JP2012139619A - Polyvinylidene fluoride porous flat membrane and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyvinylidene fluoride flat membrane allowed to be manufactured by a simple process and having homogeneous and high water permeability.SOLUTION: A porous membrane composed of polyvinylidene fluoride resin is a polyvinylidene fluoride porous membrane having pores of which the average pore diameter is 0.01 to 10 μm in surface and cross-sectional directions of the porous membrane, having a pure water permeability coefficient of 1×10m/msPa and more, and including no skin layer. The polyvinylidene fluoride porous membrane is manufactured by applying a solution containing polyvinylidene fluoride resin of 5 to 35 wt.% to one side of a base material, bringing the resin solution into contact with a gas phase into which waterdrops whose average particle size is 1 to 30 μm are uniformly dispersed to semi-solidify the polyvinylidene fluoride resin, and the base material to which the resin solution is applied is dipped into water to completely solidify the polyvinylidene fluoride resin.

Description

The present invention relates to a porous flat membrane containing a hydrophilic or hydrophobic polyvinylidene fluoride resin preferably used for various microfiltration applications, and a method for producing the same.

  In recent years, technology related to porous membranes made of polymer compounds has made remarkable progress, and in particular, porous membranes having pores in the form of continuous pores have been increasingly used as various filter elements. Among these, polyvinylidene fluoride membranes are used as an oxidizing environment including ozone, which is widely used in water sterilization, and as a disinfectant such as sodium hypochlorite, which is used for the purpose of sterilization and water biofouling prevention in water purification treatment. It is also resistant to the effects of most inorganic and organic acids, aliphatic and aromatic hydrocarbons, alcohols and halogenated solvents.

  Several techniques have been disclosed for producing a flat membrane using a polyvinylidene fluoride resin, but most of them are obtained by casting a polyvinylidene fluoride resin solution dissolved in a good solvent on a glass plate. And then forming a porous structure by non-solvent induced phase separation by contacting with a liquid containing a non-solvent of polyvinylidene fluoride resin.

  In such a conventional wet solution method, a coagulating liquid containing water as a main component is used. In this case, only the film surface in contact with the coagulating liquid rapidly solidifies, resulting in a skin layer on the surface, and a cross section of the film. Solidification in the direction is delayed, resulting in a so-called asymmetric structure consisting of a skin layer and a support layer. The skin layer becomes a resistance during permeation of the substance, and the support layer has macrovoids generated during solidification, resulting in a decrease in mechanical strength.

  In order to solve these problems, for example, in Patent Document 1, a polyvinylidene fluoride resin, an organic liquid and an inorganic fine powder are mixed and then melt-molded, and then the organic liquid and the inorganic fine powder are formed from the molded product. It is disclosed that a porous film having a homogeneous porous structure excellent in mechanical strength can be obtained in the method for producing a porous film characterized by extracting the above. However, in this method, in order to extract the inorganic fine powder from the molded film, it is necessary to immerse in an alkaline solution for a long time, so that the process load may become a problem.

  Patent Document 2 discloses that a film-forming stock solution comprising a polyvinylidene fluoride resin, a good solvent for the resin, a poor solvent for the resin, and a hydrophilic resin is cast, and a solidified phase is formed in a gas containing air or water vapor. A manufacturing method is disclosed in which separation is advanced and then components other than the polyvinylidene fluoride resin are removed in a washing bath. The film obtained by the production method has a group of pores with a high porosity on the surface and in the structure, and has high water permeability. However, in this method, in order to induce and advance the phase separation, a contact time with the atmosphere or water vapor of about 5 minutes is required, which may cause a process load.

JP-A-3-215535 JP 60-97001 A

  In view of the problems as described above, an object of the present invention is to provide a polyvinylidene fluoride flat membrane that is homogeneous and has high water permeability through a simple process.

The present invention for achieving the above object is (1) a porous membrane made of a polyvinylidene fluoride-based resin, having pores having an average pore diameter of 0.01 to 10 μm on the surface and in the cross-sectional direction of the porous membrane, This is a polyvinylidene fluoride porous flat membrane having a pure water permeability coefficient of 1 × 10 ⁻⁹ m ³ / m ² · s · Pa or more and having no skin layer.
Moreover, after apply | coating the solution containing 5-35 weight% of polyvinylidene fluoride resin to (2) on the single side | surface of a base material, the gas phase in which the water droplet whose average particle diameter is 1-30 micrometers is disperse | distributed uniformly and A method for producing a polyvinylidene fluoride-based porous flat film, characterized in that the polyvinylidene fluoride-based resin is semi-solidified by contact, and then the substrate coated with the resin solution is immersed in water and completely solidified. is there.
(3) The method for producing a polyvinylidene fluoride-based porous flat membrane according to (2), wherein the contact with the gas phase is performed by exposing the resin-coated surface in the gas phase. It is.
Further, (4) is the method for producing a polyvinylidene fluoride porous flat membrane according to (2), wherein the contact with the gas phase is performed by spraying the gas phase on the resin coating surface.

