JP2004098028A - Production method for high-performance hollow-fiber precision filtration film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a precision filtration film which has an anisotropic structure, is excellent in strengths and water permeability, and hardly causes clogging in internal pressure filtration. <P>SOLUTION: This method for producing the hollow-fiber precision filtration film comprises causing a film-forming stock solution and an internal liquid to be delivered from a double ring nozzle, followed by passing through an air gap and coagulating them in a coagulation bath. (a) The film-forming stock solution comprises a film-forming polymer, a solvent thereof, and a hydrophilic polymer, the ratio of the hydrophilic polymer to the film-forming polymer being 20-60wt%. (b) The internal liquid comprises water and at least one solvent, the water content being 35-55wt%. (c) The temperature of the film-forming stock solution at the nozzle section is 50°C or higher, and (d) the coagulation bath temperature is 85-100°C. (e) The ratio of the air gap to the spinning speed is set at 0.01-0.1m/(m/min). <P>COPYRIGHT: (C)2004,JPO

Description

【００５３】
【表２】

【００５４】
【発明の効果】
本発明の製造方法から得られた膜は、高い強度と優れた透水性能を有する異方性構造の精密濾過膜であって、特に内圧濾過において目詰まりが少ない優れた精密濾過膜であることから医薬用途、医療用途、及び一般工業用途に用いることができる。[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a method for producing an anisotropic microfiltration membrane, which has high strength and excellent water permeability, and has little clogging in internal pressure filtration.
[0002]
[Prior art]
Hollow fiber membranes are widely used in industrial applications from microfiltration to ultrafiltration, and polyethylene, cellulose acetate, polysulfone, polyvinylidene fluoride, polycarbonate, polyacrylonitrile, and the like are used as membrane materials. Conventional hollow fiber membranes made of these materials have been developed with an emphasis on improving filtration performance, so the hollow fiber membranes have low breaking strength and low elongation at break, and are subject to rapid temperature changes and backwashing. It has been pointed out that the hollow fiber membrane is often broken by the pressure change.
[0003]
Various attempts have been made to solve this problem. However, as generally suggested in the invention described in Patent Document 1, a hollow fiber membrane is prepared by increasing the polymer concentration in a stock solution for film formation. A method of increasing the overall polymer density is conceivable. However, in this method, while the strength of the membrane is improved, the pore diameter of the membrane is reduced and the amount of water permeation of the membrane is significantly reduced, so that a hollow fiber membrane excellent in balance between strength and water permeation performance has not been obtained.
[0004]
On the other hand, in order to improve the water permeability of the membrane, a method of increasing the pore size of the membrane is generally performed, but an increase in the pore size generally causes a decrease in the fractionation performance and strength of the membrane.
As described above, in the related art, a high-performance hollow fiber membrane in which strength, water permeability, and fractionation performance are balanced has not been obtained. For example, Patent Document 2 proposes a method for producing a membrane having high strength and excellent water permeability, but the membrane produced by this method has a large pore diameter, and balances water permeability and fractionation performance. Not.
[0005]
Patent Document 3 discloses a hollow fiber microfiltration membrane in which the pore size continuously decreases from the outer surface of the membrane toward the inside, gradually increases through the minimum pore size in the inside, and opens again on the inner surface. ing. However, when a liquid or the like is filtered from the hollow portion side (inner surface side) of the membrane using the membrane having this structure, rapid clogging occurs, and stable filtration cannot be performed for a long time.
[0006]
[Patent Document 1]
JP-A-59-228016 [Patent Document 2]
JP-A-4-260424 [Patent Document 3]
JP-A-2-102722
[Problems to be solved by the invention]
An object of the present invention is to provide a method for producing an anisotropic microfiltration membrane having high strength and excellent water permeation performance, and in particular, having less clogging in internal pressure filtration.
[0008]
[Means for Solving the Problems]
As described above, when liquid or the like is filtered from the hollow side of the membrane (hereinafter also referred to as “internal pressure filtration”), there has been no high-strength microfiltration membrane with little clogging and excellent water permeability. This is because, on the inner surface of the membrane having a gradient structure in which the pore diameter continuously decreases from the outer surface to the inner surface of the membrane, while maintaining high membrane strength, 0.01 μm or more (of the microfiltration region). This is because opening pores has been impossible in the past particularly with a hydrophobic polymer such as polysulfone.
