Radiation imagery chemistry: process – composition – or product th – Thermographic process – Heat applied after imaging
Reexamination Certificate
2000-07-21
2002-11-12
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Thermographic process
Heat applied after imaging
C430S523000, C430S531000, C430S536000, C430S537000, C430S961000, C430S533000
Reexamination Certificate
active
06479222
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to photographic imaging elements having a protective overcoat that resists fingerprints, common stains, and spills. More particularly, the present invention provides a processing-solution-permeable overcoat that becomes water resistant in the photochemically processed product. The overcoat formulation comprises at least one water-dispersible hydrophobic polymer interspersed with a water-soluble polymer. During development or thereafter, before drying, the water-soluble polymer is removed to a significant extent, facilitating coalescence of the residual water-dispersible polymer, thereby forming a water-resistant continuous protective overcoat.
BACKGROUND OF THE INVENTION
Silver halide photographic elements contain 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. Thus, gelatin or similar natural or synthetic hydrophilic polymers have proven to be the binders of choice for silver halide photographic elements. Unfortunately, when gelatin or similar polymers are formulated so as to facilitate contact between the silver halide crystals and aqueous processing solutions, the resultant coatings are not as fingerprint and stain resistant as would be desirable, particularly in view of the handling or environment that an imaged photographic element may commonly experience at various times and circumstances. Thus, fingerprints can permanently mark the imaged element. The imaged element can be easily stained by common household products, such as foods or beverages, for example, coffee spills.
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. U.S. Pat. No. 2,173,480 describes a method of applying a colloidal suspension to moist film as the last step of photographic processing before drying. A series of patents describes methods of solvent coating a protective layer on the image after photographic processing is completed and are described in U.S. Pat. Nos. 2,259,009, 2,331,746, 2,798,004, 3,113,867, 3,190,197, 3,415,670 and 3,733,293. U.S. Pat. No.5,376,434 describes a protective layer formed on a photographic print by coating and drying a latex on a gelatin-containing layer bearing an image. The latex is a resin having a glass transition temperature of from 30° C. to 70° C. The application of UV-polymerizable monomers and oligomers on processed image followed by radiation exposure to form crosslinked protective layer is described in U.S. Pat. Nos. 4,092,173, 4,171,979, 4,333,998 and 4,426,431. A drawback for both the solvent coating method and for the radiation cure method is the health and environmental concern of those chemicals or radiation to the coating operator. Another drawback is that the photographic materials need to be coated after the processing step. Thus, the processing equipment needs to be modified and the personnel running the processing operation need to be trained to apply the protective coating.
Various lamination techniques are known and practiced in the trade. U.S. Pat. Nos. 3,397,980, 3,697,277 and 4,999,266 describe methods of laminating a polymeric sheet film, as a protective layer, on a processed image. U.S. Pat. No. 5,447,832 describes the use of a protective layer containing a mixture of high and low Tg latices as a water-resistant layer to preserve the antistat property of a V
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layer through photographic processing. This protective layer is not applicable to the image formation layers, however, since it will detrimentally inhibit the photographic processing. U.S. Pat. No. 3,443,946 provides a roughened (matte) scratch-protective layer, but not one designed to be water-impermeable or resistant. U.S. Pat. No. 3,502,501 is intended to provide protection against mechanical damage only; the layer in question contains a majority of hydrophilic polymeric materials, and must be permeable to water in order to maintain processibility. U.S. Pat. No. 5,179,147 likewise provides an overcoat that is not water-protective.
Protective coatings that need to be applied to the image after it is formed, several of which were mentioned above, adds a significant cost to the final imaged product. A number of patents have been directed to water-resistant protective coatings that can be applied to a photographic element prior to development. For example, U.S. Pat. No. 2,706,686 describes the formation of a lacquer finish for photographic emulsions, with the aim of providing water-and fingerprint-resistance by coating the light-sensitive layer, prior to exposure, with a porous layer that has a high degree of water permeability to the processing solutions. After processing, the lacquer layer is fused and coalesced into a continuous, impervious coating. The porous layer is achieved by coating a mixture of a lacquer and a solid removable extender (ammonium carbonate), and removing the extender by sublimation or dissolution during processing. The overcoat as described is coated as a suspension in an organic solvent, and thus is not desirable for large-scale application. More recently, U.S. Pat. No. 5,853,926 to Bohan et al. discloses a protective coating for a photographic element, involving the application of an aqueous coating comprising polymer particles and a soft polymer latex binder. This coating allows for appropriate diffusion of photographic processing solutions, and does not require a coating operation after exposure and processing. Again, however, the hydrophobic polymer particles must be fused to form a protective coating that is continuous and water-impermeable.
U.S. Pat. No. 5,856,051 describes the use of hydrophobic particles with gelatin as the binder in an overcoat formulation. This invention demonstrated an aqueous coatable, water-resistant protective overcoat that can be incorporated into the photographic product, allows for appropriate diffusion of photographic processing solutions, and does not require a coating operation after exposure and processing. The hydrophobic polymers exemplified in U.S. Pat. No. 5,856,051 include polyethylene have a melting temperature (Tm) of 55 to 200° C., and are therefore capable of forming a water-resistant layer by fusing the layer at a temperature higher than the Tm of the polymer after the sample has been processed to generate the image. The coating solution is aqueous and can be incorporated in the manufacturing coating operation without any equipment modification. Again, however, fusing is required by the photofinishing laboratories to render the protective overcoat water-resistant. Similarly, commonly assigned U.S. Ser. Nos. 09/353,939 and 09/548,514, respectively, describe the use of a polystyrene-based material and a polyurethane-based material, with gelatin as the binder, in an overcoat for a photographic element, which overcoat can be fused into a water resistant overcoat after photographic processing is accomplished to generate an image.
Commonly assigned U.S. Ser. No. 09/235,436 discloses the use of a processing solution permeable overcoat that is composed of a urethane-vinyl copolymer having acid functionalities. Commonly assigned U.S. Ser. Nos. 09/235,437 and 09/448,213 disclose the use of a second polymer such as a gelatin or polyvinyl alcohol to improve
Jones Tamara K.
Lobo Lloyd A.
Nair Mridula
O'connor Kevin M.
Qiao Tiecheng A.
Eastman Kodak Company
Konkol Chris P.
Schilling Richard L.
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