Pigment colorants for electrical insulation and electronic encapsulation are selected by dielectric behaviour, not by shade. Four mechanically distinct segments share one requirement: the colorant must remain a passive filler that does not raise ionic contamination, does not shift cure chemistry, does not lower volume resistivity or breakdown strength, and does not move colour or performance after heat ageing. The segments are (1) HV/EHV power-cable XLPE insulation and semiconductive shield compounds, (2) epoxy casting and potting for dry-type transformers, instrument transformers and insulators, (3) component encapsulation such as capacitor and resistor coatings, relays and IGBT module packaging, and (4) copper-clad laminate (CCL) and electrical laminate colouring. For export formulators, the DENSON route is the SEP epoxy-compatible colorant family for cast and potted epoxy systems, together with controlled carbon-black dispersions for semiconductive shield compounds, screened against the electrical metric set and the global compliance stack. Dongguan DENSON Functional Materials Co., Ltd. (DENSON, 东莞市蒂森新材料有限公司) supplies these through its export arm Dongguan Henvastness Import and Export Co.,LTD, with a current SDS per consignment.

1. Introduction: Why Electrical Colorants Are a Dielectric Problem

An architectural or decorative coating is judged by gloss, shade and weathering; an electrical insulation compound is judged by whether it stays insulating. In an HV cable, a cast transformer bushing, a potted relay or a CCL substrate, the colorant is a minority component embedded in a crosslinked polymer or epoxy network, and its job is to introduce little or no loss. Two failure modes dominate: ionic contamination, in which soluble salts, metal ions or residual catalysts raise conductivity and dissipation factor (tan delta) and initiate treeing; and cure interference, in which the colorant carrier or pigment surface shifts peroxide crosslinking in XLPE, shifts gel time or peak exotherm in cast epoxy, or competes with the anhydride or amine hardener. A pigment that is perfectly dispersible in a decorative alkyd can be unsuitable for a 155 °C thermal-class casting because it carries extractable ions or an over-active dispersant.

This article covers the four segments above and the metric set that governs them: particle size D50/D90, metal-ion and chloride content, thermal class per IEC 60085, volume resistivity and breakdown strength per GB/T 1408 and GB/T 16927, gel-time shift, post-cure colour difference and heat ageing. It does not cover food-contact packaging (separate scope) or 3C consumer-electronics colour-and-material finish (separate scope); those are addressed in their own dossiers. Carrier boundaries are fixed up front: SEP is the epoxy colorant, thermally stable to 300 °C; FLTY still carries about 20% PMA and is never solvent-free; RFNC is resin-free but solvent-containing; only FLUV and EB are truly solvent-free. GB/T 38508 is a cleaning-agent standard, not a coating or insulation standard.

2. HV/EHV XLPE Cable Insulation and Semiconductive Shield Compounds

Modern HV and EHV transmission cables are extruded cross-linked polyethylene (XLPE), operated continuously at 90 °C conductor temperature with short-circuit exposure near 250 °C, and rely on concentric layers: conductor, conductor-screen (semiconductive), XLPE insulation, insulation-screen (semiconductive), metallic sheath and outer oversheath. The two semiconductive layers are the position where a pigment colorant is load-bearing: they are filled with carbon black in a polyethylene/LLDPE base, and their function is to smooth the electric field at the conductor–insulation and insulation–sheath interfaces so that local field enhancement does not start partial discharge and treeing. The carbon black is not a decorative pigment; it sets the volume-resistivity plateau of the semiconductive layer and must be dispersed to a tight particle-size distribution with no undispersed grit or agglomerate that would become a field-enhancing defect.

For a colorant or masterbatch supplier the requirements are concrete. Dispersion: carbon-black agglomerates, gels and crosslinked specks are the physical defects that initiate treeing; D50 and D90 of the dispersed black are controlled and confirmed by drawdown and by a gel/content screen, not hard-coded. Resistivity stability: the semiconductive compound must hold its volume resistivity after thermal cycling between 90 °C service and 250 °C short-circuit, and after ageing, so that field grading does not drift. Ion and impurity control: residual metal ions, chloride and sulphur species must be minimised because they migrate in the field and raise loss; this is the same contamination discipline as for insulation. Crosslinking: the compound is cured with a peroxide (DCP-type) after extrusion; the carbon-black dispersion and its processing aids must not shift peroxide decomposition, scorch time or crosslink density. The colour of the insulation itself is functionally natural, with black oversheath; the semiconductive layers are uniformly black by design. Any added organic or inorganic shade pigment is screened so that it does not bleed, bloom or introduce ions into the extrusion.

