JP5433921B2 - Polymer porous hollow fiber membrane - Google Patents

Description

  The present invention relates to a polymer porous hollow fiber membrane used for treatment of an aqueous fluid. Specifically, it comprises a hydrophobic polymer and a hydrophilic polymer, has a dense layer on the inner surface and the outer surface, the initial porosity increases from the inner surface toward the outer surface, and at least one local maximum After passing through the material, it has a characteristic structure in which the porosity decreases again on the outer surface side, and the pore size of the inner surface that mainly defines the separation characteristics and the exclusion limit particle size have a specific relationship, The present invention relates to a polymer porous hollow fiber membrane excellent in stable membrane performance and recoverability of membrane performance by washing.

  Hollow fiber membranes for the treatment of aqueous fluids are widely used in industrial applications such as microfiltration and ultrafiltration, and medical applications such as hemodialysis, hemofiltration, and hemodiafiltration. Cellulose acetate, polyethylene, polysulfone, polyvinylidene fluoride, polycarbonate, polyacrylonitrile and the like are used.

Examples of basic characteristics required for such a hollow fiber membrane include the following points.
(1) High removability of the substance to be removed (2) High permeability of the permeating substance (Fractionation characteristics in combination with (1) and (2))
(3) High permeability of processing fluid (permeability)
(Membrane properties combined with (1), (2), (3))
(4) Strength is high enough to prevent breakage and leakage (strength)
(5) The fractionation characteristics do not deteriorate over time (retention property of fractionation characteristics)
(6) The permeability of the processing fluid does not decrease over time (permeability retention)
(Retaining properties of film characteristics by combining (5) and (6))
In addition, in membranes other than medical uses that are basically discarded after a single use,
(7) Excellent recovery of fractionation characteristics by washing (Recovery of fractionation characteristics)
(8) Excellent recovery of permeability by washing (recoverability of permeability)
(Restoration of film characteristics by combining (7) and (8))
Is also added.

  Conventionally, many hollow fiber membranes have been developed by paying attention to the improvement in the filtration performance of (3) above, and other characteristics may be sacrificed. In order to improve the permeability of the membrane, a method of increasing the pore diameter is generally used, but this tends to cause a decrease in fractionation performance and strength at the same time.

  The hollow fiber membrane has a symmetrical structure in which the pore diameter does not change substantially in the thickness direction of the hollow fiber membrane, and the pore diameter changes continuously or discontinuously from the membrane structure. Are roughly classified into different asymmetric membranes. Among them, the symmetric membrane has a drawback that the entire film thickness portion shows a large resistance to the flow of fluid during filtration, and it is difficult to obtain a large flow rate, and the solute (substance to be removed) is likely to be clogged. .

  Removal of a substance to be removed by fluid filtration has contributions by both the surface layer effect due to the pore diameter on the membrane surface and the depth effect due to the film thickness portion. Of these, separation that mainly depends on the depth effect can be expected to be sensitive to fractionation characteristics, but it is difficult to obtain a large flow rate because it is a separation using a certain amount of thickness. There is a disadvantage that the flow rate decreases with time due to clogging. In the above-mentioned symmetrical film, since the contribution of the deep layer effect is relatively large, it is considered that the above-mentioned defects are easily manifested.

Against this background, studies have been made on asymmetric membranes provided with a thin dense layer that mainly defines fractionation characteristics and permeability. In Patent Document 1, an aromatic polysulfone hollow having a smooth circumference with an elliptical to circular shape having a smooth circumference and a maximum major axis of at least 0.1 μm, a skin layer on the outer surface, and no macrovoids on the cross section A yarn membrane is disclosed. In this technology, the shape of the hole is made oval to circular to achieve sharp fractionation characteristics, and the local force applied to blood cell components during blood filtration is reduced to solve problems such as hemolysis. It is supposed to be possible.
Certainly, such an effect can be expected by controlling the shape of the hole, but here, the consideration of the structure at the cross-section is insufficient, especially the retention of the membrane properties and the recovery of the membrane properties. There is a lack of consideration for sex.

Patent Document 2 discloses a hollow fiber microfiltration membrane comprising an aromatic polysulfone and polyvinylpyrrolidone and having a specific polyvinylpyrrolidone content, membrane structure, and breaking strength. In order to improve the permeability, it is preferable to control the pore size of the inner surface of the membrane. Specifically, the membrane must have a pore size smaller than the size of the substance to be blocked by filtration. It is said that it is 01-1 micrometer, Preferably it is 0.05-0.5 micrometer. However, depending on the shape and size of the hole, even if the hole diameter is measured, the error becomes large. Therefore, the blocking diameter at the time of internal pressure filtration is required to be 0.015 to 1 μm. Further, when the breaking strength of the film is less than 50 kgf / cm ² , leaks and the like occur frequently and are not practical, and therefore, it is described that it is at least 50 kgf / cm ² or more. Further, as a consideration when the filtrate is blood, the concentration of polyvinylpyrrolidone, which is hydrophilic, on the inner surface of the membrane in order to suppress the adsorption of plasma proteins is said to be 20 to 45% by weight. In this technology, high strength, high water permeability (high permeability), and less clogging (retention property of fractionation characteristics) are taken into consideration, and in fact, some of these problems have been solved. However, there is no description about the retention of membrane performance when used as a water film or a beverage treatment membrane for a long period of time, and the recovery of membrane properties by washing, and the consideration is still insufficient. I must say.

  In Patent Document 3, a separation layer A made of a polymer soluble in ε-caprolactam and having a separation limit of 500 to 5000000 daltons, a support layer B having a small hydrodynamic resistance with respect to the separation layers A and C, and a pore diameter Is disclosed as a problem to be solved in this technology, which is a separation limit and a semi-permeable membrane having a multilayer multi-layer structure of layer C larger than separation layer A but smaller than support layer B. The hydrodynamic permeability can be adjusted precisely, in which case the hydrodynamic permeability can be adjusted accurately independently of the separation limit, which allows the low, middle or high frequencies to be adjusted as required. It is considered to provide a membrane capable of producing a membrane having a specified separation limit, and no consideration is given to strength, retention of membrane characteristics, and recovery of membrane performance.

Further, as a structurally similar film, in Patent Document 4, the hole diameter of the micropores in the layer near the surface of the inner wall of the film is 500 nm or less, and at least one or more in the distribution of micropores distributed in the film thickness direction cross section. There is disclosed a membrane having a maximum pore diameter of a specific value. This technology is for medical membranes that are substantially superior in biocompatibility. Densification of the inner surface of the membrane that comes into contact with blood suppresses the entry of high molecular weight proteins into the membrane, and the high molecular weight proteins and membranes. The aim is to improve the biocompatibility by reducing the contact area. The reason why the dense structure is formed again in the vicinity of the outer surface through the pore diameter maximum portion of the membrane cross section is to suppress the entry of endotoxin fragments from the outer surface of the membrane. That is, the dense-sparse-dense structure of the membrane is a structure necessary for the substance removal ability, biocompatibility, and endotoxin invasion suppression as a blood treatment membrane. Other than that, for example, retention of membrane characteristics, membrane performance There is no description of the relationship with the recovery of
Japanese Patent Publication No. 07-022690 Japanese Patent No. 3594946 Japanese National Patent Publication No. 11-506387 JP 09-047645 A

  The problem of the present invention is that various water-based fluid treatment membranes such as clean water (purified water) membranes, beverage treatment membranes, blood treatment membranes, etc. have excellent fractionation characteristics and permeability. Providing a polymer porous hollow fiber membrane that has sufficient strength that does not cause breakage or leakage, suppresses deterioration of these performances and properties over time, and is excellent in recovering membrane properties by washing There is to do.

  The inventors of the present invention have fundamental characteristics required for hollow fiber membranes used in the treatment of aqueous fluids: membrane characteristics (fractionation characteristics and permeability), strength, retention of membrane characteristics, recoverability of membrane characteristics, As a result of intensive investigations to obtain a polymer porous hollow fiber membrane that realizes all of these at the same time at a high level, the above problems can be solved by a specific configuration, leading to the present invention.

