JPH07109669A - Metal-supporting porous fluorofiber sheet and its production - Google Patents

Abstract

PURPOSE:To prepare a metal-supporting porous fluorofiber sheet exhibiting excellent water-repellency and having small specific gravity, uniform pore diameter, excellent heat-resistance and chemical resistance and easily adjustable electrical properties and chemical properties and to provide a production process therefor. CONSTITUTION:This metal-supporting porous fluorofiber sheet is produced by forming a sheet of polytetrafluoroethylene fiber by wet paper-making process, sintering the sheet and supporting a metal on the obtained porous sheet. This invention also relates to a process for the production of the fluorofiber sheet.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal-supporting porous fluorofiber sheet useful as a porous solid catalyst used for a reaction such as oxidation and reduction of a solute with a poorly soluble gas, and a method for producing the same. More specifically, a polytetrafluoroethylene (hereinafter also referred to as PTFE) fiber carrying a metal thin film on one or both sides thereof is water-repellent and adsorbs a hardly water-soluble gas to react with a solute in an aqueous solution. The present invention relates to a metal-supporting porous fluorofiber sheet having excellent gas permeability, heat resistance, and chemical resistance, and a method for producing the same.

[0002]

2. Description of the Related Art Porous fluorofiber sheets include woven cloth, non-woven cloth, sintered bodies and the like. The woven fabric is a mesh-shaped, cloth-shaped braided, spun-woven fabric.
Pore size too large. Further, there are problems that the fibers are loosened, too thick, and the specific surface area is too small. The dry non-woven fabric is thick, has a low density, has a non-uniform surface condition, and has a poor texture. The sintered body is produced by spraying fluororesin powder or short fibers by a dry method, heating this to a temperature close to the melting point of the fluororesin, and fusing. This has the problem that long sheets cannot be created. In order to solve these problems, the applicant of the present application has filed Japanese Patent Application Laid-Open No. 63-16559.
8 and JP-A-63-165599,
We proposed a method for producing fluorofiber sheets by the wet papermaking method. However, a fiber sheet containing only fluorine fibers or a mixed paper sheet containing fluorine fibers and inorganic fibers according to this proposal is
Its scope is limited by its unique characteristics,
There has been a problem that applications are limited in terms of electrical characteristics, chemical characteristics, and filtration characteristics.

In the industrial fields such as electronic industry and chemical industry, precious metals such as platinum, gold and silver, and other metallic materials such as nickel, chromium, titanium, palladium, rhodium, copper, zinc, iron and stainless are used as catalysts, It is used in various fields such as conductive materials. For example, hydrogen and oxygen are industrially used in various fields, but are rarely used in reactions in an aqueous solution. This is because these gases are poorly soluble in water. Although the reduction reaction of copper (II) ion by hydrogen should proceed in chemical equilibrium, metallic bubbling does not precipitate even if hydrogen gas is simply bubbled into an aqueous solution of copper sulfate. Further, the reaction does not proceed even in the presence of a usual catalyst having alumina, silica, titania, activated carbon or the like as a carrier. This is because these catalysts are hydrophilic, so that the surface is covered with water and no gas is adsorbed. Therefore, reduction of copper ions is carried out at high temperature (100 to 200 ° C.) and high pressure (1 to 5 MPa) with the addition of a uniform catalyst such as arsenic and antimony. If the surface of the catalyst is water repellent,
A gas that is poorly soluble in water is adsorbed on the surface, and the reaction in the aqueous solution is promoted. Moreover, if a catalyst having water repellency can be applied to a gas-liquid system reaction, it can also be applied to a heavy water production process by an isotope exchange reaction. Further, noble metals have unique chemical properties and excellent conductivity, but since they are expensive, their applications are limited as industrial materials. However, in recent years, there has been an increasing demand for using precious metals.

[0004]

DISCLOSURE OF THE INVENTION The present invention is suitable for solving the above various problems, exhibits excellent water repellency, has a small specific gravity, a uniform pore size, excellent heat resistance, chemical resistance, and electrical properties. It is intended to provide a metal-supported porous fluorofiber sheet which can easily adjust properties and chemical properties, and a method for producing the same.

[0005]

The present invention relates to a porous sheet obtained by sintering polytetrafluoroethylene fiber or a mixed fiber of polytetrafluoroethylene fiber and inorganic fiber, which is formed into a sheet by a wet papermaking method. Provided is a metal-supporting porous fluorofiber sheet, which is characterized in that a metal is supported on one side or both sides. The present invention further comprises a step of forming a sheet of polytetrafluoroethylene fiber or polytetrafluoroethylene fiber and an inorganic fiber by a wet papermaking method, a step of sintering the sheet, one or both sides of the sintered porous sheet. Provided is a method for producing a metal-supporting porous fluorofiber sheet, which comprises a step of supporting a metal.

