multi-stage polymer having at least one stage polymerized from monomer comprising carboxylic acid monomer and at least one subsequent stage encapsulating said acid-containing stage(s) as evidenced by titration of said polymerised acid with aqueous alkali metal hydroxide providing a titer for less than 50% of the acid, thereby indicating more than 50% encapsulation, said acid stage(s) being swellable upon at least partial neutralisation with volatile base and said emcapsulating stage(s) being permeable to said base, the exterior sheath having a T i of below 50°C and the particles being film-forming.

Claim 13

A multi-stage polymer having at least one stage polymerized from monomer comprising carboxylic acid monomer and at least one subsequent stage encapsulating said acid-containing stage(s) as evidenced by titration of said polymerised acid with aqueous alkali metal hydroxide providing a titer for less than 50% of the acid, thereby indicating more than 50% encapsulation, said acid stage(s) being swellable upon at least partial neutralisation with volatile base and said emcapsulating stage(s) being permeable to said base, the exterior sheath having a T i of below 50°C and the particles being film-forming.

Claim 14

A polymer as claimed in claim 11 wherein the degree of encapsulation is at least 85%.

Claim 15

A product according to claim 11 or 12 or obtained by the process of any of claims 1 to 10 when used as a thickening agent in an aqueous medium containing sufficient volatile base to at least partially neutralize the product to a pH of at least 6.

Claim 16

A process which comprises mixing an aqueous core/sheath heteropolymer dispersion obtained by a process according to any of claims 1 to 10 or a dispersion of polymer particles of claim 11 or 12 with a dispersion of a particulate material selected from pigments, extenders, vinyl addition emulsion polymers, and mixtures thereof to form a coating composition, adding a volatile basic swelling agent to raise the pH of the composition to 6 to 10 or higher, thereby at least partially neutralising the acid of the cores and swelling the heteropolymer cores.

Claim 17

A process according to Claim 14 which comprises the further step of depositing a film of the coating composition on a solid substrate to be coated and/or impregnated and subsequently drying the film.

Claim 18

A composition for coating/or impregnating a substrate comprising a core/sheath polymer according to claim 11 or 12 or prepared according to any of claims 1 to 10 in which the core/sheath polymer is in swollen condition by virtue of neutralisation with a volatile base.

Claim 19

A composition for coating or impregnating a substrate comprising (1) a film-forming vinyl addition polymer either dissolved or dispersed in an aqueous medium and (2) a core/sheath particulate polymer dispersion prepared by a process according to any of claims 1 to 10 or a dispersion of polymer particles of claim 11 or 12.

Claim 20

A composition according to claim 17 comprising an aqueous dispersion of a water-insoluble emulsion vinyl addition polymer, the core/sheath polymer, inorganic pigment and optionally an extender.

Claim 21

A composition or product according to any of claims 13 and 15 to 18 in which the exterior sheath of the core/sheath product has a T. of -40°C to +23°C.