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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to a silver halide photographic
light-sensitive material, and more particularly to a silver halide
photographic light-sensitive material suitable for radiographic use having
a high sensitivity, wide exposure range, excellent graininess sharpness
and preservability, and producing little or no fog under a safelight.
More and more complex and diverse demands have lately been made for
improving the characteristics of silver halide photographic
light-sensitive materials, and especially for the realization of a
high-speed or ultra-high-speed silver halide photographic light-sensitive
material having stable photographic characteristics. Particularly, in
photographic light-sensitive materials for radiography use, in order to
lessen the exposure dose of X rays against the human body, the
photographic light-sensitive material is strongly desired to be so highly
sensitive as to enable the obtaining of more information with less
exposure dose of X rays and so improved as to produce a high-quality image
with less fog.
Increasing the sensitivity of the silver halide photographic
light-sensitive material (hereinafter may be called light-sensitive
material) is carried out most generally by making larger the size of the
silver halide contained in an emulsion layer, by the optical sensitization
with use of sensitizing dyes, or the like.
It is well-known that, if the silver halide grain size is made larger, the
sensitivity thereof increases. However, the light-sensitive material which
uses a large-grain-size silver halide emulsion has the disadvantage that
it tends to produce an increased fog or to be desensitized during the
storage thereof; i.e., the preservability thereof is deteriorated, and to
produce a fog due to a safelight.
A large number of prior-art techniques such as the incorporation of various
additives have hitherto been disclosed for the improvement of the
preservability of the silver halide photographic light-sensitive material
and also for reducing the safelight fog of the photographic
light-sensitive material, but it is the status quo that many of them are
accompanied by undesirable secondary effects such as desensitization, and
no satisfactory techniques for improving particularly the preservability
of high-speed light-sensitive materials containing large-size silver
halide grains have yet been obtained. In addition, such undesirable
phenomena as the deterioration of the covering power with the increase in
the grain size, the increase in the desensitization of the light-sensitive
mateial when subjected to a mechanical pressure such as fold, and the
like, also increase, so that raising the sensitivity by increasing the
grain size has its limit.
Inparticular, most of the silver halide emulsions of conventional type
silver halide photographic light-sensitive materials have so far used a
silver halide grains having a wide grain-size distribution. Therefore, it
has not always positively affirmed that an optimum chemical sensitization
have been applicable to silver halide grains having every grain-size,
accordingly the intrinsic sensitivity of each silver halide grain has not
satisfactorily been displayed.
From the above-mentioned aspects, the techniques for making a photographic
speed higher have very often been applied to silver halide photographic
light-sensitive materials. The techniques of using a twin-crystal type
silver halide grain are disclosed in Japanese Patent O.P.I. Publication
Nos. 153428/1977, 145827/1979 and 142329/1980 and others; the techniques
of using a flat-plate shaped silver halide grain are disclosed in Japanese
Patent O.P.I. Publication Nos. 12792/1983, 95337/1983, 108526/1983,
111937/1983 and 113928/1983, and others; and the techniques of using a
monodisperse emulsion are disclosed in Japanese Patent O.P.I. Publication
Nos. 207597/1981, 178235/1982 and 49938/1983; Japanese Patent Application
Nos. 53043/1983 and 54949/1983; and others. In the above-mentioned
techniques, however, it has been hard to manufacture any silver halide
photographic light-sensitive material which displays few fogginess and
high sensitivity without affecting any other photographic characteristics.
For raising the sensitivity with the same grain size; i.e., for sensitizing
methods, there are a variety of techniques. For example, a method for
incorporating a development accelerator such as a thioether into an
emulsion, a method for the supersensitization of a spectrally sensitized
silver halide emulsion by the combined use of appropriate optical
sensitizers, improved chemical sensitization techniques, and the like,
have been reported. However, these methods or techniques are not
necessarily applicable widely to high-speed silver halide photographic
light-sensitivematerials. The silver halide emulsion to be used in a
high-speed silver halide photographic light-sensitive material, since it
is chemically sensitized to the utmost possible extent, when such above
methods are applied, has the disadvantage that it tends to produce a fog
during the storage thereof or a fog due to a safelight, or the like.
