JP2003147629A - Method for producing hollow fiber membrane and hollow fiber membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a hollow fiber membrane, by which the hollow fiber membrane having a high strength and a high water- penetrable performance can be produced from a polyvinylidene fluoride-based resin having high chemical resistance at a low cost in a state scarcely giving loads to the environments. SOLUTION: The method for producing the hollow fiber membrane is characterized by extruding and coagulating a solution containing at least a polyvinylidene fluoride-based resin and having a viscosity of 10 to 200 Pa.s into a cooling bath.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hollow fiber membrane for separation, which can be suitably used for clarification of river water, groundwater, etc. and clarification of industrial water, and a method for producing the same.

[0002]

2. Description of the Related Art Membrane separation method is energy saving, space saving,
It is a technology used in various fields because it has features such as labor saving. It uses flat membranes such as microfiltration membranes, ultrafiltration membranes and reverse osmosis membranes, and hollow fiber membranes. Conventionally, in the field of microfiltration, a cartridge type that is premised on being disposable, such as a small-sized household water purifier, has been widely used. In recent years, as a separation membrane for microfiltration or ultrafiltration, there has been active movement to apply hollow fiber membranes to fields such as river water and groundwater clarification, clarification of industrial water, and advanced treatment of wastewater. Has been done. However, when applied to the field of water purification treatment intended for long-term operation instead of being disposable, high properties such as water permeability, mechanical properties, chemical resistance, and sterilization properties are required. When a polyvinylidene fluoride resin is used as a material, it is highly expected as a separation membrane because it has excellent properties such as chemical resistance, heat resistance, and mechanical properties. Conventional methods for producing hollow fiber membranes made of polyvinylidene fluoride resin include, for example, Japanese Patent Publication No. 1-22.
A wet spinning method is disclosed in Japanese Patent Laid-Open No. 003, which uses a surfactant to dissolve the polyvinylidene fluoride resin in a solvent and cause phase separation. However, mechanical voids were insufficient due to the generation of macrovoids inside the film. Next, as disclosed in Japanese Patent No. 2899903, a method of extracting a solvent or an inorganic fine powder from a melt-molded product has been proposed, but it takes a lot of time to extract the inorganic fine powder to form pores, and it is used. There is concern about the environmental impact of the solvents used.

[0003]

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a hollow fiber membrane using a polyvinylidene fluoride resin which exhibits excellent characteristics in a simple process.

[0004]

[Means for Solving the Problems] In order to achieve the above-mentioned object, it has the following constitution. That is, the method for producing a hollow fiber membrane of the present invention uses a solution containing at least a polyvinylidene fluoride resin and having a viscosity in the range of 10 to 200 Pa · s,
It is characterized by being discharged into a cooling bath to solidify. Further, the present invention has a pure water permeation amount of 1.6 m ³ / m ² · h.
・ 100 kPa or more and tensile strength of 4 MN / m ²
The hollow fiber membrane produced by the production method of the present invention having the elongation of 50% or more and the hollow fiber membrane element for water purification using the hollow fiber membrane.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The polyvinylidene fluoride resin in the present invention includes vinylidene fluoride homopolymer, vinylidene fluoride copolymer, a mixture of both, and the like, but vinylidene fluoride homopolymer is preferable. Is contained in an amount of 85% by weight or more (more preferably 90% by weight or more, further preferably 95% by weight or more). As the vinylidene fluoride copolymer, there is a polymer having a vinylidene fluoride monomer residue structure in the polymer structure, such as vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-6-fluorinated propylene copolymer and the like. In addition to the polymer which can be produced using vinylidene fluoride as the raw material monomer, those which can be produced from a raw material monomer other than vinylidene fluoride, such as an ethylene-4 fluoroethylene copolymer, are also included. The weight average molecular weight of the polyvinylidene fluoride resin is preferably 50,000 to 700,000 in consideration of the mechanical properties and water permeability of the hollow fiber membrane, and 100,000 to 100,000 in consideration of the solvent solubility and spinnability.
500,000 is preferable. More preferably, it is 150,000 to 450,000.

