Method of making a lithographic printing plate

1. A method of making a lithographic printing plate comprising the steps of:

a) providing a lithographic printing plate precursor including a support having a hydrophilic surface or which is provided with a hydrophilic layer, a coating on the support including a photopolymerizable layer, optionally, an intermediate layer between the photopolymerizable layer and the support, and an adhesion promoting compound including a functional group that interacts with the support, wherein the adhesion promoting compound is in the photopolymerizable layer or the optional intermediate layer, and the photopolymerizable layer includes a polymerizable monomer or oligomer including an ethylenically unsaturated compound having at least one terminal ethylenic group, a polymerization initiator, and a reactive binder;

b) image-wise exposing the coating by a laser in a plate setter;

c) optionally, heating the precursor in a pre-heating unit;

d) developing the precursor off-press in a gumming unit by treating the coating of the precursor with a gum solution, thereby removing the non-exposed areas of the photopolymerizable layer from the support; wherein

the reactive binder is a polymer containing a monomeric unit which includes a group having an ethylenically unsaturated bond; and

the gum solution has a pH-value ranging between 3 and 9.

2. A method according to claim 1 , wherein the group having the ethylenically unsaturated bond is in a side chain of the monomeric unit.

3. A method according to claim 1 , wherein the group having the ethylenically unsaturated bond has a terminal ethylenically unsaturated bond in a side chain.

4. A method according to claim 1 , wherein the group having the ethylenically unsaturated bond is a vinyl group or a (meth)acrylate group.

5. A method according to claim 1 , wherein the monomeric unit has the structure of the following formula:

wherein

R 1 to R 4 independently represent hydrogen or an alkyl group;

L 1 and L 2 represent a linking group;

p and q are 0 or 1;

G is a bifunctional group represented by —O—, —S—, —C(═O)—, —NR 5 —, —CR 6 R 7 —, —CR 8 (OH)—, or a combination of at least two of them; and

R 5 to R 8 independently represent hydrogen or an optionally substituted alkyl or aryl group.

6. A method according to claim 1 , wherein the polymer is a product of a reaction of a polymer having a reactive group A and a monomer having a reactive group B, wherein the group A and the group B are capable of reacting with each other to form group G.

7. A method according to claim 6 , wherein the group A is selected from a hydroxyl group, a carboxylic acid group, a carboxylic acid anhydride group, a carboxylic acid chloride group, and an epoxy group.

8. A method according to claim 6 , wherein the group B is selected from a hydroxyl group, a carboxylic acid group, a carboxylic acid anhydride group, a carboxylic acid chloride group, an epoxy group, an amino group, or an isocyanate group.

9. A method according to claim 6 , wherein the polymer having the reactive group A is a polyvinylalcohol, a partially hydrolyzed polyvinylacetate, a copolymer of hydroxy ethyl (meth)acrylate, a copolymer of (meth)acrylic acid, or a copolymer of maleic acid anhydride.

10. A method according to claim 6 , wherein the monomer having the reactive group B is hydroxy alkyl (meth)acrylate, (meth)acrylic acid, (meth)acrylic acid anhydride, (meth)acrylic acid chloride, isocyanato alkyl (meth)acrylate, glycidyl (meth)acrylate, or amino alkyl (meth)acrylate.

11. A method according to claim 1 , wherein the gum solution has a pH-value ranging between 4.5 and 8.5.

12. A method according to claim 1 , wherein the laser emits violet light.

13. A method according to claim 1 , wherein the laser emits infrared light.