Low-Viscosity Polyurethane Laminating Adhesive for Rapid Curing
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Solution Overview
Problem
Existing polyurethane-based 2-component laminating adhesives have issues with excess monomeric isocyanate groups leading to the formation of primary aromatic amines, which are harmful, and require long curing times, while also causing misting during high-speed processing.
Innovation Solution
A polyurethane adhesive system using an NCO-terminated polyurethane prepolymer with at least 40 wt.% diphenylmethane diisocyanate and a polyol mixture with three different polyols, which reduces primary aromatic amine formation and accelerates curing, allowing high-speed processing without misting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If polyurethane-based 2-component systems with excess monomeric isocyanate groups are used, then low viscosities and good processability are achieved, but primary aromatic amines are formed which are harmful to health and curing times are extended
Solution Approach 1:
The invention changes the chemical composition parameters by using a specific polyol mixture (containing at least three different polyols with specific OH values and molecular weights) to react with MDI-based prepolymer. This parameter change reduces the excess monomeric isocyanate groups and accelerates the reaction kinetics, thereby reducing PAA formation and shortening curing time while maintaining low viscosity and good processability
Solution Approach 2:
The invention uses a composite curing system combining at least three different polyols (including polyester polyols, polyether polyols, and/or polycarbonate polyols) with specific properties. This composite approach creates a multi-functional curing system that simultaneously achieves low viscosity, fast curing, and reduced PAA formation by distributing the reaction pathways across multiple polyol components
2Strength
If polyester polyols are used to increase adhesion, then bond strength is improved, but viscosities become relatively high causing misting during high-speed processing
Solution Approach 1:
The invention carefully controls the molecular weight and OH value parameters of the polyester polyols used, combining them with other polyol types in specific ratios. This parameter optimization maintains the adhesion benefits of polyester polyols while preventing excessive viscosity increase that would cause misting during high-speed processing
Solution Approach 2:
The invention creates a composite polyol system combining polyester polyols (for adhesion), polyether polyols (for flexibility and low viscosity), and/or polycarbonate polyols (for durability). This composite approach balances adhesion requirements with processability by distributing functional properties across different polyol components
3Object-affected harmful factors
If the content of monomeric isocyanate groups is reduced through prepolymerization, then PAA degradation is improved, but curing times are extended
Solution Approach 1:
The invention performs preliminary prepolymerization to reduce monomeric isocyanate content before the final curing stage. The specific polyol mixture then accelerates the remaining curing reaction, ensuring that PAA degradation is achieved while minimizing the time penalty through optimized reaction kinetics
4Productivity
If run speed is increased above 250 m/min in laminating machines, then productivity is improved, but misting occurs during processing
Solution Approach 1:
The invention optimizes the viscosity parameters of the adhesive composition by selecting polyols with specific molecular weights and OH values. This parameter control ensures the adhesive remains fluid enough for high-speed application above 250 m/min without becoming so thin that misting occurs during processing
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 system effectively minimizes primary aromatic amine release, achieves rapid curing, and prevents misting, ensuring high-speed processing and improved bond adhesion, suitable for food and medical packaging applications.
Implementation Method 1
a polyurethane adhesive, in particular for laminating films, wherein the PU adhesive contains, based on the total weight of the laminating adhesive composition, (a) as a resin component at least one NCO-terminated polyurethane prepolymer having a content of at least 40 wt. % diphenylmethane diisocyanate (MDI)... and (b) as a curing component a polyol mixture comprising at least three different polyols
Implementation Method 2
These systems as described herein are characterized by good processability (low viscosities, >300 m/min in laminating machines) and fast chemical (PAA degradation) as well as physical cure rates
Data Source
AI summary
The invention relates to a 2-component polyurethane adhesive, in particular for laminating films, wherein the PU adhesive, based on the total weight of the laminating adhesive composition, (a) contains as resin component at least one NCO-terminated polyurethane pre-polymer having a content of at least 40% by weight of diphenylmethandiisocyanate (MDI), wherein the MDI is 4,4′-diphenylmethandiisocyanate or a mixture thereof with 2,4′-diphenylmethandiisocyanate, and (b) contains as hardener component a polyol mixture comprising at least three different polyols. The invention further relates to the use of the adhesive for adhesively bonding films, to methods for producing composite films, and to composite films bonded by means of the described adhesive.