1. Introduction

Functional epoxy coatings with conductive or insulating properties are critical components in modern electronics, electrical equipment, and electromagnetic shielding applications. The colorants used in these functional coatings must not only provide consistent color but also maintain the coating's electrical properties without interfering with conductivity or insulation performance. DENSON SEP series epoxy resin colorants, developed by Dongguan DENSON Functional Materials Co., Ltd., are specially formulated to be compatible with both conductive and insulating epoxy coating systems. This article examines the technical requirements for colorants in functional coatings, three application cases in electromagnetic shielding, anti-static flooring, and high-voltage insulation, and provides selection parameters and market trend analysis.

2. Technical Features and Mechanism

Conductive epoxy coatings are coatings that provide electrical conductivity through the incorporation of conductive fillers such as carbon black, carbon nanotubes, graphene, or metallic pigments (silver, copper, nickel). The conductivity is measured as surface resistivity (Ω/sq) per ASTM D257 or IEC 60093. Insulating epoxy coatings, conversely, are designed to prevent electrical current flow, with volume resistivity typically ≥ 10^12 Ω·cm.

The key challenge for colorants in functional coatings is maintaining electrical performance:

(1) For conductive coatings: The colorant must not disrupt the conductive network formed by conductive fillers. Insulative pigment particles can break the percolation network if not properly dispersed. DENSON SEP colorants use ultra-fine pigment particles (D90 ≤ 3μm) that do not interfere with the conductive filler network, maintaining surface resistivity within 10^3-10^6 Ω/sq for anti-static applications.

(2) For insulating coatings: The colorant must not introduce conductive impurities or ionic contaminants that could reduce insulation resistance. SEP colorants use high-purity pigments with low ionic impurity content (conductivity of water extract ≤ 50 μS/cm per IEC 60454-2), ensuring volume resistivity ≥ 10^14 Ω·cm in cured epoxy systems.

(3) Dispersion compatibility: The hyperdispersant technology in SEP colorants ensures uniform pigment distribution without agglomeration, preventing local conductivity variations or insulation weak points that could cause electrical breakdown.

(4) Thermal stability: SEP colorants maintain color stability up to 180°C, suitable for high-temperature curing cycles (150-180°C) common in electrical insulation coatings.

The market trend: The global conductive coatings market is projected to grow at a CAGR of 7.2% from 2025 to 2030, driven by increasing demand for electromagnetic interference (EMI) shielding in consumer electronics, electric vehicles, and 5G infrastructure. The insulating coatings market is growing at 5.8% CAGR, fueled by renewable energy (wind turbine generators, solar inverters) and electric vehicle motor insulation requirements.

3. Application Case Study 1: Electromagnetic Shielding Coatings

An electronics manufacturer required conductive epoxy coatings for EMI shielding of plastic enclosures used in industrial control equipment. The coating needed a surface resistivity of 10^3-10^5 Ω/sq and consistent dark gray color. Using DENSON SEP-700 colorants at 4% dosage in a carbon-nanotube-filled conductive epoxy system, the manufacturer achieved stable conductivity and uniform color.

Key performance: Surface resistivity was 5×10^4 Ω/sq (ASTM D257), with variation ≤ ±15% across the coated surface. EMI shielding effectiveness reached 40-50 dB in the 30 MHz-1 GHz range (IEEE 299). Adhesion to ABS/PC substrate was ≥ 4MPa (ASTM D4541), and the coating passed 1000 hours of salt spray testing (ASTM B117) without conductivity degradation.

4. Application Case Study 2: Anti-static Epoxy Flooring

A semiconductor manufacturing facility required anti-static epoxy flooring with surface resistivity of 10^6-10^9 Ω/sq (per ANSI/ESD S20.20) to protect sensitive electronic components from electrostatic discharge. Using SEP-750 colorants at 5% dosage in a carbon-fiber-filled anti-static epoxy flooring system, the facility achieved consistent anti-static performance with customizable colors.

Key performance: Surface resistivity was 2×10^8 Ω/sq (ANSI/ESD STM11.11), meeting the ESD-protective flooring requirement. The flooring had a compressive strength of 90MPa (ASTM D695) and abrasion resistance of ≤ 0.05g/1000 cycles (ASTM D4060). Color uniformity ΔE ≤ 0.6 across a 2000m² installation area, and the anti-static performance remained stable after 5 years of service with regular maintenance.

5. Application Case Study 3: High-voltage Motor Insulation Varnish

A motor manufacturer required insulating epoxy varnish for high-voltage (6kV-10kV) motor stator windings. The varnish needed volume resistivity ≥ 10^14 Ω·cm and dielectric strength ≥ 20 kV/mm, with color coding for voltage level identification. Using SEP-800 high-purity colorants at 3% dosage in an epoxy anhydride insulation varnish, the manufacturer achieved excellent insulation performance with reliable color coding.

