[0001] The invention is directed to photographic emulsions. More specifically, the invention
is directed to high bromide ultrathin tabular grain emulsions containing selected
peptizers.
[0002] The term "equivalent circular diameter" or "ECD" is employed to indicate the diameter
of a circle having the same projected area as a silver halide grain.
[0003] The term "aspect ratio" designates the ratio of grain ECD to grain thickness (t).
[0004] The term "tabularity" is defined as ECD/t
2, where ECD and t are both measured in micrometers (µm).
[0005] The term "tabular grain" indicates a grain having two parallel crystal faces which
are clearly larger than any remaining crystal face and having an aspect ratio of at
least 2.
[0006] The term "tabular grain emulsion" refers to an emulsion in which tabular grains account
for greater than 50 percent of total grain projected area.
[0007] The term "ultrathin tabular grain emulsion" refers to a tabular grain emulsion in
which the average thickness of the tabular grains is less than 0.07 µm.
[0008] The term "high bromide" or "high chloride" in referring to grains and emulsions indicates
that bromide or chloride, respectively, are present in concentrations of greater than
50 mole percent, based on total silver.
[0009] In referring to grains and emulsions containing two or more halides, the halides
are named in order of ascending concentrations.
[0010] The term "{111} tabular" is employed in referring to tabular grains and tabular grain
emulsions in which the tabular grains have {111} major faces.
[0011] The term "gelatino-peptizer" is employed to designate gelatin and gelatin-derived
peptizers.
[0012] The terms "selected cationic starch peptizer" and "selected peptizer" are employed
to designate a water dispersible cationic starch.
[0013] The term "cationic" in referring to starch indicates that the starch molecule has
a net positive charge at the pH of intended use.
[0014] The term "water dispersible" in referring to cationic starches indicates that, after
boiling the cationic starch in water for 30 minutes, the water contains, dispersed
to at least a colloidal level, at least 1.0 percent by weight of the total cationic
starch.
[0015] The term "middle chalcogen" designates sulfur, selenium and/or tellurium.
[0016] Photographic emulsions are comprised of a dispersing medium and silver halide microcrystals,
commonly referred to as grains. As the grains are precipitated from an aqueous medium,
a peptizer, usually a hydrophilic colloid, is adsorbed to the grain surfaces to prevent
the grains from agglomerating. Subsequently binder is added to the emulsion and, after
coating, the emulsion is dried. The peptizer and binder are collectively referred
to as the photographic vehicle of an emulsion.
[0017] Gelatin and gelatin derivatives form both the peptizer and the major portion of the
remainder of the vehicle in the overwhelming majority of silver halide photographic
elements. An appreciation of gelatin is provided by this description contained in
Mees
The Theory of the Photographic Process, Revised Ed., Macmillan, 1951, pp. 48 and 49:
Gelatin is pre-eminently a substance with a history; its properties and its future
behavior are intimately connected with its past. Gelatin is closely akin to glue.
At the dawn of the Christian era, Pliny wrote, "Glue is cooked from the hides of bulls."
It is described equally shortly by a present-day writer as "the dried down soup or
consommé of certain animal refuse." The process of glue making is age-old and consists
essentially in boiling down hide clippings or bones of cattle and pigs. The filtered
soup is allowed to cool and set to a jelly which, when cut and dried on nets, yields
sheets of glue or gelatin, according to the selection of stock and the process of
manufacture. In the preparation of glue, extraction is continued until the ultimate
yield is obtained from the material; in the case of gelatin, however, the extraction
is halted earlier and is carried out at lower temperatures, so that certain strongly
adhesive but nonjelling constituents of glue are not present in gelatin. Glue is thus
distinguished by its adhesive properties; gelatin by its cohesive properties, which
favor the formation of strong jellies.
[0018] Photographic gelatin is generally made from selected clippings of calf hide and ears
as well as cheek pieces and pates. Pigskin is used for the preparation of some gelatin,
and larger quantities are made from bone. The actual substance in the skin furnishing
the gelatin is
collagen. It forms about 35 per cent of the coria of fresh cattle hide. The corresponding tissue
obtained from bone is termed
ossein. The raw materials are selected not only for good structural quality but for freedom
from bacterial decomposition. In preparation for the extraction, the dirt with loose
flesh and blood is eliminated in a preliminary wash. The hair, fat, and much of the
albuminous materials are removed by soaking the stock in limewater containing suspended
lime. The free lime continues to rejuvenate the solution and keeps the bath at suitable
alkalinity. This operation is followed by deliming with dilute acid, washing, and
cooking to extract the gelatin. Several "cooks" are made at increasing temperatures,
and usually the products of the last extractions are not employed for photographic
gelatin. The crude gelatin solution is filtered, concentrated if necessary, cooled
until it sets, cut up, and dried in slices. The residue, after extraction of the gelatin,
consists chiefly of elastin and reticulin with some keratin and albumin.
[0019] Gelatin may also be made by an acid treatment of the stock without the use of lime.
The stock is treated with dilute acid (pH 4.0) for one to two months and then washed
thoroughly, and the gelatin is extracted. This gelatin differs in properties from
gelatin made by treatment with lime.
[0020] In addition to the collagen and ossein sought to be extracted in the preparation
of gelatin there are, of course, other materials entrained. For example, James
The Theory of the Photographic Process, 4th Ed., Macmillan, 1977, p. 51, states:
Although collagen generally is the preponderant protein constituent in its tissue
of origin, it is always associated with various "ground substances" such as noncollagen
protein, mucopolysaccharides, polynucleic acid, and lipids. Their more or less complete
removal is desirable in the preparation of photographic gelatin.
Superimposed on the complexity of composition is the variability of composition, attributable
to the varied diets of the animals providing the starting materials. The most notorious
example of this was provided by the forced suspension of manufacturing by the Eastman
Dry Plate Company in 1882, ultimately attributed to a reduction in the sulfur content
in a purchased batch of gelatin.
[0021] Considering the time, effort, complexity and expense involved in gelatin preparation,
it is not surprising that research efforts have in the past been mounted to replace
the gelatin used in photographic emulsions and other film layers. However, by 1970
any real expectation of finding a generally acceptable replacement for gelatin had
been abandoned. A number of alternative materials have been identified as having peptizer
utility, but none have found more than limited acceptance. Of these, cellulose derivatives
are by far the most commonly named, although their use has been restricted by the
insolubility of cellulosic materials and the extensive modifications required to provide
peptizing utility.
[0022] Research Disclosure, Vol. 365, Sept. 1994, Item 36544, II. Vehicles, vehicle extenders, vehicle-like
addenda and vehicle related addenda, A. Gelatin and hydrophilic colloid peptizers,
paragraph (1) states:
(1) Photographic silver halide emulsion layers and other layers on photographic elements
can contain various colloids alone or in combination as vehicles. Suitable hydrophilic
materials include both naturally occurring substances such as proteins, protein derivatives,
cellulose derivatives--e.g., cellulose esters, gelatin--e.g., alkali-treated gelatin
(pigskin gelatin), gelatin derivatives--e.g., acetylated gelatin, phthalated gelatin
and the like, polysaccharides such as dextran, gum arabic, zein, casein, pectin, collagen
derivatives, collodion, agar-agar, arrowroot, albumin and the like....
This description is identical to that contained in
Research Disclosure, Vol. 176, December 1978, Item 17643, IX. Vehicles and vehicle extenders, paragraph
A.
Research Disclosure is published by Kenneth Mason Publications, Ltd., Dudley House, 12 North St., Emsworth,
Hampshire P010 7DQ, England.
[0023] During the 1980's a marked advance took place in silver halide photography based
on the discovery that a wide range of photographic advantages, such as improved speed-granularity
relationships, increased covering power, both on an absolute basis and as a function
of binder hardening, more rapid developability, increased thermal stability, increased
separation of native and spectral sensitization imparted imaging speeds, and improved
image sharpness in both mono- and multi-emulsion layer formats, can be realized by
increasing the proportions of selected high (>50 mole %) bromide tabular grain populations
in photographic emulsions.
[0024] In descriptions of these emulsions, as illustrated by Kofron et al U.S. Patent 4,439,520,
the vehicle disclosure of
Research Disclosure Item 17643 was incorporated verbatim. Only gelatin peptizers were actually demonstrated
in the Examples.
[0025] Recently, Antoniades et al U.S. Patent 5,250,403 disclosed tabular grain emulsions
that represent what were, prior to the present invention, in many ways the best available
emulsions for recording exposures in color photographic elements, particularly in
the minus blue (red and/or green) portion of the spectrum. Antoniades et al disclosed
tabular grain emulsions in which tabular grains having {111} major faces account for
greater than 97 percent of total grain projected area. The tabular grains have an
equivalent circular diameter (ECD) of at least 0.7 µm and a mean thickness of less
than 0.07 µm--i.e., ultrathin. They are suited for use in color photographic elements,
particularly in minus blue recording emulsion layers, because of their efficient utilization
of silver, attractive speed-granularity relationships, and high levels of image sharpness,
both in the emulsion layer and in underlying emulsion layers.
[0026] A characteristic of ultrathin tabular grain emulsions that sets them apart from other
tabular grain emulsions is that they do not exhibit reflection maxima within the visible
spectrum, as is recognized to be characteristic of tabular grains having thicknesses
in the 0.18 to 0.08 µm range, as taught by Buhr et al,
Research Disclosure, Vol. 253, Item 25330, May 1985.
Research Disclosure is published by Kenneth Mason Publications, Ltd., Dudley House, 12 North St., Emsworth,
Hampshire P010 7DQ, England. In multilayer photographic elements overlying emulsion
layers with mean tabular grain thicknesses in the 0.18 to 0.08 µm range require care
in selection, since their reflection properties differ widely within the visible spectrum.
The choice of ultrathin tabular grain emulsions in building multilayer photographic
elements eliminates spectral reflectance dictated choices of different mean grain
thicknesses in the various emulsion layers overlying other emulsion layers. Hence,
the use of ultrathin tabular grain emulsions not only allows improvements in photographic
performance, it also offers the advantage of simplifying the construction of multilayer
photographic elements.
[0027] Whereas Kofron et al suggested that any conventional peptizer could be present during
the preparation of tabular grain emulsions, even though actual precipitations demonstrated
only gelatino-peptizers, Antoniades et al quite conspicuously requires the peptizers
employed through grain nucleation to be selected from among gelatino-peptizers only.
It is only after tabular grain nuclei have been formed that using other conventional
peptizers is viewed as a possible alternative. However, Antoniades et al, like Kofron
et al, demonstrates only gelatino-peptizers to be effective in preparing tabular grain
emulsions.
[0028] Maskasky U.S. Patent 5,284,744 taught the use of potato starch as a peptizer for
the preparation of cubic (i.e., {100}) grain silver halide emulsions, noting that
potato starch has a lower absorption, compared to gelatin, in the wavelength region
of from 200 to 400 nm. Maskasky '744 does not disclose tabular grain emulsions.
[0029] In one aspect this invention is directed to a radiation-sensitive emulsion comprised
of silver halide grains including tabular grains (a) having {111} major faces, (b)
containing greater than 50 mole percent bromide, based on silver, (c) accounting for
greater than 70 percent of total grain projected area, (d) exhibiting an average equivalent
circular diameter of at least 0.7 µm, and (e) exhibiting an average thickness of less
than 0.07 µm, and a dispersing medium including a peptizer adsorbed to the silver
halide grains, characterized in that the peptizer is a water dispersible cationic
starch.
[0030] In another aspect this invention is directed to a photographic element comprised
of (i) a support, (ii) a first silver halide emulsion layer coated on the support
and sensitized to produce a photographic record when exposed to specular light within
the minus blue visible wavelength region of from 500 to 700 nm, and (iii) a second
silver halide emulsion layer capable of producing a second photographic record coated
over the first silver halide emulsion layer to receive specular minus blue light intended
for the exposure of the first silver halide emulsion layer, the second silver halide
emulsion layer being capable of acting as a transmission medium for the delivery of
at least a portion of the minus blue light intended for the exposure of the first
silver halide emulsion layer in the form of specular light, characterized in that
the second silver halide emulsion layer is comprised of an improved emulsion according
to the invention.
[0031] It has been discovered quite surprisingly that cationic starches are better suited
for preparing high bromide ultrathin {111} tabular grain emulsions than noncationic
starches and that cationic starches, when present in place of gelatin, facilitate
photographic advantages.
[0032] Cationic starches exhibit lower levels of viscosity than have previously been present
in preparing ultrathin tabular grain emulsions. Reduced viscosity facilitates more
uniform mixing. Both micromixing, which controls the uniformity of grain composition,
mean grain size and dispersity, and bulk mixing, which controls scale up of precipitations
to convenient manufacturing scales, are favorably influenced by the reduced viscosities
made possible by cationic starch peptizers. Precise control over grain nucleation,
including the monodispersity of the grain nuclei, is particularly important to successfully
achieving and improving the properties of ultrathin tabular grain emulsions.
[0033] Under comparable levels of chemical sensitization higher photographic speeds can
be realized with cationic starches. Alternatively, lower temperatures can be employed
during chemical sensitization of cationic starch peptized ultrathin tabular grain
emulsions to achieve photographic speeds equal or superior to those of gelatino-peptized
ultrathin tabular grain emulsions. Lower temperatures have the advantage of protecting
the ultrathin tabular grains from unwanted ripening, particularly thickening, during
chemical sensitization.
[0034] The present invention is generally applicable to high bromide ultrathin {111} tabular
grain emulsions. The emulsions are specifically contemplated for incorporation in
camera speed color photographic films.
[0035] More specifically, the high bromide ultrathin {111} tabular grain emulsions of the
invention are comprised of silver halide grains including tabular grains
(a) having {111} major faces,
(b) containing greater than 50 mole percent bromide, based on silver,
(c) accounting for greater than 70 percent of total grain projected area,
(d) exhibiting an average equivalent circular diameter of at least 0.7 µm, and
(e) exhibiting an average thickness of less than 0.07 µm.
[0036] The emulsions of the present invention can be readily distinguished from conventional
high bromide ultrathin {111} tabular grain emulsions, such as those disclosed by Atoniades
et al, in that a water dispersible cationic starch is adsorbed to the grain surfaces,
thereby acting as a peptizer. Any conventional water dispersible cationic starch can
be employed as a peptizer.
[0037] The term "starch" is employed to include both natural starch and modified derivatives,
such as dextrinated, hydrolyzed, alkylated, hydroxyalkylated, acetylated or fractionated
starch. The starch can be of any origin, such as corn starch, wheat starch, potato
starch, tapioca starch, sago starch, rice starch, waxy corn starch or high amylose
corn starch.
[0038] Starches are generally comprised of two structurally distinctive polysaccharides,
α-amylose and amylopectin. Both are comprised of α-D-glucopyranose units. In α-amylose
the α-D-glucopyranose units form a 1,4-straight chain polymer. The repeating units
take the following form:

In amylopectin, in addition to the 1,4-bonding of repeating units, 6-position chain
branching (at the site of the -CH
2OH group above) is also in evidence, resulting in a branched chain polymer. The repeating
units of starch and cellulose are diasteroisomers that impart different overall geometries
to the molecules. The α anomer, found in starch and shown in formula I above, results
in a polymer that is capable of crystallization and some degree of hydrogen bonding
between repeating units in adjacent molecules, but not to the same degree as the β
anomer repeating units of cellulose and cellulose derivatives. Polymer molecules formed
by the β anomers show strong hydrogen bonding between adjacent molecules, resulting
in clumps of polymer molecules and a much higher propensity for crystallization. Lacking
the alignment of substituents that favors strong intermolecular bonding, found in
cellulose repeating units, starch and starch derivatives are much more readily dispersed
in water.
[0039] The water dispersible starches employed in the practice of the invention are cationic--that
is, they contain an overall net positive charge when dispersed in water. Starches
are conventionally rendered cationic by attaching a cationic substituent to the α-D-glucopyranose
units, usually by esterification or etherification at one or more free hydroxyl sites.
Reactive cationogenic reagents typically include a primary, secondary or tertiary
amino group (which can be subsequently protonated to a cationic form under the intended
conditions of use) or a quaternary ammonium, sulfonium or phosphonium group.
[0040] To be useful as a peptizer the cationic starch must be water dispersible. Many starches
disperse in water upon heating to temperatures up to boiling for a short time (e.g.,
5 to 30 minutes). High sheer mixing also facilitates starch dispersion. The presence
of cationic substituents increases the polar character of the starch molecule and
facilitates dispersion. The starch molecules preferably achieve at least a colloidal
level of dispersion and ideally are dispersed at a molecular level--i.e., dissolved.
[0041] The following teachings illustrate water dispersible cationic starches within the
contemplation of the invention:
Rutenberg et al U.S. Patent 2,989,520;
Meisel U.S. Patent 3,017,294;
Elizer et al U.S. Patent 3,051,700;
Aszolos U.S. Patent 3,077,469;
Elizer et al U.S. Patent 3,136,646;
Barber et al U.S. Patent 3,219,518;
Mazzarella et al U.S. Patent 3,320,080;
Black et al U.S. Patent 3,320,118;
Caesar U.S. Patent 3,243,426;
Kirby U.S. Patent 3,336,292;
Jarowenko U.S. Patent 3,354,034;
Caesar U.S. Patent 3,422,087;
Dishburger et al U.S. Patent 3,467,608;
Beaninga et al U.S. Patent 3,467,647;
Brown et al U.S. Patent 3,671,310;
Cescato U.S. Patent 3,706,584;
Jarowenko et al U.S. Patent 3,737,370;
Jarowenko U.S. Patent 3,770,472;
Moser et al U.S. Patent 3,842,005;
Tessler U.S. Patent 4,060,683;
Rankin et al U.S. Patent 4,127,563;
Huchette et al U.S. Patent 4,613,407;
Blixt et al U.S. Patent 4,964,915;
Tsai et al U.S. Patent 5,227,481; and
Tsai et al U.S. Patent 5,349,089.
[0042] The water dispersible cationic starch is present during the precipitation (during
nucleation and grain growth or during grain growth) of the high bromide {111} tabular
grains. Preferably precipitation is conducted by substituting the water dispersible
cationic starch for all conventional gelatino-peptizers. In substituting the selected
cationic starch peptizer for conventional gelatino-peptizers, the concentrations of
the selected peptizer and the point or points of addition can correspond to those
employed using gelatino-peptizers.
[0043] In addition, it has been unexpectedly discovered that emulsion precipitation can
tolerate even higher concentrations of the selected peptizer. For example, it has
been observed that all of the selected peptizer required for the preparation of an
emulsion through the step of chemical sensitization can be present in the reaction
vessel prior to grain nucleation. This has the advantage that no peptizer additions
need be interjected after tabular grain precipitation has commenced. It is generally
preferred that from 1 to 500 grams (most preferably from 5 to 100 grams) of the selected
peptizer per mole of silver to be precipitated be present in the reaction vessel prior
to tabular grain nucleation.
[0044] At the other extreme, it is, of course, well known, as illustrated by Mignot U.S.
Patent 4,334,012, that no peptizer is required to be present during grain nucleation,
and, if desired, addition of the selected peptizer can be deferred until grain growth
has progressed to the point that peptizer is actually required to avoid tabular grain
agglomeration.
[0045] The procedures for high bromide ultrathin {111} tabular grain emulsion preparation
through the completion of tabular grain growth require only the substitution of the
selected peptizer for conventional gelatino-peptizers. Although criteria (a) through
(e) are too stringent to be satisfied by the vast majority of known tabular grain
emulsions, a few published precipitation techniques are capable of producing emulsions
satisfying these criteria. Antoniades et al, cited above, demonstrates preferred silver
iodobromide emulsions satisfying these criteria. Zola and Bryant published European
patent application 0 362 699 A3, also discloses silver iodobromide emulsions satisfying
these criteria.
[0046] For camera speed films it is generally preferred that the tabular grains contain
at least 0.25 (preferably at least 1.0) mole percent iodide, based on silver. Although
the saturation level of iodide in a silver bromide crystal lattice is generally cited
as about 40 mole percent and is a commonly cited limit for iodide incorporation, for
photographic applications iodide concentrations seldom exceed 20 mole percent and
are typically in the range of from about 1 to 12 mole percent.
[0047] As is generally well understood in the art, precipitation techniques, including those
of Antoniades et al and Zola and Bryant, that produce silver iodobromide tabular grain
emulsions can be modified to produce silver bromide tabular grain emulsions of equal
or lesser mean grain thicknesses simply by omitting iodide addition. This is specifically
taught by Kofron et al.
[0048] It is possible to include minor amounts of chloride ion in the ultrathin tabular
grains. As disclosed by Delton U.S. Patents 5,372,927 and 5,460,934, ultrathin tabular
grain emulsions containing from 0.4 to 20 mole percent chloride and up to 10 mole
percent iodide, based on total silver, with the halide balance being bromide, can
be prepared by conducting grain growth accounting for from 5 to 90 percent of total
silver within the pAg vs. temperature (°C) boundaries of Curve A (preferably within
the boundaries of Curve B) shown by Delton, corresponding to Curves A and B of Piggin
et al U.S. Patents 5,061,609 and 5,061,616. Under these conditions of precipitation
the presence of chloride ion actually contributes to reducing the thickness of the
tabular grains. Although it is preferred to employ precipitation conditions under
which chloride ion, when present, can contribute to reductions in the tabular grain
thickness, it is recognized that chloride ion can be added during any conventional
ultrathin tabular grain precipitation to the extent it is compatible with retaining
tabular grain mean thicknesses of less than 0.07 µm.
[0049] The high bromide ultrathin {111} tabular grain emulsions that are formed preferably
contain at least 70 mole percent bromide and optimally at least 90 mole percent bromide,
based on silver. Silver bromide, silver iodobromide, silver chlorobromide, silver
iodochlorobromide, and silver chloroiodobromide tabular grain emulsions are specifically
contemplated. Although silver chloride and silver bromide form tabular grains in all
proportions, chloride is preferably present in concentrations of 30 mole percent or
less. Iodide can be present in the tabular grains up to its solubility limit under
the conditions selected for tabular grain precipitation. Under ordinary conditions
of precipitation silver iodide can be incorporated into the tabular grains in concentrations
ranging up to about 40 mole percent. It is generally preferred that the iodide concentration
be less than 20 mole percent. Significant photographic advantages can be realized
with iodide concentrations as low as 0.5 mole percent, with an iodide concentration
of at least 1 mole percent being preferred.
[0050] When the ultrathin tabular grains include iodide, the iodide can be uniformly distributed
within the tabular grains. To obtain a further improvement in speed-granularity relationships
it is preferred that the iodide distribution satisfy the teachings of Solberg et al
U.S. Patent 4,433,048.
[0051] The high bromide ultrathin {111} tabular grain emulsions exhibit mean grain ECD's
ranging from 0.7 to 10 µm. The minimum mean ECD of 0.7 µm is chosen to insure light
transmission with minimum high angle light scattering. In other words, tabular grain
emulsions with a mean ECD of at least 0.7 µm produce sharper images, particularly
in coating formats in which another emulsion layer of any conventional type underlies
the emulsion of the invention. Although the maximum mean ECD of the tabular grains
can range up to 10 µm, in practice, the tabular grain emulsions of the invention typically
exhibit a mean ECD of 5.0 µm or less. An optimum ECD range for moderate to high image
structure quality is in the range of from 1 to 4 µm.
[0052] The ultrathin tabular grains typically have triangular or hexagonal major faces.
The tabular structure of the grains is attributed to the inclusion of parallel twin
planes.
[0053] The tabular grains of the emulsions of the invention account for greater than 70
percent and preferably greater than 90 percent of total grain projected area. Emulsions
according to the invention can be prepared following the procedures of Antoniades
et al or Delton, both cited above, in which "substantially all" (>97 %) of the total
grain projected area is accounted for by tabular grains.
[0054] Ultrathin (<0.07 µm) tabular grains are specifically preferred for minus blue recording
in photographic elements forming dye images (i.e., color photographic elements). An
important distinction between ultrathin tabular grains and those having greater (≧0.07
µm) thicknesses resides in the difference in their reflective properties. Ultrathin
tabular grains exhibit little variation in reflection as a function of the wavelength
of visible light to which they are exposed, where as thicker tabular grains exhibit
pronounced reflection maxima and minima as a function of the wavelength of light.
Hence ultrathin tabular grains simplify construction of photographic element intended
to form plural color records (i.e., color photographic elements). This property, together
with the more efficient utilization of silver attributable to ultrathin grains, provides
a strong incentive for their use in color photographic elements.
