阅读说明：本技术 拒油性片材的制造方法和气体传感器 (Method for producing oil-repellent sheet, and gas sensor ) 是由 福永笃史 林文弘 于 2018-10-25 设计创作，主要内容包括：根据本公开的一个实施方式的拒油性片材的制造方法包括在多孔片上涂布拒油层形成用组合物的步骤,所述拒油层形成用组合物含有溶剂和分散在所述溶剂中的无定形含氟树脂；和在所述涂布步骤之后对所述多孔片进行型锻的步骤,其中所述多孔片具有主要由聚四氟乙烯构成的纤维状骨架,并且所述拒油性片材的制造方法在所述型锻步骤之前或之后还包括对涂布有所述拒油层形成用组合物的所述多孔片进行加热的热处理步骤。(A method for manufacturing an oil-repellent sheet according to one embodiment of the present disclosure includes a step of coating a porous sheet with an oil-repellent layer-forming composition containing a solvent and an amorphous fluorine-containing resin dispersed in the solvent; and a step of swaging the porous sheet after the coating step, wherein the porous sheet has a fibrous skeleton mainly composed of polytetrafluoroethylene, and the method for producing the oil-repellent sheet further includes a heat treatment step of heating the porous sheet coated with the oil-repellent layer-forming composition before or after the swaging step.)

1. A method for producing an oil-repellent sheet, comprising:

a step of coating a porous sheet with an oil-repellent layer-forming composition containing a solvent and an amorphous fluorine-containing resin dispersed in the solvent; and

a step of swaging the porous sheet after the coating step, wherein,

the porous sheet has a fibrous skeleton mainly composed of polytetrafluoroethylene, and

the method for producing an oil-repellent sheet further comprises a heat treatment step of heating the porous sheet coated with the oil-repellent layer-forming composition before or after the swaging step.

2. The method for producing an oil repellent sheet according to claim 1, wherein the heat treatment step is performed before the swaging step.

3. The method for producing an oil-repellent sheet according to claim 2, wherein the heating temperature in the heat treatment step is more than 250 ℃ and less than 340 ℃, and the heat treatment time is 5 minutes or more.

4. The method for producing an oil-repellent sheet according to claim 3, wherein the heating temperature is 300 ℃ or higher and 335 ℃ or lower.

5. The method for producing an oil-repellent sheet according to any one of claims 1 to 4, wherein in the coating step, the oil-repellent layer-forming composition is sprayed.

6. The method for producing an oil-repellent sheet according to claim 5, wherein the coating amount of the amorphous fluorine-containing resin is 10 μ g/cm in terms of solid content per unit area of the porous sheet²Above and 75. mu.g/cm²The following.

7. The method for producing an oil-repellent sheet according to any one of claims 1 to 6, wherein the amorphous fluorine-containing resin is a tetrafluoroethylene-perfluorodioxole copolymer, a tetrafluoroethylene-perfluoromethyl vinyl ether copolymer, a tetrafluoroethylene-perfluoroethyl vinyl ether copolymer, a tetrafluoroethylene-perfluoropropyl vinyl ether copolymer, a perfluoro (4-ethyleneoxy-1-butene) cyclopolymerized polymer, or a combination thereof.

8. The method for manufacturing an oil-repellent sheet according to any one of claims 1 to 7, wherein the oil-repellent sheet is an air filter.

9. A gas sensor comprising the oil-repellent sheet obtained by the method for producing an oil-repellent sheet according to any one of claims 1 to 8.

Technical Field

The present disclosure herein relates to a method for manufacturing an oil-repellent sheet and a gas sensor.

This application is based on and claims priority from japanese patent application 2018-2896 filed on 11/1/2018, and the entire contents of which are hereby incorporated by reference.

Background

The gas sensor is used for detecting the oxygen concentration and the like in the gas discharged from the automobile. The gas sensor has a gas inlet for introducing external gas. The gas inlet is provided with a porous filter having gas permeability. The porous filter is fixed by swaging to a cylindrical body communicating with a gas inlet for introducing gas into the sensor device. In addition to air permeability, the porous filter is also required to have high heat resistance to withstand the exhaust gas of an automobile. In view of this, a porous sheet mainly containing polytetrafluoroethylene is currently used as the porous filter (see japanese patent application publication No. 2007-147586).

