Compositions and processes for producing scratch resistant polysiloxane coatings

Claim 2

A prepolymer composition for forming a scratch-­resistant coating, comprising an acidic, aqueous solution of a polysiloxane prepolymer having non-co-reactive side groups and co-reactive side groups other than alkoxy groups or other hydrolysable derivatives thereof, the composition being curable by evaporation of solvent and an increase in pH causing the alkoxy, hydroxy and/or carboxy, and also the co-reactive side groups to react together to cross-link the polymer.

Claim 3

A prepolymer composition according to claim 1 wherein the prepolymer also has alkoxy groups or acid-stabilised hydrolysable derivatives thereof, whereby the curing process involves further formation of siloxane linkages through the interaction of these groups.

Claim 4

A process for producing a polysiloxane prepolymer composition for forming a scratch-resistant coating, which comprises: (i) forming an aqueous acidic solution of two or more silanes or their oligomers, said silanes or oligomers having hydrolysable groups, at least one of the silanes or oligomers having at least one non-coreactive side group, and at least one of the silanes or oligomers having a co-­reactive group other than alkoxy or hydrolysable derivative thereof, and allowing the solution to form siloxane linkages by the interaction of the hydrolysable groups; and (ii) adding at least one further silane or its oligomer which has at least one hydrolysable group and a group which is capable of co-reacting with said co-reactive group in (i) under conditions of lower dilution and increased pH, and allowing the solution to form siloxane linkages between the existing polysiloxane and the added silane or oligomer.

Claim 5

A process for producing a polysiloxane prepolymer composition for forming a scratch-resistant coating, which comprises: (i) forming an aqueous acidic solution of two or more silanes or their oligomers, said silanes or oligomers having hydrolysable groups, at least one of the silanes or oligomers having at least one non-coreactive side group, and at least one of the silanes or oligomers having a co-­reactive group other than alkoxy or hydrolysable derivative thereof, and allowing the solution to form siloxane linkages by the interaction of the hydrolysable groups; and (ii) adding at least one further silane or its oligomer which has at least one hydrolysable group and a group which is capable of co-reacting with said co-reactive group in (i) under conditions of lower dilution and increased pH, and allowing the solution to form siloxane linkages between the existing polysiloxane and the added silane or oligomer.

Claim 6

A process according to claim 3 which includes the further step of (iii) adding further acid to stabilise the prepolymer solution.

Claim 7

A composition or process of any one of the preceding claims wherein the solvent also comprises one or more volatilisable alcohols.

Claim 8

A composition or process according to any one of the preceding claims wherein acidity is provided by the presence of a volatilisable organic acid.

Claim 9

A composition or process according to any one of the preceding claims wherein the non-coreactive side groups are selected from alkyl, aryl, and methacrylic.

Claim 10

A composition or process according to any one of the preceding claims wherein the co-reactive side groups comprise amino and epoxy groups.

Claim 11

A composition or process according to any one of claims 1 to 7 wherein the co-reactive side groups comprise thiol reacting with epoxy, vinyl, acrylic or methacrylic groups.

Claim 12

A composition or process according to any one of the preceding claims wherein at least one of the co-reactive side groups forms part of a larger group in which the co-­reactive group is separated from the silicon atom by a connecting group which has at least one single bond allowing rotation of the co-reactive group.

Claim 13

A composition or process according to claim 10 wherein the connecting group comprises -(CH₂) n - or -(CH₂) n -O-, where n = 1 to 3.

Claim 15

A method according to claim 12 wherein the increase in pH is brought about by using a volatilisable acid in the prepolymer composition, whereby the acid evaporates with the solvent during the curing process.