Thermohardenable Structural Adhesive High Tg Elongation
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Solution Overview
Problem
Current structural adhesives face challenges in achieving a balance between high glass transition temperature (Tg), high elongation at break, and high strength, often requiring compromises that result in undesirable brittleness or reduced durability, especially in applications like the automotive and aerospace industries where temperature variability and impact resistance are critical.
Innovation Solution
A thermohardenable epoxy-based adhesive composition that includes a thermoplastic modifier, such as a phenoxy resin, and a flexibilizer, along with impact modifiers and blowing agents, to achieve a high Tg of 80°C or higher and an elongation at break of at least 15%, maintaining mechanical properties across a broad temperature range and providing impact resistance without brittleness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If rubbery materials or other polymers are added to increase elongation at break, then elongation improves, but Tg and strength are reduced
Solution Approach 1:
The patent changes the chemical composition parameters by introducing a specific epoxy-terminated polymer with controlled molecular weight (5,000-50,000) and epoxy equivalent weight (180-300). This parameter optimization allows achieving high elongation (≥5%) while maintaining high Tg (≥80°C) and acceptable strength, resolving the contradiction between ductility and thermal stability.
Solution Approach 2:
The patent creates a composite adhesive system combining epoxy resin, curing agent, and epoxy-terminated polymer in specific weight ratios (10-50%, 5-20%, 5-30% respectively). This composite formulation synergistically integrates the strength of epoxy with the flexibility of the terminated polymer, achieving both high elongation and high Tg without the trade-off present in conventional single-material approaches.
2Stability of the object's composition
If rubbery materials or other polymers are added to increase elongation at break, then elongation improves, but strength is reduced
Solution Approach 1:
The patent optimizes the epoxy equivalent weight of the epoxy-terminated polymer to be within 180-300, which controls the crosslinking density and network structure. This parameter control ensures that the polymer provides sufficient elongation (≥5%) while maintaining adequate adhesive strength, preventing the strength reduction that occurs with conventional rubbery additives.
Solution Approach 2:
The epoxy-terminated polymer introduces localized flexible segments within the rigid epoxy crosslinked network. These localized soft zones provide ductility and elongation without compromising the overall structural integrity and strength of the adhesive bond, resolving the contradiction between flexibility and strength.
3Temperature
If high Tg is achieved to maintain stiffness at elevated temperatures, then temperature resistance improves, but elongation at break is reduced
Solution Approach 1:
The patent formulates a composite system where epoxy resin provides the rigid crosslinked network for high Tg (≥80°C), while the epoxy-terminated polymer contributes flexible chains for high elongation (≥5%). The synergistic interaction between these components allows simultaneously achieving temperature resistance and ductility, overcoming the inverse relationship present in conventional adhesives.
Solution Approach 2:
The adhesive structure incorporates localized flexible domains from the epoxy-terminated polymer within the global rigid epoxy network. These local flexible regions enable high elongation at break while the predominant rigid structure maintains high Tg and stiffness at elevated temperatures, resolving the contradiction between thermal stability and ductility.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The adhesive composition maintains structural integrity and impact resistance while avoiding brittleness, ensuring durability and corrosion protection across a wide temperature range, making it suitable for applications in the automotive and aerospace sectors.
Implementation Method 1
The present invention provides a thermohardenable structural adhesive with the desirable combination of Tg and high elongation to break
Implementation Method 2
Epoxy resins are widely used in adhesives due to their ability to be cured (crosslinked), typically by heating, to produce strong, resilient bonds
Data Source
AI summary
A thermohardenable structural adhesive material that upon curing has an elongation at break of at least 10% and has a glass transition temperature (Tg) of 80°C or higher and is useful as a structural adhesive in automobiles to reduce the deformation of bonds particularly during accidents, the adhesive is dry to the touch at ambient temperature and can be melt processed at temperature below that at which thermohardening occurs. The adhesives are useful in applications requiring a combination of high strain to failure, glass transition temperature more than 80°C, high stiffness and high strength. This combination is of particular interest in the aerospace and automotive industries.