Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Structurally defined
Reexamination Certificate
2001-04-12
2002-09-24
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Structurally defined
C430S350000, C430S531000, C430S536000, C430S961000
Reexamination Certificate
active
06455238
ABSTRACT:
FIELD OF THE INVENTION
A protective overcoat for photographic elements is disclosed. More particularly, the protective overcoat comprises a porous membrane that is present on the photographic element before exposure and processing and which is permeable to processing solutions. Subsequent to processing, the photographic element is heated to substantially close the pores of the overcoat, so that it provides water resistance, fingerprint resistance, and scratch protection to the surface of the photographic element.
BACKGROUND OF THE INVENTION
Typically, a silver-halide photographic element contains light sensitive silver halide in a hydrophilic emulsion. An image is formed in the element by exposing the silver halide to light, or to other actinic radiation, and developing the exposed silver halide to reduce it to elemental silver. In color photographic elements, a dye image is formed as a consequence of silver halide development by one of several different processes. The most common is to allow a by-product of silver halide development, oxidized silver-halide developing agent, to react with a dye forming compound called a coupler. The silver and unreacted silver halide are then removed from the photographic element, leaving a dye image.
In either case, formation of the image commonly involves liquid processing with aqueous solutions that must penetrate the surface of the element to come into contact with silver halide and coupler. Gelatin has been used exclusively in a variety of silver halide photographic systems as the primary binder due to its many unique properties, one of which is the water-swellable property. This rapid swelling allows processing chemistry to proceed and images to be formed. However, due to this same property, photographic images, whether they are on film or paper, need to be handled with extreme care so as not to come in contact with any aqueous solutions that may damage the images. Thus, although gelatin, and similar natural or synthetic hydrophilic polymers, have proven to be the binders of choice for silver-halide photographic elements to facilitate contact between the silver halide crystal and aqueous processing solutions, they are not as tough and mar-resistant as would be desired. This is especially true in view of the handling commonly encountered by an imaged photographic element. The imaged element can be easily marked by fingerprints, it can be scratched or torn, and it can swell or otherwise deform when it is contacted with liquids.
There have been attempts over the years to provide protective layers for gelatin based photographic systems that will protect the images from damages by water or aqueous solutions. Many protective layers have been proposed for photographic elements that need to be applied after photoprocessing. However, there is a need for a protective layer that could be incorporated as part of the photographic element as manufactured.
Commonly assigned, copending application U.S. Pat. No. 6,203,970 describes a non-porous overcoat layer that is present on the photographic element prior to exposure, which layer comprises a hydrophobic thermoplastic polymer and a hydrophilic component. The processing solutions permeate the layer by dissolving away the hydrophilic component and creating pores. After processing, the layer is heated so as to close the pores and provide a protective layer. With this invention, a significant amount of material must be removed from the layer during processing and this leads to waste and contamination of the processing solutions.
U.S. Pat. No. 5,856,051 describes a protective overcoat comprising a mixture of gelatin and hydrophobic polymer particles that have a particular melting point range. After photoprocessing, including development, to produce the image, the photographic element is thermally fused, so that the hydrophobic polymer particles form a water-resistant protective overcoat. The element described in the '051 patent, however, suffers in that this protective overcoat is easily scratched.
Commonly assigned, copending application U.S. Ser. No. 09/312,378 (Docket 79332) describes a protective overcoat comprising two layers, an uppermost layer comprising abrasion resistant particles and a second layer below this comprising gelatin in admixture with hydrophobic polymer particles that have a particular melting point range. After photoprocessing, including development, to produce the image, the photographic element is thermally fused so as to provide a water-resistant and dry scratch-resistant protective overcoat. The element described in this patent, however, suffers in that this protective overcoat is easily scratched when the element is wet.
U.S. Pat. No. 5,853,926 describes a protective overcoat applied during manufacturing that comprises polymer particles and a polymer latex binder. The element described in this patent, however, suffers in that the overcoat is not porous prior to processing and the speed of development is slow.
There remains a need for a water-resistant protective overcoat that can be incorporated into the photographic product during manufacturing, allows for appropriate diffusion of photographic processing solutions, and does not require coating operation after exposure and processing.
The present invention discloses a uniquely structured overcoat that allows the photographic processing solutions to diffuse through for image formation, and then provides water resistance, fingerprint resistance, and improved scratch resistance properties.
SUMMARY OF THE INVENTION
The present invention relates to a photosensitive photographic element comprised of a support, at least one silver-halide light-sensitive emulsion layer, and a porous-membrane layer, said layer comprising an open-pore membrane of a water-insoluble polymer, the membrane layer being made by homogeneously dissolving the polymer in a solvent mixture, the solvent mixture comprising at least one solvent which is a relative good solvent for the water-insoluble polymer and at least one solvent which is a relatively poor solvent for the water-insoluble polymer, wherein the relatively poor solvent has a higher boiling point than the relatively good solvent, coating the dissolved mixture onto the at least one silver halide light-sensitive emulsion layer, and then drying to remove approximately all of the solvents to obtain the open-pore membrane.
The invention is also directed to a method of processing the above-described photographic element, in which the imaging element is developed to provide an imaged photographic element, and the porous-membrane layer is fused to form a protective overcoat.
By means of the present invention, an imaging element can be obtained that will provide, in the imaged product, improved wet and dry abrasion resistance, scratch resistance, fingerprint resistance, water resistance, and stain resistance.
DETAILED DESCRIPTION OF THE INVENTION
As indicated above, the present invention provides an imaged photographic element having an overcoat that imparts both water resistance, fingerprint resistance, and abrasion resistance. The protective overcoat of this invention can be achieved in the following manner. An uppermost porous membrane is coated over the photosensitive layers. In order for the membrane layer to be sufficiently porous, however, the water-insoluble polymer must be coated from a solvent mixture combination such that an open-pore membrane structure will be formed when the solution is coated and dried, in accordance with the known technique of “dry-phase inversion.” The formation of an open-pore membrane is accomplished by using a mixture of an essentially good and an essentially poor solvent for the water-insoluble polymer. As noted above, the essentially poor solvent has a boiling point that is higher than that of the good solvent. When the solution is coated or cast onto a support and dried, the essentially good solvent evaporates faster than the poor solvent, forming the membrane structure of the layer when the polymer phase separates from the solvent mixture. The open-pore structure resul
Franklin Linda M.
Landry-Coltrain Christine J.
Eastman Kodak Company
Konkol Chris P.
Schilling Richard L.
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