Key performance: Volume resistivity was 5×10^14 Ω·cm (ASTM D257) at 25°C, and dielectric strength was 25 kV/mm (ASTM D149). The varnish had a thermal class of F (155°C continuous operation, per IEC 60085) and passed the 1000-hour thermal aging test at 180°C without insulation degradation. The color coding (red for 6kV, blue for 10kV) remained stable with ΔE ≤ 1.0 after thermal aging.

6. Key Selection Parameters and Usage Recommendations

| Parameter | Conductive Coatings | Insulating Coatings |

| Pigment particle size | D90 ≤ 5μm | D90 ≤ 3μm |

| Ionic impurity | ≤ 200 μS/cm | ≤ 50 μS/cm |

| Recommended dosage | 3-6% | 2-4% |

| Target resistivity | 10^3-10^6 Ω/sq | ≥ 10^12 Ω·cm |

| Key test standard | ASTM D257, IEEE 299 | ASTM D149, IEC 60085 |

| Market growth (CAGR) | 7.2% (2025-2030) | 5.8% (2025-2030) |

Usage recommendations:

(1) For conductive coatings, always test the colorant's effect on surface resistivity before full production, as even small amounts of insulative pigment can shift resistivity by an order of magnitude.

(2) For insulating coatings, request a low-ionic-impurity certificate from the colorant supplier, and verify the water extract conductivity per IEC 60454-2.

(3) When using colorants in conductive systems, add the colorant before the conductive filler to ensure uniform dispersion, and avoid high-shear mixing that could break conductive filler networks.

(4) For high-temperature insulation applications, verify the colorant's thermal stability at the curing temperature and service temperature.

(5) For more information on DENSON SEP functional colorant applications, refer to the DENSON technical library.

7. Conclusion

Conductive and insulating functional epoxy coatings require colorants that are carefully formulated to maintain electrical performance while providing consistent color. DENSON SEP epoxy resin colorants, through ultra-fine particle size control, low ionic impurity content, hyperdispersant technology, and thermal stability, enable reliable performance in electromagnetic shielding, anti-static flooring, and high-voltage insulation applications. With the growing demand for functional coatings in electronics, renewable energy, and electric vehicles, selecting the right colorant partner is essential for maintaining both electrical performance and color consistency.

8. FAQ

Q1: How do colorants affect the conductivity of epoxy coatings?

A: Colorants can affect conductivity in two ways: (1) Insulative pigment particles can physically separate conductive filler particles, breaking the percolation network and increasing resistivity. (2) Ionic impurities in the colorant can create unintended conductive paths, reducing insulation resistance. For conductive coatings, use ultra-fine colorants (D90 ≤ 5μm) at low dosage (3-6%) to minimize network disruption. For insulating coatings, use high-purity colorants with water extract conductivity ≤ 50 μS/cm.

Q2: What is the difference between surface resistivity and volume resistivity?

A: Surface resistivity (Ω/sq) measures the electrical resistance across the surface of a material, used for anti-static and EMI shielding coatings (ASTM D257). Volume resistivity (Ω·cm) measures the resistance through the bulk material, used for insulating coatings (ASTM D257). Anti-static flooring typically requires surface resistivity of 10^6-10^9 Ω/sq, while motor insulation requires volume resistivity ≥ 10^12 Ω·cm.

Q3: Can organic pigments be used in high-voltage insulation coatings?

A: Yes, but only high-purity organic pigments with low ionic impurity content. Some organic pigments may contain residual salts or surfactants from manufacturing that can reduce insulation resistance. DENSON SEP-800 series colorants use purified organic pigments with water extract conductivity ≤ 50 μS/cm, making them suitable for high-voltage insulation applications. Always request a purity certificate and conduct validation testing.

Q4: What is the maximum service temperature for SEP colorants in functional coatings?

A: DENSON SEP epoxy colorants maintain color stability up to 180°C for continuous service, suitable for thermal class F (155°C) and class H (180°C) insulation systems per IEC 60085. For higher temperature applications (above 180°C), inorganic pigment-based colorants such as iron oxide or mixed metal oxide pigments are recommended, as they offer better thermal stability than organic pigments.

Q5: What are the key growth drivers for functional epoxy coatings?

A: The main growth drivers are: (1) Electric vehicle production, requiring conductive coatings for battery EMI shielding and insulating coatings for motor windings. (2) 5G infrastructure, needing EMI shielding for base station electronics. (3) Renewable energy, with wind turbine generators and solar inverters requiring high-performance insulation. (4) Semiconductor manufacturing, demanding anti-static flooring and ESD-protective coatings. The global functional coatings market is expected to reach $18.5 billion by 2030.