Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
1999-12-22
2001-07-24
Letscher, Geraldine (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S567000, C430S944000, C430S570000, C430S559000, C430S599000
Reexamination Certificate
active
06265144
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to silver halide light sensitive color photographic materials and in particular, to silver halide color photographic materials having infrared-sensitivity and exhibiting high sensitivity and low fog.
BACKGROUND OF THE INVENTION
Recent pronounced advancements of solid state image sensors such as CCD and magnetic, electronic or optical recording medium in the field of electronics enabled easy picture-taking as in conventional silver photography, images can be instantly reproduced on television and stored in various recording mediums. Further, as a result of advances in scanners and image processing apparatuses in the field of printing and plate-making, operations such as editing or correcting with watching a color display and treatments such as magnification-reduction or contrast adjustment, after the original images are read, can be easily conducted. Along with such advances, a technique for obtaining high quality images from an image processing apparatus and a recording medium are desired and various types of outputting systems have been put to practical use, including a thermal transfer system, an ink-jet system and an electrophotography system.
Silver halide photographic materials are superior in representation of highlight and image lasting quality and techniques for applying them to digital image output have been developed. The reason why silver halide photographic materials are superior in representation is that silver halide photographic material, as a print material, can form images with little electronic noise. Accordingly, the difference in density which is perceptible in prints is regarded to be substantially in accord with the density difference perceptible by human eyesight.
Silver halide photographic materials are employed not only in photography but also in printing, in terms of high sensitivity, superior color reproducibility and suitability to rapid access. Specifically, the photographic material are employed in the field of so-called proofs to check the finished state prior to actual printing.
Although silver halide photographic materials are quite superior in representation and are broadly employed, conventional silver halide photographic materials have blue-, green- and red-sensitive silver halide emulsion layers, leading to problems such that light sources usable for recording are limited. To expose the silver halide photographic material to light for the purpose described above, gas lasers such as helium-neon, argon gas and helium cadmium have been employed. However, disadvantages of these lasers are that they are too expensive, large and short life. Although a method using a semiconductor laser and a non-linear optical element is known, there were also problems with this method such that its conversion efficiency was insufficient and light with a wavelength suitable for silver halide photographic materials was not available, so that its practical application was not achieved. However, the use of a semiconductor laser and a silver halide infrared-sensitive photographic material makes it possible to readily obtain images using a low-priced compact exposure apparatus.
However, it is generally known that in cases when a silver halide emulsion is spectrally sensitized with an infrared-sensitizing dye, the dye becomes highly unstable in the emulsion, due to its specific structure, producing problems such as increased fogging in spectral sensitization.
To restrain fogging of emulsions, a technique of varying the pAg or the temperature at the time of chemical sensitization is disclosed in JP-A 58-125612 (herein, the term, JP-A means an examined, published Japanese Patent Application). However, this is a technique in chemical sensitization, not a technique for infrared spectral sensitization. JP-A 5-80445 discloses a technique of spectral sensitization, in which a sensitizing dye is added and then the temperature is raised. Thus, the sensitizing dye is added at a temperature 25 to 55° C. and chemical ripening is conducted at a still higher temperature, thereby producing a silver halide emulsion exhibiting superior linearity in the region of from intermediate to high densities. However, there is disclosed nothing with respect to problems concerning specific fogging of a infrared sensitizing dye. Further, the sensitizing dye was added before starting chemical sensitization.
In view of the foregoing, there is continuous strong desire for a technique for achieving reduced fog and enhanced sensitivity, even when subjecting a silver halide emulsion to infrared spectral sensitization.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a silver halide emulsion with reduced fog, even when subjected to infrared spectral sensitization and a silver halide light sensitive photographic material by use thereof.
The above-described object of the invention can be accomplished by the following constitution:
(1) a method of preparing a silver halide emulsion comprising silver halide grains, the method comprising the steps of:
(i) forming a silver halide emulsion,
(ii) subjecting the silver halide emulsion to chemical sensitization, and
(iii) adding a sensitizing dye the silver halide emulsion, wherein the sensitizing dye exhibits an absorption maximum at a wavelength of not less than 730 nm, the pAg of the emulsion being adjusted to a range of from 7.50 to 8.25 after starting the chemical sensitization and before adding said sensitizing dye; and
(2) a silver halide light sensitive photographic material, comprising a support having thereon a silver halide emulsion layer comprising a silver halide emulsion containing a sensitizing dye exhibiting an absorption maximum at the wavelength of not less than 730 nm (hereinafter, also denoted as &lgr;max≧730 nm) and which has been chemically sensitized, wherein the pAg of the emulsion is adjusted to 7.50 to 8.25 at the time after starting chemical sensitization and before adding the sensitizing dye.
DETAILED DESCRIPTION OF THE INVENTION
Silver halide emulsions relating to the invention are those which are chemically sensitized and are further spectrally sensitized with a sensitizing dye exhibiting an absorption maximum (&lgr;max) at a wavelength of not less than 730 nm.
The process of preparing a silver halide emulsion generally comprises various stages, including silver halide grain formation, chemical sensitization and spectral sensitization step, and chemical sensitization-stopping. In the silver halide formation stage, an aqueous silver salt solution and an aqueous halide salt solution are conventionally added into a protective colloid solution such as gelatin to form nucleus grains and the formed nucleus grains are allowed to grow to silver halide grains with desired sizes. In the final step of this stage, excessive soluble salts are removed or the temperature is lowered to reduce variation of the form or size of silver halide grains.
In the conventional subsequent stage, chemical sensitization is conducted, in which an additive, so-called chemical sensitizer is added to a silver halide emulsion maintained at a high temperature to allow chemical sensitization to start. Further, a sensitizing dye is added to the emulsion to allow spectral sensitization to start. The chemical sensitization and the spectral sensitization may not be separated to two steps. For example, to a silver halide emulsion which has completed the grain formation stage, a sensitizing dye is added, then, sodium thiosulfate and chloroauric acid are further added thereto to perform chemical sensitization, as described in Example 1 of JP-A 5-80445.
One feature of the silver halide emulsion used in the invention is that after the start of chemical sensitization, a sensitizing dye having a &lgr;max of 730 nm or more is added. Before adding the dye, various specified compound(s) are added and characteristic values of the emulsion are adjusted to a specified region. According the invention, a silver halide emulsion with a high sensitivity can be obtained without causing an increase of
Okuyama Masato
Tanaka Shigeo
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Konica Corporation
Letscher Geraldine
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