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Description  |
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FIELD OF THE INVENTION
This invention is directed to a negative-working photographic emulsion, to
a photographic element containing a negative-working emulsion layer and to
a process forming an image with such a photographic element.
DESCRIPTION OF THE STATE OF THE ART
Relatively high contrast negative-working photographic elements have been
recognized to have practical photographic imaging applications. For
example, hydrazine compounds have been employed to increase contrast,
preferably in combination with an antifoggant. Smith et al U.S. Pat. Nos.
2,410,690, Stauffer et al 2,419,974, Trivelli et al 2,419,975, Hunsberger
2,892,715 and Stauffer, Smith and Trivelli, "The Influence of Photographic
Developers Containing Hydrazine Upon the Characteristic Curves of
Photographic Materials", Journal of the Franklin Institute. Vol. 238,
October 1944, pp. 291-298, illustrate basic discoveries pertaining to
relatively high contrast imaging with negative-working silver halide
photograhic elements.
Very high contrast (.gamma.>10) negative-working silver halide emulsions
and photographic elements are commonly referred to as "lith" emulsions and
photographic elements, since they are useful in forming halftone masters
for plate exposures in photolithography. Typical lith silver halide
photographic elements contain high chloride emulsions (at least about 60
percent by weight silver chloride, based on total silver halide),
typically in the form of silver chlorobromides or silver
chlorobromoiodides. Very high contrast is achieved using a phenolic
developing agent, such as a hydroquinone, limiting the use of secondary
developing agents and limiting sulfite preservatives to avoid interference
with hydroquinone oxidation products. Hydrazine compounds have not been
employed in these very high contrast emulsions and photographic elements.
Conventional approaches to obtaining very high contrast images with
negative-working silver halide photographic elements have exhibited a
number of disadvantages. First, using silver chloride-containing
emulsions, the higher photographic speeds of silver bromide and silver
bromoiodide emulsions have not been achieved. Second, the requirement of
using hydroquinone developing agents has limited the selection of
photographic developer compositions. Third, the need to limit sulfite
preservative concentrations has resulted in lack of stability during
storage of developers.
SUMMARY OF THE INVENTION
The present invention achieves the unexpected advantages of higher speed
and very high contrast through the use of selected hydrazine compounds. In
a preferred form advantages are obtained by employing these hydrazine
compounds in combination with a specific class of antifoggants. This
invention obtains very high contrasts using silver halide emulsions
generally, rather than just high chloride emulsions. Further, very high
contrast images are obtained using conventional photographic developers
having higher sulfite concentrations than have heretofore been employed in
processing of lith photographic elements. Specifically, this invention
achieves the advantage of being able to employ developers which are more
storage stable. Further, auxiliary, nonphenolic developing agents can be
employed to increase developer capacity and reduce induction times. This
invention then expands both the choice of silver halide emulsions and
developers which can be employed in obtaining relatively high contrast
photographic images.
In one aspect this invention is directed to a negative-working photographic
emulsion comprised of radiation-sensitive silver halide grains capable of
forming a surface latent image, a binder and, in an amount sufficient to
increase contrast, a hydrazine compound of the formula
##STR2##
wherein R.sup.1 is a phenyl nucleus having a Hammett sigma value-derived
electron withdrawing characteristic of less than +0.30.
In another aspect this invention is directed to a photographic element
comprising a support, coated on the support at least one negative-working
photographic emulsion comprising radiation-sensitive silver halide grains
capable of forming a surface latent image and a binder and, in the
emulsion or in a remaining hydrophilic colloid layer coated on the support
in an amount sufficient to increase contrast, a hydrazine compound of the
formula
##STR3##
wherein R.sup.1 is a phenyl nucleus having a Hammett sigma value-derived
electron withdrawing characteristic of less than +0.30.
In an additional aspect this invention is directed to an improvement in
developing an imagewise exposed photographic element as described above
wherein the developer contains about 0.15 mole or more of sulfite ion per
liter and has a pH of from about 11.0 to 12.3.
