Laminated PTFE Membrane for High Heat Resistance and Air Permeability
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Solution Overview
Problem
Conventional water-proof air permeable filters with porous polytetrafluoroethylene (PTFE) membranes face challenges in achieving high heat resistance and maintaining air permeability and water pressure resistance when used in applications like automobile components and sensors, as increasing membrane thickness lowers air permeability and stretching factors compromise water pressure resistance.
Innovation Solution
A method involving the production of a laminated PTFE membrane by stretching a first porous body uniaxially and a second porous body biaxially, then integrating them while heating above the melting point of PTFE, using PTFE sheets with specific gravities and molecular weights to achieve a balance between thickness, air permeability, and water pressure resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the thickness of the porous PTFE membrane is increased to ensure strength and heat resistance, then the membrane can be used directly without support material, but the air permeability of the membrane is lowered
Solution Approach 1:
The membrane is divided into multiple layers with different functions: a thick first porous body (50-200 μm) made from high molecular weight PTFE for strength and heat resistance, and a thin second porous body (10-50 μm) made from low molecular weight PTFE for air permeability. This segmentation allows each layer to optimize its thickness for its specific function while working together as a unified membrane structure.
2Productivity
If the stretching factor of the sheet is increased to increase air permeability, then the membrane becomes more porous, but the water pressure resistance is lowered
Solution Approach 1:
Different regions of the membrane structure have different porosity characteristics: the first porous body has controlled porosity (30-70%) optimized for strength and water resistance, while the second porous body has higher porosity (50-80%) optimized for air permeability. This local differentiation of quality allows the membrane to achieve high air permeability without compromising water pressure resistance.
3Ease of manufacture
If a support material such as nonwoven fabric is used to enable welding to housing, then the filter can be attached to housing, but the heat resistance of the filter is reduced
Solution Approach 1:
The invention replaces the disposable support material (nonwoven fabric with limited heat resistance) with a self-sufficient thick PTFE membrane structure that inherently provides both mechanical strength and heat resistance. The membrane itself becomes the structural component that can be directly welded to housing, eliminating the need for separate support materials with poor thermal properties.
4Productivity
If PTFE with low molecular weight is used to increase air permeability, then the membrane becomes more breathable, but the water pressure resistance and structural integrity are reduced
Solution Approach 1:
The membrane is constructed as a composite of two different PTFE materials: high molecular weight PTFE (standard specific gravity 2.130-2.160) for the first porous body providing structural integrity and water resistance, and low molecular weight PTFE (standard specific gravity 2.165-2.200) for the second porous body providing high air permeability. The composite structure synergistically combines the advantages of both 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 method results in a porous PTFE membrane with a thickness of 70 µm to 400 µm, air permeability of 2 to 40 seconds/100mL, and water pressure resistance of 40 kPa to 300 kPa, effectively addressing the need for high heat resistance and air permeability while preventing water entry.
Implementation Method 1
stretching, in a uniaxial direction, a sheet made of PTFE having a standard specific gravity of 2.155 or more
Implementation Method 2
stretching the stacked films at least uniaxially at a temperature higher than Tm
Implementation Method 3
heating the laminate at a temperature equal to or higher than a melting point of PTFE
Implementation Method 4
integrating the first porous body with the second porous body by stretching a laminate of the first porous body and the second porous body in the same direction as the uniaxial direction while heating the laminate at a temperature equal to or higher than a melting point of PTFE
Implementation Method 5
a porous PTFE membrane with a satisfactory air permeability and high water pressure resistance
Data Source
Figure 1A~1C
Figure 2A~2B
AI summary
First, a first porous body is manufactured by stretching, in a uniaxial direction, a sheet made of polytetrafluoroethylene having a standard specific gravity of 2.155 or more, and a second porous body is manufactured by stretching, in biaxial directions, a sheet made of polytetrafluoroethylene. Next, the first porous body is integrated with the second porous body by stretching a laminate of the first porous body and the second porous body in the same direction as the uniaxial direction while heating the laminate at a temperature equal to or higher than a melting point of polytetrafluoroethylene. Thus, a porous polytetrafluoroethylene membrane is produced.