IE41719B1 - Improvements in or relating to the processing of printing plates - Google Patents

Abstract

1523877 Developing photo-sensitive polymers VICKERS Ltd 19 Nov 1975 [19 Sept 1974] 40949/74 Heading G2C A developer for an exposed photo-sensitive polymer layer includes a lactam of the Formula: in which n is 0 or an integer of from 1 to 9; h is a hydrogen atom, or an alkyl, alkenyl, aralkyl, aryl or acyl group; and R' and R" are each a hydrogen atom or an alkyl or aryl group, together with a wetting agent and/or a colourant. The colourant is preferably an organic solvent soluble dye. Preferred lactams are 1-methyl-2pyrrolidinone, 1-butyl- 2-pyrrolidinone, 1-cyclohexyl-2-pyrrolidinone, 2-pyrrolidinone, 1-vinyl-2-pyrrolidinone and #-caprolactam. The developer may further include (i) an acid e.g. phosphoric, hydrochloric [or] sulphuric, acetic, lactic, glycollic or α-pentenoic acid (ii) an inert diluent e.g. water, ethanolamine or 2-ethoxy ethanol and (iii) an additional organic solvent which dissolves the polymer e.g. tetrahydrofurfuryl alcohol, 2-methoxy ethyl acetate or γ-butyrolactone. The light-sensitive polymer is negative working containing groups of the structure -CH=CH-CO- e.g. polyvinyl cinnamate, or a cinnamoylated epoxy resin.

Description

This invention relates to the processing of image-wise exposed light-sensitive polymer layers.

Such layers axe widely used to form images on a variety of substrates and thereby provide different products such as etched patterns, printed circuits, and printing plates or masters. A particularly important application of the present invention is in the production of lithographic printing plates, although it can also be used in the production of other types of printing plate such asa letterpress plate where the image is etched into relief and in the production of printed, circuits, integrated circuits and the like.

The printing of patterns, typography and pictorial subjects on various materials such as paper, carton board, plastics and metal is frequently carried out by means of lithography. The lithographic method of printing employs a special printing plate which, when wetted with water selectively accepts oleo ink from one or more ink covered rollers and transfers it either directly or indirectly to the paper or other material to be printed. A lithographic printing plate is alternatively known as a planographic plate or a surface plate. The printing image on a litho20 - 3 graphic printing plate is neither raised above nor recessed below the level or plate of the surrounding non-image areas, hence the term planographic. In this it is unlike the plates, formes and cylinders used by the other two major printing methods, namely letterpress and gravure. The printing image of the letterpress plate is substantially raised above its supporting non-image material, and that of the gravure plate or cylinder is recessed below its surrounding non-image area. In the lithographic method the plate needs to process suitable surface characteristics which enable the ink to adhere to the required image areas and not to adhere to the clear non-image areas, and the correct choice of the component mater15 ials used to construct the lithographic plate is important. It is also important that the plate and materials on it be correctly processed otherwise the essential oleophilic and hydrophilic properties of the image and non-image areas respectively may not be obtained.

During recent years the photographic methods used to form lithographic printing images have changed. Whereas dichromatesensitised natural colloids (e.g. albumen) were commonly used to produce what are known as surface images by exposure behind a photographic negative, two alternative systems are now commonly employed for this so-called negative-working process. One of these systems uses a light-sensitive plate comprising a diazo resin coated to form a very thin layer on the surface of a metal support which is usually made of aluminium. In the other system there is used a light sensitive plate comprising a support coated with a thicker layer of a light-sensitive polymer(e.g,, a cinnamoylated resin) for the same purpose. - 4 41719 These light-sensitive polymers are negative-working i.e. photohardenable and may be defined as polymers containing a plurality of groups of the structure - CH=CH-CO-. Such polymers are described in British Patent Specifications Nos. 695,197} 794,572; 813,605; 838,547; 846,908; 913,764} 921,530; 949,919; 966,296; 966,297} 1,112,277; 1,117,197; 1,311,692; 1,313,390; 1,314,689; 1,317,818; 1,338,020; 1,341,004; l,35O;351; 1,353,501; 1,363,214; l,377;74O; 1,377,747; 1,378,535 and in aany other documents.

Such polymer systems are processed by a procedure which is said to be subtractive and it is with light sensitive plates incorporating layers of such negative-working polymers that the present invention is concerned.

