Photosolubilisable compositions

Claim 2

A radiation-sensitive composition comprising an alkali-soluble phenolic resin and a radiation-sensitive onium salt, characterised in that the composition is yhotosolubilisable.

Claim 3

A radiation-sensitive composition as claimed in Claim 1, characterised in that the onium salt is selected from iodonium, sulphonium, phosphonium, bromonium, chloronium, oxysulphoxonium, oxysulphonium, sulphoxonium, selenonium, telluronium and arsonium salts.

Claim 4

A composition as claimed in Claim 1 or Claim 2, characterised in that the resin is a novolac resin and the onium salt is present in an amount from 1 to 40% by weight of the total weight of phenolic resin and onium salt.

Claim 5

A composition as claimed in Claim 1 or Claim 2, characterised in that the resin is a resole resin and the onium salt is present in an amount from 5 to 40% by weight of the total weight of phenolic resin and onium salt.

Claim 6

A composition as claimed in any preceding claim, characterised in that the onium salt has one of the following formulae: in which. at least one of R 1 , R 2 and R 3 is an optionally substituted aromatic group, Q is a carbon-to-carbon bond or a linking group selected from O, S, > S=O, > C=O, or > N-R 6 , in which R 4 and R 5 are independently selected from H, an alkyl group having from 1 to 4 carbon atoms, and an alkenyl group having from 2 to 4 carbon atoms, and R 6 is an aryl group having from 6 to 20 carbon atoms or an acyl group having from 2 to 20 carbon atoms; and X⊖ is an anion, in which: Ar l and Ar 2 independently represent aromatic groups which are optionally substituted and optionally linked together to include the iodine atom within a ring structure; and X⊖ represents an anion, in which R 1 to R 3 are as defined above, with the exception that each of R 1 to R 3 may represent optionally substituted aliphatic groups, in which R l to R 3 are as defined above, with the exception that each of R 1 to R 3 may represent optionally substituted aliphatic groups, in which R l to R 3 are as defined above, with the exception that each of R l to R 3 may represent optionally substituted aliphatic groups, and a polymer including the monomeric units of the formula: in which X⊖ is an anion.

Claim 7

A composition as claimed in Claim 5, characterised in that the anion is selected from halide, H 2 SO 4 ⊖; R 8 CO 2 ⊖, in which R 8 represents an optionally substituted alkyl or phenyl group, and a halogen-containing complex ion.

Claim 8

A composition as claimed in any preceding claim, additionally comprising a spectral sensitiser in an amount up to 10% by weight of the total weight of phenolic resin, onium salt and spectral sensitiser.

Claim 9

composition as claimed in Claim 7, characterised in that the spectral sensitiser is selectea from one of the following classes diphenylmethane, xanthene, acridine, methine and polymethine (incluaing oxonol, cyanine and merocyanine) dye, thiazole, thiazine, azine, aminoketone, porphyrin, coloured aromatic polycyclic hydrocarbon, p-substituted aminostyryl compound, aminotriazyl methane, polyarylene, polyarylpolyene, 2,5-diphenylisobenzofuran, 2,5-diarylcyclopentadiene, diarylfuran, diarylthiofuran, diarylpyrrole, polyarylphenylene, coumarin and polyaryl-2-pyrazoline.

Claim 10

A composition as claimed in Claim 7 or b, characterised in that the spectral sensitiser has the formula: or in which: R 7 represents an alkyl group of 1 to 6 carbon atoms, Y⊖ represents 4-perfluoroethylcyclohexyl- sulphonate or ClO 4 ⊖, and p is 1 or 2.

Claim 11

A composition as claimed in any preceding claim, additionally comprising an amine in an amount up to 25% by weight of the total weight of phenolic resin, onium salt and amine.

Claim 12

A composition as claimed in Claim 10, characterised in that the molar ratio of amine to onium salt is approximately 1:1.

Claim 13

A composition as claimed in any one of Claims 10 or 11, characterised in that the amine is tri-n-butylamine or bis(4-dimethylaminophenyl)methane.

Claim 14

A radiation-sensitive element comprising a layer of the composition of any one of the preceding claims coated on a substrate.

Claim 15

An element as claimed in Claim 13, characterised in that the substrate is paper, aluminium, copper, copper-epoxy laminated board, polyester film or silica.

Claim 16

A method of producing a lithographic image on an element as claimed in Claim 13 or Claim 14 comprising image-wise exposing said element to actinic radiation, and developing the plate with an alkali-based developer so that the composition is removed in the irradiated areas thereby producing said image.

Claim 17

A method of producing a lithographic image on an element as claimed in Claim 13 or Claim 14 comprising image-wise exposing said element to actinic radiation, heating the element so as to convert the coating in the irradiated areas to a form insoluble to alkali, further exposing the element overall to actinic radiation so that areas not previously exposed are rendered alkali-soluble, and developing the element with an alkali-based developer so that the coating is removed from those areas of the element rendered soluble by said further exposure thereby producing said image.

Claim 18

A method as claimed in Claim 15 or Claim 16, characterised in that the developer is aqueous sodium metasilicate.