US3502471A

US3502471A - New light-developable photographic material and recording process

Info

Publication number: US3502471A
Application number: US585731A
Authority: US
Inventors: Paul Desire Van Pee; Jozef Frans Willems
Original assignee: Agfa Gevaert NV
Current assignee: Agfa Gevaert NV
Priority date: 1965-10-11
Filing date: 1966-10-11
Publication date: 1970-03-24
Anticipated expiration: 1987-03-24
Also published as: FR1496596A; NL6615205A; DE1522401A1; BE688065A; NL6614290A; US3431108A; DE1522403A1; BE688068A; GB1160955A

Description

United States Patent 3,502,471 NEW LIGHT-DEVELOPABLE PHOTOGRAPHIC MATERIAL AND RECORDING PROCESS Paul Desire Van Pee, Edegem, and Jozef Frans Willems, Wilrijk-Antwerp, Belgium, assignors to Gevaert-Agfa N.V., Mortsel-Belgium, a Belgian company No Drawing. Filed Oct. 11, 1966, Ser. No. 585,731 Claims priority, application Great Britain, Oct. 11, 1965, 42,969/ 65 Int. Cl. G03c /32 US. Cl. 9645.2 .22 Claims ABSTRACT OF THE DISCLOSURE Photographic elements are defined which comprise a radiation-sensitive silver halide emulsion layer of the light developable type. The layer is applied from a coating composition containing a silver iodide sol and/or a compound which will release free iodide ions and a halogen acceptor corresponding to the formula or to a tautomeric structure thereof as follows:

wherein each of R R R R and R is hydrogen, an alkyl group or an aryl group, with the proviso, however, that at least one of the substituents R and R is hydrogen; R, and R may also be the atoms necessary to complete a carbocylic ring. These light-developable silver halide materials are useful in high-speed recording such as high-speed oscillographic recording of events which occur in rapid sequence, and the like.

' The present invention relates to photographic elements comprising an improved light-developable radiation-sensitive silver halide emulsion layer, as well as to a process for making records employing said elements.

The light-developable silver halide materials have become of increasing interest, for they possess desirable properties for high speed recording, such as high speed oscillographic recording of events, which occur in rapid sequence, and the like.

Light-developable silver halide materials for direct recording are radiation-sensitive materials in which a visible image can be obtained, after an exposure to a high intensity source of radiation has been initially utilised to form a latent image, by an additional exposure to a radiation of lower intensity such as ditfuse daylight or artificial light. The secondary exposure, also called latensification, is an overall exposure, including exposing the areas in which the initial latent image was formed as well as the surrounding background to an additional amount of radiation.

It is known that in general, intense exposure favours the formation of a latent image in the interior of the grains while low-intensity exposure forms almost exclusively a surface latent image. The surface latent image is the one developed by a usual chemical development whereas the internal latent image is practically not developed by such processing. The light absorbed by the silver halide in the secondary exposure provides the energy for the development of the internal latent image to a visible form (cf. H. Hunt High Speed Direct Recording Papers, Phot. Sci. Eng, vol. 5, No. 2, 1961).

3 ,5 02,47 1 Patented Mar. 24, 1970 wherein each of R R R R and R represents a hydrogen atom, an alkyl group including a substituted alkyl group or an aryl group including a substituted aryl group, with the proviso, however, that at least one of the substituents R and R represents a hydrogen atom; R and R may also represent the atoms necessary to complete a carbocyclic ring including a substituted carbocyclic ring, to light-developable radiation-sensitive silver halide emulsions results unexpectedly and surprisingly in the production of a light-developable material in which an improved image can be obtained, showing a favourable contrast between the image and the background (i.e. having a good net density) and having a very good stability as well as a good chemical developability. As will be seen from the examples hereinafter, the effect of the simultaneous addition of the above compounds is much more important than the effects obtained on the one hand by the addition of the halogen acceptor alone and on the other hand by the addition of the silver iodide sol and/ or the compound splitting off iodide ions alone. When only a member of one of these two groups of compounds is incorporated into the light-developable radiation-sensitive emulsion layer the difierence between the maximum and minimum density is considerably lower than when both groups are present together. This additive effect is the more surprising since it was found that this effect could not be obtained in the case of a combination of a compound setting free iodide ions with many other generally known and often used halogen-acceptors e.g. hydrazothiocarbonamide, thiosemicarbazide and thiourea.