That is, the polymer porous hollow fiber membrane of the present invention is
(1) comprising a hydrophobic polymer and a hydrophilic polymer;
(A) having a dense layer on the inner and outer surfaces;
(B) the hole diameter on the inner surface is smaller than the hole diameter on the outer surface;
(C) The initial porosity increases from the inner surface toward the outer surface, and after passing through at least one local maximum, the porosity decreases again on the outer surface side,
(D) When the exclusion limit particle diameter obtained by the fine particle passage test is φmax [μm], the pore diameter of the inner surface is dIS [μm], and the existence ratio of dIS exceeding φmax is DR [%], 2 [%] ≦ DR ≦ 20 [%].
(2) The inner surface of the hollow fiber membrane is IS, the outer surface of the hollow fiber membrane is OS, the maximum porosity in the cross section of the hollow fiber membrane is CSmax, and the pore diameter of each part is dIS, dOS, dCSmax, When the porosity of the part is pIS, pOS, pCSmax,
(A) 0.001 [μm] ≦ dIS ≦ 1 [μm] and (b) 0.1 [μm] ≦ dCSmax ≦ 10 [μm] and (c) 5 [%] ≦ pIS ≦ 30 [%] and ( d) 40 [%] ≦ pCSmax ≦ 80 [%]
It is characterized by being.
(3) IS is the inner surface of the hollow fiber membrane, OS is the outer surface of the hollow fiber membrane, and each portion when the cross section of the hollow fiber membrane is divided into eight equal parts from the inner surface toward the outer surface is CS1, CS2, CS3, CS4, CS5, CS6, CS7, CS8, the hole diameter of each part is dIS, dOS, dCS1, dCS2, dCS3, dCS4, dCS5, dCS6, dCS7, dCS8, the porosity of each part is pIS, When pOS, pCS1, pCS2, pCS3, pCS4, pCS5, pCS6, pCS7, pCS8,
(A) dIS ≦ dCS1 <dCS2 ≦ dCS3 ≧ dCS4>dCS5>dCS6>dCS7> dCS8 ≧ dOS and (b) pIS <pCS1 ≦ pCS2 <pCS3> pCS4 ≧ pCS5 ≧ pCS6 ≧ pCS7 ≧ pCS8> pOS
It is characterized by being.
(4) When the maximum pore diameter obtained by the bubble point is dBmax [μm] and the permeability of pure water at 25 ° C. is F [L / (h · m ² · bar)],
(A) (1/10000) · F ≦ dBmax ≦ (1/4000) · F and (b) 0.05 [μm] ≦ dBmax ≦ 1 [μm]
It is characterized by being.
(5) The content of hydrophilic polymer in the entire hollow fiber membrane is Ca [wt%], the content of hydrophilic polymer on the inner surface is Ci [wt%], and the content of hydrophilic polymer on the outer surface is Co [weight] %]
(A) 1 [wt%] ≦ Ca ≦ 10 [wt%] and (b) Ca ≦ Ci and Ca ≦ Co and (c) Co ≦ Ci
It is characterized by being.
(6) The hydrophobic polymer is a polysulfone polymer.
(7) The hydrophilic polymer is polyvinylpyrrolidone.

  The polymer porous hollow fiber membrane of the present invention can be used for various aqueous fluid treatment membranes such as clean water (purified water) membranes, beverage treatment membranes, blood treatment membranes, and in particular, retention of membrane properties, membranes by washing Since it is excellent in the recoverability of characteristics, it can be preferably used as industrial membranes such as clean water (purified water) membranes and beverage treatment membranes.

Hereinafter, the present invention will be described in detail.
The polymer porous hollow fiber membrane of the present invention preferably comprises a hydrophobic polymer and a hydrophilic polymer. Examples of the hydrophobic polymer include polyester, polycarbonate, polyurethane, polyamide, polysulfone (hereinafter referred to as PSf). And a polyethersulfone (hereinafter abbreviated as PES), polymethyl methacrylate, polypropylene, polyethylene, polyvinylidene fluoride, and the like. Among them, polysulfone-based polymers such as PSf and PES having repeating units represented by the following chemical formulas 1 and 2 are advantageous and preferable for obtaining a highly water-permeable membrane. The polysulfone polymer referred to here may contain a substituent such as a functional group or an alkyl group, and the hydrogen atom of the hydrocarbon skeleton may be substituted with another atom such as halogen or a substituent. These may be used alone or in combination of two or more.

  Examples of the hydrophilic polymer in the present invention include polymer carbohydrates such as polyethylene glycol, polyvinyl alcohol, polyvinyl pyrrolidone (hereinafter abbreviated as PVP), carboxymethyl cellulose, and starch. Among these, PVP is preferable from the viewpoint of compatibility with polysulfone and its use as an aqueous fluid treatment membrane. These may be used alone or in admixture of two or more. As the molecular weight of PVP, those having a weight average molecular weight of 10,000 to 1500,000 can be preferably used. Specifically, it is preferable to use those having a molecular weight of 9000 (K17) commercially available from BASF, and 45,000 (K30), 450,000 (K60), 900000 (K80), and 1200000 (K90).

The polymer porous hollow fiber membrane of the present invention has a dense layer on the inner surface and the outer surface, the pore diameter on the inner surface is smaller than the pore diameter on the outer surface, and the initial porosity from the inner surface toward the outer surface is The structure is characterized in that, after passing through at least one local maximum, the porosity decreases again on the outer surface side. The pore diameter and porosity in the present invention can be determined by taking an electron micrograph of the dried film into a computer, analyzing it with image analysis software, and digitizing it. Specifically, based on the total area of the image read into the image analysis software, the total area of the hole portions, and the number of the hole portions, the porosity is expressed by the following equations [1] and expressed by the equations [2] and [3]. ], The pore diameter (average pore diameter) is obtained.
Porosity [%] = 100 × (total area of holes / total area of read image) [1]
Hole area (average hole area) [μm ² ] = total area of holes / number of holes [2]
Pore diameter (average pore diameter) [μm] = (average pore area / π) ^1/2 [3]

  In the present invention, the shape of the hole is not particularly limited, but as can be seen from the above equation [3], the hole diameter is calculated from the area by approximating the hole as a circle, so that a slit shape, a spindle shape, an indefinite shape, etc. When the shape is significantly different from the circle, the difference between the calculated value and the actual state becomes large, and therefore, it is more preferably an ellipse or a circle.

  Having a dense layer on the inner and outer surfaces, and the pore size on the inner surface being smaller than the pore size on the outer surface, the inner and outer surfaces define fractionation characteristics and permeability, and the fractionation characteristics and transmission The contribution to the property means that the dense layer on the inner surface side is the main and the dense layer on the outer surface side is the subordinate. When an aqueous fluid is processed by cross flow filtration with internal perfusion, shearing force is generated by the fluid on the inner surface, so that it is easy to avoid the deposition of a substance to be removed on the surface. At this time, the effect is further enhanced by the presence of the dense layer on the surface. In addition, it is advantageous that the portion behind the dense layer is a sponge-like support layer having a large pore diameter and a large porosity because the fluid resistance is low and high permeability can be easily obtained. That is, the film structure is preferably a structure in which the inner surface is dense and sparse within the film. A sparse-dense structure opposite to this is not preferable because clogging of the substance to be removed proceeds to the film thickness portion. However, since the pore diameter necessarily has a distribution, it is difficult to avoid that the substance to be removed is not trapped and slips through to some extent. For this reason, in membranes whose fractionation characteristics are defined only by a dense layer with a thin inner surface, the fractionation characteristics are slowed down, and the productivity of hollow fiber membranes is sacrificed to obtain sensitive fractionation characteristics. turn into.

  Since the porous polymer hollow fiber membrane of the present invention has dense layers on both the inner and outer surfaces, the substance to be removed that has passed through the dense layer on the inner surface may be trapped by the dense layer on the outer surface. Sensitive fractionation characteristics can be obtained.

Here, it is preferable that the portion where the porosity is maximum in the membrane wall portion is present slightly from the inner surface from the center of the membrane wall. By adopting such a structure, in the vicinity of the inner surface, the inclination of the pore size distribution from the surface to the inner direction becomes larger, and the fractionation predetermined layer becomes thinner, which contributes to the improvement of permeability. In addition, in the vicinity of the outer surface, the inclination of the pore size distribution from the inside to the surface direction becomes small, and contributes to fractionation by the effect of depth filtration. Specifically, the inner surface of the hollow fiber membrane is IS, the outer surface of the hollow fiber membrane is OS, and each section when the cross section of the hollow fiber membrane is divided into eight equal parts from the inner surface to the outer surface direction in order from the inner surface direction. CS1, CS2, CS3, CS4, CS5, CS6, CS7, CS8, and the hole diameter of each part is dIS, dOS, dCS1, dCS2, dCS3, dCS4, dCS5, dCS6, dCS7, dCS8, and the porosity of each part. When pIS, pOS, pCS1, pCS2, pCS3, pCS4, pCS5, pCS6, pCS7, pCS8,
(A) dIS ≦ dCS1 <dCS2 ≦ dCS3 ≧ dCS4>dCS5>dCS6>dCS7> dCS8 ≧ dOS and (b) pIS <pCS1 ≦ pCS2 <pCS3> pCS4 ≧ pCS5 ≧ pCS6 ≧ pCS7 ≧ pCS8> pOS
It is preferable that

  In the polymer porous hollow fiber membrane of the present invention, since the inner surface is a dense layer, the effect of shearing force on the inner surface by crossflow filtration is also effective, and the membrane characteristics are easily maintained. Furthermore, since the inner surface of the dense-sparse-dense structure is a dense layer, the substance to be removed is easily removed during backwashing, and the film characteristics are highly recoverable. It is considered that the substance to be removed is trapped even in the outer dense layer. However, since the cleaning liquid flows in the direction from the small pore diameter to the large pore diameter during backwashing, the trapped substance to be removed is likely to come off. Although the detailed mechanism is unknown, it is probably a dense-sparse-dense structure, and the flow of the cleaning liquid inside the membrane wall is randomized non-linearly, so that the cleaning effect is further enhanced.

  In the polymer porous hollow fiber membrane of the present invention, the exclusion limit particle diameter obtained by the fine particle passage test is φmax [μm], the pore diameter of the inner surface is dIS [μm], and the presence ratio of dIS exceeding φmax is DR [%. ], It is one of the major features that 2 [%] ≦ DR ≦ 20 [%].