  According to the production method of the present invention, it is possible to provide a polyvinylidene fluoride flat membrane that is homogeneous and has high water permeability through a simple process and a method for producing the same.

Embodiments of the present invention will be described below.
In the present invention, as the polyvinylidene fluoride resin solution, a solution in which a polyvinylidene fluoride resin is dissolved in a good solvent for the polyvinylidene fluoride resin is used.
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. Examples of the vinylidene fluoride copolymer include a copolymer of vinylidene fluoride and at least one selected from the group consisting of vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, and ethylene trifluoride chloride. . Among these, vinylidene fluoride homopolymer is more preferably used from the viewpoint of film forming property, chemical durability, and cost.

  Examples of the good solvent for the polyvinylidene fluoride resin include N-methyl-2-pyrrolidone, diethylacetamide, diethylformamide, hexamethylphosphoramide, tetramethyluric acid, dimethylsulfoxide, and the like. However, N-methyl-2-pyrrolidone, dimethylacetamide, and dimethylformamide, which have a large dissolving power and are water-soluble, are preferably used.

  Moreover, it is preferable to add a non-solvent of polyvinylidene fluoride resin to the polyvinylidene fluoride resin solution. The non-solvent does not dissolve the polyvinylidene fluoride resin and acts to control the size of the pores by controlling the solidification rate of the polyvinylidene fluoride resin. As the non-solvent, water, alcohols such as methanol and ethanol, and mixtures thereof can be used. Of these, water and methanol are preferred from the viewpoint of wastewater treatment and price.

  Furthermore, it is preferable to add inorganic fine particles to the polyvinylidene fluoride resin solution. The inorganic fine particles preferably have a high affinity with a good solvent for the polyvinylidene fluoride resin. As the inorganic fine particles, calcium carbonate fine particles or silicon dioxide fine particles whose surface has been subjected to a hydrophobic treatment are preferable. The inorganic fine particles act to suppress formation of macrovoids having a pore diameter of 5 μm or more and to form pores having a uniform pore diameter.

  The average particle size of the inorganic fine particles is preferably 0.01 to 2 μm, and more preferably 0.15 to 2 μm. For the formation of the pores, the smaller the particle diameter, the better. However, those having an average particle diameter of less than 0.01 μm are expensive and may increase the cost. When the average particle diameter exceeds 2 μm, a hole having a large hole diameter is formed, and there is a possibility that sufficient filtration performance cannot be obtained.

  A water-soluble polymer may be added to the polyvinylidene fluoride resin solution. The water-soluble polymer acts to impart hydrophilicity to the polyvinylidene fluoride porous membrane. The water-soluble polymer used in the present invention must be miscible with the aforementioned good solvent and non-solvent. Since the polymer is water-soluble, excess water-soluble polymer is easily removed from the membrane by washing with water, while a trace amount of water-soluble polymer remaining in the membrane imparts hydrophilicity to the membrane of the present invention. As the water-soluble polymer, polyether (polyethylene glycol, polypropylene glycol, etc.) and polyvinyl pyrrolidone are preferable, and at least one of these water-soluble polymers is used. If necessary, the same or different polymers having different properties may be mixed. May be used. Of these, polyvinylpyrrolidone is particularly preferably used from the viewpoint of viscosity.

  The polyvinylidene fluoride resin solution of the present invention is a resin solution in which a polyvinylidene fluoride resin is dissolved in a good solvent in a concentration range of 5 to 35% by weight, and preferably contains a non-solvent and inorganic fine particles. If the polyvinylidene fluoride content is less than 5% by weight, the film strength may be weak and the film formation may not be possible. If it exceeds 35% by weight, the resin solubility is impaired, or the viscosity is too high to make the film formation difficult. The non-solvent and the inorganic fine particles are each preferably added in a concentration range of 2 to 10% by weight, and more preferably 2 to 5% by weight. If the amount of the non-solvent and inorganic fine particles is less than 2% by weight, the effect of addition is not exhibited, and if the amount exceeds 10% by weight, the resin solution undergoes phase separation or gelation.

  The concentration range of the water-soluble polymer to be added is preferably 2 to 30% by weight. When the water-soluble polymer is less than 2% by weight, the effect of addition is not expressed, and when it exceeds 30% by weight, the resin solution is phase-separated or gelled. It also affects chemical durability.

  In the method for producing a polyvinylidene fluoride porous flat membrane of the present invention, after preparing a polyvinylidene fluoride-based resin solution, the resin is applied to one side of a substrate and brought into contact with water droplets in a gas phase to form polyvinylidene fluoride. The base resin is semi-solidified, and then the base material coated with the resin solution is immersed in water to be completely solidified and molded.

