Photographic element and emulsion having enhanced sensitometric properties and process of development

A photographic element and emulsion are described which comprise a negative working silver halide emulsion layer, a hydrazine compound nucleating agent and an electron accepting antifogging dye. Enhanced sensitometric properties are obtained. A process for developing such element or emulsion is also described.

The present invention relates to improved photographic element and 
emulsion. More particularly, this invention relates to both a photographic 
element and a photographic emulsion having enhanced sensitometric 
properties and to a process for developing same. 
Hydrazine type compounds have been used as nucleating agents to enhance the 
photographic response of silver halide emulsions, particularly to increase 
contrast values thereof. For example, U.S. Pat. Nos. 2,419,975; 4,224,401; 
4,237,214 and 4,272,606 relate to the use of hydrazine type compounds 
which can be incorporated in photographic elements or employed in 
developer solutions. The silver halide emulsions described in these 
patents may be chemically sensitized. 
However, when hydrazine type compounds are used with silver halide 
emulsions, particularly with emulsions which have been chemically 
sensitized, the usual high level of discrimination between a desirable 
image and fog becomes much less perceptible. 
Attempts to reduce fog in silver halide emulsions containing hydrazine type 
compounds are described in U.S. Pat. No. 2,892,715. Such attempts 
recognize the use of conventional antifogging agents, such as for example 
6-nitrobenzimidazole nitrate, and also the use of a combination of sodium 
xylene sulfonate and octylphenoxy polyoxyethylene ethanol with 
conventional antifoggants. 
Notwithstanding attempts to reduce fog formation caused by hydrazine type 
compounds the problem of unwanted fogging in silver halide emulsions 
containing hydrazine type compounds is still basically unresolved, 
particularly with respect to silver halide emulsions which are chemically 
sensitized. 
It is therefore an object of the present invention to provide for the 
reduction, or the substantial elimination, of undesirable fogging in 
silver halide emulsions, particularly in chemically sensitized silver 
halide emulsions, comprising hydrazine type compounds. 
It is also an object of this invention to provide for the reduction, or 
substantial elimination, of undesirable fogging in sensitized silver 
halide emulsions by processing such emulsions in the presence of hydrazine 
compounds. 
Hereinafter, use of the term "hydrazine" or "hydrazine type" compound is 
intended to include both hydrazine and hydrazide compounds, as well as 
salts and derivatives thereof, which are capable of functioning as 
nucleating agents to enhance the contrast and photographic speed of silver 
halide emulsions. 
The present invention provides a photographic element comprising a support 
having thereon a chemically sensitized, negative working photographic 
silver halide emulsion layer and a hydrazine compound nucleating agent 
wherein said element also comprises an electron accepting antifogging dye 
which has a reversible reduction potential more positive than about -0.8 
volt. 
The present invention also provides a process for developing an imagewise 
exposed, chemically sensitized, negative working photographic silver 
halide emulsion comprising an electron accepting antifogging dye having a 
reversible reduction potential more positive than about 31 0.80 volt 
wherein processing is carried out in an alkaline solution comprising a 
hydrazine compound nucleating agent. 
The present invention also provides a chemically sensitized, negative 
working photographic silver halide emulsion comprising a hydrazine 
compound nucleating agent and an electron accepting antifogging dye having 
a reversible reduction potential more positive than about -0.80 volt. 
The electron accepting antifoggin dye (EAD) which is suitable for use in 
this invention has a reversible reduction potential which is more positive 
than about -0.80 volt. Preferably, such EDA has a reversible reduction 
potential of from about -0.10 to about -0.80 volt. 
Measurement of reversible polarographic reduction potential is accomplished 
by the method of J. Lenhard in Journal of Imaging Science, 30 No. 1, 27-35 
(1986), which description is incorporated herewith by reference. 
Applicants have found that the combination of an EAD, as defined above, 
with a fogging or a nucleating speed-increasing or contrast-enhancing 
hydrazine compound, provides improved photographic speed in chemically 
sensitized silver halide emulsions without a concomitant increase in fog. 
The EAD compound used in this invention is believed to be a deep electron 
trapping agent and, as such, is able selectively to trap electrons away 
from chemical sensitization centers on silver halide grains. This function 
of selective electron trapping is dependent upon the reduction potential 
which, as noted above, must be more positive than about -0.80 volt. 
The concentration of an EAD which is useful in this invention depends at 
least in part upon its reduction potential. It has been found that as the 
reduction potential becomes less negative, moving for example from a value 
of about -0.80 to about -0.40 volt, the amount of EAD required to reduce 
fog caused by the hydrazine type compound decreases. This effect is 
demonstrated in Table I below. 