The improved light developable radiation sensitive photographic silver halide elements according to the pres ent invention permit a rapid access to and prolonged examination of the image formed on photodevelopment and also permit a chemical development and fixing treatment in order to obtain permanent records of the traces or images. The material according to the present invention shows a high degree of sensitivity to the trace beam coupled with a highly stable background i.e. a background which is not very sensitive to low intensity radiation, thus resulting in a maximum contrast between the image and background. Thus, the images or traces obtained on lightdevelopment with elements according to the present invention are characterized by a high net density, i.e. an optimum contrast between the image and background, a good resistance to fogging of the non-image areas even when exposed for a long time to ambient lighting and even when no chemical development occurs. Of course, when the traces or images produced on latensification are exposed to ambient lighting for a long time the back ground darkens slowly, however, the contrast between image and background will remain for many hours. The

mages'or traces will not remain visible when permanently Compound 4 :xposed to light. To keep a permanent record of the races or images, the material has to be chemically develped and fixed, preferably not too long after the light- CHz-CH: N levelopment. Without said development and fixing step, he record will remain permanently only when the lightleveloped images are exposed to light infrequently and CHT'O :ept in the dark when not in use. Indeed, the image will :0 0:8 ast practically indefinite if protected from prolonged exlosure to strong light. 6

Another advantage offered by the hght'developable 4-methyl-3-thio-1,2,4-triazfospiro[5,5]undecane-35-dione :lements of the invention is that it is possible to carry out a he light-development while supplying heat, whereby the Melnng o 210 Tjhls compound F be P ecorded image becomes almost immediately visible for pared accofdlng to Pfoparatlon as descl'lbed further he reason that, when heating, it is possible to increase the hereinafteright-intensity of the secondary exposure without produe- ComP 5 ng fog. A probable explanation of this phenomenon has 0,11, een given by Jacobs, Phot. Sci. & Eng, vol. 5, No. 1, 1 .961. By the fact that when operating at elevated tem- )erature a more rapid image access is obtained, it is not i lecessary in those instances Where there is recorded at 0:0 0:8 righ writing speeds and thus at high paper transport peeds, to expose considerable meters of paper to ambient I ight at the Same time, which would lead to a handling CH3 roblem. Some oscillographs operate according to this -p y 'et xy3 t io-1,6-dihydro'as-triazinerrinciple: after the high-intensity exposure the print-out material is passed over a heated plate while being ex- Melnng P This compound can be P :osed to fluorescent U.V. lamps so that a visible image pared according to Preparation as described further s produced almost immediately. e te The following is a non-restrictive list of halogen ac- Compound 6 eptors, which have proved to be particularly suitable For use according to the present invention, and which (IJHHH :orrespond to the above general formula: N

Compound 1 nio NH E l 0:1 o=s HzC N NH H3C C T 1-phenyl-3-thio-1, 6-dihydro-as-tri azine-3, 5 (2H,1H) -dione Melting point: 172-173 C. Preparation described by f Busch and Meussdorfier, Ber. 40, 1021 (1907). .H Compound 7 6,6-dimethyl-3-thio 1,fi-dihydro as-trrazine-lpfi 2H,4H) -dione Melting point: 248249 C. Preparation described by cm Fusco and Rossi, Gazz. Chim. Ital. 89, 373 1954 1,

