For plastic products containing white pigments, their optical properties, such as whiteness and yellowness, directly affect the appearance of plastic products. Accordingly, optical performance is an important basis for determining the processing feasibility titanium white powder in the plastic mechanical activation process. We can see that in different resin systems, the whiteness of the product increases with the increase of the mass percentage of the pigment treated by the mechanical activation method, and the law is basically consistent with the non-mechanical treatment of titanium dioxide. Due to the mechanical activation method, the titanium dioxide is coated on the surface of the core material in a proportion of 30%-40%, so the maximum effective mass percentage is much higher than that of the untreated titanium dioxide. It can be seen that the opacity of the titanium dioxide after its mechanical activation treatment is reduced. It is well known that the hiding power of a pigment is determined by the crystal structure of the pigment. Titanium dioxide is the most opaque of known white pigments. Other pigments, such as heavy calcium, kaolin , magnetic white powder, etc., are not as good as titanium dioxide. Therefore, with heavy calcium and kaolin as the core and titanium dioxide as the mechanical activated pigment of the coating layer, the hiding power will be reduced. The higher the mass percentage of titanium dioxide in the pigment, the stronger the hiding power. [next] In the mechanical activation method, after the core material is mechanically activated, the active center of the particle surface is intensified, forming a new active center on the primary gap of the crystal particles, so that the finer pigment particles are optimally on the core crystal. The central distribution of the activity forms a mosaic fixation. Since the core material and the coating material are inlaid and fixed by the charge between the two kinds of seeds, the stability of the coating material on the surface of the core material particles is ensured. Further, the mechanically activated treated pigment obtained by coating in the form of a single layer of discontinuous film has uniformity which cannot be achieved by a mechanical mixing method. This stability and uniformity make mechanical activation of pigments a viable pigment surface treatment. Water Tank Water Tank FOSHAN UWOTEC NEW ENERGY CO., LTD. , https://www.uwo-heatpump.com
(1) Effect of mechanical activation on the whiteness of titanium dioxide. We first investigated the relationship between the whiteness of untreated titanium dioxide and the content of titanium dioxide in PP samples.
It can be seen from Figure 1 that at low concentrations, the whiteness of the PP template increases rapidly with increasing titanium dioxide content. However, when the mass percentage exceeds 1.8%, the whiteness rises slowly. From 1.8% to 8%, whiteness only increased by 2.8%. This indicates that there is a maximum effective mass percentage (C e ) in the coloration of the plastic. When the pigment mass percentage C
We believe that, when the percentage mass of the pigment is less than C e, increasing the number of the pigment particles in the plastic mass percentage of pigment per unit area can be increased. Since whiteness depends on the intensity of reflected light, and titanium dioxide is a substance with a high refractive index, most of the human light is reflected and refracted. Therefore, increasing the mass percentage of iron powder can increase the reflectivity of the product to light. The higher the mass percentage of titanium dioxide, the higher the whiteness. However, when the mass percentage of titanium dioxide reaches a certain level, the particles will overlap vertically. Thus, the titanium dioxide under the surface titanium dioxide particles does not function to reflect light at all. Therefore, even if the titanium dioxide mass percentage is increased, the whiteness will not be increased.
We selected the same core material, titanium white powder, and treated the surface treatment of the mechanical activation method with the same formula. The prepared titanium dioxide powder was made into masterbatch, and then injected into PP, PVC and ABS samples with the same pigment mass percentage. The results of the whiteness test are shown in Table 1 and Figure 2. 
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Comparing Table 3-6 and Figure 3-7, it can be found that when the mass percentage of the pigment treated by the mechanical activation method in the PP template reaches 2%, the whiteness is similar to the whiteness of the 1% untreated titanium dioxide PP sample. That is to say, the whiteness of the PP white plate containing 2 parts of the mechanical activation method is similar to the whiteness of the PP sample containing 1 part of the untreated titanium dioxide. Since titanium dioxide actually accounts for only 40% in the treatment of titanium dioxide by this mechanical activation method, the PP sample of 0.8% by mass of titanium dioxide is similar to the whiteness of PP sample of 1% by mass of titanium dioxide. Therefore, the use of mechanical activation to treat titanium dioxide can save 20% of untreated titanium dioxide.
(2) Effect of mechanical activation treatment of titanium dioxide on hiding power We prepared various mechanical activation methods of titanium dioxide into masterbatch, and then blown into PE film. The pigment mass percentage in the film was 1%. At a wavelength of 460 nm, eight test positions were selected, and the optical density at each point was measured with a spectrophotometer. At the same time, the thickness of each point is measured, and finally the optical density per unit thickness is calculated. The test results are shown in Table 2.
(3) Effect of mechanical activation treatment of titanium dioxide on whiteness From the whiteness data of Table 1, it can be seen that under the condition of the same pigment mass percentage, the whiteness of the titanium dioxide containing mechanically treated method is higher than that of untreated titanium dioxide. The whiteness of the sample has been reduced. This is because the titanium dioxide having a high refractive index is coated on the surface of the core material in the form of a single layer of discontinuous film. Although this single-layer coating method can control the particle size of the pigment by the mechanical activation method to a certain extent, it also brings a problem that cannot be ignored for the whiteness of the pigment. Because the light enters the plastic, after the complex reflection, refraction, scattering, the intensity of the part of the light that is finally reflected back directly determines the whiteness of the plastic. The stronger the reflected light, the higher the whiteness; the weaker the reflected light, the lower the whiteness. Usually, the iron white powder has a diameter of 0.2-0.4 μm. When a single layer of titanium dioxide is coated on the surface of the core material, the light passes through the transparent titanium dioxide layer and enters the core inner layer. Since the refractive index of the core material (CaC0 3 , kaolin is about 1.6) is smaller than that of titanium dioxide, it can absorb more light than titanium dioxide. Therefore, the mechanically activated titanium dioxide generally absorbs more light than the untreated titanium dioxide, resulting in reduced reflected light and reduced whiteness.
At the same time, it can be seen that the lower the content of titanium dioxide in the pigment treated by the mechanical activation method, the lower the whiteness of the sample to be injected. This again confirms the above assumption that the whiteness depends on the intensity of the reflected light, which in turn depends on the refractive and reflective properties of the pigment. In general, the thicker the titanium dioxide coating with high refractive power, the stronger the refractive power and the higher the whiteness.
(4) Effect of mechanical activation treatment on whiteness of titanium dioxide Titanium dioxide is injected into the same mass percentage of PP template by mechanical activation method and ordinary mixing, and the whiteness is different.
It can be seen from Fig. 3 that the whiteness of the sample containing the mechanically activated titanium dioxide is higher. We believe that in the ordinary mixing process, the mixed system is transmitted through the resin matrix by applying shear stress through the screw. In this way, it is not only impossible to ensure that the agglomerates of the core material and the coating material are completely opened and uniformly dispersed in the resin matrix, and it is impossible for the coating layer to cover the surface of the core material in the form of a monomolecular film.