Negative-working imageable materials

Abstract

A negative-working imageable element includes a combination of a specific polymeric binder comprising pendant allyl ester groups with an highly efficient iodonium borate free radical initiator to provide solvent resistance, excellent digital imaging speed (sensitivity) and can be imaged and developed without a preheat step to provide lithographic printing plates. The polymeric binder can be prepared with a precursor polymer having pendant carboxy groups that are converted to allyl ester groups using an allyl-containing halide in the presence of a base in order to avoid gelation. The desired iodonium borates are diaryliodonium borates having substituents on the aryl rings.

1 . An imageable element comprising a substrate having thereon an imageable layer comprising: 
 a free radically polymerizable component,    an initiator composition capable of generating radicals sufficient to initiate polymerization of said radically polymerizable component upon exposure to imaging radiation,    a radiation absorbing compound, and    a polymeric binder that is represented by the following Structure (I):      -(A) x -(B) y -(C) z -   (I)    wherein A represents recurring units comprising a pendant —C(═O)O—CH 2 CH═CH 2  group, B represents recurring units comprising pendant cyano groups, and C represents recurring units other than those represented by A and B,    x is from about 1 to about 70 mol %, y is from about 10 to about 80 mol %, and z is from about 20 to about 90 mol %,    wherein said initiator composition comprises at least 0.5 weight % of an iodonium borate comprising a diaryliodonium borate compound represented by the following Structure (II):                          wherein X and Y are independently halo, alkyl, alkyloxy, or cycloalkyl groups or two or more adjacent X or Y groups can be combined to form a fused ring with the respective phenyl rings, p and q are independently 0 or integers of 1 to 5, provided that either p or q is at least 1, and    Z −  is an organic anion represented by the following Structure (III):                          wherein R 1 , R 2 , R 3 , and R 4  are independently alkyl, aryl, alkenyl, alkynyl, cycloalkyl, or heterocyclyl groups, or two or more of R 1 , R 2 , R 3 , and R 4  can be joined together to form a heterocyclic ring with the boron atom.    
   
   
       2 . The element of  claim 1  wherein B represents recurring units derived from (meth)acrylonitrile, x is from about 5 to about 50 mol %, y is from about 10 to about 60 mol %, and z is from about 30 to about 80 mol %.  
   
   
       3 . The element of  claim 1  wherein C represents recurring units derived from one or more (meth)acrylic acid esters, (meth)acrylamides, vinyl carbazole, styrene and styrenic derivatives thereof, N-substituted maleimides, maleic anhydride, vinyl acetate, vinyl ketones, vinyl pyridine, N-vinyl pyrrolidones, 1-vinylimidazole, (meth)acrylic acid, and vinyl polyalkylsilanes.  
   
   
       4 . The element of  claim 1  wherein said polymeric binder represents from about 10 to about 80 weight %, based on the total imageable layer dry weight.  
   
   
       5 . The element of  claim 1  wherein said polymeric binder has a solubility of less than 50 mg in 1 gram of an 80 weight % solution of 2-butoxyethanol in water, at 25° C.  
   
   
       6 . The element of  claim 1  wherein X and Y are independently alkyl, alkyloxy, or cycloalkyl groups, both p and q is at least 1, and R 1 , R 2 , R 3 , and R 4  are independently alkyl or aryl groups.  
   
   
       7 . The element of  claim 1  wherein X and Y are independently alkyl groups, from about 3 of R 1 , R 2 , R 3 , and R 4  are independently aryl groups, and Z −  is a tetraphenylborate.  
   
   
       8 . The element of  claim 1  wherein said iodonium borate is present in an amount of at least 2 weight %.  
   
   
       9 . The element of  claim 1  wherein said radiation absorbing compound is an infrared radiation absorbing compound.  
   
   
       10 . The element of  claim 1  wherein the sum of carbon atoms in said X and Y substituents is at least 6.  
   
   
       11 . The element of  claim 1  wherein B represents recurring units derived from (meth)acrylonitrile, x is from about 5 to about 50 mol %, y is from about 10 to about 60 mol %, z is from about 30 to about 80 mol %, C represents recurring units derived from one or more (meth)acrylic acid esters, (meth)acrylamides, vinyl carbazole, styrene and styrenic derivatives thereof, N-substituted maleimides, maleic anhydride, vinyl acetate, vinyl ketones, vinyl pyridine, N-vinyl pyrrolidones, 1-vinylimidazole, (meth)acrylic acid, and vinyl polyalkylsilanes, and the sum of carbon atoms in said X and Y substituents is at least 8.  
   
   
       12 . The element of  claim 1  wherein said imageable layer is the outermost layer.  
   
   
       13 . A method of making an imaged element comprising: 
 A) imagewise exposing the negative-working imageable element of  claim 1  to form exposed and non-exposed regions, and    B) with or without a preheat step, developing said imagewise exposed element to remove only said non-exposed regions.    
   
   
       14 . The method of  claim 13  wherein said radiation absorbing compound is an IR-sensitive dye and said imagewise exposing step A is carried out using radiation having a maximum wavelength of from about 700 to about 1200 nm at an energy level of from about 20 to about 500 mJ/cm 2 .  
   
   
       15 . The method of  claim 13  wherein said developing is carried out without a preheat step.  
   
   
       16 . A method of making a polymer that is represented by the following Structure (I):  
       -(A) x -(B) y -(C) z -   (I)  
     wherein A represents recurring units comprising a pendant —C(═O)O—CH 2 CH═CH 2  group, B represents recurring units comprising pendant cyano groups, and C represents recurring units other than those represented by A and B and optionally including recurring units comprising pendant carboxy groups, 
 x is from about 1 to about 70 mol %, y is from about 10 to about 80 mol %, and z is from about 20 to about 90 mol %,  
 said method comprising:  
 A) providing or preparing a precursor polymer that is represented by the following Structure (Ia):  
   -(A′) x -(B) y -(C) z -   (Ia)  
 wherein A′ represents recurring units comprising a pendant carboxy group, and B, C, x, y, and z are as defined above, and  
 B) reacting said precursor polymer with an allyl-containing halide in the presence of a base under conditions to convert said pendant carboxy groups to pendant —C(═O)O—CH 2 CH═CH 2  groups.  
 
   
   
       17 . The method of  claim 16  wherein said allyl-containing halide is vinyl benzyl chloride, allyl chloride or allyl bromide, and said base is a hydroxide, trialkylamine, pyridine, or 1,8-diazabicyclo[5,4,0]-undec-7-ene.  
   
   
       18 . The method of  claim 16  wherein reacting step B is carried out for from about 1 to about 48 hours at a temperature of from about 20 to about 150° C.