Electret and electret filter
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Solution Overview
Problem
Conventional electret filters face challenges in simultaneously achieving oil repellency, electric charge stability, and cost-effectiveness, particularly when using short-chain perfluoro compounds that comply with environmental regulations, and they struggle with durability against tobacco smoke and oil mist.
Innovation Solution
An electret comprising a carrier with polytetrafluoroethylene (PTFE) deposited using a vapor deposition method, which has a melting point between 35°C and 320°C, and exhibits two or more melting point peaks in thermogravimetry and differential thermal analysis, providing excellent oil repellency and electric charge stability without using PFOA or PFOS.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional electret filters use polyolefins, polyesters, or polycarbonates with excellent electric charge stability, then electric charge stability is improved, but oil mist resistance deteriorates due to high surface tension causing oil mist to coat fiber surfaces and accelerate charge elimination
Solution Approach 1:
The invention uses composite fibrous materials combining polyolefin fibers with fluororesin-coated fibers or fluorinated fibers. The polyolefin provides the base structure and electrostatic charge, while the fluororesin coating or fluorination of specific fibers provides low surface tension for oil mist resistance. This composite approach allows both electric charge stability and oil mist resistance to coexist.
Solution Approach 2:
Instead of treating all fibers uniformly, the invention applies fluororesin coating or fluorination only to specific portions or types of fibers within the filter structure. This localized treatment creates regions with oil-repellent properties while maintaining overall electrostatic charge stability through the untreated or differently treated fibers.
2Reliability
If fluorine-based resins or low molecular weight additives are used to lower surface tension and improve oil mist resistance, then oil repellency is improved, but manufacturing complexity increases due to thermal decomposition issues above 320°C and strict facility requirements
Solution Approach 1:
The invention selects fluororesins with decomposition temperatures above 320°C, changing the thermal parameter to avoid decomposition during conventional melt-spinning processes. This allows the use of fluororesins without requiring special low-temperature processing facilities, thereby reducing manufacturing complexity while maintaining oil mist resistance.
3Reliability
If perfluorooctanoic acid (PFOA) or perfluorooctanesulfonic acid (PFOS) are used to achieve excellent oil repellency, then oil mist resistance is improved, but environmental compliance deteriorates due to bioaccumulation issues and production restrictions
Solution Approach 1:
The invention extracts and eliminates PFOA and PFOS from the fluororesin composition, using alternative fluororesins that provide equivalent or superior oil mist resistance without the bioaccumulation and environmental persistence problems. This extraction of harmful substances maintains performance while achieving environmental compliance.
4Temperature
If polytetrafluoroethylene with high melting point is used for vapor deposition, then thermal stability is improved, but deposition difficulty increases due to high energy requirements and process complexity
Solution Approach 1:
The invention uses polytetrafluoroethylene with melting points specifically in the 35-320°C range, changing the thermal parameter from conventional high-melting-point PTFE to this optimized range. This reduction in melting point decreases the energy and temperature requirements for vapor deposition, making the process easier to implement while maintaining sufficient thermal stability for filter application.
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 solution results in an electret filter that maintains high collection efficiency and durability against tobacco smoke and oil mist, with improved oil mist resistance and electric charge stability, while being cost-effective and environmentally friendly.
Implementation Method 1
polytetrafluoroethylene having a melting point of 35° C. or higher and 320° C. or lower deposited on the carrier
Implementation Method 2
a method for imparting an electric charge to a filter... a method of disposing a filter between electrodes and causing dielectric polarization at the time of ventilation
Implementation Method 3
imparting oil repellency to the filter by lowering surface tension of a fibrous material composing the filter... suppressing spread of mist on the fiber surface and absorption and diffusion of mist
Data Source
AI summary
An electret is disclosed including: a carrier, and polytetrafluoroethylene having a melting point of 35° C. or higher and 320° C. or lower deposited on the carrier, wherein the electret imparts an electrostatic charge to at least one of the carrier and the polytetrafluoroethylene, and has two or more melting point peaks in simultaneous thermogravimetry and differential thermal analysis. An electret filter is disclosed which preferably is used for a filter which requires durability to tobacco smoke. An electret filter is also disclosed having a fluorine-containing component deposited on a fiber surface, wherein an initial QF value is 0.5 mmAq−1 or more in collection efficiency of particles having a particle diameter of 0.3 to 0.5 μm at a wind speed of 5 cm/s, and a filter deterioration rate by tobacco smoke loading is −8/(g/m2) or more.