KR102219541B1 - Hollow fiber membrane - Google Patents

Abstract

^{The hollow fiber membrane of the present invention has a dense layer having only pores with a pore area of 0.28 μm 2} or less in a state observed from a cross section perpendicular to the longitudinal direction of the hollow fiber membrane, and the dense layer is the outer surface side or the inner surface of the hollow fiber membrane. It is arranged on the side, the outer diameter is 350 μm or less, the inner diameter is 150 μm or more, the film thickness is 30 μm or more and 90 μm or less, and the surface of the hollow fiber membrane on which the dense layer is disposed has a plurality of pores, and The average pore diameter observed from the surface of the hollow fiber membrane of the pores is 0.3 µm or more and 0.9 µm or less, and the ratio (DT/WT) of the thickness of the dense layer (DT) to the film thickness (WT) of the hollow fiber membrane is 0.24 or more.

Description

Hollow fiber membrane

The present invention relates to a hollow fiber membrane.

Hollow fiber membranes have been widely used conventionally in fields ranging from reverse osmosis to microfiltration. As a use, it is widely used in medical applications such as blood purifiers for patients with renal failure and water treatment applications such as water purifiers.

Hydrophobic polymers such as polyethylene and polysulfone are known as the material of the hollow fiber membrane, and it is known that a hollow fiber membrane using these materials is subjected to a hydrophilic treatment. The hydrophilization treatment includes a method of coating the hollow fiber membrane with a hydrophilic polymer after film formation, or a method of imparting hydrophilicity by discharging an infusion solution containing a hydrophilic polymer together with the spinning dope of the hollow fiber membrane from a bicyclic detention. By carrying out such a hydrophilic treatment, the water permeability of the hollow fiber membrane is improved.

In addition, the characteristics required for the cartridge for a water purifier include resistance to high water pressure, high water permeability, high material removal characteristics, and long cartridge life. To this end, as a hollow fiber membrane for a water purifier, development of a hollow fiber membrane having high water permeability and sharp material fractionation performance while having strength to withstand water pressure has been conducted.

For example, Patent Document 1 discloses a method of spinning a hollow fiber membrane at a high spinning draft rate of 100 or 185 in the melt spinning method in order to improve resistance to high water pressure.

Patent Document 2 discloses a method of controlling the pore structure of the membrane by controlling the spinning draft rate and increasing the water permeability in a hollow fiber membrane having an asymmetric structure in which a dense layer is formed.

In addition, it is known that it is effective to increase the area of the hollow fiber membrane in order to extend the life of the water purifier cartridge.

Japanese Patent Laid-Open Publication No. Hei 04-018112 International Publication No. 2010/029908

However, the hollow fiber membrane obtained by the manufacturing method disclosed in Patent Document 1 is excellent in resistance to high water pressure, but the cross-sectional structure of the hollow fiber membrane is uniform, that is, because all the micropores present in the cross section of the hollow fiber membrane are dense, the water permeability is lowered. There is a task of falling. Here, as a means of increasing the water permeability of the hollow fiber membrane, it is considered to increase the pore area of the micropores, but in this case, there is a problem that the hollow fiber membrane becomes inferior in the fractionation performance.

Further, although the hollow fiber membrane disclosed in Patent Document 2 has a dense layer and a non-tight layer, and the pore structure is controlled, the water permeability is excellent, but there is a problem that resistance to high water pressure is inferior.

In addition, when the membrane area of the hollow fiber membrane provided in the water purifier cartridge is increased in order to prolong the product life of the water purifier cartridge (hereinafter, referred to as a cartridge) having a hollow fiber membrane, there is a problem that the cartridge becomes large. Therefore, in order to increase the membrane area of the hollow fiber membrane and to suppress the enlargement of the cartridge, it is considered that the hollow fiber membrane is thinner, but in this case, this hollow fiber membrane tends to be inferior in resistance to high water pressure and inferior water permeability. . Further, when the hollow fiber membrane having a dense layer is thinned, the resistance of the hollow fiber membrane to a high water pressure is further inferior.

Therefore, in view of the above problems, an object of the present invention is to provide a hollow fiber membrane having excellent resistance to high water pressure and excellent water permeability, and to achieve a long life of a water purifier cartridge equipped with a hollow fiber membrane.

In order to solve the above problems, the present invention is characterized by the following (1) to (5).

^{(1) A hollow fiber membrane having a dense layer having only pores having a pore area of 0.28 μm 2} or less in a state observed from a cross section perpendicular to the longitudinal direction of the hollow fiber membrane, wherein the dense layer is at the outer surface side of the hollow fiber membrane or It is disposed on the inner surface side, the outer diameter of the hollow fiber membrane is 350 μm or less, the inner diameter of the hollow fiber membrane is 150 μm or more, the thickness of the hollow fiber membrane is 30 μm or more and 90 μm or less, and the dense layer is disposed The surface of the hollow fiber membrane formed has a plurality of pores, the average pore diameter observed from the surface of the hollow fiber membrane of the plurality of pores is 0.3 μm or more and 0.9 μm or less, and the thickness of the dense layer (DT) and the A hollow fiber membrane having a film thickness (WT) ratio (DT/WT) of 0.24 or more.

(2) The hollow fiber membrane according to (1) above, wherein the dense layer is disposed on the outer surface side of the hollow fiber membrane.

(3) The hollow fiber membrane according to (1) or (2) above, wherein the surface opening ratio of the hollow fiber membrane on which the dense layer is disposed is 15% or more and 45% or less.

(4) The hollow fiber membrane according to any one of (1) to (3) above, comprising a polysulfone-based polymer and polyvinylpyrrolidone.

(5) A cartridge for a water purifier equipped with the hollow fiber membrane according to any one of (1) to (4) above.

(Effects of the Invention)

Advantageous Effects of Invention According to the present invention, a hollow fiber membrane having excellent resistance to high water pressure and excellent water permeability can be provided, and a longer life of a cartridge for a water purifier equipped with a hollow fiber membrane can be realized.

Hereinafter, preferred embodiments of the present invention will be described in detail.

In addition, in this specification, all percentages and parts expressed by mass are the same as percentages and parts expressed by weight.

