US3508921A - Light-developable photographic material and recording process - Google Patents

Description

United States Patent O 3,508,921 LIGHT-DEVELOPABLE PHOTOGRAPHIC MATE- RIAL AND RECORDING PROCESS Paul Desire van Pee, Edegem, and Jozef Frans Willems,

Wilrijk-Antwerp, Belgium, assignors to Gevaert-Agfa N.V., Mortsel, Belgium, a Belgium company No Drawing. Filed Oct. 11, 1966, Ser. No. 585,733 Claims priority, application Great Britain, Oct. 11, 1965, 42,373/ 65 Int. Cl. G03c /32 US. Cl. 9645.2 22 Claims ABSTRACT OF THE DISCLOSURE Photographic elements are described which comprise a radiation-sensitive silver halide emulsion layer of the lightdevelopable type applied from a coating composition containing (1) a silver iodide sol and/or a compound which will release iodide ions, and (2) at least one halogen acceptor corresponding to the following general formula wherein:

each of R R R and R is hydrogen, an alkyl radical or an aryl radical, or

R and R and/ or R and R together are the atoms necessary to close a heterocyclic ring, and

n is an integer from 1 to 4.

The photographic element has application in light-development recording 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 utilized to form a latent image, by an additional exposure to a radiation of lower intensity such as diffuse daylight or artificial light. The secondary enclosure, 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).

Many of the known light-developable, radiation-sensitive materials have the disadvantage that on latensification the image becomes very slowly visible, that the background tends to darken fast and that the maximum density of the image decreases on a prolonged secondary exposure.

It has now been found that the addition of at least one 3,508,921 Patented Apr. 28, 1970 member selected from a silver iodide sol and a compound that sets free iodide ions together with at least one halogen-acceptor corresponding to the following general formula:

each of R R R and R represents a hydrogen atom, an alkyl radical including a substituted alkyl radical, an aralkyl radical and a substituted aralkyl radical, or an aryl radical including a substituted aryl radical, or

R and R and/ or R and R together represent the atoms necessary to close a heterocyclic ring including a substituted heterocyclic ring, and

n is an integer from 1 to 4,

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 oif 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 difference between the maximum and minimum density is considerably lower than when both groups are present together. This additive eifect 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 present 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 background darkens slowly, however, the contrast between image and background will remain for many hours. The images or traces will not remain visible when permanently exposed to light. To keep a permanent record of the traces or images, the material has to be chemically developed and fixed, preferably not too long after the light-development. Without said development and fixing step, the record will remain permanently only when the lightdeveloped images are exposed to light infrequently and kept in the dark when not in use. Indeed, the image will last practically indefinite if protected from prolonged exposure to strong light.

Another advantage oifered by the light-developable elements of the invention is that it is possible to carry out the light-development while supplying heat, whereby the recorded image becomes almost immediately visible for the reason that, when heating, it is possible to increase the light-intensity of the secondary exposure without producing fog. A probable explanation of this phenomenon has been given by Jacobs, Phot. Sci. & Eng, vol. 5, No. 1, 1961. By the fact that when operating at elevated temperature a more rapid image access is obtained, it is not necessary in those instances where there is recorded at high writing speeds and thus at high paper transport speeds, to expose considerable meters of paper to ambient light at the same time, which would lead to a handling problem. Some oscillographs operate according to this principle: after the high-intensity exposure the print-out material is passed over a heated plate While being exposed to fluorescent U.V. lamps so that a visible image is produced almost immediately.

The following is a non-restrictive list of halogen acceptors, which have proved to be particularly suitable for use according to the present invention, and which correspond to the above general formula:

(1 Bis-(dimethyl-thiocarbamoyl) -sulphide ao g (2) Bispiperidino-thiocarbonyl)-su1phide CH2C H2 CH2C H2 NC-SCN CH2 (3 Bis- (dimethyl-thiocarbarnoyl) -disulphide Q- -tt- Q S S (7) Bis- (piperidino-thiocarbonyl)-disulphide CHzCH2 CH2C H2 HzC \CH2-C2 S S (8) Bis- (ethyl-phenyl-thiocarbarnoyl) -tetrasulphide CHz-CH GHz-GHa (9) Bispiperidino-thiocarbonyl) -tetrasulphite CHr-CHz CHz-G H2 H2O NCS--SSSON CH2 CH2C2 CHzOI z i l The amount of halogen acceptor according to the above general formula that is incorporated into the silver halide 75 4 emulsion layer according to the present invention 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 acceptors corresponding to the above general formula may also be used 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 application entitled Light-Developable Photographic Material and Recording Process filed on even date herewith.

