JP5655963B1 - Polymeric porous flat membrane sheet made of polyvinylidene fluoride - Google Patents

Abstract

An object of the present invention is to provide a high-strength polymer porous flat membrane sheet for MBR in which the surface of a polymer porous membrane is maintained hydrophilic for a long period of time and high water permeability and fouling resistance are maintained for a long period of time. A flat membrane sheet comprising a flat membrane structure comprising a sheet-like substrate made of nonwoven fabric and a polymer porous membrane containing polyvinylidene fluoride, wherein hydroxypropylcellulose is in a state of fine particles on the flat membrane sheet The polymer porous flat membrane sheet for MBR, wherein the size of the fine particles of hydroxypropylcellulose in the range of 5 μm depth from the outermost surface of the flat membrane sheet is 5 to 100 nm . [Selection figure] None

Description

  The present invention relates to a polymer porous flat membrane sheet made of polyvinylidene fluoride used in a membrane separation activated sludge method (MBR), which maintains high water permeability and fouling resistance even when used for a long period of time.

  In recent years, the quality and quantity required for domestic and industrial water has increased against the background of global population growth, industrialization, urbanization, and improvement in living standards.

  In general, water resources can be obtained by using natural water obtained from nature or by obtaining fresh water from seawater using evaporation or reverse osmosis, or by reverse osmosis from salt-containing brine. There is a way to get fresh water using. However, natural resources of fresh water are limited, and it is said that the availability tends to become narrower due to the influence of abnormal weather in recent years. Moreover, in order to produce fresh water using the evaporation method or reverse osmosis, energy for heating and pressurization is required, so the area used is limited.

  Another method is to reuse sewage. In the conventional sewage treatment, the organic components in the sewage are decomposed with activated sludge, and the treated water is discharged through sedimentation filtration or the like, but it is difficult to completely remove bacteria such as Escherichia coli. However, in MBR, water treated with activated sludge is filtered using a separation membrane, so it is possible to completely remove the above-mentioned harmful bacteria group, such as compactness of equipment and ease of operation management. There are many advantages, and it has become a technology that attracts much attention in recent years. The water separated by the membrane separation activated sludge method can be used not only as life scenery maintenance water and middle water, but also can be obtained in combination with the reverse osmosis method. The reverse osmosis method using seawater requires a high pressure against the salinity, but is characterized in that it can be produced safely and with low energy by using treated water obtained by MBR as raw water.

  Thus, MBR is attracting attention as a method for solving the water shortage expected in the future. In order to further improve this method and complete a low-cost and high-efficiency system, there is a need to ensure water permeability while maintaining membrane separation performance. The general characteristics required for membranes used in the membrane separation activated sludge method are shown below.

  First, in MBR, a bare membrane is used by immersing it in activated sludge, so that it is a rough usage pattern compared to separation membranes in other technical fields. Therefore, physical strength that can withstand use is required. More specifically, the membrane is not damaged, deformed, or deteriorated in performance even when it is impacted by various contaminants in the activated sludge or the transmembrane pressure difference (TMP) is increased by filtration. In order to achieve this, high strength and film properties that are difficult to stretch are required.

  In addition, if the membrane is used for a long time in a state where it is immersed in activated sludge, the pores will be blocked by secretions, dead bodies themselves, and foreign substances contained in the sludge. In order to cope with this, it is necessary to increase the pump pressure. This is the biggest problem when using a membrane called fouling, but this problem is solved by washing the membrane with chemicals such as sodium hypochlorite and hydrochloric acid, An operation is performed to return the membrane to a fresh state. Therefore, chemical resistance that does not deteriorate the membrane against these drugs is also important.

  However, these chemical cleaning operations have many problems in terms of economy and environment, such as the inability to perform a filtration operation, chemical costs, labor, and drainage treatment of chemicals. Therefore, the biggest issue is how to prevent fouling and allow it to be used for a longer period of time so that the cleaning operation with the medicine is reduced.

  Although methods for suppressing fouling have been intensively studied, effective examples include membrane structure control (particularly control of pore diameter and distribution thereof) and membrane hydrophilization. If there is a width in the pore diameter, there will always be pores that are likely to close, so fouling will proceed rapidly from there. In addition, when the pore diameter on the membrane surface is too small or the degree of opening is low, it is considered that the suction pressure per pore increases and the probability of clogging increases. Another is the hydrophilization of membranes. In general, many substances (foulants) that cause fouling are hydrophobic. If the separation membrane is hydrophobic, the foulant is likely to be adsorbed on the membrane surface due to the hydrophobic interaction. As a result, it is considered that fouling occurs easily and progresses rapidly.

  Furthermore, what is important in practical use of the membrane is that the hydrophilicity lasts as long as possible. As a result, it is possible to save the labor and cost of making the membrane after use washed and dried and then making it hydrophilic again, and the anti-fouling effect lasts even during actual use, thereby contributing to energy saving and cost reduction.

  As an MBR membrane considering the problems of water permeability and hydrophilization, a membrane using chlorinated polyvinyl chloride (CPVC) as a membrane material has been proposed (for example, see Patent Document 1). Specifically, in Patent Document 1, a chlorinated polyvinyl chloride is dissolved in tetrahydrofuran, and a solution obtained by further adding isopropyl alcohol (IPA) and sucrose ester is impregnated with a polyester nonwoven fabric, followed by phase separation by drying. Raises to form a microporous body. However, since the film using the above-described conventional CPVC is formed by a dry method, there is a problem in the process of treating the solvent vapor from the manufacturing process. In addition, there is a problem in the degree of hydrophilization, particularly in maintaining hydrophilicity when used for a long time.

  As an example using a different hydrophilizing agent, a method using cellulose introduced with a hydrophobic group or hydroxypropylmethylcellulose (HPMC) introduced with a hydrophobic group has been proposed (for example, see Patent Document 2). Specifically, polyvinyl chloride (PVC) or CPVC is dissolved in tetrahydrofuran (THF), and a non-solvent such as the above-described cellulose derivative and IPA is further impregnated with a nonwoven fabric, followed by drying. Separation is caused to form a microporous body. However, in this method, the hydrophilizing agent is only dispersed in the membrane components, and the hydrophilizing agent is easily eluted in the membrane cleaning performed in actual use, particularly in the membrane cleaning using chemicals, and the hydrophilicity is maintained. There is a problem that the effect is weak. Further, in Patent Document 2, it is necessary to use a hydrophilizing agent at least 3% by weight with respect to the resin material, and there is a problem that costs increase.

  As an example of immobilizing a hydrophilizing agent on the membrane surface, a method aimed at immobilizing hydroxyalkyl cellulose on a hydrophobic ultrafiltration membrane has been proposed (see, for example, Patent Document 3). Specifically, an ultrafiltration membrane made of a sulfone-based polymer is immersed in an alcohol solution containing hydroxyalkyl cellulose, and then subjected to treatment including autoclaving in the presence of steam or water, and immersion in boiling water. Is what you do. However, in this method, as will be described later, the hydrophilic effect may be lowered by excessively promoting the thermal denaturation of the hydroxyalkyl cellulose at a high temperature, and the original hydrophilic properties of the hydroxyalkyl cellulose are fully expressed. There is a problem that cannot be done. In addition, providing an autoclave treatment or boiling water treatment process is not an excellent method from the viewpoint of energy saving and cost because of increased energy consumption, and may complicate equipment and processes. . As an example of a surface modification method for various polymeric support materials, a method of irreversibly adsorbing a hydrophilic polymer on the surface of a hydrophobic membrane has been proposed (see, for example, Patent Document 4). Specifically, a polysulfone (PSf) membrane is impregnated with a deionized solution of hydroxypropyl cellulose (HPC) for 16 hours, and then washed with deionized water for 16 hours. However, this method has a problem in that HPC does not stay on the surface of the membrane and is eluted at the time of washing because the insolubilization treatment for fixing the HPC on the surface of the hydrophobic membrane and preferable heat denaturation are not performed.

  An example of a spontaneously wettable porous membrane composed of HPC and polyethersulfone (PES) has been proposed for the purpose of imparting high-temperature sterilization treatment resistance such as steam sterilization (see, for example, Patent Document 5). Specifically, HPC is applied to a porous membrane made of PES, and then steam sterilization is performed. However, in this example as well as Patent Document 3, as described later, the thermal modification of HPC is accelerated too much at a high temperature, and the hydrophilic effect may be lowered. May not be expressed in

  In order to prevent a decrease in the filtration rate and clogging of the hydrophobic membrane filter, an example in which a cellulose derivative is adsorbed on the membrane surface in order to modify the hydrophobic membrane to hydrophilic has been proposed (for example, (See Patent Document 6). Specifically, an aromatic polymer-based hydrophobic membrane is impregnated with a solution of a hydrophilic cellulose derivative at a temperature lower by 10 ° C. or more than the gelation or cloudiness temperature of the solution, and then the gelation or cloudiness temperature of the solution is exceeded. Is also washed with water at a temperature not lower than 20 ° C. However, the content of this patent document only shows the temperature of gelation or cloudiness of HPC, and teaches that the hydrophilic treatment of HPC is performed below that temperature in order to prevent clogging of the film.

