Aliphatic Polyurethane Lamination Adhesive for Sterilization Films
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Solution Overview
Problem
Existing solvent-based two-component polyurethane adhesives used in laminating processes for flexible packaging face issues such as the formation of harmful primary aromatic amines due to residual diisocyanate monomers, lengthy crosslinking times, and inadequate cohesion during and after sterilization treatments, which affect industrial efficiency and safety.
Innovation Solution
A two-component polyurethane adhesive composition comprising an -OH component with amorphous prepolymers and an -NCO component using aliphatic monomers, specifically meta-xylylene diisocyanate with triols or isocyanurate, ensuring rapid crosslinking within 2 days and preventing the formation of primary aromatic amines, while maintaining cohesion under high temperatures and mechanical stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If aromatic diisocyanate monomers are used in solvent-based two-component polyurethane adhesives, then initial tack and crosslinking density are improved, but harmful primary aromatic amines are formed during sterilization due to residual monomers
Solution Approach 1:
The patent changes the chemical parameter of the diisocyanate monomer from aromatic to aliphatic type. This substitution maintains the reactivity and crosslinking capability needed for initial tack while eliminating the formation of harmful primary aromatic amines during sterilization, as aliphatic diisocyanates do not produce aromatic amine byproducts
Solution Approach 2:
The patent converts the potential harm of residual diisocyanate monomers (which form harmful aromatic amines) into a benefit by selecting aliphatic diisocyanates. These monomers still provide the necessary reactivity for crosslinking and initial tack but produce benign degradation products that do not pose health risks during sterilization
2Strength
If conventional two-component polyurethane adhesives are used, then good initial tack is achieved, but crosslinking time is excessively long (3-7 days) requiring intermediate storage
Solution Approach 1:
The patent applies preliminary action by incorporating a catalyst into the adhesive composition before application. This catalyst is specifically designed to accelerate the crosslinking reaction between the polyol and diisocyanate components, enabling the crosslinking process to complete within 2 days rather than the conventional 3-7 days, thereby eliminating the need for intermediate storage
3Reliability
If high crosslinking density is achieved for sterilization resistance, then thermal stability is improved, but cohesion during heat sealing deteriorates due to excessive rigidity
Solution Approach 1:
The patent applies local quality by creating different functional zones within the adhesive layer. The crosslinked polyurethane network provides localized rigidity and thermal stability for sterilization resistance, while the polyol component and catalyst system maintain localized flexibility and adhesion properties that enable proper cohesion during heat sealing processes
Solution Approach 2:
The patent uses a composite adhesive system combining polyol, aliphatic diisocyanate, catalyst, and solvent. This composite formulation achieves synergistic effects where the crosslinked structure provides sterilization resistance while the overall composition maintains appropriate flexibility and cohesion for heat sealing applications
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 provides rapid crosslinking, excellent cohesion, and prevents the formation of harmful compounds, enabling efficient production of multilayer films suitable for sterilization-resistant packaging without the need for intermediate storage, with improved mechanical resistance and safety.
Implementation Method 1
the isocyanate groups of the -NCO component react with the hydroxyl groups of the -OH component, according to a so-called crosslinking reaction, to form a polyurethane which is in the form of a three-dimensional network with urethane groups
Implementation Method 2
The implementation of said solvent-based adhesives in the laminating process requires an evaporation step of the organic solvent
Data Source
AI summary
1) Solvent-based two-component polyurethane adhesive composition, comprising an -OH component and an -NCO component such that: - the -OH component comprises an amorphous prepolymer including 2 –OH end groups, with a number average molar mass Mn of between 8000 and 12000 g and chosen from: - a copolyester (A1) obtained by a polycondensation reaction of at least one aliphatic diol (i) with at least one aromatic diacid (ii) and at least one aliphatic diacid (iii); and - a polyurethane (A2) obtained by a polyaddition reaction between an aliphatic diisocyanate compound and an amorphous copolyester diol with a number average molecular mass Mn of between 4000 and 11500 g/mole, - the –NCO component comprises a compound (B1) including 3 –NCO end groups, obtained by the reaction of meta-xylylene diisocyanate (m-XDI) with a triol, the compound (B1) being alone or in a mixture with a compound (B2) derived from an aliphatic diisocyanate. 2) Multilayer film comprising 2 thin layers of material connected together by a continuous layer of two-component adhesive composition, in the cross-linked state, 3) Method for preparing the film and use thereof for manufacturing flexible packaging.