JP2010094670A - Polyvinylidene fluoride-based multiple membrane and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polyvinylidene fluoride-based multiple membrane having good capability of removing viruses, pure water permeation performance, and physical strength in a simple process in order to stabilize the water quality of permeation water through improvement of separation functions to a greater extent than conventional water treatment membranes. <P>SOLUTION: The polyvinylidene fluoride-based multiple membrane contains 50 wt.% or more and 88 wt.% or less of a polyvinylidene fluoride-based resin with viscosity of 2,500 Pa s or more and 12 wt.% or more and 50 wt.% or less of cellulose ester and having a three-dimensional network structure with an average bore size of 0.01 μm or more and 1 μm or less and a thickness of 5 μm or more and 100 μm or less, wherein the multiple membrane is formed via lamination of a separation function layer having no macrovoid of substantially 5 μm or more on a polyvinylidene fluoride-based supporting membrane having a spherical structure with an average diameter of 0.1 μm or more and 5 μm or less. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a separation membrane suitably used in the fields of water treatment, pharmaceutical production, food industry and the like. More specifically, the present invention relates to a method for producing a polyvinylidene fluoride composite film that can be suitably used in the field of efficiently removing fine substances such as viruses in a liquid.

  In recent years, fluororesin hollow fiber membrane modules have been applied to water purification fields such as turbidity of river water and groundwater, clarification of industrial water, and advanced treatment of wastewater. For these hollow fiber membrane modules used in the water purification field, chemical cleaning such as acid, alkali, chlorine and surfactant is applied to the hollow fiber membrane module for the purpose of long-term operation, and regeneration is used repeatedly. The hollow fiber membranes used for this purpose require high chemical resistance (chemical strength) and physical strength, and in addition, separation characteristics that prevent pathogenic microorganisms such as Cryptosporidium from entering the permeated water are required. ing. In the fields of drinking water production, pharmaceutical production, and food industry, if a pathogen such as a virus is mixed in the production process, the production line is contaminated and there is a risk of causing a virus infection. For this purpose, various sterilization techniques have been used, and the use of separation membranes that can physically remove viruses with pores has attracted attention. Thus, the separation membrane is required to have excellent separation performance, chemical strength (chemical resistance), physical strength, and permeation performance.

  Polyvinylidene fluoride resin separation membranes that have both chemical strength (chemical resistance) and physical strength have been used in response to such characteristic requirements. However, although the separation membrane made of polyvinylidene fluoride resin has high chemical strength (chemical resistance) and physical strength, it has a hydrophobic interaction on the membrane surface and is easily soiled, resulting in a decrease in water permeability.

  For this reason, improvement in stain resistance, water permeability, or virus removal properties such as hydrophilicity of polyvinylidene fluoride resin has been performed. For example, the method described in Patent Document 1 discloses a method for producing a separation membrane in which cellulose acetate and a polyvinylidene fluoride resin are blended. However, when cellulose acetate is blended until a hydrophilic effect is exhibited in a single-layer film, chemical resistance such as acid, alkali, and chlorine is low, and there is a concern that mechanical strength is lowered. Patent Document 2 discloses a composite film having a high physical strength, water permeability, and the like by forming a fluororesin containing a hydrophilic polymer on the surface layer. However, since this composite membrane contains macrovoids and the membrane pores are coarse, the separation characteristics for removing microscopic substances such as viruses are low. Patent Document 3 discloses that a composite membrane formed of a fluororesin containing a hydrophilic polymer on the surface layer has high separation characteristics. However, virus removability was still insufficient. Patent Document 4 describes a hollow fiber membrane for medical use. However, although it exhibits high virus removal performance, its physical strength is low due to the thin film thickness, and the permeation performance is also low.

JP-A-2-78425 JP 2006-239680 A JP 2006-263721 A International Publication No. 03/26779 Pamphlet

  In view of the above problems, an object of the present invention is to provide a polyvinylidene fluoride composite membrane having excellent virus removal performance, pure water permeation performance, and physical strength by a simple process.

In order to achieve the above-mentioned problems, the following configurations (1) to (2) are included.
(1) A tertiary resin having a melt viscosity of 2500 Pa · s or more and a polyvinylidene fluoride-based resin of 50% by weight or more and 88% by weight or less and a cellulose ester of 12% by weight or more and 50% by weight or less and an average pore diameter of 0.01 μm or more and 1 μm or less. Polyvinylidene fluoride having an original network structure, a separation functional layer having a thickness of 5 μm or more and 100 μm or less and substantially having no macrovoids of 5 μm or more has a spherical structure having an average diameter of 0.1 μm or more and 5 μm or less A polyvinylidene fluoride-based composite membrane, characterized by being laminated on a system support membrane.
(2) Polyvinylidene fluoride resin having a melt viscosity of 2500 Pa · s or more is contained in an amount of 8 wt% or more and 14 wt% or less, and a cellulose ester is contained in an amount of 2 wt% or more and 12 wt% or less, and the solution viscosity is 1 Pa · s or more and 100 Pa · s. Forming a separation functional layer on the polyvinylidene fluoride-based support membrane by coating the following coating solution on the polyvinylidene fluoride-based support membrane and solidifying it in a coagulation bath after a free running time of 2 seconds or less. A process for producing a polyvinylidene fluoride-based composite film characterized by

  The production method of the present invention can provide a polyvinylidene fluoride composite membrane having excellent virus removal performance, pure water permeation performance, and physical strength by a simple process, and a production method thereof.

It is an electron micrograph (magnification 600 times) which shows the cross section (part) of the uniform state regarding the hollow fiber-shaped separation membrane which concerns on this invention. It is an electron micrograph (magnification 3000 times) which shows the cross section (part) of the uniform state regarding the hollow fiber-shaped separation membrane which concerns on this invention. It is the schematic of the evaluation module of the filtration resistance raise degree used in the Example.

  Hereinafter, specific embodiments of the polyvinylidene fluoride resin composite film and the method for producing the polyvinylidene fluoride resin composite film of the present invention will be described.

  The polyvinylidene fluoride resin in the present invention is a resin containing a vinylidene fluoride homopolymer and / or a vinylidene fluoride copolymer, and may contain a plurality of vinylidene fluoride copolymers. The vinylidene fluoride copolymer is a polymer having a vinylidene fluoride residue structure, and is typically a copolymer of a vinylidene fluoride monomer and other fluorine-based monomers. Examples of such a copolymer include a copolymer of vinylidene fluoride and one or more selected from vinyl fluoride, ethylene tetrafluoride, propylene hexafluoride, and ethylene trifluoride chloride. Further, a monomer such as ethylene other than the fluorine-based monomer may be copolymerized to such an extent that the effects of the present invention are not impaired. Among them, a resin made of vinylidene fluoride homopolymer is preferably used because of its high chemical strength and physical strength.

