Co-Extruded Multilayer Structure for Stable High Draw-Down Extrusion
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Solution Overview
Problem
Existing polymer extrusion processes face limitations in speed and thickness due to shear and extensional flow instabilities, leading to melt shark skin, stick-lip, melt breakage, and draw resonance, which are challenging to predict and improve in multilayer structures.
Innovation Solution
A co-extruded multilayer structure is created using polymers with differing extensional viscosities, where one polymer increases and the other decreases viscosity under tensile stress, supported by an inter-layer interaction, allowing for higher draw-down ratios without instability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If polymer extrusion is performed at high speed and low thickness, then productivity is improved, but extensional flow instabilities occur leading to melt breakage and draw resonance
Solution Approach 1:
The patent employs multilayer composite structures combining polymers with different extensional viscosity behaviors (thickening and thinning polymers) to achieve high-speed extrusion without melt instabilities. The composite structure allows each layer to contribute its rheological properties, enabling stable processing at high draw-down ratios that would cause failure in single-polymer systems.
Solution Approach 2:
The patent changes the rheological parameters of the extrusion system by selecting polymers with specific extensional viscosity characteristics and adjusting their proportions in the multilayer structure. This parameter optimization allows the system to maintain stability at high extrusion speeds and low thicknesses where conventional single-polymer systems would fail.
2Manufacturing precision
If draw-down ratio is increased to reduce film thickness, then manufacturing precision is improved, but extensional flow instabilities cause melt breakage
Solution Approach 1:
The multilayer composite structure combines polymers with complementary extensional viscosity behaviors, where thickening polymers provide stability at high draw-down ratios while thinning polymers ensure processability. This composite approach enables achieving low film thicknesses with high precision without encountering melt breakage that limits single-polymer systems.
Solution Approach 2:
Different layers in the multilayer structure have locally optimized rheological properties tailored to specific functional requirements. The thickening polymer layers provide structural stability during high-rate drawing, while thinning polymer layers facilitate processing, creating a locally optimized system that achieves both high precision and stability.
3Device complexity
If single polymer is used for extrusion, then device complexity is reduced, but extensional viscosity behavior limits critical draw-down ratio
Solution Approach 1:
The patent uses multilayer composite structures to overcome the inherent limitations of single-polymer systems. By combining polymers with different extensional viscosity behaviors, the system achieves higher critical draw-down ratios and improved productivity while maintaining relatively simple co-extrusion equipment configuration.
Solution Approach 2:
The extrusion system is segmented into multiple layers, each with distinct rheological properties optimized for specific functions. This segmentation allows the system to achieve performance levels unattainable by single-polymer systems while using standard co-extrusion technology, balancing complexity and productivity.
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 method enhances the critical draw-down ratio by up to 300% compared to individual polymers, enabling thinner coatings and filaments with improved stability and reduced waste, suitable for high-speed production.
Implementation Method 1
the inter-layer chemically or physically interacts with the first polymer and the second polymer, adhering both layers either in molten and after polymers solidification
Implementation Method 2
the inter-layer chemically or physically interacts with the first polymer and the second polymer, adhering both layers either in molten and after polymers solidification
Implementation Method 3
stretching the molten co-extruded layers under tensile stress, whereby the resulted coextruded multilayer structure has a draw-down ratio which is higher than the critical draw-down ratio
Implementation Method 4
cooling down the co-extruded multi-layer structure to room temperature
Data Source
AI summary
The present invention is directed to a novel co-extruded multilayer structure that possess a draw down ratio superior than the critical draw-down ratio of each one of the polymeric layers, extruded individually. The present invention is also directed to a method for obtaining the co-extruded multilayer structure. The co-extruded multilayer structure obtainable by the method described herein allows preparing films, filaments or spun-melt non-wovens of low weight at high speed using conventional extrusion equipments. The co-extruded multilayer structure is especially suitable as diaper back-sheets or flexible packaging coatings.