  Although it has already been described that the removal of the substance to be removed by membrane filtration has a contribution from both the surface layer effect due to the pore diameter of the membrane surface and the depth effect due to the film thickness portion, it has the characteristics as in the present invention. This means that the contribution of the surface effect to the fractionation characteristic is relatively large. Since it is the depth effect that separates according to the thickness of the membrane wall, the separation mechanism depending on this effect tends to clog the substance to be removed inside the membrane. This means a decrease in film characteristics over time, which is not a preferable behavior. Further, when separated by the surface layer effect, the substance to be removed stays on the surface of the film and is easily removed by backwashing. In other words, a film having a separation mechanism in which the surface layer effect is more dominant than the deep layer effect leads to the design of a film having excellent retention of membrane characteristics and excellent recovery of membrane characteristics. In the present invention, when the exclusion limit particle diameter obtained by the fine particle passage test is φmax [μm], the pore diameter of the inner surface is dIS [μm], and the presence ratio of dIS exceeding φmax is DR [%] By setting 2 [%] ≦ DR ≦ 20 [%], a polymer porous membrane excellent in retention of membrane characteristics and recoverability of membrane properties was obtained. Here, when DR exceeds 20%, the contribution of the depth filtration becomes too large, and the retention of the membrane characteristics and the recovery of the membrane characteristics are undesirably lowered. Further, a certain degree of distribution is inevitable in the pores on the surface, and it is not preferable to extremely narrow the pores because it causes a significant decrease in productivity. For this reason, it is preferable that DR is 2% or more. From such a viewpoint, a more preferable DR range is 2 [%] ≦ DR ≦ 15 [%], and further preferably 3 [%] ≦ DR ≦ 10 [%].

  The pore diameter on the inner surface of the polymer porous hollow fiber membrane of the present invention is preferably 0.001 μm to 1 μm, and more preferably 0.01 μm to 1 μm. If the pore size is smaller than this, the permeability is low, which is not preferable, and if the pore size is larger than this, the strength of the membrane is lowered, which is not preferable. The porosity on the inner surface is preferably 5% to 30%, more preferably 7% to 25%. If the porosity is lower than this, the permeability is low, which is not preferable, and if it is higher than this, the strength of the film is lowered, which is not preferable. The polymer porous hollow fiber membrane of the present invention is characterized in that there is a portion where the porosity is maximized in the membrane wall portion. The pore diameter at this maximum portion is the pore diameter at the inner surface and the outer surface. And is preferably 0.1 μm to 10 μm, and more preferably 0.2 μm to 8 μm. If the pore diameter is smaller than this, the inclination of the film structure becomes too gentle, and the film characteristics, the retention of the film characteristics, and the recoverability of the film characteristics deteriorate, which is not preferable. If it is larger than this, the strength of the film decreases, which is not preferable. Moreover, the porosity in the maximum portion is larger than the porosity on the inner surface and the outer surface, and is preferably 40% to 80%, and more preferably 45% to 70%. If the porosity is smaller than this, the inclination of the film structure becomes too gentle, and the film characteristics, the retention of the film characteristics, and the recoverability of the film characteristics deteriorate, which is not preferable. If it is larger than this, the strength of the film decreases, which is not preferable. The pore diameter on the outer surface is not particularly limited as long as it is larger than the pore diameter on the inner surface, but is preferably 0.02 to 2 μm. If the pore size is smaller than this, the permeability is low, which is not preferable. The porosity on the outer surface is not particularly limited, but is preferably 5% to 30%, and more preferably 7% to 25%. If the porosity is lower than this, the permeability is low, and the adjacent hollow fiber membranes are likely to stick to each other, which is not preferable, and if it is higher than this, the strength of the membrane is reduced, which is not preferable. Here, the porosity and the pore diameter are the porosity obtained by the above formula [1] and the average pore diameter obtained by [2] and [3], respectively.

In the polymer porous hollow fiber membrane of the present invention, the maximum pore diameter obtained by the bubble point is dBmax [μm], and the permeability of pure water at 25 ° C. is F [L / (h · m ² · bar)]. When
(A) (1/10000) · F ≦ dBmax ≦ (1/4000) · F and (b) 0.05 [μm] ≦ dBmax ≦ 1 [μm]
It is preferable that the relationship is In order to realize a certain water permeability, it is thought that the diameter and number of pores contribute. If the number of pores is greatly increased in order to improve water permeability, the strength of the membrane decreases, and the possibility of leakage or breakage during actual use increases. Moreover, if the diameter of the pores is greatly increased, the possibility that the substance to be removed leaks increases. When dmax is smaller than (1/10000) · F, the number of holes must be increased in order to realize F, which causes a decrease in film strength. On the other hand, if dmax is larger than (1/4000) · F, the pore diameter becomes large, which causes undesirable separation characteristics. When dmax is in the range of (1/10000) · F ≦ dmax ≦ (1/4000) · F, sufficient film strength and separation characteristics are realized.

In order to obtain long-term stable permeability and separation characteristics, it is necessary to suppress nonspecific adsorption of the substance derived from the liquid to be treated to the membrane. In the case of membrane treatment of an aqueous fluid, such non-specific adsorption can be reduced by increasing the hydrophilicity of the membrane material, but there is also the possibility of hydrophilic polymer elution, and the amount of effectively suppressed as much as possible. Introduction is preferred. In the present invention, the content of the hydrophilic polymer in the entire hollow fiber membrane is Ca [wt%], the content of the hydrophilic polymer on the inner surface is Ci [wt%], and the content of the hydrophilic polymer on the outer surface is Co. [Weight%]
(A) 1 [wt%] ≦ Ca ≦ 10 [wt%] and (b) Ca ≦ Ci and Ca ≦ Co and (c) Co ≦ Ci
It is preferable that By satisfying this, the total amount necessary and sufficient for imparting hydrophilicity should be concentrated on the surface of the membrane that is mainly in contact with the liquid to be treated, especially concentrated on the inner surface that defines the separation characteristics. It is preferable.

  It is conceivable that a hydrophilic polymer having a part of its structure modified by a treatment such as cross-linking exhibits a behavior slightly different from the characteristics inherent to the hydrophilic polymer. In order to ensure the membrane characteristics and retention during aqueous fluid treatment, the hydrophilic polymer contained in the polymer porous hollow fiber membrane of the present invention is preferably not substantially insolubilized, specifically The content of insoluble components is preferably less than 2% by weight based on the entire film. The content rate of the insoluble component mentioned here means the ratio of the component that remains without being dissolved when the hollow fiber membrane that has been molded and dried is dissolved in the solvent used for the membrane forming raw solution. Specifically, the content rate calculated by the following method is meant. That is, 10 g of a hollow fiber membrane is taken, a solution dissolved in 100 ml of dimethylformamide is applied at 1500 rpm for 10 minutes with a centrifuge, and then the supernatant is removed. 100 ml of dimethylformamide is again added to the remaining insoluble matter, and the mixture is stirred and then centrifuged under the same conditions to remove the supernatant. Again, 100 ml of dimethylformamide is added and stirred, the same centrifugation operation is performed, and then the supernatant is removed. The remaining solid is evaporated to dryness, and the content of insoluble components is determined from the amount.

  The diameter and thickness of the polymeric porous hollow fiber membrane of the present invention may be appropriately selected according to the intended use, and are not particularly limited, but the inner diameter is preferably 100-1500 μm, more preferably 130-1300 μm. is there. The film thickness is preferably 5 to 600 μm, more preferably 10 to 500 μm. If the inner diameter is smaller than this, depending on the use, there is a possibility that the lumen is blocked by a component in the liquid to be treated, which is not preferable. If the inner diameter is larger than this, the hollow fiber membrane tends to be crushed and distorted, which is not preferable. If the film thickness is smaller than this, the hollow fiber membrane tends to be crushed, distorted, etc., which is not preferable. A film thickness larger than this is not preferable because the resistance when the processing fluid passes through the membrane wall increases and the permeability decreases.

  The method for producing the polymer porous hollow fiber membrane of the present invention is not limited in any way, but a membrane-forming solution is prepared by mixing and dissolving a hydrophobic polymer, a hydrophilic polymer, a solvent, and a non-solvent and degassing the solution. As the core liquid is discharged simultaneously from the annular part and center part of the double-tube nozzle, it is guided to the coagulation bath through the idle part (air gap part) to form a hollow fiber membrane (dry wet spinning method), and after washing with water The method of winding and drying is illustrated.

  Solvents used in the film-forming solution are N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP), N, N-dimethylformamide (hereinafter abbreviated as DMF), N, N-dimethylacetamide (hereinafter abbreviated as DMAc). ), Dimethyl sulfoxide (hereinafter abbreviated as DMSO), ε-caprolactam, etc., can be widely used as long as they are good solvents for hydrophobic polymers and hydrophilic polymers. When a polysulfone polymer such as PSf or PES is used, an amide aprotic solvent such as NMP, DMF, or DMAc is preferable, and NMP is particularly preferable. In the present invention, the amide solvent means a solvent containing an N—C (═O) amide bond in the structure, and the aprotic solvent is directly bonded to a hetero atom other than a carbon atom in the structure. Means a solvent containing no hydrogen atom.

  It is also possible to add a polymer non-solvent to the film forming solution. Examples of the non-solvent used include ethylene glycol, propylene glycol, diethylene glycol (hereinafter abbreviated as DEG), triethylene glycol (hereinafter abbreviated as TEG), polyethylene glycol (hereinafter abbreviated as PEG), glycerin, water, and the like. In the case of using a polysulfone polymer such as PSf and PES as the hydrophobic polymer and PVP as the hydrophilic polymer, ether polyols such as DEG, TEG, and PEG are preferable, and TEG is particularly preferable. . In the present invention, the ether polyol means a substance having at least one ether bond and two or more hydroxyl groups in the structure.

