JP2010075851A - Porous film and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a porous film suitable for liquid separation which has high physical durability against a liquid to be treated and high permeability even when it is used in an activated sludge vessel for solid-liquid separation. <P>SOLUTION: The porous film is characterized in that the porous film has a single layer of a porous resin layer on the surface of a porous substrate, that the porous resin layer includes a spherical member of an average diameter of 0.5 to 10 μm, that at least one of the pores of an average pore diameter of 0.05 to 5 μm inclusive is formed on the surface of the spherical member and that the average diameter of at least one side of the porous film is 0.05 to 5 μm inclusive. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a porous membrane suitable for water treatment such as drinking water production, water purification treatment, wastewater treatment, and solid-liquid separation treatment in the food industry. In particular, the present invention relates to a porous membrane which is immersed in an activated sludge tank and suitably used for solid-liquid separation in wastewater treatment.

  In recent years, porous membranes in the form of flat membranes and hollow fiber membranes that have come to be used for purification of sewage and wastewater include membrane separation elements in which membranes are arranged, and membrane separation modules in which a plurality of such elements are arranged It is used for water purification treatment as a device.

  There are various types and forms of membranes to be disposed in such membrane separation elements, but a polyvinylidene fluoride resin solution containing a surfactant is applied to the surface of a substrate such as a woven or non-woven fabric. Or after impregnating the base material, the polyvinylidene fluoride resin is solidified, and a porous polyvinylidene fluoride resin layer is formed on the surface of the base material layer. A composite separation membrane is known (Patent Document 1).

  In this composite separation membrane, the porous polyvinylidene fluoride resin layer acts as a separation functional layer, but in such a flat membrane, an effective membrane per unit volume compared to other forms of separation membrane, for example, a hollow fiber membrane. Since it is difficult to increase the area, it is required to increase the water permeation amount while maintaining the pore diameter according to the filtration target. However, if the porosity is increased to increase the water permeation amount, the pore size becomes too large or the surface cracks and the blocking rate decreases. On the other hand, if the pores are made small in order to increase the blocking rate, the water permeability will be lowered this time. That is, the improvement in the rejection rate and the improvement in water permeability are in a contradictory relationship, and it is difficult to balance the two.

  In addition, in the separation membrane for sewage wastewater, during the membrane filtration operation, inorganic substances such as sand, sludge, and other solids in the treated water violently collide with the membrane surface, or oxygen to the activated sludge If bubbles or air bubbles are violently colliding with the membrane surface due to aeration operations to prevent supply or clogging, membrane damage and liquid leakage are likely to occur if significant impact or vibration is applied to the membrane surface. It is required to have a sufficiently strong film strength.

  For example, in Patent Document 2, a polymer solvent obtained by dissolving a polyvinylidene fluoride resin in a good solvent is extruded from a die at a temperature considerably lower than the melting point of the polyvinylidene fluoride resin or cast on a glass plate. Then, a wet solution method is disclosed in which an asymmetric porous structure is formed by contact with a liquid containing a non-solvent of polyvinylidene fluoride resin by non-solvent induced phase separation. However, in the wet solution method in which an asymmetric porous structure is formed by non-solvent-induced phase separation by contacting a liquid containing a non-solvent of polyvinylidene fluoride resin, it is difficult to cause phase separation uniformly in the film thickness direction. , There is a problem that the physical strength is not sufficient because of the asymmetric film containing macrovoids.

  Patent Document 3 discloses a porous film in which the porous film has both a three-dimensional network structure and a spherical structure. In this porous membrane, the three-dimensional network structure part is a separation functional layer having an asymmetric porous structure formed by non-solvent induced phase separation, and the spherical structure part has a symmetric porous structure formed by a thermally induced phase separation method. Although it is a support part structure that supports the separation functional layer, the three-dimensional network structure part has an asymmetric porous structure, so that there is a problem that the physical strength is not sufficient.

  Further, as disclosed in Patent Document 4, inorganic fine particles and an organic liquid are kneaded with polyvinylidene fluoride resin, and the polyvinylidene fluoride resin is extruded from a die at a temperature equal to or higher than the melting point or pressed with a press. For example, a melt extraction method is disclosed in which a porous structure is formed by cooling and solidifying after molding, and then extracting an organic liquid and inorganic fine particles. In the case of the melt extraction method, it is easy to control the porosity, and macrovoids are not formed, and a relatively homogeneous and high strength film can be obtained. However, if the dispersibility of the inorganic fine particles is poor, defects such as pinholes are generated. there is a possibility. Furthermore, the melt extraction method has the disadvantage that the production cost is extremely high.

Patent Document 5 discloses a composite membrane in which an ultrafiltration membrane is further placed on a porous membrane. This composite membrane is treated with a glycerin alcohol solution, etc., dried, coated with a polymer solution, and coagulated with a non-solvent to improve its ability to bind to a porous membrane as a base material. Thus, since the ultrafiltration membrane is formed, the process is complicated and the manufacturing cost is extremely high.
JP 2003-135939 A European Patent No. 0037836 International Publication No. 03/106545 Pamphlet US Pat. No. 5,022,990 European Patent Application No. 0245863

  The present invention is suitable for liquid separation that has high physical durability against a liquid to be treated such as activated sludge and can achieve high water permeability even when used for solid-liquid separation in an activated sludge tank. The main purpose is to provide a porous membrane.

In order to achieve the above object, the present invention comprises the configurations described in the following (1) to (7).
(1) A porous film having a single porous resin layer on the surface of a porous substrate, the porous resin layer comprising a spherical body having an average diameter of 0.5 μm to 10 μm, At least one pore having an average pore diameter of 0.05 μm or more and 5 μm or less is formed on the surface of the spherical body, and the average pore diameter of the surface of at least one side of the porous membrane is 0.05 μm or more and 5 μm or less. A porous membrane characterized by being.
(2) The porous membrane according to (1), wherein the porous resin layer is made of a thermoplastic resin.
(3) The porous film according to (2), wherein the thermoplastic resin is a polyvinylidene fluoride resin.
(4) The rejection rate (%) of latex fine particles having an average particle size of 0.09 μm before and after the sandfall wear test was A (%) before the sandfall wear test, and after the sandfall wear test. When the rejection rate is B (%), the following inequality A−B ≦ 50 (%)
The porous film according to any one of (1) to (3), which satisfies the following relationship:
(5) The porous membrane according to any one of (1) to (4), which is a flat membrane.
(6) 20 to 60% by weight of a polyvinylidene fluoride resin, 1 to 30% by weight of a hydrophilic porogen and a poor solvent for the polyvinylidene fluoride resin, and the temperature is in the range of 80 to 175 ° C. The porous material according to any one of (1) to (5), which is obtained by bringing a polyvinylidene fluoride resin solution into contact with the surface of a porous substrate and then immersing it in a coagulation bath. A method for producing a membrane.
(7) The liquid in the coagulation bath has a temperature in the range of 0 to 50 ° C., and contains 60 to 100% by weight of a poor solvent for the polyvinylidene fluoride resin. The manufacturing method of the porous membrane of description.