Disclosure of Invention

A method for manufacturing an oil-repellent sheet according to one embodiment of the present disclosure includes a step of coating a porous sheet with an oil-repellent layer-forming composition containing a solvent and an amorphous fluorine-containing resin dispersed in the solvent; and a step of swaging the porous sheet after the coating step, wherein the porous sheet has a fibrous skeleton mainly composed of polytetrafluoroethylene, and the method for producing the oil-repellent sheet further includes a heat treatment step of heating the porous sheet coated with the oil-repellent layer-forming composition before or after the swaging step.

Further, a gas sensor according to one embodiment of the present disclosure includes an oil-repellent sheet manufactured by the method of manufacturing an oil-repellent sheet.

Drawings

Fig. 1 is a flowchart illustrating a method of manufacturing an oil repellent sheet according to one embodiment of the present disclosure.

Fig. 2 is a schematic view illustrating a gas sensor according to an embodiment of the present disclosure.

Fig. 3 is an enlarged cross-sectional view taken along line a-a of the gas inlet of the gas sensor shown in fig. 2.

Fig. 4 is an enlarged cross-sectional view taken along line B-B of the gas inlet of the gas sensor shown in fig. 2.

Fig. 5 is a partially enlarged sectional view taken along an axial direction of a gas inlet of the gas sensor shown in fig. 2.

Detailed Description

[ problem to be solved by the present disclosure ]

The conventional porous filter disclosed in the above publication has a high risk of a reduction in air permeability because pores may be clogged due to adhesion of oil used for repair of automobiles and the like during continuous use thereof.

The present disclosure is provided based on the above-described circumstances, and aims to provide a gas sensor and a method for manufacturing an oil-repellent sheet that can maintain high gas permeability and oil-repellent performance.

[ advantageous effects of the present disclosure ]

The method for producing an oil-repellent sheet according to the present disclosure is used for producing an oil-repellent sheet maintaining high air permeability and oil-repellent performance. Further, the gas sensor according to the present disclosure maintains high gas permeability and oil repellency.

[ description of embodiments of the present disclosure ]

Embodiments of the present disclosure will be listed and explained first.

A method for producing an oil-repellent sheet according to one embodiment of the present disclosure includes a step of coating a porous sheet with a composition for forming an oil-repellent layer containing a solvent and an amorphous fluorine-containing resin dispersed in the solvent (hereinafter referred to as a coating step); and a step of swaging the porous sheet after the coating step (hereinafter referred to as a swaging step), wherein the porous sheet has a fibrous skeleton mainly composed of polytetrafluoroethylene, the method for producing the oil-repellent sheet further includes a heat treatment step of heating the porous sheet coated with the oil-repellent layer-forming composition before or after the swaging step.

The method for producing an oil-repellent sheet comprises applying an oil-repellent layer-forming composition containing a solvent and an amorphous fluorine-containing resin dispersed in the solvent onto a porous sheet having a fibrous skeleton mainly composed of polytetrafluoroethylene, thereby providing an oil-repellent sheet having excellent air permeability and excellent oil-repellent performance. The method for producing an oil-repellent sheet has a heat treatment step of heating the porous sheet coated with the oil-repellent layer-forming composition before or after the swaging step, thereby reducing the possibility of occurrence of reduction in air permeability and oil-repellent performance after swaging. This enables to maintain high air permeability and high oil-repellent performance.

In the method for producing an oil-repellent sheet, the heat treatment step is preferably performed before the swaging step. As described above, provision of performing the heat treatment step before the swaging step more easily reduces the decrease in oil repellency caused by swaging.

In the case where the heat treatment step is performed before the swaging step, the heating temperature in the heat treatment step is preferably more than 250 ℃ and less than 340 ℃, and the heat treatment time is preferably 5 minutes or more. The use of both the heating temperature in the heat treatment step in the above range and the heat treatment time of the above lower limit or more makes it possible to easily and reliably reduce the decrease in oil repellency caused by swaging.

In the case where the heat treatment step is performed before the swaging step, the heating temperature is more preferably 300 ℃ or more and 335 ℃ or less. The use of the heating temperature within the above range makes it possible to more easily and reliably reduce the decrease in oil repellency caused by swaging.

In the coating step, the oil repellent layer forming composition may be sprayed. Spraying the oil-repellent layer-forming composition in the coating step enables oil-repellent performance to be selectively improved at a location where oil-repellent performance is required, which enables manufacturing costs to be reduced.

