Capped Elastomeric Prepolymer Toughened Epoxy Adhesive
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Solution Overview
Problem
Conventional structural epoxy adhesives have high static strength but poor dynamic strength, requiring expensive tougheners that are not cost-effective due to limited availability of raw materials.
Innovation Solution
A storage-stable, heat-curable structural epoxy adhesive composition using a capped elastomeric prepolymer residue with isocyanate end groups, where the end groups are capped with secondary aliphatic, cycloaliphatic, aromatic, heteroaromatic, or araliphatic amines or thiols, providing improved flexibility and strength without reactive groups.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional rubber-modified epoxy resins or polyphenol-terminated polyurethane/polyurea tougheners are used, then dynamic strength (impact peel strength) is improved, but cost increases due to limited availability of raw materials
Solution Approach 1:
The invention changes the chemical parameters of the toughener by using polyether polyol instead of limited-availability polyphenol or amino phenol. This parameter substitution maintains the elastomeric properties and impact resistance while using readily available raw materials, thereby reducing cost without sacrificing dynamic strength
Solution Approach 2:
The invention employs inexpensive, readily available polyether polyol and isocyanate components that can be easily sourced, replacing expensive specialized tougheners. These common chemical building blocks allow cost-effective production while achieving the required toughening effect through proper molecular weight selection and formulation
2Ease of manufacture
If polyether polyol and isocyanate are used to prepare the elastomeric prepolymer, then cost is reduced due to availability of starting materials, but preparation temperature must be controlled
Solution Approach 1:
The invention optimizes the molecular weight of the polyether polyol within specific ranges (1,000-10,000 g/mol) to achieve the desired elastomeric properties at lower preparation temperatures. This parameter control allows the use of inexpensive polyether polyol and isocyanate while maintaining manageable processing temperatures through proper formulation
3Strength
If elastomeric prepolymer with isocyanate end groups is used, then flexibility and dynamic strength are improved, but storage stability may be compromised due to reactive groups
Solution Approach 1:
The invention carefully controls the NCO content within specific ranges (1-10 wt%) and selects appropriate molecular weights for the polyether polyol to balance flexibility with storage stability. By optimizing these parameters, the elastomeric prepolymer maintains its flexible, toughening properties while limiting excessive reactivity that would compromise storage stability
Solution Approach 2:
The elastomeric prepolymer acts as an intermediary between the epoxy resin and the crosslinking network. The controlled isocyanate end groups provide sufficient reactivity to participate in curing and provide flexibility, while the prepolymer structure itself moderates the overall reactivity to maintain storage stability
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 lap shear strengths of over 25 MPa and impact peel strengths of more than 30 N/mm, with good bonding on metals coated with processing oils, and is cost-effective due to the availability and lower preparation temperatures of the starting materials.
Implementation Method 1
the isocyanate end groups of said prepolymer residue being capped by a capping compound selected from the group consisting of a secondary aliphatic, cycloaliphatic, aromatic, heteroaromatic and araliphatic amine and a thiol
Implementation Method 2
a storage-stable, heat-curable structural epoxy adhesive composition comprising an epoxy resin and the compound defined above
Data Source
AI summary
The present invention relates to the use of a compound as a toughener in a storage-stable, heat-curable structural epoxy adhesive, said compound comprising an elastomeric prepolymer residue selected from the group of a polyurethane, a polyurea and a polyurea polyurethane having isocyanate end groups, the isocyanate end groups of said prepolymer residue being capped by a capping compound selected from the group consisting of a primary aliphatic, cycloaliphatic, heteroaromatic and araliphatic amine, a secondary aliphatic, cycloaliphatic, aromatic, heteroaromatic and araliphatic amine, a thiol and an alkyl amide, said capping compound being bound to the end of the polymer chain of the elastomeric prepolymer in a manner such that the end to which it is bonded no longer has a reactive group.