JPH09255808A - Method for producing porous polyvinylidene fluoride - Google Patents

Abstract

(57) [PROBLEMS] To obtain a polyvinylidene fluoride porous body in which open cells are uniformly distributed. SOLUTION: A fluororesin soluble in an organic solvent and polyvinylidene fluoride are mixed and then heat-molded, or a solution of a fluororesin soluble in an organic solvent and a polyvinylidene fluoride solution are mixed, and then the solvent is removed. What was later heat molded, dissolved in a fluororesin that is soluble in an organic solvent,
It is immersed in an organic solvent that does not dissolve polyvinylidene fluoride to dissolve and remove the fluororesin that is soluble in the organic solvent.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a fluororesin porous body suitable for a separation membrane, a diaphragm, a battery separator, a dielectric material and a sensor material.

[0002]

2. Description of the Related Art Microporous porous bodies made of synthetic resin are widely used by being made of materials according to their respective uses. Especially for applications requiring heat resistance and chemical resistance, a fluororesin porous material is used, but due to the unique properties of fluororesin, the porous material is also manufactured by a special manufacturing method. There is. A porous film obtained by stretching and cleaving a film of polytetrafluoroethylene, which is a typical fluororesin, is known.
When the shape of the hole by stretching is uniaxially stretched, it is limited to an oblong shape. Since the tubular shape is uniaxially stretched, the shape of the opening is limited to a long shape in the length direction. on the other hand,
When biaxially stretched to make the shape of the hole circular, there is a problem that the mechanical strength is not sufficient. Further, since the film is produced by cleavage by stretching, the biaxial stretching is limited to a flat film-like porous body.

Therefore, it has been proposed to manufacture a porous body using polyvinylidene fluoride, which is a fluororesin that is soluble in a solvent. The microporous porous body made of polyvinylidene fluoride resin is made of N-vinylidene fluoride resin.
After being dissolved in an organic solvent such as methylpyrrolidone (NMP) or dimethylformamide (DMF) and thinly applied to the substrate, the polyvinylidene fluoride resin is not dissolved, but it is immersed in a treatment liquid that is compatible with the organic solvent to make it organic. A method of extracting a solvent to form holes, and JP-A-49-126572.
As described in the publication, a polyvinylidene fluoride resin and a slow-drying solvent that dissolves it, a resin solution consisting of a fast-drying solvent with a large volatility that dissolves or swells the resin is formed into a sheet, and after the quick-drying solvent is volatilized to some extent , A method of producing a porous sheet by immersing the resin in a treatment solution that does not dissolve the resin and eluting the solvent has been proposed.

However, in the porous sheet produced by these methods, the resin is not sufficiently bonded to each other, and the extraction state of the solvent from the sheet is affected by the difference in the contact state with the extraction liquid. It was difficult to obtain a uniform porous body in which the size of the pores formed was different between the front and back and the quality was constant.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing a porous body of polyvinylidene fluoride having a uniform size and distribution of open pores.

[0006]

The present invention is a method for producing a polyvinylidene fluoride porous body, in which a fluororesin soluble in an organic solvent compatible with polyvinylidene fluoride and polyvinylidene fluoride are heat-molded. Or a mixture of a solution of a fluororesin soluble in an organic solvent compatible with polyvinylidene fluoride and a solution of polyvinylidene fluoride and then heat-molded after removing the solvent to obtain a fluorine-soluble solution in an organic solvent. Dissolve the resin, dip it in an organic solvent that does not dissolve polyvinylidene fluoride,
A method for producing a polyvinylidene fluoride porous body, which comprises dissolving and removing a fluororesin soluble in an organic solvent.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for producing a polyvinylidene fluoride porous body of the present invention, polyvinylidene fluoride is mixed with a fluororesin soluble in an organic solvent in a solid state, or a fluororesin soluble in an organic solvent is used. The solution is mixed with the solution of polyvinylidene fluoride and then gelled to remove the solvent to form a solid mixture which is heat-formed at a temperature not lower than the melting temperature of polyvinylidene fluoride. Fluorine resin soluble in organic solvent compatible with vinylidene can evenly disperse polyvinylidene fluoride, and it is possible to uniformly agglomerate and bond polyvinylidene fluoride resins, and also to bond polyvinylidene fluoride to each other. It is possible to raise it. As a result, by eluting the fluororesin soluble in the organic solvent, it is possible to obtain a porous body having three-dimensionally bonded continuous fine pores of extremely fine network structure without having orientation.

The organic solvent-soluble fluororesin usable in the present invention includes a copolymer of tetrafluoroethylene and vinylidene fluoride, a copolymer of tetrafluoroethylene, vinylidene fluoride and hexafluoropropylene. Can be used. Specifically, examples of the copolymer of tetrafluoroethylene and vinylidene fluoride include NEOFLON VDF (manufactured by Daikin), and examples of the copolymer of tetrafluoroethylene, vinylidene fluoride and hexafluoropropylene include THV (manufactured by 3M). You can
The fluororesin may be in any shape such as powder or pellets.

When polyvinylidene fluoride and a fluororesin soluble in an organic solvent are mixed and heat-molded, the mixing ratio of polyvinylidene fluoride and the fluororesin soluble in an organic solvent is 1: 9 to. It is preferably 9: 1 and 2:
It is more preferable to use 8 to 8: 2, and it is preferable to use powdery polyvinylidene fluoride. Then, after mixing the two, they are heat-molded at a temperature equal to or higher than the melting point of polyvinylidene fluoride.