[0009]
The inventor of the present invention has made intensive studies on an inclined structure in which the pore diameter is continuously reduced from the outer surface to the inner surface of the membrane in order to prevent clogging, and as a result, the present invention has been achieved.
[0010]
That is, the present invention
(1) In a method for producing a hollow fiber membrane in which a membrane-forming stock solution and an internal solution are discharged from a double annular nozzle and then passed through an air gap and then coagulated in a coagulation bath,
a) The membrane-forming stock solution is composed of an additive consisting of a film-forming polymer, a solvent for the polymer, and a hydrophilic polymer, wherein the ratio of the additive to the film-forming polymer is 20 to 60% by weight;
b) the internal liquid is composed of water and at least one solvent, and has a water content of 35 to 55% by weight;
c) the temperature of the stock solution at the nozzle is 50 ° C. or more,
d) the coagulation bath temperature is 85 to 100 ° C., and e) the ratio of the air gap to the spinning speed is 0.01 to 0.1 m / (m / min).
A method for producing a hollow fiber microfiltration membrane,
(2) The production method according to (1), wherein irradiation is further performed.
(3) The method according to (1) or (2), wherein the ratio of the film thickness to the inner diameter of the film is 0.15 to 0.4.
(4) The production method according to any one of (1) to (3), wherein the outer diameter of the membrane is 500 μm or less;
(5) The method according to (1) to (4), wherein the membrane-forming polymer is a polysulfone-based polymer;
(6) The method according to (1) to (5), wherein the hydrophilic polymer is polyvinylpyrrolidone having a weight average molecular weight of 900,000 or more.
(7) The production method according to (1) to (6), wherein the solvent of the film-forming polymer is N-methyl-2-pyrrolidone, and (8) the spinning speed is 60 m / min or more. The production method according to any one of (1) to (7),
It is about.
[0011]
According to the production method of the present invention, an excellent hollow having a sponge structure in which the pore size is continuously reduced from the outer surface to the inner surface of the membrane, and having a blocking diameter in internal pressure filtration of 0.015 to 1 μm. A fibrous microfiltration membrane is obtained.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a method for producing the hollow fiber microfiltration membrane (hereinafter, also simply referred to as “membrane” or “hollow fiber membrane”) of the present invention will be described.
The hollow fiber microfiltration membrane obtained in the present invention is used in water supply fields such as river water, lake water, groundwater, removal of microorganisms from natural water such as seawater, removal of microorganisms, and preparation of aseptic water, and from electrodeposition paint solutions. It can be applied to a wide range of applications such as paint recovery field, ultrapure water production field for electronics industry, use in medicine / fermentation and food fields.
[0013]
The production method of the present invention comprises the steps of: forming a film-forming stock solution at a specific temperature consisting essentially of a film-forming polymer, a solvent for the polymer, and an additive consisting of a hydrophilic polymer; The liquid is discharged from a double annular nozzle together with the liquid, passed through an air gap having a specific ratio to the spinning speed, and then coagulated in a coagulation bath at a specific temperature.
[0014]
The film-forming polymer used in the production method of the present invention may be any polymer capable of forming a film by wet film formation, such as a polysulfone-based polymer, a polyvinylidene fluoride-based polymer, a polyacrylonitrile-based polymer, and a polymethacrylic acid-based polymer. Examples thereof include polymers, polyamide polymers, polyimide polymers, polyetherimide polymers, and cellulose acetate polymers. Among them, aromatic polysulfone is excellent in thermal stability, acid resistance, alkali resistance and mechanical strength, but because of its hydrophobicity, it can remove turbidity from natural water such as river water, lake water, groundwater, seawater, and remove microorganisms. In the field of paint recovery from an electrodeposition coating solution and in general industrial fields such as medicine and fermentation, there is a problem that clogging is likely to occur. By adding a hydrophilic polymer to a membrane-forming stock solution to form a membrane, it can be used in general industrial fields, and is also preferably used in the medical field because it can improve blood compatibility. As the aromatic polysulfone, bisphenol A type polysulfone is particularly preferably used.
[0015]
Examples of the aromatic polysulfone used in the present invention include those having a repeating unit represented by the following formula (1) or (2). In the formula, Ar represents a para-substituted phenyl group, and the degree of polymerization and molecular weight are not particularly limited.