In the present invention, the solvent of the solution containing the polyvinylidene fluoride resin is an organic aprotic solvent such as dimethylsulfoxide, N-methyl-2pyrrolidone, dimethylacetamide, dimethylformamide, methylethylketone, acetone or tetrahydrofuran. Examples of the solvent include dimethyl sulfoxide, which has a high melting point, and is preferably used.

It is preferable that the polyvinylidene fluoride resin is completely dissolved in the solvent, but even if undissolved solid matter remains, there is no problem if it is removed by filter filtration. Moreover, the viscosity of the solution containing the polyvinylidene fluoride resin thus prepared (hereinafter, also simply referred to as a polymer solution) has a viscosity of 10 to 200 (preferably 20 to 180, more preferably 30 to 150) Pa.
must be s. Here, the solution viscosity is 200 Pa
If it exceeds s, melt fracture and nozzle clogging tend to occur during film formation. Further, if the viscosity is lower than 10 Pa · s, the solidification is delayed, and extrusion failure such as yarn breakage easily occurs. The viscosity is 80 using a rotary type B viscometer.
It was measured at ° C. The solvent may be a single solvent or a combination of two or more solvents.

Next, the polymer solution prepared as described above is filtered through a stainless filter having a thickness of preferably 5 to 100 μm, and then shaped into a hollow fiber. For example, a hollow fiber membrane can be produced by a wet or dry-wet spinning method using a tube-in orifice. Here, the tube-in-orifice means a double tube-shaped nozzle in which a circular tube (pipe) is inserted in a circular nozzle made of metal or the like, and a constant gap is provided between the circular nozzle and the circular tube. The size of the tube-in-orifice to be used may be appropriately selected depending on the size of the hollow fiber membrane to be manufactured and the membrane structure, but the outer diameter of the orifice is approximately 0.7 to 10 mm, the outer diameter of the tube is 0.5 to 4 mm, and the tube is Inner diameter 0.25
It is preferably in the range of 2 mm. The polymer solution is caused to flow in the gap between the outer diameter of the orifice and the outer diameter of the tube, and the liquid for forming a hollow portion is caused to flow in the inner diameter of the tube. In addition, the spinning draft (take-off speed / the linear discharge speed of the stock solution) is preferably 0.8 to 100, more preferably 0.9 to 50, still more preferably 1 to 30, and the dry length is preferably 10 to 1000 mm, More preferably 15-80
It is 0 mm, more preferably 15 to 600 mm.

The temperature of the orifice, that is, the spinning temperature is 60 to 160 ° C., preferably 70, like the melting temperature.
The temperature is preferably in the range of to 140 ° C., and the die temperature and the melting temperature may be different. Regarding the melting temperature, it is also preferable to set the melting temperature to a temperature higher than the die temperature from the viewpoint of uniformly melting in a short time.

As described above, when the polymer solution is formed into a hollow fiber film by discharging the polymer solution from the orifice, it is preferable to use a hollow portion forming liquid that forms the hollow portion of the hollow fiber membrane. A low coagulating liquid is suitable for this. Here, the low-coagulable liquid is preferably a mixed liquid of a solvent containing the above-mentioned solvent in the range of 75 to 95% by weight and a non-solvent. Examples of the non-solvent include water, hexane, pentane, benzene, methanol, ethanol, toluene and other protic or non-polar solvents, but water that is easy to handle is preferably used. When injecting a low-coagulable liquid into the tube, if the solvent concentration is less than 75% by weight, agglomeration is rapid and the inner surface of the membrane is densified, which tends to decrease water permeability. On the other hand, when the solvent content exceeds 95% by weight, aggregation of the polymer is slow and it becomes difficult to form filaments. The solvent or non-solvent may be used alone or in combination of two or more. As such a low-coagulable liquid, a dimethyl sulfoxide aqueous solution containing dimethyl sulfoxide in the range of 75 to 95% by weight is preferably used. In the present invention, such a low-coagulation liquid is preferably used at 30 ° C. or lower as the hollow part forming liquid.
More preferably below 20 ° C, even more preferably 15 ° C
It can be used below. By injecting the low coagulation liquid under the above temperature conditions into the tube of the tube-in-orifice, the temperature inside the hollow solution can be effectively lowered and solidified.

