Silver bromide emulsions of narrow grain size distribution and processes for their preparation

Claim 2

A radiation-sensitive emulsion comprised of a dispersing medium and silver bromide grains, wherein tabular silver bromide grains bounded by two substantially parallel square or rectangular major crystal faces and having an average aspect ratio of at least 8.5:1 account for at least 50 percent of the total projected surface area of the silver bromide grains present in the emulsion.

Claim 3

A radiation-sensitive emulsion according to claim 1 wherein said tabular silver bromide grains exhibit a coefficient of variation of less than 30.

Claim 4

A radiation-sensitive emulsion according to claim 1 wherein said tabular silver bromide grains exhibit a thickness of less than 0.3 micron.

Claim 5

A radiation-sensitive emulsion according to claim 1 in which said tabular silver bromide grains exhibit an average aspect ratio of greater than 10:1.

Claim 6

A radiation-sensitive emulsion according to claim 1 wherein said tabular silver bromide grains account for at least 70 percent of the total projected surface area of the silver bromide grains present in the emulsion.

Claim 7

A radiation-sensitive emulsion according to claim 1 wherein said tabular silver bromide grains account for at least 90 percent of the total projected surface area of the silver bromide grains present in the emulsion.

Claim 8

A radiation-sensitive emulsion comprised of a dispersing medium and silver bromide grains, wherein tabular silver bromide grains having a thickness of less than 0.3 micron bounded by (100) crystallographic planes and having two substantially parallel square or rectangular major crystal faces have an average aspect ratio of greater than 10:1, account for at least 70 percent of the projected surface area of the silver bromide grains, and exhibit a coefficient of variation of less than 20.

Claim 9

A radiation-sensitive emulsion comprised of a dispersing medium and silver bromide grains, wherein tabular silver bromide grains having a thickness of less than 0.3 micron bounded by (100) crystallographic planes and having two substantially parallel square or rectangular major crystal faces have an average aspect ratio of greater than 10:1, account for at least 70 percent of the projected surface area of the silver bromide grains, and exhibit a coefficient of variation of less than 20.

Claim 10

A radiation-sensitive emulsion comprised of a dispersing medium and silver bromide grains, wherein tabular silver bromide grains having a thickness of less than 0.2 micron bounded by (100) crystallographic planes and having two substantially parallel square or rectangular major crystal faces have an average aspect ratio of greater than 10:1, account for at least 90 percent of the projected surface area of the silver bromide grains, and exhibit a coefficient of variation of less than 20.

Claim 11

A radiation-sensitive emulsion comprised of a dispersing medium and silver bromide grains, wherein tabular silver bromide grains having a thickness of less than 0.2 micron bounded by (100) crystallographic planes and having two substantially parallel square or rectangular major crystal faces have an average aspect ratio of greater than 10:1, account for at least 90 percent of the projected surface area of the silver bromide grains, and exhibit a coefficient of variation of less than 20.

Claim 12

A radiation-sensitive emulsion according to claim 8 wherein said tabular silver bromide grains consist essentially of silver bromide as the sole silver halide present.

Claim 13

In a photographic element comprised of a support and, located on said support, at least one silver halide emulsion layer, the improvement comprising said silver halide emulsion layer comprising an emulsion according to claim 1, 2, 3, 4, 5, 6, 7, 8, or 9.

Claim 14

In a process of producing a silver bromide emulsion containing tabular silver bromide grains bounded by two substantially parallel square or rectangular major crystal faces comprising providing a monodisperse silver bromide emulsion containing cubic seed grains having an edge length of less than 0.15 micron and ripening the seed grains to produce tabular grains, the improvement comprising while maintaining the pAg of the seed grain emulsion in the range of from 5.0 to 8.0, ripening the emulsion in the substantial absence of nonhalide silver ion complexing agents to produce tabular silver bromide grains having an average aspect ratio of at least 8.5:1.

Claim 15

In a process of producing a silver bromide emulsion containing tabular silver bromide grains bounded by two substantially parallel square or rectangular major crystal faces comprising providing a monodisperse silver bromide emulsion containing cubic seed grains having an edge length of less than 0.15 micron and ripening the seed grains to produce tabular grains, the improvement comprising while maintaining the pAg of the seed grain emulsion in the range of from 5.0 to 8.0, ripening the emulsion in the substantial absence of nonhalide silver ion complexing agents to produce tabular silver bromide grains having an average aspect ratio of at least 8.5:1.

Claim 16

A process according to claim 11 wherein the seed grains have an edge length of less than 0.08 micron.

Claim 17

A process according to claim 11 wherein ripening is conducted at a pH in the range of from 5.5 to 7.0.

Claim 18

A process according to claim 11 wherein ripening is conducted at a temperature in the range of from 50° to 80° C.

Claim 19

A process according to claim 11, 12, 13, or 14 wherein the seed grains are produced by a double-jet precipitation reaction of an aqueous silver salt solution and an aqueous alkali halide salt solution at a pAg in the range of from 5.0 to 8.0.

Claim 20

A process according to claim 15 wherein said aqueous salt solutions are of less than 2 molar concentration.

Claim 21

A process according to claim 16 wherein said aqueous salt solutions are of less than 1 molar concentration.

Claim 22

A process according to claim 15 wherein the double-jet precipitation is undertaken at a temperature of greater than 20° C.

Claim 23

A process according to claim 15 wherein the double-jet precipitation is undertaken at a pH in the range of from 2.0 to 4.5.

Claim 24

In a process of producing a silver bromide emulsion comprised of a dispersing medium and tabular grains bounded by (100) crystal faces comprising providing a monodisperse emulsion containing cubic seed grains and ripening the seed grains to produce tabular grains the improvement comprising precipitating at a pAg of from 6.5 to 7.5, a pH of from 2.0 to 4.5, and a temperature of greater than 20° C. a monodisperse silver bromide emulsion comprised of a dispersing medium and cubic seed grains having an average edge length of less than 0.08 micron, and while maintaining the seed grain emulsion at a pAg in the range of from 6.5 to 7.5, a pH in the range of 6.0 to 7.0, and a temperature of from 50° to 70° C., ripening the seed grain emulsion in the absence of silver ion complexing agents other than bromide to produce tabular silver bromide grains having an average aspect ratio of at least 10:1 and a coefficient of variation of less than 20.

Claim 25

In a process of producing a silver bromide emulsion comprised of a dispersing medium and tabular grains bounded by (100) crystal faces comprising providing a monodisperse emulsion containing cubic seed grains and ripening the seed grains to produce tabular grains the improvement comprising precipitating at a pAg of from 6.5 to 7.5, a pH of from 2.0 to 4.5, and a temperature of greater than 20° C. a monodisperse silver bromide emulsion comprised of a dispersing medium and cubic seed grains having an average edge length of less than 0.08 micron, and while maintaining the seed grain emulsion at a pAg in the range of from 6.5 to 7.5, a pH in the range of 6.0 to 7.0, and a temperature of from 50° to 70° C., ripening the seed grain emulsion in the absence of silver ion complexing agents other than bromide to produce tabular silver bromide grains having an average aspect ratio of at least 10:1 and a coefficient of variation of less than 20.