Gas Transmitting Polyurethane Adhesive for Flexible Packaging
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Solution Overview
Problem
Conventional isocyanate-based adhesives used in flexible packaging laminates can significantly reduce the oxygen transmission rate, which is undesirable for packaging perishable food items that require gas exchange to maintain freshness.
Innovation Solution
A solvent-free, two-part laminating adhesive composition comprising a mixture of polyol and isocyanate-terminated polyurethane prepolymer, where the polyol is combined with a hydroxyl functional acrylic polymer to form a homogeneous liquid solution, maintaining a high oxygen transmission rate by minimizing the adhesive's contribution to the laminate's gas barrier properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional isocyanate-based adhesives are used to manufacture laminates for flexible packaging, then strong bonding between substrate layers is achieved, but the oxygen transmission rate is significantly reduced
Solution Approach 1:
The invention modifies the chemical composition parameters of the adhesive by incorporating specific polyols (polyester polyols, polyether polyols, natural oil polyols) with controlled molecular weights and hydroxyl values, along with hydroxyl-functional acrylic polymers of specific molecular weights (5,000-15,000 g/mol). These parameter changes in the adhesive formulation enable maintenance of bonding strength while improving oxygen transmission characteristics.
Solution Approach 2:
The adhesive comprises a composite system combining isocyanate-terminated polyurethane prepolymer with hydroxyl-functional acrylic polymers and various polyols. This composite material approach allows the adhesive to achieve both strong bonding properties and improved gas transmission characteristics that single-component adhesives cannot provide.
2Strength
If adhesive is applied between polymeric films in a laminate, then the films are strongly adhered, but the gas exchange properties of the laminate are degraded
Solution Approach 1:
The invention applies the principle of local quality by ensuring the adhesive provides strong bonding locally at the interface between substrate layers, while maintaining gas permeability in the bulk laminate structure. The specific adhesive formulation achieves strong interfacial adhesion without creating a continuous barrier that would block gas exchange throughout the laminate.
Solution Approach 2:
By changing the molecular weight parameters of the acrylic polymer (5,000-15,000 g/mol) and the polyol components, and by controlling the NCO/OH ratio (1.05-2.0), the adhesive achieves optimal balance between adhesion strength and gas transmission properties, preventing the formation of a dense barrier 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 composition provides a strong bond while maintaining a low oxygen transmission rate decrease, ensuring the freshness of packaged food items by allowing minimal impact on the gas exchange properties of the laminate, and is safe for indirect food contact according to FDA guidelines.
Implementation Method 1
Part B is an isocyanate-terminated polyurethane (prepolymer having a percent isocyanate (NCO %) of from about 4% to about 20%, based on the weight of the prepolymer. Part B is present relative to Part A at an NCO/OH ratio of at least about 1.1:1.
Data Source
AI summary
A two-part, solvent-free laminating adhesive including a Part A that is a liquid mixture of a first polyol and a hydroxyl functional acrylic polymer having a molecular weight of no greater than 15,000 g/mole, and a Part B that is an isocyanate-terminated polyurethane prepolymer. The adhesive is especially suited for making flexible laminates for use in food packaging. When adhered two polymeric film materials and in cured form, the adhesive provides substantially no contribution to the oxygen barrier properties of the laminate.