As described above, the hollow fiber-shaped polymer is discharged into a cooling bath and solidified to form a hollow fiber membrane. The solidification step is required to be predominantly the cooling solidification in which spherulites easily develop, and the present invention uses a cooling bath.

The form of the cooling bath is not particularly limited as long as the cooling liquid and the polymer solution formed into a hollow fiber are sufficiently brought into contact with each other for cooling and the like. It may be in the form of a liquid tank in which a liquid is stored, or if necessary, the liquid tank may be circulated or renewed with a liquid whose temperature and composition are adjusted. The above-mentioned form is the most preferable, but in some cases, the cooling liquid may be flowing in the pipe, or the cooling liquid may be jetted to the hollow fiber membrane which is striking in the air. May be.

As the cooling liquid, the above-mentioned low solidification liquid is preferable. The cooling liquid and the hollow part forming liquid may be the same solvent or a combination of non-solvents, or may have the same mixed composition, or may not have the same composition, but in terms of process control such as solvent recovery. Are preferably the same in solvent, non-solvent, and mixed composition. When the polymer solution is cooled to 30 ° C. or lower using a low coagulation liquid, phase separation is induced, and the phase separation of the polymer in the solution proceeds to nucleate to form a preferable spherical particle structure. With low coagulation liquids above 30 ° C., the polymer in solution does not form a particle structure due to coagulation before phase separation into particles. That is, in order to take a particle structure, phase separation is induced in the process of cooling the solution and the temperature and time for nucleation are important, and the temperature and time for nucleation can be easily controlled by the method described above.

Further, in the production method of the present invention, after coagulation, the hollow fiber membrane is made to have a thickness of 1.1 to 3 (more preferably 1.1).
It is preferable to perform stretching in the range of up to 2.5 times, more preferably 1.1 to 2 times, because the properties such as water permeability and blocking rate can be easily controlled. If the draw ratio exceeds 3 times, the mechanical strength of the hollow fiber membrane tends to decrease. Also, FIG.
4 to 4 are examples of scanning electron micrographs for explaining the membrane wall structure of the hollow fiber membrane obtained by the present invention in detail.
1 and 4 are drawings-substituting photographs (magnification: 6000, 1000 times) showing the inner surface morphology of the hollow fiber membrane according to the production method of the present invention, in which spherical particles are superposed and joined, and a part between spherical particles is used. Shows a form in which they are joined and connected in a streak shape. FIG. 2 is a drawing-substituting photograph (magnification: 5000 times) showing a fractured cross-sectional shape of the hollow fiber membrane, in which a plurality of particles are joined in a planar shape and connected. FIG. 3 is a drawing-substituting photograph (magnification: 3000 times) showing the outer surface morphology of the same hollow fiber membrane, in which spherical particles are formed around a lump-shaped portion. Here, the shape of the particles is spherical or elliptical, and substantially a part of the particles is joined and connected to the adjacent particles. The average particle size of such particles is preferably in the range of 0.5 to 10 μm, and the particle size is 10 μm.
If it exceeds m, the voids to be formed become rough. The particle size is 0.
When it is less than 5 μm, voids formed by joining between particles
The (interval) becomes narrow and the water permeability decreases. The average particle diameter is more preferably 0.5 to 5 μm, further preferably 0.5 to
2 μm. Regarding such a particle structure, on the inner surface of the hollow fiber membrane or on the fractured surface (from the viewpoint of the mechanism of action, the fractured surface is presumed to be more strict, but it is considered that the inner surface can be substituted). Preferably 0.01 mm ²
3 to 3000 (more preferably 300 to 300)
Particles are present in the range of 0, more preferably 1000 to 3000), and the length of the communicating gap formed by the connection of the particles is preferably 0.05 to 30.
(More preferably 0.1 to 5, and even more preferably 0.1 to
1) It is in the range of μm. If the length of the gap is less than 0.05 μm, sufficient water permeability cannot be obtained. Also, 30
When the pore length exceeds μm, there is concern about the rejection rate of bacterial cells. The porosity formed by such a particle structure is preferably in the range of 40 to 75 (more preferably 45 to 70, further preferably 50 to 65)%. When the porosity is less than 40%, mechanical strength is high, but high water permeability cannot be expected due to the densification of the membrane structure. If the porosity exceeds 75%, the mechanical strength tends to decrease.

