JPH10266014A - Production of fluororesin hollow yarn - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a hollow yarn of a fluororesin suitable for a filtration membrane, a dialytic membrane, a gas separation membrane, a reverse osmosis membrane, an ultrafiltration membrane or a precise filtration membrane. SOLUTION: A solution prepared dissolving a fluororesin in a solvent is applied onto a core wire 1 and dried to form a solvent-soluble fluororesin layer 2 and a dispersion of a solvent-insoluble fluororesin is then applied onto the layer 2, dried and baked. The operations are performed at least once to form a laminate having the solvent-insoluble fluororesin layer 3. The resultant laminate is further dipped in a solvent 5 to dissolve the solvent-soluble fluororesin or the laminate is drawn in a drawing step 4 together with the core wire 1 under heating and then dipped in the solvent 5 to dissolve the solvent-soluble fluororesin. The core wire 1 is subsequently separated from the laminate to afford the objective fluororesin hollow yarn 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a porous or dense hollow fiber of a fluororesin suitable for a filtration membrane, a dialysis membrane, a gas separation membrane, a reverse osmosis membrane, an ultrafiltration membrane, and a microfiltration membrane.

[0002]

2. Description of the Related Art A hollow porous material such as a hollow fiber is used for an apparatus for separating various substances. The hollow porous body is
Hollow synthetic resin, which uses the wall portion of the hollow fiber as a permeable membrane, the module containing a large number of hollow fibers in a cylindrical outer cylinder, compared to the one using a flat membrane,
It is characterized in that the packing density of the film can be increased and a compact device can be obtained.

[0003] A porous body made of a fluororesin has excellent chemical resistance and heat resistance as compared with a material made of a general hydrocarbon-based synthetic resin as a raw material. And various other fields.

[0004] However, polytetrafluoroethylene, which is a typical fluororesin, has a very high melt viscosity and is inferior in workability, and cannot be produced by a method such as melt molding. A hollow member was extruded and then fired to produce a fluororesin hollow tube, which was then stretched or stretched and fired to produce a porous hollow fiber of any diameter. .

[0005] However, if it is attempted to produce by such a method, the fluororesin is broken at the time of stretching, and it is difficult to produce a thin-walled tube. There was a problem that it could not be manufactured.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to produce a uniform and thin hollow fiber which is difficult to produce by extrusion.

[0007]

SUMMARY OF THE INVENTION The present invention relates to a method of manufacturing a fluororesin hollow fiber, which comprises applying a solution obtained by dissolving a fluororesin in a solvent on a core wire and drying the resulting resin layer. A layer of the fluororesin layer insoluble in the solvent is formed by applying at least one operation of coating, drying and baking a dispersion of the fluororesin insoluble in the solvent, and immersing the laminate in the solvent. After dissolving, or after dissolving the solvent-soluble fluororesin by immersing in a solvent after stretching the laminate together with the core under heating,
This is a method for producing a fluororesin hollow fiber produced by drawing a core wire.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a fluororesin hollow fiber of the present invention comprises forming a thin layer of a fluororesin soluble in an organic solvent on a metal core wire, Containing dispersion, for example, polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FE)
P), aqueous solutions of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene-perfluoroalkyl vinyl ether copolymer (EPA), and tetrafluoroethylene-ethylene copolymer (ETFE) The dispersion or a mixture thereof is applied, dried and then heated at a temperature equal to or higher than the melting point of the fluororesin contained in each of the dispersions, thereby melting or calcining the fluororesin and integrating the fluorine onto the core wire. The resin-laminated laminate is immersed in an organic solvent as it is to dissolve the fluorine resin soluble in the solvent, and then the core wire is pulled out to obtain a fluororesin hollow body. Then, the hollow body is drawn into a hollow fiber by stretching.
Alternatively, before immersing the above-mentioned laminate in an organic solvent, after forming a fine hole in the fluororesin layer by stretching together with the core wire under heating, and immersing in the organic solvent to form a fluororesin soluble in the solvent, The microporous hollow fiber is obtained by melting and then drawing out the core wire.

The present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating the steps of the method for producing a fluororesin hollow fiber of the present invention. First, as shown in FIG. 1A, a coating layer 2 of a fluororesin soluble in an organic solvent is formed on a core wire 1. The core wire is preferably made of a metal having good ductility such as copper. The diameter of the core wire can be arbitrarily determined according to the inner diameter of the hollow fiber to be produced, and a fiber having an inner diameter of several millimeters, for example, 10 μm to 10 mm can be manufactured from an extremely fine diameter.

The formation of the fluororesin layer soluble in the organic solvent on the core wire is preferably performed by coating or stretching. The thickness of the fluororesin layer soluble in organic solvent after drying is
It is preferably in the range of 0.1 to 50 μm,
It is more preferable that the thickness be 30 μm. 0.1μ thickness
If it is less than m, the surface becomes uneven, which is not preferable.
If it is larger than 0 μm, it takes a long time for dissolution, which is not preferable.

As the fluorine resin soluble in the organic solvent, a copolymer with tetrafluoroethylene-vinylidene fluoride, a copolymer of tetrafluoroethylene-vinylidene fluoride-hexafluoropropylene and the like can be used. Specifically, NEOFLON VDF (manufactured by Daikin) can be mentioned as the tetrafluoroethylene-vinylidene fluoride copolymer, and THV (manufactured by 3M) can be mentioned as the tetrafluoroethylene-vinylidene fluoride-hexafluoropropylene copolymer. Organic solvents that dissolve these fluororesins include N-methylpyrrolidone, dimethylformamide, acetone and the like.

