BACKGROUND OF THE INVENTION
1. Field of the Invention:
[0001] 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:
[0002] 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.
[0003] 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.
SUMMARY OF THE INVENTION
[0004] 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
[0005] 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.
[0006] 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.
[0007] In the practice of my invention, I prefer encapsulating 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.
[0008] 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.
[0009] This invention will now be illustrated by the following examples:
EXAMPLE 1
[0010] This example demonstrates the use of encapsulated, photographic sensitizing dye within
a gelatino, silver halide emulsion.
[0011] 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.
[0012] 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
[0013] This example demonstrates the use of the encapsulation process for the preparation
of an antihalation layer.
[0014] 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.
[0015] 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.
1. In a process for the addition of powder to a photographic emulsion wherein the
improvement comprising the addition of said powder is within a plurality of gelatin
capsules with the proviso that the capsule is not a microcapsule.
2. The process of claim 1 wherein the powder is a dye.
3. The process of Claim 2 wherein said dye is a photographic sensitizing dye.
4. The process of Claim 2 wherein said dye is an antihalation dye.
5. The process of Claim 2 wherein said dye is a filter dye.
6. A photographic emulsion containing a powder encapsulated within a plurality of
gelatin capsules with the proviso that the capsule is not a microcapsule.
7. The photographic emulsion wherein the powder is a dye.
8. The emulsion of claim 7 wherein said dye is a photographic sensitizing dye.
9. The emulsion of claim 7 wherein said dye is an antihalation dye.
10. The emulsion of claim 7 wherein said dye is a filter dye.