In the prior art, when the hollow fiber membrane having a dense layer is thinned, the resistance of the hollow fiber membrane to high water pressure is inferior (deterioration of the strength of the hollow fiber membrane occurs), and sufficient water permeability performance cannot be obtained. Therefore, the present inventors found that the outer diameter, inner diameter, and film thickness of the hollow fiber, and the structure of the dense layer greatly affect the strength improvement and water permeability of the hollow fiber membrane, and the state observed from the cross section perpendicular to the length direction of the hollow fiber membrane WHEREIN: A hollow fiber membrane comprising a dense layer having only pores having a pore area of 0.28 ^{μm 2} or less, wherein the dense layer is disposed on the outer or inner surface side of the hollow fiber membrane, and the outer diameter of the hollow fiber membrane is 350 μm or less, The inner diameter of the hollow fiber membrane is 150 μm or more, the thickness of the hollow fiber membrane is 30 μm or more and 90 μm or less, and the surface of the hollow fiber membrane on which the dense layer is disposed has a plurality of pores, and on the surface of the hollow fiber membrane of the plurality of pores The hollow fiber membrane of the present invention was created in which the observed average pore diameter was 0.3 µm or more and 0.9 µm or less, and the ratio (DT/WT) of the thickness of the dense layer (DT) to the film thickness (WT) of the hollow fiber membrane was 0.24 or more.

As described above, since the hollow fiber membrane of the present invention has an outer diameter of 350 μm or less, it can be mounted in a number of compact hollow fiber membrane modules (hereinafter sometimes referred to as modules) or cartridges for water purifiers. The product life of can be made excellent.

Further, from the viewpoint of improving the water permeability and product life of the cartridge, it is preferable that the outer diameter of the hollow fiber membrane is small, the inner diameter is large, and the thickness is thin. Further, from the viewpoint of making the hollow fiber membrane excellent in strength, it is preferable that the outer diameter of the hollow fiber membrane is large, the inner diameter is small, and the thickness is thick. It is important to control the structure of the dense layer in order to satisfy these conflicting conditions. The structure of the dense layer greatly affects the strength maintenance and water permeability of the membrane. From the above point of view, it is important that the outer diameter of the hollow fiber membrane is 350 µm or less, and the lower limit is preferably 190 µm or more, more preferably 220 µm or more, and even more preferably 260 µm or more. On the other hand, the upper limit is preferably 330 µm or less, and more preferably 310 µm or less. In addition, it is important that the hollow fiber membrane has an inner diameter of 150 µm or more, and the lower limit thereof is preferably 155 µm or more, and more preferably 160 µm or more. On the other hand, the upper limit is preferably 220 µm or less, more preferably 210 µm or less, and even more preferably 200 µm or less.

It is important that the thickness of the hollow fiber membrane is 30 µm or more and 90 µm or less, and the lower limit is preferably 40 µm or more, and more preferably 50 µm or more. On the other hand, the upper limit is preferably 80 µm or less, and more preferably 70 µm or less.

The hollow fiber membrane of the present invention has a dense layer, and this dense layer is disposed on the outer surface side or the inner surface side of the hollow fiber membrane. In addition, since the hollow fiber membrane of the present invention has a plurality of pores on the surface of the hollow fiber membrane on which the dense layer is disposed, and the average pore diameter observed from the surface of the hollow fiber membrane of the plurality of pores is 0.3 μm or more, the water permeability of the hollow fiber membrane is It becomes extremely good. On the other hand, since the average pore diameter of the pores observed from the surface of the hollow fiber membrane is 0.9 μm or less, the strength of the hollow fiber membrane can be made excellent, and the performance of removing turbid substances such as bacteria and fine particles can be improved. From the above point of view, the lower limit of the average pore diameter of the plurality of pores is preferably 0.35 μm or more, and more preferably 0.40 μm or more. On the other hand, the upper limit of the average pore diameter of the plurality of pores is preferably 0.85 µm or less, and more preferably 0.80 µm or less. Here, the dense layer means that when a cross section perpendicular to the length direction of the hollow fiber membrane is observed with a scanning electron microscope (SEM), ^{the existence of a hole having a hole area exceeding 0.28 µm 2} is not confirmed, that is, the hole area is 0.28 µm ² It refers to a layer having only the following holes. In addition, in the hollow fiber membrane of the present invention, it is preferable that macro voids or finger voids are not formed in the cross section of the membrane.

In addition, since the hollow fiber membrane of the present invention has a ratio (DT/WT) of the dense layer thickness (DT) and the thickness (WT) of the hollow fiber membrane to 0.24 or more, the strength of the hollow fiber membrane can be sufficiently maintained. Not only resistance to high water pressure, but also workability and handling required for modularization can be excellent. The thickness of the dense layer can be measured by the method described in Examples.

In addition, it is preferable that the dense layer of the hollow fiber membrane is disposed on the surface of the hollow fiber membrane in contact with the water to be treated. For example, when the water to be treated is allowed to permeate from the outer surface side of the hollow fiber membrane to the inner surface side, it is preferable to arrange a dense layer on the outer surface side of the hollow fiber membrane. The reason is that since it is possible to prevent the turbidity contained in the water to be treated from entering the interior of the hollow fiber membrane, deterioration in filtration resistance due to clogging of pores can be suppressed, and a decrease in water permeability of the membrane can be suppressed.

Further, the hollow fiber membrane of the present invention has a plurality of pores on the surface of the hollow fiber membrane on which the dense layer is disposed, and the porosity on this surface is preferably 15% or more and 45% or less. If the pore rate on the surface of the dense layer side of the hollow fiber membrane is 15% or more, it is preferable because the water permeability is excellent. On the other hand, when the porosity on the surface of the dense layer side of the hollow fiber membrane is 45% or less, its strength and removal performance can be sufficiently maintained. From the above viewpoint, the lower limit of the porosity is more preferably 18% or more, and still more preferably 21% or more. In addition, the upper limit of the porosity is more preferably 42% or less, and even more preferably 39% or less. In addition, as a means for adjusting the porosity on the surface of the dense layer side of the hollow fiber membrane to the above range, in the method for producing a hollow fiber membrane, controlling the phase separation rate of the polymer by adjusting the atmosphere of the dry part, or adjusting the content of the hydrophilic polymer. Can be mentioned.

In addition, it is preferable that the hollow fiber membrane of the present invention contains a hydrophilic polymer. The reason is that by imparting hydrophilicity to the membrane surface, it is possible to improve the water permeability and also suppress the adhesion of the turbidity to the membrane. On the other hand, when the content of the hydrophilic polymer is large, the hydrophilic polymer itself has a permeability resistance in order to retain water, and the water permeability decreases. Therefore, the upper limit of the content of the hydrophilic polymer is preferably 20 parts by mass or less, and more preferably 15 parts by mass or less with respect to the total mass of the hollow fiber membrane. On the other hand, the lower limit is preferably 3 parts by mass or more, and more preferably 5 parts by mass or more. In addition, when a large number of crosslinked hydrophilic polymers exist on the membrane surface of the hollow fiber membrane, there is a tendency that a decrease in water permeability is observed. Therefore, the ratio of the hydrophilic polymer and the hydrophobic polymer (hydrophilic polymer/hydrophobic polymer) on the surface of the hollow fiber membrane in which the dense layer is present is preferably 0.80 or less, and more preferably 0.70 or less. In addition, from the above viewpoint, the ratio of the hydrophilic polymer and the hydrophobic polymer (hydrophilic polymer/hydrophobic polymer) on the surface opposite to the surface of the hollow fiber membrane in which the dense layer is present is also preferably 0.80 or less, and more preferably 0.70 or less.

