WO2015041286A1

WO2015041286A1 - Porous hollow fiber membrane and method for manufacturing same

Info

Publication number: WO2015041286A1
Application number: PCT/JP2014/074680
Authority: WO
Inventors: 正史寺町; 真理子岡; 芳則福場; 隅　敏則; 泰夫広本; 藤木　浩之; 祐吾溝越
Original assignee: 三菱レイヨン株式会社
Priority date: 2013-09-18
Filing date: 2014-09-18
Publication date: 2015-03-26
Also published as: JPWO2015041286A1; KR101826451B1; CN105722585A; JP6020592B2; JP2016196004A; KR20160044582A

Abstract

　Provided is a porous hollow fiber membrane and a method for manufacturing same, the porous hollow fiber membrane being able to be used suitably in devices for processing various water-based fluids for use in applications such as water purification, drinking-water processing, and seawater clarification; having excellent fractionation characteristics and permeability with minimal decrease in performance over time; having excellent recovery in membrane separation characteristics by washing: and having excellent separation characteristics, filtration stability, and mechanical strength. The present invention is a porous hollow fiber membrane having a porous layer made of a thermoplastic resin in at least an outer surface and the vicinity thereof, the average pore diameter (Ad) at a depth of 1 μm from the surface as seen in cross-section being no more than 0.6 of the average pore diameter (Bd) from a depth of 2 to 3 μm, and a method for manufacturing said membrane.

Description

Porous hollow fiber membrane and method for producing the same

The present invention relates to a porous hollow fiber membrane having excellent anti-fouling performance, which is mainly used for removing bacteria, viruses, SS components and the like in water. Specifically, the present invention relates to a porous hollow fiber membrane that is excellent in stable membrane performance over a long period of time and excellent in recoverability of membrane performance by washing. The present invention also relates to a porous hollow fiber membrane suitable for water treatment such as water purification treatment that can be used as a microfiltration membrane or an ultrafiltration membrane, and a method for producing the same.
This application claims priority based on Japanese Patent Application No. 2013-193213 filed in Japan on September 18, 2013 and Japanese Patent Application No. 2013-193214 filed on September 18, 2013 in Japan. Is hereby incorporated by reference.

Conventionally, sand filtration and combined use of coagulation sedimentation and sand filtration have been widely used in the filtration process in the water supply field, where tap water is produced from fresh water sources such as river water, lake water, and groundwater. However, in these treatments, there is a concern such as water source contamination due to Cryptosporidium which has high chlorine resistance and may not be completely rendered harmless by chlorine sterilization after filtration. Against this background, membrane filtration methods that can remove turbidity more easily and accurately are becoming more and more used alone or in combination with other water treatment technologies such as coagulation sedimentation and sand filtration. . On the other hand, when desalinating seawater using a reverse osmosis membrane, the seawater supplied to the reverse osmosis membrane is subjected to a turbidity treatment in advance by a pretreatment such as coagulation sedimentation or sand filtration, and then supplied to the reverse osmosis membrane to be removed. Salt treatment is performed. For these treatments, there is an increasing number of cases where turbidity by membrane filtration is employed instead of coagulation sedimentation or sand filtration or in combination with other water treatment techniques.

Examples of the required characteristics required for the porous hollow fiber membrane used for membrane separation include the following points.
(1) The removability of the substance to be removed is high.
(2) The permeability of the permeable substance is high.
(3) The permeability of the processing fluid is high.
(Hereinafter, (1), (2), and (3) are collectively referred to as membrane separation characteristics.)
(4) The rupture strength against tension or the like is sufficiently high, and it is difficult to break or leak.
(5) The fractionation characteristics are unlikely to deteriorate over time.
(6) The permeability of the processing fluid is difficult to decrease over time.
(Hereinafter, (5) and (6) are collectively referred to as retention of membrane separation characteristics.)
(7) Excellent recovery of fractionation characteristics by washing.
(8) It is excellent in recovering permeability by washing.
(Hereinafter, (7) and (8) are collectively referred to as recoverability of membrane separation characteristics.)

In general, in the membrane filtration process, as the membrane filtration operation time elapses, fouling substances adhere and accumulate on the membrane surface on the side where raw water is supplied, and membrane filtration resistance increases and membrane filtration efficiency decreases. A phenomenon occurs. At that time, in order to remove the fouling substances adhering to the membrane surface, washing operation such as washing, air scrub, draining of feed water, or chemical washing is performed to restore membrane filtration resistance, and membrane filtration is resumed. . The membrane filtration process is operated by repeating the membrane filtration operation and the washing operation on the left. The washing operation requires utilities such as electricity and water, and during the washing operation, since production water is not obtained, the washing operation frequency is low and the washing operation time is preferably short. Therefore, it is very useful if a separation membrane can be obtained in which the increase in the membrane filtration resistance that occurs with the passage of the membrane filtration operation is small and the recovery of the membrane filtration resistance by the washing operation is large.

In the prior art, many technical developments have been made in the direction of improving the fouling resistance by hydrophilizing the membrane surface and suppressing the increase in filtration resistance during the membrane filtration operation. For example, a hydrophilic polymer such as polyvinyl pyrrolidone (PVP) or polyvinyl alcohol (PVA) is mixed in a film-forming stock solution used to obtain a porous film made of a hydrophobic polymer. The molecule remains, and the hydrophilicity of the film surface is improved to improve the fouling resistance. Although this method is simple and easy to form and has high production efficiency of the membrane, it is an excellent method, but the fouling resistance is still insufficient.

In addition, in the prior art, a membrane made of a hydrophobic polymer is first formed, and then various surface treatments are performed to coat the surface of the hydrophobic polymer membrane with a hydrophilic polymer, thereby improving fouling resistance. There is something to try. These methods have many practical problems such as a complicated manufacturing process and difficulty in controlling the process as compared with a method of forming a film by mixing a hydrophilic polymer in a film forming stock solution.

Both of these technologies focus on the chemical properties and chemical composition of the membrane surface, and the technical idea of improving the fouling resistance by making the membrane surface hydrophilic is fundamental. On the other hand, Patent Documents 1 and 2 can be cited as examples referring to the relationship between the shape of the membrane surface and the membrane separation characteristics. Patent Document 1 discloses an invention related to a composite reverse osmosis membrane having a polyamide-based skin layer. By making the specific surface area of the membrane surface on the side to which raw water is supplied into a specific range, It has been shown that water permeability is improved. Further, Patent Document 2 discloses an invention related to a composite reverse osmosis membrane having a polyamide-based skin layer as well, and the average value X of the horizontal distance between adjacent vertices of the surface irregularities on the membrane surface on the raw water supply side is disclosed. It is disclosed that a composite reverse osmosis membrane exhibiting high blocking performance can be obtained when the average value Z of the unevenness difference between the apex adjacent to each other and the bottom side satisfies a specific relationship. However, neither of Patent Documents 1 and 2 is a study on a composite reverse osmosis membrane, and further, no mention is made regarding improvement of fouling resistance.

On the other hand, in recent years, due to increasing interest in environmental pollution and stricter regulations, water treatment by a membrane method using a filtration membrane having excellent separation completeness and compactness has attracted attention. In such water treatment applications, filtration membranes are required to have excellent separation characteristics, water permeability, and high mechanical strength.

Conventionally, filtration membranes made of polysulfone, polyacrylonitrile, cellulose acetate, or polyvinylidene fluoride manufactured by a wet or dry wet spinning method are known as filtration membranes having excellent water permeability. These filtration membranes are manufactured by microphase-separating a polymer solution and then coagulating the polymer solution in a non-solvent, and have a high porosity and an asymmetric structure.

Among the above filtration membrane materials, polyvinylidene fluoride resin is suitably used as a material for separation membranes because it is excellent in chemical resistance and heat resistance. However, many of the proposed filtration membranes made of polyvinylidene fluoride hollow fiber membranes are not sufficient in any one of separation characteristics, filtration stability, and mechanical strength, and those satisfying all of them There was a problem that the manufacturing method was complicated.

In order to increase the mechanical strength of the separation membrane, a separation membrane in which a hollow braid is used as a support and a porous layer is provided on the surface has been proposed (Patent Document 3). However, this porous layer has a large macro void inside the membrane structure due to its production method, and there is a problem that the separation characteristics are liable to be deteriorated due to damage to the outer surface of the membrane due to external factors.

On the other hand, a separation membrane has been proposed in which the dense layer is made thick to some extent by controlling the phase separation, and at the same time, macrovoids are suppressed to improve the separation characteristics (Patent Document 4). However, when the dense layer is thickened in this way, there is a problem that ultrafine objects and soluble organic polymers are clogged with the dense layer, which may reduce the filtration stability.

On the other hand, a polyvinylidene fluoride resin and a plasticizer are melt-kneaded, extruded, cooled and solidified, then the plasticizer is extracted to obtain a porous hollow fiber membrane, and then the outer surface dense layer is stretched in a wet state However, a separation membrane has been proposed in which the porosity of the surface dense layer is increased to make it less likely to be contaminated by turbid water (Patent Document 5). However, the separation membrane of this technique has a high porosity, but the pore diameter of the dense layer is almost uniform, so that the problem that microscopic objects and soluble organic polymers that have passed through the surface are easily clogged inside the dense layer still remains. In addition, there is a problem that it is difficult to combine with a support because the manufacturing method substantially requires stretching, and it is difficult to achieve both mechanical strength.

Japanese Patent Laid-Open No. 09-19630 JP 2005-169332 A US Pat. No. 5,472,607 International publication 09/142279 pamphlet International Publication 2011/007714 Pamphlet

The problem of the present invention is that it can be used in the treatment of various aqueous fluids such as water purification treatment, beverage treatment, or seawater turbidity, and has excellent fractionation characteristics and permeability, An object of the present invention is to provide a porous hollow fiber membrane in which a decrease is suppressed and the membrane separation property recoverability by washing is excellent.

Another object of the present invention is to solve the above problems and provide a porous hollow fiber membrane having excellent separation characteristics, filtration stability, and mechanical strength.

In order to solve the above-described problems, the present invention has the following embodiments.
(1) A porous hollow fiber membrane having a porous layer on at least an outer surface, wherein an average pore diameter (Ad) from the outer surface to a depth of 1 μm in a cross-sectional structure of the porous hollow fiber membrane is from a depth of 2 μm A porous hollow fiber membrane having a ratio (Ad / Bd) to an average pore diameter (Bd) of up to 3 μm of 0.6 or less.
(2) The porous hollow fiber membrane according to (1), wherein the outer surface has an average pore diameter P1 of 0.05 to 1.0 μm and an open area ratio A1 of 15 to 65%.
(3) The average pore diameter P2 of the layer from the outer surface to the depth of 10 μm in the cross-sectional structure is 0.1 to 5.0 μm, and the open area ratio A2 is 10 to 50%, as described in (1) or (2) Porous hollow fiber membrane (4) The structure from the outer surface to a depth of 5 μm is a three-dimensional network structure in which the pore diameter gradually increases in the direction away from the outer surface (1) to (3) Porous hollow fiber membrane.
(5) The average pore diameter of the porous layer from the outer surface to a depth of 5 μm is smaller than the average pore diameter of the porous layer existing at a position farther from the outer surface than the depth of 5 μm (1) to (4) The porous hollow fiber membrane according to any one of the above.
(6) The porous hollow fiber membrane according to any one of (1) to (5), wherein an average pore diameter of the porous layer existing at a part farther from the outer surface than a depth of 5 μm is 10 μm or less.
(7) The porous hollow fiber membrane according to any one of (1) to (6), wherein the thermoplastic resin constituting the depth of 5 μm from the outer surface is made of the same thermoplastic resin.
(8) The porous hollow fiber according to any one of (1) to (7), which does not contain a macrovoid exceeding 10 μm in pore diameter and a part thereof in the porous layer at a part not more than 10 μm deep from the outer surface. film.
(9) The porous hollow fiber membrane according to any one of (1) to (8), which is formed by a non-solvent phase separation method.
(10) The porous hollow fiber membrane according to any one of (1) to (9), wherein the porous layer is formed on the outer surface side of a hollow fiber-like support.
(11) The porous hollow fiber membrane according to (10), wherein the hollow fiber-shaped support is a heat-treated support.
(12) The porous hollow fiber membrane according to (10) or (11), wherein the hollow fiber-shaped support is a hollow knitted string.
(13) The porous hollow fiber membrane according to (11) or (12), wherein the support is a hollow knitted string obtained by circularly knitting a single yarn made of multifilament.
(14) A film-forming resin solution containing a thermoplastic resin and a hydrophilic compound is discharged from a spinning nozzle, and then the discharged film-forming resin solution is used as a component of the film-forming resin solution to saturate a non-solvent. A method for producing a porous hollow fiber membrane, which is brought into contact with steam and then solidified by being immersed in a coagulating liquid to form a porous hollow fiber membrane, wherein the spinning nozzle is a single or double tubular nozzle And the said porous hollow fiber membrane is a manufacturing method of the porous hollow fiber membrane which forms the site | part of 5 micrometers in depth from an outer surface with the same film forming resin solution.
(15) The method for producing a porous hollow fiber membrane according to (14), wherein the non-solvent saturated vapor is saturated water vapor.
(16) Using a spinning nozzle, a film-forming resin solution is applied to the outer peripheral surface of the hollow support to form a film-forming resin layer, and then the film-forming resin layer is brought into contact with a non-solvent saturated vapor. (14) The manufacturing method of the porous hollow fiber membrane as described in (15).
(17) The method for producing a porous hollow fiber membrane according to (16), wherein the support is a heat-treated support.
(18) The method for producing a porous hollow fiber membrane according to (16) or (17), wherein the support is a knitted string.
(19) The method for producing a porous hollow fiber membrane according to (17) or (18), wherein the support is a hollow knitted string obtained by circularly knitting a single yarn made of multifilament.

