GB1565903A - Vesicular image recording materials - Google Patents

Description

(54) VESICULAR IMAGE RECORDING MATERIALS (71) We, BEXFORD LIMITED, of Imperial Chemical House, Millbank, London SWIP 3JF, a British Company, 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:- The present invention relates to photographic recording materials which may be used for vesicular imaging.

Such materials are known in the art and generally comprise a transparent or opaque film or sheet support carrying an imaging layer comprising a plastics vehicle and a sensitising agent dispersed through the vehicle. The sensitising agent is decomposable on exposure to a light image to evolve a gas such as nitrogen thereby forming a latent gas image in the vehicle. Generally, the latent image may be developed by heating the material, usually above the glass transition temperature of the plastics vehicle, to enable the gas in the light-struck areas to expand into bubbles or vesicles which have a light-scattering or reflecting activity.

A typical assembly is described in British patent specification 861 250.

Various plastics vehicles have been disclosed in the art for inclusion in the imaging layer. For example, British patent specification 861 250 discloses the use of various plastics vehicles such as copolymers derived from acrylonitrile, including copolymers of acrylonitrile with vinyl chloride, styrene, l,l-difluoroethylene or vinylidene chlorofluoride.

Certain terms employed throughout this specification have the following meaning: "DmaX" (maximum projection density) relates to the densest image which can be produced in a process material, the values quoted hereinafter being measured by a Macbeth densitometer TD 528 at an aperture of f4.5 using a Wratten (registered Trade Mark) 106 filter.

"din" relates to the lowest density which can be obtained in a processed material, the values quoted hereinafter being measured by a Macbeth densitometer TD 528 at an aperture of f4.5 using a Wratten 106 filter.

"Gamma" represents the rate of change of image density with respect to changes in the logarithm (base 10) of the exposure and is derived from the characteristic curve, i.e. the curve of density/log10 exposure, of the material, as the slope of the straight-line portion of the curve. For low gamma a small change in exposure produces a small change in density whilst for high gamma the same small change in exposure produces a larger change in density.

"Tonal range" relates to the relative ability of the material to reproduce accurately the varying tones in an object, the values quoted hereinafter being assessed as the number of visible image steps upon the material after exposure through a Kodak (registered Trade Mark) No. 2 step tablet and development. The first step of the tablet is transparent and each subsequent step increasingly opaque.

The ability of the material to reproduce images of the successive steps is a measure of its tonal range.

"Nitrogen permeability constant" refers to the volume of nitrogen in cm3 which diffuses in one second through one cm of a sample of the polymeric vehicle, one cm in area, and under a pressure gradient of one cm of mercury at a constant temperature of 25"C.

"Speed at Dmjn+o t" relates to the speed of the material at a density corresponding to Admin determined as described above plus 0.1 of the density at Dmin.

"Thermal Stability" is assessed by measuring Dmax at ambient temperature and after ageing the material at 950C for 5 minutes and relates to the reduction in D,,ax caused by ageing.

According to the present invention a recording material for vesicular imaging comprises a polymeric vehicle and dispersed uniformly therein a sensitising agent which releases a vesicle-forming gas upon exposure to light, said polymeric vehicle comprising a copolymer derived from 62 to 95 mole % of a comonomer having the formula:

wherein R represents hydrogen or an alkyl group having from 1 to 5 carbon atoms and another comonomer having the formula:

wherein R' represents hydrogen or an alkyl group having from 1 to 5 carbon atoms and R2 represents hydrogen, an alkyl group having from 1 to 5 carbon atoms, -CH2OH or

wherein R3 is an alkyl group having from 1 to 5 carbon atoms, said copolymer having a nitrogen permeability constant in the range 1 x 10-15 to 1 x 10-'0 and being softenable upon heating above its glass transition temperature to permit the gas released by the sensitising agent in the light-struck areas to form light-scattering or reflecting vesicles therein.

