JP4564758B2 - Method for producing vinylidene fluoride resin porous membrane - Google Patents

Description

The present invention uses a thermally induced phase separation method, and is excellent in mechanical strength, heat resistance, chemical resistance, large pore diameter, large water permeability, high separation performance, and excellent pore formation. The present invention relates to a method for producing a vinylidene resin porous membrane.

  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.

  Moreover, important characteristics required for the filtration membrane include not only separation accuracy but also strength, elongation, and chemical resistance. These characteristics largely depend on the membrane material. Therefore, in recent years, the development of a filtration membrane using a vinylidene fluoride resin has been promoted. Filtration membranes using vinylidene fluoride resin not only excel in strength, elongation, and chemical resistance, but also in oxidation resistance, so they can be used for advanced water treatment using ozone, which has recently been attracting attention. Is possible.

  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).

On the other hand, regarding a method for producing a polyvinylidene fluoride resin porous membrane using a thermally induced phase separation method, a spinning stock solution comprising a polyvinylidene fluoride resin and a solvent such as diethyl phthalate or acetophenone is dissolved at a high temperature and then heated by cooling. A method of expressing induced phase separation and obtaining a porous membrane through an extraction or stretching process is known (see, for example, Patent Document 1). The average pore size of the porous membrane obtained by this method is about 0.5 μm at the maximum, and the pure water permeation rate (water permeation amount) is less than 10,000 L / m ² / hr / 98 kPa.
JP 11-319522 A “Chemical Engineering” Chemical Industry Co., Ltd. June 1998, pages 453-464

The object of the present invention is to use a thermally induced phase separation method, which is excellent in mechanical strength, heat resistance and chemical resistance, and has a large pore diameter, large water permeability, high separation performance, and excellent pore formation. It is providing the manufacturing method of a vinylidene fluoride resin porous membrane.

In order to achieve the above object, the method for producing a vinylidene fluoride resin porous membrane of the present invention is compatible with a vinylidene fluoride resin and the vinylidene fluoride resin in a specific temperature region to be in a one-phase state. In addition, a predetermined solvent capable of causing phase separation due to a temperature change, inorganic particles, and an aggregating agent having an affinity for the inorganic particles were kneaded at a temperature at which the vinylidene fluoride resin and the solvent are compatible with each other. After preparing the liquid mixture, cooling causes heat-induced phase separation and precipitation of the vinylidene fluoride resin, followed by stretching in the presence of inorganic particles, and then the solvent, inorganic particles, and agglomeration The porous membrane is produced by extracting the agent. The membrane surface has circular or elliptical micropores with an average pore diameter of 3 μm or more, and the porosity, which is the volume ratio of the space in the porous membrane, is 50%. In the range of ~ 90% Pure water permeation rate 30000L ^/ m 2 ^/ hr ^/ 98kPa above, fractionated particle diameter and wherein the obtaining a more porous membrane of vinylidene fluoride resin 1 [mu] m.

  The vinylidene fluoride resin used in the present invention is a resin containing a vinylidene fluoride homopolymer and / or a vinylidene fluoride copolymer, and is compatible with a solvent in a specific temperature range to become a one-phase state. In addition, there is no particular limitation as long as phase separation can be caused by temperature change. The vinylidene fluoride copolymer is not particularly limited as long as it is a polymer having a vinylidene fluoride residue structure, and is typically a copolymer of a vinylidene fluoride monomer and other fluorine-based monomers. For example, a copolymer of at least one fluorine-based monomer selected from vinyl fluoride, ethylene tetrafluoride, propylene hexafluoride, and ethylene trifluoride chloride and vinylidene fluoride can be given. In some cases, a monomer such as ethylene other than the fluorine-based monomer may be included. The higher the molecular weight of the vinylidene fluoride resin, the higher the strength of the film. However, in consideration of processability, the weight average molecular weight is preferably in the range of 100,000 to 600,000, more preferably 200,000 to 500,000. A range is preferred.

