High temperature epoxy adhesive formulations
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Solution Overview
Problem
Existing structural toughened epoxy adhesives fail to provide a balance of mechanical strength and elastic modulus at elevated temperatures, leading to cohesive failure and inadequate thermal stress resistance in vehicles with diverse materials.
Innovation Solution
A formulation combining diglycidyl ether bisphenol epoxy resin, epoxy novolac resin, polyurethane toughener, hardener, and cure accelerator, characterized by specific viscosities and molecular weights, achieves a balance of mechanical strength and elastic modulus, with a single-component system activated by heat.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the mechanical strength at high temperature is increased, then the adhesive can resist thermal stresses better, but the elastic modulus becomes undesirably high
Solution Approach 1:
The patent applies parameter changes by carefully controlling the molecular weight and epoxide group concentration of the epoxy novolac resin, and the amount of polyurethane toughener, to achieve a balance between mechanical strength and elastic modulus at elevated temperatures
Solution Approach 2:
The patent uses a composite epoxy resin system combining diglycidyl ether of bisphenol A (30-70 wt%) with epoxy novolac resin (10-30 wt%), along with polyurethane toughener (1-10 wt%), to achieve both low elastic modulus and high mechanical strength at high temperatures
2Strength
If adhesive formulations use higher epoxy resin content to improve strength, then mechanical strength increases, but the elastic modulus becomes too high for thermal stress resistance
Solution Approach 1:
The patent changes the parameters of the epoxy resin system by using epoxy novolac resin with specific molecular weight (less than 750 g/mol) and epoxide group concentration (more than 2 but less than 3.7 per molecule), along with controlled polyurethane toughener content, to achieve both high strength and appropriate elastic modulus
Solution Approach 2:
The patent applies local quality by selecting epoxy novolac resin with specific local molecular characteristics (viscosity less than 3000 mPa-s at 25°C, specific epoxide group density) to achieve the desired balance of properties
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 formulation exhibits high mechanical strength and low elastic modulus, ensuring cohesive failure modes and effective thermal stress resistance up to 140°C, with Lap shear strength and impact peel strength exceeding industry standards.
Implementation Method 1
cure is initiated by heating, preferably to a temperature in the range of above 150°C and preferably between 160 and 210°C
Implementation Method 2
the different thermal expansion rates of the different materials can cause significant mechanical stresses in the joints between the materials
Implementation Method 3
The formulation exhibits high mechanical strength and low elastic modulus, ensuring cohesive failure modes and effective thermal stress resistance up to 140°C
Data Source
AI summary
The invention is an epoxy resin system useful as an adhesive for high temperature applications. The system is a combination of a diglycidyl ether a bisphenol epoxy resin(s), at amounts of 30-70% by weight, with 1-10% by weight of an epoxy novolac resin 10-30% by weight of a polyurethane toughener which preferably has the terminal isocyanate functional group blocked,1-8% by weight of a hardener, 0.1-% by weight of a cure accelerator, preferably a latent urea cure accelerator, provides the desired balance of mechanical strength and elastic modulus. The epoxy novolac resin is characterized by at least one of the following features: (i) having a viscosity at 25 degrees C of less than 3000 mPa-s according to ASTM D-445, (ii) an average number of epoxide groups per molecule of more than 2 but less than 3.7, and (iii) a molecular weight of less than 750 g/mol.