  Base materials include polyester fiber, nylon fiber, polyurethane fiber, acrylic fiber, rayon fiber, woven fabric made of organic fibers such as cotton and silk, knitted fabric, non-woven fabric and other porous substrates, and glass fibers and metal fibers. A porous substrate such as a woven fabric or a knitted fabric can be used. Among these, from the viewpoint of stretchability and cost, a porous substrate made of organic fibers is particularly preferable.

  Examples of the method of applying the polyvinylidene fluoride resin solution to the substrate include a method using a floating knife coater, a roll-on knife coater, a comma coater, a reverse coater, a lip coater, a roll coater, a die coater, and the like. Among these, a roll-on knife coater and a comma coater are preferably used because the polyvinylidene fluoride resin solution can be stably applied with a uniform thickness.

  The thickness of the polyvinylidene fluoride porous membrane is preferably 20 to 200 μm. If the thickness of the microporous film is less than 20 μm, sufficient strength may not be obtained, and if it exceeds 200 μm, the porous film may become hard and handleability may be impaired.

Next, the polyvinylidene fluoride resin solution coated on the substrate is brought into contact with a gas phase in which water droplets having an average particle diameter of 1 to 30 μm are uniformly dispersed.
Here, the gas phase in which water droplets are uniformly dispersed refers to an atmosphere in which liquid water (H ₂ O) is uniformly dispersed in the air as fine droplets having an average particle diameter of 1 to 30 μm. It is different from the atmosphere where water is a gas, that is, water vapor and dispersed in the air. Such a gas phase is often expressed as “mist” (mist, fog, haze). The gas phase in which water droplets are uniformly dispersed is in a saturated vapor state, and further water droplets that cannot be vaporized are dispersed in the gas phase. As a result, the gas phase can hold a large amount of moisture exceeding the saturated vapor state.

  The average particle size of water droplets dispersed in the gas phase is required to be 1 to 30 μm, and more preferably 1 to 20 μm. It is difficult to produce water droplets having an average particle diameter of less than 1 μm in a preferable temperature range described later. When the average particle diameter exceeds 30 μm, water droplet marks remain on the surface of the semi-solidified layer, and the quality of the resulting polyvinylidene fluoride porous film may be deteriorated.

  In addition, the average particle diameter of the water droplets dispersed in the gas phase can be measured using a particle size distribution measuring apparatus applying the laser diffraction principle. The particle size distribution measurement method applying the laser diffraction principle applies an intensity pattern of scattered light that changes according to the particle diameter when light is applied to the particle.

  The gas phase can be prepared using an apparatus that atomizes water and atomizes the water. As such an apparatus, for example, a water spray type humidifier such as an ultrasonic type, a two-fluid spray type, a centrifugal type, and the like can be cited. Among these, an ultrasonic humidifier capable of generating water droplets having a small particle diameter by ultrasonic vibration is preferable.

  In order to adjust the water droplets dispersed in the gas phase to a desired average particle size, the type of water spray humidifier and the spray conditions may be adjusted. For example, when water droplets having an average particle diameter of 1 to 10 μm are generated, water droplets having a small particle diameter can be stably supplied by using an ultrasonic sprayer. When water droplets having an average particle size of 10 to 30 μm are generated, the particle size can be adjusted by using a two-fluid spray method and changing the amount of supplied water and the pressure of compressed air. In the case of a centrifugal sprayer, water droplets having an average particle diameter of 10 to 30 μm can be generated by adjusting the number of rotations of a rotating plate that scatters water by centrifugal force.

  The gas phase temperature is preferably 5 to 50 ° C, more preferably 5 to 30 ° C. If the temperature is less than 5 ° C., the saturated vapor pressure is low, and there is a possibility that a sufficient amount of moisture cannot be retained for semi-solidifying the polyvinylidene fluoride resin. Further, water condensation occurs, and large water droplets adhere to the surface of the polyvinylidene fluoride resin solution, so that water droplet traces remain, and the quality of the obtained polyvinylidene fluoride porous membrane may be deteriorated. When the temperature exceeds 50 ° C., the good solvent contained in the polyvinylidene fluoride resin solution is greatly vaporized, and the coagulation on the surface of the polyvinylidene fluoride resin solution becomes uneven, and the performance such as moisture permeability and waterproofness varies. There is a risk of getting on.

  In the present invention, by bringing the base material coated with the polyvinylidene fluoride resin solution into the gas phase, water droplets uniformly dispersed in the gas phase are allowed to adhere to the surface of the polyvinylidene fluoride resin solution (in the gas phase). The surface of the polyvinylidene fluoride resin solution starts to solidify on the surface of the polyvinylidene fluoride resin solution. And the layer of the state which coagulation | solidification is incomplete and coagulation | solidification is progressing is formed in the surface of a polyvinylidene fluoride resin solution in a short time. At this time, it is considered that the inside of the polyvinylidene fluoride resin solution (referring to a portion not in contact with the gas phase) is hardly solidified. In the present invention, such a state of the polyvinylidene fluoride-based resin or the polyvinylidene fluoride-based resin solution is called semi-solidified, and a layer in a state where solidification is progressing, which is formed on the surface of the polyvinylidene fluoride-based resin solution. Called the semi-solidified layer.

