Planographic printing plate precursor

1. A planographic printing plate precursor comprising a support, and a photosensitive layer and a protective layer, which are formed in this sequence on or above the support, wherein:

the photosensitive layer comprises an infrared absorbing agent, a polymerization initiating agent, a polymerizable compound and a binder polymer comprising repeating units as represented by the following Formula (i); and

the protective layer comprises an inorganic lamellar compound:

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

2. A planographic printing plate precursor according to claim 1 , wherein a coating amount of the protective layer when dry is 0.5 to 2.0 g/m 2 .

3. A planographic printing plate precursor according to claim 1 , wherein an amount of the inorganic lamellar compound contained in the protecting layer is in a range of 5 to 55% by mass relative to a total solid content of the protecting layer.

4. A planographic printing plate precursor according to claim 1 , wherein the inorganic lamellar compound is mica.

5. A planographic printing plate precursor according to claim 1 , wherein the inorganic lamellar compound is swelling synthetic mica.

6. A planographic printing plate precursor according to claim 1 , wherein the inorganic lamellar compound is fluorine-containing swelling synthetic mica.

7. A planographic printing plate precursor according to claim 1 , wherein the inorganic lamellar compound is in a form of particles having an aspect ratio of 20 or more, an average major axis of 0.3 to 20 μm, and an average thickness of 0.1 μm or less.

8. A planographic printing plate precursor according to claim 1 , wherein the protective layer comprises polyvinyl alcohol as a binder component.

9. A planographic printing plate precursor according to claim 1 , wherein the protective layer comprises polyvinyl alcohol and polyvinyl pyrrolidone as binder components.

10. A planographic printing plate precursor according to claim 9 , wherein an addition ratio by mass of polyvinyl alcohol/polyvinyl pyrolidone is 3/1 or less.

11. A planographic printing plate precursor according to claim 1 , wherein the connecting group represented by R 2 in Formula (i) is a hydrocarbon group having an alicyclic structure having 3 to 30 carbon atoms and a valency of (n+1).

12. A method for forming the planographic printing plate precursor of claim 1 , comprising:

preparing a dispersion liquid of the inorganic lamellar compound;

preparing a protecting layer coating liquid, by blending the dispersion on liquid and a binder component; and

coating the protecting layer coating liquid over the photosensitive layer so as to form the protecting layer.

13. A planographic printing plate precursor according to claim 1 , wherein the binder polymer comprising repeating units as represented by the following Formula (i);

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