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Home / News / Industry News / Paint Film Keeps Peeling? It's Likely Adhesion and Interlayer Bonding That's Failing
Industry News
Adhesion Promoter Technology
A coating that passes initial quality checks can still fail weeks later — peeling at the edges, blistering after water exposure, or a topcoat that lifts cleanly off the primer during recoat testing. In most of these cases, the resin chemistry is not the problem; the weak link is the interface itself, where adhesion to the substrate and bonding between coating layers were never fully developed.
Where Interlayer Bonding Typically Breaks Down
Multi-coat systems rely on a continuous chain of adhesion: primer to substrate, basecoat to primer, and topcoat to basecoat. If any single link in that chain is weak, the entire film can fail under mechanical stress, humidity, or thermal cycling — even if every other property of the formulation looks correct on paper.
Edge & Impact Lift-Off
Coating chips or peels away from corners, edges, or impact points first, indicating insufficient anchoring to the substrate surface.
Recoat Delamination
A second or third coat separates cleanly from the layer beneath it during cross-cut or tape-pull testing, even when both layers cured correctly on their own.
Water & Salt-Spray Failure
Blistering, whitening, or loss of gloss appears after humidity chambers, water immersion, or salt-spray exposure, pointing to moisture penetrating the interface.
Reduced Flexibility & Tensile Strength
The film cracks or loses elasticity under bending or stretching, suggesting the cross-linked network at the interface is too rigid or poorly bonded.
Why Simply Increasing Resin or Hardener Doesn't Solve It
A common first response is to raise the resin-to-hardener ratio or extend cure time, hoping a denser film will bond better. In practice this only shifts the problem: bulk film hardness may improve, but the resin network at the substrate or interlayer boundary is what actually determines peel strength — and bulk-property changes rarely reach that thin interfacial zone in a meaningful way. Pot life, application window, and storage stability can also suffer as a side effect.
A Formulation-Level Approach: DH-7326N Adhesion Promoter
DH-7326N is a polyether-modified siloxane copolymer adhesion promoter designed to strengthen the bond both between the coating and the substrate, and between successive coating layers. Rather than changing the bulk resin system, it works at the interface — optimizing interfacial bonding and the cross-linked network so the film behaves as one continuous structure rather than a stack of weakly connected layers.
Without DH-7326N
- Edge and corner adhesion below specification
- Interlayer peel visible on cross-cut test
- Reduced salt-spray and water-soak resistance
- Limited working time in 2K systems
- Lower tensile elongation, brittle feel
With DH-7326N
- Improved adhesion to substrate and between coats
- Stronger cross-cut and tape-pull performance
- Better water immersion, salt-spray and boiling resistance
- Extended pot life in two-component formulations
- Improved tensile strength and elasticity
Key Performance Contributions
| Adhesion Improvement | Strengthens bonding between the coating film and substrate, reducing edge lift and peeling under mechanical stress |
| Interlayer Bonding | Improves anchoring between successive coats, lowering the risk of delamination during multi-coat builds |
| Mechanical Properties | Contributes to higher tensile strength and elongation, giving the film better overall toughness |
| Water & Salt-Spray Resistance | Helps the film withstand water immersion, salt-spray testing, and boiling-water exposure without blistering |
| Wipe Resistance | Supports surface durability under repeated cleaning or wiping cycles |
| Two-Component Pot Life | Helps extend the usable working time of 2K formulations after mixing |
Where It Fits
| Amino Baking Finishes | Improves interlayer adhesion and durability in high-temperature curing systems for appliances, furniture and metal parts |
| 2K Polyurethane (2K PU) | Enhances bonding and extends working time in two-component PU topcoats and primers |
| General Multi-Coat Builds | Suitable for primer-basecoat-topcoat structures where overall system integrity depends on every interface |
Frequently Asked Questions
Does DH-7326N replace the primer in a coating system?
No. It is added to the formulation as an additive to reinforce interfacial bonding; it does not replace primer design, surface preparation, or proper cure schedules.
Will it affect the gloss or appearance of the finished film?
DH-7326N is formulated to improve interfacial bonding without significantly altering the visual properties of the cured film, so existing gloss and color targets can generally be maintained.
Is it suitable for both primer and topcoat layers?
Yes — because it strengthens both substrate adhesion and interlayer bonding, it can be evaluated in primers, intermediate coats, and topcoats depending on where bonding is weakest in a given system.
How is dosage typically determined?
Dosage depends on the resin system, substrate, and target performance (e.g. salt-spray hours, cross-cut rating). Our technical team can recommend a starting dosage range and help design a small-batch trial.
Key Takeaway
Long-term coating performance is decided at the interface — not just in the bulk resin. When peeling, recoat delamination, or water/salt-spray failures occur, the most effective fix is usually to reinforce interfacial bonding directly rather than reformulating the entire system.
- DH-7326N strengthens both substrate adhesion and interlayer bonding
- Improves tensile strength, elongation and overall film toughness
- Enhances water immersion, salt-spray, boiling and wipe resistance
- Extends pot life in 2K systems while supporting amino baking and 2K PU formulations
Seeing adhesion or interlayer bonding failures in your coating line? Talk to our formulation team about DH-7326N adhesion promoter and request a technical data sheet or sample for trial.
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