Japanese Patent Examined Publication No. 8831/1970 discloses a method of
carrying out chemical sensitization by use of gold(I) mercaptide, but this
method also has the disadvantage that, when the method is used alone, the
stability of the light-sensitive material against heat is largely
deteriorated and besides, the actual sensitivity of the light-sensitive
material when exposed for a long period to a low-illuminance light is
deteriorated, thereby causing the deterioration of the low-intensity
reciprocity law failure characteristic.
Further, Japanese Patent Examined Publication No. 24937/1981 discloses the
use of thiosuccinimide-type compounds for chemical sensitization, but this
method is not enough to provide any adequate sensitization.
On the other hand, optical sensitization also is a useful sensitization
means. For example, in the field of medical radiography, those
conventional regular-type films sensitive to a wavelength region around
450 nm have now been replaced by orthochromatic-type photographic films
orthochromatically sensitized to be further sensitive to the wavelength
region range of from 540 to 550 nm. The wavelength region to which thus
sensitized light-sensitive materials are sensitive is extended and at the
same time the sensitivity of such materials is increased, thus allowing to
reduce the exposure dose of X rays to thereby lessen its influence upon
the human body. Thus, the optical sensitization is a very useful
sensitization means, but there are many problems yet to be solved. For
example, there are many cases where, if the combination of or the using
quantities in combination of photographic emulsions, sensitizers and other
additives are inappropriate, they lead to the impairment of the
sensitizability or to the deterioration of the preservability of the
resulting light-sensitive material, thus making it difficult to obtain
adequate effects. Particularly in a high-speed light-sensitive material
which uses large-size silver halide grains, the above-mentioned
disadvantage tends to appear significantly, so that there is much room for
further improvement.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a silver
halide photographic light-sensitive material suitable for radiographic use
which is free of the above-mentioned disadvantage of conventional
techniques and has a high sensitivity and a wide exposure range and which
is excellent in the graininess, sharpness and preservability, and produces
little or not fog due to a safelight.
The above object is accomplished by a silver halide photographic
light-sensitive material comprising a support and at least one silver
halide photographic emulsion layer provided on the support, at least one
silver halide emulsion layer containing a silver halide grain which has a
localized portion containing 20 mol% or more silver iodide and average
silver iodide content of which grain is from 0.1 to 10 mol%, provided that
said silver halide grain is prepared by mixing an aqueous solution
containing a water soluble halide compound and an aqueous solution
containing a water soluble silver salt under a condition that pAg of the
mixture is raised to between 9.7 and 12.5 during a period after a half
amount of the silver salt to be used has been added to the mixture.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a chart illustrating the pAg variation patterns in preparing
silver halide grains;
FIG. 2 is a graph illustrating the grain-size distribution of silver halide
grains used in the radiographic light-sensitive material relating to the
invention; and
FIG. 3 is a graph illustrating a model of change on standing of flow rates
of a silver salt solution and a halide solution added in a double-jet
process, in the course of preparing the emulsions in the examples.
DETAILED DESCRIPTION OF THE INVENTION
In the preparation of the silver halide grains in accordance with the
invention, it is preferred that a pAg value is to be adjusted to not less
than 9.7 and not more than 12.5 at the time when completing the
preparation by changing a pAg value instantly or gradually in the stage
after an amount of silver formed or deposited reaches not less than one
half of a total amount of silver to be prepared; and it is further
preferred that a pAg value is to be adjusted to not less than 9.7 and not
more than 12.5 at the time when completing a preparation by changing a pAg
value gradually at the point of time when an amount of silver formed or
deposited is from 2/3 to 9/10 of a total amount of silver to be prepared.
