Polyisocyanate Mixture for Moisture-Curing Adhesives
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Solution Overview
Problem
Existing moisture-curing adhesives based on isocyanate prepolymers face challenges with storage stability and curing speed, particularly under temperature stress, and often require external catalysts that can negatively impact properties.
Innovation Solution
A polyisocyanate mixture comprising diphenylmethane diisocyanate and nitrogen-containing polyetherol components, with specific isocyanate functionality and viscosity, that reacts rapidly with atmospheric moisture without external catalysts, providing improved storage stability and rapid curing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If external catalysts are added to accelerate the curing process, then the curing speed is improved, but the storage stability deteriorates
Solution Approach 1:
The prepolymer contains built-in amino groups that act as internal catalysts, eliminating the need for external catalysts. The amino groups are incorporated into the polymer structure during synthesis, allowing the material to self-accelerate curing without compromising storage stability, as the catalytic function is integrated rather than added separately.
Solution Approach 2:
The invention changes the chemical structure of the prepolymer by incorporating amino groups into the polyol component. This structural modification inherently provides catalytic activity for moisture curing, transforming the prepolymer from a passive material to one with built-in catalytic functionality, thus achieving rapid curing without external catalysts.
2Productivity
If the reaction with atmospheric moisture is accelerated, then the curing completeness is improved, but the storage stability under temperature stress deteriorates
Solution Approach 1:
The prepolymer contains built-in amino groups that act as internal catalysts, eliminating the need for external catalysts. The amino groups are incorporated into the polymer structure during synthesis, allowing the material to self-accelerate curing without compromising storage stability, as the catalytic function is integrated rather than added separately.
Solution Approach 2:
The invention creates a composite prepolymer structure combining polyol, isocyanate, and amino groups into a single integrated molecule. This composite structure provides both the polyurethane backbone for structural integrity and the amino groups for catalytic activity, achieving synergistic effects that balance curing performance and storage stability.
3Speed
If amino-polyetheralcohol is used to increase reactivity to moisture, then the curing speed is improved, but the product becomes unsuitable for adhesive formulations
Solution Approach 1:
The invention introduces amino groups at specific locations within the polyol structure (as side chains or terminal groups) rather than using fully amino-substituted polyethers. This localized incorporation provides sufficient catalytic activity for rapid curing while maintaining the bulk polyol properties necessary for adhesive performance, such as flexibility and bonding characteristics.
Solution Approach 2:
The invention optimizes the concentration of amino groups within a specific range (0.1-5.0 wt%) to achieve the desired balance between reactivity and adhesive performance. By precisely controlling this parameter, the prepolymer attains rapid moisture curing capability while retaining compatibility with adhesive formulations and substrate bonding properties.
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 solution achieves rapid dry-hard and set-to-touch times with high initial and ultimate strength, maintaining storage stability even at elevated temperatures, eliminating the need for catalysts and ensuring favorable viscosity for application.
Implementation Method 1
All isocyanate group-containing prepolymers that are not stored in an absolutely moisture-tight container lose isocyanate groups over time due to reaction with atmospheric moisture
Implementation Method 2
These prepolymers are preferably used in one-component, moisture-curing foam applications
Data Source
AI summary
Polyisocyanate mixtures, their preparation by reacting aromatic polyisocyanate mixtures and nitrogen-containing polyetherol mixtures, and their use as an isocyanate component for the preparation of moisture-curing adhesives, said polyisocyanate mixtures comprising: (A) 15 to 35 wt. % of diphenylmethane diisocyanate with 2 aromatic rings; (3) 10 to 30 wt. % of polymeric diphenylmethane diisocyanate with 3 or more aromatic rings; and (C) 40 to 75 wt. % of an isocyanate-functional polyurethane; wherein the polyisocyanate mixture has an isocyanate content of 12 to 20 wt. %, an isocyanate functionality of >2.4, a viscosity of <10,000 mPa·s at 25° C., and a shear rate of 80 l/s.