Title:
Mixed grain emulsions
United States Patent 2388859
Abstract:
This invention relates to color photography and more particularly to a duplicating and printing material having a mixed grain emulsion layer. Photographic films provided with emulsions of the mixed grain type are well known. These consist essentially of emulsions containing a mixture of sensitive...


Inventors:
Mannes, Leopold D.
Godowsky Jr., Leopold
Application Number:
US37379041A
Publication Date:
11/13/1945
Filing Date:
01/09/1941
Assignee:
EASTMAN KODAK CO
Primary Class:
Other Classes:
430/365
International Classes:
G03C7/26; G03C7/30
View Patent Images:
Description:

This invention relates to color photography and more particularly to a duplicating and printing material having a mixed grain emulsion layer.

Photographic films provided with emulsions of the mixed grain type are well known. These consist essentially of emulsions containing a mixture of sensitive silver halide grains sensitized to record different regions of the spectrum coated on a support with or without additional emulsion layers. In the mixed grain emulsion system it is common to use a mixture of silver halide grains sensitized to record the primary regions of the visible spectrum, the red, the green and the blue.

Since the red and green sensitive grains retain the inherent blue sensitivity of a silver halide it is necessary to restrict this blue sensitivity so that a blue record is not printed on grain intended to record red or green. In a system employing a multilayer material this same problem is also present and may be solved by coating the red and green sensitive layers under a blue sensitive layer and screening these layers from blue light by means of a filter dye. Such an expedient is not possible in a mixed grain system where particles sensitive to all three color components are exposed to the action of light rays at a common surface. It has been suggested to bath the red and green sensitive particles in a yellow dye solution thereby reducing their blue sensitivity.

Another proposal is to use silver chloride emulsions for the green and red components and silver bromide for the blue component emulsion, thereby utilizing the sensitivity of silver chloride to shorter wave lengths than silver bromide.

The object of the present invention is to provide a mixed grain emulsion which avoids the difficulties of the prior art.

Another object is to provide a mixed grain emulsion consisting of silver halide grains of high sensitivity and wide latitude.

Another object is to described the method of using a film provided with the mixed grain emulsion of this invention, as a printing and duplicating material.

Another object is to provide a two or three color component mixed grain emulsion, certain grains of which are sensitive to a region of the visible spectrum other than the blue and are not especially screened against blue light.

Another object is to provide sensitizing dyes which restrict sensitivity to the grains of a mixed grain emulsion which they are intended to sensitize and do not confer .sensitivity on other grains.

These objects are accomplished in the present invention by the use of a photographic printing material consisting of a support upon which is coated a mixed grain emulsion layer containing fast silver halide grains sensitive to the blue spectral region, and slow silver halide grains sensitive to a region of the visible spectrum other than the blue, as well as the blue spectral region, the sensitivity of the grains primarily sensitive to blue light being considerably greater than the sensitivity of any other grains to blue light.

The silver halide emulsions which may be used are those containing silver bromide or silver bromo-iodide, preferably silver bromo-iodide.

The silver halide emulsion component sensitive to the blue spectral region is provided by a fast negative emulsion of the type used in motion picture negative or press film, such as that described by Carroll, Bureau of Standards Scientific Paper No. 340, and having a high sensitivity to blue light. The emulsion components sensitive to a spectral region other than the blue are provided by emulsions of the type used in positive films or enlarging papers and which have a blue speed many times less than that of the high speed negative emulsion. We may use as a mixed grain emulsion component sensitive to red light, a silver bromide emulsion sensitized with an 8-alkyl or 8-phenyl-3, 4, 3', 4'-dibenzothiacarbocyanine dye as described in Brooker U. S. Patents 1,969,444 and 1,969,447, granted August 7, 1134.

For another component sensitive to a region such as the green spectral region we may use an emulsion sensitized with a thia- or selena-2'-cyanine dye as described in Brooker U. S. Patent 2,189,599, granted February 6, 1940, or a 3,4-benzothia-2'cyanine dye as described in Brooker U. S. Patent 1,935,696 granted November 21, 1933. These dyes are also disclosed in our pending application Serial No. 307,140 filed December 1, 1939, which describes their use in the narrow band sensitization of multilayer color films.