  According to the present invention, a porous membrane suitable for liquid separation can be obtained which has high physical durability even for liquids to be treated such as activated sludge liquid and can achieve high water permeability. Accordingly, the durability of the porous membrane is improved, and long-term operation is facilitated.

  The porous membrane according to the present invention is a porous membrane having a single porous resin layer on the surface of a porous substrate, and the porous resin layer has an average diameter of 0.5 μm or more and 10 μm or less. The spherical body has at least one pore having an average pore diameter of 0.05 μm or more and 5 μm or less on the surface of the spherical body, and the average pore diameter of the surface of at least one side of the porous membrane is 0. A porous film characterized by having a thickness of not less than 05 μm and not more than 5 μm.

  Here, the spherical body means a structure having a structure in which a large number of spherical or substantially spherical solid components are connected directly or via a streaky solid component. The spherical body is presumed to consist exclusively of spherulites. The spherulite is a crystal in which a thermoplastic resin is precipitated and solidified into a spherical shape when a thermoplastic resin solution is phase-separated to form a porous structure.

  The average diameter of the spherical body needs to be not less than 0.5 μm and not more than 10 μm. The diameter of the spherical body is 10 or more, preferably 20 or more, by taking a photograph using a scanning electron microscope (SEM) or the like at a magnification at which the spherical body can clearly confirm the surface or cross section of the porous membrane. It can be obtained by measuring the diameter of the spherical body and averaging the number. It is also possible to preferably employ an average of equivalent circle diameters as an average diameter by analysis with a photo resolution processor.

  At least one or more pores need to be formed on the surface of the spherical body. Further, the average pore diameter of the pores needs to be 0.05 μm or more and 5 μm or less. Here, the average pore diameter of the fine pores on the surface of the spherical body is measured with a scanning electron microscope (SEM) or the like at a magnification at which the fine pores on the spherical body surface can be clearly confirmed on the surface or cross section of the porous membrane. The diameter can be obtained by measuring the diameter of 10 or more, preferably 20 or more arbitrary pores and averaging the number. It is also possible to preferably employ an average of equivalent circular hole diameters as an average hole diameter by analyzing with a photographic resolution processing apparatus.

  The porous membrane preferably has a blocking rate of 90% or more of fine particles having an average particle size of about 0.09 μm or less. When the fine particle rejection rate is 90% or more, long-term operation can be performed without causing clogging or leakage due to bacterial cells or sludge, or an increase in filtration differential pressure.

This fine particle blocking rate is set by using a porous membrane in a stirring cell (VHP-43K manufactured by Advantech Co., Ltd.), an evaluation pressure of 9.8 kPa, a stirring speed of 600 rpm, and a reverse osmosis membrane (SUL- manufactured by Toray Industries, Inc.). An evaluation stock solution in which polystyrene latex fine particles (nominal pore size 0.083 μm manufactured by Celadin Co., Ltd.) are dispersed as fine particles having an average particle size of 0.09 μm or less in filtered water according to G10) to a concentration of 25 ppm is filtered and evaluated. About the undiluted | stock solution and the obtained filtrate permeation | transmission liquid, the light absorbency of the ultraviolet-ray with a wavelength of 250 nm can be measured, and fine particle blocking rate can be calculated | required by following Formula.
Fine particle blocking rate = [(absorbance of raw water−absorbance of permeate) / absorbance of stock solution] × 100
Here, a spectrophotometer (U-3200 manufactured by Hitachi, Ltd.) can be used for absorbance measurement.

Further, the porous membrane of the present invention measures the rejection rate of latex fine particles having an average particle size of 0.09 μm before and after the sandfall wear test, and the rejection rate before the sandfall wear test is A (%). When the rejection after the sand type abrasion test is B (%), it is preferable to satisfy the following inequality relationship.
A-B ≦ 50 (%)
If the difference between A and B is greater than 50%, the cells and sludge will leak, the cells will clog with sludge, the filtration differential pressure will increase, and the life will be extremely short . Usually, a range of AB ≦ 10 is more preferable.

  Here, the abrasion test of the porous membrane was carried out by using a sand drop type abrasion tester (ASTM D673 # 80, manufactured by Toyo Seiki Seisakusho Co., Ltd.) on the pedestal held at an angle of 45 ° with the horizontal plane. Can be performed by a wear test in which SiC (45 #) having a height of 650 mm to 400 g is dropped from the sample.

  Moreover, the value of the blocking rate (%) of latex fine particles having an average particle size of 0.09 μm can be determined by measuring in the same manner as described above.

Furthermore, the porous membrane of the present invention preferably has a pure water permeability coefficient of 1 × 10 ⁻⁹ m ³ / m ² / Pa / s or more. When this pure water permeability coefficient is less than 1 × 10 ⁻⁹ m ³ / m ² / Pa / s, it is necessary to operate at a high pressure because the water permeability of the membrane is inferior. There is. Here, the pure water permeability coefficient is obtained by filtering drinking water with a dialysis membrane (Filtriser (registered trademark) B2-1.5H, manufactured by Toray Industries, Inc.) as raw water, at a temperature of 25 ° C. and a head pressure of 1 m. It can be measured by membrane filtration under. The pure water permeability coefficient may be obtained by converting a value obtained by applying pressure or suction with a pump or the like. The water temperature may also be converted by the viscosity of the evaluation liquid.

  The resin used for the porous resin layer according to the present invention is not particularly limited, but is preferably a thermoplastic resin because a spherical body can be easily formed.

  Here, the thermoplastic resin refers to a resin that is made of a chain polymer and that exhibits a property of being deformed / flowed by an external force when heated. Examples of thermoplastic resins include polyethylene, polypropylene, acrylic resin, polyacrylonitrile, acrylonitrile-butadiene-styrene (ABS resin), polystyrene, acrylonitrile-styrene (AS resin), vinyl chloride resin, polyethylene terephthalate, polyamide, polyacetal, Examples include polycarbonate, modified polyphenylene ether, polyphenylene sulfide, polyvinylidene fluoride, polyamideimide, polyetherimide, polysulfone, polyethersulfone, and mixtures and copolymers thereof. Any resin miscible with these may be mixed.