Here, the hydrophilic polymer refers to a water-soluble polymer compound or a polymer compound that interacts with water molecules by electrostatic interaction or hydrogen bonding even if it is water-insoluble. Specifically, polyalkylene oxides such as polyethylene oxide and polypropylene oxide, polyvinyl alcohol, polyvinylpyrrolidone (hereinafter sometimes referred to as PVP), polyvinyl acetate, polydimethyl methoxyacrylate, polydimethylacrylic Amides, copolymers of vinylpyrrolidone and acrylic acid, nonionic hydrophilic polymers such as copolymers of vinyl acetate and vinylpyrrolidone, anionic hydrophilic polymers such as polyacrylic acid, polyvinylsulfuric acid, and carboxymethylcellulose, polyallylamine, Cationic hydrophilic polymers such as polylysine, chitosan, and poly[methacrylic acid {2(dimethylamino)ethyl}] are used in polymethacryloyloxyethylphosphorylcholine, polymethacryloyloxyethyldimethylammoniumpropionate, etc. Amphoteric ionic hydrophilic polymers of. Further, the number of hydrophilic polymers contained in the hollow fiber membrane may be two or more. In particular, nonionic hydrophilic polymers and amphoteric ionic hydrophilic polymers are suitably used from the viewpoint of suppressing the adhesion of the suspension.

As the material (component) constituting the base of the hollow fiber membrane, a hydrophobic polymer is preferable, and the hydrophobic polymer is a polysulfone polymer such as polysulfone (hereinafter sometimes referred to as PSF), polyethersulfone, polyallylate, and poly Fluorinated resins such as vinylidene fluoride, cellulose resins such as cellulose triacetate, cellulose diacetate, polymethyl methacrylate, polyacrylonitrile, polyamide, etc. are suitably used. Among them, the strength of the hollow fiber membrane, Polysulfone-based polymers are suitably used from the viewpoint of water permeability. The addition of PVP to the spinning dope made of a polysulfone polymer is particularly preferred from the viewpoint of easy control of the film structure of the present invention.

The composition ratio of the hollow fiber membrane is a mass ratio (%), and the polysulfone-based polymer is preferably 5 to 20% with respect to the entire constituent components of the hollow fiber membrane.

In addition, the hollow fiber membrane preferably contains polyvinylpyrrolidone in addition to the polysulfone-based polymer. In addition, although polyvinylpyrrolidone can use various molecular weights, K90 (trade name, manufactured by ISP, weight average molecular weight 1.3 million), K60 (trade name, manufactured by Tokyo Chemical Industry Co., Ltd., weight average molecular weight) 160,000), K30 (brand name, manufactured by BASF, weight average molecular weight 40,000), K17 (brand name, manufactured by ISP, weight average molecular weight 10,000), etc., are convenient to use. These mixtures or those having a molecular weight range other than the above may be used by polymerization.

In addition, in the manufacturing process of the hollow fiber membrane, constituents of the hollow fiber membrane such as polysulfone polymer or PVP are dissolved in a solvent to obtain a spinning dope. Here, the solvent is preferably a high-boiling polar solvent such as dimethylacetamide (hereinafter abbreviated as DMAc) or N-methylpyrrolidone, but other combinations may be used as long as it can be dissolved uniformly.

The water permeability of the hollow fiber membrane of the present invention is preferably 30 ml/Pa/hr/m 2 or more, more preferably 35 ml/Pa/hr/m 2 or more, and still more preferably 40 ml/Pa/hr/m 2 or more. . In addition, the upper limit of the water permeability of the hollow fiber membrane is not particularly limited, but the upper limit of the water permeability of the hollow fiber membrane is preferably 120 ml/Pa/hr/m2 or less, since there is a possibility that the fractionation performance may be lowered if the water permeability is too high. , It is more preferable that it is 110 ml/Pa/hr/m 2 or less, and it is more preferable that it is 100 ml/Pa/hr/m 2 or less.

As the fractionation performance of the hollow fiber membrane, the removal rate of latex bead particles having a particle diameter of 0.2 µm is preferably 80% or more, and more preferably 90% or more.

The hollow fiber membrane of the present invention includes the composition of the spinning dope and the composition of the injection liquid, the discharge linear speed and the injection liquid discharge linear speed when discharging the spinning dope from the detention center, the dew point and temperature of the cold air of the dry part after discharge, the cold wind speed, and the spinning dope discharge. It is obtained by controlling the draft ratio at the time, the coagulation bath temperature, the water washing conditions, and the like.

Subsequently, the method for producing the hollow fiber membrane of the present invention will be described. The hollow fiber membrane of the present invention is not particularly limited, but a dry method by discharging the spinning dope containing a polymer used as the material of the hollow fiber membrane from the outer annular slit and the injected liquid from the inner central pipe using an orifice-type double ring confinement. After passing through the part, it is solidified in a coagulation solution and then washed with warm water to form a hollow fiber membrane having an asymmetric structure.

When manufacturing the hollow fiber membrane of the present invention, the spinning draft rate is preferably 2 or more and 6 or less. Here, the spinning draft rate is a ratio of the discharge linear speed of the film-forming composition from the outer circumferential slit portion of the bi-ring cap and the take-up speed of the hollow fiber membrane, and represents a value obtained by dividing the take-up speed by the discharge line speed of the film-forming composition. In addition, the discharge line speed is the linear speed when the film forming composition is discharged from the outer circumferential slit of the double ring cap, and is a value obtained by dividing the discharge flow rate by the outer slit cross-sectional area.

By setting the spinning draft rate to 2 or more, the water permeability of the hollow fiber membrane is improved. On the other hand, by setting the spinning draft rate to 6 or less, spinning stability is improved and the frequency of yarn breakage can be reduced. In particular, when the thread diameter (outer diameter) of the hollow fiber membrane is thin, when the spinning draft rate is high, when the injected liquid has non-coagulation, the outer surface of the hollow fiber membrane is affected by the spinning draft, the smoothness of the outer surface is lost, and the plate structure Is formed, and the thickness of the dense layer tends to be thin. When the thickness of the dense layer decreases, the fractionation performance of the hollow fiber membrane decreases, and the resistance to high water pressure (hereinafter, referred to as pressure resistance) of the hollow fiber membrane decreases, and in some cases, there is a risk of thread breakage.

