There are many common test methods for defoaming performance and defoaming performance. The main difference lies in the cause of foam generation, the timing of addition of defoaming agent and the static and dynamic types of foam, etc. The common point is that they all use the change of foam volume to compare the action performance of defoaming agent, but the method of using foam height is very poor in many actual production.


In addition, there is no fixed standard for the performance evaluation of defoamer, and the performance of defoamer is evaluated by comparing with each other in the test.






01 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 sample into a stopper 50ml measuring cylinder, then add a certain amount of defoamer as needed, cover the stopper, and turn 20 times at the rate of 1 time /S. Then stop immediately and record the height of the foam, let it stand for a certain period of time and record the height of the foam again, and compare the recorded data with the data of various other defoamer. This method can be used to estimate the defoamer's defoamer, but the measurement method determines that the measurement accuracy is not too high.








02 High speed mixing method






Compared with the measuring cylinder method, the high speed stirring method has the advantages of accurate measurement standards and wide application. The high speed stirring method can be evaluated in two ways. Foam level measurement method, this method is suitable for low viscosity coating systems and emulsions; Specific gravity cup method, this method is suitable for high viscosity systems and emulsions.


① Foam liquid level measurement method


Add a certain amount of paint sample in a beaker with a minimum measuring scale of 1ml, such as 100ml, add a certain amount of defoamer, and then use a high-speed mixing and dispersing machine to stir at a certain speed, such as 3000~6000r/min for a certain time, and let it stand. Observe the change of foam volume in a certain time interval and record it. The smaller the foam volume, the stronger the defoamer, or observe the time required when the foam reaches a certain volume. The longer the time, the weaker the defoamer.


② Specific gravity cup method


Put a certain amount of paint sample (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 stirring, put the stirred paint sample into the specific gravity cup to measure its density, and interval of time. If the measurement is performed after 15 minutes, record 4 to 6 groups of data for comparison and analysis.








03 Coating experiment method






After the performance evaluation of the defoamer, it is necessary to further test the effect of the defoamer on the quality of the coating film, such as whether there is shrinkage hole, miscibility, gloss change and other properties. Use a 75um coater to apply a coating film on a clean glass plate, and then observe whether it has shrinkage holes, and then use a gloss meter to measure its gloss.








04 Storage stability method






A certain amount of defoamant sample is placed in a covered bottle, and then placed in a constant temperature oven at 50 ° C, taken out at intervals and then tested its various properties, and 3 to 4 groups of data are recorded for comparative analysis. It is generally believed that storage in a constant temperature drying oven at 50 ° C for 1 to 2 weeks is equivalent to storage at normal temperature for 6 months.