Process for dispersing sensitizing dyes

Claim 2

A process for forming a colloidally stable dispersion of a spectral sensitizing dye directly in water, which comprises the steps of: a. mixing substantially water-insoluble spectral sensitizing dye particles with water in the absence of an organic solvent to form a slurry having a dye concentration of about 0.5% to about 30% on a weight/weight basis; and b. homogenizing or milling said slurry at an elevated temperature of from about 40° C. to about 50° C. in the presence of a surfactant to provide finely divided dye particles having particle sizes in the range from about 0.5 to about 1.0 μ which are uniformly dispersed in said water.

Claim 3

A process as defined in claim 1 wherein said sensitizing dye is a cyanine dye.

Claim 4

A process as defined in claim 2 wherein said cyanine dye is a thiacyanine dye.

Claim 5

A process as defined in claim 1 wherein said surfactant is a solubilizing surfactant.

Claim 6

A process as defined in claim 4 wherein said solubilizing surfactant is an alkyl naphthalene sulfonate.

Claim 7

A process as defined in claim 1 wherein said surfactant is presented at about 5% of the quantity of said sensitizing dye.

Claim 8

A process as defined in claim 1 wherein said homogenizing or milling step is carried out in the presence on an antiflocculating agent.

Claim 9

A process as defined in claim 7 wherein said antiflocculating agent is polyvinyl pyrrolidone present in a quantity less than about 0.05% of the dye amount.

Claim 10

A process as defined in claim 1 wherein the dye concentration of said slurry is about 10%.

Claim 11

A process as defined in claim 1 wherein said temperature is 45° C. ± 3° C.

Claim 12

A process for spectrally sensitizing a photographic silver halide emulsion which comprises: a. mixing substantially water-insoluble particles of a silver halide spectral sensitizing dye with water to form a slurry having a dye concentration of about 10% on a weight/weight basis; b. homogenizing or milling said slurry at an elevated temperature of from about 40° C. to about 50° C. in the presence of an alkyl aryl sulfonate surfactant, present at about 5% of the quantity of said dye, to provide finely divided dye particles having particle sizes in the range from about 0.5 to about 1.0 μ which are uniformly dispersed in said water; c. diluting said dispersion with water to a concentration less than 1% on a weight/weight basis; and d. incorporating said diluted dispersion into a melted silver halide emulsion thereby to spectrally sensitize said emulsion.

Claim 13

A process for spectrally sensitizing a photographic silver halide emulsion which comprises: a. mixing substantially water-insoluble particles of a silver halide spectral sensitizing dye with water to form a slurry having a dye concentration of about 10% on a weight/weight basis; b. homogenizing or milling said slurry at an elevated temperature of from about 40° C. to about 50° C. in the presence of an alkyl aryl sulfonate surfactant, present at about 5% of the quantity of said dye, to provide finely divided dye particles having particle sizes in the range from about 0.5 to about 1.0 μ which are uniformly dispersed in said water; c. diluting said dispersion with water to a concentration less than 1% on a weight/weight basis; and d. incorporating said diluted dispersion into a melted silver halide emulsion thereby to spectrally sensitize said emulsion.

Claim 14

A process as defined in claim 11 wherein said sensitizing dye is a thiacyanine dye.

Claim 15

A process as defined in claim 11 wherein said homogenizing or milling step is carried out in the presence of polyvinyl pyrrolidone in a quantity less than about 0.05% of the dye amount.

Claim 16

A process as defined in claim 11 wherein a small quantity of a dilute salt solution is added to the dispersion after the dilution step to improve the colloidal stability of said diluted dispersion.