  When the above-mentioned polyvinylidene fluoride resin is used for the support membrane, it is preferable that the weight average molecular weight is in the range of 50,000 to 700,000 in view of physical strength and water permeability, and the solubility in a solvent and spinnability are improved. In consideration, those having a weight average molecular weight of 100,000 to 500,000 are preferably used.

  In the case of the polyvinylidene fluoride resin used for the coating layer, a polyvinylidene fluoride resin having a melt viscosity of 2500 Pa · s or more is used, but generally, the relationship between the melt viscosity and the weight average molecular weight is uniquely determined. A polyvinylidene fluoride resin having a weight average molecular weight corresponding to a melt viscosity of 2500 Pa · s or more may be used. The weight average molecular weight of the polyvinylidene fluoride resin having a melt viscosity of 2500 Pa · s or more is generally 700,000 or more, but is more reliably achieved if it is 900,000 or more. When the melt viscosity is 2500 Pa · s or more, or the weight average molecular weight is 700,000 or more, generation of macrovoids can be suppressed and separation characteristics such as virus removal can be improved. Here, the upper limit of the melt viscosity of the polyvinylidene fluoride resin is not particularly limited, but if it exceeds 7000 Pa · s or the weight average molecular weight exceeds 1.3 million, the solubility in a solvent is reduced, or the composite film There is a concern that the water permeability will decrease.

  The support membrane of the present invention is produced mainly by a thermally induced phase separation method by cooling a polyvinylidene fluoride resin solution. Here, a polyvinylidene fluoride resin having a weight average molecular weight of 50,000 to 700,000 is dissolved in a poor solvent or a good solvent of the polyvinylidene fluoride resin at a concentration higher than the crystallization temperature at a concentration of 20 wt% to 60 wt%. . If the concentration of the polyvinylidene fluoride resin increases, a support membrane having high physical strength can be obtained. However, since the porosity of the separation membrane decreases and the permeation performance tends to decrease, it is necessary to consider. Accordingly, the concentration of the polyvinylidene fluoride resin is preferably in the range of 30 wt% to 50 wt%.

  The polyvinylidene fluoride resin solution is shaped into a sheet shape or hollow fiber shape with a T-die, a double tube die, or the like, and cooled and solidified in a cooling bath. The cooling bath is preferably a mixed liquid composed of a poor solvent or a good solvent having a concentration of 50% to 95% by weight and a non-solvent having a concentration of 5% to 50% by weight at 0 ° C. to 30 ° C. Further, when forming into a hollow fiber shape, it is preferable to discharge the hollow portion forming liquid from the central pipe of the double tube type die simultaneously with the polyvinylidene fluoride resin solution. The hollow portion forming liquid is preferably a mixed liquid comprising a poor solvent or a good solvent having a concentration of 50% by weight to 95% by weight and a non-solvent having a concentration of 5% by weight to 50% by weight, as in the cooling bath. Further, it is preferable to use the same poor solvent as the resin solution as the poor solvent.

  In addition to the above method for producing a support membrane, it is also preferable to perform stretching in order to improve the permeation performance. The stretching temperature is preferably 50 ° C. or higher and 165 ° C. or lower. When the temperature is 50 ° C. or higher, stretching orientation tends to occur uniformly, and when the temperature is 165 ° C. or lower, the melting point of polyvinylidene fluoride is close to the melting point, so that the partial disappearance of fine pores on the film surface can be suppressed. The draw ratio is preferably 1.1 to 4 times, more preferably 1.1 to 2 times. If it is 1.1 times or more, the transmission performance is improved, and if it is 4 times or less, a decrease in physical strength such as buckling pressure can be suppressed.

  The poor solvent in the present invention cannot dissolve 5% by weight or more of polyvinylidene fluoride resin at a low temperature of less than 60 ° C., but it is 60 ° C. or more and below the melting point of the polyvinylidene fluoride resin (for example, polyvinylidene fluoride resin). Is a solvent that can be dissolved by 5 wt% or more in a high temperature region of about 178 ° C. when the polyvinylidene fluoride homopolymer is used alone. Examples of the poor solvent in the present invention include cyclohexanone, isophorone, γ-butyrolactone, methyl isoamyl ketone, propylene carbonate, and other medium chain length alkyl ketones, esters, organic carbonates, and the like, and mixed solvents thereof.

  The good solvent is not particularly limited as long as it dissolves polyvinylidene fluoride resin and preferably forms a three-dimensional network structure by non-solvent induced phase separation, but dimethyl sulfoxide, N, N-dimethylformamide, N, Examples thereof include N-dimethylacetamide, N-methyl-2-pyrrolidone, methyl ethyl ketone, acetone, tetrahydrofuran, tetramethylurea, lower alkyl ketones such as trimethyl phosphate, esters, amides, and the like, and mixed solvents thereof. Here, the good solvent is a solvent capable of dissolving 5% by weight or more of the polyvinylidene fluoride resin even at a low temperature of less than 60 ° C.

  The non-solvent is defined as a solvent that does not dissolve or swell the polyvinylidene fluoride resin up to the melting point of the polyvinylidene fluoride resin or the boiling point of the solvent. Here, as the non-solvent of the polyvinylidene fluoride resin, water, hexane, pentane, benzene, toluene, methanol, ethanol, carbon tetrachloride, o-dichlorobenzene, trichloroethylene, ethylene glycol, diethylene glycol, triethylene glycol, propylene Aliphatic hydrocarbons such as glycol, butylene glycol, pentanediol, hexanediol, low molecular weight polyethylene glycol, aromatic hydrocarbons, aliphatic polyhydric alcohols, aromatic polyhydric alcohols, chlorinated hydrocarbons, or other chlorinations Examples thereof include organic liquids and mixed solvents thereof.

  The coating solution used in the present invention is a resin solution containing 8 to 14% by weight of a polyvinylidene fluoride resin having a melt viscosity of 2500 Pa · s or more and 2 to 12% by weight of a cellulose ester. Normally, when a polyvinylidene fluoride resin solution with a single composition is used as a coating solution and solidified by a non-solvent-induced phase separation method, a large number of macrovoids are generated on the formed film wall due to the high cohesiveness of the coating solution. Therefore, it is difficult to develop high separation characteristics and permeation performance. In addition, in this invention, a macro void refers to the coarse hole in which the hole diameter formed in the isolation | separation functional layer exceeds 5 micrometers. In addition, macrovoids can be reduced by using a polyvinylidene fluoride resin having a high melt viscosity, but the permeation performance decreases due to the formation of a dense layer on the membrane wall. In the present invention, by blending a cellulose ester which is a hydrophilic polymer, the cohesiveness of the polyvinylidene fluoride resin can be lowered and the compatibility can be increased. Furthermore, by using a polyvinylidene fluoride resin having a high melt viscosity, the pores of the separation functional layer can be uniformly formed, and higher separation characteristics and permeation performance can be exhibited compared to conventional membranes.

