Radiation imagery chemistry: process – composition – or product th – Retrieving image made using radiation imagery
Reexamination Certificate
2001-08-27
2002-12-10
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Retrieving image made using radiation imagery
C430S351000, C430S502000, C430S510000, C430S511000, C430S513000, C430S517000, C430S522000, C430S566000, C430S617000, C430S619000, C430S959000, C430S964000
Reexamination Certificate
active
06492076
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to colored, aqueous heat-bleachable compositions that can undergo a change in electromagnetic absorption characteristics upon application of heat. These compositions are useful as antihalation or filter components of photothermnographic elements. In particular, zwitterionic 1-aminopyridinium dyes have been found to provide improved bleaching characteristics in photothermographic elements.
BACKGROUND OF THE INVENTION
Photographic materials usually contain various layers and components, including antihalation or filter layers, overcoats and radiation sensitive layers. The antihalation layer of an imaging element helps to prevent light that has passed through the radiation sensitive layer(s) from reflecting back into those layers. If reflection is not prevented, the resulting image is less sharp. In wet processes, the antihalation layer is generally removed or rendered colorless during wet-chemical processing. A filter layer is used to absorb light of a color not completely absorbed by a color layer or color layer unit above the filter layer, while transmitting light of a color intended to be absorbed by a color layer or a color layer below the filter layer. In other words, a filter layer is used to selectively absorb light not used for image capture. An antihalation layer can be viewed as a type of filter layer positioned below all the color layers, wherein no light needs to be transmitted to any color layer below the antihalation layer, but reflection of light back through the antihalation unit is prevented or minimized. Both an antihalation layer and a filter layer will typically employ a filter dye which absorbs, or filters out, light not intended to be absorbed by a color layer.
Imaging elements that can be processed, after imagewise exposure, simply by heating the element are referred to as photothermographic elements. It is often desired that such elements include an antihalation or filter layer. In most cases, the antihalation layer must be rendered substantially transparent upon heat processing in order to avoid unwanted absorption of light during scanning, which would undesirably result in a higher level of minimum density (an increased “D
min
”). Particularly in the case of a color film, bleaching to transparency and avoiding or minimizing any tint is desirable.
It is generally desirable to employ light-filtering dyes which can be quickly and readily rendered ineffective, i.e., decolorized or destroyed and removed prior to or during or after photographic processing. For conventional processing of conventional film, it has been found to be particularly convenient to employ dyes which are rendered ineffective by one of the photographic baths used in processing the exposed element, such as a photographic developer or fixer. The de-coloration or destruction of a light-absorbing dye will hereinafter be referred to as bleaching.
Prior-art dyes having desirable absorption characteristics have not always had good thermal bleaching characteristics. Some of these dyes have been subject to undesirable stains in the visible images made from photographic elements containing the dyes. Other dyes have not had the desired stability that is required for normal storage of the photographic element. Many dry photographic processes, that is, those photographic processes that require no liquids for the preparation of a visible image, have employed light-absorbing dyes that could only be removed by subjecting them to some form of liquid treatment, for example, an acid bath or an alkaline bath. Many of these dry processes lose a good part of their attractiveness when liquids are required for the dye removal. Typical processes employing prior art light-absorbing layers are described in U.S. Pat. Nos. 3,260,601 and 3,282,699.
Furthermore, many if not most of the bleachable antihalation compositions in the prior art were designed for solvent systems in which the dyes and the bleaching agents were soluble as individual molecules. Furthermore, most of the bleachable antihalation compositions in the prior art have been directed to health imaging or graphic arts (monochrome systems), as compared to photothermographic color film for consumer use. In the latter context, the dark keeping of a thermally bleachable dye composition is a challenge. For such compositions to be useful, it would be important that they have the least amount of dark-keeping loss, while at the same time undergo almost complete bleaching at higher temperatures.
A variety of antihalation compositions have been reported in the literature for use in photothermographic systems that avoid the use of processing solutions. Such compositions generally include heat-bleachable antihalation dyes or incorporated addenda that act as bleaching agents. Furthermore, many if not most prior arts (references cited below) describing thermally bleachable dye compositions use many-fold excesses of the bleaching reagents to decolorize the dyes. For example, prior patents teaching the use of excess of bleaching reagents: include, for example, Fuji EP 911,693 A1, DuPont U.S. Pat. No. 5,312,721, 3M U.S. Pat. No. 5,258,274, and Kodak U.S. Pat. Nos. 4,201,590, 4,196,002, and 4,081,278.
Prior art not using bleaching reagents to decolorize the dyes is very limited. Dyes containing 1-aminopyridinium nucleus represent one such class of dyes. In particular, the use of 1-aminopyridinium dyes in antihalation or filter compositions for photographic imaging systems is known, being described in U.S. Pat. No. 3,619,194 (Mitchell). Various substituents on the dyes are listed in column 4 of the patent, including carboxyalkyl and sulfoalkyl that would comprise a zwitterionic compound. The examples, however, disclose the non-zwitterionic perchlorate, tetrafluoroborate or similar salt forms of the cyanine type of 1-aminopytidinium dyes. But these dyes, as disclosed in this prior art, are not useful as they do not bleach efficiently enough at acceptable processing temperatures.
PROBLEM TO BE SOLVED BY THE INVENTION
There is a need for antihalation compositions that can be permanently and quickly bleached at lower temperatures in aqueous systems. Particularly in the field of color photothermographic film for consumer use, the requirements in terms of bleaching and keeping are high. Bleaching of an antihalation layer or filter-dye layer is desired to improve scanning of the film.
Also, the need to use excesses of bleaching reagents in a bleachable AHU or filter layer adds to the cost of thermally bleachable dye compositions. It would be desirable to obtain useful AHU dyes that do not require excessive amounts of bleaching reagents to undergo decolorization. Most preferable are the dyes that do not need any additional reagents to undergo successful bleaching and yet have good keeping characteristics.
SUMMARY OF THE INVENTION
The present invention relates to a photothermographic element comprising a support, at least one photothermographic layer, and at least one antihalation layer or a filter layer, wherein the antihalation or filer layer comprises a heat-bleachable composition comprising at least one light-absorbing filter dye that is a zwitterionic 1-aminopyridinium dye comprising a methine linkage terminated by a substituted or unsubstituted heterocyclic nucleus of the type contained in cyanine dyes.
The term “filter dye” encompasses dyes used in filter layers or antihalation layers and excludes dyes resulting from developing agents or coupling agents. In one embodiment of the invention, the particles are dispersed in a matrix comprising a hydrophilic polymer or water-dispersible hydrophobic polymer.
The invention is also directed to a method of making a photothermographic element and the use of the photothermographic element, wherein the antihalation or filter layer becomes at least 40%, preferably at least 50%, more preferably at least 90%, colorless within about 20 minutes, preferably within about 5 minutes, more preferably within about 0.5 minutes, upon heating to a temperature of at least about 90° C. (according to control
Goswami Ramanuj
Irving Mark E.
Levy David H.
Chea Thorl
Eastman Kodak Company
Konkol Chris P.
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