In the case of using a double ring pin such as an orifice type double ring pin for spinning the hollow fiber membrane, the viscosity of the spinning dope is preferably 2 Pa·s or more and 11 Pa·s or less. By setting the viscosity of the spinning dope to be 2 Pa·s or more, the sharpness of the hollow fiber membrane is improved. On the other hand, by setting the viscosity of the spinning dope to be 11 Pa·s or less, the pressure in the double ring detention can be suppressed, and a stable discharging state of the spinning dope can be maintained. In addition, from the viewpoint of controlling the thickness of the dense layer, when the viscosity of the spinning dope is too low, the phase separation speed of the polymer is accelerated, and the thickness of the dense layer is too thin. The viscosity of the spinning dope is preferably 2 Pa·s or more.

On the other hand, the liquid injected into the central pipe of the double ring confinement may be appropriately selected from a solidifying or non-coagulating liquid according to a desired shape of the hollow fiber membrane. There is a coagulation value as an indicator of the coagulation property of the injected liquid. This coagulation value represents the added mass of the injection liquid at the time when the injection liquid was added in small portions to 50 g of the 1% by mass solution of the main polymer constituting the membrane, and the inside of the system became cloudy. The smaller the value of this solidification value, the higher the solidification property of the injected liquid. From the past rule of thumb, if the coagulation value is 40 g or more (80% or more of the original liquid amount), it is judged to have non-coagulation in that the particle structure of the agglomerated polymer is not visible on the surface of the film where the dense layer is formed.

When a solidifying liquid is used for the injection liquid, since solidification starts from the inner surface, a dense layer is formed on the inner surface side of the hollow fiber membrane. On the other hand, in the case of using a non-coagulating liquid, a dense layer is formed on the outer surface side of the hollow fiber membrane because coagulation starts from the outer surface by the coagulation bath provided on the downstream side. Therefore, in the case of a water purifier used as a flow filtering from the outer surface side to the inner surface side of the hollow fiber membrane, a non-coagulating liquid is particularly suitably used.

In particular, the absolute value of the discharge linear velocity of the spinning dope and the injected liquid and the relative value of both have a great influence on the formation of the dense layer structure. It is assumed that this is because the orientation of the polymer is determined by the discharge linear velocity.

If the absolute value of the discharge linear velocity of the spinning dope is too high, the water permeability of the obtained hollow fiber membrane decreases, and if the absolute value of the discharge linear speed is too low, the smoothness of the outer surface of the obtained hollow fiber membrane is lost, resulting in a plate structure forming a dense layer. Tends to become thinner. In both cases, the fractionation performance of the hollow fiber membrane decreases, and the resistance of the hollow fiber membrane to high water pressure decreases, and in some cases, it is not preferable because it causes thread breakage. Therefore, the absolute value of the discharge linear velocity of the spinning dope is preferably 0.05 m/s or more, and more preferably 0.1 m/s or more. On the other hand, it is preferably 0.3 m/s or less, and more preferably 0.25 m/s or less.

If the absolute value of the discharge linear velocity of the injected liquid is too high, the pressure loss in the central pipe of the double ring cage increases, and the deviation of the outer diameter of the obtained hollow fiber membrane increases. In addition, if the absolute value of the discharge linear velocity is too low, a plate structure is formed on the inner surface of the obtained hollow fiber membrane, and the resistance to high water pressure of the hollow fiber membrane decreases, and in some cases, it is not preferable because it causes thread breakage. Therefore, the absolute value of the discharge linear velocity of the injected liquid is preferably 0.05 m/s or more, and more preferably 0.1 m/s or more. On the other hand, it is preferably 0.5 m/s or less, and more preferably 0.3 m/s or less.

When the relative value of the discharge linear velocity of the spinning dope and the injected liquid is too high, a plate structure is formed on the outer surface of the obtained hollow fiber membrane, and the thickness of the dense layer tends to be thin. When the thickness of the dense layer decreases, the fractionation performance of the hollow fiber membrane decreases, and the resistance to high water pressure of the hollow fiber membrane decreases, and in some cases, it is not preferable because it causes thread breakage. Further, if the relative value of the discharge linear velocity of the spinning dope and the injected liquid is too small, the water permeability of the resulting hollow fiber membrane is lowered, which is not preferable. Here, the relative value of the discharge linear speed of the spinning dope and the injected liquid is a value obtained by dividing the discharge linear speed of the injected liquid by the discharge linear speed of the spinning dope. Therefore, it is preferable that it is 0.5 or more, and it is more preferable that it is 0.6 or more as a relative value of the discharge linear velocity of a spinning dope and injection liquid. On the other hand, it is preferably 2.0 or less, and more preferably 1.5 or less.

If the thread diameter of the hollow fiber membrane is decreased, the deviation of the outer diameter tends to be large, and the structure of the hollow fiber membrane is disturbed, causing problems in the quality of pressure resistance, water permeability, and fractionation performance. Therefore, as the variation in the outer diameter of the hollow fiber membrane, 15% or less is preferable, and 10% or less is more preferable. The deviation of the outer diameter was evaluated by the method described in Examples. As a means of making the deviation of the outer diameter of the hollow fiber membrane into the above range, there may be mentioned controlling the size of the annular slit of the double ring cap or the pressure loss of the central pipe of the double ring cap.

In the case of causing phase separation of the hollow fiber membrane by heat in the spinning process of the hollow fiber membrane, it is cooled in the dry part and then rapidly cooled in a coagulation bath to solidify. In the case of causing phase separation of the hollow fiber membrane with the injection liquid in the spinning process of the hollow fiber membrane, it is discharged by contacting the injection liquid containing a poor solvent in the spinning dope, and solidified in a coagulation bath containing a poor solvent. In addition, in the method of causing phase separation of the hollow fiber membrane with a poor solvent, since the poor solvent is supplied to the interior of the hollow fiber membrane by diffusion, the supply amount of the poor solvent changes in the thickness direction of the hollow fiber membrane. Accordingly, a structure in which the pore diameter of the cross section in the thickness direction of the hollow fiber membrane increases from one surface to the other surface of the hollow fiber membrane. Therefore, it is preferable to bring the injection liquid containing a poor solvent into contact with the spinning dope immediately after discharge. When the concentration of the injection liquid is adjusted as a mixture of the poor solvent and the good solvent, the coagulation property is changed, so that the pore size of the hole on the side in contact with the injection liquid and the thickness of the dense layer can be controlled.

In addition, phase separation is induced on the side where the injection liquid and the spinning dope are in contact, so that solidification proceeds quickly, resulting in a compact structure with a small pore diameter. Further, the hole diameter continuously increases toward the opposite direction to the side in which the injected liquid and the spinning dope were contacted. Here, if the passage time of the dry part is sufficiently long, the diameter of the hole on the side not in contact with the injected liquid increases. Therefore, by shortening the passing time of the dry portion and immersing it in the coagulation bath immediately, solidification of the side not in contact with the injection liquid proceeds due to the contact of the poor solvent in the coagulation bath, thereby forming a compact structure with a small pore diameter.