_{-O-Ar-C (CH 3} ) 2 -Ar-O-Ar-SO 2 -Ar- (1)
—O—Ar—SO ₂ —Ar— (2)
[0016]
As the additive, a hydrophilic polymer that is compatible with the solvent and does not dissolve the film-forming polymer is used. If the film-forming polymer is a polysulfone-based polymer, polyvinylpyrrolidone is preferably used as an additive. Polyvinylpyrrolidone is preferred because of its particularly low toxicity among hydrophilic polymers. When the film-forming polymer is aromatic polysulfone, the use of an additive other than polyvinylpyrrolidone makes it difficult to obtain the film of the present invention.
[0017]
Polyvinylpyrrolidone has a higher effect of hydrophilizing the film as it has a higher molecular weight. Therefore, a smaller amount of polyvinylpyrrolidone can exert a sufficient effect. You. A large amount of polyvinylpyrrolidone needs to remain in the membrane in order to impart a hydrophilizing effect to the membrane using polyvinylpyrrolidone having a weight average molecular weight of less than 900,000. Will increase. Conversely, if the residual amount of polyvinylpyrrolidone having a weight average molecular weight of less than 900,000 in the film is reduced in order to reduce the eluate, the hydrophilizing effect becomes insufficient. In addition, if polyvinylpyrrolidone having a weight-average molecular weight of 900,000 or more is not used, the hydrophilicity in the film thickness portion is insufficient. At the part, so that good separation characteristics cannot be exhibited.
[0018]
Examples of the solvent for the polymer include N-methyl-2-pyrrolidone, N, N-dimethylformamide, and N, N-dimethylacetamide. When the film-forming polymer is a polysulfone-based polymer, N-methyl-2 -Pyrrolidone (hereinafter also simply referred to as "NMP") is preferred. NMP is the solvent having the highest dissolving power for the polysulfone-based polymer. For example, it has about 1.5 times the dissolving power at room temperature as compared with N, N-dimethylacetamide which is another good solvent. Non-solvent in the internal liquid induces liquid-liquid phase separation to open a large pore size of 0.01 μm or more on the inner surface of the membrane in a gradient structure where the pore size decreases continuously from the outer surface to the inner surface of the membrane. It is necessary to increase the time from the completion of the phase separation (solidification), that is, the particle growth time. In a polysulfone-based polymer, the particle growth time can be made longer by using NMP having a very high dissolving power than by using any solvent. Further, since NMP is the best solvent in the polysulfone-based polymer, the molecular chains of the polysulfone-based polymer in the membrane-forming stock solution are well entangled with each other, and as a result, a high-strength membrane can be obtained. For the above reasons, when the film-forming polymer is a polysulfone-based polymer, the use of a solvent other than NMP makes it difficult to obtain the film of the present invention.
[0019]
The film-forming stock solution consists essentially of a film-forming polymer, a specific additive such as polyvinylpyrrolidone, and a solvent of a specific polymer such as N-methyl-2-pyrrolidone. When other additives such as water and metal salts which are conventionally known as additives are added to the film forming stock solution, the film of the present invention is hardly obtained.
[0020]
From the above, it is most preferable that the membrane obtained by the production method of the present invention comprises aromatic polysulfone and polyvinylpyrrolidone. Furthermore, since the microfiltration membrane obtained from the production method of the present invention is used by internal pressure filtration, the concentration of polyvinylpyrrolidone on the inner surface of the membrane with which the liquid to be filtered comes into contact is preferably 20 to 45% by weight. . When the liquid to be filtered is blood or the like, an important factor for the blood compatibility of the membrane is the hydrophilicity of the inner surface of the membrane with which the blood comes into contact, and a polysulfone-based polymer containing polyvinylpyrrolidone (hereinafter also simply referred to as “PVP”). In a film, the PVP concentration on the inner surface of the film is important. If the PVP concentration on the inner surface of the membrane is too low, the inner surface of the membrane becomes hydrophobic, plasma proteins are easily adsorbed, and blood coagulation tends to occur. That is, the blood compatibility of the membrane becomes poor. Conversely, if the PVP concentration on the inner surface of the membrane is too high, the amount of PVP eluted into the blood system will increase, giving undesirable results. Therefore, the concentration of PVP when blood, plasma and serum are subjected to internal pressure filtration is in the range of 20 to 45% by weight, preferably 25 to 40% by weight.
