US3817752A

US3817752A - Free radical photographic system containing a pyrylium dye former

Info

Publication number: US3817752A
Application number: US00288780A
Authority: US
Inventors: U Laridon; Den Houte J Van
Original assignee: Agfa Gevaert NV
Current assignee: Agfa Gevaert NV
Priority date: 1971-09-14
Filing date: 1972-09-13
Publication date: 1974-06-18
Anticipated expiration: 1991-06-18
Also published as: FR2152997A1; JPS4838727A; GB1398265A; BE787339A; FR2152997B3; CA990569A; DE2244783A1

Abstract

WHEREIN: R1 REPRESENTS AN ALIPHATIC GROUP, AN ARYL GROUP, OR REPRESENTS TOGETHER WITH R'' THE NECESSARY ATOMS TO CLOSE A HOMOCYCLIC RING, R'' REPRESENTS HYDROGEN, A C1-C5 ALKYL GROUP, A PHENYL GROUP, OR A PHENOXY GROUP, Z1 REPRESENTS THE NECESSARY ATOMS TO CLOSE A HOMOCYCLIC RING OR RING SYSTEM. Z2 REPRESENTS THE NECESSARY ATOMS TO CLOSE A HOMOCYCLIC NUCLEUS, R2 REPRESENTS A C1-C5 ALKYL GROUP, AND N REPRESENTS 1 OR 2.

2-R2,5,6-(-Z2-)-2H-PYRAN-2-OL

R1-(CO)(N-1)-C(-R'')=CH-C<(=C(-OH)-Z1-) AND

A PHOTOGRAPHIC PROCESS WHEREIN A VISIBLE IMAGE IS FORMED BY IMAGE-WISE EXPOSURE TO ACTIVE ELECTROMAGNETIC RADIATION OF A RECORDING MATERIAL WHICH COMPRISES IN INTIMATE ADMIXTURE: (1) AT LEAST ONE ORGANIC POLYHALOGEN COMPOUND OF WHICH A HALOGEN CONTAINING RADICAL CAN BE SEPARATED PHOTOLYTICALLY, AND (2) AT LEAST ONE COLOUR FORMING COMPOUND CORRESPONDING TO ONE OF THE FOLLOWING GENERAL FORMULAE:

Description

United States Patent 3,817,752 FREE RADICAL PHOTOGRAPHIC SYSTEM CON- TAINING A PYRYLIUM DYE FORMER Urbain Leopold Laridon, Wilrijk, and Jozef Willy Van den Houte, Berchem, Belgium, assignors to Agfa- Gevaert N.V., Mortsel, Belgium No Drawing. Filed Sept. 13, 1972, Ser. No. 288,780 Claims priority, application Great Britain, Sept. 14, 1971,- 42,802/71 Int. Cl. G03c 1/52, 5/24 US. CI. 96-48 R 18 Claims ABSTRACT OF THE DISCLOSURE A photographic process, wherein a visible image is formed by image-wise exposure to active electromagnetic radiation of a recording material which comprises in intimate admixture:

(1) at least one organic polyhalogen compound of which a halogen containing radical can be separated photolytically, and

(2) at least one colour forming compound corresponding to one of the following general formulae:

wherein:

R represents an aliphatic group, an aryl group, or represents together with R' the necessary atoms to close a homocyclic ring,

R represents hydrogen, a C -C alkyl group, a phenyl group, or a phenoxy group,

2; represents the necessary atoms to close a homocyclic ring or ring system,

2,, represents the necessary atoms to close a homocyclic nucleus,

R represents a C -C alkyl group, and

n represents 1 or 2.

The invention relates to photographic recording and reproduction of information and to materials suited therefor.

Free radical photography has been described already by A. Fotland in J. Photo. Sci, Vol. :18 (1970), 33-37.

A typical photosystem which has been investigated in detail comprises leuco crystal violet, carbon tetrabromide, triphenylstibine and polystyrene as a binder.

These materials are commercially available but must be carefully handled to prevent the production of a triphenylmethane dye during the preparation and storage since the leuco dye bases are very sensitive to oxygen. This is a real disadvantage for handling the materials before and during exposure and makes it diflicult to keep the obtained images completely free from background colouration.

It is an object of the present invention to provide a photographic colour forming system of the free radical ICC type that oliers the possibility to produce photographic materials having a particularly good stability, printout and optical development speed.

