Latent Curative System for Epoxy Adhesives
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Solution Overview
Problem
One-part curable epoxy compositions face limitations in controlling cure time, temperature, and shelf life, which are essential for various industrial applications, particularly in automotive sectors, where conventional one-part systems fall short in efficiency and stability.
Innovation Solution
The use of a combination of two or more latent accelerators, including dicyandiamide derivatives, substituted imidazoles, and substituted ureas, in a heat curable epoxy resin system, allowing for reduced cure temperature, shorter cure time, and extended shelf life, while maintaining mechanical strengths such as shear and peel resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If conventional latent curatives are used in one-part epoxy formulations, then shelf life is extended, but cure temperature is limited to above 170°C
Solution Approach 1:
The patent combines multiple accelerator types (imidazole compounds and urea compounds) with latent curatives to create a composite curative system. This composite approach allows the system to maintain shelf stability through the latent curative while the accelerator combination enables curing at lower temperatures (below 170°C) by catalyzing the reaction more effectively.
Solution Approach 2:
The patent changes the chemical parameters of the curative system by introducing specific accelerator compounds (imidazoles and ureas) that modify the curing behavior. These parameter changes allow the system to cure at lower temperatures while maintaining the shelf-life benefits of latent curatives, effectively decoupling the temperature-cure rate relationship from the shelf-life constraint.
2Loss of time
If conventional accelerators are used individually, then cure time can be controlled, but cure temperature and shelf life stability cannot be optimized across broad ranges
Solution Approach 1:
The patent merges multiple accelerator types (imidazole compounds and urea compounds) into a single curative system. This combination allows the system to achieve cure times and temperature profiles that neither accelerator could achieve alone, while also maintaining shelf life stability across a broader temperature range. The synergistic effect of the combined accelerators provides versatility in controlling cure parameters.
3Ease of operation
If one-part formulations are used to eliminate mixing, then application is simplified, but shelf life is significantly reduced compared to two-part formulations
Solution Approach 1:
The patent uses latent curatives as intermediaries that remain dormant during storage and only activate under specific conditions (heat, moisture). This intermediary approach allows the one-part formulation to maintain long shelf life by preventing premature reaction, while still providing the application simplicity of a single-component system. The latent curative mediates between the need for long shelf life and the need for easy application.
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
This approach enables one-part curable epoxy compositions to achieve reduced cure temperatures and times, along with improved shelf life, resulting in more efficient manufacturing and enhanced performance in automotive applications with stable mechanical properties and minimal viscosity change upon aging.
Implementation Method 1
The cure of one-part epoxy adhesives can be catalyzed by the use of various accelerators. Conventional accelerators include ureas and imidazoles... The presently disclosed one-part curable epoxy compositions having a combination of two or more accelerators allows for a longer shelf life
Data Source
Figure 1
AI summary
There is provided a one -part curable epoxy composition comprising a heat curable epoxy resin; and a latent curative system in an amount sufficient to cure the epoxy resin, where the latent curative system comprises at least one epoxy resin miscible first curative comprising a latent hardener, selected from dicyandiamide and its derivatives, and two or more latent accelerators selected from at least one of substituted ureas, substituted imidazoles, and combinations thereof. There are also provided adhesive compositions, cured adhesives and articles made using such one -part curable epoxy compositions.