LITHOGRAPHIC PRINTING PLATE PRECURSOR AND METHOD OF USE
IR-sensitive lithographic printing plate precursors provide a stable print-out image using a unique IR radiation-sensitive composition in an infrared radiation-sensitive image-recording layer. This IR radiation-sensitive composition includes: (1) a free radical initiator composition that comprises an electron-donating agent; (2) a free radically polymerizable composition; and (3) a color-changing compound that is represented by the Structure (I) having an indene ring in the conjugated chain between the aromatic terminal groups. The compound can also have a —C(═O)—OR 7 , —SO 2 —R 3 , or —SO 2 NR 8 R 9 group wherein R 7 represents a substituted or unsubstituted alkyl group having a secondary or tertiary connecting carbon that connects to the rest of the —C(═O)—OR 7 group; and R 8 , R 9 , and R 10 independently represent substituted or unsubstituted alkyl, aryl, or heteroaryl groups. After IR imaging, these precursors exhibit desirable printout images both fresh and after dark storage. The precursors can be developed off-press or on-press.
1 . A lithographic printing plate precursor comprising:
a substrate, and
an infrared radiation-sensitive image-recording layer disposed on the substrate, the infrared radiation-sensitive image-recording layer comprising the following components (1), (2), and (3):
(1) a free radical initiator composition that is capable of generating free radicals upon exposure to infrared radiation, and which comprises an electron-donating agent;
(2) a free radically polymerizable composition; and
(3) a color-changing compound that is represented by the following Structure (I)
wherein:
Ar1, Ar2, and Ar3 independently represent the atoms necessary to complete substituted or unsubstituted aromatic rings or to complete substituted or unsubstituted heteroaromatic rings;
Y represents an oxygen atom, a sulfur atom, or a dialkylmethylene group represented by >C(R 4 R 5 ) wherein R 4 and R 5 are independently substituted or unsubstituted alkyl groups having 1 to 4 carbons;
R 1 and R 2 are independently substituted or unsubstituted alkyl groups;
X represents a single bond or a divalent linking group selected from —S—, —O—, and >N(R 6 ) wherein R 6 is hydrogen, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heteroaryl group, or L;
L represents a —C(═O)—OR 7 group, —SO 2 —R 3 group, or —SO 2 NR 8 R 9 group, wherein R 7 represents a substituted or unsubstituted alkyl group that has a secondary or tertiary connecting carbon that connects to the remainder of the —C(═O)OR 7 group; and R 3 , R 8 , and R 9 independently represent substituted or unsubstituted alkyl groups, substituted or unsubstituted aryl groups, or substituted or unsubstituted heteroaryl groups; and
Za represents one or more counter ions to balance the electric charge in the rest of the color-changing compound according to Structure (I).
2 . The lithographic printing plate precursor of claim 1 , wherein the (3) color-changing compound is represented by the following Structure (II):
wherein Ar1, Ar2, Ar3, R 1 , R 2 , R 3 , R 6 , Y, and Za are as defined above.
3 . The lithographic printing plate precursor of claim 1 , wherein Ar1 and Ar2 are the atoms necessary to complete substituted or unsubstituted aromatic rings.
4 . The lithographic printing plate precursor of claim 1 , wherein one or both of the aromatic rings completed by the atoms of Ar1 and Ar2 are substituted with one or two halo groups that can be the same or different.
5 . The lithographic printing plate precursor of claim 1 , wherein R 3 is a trifluoromethyl group.
6 . The lithographic printing plate precursor of claim 1 , wherein Ar3 represents the carbon and hydrogen atoms needed to complete a benzene ring.
7 . The lithographic printing plate precursor of claim 1 , wherein Za comprises a tetraaryl borate anion.
8 . The lithographic printing plate precursor of claim 1 , wherein the electron donating agent is an organic borate salt represented by the following Structure (III):
[B(R 10 R 11 R 12 R 13 ) − ] n M n+ Structure (III)
wherein R 10 , R 11 , R 12 , and R 13 are independently substituted or unsubstituted alkyl groups or substituted or unsubstituted aryl groups, and at least three of R 10 , R 11 , R 12 , and R 13 are the same or different substituted or unsubstituted aryl groups, n is an integer equal to or greater than 1, and M n+ is an n-valent cation.
9 . The lithographic printing plate precursor of claim 8 , wherein all of R 10 , R 11 , R 12 , and R 13 are substituted or unsubstituted aryl groups.
10 . The lithographic printing plate precursor of claim 8 , wherein all of R 10 , R 11 , R 12 , and R 13 are the same substituted or unsubstituted phenyl groups.
11 . The lithographic printing plate precursor of claim 1 , wherein one or both of R 1 and R 2 independently comprises a chain of carbon atoms interrupted by one or more ether or ester linkages.
12 . The lithographic printing plate precursor of claim 1 , wherein the infrared radiation-sensitive image-recording layer further comprises a component (4) infrared absorbing material that is different from the component (3) color-changing compound.
13 . The lithographic printing plate precursor of claim 1 , wherein the component (1) free radical initiator composition comprises an onium salt.
14 . The lithographic printing plate precursor of claim 1 , wherein the component (1) free radical initiator composition comprises an iodonium cation.
15 . The lithographic printing plate precursor of claim 14 , wherein the iodonium cation is a diaryliodonium cation.
16 . The lithographic printing plate precursor of claim 1 , wherein the infrared radiation-sensitive image-recording layer further comprises a component (5) acid-sensitive dye precursor that is different from all of the components (1), (2), (3), and (4) defined above.
17 . The lithographic printing plate precursor of claim 1 , wherein the infrared radiation-sensitive image-recording layer further comprises a component (6) non-free radically polymerizable polymeric material that is different from all of the components (1), (2), (3), and (4) defined above and is present in particulate form.
18 . The lithographic printing plate precursor of claim 1 , wherein, the infrared radiation sensitive image-recording layer is the outermost layer.
19 . The lithographic printing plate precursor of claim 1 , wherein the component (3) color-changing compound represented by Structure (I) is present in the infrared radiation-sensitive image-recording layer in a coverage amount of at least 0.5 weight % and up to and including 15 weight %, based on the total weight of the infrared radiation-sensitive image-recording layer.
20 . A method for providing a lithographic printing plate, comprising:
A) imagewise exposing the lithographic printing plate precursor according to claim 1 to infrared radiation, to provide exposed regions and non-exposed regions in the infrared radiation-sensitive image-recording layer, and
B) removing the non-exposed regions in the infrared radiation-sensitive image-recording layer from the substrate on-press using a lithographic printing ink, a fountain solution, or a combination of a lithographic printing ink and a fountain solution.