Light-sensitive plates based on such photosensitive polymer systems comprise a support having a surface completely covered with a layer of the lightsensitive polymer. The support is usually of metal which may be grained and suitably anodised to improve its properties. The polymer layer is image-wise exposed to actinic light using a suitable negative. Those parts of the polymer which are struck by the light become hardened. The image-wise exposed plate is processed by selectively removing the non-light struck, and unwanted areas, of the polymer from the support surface (i.e. the plate is developed) and by making adequately water receptive the underlying areas of the support surface which are revealed when the non-light struck areas are removed, (i.e. the plate is gummed or desensitised).

Poly(vinyl cinnamate) is a typical example of a polymer system of the type with which the present - 5 invention is concerned. This and similar lightsensitive polymers, which often have admixed with them suitable sensitisers to enhance their response to light and also colourants, are developed by applying a developer comprising one or more suitable organic solvent liquids. The developers used are such that they dissolve the non-light struck areas of the polymer but not the light struck areas of the polymer, fiesensitising of the support surface revealed on development is done in the traditional manner by using suitable film or layer forming materials to make contact and possibly react with the metal surface. Such materials are well known and may be colloidal desensitisers for example, gum arable or sodium carboxymethyl cellulose or desensitising acids such as phosphoric acid.

The procedure of lithographic plate making above described enables factory coated presensitised plates to be supplied to the user, and enables the user to rapidly and economically produce printing plates.

Such printing plates are capable of yielding 50,000 or more satisfactory copies. When a suitable metal support is used the edition obtained from a single plate can be as large as 400,000.

The choice of organic solvent for use in the developer is not simple due to the numerous limitations which exist. If a solvent is too powerful, the image constituted by the light struck areas of the polymer, is weakened. If the solvent is not powerful enough, the unwanted, non-light struck areas of the polymer are not sufficiently removed. Furthermore, if the solvent evaporates excessively at room temperature it is inconvenient and perhaps costly to use, and if it is toxic to any degree it must be avoided. Finally, - 6 it is usually necessary to include a desensitising acid in the developer and hence the solvent used should not be readily hydrolysed by the acid.

The organic solvents conventionally used for developing photo sensitive polymers all suffer from one or more of the above disadvantages. For instance, cyclohexanone is toxic and smells objectionably, particularly at the elevated temperature of some work rooms; tetrahydrofurfuryl alcohol is non-toxic but is not sufficiently powerful; butyrolactone is non-toxic but is readily hydrolysed in the presence of acids; methoxybutyl acetate is toxic, possesses a sickly odour and is hydrolysed in the presence of acids; 2 - methoxyethyl acetate is toxic, possesses an objectionable odour and is readily hydrolysed in the presence of acids; and dimethylformamide is extremely toxic.

According to one aspect of the present invention there is provided a method of processing a photo sensitive polymer layer which has been image-wise exposed, which method comprises selectively removing the non-light struck areas of the layer by contacting the layer with a developer comprising a lactam having the general formula; R> - 7 where n is 0 or is an integer of from 1 to 9, R is a hydrogen atom or an alkyl, alkenyl, aralkyl, aryl, or acyl radical and each of R' and R”, which may be the same or different, represents a hydrogen atom or an alkyl or aryl radical.

According to another aspect of the present invention there is provided a developer for use in processing a photo sensitive polymer layer which has been image-wise exposed, which developer comprises a lactam having the general formula: •C = 0 C n wherein n, R, R' and R have the above meanings, said developer further including a wetting agent and/ or a colourant.

Optionally, the developer additionally contains an acid, an inert diluent, and/or an additional organic liquid which is a selective solvent for the non-light struck areas of an image-wise exposed photo sensitive polymer.

Preferably, n has a value of from 0 to 3. - 8 Examples of γ - lactams are 2 - pyrrolidinone (melting point 25°C) and. its hydrate (m.p. 35°C), 1 methyl - 2 - pyrrolidinone, 5 - methyl - 2 - pyrrolidinone (m.p. 41°C), ί - vinyl - 2 - pyrrolidinone, 1 5 ethyl - 2 - pyrrolidinone, 1 - isopropyl - 2 - pyrrolidinone, 1 — n — butyl - 2 - pyrrolidinone, 1 - pentyl - 2 - pyrrolidinone, 1 - phenyl - 2 - pyrrolidinone (m.p. 68°C), l-(£- tolyl) - 2 - pyrrolidinone (m.p. 88.5°C), 1 - acetyl - 2 - pyrrolidinone, and 1,5 - dimethyl - 2 - pyrrolidinone. Examples of § - lactams are 2 - piperidone (m.p. 39°C) 1 - methyl 2 - piperidone, 3 - methyl - 2 - piperidone (m.p. 53°C) - ethyl - 2 - piperidone (m.p. 68°C), 3-2.” propyl - 2 - piperidone (m.p. 59°C) and 6 - a - propyl - 2 15 piperidone (84°C). An example of an f- lactam is 6 hexano - lactam. It will be appreciated that, in the case where the lactam is a solid at room temperature, it must be transformed into a liquid before use by heat ing or by dissolution.

