GB1580042A - Radiation sensitive compositions - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO RADIATION SENSITIVE COMPOSITIONS (71) We, VICKERS LIMITED, a British company, of Vickers House, Millbank Tower, Millbank, London SWI, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to radiation sensitive compositions.

According to the present invention there is provided a radiation sensitive composition comprising (i) a quaternary ammonium salt of the type which will accept at least one electron on exposure to radiation to form a substance capable of causing metal to be deposited onto said substance from an electroless plating solution in contact with said substance which electroless plating solution comprises a salt of said metal and a reducing agent and (ii) a chemical sensitiser for improving the speed of photoreduction of the salt said sensitiser having the general formula

wherein R2' is a substituted or unsubstituted aryl group, an arylalkenyl group, or an arylalkyl group; R22 is a substituted or unsubstituted aryl group, an alkyl group, an arylalkyl group, an arylalkenyl group, a carboxylic acid group, a carboxylic acid salt group, or a hydrogen atom; or R21 and R22 together represent a bivalent species; and X represents a carboxylic acid group or a carboxylic acid salt group.

The quaternary ammonium salt may be of the type described in British Patent Specification No. 1,310,812 and having the general formula:

wherein R' to R10 are hydrogen or halogen atoms or organic substituents; R" and R'2, if present, are each halogen atoms or organic substituents or together represent a divalent organic substituent; Z is zero or an integer; X- is an anion; m=l or 2; and at least one of the nitrogen atoms is quaternary. In an embodiment, R" and R12 are not each -CM3 groups or are not together a -CH2-CH2- group when each or R' to R10 is a hydrogen atom and Z is zero.

The quaternary ammonium salt is preferably a diquaternary cyclic ammonium salt which by the addition of one electron forms Weitz radicals. Such salts are dicationic and contain nitrogen atoms in the molecule, at least two of the nitrogen atoms being quaternised and being constituents of ring structures which are linked and are at least partially aromatic, the link between the ring structures providing a chain of conjugated unsaturation between the nitrogen atoms. Particularly suitable diquaternary ammonium salts for the compositions of the present invention are the bypyridylium salts exemplified by

Compounds (1) and (2) are commercially available materials marketed under the trade names of PARAQUAT and DIQUAT respectively. Compound (3) is N,N' bis-(paracyanophenyl)-4,4'.bipyridylium dichloride and will hereinafter be referred to as CPP++.

Preferably the quaternary ammonium salt is colourless or only slightly coloured prior to exposure and the substance formed therefrom on exposure is coloured, so that a readily visible image is produced on exposure. For example, the dication CPP++ is almost colourless, the radical cation formed by the addition of one electron to the dication CPP++ is green, and the corresponding neutral molecule formed by the addition of two electrons to the dication CPP++ is red.

The quaternary ammonium salt may include a simple cation or it may be part of a more complex molecule such as a dimeric cationic compound. It may be a polymeric material with one or more of the ring structures containing the quaternary nitrogens being in the polymer backbone, in end groups, in side chains or in combinations of such positions.

The anions of the quaternary ammonium salts may be, for example, halides, perchlorates, tetrafluoroborates, silico.fluorides, methyl sulphates, bisulphates, or polymeric anions such as, for example, poly(acrylate). The presence of iodine atoms is less desirable than the presence of chlorine or fluorine atoms because iodine acts as a quencher for the excited state of the cation. The anions should not be oxidising or reducing agents.

In an embodiment, in the formula for the chemical sensitiser, R21 is not a phenyl group when R22 is a phenyl group. Examples of suitable chemical sensitizers of the specified formula are mandelic acid and derivatives thereof such as pbromomandelic acid, p-chloromandelic acid, p-fluoromandelic acid, mmethoxybenzilic acid and 3,4-dimethoxy 2'-chlorobenzilic acid; 3-phenyllactic nitromandelic acid; benzilic acid and derivatives thereof such as di-pmethoxybenzilic acid and 3e,4-dimethoxy 2'-chlorobenzilic acid; 3-phenyllactic acid; atrolactic acid; 9-hydroxy-fluorine-9-carboxylic acid; and styryl glycollic acid. It is particularly preferred to use water soluble sensitisers such as potassium atrolactate or mandelic acid salts, for example, sodium mandelate, ammonium mandelate, tetramethyl ammonium p-fluoro mandelate, and hexamethylene tetramine mandelate. The chemical sensitisers appear to act as electron donors in the photoreduction action. The molar ratio of quaternary ammonium salt to chemical sensitiser may be, for example, from 10:1 to 1:50 respectively.

