Photothermographic element

Details Photothermographic element Photothermographic element

1999-04-28

2001-12-18

Chea, Thorl (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Radiation sensitive product

Silver compound sensitizer containing

C430S264000, C430S531000, C430S607000, C430S613000, C430S614000, C430S615000

Reexamination Certificate

active

06331386

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 for use in a photomechanical process and capable of forming images with a high maximum density (Dmax).
BACKGROUND OF THE INVENTION
One well-known method for the exposure of photographic photosensitive elements is an image forming method of the scanner system comprising the steps of scanning an original to produce image signals, subjecting a photographic silver halide photosensitive element to exposure in accordance with the image signals, and forming a negative or positive image corresponding to the image of the original.
There is a desire to have a procedure of providing outputs of a scanner to a film and directly printing on a printing plate without a transfer step as well as a scanner photosensitive element having an ultrahigh contrast and high Dmax with respect to a scanner light source having a soft beam profile. It is well known to utilize the nucleation infectious development using hydrazine derivatives.
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 wet 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.
Photothermographic elements of this type are well known in the art. In most of these elements, photosensitive layers are formed by applying coating solutions based on organic solvents such as toluene, methyl ethyl ketone (MEK) and methanol, followed by drying.
It was also contemplated to form photosensitive layers using coating solutions based on water. Such photosensitive layers are sometimes referred to as “aqueous photosensitive layers,” hereinafter. For example, JP-A 52626/1974 and 116144/1978 disclose the use of gelatin as the binder. JP-A 151138/1975 discloses polyvinyl alcohol as the binder. Further, JP-A 61747/1985 discloses a combined use of gelatin and polyvinyl alcohol. Besides, JP-A 28737/1983 discloses a photosensitive layer containing water-soluble polyvinyl acetal as the binder.
EP 762,196 and JP-A 90550/1997 disclose that photothermographic image-recording elements exhibit high-contrast photographic properties when photosensitive silver halide grains contain metal ions or metal complex ions belonging to Group VII or VIII (Group 7 to 10) in the Periodic Table and the photothermographic elements contain hydrazine derivatives.
It is known for photothermographic elements that the use of hydrazine derivatives achieves sufficient properties including high contrast and high Dmax for use in the photomechanical process. On the other hand, the use of hydrazine derivatives has serious drawbacks in practical use including a decline of Dmax during long-term storage and an increase of Dmin (minimum density) upon printing to presensitized (PS) plates.
SUMMARY OF THE INVENTION
Therefore, an object of the invention is to provide a photothermographic element suitable for use in a photomechanical process and exhibiting excellent properties including a high contrast, long-term storage stability, and no increase of Dmin upon printing to PS plates.
According to the invention, there is provided a photothermographic element comprising a non-photosensitive organic silver salt, a photosensitive silver halide formed independent of the non-photosensitive organic silver salt, and a binder on a support. A polymer latex constitutes at least 50% by weight of the binder in an image forming layer on one surface of the support containing the photosensitive silver halide. The image forming layer has been formed by applying a coating solution in which at least 60% by weight of a solvent is water. The image forming layer or another layer on the one surface of the support contains at least one compound selected from compounds of the following formulae (A) and (B) and has been formed by applying a coating solution having added thereto a water dispersion of the compound. formula (A)
In formula (A), Z
1
is a group of non-metallic atoms completing a 5- to 7-membered cyclic structure, Y
1
is —C(═O)— or —SO
2
—, X
1
is —O.(1/k)M or —S.(1/k)M, M is a cation, and k is the valence of M.
In formula (B), Z
2
is a group of non-metallic atoms completing a 5- to 7-membered cyclic structure, Y
2
is —C(═O)— or —SO
2
—, X
2
is —O.(1/k)M or —S.(1/k)M, M is a cation, k is the valence of M, and Y
3
is hydrogen or a substituent.
Preferably, the compound of formula (A) has at least 6 carbon atoms in total and the compound of formula (B) has at least 12 carbon atoms in total. Preferably, the compound of formula (A) or (B) has been added to the coating solution as a water dispersion free of a surfactant.
The preferred polymer latex is a latex of a polymer having a glass transition temperature of −30° C. to 40° C.


REFERENCES:
patent: 4123274 (1978-10-01), Knight et al.
patent: 5545515 (1996-08-01), Murray et al.
patent: 762196A1 (1997-03-01), None
patent: 0897130 (1999-02-01), None
patent: 53116144 (1978-10-01), None
patent: 58 28737 (1983-02-01), None
patent: 60 61747 (1985-04-01), None

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