Particularly preferred lactams are 1 - methyl - 2 pyrrolidinone, 1 - butyl - 2 - pyrrolidinone, 1 cyclo - hexyl - 2 - pyrrolidinone, 2 - pyrrolidinone, - vinyl - 2 - pyrrolidinone and ε - caprolactam.

These lactams have been found to have a particularly good solvent action on the non-light struck areas of the photopolymer and thus can be used in diluted form but do not cause undue swelling of the light hardened polymer, 1 - Methyl 2 - pyrrolidinone is particularly advantageous as it is non-toxic, possesses a low vapour pressure, and a negligible odour. Also it is stable in acidic conditions.

In the case where the developer additionally contains an acid, this may be a mineral acid for example, phosphoric acid, sulphuric acid or hydro41719 chloric acid or an organic carboxylic acid, especially a monocarboxylic acid, such as acetic acid, a hydroxycarboxylic acid such as lactic acid and glycollic acid, or an unsaturated carboxylic acid such as a - pentenoic acid. The amount of acid present may be from 1-5% by volume, based on the volume Of lactam employed, and is preferably such that the developer has a pH of from about 2 to 6.

The presence of one or more wetting agents is preferred to impart good spreading characteristics to the developer and to help to maintain in suspension in the developer, polymer and colourant (in the case where the photopolymer layer includes a colourant) removed from the non-light struck areas. Examples of wetting agents are Texofor FP 85 and 65 A9P (polyoxyethylene ether condensates obtainable from Glovers Chemicals Ltd.), Perminal BX (sodium salt of an alkylated naphthalene sulphonic acid obtainable from ICI Ltd.), Aerosol 0T, and Tergitol MPX (a nonyl phenol ethylene oxide condensation product obtainable from Union Carbide). (The words Texofor Perminal and Tergitol are Trade Marks).

In the case where the developer includes one or more inert diluents, suitable diluents are for example, water, ethanolamine, ethylene glycol monoethyl ether (i.e. 2 - ethoxy-ethanol), ethylene glycol, diethylene glycol, diethylene glycol monoethyl ether (i.e. 2 (2 - ethoxy ethoxy) ethanol), diacetone alcohol, isopropanol or other liquid which, when used alone, has no appreciable solvent action on the image-wise exposed layer.

In the case where the developer includes an additional organic liquid which is a selective solvent for the non-light struck areas, this may be any compatible organic solvent liquid conventionally used for developing the photopolymer. Examples of such additional organic solvent liquids are 2 - methoxyethyl acetate, γ - butyrolacetone, tetrahydrofurfuryl alcohol, n - propyl alcohol and methoxybutyl acetate. More than one additional organic liquid may be present.

Ih the case where the developer includes a colourant, this is preferably a water insoluble organic 10 solvent, soluble dye having a good affinity for printing ink. Examples of such dyes are Oil Orange E; Oil Red Dye No. 152008; Waxoline, Yellow; and Waxoline Blue AS.

The method of the present invention has been found to be useful for developing many image-wise exposed photosensitive polymer layers and particularly for developing layers of polymers containing a plurality of groups of the structure -CH=CH-C0- as described in the previously mentioned documents. Specific examples 20 of such polymers are photopolymerisable resin esters such as those derived from polymers containing free hydroxy groups e.g. polyvinyl alcohol or an epoxy resin, and unsaturated carboxylic acids such as cinnamic acid.

In use of the method of the present invention, in printing plate production, a light sensitive plate comprising a layer of photosensitive polymer coated on the surface of a support is suitably image-wise exposed to actinic light. Then the image-wise exposed 20 layer is developed by applying the developer for a period of time sufficient to remove the polymer from the non-light struck areas; gentle mechanical action - 11 41719 action aids the removal. Thus, swabbing is a highly useful method of applying the developer to the plate.

