Planographic printing plate precursor and plate-making method thereof

1 . A planographic printing plate precursor, comprising a photosensitive layer containing an infrared absorbent, a polymerization initiator, a polymerizable compound, and a binder polymer, and a protective layer formed in this order on a hydrophilic aluminum support surface, wherein the protective layer contains polyvinyalcohol having a saponification value of 91 mole % or more and a mica compound in an amount of 5 wt % to 50 wt % relative to the total weight of the protective layer.

2 . The planographic printing plate precursor according to claim 1 , wherein the oxygen permeability of the protective layer at 25° C. and −1 atm is 0.5 ml/m 2 ·day to 100 ml/m 2 ·day.

3 . The planographic printing plate precursor according to claim 1 , wherein the binder polymer is a binder polymer having a repeating unit represented by the following Formula (i):

wherein R 1 represents a hydrogen atom or a methyl group, R 2 represents a connecting group which contains two or more atoms selected from the group consisting of a carbon atom, a hydrogen atom, an oxygen atom, a nitrogen atom, and a sulfur atom and which has 2 to 82 atoms in total, A represents an oxygen atom or —NR 3 —; R 3 represents a hydrogen atom or a monovalent hydrocarbon group having 1 to 10 carbon atoms; and n represents an integer of 1 to 5.

4 . The planographic printing plate precursor according to claim 1 , wherein the polyvinylalcohol is a polyvinylalcohol having an average degree of polymerization in the range of 300 to 2,400.

5 . The planographic printing plate precursor according to claim 1 , wherein the polyvinylalcohol having a saponification value of 91 mol % or more is an acid-modified polyvinylalcohol having an average degree of polymerization of the vinylalcohol unit at 100 to 800.

6 . The planographic printing plate precursor according to claim 1 , wherein the polyvinylalcohol is used in combination with a binder component selected from the group consisting of polyvinylpyrrolidone, acidic celluloses, gelatin, Arabic gum, polyacrylic acid, and the copolymers thereof.

7 . The planographic printing plate precursor according to claim 1 , wherein the mica compound is a mica selected from the group consisting of the natural and synthetic micas represented by Formula: A(B,C) 2 -5D 4 O 10 (OH,F,O) 2 wherein A represents K, Na, or Ca; each of B and C represents Fe(II), Fe(III), Mn, Al, Mg, or V; and D represents Si or Al.

8 . The planographic printing plate precursor according to claim 7 , wherein the mica compound is a synthetic mica selected from the group consisting of non-swelling micas such as fluorine phlogopite KMg 3 (AlSi 3 O 10 )F 2 , and K tetrasilicic mica KMg 2.5 (Si 4 O 10 )F 2 ; and swelling micas such as Na tetrasilicic mica NaMg 2.5 (Si 4 O 10 )F 2 , Na or Li teniolite (Na,Li)Mg 2 Li(Si 4 O 10 )F 2 , and montmorillonite-based Na or Li hectorite (Na,Li) 1/8 Mg 2/5 Li 1/8 (Si 4 O 10 )F 2 .

9 . The planographic printing plate precursor according to claim 8 , wherein the mica compound is a fluorine-containing swelling mica.

10 . The planographic printing plate precursor according to claim 1 , wherein the infrared absorbent is a dye or pigment having an absorption maximum at a wavelength of 750 to 1,400 nm.

11 . The planographic printing plate precursor according to claim 1 , wherein the coating amount of the protective layer is 0.1 to 2.0 g/m 2 .

12 . A method of making the planographic printing plate precursor according to claims 1 , comprising:

placing a laminate of planographic printing plate precursors formed by laminating multiple layers of a protective layer on an aluminum plate, the rear surface of which is brought into contact with the surface of the protective layer in a plate setter,

conveying each of the planographic printing plate precursors automatically,

exposing the precursor with a light having a wavelength of 750 nm to 1,400 nm, and

developing the precursor practically without conducting heat treatment under the condition of a conveyance speed of 1.25 m/min or more.