TW201306930A - Porous polymer membrane for discharge water treatment - Google Patents

Abstract

The object of the present invention is to provide a flat film of a porous polymer membrane for MBR method having a structure of that can keep sufficient strength suitable for using in a discharge water treatment for a long term and also has high membrane performance. The solution means of the present invention is a porous polymer membrane. The porous polymer membrane is a flat membrane immersed in an actived sludge to obtain a filtration from the actived sludge, and is characterized by satisfying conditions of (A) to (E) as follows: (A) the pure water flux is 20 to 50mL/cm<SP>2</SP>/min/bar; (B) the bubble point in pure water is 0.08 to 0.3MPa; (C) the porous polymer membrane comprises a polyvinyl chloride and / or a chlorinated polyvinyl chloride; (D) in the observation of a surface of the porous polymer membrane contacted with a liquid to be treated through a 5000 times electron microscope, it is found that the porous polymer membrane has 25 to 45% of aperture ratio of the membrane surface, 0.2 to 1.0 μ m average fine-pore diameter, and 0.5 to 5 numbers of fine-pores occurred in 1 μ m<SP>2</SP>; (E) in the observation of a membrane cross section of the porous polymer membrane through a 5000 times electron microscope, it is found that the structure becomes gradually loosen from the surface contacted with a liquid to be treated to the inner layer portion; and the porosity of a polymer network of the inner layer portion is 1 to 3 times with respect to that of surface nearby the portion contacted with the liquid to be treated.

Description

Polymer porous membrane for drainage treatment

The present invention relates to a polymer porous membrane suitable for a flat membrane which is subjected to a wastewater treatment by a membrane separation activated sludge method (MBR).

In recent years, in the context of increasing world population, industrialization, urbanization, and rising living standards, the quality and quantity necessary for domestic and industrial water use are gradually increasing.

In general, water resources are ensured by the use of natural water obtained from nature in the past, as well as the method of obtaining fresh water from seawater by evaporation and reverse osmosis, or by using reverse osmosis to obtain fresh water from brine containing salt. . However, natural freshwater resources are limited, and due to the impact of weather anomalies in recent years, availability is increasingly narrow. Further, in order to produce fresh water using an evaporation method and reverse osmosis, since the energy for heating or pressurization is required, the area in which utilization is enabled is limited.

As for other methods, there is also the direction of sewage reuse. In the past, sewage treatment was carried out by decomposing the organic components in the sewage by activated sludge, and then discharging the treated water by precipitation filtration or the like, but it was difficult to completely remove the bacteria such as Escherichia coli. However, the membrane separation activated sludge method is very attractive in recent years because it uses a separation membrane to filter water treated with activated sludge, and may completely remove the above-mentioned harmful microflora, and has many advantages such as exquisite equipment and easy management operation. Attention technology. The water separated by the membrane separation activated sludge method can be used not only as a living landscape to maintain water or reclaimed water, but also by tapping the reverse osmosis method. It is necessary to use the treated water obtained by the membrane separation activated sludge method as the raw water, as opposed to the use of the reverse osmosis method for seawater to have a high pressure against the salt concentration. A feature that makes water safe and low-energy.

Therefore, the membrane separation activated sludge method has attracted attention as a method for solving the shortage of water expected in the future. In order to further improve this method, it is necessary to maintain a high-efficiency system at a low cost, while maintaining the separation performance of the membrane while ensuring water permeability. The general characteristics required for the membrane used in the membrane separation activated sludge process are indicated below.

First, the membrane separation activated sludge method uses a membrane without a covering to be immersed in activated sludge, and is more severely used than a separation membrane of other technical fields. Therefore, the physical strength required is sufficient. More specifically, in order to be damaged by various kinds of inclusions in the activated sludge, or when the pressure difference between the membranes (TMP) increases during filtration, the membrane is not damaged or deformed, and the performance is not lowered. High strength and film properties that are not easily stretched.

Next, if the membrane is used in a state of being immersed in activated sludge for a long period of time, the secretions generated by the activated sludge and the remains contained in the sludge, etc., may block the pores, thereby lowering the water permeability, and corresponding to This will create the need to increase the pressure on the pump. This is called fouling, which is the biggest problem when using a film. For this problem, it is possible to clean the membrane by using a drug such as sodium hypochlorite or hydrochloric acid to solve the fouling and return the membrane to a fresh state. Operation. Therefore, it is also important that the film is resistant to liquid chemicals in which the agents do not deteriorate.

