Radiation imagery chemistry: process – composition – or product th – Diazo reproduction – process – composition – or product – Composition or product which contains radiation sensitive...
Reexamination Certificate
2001-07-12
2003-02-11
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...
C430S191000, C430S192000, C430S193000, C430S302000
Reexamination Certificate
active
06517988
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to radiation-sensitive, positive working coating compositions useful for the preparation of lithographic printing plates. In particular, this invention relates to coating compositions that produce lithographic printing plates that show high print run stability.
BACKGROUND OF THE INVENTION
The art of lithographic printing is based upon the immiscibility of oil and water, in which oily material or ink is preferentially retained by the image areas and the water or fountain solution is preferentially retained by the non-image areas of the printing plate. When a suitably prepared surface is moistened with water and ink is applied, the background or non-image areas retain the water and repel the ink while the image areas accept the ink and repel the water. The ink on the image areas is then transferred to the surface of a material upon which the image is to be reproduced, such as paper, cloth and plastics. Commonly, the ink is transferred to an intermediate material called the blanket, which in turn transfers the ink to the surface of the material upon which the image is to be reproduced.
Lithographic printing plates can be either negative working or positive working, and comprise one or more radiation-sensitive layers on a suitable substrate, such as a metal or polymeric support. The radiation-sensitive layer generally includes one or more radiation-sensitive components that may be dispersed in a suitable binder. Alternatively, the radiation-sensitive component can also be the binder material.
Upon exposure to light, the exposed areas of a negative working printing plate are hardened, leaving non-exposed areas removable during development. Negative working printing plates can be divided into two different types depending on the mechanism of “insolubilization” during exposure:
In the first type the presence of a diazonium compound in the radiation-sensitive composition is responsible for the insolubilization upon exposure to radiation. In the second type the radiation-sensitive composition contains a photocrosslinkable component which is subjected to crosslinking upon exposure to radiation, the crosslinking being responsible for the insolubilization. Certain negative working printing plates contain novolac resins, a cross-linking agent, and a radiation-sensitive component that produces acid on exposure.
An alkaline developable positive working printing plate generally has a light sensitive layer comprising a novolac resin and a radiation-sensitive component such as an o-diazoquinone or diazonaphthoquinone compound (see, for example Lawson, U.S. Pat. No. 3,802,885). Upon exposure to light the radiation-sensitive component is converted to the corresponding carboxylic acid. The use of an alkaline developer will remove only the exposed areas of the radiation-sensitive layer, releasing the surface of the support. Because the surface of the support is hydrophilic, the uncovered non-image area attracts water and repels the oily ink. The image area remaining after development is oleophilic thereby repelling water and attracting the printing ink.
Developers used for positive working precursors (hereafter abbreviated as positive developers) are characterized by a high pH value, i.e. a pH of clearly more than 10, usually in the range of about 12 to about 14. Compared thereto, developers used for negative working precursors (hereafter abbreviated as negative developers) have a relatively low pH value, i.e. around 10.
DE-A-44 26 141 discloses radiation-sensitive compositions comprising a naphthoquinonediazide compound and a polymeric binder obtained by polymerizing an unsaturated compound comprising an aromatic carboxyl ground (i.e. a carboxyl group bonded to a phenyl or naphthyl ring). A printing plate precursor comprising a radiation-sensitive layer of said composition can be developed after imagewise exposure with an aqueous alkaline developer having a pH of 12.5 or less. However, an improvement of the print run stability of printing plates obtained therefrom is desirable.
Today the demands on radiation-sensitive compositions used for the preparation of lithographic printing plates are quite high. Besides high sensitivity a high print run stability is required. For improving the print run stability of radiation-sensitive compositions and thus also of the corresponding printing plates, basically two methods have been pursued. One of them relates to the improvement of the components of the radiation-sensitive compositions especially the polymeric compounds (“binders”) thereof which are supposed to control the physical properties of the radiation-sensitive layers like developability, scratch resistance and print run stability. The other one refers to the incorporation of particles into the radiation-sensitive layer for improving the print run stability.
Coating solutions for in-situ formation of particles in the radiation-sensitive layer during drying are for instance disclosed in the pending U.S. application Ser. No. 09/493,837 based on PCT/DE 99/016730.
The development of new binder materials is for instance described in EP-A-0 722 171, EP-A-0 544 264 and EP-A-0 440 086.
Therefore, a need exists for provide coating compositions for positive working printing plate precursors in which the radiation-sensitive composition contains only a very few components yet produces in a radiation-sensitive layer having high printrun stability. The coating composition should produce printing plates in which the ink-water balance can be reached faster and which show less problems after restart. In addition, the printing plate precursors should have reduced sludge formation in the developer. Sludge formation in the developer often occurs due to precipitation of silicates.
SUMMARY OF THE INVENTION
The invention is a radiation-sensitive composition comprising:
(a) at least one quinonediazide compound, and
(b) at least one copolymer comprising the units A, B, C and D,
wherein:
unit A has the formula
wherein R is hydrogen or C
1
-C
4
alkyl,
unit B has the formula
unit C has the formula
wherein R
1
is C
1
-C
4
alkyl and
unit D is a unit comprising at least one free carboxyl group selected from the group consisting of straight chain C
1
-C
4
alkylenes having at least one carboxyl substituent, straight-chain C
2
-C
4
alkenylenes having at least one carboxyl substituent, divalent groups represented by formula (D1),
divalent groups represented by formula (D2),
and divalent groups represented by formula (D3)
where X is selected from the group consisting of phenylene, phenylenes substituted with one or more C
1
-C
4
alkyl groups, benzofused phenylenes, and divalent groups of the following formula
where Z is an aliphatic, aromatic or araliphatic spacer group, R
2
is hydrogen or an aliphatic, aromatic or araliphatic group, and Y is a saturated or unsaturated chain-or ring-shaped spacer group.
Preferably the carboxylic copolymer comprises 0.5 to 25 mol % of unit A, 30 to 55 mol % of unit B, 25 to 65 mol % of unit C, and 1 to 10 mol % of unit D.
In another aspect, the invention is a printing plate precursor, sometimes called printing plate or a printing form, comprising the radiation-sensitive composition. In another aspect, the invention is a method for forming an image useful as a printing late using the printing plate precursor. In yet another aspect, the invention is a printing plate formed by the method of the invention.
DETAILED DESCRIPTION OF THE INVENTION
The radiation-sensitive composition of the invention comprises two essential components: a quinonediazide compound and a polymeric binder.
Examples of suitable quinonediazide compounds are benzoquinonediazide (BQD) compounds and naphthoquinonediazide (NQD) compounds. A BQD compound may, for example, comprise a 1,4- or, preferably 1,2-benzoquinonediazide. A NQD compound may, for example, comprise a 1,4-, 2,1- or, most preferably, 1,2-naphthoquinonediazide. Generally, NQDs are preferred to BQDs. Most preferred is 1,2-naphthoquinonediazide. The composition can comprise a BQD or NQD ester of a phenol
Hauck Gerhard
Jarek Mathias
Chu John S.
Kodak Polychrome Graphics LLC
RatnerPrestia
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