Various techniques are known for dispersing hydrophobic photographically useful compounds such as photographic couplers into photographic element layer coating compositions comprising hydrophilic colloids.
Photographic dye forming couplers, as well as other hydrophobic photographically useful compounds, are typically incorporated into a hydrophilic colloid layer of a photographic element by first forming an aqueous dispersion of the couplers and then mixing such dispersion with the layer coating solution. An organic solvent is typically used to dissolve the coupler, and the resulting organic solution is then dispersed in an aqueous medium to form the aqueous dispersion.
The organic phase of these dispersions frequently includes high boiling or permanent organic solvents, either alone or with low boiling or water miscible solvents which are removed after dispersion formation. Permanent high boiling solvents have a boiling point sufficiently high, generally above 150° C. at atmospheric pressure, such that they are not evaporated under normal dispersion making and photographic layer coating procedures. Permanent high boiling coupler solvents are primarily used in the conventional “oil-protection” dispersion method whereby the organic solvent remains in the dispersion, and thereby is incorporated into the emulsion layer coating solution and ultimately into the photographic element.
The conventional “oil in water” dispersion method for incorporating hydrophobic couplers is described, e.g., in U.S. Pat. No. 2,322,027 by Jelly and Vittum. In such conventional process, the coupler is dissolved in a high boiling water immiscible solvent, mixed with aqueous gelatin, and dispersed using a colloid mill or homogenizer. The presence of the high boiling solvent provides a stable environment for the hydrophobic coupler, as well as generally increasing the reactivity of the coupler upon photographic processing. The presence of high levels of permanent solvent in photographic elements, however, may adversely impact the physical integrity of such elements.
Photographic dispersions and layers of photographic elements that contain relatively low levels of permanent solvent or essentially no coupler solvent at all are known in the art. Dispersions of photographic compounds made without permanent solvent are described, e.g., in U.S. Pat. No. 2,801,170. Co-dispersions of yellow dye forming couplers and yellow dye light stabilizers made with no coupler solvent to improve light stability are described in U.S. Pat. No. 5,891,613. Yellow coupler dispersions featuring high coupler reactivity in a no solvent environment to facilitate layer thinning and to improve light stability are described in U.S. Pat. No. 5,879,867. In general, however, coupler dispersions containing little or no permanent solvent have lower coupler reactivity than solvent-rich dispersions, which is undesirable since higher material laydowns are required resulting in higher manufacturing cost. This is especially true with dispersions of cyan dye forming couplers. U.S. Pat. No. 5,112,729 describes a photographic material containing a cyan naptholic coupler and a high-boiling solvent present in a weight ratio with respect to the coupler in the layer of not more than 0.3. Low solvent dispersions of cyan dye forming couplers to provide high coupler reactivity and enable reduced coated dry thickness are disclosed in U.S. Pat. No. 5,834,175. Use of cyan coupler dispersions with reduced levels of a saturated alcoholic high boiling solvent as permanent solvent to improve scratch resistance while maintaining high coupler reactivity are described in commonly assigned, copending U.S. Ser. No. 11/261,047, filed Oct. 28, 2005, the disclosure of which is incorporated by reference herein.
It is also known in the art to use various lubricants in the outermost layer of photographic elements to reduce friction and to improve their abrasion resistance. It is understood that the addition of such lubricants lowers the contact friction between the imaging element and potentially damaging surfaces as the two surfaces slide past one another in intimate contact. Examples of lubricants used to lower contact friction include silicone fluids as described in U.S. Pat. No. 3,489,567 and wax esters of fatty acids or alcohols contained in U.S. Pat. No. 3,121,060. Materials known to reduce sliding friction of silver halide containing photographic elements include dimethylsilicones and specific surfactants disclosed in U.S. Pat. No. 3,042,522, GB 1,143,118, and JP-A-51-14163. A surface layer having improved antistatic properties and lubricity is described in U.S. Pat. No. 4,623,614. The combination of a silicone copolymer and colloidal silica in the outermost protective layer of a photographic element having a dynamic friction coefficient of 0.35 or less is described in U.S. Pat. No. 5,208,139. Use of some of these lubricants may suffer the disadvantage of creating light scatter, which may reduce the maximum achievable densities in the imaging layers. Also, some of such lubricants have a propensity to transfer from the protective overcoat layer to the backside of the photographic element, or they may be partially removed during photographic processing thereby reducing their effectiveness.
Methods for providing lubricant droplets having narrow particle size distributions using a limited coalescence process to improve the lubricating properties of photographic elements are given in U.S. Pat. No. 5,541,048 and U.S. Pat. No. 6,068,957. The use of fluoro-containing compounds as lubricants for imaging elements is also known in the art. The incorporation of sub-micron particles of fluoroethylene polymers into a transparent magnetic layer on photographic film, e.g., is described in U.S. Pat. No. 5,807,661. A lubricant layer comprising a fluoropolymer resin coated on a transparent magnetic layer by vapor deposition is disclosed in U.S. Pat. No. 6,228,570. The use of tetrafluoroethylene telomers for improving the lubricity and abrasion resistance of photographic films is described in U.S. Pat. No. 3,862,860. A method of forming polymer particles containing a fluorinated lubricant for use in the overcoat layer of an imaging element is given in U.S. Pat. No. 6,165,702. Lubricant particles having a mean size greater than 1 micron employed in the protective overcoat of a photographic paper is described in U.S. Pat. No. 6,613,503. A photographic element with improved scratch resistance containing lubricant particles having a narrow size distribution and a droplet size related to the thickness of the overcoat layer is disclosed in U.S. Pat. No. 5,529,891. Photographic elements comprising highly lubricated protective outermost layers in combination with both relatively low Tg crosslinked elastomeric matte particles and higher Tg permanent matte particles to provide good manufacturability of the imaging element while also maintaining wear and other desired film performance properties are described in U.S. Pat. No. 6,913,874.