Study on application of ultrafine barium sulfate in coatings
Barium sulfate is widely used in coatings as a physical pigment, which plays a very important role in improving the thickness, wear resistance, water resistance, heat resistance, surface hardness and impact resistance of the coating film. In addition, barium sulfate is highly reflective in the wavelength range of 300-400lm, which can protect the paint film from light aging and is an effective white inorganic light stabilizer.
Ultrafine barium sulfate made by special process has many characteristics that other similar products do not have. Its needle-like crystal structure makes it a good leveling agent and can enhance the leveling property of the coating. It can be used as strengthening agent in self-cleaning coatings. Because its oil absorption is low, there is a high amount of filling, so it can reduce the cost of paint, can be used for water-based paint, primer, intermediate coating, oil coating and so on. Use it to replace 10%-25% of titanium dioxide in waterborne paint, whiteness increased, no decrease in covering power.
Mechanism of ultrafine barium sulfate used in coatings: Barium sulfate is crushed to 1-8LM particle size, which can replace part of titanium dioxide when applied to latex coatings, and the whiteness and hiding power will not decrease, as shown in the figure. Although the crushed barium sulfate is very fine, it still forms particles of medium size as aggregates. Because the crystal size of precipitated barium sulfate is between 0.2-0.8lm at the time of formation, the gap between these particles is too small for the dispersed resin to enter the polymer. When the paint film dries, these tiny air gaps are preserved in the form of air, thus improving the refraction difference between the components. In such a paint film, the refractive index of each substance is as follows: titanium dioxide is 2.76, polymer is 1.55, water is 1.33, air is 1.0. In dry paint film and wet paint film, mainly by the following refractive index difference determines the size of covering power: titanium dioxide - polymer =2.76-1.55=1.21, titanium dioxide - water =2.76-1.33=1.43, titanium dioxide - filler =1.11, titanium dioxide - air =1.76. It can be seen that, due to the existence of ultrafine barium sulfate powder, when the coating film, in addition to other refractive index difference, there are titanium dioxide and water refractive index difference. After the paint film becomes dry film, due to the evaporation of water, air bubbles are produced in the paint film, which produces the refractive index difference between titanium dioxide and air, which objectively improves the scattering ability of titanium dioxide, thereby increasing the covering power, so ultrafine barium sulfate can replace part of titanium dioxide, and the covering power does not decrease.
Application of ultrafine barium sulfate in coatings
In order to detect the various characteristics of ultrafine barium sulfate in coatings, we conducted a series of experimental studies and performance tests on the application of ultrafine barium sulfate in benzene-acrylic matt emulsion paint:
Comparison of whiteness and hiding power of paint film
Artificial aging test of paint film
The paint of different formulations is sprayed on cement board, and artificial aging test is carried out on sunshine aging machine. It is known that the discoloration time of the original production formula is 580 hours, and the discoloration time of the present production formula is 1200 hours, indicating that the weatherability of the paint film can be significantly improved after the addition of ultrafine barium sulfate.
Coating stored at room temperature
Due to the small particle size of ultrafine barium sulfate, its agglomeration morphology also determines that its density is not lower than that of ordinary barium sulfate, so it overcomes the disadvantages of ordinary barium sulfate, such as easy precipitation and easy stratification. The emulsioni paint test sample placed for a year without obvious delamination, no settlement phenomenon, good stability. Additional, its paint film is in be able to bear water, be able to bear wet swabbing sex, the respect such as fight pollution sex all has outstanding advantage.
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