The embodiment of the present invention has the following aspects. The first gist of the present embodiment that solves the above-mentioned problems is a porous hollow fiber membrane having an outer surface open area ratio of 15 to 65%.
The second gist of the present embodiment is a method for evaluating a porous hollow fiber membrane having the following steps.
Step (1): A step of observing a cross section of the porous hollow fiber membrane with a scanning electron microscope and measuring an area of each hole appearing on the surface of the cross section. Step (2): Area of each hole measured in step (1) Of calculating the average pore diameter index for the holes corresponding to 50% of the total area

Further, this embodiment is a porous hollow fiber membrane having a porous layer made of a thermoplastic resin at least on the outer surface and in the vicinity thereof, and the average pore diameter Ad from the surface in the cross-sectional structure to the depth of 1 μm is the depth. The porous hollow fiber membrane has a mean pore diameter Bd of 2 μm to 3 μm that is 1/2 or less.
Furthermore, in this embodiment, a film-forming resin solution containing a thermoplastic resin and a hydrophilic compound is discharged from a spinning nozzle, immediately after being brought into contact with a non-solvent saturated vapor of the film-forming resin, and then into a coagulating liquid. This is a method for producing a porous hollow fiber membrane that is solidified by dipping.

The embodiment of the present invention has the following aspects.
(1A) A porous hollow fiber membrane in which at least the outer surface side is composed of a porous layer, and the porosity of the outer surface is 15 to 65%.
(2A) The porous hollow fiber membrane according to (1A), wherein the outer surface has an average pore diameter index P1 of 0.05 to 1.0 (μm).
(3A) As described in (1A) or (2A), the dense layer has a dense layer up to 10 μm near the outer surface, and the average pore diameter index P2 (μm) of the dense layer is in the range of 0.1 to 5.0 (μm). Porous hollow fiber membrane.
(4A) The porous hollow fiber membrane according to (3A), wherein the open area ratio A2 (%) of the dense layer is 10 to 50%.
(5A) The porous hollow fiber membrane according to (1A) to (4A), wherein the total thickness of the porous layer is 200 μm or less.
(6A) The porous membrane according to (1A) to (5A), wherein the pore diameter index of the porous layer continuous from the outer surface gradually increases.
(7A) A method for evaluating a porous hollow fiber membrane comprising the following steps, wherein the outer surface side is a porous layer.
Step 1: A step of observing the cross section of the porous hollow fiber membrane with a scanning electron microscope and measuring the area of each hole appearing on the surface of the cross section. Step 2: The area value of each hole measured in Step 1 is small. Step of calculating the average pore diameter index using the holes corresponding to 50% of the total area

The embodiment of the present invention further has the following aspects.
(1B) A porous hollow fiber membrane having a porous layer made of a thermoplastic resin at least on the outer surface and in the vicinity thereof, wherein the average pore diameter Ad from the surface to the depth of 1 μm in the cross-sectional structure is from the depth of 2 μm to 3 μm A porous hollow fiber membrane having a mean pore diameter Bd of ½ or less.
(2B) The porous hollow fiber membrane according to (1B), wherein the structure from the outer surface to a depth of 5 μm is a three-dimensional network structure in which the pore diameter gradually increases toward the center.
(3B) The porous hollow fiber according to (1B) or (2B), wherein the average pore diameter of the porous layer from the outer surface to a depth of 5 μm is smaller than the average pore diameter of the porous layer existing inside the depth of 5 μm. film.
(4B) The porous hollow fiber membrane according to any one of (1B) to (3B), wherein the average pore diameter of the porous layer existing inside the depth of 5 μm is 10 μm or less.
(5B) The porous hollow fiber membrane according to any one of (1B) to (4B), wherein the thermoplastic resin constituting the depth of 5 μm from the outer surface is made of the same thermoplastic resin.
(6B) The porous hollow fiber membrane according to any one of (1B) to (5B), wherein the porous layer from the outer surface to a depth of 10 μm does not contain macrovoids having a pore diameter exceeding 10 μm.
(7B) The porous hollow fiber membrane according to any one of (1B) to (6B), wherein the porous layer is formed on the outer surface side of a hollow fiber-like support.
(8B) The porous hollow fiber membrane according to (7B), wherein the hollow fiber-shaped support is a hollow knitted string.
(9B) The porous hollow fiber membrane according to (8B), wherein the hollow fiber-shaped support is a heat-treated hollow knitted string.
(10B) The porous hollow fiber membrane according to (8B) or (9B), wherein the support is a hollow knitted string obtained by circularly knitting a single yarn made of multifilament.
(11B) A film-forming resin solution containing a thermoplastic resin and a hydrophilic compound is discharged from a spinning nozzle, then contacted with a non-solvent saturated vapor of the film-forming resin, and then immersed in a coagulation liquid. A method for producing a porous hollow fiber membrane, which is solidified by the method.
(12B) The production of the porous hollow fiber membrane according to (11B), wherein the spinning nozzle is a single or double or more tubular nozzle, and at least 4 μm in depth is formed from the outer surface with the same membrane-forming resin solution. Method.
(13B) The method for producing a porous hollow fiber membrane according to (12B), wherein the non-solvent saturated vapor is saturated steam at 100 ° C.
(14B) The porous hollow film according to (12B) or (13B), wherein the film-forming resin solution discharged from the spinning nozzle is contacted with dry air before contacting with the non-solvent saturated vapor of the film-forming resin. Yarn membrane manufacturing method.
(15B) The method for producing a porous hollow fiber membrane according to (14B), wherein the dry air is supplied vertically downward from a nozzle discharge surface, and then comes into contact with the saturated vapor of the non-solvent.
(16B) The method for producing a porous hollow fiber membrane according to (14B) or (15B), wherein the relative humidity of the non-solvent in the atmosphere near the spinning nozzle is made less than 10% by the dry air.

The porous hollow fiber membrane of the present invention is a porous hollow fiber membrane having a porous layer containing a thermoplastic resin at least on the outer surface and in the vicinity of the outer surface, and is in the thickness direction of the porous hollow fiber membrane. The size of the average pore diameter (Ad) from the surface to the depth of 1 μm in the cross-sectional structure is not more than 0.6 in terms of the ratio of the average pore diameter (Bd) from the depth of 2 μm to 3 μm. As a result, a porous hollow fiber membrane excellent in separation characteristics, filtration stability and mechanical strength is obtained.

Further, according to the present invention, by forming a porous hollow fiber membrane having a porous layer at least on the outer surface side and a porosity of 15 to 65% on the outer surface, Since the structure has an inclined structure coarser than the surface, it is considered that there is no clogging inside and the cleaning recovery is high. Moreover, a porous hollow fiber membrane excellent in retention and recovery of membrane separation characteristics can be obtained.

The porous hollow fiber membrane of the present invention can be used in the treatment of various aqueous fluids such as water purification membranes, beverage treatment membranes and seawater turbidity membranes, and provides a porous hollow fiber membrane particularly suitable for water purification treatments. Can do. Moreover, the porous hollow fiber membrane of the present application has sufficient membrane strength that does not cause breakage or leakage during module molding or actual use, while having excellent fractionation characteristics and permeability. In this way, it is possible to suppress the deterioration of the characteristics of the film over time, and it is excellent in recovering the membrane separation characteristics by washing.

The porous hollow fiber membrane of the present invention has a so-called dense layer because the average pore diameter Ad from the surface to the depth of 1 μm in the cross-sectional structure is ½ or less of the average pore diameter Bd from the depth of 2 μm to 3 μm. As a result, a porous hollow fiber membrane excellent in separation characteristics, filtration stability and mechanical strength is obtained.

2 is a cross-sectional photograph of a porous layer of a porous hollow fiber membrane obtained in Reference Example 1. 4 is a cross-sectional photograph of a porous layer of a porous hollow fiber membrane obtained in Reference Example 2. 4 is a cross-sectional photograph of a porous layer of a porous hollow fiber membrane obtained in Reference Example 3. 4 is a cross-sectional photograph of a porous layer of a porous hollow fiber membrane obtained in Reference Example 4. 2 is a cross-sectional photograph of a porous layer of a porous hollow fiber membrane obtained in Reference Comparative Example 1. 2 is a cross-sectional photograph of the porous layer in the vicinity of the outer surface portion of the porous hollow fiber membrane obtained in Reference Example 1. 4 is a cross-sectional photograph of the porous layer in the vicinity of the outer surface portion of the porous hollow fiber membrane obtained in Reference Example 2. 4 is a cross-sectional photograph of the porous layer in the vicinity of the outer surface portion of the porous hollow fiber membrane obtained in Reference Example 3. 4 is a cross-sectional photograph of the porous layer in the vicinity of the outer surface portion of the porous hollow fiber membrane obtained in Reference Example 4. 2 is a cross-sectional photograph of a porous layer in the vicinity of an outer surface portion of a porous hollow fiber membrane obtained in Reference Comparative Example 1. It is a graph which shows the time-dependent change of the differential pressure | voltage at the time of filtration operation in a reference example and a reference comparative example. It is a schematic diagram which shows the manufacturing apparatus used for manufacture of the porous hollow fiber membrane which concerns on one Embodiment of this invention. It is a bottom view which shows the ventilation nozzle which comprises the manufacturing apparatus of the hollow porous membrane of FIG.

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

(First embodiment)
The porous hollow fiber membrane of the present embodiment is a porous hollow fiber membrane in which at least the outer surface side of the present embodiment is composed of a porous layer, and the porosity of the outer surface is from 15 to the total area of the outer surface. It is a porous hollow fiber membrane that is 60%. Here, the outer surface refers to the surface on the side facing the outer periphery of the cylinder when the membrane is formed into a hollow fiber shape (cylindrical shape) to form a porous hollow fiber membrane. The surface on the side facing the inner periphery of the cylinder is defined as the inner surface. Here, the porous layer refers to a layer having pores having the properties described later in a form dispersed in almost the entire layer. Further, here, the open area ratio means that the outer surface of the porous hollow fiber membrane is observed with a microscope or the like, the area of the holes is measured by image analysis or the like, and the total area of all the holes is totaled. It is a value obtained as the sum of the areas of all the holes / the area of the entire observed outer surface (film area in the field of view). A porous hollow fiber membrane having a porous layer at least on the outer surface side, and the porosity of the outer surface is 15 to 60% with respect to the entire area of the outer surface. It becomes an excellent porous hollow fiber membrane. The porosity of the outer surface is preferably 20% or more and 60% or less, and more preferably 25% or more and 55% or less with respect to the entire area of the outer surface.

Further, the average pore diameter index (or average pore diameter P1) of each pore of the porous layer of the porous hollow fiber membrane of the present embodiment may be 0.05 to 1.0 (μm). Thereby, it becomes a porous hollow fiber membrane excellent in recoverability. The average pore diameter index of the porous hollow fiber membrane is preferably 0.06 to 0.9 (μm), more preferably 0.75 to 0.8 (μm).
The average pore size index refers to the pore size calculated by performing arithmetic processing on the pore size read from the micrograph using image analysis software. As a result, there is an effect of excluding minute noise due to the density of pixels. In the present embodiment, the outer surface of the porous hollow fiber membrane is photographed with a microscope, and the average value of the pore diameters in the photograph is measured.

