Core-Sheath Fiber Electret Charge Retention

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Solution Overview

Problem

Existing methods for creating electrets, such as corona treatment and tribocharging, typically involve surface treatments that limit the distribution and retention of electrostatic charges within fibrous materials, whereas placing a charge-enhancing additive in the core of a core-sheath fiber allows for the generation of electrets with improved charge retention and distribution.

Innovation Solution

A thermoplastic core-sheath fiber is developed, where the core contains a first polymeric resin and an electrostatic charge-enhancing additive, and the sheath is made of a second polymeric resin, with the option to use poly(4-methyl-1-pentene) in the sheath without comprising 100% of it, allowing for effective charging via corona treatment, hydrocharging, or tribocharging to form electrets.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If charge-enhancing additives are placed in the surface layer through corona treatment or tribocharging, then the electret can be formed, but the charge distribution and retention are limited

Engineering Contradiction:

Improvecharge retentionVSAvoidsurface treatment complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies local quality by placing the charge-enhancing additive specifically in the core region of the fiber rather than uniformly throughout or only on the surface. This localized placement allows the core to generate and retain electrostatic charge while the sheath provides structural integrity and controlled charge distribution, resolving the contradiction between charge retention and treatment complexity

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent uses composite materials by creating a core-sheath fiber structure where the core contains both the polymeric resin and the charge-enhancing additive, while the sheath is made of a different polymeric resin. This composite structure enables the fiber to simultaneously achieve good charge retention and controlled surface properties without requiring complex surface treatment processes

Inventive Principle:

Principle #40Composite materials

2Reliability

If surface treatment techniques are used to create electrets, then the electret can be formed, but the charge distribution within the fibrous material is limited

Engineering Contradiction:

Improvecharge distributionVSAvoidmanufacturing simplicity

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent applies preliminary action by incorporating the charge-enhancing additive into the core during the fiber formation process itself, rather than adding it later through separate surface treatment steps. This preliminary incorporation ensures uniform charge distribution throughout the fibrous material and simplifies manufacturing by eliminating the need for complex post-processing treatments

Inventive Principle:

Principle #10Preliminary action

3Reliability

If the sheath is made of 100 wt % poly(4-methyl-1-pentene), then the fiber has good properties, but the electret charge retention is compromised

Engineering Contradiction:

Improvecharge stabilityVSAvoidpolymer composition flexibility

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The patent applies parameter changes by modifying the composition parameter of the sheath from 100 wt % poly(4-methyl-1-pentene) to a copolymer containing poly(4-methyl-1-pentene) and another polymeric resin. This compositional parameter change maintains the structural benefits of poly(4-methyl-1-pentene) while improving charge stability and electret performance

Inventive Principle:

Principle #35Parameter changes

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 approach enables the creation of electrets with enhanced charge stability and filtration performance, as evidenced by improved Quality Factor retention and penetration ratios, suitable for applications in filtering articles like respirators.

Implementation Method 1

charging the thermoplastic core-sheath fiber via corona treatment, hydrocharging, tribocharging, or combinations thereof to form the electret

Methodology Applied

Scientific EffectCorona treatment: Corona Discharge

Implementation Method 2

charging the thermoplastic core-sheath fiber via corona treatment, hydrocharging, tribocharging, or combinations thereof to form the electret

Methodology Applied

Scientific EffectTribocharging: Triboelectric Effect

Implementation Method 3

enhanced charge stability and filtration performance, as evidenced by improved Quality Factor retention and penetration ratios

Methodology Applied

Scientific EffectElectrostatic filtration: Electrostatic Deposition

Data Source

PatentUS20230390678A1Core-sheath fibers, nonwoven fibrous web, and filtering articles including the same

Publication Date: 2023.12.07 3M INNOVATIVE PROPERTIES CO

AI summary

Described herein is a thermoplastic core-sheath fiber. The thermoplastic core-sheath fiber comprises a core having a coextensive sheath layer disposed thereon, wherein the core comprises a first polymeric resin and an electrostatic charge enhancing additive, and the sheath layer comprising a second polymeric resin, with the proviso that if the second polymeric resin comprises poly(4-methyl-1-pentene), then the second polymeric resin does not comprise 100 wt % of poly(4-methyl-1-pentene). These thermoplastic core-sheath fibers can be used in filtering applications.