FIG. 1 is the examples of various patterns of pAg value adjustments in the
preparation of the emulsions of the invention; wherein (2) and (3) show
the examples that pAg values are raised intermittently up to 11 at the
point of time when an amount of silver added reaches 1/2 and 2/3,
respectively, and (4), (5), (6), (7), (9) and (10) show the examples that
pAg values are raised continuously from the point of time when an amount
of silver added reaches a prescribed proportion up to the prescribed value
of between 9.7 and 12.5, i.e., pAg=11, 10.1 and 9.85.
To simplify the drawing, it illustrates only the case where the variations
of pAg values are linear. In the invention, however, a pAg value may be
adjusted up to between 9.7 and 12.5, provided the adjustment is to be made
within the range where a content of silver added is not less than one half
of a total amount of silver added. There are also many variations of such
adjustments including, for example, one case that a pAg raising line is
curved or another case that a pAg reaches a prescribed value before a
total amount of silver is added and the value is kept constant.
In the meantime, FIG. 1 shows an example that the pAg is 7.3 in the initial
stage of mixing operation and the pAg is 9.0 in the stage before starting
the adjustment. These pAg values may be determined in accordance with the
composition, grain-size, configuration and the like of silver halide
grains aimed to obtain. It is the matter of course that such values shall
not be limited to the values indicated in the drawing.
In the drawing, (1) and (8) are the examples of the patterns not in
accordance with the invention.
More particularly, it is preferred that, when using the above-mentioned
silver halide grain, it is of the mono-dispersion type in grain-size
distribution. The term, `mono-dispersion`, mentioned herein means a grain
dispersion within the range that 95% of the grains are not more than
.+-.60% and more preferably not more than .+-.40% in number-average
grain-size. The term, `number-average grain-size`, means a number-average
value of the respective diameters of the projective areas of grains.
It is allowed in the invention to select any contents of silver halide
grains in an emulsion layer, however, the contents thereof is preferably
not less than 40% and more preferably not less than 90%, in terms of
silver, to a total quantity of silver halide grains.
It is also allowed to use a plurality of different sized emulsions relating
to the invention mixed together.
The sizes of silver halide grains used in the invention are preferably from
0.1 to 8.0 .mu.m and more preferably from 0.3 to 1.5 .mu.m.
The silver halide grains may be comprised of such a silver halide as silver
chloroiodobromide, silver chloride, silver chlorobromide, silver bromide,
silver iodobromide, silver iodide and the like, and silver iodobromide is
preferable from the viewpoint of obtaining a high sensitivity. Further, an
average silver iodide content in silver iodobromide is from 0.1 to 10 mol%
and preferably from 1 to 8 mol%.
The silver halide grains of the invention have some portions inside
thereinside where localize silver iodide of such a high content as is not
less than 20 mol%, and the silver iodide localized portions are to
preferably be as far inside as possible from the outer surface of each
grain and more preferably be not less than 0.01 .mu.m far from the outer
surface thereof.
Such localized parts may be present in the layer-form in the grains of the
whole core body of the grain may be so formed into the so-called
core/shell type structures as to serve as such a localized part. In this
instance, it is preferred that a part of or the whole of the core portion
of a grain except the shell portions of not less than 0.01 .mu.m in
thickness from the outer surface of the grain is to be a localized part
containing silver iodide in an amount of not less than 20 mol%.
A silver iodide content in the localized parts is to preferably be within
the range of from 30 to 40 mol%.
It is preferred that a silver iodide content in the localized portions is
to be not less than 20 mol% greater than that of the layer inner than the
localized portions.
As for the processes for providing a localized part of such a high silver
iodide content as is at least 20 mol% or higher to the inside of each
silver halide grain used in the invention (that is, preferably, the inside
of each grain not less than 0.01 .mu.m far from the outer wall of each
grain), it is preferable to use a seed crystal, however, it is also
allowed not to use such a seed crystal.
