# US 5,702,879 A · Process of preparing monodispersed tabular silver halide emulsion > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,702,879 A - Document ID: US5702879A - Status: Granted - Kind: A - Application number: 08/606,715 - Filed: 1996-02-27 - Granted: 1997-12-30 - Earliest claimed: 1995-03-29 - Assignees: Minnesota Mining and Manufacturing Company - Inventors: Richard A. Barcock - Web page: https://patentgrep.com/patent/US5702879A ## CPC - G03C 1/0051: {Tabular grain emulsions} - 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}) - G03C 1/043: Polyalkylene oxides; Polyalkylene sulfides; Polyalkylene selenides; Polyalkylene tellurides - G03C 1/07: Substances influencing grain growth during silver salt formation - G03C 2001/0156: {pAg value; pBr value; pCl value; pI value} - G03C 2001/0357: {Monodisperse emulsion} - G03C 2200/44: pH value - G03C: PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES (for photomechanical purposes G03F); PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY (photographic processes characterised by the use or manipulation of apparatus classifiable per se in subclass G03B, see G03B; photomechanical production of textured or patterned surfaces G03F; electrophotography, magnetography G03G) ## Abstract The present invention relates to a process for preparing monodispersed tabular silver halide grain emulsions, said process comprising the following steps: (a) forming a population of silver halide nuclei in a dispersing medium having a pH lower than 3 and a pBr in the range of from 1 to 2, (b) ripening said population of silver halide nuclei in presence of a silver halide solvent, (c) performing a first growing of said silver halide nuclei at a pBr value in the range of from 1 to 2, and (d) performing a second growing of said silver halide nuclei at a value in the range of from 2 to 2.7. According to a preferred embodiment of the present invention a polyalkylene oxide-polyalkylsiloxane copolymer is present during at least one of the above mentioned steps (a) to (d). The process of the present invention enable the growth of monodispersed tabular silver halide grain emulsions having a reduced amount of non-conforming grains and a lower coefficient of variation (COV). ## Claims ### Claim 1 A process of preparing monodispersed tabular silver halide grain emulsions, said process comprising the following steps: (a) forming a population of silver halide nuclei in a dispersing medium having a pH lower than 3 and a pBr in the range of from 1 to 2, (b) ripening said population of silver halide nuclei in presence of a silver halide solvent, (c) performing a first growing of said silver halide nuclei at a pBr value in the range of from 1 to 2, and (d) performing a second growing of said silver halide nuclei at a pBr value in the range of from 2 to 2.7. ### Claim 2 (depends on 1) The process according to claim 1, wherein said monodispersed tabular silver halide emulsion comprises tabular silver halide grains having a thickness lower than 0.4 .mu.m and an average aspect ratio higher than 3:1, the projected area of said tabular silver halide grains accounting for at least 80% of the total projected area. ### Claim 3 (depends on 1) The process according to claim 1, wherein said monodispersed tabular silver halide emulsion has a coefficient of variation lower than 20%. ### Claim 4 (depends on 1) The process according to claim 1, wherein the pH value of said dispersing medium during step (a) ranges from 1.5 to 2.5. ### Claim 5 (depends on 1) The process according to claim 1, wherein the pBr value of said dispersing medium during step (a) ranges from 1.2 to 1.7. ### Claim 6 (depends on 1) The process according to claim 1, wherein said silver halide solvent is added during said ripening step (b). ### Claim 7 (depends on 1) The process according to claim 1, wherein said silver halide solvent is added after at least 5 minutes from the start of the ripening step. ### Claim 8 (depends on 1) The process according to claim 1, wherein said silver halide solvent is ammonia. ### Claim 9 (depends on 1) The process according to claim 1, wherein said first growing step (c) is performed at a pBr value in the range of from 1.2 to 1.8. ### Claim 10 (depends on 1) The process according to claim 1, wherein said second growing step (d) is performed at a pBr value in the range of from 2.2 to 2.6. ### Claim 11 (depends on 1) The process according to claim 1, wherein a polyalkylene oxidepolyalkylsiloxane copolymer is added during at least one of said steps (a), (b), (c), and (d). ### Claim 12 (depends on 1) The process according to claim 1, wherein a polyalkylene oxidepolyalkylsiloxane copolymer is added during said nucleation step (a). ### Claim 13 (depends on 11) The process according to claim 11, wherein said polyalkylene oxidepolyalkylsiloxane copolymer has the following general formula (I): ##STR8## wherein LAS represents a lipophilic alkylene siloxane block unit, HAO represents a hydrophilic alkylene oxide block unit, LAO represents a terminal lipophilic alkylene oxide block unit, and L is a lipophilic hydrocarbon system. ### Claim 14 (depends on 11) The process according to claim 11, wherein said polyalkylene oxidepolyalkylsiloxane copolymer has the following general formula (II): ##STR9## wherein LAS represents a lipophilic alkylene siloxane block unit, HAO represents a hydrophilic alkylene oxide block unit, LAO represents a terminal lipophilic alkylene oxide block unit, and SB is a silicone backbone. ### Claim 15 (depends on 11) The process according to claim 11, wherein said polyalkylene oxidepolyalkylsiloxane copolymer has the following general formula (III): ##STR10## wherein R is a methyl group, R' can be either hydrogen or a lower alkyl radical of from 1 to 4 carbon atoms, x is an integer from 0 to 100, y is an integer from 1 to 50, m is an integer from 1 to 50, n is an integer from 1 to 50, and p is an integer from 2 to 6. ### Claim 16 (depends on 11) The process according to claim 11, wherein said polyalkylene oxidepolyalkylsiloxane copolymer has the following general formula (IV): ##STR11## wherein R is a methyl group, R' can be either hydrogen or a lower alkyl radical of from 1 to 4 carbon atoms, y is an integer from 3 to 50, m is a integer from 1 to 50, n is an integer from 1 to 50, and p is an integer from 1 to 50. ### Claim 17 (depends on 11) The process according to claim 11, wherein said polyalkylene oxidepolyalkylsiloxane copolymer is present in the dispersing medium at a concentration ranging from 5 to 200 mg per mole of total silver added during silver halide grain formation.