Expandable Epoxy Adhesive With Thermoplastics for Large Gaps

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Solution Overview

Problem

Existing thermally expandable structural epoxy adhesives for automotive metal bonding face limitations in large gap applications due to high peak core temperatures during ring-opening polymerization, leading to thermal degradation.

Innovation Solution

Incorporating semi-crystalline thermoplastics in particulate form into an expandable adhesive composition comprising liquid epoxy resin, blowing agents, and hardeners to reduce peak core temperatures during curing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If expandable structural epoxy adhesives are used for automotive metal bonding, then superior strength, water absorption characteristics and metal adhesion are achieved, but large amount of heat is released during ring-opening polymerization leading to peak core temperatures above cure temperature and thermal degradation

Engineering Contradiction:

Improveadhesive strengthVSAvoidpeak core temperature

Core Design Contradiction:

StrengthVSTemperature

Solution Approach 1:

The patent introduces a heat transfer medium (typically a metal substrate or filler material) as an intermediary to conduct heat away from the adhesive layer during curing. This mediator prevents heat accumulation by providing a thermal pathway that dissipates the exothermic heat to surrounding structures, thereby controlling peak core temperatures while maintaining cure effectiveness

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent modifies the curing parameters by controlling the rate and distribution of heat generation through adjusted formulation (epoxy-to-hardener ratio, catalyst concentration) and processing conditions (cure cycle temperature profile, heating rate). These parameter changes reduce the intensity of the exothermic reaction peak while ensuring complete cure, balancing adhesive strength development with thermal control

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If expandable structural epoxy adhesives are used in large gap applications, then cavity sealing and reinforcement are achieved, but thermal degradation occurs due to high peak core temperatures

Engineering Contradiction:

Improvelarge gap application capabilityVSAvoidadhesive reliability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent creates a composite adhesive system combining epoxy resin with thermally conductive fillers (such as metal powders, oxide particles, or ceramic beads). This composite formulation enhances thermal conductivity to dissipate heat more effectively while maintaining the adhesive's structural properties and gap-filling capability, thereby preventing thermal degradation in large gap applications

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The thermally conductive filler particles act as microscopic heat transfer intermediaries distributed throughout the adhesive layer. These particles create thermal pathways that conduct heat away from reaction zones, preventing localized overheating and thermal degradation while allowing the adhesive to maintain its reliability in large gap applications

Inventive Principle:

Principle #24Intermediary (Mediator)

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 inclusion of semi-crystalline thermoplastics allows for the use of expandable epoxy adhesives in large gap applications with reduced peak temperatures, enabling robotic application to oily vehicle panels, saving time and money in automated assembly processes.

Implementation Method 1

incorporating at least one semi-crystalline thermoplastic in particulate form. Such thermally expandable epoxy adhesive pastes can be applied robotically to oily vehicle panels to fill and reinforce cavities during an automated assembly process

Methodology Applied

Scientific EffectHeat absorption: Absorption (EM radiation)

Implementation Method 2

it was found that particulate semi-crystalline thermoplastic resins, such as polyamides, copolyetheresters and polyesters, afford significant reductions in the peak core temperatures reached within the expandable epoxy pastes during cure

Methodology Applied

Scientific EffectThermal mass effect: Heat Sink