Porous PTFE Membrane Composite with Graded Pore Structure
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Solution Overview
Problem
Conventional porous PTFE membranes with small pore diameters struggle to achieve high porosity and are prone to clogging when used as filters, as they are difficult to produce with both small pore diameters and high porosity, leading to reduced filtration efficiency and rapid clogging due to varying particle sizes in the treatment liquid.
Innovation Solution
A process involving the stacking and bonding of nonporous PTFE membranes with different heat of fusion values, followed by stretching, to create a porous membrane with a gradual pore diameter distribution, which reduces pore diameter differences between layers and increases porosity, allowing for a filter with a larger upstream pore diameter to mitigate clogging and enhance filtration efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a porous PTFE membrane is produced by stretching a PTFE membrane with small pore diameter, then the pore diameter is reduced for better filtration of microscopic particles, but the porosity decreases and the membrane becomes prone to clogging
Solution Approach 1:
The membrane is divided into multiple layers with different pore diameters, where the upstream layer has larger pores and the downstream layer has smaller pores. This segmentation allows the upstream layer to capture larger particles while maintaining high porosity, and the downstream layer to filter microscopic particles, thereby resolving the contradiction between small pore diameter and high porosity
Solution Approach 2:
Different regions of the membrane (upstream and downstream layers) are given different pore diameter characteristics. The upstream layer is designed with larger pores for high porosity and reduced clogging, while the downstream layer has smaller pores for microscopic particle filtration, allowing each region to perform its specific function optimally
2Productivity
If the porosity is increased to achieve high treating rate, then the filtration efficiency improves, but the pore diameter increases which reduces the ability to filter microscopic particles
Solution Approach 1:
The membrane is segmented into multiple layers with different porosity and pore diameter characteristics. The upstream layer has higher porosity for high treating rate, while the downstream layer has controlled smaller pore diameter for microscopic particle filtration, allowing both high productivity and precise pore diameter control to coexist
Solution Approach 2:
The problem is solved by transitioning from a single-layer membrane to a multi-layer structure, adding the dimension of layering. This allows different layers to have different porosity and pore diameter characteristics, enabling the system to achieve both high treating rate and precise pore diameter control simultaneously
3Device complexity
If a single-layer porous membrane is used, then the structure is simple, but the membrane develops clogging rapidly due to varying particle sizes in the treatment liquid
Solution Approach 1:
The single-layer membrane is segmented into multiple layers with different pore diameters. The upstream layer with larger pores captures larger particles, preventing them from clogging the downstream layer with smaller pores. This segmentation significantly reduces clogging while maintaining relatively simple structure
Solution Approach 2:
The upstream layer with larger pores performs preliminary filtration of larger particles before the liquid reaches the downstream layer with smaller pores. This preliminary action prevents larger particles from entering and clogging the finer pores, thereby enhancing clogging resistance
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 porous PTFE membrane composite exhibits high porosity, reduced clogging, and improved mechanical strength, enabling efficient filtration with a higher treating rate and reduced Gurley second, making it suitable for filtering microscopic particles.
Implementation Method 1
heating each membrane to its melting point or above to bake it
Implementation Method 2
heating each membrane to its melting point or above to bake it
Implementation Method 3
stretching the bonded membranes to form the porous resin membrane
Implementation Method 4
a porous PTFE membrane having through pores having a microscopic and uniform diameter of 50 nm or less, can achieve superior efficiency in filtering treatment
Data Source
Figure 1(a)~1(b)
Figure 2(a)~2(b)
Figure 3(a)~3(b)
AI summary
The invention offers a porous polytetrafluoroethylene membrane, which is a porous resin membrane produced by the following steps: preparing multiple types of polytetrafluoroethylene each having a different quantity of heat of fusion; using each of the multiple types of polytetrafluoroethylene to form a membrane composed of a fluororesin consisting mainly of polytetrafluoroethylene; heating each membrane to its melting point or above to bake it, so that multiple types of nonporous resin membranes are produced; stacking the multiple types of nonporous resin membranes in the order of the magnitude of the quantity of heat of fusion of the polytetrafluoroethylene used to produce each of the nonporous resin membranes; bonding the stacked membranes with each other; and stretching the bonded membranes to form the porous resin membrane. The porous polytetrafluoroethylene membrane has a mean flow pore diameter of 50 nm or less. It has through pores having a microscopic and uniform diameter, and when used as a filter, it has excellent efficiency in filtering treatment and is less likely to develop clogging. The invention also offers a composite of the membrane, a process of producing the composite, and a separation membrane element incorporating the composite as a filtering membrane.