Radiation imagery chemistry: process – composition – or product th – Silver halide colloid tanning process – composition – or product
Reexamination Certificate
2001-04-26
2002-07-16
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Silver halide colloid tanning process, composition, or product
C430S204000, C430S227000, C430S264000, C430S525000, C430S935000, C430S276100
Reexamination Certificate
active
06420081
ABSTRACT:
The invention relates to a process for the production of a photosensitive recording material for the production of offset printing plates, having a dimensionally stable, two-dimensional support of a metal or metal alloy, a silver halide-containing, photosensitive layer on the front of the support, and a layer which essentially consists of an organic polymeric material and is resistant to processing chemicals on the back of the support.
If recording materials having a metal support and a silver halide-containing layer are stored one on top of the other, the contact between the silver-containing layer and the metallic back of the recording material on top frequently causes the formation of local elements, resulting in corrosion phenomena. This is the case in particular if the metallic back has scratches. The passivating layer on the aluminium is damaged at these points, and the reactive metal comes into direct contact with the silver-containing layer. In order to prevent this, sheets of paper are generally placed between the individual recording materials. However, the stacks with the light-sensitive materials are increasingly being processed in automatic equipment, in particular automatic plate setters. The separating paper frequently causes faults in the process. Materials which are to be processed in computer-to-plate (CTP) equipment are therefore frequently unstacked in order to remove the paper. However, this means an additional working step. In addition, scratches can very easily occur on removal of the plates from the stack.
In order to avoid these problems, recording materials of the type mentioned at the outset are used. Thus, in accordance with WO 98/47719, a continuous or discontinuous layer of an inert material is applied to Thus, in accordance with WO 98/47719, a continuous or discontinuous layer of an inert material is applied to the back of the support. The weight of this layer is preferably from 0.5 to 2.0 g/m
2
. In the description of GB-A 2,324,381, it is additionally emphasized, as an essential feature, that the silver halide layer is applied to the aluminium support first, before the back coating. However, the process and the products produced thereby are associated with significant disadvantages. For example, excessively high temperatures must not prevail during production of the back coating so as to avoid damage to the light-sensitive layer. However, warming or heating is necessary if the back coating is initially applied as a solution or dispersion and the solvent is then removed by drying. Furthermore, elevated temperatures are necessary if thermally induced crosslinking and thus curing of the back coating is to be achieved. Although curing using UV radiation avoids high temperatures, scattered light can, however, result in partial exposure of the photosensitive layer.
In addition, known problems occur in the recutting of offset printing plates in stacks. The separating paper normally used prevents the aluminium acting as a solid block in the stacks, and in addition the lubricating action of the commercially available separating papers ensure that the cutting tool blades remain sharp for longer. Very thin back layers, as described in GB-A 2,324,381, generally do not exhibit this action, which results in greater wear of the blades in the cutting tools and in addition in unacceptable cutting burrs on the made-up printing plates.
It is likewise not without problems, when a back coating is applied before the silver halide layer, if an aluminium oxide layer is formed as corrosion protection on the back of the support by anodic oxidation. In this case, coating flaws frequently occur on application of the silver halide layer. White spots are then evident on the copying layer. These so-called “horseshoe flaws” make the recording material unusable.
The object was therefore to provide a process which allows the production of light-sensitive recording materials of the type mentioned at the outset, but which overcomes the disadvantages of the known processes. In particular, the aim was to develop processes which involve less restrictive conditions in the production of the back coating and thus allow a broader choice of materials. Under no circumstances should the back coating result in flaws or impairment of the silver halide layer, as was frequently the case in the previous processes. In addition, it should be possible to make up plates in a stack without problems for greater wear of the blades and in particular also without cutting burrs at the edges of the offset printing plates.
It has now been found that said problems can be solved if a layer of an essentially organic, polymeric material is firstly produced on the back of the metallic support and only then is the silver halide layer produced on the front. The problems in re-cutting in the stack can be avoided if the layer thickness of the organic back layer is at least 1.5 g m
−2
, better at least 2 g m
−2
.
The present application accordingly relates to a photosensitive recording material for the production of offset printing plates which comprises a dimensionally stable, two-dimension support of a metal or metal alloy and a silver halide-containing, photosensitive layer on the front of the support and a layer which essentially consists of an organic polymeric material and is resistant to processing chemicals on the back of the support, which is characterized in that the layer on the back of the support is applied before the photosensitive layer on the front. The term “front” here and below always denotes the side of the support on which the silver halide-containing layer is located.
In a preferred embodiment, the layer on the back comprises at least one organic polymer having a glass transition temperature T
g
of 50° C. It is also preferably crosslinked. The crosslinking can be effected here by the action of heat, radiation and/or oxidants.
The back coating generally consists of an organic polymeric material which is virtually insoluble in water and aqueous/alkaline developers. Particularly suitable materials are polyolefins (such as polyethylene, polypropylene, polybutylene, polybutadiene or polyisoprene), polyesters, polycarbonates, polyamides, polysiloxanes, polystyrene, homopolymers or copolymers of or with alkyl acrylate or alkyl methacrylate units (such as polymethyl methacrylate (PMMA) or styrenemethyl methacrylate copolymers), polyvinylacetal, phenoxy resins (for example resins made from bisphenol A and epichlorohydrin), polyvinyl chloride (PVC) or polyvinylidene chloride (PVDC). If necessary, the layer may in addition contain additives in secondary amounts. These include, for example, plasticizers, dyes, pigments, silicone compounds or surfactants. Besides polymeric materials, the layer can also comprise monomeric or oligomeric compounds which polymerize, condense or crosslink under the action of radiation, heat and/or oxidants and thus effect curing of the layer. Particularly suitable for this purpose are addition-polymerizable acrylates or methacrylates, such as ethyl meth(acrylate), propyl (meth)acrylate, butyl (meth)acrylate, 2-hydroxyethyl (meth) acrylate, trimethylolpropane mono-, di- or tri(meth)acrylate or pentaerythritol tri(meth)acrylate. Also suitable are (meth)-acrylamides, such as N-methyl-, N-ethyl-, N-propyl-, N-butyl- or N-isobutyl(meth)acrylamide; furthermore allyl esters, such as allyl acetate; vinyl ethers, such as butyl vinyl ether, octyl vinyl ether, decyl vinyl ether, 2-methoxyethyl vinyl ether, diethylene glycol vinyl ether or benzyl vinyl ether; polyfunctional urethane acrylates which cure under the action of UV radiation, and polyurethanes which cure under the action of heat. In this connection, “(meth)acrylate” means “acrylate and/or methacrylate”. A corresponding situation applies to “(meth)acrylamide” and other derivatives of acrylic and methacrylic acid. The back coating may thus also be light-sensitive. For distinction therefrom, the photosensitive layer on the front of the support is referred to as the “silver halide layer” or “image layer”, since only thi
Coppens Paul
Denzinger Steffen
Dörr Michael
Elsässer Andreas
Agfa-Gevaert
Leydig , Voit & Mayer, Ltd.
Schilling Richard L.
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