The hollow fiber membrane obtained by the production method of the present invention has a membrane wall structure in which at least a part of such adjoining particles are joined and connected in a streak-like, plane-like, or block-like shape. When formed, the pure water permeation amount is preferably 1.6 (more preferably 1.8) m ³ / (m ² · h · 100).
kPa) or more and tensile strength 4 (more preferably 5)
It exhibits an elongation of 50 (more preferably 60)% or more at MN / m ² or more. If there is tensile strength and elongation in this range,
The handling property of the hollow fiber membrane is improved, and the membrane is less likely to be broken or crushed during filtration.

The outer diameter and thickness of the hollow fiber membrane of the present invention are
As long as the strength of the membrane is not impaired, pressure loss in the longitudinal direction inside the hollow fiber membrane may be taken into consideration so that the membrane module may be determined so that the water permeation amount becomes a target value. That is, if the outer diameter is large, it is advantageous in terms of pressure loss, but the number of filling is reduced, which is disadvantageous in terms of membrane area. On the other hand, when the outer diameter is small, the number of filling tubes can be increased, which is advantageous in terms of the membrane area, but is disadvantageous in terms of pressure loss. Further, the film thickness is preferably as thin as possible without impairing the strength. Therefore, if you give a rough guide,
The outer diameter of the hollow fiber membrane is preferably 0.3 to 3 mm, more preferably 0.4 to 2.5 mm, and further preferably 0.5.
~ 2 mm. The film thickness is preferably 0.
08-0.4 times, more preferably 0.1-0.35 times,
More preferably, it is 0.12-0.3 times.

The hollow fiber membrane of the present invention preferably has substantially no macrovoids. Here, the macrovoids are pores having a major axis of 50 μm or more observed in the substantial part of the membrane in the cross section of the hollow fiber membrane. The term “substantially not having” means 10 pieces / mm ² or less, more preferably 5 pieces / mm ² or less in a cross section, and it is most preferable not to have it at all.

Further, a hollow fiber membrane module using the hollow fiber membrane produced by the above-mentioned production method is also preferable because it can be utilized for water purification treatment, wastewater treatment and industrial water production.

Specific examples will be described below.

Here, the morphology of the hollow fiber membrane of the present invention was evaluated as follows. (1) The average particle size of the particles was obtained by measuring the major axis and the minor axis of the particles from the scanning electron micrograph of the inner surface of the film and using the following formula to find the average of 20 particles. Average particle size = (particle major axis + particle minor axis) / 2 (2) The number of particles was determined from the number of particles per 0.01 mm ² from the scanning electron micrograph of the inner surface of the film. (3) The range of the gap length of the membrane is measured by arbitrarily selecting the magnification and the width of the region from the scanning micrograph of the membrane surface or cross section, and perpendicular to the longitudinal direction of the hollow fiber membrane at regular intervals at arbitrary lengths. Draw 30 straight lines parallel to different directions, measure the length of 50 points selected arbitrarily among the points where the line segment crosses the void, and determine the maximum value (Max) and minimum value (Min) of the membrane. It was set to the range of the gap length. (4) The method of measuring the porosity of the film was obtained by quantifying the ratio of the voids formed by the particles or the particle structure from the inner surface of the film as image data using an image analysis system. (5) Pure water permeation rate (m ³ / m ² · h · 100 kPa)
A miniature module having a length of 200 mm composed of two hollow fiber membranes was produced, and under the conditions of a temperature of 25 ° C. and a filtration pressure difference of 16 kPa, external pressure full filtration of pure water containing substantially no solid matter such as fine particles was performed for 30 minutes. The amount of permeation (m ³ ) was converted into a value per unit time (h) and effective membrane area (m ² ) and converted into pressure (100 kPa). (6) Tensile strength and elongation are measured by a tensile tester (TENSI
LON / RTM-100) (manufactured by Toyo Baldwin)
A sample with a length of 50 mm and a pulling speed of 50 mm /
The sample was changed for 30 minutes and measurement was performed 30 times, and the average thereof was used as the measurement value.

