1. Introduction

Electron Beam (EB) curing technology has emerged as a transformative high-energy radiation curing process in the packaging printing and composite materials manufacturing sectors. Compared with conventional thermal curing and UV photocuring, EB curing offers distinct advantages including no photoinitiator residue, ambient-temperature deep-through curing, zero VOC emissions, and exceptional production speed. These benefits make EB curing particularly well-suited for applications demanding high safety standards, environmental compliance, and manufacturing efficiency, such as food packaging, metal packaging, and advanced composite materials. In these applications, colorants serve as critical coloring components that not only determine product appearance but also directly influence curing system reactivity, coating performance, and long-term stability. DENSON (Dongguan DENSON Functional Materials Co., Ltd.), a specialized pigment colorant manufacturer, has developed a dedicated series of EB-curable colorants engineered specifically for the unique requirements of EB curing in packaging and composite industries. These colorants have undergone rigorous validation in pigment radiation resistance, dispersion stability, and curing compatibility. This article presents three detailed application cases that systematically demonstrate the practical performance and effectiveness of DENSON EB colorants in food packaging printing inks, composite prepreg resin systems, and metal packaging coatings, providing valuable technical reference for industry professionals.

2. Technical Features and Mechanism

The core technical characteristic of EB-curable colorants is their ability to maintain pigment stability and achieve excellent curing compatibility under high-energy electron beam radiation. EB curing employs high-energy electron beams with acceleration voltages of 150-300 kV to bombard coatings, ionizing resin molecules to generate free radicals that initiate chain polymerization of acrylate double bonds. Unlike UV curing, EB curing does not rely on photoinitiators, eliminating the ultraviolet light absorption competition between pigments and photoinitiators. This fundamental difference enables EB-curable colorants to achieve complete deep-through curing even at higher pigment loading levels and darker colors.

DENSON EB colorants employ radiation-resistant pigment selection and acrylate-functionalized dispersant systems. All pigments undergo electron beam irradiation aging testing at standard doses of 50-100 kGy, ensuring post-irradiation color difference ΔE ≤2.0. The dispersant molecules feature anchoring groups that adsorb onto pigment surfaces at one end, while solvated chains bearing acrylate double bonds at the other end participate in free radical polymerization during EB curing, permanently bonding dispersants into the crosslinked network. This in-situ fixation mechanism effectively prevents pigment migration and floating. Additionally, DENSON EB colorants receive specialized optimization for packaging and composite applications, including low migration properties, high purity, and broad compatibility with multiple resin systems.

3. Application Case Study 1: EB Curing Food Packaging Printing Inks

A major food packaging printing enterprise adopted EB offset printing technology to produce premium food packaging boxes (chocolate boxes, biscuit tins, tea can outer packaging), requiring printing inks with no photoinitiator residue, no odor, and compliance with food contact material safety standards. The enterprise previously experienced photoinitiator migration risks and incomplete curing of dark inks with UV curing systems, and required specialized compatible colorants after switching to EB curing.

DENSON EB colorants were added at 8%-15% loading (by total ink mass) for four-color offset inks (cyan, magenta, yellow, black) and spot color inks. Production parameters included printing speed of 15,000-20,000 sheets/hour, EB curing dose of 20-40 kGy, acceleration voltage of 200 kV, and beam current of 30-50 mA. DENSON EB colorants utilize pigments compliant with FDA 21 CFR 178.3297 and EU 10/2011 food contact material regulations, with specially purified acrylate-functionalized polymeric dispersants ensuring migratable substance content below detection limits.

Performance test results demonstrated: EB-cured ink curing degree (gel content by solvent extraction) ≥95%, no odor on printed products, total migration (4% acetic acid, 10 days, 40°C) ≤0.5 mg/dm², well below the regulatory limit of 10 mg/dm². Ink printability was excellent, with viscosity stability (25°C, No. 4 Zahn cup) maintained at 20-30 seconds without significant viscosity drift during press runs. Compared with UV-cured inks, EB-cured ink rub resistance (GB/T 7706) improved by approximately 30%, and lightfastness (xenon arc aging 500 hours) color difference ΔE ≤1.5. This case confirms that DENSON EB colorants can meet the comprehensive requirements of food packaging printing for safety, printability, and curing performance.

4. Application Case Study 2: EB Curing Composite Prepreg Resin Systems

An aerospace composite manufacturer adopted EB curing technology to produce carbon fiber/glass fiber prepregs for aircraft interior components and sports equipment (skis, bicycle frames). Conventional thermally cured prepregs require prolonged high-temperature high-pressure curing (120-180°C, 1-4 hours), resulting in high energy consumption, long production cycles, and potential fiber distribution irregularities caused by resin flow during thermal curing. EB-cured prepregs can be rapidly cured at ambient temperature (typically seconds to minutes), with controllable resin viscosity changes during curing that help maintain precise fiber alignment.

DENSON EB colorants were added at 2%-5% loading for colored prepreg pigmentation, including black, dark gray, dark blue, and red colors. The prepreg resin system was an epoxy acrylate/polyurethane acrylate hybrid, with carbon fiber areal weight of 200 g/m² and resin content of 35%-40%. EB curing parameters included curing dose of 50-80 kGy, acceleration voltage of 300 kV (to ensure electron beam penetration through prepreg thickness), and beam current of 50-100 mA.

Key technical challenges in this application included: colorants must not affect prepreg shelf life (typically requiring ≤10% viscosity change after 6 months storage at -18°C); pigments must not impede electron beam penetration or affect resin curing degree during EB curing; and cured composite mechanical properties must not significantly degrade due to colorant addition. DENSON EB colorants achieved high tinting strength at low loading while minimizing impact on resin system rheological properties and curing reactions through precise control of pigment particle size (D50 ≤200 nm) and dispersant dosage.

