In general, photographic elements comprise a base having photographic layers coated on one or both sides thereof. Photographic layers are for example light-sensitive silver halide emulsion layers, intermediate layers, protective layers, antihalation layers, etc.
The base in particular comprises a film of a self-supporting natural or synthetic polymeric compound such as a poly-alpha-olefin (e.g. polyethylene or polystyrene), a cellulose ester (e.g. cellulose triacetic), polyester (e.g. polyethyleneterephthalate), a polycarbonate or paper.
Most photographic light-sensitive elements have photographic layers coated on only one side of the support, the other side being free of photographic layers. A photographic elements suitable for color reproduction comprises for example a base having coated on one side thereof blue-sensitive silver halide emulsion gelatin layer or layers, green-sensitive silver halide emulsion gelatin layer or layers and red-sensitive silver halide emulsion gelatin layer or layers associated with protective, intermediate and antihalation layers. To obtain the photographic image, said silver halide photographic elements are generally exposed and processed in developer, bleaching and fixing baths.
It is known that electrostatic charges tend to accumulate during the production and the use of photographic elements, because of some surface friction resulting from contact with other surfaces. The light-sensitive layers are sensitized by the discharge of accumulated electrostatic charges and this results in the formation of dots or branched line marks (called "static marks") upon development.
To overcome the adverse effects resulting from the accumulation of static electrical charges, it is conventional practice to include an antistatic layer in the photographic elements.
Electroconductive water-soluble polymers, such as quaternary polyelectrolyte compounds (polymeric quaternary ammonium salts), have been described for use in photographic elements as backing layers to provide static protection by preventing the static built-up through electrical conductivity. A problem with these antistatic layers is their inhability to withstand photographic processing baths and their tendency to cause photographic sheets or films to stick together or to stick to other surfaces. Such problems have been partially solved by coating onto said antistatic layers a protective layer comprising hydrophobic polymers. Such antistatic double layer constructions still suffer from other disadvantages. Thus, for example, sticking under severe temperature and humidity conditions between said double layer antistatic layer and the emulsion side of the same element or other element causes stains and ferrotyping defects (by the term "ferrotyping" in the photographic art it is meant opacity stains on the hydrophilic surface of a light-sensitive material caused by sticking). Improved antistatic compositions have been described in U.S. Pat. No. 4,070,189, in EP Patent Appln. 18,601 and in Japanese Patent Appln. J5 5057-842 and J5 5065-950. These patents describe antistatic compositions comprising highly crosslinked quaternary ammonium or phosphonium salt copolymers as electroconductive compounds, obtained by copolymerizing quaternary ammonium or phosphonium salt monomers with a copolymerizable monomer containing at least two ethylenically unsaturated groups. However, under extremely severe temperature and humidity conditions, some sticking still continues to occur. Moreover, said highly crosslinked quaternary ammonium and phosphonium salt copolymers need to be used in combination with special crosslinkable latex binders, as described for example in the before mentioned EP 18,601, in order to reduce substantially ferrotyping occurrence. These methods present a number of disadvantages, such as for example cost and difficulty in preparation of said crosslinked copolymers and binders, and troubles in separating the antistatic layer from the support to recycle the latter.
Therefore, there is a continuous need for antistatic compositions which can be coated on one side of a photographic support to provide layers having the necessary antistatic chracteristics without negatively affecting the physical characteristics, especially when said layers are put in intimate contact under extremely severe conditions with the hydrophilic radiation sensitive layers coated on the other side of the support.
U.S. Pat. No. 3,607,286 describes antistatic layers of homopolymers or copolymers of a diallyldi-alkyl ammonium salt compound coated, on the back of a photographic material, from aqueous solution or from a lower primary alcohol solution. It has been found that said binderless antistatic layers have poor adhesion to the support, poor abrasion resistance and when put in contact with hydrophilic light-sensitive layers of photographic materials cause ferrotyping and other undesirable physical defects.