Multimodal Polyethylene Extrusion Coating Composition
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Solution Overview
Problem
Low density polyethylene (LDPE) extrusion compositions lack sufficient abuse resistance and toughness for many applications, and traditional high density polyethylene (HDPE) and linear low density polyethylene (LLDPE) compositions exhibit poor extrusion processability, leading to limitations in extrusion drawdown rates and neck-in issues during high-speed processing.
Innovation Solution
Development of multimodal polyethylene compositions comprising a high molecular weight component with substantial long chain branching and a low molecular weight component, blended with LDPE, which provides improved processability and resistance to draw resonance, allowing for high line speeds and reduced neck-in, even with less than 20% LDPE by total resin weight.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If LDPE is used for extrusion coating, then excellent extrusion processability and high extrusion drawdown rates are achieved, but sufficient abuse resistance and toughness are lacking
Solution Approach 1:
The patent creates a composite polymer system by blending LDPE (2-20% by weight) with a linear polyethylene copolymer containing long chain branches. This composite structure combines the processability benefits of LDPE with the toughness and abuse resistance of the linear copolymer, resolving the contradiction between ease of operation and strength.
Solution Approach 2:
The invention introduces long chain branches at specific locations within the linear polyethylene backbone. These localized structural modifications create regions of enhanced entanglement and strength without compromising the overall linearity needed for good processability, thereby achieving both toughness and ease of operation.
2Strength
If linear polyethylene resins (HDPE, LLDPE, ULDPE) are used, then improved abuse resistance, toughness properties and barrier resistance are achieved, but poor extrusion processability results in high neck-in, draw resonance and high motor load
Solution Approach 1:
The patent modifies the molecular architecture parameters of linear polyethylene by introducing long chain branches (at least 10 carbon atoms) while maintaining the linear backbone structure. This parameter change enables the polymer to achieve both improved strength properties and acceptable extrusion processability by balancing molecular weight distribution and chain architecture.
Solution Approach 2:
The invention creates a composite molecular structure combining linear polyethylene segments with attached long chain branches. This composite architecture integrates the high strength and toughness of linear polymers with the improved processability characteristics introduced by the branched segments.
3Strength
If high molecular weight LDPE compositions are provided to improve properties, then abuse resistance improves, but too much melt strength prevents successful drawdown at high line speeds
Solution Approach 1:
The patent changes the molecular weight distribution parameters by using a bimodal system: a high molecular weight component (Mw > 100,000) providing toughness and a low molecular weight component (Mw < 50,000) providing processability. This parameter optimization enables both high abuse resistance and high drawdown rates at production speeds.
Solution Approach 2:
The invention segments the molecular weight distribution into distinct high and low molecular weight populations. The high molecular weight fraction contributes to mechanical strength and abuse resistance, while the low molecular weight fraction reduces melt viscosity enough to enable high-speed drawdown, resolving the contradiction between strength and productivity.
Data Source
AI summary
Multimodal polyethylene compositions are provided. Extrusion compositions including the multimodal polyethylene are provided. The extrusion composition further include a high pressure low density polyethylene and optionally other additives and/or polyethylenes. Extruded articles made from the polyethylene extrusion compositions are also provided.