The inherent spectral sensitivity of the quaternary ammonium salts can be extended well into the visible region of the spectrum by the inclusion of spectral sensitisers and such sensitisers may be included in the composition of the present invention. Suitable spectral sensitisers are riboflavin, 7 chloro-9-(N-methyl-2diethylaminoethyl) isoalloxazine chloride (hereinafter referred to as compound RD) and other very similar compounds, and Arconol Yellow (3,6-dimethyl-2-(4dimethylamino-phenyl)benzthiazolium chloride). Other sensitisers which can be used include 3,3'-diethylthiacyanine iodide, proflavin, acridine orange, acriflavin, N-methylphenazinium methyl sulphate, 4-cyanoquinolinium methiodide and erythrosin.

The composition of the present invention may additionally include a filmforming polymeric binder. The binder may be such that it is inert towards the substance formed on exposure of the quaternary salt or such that it has a stabilising influence on that substance. Suitable water soluble or swellable film forming polymers for use as the binder include poly(vinyl alcohol), poly(ammonium methacrylate), gelatin, alginates and maleic anhydride copolymers e.g. a copolymer of maleic anhydride with styrene vinyl ether or ethylene. Soluble polysaccharides such as polysucrose may also be used as binder as may poly-(Nvinylpyrrolidone) either alone or in admixture with poly(vinylalcohol).

Poly(vinylalcohols) of many viscosities and degrees of hydrolysis may be used but low- and medium-viscosity and maximum degree of hydrolysis grades are preferred. The relative amounts (in parts by weight) of quaternary salt to binder may be, for example, from 1:200 respectively to 10:1 respectively.

Other materials may be present in the composition as required. For example surface active agents may be included. Other compounds may also be present in the composition such as ethylene diamine-tetracetic acid (disodium salt), diammonium hydrogen citrate, ammonium chloride, and the fumed silica known under the Trade Mark Cab-o-sil.

The composition of the present invention can be used as an image-forming system of general application for forming high contrast positives from negatives and vice-versa. The composition may be reduced in an image-wise manner by means of actinic light, bymeans of an electron beam or a laser beam or by means of a spark cutting machine. The composition may be applied to a suitable substrate, e.g. of metal or plastics materal, to form a radiation sensitive plate which, after imagewise reduction may be contacted with an electroless plating solution, for example a solution containing a silver salt and a reducing agent, to form an image as a result of deposition of metal from the electroless plating solution onto the reduced areas of the composition. Such solutions are well known per se and are capable of depositing metal without the external application of an electrical field.

In the case where the composition is used in the form of a coating on a substrate, it is preferred to use a coating solution having a pH of from about 1 to 7.

In general, the higher the pH the more sensitive is the composition.

The following Examples illustrate the invention. In all cases except where otherwise stated, the quantities of the various ingredients used are expressed in parts by weight. The amount of radiation sensitive composition applied in the Examples was of the order of 0.2 g/m2. The silver electroless plating solution used in the Examples was prepared by admixing 1 part by wt of solution II and 4 parts by wt of solution I followed by the addition of 1 part by wt of solution III, the solutions being, as follows:- Solution I Ferrous ammonium sulphate 100g Ferric nitrate 40g Citric acid 100g water to 1 litre Solution II n-Dodecylamine 1.6g Lissapol N 0.97g Acetic acid 2.4g Oleylamine 0.8g Water to 1 litre Solution III Silver Nitrate 120g Water to 1 litre Lissapol N is a non-ionic wetting agent and is an ethylene oxide condensate with a nonyl phenolic alcohol.