[0055] As the mean thicknesses of the tabular grains are further reduced below 0.07 µm,
the average reflectances observed within the visible spectrum are also reduced. Therefore,
it is preferred to maintain mean grain thicknesses at less than 0.05 µm. Generally
the lowest mean tabular grain thickness conveniently realized by the precipitation
process employed is preferred. Thus, ultrathin tabular grain emulsions with mean tabular
grain thicknesses in the range of from about 0.03 to 0.05 µm are readily realized.
Daubendiek et al U.S. Patent 4,672,027 reports mean tabular grain thicknesses of 0.017
µm. Utilizing the grain growth techniques taught by Antoniades et al these emulsions
could be grown to average ECD's of at least 0.7 µm without appreciable thickening--e.g.,
while maintaining mean thicknesses of less than 0.02 µm. The minimum thickness of
a tabular grain is limited by the spacing of the first two parallel twin planes formed
in the grain during precipitation. Although minimum twin plane spacings as low as
0.002 µm (i.e., 2 nm or 20 Å) have been observed in the emulsions of Antoniades et
al, Kofron et al suggests a practical minimum tabular grain thickness about 0.01µm.
[0056] Conventional dopants can be incorporated into the tabular grains during their precipitation,
as illustrated by the patents cited above and
Research Disclosure , Item 36544, cited above, Section I. Emulsion grains and their preparation, D. Grain
modifying conditions and adjustments, paragraphs (3), (4) and (5). It is specifically
contemplated to incorporate shallow electron trapping site providing (SET) dopants
in the tabular grains as disclosed in
Research Disclosure , Vol. 367, November 1994, Item 36736.
[0057] It is also recognized that silver salts can be epitaxially grown onto the tabular
grains during the precipitation process. Epitaxial deposition onto the edges and/or
corners of tabular grains is specifically taught by Maskasky U.S. Patent 4,435,501.
In a specifically preferred form high chloride silver halide epitaxy is present at
the edges or, most preferably, restricted to corner adjacent sites on the tabular
grains.
[0058] Although epitaxy onto the host tabular grains can itself act as a sensitizer, the
emulsions of the invention show unexpected sensitivity enhancements with or without
epitaxy when chemically sensitized in the absence of a gelatino-peptizer, employing
one or a combination of noble metal, middle chalcogen and reduction chemical sensitization
techniques. Conventional chemical sensitizations by these techniques are summarized
in
Research Disclosure , Item 36544, cited above, Section IV. Chemical sensitizations. All of these sensitizations,
except those that specifically require the presence of gelatin (e.g., active gelatin
sensitization) are applicable to the practice of the invention. It is preferred to
employ at least one of noble metal (typically gold) and middle chalcogen (typically
sulfur) and, most preferably, a combination of both in preparing the emulsions of
the invention for photographic use.
[0059] Between emulsion precipitation and chemical sensitization, the step that is preferably
completed before any gelatin or gelatin derivative is added to the emulsion, it is
conventional practice to wash the emulsions to remove soluble reaction by-products
(e.g., alkali and/or alkaline earth cations and nitrate anions). If desired, emulsion
washing can be combined with emulsion precipitation, using ultrafiltration during
precipitation as taught by Mignot U.S. Patent 4,334,012. Alternatively emulsion washing
by diafiltration after precipitation and before chemical sensitization can be undertaken
with a semipermeable membrane as illustrated by
Research Disclosure, Vol. 102, October 1972, Item 10208, Hagemaier et al
Research Disclosure , Vol. 131, March 1975, Item 13122, Bonnet
Research Disclosure , Vol. 135, July 1975, Item 13577, Berg et al German OLS 2,436,461 and Bolton U.S.
Patent 2,495,918, or by employing an ion-exchange resin, as illustrated by Maley U.S.
Patent 3,782,953 and Noble U.S. Patent 2,827,428. In washing by these techniques there
is no possibility of removing the selected peptizers, since ion removal is inherently
limited to removing much lower molecular weight solute ions.
[0060] A specifically preferred approach to chemical sensitization employs a combination
of sulfur containing ripening agents in combination with middle chalcogen (typically
sulfur) and noble metal (typically gold) chemical sensitizers. Contemplated sulfur
containing ripening agents include thioethers, such as the thioethers illustrated
by McBride U.S. Patent 3,271,157, Jones U.S. Patent 3,574,628 and Rosencrants et al
U.S. Patent 3,737,313. Preferred sulfur containing ripening agents are thiocyanates,
illustrated by Nietz et al U.S. Patent 2,222,264, Lowe et al U.S. Patent 2,448,534
and Illingsworth U.S. Patent 3,320,069. A preferred class of middle chalcogen sensitizers
are tetrasubstituted middle chalcogen ureas of the type disclosed by Herz et al U.S.
Patents 4,749,646 and 4,810,626. Preferred compounds include those represented by
the formula:

wherein
X is sulfur, selenium or tellurium;
each of R1, R2, R3 and R4 can independently represent an alkylene, cycloalkylene, alkarylene, aralkylene or
heterocyclic arylene group or, taken together with the nitrogen atom to which they
are attached, R1 and R2 or R3 and R4 complete a 5 to 7 member heterocyclic ring; and
each of A1, A2, A3 and A4 can independently represent hydrogen or a radical comprising an acidic group,
with the proviso that at least one A1R1 to A4R4 contains an acidic group bonded to the urea nitrogen through a carbon chain containing
from 1 to 6 carbon atoms.
[0061] X is preferably sulfur and A
1R
1 to A
4R
4 are preferably methyl or carboxymethyl, where the carboxy group can be in the acid
or salt form. A specifically preferred tetrasubstituted thiourea sensitizer is 1,3-dicarboxymethyl-1,3-dimethylthiourea.
[0062] Preferred gold sensitizers are the gold(I) compounds disclosed by Deaton U.S. Patent
5,049,485. These compounds include those represented by the formula:
AuL
2+X
- or AuL(L
1)
+X
- (III)
wherein
L is a mesoionic compound;
X is an anion; and
L1 is a Lewis acid donor.
[0063] In another preferred form of the invention it is contemplated to employ alone or
in combination with sulfur sensitizers, such as those formula I, and/or gold sensitizers,
such as those of formula II, reduction sensitizers which are the 2-[N-(2-alkynyl)amino]-
meta-chalcoazoles disclosed by Lok et al U.S. Patents 4,378,426 and 4,451,557.
[0064] Preferred 2-[N-(2-alkynyl)amino)-
meta-chalcoazoles can be represented by the formula:

where
X = O, S, Se;
R1 = (IVa) hydrogen or (IVb) alkyl or substituted alkyl or aryl or substituted aryl;
and
Y1 and Y2 individually represent hydrogen, alkyl groups or an aromatic nucleus or together
represent the atoms necessary to complete an aromatic or alicyclic ring containing
atoms selected from among carbon, oxygen, selenium, and nitrogen atoms.
[0065] The formula IV compounds are generally effective (with the IVb form giving very large
speed gains and exceptional latent image stability) when present during the heating
step (finish) that results in chemical sensitization.
[0066] Spectral sensitization of the emulsions of the invention is not required, but is
highly preferred, even when photographic use of the emulsion is undertaken in a spectral
region in which the tabular grains exhibit significant native sensitivity. While spectral
sensitization is most commonly undertaken after chemical sensitization, spectral sensitizing
dye can be advantageous introduced earlier, up to and including prior to grain nucleation.
Kofron et al discloses advantages for "dye in the finish" sensitizations, which are
those that introduce the spectral sensitizing dye into the emulsion prior to the heating
step (finish) that results in chemical sensitization. Maskasky U.S. Patent 4,435,501
teaches the use of aggregating spectral sensitizing dyes, particularly green and red
absorbing cyanine dyes, as site directors for epitaxial deposition. These dyes are
present in the emulsion prior to the chemical sensitizing finishing step. When the
spectral sensitizing dye present in the finish is not relied upon as a site director
for the silver salt epitaxy, a much broader range of spectral sensitizing dyes is
available. The spectral sensitizing dyes disclosed by Kofron et al, particularly the
blue spectral sensitizing dyes shown by structure and their longer methine chain analogous
that exhibit absorption maxima in the green and red portions of the spectrum, are
particularly preferred for incorporation in the tabular grain emulsions of the invention.
A more general summary of useful spectral sensitizing dyes is provided by
Research Disclosure , Item 36544, cited above, Section V. Spectral sensitization and desensitization.
