GB2176796A - Photopolymerisable compositions - Google Patents

Abstract

Two different photopolymerisable (photocross linkable) systems, (1) and (2) below, can be incorporated into a single composition. The composition comprises (i) a first polymer having ethylenically unsaturated groups and free radical-generating polyhalo groups, (ii) a second polymer, free from ethylenically unsaturated groups, having nucleophilic substituents and (iii) an arene transition metal carbonyl having attached to the arene ligand an ethylenically unsaturated group. On exposure to actinic radiation (1) free radicals generated by the carbonyl (iii) and polyhalo groups in polymer (i) cause addition polymerisation of ethylenically unsaturated groups in polymer (i) and (2) the carbonyl (iii) forms cross links in the second polymer (ii). The various reactions possible combine to give good sensitivity.

Description

SPECIFICATION Photopolymerisable compositions The invention relates to photopolymerisable compositions useful in the manufacture of photoresists and presensitised lithographic printing plates.

Imagewise exposure of a layer of a conventional, negative working, photoresit composition to actinic radiation reduces the solubility of the composition in the exposed areas so that by treating the layer with a suitable solvent it is possible to remove the unexposed composition and thereby produce a resist image. If the layer is carried by a hydrophilic support, the resist image may be suitable for use as a lithographic printing image.

A variety of negative-working photoresist compositions have been proposed, and many of them function as a result of polymerisation, or of cross-linking between polymer chains or, sometimes, of both these mechanisms.

It was discovered in 1959 that metal carbonyls brought about telomerisation of ethylene and carbon tetrabromide to give products of formula Rr(CH2CH2)#CBr#. As described in a paper by the present inventors in J. Photographic Science 29 230-5 (1981), Bamford studied the mechanism of this kind of reaction and concluded that, on exposure, the carbonyl lost CO and produced a species which abstracted a halogen atom from the carbon tetrahalide to form a free radical which initiated polymerisation of the ethylenically unsaturated compound. A process based on the results of this work is described in U.K. patent specification 1,027,148.In this process a soluble or swellable preformed polymer or copolymer containing at least one CX3 group where X represents chlorine or bromine, an ethylenically unsaturated material normally polymerisable by a free radial mechanism, and a metal carbonyl are brought into contact with each other under such conditions as to cause a thermal or photochemical reaction. The words 'soluble or swellable' are used to indicate that the preformed polymer or copolymer is soluble in or swollen by the ethylenically unsaturated material or any liquid miscible with the latter. The process may be used for the formation of cross links between the preformed polymer or copolymer molecules or for the preparation of graft or block copolymers.

It was later discovered that the CX3 (or a similar) group and the ethylenically unsaturated material could be constituents of a single polymer and, accordingly U.K. Patent Specification 1,463,816 describes a photosensitive layer comprising (i) a polymer containing repeating units containing a polyhalogen group having two or three halogen atoms bonded to the same carbon atom and repeating units containing an olefinically unsaturated group, and (ii) at least one metal carbonyl (or derivative as defined), the proportion of the polyhalogen groups and of the unsaturated groups being at least sufficient for the polymer to be insolubilised by actinic radiation.

The use of a metal carbonyl compound and a trihalomethane derivative as a photoinitiator system has been suggested, amongst other systems, for a water-coatable composition containing (1) a non-light-sensitive water-soluble addition polymer containing ethylenically unsaturated groups and (2) a latex copolymer which renders a dried layer of the composition less watersoluble than a layer of (1) alone, in European Patent Application 0 029 358 Al.

A practical disadvantage of processes such as those outlined above which depend upon polymerisation induced by free radicals is that free radicals react with oxygen molecules so that the polymerisation is inhibited by the presence of air. This disadvantage can be overcome by overcoating the photosensitive layer with an oxygen impermeable barrier layer, a satisfactory layer of this kind, formed from a polyvinyl alcohol in which at least two per cent of the available secondary hydroxyl groups have been esterified with a dicarboxylic acid anhydride, being described in U.K. Patent Specification 1,553,823.

