Nacreous Pigment of Black Pearl Tone

摘要

1,160,173. Lead Pigment. NIHON KOKEN KOGYO K.K. 15 Sept., 1967, No. 42245/67. Heading C1A. A highly lustrous nacreous pigment of black pearl tone comprises substantially uniform crystalline platelets characterized by strong reflectance and weak transmittance of incident light, the platelets having an optical thickness of 180-2000 mÁ, and the individual platelets consisting of a core of crystalline, light-transmitting lead salt having an index of refraction of 1À8-2À1 and substantially uniform surface layer on the upper and lower surface of a mixture of lead sulphide [salt] and PbS.Pb(OH) 2 , each of which surface layers has an optical thickness of 10-30 mÁ. The pigment may be prepared by suspending the core material in an aqueous medium, preferably having a lead ion concn. of up to 0.01 mole/litre, and adding thereto, at a rate of 0À001-0À02 mole of sulphide ion per minute, a soln. of an inorganic sulphide, the soln. having a sulphide ion concn. of 0À0001-0À03 mole per litre to form by chemical reaction on the surface of the platelets the mixture of PbS and PbS.Pb(OH) 2 . The core may be basic lead carbonate, lead hydrogen arsenate, lead phosphate, lead hydrogen phosphate or lead iodide. The inorganic sulphide may be sodium sulphide, potassium sulphide, hydrogen sulphide or ammonium sulphide. Lead acetate, lead nitrate or lead chloride may be used to provide the aqueous medium with lead ion. The suspension may be formed with conventional surfactants such as polyoxyethylene esters and ethers, alkylbenzene sulphonates, polyoxyethylene alkylbenzene sulphonates and polyoxyethylene alkylamines. A buffer soln. made from combinations of ammonium acetate, sodium acetate, sodium citrate, sodium hydrogen phosphate, potassium hydrogen phosphate, borax and sodium chloride may be added to maintain a steady rate of reaction.