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Structural bonding is increasingly important in industries such as automotive, aircraft manufacturing, shipbuilding, electronics, and construction. Adhesive bonding technology has advanced to meet the technical requirements of lightweight and multi-material designs, progressive integration, miniaturization, and increasing complexity. Structural bonding offers practical advantages over other joining processes, allowing for the realization of material composites and composite materials consisting of different materials. Adhesive bonding also provides homogeneous stress distribution, stress compensation, the ability to compensate for component tolerances, and additional functions such as sealing, corrosion protection, and vibration damping. Despite some challenges, such as lower thermal resistance and the issue of de-bonding, structural bonding is now an optimum solution for many bonding options and manufacturing processes, with epoxides being among the most widely used structural adhesives.

Performance characteristics of system types

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One-component adhesives are used for simple bonding applications, while two-component adhesives are used for complex bonding applications where a stronger bond is required.

Evonik offers a comprehensive portfolio of products for adhesive formulators to optimize their products in terms of performance, efficiency, and sustainability. The Epoxy Curing Agents product line includes high-quality amine-based curing agents and accelerators for structural one-component and two-component epoxy adhesives. The range covers almost all current amine curing technologies, including aliphatic and cycloaliphatic amines, polyamides, amidoamines, imidazoles, and dicyandiamide. The brands Ancamine®, Ancamide®, Amicure®, Dicyanex®, Curezol®, and Imicure® are included in the product line. Evonik's expertise in this area allows them to provide innovative solutions to meet the evolving needs of the market.

Amine curing technologies for structural epoxy adhesives, their property profiles, typical application rates and product examples

One-component structural epoxy adhesives are pre-mixed and do not require additional mixing during application. They have a storage stability of a few days to several months, depending on the curing agent's reactivity and solubility. Curing takes place at high temperatures of up to 200°C, producing adhesive bonds with excellent mechanical strength and high resistance to moisture, chemicals, and temperature. Flexibilization and impact modification can be achieved through additives and performance modifiers. Evonik's product portfolio for one-component epoxy adhesives includes modified aliphatic amines, imidazoles, and substituted ureas that can be used as accelerators for dicyandiamide, improving the system's reactivity and activation temperature. Modified aliphatic amines, such as Ancamine® 2014 AS/FG, Ancamine® 2441, and Ancamine® 2442, reduce the activation temperature significantly while offering long storage stability. They can achieve acceptable curing times from 120°C onwards and high initial strengths with very short curing times of less than one minute at higher temperatures, making them suitable for induction curing.

Accelerators for dicyanamide-based structural one-component epoxy adhesives

Modified aliphatic amines, such as Ancamine® 2337S, 2441, and 2442, can be used as sole curing agents for one-component systems, providing fast curing at low temperatures and long storage stability. Ancamine® 2337S allows curing from 80°C, while Ancamine® 2441 and 2442 offer higher thermal stabilities starting at 100°C. Imidazoles Imicure® EMI-24 and Curezol® 2MZ Azine can improve thermal stability >150°C, but require higher curing temperatures.

Curing agents for structural one-component epoxy adhesives

Two-component structural epoxy adhesives consist of separate curing agent and resin components, allowing for high storage stability. The curing reaction is initiated by mixing the components before application and can take place at room temperature, producing adhesive bonds with good resistance to environmental factors. Evonik's product portfolio for two-component epoxy adhesives includes a range of modified and non-modified, cyclic and non-cyclic amines, amidoamines, and polyamides. Ancamide® 3030 is a standard product with medium gel time and good all-round properties. Ancamine® 2919 and Ancamine® 2927 offer longer gel times of up to 800 minutes but require curing at higher temperatures to achieve the final properties. Hot curing can also be used to accelerate the curing reaction and achieve higher thermal resistance.

Ancamine® 1769 and Ancamine® 2914UF are suitable for two-component structural epoxy adhesives that require short curing times at room temperature. They reduce the gel time to 8 minutes. For high thermal resistance, polycycloaliphatic amines such as Ancamine® 2167 and Ancamine® 2264 are recommended for curing at higher temperatures.

Curing agents for structural two-component epoxy adhesives

Curing agents for structural two-component epoxy adhesives with long gel times

Fast curing agents for structural two-component epoxy adhesives

Curing agents for structural two-component epoxy adhesives with high thermal resistance