US3749912A

US3749912A - Silver complex diffusion transfer process

Info

Publication number: US3749912A
Application number: US00168749A
Authority: US
Inventors: Haes L De
Original assignee: Agfa Gevaert AG
Current assignee: Agfa Gevaert NV; Agfa Gevaert AG
Priority date: 1968-03-20
Filing date: 1971-08-03
Publication date: 1973-07-31
Anticipated expiration: 1990-07-31

Abstract

A continuous tone transparency is produced from X-ray or radioactive radiation by means of the silver complex diffusion transfer process by exposing a light-sensitive material carrying a silver halide emulsion layer to a beam of such X-rays or radiation, treating the exposed layer with a photographic developing compound for 3-30 seconds with an aqueous developing solution having a pH between 10.5 and 11.5 at a temperature between 25* and 35*C, bringing the light-sensitive material in the presence of a silver halide complexing agent into contact with image-receiving material including a transparent hydrophobic film support and an image-receiving layer containing development nuclei for the complexed silver halide, maintaining the two materials in contact for a period of 10-60 seconds while at a temperature between 30* and 60*C, and finally separating the materials from one another. The exposure can be made directly to the beam of X-rays or radiation or, alternatively, a fluorescent intensifying screen can be associated with the light-sensitive material whereby a visible image is first formed in such screen by exposure to the X-rays or radiation and the light-sensitive material is exposed from such visible image.

Description

lluite States atet 1 De lilacs [451 .luly 31, B973 1 SILVER COMPLEX DIFFUSION TRANSFER PROCESS [75] Inventor: Louis Maria De Haes, Edegem,

Belgium [73] Assignee: Ag1a-GevaertN.V., Mortsel,

Belgium [22] Filed: Aug. 3, 1971 [21] Appl. No.: 168,749

Related US. Application Data [63] Continuation of Ser. No. 714,467, March 20, 1968,

abandoned.

[52] 11.8. Cl. 250/65 F, 96/29 R, 96/82, 96/76 R [51] Int. Cl. G01n 21/34 [58] Field of Search 96/29, 76; 252/62.l; 250/65 [56] References Cited UNITED STATES PATENTS 2,887,379 /1959 Blake.... 96/82 3,185,841 5/1965 Land..." 250/65 2,765,240 /1956 Land..... 117/34 3,351,466 11/1967 Land 96/29 OTHER PUBLICATIONS Larmore Introduction to Photographic Principles Prentice1-1all 1958 page 112-119 Primary Examiner-Norman G. Torchin Assistant Examiner.lohn L. Goodrow Attorney-William J. Daniel [57] ABSTRACT A continuous tone transparency is produced from X-ray or radio-active radiation by means of the silver complex diffusion transfer process by exposing a lightsensitive material carrying a silver halide emulsion layer to a beam of such X-rays or radiation, treating the exposed layer with a photographic developing compound for 330 seconds with an aqueous developing solution having a pH between 10.5 and 11.5 at a temperature between and C, bringing the lightsensitive material in the presence of a silver halide complexing agent into contact with image-receiving material including a transparent hydrophobic film support and an image-receiving layer containing development nuclei for the complexed silver halide, maintaining the two materials in contact for a period of 10-60 seconds while at a temperature between 30 and C, and finally separating the materials from one another. The exposure can be made directly to the beam of X- rays or radiation or, alternatively, a fluorescent intensifying screen can be associated with the light-sensitive material whereby a visible image is first formed in such screen by exposure to the X-rays or radiation and the light-sensitive material is exposed from such visible image 5 Claims, No Drawings SILVER COMPLEX DIFFUSION TRANSFER PROCESS This is a continuation of Ser. No. 714,467, filed Mar. 20, 1968, now abandoned.

It is an object of the present invention to provide a method for quickly producing, according to silver complex diffusion transfer process, a continuous tone transparency of an object exposed to a beam of X-rays or of a radio-active radiation. The darkest parts of the transparency thus obtained correspond with those parts of the object which absorb the radiation beam in the strongest way. Consequently, the transparency may be considered as a positive copy of the object to be reproduced.

Another object of the present invention is to provide a method for obtaining such continuous tone transparencies with a high maximal density and a neutral image tone.

