Negative type silver halide photographic emulsions

Negative type silver halide photographic emulsions are provided, formed by growing silver halide grains in the presence of a water-soluble iridium salt in a molar ratio of 3.times.10.sup.-4 mol or more to the amount of the total silver halides used in the formation of the silver halide grains and then chemically sensitizing the surfaces of the grains formed with a sulfur compound or with a sulfur compound and a gold compound. The present emulsions have high sensitivity and extremely improved variation of sensitivity and gradation under broad exposure conditions of high intensity exposure and low intensity exposure.

FIELD OF THE INVENTION 
The present invention relates to light-sensitive negative type silver 
halide emulsions and, more precisely, to those of high sensitivity which 
have extremely improved variation of sensitivity and gradation under high 
intensity exposure and low intensity exposure. 
BACKGROUND OF THE INVENTION 
Recently, negative films of higher sensitivity and broader exposure 
aptitude have been required with the variation of color negative films 
into small format styles under various photographic conditions. 
Under such circumstances, various proposals have been made for the purpose 
of improving the photographic properties by the addition of iridium to the 
silver halide emulsions thereof, including one typical embodiment where 
silver halide grains are formed in the presence of 10.sup.-8 to 10.sup.-5 
mol of iridium per 1 mol of silver, which is to be added to the emulsion 
at a certain stage of the formation thereof, resulting in various effects 
of intensification of sensitization, improvement of high intensity 
reciprocity low failure and improvement of fogging inhibition. These 
techniques are described in, for example, Japanese Patent Publication Nos. 
4935/68 and 32738/70 or Japanese Patent Application (OPI) Nos. 221839/83 
and 152438/84 (the term "OPI" as used herein refers to a "published 
unexamined Japanese patent application"). In these publications, however, 
it is reported that the amount of the iridium to be added is preferably 
10.sup.-7 to 10.sup.-6 mol/mol AgX and that any sufficient effect cannot 
be attained when 10.sup.-8 mol or less iridium is added, and further it is 
additionally reported in the publications that the addition of 10.sup.-5 
mol or more iridium results in a noticeable reduction of the sensitivity 
with no improvement of the characteristics of the emulsions and, 
therefore, is no more practicable. However, this conclusion almost is 
based upon the results of examples where at most 10.sup.-4 mol or less 
iridium is used. 
In such background, examples for the preparation of silver halide fine 
grains containing iridium of high concentration, as found in the present 
invention, are almost merely those for the measurement of the physical 
properties of the grains (for example, refer to Journal of Japan 
Photographic Society, Vol. 31, No. 3, page 139 (1968)), and there are few 
examples for the evaluation of photographic characteristics of the 
photographic materials. In fact, there is only one example, where 
3.times.10.sup.-4 mol/mol AgX of iridium is added to silver halide grains 
which are not chemically sensitized. (Refer to Photographic Science and 
Engineering, Vol. 19, No. 4, page 214 (1975)). 
On the other hand, some examples are noted where a large amount of iridium 
is added to direct positive type silver halide emulsions, as so defined in 
the present invention. (For instance, refer to Japanese Patent Publication 
Nos. 37530/75 and 186739/83.) However, the direct positive type silver 
halide emulsions are those for the formation of positive images by the use 
of such mechanisms as bleaching the fogged nuclei in the previously fogged 
surface, and, therefore, are fundamentally different from the other 
negative type emulsions for the formation of latent images on the surfaces 
of grains when exposed to light. 
SUMMARY OF THE INVENTION 
The essential object of the present invention is to provide negative type 
silver halide emulsions of high sensitivity, which are highly sensitive 
under broad exposure conditions. 
The present inventors have earnestly investigated various problems in order 
to attain the object and have found that the object is attained by growing 
silver halide grains in the presence of a water-soluble iridium salt in an 
amount of 3.times.10.sup.-4 mol or more per 1 mol of the silver halides in 
the formation of the silver halide grains followed by chemical 
sensitization of the resulting silver halide emulsion with a sulfur 
compound or with a sulfur compound and a gold compound. 