First, the method for producing the metal-supporting porous fluorofiber sheet of the present invention will be described. Polytetrafluoroethylene fiber in the present invention, viscose in the dispersion of stretched or unstretched polytetrafluoroethylene,
Fibers obtained by blending a binder such as carboxymethyl cellulose or polyvinyl alcohol as a matrix and spinning the mixture through the pores into a coagulation bath are preferably used. The obtained stretched or unstretched polytetrafluoroethylene fiber is cut into a length of 3 to 15 mm, and this is dispersed in water together with a dispersant such as polyacrylamide to prepare a papermaking raw material. This papermaking raw material is paper-made by a paper machine such as a cylinder paper machine or a Fourdrinier paper machine to prepare a sheet of polytetrafluoroethylene fiber. In forming a sheet of polytetrafluoroethylene fiber, the matrix substance mixed with the polytetrafluoroethylene fiber exerts a binding function between fibers during papermaking.

Inorganic fibers such as glass fibers, silica fibers, alumina fibers, and aluminum silicate may be added to the papermaking raw material. Next, the sheet of polytetrafluoroethylene fiber is heated to a temperature above the melting point of the fiber (for example, 380 ° C.), and the fibers are fused and sintered. Further, if necessary, an operation of heating to about 300 to 330 ° C. may be added in order to thermally decompose and remove a matrix substance such as viscose existing between the fibers. In order to improve the adhesion between the obtained sintered porous sheet and the metal, the surface of the sintered porous sheet is subjected to pretreatment such as corona treatment, plasma treatment, ultraviolet treatment and acid treatment. May be added. Alternatively, a metal film having a high affinity for the sheet may be provided on the surface of the sintered porous sheet, and then a target metal may be attached.

The metal is preferably attached to the sintered porous sheet by a vacuum thin film forming method such as a vapor deposition method, a sputtering method or an ion plating method.
The metal to be attached is appropriately selected depending on the application. Generally, the following metals are exemplified. Gold, silver, copper, platinum, chrome,
Nickel, palladium, rhodium, titanium, zinc, iron,
Stainless steel etc. The porous sheet to which a metal is attached has various properties such as heat resistance and chemical resistance improved, although it varies depending on the type of metal. It is also possible to further increase the thickness of the metal film to improve the conductivity. In this case, the electrolytic plating method and the electroless plating method are preferably adopted. The metal film may be on one side or both sides of the porous sheet. It is appropriately selected according to the application.

In the present invention, the compounding ratio of the inorganic fiber to the polytetrafluoroethylene fiber, the thickness of the metal film provided on the polytetrafluoroethylene fiber sheet, the type of metal, the thickness of the sintered sheet, the pore size, etc. are selected. As a result, various characteristics can be exhibited depending on the application. For example, various characteristics such as catalyst capacity, presence / absence of antibacterial property, rigidity, flame retardancy, gas / liquid permeability, conductivity, other insulation, heat resistance, chemical resistance, etc. Can be controlled within an arbitrary range. The thickness of the sintered porous sheet is generally in the range of 40 μm to 5 mm and the average pore size is generally in the range of 5 to 100 μm. The thickness of the metal film is also generally in the range of 500 to 5000Å, but it should be appropriately selected.

The sintered porous sheet of the present invention comprises:
The base is a thin porous fluorofiber sheet obtained by a wet papermaking method. Therefore, it has a feature that the surface area of the sheet is large. Moreover, since a metal is supported on the surface of the porous sheet that has been sintered, it is excellent as a hydrophobic solid catalyst. The usage ratio of expensive precious metals and rare metals can be significantly reduced. In addition, since the metal-supporting porous fluorofiber sheet of the present invention is mostly fluorofiber, it is light in weight and excellent in heat insulating effect, heat resistance, and chemical resistance.

EXAMPLES The present invention will be described in detail below with reference to examples. Unless otherwise specified,% in the examples means% by weight.

