JP-2026075596-A - Separators for nonwoven fabrics and electrochemical elements, and membrane supports.

Abstract

[Problem] To provide a highly versatile nonwoven fabric that is excellent in heat resistance and mechanical strength and can be applied to applications requiring heat resistance, or a nonwoven fabric that is excellent in heat resistance, mechanical strength and permeability. [Solution] The nonwoven fabric of the present invention contains core-sheath type composite fibers having a polyethylene component as a sheath component and a polymethylpentene component as a core component, and the polyethylene component, which is the sheath component of the core-sheath type composite fiber, is fused to the nonwoven fabric, wherein the polymethylpentene component accounts for 30% or more by volume of the total nonwoven fabric constituent fibers, and the polyethylene component accounts for 30% or more by volume of the total nonwoven fabric constituent fibers. In particular, the thickness of the nonwoven fabric is 100 μm or less, and the tensile strength per unit basis weight is 2.0 N/5 cm width or more in a direction, or the ratio (L/D) of the fiber diameter (D, unit: μm) of the core-sheath type composite fiber to the length (L, unit: μm) is 350 or more. [Selection Diagram] Figure 5

Inventors

• 川野 明彦
• 澤田 峻一
• 村田 修一
• 田中 政尚

Assignees

• 日本バイリーン株式会社

Dates

Publication Date

20260508

Application Date

20250909

Priority Date

20241022

Claims (17)

1. A nonwoven fabric comprising a polymethylpentene component and a polyethylene component, wherein the polyethylene component is fused, characterized in that the polymethylpentene component accounts for 30% or more by volume of the total nonwoven fabric fibers, and the polyethylene component accounts for 30% or more by volume of the total nonwoven fabric fibers.
2. The nonwoven fabric according to claim 1, characterized in that it contains a core-sheath type composite fiber as a nonwoven fabric constituent fiber, wherein the polyethylene component is the sheath component and the polymethylpentene component is the core component.
3. The nonwoven fabric according to claim 2, further characterized by containing ultrafine fibers with a fiber diameter of 4.5 μm or less as nonwoven fabric constituent fibers.
4. The nonwoven fabric according to claim 1, characterized in that it has a tensile strength of 2.5 N/5 cm width or more per unit basis weight in one direction.
5. The nonwoven fabric according to claim 1, characterized in that its porosity is 50 to 80%.
6. The nonwoven fabric according to claim 1, characterized in that the liquid retention rate after pressurization at 5.7 MPa is 5% or more.
7. A separator for electrochemical elements, characterized by comprising any nonwoven fabric described in claims 1 to 6.
8. A nonwoven fabric comprising a polymethylpentene component and a polyethylene component, wherein the polyethylene component is fused, and the polymethylpentene component accounts for 30% or more by volume of the total nonwoven fabric fibers, and the polyethylene component accounts for 30% or more by volume of the total nonwoven fabric fibers, characterized in that the thickness of the nonwoven fabric is 100 μm or less, and the tensile strength per unit basis weight is 2.0 N/5 cm width or more in a direction.
9. The nonwoven fabric according to claim 8, characterized in that it contains a core-sheath type composite fiber as a nonwoven fabric constituent fiber, wherein the polyethylene component is the sheath component and the polymethylpentene component is the core component.
10. The nonwoven fabric according to claim 9, characterized in that the ratio (L/D) of the fiber diameter (D, unit: μm) of the core-sheath type composite fiber to its length (L, unit: μm) is 350 or more.
11. The nonwoven fabric according to claim 8, characterized in that its porosity is 60% or more.
12. The nonwoven fabric according to claim 8, characterized in that its basis weight is 20 g/ m² or less.
13. A nonwoven fabric comprising core-sheath type composite fibers having a polyethylene component as the sheath component and a polymethylpentene component as the core component, wherein the polyethylene component, which is the sheath component of the core-sheath type composite fiber, is fused, and the polymethylpentene component accounts for 30% or more by volume of the total nonwoven fabric constituent fibers, and the polyethylene component accounts for 30% or more by volume of the total nonwoven fabric constituent fibers, characterized in that the thickness of the nonwoven fabric is 100 μm or less, and the ratio of the fiber diameter (D, unit: μm) to the length (L, unit: μm) of the core-sheath type composite fiber (L/D) is 350 or more.
14. The nonwoven fabric according to claim 13, characterized in that it has a direction in which the tensile strength per unit basis weight is 2.0 N/5 cm width or more.
15. The nonwoven fabric according to claim 13, characterized in that its porosity is 60% or more.
16. The nonwoven fabric according to claim 13, characterized in that its basis weight is 20 g/ m² or less.
17. A membrane support characterized by comprising any nonwoven fabric described in claims 8 to 16.

