US2728290A

US2728290A - Photographic reproduction process, including transfer of azo dyes

Info

Publication number: US2728290A
Application number: US345798A
Authority: US
Inventors: Marriage Anthony; Philip K Brooks
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1953-03-31
Filing date: 1953-03-31
Publication date: 1955-12-27
Anticipated expiration: 1972-12-27

Description

Dec. 27, 1955 A. MARRIAGE ET L 2,728,290

PHOTOGRAPHIC REPRODUCTION PROCESS INCLUDING TRANSFER OF AZO DYES Filed March 51, 1953 NEGATIVE llllllll Ill ,2 i SILVER-DYE -BLEACH lllllll T fUJlllllllllHl ll AnfbonyMarriage Felix .Pollak Philip K. Brooks INVENTORS ATTORNEY AGENT United States Patent PHOTOGRAPHIC REPRODUCTION PROCESS, INCLUDING TRANSFER OF AZO DYES Anthony Marriage, Felix Pollak, and Philip K. Brooks,

Harrow, England, assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application March 31, 1953, Serial No. 345,798

4 Claims. (Cl. 101--149.1)

This invention relates to photographic reproduction processes.

In the field of color photography, the production of dye images by the so-called silver-dye-bleach process is well known. In this process, a silver image in a photographic layer containing a dyestuff uniformly dispersed therein is bleached by treatment with a suitable bleaching agent whereby the dyestuff is destroyed in the layer at the places where silver is present. The dyestuff is then left in the layer as a positive dye image complementary to the negative silver image. The dyestuffs which have been proposed for this process are chiefly azo dyes.

We have found that dye from a dye image so formed in a single photographic layer may be transferred onto an absorbent support to form a dye image thereon; provided of course the dye is one which will diffuse or can be made to diffuse.

According to the present invention, therefore, there is provided a method of photographic reproduction in which a photographic emulsion layer containing a silver image preferably a two-tone image such as a line or halftone image, or a continuous tone silver image, is treated with a silver dye bleach bath in the presence of a dye capable of being bleached in the presence of metallic silver to form a positive dye image in the layer, preferably a difiusible acid azo dye, and is then brought into contact with a receiving absorbent support whereby part or all of the dye is transferred so as to form a positive dye image in the absorbent support.

It is apparent that the transferred image will be laterally reversed with respect to the dye image first formed in the emulsion layer.

When performing the invention, a light-sensitive silver halide emulsion layer is exposed to an object or image and then developed to form the said silver image.

The image dye may be introduced into the layer at any one of various stages; thus, it may be incorporated in the emulsion before coating or the layer may take up dye from the developer, from a separate bath or from the bleach bath.

The production of several copies from a layer containing a positive dye image formed as described above can be effected by transferring only a part of the dye forming the dye image in the emulsion layer. The proportion transferred depends on several factors including the time of contact of the layer and the support.

This time of contact must be long enough to allow the transfer of suflicient dye to form a clear image on the support.

Any of the known silver dye bleach baths are suitable for use in the present invention such as acid thiourea solutions. If desired, a compound such as anthraquinone- 2-sulfonic acid or 2:3-dimethyl quinoxaline may be used with the bleaching agent to accelerate the bleaching action, as is also well-known in the art.

The time of transfer of sufiicient dye to form a clear copy image can usually be reduced by treating the support before transfer with water or preferably dilute alkali, e. g. a solution of sodium carbonate or ammonia. This treatment appears to facilitate the transfer of the dye.

If it is desired to obtain as many copies as possible from a single exposure of the photographic emulsion, it is preferable to use a high contrast emulsion, by which term we mean an emulsion which produces a large change in the amount of silver for a given change in the logarithm of the exposure, and not necessarily one which produces a high visual density.

Using such an emulsion, it is possible to obtain several copies from the first dyeing of the emulsion layer, and then, when the dye in this layer has been partially or completely exhausted, to redye and rebleach the layer after which further copies may be obtained from the fresh positive dye image in the layer. This procedure of transferring a number of copies, redyeing, and rebleaching may be repeated as long as enough silver is present to bleach dye sufliciently to form a clear image when transferred.

