Insulated Wire Construction with Fire-Resistant Polymer Liner

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Solution Overview

Problem

Fire safety cables face challenges in maintaining electrical circuit integrity and long-term insulation resistance, particularly when exposed to high temperatures and water, as existing silicone rubber insulation materials fail to meet the requirements of UL 44 standards.

Innovation Solution

The use of a wire construction featuring an oxygen-free high thermal conductivity conductor with a thermoplastic polymer liner, a non-ceramifiable silicone first insulation layer, and a ceramifiable silicone second insulation layer, coextruded into inseparable layers, surrounded by a metal shield and a flame retardant polyethylene jacket, which provides improved thermal resistance and moisture barrier properties.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If ceramifiable silicone rubber is applied as insulation layer, then fire performance is improved, but moisture barrier properties deteriorate

Engineering Contradiction:

Improvefire performanceVSAvoidmoisture barrier

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The protective function is segmented between two layers: the thermoplastic polymer liner layer provides the moisture barrier function, while the ceramifiable silicone rubber outer layer provides the fire performance function. This segmentation allows each material to optimize its specialized function.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The thermoplastic polymer liner acts as an intermediary layer between the conductor and the silicone rubber insulation. It provides the moisture barrier function that silicone rubber lacks, while allowing the silicone rubber to perform its fire protection function without being compromised by moisture exposure.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If glass fiber tape with mica is used for fire protection, then circuit integrity during fire is improved, but manufacturing complexity increases

Engineering Contradiction:

Improvecircuit integrity during fireVSAvoidmanufacturing complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces the mechanical wrapping process of glass fiber tape with mica with a continuous extrusion process. The thermoplastic polymer liner and silicone rubber insulation are co-extruded in a single continuous operation, eliminating the manual or semi-automatic wrapping steps required for glass fiber tape.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent uses a composite extrusion of thermoplastic polymer and silicone rubber that combines the fire protection function previously achieved with glass fiber and mica into a single integrated insulation structure, simplifying both material application and manufacturing process.

Inventive Principle:

Principle #40Composite materials

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

This configuration enhances the wire's ability to maintain electrical functionality and insulation resistance during fire exposure and water immersion, meeting the stringent requirements of UL 2196 and UL 44 tests by preventing oxygen exposure and ensuring the conductor remains malleable and protected.

Implementation Method 1

maintain electrical functionality and insulation resistance during fire exposure and water immersion, meeting the stringent requirements of UL 2196 and UL 44 tests by preventing oxygen exposure

Methodology Applied

Scientific EffectOxygen barrier: Permeation

Implementation Method 2

a material of choice for wire insulation is a silicone rubber that has been specially formulated to form a ceramic-like layer when heated to the temperatures that are present in a fire

Methodology Applied

Scientific EffectCeramification: Vitrification