Organic compounds -- part of the class 532-570 series – Organic compounds – Carboxylic acid esters
Reexamination Certificate
2000-10-18
2002-05-07
Davis, Brian J. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carboxylic acid esters
C560S163000
Reexamination Certificate
active
06384264
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to photoactive materials which are useful in imaging systems. More particularly, the invention is concerned with materials which are capable of generating free bases on interaction with radiation.
Photogeneration of active species has proved to be extremely important in many areas and photolabile protecting groups have been used widely in organic and bio-organic synthesis. Photocurable polymers have found many applications in coating technology and photoresists are important in fabrication of microelectronic devices. Although some such applications involve very short wavelength ultraviolet irradiation or even electron beams, most commercial systems use ultraviolet or visible light sources because of their ease of use for low cost.
In lithography, compounds that produce radicals and/or acids on photolysis have been used extensively as photoinitiators in positive and negative working imaging systems. Thus, irradiation with light may be used to effect polymer formation, or polymer side-chain modification. In situ generation of acid is used as a means of inducing polymerisation of monomers or oligomers or to effect cross-linking, and both of these processes normally lead to less soluble materials. Despite the possibilities for application of base catalysts, the use of photogenerated bases in imaging systems has attracted little attention. In most photochemical reactions that liberate a base (usually an amine), it is trapped in solution in its largely neutral protonated form so that such processes are of little utility with systems that require base catalysts. Major exceptions lie in deep-UV irradiation of transition metal-amine complexes with negative photoresist systems, which photogenerate ammonia in a quantum efficient process and short wavelength irradiation of &agr;,&agr;-dimethyl-3,5-dimethoxybenzyloxy carboxamides, which yield amines. Thus, compared with acid-release systems, there are few general base-release agents useful for short- and long-wavelength lithographic applications.
The present invention seeks to provide organic photoprecursors of amines which may find application in lithographic printing plates or photoresist systems, and methods for the production of said photoprecursors.
Advantageously, said photoprecursors may be caused to photochemically generate free amines via interaction with long wavelength UV or visible radiation and may then serve to cause a change in the dissolution properties of a coating composition in developer solutions, thereby effecting differences in solubility properties in exposed and unexposed regions and facilitating image formation. Alternatively, changes in colour between irradiated and non-irradiated areas may be caused to occur with the incorporation of base-sensitive dyes into the coatings, thereby allowing for ready distinction between image and non-image areas.
The conception of generation of amines by irradiation of systems with light is well known from the synthesis of peptides or nucleotides, wherein photolabile protecting groups are used until the final steps of the synthesis in order to protect the amine. Cleavage of the masking groups then allows the amine to be regenerated, preferably by irradiation with visible or long-wavelength UV light, in a process having high quantum efficiency.
An especially suitable photolabile group for systems of this type is the 2-nitrobenzyl group. Particular attention has focused on 2-nitrobenzyl compounds, in which the benzylic group carries at least one &agr;-hydrogen atom; these derivatives are known to undergo photoinduced intermolecular oxygen transfer with reduction of the nitro group to a nitroso group and simultaneous oxidation of the benzylic side chain. This process is initiated by photoinduced hydrogen abstraction by an ortho-nitro group from the nearby benzylic carbon functionality, followed by transfer of a hydroxyl group from the nitro group back on to the carbon atom from which the hydrogen was abstracted.
Several derivatives of this type have been reported in the prior art. Photosensitive polymers which are used to form resist patterns, and which contain o-nitro benzyl oxy units are disclosed in unexamined Japanese Patent Specification No. 63-146032 and unexamined Japanese Patent Specification No. 63-247749 describes a range of o-nitro aryl oxy and o-nitro hetaryl oxy unit-containing polymers useful in the photosensitive layers of offset printing plates.
Subsequently, unexamined Japanese Patent Specifications Nos 03-131626 and 03-141357 have disclosed photosensitive amphipathic high molecular weight compounds which comprise polyesters or polyester acids or their esters which are prepared from tetracarboxylic acid dianhydrides and diols containing o-nitrobenzyl groups, the acid dianhydride optionally being reacted with an alcohol and converted to an acid halide prior to reaction with the diol. The compounds are utilised in light sensitive ultra-thin films.
More recently, improved quantum efficiency of photoreaction has been reported when employing dinitrobenzyl derivatives as precursors for photoreactive compounds as disclosed, for example, in U.S. Pat. Nos. 5,449,834 and 5,600,035. Thus, various 2,5- and, most preferably, 2,6-dinitro-benzyl derivatives have been used as monomers for the preparation of photosensitive polymers, having especially enhanced sensitivity at longer wavelengths. Particular use has been made of dichlorodinitro compounds and dinitrodiols in this regard, with 2,6-dinitro-4-methoxycarbonylbenzaldehyde having found particular application. Various polyurethanes, polysulphides, polyesters, and polyamines have been prepared from these precursors.
Unfortunately, however, whilst a high degree of photosensitivity is achieved with these products, their synthesis is not a trivial matter and the materials are only obtained with difficulty. Additionally, the compounds, like many polynitro derivatives, suffer from poor solubility in a range of common organic solvents, such as hydrocarbons, alcohols, ketones and the like.
It is, therefore, an object of the present invention to provide highly photosensitive compounds, capable of efficient photoreaction allowing for the production of basic materials during said photoreaction, wherein the photosensitive compounds and corresponding precursors may be simply and efficiently prepared by means of standard synthetic techniques.
It is a further object of the present invention to provide highly photosensitive compounds as hereinbefore described, having a high level of solubility in a range of common organic solvents.
The present inventors have found that the general principles discussed may be applied to urethanes having the general structural formula I.
Thus, on irradiation, the compound I undergoes light induced internal rearrangement to produce nitroso derivative II and carbamic acid III. Due to the instability of the acid III. its formation is followed rapidly by spontaneous release of carbon dioxide to give the free amine IV. Hence, suitable urethanes I are photoprecursors of amines and may be used as photoactive compounds for photoimaging.
Furthermore, it has also been found that polymeric derivatives, including for example polycarbonates or polycarbamates which include the 2-nitrobenzyl functionality will undergo similar light-induced degradation. Thus, photolysis of a polycarbamate results not only in polymer degradation by cleavage at the carbamate linkages, but also in functional changes on the resulting fragments which contain terminal basic amino groups, whereas the original polymer is neutral. Therefore, such polymers may be used to provide a positive-working photoimaging system wherein the irradiated areas of a coating may be washed away with an aqueous acidic developer, thereby producing a three-dimensional relief image, for example via the degradation of a polymer V to a nitroso derivative VI and a diamine VII. It has also been found that these polymers are of value in the production of negative-working photoimaging systems, since the breakdown products—containing bas
Cristiano Maria de Lurdes dos Santos
Davies John Kynaston
Dowd Sharon
Johnstone Robert Alexander Walker
Pratt Michael John
Agfa-Gevaert
Breiner & Breiner L.L.C.
Davis Brian J.
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