EXAMPLE 1.

A composition was prepared comprising the following ingredients: CPP++ 1.50 (0.0035 moles) Triton X-100 0.10 Lemol 16-98 3.00 Dimethylformamide 30.00 Water 70.00 Triton X-100 is octylphenoxypolyethoxyethanol. (The word "Triton" is a Trade Mark.) Lemol 16-98 is a poly(vinylalcohol) produced by the Borden Chemical Company.

The composition was applied by roller coating to a sheet of aluminium which had been electro-grained in nitric acid, desmutted in phosphoric acid and finally anodised in sulphuric acid to form a radiation sensitive plate having a dry coating weight of from about 0.1 to 0.2 g/m2.

Using a Kodak No. 2 step-wedge and a contact printing frame, the radiation sensitive plate was exposed for 2 minutes to the radiation from four Phillips 300 W MLU lamps 600 mm from the frame. (The words "Kodak" and "Phillips" are Trade Marks.) The resultant print out image was then examined and its reflected optical density was measured through a red filter. Then the plate was immersed in the above silver electroless plating solution for 3 minutes at room temperature.

Further identical aluminium sheets were coated as above except that the composition contained 3.0 parts of various chemical sensitisers. The resulting plates were then exposed, examined, developed, and measured as above. The results are shown in table 1.

The above experiments were then repeated using an exposure time of 30 seconds instead of 2 minutes. The results are shown in Table 1.

TABLE 1

Number of Solid Steps on Developed Increase in Reflected Optical Density CHEMICAL SENSITIZER Coating Plate (After and amount of same in moles Solution Z Minutes After 30 Seconds After 2 Minutes pH. Exposure) Exposure Exposure Mandelic acid (0.020) 3.2 7 0.15 0.24 Hexamethylenetetramine Mandelate (0.010) 4.8 2 0.27 0.25 p-Methoxymandelic acid (0.016) 3.0 4 0.20 0.32 o-Methoxymandelic acid (0.016) 3.2 3 0.22 0.24 Atrolactic acid (0.018) 3.0 1 0.27 0.27 3-Phenyliactic acid (0.018) 3.1 1 0.12 0.25 9-Hydroxyfluorene-9-carboxylic acid (0.013) 1.9 6 0.15 0.16 Benzilic acid (0.013) 3.0 5 0.28 0.23 p-fluoromandelic acid (0.018) 3.2 7 0.14 0.24 None 6.0 None 0.01 0.01 The dimethyl formamide (DMF) was included because some of the sensitisers had low solubility in water.

Any decrease in image density with increase of exposure time was due to the formation of a red colour in the image areas.

EXAMPLE 2.

To test the effect of using different amount of mandelic adic, p-fluoro mandelic acid, and benzilic acid as sensistiser, the procedure of Example 1 was repeated using CPP++ and sensitiser as shown in Table 2.

TABLE 2

Sensitiser Mandelic acid p-fluoro mandelic acid benzilic acid Amount of part by Sensitiser weight 0.5 1.0 1.5 3.0 0.5 1.0 1.5 3.0 0.5 1.0 1.5 3.0 moles 0.0033 0.0066 0.0099 0.020 0.0029 0.0059 0.0088 0.018 0.0022 0.0043 0.0067 0.013 Highest Stepwedge number appearing after exposure 13 14 15 16 13 13 16 16 16 16 16 16 Immersion time (seconds) before silver image first appears 15 10 5 3 10 4 3 3 25 20 10 8 Highest step wedge number which is solid silver 3 4 5 7 3 5 6 7 2 3 4 5 EXAMPLE 3.

A composition was prepared comprising the following ingredients: CPP++ 1.5 (0.0035 moles) Triton X-100 0.10 Lemol 16-98 3.00 Water 97.00 Mandelic acid 1.5 (0.0099 moles) The composition was applied by a two roll roller coater to a sheet of aluminium as in Example I to give a dry coating weight of about 0.2 g/m2.