  As the solvent used in the present invention, a solvent that is compatible with the vinylidene fluoride resin in a specific temperature range and causes phase separation with the vinylidene fluoride resin due to temperature change is used. Solvents that can be in a solid-liquid phase separation state with polyvinylidene fluoride include acetophenone, isophorone, cyclohexanone, dimethyl phthalate, diethyl phthalate, and the like. Examples of the solvent capable of taking a phase separation state include acetophenone, dibutyl sebacate, tricresyl phosphate, and the like. Examples of the solvent that can take a liquid-liquid phase separation state with polyvinylidene fluoride include hexyl benzoate, and the solvent that can take a liquid-liquid phase separation state with a polyvinylidene fluoride-hexafluoropropylene copolymer, Examples include propyl salicylate and pyridine. Among these, it is preferable to use a combination of a vinylidene fluoride resin and a solvent that exhibits a liquid-liquid phase separation state in order to produce a separation membrane having excellent permeation performance and fractionation performance. Furthermore, it is preferable to use a solvent having a weight loss rate of 10% or less at 30 ° C. at (thermally induced phase separation temperature + 30) ° C., because the pore opening property (opening rate) on the membrane surface becomes better. The weight loss rate of the solvent is measured using, for example, a differential thermal / thermogravimetric measuring device (hereinafter sometimes abbreviated as TG (thermogravimetric) -DTA (differential heat)).

  The inorganic particles used in the present invention are the core for the porous membrane to have a large pore size, and are desirably fine particles that can be easily extracted with chemicals and have a relatively narrow particle size distribution. Examples thereof include, for example, metal oxides or hydroxides such as silica, calcium silicate, aluminum silicate, magnesium silicate, calcium carbonate, magnesium carbonate, calcium phosphate, iron and zinc, and salts such as sodium, potassium and calcium. be able to. In particular, the inorganic particles having a cohesive property are usually compatible with each other by adding to a composition in which the vinylidene fluoride resin and the solvent are phase-separated. As a result of improving the stability at the time, it becomes possible to produce a homogeneous porous film, and a porous film 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 improving the pore diameter control of the porous membrane, in particular, improving the pore connectivity.

  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 these requirements, the flocculant needs to have a boiling point equal to or higher than the temperature at which the vinylidene fluoride resin 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, it is not necessary to add a new flocculant when the solvent also satisfies the requirements for the 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 composition of the mixed liquid composed of the above-mentioned vinylidene fluoride resin, solvent, inorganic particles, and aggregating agent has such a strength that the manufactured porous film can withstand practical use, and the desired pore diameter and pores satisfy the desired performance. It can be freely set within a possible range. The composition of the mixed solution varies depending on the chemical structure of each component described above, but when the total composition ratio of the vinylidene fluoride resin, the solvent, the inorganic particles, and the flocculant is 120 (the same applies hereinafter) It is desirable that it is in the range of vinylidene resin: solvent: inorganic particles: flocculant = 15-30: 25-85: 5-30: 5-50. When the composition of the mixed solution is out of this range, the stability is lowered when producing the porous membrane from the mixed solution, and it becomes difficult to produce a homogeneous porous membrane. Further, when the amount of the vinylidene fluoride resin is larger than the above-mentioned amount, the pore diameter of the obtained porous membrane is reduced even if it is possible to produce a homogeneous porous membrane. It tends to be difficult to obtain a high pure water permeation rate.

  In the mixed liquid comprising the above-mentioned vinylidene fluoride resin, solvent, inorganic particles, and aggregating agent, an antioxidant, an ultraviolet absorber, a lubricant, an antiblocking agent, a dye, a hydrophilizing agent, and a thickener are added as necessary. Such various additives can be added as long as the object of the present invention is not impaired.