  Although the detailed mechanism is unknown, phase separation (coagulation) in the spinning process is controlled by using a membrane forming stock solution prepared using these solvents and non-solvents, and the preferred membrane structure of the present invention is formed. It is thought that it becomes advantageous to do. For controlling the phase separation, the composition of the core liquid described later and the composition of the liquid in the coagulation bath (external coagulation liquid) are also important.

  The concentration of the hydrophobic polymer in the film-forming stock solution is not particularly limited as long as film formation from the stock solution is possible, but is preferably 10 to 35% by weight, and more preferably 10 to 30% by weight. In order to obtain high permeability, it is preferable that the concentration of the hydrophobic polymer is low. However, if the concentration is too low, strength may be lowered and fractionation characteristics may be deteriorated, so 10 to 25% by weight is preferable. The amount of hydrophilic polymer added is not particularly limited as long as it is sufficient to impart hydrophilicity to the hollow fiber membrane and suppress non-specific adsorption during aqueous fluid treatment. The polymer ratio is preferably 10 to 30% by weight, more preferably 10 to 20% by weight. If the amount of the hydrophilic polymer added is less than this, the imparting of hydrophilicity to the film will be insufficient, and the retention of film characteristics may be reduced. On the other hand, if the amount is larger than this, the hydrophilicity-imparting effect is saturated and the efficiency is not good, and the phase separation (coagulation) of the film-forming solution tends to proceed excessively, thereby forming the preferred membrane structure of the present invention. Disadvantageous.

  The ratio of solvent / non-solvent in the film-forming stock solution is an important factor for controlling phase separation (coagulation) in the spinning process. Specifically, the content of the solvent / non-solvent is preferably 30/70 to 70/30 by weight, more preferably 35/65 to 60/40, and 35/65 to 55/45. More preferably. If the content of the solvent is less than this, solidification tends to proceed, the membrane structure becomes too dense, and the permeability is lowered. On the other hand, if the solvent content is higher than this, the progress of the phase separation is excessively suppressed, and pores having a large pore diameter are likely to be generated, and the possibility of a decrease in fractionation characteristics and strength is increased.

The film-forming stock solution is obtained by mixing a hydrophobic polymer, a hydrophilic polymer, a solvent, and a non-solvent, and dissolving them by stirring. At this time, the solution can be efficiently dissolved by appropriately applying the temperature, but excessive heating may cause decomposition of the polymer, so that it is preferably 30 to 100 ° C, more preferably 40 to 80 ° C. is there. When PVP is used as the hydrophilic polymer, PVP tends to undergo oxidative degradation due to the influence of oxygen in the air. Therefore, the spinning solution is preferably dissolved in an inert gas. Nitrogen, argon, etc. are raised as the inert gas, but nitrogen is preferably used. At this time, the residual oxygen concentration in the dissolution tank is preferably 3% or less. If the nitrogen filling pressure is increased, the melting time can be shortened. However, in order to increase the pressure, the equipment cost is increased, and from the viewpoint of work safety, atmospheric pressure and 2 kgf / cm ² or less are preferable.

  When film formation is performed, it is preferable to use a film-forming stock solution from which foreign matters are excluded in order to avoid generation of defects in the membrane structure due to foreign matters mixed into the hollow fiber membrane. Specifically, a method of reducing a foreign material by filtering a film forming stock solution using a raw material with few foreign materials is effective. In the present invention, it is preferable to filter the membrane-forming stock solution using a filter having a pore diameter smaller than the film thickness of the hollow fiber membrane bundle and then discharge from the nozzle. Specifically, the uniformly dissolved spinning solution is discharged from the dissolution tank to the nozzle. Is passed through a sintered filter having a pore diameter of 10 to 50 μm. The filtration process may be performed at least once. However, when the filtration process is performed in several stages, it is preferable to reduce the pore size of the filter as the latter stage in order to extend the filtration efficiency and the filter life. The pore size of the filter is more preferably 10 to 45 μm, further preferably 10 to 40 μm. If the filter pore size is too small, the back pressure may increase and productivity may decrease.

  Moreover, it is effective to eliminate the bubbles from the membrane forming stock solution to obtain a hollow fiber membrane having no defects. As a method for suppressing the mixing of bubbles, it is effective to defoam the film forming stock solution. Depending on the viscosity of the film-forming stock solution, stationary defoaming or vacuum defoaming can be used. In this case, after the inside of the dissolution tank is reduced from normal pressure to −100 to −750 mmHg, the inside of the tank is sealed and allowed to stand for 30 minutes to 180 minutes. This operation is repeated several times to perform defoaming treatment. If the degree of vacuum is too low, the treatment may take a long time because it is necessary to increase the number of defoaming times. On the other hand, when the degree of vacuum is too high, the cost for increasing the degree of sealing of the system may increase. The total treatment time is preferably 5 minutes to 5 hours. If the treatment time is too long, the constituent components of the film-forming stock solution may be decomposed and deteriorated due to the effect of reduced pressure. If the treatment time is too short, the defoaming effect may be insufficient.

  As the composition of the core liquid used at the time of forming the hollow fiber membrane, it is preferable to use a mixed solution of a solvent and a non-solvent contained in the membrane forming stock solution and water. At this time, the ratio of the solvent and the non-solvent contained in the core liquid is preferably the same as the solvent / non-solvent ratio of the film-forming stock solution. Preferably, the same solvent and non-solvent used in the film-forming stock solution are mixed in the same ratio as in the film-forming stock solution and then diluted by adding water. The content of water in the core liquid is 10 to 40% by weight, preferably 15 to 30% by weight. If the water content is higher than this, solidification tends to proceed, the membrane structure becomes too dense, and the permeability decreases. On the other hand, if the water content is less than this, the progress of the phase separation is excessively suppressed, and pores having a large pore diameter are likely to be generated, which increases the possibility of causing a decrease in fractionation characteristics and strength.

  As the composition of the external coagulation liquid, it is preferable to use a mixed liquid of a solvent and a non-solvent contained in the film-forming stock solution and water. At this time, the ratio of the solvent and the non-solvent contained in the core liquid is preferably the same as the solvent / non-solvent ratio of the film-forming stock solution. Preferably, the same solvent and non-solvent used in the film-forming stock solution are mixed in the same ratio as in the film-forming stock solution and then diluted by adding water. The content of water in the external coagulation liquid is 30 to 85% by weight, preferably 40 to 80% by weight. If the water content is higher than this, solidification tends to proceed, the membrane structure becomes too dense, and the permeability decreases. On the other hand, if the water content is less than this, the progress of the phase separation is excessively suppressed, and pores having a large pore diameter are likely to be generated, which increases the possibility of causing a decrease in fractionation characteristics and strength. On the other hand, when the temperature of the external coagulation liquid is low, coagulation tends to proceed, the membrane structure becomes too dense, and the permeability is lowered. On the other hand, if it is high, the progress of the phase separation is excessively suppressed, and pores having a large pore diameter are likely to be generated, and the possibility of causing a decrease in fractionation characteristics and strength is increased. Therefore, 30 to 80 ° C., preferably 40 ~ 70 ° C.

  In the present invention, one of the factors controlling the film structure is the temperature of the nozzle. If the temperature of the nozzle is low, solidification tends to proceed, the membrane structure becomes too dense, and the permeability decreases. On the other hand, if it is high, the progress of phase separation is excessively suppressed, and pores having a large pore diameter are likely to be generated, and the possibility of causing a decrease in fractionation characteristics and strength is increased. Therefore, 30 to 90 ° C., preferably 40 ~ 80 ° C.

  As a preferred production method for obtaining the polymer porous hollow fiber membrane of the present invention, the membrane forming stock solution discharged from the double tube nozzle together with the core solution is introduced into a coagulation bath filled with an external coagulation solution through an air gap portion. The dry-wet spinning method for forming the hollow fiber membrane is exemplified, but the residence time of the membrane-forming stock solution discharged from the nozzle in the air gap portion can be one of the factors controlling the membrane structure. If the residence time is short, the outer coagulating liquid quenches the growth of aggregated particles due to phase separation in the air gap portion, so that the outer surface becomes dense and the permeability is lowered. In addition, the densification of the outer surface is not preferable because the obtained hollow fiber membrane tends to stick. When the residence time is long, pores having a large pore diameter are likely to be generated, and the possibility that the fractionation characteristics and the strength are reduced is increased. A preferable range of the residence time in the air gap is 0.05 to 4 seconds, and more preferably 0.1 to 3 seconds.

  The hollow fiber membrane guided to the coagulation bath through the air gap portion having a relatively short residence time is relatively coagulated in a state in which coagulation from the core liquid proceeds while coagulation from the outside is suppressed to some extent. Contact with a mild external clotting solution. That is, the hollow fiber membrane immediately after entering the coagulation bath is in a “live” state in which the structure is not yet completely determined, but this “live” hollow fiber membrane is completely solidified in the coagulation bath, and the structure is Determined and raised. As described above, since the coagulability of the external coagulation liquid is relatively mild, the residence time in the coagulation bath needs to be sufficient until the coagulation is completely completed. Specifically, 5 to 20 seconds is preferable, and 10 to 20 seconds is more preferable. If the residence time in the coagulation bath is shorter than this, coagulation is insufficient, and if it is longer than this, it is not preferable because it is necessary to decrease the film forming speed or enlarge the coagulation bath.

