Negative-working radiation-sensitive compositions and imageable materials
View Patent ↗A radiation-sensitive composition and negative-working imagable element includes a polymeric binder that has a hydrophobic backbone and pendant salt groups that comprise a cation covalently attached to the hydrophobic backbone and a boron-containing anion forming a salt with the cation. The use of these particular polymers provides fast digital speed (high imaging sensitivity) and good printability (good shelf-life) even when the preheat step normally used between exposure and development, is omitted.
1. A method of making an imaged element comprising:
A) imagewise exposing a negative-working imagable element having a hydrophilic substrate having thereon an imagable layer to imaging radiation having a maximum wavelength of from about 700 to about 1200 nm to form exposed and non-exposed regions in the imaged imagable layer, and
B) with or without a preheat step, developing said imagewise exposed element off-press using an aqueous alkaline or organic solvent-containing developer having a pH of at least 6.5, a plate cleaner, or heated aqueous developer consisting essentially of water, to remove only said non-exposed regions of the imaged imagable layer,
said negative-working imagable element being sensitive to radiation at a wavelength of from about 700 to about 1200 nm, and comprising the hydrophilic substrate having a hydrophilic surface and having thereon the imagable 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 said imaging radiation, and
a polymeric binder that has a hydrophobic backbone and pendant salt groups that comprise a cation covalently attached to said hydrophobic backbone and a boron-containing anion forming a salt with said cation.
2. The method of claim 1 wherein said imagewise exposing step A is carried out at an energy level of from about 20 to about 300 mJ/cm 2 .
3. The method of claim 1 wherein said initiator composition comprises an onium or triazine.
4. The method of claim 1 wherein said cation is an ammonium, sulfonium, or phosphonium ion, and said boron-containing anion is represented by the following Structure (I):
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.
5. The method of claim 4 wherein said cation is an ammonium ion and said boron-containing anion is an alkyltriarylborate or tetraarylborate.
6. The method of claim 1 wherein said polymeric binder represents from about 20 to about 70 weight %, based on the total imagable layer weight.
7. The method of claim 1 wherein said polymeric binder is represented by the following Structure (II):
wherein A represents recurring units comprising said pendant salt groups comprising said cation and boron-containing anion, B represents recurring units other than those represented by A, x is from about 0.5 to 30 mol %, and y is from 70 to about 99.5 mol %.
8. The method of claim 7 wherein x is from about 0.5 to about 15 mol %, and y is from about 85 to about 99.5 mol %.
9. The method of claim 7 wherein B represents recurring units derived from one or more (meth)acrylic acid esters, (meth)acrylamides, (meth)acrylonitriles, poly(alkylene oxide) methyl ether (meth)acrylates, 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.
10. The method of claim 1 wherein said initiator composition comprises an onium salt, said free radically polymerizable component comprises an ethylenically unsaturated free-radical polymerizable monomer or oligomer, or a free-radical crosslinkable polymer, and said radiation absorbing compound is an infrared radiation absorbing compound.