Polymerizable composition and lithographic printing plate precursor

1. A lithographic printing plate precursor comprising: an aluminum support subjected to a surface roughening treatment; and a photosensitive layer formed from a polymerizable composition comprising:

(A) at least one saccharide selected from the group consisting of an oligosaccharide and a polysaccharide, the polysaccharide containing an amino group, an alkylamino group, an acetylamino group, an ethyleneoxy group, a sulfonic acid group, a phosphoric acid group, a urethane group, a urea group, or a thiol group as a hydrophilic group;

(B) a film-forming binder polymer which is not the at least one saccharide (A);

(C) a compound having an addition polymerizable ethylenic unsaturated bond;

(D) a polymerization initiator; and

(E) a sensitizing dyestuff having an absorption maximum at a wavelength of from 300 to 600 mn.

2. A lithographic printing plate precursor comprising:

a support;

a layer comprising at least one saccharide selected from the group consisting of an oligosaccharide and a polysaccharide, wherein the polysaccharide has at least one substituent selected from the group consisting of a hydrophilic group and a salt of the hydrophilic group, wherein the hydrophilic group is selected from the group consisting of an amino group, an alkylamino group, an acetylamino group, an ethyleneoxy group, a sulfonic acid group, a phosphoric acid group, a urethane group, a urea group and a thiol group; and a photosensitive layer, in this order, wherein the photosensitive layer comprises:

(B) a binder polymer having an ethylenic unsaturated double bond in a side chain of the binder polymer;

(C) a compound having an addition polymerizable ethylenic unsaturated bond;

(D) a polymerization initiator; and

(E) a sensitizing dyestuff having an absorption maximum at a wavelength of from 300 to 600 nm.

3. The lithographic printing plate precursor according to claim 2 , wherein the polysaccharide has a property that a part or an entire structure of the polysaccharide takes a helical structure in an aqueous solution having a concentration of 50 mass % or less.

4. A process for producing a lithographic printing plate comprising:

imagewise exposing a lithographic printing plate precursor according to claim 1 to thereby cure an exposed area; and

subjecting the exposed lithographic printing plate precursor to wet development processing.

5. The lithographic printing plate precursor according to claim 2 , wherein the at least one substituent selected from the group consisting of a hydrophilic group and a salt of the hydrophilic group is a least one of a sulfonic acid group and a salt of a sulfonic acid group.

6. The lithographic printing plate precursor according to claim 3 , which is produced by, at the time of preparation and coating of an undercoat layer coating solution comprising the polysaccharide, stirring and heating the coating solution at 60 to 100 degrees C. for 30 minutes or more; and then coating and drying the coating solution while maintaining the solution at coating and at drying at 60 to 100 degrees C.

7. The polymerizable composition according to claim 1 , wherein the film-forming binder polymer (B) contains a structural unit represented by formula (2):

wherein X represents O, S or —NR 4 —;

Y represents a divalent organic group;

A represents an acid group having an acid dissociation constant pKa of from 0 to 11; and

R 1 , R 2 , R 3 , and R 4 each represents a hydrogen atom, a halogen atom, a monovalent organic group, a cyano group, or a nitro group.