A novel method for the addition of powders to photographic systems

Abstract: A process for improving the method by which a powder such as a dye is added to a gelatino silver halide element is described. This process involves encapsulating the powder within a gelatin capsule. This process avoids cross-contamination and dusting when powder is added to solvent and also reduces the use of extra solvent in the manufacture of the element.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention : This invention relates to a process of preparing and making of photographic emulsions. Specifically, this invention relates to a particular method for the addition of a powdered material such as dyes to a photographic system. Examples of dyes include spectral sensitizing dyes, filter dyes and antihalation dyes. Also the present invention relates to emulsions containing such powders. 2. Discussion of the Prior Art : During the preparation of gelatino, silver halide emulsions, the addition of a powder such as a dye is useful such as for spectral sensitization, image quality improvement or antihalation. Illustratively in the case of sensitiza-tion, such property may take the form of so-called "chemical sensitization" wherein various ingredients are added to change the sensitometry thereof. Alternatively, it may also be necessary to alter the spectral response of the emulsions for one reason or another. If this is required, so-called "spectral sensitizing" dyes are added to this aqueous dispersion of gelatin and silver halide. The dyes are conventionally large, organic molecules as is well-known and these are sometimes not very soluble in either an aqueous or in a mixture of organic/aqueous solvents. Thus, very dilute mixtures are made in order to dissolve the dye before adding the dye to the emulsion. Several problems occur. One concern is the solution handling of a formulation containing a dye. The addition of the dry, powdered dye to the solvent or into a formulation can cause dusting problems which is a great inconvenience. This dust may cause respiratory problems to the handlers and also causes airborne contamination of what is supposed to be an ultra-clean environment. Thus, there is a pressing need to find an alternative method for the addition of spectral sensitizing dyes to a photographic system. Examples of prior art are FR-A-2 381 337 and FR-A-2 381 335 (where powders are incorporated into photographic coating compositions in the form of granules or pellets), as well as US-A-4,755,446 and US-A-4,798,741 (where additives are present in photosensitive materials within microcapsules). SUMMARY OF THE INVENTION It is an object of this invention to provide a system for the addition of a powder such as a dye to gelatino, silver halide emulsion without the necessity of forming a solution of the powder. It is yet another object to provide a system which avoids dusting and the like. These and yet other objects are achieved in a process for the addition of powder to a photographic emulsion wherein said powder is contained within a plurality of gelatin capsules. DETAILED DESCRIPTION OF THE INVENTION The encapsulation of various ingredients is a well-known process in the prior art. For example, it is known to make capsules in the pharmaceuticals industry to assist in taking and controlling the specific dose of a medicine, for example. When these capsules are made from gelatin, for example, they may be consumed or dissolved in water. It is also known to encapsulate various other ingredients for various other purposes. However such technique has not not been employed in conjunction with a dye for use in a photographic emulsion and particularly a gelatino silver halide emulsion. In the photographic industry it is sometimes necessary to add powdered materials such as dyes to the system. These dyes for example can be of the sensitizing, filter or antihalation type and they can be added to an under or backing layer. Dyes of this type often are generally large, organic compounds and some have very complex structures. Many of the compounds are usually not very soluble in water and thus generally are either dispersed as a dilute water solution or some water miscible combination such as the lower alcohols or ketones. The problem of adding the dye to the solvent is obvious. These dyes are conventionally fine, powdered materials and will color, stain and even cause physical problems if ingested while airborne. It has long been a practice in the prior art to add these dyes dissolved since it was thought that only in this manner would the dye be properly adsorbed to the silver halide grains or dispersed within the gelatin binder, for example. Thus, no efforts have been made to add dyes of this nature in an encapsulated form. Other methods have been tried with varying results in addition of dyes to photographic systems such as by granulating or pelletizing the dye prior to addition of this material to the emulsion. Although these processes avoid the addition of extra solvent and the dusting problems in making up the solution of the dye, the pelletizing or granulating retards the solution of the dye within the gelatin or emulsion materials. Thus, sometimes, good dispersion of the dye is not achieved by these methods. In the practice of my invention, I encapsulate the dry dye powder within a gelatin capsule. In the present invention the term "capsule" excludes a microcapsule The process for achieving an encapsulation is well-known in the prior art. The capsules are formed and the dry dye powder can be inserted therein using a conventionally known machine such as the Type 8 Standard Hard Capsule Filling Machine designed by CAPSUGEL, a Division of Warner-Lambert Co., Highland