  In order to obtain long-term water permeability of the membrane, there is a proposal using polyvinylidene fluoride (PVDF) (see, for example, Patent Document 7). In order to improve the hydrophobicity of PVDF, hydrophilicity is imparted by adding a polymer component having hydrophilicity. However, in this proposal, since the hydrophilic component is simply blended, the hydrophilizing agent falls off during use, and thus there is a problem that the effect of anti-fouling does not continue for a long time.

  In addition, as an example of hydrophilizing a PVDF membrane, a technique has been disclosed in which a flat membrane formed by casting a PVDF solution is immersed in an HPC aqueous solution to impart hydrophilicity (for example, Patent Document 8). reference). In this technique, a hydrophobic film is immersed in an aqueous HPC solution and then dried. However, in this method, the water content of the aqueous solution on the film may become non-uniform in the drying process. Heating at the time of drying does not allow the HPC to be heat-treated uniformly at an appropriate temperature, or the concentration of HPC may be locally increased / decreased. As a result, there is a possibility that the hydrophilic expression of the film is insufficient and non-uniform. In the case where only air drying is performed at the time of drying, there is a problem that the hydrophilicity of the film and the persistence of the hydrophilic effect are insufficient because the adhesion of the HPC to the film becomes insufficient.

JP 58-088011 A Japanese Patent No. 4395904 Japanese Patent No. 4504963 JP-A-62-176508 JP 2003-251152 A Japanese Patent Application Laid-Open No. 09-075694 JP 2012-106235 A Special Table 2000-505719

  The present invention has been made to overcome the problems of the prior art, and its purpose is to maintain the surface of the polymer porous membrane for a long period of time and to maintain high water permeability and fouling resistance for a long period of time. It is to provide a high-strength polymer porous flat membrane sheet for MBR that is maintained.

  As a result of intensive studies to achieve the above object, the present inventor has selected a film material having a strength that can withstand long-term use, and has developed excellent film surface properties that prevent sludge from adhering. Specifically, MBR that maintains high water permeability and fouling resistance for a long period of time by dispersing and fixing HPC in the form of fine particles on the surface of the porous polymer membrane using PVDF and further insolubilizing it. The present inventors have found that a polymeric porous flat membrane sheet can be provided for use in the present invention.

That is, this invention is comprised by the following (1) and (2).
(1) High molecular porous material including a sheet-like base material made of nonwoven fabric and polyvinylidene fluoride (excluding polyvinyl chloride, chlorinated polyvinyl chloride, polyether sulfone, polytetrafluoroethylene, or a mixture thereof) A flat membrane sheet comprising a flat membrane structure comprising a membrane, wherein hydroxypropylcellulose is dispersed and fixed in the form of fine particles on the flat membrane sheet, and is 5 μm deep from the outermost surface of the flat membrane sheet A polymer porous flat membrane sheet for MBR, wherein the size of the fine particles of hydroxypropylcellulose in the range is 5 to 100 nm.
(2) The flat film sheet according to (1), wherein the dispersion degree of the fine particles of hydroxypropylcellulose is in the range of 0.2 to 1.5.

  In the flat membrane sheet of the present invention, the membrane material is PVDF, can withstand long-term use, and has extremely high membrane performance such as water permeability. In addition, since HPC is used as a hydrophilizing agent, a high hydrophilizing effect is obtained, and HPC is dispersed in fine particles and fixed and then insolubilized, so that high fouling resistance is exhibited and sustained. Sexual expression is possible.

FIG. 1A is an enlarged view of the film cross-sectional structure near the outer surface of the flat film sheet obtained in the present invention, using a scanning electron microscope (SEM). FIG. 1B is an enlarged view of the film cross-sectional structure near the inner surface of the flat film sheet, using a scanning electron microscope (SEM). FIG. 2 is an image obtained by enlarging a film cross-sectional structure near the outer surface of a typical flat film sheet obtained by the present invention at a magnification of 2,000 using a transmission electron microscope (TEM). Stained and indicated by black dots are HPC, the amorphous island is the polymer porous membrane, and the sea is the embedding epoxy resin.

  Hereinafter, the present invention will be described based on the embodiments. The feature of the polymer porous flat membrane sheet according to the embodiment of the present invention is that it has high water permeability even if it is used for a long time by dispersing and fixing HPC in the form of fine particles to a membrane containing PVDF suitable for MBR application. Characteristics and fouling resistance are maintained. In particular, such HPC sticking is achieved by immersing the above-mentioned flat membrane structure in a clear hydrophilizing impregnation liquid (alcohol aqueous solution) composed of HPC, alcohol, and water, and then a part of the alcohol component in the film. It is characterized in that it is fixed at a specific temperature after volatilizing.

  The flat membrane sheet of the present invention is used for MBR which is immersed in activated sludge to obtain a clear filtrate from the activated sludge liquid. In the MBR method, wastewater is guided into activated sludge, and pollutants in wastewater, mainly organic matter, are captured by microorganisms that have propagated in large quantities in the reaction tank, that is, activated sludge, and consumed by metabolism or respiration. Or let it drain as sludge while attached. In this way, the organic matter in the wastewater is decomposed by activated sludge, and on the other hand, filtration is performed using a membrane to extract only clear water.

  When separating purified water from activated sludge, in the conventional method, it was separated by a precipitation method. However, when this method is adopted, it takes a long time for separation, and therefore it is indispensable to install a sedimentation basin that requires a large area. Moreover, since it is processed through the grain of the sedimentation tank, there is an inevitable risk that bacteria and sludge components contained in activated sludge such as Escherichia coli are mixed into the treated water. On the other hand, in the MBR method using a separation membrane, since almost complete solid-liquid separation is possible depending on the pore size of the membrane, the above risk can be remarkably reduced and the precipitation tank can be omitted. It can also contribute greatly to downsizing and space saving. However, as described above, the use of a film causes fouling, which is the biggest problem. Bacterial metabolites and carcasses, metabolites such as sugars and polypeptides adhere to the membrane surface with use and block the membrane. If MBR has a membrane with high resistance to fouling, equipment management This also makes it possible to greatly contribute to improvement of processing capacity and cost reduction. As described above, the membrane of the present invention has succeeded in reducing fouling, which is a problem in the use of the membrane, and improving membrane performance such as water permeability.

  The flat membrane sheet of the present invention is configured by combining a base material made of a nonwoven fabric and a membrane material containing PVDF that forms a network structure. The nonwoven fabric constituting the base material not only supports the membrane material and maintains the form of the membrane, but also serves to absorb stress applied to the membrane. The polymer material constituting the membrane material can have a function as a separation membrane by taking an appropriate porous structure while being appropriately entangled with the base material.

  The nonwoven fabric is not limited as long as it is made of a polymer material that is insoluble in an organic solvent or water, and has an ability to retain a film component and retain a stress applied to the film. The nonwoven fabric is preferably made of a hydrocarbon-based, olefin-based, or condensation-based polymer. For example, polyethylene (PE), polyolefin, polyvinyl alcohol (PVA), polyethylene terephthalate (PET), nylon (Ny), polyimide (PI). , Polytetrafluoroethylene (PTFE), PVC and the like.

The thickness of the nonwoven fabric is preferably 80 to 150 μm. Since the nonwoven fabric is used as the base material of the water permeable membrane, if it is too thick, there is a risk of inhibiting water permeation, and if it is too thin, the strength may not be sufficient and it may not withstand long-term use. The fiber diameter and basis weight of the nonwoven fabric are important for ensuring water permeability. The fiber diameter is preferably 5 to 12 μm. If the fiber diameter is too small, the strength will be small and it will not withstand long-term use, and if it is too thick, the overall appearance will be reduced and the strength will not be sufficient, and this may not withstand long-term use. In addition, if the fiber diameter is too thick with respect to the film thickness, the nonwoven fabric has an overall rough structure, and as a result, the polymer components constituting the film are not sufficiently retained in the nonwoven fabric, resulting in problems such as defects. The amount of polymer to be filled becomes insufficient, and voids may be generated in the film. The basis weight per 1 μm thickness is preferably 0.4 to 0.8 g / m ² . The basis weight is preferably small, but if it is too small, the strength becomes small, so that it cannot withstand long-term use as a membrane, and if it is too large, voids may be reduced and water permeability may be reduced.