  The porous polymer membrane of the present invention has a dense layer on the inner surface and the outer surface, the pore diameter on the inner surface is smaller than the pore diameter on the outer surface, and the initial porosity increases from the inner surface toward the outer surface. The main feature is that after passing through at least one local maximum, the porosity decreases again on the outer surface side, but in order to realize such a structure, the above film forming stock solution is used. It is preferable to adopt a method for obtaining a hollow fiber membrane under the above spinning conditions. To form a dense-sparse-dense asymmetric structure from the inner surface to the outer surface, solidification from the inside of the hollow fiber membrane (mainly phase separation / coagulation by the core liquid) and solidification from the outside (mainly the air gap, It is necessary to control the coagulation from the inner and outer surfaces toward the inside of the membrane wall by balancing the phases and coagulating them. Effective control means for that purpose are the composition of the core liquid, the composition / temperature of the external coagulation liquid, the residence time in the air gap portion, and the residence time in the coagulation bath. By setting these within the above range, the characteristic film structure of the present invention can be obtained.

  In order to obtain the polymer porous hollow fiber membrane of the present invention, it is necessary to delicately control the progress of solidification from both the inner and outer surfaces. There is a bend. In dry-wet spinning, the film-forming stock solution is usually discharged from the nozzles arranged downward in the direction of gravity, led to the coagulation bath through the air gap part, the direction of travel is changed upward in the coagulation bath, and pulled up from the coagulation bath. It is common to wind up after washing in a water bath. Since the polymer porous hollow fiber membrane of the present invention is in a “live” state in which the structure is not completely determined immediately after entering the coagulation bath, the membrane structure is changed when the direction is rapidly changed in the coagulation bath. This is not preferable because it causes defects and destruction. Specifically, the radius of curvature at the time of changing the direction is preferably 20 to 300 mm, more preferably 30 to 200 mm. Also preferred is a method of gradually changing direction at a plurality of points using a multipoint guide.

  In the production of the polymer porous hollow fiber membrane of the present invention, it is preferable that stretching is not substantially applied before the hollow fiber membrane structure is completely fixed. The fact that the film is not substantially stretched means that the roller speed during the spinning process is controlled so that the spinning solution discharged from the nozzle is not loosened or excessively tensioned. The discharge linear speed / coagulation bath first roller speed ratio (draft ratio) is preferably in the range of 0.7 to 1.8. If the ratio is less than 0.7, the traveling hollow fiber membrane may be loosened, leading to a decrease in productivity. Therefore, the draft ratio is more preferably 0.8 or more, more preferably 0.9 or more, and More preferably 95 or more. If it exceeds 1.8, the membrane structure may be destroyed, for example, the dense layer of the hollow fiber membrane is torn. Therefore, the draft ratio is more preferably 1.7 or less, still more preferably 1.6 or less, still more preferably 1.5 or less, and particularly preferably 1.4 or less. By adjusting the draft ratio within this range, it is possible to prevent the deformation and destruction of the pores, and to maintain the membrane performance and to exhibit sharp fractionation characteristics.

  The film forming speed (spinning speed) is not particularly limited as long as a hollow fiber membrane having no defect is obtained and productivity can be secured, but is preferably 5 to 40 m / min, more preferably 7 to 20 m / min. If the spinning speed is lower than this, productivity is lowered, which is not preferable. If the spinning speed is higher than this, it is difficult to secure the above spinning conditions, particularly the residence time in the air gap portion and the residence time in the coagulation bath, which is not preferable.

  The hollow fiber membrane obtained by rolling after washing in a washing bath after film formation suppresses changes in membrane properties during use and washing operations, and retains and stabilizes membrane properties and restores membrane properties. In order to ensure the property, it is preferable to perform heat treatment. By making this heat treatment an immersion treatment in hot water, the effect of washing and removing the solvent, non-solvent, etc. remaining in the hollow fiber membrane can be expected at the same time. The temperature of the hot water is 60 to 100 ° C., more preferably 70 to 90 ° C., and the treatment time is 30 to 120 min, more preferably 40 to 90 min, and still more preferably 50 to 80 min. If the temperature is lower than this and the treatment time is shorter than this, the heat history applied to the hollow fiber membrane may be insufficient, and the retention and stability of the membrane characteristics may be lowered, and the cleaning effect is insufficient. Therefore, there is a high possibility that the amount of eluate increases, which is not preferable. If the temperature is higher than this and the treatment time is longer than this, water will boil or the treatment will take a long time, resulting in decreased productivity. The bath ratio of the hollow fiber membrane to the hot water is not particularly limited as long as the hollow fiber membrane is sufficiently soaked in hot water, but using a large amount of hot water is not preferable because the productivity decreases. .

  The hollow fiber membrane that has been subjected to film formation and heat treatment is finally completed by drying. As a drying method, commonly used drying methods such as air drying, reduced pressure drying, and hot air drying can be widely used. Recently, microwave drying, which has been used for drying blood treatment membranes, can be used. However, hot air drying can be preferably used in that a large amount of hollow fiber membranes can be efficiently dried with a simple apparatus. By performing the above heat treatment prior to drying, changes in film properties due to hot air drying can also be suppressed. The hot air temperature at the time of hot air drying is not particularly limited, but is preferably 40 to 100 ° C, more preferably 50 to 80 ° C. If the temperature is lower than this, it takes a long time to dry, and if the temperature is higher than this, the energy cost for generating hot air becomes high, which is not preferable. The temperature of the hot air is preferably lower than the temperature of the hot water heat treatment.

  Hereinafter, the effectiveness of the present invention will be described with reference to examples, but the present invention is not limited thereto. In addition, the evaluation methods in the following examples are as follows.

1. Structure observation and analysis of hollow fiber membrane by electron microscope The dried hollow fiber membrane was cut, and a scanning electron microscope (SEM) photograph of the inner surface, outer surface, and cross section was taken at a magnification of 10,000 or 2000 times. SEM photographs were taken into a computer at a resolution of 466 dpi and analyzed using image analysis software to determine porosity, average pore area, and pore distribution. Specifically, first, the captured image was binarized to obtain an image in which the hole portion was black and the constituent polymer portion was white. By analyzing this image, the total number of holes, the area of each hole, and the area of the holes was obtained. From the total area of the read image and the total area of the pore term portion, the porosity was calculated by the following equation [1].
Porosity [%] = 100 × (total area of holes / total area of read image) [1]
The average hole area was calculated from the total area of the hole portions and the number of the hole portions, and the shape of the holes was approximated to a circle, and the average hole diameter was calculated from the average hole area. (Formulas [2] and [3])
Hole area (average hole area) [μm ² ] = total area of holes / number of holes [2]
Pore diameter (average pore diameter) [μm] = (average pore area / π) ^1/2 [3]
Further, as described above, the hole diameter when the hole shape was approximated to a circle was calculated from the area of each hole portion, and the result was taken into spreadsheet software to create a histogram and summarize it as a pore distribution.

2. Production of Mini Module A hollow fiber membrane was cut into a length of about 30 cm and both ends were bundled with a paraffin film to produce a hollow fiber membrane bundle. Both ends of this hollow fiber membrane bundle were inserted into a pipe (sleeve) and hardened with a urethane potting agent. The ends were cut to obtain a double-end open mini-module with both ends fixed by sleeves. The number of hollow fiber membranes was appropriately set so that the surface area of the inner surface was 50 to 100 cm ² .

3. Production of Module A hollow fiber membrane was cut into a length of about 30 cm and wound with a polyethylene film to obtain a hollow fiber membrane bundle. This hollow fiber membrane bundle was inserted into a cylindrical polycarbonate module case, and both ends were hardened with a urethane potting agent. The edge part was cut | disconnected and the module which both ends opened was obtained. The number of hollow fiber membranes was appropriately set so that the surface area of the inner surface was about 200 cm ² . The cylindrical module case is provided with ports at two locations on the cylindrical surface so that fluid can perfuse the outer surface of the hollow fiber membrane. End caps are attached to both ends, and the fluid perfuses the inner surface of the hollow fiber membrane. I was able to do it.

4). Production of Loop Type Mini-Module A hollow fiber membrane was cut to a length of about 40 cm, bundled into a loop type, and the end was fixed with a paraffin film. The end of this loop type hollow fiber membrane bundle was inserted into a pipe (sleeve) and hardened with a urethane potting agent. The end portion was cut to obtain a loop type mini module having the end portion fixed by a sleeve. The number of hollow fiber membranes was appropriately set so that the surface area of the inner surface was 20 to 50 cm ² .

5. Calculation of membrane area The membrane area of the module was determined based on the inner diameter of the hollow fiber membrane. The membrane area of the module can be calculated by the following equation [4].
A = n × π × d × L [4]
Here, n is the number of hollow fiber membranes, π is the circumference, d is the inner diameter [m] of the hollow fiber membrane, and L is the effective length [m] of the hollow fiber membrane in the module.