The developer has sufficient activity that it can be employed at room temperature. If desired, however, it can be employed at elevated temperatures of up to about 50°C. After an initial application of developer a second application can be made followed by either a single or multiple application of a desensitizing material to render hydrophilic those areas of the support surface revealed when the nonlight struck areas are removed. The plate is then dried and comprises a printing image constituted by the light struck areas and non-printing areas constituted by the revealed areas of the support surface.

The following non-limiting Examples illustrate the invention. All parts are by weight unless otherwise stated.

Example 1 A Super Sensalith presensitised printing plate of Howson-Algraphy and comprising a support of anodised aluminium carrying a photo sensitive polymer layer comprising a cinnamoylated epoxy resin was placed in contact with a '’line” photographic negative and exposed to light emitted from a carbon arc lamp for five minutes (The word Sensalith” is a Trade Mark). It was then manually processed by rubbing with 1 - methyl - 2 pyrrolidinone for thirty seconds. It was then desensitised with a solution containing 46% by volume water, 50% by volume gum arabic (S.G. 1.17), 0.9% by volume Perminal BX, 2% by volume ammonium dihydrogen phosphate, and 1.1% by volume phosphoric acid (S.G. 1.75).

When the resultant printing plate was moistened with water and inked with oleo ink, a well defined inked printing image was visible.

Example 2 Example 1 was repeated except that the presensitised plate was one comprising an anodised aluminium support coated with a layer of Waycoat photoresist (Phillip A. Hunt Chemical Corporation). Waycoat photoresist comprises a photopolymer which is believed to be poly(vinyl cinnamate). A well defined inked printing image was visible.

Example 3 Example 1 was repeated with equally satisfactory results using as developer the following developing solution. parts - Methyl - 2 - pyrrolidinone 5 - hydroxy - 4 - methyl - 2 pentanone (diluent 4.6 phosphoric acid (S.G 1.75) 0.4 Example 4 A Super Sensalith plate (Howson-Algraphy) was automatically processed in a 30 inch wide HowsonAlgraphy negative plate processor running at 36n per minute after exposure beneath a dot structured photographic negative to a pulsed-Xenon light source. The desensitising section of the processor was filled with a 10% aqueous solution of polyacrylamide, and, the - 13 the developing section was filled with: parts - methyl - 2 - pyrrolidinone 6 tetra - hydrofurfuryl alcohol 3 Texofor 65A9P (Glovers Chemicals Ltd.) sulphuric acid 1 2 Waxoline Blue AS.

(I.C.I. Ltd.) 0.1 1° Texofor 05A9P is a wetting agent and is a polyoxyethylene ether condensate of the formula R.O. (C-H.O) H wherein R is a long chain fatty group. ΛΙ if Ω No difficulty was experienced in obtaining dense black prints from the blue imaged planographic plate when it was used on a lithographic printing press. The temperature of the solution in the devel oping section was 24°C.

Example 5 Example 4 was repeated with similar success whilst using the developing solution at 40°C. No objectionable odours were noticed in the work area. Development could be carried out at a faster running speed.

Example 6 A light sensitive plate was produced by coating a grained and anodised aluminium sheet with a light41719 - 14 sensitive cinnamoylated epoxy resin at 0.5 gram per square metre. When thoroughly dry the plate was exposed in contact with a line and half-tone negative for minutes to a mercury halide lamp.

The plate was cut into four sections which were developed as follows: A - developed with 1 - butyl 2 - pyrrolidinone at 22°C.

B - developed with 1 - cyclohexyl - 2 10 pyrrolidinone at 50°C.

C - developed with 2 - pyrrolidinone at 50°C D - developed with 1 - vinyl 2 - pyrrolidinone at 22°C.

The sections were desensitised with the desensit15 ising solution of Example 1 and inked whilst wet with oleo black ink. In each case a well defined printing image was obtained.

Example 7 This demonstrates how a suitable lactam can be 20 considerably diluted to achieve economy without upsetting its usefulness.

Example 1 was repeated using the following developers. Satisfactory printing plates were obtained in each case. - 15 A: 9 parts 1 - methyl - 2 - pyrrolidinone and part water B: 8 parts 1 - methyl - 2 - pyrrolidinone and parts ethanolamine.

