1.What are the steps involved in a basic adhesion test?
Test Method: Use a specialized tool to score a certain number of squares (e.g., 1mm × 1mm) on the coating surface, ensuring the cuts penetrate the coating to the substrate. Then, secure the cuts with special adhesive tape and forcefully peel them off, observing the coating peeling off from the square areas.
Result Evaluation (Grading): Graded from 0 to 5 according to national standards (e.g., GB/T 9286) or international standards (ISO 2409).
Grade 0 (Best): The cut edges are completely smooth, with no peeling.
Grade 1: Small pieces peel off at the cut intersections, with a peeling area ≤ 5%.
Grade 2: Peeling occurs at the cut edges and/or intersections, with an area > 5% and ≤ 15%.
...Grade 5 (Worst): The peeling area far exceeds 65%.
Application Significance: Achieving Grade 0 or 1 is generally required. This directly reflects the overall quality of the coating system (pretreatment + coating).
2.How are the T-bend test methods and results evaluated?
Test Method: Gradually bend the sample 180°, using shims of varying thicknesses to control the bending radius, and observe the coating cracking at the bend.
Result Evaluation (Grading): Expressed as "T-value", such as 0T, 1T, 2T, 3T, etc.
0T: No cracking in the coating after bending (optimal, requires an excellent substrate and excellent coating flexibility).
1T: Bend the sample 180° and press it firmly until it fits (bending radius approximately equal to the board thickness), then inspect the outer coating. Generally, ≤3T is considered acceptable; high-requirement applications require ≤2T or even 1T.
Application Significance: Directly determines whether the sheet material can be used for bending, edge rolling, and other forming processes. The smaller the T-value, the better the formability.
3.How are impact test methods and results evaluated?
Test Method: A punch of a certain mass is used to impact the back (front impact) or front (reverse impact) of the sample from a specific height, creating a dent. The extent of coating peeling at and around the dent is then examined.
Result Evaluation: Results are expressed as impact energy (Joules, J) and describe whether the coating has cracked or peeled. For example, "9J front impact, no coating peeling."
Application Significance: Evaluates the coating's ability to resist sudden deformation or external impacts (such as hail or installation bumps).
4.What are the adhesion testing methods related to overall durability?
Water Resistance/Boiling Water Resistance
Test Method: Immerse the sample in boiling water for a certain period of time (e.g., 2 hours), remove and dry, then immediately perform a cross-cut test.
Application Significance: Simulates high-temperature and high-humidity environments (e.g., outdoor sun and rain, high-temperature cleaning in food processing plants) to test the coating's resistance to water vapor penetration and erosion. Passing this test is an important indicator of a high-performance coating.
Salt Spray Resistance/Adhesion After Damp Heat Resistance
Test Method: After the sample undergoes a salt spray test or damp heat test for a certain period of time, perform a cross-cut test.
Application Significance: Evaluates the coating's ability to resist "loss of adhesion" and "blistering" in corrosive environments.
5.How to understand and choose "levels"?
In actual procurement and technical requirements, you won't simply say "I need Grade 1 adhesion." Instead, specific test items and indicators should be clearly defined in the technical agreement based on the end use.
For general building roof and wall panels: Focus on standard specifications (0-1) and T-bend (≤3T).
For components requiring molding (such as appliance panels, air ducts): Strict requirements must be placed on T-bend (≤2T or 1T), impact, and cupping performance.
For harsh corrosive environments or high-end applications (such as industrial plants, coastal buildings, food processing plants): Requirements for adhesion after boiling and adhesion after salt spray must be added.
Substrate pretreatment is crucial: all excellent adhesion is built upon a high-quality substrate (e.g., zinc plating weight, surface cleanliness) and a good chemical conversion coating treatment.