Heat developable silver image forming materials

A heat developable silver image forming material comprising: PA1 (a) an organic silver salt oxidizing agent; PA1 (b) a compound or a composition capable of forming a photosensitive silver compound by reaction with the organic silver salt oxidizing agent (a); PA1 (c) a reducing agent for silver ion; and PA1 (d) a compound having a unit of ##STR1##

BACKGROUND OF THE INVENTION 1. Field of the Invention 
This invention relates to a heat developable silver image forming material. 
More particularly, it relates to a heat developable silver image forming 
material having good sensitivity and storage stability capable of forming 
a silver image thereon by reduction of the silver ion of an organic silver 
salt oxidizing agent with a reducing agent for silver ion by heat 
development. 
2. Description of the Prior Art 
Conventional wet processing photosensitive materials containing a silver 
halide require complicated and time consuming processes using various 
treating chemicals in obtaining stable images and further, the chemicals 
used give rise to a pollution problem. Accordingly, in order to avoid 
these disadvantages there have been made many attempts to develop 
photosensitive materials having high sensitivity capable of forming stable 
images thereon only by dry processing without using treating chemicals. 
For example, U.S. Pat. No. 3,152,902 describes a heat developable silver 
image forming material comprising an organic silver salt having rather 
good light stability, a reducing agent for silver ion and a photosensitive 
silver halide. U.S. Pat. No. 3,457,075 describes a heat developable silver 
image photosensitive material whose sensitivity is increased by the 
photosensitive silver halide formed by halogenation of a small portion of 
the organic silver salt. However, the sensitivity of these photosensitive 
materials is still insufficient for practical purposes and the storage 
stability thereof are markedly low. Further, U.S. Pat. Nos. 3,802,888 and 
3,764,329 describe heat developable silver image forming materials which 
are non-photosensitive under normal light conditions and can be rendered 
photosensitive by the preliminary heating prior to the imagewise exposure 
to light. The heat developable silver image forming materials of this type 
are hereinafter referred to as "post activatable type heat developable 
silver image forming materials". These post activatable type heat 
developable silver image forming materials can be advantageously prepared 
and handled in normal light conditions, but according to U.S. Pat. No. 
3,802,888, their minimum optical density (fog density) increase when they 
are stored under normal light conditions, and hence their storage 
stability (shelf life) is still insufficient for practical purposes. The 
post activable type heat developable silver image forming materials 
described in U.S. Pat. No. 3,764,329 have higher storage stability but 
instead lower sensitivity than those of U.S. Pat. No. 3,802,888. In 
general, use of a sensitizer reduces the storage stability, increases the 
minimum optical density and decreases or, in some cases, increases the 
sensitivity. The change of the sensitivity due to their storage under 
normal light conditions is also undesirable for post activable type heat 
developable silver image forming materials. 
Furthermore, the heat developable silver image forming materials produce 
images by reduction of the silver ion of an organic silver salt upon the 
imagewise exposure to light, followed by heat development and differs from 
conventional silver halide photosensitive materials in their image forming 
mechanism as well as in their compositions. Thus, it is well known in this 
field that the techniques for increasing the sensitivity or the storage 
stability of conventional silver halide photosensitive materials cannot be 
applied directly for heat developable silver image forming materials. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide a heat developable silver image 
forming material having good sensitivity. 
Another object of this invention is to provide a heat developable silver 
image forming materials having good storage stability under normal light 
conditions. 
Accordingly, the present invention provides a heat developable silver image 
forming material comprising: 
(a) an organic silver salt oxidizing agent; 
(b) a compound or a composition capable of forming photosensitive silver 
compound by reaction with the organic silver salt oxidizing agent (a); 
(c) a reducing agent for silver ion; and 
(d) a compound having a unit of 
##STR2## 
Thus, by using the above-described component (d) the sensitivity of the 
heat developable silver image forming materials of this invention can be 
increased. Further, with regard to the post activable type heat 
developable silver image forming materials of this invention, their 
sensitivity and storage stability under normal light conditions can be 
increased at the same time. 