The polymerisation processes described above are all based upon the addition polymerisation of ethylenically unsaturated compounds. A different type of process is described in U.K. Specification 2 106 522A wherein the photosensitive layer is made from a composition comprising a polymer comprising a recurring unit having any one of a number of specified nucleophilic groups, and as the sole crosslinking agent for said polymer, a radiation-sensitive transition metal carbonyl (possibly an arene metal carbonyl), the composition being substantially free of any compound which reacts in response to activating radiation to form a free radical.Thus in this process the carbonyl is not used as an intermediate in the formation free radicals but as compound which forms links between adjacent polymer molecules, doing so by a mechanism believed to involve oxidation of the metal atom and substitution of the carbonyl groups by the nucleophilic groups on the polymer.

In devising photopolymerisable systems, the usual practice is to select a particular polymerisation process and then to choose the necessary constituents, including any polymerisable monomer or crosslinkable polymer, any sensitizer and any inert components, so as to provide the desired photochemical and physical properties. It is most unusual to choose constituents which will give rise to two or more polymerisation processes because the constituents for each process dilute those for each other's process and the simultaneous optimisation of all the processes is unlikely to be possible, particularly in view of possible interactions between the processes.

In the present invention, a photopolymerisable composition is employed comprising (i) a first polymer having ethylenically unsaturated groups and free radical-generating polyhalo groups, (ii) a second polymer, free from ethylenically unsaturated groups, having nucleophilic substituents and (iii) an arene transistion metal carbonyl having attached to the arene ligand an ethylenically unsaturated group.

Thus a composition of the invention contains constituents enabling polymerisation by the two different processes described above to occur. The arene transistion metal carbonyl (iii) participates in both processes and by virtue of the group attached to the arene ligand can function in a variety of additional ways as outlined below. Not only can the composition have properties including the photosensitivity, at least as good as obtainable using either of the main participating processes alone, but it provides a valuable and unexpected advantage: an oxygen barrier layer is not required in order to retain the photosensitivity for low intensity exposure.

Upon absorption of actinic radiation by the arene transistion metal carbonyl (iii) five processes, in addition to simple photodecomposition, may occur, these being listed as (a) to (e) below.

(a) The reaction of the photoexcited metal carbonyl (iii) with the polyhalo groups of the first polymer (i) to produce free radicals which cause crosslinking by addition of the ethylenically unsaturated groups.

(b) The reaction of the photoexcited metal carbonyl (i) with nucleophilic substituents of the second polymer (ii) to give crosslinks.

(c) The crosslinking of the first polymer (i) by the reaction (a) above, but with molecules of the metal carbonyl incorporated into the crosslinks by reaction of the polymerisable groups attached to the arene ligand.

(d) The reaction of a metal carbonyl molecule incorporated into a crosslink by the process (c) with a polyhalo group of the first polymer (i) to produce free radicals and so cause process (a).

(e) The reaction of a metal carbonyl molecule incorporated into a crosslink by the process (c) with a nucleophilic substituent of the second polymer (ii) to give a cross-link.

As the result of all these processes, an exposed composition of the invention is insolubilised by cross linking and entanglement of the polymer molecules.

The essential constituents of a composition of the invention are now described in more detail.

(i) The first polymer having ethylenically unsaturated groups and free radical-generating polyhalo groups.