The resulting radiation sensitive plate was exposed through a negative transparency as in Example 1. The exposed plate was then immersed in the silver electroless plating solution for 3 minutes at room temperature. The plating surface was then washed with water and then swabbed over with a pad of cotton wool soaked in a dispersion of an organic mercapto compound and wetting agent in water to increase the initial ink receptivity of the image. After inking and gumming in the normal manner the plate was placed on a sheet-fed offset printing press. A run of 500,000 high quality prints was obtained. The residual radiation sensitive layer in the non-light struck areas was hydrophilic and served as the water receptive background of the plate until it had been completely removed by the abrasive forces etc. to which it was subjected on the press. Thereafter the underlying grained and anodised aluminium surface constituted the background.

EXAMPLE 4.

Example 3 was repeated using a composition comprising: CPP++ 1.5 (0.0035 moles) BRIJ35 0.10 Lemol 16-98 3.00 RD 0.50 p-fluoromandelic acid 1.5 (0.0088 moles) water 97 BRIJ 35 is a non-ionic wetting agent and is an ethylene oxide condensate of an aliphatic alcohol. (The word "Brij" is a Trade Mark.) A satisfactory printing plate was obtained.

EXAMPLE 5.

Example 3 was repeated using a composition comprising CPP++ 2.50 (0.0058 moles) BRIJ 35 0.10 Gelatin 2.00 9-hydroxyfluorene-9-carboxylic acid 2.00 (0.0087 moles) Riboflavin 0.50 Dimethyl formamide 30.00 Water 70.00 A satisfactory printing plate was obtained.

EXAMPLE 6.

A composition was prepared comprising the following ingredients; CPP++ 2.50 (0.0058 moles) Lemol 16-98 3.00 RD 0.50 benzilic acid 2.00 (0.0087 moles) Dimethyl-formamide 30.00 Water 67.00 The composition was applied, by roller coating to a sheet of aluminium, which had been electrograined in a mixture of nitric acid and acetic acid, desmutted in phosphoric acid and anodised in sulphuric acid, to give a dry coating weight of about 0.2 g/m2.

The resulting radiation sensitive plate was exposed and further processed as in Example 3 and a satisfactory printing plate was obtained.

EXAMPLE 7.

Example 6 was repeated using the following composition: CPP++ 1.5 (0.0035 moles) Kuraray Poval 105 6.0 Riboflavin 0.5 p-methoxy 3.0 (0.016 moles) mandelic acid Lissapol N 0.1 water 94 Kuraray Poval 105 is a low molecular weight fully hydrolysed poly(vinyl alcohol) made by Kuraray Limited. A similar result was obtained.

EXAMPLE 8.

Example 6 was repeated using the following composition CPP++ 1.5 (0.0035 moles) Kuraray Poval 105 5.0 Ammonium mandelate 1.5 (0.0088 moles) Triton X-100 0.10 EDTA (disodium salt) 1.00 Water 95.00 A satisfactory printing plate was obtained.

EXAMPLE 9.

A sheet of polyester film subbed with a layer of gelatin was roller coated with the composition of Example 3. After exposure for 2 minutes through a negative transparency a green image was obtained, which after 3 minutes immersion in silver electroless plating solution was replaced by a black image of silver metal which could be polished to obtain lustrous silver.

EXAMPLE 10.

A composition was prepared comprising CPP++ 1.0 (0.0023 moles) RD 0.5 Ammonium chloride 0.57 Mandelic acid 1.0 (0.0066 Moles) Ammonium mandelate 1.0 (00.59 Moles) BRIJ 35 0.1 Gelatine 2.0 Water 98.0 The composition was roller coated onto a sheet of aluminium which had been grained in nitric acid, desmutted in phosphoric acid, and finally anodised in sulphuric acid. The resultant tradiation sensitive plate was exposed through a negative transparency in a printing down frame for 2 minutes to the radiation from four Philips 300w MLU lamps suspended 600 mm above the frame. A green printout image was obtained. The exposed plate was then immersed in the silver electroless plating solution for three minutes at room temperature. The green image was replaced by a black image of silver metal which could be polished to obtain lustrous silver which was in conductive contact with the aluminium substrate.

