Radiation imagery chemistry: process – composition – or product th – Imaged product – Multilayer
Reexamination Certificate
2001-04-30
2003-01-14
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaged product
Multilayer
C430S350000, C430S533000, C430S432000, C430S961000
Reexamination Certificate
active
06506527
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to imaged photographic elements having a protective overcoat that resists fingerprints, common stains, and spills. More particularly, the present invention provides a protective overcoat comprising an improved polyester material that is applied to photographic elements following image development.
BACKGROUND OF THE INVENTION
Gelatin has been used extensively in a variety of photographic elements as the binder because of its many unique and advantageous properties. For example, its property of water swellability allows processing chemistry to be carried out to form silver halide-based photographic images. However, due to this same property, photographic elements with exposed gelatin-containing materials, no matter if they are formed on transparent or reflective media, have to be handled with extreme care so as not to be in contact with any solutions that may stain and damage the images. Accidental spillage of common household solutions such as coffee or punch can damage photographic elements such as photographic prints.
There have been attempts over the years to provide protective layers for gelatin-based photographic systems that will protect the images from damage from staining 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 number of patents describe methods of solvent coating a protective layer on the image after photographic processing is completed and are described, for example, 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. More recently, 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. Another type of protective coating involves the application of UV-polymerizable monomers and oligomers on a processed image followed by radiation exposure to form crosslinked protective layer, which 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.
U.S. Pat. No. 6,087,051 relates to an imaging element containing a protective overcoat layer of an aqueous polyurethane resin or an aqueous polyacryl resin. In addition, there are comparison examples in that patent which use a polyester resin, and the aqueous polyurethane resin and polyacryl resins are said to have advantages over the polyester resin. However, there are problems using a polyurethane resin or an aqueous polyacryl resin in that these resins have to be synthesized from virgin raw materials and the resins cannot be recycled. Preferably, the protective overcoat is composed of a water-dispersible polyurethane polycarbonate resin to provide water-resistance, scratch resistance, glossiness, image storage stability, and resistance to fingerprints. The expense of such materials, in addition to the difficulty of coating a print in a photoprocessing lab, has continued to hinder the commercialization of such technology. Another disadvantage of a polyurethane coating is that it is not environmentally friendly. Typical polyester materials such as unmodified polyethylene terephthalate (PET), on the other hand, are known to be environmentally friendly, but are do not provide good stain resistance in a protective overcoat.
U.S. Pat. No. 5,958,601 to Salsman discloses the use of water dispersible hydrophobic polyester resins derived typically from PET having improved hydrophobicity or non-polar characteristics. This resin can be used to coat substrates such as cellulosic or synthetic substrates such as paper. For example, printing paper coated with the resins of U.S. Pat. No. 5,958,601 are disclosed as having excellent water repellency and ink holdout as well as increased strength and gloss. Salsman does not coat a gelatin substrate, nor an imaged substrate. Applicants have found that traditional photographic elements using cross-linked gelatin as a binder already have a water resistance comparable to the polyester material of Salsman.
PROBLEM TO BE SOLVED BY THE INVENTION
There is a need for an imaged photographic element with improved durability, particularly with improved stain resistance. There is also a need for a photographic element containing an overcoat layer made with a material that can be made from recycled materials and is capable of being recycled.
SUMMARY OF THE INVENTION
The present invention provides an aqueous-coatable overcoat that can be coated onto an imaged photographic element to form a stain-resistant protective overcoat. More particularly, the present invention describes an uppermost-layer or overcoat composition that can be applied to the photographic element after image development. These and other objects are achieved in accordance with the present invention which comprises a photographic element comprising a support having one or more imaged layers, derived from a silver halide emulsion comprising a colored dye formed from the reaction product of an oxidized developer and a dye forming coupler, and overlying the imaged layers, an overcoat layer of a water-dispersible, hydrophobic polyester resin having the following general formula:
I
n
—P—A
m
Formula (I)
Wherein I is an ionic group; n is an integer from 1-3; P is a polyester backbone; A is an Asiatic group comprising a straight or branched chain fatty acid or triglyceride thereof having from about 6 to about 24 carbon atoms; and m is an integer from 3-8.
In another preferred embodiment of the invention, the water-dispersible, hydrophobic polyester as described above is physically mixed or blended with a thermoplastic or thermosetting polymer that is a polyurethane and copolymers thereof, acrylate or methacrylate esters and copolymers thereof. The thermoplastic or thermosetting polymer lends added hydrophobicity to the layer, as well as enhanced coating flexibility and serves as a diluent to the polyester component to minimize cross-linking which would deleteriously alter coating properties. In another preferred embodiment of the invention, the water-dispersible, hydrophobic polyester as described above is physically mixed or blended with a microgel. In the preferred embodiment, the Tg of the overcoat composition is at least 70° C.
Another aspect of the invention provides for a method of forming a stain-resistant coating image on an imaged photographic element.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides an improved overcoat formulation for the imaged side of a photographic element or material, including photographic prints, which encounter frequent handling and abuse by end users. The preferred overcoat formulation of this invention comprises 5% to 95% by weight, preferably 50% to 80% by weight, (based on the dry laydown of the total overcoat) of a polyester material as described herein and 5% to 95% by weight, preferably 20% to 50% by weight (based on the dry laydown of the total overcoat) of a hydrophobic thermoplastic or thermosetting polymer.
The polyester material of the invention are preferably water dispersible polyesters of Formula (I) above, wherein the ionic groups I in the above formula which provide the polymer with water-dispersibility are typically derived from a carboxylic acid group which is introduced into the resin by polyacid monomers such as trimellitic anhydride, trimellitic acid, or maleic anhydride or sulfonate groups which come from monomers such as dimethyl 5-sulfoisophthalate, dimethyl 5-sulfo,1,3-benzenedicarboxylate, sulfoisophthalate ethylene
Demejo Lawrence P.
Nesbitt Sandra D.
Romano, Jr. Charles E.
Eastman Kodak Company
Konkol Christ P.
Schilling Richard L.
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