  The liquid mixture composed of the above-mentioned vinylidene fluoride resin, 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 vinylidene fluoride resin and the solvent are compatible with each other and each component of the mixture is not decomposed. After the mixed solution is kneaded, bubbles are sufficiently removed, measured with a metering pump such as a gear pump, and then extruded through a sheet die or a nozzle having a double ring structure, and formed into a desired shape. When forming a hollow fiber, a gas such as air or nitrogen or a liquid having a boiling point equal to or higher than the extrusion temperature of the above mixed liquid is extruded from the center of the nozzle having a double ring structure. 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 more effective in obtaining a large pore size by coarsening the structure.

  In the extruded product extruded from the sheet die or nozzle, for example, the vinylidene fluoride resin and the solvent undergo phase separation due to a temperature change such as cooling, and the vinylidene fluoride resin is solidified. When the mixture of the vinylidene fluoride resin and the solvent compatible with the vinylidene fluoride resin is solidified by contact with the poor solvent of the vinylidene fluoride resin, the portion corresponding to the interface between the mixture and the non-solvent is a dense layer. The resulting porous membrane has a non-uniform structure, and high separation accuracy may not be obtained. The cooling method includes a method of performing in air, a method of introducing into the liquid, a method of once passing through the air and then introducing into the liquid, and any method may be used. Therefore, 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, a solvent, inorganic particles, and an aggregating agent are extracted from the molded product formed as described above to obtain a porous film. The extraction of these components can be carried out continuously in the process together with operations such as extrusion and solidification, and can be carried out after the molded product is once wound up on a frame or a cassette, or the molded product can be formed into a predetermined shape. You may carry out after storing in the case and modularizing. The solvent used for extraction of each component must be a non-solvent of vinylidene fluoride resin at the extraction temperature. Although the extraction solvent varies depending on the chemical structure of the extraction component, for example, when the solvent is acetophenone, acetone, methanol 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. The porous film is dried after being subjected to these treatments, for example, in a state of being wound around a frame or a cassette.

  In the present invention, it is also possible to perform a stretching treatment in order to improve the strength of the porous 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 excessive, the resulting porous 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 and inorganic particles are present after formation, and is performed in a state where inorganic particles are present after extracting the solvent and the flocculant. After extracting the solvent, inorganic particles and the flocculant This may be done by any method. When stretching in a state where inorganic particles are present at the time of stretching, it is preferable because the inorganic particles serve as nuclei for pore formation, so that a porous film having a large pore diameter can be obtained. 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 vinylidene fluoride resin porous membrane of the present invention thus obtained has circular or elliptical micropores with an average pore diameter of 3 μm or more on the membrane surface. The porosity, which is the volume ratio of the space in the porous 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 porous membrane of the present invention has such a membrane structure, the pure water permeation rate is 30000 L / m ² / hr / 98 kPa or more, which is much higher than conventional membranes, and the fractional particle diameter is 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 membrane module is obtained by bundling a predetermined number of porous membranes after drying and storing them in a case having a predetermined shape, and then fixing the ends with urethane resin, epoxy resin or the like. For example, in the case of a hollow fiber membrane, the membrane module is of a type in which both ends of the hollow fiber membrane are fixed open, one end of the hollow fiber membrane is fixed open and the other end is sealed but not fixed Various types are known, such as types.

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

Example 1
Polyvinylidene fluoride (hereinafter sometimes abbreviated as PVDF) as a vinylidene fluoride-based resin (SOLEF6010 manufactured by Solvay Advanced Polymers Co., Ltd.), and hexyl benzoate (manufactured by Wako Pure Chemical Industries, Ltd., reagent grade 1) as a solvent; Silica as inorganic particles (Tokuyama Co., Ltd., Fine Seal X-45, average agglomerated particle size 4.0 to 5.0 μm) and hexaglyceryl monolaurate as a flocculant (Hexaglyn 1-L, manufactured by Nikko Chemicals Co., Ltd.) Were mixed so that the weight ratio was 20: 80: 10: 10. The composition of this mixed solution is shown in Table 1.

  The above mixed solution was heated and kneaded (temperature 240 ° C.) in a twin-screw kneading extruder, and the extruded strand was passed through a pelletizer to form chips. This chip was extruded using an extruder (230 ° C.) equipped with a nozzle having a double ring structure 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 obtained hollow fiber was immersed in methanol at 50 ° C. for 60 minutes twice to extract and remove the solvent (hexyl benzoate), the flocculant (hexaglyceryl monolaurate), and the injection solution (tetraethylene glycol). did.