If not to use such a seed crystal, there is not such a silver halide as is
capable of becoming a nucleus growable before starting a ripening in a
reaction liquid phase containing a protective gelatin (hereinafter called
a mother liquid). Therefore, a grown nucleus is formed by supplying a
silver ion and a halide ion containing a highly concentrated iodine of at
least 20 mol% or more. A further supply thereof is still continued so as
to grow a grain out of the grown nucleus. Thereafter, at least one or more
layers containing silver bromide or silver iodobromide (hereinafter called
a shell layer) are formed.
When a seed crystal is used, it is allowed either to form silver iodide of
at least 20 mol% or more in the seed crystal and then to coat the seed
crystal with a shell layer or to contain silver iodide in an amount within
the range of from zero to 10 mol% in the seed crystal so as to form silver
iodide of at least 20 mol% within the grain in the course of growing the
seed crystal and then to coat the seed crystal with a shell layer.
Provided that a proportion of silver iodide is within the range of from 0.5
to 10 mol% to every silver halide used in all the grains, the seed crystal
becomes larger in size and the grain-size distribution becomes broader in
the former process than in the latter process. It is, therefore,
preferable in the invention to use such a grain having a multi-layered
structure as those used in the latter process, because a monodisperse type
emulsion may readily be prepared therein.
In addition to the above, as for the processes for forming a layer having a
localized part, a halogen-substitution process may be used. Such a
halogen-substitution process may be carried out, for example, in such a
manner that an inner core is formed and an aqueous solution of an iodide
compound is then added. To be more concrete, this type of processes may be
performed in the processes described in detail in U.S. Pat. Nos. 2,592,250
and 4,075,020, Japanese Patent O.P.I. Publication No. 127549/1980 and the
like.
When using a monodisperse type emulsion, such a sensitization as a chemical
sensitization may satisfactorily be so applied as to obtain a remarkably
high sensitivity and a contrast may not much be reduced even in such a
sensitization process, so that the contrast may be hardened.
The above-mentioned monodisperse type emulsion may be prepared in such a
manner that the crystal growth of emulsion grains are carried out first,
and when growing the grains, it is allowed to add silver ions and a halide
solution alternately in a time series, and it is, however, preferred to
use the so-called double-jet process.
In the case of supplying the silver ions and halide ions, either a critical
growth rate is to be applied so as not to dissolve the existing crystal
grains away and conversely not to allow any formation or growth of new
grains and further to supply a satisfactory amount of a silver halide
necessary for growing only the existing grains, or a growth rate is to be
gradually increased continuously or stepwise within the allowable range,
as the crystal grains are being grown. How to gradually increasing the
rate is described in, for example, Japanese Patent Examined Publication
Nos. 36890/1973 or 16364/1977, or Japanese Patent O.P.I. Publication No.
142329/1980.
The above-mentioned critical growth rate is varied according to a
temperature, pH value, pAg value, stirring frequency, silver halide grain
composition, solubility, agrain-size, intergrain distance, crystal habit
or kind of protective colloids and the concentration thereof, and the
like. However, the critical growth rates may readily be obtained in such
an experimental way as a microscopic observation or turbidity measurement
of emulsion grains being suspended in a liquid phase.
In order to obtain the above-mentioned monodisperse type emulsion, it is
preferred that such grain is to be grown by using the seed crystal to
serve as the growing nucleus and supplying thereto silver ions and halide
ions.
The broader the grain-size distribution of the above-mentioned seed crystal
is, the broader the grain-size distribution thereof is, after the grains
are grown up. Accordingly, it is preferred to use such a grain as is
narrow in the grain-size distribution in the stage of the seed crystal, so
as to obtain the monodisperse type emulsion.
In practicing this invention, the silver halide grains to be used in the
silver halide emulsion may be prepared by the application of any of those
neutral method, acid method, ammoniacal method, orderly mixing method,
inverse mixing method, double-jet method, controlled double-jet method,
conversion method, core/shell method, and the like, as described in, e.g.,
T. H. James, The Theory of the Photographic Process, 4th ed., published by
MacMillan (1977) p. 38-104, and the like.