EXAMPLE 11.

A composition was prepared comprising: CPP++ 1.0 (0.0023 moles) Lemol 16-98 3.0 Water 67.0 RD 0.5 Benzilic acid 2.0 (0.0086 moles) DMF 30.0 The composition was used to form a radiation sensitive plate as in Example 10 and the plate was exposed as in Example 10 except that the exposure time was 30 seconds.

The green print out image of the exposed plate was replaced by a black image of metallic silver after the plate had been immersed in the silver plating solution described above for three minutes at room temperature. The plate surface was then washed with water and swabbed over with a pad of cotton wool soaked in a dispersion of an organic mercapto compound and wetting agent in water to increase the initial ink-receptivity of the image. After inking and gumming in the normal manner the plate was placed on a sheet-fed, offset, lithographic printing press and several hundred good, clean, high quality prints were run off. As in the case of Example 3, the residual radiation sensitive layer in the non-light struck areas was hydrophilic and served as the water receptive background of the plate until it had been completely removed by the abrasive forces etc. to which it was subjected on the press. Thereafter, the underlying grained and anodised aluminium surface constituted the background.

EXAMPLE 12.

A composition was prepared comprising CPP++ 1.0 (0.0023 moles) RD 0.5 Ammonium chloride 0.6 Mandelic acid 2.0 (0.014 moles) BRIJ35 0.1 Lemol 16-98 5.0 Water 95.0 The composition was used to form a radiation sensitive plate as in Example 11 and the plate was exposed, processed, and used for printing as in Example 11 except that the exposure time was 2 minutes. Good clean, high quality prints were obtained.

EXAMPLE 13.

A composition was prepared comprising: CPP++ 1.0 (0.0023 moles) RD 0.5 Ammonium chloride 0.6 Mandelic acid 2.0 (0.014 moles) Sodium bicarbonate 0.5 BRIJ35 0.1 Cab-o-sil M5 0.5 Lemol 16-98 4.6 Water 95.0 The composition was used in a repeat of Example 11 but using an exposure time of 15 seconds.

EXAMPLE 14.

A composition was prepared comprising: Benzyl Viologen 1.0 Lemol 16-98 1.0 Water 69.0 RD 0.5 Benzilic acid 2.0 Dimethylformamide 30.0 Benzyl viologen is similar to paraquat but with the methyl groups replaced by benzyl groups.

The composition was roller coated on to a fine grained and anodised aluminium sheet. The resultant plate was imagewise exposed as in Example 10 for 2 minutes. A pale purple, print-out image was obtained.

As stated above, exposure to radiation in the presence of an electron donor causes CPP++ to be reduced to the green radical cation CPP4; the degree of colour change to green being a measure of the reduction. Thus, an indication of the effectiveness of materials as chemical sensitisers in acting as electron donors can be tested by measuring the reflected optical density of the green image resulting from an exposure of a composition containing CPP++ and a chemical sensitiser.

The following method may be used for testing the effectiveness of a chemical sensitiser.

A solution of 0.0025M CPP++, 0.01M sensitiser, 0.02M malonic acid and 10gel of polyvinylbutyral in methanol is used. Methanol is used as it is the most suitable solvent for both CPP++ and most sensitiser materials. The purpose of the malonic acid is to keep the pH of the solution approximately constant and the purpose of the polyvinylbutyral is to act as a binder and to reduce the rate of air oxidation of the radical cation CPP+*.

A piece of filter paper is dipped in the solution for 5 seconds, dried at 500C for 15 minutes and exposed for 30 seconds on an exposure frame. The reflected optical density of the resulting green image is then measured through a red filter 5 minutes after the exposure.

The results of this test for various sensitisers are shown in Table 3.

TABLE 3.

