Printing – Planographic – Lithographic plate making – and processes of making or using...
Reexamination Certificate
2000-07-18
2001-07-31
Funk, Stephen R. (Department: 2854)
Printing
Planographic
Lithographic plate making, and processes of making or using...
C101S457000, C430S303000
Reexamination Certificate
active
06267055
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the imaging of a plate having a coating imageable by infrared radiation and more specifically to infrared imaging with simultaneous supplemental infrared heating to improve the imaging process. The invention is particularly directed to the imaging of lithographic printing plates.
Positive-working lithographic printing plates or other imageable plates which have a coating selectively removed from the plate by exposure to imaging infrared laser radiation are known in the prior art. One category of these plates has a coating on a substrate wherein the coating is transparent to the imaging infrared radiation and wherein the substrate absorbs the infrared radiation generating heat. The generated heat then removes the coating in the imaged areas by ablation or combustion of the coating. International Patent Application Publication No. WO 98/52743, published Nov. 26, 1998 and the related U.S. patent application Ser. No. 09/079,735, filed May 15, 1998, now U.S. Pat. No. 6,145,565, discloses a laser imageable printing plate having a coating which is transparent to the laser imaging radiation and having a substrate which absorbs the radiation. In that patent application, the coating is ablated from the substrate by the heat generated as a result of the substrate absorbing the radiation. The ablation is a function of the heat disrupting the physical bond between the substrate and the coating and pulverizing the coating probably by expansion of the substrate beneath the relatively brittle coating. Another known type of a coating which can be removed by heating the substrate with the infrared laser radiation is a coating which will undergo a thermally induced chemical reaction such as combustion. In either case, certain minimum laser power levels and exposure times are required to produce the heating required.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an improved method of infrared laser imaging an imageable plate having a substrate with a coating which is removed in the imaged areas by a chemical reaction initiated by heat from the infrared radiation. The chemical reaction is a reaction which rapidly produces gaseous reaction products which blow or propel the coating off the substrate in the imaged areas. The heating is effected by dual lasers with one laser being a modulated imaging laser of a selected wavelength and the other being an unmodulated, non-imaging laser of a different wavelength. The coating is transparent to the modulated imaging laser radiation with this radiation being absorbed by the substrate and thereby heating the substrate and the adjacent coating. The coating contains an absorber for the unmodulated, non-imaging laser radiation whereby this radiation directly supplies supplemental heat to the coating. The supplemental heating is limited to a temperature below the threshold reaction temperature of the coating and the heating from the imaging radiation is sufficient to take the coating temperature over that threshold. The advantage of the invention is that the power needed for the modulated imaging infrared laser is reduced.
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Fromson Howard A.
Rozell William J.
Alix Yale & Ristas, LLP
Fromson Howard A.
Funk Stephen R.
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