Titanium Dioxide in Coatings, Color
The bright, clean tone achieved with Tiona® TiO2 allows you maximum flexibility in producing a range of bright, clean colors. The excellent color of Tiona pigments also enables you to meet the more exacting specifications demanded by manufacturers of such items as light fittings and domestic appliances where high reflectivity is an important component of showroom appeal.
Metallic Impurities
Any metallic impurities present in TiO2 pigments can catalyze the formation of compounds responsible for the discoloration of coatings when subjected to heat in excess of that required for normal curing. This "overstoving" is always a problem on multi-tone items and in reject repair processes. Items such as radiators, bake-wire and heating appliances are subject to excess temperature throughout their service life. The purity of Tiona pigment ensures that overstoving discoloration is minimized.
Discoloration can also be caused by metallic impurities introduced to the millbase during dispersion of the pigment. One frequent cause of this is extended running of the mill. This is particularly the case with bead mills, sand mills and high speed dispersers where iron can be worn from the sides of the milling vessel giving the white paint a distinct gray shade. A similar graying will be obtained if a bead mill, sand mill or similar equipment is run with too low a millbase charge. This "dry" milling causes serious wear on the mill vessel.
Dispersion
A pigment only develops its full tint strength when it is fully dispersed to its optimum particle size and distribution. Tint strength is normally only considered when discussing the coloring ability of TiO2 and other colored pigments. However, if a colored resin system is being used, for example a typical long oil alkyd, then the color of the resin will influence the final color of the paint. To minimize this, pigment dispersion should be maximized. Thus to reduce the yellow tone of typical alkyd systems it is essential that the pigment is fully dispersed.
Paint Composition
Many of the ingredients, other than the pigments, used in a paint can influence its color. One obvious cause could be something as simple as using "dirty" toned extenders, often chosen for their low cost. However, this would be immediately noticeable. Other causes may not be so obvious. One that occurs frequently is the use of a reactive raw material, which goes through a colored stage during its reaction. If excess of this material is used then complete reaction will not take place. This opens the opportunity for some of the colored intermediate stage to remain, adversely influencing paint color.
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