  Nonwoven fabric is a member that supports a membrane, and its strength and elongation properties are important properties that govern membrane strength. The yield strength of the nonwoven fabric is preferably 15 to 50 N per 15 mm width in both the longitudinal direction and the transverse direction. When the yield strength is low, it is preferable that the yield strength is high, because when a force is applied to the film, plastic deformation occurs immediately and the film does not return. However, if it is too high, it is technically difficult to obtain an inexpensive nonwoven fabric that can maintain water permeability. The yield elongation of the nonwoven fabric is preferably 1 to 5%. If the yield elongation is high, the elongation of the nonwoven fabric increases, so there is a higher risk of damage to the network when the membrane is formed, and it is deformed by water pressure or pressure during filtration, so that sufficient water permeability is obtained. There is a risk of being lost. Further, if the film does not stretch at all, it may not be absorbed when the film is subjected to an impact and may be damaged. In addition, let the longitudinal direction of the obtained sheet | seat be a vertical direction.

  PVDF is used as the polymer material constituting the membrane material, and a polymer network having submicron-sized pores is formed by a phase separation method to form a membrane. The reason for using PVDF is that the balance between the material cost and the chemical resistance, strength, and stability which are not problematic in actual use is very excellent. In the application of the present invention, strength characteristics that can withstand suction pressure during use and sponge cleaning during cleaning, chemical resistance characteristics that can withstand treatment with sodium hypochlorite, acid and alkaline chemicals, and decomposition and deformation even after long-term use , Stability that does not break is required.

  PVDF 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 the copolymer include a copolymer of vinylidene fluoride and at least one selected from vinyl fluoride, tetrafluoroethylene, hexafluoropropylene, and trifluoroethylene 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. The weight average molecular weight is preferably in the range of 50,000 to 700,000. In consideration of solubility in a solvent, film-forming property, and compatibility with other resins, those having a weight average molecular weight of 100,000 to 500,000 are preferable. preferable.

  PVDF is dissolved in a solvent and applied to a substrate as described later. At this time, if a solution is made with only a single polymer, it may become cloudy during long-term storage. In order to prevent this, it may be preferable to mix the second component. The polymer to be mixed may be any polymer that can be dissolved in a solvent. However, PSf, polyether sulfone (PES), polyacrylic acid ester, polymethacrylic acid ester, polyvinylpyrrolidone (PVP) and the like are preferable from the standpoint of quality after the film is formed. The amount to be added is preferably 0.1 to 5% by weight with respect to PVDF.

  As a solvent for dissolving the polymer material, it is necessary to dissolve the polymer constituting the film but not the nonwoven fabric, and a water-soluble solvent having a boiling point of 210 ° C. or lower can be used. Specifically, dimethylformamide (DMF), dimethylacetamide (DMAC), N-methyl-2-pyrrolidone (NMP), acetone, methyl ethyl ketone (MEK), ethylene glycol monomethyl ether acetate (EGMMA), ethylene glycol monoethyl ether acetate (EGMEA), diethylene glycol monoethyl ether acetate (DEGMEA), diethylene glycol monobutyl ether acetate (DEGMBA), propylene glycol monomethyl ether acetate (PGMMA), dipropylene glycol monomethyl ether acetate (DPGMMA), triethyl phosphate (TEP) are preferred. You may use independently or may mix multiple types.

  When using a non-solvent, water, alcohol, and glycol are preferable, and they may be used alone or in combination of two or more. With regard to the alcohol, ethanol (EtOH), propanol (1- or 2-propanol, IPA), butanol (1- or 2-butanol, BuOH) are particularly suitable. Regarding glycol, ethylene glycol (EG), diethylene glycol (DEG), and triethylene glycol (TEG) are more preferable. These may be used alone or in combination.

  The polymer concentration in the solution is 5 to 40% by weight. If the polymer concentration is too low, the network structure of the membrane will not develop sufficiently, the membrane part itself cannot withstand long-term use, and if the concentration is too high, the solution will not penetrate into the nonwoven fabric, May not function. The ratio of the solvent (solvent / non-solvent) in the mixed solution consisting of the solvent and the non-solvent is preferably 10 to 100% by weight. If the proportion of the non-solvent is too high, the ability to dissolve the polymer is impaired, a uniform solution cannot be produced, and sufficient impregnation may not be achieved. If it is too low, it may not be able to serve to promote phase separation.

  As a method for applying / impregnating the polymer solution to the nonwoven fabric substrate, any method such as a dipping method, a coater method, a die method, or a spray method may be used. However, the coater method is preferable in order to maintain the smoothness of the coated surface. After application / impregnation of the polymer solution, a membrane structure is formed by phase separation. For phase separation, a polymer material is mixed with a solvent to create a solution, and then applied to and impregnated into a non-woven fabric substrate and dried in the air (dry method). A method (wet method), a method of rapidly changing temperature (thermally induced phase separation method, TIPS), and the like are known. Any method can be used, but the TIPS method, the wet method of solidifying the substrate coated / impregnated with a polymer solution in a liquid, or a combination of these methods is easy and complicated in film formation. This is preferable because it does not require any equipment.

  The polymer material constituting the membrane is hydrophobic. For this reason, not only is it difficult to pass water at the beginning of use of the membrane, but also due to hydrophobic interactions, metabolic components, sugars, dead bodies, etc. generated by activated sludge bacteria are adsorbed on the membrane during use. It tends to cause a so-called fouling problem. As one method for avoiding this, it is preferable to make the membrane hydrophilic. In the present invention, the sheet-like base material and the polymer porous membrane are integrated means that the polymer porous layer is a composite layer in which the polymer porous layer enters at least a part of the sheet-like base material. And a sheet-like base material may be laminated, or a sheet-like base material may be embedded in a polymer porous membrane. It means that the molecular porous membrane and the sheet-like substrate are integrated so as not to peel off.

  As a general hydrophilization treatment method, a method of adding a hydrophilizing agent to a polymer solution, a method of adding a hydrophilizing agent after creating a flat membrane constituent, and a method of surface-treating the flat membrane constituent Etc. Among these, a method of adding a hydrophilizing agent after preparing a flat membrane constituent, a method of subjecting the flat membrane constituent to a surface treatment, and the like are preferable. A hydrophilizing agent is a chemical substance having both a hydrophobic part and a hydrophilic part in one molecule, and has a function of adhering to a membrane surface or an internal network. Examples thereof include saccharides, cellulose derivatives, and surfactants. Specific examples include sucrose fatty acid esters, HPC, sodium lauryl sulfate, and the like. In addition, as a method of hydrophilizing after producing the flat membrane constituent, a method of fixing the flat membrane constituent by immersing the flat membrane constituent in a solution comprising the above-mentioned hydrophilizing agent and then applying a temperature or drying. Is mentioned. In addition, although it becomes difficult to control, the membrane itself can be sulfonated by a direct method or a sulfate group can be attached. In addition, a method of applying a carboxylic acid by irradiating an electron beam, plasma, gamma rays, ultraviolet rays or the like to oxidize the whole film surface or the film surface may be considered. In addition, a method of crosslinking or grafting a hydrophilizing agent in post-processing is also effective in terms of sustaining the hydrophilic effect.

  As described above, various methods for hydrophilizing the membrane can be employed, but it is preferable to impart HPC to the flat membrane structure from the viewpoint of cost reduction. Also, from the viewpoint of anti-fouling against actual drainage, it is preferable to provide HPC. The type and characteristics of the HPC used are not limited in the present invention, but in particular, the ease of preparing the HPC solution used for imparting to the flat membrane structure, the control of the viscosity of the solution, and the ease of maintenance and management. Furthermore, HPC-L manufactured by Nippon Soda Co., Ltd. was selected in view of the balance between anti-fouling characteristics and water permeability. According to the specifications of Nippon Soda Co., Ltd., HPC-L has a 2% HPC concentration solution at a temperature of 20 ° C. in the range of 6.0 to 10.0 mPa · s, and a hydroxypropoxy group of 53.4 to 77. It is in the range of 5%.

  Next, an example of a method for producing the polymer porous flat membrane sheet of the present invention will be described. As long as the object of the present invention can be achieved, the flat membrane structure before hydrophilization by HPC used in the present invention may be actually produced or commercially available. First, the nonwoven fabric is impregnated with a solution in which a polymer that forms a film is dissolved. As the impregnation method, any method such as an immersion method or impregnation using a die may be used.