However, the cleaning operation of these chemicals has many problems in the economical and ecological environment, such as the inability to operate the filtration at present, the cost of the medicine, the operation process, and the liquid discharge treatment of the medicine. Therefore, it has become the biggest problem to reduce the cleaning operation of the drug, how to prevent fouling, and to use it for a long time.

In view of such a water permeable membrane for MBR, it has been proposed to use chlorinated polyvinyl chloride or polyvinylidene fluoride resin as a film material (refer to the patent literature). 1, 2). Specifically, in Patent Document 1, a polyester nonwoven fabric is impregnated with a solution obtained by dissolving chlorinated polyvinyl chloride in tetrahydrofuran and further adding isopropanol and sucrose ester, and drying to form a phase separation to form a microparticle. Hole body. Further, in Patent Document 2, a polyvinylidene fluoride, a polymethyl methacrylate, a graft copolymer with polyvinylpyrrolidone, and N,N-dimethylacetamide, which are excellent in chemical resistance, are produced. A film forming raw material liquid of polyvinyl alcohol is applied to a polyester nonwoven fabric and impregnated into a water coagulation bath to obtain a porous substrate in which a porous resin layer is formed.

However, the use of the above-mentioned conventional chlorinated polyvinyl chloride film cannot be said to have increased the opening ratio to the limit, and the degree of hydrophilization, particularly the hydrophilicity at the time of maintaining long-term use. On the other hand, if a material other than chlorinated polyvinyl chloride is used as a raw material having chemical resistance, the film forming method is limited, and it is practically impossible to form a film by a dry method in which equipment investment is small and film formation can be easily performed. For example, a flat film of a polyvinylidene fluoride-based resin is excellent in chemical resistance and micropore density, and a solvent or a non-solvent can be selected by a wet method or a thermally induced phase separation method. According to the wet method, since a skin layer is formed on the surface of the film and a large void is formed inside the film, sufficient performance and strength are not easily obtained. According to the heat-induced phase separation method, since the membrane pores are formed due to temperature changes, strict temperature management is required, resulting in an increase in equipment investment and a high disaster risk in high-temperature operation. Further, since the price of the polymer is very high with respect to the polyvinyl chloride resin, there is a problem that the cost in industrial production becomes high.

[prior technical literature] [Patent Document]

Patent Document 1 Japanese Patent Laid-Open No. 58-88011

Patent Document 2 Japanese Patent Laid-Open Publication No. 2006-205067

In view of the current state of the art, the present invention has an object of providing a polymer porous film for a flat film of MBR capable of maintaining a structure suitable for long-term use in drainage treatment and having excellent film properties.

As a result of intensive research to achieve the above object, the present inventors have found that on the basis of selecting a film substrate and a film material which can withstand the strength for a long period of use, it is difficult to adhere to the film while maintaining a high surface opening ratio and a pore diameter. The polymer porous film of the MBR flat film which can maintain high film performance and strength for a long period of time can be provided to the surface of the mud, and the structure of the inner layer is appropriately loosened.

That is, the present invention has the following configurations (1) to (8).

(1) A polymer porous membrane which is a polymer porous membrane which is immersed in an activated sludge and obtains a flat membrane of a filtrate from an activated sludge liquid, and is characterized in that it satisfies the following A) to E Conditions: A) pure water flux is 20~50mL/cm ² /min/bar; B) foaming point in pure water is 0.08~0.3MPa; C) polymer porous membrane system is made of polyvinyl chloride And/or chlorinated polyvinyl chloride; D) when the surface of the porous polymer membrane is in contact with the liquid to be treated by a 5,000-fold electron microscope, the membrane surface opening ratio is 25 to 45%, and the average pore diameter is 0.2 to 1.0 μm, the number of pores present in 1 square micrometer is 0.5 to 5 pores; E) when the membrane cross section of the porous membrane of the polymer is observed by a 5,000-fold electron microscope, the surface in contact with the liquid to be treated The inner layer portion has a gradually sparse structure, and the void ratio of the polymer network in the inner layer portion is 1 to 3 times with respect to the portion near the surface in contact with the liquid to be treated.

