DE3226177A1 - Process for producing photographic reproductions - Google Patents

Abstract

The invention relates to a photographic reproduction process which is based on the light sensitivity of dichromate and in which the light-sensitive layer is provided with a grainy structure by prolonged rolling onto the base. Above all a simple and reliable halftone reproduction, particularly effective image action and rapid developability are achieved by this simple measure. Expediently, additives which promote the grain structure during coating are added to the image layer.

Description

Process for making photographic reproductions the photographic processes, which come together under the name of noble printing processes can be tough ion to the oldest photographic copying processes. You experienced their heyday at the turn of the century. These methods are based on photosensitivity of chromium VI salts (dichromates) in connection with gelatine or gum arabic. When exposed to light, Cr (VI) is reduced to Cr (III), the resulting Cr (III) has a tanning effect on the gelatine. As a result, the gelatine loses its solubility or Swellability in warm water. At this point we want to refer to two of these historical Procedures are discussed in more detail because they are related to the present procedure stand in a certain 13cziel1ullg.

In the pigment printing process, an aqueous solution of gelatin is used and potassium dichromate with color pigment additives in a relatively thick layer on a carrier paper upset. The exposure takes place through a transparent contact copy negative.

The gelatine becomes more or less deep depending on the light intensity tanned. The pigment paper is then soaked in water and the pigment layer transferred by pressing onto a transfer paper. Only then does the Treatment with warm water, whereby the unexposed gelatin together with the pigment is washed away from the (unexposed) back. Depending on the exposure intensity This creates a gelatin pigment relief; so the semitones are through different layer thicknesses of the image layer are generated.

It is different with the rubber printing process: here, the thinnest possible layer is created of gum arabic, potassium dichromate and pigment applied to a suitable paper and exposed. The result is an image that shows almost no semitones. These arise only when you have several layers with different exposure times on top of each other copied.

The other fine printing processes are based on a different principle: tanned gelatin loses its swellability in water and is bold in color (e.g. Ulfarben) can be dyed, while the untanned gelatine repels the greasy color. In this way, too, one can achieve an image-like reproduction.

The photographic processes briefly outlined here have a few Disadvantages: they require a great deal of technical skill to be carried out, it is complicated to carry out, the exposure times are very long, and it is a contact copy negative in the same format as the reproduction is required, the development is time-consuming, the halftone reproduction is either carried out by cumbersome transmission methods (Pigment printing) or by copying multiple copies with different ones Exposure times (rubber pressure). Sourcing the materials in today Time is difficult to achieve the uniform application of the image layer on the Carrier is also difficult.

In conclusion it can be said that the fine printing process, in spite of interesting artistic properties (hollow l: flexibility in color, large Ccstaltullgsireihe it through many intervention possibilities), not being bound to a darkroom and developability of the reproductions in ordinary water, almost completely forgotten due to the listed disadvantages are.

The present invention relates to a photographic reproduction process, which is based on the light sensitivity of dichromate, also a tanning process is, but due to the special concept: #eption of the layer of layer is much easier, is much faster and cheaper to do. It is different from the traditional ones Procedure essential in the following points: 1.) Instead of a relatively thick one Image layer a very thin, grainy structured image layer is used, the is made with a special rolling process. Due to the grain structure that practically consists of fine, closely spaced image layer dots, becomes a simple and reliable sound reproduction, a particularly effective one Image effect and rapid developability achieved.

2.) The composition of the image layer is in addition to the usual Chemicals like gelatin, dichromate and color pigment preferably still come from others Additives that promote the grain structure during coating, the photosensitivity and improve developability.

3.) The exposure does not take place as with conventional methods by contact copying, but preferably with a slide projector. Through this Measure one is able to produce enlargements directly from the 35mm negative, without first having to make an (expensive) contact copy negative.

The inventive method for the production of photographic Reproductions using chromium VI salts and color pigments in one layer a gel former, whereby an aqueous suspension of chromium VI salt (s), gel former, Applies color pigment (s) and possibly other additives to a base, then exposed, preferably by means of a projector, and finally by washing out the underexposed or unexposed parts developed, is characterized in that the photosensitive layer, which preferably also improves grain formation Contains additives during or after application as long as a roller treatment subject until a grainy layer is formed.

I) The chemicals for the image layer come for durability reasons expediently used in powder form, the pigmented in different colors and ready-to-use chemical mixtures for use only with warm water must be mixed.

