Dual PTFE Membrane Air Filter for Oil Mist Clogging

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Solution Overview

Problem

Air filter media for clean rooms and medical/pharmaceutical applications face clogging issues due to both dust and oil mist, leading to increased pressure drop, and existing solutions either fail to resist oil mist clogging or result in high manufacturing costs and pleating difficulties.

Innovation Solution

An air filter medium comprising a first porous PTFE membrane with a specific surface area of 0.5 m2/g or less and a thickness of 4 to 40 μm, stacked with a second porous PTFE membrane, where the air flow passes through both membranes, effectively collecting large particles of dust and oil mist while minimizing pressure drop.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a porous PTFE membrane is used to filter air dust, then dust collection performance is improved, but the membrane collects dust only on its surface and becomes clogged, causing increased pressure drop

Engineering Contradiction:

Improvedust collection performanceVSAvoidclogging and pressure drop increase

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The single porous PTFE membrane is segmented into two distinct porous PTFE membranes with different pore sizes arranged in sequence. The first membrane (upstream) has larger average pore diameter to capture large dust particles, while the second membrane (downstream) has smaller average pore diameter to capture finer particles. This segmentation prevents clogging of the fine-pore membrane by large particles, maintaining reliable dust collection performance without excessive pressure drop.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first porous PTFE membrane with larger pores performs preliminary filtration by collecting large-diameter dust particles before the air reaches the second membrane with smaller pores. This preliminary action protects the second membrane from clogging by large particles, allowing it to maintain its dust collection efficiency over extended periods with minimal pressure drop increase.

Inventive Principle:

Principle #10Preliminary action

2Duration of action of stationary object

If a prefilter layer is thickened to prevent clogging of the porous PTFE membrane, then service life is improved, but manufacturing cost increases and pleating becomes difficult

Engineering Contradiction:

Improveservice lifeVSAvoidmanufacturing cost and pleating

Core Design Contradiction:

Duration of action of stationary objectVSEase of manufacture

Solution Approach 1:

Instead of increasing the thickness of a single prefilter layer, the invention changes the parameter of pore diameter by using two porous PTFE membranes with different average pore diameters. The first membrane has larger pores for preliminary filtration, while the second has smaller pores for fine filtration. This parameter change allows effective clogging prevention without requiring excessive thickness, thereby reducing manufacturing cost and maintaining pleating feasibility.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If existing air filter media are used, then dust filtration is achieved, but they are not resistant to clogging from oil mist

Engineering Contradiction:

Improvedust filtrationVSAvoidoil mist clogging

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The invention uses a composite structure of two porous PTFE membranes with different pore size characteristics. PTFE material itself has oil resistance properties, and by combining two membranes with different pore diameters, the system achieves both dust filtration and oil mist resistance. The larger-pore first membrane prevents oil mist accumulation that would clog the smaller-pore second membrane, maintaining reliable filtration performance against both dust and oil mist.

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

The solution provides resistance to clogging from both dust and oil mist, reducing structural pressure drop and extending the service life of the air filter medium while maintaining manufacturability and pleating feasibility.

Implementation Method 1

a first porous PTFE membrane and a second porous PTFE membrane, wherein the air filter medium has a first main surface and a second main surface, the first porous PTFE membrane and the second porous PTFE membrane are arranged so that an air flow moving from the first main surface to the second main surface passes through the first porous PTFE membrane and subsequently through the second porous PTFE membrane

Methodology Applied

Scientific EffectPhysical filtration: Filter (physical)

Data Source

PatentUS11213782B2Air filter medium, air filter pack, and air filter unit

Publication Date: 2022.01.04 NITTO DENKO CORP

AI summary

An air filter medium includes a first porous PTFE membrane and a second porous PTFE membrane. The air filter medium (10) has a first main surface and a second main surface, and the first porous PTFE membrane and the second porous PTFE membrane are arranged so that an air flow moving from the first main surface to the second main surface passes through the first porous PTFE membrane and subsequently through the second porous PTFE membrane. A thickness of the first porous PTFE membrane is in the range of 4 to 40 μm and a specific surface area of the first porous PTFE membrane is 0.5 m2/g or less.