Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Radiation sensitive composition or product or process of making
Reexamination Certificate
2001-04-04
2003-12-02
Chu, John S. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Radiation sensitive composition or product or process of making
C430S162000, C430S166000, C430S273100, C430S303000, C524S264000, C526S279000
Reexamination Certificate
active
06656661
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an imageable element, which can be imaged by analog or digital imaging and used in the preparation of negative or positive-working waterless lithographic printing plates. More particularly, the present invention relates to an imageable element, wherein the imaging layer is overcoated with a crosslinked silicone polymer which is the curing product of: a vinyl functional polysiloxane copolymer and a hydrosiloxane compound.
2. Description of the Prior Art
Waterless printing plates have existed since 1970. Most waterless printing plate precursors have an ink abhesive layer such as silicone overlying a light absorbing imaging layer. Imaging is typically achieved by exposing the imaging layer to an ultraviolet radiation source followed by selectively removing the ink abhesive coating. For positive working waterless plates, the imaging layer is a light absorbing layer typically containing a negative working diazo resin as disclosed in U.S. Pat. Nos. 3,511,178; 3,677,178; and 4,775,607; or a light absorbing layer containing a photopolymerizable compound as described in U.S. Pat. Nos. 3,894,873; 5,232,813, and 5,503,074. For negative working waterless plates, imaging has been achieved by solubilizing, via ultraviolet radiation, the imaging layer, which typically contains diazonaphthoquinones, as described in U.S. Pat. Nos. 4,342,820; 4,358,522 and 5,866,294. Solubilization has also been achieved by imagewise exposing a layer that undergoes light-induced acid-catalyzed hydrolysis as described in U.S. Pat. No. 4,842,990. U.S. Pat. No. 3,933,495 describes a dual-tone waterless plate wherein the solubility of the imaging layer is either enhanced or reduced by the developer in the developing step, depending upon developer used.
The printing plate precursors described above generally require a photographic film for imagewise exposure, corresponding to analog imaging. More recently, waterless plate precursors have been adapted for direct, imagewise exposure utilizing a computer-directed laser, corresponding to computer-to-plate, digital imaging. Typically, a material, which is capable of converting electromagnetic radiation into heat, known as a photothermal converter, is present in the radiation sensitive imaging layer. The photothermal converter is generally a pigment or a dye, which absorbs infrared radiation, and the imaging step is carried out using an infrared laser.
For negative working waterless plates, digital imaging has been achieved by solubilizing the imaging layer, which may contain a diazonaphthoquinone, as described in U.S. Pat. No. 5,919,600. Solubilization of the imaging layer has also been accomplished by overall, ultraviolet light-induced acid generation, followed by imagewise digital exposure, as described in U.S. Pat. No. 5,955,238. Digitally-imaged, negative working waterless plates have also been prepared by selectively reducing the adhesive forces between the imaging layer and the overlying silicone layer, as described in U.S. Pat. No. 5,888,696.
U.S. Pat. No. 5,786,125 describes a dual-tone waterless plate precursor for digital imaging. The imaging layer is solubilized by imagewise exposure with an infrared laser, followed by development. Alternatively, imagewise infrared exposure followed by overall heating prior to development, results in a positive-working printing plate. An alternative approach to positive-working digital plates has been the thermal insolubilization of the imaging layer by coalescence of polymer particles, as described in U.S. Pat. No. 6,197,478.
For both positive and negative working waterless plates prepared by either analog or digital imaging methods, the radiation sensitive layer is typically overcoated with an ink-repellant, crosslinked silicone rubber layer. The following two methods have generally been utilized for hardening the silicone rubber layer:
(1) Condensation reaction in which an organopolysiloxane having hydroxyl groups at both ends and/or along the polymer chain is crosslinked with a silane or siloxane having a hydrolyzable functional group directly bonded to the silicon atom thereof to give a silicone rubber; and
(2) Addition reaction in which a polysiloxane having Si—H groups and a polysiloxane having —CH
2
═CH— groups are crosslinked by hydrosilylation to give a silicone rubber.
U.S. Pat. No. 5,464,686 discloses that in cases of hardening by condensation, curing properties and adhesion to a radiation sensitive layer may change depending on the moisture content of the atmosphere during hardening. This would produce plates of variable sensitivity, making stable production very difficult. Because of this problem, it was concluded that hardening by addition reaction was superior because it did not involve such drawbacks. This patent describes positive working waterless plates having a silicone rubber layer crosslinked by an addition reaction utilizing platinum catalysts such as elemental platinum, platinum chloride, chloroplatinic acid and platinum coordinated with olefins. The commonly owned U.S. Pat. Nos. 5,919,600 and 6,045,963 also utilize platinum compounds to catalyze the addition reaction of a vinyl functional polysiloxane copolymer and a hydrosiloxane compound to form the crosslinked silicone polymer.
U.S. Pat. Nos. 4,842,988 and 4,842,990 disclose a silicic acid interlayer between the silicone and photosensitive layer to enhance adhesion. U.S. Pat. No. 4,842,988 includes radiation sensitive layers, which undergo both photosolubilization and photoinsolubilization. The radiation sensitive layers in U.S. Pat. No. 4,842,990 undergo photosolubilization. This approach of enhancing adhesion by providing a silicic acid interlayer requires the additional step of applying the interlayer and thus, adds to the manufacturing cost.
The above references point out the importance of adhesion of the crosslinked silicone rubber layer to the radiation-sensitive layer, which is generally regarded as one of the most important factors determining press life of waterless plates. Furthermore, the method of crosslinking the silicone rubber layer is recognized as an important contributing factor to the adhesion as well as to the durability of the adhesive forces.
Platinum carbonyl catalysts have been used in hydrosilylation reactions. For example, U.S. Pat. No. 3,865,858 discloses dichloroplatinum dicarbonyl as a hydrosilylation catalyst for the production of organosilicone compounds. U.S. Pat. No. 5,359,111 discloses methods of controlling the rate of hydrosilylation in reaction mixtures, methods for isomerization and methods for producing cyclosiloxanes, in which dichloroplatinum dicarbonyl, as well as other platinum catalysts, are utilized. However, none of the above references discloses the use of platinum carbonyl catalysts for crosslinking vinyl functional polysiloxanes with hydrosiloxanes. Furthermore, none of the above references discloses the use of platinum carbonyl catalysts to improve interlayer adhesion.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a radiation sensitive waterless plate having a highly durable crosslinked silicone polymer, which exhibits superior adhesion to the radiation sensitive imaging layer, high resistance to delamination under humid conditions, high durability and long press life. As a result of extensive studies, it has now been found that these objectives can be accomplished with vinyl-functional siloxane polymers that are crosslinked with hydrosiloxanes by a catalyzed hydrosilylation reaction in which a platinum carbonyl complex is utilized as the addition catalyst.
Accordingly, the present invention includes an imageable element comprising a sheet substrate, an imaging layer and a silicone layer. The imaging layer is a radiation-sensitive imaging layer. The silicone layer comprises a crosslinked silicone polymer which is the curing product of a vinyl functional polysiloxane copolymer having a molecular weight of at least 1,000 g/mol and a hydrosiloxane compound. The curing is catalyzed
Hong Suck-Ju
Pappas S. Peter
Chu John S.
Faegre & Benson LLP
Kodak Polychrome Graphics LLC
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