A further object of the present invention is to provide a method for obtaining such continuous tone transparencies which can be considered as being dry for all practical purposes immediately after the diffusion transfer image has been formed and the light-sensitive and the image-receiving materials have been separated from eaCh other.

Still another object of the present invention is to provide a method for obtaining two of such continuous tone transparencies at the same time and from a single object-wise exposed light-sensitive material.

Further objects of the present invention will in part be obvious and in part appear hereinafter.

The method of the invention comprises the consecutive steps of exposing an object to be reproduced to a beam of X-rays or of a radio-active radiation, recording the objectwise modified beam either directly or indirectly on a light-sensitive photographic material comprising a silver halide emulsion layer, treating the lightsensitive material carrying the recorded latent image in the presence ofa developing compound for 3 to 30 seconds with an aqueous alkaline processing composition having a pH between 10.5 and 11.5 and a temperature between 25 and 35C, bringing the light-sensitive material in the presence of a complexing agent for the silver halide into contact with an image-receiving material comprising a transparent hydrophobic film support provided with an image-receiving layer comprising a substance or substances in order to form a silver containing image from the diffusing complexed silver halide, keeping the light-sensitive material and the imagereceiving material for to 60 seconds in contact with each other whilst being heated between 30 and 60C, and finally separating both the light-sensitive material and the image-receiving material from each other.

By proceeding in this way, it is possible to obtain in a very short time, mostly comprised between about 30 seconds and about 3 minutes, an excellent and positive continuous tone transparency of an object exposed to a beam of X-rays or of a radioactive radiation. The method of the present invention possesses the further advantage that no extensive but rather only a compact processing unit is necessary and that the copies obtained are dry whereby they can be stored immediately without first drying them. Consequently, the method of the present invention is particularly suitable for being applied in cases wherein quick information of an X-ray or a radioactive radiation examination is necessary, and this quick information often has to be obtained in little ideal working circumstances such as e.g. during a chirurgical intervention, in war circumstances, in accident rooms to quickly determine the seriousness of a wounding, in industrial applications for tracing defects, and so on.

The light-sensitive silver halide emulsion for use in the method of the present invention is preferably a high sensitive emulsion layer. Silver bromide emulsion layers which contain minor amounts of silver iodide are particularly suitable. The desirable high sensitivity of the light-sensitive layer can be obtained in the usual way by physical and chemical ripening of the silver halide emulsion. The light-sensitive material can also spectrally be sensitized, especially when it is intended to record indirectly the object-wise modified radiation beam. Thus, in case of screen image photography, it should mostly be sensitized ortho-chromatically.

The object-wise modified radiation beam may be recorded directly by the light-sensitive material, but mostly is recorded indirectly.

This indirect recording may occur by first converting the oject-wise modified radiation beam into a visible screen image which will be recorded on the lightsensitive material, in other words by the so-called screen image photography.

Preferably, however, the object-wise modified radiation beam is substantially indirectly recorded in that it is for the greater part detected by one or more fluorescent or luminescent intensifying or reinforcing screens in contact with the light-sensitive material and the fluorescent or luminescent image thus produced is recorded in the silver halide emulsion layer in addition to the part of the radiation beam that has been directly recorded. The sensitivity attained by processing the silver halide emulsion layer thus exposed according to the method of the present invention may be from two to five times as high as that attained by producing a negative image of the object by normal negative development. The said gain in sensitivity is evidently of great importance in that it enables a corresponding reduction of the dosage radiation on the object. Especially in medicine, where said objects are human beings, it is very important that said dosage be as small as possible. According to the present invention, the highest sensitivity is attained by using two screens, one at either side of a light-sensitive material with a transparent support.

All the usual and generally known fluorescent or luminescent intensifying screens are suited for being used according to the latter embodiment of the present invention. As a matter of fact, the screen should be chosen according to the characteristics of the lightsensitive material. A fluorescent or-luminescent intensifying screen can also be built in the light-sensitive material by incorporating adapted fluorescent or luminescent substances into at least one layer. This layer may be the emulsion layer itself. It is also possible to incorporate said substances into the support of the lightsensitive material. Frequently used and particularly suitable fluorescent or luminescent screens are among others calcium tungstate screens, barium tungstate screens, zinc sulphide screens and leadand barium sulphate screens.