  As the thermoplastic resin used for the porous resin layer according to the present invention, one selected from polyethylene resin, polypropylene resin and polyvinylidene fluoride resin is particularly preferable because of its high chemical resistance.

  Of these, polyvinylidene fluoride resins and those containing them as the main component are most preferred. The polyvinylidene fluoride resin is a resin containing a vinylidene fluoride homopolymer and / or a vinylidene fluoride copolymer. A plurality of types of vinylidene fluoride copolymers may be contained. 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, Examples thereof include a copolymer of at least one fluorine-based monomer selected from vinyl fluoride, tetrafluoroethylene, propylene hexafluoride, and ethylene trifluoride chloride and vinylidene fluoride. In some cases, a monomer such as ethylene other than the fluorine-based monomer may be included.

  The weight average molecular weight of the polyvinylidene fluoride resin may be appropriately selected depending on the required strength and water permeability of the porous membrane, but is preferably in the range of 50,000 to 1,000,000. As the porous membrane, when considering the film-forming property to a flat membrane, the range of 100,000 to 600,000 is preferable, and the range of 250,000 to 450,000 is more preferable. When the weight average molecular weight is larger than this range, the viscosity of the resin solution becomes too high. When the weight average molecular weight is smaller than this range, the viscosity of the resin solution becomes too low, and it becomes difficult to form a porous film in any case. .

  In the present invention, the poor solvent for the polyvinylidene fluoride resin means that the polyvinylidene fluoride resin cannot be dissolved at 5% by weight or more at a low temperature of less than 60 ° C., but the melting point of the polyvinylidene fluoride resin at 60 ° C. or more and For example, when the polyvinylidene fluoride resin is composed of a vinylidene fluoride homopolymer alone, it is a solvent that can be dissolved by 5% by weight or more in a high temperature region of about 178 ° C. or less. A solvent capable of dissolving 5% by weight or more of a polyvinylidene fluoride resin at a low temperature of less than 60 ° C. with respect to a poor solvent is a good solvent, the polyvinylidene fluoride resin up to the melting point of the polyvinylidene fluoride resin or the boiling point of the liquid A solvent that does not dissolve or swell is defined as a non-solvent.

  Examples of the poor solvent include cyclohexanone, isophorone, γ-butyrolactone, methyl isoamyl ketone, dimethyl phthalate, propylene glycol methyl ether, propylene carbonate, diacetone alcohol, glycerol triacetate, etc., medium chain length alkyl ketone, ester, glycol ester And organic carbonates. Examples of good solvents include N-methyl-2-pyrrolidone, dimethyl sulfoxide, N, N-dimethylacetamide, N, N-dimethylformamide, methyl ethyl ketone, acetone, tetrahydrofuran, tetramethylurea, lower alkyl ketones such as trimethyl phosphate, Examples include esters and amides. Non-solvents include water, hexane, pentane, benzene, toluene, methanol, ethanol, carbon tetrachloride, o-dichlorobenzene, trichloroethylene, low molecular weight polyethylene glycol and other aliphatic hydrocarbons, aromatic hydrocarbons, Examples include chlorinated hydrocarbons and other chlorinated organic liquids.

  The hydrophilic porosifying agent according to the present invention is not limited at all as long as it has hydrophilicity and has the property of promoting the porous formation of the porous resin layer, preferably a hydrophilic organic substance. These are high molecular weight or low molecular weight substances. Specifically, water-soluble polymers such as polyethylene glycol, polypropylene glycol, polyvinyl alcohol, polyvinyl acetate, polyvinyl pyrrolidone, polyacrylic acid, ester bodies of polyhydric alcohols such as sorbitan fatty acid esters (mono, triesters, etc.) Ethylene oxide low mole adduct of sorbitan fatty acid ester, ethylene oxide low mole adduct of nonylphenol, pluronic type ethylene oxide low mole adduct, etc., polyoxyethylene alkyl ester, alkylamine salt, polyacrylic acid Surfactants such as soda, polyhydric alcohols such as glycerin, and glycols such as tetraethylene glycol and triethylene glycol. These may be used alone or in a mixture of two or more. These hydrophilic porosifiers preferably have a weight average molecular weight of 50,000 or less, more preferably 30,000 or less. Those having a higher molecular weight than this are not preferable because they are poorly extractable into the liquid in the coagulation bath and are difficult to uniformly dissolve in the polyvinylidene fluoride resin solution. This hydrophilic porous agent is considered to remain in the porous resin for a relatively long time compared to the solvent when the solvent is extracted in the liquid of the coagulation bath and structural aggregation occurs.

  Since the hydrophilic porous agent is extracted after the structure aggregation accompanying the solvent extraction becomes gentle, the obtained porous resin layer has high porosity. The structure obtained depends on the type, molecular weight, added amount, etc. of the hydrophilic porogen, but in the present invention, a porous resin layer composed of spherical bodies having an average diameter of 0.5 μm or more and 10 μm or less is obtained. Here, it has a structure in which spherical bodies are connected, or pores are distributed at the boundaries and gaps between the spherical bodies, or the gaps between the spherical bodies themselves become large, or the spherical bodies themselves have a fineness of 5 μm or less. A large number of pores are distributed or a combination of these factors makes the porous membrane of the present invention highly porous and highly permeable.

  A porous film having such a structure can have higher physical strength than a porous film having a network structure obtained by a conventional wet solution method.

  In the production method of the present invention, first, a polyvinylidene fluoride resin (hereinafter also simply referred to as a polymer) is contained in a concentration range of 20 to 60% by weight, preferably 30 to 50% by weight. It contains a poor solvent for the polyvinylidene fluoride resin in a concentration range of 1 wt%, preferably 1-20 wt%, more preferably 1-10 wt%, and the temperature is 80-175 ° C, preferably 100-150 ° C. The polyvinylidene fluoride resin solution dissolved in the following temperature range is used.

  If the polymer concentration of the polyvinylidene fluoride resin is increased, a porous film having high strength can be obtained. However, if the polymer concentration is too high, the porosity of the produced porous film is decreased, and the water permeability is deteriorated. Moreover, if the viscosity of the prepared polymer solution is not within an appropriate range, it is difficult to form a flat film. In the preparation of the polymer solution, a plurality of poor solvents may be used. In addition, a good solvent or a non-solvent may be mixed in the poor solvent as long as the solubility of the polymer is not hindered. In the present invention, high strength characteristics are expressed by increasing the polymer concentration to 20 to 60% by weight as described above.

