Thermographic recording elements

Details Thermographic recording elements Thermographic recording elements

1998-11-17

2001-01-23

Chea, Thorl (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Radiation sensitive product

Silver compound sensitizer containing

C430S531000, C430S598000, C430S613000, C430S617000, C430S620000

Reexamination Certificate

active

06177240

ABSTRACT:

This invention relates to thermographic recording elements and more particularly, to thermographic recording elements suitable for the manufacture of printing plates.
BACKGROUND OF THE INVENTION
Photothermographic materials which are processed by a thermographic process to form photographic images are disclosed, for example, in U.S. Pat. Nos. 3,152,904 and 3,457,075, D. Morgan and B. Shely, “Thermally Processed Silver Systems” in “Imaging Processes and Materials,” Neblette, 8th Ed., Sturge, V. Walworth and A. Shepp Ed., page 2, 1969.
These photothermographic materials generally contain a reducible silver source (e.g., organic silver salt), a catalytic amount of a photocatalyst (e.g., silver halide), a toner for controlling the tone of silver, and a reducing agent, typically dispersed in a binder matrix. Photothermographic materials are stable at room temperature. When they are heated at an elevated temperature (e.g., 80° C. or higher) after exposure, redox reaction takes place between the reducible silver source (functioning as an oxidizing agent) and the reducing agent to form silver. This redox reaction is promoted by the catalysis of a latent image produced by exposure. Silver formed by reaction of the organic silver salt in exposed regions provides black images in contrast to unexposed regions, forming images.
Such photothermographic materials have been used as microphotographic and medical photosensitive materials. However, only a few have been used as a graphic printing photosensitive material because the image quality is poor for the printing purpose as demonstrated by low maximum density (Dmax) and soft gradation.
With the recent advance of lasers and light-emitting diodes, scanners and image setters having an oscillation wavelength of 600 to 800 nm find widespread use. There is a strong desire to have a high contrast photosensitive material which has so high sensitivity and Dmax that it may comply with such output devices.
From the contemporary standpoints of environmental protection and space saving, it is strongly desired in the graphic printing field to reduce the quantity of spent solution. Needed in this regard is a technology relating to photothermographic materials for use in the graphic printing field which can be effectively exposed by means of laser image setters and produce clear black images having a high resolution and sharpness. These photothermographic materials offer to the customer a simple thermographic system which eliminates a need for solution type chemical agents and is not detrimental to the environment.
U.S. Pat. No. 3,667,958 discloses that a photothermographic element comprising a polyhydroxybenzene combined with a hydroxylamine, reductone or hydrazine has high image quality discrimination and resolution. This combination of reducing agents, however, was found to incur an increase of fog.
For producing a thermographic recording element having high Dmax and high contrast, it is effective to add to the element the hydrazine derivatives described in U.S. Pat. No. 5,496,695. Although this results in a thermographic recording element having high Dmax and high contrast, all of sensitivity, contrast, Dmax, Dmin, gradation reproducibility, and storage stability of compounds are not fully satisfied.
Improvements in contrast and storage stability of compounds are achieved by using the hydrazine derivatives described in EP 762196A1, but the fully satisfactory level has not been reached.
Further, U.S. Pat. Nos. 5,545,515 and 5,635,339 disclose the use of acrylonitriles as the co-developer. With these acrylonitrile compounds, a fully satisfactory high contrast is not achieved and the photographic properties largely depend on the developing time.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a thermographic recording element having high sensitivity, high Dmax, and high contrast, and improved in developing condition dependency in that photographic properties vary little with developing conditions such as developing time and temperature. Another object of the present invention is to provide a recording element for use in the manufacture of graphic printing plates which forms an image of quality and can be processed in a fully dry basis without a need for wet processing. A further object of the present invention is to provide a photothermographic element having such improved properties.
According to the invention, there is provided a thermographic recording element having at least one image forming layer and comprising an organic silver salt, a reducing agent, and a compound of the following formula (1).
In formula (1), Z is an aromatic, heterocyclic or amino group; M is a hydrogen atom, silver atom, alkali metal or alkaline earth metal; m is an integer of 1 or 2, m is 1 when M is a monovalent atom, and 2 when M is a divalent atom, n is an integer of 0 or 1; and each of R
1
and R
2
, which may be the same or different, is hydrogen or a substituent or may form a cyclic structure with Z.
In one preferred embodiment wherein a photosensitive silver halide is further contained, a photothermographic recording element is provided.
DETAILED DESCRIPTION OF THE INVENTION
The thermographic recording element of the invention has at least one image forming layer and contains an organic silver salt and a reducing agent. Preferably it further contains a photosensitive silver halide, providing a photothermographic recording element. More preferably, it is a high contrast photothermographic recording element suitable as a printing plate.
According to the invention, a compound of formula (1) is contained as a nucleating agent in the thermographic recording element for achieving a fully satisfactory high contrast and minimizing the variation of photographic properties with developing conditions such as developing time and temperature, thus providing consistent photographic properties independent of developing conditions. The containment of this compound is also effective for achieving a high Dmax and high sensitivity. In contrast, the sole use of different compounds outside the scope of formula (1), for example, hydrazine derivatives fail to achieve both the effects of contrast enhancement and restrained developing condition dependency.
Now the compounds of formula (1) are described in detail.
In formula (1), Z represents aromatic, heterocyclic or amino groups. The aromatic groups represented by Z include monocyclic and fused aryl groups, for example, phenyl, naphthyl and anthryl groups derived from benzene, naphthalene, and anthracene rings. The heterocyclic groups represented by Z include monocyclic or fused ring, saturated or unsaturated, aromatic or non-aromatic heterocyclic groups.
When Z represents aromatic or heterocyclic groups, these groups may be substituted ones. Typical substituents include halogen atoms (e.g., fluorine, chlorine, bromine and iodine atoms), alkyl groups (including aralkyl, cycloalkyl and active methine groups), alkenyl groups, alkynyl groups, aryl groups, heterocyclic groups, quaternized nitrogen atom-containing heterocyclic groups (e.g., pyridinio), acyl groups, alkoxycarbonyl groups, aryloxycarbonyl groups, carbamoyl groups, carboxy groups or salts thereof, formyl groups, sulfonylcarbamoyl groups, acylcarbamoyl groups, sulfamoylcarbamoyl groups, carbazoyl groups, oxalyl groups, oxamoyl groups, oxalo groups, cyano groups, isocyanato groups, isothiocyanato groups, thiocarbamoyl groups, hydroxy groups, alkoxy groups (including groups containing recurring ethylenoxy or propylenoxy units), aryloxy groups, heterocyclic oxy groups, acyloxy groups, (alkoxy or aryloxy)carbonyloxy groups, carbamoyloxy groups, sulfonyloxy groups, amino groups, (alkyl, aryl or heterocyclic) amino groups, N-substituted nitrogenous heterocyclic groups, acylamino groups, sulfonamide groups, ureido groups, thioureido groups, imide groups, (alkoxy or aryloxy)carbonylamino groups, sulfamoylamino groups, semicarbazide groups, thiosemicarbazide groups, hydrazino groups, amidino groups, quaternary ammonio groups, oxamoylamino groups, (alkyl or aryl) sulf

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