Photopolymerizable radiation-sensitive resin composition and radiation-sensitive sheet material
BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings will be briefly described. In these drawings: 
     FIG. 1 is a cross-sectional view of the radiation-sensitive sheet material according to the present invention, which comprises a layer of the photopolymerizable radiation-sensitive resin composition and a protective coating, 
     FIG. 2 is a cross-sectional view of the radiation-sensitive sheet material as is shown in FIG. 1, which has been exposed to an actinic radiation, and 
     FIG. 3 is a cross-sectional view of the exposed sheet material as is shown in FIG. 2, which has been processed with a processing solution. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The photopolymerizable radiation-sensitive resin compositions according to the present invention comprise polymers which are photopolymerizable and alkali-soluble. As the polymers of this type, for example, novolak type phenol-formaldehyde resins, copolymers of acrylic or methacrylic acid, alkyd resins having a high acid value, shellac-acrylic acid copolymers, styrene-maleic acid copolymeric resins and the like are well-known. Among these polymers, particular styrene-maleic acid copolymeric resins are selected and used in the present invention. The reason why the above particular polymers are used in the present invention is based on the following facts. Namely, while the styrene-maleic acid copolymeric resin is photopolymerized by actinic radiation in the presence of a photopolymerization initiator and, as a result of this, its inherent alkali-solubility is lost, the unpolymerized styrene-maleic acid copolymeric resin, when it has added thereto an unsaturated compound with a polymerizable ethylene bond, its alkali-solubility is increased greatly. Accordingly, the polymer having added thereto an unsaturated compound can be dissolved with alkali weaker than that used in dissolving the polymer, comprising only styrene-maleic acid copolymeric resin having no unsaturated compound added thereto, and the photopolymerization initiator. Although many similar experiments were repeated using other polymers, an alkali-solubility which was equivalent to or more than than of the above-mentioned styrene-maleic acid copolymeric resin could not be attained. 
     Styrene-maleic acid copolymeric resins which are copolymeric resins of styrene and maleic anhydride are widely used in many applications such as paints, sizing agents for textiles, aqueous printing inks and the like. These resins are commercially available, e.g., from Sinclair Petrochemicals, Inc. under the trade name: SMA Resin, from Monsanto Chemical Co. under the trade name: LYTRON Resin, and from Daido Industrial Co., Ltd. under the trade name: Stylite, respectively. The styrene-maleic acid copolymeric resins generally have a molecular weight of from 700 to 50,000. The molecular weight varies depending upon various factors such as amounts of monomers used in the production of the copolymeric resins, reaction period of time, degree of esterification and the like. Furthermore, the acid value of these copolymeric resins usually ranges from 130 to 500. The styrene-maleic acid copolymeric resins useful in embodying the present invention have a molecular weight of from 1,000 to 2,000 and an acid value of from 130 to 220. Styrene-maleic acid copolymeric resins, which are partially esterified styrene-maleic anhydride resins and contain carboxyl groups yet remaining in the molecule, are particularly preferred. 
     The following Table I illustrates the results which are obtained when the amount of an ethylenically unsaturated compound to be added to the styrene-maleic acid copolymeric resin is widely varied. It will be understood from this table that the alkali-solubility of the styrene-maleic acid copolymeric resin is more and more increased with the increase in the amount of the unsaturated compound added thereto. In the Table I below, all parts used herein are by weight, and alkali used herein is a 0.0005% solution of anhydrous sodium carbonate. The thickness of the dried coating is 10 microns. 
     
                                           TABLE I                                 
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Styrene-maleic                      Exposed and                           
acid copolymeric                                                          
         Unsaturated Speed of                                             
                             Unexposed                                    
                                    developed                             
resin    compound                                                         
                Initiator                                                 
                     development                                          
                             coating                                      
                                    coating                               
__________________________________________________________________________
94 parts 0      6 parts                                                   
                     more than 180&#34;                                       
                             hard,  hard, non-tacky,                      
                             non-tacky                                    
                                    cracks when bent                      
80 parts 14 parts                                                         
                6 parts                                                   
                     60&#34;-90&#34; hard,  hard, non-tacky,                      
                             non-tacky                                    
                                    slightly poor                         
                                    solvent resistance                    
72 parts 22 parts                                                         
                6 parts                                                   
                     35&#34;-45&#34; hard,  hard, non-tacky,                      
                             non-tacky                                    
                                    good coating                          
64 parts 30 parts                                                         
                6 parts                                                   
                     30--40&#34; hard,  hard,                                 
                             non-tacky                                    
                                    good coating                          
58 parts 36 parts                                                         
                6 parts                                                   
                     20&#34;-30&#34; hard,  hard,                                 
                             non-tacky                                    
                                    good coating                          
52 parts 42 parts                                                         
                6 parts                                                   
                     15&#34;-25&#34; slightly hard,                               
                                    slightly brittle,                     
                             slightly tacky                               
                                    cracks when bent                      
35 parts 59 parts                                                         
                6 parts                                                   
                     10&#34;-20&#34; soft,  brittle,                              
                             tacky  easily cracks                         
__________________________________________________________________________
 