[0067] While in specifically preferred forms of the invention the spectral sensitizing dye
can act also as a site director and/or can be present during the finish, the only
required function that a spectral sensitizing dye must perform in the emulsions of
the invention is to increase the sensitivity of the emulsion to at least one region
of the spectrum. Hence, the spectral sensitizing dye can, if desired, be added to
an emulsion according to the invention after chemical sensitization has been completed.
[0068] At any time following chemical sensitization and prior to coating additional vehicle
is added to the emulsions of the invention. Conventional vehicles and related emulsion
components are illustrated by
Research Disclosure , Item 36544, cited above, Section II. Vehicles, vehicle extenders, vehicle-like
addenda and vehicle related addenda.
[0069] Aside from the features described above, the emulsions of this invention and their
preparation can take any desired conventional form. For example, although not essential,
after a novel emulsion satisfying the requirements of the invention has been prepared,
it can be blended with one or more other novel emulsions according to this invention
or with any other conventional emulsion. Conventional emulsion blending is illustrated
in
Research Disclosure , Item 36544, Section I. Emulsion grains and their preparation, E. Blends, layers
and performance categories. Other common, but optional features are illustrated by
Research Disclosure , Item 36544, Section VII, Antifoggants and stabilizers; Section VIII, Absorbing
and scattering materials; Section IX, Coating physical property modifying agents;
Section X, Dye image formers and modifiers. The features of Sections II and VII-X
can alternatively be provided in other photographic element layers.
[0070] The photographic applications of the emulsions of the invention can encompass other
conventional features, such as those illustrated by
Research Disclosure , Item 36544, Sections:
- XI.
- Layers and layer arrangements
- XII.
- Features applicable only to color negative
- XIII.
- Features applicable only to color positive
- XIV.
- Scan facilitating features
- XV.
- Supports
- XVI.
- Exposure
- XVII.
- Physical development systems
- XVIII.
- Chemical development systems
- XIX.
- Development
- XX.
- Desilvering, washing, rinsing and stabilizing (post-development)
[0071] The high bromide ultrathin {111} tabular grain emulsions of this invention can be
employed in any otherwise conventional photographic element. The emulsions can, for
example, be included in a photographic element with one or more silver halide emulsion
layers. In one specific application a novel emulsion according to the invention can
be present in a single emulsion layer of a photographic element intended to form either
silver or dye photographic images for viewing or scanning.
[0072] In one important aspect this invention is directed to a photographic element containing
at least two superimposed radiation sensitive silver halide emulsion layers coated
on a conventional photographic support of any convenient type. Exemplary photographic
supports are summarized by
Research Disclosure, Item 36544, cited above, Section XV. The emulsion layer coated nearer the support
surface is spectrally sensitized to produce a photographic record when the photographic
element is exposed to specular light within the minus blue portion of the visible
spectrum. The term "minus blue" is employed in its art recognized sense to encompass
the green and red portions of the visible spectrum--i.e., from 500 to 700 nm. The
term "specular light" is employed in its art recognized usage to indicate the type
of spatially oriented light supplied by a camera lens to a film surface in its focal
plane--i.e., light that is for all practical purposes unscattered.
[0073] The second of the two silver halide emulsion layers is coated over the first silver
halide emulsion layer. In this arrangement the second emulsion layer is called upon
to perform two entirely different photographic functions. The first of these functions
is to absorb at least a portion of the light wavelengths it is intended to record.
The second emulsion layer can record light in any spectral region ranging from the
near ultraviolet (≧300 nm) through the near infrared (≦1500 nm). In most applications
both the first and second emulsion layers record images within the visible spectrum.
The second emulsion layer in most applications records blue or minus blue light and
usually, but not necessarily, records light of a shorter wavelength than the first
emulsion layer. Regardless of the wavelength of recording contemplated, the ability
of the second emulsion layer to provide a favorable balance of photographic speed
and image structure (i.e., granularity and sharpness) is important to satisfying the
first function.
[0074] The second distinct function which the second emulsion layer must perform is the
transmission of minus blue light intended to be recorded in the first emulsion layer.
Whereas the presence of silver halide grains in the second emulsion layer is essential
to its first function, the presence of grains, unless chosen as required by this invention,
can greatly diminish the ability of the second emulsion layer to perform satisfactorily
its transmission function. Since an overlying emulsion layer (e.g., the second emulsion
layer) can be the source of image unsharpness in an underlying emulsion layer (e.g.,
the first emulsion layer), the second emulsion layer is hereinafter also referred
to as the optical causer layer and the first emulsion is also referred to as the optical
receiver layer.
[0075] How the overlying (second) emulsion layer can cause unsharpness in the underlying
(first) emulsion layer is explained in detail by Antoniades et al and hence does not
require a repeated explanation.
[0076] It has been observed that a favorable combination of photographic sensitivity and
image structure (e.g., granularity and sharpness) are realized when high bromide ultrathin
{111} tabular grain emulsions satisfying the requirements of the invention are employed
to form at least the second, overlying emulsion layer. Obtaining sharp images in the
underlying emulsion layer is dependent on the ultrathin tabular grains in the overlying
emulsion layer accounting for a high proportion of total grain projected area; however,
grains having an ECD of less than 0.2 µm, if present, can be excluded in calculating
total grain projected area, since these grains are relatively optically transparent.
Excluding grains having an ECD of less than 0.2 µm in calculating total grain projected
area, it is contemplated that the overlying emulsion layer containing the ultrathin
tabular grain emulsion of the invention account for greater than 70 percent, preferably
greater than 90 percent, and optimally "substantially all" (i.e., >97%), of the total
projected area of the silver halide grains.
[0077] Except for the possible inclusion of grains having an ECD of less than 0.2 µm (hereinafter
referred to as optically transparent grains), the second emulsion layer consists almost
entirely of ultrathin tabular grains. The optical transparency to minus blue light
of grains having ECD's of less 0.2 µm is well documented in the art. For example,
Lippmann emulsions, which have typical ECD's of from less than 0.05 µm to greater
than 0.1 µm, are well known to be optically transparent. Grains having ECD's of 0.2
µm exhibit significant scattering of 400 nm light, but limited scattering of minus
blue light. In a specifically preferred form of the invention the tabular grain projected
areas of greater than 90% and optimally greater than 97% of total grain projected
area are satisfied excluding only grains having ECD's of less than 0.1 (optimally
0.05) µm. Thus, in the photographic elements of the invention, the second emulsion
layer can consist essentially of tabular grains contributed by the ultrathin tabular
grain emulsion of the invention or a blend of these tabular grains and optically transparent
grains. When optically transparent grains are present, they are preferably limited
to less than 10 percent and optimally less than 5 percent of total silver in the second
emulsion layer.
[0078] The advantageous properties of the photographic elements of the invention depend
on selecting the grains of the emulsion layer overlying a minus blue recording emulsion
layer to have a specific combination of grain properties. First, the tabular grains
preferably contain photographically significant levels of iodide. The iodide content
imparts art recognized advantages over comparable silver bromide emulsions in terms
of speed and, in multicolor photography, in terms of interimage effects. Second, having
an extremely high proportion of the total grain population as defined above accounted
for by the tabular grains offers a sharp reduction in the scattering of minus blue
light when coupled with an average ECD of at least 0.7 µm and an average grain thickness
of less than 0.07µm. The mean ECD of at least 0.7 µm is, of course, advantageous apart
from enhancing the specularity of light transmission in allowing higher levels of
speed to be achieved in the second emulsion layer. Third, employing ultrathin tabular
grains makes better use of silver and allows lower levels of granularity to be realized.
Finally, the presence of ultrathin tabular grains that are peptized by cationic starch
and sensitized in the absence of a gelatino-peptizer allows unexpected increases in
photographic sensitivity to be realized.
[0079] In one simple form the photographic elements can be black-and-white (e.g., silver
image forming) photographic elements in which the underlying (first) emulsion layer
is orthochromatically or panchromatically sensitized.
[0080] In an alternative form the photographic elements can be multicolor photographic elements
containing blue recording (yellow dye image forming), green recording (magenta dye
image forming) and red recording (cyan dye image forming) layer units in any coating
sequence. A wide variety of coating arrangements are disclosed by Kofron et al, cited
above, columns 56-58.
Examples
[0081] The invention can be better appreciated by reference to the following specific examples.
Except as otherwise indicated all weight percentages (wt%) are based on total weight.
