US3776733A - Photographic material of emulsions of different gamma and sensitivity - Google Patents

Abstract

Photographic copy of image that is partly continuous tone and partly line is made with a single exposure of entire image on combination of two silver halide emulsions carried by a supporting surface that reflects at least half the light reaching it, one emulsion having a gamma between 0.8 and 1.2 and a maximum density of at least 1.4, the other being slower than the first by at least 6* DIN, having a gamma between 2.0 and 4.0 and at least 1.0 greater than the first and having a maximum density about the same as the first. The emulsions can have their respective maximum sensitivities in different portions of the spectrum and can contain dyes that absorb in such spectrum portion to adjust respective sensitivities.

Description

United States Patent Lohmer et al. Dec. 4, 1973 [54] PHOTOGRAPHIC MATERIAL 0F 3,411,908 11/1968 Crawford 96/87 g gg il gis DIFFERENT GAMMA AND FOREIGN PATENTS OR APPLICATIONS 604,761 9/1960 Canada 96/68 [75] Inventors: Karl Lohmer; Werner Verburg, both of Leverkusen, Germany [63] Continuation of Ser. No. 688,354, Dec. 6, i967,

abandoned.

[30] Foreign Application Priority Data Dec. 14, 1966 Germany A 54364 [52] US. Cl 96/68, 96/44, 96/45 [51] G03c l/76, G03f 5/00 [58] Field of Search 96/68 [56] References Cited UNITED STATES PATENTS 7/1964 Hellmig 96/68 Primary Examiner-Norman G. Torchin Assistant ExaminerAlfonso T. Suro Pico Att0rneyConnolly & l-lutz [57] ABSTRACT Photographic copy of image that is partly continuous tone and partly line is made with a single exposure of entire image on combination of two silver halide emulsions carried by a supporting surface that reflects at least half the light reaching it, one emulsion having a gamma between 0.8 and 1.2 and a maximum density of at least 1.4, the other being slower than the first by at least 6 DIN, having a gamma between 2.0 and 4.0 and at least 1.0 greater than the first and having a maximum density about the same as the first. The emulsions can have their respective maximum sensitivities in different portions of the spectrum and can contain dyes that absorb in such spectrum portion to adjust respective sensitivities.

3 Claims, No Drawings PHOTOGRAPHIC MATERIAL OF EMULSIONS OF DIFFERENT GAMMA ANlD SENSITIVITY This application is a continuation of Ser. No. 688,354 filed on Dec. 6, 1967, now abandoned.

This invention relates to a photographic material for use in the production of reflection copies for the photomechanical production of printing forms.

In the photomechanical production of printing forms, one generally starts with an original which has been obtained photographically. The density values of this original are converted into electrical values by point-bypoint scanning with a measuring beam. These measured values are used in a mechanical apparatus which operates synchronously with the scanning device to produce a printing form by mechanical means.

In the production of cylindrical printing forms, the original may be arrangedcylindrically in order to facilitate synchronization between the scanning device and the cylindrical printing form, so that in the simplest case, where the conversion scale is 1:1, very simple geometrical relationships are obtained.

The photographic original used for the photomechanical production of printing form must meet high requirements. This material must render both continuous-tone and line images of optimum quality and in addition it should have good dimensional stability. This requirement of yielding optimum reproduction both of continuous-tone and of line images would appear to be a contradiction in terms in that a relatively low contrast is required for a continuous-tone image whereas a steep gradation is required for optimum reproduction of a line image.

These contradictory requirements can be met if a photographic material is produced in such a way that either a high or low gamma value results, depending on the choice of copying light. This is achieved, for example, either by mixing an orthochromatic (green sensitive) line emulsion with a blue-sensitive continuoustone emulsion or applying one such emulsion over the other. If this material is exposed through a blue filter, only the silver halide emulsion which yields a low gamma will be photographically active provided the threshold sensitivity of the green-sensitive silver halide emulsion is sufficiently high compared with the bluesensitive emulsion.

The use of such a material, however, requires considerable waste of time because the line image in a combined original which contains partly continuous-tone and partly line images must be covered by a black mask while the continuous image is exposed behind a blue filter, and conversely the continuous-tone image must be covered with a mask during exposure of the line image behind a yellow filter.

The object of the present invention is to provide a photographic material by means of whichboth continuous-tone and line image of good quality can be. reproduced by a single exposure.