Although depending on conditions that affect the progress of phase separation, such as the composition of the spinning dope or temperature, the passing time of the dry portion is preferably 0.02 seconds or more, and more preferably 0.14 seconds or more. On the other hand, 0.40 second or less is preferable, and 0.35 second or less is more preferable.

The concentration of the poor solvent in the coagulation bath is preferably 30 parts by mass or more, more preferably 50 parts by mass or more, and even more preferably 80 parts by mass or more with respect to the whole liquid in the coagulation bath.

Since the temperature of the coagulation bath is high, solvent exchange in the coagulation bath is likely to occur, and since the amount of residual solvent in the hollow fiber membrane can be reduced, the coagulation bath temperature is preferably 50°C or higher, and 60°C or higher. It is more preferable, and 70 degreeC or more is still more preferable.

When the temperature of the coagulation bath is high, condensation is formed on the orifice, and the possibility of thread breakage is considered accordingly. Therefore, the discharge temperature of the spinning dope is preferably 25° C. or higher from the viewpoint of preventing condensation on the mouth surface. In addition, when the discharge temperature of the spinning dope is too high, the discharge temperature of the spinning dope is preferably 70°C or less, and more preferably 55°C or less from the point that the spinning property is liable to become unstable.

The coagulation bath concentration changes over time by supply of a solvent from the spinning dope or the injection liquid. Therefore, it is preferable to increase the amount of liquid in the coagulation bath to suppress the change in concentration, or to monitor the concentration and adjust the concentration at any time.

In addition, in the dry section, setting a running section in which the temperature and humidity are more actively regulated is also effective for controlling the opening of the hollow fiber membrane, and it is preferable in terms of reducing unevenness in the performance of the obtained hollow fiber membrane.

In addition, in the dry part, although it is not particularly limited, in order to more actively regulate the atmosphere of the dry part, a cooling air box is installed on both sides of the spinning dope discharged from the double ring confinement, or around the spinning dope discharged from the double ring confinement. Enclosing the tube with an annular cooler is considered. In the case of installing cold air cylinders on both sides of the spinning dope discharged from the double ring detention center, the method of supplying cold air from one side of the cold air cylinder and exhausting the cold air from the other side, or the method of supplying cold air from both sides of the dry area It is preferable in that it can control humidity more actively. Further, it is preferable that the dry portion is less susceptible to the influence of the outside air even when the periphery of the spinning dope discharged from the double ring confinement is surrounded by an annular cool air cylinder, and the performance unevenness of the obtained hollow fiber membrane can be reduced.

In the dry section, as the dew point and wind speed of the cold air increase, the amount of water supplied as a poor solvent increases. Therefore, it is effective when the pore diameter of the hole on the outer surface is increased to increase the porosity. The dew point of the dry part is preferably 18°C or higher, and more preferably 21°C or higher. In addition, the wind speed of the cold air in the dry section is preferably 0.1 m/s or more, and more preferably 0.5 m/s or more. On the other hand, by lowering the wind speed of the cold air, it is possible to suppress disturbance of the surface of the spinning dope under discharge and shaking under discharge, so that the wind speed of the dry part is preferably 10 m/s or less, and more preferably 5 m/s or less.

In addition, the length of the dry portion is preferably 10 to 200 mm in order to prevent thread shaking during film formation while making the hole diameter of the surface of the hollow fiber membrane suitable.

Poor solvent is a solvent that does not dissolve a polymer that is mainly a structure of a hollow fiber membrane at the film forming temperature.

Poor solvent may be appropriately selected according to the type of polymer, but water is suitably used. A good solvent may be appropriately selected according to the type of polymer, but when the polymer constituting the hollow fiber membrane is a polysulfone-based polymer, N,N-dimethylacetamide is suitably used.

According to the above production method, the hollow fiber membrane is obtained in a wet state, but as it is, since the water permeability of the hollow fiber membrane is unstable, drying of moisture and a crosslinking reaction of a hydrophilic polymer (PVP, etc.) are required. As described above, when a hydrophilic polymer (PVP, etc.) is contained, hydrophilicity can be imparted to the hollow fiber membrane, and water permeability can be improved and the adhesion of the turbidity to the membrane can be suppressed. However, the hydrophilic polymer remaining in the membrane may be slightly eluted. This is not desirable for medical use and food industry use. As a crosslinking reaction for insolubilization, γ-ray irradiation is effective in vinyl hydrophilic polymers. In addition, in particular, when the hydrophilic polymer is polyvinylpyrrolidone, it can be crosslinked by heating. The drying temperature is preferably 100°C or higher from the viewpoint of evaporating water. The heat treatment temperature for crosslinking is preferably about 5 hours at 170°C, about 2.5 hours at 180°C, and about 1.5 hours at 190°C. The higher the temperature, the shorter the processing time. At 150° C. or lower, the treatment time is too long, which is not practical.

When drying the hollow fiber membrane while the hydrophilic polymer in the hollow fiber membrane is contained in a large amount, hydrophilic polymers are unevenly distributed on the surface of the hollow fiber membrane, thereby reducing the water permeability of the hollow fiber membrane or the filtration flow rate when modularized. From this point of view, it is preferable to wash the hollow fiber membrane obtained as a pretreatment with warm water. The temperature of the hot water is preferably 60°C or higher, more preferably 70°C or higher, and even more preferably 80°C or higher. Moreover, it is preferable that it is 99 degreeC or less. The mass of the hydrophilic polymer after washing with warm water is preferably 3 parts by mass or more and 20 parts by mass or less, and more preferably 5 parts by mass or more and 10 parts by mass or less based on the total mass of the membrane.

It is as described above that the hollow fiber membrane of the present invention can be suitably used for a water purifier cartridge. In addition, as a method for manufacturing a cartridge for a water purifier equipped with a hollow fiber membrane, a method conventionally used can be adopted.

Example

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited thereto.

(Analysis method and evaluation method)

(1) Viscosity measurement:

It was measured using the B-type viscometer shown in JIS K7117 (1999), and the average value of n=3 was taken as the measured value.

(2) Measurement of water permeability

Hollow fiber membranes are inserted into a case with holes for reflux at both ends, and potted with an epoxy resin adhesive "Quick Mender" (registered trademark) manufactured by Konishi Co., Ltd., and a hollow fiber membrane and potting agent protruding from both ends of the case By cutting, a small module with an effective length of 12 cm was produced. Water permeation performance is measured by calculating from the amount of water passing through the hollow fiber membrane within a certain period of time, the effective membrane area, and the pressure difference between the membranes by maintaining it at 37℃ in a constant temperature water tank and applying water pressure to the inside of the hollow fiber membrane. did. That is, the water permeability performance (UFRS) of the hollow fiber membrane was calculated by the following formula.