  In the present invention, the average pore size on the surface of the spherical body can be controlled by adding a hydrophilic porous agent to the polyvinylidene fluoride resin solution so that when the spherical particles form crystals, the droplets of the hydrophilic porous agent are formed. When it is left inside the sphere and is extracted in the liquid of the coagulation bath and structural aggregation occurs, it remains in the porous resin for a relatively long time compared to the solvent, thereby forming pores on the surface of the sphere and making it hydrophilic. Since the average pore size is considered to depend on the type, molecular weight, added amount, etc. of the porous porous agent, the average pore size is controlled by the type, molecular weight, added amount, etc.

  If the polyvinylidene fluoride resin solution does not contain a hydrophilic porogen or is less than 1% by weight, the resulting porous membrane does not have sufficient porosity, making it difficult to obtain water permeability. On the other hand, if it contains more than 30% by weight of the hydrophilic porogen, it cannot be uniformly dissolved in the polyvinylidene fluoride resin solution and cannot be formed into a flat film. Further, streaks and pinhole-like defects are given to the porous membrane, the separation characteristics are lowered, and the strength is also weakened. In the present invention, pores are formed on the surface of the spherical body by setting the hydrophilic porogen concentration in the polyvinylidene fluoride resin solution to 1 to 30% by weight as described above.

  Further, in the production method of the present invention, by using a poor solvent, a spherical film structure presumed to be composed of spherical crystals is preferentially formed over a network structure obtained by a wet solution method. When the solvent system is not used, or when a solvent other than the poor solvent is added too much to the poor solvent and the solvent system deviates from the solubility characteristics as the poor solvent, the following problems occur. That is, when the solvent or solvent system is a good solvent or has good solvent characteristics, the ability of the polyvinylidene fluoride resin solution to dissolve in the polymer is increased even at low temperatures. Thus, the spherical body separated by the thermal phase is difficult to solidify and precipitate, and the spherical sphere grows larger. As a result, there are few films, and the spherical bodies are closely connected to each other, and the porous film is weak in strength. On the other hand, when the solvent or the solvent system is a non-solvent or has non-solvent characteristics, the polymer is difficult to be uniformly dissolved in the solvent or the solvent system, which is disadvantageous in terms of film formation stability.

  The content of the poor solvent of the polyvinylidene fluoride resin used in this case is preferably in the range of 80 to 100% by weight, more preferably 90 to 100% by weight.

  Furthermore, when preparing a polyvinylidene fluoride resin solution, an inorganic substance other than the above is added to the polyvinylidene fluoride resin solution in order to control the functional layer formed on the surface of the porous film and the pores of the spherical body. Etc. may be added. For example, examples of the inorganic substance include lithium chloride, calcium chloride, silica fine particles, titanium oxide fine particles, and activated carbon fine particles.

  In the method for producing a porous membrane of the present invention, after preparing a polyvinylidene fluoride resin solution, the polyvinylidene fluoride resin solution is brought into contact with the surface of the porous substrate and immersed in a coagulation bath. To form the desired shape.

  For example, a polyvinylidene fluoride resin solution is discharged from a base for a flat membrane and applied onto a porous substrate, and after passing through a dry part of a predetermined length as necessary, is guided to a coagulation bath. Solidify. When using a die, it is preferable to filter the polyvinylidene fluoride resin solution with a 5-100 μm stainless steel filter or the like before discharging from the die. The size of the die to be used may be appropriately selected depending on the size of the flat membrane to be produced and the membrane structure, but the slit width is preferably in the range of 0.1 mm to 10 mm.

  Further, the temperature of the die, that is, the film forming temperature may be in the range of 80 to 175 ° C., preferably 100 to 170 ° C., similarly to the melting temperature, and the die temperature and the melting temperature may be different. Regarding the melting temperature, it is also possible to preferably employ a temperature higher than the die temperature from the viewpoint that the melting is performed uniformly in a short time.

  The thickness of the porous membrane is preferably 10 μm to 1 mm, more preferably 30 μm to 500 μm. The porous film is formed by providing a single porous resin layer on the surface of the porous substrate, but a layer in which the porous substrate and the porous resin layer overlap may be present. Examples of porous substrates include polyester, nylon fibers, polyurethane fibers, acrylic fibers, rayon fibers, woven fabrics made of organic fibers such as cotton and silk, knitted fabrics and nonwoven fabrics, glass fibers, metal fibers, etc. Porous substrates such as woven fabrics and knitted fabrics made of these inorganic fibers can be used. Among these, a porous substrate made of organic fibers is particularly preferable from the viewpoint of stretchability and cost.

  As described above, the polyvinylidene fluoride resin solution applied on the porous substrate enters the coagulation bath and coagulates to form a porous resin layer.

  Further, the functional layer on the membrane surface contains a non-solvent such as water in the liquid in the coagulation bath, so that non-solvent induced separation occurs and the functional layer is formed on the membrane surface.

  The liquid in the coagulation bath used here has a temperature of preferably 0 to 50 ° C., more preferably 5 to 30 ° C., and a concentration of the poor solvent of the polyvinylidene fluoride resin is preferably 60 to 100% by weight, More preferably, it is in the range of 70 to 90% by weight, and the concentration of the non-solvent of the polyvinylidene fluoride resin is preferably 1 to 35% by weight, more preferably 5 to 30% by weight. When the coagulation bath is in this temperature range, the cooling coagulation that tends to develop a spherical shape becomes dominant in the coagulation process. A plurality of poor solvents may be used as a mixture. In addition, a solvent other than the poor solvent may be mixed with the poor solvent as long as the concentration range is not deviated. Preferably, a non-solvent is mixed, but depending on the case, a good solvent may be mixed or a hydrophilizing porous agent may be mixed.

  By giving a large temperature difference from the dissolution temperature of the polyvinylidene fluoride resin solution in the coagulation bath and rapidly cooling, the spheres become minute, and at the same time, there are moderately aggregates of polymer molecules between the spheres. A film structure having high strength characteristics is expressed.

  Further, by incorporating a non-solvent having a high concentration to some extent in the liquid in the coagulation bath, a functional layer can be formed on the membrane surface by non-solvent induced phase separation.

  When a non-solvent such as water is contained at a high concentration in the liquid in the coagulation bath, a very dense functional layer is formed on the membrane surface, and the water permeation performance is not exhibited.

  The form of the coagulation bath is not particularly limited as long as the liquid in the coagulation bath and the polyvinylidene fluoride resin applied to the porous substrate are sufficiently in contact and can be cooled and coagulated. However, it may literally be in the form of a liquid tank in which the cooling and solidification liquid is stored, and the liquid tank may be circulated or updated with a liquid whose temperature and composition are adjusted as necessary. The liquid tank form is the most suitable, but depending on the case, the liquid may flow in the pipe, or the cooling liquid is sprayed onto the polyvinylidene fluoride resin running in the air. Form may be sufficient.