Compound 2 1 =S CH CH N 2- H2C\ O NH 02H CHz-Cg 1-methyl-4ethyI-3-thio-1,'6-dihydro=as-trlazine- O=O\ /C=S 3,5(2H,4H)-dione N Melting point: 129 C. This compound can be prepared k according to Preparation 4 as described further herein- 3-thio-1,2,4-triazaspiro['5,5]undecane-3,5-dione after' PREPARATION 1 Melting 224 Preparation descnbed by Fusco A. Preparation of the intermediate product 1-(1'-cyano- 1nd ROSSI, GaZz. Chlm- Ital. 89, r e y1 y 4 et y th s m ca ba de Compound 3 21 g. of 4-methyl thiosemicarbazide are dissolved in H 80 ccs. of a mixture of ethanol and water (1:1). Whilst H30 5 stirring the solution, there are successively added at room temperature: 11.5 ccs. of acetic acid, a solution of 13 g. Hie-C I of potassium cyanide in 25 ccs. of Water and 12.6 ccs. of 0:0 0:8 acetone. The reaction mixture is refluxed for 1 hour. After cooling, the crystals formed are filtered by suction (yield: 34.5 g.melting point: 197-203 C.) and recrys- CH3 tallized from 1600 ccs. of ethanol. 4,6,(i-trimethyl-S-thio-l,G-dihydro-as-triazine- Yield: 25.5 g. 1-(1'-cyano-1'-methyl-ethyl)-4-methylthio-semicarbazide. Melting point: 210 C. Melting point: 190 C. This compound can be pre Microanalysis.-Calculated for C H N S, molecular pared according to Preparation 1 as described further weight: 172 (percent): C, 41.90; H, 7.03; S, 18.64. lereinafter. Found (percent): C, 42.45; H, 6.87; S. 18.39.

B. Preparation of Compound 3 800 g. of the obtained 1-(1-cyano-1'- methyl-ethyl)-4- methyl-thiosemicarbazide are dissolved in 3300 ccs. of an aqueous hydrochloric acid solution (d.: 1.17) and heated for 24 h. at 80 C. On cooling, ammonium chloride crystallizes and is filtered by suction. The filtrate is brought at pH 3-4 by means of 2200 ccs. ammonium hydroxide, whereby 4,6,6-trimethyl-3-thio-1,6-dihydro-astriazine-3,5 (2H, 4H)-di0ne precipitates together with ammonium chloride. The precipiate is crystallized from water (5500 ccs.).

Yield: 160 g. of 4,6,6-trimethyl-3-thio-1,6-dihydro-astriazine-3,5 (2H, 4H)-dione. Melting point: 190 C.

Microanalysis.-Calculated for C H ON S, molecular weight: 173 (percent): C, 41.65; H, 6.41; S, 18.54. Found (percent): C, 41.92; H, 6.38; S, 18.33.

PREPARATION 2 A. Preparation of the intermediate product 1-(1'-cyanocyclohexyl) -4-methy1-thio semicarbazide 105 g. of 4-methyl-thiosemicarbazide are dissolved in 400 ccs. of a mixture of ethanol and water (1 :1). Whilst stirring the solution at C. there are successively added: 57.5 ccs. of acetic acid, a solution of 65 g. of potassium cyanide in 125 ccs. of water and 98 g. of cyclohexanone. The reaction mixture is refluxed for 2 hours, whilst stirring. After cooling, the crystals formed are filtered by suction and washed with ethanol and ether.

Yield: 189 g. 1-(1-cyano-cyclohexyl)-4-methyl-thiosemicarbazide. Melting point: 200 C.

Microanalysis.Calculated for C H N S, molecular weight: 212 (percent): C, 50.99; H, 7.61; S, 15.13. Found (percent): C, 51.22; H, 7.84; S, 15.00.

B. Preparation of Compound 4 189 g. of l-(1'-cyano-cyclohexyl)-4-methyl-thiosemicarbazide are dissolved in 1375 ccs. of an aqueous hydrochloric acid solution (d.=l.17) and heated for 24 hours at 80 C. After cooling, the precipitate formed is filtered by suction and washed with water, whereafter it is recrystallized from 3500 ccs. of ethanol.

Yield: 125 g. of 4-methyl-3-thio-1,2,4-triazospiro[5,5] undecane-3,5-dione. Melting point: 210 C.

Microanalysis.Calculated for C H ON S, molecular weight 213 (percent): C, 50.75; H, 7.10; S, 15.05. Found (percent): C, 50.47; H, 7.08; S, 15.05.