The coating amount of the amorphous fluorine-containing resin is preferably 10. mu.g/cm in terms of solid content per unit area of the porous sheet²Above and 75. mu.g/cm²The following. By ensuring that the coating amount of the amorphous fluororesin per unit area of solid content of the porous sheet falls within the above range, clogging of pores in the porous sheet caused by coating of the amorphous fluororesin is reduced while the oil-repellent performance is sufficiently improved, thereby reliably reducing the reduction in air permeability.

The amorphous fluororesin may be a tetrafluoroethylene-perfluorodioxole copolymer, a tetrafluoroethylene-perfluoromethyl vinyl ether copolymer, a tetrafluoroethylene-perfluoroethyl vinyl ether copolymer, a tetrafluoroethylene-perfluoropropyl vinyl ether copolymer, a perfluoro (4-ethyleneoxy-1-butene) cyclopolymer, or a combination thereof. With this arrangement, the oil repellency of the oil repellent sheet obtained is easily and reliably improved.

The oil-repellent sheet may be an air filter. Such a method for producing an oil-repellent sheet is used to easily and reliably produce an air filter that maintains high air permeability and oil-repellent performance.

Further, a gas sensor according to another embodiment of the present disclosure includes an oil-repellent sheet manufactured by the method of manufacturing an oil-repellent sheet.

With the oil-repellent sheet produced by the method for producing an oil-repellent sheet, such a gas sensor can maintain high gas permeability and oil-repellent performance.

In the present disclosure, the term "main component" refers to a component that accounts for the highest content by mass, and may refer to a component having a content of 50 mass% or more, for example. The term "unit area of the porous sheet" refers to a unit area of the porous sheet in a plan view.

[ details of embodiments of the present disclosure ]

Hereinafter, a method of manufacturing an oil repellent sheet and a gas sensor according to one embodiment of the present disclosure will be described with reference to the drawings.

[ method for producing oil-repellent sheet ]

The method for producing an oil-repellent sheet shown in fig. 1 includes a step of coating a composition for forming an oil-repellent layer containing a solvent and an amorphous fluorine-containing resin dispersed in the solvent on a porous sheet, and a step of swaging the porous sheet after the coating step. The method for producing an oil-repellent sheet further comprises a heat treatment step of heating the porous sheet coated with the oil-repellent layer-forming composition before or after the swaging step. In the method for producing an oil-repellent sheet, the porous sheet has a fibrous skeleton mainly composed of Polytetrafluoroethylene (PTFE).

Since the method for producing an oil-repellent sheet uses a porous sheet having a fibrous skeleton composed mainly of PTFE, the produced oil-repellent sheet has excellent air permeability and excellent heat resistance. Specifically, the method for producing an oil-repellent sheet can produce an oil-repellent sheet having high heat resistance for withstanding automobile exhaust gas exceeding 300 ℃. Further, the method for producing an oil-repellent sheet comprises applying an oil-repellent layer-forming composition comprising a solvent and an amorphous fluorine-containing resin dispersed in the solvent onto a porous sheet having a fibrous skeleton mainly composed of PTFE, thereby providing an oil-repellent sheet having excellent oil-repellent properties. The method for producing an oil-repellent sheet has a heat treatment step of heating the porous sheet coated with the oil-repellent layer-forming composition before or after the swaging step, thereby reducing the possibility of a reduction in air permeability, oil-repellent performance, and water pressure resistance occurring after swaging. This enables to maintain high air permeability, high oil-repellent performance and high water pressure resistance.

The method for producing an oil-repellent sheet is suitable for producing an air filter provided in a gas sensor or the like. That is, the oil-repellent sheet obtained by the method for producing an oil-repellent sheet is preferably an air filter. The use of the method for producing an oil-repellent sheet allows an air filter capable of maintaining high air permeability, high oil-repellent performance, and high water pressure resistance to be easily and reliably produced.

(coating step)

In the coating step, an oil-repellent layer-forming composition containing a solvent and an amorphous fluorine-containing resin dispersed in the solvent is coated on a porous sheet. The porous sheet and the amorphous fluorine-containing resin used in the coating step will first be described before the description of the coating step.

(porous sheet)

The porous sheet has a single-layer structure mainly composed of PTFE and is excellent in heat resistance, chemical stability, weather resistance, flame retardancy, strength, and the like. The porous sheet has a fibrous skeleton, and a plurality of pores are formed in a region surrounded by the fibrous skeleton. The fibrous skeleton has a network structure in which particle aggregates (i.e., secondary particles) called nodes are connected by fibrous portions called fibrils. In the porous sheet, the above-mentioned pores are formed by gaps between fibrils or between fibrils and nodes. The porous sheet is not limited to a specific shape, and may be, for example, a flat film shape or a tubular shape.