  In addition, as another approach of high water permeability expression, polyvinylidene fluoride resin as a liquid in a coagulation bath has a temperature of 0 to 50 ° C, preferably 3 to 30 ° C, and a concentration of 1 to 100. A method of coagulating using a liquid containing a hydrophilic porosifying agent in the range of wt%, preferably 1 to 50 wt% is also preferably employed. As the hydrophilic porogen, it is desirable to use one or more of the same types as those contained in the polyvinylidene fluoride resin solution, but other hydrophilic porogens may be used. Moreover, as long as it does not deviate from the above-mentioned concentration range, a solvent other than the hydrophilic porous agent may be mixed with the hydrophilic porous agent. A non-solvent or a poor solvent is preferably mixed, but a good solvent may be mixed in some cases. By containing a hydrophilic porosifying agent in the cooling bath, the concentration of the porous membrane discharged compared to the solvent extraction rate of the polyvinylidene fluoride resin solution when the solvent is extracted and solidified and precipitated in the cooling bath and the coagulation bath. The gradient reduces the extraction rate of the hydrophilic porogen. As a result, the hydrophilic porosifying agent remains in the structure for a longer period of time even when the structure contracts due to solvent extraction, and a highly porous film with high porosity is developed.

  Furthermore, in the porous film in which the porous resin layer is formed on the porous substrate, a part of the polyvinylidene fluoride resin constituting the porous resin layer enters the porous substrate, and the porous resin layer It is preferable that a layer in which the resin and the base material constituting the material are mixed is interposed between the porous resin layer and the porous base material. By inserting the polyvinylidene fluoride resin inside the substrate surface side, the porous resin layer is firmly fixed to the porous substrate by the so-called anchor effect, and the porous resin layer is prevented from peeling off from the porous substrate. become able to. The porous resin layer may exist on one side with respect to the porous base material, or may exist on both sides. The porous resin layer may have a symmetric structure or an asymmetric structure with respect to the porous substrate. Further, when the porous resin layer is present on both sides with respect to the porous substrate, the porous resin layers on both sides may be continuous through the porous substrate, or discontinuous It does not matter.

  Next, a method for producing a porous membrane used in the present invention will be described. This porous membrane is obtained by, for example, bringing a polyvinylidene fluoride resin solution containing a polyvinylidene fluoride resin and a hydrophilic porosizing agent into contact with one surface or both surfaces of a porous substrate, and removing a poor solvent and a non-solvent. It can be produced by coagulating in a coagulating bath liquid to form a porous resin layer. At this time, the means for bringing the polyvinylidene fluoride resin solution into contact with the surface of the porous substrate may be application of a polyvinylidene fluoride resin solution, or a method of immersing the porous substrate in the polyvinylidene fluoride resin solution But you can. When the polyvinylidene fluoride resin solution is applied to the porous substrate, it may be applied to one side or both sides of the porous substrate. A method of joining both layers after forming only the porous resin layer separately from the porous substrate may be used.

  In coagulating the polyvinylidene fluoride resin solution, a method may be used in which only the polyvinylidene fluoride resin solution film on the porous substrate is brought into contact with the coagulation liquid, or based on the polyvinylidene fluoride resin solution film. A method of immersing the whole material in a coagulating liquid may be used. In order to bring only the polyvinylidene fluoride resin solution film into contact with the coagulation liquid, for example, a method of bringing the polyvinylidene fluoride resin solution film formed on the substrate into contact with the surface of the coagulation bath such that A porous substrate having a polyvinylidene fluoride resin solution coating by contacting a porous substrate on a smooth plate such as a glass plate or a metal plate so that the coagulation bath does not enter the porous substrate side. There is a method of immersing the substrate together with the plate in a coagulation bath. In the latter method, the film of the polyvinylidene fluoride resin solution may be formed after the porous substrate is attached to the plate, or after the film of the polyvinylidene fluoride resin solution is formed on the substrate, You can paste it.

  In addition to the above-mentioned polyvinylidene fluoride resin, etc., a pore opening agent or a solvent for dissolving them may be added to the polyvinylidene fluoride resin solution, if necessary.

  The porous membrane of the present invention produced as described above is used, for example, as a separation membrane for a plate-and-frame type membrane module. The solid-liquid separator is immersed in a treatment tank containing a liquid to be treated such as activated sludge, such as an activated sludge tank, and is provided with pressure means on the processing stock solution side or suction means on the permeate side by a pump. Membrane filtration is performed. Of course, you may perform membrane filtration by a water level difference without providing a pump. In order to obtain the membrane cleaning effect, the solid-liquid separation device may include means for allowing the liquid to be processed to flow in parallel to the membrane surface, such as disposing an aeration device below the membrane.

The present invention will be described below with reference to specific examples, but the present invention is not limited to these examples. In addition, the film performance evaluation of the obtained porous film was performed by the following method.
(1) Average diameter of spheres Photographed with a scanning electron microscope (SEM) at a magnification at which the spheres can be clearly confirmed on the surface or cross section of the porous membrane, and measured the diameter of 20 arbitrary spheres Then, the number average was obtained.
(2) Average pore diameter of the pores on the surface of the spherical body Take a photograph with a scanning electron microscope (SEM) at a magnification that allows the pores on the surface of the spherical body to be clearly confirmed on the surface or cross section of the porous membrane. The diameter of each of the individual pores was measured and obtained by number averaging.
(3) Polystyrene latex fine particle rejection rate A porous membrane was set in a stirring type cell (VHP-43K manufactured by Advantech Co., Ltd.), and a reverse osmosis membrane (manufactured by Toray Industries, Inc.) at an evaluation pressure of 9.8 kPa and a stirring speed of 600 rpm. An evaluation stock solution in which polystyrene latex fine particles (Nominal pore size 0.083 μm manufactured by Celadin Co., Ltd.) are dispersed as fine particles having an average particle size of 0.09 μm or less in filtered water by SUL-G10) to a concentration of 25 ppm is filtered. The absorbance of ultraviolet rays having a wavelength of 250 nm was measured for the evaluation stock solution and the obtained filtrate permeate, and the fine particle blocking rate was determined by the following formula.
Fine particle blocking rate = [(absorbance of raw water−absorbance of permeate) / absorbance of stock solution] × 100
Here, a spectrophotometer (U-3200, manufactured by Hitachi, Ltd.) was used for the absorbance measurement.
(4) Drop type wear test The porous resin layer of the porous membrane sample appears on the upper surface of the pedestal held at a 45 ° angle with the horizontal surface by the sand fall type wear test device (ASTM D673 # 80 manufactured by Toyo Seiki Seisakusho). In this manner, SiC (45 #) having a height of 650 mm to 400 g is dropped from the sample, and the rejection rate B after the sandfall wear test is calculated from the rejection rate A (%) before the sandfall wear test. (%) Was subtracted.
(5) Pure water permeability coefficient The raw water is obtained by filtering drinking water with a dialysis membrane (Filtrizer (registered trademark) B2-1.5H, manufactured by Toray Industries, Inc.) under conditions of a temperature of 25 ° C. and a head pressure of 1 m. Measured by membrane filtration. The pure water permeability coefficient was obtained by converting a value obtained by applying pressure or suction with a pump or the like.
Example 1
Polyvinylidene fluoride (PVDF / Kureha Chemical Co., Ltd., KF # 1300) was used as a resin component for the film-forming stock solution. Further, polyethylene glycol (average molecular weight 20,000) was used as the hydrophilic porogen, and γ-butyrolactone was used as the poor solvent. These were sufficiently stirred at a temperature of 160 ° C. to prepare a polyvinylidene fluoride resin solution having the following composition.

