Sterilization-Resistant Polyurethane Adhesive for Multilayer Films
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Solution Overview
Problem
Existing two-component polyurethane compositions used in multilayer films for flexible packaging pose health and environmental risks due to the formation of primary aromatic amines from unreacted polyisocyanate monomers and the use of harmful solvents like GLYMO, while lacking sufficient thermal resistance and bonding strength after sterilization.
Innovation Solution
A two-component composition comprising an aliphatic polyisocyanate, crystalline polyester polyol, polyester polyol, chain extender, and silane coupling agent, which forms a solvent-free adhesive layer with high bonding strength, preventing the formation of primary aromatic amines and ensuring thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If aromatic polyisocyanate monomers are used in the NCO component, then the adhesive forms a polyurethane network providing cohesion, but unreacted monomers migrate and form harmful primary aromatic amines through hydrolysis
Solution Approach 1:
The patent changes the chemical parameter of the polyisocyanate from aromatic to aliphatic type. This substitution maintains the crosslinking functionality and cohesion properties while eliminating the formation of harmful primary aromatic amines, as aliphatic polyisocyanates do not produce carcinogenic aromatic amines upon hydrolysis
Solution Approach 2:
The patent converts the potentially harmful aromatic polyisocyanate system into a beneficial aliphatic polyisocyanate system. The aliphatic variant provides the same adhesive performance and crosslinking capability without the harmful byproduct formation, effectively transforming a harmful chemical pathway into a safe one
2Ease of operation
If solvents like GLYMO are used in the adhesive composition, then the adhesive can be applied and processed, but harmful solvents pose health and environmental risks
Solution Approach 1:
The patent extracts and removes the harmful solvent component from the adhesive composition. By formulating a solvent-free adhesive system, the invention eliminates health and environmental risks associated with solvents like GLYMO while maintaining the adhesive's functionality through proper formulation of the polyol and polyisocyanate components
Solution Approach 2:
The patent changes the physical state parameter of the adhesive from a solvent-based liquid to a solvent-free formulation. This is achieved by adjusting the molecular weight and composition of polyester polyols to ensure proper viscosity and reactivity without requiring volatile organic solvents for application
3Reliability
If the multilayer film is exposed to high temperatures during heat-sealing and sterilization, then the packaging is properly sealed and sterilized, but the adhesive layer may separate causing delamination
Solution Approach 1:
The patent employs a composite adhesive system combining polyester polyol with specific molecular weight characteristics and aliphatic polyisocyanate. This composite formulation creates a crosslinked polyurethane network with enhanced thermal stability, preventing delamination during heat-sealing and sterilization while maintaining bonding strength
Solution Approach 2:
The patent performs preliminary crosslinking preparation by selecting polyester polyols with specific molecular weights (500-3000 g/mol) that react efficiently with aliphatic polyisocyanates to form a pre-stabilized adhesive network before thermal exposure. This preliminary structural formation ensures the adhesive can withstand subsequent high-temperature 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 composition provides multilayer films with enhanced thermal properties and bonding strength after sterilization, without the risk of primary aromatic amine formation and the need for solvents or epoxysilanes, ensuring safety and environmental compliance.
Implementation Method 1
These prepolymers comprising —NCO groups are generally themselves polyurethanes produced by the polyaddition reaction of a molar excess of a polyisocyanate monomer
Implementation Method 2
the isocyanate groups of the —NCO component react with the hydroxyl groups of the —OH component, according to a reaction referred to as crosslinking, to form a polyurethane which exists in the form of a three-dimensional network
Implementation Method 3
a silane coupling agent
Data Source
AI summary
A two-component composition comprises component A and component B. Component A comprises a reaction product obtained by reacting at least an aliphatic polyisocyanate and a crystalline polyester polyol having a number average molecular weight of less than 3000 g/mol. Component B comprises at least one polyester polyol, a chain extender, and a silane coupling agent. The composition can be used as an adhesive to manufacture an article having a bonding strength value after sterilization greater than or equal to 3.5 N/15 mm. A multilayer film comprises at least two layers of substrates bonded together by a continuous layer, wherein the continuous layer consists of the two-component composition. The multilayer film can be used to manufacture flexible packaging intended for sterilization treatments.