DETAILED DESCRIPTION OF THE INVENTION 
The water-soluble iridium salts which are used in the present invention are 
not specifically limitative, and, for example, include the following 
compounds: 
K.sub.3 IrCl.sub.6, K.sub.2 IrCl.sub.6, (NH.sub.4).sub.2 IrCl.sub.6, 
NA.sub.2 IrCl.sub.6, IrCl.sub.4, IrBr.sub.4, IrBr.sub.3.4H.sub.2 O 
Among these compounds, K.sub.3 IrCl.sub.6, K.sub.2 IrCl.sub.6, 
(NH.sub.4).sub.2 IrCl.sub.6 and Na.sub.2 IrCl.sub.6 are preferably used in 
the present invention. 
In the present invention, any combinations of trivalent compounds and 
tetravalent compounds among these compounds may be used. 
These iridium compounds are used dissolved in water or in a pertinent 
solvent, and some conventional means for the stabilization of the iridium 
compound-containing solutions may be adapted thereto, including the 
addition of a hydrogen halide aqueous solution (such as HCl, HBr or HF 
aqueous solution) or an alkali halide (such as KCl, NaCl, KBr or NaBr) to 
the iridium compound-containing solution. 
The amount of the water-soluble iridium compound to be used in the 
preparation of silver halide emulsions in the present invention is 
3.times.10.sup.-4 mol or more per 1 mol of the finally formed total silver 
halides, and is preferably 5.times.10.sup.-4 to 3.times.10.sup.-3 mol. The 
use of the water-soluble iridium salt within the range of 
1.times.10.sup.-5 to 3.times.10.sup.-4 mol per 1 mol of the silver halides 
is not desirable, as it causes extreme reduction of sensitivity or 
solarization, even though the conditions in the chemical sensitization are 
properly regulated. On the other hand, if the amount of the iridium salt 
to be used is larger than 5.times.10.sup.-3 mol, the salt will cause 
cross-linking of the gelatin already existing in the emulsion when the 
salt is added, and, therefore, the formed emulsions are no longer usable 
as photographic emulsions. In such a case, some care should be taken with 
respect to the concentration of the gelatin to be used. 
Regarding the means for the addition of the iridium salts, the total amount 
of the necessary salts may be added all at once at any desired stage 
during the formation of silver halide grains. Further, the salts may be 
added at intervals in several separate amounts or the salts may be 
gradually added continuously. 
In the addition of the iridium salts, it is more preferred that 80% or more 
of the total amount to be added is added after the silver halide grains 
have grown to 70% or more of the average grain size thereof. For the 
continuous addition of the salts, for example, the iridium salt may be 
added to a silver halide aqueous solution when the halide grains are grown 
by means of a double jet method. 
The silver halide grains which may be used in the present invention may be 
either polydispersed or monodispersed ones, and are preferably 
monodispersed grains. 
The "monodispersed grains" means that 95% or more of the total grains fall 
within the range of an average grain size .+-.40%. 
Regarding the structure of the grains, these may be any one of cubic, 
octahedral, tetradecahedral, tabular or potato-like shaped ones, and are 
preferably cubic grains. The halogen compositions of the grains may be any 
one of AgI, AgBr, AgCl or mixed crystals thereof such as AgBrI or AgBrCl, 
and are preferably AgBr or AgBrI. The grain size is 3.0 .mu.m or less, 
preferably 1.0 .mu.m or less, more preferably 0.5 .mu.m or less, as based 
upon the diameter of the corresponding spheres. 
The formation of the silver halide grains in the present invention is not 
specifically limitative, and the grains may be formed, in general, by 
mixing a solution of a water-soluble silver salt (such as silver nitrate) 
and a solution of a water-soluble halide (such as potassium bromide) in 
the presence of a water-soluble high molecular compound solution such as a 
gelatin solution. 
For instance, these grains may be formed by means of known methods as 
described in The Theory of the Photographic Process, 4th Ed. (written by 
Mees and published by Macmillan, 1976); Chimie Photographique (written by 
P. Glafkides and published by Paul Montel, 1957); Photographic Emulsion 
Chemistry (written by C. F. Duffin and published by The Focal Press, 
1966); and Making and Coating Photographic Emulsion (written by V. L. 
Zelikman, et al., and published by The Focal Press, 1960). As described in 
the literature, the present silver halide grains may be formed by any of 
an acidic method, a neutral method or an ammonia method; and for the 
reaction of the soluble silver salt and the soluble halide, any of single 
jet method, double jet method or combination thereof may be used. 
