Multilayer Foil Retains Heat Shrinkability After Thermoforming
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Solution Overview
Problem
Existing multilayer foils struggle to maintain heat-shrinkability and mechanical strength after thermoforming and heat-sealing processes, making it difficult to achieve both thermoformability and heat-shrinkability in packaging trays without significant shrinkage.
Innovation Solution
A thermoformable, deep-draw-thermoformable, and heat-shrinkable multilayer foil with a specific layer structure, including a central inner layer and adhesion-promoter layers, which retains heat-shrinkability of at least 20% at 93°C, unaffected by the thermoforming process, and maintains excellent mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a multilayer foil is made thermoformable to produce packaging trays, then the foil can be formed into the required shape, but the heat-shrinkability is reduced or lost
Solution Approach 1:
The multilayer foil is divided into distinct functional layers: a thermoformable outer layer for shaping, a heat-shrinkable inner layer for dimensional stability and shrinkage, and intermediate adhesion layers. This segmentation allows each layer to perform its specific function independently, resolving the contradiction between thermoformability and heat-shrinkability retention.
Solution Approach 2:
The invention uses a composite multilayer structure combining different polymer materials with complementary properties. The outer layer provides thermoformability while the inner layer maintains heat-shrinkability, creating a composite material that exhibits both properties simultaneously, thus resolving the technical contradiction.
2Strength
If the foil thickness is increased to improve mechanical strength, then puncture resistance improves, but heat-shrinkability is compromised
Solution Approach 1:
The foil structure segments the mechanical strength function into the outer thermoformable layer and the heat-shrinkability function into the inner layer. This allows the total thickness to be increased for strength while the inner layer retains its heat-shrinkability property, resolving the contradiction between thickness/strength and heat-shrinkability.
3Ease of manufacture
If the foil is subjected to heat-sealing process, then sealing is achieved, but significant shrinkage occurs before packaging is complete
Solution Approach 1:
The sealing process heats only the outer thermoformable layer to achieve bonding, while the inner heat-shrinkable layer remains at lower temperature to maintain dimensional stability. This layered segmentation allows heat-sealing to occur without causing significant shrinkage, resolving the contradiction between sealability and dimensional stability.
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 multilayer foil achieves significant heat-shrinkability and mechanical strength, ensuring packaging trays remain effective in sealing and handling perishable foods without significant shrinkage during processing, with heat-shrinkability retention and enhanced puncture resistance.
Implementation Method 1
The packaging trays are usually produced by thermoforming, mostly by deep-draw-thermoforming, from a thermoformable multilayer foil, with exposure to heat
Implementation Method 2
Heat-shrinkable multilayer foils have the property of shrinking back to their original, unoriented dimensions when they are heated to temperatures above 60° C
Implementation Method 3
the sealing of the packaging tray with the lid foil usually takes place with exposure to heat, i.e. by heat-sealing
Data Source
AI summary
Sealable, thermoformable, heat-shrinkable multi-layer film having a symmetrical construction around a two-ply inner layer, and having a heat shrinkability in machine direction and in cross direction of in each case at least 20% at 93° C., the heat-shrinkability being substantially unaffected by thermoforming, and use thereof with specially equipped packaging machines.