UV-Curing Hot Melt Adhesive with Low Oligomer Content
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Solution Overview
Problem
Hot melt adhesives require high temperatures for application, which can damage substrates and involve hazardous low molecular weight monomers, and UV-curing systems have lower adhesion and environmental concerns due to reactive acrylate components.
Innovation Solution
A reactive hot melt adhesive composition comprising a blend of (meth)acrylate polymer, polyurethane polymer with (meth)acrylate groups, and polyurethane prepolymer with NCO-groups, minimizing low molecular weight (meth)acrylate urethanes and monomeric isocyanates, allowing for lower temperature application and in-line bonding with improved green strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high molecular weight polymers are used in hot melt adhesives, then green strength is improved, but melt viscosity increases requiring elevated application temperatures
Solution Approach 1:
The patent uses a composite system combining thermoplastic polyurethane polymers with reactive oligomers containing (meth)acrylate groups. This composite approach allows the adhesive to exhibit both high green strength (from the polymeric component) and low melt viscosity (from the oligomeric component), eliminating the need for elevated application temperatures while maintaining substrate integrity.
Solution Approach 2:
The patent changes the molecular weight parameters of the adhesive components, specifically using oligomers with low molecular weight (to reduce viscosity) combined with polymeric substances (to provide green strength). This parameter optimization allows application at moderate temperatures below the substrate damage threshold while achieving the required bonding performance.
2Temperature
If low molecular weight acrylate monomers are used to reduce viscosity, then application temperature decreases, but adhesion performance deteriorates and environmental concerns increase
Solution Approach 1:
The patent changes the molecular weight parameter of the acrylate component from monomeric (low molecular weight) to oligomeric (low to medium molecular weight). This parameter change maintains low viscosity for easy application at moderate temperatures while improving adhesion performance and reducing environmental concerns associated with monomeric substances.
Solution Approach 2:
The patent replaces permanent monomeric substances with oligomeric reaction products that are less hazardous and more stable. The oligomers represent a more stable, less volatile alternative to monomers, reducing environmental and health concerns while maintaining the desired rheological properties for application.
3Productivity
If monomeric isocyanates and acrylic monomers are present in the adhesive, then reactivity is improved, but hazardous substance content increases
Solution Approach 1:
The patent extracts and removes monomeric isocyanates and acrylic monomers from the adhesive composition, replacing them with oligomeric and polymeric substances. This extraction eliminates the hazardous substances while maintaining the necessary reactivity through the oligomeric components that contain reactive functional groups but lack the volatility and hazards of monomers.
Solution Approach 2:
The patent converts the potentially harmful monomeric substances into beneficial oligomeric reaction products. The oligomers retain the reactive functionality needed for curing but eliminate the hazardous properties of monomers, such as volatility and toxicity, effectively transforming a harmful component into a beneficial one.
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
Enables bonding at moderate temperatures without substrate fixation during curing, reduces hazardous substance content, and achieves high green strength and adhesion with fast curing properties.
Implementation Method 1
a reactive PU prepolymer which shall include NCO-groups which can be cross-linked by reaction with moisture
Implementation Method 2
a PU polymer which shall comprise unsaturated double bonds which may react under UV-radiation
Data Source
AI summary
A reactive hot melt adhesive comprising a blend of a (meth)acrylate polymer, a polyurethane polymer containing (meth)acrylate groups and a polyurethane prepolymer containing NCO-groups wherein the content of low molecular weight (meth)acrylate urethanes is less than 1 wt % of the adhesive. The adhesive provides a fast and improved green strength during application.