This invention can be better appreciated by reference to the following
detailed description considered in conjunction with the drawing, in which
characteristic curves for photographic elements containing
1-formyl-2-phenylhydrazines according to this invention are compared with
similar photographic elements containing pyridinium hydrazide and
semicarbazide compounds in similar and higher concentrations.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The hydrazine compounds employed in the practice of this invention exhibit
the following general formula:
##STR4##
wherein R.sup.1 is a phenyl nucleus having a Hammett sigma value-derived
electron withdrawing characteristic of less than +0.30.
R.sub.1 can take the form of a phenyl nucleus which is either electron
donating (electropositive) or electron withdrawing (electronegative);
however, phenyl nuclei which are highly electron withdrawing produce
inferior nucleating agents. The electron withdrawing or electron donating
characteristic of a specific phenyl nucleus can be assessed by reference
to Hammett sigma values. The phenyl nucleus can be assigned a Hammett
sigma value-derived electron withdrawing characteristic which is the
algebraic sum of the Hammett sigma values of its substituents (i.e., those
of the substituents, if any, to the phenyl group). For example, the
Hammett sigma values of any substituents to the phenyl ring of the phenyl
nucleus can be determined algebraically simply by determining from the
literature the known Hammett sigma values for each substituent and
obtaining the algebraic sum thereof. Electron withdrawing substituents are
assigned negative sigma values. For example, in one preferred form R.sup.1
can be a phenyl group which is unsubstituted. The hydrogen attached to the
phenyl ring each have a Hammett sigma value of 0 by definition. In another
form the phenyl nuclei can include halogen ring substituents. For example,
ortho- or para-chloro or fluoro substituted phenyl groups are specifically
contemplated, although the chloro and fluoro groups are each mildly
electron withdrawing.
Preferred phenyl group substituents are those which are not electron
withdrawing. For example, the phenyl groups can be substituted with
straight or branched chain alkyl groups (e.g., methyl, ethyl, n-propyl,
isopropyl, n-butyl, isobutyl, n-hexyl, n-octyl, tert-octyl, n-decyl,
n-dodecyl and similar groups). The phenyl groups can be substituted with
alkoxy groups wherein the alkyl moieties thereof can be chosen from among
the alkyl groups described above. The phenyl groups can also be
substituted with acylamino groups. Illustrative acylamino groups include
acetylamino, propanoylamino, butanoylamino, octanoylamino, benzoylamino
and similar groups.
In one particularly preferred form the alkyl, alkoxy and/or acylamino
groups are in turn substituted with a conventional photographic ballast,
such as the ballasting moieties of incorporated couplers and other
immobile photographic emulsion addenda. The ballast groups typically
contain at least eight carbon atoms and can be selected from both
aliphatic and aromatic relatively unreactive groups, such as alkyl,
alkoxy, phenyl, alkylphenyl, phenoxy, alkylphenoxy and similar groups.
The alkyl and alkoxy groups, including ballasting groups, if any,
preferably contain from 1 to 20 carbon atoms, and the acylamino groups,
including ballasting groups, if any, preferably contain from 2 to 21
carbon atoms. Generally, up to about 30 or more carbon atoms in these
groups are contemplated in their ballasted form. Methoxyphenyl, tolyl
(e.g., p-tolyl and m-tolyl) and ballasted butyramidophenyl nuclei are
specifically preferred.
Although the hydrazine compounds intended for use in the practice of this
invention each contain a formyl moiety, it is appreciated that otherwise
comparable hydrazine compounds containing a benzoyl moiety which is
substituted with a highly electron withdrawing substituent, such as a
cyano group, are operative. Such compounds have, however, been found to be
inferior to the hydrazine compounds containing a formyl moiety.
The synthesis of 1-formyl-2-phenylhydrazine compounds employed in the
practice of this invention is well known in the art and need not be
described in detail. Generally such compounds can be formed by reacting
formic acid or its salt with the corresponding phenylhydrazine. The
conventional nature of the 1-formyl-2-phenylhydrazine compounds as such is
illustrated by Honig et al U.S. Pat. No. 3,386,831, which shows
1-acetyl-2-phenylhydrazine and homologues formed by higher molecular
weight carboxylic acid adducts, and Olivares et al U.S. Pat. No.
