Natural drying has the advantages of simple method and wide application, but also has the disadvantage of slow drying speed. Under natural conditions, the temperature, humidity and wind speed are constantly changing, and the drying speed and film quality are unstable. If the temperature is high, the humidity is high or the humidity is high, the coating tends to turn white and the drying speed is slow. At low temperature, the drying speed is very slow, especially at 5℃, the film formation of water-based coatings is difficult. These are the important reasons that restrict the application of water-based coatings.
The calculation formula of plane roughness is as follows:
R. is the ratio of the total area of the measured peaks and valleys to the measured distance Im, that is, the arithmetic average value from the average line to the absolute value of the roughness value Y on the long measured surface of I, expressed in um.
R can be determined using the scanning fragment method. The method was developed by Hommel we ke, Germany, and measured using a Hommel tester. Its standard is German DIN 4762/1E. Some wax emulsion manufacturers in india documents also use the average roughness depth RZ D for measurement. The standard is German DIN 4768.
When the thickness of the coating film of a certain coating is constant, the larger the particle size of the matting agent used, the R. value of the coating film is also large, and the gloss is low. From Table 12-2, we can see their correlation.
The relationship between 85° glossiness and matting agent particle size and average roughness R. is more obvious.
At present, the 3D surface morphology map of the paint film can be drawn using the laser surface roughness tester.
The 3D image of the matte surface of the amino alkyd enamel (OK412, 3.3% of the coating amount) can be intuitively understood from the 3D morphology image of the surface state of the coating film. It can be seen from the comparison of the two pictures that the surface roughness of the coating film in Fig. 12-3 is higher than that in Fig. 12-4, and the gloss of 60° and 85° is low.
The current view on the mechanism of coating surface extinction is the same.
The light irradiates the surface of the coating at a certain angle. If the surface is close to the optical plane, it will cause total reflection. The reflection angle is equal to the angle of shot, and the gloss is high. When the light from a person reaches the surface with tiny bumps, as the average roughness of the coating surface increases, scattered light gradually replaces the reflected light, causing its gloss to continue to decline, and eventually a matte coating will be formed.
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