(2) The porous polymer membrane according to (1), which is characterized by satisfying the following conditions F) to H): F) pure water passing after being immersed in hot water at 60 ° C for 4 weeks and then dried. The retention of the amount is above 80%; G) the thickness of the film is 80~150μm; H) the tensile strength of each 15mm width in the longitudinal and transverse directions is 17~52N, and the elongation at break is 1~5 %.

(3) The porous polymer membrane according to (1) or (2), wherein the polymer porous membrane is composed of a membrane material composed of a polymer material for forming a mesh network structure, and is used for It is formed by supporting a film substrate composed of a non-woven fabric.

(4) The porous polymer membrane according to (3), wherein the membrane substrate satisfies the following conditions I) to K): I) a fiber diameter of 5 to 12 μm; and J) a thickness of 80 to 150 μm. And the weight per unit area of the thickness of 1 μm is 0.4-0.8 g/m ² ; K) the tensile strength of each 15 mm width in the longitudinal direction and the lateral direction is 15 to 50 N, and the elongation at break is 1 to 5%.

(5) The porous polymer membrane according to any one of (1) to (4), wherein the surface of the porous polymer membrane is hydrophilized by hydroxypropylcellulose.

(6) A manufacturing method comprising the steps (1) to (5) of a step of containing a film substrate composed of a nonwoven fabric in a polymer solution containing a polymer material, a solvent, and a non-solvent and drying the polymer substrate. The method for producing a porous polymer membrane according to any one of the preceding claims, wherein the polymer material is polyvinyl chloride and/or chlorinated polyvinyl chloride, The non-solvent comprises isopropanol and butanol, and the weight percentage of isopropanol/butanol in the aforementioned non-solvent is 20-80%.

(7) The production method according to (6), wherein the polymer concentration in the polymer solution is 5 to 20% by weight, and the solvent/non-solvent weight ratio is 1 to 3.

(8) The production method according to (6) or (7), characterized in that the temperature at the time of drying is 10 to 40 ° C and the relative humidity is 50 to 90%.

The polymer porous membrane of the present invention is formed of polyvinyl chloride and/or chlorinated polyvinyl chloride, and has a surface open porosity, an average pore diameter, and a fine pore, while having a strength capable of withstanding long-term use. The number, the structure of the cross section of the film, and the porosity of the polymer network are controlled to a specific range, and the film performance such as water permeability is extremely high.

[Formation of the Invention]

The porous polymer membrane of the present invention can be used as a membrane separation activated sludge method (MBR) for immersing in activated sludge and obtaining a clear filtrate from an activated sludge liquid. The MBR method is to introduce the drainage into the activated sludge, and capture the pollutants in the organic-based drainage into the microorganisms in the reaction tank, that is, the activated sludge, which is consumed by metabolism or respiration. In this way, the sludge is discharged, and the organic matter in the drainage is decomposed by the activated sludge, and the membrane is used for filtration, and only the clarified water is taken out.

Generally, the water treatment film has the following three types according to the separation ability. First, a reverse osmosis (RO) membrane and an NF membrane having a molecular level separation ability of a nanometer size or less can be used for saltwater desalination, salinity removal of brine, softening, etc. by separating salts dissolved in water. . Next, it is a UF membrane with a separation capacity of several nanometers to several hundred nanometers, which can be used as a filter for removing viruses and bacteria in a water purification field. Membrane, or used as a water purifier or membrane for blood purification. This is followed by an MF film having a separation ability of several hundred nanometers to several micrometers. The membrane used in MBR belongs to the range of UF membrane to MF membrane, and plays a role in separating the inclusions and bacteria in the activated sludge from the purified water.

