Styrenic Polymer Blend for Power Cable Shield Strippability
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Solution Overview
Problem
Existing strippable shield formulations for electric power cables, such as those using ethylene vinyl acetate (EVA) and nitrile rubber, face challenges with high vinyl acetate content leading to a rubbery consistency unsuitable for high-speed extrusion, high cost, and poor thermal stability, while alternative additives have limited commercial success in achieving the desired adhesion and crosslinkability.
Innovation Solution
A power cable with an insulation shield layer comprising a blend of ethylene copolymer, carbon black, and a styrenic polymer, where the ethylene copolymer constitutes at least 45 wt%, and a polyolefin insulation layer, which allows for strippability while maintaining sufficient adhesion and exhibiting improved thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If highly polar polymer blends comprising ethylene vinyl acetate (EVA) and nitrile rubber are used to achieve strippability, then the shield layer can be peeled away from the insulation layer, but the formulations require relatively high vinyl acetate content which results in more rubbery consistency unsuitable for high speed extrusion
Solution Approach 1:
The patent changes the chemical composition parameters of the polymer blend by replacing EVA and nitrile rubber with a blend of polypropylene and styrenic block copolymer. This parameter change achieves strippability through the styrenic block copolymer's adhesive properties while maintaining suitable consistency for high-speed extrusion, as the polypropylene base provides appropriate rigidity and processability.
Solution Approach 2:
The patent uses a composite material system consisting of polypropylene blended with styrenic block copolymer (SBS or SEBS). This composite combines the structural properties of polypropylene with the adhesive and strippable characteristics of styrenic block copolymer, achieving both strippability and extrusion suitability simultaneously.
2Ease of operation
If nitrile rubber is used in strippable shield formulations, then adhesion control is achieved, but the cost increases and thermal stability deteriorates
Solution Approach 1:
The patent replaces expensive nitrile rubber with polypropylene, which is a cheaper and more thermally stable material. The styrenic block copolymer component provides the necessary adhesion control at lower cost and with superior thermal stability, making the overall formulation more economical and reliable.
Solution Approach 2:
The patent changes the material selection parameters by substituting nitrile rubber with the polypropylene-styrenic block copolymer system. This parameter change improves thermal stability because polypropylene has better thermal resistance than nitrile rubber, while the styrenic block copolymer maintains adhesion control through its polar interactions with the insulation layer.
3Ease of operation
If EVA and nitrile rubber blends are used for strippable shields, then adhesion is achieved, but the formulations exhibit poor thermal stability after thermal aging
Solution Approach 1:
The patent employs a composite material system of polypropylene and styrenic block copolymer that maintains adhesion properties after thermal aging. The polypropylene provides thermal stability and resistance to degradation, while the styrenic block copolymer maintains its adhesive characteristics, ensuring the shield remains strippable even after prolonged thermal exposure.
Solution Approach 2:
The patent replaces thermally unstable nitrile rubber with thermally stable polypropylene, which resists degradation during thermal aging. This substitution ensures the shield formulation maintains its adhesion and strippability properties throughout the service life of the cable under thermal stress.
Data Source
AI summary
The insulation shield layer of a power cable comprises a blend of ethylene copolymer, e.g., vinyl acetate, and a styrenic polymer, e.g., polystyrene. The insulation shield layer is adjacent to a polyolefin insulation layer of the power cable. The insulation shield layer exhibits cross-linkability. strippability from the insulation layer, and good thermal stability.