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Home / News / Industry News / Difficult-to-Coat Substrates Keep Losing Paint — Why Substrate Treatment Is the Key
Industry News
Substrate Pre-Treatment · Low-Surface-Energy & Inert Substrates · DH-7208
In coating applications, substrates such as PP, PE, POM, rubber, and stainless steel have low surface energy or insufficient chemical reactivity — making it difficult for coatings to fully wet and bond to them. Adhesion failure and film peeling are common results. This is especially the case in plastic parts, metal parts, and vacuum-plated components, where standard coating systems often cannot achieve adequate adhesion — making substrate pre-treatment necessary to improve interfacial bonding performance.
Common Problems
| Insufficient Film Adhesion | The coating does not bond firmly to the substrate — it peels after use or testing. |
| Plastic Substrates Difficult to Coat | Non-polar materials such as PP and PE have low surface activity — coatings cannot adhere adequately. |
| Film Fails After Water-Boil Testing | Some substrates develop blistering and peeling after water-boil or extended use. |
| Poor Adhesion on Metal Surfaces | Special surfaces such as aluminium and stainless steel have characteristics that standard coatings struggle to form stable bonds with. |
Limitations of Traditional Improvement Approaches
Some processes improve substrate surface roughness or activity through sanding or flame treatment, but these methods are susceptible to application condition variation and cannot fully resolve interfacial bonding issues across different substrate types. Using a substrate treatment agent to improve the bonding state between substrate and coating is the more systematic approach to improving adhesion and stability.
DH-7208: Halogen-Free Graft Copolymer Substrate Treatment Agent
DH-7208 is a halogen-free special graft copolymer substrate treatment agent, primarily used for surface treatment of difficult-to-coat substrates including PP, PE, POM, EPDM rubber, and stainless steel.
The product improves the bonding performance between substrate and coating, increases film adhesion, and provides good water-boil resistance and low shrinkage. It is applicable in PU coatings, thermoplastic coatings, and vacuum plating applications.
For use: dilute DH-7208 with xylene at the recommended ratio according to process requirements, spray onto the substrate surface, allow to surface-dry or bake, then proceed with subsequent coating application.
Summary
For low-surface-energy plastics and special metal substrates, adhesion has always been a key challenge in the coating process. Using a substrate treatment agent appropriately can improve interfacial bonding, increase film stability, and allow the coating to maintain better performance across different application environments.
Frequently Asked Questions
How does DH-7208 differ from flame treatment or plasma treatment for PP/PE?
Flame and plasma treatment physically and chemically activate the substrate surface, which is effective but dependent on exposure uniformity, distance, and dwell time — all of which are difficult to control consistently on complex 3D geometry. DH-7208 chemical pre-treatment provides more uniform surface modification regardless of part geometry, and the modified surface is more stable over time before coating is applied. Both approaches address the same surface energy problem; the optimal choice depends on the specific production environment.
Does DH-7208 need to be fully dried before applying the topcoat?
The treated surface should be allowed to surface-dry or baked per the recommended process before the subsequent coat is applied. Applying the topcoat while the treatment agent is still wet may affect the final adhesion result. The specific drying window should be confirmed for the substrate type and production environment.
Can it be used on substrates other than the five listed?
DH-7208 is developed and characterised for PP, PE, POM, EPDM rubber, and stainless steel as its primary target substrates. For other difficult-to-coat materials, a trial evaluation is recommended to determine whether the surface modification mechanism is compatible with the specific substrate chemistry.