The lower limit of the PTFE content in the porous sheet is preferably 90 mass%, more preferably 95 mass%, and still more preferably 98 mass%. The use of a PTFE content less than the lower limit poses a risk of insufficient heat resistance of the oil-repellent sheet obtained.

The PTFE may contain polymerized units derived from other copolymerizable monomers within a range not impairing the effects of the present disclosure. For example, the PTFE may contain polymerized units such as perfluoro (alkyl vinyl ether), hexafluoropropylene (perfluoroalkyl) ethylene, chlorotrifluoroethylene, and the like. The upper limit of the content of polymerized units derived from these other copolymerizable monomers is, for example, 3 mol% of the total polymerized units constituting PTFE.

The porous sheet may contain other fluorine-containing resin, other optional components, and the like within a range not to impair the effects of the present disclosure. Examples of such other fluorine-containing resins include tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyvinylidene fluoride (PVDF), tetrafluoroethylene-ethylene copolymer (ETFE), Polychlorotrifluoroethylene (PCTFE), chlorotrifluoroethylene-Ethylene Copolymer (ECTFE), polyvinyl fluoride (PVF), fluoroolefin-vinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, and the like.

The porous sheet has a substantially uniform thickness. The lower limit of the average thickness of the porous sheet may be set according to the use. When the oil-repellent sheet obtained is an air filter for a gas sensor, the lower limit may be, for example, 0.2mm or more and 3.0mm or less.

(oil repellent layer-forming composition)

Examples of the amorphous fluorine-containing resin contained in the oil-repellent layer-forming composition include tetrafluoroethylene-perfluorodioxole copolymer (TFE/PDD), tetrafluoroethylene-perfluoromethyl vinyl ether copolymer (TFE/MFA), tetrafluoroethylene-perfluoroethyl vinyl ether copolymer (TFE/EFA), tetrafluoroethylene-perfluoropropyl vinyl ether copolymer (TFE/PFA), perfluoro (4-ethyleneoxy-1-butene) cyclic polymer (BVE), and combinations of these. The use of these copolymers and/or polymers as the above-mentioned amorphous fluorine-containing resin makes it possible to easily and reliably improve the oil-repellent performance of the oil-repellent sheet obtained by the method for producing an oil-repellent sheet. For example, examples of the above-mentioned TFE/PDD include AF series (manufactured by Mitsui-DuPont fluorine chemical Co., Ltd.), such as "AF 1600" and "AF 2400"; algoflon series (manufactured by solveld specialty polymers japan ltd.), such as "Algoflon (registered trademark) AD" and the like. Examples of the above BVE include "CYTOP (registered trademark)" manufactured by AGC co.

Examples of the solvent contained in the oil-repellent layer-forming composition include, for example, fluorine-based organic solvents such as heptacosyl tributylamine, hexafluorobenzene, perfluorooctane, perfluoroheptane, perfluorotriethylamine, perfluorononane, perfluoropolyether, 2H, 3H-decafluoropentane, 1H, 10H-hexadecafluoro-1, 10-decanediol, 1H-nonafluoro-1-pentanol, 2,3,3, 3-pentafluoro-1-propanol, 2,3,3,4,4, 4-heptafluoro-1-butanol, and methyl heptafluorobutyrate. The solvent preferably has a property of being incompatible with the amorphous fluorine-containing resin. The use of a solvent having the characteristic of being incompatible with the amorphous fluororesin allows stable dispersion of the amorphous fluororesin.

The lower limit of the content of the amorphous fluorine-containing resin is preferably 0.02 parts by mass and more preferably 0.06 parts by mass with respect to 100 parts by mass of the solvent. The upper limit of the content is preferably 2.0 parts by mass and more preferably 0.5 parts by mass. The use of a content less than the lower limit poses a risk that the amorphous fluorine-containing resin does not sufficiently cover the fibrous skeleton of the porous sheet. The use of a content greater than the upper limit poses a risk that the amount of coverage provided by the amorphous fluorine-containing resin is unnecessarily large to cause the amorphous fluorine-containing resin to block the pores of the porous sheet.

The oil repellent layer forming composition may contain the amorphous fluorine-containing resin and the solvent, and other components, within a range not to impair the desired effects of the present disclosure.