3,782,949, which shows 1-formyl-2-phenylhydrazine, there designated
formyl-.beta.-phenylhydrazine.
The following are illustrative of specifically preferred hydrazine
compounds useful in the practice of this invention:
##STR5##
The hydrazine compounds are present in the photographic elements of this
invention in a concentration of from about 10.sup.-4 to about 10.sup.-1
mole per mole of silver. A preferred quantity of the hydrazine compound is
from 5.times.10.sup.-4 to about 5.times.10.sup.-2 mole per mole of silver.
Optimum rests are obtained when the hydrazine compound is present in a
concentration of from about 8.times.10.sup.-4 to about 5.times.10.sup.-3
mole per mole of silver. The hydrazine compound can be incorporated in a
silver halide emulsion used in forming the photographic element.
Alternatively the hydrazine compound can be present in a hydrophilic
colloid layer of the photographic element, preferably a hydrophilic
colloid layer which is coated to be contiguously adjacent to the emulsion
layer in which the effects of the hydrazine compound are desired. The
hydrazine can, of course, be present in the photographic element
distributed between or among emulsion and hydrophilic colloid layers, such
as undercoating layers, interlayers and overcoating layers.
The hydrazine compounds are employed in combination with negative-working
photographic emulsions comprised of radiation-sensitive silver halide
grains capable of forming a surface latent image and a binder. The silver
halide emulsions include the high chloride emulsions conventionally
employed in forming lith photographic elements as well as silver bromide
and silver bromoiodide emulsions, which are recognized in the art to be
capable of attaining higher photographic speeds. Generally the iodide
content of the silver halide emulsions is less than about 10 mole percent
silver iodide, based on total silver halide.
The silver halide grains of the emulsions are capable of forming a surface
latent image, as opposed to being of the internal latent image-forming
type. Surface latent image silver halide grains are employed in the
overwhelming majority of negative-working silver halide emulsions, whereas
internal latent image-forming silver halide grains, though capable of
forming a negative image when developed in an internal developer, are
usually employed with surface developers to form direct-positive images.
The distinction between surface latent image and internal latent image
silver halide grains is generally well recognized in the art. Generally
some additional ingredient or step is required in preparation to form
silver halide grains capable of preferentially forming an internal latent
image as compared to a surface latent image.
Although the difference between a negative image produced by a surface
latent image emulsion and a positive image produced by an internal latent
image emulsion when processed in a surface developer is a qualitative
difference which is visually apparent to even the unskilled observer, a
number of tests have been devised to distinguish quantitatively surface
latent image-forming and internal latent image-forming emulsions. For
example, according to one such test when the sensitivity resulting from
surface development (A), described below, is greater than that resulting
from internal development (B), described below, the emulsion being
previously light exposed for a period of from 1 to 0.01 second, the
emulsion is of a type which is "capable of forming a surface latent image"
or, more succinctly, it is a surface latent image emulsion. The
sensitivity is defined by the following equation:
##EQU1##
in which S represents the sensitivity and Eh represents the quantity of
exposure necessary to obtain a mean density--i.e., 1/2(D.sub.max
+D.sub.min).
Surface Development (A)
The emulsion is processed at 20.degree. C. for 10 minutes in a developer
solution of the following composition:
______________________________________
N--methyl- -p-aminophenol (hemisulfate)
2.5 g
Ascorbic acid 10 g
Sodium metaborate (with 4 molecules of water)
35 g
Potassium bromide 1 g
Water to bring the total to
1 liter.
______________________________________
Internal Development (B)
The emulsion is processed at about 20.degree. C. for 10 minutes in a
bleaching solution containing 3 g of potassium ferricyanide per liter and
0.0125 g of phenosafranine per liter and washed with water for 10 minutes
and developed at 20.degree. C. for 10 minutes in a developer solution
having the following composition:
______________________________________
N--methyl- -p-aminophenol (hemisulfate)
2.5 g
Ascorbic acid 10 g
Sodium metaborate (with 4 moles of water)
35 g
Potassium bromide 1 g
Sodium thiosulfate 3 g
Water to bring the total to
1 liter.