A photosensitive composition has now been found, which is capable of producing directly a visible image as a result of an image-wise modulated exposure to actinic electromagnetic radiation and of producing a visible image by the steps of (1) image-wise exposing the recording material to activating electromagnetic radiation of a dose sufiicient to bring about a latent or barely visible image and of (2) subsequently overall exposing the recording material to light of the wavelength range for which it has been made more sensitive in the image-wise exposure, said composition comprising in admixture:

(1) at least one organic polyhalogen compound of which a halogen containing radical can be photolytically separated and (2) at least one colour forming compound corresponding to one of the following general formulae (1) or wherein:

R represents an organic group, e.g. a saturated or unsaturated aliphatic group, e.g. an alkyl group including a substituted alkyl group, or an aryl group including a substituted aryl group, or together with IR represents the necessary atoms to close a homocyclic ring, e.g. a cyclohexylen-Z-one R' represents hydrogen, a lower alkyl group, e.g. methyl, or a substituted lower alkyl group, e.g. benzyl, a phenyl group including a substituted phenyl group or phenyloxy,

Z represents the necessary atoms to close a homocyclic ring or ring system including such a ring or ring system in substituted form, e.g. a phenyl group, a naphthyl group or such groups carrying in addition to the hydroxyl group one or more substituents, e.g. a methoxy group or a benzyl group that is further substituted with a hydroxy group and a CH=CH-COR group, R having the significance as defined above,

Z represents the necessary atoms to close a homocyclic nucleus including a substituted homocyclic nucleus e.g. a benzene or a naphthalene nucleus including a substituted benzene or naphthalene nucleus,

R represents a lower alkyl (C -C group, and

n represents 1 or 2.

The following Table 1 contains an illustrative list of compounds according to the general formula 1) with their melting point and the colour formed by exposure in the presence of OBr in polystyrene as binding agent.

TABLE 1 Number Melting of the point, compound Structural formula 0. Colour 1 Yellowlslr green.

TABLE 1-Continued Number Melting of the point, compound Structural formula 0. Colour 250 Blue om CH=CH-O o-Q 16 115 Cyan:

CH=C H-0 0 J) CH:

17 CH3 115 D0.

CH=CHC O CH:

18 139 Magenta:

CH=CHC 0 OH:

CHa on 20 Homopolymer containing recurring units of the following formula: Yellow;

XCHz-CH L .I

The compounds of general formula (I) can be prepared e.g. according to:

Heilbron and Whitworth, J. Chem. Soc., 123, 243 (1923). C. D. Harries, Ber. 24, 3180 (1891). Decker and V. Fellenberg, Ann. 364, 21 (1909).

A suitable compound according to the general formula (II) has the following structure:

the preparation of which may proceed as follows:

In a 250 ml. flask fitted with a reflux condenser and a gas inlet tube reaching nearly the bottom of the flask are introduced:

Z-hydroxy-l-naphthaledhyde g 10 Acetone ml 50 residue treated with 50 m1. of methanol by means of which treatment the residue solidifies. The obtained solid is pulverised, washed again with 50 ml. of methanol and dried. Yield: 9 g. Melting point: 200 C.

A high photosensitivity combined with a very low fog formation is obtained by the use of the compounds according to general formula I and more particularly by those having a methoxy group in the ortho-position to the hydroxyl group.

Suited organic polyhalogen compounds from which a halogen containing radical can be separated photolytical- 1y are within the scope of the following general formula:

each of A, B, X and Y is a halogen atom of the group of chlorine, bromine or iodine, or

wherein one of said symbols A, B, X or Y represents an alkyl group, including a substituted alkyl group e.g. a halogen substituted alkyl group, a hydroxyalkyl group or an aralkyl group e.g. benzyl, an aryl group, a substituted aryl group or an aroyl group, and the other symbols chlorine, bromine or iodine, or wherein at least two of said symbols A, B, X or Y represent an aromatic acyl group, e.g. benzoyl, and the other symbols chlorine, bromine or iodine.

Suitable representatives falling within the scope of that general formula are organic halides such as carbon tetrabromide, bromoform, iodoform, hexachloroethane, hexabromoethane, pentabromoethane, 1,1,2,2 tetrabromoethane, a,a,a-tribromoacetophenone and tribromoethanol.

wherein Z represents sulphur or a single bond, 7

A represents a single bond or a divalent hydrocarbon group e.g. -CH

R represents hydrogen or a lower alkyl group, e.g.

methyl,

R represents hydrogen or a lower alkyl group, e.g. methyl or ethyl,

each of Q and Q represents hydrogen or together represent the necessary atoms to close an adjacent carbocyclic ring or ring system including such ring or ring system in substituted form, preferably an aromatic ring (e.g. a benzene ring) including a substituted aromatic ring e.g. a halogen substituted (chlorine, bromine or iodine substituted) benzene ring,

each of Q and Q represents hydrogen or together represent the necessary atoms to close an adjacent carbocyclic nucleus or ring system including such a ring or ring system in substituted form, preferably an aromatic ring (e.g. a benzene ring) including a substituted aromatic ring e.g. a halogen substituted (chlorine, bromine or iodine'substituted) benzene ring, and

n represents 1 or 2.