In the porous hollow fiber membrane of this embodiment, when the cross section in the thickness direction is observed, the average pore diameter P2 of the layer from the surface to the depth of 10 μm in the cross-sectional structure is 0.1 to 5.0 (μm It is preferable that the porosity A2 in this layer is 10 to 50%. If it is this range, there exists an effect which can make clogging-proof property and intensity | strength compatible.

The porous membrane layer constituting the porous hollow fiber membrane of the present embodiment preferably has a thickness of 200 μm or less. This is because when the thickness of the porous membrane layer is 200 μm or less, the permeation resistance at the time of membrane separation is reduced, and excellent water permeability is obtained. This is because the coagulation time when forming the membrane layer can be shortened, and it is effective in suppressing macrovoids (defects), and excellent productivity tends to be obtained. More preferably, the thickness of the porous membrane layer is 150 μm or less.
Moreover, in the porous membrane layer which comprises the porous hollow fiber membrane of this embodiment, it is preferable that the thickness is 100 micrometers or more. This is because when the thickness of the porous membrane layer is 100 μm or more, there is a tendency that mechanical strength having no practical problem can be obtained. However, when the outer diameter of the membrane is small, the mechanical strength may be maintained even if the thickness is less than 100 μm, so this is not the case.

The porous membrane layer has a dense layer at least near the outer surface. Here, the vicinity of the outer surface refers to a portion adjacent to the outer surface of the porous membrane layer (inside the porous membrane layer) at a portion inside the porous membrane layer. Here, the dense layer refers to a region in which fine pores having smaller pore diameters are gathered in the porous membrane layer. In this embodiment, the water permeability and separation of the porous hollow fiber membrane are used. In order to achieve both performances, in the dense layer near the surface, the average pore diameter index is preferably in the range of 0.01 to 1 μm.

The thickness of the dense layer in this embodiment is preferably in the range of 10 to 125 μm from the viewpoints of both improving the stability of separation characteristics and improving water permeability.
In the dense layer near the outer surface, the thickness is more preferably in the range of 25 to 100 μm from the viewpoint of improving the stability of the separation characteristics. More preferably, the dense layer has a thickness in the range of 40 to 75 μm.

The position of the dense layer in the vicinity of the outer surface is preferably present at a position within 20 μm from the outer surface of the porous membrane layer from the viewpoint of avoiding an increase in water permeability resistance inside the membrane. Furthermore, it is particularly preferred that this dense layer constitutes the outer surface of the porous membrane layer.

The porous membrane layer preferably has a sponge layer having an average pore diameter index of 2 μm or more inside the dense layer near the outer surface (a portion further away from the outer surface and a portion deeper when viewed from the outer surface). . Since this intermediate porous layer contributes to the water permeability in the porous hollow fiber membrane of this embodiment in particular, the larger the pore diameter, the better. However, if it is too large, it becomes a macrovoid and reduces its mechanical strength. . Therefore, the average pore diameter index is preferably 8 μm or less, and more preferably substantially no pores of 10 μm or more are present. More preferably, it is in the range of 3 to 5 μm.
In addition, from the viewpoint of improving water permeability, this intermediate porous layer, particularly at a part away from the outer surface by a depth of 5 μm, is directed away from the dense layer near the outer surface toward the outer surface, that is, near the inner surface. It is preferable to have an inclined structure in which the hole diameter gradually increases. In particular, the intermediate porous layer preferably has a three-dimensional network structure in which the pores sterically intersect with each other.
Moreover, it is preferable that the average pore diameter of the porous layer from the outer surface to a depth of 5 μm is smaller than the average pore diameter of the porous layer existing at a site deeper than the depth of 5 μm from the outer surface. Furthermore, it is particularly preferable that the average pore diameter of the porous layer existing at a site deeper than 5 μm from the outer surface is 10 μm or less. With this configuration, it is possible to prevent substances that have passed through the dense layer in the vicinity of the outer surface from being clogged inside, and to achieve both effects of quality.
The porous layer described so far may be discontinuously divided into a plurality of layers (for example, a dense layer and a layer other than the dense layer) depending on the material and the average pore diameter. (For example, the average value of the diameter gradually changes according to the distance from the surface). In this case, the layer may be referred to as a part (for example, a dense part and other parts).

Next, the manufacturing method of the porous hollow fiber membrane of this embodiment is demonstrated.
The porous hollow fiber membrane of the present embodiment includes an annular nozzle and a first membrane undiluted solution and a second membrane undiluted solution containing the material and solvent for the porous membrane layer on the outer peripheral surface of the hollow support. The film-forming stock solution can be continuously applied and laminated, and these film-forming stock solutions can be coagulated at the same time.
In this case, the solidification may be from only one side, and an integral porous membrane structure can be obtained from two types of film-forming stock solutions by this method.

For example, a double annular nozzle as shown in FIG. 1 of Patent Document 7 is used, a hollow support (knitted string) is passed through the support passage, and the first film is formed from the first supply port. After discharging the stock solution (inner layer side film forming stock solution) and the second film forming stock solution (outer layer side film forming stock solution) from the second supply port at the same time, and applying the first film forming stock solution to the outer peripheral surface of the hollow knitted string The second film-forming stock solution is applied onto the coating layer of the first film-forming stock solution. After this, the hollow knitted string coated with the film-forming stock solution is idled for a predetermined time, and then immersed in a coagulation liquid to solidify the film-forming stock solution, washed with water, and dried, so that the porous hollow specified in this embodiment is used. A thread membrane structure can be obtained.

When a double annular nozzle is used, the first film-forming stock solution and the second film-forming stock solution can be combined in the nozzle in advance, and these can be simultaneously discharged from the nozzle surface and applied to the hollow support. .
Furthermore, using a triple annular nozzle having a central part, an inner part and an outer part, while passing a hollow support through the central part, the first film-forming stock solution from the inner part and the second film-forming stock solution from the outer part Can be simultaneously discharged to apply the film-forming stock solution to a hollow support.
By using the annular nozzle as described above, each of the first film-forming stock solution and the second film-forming stock solution can be uniformly applied, and the first film-forming stock solution and the second film-forming stock solution are laminated. In this case, bubbles can be prevented from being generated between the layers. The first film-forming stock solution and the second film-forming stock solution may be applied in sequence. In this case, when the first film-forming stock solution and the second film-forming stock solution are applied, the first film-forming stock solution and the second film-forming solution may be applied either continuously or at intervals. In order to prevent bubbles from being generated between the layers when laminating the membrane stock solution, it is preferably performed continuously.

In the above case, two types of film-forming stock solutions are used, both of which contain a polymer resin, an additive, and an organic solvent.
Examples of the polymer resin used in these film-forming stock solutions include polysulfone resin, polyethersulfone resin, sulfonated polysulfone resin, polyvinylidene fluoride resin, polyacrylonitrile resin, polyimide resin, polyamideimide resin, or polyesterimide resin. be able to. These can be appropriately selected and used as necessary, but among these, polyvinylidene fluoride resin is preferred because of its excellent chemical resistance.

As an additive, it can be used for the purpose of controlling phase separation and the like, for example, a hydrophilic polymer resin such as monool, diol, triol, or polyvinylpyrrolidone represented by polyethylene glycol is used. be able to. These can be appropriately selected and used as necessary, and among them, polyvinylpyrrolidone is preferred because of its excellent thickening effect.

The organic solvent is not particularly limited as long as it can dissolve the above-described polymer resin and additives, and for example, dimethyl sulfoxide, dimethylacetamide, or dimethylformamide can be used.

The composition of the two types of film-forming stock solutions described above is not particularly limited, and the same film-forming stock solution or different film-forming stock solutions may be used. However, from the viewpoint of preventing delamination and improving mechanical strength, it is preferable that the solvent and polymer resin used are the same type in order to form an integral structure from two types of film-forming stock solutions during solidification.

In the case of producing the porous hollow fiber membrane of the present embodiment by the above method, the viscosity of the first membrane forming stock solution that is the inner layer side membrane forming stock solution is higher than that of the second membrane forming stock solution that is the outer layer side membrane forming stock solution. It is preferable to increase the height.
This is because the first membrane-forming solution having a higher viscosity is applied to the outer peripheral surface of the hollow support, thereby preventing the membrane-forming stock solution from excessively penetrating into the hollow support, This is because blockage of the hollow portion of the yarn membrane can be prevented.
In order to achieve this, the first film-forming stock solution needs to have a sufficient viscosity, and the viscosity at 40 ° C. is preferably 50,000 mPa · sec or more. More preferably, it is 100,000 mPa * sec or more, More preferably, it is 150,000 mPa * sec or more. Specifically, for example, the viscosity of the first film forming stock solution at 40 ° C. is in the range of 5 to 250,000 mPa · sec, and the viscosity of the second film forming stock solution at 40 ° C. is in the range of 100,000 to 300,000 mPa · sec. It is.

The method for adjusting the viscosity of the film-forming stock solution described above is not particularly limited. For example, the viscosity can be changed by changing the molecular weight of the polymer resin or changing the concentration of the polymer resin. As a method of changing the molecular weight of the polymer resin, a method of blending two kinds of polymer resins having different molecular weights can also be used.

The viscosity adjustment of the film-forming stock solution can be appropriately selected as described above. However, in the first film-forming stock solution, adjusting the concentration of the polymer resin and increasing the concentration is a slow coagulation rate. The inner layer is also preferred because it tends to suppress the generation of macrovoids. Further, it is preferable because the structural stability of the entire porous layer can be improved by increasing the concentration of the first film-forming stock solution.
On the other hand, in the second membrane forming undiluted solution, it is preferable to adjust the molecular weight of the polymer resin because the porosity of the outer surface of the porous membrane layer tends to be maintained high.

As described above, when the film-forming stock solution is solidified to form a film, a porous structure is formed by phase separation. As the porous structure, various structures can be obtained depending on the film forming conditions, but as a typical porous structure, a sponge structure derived from a sea-island structure in which the polymer resin is on the sea side, and the polymer resin is on the island side. The particle aggregation structure derived from the sea-island structure, and the three-dimensional network structure derived from the co-continuous structure in which the polymer resin and the solvent are entangled in a network form by spinodal decomposition.
The porous structure can be appropriately selected from these structures, but the particle aggregate structure tends to be a structure in which the polymer resin layer is aggregated and tends to be inferior in mechanical strength. It is preferable to adopt a sponge structure or a three-dimensional network structure.
The sponge structure tends to be a homogeneous structure in which the pore diameter does not change greatly in the film thickness direction, and is a structure suitable for improving the stability of the separation characteristics.
On the other hand, the three-dimensional network structure tends to be a structure having a higher degree of communication between pores than the sponge structure, and is a structure suitable for improving the permeation performance.

The composition of the first film-forming stock solution that is the inner-layer side film-forming stock solution can be appropriately selected according to the film structure to be formed.
The conditions for obtaining the sponge structure from the first film-forming stock solution are the same, and the composition is not particularly limited, but the mass ratio of the additive to the polymer resin in the film-forming stock solution (additive / polymer resin) ) Is 0.45 or less, more preferably 0.40 or less.
By setting the mass ratio to 0.45 or less, the homogeneous structure tends to be densified, and macrovoids tend not to occur easily.
On the other hand, if this mass ratio is too low, the pore size tends to be too small and the permeation performance tends to be lowered, so this mass ratio is preferably 0.3 or more.
Examples of the composition of the film-forming stock solution include 20-30% by weight of polyvinylidene fluoride resin, 5-12% by weight of polyvinylpyrrolidone, 60-85% by weight of dimethylacetamide, and polyvinyl There may be mentioned those having a mass ratio of pyrrolidone to polyvinylidene fluoride resin (polyvinylpyrrolidone / polyvinylidene fluoride resin) in the range of 0.3 to 0.45.

The conditions for obtaining the three-dimensional network structure of the porous layer from the first film-forming stock solution are not particularly limited, but the mass ratio of the additive to the polymer resin in the film-forming stock solution (additive / polymer resin) ) Is 0.45 or more, more preferably 0.51 or more.
Moreover, it is preferable that the ratio of an organic solvent shall be 68 mass% or less with respect to the whole mass of a film-forming stock solution. This is because the generation of macrovoids tends to be suppressed, and the structural stability of the entire porous layer tends to be improved. More preferably, it is 60% by weight or less based on the total mass of the film-forming stock solution.
Examples of the composition of the film-forming stock solution include 20-30% by weight of polyvinylidene fluoride resin, 10-20% by weight of polyvinylpyrrolidone, 55-68% by weight of dimethylacetamide, and polyvinyl The thing whose mass ratio (polyvinyl pyrrolidone / polyvinylidene fluoride resin) of a pyrrolidone and a polyvinylidene fluoride resin is 0.45 or more can be mentioned.