    
     The ethylenically unsaturated compounds useful in the present invention are polymerizable compounds which contain one or more ethylenically unsaturated double bonds in one molecule thereof. The term &#34;ethylenic compounds&#34;, when used herein, is intended to mean the compounds (including monomers, prepolymers, dimers, trimers and other oligomers) which contain at least one ethylenically unsaturated double bond in their chemical structure. 
     The ethylenic compound which is advantageously usable in embodying the present invention is a mixture of (A) one or more ethylenic compounds (with a terminal hydroxyl group) having a molecular weight of 150 or more and a boiling point, under normal pressure, of 100° C. or more and containing at least one acryloyl or methacryloyl group, and (B) one or more ethylenic compounds having a molecular weight of 150 or more and a boiling point, under normal pressure, of 100° C. or more and containing at least one acryloyl or methacryloyl group, but containing no terminal hydroxyl group. 
     Examples of the above-mentioned ethylenic compounds (A) include, for example, polyester monoacrylate represented by the structural formula: ##STR1## where R is H or CH 3 , 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate, 1,4-butylene glycol monoacrylate and the like. 
     Examples of the above-mentioned ehtylenic compounds (B) include, for example, polyethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,4-butylene glycol diacrylate, 1,6-hexane glycol diacrylate, neopentyl glycol diacrylate, 2,2-bis (4-acryloxy diethoxy phenyl) propane, 2,2-bis (4-acryloxy propyloxy phenyl) propane, trimethylol propane triacrylate, tetramethylol methane triacrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, 1,6-hexane glycol dimethacrylate, polypropylene glycol dimethacrylate, 2,2-bis (4-methacryloxy ethoxy phenyl) propane, 2,2-bis (4-methacryloxy diethoxy phenyl) propane, trimethylol propane trimethacrylate, polyester acrylate oligomer, polyamide acrylate, epoxy acrylate, polyurethane acrylate, polyester monoacrylate represented by the structural formula: ##STR2## wherein R is H or CH 3 , and the like. 
     Examples of the photopolymerization initiators usable in the present invention are, for example, one or more compounds selected from the group consisting of acyloin such as benzoin and the like; acyloin derivatives such as benzoin methyl ether, benzoyl ethyl or isopropyl or benzoin isobutyl ether and the like; ketones such as benzophenone, acetophenone, methyl ethyl ketone, benzyl and the like; substituted benzophenones such as Michler&#39;s ketone, halogenated benzophenone and the like; aldehydes such as benzaldehyde, dimethyl amino benzaldehyde, 4-hydroxy-3-methoxy benzaldehyde, naphthal-aldehyde, cinnamaldehyde and the like, and; substituted or unsubstituted polynuclear quinones such as xanthone, 3-chloroxanthone, 3,9-dichloroxanthone, anthraquinone, 1-chloroanthraquinone, 2-ethylanthraquinone, 1,4-naphthoquinone and the like. 
     In the radiation-sensitive resin compositions according to the present invention, various pigments may be optionally incorporated therein depending upon the desired hue. As typical examples of useful pigments, for example, the following compounds can be mentioned. However, the present invention should not be restricted to these compounds: 
     Yellow pigments: Benzidine yellow, hansa yellow, chrome yellow and the like 
     Red pigments: Brilliant carmine, permanent reds, lithol rubine, watchung red and the like 
     Blue pigments: Phthalocyanine blue, alkali blue and the like 
     Black pigments: Carbon black, iron black and the like. 
     In addition to these pigments, finely divided silicic acid may be used as a filler or a viscosity modifier. 
     The photopolymerizable radiation-sensitive resin composition in accordance with the invention comprises a styrene-maleic acid copolymeric resin as an alkali-soluble polymer as well as 10 through 60% by weight, based on the weight of said copolymeric resin, of ethylenically unsaturated compound and 1 through 10% by weight, based on the total weight of the copolymeric resin and the ethylenically unsaturated compound, of the photopolymerization initiator. With regard to the ethylenically unsaturated compound, it is further added that a ratio, of percentage by weight, of the compound (A) having a molecular weight of 150 or more, a boiling point, under normal pressure, of 100° C. or more, at least one acryloyl or methacryloyl group, and a terminal hydroxyl group to the compound (B) having a molecular weight of 150 or more, a boiling point, under normal pressure, of 100° C. or more, and at least one acryloyl or methacryoyl group is 40 through 60%. If the above ethylenic compound (B) is used in an amount which is less than the lower limit of the above range, drawbacks such as delay of photopolymerization and the like will be caused. On the other hand, if the ethylenic compound (B) is used in an amount more than the upper limit of the above range, drawbacks such as insufficient adhesion of the photocured coating to vinyl chloride and the like will result. 
     In the photopolymerizable radiation-sensitive resin composition of the present invention, it is preferred that benzyl and dimethyl amino benzaldehyde are selected as the photopolymerization initiator among the above-listed photopolymerization initiators, and they are optionally combined and used so that a ratio, of percentage by weight, of dimethyl amino benzaldehyde to benzyl is within the range of from 10 to 90%. The use of a combination of the photopolymerization initiators is preferred due to the following reasons. Namely, in the composition comprising the above-discussed styrene-maleic acid copolymeric resin having incorporated therein the ethylenic compound, the resulting rate of photopolymerization is remarkably slow and therefore a practically effective sensitivity can not be obtained if each of benzyl and dimethyl amino benzaldehyde is added separately to the composition, while a very fast rate of photopolymerization can be attained if benzyl and dimethyl amino benzaldehyde are used in combination and furthermore if they are combined at a specific ratio. In addition, it was found that, although the reasons have not yet been completely grasped, the radiation-sensitive resin composition of the present invention can be kept stably for a remarkably long duration without adding any shelf stabilizer such as a thermal polymerization inhibitor and the like, if a combination of benzyl and dimethyl amino benzaldehyde is used as the photopolymerization initiator. Though similar comparison was tried using other combinations of the photopolymerization initiators, notably excellent results, which were obtained when benzyl and dimethyl amino benzaldehyde were used in combination, could not be attained. 
     In the photopolymerizable radiation-sensitive resin composition in accordance with the present invention, if any pigment is added to the composition, it may be added thereto in an amount of 1 through 50 parts by weight based on the weight of the composition, and if any thermal polymerization inhibitor is added to the composition, it may be added thereto in an amount of 0.01 through 2% by weight based on the weight of the composition. 
     The photopolymerizable radiation-sensitive resin compositions in accordance with the present invention will be further described with reference to the following examples. While the examples mentioned below illustrate the radiation-sensitive resin compositions which are suitable in the production of cards, it should be appreciated that these examples illustrate only one example of the present invention and they do not restrict the applications of the present invention and the compositions or proportions of the ingredients of the present invention. The &#34;parts&#34; used in the examples is intended to mean &#34;parts by weight&#34; unless otherwise stated. 
     Example 1-1 
     
