Capped Polyurethane Tougheners for Epoxy Adhesives
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Solution Overview
Problem
Epoxy adhesives used in the automotive industry face challenges with brittleness, impacting peel strength and elastic moduli, and require expensive auxiliary tougheners to meet mechanical and corrosion resistance requirements.
Innovation Solution
A capped polyurethane (PU) toughener composition comprising soft and rubbery units, specifically formulated with polytetramethylene ether glycol (PTMEG) and polybutadiene-diol (PBD) with aliphatic diisocyanate and bisphenol, and protected with capping groups, which eliminates the need for secondary tougheners and reduces material costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If epoxy resins are used in adhesives to provide strength, then the adhesive gains high strength, but the adhesive becomes brittle which compromises impact peel strength and elastic moduli
Solution Approach 1:
The patent uses a composite toughener system combining polybutadiene (rubbery phase) and polytetramethylene ether glycol (soft phase) within a single polyurethane architecture. This composite structure provides both flexibility to reduce brittleness and controlled reactivity for strength, resolving the contradiction between strength and brittleness in epoxy adhesives
2Strength
If auxiliary tougheners comprising rubbery portions such as polybutadiene or polyisoprene are added to meet mechanical property requirements, then impact peel strength and elastic moduli are improved, but the formulation cost increases significantly
Solution Approach 1:
The patent merges the functions of multiple auxiliary tougheners (polybutadiene and polytetramethylene ether glycol) into a single polyurethane toughener molecule. This consolidation achieves the required impact peel strength and elastic moduli while reducing formulation complexity and cost by eliminating the need for separate expensive rubbery toughener additives
3Reliability
If the adhesive formulation is exposed to cyclic climate storage and corrosive environments, then the adhesive must maintain strength, but corrosion causes strength decrease of more than 40% in typical formulations
Solution Approach 1:
The patent modifies the chemical parameters of the toughener by incorporating carboxylic acid groups that can neutralize basic contaminants and form protective complexes with metal surfaces. This chemical modification enables the adhesive to maintain strength in corrosive environments by preventing the corrosive attack that would otherwise cause more than 40% strength decrease
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 provides enhanced corrosion resistance, improved tackiness, and higher elastic modulus without the use of expensive auxiliary tougheners, maintaining strength and stability over time with minimal viscosity increase, even when exposed to oily metal panels.
Implementation Method 1
the isocyanate prepolymer may be protected by a capping group that dissociates from the PU-toughener when exposed to heat (curing conditions)
Implementation Method 2
the tips have been modified with isocyanate and bisphenol to allow them to react with epoxy resin when curing conditions are obtained
Data Source
AI summary
The invention is directed to a toughener for epoxy adhesives, the toughener comprising both soft and rubber units, and may be described as a capped soft-rubber PU toughener. The invention includes the tougheners and methods of making them, as well as adhesives comprising the inventive tougheners, methods of using the tougheners and adhesives comprising them, and cured inventive adhesives and products comprising them.