What sets HT adhesives apart

High temperature-resistant adhesives (HT adhesives) perform reliably, even under demanding conditions, and maintain stable performance under extreme thermal stress. Here are some key terms and concepts to better understand these materials.

• Temperature Resistance: This refers to an adhesive's capacity to preserve its adhesive (surface bonding) and cohesive (internal bonding) properties, even after prolonged exposure to high temperatures. An adhesive with high temperature resistance will continue to perform effectively after being subjected to conditions such as sustained exposure to 150 °C, indicating strong long-term performance under heat.
• Thermal Stability: This relates to the maximum mechanical load an adhesive can endure briefly at high temperatures. A high thermal-stability adhesive can support weight at temperatures as high as 200 °C without failing. Unlike temperature resistance, temperature stability focuses on short-term load capacity.
• Glass Transition Temperature (Tg): This is the temperature at which a polymer transitions from a hard, glass-like state to a softer, potentially more elastic state. This change can lead to a loss of strength and shape stability. A high glass transition temperature indicates that an adhesive starts to change its properties at a higher temperature, potentially losing strength. Thus, a high Tg is indicative of high temperature stability.
• Exception: Some materials remain stable, even above their glass transition temperature. For example, silicones and polyimides retain useful mechanical properties in a flexible, rubber-like state, known for their excellent thermal stability and chemical resistance.

Flexibility is crucial in the development of HT adhesives, enabling them to absorb stress peaks, and is particularly important for peel stresses. Peel stress refers to a force that acts perpendicular to the bondline and attempts to separate bonded materials.

Imagine lifting stuck-on tape at its edge and pulling it sharply. This depicts peel stress. Flexible adhesives can deform to absorb such stresses without breaking or losing adhesion, making them more resistant to cracking or delamination than stiffer ones. They also help accommodate thermal expansion differences in bonded materials, enhancing overall strength and durability through temperature fluctuations.

• Summary: Effective HT adhesives combine good temperature resistance, high temperature strength, and sufficient flexibility to manage mechanical stresses effectively. This results in adhesive bonds that remain reliable at high temperatures, even when subjected to constantly changing conditions or mechanical stresses.