Radiation imagery chemistry: process – composition – or product th – Diazo reproduction – process – composition – or product – Composition or product which contains radiation sensitive...
Reexamination Certificate
2000-03-30
2001-05-15
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...
C430S190000, C430S191000, C430S192000, C430S193000, C430S302000
Reexamination Certificate
active
06232031
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an infrared sensitive composition and to a positive-working element using such a composition. More particularly, this invention relates to positive-working lithographic printing plates.
Lithographic printing depends upon the immiscibility of oily ink and water with the ink being retained on the oleophilic image areas of the plate and the water being retained on the hydrophilic non-image areas. Most lithographic printing plates have a radiation-sensitive coating applied to an aluminum printing plate substrate. These coatings can be selected to be sensitive to a wide range of radiations including ultraviolet radiation, visible radiation and infrared radiation. The coating may react to the radiation such that the portions of the coating exposed become soluble and are removed during development, thus becoming hydrophilic non-image areas. Such plates are known as positive-working printing plates. On the other hand, the coating may react to the radiation such that the exposed areas become hardened and insoluble and remain during development, becoming the oleophilic image areas. Such plates are known as negative-working printing plates.
One prior art lithographic plate of the negative-working type is described in U.S. Pat. No. 5,705,308. The coating is an infrared imaging composition containing a phenolic resin that is either mixed with or reacted with an o-diazonaphthoquinone derivative and which also contains a specific infrared radiation absorber.
Another prior art lithographic plate which is related but which is of the positive-working type is described in U.S. Pat. No. 5,858,626. The coating is also an infrared imaging composition containing a phenolic resin that is either mixed with or reacted with an o-diazonaphthoquinone derivative and which also contains an infrared radiation absorber. In this patent, the dry weight ratio of o-diazonaphthoquinone moiety to the infrared absorber in the coating composition is quite high and the diazonaphthoquinone moiety is at least 5 weight percent and more preferably 15 to 40 weight percent of the coating.
In the PCT International Application Publication Number WO 96/20429, another coating is described which is a naphthoquinone diazide ester of a phenolic resin or a naphthoquinone diazide ester mixed with a phenolic resin containing an infrared absorber. The plate is blanket (overall) exposed to ultraviolet radiation which solubilizes the entire coating as with a positive-working plate. The plate is then laser imaged to insolubilize the coating in the image areas as with a negative-working plate.
In the PCT International Application Publication Number WO 97/39894, the coating is an alkali soluble phenolic resin containing a compound which complexes with the resin and reduces the solubility. The coating also contains an infrared absorber which may also be the complexing compound. When exposed, the heating breaks down the complex so that the exposed areas become soluble. The complexing compound increases the solubility differential between the exposed and unexposed areas. The solubility of the coating is not affected by ultraviolet radiation.
Further prior art is disclosed in U.S. Pat. No. 5,962,192 which discloses a positive-working plate having a polymeric resin coating containing an organo azide compound and an infrared radiation sensitive dye. In this patent, the suitable resins are polyvinyl formal, acrylates, methacrylates and styrene. The radiation is absorbed by the dye to raise the temperature above the decomposition temperature of the organo azide. The plate is then blanket exposed to ultraviolet radiation which hardens the coating in the areas which were not exposed to the infrared radiation. This blanket exposure is necessary to increase the solubility contrast between the infrared exposed and non-exposed areas to a practical, workable level. The infrared exposed, non-image areas of the coating are then dissolved away. Alternately, the coating can first be blanket exposed to cross link and harden the coating. The coating is then infrared exposed in the non-image areas to solubilize the coating in those areas. An acidic organic solvent is used in the development process.
SUMMARY OF THE INVENTION
The invention relates to a positive-working coating composition and to a lithographic printing plate formed with a coating of that composition. The object is to provide an infrared imageable lithographic printing plate having a phenolic resin coating containing an o-diazonaphthoquinone derivative coupled to or reacted with the resin and an infrared radiation absorbing compound. More specifically, the invention provides a low cost plate with a resin coating containing a quantity of infrared absorber sufficient to be infrared imageable but with only a low level of o-diazonaphthoquinone derivative loading. More specifically the o-diazonaphthoquinone moiety comprises less than 5 weight percent and preferably about 2.5 weight percent of the dried coating and the dry weight ratio of the infrared absorber to the o-diazonaphthoquinone moiety is greater than 1:5 and preferably 1:2 or greater. The most preferred ratio is about 3:1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The coating of the invention is particularly suitable for lithographic printing plates and the invention will be described in that environment. However, it is recognized that the coating can be used with other substrates such as for imageable printed circuit boards. With respect to lithographic printing plates, the substrate is most commonly a conventional grained and anodized aluminum substrate although other metal substrates can be used. For a teaching of one type of graining process, see U.S. Pat. No. 4,183,788 to Fromson et al and for a teaching of anodizing see U.S. Pat. RE 29754 to Fromson.
The basic and predominant component of the coating of the invention is a film-forming resin of the type normally used for lithographic printing plate coatings. These resins are light-stable, water-insoluble and alkali soluble. The typical resins are polyhydroxy polymers capable of forming hydrogen bonds with o-diazonaphthoquinones such as novolac resins, resole resins and polyvinyl resins with phenolic hydroxide groups. Novolac resins such as phenol formaldehyde resin and cresol formaldehyde resin are preferred.
The resin coating of the invention contains two essential components. The first is the o-diazonaphthoquinone derivative which interacts with the resin to insolubilize the resin coating in the typical alkaline developers. The o-diazonaphthoquinone derivative may be mixed with and merely couple with the resin by hydrogen bonding or it may be an o-diazonaphthoquinone derivative which has a functional group, such as chloride or imide groups, that can react with a reactive group of the resin and become part of the resin. In either case, the result is to insolubilize the coating. The preferred embodiment of the invention employs an o-diazonaphthoquinone derivative which is mixed with the resin and hydrogen bonds. The second component is the infrared radiation absorbing compound which also couples with the resin by hydrogen bonding to insolubilize the resin coating. The infrared radiation absorbing compound is usually a dye compound but pigments can also be used. The use of the term dye herein is intended to include both dyes and pigments. The dye compound also serves the function of absorbing the infrared imaging radiation to produce heat which decouples the components from the resin and thereby solubilizes the coating in the exposed areas. Because both of these components function to insolubilize the coating, it has been found that a positive-working coating can be prepared which is infrared imageable but which has such a low sensitivity to ultraviolet light that it can be handled in daylight at least for some periods of time. The coating contains only that quantity of infrared radiation absorbing dye necessary to be imageable in that mode and only that small quantity of o-diazonaphthoquinone derivative necessary to supplement the ins
Fromson Howard A.
Gracia Robert F.
Ren Yijin
Rozell William J.
Alix Yale & Ristas, LLP
Ano-Coil Corporation
Chu John S.
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