The N-vinyl polymers and copolymers can be prepared by application of one of the various known polymerization procedures, e.g., by pearlor emulsion polymerization or by polymerization in solution, whereby the initiation of the polymerization can occur by free radicals, by ion formation, or by radiation eg, with actinic light. It is to be noted that the polymerization degree is not critical and can vary between wide limits. As far as the copolymers are concerned, it is further to be noted that the content of groups corresponding to the general formula given hereinbefore is not critical and, as shown furtheron in the table of copolymers containing N-vinylcarbazole units, can vary between wide limits, say, e.g. between 20 and 95%, when the properties of the compounds used in the preparation of the copolymers as well as the required sensitizing and/or mechanical properties are taken into account. In general, the best results are attained with copolymers having a content of vinyl carbazole units between 40 and 90%.

The preparation of suitable poly-N-vinylcarbazoles is described, e.g., in the German patent specifications 931,- 731-936,421-1,097,680 and 1,158,367 and the United States patent specification 2,072,465. The preparation of poly-N-vinyl-pyrrole proceeds analogously.

The preparation of suitable N-vinylcarbazole copolymers is described in the United Kingdom patent specification 964,875 which specification also contains a preparation receipt for poly(N-allylcarbazole) (R =CH and "R =H) and for poly(N-propenylcarbazole') (R =H,

The poly-N-vinyl indoles are described in the published German patent applications 1,906,831 and 1,917,747. The poly-N-vinyldiphenylamine is described in the published German patent application 2,007,692. Halogen-substituted poly-N-vinylcarbazoles are described in the published Japanese patent applications 7,592/68l9,751/67 and 7,591/68.

For illustrative purposes suitable vinyl copolymers containing N-vinyl carbazole units are enumerated in the following Table 2.

TABLE 2 Mole percent of Copolymer N-vinylcarbazole Copolymer of N-vinylcarbazole and vinylidene chloride 85.4 Copolymer of N-vinylcarbazole and 3,3,5 trimethylisononylether 93 Copolymer of N-vinylcarbazole and vinyl acetate 88.6 Copolymer of N-vinylcarbazole and isopropenyl acetate 94.5 Copolymer of N-vinylcarbazole and vinyl stearate 37.5 Copolymer of N-vinylcarbazole and methyl acrylate 67.6 Copolymer of N-vinylcarbazole and ethyl acrylate 41 Graft copolymer of N-vinylcarbazole and ethyl acrylate 90.3 Emulsion polymer of N-vinylcarbazole and polyethylacrylate 94.5 Copolymer of N-vinylcarbazole and n-butyl acrylate 58.3 Copolymer of N-vinylcarbazole and 2-ethyl hexylacrylate 51.6 Copolymer of N-vinylcarbazole and acryloxyethyldiethylamine 76.6 Copolymer of N-vinylcarbazole and vinyl cinnamate 92.5 Copolymer of N-vinylcarbazole and methyl methacrylate 62.7 Copolymer of N-vinylcarbazole and isobutyl methacrylate 51.8 Copolymer of N-vinylcarbazole and lauryl methacrylate 77.4 Copolymer of N-vinylcarbazole and methylacryloxyethyl diethylamine 9.7 Copolymer of N-vinylcarbazole and acrylonitrile 88 Graft copolymer of N-vinylcarbazole and butylaldehyde acetal of polyvinyl alcohol 30 Copolymer of N-vinylcarbazole and di(2-di-chloroethyl)-vinyl phosphonate 82.4 Copolymer of N-vinylcarbazole and styrene 49. Graft copolymer of N-vinylcarbazole and polystyrene 27.3 Copolymer of N-vinylcarbazole and vinylnapl1- thalene 47.1 Copolymer of N-vinylcarbazole and anthracene- (9,10) 91.5 Copolymer of N-vinylcarbazole and 2-vinylpyridine 31.8 Copolymer of N-vinylcarbazole and 4-vinylpyridine 32.4 Copolymer of N-vinylcarbazole and N-vinylpyrrolidine 69.1 Terpolymer of N-vinylcarbazole, acrylonitrile and styrene 2O Graft copolymer of a terpolymer of vinyl chloride,

vinyl acetate and vinyl alcohol with poly-N-vinylcarbazole 29.4 Graft copolymer of a terpolymer of vinyl chloride,

vinyl acetate and maleic anhydride with poly-N- vinylcarbazole 55.1

A preferred photosensitive recording material according to the present invention contains the color forming 9 compounds and poly-N-vinylcarbazole in a ratio b weight within the range of 80: 100 to 10:400.

