ASTM D3359-02, developed by the American Society for Testing and Materials, applies to dry film thicknesses above 125pmm, with no limit to the maximum paint film thickness. The corresponding cross-cut method is generally applicable to dry film thicknesses below 250um.
The tools used for testing are relatively simple, including sharp blades, such as utility knives and scalpels; 25mm (lin) translucent pressure-sensitive tape, rubber pens, and light sources, such as flashlights.
The test procedure is as follows:
1. The coating surface should be clean and dry. High temperature and high humidity will affect the adhesive force of the tape;
2. The soaked samples should be cleaned with a solvent without damaging the coating, and then dried;
3. Cut the paint film onto the substrate stably with a knife along a straight line with an included angle of 30-45°. The length of the dash line is 40mm (15in), and the intersection point is in the middle of the line length;
4. Check the reflection of the steel substrate with light to determine whether there are scratches on the substrate: if there are no scratches on the substrate, cut at another position;
5. Remove the two circles above the pressure sensitive tape, then pull the tape at a steady speed to cut a 75mm (3 inch) length of tape;
6. Place the middle of the tape at the intersection of the cutting points, smooth it with your fingers, and then smooth the tape with an eraser. The color of scotch tape can help you see the density of the state of contact with the paint film;
7. Within (9030) seconds, tear off the tape from the surface of the paint film at an angle of 180°, and observe the state of the coating after it is pulled up. There are 6 states defined in the standard for reference (Figure 7-4), among which 5A~3A are acceptable adhesion states;
a. 5A No desquamation or flaking.
b. There are traces of peeling along the knife marks
c. Cut off 1.6mm on both sides of the 3A knife mark
d. Both sides of the 2A knife mark are cut off by 3.2mm
e. Most of the X area under the 1A tape is peeled off
f. 0A shedding area exceeds X area