Polyvinylidene fluoride (PVDF): 30.0% by weight
γ-butyrolactone: 65.0% by weight
Polyethylene glycol: 5.0% by weight
Next, after filtering the polyvinylidene fluoride resin solution with a 50 μm stainless steel filter or the like, the density is 0.42 g / cm ³ so that the thickness becomes 100 μm from the flat film die having a slit width of 1 mm adjusted to 160 ° C. And coated on a non-woven polyester fiber having a thickness of 160 μm, and immediately immersed in a coagulating solution at 15 ° C. containing 80% by weight of a poor solvent γ-butyrolactone and 20% by weight of a non-solvent water for 5 minutes. A porous membrane having a layer formed thereon was produced.

  A porous resin layer in which a polyvinylidene fluoride resin solution was applied to a porous substrate was immersed in hot water at 95 ° C. for 2 minutes to wash away γ-butyrolactone and polyethylene glycol to obtain a porous film.

As a result of evaluating the membrane performance of the obtained porous membrane, the average pore diameter of the functional layer on the surface of the porous membrane was 0.4 μm, the average diameter of the spherical body was 5 μm, and the average pore diameter of the spherical body surface was 0.45 μm. there were. The thickness of the porous membrane was 102 μm, and it was a communication hole structure from the interface of the functional layer to the other end, and the pure water permeability coefficient was as high as 38 × 10 ⁻⁹ m ³ / m ² / s / Pa.

  With respect to the porous film, the initial value (before wear test) of polystyrene latex fine particles having an average particle diameter of 0.09 μm was 98%. The polystyrene latex rejection after the wear test was 95%. Thus, the decrease rate (AB) of the rejection rate performance of the polystyrene latex fine particles by the abrasion test is as extremely small as 3.0%, and the performance degradation of the porous film by the abrasion test is not recognized, and even after the abrasion test. A good level of 90 or more could be maintained.

Further, FIG. 1 (surface of the porous membrane) and FIG. 2 (cross section of the porous membrane) show structural photographs of the obtained porous membrane, and Table 1 shows the evaluation results of the membrane performance.
(Example 2)
Polyvinylidene fluoride (PVDF / Kureha Chemical Co., Ltd., KF # 1300) was used as a resin component for the film-forming stock solution. Further, polyethylene glycol (average molecular weight 20,000) was used as the hydrophilic porogen, and γ-butyrolactone was used as the poor solvent. These were sufficiently stirred at a temperature of 160 ° C. to prepare a polyvinylidene fluoride resin solution having the following composition.

Polyvinylidene fluoride (PVDF): 30.0% by weight
γ-butyrolactone: 60.0% by weight
Polyethylene glycol: 10.0% by weight
Next, after filtering the polyvinylidene fluoride resin solution with a 50 μm stainless steel filter or the like, the density is 0.42 g / cm ³ so that the thickness becomes 100 μm from the flat film die having a slit width of 1 mm adjusted to 160 ° C. And coated on a non-woven polyester fiber having a thickness of 160 μm, and immediately immersed in a coagulating solution at 15 ° C. containing 80% by weight of a poor solvent γ-butyrolactone and 20% by weight of a non-solvent water for 5 minutes. A porous membrane having a layer formed thereon was produced.

  A porous resin layer in which a polyvinylidene fluoride resin solution was applied to a porous substrate was immersed in hot water at 95 ° C. for 2 minutes to wash away γ-butyrolactone and polyethylene glycol to obtain a porous film.

As a result of evaluating the membrane performance of the obtained porous membrane, the average pore diameter of the functional layer on the surface of the porous membrane was 0.60 μm, the average diameter of the spherical body was 7 μm, and the average pore diameter of the spherical body surface was 0.60 μm. there were. The thickness of the porous membrane was 104 μm, and it was a communicating hole structure from the interface of the functional layer to the other end, and the pure water permeability coefficient was a high level of 33 × 10 ⁻⁹ m ³ / m ² / s / Pa.

  With respect to the porous film, the initial value (before the wear test) of polystyrene latex fine particles having an average particle size of 0.09 μm was 93%. The polystyrene latex rejection after the wear test was 91%. As described above, the decrease width (AB) of the rejection rate performance of the polystyrene latex fine particles by the wear test is as extremely small as 2.0%, and the deterioration of the performance of the porous film by the wear test is not recognized, and even after the wear test. A good level of 90 or more could be maintained.

Further, FIG. 3 (surface of the porous membrane) and FIG. 4 (cross section of the porous membrane) show structural photographs of the obtained porous membrane, and Table 1 shows the evaluation results of the membrane performance.
(Example 3)
Polyvinylidene fluoride (PVDF / Kureha Chemical Co., Ltd., KF # 1300) was used as a resin component for the film-forming stock solution. Further, polyethylene glycol (average molecular weight 20,000) was used as the hydrophilic porogen, and γ-butyrolactone was used as the poor solvent. These were sufficiently stirred at a temperature of 160 ° C. to prepare a polyvinylidene fluoride resin solution having the following composition.