We now have found that a photographic material which contains at least two silver halide emulsions differing from each other in gamma and sensitivity, which emulsions may be either mixed in one layer or arranged separately in two layers, may be used for this purpose. A dye which absorbs light from that range of wavelengths to which the low contrast silver halide emulsion is sensitive is added at least to that emulsion which is responsible for reproduction of the continuous-tones.

The density of the dye in this region is preferably about 0.8 to 1.2.

The light-sensitive silver halide emulsion layer or layers of the photographic material according to the invention are applied direct to a dimensionally stable support which reflects diffusely from its surface essentially all light, but at least 50 percent. In order to achieve sufficient sharpness, the light must not penetrate to any significant extent into the support but must be reflected on the surface. Surprisingly with this material one obtains such good reproduction of detail that copied line images suffer no detectable loss in sharpness even if they are copied on a photographic material having a gamma suitable for continuous-tone images.

A suitable support is, for example, a polyester film especially, polyethylene terephtylene', containing white pigments. Alternatively, paper the surface of which has been rendered water-resistant by application of layers of synthetic resin containing white pigment, may be 'used. The dimensional stability of the paper'may be improved by backing it with metal foils. Thus, good results were obtained with paper which had been rendered dimensionally stable by backing with an aluminium foil and which had been made waterproof by coating the surface with polyolefine, preferably polyethylene, layers containing TiO The white pigment content inthe layer immediately below the light-sensitive silver halide emulsion layer is necessary if one is to achieve the required sharpness.

The light-sensitive silver halide emulsions are prepared in the usual manner. The emulsions with flatter gamma for reproduction of continuous-tone images generally contain silver bromide, optionally with a small addition of silver chloride and a minor quantity of silver iodide. The emulsions with steeper gamma, which are higher in contrast, generally contain mixtures of silver chloride and silver bromide. The usual hydrophilic film-forming binding agents such as polyvinyl alcohol, alginic acid derivatives or preferably gelatin, may be used as binding agents for the silver halide emulsion layers.

The usual photographically inactive dyes are applied as masking dyes. Suitable products are described in the literature.

The thickness of the silver halide emulsion layer where only one is used is about 3 to 10 u, preferably about 5 p..

The emulsion with the flatter gamma is preferablyonly blue-sensitive whereas the emulsion with the steeper gamma and higher contrast may in addition he green-sensitive and/or red-sensitive. The emulsion with the flatter gamma, which records the continuous tones, should be so composed as regards its silver concentration and other photographic properties that it has a maximum density of at least 1.4 under the usual conditions of development.

The low contrast silver halide emulsion has a gamma between 0.8 and 1.2, the high contrast silver halide emulsion a gamma of 2.0 and 4.0. The difference in gamma between the two emulsions should be at least 1.0.

The sensitivity to white light of the high contrast silver halide emulsions is at least 6 DIN less than that of the low contrast emulsion. This amounts to a difference of two or more shutter stops.

Example 1 A silver iodobromide gelatin emulsion containing 5 mol% of silver iodide based on the total silver halide, and which has not been optically sensitized, contains a yellow masking dye (as described in Ullmann, Encyklopadie der Techn. Chemie, Vol. 13, page 627, 3rd edition) and reproduces continuous tones with gamma of one, is applied to a biaxially prestretched support of polyethylene terephthalate that has been rendered opaque by incorporation of titanium dioxide. The emulsion is applied in such the way that a maximum density of developable silver is .4. The concentration of the masking dye is so calculated that a yellow density of about D 1.0 is obtained in the unprocessed material.

A high contrast silver chlorobromide gelatin emulsion (containing 70 mol% of silver chloride based on the total silver halide) which has not been optically sensitized and which has a 'y 4, the sensitivity to white light of which is only one-twentieth of the sensitivity of the first emulsion, is applied onto this first emulsion layer in such a way that the second emulsion has the same silver content per square meter. The above masking dye may also be added to this second layer to correct the sensitivity.

A material is thereby obtained which on exposure behind a grey test wedge and the usual photographic processing including development and fixing in the following baths:

Developer: 1 g. p-methylamino phenol 3 g. hydroquinone 13 g. of sodium carbonate g. of sodium sulfite sicc.