DETAILED DESCRIPTION OF THE INVENTION 
The organic silver salt oxidizing agents which can be employed as component 
(a) in this invention include silver salts of long chain aliphatic 
carboxylic acids having 12 to 24 carbon atoms such as silver laurate, 
silver myristate, silver palmitate, silver stearate, silver arachidate and 
silver beherate; silver salts of organic compounds having an imino group 
such as benztriazole silver salt, benzimidazole silver salt, carbazole 
silversalt and phthalazinone silver salt; silver salts of sulfur 
containing compounds such as S-alkylthioglycollates; silver salts of 
aromatic carboxylic acids such as silver benzoate and silver phthalate; 
silver salts of sulfonic acids such as silver ethanesulfonate; silver salt 
of sulfinic acids such as silver o-toluenesulfinate; silver salts of 
phosphoric acids such as silver phenylphosphate; silver barbiturate; 
silver saccharate; silver salts of salicylaldoxime; and any mixtures 
thereof. Of these compounds, silver salts of long chain aliphatic 
carboxylic acids having 12 to 24 carbon atoms are preferred. 
The amount of the organic silver salt oxidizing agent which can be employed 
in this invention typically ranges from about 0.1 g/m.sup.2 to about 50 
g/m.sup.2 of the support area of the dry image forming material. A 
preferred amount of the organic silver salt oxidizing agent ranges from 
about 1 g/m.sup.2 to about 10 g/m.sup.2 of the support area of the dry 
image forming material. 
The compounds or the compositions capable of forming a photosensitive 
silver compound by reaction with the organic silver salt oxidizing agent 
(a) which can be employed as component (b) in this invention includes (I) 
silver halides, (II) inorganic halides, (III) metal complexes containing a 
halogen atom, (IV) onium halides, (V) halogenated hydrocarbons, (VI) 
organic haloamides having a unit of -CONX- or -SO.sub.2 NX-, wherein X 
represents a chlorine atom, a bromine atom or an iodine atom, (VII) 
iodine, (VIII) compounds or compositions comprising a halogen atom as a 
halogen component and an organic component containing an element of the IV 
group, the V group or the VI group of the Periodic Table except the sulfur 
whose atomic number is 14 or more, and any mixtures thereof. 
The silver halides (I) used in this invention include silver chloride, 
silver bromide and silver iodide. 
The inorganic halides (II) includes the compounds of the formula MX.sub.n, 
wherein M is H, NH.sub.4 or a metal atom; X is Cl, Br or I; in case of M 
being H or NH.sub.4 n is 1 and in case of M being the metal atom n is its 
valence; and the metal atom is lithium, sodium, potassium, rubidium, 
cesium, copper, gold, beryllium, magnesium, calcium, strontium, barium, 
zinc, cadmium, mercury, aluminum, gallium, indium, lathanum, ruthenium, 
thallium, germanium, tin, lead, antimony, bismuth, chromium, molybdenum, 
tungsten, manganese, rhenium, iron, cobalt, nickel, rhodium, palladium, 
osmium, iridium, platinum or cerium. 
Specific examples of the metal complexes containing a halogen atom (III) 
include K.sub.2 PtCl.sub.6, K.sub.2 PtBr.sub.6, HAuCl.sub.4, 
(NH.sub.4).sub.2 IrCl.sub.6, (NH.sub.4).sub.3 IrCl.sub.6, (NH.sub.4).sub.2 
RuCl.sub.6, (NH.sub.4).sub.3 RhCl.sub.6 and (NH.sub.4).sub.3 RhBr.sub.6. 
Specific examples of the onium halides (IV) include quaternary ammonium 
halides such as trimethylphenylammonium bromide, 
cetylethyldimethylammonium bromide and trimethylbenzylammonium bromide; 
quaternary phosphonium halides such as tetraethylphosphonium bromide; and 
tertiary sulfonium halides such as trimethylsulfonium iodide. 
Specific examples of the halogenated hydrocarbons (V) include iodoform, 
bromoform, tetraiodocarbon and 2-bromo-2-methylpropane. 
