Crosslinked Cable Insulation With High Melt Strength Polymer Extrusion
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Solution Overview
Problem
Existing ethylene-based polymers, particularly low-density polyethylene (LDPE), face challenges in maintaining high melt strength at lower viscosities, which affects extrusion processes for power cables, leading to issues like sag resistance and insulation concentricity, especially in high-voltage applications.
Innovation Solution
A high melt strength ethylene-based polymer is developed using a tubular reactor, modified with branching agents such as poly(propylene glycol) allyl ether methacrylate (PPG AEMA), di- or higher functional (meth)acrylates, or monomeric chain transfer agents, achieving enhanced melt strength and low dissipation factors to improve extrusion processes and electrical insulation performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the viscosity of ethylene-based polymer is decreased to enable faster extrusion, then extrusion speed is improved, but melt strength decreases leading to poor sag resistance
Solution Approach 1:
The patent changes the molecular architecture parameters of the ethylene-based polymer by introducing long chain branches through copolymerization with alpha-olefins (1-butene, 1-hexene, or 1-octene) at controlled levels (0.5-5.0 wt%). This parameter change enables the polymer to maintain high melt strength while achieving lower viscosity for faster extrusion, resolving the contradiction between extrusion speed and melt strength
Solution Approach 2:
The patent creates a composite molecular structure within the polymer by combining linear ethylene chains with grafted alpha-olefin branches. This composite architecture provides both the flow characteristics of linear chains and the entanglement strength of branched structures, enabling simultaneous improvement of extrusion speed and maintenance of melt strength
2Stress or pressure
If the viscosity of ethylene-based polymer is decreased to reduce head-pressure, then extrusion pressure is reduced, but melt strength decreases compromising sag resistance
Solution Approach 1:
The patent modifies the polymer's molecular weight distribution and branching parameters to achieve a material that flows more easily (lower head-pressure) while maintaining structural integrity (melt strength). The controlled copolymerization with alpha-olefins creates optimal branch length and frequency that reduce viscosity without sacrificing sag resistance
3Reliability
If conventional ethylene-based polymer is used to maintain low dissipation factor, then electrical performance is good, but melt strength is insufficient for high-voltage cable extrusion
Solution Approach 1:
The patent applies local quality modification by introducing branching at specific locations within the polymer chains through controlled copolymerization. The alpha-olefin branches are distributed throughout the molecular structure at controlled densities, providing localized entanglement points that enhance melt strength while preserving the overall low dissipation factor required for high-voltage cable insulation
4Strength
If branching agents are added to increase melt strength, then sag resistance is improved, but dissipation factor may increase affecting electrical performance
Solution Approach 1:
The patent carefully controls the branching parameters including branch length, branch frequency, and comonomer content to optimize the balance between melt strength and dissipation factor. By adjusting these parameters within specific ranges (0.5-5.0 wt% alpha-olefin), the patent achieves high melt strength while maintaining dissipation factor levels suitable for electrical insulation applications
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 modified polymers exhibit improved melt strength and sag resistance, allowing for faster extrusion, longer run lengths, and lower head-pressures, while maintaining low dissipation factors, thus enhancing the quality and reliability of high-voltage cable insulation.
Implementation Method 1
a high melt strength ethylene-based polymer made in a tubular reactor
Implementation Method 2
modified with a branching agent, e.g., poly(propylene glycol) allyl ether methacrylate (PPG AEMA)
Implementation Method 3
the peroxide is completely decomposed to enable crosslinking of the polymers
Implementation Method 4
peroxide crosslinkable power cable insulations
Implementation Method 5
Extrusion of the polymer compounds is typically done at temperatures below 140° C.
Data Source
AI summary
An insulated wire or cable is made by a process comprising the steps of:(A) extruding onto a covered or uncovered metal conductor or optical fiber a composition having a DF measured at 130° C. (60 Hz, 2 kV) or 120° C. (60 Hz, 8 kV) or 100° C. (60 Hz, 8 kV) of ≤0.5% and comprising:(1) a high melt strength ethylene-based polymer made in a tubular reactor, and(2) a peroxide, and(B) crosslinking the high melt strength ethylene-based polymer.