Positive working lithographic printing plate precursor and process for preparing lithographic printing plate

1. A positive working lithographic printing plate precursor, comprising:

(1) a substrate; and

(2) an imaging layer, formed on the substrate, comprising a water-insoluble and an alkaline aqueous solution-soluble or dispersible resin and a photo-thermal converting material,

wherein

the imaging layer comprises either polyurethane or polyurethane urea or both of the polyurethane and the polyurethane urea, the polyurethane and the polyurethane urea comprising a unit having a substituent having an acidic hydrogen atom and a unit having a polysiloxane moiety in a side or main chain.

2. A positive working lithographic printing plate precursor, comprising:

(1) a substrate;

(2) a bottom layer formed on the substrate; and

(3) a top layer formed on the bottom layer,

wherein

the (2) bottom layer and the (3) top layer comprise a water-insoluble and alkaline aqueous solution-soluble or dispersible resin;

either of the (2) bottom layer or the (3) top layer or both of the (2) bottom layer and the (3) top layer comprise(s) a photo-thermal converting material; and

the top layer (3) comprises either polyurethane or polyurethane urea or both of the polyurethane and the polyurethane urea, the polyurethane and the polyurethane urea comprising a unit having a substituent having an acidic hydrogen atom and a unit having a polysiloxane moiety in a side or main chain.

3. The positive working lithographic printing plate precursor according to claim 1 , wherein the polyurethane is obtainable from the reaction of

at least one diisocyanate component, and

a diol component comprising a diol comprising a substituent having an acidic hydrogen atom and a diol having a polysiloxane moiety in a side or main chain.

4. The positive working lithographic printing plate precursor according to claim 1 , wherein the polyurethane urea is obtainable from the reaction of:

at least one diisocyanate component,

a diol component comprising either a diol comprising a substituent having an acidic hydrogen atom, a diol having a polysiloxane moiety in a side or main chain, or a diol comprising both a substituent having an acidic hydrogen atom and a polysiloxane moiety in a side or main chain, and

at least one diamine component.

5. The positive working lithographic printing plate precursor according to claim 4 , wherein the at least one diamine component is a diamine having a polysiloxane moiety in a main chain.

6. The positive working lithographic printing plate precursor according to claim 1 , wherein the substituent having an acidic hydrogen atom is selected from the group consisting of a carboxy group, —SO 2 NHCOO—, —CONHSO 2 —, —CONHSO 2 NH—, and —NHCONHSO 2 —.

7. The positive working lithographic printing plate precursor according to claim 3 , wherein the dial having a polysiloxane moiety in a side or main chain has no silicon atom-bonded hydroxy group.

8. The positive working lithographic printing plate precursor according to claim 3 , wherein the diol having a polysiloxane moiety in a main chain is a both terminal hydroxy-modified diorganopolysiloxane which has at both terminals a group represented by the formula:

—(C l H 2l ) p —(OC m H 2m ) q —(OC n H 2n ) r —(C 6 H 4 ) s —OH

wherein

l, m and n each independently denotes an integer from 1 to 3,

p is an integer of 1 or more,

q is an integer of from 0 to 100,

r is an integer of from 0 to 100, and

s is an integer of from 0 to 3.

9. The positive working lithographic printing plate precursor according to claim 3 , wherein the diol having a polysiloxane moiety in a side chain is a one terminal diol-modified diorganopolysiloxane represented by the formula:

R 1 3 SiO—(R 1 2 SiO) t —SiR 1 2 R 2

wherein

R 1 independently denotes a C 1 -C 20 alkyl group, a C 6 -C 20 aryl group or a C 7 -C 20 aralkyl group;

R 2 denotes —(C l H 2l ) u —(OC m H 2m ) v —(OC n H 2n ) w —(C 6 H 4 ) x —CR 1 R 3 2

wherein

l, m, n and R 1 are as defined above,

u is an integer of 1 or more,

v is an integer of from 0 to 100,

w is an integer of from 0 to 100,

x is an integer from 0 to 3, and

R 3 independently denotes —(C y H 2y ) z OH where y is an integer of from 1 to 3 and z is an integer of from 1 to 100; and

t is an integer of from 1 to 10,000.

10. The positive working lithographic printing plate precursor according to claim 1 , wherein the amount in the imaging layer of either polyurethane or polyurethane urea or both of the polyurethane and the polyurethane urea is from 10 to 99% by weight relative to the total weight of the imaging layer.

11. The positive working lithographic printing plate precursor according to claim 2 , wherein the amount in the (3) top layer of either polyurethane or polyurethane urea or both of the polyurethane and the polyurethane urea is from 10 to 99% by weight relative to the total weight of the (3) top layer.

12. A process for preparing a lithographic printing plate, comprising the steps of:

imagewise exposing the positive working lithographic printing plate precursor according to claim 1 ; and

developing the exposed positive working lithographic printing plate precursor with an alkaline developer to remove exposed regions in order to form imaging and non-imaging regions.

13. The process for preparing a lithographic printing plate according to claim 12 , wherein the step of imagewise exposing is performed by using an IR laser.

14. The process for preparing a lithographic printing plate according to claim 12 , wherein the alkaline developer has a pH of 12 or less.

15. The positive working lithographic printing plate precursor according to claim 2 , wherein the polyurethane is obtainable from the reaction of

at least one diisocyanate component, and

a diol component comprising a diol comprising a substituent having an acidic hydrogen atom and a diol having a polysiloxane moiety in a side or main chain.

16. A process for preparing a lithographic printing plate, comprising the steps of:

imagewise exposing the positive working lithographic printing plate precursor according to claim 2 ; and

developing the exposed positive working lithographic printing plate precursor with an alkaline developer to remove exposed regions in order to form imaging and non-imaging regions.