  After impregnating the non-woven fabric with the polymer solution, it is led to a coagulation zone for film structure formation. At this time, it is necessary to pay attention to the solidification temperature in order to ensure sufficient opening. A preferred temperature is 5 to 90 ° C. If the temperature is too low, the surface structure becomes dense and the pore diameter decreases, such being undesirable. If the temperature is too high, the pore size distribution becomes wide and the fractionation ability of the membrane decreases.

  The component of the coagulation bath may be any liquid as long as it solidifies the polymer solution. Preferably, water or alcohol alone or a mixture. In order to form a preferred membrane structure, it is necessary to adjust the rate of penetration of coagulant molecules into the membrane. For this purpose, the solvent and non-solvent components used in preparing the polymer solution may be added to the coagulation bath. As the additive, ethanol (EtOH), propanol (1- or 2-propanol, IPA), butanol (1- or 2-butanol, BuOH) is preferable. These may be used alone or in combination.

  In the subsequent step of the coagulation bath, a washing step for the obtained flat membrane structure may be introduced if necessary. This is because the solvent and non-solvent remaining in the film are washed away, and there is an advantage that the subsequent steps can be performed more smoothly. As the cleaning liquid, water, alcohol, or a mixture thereof is suitable. The temperature is preferably used in the range of 5 ° C. to less than the boiling point. When used at a higher temperature, the cleaning effect tends to be higher, but in that case, it is necessary to pay attention to the boiling point of the liquid used.

  The membrane is dried after coagulation, but as it is, PVDF is hydrophobic and membrane fouling proceeds rapidly, so it cannot be used as a wastewater treatment membrane. Therefore, the surface of the membrane is hydrophilized using the method described below.

  The flat membrane structure produced by the above-described method is subjected to the following impregnation, volatilization, fixation, and drying steps to achieve hydrophilicity of the membrane. Hereinafter, the hydrophilization method of the present invention and the structural characteristics of the resulting film will be described in detail.

  Generally, HPC is said to have a property of becoming insoluble (white turbidity) in water by heating an aqueous solution at a temperature of 50 ° C. or higher. However, in the present invention, it has been found that when alcohol is dissolved in this aqueous solution, HPC is not insolubilized even when the solution is heated at a temperature of 50 ° C. or higher, and the solution remains transparent. This phenomenon indicates that the presence of alcohol does not cause aggregation or insolubilization of HPC even when heated (fixing step), that is, alcohol has an effect of dispersing HPC in the solution. Utilizing this property, hydrophilicity was effectively achieved by dispersing and fixing fine particles of HPC uniformly on the surface of the film. First, the flat membrane structure is immersed in a hydrophilization impregnation liquid (alcohol aqueous solution) composed of HPC, alcohol (preferably methanol, ethanol, or IPA, more preferably IPA), and water (impregnation step). Then, an alcohol aqueous solution made of HPC is widely dispersed in the membrane pores. Thereafter, the alcohol is selectively volatilized (volatilization process) and / or washed from the membrane to reduce the alcohol content. As a result, in the fixing step described later, the HPC is fixed on the surface of the film and the surface of the micropores existing in the film in a desired form without being blocked in a properly dispersed state in the form of fine particles. As a result, in addition to the expression / maintenance of anti-fouling properties and hydrophilic properties, it contributes to the suppression of deterioration of water permeability (inhibition of blockage of membrane pores by a hydrophilic agent). However, the alcohol component must not be volatilized completely. Then, it is heated to a predetermined temperature using hot water to be insolubilized and fixed to the polymer constituting the film (fixing step). At this time, alcohol remains in the impregnation liquid. As described above, the alcohol component has an effect of inhibiting the white turbidity (gelation) of HPC. For this reason, by fixing in the presence of alcohol, the HPC component is not unevenly distributed or localized in a part of the pores of the membrane, and is effective on the surface of the pores in the membrane in a dispersed state with fine particles. Can be granted. The term “fine particles” as used herein refers to particles in which HPC aggregates (aggregates) into a granular shape or a lump shape. FIG. 2 shows a TEM image as an example of a film in which the adhered HPC is dispersed in the form of fine particles. In this case, the HPC is dyed by a dyeing process described later and shown in black.

The structural characteristics of the film of the present invention will be described in detail. In the present invention, an image obtained by enlarging a cross section of a polymer porous membrane (a region having a depth of 5 μm from the outermost surface of the polymer porous membrane and an observation area of 20 μm ² ) by TEM to 5,000 times The size of the HPC fine particles (defined as the average of the average values of the maximum length and the minimum width of the fine particles) is 5 to 100 nm. If this value is too small, the interaction between the foulant and the film surface cannot be sufficiently inhibited, so that the foulant is easily adsorbed, resulting in a problem that the anti-fouling property is lowered. When this value is too large, the fine pores of the membrane are blocked by the HPC fine particles themselves, and the water permeation space becomes narrow, which may cause problems such as degradation of water permeation characteristics and increase of pressure loss. In the present invention, the dispersion degree of the fine particles of HPC (defined as the average deviation of the interparticle distance divided by the average interparticle distance) in the above-mentioned image is in the range of 0.2 to 1.5. It is characterized by that. If this value is too large, it means that the dispersion / distribution state of the fine particles is remarkably biased, and the water permeation performance is lowered by excessively occupying a part of the space inside the pores (uneven distribution / localization). Or the problem of an increase in pressure loss occurs, and further, the exposed portion of the polymer porous membrane surface becomes too large and large, so that the foulant is easily adsorbed and the anti-fouling property is deteriorated. There is a risk of degrading the hydrophilic properties of the membrane. On the contrary, the case where this value is small means that the dispersion / distribution state of the fine particles is more uniform, but there is a region of the polymer porous membrane (amorphous island portion in the TEM image). Therefore, the value is not likely to be small. Still, in the case where the value can be smaller than the above range, the HPC fine particles are unevenly distributed and evenly present in the minute region of the membrane pore, and the HPC fine particles are not present in the region other than the above region in the TEM image. means. In this state, the region where the fine particles are not present, that is, the exposed portion of the surface of the polymer porous membrane becomes too wide and the foulant is easily adsorbed, resulting in a problem that the anti-fouling property is deteriorated, Since it leads to the problem of causing the fall of a hydrophilic property, it is not preferable.

  The impregnation process will be described. The flat membrane structure obtained as described above is guided to the impregnation step, and is impregnated with an impregnation liquid for developing hydrophilicity. In order to maintain the anti-fouling performance as long as possible, it is necessary to apply an appropriate amount of HPC to the film. As the impregnation liquid, it is preferable to use an aqueous alcohol solution in which HPC is uniformly dissolved in a range of preferably 0.5 wt% to 1.0 wt%. Depending on the characteristics of the porous membrane used, the ratio of alcohol to pure water and the concentration of HPC may be changed. When the concentration of HPC in the aqueous alcohol solution is too low, the amount of HPC fixed to the film is reduced, the hydrophilic properties of the finally obtained flat membrane sheet are deteriorated, and the preferred anti-fouling properties may not be exhibited. is there. On the contrary, when the HPC concentration is too high, the degree of dispersion of the HPC fine particles cannot be controlled within a preferable range. As a result, the flat membrane sheet to be finally obtained is not preferable because the fouling resistance may not be sufficiently exhibited or the pores of the membrane may be blocked to deteriorate the water permeability. Examples of the method for applying the solution to the flat membrane constituent include a method of immersing the flat membrane constituent with the aqueous solution as an impregnating liquid, a method of applying the flat membrane constituent using a die, and the like. The impregnation method is most convenient and preferable from the viewpoint of cost. After immersing the flat membrane component in the impregnating solution, a step of removing excess solution with a scraper or a roller bar may be performed.

  A preferable ratio of the solvent in the impregnating solution for forming the HPC and the aqueous alcohol solution is 30 to 90%, preferably 40 to 70% in terms of alcohol weight fraction. If the fraction of alcohol in the solvent is too low, the membrane is hydrophobic, so that it cannot be sufficiently impregnated into the pores of the membrane structure, which is not preferable. If the alcohol fraction is too high, fine particles composed of HPC in a desired form cannot be formed in the fixing step described later, which is not preferable.