Specific examples of the organic haloamides (VI) include 
N-chlorosuccinimide, N-bromosuccinimide, N-iodosuccinimide, 
N-chlorophthalimide, N-bromophthalimide, N-iodophthalimide, 
N-chlorophthalazinone, N-bromophthalazinone, N-iodophthalazinone, 
N-chloracetamide, N-bromoacetamide, N-iodoacetamide, N-chloroacetanilide, 
N-bromoacetanilide, N-iodoacetanilide, 
1-chloro-3,5,5-trimethyl-2,4-imidazolidinedione, 
1-bromo-3,5,5-trimethyl-2,4-imidazolidinedione, 
1-iodo-3,5,5-trimethyl-2,4-imidazolidinedione, 
1,3-di-chloro-5,5-dimethyl-2,4-imidazolidinedione, 
1,3-dibromo-5,5-dimethyl-2,4-imidazolidinedione, 
1,3-diiodo-5,5-dimethyl-imidazolidinedione, 
N,N-dichlorobenzenesulfonamide, N,N-dibromobenzenesulfonamide, 
N-bromo-N-methyl-benzenesulfonamide, N-chloro-N-methylbenzenesulfonamide, 
N,N-diiodobenzenesulfonamide, N-iodo-N-methyl-benzenesulfonamide, 
1,3-dichloro-4,4-dimethylhydantoin, 1,3-dibromo-4,4-dimethylhydantoin and 
1,3-diiodo-4,4-dimethylhydantoin. 
Specific examples of the compounds or compositions (VIII) include 
##STR3## 
wherein X represents a chlorine atom, a bromine atom or an iodine atom; 
and mixtures of the compounds (II) to (III) with the compounds shown 
below; 
##STR4## 
Of these compounds and compositions (II) to (VIII), the compounds and 
compositions (VI), (VII) and (VIII) are preferably employed as the 
component (b) for the post activatable type heat developable silver image 
forming materials according to this invention. 
The amount of the compounds or the compositions capable of forming a 
photosensitive silver compound by reacton with the organic silver salt 
oxidizing agent which can be employed in this invention typically ranges 
from about 0.1 mole to about 0.5 mole, and preferably 0.05 mole to 0.3 
mole, based on the mole of the organic silver salt oxidizing agent. 
The reducing agents for silver ion which can be used as component (c) in 
this invention sterically hindered phenols in which a sterically bulky 
grop is bonded to the carbon atom adjacent to the carbon atom bonded to 
the hydroxyl group; substituted phenols; hydroquinones; hydroquinone 
ethers; and other reducing agents for conventional wet processing silver 
salt type photosensitive materials. 
Specific examples of reducing agent for silver ion include 
2,6-di-tert-butyl-4-methylphenol, 
2,2'-methylenebis(4-methyl-6-tertbutylphenol), 
2,6-methylenebis(2-hydroxy-3-tert-butyl-5-methylphenyl)4-methylphenol, 
2,2'-methylenebis(4-ethyl-6-tert-butylphenol), 
2,4,4-trimethylpentylbis(2-hydroxy-3,5-dimethylphenyl)methane, 
2,2'-methylenebis[4-methyl-6-(1-methylcyclohexyl)phenol, 
2,5-di-tert-butyl-4-methoxyphenol, p-phenylphenol, p-methoxyphenol, 
p-aminophenol, catechol, pyrogallol, resorcin, bisphenol A, 
2,4-dihydroxybenzoic acid, hydroquinone, methylhydroquinone, 
chlorohydroquinone, bormohydroquinone, phenylhydroquinone, 
tert-butylhydroquinone, tert-octylhydroquinone, 2,5-dimethylhydroquinone, 
2,6-dimethylhydroquinone, methoxyhydroquinone, hydroquinone monobenzyl 
ether, .alpha.-naphthol, .beta.-naphthol, 1,3-dihydroxynaphthalene, 
2,2'-dihydroxy-1,1'-binaphthyl; phenidone, methyl gallate, and any 
mixtures thereof. 
A preferred reducing agent for silver ion can be chosen depending upon the 
organic silver oxidizing agent employed. For example, with no organic 
silver salt oxidizing agent such as silver behenate which is relatively 
hard to be reduced, a relatively strong reducing agent for silver ion such 
as a sterically hindered phenol including 
2,2'-methylenebis(4-ethyl-6-tert-butylphenol) is suitably chosen. On the 
other hand, with an organic silver salt oxidizing agent such as silver 
laurate which is relatively easy to be reduced, a relatively weak reducing 
agent for silver ion such as a substituted phenol including p-phenylphenol 
is suitably chosen, and with an organic silver salt oxidizing agent such 
as silver salt of benztriazole which is very hard to be reduced, a strong 
reducing agent for silver ion such as ascorbic acid is suitably chosen. 
