Diffusion transfer process for producing silver-free azo dye images



United States Patent 3,340,059 DIFFUSION TRANSFER PROCESS FOR PRODUCING SILVER-FREE AZO DYE IMAGES Otto Boes, Neu-Isenburg, Germany, assignor to E. L du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Sept. 27, 1963, Ser. No. 311,980 Claims priority, application Germany, Feb. 27, 1963,

6 Claims. (51. 96-29 This invention pertains to a novel process for producing silver-free images from photographic silver images by image-true contact transfer of a compound to an image acceptor film containing a reagent suitable for coupling.
An object of this invention is to provide new imageforming processes. A related object is to provide new processes for forming and transferring images. A further object is to provide such processes which are simple and dependable. Still further objects will be apparent from the following description of the invention.
 According to the invention, a photographic silver image is treated with a solution of a diazonium compound in the presence of a substance having catalytic activity and the diazonium compound is transferred, true to the image, to an image acceptor film which is placed in intimate contact with the original silver image. The process of image formation takes the following course:

In treating the silver image, e.g., a developed silver image in an original photographic silver halide emulsion layer, with a diazonium compound solution, the latter, under the catalytic influence of suitable additives, is decomposed at points containing image silver, with formation of noncoupling degradation products. At points free from image silver, on the other hand, in the reverse areas or non-developed areas of the layer the diazonium compound is retained unchanged. By pressing the treated layer against the surface of an image acceptor element, e.g., paper or film, the diazonium compound can be transferred thereto. There is then formed in the image acceptor element, by coupling the diazonium compound with a reagent which is present in that film, an azo dye image with gradation opposite to that of the original, i.e., if the start is made with an ordinary photographic negative, then a positive image is obtained after the transfer, whereas when a positive is used as the original a negative image is obtained by diffusion.
Not only half-tones but also line negatives and screen images can serve as originals, and their base may consist of the usual transparent or opaque materials, is. film base or paper.
 Chloride, thiocyanate, bromide and iodide ions have been found particularly suitable for use as additives which effect the catalytic decomposition of the diazo compound by the image silver, the catalytic activity of the specified ions being in ascending order as listed. In practice, this rising activity results in an apparent increase in speed and contrast. Thus, when iodide ions are used, the apparent speed is higher and the pictures exhibit high contrast, whereas when chloride ions are used relatively lower speed and contrast are obtained. The choice of a suitable catalyst for each case depends on the character of the original as well as on the requirements imposed on the finished picture, and can be easily decided from case to case by one skilled in the art.
Suitable compounds that will provide the ions referred to above include sodium and potassium chloride, bromide, iodide and thiocyanate which are illustrated in the examples. Mixtures of two or more of these compounds can be used. Other useful compounds are: the corresponding magnesium, calcium, strontium and barium salts and mixtures of two or more of the foregoing salts.
In addition, there is the possibility of influencing the sensitivity and gradation of the picture to a certain extent by varying the quantity of catalyst.
The catalytically active substances may be added to the diazonium solution singly or in combination. Practically all coupling reagents and diazonium salts which are capable of azo coupling are suitable for carrying out the processes, so that a very wide selection of dyes is avail; able. Usable compounds are listed, for example, in the following tables:

TABLE I No. Coupling Reagent Color 1.--. HOOC$|I-(FH: Yellow.
N\ /C :O

H=N-fi-OH1 Bright yellowi 3-- HO O C-(i/'-CH: Yellow.
 ' N C :O

NBC 0 01111::

TABLE I-Contin11ed N0. Coupling Reagent Color 4- HnC1-}EIJ C H1 Bright yellow.
HaaCnC ONE-(6*? H; Bright yellow. C 0

6---- HuCnC ONH-(I?-('3 H, 'Brlght yellow.
N\ /C O ONHC o cum, Yellow. HI ICHIOH2CHZBO3H ONHC 000 018E Orange-yellow.
| I .N (C H3) 2 S OaH 9. OH Red.
I HNO 0 0111115 10. Orange red.
35C110 ONH SOaH OH 11--- w Bright red.
I HN-E O C18H37 03H 7 12 -CONHCH2CH2CONHOO Orange.
O CIBHH OH 7 V V 7 13--. we og-O-o ON-C1sH31 Orange red.
HO O C C O OH TA BLE Elk-Continued No. Coupling Reagent Color OH H=CI?'-C1a a1 14 c ONE-O Purple. aloa OH NH0 0 CI'IH35 15 Bluish red.
s oaH H0 NBC 0 C17H 16. Purple.
H0 8 SOaH H 0 NBC 0 C17H35 17 Purple.
HOaS

S OaH 18--. 13150110 ONE-Q COCHzCONH v Bright yellow.
HO 0 0g: O OH 19- GO EQUITY-(3181131 Orange.
11( 3 ONHQ SlOgH 20- OH HzC-ITL-CmHz-l Red. 0