Polyvinylidene fluoride (PVDF): 35.0% by weight
γ-butyrolactone: 60.0% by weight
Polyethylene glycol: 5.0% by weight
Next, after filtering the polyvinylidene fluoride resin solution with a 50 μm stainless steel filter or the like, the density is 0.42 g / cm ³ so that the thickness becomes 100 μm from the flat film die having a slit width of 1 mm adjusted to 160 ° C. , Coated on a polyester fiber nonwoven fabric having a thickness of 160 μm, and immediately immersed in a coagulating solution at 10 ° C. containing 80% by weight of a poor solvent γ-butyrolactone and 20% by weight of non-solvent water for 5 minutes. A porous membrane having a layer formed thereon was produced.

  A porous resin layer in which a polyvinylidene fluoride resin solution was applied to a porous substrate was immersed in hot water at 95 ° C. for 2 minutes to wash away γ-butyrolactone and polyethylene glycol to obtain a porous film.

As a result of evaluating the membrane performance of the obtained porous membrane, the average pore diameter of the functional layer on the surface of the porous membrane was 0.50 μm, the average diameter of the spherical body was 4 μm, and the average pore diameter of the surface of the spherical body was 0.55 μm. there were. The thickness of the porous membrane was 99 μm, and it was a communicating hole structure from the interface of the functional layer to the other end, and the pure water permeability coefficient was as high as 26 × 10 ⁻⁹ m ³ / m ² / s / Pa.

With respect to the porous film, the initial value (before the wear test) of polystyrene latex fine particles having an average particle diameter of 0.09 μm was 97%. Further, the polystyrene latex rejection after the abrasion test was 92%. Thus, the decrease rate (AB) of the rejection rate performance of the polystyrene latex fine particles by the wear test is as small as 6.0%, and the performance decrease of the porous film by the wear test is not recognized. The above good level could be maintained.
Example 4
Polyvinylidene fluoride (PVDF / Kureha Chemical Co., Ltd., KF # 1300) was used as a resin component for the film-forming stock solution. In addition, glycerin was used as the hydrophilic porogen and γ-butyrolactone was used as the poor solvent. These were sufficiently stirred at a temperature of 160 ° C. to prepare a polyvinylidene fluoride resin solution having the following composition.

Polyvinylidene fluoride (PVDF): 30.0% by weight
γ-butyrolactone: 65.0% by weight
Glycerin: 5.0% by weight
Next, after filtering the polyvinylidene fluoride resin solution with a 50 μm stainless steel filter or the like, the density is 0.42 g / cm ³ so that the thickness becomes 100 μm from the flat film die having a slit width of 1 mm adjusted to 160 ° C. And coated on a non-woven polyester fiber having a thickness of 160 μm, and immediately immersed in a coagulating solution at 15 ° C. containing 80% by weight of a poor solvent γ-butyrolactone and 20% by weight of a non-solvent water for 5 minutes. A porous membrane having a layer formed thereon was produced.

  A porous resin layer in which a polyvinylidene fluoride resin solution was applied to a porous substrate was immersed in hot water at 95 ° C. for 2 minutes to wash away γ-butyrolactone and glycerin to obtain a porous film.

As a result of evaluating the membrane performance of the obtained porous membrane, the average pore diameter of the functional layer on the surface of the porous membrane was 0.80 μm, the average diameter of the spherical body was 6 μm, and the average pore diameter of the spherical body surface was 0.85 μm. there were. The thickness of the porous membrane was 98 μm, and it had a communicating hole structure from the interface of the functional layer to the other end, and the pure water permeability coefficient was a high level of 27 × 10 ⁻⁹ m ³ / m ² / s / Pa.

With respect to the porous film, the initial value (before wear test) of polystyrene latex fine particles having an average particle diameter of 0.09 μm was 91%. Further, the polystyrene latex rejection after the abrasion test was 90%. Thus, the decrease rate (AB) of the rejection rate performance of the polystyrene latex fine particles by the abrasion test is as small as 1.0%, and the performance degradation of the porous film by the abrasion test is not recognized, and even after the abrasion test, 90%. The above good level could be maintained.
(Comparative Example 1)
Polyvinylidene fluoride (PVDF / Kureha Chemical Co., Ltd., KF # 1300) was used as a resin component for the film-forming stock solution. Further, polyethylene glycol (average molecular weight 20,000) was used as the hydrophilic porogen, and γ-butyrolactone was used as the poor solvent. These were sufficiently stirred at a temperature of 160 ° C. to prepare a polyvinylidene fluoride resin solution having the following composition.

Polyvinylidene fluoride (PVDF): 30.0% by weight
γ-butyrolactone: 65.0% by weight
Polyethylene glycol: 5.0% by weight
Next, after filtering the polyvinylidene fluoride resin solution with a 50 μm stainless steel filter or the like, the density is 0.42 g / cm ³ so that the thickness becomes 100 μm from the flat film die having a slit width of 1 mm adjusted to 160 ° C. The film was coated on a 160 μm thick polyester fiber nonwoven fabric and immediately immersed in a non-solvent 100 wt% water coagulating solution at 15 ° C. for 5 minutes to produce a porous film on which a porous resin layer was formed. .

  A porous resin layer in which a polyvinylidene fluoride resin solution was applied to a porous substrate was immersed in hot water at 95 ° C. for 2 minutes to wash away γ-butyrolactone and polyethylene glycol to obtain a porous film.

As a result of evaluating the membrane performance of the obtained porous membrane, the average pore diameter of the functional layer on the surface of the porous membrane was 0.01 μm or less, the average diameter of the spherical body was 5 μm, and the average pore diameter of the surface of the spherical body was 0.40 μm. Met. The thickness of the porous film was 101 μm, and almost no pores were observed in the functional layer, and the pure water permeability coefficient was a low level of 1 × 10 ⁻⁹ m ³ / m ² / s / Pa or less.

  With respect to the porous membrane, measurement of the rejection rate of polystyrene latex fine particles having an average particle size of 0.09 μm before and after the abrasion test by the abrasion test could not be performed because the value of the pure permeability coefficient was not obtained.

Further, FIG. 5 (the surface of the porous membrane) and FIG. 6 (the cross section of the porous membrane) show structural photographs of the obtained porous membrane, and Table 1 shows the evaluation results of the membrane performance.
(Comparative Example 2)
Polyvinylidene fluoride (PVDF / Kureha Chemical Co., Ltd., KF # 1300) was used as a resin component for the film-forming stock solution. Further, polyethylene glycol (average molecular weight 20,000) was used as the hydrophilic porogen, and γ-butyrolactone was used as the poor solvent. These were sufficiently stirred at a temperature of 160 ° C. to prepare a polyvinylidene fluoride resin solution having the following composition.

