Abstract: Photopolymerizable polyvinyl alcohols including a group of formula ##STR1## wherein R.sub.1 represents a substituted or unsubstituted alkyl group, a substituted or unsubstituted aralkyl group, or a hydrogen atom; R.sub.2 represents a substituted or unsubstituted alkyl group, a primary, secondary or tertiary amino group, a cyano, hydroxy or nitro group, a halogen or hydrogen atom or, together with the pyridine ring to which it is attached, part of a quinolyl group; R.sub.3 represents a chlorine or hydrogen atom or, together with the benzene ring to which it is attached, part of a naphthyl group; and X.sup.- represents an anion, and photocurable compositions for producing screen printing stencils including such polyvinyl alcohol derivatives. Compositions of the invention show high light sensitivity with low levels of photocrosslinkable groups grafted to the polyvinyl alcohol.

Abstract: This invention relates to compositions for forming opaque, abrasion-removable masks on substrates. The compositions, which include a texture modifying amount of solid or hollow microspheres, have enabled depression or embossing of the surface of the printed substrates to be obscured so that they cannot be seen by the naked eye. The compositions can be based on plastisols, pigmented polymer solution, or pigmented aqueous emulsions. The invention further provides substrates, for example lottery tickets, having abrasion-removable masks formed from compositions of the invention.

Abstract: The invention provides new compositions which change color on exposure to actinic radiation and contain a photosensitive onium, e.g. iodonium or sulphonium, salt and a dyestuff which changes color when protonated. The compositions may also include a resin, especially a resin curable by the onium salt when the latter is exposed, and preferably an epoxy resin. The compositions are useful especially as coatings, e.g. for making screen stencils or for producing lithographic printing plates.

Abstract: The invention provides photosensitive compositions useful in the production of screen printing stencils which comprise, in addition to the usual ingredients, also an indicator to show when a layer formed from the said composition has been isolubilized by exposure to actinic light.

Abstract: Aqueous dispersions comprising water, a cationically curable compound, and a photosensitive onium salt, and preferably other ingredients such as sensitizers, fillers, and plasticizers, are useful for making printing screens, lithographic plates, and printed circuit resists. After exposure, the un-cured composition is easily removed by washing with water.

Abstract: Aqueous compositions useful in making stencils for screen printing comprise a solution of an unsaturated prepolymer dispersed in an aqueous solution of a colloid, and a photo-initiator. Such compositions may be coated on suitable support sheets to produce photosensitive sheets useful for making stencils for screen printing by the direct, indirect, or direct/indirect methods.

Abstract: Aqueous compositions useful in making stencils for screen printing by the direct, indirect or direct/indirect method comprise a photopolymerizable monomer, a water-insoluble photoinitiator, a tertiary amine accelerator, a water-soluble colloid, water, and a water-miscible organic solvent.

Abstract: The invention provides novel thioxanthone photoinitiators having the formula: ##STR1## wherein R.sub.1 alkyl, alkoxy, alkylthio, halogeno, nitro, amino, alkyl-amino, di-alkyl-amino, hydroxy alkyl-amino, alkanoylamino, benzoylamino, N-alkanoyl-N-benzoyl-amino, sulphonamido, or acetyl, R.sub.2 is alkylene, A is --COOH, --SO.sub.3 H, --OSO.sub.3 H, or --O--CO--X--COOH (where X is such that HO--CO--X--COOH is a di- or tri-carboxylic acid of up to 8 carbon atoms), n is 0, 1, or 2 and m is 1 or 2, provided that when A is --COOH, m is 2, the aforesaid alkyl, alkoxy, alkanoyl, and alkylene residues containing up to 4 carbon atoms each, as the free acid or as a salt thereof. The photoinitiators may advantageously be used in water-based photopolymerizable compositions, e.g. for use in screen stencil production.

Abstract: Aqueous compositions useful in making stencils for screen printing comprise one or more unsaturated monomers, a tertiary amino compound, a colloid, and a water-soluble, carboxy- or sulpho-alkyleneoxy-thioxanthone photoinitiator. When coated on to a suitable support sheet and dried, photosensitive sheets are obtained useful for making stencils for screen printing by the direct, indirect, or direct/indirect methods.