In the present invention, the melt viscosity of the polyvinylidene fluoride resin is required to be 2500 Pa · s or more, preferably 3000 Pa · s or more, and more preferably 3300 Pa · s or more. When the melt viscosity is 2500 Pa · s or more, the physical strength is improved, and the occurrence of voids that deteriorate the separation characteristics such as virus removal can be suppressed, and thus the present invention is achieved. The upper limit is not particularly limited, but if it exceeds 7000 Pa · s, there is a manufacturing concern such as a decrease in the solubility of the resin. Here, the melt viscosity of the polyvinylidene fluoride resin can be measured under the conditions of ASTM D3835 / 232 ° C. and a shear rate of 100 seconds− ¹ .

  Further, the concentration of the polyvinylidene fluoride resin in the coating solution needs to be 8% by weight or more and 14% by weight or less, and preferably 8% by weight or more and 12% by weight or less. When the concentration of the polyvinylidene fluoride resin is 8% by weight or more, the physical characteristics are improved. On the other hand, when it is 14% by weight or less, the separation characteristics and the water permeability are improved, so that the present invention is achieved.

  In the present invention, the concentration of the cellulose ester blended in the coating solution in the coating solution needs to be 2% by weight to 12% by weight, preferably 3% by weight to 12% by weight, and more preferably 5%. % By weight or more and 12% by weight or less. When the cellulose ester content is 2% by weight or more, the cohesiveness of the polyvinylidene fluoride resin is reduced to suppress generation of large voids, and virus separation characteristics and fouling resistance are improved by uniform pore formation. On the other hand, when the content is 12% by weight or less, a decrease in chemical resistance and physical strength can be reduced, so that the present invention is achieved. Here, the cellulose ester is one selected from cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate having three ester groups in the repeating unit and adjusting the degree of hydrolysis thereof. is there.

  In the production method of the present invention, a coating solution having a solution viscosity of 1 Pa · s or more and 100 Pa · s or less is solidified in a coagulation bath after a free running time of 2 seconds or less while being coated on a polyvinylidene fluoride support film. In the case of forming into a hollow fiber shape, coating is performed using a coating nozzle made of an elastic body described in, for example, Japanese Patent Application Laid-Open No. 2004-314059, or a circular nozzle made of metal, ceramics, or the like according to the solution viscosity. It is possible. Further, when forming into a sheet shape, for example, it is possible to coat the support film drawn from the T-die with a slit coater.

  The solution viscosity of the coating solution needs to be 1 Pa · s or more and 100 Pa · s or less, and preferably 5 Pa · s or more and 80 Pa · s or less. If the viscosity of the coating solution is 1 Pa · s or more, excessive penetration of the coating solution into the support membrane can be suppressed, and if it is 100 Pa · s or less, coating spots due to an increase in shear stress are reduced, The invention is achieved. Here, the solution viscosity of the coating solution can be measured with a rotary digital viscometer (model: PV-II + Pro, manufactured by Brookfield, USA) while keeping the solution at 50 ° C.

  The idle time after coating needs to be 2 seconds or less, preferably 1 second or less. By solidifying in 2 seconds or less after coating, the development of voids due to the progress of phase separation of the coating solution induced by moisture in the gas phase can be suppressed and the separation characteristics can be improved. The As the coagulation liquid, the above-mentioned mixed solution of 40% by weight or less of a good solvent and a non-solvent is preferably used, but it is also preferable to use water that is easy to handle alone. The coagulation bath temperature is preferably 5 ° C. or higher and 80 ° C. or lower. Since the pores of the membrane wall can be controlled by controlling the phase separation according to the viscosity of the coating solution by adjusting the temperature to 5 ° C. or more and 80 ° C. or less, macrovoids can be reduced.

  The composite film of polyvinylidene fluoride resin according to the present invention will be described below. FIG. 1 and FIG. 2 are scanning electron micrographs in place of drawings for explaining the form of the composite hollow fiber membrane of the present invention.

  FIG. 1 is a drawing-substituting photograph (600 times) showing a membrane wall sectional structure constituting the hollow fiber-like composite membrane according to the present invention, and FIG. 2 shows a membrane wall sectional structure constituting the hollow fiber-like composite membrane according to the present invention. It is a drawing substitute photograph (3000 times).

  The structure of these composite membranes is a three-dimensional network structure containing a polyvinylidene fluoride resin having a melt viscosity of 2500 Pa · s or more in a range of 50 wt% to 88 wt% and a cellulose ester of 12 wt% to 50 wt%. It is formed of a functional layer followed by a support film having a spherical structure. When the polyvinylidene fluoride-based resin is 50% by weight or more, a separation property and physical strength are improved, and when it is 88% by weight or less, a three-dimensional network structure in which water permeability is improved is formed. Further, the fouling resistance is improved by containing 12% by weight or more of the cellulose ester, and the chemical resistance is improved by containing 50% by weight or less. Since the composite membrane in the present invention is formed by laminating a separation functional layer on a support membrane having a spherical structure, the composite membrane is formed by laminating layers at the interface. That is, in the case of a support film having a spherical structure, since the support films are joined at wide intervals when the spherical average diameter is increased, the separation functional layers are laminated in a deeply intricate manner. On the other hand, when the spherical average diameter is reduced, the bonding interval is narrowed, and a shallow structure is formed in an interlaced manner at the interface. Here, the three-dimensional network structure refers to a structure in which the solid content spreads in a three-dimensional network. In addition, the three-dimensional network structure has pores and voids partitioned by solid contents forming a network. The spherical structure refers to a structure in which a large number of spherical or substantially spherical solid components are connected directly or in a streak shape through the solid components.

  The separation functional layer according to the present invention needs to have a three-dimensional network structure with an average pore diameter of 0.01 μm or more and 1 μm or less and a thickness of 5 μm or more and 100 μm or less. As the functional layer, a separation functional layer having a three-dimensional network structure including a pore size slightly larger than the size of the smallest poliovirus (about 0.03 μm) is present with a thickness of a certain level or more. In fact, since it has such a property, viruses and the like can be removed more preferably, the separation function layer according to the present invention is smaller than the sieve (sieving) filtration that performs filtration with a pore size smaller than that of the virus. It is thought that so-called depth filtration that traps particles and viruses in the pores occurs predominantly.

  For the above reasons, the average pore size of the three-dimensional network structure in the separation functional layer according to the present invention needs to be 0.01 μm or more and 1 μm or less, preferably 0.03 μm or more and 0.5 μm or less, more preferably Is 0.05 μm or more and 0.2 μm or less. When the average pore diameter is less than 0.01 μm, the membrane permeability tends to be lowered, and when it exceeds 1 μm, there is a concern that the virus blocking rate is lowered. Here, the average pore diameter of the three-dimensional network structure in the separation functional layer was photographed with a scanning electron microscope at a cross section of the composite membrane at 6,000 times and 10,000 times, and 5 μm from the outer surface layer. The result of measuring the major and minor diameters of a total of 20 holes arbitrarily selected by depth can be obtained by number averaging.

