DH-7325 Adhesion Promoter for Stainless Steel and Difficult Metal Substrates

Difficult Inorganic Substrate Adhesion

Stainless steel, aluminium, electroplated surfaces, and glass share one characteristic that makes them consistently harder to coat than carbon steel: their surfaces are chemically stable and low in surface energy, which is exactly what makes them valuable materials — and exactly what makes coatings reluctant to bond to them durably. The passive oxide layers on stainless steel and aluminium, the smooth inert surfaces of electroplated parts, and the hydrophilic but low-reactivity surface of glass all present the same fundamental challenge at the coating interface.

Why These Substrates Resist Durable Coating Adhesion

Stainless Steel Passive Layer

The chromium-oxide passive film that prevents corrosion is chemically inert and low-energy — both properties that limit the interfacial bonding reactions that coatings depend on for adhesion. Mechanical abrasion helps, but the passive layer reforms quickly on exposure to air.

Aluminium Oxide Surface

Aluminium develops a dense, stable oxide layer almost immediately. Like stainless steel, this layer provides corrosion protection but acts as a barrier between the metal and the coating at the interface where adhesion is formed.

Zinc and Galvanised Surfaces

Zinc surfaces develop zinc oxide and zinc carbonate layers on exposure. These affect the surface chemistry differently from iron oxide and create interface conditions that standard coating adhesion chemistry is often not optimised for.

Electroplated Surfaces

Chrome, nickel, and gold plating are smooth, chemically stable, and have very low surface roughness — minimising both mechanical interlocking and chemical bonding opportunities for the applied coating.

Glass Surfaces

Glass is hydrophilic and can be chemically reactive under the right conditions, but standard organic coating adhesion chemistry is not inherently optimised for a silicate surface without specific interfacial agents.

Why Increasing Resin Content or Baking Temperature Doesn't Fully Solve It

The standard responses to adhesion problems on difficult substrates — raising resin content, extending baking time, or increasing temperature — improve the bulk mechanical properties of the film and the completeness of cure, but do not change what happens at the coating-substrate interface. If the interface lacks adequate chemical bonding sites or compatibility with the substrate surface chemistry, no amount of bulk film optimization can compensate for the weak interfacial bond.

DH-7325: Epoxy Polymer Adhesion Promoter for Difficult Substrates

DH-7325 uses an epoxy polymer structure to improve the bonding between coating and difficult inorganic substrates — aluminium, zinc, stainless steel, electroplated surfaces, and glass. It works at the coating-substrate interface, improving the interfacial compatibility that determines adhesion strength, chemical resistance, and corrosion protection durability.

Without Interface Optimisation

Adhesion relies on physical contact with passive/inert surfaces
Chemical resistance performance limited by weak interface
Corrosion resistance degrades faster at interface entry points
Film flexibility and elongation at interface insufficient for forming
Short service life on difficult substrates despite adequate bulk film quality

With DH-7325

Epoxy polymer chemistry improves bonding to passive/inert substrate surfaces
Enhanced chemical resistance including media and water immersion
Improved corrosion protection through stronger interfacial bonding
Better flexibility and elongation performance retained across the interface
Suitable for both baking (amino, alkyd-amino) and industrial 2K systems

Performance Contributions

Adhesion to Difficult Substrates	Improves bonding to aluminium, zinc, stainless steel, electroplated surfaces, and glass at the coating-substrate interface
Chemical and Media Resistance	Stronger interface bonding supports improved resistance to chemical exposure and liquid immersion
Corrosion Protection	Reduced interface permeability to moisture and ions improves corrosion protection durability
Flexibility and Elongation	Contributes to improved film flexibility and elongation performance, supporting forming and bending after coating
Storage Stability	Good formulation compatibility with limited effect on storage stability of the base system
System Compatibility	Applicable in alkyd-amino and acrylic-amino baking systems, and medium/high-temperature single- and two-component industrial coatings

Frequently Asked Questions

Can DH-7325 be used on all five substrate types simultaneously in a mixed-substrate production line?

Yes — its adhesion improvement mechanism operates through interfacial chemistry that is relevant across aluminium, zinc, stainless steel, electroplated surfaces, and glass. In mixed-substrate production environments, it can provide a more consistent baseline adhesion without requiring separate formulation optimisation for each substrate type.

Does it replace the need for surface pre-treatment on difficult substrates?

DH-7325 improves adhesion through the formulation, complementing rather than replacing surface pre-treatment. On difficult substrates, both interfacial chemistry (through the additive) and surface condition (through pre-treatment) contribute to the final adhesion result, and both remain relevant.

Is it suitable for direct-to-metal application without a primer?

Its adhesion improvement is applicable in both primer and direct-to-metal topcoat formulations. For applications requiring both adhesion and corrosion protection, use in a primer system typically delivers better overall performance than in a topcoat alone.

Will it affect the gloss or colour of the finished coating?

At normal dosage levels, DH-7325 is formulated to improve interfacial adhesion without significant effect on the visual properties of the cured film. A drawdown evaluation on the specific formulation is recommended to confirm.

Key Takeaway

Paint peeling on stainless steel, aluminium, zinc, and electroplated surfaces is an interfacial problem — the passive or chemically stable surfaces that make these materials useful also limit the bonding mechanisms that coatings rely on. Bulk resin and cure adjustments don't reach the interface where the problem originates.

DH-7325 uses epoxy polymer chemistry to improve bonding at the coating interface on passive and chemically stable inorganic surfaces
Contributes to improved adhesion, chemical resistance, corrosion protection, and film flexibility
Compatible with alkyd-amino, acrylic-amino baking systems, and single- or two-component industrial coatings
Works alongside surface pre-treatment rather than replacing it, providing complementary formulation-level adhesion improvement

Coating stainless steel, aluminium, electroplated parts, or glass and experiencing adhesion or corrosion durability issues? Request technical data on DH-7325 adhesion promoter.