According to another aspect of the invention, a process for the production of a recording material for vesicular imaging comprises producing a polymeric vehicle having dispersed uniformly therein a sensitising agent which releases a vesicles forming gas upon exposure to light, said polymeric vehicle comprising a copolymer derived from 62 to 95 mole % of a comonomer having the formula:

wherein R represents hydrogen or an alkyl group having from I to 5 carbon atoms and another comonomer having the forula:

wherein R' represents hydrogen or an alkyl group having from 1 to 5 carbon atoms and R2 represents hydrogen, an alkyl group having from I to 5 carbon atoms, -CH2OH or

wherein R3 is an alkyl group having from 1 to 5 carbon atoms, said copolymer having a nitrogen permeability constant in the range 1 x 10-15 to 1 x 10-'0 and being softenable upon heating above its glass transition temperature to permit the gas released by the sensitising agent in the light-struck areas to form light-scattering or reflecting vesicles therein.

The recording layer comprising the polymeric vehicle and the sensitising agent is preferably applied to a carrier sheet or film. Opaque carriers may be used in recording materials when the image is to be viewed by reflection. In such an assembly, the image vesicles appear white upon reflection of incident light. The opaque carrier is preferably dark in colour to contrast with the image and may comprise a pigmented or coloured plastics film or sheet or paper or card. When the image is to be viewed by light-scattering the carrier is preferably a transparent plastics sheet or film which may consist of any suitable plastics material such as cellulose esters, e.g. cellulose acetate, polystyrene, poiyamides, polymers and copolymers of vinyl chloride, polycarbonate, polymers and copolymers of olefines, e.g. polypropylene, polysulphones and linear polyesters which may be obtained by condensing one or more dicarboxylic acids or their lower alkyl diesters, e.g. terephthalic acid, isophthalic, phthalic, 2,5-, 2,6- and 2,7-naphthalene dicarboxylic acid, succinic acid, sebacic acid, adipic acid, azelaic acid, diphenyl dicarboxylic acid, and hexahydroterephthalic acid or bis-p-carboxyl phenoxy ethane, optionally with a monocarboxylic acid, such as pivalic acid, with one or more glycols, e.g. ethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol and 1,4-cyclohexanedimethanol. Biaxially oriented and heat-set films of polyethylene terephthalate are particularly useful as carriers according to this invention.

The copolymeric vehicle included in the recording materials according to the present invention may be derived from one or more other comonomers in addition to the comonomers having the general formulae (1) and (2) above provided the copolymer has a nitrogen permeability constant in the range I x 10-'5 to 1 x 10-'0 and is softenable upon heating above its glass transition temperature to facilitate the formation of light-scattering vesicles. However, the copolymer is preferably derived exclusively from two comonomers of the above general formulae (1) and (2).

The preferred comonomers covered by the general formula (1) comprise acrylonitrile and methacrylonitrile, acrylonitrile being especially preferred.

For comonomers according to formula (2), R' is preferably hydrogen or methyl and R2 is preferably hydrogen, isopropyl, tert.butyl, -CH2OH or

Preferred comonomers according to formula (2) include acrylamide, methacrylamide, N-isopropyl acrylamide, N-tert.butyl acrylamide, N-methylol acrylamide and diacetone acrylamide, the latter having the formula:

Polymeric vehicles based upon copolymers derived from the preferred comonomers exhibit a beneficial combination of vesiculation properties including properties such as Dmax gamma, tonal range, speed at Dm1n+O. 1 and thermal stability.

Copolymers derived from preferred amounts of 65 to 90 mole % of the formula (1) comonomer provide particularly effective vesiculation properties, the most beneficial combination of the above properties being obtained with copolymers derived from 75 to 85 mole % of the formula (1) comonomer.

Particularly useful polymeric vehicles comprise copolymers of75 to 85 mole V acrylonitrile with one formula (2) comonomer chosen from N-tert.butyl acrylamide, diacetone acrylamide, or N-methylol acrylamide.

The copolymer comprising the polymeric vehicle is preferably homogeneous by which is meant that all the copolymer molecules contain substantially the same proportions of the comonomeric constituents. Such homogeneous copolymers may be produced by metering the comonomeric ingredients to the polymerisation medium so as to maintain compositional homogeneity and to achieve the desired copolymer formulation, e.g. as described in United States patent specification 2 559 155 or British patent specification 1197 721.