Such silver halide grains or such a silver halide emulsion is desirable to
contain at least one of those salts (water-soluble salts) of iridium,
thalium, palladium, rhodium, zinc, nickel, cobalt, uranium, thorium,
strontium, tungsten and platinum. The salt content of the emulsion is
preferably from 10.sup.-1 to 10.sup.-6 per mole of silver, and more
preferably the emulsion contains at least one of those salts of thalium,
palladium and iridium. These salts may be used alone or in a mixture, and
the adding stage (adding point of time) thereof is discretional. The
grains each may also be endowed thereinside with a reduction sensitization
nucleus by making use of a suitable reducing agent or under a relatively
lower pAg atmosphere.
By doing this, the improvement of the flash exposure characteristics,
prevention of the pressure desensitization, prevention of the latent image
fading, sensitization and other effects can be expected. Silver halide
grains may be made more finer in size, provided that a sensitivity of an
optically sensitized light-sensitive material may be kept in the same
level as that before it is sensitized. It is, therefore, possible to
obtain the light-sensitive materials excellent in image quality, pressure
resistance and the like.
The term `average grain size r` used herein means the average value, in the
case of spherical silver halide grains, of the diameters thereof and, in
the case of cubic grains, of the lengths of the sides thereof and, in the
case of other forms, of the diameters of assumed circular images
corresponding in the area to the projected images thereof. When each
individual grain size is regarded as r.sub.i and the number of the grains
as n.sub.i, the average grain size r is defined by the following equation:
##EQU1##
As for the monodisperse silver halide (grains) in this invention, when the
silver halide grain size distribution's standard deviation S as defined by
the following equation is divided by the average grain size r, the
quotient is desirable to be not more than 0.20.
##EQU2##
Further, the S/r is more desirable to be equal to or less than 0.15.
In a silver halide emulsion used in the invention, it is usual that the
furfaces of the grains thereof are chemically sensitized. As for the
chemical sensitization processes, a sulfur sensitization process using a
compound containing sulfur capable of reacting with silver ions and an
active gelatin, a reduction sensitization process using a reducible
substance, a noble metal sensitization process using gold or other noble
metal compounds, and the like may be used independently or in combination.
The sulfur sensitizers useful therein include, for example, a thiosulfate,
a thiourea, a thiazole, a rhodanine and other compounds. The reduction
sensitizers useful therein include, for example, a stannous salt, an
amine, a hydrazine derivative, a formamidinesulfinic acid, a silane
compound and the like. The noble metal sensitizers useful therein include,
for example, such a metal complex which belongs to the VIII group of the
periodic table, such as the complex salts of platinum, iridium or
palladium, as well as the complex salts of gold.
A photosensitive layer containing the above-mentioned grains is to be
present on at least one side of a support.
The silver halide photographic light-sensitive material of this invention
is desirable to be sensitized by a gold sensitizer in a quantity of from
1.0.times.10.sup.-16 to 1.0.times.10.sup.-20 moles per .mu.m.sup.2 of the
surface area of the silver halide grain. By doing this, a high-speed
light-sensitive material excellent in the preservability and producing
little or no fog due to a safelight can be obtained. This effect is
significant also in a color-sensitized silver halide emulsion.
The surface area of the silver halide grain, if the average grain size is
regarded as r, where the grain is in the form of a cube, can be calculated
by 6.times.r.sup.2, and where the grain is in the spherical form, can be
calculated by .pi.r.sup.2 (the average grain size r will be defined
hereinafter). The foregoing gold sensitizer is desirable to be used in the
above quantity per unit area of the surface area of such the grain.
As for the gold sensitizer, those various gold compounds known as gold
sensitizers may be used, which include, for example, chloroaurates, gold
chloride, gold thiocyanate, etc., which is advantageously usable. And
those compounds as described in U.S. Pat. No. 2,399,083 may also be used.
