Water based photopolymerisable compositions and their use

Claim 2

A composition in the form of an aqueous dispersion comprising water, at least one dispersed cationically curable compound, and a photosensitive onium salt capable on exposure to actinic radiation of effecting cationic polymerisation of the said curable compound.

Claim 3

A composition according to claim 1 in which the curable compound is a mixture of one or more low viscosity epoxy diluents selected from glycidyl ethers, glycidyl acrylates, 4-vinylcyclohexene dioxide, limonene dioxide, 1,2-cyclohexene dioxide and 3,4-epoxycyclohexylmethyl-3,4-cyclohexanecarboxylate, and one or more higher molecular weight epoxy resins.

Claim 4

A composition according to claim 1 or 2 in which the photoinitiator is an iodonium salt of the formula:- where X is tetrafluoroborate, hexafluorophosphate, hexafluoroarsenate, hexafluoroantimonate, trifluoromethanesulphonate, or perchlorate, and R 1 and R 2 are each selected from hydrogen, halogen,straight or branched alkyl, alkoxy, aryl, acyl, nitro or cyano.

Claim 5

A composition according to claim 3 in which the photoinitiator is 4,4-dimethyldiphenyliodonium hexafluorophosphate or diphenyliodonium hexafluorophosphate.

Claim 6

A composition according to claim 1 or 2 in which the photoinitiator is a sulphonium salt of the formula:- where X is tetrafluoroborate, hexafluorophosphate, hexafluoroarsenate, trifluoromethanesulphonate, perchlorate or hexafluoroantimonate, R 3 is a monovalent aromatic radical, which may be substituted by one or more alkyl, aryl, alkoxy, hydroxy, phenoxy, thiophenoxy, mercaptan or acyl groups or halogen atoms, R4is a monovalent organic aliphatic radical selected from alkyl, cycloalkyl and substituted alkyl, R 5 is a polyvalent organic radical + forming a heterocyclic or fused ring structure with S, a is a whole number from 0 to 3 inclusive, b is a whole number from 0 to 2 inclusive, and c is 0 or 1, and a + b + c = 3.

Claim 7

A composition according to claim 5 in which the photoinitiator is a sulphonium salt of the formula:-

Claim 8

A composition according to any one of claims 1 to 6 which also comprises a sensitizer to increase the spectral sensitivity of the photosensitive onium salt.

Claim 9

A composition according to claim 7, in which the said sensitiser is 9,10-diethoxyanthracene or an alkylated 9,10-diethoxyanthracene.

Claim 10

A composition according to any of claims 1 to 8 comprising, by weight of the said composition, 40 - 80% of water, 10-60% of epoxy resin (including reactive diluent), 1 to 10% of onium salt, and 0 to 5% of sensitiser.

Claim 11

A composition according to any of claims 1 to 9 which also comprises a water-soluble colloid and a surfactant as dispersion stabilizers.

Claim 12

A composition according to claim 10 in which the said colloid is polyvinylalcohol, polyvinylpyrrolidone, gelatin, hydroxyethylcellulose or hydroxypropylcellulose, and the said surfactant is a non-ionic surfactant.

Claim 13

A composition according to any one of claims 1 to 11 which also comprises one or more of an inert polymeric filler, an inert inorganic filler, a plasticiser, an organic solvent, a biocide, a defoamer, a pigment, or a dye which may change colour contrast on exposure to actinic radiation.

Claim 14

A composition according to claim 12 in which the said plasticiser is dibutylphthalate.

Claim 15

A composition according to claim 12 or 13, in which the said inert filler is a polyvinylacetate homopolymer, a polyvinylacetate-polyvinylchloride copolymer, starch, silica, kaolin or titanium dioxide.

Claim 16

A composition according to claim 12, 13 or 14 comprising, by weight of the said composition, 50 to 70% of water, 25 to 50% of epoxy resin (including reactive diluent}, 2 to 5% of onium salt, 0 to 3% of sensitiser, 0 to 2% of an inert polymer, 0 to 2% of a surfactant, 0 to 3% of a plasticiser, 4 to 14% of a water-soluble colloid, and 0 to 15% of organic solvent.

Claim 17

A screen for screen printing coated with a composition according to any of claims 1 to 15 and dried.

Claim 18

A method of producing a stencil for screen printing which comprises irradiating a coated screen, as claimed in claim 16, with actinic radiation and then developing the insolubilised image.

Claim 21

A method according to claim 17, 18 or 19 in which the insolubilized image is developed by washing away with water the un-irradiated coating.