Thermographic recording element

Details Thermographic recording element Thermographic recording element

1998-10-16

2001-08-21

Chea, Thorl (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Radiation sensitive product

Silver compound sensitizer containing

C430S264000, C430S611000, C430S613000, C430S614000, C430S619000

Reexamination Certificate

active

06277553

ABSTRACT:

This invention relates to a thermographic recording element and more particularly, to a thermographic recording element suitable for the manufacture of graphic 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 an image.
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 thermographic photosensitive 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 thermographic photosensitive 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 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 sometimes black pepper develops.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a thermographic recording element having a fully high contrast, least black pepper, high sensitivity and high Dmax. 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.
The invention provides a thermographic recording element comprising at least one image forming layer and containing an organic silver salt, a reducing agent, and at least one compound of the following general formula (A).
In formula (A), R
1
and R
2
are independently hydrogen or monovalent substituents, X
1
is an oxygen, sulfur or nitrogen atom, Y
1
is a group represented by —C(═O)—, —C(═S)—, —SO—, —SO
2
—, —C(═NR
3
)— or —(R
4
)C═N—, R
3
and R
4
are independently hydrogen or substituents, Zis a group of non-metallic atoms forming a 5- to 7-membered ring containing X
1
and Y
1
, with the proviso that R
1
and R
2
do not form a cyclic structure together.
In one preferred embodiment, the thermographic recording element further contains a hydrazine derivative of the following general formula (I).
In formula (I) , R
100
is hydrogen or a block group, R
200
is an aliphatic, aromatic or heterocyclic group, G
1
is —C(═O)—, —C(═O)C(═O)—, —C(═S)—, —SO
2
—, —SO—, —PO(R
300
)— or iminomethylene group, R
300
is selected from the same range as defined for R
100
and may be different from R
100
, A
1
and A
2
are independently hydrogen, alkylsulfonyl, arylsulfonyl or acyl groups, at least one of A
1
and A
2
is hydrogen, letter m
1
is equal to 0 or 1, with the proviso that R
100
is an aliphatic, aromatic or heterocyclic group when m
1
is 0.
Also preferably, the thermographic recording element further contains a photosensitive silver halide. The invention then provides a photothermographic recording element.
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 (A) is contained as a nucleating agent in the thermographic recording element for achieving a fully satisfactory high contrast and restraining occurrence of black pepper. The containment of this compound is also effective for achieving a high Dmax and high sensitivity. For producing high contrast images, the concurrent use of a hydrazine derivative nucleating agent is also preferred.
In contrast, acrylonitrile compounds analogous to formula (A) fail to achieve both the effects of contrast enhancement and black pepper restraint.
Now the compounds of formula (A) are described in detail.
In formula (A), X
1
represents an oxygen, sulfur or nitrogen atom. When X
1
is nitrogen, the bond between X
1
and Z
1
may be either a valence bond or a double bond. In the case of a valence bond, the nitrogen atom may have a hydrogen atom or an arbitrary substituent thereon. The substituent is selected from among, for example, alkyl (including aralkyl, cycloalkyl and active methine groups), alkenyl, alkynyl, aryl, heterocyclic, acyl, alkoxycarbonyl, aryloxycarbonyl, carbamoyl, and (alkyl, aryl or heterocyclic) sulfonyl groups. Y
1
is a group represented by —C(═O)—, —C(═S)—, —SO—, —SO
2
—, —C(═NR
3
)— or —(R
4
)C═N—.
Z
1
is a group of non-metallic atoms forming a 5-, 6- or 7-membered ring containing X
1
and Y
1
. The ring-forming atom group is a group of two to four atoms other than metal atoms wherein the atoms may be connected through a valence bond or a double bond and the atoms each may have thereon a hydrogen atom or arbitrary substituent. The substituent is selected from among, for example, alkyl, aryl, heterocyclic, alkoxy, alkylthio, acyl, amino, and alkenyl groups. When Z
1
forms a 5- to 7-membered ring with X
1
and Y
1
, the ring is a saturated or unsaturated heterocycle which may be monocyclic or have a fused ring. When yis a group represented by —C(═NR
3
)— or —(R
4
) C═N—, R
3
or R
4
can bond with t

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