Radiation imagery chemistry: process – composition – or product th – Imaged product – Multilayer
Reexamination Certificate
1999-07-15
2002-07-30
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Imaged product
Multilayer
C430S350000, C430S537000, C430S961000, C430S527000, C347S105000
Reexamination Certificate
active
06426167
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to image recording materials. More particularly the present invention provides a protective overcoat which provides excellent scratch and spill resistance to image recording materials.
BACKGROUND OF THE INVENTION
Gelatin has been used extensively in a variety of image recording systems as the binder for its many unique properties. For example, its water-swellable property allows processing chemistry to be carried out to form silver halide-based photographic images, and its hydrophilic nature allows gelatin to function as an ink-receiver in ink-jet printing systems. However, due to this same property, recorded images, no matter if they are formed on transparent or reflective media, have to be handled with extreme care so as to not be in contact with any aqueous solutions to damage the images.
There have been attempts over the years to provide protective layers for gelatin-based photographic systems that will protect the images from damage by water or any aqueous solution. For example, 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 describe the methods of solvent-coating a protective layer on the image after photographic processing was completed. See, for example, 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. There is also teaching describing the application of UV-polymerizable monomers and oligomers on processed images followed by radiation exposure to form a crosslinked protective layer. Radiation curable layers are exemplified in U.S. Pat. Nos. 4,092,173, 4,171,979, 4,333,998, and 4,426,431.
The obvious drawback for the solvent coating method and radiation cure method is the health and environmental concern of those chemicals to the coating operator. U.S. Pat. Nos. 3,397,980, 3,697,277 and 4,999,266 describe the method of laminating polymeric sheet film on the processed image as the protective layer. U.S. Pat. No. 5,447,832 describes the use of a protective layer containing a mixture of high and low Tg latices as the water-resistant layer to preserve the anti-static property of the V
2
O
5
layer through photographic processing. This protective layer is not applicable to the image formation layers since it will detrimentally inhibit the photographic processing. U.S. Pat. No. 2,706,686 describes the use of a lacquer layer containing inorganic compound NH
4
HCO
3
particles in the overcoat, followed by sublimation or dissolving of such compound in photographic processing and heat fusing to obtain a water resistant layer. However, the lacquer overcoat was applied as a suspension in an organic solvent and the volatiles or salts released from NH
4
HCO
3
were major disadvantages in manufacturing as well as to photoprocessing laboratories. In addition, there are many patents disclosing overcoat formulations to improve scratch resistance of dry gelatin coatings, such as U.S. Pat. No. 5,179,147 among many others. However these overcoat formulations do not impart water resistance.
In general, all methods of protection requiring the application or coating of a layer after image formation suffer from the drawbacks of additional cost, the need for modifications to the processing equipment and additional operator training.
U.S. Pat. No. 5,853,926 describes the application of an aqueous coating comprising polymer particles in a polymer latex binder, allowing for development of a photographic image and after processing, fusing by heat to form a protective surface. The disadvantages of such a method include the limited photographic processing rates achievable when a polymer latex binder is used in the protective layer.
European Patent Application 0,858,905A1 describes a porous, particulate outermost layer applied to ink-jet recording media, that is heat-fused after ink absorption to form a protective surface. Such porous surface layers are often mechanically weak and in particular can be prone to scratching damage or material removal during transport and handling prior to image formation and subsequent fusing, thus compromising the usefulness of their protective function.
U.S. Pat. No. 5,856,051 describes the use of hydrophobic particles with gelatin as the binder in the 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 polyethylenes having a melting temperature (Tm) of 55 to 200° C., and 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. The fusing step is simple and environmentally friendly to photofinishing laboratories. Since the particles are incorporated entirely within the uppermost layer, this approach does not suffer from a lack of mechanical strength and integrity during transport and handling prior to image formation and fusing. However, the scratch resistance of such an overcoat after fusing is a serious concern, since polyethylene is a very soft material.
Thus, there remains a need for an aqueous coatable, water-resistant protective overcoat that can be incorporated into the image recording material during manufacturing, that is not damaged during machine transport and handling, that allows for appropriate diffusion of photographic processing solutions or uptake of ink, that does not require a coating operation after exposure and processing and that offers good scratch resistance.
SUMMARY OF THE INVENTION
The present invention provides an aqueous-coatable protective overcoat that can be coated on to the image recording material (either sequentially or simultaneously), allows for appropriate diffusion of photographic processing solutions or uptake of ink, and can be fused after photographic processing or ink-jet printing to form a water-resistant protective overcoat with good scratch resistance.
The present invention describes an uppermost-layer or overcoat composition that can be incorporated and coated directly in the image recording material during manufacturing, that does not inhibit photographic processing or uptake of ink, and that can become water-resistant by fusing the layer after it goes through photographic processing or ink-jet printing. A component of the invention is the hydrophobic polymer particles of polystyrene-type homo- or co-polymers consisting of at least 30% styrene-type monomers. The polymer can be either liner, graft or hyperbranched. The material of the invention can be introduced to the overcoat coating melt in a latex form or as a conventional colloidal dispersion in gelatin. When used at 50-70% by weight, based on total laydown of the overcoat where gelatin is the binder, it allows photographic processing to proceed at an acceptable rate. After processing to obtain images, the image recording media can be fused at a temperature above 300° F. to form a water-resistant surface. Compared to U.S. Pat. No. 5,856,051 which describes the use of commercially available polyethylene particles, the polystyrene particles of the present invention offer improved dry scratch resistance.
Hence, the present invention provides:
An overcoat composition for image recording elements comprising:
30 to 95 weight percent, based on the dry laydown of the overcoat, of hydrophobic polymer particles having an average size of 0.01 to 0.5 micrometers, said hydrophobic polymer being a homopolymer of the monomer described in Structure 1 or a copolymer containing at least 30 weight percent, based on the total weight of monomers, of the monomer described in Structure 1 and 5 to 70 w
Chen Tien-teh
Thai Lan B.
Wang Jin-Shan
Yau Hwei-Ling
Eastman Kodak Company
Konkol Chris P.
Schilling Richard L.
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