  Moreover, the average pore diameter of the outermost surface of the separation functional layer of the present invention is preferably 1 μm or less, more preferably 0.1 μm or less, and still more preferably 0.01 μm or less. If the average pore diameter on the outermost surface exceeds 1 μm, membrane fouling tends to occur. Here, the average pore diameter of the outermost surface of the separation functional layer is 20 holes selected arbitrarily by taking a picture of the surface of the composite membrane at 30,000 times and 60,000 times using a scanning electron microscope. The results of measuring the major axis and minor axis of the film can be obtained by number averaging.

  The separation functional layer needs to have a thickness of 5 μm or more and 100 μm or less, substantially not having a macrovoid of 5 μm or more, and preferably 5 μm or more and 80 μm or less. When the thickness of the coat layer is 5 μm or more, the virus removability is improved, and when the thickness is 100 μm or less, the permeation performance is improved. Here, the thickness of the separation functional layer is arbitrarily set to the length of the range in which the three-dimensional network structure is observed by taking a picture of a cross section of the composite film at a magnification of 3,000 using a scanning electron microscope. It is possible to obtain a result obtained by averaging the results measured at 10 selected places.

  The support membrane according to the present invention preferably has a thickness of 60 μm or more and 400 μm or less, more preferably 120 μm or more and 350 μm or less. If the thickness of the support film is 60 μm or more, the buckling pressure due to the external pressure is improved, and if it is 400 μm or less, the permeation performance is improved. Here, the thickness of the support film was arbitrarily selected by using a scanning electron microscope, taking a cross-sectional view of the composite film at 100 times and 1000 times, and photographing the length of the range in which the spherical structure was observed. The results measured at a total of 10 locations can be obtained by number averaging.

  The average diameter of the spherical structure is preferably from 0.1 μm to 5 μm, more preferably from 0.5 μm to 3 μm. In the case of a spherical structure having an average diameter of 0.1 μm or more, the transmission performance is improved. Moreover, when it comprises a spherical structure with an average diameter of 5 micrometers or less, physical strength improves. Here, the average diameter of the spherical structure is obtained by measuring the diameter of the spherical shape in a total of 20 locations by taking an image photograph of the cross-section of the composite film at a magnification of 6,000 times using a scanning electron microscope. It can be obtained on average.

The virus removal performance of the separation membrane of the present invention is a performance determined by a non-destructive test for determining whether the membrane has an appropriate performance to be captured and whether there is a defect. As a test method, for example, indicator bacteria of a predetermined size are cultured, and the virus stock solution is prepared in distilled water so that the indicator bacteria contain a concentration of about 1.0 × 10 ⁷ PFU / ml. Do. The concentration of bacteria in the stock solution is taken as the numerator, the concentration of bacteria in the permeate as the denominator, and the ratio is expressed in common logarithm. The virus removal performance of this separation membrane can be performed using bacteriophage MS-2 (Bacteriophage MS-2 ATCC 15597-B1) having a size of about 25 nm. For example, in the case of a hollow fiber membrane, a glass module having a length of about 20 cm consisting of about 2 to 4 hollow fibers is produced, and a temperature of about 20 ° C. and a filtration differential pressure of about 10 kPa (external pressure) are evaluated. Under conditions, the virus stock solution can be fed and completely filtered. In the case of a flat membrane, the membrane can be obtained, for example, by cutting the membrane to a diameter of 43 mm, setting it in a cylindrical filtration holder, and performing the same operation as for the hollow fiber membrane.

  The pure water permeation performance in the present invention can be evaluated by incorporating a membrane in a container (module) that separates supply water and permeate and measuring the amount of permeate with an applied pressure. It is carried out using pure water or distilled water which does not substantially contain fine particles in the feed water. For example, in the case of a hollow fiber membrane, a glass module having a length of about 20 cm consisting of about 2 to 4 hollow fibers is prepared, and pure water is fed under conditions of a temperature of about 20 ° C. and a filtration differential pressure of about 10 kPa (external pressure). And can be completely filtered. In the case of a flat membrane, the membrane can be obtained, for example, by cutting the membrane to a diameter of 43 mm, setting it in a cylindrical filtration holder, and performing the same operation as for the hollow fiber membrane.

The breaking strength and breaking elongation in the present invention are determined by measuring the strength and elongation at the time of breaking indicated by a load-elongation curve when pulled in the length direction of the test length using a physical property tester. For these measurements, using a tensile tester (TENSILON (registered trademark) / RTM-100 manufactured by Toyo Baldwin Co., Ltd.), a composite membrane wetted with water was tested with a test head length of 50 mm and a full scale load of 5 kg. It can be determined by measuring at a speed of 50 mm / min, and by averaging the results of measurement of the breaking strength / elongation performed 10 times by changing the composite film. In addition, the breaking strength can be obtained by breaking strength (N) as breaking strength (N / mm ² = Pa) in a unit sectional area (mm ² ) of the composite membrane.

  The composite membrane of the present invention is also characterized by excellent stain resistance due to the formation of uniform pores in the separation functional layer and the hydrophilic effect of the cellulose ester. The stain resistance will be described below. In a water treatment method using a general microfiltration membrane or an ultrafiltration membrane, blocking of turbid components and the like in the water to be treated is prevented in the filtration step, so that the membrane surface pores are blocked and the filtration resistance is increased. For this reason, in the physical cleaning process, in order to remove turbid components adhering to the membrane surface from the membrane pores, back pressure cleaning is performed by flowing a fluid such as permeate or compressed air from the permeate side toward the outer surface of the membrane. Apply. In this physical cleaning process, a part of the blocked components is peeled off from the membrane, and the filtration resistance is lowered. However, it is difficult to completely remove all the components blocked on the membrane surface, and the filtration resistance continues to increase as the operation continues due to the adhering components remaining on the membrane. Finally, chemical cleaning using chemicals is performed, but if the filtration resistance does not recover, the membrane module itself is replaced.

  In order to suppress such a long-term increase (degree) in filtration resistance and enable a constant flow rate (stable) operation, the increase in filtration resistance in a single filtration step is suppressed, and a continuous process including a physical cleaning step is included. It is required to suppress an increase in filtration resistance during operation. In other words, for long-term stable operation, it is important to reduce the degree of increase in the filtration resistance value including the recoverability of physical cleaning. The increase in filtration resistance in continuous operation is quantitatively represented by the following technique as the degree of filtration resistance increase.