  After that, by immersing the substrate coated with the polyvinylidene fluoride resin solution in water, the semi-solid layer formed on the surface of the polyvinylidene fluoride resin solution causes water to enter the polyvinylidene fluoride resin solution. Intrusion and outflow of the good solvent contained in the polyvinylidene fluoride resin solution into water are suppressed. For this reason, the solidification rate of the polyvinylidene fluoride resin becomes slow, and a porous film having a large number of micropores with small pore diameters can be formed.

  When a steam atmosphere (or a gas phase in which water is dispersed as a gas (steam)) is used instead of the gas phase, there is a limit to the amount of water that can be retained, and the polyvinylidene fluoride resin It takes a long time to semi-solidify, which is not preferable because productivity is lowered.

The amount of water droplets attached to the surface of the polyvinylidene fluoride-based resin solution varies depending on the composition of the polyvinylidene fluoride-based resin solution, and thus cannot be generally specified, but is preferably 0.15 to 20 g / m ² . more preferably 25~10g / ^{m 2,} further preferably 0.25~5g / ^{m 2.}
If the water droplet amount is less than 0.15 g / m ² , the semi-solidified layer may not be formed. When the amount of water droplets exceeds 20 g / m ² , water marks of water droplets are generated on the surface of the semi-solidified layer, or good solvents contained in the polyvinylidene fluoride resin solution ooze out on the surface, resulting in point marks. As a result, the quality of the obtained polyvinylidene fluoride porous film may be deteriorated. In addition, the surface state of the polyvinylidene fluoride resin solution is completely solidified, and when immersed in water in the next step, water penetration into the polyvinylidene fluoride resin solution is completely blocked, There is a possibility that the solidified layer is peeled off and resin residue is generated.

  As a method of bringing the substrate coated with the polyvinylidene fluoride resin solution into contact with a gas phase in which water droplets having an average particle size of 1 to 30 μm are uniformly dispersed, water droplets uniformly dispersed in the gas phase may be used. Although not particularly limited as long as it uniformly and quickly adheres to the entire surface of the polyvinylidene fluoride resin solution, specifically, in the gas phase (atmosphere in which water droplets having an average particle diameter of 1 to 30 μm are uniformly dispersed) And a method of exposing the substrate coated with the polyvinylidene fluoride-based resin solution, and a method of directly spraying the gas phase onto the polyvinylidene fluoride-based resin solution coated on the substrate.

  In the exposure to the gas phase, for example, a substrate coated with the polyvinylidene fluoride resin solution is continuously run in an apparatus (exposure apparatus) whose interior is adjusted to an atmosphere satisfying a predetermined condition. Can be done. In that case, the amount of water droplets attached can be adjusted by adjusting the time during which the substrate stays in the exposure apparatus. Specifically, it adjusts by changing the speed (traveling speed) at which the base material travels within the exposure apparatus. Furthermore, since the moisture state in the exposure device also changes depending on the device volume and the spray amount of the water spray type humidifier, the water spray type humidifier so that the water droplets in the device float stably according to the device volume. It is preferable to adjust the spray amount.

  The time for exposing the substrate coated with the polyvinylidene fluoride resin solution in the gas phase is preferably 1 to 60 seconds, and more preferably 1 to 30 seconds. By setting the exposure time within this range, the amount of water droplets attached to the surface of the polyvinylidene fluoride resin solution can be adjusted to the above range.

  In the method of exposing to the gas phase, the amount of water droplets adhering to the surface of the polyvinylidene fluoride resin solution is determined by running the inside of the exposure apparatus with filter paper placed on the substrate surface to be actually treated. It can be calculated from the change in weight of the filter paper after adhesion.

