Low Monomer Hot Melt Polyurethane Adhesive for Roll Coating
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Solution Overview
Problem
Conventional reactive polyurethane hot melt adhesives contain toxic and irritating monomeric diisocyanates, which pose health risks, and lack heat stability necessary for roll coating applications.
Innovation Solution
A reactive hot melt adhesive composition is formulated with an isocyanate functional prepolymer partially reacted with active hydrogen organofunctional silane and fully capped with active hydrogen non-silane capping agents, reducing monomeric diisocyanate content and maintaining heat stability, comprising a polyfunctional isocyanate, polyol, thermoplastic polymer, and optional tackifying agents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional reactive polyurethane hot melt adhesives are used, then green strength and heat resistance are achieved, but toxic monomeric diisocyanates are present causing health risks
Solution Approach 1:
The harmful monomeric diisocyanates are extracted and removed from the adhesive formulation through a two-stage reaction process. First, isocyanate groups react with polyol to form prepolymer. Second, remaining isocyanate groups react with capping agents (oxazolidines, amino compounds, or hydroxyl compounds) to eliminate free isocyanates that would vaporize and cause health issues, while maintaining the crosslinking functionality through silane groups.
Solution Approach 2:
The formulation changes the chemical parameters by introducing silane-terminated polyols and controlling the stoichiometry of isocyanate groups. The isocyanate content is reduced to less than 0.1% by weight through precise control of reaction conditions and component ratios, transforming the adhesive from toxic to safe while preserving performance.
2Object-affected harmful factors
If silane terminated reactive polyurethane hot melt adhesives are used to eliminate monomeric diisocyanates, then health safety is improved, but heat stability necessary for roll coating applications is lost
Solution Approach 1:
The adhesive uses a composite formulation combining silane-terminated polyurethane prepolymer with additional crosslinking agents (oxazolidines, amino compounds, or hydroxyl compounds). This composite approach provides both the low diisocyanate content for safety and the heat stability for roll coating through the synergistic interaction of multiple functional components.
Solution Approach 2:
The silane groups act as intermediaries that bridge the polyol and crosslinking agents. The silane-terminated prepolymer provides reactive sites for moisture crosslinking while the added capping agents with active hydrogens provide additional crosslinking pathways, maintaining heat stability without requiring free monomeric diisocyanates.
3Object-affected harmful factors
If isocyanate groups are fully reacted to eliminate monomeric diisocyanates, then toxicity is reduced, but crosslinking functionality and heat resistance are compromised
Solution Approach 1:
The crosslinking functionality is segmented into two parts: silane groups that provide moisture-cure crosslinking and additional crosslinking agents (oxazolidines, amino compounds, or hydroxyl compounds) that provide thermal stability. This segmentation allows the adhesive to achieve both low toxicity and maintained heat resistance through distributed crosslinking mechanisms.
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 low monomeric diisocyanate content, excellent green strength, and heat stability, allowing safe and effective roll coating with minimal health risks and maintaining desirable properties.
Implementation Method 1
the isocyanate groups of the isocyanate functional prepolymer are partially reacted with the active hydrogen of the organofunctional silane
Implementation Method 2
essentially all of the remaining isocyanate groups are capped by reaction with the active hydrogen non-silane capping agent
Implementation Method 3
Chemical reaction of the isocyanate groups still present with moisture from the environment to form a cross-linked adhesive
Data Source
AI summary
The invention includes a reactive hot melt adhesive composition including an isocyanate functional prepolymer derived from a polyfunctional. isocyanate having a functionality of about 2 or more and a polyol, an active hydrogen organofunctional silane, an active hydrogen non-silane capping agent and a thermoplastic polymer.