Special Function
Engineered for Specific Service Conditions and Functional Targets
This category covers engineered powders for applications that cannot be defined by appearance alone, including wheel clearcoats and primers, electrical-insulating epoxies and heavy-duty anticorrosive systems.
Clearcoats focus on transparency, flow and intercoat compatibility. Wheel primers combine filling, adhesion and compatibility with subsequent coating stages. Insulating epoxies rely on continuous coverage and controlled film build to provide dielectric performance. Heavy-duty epoxies support high film builds, multilayer application or use beneath polyester topcoats.
Selection should consider substrate, component geometry, pretreatment, film thickness, curing conditions and final qualification tests, followed by validation on representative panels or production parts.
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Special Function FAQ
What products are currently included in the Specialty & Functional category?
The Specialty & Functional category currently includes three types: insulating powder coatings, heavy-duty anti-corrosion powder coatings, and automotive wheel primer powder coatings.
EP1S Insulating Epoxy Powder Coating:
used for insulation protection of traction-battery components, motor systems, electrical equipment, and similar applications.
EP4S Heavy-Duty Anti-Corrosion Pure Epoxy Powder Coating: used for steel structures, pipelines, energy-storage equipment, and other high-corrosion applications.
HY0S_Wheel Automotive Wheel Primer Powder Coating: an epoxy-polyester hybrid smooth primer for automotive wheels, focused on primer compatibility, surface hiding, and subsequent topcoat requirements.
What are the main functions of automotive wheel primer powder coating?
Automotive wheel primer powder coating is mainly used to establish a stable base layer between the aluminum-alloy substrate and subsequent color paint or clear powder.
- Its core functions include providing good adhesion and basic corrosion protection
- improving minor defects on cast-wheel surfaces through high flow and filling ability
- improving powder deposition and coverage in complex areas such as bolt holes and recesses
- and ensuring intercoat compatibility with subsequent color paint and clear powder.
For actual wheel-service requirements such as corrosion, mechanical impact, and thermal cycling, performance should be verified as part of the complete coating system rather than judged from the primer layer alone.
How is compatibility between wheel primer powder and subsequent paint or clear powder verified?
Compatibility validation focuses on three core dimensions: intercoat adhesion, material compatibility, and curing compatibility.
Poor compatibility can cause defects such as peeling, cratering, and uneven gloss.
Laboratory pre-validation:
- contact-angle testing to ensure primer surface energy is 38–48 mN/m
- cross-cut (≥4B), X-cut, and pull-off tests to measure intercoat adhesion
- recoat-window tests to determine the optimum recoat time from 0–72 h
- solvent spot tests to assess compatibility.
Process simulation:
- control curing-temperature difference within ±10°C
- match primer film thickness of 60–80 μm with clear-powder thickness of 40–60 μm
- conduct 50–100 thermal cycles from -40°C to 150°C to check intercoat stability.
On-site quick checks:
- immediate cross-cut testing with a cross-hatch cutter and 3M tape peel evaluation
- tapping for a rough adhesion check
- 180° bend testing to detect intercoat cracking.
Common failure responses:
- control cure level or apply surface treatment for over-cured primer
- improve cleaning for intercoat contamination
- optimize oven temperature for curing mismatch
- and use verified material combinations where coating systems conflict.
A compatibility database is recommended from material selection through mass production.
What is the difference between using heavy-duty anti-corrosion powder coating alone and using it as a primer?
EP4S can be used either as a standalone heavy-duty anti-corrosion coating or as an anti-corrosion primer paired with a polyester topcoat.
When used alone, corrosion protection mainly comes from the pure epoxy coating's adhesion, thick-film capability, and barrier effect.
Higher film thickness can be used according to project needs, making it suitable for corrosion-protection applications where long-term outdoor weathering appearance is not a priority.
When used as a primer, EP4S mainly provides substrate adhesion, edge coverage, and a corrosion barrier, while the polyester topcoat provides outdoor weathering resistance and decorative performance.
The TDS states that a single epoxy coating achieves C2–C4 after ISO 9227 NSS 1,000 h testing; when combined with a topcoat as a complete system, it can meet relevant ISO 12944-6 C4–C5 corrosion-protection grades.
For highly corrosive or long-term outdoor projects, a complete primer + topcoat system is generally more suitable and should be designed according to the environmental category.
Is the insulation performance of insulating powder coating stable under high-temperature and high-humidity conditions?
After 1,000 h at 85°C/85% RH, the EP1S coating showed no obvious discoloration, blistering, or peeling and still met the dielectric withstand-voltage requirement.
After 500 thermal-shock cycles from -40°C to 85°C, it also maintained dielectric withstand performance.
Why does EP1S support relatively high film thickness, and is thicker always better?
EP1S is designed for a wide film-thickness range of 60–500 μm and can use fluidized-bed dipping or multiple coating passes to meet different insulation-protection requirements.
Increasing film thickness generally helps improve insulation protection and edge coverage, but thicker is not always better.
Excessive film thickness may increase the risk of internal coating defects, uneven curing, or stress, affecting long-term reliability.
The optimum thickness should therefore be determined according to working voltage, structural design, insulation requirements, and application process.
For high film thickness, multiple coating passes with performance verification are recommended.
How is compatibility between wheel primer powder and subsequent paint or clear powder verified?
Key factors are intercoat adhesion, material compatibility, and curing compatibility.
Begin with laboratory panel testing, including appearance after recoating, intercoat adhesion, solvent resistance, and thermal-cycle evaluation, confirming that there is no cratering, blistering, peeling, or other abnormality.
Then conduct a small production trial under actual process conditions to verify the stability of spraying parameters, film thickness, and curing conditions.
For wheel primers such as HY0S_Wheel, particular attention should be paid to bonding with subsequent color paint and clear powder to ensure that the complete coating system meets appearance and long-term performance requirements.