In the filtration step, the permeated water amount is 0.065 m ³ / m ² at a filtration pressure of 100 kPa, and then in the back pressure washing step, 0.0025 m ³ / m ² of water is passed from the permeate side to the outer surface of the membrane at a back washing pressure of 150 kPa. The filtration process and the back pressure washing process are repeated 10 times in a cycle. The total filtration water amount is plotted on the horizontal axis, and the calculated filtration resistance is plotted on the vertical axis. The permeated water amount obtained per fixed time in the filtration step is recorded, and the filtration resistance value at that time is obtained by dividing the filtration pressure 100 kPa by the permeated water amount. In this plot, the slope of the straight line connecting 9 points of filtration resistance at the start of the second to 10th filtration steps is defined as the increase in filtration resistance. However, if 9 points are not on the straight line, the slope of the straight line is obtained by linear approximation to obtain the degree of increase in filtration resistance. Usually, in a membrane filtration operation in which the filtration step and the back pressure washing step are repeated, the smaller the degree of increase in filtration resistance, the better the stain resistance and the better the membrane that can be stably operated over the long term. In the composite membranes of the present invention, filtration resistance increases degree calculated by said method is preferably ² × ¹⁰ 12 / ^m 2 or less, more preferably 1 × ¹⁰ 12 / ^{m 2} or less.

Hereinafter, the present invention will be described with reference to specific examples, but the present invention is not limited to these examples. Here, the physical property value and form of the polyvinylidene fluoride composite film of the present invention were measured by the following methods.
(1) Melt viscosity The melt viscosity was measured under the conditions of ASTM D3835 / 232 ° C and a shear rate of 100 sec- ¹ .
(2) Solution viscosity The solution viscosity was measured with a rotary digital viscometer (model: PV-II + Pro, manufactured by Brookfield, USA) while keeping the solution at 50 ° C.
(3) Virus removal performance The virus stock solution is distilled so that bacteriophage MS-2 (Bacteriophage MS-2 ATCC 15597-B1) having a size of about 25 nm contains a concentration of about 1.0 × 10 ⁷ PFU / ml. Prepared in water. The distilled water used here was distilled water from a pure water production apparatus Auto Still (manufactured by Yamato Kagaku) and subjected to high-pressure steam sterilization at 121 ° C. for 20 minutes. The virus stock solution removal performance was evaluated by preparing a glass module with a length of about 20 cm consisting of about 2 to 4 hollow fiber membranes, and sending the virus stock solution under conditions of a temperature of about 20 ° C. and a filtration differential pressure of about 10 kPa (external pressure). The whole was filtered. In collecting the filtrate, about 10 ml of the filtered initial permeate was discarded, and about 5 ml of the permeate for measurement was collected and diluted with distilled water to 0 to 1000 times. Based on the method of Overlay agar assay, Standard Method 9211-D (APHA, 1998, Standard methods for the examination of water and wastewater, 18th ed.) To determine the concentration of bacteriophage MS-2. Removal performance was expressed logarithmically. For example, 2 log means 2 log ₁₀ and means that the residual concentration is 1/100. Further, when no plaque was measured in the permeate, it was set to> 7 log.
(4) Pure water permeation performance Water permeation performance was achieved by preparing a glass mini-module consisting of about 2 to 4 composite membranes and sending distilled water under conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa (external pressure). The value obtained by performing filtration and measuring the amount of permeated water (m ³ ) for a certain period of time was calculated by converting into values at unit time (hr), unit effective membrane area (m ² ), and 50 kPa.
(5) Breaking strength / elongation Using a tensile tester (TENSILON (registered trademark) / RTM-100 manufactured by Toyo Baldwin Co., Ltd.), the composite membrane wetted with water was tested with a test length of 50 mm and a full scale load of 5 kg. The measurement was performed at a crosshead speed of 50 mm / min, and the number averaged from the measurement results of the breaking strength / elongation performed 10 times by changing the composite film. In addition, the breaking strength was determined as the breaking strength (N / mm ² = Pa) at the unit cross-sectional area (mm ² ) of the composite membrane.
(6) Thickness of separation functional layer Using a scanning electron microscope, the cross section of the composite film was photographed at 3,000 times, and the length of the range in which the three-dimensional network structure was observed was arbitrarily selected. The results measured at a total of 10 locations were obtained by number averaging.
(7) Thickness of the support film Using a scanning electron microscope, the composite film was photographed at 100 times and 1000 times, and the length of the range in which the spherical structure was observed was arbitrarily selected. The results measured at the places were obtained by number averaging.
(8) Average pore diameter on the outer surface of the separation function layer Using a scanning electron microscope, the surface of the composite membrane was photographed at 30,000 times and 60,000 times, and the long diameters of a total of 20 holes selected arbitrarily. The number average of the results of measuring the minor axis was obtained.
(9) Average pore diameter of three-dimensional network structure Using a scanning electron microscope, the composite membrane was photographed at 6,000 times and 10,000 times in cross section, and the pore diameters of a total of 20 holes selected arbitrarily. The result of measuring the minor axis was obtained by number averaging.
(10) Average diameter of spherical structure Using a scanning electron microscope, a cross-section of the composite film was photographed at a magnification of 6,000 times, and the results of measuring the major and minor diameters of a total of 20 arbitrarily selected spherical shapes were obtained. Obtained by number average.
(11) Average outer diameter / inner diameter of composite membrane (hollow fiber membrane) Using a scanning electron microscope, the cross-section of the hollow fiber-like composite membrane was photographed at 60 times and 100 times, and a total of 10 arbitrarily selected locations The results of measuring the major and minor diameters of the outer and inner diameters were obtained by number averaging.
(12) Average thickness of composite membrane (hollow fiber membrane) Using a scanning electron microscope, the cross section of the composite membrane was photographed at 60 times and 100 times, and the length from the outermost layer to the innermost layer end was The measurement results at a total of 10 arbitrarily selected sites were obtained by number averaging.
(13) Degree of increase in filtration resistance A glass membrane module was produced in which both ends of a hollow fiber membrane having a length of about 15 cm consisting of six hollow fiber membranes were opened (FIG. 3). Raw water is put into a stainless steel pressurized tank (ADVANTEC PRESSURE VESSEL DV-10, capacity 10L) (hereinafter referred to as raw water tank), and pure water is produced in a stainless steel pressurized tank (ADVANTEC PRESSURE VESSEL DV-40, capacity 40L). Distilled water obtained by autoclaving distilled water from a device auto still (manufactured by Yamato Kagaku) at 121 ° C. for 20 minutes was added (hereinafter referred to as a distilled water tank). For raw water, Lake Biwa water (turbidity 1.0 NTU or less, TOC (total organic carbon) 1.2 mg / L, calcium concentration 15 mg / L, silicon concentration 0.5, manganese concentration 0.01 mg / L or less, iron concentration) 0.01 mg / below) was used.

  The configuration of the evaluation apparatus was such that a connection type two-way cock (made of PTFE) was attached to the ends of A and D of the glass membrane module, and a connection type three-way cock (made of PTFE) was attached to the ends of C and D. The two-way cock at the B end of the glass membrane module and the raw water tank supply port were connected with a PTFE tube having an inner diameter of φ6 mm to form a raw water supply line. A similar tube was connected to the cocks at the ends of A and C and a distilled water tank supply port to form a distilled water supply line. First, the A and C end cocks are closed, compressed air adjusted to 100 KPa is applied to the raw water tank, and the B and D end cocks are opened to open the raw water tank into the glass membrane module. It was set as the filtration process which supplies raw | natural water (lake water) and performs external pressure total filtration.

