DE1170779B - Direct positive photographic material - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Boarding school Class: G 03 c

Number:
File number:
Registration date:
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German KL: 57 b - 9

J 21412 IX a / 57 b
March 9, 1962
May 21, 1964

The invention relates to direct positive photographic materials with photographic emulsions, which can be processed directly into positive images.

It is known that direct positive photographic emulsions can be prepared by a small amount of a desensitizing compound is incorporated into a silver chloride emulsion, and obscured the emulsion by light or chemical means. When this emulsion is exposed and de- ίο is wound, a positive image emerges immediately after the development.

Although such a method of making a direct positive photographic emulsion is general Has found recognition and is widely practiced on a technical scale, represents the actually producing such materials to the required standard is a difficult one In particular, it has been found that the selection of the desensitizer is difficult that not all desensitizers show their effect to a useful extent and that practically only very much result in few products of technical merit. There has therefore been extensive research to find suitable desensitizers and many suggestions have been made in the literature which are of varying value in practice.

In general, the emulsions were applied as a coating on paper substrates and the products for Document rendering used. Desired properties for these emulsions for use for such purposes the following may be mentioned:

In the first place, it is desirable that the emulsion have good bleach sensitivity; H. the Sensitivity with which the fogged emulsion is reactive on exposure so that results in a white background in the exposed areas during development. However, as the materials are generally used in offices or the like without using a dark room, it is important that the effect of ordinary exposure on the exposed areas of the emulsion is not such that these areas become viable again, d. H. in the period between exposure to picture taking and the development, otherwise a gray or cloudy background instead of the preferred one clear, white background is obtained. This tendency to have a viable picture in the at Exposure to re-form bleached areas is called the "forward" sensitivity of the material Direct positive photographic material

Applicant:

Ilford Limited, Ilford, Essex (Great Britain)

Representative:

Dr. E. Wiegand and Dipl.-Ing. W. Niemann,

Patent Attorneys, Munich 15, Nussbaumstr. 10

Named as inventor:

Douglas lames Fry,

Bernard Alan Lea, Ilford, Essex

(Great Britain)

Claimed priority:.

Great Britain March 10, 1961 (8928)

and in the selection of a desensitizer for use in direct positive photographic emulsions of the type in question here, it is desirable to carry out the election in such a way that this Forward sensitivity as low as is practical.

It also follows that since a copy with a clear, white background is desired, the The desensitizer itself should not be so strongly colored that it becomes a part of the thinly applied emulsion layer gives perceptible color.

Furthermore, it is sometimes desirable to have a "double copy" on a photographic material of this effect in question. This allows the material to be exposed to yellow light for the first time an outline or line image (black on white background) are subjected and in this way the emulsion can be "bleached" in the exposed areas. When the emulsion develops at this stage it gives a simple, positive image when it is developed; H. black lines on white Underground. If, instead of direct development, the exposed material is exposed to white light with a second original (again e.g. black lines on a white background) is exposed again, then becomes in the areas bleached by the first exposure, provided that the forward speed of the material is sufficient, a negative record of the second original of the first

409 590/394

Record formed superimposed. In this way the material shows a record when developed of the first original in black lines and a record of the second original in white Lines.

One purpose of the invention is to use a particular class of desensitizers in Direct positive photographic emulsions made from the viewpoint of the above requirements are particularly satisfactory.

The photographic material according to the invention contains a fogged gelatin-silver halide emulsion, in which at least 95% and preferably at least 99% of the silver halide is comprised of silver chloride exist, the emulsion as a desensitizer a bisquaternary 2,2-pyridyl salt of the general formula

4 ecm 2,3-dibromobutane instead of 4 ecm 1,2-dibromo-2-methylpropane. The product had a melting point of 290 to 295 ^° C. (decomposition).

