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
1999-06-03
2002-04-09
Baxter, Janet (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
C430S283100, C430S285100, C430S287100, C522S076000, C522S079000, C522S021000, C525S059000, C525S061000
Reexamination Certificate
active
06368772
ABSTRACT:
The present invention relates to a process for functionalizing a water-soluble or water-dispersible polymeric binder, in which an unmodified, water-soluble or water-dispersible polymeric binder is reacted with one or more polar aprotic swelling agents which are compatible with the binder, with thorough mixing with one or more compounds which have groups capable of free radical polymerization.
It furthermore relates to a composition which essentially contains a water-soluble or water-dispersible polymeric organic binder having groups capable of free radical polymerization and a polar, aprotic swelling agent, and a radiation-sensitive mixture which contains, as essential components, said composition, at least one photopolymerization initiator, if required one or more ethylenically unsaturated, photopolymerizable low molecular weight compounds, compatible with the polymeric binder, and further conventional additives and/or assistants. It also relates to radiation-sensitive letterpress or relief printing plates which can be produced from said radiation-sensitive mixture.
Photosensitive photopolymeric recording materials from which printing plates can be produced have to meet a wide range of requirements. For example, the recording materials should have high photosensitivity in order to ensure crisp reproduction of the film. The exposed recording materials should have high mechanical strength in order to withstand long print runs without damage, in particular in letterpress and gravure printing applications.
Photosensitive recording materials based on polymers and monomers which can be washed out with water for the production of printing plates and relief plates are in principle known and are disclosed, for example, in U.S. Pat. No. 4,361,640, EP-A-079 514 or EP-A-224 164.
It is known that the polymeric binder used for letterpress printing plates which can be developed in an aqueous medium may comprise various types of polyvinyl alcohol, which are mixed with suitable monomers, photoinitiator and stabilizer and are cast from solution to give photosensitive recording materials.
Owing to the polarity of polyvinyl alcohol, such recording materials can, after imagewise exposure, be washed out in a short time in water or aqueous solution. In order to achieve sufficient photosensitivity, however, large amounts of photopolymerizable monomers, for example mono-, bi- or polyfunctional acrylates or acrylamides, have to be added to the polyvinyl alcohol. Such monomers are expensive, generally have an irritant effect on the skin and have an unpleasant odor. Furthermore, recording materials obtained from polyvinyl alcohol, monomers and photoinitiator have insufficient mechanical cohesion, which can lead to damage, for example cracks or scratches, during printing.
It has therefore been proposed to use functionalized polyvinyl alcohols in which some of the hydroxyl groups have been reacted with an agent containing double bonds. Photosensitive recording materials having functionalized polyvinyl alcohol as the polymeric binder have the advantage that less monomers have to be added for their crosslinking, shorter exposure times are required and the mechanical resistance is substantially improved compared with recording materials containing unmodified polyvinyl alcohol.
The functionalization of polyvinyl alcohol can be carried out by reacting the hydroxyl group with unsaturated glycidyl compounds, such as glycidyl methacrylate, with unsaturated anhydrides, for example methacrylic anhydride or maleic anhydride, or with unsaturated acids. In carrying out the reaction, however, the problem arises that polyvinyl alcohols are soluble only in protic solvents, such as water, ethanol or propanol. However, since the stated agents react more rapidly with alcohols or water than the hydroxyl groups of the polyvinyl alcohol, a polymer-analogous reaction in solution cannot be realized.
EP-A-670 521 proposes carrying out the reaction in the melt. However, this procedure is disadvantageous since polyvinyl alcohol does not melt until about 200° C. in the absence of additives, and elimination of water may already have occurred. The agents containing double bonds also tend to decompose at 200° C. Before further processing, the modified polymers obtained must therefore first be purified by reprecipitation from a mixture of water and organic solvents.
WO 96/18133 describes a process in which polyvinyl alcohol in aqueous solution is reacted with unsaturated aldehydes or their acetals. Since the reaction is an acid-catalyzed equilibrium reaction, acid must be added to the reaction mixture or the mixture must be passed over an acidic ion exchanger. Furthermore, few unsaturated compounds having an aldehyde or acetal function are commercially available economically.
EP-A-079 514, DE-A-33 22 993 and DE-A-33 22 994 describe a process in which polyvinyl alcohol, after suspension in toluene or halogenated hydrocarbons, is subjected to a heterogeneous reaction with methacrylic anhydride. The disadvantage of this process is that the organic solvent required for suspending has to be removed in an expensive procedure after the reaction is complete, since even small residual amounts of the organic solvents adversely affect the transparency of the recording materials. Since the reaction is carried out in the heterogeneous phase, it is furthermore difficult to achieve homogeneous functionalization.
It is an object of the present invention to provide a simple and economical process for functionalizing a water-soluble or water-dispersible polymeric binder and, from the compositions thus obtainable, to provide improved photosensitive recording materials which are used for the production of letterpress printing plates, coating materials for screen printing and film primers. The invention also relates to the novel compositions containing polar, aprotic swelling agents, radiation-sensitive mixtures and letterpress printing plates containing them.
We have found that this object is achieved by a process for functionalizing a water-soluble or water-dispersible polymeric organic binder, in which an unmodified, water-soluble or water-dispersible polymeric binder is reacted with one or more polar aprotic swelling agents which are compatible with the binder, with thorough mixing with one or more compounds which have groups capable of free radical polymerization.
Surprisingly, it has been found that the resulting composition comprising a water-soluble or water-dispersible polymeric organic binder having groups capable of free radical polymerization and polar, aprotic swelling agents is very useful for the preparation of radiation-sensitive mixtures, without separating off the swelling agent and without further purification.
The radiation-sensitive mixture found contains, as essential components, the above composition, at least one photopolymerization initiator and, if required, further conventional additives and/or assistants. Furthermore, one or more ethylenically unsaturated, photopolymerizable low molecular weight or oligomeric compounds compatible with the polymeric binder and/or further water-soluble or water-dispersible binders may be present. Finally, we have found letterpress or relief printing plates which can be produced from said radiation-sensitive mixture.
The unmodified water-soluble or water-dispersible polymeric binders used as starting material are preferably polyvinyl alcohol or polyvinyl alcohol copolymers. For the purposes of the present invention, the term polyvinyl alcohol is intended to be understood below as meaning partially hydrolyzed polyvinyl acetates in which more than 50% of the acetate groups have been hydrolyzed. The degree of hydrolysis is determined on the one hand by the condition of water solubility or water dispersibility and on the other hand by the desired conversion or degree of functionalization. Preferably, the degree of hydrolysis is 72-92%, very particularly preferably 80-88%. The average degree of polymerization is preferably from 350 to 2500 and is chosen according to the intended use by a person skilled
Leinenbach Alfred
Stebani Uwe
Telser Thomas
Tönnessen Markus
BASF Drucksytems GmbH
Baxter Janet
Clarke Yvette M.
Keil & Weinkauf
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