[0021]
The PVP concentration on the inner surface of the film is determined by X-ray photoelectron spectroscopy (XPS). That is, the XPS of the inner surface of the film is measured by a usual method after arranging the samples on a double-sided tape, incising in the fiber axis direction with a cutter, spreading the film so that the inside of the film is exposed, and then spreading it. . That is, the concentration obtained from the surface intensity of nitrogen (nitrogen atom concentration) and the surface concentration of sulfur (nitrogen atom concentration) using the relative sensitivity coefficient attached to the device from the area intensity of the C1s, O1s, N1s, and S2p spectra. When the polysulfone-based polymer has the structure of the formula (2), it can be calculated by the formula (3).
PVP concentration (% by weight) = C ₁ M ₁ × 100 / (C ₁ M ₁ + C ₂ M ₂ ) (3)
Here, C ₁ : nitrogen atom concentration (%)
C ₂ : Sulfur atom concentration (%)
M ₁ : molecular weight of the repeating unit of PVP (111)
M ₂ : molecular weight of the repeating unit of the polysulfone-based polymer (442)
[0022]
The polymer concentration of the membrane-forming stock solution used in the present invention is not particularly limited as long as the membrane can be formed from the stock solution, and the obtained membrane has a performance as a membrane in a concentration range. It is 35% by weight, preferably 10 to 30% by weight. In order to achieve high water permeability or a large molecular weight cut-off, the lower the polymer concentration, the better, and preferably 10 to 25% by weight.
[0023]
What is more important is the amount of the additive (hydrophilic polymer) in the film forming stock solution, and the mixing ratio of the additive to the polymer is 20 to 60% by weight, preferably 27 to 60% by weight. If the mixing ratio of the additive to the polymer is less than 20% by weight, the pore diameter on the inner surface of the film tends to be small, 0.01 μm or less, and if it exceeds 60% by weight, the viscosity of the film forming stock solution increases, and It is not preferable because the spinnability tends to deteriorate.
[0024]
Further, the temperature of the film forming solution is important, and the temperature of the film forming solution at the time of discharge by the nozzle is 50 ° C. or more, preferably 60 to 100 ° C. If the temperature is lower than 50 ° C., spinnability during film formation is poor.
[0025]
The internal liquid is used to form the hollow portion of the hollow fiber membrane, and is composed of water and a good solvent for at least one or more types of the film-forming polymers. The water content is preferably from 35 to 55% by weight. If the water content is less than 35% by weight, the spinnability at the time of film formation is poor, and if it exceeds 55% by weight, the pore size on the inner surface of the film tends to be as small as 0.01 μm or less.
[0026]
Air gap refers to the gap between the nozzle and the coagulation bath. The ratio of the air gap (m) to the spin speed (m / min) is very important for obtaining the membrane of the present invention. Because, in the membrane structure of the present invention, the non-solvent in the internal solution comes into contact with the stock solution to induce phase separation over time from the inner surface portion to the outer surface portion side of the stock solution. This is because if the phase separation from the inner surface portion of the membrane to the outer surface portion is not completed before the film forming stock solution enters the coagulation bath, it cannot be obtained.
[0027]
The ratio of the air gap to the spinning speed is preferably from 0.01 to 0.1 m / (m / min), and more preferably from 0.01 to 0.05 m / (m / min). If the ratio of the air gap to the spinning speed is less than 0.01 m / (m / min), it is difficult to obtain a film having the structure and performance of the present invention. This is not preferable because the film tension tends to be high in the air gap portion due to high tension, and the production tends to be difficult.
[0028]
The spinning speed greatly contributes to the production efficiency. Therefore, the higher the spinning speed, the better. However, it is impossible to increase the spinning speed because the spinning speed increases and the tension increases. However, the spinning speed is 60 m / m in the present invention. Min or more, and even 70-120 m / min.
Here, the spinning speed refers to a film forming stock solution discharged from the nozzle together with the internal solution, passes through an air gap, and is wound in a coagulation bath. It means the winding speed when there is no operation. Further, when the air gap is surrounded by a cylindrical tube or the like, and a gas having a certain temperature and humidity flows through the air gap at a certain flow rate, the hollow fiber membrane can be manufactured in a more stable state.
[0029]
As the coagulation bath, a liquid that does not dissolve the polymer such as water; alcohols such as methanol and ethanol; ethers; and aliphatic hydrocarbons such as n-hexane and n-heptane is used, but water is preferable. It is also possible to control the coagulation rate and the like by adding a small amount of a solvent that dissolves the polymer to the coagulation bath.
