Photothermographic element

Details Photothermographic element Photothermographic element

1999-04-01

2001-10-09

Chea, Thorl (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Radiation sensitive product

Silver compound sensitizer containing

C430S510000, C430S513000, C430S517000, C430S603000, C430S955000

Reexamination Certificate

active

06300053

ABSTRACT:

This invention relates to a photothermographic element and more particularly, to a photothermographic element which is improved in dye decolorization and produces water-resistant images.
BACKGROUND OF THE INVENTION
Photothermographic elements are known from the past and described, 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. The photothermographic elements generally have photosensitive layers which contain a reducible silver salt (e.g., organic silver salt), a catalytic amount of a photocatalyst (e.g., silver halide), a reducing agent, and optionally a toner for controlling the tone of silver, typically dispersed in an binder matrix. After imagewise exposure, photothermographic elements are heated at an elevated temperature (e.g., 80° C. or higher), whereby redox reaction takes place between the reducible silver salt (functioning as an oxidizing agent) and the reducing agent to form a black silver image. This redox reaction is promoted by the catalysis of a latent image of silver halide produced by exposure. The black silver image is thus formed in the exposed area.
Thermography or heat development has the advantage of easy and quick processing because it eliminates a need for processing solution as used in the wet development process. However, the image forming process by wet development is still the mainstream in the photographic art. This is because the thermographic process yet leaves an outstanding problem which never occurs with the wet development process.
It is a common practice to add dyes to photographic photosensitive materials as a filter or for the anti-halation or anti-irradiation purpose. Specifically, the dye is added to a non-photosensitive layer and exerts its function upon imagewise exposure. If the dye having exerted its function is left in the photographic photosensitive material, the image formed therein can be colored with that dye. Therefore, the dye must be removed from the photographic photosensitive material during development. In the wet development process, the dye can be readily removed from the photographic photosensitive material into the processing solution. By contrast, the thermographic process is very difficult or substantially impossible to remove the dye.
A simple and quick development process is required for the modern photographic art, especially in the fields of medical photography and printing photography. Improvements in the wet development process, however, have approached the plateau. For this reason and others, engineers in the fields of medical photography and printing photography now pay attention to the thermographic image formation.
With respect to the problem of difficult removal of dyes in the thermographic process, it was proposed to decolorize the dye by the heat applied during heat development. For example, U.S. Pat. No. 5,135,842 discloses that polymethine dyes of a specific structure can be decolorized by heating. U.S. Pat. Nos. 5,314,795, 5,324,627, and 5,384,237 disclose that polymethine dyes are heated for decolorization using carbanion generators.
Some of the prior art methods, however, are short in decolorization, failing to reach a sufficient degree of transparency within the desired time. Some dyes are quickly bleachable, but a problem is left with respect to the water resistance of processed images. When the processed elements are incidentally contacted with water droplets or stored in high-humidity conditions, a loss of transparency occurs, resulting in alterations.
SUMMARY OF THE INVENTION
Therefore, an object of the invention is to provide a photothermographic element having an increased rate of decolorization of a dye by the heat applied during heat development and the improved water resistance of a coating.
According to a first aspect of the invention, there is provided a photothermographic element comprising a support having a first surface and a second surface, at least one photosensitive layer on the first surface of the support, and a first non-photosensitive layer on the first or second surface of the support. The first non-photosensitive layer contains (1) a base-bleachable dye or a salt thereof and (2) a binder. The first non-photosensitive layer or a second non-photosensitive layer disposed adjacent thereto contains (3) a base precursor and (4) a melting point depressant which, when mixed with the base precursor, acts to depress the melting point by at least 3° C., or a mixture of melting point depressants which, when mixed with the base precursor, cooperate to depress the melting point by at least 3° C.
Preferably, a co-dispersion of the base precursor (3) and the melting point depressant or the melting point depressant mixture (4) is contained in the non-photo-sensitive layer. Typically the photosensitive layer contains a photosensitive silver halide, an organic silver salt, a reducing agent, and a binder. The first and second non-photosensitive layers are preferably disposed on the second surface of the support.
According to a second aspect of the invention, there is provided a photothermographic element comprising a support having a first surface and a second surface, at least one photosensitive layer on the first surface of the support, and a non-photosensitive layer on the first or second surface of the support. The non-photosensitive layer contains a compound of the following formula (I):
wherein R
01
and R
02
independently represent an aliphatic, aromatic or heterocyclic group which is free of a carboxyl group and carboxyl group salt.
Typically, the photosensitive layer contains a photo-sensitive silver halide, an organic silver salt, a reducing agent, and a binder. Preferably, the non-photosensitive layer or another non-photosensitive layer disposed adjacent thereto contains a base-bleachable dye or a salt thereof and a base precursor. Preferably, a co-dispersion of the base precursor and the compound of formula (I) is contained in the non-photosensitive layer. The non-photosensitive layer is preferably disposed on the second surface of the support.
In the photothermographic elements of the first and second aspects, the base-bleachable dye or salt thereof is preferably a cyanine dye or salt thereof having the following formula (II):
wherein R
1
represents an electron attractive group; R
2
represents hydrogen or an aliphatic or aromatic group; R
3
and R
4
independently represent hydrogen, a halogen atom, an aliphatic group, an aromatic group, —NR
6
R
7
, —OR
6
, or —SR
7
; R
6
and R
7
independently represent hydrogen or an aliphatic or aromatic group; R
5
represents an aliphatic group; each of L
1
, L
2
, and L
3
independently represents a substituted or unsubstituted methine group in which substituents on the methine group may bond together to form an unsaturated aliphatic ring or an unsaturated heterocyclic ring; each of Z
1
and Z
2
independently represents a group of atoms that form a 5- or 6-membered nitrogenous heterocyclic ring which may have an aromatic ring fused thereto, and the nitrogenous heterocyclic ring or the ring fused thereto may have a substituent; and m represents 0, 1, 2 or 3.
Also preferably, the base precursor is a diacidic base precursor.


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patent: 5314795 (1994-05-01), Helland et al.
patent: 5324627 (1994-06-01), Stevenson et al.
patent: 5384237 (1995-01-01), Stevenson et al.
patent: 5817598 (1998-10-01), Defieuw et al.

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