Presensitized plate and lithographic printing method

1 . A presensitized plate, comprising:

a support for a lithographic printing plate obtainable by forming on an aluminum plate at least an anodized layer, then performing sealing treatment; and

an image recording layer which is provided on the support, includes an infrared absorber (A), a polymerization initiator (B), and a polymerizable compound (C), and can be removed with printing ink and/or dampening water.

2 . The presensitized plate according to claim 1 , wherein the sealing treatment is carried out with an aqueous solution containing an inorganic fluorine compound.

3 . The presensitized plate according to claim 2 , wherein the inorganic fluorine compound has a concentration in the aqueous solution of 0.01 to 1 wt %.

4 . The presensitized plate according to claim 2 , wherein the aqueous solution contains also a phosphate compound.

5 . The presensitized plate according to claim 4 , wherein the aqueous solution contains as the inorganic fluorine compound at least sodium hexafluorozirconate and contains as the phosphate compound at least sodium dihydrogenphosphate.

6 . The presensitized plate according to claim 4 , wherein the phosphate compound has a concentration in the aqueous solution of 0.01 to 20 wt %.

7 . The presensitized plate according to claim 2 , wherein the sealing treatment is carried out at a temperature in the range of 20 to 100° C.

8 . The presensitized plate according to claim 2 , wherein the sealing treatment is carried out for a period of from 1 to 100 seconds.

9 . The presensitized plate according to claim 1 , wherein the sealing treatment is carried out with steam.

10 . The presensitized plate according to claim 9 , wherein the sealing treatment is carried out at a temperature in the range of 80 to 105° C.

11 . The presensitized plate according to claim 1 , wherein the sealing treatment is carried out with hot water.

12 . The presensitized plate according to claim 11 , wherein the sealing treatment is carried out at a temperature in the range of 80 to 100° C.

13 . The presensitized plate according to claim 9 , wherein the sealing treatment is carried out for a period of from 1 to 100 seconds.

14 . The presensitized plate of claim 1 , wherein the anodized layer after the image recording layer has been provided on the support has a fracture plane in which the atomic ratio of carbon to aluminum (C/Al) expressed by formula (1) below is at most 1.0;

C/Al=( I c /S c )/( I al /S al )   (1),

wherein

I c is the carbon (KLL) Auger electron differential peak-to-peak intensity,

I al is the aluminum (KLL) Auger electron differential peak-to-peak intensity,

S c is the carbon (KLL) Auger electron relative sensitivity factor, and

S al is the aluminum (KLL) Auger electron relative sensitivity factor.

15 . The presensitized plate according to claim 1 , wherein the support is obtainable by performing hydrophilizing treatment after the sealing treatment.

16 . The presensitized plate according to claim 15 , wherein the hydrophilizing treatment is carried out with an aqueous solution containing an alkali metal silicate.

17 . The presensitized plate according to claim 15 , wherein the hydrophilizing treatment is carried out at a temperature in the range of 20 to 100° C.

18 . The presensitized plate according to claim 1 , wherein at least some of the infrared absorber (A), polymerization initiator (B) and polymerizable compound (C) is microencapsulated.

19 . A lithographic printing method which includes the steps of imagewise exposing the presensitized plate according to claim 1 with an infrared laser, supplying printing ink and dampening water to the exposed plate to print.