Description

This invention relates to a nonwoven fabric. Because the nonwoven fabric of this invention has excellent heat resistance and mechanical strength, it can be suitably used in applications requiring these properties, such as separators for electrochemical elements, diaphragm supports for batteries, and diaphragm supports for water electrolysis. Furthermore, the nonwoven fabric of the present invention not only has excellent heat resistance, but also excellent mechanical strength despite its thinness, and excellent permeability. Therefore, it can be suitably used in applications requiring these properties, such as diaphragm supports for batteries, diaphragm supports for water electrolysis, and separators for electrochemical elements. Unlike woven or knitted fabrics, nonwoven fabrics can have randomly oriented fibers, allowing them to possess various properties such as dust removal, liquid retention, wipeability, opacity, flexibility, separation, isolation, and strength-enhancing capabilities, making them suitable for a wide range of applications. However, depending on the fibers constituting the nonwoven fabric, insufficient heat resistance or mechanical strength may make them unsuitable for applications requiring heat resistance. For example, nonwoven fabrics are used as separators to isolate electrodes in nickel-metal hydride batteries, taking advantage of their liquid-retaining and insulating properties. In recent years, nickel-metal hydride batteries have increasingly been installed in automobiles as power sources and as backup power sources for systems such as T-BOX, GPS, and T-CONNECT. However, due to insufficient heat resistance or mechanical strength of nonwoven fabrics, it has sometimes been impossible to provide nickel-metal hydride batteries that are reliable over long periods. To address these heat resistance challenges, a nonwoven fabric (separator) utilizing polyolefin-based split-type composite fibers, a combination of polymethylpentene (a highly heat-resistant polyolefin resin) and polypropylene, has been proposed (Patent Document 1). However, even nonwoven fabrics utilizing polyolefin-based splittable fibers composed of a combination of polymethylpentene and polypropylene did not possess sufficient heat resistance and mechanical strength. These issues with heat resistance and mechanical strength are not limited to separators in nickel-metal hydride batteries and the like, but also arise when nonwoven fabrics are used as diaphragm supports for batteries or water electrolysis. For example, nonwoven fabrics are used as a support for the diaphragm that isolates the electrodes of nickel-zinc batteries, taking advantage of their strength-enhancing properties. Nickel-zinc batteries are prone to short circuits due to dendrites, so resin films are often used as diaphragms. However, because resin films lack sufficient mechanical strength, nonwoven fabrics are used as the support (Patent Document 2). Such diaphragms made of resin films are formed by filling the voids in the nonwoven fabric with a resin solution and then removing the solvent from the resin solution to form a film. However, conventionally used nonwoven fabrics, which are composed of polyolefin resins such as polyethylene and polypropylene, tend to shrink easily due to the heat generated during volatilization and use, resulting in poor heat resistance and an inability to provide sufficient strength as a support. On the other hand, while polyphenylene sulfide resin is known as a nonwoven fabric resin with excellent heat resistance, constructing a nonwoven fabric support using polyphenylene sulfide fibers requires adhesive fibers to fix the polyphenylene sulfide fibers. Adhesive fibers made of polyolefin fibers have poor heat resistance, and plasticizing and fixing undrawn polyphenylene sulfide fibers, which have excellent heat resistance, requires heating and pressurizing. This results in fewer voids in the support and poor ion permeability. To address these heat resistance challenges, a nonwoven fabric (separator) utilizing polyolefin-based split-type composite fibers, a combination of polymethylpentene (a highly heat-resistant polyolefin resin) and polypropylene, has been proposed (Patent Document 1). However, even nonwoven fabrics utilizing polyolefin-based splittable fibers composed of a combination of polymethylpentene and polypropylene did not possess sufficient heat resistance, mechanical strength, and permeability (ion permeability). These issues regarding heat resistance, mechanical strength, and permeability were not limited to the battery diaphragm supports mentioned above, but also occurred when nonwoven fabrics were used as diaphragm supports for electrolysis or as separators for electrochemical elements. Japanese Patent Publication No. 2021-161563Japanese Patent Publication No. 2019-179678 schematic cross-section of a splittable fiber that can be used in the production of the nonwoven fabric of the present invention.A schematic