Regarding the composition of the second membrane forming stock solution, which is the outer layer side membrane forming stock solution, the gradient structure has a dense layer near the outer surface of the porous membrane layer and the pore diameter gradually increases toward the inner surface of the porous membrane layer. If it can form by this, it will not specifically limit.
The composition of the second membrane forming stock solution can be appropriately selected according to the target membrane structure, but from the viewpoint that the surface porosity of the porous membrane layer can be increased, the ratio of the organic solvent is 70% by mass or more. It is preferable to do.
Moreover, since there exists a tendency which can form the inclination structure without a big macrovoid, it is preferable that mass ratio of an additive / polymer resin is 0.45 or more. Examples of the composition of the film forming stock solution include 15 to 25% by weight of polyvinylidene fluoride resin, 5 to 15% by weight of polyvinylpyrrolidone, 70 to 80% by weight of dimethylacetamide, and (polyvinylpyrrolidone / polyvinylidene fluoride resin) The thing which is 0.45 or more can be mentioned.

The thickness at the time of application of each of the outer layer and the inner layer can be set as appropriate, but if the outer layer tends to have a higher ratio of organic solvent, macro voids tend to occur during film formation, The thickness of the outer layer is preferably 150 μm or less. More preferably, it is 100 micrometers or less, More preferably, it is 80 micrometers or less. On the other hand, the lower limit of the thickness of the outer layer is 5 μm.

When a hollow knitted string is used as the support, the support may be previously impregnated with a non-solvent for the film-forming stock solution in order to prevent excessive infiltration of the film-forming stock solution into the support. An example of the non-solvent in the case of using the film-forming stock solution having the above composition is glycerin. However, non-solvents with too high coagulation ability for the film-forming stock solution to be used and non-solvents with too high viscosity hinder the penetration of the porous membrane layer into the support and greatly reduce the peel resistance. Absent.

Further, when polyvinylpyrrolidone is used as an additive, it is preferable to perform chemical cleaning of the porous hollow fiber membrane using sodium hypochlorite or the like in the cleaning after the formation of the membrane structure from coagulation.

(Porous membrane)
Examples of the material for the porous membrane layer include polyvinylidene fluoride, polysulfone, polyacrylonitrile, polyvinyl pyrrolidone, and polyethylene glycol. From the viewpoint of chemical resistance and heat resistance, polyvinylidene fluoride, or polyvinylidene fluoride and polyvinyl A combination with pyrrolidone is preferred.
The porous membrane layer may be a single layer composed of any one of these constituent materials, or may be a composite porous membrane layer formed by laminating two or more of these single layers.

(Second embodiment)
Hereinafter, another preferred embodiment of the present embodiment will be described.
The hollow porous hollow fiber membrane of this embodiment has an average pore diameter Ad of a layer from the surface to a depth of 1 μm (hereinafter referred to as porous layer A) in the cross-sectional structure when cut and observed in the thickness direction. Is a porous layer whose ratio to the size of a layer having a depth of 2 to 3 μm (hereinafter referred to as porous layer B) Bd is 0.6 or less, preferably ½ or less (0.5 or less) It is in a hollow fiber membrane.

This is because the porous hollow fiber membrane of the present embodiment has a membrane having the smallest pore diameter in the porous layer A forming the outer surface, which is substantially less than 1 μm. Or a soluble organic polymer has a characteristic that it is difficult to be clogged inside the film.

Further, it is more preferable that the porous hollow fiber membrane porous layer A of the present embodiment and a structure in which the pore diameter gradually increases to a layer having a depth of 4 μm to 5 μm (hereinafter referred to as porous layer C) are more preferable. When the pore diameter is uniform, the very small objects or the soluble organic polymer that have passed through the outer surface are likely to be clogged with the layer near the outer surface, which causes a decrease in filtration stability. A film formed by a heat-induced phase separation method, a plasticizer extraction method, or a stretching method easily forms such a structure. On the other hand, when the pore diameter increases discontinuously, the thickness of the layer including the outer surface becomes thin, the mechanical strength decreases, and problems such as peeling of the outer surface occur.

As the rate of the gradual increase in the pore diameter increases, the filtration stability improves because the microscopic matter and the soluble organic polymer that have passed through the porous layer A are less likely to be clogged by the layer on the inner surface side of the porous layer A. If it is too large, the layer that contributes to filtration becomes only the layer including the outer surface, and the separation characteristics are likely to deteriorate due to external factors and the like. Therefore, in the cross-sectional structure, the pore diameter Bd of the porous layer B may be 5/3 or more (that is, Ad / Bd is 0.6 or less) with respect to the pore diameter Ad of the porous layer A forming the outer surface. . Further, Bd is preferably 2 times or more (Ad / Bd is 0.5 or less) with respect to Ad, more preferably 3 times or more (Ad / Bd is 0.33 or less), and 4 times or more (Ad / B). More preferably, Bd is 0.25 or less. When the separation characteristics can be maintained, it is more preferable that the separation characteristic is 5 times or more (Ad / Bd is 0.2 or less).
The porous layer B preferably means a layer adjacent to the porous layer A constituting the outer surface with one layer interposed therebetween. Even in the non-solvent-induced phase separation method, where the pore diameter of the porous layer gradually increases toward the inside (in the direction away from the outer surface), this region directly under the outer surface has a high diffusion diffusion rate of the coagulating liquid, which is sufficient. Since solid phase separation does not proceed, it is difficult to form a porous layer B having a sufficiently large structure with respect to the porous layer A.

The pore size Ad substantially determines the filtration characteristics and is appropriately selected depending on the material to be filtered. In this embodiment, since the water permeability and separation characteristics of the porous hollow fiber membrane can be compatible, 0.01 to The range is preferably 1 μm, more preferably 0.02 to 0.5 μm, and still more preferably 0.04 to 0.2 μm.

In the porous hollow fiber membrane in the present embodiment, it is preferable that the pore diameter from the porous layer C to the layer forming the inner surface is larger than the pore diameter from the porous layer A to the porous layer C. When the pore diameter from the porous layer C to the layer forming the inner surface becomes smaller, the microscopic matter and the soluble organic polymer that have passed through the porous layer C tend to be clogged inside the membrane.

The pore diameter from the porous layer C to the layer forming the inner surface is appropriately selected according to the purpose. If the system is prioritized for water permeability, the larger one is preferable, and if the system is prioritized for separation characteristics, it is preferable to maintain a pore diameter close to Cd. In many separation membranes, separation characteristics are given priority. In that case, the pore diameter from the porous layer C to the layer forming the inner surface is preferably 8 μm or less, and there are substantially no pores of 10 μm or more. Is more preferable. More preferably, it is 5 μm or less. In forming the structure from the porous layer C to the layer forming the inner surface, there are a method of stacking different dopes to form a multilayer structure of two or more layers, and a method of controlling by the composition and temperature of the coagulation liquid. obtain.

On the other hand, the layers from the porous layer A to the porous layer C are preferably formed from one dope. That is, it includes the same constituent material, more specifically, a thermoplastic resin of the same compound that substantially constitutes the layer, and other film constituent additives. If a multi-layer structure is used, an interfacial structure will be generated between the layers, which may cause clogging of microscopic objects and soluble organic polymers that have passed through the outer surface, and the strength of each layer will decrease, causing a peeling problem. This is because there is a possibility of occurrence.

It is preferable that the porous hollow fiber membrane in the present embodiment does not have a defect site called a macrovoid having a pore diameter of 10 μm or more. As a method of gradually increasing the structure in the vicinity of the outer surface toward the inside, it can be considered that the dope viscosity is greatly reduced. However, in this method, macro voids are likely to occur near the outer surface at the same time. Separation characteristics are greatly reduced. Therefore, in this embodiment, it is preferable that the macro void or part of the macro void is not provided between the porous layer A and the porous layer C. In particular, it is more preferable that the porous layer from the outer surface to the layer having a depth of 10 μm does not contain a macro void having a pore diameter exceeding 10 μm and a part thereof, and the macro void is observed over the entire cross section when the cross-sectional structure is observed. It is further preferable not to contain.
In the present embodiment, “including a macro void and a part thereof from the outer surface to a layer having a depth of 10 μm” means that a part of the macro void is outside the outer surface by a depth of 10 μm (near the outer surface). It is also included when it is hung.

The hollow porous hollow fiber membrane of the present embodiment may be composed only of the above-mentioned porous layer, but since excellent mechanical strength is obtained, the porous porous fiber membrane is formed on the hollow support. Those having a layer are particularly preferred. Here, in order to clarify the positional relationship between the porous layer and the support, it is expressed as on the support, but the porous layer may be impregnated inside the support through the gap of the support. . In the present embodiment, the porous layer is formed on the outer surface side of the hollow fiber support.

The support is not particularly limited as long as it has high mechanical strength and can be integrated with the porous layer, and is not particularly limited. Knitted cords are preferable because they can achieve both the stability and shape stability (roundness) of the cross section and are excellent in adhesion to the porous layer. Among these, a hollow knitted string obtained by circularly knitting a single yarn made of multifilament is preferable. The constituent material of the support is preferably a polyester fiber, an acrylic fiber, a polyvinyl alcohol fiber, a polyamide fiber, a polyolefin fiber, or a polyvinyl chloride fiber from the viewpoint of excellent chemical resistance, a polyester fiber, Acrylic fibers or polyvinyl chloride fibers are particularly preferred. The support is preferably heat-treated at a temperature higher than the thermal deformation temperature of the fiber and lower than the melting temperature of the fiber while regulating the outer diameter. With this configuration, there are effects of stabilizing the outer diameter of the support, suppressing stretchability, and densifying the voids of the support.

In this case, the porous layer and the support (hollow knitted string) do not necessarily need to be in close contact with each other. However, if their adhesiveness is low, they are separated when the hollow fiber membrane is pulled, Layers can escape. Therefore, in the hollow porous hollow fiber membrane of the present embodiment, a part of the porous layer is infiltrated into the knitted string through the stitch of the hollow knitted string, and the porous layer and the hollow knitted string are integrated. It is preferable to make it.
In order to provide sufficient adhesion between the porous layer and the support, it is more preferable that the porous layer penetrates 50% or more of the thickness of the hollow knitted string. Furthermore, it is more preferable from the viewpoint of peeling resistance that the porous layers that have penetrated 50% or more through different stitches are connected to each other and wrap around a part of the support. In addition, it is preferable that a portion that wraps a part of the support is connected in the fiber axis direction because the peel resistance is further increased. Furthermore, if the connection in the fiber axis direction is spiral, it is more preferable because the peel resistance is remarkably improved. Even in such a case, the above-described film thickness in the present embodiment means the thickness of the portion exposed on the support.

The porous layer is formed of a film-forming resin. As the film-forming resin, a thermoplastic resin can be used as described above, for example, polysulfone resin, polyethersulfone resin, sulfonated polysulfone resin, polyfluorinated vinylidene resin, polyacrylonitrile resin, polyimide resin, polyamideimide resin. Or polyesterimide resin. Among these, polyvinylidene fluoride resin is preferable because of excellent chemical resistance.

Next, the manufacturing method of the hollow porous hollow fiber membrane of this embodiment is demonstrated.
The porous hollow fiber membrane of this embodiment is preferably formed by a non-solvent phase separation method. The non-solvent phase separation method is a method for making a porous layer that induces phase separation by incorporating a non-solvent (water or the like).
In the thermally induced phase separation method in which phase separation is induced by heat, since the heat propagation speed is high, it is difficult to form a structure in which the pore diameter of the porous layer gradually increases toward the inside. In the method of making porous by electron beam irradiation, fine particle filling or stretching, a homogeneous structure is formed in terms of the production method. In contrast to these methods, the non-solvent phase separation method has an effect of easily forming a structure that gradually increases toward the inside because the diffusion rate of the non-solvent into the inside is slow.
Specifically, the porous hollow fiber membrane of this embodiment is formed by applying a film-forming resin containing a porous layer material and a solvent to the outer surface of a hollow support using an annular nozzle. After forming the resin layer, it can be produced by bringing saturated water vapor (conditions such as temperature will be described later) into contact with the surface of the film-forming resin layer and then coagulating with a coagulating liquid.