Examples 1 through 7
[0082] These examples demonstrate the precipitation of ultrathin tabular grain emulsions
using a cationic starch derived from different plant sources, including a variety
of potato and grain sources. The starches were selected to demonstrate a wide range
of nitrogen and phosphorus contents. Variations in emulsion precipitation conditions
are also demonstrated. Particularly significant is the demonstration that all of the
cationic starch used for the entire precipitation can be added prior to grain nucleation.
Example 1 AgIBr (3 mole % I) Ultrathin Tabular Grain Emulsion Made Using a Cationic Potato
Starch
[0083] A starch solution was prepared by boiling for 30 min a stirred mixture of 80 g cationic
potato starch (STA-LOK ® 400, obtained from A. E. Staley Manufacturing Co., Decatur,
IL.), 27 mmoles of NaBr, and distilled water to 4 L. The cationic starch was a mixture
of 21% amylose and 79% amylopectin and contained 0.33 wt% nitrogen in the form of
a quaternary trimethyl ammonium alkyl starch ether and 0.13 wt% natural phosphorus.
The cationic starch had an average molecular weight is 2.2 million. The resulting
solution was cooled to 35°C, readjusted to 4 L with distilled water, and the pH was
adjusted to 5.5. To a vigorously stirred reaction vessel of the starch solution at
35°C, a 2 M AgNO
3 solution was added at 100 mL per min for 0.2 min. Concurrently, a salt solution of
1.94 M NaBr and 0.06 M KI was added initially at 100 mL per min and then at a rate
needed to maintain a pBr of 2.21. Then the addition of the solutions was stopped,
25 mL of 2 M NaBr solution was added rapidly and the temperature of the contents of
the reaction vessel was increased to 60°C at a rate of 5°C per 3 min. At 60°C, the
AgNO
3 solution was added at 10 mL per min for 1 min then its addition rate was accelerated
to 50 mL per min in 30 min until a total of 1.00 L had been added. The salt solution
was concurrently added at a rate needed to maintain a constant pBr of 1.76. The resulting
tabular grain emulsion was washed by ultrafiltration at 40°C to a pBr of 3.38.
[0084] The tabular grain population of the resulting tabular grain emulsion was comprised
of tabular grains with an average equivalent circular diameter of 1.2 µm, an average
thickness of 0.06 µm, and an average aspect ratio of 20. The tabular grain population
made up 92% of the total projected area of the emulsion grains. The emulsion grains
had a coefficient of variation in diameter of 18%.
Example 2 AgIBr (3 mole% I) Ultrathin Tabular Grain Emulsion Made Using a Cationic Corn Starch
[0085] A starch solution was prepared by boiling for 30 min a stirred 400 g aqueous mixture
containing 2.7 mmoles of NaBr and 8.0 g of a cationic hybrid corn starch (CATO ® 235,
obtained from National Starch and Chemical Company, Bridgewater, NJ.) containing 0.31
wt% nitrogen and 0.00 wt% phosphorus.
[0086] The resulting solution was cooled to 35°C, readjusted to 400 g with distilled water.
To a vigorously stirred reaction vessel of the starch solution at 35°C, pH 5.5 was
added 2 M AgNO
3 solution at a constant rate of 10 mL per min. Concurrently, a salt solution of 1.94
M NaBr and 0.06 M KI was added initially at 10 mL per min and then at a rate needed
to maintain a pBr of 2.21. After 0.2 min., the addition of the solutions was stopped,
2.5 mL of 2M NaBr was added rapidly, and the temperature of the contents of the reaction
vessel was increased to 60°C at a rate of 5°C per 3 min. At 60°C, the AgNO
3 solution was added at 1.0 mL per min for 1 min then its addition rate was accelerated
to reach a flow rate of 5 mL per min in 30 min until a total of 100 mL of the AgNO
3 solution had been added. The salt solution was concurrently added at a rate needed
to maintain a constant pBr of 1.76.
[0087] The tabular grain population of the resulting emulsion was comprised of tabular grains
with an average equivalent circular diameter of 1.6 µm, an average thickness of 0.06
µm, and an average aspect ratio of 27. The tabular grain population made up 85% of
the total projected area of the emulsion grains.
Example 3 AgIBr (3 mole% I) Ultrathin Tabular Grain Emulsion Made Using a Cationic Amphoteric
Potato Starch
[0088] This emulsion was prepared similarly to Example 2, except that the starch used was
a cationic amphoteric potato starch (Wespol A ®, obtained from Western Polymer Corporation,
Moses Lake, WA.) containing both a quaternary trimethyl ammonium alkyl starch ether
(0.36 wt% nitrogen) and orthophosphate (0.70 wt% phosphorus) substituents.
[0089] The tabular grain population of the resulting emulsion was comprised of tabular grains
with an average equivalent circular diameter of 1.7 µm, an average thickness of 0.05
µm, and an average aspect ratio of 34. The tabular grain population made up 95% of
the total projected area of the emulsion grains.
Example 4 AgIBr (3 mole% I) Ultrathin Tabular Grain Emulsion Made Using a Cationic Amphoteric
Potato Starch
[0090] This emulsion was prepared similarly to Example 3, except that the precipitation
was stopped after 50 mL of the AgNO
3 solution was added.
[0091] The tabular grain population of the resulting emulsion was comprised of tabular grains
with an average equivalent circular diameter of 1.0 µm, an average thickness of 0.045
µm, and an average aspect ratio of 25. The tabular grain population made up 95% of
the total projected area of the emulsion grains.
Example 5 AgIBr (3 mole% I) Ultrathin Tabular Grain Emulsion Made Using a Cationic Potato Starch
and at pH 2.0.
[0092] This emulsion was prepared similarly to Example 2, except that the emulsion was precipitated
at pH 2.0 and the starch used was cationic potato starch (STA-LOK ® 400).
[0093] The tabular grain population of the resulting emulsion was comprised of tabular grains
with an average equivalent circular diameter of 1.5 µm, an average thickness of 0.06
µm, and an average aspect ratio of 22. The tabular grain population made up 80% of
the total projected area of the emulsion grains.
Example 6 AgIBr (3 mole% I) Ultrathin Tabular Grain Emulsion Made Using a Cationic Corn Starch
[0094] This emulsion was prepared similarly to Example 2, except that the emulsion was precipitated
at pH 6.0, and the starch used was a cationic waxy corn starch (STA-LOK ® 180, obtained
from A. E. Staley Manufacturing Co.) made up of 100% amylopectin derivatized to contain
0.36 wt% nitrogen in the form of a quaternary trimethyl ammonium alkyl starch ether
and 0.06 wt% phosphorus, average molecular weight 324,000.
[0095] The tabular grain population of the resulting emulsion was comprised of tabular grains
with an average equivalent circular diameter of 1.6 µm, an average thickness of 0.06
µm, and an average aspect ratio of 27. The tabular grain population made up 91% of
the total projected area of the emulsion grains.
Example 7 AgBr Ultrathin Tabular Grain Emulsion Made by Adding 94% of a Cationic Potato Starch
After Grain Nucleation
[0096] A starch solution was prepared by boiling for 30 min a stirred 200 g aqueous mixture
containing 3.75 mmoles of NaBr and 8.0 g of the cationic potato starch STA-LOK ® 400.
[0097] To a vigorously stirred reaction vessel of 12.5 g of the starch solution (0.5 g starch),
387.5 g distilled water, and 2.2 mmole of NaBr at pH of 6.0 and 35°C was added 2M
AgNO
3 solution at a constant rate of 10 mL per min. Concurrently, a 2.5 M NaBr solution
was added initially at 10 mL per min and then at a rate needed to maintain a pBr of
2.21. After 0.2 min, the addition of the solutions was stopped, 2.5 mL of 2 M NaBr
was added rapidly, and the temperature of the contents of the reaction vessel was
increased to 60°C at a rate of 5°C per 3 min. At 60°C, 187.5 g of the starch solution
(7.5 g starch) was added, the pH was adjusted to 6.0 and maintained at this value
throughout the remainder of the precipitation, and the AgNO
3 solution was added at 1.0 mL per min for 3 min and the NaBr solution was concurrently
added at a rate needed to maintain a pBr of 1.76. Then the addition of the NaBr solution
was stopped but the addition of the AgNO
3 solution was continued at 1.0 mL per min until a pBr of 2.00 was obtained. Then the
addition of the AgNO
3 was accelerated at 0.05 mL per min squared and the NaBr solution was added as needed
to maintain a pBr of 2.00 until a total of 0.20 mole of silver had been added.