In general, from about 10.sup.-8 to about 10.sup.-3 mol of EAD per mol of 
silver has been found to be capable of imparting desired speed increases 
while maintaining low levels of fog. A preferred range of EAD is from 
about 10.sup.-7 to about 10.sup.-4 mol per mol of silver to achieve the 
desired results without causing desensitization of the silver halide. As 
can be seen from results presented below, particular EAD compounds 
function very well at low levels of concentration. 
Mixtures of EAD compounds and of hydrazine type compounds can be employed 
to achieve the desired speed increases with low fog levels. 
EAD compounds which have been found to be useful in this invention include 
electron trapping and desensitizing dyes which are already known in the 
art. References which describe such dyes and their preparation include 
U.S. Pat. Nos. 3,772,030 and 4,011,081 and J. Photographic Science, 31, 
185 (1983). Accordingly, preparation of such compounds can be accomplished 
by known synthetic procedures. 
Representative EAD compounds suitable for use in this invention include: 
##STR1## 
The hydrazine compound nucleating agent suitable for use in this invention, 
coated in combination with an EAD compound or employed separately in a 
developer solution, is a nonselective reducing agent, that is the 
hydrazine compound is capable of reducing both exposed and unexposed 
silver halide grains. Such nucleating agents are well known and can be any 
of a number of agents already recognized as being capable of enhancing the 
speed or contrast of negative working silver halide. 
Typical but not limiting examples of such hydrazine compound nucleating 
agents include those described in U.S. Pat. Nos. 2,419,975; 4,221,857; 
4,224,401; 4,237,214; 4,243,739; 4,272,606; 4,323,643; 4,358,530; 
4,269,929; 4,540,655; 4,560,638; 4,650,746; 4,681,836 and 4,722,884, and 
also in pending U.S. pat. application Ser. Nos. 167,814 of Looker et al, 
filed Mar. 14, 1988 and 200,273 of Machonkin et al, filed May 31, 1988, 
which disclosures are incorporated herein by reference. 
Preferred hydrazine compound nucleating agents include those disclosed in 
U.S. Pat. No. 4,650,746 which have the structural formula: 
##STR2## 
wherein; R is a phenyl nucleus having a Hammet sigma value-derived 
electron withdrawing characteristic of less than +0.30; 
also those disclosed in U.S. Pat. No. 4,323,643 which have the structural 
formula: 
##STR3## 
wherein; R.sup.2 and R.sup.3 represent hydrogen, an aliphatic group, an 
aromatic group or a heterocyclic group; 
R.sup.4 represents hydrogen or an aliphatic group and 
X is a divalent aromatic group; 
and also the hydrazine compounds described in U.S. Pat. No. 4,681,836 
having the structural formula: 
##STR4## 
wherein; R.sup.5 is an aliphatic or an aromatic group. 
The electron withdrawing or electron donating characteristic of an R.sup.1 
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. 
The hydrazine compound nucleating agents which can be employed in this 
invention are well known in the art and need not be described in detail. 
Generally such compounds can be obtained by reacting formic acid, or a 
salt thereof, with a hydrazine compound, for example a phenylhydrazine. 
Specific hydrazine compounds include the following: 
##STR5## 
The hydrazine compounds can be employed in the described photographic 
elements and emulsions in a concentration of from about 10.sup.-4 to about 
10.sup.-1 mol per mol of silver. A preferred quantity of the hydrazine 
compound is from about 5.times.10.sup.-4 to about 5.times.10.sup.-2 mol 
per mol of silver. Optimum results are obtained when the hydrazine 
compound is present in a concentration of from 8.times.10.sup.-4 to about 
5.times.10.sup.-3 mol per mol of silver. 
The hydrazine compound can be incorporated in a photographic silver halide 
emulsion layer or, alternatively, in another hydrophilic colloid layer. 
Preferably, the hydrazine is coated in the same layer which contains the 
EAD compound. The compound may be added to the photographic emulsion at 
any stage of preparation from the beginning of the chemical ripening to 
just before coating of the emulsion. 
When the hydrazine compound nucleating agent is incorporated in a developer 
solution the amount of such compound to be used is from about 10.sup.-5 to 
about 10.sup.-2 mol thereof/liter of developer solution. Equally 
satisfactory results are obtained by incorporating the hydrazine compound 
in the photographic element or emulsion or in the alkaline developer 
solution as is demonstrated hereafter by test results. 