  The volatilization process will be described. A portion of the alcohol present in the flat membrane structure after the impregnation step is volatilized. At this time, it is preferable that water is more than alcohol in the membrane sheet. If the concentration of the alcohol in the solvent is too low, HPC is not dispersed but localized in a part of the region, which may clog the pores in the region and cause a decrease in water permeability. As a result, the preferable dispersion state of the HPC fine particles described later cannot be achieved. If it is too high, fine particles having a size that exhibits an effective effect cannot be formed, or the HPC fine particles may not be sufficiently fixed in the fixing step described later. The temperature and humidity of the volatilization step are not particularly limited as long as they satisfy the range of the alcohol weight fraction described later, but a preferable range of the temperature is 18 ° C. or more and less than 50 ° C. If the temperature is too low, the volatilization of the alcohol will be suppressed so that no effect will be exhibited. If the temperature is too high, the alcohol volatilizes rapidly or the volatilization of the alcohol is promoted too much. In this case, a high-concentration HPC solution is unevenly distributed near the outermost surface of the flat membrane structure, which is not preferable. Further, in the volatilization step, it is necessary to flow air around the flat membrane structure in order to control the volatilization of the alcohol in more detail. If the range of the alcohol weight fraction can be satisfied, the condition of the wind speed to be applied is not particularly limited, but is preferably 0.01 to 0.5 m / second. If the wind speed is too low, the volatilization of alcohol is suppressed, and the alcohol weight fraction may not be reduced. On the other hand, if the wind speed is too high, the volatilization of the alcohol is promoted too much and the alcohol weight fraction may be reduced too much. The formation of HPC microparticles is a nucleation process. That is, when the solution concentration and composition satisfy certain conditions, the interaction between molecules starts and nuclei that form the basis of fine particles are formed. Eventually, more nuclei gather to reach fine particles. At this time, the volatilization rate of alcohol becomes important. Fine particle nuclei form when volatilized at a specific range of rates. If the volatilization rate is slow, it will fall into a kind of quasi-equilibrium state, so fine particle nuclei cannot be formed. Therefore, the fine particles of HPC that exhibit a sufficient hydrophilic effect are not formed. After the volatilization step, the flat membrane structure may be immersed in a water washing tank for a short time and washed as necessary. The immersion time is preferably 3 seconds or less. When the immersion time exceeds 3 seconds, the impregnating liquid is drawn back to the outermost surface of the flat membrane constituent, and therefore, the problem that HPC agglomerates on the outermost surface of the flat membrane constituent and the pores are blocked in the fixing process. May occur. In addition, if washed with water for a very long time, the HPC before fixing may be washed away. As a result, in the flat membrane structure after the volatilization / water washing step, the weight fraction of alcohol in the HPC alcohol aqueous solution is reduced to a range of 25 to 55% during a residence time of 30 seconds to 5 minutes. Volatilization is controlled.

  The fixing process will be described. Heat treatment is performed to fix the HPC to the polymer porous membrane. This heat treatment is not limited by a method such as hot water, hot air, and infrared irradiation, but heat treatment using hot water is preferable because it can be uniformly processed over the entire film including the inside of the film at low cost and with ease. The heat treatment temperature at this time is preferably 50 ° C to 72 ° C. When the treatment is performed at a temperature less than 50 ° C., it becomes difficult to fix the HPC fine particles to the film. In that case, there is a possibility that HPC dissolves in water when the obtained flat membrane sheet is washed or actually used, and the hydrophilicity is easily lowered or lost. This can also be known from the fact that the degree of differential pressure increase in the actual liquid test and filtration suction during actual use is increased. On the other hand, it has been found that when heat treatment is performed at a high temperature exceeding 72 ° C., the obtained membrane significantly reduces the fouling resistance in a filtration test using an actual solution. This is because, when the heating temperature is too high, HPC is chemically modified, and the inherent properties such as hydrophilicity cannot be sufficiently exhibited.

  The film performance can vary depending on the heat treatment time. A preferable treatment time is 5 minutes to 75 minutes. If the treatment time is short, the HPC may not be sufficiently fixed to the film. A long treatment time is not preferable from the viewpoint of industrial productivity.

  Furthermore, the fixing temperature is also involved in the formation and distribution of fine particles. As described above, it is preferable that the HPC forms fine particles having an appropriate size and is fixed to the film surface in a dispersed state. In order to achieve the formation of fine particles and fine dispersion fixing, the composition of the HPC solution and the fixing temperature are involved. That is, if the alcohol fraction is too low, the solubility of HPC falls, so that dispersion cannot be achieved. On the other hand, if it is too high, the solubility is too high, so that it is impossible to form fine particles having a size that exhibits an effective effect. If the fixing temperature is too low, fine particles having a size that exhibits an effective effect are not formed. If the particle size is too high, the resulting fine particles interact with each other, so that fusion occurs and a preferable dispersed state cannot be achieved.

  The drying process will be described. The flat membrane sheet after the hydrophilic treatment by HPC is dried and wound up. The drying conditions are a temperature range of 40 ° C. to 70 ° C. and a relative humidity of 1% to 20% in order to efficiently remove moisture and suppress HPC denaturation. If the temperature is too high, denaturation of HPC may be promoted. If the temperature is too low, drying may be insufficient, and problems may occur when storing the film roll after winding. Further, if the relative humidity is too high, drying may be insufficient, and if the relative humidity is too low, the burden may be increased in terms of energy and equipment.

  Since the impregnation step, the volatilization step, the fixing step, and the drying step as described above are continuously processed, there is an advantage that it is easy to study production efficiency improvement and cost reduction. In addition, if necessary, treatment equipment that crosslinks the hydrophilizing agent or reacts and binds the membrane with the hydrophilizing agent may be introduced online, or as post-processing, gamma irradiation or grafting reaction is performed. Also good.

  It was also found that not only the vicinity of the membrane surface of the flat membrane sheet but also the proportion of HPC adhered to the flat membrane sheet when paying attention to the entire membrane affects the anti-fouling characteristics in the actual liquid test. That is, there is an appropriate range for the HPC sticking ratio in order to maintain the hydrophilic expression and anti-fouling effect as much as possible. The fixing ratio of HPC is 0.4% by weight to 1.0% by weight per film. If the sticking ratio is too small, the degree of hydrophilicity of the film may be weakened, resulting in a problem that the period for maintaining the anti-fouling characteristics during actual use of the film is shortened. On the other hand, if the sticking ratio is too large, there is a possibility that water permeability is lowered, or that the degree of increase in the transmembrane pressure difference during actual use is increased or increased in a short period of time.

  The film properties and performance will be described. The flat membrane sheet of the present invention thus produced has an average pore diameter of 0.2 μm to 0.5 μm as measured with a porous material (PPM) manufactured by Porous Materials. This range of pore diameters is a practical aspect considering fractionation performance and water permeability. In this PPM measurement, the flow rate when the flat membrane sheet is in a dry state is 20 L / min. When the pressure is 150 kPa. ~ 60 L / min. It is. This range considers membrane strength and filtration efficiency in long-term use. This value of the flow rate also indirectly represents the degree of opening of the film surface and the density of the film structure. The larger this value, the greater the degree of opening on the membrane surface, or the membrane structure tends to be rough. Conversely, it can be said that the smaller the value, the smaller the degree of opening or the denser the membrane structure. Since these are closely related to the strength of the membrane and the filtration efficiency, they can be indicators of whether the membrane can be used over a long period of time.

The initial performance of the flat membrane sheet is evaluated by pure water flux (FR) and bubble point (BP). The pure water FR is a volume of water through which pure water can pass per unit area per unit time. P. Is an index indicating the maximum pore diameter of the pores and represents fractionation performance. The pure water FR (unit: mL / cm ² / min / bar) is 15-50. If the pure water FR is too small, it is necessary to increase the number of flat membrane sheets or increase the pressure by the pump in order to secure the necessary amount of water when it is put to practical use. The problem is big. On the other hand, if it is too large, it is necessary to increase the pore diameter of the membrane, resulting in poor fractionation performance and the possibility of failing to function sufficiently as a membrane. B. P. Is 0.08 to 0.3 MPa. B. P. If it is too small, fractionation performance will not be achieved (the pore size will be too large), and sludge components may be mixed in the filtered water. If it is too large, there is a high possibility that sufficient water permeability will not be secured. There is a risk that the efficiency of filtration will deteriorate.

  The flat membrane sheet of the present invention preferably has a thickness of 80 to 150 μm. Since the flat membrane sheet is held in shape by the non-woven fabric that is the base material, it has substantially the same thickness as the base material. If the thickness is too thick, the resistance at the time of passing water is increased, so there is a possibility that the water permeability is lowered. If the thickness is too thin, the film strength may be insufficient.