A method for the formation of the grains in the presence of an excess 
silver ion (or a so-called reverse mixing method) may also be used. In 
addition, a so-called controlled double jet method, which is one 
embodiment of the double jet method, may also be used, where the pAg value 
in the liquid phase in which silver halide grains are formed is kept 
constant. 
By the aforesaid method may be obtained silver halide emulsions containing 
grains of regular crystalline form and uniform grain size. 
Regarding the addition rate of the water-soluble silver salt and the 
water-soluble halide, the addition rate may be accelerated with the lapse 
of time, as described in U.S. Pat. No. 3,650,757, or the concentration of 
the salts to be added may be elevated with the lapse of time, as described 
in U.S. Pat. No. 4,242,445, and the latter may be preferably used in the 
present invention. 
In addition, seed crystals may previously be present in the reaction 
container, and the water-soluble silver salt and the water-soluble halide 
may be added thereto later, as described in British Pat. No. 1,469,480. 
Silver halide solvents are preferably used in the formation of the silver 
halide grains. 
Ammonia and thioether compounds are preferably used as the silver halide 
solvent, as described in U.S. Pat. Nos. 3,574,628 and 3,790,387. 
The soluble salts are generally removed from the emulsion formed after the 
formation of precipitates or after the physical ripening thereof; and for 
this removal, a conventional and well known noodle washing method 
comprising gelling the gelatin may be used, or otherwise, a flocculation 
method may be used where a polyvalent anion-containing inorganic salt such 
as sodium sulfate, anionic surfactant, anionic polymer (e.g., 
polystyrenesulfonic acid) or a gelatin derivative such as aliphatic 
acylated gelatin, aromatic acylated gelatin or aromatic carbamoylated 
gelatin is used. 
For the chemical sensitization of the silver halide grains in the present 
invention, a sulfur sensitization or a sulfur sensitization and a gold 
sensitization may be carried out, and the combination of the sulfur and 
gold sensitization is preferred. 
In the addition of gold and sulfur compounds for the sensitization, the 
preferred amounts to be added are 10.sup.-7 to 10.sup.-4 mol and 10.sup.-7 
to 10.sup.-3 mol, respectively, per 1 mol of the existing silver halide. 
The temperature in the chemical sensitization is preferably a lower 
temperature than that in the formation of the silver halide grains. 
In the present invention, some other sensitization such as selenium 
sensitization or reduction sensitization may be carried out along with the 
sulfur sensitization and gold sensitization. 
Active gelatins and sulfur-containing compounds capable of reacting with 
silver may be used as the sulfur sensitizer, including, for example, 
thiosulfates, thioureas, mercapto compounds and rhodanines. 
Chloroaurates may be used as the gold sensitizer. 
Stannous salts, amines and hydrazine derivatives may be used as the 
reduction sensitizer. 
Regarding the chemical sensitization, the disclosure of Research 
Disclosure, Vol. 176, page 23 (December 1978) may be referred to. 
The photographic emulsions to be used in the present invention may contain 
various compounds for the purpose of prevention of fog in the preparation 
or preservation of the light-sensitive materials or in the photographic 
treatment thereof or for the purpose of stabilization of the photographic 
characteristics of the materials. For instance, various kinds of compounds 
which are known as an antifogging agent or a stabilizer may be added to 
the present photographic emulsions for these purposes, including azoles 
(such as benzothiazolium salts, nitroimidazoles, nitrobenzimidazoles, 
chlorobenzimidazoles, bromobenzimidazoles, nitroindazoles, benzotriazoles, 
aminotriazoles); mercapto compounds (such as mercaptothiazoles, 
mercaptobenzothiazoles, mercaptobenzimidazoles, mercaptothiadiazoles, 
mercaptotetrazoles especially 1-phenyl-5-mercaptotetrazole, 
mercaptopyrimidines, mercaptotriazines); thioketo compounds such as 
oxazolinethione; azaindenes (such as triazaindenes, tetraazaindenes 
especially 4-hydroxy-substituted(1,3,3a,7)tetraazaindenes, 
pentaazaindenes); and benzenethiosulfonic acids, benzenesulfinic acids and 
benzenesulfonic acid amides. 
Further detailed examples of these compounds and the use thereof are 
described in, for example, U.S. Pat. Nos. 3,954,474 and 3,982,947 and 
Japanese Patent Publication No. 28660/77, and the related disclosures may 
be referred to. 