The N-vinylcarbazole polymers are preferably used in admixture with carbon tetrabromide or iodoform or in a mixture of both of said polyhalogen compounds. Said polyhalogen compounds are preferably used with respect to poly-N-vinylcarbazole in a ratio by weight in the range of 160: 100 to 20:100.

If the above sensitizing polymers and copolymers do not serve themselves as binding agent for the formation of a recording layer according to the present invention one or more other binding agents for forming a selfsupporting or supported layer are used. For that purpose preferably hydrophobic polymers are elected that shield as much as possible to ingredients from a direct contact with the atmosphere and more especiall from oxygen.

Particularly suitable binders for use in the present invention are hydrophobic polymers and copolymers e.g. containing styrene, vinyl acetate, acrylonitrile, acrylate, methacrylate, or butadiene units, hydrophobic cellulose derivatives, phenoxy resins or polycondensates of the polyester type, e.g. polycarbonates.

These polymers may be used in admixture for improvement of the mechanical strength or adhering power of the recording layer to its support when no self-supporting layer is produced.

In order to diminish the rate of spontaneous thermal color formation over long periods of time as might be encountered during storage and processing of the photographic materials so-called anti-foggants may be added to the photosensitive composition. Suitable anti-foggants include sterically hindered phenols, e.g. 2,6-ditert.butyl p-cresol and other reducing compounds or agents accepting atmospheric oxygen.

Preferred amounts of anti-fogging agent such as said cresol compound with respect to photosensitive carbon tetrabromide and/ or iodoform are within the weight ratio range of 1:100 to 2.5:100.

A dry photographic coating containing the above mentioned ingredients can be formed by dissolving the binding agent(s) in a suitable inert solvent, which acts as dispersing or dissolving medium for the other ingredients, and by removing the solvent from the coating composition by evaporation so that a solid photographic recording layer is left on a properly chosen support. The supports may be of any kind encountered in silver halide photographic materials, e.g. paper and film supports, e.g. subbed and unsubbed polyethylene terephthalate ester supports.

The recording materials of the present invention containing the color-forming compounds of the general formulae especially in combination with polymers and copolymers containing N-vinylcarbazole units and that serve as binding agent show a remarkable high sensitivit to U.V. radiation. This high sensitivity is still increased when during the U.V. exposure the temperature of the recording layer composition is raised above 40 C. A very suitable operating temperature is in the range of 40-70 C.

The recording materials according to the present invention are suited to produce print-out images of different color according to the particular color forming compound applied.

In a particular preferred composition for forming printout prints a mixture of carbon tetrabromide and iodoform is used, which yields a superadditive sensitivity effect.

The stabilisation of the obtained prints may proceed by Washing out the residual free radical generator with a suitable solvent or solvent mixture, e.g. a hydrocarbon liquid such as petroleum ether optionally mixed with acetone, or by simply evaporating it by raising the temperature when the compound involved is sufliciently volatile. For the latter purpose and the high photosensitivity, carbon tetrabromide or a mixture of carbon tetrabromide and iodoform is preferred. A useful stabilisation tempera- 10 ture is in the range of to C. During the heat stabilisation an increase of the image density is obtained.

According to a preferred recording and reproduction process of the present invention the information-wise exposure is carried out in such a way that first a latent image is produced, which subsequently is transformed into a visible dye image by means of a so-called optical developmen The optical development proceeds by overall exposing the recording layer containing the latent or barely visible image with visible radiation that lies in the spectral absorption band of the products formed by the image-wise exposure and image-wise interaction of the photoexposed ingredients (1) and (2) of the mentioned photosensitive composition. In the overall exposure no light is applied to which the photosensitive polyhalogen compound is inherently sensitive since thereby the effect of the imagewise exposure is masked by an overall colouration. It is advantageous to use in the optical development exposure a filter absorbing all the light corresponding with the wavelength range that is inherently absorbed by the ingredients of the non-previously exposed recording layer.

