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The common test methods of defoamer performance and foaming inhibition performance are: Ross-Meyers method, West German industrial standard method, air method, stirring method, titration method, high-speed dispersion method and cyclic bubbling method, and some such as ASTM D892-06E1 standard, ASTM-E2407-04, shock method (or flask shaking method), Gao Schmidt evaluation method, Q/XGY014-91 standard, ASTM D892-46T standard and the above test methods are similar.
The differences between these methods are the causes of foam generation, the timing of adding defoaming agent and the static and dynamic types of foam. The common point is that they compare the performance of defoamer with the change of foam volume, but the method of using the height of foam is very poor in practical production. In addition, there is no fixed standard for the evaluation of the performance of defoaming agent, which is judged by comparing the performance of defoaming agent in the test .
One, measuring cylinder method
The measuring cylinder method is mainly used in low viscosity coating systems and pure emulsion systems. Add a certain amount of about 20ml of the sample into a 50ml measuring cylinder with stopper, and then add a certain amount of antifoaming agent as required. After the stopper is covered, shake it violently by hand for a certain number of times, such as 20 times. Then stop immediately and record the height of the foam. After standing for a certain period of time, record the height of the foam again and compare the recorded data with the data of other kinds of antifoaming agents. This method can be used to preliminarily estimate the defoaming ability of defoaming agent, but its measurement method determines the accuracy of its measurement is not too high.
Two, high-speed mixing method
Compared with the measuring cylinder method, the high speed mixing method has the advantages of accurate measurement standard and wide application. The high speed mixing method can be evaluated by two methods. Foam level measurement method, this method is suitable for low viscosity coating system and emulsion; The specific gravity cup method is suitable for high viscosity systems and emulsions.
(1) foam level measurement method in a minimum measurement scale of 1ml in a beaker to add a certain amount of paint sample, such as 100ml, add a certain amount of defoaming agent, and then use a high-speed mixing and dispersing machine at a certain speed, such as 3000~6000r/min stirring for a certain time, standing. The change of foam volume within a certain time interval was observed and recorded. The smaller the foam volume, the stronger the defoaming ability of the defoaming agent was, or the longer the time required for the foam to reach a certain volume, the weaker the defoaming ability of the defoaming agent was.
(2) the specific gravity cup method will be a certain amount of paint samples (150~200g) into a fixed size beaker, and then use a high speed mixing and dispersing machine to stir at a certain speed, such as 3000~6000r/min stirring for a certain time, and then immediately stop mixing, will be mixed after the paint sample into the specific gravity cup to measure its density, After a period of time, such as 15min, the measurement was carried out, and 4-6 groups of data were recorded for comparative analysis.
Three, coating experiment method
After the performance evaluation of defoaming agent, it is necessary to further test the influence of defoaming agent on the quality of paint film, such as whether there is shrinkage, miscibility, gloss changes and other properties. Use a 75um coater to coat a layer of paint film on a clean glass plate, and then observe whether it has shrinkage holes, and then use a glossiness meter to measure its glossiness.
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