The temperature of the coagulation bath is 85-100 ° C, preferably 90-100 ° C. If the temperature of the coagulation bath is lower than 85 ° C., the pore diameter on the inner surface of the film tends to be small, less than 0.01 μm.
[0030]
Further, in order to obtain the film of the present invention, the ratio of the film thickness to the inner diameter of the film after coagulation is 0.15 to 0.4, preferably 0.2 to 0.3. If the ratio of the film thickness to the inner diameter of the film is less than 0.15, the absolute strength of the film tends to be weak. On the other hand, if the ratio exceeds 0.4, it tends to be difficult to obtain an inclined structure in which the pore diameter decreases from the outer surface to the inner surface (or the inner surface portion) of the film as in the present invention. Because the ratio of the amount of solvent in the stock solution to the amount of non-solvent in the internal solution is large, the amount of non-solvent in the internal solution alone means that from the inner surface of the film of the stock solution before entering the coagulation bath. This is because phase separation up to the outer surface cannot be completed.
[0031]
Further, the outer diameter of the film is 500 μm or less, preferably 400 μm or less, and more preferably 300 μm or less. If the outer diameter of the membrane is large, the area (filling amount) of the membrane in the module must be reduced, and as a result, the processing capacity per unit time is inferior, which is not preferable. Conversely, in order to increase the outer diameter of the membrane and make the membrane area (filling amount) in the module the same, the module container must be enlarged, which results in an increase in cost, which is not preferable. In particular, it is necessary to avoid using large modules that are expensive for medical use in order to reduce the burden of medical expenses on patients. The outer diameter of the film is preferably 500 μm or less in view of the relationship between the processing capacity and the cost.
[0032]
Further, the membrane of the present invention can be dried, and does not have to be impregnated with a humectant such as glycerin at the time of drying.
In addition, by irradiating the film with radiation such as an electron beam and γ-ray, a part of PVP in the film can be insolubilized in water, so that the amount of elution from the film can be reduced. Irradiation with radiation may be performed before or after modularization. Further, if all the PVP in the membrane is insolubilized, the swelling property of the membrane deteriorates and the separation performance deteriorates, which is not preferable.
[0033]
The term "PVP insoluble in water" as used in the present invention is obtained by subtracting the amount of PVP soluble in water from the total amount of PVP in the membrane. The total amount of PVP in the film can be easily calculated by elemental analysis of nitrogen and sulfur.
The amount of PVP soluble in water can be determined by the following method.
For example, when the membrane-forming polymer is a polysulfone-based polymer, after completely dissolving the membrane with N-methyl-2-pyrrolidone, water is added to the obtained polymer solution to completely precipitate the membrane-forming polymer. Further, after the polymer solution is allowed to stand, PVP soluble in water can be determined by determining the amount of PVP in the supernatant by liquid chromatography.
[0034]
【Example】
Hereinafter, examples of the present invention will be described, but the present invention is not limited thereto.
Each measuring method is as follows.
The hollow fiber membranes used as the measurement samples were all fully impregnated with water.
[0035]
(Measurement of water permeability)
A thread bundle having an effective length of 180 mm (both mini-modules having the same number of membranes so as to have an inner surface area of 110 ± 10 cm ² ) whose both ends are fixed with an adhesive is transmitted from the inner surface to the outer surface, and the amount is mL (milliliter). ) / (M ² · hr · mmHg). However, the effective film area was converted to the inner surface.
[0036]
(Measurement of breaking strength)
The film strength was measured using an Autograph AGS-5D manufactured by Shimadzu Corporation at a sample length of 20 mm and a pulling speed of 300 mm / min.
[0037]
(Measurement of blocking diameter)
If the pore diameter of the inner surface of the membrane is smaller than 0.05 μm or a slit-shaped pore, measuring the pore size increases the error and has no meaning. The diameter was used as an index of the pore diameter on the inner surface of the membrane. The inhibition diameter in the internal pressure filtration in the present invention was determined by the following method.