  The weight of the permeated water was measured every 5 seconds with an electronic balance (AND HF-6000) connected to a personal computer, and the continuous recording program AND RsCom ver. Recorded using 2.40. The data obtained in this experiment was calculated from the permeated water weight (g) per 5 seconds using the following formula for filtration resistance.

Filtration resistance (1 / m) = filtration pressure (kPa) × 10 ³ × 5 × membrane area (m ² ) × 10 ⁶ / (viscosity (Pa · s) × (permeated water weight per 5 seconds) × density (g / Cm ³ ))
When the permeate reaches a flow rate of 0.00025 (m ³ / m ² ), the raw water supply is stopped by closing the 3-way cock at the B-end of the glass membrane module and the 2-way cock at the D-end. did. Subsequently, compressed air adjusted to 150 kPa is applied to the distilled water tank, the two-way cock at the A end is opened as backwash water, distilled water is allowed to flow inside the hollow fiber, and the three-way cock at the C end is moved to the discharge side. It was opened and flowed out of the system until the backwash drainage reached 10 ml, and the backwash process was performed. The above filtration step and backwashing step were carried out 10 times continuously with respect to the installation module as one operation, and the total filtration water amount was plotted on the horizontal axis and the calculated filtration resistance was plotted on the vertical axis.

  Here, the plot was started 30 seconds after the start of each filtration. Moreover, since the water permeation amount decreases as the filtration resistance increases, the absolute value of the increase amount every 5 seconds decreases. Since the filtration resistance is calculated from the increase amount according to the above formula, when the increase amount decreases, the variation has a greater effect on the calculated filtration resistance. Therefore, when the decrease in water permeability was significant, the graph was corrected by taking a moving average approximation of the graph created as appropriate.

In the graph of the total filtered water amount-filtration resistance created from the results of the filtration experiment, and in some cases the moving average approximation of the graph, the relationship between the total filtered water amount and the filtration resistance, and the 2-10th filtration process start time The slope of the straight line connecting 9 filtration resistances was defined as the increase in filtration resistance. However, when 9 points did not lie on the straight line, the slope of the straight line was obtained by linear approximation to obtain the degree of increase in filtration resistance (× 10 ¹² / m ² ).
<Example 1>
A support membrane solution was obtained by dissolving 38% by weight of vinylidene fluoride homopolymer having a weight average molecular weight of 420,000 and 62% by weight of γ-butyrolactone at 160 ° C. Further, vinylidene fluoride homopolymer having a melt viscosity of 4700 Pa · s is 10% by weight, cellulose acetate (Eastman Chemical Co., CA435-755: cellulose triacetate, CA398-3: cellulose diacetate) 6% by weight, N-methyl-2- Pyrrolidone was dissolved at a temperature of 140 ° C. at a ratio of 84% by weight to obtain a coating solution having a solution viscosity of 46 Pa · s. The support membrane solution was extruded from the outer slit of the double tubular spinning nozzle and a 85% by weight aqueous solution of γ-butyrolactone was extruded concentrically from the center pipe of the double tubular spinning nozzle, and the solidification temperature was 10 ° C. and 85 weight of γ-butyrolactone. After solidifying in an aqueous solution, a support film was obtained through a 1.5-fold stretching process, a solvent removal process, and a drying process. Supplying the support film into a coating nozzle, and on the other hand, supplying the obtained coating solution and drawing it out while coating the support film, coagulating in water with a freezing time of 1 second and a coagulation bath temperature of 25 ° C .; A hollow fiber composite membrane (hereinafter referred to as a composite hollow fiber membrane) was obtained through a solvent removal step.

The structure of the obtained composite hollow fiber membrane has an outer diameter of 1352 μm, an inner diameter of 728 μm, an average thickness of the separation functional layer of 50 μm, an average pore diameter of the outer surface of the separation functional layer of 0.03 μm, and an average of the three-dimensional network structure The pore diameter was 0.3 μm, the thickness of the support membrane was 262 μm, and the average diameter of the sphere (structure) was 2.6 μm. Pure water permeation performance is 0.43 m ³ / m ² / hr, virus removal performance is> 7 log, breaking strength is 11.9 MPa, breaking elongation is 53%, and filtration resistance increase in Lake Biwa water is 0.55 × 10 It was a composite hollow fiber membrane showing ¹² / m ² and excellent in stain resistance. The evaluation results are summarized in Table 1.
<Example 2>
10% by weight of vinylidene fluoride homopolymer having a melt viscosity of 4700 Pa · s, 9.6% by weight of cellulose acetate (Eastman Chemical Co., CA435-75S: cellulose triacetate, CA398-3: cellulose diacetate), N-methyl-2 -Pyrrolidone was dissolved at a temperature of 140 ° C as a proportion of 80.4% by weight to obtain a coating solution having a solution viscosity of 76 Pa · s. A support membrane was obtained using the same support membrane solution as in Example 1. Supplying the support film into a coating nozzle, and on the other hand, supplying the obtained coating solution and drawing it out while coating the support film, coagulating in water with a freezing time of 1 second and a coagulation bath temperature of 25 ° C .; A composite hollow fiber membrane was obtained through a solvent removal step.

The resulting composite hollow fiber membrane has an outer diameter of 1360 μm, an inner diameter of 736 μm, an average thickness of the separation functional layer of 52 μm, an average pore diameter of the outer surface of the separation functional layer of 0.02 μm, and an average of the three-dimensional network structure. The pore diameter was 0.4 μm, the thickness of the support membrane was 260 μm, and the average diameter of the sphere (structure) was 2.6 μm. Pure water permeation performance is 0.32 m ³ / m ² / hr, virus removal performance is> 7 log, breaking strength is 12.9 MPa, breaking elongation is 45%, and filtration resistance increase in Lake Biwa water is 0.21 × It was a composite hollow fiber membrane exhibiting 10 ¹² / m ² and excellent in stain resistance. The evaluation results are summarized in Table 1.
<Example 3>
12% by weight of vinylidene fluoride homopolymer having a melt viscosity of 4700 Pa · s, 6% by weight of cellulose acetate (Eastman Chemical Co., CA435-75S: cellulose triacetate, CA398-3: cellulose diacetate), 82% by weight of dimethyl sulfoxide A coating solution having a solution viscosity of 80 Pa · s was obtained by dissolving at a temperature of 140 ° C. as a ratio. A support membrane was obtained using the same support membrane solution as in Example 1. Supplying the support film into a coating nozzle, and on the other hand, supplying the obtained coating solution and drawing it out while coating the support film, coagulating in water with a freezing time of 1 second and a coagulation bath temperature of 25 ° C .; A composite hollow fiber membrane was obtained through a solvent removal step.