The amount of the reducing agent for silver ion may vary depending upon the 
organic silver salt oxidizing agent selected and the reducing agent for 
silver ion selected. In general, the amount of the reducing agent for 
silver ion used ranges from about 0.1 percent by weight to about 200 
percent by weight based on the weight of the organic silver salt oxidizing 
agent. A preferred amount of the reducing agent for silver ion ranges from 
about 1 percent by weight to about 100 percent by weight. 
The compounds having a unit of 
##STR5## 
which can be employed as component (d) in this invention include the 
compounds of the formula, 
##STR6## 
and their salts of hydrochloric acid, carbonic acid, acetic acid, sulfuric 
acid or phosphoric acid. 
In the above-described formula, 
##STR7## 
R.sup.1 and R.sup.2 independently represent an aryl group; an aryl group 
substituted with an acetyl group, an amino group, an alkyl group or an 
alkoxy group; an alkyl group; an alkyl group substituted with an amino 
group, a carboxyl group, a mercapto group or an acetyl group; a cycloalkyl 
group; a S-, Se-, O- or N-containing heterocyclic group; an amidinyl 
group; a sulfanil group; a cyano group; an amino group; a nitro group and 
a hydrogen atom, and R.sup.1 and R.sup.2 may be coupled with each other to 
form a ring. 
Preferably, R.sup.1 and R.sup.2 independently represents a phenyl group as 
the aryl group; an acetylphenyl, an aminophenyl group, a methylphenyl 
group, a methoxyphenyl and an ethoxyphenyl as the substituted aryl group; 
an alkyl group having 1 to 18 carbon atoms as the alkyl group; an alkyl 
group having 1 to 4 carbon atoms substituted with a carboxyl group, an 
amino group or a mercapto group as the substituted alkyl group, a 
cyclohexyl group as the cycloalkyl group; a 2-benzimidazolyl group, a 
2-benzthiazolyl group, a 2-benzoxazolyl group and 5-quinolyl group as the 
heterocyclic group; an amidinyl group; a sulfanil group; a cyano group; 
and a hydrogen atom, and R.sup.1 and R.sup.2 is coupled with each other to 
form a ring such as malonylguanidine and guanidine. 
Specific examples of the compounds having a unit of 
##STR8## 
include diphenylguanidine, o-, m- or p-acetylphenylguanidine, 
bis(p-methoxyphenyl)guanidine, bis(2-methylphenyl)guanidine, 
4-aminophenylguanidine, methylguanidine, octylguanidine, 
4-aminobutylguanidine, arginine, N-amidinoalanine, dicyclohexylguanidine, 
2-benzimidazolylguanidine, 2-imidazolylguanidine, 
2-benzothiazolylguanidine, benzoselenazoylguanidine, 
4-morphorinylguanidine, 5-quinolinylguanidine, 2-pyrimidinylguanidine, 
malonylguanidine, guanoxan, methylthioethylguanidine, guanylguanidine, 
dimethlyguanylguanidine, sulfaguanidine, nitrosulfanilguanidine, 
butylsulfanilguanidine, (N-acetylsulfanil)phenylguanidine, glycocyamine, 
cyanoguanidine, aminoguanidine, aminonitroguanidine, guanine, 
N-phenyl-N'-cyanoguanidine, N-(4-methylphenyl)-N'-cyanoguanidine, 
N-(4-methoxyphenyl)-N'-cyanoguanidine, N,N'-bis(4-ethoxyphenyl)guanidine, 
dodecylguanidine, N-dodecyl-N'-cyanoguanidine, N-octyl-N'-cyanoguanidine, 
octadodecylguanidine, 2-mercaptoethylguanidine, 
N-mercaptoethyl-N'-methylguanidine, cyclohexylguanidine, 
(5-methyl-1H-benzimidazole-2-yl)guanidine, 
N-(4,5-dihydro-1H-imidazole-2-yl)-N'-[(4-methoxyphenyl)ethyl]guanidine, 
2-benzoxazolylguanidine, guanacline, 2-tolylbiguanido, 
N-acteylsulfaguanidine, N,N'-dicyanoguanidine, their salts of hydrochloric 
acid, carbonic acid, acetic acid, sulfuric acid or phosphoric acid and any 
mixtures thereof. 