The manufacturing apparatus of this embodiment will be described. FIG. 12 shows the manufacturing apparatus of this embodiment. The manufacturing apparatus 1g of the present embodiment is for scavenging a spinning nozzle 10, a processing container 20A disposed on the downstream side of the spinning nozzle 10, a coagulating tank 30 for storing the coagulating liquid B, and a discharge surface 10a of the spinning nozzle. Scavenging means 40A for scavenging gas.

(Processing container)
The processing container 20A contains a gas containing a non-solvent of the film-forming resin (hereinafter referred to as “processing gas”), and brings the filament A ′ discharged from the spinning nozzle 10 into contact with the processing gas. The container is configured as described above.
Here, the non-solvent refers to a solvent that does not have the ability to dissolve the film-forming resin under the reaction conditions in this step (for example, the solubility is less than 1% by mass at room temperature). As the non-solvent, water, alcohols such as ethanol, acetone, toluene, ethylene glycol, or a mixture of water and a good solvent used for the film-forming resin solution can be used. Of these, water is particularly preferred.

The processing container 20A used in the present embodiment is a cylindrical body having a flat ceiling portion 21, a flat bottom portion 22 and a cylindrical side portion 23, and the filament A ′ is introduced into the ceiling portion 21. The first opening 21a is formed, and the bottom 22 is formed with a second opening 22a into which the filament A ′ is introduced. The openings of the first opening 21a and the second opening 22a are the same, or more processing gas in the processing container 20A flows out of the first opening 21a than the second opening 22a due to thermal buoyancy. In order to suppress this, the opening diameter of the second opening 22a may be made larger than the opening diameter of the first opening 21a. Further, the second opening 22 a is disposed above the liquid level of the coagulating liquid B in the coagulating tank 30. That is, in the present embodiment, the processing container 20A and the coagulation liquid B in the coagulation tank are separated from each other, and the second opening 22a is not closed with the coagulation liquid B.

In the processing container 20A, the filament A ′ is introduced from the first opening 21a, and the filament A ′ brought into contact with the processing gas in the processing container 20A is exposed to the outside from the second opening 22a. Has been derived.
Further, the processing gas supplied from the gas supply pipe 24 passes through the inside of the processing container 20A, and is then discharged from the first opening portion 21a and the second opening portion 22a.

(Scavenging means)
The scavenging means 40A is a gas removing means configured to replace the processing gas flowing out in the vicinity of the spinning nozzle 10 with the scavenging gas and remove it, and the scavenging nozzle 41 provided on the discharge surface 10a of the spinning nozzle 10. And a gas supply means 42 for supplying a scavenging gas to the scavenging nozzle 41.
The scavenging nozzle 41 is formed of an annular member, and has a central circular opening 41a, a gas introduction chamber 41b that is connected to the gas supply means 42 and is formed of an annular space into which scavenging gas is introduced, and a circular opening 41a. And an annular gas discharge port 41c for discharging the scavenging gas supplied from the gas introduction chamber 41b toward the discharge surface 10a of the spinning nozzle 10 exposed.
The circular opening 41a is arranged so that the center thereof coincides with the center of the support discharge port and the resin solution discharge port of the spinning nozzle 10. Accordingly, the filament A ′ passes through the circular opening 41a. The gas introduction chamber 41b is formed concentrically with the scavenging nozzle 41 on the outer peripheral side of the circular opening 41a. Since the gas discharge port 41c communicates with the gas introduction chamber 41b and opens toward the center of the circular opening 41a as shown in FIG. 123, the scavenging gas is centered from the outer peripheral side of the circular opening 41a. It discharges toward

In the present embodiment, a protective cylinder 50 is provided on the lower surface of the scavenging nozzle 41 in the scavenging means 40A to cover and protect the filament A ′.

The protective cylinder 50 is a cylindrical member and has a through hole 50a. Further, the upper end portion 51 of the protective cylinder 50 is closely fixed to the lower surface of the scavenging nozzle 41 so that the through hole 50 a communicates with the circular opening 41 a of the scavenging nozzle 41. The lower end portion 52 of the protective cylinder 50 is spaced apart from the processing container 20A, and a gap Q is formed between the protective cylinder 50 and the treatment container 20A.

It is preferable that the opening area of the through-hole 50a and the opening area of the opening 52a on the lower end 52 side are small as long as the filament A ′ can pass without contacting. The smaller the cross-sectional area of the through-hole 50a, the higher the flow rate can be achieved and the scavenging ability can be improved even if the supply amount of the scavenging gas is small. Further, as the opening area of the opening 52a on the lower end 52 side is smaller, the processing gas flowing out from the first opening 21a can be prevented from flowing into the through hole 50a.
However, it is preferable that the flow rate of the scavenging gas from the lower end 52 side toward the first opening 21a is not made faster than necessary, and the opening area of the opening 52a on the lower end 52 side is not made smaller than necessary. . When the flow rate of the scavenging gas toward the first opening 21a is excessively high, or the opening area of the opening 52a of the lower end 52 is excessively small, the scavenging gas passes through the first opening 21a. There is a risk of entering the processing container 20A and changing the temperature and humidity of the gas in the processing container 20A.

The material of the protective cylinder 50 is preferably a material that is not corroded or attacked by the gas flowing out of the processing container 20A. Examples of materials that satisfy these requirements include polyethylene, polypropylene, fluororesin, stainless steel, aluminum, ceramic, and glass. In addition, the material of the protective cylinder 50 preferably has a low thermal conductivity in order to suppress heat dissipation of the scavenging gas flowing through the through hole 50a and temperature change of the scavenging gas due to heat received from the external atmosphere. Examples of the material having low thermal conductivity include polyethylene, polypropylene, fluorine-based resin, ceramic, or glass. Further, the material of the protective cylinder 50 is preferably highly transparent because the state of the filament A ′ running through the through hole 50a can be observed from the outside. Highly transparent polyethylene, highly transparent polypropylene, transparent Particularly preferred is a highly fluoropolymer tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA) or glass.

The protective cylinder 50 is preferably detachable from the scavenging nozzle. If the protective cylinder 50 is detachable, it can be removed from the scavenging nozzle 41, so that the hand can easily reach the vicinity of the discharge surface 10a, and the operability at the start of film formation can be improved. As the attachment / detachment means, a mechanical attachment / detachment means such as a screw or a clamp, or a magnet adsorption attachment / detachment means using a magnet and a metal adsorbed to the magnet is simple and suitable.

In the present embodiment, the filament A ′ discharged from the spinning nozzle 10 passes through the through hole 50a of the protective cylinder 50 after passing through the gas discharge port 41c.
Further, the scavenging gas discharged from the gas discharge port 41c of the scavenging nozzle 41 flows from the upper end 51 toward the lower end 52 in parallel with the filament A 'passing through the through hole 50a. To do. And it discharges toward the process gas which flows out out of the 1st opening part 21a from the through-hole 50a. Thereafter, the scavenging gas flows outward in the gap Q so as to be separated from the first opening 21a together with the processing gas flowing out from the first opening 21a.

The treatment gas flowing out from the first opening 21a can be replaced with the scavenging gas by the scavenging means 40A and removed from the vicinity of the ejection surface 10a, so that condensation on the ejection surface 10a due to a non-solvent can be prevented. Thereby, precise control of the membrane surface structure of the obtained porous hollow fiber membrane A, uniformity of the membrane surface structure, and quality of the porous hollow fiber membrane A can be improved.

As the scavenging gas, dry air is preferable. In this embodiment, dry air refers to a gas having a relative humidity (vapor pressure with respect to saturated vapor pressure) of 0 to 9%. When dry air having a relative humidity of about 1% at room temperature is supplied in a factory or the like, the dry air is adjusted to a predetermined temperature by a gas temperature adjusting means to be heated dry air, which is supplied to the scavenging nozzle 41. It is preferable to supply.

(Method for producing porous hollow fiber membrane)
The manufacturing method of the porous hollow fiber membrane A using the said manufacturing apparatus 1a is demonstrated. This manufacturing method has a spinning process, a scavenging process, and a coagulation process.

[Spinning process]
In the spinning step in the present embodiment, the hollow string-like support A1 is discharged downward from the support discharge port of the spinning nozzle 10 while the film-forming resin solution is discharged downward from the resin solution discharge port, thereby forming the hollow string. A film A2 of a film-forming resin solution is formed on the outer peripheral surface of the support A1 to produce a hollow filamentous body A ′.

The film-forming resin solution usually contains a film-forming resin, a hydrophilic resin, and a solvent for dissolving them. The film-forming resin solution may contain other additive components as necessary. The hydrophilic resin is added to adjust the viscosity of the film-forming resin solution to a range suitable for the formation of the hollow porous hollow fiber membrane A, and to stabilize the film-forming state. Glycol or polyvinyl pyrrolidone is preferably used. Among these, polyvinyl pyrrolidone or a copolymer obtained by copolymerizing other monomers with polyvinyl pyrrolidone from the viewpoint of controlling the pore diameter of the obtained hollow porous hollow fiber membrane and the strength of the hollow porous hollow fiber membrane. preferable.
Moreover, 2 or more types of hydrophilic resin can also be mixed and used. For example, when a higher molecular weight hydrophilic resin is used, a hollow porous hollow fiber membrane having a good membrane structure tends to be formed. On the other hand, a low molecular weight hydrophilic resin is preferable in that it is more easily removed from the hollow porous hollow fiber membrane A. Therefore, the same kind of hydrophilic resins having different molecular weights may be appropriately blended depending on the purpose.

Examples of the solvent include N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, or N-methylmorpholine-N monooxide, and one or more of these can be used. . In addition, a poor solvent or a non-solvent of the film-forming resin or the hydrophilic resin may be mixed and used as long as the solubility of the film-forming resin or the hydrophilic resin in the solvent is not impaired.

The temperature of the film-forming resin solution is not particularly limited, but is usually 20 to 40 ° C. The viscosity of the film-forming resin solution at 40 ° C. is preferably 20,000 to 500,000 mPa · second, more preferably 50,000 to 300,000 mPa · second, and 70,000 to 250,000 mPa · second. More preferably it is. If the viscosity is too low, the phase separation rate increases, and Ad and Bd become too large, and the separation characteristics deteriorate. On the other hand, if the viscosity is too high, the speed of phase separation decreases, and it becomes difficult to make Bd sufficiently larger than Ad.

If the concentration of the film-forming resin in the film-forming resin solution is too thin or too thick, the stability during film formation tends to decrease, and the desired hollow porous hollow fiber membrane tends to be difficult to obtain. Therefore, the lower limit is preferably 10% by mass and more preferably 15% by mass with respect to the total mass of the film-forming resin solution. Further, the upper limit is preferably 30% by mass, and more preferably 25% by mass with respect to the total mass of the film-forming resin solution. Specifically, the film-forming resin may be in the range of 10 to 30% by mass, preferably 15 to 25% by mass, based on the total mass of the film-forming resin solution.
On the other hand, the lower limit of the concentration of the hydrophilic resin is preferably 1% by mass, preferably 5% by mass with respect to the total mass of the film-forming resin solution in order to make it easier to form a hollow porous hollow fiber membrane. More preferred. The upper limit of the concentration of the hydrophilic resin is preferably 20% by mass and more preferably 12% by mass with respect to the total mass of the film-forming resin solution from the viewpoint of the handleability of the film-forming resin solution. Specifically, it may be in the range of 1 to 20% by mass, preferably 5 to 20% by mass with respect to the total mass of the film-forming resin solution.

The composition of the film-forming resin solution is not particularly limited as long as the structure that gradually increases from the porous layer A to the porous layer C can be formed by phase separation, but the surface porosity of the porous layer can be increased. Therefore, the ratio of the solvent is preferably 68% by mass or more, more preferably 70% or more with respect to the total mass of the film-forming resin solution.
Moreover, since there exists a tendency which can form the gradual increase structure without a big macrovoid, it is preferable that the mass ratio of hydrophilic resin / film-forming resin is 0.45 or more. Below this value, it tends to form macrovoids and tends to form a sea-island structure rather than a co-continuous structure, resulting in a decrease in surface porosity and formation of a homogeneous structure, It is not preferable.

