Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Identified backing or protective layer containing
Reexamination Certificate
2001-11-01
2002-08-20
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Identified backing or protective layer containing
C430S531000, C430S533000, C430S534000, C430S536000, C430S617000, C430S964000
Reexamination Certificate
active
06436622
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to thermographic materials having two or more layers on a polymeric support. A layer next to the support has a single-phase mixture of polymers that provides multiple properties including adhesion of the layer to the polymeric support. The invention also relates to a method of preparing the noted thermographic materials.
BACKGROUND OF THE INVENTION
Thermographic imaging materials (that is, non-photosensitive, heat-developable materials) processed with heat, and without liquid development, are widely known in the imaging arts and rely on the use of heat to help produce an image. These materials generally comprise a support or substrate (such as paper, plastics, metals, glass, and the like) having coated thereon: a thermally-sensitive, reducible silver source, a reducing agent for the thermally-sensitive, educible silver source (that is, a “developer” that can reduce silver ion to metallic silver), and a binder.
In a typical thermographic construction, the image-forming layers re based on silver salts of long chain fatty acids. Typically, the preferred n-photosensitive reducible silver source is a silver salt of a long chain aliphatic carboxylic acid having from 10 to 30 carbon atoms (such as, silver behenate or silver salts of other fatty acids of similar molecular weight).
Upon exposure of the thermographic material to thermal energy, silver salt is reduced by the incorporated reducing agent whereby a black-and-white image of elemental silver is formed. Typical reducing agents for silver ion are methyl gallate, hydroquinone, substituted-hydroquinones, hindered phenols, catechol, pyrogallol, ascorbic acid, ascorbic acid derivatives, and the like,
Some thermographic constructions are imaged by contacting them with the thermal head of a thermographic recording apparatus, such as in a thermal printer, thermal facsimile, and the like. Other thermographic constructions are imaged by using the heat of a scanning laser. Still others are imaged by contact with a thermal blanket or roller.
The preparation of thermographic imaging materials requires solving several problems. One major problem is that of coating the thermographic material. Because the necessary image-forming chemistry is within the material itself, the binders used in thermographic elements must be stable for thermal imaging processing and provide both layer cohesion and interlayer adhesion. In addition, all coatings usually require a specific range of adhesion with underlying coatings or supports (such as polyester substrates) to meet useful end purposes. The conventional state of the art is to treat the support surface in some manner, such as with electrical corona treatment, flame treatment and glow discharge, to increase wettability and bonding strength. While these treatments do provide increased adhesion, they also leave charge or surface irregularities on the support that result in surface irregularities when an organic solvent based coating is applied. Other disadvantages with such treatments are high inherent capital costs, maintenance and upkeep of the equipment and in some cases the need for inert gases.
Another manner for improving adhesion is to apply a primer layer on the support prior to applying other layers including imaging layers. Such coatings include a wide range of formulations, and are usually aqueous in nature to provide the desired adhesion to subsequent layers. These methods are generally inadequate when organic solvent-based coatings are applied to the primer layer due to poor adhesion and/or migration of the components from the primer layer into upper layers. This results in a variety of unwanted physical and chemical problems (for example, coating discoloration, haze, static discharge, poor coating quality and poor sensitometry.
WO 96/15478 (Geisler et al.) and U.S. Pat. No. 5,928,857 (Geisler et al.) describe spectrally sensitized photothermographic elements having improved adhesion using additional adhesive materials in the photosensitive layer. Thus, besides the usual polyvinyl butyral binder, the photosensitive layer also includes a polymeric component that is not a polyvinyl acetal. This polymeric component has a higher strength of adhesion to polyester film than a polyvinyl acetal and the improved adhesion is readily observed in high-density image areas.
Primer layers for photothermographic materials are described for example in U.S. Pat. No. 4,752,559 (Helland et al.) to include a pigmented acrylic polymer binder system. This binder system is said to adhere to a photosensitive layer containing a variety of polymer binders including polyvinyl acetals. Polymeric substrates can also be coated with a polyacrylate/gelatin composition that either adheres the photosensitive layer to the substrate or includes the photo-sensitive materials, as described in U.S. Pat. No. 5,244,780 (Strobel et al.).
Block and graft copolymers are described as adhesion-promoting materials in U.S. Pat. No. 5,384,192 (Long et al.) between the support and the organic polymer layer (photosensitive layer). The copolymers have a component compatible with the organic polymer layer and a polyvinyl phenol. Other more complicated polymer subbing layer materials are described in U.S. Pat. No. 5,639,589 (Bauer et al.).
The use of primer layers may be necessary in some instances, but as noted above, their use presents a number of problems. In addition, they require additional coating passes, capital investment and film waste. Curl may also result from application of the additional layer.
There are several known techniques for simultaneous coating of multiple layers. For example, U.S. Pat. No. 4,001,024 (Dittman et al.) describes what is known in the industry as “slide” coating technology in which a plurality of thin layers are applied to a moving web (support) to prepare photographic elements. This technology is best used with the lowermost layer being thinner (wet thickness) than the upper layers. This thinner layer has become known as a “carrier” layer and can be chosen from a wide range of materials that are compatible with the silver/gelatin containing photosensitive layers coated on top so that interlayer mixing can occur without adverse effect.
Thin “accelerating” or carrier layers are described in U.S. Pat. No. 4,569,863 (Koepke et al.) for use in what is known as “curtain” coating methods for preparing multilayer photographic elements. Still other coating techniques are described in U.S. Pat. No. 4,572,849 (Koepke et al.) in which thin accelerating layers are composed of various hydrophilic coating materials. In U.S. Pat. No. 5,641,544 (Melancon et al.), U.S. Pat. No. 5,733,608 (Kessel et al.), U.S. Pat. No. 5,849,363 (Yapel et al.), and U.S. Pat. No. 5,861,195 (Bhave et al.) thin “carrier fluids” and coating fluids are described as comprising non-miscible materials. The carrier layers applied in these procedures are used for some aspect of coating quality such as streak reduction, reducing air entrapment, increased line speed and reduction in “strike through”.
While WO 96/15478 and U.S. Pat. No. 5,928,857 (both noted above) describe an advance in the art to adhere photothermographic imaging layer to polyester supports, there is a desire to avoid adding additional components, particularly additional binders, to the imaging layers. Yet, polyvinyl butyral, the most common binder does not satisfactorily bind the imaging layer to the polyester support.
While some polymers effectively adhere imaging layers to a polymeric film support, it has been observed that use of some adhering polymers causes physical or coating defects.
There remains a need then, for increased adhesion between polymeric supports and organic solvent based polymeric layers coated thereon, particularly in imaging materials such as thermographic materials where other properties of the imaging materials are not adversely affected.
SUMMARY OF THE INVENTION
The problems noted above with known coating technologies for providing improved adhesion are solved with the present invention. In particular, this invention p
Eastman Kodak Company
Schilling Richard L.
Tucker J. Lanny
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