One-Part Polyurethane Adhesive Green Strength and Storage Stability
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Solution Overview
Problem
One-part polyurethane compositions used as warm melt adhesives often suffer from short open times, poor storage stability, and adverse effects due to incompatible melt components, limiting their application in requiring high green strength and long open time.
Innovation Solution
A one-part polyurethane composition comprising a reaction product of polyether polyol, thermoplastic polyester polyol, hydrophobic polyol, and polyisocyanate, with a specific isocyanate content, which can be applied warm and exhibits high green strength, long open time, and excellent mechanical properties while maintaining good storage stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a nonreactive polyurethane polymer is used as melting component, then green strength is improved, but chemical resistance and adhesion properties deteriorate
Solution Approach 1:
The patent changes the chemical parameters of the melting component from nonreactive to reactive polyurethane polymer, and optimizes the isocyanate content to 0.5-5 wt% to achieve both high green strength and good chemical resistance/adhesion properties
Solution Approach 2:
The patent creates a composite adhesive system combining reactive polyurethane polymer with specific isocyanate content, polyol components, and optional fillers to achieve synergistic effects of green strength, chemical resistance, and adhesion properties
2Strength
If reactive melting component is used to improve green strength, then green strength is improved, but storage stability deteriorates
Solution Approach 1:
The patent optimizes the isocyanate content parameter to a specific range of 0.5-5 wt% and controls the NCO:OH ratio to prevent premature crosslinking while maintaining high green strength and excellent storage stability
Solution Approach 2:
The patent uses a controlled excess of isocyanate groups (0.5-5 wt% remaining isocyanate content) to ensure complete reaction with moisture during application while preventing premature crosslinking during storage
3Strength
If high viscosity is achieved through physical solidification, then green strength is improved, but open time deteriorates
Solution Approach 1:
The patent adjusts the melting point and viscosity parameters of the polyurethane polymer to achieve optimal balance between green strength and open time, allowing sufficient working time while maintaining high green strength
Solution Approach 2:
The patent uses polyol components as intermediaries to modulate the viscosity and solidification behavior of the adhesive, extending open time while maintaining green strength through controlled physical solidification
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 high green strength, long open time, and excellent mechanical properties, along with improved storage stability, making it suitable for industrial bonding applications without the drawbacks of previous warm melt adhesives.
Implementation Method 1
The high green strength of such an adhesive stems primarily from a sharp increase in viscosity upon cooling, as result of the physical solidification of one constituent of the adhesive, known as the melting component. This melting component represents a substance which is solid at room temperature but melts when the adhesive is heated to the application temperature
Implementation Method 2
which solidifies again within a certain time, by crystallization, for example, when the adhesive is again cooled
Implementation Method 3
They are especially suitable for elastic sealing and bonding, because, depending on the formulation, they can combine high adhesion strength with toughness and elasticity. Generally, such one-component polyurethane compositions are applied in the form of a viscous liquid or paste that cures to a soft elastic, rubberlike or tough solid, mostly by influence of humidity from air
Data Source
AI summary
The invention relates to a one-part polyurethane composition, comprising the reaction product of A) at least one polyether polyol PO; B) at least one thermoplastic polyester polyol PE; C) at least one hydrophobic polyol PH; D) at least one polyisocyanate PI, preferably methylene diphenyl diisocyanate (MDI), wherein the composition has a remaining isocyanate content of between 0.8 and 3.5 wt.-%, preferably between 1.4 to 1.8 wt.-%, based on the total weight of the isocyanate-functional polymers comprised therein, and wherein said polyether polyol PO comprises a bifunctional polyether polyol PO1 and a trifunctional polyether polyol PO2 and wherein said hydrophobic polyol PH is a polyester polyol based on fatty acids. The inventive one-component composition exhibits high green strength and long open time, as well as high storage stability. It is especially suitable as adhesive, in particular for automotive windshields and is preferably applied warm.