  The strength and elongation properties of the flat membrane sheet are also basically governed by the nonwoven fabric as the substrate. When the yield strength is low, when a force is applied to the flat membrane sheet, plastic deformation occurs immediately and the original film does not return, so a higher value is preferable. The yield strength of the flat membrane sheet of the present invention is preferably 15 to 52 N per 15 mm width in both the machine direction (MD) and the transverse direction (TD). In addition, if the yield elongation is large, the elongation of the flat membrane sheet increases, so the risk of damaging the membrane structure increases, and it becomes deformed by water pressure or pressure during filtration, and sufficient water permeability is obtained. There is a risk of disappearing. Moreover, if it does not extend at all, there is a possibility that the flat membrane sheet cannot be absorbed when an impact is applied and may be damaged. Therefore, the yield elongation of the flat membrane sheet of the present invention is preferably 1 to 5%. In addition, let the longitudinal direction of the obtained sheet | seat be MD.

  In order to evaluate the characteristics of the flat membrane sheet for MBR, a filtration test in an actual liquid using activated sludge is effective. In general, filtration is continued while maintaining a constant filtration flow rate, and the degree of increase in transmembrane pressure difference is observed. It can be said that the higher the differential pressure increase is, the better the MBR film is and the more practical it is. In the present invention, when an actual liquid test was performed under the conditions shown in the examples, whether or not the transmembrane pressure difference exceeded 10 kPa in one week of continuous operation was used as an index of fouling resistance.

  The flat membrane sheet of the present invention is made of a nonwoven fabric having characteristics that can withstand long-term use as a base material, and HPC is dispersed and fixed to the membrane in the form of fine particles on a membrane prepared by controlling the membrane structure and pore size. Therefore, it can withstand actual use in MBR applications and can exhibit excellent water permeability, high hydrophilicity and anti-fouling properties.

  The excellent effects of the flat membrane sheet of the present invention are shown by the following examples, but the present invention is not limited thereto. In addition, the evaluation method of the characteristic value measured in the Example was described below.

(1) Used raw material The raw material used by this invention is described. (Polymer) PVDF; SOLVAY: SOLEF6020, (Solvent) DEGMEA; Daicel Chemical Industries, Ltd. (Hydrophilic agent) HPC; Nippon Soda Co., Ltd. HPC-L, IPA; Daisho Kasei Co., Ltd. (Substrate) PET paper Respectively; Hirose Paper Co., Ltd. 05TH-60 was used.

(2) Pure water flux (pure water FR)
The prepared flat membrane sheet was cut into a circle of φ90 mm and set in a filter holder (excluding UHP-90K stirrer manufactured by Toyo Roshi Kaisha Co., Ltd.), then water pressure 0.5 bar was applied for 1 minute from the holder outlet The pure water FR was determined from the following equation from the amount of water permeated in The water used for the filtration was RO water at 25 ° C., and 30 seconds after the water pressure was applied as the sampling start time. Moreover, the water surface height from the film surface was adjusted to be 3 cm ± 1 cm.
(Pure water FR [mL / cm ² / min / bar])
= (Q [mL / min]) / (A [cm ² ]) / (P [bar])
(Q: water permeability for 1 minute, A: effective membrane area = 48 cm ² , P: water pressure = 0.5 bar)

(3) B. P.
Set the prepared flat membrane sheet in the holder used in (2), add RO water so that the height is 5 cm from the membrane surface, and open the pressure relief valve in the holder, and then open the holder outlet (under the membrane surface). )), And the pressure at which bubbles continuously emerged from the membrane surface into the water was measured. P. [MPa]. In addition, the member which can support a film | membrane without disturbing observation of a bubble was set to the film | membrane upper surface, and it devised so that a film | membrane might not remove | deviate from a holder with respect to the pressure from a lower surface. The rate of increase in nitrogen pressure was 0.02 MPa per minute.

(4) Average pore diameter of flat membrane structure and flat membrane sheet The average pore diameter of the produced flat membrane sheet was measured using a Palm Porometer (PPM, CFP-1200AEX) apparatus manufactured by Porous Materials. The test type was Wet Up / Dry Up of Capillary Flow Poromory, and GalWick (surface tension 15.7 dyne / cm) was used as a test solution. The membrane sample was set to fit the sample holder attached to the apparatus (o-ring inner diameter 30 mm, holder opening 25.4 mm). After inputting the measurement parameters described below into the measurement software attached to the apparatus, a membrane sample that had been preliminarily immersed in GalWick for 5 minutes was set in a sample holder, and the holder was further set in the apparatus. The measurement was first performed under Wet, and then the measurement was performed under Dry.
<Automatic test parameter values for pore diameter distribution measurement test>
・ Minimum pressure: 0 (KPA), maximum pressure: 300 (KPA)
(I) Bubble point test / integrity test; 10 bubbleflow (cc / m), 50 F / PT (old bubbletime), 0 minbppres (KPA), 0 minbppres (KPA), 1.0 zerotime (sec)
(Ii) Motor valve control; 10 v2 incr (cts * 3)
(Iii) Regulator control; 1 preginc, 2 pulse delay
(Iv) Lohm calibration; 1378.9466 maxpress (KPA), 0.2 pulsewidth (sec)
(V) Data determination routine; 30 mineqtime (sec), 10 presslew (cts * 3), 50 flowslew (cts * 3), 20 equiter (0.1 sec), 20 aveiter (0.1 sec), 0.69 maxpdif ( KPA), 50 maxfdif (cc / m)

(5) Thickness of membrane base material The thickness of the membrane base material was measured from an arbitrary five points using a thickness meter from the base material used for the membrane, and the average value was obtained. The measurement was performed by immersing the film after film formation in a solvent that dissolves only the film component and removing the film component to expose the film substrate.

(6) Fiber Diameter of Membrane Substrate The fiber diameter of the membrane substrate was calculated from the substrate fiber photographed and the scale information obtained by photographing the substrate with SEM. The calculation was performed for 10 fibers, and the average value was defined as the fiber diameter [μm] of the membrane substrate.

(7) The basis weight of the membrane base material per unit thickness The basis weight of the membrane base material is obtained by weighing the weight of the base material cut into 10 cm square with an electronic balance, and calculating the weight per 1 m ² from the result. After obtaining the basis weight, it was divided by the thickness of the membrane substrate to obtain the basis weight per 1 μm thickness [g / m ² / μm].

(8) Yield strength and yield elongation of membrane substrate and flat membrane sheet The yield strength and yield elongation of the membrane substrate and membrane were measured using a Tensilon tensile measuring instrument. The membrane substrate was cut into a strip having a width of 15 mm (length of about 60 mm) and set on a Tensilon tensile measuring instrument so that the distance between chucks was 40 mm. A load cell condition was set to 100 kgf and a range of 10%, and a tensile test was performed at a tensile speed of 20 mm / min to obtain a stress-strain curve. From the obtained curve, the tangent line between the elastically deformed part and the plastically deformed part was drawn with a straight line, and the intersection and the yield point were taken as the yield point, and the strength and yield elongation were determined. Five samples were measured for each of the longitudinal direction and the transverse direction of the film, and the average values were taken as the yield strength [N / 15 mm] and the yield elongation [%].

(9) Structure observation The observation of the cross section of the vicinity of the outer surface of the flat membrane sheet and the vicinity of the inner surface of the flat membrane sheet was carried out in the following manner. The flat membrane sheet was immersed in liquid nitrogen and frozen to expose the cross section of the flat membrane sheet, and then fixed to a sample stage for SEM observation with a double-sided tape. These samples were subjected to platinum coating and observed at a magnification of 5,000 using a scanning electron microscope (S-4500) manufactured by Hitachi.