1) A stock solution prepared by suspending polystyrene latex particles having a particle size accuracy of within ± 4% at a concentration of 0.02% by volume in a 0.2% by weight aqueous solution of sodium dodecyl sulfate was added to both ends. The average pressure of the input pressure and the output pressure is 0.5 kgf / with respect to a yarn bundle having an effective length of 180 mm (the number of membranes is adjusted so as to be 110 ± 10 cm ² in terms of the internal surface area) in which is fixed with an adhesive. Internal pressure filtration was performed under the conditions of cross flow of cm ² and a fluid linear velocity of 1 cm / sec, and the rejection of the concentration of the filtrate and the original solution after 40 minutes was determined. At this time, it is necessary that the rejection rate does not change with time, and the deviation of the absolute value of the rejection rate after 20 minutes, 40 minutes, and 60 minutes must be within ± 10%. The concentrations of the obtained filtrate and the original solution are measured at a wavelength of 280 nm using an ultraviolet spectrophotometer, and substituted into the following equation (4) to calculate the rejection. 2) Next, the minimum particle size of the latex particles used in 1) in which the rejection was 90% or more was defined as the rejection diameter of the film.
Inhibition rate (%) = {1- (absorbance of filtrate) / (absorbance of original solution)} × 100 (4) For measuring the inhibition diameter, 0.0147 μm (manufactured by Magsphere, polystyrene-based polymer, 0.0147 μm) 0.028 μm (manufactured by Magsphere, polystyrene-based polymer, 0.028 μm), 0.037 μm (manufactured by Magsphere, polystyrene-based polymer, 0.037 μm), 0.062 μm (manufactured by Seradyn, polystyrene-based polymer, 0.062 μm) ), 0.088 μm (Seradyn, polystyrene-based polymer, 0.088 μm) and 0.102 μm (Seradyn, polystyrene-based polymer, 0.102 μm) latex particles (each particle size accuracy ± 4%) did.
[0038]
(Measurement of porosity on membrane surface)
The aperture ratio was determined by numerically analyzing an electron micrograph of the outer surface of the film and analyzing the image. The aperture ratio according to the present invention is defined as a percentage of the sum of the area of the opening portion and the area of the worked image, and is given by the following equation (5). In addition, 10 pixels or less were considered as noise and were excluded from the count.
Perforation rate (%) = (total of perforated area of perforated part / area of captured image) × 100 (5)
[0039]
(Measurement of average pore diameter on membrane surface)
The shape and size of the holes opened on the surface of the film were observed and measured using an electron microscope.
The average pore diameter D of the pores opened on the inner surface and the outer surface is a value represented by the following equation (6).
D = [{(D _i ² ) ² +... + (D _n ² ) ² } / {D _i ² +... + D _n ² }] ^1/2 (6)
Here, D is the average pore diameter, _Di is the measured diameter of the _i- th hole, and Dn is the measured diameter of the _n- th hole. However, the measured diameters of D _i and D _n are represented by the diameter of the hole when the hole is close to a circle, and by the diameter of a circle having the same area as the hole when the hole is not circular.
[0040]
Embodiment 1
(Film formation and removal of residual solvent)
20.0% by weight of polysulfone (P-1700 manufactured by Amoco Engineering Polymers) and 4.4% by weight of polyvinylpyrrolidone (K90 manufactured by BASF, weight average molecular weight 1,200,000) were added to N-methyl-2-pyrrolidone 75. It was dissolved in 6% by weight to obtain a uniform solution. Here, the mixing ratio of polyvinylpyrrolidone to polysulfone in the membrane-forming stock solution was 22.0% by weight. This membrane-forming stock solution was kept at 60 ° C., and an internal solution (water content was 46% by weight) consisting of a mixed solution of 54% by weight of N-methyl-2-pyrrolidone and 46% by weight of water was spun (dual cyclic). Nozzle 0.1mm-0.2mm-0.3mm, Nozzle temperature 60 ° C, Temperature of film forming stock solution at the nozzle part 60 ° C), water through a 0.96m air gap, 95 ± 1 ° C water In a coagulation bath consisting of
At this time, the space from the spinneret to the coagulation bath was surrounded by a cylindrical tube, and was sealed so that outside air did not enter. The spinning speed was fixed at 80 m / min. Here, the ratio of the air gap to the spinning speed was 0.012 m / (m / min).
After the wound yarn bundle was cut, the remaining solvent in the film was removed by washing with a hot water shower at 80 ° C. for 2 hours from above the cut surface of the yarn bundle. Further, a part of PVP in the film was insolubilized by irradiating 2.5 Mrad of γ-ray.
