LITHOGRAPHIC PRINTING PLATE PRECURSOR
A lithographic printing plate precursor is disclosed including a support and a coating comprising a sensitizer and an onium salt wherein the onium salt and the sensitizer are capable of inducing a print-out image upon UV light exposure.
1 . A negative-working lithographic printing plate precursor comprising:
a coating comprising at least one sensitizer and an onium salt;
wherein the sensitizer and the onium salt are capable of inducing a print-out image upon UV light exposure.
2 . The lithographic printing plate precursor according to claim 1 wherein the coating is stable for at least five minutes in office light.
3 . The lithographic printing plate precursor according to claim 1 wherein the sensitizer is represented by Formula II:
wherein
R 1 to R 14 independently represent hydrogen, an alkyl group, an alkoxy group, a cyano group or a halogen.
4 . The lithographic printing plate precursor according to claim 3 wherein at least one of R 1 to R 10 represents an alkoxy group having more than 1 carbon atom.
5 . The lithographic printing plate precursor according to claim 1 wherein the sensitizer is a mixture comprising Formulas III, IV, and V:
6 . The printing plate precursor according to claim 1 wherein the sensitizer has an absorption maximum in a wavelength range from 320 nm and 500 nm.
7 . The printing plate precursor according to claim 1 wherein the onium salt is an optionally substituted iodonium or sulfonium compound.
8 . The printing plate precursor according to claim 1 wherein the onium salt is an optionally substituted diaryliodonium or triaryl sulfonium compound.
9 . The printing plate precursor according to claim 1 wherein the onium salt has hexafluorophosphate as counter ion.
10 . The printing plate precursor according to claim 1 wherein the onium salt is present in an amount comprised between 1% wt and 25% wt.
11 . The printing plate precursor according to claim 1 wherein the coating further comprises a radical polymerisation initiator, a radically polymerisable compound, and a binder polymer.
12 . The printing plate precursor according to claim 1 wherein the coating further comprises a diazonium compound.
13 . A method for making a printing plate comprising:
image-wise exposing the printing plate precursor as defined in claim 1 to UV radiation whereby a lithographic image consisting of image areas and non-image areas is formed and whereby a colour change in the image areas is induced; and
developing the exposed precursor.
14 . The method according to claim 13 wherein the colour change is characterized by a CIE 1976 colour distance ΔE between the image and non-image areas of at least 5.
15 . The method according to claim 13 wherein the energy density of the UV radiation is between 10 mJ/cm 2 and 150 mJ/cm 2 .
16 . A method for making a printing plate comprising:
image-wise exposing the printing plate precursor as defined in claim 3 to UV radiation whereby a lithographic image consisting of image areas and non-image areas is formed and whereby a colour change in the image areas is induced; and
developing the exposed precursor.
17 . The method according to claim 16 wherein the colour change is characterized by a CIE 1976 colour distance ΔE between the image and non-image areas of at least 5.
18 . The method according to claim 16 wherein the energy density of the UV radiation is between 10 mJ/cm 2 and 150 mJ/cm 2 .
19 . A method for making a printing plate comprising:
image-wise exposing the printing plate precursor as defined in claim 5 to UV radiation whereby a lithographic image consisting of image areas and non-image areas is formed and whereby a colour change in the image areas is induced; and
developing the exposed precursor.
20 . The method according to claim 19 wherein the colour change is characterized by a CIE 1976 colour distance ΔE between the image and non-image areas of at least 5.