The structure of the obtained composite hollow fiber membrane has an outer diameter of 1363 μm, an inner diameter of 713 μm, an average thickness of the separation functional layer of 64 μm, an average pore diameter of the outer surface of the separation functional layer of 0.02 μm, and an average of a three-dimensional network structure. The pore diameter was 0.4 μm, the thickness of the support membrane was 261 μm, and the average diameter of the sphere (structure) was 2.7 μm. Pure water permeation performance is 0.32 m ³ / m ² / hr, virus removal performance is> 7 log, breaking strength is 12.2 MPa, breaking elongation is 43%, and filtration resistance increase in Lake Biwa water is 2.0 × It was a composite hollow fiber membrane exhibiting 10 ¹² / m ² and excellent in stain resistance. The evaluation results are summarized in Table 1.
<Example 4>
10% by weight of vinylidene fluoride homopolymer having a melt viscosity of 2800 Pa · s, 4% by weight of cellulose acetate (Eastman Chemical Co., CA435-75S: cellulose triacetate, CA398-3: cellulose diacetate), N-methyl-2-pyrrolidone Was coated at a temperature of 140 ° C. at a temperature of 140 ° C. to obtain a coating solution having a solution viscosity of 8.6 Pa · s, and the composite hollow fiber membrane was coated on the support membrane under the same conditions as in Example 1. Obtained.

The structure of the obtained composite hollow fiber membrane has an outer diameter of 1371 μm, an inner diameter of 717 μm, an average thickness of the separation functional layer of 60 μm, an average pore diameter of the outer surface of the separation functional layer of 0.02 μm, and an average of the three-dimensional network structure The pore diameter is 0.4 μm, the support membrane thickness is 267 μm, the spherical (structure) average diameter is 2.5 μm, the pure water permeation performance is 0.39 m ³ / m ² / hr, and the virus removal performance is> 7 log. Met. Moreover, it was a composite hollow fiber membrane excellent in stain resistance, having a breaking strength of 8.2 MPa, a breaking elongation of 43%, and an increase in filtration resistance in Lake Biwa water of 1.3 × 10 ¹² / m ² . . The evaluation results are summarized in Table 1.
<Example 5>
14% by weight of vinylidene fluoride homopolymer having a melt viscosity of 4700 Pa · s, 2% by weight of cellulose acetate (Eastman Chemical Co., CA435-75S: cellulose triacetate, CA398-3: cellulose diacetate), N-methyl-2-pyrrolidone Was dissolved at a temperature of 140 ° C. at a ratio of 84% by weight to obtain a coating solution having a solution viscosity of 68 Pa · s. A support membrane was obtained using the same support membrane solution as in Example 1. Supplying the support film into a coating nozzle, and on the other hand, supplying the obtained coating solution and drawing it out while coating the support film, coagulating in water with a freezing time of 1 second and a coagulation bath temperature of 25 ° C .; A composite hollow fiber membrane was obtained through a solvent removal step.

The structure of the obtained composite hollow fiber membrane has an outer diameter of 1383 μm, an inner diameter of 713 μm, an average thickness of the separation functional layer of 74 μm, an average pore diameter of the outer surface of the separation functional layer of 0.02 μm, and an average of the three-dimensional network structure. The pore diameter is 0.4 μm, the support membrane thickness is 261 μm, the spherical (structure) average diameter is 2.7 μm, the pure water permeation performance is 0.30 m ³ / m ² / hr, and the virus removal performance is> 7 log. The composite hollow fiber membrane was excellent in stain resistance, having a breaking strength of 11.2 MPa, a breaking elongation of 44%, and an increase in filtration resistance in Lake Biwa water of 1.9 × 10 ¹² / m ² . . The evaluation results are summarized in Table 1.

<Comparative Example 1>
The test was carried out under the same conditions as in Example 1 except that the idling time was 10 seconds.

The structure of the obtained composite hollow fiber membrane has an outer diameter of 1348 μm, an inner diameter of 722 μm, an average thickness of the separation functional layer of 51 μm, an average pore diameter of the outer surface of the separation functional layer of 0.06 μm, and an average of a three-dimensional network structure. The pore diameter was 1.3 μm, the support membrane thickness was 262 μm, and the average diameter of the sphere (structure) was 2.6 μm. Pure water permeation performance is 0.41 m ³ / m ² / hr, virus removal performance is 4.8 log, breaking strength is 11.2 MPa, breaking elongation is 48%, and filtration resistance increase in Lake Biwa water is 0.61 × 10 ¹² / m ² was shown. As membrane characteristics, pure water permeation performance, breaking strength and elongation were maintained high, and the degree of filtration resistance increase was low and the stain resistance was excellent, but the virus removability decreased. The evaluation results are summarized in Table 2.
<Comparative example 2>
Temperature of 10% by weight of vinylidene fluoride homopolymer having a melt viscosity of 700 Pa · s, 4% by weight of cellulose acetate (Eastman Chemical Co., CA435-75S: cellulose triacetate), and 86% by weight of N-methyl-2-pyrrolidone A composite hollow fiber membrane was obtained by coating the support membrane under the same conditions as in Example 1 except that the coating solution was dissolved at 110 ° C. to obtain a coating solution having a solution viscosity of 0.4 Pa · s.

The structure of the obtained composite hollow fiber membrane has an outer diameter of 1340 μm, an inner diameter of 750 μm, an average thickness of the separation functional layer of 35 μm, an average pore diameter of the outer surface of the separation functional layer of 0.04 μm, and a thickness of the support membrane. Although 260 μm and the average diameter of the sphere (structure) were 2.6 μm, many macrovoids having a pore diameter exceeding 5 μm were observed in the three-dimensional network structure (cross section). The pure water permeation performance was 0.18 m ³ / m ² / hr, and the virus removal performance was 1.2 log. The breaking strength was 7.0 MPa, the breaking elongation was 55%, and the filtration resistance increase in Lake Biwa water was 0.73 × 10 ¹² / m ² , but the virus removal performance, pure water permeation performance, and breaking strength The strength decreased significantly. The evaluation results are summarized in Table 2.
<Comparative Example 3>
Temperature of 10% by weight of vinylidene fluoride homopolymer having a melt viscosity of 700 Pa · s, 8% by weight of cellulose acetate (Eastman Chemical Co., CA435-75S: cellulose triacetate), 82% by weight of N-methyl-2-pyrrolidone A composite hollow fiber membrane was obtained by coating the support membrane under the same conditions as in Example 1 except that the coating solution having a solution viscosity of 4.7 Pa · s was obtained by dissolving at 110 ° C.