Claims (49)

1. Optical Optical Sensitiser Density Sensitiser Density Mandelic acid 0.87 m-methoxy mandelic acid 0.58 benzilic acid 0.81 p-methoxy mandelic acid 0.62 p-bromomandelic acid 0.80 3-phenyllactic acid 0.58 p-chloromandelic acid 0.80 atrolactic acid 0.79 I-napthylglycollic acid 0.79 p-fluoromandelic acid 0.75 m-nitromandelic acid 0.50 9-hydroxyfluorene-9 carboxylic acid 0.70 o-methoxymandelic acid 0.51 3,4-dimethoxy 2' chloro benzilic acid 0.65 styrylglycollic acid 0.72 In Claim 18 of our copending Patent Application No. 27435/75 (Serial No.

   1556362) there is claimed a radiation sensitive plate comprising a metallic substrate having a surface coated with a radiation sensitive layer comprising (i) a chemical sensitiser which is a substituted or unsubstituted mono or diaryl or l-aryl l-alkyl glycollic acid or salt or ether thereof and (ii) a quaternary ammonium salt of the type which will accept at least one electron on exposure to radiation to form a substance capable of causing metal to be deposited onto said substance from an electroless plating solution in contact with said substance, which electroless plating solution comprises a salt of said metal and a reducing agent. Insofar as the chemical sensitiser of the radiation sensitive composition of the present invention may be a substituted or unsubstituted mono or di aryl or l-aryl l-alkyl glycollic acid or salt thereof, we make no claim in the present Application to a radiation sensitive composition comprising such a chemical sensitiser when the composition is coated on to the surface of a metallic substrate.

   Subject to the foregoing disclaimer, WHAT WE CLAIM IS: 1. A radiation sensitive composition comprising (i) a quaternary ammonium salt of the type which will accept at least one electron on exposure to radiation to form a substance capable of causing metal to be deposited onto said substance from an electroless plating solution in contact with said substance, which electroless plating solution comprises a salt of said metal and a reducing agent and (ii) a chemical sensitiser for improving the speed of photoreduction of the salt, said sensitiser having the general formula

   wherein R2' is a substituted or unsubstituted aryl group, an arylalkenyl group, or an arylalkyl group; R22 is a substituted or unsubstituted aryl group, an alkyl group, an arylalkyl group, an arylalkenyl group, a carboxylic acid group, a carboxylic acid salt group, or a hydrogen atom; or R2' and R22 together represent a bivalent species; and X represents a carboxylic acid group or a carboxylic acid salt group.
2. 2. A radiation sensitive composition comprising (i) a quaternary ammonium salt of the type which will accept at least one electron on exposure to radiation to form a substance capable of causing metal to be deposited onto said substance from an electroless plating solution in contact with said substance, which electroless plating solution comprises a salt of said metal and a reducing agent and (ii) a chemical sensitiser for improving the speed of photoreduction of the salt, said sensitiser having the general formula

   wherein R21 is a substituted or unsubstituted aryl group; R22 is a substituted or unsubstituted aryl group, an alkyl group, or a hydrogen atom; and X represents a carboxylic acid group or a carboxylic acid salt group.
3. 3. A radiation sensitive composition comprising (i) a quaternary ammonium salt of the type which will accept at least one electron on exposure to radiation to form a substance capable bf causing metal to be deposited onto said substance from an electroless plating solution in contact with said substance, which electroless plating solution comprises a salt of said metal and a reducing agent and (ii) a chemical sensitiser for improving the speed of photoreduction of the salt, said sensitiser having the general formula

   wherein R2' is an arylalkenyl group, or an arylalkyl group; R22 is an alkyl group, an arylalkyl group, an arylalkenyl group, a carboxylic acid group, or a carboxylic acid salt group or R2' and R22 together represent a bivalent species; and X represents a carboxylic acid group or a carboxylic acid salt group.
4. 4. A composition according to Claim 2 wherein the chemical sensitiser is mandelic acid, a mandelic acid salt, benzilic acid, or p-bromo mandelic acid.
5. 5. A composition according to Claim 4 wherein the mandelic acid salt is ammonium mandelate.
6. 6. A composition according to Claim 2 wherein the chemical sensitiser is pchloromandelic acid.
7. 7. A composition according to Claim 2 wherein the chemical sensitiser is sodium mandelate or p-fluoromandelic acid.
8. 8. A composition according to any one of Claims 1 to 7 wherein the quaternary ammonium salt has the general formula