(10) HPC ratio of membrane (a) About 130 mg (W ₁ , weight is recorded) of a flat membrane sheet sample was cut into about 1 cm square, and then placed in a vial. On the other hand, (b) About 10 mg of HPC was collected (W ₂ , weight recorded) and placed in different vials. In these bottles, 6 ml (C) of a mixed solution of deuterated chloroform (CDCl ₃ ) / deuterated dimethyl sulfoxide (DMSO-d6) = 2/1 vol% was used, and BHT (Butylhydroxy toluene, 3,5-di-tert. -Butyl-4-hydroxytoluene, 8 mg (D)) was added 1 ml at a time and immersed for 2 days to dissolve components other than the base material. Then, the solution of (a) * (b) was extract | collected separately and 400 MHz-proton NMR measurement was performed, respectively. The measurement apparatus used was the same as (6), and the measurement conditions were a resonance frequency of 399.796 MHz, a lock solvent DMSO-d6, a total number of times of 128, a waiting time of 1 second, and a flip angle of 45 degrees. The spectrum peak derived from BHT was determined to be 6.8 ppm, and attention was paid to the spectrum peak derived from HPC in the vicinity of 3.8 ppm. The integral value of the BHT-derived spectrum peak in measurement (a) is I, the integral value of the HPC-derived spectrum peak is II, the integral value of the BHT-derived spectrum peak in measurement (b) is I ′, and the integral value of the HPC-derived spectrum peak is When II ′, the HPC ratio per film was calculated using the following formula.
<Ratio of hydroxypropyl cellulose per membrane
= II × I ′ × W ₂ / (I × II ′ × W ₁ ) × 100 [wt% / film]>
<Preparation amount of (C) and (D); when the number of simultaneously measured samples is 6 or more,
C = (n + 1) [ml] as n measurement samples
D = (n + 1) / 5 × 8 [ml]. >

(11) Alcohol weight fraction (alcohol aqueous solution) About 50 mg of alcohol aqueous solution used in the impregnation step (record the weight with three significant digits, W ₃ ) is weighed and deuterated solvent (eg deuterated methanol) is added. It poured into the vial bottle which put 1 mL beforehand. Next, 10 mg of BHT as a standard substance was put into the vial and dissolved in a liquid, and this solution was put into an NMR tube. Using this, 400 MHz-proton NMR measurement was performed. The measurement apparatus used was Varian 400MR, the measurement conditions were a resonance frequency of 399.796 MHz, the lock solvent was deuterated methanol, the number of integrations was 64, and the waiting time was 1 second. The spectrum peak derived from BHT is defined as 6.9 ppm, and this and an alcohol-derived peak (for example, around 3.9 ppm or around 1.2 ppm in the case of 2-propanol) are used, and the integrated intensity corresponds to each peak. The weight (W ₄ ) of alcohol in the aqueous alcohol solution was calculated from the number of hydrogen atoms and the amount of BHT input. From this value and the weight (W ₃ ) of the first aqueous alcohol solution weighed, the alcohol weight fraction was calculated using the following formula.
Alcohol weight fraction (%) = W ₄ / W ₃ × 100
(Flat membrane sheet) A flat membrane sheet sample that has passed through the volatilization process is cut into 4 × 5 cm squares and weighed (W ₅ , 3 significant digits). All of the deuterated solvent (for example, deuterated methanol) that can be selectively dissolved was put into a vial bottle in which 1 mL was previously placed. (The series of operations should be performed quickly.) The vial is sealed, and the membrane sample is completely immersed in the deuterated solvent and kept at room temperature for 24 hours or more to completely remove the alcohol aqueous solution adhering to the membrane sample. Extracted. Next, 2 mg of BHT as a standard substance was put into the vial so as to be well blended with the extract, and the extract in the vial was put into the NMR tube. Using this NMR tube, 400 MHz-proton NMR measurement was performed. The measurement conditions used were the same as the content of the alcohol aqueous solution described above except that the number of integrations was 256. The spectrum peak derived from BHT is defined as 6.9 ppm, and this and an alcohol-derived peak (for example, around 3.9 ppm or around 1.2 ppm in the case of 2-propanol) are used, and the integrated intensity corresponds to each peak. From the number of hydrogen atoms and the amount of BHT input, the weight (W ₆ ) of alcohol in the aqueous alcohol solution adhered to the flat membrane sheet was calculated. Furthermore, when the weight of the membrane sample after taking out the membrane sample and allowing it to dry completely is (W ₇ , 3 significant digits), the alcohol weight in the aqueous alcohol solution attached to the flat membrane sheet using the following formula: The fraction was calculated.
Alcohol weight fraction (%) = W ₆ / (W ₅ −W ₇ ) × 100

(12) Real liquid test (degree of fouling)
Using actual sludge liquid, the fouling characteristics of the membrane were investigated. The apparatus used was an immersion type membrane separation activated sludge method test apparatus (Model IMF-5) manufactured by Miyamoto Seisakusho. An activated sludge solution was prepared so that the concentration of MLSS (Mixed Liquor Suspended Solids) in the apparatus tank was about 10,000 mg / L, and a membrane cartridge in which the produced membrane was attached to both sides was set. A suction filtration operation with a tube pump was performed at a filtration rate of 0.6 m ³ / day per 1 m ^{2 of} membrane area. During the filtration operation, the temperature was kept at 30 ° C., and aeration was continuously performed from the lower part of the membrane cartridge as a continuous operation without providing an operation stop time. The aeration amount is 2 L / min. Per membrane cartridge. It adjusted so that it might become. The operation was continued for one week in this state, and the degree of fouling was determined by monitoring the increase in transmembrane pressure difference. Whether or not the differential pressure increase in one week exceeded 10 kPa was used as a guide.

(13) TEM observation A flat membrane sheet sample was cut out and degassed and embedded with an epoxy resin. The embedded sample was made into an ultrathin section having a thickness of about 100 nm with a microtome equipped with an ultrasonic knife, and immersed and dyed in an aqueous phosphotungstic acid solution with a concentration of 0.5% for 30 minutes. Thereafter, it was washed with water and subjected to carbon deposition to prepare a sample for TEM observation. JEM2100 transmission electron microscope was used as the device, and the acceleration voltage was 200 kV, the measurement magnification was 5,000 times, and the vicinity of the film surface (from the film outermost surface to about 5 μm in the depth direction, and the observation area was 20 μm ² ) The cross section was observed and photographed. The size of the TEM image at this time was set to 4008 × 2672 pixels.

(14) Dispersion degree and size of HPC fine particles A TEM image (BMP file or JPEG file) of the flat membrane sheet obtained in (13) is obtained from A image-kun (ver. 2.52) manufactured by Asahi Kasei Engineering Corporation. The following analysis was performed.
(Dispersion degree of HPC fine particles) The above-described analysis software was started up, and “JPEG file input” or “BMP file input” was selected from “image input / output” on the menu bar to capture a TEM image. Using “new scale setting”, the reference scale line in the image and the length of the reference line were input and “registered”, and then the image information was transferred to the analysis software by “image transfer”. From the "Image Analysis" menu bar, select "Dispersion Measurement" and then select the following in the "Parameters" window that appears. Measurement method; wall distance method, particle brightness; darkness, binarization method; manual, range specification; no, outer edge correction; no, hole filling; yes, small figure removal area; 10 pixels, correction method; no, noise Removal filter; yes, shading; no, result unit display; nm. Press “Execute” and select the smallest value among the continuous bottoms of the histogram shown in a mountain shape in the “Threshold Setting” window (At this time, the smaller side of the bottom of the histogram peak continues to 0. If the height of the longest part of the mountain is the standard, select the value of the edge of the mountain (the heel part) that is 2% of the height. There are two types, the larger side (bright part) and the smaller side (dark part), but the smaller one (dark part) should be selected. This was “determined” as the threshold value, and only the fine particle region derived from HPC was selected. Among the values displayed in the obtained measurement result window, the value indicated by “dispersion degree” was used. The definition is as follows: (It is described in the manual of the software.)
Dispersion of HPC fine particles = average deviation of distance between particles / average distance between particles (size of HPC fine particles) Launch the above analysis software, select “Particle Analysis” from “Image Analysis” on the menu bar, and then display In the "Parameter" window, select as follows. Particle brightness: Dark, Binarization method: Manual, Range specification; None, Outer edge correction; None, Fill in hole; None, Small figure removal area; 10 pixels, Correction method; None, Noise removal filter; , Result unit display; nm, measurement item; area, circumference, maximum length, minimum width. Press “Execute” and set in the threshold setting window in the same way as described above (in the case of the same image as the TEM image handled by the degree of dispersion, the threshold is set to the same value). Only to be selected. Among the values displayed in the obtained “measurement result” window, the average value (X) of the maximum length and the average value (Y) of the minimum width were confirmed, and the size of the fine particles was obtained from the following formula.
HPC fine particle size (nm) = (X + Y) / 2

