Minimum thickness of wet film method for measuring covering power

Fan Guo and Description

This method uses the minimum wet film thickness required to cover the bottom surface to measure the hiding power of the paint, and the result is expressed in µm. This method uses less paint and has a fast test speed. It is suitable for production control in factories and can be converted into a coating rate expressed in m2/L (meter 2/liter).

Instruments and Materials

Capping force Tester: see the picture. The instrument is a black and white optical glass plate with millimeter scale engraved on the side, and a transparent glass top plate with a certain height at one end is covered on it, so as to form a mold with the bottom plate. shape space, see Fig.

The English name of the hiding power Tester is Cryptometer. The bottom plate is half black and half white, the black one is used for white and light-colored paint, the white one is used for colored and dark-colored paint, and is equipped with two top plates, the constants are K1=0.004 and K2=0.008 respectively. Through the conversion table provided by the instrument, the average number of square meters per liter can also be obtained.

test methods

(1) Pour a small amount of sample in the middle of the bottom plate. Press the upper transparent glass top plate, and the sample will unfold in the space.

(2) Move the top plate back and forth, the excess samples are squeezed into the flow control grooves on both sides of the bottom plate, and the top plate moves steadily and slowly along the millimeter scale until the black dividing line on the bottom plate cannot be seen through the top plate and the paint layer until.

(3) When observing, the illuminance is required to be 540 lx, and the covering power meter is illuminated vertically at 90°, while the Tester observes at an angle of 45°, and records the reading from the black self-demarcation line to the front of the top plate.

The result shows

WFT=LK×1000

K = tan α

In the formula, WFT is the wet film thickness (μm), L is the black and white dividing line to the top reading (mm), K is the instrument constant, α is the wedge -shaped space angle formed by the top plate and the bottom plate