   wherein R' to R10 are hydrogen or halogen atoms or organic substituents; R11 and R12, if present, are each halogen atoms or organic substituents or together represent a divalent organic substituent; Z is zero or an integer; X- is an anion; m=l or 2; and at least one of the nitrogen atoms is quaternary; provided that R11 and R12 are not each -CM3 groups or are not together a -CH2-CH2- group when each of R1 to R10 is a hydrogen atom and Z is zero.
9. 9. A composition according to Claim 8 wherein the quaternary ammonium salt is a bipyridilium salt.
10. 10. A composition according to Claim 8 or 9 wherein the quaternary ammonium salt is a halide, a perchlorate, a tetrafluoroborate, a silicofluoride, a methyl sulphate or a bisulphate.
11. I I. A composition according to Claim 10 wherein the halide is chloride or bromide.
12. 12. A composition according to Claim 8 or 9 wherein the anion of the quaternary ammonium salt is a polymeric anion.
13. 13. A composition according to Claim 12, wherein the polymeric anion is a poly (acrylate).
14. 14. A composition according to Claim 11 when appendant to claim 9 wherein the quaternary ammonium salt is N,N'-bis-(paracyano phenyl)-4,4'-bipyridylium dichloride.
15. 15. A composition according to Claim 1, or to any one of Claims 8 to 14 when appendant to Claim 1, wherein the chemical sensitiser is mandelic acid.
16. 16. A composition according to Claim 1, or 2 or to any one of Claims 8 to 14 when appendant to Claim 1 or 2 wherein the chemical sensitiser is a mandelic acid derivative.
17. 17. A composition according to Claim 16 wherein the mandelic acid derivative is p-bromo mandelic acid or ammonium mandelate.
18. 18. A composition according to Claim 16 wherein the mandelic acid derivative is p-chloro mandelic acid, p-fluoromandelic acid, m-methoxy mandelic acid, omethoxy mandelic acid, p-methoxy mandelic acid, m-nitro mandelic acid, sodium mandelate, tetramethyl ammonium p-fluoro mandelate, or hexamethylene tetramine mandelate.
19. 19. A composition according to Claim 1 or 2 or to any one of Claims 8 to 14 when appendant to Claim 1 or 2 wherein the chemical sensitiser is benzilic acid.
20. 20. A composition according to Claim I or 2 or to any one of Claims 8 to 14 when appendant to Claim 1 or 2 wherein the chemical sensitiser is a derivative of benzilic acid.
21. 21. A composition according to claim 20 wherein the benzilic acid derivative is 3,4-dimethoxy 2'-chloro benzilic acid or di-p-methoxy benzilic acid.
22. 22. A composition according to Claim 1, 2 or 3 or to any one of Claims 8 to 14 when appendant to Claim 1, 2 or 3 wherein the chemical sensitiser is 3-phenyl lactic acid, atrolactic acid, potassium atrolactate, 9-hydroxy fluorene-9-carboxylic acid, styryl glycollic acid, or l-naphthyl glycollic acid.
23. 23. A composition according to Claim 1, 2 or 3 wherein the chemical sensitiser has the general formula

