Thixotropic Polyurethane Adhesive with Hindered Amines
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Solution Overview
Problem
Existing two-component polyurethane adhesives have high viscosity and short open time, making them difficult to apply to large surfaces and prone to flowing, which compromises their mechanical properties and adhesion under mechanical stress and environmental conditions.
Innovation Solution
A two-component polyurethane adhesive system with a polyol component containing sterically hindered amines and a polyisocyanate component, designed to maintain low viscosity after mixing while developing a thixotropic effect, ensuring the adhesive does not flow without external pressure and providing excellent adhesion and mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If conventional polyurethane adhesives are used, then the adhesive provides good initial bonding, but the viscosity increases rapidly leading to short open time and difficulty in application to large surfaces
Solution Approach 1:
The patent changes the chemical composition parameters by introducing sterically hindered amines (0.1-5 wt%) and controlling polyol molecular weight (>500 g/mol) to modify the reaction kinetics. This extends the open time while maintaining manageable viscosity levels during application.
Solution Approach 2:
The sterically hindered amines act as intermediaries that control the reaction between polyol and polyisocyanate. They provide a thixotropic effect that temporarily increases viscosity to prevent flow during application, then allows controlled curing without premature crosslinking.
2Ease of operation
If the adhesive is made fluid for easy application, then it can be applied to large surfaces, but it flows from the substrate and cannot maintain thick layers
Solution Approach 1:
The adhesive exhibits dynamic viscosity changes through thixotropy. During application, the adhesive remains relatively fluid for easy spreading, then develops increased viscosity to prevent flow and maintain thickness. This time-dependent viscosity control enables both ease of application and flow prevention.
Solution Approach 2:
The sterically hindered amines serve as intermediaries that mediate between the polyol and polyisocyanate components, creating a thixotropic network that provides temporary structural support to prevent flow while maintaining applicability during the open time period.
3Strength
If the adhesive cures quickly to provide strong bonding, then mechanical strength is improved, but the reactivity is too high causing premature reaction and poor wetting
Solution Approach 1:
The patent modifies the reaction parameters by using sterically hindered amines with specific molecular structures that control reaction rate. This provides optimal balance between initial wetting ability and subsequent curing strength, preventing premature reaction while ensuring strong bonding.
Solution Approach 2:
The sterically hindered amines act as intermediaries that control the reaction kinetics between polyol and polyisocyanate. They provide sufficient reactivity for strong bonding while maintaining controlled reaction rate that allows proper wetting and application before curing begins.
4Loss of time
If the adhesive is applied to large surfaces requiring time for processing, then application flexibility is improved, but the viscosity increase makes application difficult
Solution Approach 1:
The adhesive exhibits dynamic viscosity behavior where initial viscosity remains low to facilitate application to large surfaces, then increases over time as curing progresses. This time-dependent viscosity change allows extended processing time without making application difficult.
Solution Approach 2:
The thixotropic effect provides continuous structural support during the entire open time period, maintaining consistent viscosity characteristics that facilitate application while preventing flow. This continuous property enables extended processing time without compromising applicability.
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 achieves a non-flowing, pumpable state for application, maintaining mechanical strength and adhesion even under mechanical stress and varying environmental conditions, with a glass transition temperature above 50°C and modulus of at least 15 MPa, ensuring stability and durability.
Implementation Method 1
Two-component polyurethane adhesives with thixotropic effect... provide a thixotropic effect to adhesive mixture... the adhesive will not be free flowing without external pressure
Implementation Method 2
two component reactive polyurethane system... curing of isocyanate groups with primary or secondary amino groups proceeds as a fast reaction
Data Source
AI summary
A two-component polyurethane adhesive is provided, which comprises a component A comprising at least one polyol with a molecular weight of more than 500 g/mol, a component B comprising at least one polyisocyanate with a molecular weight of less than 1000 g/mol, and additional additives. The component A contains 0.1 to 10 wt. % sterically hindered amines having primary amino groups.