         ______________________________________                                    
First group:                                                              
Styrene-maleic acid copolymeric                                           
                         22    parts                                      
resin                                                                     
Ethylene glycol monoethyl ether                                           
                         20    parts                                      
Second group:                                                             
Carbon black             3.5   parts                                      
Phthalocyanine blue      0.5   parts                                      
Third group:                                                              
2-hydroxy ethyl acrylate 7     parts                                      
Trimethylol propane triacrylate                                           
                         9     parts                                      
Benzyl                   1.6   parts                                      
Dimethyl amino benzaldehyde                                               
                         0.4   parts                                      
Ethanol                  36    parts                                      
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     Firstly, the substances of the above-mentioned first group are added to a vessel equipped with a reflux condenser, and are dissolved while stirring at a temperature of 80 to 90° C. Heating is stopped after the substances added to the vessel are completely dissolved. Thereafter the solution is allowed to cool to room temperature while stirring. The resulting solution is transferred to a porcelain or stainless steel ball mill, wherein it is milled with the substances of the above-mentioned second group for a period of about 24 hours. Thereafter, the resulting mixture is transferred to a vessel equipped with a mixer or stirrer and the like, to which the substances of the above-mentioned third group are added. Stirring is continued for a period of about 2 hours. A black-coloured radiation-sensitive resin composition can be obtained. 
     Example 1-2 
     