[Scavenging process]
The scavenging step in the present embodiment is a step of feeding a scavenging gas to the discharge surface 10a of the spinning nozzle 10.
Specifically, in the scavenging step, first, the scavenging gas supplied from the gas supply unit 432 is filtered by the gas filtering unit 43, the temperature and humidity are adjusted by the gas adjusting unit 44, and then supplied to the gas introduction chamber 41 b. At this time, since the condensation on the discharge surface 10a can be further spun, the scavenging gas is preferably adjusted by the gas adjusting means 44 so that the dew point is lower than the surface temperature of the discharge surface of the spinning nozzle 10. In order to keep the temperature of the spinning nozzle 10 and the filament A ′ from changing from the set state, it is preferable to supply the scavenging gas at the same temperature as the set temperature of the spinning nozzle 10.
Next, in the gas introduction chamber 41b, the pressure distribution of the scavenging gas is made uniform by the resistance applying body 41d provided in the gas discharge port 41c. Next, the scavenging gas in the gas introduction chamber 41b is discharged toward the center of the circular opening 41a through the resistance applying body 41d of the gas discharge port 41c, and the scavenging gas is sent to the discharge surface 10a. The scavenging gas discharged from the gas discharge port 41c flows from the upper end 51 toward the lower end 52 around the filament A ′ passing through the through hole 50a in parallel with the filament A ′. And it discharges toward the process gas which flows out out of the 1st opening part 21a from the through-hole 50a. Thereafter, the scavenging gas is discharged toward the outside in the gap Q together with the processing gas flowing out from the first opening 21a so as to be separated from the first opening 21a.

In the scavenging step, the dew point of the non-solvent in the atmosphere in the vicinity of the spinning nozzle 10 is made lower than the surface temperature of the spinning nozzle 10. When the dew point of the non-solvent in the atmosphere in the vicinity of the spinning nozzle 10 is equal to or higher than the spinning nozzle 10, spinning of condensation becomes difficult. Here, “the dew point of the non-solvent in the atmosphere” means that when the amount of the non-solvent that the atmosphere can contain matches the amount of the non-solvent contained in the atmosphere and the ambient temperature decreases, This is the temperature at which the non-solvent that cannot be used begins to condense.
In addition, since the above-described scavenging step can prevent condensation more, it is preferable that the relative humidity of the non-solvent in the atmosphere near the spinning nozzle is less than 10%. Here, “the relative humidity of the non-solvent in the atmosphere” It is a value (unit:%) determined by the amount of non-solvent contained in an atmosphere at a certain temperature / the amount of saturated non-solvent at that temperature × 100.

[Coagulation process]
The coagulation step is a step in which the film-forming resin solution discharged from the spinning nozzle 10 is immersed in the coagulation liquid B in the coagulation tank 30 after being brought into contact with the processing gas in the processing vessel 20A.
In the solidification step in the present embodiment, the filament A ′ is brought into contact with the processing gas in the processing vessel 20A and the coagulation liquid B in the coagulation tank 30 to thereby form a coating film of the film-forming resin solution of the filament A ′. A2 is solidified to obtain a porous hollow fiber membrane A.
Specifically, the filament A ′ formed with the coating film A2 of the film-forming resin solution in the spinning process is introduced into the processing container 20A from the first opening 21a of the processing container 20A. Contact with processing gas. The non-solvent component contained in the processing gas diffuses and enters the coating film A2 that has come into contact with the processing gas, and phase separation starts.

Here, examples of the processing gas include air in which the non-solvent is saturated, air in which the non-solvent is non-saturated, and saturated vapor of the non-solvent. In order to obtain the porous hollow fiber membrane of this embodiment For this, a non-solvent saturated vapor is preferred.
When the film-forming resin is a hydrophobic polymer, water, alcohols such as ethanol, acetone, toluene, ethylene glycol, or the like can be used as the non-solvent, but water is particularly preferable.

In the case where the processing gas is a non-solvent saturated vapor, the entire periphery of the filament A ′ passing through the processing container 20A is filled with the non-solvent. Hereinafter, characteristics when the processing gas is saturated water vapor at atmospheric pressure will be described.
The temperature of the saturated water vapor under atmospheric pressure is about 100 ° C., and the space in the processing vessel 20A filled with the saturated water vapor is filled with 100% water molecules. Therefore, when saturated steam is used as the processing gas, the ambient temperature and humidity around the filament A ′ can be easily made uniform.
Further, the saturated water vapor can increase the amount of water and the amount of heat supplied per unit time to the filament A ′ passing through the processing container 20A, as compared with gases containing other moisture. Further, the amount of heat of condensation when water vapor condenses is extremely large, and the heat of condensation heat transfer is high, so that the temperature near the surface layer of the filament A ′ can be instantaneously raised to near 100 ° C.
Therefore, the phase separation behavior is completely different from the case where the filament A ′ is passed through a gas containing water in an unsaturated state by water supply and heat supply in saturated steam condensation due to a temperature difference from the filament A ′. Can be generated.
In other words, since a large amount of water is supplied, the outer surface of the membrane proceeds to solidification immediately after phase separation. Therefore, if the viscosity of the film-forming resin solution is adjusted to a relatively high value, a dense structure suitable for filtration can be obtained. It can be formed on the surface. A large amount of moisture immediately diffuses and penetrates to the inside of the membrane, and can cause up to phase separation of the surface layer portion of the filament A ′ while the filament A ′ is in the processing container 20A.
Here, since the temperature in the vicinity of the surface layer of the filament A ′ has risen to nearly 100 ° C., the phase separation rate is very high, and thereby a structure sufficiently large with respect to the structure of the porous layer A is obtained. The porous layer A can be formed on the inner surface layer.

In this way, the filament A ′ whose outer surface structure is fixed and the phase separation has proceeded to the inner surface layer in the processing vessel 20A is then introduced into the coagulation tank 30 and brought into contact with the coagulation liquid B. . Thereby, the non-solvent component of the coagulation liquid B diffuses and penetrates into the coating film A2 of the film-forming resin solution. Since the coagulating liquid B is a liquid, a large amount of non-solvent rapidly enters even when compared with saturated water vapor, and solidifies through phase separation to the inside, so that the porous hollow fiber membrane A is obtained.

The coagulation liquid B is a non-solvent for the film-forming resin and a good solvent for the hydrophilic resin, and examples thereof include water, techanol, methanol, and mixtures thereof. Among them, the coagulating liquid B is used for the film-forming resin solution. A mixed solution of a solvent and water is preferable from the viewpoints of safety and operation management.
When a mixed solution of the solvent and water used for the film-forming resin solution is used, the concentration of the solvent is preferably in the range of 5 to 50% by mass with respect to the total mass of the solvent, water and the mixed solution. The range of 10 to 40% by mass is more preferable. Below this range, the rate of increase of the non-solvent increases and the internal structure may become too dense. Moreover, if it exceeds this range, a sufficient amount of non-solvent cannot enter and solidification may not be completed in the coagulation tank.

The temperature of the coagulation liquid B is in the range of 30 to 95 ° C, preferably 40 to 85 ° C. By setting the temperature of the coagulation liquid B to the lower limit value or more, the water permeability of the obtained hollow porous hollow fiber membrane is increased, and by setting the temperature to the upper limit value or less, the resulting hollow porous hollow fiber membrane The film quality is improved.

When a polymer such as polyvinylpyrrolidone is used as the hydrophilic resin, the porous hollow fiber membrane A can be washed with hot water and then treated with an oxidant-containing liquid to decompose and remove the hydrophilic resin. preferable.

The method for producing a porous hollow fiber membrane of the present embodiment and the hollow fiber membrane produced thereby can be applied mainly in the field of water treatment. For example, it can be used in a method for producing a porous hollow fiber membrane of the present embodiment, a water purification treatment method using the hollow fiber membrane produced thereby, and other water treatment methods. Moreover, the manufacturing method of the porous hollow fiber membrane of this embodiment and the hollow fiber membrane manufactured thereby can be used in a water purification device or the like provided with the structure, and used in the manufacturing method of the water purification device or the like. Can do.
In these applications, each of the configurations of the above-described embodiments can be used in appropriate combination.

Further, the present embodiment will be specifically described with reference to the following examples.
(Image analysis)
Various physical properties of the porous membrane were measured by image analysis as follows.

(1) Average pore size index of porous membrane Using a scanning electron microscope (SEM), the cross-section and surface of the porous membrane are photographed, and the internal structure and the average pore size of the surface are analyzed by image analysis using a computer. The index was determined. The average pore size index obtained by image analysis varies slightly depending on image quality adjustment for image analysis and image analysis software, but the difference is within the range of normal experimental error.

The outer surface of the obtained porous film is observed with a scanning electron microscope (SEM). When the porous membrane is a porous hollow fiber membrane, a reference point on the outer surface of the porous hollow fiber membrane is determined, and this is set to 0 °, and SEM photographs are taken from four directions of 90 °, 180 °, and 270 °. To do. Although the observation magnification depends on the desired fractional pore diameter, it cannot be generally stated, but in the case of a microfiltration membrane, it is 10,000 to 100,000 times. When outside this range, the pore diameter on the outer surface cannot be sufficiently observed at 5000 times or less, and when it is 100,000 or more times, the number of holes in the field of view decreases, and the average pore diameter is May be difficult to say. The diameter of the hole recognized by the image analysis software is taken as the hole diameter, the hole diameter of all the holes in the SEM photograph is calculated, the hole diameter index is calculated from the average value, and the surface or cross-sectional structure of the porous membrane is calculated accordingly. Assess quantitatively. Here, the data is arranged so that the calculated total holes are in descending order by area, the area is integrated from the upper holes, and the holes up to a place corresponding to an arbitrary ratio of 50% with respect to the total area are used. Calculate the pore size index. For example, although not limited, this arbitrary ratio A is assumed.

(2) Porosity of Porous Membrane The area of the pores was measured from the SEM photograph of the porous membrane using the above image analysis, and the porosity of the porous membrane was determined.
Open area ratio (%) = sum of all hole areas recognized by image analysis / film area in field of view in SEM photograph

(Outer diameter of support)
The outer diameter of the support was measured by the following method.
A sample to be measured was cut into approximately 10 cm, several bundles were bundled, and the whole was covered with a polyurethane resin. The polyurethane resin also entered the hollow part of the support.
After the polyurethane resin was cured, a thin piece having a thickness (longitudinal direction of the film) of about 0.5 mm was sampled using a razor blade.
Next, the sampled cross section of the support was observed with a projector (Nikon Corporation, PROFILE PROJECTOR V-12) at an objective lens magnification of 100 times.
A mark (line) was aligned with the position of the outer surface in the X direction and Y direction of the cross section of the support being observed, and the outer diameter was read. This was measured three times to determine the average value of the outer diameter.

(Inner diameter of support)
The inner diameter of the support was measured by the following method.
The sample to be measured was sampled in the same manner as the sample whose outer diameter was measured.
Next, the sampled cross section of the support was observed with a projector (Nikon Corporation, PROFILE PROJECTOR V-12) at an objective lens magnification of 100 times.
A mark (line) was aligned with the position of the inner surface in the X direction and Y direction of the cross section of the support being observed, and the inner diameter was read. This was measured three times to determine the average inner diameter.

(Outer diameter of porous hollow fiber membrane)
The outer diameter of the porous hollow fiber membrane was measured by the following method.
A sample to be measured was cut into approximately 10 cm, several bundles were bundled, and the whole was covered with a polyurethane resin. The polyurethane resin also entered the hollow part of the support.
After the polyurethane resin was cured, a thin piece having a thickness (longitudinal direction of the film) of about 0.5 mm was sampled using a razor blade.
Next, a cross section of the sampled porous hollow fiber membrane was observed with a projector (Nikon Corporation, PROFILE PROJECTOR V-12) at an objective lens of 100 times.
A mark (line) was placed at the position of the outer surface in the X direction and Y direction of the cross section of the porous hollow fiber membrane being observed, and the outer diameter was read. This was measured three times to determine the average value of the outer diameter.

(Inner diameter of porous hollow fiber membrane)
The inner diameter of the porous hollow fiber membrane was measured by the following method.
The sample to be measured was sampled in the same manner as the sample whose outer diameter was measured.
Next, a cross section of the sampled porous hollow fiber membrane was observed with a projector (Nikon Corporation, PROFILE PROJECTOR V-12) at an objective lens of 100 times.
A mark (line) was aligned with the position of the inner surface of the support in the X and Y directions of the cross section of the porous hollow fiber membrane being observed, and the inner diameter was read. This was measured three times to determine the average inner diameter.