PREPARATION 3 70 g. of 1-phenyl-l-ethoxyacetyl-hydrazine hydrochloride are dissolved in 450 ccs. of water. By adding 17.1 g. of ammonium carbonate 1 aq., the base is set free from its hydrochloride whereupon it is extracted with ether. After drying the etheric solution over molecular sieves, a

solution of 15.6 g. of methylisothiocyanate in 220 ccs. of-

PREPARATION 4 45 g. of l-methyl-l-ethoxyacetyl hydrazine hydrochloride are suspended in 230 ccs. anhydrous ether and whilst thoroughly stirring at 0 C. ammonia gas is introduced. The formed ammonium chloride is removed by filtration. By evaporation of the ether of the filtrate, an oil is left which is again dissolved in 205 ccs. anhydrous ether and this solution is added to a solution of 21.6 ccs. of ethylisothiocyanate in 205 ccs. of anhydrous ether. After stirring for half an hour at room temperature, the ether is evaporated. The residue is dissolved in ccs. of anhydrous ethanol and whilst stirring at 0 C., a solution of 16.2 g. of potassium hydroxide in ccs. of anhydrous ethanol is dropwise added. After stirring for one hour, the ethanol is evaporated. The remaining yellow oil is added to 200 ccs. of water and acidified with acetic acid. The precipitate is crystallized from 50 ccs. of ethanol.

Yield: 13 g. of 1-methyl-4-ethyl-3-thio-1,6-dihydro-astriazine-3,5(2H, 4H)-dione. Melting point: 129 C.

Microanalysis.Calculated for C H ON S, molecular weight: 173 (percent): C, 41.65; H, 6.41; S, 18.54. Found (percent): C, 41.73; H, 6.29; S, 18.60.

The amount of halogen acceptor according to the above general formula that is incorporated into the silver halide emulsion layer according to the present in- 'vention may vary within very wide limits viz from about 0.01 g. to about 20 g. per mole of silver halide, but is preferably comprised between about 0.1 g. and about 5 g. per mole of silver halide.

According to the invention, the halogen acceptor corresponding to the above general formula may also be applied together with other halogen acceptors. Very good results have been obtained when using in combination with the halogen acceptors of the present invention the halogen acceptors described in our co-pending applications entitled Light-Developable Photographic Material and Recording Process and Improved Light-Developable Photographic Material and Recording Process, both filed on even date herewith.

Suitable compounds setting free iodide ions are among others inorganic and organic iodides, organic compounds with labile iodine atom and onium chloroiodates.

Suitable inorganic iodides are for instance the following water-soluble iodides: calcium iodide, ammonium iodide, lithium iodide, magnesium iodide, potassium iodide and sodium iodide.

Suitable organic iodides are for instance the iodides having the following structural formulae:

1-methyl-8-hydroxy-qui1roliniun1 iodide lCH3 1-methyl-2-iodo-quinolinium iodide 1,2,3,4-tetrahydro-8-hydroxy-1,l-dimethyl-quinolinlum iodide benzyltriphenylphosphonium iodide 3,5-dimorpholino-dithiolium dio'de COO CH3 [Cla- 31 3):

#crimethyl o-methoxycarbonyl-auilinium) dichloroio'date benzyltriphenyl-phosphonium dichloroiodate Instead of or in addition to a compound setting free Iodide ions, a silver iodide sol comprising an appropriate protective colloid can be added with the same effect to :he silver halide emulsion. A very suitable silver iodide sol can be prepared by slowly adding while strongly rtirring the following solution A to the following solu- :ion B, both solutions being heated to 35 C.

Solution B:

3NKI.17 ccs. gelatin.40 g. water up to 1 litre Solution A:

3NAgNO .17 ccs. water up to 1 litre The amount of compound setting free iodide ions may also vary within very wide limits. In general an amount rom about 0.01 g. to about 20 g. preferably from about ).1 g. to about 5 g. per mole of silver halide is applied. lhe same applies to the limits within which the silver odide sol is used. In the latter case the above amounts -elate to the silver iodide and not to the total sol. The lddition of a member selected from a. silver iodide sol and at least one compound setting free iodide ions, and

preferably also the addition of the halogen-acceptor occurs after the emulsion preparation and preferably just before coating on a suitable support. Except the addition of the silver iodide sol, any other addition can occur from a solution of the compound involved in a suitable slvent, which is mostly water but may also be an organic solvent.

