Photothermographic element

Details Photothermographic element Photothermographic element

1999-05-14

2001-08-14

Chea, Thorl (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Radiation sensitive product

Silver compound sensitizer containing

C430S531000, C430S600000, C430S607000

Reexamination Certificate

active

06274302

ABSTRACT:

This invention relates to a photothermographic element, and more particularly, to a photothermographic element suitable for use in a photomechanical process and especially adapted for scanners and image setters. More specifically, it relates to such a photothermographic element exhibiting an ultrahigh contrast, very low fog (Dmin), high activity, and storage stability.
BACKGROUND OF THE INVENTION
There are known a number of photosensitive elements having a photosensitive layer on a support wherein images are formed by imagewise exposure. Among these, a technique of forming images through heat development is known as a system capable of simplifying image forming means and contributing to the environmental protection.
From the contemporary standpoints of environmental protection and space saving, it is strongly desired in the photomechanical process field to reduce the quantity of spent solution. Needed in this regard is a technology relating to photothermographic elements for use in photomechanical process which can be effectively exposed by means of laser scanners or laser image setters and produce distinct black images having a high resolution and sharpness. These photothermographic elements offer to the customer a simple thermographic system that eliminates a need for solution type chemical agents and is not detrimental to the environment.
The technology of forming images through heat development is 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 elements generally contain a reducible non-photosensitive silver source (e.g., organic silver salt), a catalytic amount of a photocatalyst (e.g., silver halide), and a reducing agent for silver, typically dispersed in an organic binder matrix. Photothermographic elements 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 reducible silver salt in exposed regions provides black images in contrast to unexposed regions, forming an image.
One of the outstanding problems associated with photothermographic elements is fog. A number of studies have been made to reduce the fog of thermographic silver halide photosensitive materials. A variety of antifoggants are disclosed in a number of patents. For example, U.S. Pat. No. 3,589,903 discloses mercury salts; U.S. Pat. No. 4,152,160 discloses carboxylic acids such as benzoic acid and phthalic acid; U.S. Pat. No. 4,784,939 discloses benzoylbenzoic acids; U.S. Pat. No. 4,569,906 discloses indane and tetraphosphorus carboxylic acids; U.S. Pat. No. 4,820,617 discloses dicarboxylic acids; U.S. Pat. No. 4,626,500 discloses hetero-aromatic carboxylic acids; U.S. Pat. Nos. 4,546,075, 4,756,999, 4,452,885, 3,874,946, and 3,955,982 disclose halogenated compounds; U.S. Pat. No. 5,028,523 discloses halogen molecules or halogen atoms associated with heterocyclic rings; U.S. Pat. No. 4,103,312 and GB 1,502,670 discloses palladium compounds; U.S. Pat. No. 4,128,428 discloses iron group metals; U.S. Pat. Nos. 4,123,374, 4,129,557 and 4,125,430 disclose substituted triazoles; U.S. Pat. Nos. 4,213,784, 4,245,033 and JP-A 26019/1976 disclose sulfur compounds; U.S. Pat. No. 4,002,479 discloses thiouracil compounds, JP-A 123331/1975 discloses sulfinic acids; U.S. Pat. Nos. 4,125,403, 4,152,160, and 4,307,187 disclose metal salts of thiosulfonic acids; JP-A 20923/1978 and 19825/1978 disclose mixtures of a metal salt of thiosulfonic acid and sulfinic acid; JP-B 50810/1987, JP-A 209797/1995 and 43760/1997 disclose thiosulfonates; and JP-A 42529/1976 and JP-B 37368/1988 disclose disulfides.
These compounds, however, have drawbacks. Some are unsatisfactory in antifogging ability, some cause a drop of maximum density (Dmax) when added in large amounts, and some exacerbate image storage stability after development. There is a desire to have a novel antifoggant.
Additionally, JP-A 26019/1976, 207244/1982, 207140/1985 and 251838/1990, U.S. Pat. Nos. 2,910,377 and 3,074,809 disclose salicylic acid and derivatives thereof, but refer nowhere to their effect in ultrahigh contrast dry silver systems.
SUMMARY OF THE INVENTION
An object of the invention is to provide a photothermographic element having a very low fog or Dmin, and especially, a photothermographic element having an ultrahigh contrast and low Dmin enough for use in a photomechanical process.
Another object of the invention is to provide a photothermographic element exhibiting a high activity, and storage stability suitable for use in a photomechanical process, especially with scanners and image setters.
The present invention provides a photothermographic element comprising on at least one surface of a support, (a) a photosensitive silver halide, (b) a reducible silver salt, (c) a reducing agent, (d) an ultrahigh contrast-providing agent, (e) a binder, and (f) at least one antifoggant of the following formula (A).
Herein M represents a hydrogen atom or a cation with a valence k, R represents a substituent, n is an integer of 1 to 4, with the proviso that plural R groups may be the same or different when n is at least 2, and k is an integer of at least 1, with the proviso that k=1 when M represents a hydrogen atom. M preferably represents a heavy metal ion.
The photothermographic element may further comprise (g) at least one compound selected from among phosphoric acid and salts thereof.
The ultrahigh contrast-providing agent (d) is preferably a substituted alkene derivative of the following formula (1), a substituted isoxazole derivative of the following formula (2), an acetal compound having the following formula (3), or a hydrazine derivative.
In formula (1), R
1
, R
2
, and R
3
independently represent hydrogen or substituents, and Z represents an electron attractive group or silyl group, and at least one pair of R
1
and Z, R
2
and R
3
, R
1
and R
2
, and R
3
and Z, taken together, may form a cyclic structure; in formula (2), R
4
represents a substituent; in formula (3), X and Y independently represent hydrogen or substituents, A and B independently represent alkoxy, alkylthio, alkylamino, aryloxy, arylthio, anilino, heterocyclic oxy, heterocyclic thio, or heterocyclic amino groups, and X and Y, and A and B, taken together, may form a cyclic structure.
In another preferred embodiment, the photothermographic element has on the at least one surface of the support a photosensitive layer containing at least components (a), (b), and (d), wherein the reducible silver salt (b) is a non-photosensitive organic silver salt, and a latex of a polymer having a glass transition temperature of up to 40° C. is used as a main binder (d) in the photosensitive layer. The photosensitive layer has been formed by preforming the photosensitive silver halide independent of the non-photosensitive organic silver salt, adding the preformed photosensitive silver halide and the binder to a solvent to form a coating solution, at least 60% by weight of the solvent being water, and applying the coating solution.


REFERENCES:
patent: 4847187 (1989-07-01), Ono et al.
patent: 5152160 (1992-10-01), Ikienoue et al.
patent: 5545515 (1996-08-01), Murray et al.
patent: 5705324 (1998-01-01), Murray
patent: 5891616 (1999-04-01), Gilliams et al.
patent: 57-207244 (1982-12-01), None
patent: 2-251838 (1990-10-01), None

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