Multi-layer Plastic Film Deep-drawing Stability
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Solution Overview
Problem
Current methods for producing multilayer plastic films with foamed layers lack sufficient stability for deep-drawing and thermal forming, especially at low densities, which limits their application in producing three-dimensionally shaped bodies like motor vehicle interior panels.
Innovation Solution
The method involves producing a foamed plastic layer by blowing a pressurized inert gas into the plastic melt during extrusion, relaxing it below the melting temperature, and then connecting it to a compact cover layer, which is crosslinked later, allowing for enhanced foam formation and stability through controlled rheological conditions and high-energy radiation crosslinking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a foamed plastic layer is produced by conventional extrusion methods, then the production process is simple, but the film lacks sufficient stability for deep-drawing and thermal forming at low densities
Solution Approach 1:
The patent applies parameter changes by controlling the rheological properties of the plastic melt through specific viscosity ranges (shear viscosity 10^5-10^7 Pa·s, elongational viscosity 10^4-10^6 Pa·s) and adjusting the blowing agent pressure (1-10 bar) to achieve optimal foam formation. These parameter optimizations enable the foam film to maintain stability during deep-drawing with stretching degrees >300% while preserving a relatively simple extrusion manufacturing process.
Solution Approach 2:
The patent creates a composite structure by combining a foamed plastic layer with a compact cover layer to form a multi-layer plastic film. This composite construction integrates the light weight and insulation properties of foam with the structural stability and surface quality of the compact cover layer, achieving both deep-drawability and thermal forming stability that neither layer could provide alone.
2Stability of the object's composition
If the foam layer is crosslinked before lamination, then the foam structure is stabilized, but the connection to the cover layer becomes difficult
Solution Approach 1:
The patent applies preliminary action by performing the lamination of the foam layer to the cover layer before the crosslinking step. The foam layer is extruded and connected to the compact cover layer in a thermoplastic state, ensuring good interlayer adhesion. Only after this connection is established is the entire multi-layer structure crosslinked, thus avoiding the problem of difficult connection that would result from pre-crosslinking the foam.
Solution Approach 2:
The patent inverts the conventional sequence of operations by reversing the order of lamination and crosslinking. Instead of crosslinking the foam first and then laminating, the method laminates the foam to the cover layer while it is still in its thermoplastic state, and only subsequently applies crosslinking to the entire assembled structure. This inversion resolves the contradiction between foam stability and connection ease.
3Reliability
If high density foam material is used, then structural stability is improved, but weight increases and deep-drawing capability decreases
Solution Approach 1:
The patent optimizes the density parameter of the foam layer to a specific range (20-800 kg/m³) that balances weight reduction with structural stability. By controlling the foam cell structure and density within this range, and combining it with the compact cover layer, the multi-layer film achieves sufficient structural stability for deep-drawing applications while maintaining low weight and high stretchability (>300% degree of stretching).
Solution Approach 2:
The patent uses a composite material system where a low-density foamed layer (providing light weight and insulation) is combined with a compact cover layer (providing structural integrity and surface quality). This composite construction allows the overall film to achieve the structural stability needed for deep-drawing without requiring the foam itself to be high density, thus maintaining low weight and high deformability.
4Reliability
If the plastic melt has high viscosity, then foam cell stability is improved, but extrusion and ironing become difficult
Solution Approach 1:
The patent precisely controls the viscosity parameters of the plastic melt within optimal ranges: shear viscosity of 10^5-10^7 Pa·s and elongational viscosity of 10^4-10^6 Pa·s. These viscosity values are high enough to stabilize foam cell formation and prevent cell collapse, yet low enough to allow proper extrusion through the die and subsequent ironing processes. The patent achieves this balance through selection of appropriate polymers (polyethylene, polypropylene) and processing temperature control.
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
This process results in a deep-drawable foam film with high stretching stability, low weight, and improved thermal and pressure stability, enabling the production of complex three-dimensional structures with reduced raw material and energy usage.
Implementation Method 1
blowing the plastic melt above the melting temperature with a pressurized blowing agent, in particular an inert gas, during the extrusion process
Implementation Method 2
relaxing this gas-loaded melt when it leaves the extrusion system and below the melting temperature is cooled
Implementation Method 3
The multi-layer plastic film is crosslinked, in particular crosslinked with high-energy radiation
Data Source
AI summary
The invention relates to a method for producing a multi-layer plastic film comprising at least one compact cover layer and at least one layer which is arranged under the cover layer and made of extruded foamed plastic (foam layer), wherein the compact cover layer is connected to the foam layer thermally or by adhesion after extrusion and cooling of the foam layer to below the melting temperature. The invention further relates to a plastic composition for the foam layer for carrying out the method and to a multi-layer plastic film produced according to the method and to the use thereof. The layer made of foamed plastic is generated by blowing a propellant which is under positive pressure into a plastic melt during the extrusion process and by subsequently relaxing the propellant which is under positive pressure, wherein the foamed plastic is at first not cross-linked and is cross-linked together with the compact cover layer, in particular by high-energy radiation, only after the foam layer and the compact cover layer have been connected.