The recording layer may be applied to a carrier sheet or film as a solution in any suitable common organic solvent such as acetone or a mixture of acetone with butan-2-one, toluene and/or methanol. However some copolymers especially those of acrylonitrile with acrylamide or methacrylamide are cross-linked and therefore insoluble in organic solvents. Recording layers comprising such copolymers must therefore be applied as aqueous latices.

Surfactants may optionally be included in the polymeric vehicle to improve the vesiculating properties of the vehicle and especially its speed at Dmln+01. The optimum amount of surfactant required may be up to 20% by weight based upon the weight of the copolymer. Generally, no more than 10% by weight of the surfactant is required to provide acceptable vesiculation and amounts in the range 0.5 to 5.0 by weight are particularly effective. Such surfactants may be incorporated into the reaction mixture from which the copolymer is derived and may be present in the resulting copolymer as residues from the reaction or alternatively they may be added separately after the copolymerisation reaction.

Residual surfactant from the polymerisation reaction may be supplemented by the addition of further surfactant to the polymeric vehicle. Mixtures of surfactants may be employed. Anionic, cationic and non-ionic surfactants are effective according to the invention and may be chosen from the following.

Anionic Surfactants Fatty alcohol sulphates, e.g. sodium lauryl sulphate; fatty alcohol ether sulphates, e.g. sodium lauryl ether sulphate; alkyl aryl sulphonates, e.g. sodium alkyl benzene sulphonate; alkyl sulphosuccinates, e.g. sodium dioctyl sulphosuccitiate; and phosphate esters, e.g. neutralised phosphate esters; and salts of fatty acids, e.g. sodium laurate and ammonium laureate.

Nonionic Surfactants Polyoxy-2-hydroxy-propylene alkyl phenols, e.g. polyoxy-2-hydroxy propylene (10) alkyl phenol; polyoxyethylene alcohols, e.g. lauryl alchol ethoxylate; polyoxyethylene esters of fatty acids, e.g. mono-oleate ester of polyethylene glycol; polyoxyethylene alkyl amines, e.g. bis(2-hydroxyethyl)lauryl amine; polyoxyethylene alkyl amides, e.g. oleyl dialkanol (5) amide; polyol surfactants, e.g. sorbitan monolaurate, sorbitan monopalmitate, sorbitan mono-oleate, and polyoxyethylene sorbitan monolaurates; polyalkylene oxide block copolymers, e.g. polyoxyethylene polyoxypropylene glycol; polyoxyethylene alkyl phenols, e.g. polyoxyethylene nonyl phenol derived from 4 moles of ethylene oxide per mole of nonyl phenol; silicone surfactants, e.g. as described in British patent specification 1 352 559: and fluorocarbon surfactants, e.g. as described in British patent specification 1 352 560.

Cationic Surfactants Quaternary ammonium compounds.

Plasticisers and additives which reduce the nitrogen permeability of the vehicle may be added to the vehicle if desired.

The sensitising agent incorporated into the vehicle should be non-reactive with the vehicle. Likewise the vesicle-forming gas which is liberated by the sensitising agent should be non-reactive with the vehicle. Sensitising agents which liberate nitrogen on exposure to actinic light, especially ultra-violet light which is widely used in vesicular processing equipment, may be employed according to this invention, suitable agents including nitrogen liberating diazonium salts, such as those which may be derived from the following amines: N,N-dimethyl-p-phenylenediamine N,N-diethyl-p-phenylenediamine N,N-dipropyl-p-phenylenediamine N-ethyl-N-p-hydroxyethyl-p-phenylenediamine N,N-dibenzyl-3-ethoxy-4-p-phenylenediamine 4-N-morpholino-aniline 2,5-diethoxy-4-N-morpholino-aniline 2,5-dimethoxy-4-N-morpholino-aniline 2,5-di-(n-butoxy)-4-N-morpholino-aniline 4-N-pyrrolidino-aniline 3-methylA-N-pyrrolidino-aniline 3-methoxy4-N-pyrrolidono-aniline 2-ethoxy-4-N,N-diethylamino-aniline 2,5-diethoxy-4-benzoylamino-aniline 2,5-diethoxy-4-thio-(4'-tolyl)-aniline Other suitable sensitising agents include quinone-diazides and especially that having the structure:

and azide compounds derived from the structure:

Alternatively, carbazido compounds (carboxylic acid azides) containing a hydroxyl or amino group in the position ortho to the carbazido group may be used.

