Patent GB-992805-A (GB)
Title: Nacreous pigment and method for preparing same
IPC: C09C1/00
Filed: 1962-04-09
Abstract: A nacreous pigment comprises platelets each comprising a plurality of adhering, light transmitting layers of nacreous material, each layer having a different refractive index from the layer or layers immediately adjacent thereto and the layers being such that, in use when white light falls on the pigment, light is reflected at the layer surface to give a nacreous effect by virture of the refractive index and thickness of each platelet. In Examples 1 and 2, pigments comprising ZnS and MgF2 layers are dispersed in cellulose nitrate and nitrocellulose lacquers and the resulting compositions used to coat beads. In Example 10, a suspension of a pigment comprising ZnS and MgF2 layers, in isopropanol is dispersed in methyl methacrylate partial polymer and the resultant composition is used to form an interference filter by heating it in a casting cell.  In Example 11, the dried pigment of Example 1 is mixed with cellulose acetate powder and then extruded to give a rod which may be made into beads of jewellery, furniture legs or shelf supports.  Specifications 957,535 and 992,804 are referred to.ALSO:A nacreous pigment comprises platelets each comprising a plurality of adhering, light transmitting layers of nacreous material, each layer having a different refractive index from the layer or layers immediately adjacent thereto and the layers being such that, in use when white light falls on the pigment, light is reflected at the layer surface to give a nacreous effect by virtue of the refractive index and thickness of each platelet. The nacreous materials mentioned are guanine, lead carbonate, lead hydrogen phosphate, bismuth oxychloride, glass, zinc oxide, zinc sulphide, titanium dioxide, lead chloride, magnesium fluoride, cryolite, and calcium carbonate.  The composite pigments are prepared by successively depositing e.g. by vacuum sublimation or evaporation, a substrate and the required number of nacreous materials on to a moving surface.  The coated surface is then washed with solvent, e.g. water, which dissolves the substrate and the pigment which flakes off, is then fractured mechanically.  The moving surface may be an endless belt of cellulose acetate, cellulose, polyfluorocarbon, polyethylene, or polyester film, which may be metallized, e.g. by coating with aluminium by evaporation, a rotating glass or metal disc or a rotating steel or chromium drum.  The surface may also be ceramic.  The substrate may be sodium and potassium chlorides, sodium bromide, sodium and potassium tetraborates, boric acid, magnesium chloride and calcium chloride and bromide.  The examples disclose the pigments of the following structures: (1) and (2) ZnS, MgF2; (3) MgF2, ZnS, MgF2; (4) ZnS, MgF2, ZnS, MgF2; (5) ZnO, cryolite, ZnO; (6) guanine, CaF2, guanine; (7) guanine, MgF2, guanine; and (8) TiO2, MgF2, TiO2.  Specifications 957,535 and 992,804 are referred to.ALSO:A nacreous composite pigment comprising a plurality of layers is prepared by successively depositing, e.g. by vacuum sublimation or evaporation, on to a moving surface a substrate and the required number of nacreous materials. The coated surface is then washed with solvent, e.g. water, which dissolves the substrate and the pigment flakes off.  The moving surface may be ceramic, an endless belt of cellulose acetate, cellulose, polyfluorocarbon, polyethylene or polyester film, which may be metallized, e.g. by coating with aluminium by evaporation, a rotating glass or metal disc, or a rotating steel or chromium drum.  The substrate may be sodium and potassium chlorides, sodium bromide, sodium and potassium tetraborates, boric acid, magnesium chloride and calcium bromide and chloride.  In the examples the layers deposited successively on the moving surface coated with substrate are (1) and (2) ZnS and MgF2; (3) MgF2, ZnS and MgF2; (4) ZnS, MgF2, ZnS and MgF2; (5) ZnO, cryolite and ZnO; (6) guanine, CaF2 and guanine; (7) guanine, MgF2 and guanine; and (8) TiO2, MgF2 and TiO2. Specifications 957,535 and 992,804 are referred to.ALSO:In Example 11 a dry pigment comprising layers of zinc sulphide and magnesium fluoride is mixed with cellulose acetate powder and from the resultant composition a rod is extruded which may be formed into beads of jewellery.  Specifications 957,535 and 992,804 are referred to.ALSO:Alabaster beads are coated, e.g. by dipping, with compositions comprising a composite nacreous pigment comprising layers of zinc sulphide and magnesium fluoride dispersed in nitrocellulose or cellulose nitrate lacquer, to make simulated pearls. Specifications 957,535 and 992,804 are referred to.