6). Measurement of Exclusion Limit Particle Size by Fine Particles A monodisperse polystyrene latex suspension (stock solution concentration: 10 w / v%) was diluted with 0.1 vol% Tween 20 aqueous solution and adjusted to 0.01 w / v% ( (Referred to as PSt-Tween solution). The PSt-Tween solution is introduced into the hollow fiber membrane lumen from one end (introduction side) of the mini-module, and the PSt-Tween solution leaks out from the other end (outflow side). The end of each was sealed, and the PSt-Tween solution was continuously introduced from the introduction side, and dead-end filtration with a hollow fiber membrane was performed. Similarly, filtration of 0.1 volume% Tween20 aqueous solution which does not contain a polystyrene latex suspension was performed. The absorbance of the liquid at 250 nm was measured, and the polystyrene latex removal rate Rj was calculated by the following equation [5].
Rj [%] = 100 × (ApPSt−ApT) / (AfPSt−AfT) [5]
However, ApPSt is the absorbance at 250 nm of the filtrate of the PSt-Tween solution, ApT is the absorbance at 250 nm of the filtrate of the 0.1 volume% Tween20 aqueous solution, AfPSt is the absorbance at 250 nm of the PSt-Tween solution introduced into the minimodule, and AfT is The light absorbency in 250 nm of 0.1 volume% Tween20 aqueous solution is shown. The Rj was determined by changing the particle size of the monodisperse polystyrene latex, and the minimum particle size satisfying Rj ≧ 95% was defined as the exclusion limit particle size.

7). Bubble Point Measurement / Maximum Pore Diameter Calculation The entire loop mini-module was immersed in a sufficient amount of 2-propanol (hereinafter abbreviated as iPA) for 1 hour or longer to spread iPA over the lumen and membrane wall. With the entire hollow fiber membrane portion of the loop type module immersed in iPA, the sleeve was connected to a nitrogen line fitted with a pressure gauge so that the pressurized pressure could be monitored, and pressurized at a rate of 1 bar per minute. . The point at which bubbles started to emerge constantly from the membrane wall portion of the hollow fiber membrane was recorded as the bubble point P [bar]. Three types of measurement were performed for one type of sample, and the average value of the measured values of bubble points was defined as the bubble point with the sample. Furthermore, the maximum pore diameter dBmax calculated from the bubble point (P [bar]) measured by iPA was obtained from the following equation [6].
dBmax [μm] = 0.0286 × 22.9 / P [6]

8). Measurement of water permeability (abbreviated as pure water flux) A circuit is connected to two end caps of the module (referred to as the inner surface inlet and the inner surface outlet, respectively), the inflow pressure of pure water into the module and the pure water from the module. The water outflow pressure can be measured. Both the inner and outer surfaces of the hollow fiber membrane were filled with pure water. Pure water is introduced into the module from the inner surface inlet, the circuit connected to the inner surface outlet (downstream from the pressure measurement point) is sealed with forceps to stop the flow, and the pure water that has entered from the inner surface inlet of the module is completely filtered. I did it. Purified water kept at 25 ° C is put into a pressurized tank, pressure is controlled by a regulator, pure water is sent to the module kept at 25 ° C constant temperature bath, and the amount of filtrate flowing out from the dialysate outlet is measured with a graduated cylinder. did. The transmembrane pressure difference (TMP) is TMP = (Pi + Po) / 2 [7]
It was. Here, Pi is the inner surface inlet side pressure of the module, and Po is the inner surface outlet side pressure of the module. The TMP was changed at four points, the filtration flow rate was measured, and the pure water flux [L / h / bar] was calculated from the slope of the relationship. At this time, the correlation coefficient between TMP and the filtration flow rate must be 0.999 or more. The pure water flux of the hollow fiber membrane was calculated from the membrane area and the water permeability of the module.
Pure water flux = pure water flux (M) / A [8]
Here, pure water Flux is the water permeability of the hollow fiber membrane [L / m ² / h / bar], pure water Flux (M) is the water permeability of the module [L / h / bar], and A is the membrane area of the module [m. ² ].

9. Measurement of PVP content on the surface of the hollow fiber membrane One hollow fiber membrane was stuck on a double-sided tape, opened with a knife and then developed to expose the inner surface. This was affixed to a sample stage and measured with Electron Spectroscopy for Chemical Analysis (ESCA). The above operation is for measuring the inner surface of the hollow fiber membrane. However, when measuring the outer surface, it is not necessary to open the laparotomy and expose the inner surface. Measurement was performed by pasting. The measurement conditions were as shown below.
Measuring device: ULVAC-Phi ESCA5800
Excitation X-ray: MgKα ray X-ray output: 14 kV, 25 mA
Photoelectron escape angle: 45 °
Analysis diameter: 400μmφ
Pass energy: 29.35 eV
Resolution: 0.125 eV / step
Degree of vacuum: about 10 ⁻⁷ Pa or less From the measured value (N) of nitrogen and the measured value (S) of sulfur, the PVP content on the film surface was calculated by the following formula [9] or [10].
<In case of PVP-added PES membrane>
PVP content [wt%]
= 100 × (N × 111) / (N × 111 + S × 232) [9]
<In the case of PVP-added PSf film>
PVP content [wt%]
= 100 × (N × 111) / (N × 111 + S × 442) [10]

10. Measurement of PVP content in whole hollow fiber membrane The hollow fiber membrane was dissolved in DMSO-d6, and 1H-NMR was measured at 60 ° C. For measurement, an Avance-500 manufactured by Brucker was used. From the integral intensity ratio of the peak (a) derived from the aromatic ring of the polysulfone polymer around 7.2 ppm in the 1H-NMR spectrum and the peak (b) derived from the pyrrolidone ring of PVP around 2.0 ppm, the following formula [11 ] To calculate the PVP content.
PVP content [wt%]
= {(B / nb) × 111 × 100} / {(a / na) × Ma + (b / nb) × 111}
[11]
Where Ma is the molecular weight of the repeating unit of the polysulfone polymer, 111 is the molecular weight of the repeating unit of PVP, na is the number of protons of the a contained in the repeating unit, and nb is the proton of b of the repeating unit contained in the repeating unit. The number of

11. Measurement of wine permeability (abbreviated as “Wine Flux”) Diluted “Tanba Shinshu Nigori 2005”, a turbid wine containing yeast marketed by Tamba Wines, with “Wine Life [White]” marketed by Mercian The turbidity was adjusted to 10 NTU (hereinafter referred to as evaluation wine). After immersing the module in RO water for 1 hour or longer, the module was replaced with evaluation wine, and both the inner and outer surfaces were filled with the evaluation wine. The container was filled with wine for evaluation and the temperature was controlled to 22 ° C. A circuit was constructed so that the wine for evaluation perfused the inner surface of the module from the container through the pump and returned to the container, and the wine for evaluation filtered by the hollow fiber membrane also returned to the container. At that time, the inflow pressure of the evaluation wine to the module and the outflow pressure of the evaluation wine from the module can be measured. The evaluation wine was introduced from the inner surface inlet so that the evaluation wine flowed through the lumen of the hollow fiber membrane at a flow rate of 1.5 m / sec. At this time, TMP was adjusted to about 1.5 bar. In this state, the evaluation wine was perfused into the lumen of the hollow fiber membrane, and cross-flow filtration for filtering a part was continued. When a predetermined time has elapsed, the amount of wine filtered in a certain time was measured (for example, the filtration amount at the time point of 10 to 11 minutes after the start of perfusion, and the filtration amount at the time point of 20 to 21 minutes). Wine Flux was calculated by the following equation [12].
Wine Flux [L / m ² / h / bar]
= (Wine filtration amount per minute [L / min] × 60 / A) / TMP [bar] [12]
Here, A is the membrane area [m ² ] of the module.

Example 1
19.0 parts by weight of PES (Sumika Excel (registered trademark) 4800P manufactured by Sumitomo Chemtech), 3.0 parts by weight of PVP (Collidon (registered trademark) K30) manufactured by BASF, 35.1 parts by weight of NMP manufactured by Mitsubishi Chemical, Mitsui Chemicals 42.9 parts by weight of TEG manufactured by KK were mixed and dissolved at 70 ° C. over 3 hours to obtain a uniform solution. Further, after reducing the pressure to 70-700 mmHg at 70 ° C., the system is immediately sealed so that the solvent composition does not volatilize and the solution composition does not change, and left to degas for 2 hours. did. On the other hand, a mixed solution of 35.1 parts by weight of NMP, 42.9 parts by weight of TEG, and 22.0 parts by weight of RO water was prepared, and this solution was used as a core solution. The film-forming stock solution is discharged from the annular part of the double tube nozzle, and the core liquid is discharged from the center part. After passing through an air gap of 20 mm, 13.5 parts by weight of NMP, 16.5 parts by weight of TEG, 70.0 parts by weight of RO water To a coagulation bath filled with an external coagulation liquid consisting of At this time, the nozzle temperature was set to 65 ° C., and the external coagulating liquid temperature was set to 55 ° C. The hollow fiber membrane was pulled out from the coagulation bath and wound up at a spinning speed of 10 m / min. In the coagulation bath, three cylindrical guides having a diameter of 50 mm were used, and the traveling direction of the hollow fiber membrane was gradually changed and pulled out from the coagulation bath. The maximum immersion depth of the hollow fiber membrane in the coagulation bath was 800 mm, and the travel distance of the hollow fiber membrane in the coagulation bath was 2000 mm. For the hollow fiber membrane, the discharge amount of the membrane forming stock solution and the core solution was controlled so that the inner diameter was about 1200 μm and the film thickness was about 340 μm.