If desired, a small quantity of a dyestuff and a stabilising acid may be included in the recording layer.

If desired, the surface of the carrier may be pretreated and/or coated with an adhesion-promoting layer prior to the application of the recording layer. The adhesion of the recording layer to a plastics sheet or film carrier may in particular be improved by such a treatment. Polyethylene terephthalate film carriers may be pretreated by coating with solutions of materials having a solvent or swelling action on the film such as halogenated phenols in common organic solvents, e.g. solutions of p-chloro-m-cresol, 2,4-dichlorophenol, 2,4,6- or 2,4,5-trichlorophenol or 4chlororesorcinol or a mixture of such materials in acetone or methanol. After application of such a solution the film surface can be dried and heated at an elevated temperature for a few minutes, e.g. 2 minutes at 600 to 100 C. If desired, the pre treating solution may also contain an adhesion-promoting polymer such as a partially hydrolysed copolymer of vinyl chloride and vinyl acetate.

As an alternative to, or in addition to, such a pretreatment, a material having a swelling or solvent action upon the film may be incorporated into the coating composition from which the recording layer is applied.

The recording layer may, if desired, be treated with an aqueous solution or steam or water vapour at temperatures of up to 100 C for up to 300 seconds prior to imagewise exposure in accordance with established practice in the art, e.g. as described in United States patent specification 3149 971. Nevertheless, it has been found that surfactants employed as specified above are effective in improving the speed of the recording layer in the absence of any treatment with an aqueous solution or steam or water vapour or when such a treatment is of short duration, e.g. not exceeding 5 seconds. Surfactants do not however increase the speed of the recording layer when such a treatment is more prolonged, e.g. at least 10 seconds.

The resulting recording materials may be exposed to a light image in a conventional manner to produce a latent image in the recording layer. The image may be developed in a conventional manner by heating immediately after light exposure to permit the gas vesicles to form in the light-struck areas. Fixing may then be accomplished by a further overall light exposure and permitting the gas evolved by the decomposition of the sensitising agent to diffuse out of the recording layer. Alternatively, the latent image may be reversal processed by permitting the gas evolved in the imagewise light-struck areas to diffuse out of the recording layer and then subjecting the material to an overall light exposure followed by immediate heating to form gas vesicles in the areas subjected to the overall exposure.

EXAMPLES 1 to 3 Homogeneous acrylonitrile/N-tert.butyl acrylamide copolymers of varying comonomeric molar proportions were prepared by emulsion polymerisation. The reaction ingredients were as set out in Table 1.

TABLE 1

Quantities used in each Example Ingredient Example 1 Example 2 Example 3 Acrylonitrile 105.4 g 93.8 g 83.7 g 85 mole % 80 mole % 75 mole % N-tert.butyl 44.6 g 56.2 g 66.9 g acrylamide 15 mole % 20 mole Yc 25 mole % Methanol 30 ml Water 500 ml Sodium alkyl benzene sulphonate 22.5 g Ammonium persulphate 0.45 g as as Sodium metabisulphite 0.45 g Example I Example 1 1% weight/volume sulphuric acid 1.0 ml Lauryl mercaptan 0.9 ml The polymerisation was carried out in a 1 litre flask fitted with a stirrer, a thermometer, a nitrogen inlet tubing, a water cooled condenser and dropping funnels. The water, sodium alkyl benzene sulphonate, sulphuric acid and lauryl mercaptan were added to the flask, heated to 800C and purged with oxygen-free nitrogen gas for 30 minutes. The monomer mixture of acrylonitrile and N-tert.butyl acrylamide in methanol and a solution of the ammonium persulphate and sodium metabisulphate in 60 ml of water as catalyst were added slowly at a rate sufficient to maintain the temperature of the reaction at 80 + 2 C. After the addition of the comonomers, the latex was coagulated in twice its volume of methanol. The copolymer was collected, washed with water and vacuum dried.

