Two-Liquid Urethane-Epoxy Adhesive for Thermal Expansion Mismatch
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Solution Overview
Problem
Existing polyurethane-based adhesives face challenges in achieving both high adhesive strength against shear force and good elongation at break, particularly when bonding components with differing thermal expansion coefficients.
Innovation Solution
A two-part curable adhesive composition comprising a main agent containing a urethane prepolymer and an epoxy compound, and a curing agent with specific polyol and polyamine compounds, optimized by controlling the equivalent ratios of isocyanate groups and active hydrogen groups, and incorporating a silane compound to enhance bonding with metals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a polyurethane-based adhesive is designed to have high adhesive strength against shear force, then the adhesive strength is improved, but the elongation at break deteriorates
Solution Approach 1:
The invention uses a composite adhesive system combining polyurethane components (providing elongation) with epoxy components (providing strength). The main agent contains a urethane prepolymer and an epoxy compound, while the curing agent contains a polyol compound and a polyamine compound. This composite approach allows the cured adhesive to exhibit both high adhesive strength (≥10 MPa) and high elongation at break (≥100%), resolving the contradiction between strength and flexibility.
2Strength
If the equivalent ratio of isocyanate groups to hydroxy groups is increased to improve crosslinking density, then the adhesive strength is improved, but the elongation at break deteriorates
Solution Approach 1:
The invention optimizes the equivalent ratio of isocyanate groups to hydroxy groups in a specific range (2.05 to 12) to achieve balanced crosslinking density. This parameter control ensures sufficient crosslinking for strength while maintaining enough flexibility for elongation, preventing the adhesive from becoming too rigid.
3Strength
If a silane compound is incorporated to enhance bonding with metals, then the adhesive strength to metal is improved, but the complexity of the composition increases
Solution Approach 1:
The silane compound serves multiple functions: it acts as a coupling agent to enhance adhesion to metal substrates, contributes to the crosslinking network formation, and provides moisture cure capability. By incorporating silane into the existing polyurethane-epoxy system, the invention achieves improved metal bonding without requiring separate primer layers or additional processing steps.
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 composition achieves excellent elongation at break and adhesive strength, with a cured product exhibiting tensile lap-shear strength of 10 MPa or greater and elongation at break of 100% or greater, effectively bonding components with varying thermal expansion.
Implementation Method 1
a urethane prepolymer (a1) and an epoxy compound (a2), and a curing agent (B) containing a polyol compound (b1) and a polyamine compound (b2), the urethane prepolymer (a1) being obtained by reacting a raw material polyisocyanate and a polyol compound (a3)
Implementation Method 2
at least one of the main agent (A) or the curing agent (B) containing a silane compound (X)
Data Source
AI summary
A two-part curable adhesive composition contains a main agent (A) containing a urethane prepolymer (a1) and an epoxy compound (a2), and a curing agent (B) containing a polyol compound (b1) and a polyamine compound (b2). The urethane prepolymer (a1) is obtained by reacting a raw material polyisocyanate and a polyol compound (a3) at an index of 2.05 to 12. The main agent (A) further contains a remaining polyisocyanate (a4). The two-part curable adhesive composition contains a silane compound (X) in at least one of the main agent (A) or the curing agent (B). The SP value of each of the polyol compounds (a3) and (b1) is from 14.0 to 21.0 (J/cm3)1/2. The difference between the SP values of the polyol compounds (a3) and (b1) is from 0.1 to 4.0 (J/cm3)1/2.