Microporous Modified-PTFE Membrane Uniform Pore Diameter
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Solution Overview
Problem
Conventional methods for producing microporous PTFE membranes struggle to achieve uniform pore diameters smaller than 30 nm, leading to broadened pore-diameter distributions and reduced filtering efficiency, especially for microscopic particles, and require large-scale apparatus due to low flow rates.
Innovation Solution
A microporous modified-PTFE membrane is produced by copolymerizing PTFE with hexafluoropropylene or perfluoroalkyl ether, followed by heating and stretching, which results in a membrane with a mean flow pore diameter of 30 nm or less and a narrow pore-diameter distribution, achieved through specific copolymerization ratios and annealing processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If PTFE is stretched in a semibaked state to produce a porous membrane, then the membrane can be formed with porosity, but the pore diameter becomes non-uniform and gaps exist between particles
Solution Approach 1:
The patent changes the physical state parameter of PTFE from semibaked to fully baked (melted) state during stretching. By heating to the melting point or higher before stretching, the PTFE particles fuse completely, eliminating gaps between particles and achieving uniform pore diameters through controlled deformation of the melted structure.
Solution Approach 2:
The patent utilizes the phase transition of PTFE from solid particles to melted state, then to porous solid upon cooling. The sequence involves: (1) heating PTFE particles to melting point to form a nonporous melted membrane, (2) stretching the melted membrane to create uniform pores, (3) cooling to solidify the porous structure. This phase transition approach ensures complete particle fusion and uniform pore formation.
2Manufacturing precision
If the pore diameter is reduced to filter microscopic particles, then filtering efficiency improves, but the pore-diameter distribution broadens and flow rate decreases
Solution Approach 1:
The patent controls the stretching parameters (temperature, stretching ratio, stretching speed) to achieve uniform pore diameters of 30 nm or less. By maintaining PTFE in a fully melted state during stretching and using controlled deformation, the pore-diameter distribution is narrowed while keeping pore sizes small enough for high-efficiency filtration of microscopic particles.
Solution Approach 2:
The patent employs a specific phase transition sequence: heating PTFE to melting point to form a homogeneous nonporous membrane, stretching while in the melted state to create uniform micro-pores, then cooling to solidify. This process ensures that even at 30 nm or smaller pore diameters, the pores remain uniform in size, preventing broadening of the pore-diameter distribution and maintaining both high filtration efficiency and adequate flow rate.
3Manufacturing precision
If a thin membrane is used to improve filtration efficiency, then the membrane can remove microscopic particles effectively, but the membrane becomes difficult to handle and may have defects
Solution Approach 1:
The patent produces thin nonporous fluororesin membranes by casting and baking to achieve uniform thickness without defects. The key is heating the cast membrane to the melting point or higher to eliminate voids and cracks, then cooling to solidify. This creates a defect-free thin membrane that can be handled more easily while maintaining high filtration efficiency when subsequently stretched to create uniform pores.
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 resulting membrane exhibits high efficiency in removing microscopic particles with a narrow pore-diameter distribution, maintaining high porosity and mechanical strength, and can be easily handled when combined with a porous supporter for enhanced filtration performance.
Implementation Method 1
heating to the melting point of the copolymer or above to perform baking
Implementation Method 2
subsequent to the above process, by stretching the thin nonporous fluororesin membrane to render it porous
Implementation Method 3
the dispersion medium is evaporated, and the fluororesin powder is baked to melt it completely
Data Source
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AI summary
The invention offers a microporous modified-polytetrafluoroethylene membrane that is a microporous membrane having a significantly small pore diameter and narrow pore-diameter distribution and that can remove microscopic foreign particles at high efficiency when used as a filtration membrane. A microporous modified-polytetrafluoroethylene membrane that is a microporous membrane produced by the steps of producing a copolymer of hexafluoropropylene or perfluoroalkyl ether and tetrafluoroethylene having the number of moles not less than 50 times that of the hexafluoropropylene or perfluoroalkyl ether, forming the copolymer into the shape of a membrane, heating the membrane to the melting point of the copolymer or above to bake the copolymer, cooling the obtained baked product, and stretching the baked product and that has a mean flow pore diameter of 30 nm or less; a porous-modified-polytetrafluoroethylene-membrane composite that incorporates the microporous membrane and a production process of the composite; and a separation membrane element incorporating the porous-modified-polytetrafluoroethylene-membrane composite.