Coating solutions comprising the resulting copolymers were made up to the following general sensitising composition: acrylonitrile/N-tert butyl acrylamide copolymer 10.0 g 2,5-diethoxy-4-N-morpholino benzene diazonium fluoroborate 0.8 g acetone 72.0g The solutions were uniformly coated on one side of 100 micron thick transparent biaxially oriented and heat-set films of polyethylene terephthalate which had been pretreated with a halogenated phenol and were dried at 1200C for 2.5 minutes to provide a 7 micron thick recording layer.

The dried films were immersed in distilled water at 800C for 10 seconds and wiped dry. The films were exposed through a Kodak (registered Trade Mark) No. 2 step tablet for 15 seconds to three parallel UV fluorescent lamps in a commercially available vesicular film printer (Canon Kal Printer 480 VC). The exposed films were developed immediately at 1300C by passing through a commercially available developer (Canon Kal Developer 360 VS).

The applied recording layer exhibited acceptable vesiculation properties as indicated in Table 2.

TABLE 2

Tonal Copolymer Range mole % acrylonitrile/ number of mole % N-tert.butyl visible Example acrylamide Dmax Dmin Gamma steps 1 85/15 2.40 0.09 5.4 8 2 80/20 2.34 0.30 3.3 9 3 75/25 2.20 0.16 3.1 8 EXAMPLES 4 to 11 Samples of the recording materials prepared in Examples I and 2 were treated for two seconds in a bath of distilled water maintained at 800C and wiped dry. The materials were then exposed and developed as described in Examples 1 to 3 and tested for vesiculation properties with the results given in Table 3 (Examples 4 and 7 respectively).

Further recording materials (Examples 5, 6 and 8 to 11) were prepared in accordance with Examples I to 3 using the acrylonitrile/N-tert.butyl acrylamide copolymers specified therein and with the addition of the sensitising coating solutions of 5% by weight based on the weight of the copolymer of the surfactants specified in Table 3. The recording materials were treated in distilled water and exposed, developed and tested as specified for Examples 4 and 7, the test results being shown in Table 3.

TABLE 3

Tonal Copolymer Range mole % acrylonitrile/ number of mole % N-tert-butyl Surfactant visible Speed at Example acrylamide added Dmax Dmin Gamma steps Dmin + 0.1 4 85/15 None 2.31 0.11 5.3 6 100% 5 85/15 Material commercially available as 'Alcopol' 0 (sodium di-octyl suphosuccinate) 2.38 0.12 3.8 7 109% 6 85/15 Material commercially available as 'Span' 40 (sorbitan monopalmitate) 2.36 0.15 2.9 8 128% 7 80/20 None 2.05 0.11 5.2 5 100% 8 80/20 'Alcopol' 0 2.24 0.12 3.1 9 208% 9 80/20 'Span' 40 2.38 0.16 3.6 6 137% 10 75/25 'Alcopol' 0 2.14 0.12 3.0 7 11 75/25 'Span' 40 1.97 0.15 3.0 5 'Span' is a registered Trade Mark The materials of Examples 4 to 11 exhibited satisfactory vesicular properties.

The increase in the speed of the recording layer resulting from the presence of the surfactant was greater for the copolymers comprising lower amounts of acrylonitrile (80 mole %) than for copolymers comprising 85 mole %. 'Alcopol' 0 also improved the tonal range of the recording material.

EXAMPLES 12 to 14 Using the 80/20 mole % acrylonitrile/N-tert.butyl acrylamide copolymer of Example 2, recording materials were prepared as described in relation to Examples 1 to 3. In Examples 13 ad 14, 2% by weight based on the weight of the copolymer of the surfactants specified in Table 4 were added to the sensitising coating solutions.

The recording materials were treated in distilled water and exposed, developed and tested as specified for Examples 4 to 11, the test results being shown in Table 4.