In the separation of purified water from activated sludge, the past method was separated by precipitation. However, if this method is required for separation for a long time, it is not necessary to provide a sedimentation tank having a large area. In order to remove and treat the particles of the sedimentation tank, there is a risk that bacteria and sludge components contained in the activated sludge such as Escherichia coli will be mixed into the treated water. On the other hand, the MBR method using a separation membrane can almost completely reduce the above-mentioned risk because the pore diameter of the membrane can be almost completely separated, because the precipitation tank can be omitted, and the processing equipment or the device can be refined and space-saving. It also contributed a lot. However, as previously described, the biggest problem - fouling - occurs due to the use of the membrane. At the same time of use, bacterial metabolites and remains, metabolites, sugars and peptides will adhere to the surface of the membrane to block the membrane. If MBR has a membrane with high resistance to this scale, it will make equipment management easier. It can also contribute significantly to the improvement of processing capacity and cost reduction. On the other hand, the film of the present invention, as described above, reduces the problem of fouling during use of the film, and successfully improves the film properties such as water permeability.

The porous film of the present invention comprises a film substrate composed of a nonwoven fabric and a film material composed of a polymer material having a mesh network structure. The non-woven fabric constituting the film substrate not only supports the form of the film material holding film but also plays the role of absorbing the stress applied to the film. The polymer material constituting the film material can have a function as a separation membrane by appropriately entanglement with the film substrate and obtaining an appropriate porous structure.

The non-woven fabric is composed of a polymer material that is insoluble in an organic solvent or water, and has an ability to retain the film component and maintain the stress applied to the film. set. The nonwoven fabric is preferably composed of a hydrocarbon-based, olefin-based or condensed polymer, such as polyethylene, polyolefin, polyvinyl alcohol, polyethylene terephthalate, nylon, polyimine, polytetrafluoroethylene. It is composed of ethylene, polyvinyl chloride, and the like.

The thickness of the non-woven fabric is preferably 80 to 150 μm. Non-woven fabrics are used as a water-permeable film substrate. If they are too thick, they may hinder the penetration of water. However, if they are too thin, the strength is insufficient and they may not be used for a long time.

In order to secure the strength of the nonwoven fabric, a method of fixing the fibers to each other with an adhesive is known. As a method of fixing, a method of forming a binder component into a core sheath structure fiber of a sheath portion, or a method of impregnating a binder component after a nonwoven fabric, or the like may be preferably used in combination with a binder fiber. After the nonwoven fabric is formed, the fibers are joined to each other by welding by heat. After a suitable combination of the drawn yarn and the undrawn yarn to form a nonwoven fabric, temperature and pressure are applied. At this time, the undrawn yarn plays a role as a binder because it is soft at a low temperature compared with the drawn yarn. Although a method of maintaining strength by embossing is known, the embossed portion may become a defect when forming a film.

There are various methods such as a melt blown, a thermal bond, and a papermaking method, and any of them can be used. However, the fiber diameter and the basis weight are important in ensuring water permeability. The fiber diameter is preferably 5 to 12 μm, more preferably 7 to 10 μm. If the fiber diameter is too small, the strength becomes small, and it is unbearable for long-term use. If it is too thick, the overall solvent balance is small and does not have sufficient strength, and it is also unbearable for long-term use. The basis weight per 1 μm thick is preferably 0.4 to 0.8 g/m ² , preferably 0.5 to 0.7 g/m ² . The weight per unit area is preferably small, but if it is too small, the strength is made small, and it is not used as a film for a long period of time, and if it is too large, the voids are reduced, and the water permeability may be deteriorated.

When applying force to the non-woven fabric, it is initially elastic. If the force is relaxed, it will return to the original, but if a force is applied beyond a certain point to deform it, even force The amount is relaxed and will not return to the original. The former is called elastic deformation, and the latter is called plastic deformation. The above point is called the drop point, the force is called the fall strength, and the stretch is called the fall elongation. The non-woven fabric is a member supporting the film, and its strength and elongation characteristics are important characteristics that govern the strength of the film. If the drop strength is low, the plastic deformation immediately occurs when a force is applied to the film, and it is impossible to return to the original state, so that it is preferable. However, if it is too high, it is technically difficult to obtain an inexpensive non-woven fabric capable of maintaining water permeability. Therefore, the lodging strength per 15 mm width of the non-woven fabric in the longitudinal direction and the lateral direction is preferably 15 to 50 N, more preferably 15 to 45 N. . Further, if the elongation at break is large, the elongation of the nonwoven fabric becomes large, and the risk of breakage of the network at the time of film formation becomes high, and the pressure at the time of water pressure or filtration becomes a state of deformation, and there is a fear that a sufficient amount of water permeability cannot be obtained. However, if it is not stretched at all, it is not absorbed when the film is applied and there is a possibility of damage. Therefore, the elongation at break of the nonwoven fabric is preferably from 1 to 5%, more preferably from 1 to 3%. Further, the longitudinal direction of the obtained sheet was set to the longitudinal direction.

