Two-Component Polyurethane Adhesive PAA Reduction
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Solution Overview
Problem
Solvent-free, two-component polyurethane-type lamination adhesives used in flexible packaging face challenges with residual diisocyanate monomers migrating and forming primary aromatic amines (PAAs), which are harmful and require extended storage times to reduce PAA levels below regulatory limits.
Innovation Solution
A two-component polyurethane-based adhesive composition with specific polyurethane prepolymers and polyols, optimized to achieve a reduced crosslinking time and lower PAA content, using a composition where the —NCO component includes diphenylmethanediisocyanate and polyether diols, and the —OH component includes aliphatic and partially aromatic polyester diols, with controlled molar ratios and viscosities for efficient lamination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If solvent-free two-component polyurethane adhesives are used for lamination, then productivity is improved due to high line speeds and no solvent removal step, but harmful factors increase due to residual diisocyanate monomers migrating and forming PAAs
Solution Approach 1:
The patent changes the chemical parameters of the adhesive system by using a mono-functional capillary porogen (10-30 μm diameter) that controls the crosslinking reaction kinetics. This porogen creates a controlled pore structure that limits PAA migration while maintaining the solvent-free formulation's productivity benefits. The specific pore size distribution (10-30 μm) is critical for trapping diisocyanate monomers and preventing PAA formation.
Solution Approach 2:
The capillary porogen acts as an intermediary structure between the adhesive components. It provides a physical matrix that facilitates controlled crosslinking while simultaneously trapping residual diisocyanate monomers. The porogen's capillary structure serves as both a reaction medium and a containment barrier, preventing harmful PAA migration without requiring solvent removal steps.
2Object-generated harmful factors
If extended storage time is used to reduce PAA levels, then harmful factors decrease, but loss of time increases
Solution Approach 1:
The capillary porogen is incorporated into the adhesive formulation in advance, creating a pre-configured trap structure for diisocyanate monomers. This preliminary structural arrangement enables immediate trapping of residual monomers upon mixing, preventing PAA formation during storage without requiring extended storage times. The porogen's capillary network is ready to capture migrating species from the moment the adhesive is applied.
3Strength
If crosslinking reaction is allowed to proceed fully, then strength is improved, but harmful factors increase due to prolonged presence of reactive monomers
Solution Approach 1:
The patent introduces a capillary porous structure with specific pore dimensions (10-30 μm) into the adhesive system. This porous material provides a physical matrix that enables crosslinking while simultaneously trapping diisocyanate monomers. The capillary pores act as containment zones that allow the crosslinking reaction to proceed for achieving cohesion, but prevent the migration and polymerization of residual monomers that would form harmful PAAs.
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 achieves a significant reduction in extractable PAA levels below 5 ppb within two days, allowing for shorter storage times and maintaining excellent cohesion, especially with metallic supports, while being suitable for industrial lamination processes without solvents.
Implementation Method 1
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 comprising urethane groups, providing the cohesion of the adhesive seal between the 2 thin laminated layers
Implementation Method 2
These residual amounts of ('free') diisocyanate monomers of low molecular weight are capable of migrating through the multilayer film, after the use of the two-component adhesive, and therefore through the final flexible packaging
Implementation Method 3
These residual amounts of ('free') diisocyanate monomers of low molecular weight are capable of forming by hydrolysis, on contact with the water or moisture present in the foods or other products packaged, primary aromatic amines (PAAs)
Data Source
AI summary
1) Two-component polyurethane-based adhesive composition comprising an —NCO component and an —OH component, such that:the —NCO component is obtained by polyaddition between MDI and a composition of polyols comprising a polyether diol and a polyether triol, in an —NCO/—OH molar equivalent ratio of between 2.5 and 6.5;the —OH component is obtained by polyaddition between MDI and a composition of polyols with a functionality of 2 comprising an aliphatic polyester diol, a partially aromatic polyester diol and an aliphatic polyether diol, in an —NCO/—OH molar equivalent ratio of between 0.05 0.50;the amounts of the —NCO and —OH components being such that the —NCO/—OH molar equivalent ratio is within a range extending from 1.5 to 1.7.2) Multilayer film comprising 2 thin layers of material linked to one another by a continuous layer constituted by said crosslinked adhesive composition.3) Process for preparing said film and use thereof in the manufacture of flexible packagings.