UFRS(mL/hr/Pa/㎡)=Qw/T/P/A

Qw: (pass) filtration amount (mL)

T: outflow time (hr)

P: pressure (Pa)

A: Membrane area of hollow fiber membrane (㎡)

(3) Measurement of the surface porosity of the hollow fiber membrane and the hole diameter of the hole of the hollow fiber membrane

An SEM (S-5500, manufactured by Hitachi High-Technologies Corporation) photographed a 5000-fold image of the outer surface of the hollow fiber membrane and introduced into a computer. Subsequently, analysis processing was performed with image processing software. The SEM image was subjected to binarization treatment, and an image obtained by inverting the pore portion to black and the structural polymer portion to white. The total area S of the holes was read, and the perforation rate (%) per image was calculated by the following equation.

Porosity (%) = S (㎛ ² ) / Image size (㎛ ² ) × 100

Moreover, similarly, analysis processing was performed with image processing software about the average hole diameter. The SEM image was subjected to binarization treatment, and an image in which the pores were black and the structural polymer portion was white was obtained. The total area S (µm ² ) of the holes and the number of black holes (hereinafter, the total number of holes) were read, and the average hole area (µm ² ) was calculated by the following equation. Further, the average pore diameter (µm) was calculated from the ^{average pore area (µm 2 ).} In addition, this calculation was performed by considering the hole shape to be a true circle.

Average hole area (㎛ ² ) = S (㎛ ² ) / Total number of holes

Average pore diameter (㎛)=2×√(Average pore area/π)

The above operation was performed for five different hollow fiber membranes, and the arithmetic average was used as the result.

(4) Measurement of dense layer thickness (DT)

After immersing the hollow fiber membrane in water for 5 minutes and soaking it, it is frozen with liquid nitrogen, and it is quickly folded and the cross section perpendicular to the length direction of the hollow fiber membrane used as a sample for observation of the cross section is measured by SEM (S-5500, manufactured by Hitachi High-Technologies Corporation). The image was introduced into a computer so that the surface side on the side where the structure portion is dense is placed on the left side of the image and the surface side on the side where the structure portion is roughened is placed on the right side of the image. In addition, in the following description, for convenience, a hollow fiber membrane in which the structure portion is dense on the outer surface side and the structure portion is roughened on the inner surface side is described as an example. In the case of a hollow fiber in which the structure portion is dense on the inner surface side and the structure portion is rough on the outer surface side, the outer surface described below may be replaced with an inner surface and the inner surface may be replaced with an outer surface.

The size of the introduced image was 640 pixels x 480 pixels. When observed by SEM and the hollow part of the hollow fiber membrane in the cross section was blocked, the sample was prepared again. The blockage of the hollow part may occur due to deformation of the hollow fiber membrane in the stress direction during the cutting treatment. Further, when the dense layer was not stable in the observation field of the measurement magnification, two or more SEM images were synthesized so that the dense layer was stabilized. An image was obtained in which the hole portion was made black and the structure portion was made white by the binarization treatment. When the structure portion and the other portions were not divided by the difference in contrast in the image, the image was divided into portions having the same contrast, subjected to binarization processing, respectively, and then pasted together to return to one image. Alternatively, image analysis may be performed by completely painting other parts of the structure in black. When the hole was observed in duplicate in the depth direction, it was measured in the shallow side hole. In addition, the hole area was obtained by analyzing the area displayed in black by the binarization process of the image, that is, the area of the single hole portion by the image processing software.

The number of pixels of the scale bar indicating the known length in the image was measured, and the length per pixel number (µm) was calculated. The size of the introduced image was 42.38 µm in width x 31.79 µm in length.

By image processing, pores with a pore area ^{exceeding 0.28 μm 2} are completely painted in fluorescent color, and ^{a layer without pores with a pore area exceeding 0.28 μm 2} is made a dense layer, from the outer surface to the inner surface of the hollow fiber membrane. The thickness of the dense layer was measured. However, in the vicinity of the surface of the dense layer due to the influence of the method of forming the hollow fiber membrane, a hole having a hole area ^{exceeding 0.28 µm 2} may be observed. In addition, this dense layer surface a plurality of holes in the vicinity of the hole area 0.28㎛ ² or less or the like even by the focus of the image that does not fit effect is recognized as one hole as the hole to the hole area exceeds 0.28㎛ ² tightly by fluorescent It may be painted. If there is such a case, it becomes impossible to accurately measure the dense layer thickness. ^{Therefore, if there is a hole with a hole area exceeding 0.28 µm 2} at a position within 10% of the film thickness from the outer surface of the hollow fiber membrane (6 µm in the case of a film thickness of 60 µm), it was neglected as noise. .

Specifically, the thickness of the dense layer was measured as follows. First, a straight line perpendicular to the outer surface was drawn in the thickness direction of the hollow fiber membrane, that is, in the direction from the outer surface to the inner surface of the hollow fiber membrane. Holes having a hole area closest to the outer surface of more ^{than 0.28 µm 2} were searched from among the holes existing on the straight line. Among the intersection points of the hole and the straight line, an intersection point on the side close to the outer surface was selected, and the distance between this intersection point and the outer surface was taken as the thickness of the dense layer.

With respect to the introduced image (42.38 µm in width x 31.79 µm in height), the image was divided into three in the vertical direction to obtain three images of 42.38 µm in width x 10.6 µm in length. Next, the thickness of the dense layer at the vertical midpoint of each visual field was measured as described above.

The thickness of each dense layer was obtained from the images of each of the three divided fields of view, and the same measurement was performed from 20 introduced images to obtain measurement data of the thickness of a total of 60 dense layers. The average value of 60 measurement data was calculated and defined as the thickness (DT) of the dense layer having only pores ^{with a pore area of 0.28 μm 2 or less.}

(5) Hydrophilic polymer/hydrophobic polymer on the surface of hollow fiber membrane

The measurement sample of the hollow fiber membrane containing hydrophilic polymer and hydrophobic polymer is set in the sample holder, the sample holder is installed on the plate, and the prism and the surface to be measured (the outer or inner surface) of the hollow fiber membrane are closely adhered by turning the handle. Made it. Next, the surface to be measured of the hollow fiber membrane was analyzed using an infrared ATR measuring device (manufactured by JASCO Corporation, infrared spectrophotometer: FT/IR-6000, infrared microscope: IRT-3000), and hydrophilic polymer contained in this surface The ratio of and hydrophobic polymer (hydrophilic polymer/hydrophobic polymer) was obtained. Hereinafter, the case of using PVP as the hydrophilic polymer and PSF as the hydrophobic polymer is exemplified, and this measurement method will be described in detail.

