Radiation imagery chemistry: process – composition – or product th – Radiation sensitive product – Silver compound sensitizer containing
Reexamination Certificate
2002-01-28
2004-06-15
Letscher, Geraldine (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Radiation sensitive product
Silver compound sensitizer containing
C430S546000, C430S631000, C430S449000, C430S572000, C430S574000, C430S581000, C430S582000, C430S583000, C430S584000, C430S585000, C430S586000, C430S587000, C430S588000
Reexamination Certificate
active
06750002
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a process for preparing concentrated dye-water compositions for use in the spectral sensitization of photographic emulsions, wherein the compositions are formed at concentrations of anionic dyes sufficient to form a liquid crystalline dye phase in the absence of organic solvent and presence of an antifoamant nonionic surfactant.
BACKGROUND OF THE INVENTION
Many dyes useful for spectrally sensitizing silver halide emulsions are known to be substantially insoluble in water for all practical purposes. Accordingly, such dyes, as well as other photographic additives which are capable of being adsorbed on the grain surfaces of silver salts, have been added to photographic silver halide emulsions in the form of solutions in suitable water miscible solvents such as methyl alcohol, dimethylformamide or the like. However, spectrally sensitizing dyes are difficult to dissolve in the usual solvents. Consequently, large quantities of solvent are often needed for satisfactory dissolution of such additives. This presents a significant problem since the presence of residual solvent generally causes diffusion and migration of spectrally sensitizing dyes in the emulsion. Further, even minute residues of solvent promote recrystallization processes in the photographic layer which, in turn, adversely affect not only the dyes and other additives introduced using solvent but other additives in the emulsion as well. Moreover, if residues of polar organic solvents miscible with water remain in a silver halide emulsion, particularly a silver-rich emulsion having a high silver packing density, the residual solvent considerably reduces the stability of the casting emulsion which in turn causes a reduced stability during processing including phase separation between hydrophilic and hydrophobic phases, agglomeration, and coalescence as well as flocculation before casting.
Additives which need not be held on the surface of silver halide crystals by adsorption after their introduction into a photographic emulsion have long been incorporated into silver halide emulsions in the form of dispersions. For that purpose, the additive is usually dissolved in a suitable solvent, which is generally immiscible with water, in the presence of an oil former and wetting agent, and then emulsified into an aqueous gelatin solution. The low boiling solvent generally used for this purpose is subsequently removed and the resulting dispersion is added to the photographic silver halide emulsion. Unfortunately, the complete removal of the solvent from the resulting dispersion is difficult to achieve, even when low boiling solvents are employed, and particularly when polar solvents are employed. Polar solvents, in particular polar protic solvents, can be removed from gelatin dispersions only by heating, a process which adversely effects the stability of the sensitizing dye molecule. Alternatively, the use of a vacuum to remove the solvent often causes considerable foaming.
One method for obviating the harmful effects of using water miscible or immiscible organic solvents to incorporate substantially insoluble additives into silver halide emulsions and dispersions as described in British Patent 1,570,362 is to sand mill such additives in water to a particle size of less than 1 micron in the presence of a surfactant which gives rise to a surface tension of not less than 38 dynes/cm in water when used in a quantity of 1 g/l. A similar process is disclosed in U.S. Pat. No. 4,006,025 which teaches milling or homogenizing at an elevated temperature in the presence of a relatively high level of surfactant in which the sensitizing dye is at least partially soluble. The process is complicated and the use of surfactant increases finish time.
U.S. Pat. No. 4,474,872 also describes a sensitizing dye dispersion process for substantially water insoluble dyes which requires mechanically milling to a fine grain size (1 micron or less), but teaches that the use of a surfactant can be eliminated if the dye is ground at elevated temperatures (60°-80° C.), and processing conditions such as pH are strictly controlled. U.S. Pat. No. 4,683,193 similarly discloses forming dispersions of sensitizing dyes having water solubility of 0.01% by weight or less by mechanically dispersing the dyes generally at temperatures of from 40 to 80° C., and in the absence of a dispersing agent at temperatures of from 60 to 80° C. While the ability to form sensitizing dye dispersions in the absence of organic solvents and surfactants is desirable, the need for relatively high temperatures is potentially problematic as the dyes are subject to decomposition damage.
EP 0 640 225 describes a process of preparing concentrated dye-water compositions of spectral sensitizing dyes in the absence of organic solvent or surfactant at moderate temperatures of from 20-50° C., wherein the spectral sensitizing dye is selected to be slightly water soluble (at least 0.005 wt %), and a dye-water composition containing dye at a concentration higher than the solubility limit of the dye is agitated for an extended time period of at least 30 minutes. JP Kokai 05-297496 similarly discloses a method of dispersing spectral sensitizing dyes which have limited levels of solubility in water (0.0002 to 0.04 mol/L) in the absence of organic solvents and surfactants, wherein the dyes are mechanically dispersed in the form of solid particles.
For most materials, it is generally accepted that only three states of matter exist; namely, solids, liquids and gases. However, some materials exhibit a fourth state of matter commonly referred to as a liquid crystal phase (or mesophase). Liquid crystal phases are neither crystalline solids nor isotropic liquids, but exhibit some of the characteristics of both. A liquid crystal phase can be described simply as being a liquid with a certain degree of molecular order. This molecular order gives rise to measurable anisotropy in the bulk properties of a material that is otherwise much like a liquid. Consequently, the physical properties of liquid crystalline materials are unique and distinct from those of solids and liquids. It has been found that many dyes may be advantageously dispersed directly in an aqueous medium at concentrations above their water solubility levels in the form of well-ordered liquid-crystalline phases (a lyotropic mesophase), such as dyes which form smectic liquid-crystalline phases (W. J. Harrison, D. L. Ma-teer & G. J. T. Tiddy, J. Phys. Chem. 1996, 100, pp 2310-2321). More specifically, many anionic sensitizing dyes will form liquid-crystalline J-aggregates in aqueous-based media (see The Theory of the Photographic Process, 4th edition, T. H. James, editor, Macmillan Publishing Co., New York, 1977, for a discussion of aggregation). Mesophase-forming dyes may be readily identified by someone skilled in the art using polarized-light optical microscopy as described by N. H. Hartshorne in The Microscopy of Liquid Crystals, Microscope Publications Ltd., London, 1974.
Because of the small size of the liquid crystalline domains in liquid crystalline dispersions or suspensions and the interactions between them, the viscosities of liquid crystalline anionic sensitizing dye dispersions are typically very high, particularly at low shear. However, because these structures are interacting, the dispersions also exhibit strong shear thinning behavior (i.e., their viscosity drops precipitously with increase in the shear rate). The manufacture of such dispersions thus requires high shear mixing of the aqueous phase to overcome the high viscosity of the final dispersions and to ensure that mixing occurs through the entire aqueous phase.
While the preparation of concentrated dye-water compositions comprising liquid crystalline dispersions in the absence of organic solvent and surfactants would be desirable, the preparation of such compositions has been found to be complicated by the problem of air entrainment. Air bubbles may be easily generated, e.g., by cavitation at the tip of impellers used to perform high shea
Baugher Jeffrey S.
Hasberg Dirk J.
Lobo Lloyd A.
Novak James E.
Anderson Andrew J.
Letscher Geraldine
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