[0098] The tabular grain population of the resulting emulsion was comprised of tabular grains
with an average equivalent circular diameter of 1.0 µm, an average thickness of 0.055
µm, and an average aspect ratio of 18. The tabular grain population made up 90% of
the total projected area of the emulsion grains.
Control Examples 8 through 12
[0099] These examples demonstrate tabular grain preparation failures resulting from choosing
noncationic starches as peptizers.
Control Example 8 AgIBr (3 mole% I) Nontabular Grain Emulsion Made Using a Water-Soluble Carboxylated
(Noncationic) Corn Starch
[0100] This emulsion was prepared similarly to Example 2, except that the starch used was
a corn starch (FILMKOTE ® 54, obtained from National Starch and Chemical Co.), which,
as purchased, was derivatized to contain carboxylate groups. The nitrogen content
was natural, 0.06 wt%.
[0101] A nontabular grain emulsion resulted.
Control Example 9 AgIBr (3 mole% I) Nontabular Grain Emulsion Made Using a Water-Soluble Orthophosphate
Derivatized (Noncationic) Potato Starch
[0102] This emulsion was prepared similarly to Example 2, except that the starch used was
an orthophosphate derivatized potato starch 0.03 wt% nitrogen (natural), and orthophosphate
substituents, 0.66 wt% phosphorus. The sample was obtained from Western Polymer Corporation.
[0103] A nontabular grain emulsion resulted.
Control Example 10 AgIBr (3 mole% I) Nontabular Grain Emulsion Made Using a Water-Soluble Hydroxypropyl-substituted
(Noncationic) Corn Starch.
[0104] This emulsion was prepared similarly to Example 2, except that the starch (STARPOL
® 530, was obtained from A. E. Staley Manufacturing Co.) used was a hydroxypropyl-substituted
corn starch, 0.06 wt% nitrogen (natural) and 0.12 wt% phosphorus.
[0105] A nontabular grain emulsion resulted.
Control Example 11 AgIBr (3 mole% I) Nontabular Grain Emulsion Made Using a Water-Soluble (Noncationic)
Potato Starch
[0106] This emulsion was prepared similarly to Example 2, except that the starch (Soluble
Potato Starch obtained from Sigma Chemical Company, St. Louis, MO.) used was a treated
and purified water soluble potato starch, 0.04 wt% nitrogen and 0.06 wt% phosphorus.
[0107] A nontabular grain emulsion resulted.
Control Example 12 AgIBr (3 mole% I) Nontabular Grain Emulsion Made Using a Water-Soluble (Noncationic)
Wheat Starch
[0108] This emulsion was prepared similarly to Example 2, except that the starch (Supergel
® 1400, obtained from ADM/Ogilvie, Montreal, Quebec, Canada) used was a water soluble
noncationic wheat starch. A nontabular grain emulsion resulted.
Control Example 13 AgIBr (3 mole% I) Nontabular Grain Emulsion Made Using the Grain Protein Zein
[0109] This example demonstrates the failure of zein, a grain protein, to act as a peptizer.
[0110] In a stirred reaction vessel, 8.0 g of zein (obtained from Sigma Chemical Co.) in
400 g distilled water containing 2.7 mmole of NaBr was boiled for 60 min. Most of
the zein did not appear to dissolve. The mixture was filtered and the filtrate was
used as the starch solution to precipitate silver halide using conditions similar
to those used in Example 2.
[0111] The resulting precipitation resulted in large clumps of nontabular grains.
Control Examples 14 through 17
[0112] These examples demonstrate tabular grain preparation failures resulting from choosing
noncationic starch-like substances as peptizers.
Control Example 14 AgIBr (3 mole% I) Nontabular Grain Emulsion Made Using the Noncationic Polysaccharide
Dextran
[0113] This emulsion was prepared similarly to Example 2, except that the polysaccharide
dextran (obtained from Sigma Chemical Co., St. Louis, MO.), having a molecular weight
of approximately 500,000, was employed.
[0114] The resulting precipitation resulted in large clumps of nontabular grains. Dextran
was unable to peptize the silver halide grains.
Control Example 15 AgIBr (3 mole% I) Nontabular Grain Emulsion Made Using the Noncationic Polysaccharide,
Agar
[0115] This emulsion was prepared similarly to Example 2 except that the polysaccharide
used was agar (purified, ash content < 2%), obtained from Sigma Chemical Co.
[0116] The resulting precipitation resulted in large clumps and isolated nontabular grains.
Agar was a poor peptizer for silver halide grains.
Control Example 16 AgIBr (3 mole% I) Nontabular Grain Emulsion Made Using the Noncationic Polysaccharide
Pectin
[0117] This emulsion was prepared similarly to Example 2, except that the polysaccharide
used was pectin from citrus fruit (obtained from Sigma Chemical Co).
[0118] A nontabular grain emulsion resulted.
Control Example 17 AgIBr (3 mole% I) Nontabular Grain Emulsion Made Using the Noncationic Polysaccharide,
Gum Arabic
[0119] This emulsion was prepared similarly to Example 2, except that the polysaccharide
used was gum arabic (obtained from Sigma Chemical Co.), having a molecular weight
of about 250,000.
[0120] A nontabular grain emulsion resulted.
Control Examples 18 through 20
[0121] These examples confirm that the experimental conditions demonstrated above to produce
tabular grain emulsions with cationic starch worked poorly using gelatin. While gelatin
is a well known peptizer for the precipitation of tabular grain emulsions, the choice
of adding all of the peptizer before grain nucleation, demonstrated above using cationic
starches, hampered tabular grain emulsion preparation.
Control Example 18 AgIBr (3 mole% I) Tabular Grain Emulsion Made Using Gelatin as Peptizer.
[0122] This emulsion was prepared similarly to Example 2, except that oxidized bone gelatin
was substituted for the starch.
[0123] The tabular grain population of the resulting emulsion was comprised of tabular grains
with an average equivalent circular diameter of 2.2 µm, an average thickness of 0.07
µm, and an average aspect ratio of 31. The tabular grain population made up 60% of
the total projected area of the emulsion grains, down from 85% in Example 2.
Control Example 19 AgIBr (3 mole% I) AgIBr Nontabular Grain Emulsion Made Using Gelatin as Peptizer.
[0124] This emulsion was prepared similarly to Control Example 28, except that precipitation
was terminated after the addition of 0.1 mole of silver nitrate.
[0125] The tabular grain population of the resulting emulsion was comprised of tabular grains
with an average equivalent circular diameter of 2.0 µm, an average thickness of 0.06
µm, and an average aspect ratio of 33. The tabular grain population made up only 30%
of the total projected area of the emulsion grains.
Control Example 20 AgBr Nontabular Grain Emulsion Made Using Gelatin as Peptizer.
[0126] This emulsion was prepared similarly to Example 2, except that oxidized bone gelatin
was substituted for the starch, the salt solution used was 2.0 M NaBr, and, after
the accelerated addition of AgNO
3, the flow of AgNO
3 was maintained at 5 mL/min until a total of 200 mL was added.
[0127] The tabular grain population of the resulting emulsion was comprised of tabular grains
with an average equivalent circular diameter of 3.2 µm, an average thickness of 0.07
µm, and an average aspect ratio of 46. The tabular grain population made up only 30%
of the total projected area of the emulsion grains.
Control Example 21 AgIBr (2.7 mole% I) Tabular Grain Emulsion
[0128] This emulsion was prepared in bone gelatin using conventional techniques favorable
for the formation of tabular grain emulsions for the purpose of providing an emulsion
with tabular grain thicknesses equal to or less than and tabular grain projected areas
equal to or greater than those of the tabular grain emulsion precipitated in cationic
starch reported in Example 1.
[0129] The emulsion was diafiltered-washed to a pBr of 3.38 at 40°C. The tabular grains
had an average equivalent circular diameter of 2.45 µm, an average thickness of 0.06
µm, and an average aspect ratio of 41. The tabular grain population made up 95% of
the total projected area of the emulsion grains.
