Application of Titanium Dioxide in Powder Coatings
The environmental advantages of powder coatings are better than those of paints and water-based coatings, and they are an important direction for the development of coatings.
Powder coating production can be divided into four stages, namely batching, extrusion and mixing, cooling and tableting, and grinding. Titanium dioxide as a pigment component can only be dispersed during extrusion and mixing. At this time, the resin becomes fluid at a certain temperature. , Infiltrate titanium dioxide and other pigments, and shear and disperse, usually for tens of seconds.
Powder coatings have relatively high requirements for titanium dioxide, requiring good dispersibility and not easy to agglomerate; strong hiding power and tinting power; good thermal stability, at least 160 ℃ temperature resistance; must have a certain light and weather resistance, such as not easy to fade , anti-pulverization, physical properties should be durable; moderate oil absorption, good anti-bleeding.
Titanium dioxide has different percentage pigment volume concentrations in powder coatings, which will show different hiding power. When the pigment volume concentration ( PVC ) of titanium dioxide is 10% , it is an economical amount to obtain better hiding power. When the PVC concentration of titanium dioxide increases to 10 % (because the density of various coatings is different, 10% PVC concentration is equivalent to about 22 to 32% by weight ), the refraction efficiency of diffracted light will decrease due to the aggregation of titanium dioxide particles. , the result of this effect will make the coating lose part of the hiding power. When the PVC concentration of titanium dioxide is between 10 % and 25% , the rate of reduction of the refraction efficiency is slower than that of increasing the PVC concentration of titanium dioxide to enhance the covering. The increase of titanium dioxide will still increase the covering power a little. However, when the PVC concentration of titanium dioxide is above 25% , the rate of reduction of the refraction efficiency is faster than that of increasing the PVC concentration of titanium dioxide to enhance the covering. With the addition of titanium dioxide, the covering power will decrease instead.
Heat resistance refers to the degree of color stability of titanium dioxide when heated. Because the local temperature of the construction baking equipment for powder coatings is between 170 ℃ and 220 ℃, when the heat resistance of titanium dioxide is not good, the workpieces hanging in different positions in the oven will appear different colors. In general, rutile-type titanium dioxide has better heat resistance than anatase-type titanium dioxide; coated titanium dioxide has better heat resistance than uncoated titanium dioxide.
Whiteness requirements are also one of the key points. Due to the difference in process routes, raw materials, equipment, and technical levels, there will also be differences in color. Of course, the color depends on the chemical composition, but the more important and often decisive factors are its particle shape, size, particle size distribution, crystallinity. type, impurity content, etc. Therefore, the whiteness of different manufacturers is still different.