         ______________________________________                                    
First group:                                                              
Styrene-maleic acid copolymeric                                           
                         22    parts                                      
resin                                                                     
2-hydroxy ethyl acrylate 9     parts                                      
Second group:                                                             
2,2-bis (4-acryloxy diethoxy                                              
                         7     parts                                      
phenyl) propane                                                           
Benzyl                   1.6   parts                                      
Dimethyl amino benzaldehyde                                               
                         0.4   parts                                      
Third group:                                                              
Carbon black             3.5   parts                                      
Phthalocyanine Blue      0.5   parts                                      
Ethylene glycol monoethyl ether                                           
                         36    parts                                      
Ethanol                  20    parts                                      
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     First, the substances of the above-mentioned first group are added to a vessel equipped with a reflux condenser, and, while bubbling with air, are dissolved while stirring at a temperature of 130 to 140°. Heating is stopped after the substance added to the vessel are completely dissolved. The solution is cooled to a temperature of about 90° C. while stirring and bubbling with air are further continued. Subsequently, the substances of the above-mentioned second group are added, and are stirred for about one hour. Thereafter, the resulting solution is transferred to a porcelain or stainless steel ball mill, to which the substances of the above-mentioned third group are then added and milled for a period of about 24 hours. A black-coloured radiation-sensitive resin composition can be obtained. 
     Example 1-3 
     
         ______________________________________                                    
First group:                                                              
Styrene-maleic acid copolymeric                                           
                          22    parts                                     
resin                                                                     
Polyester monooligoacrylate having                                        
                          9     parts                                     
a terminal - OH group (Allonix                                            
M5700 commercially available from                                         
Toagosei Chemical Industry Co., Ltd.)                                     
Second group:                                                             
Epoxy acrylate (Lipoxy VR80                                               
                          7     parts                                     
commercially available from                                               
Showa Koubunshi Kogyo Kabushiki                                           
Kaisha)                                                                   
Benzyl                    1.6   parts                                     
Dimethyl amino benzaldehyde                                               
                          0.4   parts                                     
Third group:                                                              
Carbon black              3.5   parts                                     
Phthalocyanine Blue       0.5   parts                                     
Ethylene glycol monoethyl ether                                           
                          36    parts                                     
Ethanol                   20    parts                                     
______________________________________                                    
 
    
     A radiation-sensitive resin composition is prepared in accordance with the procedure similar to that as described in Example 1-2. 
     Example 1-4 
     
         ______________________________________                                    
First group:                                                              
Styrene-maleic acid copolymeric                                           
                          22    parts                                     
resin                                                                     
2-hydroxy ethyl acrylate  9     parts                                     
Second group:                                                             
Polyester monooligoacrylate having                                        
                          7     parts                                     
a terminal - COOH group (Allonix                                          
M 8060 commercially available from                                        
Toagosei Chemical Industry Co., Ltd.)                                     
Benzyl                    1.6   parts                                     
Dimethyl amino benzaldehyde                                               
                          0.4   parts                                     
Third group:                                                              
Carbon black              3.5   parts                                     
Phthalocyanine Blue       0.5   parts                                     
Ethylene glycol monoethyl ether                                           
                          36    parts                                     
Ethanol                   20    parts                                     
______________________________________                                    
 
    
     A radiation-sensitive resin composition is prepared in accordance with the procedure similar to that as described in Example 1-2. 
     Example 1-5 
     
         ______________________________________                                    
First group:                                                              
Styrene-maleic acid copolymeric resin                                     
                         22    parts                                      
Polyester monooligoacrylate having                                        
                         16    parts                                      
a terminal - OH group                                                     
Second group:                                                             
Benzyl                   1.6   parts                                      
Dimethyl amino benzaldehyde                                               
                         0.4   parts                                      
Third group:                                                              
Carbon black             2.5   parts                                      
Phthalocyanine Blue      0.5   parts                                      
Ethylene glycol monoethyl ether                                           
                         36    parts                                      
Ethanol                  20    parts                                      
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     A radiation-sensitive resin composition is prepared in accordance with the procedure similar to that as described in Example 1-2. 
     Example 1-6 
     