[0041]
Observation of the obtained film with an electron microscope revealed that the film had a sponge structure in which the pore diameter was continuously reduced from the outer surface to the inner surface. Table 1 shows other film structures and film performances. The breaking strength of the membrane was as high as 50 kgf / cm ² or more, and it was revealed that the membrane was a microfiltration membrane having excellent water permeability of 1,000 mL / m ² · hr · mmHg or more. Furthermore, even when the latex particles having an average particle size of 0.062 μm were subjected to internal pressure filtration, the amount of filtrate remained stable for a long time without a rapid clogging.
[0042]
Embodiment 2
The same operation as in Example 1 was carried out except that polyvinylpyrrolidone was 10% by weight and N-methyl-2-pyrrolidone was 70% by weight in the film-forming stock solution. At this time, the mixing ratio of polyvinylpyrrolidone to polysulfone in the membrane-forming stock solution was 50.0% by weight. Observation of the obtained film with an electron microscope revealed that the film had a sponge structure in which the pore diameter was continuously reduced from the outer surface to the inner surface. Table 1 shows other film structures and film performances. The breaking strength of the membrane was as high as 50 kgf / cm ² or more, and it was revealed that the membrane was a microfiltration membrane having excellent water permeability of 1,000 mL / m ² · hr · mmHg or more. Further, even when the latex particles having an average particle size of 0.037 μm used for the measurement of the blocking diameter were subjected to the internal pressure filtration, the amount of the filtrate remained stable for a long time without rapid clogging.
[0043]
Embodiment 3
The same operation as in Example 1 was performed except that an internal liquid (water content: 37% by weight) composed of a mixed solution of 63% by weight of N-methyl-2-pyrrolidone and 37% by weight of water was used. Observation of the obtained film with an electron microscope revealed that the film had a sponge structure in which the pore diameter was continuously reduced from the outer surface to the inner surface. Table 1 shows other film structures and film performances. The breaking strength of the membrane was as high as 50 kgf / cm ² or more, and it was revealed that the membrane was a microfiltration membrane having excellent water permeability of 1,000 mL / m ² · hr · mmHg or more. Further, even when the latex particles having an average particle diameter of 0.102 μm used for the measurement of the inhibition diameter were subjected to internal pressure filtration, the amount of filtrate remained stable for a long time without a rapid clogging.
[0044]
Embodiment 4
The same operation as in Example 1 was performed except that an internal liquid (water content was 54% by weight) composed of a mixed solution of 46% by weight of N-methyl-2-pyrrolidone and 54% by weight of water was used. Observation of the obtained film with an electron microscope revealed that the film had a sponge structure in which the pore diameter was continuously reduced from the outer surface to the inner surface. Table 1 shows other film structures and film performances. The breaking strength of the membrane was as high as 50 kgf / cm ² or more, and it was revealed that the membrane was a microfiltration membrane having excellent water permeability of 1,000 mL / m ² · hr · mmHg or more. Further, in the internal pressure filtration of the latex particles having an average particle size of 0.028 μm used for the measurement of the inhibition diameter, the amount of filtrate maintained without a sudden clogging was maintained for a long time.
[0045]
Embodiment 5
The same operation as in Example 1 was performed except that the polyvinylpyrrolidone in the film forming solution was 6.6% by weight and the N-methyl-2-pyrrolidone was 73.4% by weight. At this time, the mixing ratio of polyvinylpyrrolidone to polysulfone in the membrane-forming stock solution was 33.0% by weight. Observation of the obtained film with an electron microscope revealed that the film had a sponge structure in which the pore diameter was continuously reduced from the outer surface to the inner surface. Table 1 shows other film structures and film performances. The breaking strength of the membrane was as high as 50 kgf / cm ² or more, and it was revealed that the membrane was a microfiltration membrane having excellent water permeability of 1,000 mL / m ² · hr · mmHg or more. Further, even when the latex particles having an average particle diameter of 0.088 μm used for the measurement of the inhibition diameter were subjected to the internal pressure filtration, the amount of the filtrate remained stable for a long time without rapid clogging.