Park, MI. These dye capsules can then be stored for long periods of time prior to use. Since a known amount of dry dye is placed within each capsule, the amount of dye added to the emulsion or gelatin layers is easily controlled. Since the gelatin capsules are compatible with the gelatin conventionally used within these photographic systems, problems of dispersion of the dye prevalent with other, dry methods, are not a problem here. Thus, one only needs to insure that the capsules have some time to dissolve and the dye will enter the emulsion properly. Since the capsules are essentially dry and dust-free, the problems of dry dye dispersion are also eliminated as is the addition of extra solvent and the like. Although the previous discussion has been in relationship to a powder which is a dye it is within the scope of the present invention that other powders are encapsulated. Other materials which are introduced into the photographic emulsion that are initially in powder form, such as a sensitizer, can be incorporated. This invention will now be illustrated by the following examples: EXAMPLE 1 This example demonstrates the use of encapsulated, photographic sensitizing dye within a gelatino, silver halide emulsion. A conventional, silver bromoiodide, tabular grain emulsion (ca. 98% Br and ca. 2% I) was prepared as well-known to those of normal skill in the art. This emulsion was then dispersed in a bulking amount of gelatin and brought to its optimum sensitivity with gold and sulfur salts as is also well-known. Standard antifoggants, wetting and coating aides were also present as well as hardeners. Since tabular grains have a low sensitivity in the green spectrum of the visible region, it is conventional to add a green spectral sensitizing dye to the emulsion in order to increase the sensitivity thereof. In this case, 800 gms of a carbocyanine dye in an amount of 2 gms per 1.5 moles silver and tartrazine, i.e., which had been encapsulated using the aforementioned Type 8 Encapsulator, were added to this emulsion and digested for a period of 60 minutes at 39°C. In this case, the dye containing capsules were of .00 size and each capsule contained about 320 mg of the aforesaid dye. In addition, 215 gms of encapsulated tartrazine dye were also added to improve the image quality of this element. For control purposes, a similar emulsion was prepared using the aforementioned dyes in a conventional manner, i.e., where the carbocyanine dye was dissolved in alcohol and tartrazine was dissolved in water . During the dissolution of these dyes in the solvent, "dusting" was observed which was undesirable. Both emulsions were coated on a standard dimensionally stable polyethylene terephthalate film support which had been previously subbed with resin and gelatin sub layers to improve the adhesion of the emulsion. The emulsion layers were coated to a coating weight of 4.7 mg Ag/dm 2 and then an overcoat layer of gelatin was applied supra thereto. After drying, samples of both elements were given a conventional exposure, developed, fixed, washed and dried. The physical and sensitometric properties of these elements were equivalent indicating that the encapsulated dyes had been dispersed and absorbed by the silver halide grains. EXAMPLE 2 This example demonstrates the use of the encapsulation process for the preparation of an antihalation layer. An emulsion suitable for preparing an antihalation layer was made by mixing 900 gms of an encapsulated Acid Violet 520 dye of the following structure: This material was encapsulated using the same equipment as Example 1 and the capsules contained in the neighborhood of 300 to 500 mg of dye per capsule. The backing solution also contained about 60,000 gms of gelatin and about 690,900 gms of water, Additionally, this solution contained the usual wetting and coating aides and hardeners. The capsules were dispersed in this solution at 60°C for about 3 minutes and appeared to be fully compatible with this mixture. For control purposes, the same dye dissolved in water was used. Both gelatin solutions were coated on standard polyester base and a standard emulsion layer coated on the opposite side thereto. Both antihalation layers were equivalent in every respect as regards optical density and ability to absorb scattered light. The sensitometry of the silver halide emulsion layers were also equivalent. Thus, the procedure described in this invention can be used with dyes used within any conventional, gelatino, silver halide element. Cross contamination of various dyes which might be used to prepare any variety of element is avoided as well as the dusting and dirt problem normally associated with the dissolution of dyes into solvents. The addition of alternate solvents to the silver halide emulsion is also avoided by the practice of this invention.

Claims: A process for the formation of a photographic emulsion containing a powder comprising the steps of: (a) forming a plurality of gelatin capsules, (b) inserting dry powder into each of the plurality of gelatin capsules, (c) adding the gelatin capsules containing the powder to a photographic emulsion, and (d) dissolving the gelatin capsules within the emulsion to allow release of the powder with the emulsion to obtain a uniform dispersion or solution of the powder. The process of claim 1 wherein the powder is a dye. The process of claim 2 wherein said dye is a photographic sensitizing dye. The process of claim 2 wherein said dye is an antihalation dye. The process of claim 2 wherein said dye is a filter dye.

Inventors: MASON EILEEN, MASON, EILEEN
Applicants: STERLING DIAGNOSTIC IMAGING, STERLING DIAGNOSTIC IMAGING, INC.
Application year: 1991
Main classification: G03C1
IPC codes: G03C1, G03C7