The adhesion of the screen printing silicone middle layer can be tested in the following ways:
1. 100-grid test
Test tools and materials:
Knife: such as a utility knife or a special 100-grid knife, the blade should be sharp to ensure that neat squares are cut.
Tape: Generally, a pressure-sensitive tape with a specific width (such as 25mm) is used, such as 3M Scotch tape, which has strong adhesion.
Magnifying glass: used to observe the cut squares and the tape after peeling.
Test steps:
After the screen printing silicone middle layer is completely cured, use a knife to cut into 1mm×1mm small squares on the coating surface. The cutting depth should reach the surface of the substrate, but not too deep to avoid damaging the substrate.
Use a soft brush to gently brush away the debris on the surface of the square.
Apply the tape flatly on the square, and press repeatedly on the tape with your fingers or a rubber roller to ensure that the tape is in full contact with the coating.
After standing for a period of time (usually 1-2 minutes), quickly peel the tape from the coating surface at an angle close to 90°.
Result evaluation:
Observe the peeling of the coating through a magnifying glass and evaluate the adhesion level. It is generally divided into 0-5 levels, 0 means that the cutting edge is completely smooth and no grid is peeled off; 1 means that there is a little coating peeling off at the intersection of the cut, but the cross-cut area affected cannot be significantly greater than 5%; 2 means that the coating peels off at the intersection of the cut and/or along the edge of the cut, and the affected cross-cut area is significantly greater than 5%, but not significantly greater than 15%; and so on, 5 means that the peeling area is greater than 65%.
2. Pull-off test
Test tools and materials:
Pull-off tester: can provide accurate pulling force and record the pulling force value.
Test fixture: used to fix the pull-off head on the substrate and the coating.
Pull-off head: usually a cylindrical or square metal block, firmly bonded to the coating surface by glue or other means.
Test steps:
Attach the pull head to the surface of the screen-printed silicone intermediate layer with appropriate glue, and ensure that it is firmly attached. Let it stand for a while to allow the glue to fully solidify.
Fix the substrate on the workbench of the pull tester, and then install the test fixture on the pull head.
Start the pull tester and apply tension at a constant speed until the coating falls off the surface of the substrate.
Result evaluation:
Record the tensile force value when the coating falls off. The greater the tensile force, the stronger the adhesion. A minimum tensile force value can be determined as a qualified standard according to different application requirements and standards. For example, for some high-demand applications, the adhesion may be required to reach more than 5MPa.
3. Friction test
Test tools and materials:
Friction tester: It can simulate different friction conditions, such as friction times, pressure, speed, etc.
Friction medium: Such as cotton cloth, sandpaper, rubber, etc., select the appropriate friction medium according to the actual application.
Weighing equipment: Used to measure the weight change of the coating before and after friction.
Test steps:
Fix the screen-printed sample on the friction tester.
Select the appropriate friction medium and set the parameters of the friction tester, such as the number of frictions, pressure, speed, etc.
Start the friction tester and let the friction medium rub on the coating surface.
After a certain number of frictions, observe the wear of the coating, and use a weighing device to measure the weight change of the coating before and after friction.
Result evaluation:
The adhesion is evaluated based on the degree of wear and weight change of the coating. If the coating is only slightly worn after friction and the weight change is small, it means that the adhesion is good; if the coating is severely worn, falls off, or the weight change is large, it means that the adhesion is poor. For example, in some demanding applications, it may be required that the coating wear area cannot exceed 5% after 1,000 frictions.