(coating method)

The coating method of the oil repellent layer forming composition in the coating step includes, for example, a spray coating method, a spin coating method, a bar coating method, a die coating method, a slit coating method, a roll coating method, a dip coating method, and the like. Among these, the spray coating method is a preferred coating method. That is, in the coating step, the oil repellent layer forming composition may be preferably applied by spraying. The use of the spray coating method as the coating method allows easy selective coating of the portion requiring oil repellency, which selectively improves the oil repellency of the portion requiring oil repellency, and also reduces the manufacturing cost.

The lower limit of the coating amount of the amorphous fluorine-containing resin is preferably 10. mu.g/cm in terms of solid content per unit area of the porous sheet²And more preferably 20. mu.g/cm². Further, the upper limit of the coating amount is preferably 75. mu.g/cm²And more preferably 60. mu.g/cm². The use of a coating amount less than the lower limit poses a risk that the oil repellency of the oil-repellent sheet obtained cannot be sufficiently improved. The use of a coating amount larger than the upper limit causes the coating of the amorphous fluorine-containing resin to cause the pores of the porous sheet to be blocked, resulting in a risk of insufficient air permeability of the oil-repellent sheet obtained. When the amorphous fluororesin is coated only on a part of the porous sheet, the term "coating amount of the amorphous fluororesin per unit area of the solid content of the porous sheet" refers to the coating amount per unit area of the coated part.

(Heat treatment step)

The method for producing the oil-repellent sheet dries the solvent after the coating step (drying step), and then performs the heat treatment step after the drying step. The method for producing an oil-repellent sheet uses the heat treatment step to form an oil-repellent layer on the outer surface of the fibrous skeleton of the porous sheet.

In the heat treatment step, the amorphous fluorine-containing resin coated in the coating step is melted so that the amorphous fluorine-containing resin adheres to the outer surface of the fibrous skeleton of the porous sheet. In the heat treatment step, the amorphous fluorine-containing resin and the fibrous skeleton of the porous sheet diffuse into each other at the interface therebetween, thereby being firmly bonded to each other. With this arrangement, the method of manufacturing the oil-repellent sheet reduces a decrease in oil-repellent performance caused by a swaging step described later. Further, the method for manufacturing an oil-repellent sheet uses the heat treatment step to relax the residual stress of the porous sheet, thereby reducing the decrease in air permeability and water pressure resistance caused by use in a high-temperature environment after the swaging step.

In the method for producing an oil-repellent sheet, the heat treatment step is preferably performed before the swaging step. As described above, provision of performing the heat treatment step before the swaging step more easily reduces the decrease in oil repellency caused by swaging.

The lower limit of the heating temperature in the heat treatment step is preferably more than 250 ℃, and more preferably 280 ℃, and still more preferably 300 ℃. The upper limit of the heating temperature is preferably less than 340 ℃ and more preferably 335 ℃. The use of a heating temperature less than the lower limit poses a risk that the fibrous skeleton of the amorphous fluorine-containing resin and the porous sheet does not sufficiently interdiffuse. Therefore, the adhesiveness between the two cannot be sufficiently increased, resulting in a risk of a reduction in oil-repellent performance due to compression or the like occurring in the swaging step. In contrast, using a heating temperature greater than the upper limit may cause a risk of thermal shrinkage causing the pores of the porous sheet to be clogged.

The lower limit of the heat treatment time in the heat treatment step is preferably 5 minutes and more preferably 10 minutes. The use of a heat treatment time shorter than the lower limit poses a risk that the fibrous skeleton of the amorphous fluorine-containing resin and the porous sheet does not sufficiently interdiffuse. Therefore, the adhesiveness between the two cannot be sufficiently increased, resulting in a risk of a reduction in oil-repellent performance due to compression or the like occurring in the swaging step. The heat treatment time is not limited by a specific upper limit, but the upper limit may be set to 20 minutes from the viewpoint of preventing the heat treatment from being unnecessarily long.

Examples of the heating method in the heat treatment step include, for example, hot air heating.

(swaging step)

In the above-described swaging step, one surface of the porous sheet having been subjected to the coating step is supported with a support structure (not shown) or the like, and the other surface of the porous sheet is held in contact with a metal-made plate material (not shown), followed by swaging the porous sheet by pressing the porous sheet with a die or the like from the plate material side. The porous sheet is held in a state in which its portion pressed by the plate material in the swaging step is depressed toward the support structure side (i.e., a plastic deformation state). The method for producing an oil-repellent sheet provides sufficiently strong adhesion between the amorphous fluorine-containing resin and the fibrous skeleton of the porous sheet using the heat treatment step as described above. Therefore, the method for producing an oil-repellent sheet reduces a decrease in adhesive strength between the amorphous fluororesin and the fibrous skeleton of the porous sheet due to plastic deformation of the porous sheet occurring in the swaging step, thereby reducing a decrease in oil-repellent performance.

