Photosensitive lithographic printing plate

1. A photosensitive lithographic printing plate comprising a hydrophilic support and a photopolymerizable photosensitive layer containing the following components (i) to (v):

(i) a sensitizing dye having an absorption maximum in a wavelength range of from 360 to 450 nm;

(ii) a hexaarylbisimidazole compound;

(iii) an addition polymerizable compound having an ethylenically unsaturated double bond;

(iv) a binder polymer; and

(v) a mercapto compound represented by the following formula (1):

wherein R 1 represents a group containing an aromatic ring and having from 6 to 20 carbon atoms; and X represents N(R 2 )— in which R 2 represents a straight chain or branched alkyl group having from 1 to 18 carbon atoms, an alkyl group containing an alicyclic structure and having from 5 to 20 carbon atoms or a group containing an aromatic ring and having from 6 to 20 carbon atoms.

2. The photosensitive lithographic printing plate as claimed in claim 1 , wherein the binder polymer comprises three structure units represented by the following formulae (B1) to (B3):

wherein R 1a , R 2a and R 3a each independently represents a hydrogen atom or an alkyl group having from 1 to 6 carbon atom; X represents a functional group selected from —COOH, —CO—W 1 -L 1 -COOH and —SO 3 H in which W 1 represents an oxygen atom, a sulfur atom or —NH— and L 1 represents a divalent organic group; Y represents —CO—O—CH 2 —CH═CH 2 or —CO—W 2 -L 2 -O—CO—C(R 0 )═CH 2 in which W 2 represents an oxygen atom, a sulfur atom or —NH—, L 2 represents a divalent organic group and R 0 represents a hydrogen atom or an alkyl group having from 1 to 6 carbon atom; W 3 represents an oxygen atom, a sulfur atom or —NH—; and R 4a represents a straight chain or branched alkyl group having from 1 to 18 carbon atoms, an alkyl group containing an alicyclic structure and having from 5 to 20 carbon atoms or a group containing an aromatic ring and having from 6 to 20 carbon atoms.

3. The photosensitive lithographic printing plate as claimed in claim 1 , wherein a ratio of a content of the component (iii) contained in the photopolymerizable photosensitive layer to a content of the component (iv) contained in the photopolymerizable photosensitive layer is 1.0 or less.

4. The photosensitive lithographic printing plate as claimed in claim 2 , wherein a ratio of a content of the component (iii) contained in the photopolymerizable photosensitive layer to a content of the component (iv) contained in the photopolymerizable photosensitive layer is 1.0 or less.

5. The photosensitive lithographic printing plate as claimed in claim 1 , further comprising an overcoat layer containing a water-soluble resin, so that the hydrophilic support, the photopolymerizable photosensitive layer and the overcoat layer are in this order.

6. The photosensitive lithographic printing plate as claimed in claim 1 , wherein the binder polymer has a weight average molecular weight of from 5,000 to 300,000 and an acid value of from 0.5 to 200.

7. The photosensitive lithographic printing plate as claimed in claim 6 , wherein the binder polymer has an acid value of from 5.0 to 180.

8. The photosensitive lithographic printing plate as claimed in claim 6 , wherein the binder polymer has an acid value of from 10 to 150.

9. The photosensitive lithographic printing plate as claimed in claim 2 , wherein a weight ratio of a total amount of the structure unit represented by the formula (B1) and the structure unit represented by the formula (B3) to an amount of the structure unit represented by the formula (B2) is from 0.1 to 3.0.

10. The photosensitive lithographic printing plate as claimed in claim 2 , wherein a weight ratio of a total amount of the structure unit represented by the formula (B1) and the structure unit represented by the formula (B3) to an amount of the structure unit represented by the formula (B2) is from 0.1 to 2.0.