______________________________________
The silver halide grains, when the emulsions are used for lith
applications, have a mean grain size of not larger than about 0.7 micron,
preferably about 0.4 micron or less. Mean grain size is well understood by
those skilled in the art, as illustrated by Mees and James, The Theory of
the Photographic Process, 3rd Ed., MacMillan 1966, Chapter 1, pp. 36-43.
The photographic emulsions of this invention are capable of producing
higher photographic speeds than would be expected from their mean grain
sizes. The photographic emulsions can be coated to provide emulsion layers
in the photographic elements of any conventional silver coverage. Common
conventional silver coating coverages fall within the range of from about
0.5 to about 10 grams per square meter.
As is generally recognized in the art, higher contrasts can be achieved by
employing relatively monodispersed emulsions. Monodispersed emulsions are
characterized by a large proportion of the silver halide grains falling
within a relatively narrow size-frequency distribution. In quantitative
terms, monodispersed emulsions have been defined as those in which 90
percent by weight or by number of the silver halide grains are within plus
or minus 40 percent of the mean grain size.
Silver halide emulsions contain in addition to silver halide grains a
binder. The proportion of binder can be widely varied, but typically is
within the range of from about 20 to 250 grams per mole of silver halide.
Excessive binder can have the effect of reducing maximum densities and
consequently also reduce contrast. Thus for contrast values of 10 or more
it is preferred that the binder be present in a concentration of 250 grams
per mole of silver halide or less.
The binders of the emulsions can be comprised of hydrophilic colloids.
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 (cattle bone or
hide gelatin) or acid-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 as described in U.S. Pat. Nos. 2,614,928 and '929, to Yutzy et al.,
Lowe et al 2,691,582, 2,614,930, '931, 2,327,808 and 2,448,534, Gates et
al 2,787,545 and 2,956,880, Himmelmann et al. 3,061,436, Farrell et al
2,816,027, Ryan 3,132,945, 3,138,461 and 3,186,846, Dersch et al U.K. Pat.
No. 1,167,159 and U.S. Pat. Nos. 2,960,405 and 3,436,220, Geary 3,486,896,
Gazzard U.K. Pat. No. 793,549, to Gates et al U.S. Pat. Nos. 2,992,213,
3,157,506, 3,184,312 and 3,539,353, Miller et al 3,227,571, Boyer et al
3,532,502, Malan 3,551,151, Lohmer et al 4,018,609, to Luciani et al U.K.
Pat. Nos. 1,186,790, 1,489,080 and Hori et al Belgian Pat. No. 856,631,
U.K. Pat. Nos. 1,490,644, 1,483,551, Arase et al 1,459,906, to Salo U.S.
Pat. Nos. 2,110,491 and 2,311,086, Fallesen 2,343,650, Yutzy 2,322,085,
Lowe 2,563,791, Talbot et al 2,725,293, Hilborn 2,748,022, DePauw et al
2,956,883, Ritchie U.K. Pat. No. 2,095, DeStubner U.S. Pat. Nos.
1,752,069, Sheppard et al 2,127,573, Lierg 2,256,720, Gaspar 2,361,936,
Farmer U.K. Pat. Nos. 15,727, Stevens 1,062,116 and Yamamoto et al U.S.
Pat. No. 3,923,517.
In addition to hydrophilic colloids the emulsion binder can be optionally
comprised of synthetic polymeric materials which are water insoluble or
only slightly soluble, such as polymeric latices. These materials can act
as supplemental grain peptizers and carriers, and they can also
advantageously impart increased dimensional stability to the photographic
elements. The synthetic polymeric materials can be present in a weight
ratio with the hydrophilic colloids of up to 2:1. It is generally
preferred that the synthetic polymer materials constitute from about 20 to
80 percent by weight of the binder.