Suitable compounds setting free iodide ions are among others inorganic and organic iodides, organic compounds with labile iodine atom an oniurn 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:

l-methyl-8-hydroxy-quinolinium iodide 1-methyl-2-iodo-quinolinium iodide 1,2,3,4-tetrahydro 8 hydroxy-l,l-dimethyl-quinolinium QLCHPQ Q benzyltriphenylphosphonium iodide H3 0 CH3 S-S-bis-(dimethyl)-hexamethyleen 1,6 disulphonium iodide C O CH ICIz" trimethyl(o-methoxycarbonyl-anilinium) dichloroiodate 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 the silver halide emulsion. A very suitable silver iodide sol can be prepared by slowly adding while strongly stirring the following solution A to the following solution B, both solutions being heated to 35 C.

Solution A 3 N AgNO -l7 ccs. Water up to 1 litre Solution B 3 N KI-l7 ccs. Gelatin 40 g.

Water up to 1 litre The amount of compound setting free iodide ions may also vary within very wide limits. In general an amount from about 0.01 g. to about 20 g., preferably from about 0.1 g. to about g. per mole of silver halide is applied. The same applies to the limits within which the silver iodide sol is used. In the latter case the above amounts relate to the silver iodide and not to the total sol. The addition 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 solvent, 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 halide 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 developer, such as:

p-Hydroxyphenyl glycine-40 g. Sodium carbonate (cryst.) 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:

Hydroquinone-15 g.

Monomethyl-p-aminophenol sulphatel.5 g.

Sodium sulphite (anhydrous)-50 g.

Potassium bromide-10 g.

Sodium hydroxide-J5 g.

Sodium thiosulphate (cryst.)-2O 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 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 sensitizers 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. Further, more specific ingredients may be incorporated also. Among these may be mentioned more particularly:

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

Compounds or mixtures of compounds reducing the background density on latensification, e.g., lead salts, and preferably 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 sq. m. of support.

Suitable supports 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, poly(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 utilized.

In order to form an image in the light-developable radiation-sensitive photographic elements according 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 length, 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 ofi'lce 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 advantageous, 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 solubilizing 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 anti-fogging 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 antifogging agents are Z-mercapto-ethyl-carbanilate, l-phenyl- 2-tetrazoline-5-thione and 4,5,6,7-tetrabromo-lH-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 addi tives according to the invention as listed in the table hereinafter. The halogen-acceptor is added in an amount of 40 cos. 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 cos. 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 fiash-sensitometer Mark VI of Edgerton, Germeshausen and Grier for 10- sec. through a step wedge with a constant of 0.3.

(2) The exposed materials are photo-developed for 15 min. by exposure to ordinary office fluorescent lights with a total light intensity of 240 Lux whereupon the density of the image-areas and non-image areas are measured in a MacBeth reflection densitometer. The difference between the maximum and minimum density AD of all materials is listed in the table hereinafter.

(3) In order to determine the stability of the image, the difference between the maximum and minimum density AD is measured again after latensification in analogous circumstances as in (2) but for 10 hours.

9 This difierence AD of all materials is also listed in the table hereinafter.

TABLE Material Additive AD AD 1 None 0. 12 0. 09 2. KI alone O. 36 0.20 3- s- Compound 1 alone- 0. 29 0.19 4 Compoundl +KI.-- 0.43 0.23 0. 33 0. 18

Compound 9 +KI. 0. 40 0. 24

Example 2 The process of Example 1 is repeated with the difference that as compounds setting free iodide ions and as halogen-acceptors according to the above general formula are used the compounds listed in the table hereinafter. Only the AD values after 15 min. of photodevelopment have been measured. In the last column of the table are listed the number of steps of the wedge that are recorded. This number is a measure of the relative sensitivity of the different radiation-sensitive photo-developable materials.