Gelatin is advantageously used as a binder or a protective colloid in the 
emulsions of the present invention, and in addition, any other hydrophilic 
colloids may also be used therefor. 
For instance, proteins such as gelatin derivatives, graft polymers of 
gelatin and other high molecular substances, albumin and casein; cellulose 
derivatives such as hydroxyethyl cellulose, carboxymethyl cellulose and 
cellulose sulfates, and saccharide derivatives such as sodium alginate and 
starch derivatives; and other various kinds of synthetic hydrophilic high 
molecular substances of mono- or copolymers such as polyvinyl alcohol, 
partially acetalized polyvinyl alcohol, poly-N-vinylpyrrolidone, 
polyacrylic acid, polymethacrylic acid, polyacrylamide, polyvinyl 
imidazole and polyvinyl pyrazole may be used. 
Regarding the gelatin, lime-treated gelatin and acid-treated gelatin as 
well as enzyme-treated gelatin (as described in Bull. Soc. Sci. Phot. 
Japan, No. 16, page 30 (1966)) may be used, and in addition, a hydrolyzed 
product or enzyme-decomposed product of gelatin may also be used. 
The photographic emulsions of the present invention may contain an 
inorganic or organic hardener. For instance, chromium salts (such as 
chromium alum, chromium acetate), aldehydes (such as formaldehyde, 
glyoxal, glutaraldehyde), N-methylol compounds (such as dimethylolurea, 
methyloldimethylhydantoin), dioxane derivatives (such as 
2,3-dihydroxydioxane), active vinyl compounds (such as 
1,3,5-triacryloyl-hexahydro-s-triazine, 1,3-vinylsulfonyl-2-propanol), 
active halogen compounds (such as 2,4-dichloro-6-hydroxy-s-triazine), 
mucohalogenic acids (such as mucochloric acid, mucophenoxychloric acid), 
etc., may be used singly or in the form of a mixture thereof. 
In particular, active vinyl compounds and active halogen compounds are 
preferably used. 
The photographic emulsions to be used in the present invention may be 
spectrally sensitized with methine dyes or other sensitizing dyes. Usable 
dyes are cyanine dyes, merocyanine dyes, complex cyanine dyes, complex 
merocyanine dyes, holopolar cyanine dyes, hemicyanine dyes, styryl dyes 
and hemioxonol dyes. Especially preferred dyes are cyanine dyes, 
merocyanine dyes and complex merocyanine dyes. Any nucleus which is 
generally used in cyanine dyes as a basic heterocyclic nucleus may be 
adapted to these dyes. For instance, various nuclei may be adapted 
thereto, including a pyrroline nucleus, an oxazoline nucleus, a thiazole 
nucleus, a selenazole nucleus, an imidazole nucleus, a tetrazole nucleus, 
a pyridine nucleus; alicyclic hydrocarbon ring-fused nuclei of these 
nuclei; and aromatic hydrocarbon ring-fused nuclei of these nuclei, such 
as an indolenine nucleus, a benzindolenine nucleus, an indole nucleus, a 
benzoxazole nucleus, a naphthoxazole nucleus, a benzothiazole nucleus, a 
naphthothiazole nucleus, a benzoselenazole nucleus, a benzimidazole 
nucleus and a quinoline nucleus. These nuclei may be substituted on the 
carbon atoms. 
To merocyanine dyes and complex merocyanine dyes may be adapted various 
ketomethylene structure-containing nuclei, including a pyrazolin-5-one 
nucleus, a thiohydantoin nucleus, a 2-thioxazolidine-2,4-dione nucleus, a 
thiazolidine-2,4-dione nucleus, a rhodanine nucleus, a thiobarbituric acid 
nucleus or the like 5- or 6-membered heterocyclic nucleus. 
These sensitizing dyes may be used singly or in the form of a combination 
of two or more of them, and the combination of the sensitizing dyes is 
often utilized for the purpose of supersensitization. 
The photographic emulsion layers in the photographic materials of the 
present invention may contain, for the purpose of intensification of 
sensitivity, intensification of contrast and acceleration of development, 
various substances such as polyalkylene oxide or ether, ester or amine 
derivatives thereof, thioether compounds, thiomorpholines, quaternary 
ammonium salt compounds, urethane derivatives, urea derivatives, imidazole 
derivatives and 3-pyrazolidones. 
