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
1999-12-22
2002-03-05
Baxter, Janet (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
C430S273100, C430S302000, C101S467000
Reexamination Certificate
active
06352811
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to thermal lithographic printing plates which are imaged with an infrared laser and processed with an aqueous alkaline developer.
2. Description of Related Art
U.S. Pat. No. 5,340,699 discloses a radiation-sensitive composition especially adapted to prepare a lithographic printing plate that is sensitive to both ultraviolet and infrared radiation and is capable of functioning in either a positive-working or negative-working manner. The disclosed composition is comprised of (1) a resole resin, (2) a novolac resin, (3) a latent Bronsted acid and (4) an infrared absorber. The solubility of the composition in aqueous alkaline developing solution is both reduced in exposed areas and increased in unexposed areas by the steps of imagewise exposure to activating radiation and heating.
U.S. Pat. No. 5,858,626 discloses a lithographic printing plate having a single sensitive layer. The sensitive layer is composed of an infrared imaging composition which contains two essential components, namely an infrared absorbing compound, and a phenolic resin that is either mixed or reacted with an o-diazonaphthoquinone derivative. These compositions are useful in positive-working elements such as lithographic printing plates that can be adapted to direct-to-plate imaging procedures.
WO 97/39894 discloses a lithographic printing plate which contains a lithographic base overcoated with a complex of a developer-insoluble phenolic resin and a compound which forms a thermally frangible complex with the phenolic resin. This complex is less soluble in the developer solution than the uncomplexed phenolic resin. However when the complex is imagewise heated the complex breaks down which allows the non-complexed phenolic resin to dissolve in the developing solution. Thus the solubility differential between the heated areas of the phenolic resin and the unheated areas is increased when the phenolic resin is complexed. Preferably a laser-radiation absorbing material is also present on the lithographic base. Examples of compounds which form a thermally frangible complex with the phenolic resin are disclosed and include quinolinium compounds, benzothiazolium compounds, pyridinium compounds and imidazoline compounds.
WO 99/11458 discloses a lithographic printing plate which contains a support with a hydrophilic surface overcoated with an imaging layer. The imaging layer contains at least one polymer having bonded pendent groups which are hydroxy, carboxylic acid, tert-butyl-oxycarbonyl, sulfonamide, amide, nitrile, urea, or combinations thereof; as well as an infrared absorbing compound. The imaging layer may contain a second polymer which has bonded pendent groups which are 1,2-napthoquinone diazide, hydroxy, carboxylic acid, sulfonamide, hydroxymethyl amide, alkoxymethyl amide, nitrile, maleimide, urea, or combinations thereof. The imaging layer may also contain a visible absorption dye, a solubility inhibiting agent, or both. A method is disclosed for directly imaging the lithographic printing surface using infrared radiation without the requirement of pre- or post- UV-light exposure, or heat treatment. In practice, the imaging layer is imagewise exposed to infrared radiation to produce exposed image areas in the imaged layer which have transient solubility in aqueous alkaline developing solution, so that solubility is gradually lost over a period of time until the imaged areas become as insoluble as non-imaged areas. Within a short time period of the imaging exposure, the imaged layer is developed with an aqueous alkaline developing solution to form the lithographic printing surface. In this method, the infrared radiation preferably is laser radiation which is digitally controlled.
U.S. Pat. No. 5,493,971 discloses lithographic printing constructions which include a grained-metal substrate, a protective layer that can also serve as an adhesion-promoting primer, and an ablatable oleophilic surface layer. In operation, imagewise pulses from an imaging laser interact with the surface layer, causing ablation thereof and, probably, inflicting some damage to the underlying protective layer as well. The imaged plate may then be subjected to a solvent that eliminates the exposed protective layer, but which does no damage either to the surface layer or to the unexposed protective layer lying thereunder.
A heat-sensitive imaging element for making positive working lithographic printing plates is disclosed in European Patent Publication EP 0864420 A1. The imaging element disclosed comprises a lithographic base, a layer comprising a polymeric material which is soluble in an aqueous alkaline solution and an IR-radiation sensitive second layer. Upon image-wise exposure and absorption of IR-radiation in the second (top) layer, the capacity of the aqueous alkaline solution to penetrate and/or solubilize the second layer is changed. Image-wise exposure can be performed with an infrared laser with a short as well as with a long pixel dwell time.
Although advances have been made in the preparation of heat-sensitive elements for the production of lithographic printing plates, there remains a need for such elements having improved sensitivity to infrared laser imaging devices. There is also a need for longer shelf-life with wider development latitude and wider exposure latitude without the production of undesired sludge in the processors.
SUMMARY OF THE INVENTION
These needs are met by the present invention which is a positive-working thermal imaging element comprising;
A. a substrate; and
B. a thermally sensitive composite layer structure having an inner surface contiguous to the substrate and an outer surface, the composite layer structure comprising:
(a) a first layer having the inner surface, the first layer comprising a first polymeric material, wherein the first polymeric material is soluble or dispersible in an aqueous solution, and a solubility inhibiting material which reduces the solubility of the first layer in the aqueous solution; and
(b) a second layer having the outer surface, the second layer comprising a second polymeric material, wherein the second layer is insoluble in the aqueous solution, and wherein when the first layer is free of photothermal conversion material, the second layer is free of photothermal conversion material;
wherein, upon heating the composite layer structure, the heated composite layer structure has an increased rate of removal in the aqueous solution.
More particularly, the present invention is a positive-working, lithographic printing plate, precursor comprising;
A. a hydrophilic substrate; and
B. a thermally sensitive composite layer structure having an inner surface contiguous to the hydrophilic substrate and an outer oleophilic surface, the composite layer structure comprising:
(a) a first layer having the inner surface, the first layer comprising a first polymeric material and photothermal conversion material, wherein the first polymeric material is soluble or dispersible in an aqueous solution, and a solubility inhibiting material which reduces the solubility of the first layer in the aqueous solution; and
(b) a second layer having the outer oleophilic surface, the second layer comprising a second polymeric material, wherein the second layer is insoluble in the aqueous solution;
wherein, upon heating the composite layer structure, the heated composite layer structure has an increased rate of removal in the aqueous solution.
An added embodiment of this invention is a method for forming a planographic printing plate comprising the steps, in the order given:
I) providing a lithographic printing plate precursor comprising;
A. a hydrophilic substrate; and
B. a thermally sensitive composite layer structure having an inner surface contiguous to the hydrophilic substrate and an outer oleophilic surface, the composite layer structure comprising:
(a) a first layer having the inner surface, the first layer comprising a first polymeric material, wherein the first polymeric material is soluble or dispersible in an
Huang Jianbing
Merchant Nishith
Mikell Frederic
Patel Jayanti
Saraiya Shahhikant
Baxter Janet
Gilmore Barbara
Kodak Polychrome Graphics LLC
Ratner & Prestia
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