  The hollow fiber-like material thus obtained was stretched in hot water at 80 ° C. so as to be about twice as long as the original length in the fiber direction, and then heat-set in hot water at 100 ° C., After being immersed in a 3N sodium hydroxide aqueous solution at 20 ° C. for 20 minutes to extract and remove inorganic particles (Fine Seal X-45, manufactured by Tokuyama Corporation), a hollow fiber membrane was obtained through a water washing and drying process. The manufactured hollow fiber membrane was tested according to the following method. The test results are shown in Tables 2 and 3.

(Ratio of major and minor diameters of holes 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 based on the measured values, the value of S in which R is 90 is obtained in the following approximate formula (1), and this is the fractional particle diameter. It was.
R = 100 / (1−m × exp (−a × log (s))) (1)
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)
Using a hollow fiber membrane module with an open end of 3 cm in effective length, using pure water as raw water, filtering from the outside to the inside of the hollow fiber membrane under conditions of a filtration pressure of 50 kPa and a temperature of 25 ° C. (external pressure filtration) Then, the water permeation amount per hour was measured and calculated by a numerical value converted into the water permeation amount per unit membrane area, unit time and unit pressure.

(Strength, elongation)
Measurement was performed using a tensile tester (manufactured by Shimadzu Corporation, Autograph AGS-100G). The measurement was carried out in water at 20 ° C., the distance between chucks was 50 mm, the tensile speed was 100 mm / min, and the strength was determined by dividing the load at break by the membrane cross-sectional area. Further, the elongation was determined using the formula (2).
Elongation (%) = (Distance between chucks at break-Distance between chucks at the start of measurement) / Distance between chucks at the start of measurement × 100 (2)

(Thermally induced phase separation temperature)
The thermally induced phase separation temperature was determined by measuring the droplet structure formation temperature and the crystallization temperature of a mixed liquid composed of polyvinylidene fluoride (PVDF) and a 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.

Example 2
Polyvinylidene fluoride (PVDF) (SOLEF6010, manufactured by Solvay Advanced Polymers Co., Ltd.) as a vinylidene fluoride resin, hexyl benzoate (manufactured by Wako Pure Chemical Industries, Ltd., reagent grade 1) as a solvent, and silica 1 (incorporated as a inorganic particle) Tokuyama, Fine seal X-45, average agglomerated particle size 4.0-5.0 μm) and silica 2 (Tokuyama, Fine seal X-30, average agglomerated particle size 2.5-4.0 μm), As a flocculant, a mixture of hexaglyceryl monolaurate (manufactured by Nikko Chemicals Co., Ltd., Hexaglyn 1-L) was used, and the weight ratio of PVDF: hexyl benzoate: silica 1: silica 2: hexaglyceryl monolaurate was 20: 60: 5: A mixed solution was prepared so as to have a ratio of 15:20. The composition of this mixed solution is shown in Table 1.

  The above mixed solution was heated and kneaded (temperature 240 ° C.) in a twin-screw kneading extruder, and the extruded strand was passed through a pelletizer to form chips. This chip was extruded using an extruder (230 ° C.) equipped with a nozzle having a double ring structure 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 obtained hollow fiber was immersed in methanol at 50 ° C. for 60 minutes twice to extract and remove the solvent (hexyl benzoate), the flocculant (hexaglyceryl monolaurate), and the injection solution (tetraethylene glycol). did.

  The hollow fiber material thus obtained was immersed in a 3N sodium hydroxide aqueous solution at 20 ° C. for 20 minutes to extract and remove inorganic particles (Fine Seal X-45 and Fine Seal X-30), and then washed with water. A hollow fiber membrane was obtained through a drying process. The manufactured hollow fiber membrane was tested according to the following method. The test results are shown in Tables 2 and 3.