The structure of the obtained composite hollow fiber membrane has an outer diameter of 1342 μm, an inner diameter of 740 μm, an average thickness of the separation functional layer of 38 μm, an average pore diameter of the outer surface of the separation functional layer of 0.02 μm, and a thickness of the support membrane. Although the average diameter of the spherical (structure) was 263 μm and 2.6 μm, many macrovoids having a pore diameter exceeding 5 μm were observed in the three-dimensional network structure (cross section). The pure water permeation performance was 0.04 m ³ / m ² / hr, and the virus removal performance was 1.7 log. The breaking strength was 7.1 MPa, the breaking elongation was 32%, and the increase in filtration resistance in Lake Biwa water was 2.3 × 10 ¹² / m ² . As membrane characteristics, virus removal performance, water permeability performance, and breaking strength were significantly reduced. The evaluation results are summarized in Table 2.
<Comparative example 4>
10% by weight of vinylidene fluoride homopolymer having a melt viscosity of 2200 Pa · s, 4% by weight of cellulose acetate (Eastman Chemical Co., CA435-75S: cellulose triacetate), 86% by weight of N-methyl-2-pyrrolidone A composite hollow fiber membrane was obtained by coating the support membrane under the same conditions as in Example 1 except that the solution was dissolved at 110 ° C. to obtain a solution viscosity of 1.7 Pa · s coating solution.

The structure of the obtained composite hollow fiber membrane has an outer diameter of 1345 μm, an inner diameter of 715 μm, an average thickness of the separation functional layer of 50 μm, an average pore diameter of the outer surface of the separation functional layer of 0.03 μm, and a thickness of the support membrane. The average diameter of 265 μm and spherical (structure) was 2.6 μm, but several macrovoids having a pore diameter exceeding 5 μm were found in the three-dimensional network structure (cross section). The pure water permeation performance was 0.26 m ³ / m ² / hr, and the virus removal performance was 4.2 log. The breaking strength was 7.6 MPa, the breaking elongation was 50%, and the increase in filtration resistance in Lake Biwa water was 0.83 × 10 ¹² / m ² . As the film characteristics, it was excellent in stain resistance, but the virus removal performance and the breaking strength were remarkably reduced. The evaluation results are summarized in Table 2.
<Comparative Example 5>
10% by weight of vinylidene fluoride homopolymer having a melt viscosity of 2200 Pa · s, 8% by weight of cellulose acetate (Eastman Chemical Co., CA435-75S: cellulose triacetate), 82% by weight of N-methyl-2-pyrrolidone A composite hollow fiber membrane was obtained by coating the support membrane under the same conditions as in Example 1 except that the solution was melted at 110 ° C. to obtain a solution viscosity of 8.6 Pa · s.

The structure of the obtained composite hollow fiber membrane has an outer diameter of 1350 μm, an inner diameter of 706 μm, an average thickness of the separation functional layer of 55 μm, an average pore diameter of the outer surface of the separation functional layer of 0.03 μm, and a thickness of the support membrane. The average diameter of 267 μm and spherical shape (structure) was 2.6 μm, but many macrovoids having a pore diameter of more than 5 μm were observed in the three-dimensional network structure (cross section). The pure water permeation performance was 0.28 m ³ / m ² / hr, and the virus removal performance was 3.8 log. The breaking strength was 7.0 MPa, the breaking elongation was 42%, and the increase in filtration resistance in Lake Biwa water was 0.78 × 10 ¹² / m ² . As the film characteristics, it was excellent in stain resistance, but the virus removal performance and breaking strength were remarkably lowered. The evaluation results are summarized in Table 2.
<Comparative Example 6>
14% by weight of vinylidene fluoride homopolymer having a melt viscosity of 700 Pa · s, 3% by weight of cellulose acetate (Eastman Chemical Co., CA435-75S: cellulose triacetate), 77% by weight of N-methyl-2-pyrrolidone, polyoxyethylene palm Oil Fatty Acid Sorbitan (Sanyo Kasei Co., Ltd., trade name Ionette (registered trademark) T-20C) 3% by weight, water 3% dissolved at a temperature of 95 ° C. to obtain a solution viscosity of 0.6 Pa · s coating solution Except for the above, a support membrane was coated under the same conditions as in Example 1 to obtain a composite hollow fiber membrane.

The structure of the obtained composite hollow fiber membrane has an outer diameter of 1345 μm, an inner diameter of 739 μm, an average thickness of the separation functional layer of 38 μm, an average pore diameter of the outer surface of the separation functional layer of 0.02 μm, and a thickness of the support membrane. 265 μm, spherical (structure) average diameter was 2.6 μm, pure water permeation performance was 0.16 m ³ / m ² / hr, and virus removal performance was 3.2 log. Many macrovoids having a pore diameter exceeding 5 μm were observed in the cross section). The breaking strength was 7.8 MPa, the breaking elongation was 85%, and the increase in filtration resistance in Lake Biwa water was 2.3 × 10 ¹² / m ² . As membrane characteristics, virus removal performance, pure water permeation performance, and breaking strength were significantly reduced. The evaluation results are summarized in Table 2.
<Comparative Example 7>
Except that 10% by weight of vinylidene fluoride homopolymer having a melt viscosity of 2000 Pa · s was dissolved at a temperature of 140 ° C. at a rate of 90% by weight of N-methyl-2-pyrrolidone, and a solution viscosity of 13 Pa · s was obtained. The support membrane was coated under the same conditions as in Example 1 to obtain a composite hollow fiber membrane.

As for the structural form of the obtained composite hollow fiber membrane, many macrovoids having an outer diameter of 1380 μm, an inner diameter of 742 μm, and a pore size exceeding 5 μm were observed in the separation functional layer. As membrane characteristics, pure water permeation performance is 0.55 m ³ / m ² / hr, virus removal performance is 2.2 log, breaking strength is 7.4 MPa, breaking elongation is 80%, and the degree of filtration resistance increase in Lake Biwa water Showed 2.4 × 10 ¹² / m ² . The evaluation results are summarized in Table 2.

  INDUSTRIAL APPLICABILITY According to the present invention, a method for producing a polyvinylidene fluoride-based composite film in which a coating layer having high virus removal performance, pure water permeation performance, and physical strength is laminated by a simple method by coating, and the polyvinylidene fluoride-based composite film I will provide a. Thereby, when it uses for a water treatment use, the water quality improvement of permeated water and long-term reproduction use are attained.

Claims (2)

  A three-dimensional network structure containing a polyvinylidene fluoride resin having a melt viscosity of 2500 Pa · s or more and 50 wt% or more and 88 wt% or less, a cellulose ester of 12 wt% or more and 50 wt% or less, and an average pore size of 0.01 μm or more and 1 μm or less. And a separation functional layer having a thickness of 5 μm or more and 100 μm or less and having substantially no macrovoid of 5 μm or more has a spherical structure having an average diameter of 0.1 μm or more and 5 μm or less. A polyvinylidene fluoride-based composite film, characterized in that it is laminated on the surface.   A coating containing 8% by weight to 14% by weight of a polyvinylidene fluoride resin having a melt viscosity of 2500 Pa · s or more, 2% by weight to 12% by weight of a cellulose ester, and a solution viscosity of 1 Pa · s to 100 Pa · s. A polyvinylidene fluoride system in which a separation functional layer is formed on the polyvinylidene fluoride support membrane by coating the solution on the polyvinylidene fluoride support membrane and coagulating in a coagulation bath after a free running time of 2 seconds or less. A method for producing a composite membrane.