The amount of the compound having a unit of 
##STR9## 
which can be employed in this invention typically ranges from about 0.03 
mole to about 2 moles and preferable from about 0.1 mole to about 0.4 mole 
based on the mole of the organic silver salt oxidizing agent. 
In addition to the above-described components (a), (b), (c) and (d) of the 
heat developable silver image forming materials according to this 
invention, the image forming materials of this invention may contain 
conventional modifiers such as a toner for silver images, an anti-foggant 
for heat development, a background-darkening preventive agent, a spectral 
sensitizer and a chemical sensitizer. 
For example, phthalazinone, mercuric acetate, 1,2,3,4-tetrabromobutane, 
merocyanine, N-methyl-2-pyrrolidone are preferably employed as the toner 
for silver images, the anti-foggant for heat development, the spectral 
sensitizer and the chemical sensitizer, respectively, in the heat 
developable silver image forming materials of this invention. 
In many cases a binder is required fo shaping the heat developable silver 
image forming materials of this invention into a film. However, when the 
components (a), (b), (c) and (d) of this invention act as the binder, use 
of a binder can be omitted. 
Exemplary binders which can be used in this invention include polyvinyl 
butyrals, polyvinyl formals, polyacrylamides, polymethyl methacrylates, 
polyvinyl acetates, ethylcelluloses, cellulose acetates, cellulose acetate 
butyrates, cellulose acetate propionates, polystyrenes, polyvinyl 
pyrrolidones, polyisoprenes, butadien-styrene copolymers, vinyl 
acetate-vinylchloride copolymers, polyvinyl alcohols, gelatin and any 
mixtures thereof. The binder can be used generally in such an amount that 
the weight ratio of the binder to the organic silver salt oxidizing agent 
ranges from about 0.1 to about 10. 
For example, a heat developable dry image forming material of this 
invention may be prepared by dispersing or suspending the organic silver 
salt oxidizing agent prepared separately into a binder solution or binder 
emulsion by a sand grinder, a mixer or a ball mill, mixing the other 
components of this invention and if necessary or if desired, other 
additives with the resulting emulsion, coating the emulsion thus prepared 
on a support by conventional method to form a layer of the heat 
developable silver image forming material and drying the layer. Also, the 
components of the heat developable silver image forming material may be 
coated on a support in a plurality of layers in any combinations. 
Exemplary support which can be used in this invention include plastics 
films such as cellulose acetate films, polyester films, polyamide films, 
polyimide films, polyviny acetal films, polystyrene films and 
polycarbonate films; glass plates; papers such as photographic base paper, 
coated paper, art paper, barite paper, waterproof paper and ordinary 
paper; and metal plates such as aluminum plates. 
The thickness of the layer or layers of the heat developable silver image 
forming material dried typically ranges from about 1.mu. to about 
1000.mu.. 
For the imagewise exposure to light there can be employed various light 
sources such as tungsten lamps, fluorescent lamps, xenon lamps, mercury 
lamps, iodine lamps and CRT light sources. Exemplary methods of the 
imagewise exposure to light include photographing with a camera, 
projective exposure, contact exposure by placing a manuscript on the image 
forming material and enlarging exposure. The period of time of the 
imagewise exposure to light varies depending upon the light source 
selected and typically ranges from about one hundredth of second to about 
10 seconds. 
The temperature of the heat development which can be used typically ranges 
from about 80.degree. C. to about 130.degree. C. and the period of time of 
the heat development varies depending upon the temperature of the heat 
development selected and typically ranges from about 1 second to about 60 
seconds. 
Of the heat developable silver image forming materials of this invention, 
the post activable type heat developable silver image forming materials 
can be rendered photosensitive by heating at a temperature of about 
80.degree. C. to about 130.degree. C. for about 1 second to about 5 
seconds prior to or during the imagewise exposure to light. The 
temperature of the preliminary heating prior to the imagewise exposure to 
light in order to render the post activable type heat developable silver 
image forming materials of this invention photosensitive may be the same 
as or lower than that of the heat development. Either in the heat 
development or in the preliminary heating, the period of time of heating 
becomes shorter with increased temperatures. Images can also be formed by 
heating the post activable type heat developable silver forming materials 
of this invention at one time at an appropriate temperaure for an 
appropriate period of time during the imagewise exposure to light. 
