Radiation imagery chemistry: process – composition – or product th – Diazo reproduction – process – composition – or product – Composition or product which contains radiation sensitive...
Reexamination Certificate
2001-08-21
2004-10-19
Chu, John S. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Diazo reproduction, process, composition, or product
Composition or product which contains radiation sensitive...
C430S157000, C430S176000, C430S270100, C430S302000
Reexamination Certificate
active
06806020
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an imageable composition. More particularly, the present invention relates to a thermally imageable composition having an acid curable composition, an acid generator, a strong acid and optionally an infrared absorber. As the strong acid, sulfonic acids are added to increase the speed of the thermally imageable, pre-heated, negatively working patterning compositions, which are useful especially as printing plates.
DESCRIPTION OF THE PRIOR ART
Printing plates having a coating of a thermally imageable composition that includes an acid curable composition and either a “free acid” cure catalyst or a “latent acid” cure catalyst, such as, an acid generator, are known. However, each of these systems suffers from disadvantages, which include difficulty of controlling the cure rates.
If a “free acid” cure catalyst is used in an amount sufficient to produce a satisfactory cure speed, the shelf life of the curable composition becomes severely limited because the curing process begins immediately upon contact of the free acid with the ingredients of the acid curable composition. If, on the other hand, lesser amounts of the cure catalyst are employed to improve the shelf life, the cure rate is reduced to unacceptably low levels.
In an alternative approach, if a “latent acid” cure catalyst is used in an amount sufficient to produce a satisfactory cure speed, the amount of energy required to generate the acid from the acid generator compound is unacceptably high even though the shelf life of the curable composition is satisfactory. If, on the other hand, lesser amounts of the “latent” cure catalyst were employed to improve the energy requirements of the acid generator, the cure rate would be reduced to unacceptably low levels.
U.S. Pat. No. 5,965,319 describes a negatively working composition having an IR absorber, novolak and resole resins, and an iodonium, sulfonium or diazonium salt, with a sulfonate group as counterion. There is no teaching that the presence of sulfonic acid as a discrete additive will improve cure rate processing latitude.
U.S. Pat. No. 6,042,987 describes a thermal negative system in which an acid is produced from a typical generator upon exposure to IR radiation. This promotes cross-linking between a novolak and a crosslinking species.
Japanese Patent Application JP 11-268,438 describes a thermal positive plate having a novolak resin and an IR absorber that has a thermally decomposable sulfonate directly attached thereto. At unimaged regions of the plate, the absorber acts as an insolubiliser and, at imaged areas, it acts as a dissolution accelerant. Japanese Patent Application JP 10-193,554 describes a negative plate having excellent run length by virtue of a new, improved polymer. Japanese Patent Application JP 3-291,665 discloses conventionally imaged negative plate systems.
U.S. Pat. Nos. 5,340,699 and 5,919,601 describe imageable compositions having a binder, a crosslinker, an acid generator and an infrared absorber. These patents do not describe the use of a strong acid in addition to the acid generator or that added sulfonic acids would improve plate speed or processing latitude.
U.S. Pat. No. 5,641,608 describes ablative and positive
egative working solubility differential systems for PCB precursors. The negative systems rely on adding an amine active ingredient just prior to use, or by employing a “UV flood then IR exposure” process. U.S. Pat. No. 5,763,134 describes a composition having an acid generator, typically a triazine, and a squarylium dye having a defined nucleus. European Patent Application EP 632,003 describes MeO- and Me- containing phenol compounds for use as improved heat curing additives in conventional positive plates.
None of the above disclosures teach or suggest that the presence of a strong acid, such as, a sulfonic acid, will improve cure rate processing latitude when included in the composition as a discrete additive.
Accordingly, it is an object of the present invention to improve the speed and processing robustness of thermal, pre-heated, negatively working patterning compositions, especially printing plates, while maintaining adequate shelf life.
The present invention provides such an imageable composition, which has an improved cure rate, long shelf life of the acid curable composition and moderate energy requirement of the acid generation step.
SUMMARY OF THE INVENTION
The present invention provides an imageable composition, which includes an acid curable composition, an acid generator and a strong acid.
The present invention further provides an imageable element, which includes a substrate and an imageable composition coated on a surface of the substrate. The composition includes an acid curable composition, an acid generator and a strong acid.
The present invention further provides methods of producing an imaged element.
The first of these methods, includes the steps of:
providing a thermally imageable element including a substrate and a thermally imageable composition coated on a surface of the substrate, the composition including an acid curable composition, an acid generator and a strong acid;
imagewise exposing the imageable element to heat with a hot stylus to produce an imagewise exposed element having exposed and unexposed regions;
baking the imagewise exposed element at a temperature and period of time sufficient to produce a cured element; and
contacting the cured element and a developer to remove the unexposed regions and thereby produce the imaged element.
The second of these methods, includes the steps of:
providing an imageable element including a substrate and an imageable composition coated on a surface of the substrate, the composition including an acid curable composition, an acid generator and a strong acid;
imagewise exposing the imageable element to radiation to produce an imagewise exposed element having exposed and unexposed regions;
baking the imagewise exposed element at a temperature and period of time sufficient to produce a cured element; and
contacting the cured element and a developer to remove the unexposed regions and thereby produce the imaged element.
It was found that incorporating a small amount of a sulfonic acid into pre-heat, thermal plate increases the speed of the thermal plate and allows maximum image density at wider pre-heat temperatures. In addition, it provides significantly improved processing latitude while maintaining an adequate shelf life.
DETAILED DESCRIPTION OF THE INVENTION
Lithographic printing plate precursors, i.e., imageable elements, typically include a radiation imageable coating applied over a support material, such as, an aluminum substrate. If after exposure to radiation, the exposed regions of the coating become soluble and are removed in the developing process, revealing the underlying hydrophilic surface of the support, the plate is called a positive-working printing plate. Conversely, if exposed regions of the plate become insoluble in the developer and the unexposed regions are removed by the developing process, the plate is called a negative-working plate. In each instance, the regions of the radiation-sensitive layer that remain (i.e., the image areas) are ink-receptive and the regions of the hydrophilic surface revealed by the developing process accept water and repel ink.
The present invention is useful in negative-working printing plates, such as Thermal Printing Plates/830, available from Kodak Polychrome Graphics, Norwalk, Conn. To improve cure rate and processing latitude of the thermally imageable layer, the present invention provides an imageable composition, which in addition to an acid generator includes as a discrete additive in the composition a strong acid, such as, a sulfonic acid. Thus, the imageable composition according to the present invention includes an acid curable composition, an acid generator, a strong acid and optionally an infrared absorber.
The term “hydrocarbyl” in the context of the present invention refers to a linear, branched or cyclic alkyl, alkenyl, aryl, aralkyl or alkary
Haley Neil
Kalamen John
Chu John S.
Faegre & Benson LLP
Kodak Polychrome Graphics LLC
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