Polymers of this kind are amongst those described in U.K. Patent Specification 1,463,813, the preferred polymers of Formula I therein being suitable. Such polymers are conveniently made by reacting a starting polymer comprising lower alkyl acrylate or methacrylate units and lower hydroxyalkyl acrylate or methacrylate or N-hydroxyalkyl acrylamide or methacrylamide units with compounds which provide the essential ethylenically unsaturated and polyhalo groups. The former can be provided by an olefinically unsaturated carboxylic acid halide; the latter by a carboxylic acid or carboxylic acid halide containing a carbon atom having attached thereto two or three halogen atoms. Suitable polymers thus include those of the formula:

wherein each of RO, R2, R4, R7 and R' is H or CH3, each R1 is an alkyl group of 1 to 4 carbon atoms, each of R3, B5 and R8 is -O(CH2);- or -NH(CH2)f- where r is 1 to 4, and each of B6 and R9 is a divalent aliphatic hydrocarbon group. This group can be, for instance, alkylene, preferably of 1 to 4 carbon atoms, cycloalkylene, preferably of 5 or 6 carbon atoms, alkenylene, preferably of 2 to 4 carbon atoms or arylene, preferably phenylene or naphthylene.

In making a polymer of formula I, it is preferred for the mole ratio of alkyl acrylate, or methacrylate, to the hydroxyalkyl acrylate, or methacrylate, in the starting polymer to be from 3:1 to 10:1. Preferred olefinically unsaturated carboxylic acid halides are acryloyl and methacryloyl chlorides and preferred carboxylic acid halides containing a carbon atom having attached thereto two or three halogen atoms are trichloroacetyl chloride and tribromoacetyl bromide.

(ii) The second polymer, having nucleophilic substituents.

A wide variety of nucleophilic substituents will substitute for a carbonyl group of the arene transition metal carbonyl, suitable substituents including those specified in U.K. Patent Application 2 106 522A, namely epoxy, carboxyl, hydroxyl, tertiary amino, morpholino, unsaturated nitrogen-containing heterocyclic, and mercapto groups. The second polymer is free from ethylenically unsaturated groups. Suitable polymers are readily made from a monomer containing the nucleophilic group and a monomer containing no such group, such as an acrylate or methacrylate ester, styrene or vinyl acetate. Instead of using a single monomer of either kind, a mixture of different monomers can be used. Preferably at least 10 mole % of the monomer, or monomers, containing the nucleophilic groups is employed.Examples of monomers having nucleophilic groups are methacrylic acid, N-[2-hydroxypropyl]methacrylamide, glycidyl methacrylate, N,N-dimethylaminoethyl methacrylate and vinyl pyridine. Copolymers containing these monomers are described in the application 2 106 522A.

(iii) The arene transition metal carbonyl.

This compound comprises at least one atom of a metal of group Va, Vla, Vlla or VIII of the Mendeleeff Periodic Table, one aromatic ring bearing an ethylenically unsaturated substituent and one carbonyl group. Examples of suitable metals are Cr, Mn, Fe, Mo, W and Be. The aromatic ring is preferably a benzene ring and with the necessary unsaturated substituent may be provided by styrene.

The synthesis of the unsaturated transition metal carbonyl compound has been described by C.U. Pittman Jr and R.L. Voges, Macromolecular Synthesis, 4 175(1972).

A composition of the invention may contain any of the usual additives, including plasticisers ~which may be ethylenically unsaturated so as to be copolymerised into the exposed layer-and substances which render the image visible by changing from colourless to coloured, or vice versa, when the layer is exposed.

A photopolymerisable composition of the invention can be used for making photoresists and lithographic plates. The composition is dispersed in a coating solvent and then coated on the chosen support to give a photosensitive element. Suitable coating solvents, which may be pure solvents or solvent mixtures, can be selected from alcohols, esters, ethers, ketones and chlorinated hydrocarbons, for example. Any of the usual supports can be chosen according to the intended use. Photoresists are commonly employed in the manufacture of printed circuits, where the support may be a copper-plastics laminate, and also of integrated circuits, where the support may comprise a slice of a semiconducting material. Lithographic plates are usually prepared from a sheet of material having a hydrophilic surface such as grained and anodised aluminium.

In making an image with an element of the invention the photosensitive layer is exposed imagewise to actinic radiation, a high pressure mercury vapour lamp being an appropriate light source. The photopolymerisable composition is thereby hardened in the more heavily exposed areas. The image is then developed by treating the layer with a solvent to remove the composition from the less heavily exposed areas. The developing solvent can be the same as the coating solvent or a different solvent, according to the desired solvent power.

