Radiation imagery chemistry: process – composition – or product th – Thermographic process – Heat applied after imaging
Reexamination Certificate
2001-08-27
2002-09-17
Chea, Thorl (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Thermographic process
Heat applied after imaging
C430S020000, C430S351000, C430S510000, C430S513000, C430S517000, C430S523000, C430S531000, C430S566000, C430S619000, C430S640000, C430S959000
Reexamination Certificate
active
06451516
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 photothermographic elements. In particular, 1-aminopyridinium dyes in combination with a thermal solvent has 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. Visible images made from photographic elements containing some such dyes have been subject to undesirable stains. 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. However, many of these dry processes lose their attractiveness when liquids are required for dye removal. Typical processes employing prior art light-absorbing layers are described in U.S. Pat. No. 3,260,601 and U.S. Pat. No. 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 would be a challenge. For such compositions to be useful, it would be crucial that they have the least amount of dark keeping loss, and 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 which 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 patents in which bleaching reagents are not used to decolorize bleachable dyes are 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 are known, being described in U.S. Pat. No. 3,619,194 (Mitchell). But these dyes, as disclosed in this patent, are not useful as they do not bleach efficiently enough at acceptable processing temperatures.
Thermal solvents for use in photothermographic and thermographic systems are generally known. Heat processable photosensitive elements can be constructed so that after exposure, they can be processed in a substantially dry state by applying heat. Because of the much greater challenges involved in developing a dry or substantially dry color photothermographic system, however, most of the activity to date has been limited to black and white photothermographic systems, especially in the areas of health imaging and microfiche.
It is known how to develop latent image in a photographic element not containing silver halide wherein organic silver salts are used as a source of silver for image formation and amplification. Such processes are described in U.S. Pat. Nos. 3,429,706 (Shepard et al.) and 3,442,682 (Fukawa et al.). Dry processing thermographic systems are described in U.S. Pat. Nos. 3,152,904 (Sorenson et al.) and 3,457,075 (Morgan and Shely). A variety of compounds have been proposed as “carriers” or “thermal solvents” or “heat solvents” for such systems, whereby these additives serve as solvents for incorporated developing agents, or otherwise facilitate the resulting development or silver diffusion processes. Acid amides and carbamates have been proposed as such thermal solvents by Henn and Miller (U.S. Pat. No. 3,347,675) and by Yudelson (U.S. Pat. No. 3,438,776). Bojara and de Mauriac (U.S. Pat. No. 3,667,959) disclose the use of non-aqueous polar solvents containing thione, —SO
2
— and —CO— groups as thermal solvents and carriers in such photographic elements. Similarly, La Rossa (U.S. Pat. No. 4,168,980) discloses the use of imidazoline-2-thiones as processing addenda in heat developable photographic materials. Takahashi (U.S. Pat. No. 4,927,731) discloses a microencapsulated base activated heat developable photographic polymerization element containing silver halide, a reducing agent, a polymerizable compound, contained in a microcapsule and separate from a base or base precursor. In addition, a sulfonamide compound is included as a development accelerator.
Thermal solvents for use in substantially dry color photothermographic systems have been disclosed by Komamura et al. (U.S. Pat. No. 4,770,981), Komamura (U.S. Pat. No. 4,948,698), Aomo and Nakamaura (U.S. Pat. No. 4,952,479), and Ohbayashi et al. (U.S. Pat. N
Goswami Ramanuj
Irving Mark E.
Chea Thorl
Konkol Chris P.
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