As described above, in the present invention, instead of the method of exposing the substrate coated with the polyvinylidene fluoride resin solution to the gas phase, the substrate coated with the polyvinylidene fluoride resin solution is described in detail. By spraying the above-mentioned gas phase, that is, a gas phase in which water droplets having an average particle diameter of 1 to 30 μm are uniformly dispersed, on the surface of the polyvinylidene fluoride resin solution applied to the substrate, the polyvinylidene fluoride resin is obtained. Semi-solidification is also possible.
In this case, the same water spray type humidifier as that used for adjusting the atmosphere in the exposure apparatus is used, and the gas phase sprayed from the water spray type humidifier is directly added to the polyvinylidene fluoride resin solution. Just spray on the surface.
According to such a method, the amount of water droplets (preferably 0.15 to 20 g / m ²⁾ required to semi-solidify the polyvinylidene fluoride resin in a shorter time than the method of exposing in the gas phase. 0.15 to 10 g / m ² , and more preferably 0.25 to 5 g / m ² ) can be adhered to the surface of the polyvinylidene fluoride resin solution, so that the polyvinylidene fluoride resin can be obtained in a shorter time. Can be semi-solidified, and is excellent in productivity.
In the method of directly spraying the vapor phase on the surface of the polyvinylidene fluoride resin solution, by adjusting the spray amount of the water spray type humidifier, the distance from the surface of the polyvinylidene fluoride resin solution, the spraying time, etc. The amount of water droplets can be adjusted. For example, using a humidifier that sprays 0.1 to 5.0 kg of water droplets per hour, the gas phase is sprayed for 1 to 15 seconds from a distance of about 2 to 50 cm from the surface of the polyvinylidene fluoride resin solution. Thus, a desired amount of water droplets can be attached to the surface of the polyvinylidene fluoride resin solution.

  Next, the base material coated with the polyvinylidene fluoride resin solution (having a semi-solidified layer formed on the surface) is immersed in water. In this process, water enters the inside of the polyvinylidene fluoride resin solution, and the good solvent contained in the polyvinylidene fluoride resin solution is almost completely replaced with water, whereby the solidification of the polyvinylidene fluoride resin is completed. . The effects of the semi-solidified layer in this process are as described above, but the semi-solidified layer also becomes a completely solidified layer when immersed in water. Note that the coagulation liquid may be water alone and does not require the presence of other components. However, in actual production, the substrate coated with the polyvinylidene fluoride resin solution continuously passes through the water (coagulation liquid). As a result, the good solvent gradually accumulates in the water (coagulating liquid). In the present invention, the presence of such a good solvent in water (coagulating liquid) is not excluded.

  The temperature of the coagulation liquid is preferably 0 to 70 ° C. When the temperature exceeds 70 ° C., there is a possibility that the solidification of the polyvinylidene fluoride resin becomes non-uniform.

  The immersion time is preferably 30 seconds to 10 minutes, and more preferably 1 to 5 minutes. If the immersion time is less than 30 seconds, the polyvinylidene fluoride resin may not be completely solidified. When immersion time exceeds 10 minutes, there exists a possibility that productivity may fall.

  Next, after washing for 3 to 15 minutes in warm water at 30 to 80 ° C. to remove the remaining good solvent, non-solvent and added hydrophilic polymer, heat treatment is performed at 50 to 100 ° C. for 1 to 10 minutes and drying is performed. . Thus, the polyvinylidene fluoride porous flat membrane of the present invention can be obtained on the substrate.

The polyvinylidene fluoride porous flat membrane obtained by the present invention preferably has a pure water permeability coefficient of 1 × 10 −9 m ³ / m ² · s · Pa or more. When this pure water permeability coefficient is less than 1 × 10 ⁻⁹ m ³ / m ² · s · Pa, it is necessary to operate at a high pressure because the water permeability of the membrane is poor, and the operating cost may increase. .

Here, the pure water permeation coefficient was obtained by filtering the ion-exchanged water with a polyvinylidene fluoride porous flat membrane having a diameter of 47 mm under the conditions of a temperature of 25 ° C. and a head pressure of 1 m, and was obtained by the following formula 1. In the evaluation, the porous flat membrane was immersed in ethanol for 15 minutes and then immersed in water for 2 hours or more and used for evaluation. The pure water permeability coefficient may be obtained by converting a value obtained by applying pressure or suction with a pump or the like.
[Formula 1]
Pure water permeability coefficient (m ³ / m ² · s · Pa) = permeated water amount (m ³ ) / (membrane area (m ² ) × permeation time (s) × evaluation pressure (Pa))

  Furthermore, the polyvinylidene fluoride porous flat membrane preferably has a collection rate of fine particles having an average particle size of 0.15 μm of 90% or more. If the collection rate is less than 90%, clogging may occur in the porous membrane or the filtration differential pressure may increase, and the life of the porous flat membrane may be shortened.

Here, the fine particle collection rate is obtained by filtering an evaluation stock solution in which polystyrene latex particles having an average particle size of 0.15 μm are dispersed in ion-exchanged water so as to have a concentration of 25 ppm, and ultraviolet rays having a wavelength of 220 nm between the evaluation stock solution and the permeate. It calculated | required by following Numerical formula 2 from the light absorbency. The spectrophotometer was used for the absorbance measurement.
[Formula 2]
Fine particle collection rate (%) = ((Evaluation stock solution absorbance (abs) −Permeate absorbance (abs)) / Evaluation stock solution absorbance (abs)) × 100

  The thickness of the polyvinylidene fluoride-based porous membrane and the pore diameter of the pores formed on the surface and cross section of the porous membrane are measured with a scanning electron microscope ("S-3000N" manufactured by Hitachi High-Technologies Corporation). Using, 100 to 5000 times cross-section and surface photographs were taken and measured.