1 g. potassium bromide 1000 ml. of water Fixingbath:

200 g. of sodium thiosulfate cryst.

50 g. potassium metabisulfite 1000 ml. of water has a higher gamma in the density region above 1.5 than in the density region below 1.5. An original which is composed of continuoustone and line transparencies suitable for photogravure is copied onto the resulting material so that the lightest density value to be reproduced in the subsequent print is reproduced as grey tone of density 1.6. The resulting copy is best suited for the photomechanical production of printing forms. This process is suitable in particular for use in the production of printing forms by the so-called heliograph block method (Hell, Kiel).

Example 2 The two emulsions used in Example 1 are so chosen that for a given concentration of masking dye, they have a sensitivity ratio of 1:20. The two emulsions, which have the same silver content, are now mixed in a ratio of 1:1 and the mixture is applied to the support described in Example 1 so that the same amount of silver is present per unit surface area as in the photographic two-layered material used in Example 1. Processing is otherwise carried out as described in Example l. A copy is obtained which is excellently suitable for the production of printing forms.

Example 3 The following emulsion mixture is applied onto the support described in Example 1. One emulsion is a continuous-tone silver chlorobromide emulsion containing 30 mol% of silver bromide bored on the total silver halide and sensitized to blue light. To this emulsion is added a high contrast silver chlorobromide emulsion containing 96 mol% silver chloride and sensitized to green light, the additive being in the ratio of 1:1. The yellow masking dye of Example 1 employed in the same manner.

It is now no longer important to observe accurately the sensitivity relationship between the two silver halide emulsions since the characteristic curve of the high contrast emulsion component can be shifted in relation to the characteristic curve of the low contrast emulsion component by suitable choice of the color of the copying light. A higher gamma in the density region of above 1.5 than that in the'density-range of below 1.5 can therefore easily be achieved.

Further processing is carried out as in Example 1, except that the color of the copying light is adjusted accordingly.

Example 4 In a manner analogous to Example 3, the emulsion mixture is applied onto paper which is coated on both sides with a polypropylene layer. TiO pigment is incorporated into that polypropylene layer onto which the silver halide emulsion layer is arranged,-so that light is reflected from the surface of the pigmented polyolefine layer. The procedure is otherwise analogous to that used in Example 3.

Example 5 In a manner analogous to Example 3, the emulsion mixture is applied onto a paper support provided with polyethylene layers as described in Example 4. This support is backed on the rear side with a thin aluminium foil to increase the dimensional stability. The procedure is otherwise as indicated in Example 3.

What is claimed is:

1. In the preparation of a reproduction of an image that is partly continuous tone and partly line the steps of preparing a light sensitive low contrast silver halide emulsion which yields a gamma suitable to a continuous tone reproduction and a high contrast silver halide emulsion which yields a gamma of at least 1.0 greater than the low contrast emulsion and the high contrast emulsion being applied to a dimensionally stable support which reflects light from its surface, exposing the photographic material to light and subjecting the exposed material to photographic processing including development and fixing in suitable baths and copying continuous-tone and line images, the improvement according to which absent masking of the line image part or the continuous image part a single undelineated exposure is used to expose to that image ,a light-sensitive photographic silver halide combination having the support white pigmented to provide a surface that diffusely reflects at least half the light reaching it, and the two silver halide emulsions coated and dried on completely cover a common area of the surface, one of the emulsions having a gamma between 0.8 and 1.2 and a maximum density of at least 1.4, the other emulsion having a speed index value at least 6.0 DlN slower than the first, having a gamma between 2.0 and 4.0 and at least 1.0 greater than the first, and having a maximum optical density substantially the same as the first emulsion,

3,776,733 6 contained in the first emulsion having the ability to abent visible wavelengths. sorb light to which that emulsion responds, the density of the dye being between 0.8 and 1.2, and developing emulsion is only blue sensitive, the other emulsion 1s and fixing the thus-exposed combination.

2. The invention of claim 1 in which the two emul- 5 sensitized to green' sions have their respective sensitivity maxima at differ- 3. The invention of claim 1 in which the low contrast

Claims (2)

1. 2. The invention of claim 1 in which the two emulsions have their respective sensitivity maxima at different visible wavelengths.
2. 3. The invention of claim 1 in which the low contrast emulsion is only blue sensitive, the other emulsion is sensitized to green.