The polymer material constituting the film material is formed by forming a polymer network having pores having a submicron size by phase separation using polyvinyl chloride and/or chlorinated polyvinyl chloride.

Phase separation is a method in which a polymer material and a solvent are mixed to form a solution, and then applied to a nonwoven fabric substrate, dried in air (dry method), and guided to a coagulation bath to be solidified (wet) Method (method)), a method of rapidly changing the temperature (heat-induced phase separation method), and the like. Any method may be used, but the dry method in which the substrate of the coated polymer solution is dried in the gas phase is preferred because of the ease of film formation management and the need for complicated equipment reclamation.

The solvent for dissolving the polymer material must be one which can dissolve the polymer constituting the film but does not dissolve the non-woven fabric, and can be used to volatilize or water-soluble at approximately 150 ° C or lower. Specifically suitable for tetrahydrofuran, toluene, DMF, NMR, DMAC, A single type or a mixture of a plurality of types can be used. In the case of dry film formation, since the solvent is volatilized in the gas phase to form a film, tetrahydrofuran and a mixed solvent thereof are preferably used.

The non-solvent is preferably water or an alcohol. Among the alcohols, ethanol, propanol and butanol are particularly suitable. These may be used alone or in combination.

The concentration of the polymer in the solution is preferably from 5 to 20% by weight, more preferably from 6 to 18% by weight, most preferably from 7 to 15% by weight. If the polymer concentration is too low, the network structure of the film is not sufficiently developed, and the film portion itself cannot be used for a long period of time. If the concentration is too high, the solution cannot penetrate into the interior of the non-woven fabric, and it may not function as a film. The ratio of the solvent to the non-solvent (solvent/non-solvent) is preferably from 1 to 3, more preferably from 1.5 to 2.8, most preferably from 2 to 2.6. If the ratio of the non-solvent is too high, the solubility of the polymer is impaired, and a uniform solution cannot be obtained, and sufficient impregnation may not be achieved. If it is too low, I am afraid that it cannot play a role in promoting separation.

The polymer material constituting the film is hydrophobic. Therefore, it is not only difficult to pass water when the membrane is used, but due to the hydrophobic interaction, it is easy to cause the metabolic components formed by the activated sludge bacteria and the sugar, the remains, etc. to be adsorbed on the membrane to block the membrane, that is, the product. The problem of scale. One of the ways to avoid this problem is to preferably hydrophilize the membrane.

The method of treating the hydrophilization includes a method of adding a hydrophilizing agent to a polymer solution, a method of adding a hydrophilizing agent after forming a film, a method of surface-treating a film, and the like. The hydrophilizing agent is a chemical substance having a hydrophobic portion and a hydrophilic portion in one molecule, and is not limited as long as it can be immobilized on the surface or internal network of the film, and examples thereof include sugars, cellulose derivatives, surfactants, and the like. . Specific examples thereof include hydroxypropylcellulose, sucrose fatty acid ester, and sodium dodecyl sulfate. Further, a method of hydrophilizing after forming a film may be a method of immersing in a solution formed of the hydrophilizing agent, applying a temperature, or drying and fixing the solution. Also, you can use straight The membrane itself sulfonates or imparts a sulfate group. Further, a method of irradiating an electron beam, a plasma, or an ultraviolet ray, or oxidizing a surface or imparting a carboxylic acid may be considered.

Although a method of hydrophilizing various membranes as described above can be employed, it is preferred to coat hydroxypropylcellulose or to add sucrose fatty acid ester from the viewpoint of cost reduction. Further, in the present invention, it is suitable to apply hydroxypropylcellulose from the viewpoint of resistance to fouling of actual discharge.

An example of a method for producing the porous polymer membrane of the present invention will be described below. First, a solution obtained by dissolving a polymer forming a film is impregnated into a nonwoven fabric. The method of impregnation may be carried out by any method such as dipping, impregnation using a mold, or the like.