  The polyvinylidene fluoride porous flat membrane may be a single membrane, or may be used in combination with a porous substrate such as a fiber fabric.

  The average pore size of the pores formed on the surface of the polyvinylidene fluoride porous flat membrane is preferably 0.01 to 10 μm, and more preferably 0.01 to 5 μm. If the average pore diameter is less than 0.01 μm, sufficient water permeability cannot be obtained, and if it exceeds 10 μm, the collection rate may decrease or the filtration differential thickness may increase due to clogging.

  Moreover, it is preferable to have a three-dimensional network structure with an average pore diameter of 0.01 to 10 μm in the film cross-sectional direction of the polyvinylidene fluoride-based porous flat membrane, and it is more preferable that the average pore diameter is 0.01 to 5 μm. If the average pore diameter is less than 0.01 μm, sufficient water permeability cannot be obtained, and if it exceeds 10 μm, the mechanical strength may be lowered.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not necessarily limited to the examples. In addition, each numerical value in an Example and a comparative example was measured with the following method.
[With or without skin layer]
Using a scanning electron microscope ("S-3000N" manufactured by Hitachi High-Technologies Corporation), a cross-section and a surface photograph were taken at 1000 times to confirm the presence or absence of a skin layer.
[Thickness]
Using a scanning electron microscope ("S-3000N" manufactured by Hitachi High-Technologies Corporation), a cross-sectional photograph was taken at a magnification of 100 and measured.
[Mean surface pore size and presence / absence of pores of 10 μm or more]
Using a scanning electron microscope (“S-3000N” manufactured by Hitachi High-Technologies Corporation), cross-sections and surface photographs were taken at a magnification of 5000 times and measured.
[Pure water permeability coefficient]
Ion-exchanged water was filtered through a polyvinylidene fluoride porous membrane having a diameter of 47 mm, immersed in ethanol for 15 minutes and then immersed in water for 2 hours under conditions of a temperature of 25 ° C. and a head pressure of 1 m. It was.
[Fine particle collection rate]
An evaluation stock solution in which polystyrene latex particles having an average particle size of 0.15 μm are dispersed in ion-exchanged water so as to have a concentration of 25 ppm is filtered, and is obtained from the ultraviolet light absorbance at a wavelength of 220 nm of the evaluation stock solution and the permeation solution by the above-described formula 2. It was. The spectrophotometer was used for the absorbance measurement.

[Example 1]
Polyvinylidene fluoride homopolymer (PVDF, weight average molecular weight 680,000), N, N-dimethylformamide (DMF), ion-exchanged water, hydrophobic silica (average particle size 1.2 μm) were used, respectively, and the following formulation 1 The solution was sufficiently stirred and dissolved at a temperature of 50 ° C. to obtain a film forming stock solution.
[Prescription 1]
PVDF 11.5% by weight
DMF 82.5% by weight
Ion exchange water 3.0% by weight
Hydrophobic silica 3.0% by weight

Next, the film-forming stock solution was cooled to room temperature and applied to a polyester fiber fabric with a roll-on knife coater. Thereafter, in the exposure apparatus (volume: approximately 5.0 m ³ , manufactured by Seiren Electronics Co., Ltd.) in which a water spray type humidifier (trade name “FT-161DH”, manufactured by UCAN Co., Ltd.) is installed, A fiber fabric coated with the coalescence solution was placed, and exposed to a gas phase of 20 ° C. in which water droplets having an average particle diameter of 7 μm were uniformly dispersed for 10 seconds to semi-solidify the synthetic polymer. At this time, the amount of water droplets adhering to the surface of the synthetic polymer solution was about 0.7 g / m ² .
The fiber fabric coated with the synthetic polymer solution was immersed in water at 25 ° C. for 2 minutes for complete solidification. Next, after washing in warm water of 50 ° C. for 5 minutes, heat treatment was performed at 80 ° C. for 2 minutes and drying to obtain a polyvinylidene fluoride porous flat membrane. The evaluation results are shown in Table 1.