The heat developable silver image forming materials of this invention can 
also be used as a heat sensitive material by conducting an imagewise 
heating under exposure to light.

The follow Examples are given to illustrate the invention more 
specifically. However, it should be understood that the invention is in no 
way limited by these Examples. All parts and percentages in these Examples 
are by weight. 
EXAMPLE 1 
8.5 g of behenic acid were dissolved under heating in 150 ml of ethanol 
with stirring and to the solution was added dropwise a 100 ml aqueous 
sodium hydroxide solution containing 1 g of sodium hydroxide under heating 
with stirring to give sodium behenate. Then, 200 ml of hot water were 
added thereto and the sodium behenate was completely dissolved with 
continuation of heeating and stirring. Subsequently, an aqueous nitric 
acid acidic solution containing silver nitrate in an amount equimolar to 
the behenic acid used was added dropwise under heating with stirring to 
convert the sodium behenate dissolved to insoluble silver behenate. The 
silver behenate thus obtained was recovered by filtration and repeatedly 
washed with hot water and hot ethanol, followed by drying. 
To 88 parts of a mixed liquid of methyl ethyl ketone and toluene in a 
weight ratio of 2 to 1 were added 12 parts by weight of the silver 
behenate obtained, and the mixture was ball-milled for 24 hours to give a 
uniform silver behenate suspension. 
An emulsion was prepared by adding 4.72 g of a methyl ethyl ketone solution 
containing 15 percent of polyvinyl butyral to 6 g of the silver behenate 
suspension with stirring; adding 0.36 ml of a mixed solution obtained by 
mixing 10 ml of 48 percent hydrogen bromide with 78 ml of methanol to the 
mixture formed with stirring; continuing to stir the resulting mixture for 
30 minutes; adding 0.04 ml of a methanol solution obtained by dissolving 
1.8 g of silver bromide in 10 ml of methanol to the mixture with stirring; 
and adding 20 mg of cyanoguanidine to the mixture produced. 
The emulsion thus obtained was coated on a polyester film as the first 
layer in a wet thickness of 100 .mu. and dried at 70.degree. C. for 5 
minutes. 
Another emulsion having Composition I as set forth below was coated on the 
first layer in a wet thickness of 100.mu. and dried at room temperature to 
obtain an image forming material A. 
______________________________________ 
Composition I 
______________________________________ 
Methyl ethyl ketone 8.3 g 
Copolymer of vinyl acetate and 
vinyl chloride 0.63 g 
Phthalazinone 0.14 g 
2,2'-Methylenebis(4-ethyl-6-tert- 
butylphenol) 0.35 g 
______________________________________ 
For comparison with the image forming material A, another image forming 
material B was prepared in the same manner as described above except that 
the cyanoguanidine was omitted from the first layer. 
The image forming materials A and B were exposed to a light of illumination 
intensity of 2,000 luxes from a tungsten lamp through a 21-step steptablet 
(manufactured and sold by Eastman Kodak Co., Ltd.) for one second and then 
heat-developed at 120.degree. C. for 5 seconds to give a clear black 
image, respectively. 
From the optical density of the image formed and the quantity of exposure 
was made a photographic characteristic curve from which a quantity of 
exposure necessary for obtaining the optical density 0.6 higher than the 
total amount of the optical density of the polyester film as a support and 
that of fog by heat development was determined, and the reciprocal of the 
quantity of exposure thus determined was obtained as a relative 
sensitivity of image forming material. 
As a result, the relative sensitivity of the image forming material A was 
10 times higher than that of the image forming material B. 
EXAMPLE 2 
An emulsion having Composition II as set forth below was prepared by each 
of the ingredients of Composition II with stirring and coated on a 
polyester film as the first layer in a wet thickness of 100.mu. and then 
dried at room temperature. 
______________________________________ 
Composition II 
______________________________________ 
The same silver behenate suspension 
as in Example 1 6.0 g 
Methyl ethyl ketone solution 
containing 15 percent of polyvinyl 
butyral 4.72 g 
N-Bromosuccinimide 0.025 g 
1,3-Diphenylguanidine 0.04 g 
______________________________________ 
Then, another emulsion having composition III as set forth below was 
prepared and coated on the first layer as the second layer in a wet 
thickness of 100.mu. and then dried at room temperature to give an image 
forming material C. 