(Thickness of porous membrane layer)
The film thickness of the porous membrane layer in Examples and the like is the thickness from the surface of the support to the surface of the porous hollow fiber membrane, and was measured by the following method.
The sample to be measured was sampled in the same manner as the sample whose outer diameter was measured.
Next, the cross section of the sampled porous hollow fiber membrane was observed with a projector (Nikon Corporation, PROFILE PROJECTOR V-12) at an objective lens of 100 times.
The film thickness was read by aligning marks (lines) at the positions of the outer surface and inner surface of the film at the 3 o'clock position on the cross section of the porous hollow fiber membrane being observed. Similarly, the film thickness was read in the order of 9 o'clock, 12 o'clock, and 6 o'clock. This was measured three times to determine the average inner diameter.

(Pore diameter of porous membrane layer)
The pore diameter of the porous layer was measured by the following method.
The cross-sectional structure to be measured was photographed at a magnification of 10,000 using a scanning electron microscope, and the average pore diameter index of the structure was obtained by image analysis processing of the obtained photograph. As image analysis processing software, IMAGE-PRO PLUS version 5.0 of Media Cybernetics was used.

(Permeability of porous hollow fiber membrane)
The water permeability of the porous hollow fiber membrane was measured by the following method.
The sample to be measured was cut into 4 cm, and one end face was sealed with a polyurethane resin at the hollow portion.
Next, the sample was decompressed in ethanol for 5 minutes or more and then immersed in pure water for replacement.
Pure water (25 ° C.) was placed in the container, connected to the other end of the sample with a tube, and an air pressure of 200 kPa was applied to the container to measure the amount of pure water coming out of the sample for 1 minute. This was measured three times to obtain an average value. This value was divided by the surface area of the sample to determine the water permeability.

(Separation characteristics of porous hollow fiber membrane)
The separation characteristics of the porous hollow fiber membrane were evaluated from the maximum pore diameter determined in accordance with JIS K3832 by the bubble point method. Ethanol was used as a measurement medium.

(Average pore diameter index, opening ratio)
The average pore size index was subjected to image analysis using an SEM photograph (30,000 times) and Image-Pro Plus manufactured by Planetron Co., Ltd., and the average pore size index of the outer surface photograph observed from each direction was obtained. The average pore diameter index and the opening ratio were calculated by the following series of steps.
Process (1)
The cross-sectional surface of the porous hollow fiber membrane is observed with an SEM, and the area of the hole diameter of all the holes captured by an electron micrograph is measured.
Step (2)
In step (1), data are arranged so that the calculated hole diameters are in descending order by area, the areas are integrated from the upper holes, and up to a place corresponding to a specific ratio B (50%) with respect to the total area. Using the holes, the area is regarded as a perfect circle, and the diameter (hole diameter) is calculated as an average hole diameter index.

Example 1
Polyester fibers (polyethylene terephthalate (PET), fineness: 84 dtex, number of filaments: 36, false twisted yarn) were used as hollow reinforcing support yarns. As bobbins used for producing the hollow reinforcing support, five pieces of polyester fiber wound around 5 kg are prepared. As a circular knitting machine, a table type string knitting machine (manufactured by Sonai Textile Machinery Co., Ltd., number of knitted needles: 12 needles, needle size: 16 gauge, spindle diameter: 8 mm) were used. A Nelson roll was used as the string supply device and the take-up device. As the heating die, a stainless steel die (outer diameter D: 5 mm, inner diameter d: 2.5 mm, length L: 300 mm) having heating means was used.
Five polyester fibers drawn from the bobbin were combined into a single yarn (total fineness: 420 dtex), and then circular knitted by a circular knitting machine to form a hollow knitted string. The hollow knitted string was passed through a heating die at 210 ° C., and the heat-treated hollow knitted string was wound as a hollow reinforcing support using a winding device at a winding speed of 200 m / hour.
The obtained hollow reinforcing support had an outer diameter of about 2.5 mm and an inner diameter of about 1.7 mm. The number of loops of the hollow braid constituting the hollow reinforcing support was 12 per round, and the maximum opening width of the stitch was about 0.1 mm. The length of the hollow reinforcing support was 12000 m.

Polyvinylidene fluoride (Arkema, trade name: Kyner 301F) 11.5% by mass, Polyvinylidene fluoride (Arkema, trade name: Kyner 9000LD) 11.5% by mass and polyvinylpyrrolidone (Nippon Shokubai, trade name) K-80) was dissolved in 65% by mass of N, N-dimethylacetamide with stirring to prepare a first film-forming resin solution. The viscosity of this first film-forming resin solution at 40 ° C. was 210,000 mP · sec.
Polyvinylidene fluoride (Arkema, trade name; Kyner 301F) 19% by mass and polyvinylpyrrolidone (Nippon Shokubai, trade name; K-80) 10% by mass were stirred into N, N-dimethylacetamide 71% by mass. This was dissolved while preparing a second film-forming resin solution. The viscosity of this second film-forming resin solution at 40 ° C. was 130,000 mP · sec.
Subsequently, the porous hollow fiber membrane was manufactured using the manufacturing apparatus shown in FIG. In this example, as a spinning nozzle, a through hole for a support that allows a hollow reinforcing support to pass through, and a flow path for resin solutions of two types of film-forming resin solutions (first flow path for resin solution, second resin) A multi-annular nozzle formed with a solution flow path) was used. In this spinning nozzle, a support discharge port, a first resin solution discharge port, and a second resin solution discharge port are formed on the lower surface.

(Manufacture of porous hollow fiber membrane)
The processing container was arranged above the coagulation tank so that a gap of 10 mm from the coagulation liquid surface was formed. The processing container and the protective cylinder were arranged such that a gap of 5 mm was formed between the lower end opening of the protective cylinder and the first opening of the processing container. The scavenging nozzle was arranged so that its upper surface and the lower surface of the spinning nozzle were bonded.
The scavenging nozzle was supplied with dry air at a temperature of 32 ° C. and a relative humidity of less than 1% at 6 L / min. 100 degreeC saturated water vapor | steam was supplied to the processing container as processing gas. The supply amount of water vapor is a flow rate adjusting valve while monitoring the temperature of a thermocouple having a diameter of 0.5 mm inserted 5 mm from the first opening while supplying dry air to the scavenging nozzle at 6 L / min. Was opened little by little and the lower limit flow rate at which the thermocouple temperature was stable at 100 ° C. for 10 minutes or more was set. In the adjusted state, the water vapor discharged from the flow rate adjusting valve is cooled and liquefied, and the mass of drain water obtained per unit time is measured and converted to a water vapor volume of 100 ° C., which is equivalent to about 5 NL / min. It was.
The coagulation tank was filled with a coagulation liquid having a composition of 10% by mass of N, N-dimethylacetamide as a solvent component and 90% by mass of pure water as a non-solvent component. The coagulation tank was kept at 75 ° C.
The film-forming resin solution 1 at 32 ° C. was supplied to the spinning nozzle at a supply rate of 23.2 cm ³ / min, and the film-forming resin solution 2 at 32 ° C. was supplied at 25.0 cm ³ / min. Next, the film-forming resin solution 1 and the film-forming resin solution 2 are discharged concentrically from the resin solution discharge port, and a film is formed on the outer peripheral surface of the hollow knitted string support drawn from the support discharge port at 20 m / min. Resin solutions 1 and 2 were applied. As a result, a filament A ′ in which the film-forming resin solution was applied to the hollow knitted string support was obtained. The filament A ′ was passed through a scavenging nozzle, a processing container, and a coagulating liquid in this order to obtain a porous hollow fiber membrane.
The obtained porous hollow fiber membrane was passed through hot water at 98 ° C. for 1 minute to remove the solvent. Next, after immersing in a 30,000 mg / L sodium hypochlorite aqueous solution, it was heat-treated in a steam bath at 98 ° C. for 2 minutes. Subsequently, it was washed in hot water at 98 ° C. for 15 minutes, dried at 110 ° C. for 10 minutes, and then wound up to obtain a porous hollow fiber membrane.
About the obtained porous hollow fiber membrane, the cross-section frozen and slipped using liquid nitrogen was enlarged and observed with SEM, and a photograph was taken. The obtained photograph was subjected to image analysis using Image-Pro Plus (manufactured by Planetron Co., Ltd.), and the average pore size of each layer was calculated. The results are shown in Table 1.

(Example 2)
As the first and second film-forming resin solutions, 19% by mass of polyvinylidene fluoride (trade name Kyner 761A, manufactured by Arkema Co., Ltd.) and 12% by mass of polyvinyl pyrrolidone (trade name, K-80, manufactured by Nippon Shokubai Co., Ltd.) Using a film-forming resin solution dissolved in 69% by mass of N-dimethylacetamide with stirring, a composition containing 20% by mass of N, N-dimethylacetamide as a coagulating liquid and 80% by mass of pure water as a non-solvent component A porous hollow fiber membrane was obtained in the same manner as in Example 1 except that the coagulating liquid was used.
The viscosity of this film-forming resin solution at 40 ° C. was 250,000 mP · sec.
For the obtained porous hollow fiber membrane, the average pore diameter of each layer was calculated in the same manner as in Example 1. The results are shown in Table 1.

Example 3
As the first and second film-forming resin solutions, 15% by mass of polyvinylidene fluoride (trade name Kyner 761A, manufactured by Arkema Co., Ltd.) and 11% by mass of polyvinyl pyrrolidone (trade name, K-80, manufactured by Nippon Shokubai Co., Ltd.) A porous hollow fiber membrane was obtained in the same manner as in Example 6 except that the membrane-forming resin solution dissolved in 74% by mass of N-dimethylacetamide with stirring was used.
The viscosity of this film-forming resin solution at 40 ° C. was 80,000 mP · sec.
For the obtained porous hollow fiber membrane, the average pore diameter of each layer was calculated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 1)
The same first and second film-forming resin solutions as in Example 1 were used.
The coagulation tank was filled with a coagulation liquid having a composition of 8% by mass of N, N-dimethylacetamide as a solvent component and 92% by mass of pure water as a non-solvent component. The coagulation tank was kept at 70 ° C.
The film forming resin solution 1 at 32 ° C. was supplied to the spinning nozzle at a supply rate of 17.4 cm ³ / min, and the film forming resin solution 2 at 32 ° C. was supplied at 18.7 cm ³ / min. Next, the film-forming resin solution 1 and the film-forming resin solution 2 are discharged concentrically from the resin solution discharge port, and a film is formed on the outer peripheral surface of the hollow knitted string support drawn from the support discharge port at 15 m / min. Resin solutions 1 and 2 were applied. As a result, a filament A ′ in which the film-forming resin solution was applied to the hollow knitted string support was obtained.
The obtained filament A ′ was introduced into a cover for forming a high-temperature and high-humidity atmosphere whose interior was filled with steam of a coagulating liquid (temperature of 70 ° C.) and subjected to a high-temperature and high-humidity treatment. At that time, the distance that the filament A ′ travels in the high temperature and high humidity atmosphere in the high temperature and high humidity atmosphere forming cover was set to 67 mm.
Subsequently, the filament A ′ subjected to the high-temperature and high-humidity treatment was passed through a coagulation liquid (temperature: 70 ° C.) in the coagulation tank. As a result, a coagulating liquid was adhered to the outer peripheral surface of the filament A ′, and the coating film of the film-forming resin solution was coagulated to obtain a porous hollow fiber membrane.
The obtained porous hollow fiber membrane was washed and dried in the same manner as in Example 1.
For the obtained porous hollow fiber membrane, the average pore diameter of each layer was calculated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 2)
For the porous hollow fiber membrane (ZeeWeed 500) manufactured by GE, the average pore size of each layer was calculated in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 3)
For the porous hollow fiber membrane made by Kubota Corporation (type 510), the average pore diameter of each layer was calculated in the same manner as in Example 1. The results are shown in Table 1.

<Evaluation of filtration>
Modules were made using the porous hollow fiber membranes obtained in Examples 1 to 3 and Comparative Example 1, respectively, and MLSS (suspended substance concentration) = 9000 mg / L using activated sludge water, water temperature 10 ° C., filtration flow rate 1 Filtration was performed at 0.0 m / day.
As a result, in the module produced using the porous hollow fiber membrane of Comparative Example 1, the filtration differential pressure increased significantly after 2 days of operation, whereas the porous hollow fiber membranes of Examples 1 to 3 were used. The produced module did not show a significant change in the filtration differential pressure, and was able to operate stably.