The optical development effect is marketdly speeded up and the image density increased by applying heat, e.g. supplied by contact with a hot body or through infrared radiation during the overall exposure to visible light.

The optical development speed obtains a particularly high value by the use of poly-N-vinylcarbazole or the copolymers containing N-vinylcarbazole units in combination with the present colour forming compounds.

The optical development speed is likewise increased by means of an organic compound corresponding to the following general formula:

wherein:

each of R R and R (same or dilferent) represents an aryl group including a substituted aryl group, e.g. phenyl or a phenyl group substituted with a hydroxyl group or a halogen atom, e.g. chlorine or iodine.

Compounds of that type and the prepartion thereof are described in the United Kingdom Patent Specification 853,880.

It is assumed that during the exposure applied in the optical development at least a part of the overall applied light energy is visible light absorbed by a dyestulf salt having the pyrylium structure. Said salt seems to act as a spectral sensitizing agent for a chemical reaction between the photosensitive polyhalogen compound or radicals formed therefrom and the colour forming compound.

According to an alternative embodiment of the optical development technique the recording material is first overall exposed to electromagnetic radiation in order to produce non-differentially over the whole recording layer latent dyestuif centres that afterwards are optically developed information-wise by a sufficiently strong information-wise exposure in the absorption band of the dyestutf centres. Optionally the information-wise exposure proceeds simultaneously with an overall heating, effected e.g., by an overall infra-red exposure.

The information-wise exposure applied in the present invention may be a contact exposure of the direct or reflex type and likewise an optical projection exposure as is used, e.g., in an optical enlarging apparatus. The infor mation-wise exposure need not be simultaneous in all parts of the recording material. The exposure may be progressive in one continuous step as, e.g., in sound track recording, or in successive intermittent steps provided that the required information-wise change is obtained. Thus the recording material may be scanned with an imagewise modulated radiant energy spot of high intensity e.g. a laser beam, or the material may be progressively exposed through a slit, e.g. to copying light of a tubular lamp that is given a translation movement along the original.

A recording material of the present invention being suited for the recording of information in the form of modulated ultraviolet radiation can be used in X-ray and electron-beam recording. X-ray beams can be absorbed in substances absorbing high energy and by means of them create so-called secondary photos, e.g. of the ultraviolet radiation energy band, and photo-electrons that are absorbed by the photosensitive polyhalogen compound forming through its photoradicals a dyestutf salt with the colour forming compound. Substances for high energy absorption that may be incorporated into the recording element contain the elements lead, mercury, bismuth, barium and/or tungsten. Lead compounds that are photosensitive by themselves are preferred, e.g. lead monoxide, lead bromide and lead iodide.

Suitable light sources for use in a recording method of the present invention are ultra-violet radiation sources, xenon-gas lamps, incandescent bulbs and flash lamps. Sunlight is also suited in the overall exposure. For the optical development an infra-red lamp emitting also in the visible spectrum is preferably used.

Electron beam and laser beam recording proceed with the apparatus suited for that purpose and known to those skilled in the art.

Recording materials of the present invention are very versatile in that by the use of a proper sensitizing agent they can be applied for continuous tone or halftone reproduction. They can offer very contrasty images so that they are very suited for the reproduction of line and screen type originals and find a successful use in a great variety of graphic art applications. Due to the very high resolving power of the recording materials (the dyestuffs are formed in molecularly divided form) the recording materials of the present invention are particularly suited for microfilm reproduction and high precision image rendering as e.g. in the production of optical mieromask masters used in the manufacturing of microelectronic circuitry.

The reflex-exposure properties of the present recording materials make them very useful in the document reproduction sector since in a reflex-contact exposure they otfer print-out images of a sufiiciently intense spectral density.

According to a special application a recording layer as described herein is used in conjunction with a magnetic recording layer and is more particularly applied to the rear side of a flexible tape support carrying the magnetic recording layer. When such a material is used a sound track is formed in the magnetic recording layer and a visual text image corresponding with the sound track is photographed on the recording layer of the present invention. Such a recording material thus allows the storing of optical and acoustic signals and makes it possible to reproduce both informations simultaneously.

The present invention is illustrated by the following examples. The percentages and ratios are by weight unless otherwise indicated.

EXAMPLE 1 A mixture of 500 mg. of carbon tetrabromide, 20 mg. of a colour forming compound indicated by number in Table 1 and 2 mg. of 2,6-di-tert.butyl-p-cresol was dissolved in 8 ml. of a poly-N-vinylcarbazole solution in methylene chloride.

The solution was coated at a thickness of 0.12 mm. onto a non-subbed polyethylene terephthalate support and dried in the dark at room temperature.

Print-out processing The recording material was exposed for 2 min. through a step wedge of constant 0.15 by means of a W. high pressure mercury vapour lamp type HPL of Philips Gloeilampenfabrieken-Eindhoven (Netherlands), placed at a distance of 10 cm.

The obtained images were stabilized by means of a 3 min. heat treatment at C.

The obtained results expressed by the number of reproduced wedge steps are listed in the following table.

Optical development processing The same recording materials as used in the print-out processing were exposed through a transparent line original operating with the same U.V. lamp and exposure distance and applying for the image-wise exposure an exposure time as indicated in the Table.

The optical development was effected by overall exposing the image-Wise exposed recording material with a 250 w. infrared lamp of Bie and Berntsen, Copenhagen, Denmark, emitting also in the visible spectrum and placed at a distance of 15 cm. The overall exposure time for reaching a maximum density (d equal to 1 is listed in the Table. During the overall exposure a cut-off filter was used absorbing all the light having a wavelength smaller than 580 nm.

A mixture of 200 mg. of iodoform, 20 mg. of a colour forming compound indicated by number in Table l and 2 mg. of 2,6-di-t.-butyl-p-cresol was dissolved in 8 ml. of a 5% poly-N-vinylcarbazole solution in methylene chloride.

The recording layer was exposed for 2 min. through a step wedge of constant 0.15 by means of an 80 w. high pressure mercury vapour lamp type HPL of Philips placed at a distance of 10 cm.

The obtained images were stabilized by means of a 3 min. heat treatment at 150 C.

13 The obtained results expressed by the number of reproduced wedge steps are listed in the following table.

The present example illustrates the image density intensification obtained by applying a heat treatment subsequent to the image-wise exposure.

A mixture of 200 mg. of iodoform, 50 mg. of a mixture of colour forming compounds 3 and 18 of table 1 in a 50:50 ratio and mg. of 2,6-di-t.butyl-p-cresol was dissolved in 8 ml. of a 10% phenoxy polymer binder solution in methylene chloride.

The solution was coated at a thickness of 0.12 mm. onto a baryta coated paper support and dried in the dark at 50 C.

The obtained recording material was exposed for 2 min. through a step wedge with constant 0.15 by means of an -80 w. high pressure mercury vapour lamp placed at a distance of 10 cm.

The image density obtained in the several reproduced steps was measured before heating the exposed recording layer for 2 sec. at 150 C. and after such heat treatment. The results are listed in the following Table. The densities were measured with white light in a Macbeth-densitometer.

EXAMPLE 4 The following coating solution was applied to an unsubbed polyethylene terephthalate support at a thickness of 0.12 mm.:

Carbon tetrabromide mg 500 2 hydroxystyryl methyl ketone (compound 18) 10% solution in butanone of Eponol (a phenoxy resin prepared from epichlorohydrin and 2,2-bis (4- hydroxyphenyl)-propane of Shell-Netherlands After drying the coating was exposed for 2 min. through a continuous tone transparency (negative) by means of an 80 w. U.V.-lamp (type HPL) held at a distance of 10 cm. The originally weak print-out magenta image was much intensified by heating the exposed recording material for 3 min. at 150 C.

EXAMPLE 5 The following coating solution was applied to an unsubbed polyethylene terephthalate support at a thickness of 0.10 mm.:

Iodoform mg 100 2 hydroxy 1 naphthavinyl methyl ketone (compound 3) m 25 2,6 di t butyl p cresol mg 10 10% solution in methylene chloride of Eponol (Shell-Netherlands) ml 4 After drying a faintly yellow coloured layer was obtained.

The recording layer was exposed for 1 min. through a continuous tone transparency (negative) 'by means of an w. U.V. lamp (type HPL) held at a distance of 10 cm.

An intense blue image was obtained by heating the exposed material at 1 80 C. for 1 min.

Preparation of the 2-hydroxy-1-naphthavinyl methyl ketone (compound 3) In a 10 ml. flask fitted with a reflux condenser were introduced:

Acetone ml 20 2 hydroxy l naphthaldehyde g 4 and 2 g. of sodium hydroxide dissolved in 25 ml. of water. The obtained solution was refluxed for 4 h. Thereupon the reaction mixture was cooled, diluted with ml. of water, filtered and acidified with 3 ml. of acetic acid. A yellowish green precipitate was obtained, which was separated with suction, washed with water and dried.

Yield g-.. 4 Melting point C..-

EXAMPLE 6 The following coating solution was applied to an unsubbed polyethylene terephthalate support at a thickness of 0.10 mm.:

Iodoform mg 100 2 hydroxy 1 naphthavinyl methyl ketone (compound 3) mg 25 Z-hydroxystyryl methyl ketone (compound 18) mg 25 10% solution of Eponol (Shell-Netherlands) in a mixture of methylene chloride and 1,1,2-trichloroethane (1:1 by volume) m1- 4 After drying a faintly yellow coating was obtained.

The recording layer was exposed for 1 min. through a continuous tone transparency (negative) by means of an 80 w. U.V. lamp (type HPL) held at a distance of 10 cm.

An intense purple image was obtained by heating the exposed material for 1 min. at 180 C.

EXAMPLE 7 The following coating solution was applied to an unsubbed polyethylene terephthalate support at a thickness of 0.12 mm.:

Bromalhydrate (CBr CHO.H O) mg 250 3 methoxy-Z-hydroxystyryl methyl ketone hydrate (compound 4) mg 60 2,6-di-t.butyl-p-cresol mg 60 5% solution of poly-N-vinylcarbazole in methylene chloride l 8 15' A fog-free magenta image was obtained by stabilisa tion for 3 min. at 150 C.

The same recording layer applied to a baryta coated paper yielded an image of the same quality.

EXAMPLE 8 The following coating solution was applied to an unsubbed polyethylene terephthalate support at a thickness of 0.12 mm.: a

After drying the recording layer was exposed for 10 see. through a continuous tone transparency (negative) by means of an 80 w. U.V. lamp (type HPL) held at a distance of 10 cm. A latent image was obtained that was optically developed by overall exposing the recording layer for 3 min. with a 250 w. infrared lamp (Bie and Berntsen) through a cut-01f filter absorbing all the light of a wavelength below 540 nm. A dense fog free magneta image was obtained. It was stabilized by heating the recording material for 3 min. at 150 C.

A same recording layer as described above but not containing said sensitizing agent yielded by an image-wise exposure of 30 sec. and an overall exposure of min. only a very faint magenta image.

Equally good results as with the 1,3-diphenyl-5-(4- chlorophenyl)-pyrazoline sensitizer were obtained by using 1,3 diphenyl-S(4-iodophenyl)-pyrazoline or 1,3-diphenyl-5 (4-hydroxyphenyl -pyrazoline.

EXAMPLE 9 The following coating composition was applied to an unsubbed polyethylene terephthalate support at a thickness of 0.12 mm.:

Carbon tetrabromide mg.. 120 Compound 20 of Table 1 mg 600 1,1,2-trichloroethane ml 12 The applied coating was dried for 1 h. at 60 C. and thereupon exposed for 2 min. through a step wedge of constant 0.15 by means of an 80 w. high pressure mercury vapour lamp (type HPL) placed at a distance of cm. A yellow wedge image was obtained, which was stabilized by heating the exposed coating for 30 sec. at 150 C.

EXAMPLE 10 The following coating composition was applied to an unsubbed polyethylene terephthalate support at a thickness of 0.12 mm.:

Carbon tetrabromide mg 120 Compound of Table 1 mg 200 1,1,2-trichloroethane ml 6 of poly-N-vinylcarb- 10% solution in CH Cl azole Preparation of compound 20 I In a reaction flask were introduced:

Polyvinylacetophenone g 2.0 Salicylaldehyde ml 3.5 Dioxan ml 20 While shaking the flask 1 ml. of 40% solution of benzyltrimethylammonium hydroxide in dioxan was added.

The solution turned yellow and was kept at room temperature for 24 h. Then 0.2 ml. of acetic acid was added and the reaction mixture was poured into methanol. The polymer was separated and purified by dissolving in methylene chloride, filtering and reprecipitation in methanol. After drying under vacuum conditions 1.8 g. of the polymeric compound 20 were obtained.

