Determination of coating film hardness includes pencil hardness test, pendulum hardness test, notch hardness test and so on.
(1) Pencil hardness test
Pencil hardness mainly refers to the use of pencil scratches to measure the hardness of the coating film, and the hardness of the coating film is mainly represented by the number of pencils that penetrate the thickness of the coating film to reach the bottom surface.
Set each: pencil Hardness Tester. (Hardness Tester)
Pencils: Generally, high-end drawing pencils (mostly Zhonghua brand) produced by the same manufacturer are used.
The test steps are:
Test under the test conditions of (23±2)°C and relative humidity of 5o%±5%. Shave the pencil out of a lead about 3mm long (do not scratch the lead). Hold the pencil with your hand and push it forward. A pen core with a length of about 3 mm goes back and forth at different parts for 5 times, and then wipe off the pencil dust with a thick or soft cloth to check the scratches on the coating film.
(2) Scoring hardness
Samples are shown in Table 6-2. Place the sample for 24h under the conditions of (23±2)°C and relative humidity of 50%±5%, and measure under these conditions. Take an unused needle and check it under a magnifying glass. The needle should be smooth, hemispherical, and free of dirt. Fix the needle on the instrument so that its axis is perpendicular to the coating. Centrally tighten the sample on the slide plate, and turn on the power supply of the electric indicator. Apply the specified load to the needle, and place it lightly on the sample, so that the slide plate moves evenly. The length of the notch shall not be less than 60mm. Observe whether the coating is pierced from the electric indicator or with a magnifying glass. Each needle can only be tested once.
Determine the minimum puncture load following the procedure above. The initial applied load should be smaller than the expected puncture value of the coating film, and increase with an appropriate load increment (such as 0.5N) until the coating film punctures, and repeat the formula i for the sample with the minimum puncture load value verification.
Results: Report whether the coating is pierced under the specified load value, and the minimum load value that pierces the coating film.