By proceeding according to this embodiment with at least one fluorescent or luminescent intensifying screen in contact with the light-sensitive material, the silver halide content of the light-sensitive emulsion layer need not be quite high. An amount per sq.m equivalent to l to 5 g of silver nitrate suffices in general. This is a further advantage over the above described method for producing a negative image of the object in a lightsensitive silver halide material wherein the latter should contain per sq.m. mostly an amount of silver halide equivalent to about to about 45 g of silver nitrate.

When the object-wise modified beam is indirectly recorded, the sensitivity attained by proceeding according to the present method in most cases can still be improved by incorporating a light-reflecting compound, such as a white pigment, e.g., titanium dioxide and barium sulphate, into at least one layer of the lightsensitive material, including the support, situated at the side of the silver halide emulsion layer opposite to that of the screen.

If it is a fluorescent or luminescent image including a screen image which is recorded by the light-sensitive material, it is also possible according to the present invention to produce at the same time two diffusion transfer prints from one and the same object-wise exposed light-sensitive material, on condition that the latter is provided with a light-sensitive layer on both sides of a transparent support. Later on an image-receiving material is pressed under about identical circumstances against either of both sides of the light-sensitive material so that after separation two diffusion transfer copies of about the same quality are obtained.

Except in the case of screen image photography, the light-sensitive material is in most cases comprised in a usual cassette during the recording of the object-wise modified beam on the light-sensitive material in the first processing step of the method of the present invention. This is generally known to those skilled in the art. Variants are also possible. Thus, the light-sensitive material can be contained in an evelope of a non-alkaliresistant synthetic product, for instance cellulose phthalate, which does not allow the visible light to pass through but does allow X-rays and radio-active rays to pass through. In this way, the light-sensitive material can be stored and exposed to the objectwise modified beam in day-light. ln contact with the aqueous alkaline composition for carrying out the diffusion transfer image formation, the envelope of synthetic product desintegrates and the light-sensitive material is set free so that it can be processed.

The support of the light-sensitive material for use in the method of the present invention may be any suitable and usual support, such as a paper support, or a hydrophobic transparent support of a synthetic product, such as a cellulose triacetate support, a polyester support, preferably a biaxially stretched polyethylene terephthalate support, further a polystyrene support and so on. A transparent support, however, is preferred and is even necessary for some embodiments such as the one for obtaining simultaneously two diffusion transfer copies from a single light-sensitive material and the one according to which also at the backside of the light-sensitive photographic material a fluorescent intensifying screen is used. The support can first be provided with one or more adhesive layers before the light-sensitive silver halide emulsion layer which in most cases is a gelatino silver halide emulsion layer, is applied thereto. As the case may be, still one or more other layers may be applied before the emulsion layer is coated. The light-sensitive material can also be provided with a layer of a water-permeable hydrophilic colloid on top of the silver halide emulsion layer. Ap-

plying such a top layer is generally known in the art of diffusion transfer. In this connection, we can refer to the United Kingdom Patent Specifications 1,052,022 filed Aug. 2, 1963, 1,054,252 filed Aug. 6, 1963, to the published Dutch Patent Application 281,744 filed Aug. 3, 1962 and to the United Kingdom Patent Specification 1,055,711 filed Jan. 30, 1964 all by Gevaert Photo-Producten N.V. Besides the usual emulsion ingredients, such as plasticizers, hardeners, emulsifying agents etc., the light-sensitive silver halide emulsion layer and/or at least one water-permeable layer in effective contact with the emulsion layer can also contain ingredients which are necessary or of great importance for the primary and/or the difiusion transfer image formation such as developing substances, among others those listed hereinafter, toning agents, especially those listed further in the description, compounds which counteract the silver sludge deposition (antisludge agents) in the aqueous alkaline treating composition, etc.

