Insulating colorants are pigment dispersions that must provide phase-color identification without degrading the dielectric performance of an electrical insulation system. This article explains the dielectric mechanism behind insulating colorants and the three parameters that matter most: volume resistivity, dielectric strength, and dielectric loss. DENSON insulating colorants from Dongguan DENSON Functional Materials Co., Ltd. are batch-tested per GB/T 1410 and GB/T 1408.

1. Introduction

As voltage platforms move from 400 V toward 800 V and charging modules become more compact, even a small amount of added colorant can affect an insulation system. An insulating colorant is therefore not an ordinary tint: it must remain compatible with the base resin and preserve electrical properties. The key point is simple—select a colorant by dielectric data, not by color alone. See the DENSON EP electronic-grade colorant series for matched grades.

2. Technical Features and Dielectric Mechanism

An insulating colorant is a high-concentration dispersion of pigment in an insulating resin carrier, designed to be added to impregnating varnishes, casting resins, or potting compounds. Its dielectric behavior is governed by three mechanisms:

1. Conduction through impurities: residual moisture, free ions, or poorly dispersed pigment agglomerates create conductive paths that lower volume resistivity.

2. Breakdown at weak points: coarse particles and voids concentrate the electric field, reducing dielectric strength and initiating partial discharge.

3. Polarization loss: polar additives increase the dielectric constant and loss tangent, causing heating in high-frequency power modules.

Fig.1 Dielectric breakdown test rig for solid insulating materials (process/QC)

3. Application Case Study 1: VPI Treatment of an 800 V Hairpin Stator

An electric-drive manufacturer added 1.2% insulating colorant to a VPI (vacuum pressure impregnation) varnish for an 800 V hairpin stator. Vacuum was held below -0.095 MPa, followed by curing at 160 °C for 2 h. The pigment identified the impregnated winding while the cured varnish met the required dielectric values.

Fig.2 VPI tanks used for motor stator impregnation (process)

4. Application Case Study 2: Epoxy Casting of a 10 kV Dry-Type Transformer

A transformer works added the colorant to an epoxy casting resin under a vacuum below 200 Pa to suppress voids. The finished coil showed partial discharge below 5 pC, meeting GB/T 1094.11 requirements for cast-resin transformers.

5. Application Case Study 3: Potting of a High-Frequency Power PCB

A power-supply maker used 2% colorant in a potting compound for a high-frequency PCB, cured at 60 °C for 4 h. The low tanδ grade limited dielectric heating, and the black compound provided both insulation and confidentiality.

Fig.3 Epoxy potting compound dispensed onto a PCB array (material/process)

6. Key Selection Parameters and Recommendations

Recommendation: always match the colorant carrier to the base resin, keep dosage within 1–3%, and require dielectric test reports per GB/T 1408 and GB/T 1410. More grades are listed on the DENSON website.

7. Conclusion

Insulating colorants must color an insulation system without lowering its dielectric performance. The controlling parameters are volume resistivity (≥1×10¹⁴ Ω·cm), dielectric strength (≥20 kV/mm), and loss tangent (≤0.020). Selecting a carrier-matched, fine-grind DENSON colorant and keeping dosage between 1% and 3% preserves insulation reliability in motors, transformers, and power modules.

8. FAQ

Q1: What is an insulating colorant?
An insulating colorant is a high-concentration dispersion of pigment in an insulating resin carrier, added to varnishes, casting resins, or potting compounds to provide phase-color identification while preserving the dielectric properties of the insulation system.

Q2: Which dielectric parameters are most important for an insulating colorant?
The three key parameters are volume resistivity (typically ≥1×10¹⁴ Ω·cm per GB/T 1410), dielectric strength (≥20 kV/mm per GB/T 1408), and loss tangent (≤0.020 per GB/T 1409), together with fineness (≤5 μm per GB/T 1724).

Q3: How much insulating colorant should be added?
A typical dosage is 1–3% by weight. Exceeding the recommended dosage can introduce excess pigment interfaces and lower dielectric performance, so the minimum dosage that achieves the target color should be used.

Q4: Why must the colorant carrier match the base resin?
A mismatched carrier can cause flocculation, poor wetting, or phase separation, which create voids and weak points that reduce dielectric strength. A 48-hour compatibility test should show no flocculation or separation before use.

Q5: Does pigment fineness affect dielectric strength?
Yes. Coarse pigment agglomerates concentrate the electric field and can initiate partial discharge and early breakdown. Keeping fineness at ≤5 μm (≤1 μm for electronic grades) per GB/T 1724 helps maintain dielectric strength and low partial discharge.