By the addition to a silver halide emulsion of a compound setting free iodide ions or of a silver iodide sol, silver iodide is produced on the surface of the silver halid grains of the emulsion, in the former case by conversion and in the latter by adsorption. The formation of silver iodide at the surface of the grains and the favourable effects resulting therefrom for the method of the present invention can also be attained by conducting the emulsion layer obtained after coating through a solution, preferably an aqueous solution of a compound setting free iodide ions, or by treating this emulsion layer in some other way therewith.

According to the invention any silver halide emulsion of the light-developable type may be used. These kinds of emulsions are very well known to those skilled in the art. They mainly or entirely form an internal latent image and only to a little extent an external latent image.

A silver halide emulsion that mainly or entirely forms an internal latent image and only to a little extent an external latent image is an emulsion in which only few or no exposed grains at all are developable into silver by a developing solution that cannot act as a developer for a latent image inside the grains i.e. a so-called surface develop-er, such as:

p-Hydroxphenyl glycine-10 g. Sodium carbonate (cryst.)l00 g. Water to 1000 ccs.

and wherein the exposed grains are well developable to silver by a developing solution that acts as a developer for latent image inside the grains i.e. a so-called internal developer such as the following solution:

Hydroquinone15 g. Monomethyl-p-aminophenol sulphate-1.5 g. Sodium sulphite (anhydrous)--50 g. Potassium bromide-10 g.

Sodium hydroxide25 g.

Sodium thiosulphate (cryst.)-20 g.

Water to 1000 ccs.

By a silver halide emulsion that mainly forms internal latent image and little external latent image there is more particularly meant a silver halide emulsion, a test layer of which upon exposure to a light intensity scale for a fixed time between A00 and 1 sec. and development for 3 min. at 20 C. in the above internal developer, exhibits a maximum density at least 5 times the maximum density obtained when an identical test layer of the said silver halide emulsion is equally exposed and then developed for 4 min. at 20 C. in the above surface developer.

Silver halide emulsions that meet the above requirement and hence are suitable for being employed in the process of the invention are generally not or only slightly chemically ripened silver halide emulsions, since the extent of the surface latent image-forming capability increases with the degree of chemical ripening.

Silver chlorobromide and silver bromide emulsions have proved to be specially suitable for the purpose of the invention. When these emulsions comprise minor amounts of silver iodide, preferably not more than 5 mole percent relative to the total amount of silver halide, they are just as Well suitable.

The silver halide emulsions for use in the present process are generally gelatin silver halide emulsions. However, the gelatin may wholly or partially be replaced for instance by another protein, a hydrophilic not proteinaceous colloid or a synthetic polymeric substance applied from an aqueous dispersion. The light-sensitive silver halide emulsions may be prepared according to all known and conventional techniques for emulsion preparation. A method according to which emulsions are prepared, and which has proved to be particularly suitable for the purpose of the invention, is the so-called conversion method according to which an emulsion of a silver salt that has a higher degree of solubility than silver bromide is converted into a silver chlorobromide or a silver bromide emulsion that occasionally contains small amounts of silver iodide. This conversion is carried out preferably very slowly for instance by several consecutive steps.

The emulsions can, if desired, be modified prior to coating by the addition of all kinds of ingredients, which are generally known in the art of emulsion preparation and some of which will be set out specifically hereinafter.

Among the said ingredients may first be mentioned the common additives, for light-sensitive silver halide material such as hardening agents e.g. formaldehyde, coating aids, e.g. saponine, plasticizers, e.g. glycerol, optical sensitisers of the class of the cyanine dyes, the merocyanine dyes, etc., development accelerators, compounds that render the material more resistant to wrinkling and less brittle etc.

