Solvent-Free Polyurethane Adhesive Composition with Controlled NCO Ratio
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Solution Overview
Problem
Conventional two-component solvent-free polyurethane laminating adhesives face challenges such as high viscosity, short pot-life, slow curing speed, and high levels of free diisocyanate monomers, which affect their performance and safety in flexible packaging applications.
Innovation Solution
A two-component solvent-free polyurethane laminating adhesive composition with a mass ratio of the OH-containing component to the NCO-containing component greater than 1:1 and a molar ratio of OH groups to NCO groups less than 1:1, reducing the total mass equivalent of the isocyanate component and thereby decreasing the monomeric diisocyanate residue.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If the adhesive is designed as a two-component system with high NCO content to achieve low viscosity at application temperature, then the viscosity at application temperature is reduced, but the pot-life becomes short due to rapid viscosity increase after mixing
Solution Approach 1:
The patent changes the chemical composition parameters of the components, specifically using a polyol with higher hydroxyl value (lower molecular weight) and controlling the NCO content in a specific range (10-25%). This parameter optimization allows the adhesive to maintain low viscosity at application temperature while extending pot-life by controlling the reaction rate between OH and NCO groups.
2Speed
If the isocyanate component content is increased to achieve fast curing speed, then the curing speed is improved, but the level of free diisocyanate monomers increases causing safety concerns and anti-sealing effects
Solution Approach 1:
The patent optimizes the NCO group content to a specific range (10-25%) and controls the molar ratio of OH to NCO groups to be less than 1:1. This parameter control ensures sufficient NCO groups for fast curing while preventing excessive free diisocyanate monomer formation, thereby eliminating anti-sealing effects and food safety concerns.
Solution Approach 2:
The patent creates a composite two-component system combining a specifically formulated polyol (with higher hydroxyl value) and an isocyanate component with controlled NCO content. This composite formulation achieves balanced performance: fast curing speed through adequate NCO groups while maintaining safety by limiting free monomer levels through proper stoichiometric control.
3Force
If the molecular weight of polyol is reduced to increase hydroxyl value and decrease viscosity, then the viscosity is reduced, but the mechanical performance and bonding strength deteriorate
Solution Approach 1:
The patent selects a polyol with a specific hydroxyl value range (50-150 mg KOH/g) and molecular weight range (500-2000 g/mol), which represents an optimal compromise. This parameter selection ensures low enough viscosity for proper application while maintaining sufficient molecular weight to preserve mechanical performance and bonding strength in the cured adhesive.
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 composition achieves a longer pot-life, faster curing speed, and comparable mechanical performance, including bonding strength, while reducing the risks associated with high diisocyanate content, such as anti-sealing effects and food safety concerns.
Implementation Method 1
reaction between hydroxyl groups and isocyanate groups starts, creating high molecular weight polyurethane polymer
Implementation Method 2
reaction between hydroxyl groups and isocyanate groups starts, creating high molecular weight polyurethane polymer
Data Source
AI summary
The present invention provides a two-component solvent free polyurethane adhesive composition, comprising: (A) a OH-containing component, and (B) an NCO-containing component; wherein the mass ratio between the OH-containing component (A) and the NCO-containing component (B) is greater than 1:1, and the molar ratio between the OH group in the component (A) and the NCO group in the component (B) is less than 1:1.