The area (Acc) of the absorption peak derived from the benzene ring C=C of the PSF near ^{1580 cm -1} from the infrared absorption spectrum obtained by the analysis by the infrared ATR measuring device and the amide bond of the PVP near ^{1650 cm -1} The area of the absorption peak (Aco) was calculated, and the ratio of the peak area (Aco)/(Acc) was calculated. For 30 hollow fiber membranes, the peak area ratio was calculated in the same manner, and the average value of the measurement data of total 30 was calculated, and the ratio (PVP/PSF) of the surface of the hollow fiber membrane to be measured was taken as the ratio (PVP/PSF).

(6) Measurement of 0.2㎛ particle removal rate

In the same manner as in (2) above, a small module was produced. A polystyrene latex bead suspension (manufactured by Invitrogen, Sulfate latex) having a concentration of 200 ppm from the outside of the hollow fiber membrane was supplied, and the concentration of the suspension transmitted to the inside through the hollow fiber membrane was measured. Using the values of the supply side concentration of 200 ppm and the permeation side concentration, the blocking rate was determined by the following equation. The particle diameter of the latex beads was 0.2 µm (actual value 0.203 µm).

Stopping rate=1-Cp/Cf

Cp: Permeate side concentration

Cf: supply side concentration

The relationship between the absorbance at 260 nm and the concentration of latex beads was measured in advance, and the concentration was determined by measuring the absorbance of the suspension on the transmission side. Measurement of the absorbance was obtained using a spectrophotometer (manufactured by Hitachi, Ltd., U-5100).

(7) Measurement of inner diameter and thickness of hollow fiber membrane

The hollow fiber membrane was cut with a single blade in the film thickness direction, and set in a micro watcher (manufactured by KEYENCE CORPORATION, VH-Z100). When the cross section of the hollow fiber was crushed by cutting, cutting was performed again until it became an approximate round. The cross section of the hollow fiber membrane was observed with a 1000-fold lens, and the range of the thickness of the hollow fiber membrane was specified on the monitor screen on which the cross section was projected, and the numerical value displayed on the monitor screen was read. In addition, the inner diameter of the hollow fiber membrane is displayed on the monitor screen by specifying a range of the width of the hollow portion. The same measurement was performed for 30 hollow fiber membranes, and the average value of the measurement data of the total 30 was calculated, and it was set as the inner diameter (ID) and the film thickness (WT) of the hollow fiber membrane.

(8) Ratio of dense layer thickness (DT) and film thickness (WT) (DT/WT)

The ratio of the thickness of the dense layer (DT) and the thickness of the hollow fiber membrane (WT) from the thickness of the dense layer (DT) calculated in (4) above and the film thickness (WT) of the hollow fiber membrane calculated in (7) above ( DT/WT) was calculated.

(9) Measurement of deviation of outer diameter and outer diameter of hollow fiber membrane

Set the hollow fiber membrane cut to 30 cm in the longitudinal direction on an outer diameter measuring device (manufactured by KEYENCE CORPORATION, controller: LS-5500, sensor head: LS-5040), and measure the outer diameter of the hollow fiber membrane at 10 cm from both ends. Measured.

The same measurement was performed about 20 hollow fiber membranes, the average value of the measurement data of total 40 was calculated, and the outer diameter (OD) of the hollow fiber membrane was calculated|required. In addition, a value (MAX) having the largest outer diameter and a value (MIN) having the smallest outer diameter were selected from the measurement data of total 40, and the outer diameter deviation (ROD) was calculated by the following equation.

ROD(%)=(MAX-MIN)/OD×100

(10) Pressure resistance performance

A small module is manufactured by inserting a hollow fiber membrane into an acrylic pipe, potting both ends with an epoxy resin adhesive "Quick Mender" (registered trademark) manufactured by Konishi Co., Ltd. and cutting the hollow fiber membrane and potting agent protruding from both ends of the case. did.

In the water tank, a small module was connected to the circuit to which the air cylinder, pressure regulator, pressure gauge, dial gauge and opening and closing cock were connected using a joint.

The pressure value at the time when the dial gauge was gradually opened and the pressure rapidly decreased due to a crack in the hollow fiber membrane in the small module was referred to as the pressure resistance performance. If air leaked on the way, it was done again from the beginning.

(11) Hollow fiber membrane module filtration flow rate

Connect a tube so that raw water can be supplied to the non-opening side of the hollow fiber membrane module, supply water at 20°C at 0.1 MPa, measure the amount of water per unit time flowing out through the hollow fiber membrane, and filter the flow rate of the hollow fiber membrane module per unit time. (L/min) was calculated.

(12) Water purifier cartridge turbid filtration ability

Activated carbon was placed on the upstream side of the produced hollow fiber membrane module to form a cartridge, and then it was carried out according to the method shown in JIS S 3201:2004 (household water purifier test method). The initial flow rate was set to 2.0 L/min.

(Example 1)

Hydrophobic polymer (PSF (Udel polysulfone (registered trademark) P-3500 manufactured by Solvay)) 15 parts by mass, hydrophilic polymer (PVP (ISP K90)) 7 parts by mass and N,N-dimethylacetamide (DMAc) 75 parts by mass And 3.0 parts by mass of water were dissolved and stirred to prepare a spinning dope. The viscosity of this spinning dope at 37°C was 5.0 Pa·s. This spinning dope was discharged from the annular slit of the double ring cage. As the injection liquid, a non-solidifying liquid consisting of 55 parts by mass of DMAc, 30 parts by mass of polyvinylpyrrolidone (BASF K30, weight average molecular weight 40,000) and 15 parts by mass of glycerin was discharged from the central pipe. The detention was kept warm at 37°C. The relative ratio between the injection liquid and the discharge linear speed of the spinning dope was the injection liquid discharge linear speed/the spinning dope discharge linear speed=0.8.

A cold air cylinder was installed in the dry portion, and a predetermined dry length was passed while flowing cold air gas from both sides of the spinning dope. The dew point of the dry part during spinning was as shown in Table 1. The spinning dope that has passed through the dry section is solidified by immersing it in a coagulation bath at 80°C containing a mixed solution consisting of 90 parts of water and 10 parts of DMAc, and after washing with warm water in a warm bath at 80°C, it is wound on a reel and a wet hollow fiber membrane Got it. The wound hollow fiber membrane had an outer diameter of 300 μm, an inner diameter of 180 μm, and a film thickness of 60 μm. The obtained hollow fiber membrane was cut into 30 cm in the longitudinal direction and washed with hot water at 90°C for 3 hours. The hollow fiber membrane was dried in a dry heat dryer and heat-treated at 160°C or higher to obtain a dried hollow fiber membrane.

The 1994 hollow fiber membranes in a dried state were folded in a U shape and inserted into a cylindrical case (26 mm inner diameter and 45 mm long), and the openings were fixed with polyurethane resin to obtain a hollow fiber membrane module.

Tables 1 and 2 show the configuration and various performances of the obtained hollow fiber membrane, the flow rate of the hollow fiber membrane module, the filtration capacity of the water purifier cartridge, and the like.

