Polymerizable composition and planographic printing plate precursor

1. A polymerizable composition comprising a binder polymer having a repeating unit represented by the following formula (I) and a repeating unit having a radical-polymerizable group represented by the following formula (A) or (C), an infrared absorbent, a polymerization initiator and a polymerizable compound,

wherein R 1 represents a hydrogen atom or a methyl group; R 2 represents a linking group which includes two or more atoms selected from the group consisting of a carbon atom, a hydrogen atom, an oxygen atom, a nitrogen atom and a sulfur atom and has a number of atoms of 2 to 30; A represents an oxygen atom or —NR 3 — in which R 3 represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 10 carbon atoms; and n represents an integer of 1 to 5;

wherein R 4 , R 5 and R 6 each independently represent a hydrogen atom, or a monovalent substituent; and X represents an oxygen atom, a sulfur atom or N—R 15 in which R 15 represents a hydrogen atom or monovalent organic group;

wherein R 12 , R 13 and R 14 each independently represent a hydrogen atom, or a monovalent substituent; and Z represents an oxygen atom, a sulfur atom or N—R 15 , in which R 15 represents a hydrogen atom or a monovalent organic group.

2. The polymerizable composition according to claim 1 , wherein the number of atoms constituting a skeleton of the linking group represented by R 2 in the binder polymer having the repeating unit represented by formula (I) is 1 to 30.

3. The polymerizable composition according to claim 1 , wherein a molecular weight of the binder polymer is 2,000 to 1,000,000.

4. The polymerizable composition according to claim 1 , wherein a glass transition point (Tg) of the binder polymer is 70 to 300° C.

5. The polymerizable composition according to claim 1 , wherein R 2 in formula (I) represents an alkylene group or an arylene group.

6. The polymerizable composition according to claim 1 , wherein a repeating unit having an amide group is contained in the binder polymer.

7. A planographic printing plate precursor comprising a support having disposed thereon a photosensitive layer that contains a polymerizable composition including a binder polymer having a repeating unit represented by the following formula (I) and a repeating unit having a radical-polymerizable group represented by the following formula (A) or (C), an infrared absorbent, a polymerization initiator and a polymerizable compound,

wherein R 1 represents a hydrogen atom or a methyl group; R 2 represents a linking group which includes one or more atoms selected from the group consisting of a carbon atom, a hydrogen atom, an oxygen atom, a nitrogen atom and a sulfur atom and has a number of atoms of 2 to 30; A represents an oxygen atom or —NR 3 — in which R 3 represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 10 carbon atoms; and n represents an integer of 1 to 5;

wherein R 4 , R 5 and R 6 each independently represent a hydrogen atom, or a monovalent substituent; and X represents an oxygen atom, a sulfur atom or N—R 15 ;

wherein R 12 , R 13 and R 14 each independently represent a hydrogen atom, or a monovalent substituent; and Z represents an oxygen atom, a sulfur atom or N—R 15 , in which R 15 represents a hydrogen atom or a monovalent organic group.

8. The planographic printing plate precursor according to claim 7 , wherein the binder polymer is used in combination with a binder having an acrylic backbone-chain or a urethane binder.

9. A method of forming an image comprising

providing a planographic printing plate precursor according to claim 7 , and

exposing the planographic printing plate precursor to a laser beam having a wavelength of 300 to 1,200 nm.

10. The planographic printing plate precursor according to claim 7 , wherein the polymerization initiator is a radical generating agent selected from the group consisting of onium salts, triazine compounds, peroxides, azo-based polymerization initiators, azide compounds, quinonediazide, oximeester compounds and triarylmonoalkylborate.

11. The planographic printing plate precursor according to claim 10 , wherein the radical generating agent is an onium salt selected from the group consisting of an iodonium salt, a diazonium salt and a sulfonium salt.

12. The planographic printing plate precursor according to claim 7 , wherein the polymerization initiator is included in an amount of 0.1 to 50% by mass relative to a total solid content in the photosensitive layer.

13. The planographic printing plate precursor according to claim 7 , wherein the polymerizable compound is included in an amount of 5 to 80% by mass relative to nonvolatile components in the photosensitive layer.

14. The planographic printing plate precursor according to claim 7 , further comprising a thermal polymerization inhibitor.

15. The planographic printing plate precursor according to claim 14 , wherein the thermal polymerization inhibitor is selected from the group consisting of hydroquinone, p-methoxyphenol, di-t-butyl-p-cresol, pyrogallol, t-butylcatecol, benzoquinone, 4,4′-thiobis(3-methyl-6-t-buthylphenol), 2,2′methylenebis(4-methyl-6-t-butylphenol) and a primary cerium salt of N-nitrosophenylhydroxyamine.

16. The planographic printing plate precursor according to claim 7 , wherein R 2 in formula (I) represents an alkylene group or an arylene group.

17. The planographic printing plate precursor according to claim 7 , wherein a repeating unit having an amide group is contained in the binder polymer.

18. The planographic printing plate precursor according to claim 7 , wherein the photosensitive layer has a developing velocity of 80 nm/sec or greater at unexposed areas with respect to an alkaline developer having a pH of 10 to 13.5, and the alkaline developer has a permeating velocity of 100 nF/sec or less at exposed areas.