    wherein R21 is a substituted or unsubstituted aryl group, an arylalkenyl group or an aryl alkyl group; R22 is a substituted or unsubstituted aryl group, an alkyl group, an aryl alkyl group, an aryl alkenyl group, a carboxylic acid group, a carboxylic acid salt group, or a hydrogen atom provided that R21 is not a phenyl group when R22 is a phenyl group; or R21 and R22 together represent a bivalent species; and X represents a carboxylic acid group, or a carboxylic acid salt group.
24. 24. A composition according to Claim 23 wherein the chemical sensitiser is mandelic acid.
25. 25. A composition according to Claim 23 wherein the chemical sensitiser is a mandelic acid derivative.
26. 26. A composition according to Claim 25 wherein the mandelic acid derivative is p-bromo mandelic acid or ammonium mandelate.
27. 27. A composition according to Claim 25 wherein the mandelic acid derivative is p-chloro mandelic acid, p-fluoromandelic acid, m-methoxy mandelic acid, o methoxv mandelic acid, p-methoxy mandelic acid, m-nitro mandelic acid, sodium mandelate, tetramethyl ammoniump-fluoromandelate or hexamethylene tetramine mandelate.
28. 28. A composition according to Claim 23 wherein the chemical sensitiser is a derivative of benzilic acid.
29. 29. A composition according to Claim 28 wherein the derivative is 3,4dimethoxy 2'-chloro benzilic acid or di-p-methoxy benzilic acid.
30. 30. A composition according to Claim 23 wherein the chemical sensitiser is 3phenyl lactic acid, atrolactic acid, potassium atrolactate, 9-hydroxy fluorene-9carboxylic acid, styryl glycollic acid, or l-naphthyl glycollic acid.
31. 31. A composition according to any one of Claims 23 to 30 wherein the quaternary ammonium salt has the general formula:

    wherein R1 to R10 are hydrogen or halogen atoms or organic substituents; R11 and R12, if present, are each halogen atoms or organic substituents or together represent a divalent organic substituent; z is zero or an integer; X- is an anion; m=l or 2; and at least one of the nitrogen atoms is quaternary.
32. 32. A composition according to Claim 31 wherein the quaternary ammonium salt is a bipyridilium salt.
33. 33. A composition according to claim 31 or 32 wherein the quaternary ammonium salt is a halide, a perchlorate, a tetrafluoroborate, a silicofluoride, a methyl sulphate or a bisulphate.
34. 34. A composition according to Claim 33 wherein the halide is chloride or bromide.
35. 35. A composition according to Claim 31 or 32 wherein the anion of the quaternary ammonium salt is a polymeric anion.
36. 36. A composition according to Claim 35 wherein the polymeric anion is a Doly(acrylate).
37. 37. A composition according to Claim 31 wherein the quaternary ammonium salt is paraquat.
38. 38. A composition according to Claim 31 wherein the quaternary ammonium salt is diquat.
39. 39. A composition according to Claim 31 wherein the quaternary ammonium salt is N,N'-bis-(paracyanophenyl)-4-4'-bipyridilium dichloride.
40. 40. A composition according to any one of the preceding claims, which additionally includes a polymeric binder.
41. 41. A composition according to Claim 40 wherein the binder is poly(vinylalcohol), poly(ammonium methacrylate), gelatin, an alginate, a maleic anhydride copolymer, a poly(saccharide), poly (N-vinyl pyrrolidinone), or mixture of two or more thereof.
42. 42. A composition according to Claim 40 or 41 wherein the ratio of quaternary ammonium salt to binder is from 1:200 to 10:1 by weight.
43. 43. A composition according to any one of the preceding claims wherein the molar ratio of quaternary ammonium salt to chemical sensitiser is from 10: I to 1:50 respectively.
44. 44. A composition according to any one of the preceding claims which additionally includes a spectral sensitiser.
45. 45. A composition according to Claim 44 in which the spectral sensitiser is riboflavin; 7-chloro-9-(N-methyl-2-diethyl amino ethyl) isoalloxazine chloride; 3,6dimethyl-2-(4-dimethyl aminophenyl) benzthiazolium chloride; 3,3'diethylthiacyanine iodide; proffavin; N-methyl phenazinium methyl sulphate; 4cyanoquinolinium methiodide; or erythrosin.
46. 46. A composition according to any one of the preceding claims which additionally includes a surface active agent.
47. 47. A composition according to any one of the preceding claims which additionally includes ammonium chloride, fumed silica, ethylene diaminetetraacetic acid (disodium salt), or diammonium hydrogen citrate.
48. 48. A composition according to Claim 8 substantially as hereinbefore described in any one of Examples I to 9.
49. 49. A composition according to Claim 8 substantially as hereinbefore described in any one of Examples 10 to 14.