  The hollow fiber membrane bundle was heat-treated by being immersed in 80 ° C. RO water for 60 minutes. Thereafter, hot air drying was performed at 60 ° C. for 10 hours to obtain a hollow fiber membrane (A) having an inner diameter of 1180 μm and a film thickness of 330 μm. SEM observation of the inner surface, outer surface, and cross-section (each of the fields divided into eight in the film thickness direction) was performed by the above method, and image analysis was performed to determine the porosity and the hole diameter in each part. The SEM photographs of the inner surface, the outer surface, and the entire cross section are shown in FIGS. 1, 2, and 3, respectively, and the measurement results of the porosity and the hole diameter are shown in Table 1. In the table, IS is the inner surface of the hollow fiber membrane, OS is the outer surface of the hollow fiber membrane, and CS1, CS2, CS3, CS4, CS5, CS6, CS7, and CS8 are the cross sections of the hollow fiber membrane from the inner surface. It means each part (1 to 8 in order from the inner surface direction) when it is divided into eight equal parts in the surface direction. There are dense layers on the inner surface and the outer surface, the hole diameter (0.05 μm) on the inner surface is smaller than the hole diameter (0.12 μm) on the outer surface, and the hole area ratio and the hole diameter are maximum (58%, 1.. 34 μm).

  FIG. 4 is a plot of pore diameter distribution on the inner surface of the hollow fiber membrane (A) and removal rates of polystyrene latexes having a diameter of 0.02 μm, 0.05 μm, 0.08 μm, 0.11 μm, and 0.23 μm simultaneously. Indicated. From the removal rate of polystyrene latex at each particle size, the exclusion limit particle size (φmax) of the hollow fiber membrane (A) can be determined to be 0.08 μm. On the inner surface of the hollow fiber membrane (A), the existing ratio DR [%] of the pore diameter exceeding φmax was 7.6%. The values of φmax and DR are also shown in Table 2.

  Furthermore, dBmax (maximum pore diameter obtained by bubble point) of hollow fiber membrane (A) measured and calculated by the above method, pure water flux, PVP content in the entire hollow fiber membrane, PVP content in the inner surface, outer surface Table 2 shows the content of PVP. In the table, dBmax is the maximum pore diameter calculated from the bubble point measured by iPA, Ca is the content of PVP in the entire hollow fiber membrane, Ci is the PVP content in the inner surface of the hollow fiber membrane, and Co is outside the hollow fiber membrane. It means the PVP content on the surface. It can be seen that dBmax (0.20 μm) falls between (1/10000) × pure water flux (0.115) and (1/4000) × pure water flux (0.2875). Further, it can be seen that Ca (1.8 wt%), Ci (29 wt%), and Co (24 wt%) have a relationship of 1 ≦ Ca ≦ 10, Ca ≦ Ci, Ca ≦ Co, and Co ≦ Ci. .

  With the module produced with the hollow fiber membrane (A), the wine flux was measured by the above method. The results are shown in Table 3. In the table, WineFlux 1-30 is a new module, wine Flux measured at the time of wine filtration (cross flow filtration) for 30 min, WineFlux 1-120 is wine filtration, and wine measured at 120 min elapsed Flux, WineFlux2-30 is a wine filtration for 120 min, and then using a module that was washed by reverse filtration of hot water at 60 ° C. for 10 min from the outside of the hollow fiber membrane to the lumen direction at a pressure of 2 bar. Wine Flux at the time of carrying out for 30 min, retention rate is a value indicating the value of WineFlux 1-120 against WineFlux 1-30 as a percentage, and recovery rate is a value indicating the value of WineFlux 1-30 relative to WineFlux 1-30 as a percentage, respectively. meansMoreover, the turbidity of the wine obtained as a filtrate was measured at the time of WineFlux 1-120 measurement. The results are shown in Table 3 as filtrate turbidity.

(Example 2)
18.5 parts by weight of PSf (P-3500 manufactured by Amoco), 3.5 parts by weight of PVP (Collidon (registered trademark) K30) manufactured by BASF, 35.1 parts by weight of NMP manufactured by Mitsubishi Chemical, and TEG42.9 manufactured by Mitsui Chemicals The parts by weight were mixed and dissolved at 70 ° C. for 3 hours to obtain a uniform solution. Further, after reducing the pressure to 70-700 mmHg at 70 ° C., the system is immediately sealed so that the solvent composition does not volatilize and the solution composition does not change, and left to degas for 2 hours. did. On the other hand, a mixed solution of 35.1 parts by weight of NMP, 42.9 parts by weight of TEG, and 22.0 parts by weight of RO water was prepared, and this solution was used as a core solution. The film-forming stock solution is discharged from the annular part of the double tube nozzle, and the core liquid is discharged from the center part. After passing through an air gap of 20 mm, 13.5 parts by weight of NMP, 16.5 parts by weight of TEG, 70.0 parts by weight of RO water To a coagulation bath filled with an external coagulation liquid consisting of At this time, the nozzle temperature was set to 63 ° C., and the external coagulating liquid temperature was set to 55 ° C. The hollow fiber membrane was pulled out from the coagulation bath and wound up at a spinning speed of 10 m / min. In the coagulation bath, three cylindrical guides having a diameter of 50 mm were used, and the traveling direction of the hollow fiber membrane was gradually changed and pulled out from the coagulation bath. The maximum immersion depth of the hollow fiber membrane in the coagulation bath was 800 mm, and the travel distance of the hollow fiber membrane in the coagulation bath was 2000 mm. For the hollow fiber membrane, the discharge amount of the membrane forming stock solution and the core solution was controlled so that the inner diameter was about 1200 μm and the film thickness was about 340 μm.

The hollow fiber membrane bundle was heat-treated by being immersed in 80 ° C. RO water for 60 minutes. Thereafter, hot air drying was performed at 60 ° C. for 10 hours to obtain a hollow fiber membrane (B) having an inner diameter of 1160 μm and a film thickness of 320 μm. SEM observation of the inner surface, outer surface, and cross-section (each of the fields divided into eight in the film thickness direction) was performed by the above method, and image analysis was performed to determine the porosity and the hole diameter in each part. IS is the inner surface of the hollow fiber membrane, OS is the outer surface of the hollow fiber membrane, CS1, CS2, CS3, CS4, CS5, CS6, CS7, and CS8 are divided into eight equal sections from the inner surface to the outer surface. The hollow fiber membrane (B) had dense layers on both the inner and outer surfaces, and the numerical values indicating the structure were as follows. Further, in the same manner as in Example 1, the pore size distribution, φmax, and DR on the inner surface of the hollow fiber membrane (B) were determined. The results are shown in Table 2.
Pore diameter in IS: 0.04 μm
IS porosity: 8%
OS pore size: 0.05 μm
Porosity in OS: 11%
Site where porosity is maximized in cross section: CS3
Hole diameter at CS3: 2.31 μm
Porosity in CS3: 59%

  Further, Table 2 shows the dBmax, pure water flux, Ca, Ci, and Co of the hollow fiber membrane (B) measured in the same manner as in Example 1. It can be seen that dBmax falls between (1/10000) × pure water flux (0.124) and (1/4000) × pure water flux (0.310). In addition, it can be seen that Ca, Ci, and Co have a relationship of 1 ≦ Ca ≦ 10, Ca ≦ Ci, Ca ≦ Co, and Co ≦ Ci.

  The wine flux was measured in the same manner as in Example 1 using the module produced with the hollow fiber membrane (B). The results are shown in Table 3.

(Comparative Example 1)
A commercially available polyethylene microfiltration membrane (hereinafter referred to as PE-MF membrane) was used, and the structure was observed by SEM in the same manner as in Example 1. IS, OS, and SEM photographs of the entire cross section are shown in FIGS. 5, 6, and 7, respectively. It can be seen from the cross-sectional image of FIG. 7 that the film is a homogeneous symmetric film, and the maximum portion of the porosity in the film wall portion is not seen. Numerical values indicating the structure of the PE-MF membrane were as follows. Further, in the same manner as in Example 1, dBmax, pure water flux, pore size distribution on the inner surface, φmax, and DR were obtained. The results are shown in Table 2. Furthermore, wine flux was measured in the same manner as in Example 1 using a module made of a PE-MF membrane. The results are shown in Table 3.
Pore diameter in IS: 0.22 μm
Porosity at IS: 31%
OS pore size: 0.22 μm
Porosity in OS: 29%
Site where porosity is maximum in cross section: None

(Comparative Example 2)
A commercially available microfiltration membrane made of polyvinylidene fluoride (hereinafter referred to as PVDF-MF membrane) was used, and the structure was observed by SEM in the same manner as in Example 1. The SEM photographs of IS, OS, and the entire cross section are shown in FIGS. 8, 9, and 10, respectively. It can be seen from the cross-sectional image of FIG. 10 that the film is a homogeneous symmetric film, and the maximum portion of the porosity in the film wall portion is not seen. Numerical values indicating the structure of the PVDF-MF membrane were as follows. Further, in the same manner as in Example 1, dBmax, pure water flux, pore size distribution on the inner surface, φmax, and DR were obtained. The results are shown in Table 2. Furthermore, wine flux was measured in the same manner as in Example 1 using a module made of a PVDF-MF membrane. The results are shown in Table 3.
Pore diameter in IS: 0.31 μm
Porosity at IS: 35%
OS pore size: 0.18 μm
Porosity in OS: 25%
Site where porosity is maximum in cross section: None