For suitable compounds which counteract the silver sludge deposition in the aqueous alkaline processing composition, we can refer among other to the German Patent Specification 962,767 filed June 16, 1954 by Agfa AG, the US. Pat. No. 3,240,603 issued Mar. 15, 1966 of Horst Schiller, Herbert Grabhofer and Hans Ulrich, the Belgian Patent Specification 677,090 filed Feb. 28, 1966 by Gevaert-Agfa N.V., the United Kingdom Patent Specifications 940,169, 959,182 and 959,661 all filed July 27, 1961 by Agfa AG and the published Dutch Patent Applications 66,14290 filed Oct. 11, 1966, and 67,02133 filed Feb. 13, 1967 both by Gevaert-Agfa N.V. A particularly suitable antisludge agent is 3-heptadecyl-4-m-f1uorosulphonylphenyl-ureido-A -l ,2,4-triazolin-5-thione.

The processing step which follows after the recording of the latent image in the light-sensitive material is rather critical and the given limits should be considered very accurately in order to reach a high sensitivity for the method according to the present invention and at the same time to obtain quickly a positive continuous tone transparency of an optimal quality. These are the most important objects of the present invention. By an optimal continuous tone transparency is understood a transparency with a sufficient maximum density, a soft gradation and a neutral image tone.

This next processing step comprises, as indicated in the statement of invention, the treatment for 3 to 30 seconds of the light-sensitive material carrying the recorded latent image in the presence of a developing compound with an aqueous alkaline treating composition, which has a pH comprised between 10.5 and 1 1.5 and a temperature comprised between 24 and 35C. The pH is preferably comprised between 10.9 and l 1.3 and the temperature between 28 and 32C. In order to obtain continuous tone transparencies of the same quality, it is of importance that the pH and the temperature of the aqueous alkaline processing composition and the period wherein the light-sensitive photographic silver halide material is wetted with this aqueous alkaline composition, be kept as constant as possible.

This processing step can be carried out in different ways, for instance by dipping the light-sensitive material into said aqueous alkaline composition, by conducting it at a constant speed through said composition contained in a usual apparatus, or by wetting the sole emulsion side of the light-sensitive material with said composition by means of a kiss roller. In order to obtain a uniform diffusion transfer copy, it is of importance that the aqueous alkaline processing composition acts for about the same time upon each part of the light-sensitive material.

The aqueous processing composition contains alkaline substances necessary to bring the pH at the desired value. The usual alkaline substances are sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate and trisodium phosphate.

The developing compounds necessary for the development of the light-sensitive material and also for the diffusion transfer image formation may be present in at least one member of the light-sensitive material, the image-receiving material and the alkaline processing composition, but are preferably at least partly present in the latter. As regards the incorporation of developing substances into the materials used (light-sensitive and image-receiving material), we can refer to the United Kingdom Patent Specification 1,012,476 filed Dec. 18, 1961 by Gevaert Photo-Producten N.V. and to the published Dutch Patent Applications 279,797 filed June 15, 1962 and 281,744 filed Aug. 3, 1962 both by Gevaert Photo-producten N.V., Photo- Producten the United Kingdom Patent Specifications 1,057,273 filed Feb. 3, 1964 by Gevaert Photo- Producten N.V. and 1,086,510 filed Dec. 16, 1964 by Gevaert-Agfa N.V. and to the Belgian Patent Specification 641,298 filed Dec. 16, 1963 by Gevaert Photo- Producten N.V.

Particularly suitable developing substances for use in the method of the present invention are hydroquinone, 1-phenyl-3-pyrazolidinone and derivatives, paminophenol, pyrocathechol, p-amino-o-cresol, pamino-m-cresol, p-mono-methyl-aminophenol sulphate, p-dimethylaminophenol sulphate, pyrogallol and 2,4-diamino-phenol. Mostly two or more developing substances are used together. Particularly favourable results can be attained by using together hydroquinone and l-phenyl-3-pyrazolidinone or a derivative thereof in the aqueous alkaline processing composition, as the case may be together with p-monomethylaminophenol sulphate. The preferred concentration of these developing substances per liter of aqueous alkaline treating composition is of about 9 to about 32 g of hydroquinone, of about 0.2 to about 5 g of l-phenyl-3- pyrazolidinone or a derivative therof, and of 0 to about 10 g of p-monomethylaminophenol sulphate.

