Negatively-working lithographic printing plate precursor and method
A negative-working infrared radiation-sensitive lithographic printing plate precursor can be imaged and developed on-press to provide a lithographic printing plate. Such precursor has an initiator composition that contains compound A of Structure (I) and one or more compounds collectively as compound B of Structure (II) or Structure (III): wherein R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are independently alkyl groups each having 3 to 6 carbon atoms; at least one of R 3 and R 4 is different from R 1 or R 2 ; the difference of total number of carbon atoms in R 1 and R 2 and the total number of carbon atoms in R 3 and R 4 is 0, 1, or 2; the difference of total number of carbon atoms in R 1 and R 2 and the total number of carbon atoms in R 5 and R 6 is 0, 1, or 2; and X 1 , X 2 and X 3 are the same or different anions.
1. A negative-working, infrared radiation-sensitive lithographic printing plate precursor comprising:
a substrate having a hydrophilic surface, and
an infrared radiation-sensitive imageable layer that is disposed on the hydrophilic surface of the substrate, and comprises:
one or more free radically polymerizable compounds;
one or more infrared radiation absorbers;
an initiator composition that provides free radicals upon exposure of the infrared radiation-sensitive imageable layer to infrared radiation, the initiator composition comprising compound A and, one or more compounds collectively as compound B; and
optionally, a primary polymeric binder,
the molar ratio of compound A to compound B is from 20:80 to and including 80:20;
the sum of the weight of both compound A and compound B is at least 7 weight % and up to and including 15 weight %, based on the total dry weight of the infrared radiation-sensitive imageable layer; and
at least one infrared radiation absorber is a cyanine dye,
wherein Compound A includes one of the following cations, and each cation is present with a tetraphenyl borate anion:
and Compound B includes one of the following cations or a mixture thereof, and each cation is present with a tetraphenyl borate anion:
or a mixture of
2. The negative-working, infrared radiation-sensitive lithographic printing plate precursor of claim 1 , wherein at least one infrared radiation absorber is a cyanine dye comprising a tetraarylborate anion.
3. The negative-working, infrared radiation-sensitive lithographic printing plate precursor of claim 1 , wherein the primary polymeric binder is present in particulate form.
4. The negative-working, infrared radiation-sensitive lithographic printing plate precursor of claim 1 , wherein the primary polymeric binder is present and comprises recurring units comprising polyalkylene oxide segments and recurring units comprising pendant cyano groups.
5. A negative-working, infrared radiation-sensitive lithographic printing plate precursor that is on-press developable, comprising:
a substrate having a hydrophilic surface, and
an infrared radiation-sensitive imageable layer that is disposed on the hydrophilic surface of the substrate, and comprises:
one or more free radically polymerizable compounds;
one or more infrared radiation absorbers;
an initiator composition that provides free radicals upon exposure of the infrared radiation-sensitive imageable layer to infrared radiation, the initiator composition comprising compound A and one or more compounds collectively as compound B; and
optionally, a primary polymeric binder that is present in particulate form,
wherein:
Compound A includes one of the following cations, and each cation is present with a tetraphenyl borate anion:
and Compound B includes one of the following cations or mixture thereof, and each cation is present with a tetraphenyl borate anion:
or a mixture of
the molar ratio of compound A to compound B is from 20:80 to and including 80:20;
the sum of the weight of both compound A and compound B is at least 7 weight % and up to and including 15 weight %, based on the total dry weight of the infrared radiation-sensitive imageable layer; and
at least one infrared radiation absorber is a cyanine dye.
6. The negative-working, infrared radiation-sensitive lithographic printing plate precursor of claim 5 , wherein the primary polymeric binder is present in particulate form and comprises recurring units comprising polyalkylene oxide segments and recurring units comprising pendant cyano groups.
7. A method for providing a lithographic printing plate, the method comprising in sequence:
imagewise exposing the negative-working, infrared radiation-sensitive lithographic printing plate precursor of claim 1 to infrared radiation to provide an exposed precursor comprising exposed regions and non-exposed regions in the infrared radiation-sensitive imageable layer,
mounting the exposed precursor onto a lithographic printing press, and
removing the infrared radiation-sensitive imageable layer in the non-exposed regions using a lithographic ink, fountain solution, or both a lithographic ink and a fountain solution to provide a lithographic printing plate.
8. The method of claim 7 , wherein the negatively-working infrared radiation-sensitive lithographic printing plate precursor is defined by:
Compound A includes one of the following cations, and each cation is present with a tetraphenyl borate anion:
and Compound B includes one of the following cations or mixture thereof, and each cation is present with a tetraphenyl borate anion:
or a mixture of
9. The method of claim 7 , wherein the primary polymeric binder is present in particulate form in the infrared radiation-sensitive imageable layer, and the primary polymeric binder comprises recurring units comprising polyalkylene oxide segments and recurring units comprising pendant cyano groups.