Example 3
A hollow fiber membrane was obtained in the same manner as in Example 1 except that a mixed solution having the same composition as in Example 2 was used. Table 1 shows the composition of the mixed solution used for the production of this hollow fiber membrane, and Tables 2 and 3 show the test results.

Example 4
A mixture of dioctyl phthalate (manufactured by Wako Pure Chemical Industries, Ltd., reagent grade 1) and dibutyl phthalate (manufactured by Wako Pure Chemical Industries, Ltd., reagent grade 1) was used as the solvent, and silica (Nippon Aerosil Co., Ltd., R-) was used as the inorganic particles. 972) and PVDF: dioctyl phthalate: dibutyl phthalate: silica: hexaglyceryl monolaurate in a weight ratio of 20: 48: 12: 20: 20 A yarn membrane was obtained. Table 1 shows the composition of the mixed solution used for the production of this hollow fiber membrane, and Tables 2 and 3 show the test results.

Example 5
A vinylidene fluoride-hexafluoropropylene copolymer (hereinafter sometimes abbreviated as PVDF-HFP) (SOLEF21216, manufactured by Solvay Advanced Polymer Co., Ltd.) is used as a vinylidene fluoride resin, and propyl salicylate (Wako Pure) A hollow fiber membrane was obtained in the same manner as in Example 1 except that Yakuhin Co., Ltd., reagent grade 1) was used and the heating and kneading temperature was 220 ° C. and the extruder head temperature was 200 ° C. Table 1 shows the composition of the mixed solution used for the production of this hollow fiber membrane, and Tables 2 and 3 show the test results.

Comparative Example 1
PVDF (made by Solvay Advanced Polymers Co., Ltd., SOLEF6010) as a vinylidene fluoride resin, hexyl benzoate (made by Wako Pure Chemical Industries, Ltd., reagent grade 1) as a solvent, and silica (made by Tokuyama Co., Ltd., Fine) as inorganic particles The seal X-45, the average aggregated particle diameter of 4.0 to 5.0 μm) is hollow in the same manner as in Example 1 except that the mixture is prepared so that the weight ratio is 20:80:10. A yarn membrane was obtained. Table 1 shows the composition of the mixed solution used for the production of this hollow fiber membrane, and Tables 2 and 3 show the test results. As a result of the test, when no flocculant was added, the pore diameter was on the order of submicrons, and high water permeability was not obtained.

4 is an electron micrograph showing a cross section of a vinylidene fluoride resin porous membrane obtained in Example 2. FIG.

Claims (4)

Affinity with vinylidene fluoride resin, a predetermined solvent that is compatible with the vinylidene fluoride resin in a specific temperature range, and that can cause phase separation by temperature change, inorganic particles, and inorganic particles A coagulant having a property to be kneaded at a temperature at which the vinylidene fluoride resin and the solvent are compatible with each other, and then cooling to thermally induce phase separation and the vinylidene fluoride resin A porous film is produced by causing precipitation and then performing a stretching process in the presence of inorganic particles, and then extracting the solvent, inorganic particles, and aggregating agent . An average pore diameter of 3 μm or more is formed on the film surface. It has circular or elliptical micropores, and the porosity, which is the volume ratio of the space in the porous membrane, is within a range of 50% to 90%, and the pure water permeation rate is 30000 L / m ² / hr / 98 kPa or more, Fractionated particle size is 1 μm Method for producing a porous membrane of vinylidene fluoride resin, characterized in that to obtain a porous membrane of vinylidene fluoride resin above. 2. The method for producing a vinylidene fluoride resin porous membrane according to claim 1 , wherein the solvent has a weight loss rate of 10% or less in 30 seconds at (thermally induced phase separation temperature + 30) ° C. 3 . The method for producing a vinylidene fluoride resin porous membrane according to claim 1 , wherein the flocculant is a compound having a hydrophilic group. The method for producing a vinylidene fluoride resin porous membrane according to any one of claims 1 to 3 , wherein the porous membrane is a hollow fiber membrane.