The photographic materials of the present invention may further contain in 
the photographic emulsion layers or in any other hydrophilic colloid 
layers, a water-insoluble or sparingly water-soluble synthetic polymer 
dispersion, for the purpose of improvement of the dimension stability of 
the materials. For instance, various kinds of homopolymers or copolymers 
may be used, which are made of monomers selected from alkyl 
(meth)acrylates, alkoxyalkyl (meth)acrylates, glycidyl (meth)acrylates, 
(meth)acrylamides, vinyl esters (such as vinyl acetate), acrylonitriles, 
olefins and/or styrenes, or made of a combination of these monomers and 
other monomers selected from acrylic acids, methacrylic acids, 
.alpha.,.beta.-unsaturated dicarboxylic acids, hydroxyalkyl 
(meth)acrylates, sulfoalkyl (meth)acrylates and styrenesulfonic acids. 
The photographic materials of the present invention may contain a color 
image-forming coupler or a compound capable of coloring by 
oxidation-coupling with an aromatic primary amine developing agent (such 
as phenylenediamine derivatives or aminophenol derivatives) in the color 
development treatment. Nondiffusible couplers having a hydrophobic group 
(a so-called ballast group) in the molecule or polymerized couplers are 
preferred. The couplers may either be tetravalent or divalent to the 
silver ion. In addition, the materials may further contain colored 
couplers having color correction effect or such couplers that may release 
a development inhibitor with the advance of the development (that is, 
so-called DIR couplers). Further, noncoloring DIR coupling compounds may 
be used which form a colorless product by a coupling reaction and release 
a development inhibitor. 
Examples of magenta couplers which may be used in the present invention are 
5-pyrazolone couplers, pyrazolobenzimidazole couplers, 
cyanoacetylcoumarone couplers and open chain acylacetonitrile couplers; 
examples of yellow couplers are acylacetamide couplers (such as 
benzoylacetanilides, pivaloylacetanilides); and examples of cyan couplers 
are naphthol couplers and phenol couplers. 
Other constitutional elements of the silver halide photographic emulsions 
of the present invention and other constitutional elements of the 
photographic materials which may be obtained by the use of the present 
photographic emulsions, than those as described in the above, are not 
specifically limitative, and the disclosure as given in, for example, 
Research Disclosure, Vol. 176, pp. 22-30 (December, 1978) may be referred 
to. 
According to the present invention, a large amount of iridium, which has 
heretofore been considered unusable, is used in the formation of silver 
halide grains and the resulting emulsion is subjected to sulfur 
sensitization or sulfur/gold sensitization, whereby a negative type 
emulsion of high sensitivity and noticeably reduce reciprocity law failure 
may surprisingly be obtained, and the effect of the present invention is 
quite unexpected.

The present invention will be explained in greater detail by reference to 
the following examples, which, however, are not intended to be interpreted 
as limiting the scope of the present invention. 
Unless otherwise specified, all ratios, percents, etc., are by weight. 
EXAMPLE 1 
The following solutions (A), (B), (C) and (D) were prepared. Using these 
solutions, one emulsion of the present invention and five other 
comparative emulsions were formed in accordance with the following 
procedure, each having an iodine content of 2 mol % and comprising 
monodispersed cubic grains having an average grain size of 0.36 .mu.m. 
______________________________________ 
Solution (A): 
Gelatin 22 g 
KBr 0.84 g 
H.sub.2 O 950 ml 
3,6-Dithia-1,8-octanediol 
0.15 g 
Solution (B): 
AgNO.sub.3 150 g 
H.sub.2 O 450 ml 
Solution (C): 
KBr 123.5 g 
KI 3.52 g 
H.sub.2 O 681 ml 
Solution (D): 
(I) Solution comprising K.sub.3 IrCl.sub.6 (1.0 wt %) and 
KCl (0.5 wt %) 
(II) Solution comprising K.sub.3 IrCl.sub.6 (0.01 wt %) and 
KCl (0.5 wt %) 
(III) Solution comprising K.sub.3 IrCl.sub.6 (0.001 wt %) and 
KCl (0.5 wt %) 
(IV) Solution comprising KCl (0.5 wt %) 
______________________________________ 
Solutions (D.sub.1) through (D.sub.6) comprised the components (I) to (IV) 
as given in the following Table 1. 
