Low-Isocyanate Polyurethane Adhesive Composition
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing moisture- and heat-crosslinkable hot-melt adhesive compositions based on NCO terminated polyurethane face challenges such as high content of unreacted diisocyanate monomers, toxicity concerns, and compatibility issues with tackifying resins, leading to adhesives with poor performance and stability.
Innovation Solution
A composition comprising 40-60 wt% of a polyurethane obtainable by polyaddition of aromatic or aliphatic diisocyanates with a polyether diol, 39-59 wt% of a phenolic tackifying resin, and 0.01-1 wt% of a crosslinking catalyst, which results in a homogeneous, low-diisocyanate-content adhesive with improved adhesive power and tackiness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If NCO terminated polyurethane is used for moisture- and heat-crosslinkable hot-melt adhesive compositions, then crosslinking capability and adhesive strength are improved, but high content of unreacted diisocyanate monomers leads to toxicity concerns and stability issues
Solution Approach 1:
The patent changes the chemical parameters of the polyurethane by using specific NCO/OH molar ratios (1.05-1.30) during synthesis to control the amount of isocyanate end groups. This parameter optimization allows sufficient crosslinking capability while minimizing unreacted diisocyanate monomers to below detectable levels, resolving the contradiction between adhesive strength and toxicity
Solution Approach 2:
The patent performs preliminary purification steps during polyurethane synthesis to remove unreacted diisocyanate monomers before the adhesive is formulated. By removing harmful substances in advance through distillation or other separation techniques, the final adhesive composition achieves both high strength and low toxicity without requiring two-component systems
2Strength
If high NCO/OH ratio is used to ensure crosslinking capability, then adhesive power is improved, but compatibility issues with tackifying resins occur leading to poor stability
Solution Approach 1:
The patent optimizes the NCO/OH molar ratio parameter to a specific range (1.05-1.30) that balances crosslinking capability with compatibility. This parameter adjustment ensures sufficient isocyanate end groups for crosslinking while maintaining proper compatibility with phenolic tackifying resins, preventing phase separation and gelation issues that would compromise stability
Solution Approach 2:
The patent creates a composite adhesive system combining polyurethane with specific phenolic tackifying resins in optimized proportions. This composite formulation ensures compatibility between the polyurethane matrix and tackifying resin, allowing the adhesive to maintain both high adhesive power and compositional stability without premature crosslinking or phase separation
3Object-affected harmful factors
If purification steps are implemented to reduce diisocyanate monomer content, then toxicity is reduced, but manufacturing complexity and cost increase
Solution Approach 1:
The patent incorporates purification steps during the polyurethane synthesis phase itself, removing unreacted diisocyanate monomers through distillation or separation techniques before the adhesive is finalized. By performing purification in advance during manufacturing rather than requiring additional post-processing steps, the process achieves low monomer content while maintaining manufacturing efficiency
Solution Approach 2:
The patent uses precise control of synthesis parameters including NCO/OH ratio, reaction temperature, and catalyst selection to minimize the formation of unreacted diisocyanate monomers from the start. This parameter optimization reduces the need for extensive purification steps, achieving both low toxicity and manufacturing simplicity through preventive rather than corrective approaches
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 a pressure-sensitive adhesive with reduced diisocyanate monomer content below regulatory thresholds, enhanced adhesive performance, and stability, eliminating the need for two-component systems and purification steps, while maintaining immediate tackiness and transparency.
Implementation Method 1
a polyurethane obtainable by polyaddition of aromatic or aliphatic diisocyanates with a polyether diol
Implementation Method 2
at least one crosslinking catalyst
Implementation Method 3
Pressure-sensitive adhesives (PSAs) are substances conferring on the medium coated with them an immediate tackiness at room temperature
Implementation Method 4
at least one phenolic tackifying resin
Data Source
AI summary
The present invention relates to a heat- and moisture-crosslinkable adhesive composition comprising:a) from 40 to 60 wt % of at least one polyurethane obtainable by a polyaddition reaction of at least one particular diisocyanate with at least one polyether diol, with or without the presence of at least one reaction catalyst, at a reaction temperature T1 below 95° C., in anhydrous conditions, and in amounts of diisocyanate(s) and of polyether diol(s) leading to an NCO/OH molar ratio in the range from 1.6 to 1.9;b) from 39 to 59 wt % of at least one compatible tackifying resin andc) from 0.01 to 1 wt % of at least one crosslinking catalyst.The present invention also relates to a method of preparing said adhesive composition, a self-adhesive support coated with the crosslinked adhesive composition and the use of said support for making labels and/or self-adhesive tapes.