The aqueous composition comprises in most cases still other usual ingredients such as conservatives for the developing substances, compounds liberating halide ions such as potassium bromide, compounds for improving the soft gradation in the low densities of the diffusion transfer copy such as polyvinylpyrrolidone, anti-sludge agents such as those identified above, toning agents for the diffusion transfer image, preferably those given hereinafter, and complexing agents for the non-developed silver halide. Suitable complexing agents are among others ammonium thiosulphate and sodium thiosulphate. These two complexing agents are often used together. The anti-sludge agents are preferably supplied by the aqueous alkaline processing composition, although in many cases they can be present with favourable result in the light-sensitive material as already stated above. In the processing composition they are in most cases supplied in concentrations of 20 to 400 mg per litre, preferably in concentrations of to 250 mg per litre.

After the light-sensitive material has been treated with the aqueous alkaline composition as described above, it is brought into contact with an imagereceiving material in the presence of a complexing agent for non-developed silver halide. This imagereceiving material is preferably dry at the moment that it is brought into contact with the light-sensitive material, but it can also be wetted previously, e.g. with the same aqueous alkaline processing composition with which the light-sensitive material was wetted. This wetting of the image-receiving material can occur by conducting the image-receiving material according to the usual and generally known method together with the light-sensitive material through the treating composition or by wetting herewith the image-receiving side of the image-receiving material by means of a kiss roller. The complexing agent for silver halide can be present in the aqueous alkaline processing composition, as already described, and/or in the receiving material as will be described hereinafter.

It is also possible to have present the image-receiving layer on top of the light-sensitive silver halide emulsion layer on a same transparent support, if necessary with a suitable separating layer between them. Hereby the steps of treating the light-sensitive material with the alkaline processing composition and of bringing it into contact with the image-receiving material become reduced to a single step of treating the multilayer material with an aqueous alkaline processing composition in the presence of a developing compound and a complexing agent for silver halide.

The image-receiving material for use in the method of the present invention comprises a transparent hydrophobic film support provided with an image-receiving layer that comprises a substance or substances in order to form a silver-containing image from the diffusing complexed silver halide.

The hydrophobic transparent film support can be a polyester preferably a biaxially stretched polyester support, e.g. of polyethylene terephthalate, a polybisphenol ester of an aliphatic and/or aromatic'dicarboxylic acid, a polyester of the polycarbonate type, etc.; it can also be prepared from a polymer of copolymer, such as polystyrene, copoly[vinyl chloride/vinyl acetate] or of a hydrophobic cellulose ester such as cellulose triacetate.

The image-receiving layer is applied in the usual thickness to the transparent film support, the latter mostly being provided with a subbing layer, from a dispersion of said substance or substances for the diffusion transfer image formation in an aqueous solution of a binder. Suitable binders are water-permeable hydrophilic colloids, such as gelatin and casein, occasionally mixed with a minor amount of a natural or snythetic product, such as gum arabic, carboxymethylcellulose sodium salt and sodium alginate. It is also possible to apply several image-receiving layers to each other.

The following so-called development nuclei and ingredients which can form development nuclei are particularly suited as substance or substances to form a silver-containing image from the diffusing complexed silver halide; the sulphides of heavy metals, e.g. of antimony, bismuth, cadmium, cobalt, lead, nickel, silver and zinc. Selenides, polysulphides, polyselenides, mercaptanes, tin(l1) halides, heavy metals or their salts and fogged silver halide are also suitable for this purpose. The complex salts of lead sulphide and zinc sulphide are effective either in themselves or mixed with thioacetamide, dithiobiuret and dithio-oxamide. The concentration wherein these nuclei or ingredients which form such nuclei are present in the image-receiving layer is in most cases situated between about 0.002 and about 0.2 g per 100 g of binding agent.

Besides the image-receiving layer, the imagereceiving material can contain still other waterpermeable layers such as a protective layer, a separating layer, etc. All these layers can occasionally be hardened in the usual way. The image-receiving material may contain in at least one of its water-permeable layers one or more compounds which take a part in the diffusion transfer image formation. In particular can be mentioned developing substances as those mentioned above, a complexing agent for non-developed silver halide, such as ammonium thiosulphate (which at the same time possesses a toning action), and sodium thiosulphate, as the case may be in an additional amount to the complexing agent already present in the aqueous alkaline processing composition, anti-oxidizing agents, alkali-consuming substances, dyestuffs, toning agents, preferably those given hereinafter, and anti-sludge agents, such as those referred to above. Incorporating the latter compounds into the image-receiving material, of course, has only sense if the image-receiving material is wetted with the alkaline processing composition before it is brought into contact with the lightsensitive material.