TABLE 1 
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(D.sub.1) (D.sub.2) 
(D.sub.3) 
(D.sub.4) 
(D.sub.5) 
(D.sub.6) 
(ml) (ml) (ml) (ml) (ml) (ml) 
______________________________________ 
(I) 5.5 55.0 
(II) 5.5 55 
(III) 5.5 
(IV) 55.0 49.5 49.5 49.5 
______________________________________ 
The solutions (B) and (C) were added to the solution (A), while stirred at 
75.degree. C., in the course of 60 minutes by means of a controlled double 
jet method, to form grains. 
After 30 minutes in the formation of the grains, the solution (D.sub.1) was 
added to obtain an emulsion (E.sub.m-1), the solution (D.sub.2) was added 
to obtain an emulsion (E.sub.m-2), and analogously, other emulsions 
(E.sub.m-3), (E.sub.m-4), (E.sub.m-5) and (E.sub.m-6) were prepared. 
During the step of the formation of the grains, the pAg value in the 
reaction system was kept at about 7.1. Thus, six kinds of emulsions were 
obtained, to which Ir was added in the formation of the grains, in an 
amount of 0, about 10.sup.-7, about 10.sup.-6, about 10.sup.-5, about 
10.sup.-4 and about 10.sup.-3 mol, per 1 mol of silver halide, 
respectively. 
These emulsions (E.sub.m-1) through (E.sub.m-6) were subjected to optimum 
chemical sensitization, while a pertinent amount of Na.sub.2 S.sub.2 
O.sub.3.5H.sub.2 O was added at the beginning of the second ripening. The 
ripening temperature was 65.degree. C. and the period of the ripening was 
90 minutes. 
To each of these emulsions were added a gelatin hardener of 
2,4-dichloro-6-hydroxy-s-triazine sodium salt and a coating aid of sodium 
dodecylbenzenesulfonate, each in a pertinent amount. 
On the other hand, a coating solution for a protective layer was prepared, 
which was a 10% gelatin aqueous solution containing the same coating aid 
as above. 
The above-prepared emulsion coating solution and protective layer coating 
solution were coated on a triacetate film and dried, the coated silver 
amount being 2.6 g/m.sup.2 and the protective layer gelatin being 1.0 
g/m.sup.2. 
These samples thus obtained were subjected to sensitometry as follows: 
Each sample was exposed to light with a light source of a color temperature 
of 4,800.degree. K., through an optical wedge, for 10 seconds and 
10.sup.-3 second. The exposed sample was developed with a surface 
developer as given below for 10 minutes at 20.degree. C., and then 
subjected to stopping, fixation, water washing and drying. 
______________________________________ 
Developer: 
______________________________________ 
Metol 5.5 g 
L-Ascorbic Acid 22 g 
Nabox (made by Fuji Photo Film Co., 
77 g 
Ltd.) 
KBr 2.2 g 
H.sub.2 O up to 2.2 liters 
______________________________________ 
The sensitivity of each of these emulsions (E.sub.m-1) through (E.sub.m-6) 
in the optimum sulfur sensitization point is given in the following Table 
2. For the presentation of the sensitivity of the emulsions, the 
sensitivity of the emulsion (E.sub.m-1) with optimum sulfur sensitization, 
as exposed for 10.sup.-3 second, was represented by "100", and the 
sensitivity of the other emulsions was represented by the corresponding 
relative sensitivity thereto. 
The relative sensitivity is based upon the reciprocal of the exposure 
amount required for providing a density of fog density +0.20. 
TABLE 2 
__________________________________________________________________________ 
Sensitivity 
Sensitivity 
Solarization 
Sample No. 