The invention is particularly applicable to document copying and a number of copies of an original document may be made as described above without having to make more than one photographic exposure. This is in distinction to most prior document copying processes in which one copy only is obtained from a single photographic exposure step. For example, if a photographic negative of a document has been made by the reflex method, this negative can be used to make several positive copies of the document by application of our invention without any further photographic exposure step.

Thus, there may be taken a photographic emulsion layer containing a laterally reversed negative silver image of a document taken by the reflex method. The following treatments can then be performed in the light provided that either the image has been fixed or the first of the treatments inhibits further development. The negative is treated in a bath of a dye bleachable in the presence of silver so that the dye is uniformly distributed in the emulsion. It is then treated with a suitable silver dye bleaching agent, e. g. acid thiourea solution, so that the dye is bleached Where it is in contact with metallic silver. A positive dye image is thereby formed in the emulsion layer. The emulsion layer containing the positive dye image is then brought into contact with a receiving absorbent support such as a paper support, whereby dye from the positive image is transferred to the support to form the laterally reversed dye image. The support is preferably treated with water or dilute alkali just before transfer as stated above.

If the positive dye image first formed in the emulsion layer is laterally reversed relative to the original document, as it would be when formed from a negative taken by reflex, then when dye is transferred to the support the dye image is again laterally reversed and is a laterally correct positive dye image of the original document.

Additional copies are made simply by bringing the already prepared and at least once used negative which still contains dye, into contact with another support so that transference of dye takes place to form another dye image. This procedure according to our invention may be repeated until silver in the negative image is practically exhausted.

The accompanying drawings illustrate in greatly enlarged cross-sectional view the appearance of representative materials at various stages in a process of our invention.

The following examples illustrate but do not limit the application of the process provided by our invention.

exposed to a document by reflex, developed for one minute, dyed up in a solution of /1 of a diffusible or poten tially diflfusible acid azo dye such as Chlorazol Fast Pink BK dye (C. I. No. 353) for 2 /2 minutes, rinsed in water for 5 seconds, bleached by immersing *for 30 seconds in an aqueous solution made up of 5 grams of thiourea, .01 gram 2'z'3-di-methyl quinoxaline and 5 cc. of concentrated hydrochloric acid made up to 100 cc. with water and rinsed for 5 seconds. The dye image thus obtained was then transferred onto an alkaline gelatin coated paper '(pretreated for 1 minute ina solution containing 1% ammonia and 0.1% sodium hex-ametaphosph-ate) by means of a dye transfer blanket. it was removed after /2 -minute and again squeegeed for 1 minute on to fresh, pretreated dye transfer paper. Another transfer was made onto fresh papen'talcing '3 minutes.

The process of this example is illustrated in the accompany-in'g drawings wherein .Stage 1 shows the developed negative having support 1-0 and emulsion layer 11 containing the silver image 12 which may be a line, ha'lftone or continuous tone image. After dyeing the element appears as in Stage 2 the emulsion layer now being uniformly colored with the 'bleachable azo dye. Stage 3 shows the emulsion layer after bleaching the dye in the region of the silver image 12, dye now remaining only in areas 13 of layer 11. In Stage-4the azo dye is shown transferring by imbibition from areas '13 of the emulsion layer 11 to areas 14 0f the hydrophilic surface of the coated paper having support 15- and the. gelatin layer 16.

Example 2 .A layer of a washed bromide-emulsion was-coated at the rate 10f 16.2 grains of gelatin per squarefoot. This was exposed and processed by the procedure of Example 1. Transfer was made onto gelatin coated paper. Transfer time'wa-s lu'ninute, and 3 minutes for a second copy.

Example 3 Naphthalene Black dye No. 30745 I. C. I. (an acid azo dye) was used instead of the Chlorazol Fast Pink BK used inExample .1.

Example 4 A sheet of light sensitive material as described in Example 2 'was exposed imagewise and treated for 4 minutes with asolution of the following composition Elon .(Metol) 0.1 gram. Sodium sulfite (:anh.) 1:5 gram. Hydroquinone 0. 4 gram. Sodium carbonate (anh) .-1.7 gram. Potassium bromide 0.1 :gram. Chlorazol Fast Pink BKdye 4.02grarns. Water lliter.

