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Features of covering polymer
Contribution to cover
Titanium dioxide is by far the most commonly used white wax for pigment in the coating industry. The refractive index of rutile titanium dioxide is about 2.76, while the refractive index of most emulsions is about 1.5. When the refractive index difference between the continuous phase and the dispersed phase is greater than 0.2, the light scattering phenomenon becomes obvious, and the dispersed phase thus has hiding power. Since the refractive index of the emulsion remains roughly constant, the higher refractive index of the titanium dioxide helps maximize the covering ability of the paint film, and the light per unit volume of the titanium dioxide
The scattering efficiency of titanium dioxide depends on its concentration. Theoretically speaking, each titanium dioxide particle can scatter a certain amount of light. The actual performance line of titanium dioxide is achieved when the particle interval is twice the diameter of the titanium dioxide particle. . When PVC<10%, the interval of titanium dioxide particles is usually
The PYC of 8%~10% of titanium dioxide can meet or exceed this requirement. Figure 20-5 The effect of over-aggregation of titanium dioxide on the hiding ability, so that the titanium dioxide can be fully and effectively used; but when the pigment volume of titanium dioxide When the concentration increases to more than 10%, the scattering efficiency of scattered light will decrease due to the aggregation of titanium dioxide particles, resulting in a decrease in the overall scattering ability of titanium dioxide.
We call this effect the phenomenon of over-aggregation of titanium dioxide. Figure 20-5 shows the effect of over-aggregation of titanium dioxide on the hiding power.
In order to obtain the required hiding power, the concentration of titanium dioxide in many coatings will exceed 8%~10%, so the titanium dioxide will produce over-aggregation, which will affect the full play of its hiding power, which will undoubtedly increase the cost of the coating. Under low PVC conditions, the unit covering cost of titanium dioxide is constant, which is a reflection of the linear region of the titanium dioxide scattering curve. With the over-polymerization of titanium dioxide dominating at high dosages, the number of timbers using titanium dioxide has risen sharply , The result is a rapid increase in the cost of coverage. To put it simply, with the continuous addition of titanium dioxide, the cost continues to rise, but the efficiency continues to decline, and a large number of people are traded in exchange for limited coverage. Fortunately, the use of masking polymers can reduce the efficiency loss caused by the overpolymerization of titanium dioxide and improve the hiding power of the coating.
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