Next, an aqueous dispersion of a fluororesin insoluble in the organic solvent, for example, a dispersion of PTFE is applied on a thin layer of the fluororesin soluble in the organic solvent formed on the core wire, and dried, and then dried. The fluororesin layer 3 is formed by heating at a temperature higher than the melting point of the fluororesin insoluble in the solvent, melting or baking. The fluororesin layer 3 is coated with a dispersion, dried,
It is preferable that a predetermined thickness is obtained by repeating a series of steps including heating, further melting or firing.
Further, if a large amount of dispersion is applied at once, cracks and the like may occur in the formed fluororesin layer, which is not preferable. The dispersion of the fluororesin used in the present invention has an average particle diameter obtained by emulsion polymerization of 0.01 to 10 μm and a solid weight of 1 to 6 μm.
An aqueous dispersion containing 0% by weight and 0.1 to 10% by weight of a surfactant is preferred.

According to the present invention, since a thin layer of a fluororesin soluble in an organic solvent is formed on a core wire, a layer made of a dispersion of a fluororesin insoluble in a solvent is formed on this thin layer to form an organic solvent. When the insoluble fluorine resin layer is heated and melted or fired and integrated, the surface tension of the lower layer formed on the core wire is similar and the affinity of both is good, so the fluorine resin insoluble in the organic solvent Can maintain the cylindrical shape of the fluororesin without agglomeration. The cylindrical laminate having the fluororesin layer insoluble in the organic solvent is immediately immersed in an organic solvent 5 that dissolves the fluororesin, as shown in FIG. As shown, the columnar laminate is stretched together with the core wire 4 to form fine holes in the solvent-insoluble fluororesin layer and then immersed in an organic solvent. Alternatively, a pore-forming process may be performed by adding a surfactant containing a fluorine compound to the PTFE dispersion.

When the cylindrical laminate having the fluororesin layer formed thereon is immersed in an organic solvent dissolving a fluororesin soluble in an organic solvent, the fluororesin soluble in the organic solvent dissolves. Thus, as shown in FIG. 1 (E), the core wire can be easily pulled out 6, and the dense or porous fluororesin hollow fiber 7 shown in FIG. 1 (F) can be obtained. Ultrasonic waves may be applied to effectively immerse the organic solvent in the cylindrical laminate.

[0015]

The present invention will be described below with reference to examples. Example 1 On a copper wire having a diameter of 0.5 mm, tetrafluoroethylene-
A 20% by weight acetone solution of a vinylidene fluoride copolymer resin (Neoflon VDF manufactured by Daikin Industries, Ltd.) was applied, dried, and heated to 150 ° C. to form a fluororesin layer soluble in a 5 μm solvent. Next, a dispersion of polytetrafluoroethylene (Teflon 30J, manufactured by DuPont-Mitsui Fluorochemicals Co., Ltd.) is applied onto the fluororesin layer soluble in the organic solvent, dried, and baked at 360 ° C. for 15 seconds in a nitrogen atmosphere to obtain a thickness. A fluororesin layer insoluble in a 5 μm solvent was formed. Furthermore, application of dispersion,
The steps of drying and baking were repeated three times to form a solvent-insoluble fluororesin layer having a total thickness of 15 μm. Next, the laminate laminated in a cylindrical shape on the core wire was placed in acetone at 50 ° C. for 1 hour.
After immersion for a time, the fluororesin layer soluble in the solvent was dissolved and removed. Next, it was taken out of the acetone and the core wire was pulled out to obtain a hollow fiber made of fluororesin having an inner diameter of 51 μm and an outer diameter of 54 μm. The obtained hollow fiber had a uniform thickness and was free from cracks.

Example 2 Example 1 was repeated except that a laminated body obtained by laminating a fluororesin in a cylindrical shape on a core wire was stretched 1.5 times with the core wire evenly before being immersed in acetone. A hollow fiber was produced in the same manner as described above. The obtained hollow fiber has an inner diameter of 52 μm and an outer diameter of 5 μm.
6 μm, and the wall surface has a pore size of 0.01 to 0.05 μm.
Was a porous hollow fiber having fine pores.

[0017]

According to the present invention, it is possible to obtain a thin hollow fiber or a porous hollow fiber having a uniform wall thickness made of a fluorine resin insoluble in a solvent.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a method for producing a fluororesin hollow fiber of the present invention.

[Explanation of symbols]

1 core wire, 2 coating layer of fluororesin soluble in organic solvent,
3: Fluororesin layer, 4: stretching, 5: organic solvent, 6: drawing, 7: fluororesin hollow fiber

Claims (1)

[Claims] 1. A method for producing a fluororesin hollow fiber, comprising:
A solution obtained by dissolving a fluororesin in a solvent on a core wire is coated and dried. On a fluororesin layer soluble in the solvent formed, a dispersion of a fluororesin insoluble in the solvent is applied, dried and baked at least. The laminate having the fluororesin layer insoluble in the solvent formed once is immersed in the solvent to dissolve the solvent-soluble fluororesin, or the laminate is stretched together with the core under heating and then immersed in the solvent. And dissolving the solvent-soluble fluororesin, and then separating the core wire from the laminate.