The material was then rinsed fora few seconds and bleached, rinsed and transferred as in Example 1.

Example ,5

Asheet ef thigh-contrast photographic paper was exposed 10 a document by reflex and developed and fixed. The [following solution was then applied byswabbing to the surface of the negative.

Concentrated hydrochloric acid 1/2 cc. Thiourea 10 grams. 2z3- dimethylquinoxaline -0,.02.grarn. Chlorazol Fast Pink BK dye 10.2 gram. Water 10.0 cc.

background was obtained. The negative still contained dye for further transfers and also still contained silver in the non-image areas for several repetitions of the dye bleaching and transfer procedure.

All operations in these examples were carried out at room temperature (70 F.).

The process of our present invention is also applicable to multicolor photography. Color separation negatives of colored objects are dyed in their respective subtractive colors with dyes capable of being bleached in the presence of silver. Treatment of such dyed -negatives-wit-h a silver dye bleach bath yields the positive dye images in the emulsions and dyes from these positive dye imagesare transferred in register onto a single base which may be paper or a transparent base, to form a positive laterally correct image of the original subject. copies of a document may be made by several transfers, so'severa'l positive reproductions of a colored object may be made from the separation negatives.

As stated above the time of transfer-of suiiioientdye to form a clear cop-y image can be reduced by treating the support before transfer with water or preferably dilute alkali e. g. .a solution of sodium carbonate or ammonia. This treatment appears to facilitate the transfer of dye.

We have also found that the presence of a thiosulfate in or on the receiving support-enables :the transfertimeof the .dyeifrom the emulsion layer .to the support to be reduced; however the amount of reduction depends on the dye used.

According 'to an alternative =method of :the present invention, therefore, thereisprovided a method of photographic vreproduction in which .a photographic emulsion layencontaininga silver image is treated witha silverd-ye bleach bath in the presence of a dye capable of :being bleached,in'theapresence.ofsmetallic silver (such asan acid azojclyel) to home positive dye image inthe layer .andis then brought into contact-wither receiving absorbent support'which hasibeen previonsly'tneated with a :thiosulfate, whereby part or. all of the-"dye is :transferred soas :to "form a positive dye: image'sin the absorbent support.

Preferably, .a thiosulfate such as :an .alkali metal or ammonium rthiosulfategis incorporated in the dilute alkali solution used to pretreatwthe receiving-support.

-Particularly good results -.are 1 obtained .when usingthe Naphthalene Blackdye :givenabove.

A suitable receiving support acomprisesa paper base coated'with alayer ofgelatin.

.In apreterredform of this variation of our invention, an emulsion layer containing a positive dye image is brought into icontact with a receiving absorbent support, whereby .dye..from';the positive dye image .is transferred to the support timagewise, the support having been first treated with a solution of sodium .or ammonium itl'LlOSUlfate made alkaline, for example, with sodium carbonate orammonia.

Wetting'the emulsion layer'containing the positive dye image by a dilute carbonate solution further improves the speed of transfer fif'ilhe dye when :takingtthe first copies.

The following examples illustrate this variation of the presentinvention.

..Examp.le.6

- (a) A sheet of high contrast photographic paper-was exposed by ireflex to .a tdocumen't andrdeveloped in acaustic developer.

(b) The negative was dyed for 20 seconds inaasolution of :1 gram Naphthalene rBlack dye lifl'llQO LCCnIl/ZS hydrochloric .acid, rinsed, bleached. :as usual, squeegeed .and transferredzby means of..a ,niangle Gilli- 118 tpapel'isuppon which had .beenwettednby immersing for a ,few seconds in .a rbathicontaining 12.5 grarns of :NazSzQs :SHzO and'3j.2 grams of Na2CO3'H2O in $00 beef-solution. Thetransfer ,paper may beranrordinary .paper base ora baryta coated paper. 'Transfer of the .dye \was .allowed ,to proceed for five seconds. The negative was removed and In the same manner that several again brought into contact for five seconds with freshly conditioned transfer paper. Thirteen transfers in all, each lasting 510 seconds, were effected in this manner.