After impregnating the non-woven fabric with the polymer solution, it is guided to the drying zone. At this point, care must be taken not to let dry wind blow directly onto the membrane. The reason for this is because the film surface is promoted to be renewed by the wind, so that only the surface of the film is rapidly phase-separated, and as a result, the opening ratio of the surface is lowered, and the water permeability may be lowered. Further, as a result of intensive studies by the present inventors, it has been found that such a film having a low surface opening ratio has poor fouling resistance.

Control of temperature and humidity in the drying zone is important. The preferred temperature is 10 to 40 ° C, more preferably 15 to 30 ° C, and most preferably 18 to 25 ° C. If the temperature is too high, the surface of the film is dried, and the surface of the film is rapidly phase-separated. As a result, the opening ratio of the surface may be lowered. If the temperature is too low, dew condensation occurs on the surface of the film, making it difficult to control the phase separation mechanism of the film. Further, the preferred relative humidity is 40 to 85%, more preferably 50 to 85%, and most preferably 60 to 85%. If the humidity is too low and the surface of the film is rapidly phase-separated, it may not be possible to ensure a sufficient opening ratio. If the humidity is too high, the pore size distribution of the pores on the surface of the membrane becomes large, which may lower the bubble point and deteriorate the separation performance, and condensation may occur on the surface of the membrane. It is also preferred to control the temperature of the impregnated polymer solution. By adjusting to a temperature preferably relative to the drying zone -15~+15°C, more preferably -10°C~+10°C, optimally -5°C~+5°C, good film formation.

Further, in the above dry film formation, in order to exhibit a good film surface opening ratio, it is necessary to use a solvent having a suitable vapor pressure and a non-solvent in combination. The solvent may be selected from tetrahydrofuran or a mixed solvent thereof. The non-solvent may be selected from isopropanol, butanol, and a mixed solvent thereof. It is preferred to use a mixed solvent of two types of isopropyl alcohol and 1-butanol. As a result of the inventors' research, it was found that a solvent mixed with the two can exhibit a good open cell surface porosity and a combination of water permeability and foaming point. In the present invention, the target properties of the present invention can be exhibited by using the above two kinds of non-solvents. The mixed weight of 1-butanol in the non-solvent is preferably from 20 to 80%, more preferably from 22 to 70%, based on the total non-solvent amount (total weight of isopropanol and 1-butanol), preferably 25~60%.

In the present invention, the surface of the polymer porous film thus produced which is in contact with the liquid to be treated has an average pore diameter of 0.2 to 1 μm, preferably 0.3 to 0.9 μm, more preferably 0.4 under a 5,000-fold electron microscope. ~0.8μm, the surface opening ratio is 25~45%, preferably 28~45%, and the number of pores present in the 1 square micrometer of the surface is 0.5~5, preferably 0.7~3, preferably It is 0.8~2. The average pore diameter of the above surface is considered to be the separation property and the water permeability, and the surface opening ratio is considered in consideration of the strength and filtration efficiency for long-term use, and the number of pores is defined by the pore diameter and the opening ratio.

When the cross-section of the film is observed by a 5,000-fold electron microscope, the polymer porous film of the present invention preferably has a structure that gradually becomes sparse from the surface in contact with the liquid to be treated, and the polymer material constituting the film is formed. The three-dimensional needles on the network are formed, and the non-woven fabric of the film substrate is moderately entangled. At this time, if the density of the network is too high, the water permeability is hindered, and if it is too low, the film component may be detached from the substrate during long-term use, and the function as a film may not be exhibited. And this property is It is the porosity of the polymer network of the inner layer portion in the vicinity of the surface of the film which is in contact with the liquid to be treated. The void ratio is 1 to 3 times, preferably 1 to 2 times. 1(a) and 1(b) show an example of a cross-sectional structure of a film obtained by the present invention, and it has been confirmed that a structure which is gradually thinned from the vicinity of the surface of the film to the inner layer portion and which is entangled with the film substrate Good network. The membrane surface portion has a partitioning ability, and the inner layer portion does not hinder the permeation of water passing through the surface, and is a membrane structure capable of efficiently filtering.

