Lithographic printing plate precursor

1. A lithographic printing plate precursor comprising a photosensitive layer comprising:

(A) a fluorescent brightening agent which is a compound capable of absorbing light at a wavelength of 350 to 450 nm and emitting the absorbed light energy as fluorescence having a wavelength of 400 to 500 nm, said fluorescent brightening agent having a skeleton of the following structure, with the proviso that the skeleton may have one or more substituents:

(B) a hexaarylbiimidazole activator compound being capable of inducing a chemical change by an interaction with light absorption of the fluorescent brightening agent to produce at least one of a radical, an acid and a base;

(C) a compound being capable of undergoing a reaction by an effect of at least one of a radical, an acid and a base to irreversibly change in its physical or chemical properties; and

(D) a polyurethane resin binder,

wherein the polyurethane resin binder is synthesized from at least following compounds (i), (ii), (iii) and (iv):

(i) a diisocyanate compound;

(ii) a diol compound having at least one carboxyl group;

(iii) a diol compound having a logP value of less than 0; and

(iv) a diol compound having a logP value of 0 or more,

with the proviso that each of the diol compound (iii) and the diol compound (iv) does not have a carboxyl group.

2. The lithographic printing plate precursor according to claim 1 , wherein the activator compound (B) is a titanocene compound or a hexaarylbiimidazole compound.

3. The lithographic printing plate precursor according to claim 1 , wherein the diol compound (iii) has a logP value of from −10 to −0.5.

4. The lithographic printing plate precursor according to claim 1 , wherein the diol compound (iii) has a logP value of from −8 to −1.

5. The lithographic printing plate precursor according to claim 1 , wherein the diol compound (iv) has a logP value of from 0.5 to 30.

6. The lithographic printing plate precursor according to claim 1 , wherein the diol compound (iv) has a logP value of from 1 to 20.

7. The lithographic printing plate precursor according to claim 1 , wherein the component (C) is an addition-polymerizable compound having an ethylenically unsaturated double bond.

8. The lithographic printing plate precursor according to claim 1 , wherein the polyurethane resin binder (D) has an acid value of from 0.2 to 4.0 meq/g.

9. The lithographic printing plate precursor according to claim 1 , wherein the polyurethane resin binder (D) has an acid value of from 0.3 to 3.0 meq/g.

10. The lithographic printing plate precursor according to claim 1 , wherein the polyurethane resin binder (D) has a molecular weight in terms of polystyrene as measured by a GPC method of from 5,000 to 500,000.

11. The lithographic printing plate precursor according to claim 1 , wherein the diol compound (iii) is represented by formula (A′):

HO—(CH 2 CH 2 O) n —H  (A′)

wherein n represents an integer of 1 or more.

12. The lithographic printing plate precursor according to claim 1 , wherein the diol compound (iv) is polypropylene glycol.

13. The lithographic printing plate precursor according to claim 1 , wherein the diol compound (iii) is a diol compound represented by formula (A′):

HO—(CH 2 CH 2 O) n —H  (A′)

wherein n represents an integer of 1 or more, and the diol compound (iv) is polypropylene glycol.

14. The lithographic printing plate precursor according to claim 1 , wherein the photosensitive layer components are soluble in neutral and/or alkalescent water.

15. The lithographic printing plate precursor according to claim 14 , which can perform exposure and development on a printing press.