The following Preparations describe the synthesis of materials used in the Example.

Preparation 1~Polymer 1 A polymer was prepared from methyl methacrylate (5 moles) and N-hydroxypropyl)-methacrylamide (1 mole). This polymer (12.89) was reacted with 3.36 g of a mixture of tribromoacetyl bromide and methacryloyl chloride (molar ration 1:3) to give Polymer 1, a polymer for use as the first polymer (i) of a composition of the invention. These steps are described in more detail in Examples 18 and 19 of U.K. Patent Specification 1,463,816.

Preparation 2~Polymer 2 A polymer, Polymer 2, of methyl methacrylate and methacrylic acid (8:1 molar ratio) was prepared as described in U.K. Patent Specification 2 106 522A (see Preparation 8). This polymer, having nucleophilic carboxyl groups, was for use as the second polymer in a composition of the invention.

Preparation 3~116(phenylethyl methacrylate)tricarbonylchromium 66(2-phenylethanol)tricarbonyl chromium was made by reacting phenylethanol with chromium hexacarbonyl and was then reacted with methacryloyl chloride to give the desired compound, as described in the reference cited above.

Example A coating composition according to the invention was made of the following composition.

Polymer 1 (see Preparation 1 above) 0.50 g Polymer 2 (see Preparation 2 above) 0.50 g Arene metal carbonyl (see Preparation 3 above) 0.053 g Acetone 10 ml A comparison composition omitting the first polymer (that containing the ethylenically unsaturated and polyhalo groups) was also made of the composition: Polymer 2 1.0 g Arene metal carbonyl 0.053 g Acetone 10 ml Coatings of wet thickness 60 ,otm on a copper-polyester laminate were made from the two compositions, the acetone then being allowed to evaporate off at the ambient temperature.

A sample of each dry coating was exposed for 5 minutes in a vacuum frame to a 0.15 log E increment step wedge and a printed circuit test negative, using four 125 W high pressure mercury vapour lamps 45cm away. The samples were developed with acetone and the resulting resist images were heated in a drying oven at 800C for 1 hour. The copper was then etched where not protected by the images using aqueous ferric chloride solution. The coating according to the invention was three steps (i.e. approximately 3 times) faster than the control and was equally resistant to the etching solution.

Claims (7)

1. A photopolymerisable composition comprising (i) a first polymer having ethylenically unsaturated groups and free radical-generating polyhalo groups, (ii) a second polymer, free from ethylenically unsaturated groups, having nucleophilic substituents and (iii) an arene transition metal carbonyl having attached to the arene ligand an ethylenically unsaturated group.

2. A composition according to claim 1 wherein the first polymer is of the general formula:

wherein each of RO, R2, R4, R7 and R10 is hydrogen or a methyl group, R1 is an alkyl group of 1 to 4 carbon atoms, each of R3, Rs and R8 is -O(CH2),- or -NH(CH2),- where r is 1 to 4, and each of R6 and R9 is a divalent hydrocarbon group.

3. A composition according to claim 1 or 2 wherein the second polymer has epoxy, carboxyl, hydroxyl, tertiary amino, morpholino, unsaturated nitrogen-containing heterocyclic or mercapto substituents.

4. A composition according to any of the preceding claims wherein the arene transition metal carbonyl is a compound of chromium, manganese, iron, molybdenum, tungsten or rhenium.

5. An element comprising a support coated with a layer of a composition according to any of the preceding claims.

6. An element according to claim 5 wherein the support is a hydrophilic lithographic plate support.

7. A method of making a resist image which comprises imagewise exposing an element according to claim 5 or 6 to actinic radiation to harden the composition in the more heavily exposed regions and then treating the element with a solvent to remove the composition from the less heavily exposed regions.