For the swaging step, the lower limit of the compression ratio of the porous sheet in the thickness direction is preferably 20% and more preferably 50%. Further, the upper limit of the compression ratio is preferably 90% and more preferably 70%. The use of a compression ratio smaller than the lower limit poses a risk that the porous sheet cannot be reliably fixed at a desired position. On the contrary, the use of a compression ratio larger than the upper limit causes a risk that the porous sheet is broken at the compression.

[ gas sensor ]

Hereinafter, the gas sensor 11 having the oil-repellent sheet 1 obtained by the method for producing an oil-repellent sheet will be described with reference to fig. 2 to 5. The gas sensor 11 is provided in an exhaust passage of an automobile engine, and is configured to measure the concentration of oxygen contained in gas exhausted from the automobile. The gas sensor 11 includes a sensor device 12 and a housing 13 for accommodating the sensor device 12. The gas sensor 11 further includes a gas inlet 14 for introducing external gas at the base end of the sensor device 12. In the gas sensor 11, the oil-repellent sheet 1 is disposed in the gas inlet 14. Specifically, the gas inlet 14 includes a cylindrical cover 14a formed as a part of the housing 13 and having a plurality of gas introduction holes 14b extending through the thickness thereof, a cylindrical oil repellent sheet 1 provided on the inner surface side of the cover 14a, and a cylindrical body 15a provided on the inner surface side of the oil repellent sheet 1 and having a plurality of gas introduction holes 15b extending through the thickness thereof. The opposite end portions of the cover 14a in the axial direction each have an annular recess 14c recessed inward in the radial direction by swaging. For example, the concave portion 14c is formed by pressing the axially opposite end portions of the cover 14a from the outside with a die while the porous sheet is provided between the cover 14a and the cylindrical body 15 a. The oil-repellent sheet 1 is held in a state in which its portion in contact with the recessed portion 14c is pressed toward the cylindrical body 15 a.

As shown in fig. 3, the gas introduction hole 14b formed through the cover 14a and the gas introduction hole 15b formed through the cylindrical body 15a are located at positions shifted in the circumferential direction. Specifically, the gas introduction hole 14b formed through the cover 14a and the gas introduction hole 15b formed through the cylindrical body 15a are circumferentially shifted by 45 degrees from each other.

The lower limit of the ratio (thickness ratio) of the thickness of the compressed portion of the oil-repellent sheet 1 pressed by the recesses 14c to the thickness of the other portion (i.e., the thickness of the uncompressed portion) is preferably 0.1 and more preferably 0.3. Further, the upper limit of the ratio is preferably 0.8 and more preferably 0.5. Using a ratio less than the lower limit causes a risk of the oil repellent sheet 1 breaking upon compression. In contrast, using a ratio larger than the upper limit poses a risk that the oil repellent sheet 1 cannot be reliably fixed at a desired position.

With the oil-repellent sheet 1 produced by the method for producing an oil-repellent sheet, the gas sensor 11 can provide the gas inlet 14 with excellent gas permeability, excellent oil-repellent performance, and excellent heat resistance. Having the oil-repellent sheet 1, the gas sensor 11 can reduce the possibility of reduction in air permeability, oil repellency, and water pressure resistance, thereby making it possible to maintain high air permeability, high oil repellency, and high water pressure resistance.

[ other embodiments ]

The embodiments disclosed herein should be considered as examples only and not limiting in all respects. The scope of the invention is defined by the claims, not limited to the configurations of the disclosed embodiments, and all modifications that fall within the spirit and equivalent scope of the claims are intended to be included.

The use of the oil-repellent sheet is not limited to the gas inlet of the gas sensor. For example, the oil-repellent sheet may be used as a medical filter, or may be used as an article different from an air filter. When the oil-repellent sheet is disposed in the gas inlet of the gas sensor, the specific arrangement structure of the oil-repellent sheet may be designed according to the structure of the gas sensor. For example, the structure may be as follows: so that an oil-repellent sheet having a flat film shape is disposed at one end of the cylindrical body in the axial direction.