The chosen bisquaternary 2,2'-dipyridyl salt, which z. B. from a bromide or another Halide salt or a sulfate, methanesulfonate or toluene-p-sulfonate salt is preferred in the photographic emulsion in an amount between 0.1 and 2 g of the compound per 100 g

ίο existing silver halide introduced. The emulsion may be obscured by previous exposure to light, but it will be chemical Obfuscation of the emulsion is preferred, e.g. B. by introducing formaldehyde into the emulsion and leaving it to stand the emulsion at an elevated temperature.

The invention is explained in more detail below with the aid of examples.

ISM

N +

2X '

contains, in which the symbols R, which may be the same or different, hydrogen atoms or alkyl groups, e.g. B. with up to 4 carbon atoms mean, η = 2, 3 or 4 and X is an anion and in which either one or both pyridine nuclei can carry alkyl-substituted groups. The emulsion can be activated by light or chemical means, e.g. B. by treatment with formaldehyde or another reducing agent, can be obscured.

A preferred compound of the class listed above is 1,1'-ethylene-2,2'-dipyridylium dibromide (R = H, R = H, η = 2 and X = Br). Other suitable compounds are the trimethylene (n- 3) and tetramethylene (n = 4) analogs analogs and the 3,3'-, 4,4'- and 5,5'-dimethyl derivatives of the first-named compound. The preparation of these compounds is described by RF H ο mer and TE T ο m-1 i η s ο η in "Journal of the Chemical Society", 1960, p. 2498. Other suitable compounds of this class are the following (with an indication of their method of preparation):

1,1 '- (1,1-Dimethylethylene) -2,2'-dipyridylium dibromide

2,2'-dipyridyl (0.8 g) and l, 2-dibromo-2-methylpropane (4 cc) were heated together at 13O ⁰ C for 15 hours. The mixture was cooled and, after the addition of ether, the solid was filtered off and washed with dry acetone. It was dissolved in methanol, refluxed with activated charcoal, and the solution was filtered. The purified product was obtained by adding ether to the filtrate; F. = 280 to 285 ^° C. (decomposition).

1,1 '- (1,2-Dimethylethylene) -2,2'-dipyridylium dibromide

This compound was, as above for 1, l '- (1,1-dimethylethylene) -2,2'-dipyridylium dibromide described, produced, but using

example 1

4.41 of a washed photographic emulsion containing 188 g of silver chloride, which had been adjusted to a pH of 10, were treated with 12 ml of a 4% strength aqueous solution of formaldehyde. The emulsion was ^{heated at 52 °} C. for 35 minutes and then neutralized by adding citric acid and cooled. 2 g of 1-ethylene-2,2'-dipyridylium dibromide, dissolved in 100 ml of ethanol, were then added. The emulsion was drawn onto a paper backing. Upon exposure and development, the product gave a high quality direct positive image in which the white areas were not stained. The product showed relatively low forward speed after exposure and before development.

Similar results were obtained with the other compounds of the general listed above Formula when used in similar amounts.

Example 2

The procedure of Example 1 was repeated but using only 0.1 g of those listed Dipyridyl compound, and the emulsion was drawn down on a film base. Of the obtained film was illuminated with yellow light using an original made of black Lines existed on a clear background, exposed. After development it gave a direct positive High quality image.

A second part of this film was exposed to the first original as described above and then with white light using a second original consisting of an array of black lines on a clear background, exposed. The film was then developed and yielded a positive image of the first original and a superimposed negative image of the second original.

Claims (3)

Patent claims: 1. Direct positive photographic material with a fogged one containing a desensitizer Gelatin-chlorosilver emulsion, characterized in that the emulsion as a desensitizer a compound of general formula 2 X " 10 contains, in which the symbols R are hydrogen atoms or alkyl groups, η = 2, 3 or 4 and X is an anion and one or both pyridine nuclei can carry alkyl substituents. 2. Photographic material according to claim 1, characterized in that the proportion of the Desensitizer in the emulsion is 0.1 to 2 g per 100 g of silver chloride 3. Photographic material according to claim 1, characterized in that it is used as a desensitizer contains a l, r-ethylene-2,2'-dipyridylium salt. 409 590/394 5.64 ® Bundesdruckerei Berlin