[0021]

Example 1 Vinylidene fluoride homopolymer 4 having a molecular weight of 360,000
0 parts by weight and 65 parts by weight of dimethyl sulfoxide were dissolved at 90 ° C. to obtain a spinning solution having a viscosity of 113 Pa · s. This spinning solution is extruded through the orifice gap of the tube-in-orifice (orifice outer diameter 2.1 mm, tube outer diameter 0.7 mm), and at the same time, 90% by weight dimethyl sulfoxide aqueous solution at 20 ° C. is injected as a hollow part forming liquid into the tube. Then, it was extruded into a hollow fiber into a cooling bath having a 90% by weight dimethylsulfoxide aqueous solution as a cooling liquid at 10 ° C. to be cooled and solidified. Continue to wash bath at 8 ℃ and 6
The solvent was removed in a warm water bath at 0 ° C to obtain a hollow fiber membrane. This hollow fiber membrane has an inner diameter of 0.89 mm, an outer diameter of 1.61 mm, a water permeability of 1.8 m ³ / (m ² · h · 100 kPa), and a strength of 6.2 M.
It was N / m ² and the elongation was 123%.

Example 2 The hollow fiber membrane of Example 1 was stretched 1.5 times at 90 ° C. to obtain a hollow fiber membrane forming the inner surface of FIG. This hollow fiber membrane has an inner diameter of 0.88 mm, an outer diameter of 1.52 mm, and a water permeability of 2.
8m ³ / (m ² · h · 100kPa), strength 6.7MN /
m ² , elongation 88%, average particle size 1.5 μm, number of particles 2240 per 0.01 mm ² , average gap length of communication holes in the range of 0.1 to 16 μm, and porosity 62%. there were.

Example 3 Vinylidene fluoride homopolymer with a molecular weight of 360,000 2
5 parts by weight and 75 parts by weight of dimethyl sulfoxide at 80 ° C
It was dissolved to obtain a spinning solution having a viscosity of 38 Pa · s. This spinning
The thread solution was added to the tube-in orifice (orifice outer diameter 2.
1 mm, tube outer diameter 0.7 mm) orifice gap
Extruded from the tube and at the same time used as a hollow part forming liquid in the tube.
Inject 88% by weight dimethylsulfoxide aqueous solution at 7 ℃
Then, in the form of a hollow fiber, 88% by weight of dilute at 10 ° C. which is a cooling liquid.
Extrusion into a cooling bath containing methyl sulfoxide aqueous solution
It was cooled and solidified. Continue to desolvate in a water bath at 10 ° C
And then stretched 1.8 times at 80 ° C. to obtain a hollow fiber membrane.
It was This hollow fiber membrane has an inner diameter of 0.87 mm and an outer diameter of 1.62.
mm, water permeability 6.2 m³/ (M²・ H ・ 100kPa),
Strength 5.2MN / m², Elongation 68%, average particle size
1.5 μm, particle number 0.01 mm²Per 1890
Individual, the gap length of the communication hole is in the range of 0.1 to 26 μm,
The porosity was 71%. Comparative Example 1 The spinning solution was made into vinylidene fluoride homo with a molecular weight of 360,000.
48 parts by weight of polymer and 52 parts by weight of dimethyl sulfoxide
Is melted at 120 ° C. to prepare a spinning solution having a viscosity of 326 Pa · s.
Obtained. This spinning solution was added to the tube-in orifice (orif
Of 2.9 mm outer diameter and 0.7 mm tube outer diameter)
Extruded from the gap of the fiss, and at the same time, the hollow part is formed on the tube.
85% by weight dimethyl sulfoxy at 25 ° C as a working liquid
Injecting a water-based liquid into a hollow fiber, a cooling liquid of 20 ° C
With 85% by weight dimethylsulfoxide aqueous solution
It was extruded into a bath and cooled and solidified. Then warm water at 70 ℃
The solvent was removed in to obtain a hollow fiber membrane. This hollow fiber membrane has an inner diameter
0.87mm, outer diameter 1.88mm, strength 9.2MN /
m², Elongation was 78%, but water permeability was 0.01 m³/ (M²
・ H · 100 kPa) was a low value. Comparative example 2 The hollow fiber membrane shown in Comparative Example 1 was stretched 1.5 times at 90 ° C.
Water permeability 0.01m ³/ (M²・ H ・ 100kPa)
And there was no change. Comparative Example 3 Spin the spinning solution into vinylidene fluoride homo with a molecular weight of 260,000.
12 parts by weight of polymer and 88 parts by weight of dimethyl sulfoxide
Was dissolved at 70 ° C. and a solution having a viscosity of 6 Pa · s was used.
The outside is shaped into a hollow fiber under the same spinning conditions as in Example 3 and cooled.
Attempted solidification, but the solution aggregated on the surface of the cooling bath and formed into a filamentous shape.
I couldn't succeed.