Suitable synthetic polymer materials can be chosen from among poly(vinyl
lactams), acrylamide polymers, polyvinyl alcohol and its derivatives,
polyvinyl acetals, polymers of alkyl and sulfoalkyl acrylates and
methacrylates, hydrolyzed polyvinyl acetates, polyamides, polyvinyl
pyridine, acrylic acid polymers, maleic anhydride copolymers, polyalkylene
oxides, methacrylamide copolymers, polyvinyl oxazolidinones, maleic acid
copolymers, vinylamine copolymers, methacrylic acid copolymers,
acryloyloxyalkylsulfonic acid copolymers, sulfoalkylacrylamide copolymers,
polyalkyleneimine copolymers, polyamines, N,N-dialkylaminoalkyl acrylates,
vinyl imidazole copolymers, vinyl sulfide copolymers, halogenated styrene
polymers, amineacrylamide polymers, polypeptides and the like as described
in Hollister et al U.S. Pat. Nos. 3,679,425, 3,706,564 and 3,813,251, Lowe
2,253,078, 2,276,322, '323, 2,281,703, 2,311,058 and 2,414,207, Lowe et al
2,484,456, 2,541,474 and 2,632,704, Perry et al 3,425,836, Smith et al
3,415,653 and 3,615,624, Smith 3,488,708, Whiteley et al 3,392,025 and
3,511,818, Fitzgerald 3,681,079, 3,721,565, 3,852,073, 3,861,918 and
3,925,083, Fitzgerald et al 3,879,205, Nottorf 3,142,568, Houck et al
3,062,674 and 3,220,844, Dann et al 2,882,161, Schupp 2,579,016, Weaver
2,829,053, Alles et al 2,698,240, Priest et al 3,003,879, Merrill et al
3,419,397, Stonham 3,284,207, Lohmer et al 3,167,430, Williams 2,957,767,
Dawson et al 2,893,867, Smith et al 2,860,986 and 2,904,539, Ponticello et
al 3,929,482 and 3,860,428, Ponticello 3,939,130, Dykstra 3,411,911 and
Dykstra et al Canadian Pat. No. 774,054, Ream et al U.S. Pat. No.
3,287,289, Smith U.K. Pat. Nos. 1,466,600, Stevens 1,062,116, Fordyce U.S.
Pat. Nos. 2,211,323, Martinez 2,284,877, Watkins 2,420,455, Jones
2,533,166, Bolton 2,495,918, Graves 2,289,775, Yackel 2,565,418, Unruh et
al 2,865,893 and 2,875,059, Rees et al 3,536,491, Broadhead et al U.K.
Pat. No. 1,348,815, Taylor et al U.S. Pat. Nos. 3,479,186, Merrill et al
3,520,857, Bacon et al 3,690,888, Bowman 3,748,143, Dickinson et al U.K.
Pat. Nos. 808,227 and 808,228, Wood 822,192 and Iguchi et al 1,398,055.
Although the term "binder" is employed in describing the continuous phase
of the silver halide emulsions, it is recognized that other terms commonly
employed by those skilled in the art, such as carrier or vehicle, can be
interchangeably employed. The binders described in connection with the
emulsions are also useful in forming undercoating layers, interlayers and
overcoating layers of the photographic elements of this invention.
Typically the binders are hardened with one or more photographic
hardeners, such as those described in Paragraph VII, Product Licensing
Index, Vol. 92, December 1971, Item 9232, here incorporated by reference.
Emulsions according to this invention having silver halide grains of any
conventional geometric form (e.g., regular cubic or octahedral crystalline
form) can be prepared by a variety of techniques--e.g., single-jet,
double-jet (including continuous removal techniques), accelerated flow
rate and interrupted precipitation techniques, as illustrated by Trivelli
and Smith, The Photographic Journal, Vol. LXXIX, May, 1939, pp. 330-338,
T. H. James, The Theory of the Photographic Process, 4th Ed., Macmillan,
1977, Chapter 3, Terwilliger et al Research Disclosure, Vol. 149,
September 1976, Item 14987, as well as Nietz et al U.S. Pat. No.
