Dual-cure thiol-acrylate polymer networks for heat-sealable food packaging coatings

Overview

This technology addresses a persistent challenge in food packaging: achieving a single coating formulation that simultaneously delivers high mechanical strength, food-contact safety, fast sealing, and compliance with restrictions on vinyl chloride and styrene. Conventional single-cure polymer systems struggle to balance these competing requirements. The proposed solution is a dual-cure polymer network built through sequential photopolymerization and heat-triggered polymerization of acrylate monomers, including thiol-acrylate chemistries.

The value proposition for packaging manufacturers and brand owners is a coating that vitrifies rapidly during the first light-triggered stage, leaves residual reactive groups, and then completes curing during the heat-sealing step itself. This dual-cure mechanism is designed to shorten sealing cycle times, reduce energy use, and produce strong, reliable seals on aluminum and film substrates without relying on chemistries that face regulatory or consumer scrutiny.

Technical specifications

• Dual-cure mechanism: A first-stage photopolymerization of multifunctional acrylates creates a high glass-transition temperature network that vitrifies at room temperature, leaving unreacted acrylate groups available for further reaction.
• Second-stage heat cure: A thermally triggered free-radical acrylate polymerization completes conversion of the remaining groups, with the heat-sealing operation itself serving as the trigger.
• Monomer platform: Readily available, low-cost thiol and acrylate (methacrylate) monomers, enabling straightforward formulation and scale-up.
• Two tunable processing knobs: Light dose and heat-sealing temperature independently control network formation, allowing formulators to balance viscosity, pot life, cure speed, and final material properties.
• Performance targets: Coating-to-aluminum adhesive strength, coating-to-coating seal strength of at least 12 N per 15 mm sample width at 180 °C, and short seal dwell time.
• Regulatory positioning: Designed to be free of vinyl chloride and styrene and suitable for food-contact applications.

Technology readiness level

The concept is currently at TRL 2, with prior laboratory demonstrations of related dual-cure thiol-acrylate polymerization in the principal investigator's lab supporting feasibility. The proposed one-year research program is structured to advance the technology to TRL 4–5 through four quarterly tasks: demonstrating dual-stage curing across more than 30 photopolymer formulations, down-selecting based on adhesive and seal strength, locking the target formulation through application-relevant stress testing, and conducting an application-relevant demonstration in collaboration with the funder's product design.

Potential limitations include the need to validate long-term food-contact compliance, scalability of UV-cure processing on commercial coating lines, and confirmation that seal strength targets are met across a range of substrate combinations. These will be addressed during the planned validation tasks.