______________________________________ 
Composition III 
______________________________________ 
Acetone 8.3 g 
Cellulose acetate 0.63 g 
Phthalazinone 0.14 g 
2,2'-Methylenebis(4-ethyl-6- 
tert-butylphenol) 0.35 g 
______________________________________ 
Another image forming material D was prepared in the same manner as 
described above except that the 1,3-diphenylguanidine was omitted from the 
first layer. 
The image forming materials C and D were preliminarily heated at 
100.degree. C. for 3 seconds, exposed to light in the same manner as in 
Example 1 and then heat-developed at 120.degree. C. for 5 seconds to give 
an image, respectively. 
Then, the relative sensitivity of the image forming materials C and D was 
determined in the same manner as in Example 1. The relative sensitivity of 
the image forming material C is 8 times higher than that of the image 
forming material D. 
EXAMPLE 3 
An emulsion having Composition IV as set forth below was prepared by mixing 
each of the ingredients of Composition IV with stirring and coated on a 
polyester film as the first layer in a wet thickness of 100.mu., and then 
dried at room temperature. 
______________________________________ 
Composition IV 
______________________________________ 
The same silver behenate suspension 
as in Example 1 6.0 g 
Methyl ethyl ketone solution 
containing 15 percent of 
polyvinylbutyral 4.72 g 
Methanol solution containing 
5 mg of mercuric acetate 0.6 ml 
1,2,3,4-Tetrabromobutane 0.096 g 
N-Iodosuccinimide 0.04 g 
N-Methyl-2-pyrrolidone 1.5 g 
Cyanoguanidine 0.04 g 
______________________________________ 
Then, the same emulsion as the emulsion having Composition III in Example 2 
was coated on the first layer as the second layer in a wet thickness of 
100.mu., and then dried to give an image forming material E. 
Then, another image forming material F was prepared in the same manner as 
described above except that the cyanoguanidine was omitted from the first 
layer. 
The relative sensitivity of the image foring materials E and F was 
determined in the same manner as in Example 2. 
Further, the image forming materials E and F were exposed to light in a 
xenon fadeometer ("FadeometerXF-1," manufactured by Suga Shikenki Co., 
Ltd.) for 2 hours prior to the imagewise exposure to light to test their 
light stability, and subsequently the relative sensitivity of the image 
forming materials after the light stability test was determined in the 
same manner as in Example 2. 
As a result, the sensitivity of the image forming material F was remarkably 
changed by the storage stability test and the relative sensitivity of the 
image forming material F after the light stability test was about 5 times 
higher than that without the light stability test. This change in the 
sensitivity is disadvantageous from the viewpoint of the storage stability 
of an image forming material. 
On the other hand, the relative sensitivity of the image forming material E 
after the light stability test was the same as that without the light 
stability test, that is, its sensitivity was kept constant. Thus, it can 
be clearly seen that the image forming material E according to this 
invention is excellent in its light stability for keeping the sensitivity 
constant. 
EXAMPLE 4 
Four image forming materials G, H, I and J were prepared in the same manner 
as in Example 3 except that Composition V as set forth below was used 
instead of Composition IV in Example 3. 
______________________________________ 
Composition V 
______________________________________ 
The same silver behenate supension 
as in Example 1 6.0 g 
Methyl ethyl ketone solution 
containing 15 percent of 
polyvinyl butyral 4.72 g 
Methanol solution containing 
10 mg of mercuric acetate 0.6 ml 
1,2,3,4-Tetrabromobutane 0.096 g 
Triphenyl phosphite 0.020 g 
Iodine 0.060 g 
N-Methyl-2-pyrrolidone 1.5 g 
Compound having a unit of 
##STR10## 
in an amount as set forth in Table 1 
below 
______________________________________ 
Then, the relative sensitivity of each of the image forming materials was 
determined in the same manner as in Example 2. The relative sensitivity of 
the image forming material J thus determined was evaluated as 1 and the 
relative value of the relative sensitivity of each of the image forming 
materials G, H and I are shown in Table 1 below. 