The main components of the mixture are ground commercial gelatine (30-70%), alkali or ammonium dichromate (1-20%) and organic or inorganic Color pigments (10 -50%). Further additions that have not yet been made in the high-quality printing process Found use, have the task of promoting the grain structure of the image layer, or to improve the development properties. Such additives are inert Fillers such as plaster of paris, silica gel or similar (10 - 30%), dextrin (5 - 20%) and methyl cellulose (0.1-5%). Furthermore, the photosensitivity is increased by the addition of organic Sensitizers (0.01 - 1%) improved.

The intimate mixing of the chemicals is expediently carried out in one Ball mill, where, if necessary, individual components that are too coarse are ground up beforehand can be.

The following exemplary embodiment is intended to serve as an illustration: 180 g edible gelatine, powdered 30 g ammonium dichromate s5 g dextrin 80 g gypsum 2 g Methyl cellulose 3 g anthraquinone-2,6-disulfonic acid, disodium salt 120 g iron oxide, become black in a three-liter pot made of hard-paste porcelain in a ball mill 1/2 to Homogenized for 1 hour and mixed thoroughly.

For other shades, other commercially available pigments are used instead of the iron oxide pigment Pigments used, e.g. 60 g of a copper phthalocyanine pigment for green, etc.

For use, 3 ml of water are now added to 5 g of the above mixture, the suspension is melted in a water bath (60 to 90 ° C) with stirring, then a further 5 ml of water are added and the mixture is stirred again. Then another 2 ml Ethanol (spirit) added, which affects the coating properties (Grain structure) still improved.

Part of this coating solution is now in a warm state a suitable carrier (glass plates, metal sheets; flolz, cardboard, various Lacquer layers, etc.) poured on in the form of an elongated lacquer (for a format of 20 x 30 cm are enough about 0.5 - 1 ml) and then immediately with a rubber roller (about 15 cm wide, smooth surface, available in paint shops) evenly Distributed over the whole area. Rolling continues until the layer by evaporation of the solvent gradually loses its stickiness, which is evident the disappearance of the "sticky" rolling noise can be heard. The rolling should be easy Pressure, briskly, up and down in one direction, overlapping and uninterrupted be performed. The rolling time is about 2 minutes, which is achieved in this way the uniform grain structure of the image layer, which is so important for the process, which, after drying, is estimated to have a thickness of 0.01 to 0.1 mm.

All work can be carried out with normal room lighting (subdued daylight or incandescent light). Only the dry image layer is sensitive to light and should be stored in the dark. The drying takes place also due to the low Layer thickness and the grain structure within a few minutes, when treated with a hair dryer much faster.

The plate is now through a slide projector (halogen lamp) Black and white exposed. After the exposure, which of course also im Contact copying can be done, the development follows.

To do this, the image layer is first rinsed with cold water for approx. 20 s, then for a few seconds with warm water (approx. 400C) until the unexposed parts of the layer are removed begin to peel off.

Then you rinse again with cold water. Repeated the whole thing do one or two times until the picture is satisfactory developed is. The image layer is then allowed to dry.

Then you have the option of using the first layer of images to be rolled up (possibly differently), to be exposed and developed. In this way you achieve great freedom of design. By copying several Image layers in the subtractive primary colors are also available in natural colors Produce pictures when you look at the individual layers through the corresponding color separation negatives exposed.

Claims (7)

Claims. 1. Process for making photographic reproductions under Use of chromium VI salts and color pigments in one layer of a gel former, whereby an aqueous suspension of chromium VI salt (cn), gel former, color pigment (s) and then optionally applying further additives to a substrate, preferably by means of a projector, exposed and finally by washing out the under- or unexposed parts developed, characterized in that the light-sensitive Layer, which preferably also contains additives that improve grain formation, subjected to a rolling treatment during or after application until a granular layer has arisen. 2. The method according to claim 1, characterized in that the suspension is applied warm Imd the rolling treatment with cooling until a granular layer with an average thickness of 0.01 to 0.1 mm is carried out. 3. The method according to claim 1 or 2, characterized in that the Rolling treatment is carried out until the granular layer is required for further treatment has reached the necessary strength. 4. The method according to any one of the preceding claims, characterized in that that the suspension as additives, fillers that improve grain formation, such as ips or silica gel as well as methylc @ llulose and dextrin Y # 1g <'are used 5. Ve r L # their according to one of the preceding claims, characterized in that ethanol is added to the suspension. 6. The method according to any one of the preceding claims, characterized in, that gelatin is used as a gelling agent. 7. Mixture for use in the method according to any one of the claims 1 to 6, characterized in that it consists of the following components: 30 up to 70% gelatine 1 to 20 tons alkali or ammond dichromate 10 to 50% color pigments and optionally 10 to 30% fillers 5 to 20% dextrin 0.1 to 5% methyl cellulose 0.01 to 1 ton of photosensitizers. - Description -