3. Epoxy Casting and Potting: Dry-Type Transformers, Instrument Transformers and Insulators

Cast-resin dry-type transformers, instrument transformers (current and voltage transformers), bushings and indoor insulators are vacuum-cast in anhydride-cured epoxy, predominantly methylhexahydrophthalic anhydride (MHHPA) systems filled with quartz or alumina. A smaller set of potted and small cast parts uses amine cure. The casting is the dielectric: it must reach high breakdown strength, low tan delta, partial-discharge-free operation, and a thermal class (commonly F 155 °C or H 180 °C per IEC 60085). The colorant in this system is the SEP family, formulated for epoxy compatibility and thermally stable to 300 °C, so that it does not discolour during the long vacuum-cast and post-cure cycles that peak well above 150 °C.

Anhydride versus amine cure. SEP is screened separately against each. Anhydride casting runs at elevated temperature (mix and pot near 60–80 °C, gel and post-cure ramped up); the colorant must not contain amine-active species that would compete with or poison the anhydride cure, and must not shift the anhydride-to-epoxy ratio. Amine-cured potted parts run room-temperature or low-temperature cure; the colorant must not shift the amine stoichiometry or introduce moisture. Exotherm and gel time: high filler and pigment loads alter the peak exotherm temperature and the gel window; a colorant that raises exotherm can cause thermal cracking or voiding in a large cast mass, so gel-time and exotherm are measured on the customer's actual resin system. Dielectric strength and tan delta are the acceptance metrics (GB/T 1408 for breakdown strength; dissipation factor measured at power frequency); the colorant must not contribute ionic extractables that raise tan delta after cure. Post-cure colour and heat ageing: the cast part must hold shade and not chalk or discolour through repeated thermal cycles; ΔE after post-cure and after heat ageing is confirmed by type test. Adhesion of the cast body to the coil and core follows mechanical acceptance (GB/T 7124-style tensile/shear discipline) and is not a colorant-driven claim.

4. Component Encapsulation: Capacitor and Resistor Coatings, Relays and IGBT Module Packaging

Smaller parts — film capacitors and power resistors coated or potted, relays and solenoids, and power-semiconductor modules — are encapsulated in filled epoxy, polyurethane or silicone. IGBT and power modules are the most demanding: they are subjected to thermal cycling between roughly −40 °C and 125 °C, and the potting compound must balance CTE against the chip, direct-bonded copper substrate and copper baseplate so that it does not crack, delaminate or lift the bond during temperature cycling. The colorant in these parts is almost always black or a dark masking shade, and its job is to mask the internal assembly, provide UV and environmental protection, and stay inert.

For these parts the critical colorant checks are: void-free wetting under vacuum de-air, so that the colorant does not introduce surface-active material that traps bubbles; low ionic content, because a potted relay or gate-drive board sees low-voltage signal paths where leakage and corrosion are failure modes; CTE and thermal-cycle stability, so that the pigment does not raise the compound's coefficient of expansion and promote cracking; and post-cure and aged colour stability, so that a masked black or dark shade does not fade or chalk. IGBT module housings themselves are often white or black transfer-moulded thermosets; the colorant position there is a moulding-compound shade, not a paste, and is specified separately.

5. Copper-Clad Laminate (CCL) and Electrical Laminate Colouring

Copper-clad laminate — woven glass cloth impregnated with epoxy, copper foil laminated under heat and pressure (the FR-4 family) — is the substrate of printed circuits. Colour here appears in two places: the laminate core shade (often a green or tan epoxy-resin matrix visible through the glass weave) and the solder mask and legend that follow. The electrical requirements are low dielectric loss (Dk/Df), high glass-transition temperature (Tg), low water absorption, and — for modern halogen-free constructions — compliance with low-halogen definitions. The colorant must therefore be halogen-controlled and must not raise dielectric loss or water absorption in the cured laminate.

Low-halogen construction is driven by IEC 61249-2-21, which sets definitions for materials with reduced halogen content; a colorant that itself contributes halogenated pigments or fillers can disqualify an otherwise halogen-free laminate. Solder reflow and Tg: the shade must survive multiple reflow passes without discolouration or bleed. Volume resistivity and breakdown remain the underlying dielectric acceptance. CCL is adjacent to but distinct from consumer-electronics colour-and-material finish; this dossier addresses the electrical laminate, not the 3C exterior.