2,222,264, Wilgus German OLS No. 2,107,118, Lewis U.K. Pat. Nos. 335,925,
1,430,465 and 1,469,480, Irie et al U.S. Pat. Nos. 3,650,757, Kurz
3,672,900, Morgan 3,917,485, Musliner 3,790,387, Evans 3,761,276 and
Gilman et al 3,979,213. Double jet accelerated flow rate precipitation
techniques are preferred for forming monodispersed emulsions. Sensitizing
compounds, such as compounds of copper, thallium, cadmium, rhodium,
tungsten, thorium, iridium and mixtures thereof, can be present during
precipitation of the silver halide emulsion, as illustrated by Arnold et
al U.S. Pat. Nos. 1,195,432, Hochstetter 1,951,933, Overman 2,628,167,
Mueller et al 2,950,972, Sidebotham 3,488,709 and Rosecrants et al
3,737,313.
The individual reactants can be added to the reaction vessel through
surface or sub-surface delivery tubes by gravity feed or by delivery
apparatus for maintaining control of the pH and/or pAg of the reaction
vessel contents, as illustrated by Culhane et al U.S. Pat. Nos. 3,821,002,
Oliver 3,031,304 and Claes et al, Photographische Korrespondenz, 102 Band,
Number 10, 1967, p. 162. In order to obtain rapid distribution of the
reactants within the reaction vessel, specially constructed mixing devices
can be employed, as illustrated by Audran U.S. Pat. Nos. 2,996,287,
McCrossen et al 3,342,605, Frame et al 3,415,650, Porter et al 3,785,777,
Saito et al German OLS Nos. 2,556,885 and Sato et al German OLS 2,555,364.
An enclosed reaction vessel can be employed to receive and mix reactants
upstream of the main reaction vessel, as illustrated by Forster et al U.S.
Pat. Nos. 3,897,935 and Posse et al 3,790,386.
The grain size distribution of the silver halide emulsions can be
controlled by silver halide grain separation techniques or by blending
silver halide emulsions of differing grain sizes. The emulsions can
include ammoniacal emulsions, as illustrated by Glafkides, Photographic
Chemistry, Vol. 1, Fountain Press, London, 1958, pp. 365-368 and pp.
301-304; thiocyanate ripened emulsions, as illustrated by Illingsworth
U.S. Pat. No. 3,320,069; thioether ripened emulsions, as illustrated by
McBride U.S. Pat. Nos. 3,271,157, Jones 3,574,628 and Rosecrants et al
3,737,313 or emulsions containing weak silver halide solvents, such as
ammonium salts, as illustrated by Perignon U.S. Pat. No. 3,784,381 and
Research Disclosure, Vol. 134, June 1975, Item 13452.
The silver halide emulsion can be unwashed or washed to remove soluble
salts. The soluble salts can be removed by chill setting and leaching, as
illustrated by Craft U.S. Pat. Nos. 2,316,845 and McFall et al 3,396,027;
by coagulation washing, as illustrated by Hewitson et al U.S. Pat. Nos.
2,618,556, Yutzy et al 2,614,928, Yackel 2,565,418, Hart et al 3,241,969,
Waller et al 2,489,341, Klinger U.K. Pat. Nos. 1,305,409 and Dersch et al
1,167,159; by centrifugation and decantation of a coagulated emulsion, as
illustrated by Murray U.S. Pat. Nos. 2,463,794, Ujihara et al 3,707,378,
Audran 2,996,287 and Timson 3,498,454; by employing hydrocyclones alone or
in combination with centrifuges, as illustrated by U.K. Pat. Nos. 336,692,
Claes U.K. Pat. No. 1,356,573 and Ushomirskii et al Soviet Chemical
Industry, Vol. 6, No. 3, 1974, pp. 181-185; by diafiltration 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 No. 2,436,46and Bolton U.S. Pat. No.
2,495,918 or by employing an ion exchange resin, as illustrated by Maley
U.S. Pat. Nos. 3,782,953 and Noble 2,827,428. The emulsions, with or
without sensitizers, can be dried and stored prior to use as illustrated
by Research Disclosure, Vol. 101, September 1972, Item 10152.