TABLE 4

Tonal Range number of visible Speed at Example Surfactant added Dmax Dmin Gamma steps Dmin + 0.1 12 None 1.60 0.10 2.5 4 100% 13 Material commercially available as 'Nansa' (registered Trade Mark) 1106 (sodium alkyl benzene sulphonate) 2.23 0.09 3.0 7 225% 14 sodium lauryl sulphate 2.20 0.10 3.2 8 245% The resulting recording materials exhibited satisfactory vesiculating properties.

EXAMPLES 15 to 22 Examples 12 to 14 were repeated, with the exception that no surfactant was added to the sensitising coating solutions of Examples 15 and 19, and with the addition of the surfactants in the amounts idicated in Table 5 to the other coating solutions and with the treatment in distilled water prolonged to four seconds. The vesiculating properties of the materials are shown in Table 5.

TABLE 5

Amount of Tonal surfactant Range % by weight number of based on weight visible Speed at Example Surfactant added of copolymer Dmax Dmin Gamma steps Dmin + 0.1 15 None None 2.12 0.14 4.0 6 100% 16 Material commercially available as 2% 2.22 0.13 2.8 8 150% 'Nansa' (registered Trade Mark) 1106 (sodium alky benzene sulphonate) 17 Sodium lauryl sulphate 2% 2.27 0.19 2.6 10 158% 18 Material commercially available as 2% 2.20 0.07 3.4 7 125% 'Ethomid' (registered Trade Mark) 0/15 (oleyl dialkanol (5) amide) 19 None None 1.70 0.10 2.8 6 100% 20 Material commercially available as 2% 1.75 0.08 2.8 6 109% 'Antarox' CO430 (polyoxyethylene (4) nonyl phenol) 21 Material commercially available as 2% 1.94 0.11 2.3 7 107% 'Empilam' BQ100 (monooleate ester of polyethylene glycol) 22 Material commercially available as 2% 2.04 0.09 3.2 7 123% 'Tween' (Registered Trade Mark) 20 (polyoxyethylene (20) sorbitan monolaurate) The recording materials of these examples exhibited satisfactory vesiculating properties.

EXAMPLES 23 to 32 Homogeneous 85/15 mole % (Examples 23 to 31) and 80/20 mole V (Example 32) acrylonitrile/diacetone acrylamide copolymers were prepared by the procedure described in Examples 1 to 3 using 96 g of acrylonitrile and 54 g of diacetone acrylamide, and 83.5 g of acrylonitrile and 66.5 g of diacetone acrylamide respectively in place of the corresponding ingredients in the reaction mixture of Examples 1 to 3.

Recording materials were prepared in accordance with Examples 1 to 3 using these acrylonitrile/diacetone acrylamide copolymers in place of the copolymers specified in the sensitising coating solutions of Examples 1 to 3 and with the addition of surfactants in the amounts shown in Table 6 to some of the solutions.

Some of the recording materials were treated in a bath of distilled water maintained at 80"C for the periods indicated in Table 6.

TABLE 6

Amount of Tonal surfactant Duration Range % by weight of water number of based on weight treatment visible Speed at Example Surfactant added of copolymer - seconds Dmax Dmin Gamma steps Dmin + 0.1 23 None None 10 2.32 0.18 3.7 11 100% 24 Material commercially 5% 10 2.38 0.20 3.4 11 100% available as 'Span' 40 (sorbitan monopalmitate) 25 Sodium lauryl sulphate 2% 10 2.43 0.14 4.0 12 100% 26 None None 2 1.60 0.12 1.9 5 100% 27 'Span' 40 5% 2 2.30 0.18 4.2 7 127% 28 Sodium lauryl <

EXAMPLES 33 to 35 and COMPARATIVE EXAMPLES A and B Recording materials were prepared in accordance with Examples 1 to 3 using in the coating solutions copolymers comprising 80/20 mole V and 75/25 mole V acrylonitrile/N-tert.butyl acrylamide and 85/15 mole V acrylonitrile/diacetone acrylamide in Examples 33 to 35 respectively and copolymers comprising 76.8/23.2 weight % acrylonitrile/vinyl acetate and 75.3/24.7 weight % acrylonitrile/methyl acrylate in Comparative Examples A and B respectively. The materials were exposed to light through a step tablet and developed as described in Examples I to 3 and Dmt was measured for each step at ambient temperature and again after ageing at 950C for five minutes. The results are shown in Table 7.