Number Material Additive AD of steps 0. l2 6 0. 29 6 3 Mono-iodo acetic acid 0. 3O 6 4 Compound 1+mono-iodo acetic 0.39 7

ac 5 3,5-dimorpholino-di-thiolium 0. 28 6 iodide. 6 Compound l+3,5-di morpholino- 0. 36 7 di-thiolium iodide.

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

Example 3 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 15 ccs. respectively of a 5% by weight solution in ethanol of l-phenyl-Z-tetrazoline-S-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 40 ccs. of a 1% by weight solution of bis-(dimethylthio-carbamoyl)-sulphide in ethylene glycol monomethyl ether and 10 ccs. of a 4% by weight aqueous solution of potassium iodide are added per kg. of emulslon.

Each of the 3 materials obtained is exposed to high intensity-radiation as described in Example 1, and photodeveloped by exposure for 20 min. to ordinary ofiice 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:

Hydroquin0ne6 g. Monomethyl-p-aminophenol sulphate3 g. Sodium sulphite (anhydrous)30 g. Potassium bromide-2.5 g.

Sodium carbonate (anhydrous)-50 g. Sodium thiosulphate (cryst.)10 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.

Sample Maximum density Minimum density AD A 1.31 1. 17 0. 14 B 1. 28 1. 05 0. 23 C 1. 23 0. 0. 28

From this table it appears that by the addition of an anti-fogging agent the maximum and minimum densities both decrease, the background-density, however, decreasing more markedly than the image-density. Thus, the

difference between maximum and minimum density, i.e. the net density, increases when an anti-fogging agent is added.

Example 4 Max. Min. Material Additive dens. dens. AD

1 O. 42 0. 26 0. 16 2 35 cos. of solution of 1 g. of 0. 65 0. 34 0. 31

compound 1 in ccs. of

ethylene glycol monomethyl ether. 3 100 g. of silver iodide sol pre- 0. 80 0. 43 0. 37

pared as described herein. 4 Both said additives oi the 0. 82 0. 40 0. 42

materials 2 and 3 together.

As can be seen from the above results, the materials into which halogen-acceptor or silver iodide 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 radiation-sensitive silver halide emulsion layer of the light-developable type, applied from a coating composition containing in addition to said silver halide emulsion 1) a silver iodide sol and/or a compound which will release iodide ions, and

(2) at least one halogen acceptor corresponding to the following general formula:

1 1 wherein:

each of R R R and R is hydrogen, an alkyl radical or an aryl radical, or

R and R and/or R and R together are the atoms necessary to close a heterocyclic ring, and

n is an integer from 1 to 4.

2. Photographic element according to claim 1, wherein said compound which releases 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 present in an amount of from 0.1 to S g. per mole of silver halide.

5. Photographic element according to claim 1, wherein the halogen-acceptor 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 cadmium bromide.

9. Photographic element according to claim 7, wherein said salt is present in an amount of from about 5 g. and 15 g. per mole of silver halide.

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

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

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

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

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

15. Photographic element according to claim 1, wherein the halogen-acceptor is added to the radiation-sensitive coating composition just before coating.

16. Photographic element comprising a radiation-sensitive silver halide emulsion layer of the light-developable type, the silver halide grains of which comprise silver iodide at their surface, said emulsion layer containing at least one halogen-acceptor corresponding to the following general formula:

wherein:

each of R R R and R is hydrogen, an alkyl radical or an aryl radical, or

R and R and/or R and R together are the atoms necessary to close a heterocyclic ring, and

n is an integer from 1 to 4.

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 exposure of 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 antifogging 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 3,226,232 12/1965 Dersch et a1. 96l07 X 3,287,137 11/1966 McBride 96-l07 NORMAN G. TORCHIN, Primary Examiner A. T. SURO PICO, Assistant Examiner US. Cl. X.R. 96107