Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Identified backing or protective layer containing
Utility Patent
1998-12-18
2001-01-02
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Identified backing or protective layer containing
C430S527000, C430S530000, C430S533000
Utility Patent
active
06168911
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to imaging elements which include a support material, one or more image forming layers, and one or more electrically conductive layers. More specifically, this invention relates to improved electrically conductive layers containing colloidal electrically conductive particles and polymeric binders or blends of polymeric binders.
BACKGROUND OF THE INVENTION
Problems associated with the generation and discharge of electrostatic charge during the manufacture and use of photographic film and paper products have been recognized for many years by the photographic industry. The accumulation of static charge on film or paper surfaces can cause irregular fog patterns in the emulsion layer. The presence of static charge also can lead to the attraction of dust, which can result in repellency spots during coating, fog, densitization, and other physical defects. The discharge of accumulated charge during or after the application of the sensitized emulsion layer(s) also can produce irregular fog patterns or “static marks” in the emulsion layer. The severity of such static problems has been exacerbated greatly 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 results primarily from the tendency of webs of high resistivity polymeric film base to charge during winding and unwinding operations (unwinding static), during transport through the coating machines (transport static), and during finishing operations such as slitting and spooling. Static charge can also be generated during the use of the final photographic film product. In an automatic camera, the winding of roll film out of and back into the film cassette, especially in a low relative humidity environment, can result in static charging and marking. Similarly, high-speed automated film processing equipment can produce static charging resulting in marking.
It is widely known and accepted that electrostatic charge can be dissipated effectively by incorporating one or more electrically conductive “antistatic” layers into the overall film structure. Antistatic layers can be applied to one or to both sides of the film support as subbing layers either beneath or on the side opposite to the sensitized emulsion layer. Alternatively, an antistatic layer can be applied as the outermost-coated layer (overcoat) either over the emulsion layers (i.e., SOC) or on the side of the film support opposite to the emulsion layers (backcoat) or both. For some applications, the antistatic function can be included in the emulsion layers. Alternatively, the antistatic layer function can be incorporated into the bulk plastic film base by means of co-extrusion or co-casting techniques.
A wide variety of electrically conductive materials can be incorporated in antistatic layers to produce a broad range of surface conductivities. Many of the traditional antistatic layers used for photographic applications employ materials, which exhibit predominantly ionic conductivity. Antistatic layers containing simple inorganic salts, alkali metal salts of surfactants, ionic conductive polymers or polymeric electrolytes containing alkali metal salts and the like have been taught in the prior art. The electrical conductivities of such ionic conductors are typically strongly dependent on the temperature and relative humidity of the surrounding environment. At low relative humidities and temperatures, the diffusional mobilities of the charge carrying ions are greatly reduced and the bulk conductivity is substantially decreased. At high relative humidities, an exposed antistatic backcoating can absorb water, swell, and soften. Especially in the case of roll films, this can result in a loss of adhesion between layers and physical transfer of portions of the backcoating to the emulsion side of the film. Also, many of the inorganic salts, polymeric electrolytes, and low molecular weight surfactants -typically used in such antistatic layers are water soluble and can be leached out during film processing, resulting in a loss of antistatic function.
In addition to alkali metal salts, colloidal metal oxide sols have been found to exhibit ionic conductivity when incorporated in antistatic layers. Typically, alkali metal salts or anionic surfactants are used to stabilize such metal oxide sols. A thin antistatic layer consisting of a gelled network of colloidal metal oxide particles (e.g., silica, antimony pentoxide, alumina, titania, stannic oxide, zirconia, etc.) with an optional polymeric binder to promote adhesion to both the support and overlying emulsion layer(s) has been disclosed in EP 250,154. An optional ambifunctional silane or titanate coupling agent can be introduced to the gelled network to improve adhesion to the overlying emulsion layers (e.g., EP 301,827; U.S. Pat. No. 5,204,219). Further, an alkali metal orthosilicate can be included to minimize the loss of conductivity by the gelled network observed when said antistatic layer is overcoated with gelatin-containing layers (U.S. Pat. No. 5,236,818). In addition, coatings containing colloidal metal oxides (e.g., antimony pentoxide, alumina, tin oxide, indium oxide, etc.) and colloidal silica with an organopolysiloxane binder have been claimed to enhance abrasion resistance as well as provide antistatic function when used as an overcoat or backcoat (U.S. Pat. No. 4,442,168).
Antistatic layers incorporating electronic rather than ionic conductors also have been described. Because their electrical conductivity depends primarily on electronic mobilities rather than on ionic mobilities, the observed conductivity is independent of relative humidity and only slightly influenced by ambient temperature. Antistatic layers containing conjugated conductive polymers, conductive carbon particles, crystalline semiconductor particles, amorphous semiconductor fibrils, and continuous semiconductive thin films or networks are well known in the prior art.
Fine particles of crystalline conductive metal oxides dispersed with polymeric binders have been used to prepare optically transparent, humidity insensitive, antistatic layers for a wide variety of imaging applications. Many binary metal oxides doped with appropriate donor heteroatoms are known to be useful in antistatic layers for photographic and electrophotographic imaging elements (e.g., U.S. Pat. Nos. 4,416,963; 4,495,276; 4,394,441; 4,418,141; 4,571,361; 4,999,276). An exhaustive listing of previously claimed conductive metal oxides includes: zinc oxide, titania, tin oxide, alumina, indium oxide, indium and zinc antimonates, silica, magnesia, zirconia, barium oxide, molybdenum trioxide, tungsten trioxide, and vanadium pentoxide. The semiconductive metal oxide most widely used in conductive layers for imaging elements is a crystalline antimony-doped tin oxide with a most preferred antimony dopant level between 0.1 and 10 atom % Sb (for Sb
x
Sn
1−x
O
2
) as disclosed in U.S. Pat. No. 4,344,441.
The present invention provides an improved imaging element having antistatic layers containing colloidal conductive metal oxide containing particles and polyesterionomer binder or polyesterionomer-gelatin blend binder system. These layers exhibit superior conductivity and dynamic wettability at a given dry weight laydown and tin oxide to binder ratio when compared to those formulated using gelatin-only binder.
This invention permits the use of substantially lower tin oxide to binder ratios and lower dry weight coverages in the antistatic layer to achieve similar or lower surface resistivities than those disclosed in Prior Art and provides superior dynamic wettability characteristics of the photographic supports subbed with antistatic layers of this invention. Additional benefits resulting from the decrease in tin oxide to gel ratio include decreased optical density and minimized image tone change.
SUMMARY OF THE INVENTION
The present invention is an imaging element which includes a support, an image-forming layer super
Lelental Mark
Noonan John M.
Young Ralph H.
Eastman Kodak Company
Ruoff Carl F.
Schilling Richard L.
Wells Doreen M.
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