Solvent-Free Retort Lamination Adhesives With Low Migratable Species
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Solution Overview
Problem
Existing solvent-based adhesives used in retort applications for packaging laminates face challenges in thermal degradation and contamination due to migratable species, while solvent-free adhesives struggle to maintain suitable viscosity and bonding strength under retort conditions.
Innovation Solution
A solvent-free, two-pack lamination adhesive kit comprising aliphatic polyurethane prepolymers with reduced free isocyanate monomer content (less than 0.1% w/w) and a polyol crosslinker, using aliphatic isocyanate monomers and polyisocyanates, is developed to enhance bonding strength and resist thermal processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If solvent-based adhesives are used to maintain suitable viscosity and bonding strength, then bonding strength is improved, but harmful migratable species are generated under retort conditions
Solution Approach 1:
The patent removes the solvent component from the adhesive composition, extracting the harmful migratable species while retaining the essential adhesive properties through high molecular weight polyurethane prepolymers and reactive diluents
Solution Approach 2:
The patent changes the molecular weight parameter of the polyurethane prepolymer to greater than 10,000 g/mol, which fundamentally alters the viscosity characteristics and reduces migratable species while maintaining bonding strength under retort conditions
2Object-generated harmful factors
If high molecular weight materials are used to reduce migratable species, then migratable species are reduced, but viscosity increases making lamination difficult
Solution Approach 1:
The patent introduces reactive diluents (polyols and carboxylic acids) as intermediary substances that react with the polyisocyanate to form crosslinked networks, mediating between the need for high molecular weight (low migration) and suitable processing viscosity
Solution Approach 2:
The patent creates a composite adhesive system combining high molecular weight polyurethane prepolymer, polyol reactive diluents, and carboxylic acid reactive diluents, where each component contributes specific properties to achieve both low migration and workable viscosity
3Object-generated harmful factors
If solvent-free adhesives are used to eliminate harmful species, then migratable species are reduced, but bonding strength and delamination resistance deteriorate under retort conditions
Solution Approach 1:
The patent performs preliminary crosslinking network formation through the reaction of polyisocyanate with polyols and carboxylic acids before the retort process, creating a pre-established bonded network that resists thermal degradation and maintains strength under retort conditions
Solution Approach 2:
The patent changes the crosslinking density and network structure parameters by selecting specific polyol and carboxylic acid reactive diluents, optimizing the balance between reducing migratable species and maintaining bonding strength under thermal stress
4Strength
If aromatic isocyanates are used to provide bonding strength, then bonding strength is improved, but harmful primary aromatic amines are generated under retort conditions
Solution Approach 1:
The patent removes aromatic isocyanate components from the adhesive formulation, extracting the source of harmful primary aromatic amine generation while compensating for bonding strength through aliphatic polyurethane prepolymers with optimized molecular weight and crosslinking structure
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 kit provides improved bonding strength and delamination resistance under retort conditions, reducing the risk of harmful amine generation and migratable species, suitable for flexible packaging laminates that withstand temperatures of 100°C and higher.
Implementation Method 1
solvent-based adhesives have high resistance to thermal degradation, partially because solvent-based adhesives allow for the use of higher molecular weight starting materials, which build stronger networks that are less susceptible to forming migratable, small-molecule species upon thermolysis
Implementation Method 2
EP3176196 relates to a one-pack lamination adhesive comprising aromatic isocyanate polyurethane prepolymers, in which the amount of free diisocyanate monomer in the polyurethane prepolymer is reduced to less than 0.1% (w/w) using of a thin-film evaporator. The residual diisocyanate monomer is removed under pressures of 0.1 mbar or less at 140 °C.
Data Source
AI summary
The present invention is related to a solvent-free, two-pack adhesive kit comprising an isocyanate-functionalised, aliphatic polyurethane prepolymer and a polyol crosslinker. The present invention is also related to laminate adhesive comprising the components of the adhesive kit of the invention and a retort pouch comprising the same.