Performance test results showed: after adding DENSON EB colorants, prepreg gel time (120°C) change ≤5%, meeting 6-month shelf life requirements. EB-cured composite interlaminar shear strength (ILSS, ASTM D2344) ≥60 MPa, tensile strength (ASTM D3039) ≥1500 MPa (carbon fiber), with performance degradation ≤3% compared with uncolored control samples. Composite surface color was uniform with no significant color difference (ΔE ≤1.0), and no discoloration or coating delamination after 1000 hours of damp heat aging (85°C/85% RH). This case demonstrates that DENSON EB colorants can meet the stringent mechanical performance and long-term stability requirements of aerospace-grade composite materials.

5. Application Case Study 3: EB Curing Metal Packaging Coatings

A metal packaging enterprise adopted EB curing technology to produce inner and outer coatings for food and beverage cans (aluminum cans and tinplate cans), requiring coatings with excellent corrosion resistance, fabrication resistance, and food safety. Traditional metal packaging coatings use thermal curing processes requiring baking at approximately 200°C for 10-15 minutes, consuming significant energy and potentially causing metal substrate deformation. EB curing achieves complete curing in seconds at ambient temperature, substantially reducing energy consumption and increasing production efficiency.

DENSON EB colorants were added at 3%-8% loading for white basecoats and colored topcoats on can exteriors, as well as light-colored identification on inner coatings. The coating system was a polyester acrylate/epoxy acrylate hybrid, with coating thickness of 8-12 μm for exterior coatings and 3-5 μm for inner coatings. EB curing parameters included curing dose of 30-50 kGy, acceleration voltage of 150-200 kV, and production line speed of 300-500 cans/minute.

Key technical requirements in this application included: colorants must promote adhesion to metal substrates; cured coatings must withstand subsequent can fabrication processes (stamping, drawing, seaming) without cracking or delamination; and inner coatings must comply with food contact safety standards with no hazardous substance migration. DENSON EB colorants employ surface-modified pigments and dispersants containing adhesion-promoting groups, enhancing the bonding force at the pigment-resin-metal interface.

Performance test results showed: EB-cured metal can coating adhesion (cross-cut method, GB/T 9286) Grade 0, impact resistance (50 cm·kg) no cracking, bending resistance (T-bend test) ≤2T. Corrosion resistance testing (salt spray test, GB/T 1771, 500 hours) showed no blistering or rust. Inner coating total migration (4% acetic acid, 10 days, 40°C) ≤0.8 mg/dm², complying with GB 4806.10 food contact coating standards. Compared with thermally cured coatings, EB-cured coatings reduced production energy consumption by approximately 60% and increased production efficiency by approximately 3 times. This case demonstrates that DENSON EB colorants achieve a unified combination of high performance, high efficiency, and high safety in metal packaging coatings.

6. Key Selection Parameters and Usage Recommendations

When selecting EB-curable colorants for packaging and composite industries, the following key parameters should be prioritized: First, pigment radiation resistance—suppliers should be required to provide electron beam irradiation aging test data, ensuring color difference ΔE ≤2.0 under the actual dose used. Second, food contact safety—food packaging and inner coating applications must use colorants complying with FDA, EU 10/2011, or GB 4806 regulations, with compliance declarations and test reports required. Third, dispersion system reactivity—the dispersant should bear acrylate functional groups capable of participating in polymerization during EB curing, avoiding post-cure migration. Fourth, pigment particle size and distribution—composite and thin coating applications should select nano-scale pigments (D50 ≤300 nm) to avoid large particles affecting coating uniformity and mechanical properties. Fifth, viscosity and rheological characteristics—appropriate viscosity ranges should be selected based on printing or coating methods (offset, gravure, roller, spray, dip coating). Sixth, curing compatibility—curing tests should be conducted under actual EB equipment parameters to verify that colorant addition does not affect curing degree and coating performance.

Usage recommendations include: food packaging applications should prioritize colorants with food contact certification and conduct regular migration testing; composite applications should perform overall compatibility testing of colorants with resin systems, including shelf life, gel time, and post-cure mechanical properties; metal packaging applications should重点 verify coating fabrication resistance and corrosion resistance; conduct small-batch trial production before mass manufacturing to confirm color, curing degree, and performance indicators meet requirements; regularly calibrate EB curing equipment electron beam output as it decays over time; store colorants away from direct sunlight and high-temperature environments, with thorough stirring before use.

7. Conclusion

EB electron beam curing technology, with its unique advantages of photoinitiator-free formulation, deep-through curing, zero VOC emissions, and high efficiency, is demonstrating tremendous application potential in the packaging printing and composite materials manufacturing sectors. DENSON EB-curable colorants successfully address key technical challenges such as pigment stability, food contact safety, and curing compatibility in EB curing environments through radiation-resistant pigment selection, acrylate-functionalized dispersion systems, and specialized optimization for packaging and composite applications. Verified through three typical application cases—food packaging printing inks, composite prepreg resin systems, and metal packaging coatings—DENSON EB colorants demonstrate excellent performance and reliable curing compatibility across different application scenarios. As EB curing equipment costs continue to decline and environmental regulations become increasingly stringent, the application of EB curing technology in packaging and composite industries will further expand. Relevant enterprises, when selecting EB colorants, should fully focus on core parameters such as pigment radiation resistance, food contact safety, dispersion system reactivity, and curing compatibility, combined with specific application scenarios and equipment conditions for thorough pre-validation, to ensure stable operation of EB curing processes and reliable achievement of product performance.