The presence of dyestuffs, especially yellow dyestuffs, in one of the water-permeable layers of the image-receiving material or in the mass of the transparent support itself is sometimes useful for giving the diffusion transfer copy obtained a more neutral appearance.

As regards the toning agents having the same function of making for a more neutral appearance of the diffusion transfer copy, it is to be noted that those for use in the method of the invention in most cases differ from the usual toning agents for use in the diffusion transfer process wherein the light-sensitive material is a less sensitive one, in most cases a silver chloride material Preferably the toning agents are present in the image-receiving material but they can also be applied successfully to the light-sensitive material and/or to the alkaline processing composition as already stated above, especially to the alkaline processing composition. In the image-receiving material the toning agents are in most cases applied in a concentration of about 20 to about 500 mg, preferably in a concentration of about 50 to about 150 mg per sq.m.

Hereinafter follows a list of toning agents with specific examples that have proved to be particularly suitable in the process according to the present invention. 1. Heterocyclic nitrogen-containing thioxo compounds, preferably of the imidazolidine-Z-thione type such as l-p tolyl-Q-imidnzolidino-l hionc,

H: O NH 1-allyl-2'imidazolidine-thionc of the thiazolidineor oxazolidine-Z-thione type such as O HgC-H C (I): S

Hz C NH 5-methyl-2-oxazolidine-thione,

methyl-di-[(2-thio-thiazolidin-3-yl )-methyl -amine, and

of the perhydro-l ,3-oxazine-2-thione type and the perhydro-l,3-thiazine-2-thione type, such as and of the tetrazoline-S-thione type, such as i w HN N 1-phenyl-2-tetraz0line-li-thione,

and

benzoxazoline-Q-thione,

, N/C Ha 1-(p-(limcthylamino-phenyl)-4,4,6-trimethyl-3,4-di-hydro-2-(1H)- pyrimidlne-thione,

a-pheuyl-5-1uetl1ylin1iuo-1,3,4-tMadiazolldjne-Z-thione,

2. Thiuram sulphides, such as bis(dimethyllhiocnrbamoyl) sulphide,

and xanthogenates, such as mtnssium-ethyl-xauthate 3. Bis-onium compounds, such as l,1'-ol hylmlc-bis-[pyridlnium chloride] l,1Hetmmotlnylene-bis-[pyridinlum chloride],

l,l-deeumethylene-bis-[pyridinium bromide] and amides, e.g.

the condensation product of 9 to 10 moles of ethylene oxide with nonylphenol 5. Compounds such as aeeto-acetanilide, and

There are also some developing substances which at the same time favourably influence the image tone of the diffusion transfer image, especially developing substances of the 0- or p-dihydroxybenzene type such as hydroquinone sulphonic acid sodium salt hydroquinone-thiosulphonic acid potassium salt,

[HOQ-O-c: 0-0113 hydroquinone monoaeetate,

and

C II:

p-tcrt-hutyl-pyrocatechol,

p-aininophenol and salts 4-amino-o-cresol and salts l S 03-N8 2-1utlroxy-S-monomethyl-aininobeuzene-sulphonic acid sodium salt p-beuzylaminoplienol hydrochloride,

3-(p-liydroxyanilino)-propi0nitrilo,

2-amino-res0rcinol hydrochloride, an (1 Calls l-thyl-G-hydroxy-l.2,3-1-tetrahydroquiuoliue hydrochloride The light-sensitive material and the image-receiving material are kept in contact with each other for to 60 seconds whilst heating as uniform as possible between 30 and 60C. This may occur by means of heated plates between which the light-sensitive material and the image-receiving material are pressed against each other as uniformly as possible. By this pressure a better contact may be obtained between the light-sensitive material and the image-receiving material whereby the sharpness of the diffusion transfer image is favourably influenced. Besides the diffusion transfer image formation is accelerated by the pressure and by the supplied heat.

