In the process of forming the paint film, due to the internal reasons of the paint base itself, it will also affect the construction quality of the paint film and cause morbidity, resulting in damage or decline in the performance of the paint film. For example, the surface tension of the paint base is an indicator that cannot be ignored. We know that the color paint film is prone to "shrinkage cavity" pathology during the formation process. The "shrinkage cavity" of the coating film is related . Therefore, in order to solve the leveling property of the colored paint, it is necessary to know the surface tension of the paint base used in the colored paint before taking corresponding measures to adjust it. The surface tension index of the paint base is a microscopic quality index and key index, and should .
At present, there are several methods for measuring surface tension:
1. Determination of the surface tension of a series of resin solutions with different concentrations in the same solvent. The resin content is plotted , and the surface tension of the resin is extrapolated to 100% content.
2. Determination by Zisman graphic method on the resin solid film, that is, to measure the contact angle of a series of liquid droplets of the same series with different surface tensions without interaction with the resin . Plot the cosine of the contact angle against the surface tension of the liquid. Extrapolated to a cosine of 1, the surface tension here is the solid critical surface tension of the resin (approximate to the surface tension)
3. According to the method of ASTMD2578 to measure the wetting tension of polyethylene and polypropylene plastics, use a series of liquids with different surface tensions that have no interaction with the paint-based film- forming resin , drop them on the solid resin film, and in 2 seconds The surface tension of the liquid that can maintain a complete continuous film within a few minutes is the wetting tension (approximate surface tension) of the resin (lacquer base film former). This method is the easiest and fastest.
4. The surface tension of the solid film-forming substance in the paint base can also be estimated by its composition, chemical structure, and specific volume. The principle is to use the model structure of the resin (lacquer-based solid film former) to estimate the surface tension. For the estimation of the surface tension change of the paint base in the process of film formation , a calculation program can also be compiled with the help of a computer. Of course, these microscopic changes can provide a reference for the design and evaluation of the paint formulation, which is very important for improving the quality of the paint and preventing the coating film from appearing sick during construction. At present, foreign paint companies and research institutions are studying the surface tension of paint bases, applying modern spectrum technology and computer technology to study the microscopic state of the interface. In order to make paint formula design and quality control more scientific, various testing instruments provide various quantitative data, so as to gradually replace the usual method of only relying on sensory judgment.
5. Use various surface tension measuring instruments.
The types of surface tension measuring instruments commonly used abroad are briefly introduced as follows for reference.
German KRuSS company K-12 automatic tensiometer has the advantages of high precision and automatic measurement. It is based on Wilhelmy hanging plate or Du-Nouy, ring principle to measure the corresponding surface and interfacial tension when changing with time and concentration. Its measurement accuracy is as high as 0.01mN/m, and the measurement range is 1 to 500mN/m. The instrument uses software K121 (according to the principle of Wilhelmy hanging plate) to measure the dynamic contact angle and the adsorption performance of porous substances and powders. The test results are displayed on the connected LCD and can be printed out by the computer.