         ______________________________________                                    
First group:                                                              
Styrene-maleic acid copolymeric resin                                     
                         22    parts                                      
Ethylene glycol monoethyl ether                                           
                         20    parts                                      
Second group:                                                             
Carbon black             3.5   parts                                      
Phthalocyanine Blue      0.5   parts                                      
Third group:                                                              
Polyurethane acrylate    16    parts                                      
(Ubitan 788 commercially available                                        
from Thiokol Chemical Corp.)                                              
Benzyl                   1.6   parts                                      
Dimethyl amino benzaldehyde                                               
                         0.4   parts                                      
Ethanol                  36    parts                                      
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     A radiation-sensitive resin composition is prepared in accordance with the procedure similar to that described in Example 1-1. 
     Example 1-7 
     
         ______________________________________                                    
First group:                                                              
Styrene-maleic acid copolymeric resin                                     
                         22    parts                                      
Ethylene glycol monethyl ether                                            
                         10    parts                                      
Second group:                                                             
Benzyl                   1.6   parts                                      
Dimethyl amino benzaldehyde                                               
                         0.4   parts                                      
Third group:                                                              
Carbon black             3.5   parts                                      
Phthalocyanine Blue      0.5   parts                                      
Ethylene glycol monoethyl ether                                           
                         26    parts                                      
Ethanol                  20    parts                                      
2,2-bis (4-acryloxy diethoxy phenyl)                                      
                         16    parts                                      
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     A radiation-sensitive resin composition is prepared in accordance with the procedure similar to that as described in Example 1-2. 
     Example 1-8 
     The procedure as described in Example 1-1 is repeated except that 2 parts of benzoin isopropyl alcohol is used in place of benzyl and dimethyl amino benzaldehyde in Example 1-1. 
     Example 1-9 
     The procedure as described in Example 1-3 is repeated except that 2 parts of benzoin isopropyl alcohol is used in place of benzyl and dimethyl amino benzaldehyde in Example 1-3. 
     Example 1-10 
     The procedure as described in Example 1-3 is repeated except that 2 parts of benzyl is separately used in place of benzyl and dimethyl amino benzaldehyde in Example 1-3. 
     The novel photopolymerizable radiation-sensitive resin composition according to the present invention will be generally usable after it is coated on a support. This is because the resulting coating is effective as a stable layer of radiation-sensitive material since its exposed areas are immediately insolubilized after exposure to radiation. Furthermore, it will be understood that the support to be laid under the layer of radiation-sensitive material may be made of vinyl chloride resins, since one or more solvents which cannot dissolve vinyl chloride or vinyl chloride-vinyl acetate copolymeric resins can be optionally selected from the group consisting of alcohols, polyhydric alcohols and derivatives thereof as the solvent for use in the production of the radiation-sensitive resin composition according to the present invention. However, the materials of the support useful in the present invention also include, for example, paper, metals and the other conventional support materials. While the present invention has been described with respect to the application of its radiation-sensitive resin compositions in the production of cards, it should be appreciated that the radiation-sensitive resin compositions of the present application are also applicable to other technical fields in which known radiation-sensitive resin compositions are used. 