Ir (mol)/AgX (mol) 
(10 sec) 
(10.sup.-3 sec) 
(10 sec) 
(10.sup.-3 sec) 
__________________________________________________________________________ 
Comparative Samples 
(E.sub.m-1) 
1 0 87 100 
(E.sub.m-2) 
2 10.sup.-7 57 60 
(E.sub.m-3) 
3 10.sup.-6 97 60 
(E.sub.m-4) 
4 10.sup.-5 100 89 Noted 
(E.sub.m-5) 
5 10.sup.-4 27 40 Noted 
Noted 
Present Sample 
(E.sub.m-6) 
6 10.sup.-3 550 537 
__________________________________________________________________________ 
Table 2 proves the following facts: When the amount of the iridium added 
was 10.sup.-4 mol, extreme desensitization occurred, and when the amount 
thereof was within the range of 10.sup.-4 to 10.sup.-5 mol, solarization 
occurred and the density noticeably decreased. Whereas, when the amount of 
the iridium added was 10.sup.-3 mol, the sensitivity rapidly increased and 
no solarization was admitted, and in addition, the sensitivity was high 
under the two exposure conditions of 10.sup.1 sec and 10.sup.-3 sec. These 
facts are surprising and unexpected. 
From the above results, it is apparent that the present invention is 
extremely effective. 
These effects of the present invention are quite unexpected and are 
extremely surprising. 
EXAMPLE 2 
In the same manner as in Example 1, the emulsions (E.sub.m-1) and 
(E.sub.m-6) were prepared and these were subjected to gold/sulfur 
sensitization. The surface sensitivity of each sample is shown in the 
following Table 3. The exposure time was 10.sup.-4 second and 1 second. 
The sensitivity of the emulsion (E.sub.m-1) with sulfur sensitization, as 
exposed for 10.sup.-3 second was considered 100, and the sensitivity of 
other cases was represented by the corresponding relative sensitivity 
thereto. 
The amount of the gold sensitizer (KAuCl.sub.4 4H.sub.2 O) and that of the 
sulfur sensitizer (Na.sub.2 S.sub.2 O.sub.3. 5H.sub.2 O) as used herein 
were made to be optimum under the exposure condition of 1 second in each 
sample. 
TABLE 3 
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Sample No. 
7 8 9 10 (present sample) 
______________________________________ 
Emulsion 
(E.sub.m-1) 
(E.sub.m-1) 
(E.sub.m-6) 
(E.sub.m-6) 
Chemical 
Not used Used Not used 
Used 
Sensitizer 
Sensitivity 
35.0 708 No image 
1,260 
(1 sec) formed 
Sensitivity 
97 396 No image 
1,390 
(10.sup.-4 sec) formed 
______________________________________ 
As is apparent from the above Table 3, Sample No. 10 (of the present 
invention) which contained iridium in an amount of 10.sup.-3 mol/mol AgX 
and which was subjected to sulfur/gold sensitization was extremely highly 
sensitive when exposed for 1 second and 10.sub.-4 second, and no 
reciprocity law failure was admitted. 
This result is extremely unexpected and surprising. 
EXAMPLE 3 
In the same manner as in Example 1, with the exception that a solution (C') 
comprising KBr (126 g) and H.sub.2 O (681 ml) and additionally containing 
about 65 ml of the solution (I) was used instead of the solution (C), an 
emulsion (E.sub.m-7) was formed. In the preparation of this emulsion 
(E.sub.m-7), the solution in Example (D) was not added, and the others 
were the same as those in Example 1. Thus, the amount of the iridium added 
during the formation of the grains was 10.sup.-3 mol/mol AgX, and the 
iridium was almost uniformly and continously added to the reaction system 
during the formation of the grains. 
The emulsion (E.sub.m-7), thus formed as well as the other previously 
formed emulsions (E.sub.m-1) and (E.sub.-6) were subjected to optimum 
sulfur sensitization and then exposed for 1 second to form Sample Nos. 11, 
12 and 13, respectively. The sensitivity of each sample was given in the 
following Table 4, where the sensitivity of Sample No. 12 was represented 
by 100 and that of the other samples was represented by the corresponding 
relative sensitivity thereto. 
TABLE 4 
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Sample No. 
Comparative Sample 
Present Sample 
12 13 14 
______________________________________ 
Emulsion (E.sub.m-1) (E.sub.m-6) 
(E.sub.m-7) 
Sensitivity 100 501 200 
______________________________________ 
The above Table 4 proves the fact that the emulsion (E.sub.m-6) which was 
formed by adding the total amount of the iridium after the grains had 
grown to about 80% or more of the average grain size thereof is more 
effective than the other emulsion (E.sub.m-7). 
While the invention has been described in detail and with reference to 
specific embodiments thereof, it will be apparent to one skilled in the 
art that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.