Two-Layer Nonwoven Fabric for Separation Membranes and Bleed-Through Control
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Solution Overview
Problem
Existing nonwoven fabrics for separation membranes face challenges in achieving both bleed-through prevention and high water permeability, with issues such as densification affecting phase separation, resin penetration rates, and pinhole formation, leading to reduced permeation flux and increased costs.
Innovation Solution
A nonwoven fabric substrate composed of multiple layers, where the surface layer has a large Laplace force and smaller pore diameter, and the back surface layer has a small Laplace force and larger pore diameter, using fine and thick fibers to control resin penetration and prevent bleed-through while enhancing water permeability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the nonwoven fabric is densified to prevent bleed-through of resin solution, then the resin solution penetration is reduced, but the water permeability of the separation membrane decreases
Solution Approach 1:
The nonwoven fabric is divided into multiple layers with different fiber compositions and pore structures. The surface layer contains fine fibers to prevent bleed-through, while the base layer contains thick fibers to maintain water permeability, resolving the contradiction between reliability and productivity
Solution Approach 2:
Different regions of the nonwoven fabric have different properties: the surface layer has high density and small pore diameter for bleed-through prevention, while the base layer has low density and large pore diameter for water permeability, allowing each region to optimize its function
2Weight of moving object
If the nonwoven fabric is thinned to reduce separation membrane weight, then the membrane area per unit weight increases, but the tensile strength decreases
Solution Approach 1:
The nonwoven fabric uses a composite structure combining fine fibers and thick fibers in different layers. The thick fibers in the base layer provide high tensile strength, allowing the overall fabric to be thinner while maintaining structural integrity and meeting strength requirements
3Reliability
If a two-layer structure with thick fibers on surface is used to prevent bleed-through, then the resin solution penetration speed is reduced, but the manufacturing complexity increases
Solution Approach 1:
Instead of placing thick fibers on the surface layer as in conventional designs, this invention inverts the arrangement by placing fine fibers on the surface and thick fibers in the base layer, achieving bleed-through prevention through a different mechanism that simplifies the overall structure
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 substrate achieves both bleed-through prevention and high water permeability, allowing for efficient production of separation membranes with improved tensile strength and reduced resin usage, thereby lowering production costs and enhancing liquid permeation performance.
Implementation Method 1
when the nonwoven fabric substrate is impregnated with the coating solution for membrane formation, the surface layer has a large Laplace force
Implementation Method 2
high water permeability of a separation membrane to be produced
Data Source
Figure 1~2
Figure 3(A)~4(B)
Figure 5~6
AI summary
The present invention provides a nonwoven fabric for a separation membrane which can prevent a bleed-through of a resin solution used for coating in a step of producing the separation membrane, can produce a separation membrane having a large permeate flux of a liquid by non-solvent induced phase separation, has high adhesiveness between a coating membrane and the nonwoven fabric, and can make the coating membrane thin, and a method of producing the same. In an exemplary aspect of the present invention, a two-layer nonwoven fabric 10 for a separation membrane is configured to have a surface layer 11 and a back surface layer 12, a coating surface of a coating solution during membrane formation is a surface 11a of the surface layer 11, and, when the nonwoven fabric 10 is impregnated with the coating solution for membrane formation, the surface layer 11 has a large Laplace force and the back surface layer 12 has a small Laplace force. The nonwoven fabric 10 for a separation membrane can be produced by sequentially papermaking a fiber dispersion liquid DS1 for a surface layer including one or more kinds of fine fibers FF having a small fiber diameter and one or more kinds of thick fibers TF having a fiber diameter larger than that of the fine fibers FF and a fiber dispersion liquid DS2 for a back surface layer consisting of the thick fibers TF using a wet papermaking method.