     The sheet material to which sensitivity is induced by the radiation-sensitive resin composition according to the present invention is illustrated in FIG. 1 of the accompanying drawings. FIG. 1 is a cross-sectional view of a support 10 having coated thereon a layer 11 of a soluble radiation-sensitive material. The radiation-sensitive resin composition which forms the layer 11 of the radiation-sensitive material has been already explained in detail. Generally, the layer 11 additionally contains a pigment. A protective coating 12 may be coated over the layer 11 of the radiation-sensitive material, as is the case with conventional photographic films. The protective coating 12 should be soluble in water or soluble in weak alkali, since the coating 12 is desirably removed with solvents for processing the layer 11. In this connection, it is necessary to take care to avoid such undesirable situations that the protective coating 12 will react with the layer 11 of the radiation-sensitive material and will become insoluble during storage. 
     The materials of the protective coating 12 which satisfy the above-mentioned requirements are, principally, water-soluble resins or alkali-soluble resins. 
     While it is well-known that the water-soluble resins include, for example, hydroxy ethyl cellulose, polyethylene oxide, carboxymethylcellulose, polyvinyl alcohol and the like, it is particularly preferred that polyvinyl alcohol is used in embodying the present invention. Preferred polyvinyl alcohol is a partially saponified polyvinyl alcohol which has a degree of polymerization of from 1,000 to 1,500 and a degree of saponification of 80% of less. In the preparation of a protective coating-forming composition containing such water-soluble resin, the resulting composition generally contains 5 through 20% by weight, based on the weight of distilled water used as a solvent, of water-soluble resin, and further contains 0.5 through 5% by weight, based on the weight of the resultant solution, of a non-ionic surfactant or saponin. The non-ionic surfactant or saponin serves to prevent repellency between the layer 11 of the radiation-sensitive material and the protective coating 12 and to increase interfacial affinity therebetween, and, in addition to this, to improve the spreadability of the protective coating-forming composition during its application to form the coating 12. In some cases, the protective coating-forming composition may further contain 5 through 10% by weight, based on its weight, of finely divided silicic anhydride as a filler. Furthermore, in order to prevent focusing of the actinic radiation at the time of exposure, a pigment may be incorporated into the protective coating-forming composition. The pigment used herein is in an amount of 10 through 20% by weight, based on the weight of the solid water-soluble resin. Useful pigment is a water-dispersible pigment and is, for example, commercially available from Dainippon Ink &amp; Chemicals, Inc. under the trade name: RIYU-DYE. Furthermore, a defoaming agent such as tributyl phosphate and the like is frequently used during the preparation of the protective coating-forming composition of the above-mentioned type. However, such a defoaming agent is not related to the composition of the protective coating itself. 
     The alkali-soluble resins have been already explained in connection with the explanation of the radiation-sensitive resin composition. Examples of these resins include novolak type phenol-formaldehyde resins, copolymers of acrylic or methacrylic acid, alkyd resins having a high acid value, styrene-maleic acid copolymeric resins or its partially esterified resins, alkali salts of styrene-maleic acid copolymeric resins and the like. In order to embody the present invention, it is particularly preferred that the partially esterified products or alkali salts of styrene-maleic acid copolymeric resins are used as the alkali soluble resins. The above-mentioned alkali salts are commercially available from Monsanto Chemical Co., U.S.A., under the trade name: Stymer S Resin. Generally, in the preparation of a protective coating-forming composition containing the above alkali-soluble resin, 5 through 20% by weight, based on the weight of the solvent used, such as ethanol, ethylene glycol monoethyl ether acetate and the like, of the alkali-soluble resin is incorporated into the composition. Furthermore, if desired, finely divided silicic anhydride as a filler and a pigment as a focusing inhibitor may be incorporated into the composition, respectively, as is the case with the above-discussed protective coating-forming composition which contains a water-soluble resin. 
     The preparations of each of the above-mentioned water-soluble protective coating-forming compositions and alkali-soluble protective coating-forming compositions will be further described with reference to their typical examples. 
     Example 2-1 
     