Furthermore specific ingredients may be incorporated also. Among these may be mentioned more particularly:

Thiocyanates, such as potassium thiocyanate, which further stabilise the light-developed image;

Compounds or mixtures of compounds reducing the background density on latensification e.g. lead salts, and prreferably cadmium salts; these salts are preferably salts that are water-soluble such as lead acetate, lead iodide, lead nitrate, cadmium iodide, cadmium chloride, cadmium bromide, cadmium nitrate, etc.; they give rise to a decrease of the minimum density without, however, decreasing the maximum density to the same extent so that as a result thereof the contrast is enhanced. Said salts may be added to the emulsion during the emulsion preparation or the conversion of the silver salt emulsion by means of a bromide as well as just before coating the emulsion on a support. They are added in amounts varying from about 1 g. to about 20 g., preferably from about 5 g. to about g. per mole of silver halide.

The amount of gelatin applied in emulsion making is preferably such that per kg. of emulsion ready for coating from about g. to about 150 g. of gelatin is present.

The amount of silver nitrate used in emulsion making preferably varies from about 50 to about 200 g. per kg. of emulsion.

The emulsion is generally coated in such a way that 1 kg. of emulsion covers approximately from about 20 to about 30 sq. m. of support.

Suitable support for the elements of this invention include the flexible supports used in the prior art for lightwriting and oscillographic recording. They may be any type of paper, as well as films of cellulose nitrate, cellulose acetate, poly(vinyl acetal), polystyrene, po1y(ethylene terephthalate) and other synthetic resins. Supports of glass, metal, and other substances are not excluded. In this connection conventional photographic base papers may be conveniently utilised.

In order to form an image in the light-developable radiation-sensitive photographic elements acccording to the present invention, said elements are first exposed to a high-intensity actinic radiation e.g. from Xenon tubes, U.V.-lamps or high-pressure mercury arc lamps as used in certain oscillographs.

The high-intensity radiation source used for the initial or first exposure of the light-developable material is generally rich in blue and ultraviolet radiation but said radiation may be any light or other electromagnetic radiation of either visible or invisible wave lengths, X-rays, gamma rays or an electron beam. After the initial exposure the material may be light-developed by exposure to low intensity daylight, incandescent light or fluorescent light, or by the use of photoflood lamps as commonly used in photography. This secondary exposure must not necessarily be performed with the aid of an actinic radiation source. When light-developing with common oflice lighting or daylight the image becomes visible after 15- 30 seconds, attaining maximum density in several minutes. In certain instances i.e. for obtaining practically immediately visible traces or images it may be advan: tageous, as already stated above, to carry out the development while supplying heat. This can be carried out by running the material over a hot plate at -180 C. in the secondary exposure step.

The sharpness of the recorded trace or image may be further increased by a short preliminary exposure of the light-developable radiation-sensitive material according to the invention to ordinary light e.g. daylight, prior to exposing the material to the high-intensity radiation. Indeed, by this short preliminary exposure the gradation in the toe of the characteristic curve and the contrast or net density of the recorded trace or image are increased.

If desired the material may be chemically developed and fixed before, during or after the photo-development, latensification, or secondary exposure. This development is of the internal type which means that it takes place in the presence of an energetic silver halide solubilising agent, e.g. sodium thiosulphate,,which is mostly present in the developer itself. Said chemical development advantageously occurs in the presence of an anti-fogging agent. The halogen acceptor used can function as such at least when it possesses good antifogging properties. The antifogging agent may be incorporated in at least one of the composing layers of the photographic element used and/ or in the developer. Examples of suitable anti-fogging agents are Z-mercapto-ethyl-carbanilate, l-phenyl-Z-tetrazoline-S-thione and 4,5, 6, 7-tetrabromo- 1 H-benzotriazole.

It was noticed that the advantage of the chemical development of light-developable silver halide material in the presence of anti-fogging agents does not only apply to the material according to the present invention but also to any photographic material of the light-developable type.

EXAMPLE 1 A light-sensitive photographic silver bromide emulsion of the light-developable type, i.e. that mainly forms an internal latent image and only to a little extent an external latent image is prepared by conversion of a silver chloride emulsion into a silver bromide emulsion. Said silver bromide emulsion is prepared so that an amount of silver bromide equivalent to g. (0.7 mole) of silver nitrate is present per kg. of emulsion. The usual emulsion ingredients and coating aids are incorporated into the emulsion, and in addition thereto an orthochromatic sensitizing agent, and 8 g. of cadmium bromide per kg. of emulsion for reducing the background density.