Polyvinylidene fluoride (PVDF): 30.0% by weight
γ-butyrolactone: 70.0% by weight
Next, after filtering the polyvinylidene fluoride resin solution with a 50 μm stainless steel filter or the like, the density is 0.42 g / cm ³ so that the thickness becomes 100 μm from the flat film die having a slit width of 1 mm adjusted to 160 ° C. And coated on a non-woven polyester fiber having a thickness of 160 μm, and immediately immersed in a coagulating solution at 15 ° C. containing 80% by weight of a poor solvent γ-butyrolactone and 20% by weight of a non-solvent water for 5 minutes. A porous membrane having a layer formed thereon was produced.

  A porous resin layer in which a polyvinylidene fluoride resin solution was applied to a porous substrate was immersed in hot water at 95 ° C. for 2 minutes to wash away γ-butyrolactone to obtain a porous film.

As a result of evaluating the membrane performance of the obtained porous membrane, the average pore diameter of the functional layer on the surface of the porous membrane is 2.0 μm, the average diameter of the spherical body is 6 μm, and the average pore diameter of the spherical body surface is 0.01 μm or less. Met. The thickness of the porous membrane is 103 μm, and it is a communicating hole structure from the interface of the functional layer to the other end, and the pure water permeability coefficient is very high at 66 × 10 ⁻⁹ m ³ / m ² / s / Pa. It was.

  With respect to the porous film, the initial rate (before the wear test) of polystyrene latex fine particles having an average particle diameter of 0.09 μm was 5.0%. Further, the polystyrene latex rejection after the abrasion test was 4.0%. Thus, the reduction rate (AB) of the rejection rate performance of the polystyrene latex fine particles by the wear test was 1.0%, but the functional layer also has a large membrane surface average pore diameter and the rejection rate is 10% or less. The value was low.

Further, FIG. 7 (surface of the porous membrane) and FIG. 8 (cross section of the porous membrane) show structural photographs of the obtained porous membrane, and Table 1 shows the evaluation results of the membrane performance.
(Comparative Example 3)
Polyvinylidene fluoride (PVDF / Kureha Chemical Co., Ltd., KF # 1300) was used as a resin component for the film-forming stock solution. Further, polyethylene glycol (average molecular weight 20,000) was used as the hydrophilic porogen, and γ-butyrolactone was used as the poor solvent. These were sufficiently stirred at a temperature of 160 ° C. to prepare a polyvinylidene fluoride resin solution having the following composition.

Polyvinylidene fluoride (PVDF): 30.0% by weight
γ-butyrolactone: 70.0% by weight
Next, after filtering the polyvinylidene fluoride resin solution with a 50 μm stainless steel filter or the like, the density is 0.42 g / cm ³ so that the thickness becomes 100 μm from the flat film die having a slit width of 1 mm adjusted to 160 ° C. The film was coated on a 160 μm thick polyester fiber nonwoven fabric and immediately immersed in a non-solvent 100 wt% water coagulating solution at 15 ° C. for 5 minutes to produce a porous film on which a porous resin layer was formed. .

  A porous resin layer in which a polyvinylidene fluoride resin solution was applied to a porous substrate was immersed in hot water at 95 ° C. for 2 minutes to wash away γ-butyrolactone and polyethylene glycol to obtain a porous film.

As a result of evaluating the membrane performance of the obtained porous membrane, the average pore diameter of the functional layer on the surface of the porous membrane is 0.1 μm or less, the average diameter of the spherical body is 6.0 μm, and the average pore diameter of the surface of the spherical body is 0. .01 μm or less. The thickness of the porous membrane was 102 μm, and there were almost no pores in the functional layer, and the pure water permeability coefficient was a low level of 1 × 10 ⁻⁹ m ³ / m ² / s / Pa or less.

  With respect to the porous membrane, measurement of the rejection rate of polystyrene latex fine particles having an average particle size of 0.09 μm before and after the abrasion test by the abrasion test could not be performed because the value of the pure permeability coefficient was not obtained.

  Further, FIG. 9 (surface of the porous membrane) and FIG. 10 (cross section of the porous membrane) show structural photographs of the obtained porous membrane, and Table 1 shows the evaluation results of the membrane performance.

2 is a structural photograph of the surface of a porous resin layer in Example 1. FIG. 2 is a structural photograph of a cross section of a porous resin layer in Example 1. FIG. 3 is a structural photograph of the surface of a porous resin layer in Example 2. 3 is a structural photograph of a cross section of a porous resin layer in Example 2. FIG. 2 is a structural photograph of the surface of a porous resin layer in Comparative Example 1. 2 is a structural photograph of a cross section of a porous resin layer in Comparative Example 1. FIG. 4 is a structural photograph of the surface of a porous resin layer in Comparative Example 2. 6 is a structural photograph of a cross section of a porous resin layer in Comparative Example 2. 5 is a structural photograph of the surface of a porous resin layer in Comparative Example 3. 6 is a structural photograph of a cross section of a porous resin layer in Comparative Example 3.

Claims (7)

  A porous film having a single porous resin layer on the surface of a porous substrate, the porous resin layer comprising a spherical body having an average diameter of 0.5 μm to 10 μm, and the spherical body At least one pore having an average pore diameter of 0.05 μm or more and 5 μm or less is formed on the surface, and the average pore diameter of the surface of at least one side of the porous membrane is 0.05 μm or more and 5 μm or less. A porous membrane characterized.   The porous membrane according to claim 1, wherein the porous resin layer is made of a thermoplastic resin.   The porous film according to claim 2, wherein the thermoplastic resin is a polyvinylidene fluoride resin. The rejection rate (%) of latex fine particles with an average particle diameter of 0.09 μm before and after the sandfall wear test is A (%) before the sandfall wear test, and the rejection rate after the sandfall wear test. When B (%), the following inequality A−B ≦ 50 (%)
The porous film according to claim 1, wherein the following relationship is satisfied.   It is a flat membrane, The porous membrane in any one of Claims 1-4.   Polyvinylidene fluoride containing 20 to 60% by weight of a polyvinylidene fluoride resin, 1 to 30% by weight of a hydrophilic porogen and a poor solvent for the polyvinylidene fluoride resin and having a temperature in the range of 80 to 175 ° C The method for producing a porous membrane according to any one of claims 1 to 5, wherein the porous resin membrane is obtained by bringing the resin solution into contact with the surface of the porous substrate and then immersing the resin solution in a coagulation bath.   7. The porous according to claim 6, wherein the liquid in the coagulation bath has a temperature in a range of 0 to 50 ° C. and contains 60 to 100% by weight of a poor solvent for the polyvinylidene fluoride resin. A method for producing a membrane.