In practicing this invention, gold sensitizers and other sensitizing means
may be used in combination. For example, sulfur sensitizers may be used in
combination with gold sensitizers, i.e., gold-sulfur sensitization may be
suitably used.
In this case, as for the sulfur sensitizer, those various inorganic and
organic compounds known as sulfur sensitizers may be used, which include,
e.g., thiosulfates, thiourea, allylthiourea, allylisothiocyanate, and the
like. And those compounds as disclosed in U.S. Pat. No. 1,623,499 may also
be used.
In addition, the gold-sulfur sensitization is desirable to be made in the
presence of a thiocyanate.
In combination with the gol-sulfur sensitization, reduction sensitization
which uses thiourea dioxide, stannous chloride, silver ripening, etc. and
selenium sensitization, and the like may be used. In the case of using a
sulfur sensitizer, in order to have it exhibit adequately the effect of
this invention for improving the preservability and prevention of the
safelight fog, the sulfur sensitizer should be used in the using quantity
range of from 1.0.times.10.sup.-13 to 1.0.times.10.sup.-19 moles per unit
surface area (.mu.m.sup.2) of silver halide.
The molar ratio in the adding quantity between the sulfur sensitizer and
the gold sensitizer is preferably from 10:1 to 1:1, and more preferably
from 7:1 to 5:1.
Such a silver halide emulsion as described above is suitable for preparing
a photographic light-sensitive material for radiographic use capable of
displaying the preferable characteristics as mentioned below.
Namely, the silver halide photographic light-sensitive material for
radiography use in the medical field is desired to be excellent in the
depictability also for the early detection of focuses as well as for the
prevention of errosneous diagnoses. The optical density range used for
diagnoses is normally from 0.05 to 1.5, and in a range exceeding the
exposure range, the detail in the shadow area becomes obscure to
deteriorate the detection. That is, the most important characteristic
which a silver halide photographic light-sensitive material for medical
radiography use should have is to be excellent in the depictability in the
optical density range of from 0.05 to 1.5.
The depictability depends on the quantity of information and image quality.
And the quantity of information is determined by the exposure range, and
the image quantity by the graininess and sharpness.
Therefore, the preferred silver halide photographic light-sensitive
material for medical radiography use shall be one capable of satisfying
all the requirements: the desirable graininess and sharpness and wide
exposure range in terms of the optical density range of from 0.05 to 1.5.
The photographic characteristics of the high density area of the silver
halide photographic light-sensitive material for radiography use differ
according to the region of the human body to be radiographed. For example,
a contrast medium is used in high X-ray-transmittance regions including
digestive organs such as the stomach. If a radiographic exposure adjusted
to the contrast medium region is used, nothing but a fill-in image is
obtained, thus being unable to contribute to diagnosis. However, if the
photographic light-sensitive material is of a low gamma, this can be
avoided.
And where a high gamma is required for the medium density region as in the
angiography, if the gamma in the high-density area is also raised, this
can be avoided also.
From the point of view as described above, the photographic light-sensitive
materials for radiographic use are particularly preferred to endow with
the following .gamma. characteristics.
On the characteristic curve thereof drawn on a rectangular coordinate
system with the equal unit length-graduated coordinate axes for optical
density (D) and for exposure (log E), gamma (.gamma..sub.1) formed between
the point of an optical density of 0.05 and the point of an optical
density of 0.30 is from 0.50 to 1.00, and gamma (.gamma..sub.2) formed
between the point of an optical density of 0.50 and the point of an
optical density of 1.5 on the characteristic curve is from 2.5 to 3.5.
The gamma herein means one obtained on the basis of a characteristic curve
formed on rectangular coordinates of optical density (D) and logarithm of
exposure (log E) whose coordinate axes' unit length is equally taken. The
.gamma..sub.1 means the inclination of the straight line formed by
connecting the density point consisting of the base (support) density+fog
density+0.05 on the characteristic curve with another density point
consisting of the base density+fog density+0.30 on the same characteristic
curve, and the .gamma..sub.2 means the inclination of the straight line
formed by connecting the density point consisting of the base density+fog
density+0.50 with another density point consisting of the base density+fog
density+1.50. Further, to express numerically, if the angles formed by
these straight lines and the exposure axis (axis of abscissa) intersecting
each other are regarded as .theta..sub.1 and .theta..sub.2, respectively,
then the .gamma..sub.1 and .gamma..sub.2 mean tan .theta..sub.1 and tan
.theta..sub.2, respectively.