(c) After effecting these transfers, the original negative still contained an appreciable amount of silver. The procedure set out in (b) above was therefore repeated, that is, the negative was redyed and rebleached and by subsequent transfers 14 copies were obtained.

(d) Since silver was still present in the negative, it was again subjected to the procedure according to (b) and 17 copies were obtained.

Thus a total of 44 copies was obtained from one negative.

Example 7 A dye solution of double the acid and dye concentration employed in Example 6 was used. Three dyeings as in Example 6 (b), (c) and (d) of 15, 20 and 3 seconds respectively followed by bleaching and transfer, yielded 12, 16 and copies which were denser than those of Example 6. In this procedure a transfer blanket was used instead of a mangle and the negative was given a short rinse after each bleaching.

Example 8 The dye bleach bath of Example 7 was used. Two dyeings of 30 seconds each as in Example 6 (b) and (c) followed by bleaching and transfer, yielded 7 and 10 dense copies respectively. The transfer time was seconds. The addition of a small amount of optical bleach to the conditioning bath after the 13th transfer gave a noticeably whiter (less yellow) background.

Strong alkalis (4% NHs or N/ 10 NaOH) have similar effects to thiosulfate but replacement of thiosulfate by an equivalent amount of sodium sulfite does not produce the same exceptional change in ease of transfer.

The following acid azo dyes are given as further examples of bleachable azo dyes giving useful results when employed in our invention in the manner of the above examples:

Direct Sky Blue GS 300 (C. I. No. 518) Acid Brown (Schultz No. 294) Chlorazol Black, I. C. I.

What we claim is:

1. A photographic reproduction process which comprises uniformly coloring a photographic emulsion layer containing a silver image, with a diffusible acid azo dye, treating the colored emulsion layer with a solution of a silver-dye-bleaching agent until the azo dye in the emulsion layer in the region of the silver image has been decolorized, pressing the emulsion layer into contact with an alkaline hydrophilic surface containing a compound of the group consisting of alkali metal and ammonium thiosulfates, in the presence of moisture to imagewise transfer a portion of the azo dye image remaining in the emulsion layer to said surface.

2. A photographic reproduction process which comprises exposing a light-sensitive silver halide emulsion layer to a subject, developing a silver image in the exposed emulsion layer and uniformly coloring the emulsion layer by means of a silver halide developing solution containing a diffusible acid azo dye, treating the colored emulsion layer with a solution of a silver-dye-bleaching agent until the azo dye in the emulsion layer in the region of the silver image has been decolorized, pressing the emulsion layer into contact with an alkaline hydrophilic surface containing a compound of the group consisting of alkali metal and ammonium thiosulfates in the presence of moisture to imagewise transfer a portion of the azo dye image remaining in the emulsion layer to said surface.

3. A photographic reproduction process which comprises uniformly coloring a photographic emulsion layer containing a silver image, with an aqueous solution of a diifusible acid azo dye, treating the colored emulsion layer with a solution of a silver-dye-bleaching agent until the azo dye in the emulsion layer in the region of the silver image has been decolorized, pressing the emulsion layer into contact with an alkaline hydrophilic surface containing a compound of the group consisting of alkali metal and ammonium thiosulfates in the presence of moisture to imagewise transfer a portion of the azo dye image remaining in the emulsion layer to said surface.

4. A photographic reproduction process which comprises treating a photographic emulsion layer containing a silver image with an aqueous solution of a mixture of a silver-dye-bleaching agent and a diffusible acid azo dye until the emulsion layer contains an azo dye image only in the region free of the silver image, pressing the emulsion layer into contact with an alkaline hydrophilic surface containing a compound of the group consisting of alkali metal and ammonium thiosulfates in the presence of moisture to imagewise transfer a portion of the azo dye image to said surface.

References Cited in the file of this patent UNITED STATES PATENTS 2,020,775 Gaspar Nov. 12, 1935 2,629,658 Sprung Feb. 24, 1953 FOREIGN PATENTS 607,792 Great Britain Sept. 6, 1948