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Aluminum is prized for its corrosion resistance and lightweight strength, making it a staple in construction and appliances. However, whether you are dealing with factory color aluminum coil or on-site spray finishing,
"paint peeling" remains a persistent headache. Bubbling, cracking, or sheet-like delamination doesn’t just ruin the look—it strips away the metal’s primary defense.
Adhesion failure on aluminum isn't bad luck; it’s science. As a non-porous material, aluminum naturally forms a "passive" oxide layer that is chemically indifferent to paint. Without the right intervention, your coating
is essentially just sitting on the surface, waiting to fall off.
Beyond the surface being "too smooth," several invisible factors undermine adhesion:
Surface Residues: Microscopic traces of rolling oils, lubricants, or dust from the mill.
Primer Mismatch: Aluminum is chemically selective. Generic primers often fail to create the necessary covalent bonds with the substrate.
Thermal Incompatibility: Aluminum has a high coefficient of thermal expansion. If the paint film lacks flexibility, temperature swings will literally tear the coating away from the metal.
Factory Process Flaws: In coil coating lines, inconsistent roll pressure or failing to hit the Peak Metal Temperature (PMT) during curing results in a finish that looks fine at delivery but fails months later.
Rinsing with water is never enough. Professional-grade adhesion requires a multi-stage process of degreasing, etching, and passivation:
Degreasing: Use industrial alkaline or acid cleaners to strip away residual rolling oils.
Etching: Use a phosphoric acid-based etchant or mechanical abrasion (400-grit) to "bite" into the smooth oxide layer. This creates the microscopic "tooth" required for mechanical bonding.
The Water Break Test: After cleaning, spray the surface with water. If the water sheets off uniformly, the surface is chemically clean and ready for priming.
Never cut corners on the primer. Aluminum requires chemically active formulas:
Self-Etching Primers: These contain a mild acid that etches the metal while depositing a resin film, creating a molecular-level bond.
Epoxy Primers: Known for exceptional grip and corrosion resistance, these are the industry standard for high-durability applications.
Zinc Chromate/Strontium Chromate: These remain the "gold standard" for marine or high-moisture environments where salt spray is a factor.
The topcoat must be chosen based on the final application:
PVDF (Fluorocarbon): The top tier for architectural exteriors. It is virtually immune to UV degradation and acid rain, offering a 20+ year lifespan.
SMP (Silicone-Modified Polyester): Offers a great balance of hardness and cost, with superior scratch resistance for industrial roofing.
PE (Polyester): Suitable for indoor appliances or interior panels. It’s cost-effective but prone to chalking if exposed to heavy sunlight.
In high-speed coil coating, we follow the "2-coat, 2-bake" (2C2B) method.
Peak Metal Temperature (PMT): The aluminum itself must reach specific temperatures (often 210°C–240°C) to ensure the polymers fully cross-link.
Field Touch-ups: If repairing on-site, avoid high humidity (>70%). The coating typically needs 72 hours to reach full chemical hardness; avoid any physical abrasion during this window.
Demand Standards, Not Just Low Prices
When sourcing painted aluminum coil, insist on AAMA 2605 (for PVDF) or equivalent regional standards. Pay close attention to "Cross-hatch Adhesion" and "T-Bend" test results in the lab reports.
Annual "Health Checks"
Even the best coating needs maintenance. Wash exterior surfaces annually with a pH-neutral detergent to remove salt and industrial pollutants that can eat into the edges.
Address Damage Early
If you see a chip or a deep scratch, seal it immediately with a matching touch-up kit. This prevents moisture from "creeping" under the paint film and causing widespread delamination.
OUR ADVANTAGES
Smoothness
There is no residual stress on the surface and no deformation after shearing
Weather resistance
The paint pattern made by roller coating and high temperature baking has high gloss, good color stability and little color difference change
Decorative
There is a fresh natural beauty, the pattern is casual and do, give customers a wide range of personality choices, can enrich the culture of the product, give people more beautiful enjoyment.
Environmental Protection
Resistant to salt, alkali and acid rain corrosion, will not corrode or produce toxic bacteria, does not release any toxic gases.
Mechanical
ACP after composite with plastic and adhesive. With the flexural and flexural strength required by the decorative plate, in the four seasons climate, the change of wind pressure, temperature, humidity and other factors will not cause bending, deformation,expansion and so on.