The silver halide emulsions can be chemically sensitized with active
gelatin, as illustrated by T. H. James, The Theory of the Photographic
Process, 4th Ed., Macmillan, 1977, pp. 67-76, or with sulfur, selenium,
tellurium, platinum, palladium, iridium, osmium, rhenium or phosphorus
sensitizers or combinations of these sensitizers, such as at pAg levels of
from 5 to 10, pH levels of from 5 to 8 and temperatures of from
30.degree.to 80.degree. C., as illustrated by Research Disclosure, Vol.
134, June 1975, Item 13452, Sheppard et al U.S. Pat. Nos. 1,623,499,
McVeigh 3,297,447, Dunn 3,297,446, Berry et al Patent 3,772,031, Gilman et
al 3,761,267, Ohi et al 3,857,711, Klinger et al 3,565,633 and Oftedahl
3,901,714 and 3,904,415. Additionally or alternatively, the emulsions can
be reduction sensitized--e.g., with hydrogen, as illustrated by Janusonis
U.S. Pat. Nos. 3,891,446 and Babcock et al 3,984,249, by low pAg (e.g.,
less than 5 ) high pH (e.g., greater than 8) treatment or through the use
of reducing agents, such as stannous chloride, thiourea dioxide,
polyamines and amineboranes, as illustrated by Allen et al U.S. Pat. No.
2,983,609, Oftedahl et al Research Disclosure, Vol. 136, August 1975, Item
13654, Lowe et al U.S. Pat. Nos. 2,518,698 and 2,743,182, Chambers et al
3,026,203 and Bigelow et al 3,361,564. Generally sulfur sensitization is
the preferred chemical sensitization for the emulsions. The emulsions need
not be chemically sensitized, however, in order to exhibit the advantages
of this invention.
The silver halide emulsions can be spectrally sensitized with dyes from a
variety of classes, including the polymethine dye class, which includes
the cyanines, merocyanines, complex cyanines and merocyanines (i.e., tri-,
tetra- and poly-nuclear cyanines and merocyanines), oxonols, hemioxonols,
styryls, merostyryls and streptocyanines.
The cyanine spectral sensitizing dyes include, joined by a methine linkage,
two basic heterocyclic nuclei, such as those derived from quinolinium,
pyridinium, isoquinolinium, 3H-indolium, benz[e]indolium, oxazolium,
thiazolium, selenazolinium, imidazolium, benzoxazolinium, benzothiazolium,
benzoselenazolium, benzimidazolium, naphthoxazolium, naphthothiazolium,
naphthoselenazolium, thiazolinium dihydronaphthothiazolium, pyrylium and
imidazopyrazinium quaternary salts.
The merocyanine spectral sensitizing dyes include, joined by a methine
linkage, a basic heterocyclic nucleus of the cyanine dye type and an
acidic nucleus, such as can be derived from barbituric acid,
2-thiobarbituric acid, rhodanine, hydantoin, 2-thiohydantoin,
4-thiohyantoin, 2-pyrazolin-5-one, 2-isoxazolin-5-one, indan-1,3-dione,
cyclohexan-1,3-dione, 1,3-dioxan-4,6-dione, pyrazolin-3,5-dione,
pentan-2,4-dione, alkylsulfonyl acetonitrile, malononitrile,
isoquinolin-4-one, and chroman-2,4-dione.
One or more spectral sensitizing dyes may be used. Dyes with sensitizing
maxima at wavelengths throughout the visible spectrum and with a great
variety of spectral sensitivity curve shapes are known. The choice and
relative proportions of dyes depends upon the region of the spectrum to
which sensitivity is desired and upon the shape of the spectral
sensitivity curve desired. Dyes with overlapping spectral sensitivity
curves will often yield in combination a curve in which the sensitivity at
each wavelength in the area of overlap is approximately equal to the sum
of the sensitivities of the individual dyes. Thus, it is possible to use
combinations of dyes with different maxima to achieve a spectral
sensitivity curve with a maximum intermediate to the sensitizing maxima of
the individual dyes.
Combinations of spectral sensitizing dyes can be used which result in
supersensitizat | | |
