Method of preparing {111} tabular silver chloro(bromo)iodide crystals

US6030762A · kind A · utility

Assignee

• Agfa-Gevaert NV · BE

Inventors

• Peter Verrept · Waregem, BE
• Ann Verbeeck · Begijnendijk, BE

Key dates

• Filing date: Mar 16, 1998
• Grant date: Feb 29, 2000
• Expiry date: Mar 16, 2018

Classification

• Technology area (CPC G): Physics
• CPC primary: G03C2200/44
• WIPO field: Optics
• WIPO sector: Instruments

Abstract

A method has been found of preparing a silver halide emulsion comprising silver chlorobromoiodide or silver chloroiodide tabular grains with at least 75 mole % of chloride and from 0.1 up to 3 mole % of iodide, based on silver, further having {111} crystal faces, an average aspect ratio of at least 2:1, with at least 50%, more preferable at least 75% and still more preferable more than 90% of the total projected area of all grains being provided by said tabular grains and with a variation coefficient on sphere equivalent diameter (SED) of said grains being lower than 0.30, more preferably lower than 0.25 and most preferable from 0.05 up to at most 0.15, said method comprising the steps of PA1 preparing a dispersion medium (preferably containing a gelatino-peptizer) and a crystal habit growth modifier in a reaction vessel; PA1 precipitating silver chlor(oiod)ide or silver chlorobrom(oiod)ide nuclei in a crystal nucleation step by mixing silver salt and halide salt solutions in the said dispersion medium, PA1 growing the said nuclei during one or more growth and/or physical ripening steps; characterized by PA1 maintaining the said dispersion medium at an initial pH value maintained b…