Also, the relative sensitivity of each of the image forming materials after 
the same light stability test as in Example 3 was determined in the same 
manner as in Example 2. The ratio of the relative sensitivity of each of 
the image forming materials after the light stability test to that without 
the light stability test is shown in Table 1 below. 
TABLE 1 
______________________________________ 
Material Forming Image 
##STR11## SensitivityRelativeofValueRelative 
SensitivityRelativeofRatio 
______________________________________ 
G Cyanoguanidine 
0.04 10 1.0 
H 1,3-Diphenyl- 
0.04 8 1.2 
guanidine 
I Guanine 0.015 5 1.4 
J None 0 1 5 
______________________________________ 
EXAMPLE 5 
A uniform silver stearate suspension was prepared in the same manner as in 
Example 1 except that stearic acid was used instead of the behenic acid. 
A dry image forming material K was prepared in the same manner as in 
Example 1 except that the silver stearate suspension, 
N-cyano-N'-phenylguanidine and 
2,6-methylenebis(2-hydroxy-3-tert-butyl-5-methylphenyl)-4-methylphenol 
were used instead of the silver behenate suspension, the cyanoguanidine 
and the 2,2'-methylenebis(4-ethyl-6-tert-butylphenol), respectively. 
Further, another image forming material L was prepared in the same manner 
as described above except that the N-cyano-N'-phenylguanidine was omitted. 
The relative sensitivity of each of the image forming materials thus 
obtained was determined in the same manner as in Example 1 and as a 
result, the relative sensitivity of the image forming material K was 8 
times higher than that of the image forming material L. 
In order to test the storage stability of the image forming materials K and 
L, they were kept for one day at a temperature of 50.degree. C. at a 
relative humidity of 90% in a dark room, and then the relative sensitivity 
were determined in the same manner as in Example 1. As a result, the 
sensitivity of the image forming material L decreased while that of the 
image forming material K according to this invention did not change. The 
minimum optical density (fog density) of the image obtained from the image 
forming material K after the storage stability test was the same as that 
without the storage stability test. 
EXAMPLE 6 
Five dry image forming materials, M, N, O, P and Q were prepared in the 
same manner as in Example 3 except that Composition VI as set forth below 
was used instead of Composition IV in Example 3. 
______________________________________ 
Composition VI 
______________________________________ 
The same silver behenate 
suspension as in Example I 
6.0 g 
Methyl ethyl ketone solution 
containing 15 percent of 
polyvinyl butyral 4.72 g 
Methanol solution containing 
10 mg of mercuric acetate 
0.6 ml 
1,2,3,4-Tetrabromobutane 
0.096 g 
N-bromosuccinimide 0.012 g 
N-Iodosuccinimide 0.02 g 
N-Methyl-2-pyrrolidone 
1.5 g 
##STR12## 15 percent by mole per mole of silver behenate 
as set forth in Table 2 
______________________________________ 
The relative sensitivity of each of the image forming materials was 
determined in the same manner as in Example 2. The relative sensitivity of 
the image forming material Q thus determined was evaluated as 1 and the 
relative value of the relative sensitivity of each of the image forming 
materials M, N, O and P is shown in Table 2 below. 
Also, the relative sensitivity of each of the image forming materials after 
the same light stability test as in Example 3 was determined in the same 
manner as in Example 2. The ratio of the relative sensitivity of each of 
the image forming materials after the light stability test to that without 
the light stability test is shown in Table 2. 
Further, the minimum optical density of the image formed from each of the 
image forming materials after the light stability test is also shown in 
Table 2. 
TABLE 2 
______________________________________ 
Relative 
Compound Value Ratio Minimum 
Having a of of Optical 
Unit of Relative Relative 
Density 
MaterialFormingImage 
##STR13## itivitySensi- 
tivitySensi- 
Imageof 
______________________________________ 
M Dicyclohexylguanidine 
5 1.0 0.9 
N N-Octyl-N'- 7 0.9 0.10 
cyanoguanidine 
O Malonylguanine 10 1.1 0.10 
P Glycocyamine 8 1.0 0.09 
Q None 1 0.5 0.35 
______________________________________ 
From Table 2, it can be clearly seen that the image forming materials of 
this invention are excellent in their sensitivity and storage stability. 
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.