Example 1 An unstretched PTFE fiber (manufactured by Showa Kogyo KK, "Toyofuron", fiber diameter 15 μm) obtained from a dispersion of polytetrafluoroethylene having viscose as a matrix was used as 6
It was cut to a length of mm and dispersed in water at a concentration of 0.5%.
A polyacrylamide dispersant was added to this to prepare a papermaking raw material. This raw material is made into a sheet by a cylinder paper machine,
A PTFE fiber sheet having a basis weight of 70 g / m ² was obtained. This sheet is heated by an infrared heater at 380 ° C for 3 minutes,
The PTFE particles in the fibers were fused and made continuous, and the inter-entangled fibers were fused. Further, in order to thermally decompose and remove viscose in the sheet, heat treatment was performed at 320 ° C. for 20 hours to obtain a white PT having a basis weight of 38 g / m ² and a thickness of 125 μm.
An FE fiber sintered sheet was obtained.

This PTFE fiber sintered sheet was subjected to plasma treatment using argon gas at an RF output of 100 W for 60 seconds. Then, platinum was supported on the surface of the PTFE fiber sintered sheet. This is done by using a sputtering machine, placing platinum on the target, and then 5 x 1 from atmospheric pressure.
After evacuating to 0 ^-6 Torr to sufficiently remove volatile substances, argon gas was gradually added to 1 while maintaining this vacuum degree.
It was introduced up to × 10 ^-3 Torr, the voltage between electrodes of the DC power supply was adjusted to 600 V, and a current was passed to load platinum to a film thickness of 1000 Å. The average pore diameter of this platinum-supported PTFE fiber sintered sheet was measured by the bubble point method,
It was 35 μm. The melting point was 327 ° C.

Comparative Example 1 A surface of a polypropylene (hereinafter referred to as PP) non-woven fabric (manufactured by Hercules) was treated in the same manner as in Example 1 to carry out plasma treatment and platinum supporting treatment. The platinum film had a thickness of 1000Å and an average pore diameter of 25 μm. The melting point was 162 ° C.

With respect to the platinum-supported PTFE fiber sintered sheet obtained in Example 1 and the platinum-supported PP fiber sheet obtained in Comparative Example 1, the quality of the hydrogen reduction reaction of copper ions was tested. Even if hydrogen gas is blown into a copper sulfate solution using an ordinary hydrophilic catalyst, copper ions are not reduced and metallic copper is not deposited. Therefore, the strip-shaped platinum-supported PTFE fiber sintered sheet and the strip-shaped platinum-supported PP fiber sheet were respectively placed in a copper sulfate aqueous solution (10 mmol / l), and hydrogen gas was blown thereinto to observe changes in the catalyst surface. In the case of the platinum-supported PTFE fiber sintered sheet, a part of the surface became metallic copper color within a few minutes after starting the introduction of hydrogen gas, and then the color became darker with time. In the case of the platinum-supported PP fiber sheet, its surface hardly changed even after 1 hour.

[0016]

According to the present invention, there is provided a metal-supporting porous fluorine fiber comprising a fluorine fiber having a surface on which a precious metal or a rare metal is supported, or a mixed fiber of a fluorine fiber and an inorganic fiber, and a method for producing the same. It The metal-supporting porous fiber fluorine fiber of the present invention can control the pore diameter, thickness, thickness of the metal thin film, and metal type in any range, and can be applied to various uses as a catalyst. In particular, it is useful for promoting the reaction between a poorly water-soluble gas such as hydrogen and oxygen and a solute in an aqueous solution by utilizing its water repellency.

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Claims (5)

[Claims] 1. A metal-supporting porous fluorofiber sheet, wherein a metal is supported on the surface of a porous sheet obtained by sintering polytetrafluoroethylene fibers formed into a sheet by a wet papermaking method. 2. A metal-supporting porous fluorofiber sheet, wherein the porous sheet according to claim 1 is formed by mixing a slurry of polytetrafluoroethylene fibers and inorganic fibers into a sheet by a wet papermaking method and sintering the sheet. 3. A metal-supporting porous material comprising a step of forming a sheet of polytetrafluoroethylene fiber by a wet papermaking method, a step of sintering the sheet, and a step of supporting a metal on the surface of the sintered porous sheet. Fluorine fiber sheet manufacturing method. 4. The method for producing a metal-supporting porous fluorofiber sheet according to claim 3, wherein the sintered porous sheet is subjected to at least one pretreatment selected from plasma treatment, corona treatment and ultraviolet treatment. Then, a method for producing a metal-supporting porous fluorofiber sheet, which subsequently carries out a metal-supporting step. 5. The method for producing a metal-supporting porous fluorofiber sheet according to claim 3, wherein the metal-supporting step is performed by a vacuum thin film forming method.