Epoxy-Modified Polyurethane Adhesive for Thermal Expansion
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Solution Overview
Problem
One-component toughened epoxy adhesives are not suitable for joining different materials in automotive assemblies due to their rigid nature, which cannot accommodate uneven thermal expansion and contraction, leading to potential assembly distortion or adhesive failure.
Innovation Solution
A one-component, epoxy-modified polyurethane adhesive with high elongation and low elastic modulus, featuring a high proportion of reactive urethane and urea groups, is developed, along with non-rubber-modified and rubber-modified epoxy resins, core-shell rubbers, and latent curing agents, to provide thermal stability and strong adhesion to various substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If one-component toughened epoxy adhesives are used to join different materials, then strong adhesion and high impact peel resistance are achieved, but the rigid nature of the adhesive cannot accommodate uneven thermal expansion and contraction, leading to assembly distortion or adhesive failure
Solution Approach 1:
The patent modifies the chemical composition parameters of the adhesive by incorporating polyether or diene rubber segments with specific molecular weights (at least 1000 atomic mass units) into the toughener structure. This changes the physical properties of the cured adhesive, specifically increasing elongation to at least 20% while maintaining strength, allowing the adhesive to accommodate thermal expansion differences between dissimilar materials.
Solution Approach 2:
The invention creates a composite adhesive system by combining epoxy resins with rubber-modified tougheners containing polyether or diene segments. This composite structure integrates the strong adhesion properties of epoxy with the flexibility and thermal expansion accommodation capabilities of rubber segments, resolving the contradiction between strength and adaptability.
2Stability of the object's composition
If polyurethane adhesives are used to achieve high elongation, then thermal stability is poor and the adhesive degrades at baking temperatures
Solution Approach 1:
The patent uses rubber-modified epoxy resins as an intermediary solution that bridges the gap between polyurethane and conventional epoxy adhesives. The polyether or diene rubber segments provide the desired elongation and flexibility, while the epoxy resin backbone maintains thermal stability and resistance to degradation at baking temperatures, achieving both high elongation and thermal stability simultaneously.
3Adaptability or versatility
If different materials are joined in automotive assemblies, then weight reduction and design flexibility are achieved, but the dissimilar materials have different coefficients of thermal expansion requiring specialized adhesives
Solution Approach 1:
The patent develops a universal adhesive formulation that can bond dissimilar materials (steel, aluminum, plastics, composites) with different thermal expansion coefficients. The rubber-modified epoxy adhesive provides multi-functionality by simultaneously delivering strong adhesion to various substrates, accommodating thermal expansion differences through high elongation, and maintaining thermal stability during baking, simplifying the joining process for multi-material automotive assemblies.
Data Source
AI summary
A one-component epoxy-modified polyurethane and/or urea adhesive includes very high levels of reactive urethane group- and/or urea group-containing tougheners, an epoxy resin and epoxy hardener. These adhesives are formulated to cure at high temperatures and surprisingly provide high elongations, excellent thermal stability and good adhesive properties.