Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Identified backing or protective layer containing
Reexamination Certificate
2000-12-01
2002-11-12
Baxter, Janet (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Identified backing or protective layer containing
C430S530000, C430S531000, C430S533000, C430S536000
Reexamination Certificate
active
06479228
ABSTRACT:
FIELD OF THE INVENTION
The invention generally relates to imaging elements, particularly those elements having an antistatic layer.
BACKGROUND OF THE INVENTION
Microscratches are scratches that are on the order of several microns in width and submicron to microns in depth. They are commonly observed on the front and back sides of photographic films, on photoconductor belts, on thermal prints, and on PhotoCD disks. They are caused by sliding contact of imaging products with dirt particles or other asperities that have micron-sized contact radii. These scratches can affect analog or digital image transfer and degrade the output image quality. Their presence on magnetic or conductive backings could lessen the performance of these functional coatings. Thus, scratch resistance protective coatings on the front or back or both sides of an imaging product are commonly required.
Since all imaging products are based on flexible substrates for ease of transport, conveyance, and manufacturing, hard metallic or ceramic tribological scratch resistant coatings are not suitable due to their mechanical incompatibility with the polymeric flexible substrates. This mechanical incompatibility can cause adhesion failure between the coating and the substrate during scratching. Polymeric coatings are thus preferable as the scratch resistant layer for imaging products. However, with the requirements for high light transmission, low material cost, low internal drying stress, and high coating speeds, the thickness of these scratch resistant coatings is preferably about 10 microns or less.
During micro-scratching of a micron-thick coating, complex stress fields develop in the coating, within which high internal shear stress, interfacial shear stress, and surface tensile stress are present. A coating can fail either by shear fracture, delamination, or tensile cracking depending on the relative shear, adhesive, and tensile strengths of the coating. Using a micro-scratching instrument with a single micron-sized stylus, the resistance to scratch damage for a coating can be measured. Combining this instrument with optical microscopy, the failure mode, such as shear fracture, delamination, or tensile cracking, can be determined. All these failure modes produce scratches that are printable and scanable and, thus, unacceptable for imaging products. A permanent scratch track resulting from plastic deformation of a ductile coating without coating failure is also printable and scanable, and thus, not desirable.
Various types of polymeric coatings have been examined as scratch resistant coatings for imaging products. These include coatings comprising brittle, ductile, elastic-plastic, or rubber-elastic polymeric materials. Brittle polymers with elongations to break less than 5%, such as poly(methyl methacrylate) and poly(styrene) are not desirable as scratch resistant coatings for imaging products. Regardless of the coating thickness, the brittleness of these materials leads to printable surface tensile cracks during scratching. Soft elastomers (rubber-elastic materials), such as urethane rubbers, acrylic rubbers, silicone rubbers, are not suitable as scratch resistant coatings since deep penetration of the asperity or stylus occurs in these soft coatings which causes these elastomeric coatings to fail at low loads during scratching. Using stiff fillers to increase the stiffness of these elastomers to reduce stylus penetration does not solve this problem since permanent and printable scratch tracks result in elastomeric coatings containing stiff fillers by the induced coating plasticity under the presence of stiff fillers.
Ductile elastic-plastic coatings with elongations to break greater than 10%, such as glassy polyurethanes, polycarbonate, cellulose esters, etc., exhibit shear-fracture-type scratch damage during scratching that result from plastic flow. Plastic flow in these ductile coatings during scratching is controlled by the coating thickness. For thin coatings of these materials, plastic flow in the coating during scratching is restricted by the coating adhesion to the substrate leading to a premature failure of the coatings at low loads. Thicker coatings for these materials may have improved resistance to coating failure, however, for imaging products these thicknesses may be impractical. In addition, although thick ductile coatings have improved resistance to coating failure during scratching, the low yield strength and modulus for these materials result in the formation of permanent scratch tracks in the coatings at low loads.
It can be seen that various approaches have been attempted to obtain an improved scratch resistant layer for imaging products. However, the aforementioned methods have met with only limited success. Recently, in commonly-assigned U.S. Ser. No. 09/089,794 a coating composition is disclosed with resistance to the formation of permanent scratch tracks and coating failure when an imaging product is exposed to sharp asperities or other conditions that may lead to scratches during the manufacture and use of the imaging product. However, such a backing does not necessarily provide any antistatic characteristics required of an imaging element for its successful manufacture, finishing and subsequent use. Although a number of oxides with electronic conductivity have been proposed as stiff fillers in U.S. Ser. No. 09/089,794, their inclusion is likely to impart unacceptable levels of color and haze to the photographic element. Moreover, due to the highly filled nature of such a backing, it cannot be used as a barrier layer, against photographic processing solutions, over vanadium oxide based antistats disclosed in U.S. Pat. No. 5,679,505 and references therein and, hence, will not insure “process-surviving” conductivity of such antistats. The present invention is intended to provide improved scratch resistance and antistatic properties, before and after film processing, all in a single layer with acceptable optical properties for application in imaging elements.
The problem of controlling static charge is well known in the field of photography. The accumulation of charge on film or paper surfaces leads to the attraction of dirt which can produce physical defects. The discharge of accumulated charge during or after the application of the sensitized emulsion layer(s) can produce irregular fog patterns or “static marks” in the emulsion. The static problems have been aggravated by increases in the sensitivity of new emulsions, increases in coating machine speeds, and increases in post-coating drying efficiency. The charge generated during the coating process may accumulate during winding and unwinding operations, during transport through the coating machines and during finishing operations such as slitting and spooling. Static charge can also be generated during the use of the finished photographic film product. In an automatic camera, the winding of roll film in and out of the film cartridge, especially in a low relative humidity environment, can result in static charging. Similarly, high speed automated film processing can result in static charge generation. Sheet films (e.g., x-ray films) are especially susceptible to static charging during removal from light-tight packaging.
It is generally known that electrostatic charge can be dissipated effectively by incorporating one or more electrically-conductive “antistatic” layers into the film structure. Antistatic layers can be applied to one or to both sides of the film base as subbing layers either beneath or on the side opposite to the light-sensitive silver halide emulsion layers. An antistatic layer can alternatively be applied as an outer coated layer either over the emulsion layers or on the side of the film base opposite to the emulsion layers or both. For some applications, the antistatic agent can be incorporated into the emulsion layers. Alternatively, the antistatic agent can be directly incorporated into the film base itself.
A wide variety of electrically-conductive materials can be incorporated into antistatic layers to produce a wi
Anderson Charles
Majumdar Dabasis
Baxter Janet
Eastman Kodak Company
Walke Amanda C.
Wells Doreen M.
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