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Industrial Coatings · Metal Substrates · DH-7326N
In industrial coating applications, adhesion has always been an important indicator for evaluating coating film performance. But many formulations encounter a situation: when application has just been completed, the cross-cut test or grid test shows normal results — but after a period of water immersion, salt spray testing, wiping, or even cold-heat cycling, the film starts to show edge lifting and interlayer delamination.
This shows that the bond between coating and substrate is not a simple "is it sticky" question. Substrate surface condition, the interaction between resin and substrate, and the internal structure formed after coating film curing all affect final adhesion stability.
4
Common adhesion failure patterns after initial test passes
Common Problems
1
Good Initial Adhesion, But Declines After Water Immersion
When the film has just formed, it can adhere firmly — but after water contacts the interface over a long period, interfacial bonding is affected and delamination may gradually appear.
2
Unstable Adhesion on Metal Substrates
Substrate surface energy and chemical properties of aluminium, electroplated metals, and similar materials differ from ordinary substrates. If the coating's bonding capability for the surface is insufficient, adhesion decline easily occurs.
3
Interlayer Delamination Readily Appears
In multi-coat application systems, if the bonding between upper and lower coating layers is insufficient, delamination may preferentially occur at interlayer positions after exposure to water, salt spray, or mechanical stress.
4
Film Strength and Adhesion Difficult to Balance
Simply increasing film hardness does not necessarily bring better actual adhesion. When the film is too hard and lacks a certain extension capability, cracking and peeling can more easily occur after impact or deformation.
Why Adhesion Problems Are Not Always Just "Poor Substrate Treatment"
Many people's reaction when solving adhesion problems is to strengthen substrate cleaning, sanding, or surface treatment. These steps are of course important — but if surface treatment has already met requirements and the film still peels easily, the interfacial bond between coating and substrate needs further observation.
After coating cures, it does not simply "sit on top of" the substrate surface — it needs to form a relatively stable interfacial bond. If the interaction between the resin system and the substrate is relatively weak, even if the film surface looks complete, the interface may still be the first position to fail when subjected to water, salt spray, or mechanical action.
At the same time, the crosslink degree, elasticity, and impact resistance of the film itself will also affect whether this interfacial bond can be maintained long-term. Therefore, improving adhesion cannot only focus on substrate treatment before application — it is also necessary to find ways to strengthen interfacial action from inside the coating formulation.
DH-7326N: Polyether-Modified Siloxane Adhesion Promoter
DH-7326N is a polyether-modified siloxane adhesion promoter. Its characteristic is that it can participate in interfacial action, helping to strengthen the bond between the coating and the contact surface, while also having a certain improving effect on the film structure. Because the product has good stability, it does not easily undergo hydrolysis when used in formulations, and has relatively little impact on system storage stability.
When applied to a coating system, it can be used to improve substrate adhesion and the interlayer bond between multiple coating films, and help improve the tensile performance and elasticity of the film. In terms of durability, DH-7326N can be used to further improve the film's resistance to water immersion at ambient temperature, salt spray, water boiling, and wiping, while also taking into account certain mechanical properties.
The product is suitable for amino baking coatings and 2K PU coating systems. Reference dosage: 0.5%–1.5% of total formulation. Actual application can be adjusted based on resin type, substrate properties, and target performance.
| Substrate Adhesion | Participates in interfacial action, strengthening the bond between coating and substrate surface |
| Interlayer Bonding | Improves bonding between coating layers in multi-coat application systems |
| Film Tensile & Elasticity | Helps improve tensile performance and elasticity — coating is more stable under external force |
| Durability | Improves resistance to ambient-temperature water immersion, salt spray, water boiling, and wiping |
| Storage Stability | Good hydrolysis resistance — does not easily affect system storage stability |
| System Compatibility | Suitable for amino baking coatings and 2K PU industrial coating systems |
Summary
Coating adhesion is not a result determined by a single indicator. In addition to substrate cleaning and surface treatment, the interfacial bond between resin and substrate, the crosslink structure inside the film, and the toughness of the coating layer itself all affect long-term adhesion performance. When the situation of "initial test passes, but peels after water immersion or salt spray" occurs, rather than simply increasing resin hardness or repeatedly treating the substrate, it is better to further adjust the formulation from two directions — interfacial bonding and the overall film structure.
Frequently Asked Questions
Why does DH-7326N's resistance to hydrolysis matter for an adhesion promoter?
Siloxane chemistry relies on Si–O bonding at the coating-substrate interface for its adhesion promotion mechanism. If the siloxane groups hydrolyse prematurely — in the wet coating before cure, or in the cured film during water or humidity exposure — the interfacial bond is broken and adhesion performance is lost. DH-7326N's polyether modification and chemical structure are designed to resist hydrolysis, maintaining interfacial bond integrity under the wet conditions the coating encounters in service.
Can DH-7326N improve adhesion in multi-layer systems where the failure is between two coating layers rather than at the substrate?
Yes — in addition to substrate adhesion, DH-7326N can also improve interlayer bonding in multi-coat systems. For interlayer failures observed after water immersion or mechanical stress, DH-7326N is added to the primer or mid-coat layer that is showing failure at its upper interface. The specific addition point and dosage should be confirmed through trial evaluation for the specific multi-coat system.