[Example 2]
Polyvinylidene fluoride homopolymer (PVDF, weight average molecular weight 680,000), N, N-dimethylformamide (DMF), ion-exchanged water, hydrophobic silica (average particle size 1.2 μm), polyvinylpyrrolidone (PVP), respectively, These were sufficiently stirred and dissolved at a temperature of 50 ° C. according to the following formulation 2 to obtain a film-forming stock solution.
[Prescription 2]
PVDF 11.5% by weight
DMF 82.5% by weight
Ion exchange water 3.0% by weight
Hydrophobic silica 3.0% by weight
PVP 3.5 wt%

Next, the film-forming stock solution was cooled to room temperature and applied to a polyester fiber fabric with a roll-on knife coater. Thereafter, in the exposure apparatus (volume: approximately 5.0 m ³ , manufactured by Seiren Electronics Co., Ltd.) in which a water spray type humidifier (trade name “FT-161DH”, manufactured by UCAN Co., Ltd.) is installed, A fiber fabric coated with the coalescence solution was placed, and exposed to a gas phase of 20 ° C. in which water droplets having an average particle diameter of 7 μm were uniformly dispersed for 30 seconds to semi-solidify the synthetic polymer. At this time, the amount of water droplets adhering to the surface of the synthetic polymer solution was about 2 g / m ² .
The fiber fabric coated with the synthetic polymer solution was immersed in water at 25 ° C. for 2 minutes for complete solidification. Next, after washing for 5 minutes in warm water at 50 ° C., heat treatment was performed at 80 ° C. for 2 minutes and drying to obtain a polyvinylidene fluoride porous flat membrane imparted with hydrophilicity. The evaluation results are shown in Table 1.

Example 3
Polyvinylidene fluoride homopolymer (PVDF, weight average molecular weight 680,000), N, N-dimethylformamide (DMF), ion-exchanged water, hydrophobic silica (average particle size 0.15 μm) were used, respectively. The solution was sufficiently stirred and dissolved at a temperature of 50 ° C. to obtain a film forming stock solution. This was formed in the same manner as in Example 1 to obtain a polyvinylidene fluoride-based porous flat film. The evaluation results are shown in Table 1.
[Prescription 3]
PVDF 11.5% by weight
DMF 82.5% by weight
Ion exchange water 3.0% by weight
Hydrophobic silica 3.0% by weight

Example 4
Polyvinylidene fluoride homopolymer (PVDF, weight average molecular weight 680,000), N, N-dimethylformamide (DMF), ion-exchanged water, hydrophobic silica (average particle size 0.15 μm) were used, respectively. The solution was sufficiently stirred and dissolved at a temperature of 50 ° C. to obtain a film forming stock solution. This was formed in the same manner as in Example 1 to obtain a polyvinylidene fluoride-based porous flat film. The evaluation results are shown in Table 1.
[Prescription 4]
PVDF 8.0 wt%
DMF 88.0% by weight
Ion exchange water 2.0% by weight
Hydrophobic silica 2.0% by weight

Example 5
Polyvinylidene fluoride homopolymer (PVDF, weight average molecular weight 680,000), N, N-dimethylformamide (DMF), ion-exchanged water, hydrophobic silica (average particle size 1.2 μm), polyvinylpyrrolidone (PVP), respectively, These were sufficiently stirred and dissolved at a temperature of 50 ° C. according to the following formulation 5 to obtain a film forming stock solution. This was formed in the same manner as in Example 2 to obtain a polyvinylidene fluoride-based porous flat film. The evaluation results are shown in Table 1.
[Prescription 5]
PVDF 11.5% by weight
DMF 71.5% by weight
Ion exchange water 3.5% by weight
Hydrophobic silica 2.0% by weight
PVP 11.5% by weight

Example 6
Polyvinylidene fluoride homopolymer (PVDF, weight average molecular weight 680,000), N, N-dimethylformamide (DMF), ion-exchanged water, hydrophobic silica (average particle size 1.2 μm) were used, respectively, and the following formulation 6 The solution was sufficiently stirred and dissolved at a temperature of 50 ° C. to obtain a film forming stock solution.
[Prescription 6]
PVDF 11.5% by weight
DMF 82.5% by weight
Ion exchange water 3.0% by weight
Hydrophobic silica 3.0% by weight

Next, the film-forming stock solution was cooled to room temperature, and a roll-on knife coater was applied to a polyester fiber fabric. Thereafter, water droplets having an average particle size of 7 μm are uniformly dispersed on the surface of the fiber fabric coated with the synthetic polymer solution using a water spray type humidifier (trade name “FT-161DH”, manufactured by UCAN Co., Ltd.). The gas phase was sprayed from a distance of about 5 cm for 5 seconds. The amount of water droplets adhering to the surface of the fiber fabric coated with the synthetic polymer solution was about 1.2 g / m ² .
The fiber fabric coated with the synthetic polymer solution was immersed in water at 25 ° C. for 2 minutes for complete solidification. Next, after washing in warm water at 50 ° C. for 5 minutes, it was heat-treated at 80 ° C. for 2 minutes and dried to obtain a polyvinylidene fluoride porous flat membrane. The evaluation results are shown in Table 1.