0 ONHQ OaH TABLE 11 No. Coupling Reagent Color 1---- C O- -N=NOaS Pink.
O OH; 2- C N N OQS C C H3 Red-brown. OaH

HO;SC -N='NO;SO

4--- N=NO:S Purple.
a--- mo 0 -,N 'N-01SC Orange.
TABLE 'IICon tinued' No. Coupling Reagent Color 7---- mooQrraw-ms-O Purple.
9. CION=NO2S Pink.
| SOzH I 1o HOOC-CHr-O-ON=NOzS- Bluish red.
I 11-.- HOaSQN=NOzS-O Orange.
12.-- HO SCH;C N=NOzS Purple. 13... nmsfiIj-rwn-ms-O Pink.
CH; MGMMS 15.-- O3S NEN] Red.
16... sCON NJX- Pink.
*1- 17 H;OOONEN]X- Bluish red.
, CHsCHnCHzCE: 18... NONEN X- Blue.
HOaSCHaCHaCfi:

19--- C -N=NON=N]X- Purple.
or dye coupling agent present in the acceptor film. 'Addi tional broadening of the color range can be obtained by using a blend of diflerent dye coupling agents in the acceptor film.
 A gelatin film, for example, may be used as thep act-V ceptor layer, which contains a reagent capable of azo coupling and may be applied to any desired film base, e.g., paper, a cellulose ester or the like. Of course, other water-permeable colloid binding agents and film-forming materials may be used instead of gelatin as the vehicle ii such as polyvinyl alcohol, polyvinyl acetate, polyvinyl 'acetals,'polyesters, etcrThe reagents are incorporated in the film by methods known in the art,in which connection it has been found advisable to use the reagents in a diifusion-r'esistingjorm. It is desirable to coat the surface of the acceptor film containing the reagent capable of azo coupling with a thin protective layer of a waterpermeable colloid, e.g., gelatin, sodium alginate, etc.
The process according to this inventionis characterized "by a number of advantages; Thus, it is possible tomake one or more copies in-a veryshort'time from a silver.-

containing original-without needing copy-making illumination. When making a number of copies it is well. to wash mmeprmal bctweenit csus nqe the. silver imaaemar.
sometimes be attacked during prolonged action of the processing solution.
Copies may be made-in ordinary: daylight, so his not necessary to provide a dark room. Therequisite processingtime for making a copy is relatively short, since in A gelatin solution containing, per liter, 6 g. of dye coupling agent No. 4 of Table I is coated in the customary manner on a transparent film base. This material serves as the acceptor film.
 A normal negative silver image is treated 30 seconds in a solution having the following composition:

Water liter 1 Diazonium compound No. 7 of Table II g Potassium bromide g 25 Sodium acetate g 25 Glacial acetic acid ml 2 N-methyloleyltaurine g 0.2

The clinging treatment solution is stripped from the silver image and the negative is pressed on the acceptor film with a squeegee. After seconds the acceptor film is stripped away from the silver image. It contains a yellow positive transparency of the black-and-white negative. The negative is washed with water and dried. It is practically unchanged. If the dye coupling agent in the acceptor film is replaced by one of the coupling agents listed in Table I, then, by otherwise identical processing, positive images are obtained in the colors stated in the table. When coupling agents 1820 are used, then the acceptor film, after stripping from the silver image, is given an additional treatment of 1 minute in 1% sodium carbonate solution to force formation of the dye.
Example 2 Water liter" 1 Diazonium compound g 10 Potassium bromide -g 25 Sodium acetate g 25 Glacial acetic acid ml 2 N-methyloleyltaurine g 0.2

If the diazonium compounds specified in Table II under Nos. 1-14 are introduced, positive transparencies are obtained in the colors there cited.
 Example 3 The same original is employed as in Example 2. The acceptor film is prepared as follows: A gelatin solution is coated on an ordinary paper base; each liter of solution containing 6 g. of dye coupling agent No. 16 of Table I. A top-coat is coated on this gelatin film from a solution of the following composition:

Water liter 1 Sodium alginate g 5 Rapid wetting solution, 4% ml 5 Processing: Bath time for the silver image, seconds. Contact with the acceptor film, 15 seconds.
A stock solution, to which another catalyst is added for each image, is used as the treatment bath.
Stock solution:

Water liter 1 Diazonium compound No. 2 of Table H g 10 Sodium acetate g 25 Glacial acetic acid ml 2 N-methyloleyltaurine g 0.2

Catalyst: Grams Image 1Sodium chloride 50 Image 2-Potassium thiocyanate 25 Image 3Potassium bromide 25 Image 4-Sodiumchloride+1.25 g. KI 4 Image 5-Sodium chloride+2.5 g. KI 25 Image 6Sodium chloride-H75 g. KI 12.5 Image 7-Potassium iodide (KI) 5 In all seven cases a purple positive is obtained. Sensitivity and gradation of the images increase from image 1 to 7. That is, catalytic activity rises in the sequence chloride, thiocyanate, bromide, iodide.
 Example 4 An ordinary silver image on photographic paper is used as the original. It is treated for 20 seconds with the following solution:

Water liter 1 Diazonium compound No. 7 of Table II g 10 Potassium iodide g 5 Sodium acetate g 25 Glacial acetic acid ml 2 N-methyloleyltaurine g 0.2

A screen negative on ordinary lithographic film is used as the original. A gelatin film on a transparent base, the dye coupling agent being compound No. 16 of Table I, is used as acceptor film. The treatment solution has the following composition:

Water liter 1 Diazonium compound No. 3 of Table II g 10 Potassium bromide g 25 Sodium acetate g 25 Glacial acetic acid ml 2 N-methyloleyltaurine g 0.2

Processing is as usual, with bath time 20 seconds and contact time 15 seconds between original and acceptor film. A red positive screen image is obtained.
Example 6 The same original is used as in Examples 2 and 3, with the acceptor film described in Example 5. The requisite treatment solution is prepared as follows:

Solution A: 2.9 g. of the amine corresponding to diazonium compound No. 18 of Table II is dissolved in 20 ml. of 5% hydrochloric acid and diazotized in the usual Way by adding a solution of 0.7 g. sodium nitrite in 5 ml. water. The resulting diazonium salt solution is adjusted to pH 6 by adding 10% sodium hydroxide solution and is then made up to 50 ml. with water.
 To prepare the completed treatment solution there is then added the following Solution B:

The original is treated 30 seconds with this solution and, after removing excess solution, the wet surface is brought into contact with the acceptor film for 20.seconds. The original is stripped oif and the acceptor film is immediatedried. A blue positive image is obtained. The correspond- .ing ready A-solutions were also obtained from the diazonium salts listed in Table II as Nos. 1517 and 19, by diazotizing the amines. They were introduced as treatment-baths after adding the same B-solutions with the same material and same processing. This gave positive images inthe colors stated in Table II. After treatment of the acceptor film with sodium carbonate solution was not necessary with these diazonium salts.
An'advantage of the present invention is that it provides a'simple'and practical process for forming azo dye images in a separate element.
Another advantage of the invention is that it is possible to prepare one or several prints from an original copy containing silver within the shortest time and without any printing exposure being. necessary. A further advantage is that production of the prints may take place in normal daylight, so that a dark room is unnecessary. A

still further advantage of the invention is that a single treating bath only is required, so that prints can be made in a relatively short time, usually about one minute.
 Iclaim:

1.'A process for making silver-free negative copies from photographic silver images of a photographic element, characterized in that the silver image is treated with a solution of a diazonium compound capable of coupling, said solution being free from strong acid and initially containing at least oneion selected from the group, consisting of chloride, bromide, iodide and thiocyanate ions, after which the unchanged diazonium compound occurring at points free from image silver is, imparted bycontact transfer to an image acceptor element containing at least one reagent capable of azo coupling whereby anazo dye image is formed.
2. A process according to claim 1, characterized in that a diazosulfone is used as the diazonium compound.
3. A process according to claim. 1, characterized in that the silver image original is washed with water after the contact transfer and the contact transfer step is repeated.
4. A process according to claim 1 wherein the silver image is in a gelatin layer and the image acceptor element has an acceptor surface of gelatin, which contains the reagent capable of azo coupling.
5. A process according to claim 1 wherein the solution of the diazonium compound is slightly acidic.
6. A process according to claim lwherein the solution of the diazonium compound is slightly acidic and the contact transfer is effected under slightly alkaline conditions.
References Cited UNITED STATES PATENTS 2,271,176 1/1942 Gaspar 9654 2,386,167 10/1945 Murray 96-3 2,465,760 3/1949 Sprung'et al. 9691 2,747,999 5/1956 Yutzy et a1. 96-29 I. TRAVIS BROWN, Acting Primary Examiner.
 1. A PROCESS FOR MAKING SILVER-FREE NEGATIVE COPIES FROM PHOTOGRAPHIC SILVER IMAGES OF A PHOTOGRAPHIC ELEMENT, CHARACTERIZED IN THAT THE SILVER IMAGE IS TREATED WITH A SOLUTION OF A DIAZONIUM COMPOUND CAPABLE OF COUPLING SAID SOLUTION BEING FREE FROM STRONG ACID AND INITIALLY CONTAINING AT LEAST ONE ION SELECTED FROM THE GROUP CONSISTING OF CHLORIDE, BROMIDE, IODIDE AND THIOCYANATE IONS, AFTER WHICH THE UNCHANGED DIAZONIUM COMPOUND OCCURRING AT POINTS FREE FROM IMAGE SILVER IS IMPARTED BY CONTACT TRANSFER TO AN IMAGE ACCEPTOR ELEMENT CONTAINING AT LEAST ONE REAGENT CAPABLE OF AZO COUPLING WHEREBY AN AZO DYE IMAGE IS FORMED..
