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Where is the adhesion of pure epoxy powder coating reflected
source：www.cnjindu.com | Release time：2026年08月08日1、 Where is adhesion reflected (actual performance)
1. Grid test (hundred grid test, the most commonly used detection)
Use a hundred grid knife to draw a cross grid, apply 3M tape to quickly tear it off, and the coating will not peel off, peel off, or break off the edges and corners.
Pure epoxy can achieve grades 0-1 for steel, cast iron, and aluminum materials that have been phosphated using normal processes; If the pre-processing is poor, the entire grid will be torn off by the tape.
2. Bending/impact testing
Impact: When the workpiece is impacted, the coating does not crack or peel off;
Cylindrical bending: The coating follows the substrate bending without cracking or delamination.
Pure epoxy powder is brittle, and the bending performance will decrease under thick coatings. The adhesion is qualified ≠ the flexibility is very good.
3. No foaming or warping in salt spray, humid and hot environments
Adhesion is not just about the initial spray, wet adhesion in a corrosion-resistant environment is the key.
Water vapor seeps under the coating, and if the adhesion is poor, it can cause the coating to bubble and peel off from the substrate.
Advantages of pure epoxy: good wet adhesion, compared to polyester powder, it is not easy to "delaminate and bubble" under humid and salt spray conditions, which is also the core reason why epoxy is widely used for anti-corrosion and insulating workpieces.
4. During cutting, polishing, and drilling, the coating does not lift up in its entirety
Subsequent machining of the workpiece (drilling, polishing, turning) will not result in the coating peeling off in patches; If the adhesion is poor, the coating at the processing position will directly lift and peel off.
5. Do not detach after thermal cycling and alternating cold and hot cycles
The workpiece is repeatedly heated and cooled, and the thermal expansion and contraction of the coating and metal are not synchronized. If the adhesion is sufficient, there will be no peeling. After the baking and solidification of high-voltage insulation powder workpieces, the cold and hot cycling is an important test.
2、 Two main sources of adhesion for pure epoxy powder
1. Mechanical bite (physical anchoring)
The surface of the workpiece is subjected to shot blasting/phosphating, forming a micro concave convex rough surface. Molten epoxy powder flows into the micro gaps of the substrate, and after cooling and solidification, it locks onto the metal surface like a "lock buckle".
The surface of the substrate is too smooth (polished mirror finish), with insufficient mechanical bite, resulting in a direct decrease in adhesion.
2. Chemical binding force
The epoxy group reacts with the hydroxyl group on the surface of the metal substrate to form a chemical bond.
Phosphating treatment will significantly enhance this chemical bonding; Oil stains, saponification residues, and salt ions can block chemical bonds and directly damage adhesion.
3、 What factors can damage the adhesion of pure epoxy powder
1. Inadequate pre-treatment: oil stains, wax, salt, and passivation residues; The workpiece is not dried properly and contains moisture.
2. The surface of the substrate is too smooth and lacks roughness.
3. Insufficient curing: Insufficient baking temperature/time, incomplete cross-linking of epoxy resin, significant decrease in adhesion (many people mistakenly think it's just poor hardness, but the actual adhesion will also be damaged).
4. Differences in substrate materials: Carbon steel and cast iron have good adhesion; Aluminum alloys and copper bars need to be passivated/phosphated properly, otherwise the adhesion may deteriorate; Galvanized parts made of pure epoxy are prone to later foaming and detachment.
5. Thick coating: The internal stress of the ultra thick coating increases, which will lower the adhesion and make it easy to peel off.
4、 Simple comparison with epoxy polyester (mixed type)
Pure epoxy: good dry adhesion, significantly better wet adhesion (salt spray wet heat) than mixed powder, suitable for anti-corrosion and insulation scenarios; Disadvantages: High brittleness and weak bending performance of thick films.
Epoxy polyester hybrid type: good flexibility, but weak wet adhesion, prone to foaming and delamination in high humidity salt spray environments, commonly used for indoor decorative parts.
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