The particularly preferred embodiment is such that the above .gamma..sub.1
and .gamma..sub.2 are obtained on the characteristic curve on rectangular
coordinates when processing is carried out under the following processing
conditions:
PROCESSING CONDITIONS
Processing is made with use of the following developer-1 in a roller
transport-type automatic processor in accordance with the following
processing steps:
______________________________________
Temperature
processing time
______________________________________
Developing 35.degree. C.
30 seconds
Fixing 34.degree. C.
20 seconds
Washing 33.degree. C.
18 seconds
Drying 45.degree. C.
22 seconds
______________________________________
Developer-1
Potassium sulfite 55.0 g
Hydroquinone 25.0 g
1-phenyl-3-pyrazolidone 1.2 g
Boric acid 10.0 g
Potassium hydroxide 21.0 g
Triethylene glycol 17.5 g
5-methylbenzotriazole 0.04 g
5-nitrobenzimidazole 0.11 g
1-phenyl-5-mercaptotetrazole
0.015 g
Glutaraldehyde hydrogensulfite
15.0 g
Glacial acetic acid 16.0 g
Potassium bromide 4.0 g
Water to make 1 liter.
______________________________________
Such the characteristic curve can be obtained, for example, by the
following photosensitometry: Speaking of a light-sensitive material for
radiography use, a light-sensitive material for radiography use comprising
a transparent support having an emulsion layer on one side thereof or
emulsion layers on both sides thereof is placed between a pair of optical
wedges whose density inclination is mirror-symmetrically arranged, and
both sides of the light-sensitive material are exposed equally
simultaneously for 1/10 second to light sources of a color temperature of
5,400.degree. K. arranged on both opposite sides. The processing of the
light-sensitive material is carried out in accordance with the foregoing
steps in a roller transport-type automatic processor. A fixer solution to
be used is not particularly restricted as long as it is an acid hardening
fixer solution; for example, Sakura FX (product of Konishiroku Photo
Industry Co., Ltd.) or the like may be used.
The silver halide photographic light-sentive material of this invention,
which shows a characteristic curve whose .gamma..sub.1 and .gamma..sub.2
are in the above range, has so high sharpness and so satisfactory
graininess that all the regions of the human body can be satisfactorily
radiographed and also has so wide latitudes in the low and high density
areas that diagnoses can be advantageously conducted.
It is more desirable that .gamma..sub.1 be from 0.60 to 0.90 and
.gamma..sub.2 be from 2.6 to 3.4.
Subsequently, the preparation of the silver halide photographic
light-sensitive material having a characteristic curve whose .gamma..sub.1
and .gamma..sub.2 are in the range of this invention will be illustrated
below:
In practicing this invention, a silver halide emulsion prepared by mixing
large-size silver halide grains, medium-size silver halide grains and
small-size silver halide grains can be used. For example, the preparation
is made by mixing properly chemically sensitized grains of three different
average sizes of 0.95.mu., 0.75.mu. and 0.55.mu. in a proportion by weight
of silver halide of (10-40):(30-80):(10-40), and preferably
(15-30):(40-70):(15-30).
In the present invention, the granularity distribution of the whole silver
halide grains of the light-sensitive material is desirable to comprise at
least two peaks and dales. Such peaks and dales, because the
large(medium)-size and small-size grains have their independent
granularity distributions, can be formed by the mixing. In the peak modes,
the interval between the highest peak mode and the peak mode adjacent
thereto is desirable to be from 0.10 .mu.m to 0.40 .mu.m.
