1.Why is the direct adhesion poor?
Low surface energy of the coating: A smooth coating has low surface tension, making it difficult for the adhesive to fully wet and spread, resulting in a "false tack" phenomenon.
Chemical inertness: High-quality coatings (especially PVDF fluorocarbon) are chemically stable and do not easily form chemical bonds or strong physical interlocks with the adhesive.
Surface contamination: During production, transportation, and storage, the coating may become contaminated with release agents, oil, or dust, further weakening adhesion.
Internal stress and aging of the coating: Over time, the coating may age, chalk, or develop internal stress, leading to failure of the adhesive interface.
2.How does coating type affect adhesion?
PVDF (fluorocarbon) coating: Most difficult to bond due to its strong inertness and smoothness.
HDP/SMP (silicone-modified polyester): Moderate difficulty.
Ordinary polyester coating: Relatively the easiest, but still requires processing.
3.How does coating condition affect adhesion?
Newly manufactured and cleaned: Optimal condition.
Aged and powdery: The powdery layer must be thoroughly cleaned, otherwise failure is inevitable.
Contaminated: Must be cleaned.
4.How to achieve good adhesion?
Deep Cleaning:
Thoroughly wipe with a solvent (such as isopropyl alcohol or a specialized cleaner) to remove all oil, dust, and release agent. Never simply rinse with water.
Physical Sanding/Roughening (Highly Recommended for High-Requirement Bonding):
Use fine sandpaper (e.g., 180-400 grit) or a scouring pad to evenly sand the coated surface of the areas to be bonded until the gloss is gone, revealing a uniform matte finish.
Purpose: To greatly increase the surface area and create mechanical interlocking points.
Further Cleaning: After sanding, remove sanding dust with a solvent.
5.What are some application suggestions and precautions?
For non-critical, non-load-bearing components (such as affixed signs and small decorative strips): After thorough cleaning and sanding, high-strength VHB double-sided tape (brands such as 3M) can be used. It is specifically designed for low surface energy coatings and is easy to apply.
For critical load-bearing structures (such as insulation layer bonding and structural reinforcement): A "sanding + specialized structural adhesive" approach must be used, along with sample testing and pull-out tests to verify that the adhesion meets design requirements.
Worst-case scenario: If bonding to an old, chalked coating, the chalked layer must be completely sanded away until a solid coating is exposed; otherwise, the bond will inevitably fail.