In order to lower the salt concentration of the diffusion transfer copy obtained, avoiding thereby the risk of a visible crystallization of these salts, it is often advantageous to rinse the ontained diffusion transfer copy before storing it, preferably in an aqueous mixture which quickly evaporates from the rinsed copy so that the latter is quickly dry. Suitable aqueous mixtures are mixtures of water and a lower aliphatic alcohol, such as methanol and ethanol. 7

Finally, after a first diffusion transfer copy has been produced the light-sensitive material can still be used for producing further diffusion transfer copies by bringing the light-sensitive material in the above described circumstances again and again into contact with further image-receiving materials and by separating it therefrom after an optimal period of contact.

More particulars concerning the silver complex diffusion transfer process in general and suitable equipment for carrying out said process can be found in Progress in Photography Vol. 1; 1940-1950, pages 76, 77 and Vol. 11, 1951-1954, pages 156-157; Vol. 111, 1955-1958, pages 24-26 and the Patent Specifications mentioned therein. For suitable equipment for carrying out the process of the present invention, there may be especially referred to the United Kingdom Patent Specification 852,838 filed Oct. 3, 1957 by Gevaert Photo- Producten N.V. and to the United Kingdom Patent Specifications 1,060,572 filed Feb. 10, 1964 by Gevaert Photo-Producten N.V. and 1,077,355 filed Sept. 10, 1964 by Gevaert-Agfa N.V. and to the published Dutch Patent Application 65,09864 filed July 29, 1965 by Gevaert-Agfa N.V.

Hereinafter follow some examples for illustrating the process of the present invention.

EXAMPLE 1 For preparing the light-sensitive material, a high sensitive gelatino silver bromo-iodide (3 moles percent iodide) emulsion with a ratio of gelatin to silver nitrate of 1.5, was applied to a gelatin-subbed cellulose triacetate support having a thickness of 0.1 mm in such a way, that per sq.m. an amount of silver halide equivalent to 2.5 g of silver nitrate was present. After drying, an unhardened gelatin layer was applied to the lightsensitve emulsion layer in a ratio of l g of gelatin per sq.m.

An image-receiving material was prepared by applying an image-receiving layer to a gelatin-subbed cellulose triacetate support having a thickness of 0.1 mm. This image-receiving layer was applied in a ratio of 1 litre per 10 sq.m. from the following coating composiuon:

water 825 ccs gelatin 41 g 0.2 by weight dispersion of nickel sulphide nuclei in a 10 aqueous solution of gelatin 41 ccs 1 solution in ethanol of bis(dimethyl-thiocarbamoyl) sulphide 82 cos 12.5 aqueous solution of saponine 4 ccs sodium thiosulphate-S-water 5 g 20 aqueous solution of formaldehyde 2 ccs The light-sensitive material was placed into a usual metal cassette with a usual calcium tungstate fluorescent screen against the emulsion side. A sheet of black paper was applied to the backside of the light-sensitive material.

At the side of the fluorescent screen the lightsensitive material was exposed to a skull phantom subjected to an X-ray radiation (distance 75 cm 75 kV 64 mAs).

The image-wise exposed light-sensitive material was removed from the cassette together with the imagereceiving material described above, and conducted in the usual way through an aqueous alkaline processing liquid of the following composition distilled water 600 ccs lphenyl-Ii-pyrazolidinone 1 g anhydrous sodium sulphite 75 8 sodium hydroxide 8 hydroquinone 16 8 p-monomethylaminophenol sulphate g potassium bromide 1 8 anhydrous sodium thiosulphate 50 g distilled xater to 1000 (365 ethanol 200 1 solution of 3-heptadecyl-4-ml,2,4-triazoline-5-thione in ethylene glycol monoethyl ether 20 CCS The pH of this treating liquid amounted to l 1.2 and the liquid was kept at 30C. The conduction of the materials through this processmg composition proceeded in such a way that each part of the light-sensitive material was wetted for about 7.5 seconds before the light-sensitive material and the image-receiving material were pressed against each other between two rubber rollers in the usual way, which was the next processing step in the diffusion transfer image formation.

The sandwich of light-sensitive and image-receiving material in contact with each other was then kept pressed for 30 seconds between two metal plates heated at 40C, whereafter the light-sensitive and the image-receiving materials were separated from each other.

