There are several methods for measuring adhesion of paint film: circle method, grid method, stretch method, twist open method and the X method in ASTM in the United States. Among them, the easiest application is the circle method to determine paint film adhesion. Focus, the most commonly used on site is the grid method.
(1) Measure the adhesion by the circle method
The adhesion tester used in the circle method is evaluated according to the integrity of the paint film within the scratch range, expressed in grades. It is fixed on the tester according to the prepared tinplate. To ensure that the paint film is penetrated, add weights as appropriate. In a clockwise direction, shake the handle evenly at 80-100r/min, and scratch with a round line. 7.5cm long, take out the model and grade it. Pay attention to the following points in the experiment:
(A) The needle of the tester must be sharp, otherwise the difference between level 1 and level 2 cannot be distinguished. You should touch it with your finger before the test to see if it is sharp, or change it as appropriate after testing several test plates.
(B) Try to make a few circles first. The scratches should just penetrate the paint film. If the bottom plate is not exposed, add weights as appropriate; but don't add too much, so as not to increase the resistance and wear the needle.
(C) When grading, you can start the evaluation at level 7 (the innermost layer) or level 1 (the outermost circle). Check the integrity of the paint film of each part in order. If the grid of a certain part is more than 705 intact, then The part is considered to be intact, otherwise it is considered damaged. For example, if the paint film of part 1 is intact and the adhesion is the best, it is rated as level 1; the paint film of part 1 is damaged and the paint of part 2 is intact, and the adhesion is secondly rated as level 2. By analogy, Level 7 has the worst adhesion. Generally, it is required that the adhesion of better primer should reach level 1, and the adhesion of topcoat can be around level 2.
(2) Cross-cut method to measure adhesion
The cross-cut method adhesion test standards mainly include ASTMD3359, ISO-2409 and GB9286-98. The test method and description are basically the same, except that the order of description of the adhesion level is just the opposite. ASTMD3359 is 5B-OB grade from good to bad, while ISO-2409 is 0-5 for good to bad. The experimental tool is a cross-cut tester, which is a multi-blade cutter with 6 cutting surfaces, and the cutter gap is 1mm, 2mm and 3mm (the cutter head can be replaced). Coat the sample on the sample plate, dry for 16 hours, pull 3-4cm in parallel with the scratcher, there are six cuts, cut through the paint film to the substrate; then use the same method to be perpendicular to the former, the same six cuts ; This forms many small squares. For soft substrates, use a soft brush to form each diagonal line along the grid map, and gently sweep forward and back several times to assess the grade; for hard substrates, clean first, then apply tape (Generally use 3M tape), and to ensure that the tape is in full contact with the experimental area, you can rub it back and forth with your fingers to make it contact well, and then quickly pull it away. Use visual inspection or a magnifying glass to compare the standards with the accompanying drawings for grading. The standard description of its classification is:
Level description
0=ASTM grade: 5B, the cutting edge is completely smooth, and no grid falls off
1=ASTM grade: 4B, there is a little coating peeling off at the intersection, and the affected area cannot be significantly greater than 5%
2=ASTM grade: 3B, the coating falls off at the intersection of the incision or along the edge of the incision, and the affected area is 5%-15%
3=ASTM grade: 2B, the coating is partly or completely peeled off in a large area along the cutting edge, and the affected cross cutting area is 15%-35%
5=ASTM grade: 1B, the whole strip falls off along the edge, some grids fall off partly or completely, and the affected area is 35%-65%
6=ASTM grade: 0B, the degree of peeling exceeds grade 4