Example 1
PVDF was used as the resin component for the film-forming stock solution, and DEGMEA was used as the solvent. These were stirred and dissolved at 160 ° C. for 4 hours, and then allowed to stand for deaeration to prepare a polymer solution of PVDF 20 wt% and DEGMEA 80 wt%. A base roll made of PET paper is set on a free roll for unwinding, the base is unwound, and the polymer solution is applied and impregnated using a heatable comma coater or die, and then 60% by weight of water. And 40% by weight of DEGMEA were immersed in a coagulating liquid at 10 ° C. The passage time of the coagulation bath was 1 minute to form a film. Thereafter, the formed film is passed through a warm water bath at 90 ° C. for about 1 minute to remove residual solvent and non-solvent, then passed through a drying zone adjusted to 60 ° C. (about 5 minutes), and wound by a winder. I took it. In this way, a flat membrane structure was prepared. Next, HPC was provided using the flat membrane structure. The roll of the flat membrane structure is set on a free roll for unwinding, and an alcohol aqueous solution composed of HPC (0.7 wt%), IPA (49.65 wt%), and water (49.65 wt%) is contained. The membrane roll was slowly dipped while being unwound into the impregnation tank (so that no bubbles were introduced). The temperature of the impregnation tank was about 20 ° C., and the immersion time of the membrane was 15 minutes. After pulling up the membrane from the impregnation tank, 2-propanol in the membrane was slowly volatilized under the conditions of a temperature of 25 ° C., a wind speed of 0.03 m / sec, and a treatment time of 2 minutes. Further, it was slightly immersed in a washing tank containing pure water (1 second or less). The alcohol weight fraction in the impregnating liquid (alcohol aqueous solution) contained in the membrane coming out of the water washing tank was about 35%. Thereafter, the membrane was immersed in a hot water treatment tank at 65 ° C. for 15 minutes. After lifting the membrane from the hot water treatment tank, the membrane was dried in a drying zone under conditions of a temperature of 40 ° C., a relative humidity of 10%, and a treatment time of 15 minutes. Finally, the membrane was slowly wound with a winder. In these series of operations, no defects were found in the base material and the membrane. Table 1 shows the post-treatment (hydrophilization) conditions, and Table 2 shows the results.

(Examples 2 and 3)
In the flat membrane structure after the volatilization step and water washing, the flat membrane was prepared in the same manner as in Example 1 except that the alcohol weight fraction of the aqueous alcohol solution contained in the membrane was adjusted to 27% and 52%, respectively. A sheet was obtained. Table 1 shows the post-treatment (hydrophilization) conditions, and Table 2 shows the results.

(Examples 4 and 5)
A flat membrane sheet was obtained in the same manner as in Example 1 except that the temperature of the hot water treatment tank was changed to 55 ° C. and 71 ° C., respectively. Table 1 shows the post-treatment (hydrophilization) conditions, and Table 2 shows the results.

(Examples 6 and 7)
A flat membrane sheet was obtained in the same manner as in Example 1 except that the immersion time of the flat membrane component in the hot water treatment tank was changed to 5 minutes and 60 minutes, respectively. Table 1 shows the post-treatment (hydrophilization) conditions, and Table 2 shows the results.

(Example 8)
A flat membrane sheet was obtained in the same manner as in Example 1 except that the alcohol component contained in the HPC solution was changed to ethanol. Table 1 shows the post-treatment (hydrophilization) conditions, and Table 2 shows the results.

(Examples 9 and 10)
In the flat membrane structure after changing the HPC concentration of the alcohol solution in the impregnation tank to 0.97 wt% and the volatilization step and the water washing, the alcohol weight fraction of the alcohol aqueous solution contained in the membrane is 52%, A flat membrane sheet was obtained in the same manner as in Example 1 except that the content was adjusted to 27%. Table 1 shows the post-treatment (hydrophilization) conditions, and Table 2 shows the results.

(Comparative Examples 1 and 2)
In the flat membrane structure after the volatilization step and water washing, the flat membrane was prepared in the same manner as in Example 1 except that the alcohol weight fraction of the alcohol aqueous solution contained in the membrane was adjusted to 20% and 60%, respectively. A sheet was obtained. Details of the HPC application conditions are shown in Table 1, and details of the film properties are shown in Table 2. Table 1 shows the post-treatment (hydrophilization) conditions, and Table 2 shows the results.

(Comparative Examples 3 and 4)
A flat membrane sheet was obtained in the same manner as in Example 1 except that the temperature of the hot water treatment tank was changed to 45 ° C. and 73 ° C., respectively. Table 1 shows the post-treatment (hydrophilization) conditions, and Table 2 shows the results.

(Comparative Example 5)
A flat membrane sheet was obtained in the same manner as in Example 1 except that the liquid component of the HPC alcohol aqueous solution was changed to only 2-propanol. Table 1 shows the post-treatment (hydrophilization) conditions, and Table 2 shows the results.

(Comparative Examples 6 and 7)
In the flat membrane structure after changing the HPC concentration of the alcohol solution in the impregnation tank to 1.1 wt% and the volatilization step and the water washing, the alcohol weight fraction of the alcohol aqueous solution contained in the membrane is 60%, A flat membrane sheet was obtained in the same manner as in Example 1 except that the content was adjusted to 20%. Table 1 shows the post-treatment (hydrophilization) conditions, and Table 2 shows the results.

(Comparative Example 8)
In the flat membrane structure after changing the HPC concentration of the alcohol solution in the impregnation tank to 0.8 wt% and the volatilization step and washing with water, the alcohol weight fraction of the aqueous alcohol solution contained in the membrane was adjusted to 60%. Except for this, a flat membrane sheet was obtained in the same manner as in Example 1. Table 1 shows the post-treatment (hydrophilization) conditions, and Table 2 shows the results.

(Comparative Example 9)
No HPC was applied to the flat membrane structure. The results are summarized in Table 2.

  As is clear from the results in Table 2, in Examples 1 to 10, films having high water permeability and good bubble points are obtained as compared with Comparative Examples 1 to 9. Further, the fine particles of HPC are dispersed and fixed on the microporous surface of the polymer porous membrane. Due to the synergistic effect of these membrane characteristics and the HPC fixing treatment on the membrane, excellent results (small degree of increase in differential pressure) are obtained in the filtration test of actual sludge liquid. On the other hand, in Comparative Example 1, as a result of lowering the alcohol weight fraction in the film, the size of the HPC fine particles was increased. Moreover, the pure water FR was low and the increase in the actual liquid test differential pressure was high. In Comparative Example 2, as a result of increasing the alcohol weight fraction in the film, the HPC fine particle size was remarkably reduced, and the particle size and the degree of dispersion were also low. Moreover, the actual liquid test differential pressure increase was also increased. In Comparative Example 3, since the heat treatment temperature of HPC was low, the adhesion to the porous membrane was insufficient, and the actual liquid test differential pressure increase was high. At this time, the size of the fine particles of HPC was reduced, and the degree of dispersion was also reduced. In Comparative Example 4, since the heat treatment temperature was too high, the size of HPC fine particles and the value of dispersity were remarkably large, and the actual liquid test differential pressure increase was high. In Comparative Example 5, when only IPA was used as the solvent of the HPC solution in the impregnation step, the HPC fine particle size was reduced and the dispersity value was low. Moreover, the pure water FR became remarkably high, and the actual liquid test differential pressure increase degree became high. In Comparative Example 6, as a result of increasing the HPC concentration of the impregnating liquid and further increasing the value of the alcohol weight fraction, the particle size was remarkably reduced and the value of the dispersity was remarkably increased. Moreover, the actual liquid test differential pressure increase was also increased. In Comparative Example 7, as a result of increasing the HPC concentration of the impregnating liquid and further decreasing the value of the alcohol weight fraction, the particle size was remarkably increased and the dispersity value was also significantly increased. Moreover, the actual liquid test differential pressure increase was also increased. In Comparative Example 8, as a result of increasing the value of the alcohol fraction in the film and increasing the HPC concentration in the impregnation tank, the HPC fine particle size was remarkably small. Moreover, the actual liquid test differential pressure increase degree became high. In Comparative Example 9, since it was a hydrophobic film not provided with HPC, a behavior in which sludge components were easily adsorbed was seen, and the actual liquid test differential pressure increase was significantly increased.

  Since the flat membrane sheet of the present invention has excellent membrane performance such as water permeability and fouling resistance that can withstand long-term use, it is extremely suitable for wastewater treatment such as MBR.

Claims (2)

From a nonwoven sheet-like base material and a polymer porous membrane containing polyvinylidene fluoride (excluding polyvinyl chloride, chlorinated polyvinyl chloride, polyether sulfone, polytetrafluoroethylene, or a mixture thereof) A flat membrane sheet comprising: a flat membrane sheet, wherein hydroxypropyl cellulose is dispersed and fixed in the form of fine particles on the flat membrane sheet, and hydroxy in a range of 5 μm from the outermost surface of the flat membrane sheet. A polymer porous flat membrane sheet for MBR, wherein the propylcellulose fine particles have a size of 5 to 100 nm. The flat film sheet according to claim 1, wherein the dispersion degree of the fine particles of hydroxypropylcellulose is in the range of 0.2 to 1.5.