Radiation imagery chemistry: process – composition – or product th – Thermographic process – Heat applied after imaging
Reexamination Certificate
2001-01-17
2002-11-05
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Thermographic process
Heat applied after imaging
C430S528000, C430S529000, C430S607000, C430S611000, C430S613000, C430S614000, C430S619000
Reexamination Certificate
active
06475710
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to thermally developable photothermographic materials and in particular to photothermographic materials having higher contrast and exhibiting enhanced uniformity in image density, specifically, enhanced uniformity in solid image density in the middle tone and an image forming process by the use thereof.
BACKGROUND OF THE INVENTION
There are known a number of photosensitive materials comprising a support having thereon a photosensitive layer, which forms images upon imagewise exposure. Of these, techniques of forming images through thermal development are cited as a system suitable for environmental preservation and yet simplifying the image forming means.
Thermally developable photothermographic materials are disclosed, for example, in D. Morgan and B. Shely, U.S. Pat. Nos. 3,152,904 and 3,457,075, and D. H. Klosterboer, “Thermally Processed Silver Systems” (Imaging Processes and Materials, Neblette, 8th Edition, edited by J. M. Sturge, V. Walworth, and A. Shepp, page 2, 1969), etc. Such photothermographic materials contain a reducible light-insensitive silver source (such as organic silver salts), a catalytically active amount of photocatalyst (such as silver halide) and a reducing agent, which are dispersed in a binder matrix. Such photothermographic materials are stable at ordinary temperature and forms silver upon heating, after exposure, at a relatively high temperature (e.g., 80° C. or higher) through an oxidation-reduction reaction between the reducible silver source (which functions as an oxidizing agent) and the reducing agent. The oxidation-reduction reaction is accelerated by the catalytic action of a latent image produced by exposure. Silver formed through reaction of the reducible silver salt in exposed areas produces a black image, which contrasts with non-exposed areas, leading to image formation.
Such image forming processes are employed for medical diagnostic imaging and graphic art materials. In a medical diagnostic imaging system, it is desired to be efficiently exposed using a laser image setter or a laser imager. However, if a photothermographic material is not relatively highly sensitive and high in contrast, the use of high power laser is dispensable, leading to disadvantages in cost. Of various lasers having different wavelengths, lasers having an oscillating wavelength of 600 nm or more are preferred in terms of cost and power, necessitating spectral sensitizers in the panchromatic or infrared region and supersensitizers. With regard to the infrared-supersensitizer used in a photothermographic system, JP-A No. 2-4241 (hereinafter, the term, JP-A refers to unexamined and published Japanese patent Application) discloses aminopolycarboxylic acid derivatives and JP-A Nos. 4-182639 and 5-341432 disclose an aromatic heterocyclic mercapto-compound and an aromatic heterocyclic disulfide compound. However, there were problems in that supersenstizing effects by the use of the aminopolycarboxylic acid derivatives were relatively low, leading to low sensitivity, and in addition, the use of the aromatic heterocyclic mercapto-compound or aromatic heterocyclic disulfide compound resulted in reduction in sensitivity after storage under high humidity.
There were proposed techniques for enhancing such storage stability, including cyclic carbonyl compounds described in JP-A No. 7-146527 and disulfide compounds having a specific structure described in JP-A Nos. 10-90823, 10-90824, 10-90825, 10-319534 and 11-4489. However, it was proved that such techniques were insufficient in the supersensitization effect and storage performance, and a further improvement is still sought.
European Patent No. 761,196 and JP-A 9-90550 both disclose light-sensitive silver halide grains used in a photothermographic image recording material which occlude metal ions of the 7th to 11th groups of the periodical table or their complex ions and incorporation of hydrazine derivatives into the photothermographic material, thereby leading to desired photographic characteristics such as high contrast. As is known in the photographic art, the use of hydrazine derivatives advantageously leads to enhanced performance such as relatively high contrast or high density, which is suitable for use in printing plate making. However, there were serious disadvantages in practical use in that it also easily produced so-called black spots which were commonly shown as sand-like fogging in unexposed areas, and unevenness in image density caused by slight fluctuations in developing temperature was rather marked.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a photothermographic material having a relatively high contrast and exhibiting enhanced uniformity in image density, and particularly, uniformity in solid image density in the middle tone region.
It is another object of the invention to provide a photothermographic material exhibiting enhanced sensitivity, high image quality and superior storage stability, a preparation method thereof and an image forming method thereby.
It is another object of the invention to provide a photothermographic material using a red- to infrared-sensitive silver halide emulsion exhibiting little variation in sensitivity caused by variation in exposure conditions.
The above object of the invention can be accomplished by the following constitution:
1. A photothermographic material comprising a light-sensitive silver halide, an organic silver salt, a reducing agent, a thiuronium salt and a binder, wherein the photothermographic material comprises a compound represented by the following formula (1):
wherein R represents a univalent substituent; m is an integer of 1 to 4 and when m is 2 or more, plural Rs may be the same with or different from each other, or adjacent Rs may combine with each other to form an aliphatic ring, aromatic ring or heterocyclic ring; R
1
and R
2
each represent a hydrogen atom or a univalent substituent;
2. A photothermographic material comprising a light-sensitive silver halide, an organic silver salt, a reducing agent, a thiuronium salt and a binder, wherein the photothermographic material comprises a compound represented by the following formula (2):
wherein Z represents a non-metallic atom group necessary to form an aromatic heterocyclic 5-membered ring; R
1
and R
2
each represent a hydrogen atom or a univalent substituent;
3. A photothermographic material comprising a light-sensitive silver halide, an organic silver salt, a reducing agent, a thiuronium salt and a binder, wherein the photothermographic material comprises a compound represented by the following formula (3):
wherein T represents a univalent substituent; k is an integer of 1 to 4 and when k is 2 or more, T may be the same with or different from each other.
DETAILED DESCRIPTION OF THE INVENTION
The photothermographic material according to this invention, comprising a light-sensitive silver halide, an organic silver salt, a reducing agent, a thiuronium salt and a binder, wherein the photothermographic material further comprises a compound represented by the following formula (1), (2) or (3). Thereby is obtained a photothermographic material having a relatively high contrast and exhibiting enhanced uniformity in image density, particularly, uniformity in solid image density in the middle tone region. On the contrary, the use of a compound other than compounds of formulas (1), (2) and (3) tends to lead to occurrence of process non-uniformity, a lowered maximum density (Dmax) and reduced high-contrast.
Formula (1) will be described. R is a univalent substituent and preferred R is an alkyl group having 1 to 8 carbon atoms, more preferably 1 to 5 carbon atoms, such as methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, tert-butyl, tert-amyl and n-octyl. Further, m is an integer of 1 to 4 and when m is 2 or more, plural Rs may be the same with or different from each other. When Rs are adjacent, the Rs may combine with each other to form an aliphatic ring, aromatic ring or heterocyclic ring. R
1
and
Chigusa Keiko
Kashiwagi Hiroshi
Kudo Shinji
Bierman, Muserlian and Lucas
Chea Thorl
Konica Corporation
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