The initial performance of the film was evaluated as pure water flux and bubble point. The pure water flux is the volume of water through which pure water can pass per unit area per unit time, and the bubble point is an index indicating the maximum pore diameter of the membrane, indicating the separation performance. The pure water flux (unit: mL/cm ² /min/bar) is 20 to 50, preferably 25 to 45. If the pure water flux is too small, in order to ensure the necessary amount of water, it is necessary to increase the number of membranes and increase the pressure of the pump, which is economically and energy-intensive. On the other hand, if it is too large, the pore diameter of the film needs to be increased to deteriorate the partitioning performance, and it may not be sufficient to function as a film. The bubble point is 0.08 to 0.3, preferably 0.09 to 0.25, more preferably 0.1 to 0.2. If the bubble point is too small, the separation performance is insufficient (the pore diameter becomes too large), and the sludge component may be mixed with the filtered water. If it is too large, the possibility of ensuring sufficient water permeability is high, and the filtration efficiency may be deteriorated. .

The retention rate of the pure water flux measured by the porous membrane of the present invention after being immersed in hot water at 60 ° C for 4 weeks is preferably 80% or more. In order to maintain the fouling resistance, it is desirable that the hydrophilicity imparted to the film does not fall off even after a long period of use. As a result of the investigation, it is known that the hydrophilicity after immersion in hot water at 60 ° C is relative to the loss of hydrophilicity. The film exhibits insufficient water permeability, and the film which can maintain hydrophilicity can exhibit sufficient water permeability and can be confirmed as a desired film property. The retention rate of pure water flux is more preferably 85% or more, and even more preferably 90% or more.

The film thickness of the polymer porous film of the present invention is preferably 80 to 150 μm. Since the film retains its shape by the non-woven fabric of the film substrate, it is substantially the same thickness as the film substrate. If the thickness is too thick, the resistance at the time of water passing is increased, and the water permeability may be lowered. If the thickness is too thin, the film strength may be insufficient.

The tensile properties of the film are essentially also governed by the nonwoven fabric of the film substrate. If the strength of the drop is low, the plastic deformation is caused immediately when the force is applied to the film, and the original shape is not restored. The film of the present invention preferably has a drop strength of 15 to 52 N, more preferably 18 to 45 N, in both the longitudinal direction and the transverse direction. Further, when the elongation at break is large, the elongation of the film is increased, and the risk of damage to the network structure of the film is increased, and it is likely to be deformed under pressure at the time of water pressure or filtration, and a sufficient amount of water permeability cannot be obtained. However, if it is not stretched at all, it may not be absorbed when the film is applied and may be damaged. Therefore, the film of the present invention preferably has an elongation at break of from 1 to 5%, more preferably from 1 to 3%. Further, the longitudinal direction of the obtained sheet was a longitudinal direction.

[Examples]

The excellent effects of the porous polymer membrane 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 by the Example is described below.

(1) Pure water flux

The produced porous film was cut into a circular shape of φ90 mm, and placed in a filter device (UHP-90K, manufactured by Toyo Filter Co., Ltd.), and then applied with a water pressure of 0.5 bar, and collected from the outlet of the device for 1 minute. The amount of water permeation, the following formula to obtain pure water flux. On the other hand, the RO water of 25 ° C in the water used for filtration was set as the collection start time after 30 seconds from the application of the water pressure. Further, the height of the water surface from the film surface was adjusted to 3 cm ± 1 cm.

(pure water flux [mL/cm ² /min/bar]) = (Q [mL / min]) / (A [cm ² ]) / (P [bar])

(Q: water permeability per minute, A: effective membrane area = 48 cm ² , P: water pressure = 0.5 bar)

(2) Purity of pure water flux

The produced film was immersed in hot water at 60 ° C for 4 weeks, and then air-dried for 1 night. Thereafter, according to the method of the above (1), the pure water flux was measured, and the flux before the immersion in hot water was divided, and the retention rate (in percent) of the pure water flux was calculated. Among them, the temperature and humidity during air drying are in the range of 20 to 30 ° C and 40 to 70% humidity.

