Test methods for defoamer performance
Common test methods for defoamer performance and antifoam performance include: Ross-Myers method, West German industrial standard method, aeration method, stirring method, titration method, high-speed dispersion method and circulating bubbling method, etc. Some other methods such as ASTM D892-06e1 standard, ASTM-E2407-04, oscillation method (or shake bottle method), Goschmidt evaluation method, Q/XGY014-91 standard, ASTM D892-46T standard are similar to the above test methods.
The differences between these methods lie in the causes of foam generation, the timing of adding defoamers, and the static and dynamic types of foam. The common point is that they all use the change of foam volume to compare the performance of defoamers, but the method using foam height is poorly operable in many actual production. In addition, there is no fixed standard for the performance evaluation of defoamers. The performance of defoamers is judged by comparing them with each other in the test.
1) Cylinder method
The cylinder method is mainly used for low-viscosity coating systems and pure emulsion systems. Add a certain amount of about 20ml of sample into a 50ml stoppered cylinder, then add a certain amount of defoamer as needed, cover the stopper, and shake it vigorously by hand for a certain number of times, such as 20 times. Then stop and record the height of the foam immediately, and record the height of the foam again after a certain period of time, and compare the recorded data with the data of various other defoamers. This method can be used to preliminarily estimate the defoaming property of the defoamer, but its measurement method determines that its measurement accuracy will not be too high.
2) High-speed stirring method
Compared with the 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. The foam level measurement method is suitable for low-viscosity coating systems and emulsions; the specific gravity cup method is suitable for high-viscosity systems and emulsions.
① Foam level measurement method Add a certain amount of paint sample, such as 100ml, to a beaker with a minimum measurement scale of 1ml, add a certain amount of defoamer, and then use a high-speed stirring disperser to stir at a certain speed, such as 3000~6000r/min for a certain time, and let it stand. Observe the change in foam volume within a certain time interval and record it. The smaller the foam volume, the stronger the defoaming property of the defoamer, or observe the time required for the foam to reach a certain volume. The longer the time, the weaker the defoaming property of the defoamer.
② Density cup method Put a certain amount of paint sample (150~200g) into a beaker of a fixed size, and then use a high-speed stirring disperser to stir at a certain speed, such as 3000~6000r/min for a certain time, and then stop stirring immediately. Put the stirred paint sample into a density cup to measure its density, and measure it again after a period of time, such as 15min, and record 4~6 groups of data for comparative analysis.
3) Coating test method
After the performance evaluation of the defoamer, it is necessary to further test the effect of the defoamer on the quality of the paint film, such as whether there are shrinkage holes, miscibility, gloss changes, etc. Use a 75um applicator to apply a layer of paint film on a clean glass plate, then observe whether there are shrinkage holes, and then use a gloss meter to measure its gloss.
