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
2000-01-21
2003-11-18
Reddick, Judy M. (Department: 1713)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C428S409000, C428S500000, C428S522000, C428S473500, C430S273100, C430S281100, C430S283100, C430S284100, C430S285100, C430S286100, C430S302000, C525S057000
Reexamination Certificate
active
06649323
ABSTRACT:
Water-soluble polymers are used as temporary coatings on organic light-sensitive substrates, for example in the manufacture of lithographic printing plates, letterpress plates, litho plates for screen printing, printed boards and in etching molded parts and the like.
In the above-mentioned uses, the water-soluble polymers have the function of protecting the substrate from aerial oxygen during storage, exposure and in particular during the time between exposure and further processing (development and the like). During that time period the temporary coating has to exhibit a sufficient adhesion to the light-sensitive substrate so that safe handling (manufacture, packing, transport, exposure etc.) is guaranteed without tearing of the layers. On the other hand, the temporary layer has to be easy to remove prior to the development, preferably by washing with water.
A great number of water-soluble polymers was tested in practice. It was found that polymers such as polyvinyl alcohol, partly saponified polyvinyl acetate which can also contain vinylether and vinylacetal units, polyvinyl pyrrolidone and copolymers thereof with vinyl acetate and vinyl ethers, hydroxy alkyl cellulose, gelatin, polyacrylic acid, gum arabic, polyacryl amide, dextrin, copolymers of alkylvinyl ethers and maleic acid anhydride as well as water-soluble high molecular polymers of ethylene oxide having molecular weights of above 5,000 are particularly suitable. This is due to the low oxygen permeability of these polymers, cf. measured values in K. Petrak, E. Pitts, J. Appl. Polym. Sci. 25 (1980) pages 879-886. Polyvinyl alcohol is mentioned as being particularly suitable.
However, many of the polymers prove to be insufficient regarding their adherence to organic, light-sensitive substrates. For example, polyvinyl alcohol layers can easily be removed over large areas by means of adhesive tapes, or in cutting substrates coated with polyvinyl alcohols the water-soluble protective coating often peels off at the edges of the cut.
Furthermore, it was found that some water-soluble polymers used as overcoats affect certain properties of the light-sensitive layers. These properties include light-sensitivity, resolution, thermal stability in storage and the influence on the ability to take on colors when the light-sensitive layer is used as a printing plate.
Therefore, many tests were carried out in order to improve the properties of the water-soluble protective layers on organic light-sensitive substrates.
In practice, polyvinyl alcohol is often used in combination with polyvinyl pyrrolidone as adhesive. However, adhesion is low if low amounts of polyvinyl pyrrolidone are used and if higher amounts of polyvinyl pyrrolidone are used in order to guarantee a sufficient degree of adhesion, the impermeability and light-sensitivity of the layers are reduced.
U.S. Pat. No. 3,458,311 describes the coating of the water-soluble overcoat in the presence of a solvent miscible with water for the provision of adhesion. However, improved adhesion can only be achieved to a minor extent since in the case of the required high contents of solvents, components of the light-sensitive layers are easily removed which considerably impairs the function of this layer.
U.S. Pat. Nos. 4,072,527 and 4,072,528 disclose that in addition to the overcoat polymers dissolved in water, water-insoluble polymers are dispersed. However, the overcoats produced therefrom have the disadvantage that their removability in particular in water or aqueous developers is reduced. Furthermore, the shelf life and the impermeability to aerial oxygen are reduced.
In EP-A-275 147 amphoteric compounds are described as additives to water-soluble layers. However, the adhesion of the overcoats prepared in this manner is too low.
In EP-A-403 096 overcoats are described which contain a maximum of 20 wt.-% of photo initiators. According to this process, however, only water-soluble initiators can be introduced into the overcoat. Furthermore, the adhesion and thermal stability of the systems are not improved.
A similar situation arises when antihalation dyes are introduced into the overcoat according to EP-A-354 475 or polymerization inhibitors according to EP-A-465 034. The slightly improved sharpness of the layers is achieved while the light-sensitivity of the layers is reduced and the poor adhesion of the overcoats remains the same.
EP-A-352 630 describes the combination of a water-soluble polymer having a low aerial oxygen permeability and an aerial oxygen-binding water-soluble polymer. In this patent application, polymers with aliphatic amino groups, preferably of the polyalkyleneimine-type, are mentioned as aerial oxygen-binding polymers. However, such combinations prove to be unsuitable for practical use since this type of amino group-containing polymer exhibits a strong tendency to absorption at the surface of the photopolymer. Therefore, the surface of the photopolymer remains hydrophilic even after the developments which results in a poor ink receptivity in the printing process.
It is the object of the present invention to provide novel water-soluble layers which not only exhibit favorable oxygen-impermeability properties but also an improved adhesion to organic substrates.
Another object of the invention is the use of such water-soluble layers as oxygen-impermeable overcoats on light-sensitive compositions.
In particular, it is the object of the present invention to apply the water-soluble layers as temporary oxygen-impermeable overcoats on light-sensitive printing plate layers and at the same time to obtain a high degree of light-sensitivity of these materials independent of the external air pressure, a high resolution and a high degree of storage stability in combination with a favorable ink receptivity after the developing step.
According to the invention, this object is achieved by the use of water-soluble layers containing polyvinyl alcohol and either poly(1-vinylimidazole) (in the following referred to as PVI) or a copolymer of 1-vinylimidazole and at least one further monomer (in the following referred to as PVI copolymer). Among the PVI copolymers, those are preferred which comprise 10 to 98 mol-% 1-vinylimidazole.
The particular advantage of the overcoats according to the present invention is their extremely good adhesion to organic substrates. This adhesion is especially strong when the organic substrates contain polar groups such as carboxyl groups. The good adhesion of the overcoats on organic substrates is above all due to the content of 1-vinylimidazole units.
It was found that, contrary to many other additives to polyvinyl alcohol layers, large amounts of PVI or PVI copolymer can be used without entailing disadvantages for other properties of the layer (in particular the oxygen impermeability). This finding is all the more surprising because poly(1-vinylimidazole) by itself shows a high degree of oxygen permeability cf. measured values in K. Petrak, E. Pitts, J. Appl. Polym. Sci. 25 (1980) pages 879-886. Furthermore, layers consisting of polyvinyl alcohol and PVI or PVI copolymer show an extraordinarily good adhesion to organic light-sensitive compositions. During the developing step of the light-sensitive systems, the layers are removed residue-free with water or aqueous developing solutions so that e.g. no negative properties such as impaired ink receptivity are entailed if the processed layers are used as printing molds.
The concentration of the PVI or PVI copolymers is preferably 5 to 80 wt.-% based on the dry layer. Especially preferred are 5 to 40 wt.-%; most preferred are 10 to 25 wt.-%.
PVI and PVI copolymers are principally known. They can easily be obtained by radical polymerization of 1-vinylimidazole or 1-vinylimidazole and the second comonomer and a free radical-forming initiator. If water-soluble initiators are used in the polymerization in an aqueous solution, the polymer solution can be introduced to the coating preparations without the additional step of isolating the polymers in solid form.
Another favorable method for the preparation of PV
Baumann Harald
Dwars Udo
Pappas Socrates Peter
Savariar-Hauck Celin M.
Timpe Hans-Joachim
Faegre & Benson LLP
Kodak Polychrome Graphics LLC
Reddick Judy M.
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