<Reference Example 1>
(Manufacture of porous hollow fiber membrane)
A porous hollow fiber membrane 1 was produced using a porous hollow fiber membrane production apparatus.
Polyvinylidene fluoride A (Arkema, trade name: Kyner 761A), Polyvinylidene fluoride B (Arkema, trade name: Kyner 301F), Polyvinylidene fluoride C (Arkema, trade name: Kyner 9000LD), polyvinylpyrrolidone (Nippon Shokubai Co., Ltd., trade name: K-80) and N, N-dimethylacetamide were mixed at a mass ratio shown in Table 2 to prepare membrane-forming stock solutions (1) and (5).
The film-forming rate is 20 m / min, the length of the 100% water vapor emphasis region is 5 mm, and the film-forming stock solution (1) is combined with the outer layer and the film-forming stock solution (5) is combined with the inner layer at a coagulation bath temperature of 75 ° C. Application and film formation were performed.

The outer diameter of the obtained porous hollow fiber membrane 1 is about 2.80 mm, the inner diameter is about 1.2 mm, the thickness of the porous membrane layer 11 is about 150 μm on average, and the bubble point (Pi) The water permeability was 210 m ³ / m ² / h / MPa. The surface opening ratio A1 was 40%, and the pore diameter index P1 was 0.21 μm. The aperture ratio A2 in the inner dense layer was 27%, and the pore diameter index P2 was 0.46 μm.

MBR filtration operation conditions were subjected to a filtration test under the conditions shown in Table 4.

<Reference Example 2>
(Manufacture of porous hollow fiber membrane)
A porous hollow fiber membrane 2 was produced in the same manner as in Reference Example 1 using a porous hollow fiber membrane production apparatus.
Polyvinylidene fluoride A (Arkema, trade name: Kyner 761A), Polyvinylidene fluoride B (Arkema, trade name: Kyner 301F), Polyvinylidene fluoride C (Arkema, trade name: Kyner 9000LD), polyvinylpyrrolidone (Nippon Shokubai Co., Ltd., trade name: K-80) and N, N-dimethylacetamide were mixed at the mass ratio shown in Table 2 to prepare membrane-forming stock solutions (2) and (5).
The film-forming speed is 20 m / Min, the length of the 100% water vapor emphasis region is 5 mm, the temperature of the coagulation bath is 75 ° C., the film-forming stock solution (2) is the outer layer, and the film-forming stock solution (5) is the inner layer. Application and film formation were performed.

The outer diameter of the obtained porous hollow fiber membrane 2 is about 2.80 mm, the inner diameter is about 1.2 mm, the thickness of the porous membrane layer 11 is about 150 μm on average, and the bubble point (Pi) Was 197 kPa, and the water permeability was 49 m ³ / m ² / h / MPa. The surface opening ratio A1 was 41%, and the pore diameter index P1 was 0.23 μm. The aperture ratio A2 in the inner dense layer was 23%, and the pore diameter index P2 was 0.45 μm.

<Reference Example 3>
(Manufacture of porous hollow fiber membrane)
A porous hollow fiber membrane 3 was produced in the same manner as in Reference Example 1 using a porous hollow fiber membrane production apparatus.
Polyvinylidene fluoride A (Arkema, trade name: Kyner 761A), Polyvinylidene fluoride B (Arkema, trade name: Kyner 301F), Polyvinylidene fluoride C (Arkema, trade name: Kyner 9000LD), polyvinylpyrrolidone (Nippon Shokubai Co., Ltd., trade name: K-80) and N, N-dimethylacetamide were mixed at the mass ratio shown in Table 2 to prepare membrane-forming stock solutions (3) and (5). The film-forming speed is 20 m / Min, the length of the 100% water vapor emphasis region is 5 mm, and the temperature of the coagulation bath is 75 ° C. Application and film formation were performed.

The outer diameter of the obtained porous hollow fiber membrane 3 is about 2.80 mm, the inner diameter is about 1.2 mm, the average thickness of the porous membrane layer 11 is about 150 μm, and the bubble point (Pi) The water permeability was 164 kPa and 98 m ³ / m ² / h / MPa. The surface opening ratio A1 was 45%, and the pore diameter index P1 was 0.31 μm. The aperture ratio A2 in the inner dense layer was 25%, and the pore diameter index P2 was 0.67 μm.

<Reference Example 4>
(Manufacture of porous hollow fiber membrane)
A porous hollow fiber membrane 4 was produced in the same manner as in Reference Example 1 using a porous hollow fiber membrane production apparatus.
Polyvinylidene fluoride B (manufactured by Arkema, product name: Kyner 301F), polyvinylidene fluoride C (manufactured by Arkema, product name: Kyner 9000LD), polyvinylpyrrolidone (manufactured by Nippon Shokubai Co., Ltd., product name: K-80), and N , N-dimethylacetamide was mixed so as to have a mass ratio shown in Table 2 to prepare membrane-forming stock solutions (4) and (5).
The film-forming speed is 20 m / min, the length of the 100% water vapor emphasis region is 5 mm, and the film-forming stock solution (4) is the outer layer and the film-forming stock solution (5) is the inner layer at a coagulation bath temperature of 75 ° C. Application and film formation were performed.

The outer diameter of the obtained porous hollow fiber membrane 4 is about 2.80 mm, the inner diameter is about 1.2 mm, the thickness of the porous membrane layer 11 is about 150 μm on average, and the bubble point (Pi) The water permeation performance was 91 kPa and 168 m ³ / m ² / h / MPa. The surface opening ratio A1 was 50%, and the pore diameter index P1 was 0.36 μm. The aperture ratio A2 in the internal dense layer was 26%, and the pore diameter index P2 was 1.1 μm.

<Reference Comparative Example 1>
(Manufacture of porous hollow fiber membrane)
The porous hollow fiber membrane 5 was manufactured using the porous hollow fiber membrane manufacturing apparatus.
Polyvinylidene fluoride B (manufactured by Arkema, product name: Kyner 301F), polyvinylidene fluoride C (manufactured by Arkema, product name: Kyner 9000LD), polyvinylpyrrolidone (manufactured by Nippon Shokubai Co., Ltd., product name: K-80), and N , N-dimethylacetamide was mixed so as to have a mass ratio shown in Table 2 to prepare membrane-forming stock solutions (4) and (5). The film forming speed is 12.5 m / min, the high humidity and high temperature region length is 63.5 mm, and the coagulation bath temperature is 75 ° C. The film forming stock solution (4) is combined with the outer layer and the film forming stock solution (5) is combined with the inner layer. The film was applied to form a film.

The outer diameter of the obtained porous hollow fiber membrane 4 is about 2.80 mm, the inner diameter is about 1.2 mm, the thickness of the porous membrane layer 11 is about 150 μm on average, and the bubble point (Pi) The water permeation performance was 170 m ³ / m ² / h / MPa. The surface opening ratio A1 was 26%, and the pore diameter index P1 was 0.17 μm. The aperture ratio A2 in the inner dense layer was 5%, and the pore diameter index P2 was 0.13 μm.

According to the present embodiment, it can be used in the treatment of various aqueous fluids such as water purification treatment, beverage treatment, seawater turbidity, etc., and it has excellent fractionation characteristics and permeability, while the performance deterioration with time. Can be provided, and a porous hollow fiber membrane excellent in recovery of membrane separation characteristics by washing, and an evaluation method thereof can be provided.

The porous hollow fiber membrane of the present embodiment has a structure in which the pore diameter of the inner layer is sufficiently large relative to the pore diameter of the layer forming the outer surface and is not easily clogged. Therefore, the hollow porous hollow fiber membrane of this embodiment has high filtration stability, and is suitable as a filtration membrane used for water treatment such as water purification such as microfiltration and ultrafiltration.

DESCRIPTION OF SYMBOLS 1 Manufacturing apparatus 10 Spinning nozzle 11 Supporting through-hole 12 Resin solution flow path 20A Processing container 21 Ceiling part 21a 1st opening part 22a 2nd opening part 22c Through-hole 23 Side part 24 Gas supply pipe 25 Pipe part DESCRIPTION OF SYMBOLS 30 Coagulation tank 31 1st guide roll 32 2nd guide roll 33

Top plate

33a, 33b Opening part 40A, 40B, 40C Ventilation means 41, Ventilation nozzle 41a Circular opening part 41b Gas introduction chamber 41c Gas discharge port 41d Resistance imparting body 42 Gas supply means 43 Gas filtration means 44 Gas adjustment means 50 Protection tube 50a Through hole 51 Upper end 52 Lower end 52a Opening A A porous hollow membrane A1 A hollow string-like support A2 A coating film of a film-forming resin solution B Coagulation liquid

Claims

A porous hollow fiber membrane having a porous layer on at least an outer surface,
The average pore diameter (Ad) from the outer surface to a depth of 1 μm in the cross-sectional structure in the thickness direction of the porous hollow fiber membrane is 0 as a ratio (Ad / Bd) to the average pore diameter (Bd) from a depth of 2 μm to 3 μm. A porous hollow fiber membrane of 6 or less.
2. The porous hollow fiber membrane according to claim 1, wherein the outer surface has an average pore diameter P1 of 0.05 to 1.0 μm and an open area ratio A1 of 15 to 65%.
3. The porous hollow according to claim 1, wherein an average pore diameter P2 of a layer from the outer surface to a depth of 10 μm in the cross-sectional structure is 0.1 to 5.0 μm, and an open area ratio A2 is 10 to 50%. Yarn membrane.
The porous hollow fiber membrane according to any one of claims 1 to 3, wherein the structure from the outer surface to a depth of 5 µm is a three-dimensional network structure in which the pore diameter gradually increases in a direction away from the outer surface.
5. The average pore diameter of the porous layer having a depth of 5 μm from the outer surface is smaller than the average pore diameter of the porous layer existing at a position farther than the depth of 5 μm from the outer surface. The porous hollow fiber membrane according to the description.
6. The porous hollow fiber membrane according to any one of claims 1 to 5, wherein an average pore diameter of the porous layer existing at a part farther than 5 μm deep from the outer surface is 10 μm or less.
The porous hollow fiber membrane according to any one of claims 1 to 6, wherein the thermoplastic resin substantially constituting the depth from the outer surface to 5 μm is made of a thermoplastic resin of the same compound.
The porous hollow fiber membrane according to any one of claims 1 to 7, which does not contain a macrovoid having a pore diameter of more than 10 µm and a part thereof in the porous layer at a portion not more than 10 µm deep from the outer surface.
The porous hollow fiber membrane according to any one of claims 1 to 8, which is formed by a non-solvent phase separation method.
The porous hollow fiber membrane according to any one of claims 1 to 9, wherein the porous layer is formed on the outer surface side of a hollow fiber-like support.
The porous hollow fiber membrane according to claim 10, wherein the hollow fiber-shaped support is a heat-treated support.
The porous hollow fiber membrane according to claim 10 or 11, wherein the hollow fiber support is a hollow knitted string.
The porous hollow fiber membrane according to claim 11 or 12, wherein the support is a hollow knitted string obtained by circularly knitting a single yarn made of multifilament.
After the film-forming resin solution containing the thermoplastic resin and the hydrophilic compound is discharged from the spinning nozzle, the discharged film-forming resin solution is brought into contact with a non-solvent saturated vapor for the components of the film-forming resin solution. A method for producing a porous hollow fiber membrane, which is then solidified by being immersed in a coagulation liquid to form a porous hollow fiber membrane,
The spinning nozzle is a single or double or more tubular nozzle, and the porous hollow fiber membrane is a porous hollow fiber membrane in which at least a part having a depth of 5 μm from the outer surface is formed by the same membrane-forming resin solution. Production method.
The method for producing a porous hollow fiber membrane according to claim 14, wherein the non-solvent saturated steam is saturated steam.
The film-forming resin solution is applied to the outer peripheral surface of a hollow support by using a spinning nozzle to form a film-forming resin layer, and then the film-forming resin layer is brought into contact with a non-solvent saturated vapor. The method for producing a porous hollow fiber membrane according to 14 or 15.
The method for producing a porous hollow fiber membrane according to claim 16, wherein the support is a heat-treated support.
The method for producing a porous hollow fiber membrane according to claim 16 or 17, wherein the support is a knitted string.
The method for producing a porous hollow fiber membrane according to claim 17 or 18, wherein the support is a hollow knitted string obtained by circularly knitting a single yarn made of multifilament.