The emulsion obtained is divided into many different emulsion samples. To these samples are added the additives accoring to the invention as listed in the table hereinafter. The halogen-acceptor is added in an amount of 40 ccs. of a 1% by weight solution in a suitable solvent per kg. of emulsion whereas the compound setting free iodide ions, in this particular case potassium iodide, is added in an amount of 10 ccs. of a 4% by weight aqueous solution per kg. of emulsion.

All emulsion samples obtained are coated on conventional photographic paper supports such that an amount of silver halide equivalent to 4 g. of silver nitrate is present per sq. m. of light-sensitive material.

All light-sensitive materials obtained are subjected to the following identical successive treatments:

1) They are exposed in a flash-sensitometer Mark VI of Edgerton, Germeshausen and Grier for 10' sec. through a step wedge with a constant of 0.3.

TABLE Number Material Additive AD of steps 1 None 12 6 KI alone 0 32 6 Compound 1 alone 0 28 6 4 Compound 1+KI 0 39 7 5 Compound 2 alone 0. 26 7 6 Compound 2+KI 0.86 7

As can be seen from the results listed in the above table the materials comprising potassium iodide or halogenacceptor alone show less difference between the image and background densities than the materials comprising both potassium iodide and halogen-acceptor; thus the contrast between image and non-image areas is enhanced.

EXAMPLE 2 A light-sensitive photographic silver bromide emulsion of the light-developable type is prepared as described in Example 1. The emulsion obtained is now divided into 3 samples A, B and C. To emulsion samples B and C is added per kg. of emulsion as anti-fogging agent 5 ccs. and ccs. respectively of a 5% by weight solution in ethanol of 1-phenyl-2-tetrazoline-5-thione. To sample A no antifogging agent is added.

Before coating in the way as described in Example 1 each emulsion sample on a conventional photographic paper support 10 ccs. of a 2.5% by weight solution of 6,6 dimethyl-3-thio-1,6-dihydro-as-triazine-3,5-(2H,4H)- dione in ethylene glycol monomethyl ether and 10 ccs. of a 4% by weight aqueous solution of potassium iodide are added per kg. of emulsion.

Each of the 3 materials obtained is exposed to high intensity-radiation as described in Example 1, and photodeveloped by exposure for min. to ordinary office fluorescent light with a total light intensity of 240 Lux.

Immediately thereafter the samples are developed at 20 C. for 1 /2 min. in an internal developer with the following composition:

Hydroquinone-6 g. Monomethyl-p-aminophenol sulphate-3 g. Sodium sulphite (anhydrous)30 g. Potassium bromide-2.5 g.

Sodium carbonate (anhydrous)50 g. Sodium thiophosphate (cryst.)-1O g. Water to 1000 ccs.

The samples are then fixed, rinsed and dried in the usual way.

After development the image densities and background densities of each of the materials are determined and listed in the following table.

TABLE Maximum Minimum Sample density density AD A 1. 23 1. 16 0. ()3 B 1. 20 0. 98 0. 27 C 0. 63 0. 30 0. 32

12 EXAMPLE 3 4 light-sensitive photographic silver bromide materials of the light-developable type are prepared as described in Example 1, however, without cadmium bromide and with additives according to the invention as listed in the table hereinafter. The mentioned concentrations of these additives are per kg. of emulsion ready for being coated.

All light-sensitive materials thus obtained are exposed and photo-developed for 15 min. as described in Example 1. The maximum and minimum densities are measured in a MacBeth reflection densitometer. The AD values too have been listed.

Max. Min. Material Additive dens. dens. AD

1 0. 42 0. 26 0. 16 2 12.5 cos. of a solution of 1 g. 0.69 0.39 0.30

of compound 1 in 100 ccs. of ethylene glycol monomethyl ether. 3 100 g. of silver iodide sol 0. 0. 48 0.37

prepared as described herein. 4 Both said additives of the 0. 82 0. 40 0. 42

materials 2 and 3 together.

As can be seen from the above results, the materials mto WhlCh halogen-acceptor or silver iodlde sol alone has been incorporated show less difference between the image and background densities than the materials to which both halogen acceptor and silver iodide sol have been added. Thus, the contrast between image and nonimage areas has been enhanced.