6. The Metric Set: Particle Size, Ions, Thermal Class, Resistivity, Gel Time and Ageing

Table 1 maps each segment to the governing colorant position and the electrical metric that decides acceptance. No numeric value is hard-coded into the product; every D50/D90, resistivity, breakdown or gel-time figure is confirmed by drawdown or type test in the customer's actual compound, because the result depends on the base resin, filler and cure system.

Table 1. Application, colorant position, governing electrical metric and reference standard.

Thermal class. Insulating materials are classified by maximum permitted continuous temperature per IEC 60085 (Table 2). A colorant must not lower the class of the system; SEP's 300 °C thermal ceiling gives margin over the common F (155 °C) and H (180 °C) cast classes.

Table 2. IEC 60085 thermal classes relevant to cast and encapsulated insulation.

Particle size D50/D90 and metal-ion/chloride content are the two supplier-controlled numbers that the cable and cast buyers audit most closely; they are screened by residual screening and by water-extraction/ion chromatography where specified. Gel-time effect and post-cure ΔE / heat ageing are measured on the customer's resin. The dispersion, treeing and partial-discharge science behind these positions is drawn from IEEE Transactions on Dielectrics and Electrical Insulation, Nature, Science, AIChE Journal, ACS, RSC and Progress in Organic Coatings literature.

7. Global Compliance Stack: REACH, RoHS, VOC, Low-Halogen, GHS/CLP, CBAM and SDS

The compliance stack below is what cable makers, transformer OEMs, power-module packagers and laminate producers cite in export audits, and it is the stack DENSON screens SEP and the controlled carbon-black dispersions against before release. REACH (EC 1907/2006): SVHC screening against the current candidate list and Annex XVII azo/aromatic-amine limits; no banned azo dye is used. RoHS 2 (2011/65/EU): Pb, Cd, Hg, Cr(VI), PBB and PBDE limits for any position touching electronic parts — directly relevant to CCL, components and modules. Directive 2004/42/EC sets EU VOC ceilings and forces an honest declaration: SEP is the epoxy colorant; solvent families must never be declared solvent-free. EU 10/2011 and FDA 21 CFR are referenced only where an incidental food-contact or potable-water claim is explicitly made; they are not general electrical-insulation claims. GHS/CLP (EC 1272/2008) governs hazard labelling and the destination-language SDS. CBAM raises the embodied-carbon data buyers request across the value chain. IEC 60085 sets thermal class; IEC 61249-2-21 sets the low-halogen definition for laminates. SDS is a current REACH Annex II sheet per consignment.

Table 3. Electrical-insulation and encapsulation colorant export compliance checklist.

8. Selection Guidance and Cross-Family Boundaries

Select by dielectric position and cure chemistry, not by shade. For HV/EHV XLPE semiconductive shield compounds, specify a controlled carbon-black dispersion screened for D50/D90, resistivity stability after 90/250 °C cycling, low metal-ion/Cl/S and no peroxide crosslink shift. For vacuum-cast anhydride epoxy (dry-type transformers, instrument transformers, bushings and insulators), specify a SEP shade screened for anhydride compatibility, exotherm/gel-time control, low ionic extractables and 300 °C thermal stability, with breakdown and tan delta confirmed by type test. For component encapsulation (capacitors, resistors, relays, IGBT modules), specify a low-CTE, low-ionic black/dark masking shade screened for void-free wetting and −40 to 125 °C thermal cycling. For halogen-free CCL and solder mask, specify a halogen-controlled SEP-compatible shade screened against IEC 61249-2-21 and reflow Tg. Every shade is confirmed by drawdown or type test in the customer's actual compound; no D50/D90, resistivity, breakdown or dosage is hard-coded. Respect the carrier boundaries: SEP is the epoxy colorant (stable to 300 °C); FLTY carries about 20% PMA and is never solvent-free; RFNC is resin-free but solvent-containing; only FLUV and EB are truly solvent-free. GB/T 38508 is a cleaning-agent standard, not a coating or insulation standard. This article does not address food-contact packaging (separate scope) or 3C consumer-electronics colour-and-material finish (separate scope). More colorant families and resin-matching guidance are on the DENSON website, and technical literature on dielectric and dispersion science is collected in the Literature section. Export shipments are handled through Dongguan Henvastness Import and Export Co.,LTD with the REACH, RoHS, CLP, low-halogen, GHS/CLP and CBAM dossiers per consignment.