Table I
Emulsion Summary |
Example (Control) |
Peptizer |
Cationic |
Wt% Nitrogen |
Wt% Phosphorus |
Tabular Grain ECD/t (mm) |
Tabular Grains as % of Total Grain Projected Area |
1 |
Potato Starch |
Yes |
0.33 |
0.13a |
1.2/0.06 |
92 |
2 |
Hybrd Corn S. |
Yes |
0.31 |
0.00 |
1.6/0.06 |
85 |
3 |
Potato Starch |
Yes |
0.36 |
0.70 |
1.7/0.05 |
95 |
4 |
Potato Starch |
Yes |
0.36 |
0.70 |
1.0/0.045 |
95 |
5 |
Potato Starch |
Yes |
0.33 |
0.13a |
1.5/0.06 |
80 |
6 |
Waxy Corn S. |
Yes |
0.36 |
0.06a |
1.6/0.06 |
91 |
7 |
Potato Starch |
Yes |
0.33 |
0.13a |
1.0/0.055 |
90 |
(8) |
Corn Starch |
No |
0.06a |
0.00 |
NT |
0 |
(9) |
Potato Starch |
No |
0.03a |
0.66 |
NT |
0 |
(10) |
Corn Starch |
No |
0.06a |
0.00 |
NT |
0 |
(11) |
Potato Starch |
No |
0.04a |
0.06 |
NT |
0 |
(12) |
Wheat Starch |
No |
NM |
NM |
NT |
0 |
(13) |
Zein |
No |
NM |
NM |
NT |
0 |
(14) |
Dextran |
No |
NM |
NM |
NT |
0 |
(15) |
Agar |
No |
NM |
NM |
NT |
0 |
(16) |
Pectin |
No |
NM |
NM |
NT |
0 |
(17) |
Gum Arabic |
No |
NM |
NM |
NT |
0 |
(18) |
Gelatin |
NA |
NA |
NA |
2.2/0.07 |
60 |
(19) |
Gelatin |
NA |
NA |
NA |
2.0/0.06 |
30 |
(20) |
Gelatin |
NA |
NA |
NA |
3.2/0.07 |
30 |
(21) |
Gelatin |
NA |
NA |
NA |
2.45/0.06 |
95 |
a Natural content |
b Calculated from the degree of substitution. |
NT = Nontabular
NM = Not Measured
NA = Not Applicable |
Example 22 Photographic Comparisons
[0130] Four emulsion samples were compared.
[0131] The tabular grain emulsion of Example 1, precipitated in the presence of cationic
starch, was divided into three portions to form three samples. Two portions received
no further treatment until sensitization, "Example 1 STA" and "Example 1 STA-Spectral".
The samples were identical, but the latter sample received only spectral sensitization,
instead of chemical and spectral sensitization, as in the case of the remaining emulsion
samples.
[0132] To 0.81 mole of the third portion, "Example 1 GEL", 20 g of bone gelatin in 100 mL
distilled water were added. The purpose of adding gelatin was to demonstrate the effect
of gelatin added as a vehicle after precipitation and before chemical sensitization,
as is conventional practice.
[0133] A fourth emulsion sample was taken from a conventional silver iodobromide (2.7 mole
% I) tabular grain precipitated in bone gelatin, Control Example 21. The purpose of
providing this sample was to compare the properties of an emulsion precipitated in
gelatin to the emulsions precipitated in the absence of gelatin and sensitized either
in the presence or absence of gelatin.
[0134] To 0.035 mole of the emulsion sample (see Table II, below) at 40°C, with stirring,
were added sequentially the following solutions containing (mmole/mole Ag); 2.5 of
NaSCN, 0.22 of a benzothiazolium salt, 1.5 of anhydro-5,5-'dichloro-3,3'-bis(3-sulfopropyl)thiacyanine
hydroxide, triethylammonium salt, and 0.08 of 1-(3-acetamidophenyl)-5-mercapto-tetrazole,
sodium salt. The pH was adjusted to 5.9. Then the following solutions were sequentially
added (mmole/mole Ag) 0.023 of 2-propargylaminobenzoxazole, 0.036 of 1,3-dicarboxymethyl-1,3-dimethyl-2-thiourea,
and 0.014 of bis(1,3,5-trimethyl-1,2,4-triazolium-3-thiolate) gold (I) tetrafluoroborate.
The mixture was heated to 55°C at a rate of 5°C/3 min, and held at 55°C for 15 min.
Upon cooling to 40°C, a solution of 1.68 of 5-bromo-4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene
was added. Example 1 STA-Spectral only had the spectral sensitizing dye added.
[0135] The resulting sensitized emulsions were mixed with gelatin, yellow dye-forming coupler
dispersion, surfactants, and hardener and coated onto clear support at 0.84 g/m
2 silver, 1.7 g/m
2 yellow dye-forming coupler, and 3.5 g./m
2 bone gelatin.
[0136] The coatings were exposed to blue light for 0.02 sec through a 0 to 4.0 log density
graduated step tablet, processed in the Kodak Flexicolor C-41 ä color negative process
using a development time of 3 min 15 sec.
[0137] The results are summarized in Table II.
Table II
Emulsion Sensitized |
Dmax |
Dmin |
Mid-Scale Contrast |
Relative Speed at 0.2 above Dmin |
Control Example 21 |
3.03 |
0.08 |
2.01 |
100 |
Example 1 GEL |
2.86 |
0.09 |
1.79 |
115 |
Example 1 STA |
3.18 |
0.13 |
2.08 |
204 |
Example 1 STA-Spectral |
0.70 |
0.05 |
1.69 |
-11 |
[0138] Control Example 21, a conventional tabular grain emulsion in which the grains were
precipitated in gelatin, was employed as the speed reference. Example 1 GEL, which
was precipitated in cationic starch, but had gelatin added before chemical sensitization,
exhibited a speed that was 15 relative speed units faster than the speed of Control
Example 21. Thus, Example 1 GEL was 0.15 log E (15 relative speed units = 0.15 log
E, where E is exposure in lux-seconds) faster than Control Example 21. This amounted
to a speed advantage of (one-half stop). It was unexpected that precipitation in cationic
starch as opposed to gelatin would produce this significant speed advantage.
[0139] Quite surprising was the large speed advantage demonstrated by Example STA. This
emulsion, which precipitated and sensitized in the absence of gelatin, was 1.04 log
E faster than Control Example 31. In other words, it was more than 10 times faster
than the conventional Control Example 21 emulsion.
[0140] Example 1 STA-Spectral was included to demonstrate that the cationic starch itself,
apart from the chemical sensitizers, was not imparting the speed observed. Example
1 STA-Spectral was 11 relative speed units (1.11 log E) slower than Control Example
31. From this it was concluded that the cationic starch was in some way permitting
better interaction of the chemical sensitizer with the grain surface than is conventionally
realized by employing gelatin as a peptizer.
Example 23 Testing for Starch Retained after Washing
[0141] A coating of Example 1 STA prepared as described in Example 22 was treated with a
0.2 wt % solution of active proteolytic enzyme (H.T.-Proteolytic 200 from Miles Labs,
Inc., Elkhart, IN) for 30 min at 35°C to degrade the gelatin. The emulsion grains
were washed twice in distilled water and examined by infra-red spectroscopy. The infra-red
absorption spectrum of the starch was clearly observed, demonstrating that the starch
remained a permanent part of the emulsion and was not removed by washing.
Example 24 Peptizer Viscosity Comparisons
CS
[0142] A 2 percent by weight cationic starch solution, CS, was prepared by boiling for 30
min a stirred mixture of 8 g STA-LOK ® 400, 2.7 mmoles of NaBr and distilled water
to 400 mL. The solution was sonicated for 3 min. The resulting solution was cooled
to 40°C, readjusted to 400 mL with distilled water, sonicated for 3 min, and the pH
adjusted to 6.0.
GEL
[0143] A 2 percent by weight gealtin solution, GEL, was prepared using bone gelatin. To
4 L was added 27 mmoles of NaBr and the pH was adjusted to 6.0 at 40°C.
[0144] The kinematic viscosities of water and the CS and GEL solutions were measured at
various temperatures. The results are given below.
Table III
Viscosity (cP) |
Solution |
Temperature |
|
40°C |
20°C |
11°C |
Water |
0.66 |
1.00 |
1.27 |
CS |
3.55 |
5.71 |
7.39 |
GEL |
1.67 |
X |
X |
X = Could not be run because the solution solidified. |
[0145] The viscosity data show that cationic starch has low viscosity at low temperatures
while the gelatin solution solidified. This makes cationic starch particularly useful
for silver halide grain nucleation and/or growth at temperatures below 25°C.
[0146] The invention has been described in detail with particular reference to preferred
embodiments thereof, but it will be understood that variations and modifications can
be effected within the spirit and scope of the invention.