TABLE 7

Comparative Comparative Example 33 Example 34 Example 35 Example A Example B 62.6/37.4 55.8/44.2 64.0/36.0 76.8/23.2 75.3/24.7 weight % weight % weight % weight % weight% (80/20 mole %) (75/25 mole %) (85/15 mole %) (84.3/15.7 (83.2/16.8 acrylonitrile/ acrylonitrile/ acrylonitrile/ mole %) mole %) N-tert.butyl N-tert.butyl diacetone acrylonitrile/ acrylonitrile/ acrylamide acrylamide acrylamide vinyl acetate methyl acrylate copolymer copolymer copolymer copolymer copolymer Dmax Dmax Dmax Dmax Dmax After After After After After ageing ageing ageing ageing ageing at 95 C at 95 C at 95 C at 95 C at 95 C Step Before for 5 Before for 5 Before for 5 Before for 5 Before for 5 No. ageing minutes ageing minutes ageing minutes ageing minutes ageing minutes 1 2.16 2.16 2.16 2.16 2.32 2.16 2.44 2.36 2.30 0.76 2 2.14 2.14 2.16 2.15 2.32 2.20 2.44 2.36 2.20 0.48 3 2.22 2.22 2.11 2.10 2.30 2.16 2.42 2.36 1.62 0.30 4 2.16 2.16 1.48 1.45 2.30 2.06 2.34 2.26 0.87 0.17 5 2.07 2.06 0.71 0.71 2.21 1.58 2.28 1.75 0.41 0.12 6 1.57 1.52 0.36 0.33 1.84 1.06 1.96 0.98 0.23 0.10 7 0.85 0.85 0.18 0.18 1.19 0.68 1.55 0.63 0.14 0.10 8 0.22 0.22 0.12 0.12 0.76 0.43 1.08 0.34 0.10 9 - - - - 0.48 0.36 0.60 0.19 - 10 - - - - 0.33 0.27 0.40 0.18 - The polymeric vehicles of Examples 33 to 35 exhibited good retention of density and better resistance to ageing than those of the comparative examples.

Claims (30)

WHAT WE CLAIM IS:

1. A recording material for vesicular imaging which comprises a polymeric vehicle and dispersed uniformly therein a sensitising agent which releases a vesicleforming gas upon exposure to light, said polymericvehicle comprising a copolymer derived from 62 to 95 mole % of a comonomer having the formula:

wherein R represents hydrogen or an alkyl group having from 1 to 5 carbon atoms, and another comonomer having the formula:

wherein R' represents hydrogen or an alkyl group having from 1 to 5 carbon atoms and R2 represents hydrogen, an alkyl group having from I to 5 carbon atoms, -CH2OH or

wherein R3 is an alkyl group having from 1 to 5 carbon atoms, said copolymer having a nitrogen permeability constant in the range 1 x 10-15 to 1 x 10-'0 and being softenable upon heating above its glass transition temperature to permit the gas released by the sensitising agent in the light-struck areas to form light-scattering or reflecting vesicles therein.

2. A recording material according to claim 1, in which a recording layer comprising the polymeric vehicle and the sensitising agent is applied to a carrier sheet or film.

3. A recording material according to claim 2, in which the carrier sheet or film comprises a biaxially oriented and heat-set film of polyethylene terephthalate.

4. A recording material according to claim 1, 2 or 3 in which the comonomer having the formula (I) comprises acrylonitrile or methacrylonitrile.

5. A recording material according to any preceding claim, in which in the comonomer according to formula (2), R' is hydrogen or methyl and R2 is hydrogen, isopropyl, tert.butyl, -CH2OH or

6. A recording material according to claim 5, in which the comonomer having the formula (2) comprises acrylamide, methacrylamide, N-isopropyl acrylamide, Ntert.butyl acrylamide, N-methylol acrylamide or diacetone acrylamide.

7. A recording material according to any preceding claim, in which the copolymer included in the polymeric vehicle is derived from 65 to 90 mole V of the comonomer having the formula (1).

