Radiation imagery chemistry: process – composition – or product th – Transfer procedure between image and image layer – image... – Diffusion transfer process – element – or identified image...
Reexamination Certificate
2001-06-29
2003-06-17
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Transfer procedure between image and image layer, image...
Diffusion transfer process, element, or identified image...
C430S227000, C430S237000, C430S248000, C430S428000, C430S432000, C430S536000
Reexamination Certificate
active
06579656
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to the synthesis and use of copolymers employed in the processing of photographic film. Specifically, the instant invention discloses half esters formed using an isobutylene/maleic anhydride copolymer used to terminate the development of photographic film.
BACKGROUND OF THE INVENTION
In general, diffusion transfer photographic products and processes involve film units having a photosensitive element including a support carrying at least one silver halide emulsion, and an image-receiving element including a support and an image-receiving layer. After photoexposure, the photosensitive element is developed, typically by uniformly distributing an alkaline processing composition over the photoexposed element, to establish an imagewise distribution of a diffusible image-providing material. The image-providing material, (e.g., image dyes or complexed silver), is selectively transferred, at least in part, by diffusion to the image-receiving layer positioned in a superposed relationship with the developed photosensitive element. The image-receiving layer is capable of mordanting or otherwise fixing the image-providing material and retains the transferred image for viewing. The image is viewed in the image-receiving layer upon separation of the image-receiving element from the photosensitive element after a suitable period. Black and white transfer images are generally formed by exposing and developing a silver halide emulsion, and subsequently dissolving and transferring silver from unexposed, or less exposed regions, to an image-receiving layer containing silver precipitating agents or nuclei. The transferred silver is reduced to metallic silver in the image-receiving layer, thus forming an image. Color images are generally formed by the imagewise transfer of image dyes from a photosensitive element to an image-receiving layer containing a dye mordant material.
In photographic film units, a strip-coat (also referred to as a “stripping layer” or “release layer”), is commonly positioned between the photosensitive element and an image-receiving element to facilitate the separation of the elements from one another after processing. In photographic applications, strip-coats may additionally serve to prevent processing solution from remaining on the image-receiving element after processing. A specific example of such a strip-coat is provided in U.S. Pat. No. 5,346,800 to Foley et al. that describes a strip-coat comprising a hydrophilic colloid.
Some photographic film units incorporate an overcoat layer. This overcoat layer can serve to facilitate separation between an image-receiving element from a photosensitive element. This layer can comprise one or more polymeric materials like polyvinyl alcohol. In some embodiments the overcoat layer can serve functionally as a strip coat.
Image-receiving elements particularly adapted for use in peel-apart diffusion transfer film units include an image-receiving layer for retaining the transferred image. This image-receiving layer is typically arranged on a substrate layer of suitable material or a combination of layers arranged on the substrate layer. In one well known photographic embodiment, the image-receiving element comprises a support material (preferably, an opaque support material carrying a light-reflecting layer for the viewing of the desired transfer image thereagainst by reflection); a polymeric acid-reacting (neutralizing) layer adapted to lower the environmental pH of the film unit subsequent to substantial transfer image formation; a spacer (or timing) layer adapted to slow the diffusion of the alkali of an aqueous alkaline processing composition toward the polymeric neutralizing layer; and an image-receiving layer to receive the transferred photographic image. Such a structure is described, for example, in U.S. Pat. No. 3,362,819 and is illustrated in other patents, including U.S. Pat. Nos. 4,322,489 and 4,547,451.
The polymeric acid-reacting layer is used to neutralize the alkaline developing solution or reagent. Currently, the butyl half ester of ethylene/maleic anhydride copolymer (EMA) is used for the neutralizing layer. The half ester of EMA is effective in reducing the pH of the developing solution so as to effectuate the termination of the development process. However, there is a desire to increase manufacturing efficiency. For example, it is desirable to directly coat the film unit with the neutralizing layer immediately following its synthesis without any intervening steps. Additionally, it is desirable to form a neutralizing layer in which the functional groups of the polymer are fully converted such that available residual anhydride groups are minimized. Furthermore, it is also desirable that the coating solution of the neutralizing layer be stable and constant in terms of acid content and viscosity. These goals however must comport with the commercial goals of a particular business enterprise. Therefore, the substrates employed for making the neutralizing layer must be readily available and be economically favorable.
SUMMARY OF THE INVENTION
The present invention pertains to a polymeric neutralizing layer within a photographic film used to attenuate the development of the film. The development of film utilizes an aqueous alkaline development processing solution, or reagent. In order to arrest the development process, a polymeric acid-reacting neutralizing layer neutralizes the alkaline processing solution. Diffusion of the aqueous alkaline processing solution is facilitated by the dissolution of a timing layer that serves as a barrier between the polymeric acid-reacting neutralizing and image receiving layers. In the present invention, the neutralizing layer comprises an acidic polymer. This acidic polymer, when in contact with the alkaline processing solution, neutralizes the base, shifting the pH thus attenuating further development of the photographic film.
The present invention provides a polymeric neutralizing layer comprising, among other features, a half ester of isobutylene/maleic anhydride copolymer, hereinafter referred to as “IBMA.” In one embodiment, the esterification of IBMA leads to a propyl half ester of IBMA. In another embodiment, the esterification reaction produces a butyl half ester. Other half esters are also envisaged to be within the scope of this invention, such as alkyl half esters containing approximately 1 to 12 carbon atoms in a normal or branched alkyl chain. The alkyl chain can contain groups like hydroxyl, halogen, phenyl, substituted phenyl as well as aryl or substituted aryl half esters, containing substituents like hydroxyl, halogen and alkyl containing about 1 to 4 carbon atoms in a linear or branched structure.
The esterification of IBMA involves the dispersion of the IBMA substrate in an appropriate alcohol. During the esterification process, the alcohol reactant opens the anhydride ring and forms an ester with one carboxylic group, while the remaining carboxylic acid group contributes the acid moiety to the polymer. For example, in the synthesis of propyl half ester of IBMA, n-propanol is the alcohol substrate and the acidic moiety is released from the cyclic anhydride by the reaction of the other carboxylic group with the alcohol. The IBMA/alcohol admixture is heated to a reflux temperature appropriate for the alcohol used and refluxed for several hours. As the esterification reaction progresses, the polymer slowly becomes swollen in the boiling alcohol, passes through a swollen gel state, and then starts to dissolve within the alcohol. As the reaction nears completion, a fine dispersion becomes clear and colorless. The progress of the reaction can be followed using different detection techniques, including infrared (“IR”) detection.
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Fehervari Agota F.
Grimm William L.
Polaroid Corporation
Schilling Richard L.
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