Silver halide emulsions used in this invention contain a vehicle in 
addition to silver halide grains. The proportion of vehicle can be widely 
varied, but typically is within the range of from about 20 to 250 grams 
per mol of silver halide. Excessive vehicle can have the effect of 
reducing maximum density and consequently also reducing contrast. Thus for 
contrast values of 10 or more it is preferred that the vehicle be present 
in a concentration of 250 grams per mol of silver halide or less. The 
specific vehicle materials present in the emulsion and any other layers of 
the photographic elements can be chosen from among conventional vehicle 
materials. Preferred vehicles are water permeable hydrophilic colloids, 
especially gelatin, employed alone or in combination with extenders such 
as synthetic polymeric peptizers, carriers, latices, and binders. Such 
materials are more specifically described in Research Disclosure, Vol. 
176, Dec. 1978, Item 17643, Section IX. Vehicles are commonly employed 
with one or more hardeners, such as those described in Section X. 
The silver halide present in the described photographic elements and 
emulsions may have any halide composition. For example, silver chloride, 
silver bromide, silver chlorobromide and silver bromoiodide are all 
suitable for use with the present invention. Conventional chemical 
sensitizing agents can be employed. These include compounds of sulfur, 
gold, selenium, copper, rhodium, iridium and mixtures thereof. A preferred 
mixture is sulfur and gold. 
Emulsions include those having silver halide grains of any conventional 
geometric form (e.g., regular octahedral or, preferably, cubic crystalline 
form) and 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, pages 330-338; 
T. H. James The Theory of the Photographic Process, 4th Ed., Macmillan, 
1977, Chapter 3; Research Disclosure, Vol. 149, Sept. 1976, Item 14987; 
Research Disclosure, Vol. 225, Jan. 1983, Item 22534; as well as U.S. Pat. 
Nos. 2,222,264; 3,650,757; 3,790,387 and 3,917,485; German OLS No. 
2,107,118; and U.K. Pat. Nos. 1,335,925; 1,430,465 and 1,469,480. 
Double-jet accelerated flow rate precipitation techniques are preferred 
for forming monodispersed emulsions. Chemical sensitizing compounds, such 
as compounds of sulfur, gold, copper, thallium, cadmium rhodium, tungsten, 
thorium, iridium and mixtures thereof, can be present during precipitation 
of the silver halide emulsion, as illustrated in U.S. Pat. Nos. 1,195,432; 
1,951,933; 2,448,060; 2,628,167; 2,950,972; 3,488,709; and 3,737,313. 
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 ammonical emulsions, as illustrated by Glafkides, Photographic 
Chemistry, Vol. 1, Fountain Press, London, 1958, pages 365-368 and pages 
301-304; thiocyanate ripened emulsions, as illustrated by U.S. Pat. No. 
3,320,069; thioether ripened emulsions as illustrated by U.S. Pat. Nos. 
3,271,157; 3,574,628 and U.S. Pat. No. 3,737,313 or emulsions containing 
weak silver halide solvents, such as ammonium salts, as illustrated by 
U.S. Pat. No. 3,784,381 and Research Disclosure, Vol. 134, Jun. 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 U.S. Pat. Nos. 2,316,845 and 3,396,027; by coagulation 
washing, as illustrated by U.S. Pat. Nos. 2,618,556, 2,614,928, 2,565,418, 
3,241,969, 2,489,341; and by U.K. Pat. Nos. 1,305,409 and 1,167,159; by 
centrifugation and decantation of a coagulated emulsion, as illustrated by 
U.S. Pat. Nos. 2,463,794; 3,707,378, 2,996,287 and 3,498,454; by employing 
hydrocyclones alone or in combination with centrifuges, as illustrated by 
U.K. Pat. Nos. 1,336,692, and 1,356,573 and Ushomirski et al Soviet 
Chemical Industry, Vol. 6, No. 3, 1974, pages 181-185; by diafiltration 
with a semipermeable membrane, as illustrated by Research Disclosure, Vol. 
102, Oct. 1972, Item 10208; Research Disclosure, Vol. 131, Mar. 1975, Item 
13122; Research Disclosure, Vol. 135, Jul. 1975, Item 13577, German OLS 
No. 2,436,461 and U.S. Pat. No. 2,495,918; or by employing an ion exchange 
resin, as illustrated by Maley U.S. Pat. Nos. 2,827,428 and 3,782,953. The 
emulsions, with or without sensitizers, can be dried and stored prior to 
use as illustrated by Research Disclosure, Vol. 101, Sept. 1972, Item 
10152. 
The invention is further illustrated by the following examples: