| 摘要 |
A pigment composition is prepared by making an aqueous mixture of a colourless, water-soluble melamine-formaldehyde condensate, an inorganic white pigment derived from Be, Mg, Ca, Sr, Ba, Zn, Cd, Hg, Al, Ga, In or Tl, and an optical brightener which is a stilbene derivative containing at least one acid group giving water solubility, then curing the condensate, and comminuting the resultant mass. The melamine-formaldehyde resin preferably derives from 2-3 mols. formaldehyde per mol. of melamine, and the white pigment may be, e.g. MgO, ZnO, CaSO4, SrSO4, Al2O3, particularly a lithopone, CaCO3, BaSO4 or ZnS. The optical brightener is preferably a triazinylaminostilbene, particularly a compound of the formula <FORM:1032057/C3/1> wherein X is a carboxylic or sulphonic acid group, and T1 and T4 are s-triazin-2-yl residues. Examples of this type are listed. There are preferably used 0.5-5 p.b.w. of brightener and 50-200 p.b.w. of resin per 100 parts by weight of pigment. The composition is usually cured by heating to 50-200 DEG C. so that the water escapes, and the resulting mass is ground to a fine powder. In examples, pigments are prepared from 100 p.b.w. melamine-formaldehyde resin in 100 p.b.w. water, with 0.7 to 3.5 p.b.w. of various optical brighteners and 100 p.b.w. of lithopone, barium sulphate, calcium carbonate, or zinc sulphide. A white polyethylene may be obtained by incorporating into the polyethylene 2-5 parts by weight per 100 of a pigment of the invention. |