A positive copy of a good quality was obtained. This copy was sufficiently dry for examination purposes. It could be dipped for some seconds into a mixture of water and ethanol (50/50) in order to wash out the major part of the absorbed salts. The minor amount of said mixture taken up the copy quickly evaporated so that said positive copy very soon was completely dry.

EXAMPLE 2 The process described in example 1 was repeated but instead of using only one fluorescent screen for the exposure, two screens were used viz. one at either side of the light-sensitive material. The sheet of black paper at the backside of the light-senstive material was omitted.

The exposure dose for the same distance and the same tension amounted to only 20 mAs.

A same good result as described in example 1 was attained.

EXAMPLE 3 The process described in example 1 was repeated, but here the light-sensitive silver halide emulsion layer and the gelatin layer on top thereof were applied to a biaxially stretched polyethylene terephthalate support provided in order with a polyethylene isophthalate layer, a gelatin-cellulose nitrate layer and a lightreflecting titanium dioxide layer. The latter was coated m a ratio of 30 g of titanium dioxide per sq.m. from a composition prepared by thoroughly mixing 60 g of gelmm with 375 g of titanium dioxide and i000 ccs of water, and by adding per litre of the mixture thus obtained 20 cos of a l 1.7 percent aqueous solution of saponine apd cos of a 5 percent aqueous solution of chromic a um.

The image-receiving layer too had another composition and was applied in a ratio of 1 litre per 12 sq.m from the following coating composition 850 ccs of water The exposure dose for the same distance and the same tension amounted to only 32 mAs. The white pigment layer containing the titanium dioxide particles was responsible therefor.

The positive copy obtained was of good quality and excelled in its neutral image tone. Immediately after it had been formed it was sufficiently dry for examination purposes.

I claim:

1. Method for producing a continuous tone transparency according to the silver complex diffusion transfer process, comprising the consecutive steps of exposing an object to be reproduced to a beam of X-rays or of a radioactive radiation, recording the object-wise modified beam on a light-sensitive photographic material comprising a silver halide emulsion layer while said emulsion layer is arranged with one side thereof in contact with at least one fluorescent or luminescent intensifying or reinforcing screen, said emulsion being a silver bromide emulsion containing a minor amount of silver iodide and having a silver halide content equivalent to l to 5 grams of silver nitrate per square meter, treating the light-sensitive material carrying the recorded latent image in the presence of a photographic developing compound for 3 to 30 seconds with an aqueous alkaline processing composition having a pH between 10.5 and l 1.5 and a temperature between 25 and 35C, bringing the light-sensitive material in the presence of a complexing agent for silver halide into contact with an image-receiving material comprising a transparent hydrophobic film support provided with an image-receiving layer containing development nuclei for forming a silver-containing image from the diffusing complexed silver halide and a toning agent in a concentration of about 20-500 mg/sq.m., keeping the lightsensitive material and the image-receiving material for l0 to 60 seconds in contact with each other whilst heating between 30 and 60C to form the difiusion transfer image in said receiving material, and finally separating both the light-sensitive material and the imagereceiving material from each other.

2. Method according to claim 1, wherein the toning agent is bis(dimethylthiocarbamoyl)sulphide.

3. Method according to claim 1, wherein an antisludge agent is present in the aqueous alkaline processing composition.

4. Method according to claim 3, wherein the anti sludge agent is 3-heptadecyl-4-m-fluorosulphonylphenyl-ureido-A l ,2,4-triazoline-5-thione.

5. Method according to claim 1 wherein said photographic material comprises a layer other than said emulsion layer containing a white pigment and situated on the side of said emulsion opposite from said screen. *9 t t 4 ll

Claims

2. Method according to claim 1, wherein the toning agent is bis(dimethylthiocarbamoyl)sulphide.
3. Method according to claim 1, wherein an anti-sludge agent is present in the aqueous alkaline processing composition.
4. Method according to claim 3, wherein the anti-sludge agent is 3-heptadecyl-4-m-fluorosulphonyl-phenyl-ureido- Delta 2-1,2,4-triazoline-5-thione.
5. Method according to claim 1 wherein said photographic material comprises a layer other than said emulsion layer containing a white pigment and situated on the side of said emulsion opposite from said screen.