(Comparative Example 3)
17.5 parts by weight of PES (Sumitomo Chemtech (registered trademark) 4800P manufactured by Sumitomo Chemtech) 4.5 parts by weight of PVP (Collidon (registered trademark) K90) manufactured by BASF, 75.0 parts by weight of DMAc, 3.0 parts by weight of RO water The parts were mixed and dissolved at 50 ° C. for 2 hours to obtain a uniform solution. Further, after reducing the pressure at 50 ° C. to normal pressure −700 mmHg, the system is immediately sealed so that the solvent composition does not volatilize and the solution composition does not change, and left to degas for 2 hours. did. On the other hand, a mixed solution of 40.0 parts by weight of DMAc and 60.0 parts by weight of RO water was prepared, and this solution was used as a core solution. The film-forming stock solution is discharged from the annular part of the double-tube nozzle, the core liquid is discharged from the center part, and the outside is made of a mixed liquid of DMAc 20.0 parts by weight and RO water 80.0 parts by weight through an air gap of 450 mm. Guided to a coagulation bath filled with coagulation liquid. At this time, the nozzle temperature was set to 65 ° C., and the external coagulating liquid temperature was set to 60 ° C. The hollow fiber membrane was pulled out from the coagulation bath and wound up at a spinning speed of 75 m / min. In the coagulation bath, one rod-shaped guide having a diameter of 12 mm was used to change the traveling direction of the hollow fiber membrane, and the hollow fiber membrane was drawn from the coagulation bath. The maximum immersion depth of the hollow fiber membrane in the coagulation bath was 200 mm, and the travel distance of the hollow fiber membrane in the coagulation bath was 600 mm. The hollow fiber membrane was controlled in terms of the amount of the membrane forming stock solution and the core solution discharged so that the inner diameter was about 200 μm and the film thickness was about 30 μm.

  The obtained hollow fiber membrane was wound with an embossed polyethylene film and then cut into a length of 27 cm to form a hollow fiber membrane bundle. The operation of immersing this hollow fiber membrane bundle in RO water at 80 ° C. for 30 min was repeated four times to perform heating and washing treatment. The obtained wet hollow fiber membrane bundle is subjected to centrifugal liquid removal treatment at 600 rpm × 5 min, and the drying apparatus is simultaneously irradiated with microwaves by a microwave generator having a structure in which a reflector can be installed in the oven and heated uniformly. The inside was depressurized to 7 kPa and dried for 60 minutes. The output of the microwave was reduced by 0.5 kW every 20 min from the initial 1.5 kW. By this drying treatment, a hollow fiber membrane (C) having an inner diameter of 195 μm and a film thickness of 29 μm was obtained.

Using the hollow fiber membrane (C), the structure was observed with SEM in the same manner as in Example 1. As a structure, it was an asymmetric membrane having a dense layer only in IS and increasing the porosity from the inner surface toward the outer surface. Numerical values indicating the structure of the hollow fiber membrane (C) were as follows. Further, the measurement of φmax on the inner surface of the hollow fiber membrane was attempted in the same manner as in Example 1, but the measurement with polystyrene latex was less than 0.02 μm, and accurate measurement was impossible. For this reason, it is impossible to calculate DR. In the measurement of dBmax, the yarn was broken before the bubble point was reached and could not be measured. Pure water flux, pure water flux, Ca, Ci, and Co were measured in the same manner as in Example 1, and the results are shown in Table 2. Furthermore, the wine flux was measured in the same manner as in Example 1 using a module made of the hollow fiber membrane (C). The results are shown in Table 3.
IS pore size: 0.01 μm
IS porosity: 8%
OS pore size: 0.53 μm
Porosity in OS: 15%
Site where porosity is maximum in cross section: None

  As clarified from the measurement results of the wine permeability, the polymer porous hollow fiber membrane of the present invention has a high wine flux retention and recovery rate and is excellent in membrane property retention and recovery. Recognize. Further, the turbidity of the wine obtained as a filtrate is low, and excellent permeability of the filtration component and removal of the retention component (non-filtration component), that is, excellent fractionation characteristics are realized at the same time. It is considered that the specific configuration and film structure that are the characteristics of the present invention contribute to the achievement of these excellent characteristics.

  The polymer porous hollow fiber membrane of the present invention can be applied as various aqueous fluid treatment membranes such as a water treatment membrane, a beverage treatment membrane and a blood treatment membrane, and has excellent fractionation characteristics and permeability. It has the advantages of suppressing deterioration over time and recovering film properties by cleaning, and contributes greatly to the industry.

2 is an electron micrograph (10,000 times) of the inner surface of the hollow fiber membrane (A) obtained in Example 1. FIG. 4 is an electron micrograph (10,000 times) of the outer surface of the hollow fiber membrane (A) obtained in Example 1. FIG. 2 is an electron micrograph (200 times) of a cross section of the hollow fiber membrane (A) obtained in Example 1. FIG. It is the figure which showed the pore distribution in the inner surface of the hollow fiber membrane (A) obtained in Example 1, and the polystyrene latex removal rate of a hollow fiber membrane (A). 2 is an electron micrograph (1000 times) of an inner surface of a PE-MF film of Comparative Example 1. FIG. 2 is an electron micrograph (1000 times) of an outer surface of a PE-MF film of Comparative Example 1. 3 is an electron micrograph (150 times) of a cross section of a PE-MF film of Comparative Example 1. FIG. 4 is an electron micrograph (1000 times) of an inner surface of a PVDF-MF film of Comparative Example 2. FIG. 4 is an electron micrograph (1000 times) of an outer surface of a PVDF-MF film of Comparative Example 2. FIG. It is an electron micrograph (150 times) of the cross section of the PVDF-MF film of Comparative Example 2.

Claims (6)

(A) having a dense layer on the inner and outer surfaces;
(B) the hole diameter on the inner surface is smaller than the hole diameter on the outer surface;
(C) The initial porosity increases from the inner surface toward the outer surface, and after passing through at least one local maximum, the porosity decreases again on the outer surface side,
(D) When the exclusion limit particle diameter obtained by the fine particle passage test is φmax [μm], the pore diameter of the inner surface is dIS [μm], and the existence ratio of dIS exceeding φmax is DR [%], 2 [%] ≦ DR ≦ 20 [%],
(E) comprising a polysulfone polymer and polyvinylpyrrolidone;
(F) tap water all SANYO used for (clean water) or beverage processing,
(G) The part behind the dense layer is a sponge-like support layer,
(H) The polymer porous hollow fiber membrane wherein the polysulfone polymer is polysulfone and / or polyethersulfone . When the inner surface of the hollow fiber membrane is IS, the maximum porosity of the cross section of the hollow fiber membrane is CSmax, the hole diameter of each part is dIS, dCSmax, and the porosity of each part is pIS, pCSmax,
(A) 0.001 [μm] ≦ dIS ≦ 1 [μm] and (b) 0.1 [μm] ≦ dCSmax ≦ 10 [μm] and (c) 5 [%] ≦ pIS ≦ 30 [%] and ( d) 40 [%] ≦ pCSmax ≦ 80 [%]
The polymer porous hollow fiber membrane according to claim 1. The inner surface of the hollow fiber membrane is IS, the outer surface of the hollow fiber membrane is OS, and the section when the cross section of the hollow fiber membrane is divided into eight equal parts from the inner surface to the outer surface direction in order from the inner surface direction is CS1, CS2, CS3 , CS4, CS5, CS6, CS7, CS8, the pore diameter of each part is dIS, dOS, dCS1, dCS2, dCS3, dCS4, dCS5, dCS6, dCS7, dCS8, and the porosity of each part is pIS, pOS, pCS1 , PCS2, pCS3, pCS4, pCS5, pCS6, pCS7, pCS8,
(A) dIS ≦ dCS1 <dCS2 ≦ dCS3 ≧ dCS4>dCS5>dCS6>dCS7> dCS8 ≧ dOS and (b) pIS <pCS1 ≦ pCS2 <pCS3> pCS4 ≧ pCS5 ≧ pCS6 ≧ pCS7 ≧ pCS8> pOS
The polymer porous hollow fiber membrane according to claim 1 or 2. When the maximum pore diameter obtained by the bubble point is dBmax [μm] and the permeability of pure water at 25 ° C. is F [L / (h · m ² · bar)],
(A) (1/10000) · F ≦ dBmax ≦ (1/4000) · F and (b) 0.05 [μm] ≦ dBmax ≦ 1 [μm]
The polymer porous hollow fiber membrane according to any one of claims 1 to 3, wherein The content of the hydrophilic polymer in the entire hollow fiber membrane is Ca [wt%], the content of the hydrophilic polymer on the inner surface is Ci [wt%], and the content of the hydrophilic polymer on the outer surface is Co [wt%]. When
(A) 1 [wt%] ≦ Ca ≦ 10 [wt%] and (b) Ca ≦ Ci and Ca ≦ Co and (c) Co ≦ Ci
The polymer porous hollow fiber membrane according to any one of claims 1 to 4, wherein A production method for producing the polymer porous hollow fiber membrane according to any one of claims 1 to 5,
A heat treatment step of immersing the hollow fiber membrane in hot water at 60 to 100 ° C. for 30 to 120 minutes is provided.
A method for producing a polymeric porous hollow fiber membrane.