One-Component Epoxy Adhesive with Latent Curing Agent Mixture
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Solution Overview
Problem
One-component toughened epoxy adhesives require high curing temperatures, which can lead to energy inefficiency, increased volatile organic compound generation, and stress in assemblies with substrates of different thermal expansion coefficients, limiting their application and bond strength.
Innovation Solution
A one-component toughened epoxy adhesive composition including a non-rubber-modified epoxy resin, a toughening agent, an epoxy curing catalyst, and a curing agent mixture of dicyandiamide and dihydrazide, with a weight ratio of 1:99 to 99:1, that exhibits a lower curing onset temperature, typically around 140°C, while maintaining storage stability and forming strong bonds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high curing temperature (165-180°C) is used to achieve adequate curing with dicyandiamide, then bond strength and curing completeness are improved, but energy consumption increases and thermal stress develops in assemblies
Solution Approach 1:
The patent changes the chemical composition parameter of the curing agent system by combining dicyandiamide with dihydrazide compounds in specific ratios (1:99 to 99:1). This parameter change in the curing chemistry enables the adhesive to achieve adequate curing at lower temperatures (130-165°C) while maintaining bond strength, thereby reducing energy consumption during the curing process
2Reliability
If high curing temperature (165-180°C) is used to ensure complete curing, then adhesive performance is improved, but volatile organic compound generation increases
Solution Approach 1:
The patent modifies the curing agent composition by incorporating dihydrazide compounds alongside dicyandiamide. This chemical parameter change alters the curing mechanism to proceed effectively at lower temperatures (130-165°C), which reduces the thermal energy available for volatilizing organic compounds, thereby decreasing VOC generation while still achieving complete curing and reliable adhesive performance
3Strength
If high curing temperature (165-180°C) is used to achieve full property development, then adhesive strength is improved, but thermal expansion stress increases in multi-material assemblies
Solution Approach 1:
The patent changes the curing temperature parameter by formulating an adhesive system that cures effectively at 130-180°C instead of requiring 165-200°C. This lower curing temperature reduces the differential thermal expansion between substrates with different coefficients of thermal expansion, minimizing thermal stress development in the bonded assembly while still achieving adequate bond strength through the modified curing chemistry
Solution Approach 2:
The patent creates a composite curing agent system combining dicyandiamide and dihydrazide compounds. This composite approach leverages the complementary properties of both curing agents: dicyandiamide provides latency and storage stability, while dihydrazide compounds enable lower temperature reactivity. The synergistic interaction of this composite curing system achieves complete curing at reduced temperatures, thereby reducing thermal expansion stress in multi-material assemblies
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 achieves lower curing onset temperatures, reducing energy consumption and stress in assemblies, while providing higher glass transition temperatures and improved bond strength compared to adhesives using dicyandiamide or dihydrazide alone, and allows for bonding of substrates with different thermal expansion coefficients.
Implementation Method 1
Curing cannot commence under ordinary conditions of storage and transportation, but instead must be delayed until the adhesive is exposed to specific curing conditions, which typically include an elevated temperature
Implementation Method 2
one-component epoxy adhesives are generally formulated with a latent curing agent. Dicyandiamide is widely used for this purpose. Dicyandiamide is a solid material that is poorly soluble in most epoxy resins. It melts at a temperature above 200° C. Its high melting temperature and low solubility in epoxy resins contribute to its latency
Implementation Method 3
curing the adhesive layer at the bondline by heating to a temperature of at least 130° C., to form a cured adhesive bonded to the two substrates at the bondline
Implementation Method 4
heating the coated assembly from step 2) to a temperature of at least 140° C. to cure the adhesive to form a cured adhesive bonded to the substrates at the bondline and simultaneously cure the coating layer
Implementation Method 5
The adhesive composition achieves lower curing onset temperatures, reducing energy consumption and stress in assemblies, while providing higher glass transition temperatures and improved bond strength compared to adhesives using dicyandiamide or dihydrazide alone
Data Source
AI summary
A one-component toughened epoxy-modified polyurethane and/or urea adhesive includes a mixture of dicyandiamide and a dihdyrazide as curing agents. The mixture of curing agents permits the adhesive to be cured at lower temperatures while developing good adhesive and mechanical properties in the cured adhesive.