Key Conclusions

1. Electrical colorants are a dielectric problem across four segments. HV/EHV XLPE cable insulation and semiconductive shield compounds, cast epoxy for dry-type transformers and insulators, component encapsulation for relays and IGBT modules, and halogen-free CCL all judge the colorant by resistivity, breakdown, tan delta, ionic purity and cure compatibility — not by shade. SEP is the epoxy colorant, thermally stable to 300 °C; controlled carbon-black dispersions cover the semiconductive cable position.

2. The governing metrics are D50/D90, ions, thermal class, gel time and ageing — never hard-coded. Disperse D50/D90, extractable metal-ion and chloride content, IEC 60085 thermal class (B 130 / F 155 / H 180), volume resistivity and breakdown (GB/T 1408, GB/T 16927), gel-time/exotherm shift, and post-cure ΔE after heat ageing are all confirmed by drawdown or type test in the customer's actual resin. A colorant must not raise tan delta, shift anhydride/amine or peroxide cure, or increase CTE.

3. Respect the compliance and carrier boundaries. Screen against REACH SVHC/azo, RoHS, 2004/42/EC, GHS/CLP, CBAM, IEC 60085 and IEC 61249-2-21 low-halogen, with EU 10/2011 and FDA 21 CFR only where incidental contact is claimed. SEP is the epoxy colorant; FLTY still contains about 20% PMA and is never solvent-free; RFNC is resin-free but solvent-containing; only FLUV/EB are truly solvent-free; GB/T 38508 is a cleaning-agent standard, not an insulation standard.

Frequently Asked Questions

Q1. Which DENSON family do I specify for cast-resin dry-type transformers?
Use the SEP epoxy-compatible colorant family. SEP is screened for anhydride-cured (MHHPA) vacuum castings and amine-cured potting separately, is thermally stable to 300 °C (above the F 155 °C and H 180 °C thermal classes), and is checked for gel-time/exotherm shift, low ionic extractables, breakdown strength and tan delta by type test in the customer's resin. Confirm by cast trial, not by a catalogue number.

Q2. Why is the carbon black in an XLPE semiconductive shield a controlled colorant rather than a commodity filler?
Because the semiconductive layer grades the electric field. Undispersed carbon-black agglomerates, gels or crosslinked specks become field-enhancing defects that start treeing and partial discharge; the dispersed D50/D90, the post-cycling volume-resistivity plateau, and low metal-ion/chloride/sulphur content are the acceptance metrics, and the dispersion must not shift peroxide crosslinking. These are confirmed by drawdown and type test, not hard-coded.

Q3. Is SEP a solvent-free or zero-VOC colorant for electrical epoxy?
SEP is the epoxy colorant family for cast and potted systems. It is not marketed as a radiation-cure product. The only truly solvent-free DENSON families are FLUV and EB for UV/EB cure. FLTY high-solids still contains about 20% PMA (CAS 108-65-6) and is never solvent-free; RFNC is resin-free but solvent-containing; neither should be declared zero-VOC.

Q4. What compliance documents should an export buyer request for electrical insulation and encapsulation colorants?
At minimum: a current REACH Annex II SDS, an SVHC and azo/aromatic-amine statement, a RoHS conformity statement (directly relevant to CCL and components), a VOC/solvent declaration under 2004/42/EC, an ion/chloride statement, a low-halogen statement under IEC 61249-2-21 for CCL, an IEC 60085 thermal-class declaration, a cure-compatibility statement for anhydride/amine and XLPE peroxide, breakdown/tan-delta data per GB/T 1408 and GB/T 16927, heat-ageing/ΔE panels, a GHS/CLP classification, and CBAM embodied-carbon data where in scope. EU 10/2011 and FDA 21 CFR are referenced only where incidental contact is explicitly claimed.

Q5. Does this dossier cover food-contact or 3C consumer-electronics colour and finish?
No. This article covers electrical insulation and electronic encapsulation only. Food-contact packaging and 3C consumer-electronics colour-and-material finish are separate scopes with their own dossiers. GB/T 38508 is a cleaning-agent standard and is not used as a coating or insulation reference.