Compared with precipitated barium sulfate in powder coatings, the particle size of calcium silicate is not much different, but the oil absorption is significantly higher than that of precipitated barium sulfate. The density of calcium silicate is about 2.7, and the whiteness of calcium silicate is relatively low. If the amount added is too high, it may affect the whiteness of the final paint film.

According to the formula, the substitution gradient of calcium silicate is 10%, and the precipitated barium sulfate in the formula is replaced from 0% to 100% respectively, and experiments are carried out. The performance indicators of the paint film of the final polyester powder coating are shown in the table. 3.

It can be seen from the experimental data that with the increase of the ratio of calcium silicate to replace barium sulfate, the gloss of the paint film shows an obvious downward trend. When the filler is 100% precipitated barium sulfate, the gloss of the paint film is 79.2°, and when the filler is 100° When % calcium silicate, the gloss of the paint film is only 56.5°, indicating that calcium silicate is a kind of dull filler compared with barium sulfate, which may be caused by the higher oil absorption of calcium silicate and barium sulfate. of. Therefore, in some powder coatings with high gloss requirements, the addition amount of calcium silicate should not be too high.

From the perspective of hardness index, with the increase of the addition amount of calcium silicate, the hardness of calcium silicate for powder coatings is obviously improved. When calcium silicate replaces 20% of precipitated barium sulfate (addition amount is 8%), the hardness of the paint film increases from the initial H to 2H. When the replacement amount reaches 90% (addition amount is 18%), the hardness of the paint film reaches 3H.

In terms of adhesion, calcium silicate and precipitated barium sulfate have basically the same contribution to adhesion. Compared with 20% precipitated barium sulfate and 20% calcium silicate, the adhesion is both grade 0.

In terms of impact performance, with the increase of calcium silicate addition, before 1:1, the impact resistance recoil 50cm can pass, after this ratio, with the increase of calcium silicate substitution, the impact performance gradually declines , indicating that calcium silicate is a more rigid material than barium sulfate.

As a functional filler, calcium silicate can significantly improve the film hardness and heat resistance temperature of the powder coating when it is used in epoxy polyester powder coatings. When the addition amount of calcium silicate is about 8%, the hardness of the paint film is 2H, and when the addition amount reaches 18%, the hardness of the paint film reaches 3H; the temperature of 5% weight loss can be increased by up to 13℃, and the maximum weight loss temperature can be increased by 9.1 °C.

Comparison of T5 and Tm of powder coatings with different calcium silicate content

It can be seen from the above figure that adding a certain proportion of calcium silicate to the epoxy powder coating can effectively improve the T5 and Tm of the powder coating. When the pure barium sulfate is used, the T5 of the epoxy powder coating is 380℃, and the Tm is 418.6℃. With the increase of calcium silicate addition, T5 and Tm basically showed an upward trend. When the ratio of calcium silicate and precipitated barium sulfate was 5:5, T5 reached a peak value of 393 °C, which was higher than pure barium sulfate. At 13°C, Tm is 424.6°C at this time, which is 6°C higher than pure barium sulfate; then with the increase of calcium silicate ratio, T5 shows a downward trend, while Tm shows a small increase. The decomposition temperature of calcium silicate is 1540 ℃, and the decomposition temperature of barium sulfate is 1580 ℃. The difference between the two is not big. The above experimental phenomenon may be due to the fact that calcium silicate is a typical needle-like structure, and barium sulfate is a granular structure. During the stacking process, the needle-like structure is more likely to form intersecting three-dimensional structures, which just echoes the three-dimensional structure network structure formed by the epoxy resin during the cross-linking and curing process. At the same time, the particles of barium sulfate are filled in the network structure. Between the voids, a denser coating is formed.

Therefore, when calcium silicate partially replaces barium sulfate, with the increase of the replacement amount, the compactness of the paint film gradually increases. When the ratio of calcium silicate and barium sulfate is 1:1, the compactness of the paint film is the best. Therefore, the heat resistance is the best. With the further increase of the replacement amount of calcium silicate, there is not enough granular barium sulfate filled in the three-dimensional network structure of calcium silicate, so the porosity of the paint film becomes larger and the density becomes larger. poor, and the thermal stability tends to decrease.

Therefore, in terms of thermal stability, when the amount of calcium silicate added is 10% (ie, calcium silicate: precipitated barium sulfate = 1:1), the overall performance is the best.