[0046]
[Comparative Example 1]
The same operation as in Example 1 was performed except that the amount of polyvinylpyrrolidone was 3.4% by weight and the amount of N-methyl-2-pyrrolidone was 76.6% by weight in the stock solution for film formation. At this time, the mixing ratio of polyvinylpyrrolidone to polysulfone in the membrane-forming stock solution was 17.0% by weight. Observation of the obtained film with an electron microscope revealed that the film had a sponge structure in which the pore diameter was continuously reduced from the outer surface to the inner surface. Table 2 shows other film structures and film performances. The average pore diameter on the inner surface of the membrane was 0.01 μm or less. In addition, since the rejection of latex particles of 0.0147 μm was 100% from the initial stage, it was clear that the rejection diameter of this film was less than 0.0147 μm.
[0047]
[Comparative Example 2]
A homogeneous solution could not be obtained in which 20% by weight of polysulfone used in Example 1, 13% by weight of polyvinylpyrrolidone, and 67% by weight of N-methyl-2-pyrrolidone were dissolved.
[0048]
[Comparative Example 3]
The same operation as in Example 1 was performed except that an internal liquid (water content was 57% by weight) composed of a mixed solution of 43% by weight of N-methyl-2-pyrrolidone and 57% by weight of water was used. Observation of the obtained film with an electron microscope revealed that the film had a sponge structure in which the pore diameter was continuously reduced from the outer surface to the inner surface. Table 2 shows other film structures and film performances. The average pore diameter on the inner surface of the membrane was 0.01 μm or less. In addition, since the rejection of latex particles of 0.0147 μm was 100% from the initial stage, it was clear that the rejection diameter of this film was less than 0.0147 μm.
[0049]
[Comparative Example 4]
The same operation as in Example 1 was performed except that an internal solution (water content was 62% by weight) composed of a mixed solution of N-methyl-2-pyrrolidone 62% by weight and water 38% by weight was used. Thread breakage occurred frequently and spinning was not possible.
[0050]
[Comparative Example 5]
The same operation as in Example 2 was performed except that the temperature of the film forming solution was set at 45 ° C. and the nozzle temperature was set at 45 ° C. (temperature of the film forming solution at the nozzle portion was 45 ° C.). could not.
[0051]
[Comparative Example 6]
The same operation as in Example 1 was performed except that the solvent was changed from N-methyl-2-pyrrolidone to N, N-dimethylacetamide. Observation of the obtained film with an electron microscope revealed that the film had a sponge structure in which the pore diameter was continuously reduced from the outer surface to the inner surface. Table 2 shows other film structures and film performances. The average pore diameter on the inner surface of the membrane was 0.01 μm or less. In addition, since the rejection of latex particles of 0.0147 μm was 100% from the initial stage, it was clear that the rejection diameter of this film was less than 0.0147 μm.
[0052]
[Table 1]

[0053]
[Table 2]

[0054]
【The invention's effect】
The membrane obtained from the production method of the present invention is a microfiltration membrane having an anisotropic structure having high strength and excellent water permeability, and is particularly an excellent microfiltration membrane having little clogging in internal pressure filtration. It can be used for pharmaceutical applications, medical applications, and general industrial applications.

Claims (8)

A method for producing a hollow fiber membrane in which a stock solution and an internal solution are discharged from a double annular nozzle and then passed through an air gap and then coagulated in a coagulation bath.
a) the membrane-forming stock solution is composed of a film-forming polymer, a solvent for the polymer, and a hydrophilic polymer, and the ratio of the hydrophilic polymer to the film-forming polymer is 20 to 60% by weight;
b) the internal liquid is composed of water and at least one solvent, and has a water content of 35 to 55% by weight;
c) the temperature of the stock solution at the nozzle is 50 ° C. or more,
d) the coagulation bath temperature is 85 to 100 ° C., and e) the ratio of the air gap to the spinning speed is 0.01 to 0.1 m / (m / min).
A method for producing a hollow fiber microfiltration membrane, characterized in that: The method according to claim 1, further comprising irradiating radiation. 3. The method according to claim 1, wherein the ratio of the film thickness to the inner diameter of the film is 0.15 to 0.4. The method according to any one of claims 1 to 3, wherein the outer diameter of the membrane is 500 µm or less. The method according to any one of claims 1 to 4, wherein the film-forming polymer is a polysulfone-based polymer. The method according to any one of claims 1 to 5, wherein the hydrophilic polymer is polyvinylpyrrolidone having a weight average molecular weight of 900,000 or more. The method according to any one of claims 1 to 6, wherein the solvent for the film-forming polymer is N-methyl-2-pyrrolidone. The method according to any one of claims 1 to 7, wherein the spinning speed is 60 m / min or more.