         ______________________________________                                    
Polyvinyl alcohol       5      parts                                      
Distilled water         100    parts                                      
Non-ionic surfactant    1      part                                       
Finely divided silicic anhydride                                          
                        5      parts                                      
Water-dispersible red pigment                                             
                        0.5    parts                                      
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     First, the distilled water and polyvinyl alcohol are added to a vessel equipped with a water bath or a steam heater, and heated to a temperature of 90° C. while stirring. The finely divided silicic anhydride is added during heating, and the same temperature is maintained for a period of about 2 hours. The thus obtained complete solution is then cooled to a temperature of 40° C., and the red pigment and the non-ionic surfactant are added while cooling. A water-soluble protective coating-forming composition can be obtained. 
     Example 2-2 
     
         ______________________________________                                    
Sodium salt of partially                                                  
                        10    parts                                       
esterified styrene-maleic                                                 
acid copolymeric resin                                                    
Purified water          20    parts                                       
Ethanol                 45    parts                                       
Plasticizer             5     parts                                       
Ethylene glycol monoethyl                                                 
                        20    parts                                       
ether acetate                                                             
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     These substances are mixed, by stirring, in a vessel equipped with a reflux condenser at a temperature of 50° through 70° C. An alkali-soluble protective coating-forming composition can be obtained. 
     Generally, the radiation-sensitive sheet material in accordance with the present invention, as has been already described, has the structure illustrated in FIG. 1. For the purpose of producing such a radiation-sensitive sheet material, the following procedure can be used, for example. Namely, a surface of the support 10 is coated with a radiation-sensitive resin composition prepared in any one of Examples 1-1 through 1-10. Then, the coated support 10 is placed in a stream of warm air at a temperature of about 40° C. to evaporate the solvent contained in the coating of the radiation-sensitive resin composition. As a result of this, a layer 11 of radiation-sensitive material is formed on the support 10. Subsequently, a protective coating-forming composition such as prepared in either Example 2-1 or 2-2 is coated on the layer 11 of the radiation-sensitive material. Thereafter, the resulting coating is completely dried in a stream of warm air at a temperature of about 40°  through 50° C., whereby a radiation-sensitive sheet material having a protective coating 12 as a topcoat is obtained. For example, if it is intended to produce the radiation-sensitive sheet material which is useful in the production of cards, a transparent sheet of a rigid vinyl chloride having a thickness of 0.08 through 0.1 mm should be preferably used, and, in addition to this, the thicknesses of the layer 11 of the radiation-sensitive material and the protective coating 12 should be desirably about 4 microns and about 5 microns, respectively. 
     In the practical production of the radiation-sensitive sheet material, it is possible to use a web of support, and to continuously coat on the surface thereof a coating composition. The coated web is suitably cut into sheets of a standard size, packaged under light shielding conditions, and supplied to the user. The user can open a package of the sheet at the time of use. 
     In FIG. 2, a cross-sectional view of the radiation--sensitive sheet material which has been exposed to actinic radiation through a transparent negative is illustrated. The actinic radiation passes through a transparent negative during exposure, and reaches exposed areas 11a in the layer 11 of the radiation-sensitive material of the shown sheet material. In this case, the protective coating 12 formed on the layer 11 of the radiation-sensitive material does not prevent the transmission of the actinic radiation therethrough. If the support 10 is composed of a transparent material, the actinic radiation may be irradiated from the reverse side of the support 10 through the transparent negative, as is well-known in the art. The exposed areas 11a in the layer 11 of the radiation-sensitive material become insoluble as a result of photoreaction, and adhere to the surface of the underlying support 10. The radiation-sensitive material in the unexposed areas 11b remains unreacted, and therefore its solubility inherent in the radiation-sensitive material is maintained without change. Exposure can be carried out in accordance with the manner well-known in the art. For example, any light source capable of richly emitting ultraviolet radiation of from 2,500 to 4,200 A, such as a three-phase arc lamp, a super-high pressure mercury vapor lamp, a chemical lamp, a metal halide lamp and the like, can be used as the exposure light source. 
     FIG. 3 illustrates the condition of the sheet material as shown in FIG. 2, after it has been immersed in a developing solution. After the sheet material is processed with the developing solution, the protective coating 12 existing thereon is completely removed, whereby only the image formed from the radiation-sensitive material in the exposed areas 11a remains. The radiation-sensitive material in the unexposed areas 11b is completely washed off as a result of development and therefore the surface of the underlying support 10 is again exposed. The remaining image coincides with the exposed areas 11a and has a counter which is clearly distinct from the surface, in the unimaged areas, of the support 10. In addition, the image has a vivid colour provided by the pigment. A processing solution used in the development is weakly alkaline. A solution suitable for the above object is, for example, a mixture consisting of 50 parts of anhydrous sodium carbonate, 5 parts of a surfactant and 10,000 parts of water. 
     The following examples illustrate the results obtained when the radiation-sensitive sheet material according to the present invention is used practically. However, it should be appreciated that the present invention is not limited to these examples. 
     Example 3-1 
     Each of the radiation-sensitive resin compositions as described in Examples 1-1 through 1-10 was separately coated on transparent, rigid vinyl chloride sheet having a thickness of 0.1 mm by means of a roll coater so that the thickness of the dried coating was 4 microns. Further, the composition as described in Example 2-1 was coated thereon to form a protective coating having a dry thickness of 5 microns. A radiation-sensitive sheet material was obtained. The resulting sheet material was placed in a vacuum printing frame, being registered with a step wedge having 21 optical photographic densities, and a negative film with transparent dotted images. The layer of the radiation-sensitive material was subjected to an exposure step by means of a 3 kw metal halide lamp, which was located 80 cm away from the radiation-sensitive sheet material, from the reverse side of the sheet material through the step wedge and the negative film, and then processed with the processing solution as described above. The processed sheet material was tested with regard to its sensitivity, developability, dot reproducibility, adherability to vinyl chloride film, and coating strength. The results shown in the following Table II were obtained. Furthermore, when the unprocessed radiation-sensitive sheet material was tested with regard to its shelf stability, the results, also shown in the following Table II, were obtained. 
     
