Thick ePTFE Membrane via Dual-Resin Blending
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Solution Overview
Problem
Existing expanded polytetrafluoroethylene (ePTFE) membranes are typically limited to a thickness of 25 micrometers, which is insufficient for certain applications requiring increased filtration efficiency, and achieving thicker membranes through layering or lamination is cumbersome.
Innovation Solution
A method involving mixing two PTFE resins with different fibril and node characteristics, followed by extrusion, calendering, and transverse stretching to produce a single-layer ePTFE membrane with a thickness of at least 100 micrometers, maintaining air permeability while enhancing durability and filtration efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ePTFE membrane thickness is increased to improve filtration efficiency, then filtration efficiency improves, but manufacturing complexity increases due to required lamination steps
Solution Approach 1:
The patent combines multiple PTFE resin functions into a single membrane layer by blending resins with different fibril-forming characteristics during extrusion. This merging approach eliminates the need for separate lamination steps while achieving both thick membrane structure and desired filtration performance in one manufacturing process.
Solution Approach 2:
The patent transitions from a two-dimensional layering approach (stacking multiple thin films) to a three-dimensional single-layer structure by controlling resin blend morphology during extrusion. The blended resins self-organize into a thick membrane with appropriate node-fibril architecture without requiring multiple lamination steps.
2Strength
If ePTFE membrane thickness is increased to improve durability, then durability improves, but manufacturing complexity increases due to required lamination steps
Solution Approach 1:
The patent merges the functions of multiple thin films into a single thick membrane by blending PTFE resins with different fibril-forming characteristics. This single-layer approach achieves the desired durability through optimized internal structure rather than through stacking multiple layers, eliminating lamination complexity.
Solution Approach 2:
The patent uses a composite blend of PTFE resins with different properties (one forming more/longer fibrils, another forming thicker nodes) to create a single membrane that achieves both thickness and durability. The composite resin blend self-organizes during extrusion to provide the mechanical strength equivalent to multiple laminated layers.
3Device complexity
If single-layer thick ePTFE membrane is produced to simplify manufacturing, then manufacturing complexity decreases, but achieving appropriate node and fibril structure becomes difficult
Solution Approach 1:
The patent applies local quality by using different PTFE resins in specific proportions within the blend, where each resin contributes specific local characteristics (one provides more/longer fibrils, another provides thicker nodes). This localized functional differentiation within the single layer achieves the desired overall structure without complex manufacturing.
Solution Approach 2:
The patent controls the node-fibril structure by changing the parameters of the resin blend composition and extrusion conditions. By adjusting resin ratios, particle sizes, and processing parameters, the patent achieves precise control over the internal morphology of the single thick membrane, producing appropriate node and fibril structures.
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 thicker ePTFE membrane exhibits improved durability, filtration efficiency, and increased peel strength, with hydrostatic Mullen strength, while maintaining air and water permeability comparable to thinner membranes.
Implementation Method 1
extruding the preform into a tape
Implementation Method 2
stretching the calendered tape in the transverse direction to form a porous membrane
Implementation Method 3
passing the tape through a plurality of opposing calender rolls to form a calendered tape having a thickness
Data Source
AI summary
A method of making a porous membrane includes, in an exemplary embodiment, mixing together a first fine powder PTFE resin and a second fine powder PTFE resin to form a PTFE resin mixture. The first PTFE resin having a characteristic of forming more and longer fibrils than fibrils formed from the second PTFE resin. The second PTFE resin having a characteristic of forming thicker nodes than nodes formed from the first PTFE resin. The method also includes forming a preform from the PTFE resin mixture, extruding the preform into a tape, passing the tape through a plurality of opposing calender rolls to form a calendered tape having a thickness of about 380 μm to about 1200 μm, and stretching the calendered tape in the transverse direction to form a porous membrane having a plurality of nodes and fibrils and having a thickness of at least about 100 μm.