(Example 2)

A wet hollow fiber membrane was obtained by the same method as in Example 1. The obtained hollow fiber membrane was cut into 30 cm in the longitudinal direction, the hollow fiber membrane was dried in a dry heat dryer, and heat-treated at 160°C or higher to obtain a dried hollow fiber membrane.

The 1994 hollow fiber membranes in a dried state were folded in a U shape, inserted into a cylindrical case (26 mm in inner diameter and 45 mm in length), and the openings were fixed with polyurethane resin to obtain a hollow fiber membrane module.

Tables 1 and 2 show the configuration and various performances of the obtained hollow fiber membrane, the flow rate of the hollow fiber membrane module, the filtration capacity of the water purifier cartridge, and the like.

(Example 3)

A wet hollow fiber membrane was obtained by the same method as in Example 1. The obtained hollow fiber membrane was cut into 30 cm in the longitudinal direction and washed with warm water at 90°C for 3 hours. The hydrophilic polymer in the hollow fiber membrane was crosslinked by gamma-ray irradiation (25 kGy).

The 1994 hollow fiber membranes after gamma irradiation were folded in a U-shape, inserted into a cylindrical case (26 mm inner diameter and 45 mm long), and fixed the openings with polyurethane resin to obtain a hollow fiber membrane module.

Tables 1 and 2 show the configuration and various performances of the obtained hollow fiber membrane, the flow rate of the hollow fiber membrane module, the filtration capacity of the water purifier cartridge, and the like.

(Comparative Example 1)

Hollow in a dry state by the same method as in Example 1, except that the spinning dope was discharged from the annular slit of the double ring crest at a linear speed of 0.003 m/s and the injected liquid was discharged from the central pipe at a discharge linear speed of 0.04 m/s. Got the desert. The hollow fiber membrane had an outer diameter of 300 µm, an inner diameter of 180 µm, and a film thickness of 60 µm. The relative ratio of the discharge linear speed of the spinning dope and the injected liquid was the injection liquid discharge linear speed/the spinning dope discharge linear speed = 13.3.

The 1994 hollow fiber membranes in a dried state were folded in a U shape, inserted into a cylindrical case (26 mm in inner diameter and 45 mm in length), and the openings were fixed with polyurethane resin to obtain a hollow fiber membrane module.

Tables 1 and 2 show the configuration and various performances of the obtained hollow fiber membrane, the flow rate of the hollow fiber membrane module, the filtration capacity of the water purifier cartridge, and the like. As a result of observing the outer surface of the hollow fiber membrane with SEM (S-5500, manufactured by Hitachi High-Technologies Corporation), the membrane structure of the outer surface was stretched in the longitudinal direction to form a plate structure. For this reason, the thickness of the dense layer in the hollow fiber membrane was reduced, resulting in a hollow fiber membrane having low pressure resistance.

(Comparative Example 2)

A hollow fiber membrane was attempted to be wound on a reel by the same operation as in Example 1, except that the spinning dope had a viscosity of 1.5 Pa·s and was discharged from the annular slit of the double ring crest. This repeatedly occurred and became difficult. The evaluation results of the hollow fiber membrane and the like are shown in Tables 1 and 2. Some of the collected hollow fiber membranes had a very large ROD at 27% due to the thin dense layer. Because of the large ROD, the performance of the hollow fiber membrane became unstable, and the quality of the hollow fiber membrane was deteriorated. In addition, the quality of the hollow fiber membrane of Comparative Example 2 was poor, and thus the hollow fiber membrane could not be U-shaped as a bundle. Therefore, in order to evaluate the module filtration flow rate, a hollow fiber membrane module could not be produced, and in the hollow fiber membrane of Comparative Example 2, evaluation of the hollow fiber membrane module filtration flow rate and the water purifier cartridge turbid filtration ability could not be performed.

(Comparative Example 3)

Hollow in a dry state by the same method as in Example 1, except that the spinning dope was discharged from the annular slit of the double ring cage at a linear velocity of 0.28 m/s and the injected liquid was discharged from the center pipe at a discharge linear velocity of 0.22 m/s. Got the desert. The hollow fiber membrane had an outer diameter of 360 µm, an inner diameter of 220 µm, and a film thickness of 70 µm. The relative ratio of the discharge linear speed of the spinning dope and the injected liquid was the injection liquid discharge linear speed/the spinning dope discharge linear speed=0.79.

The 1384 hollow fiber membranes in a dried state were folded in a U shape and inserted into a cylindrical case (26 mm in inner diameter and 45 mm in length), and the openings were fixed with polyurethane resin to obtain a hollow fiber membrane module.

Tables 1 and 2 show the configuration and various performances of the obtained hollow fiber membrane, the flow rate of the hollow fiber membrane module, the filtration capacity of the water purifier cartridge, and the like.

Although the present invention has been described in detail with reference to specific embodiments, it is clear for those skilled in the art that various changes and modifications can be added without departing from the spirit and scope of the present invention. This application is based on the Japanese patent application (Japanese patent application 2016-056695) filed on March 22, 2016, the content of which is incorporated herein by reference.

(Industrial availability)

The present invention can be used as a hollow fiber membrane module or a hollow fiber membrane applicable to a cartridge for a water purifier in the field of water treatment. In addition, in addition to water purifiers, it can also be used for medical applications such as plasma separation membranes.

Claims (5)

A hollow fiber membrane comprising a dense layer having only pores having a ^{pore area of 0.28 μm 2} or less in a state observed from a cross section perpendicular to the longitudinal direction of the hollow fiber membrane,
The dense layer is disposed on the outer surface side or the inner surface side of the hollow fiber membrane,
The outer diameter of the hollow fiber membrane is less than 350㎛,
The inner diameter of the hollow fiber membrane is 150㎛ or more,
The thickness of the hollow fiber membrane is 30 μm or more and 90 μm or less,
The surface of the hollow fiber membrane on which the dense layer is disposed has a plurality of pores, and the average pore diameter observed from the surface of the hollow fiber membrane of the plurality of pores is 0.3 μm or more and 0.9 μm or less,
A hollow fiber membrane in which a ratio (DT/WT) of the thickness (DT) of the dense layer and the film thickness (WT) of the hollow fiber membrane is 0.24 or more. The method of claim 1,
The hollow fiber membrane in which the dense layer is disposed on the outer surface side of the hollow fiber membrane. The method according to claim 1 or 2,
A hollow fiber membrane having an opening rate of 15% or more and 45% or less of the surface of the hollow fiber membrane on which the dense layer is disposed. The method according to claim 1 or 2,
Hollow fiber membrane containing polysulfone-based polymer and polyvinylpyrrolidone. A cartridge for a water purifier equipped with the hollow fiber membrane according to claim 1 or 2.