Also, in this invention, as for the form of the granularity distribution
curve, when the grain size in the dale formed between the foregoing
highest peak mode A(.mu.) and the peak mode B(.mu.) adjacent thereto (if
there are two adjacent peaks, the higher one of them) is regarded as
C(.mu.), the frequency of the C is preferably from 90% to 5%, and more
preferably from 80% to 10% (for A, B and C, see the example shown in FIG.
1). There are cases where no very satisfactory effects can be obtained in
respect of the sharpness in the form of the characteristic curve if this
ratio is less than 5%, and in respect of the sensitivity if the ratio
exceeds 90%.
The proportion of the highest peak mode A to the peak mode B is preferably
from 1:1 to 1:0.3, and more preferably from 1:0.9 to 1:0.4. If this
proportion is too small, the mixing will mean little. As long as the
proportion is in the above range, good results can be attained. Where the
highest peak mode is a mode of small grains, if the proportion is smaller
and the ratio of large-size grains is reduced, the sensitivity may be
lowered. And where the highest peak mode is a mode of small grains, if the
peak mode of large-size grains is extremely close to the peak mode of
small-size grains, the sharpness of the high density area may be
deteriorated. On the other hand, where the highest peak mode is a mode of
large-size grains, if the proportion is smaller and the ratio of
small-size grains is reduced, the improvement on the maximum density
attributable to small-size grains may not be expected. Also, where the
highest peak mode is a mode of large-size grains, if the mode of
small-size grains is close to the mode of large-size grains, the
sensitivity may be lowered or the sharpness in the medium density area may
be deteriorated. If the above proportion falls under the range of from 1:1
to 1:0.3 or from 1:0.9 to 1:0.4, in any case good effects can be
adequately displayed.
In practicing this invention, when discriminating between the modes like
this, the different silver halide grains as such may be used either
together in a single layer or separately in two or more layers to have
these layers attain the above modes as a whole. For example, where two
layers, a high-speed layer and a low-speed layer, are provided, the two
layers may be so constructed as to have the above-described mode
differential as a whole.
In the present invention, the obtaining of a silver halide photographic
light-sensitive material of a characteristic curve whose high-density
portion is of a low-gamma type can be carried out by reducing the ratio of
small-size silver halide grains or by minimizing the grain size of
small-size silver halide grains, and further by increasing the hardness of
the emulsion with use of a large quantity of a hardener. Increasing the
hardening is useful means for making the gamma of the high-density portion
of the characteristic curve lower than that of the medium-density portion.
Lowering the gamma of the high-density portion of the characteristic curve
can be attained also by preferentially softening the high-density portion
of the curve by means of adding a certain development restrainer to the
emulsion. There are various additives usable as the hardener or the
development restrainer.
The gamma of the low-gamma-type silver halide emulsion is desirable to be
from 0.7 to 1.4 with an optical density of from 2.0 to 2.6. The preferred
grain size mixing proportion by weight of silver halide grains of
0.95.mu.:0.75.mu.:0.40.mu. in the low-gamma-type silver halide emulsion
should be (20-60):(30-60):(5-25).
The grain size of the silver halide grains is further desirable to be from
0.1 to 3.0.mu.. In practicing this invention, as has been described above,
the silver halide grains are desirable to be of a grain size distribution
curve having preferably peaks and dales, and more preferably two or more
peaks, the interval between the highest peak mode (e.g., A of FIG. 2) and
the peak mode adjacent thereto (e.g., B of FIG. 2) of which is not less
than 0.10.mu. and not more than 0.40.mu..
If the above construction is taken, the sensitivity can be raised by the
grains whose mode (most frequent value) in the grain-size distribution
curve is large, i.e., by the group of large-size silver halide grains,
while the covering power can be raised by the grains whose mode in the
grain-size distribution curve is small, i.e., the group of small-size
silver halide grains.
Particularly, the above-mentioned interval is desirable to be from 0.15.mu.
to 0.37.mu..
In the present | | |
