Photosensitive lithographic printing plate

1 . A photosensitive lithographic printing plate comprising: an aluminum support; a photopolymerizable photosensitive layer; and an oxygen blocking layer in this order, wherein the photopolymerizable photosensitive layer contains (1) a polyurethane binder, (2) a polymerizable compound having a urethane bond and two ethylenically unsaturated bonds, (3) a polymerizable compound having a urethane bond and four or more ethylenically unsaturated bonds, and (4) a photopolymerization initiator.

2 . The photosensitive lithographic printing plate as claimed in claim 1 , wherein the polyurethane binder (1) has an ethylenically unsaturated bond.

3 . The photosensitive lithographic printing plate as claimed in claim 1 , wherein the polymerizable compound (2) is a compound represented by the following formula (1):

X—R—U-A-U—R—X  (1)

wherein A represents an alkylene group, an aralkylene group, an arylene group or an oxyalkylene group; U each represents a urethane bond; X each represents a methacryloyl group, an acryloyl group or a vinyl group; R each represents a divalent linking group.

4 . The photosensitive lithographic printing plate as claimed in claim 2 , wherein the polymerizable compound (2) is a compound represented by the following formula (1):

X—R—U-A-U—R—X  (1)

wherein A represents an alkylene group, an aralkylene group, an arylene group or an oxyalkylene group; U each represents a urethane bond; X each represents a methacryloyl group, an acryloyl group or a vinyl group; R each represents a divalent linking group.

5 . The photosensitive lithographic printing plate as claimed in claim 1 , wherein a content of the polymerizable compound (2) is from 10 to 60% by weight based on a total solid content of the photopolymerizable photosensitive layer.

6 . The photosensitive lithographic printing plate as claimed in claim 2 , wherein a content of the polymerizable compound (2) is from 10 to 60% by weight based on a total solid content of the photopolymerizable photosensitive layer.

7 . The photosensitive lithographic printing plate as claimed in claim 3 , wherein a content of the polymerizable compound (2) is from 10 to 60% by weight based on a total solid content of the photopolymerizable photosensitive layer.

8 . The photosensitive lithographic printing plate as claimed in claim 1 , wherein a content of the polymerizable compound (2) is from 20 to 50% by weight based on a total solid content of the photopolymerizable photosensitive layer.

9 . The photosensitive lithographic printing plate as claimed in claim 1 , wherein the polymerizable compound (3) is a compound represented by the following formula (3):

D-(-U—R—X) 2-3   (3)

wherein D represents a divalent or trivalent group; U represents a urethane bond; R represents a linking group comprising a trivalent or tetravalent carbon atom or a linking group comprising a carbon atom and an oxygen atom; and X represents a methacryloyl group, an acryloyl group or a vinyl group.

10 . The photosensitive lithographic printing plate as claimed in claim 2 , wherein the polymerizable compound (3) is a compound represented by the following formula (3):

D-(-U—R—X) 2-3   (3)

wherein D represents a divalent or trivalent group; U represents a urethane bond; k represents a linking group comprising a trivalent or tetravalent carbon atom or a linking group comprising a carbon atom and an oxygen atom; and X represents a methacryloyl group, an acryloyl group or a vinyl group.

11 . The photosensitive lithographic printing plate as claimed in claim 3 , wherein the polymerizable compound (3) is a compound represented by the following formula (3):

D-(-U—R—X) 2-3   (3)

wherein D represents a divalent or trivalent group; U represents a urethane bond; R represents a linking group comprising a trivalent or tetravalent carbon atom or a linking group comprising a carbon atom and an oxygen atom; and X represents a methacryloyl group, an acryloyl group or a vinyl group.

12 . The photosensitive lithographic printing plate as claimed in claim 4 , wherein the polymerizable compound (3) is a compound represented by the following formula (3):

D-(-U—R—X) 2-3   (3)

wherein D represents a divalent or trivalent group; U represents a urethane bond; R represents a linking group comprising a trivalent or tetravalent carbon atom or a linking group comprising a carbon atom and an oxygen atom; and X represents a methacryloyl group, an acryloyl group or a vinyl group.

13 . The photosensitive lithographic printing plate as claimed in claim 1 , wherein a content of the polymerizable compound (3) is from 10 to 60% by weight based on a total solid content of the photopolymerizable photosensitive layer.

14 . The photosensitive lithographic printing plate as claimed in claim 2 , wherein a content of the polymerizable compound (3) is from 10 to 60% by weight based on a total solid content of the photopolymerizable photosensitive layer.

15 . The photosensitive lithographic printing plate as claimed in claim 9 , wherein a content of the polymerizable compound (3) is from 10 to 60% by weight based on a total solid content of the photopolymerizable photosensitive layer.

16 . The photosensitive lithographic printing plate as claimed in claim 1 , wherein a content of the polymerizable compound (3) is from 20 to 50% by weight based on a total solid content of the photopolymerizable photosensitive layer.

17 . The photosensitive lithographic printing plate as claimed in claim 1 , wherein the photopolymerizable photosensitive layer further contains a chain transfer agent.

18 . The photosensitive lithographic printing plate as claimed in claim 2 , wherein the photopolymerizable photosensitive layer further contains a chain transfer agent.

19 . The photosensitive lithographic printing plate as claimed in claim 3 , wherein the photopolymerizable photosensitive layer further contains a chain transfer agent.

20 . The photosensitive lithographic printing plate as claimed in claim 9 , wherein the photopolymerizable photosensitive layer further contains a chain transfer agent.

21 . The photosensitive lithographic printing plate as claimed in claim 1 , wherein the photopolymerization initiator is at least one member selected from the group consisting of a hexaarylbiimidazole compound, an onium salt, a trihalomethyl compound and a metallocene compound.

22 . The photosensitive lithographic printing plate as claimed in claim 1 , wherein the photopolymerization initiator is a hexaarylbiimidazole compound.