Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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IM-0367
TITLE
A NOVEL METHOD FOR THE ADDITION
OF POWDERS TO PHOTOGRAPHIC SYSTEMS
5BACKGROUND OF THE I~VENTION
1. Field gf 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
0 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. Pi~cussion 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
dlsperslon of gelatin and sllver hallde. The dyes are
conventionally large, organic molecule~ a9 19 well-known
and these a~e 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
801utlon handllng o~ a formulatlon contalning a dye.
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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 ~H~ 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 technlque has not not been employed ln
con~unction 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
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sensitizing, filter or antlhalation type and they can be
added to an under or ~acking 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
pelletiz$ng 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
~5 gelatin or emulsion materials. Thus, sometimes, good
dispersion of the dye is not achieved by these methods.
In the practice of my invention, I prefer
encapsulatlng the dry dye powder withln a gelatln
capaul-. In tho pro~ont lnvontlon tho torm ~capaulo~
excludes a m~crocapsule The process for achieving an
encapsulatlon ls well-known in the prior art. The
oapsules are fo~med and th- d~y dy- ~owdor o-n b-
lnserted thereln uslng a oonventlon~lly known m-chlne
such as the Type 8 Standard Hard Capsule Filllng Mach~ne
.
~04728a
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:
~AMPLE 1
This example demonstrates the use of encapsulated,
photographic sensitizing dye within a gelatino, silver
halide emulsion.
A conventisnal, 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
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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
S 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.,
NaO3S~N N=N2~,~0H
\[~SO3Na
1 0
which had been encapsulated using the aforementioned
Type 8 Encapsulator, were added to this emulsion and
digested for a period of 60 minutes at 39C. In this
case, the dye containing capsuIes 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.
~oth 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
welght of 4.7 mg Ag/dm2 an~ then an overcoat layer of
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gelatin was applled supra thereto. After drying,
samples of both elements were glven 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 dlspersed and absorbed by the silver halide
grains.
~AM~h~_~
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:
,~ SO3~M+
CH3
CH3 ~ ~N
CH
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 gm~ O~ water. Additionally,
thl~ ~olutlon contalned the usual wetting and coatlng
aides and hardeners. The capsules were dispersed in
this solution at 60C 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
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opposite side thereto. Both antihalatlon 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.
