The latent heat of evaporation of water is very large, reaching 2457.7kj/kg. the evaporation of water-based paint needs to absorb a large amount of heat. The evaporation of water is influenced by the atmospheric temperature, humidity and wind speed. The volatilization rate increases with the increase of temperature, decreases with the increase of air humidity, and increases with the increase of wind speed. This is because the temperature increases, the thermal movement of molecules more intense, liquid water molecules are more likely to get rid of the attraction of other water molecules and become water vapor molecules. However, with the increase in air humidity, the proportion of water vapor in the air increases, the partial pressure of water vapor increases, and more water vapor molecules become liquid water molecules per unit time. Therefore, the evaporation rate of water decreases with the increase of air humidity. The higher the wind speed, the more water molecules taken away from the volatile surface per unit of time, the faster the evaporation rate.
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 gloss of the coating film is an important physical property, which indicates the ability of the surface of the coating film to reflect the light projected on it in the same direction. The more the amount of reflected light, the higher the gloss; conversely, the less the amount of reflected light, the worse the gloss. A matting agent is a substance that can significantly reduce the gloss of the surface of the coating film. The gloss of the coating film is quantitatively characterized by gloss. The definition is as follows; the ratio of the amount of regular reflection of the light beam irradiating the surface of the coating film from a specified angle of incidence to the amount of regular reflection from the standard plate surface under the same conditions, expressed as a percentage, is called the gloss of the coating film.
The gloss of the coating film was measured with a gloss meter. The shooting angles are 20°, 60° and 85°, suitable for varnishes and colored paints other than metallic pigments. 60° is suitable for all coating films, ptfe powder perth but 20° or 85° is more suitable for coating films with high gloss or close to matt. 20*For high-gloss paints, it can improve the discrimination, suitable for paints whose gloss is higher than 70% when measured at 60°; 85° can improve the discrimination for low-gloss paints, and it is suitable for paints whose gloss is less than 30% when measured at 60°. Color paint. The current advanced gloss meter can transmit data to personal computers and printers through the RS232 interface, which is convenient for documentation.
There is no standard for classification of coatings according to gloss in our country. German and European standards DINEN13300:2001 “Waterborne Coatings and Coating Systems for Interior Walls and Ceilings” are classified according to gloss.
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