Crosslinkable Polyethylene Composition for Scorch and Water Tree Resistance
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Solution Overview
Problem
Existing crosslinkable polymer compositions for electric cables face challenges in achieving a balance of water tree retardancy, degree of crosslinking, scorch resistance, thermo-oxidative stability, and storage stability, particularly in preventing the migration of additives to the pellet surface during storage and maintaining electrical breakdown strength after wet aging.
Innovation Solution
A crosslinkable polymer composition comprising a low-density polyethylene copolymer with a polyunsaturated comonomer, an additive composition of polyethylene glycol and 4,4'-thiobis(2-tertbutyl-5-methylphenol) plus thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], and a peroxide crosslinking agent, which provides enhanced scorch retarding and crosslinking performance while maintaining stability and electrical integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If peroxide crosslinking agents are used to achieve high degree of crosslinking, then electrical insulation performance is improved, but scorch formation occurs during extrusion
Solution Approach 1:
The patent introduces scorch retarders that act preliminarily during extrusion to suppress premature crosslinking reactions. These agents prevent scorch formation by inhibiting free-radical formation at extrusion temperatures, while allowing crosslinking to proceed later under controlled conditions, thus resolving the contradiction between achieving high crosslinking and preventing scorch during processing
Solution Approach 2:
The patent employs scorch retarders as intermediary substances that mediate between the peroxide crosslinking agent and the polymer matrix. These intermediaries control the timing and rate of crosslinking reactions, preventing harmful scorch during extrusion while enabling sufficient crosslinking for electrical insulation performance
2Reliability
If scorch retarders are added to prevent scorch during extrusion, then scorch resistance is improved, but additive migration to pellet surface occurs during storage
Solution Approach 1:
The patent optimizes the concentration parameters of scorch retarders and crosslinking agents within specific ranges to balance scorch resistance and storage stability. By carefully controlling additive concentrations, the patent achieves sufficient scorch protection during extrusion while minimizing excessive additive migration during storage
Solution Approach 2:
The patent uses composite additive systems combining scorch retarders with crosslinking agents and other functional additives. This composite approach creates synergistic effects where the combined additive system provides scorch resistance while the interactions between components reduce individual additive migration, improving overall storage stability
3Strength
If crosslinking is performed to improve electrical insulation strength, then electrical breakdown strength is improved, but water treeing degradation occurs in wet environments
Solution Approach 1:
The patent converts the potential harm of water exposure into a benefit by using crosslinked polymer networks that are specifically designed to resist water treeing. The crosslinking structure, while potentially creating inhomogeneities, is controlled to create a dense network that prevents water penetration and tree formation, thus converting the usual water degradation mechanism into a protective feature
Solution Approach 2:
The patent optimizes crosslinking density and uniformity parameters to achieve the right balance between electrical breakdown strength and water tree resistance. By controlling crosslinking parameters within specific ranges and using appropriate crosslinking agents, the patent creates a network structure that provides both high electrical strength and resistance to water treeing degradation
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 composition achieves a high electrical breakdown strength of at least 75.0 kV/mm after 1000 hours of wet aging, with low additive migration during storage, and exhibits improved scorch resistance and thermo-oxidative stability, effectively addressing the balance of properties required for cable insulation.
Implementation Method 1
The crosslinking by peroxides may result in the formation of so-called 'scorch'
Implementation Method 2
a high degree of crosslinking and good thermo-oxidative stability is important for applications such as cables
Implementation Method 3
In electrically strained polymer materials, subjected to the presence of water, so called 'water treeing' can occur
Data Source
AI summary
The invention is directed to a crosslinkable polyethylene composition comprising an additive composition consisting of polyethylene glycol and a mixture of 4,4'-thiobis (2-tertbutyl-5-methylphenol) plus thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate].