JP2005193201A - Hydrophilic hollow fiber membrane and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hollow fiber membrane with an excellent pure water permeation performance, a fractioning performance, strength, heat resistance, chemical resistance, a low water absorption property, a process controlling property, a cost efficiency and a pore formation property and excellent mechanical strength using a heat induction phase separation method, and to provide its production method. <P>SOLUTION: The hollow fiber membrane is a hollow fiber membrane formed by heat induction phase separation of a polymer compound and a solvent. The membrane has circular or elliptic fine pores having an average pore diameter of 3 μm or more on an outer surface and an inner surface and has a pure water permeation speed of 30,000 L/m<SP>2</SP>/hr/98kPa or more, and a fraction particle diameter of 1 μm or more. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a hydrophilic hollow fiber membrane and a method for producing the same. More specifically, using heat-induced phase separation, pure water permeation performance and fractionation performance, strength, heat resistance, chemical resistance, low water absorption, process controllability, cost, pore formation, and mechanical strength The present invention relates to a hollow fiber membrane excellent in hydrophilicity and a method for producing the same.

  In recent years, the technology of separation means using a separation membrane having selective permeability has been remarkably advanced. Such separation operation technology has been put to practical use as a series of purification systems including separation means, washing means, sterilization means, etc., for example in the production process of drinking water, ultrapure water and pharmaceuticals, sterilization and finishing of brewed products, etc. Has been. In these fields of application, the use of separation membranes has become widespread because finer water (advanced processing), improved safety, and improved accuracy are required at a high level. However, in spite of the widespread use of separation membranes as described above, from the viewpoint of filtration and separation, filtration with sand is still the mainstream at present. For example, in the production of tap water, coagulation precipitation and sand are used. Separation means combined with filtration accounts for the overwhelming majority.

  The reason why separation means using separation membranes in the production of tap water is not so popular is that sand filtration has a higher permeate flow rate per unit filtration area than filtration by separation membranes, and sand filtration is therefore less expensive. Because it is possible to produce fresh water at

However, since separation membranes are overwhelmingly superior to sand filtration in the following points, if the cost required for filtration can be reduced, it will be rapidly spread as a new filtration technique that replaces sand filtration.
1. Since the separation accuracy is high, a stable filtrate can be obtained regardless of the quality of raw water, and the safety is also high.
2. There is little troublesome maintenance such as replacement of sand and less waste.
3. In the case of sand filtration, a coagulation sedimentation treatment is required to improve the separation accuracy, but in the case of membrane filtration, the coagulation sedimentation treatment can be omitted or simplified, and the system can be saved and processed. The process can be simplified.
4). In membrane filtration, the recovery rate of the filtrate is high and the amount of water used for backwashing is small, so that wastewater treatment by backwashing is simplified.

  The reason why the permeation rate by membrane filtration is extremely low compared with the permeation rate by sand filtration is that conventional separation membranes are mainly microfiltration membranes and ultrafiltration membranes with a fractional particle size of 0.2 μm or less. In addition, the fractional particle size is small and the pure water permeation rate is originally low, and most of the impurities and suspended solids present in the treated water are trapped by the separation membrane, and the permeation rate is increased by the increase in resistance due to the trapped substance. May be even lower. On the other hand, the separation accuracy of sand filtration is about 5 to 10 μm, the original pure water permeation rate is high, and even if there are impurities and suspended solids in water, it will permeate if the size is 5 μm or less. Therefore, it is difficult to receive resistance due to trapped substances and the like, and a high filtration rate can be maintained. Although sand filtration cannot completely remove impurities of 5 μm or less, etc., separation accuracy of 0.2 μm or less, such as microfiltration or ultrafiltration, is not necessarily required as it has already been put to practical use in most applications. It was not necessary.

  Recently, however, the presence of protozoa such as Cryptosporidium and Giardia in tap water has been a problem in terms of safety. However, removal by sand filtration is not sufficient. Although some separation means using a filtration membrane has been introduced, the low water production efficiency in membrane filtration has not been improved. If there is a separation membrane with a high separation accuracy, the pore size of the hollow fiber membrane is large enough to satisfy safety as tap water by removing protozoa, High filtration rate can be expressed and maintained by suppressing clogging of membranes by bacteria and suspended solids of 1 μm or less while having a certain advanced separation performance. It is considered to be used in applications.

  An example of a method for producing a filtration membrane having a large pore diameter is a stretch pore opening method. The method is characterized in that the membrane material is annealed and stretched under specific conditions, and as a result, a filtration membrane having a fibrillated lamellar structure can be produced. However, the filtration membrane produced by this method has a problem that the strength in the circumferential direction is greatly reduced because it is oriented in the fiber direction by stretching. In particular, since the strength tends to decrease as the pore diameter increases, it is difficult to produce a filtration membrane having practical strength by this method. In addition, since the shape of the hole to be formed is a slit shape, a long and narrow substance is easily transmitted and the separation accuracy is likely to be lowered.

  Phase separation is often used as a method for producing a filtration membrane with excellent separation accuracy. Production methods using such phase separation can be broadly divided into non-solvent induced phase separation methods and thermally induced phase separation methods. In the non-solvent induced phase separation method, a uniform polymer solution composed of a polymer and a solvent undergoes phase separation by the ingress of the non-solvent or evaporation of the solvent to the outside atmosphere. This non-solvent induced phase separation method is very general as a method for producing a filtration membrane. However, this method is difficult to control the phase separation in a non-solvent, and the non-solvent is essential, so the production cost is high and macro voids (coarse pores) are easily generated. There is a problem in terms of.

  On the other hand, the thermally induced phase separation method usually comprises the following steps. (1) A mixture of a polymer and a solvent having a high boiling point is melted at a high temperature. (2) After molding, the polymer is solidified by cooling at an appropriate rate to induce phase separation. (3) Extract the used solvent.

The advantages of the thermally induced phase separation method compared to the non-solvent induced phase separation method are as follows. (A) Macrovoids that cause a decrease in film strength are not generated. (B) In the non-solvent induced phase separation method, a non-solvent is required in addition to the solvent, so that control in the production process is difficult and reproducibility is low. On the other hand, the heat-induced phase separation method does not require a non-solvent, so it has excellent controllability and cost, and has high reproducibility. (C) The pore diameter control is relatively easy, the pore diameter distribution is sharp, and the hole forming property for forming good holes is excellent.

  Thermally induced phase separation includes solid-liquid type thermally induced phase separation and liquid-liquid type thermally induced phase separation, and it is attributed to the compatibility between the polymer and the solvent. When the compatibility of both is very high, solid-liquid type thermally induced phase separation is developed, but when compatibility is low, liquid-liquid type thermally induced phase separation is developed, and finally both become incompatible. . In general, in liquid-liquid type thermally induced phase separation, since phase separation proceeds by spinodal decomposition, it has a feature that a co-continuous structure is easily developed compared to solid-liquid type thermally induced phase separation. A separation membrane having excellent pore forming properties such as communication and uniformity can be produced. That is, in order to produce a separation membrane excellent in permeation performance and fractionation performance, it is preferable to select an appropriate polymer and solvent combination that exhibits liquid-liquid type thermally induced phase separation. In general, since the region where a polymer and a solvent exhibit liquid-liquid type thermally induced phase separation is small, it is known that it is extremely important to select an appropriate combination of a polymer and a solvent when producing a separation membrane by this method. (See, for example, Non-Patent Document 1).

  A method for producing a separation membrane using the above-described thermally induced phase separation method is known (see, for example, Patent Documents 1 and 2). However, the average pore diameter of the porous membranes obtained by these methods is that of the hollow fiber membrane described in the above-mentioned prior art is at most submicron order, and the pore diameter is about several μm using the thermally induced phase separation method. There is no description at all about a method for obtaining a separation membrane having s.

  In addition, when a hydrophilic polymer compound is used as the membrane material, a hollow fiber membrane can be formed, but a hydrophilic liquid such as water can be permeated through the membrane made of such a hydrophilic polymer compound. Since the membrane itself swells and the separation performance changes greatly, most of the membrane material is a hydrophobic polymer, but as it is, it is difficult to permeate water, and hydrophilic liquids such as water are used. In order to allow permeation, a hydrophilic treatment is necessary. For example, as a method for hydrophilizing a polyolefin porous membrane, the entire surface including the microporous portion of the polyolefin porous membrane is wet-treated with an organic solvent such as alcohol or ketone having good compatibility with water, Organic solvent wetting and water replacement methods that replace organic solvents with water, and physical adsorption methods that impart hydrophilicity to porous membranes by adsorbing hydrophilic substances such as polyethylene glycol and surfactants to the surface of the porous membrane. Known (for example, see Patent Documents 1 and 2).

  However, in the organic solvent wetting and water replacement method, once the water in the pores is removed during storage or use, the portion returns to hydrophobic and water cannot permeate, so the porous membrane is always filled with water. Therefore, it has a problem that handling is complicated. Furthermore, if the hydrophilizing agent is attached to the porous membrane and used for filtration, the hydrophilizing agent will migrate from the porous membrane into the filtrate and contaminate it. An operation of sufficiently washing and removing from the membrane is necessary. Although the physical adsorption method is simple in terms of operation, it cannot be said that it is necessarily a sufficient hydrophilization method because the hydrophilic substance is detached while it is used for a long time.

JP 54-153872 A JP 59-24732 A “Chemical Engineering” Chemical Industry Co., Ltd. June 1998, pages 453-464

  The purpose of the present invention is to use purely water permeation performance and fractionation performance, strength, heat resistance, chemical resistance, low water absorption, process controllability, cost, and pore formation using a heat-induced phase separation method. Another object of the present invention is to provide a hollow fiber membrane excellent in mechanical strength and a method for producing the same.

The hollow fiber membrane of the present invention that solves the above problems is a hollow fiber membrane formed by thermally induced phase separation of a polymer compound and a solvent, and at least a polymer compound having a viscosity average molecular weight of 1,000,000 or more It contains 1% by weight or more of the hollow fiber membrane, has circular or elliptical micropores with an average pore diameter of 3 μm or more on the outer surface and inner surface, and a pure water permeation rate of 30000 L / m ² / hr / 98 kPa or more, The image particle diameter is 1 μm or more and has hydrophilicity.

  The method for producing a hollow fiber membrane according to the present invention includes a polymer compound, a solvent that can be mixed with the polymer compound in a specific temperature range to be in a one-phase state and can undergo phase separation due to temperature change, inorganic particles, and inorganic After preparing a mixed solution in which the flocculant having affinity for particles is kneaded at a temperature at which the polymer compound and the solvent are compatible, it is extruded into a hollow fiber shape and cooled to thermally induce phase separation and precipitation of the polymer compound. Is caused to form a hollow fiber-like material, and components other than the polymer compound are extracted.

The polymer compound used in the present invention is not particularly limited as long as it is compatible with a solvent in a specific temperature range to become a one-phase state and can cause phase separation due to temperature change. Examples of the hydrophobic polymer usually used as the polymer compound of the membrane material include, for example, high density polyethylene, low density polyethylene, polypropylene, polystyrene, polyvinylidene fluoride, polyphenylene sulfide, polybutene, poly (4-methyl-1- Pentene), polychlorotrifluoroethylene, polyphenylene ether, nylon 6, nylon 11, polycarbonate and the like. Among these, olefin polymers such as high density polyethylene, low density polyethylene, linear low density polyethylene, polypropylene, polybutene, poly (4-methyl-1-pentene), polyisobutylene, polyisopentene, and polypentene, particularly Polyethylene is preferable because it is economically advantageous because it induces thermally induced phase separation at room temperature because the temperature at which it becomes the one-phase state is low, and it can be oriented and strengthened by stretching. A higher molecular weight of the polymer compound is preferable because the strength of the film is increased. For example, a polymer having a weight average molecular weight of 300,000 or more is suitably used for polyethylene.

  As the solvent used in the present invention, a solvent that is compatible with the polymer compound in a specific temperature range and causes phase separation from the polymer compound due to temperature change is used. Solid-liquid phase separation and liquid-liquid phase separation exist as forms of thermally induced phase separation, but the present invention is applicable to any of these phase separation forms. In general, it is known that a solid-liquid phase separation state is obtained when the compatibility between the polymer compound and the solvent is very high, and a liquid-liquid phase separation state is obtained otherwise. Examples of polymer / solvent combinations that can be in a solid-liquid phase separation include polyethylene / paraffin, polyethylene / stearyl alcohol, polypropylene / paraffin, poly (4-methyl-1-pentene) / mineral oil, polyphenylene ether / Combinations such as decalin are listed. Examples of polymer / solvent combinations that can be in liquid-liquid phase separation include polyethylene / dibutyl phthalate, polyethylene / diisodecyl phthalate / dioctyl phthalate, polymethyl methacrylate / dioctyl phthalate, polystyrene / nitrobenzene, Examples include combinations of polyacrylonitrile / maleic anhydride, polypropylene / diphenyl ether, and the like. Moreover, it is preferable to use a solvent having a weight loss rate of 10% or less in 30 seconds at (thermally induced phase separation temperature + 30) ° C. measured using TG-DTA because the structure of the film surface becomes good.

  The inorganic particles used in the present invention are the core for the hollow fiber membrane to have a large pore size, and are preferably fine particles that are easy to extract with chemicals and have a relatively narrow particle size distribution. Examples thereof include metal oxides or hydroxides such as silica, calcium silicate, aluminum silicate, calcium carbonate, magnesium carbonate, calcium phosphate, iron and zinc, and salts such as sodium, potassium and calcium. . In particular, the cohesive inorganic particles are usually added to a composition in which the polymer compound and the solvent are phase-separated so that the stability when the polymer compound and the solvent are in a compatible state. As a result of this, homogeneous spinning becomes possible and a membrane having a larger pore diameter can be produced. From such a cohesive point, silica is the best inorganic particle. In addition, inorganic particles having different agglomerated particle diameters can be mixed for the purpose of controlling the pore diameter of the hollow fiber membrane, in particular, improving the connectivity of the pores.

  The aggregating agent used in the present invention refers to a compound that has an affinity for inorganic particles and has a function of improving the aggregating properties of the inorganic particles. In addition to such requirements, the flocculant must have a boiling point equal to or higher than the temperature at which the polyolefin polymer and the solvent are compatible. In addition, it is more preferable that the aggregating agent is a compound having a hydrophilic group from the viewpoint of improving the aggregation property of the inorganic particles. However, if the solvent satisfies the above requirements, it is not necessary to add a new flocculant. Examples of flocculants include polyhydric alcohols such as ethylene glycol, propylene glycol, triethylene glycol, polyethylene glycol, and glycerin, polyglycerin fatty acid esters such as decaglyceryl monolaurate, and polyoxyethylene glyceryl monostearate. Polyoxyethylene glycerin fatty acid esters, polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether and polyoxyethylene cetyl ether, polyoxyethylene polyoxypropylene alkyl ethers such as polyoxyethylene polyoxypropylene cetyl ether , Polyoxyethylene alkylphenyl ethers such as polyoxyethylene nonylphenyl ether, polyoxyethylene monopalmitate Polyoxyethylene sorbitan fatty acid esters such as Nsorubitan thereof. Furthermore, in order to control the aggregation state of the inorganic particles or to stabilize the molten state of the entire system, they can be mixed at an arbitrary ratio. The flocculant mixed to stabilize the melt state of the entire system includes a solubility parameter (SP value) or a hydrophilic / lipophilic balance (HLB value) between each of the solvent and the flocculant already added. Those that take values are preferred. As for the SP value, Joel R. Fried's “Polymer Science AND Technology” and the HLB values are described in detail in “Handbook of Surfactants” written by Nishiichiro, Ima Tomoaki and Masai Kasai.

  As a method for imparting hydrophilicity to the hollow fiber membrane, a method of irradiating radiation with a hydrophilic monomer held on the surface of the porous film, or a porous structure made of a hydrophobic polymer by plasma treatment or A chemical surface modification method such as a treatment method using a fluorine-containing gas, and further a high molecular weight compound and a hydrophilic polymer in an amount of 40 parts by weight or less and 0.5 parts by weight or more based on the hydrophobic polymer and the hydrophobic polymer. And a method of using a blend comprising the above as a polymer compound. Among these, the method of blending the hydrophilic polymer is the most excellent method in terms of industrial cost and processability.

  In the case of using, as the polymer compound, a hydrophobic polymer and a blend comprising a hydrophilic polymer of 40 parts by weight or less and 5 parts by weight or more based on the hydrophobic polymer, the hydrophilic polymer may be, for example, ethylene-acetic acid. Examples thereof include vinyl copolymers, ethylene-vinyl alcohol copolymers, polyvinyl alcohol, polyvinyl pyrrolidone and the like, and modified polymers thereof, which are hydrophilic and high enough not to be eluted in the precipitation treatment after thermally induced phase separation. As long as it has viscosity or molecular weight, it is not limited to these. In particular, from the viewpoint of compatibility with a hydrophobic polymer, an ethylene-vinyl acetate copolymer is preferably used. The hydrophilic polymer is used in an amount of 40 parts by weight or less, preferably 20 parts by weight or more, and more preferably 5 parts by weight or more, more preferably 5 parts by weight or more based on the hydrophobic polymer. When the amount of the hydrophilic polymer is larger than the above range, when the hydrophilic liquid such as water is permeated, the membrane itself swells and the separation performance changes significantly. If the amount is less than the above range, any hydrophilic effect will not be obtained, which is not preferable.

  The composition of the mixed liquid composed of the polymer compound, the solvent, the inorganic particles and the flocculant described above is such that the produced hollow fiber membrane has excellent mechanical strength, and has a desired pore diameter and from the outer surface to the inner surface of the hollow fiber. Can be freely set within a range in which the through hole penetrating the hole can exist to the extent that the desired performance is satisfied. The composition of the mixed solution varies depending on the chemical structure and the like of each component described above, but when the total composition ratio of the polymer compound, the solvent, the inorganic particles, and the flocculant is 120 (the same applies hereinafter), the polymer compound: Solvent: inorganic particles: flocculant = 15-25: 25-50: 10-30: 20-50 is desirable. If the composition of the mixed solution is out of this range, the stability when spinning the mixed solution into a hollow fiber shape is lowered, making it difficult to spin a homogeneous hollow fiber material, and the amount of the polymer compound is as described above. When the amount is more than the amount, the porosity of the hollow fiber membrane obtained is low even if it is possible to spin a homogeneous hollow fiber-like material, and the large pore diameter and the large pure water permeation rate that are the characteristics of the present invention are obtained. It tends to be difficult.

  If necessary, various additives such as antioxidants, ultraviolet absorbers, lubricants, antiblocking agents, dyes, thickeners, etc., may be added to the liquid mixture composed of the polymer compound, solvent, inorganic particles and aggregating agent. It can add in the range which does not impair the objective of this invention.

  The mixed liquid composed of the above-described polymer compound, solvent, inorganic particles and aggregating agent is kneaded in a biaxial kneading equipment, a plast mill, a mixer or the like. The kneading temperature is set in such a range that the polymer compound and the solvent are compatible and each component of the mixture is not decomposed. After the mixture is kneaded, the bubbles are sufficiently removed, measured by a measuring pump such as a gear pump, and extruded from a nozzle having a double ring structure. At this time, in order to form a hollow fiber shape from the center of the nozzle having a double ring structure, a boiling point equal to or higher than the extrusion temperature of the above mixture without dissolving a gas such as air or nitrogen, or a polymer compound. The liquid it has is extruded at the same time. Examples of the liquid used for extruding from the center of the nozzle having the double ring structure include tetraethylene glycol, propylene glycol, and glycerin. When these are used, the inner surface of the hollow fiber to be obtained is used. It is effective in obtaining a large pore size by coarsening the structure.

  The extruded product extruded from the nozzle causes a phase separation between the polymer compound and the solvent due to a change in temperature such as cooling, and the polymer compound is solidified to form a hollow fiber-like product. In the present invention, it is important that the polymer compound is solidified by causing heat-induced phase separation. When a mixture of a polymer compound and a solvent compatible with the polymer compound is solidified by contact with the poor solvent of the polymer compound, a portion corresponding to the interface between the mixture and the non-solvent forms a dense layer, and is obtained. There is a possibility that the membrane has a non-uniform structure and high separation accuracy cannot be obtained. The method of cooling includes a method in air, a method of introducing into a liquid, a method of once passing through air, and a method of introducing into a liquid, and any method may be used. Since the strength and elongation of the membrane and the pore diameter control are greatly affected, it is desirable to control the ambient temperature with warm air so that the cooling rate can be controlled, or to control the temperature of the liquid used for cooling. As the liquid used for cooling, water is industrially preferable, but an organic liquid compatible with the flocculant or solvent can also be used.

  Next, the hollow fiber membrane is obtained by extracting the solvent, the inorganic particles, and the flocculant from the hollow fiber formed as described above. The extraction of these components can be carried out continuously in the process together with operations such as spinning and solidification, or can be carried out after the hollow fiber-like product is once wound on a frame or a cassette, or the hollow fiber-like product can be obtained in a predetermined manner. It may be carried out after being housed in a case of the shape and modularized. The solvent used for extraction of each component needs to be a non-solvent for the polymer compound at the extraction temperature. Although the extraction solvent varies depending on the chemical structure of the extraction component, for example, when the solvent is paraffin, hexane, tetrachloroethane, trichlorofluoromethane, trichloroethylene and the like can be mentioned. In addition, when the inorganic particles are silica, extraction with an alkaline solution is preferable. Further, when the flocculant is polyoxyethylene polyoxypropylene cetyl ether, hexane, acetone, methanol, water and the like can be mentioned. After performing these treatments, the hollow fiber membrane is dried, for example, in a state of being wound around a frame or a cassette.

  Further, in the present invention, stretching can be performed in order to improve the strength of the hollow fiber membrane. As the stretching method, methods such as hot stretching, cold stretching, and heat setting can be appropriately combined according to the intended strength. However, if the degree of stretching is too high, the resulting hollow fiber membrane is fibrillated and the micropores become slit-like, so that the separation accuracy is lowered and the strength in the circumferential direction is adversely decreased. . In the filtration of the membrane, the strength in the circumferential direction is also important. Therefore, it is necessary to control the stretching ratio within a range in which the membrane surface does not become slit-like micropores but maintains a circular or elliptical shape. Stretching is performed in a state where a solvent or inorganic particles are present after forming the hollow fiber-like material, and is performed in a state where inorganic particles are present in the hollow fiber-like material after extracting the solvent and the flocculant. It may be performed by any method, for example, after the particles and the flocculant are extracted. When stretching is performed in a state where inorganic particles are present in the hollow fiber-like material at the time of stretching, it is preferable because a hollow fiber membrane having a large pore diameter can be obtained by the inorganic particles becoming the core of pore formation. By performing such stretching, not only the strength is improved but also the porosity is increased, and as a result, a membrane having a high pure water permeation rate can be produced.

The hollow fiber membrane of the present invention thus obtained has an inner diameter of 0.2 to 2 mm, an outer diameter of 0.4 to 5 mm, and has a circular or elliptical shape with an average pore diameter of 3 μm or more on the outer surface and the inner surface. Has micropores. The average pore diameter here means taking a photograph (for example, 600 times magnification) using an electron microscope at least two places on the outer surface and the inner surface, and measuring the inner radius of all the fine holes visible in the field of view of the photograph. The above operation is repeated until the number of fine pores measured for the above operation exceeds at least 100, the average value of the measured values is obtained, and this is the average pore diameter. The circular or elliptical diameter means that the ratio of the major axis to the minor axis of the micropores measured by the electron micrograph is 1: 1 to 6: 1 or less on average. The cross section of the membrane is preferably a network structure having a larger pore diameter than the inner and outer surfaces, but may have a symmetric structure, an asymmetric structure, a finger-like structure, or a void. Moreover, the porosity which is the volume ratio of the space in the hollow fiber membrane is 50 to 95%, preferably 70 to 90%. When the porosity is less than 50%, it is difficult to obtain a sufficient pure water permeation rate. When the porosity exceeds 90%, the strength of the membrane is lowered, and the hollow fiber membrane is broken or broken during membrane filtration. It lacks durability as a thin film. Since the hollow fiber membrane of the present invention has such a membrane structure, the pure water permeation rate is 30000 L / m ² / hr / 98 kPa or higher, which is much higher than conventional membranes and has a fractional particle diameter of 1 μm or more. Have. Furthermore, according to the production method of the present invention, it is possible to produce a membrane having a pure water permeation rate of 150,000 L / m ² / hr / 98 kPa or more and a fractional particle diameter of 3 μm or more. Further, since the pore diameter is increased, a gas such as air can be permeated at a low pressure of 100 kPa or less even in a wet state, so that cleaning by physical means such as gas backwashing is possible.

  A hollow fiber membrane module can be obtained by bundling a predetermined number of hollow fiber membranes after drying and storing the hollow fiber membranes in a case having a predetermined shape, and then fixing the ends with urethane resin, epoxy resin, or the like. As the hollow fiber membrane module, a type in which both ends of the hollow fiber membrane are fixed open, a type in which one end of the hollow fiber membrane is fixed open and the other end is sealed but not fixed, etc. Various forms are known.

  Hereinafter, the present invention will be described specifically by way of examples. In addition, this invention does not receive any limitation by this.

  High-density polyethylene as a polymer compound (manufactured by Nippon Polychem Co., Ltd .: “Novatec” HB214R weight average molecular weight 430,000), ethylene-vinyl acetate copolymer (Mitsui / DuPont Polychemical Co., Ltd. as a hydrophilic polymer: “ EVAFLEX "P-1905), liquid paraffin as a solvent (Chuo Kasei Co., Ltd .: 350-S), inorganic particles as silica (Tokuyama Co., Ltd .:" Fine Seal "X-45; average aggregated particle size 4.0- 5.0 μm), and ethylene glycol (manufactured by Nippon Shokubai Co., Ltd.) (hereinafter referred to as EG) as a flocculant was prepared so that the weight ratio was 18: 2: 50: 20: 30. The composition of this mixed solution is shown in FIG.

(HLB value)
In addition, the HLB value described in Table 1 was determined by calculating from the following formula according to the method described in “Surfactant Handbook” by Nishiichiro Nishi, Ichiro Imai and Masai Kasai.
(HLB value) = 20 × (molecular weight of hydrophilic part in substance) / (molecular weight of substance) (1)
In the formula (1), the molecular weight is calculated using the value of the International Pure and Applied Chemical Association (IUPAC) atomic weight.

(SP value)
Moreover, the SP value described in Table 1 was determined by calculating from the following formula.
(SP value) = ρ × ΣF / M (2)
In the formula (2), ρ is the density of the substance at 25 ° C., M is the molecular weight of the substance, and F is a constant determined for each bond by the molar attraction constant. Here, the numerical value reported by Hoy (Joel R. Fried's "Polymer Science AND Technology"). The unit of SP value is (MPa) ^1/2 .

The above mixed solution was heated and kneaded (temperature: 165 ° C.) in a twin-screw kneading extruder, and the extruded strand was passed through a pelletizer to form chips. The chip was extruded using an extruder (165 ° C.) equipped with a double ring nozzle having an outer diameter of 2.5 mm and an inner diameter of 1.1 mm. At this time, tetraethylene glycol was injected into the hollow portion of the extrudate.
The extruded product extruded from the spinning nozzle into the air was placed in a water bath (temperature 20 ° C.) through an air travel distance of 2 cm, and passed through an approximately 50 cm water bath to be cooled and solidified. Next, the hollow fiber thus obtained was immersed twice in hexane at 50 ° C. for 60 minutes to extract and remove the solvent (350-S), and then immersed in methanol at room temperature for 60 minutes twice. The flocculant (EG) and the injection solution (tetraethylene glycol) were extracted and removed.

  The hollow fiber-like material thus obtained was stretched in hot water at 80 ° C. so as to be about 3 times the original length in the fiber direction, and then heat-set in hot water at 100 ° C., Extraction and removal of inorganic particles (“Fine Seal” X-45) by repeating immersion for 60 minutes in 80 ° C. 3N sodium hydroxide solution twice and hydrolysis of acetyl group in ethylene-vinyl acetate copolymer By doing so, hydrophilicity was imparted to the membrane. Then, the hollow fiber membrane was obtained through the water washing and the drying process. The manufactured hollow fiber membrane was tested according to the following method. The test results are shown in Table 2.

(Ratio of major and minor diameters of pores and average pore diameter)
At least two locations on the outer and inner surfaces are photographed using an electron microscope, and the major, minor, and inner radii of all micropores that are visible within the field of view of the photograph are measured. The number of micropores to be measured is 100 The above operation is performed until the above is reached. Thereafter, for each of the outer surface and the inner surface, the measured ratio of the major axis and minor axis of the hole and the average value of the inner radius were obtained, and this was defined as the ratio of the major axis and minor axis of the hole and the average pore diameter.

(Fractional particle size)
The rejection rate of at least two kinds of particles having different particle diameters is measured, and the value of S at which R is 90 is determined in the following approximate expression (3) based on the measured values. It was.
R = 100 / (1−m × exp (−a × log (s))) (3)
In the formula (1), a and m are constants determined by the hollow fiber membrane, and are calculated based on measured values of two or more types of rejection. However, the fractional particle size in the case where the rejection rate of 0.1 μm diameter particles is 90% or more is expressed as <0.1 μm.

(Pure water transmission rate)
The measurement was performed in a dry state and a wet state. In the wet state, the hollow fiber membrane was immersed in a 70% ethanol aqueous solution for 12 hours, and then a hollow fiber membrane module having an effective length of 3 cm was used, and pure water was used as raw water, and the filtration pressure was 50 kPa. Measure the water permeability per hour by filtering from the outside to the inside of the hollow fiber membrane at a temperature of 25 ° C (external pressure filtration), and calculate with the numerical value converted to the water permeability per unit membrane area, unit time, and unit pressure did. Measure the pure water permeation rate by the same method as above except that the wet state is measured and the hollow fiber membrane is dried and then not immersed in a 70% aqueous ethanol solution. did.

(Thermally induced phase separation temperature)
The thermally induced phase separation temperature was determined by measuring the temperature at which the droplet structure was formed and the crystallization temperature of the mixed solution composed of the polymer compound and the solvent. The droplet structure formation temperature was measured using an optical microscope (Nikon Corporation, ECLIPSE E600POL) with a temperature controller (Limka, TH-600PM). The liquid mixture previously kneaded was dissolved by holding for 2 minutes at the temperature at the time of kneading, and then cooled at 10 ° C./min, and the temperature of droplet structure formation observed in the process was measured. On the other hand, the crystallization temperature was measured using DSC (manufactured by PERKIN ELMER, Pyris 1). After the pre-kneaded mixture was heated from room temperature to the kneading temperature at 90 ° C./min, held at the kneading temperature for 2 minutes, then cooled at 10 ° C./min, from the endothermic peak observed in the process The crystallization temperature was estimated. Both measurements were performed at least twice, and both temperatures were determined from the average value. If the difference between the droplet structure formation temperature and the crystallization temperature obtained from the above measurement was in the range of ± 5 ° C., it was judged as solid-liquid type thermally induced phase separation, and the crystallization temperature was defined as the thermally induced phase separation temperature. On the other hand, if the droplet structure forming temperature is higher than the crystallization temperature by 5 ° C. or more, it is determined that the liquid-liquid type thermally induced phase separation is used, and the droplet structure forming temperature is defined as the thermally induced phase separation temperature.

(Weight loss rate of solvent)
10 mg of solvent is set in TG-DTA (Rigaku Denki Co., Thermo Plus TG8120), heated to 500 ° C / min to (thermally induced phase separation temperature +30) ° C, and then (thermally induced phase separation temperature +30) ° C. Holding for 30 seconds, the weight loss rate of TG (thermal weight) of the solvent within this time was estimated.

  A hollow fiber membrane was obtained in the same manner as in Example 1 except that the weight ratio of high density polyethylene: ethylene-vinyl acetate copolymer: liquid paraffin: silica: EG was 15: 5: 40: 20: 40. Table 1 shows the composition of the mixed solution used for the production of this hollow fiber membrane, and Table 2 shows the test results.

  As inorganic particles, silica 1 (manufactured by Tokuyama Co., Ltd .: “Fine Seal” X-45; average aggregate particle diameter 4.0 to 5.0 μm) and silica 2 (manufactured by Tokuyama Co., Ltd .: “Fine Seal” X-30, A mixture having an average aggregated particle size of 2.5 to 4.0 μm), EG and decaglycerin laurate (manufactured by Mitsubishi Chemical Foods, Inc .: L-7D) as an aggregating agent, and high-density polyethylene: Example 1 except that the weight ratio of ethylene-vinyl acetate copolymer: liquid paraffin: silica 1: silica 2: EG: decaglycerin laurate was 15: 5: 40: 5: 15: 30: 10 In the same manner, a hollow fiber membrane was obtained. Table 1 shows the composition of the mixed solution used for the production of this hollow fiber membrane, and Table 2 shows the test results.

  Solvents: Solvent 1: Dioctyl phthalate (Wako Pure Chemical Industries, Wako Grade 1) (hereinafter sometimes abbreviated as DOP) and Solvent 2: Diisodecyl phthalate (Wako Pure Chemical Industries, Wako Grade 1) (hereinafter DIDP) And silica (manufactured by Tokuyama Co., Ltd .: “Fine Seal” X-30, average agglomerated particle diameter of 2.5 to 4.0 μm) and a high density. A hollow fiber membrane was obtained in the same manner as in Example 1 except that the weight ratio of polyethylene: ethylene-vinyl acetate copolymer: DOP: DIDP: silica: EG was changed to 20: 5: 10: 30: 20: 35. . Table 1 shows the composition of the mixed solution used for the production of this hollow fiber membrane, and Table 2 shows the test results.

Reference example 1
High density polyethylene (“Novatec” HB214R) as a polymer compound, liquid paraffin (350-S) as a solvent, silica (“Fine Seal” X-45) as inorganic particles, and EG as a flocculant, and high density A hollow fiber membrane was obtained in the same manner as in Example 1 except that polyethylene: liquid paraffin: silica: EG was used at a weight ratio of 20: 50: 20: 30. Table 1 shows the composition of the mixed solution used for the production of this hollow fiber membrane, and Table 3 shows the test results.

Reference example 2
A mixture of solvent 1: DOP and solvent 2: DIDP as the solvent, silica (“fine seal” X-30) as the inorganic particles, and a high-density polyethylene: DOP: DIDP: silica: EG ratio by weight A hollow fiber membrane was obtained in the same manner as in Example 1 except that the ratio was 25: 10: 30: 20: 35. Table 1 shows the composition of the mixed solution used for the production of this hollow fiber membrane, and Table 3 shows the test results.

4 is an electron micrograph showing the outer surface of the hollow fiber membrane obtained in Example 3. FIG. 3 is an electron micrograph showing a cross section of the hollow fiber membrane obtained in Example 3. FIG. 3 is an electron micrograph showing the inner surface of the hollow fiber membrane obtained in Example 3. FIG.

Claims (11)

A hollow fiber membrane formed by thermally induced phase separation between a polymer compound and a solvent, and has circular or elliptical micropores with an average pore diameter of 3 μm or more on the outer surface and inner surface, and a pure water permeation rate of 30000 L A hollow fiber membrane characterized by having / m ² / hr / 98 kPa, a fractional particle size of 1 μm or more, and hydrophilicity. The hydrophilic hollow fiber membrane according to claim 1, wherein the polymer compound is an olefin polymer. The hollow fiber membrane is a polymer compound, a solvent that is compatible with the polymer compound in a specific temperature range to be in a one-phase state, and can cause phase separation by temperature change, an inorganic particle, and a flocculant having an affinity for the inorganic particle The mixture is prepared by kneading the mixture at a temperature at which the polymer compound and the solvent are compatible with each other, and then cooling it to cause thermally induced phase separation between the polymer compound and the solvent and precipitation of the polymer compound. The hydrophilic hollow fiber membrane according to claim 1, wherein The hydrophilic hollow fiber membrane according to claim 3, wherein the polymer compound comprises a hydrophobic polymer and a hydrophilic polymer in an amount of 40 parts by weight or less and 0.5 parts by weight or more based on the hydrophobic polymer. The hydrophilic hollow fiber membrane according to claim 3 or 4, wherein the hydrophilic hollow fiber membrane is stretched after thermally induced phase separation between the polymer compound and the solvent. The hydrophilic hollow fiber membrane according to any one of claims 3 to 5, wherein the flocculant is a compound having a hydrophilic group. A polymer compound, a solvent that is compatible with the polymer compound in a specific temperature range to be in a one-phase state and can cause phase separation due to temperature change, an inorganic particle, and a flocculant having an affinity for the inorganic particle After preparing a liquid mixture kneaded at a temperature at which the compound and the solvent are compatible, the mixture is extruded into a hollow fiber shape and cooled to cause heat-induced phase separation and precipitation of the polymer compound, thereby forming a hollow fiber material. A method for producing a hydrophilic hollow fiber membrane, comprising extracting inorganic particles and a flocculant having affinity for inorganic particles. The method for producing a hydrophilic hollow fiber membrane according to claim 7, wherein the polymer compound is an olefin polymer. The hydrophilic hollow fiber membrane according to claim 7, wherein the polymer compound comprises a hydrophobic polymer and a hydrophilic polymer in an amount of 40 parts by weight or less and 5 parts by weight or more based on the hydrophobic polymer. The method for producing a hydrophilic hollow fiber membrane according to any one of claims 7 to 9, wherein a stretching treatment is performed after thermally induced phase separation between the polymer compound and the solvent. The method for producing a hydrophilic hollow fiber membrane according to any one of claims 7 to 10, wherein the flocculant is a compound having a hydrophilic group.

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