Process for the preparation of silver halide photographic emulsions containing grains having (100) faces with cavities and photographic emulsions so prepared

• US 5,541,053 A
• Filed: 06/05/1995
• Issued: 07/30/1996
• Est. Priority Date: 10/20/1993
• Status: Expired due to Fees

• Current Assignee: Eastman Kodak Company
• Original Assignee: Eastman Kodak Company
• Inventors: Martin, Didier J.
• Primary Examiner(s): Baxter, Janet C.
• Application Number:
  US08/465,035
• Time in Patent Office: 421 Days
• Field of Search: 430/567, 430/569
• US Class Current: 430/567
• CPC Class Codes: G03C 1/015 Apparatus or processes for the preparation of emulsions coating, drying G03C1/74 ; G03C1/07 takes precedence; special processes for tabular grains G03C1/0051
• CPC Class Codes: G03C 1/035 characterised by the crystal form or composition, e.g. mixed grain
• CPC Class Codes: G03C 1/18 with three CH groups
• CPC Class Codes: G03C 2001/0156 pAg value; pBr value; pCl value; pI value
• CPC Class Codes: G03C 2001/03535 Core-shell grains
• CPC Class Codes: G03C 2200/44 pH value

Abstract

The present invention concerns a process for obtaining silver halide photographic emulsions containing grains of the core/shell type having {100} faces with cavities, and the corresponding photographic emulsions.

These emulsions present an improved sensitivity.

Claims

1. A process for preparing silver halide emulsions containing silver halide grains having {100} crystal faces comprised of a silver bromide or bromoiodide core and a silver bromochloride shell surrounding the core wherein the shell presents at least one {100} crystal face laterally surrounding a concave surface, and from 10 to 90 percent of the projected area of the concave surface and the laterally surrounding {100} crystal face being accounted for by the concave surface, comprising the following stages :

(a) providing silver bromide or silver bromoiodide nuclei in a colloidal dispersion medium, at a pAg from about 8.5 to about 9.5, a temperature from about 40°

C. to about 70°

C. and a pH from about 5.0 to about 7.0,

(b) precipitating silver bromide or silver bromoiodide on the nuclei, at the same pAg, pH, and temperature as in stage (a) until cores with a mean equivalent spherical diameter of between 0.1 and 2.0 μ

m are obtained;

(c) successively adjusting the pAg to a value between 7.5 and 8.0 and then to a value between 6.0 and 7.5, while maintaining the temperature at approximately 60°

C.;

(d) forming a silver bromochloride shell on the cores by double jet addition with a first step of introduction of reactants at an accelerated flow rate and a second step of introduction of reactants at a constant flow rate, while maintaining pAg at a value between 6.0 and 7.5, temperature between 50° and

80°

C., and pH between 5.0 and 7.0, during a period of time sufficient for the formation of at least one concave surface surrounded by a {100} crystal face.

2. A process according to claim 1, wherein in (d) the accelerated flow rate is defined by introducing from 5 to 50 percent of total silver with a rate of introduction increased from 2 to 20 times during said first step.

3. A process according to claim 2, wherein in (d) the accelerated flow rate is defined by introducing from 30 to 40 percent of total silver with a rate of introduction increased from 4 to 10 times during said first step.

4. A photographic silver halide emulsion containing silver halide grains comprised of a silver bromide or bromoiodide core and a silver bromochloride shell surrounding the core, wherein the shell presents a {100} crystal face laterally surrounding a concave surface, and from 10 to 90 percent of the projected area of the concave surface and the laterally surrounding {100} crystal face is accounted for by the concave surface.

5. A photographic silver halide emulsion according to claim 4, wherein from 10 to 40 percent of the projected area of the concave surface and the laterally surrounding {100} crystal face is accounted for by the concave surface.

6. A photographic silver halide emulsion according to claim 4, wherein the silver halide grains have an equivalent spherical diameter of from 0.3 to 5.0 μ

m and a volume coefficient of variation less than 10 percent.

7. A photographic silver halide emulsion according to claim 4, wherein the shell is a silver bromochloride shell containing from 3 to 70% mole percent chloride based on total silver in the grain.

8. A photographic silver halide emulsion according to claim 4, wherein the core is a silver bromoiodide core and the shell is a silver bromochloride shell containing from 3 to 15% mole percent chloride based on total silver in the grain.

9. A photographic silver halide emulsion according to claim 8, wherein the silver bromoiodide core contains between 2 and 5 mole percent iodide and the silver bromochloride shell contains from 3 to 15 mole percent chloride, the mole percentages being based on total silver in the grain.

10. A photographic silver halide emulsion according to claim 4, wherein the core is a silver bromide core and the shell is a silver bromochloride shell containing from 15 to 70% mole percent chloride based on total silver in the grain.

11. A photographic silver halide emulsion according to claim 4, wherein the core is a silver bromoiodide core containing up to 30% mole percent iodide based on total silver in the core.

12. A photographic silver halide emulsion according to claim 4, wherein the shell:

core mole ratio in the grains is between approximately 1;

1 and 5;

1.

13. A photographic product comprising at least one layer of photographic silver halide emulsion according to claim 4.