Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2000-07-17
2003-06-10
Ashton, Rosemary (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S281100, C430S286100, C430S176000, C524S425000, C525S057000
Reexamination Certificate
active
06576396
ABSTRACT:
The present invention relates to a dispersed coloured pigment and a photosensitive mixture containing the dispersed coloured pigment. The present invention also relates to a photosensitive recording material comprising a support and a layer of the mixture. The recording material is meant in particular for the preparation of lithographic printing plates.
Recording materials comprising a coloured photosensitive layer are known. As a result of the colouring, coating defects that may arise in the preparation of the materials are more readily identifiable. The visibility of the image arising in development is also better. (Insoluble) coloured pigments are generally used for the colouring, but not (soluble) dyes. Dyes almost always influence photoreactions that take place during the image-wise exposure of the recording material, and consequently give rise to an undesirable change in sensitivity. Coloured pigments, on the other hand, largely behave inertly and do not change the sensitivity. Their proportion in the photosensitive layer is therefore not particularly limited either and may vary within wide limits. However, if they are dispersed, together with the other constituents of a photosensitive mixture, in an organic solvent, they tend to agglomerate, leading to coating defects. The pigments are frequently also precipitated out of the coating liquid and form a sediment. The coating liquids are then only stable for a very short time and have to be processed almost immediately. In order to improve storage stability, the pigments according to WO 82/02780 are dispersed with substantially amorphous polyesters, which contain anionic groups. The viscosity of the pigment dispersion is additionally reduced by the dispersion with the polyesters. However, the anionic groups also give rise to increased solubility in water. Printing plates that contain such dispersed pigments in their printing layer therefore show a reduced print run, especially in wet offset printing.
The object of EP-A 695 971 is a photosensitive recording material for the preparation of lithographic printing plates, the photosensitive layer of which contains a coloured pigment dispersed in a polymerisable compound. Dispersion of the pigment takes place in the presence of a polymer containing (at least) one aliphatic double bond in the main chain or side chain, for example of an allyl methacrylate/methacrylic acid copolymer. Higher sensitivity of the recording material is additionally to be achieved by dispersion containing the special polymer. However, the said polymers are generally less stable in storage and only sufficient in highly alkaline (pH 12.5) aqueous developers, but still not readily soluble. As they are in addition relatively soft, they are not particularly suitable for long-run printing plates.
The recording material developable with water according to EP-A 738 931 contains in the photosensitive layer a polyvinyl alcohol, a diazo compound or a diazonium salt, a cationic surfactant and a metal-free phthalocyanine pigment. The pigment is pre-dispersed in water or an aqueous solvent mixture in the presence of the cationic surfactant and the polyvinyl alcohol. In order to prepare the recording material, the pre-dispersed pigment is then mixed with the diazo compound or the diazonium salt and further polyvinyl alcohol, applied to a support in the form of a thin layer and the layer is dried. In coating mixtures not based on water but on organic solvents, however, the pre-dispersed pigments according to EP-A 738 931 are not stable. They form precipitations or even prove to be completely insoluble.
The pigments which are used in the positive- or negative-working, photosensitive mixture according to EP-A 519 591 are dispersed with acid-modified polyvinyl acetals. The mixture is primarily envisaged for the preparation of colour proofs. It is less suitable for the preparation of printing plates. The plates do not achieve a sufficient print run, and tone-value stability is also poor.
Pigment dispersions and negative-working, photosensitive mixtures produced therewith are disclosed in EP-A 778 497. The pigments are in particular copper phthalocyanines. They are dispersed in a solvent mixture which comprises an aliphatic (C
1
-C
8
) alcohol, a (C
1
-C
8
) alkylene-glycol-mono- or di-(C
1
-C
8
) alkyl ether or a cyclic ketone. The dispersion takes place with a polymer, which for its part was obtained by the conversion of a polymer containing a hydroxyl group with a di- or polycarboxylic anhydride in the presence of a tertiary amine acting as a catalyst. Preferred hydroxyl group-containing polymers are those having vinyl alcohol groups. The photosensitive component is a diazonium salt polycondensation product or a combination of a polymerisable compound with a photoinitiator. As a result of the pigment dispersion, the image areas stand out with high contrast from the non-image areas, in which the layer was removed in development. However, in photopolymer systems the pigment dispersions are frequently not sufficiently stable. In addition, they cannot meet the requirements for good solubility in the developer and long print run at the same time. If the print run is sufficient, the solubility in the developer is so low that deposits form and vice-versa.
Dispersions have also long been known which were prepared by mixing a coloured pigment with a polyvinyl acetal in the melt, extruding the melt and then pulverising. The powders obtained can be readily redispersed in alcohols, ketones or ethers. The dispersions also remain stable if alkyl acrylate polymers and monomers as well as initiators are added. However, the pigment dispersions are only poorly soluble in aqueous-alkaline developers. There they very rapidly form tacky, insoluble residues.
Water-dispersible graft polyvinyl acetals and their use as dispersing agents are described in EP-A 482 517. In the graft polyvinyl acetals, polyvinyl alcohols are grafted onto a polyalkylene oxide or polyurethane base. Pigment dispersions prepared therewith can be readily processed in alcoholic and aqueous media and have only a slight tendency towards the formation of insoluble deposits in aqueous-alkaline developers. Printing plates that contain these pigment dispersions in the printing layer, however, show reduced printing stability. The ink-accepting printing layer is worn relatively rapidly, so that only a short print run can be achieved.
Surfactants are frequently added in the dispersion of the pigments. However, pigments have also been developed with which surfactant-free pigment dispersions can be prepared. In EP-A 594 026 vinyl acetal copolymers are disclosed which as well as the monomer units of vinyl acetal also contain units of monomers having alkaline metal, alkaline-earth metal or ammonium sulphonate groups. Their use in photosensitive layers, photoprinting plates or photoresists is also described. Dispersions prepared with these copolymers are stable in aqueous media; on the other hand in non-aqueous media incompatibilities with other constituents of photosensitive mixtures occur more frequently. However, the stability of offset printing plates prepared with these pigment dispersions and their print run are generally not sufficient.
A photoresist mixture with which colour filters for liquid-crystal displays can be produced is disclosed in EP-A 725 285. Besides other constituents, it contains a polymerisable acrylate compound, a photopolymerisation initiator and a coloured pigment, which is dispersed with a polyamine, a polyacrylate, a polyurethane, a polycaprolactam, a long-chain alkyl polyaminoamide, a polyisocyanate and/or a polyester. Layers of this mixture are light-fast, thermally stable, allow high resolution and also adhere well to the substrate. However, they are not suitable for the production of printing plates, as their printing stability is too low.
Therefore, there is still a need for a pigment dispersion that is stable and does not form any deposits during storage. The pigment dispersion is to be evenly distributed in photosensitive mixtures, particularly photop
Konrad Klaus-Peter
Leichsenring Thomas
Lifka Thorsten
Pink Armin
Schlosser Hans-Joachim
Agfa-Gevaert
Ashton Rosemary
Connolly Bove & Lodge & Hutz LLP
Thornton Yvette C.
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