When a solution of polyvinylidene fluoride and a solution of fluororesin soluble in an organic solvent are mixed,
The concentration of the polyvinylidene fluoride solution is preferably 5 to 40% by weight, and examples of the solvent include N-methylpyrrolidone and dimethylformamide. The concentration of the fluororesin solution soluble in an organic solvent is preferably 5 to 40% by weight, and examples of the solvent include acetone, N-methylpyrrolidone and dimethylformamide. It is preferable to mix a solution of polyvinylidene fluoride and a solution of a fluororesin soluble in an organic solvent in a volume ratio after drying of 1: 9 to 9: 1, preferably 2: 8 to 8: 2. Is more preferable. After mixing both solutions, the organic solvent is dried and solidified, or both solutions are mixed and then poured into water to remove the solvent and precipitate the resin, which is further heated to completely remove water and then kneaded. Heat molding. Further, in the method for producing a porous body of the present invention, not only is it heat-molded by various heat-molding methods, but a mixed solution of a resin is applied to a base material, dried and heated and melted, and then dissolved in an organic solvent. It is possible to produce a thin porous film by extracting various fluororesins,
Further, a hollow porous body can be obtained by similarly treating the filamentous body and the rod-shaped body as a base material. Further, in the method of the present invention, the porosity and the size of the open pores can be easily adjusted by changing the mixing ratio of the fluororesin and polyvinylidene fluoride that are soluble in an organic solvent, or by changing their particle diameters. The smaller the particle size, the smaller the diameter of the pores that can be formed.

For the heat molding of a mixture of polyvinylidene fluoride and a fluororesin soluble in a solvent, any method such as heat compression molding, extrusion molding, calender molding, etc. can be used, and a film shape, a sheet shape, a tube shape, etc. can be used. Molding is possible, and not only one having a uniform thickness but also one having irregularities or one having an arbitrary shape can be formed. After heat molding into a prescribed shape, dissolve the fluororesin soluble in an organic solvent such as acetone, immerse the molded product in an extract that does not dissolve polyvinylidene fluoride, and extract and remove the fluororesin soluble in the organic solvent. By doing so, a polyvinylidene fluoride porous body having fine cells and open cells can be obtained.

Further, the polyvinylidene fluoride porous material is not hydrophilic, but when hydrophilicity is required, when polyvinylidene fluoride and a fluororesin soluble in an organic solvent are kneaded. Hydrophilicity can be imparted by adding fine particles of silica or alumina or by forming a porous body and coating it with a hydrophilic resin. The PVdF porous material obtained by the present invention can be used for a separation membrane, a diaphragm, a battery separator, a dielectric material, and a sensor material.

[0013]

The present invention will be described below with reference to examples. Example 1 2 g of 60 g of tetrafluoroethylene-vinylidene fluoride copolymer resin (Daikin Industries, Neoflon VDF) and 60 g of polyvinylidene fluoride (Audimont 301F)
After kneading at 00 ℃, heat press at 240 ℃ to a thickness of 10
It was formed into a 0 μm sheet. This sheet was dipped in acetone to completely dissolve and remove the tetrafluoroethylene-vinylidene fluoride copolymer resin. The obtained polyvinylidene fluoride porous sheet has a porosity of 60%,
Fig. 1 (A) is a photograph of the surface observed with a scanning electron microscope (2500CX manufactured by Hitachi, Ltd.) at a magnification of 5000 times.
Shown in A porous body with uniformly distributed pores was obtained. The maximum pore size was 0.1 μm. A photograph of the cross section observed at 6000 times is shown in FIG.

Example 2 20 g of a tetrafluoroethylene-vinylidene fluoride copolymer resin (Daikin Industries, Neoflon VDF) is dissolved in 80 g of N-methylpyrrolidone. 20 g of polyvinylidene fluoride (Audimont 301F) are dissolved in 80 g of N-methylpyrrolidone. Both solutions are mixed with sufficient stirring and the mixed solution is poured into water to remove N-methylpyrrolidone. After drying, it is thermoformed at 230 ° C. into a film having a thickness of 100 μm. This film was immersed in acetone to completely dissolve and remove the tetrafluoroethylene-vinylidene fluoride copolymer resin. The porosity of the obtained polyvinylidene fluoride porous film was 50%.
Further, as in Example 1, the maximum hole diameter was 0.5 μm as observed with a scanning electron microscope.

Comparative Example 1 Polyvinylidene fluoride (Ausimont 741) 20 g
A solution of 80 g of N-methylpyrrolidone was applied on a glass plate, and the whole glass plate was immersed in water to prepare a porous body of polyvinylidene fluoride. The result of observing the obtained polyvinylidene fluoride porous film with a scanning electron microscope at 110 times as in Example 1 is shown in FIG. The pore size formed was different between the front and back.

[0016]

According to the present invention, since a fluororesin soluble in an organic solvent and a polyvinylidene fluoride mixture are heated and molded, the fluororesin soluble in an organic solvent is eluted and removed.
Since the dispersion and bonding of polyvinylidene fluoride are good, it is possible to obtain a polyvinylidene fluoride porous body having open cells and uniform distribution of pores and high strength.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph of a polyvinylidene fluoride porous body of the present invention, (A) showing the surface, and (B).
Indicates a cross section.

FIG. 2 is a scanning electron micrograph showing a cross section of a polyvinylidene fluoride porous body produced by a conventional method.

Claims (1)

[Claims] 1. A method for producing a polyvinylidene fluoride porous body, wherein a fluororesin soluble in an organic solvent having compatibility with polyvinylidene fluoride and polyvinylidene fluoride are heat-molded, or polyvinylidene fluoride and A solution of fluororesin soluble in a compatible organic solvent and a solution of polyvinylidene fluoride are mixed and heat-molded after the solvent is removed, and the fluororesin soluble in an organic solvent is dissolved to obtain polyvinylidene fluoride. A method for producing a polyvinylidene fluoride porous body, which comprises immersing in a non-dissolving organic solvent to dissolve and remove a fluororesin soluble in the organic solvent.