Multifunctional type II photoinitiators and curable compositions

1. A multifunctional Type II photoinitiator according to Formula (I):

wherein X represents a structural moiety according to Formula (II):

wherein:

A represents a Norrish Type II initiating group;

L represents a divalent linking group positioning the Norrish Type II initiating group A and the CR2R3-group in a 1-5 to a 1-9 position wherein position 1 is defined as the first atom in the aromatic or alicyclic ring of A to which L is covalently bonded and the position 5 to 9 is defined as the carbon atom of the CR2R3-group to which L is covalently bonded, with the proviso that L does not contain an amine;

R1 represents an optionally substituted group selected from the group consisting of an alkyl group, an alkynyl group, an aralkyl group, an alkaryl group, an aryl group, and a heteroaryl group;

R2 to R6 each independently represent a hydrogen or an optionally substituted group selected from the group consisting of an alkyl group, an alkenyl group, an alkynyl group, an aralkyl group, an alkaryl group, an aryl group, and a heteroaryl group, with the proviso that at least one of R2 to R6 represents a hydrogen;

any two or three groups of the group selected from R1 to R6 and L may represent the necessary atoms to form a five to eight membered ring, and with the proviso that L is not substituted with a (meth)acrylate group and that none of R1 to R6 is substituted with an ethylenically unsaturated polymerizable group;

Q represents an n-valent linking group having a number average molecular weight of at most 5,000;

Q is bonded to each of the moieties X via a single bond to a group selected from R1 to R6, L, and A; and

n represents an integer from 2 to 8.

2. The multifunctional Type II photoinitiator according to claim 1 , wherein the Norrish Type II initiating group A is selected from the group consisting of an optionally substituted benzophenone and an optionally substituted thioxanthone.

3. The multifunctional Type II photoinitiator according to claim 2 , including an optionally substituted benzophenone and an optionally substituted thioxanthone.

4. The multifunctional Type II photoinitiator according to claim 1 , wherein the n-valent linking group Q includes at least one ethylene oxide and/or propylene oxide moiety.

5. The multifunctional Type II photoinitiator according to claim 1 , wherein R1 is selected from the group consisting of a substituted or unsubstituted alkyl group and a substituted or unsubstituted aryl group.

6. The multifunctional Type II photoinitiator according to claim 5 , wherein R1 represents an aryl group according to Formula (III):

wherein the dotted line represents a chemical bond to the nitrogen atom in Formula (II), and E represents a group selected from the group consisting of an ester, an aldehyde, a ketone, and an amide.

7. The multifunctional Type II photoinitiator according to claim 6 , wherein the group E represents an ester group.

8. The multifunctional Type II photoinitiator according to claim 1 , wherein the divalent linking group L is represented by the group —O—(CH 2 ) n — with n representing an integer selected from 3 to 7.

9. A radiation curable composition comprising:

the multifunctional Type II photoinitiator according to claim 1 .

10. The radiation curable composition according to claim 9 , wherein the radiation curable composition is a radiation curable inkjet ink including a colorant.

11. A radiation curable ink set comprising:

the radiation curable composition according to claim 9 .

12. An inkjet printing method comprising the steps of:

a) providing the radiation curable composition according to claim 9 ; and

b) at least partially curing the radiation curable composition.

13. The inkjet printing method according to claim 12 , further comprising the step of:

applying the radiation curable composition to a substrate by flexographic printing; and

printing an inkjet ink upon the at least partially cured radiation curable composition.

14. The inkjet printing method according to claim 12 , further comprising the step of:

jetting the radiation curable composition upon a substrate.