[0024]

INDUSTRIAL APPLICABILITY The hollow fiber membrane of the present invention is suitably used in fields of use such as microfiltration membranes, ultrafiltration membranes and various filters having excellent water permeability, mechanical properties and chemical resistance.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph showing the particle shape on the inner surface of a hollow fiber membrane according to an embodiment of the present invention.

FIG. 2 is a scanning electron micrograph showing a particle shape on a split cross section of a hollow fiber membrane according to an embodiment of the present invention.

FIG. 3 is a scanning electron micrograph showing the particle shape on the outer surface of the hollow fiber membrane according to the embodiment of the present invention.

FIG. 4 is a scanning electron micrograph showing the particle shape on the inner surface of the hollow fiber membrane according to the embodiment of the present invention, the magnification being changed.

Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) D01F 1/08 D01F 1/08 (72) Inventor Masahiro Hemi 1-1-1, Sonoyama, Otsu City, Shiga Toray Co., Ltd. Shiga F-term in business site (reference) 4D006 GA07 HA01 MA01 MA33 MB02 MB16 MC29X NA04 NA05 NA10 NA18 NA29 NA34 NA52 PA01 PB04 PB05 4L035 BB03 BB15 BB72 DD03 FF01 MB15

Claims (9)

[Claims] 1. A solution containing at least a polyvinylidene fluoride resin and having a viscosity in the range of 10 to 200 Pa · s,
A method for producing a hollow fiber membrane, which comprises discharging into a cooling bath to solidify. 2. The method for producing a hollow fiber membrane according to claim 1, wherein a liquid at 30 ° C. or lower is used as the hollow portion forming liquid for forming the hollow portion of the hollow fiber membrane. 3. The method for producing a hollow fiber membrane according to claim 1, wherein the cooling bath contains a liquid at 30 ° C. or lower. 4. The method for producing a hollow fiber membrane according to claim 2, wherein the liquid is a mixed solution of a solvent containing a solvent in the range of 75 to 95% by weight and a non-solvent. 5. A polyvinylidene fluoride resin is 85
The method for producing a hollow fiber membrane according to any one of claims 1 to 4, which comprises a vinylidene fluoride homopolymer in an amount of not less than 5% by weight. 6. The method for producing a hollow fiber membrane according to claim 1, wherein the solvent of the solution is dimethyl sulfoxide. 7. The method for producing a hollow fiber membrane according to claim 4, wherein the solvent is dimethyl sulfoxide and the non-solvent is water. 8. A pure water permeation amount of 1.6 m ³ / (m ² · h · 10)
The hollow fiber membrane produced by the production method according to claim 1, having a tensile strength of 4 MN / m ² or more and an elongation of 50% or more. 9. A hollow fiber membrane element for water purification, which comprises the hollow fiber membrane according to claim 8.