                       TABLE II                                                    
______________________________________                                    
                       Dot   Ad-                                          
Com-                   repro-                                             
                             hera-                                        
posi- Sensi-  Develop- duci- bili-                                        
                                  Coating                                 
                                         Shelf                            
tion  tivity  ability  bility                                             
                             ty   strength                                
                                         stability                        
______________________________________                                    
1-1   120 sec ⊚                                            
                       ○                                           
                             ⊚                             
                                  ○                                
                                         less than                        
                                          6 months                        
1-2    90 sec ○ ○                                           
                             ⊚                             
                                  ⊚                        
                                         less than                        
                                          8 months                        
1-3    20 sec ⊚                                            
                       ⊚                                   
                             ⊚                             
                                  ⊚                        
                                         more than                        
                                         12 months                        
1-4    20 sec ⊚                                            
                       ⊚                                   
                             ⊚                             
                                  ⊚                        
                                         more than                        
                                         12 months                        
1-5   more    ⊚                                            
                       --    --   --     more than                        
      than                               12 months                        
      400 sec                                                             
1-6    90 sec Δ  ○                                           
                             Δ                                      
                                  ⊚                        
                                         more than                        
                                         12 months                        
1-7    40 sec Δ  Δ                                            
                             ○                                     
                                  ⊚                        
                                         more than                        
                                         12 months                        
1-8   360 sec ⊚                                            
                       Δ                                            
                             ⊚                             
                                  ○                                
                                         less than                        
                                          2 months                        
1-9   180 sec ⊚                                            
                       ○                                           
                             ⊚                             
                                  ○                                
                                         less than                        
                                          2 months                        
 1-10 240 sec ⊚                                            
                       Δ                                            
                             ⊚                             
                                  ⊚                        
                                         less than                        
                                          6 months                        
______________________________________                                    
 As to the symbols in Table II                                            
 1. Each of the sensitivities described in the table refers to time       
 (seconds) which was necessary to completely cure the sheet material      
 corresponding to the first four steps of the 21 steps in the step wedge. 
 2. Developability:                                                       
 ⊚ A vivid image is formed within 30 seconds, and there is 
 no residue in unexposed areas on the support.                            
 ○ A vivid image is formed within 60 seconds, and there is no      
 residue in unexposed areas on the support.                               
 Δ A part of the composition remains on the support, and fogging is 
 caused in spite of development for more than 60 seconds.                 
 3. Dot Reproducibility:                                                  
 ⊚ 5% of the dots of the corresponding halftone negative ar
 correctly reproduced.                                                    
 ○ 10% of the dots of the corresponding halftone negative are      
 correctly reproduced.                                                    
 Δ Reproducible dots are at most 25% of the dots of the correspondin
 halftone negative.                                                       
 4. Adherability: (According to peeling test)                             
 ⊚ Adhesion of 100/100                                     
 ○ Adhesion of 10/100                                              
 Δ Adhesion of 0/100                                                
 5. Coating Strength:                                                     
 ⊚ Coating is not peeled off after rubbing 50 times using a
 cotton ball moistened with ethanol.                                      
 ○ Coating is slightly peeled off after rubbing 50 times using a   
 cotton ball moistened with ethanol.                                      
 Δ Coating is completely peeled off after rubbing 50 times using a  
 cotton ball moistened with ethanol.                                      
 6. Shelf Stability:                                                      
 Storageable duration at room temperature.                                
 
    
     Example 3-2 
     The procedure similar to that as described in Example 3-1 was repeated except that the composition as described in Example 2-2 was used in place of the composition of Example 2-1 used in Example 3-1. Results similar to those described in the above Table II were obtained.