1. Introduction

Epoxy resin is one of the most widely used thermosetting resins globally, with annual consumption exceeding 3.5 million tons in 2025. It finds extensive applications in industrial flooring, electronic potting, anti-corrosion coatings, composite materials, and adhesives. In epoxy resin systems, color serves not only as an aesthetic requirement but also as a critical means for product identification, safety warning, and functional differentiation. DENSON SEP series epoxy resin colorants are specifically developed for epoxy resin systems, achieving excellent color performance and curing compatibility through scientific pigment selection and surface treatment technology. This article provides an in-depth study of pigment selection strategies and color performance of SEP epoxy resin colorants from four dimensions: pigment type selection, CIELAB color parameters, weatherability and chemical resistance, and tinting strength and hiding power, offering technical reference for formulation design in the epoxy industry.

2. Technical Features and Mechanism

SEP series epoxy resin colorants use epoxy resin as the carrier resin, with pigment content typically ranging from 30% to 70%, and fineness controlled below 5 μm ( Hegman gauge according to GB/T 1724-1979). Pigment selection follows these principles:

Inorganic pigments: primarily iron oxide red (Fe2O3, Pigment Red 101), iron oxide yellow (FeOOH, Pigment Yellow 42), iron oxide black (Fe3O4, Pigment Black 11), titanium dioxide (TiO2, Pigment White 6), and ultramarine blue (Pigment Blue 29). These pigments offer excellent weatherability (QUV 1000h ΔE ≤ 2.0), chemical resistance, and thermal stability (withstanding temperatures above 250°C), making them suitable for outdoor epoxy flooring and anti-corrosion coatings with high durability requirements.

Organic pigments: primarily phthalocyanine blue (Pigment Blue 15:3), phthalocyanine green (Pigment Green 7), azo yellow (Pigment Yellow 74/83), and quinacridone red (Pigment Red 122). These pigments feature vivid colors, strong tinting strength (3-5 times higher than inorganic pigments), and good transparency, suitable for electronic potting and artistic flooring with high color saturation requirements.

Carbon black: primarily furnace black (Pigment Black 7), achieving high jetness (L* ≤ 15) and excellent conductive/insulating performance control by managing particle size (20-80 nm) and structure (DBP absorption value 80-120 mL/100g).

Effect pigments: primarily aluminum paste, pearlescent pigments, and metal oxide-coated mica, suitable for decorative epoxy flooring and high-end composite materials.

The pigment surface treatment of SEP colorants employs hyperdispersant anchoring technology, forming strong adsorption with pigment surfaces through anchoring groups (such as phosphate ester groups, carboxyl groups, amine groups), while the solvated chain segments are compatible with the epoxy resin carrier, achieving stable pigment dispersion in epoxy systems and preventing flocculation and re-coarsening.

3. Application Case Study 1: Inorganic Pigments in Epoxy Floor Coatings

An industrial flooring project required epoxy floor coatings to maintain color change ΔE ≤ 3.0 after more than 5 years of outdoor exposure. SEP series iron oxide red (Pigment Red 101) and iron oxide yellow (Pigment Yellow 42) colorants were selected, blended at a 7:3 ratio to achieve a brick red color.

Test results: Initial color L*=42.5, a*=28.3, b*=18.7; after QUV-A 1000 hours accelerated aging, L*=43.1, a*=27.8, b*=19.2, ΔE=0.82, well below the 3.0 requirement. Chemical resistance testing: 5% H2SO4 immersion for 7 days ΔE=1.2, 5% NaOH immersion for 7 days ΔE=0.9, both meeting the requirements of GB/T 22374-2018 "Floor Coating Materials" standard. Tinting strength test: at 8% addition, hiding power reached 98% (contrast ratio method GB/T 1726-1979), and the application area increased by approximately 15% compared to traditional pigment powder.

4. Application Case Study 2: Organic Pigments in Electronic Potting Compounds

An LED driver power supply potting project required the potting compound to have high jetness (L* ≤ 18) and certain light transmittance (for optocoupler signal transmission), while not affecting the curing reaction and electrical properties of epoxy resin.

SEP series high-color carbon black colorant (Pigment Black 7, particle size 25 nm, DBP=95 mL/100g) was selected at 3% addition. Test results: After curing, L*=16.8, a*=0.3, b*=0.5, with excellent jetness; volume resistivity ≥ 1×10^14 Ω·cm, meeting insulation requirements; gel time deviation from blank sample ≤ 5%, with no significant impact on curing reaction; light transmittance (550 nm) was 12%, meeting optocoupler signal transmission requirements. Compared to traditional direct addition of carbon black powder, SEP colorants offer better dispersion, no particle precipitation, and the surface gloss of potting components increased by 20%.

5. Application Case Study 3: Effect Pigments in Wind Turbine Blade Epoxy Matrix

A wind turbine blade project required the leading edge protective coating to have a metallic luster effect while maintaining color fastness for 20 years in outdoor environments. SEP series aluminum paste colorant (non-leafing, particle size 15-25 μm) was selected at 5% addition.

Test results: Initial 60° gloss 85, metallic flop value 12.5; after QUV-B 2000 hours accelerated aging, gloss retention rate 82%, ΔE=2.1, meeting ISO 12944-6 C5-M (marine high-corrosion environment) durability requirements. Aluminum flakes arranged in parallel within the epoxy matrix, forming a "labyrinth effect" that reduced water vapor permeability by approximately 40% while improving coating salt spray resistance (1000 hours without blistering or rusting).

6. Key Selection Parameters and Usage Recommendations

Pigment type selection: For outdoor weatherability, prioritize inorganic pigments (iron oxide series, titanium dioxide, ultramarine); for high color saturation, select organic pigments (phthalocyanine series, quinacridone series); for high jetness, choose high-color carbon black; for decorative effects, select effect pigments.

Color parameter control: Use a spectrophotometer (such as X-Rite Ci64) to measure CIELAB values, with batch-to-batch ΔE ≤ 1.0; establish a standard color card database to ensure mass production consistency.

Addition recommendations: Inorganic pigments 8%-15%, organic pigments 3%-8%, carbon black 2%-5%, effect pigments 3%-10%; specific addition should be determined through gradient testing based on target hiding power and color depth.

Compatibility verification: Before use, compatibility testing must be conducted with the target epoxy resin (E-51, E-44, novolac epoxy, etc.) and curing agent (amine, anhydride), observing for delamination, flocculation, or curing abnormalities.

Storage conditions: Store sealed at 5-35°C, avoid direct sunlight, shelf life 12 months; stir thoroughly before use to ensure uniform pigment dispersion.

7. Conclusion

DENSON SEP epoxy resin colorants demonstrate excellent performance in inorganic pigment weatherability, organic pigment color saturation, carbon black jetness, and effect pigment decorative effects through scientific pigment selection strategies and hyperdispersant surface treatment technology. Three application cases show that SEP colorants can meet strict color performance and durability requirements in epoxy flooring, electronic potting, and wind turbine blades. As the epoxy resin industry develops toward high performance, functionalization, and greenization, precise pigment selection and color performance control will become key factors in enhancing product competitiveness. Dongguan DENSON Functional Materials Co., Ltd. will continue to deepen pigment surface treatment technology and color management systems, providing more professional coloring solutions for the epoxy industry.