Radiation imagery chemistry: process – composition – or product th – Retrieving image made using radiation imagery
Reexamination Certificate
2000-11-20
2002-10-29
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Retrieving image made using radiation imagery
C430S404000, C430S443000, C430S448000, C430S496000, C430S502000, C430S505000, C430S380000, C430S566000, C430S619000, C430S955000, C430S959000, C430S964000
Reexamination Certificate
active
06472111
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a color photothermographic element containing a mixture of blocked developing agents. In particular, a mixture of at least two blocked developers having different onset temperatures can be used to balance the image formed in different imaging layers during thermal development, for example imaging layers in different color units.
BACKGROUND OF THE INVENTION
In conventional color photography, films containing light-sensitive silver halide are employed in hand-held cameras. Upon exposure, the film carries a latent image that is only revealed after suitable processing. These elements have historically been processed by treating the camera-exposed film with at least a developing solution having a developing agent that acts to form an image in cooperation with components in the film. Developing agents commonly used are reducing agents, for example, p-aminophenols or p-phenylenediamines.
Typically, developing agents (also herein referred to as developers) present in developer solutions are brought into reactive association with exposed photographic film elements at the time of processing. Segregation of the developer and the film element has been necessary because the incorporation of developers directly into sensitized photographic elements can lead to desensitization of the silver halide emulsion and undesirable fog. Considerable effort, however, has been directed to producing effective blocked developing agents (also referred to herein as blocked developers) that might be introduced into silver halide emulsion elements without deleterious desensitization or fog effects. Accordingly, blocked developing agents have been sought that would unblock under preselected conditions of development after which such developing agents would be free to participate in image-forming (dye or silver metal forming) reactions.
U.S. Pat. No. 3,342,599 to Reeves discloses the use of Schiff-base developer precursors. Schleigh and Faul, in a
Research Disclosure
(129 (1975) pp. 27-30), describes the quaternary blocking of color developers and the acetamido blocking of p-phenylenediamines. (All Research Disclosures referenced herein are published by Kenneth Mason Publications, Ltd., Dudley Annex, 12a North Street, Emsworth, Hampshire P010 7DQ, ENGLAND.) Subsequently, U.S. Pat. No. 4,157,915 to Hamaoka et al. and U.S. Pat. No. 4,060,418 to Waxman and Mourning describe the preparation and use of blocked p-phenylenediamines in an image-receiving sheet for color diffusion transfer. In addition to the aforementioned U.S. Pat. No. 4,157,915, blocked developing agents involving &bgr;-elimination reactions during unblocking have been disclosed in European Patent Application 393523 and kokais 57076453; 2131253; and 63123046, the latter specifically in the context of photothermographic elements.
All of these approaches have failed in practical product applications because of one or more of the following problems: desensitization of sensitized silver halide; unacceptably slow unblocking kinetics; instability of blocked developer yielding increased fog and/or decreased Dmax after storage, lack of simple methods for releasing the blocked developer, inadequate or poor image formation, and other problems. Especially in the area of photothermographic color films, other potential problems include poor discrimination and poor dye-forming activity.
Recent developments in blocking and switching chemistry have led to blocked developing agents, including p-phenylenediamines, that perform relatively well. In particular, compounds having “&bgr;-ketoester” type blocking groups (strictly, &bgr;-ketoacyl blocking groups) are described in U.S. Pat. No. 5,019,492. With the advent of the &bgr;-ketoester blocking chemistry, it has become possible to incorporate p-phenylenediamine developers in film systems in a form from which they only become active when required for development. The &bgr;-ketoacyl blocked developers are released from the film layers in which they are incorporated by an alkaline developing solution containing a dinucleophile, for example hydroxylamine.
It is an object of the invention to obtain improved color photothermographic imaging elements and methods for their development employing incorporated blocked developing agents, also referred to herein as blocked developers. With respect to color photothermographic imaging elements, it is desirable to employ a blocked developer that is stable until development yet can rapidly and easily develop a high quality image once processing has been initiated by heating the element or by applying to the element a processing solution during or after heating, such as a solution of a base or acid or pure water. A completely dry process or an apparently dry process (for example, in which the volume of aqueous solutions is small enough to be applied by a laminate) is most desirable and, in fact, the eliminating the application of all or most solutions and photochemical processing chemicals is one of the main advantages of a dry or apparently dry photothermographic system. The existence of such a process would allow for very rapidly processed films that can be processed simply and efficiently in photoprocessing kiosks. Such kiosks, with increased numbers and accessibility, could ultimately allow for, relatively speaking, anytime and anywhere silver-halide film development.
One of the factors to be considered, with respect to a blocked developer in a color photothermographic element, is the onset temperature of the blocked developer, that is, the temperature at which the compound becomes substantially unblocked or activated, which is generally a measure or indication of the temperature at which the development process will need to be performed. In generally, other factors being equal, the higher the onset temperature, the higher the process temperature. A process at lower temperatures generally has less side reactions and is less expensive to accomplish. There is less potential deformation of the film base which can adversely affect image quality. Also, higher temperatures tend to undesirably decompose components in the photographic element and release volatile vapors.
Another factor to be considered, with respect to a blocked developer in a photothermographic element, is the discrimination of the image, generally defined as the difference of between Dmin and Dmax at the process temperature. Since the discrimination of an image, using a blocked developer, will generally vary with process temperature, it is usually desirable to process the film at the temperature of peak discrimination (in the photographic element). It is further desirable that the film have a high peak discrimination. Discrimination of a film can be affected by a number of factors, including photographic emulsion type and finish, the kind and amount of couple, the thermal solvent, and other factors. However, a key factor is the blocked developing agent incorporated in the photothermographic film.
A problem with a blocked developer is that discrimination may be poor if the blocked developer unblocks to quickly or does not unblock quickly enough. It is advantageous to appropriately balance the reactivity of the developing agent, during developing, with the rate of release of the developing agent from the blocked developing agent. If the reactivity of developing agent with the coupling agent (or “coupler”) to form the image dye is too much less than the rate of release of the developing agent, at a particular temperature, then there is the opportunity for side reactions to occur which may decrease the discrimination. (usually by increasing fog) and consequently decrease image quality. On the other hand, if the reactivity of the developing agent with the coupling agent is too much greater than the rate of release of the developing agent, at the temperature of development, then there may not be enough developing agent for image formation to occur which may also decrease discrimination (this time, usually by decreasing Dmax) which again will consequently decrease image quality
Levy David H.
Reynolds James H.
Southby David T.
Chea Thorl
Eastmank Kodak Company
Konkol Chris P.
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