We claim:

1. Photographic element comprising a radiationsensitive silver halide emulsion layer of the lightdevelopable type, applied from a coating composition, to which are added (1) at least one member selected from a silver iodide sol and a compound setting free iodide ions, and

(2) at least one halogen acceptor corresponding to the following general formula or to a tautomeric structure thereof:

wherein each of R R R R and R is hydrogen, an alkyl group or an aryl group, with the proviso, however, that at least one of the substituents R and R is hydrogen; R and R may also be the atoms necessary to complete a carbocyclic ring.

2. Photographic element according to claim 1, wherein said compound setting free iodide ions is an organic or a water-soluble inorganic iodide.

3. Photographic element according to claim 2, wherein said water-soluble inorganic iodide is potassium iodide.

4. Photographic element according to claim 1, wherein the silver iodide of the sol and/or the compound setting free iodide ions is (are) present in an amount of from 0.1 to 5 g. per mole of silver halide. 9

5. Photographic element according to claim 1, wherein the halogen-acceptor corresponding to the general formula:

t. wherein each of R R R R and R is hydrogen, an alkyl group or an aryl group, with the proviso, however,

13 that at least one of the substituents R and R is hydrogen; R and R may also be the atoms necessary to complete a carbocyclic ring, is present in an amount of from 0.1 to 5 g. per mole of silver halide.

6. Photographic element according to claim 1, wherein said emulsion layer is essentially a silver bromide emulsion layer.

7. Photographic element according to claim 1, wherein said emulsion layer also comprises a cadmium and/or a lead salt.

8. Photographic element according to claim 7, wherein said salt is added in an amount comprised between 5 g. and g. per mole of silver halide.

9. Photographic element according to claim 1, wherein said emulsion layer also comprises a thiocyanate.

10. Photographic element according to claim 9, wherein said thiocyanate is potassium thiocyanate.

11. Photographic element according to claim 1, wherein said emulsion layer also comprises an anti-fogging agent.

12. Photographic element according to claim 11, wherein said anti-fogging agent is 1-phenyl-2-tetrazoline-5- thione.

13. Photographic element according to claim 1, wherein said emulsion layer also comprises an optical sensitising agent.

14. Photographic element according to claim 1,.wherein the member selected from a silver iodide sol and a compound setting free iodide ions is added to the radiationsensitive coating composition just before coating.

15. Photographic element according to claim 1, wherein the halogen-acceptor corresponding to the general formula:

wherein each of R R R R and R is hydrogen, an alkyl group or an aryl group, with the proviso, however, that at least one of the substituents R and R is hydrogen; R and R may also be the atoms necessary to complete a carbocyclic ring, is added to the radiation-sensitive coating composition just before coating.

16. Photographic element comprising a radiationsensitive silver halide emulsion layer of the lightdevelopable type, the silver halide grains of which contain silver iodide at their surface, wherein said emulsion layer contains at least one halogen-acceptor corresponding to the following general formula or to a tautomeric structure thereof:

17. Process for recording traces or images comprising exposing to a high intensity actinic radiation a photographic element according to claim 1, and light-developing the latent image formed by said initial exposure by overall exposing said element to a radiation of lower intensity.

18. Process according to claim 17, wherein an internal development step and a fixing step are included before, during or shortly after said light-development.

19. Process according to claim 18, wherein the development step takes place in the presence of an anti-fogging agent.

20. Process according to claim 19, wherein said antifogging agent is 1-phenyl-2-tetrazoline-5-thione.

21. Process according to claim 17, wherein said lightdevelopment is carried out while applying heat.

22. Process according to claim 21, wherein said heat is supplied by running the element over a hot plate heated at -180 C.

References Cited UNITED STATES PATENTS 3,260,605 7/1966 Sutherns 96107 3,287,137 11/1966 McBride 96107 3,367,780 2/1968 Fix et al. 96-l02 NORMAN G. TORCHIN, Primary Examiner ALFONSO T. SURO PICO, Assistant Examiner US. Cl. X.R. 9666.5, 107