8. A recording material according to claim 7, in which the copolymer included in the polymeric vehicle is derived from 75 to 85 mole % of the comonomer having the formula (1).

9. A recording material according to claim 4, in which the copolymer included in the polymeric vehicle comprises a copolymer of 75 to 85 mole zÓ acrylonitrile with a formula (2) comonomer selected from the group consisting of N-tert.butyl acrylamide, diacetone acrylamide, and N-methylol acrylamide.

10. A recording material according to any preceding claim, in which the polymeric vehicle includes a surfactant.

11. A recording material according to claim 10, in which the surfactant comprises no more than 10% by weight based upon the weight of the copolymer in the polymeric vehicle.

12. A recording material according to any preceding claim, which has been treated with an aqueous solution or steam or water vapour at a temperature of up to 1000C and for a time up to 300 seconds.

13. A recording material according to any preceding claim, in which the sensitising agent comprises a nitrogen-liberating diazonium salt.

14. A process for the production of a recording material for vesicular imaging which comprises producing a polymeric vehicle having dispersed uniformly therein a sensitising agent which releases a vesicle-forming gas upon exposure to light, said polymeric vehicle comprising a copolymer derived from 62 to 95 mole % of a comonomer having the formula:

wherein R represents hydrogen or an alkyl-group having from I to 5 carbon atoms and another comonomer having the formula:

wherein R represents hydrogen or an alkyl group having from 1 to 5 carbon atoms and R represents hydrogen, an alkyl group having from 1 to 5 carbon atoms, -CH2OH or

wherein R3 is an alkyl group having from 1 to 5 carbon atoms, said copolymer having a nitrogen permeability constant in the range 1 x 10-'5 to I x 10-10 and being softenable upon heating above its glass transition temperature to permit the gas released by the sensitising agent in the light-struck areas to form light-scattering or reflected vesicles therein.

15. A process according to claim 14, which comprises applying a recording layer comprising the polymeric vehicle and the sensitising agent to a carrier sheet or film.

16. A process according to claim 15, in which the carrier sheet or film comprises a biaxially oriented and heat-set film of polyethylene terephthalate.

17. A process according to claim 14, 15 or 16, in which the comonomer having the formula (1) comprises acrylonitrile or methacrylonitrile.

18. A process according to any of claims 14 to 17, in which in the comonomer according to formula (2), R' is hydrogen or methyl and R2 is hydrogen, isopropyl, tert.butyl, -CH2OH or

19. A process according to claim 18, in which the comonomer having the formula (2) comprises acrylamide, methacrylamide, N-isopropyl acrylamide, Ntert.butyl acrylamide, N-methylol acrylamide or diacetone acrylamide.

20. A process according to any of claims 14 to 19, in which the copolymer included in the polymeric vehicle is derived from 65 to 90 mole % of the comonomer having the formula (1).

21. A process according to claim 20, in which the copolymer included in the polymeric vehicle is derived from 75 to 85 mole V of the comonomer having the formula (1).

22. A process according to claim 17, in which the copolymer included in the polymeric vehicle comprises a copolymer of 75 to 85 mole V acrylonitrile with a formula (2) comonomer selected from the group consisting of N-tert.butyl acrylamide, diacetone acrylamide, and N-methylol acrylamide.

23. A process according to any of claims 14 to 22, in which the polymeric vehicle includes a surfactant.

24. A process according to claim 23, in which the surfactant comprises no more than 10% by weight based upon the weight of the copolymer in the polymeric vehicle.

25. A process according to any of claims 14 to 24, in which the polymeric vehicle is treated with an aqueous solution or steam or water vapour at a temperature of up to 1000C and for a time up to 300 seconds.

26. A process according to any of claims 15 to 25, in which the recording layer is applied to the carrier sheet or film as a solution in an organic solvent.

27. A process according to any of claims 14 to 26, in which the sensitizing agent comprises a nitrogen-liberating diazonium salt.

28. A recording material when produced by a process according to any of claims 14 to 27.

29. A recording material suitable for vesicular imaging, substantially as described in any one of the Examples.

30. A process for the production of a recording material suitable for vesicular imaging, substantially as described in any one of the Examples.