C: 6.5 parts 1 - methyl - 2 - pyrrolidinone and 3.5 parts ethanolamine D: 10 parts 1 - methyl - 2 - pyrrolidinone and parts 2 - ethoxyethanol E: 6 parts 1 - methyl - 2 - pyrrolidinone and 10 4 parts 2-(2- ethoxy ethoxy) - ethanol F: 10 parts 1 - methyl - 2 - pyrrolidinone and parts 4 - hydroxy - 4 - methyl - 2 pentanone.

Example 1 was also repeated using the lactams in 15 combination with 2 - methoxy-ethyl acetate on the one hand and γ - butyro-lactone on the other hand. Satisfactory results were also obtained in each case.

Example 8 Example 4 was repeated using, as developer, a warm 20 solution of 10 parts ε- caprolactam in 9 parts 2 ethoxy ethanol. Similar results were obtained.

Example 9 Example 1 was repeated except that an LNL lithographic plate (Kodak Limited) was used. This plate is - 16 a negative working plate and comprises a support coated with a photosensitive polymer. A well defined printing image was obtained.

Example 10 The front of an unused sheet of photoengraving ainc (S.D. Syndicate Ltd.) was cleaned and coated with a layer of KPR (Kodak Limited). KPR comprises a photosensitive polymer which is believed to be poly(vinyl cinnamate). When dried, the resultant light-sensitive plate was exposed to actinic light whilst in contact with a contrasty line negative for several minutes. The plate was then developed using 1 - methylene - 2 - pyrrolidinone and dried.

The image remaining on the sheet after development was used as a resist whilst etching the plate with an etchant containing nitric acid to produce a relief imaged letterpress printing plate.

Example 11 A smooth piece of copper clad resin laminate board, as used in the production of printed circuits, was coated with Waycoat photo-resist (Philip A. Hunt Chemical Corporation). The resultant light sensitive plate was exposed beneath a photographic negative developed with a solution containing 10 parts of 1 25 methyl - 2 - pyrrolidinone and 8 parts of isopropyl alcohol (diluent). A cleanly developed well defined etch resistant image was obtained.

Example 12 Example 1 was repeated using as developer on separate exposed plates the following lactams: - 17 1 - ethyl-2 - pyrrolidinone - acetyl - 2 - pyrrolidinone (1 - acetyl 2 - oxohexamethylene imine) 1,5 - dimethyl - 2 - pyrrolidinone 5 - methyl - 2 - pyrrolidinone 3 - piperidone ( 6- valerolactam) In the case of the last two lactams, it was necessary to warm them to their melting points (about 40°C).

In all cases clean plates with well-defined printing images were obtained.

Example 13 Example 1 was repeated using 1 - methyl - 2 pyrrolidinone in which had been dissolved 1 g of oil soluble red dyestuff ('TAX* Williams (Hounslow) Ltd.) for each 100 ml of 1 - methyl - 2 - pyrrolidinone. A coloured image of good visibility was obtained which accepted oleo ink without difficulty.

Example 14 Example 1 was repeated successfully using 1 methyl - 2 - pyrrolidinone containing 2% acetic acid followed by a non-acidified gum arabic desensitiser.

Example 15 A presensitised photopolymer negative-working plate (Marathon supplied by Vickers Ltd.) was exposed to actinic light emitted from a mercury halide source whilst in contact with a half-tone negative for 1 minute. It was subsequently developed with a solution comprising : 490 el of 1 - methyl - 2 - pyrrolidinone 49Ο ml qf 4 - hydroxy - 4 - methyl - 2 pentanone (diluent) ml of phosphoric acid (S.G. 1.750) g of Waxoline Purple (I.C.I. Ltd.) Immediately following this it was desensitised with an aqueous solution of sodium carboxymethyl cellulose to give a well defined visible red coloured image.

Claims (36)

1. A method of processing a photosensitive polymer layer which has been image wise exposed, which method comprises selectively removing the non-light struck 5 areas of the layer by contacting the layer with a developer comprising a lactam having the general formula: R< where n is 0 or an integer of from 1 to 9, R is a hydrogen atom or an alkyl, alkenyl, aralkyl, aryl, 10 or acyl radical and each of R' and R, which may be the same or different, represents a hydrogen atom or an alkyl or aryl radical.