We claim:

1. A photographic process wherein a visible image is formed in a recording material which comprises in intimate admixture:

(1) at least one organic polyhalogen compound corresponding to the following general formula:

wherein:

each of A, B, X and Y is chlorine, bromine and iodine, or one of A, B, X or Y represents an alkyl group, an aryl group or an aroyl group and the others represent chlorine, bromine or iodine, or at least two of A, B, X or Y represent an aromatic acyl group and the others represent chlorine, bromine or iodine, and p (2) at least one color forming compound corresponding to one of the following general formulae:

wherein:

R represents an alkyl group, a phenyl group, a

naphthyl group, or together with R the neces-.

sary atoms to close a cyclohexanyl ring, R represents hydrogen, a C -C alkyl group, a

phenyl group or a phenoxy group, Z represents the necessary atoms to close a phenyl or naphthyl nucleus, Z represents the necessary atoms to close a benzene or naphthalene nucleus, R represents a C -C alkyl group, and n represents 1 or 2, said visible image being formed by the step of: imagewise exposing the recording material to activating electromagnetic radiation of a dose being sufiicient to bring about a directly visible image, or by the steps of: imagewise exposing the recording material to activating electromagnetic radiation of a dose sufficient to create therein an at most barely visible image which has a spectral sensitivity in a wawelength range outside the inherent sensitivity range of the organic polyhalogen compound, and overall exposing the imagewise exposed recording material to light within the wavelength range to which the initially exposed portions were made more sensitive than the initially non-exposed portions, to thereby increase the visibility of said image, or by the steps of: overall exposing the recording materal to electromagnetic radiation of a dose sufiicient to bring about in the recording material an increase in spectral sensitivity in a wavelength range outside the inherent sensitivity range of the polyhalogen compound, and imagewise exposing the overall exposed recording material within the wavelength range for which the overall exposed recordin material was made more 17 sensitive in order to form a visible image corresponding with said imagewise exposed portions.

2. A photosensitive recording material for producing directly a visible image upon imagewise exposure to activating electromagnetic radiation, said material containing an intimate mixture consisting essentially of:

wherein:

each of A, B, X and Y is chlorine, bromine and iodine, or one of A, B, X'or Y represents an alkyl group, an aryl group, or an aroyl group and the others represent chlorine, bromine or iodine, or at least two of A, B, X or Y represent an aromatic acyl group and the others represent chlorine, bromine or iodine, and (2) at least one color forming compound corresponding to one of the following general formulae (1) or (H):

R represents an alkyl group, a phenyl group, a

naphthyl group, or together with R the necessary atoms to close a cyclohexyl ring,

R represents hydrogen, a C -C alkyl group, a

phenyl group of a phenoxy group,

Z represents the necessary atoms to close a phenyl or naphthyl nucleus,

Z represents the necessary atoms to close a henzene or naphthalene nucleus,

R represents a C -C alkyl group, and

n represents 1 or 2.

Z represents sulphur or a single bond,

A represents a single bond or a. divalent hydrocarbon group,

each of R and R represents hydrogen or a lower alkyl radical,

wherein:

each of Q and Q represents hydrogen or together represent the necessary atoms to close an adjacent carbocyclic nucleus,

each of Q and Q represents hydrogen or together rep resent the necessary atoms to close an adjacent carbocyclic nucleus, and

n represents 1 or 2.

7. A process according to claim 6, wherein said polymeric compound is poly-N-vinylcarbazole or a copolymer containing N-vinylcarbazole units.

8. A process according to claim 1, wherein said mixture is used in combination with an organic compound having the following general formula:

R represents hydroxyl, chlorine or iodine.

9. A process according to claim 1, wherein the recording material in combination with said mixture contains as anti-fogging agent a sterically hindered phenol.

10. A photosensitive recording material according to claim 2, wherein the compound of general formula (1) contains a methoxy group in ortho-position to the hydroxyl group on the Z nucleus.

11. A photosensitive recording material according to claim 2, wherein said ultraviolet-sensitive compound is carbon tetrabromide or iodoform.

12. A photosensitive recording material according to claim 2, which contains a mixture of carbon tetrabromide and iodoform.

13. A photosensitive recording material according to claim 2, which in addition to said mixture contains a polymeric compound containing recurring units of the following general structure:

l Q1 Q2 wherein zole units.

15. A photosensitive recording material according to claim 2, which in addition to said mixture contains an organic compound having the following general formula:

' wherein:

R represents hydroxyl, chlorine or iodine.

'16. A photosensitive recording material according to claim 14, wherein said mixture is present in layer form and 20 said polymeric compound is the sole binding agent for said layer.

References Cited UNITED STATES PATENTS Arcesi et al. 96-115 P Hartman et al. 96-90 R Hori et al 96--90 R Thomo et al. 96-115 R Van Allan et al. 96-90 PC RONALD H. SMITH, Primary Examiner W. H. LOUIE, JR., Assistant Examiner 9648 QP, 90 R US. Cl. X.R.