Example 7
Polyvinylidene fluoride homopolymer (PVDF, weight average molecular weight 680,000), N, N-dimethylformamide (DMF), ion-exchanged water, and hydrophobic silica (average particle size 1.2 μm) were used, respectively. The solution was sufficiently stirred and dissolved at a temperature of 50 ° C. to obtain a film forming stock solution.
[Prescription 7]
PVDF 11.5% by weight
DMF 82.5% by weight
Ion exchange water 3.0% by weight
Hydrophobic silica 3.0% by weight

Next, the film-forming stock solution was cooled to room temperature and applied to a polyester fiber fabric with a roll-on knife coater. Thereafter, the synthetic polymer solution was placed in an exposure apparatus (volume: about 5.0 m ³ , manufactured by Seiren Electronics Co., Ltd.) in which a water spray type humidifier (trade name “FT-161DH”, manufactured by Yucan Co., Ltd.) was installed. The synthetic polymer was semi-solidified by placing it in a gas phase at 50 ° C. where water droplets having an average particle diameter of 7 μm were uniformly dispersed for 10 seconds. At this time, the amount of water droplets adhering to the surface of the synthetic polymer solution was about 0.9 g / m ² .
The fiber fabric coated with the synthetic polymer solution was immersed in water at 25 ° C. for 2 minutes for complete solidification. Next, after washing in warm water at 50 ° C. for 5 minutes, it was heat-treated at 80 ° C. for 2 minutes and dried to obtain a polyvinylidene fluoride porous flat membrane. The evaluation results are shown in Table 1.

[Comparative Example 1]
Polyvinylidene fluoride homopolymer (PVDF, weight average molecular weight 680,000), N, N-dimethylformamide (DMF), ion-exchanged water, hydrophobic silica (average particle size 1.2 μm) were used, respectively. The solution was sufficiently stirred and dissolved at a temperature of 50 ° C. to obtain a film forming stock solution.
[Prescription 8]
PVDF 11.5% by weight
DMF 82.5% by weight
Ion exchange water 3.0% by weight
Hydrophobic silica 3.0% by weight

Next, the film-forming stock solution was cooled to room temperature and applied to a polyester fiber fabric with a roll-on knife coater. Thereafter, the fiber fabric coated with the film-forming stock solution was immersed in water at 25 ° C. for 2 minutes to be completely solidified. Next, after washing in warm water at 50 ° C. for 5 minutes, it was heat-treated at 80 ° C. for 2 minutes and dried to obtain a polyvinylidene fluoride porous flat membrane. A skin layer and a support layer were formed on the film surface. The evaluation results are shown in Table 1.

[Comparative Example 2]
Polyvinylidene fluoride homopolymer (PVDF, weight average molecular weight 680,000), N, N-dimethylformamide (DMF), ion-exchanged water, and hydrophobic silica (average particle size 1.2 μm) were used, respectively, and the following formulation 9 The solution was sufficiently stirred and dissolved at a temperature of 50 ° C. to obtain a film forming stock solution.
[Prescription 9]
PVDF 11.5% by weight
DMF 82.5% by weight
Ion exchange water 3.0% by weight
Hydrophobic silica 3.0% by weight

Next, the film-forming stock solution was cooled to room temperature and applied to a polyester fiber fabric with a roll-on knife coater. Thereafter, the fiber fabric coated with the synthetic polymer solution was humidified for 10 seconds using a spray. The particle diameter of the water droplets dispersed from the spray was 50 μm to 200 μm.
The fiber fabric coated with the synthetic polymer solution was immersed in water at 25 ° C. for 2 minutes for complete solidification. Next, after washing in warm water at 50 ° C. for 5 minutes, it was heat-treated at 80 ° C. for 2 minutes and dried to obtain a polyvinylidene fluoride porous flat membrane. A skin layer and a support layer were formed on the film surface. The evaluation results are shown in Table 1.

Claims (4)

A porous membrane made of a polyvinylidene fluoride resin has pores having an average pore diameter of 0.01 to 10 μm on the surface and cross-sectional direction of the porous membrane, and a pure water permeability coefficient of 1 × 10 ⁻⁹ m ³ / A polyvinylidene fluoride-based porous flat membrane having a skin layer of m ² · s · Pa or more. After a solution containing 5 to 35% by weight of a polyvinylidene fluoride resin is applied to one side of a substrate, it is brought into contact with a gas phase in which water droplets having an average particle diameter of 1 to 30 μm are uniformly dispersed to make a polyvinylidene fluoride system A method for producing a polyvinylidene fluoride porous flat membrane, characterized by semi-solidifying a resin and then completely solidifying the substrate coated with the resin solution by immersing it in water. 3. The method for producing a polyvinylidene fluoride porous flat membrane according to claim 2, wherein the contact with the gas phase is performed by exposing the resin-coated surface in the gas phase. 3. The method for producing a polyvinylidene fluoride porous membrane according to claim 2, wherein the contact with the gas phase is performed by spraying the gas phase on the resin coating surface.