2. A method according to claim 1 wherein the lactam is 1 - methyl - 2 - pyrrolidinone. 15

3. A method according to claim 1 wherein the lactam is 1 - butyl - 2 - pyrrolidinone, 1 - cyclohexyl - 2 pyrrolidinone, 2 - pyrrolidinone, 1 - vinyl - 2 pyrrolidinone or £.- caprolactam.

4< A method according to claim 1, 2 or 3» wherein the developer further comprises an acid.

5. A method according to claim 4, wherein the acid is phosphoric acid. 5

6. A method according to any one of the preceding claims wherein the developer further comprises a wetting agent.

7. A method according to any one of the preceding claims wherein the developer further comprises an 10 inert diluent.

8. A method according to Claim 7 wherein the diluent is water, ethanolamine or 2 - ethoxy ethanol.

9. A method according to any one of the preceding claims wherein the developer further comprises an 15 additional organic liquid which is a selective solvent for the non-light struck areas of the polymer layer.

10. A method according to Claim 9 wherein the additional organic liquid is tetrahydrofurfuryl alcohol. 20 ii.

A method according to Claim 9 wherein the additional organic liquid is 2 - methoxyethyl acetate or γ - butyrolactone.

12. A method according to any one of the preceding claims wherein the developer further comprises a 25 colourant.

13. A method according to any one of the preceding claims wherein the photosensitive polymer is a photo21 polymerisable resin ester.

14. A method according to Claim 13 wherein the photopolymerisable resin ester is derived from a polymer containing hydroxyl groups and from an un5 saturated carboxylic acid.

15. A method according to Claim 14 wherein the photopolymerisable resin ester is poly(vinyl cinnamate) .

16. A method according to claim 14 wherein the 10 photoplymerisable resin ester is a cinnamoylated epoxy resin,

17. A method of processing in accordance with claim 1 substantially as hereinbefore described in any one of Examples 1, 3, 4, 5, 10 and 11. 15

18. A method of processing in accordance with Claim 1 substantially as hereinbefore described in any one of Examples 2, 6, 7, 8 and 9· I

19. A developer for use in processing a photosensitive polymer layer which has been image wise exposed, 20 which developer comprises a lactam having the general formula: R' \ C-C = 0 z R R* wherein n is 0 or ah integer of from 1 to 9, R is a hydrogen atom or an alkyl, alkenyl, aralkyl, aryl or acyl radical and each of R 1 and R rt , which may be the 5 same or different, represents a hydrogen atom or an alkyl or aryl radical, said developer further including a wetting agent and/or a colourant.

20. A developer according to Claim. 19 wherein the lactam is 1 - methyl - 2 - pyrrolidinone. 10

21. A developer according to claim 19 wherein the lactam is 1 - butyl - 2 - pyrrolidinone, 1 - cyclohexyl - 2 - pyrrolidinone, 2 T pyrrolidinone or ε - caprolactam.

22. A developer according to claim 19, 20 or 21 15 which also.includes an acid.

23. A developer according to claim 22 wherein the acid is a mineral acid.

24. A developer according to Claim 23 wherein the acid is phosphoric acid.

25. A developer according to Claim 23 wherein the acid is hydrochloric acid.

26. A developer according to Claim 23 wherein the acid is sulphuric acid.

27. A developer according to Claim 22 wherein the acid is an organic carboxylic acid.

28. A developer according to claim 27, wherein the acid is acetic acid, lactic acid, glycollic acid, or a - pentenoic acid.

29. A developer according to any one of Claims 22 to 28 and containing sufficient of said acid such that it has a pH of from 2 to 6.

3. Q. A developer according to any one of Claims 19 to 29, and also including an inert diluent.

31. A developer according to Claim 30, wherein the diluent is water, ethanolamine, or 2 - ethoxyethanol.

32. A developer according to any one of Claims 19 to 31 and also including an additional organic liquid which is a selective solvent for the non-light struck areas of an image-wise exposed photosensitive polymer.

33. A developer according to Claim 32 wherein the additional organic liquid is tetrahydrofurfuryl alcohol.

34· A developer according to Claim 32 wherein the - 24 additional organic liquid is 2 - methoxy· ethyl acetate or γ - butyrolactone.

35· A developer according to Claim 19 substantially as hereinbefore described in either of Examples 4 5 and 5.

36. A developer according to claim 19 substantially as hereinbefore described in Example 13 or 15. 37· The product of the method claimed in any one of Claims 1 to 18. F. R. KELLY & CO.