In the accompanying drawing is shown a sensitive photographic printing material made according to our invention and printed by use of a yellow filter 12 interposed between the light sourc and the printing material. The support 0 may be any suitable material such as paper, glass, synthetic resin, a cellulose ester or a metal plate, such as aluminum. The emulsion layer ii of our invention consists of grains of silver halide sensitized to record different regions of the visible spectrum, joined to the support by any suitable subbing means (not shown). The yellow filter 12 may be composed of a yellow dye such as tartrazine in gelatin and may be applied as a filter layer over the mixed grain emulsion layer.

Our invention may be further illustrated by the following example: Example One liter of a slow silver bromide paper emulsion is divided into two equal portions. To the first portion is added 2.0 gm. of 2,2'-dimethyl8 - ethyl - 3,4,3',4' - dibenzthiacarbocyanine bromide, and to the second.portion is added 2.0 gm. of 2,1'-diethyl-3,4-benzthia-2'-cyanine bromide.

The two portions are held at a temperature of 50° C. for 10 minutes then mixed,' combining with this mixture 500 cc. of a fast negative type emulsion, such as is used in motion picture negative or press films. The mixed grain emulsion is then coated on a support in a known manner.

The photographic printing material prepared as described above may be used for the reproduction of natural color pictures by printing from a transparency through a filter. The filter is one which absorbs just enough blue light so that the printing speed of the fast blue sensitive component of the mixed grain emulsion is reduced to a value equivalent to those of the red and green speeds of the two other compoents. Where the blue speed differential between the fast and slow emulsions is, for instance, as great as fifty times, a yellow filter absorbing 98% of the overall blue light may be used. Such a filter is one containing a dye of the pyrazalone type exemplified by tartrazine. This filter would reduce the blue speed of the red and green sensitive components of the mixed grain emulsion to approximately 2% of the speeds of the red and green thereby rendering the blue sensitivity of these grains negligible for printing purposes.

The high speed blue sensitive emulsion still prints the blue record at the same speed required for printing the red and green records onto the other two components.

If it is desired we may provide a mixed grain emulsion consisting of particles sensitized to record only two regions of the spectrum, one of which is the blue, and coat this emulsion on one side of a support and a second emulsion sensitive to the third color component is coated on the opposite side of the support. In this case we prepare a homogeneous mixture of a high speed blue sensitive silver bromide emulsion with a slow silver bromide emulsion sensitized to record red or green light in a manner similar to that described in the preceding example. Here again it is necessary to have a considerable blue speed differential between the two mixed grain emulsion components and between the blue component and the emulsion layer coated on the opposite side of the support. In printing we may use the same type of yellow filter as above described for use with a three component mixed grain emulsion.

The films constructed in the manner of our invention may have color couplers or dyestuff formers incorporated in the emulsion layers but preferably these are in the developing solution and form a dye simultaneously and in situ with the oxidation product of the developer. The color forming developers which we may use are the primary aromatic amino developing agents such as diethyl-p-phenylene diamine. The couplers which may be used are those having a methylene group or phenolic hydroxyl group reactive in the coupling process.

It is to be understood that the disclosure herein is by way of example and that we consider as included in our invention all modifications and equivalents falling within the scope of the appended claims.

What we claim is new and wish to secure by Letters Patent of the United States is: 1. A photographic material sensitive to different regions of the visible spectrum, comprising a support having thereon a single mixed grain emulsion layer containing coarse, highspeed silver bromide grains sensitive to only the blue region of the spectrum, and fine, slow-speed silver bromide grains sensitive to the blue region and also to another region of the visible spectrum, the sensitivity to blue light of said highspeed grains being approximately 50 times the sensitivity to blue light of said slow-speed grains.

2. A photographic material sensitive to different regions of the visible spectrum, comprising a support having thereon a single mixed grain gelatine emulsion layer containing coarse, high-speed silver bromide grains sensitive to only the blue region of the spectrum, fine, slow-speed silver bromide grains sensitive to the blue and green regions of the spectrum, and fine, slowspeed silver bromide grains sensitive to the blue and red regions of the spectrum, the sensitivity to blue light of said high-speed grains being ap60 proximately 50 times the sensitivity to blue light of both of said slow-speed grains.

LEOPOLD D. MANNES.

LEOPOLD GODOWSKY, JR.