(3) bubble point

The produced membrane was placed in the apparatus used in (1), RO water was injected in such a manner that the membrane surface was 5 cm high, and nitrogen pressure was applied from the outlet of the apparatus (below the membrane) in a state where the pressure relief valve in the apparatus was opened. The pressure at which the bubble continuously emerges from the film surface into the water is taken as the bubble point [MPa]. Among them, the member capable of supporting the film was not hindered from observing the bubble on the film, and the film was designed to be detached from the device without being subjected to pressure from the lower surface. Further, the rate of increase in the nitrogen pressure was set to 0.02 MPa per minute.

(4) Surface open porosity of the film

From the scanning electron microscope (SEM) photograph of the surface of the produced film, the surface open ratio was calculated in the following order. A 5000-times SEM photograph of the surface of the film was prepared, and the soft body was processed by the image, and the pore portion of the film surface was changed, and the polymer portion of the film was whitened, and binarization treatment was performed. Among them, the polymer portion seen from the depth of the film hole is appropriately blackened. Thereafter, the image analysis software (Image-J) was used to calculate the surface opening ratio of the film. In addition, in order to reduce noise, the minimum value of the measurement size is set to 10. "Area Fraction [%]" corresponds to the surface opening ratio of the film.

(5) Average pore diameter of the membrane surface

The average pore diameter of the film surface was calculated using the image analysis software (Image-J) in the same manner as in (4). From the "Average Size [pixel ² ]" calculated by the image analysis software and the scale data [pixel/μm] of the SEM image used for analysis, the average pore area [μm ² ] of the film pore was determined, and the pore size was assumed. In the case of a circle, the average pore diameter (diameter) [μm] was calculated.

(6) The number of pores on the surface of the membrane

Similarly to (4), the number of pores on the surface of the film was calculated using an image analysis software (Image-J). The number of pores (number/μm ² ) was calculated from the "count" calculated from the image analysis software, the total field of view area (pixel ² ) and the scale data [pixel/μm] of the SEM image used for analysis.

(7) Observing the structure of the film surface to the inner layer

Using a scanning electron microscope (SEM) on the cross section of the produced film, the film surface portion was sequentially printed to the inside of the film at 5000 times, and the structure of the entire film cross section was confirmed.

(8) Void ratio of the polymer network of the film cross section

From the cross-sectional photograph of the film taken by SEM, the image analysis software (W inROOF experience version) was used to calculate the void ratio of the polymer network of the film. In the calculation, the calculation range is selected so as not to calculate the range of the film substrate portion. Calculate the polymer network in the vicinity of the surface in contact with the liquid to be treated (the portion from 0.5 μm to 5 μm thick from the surface of the film) and the inner portion (the central portion of the film) to obtain the inner layer portion of the portion near the surface. The ratio of void ratios (expressed as a percentage).

(9) Total thickness of the film

Regarding the total thickness of the film, any five points were measured using a thickness gauge, and the average value thereof was taken.

(10) Falling strength and elongation at break of the film

The fall strength and the elongation at break of the film were calculated in the following order. Will be made The film was cut into a strip shape having a width of 15 mm (about 60 mm in length), and a Tensilon tensile tester was set in such a manner that the detection pitch was 40 mm. The dynamometer conditions were set to 100 kgf and the range was 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 wiring of the elastically deformed portion and the plastically deformed portion is drawn in a straight line, and the intersection point of the two is taken as the falling point, and the corresponding strength and the elongation at break of the point are obtained. Five samples were measured in the longitudinal direction and the transverse direction of the film, and the average value was taken as the drop strength [N/15 mm] and the elongation at break [%].

(11) Thickness of film substrate

The thickness of the film substrate was measured by arbitrarily measuring 5 points using the thickness of the substrate for the film. Further, a method of immersing in a solvent which can dissolve a film component only from a film after film formation, and removing the film component to expose the film substrate is also carried out.

(12) Fiber diameter of the film substrate

The fiber diameter of the film substrate was photographed by SEM, and the fiber diameter and scale data of the film were taken. Ten fibers were counted, and the average value was taken as the fiber diameter [μm] of the film substrate.

(13) Unit weight per unit thickness of the film substrate

The weight per unit area of the film base material was measured by weighing 10 square centimeters of the substrate on an electronic scale, and the weight per 1 m ² was calculated to obtain the basis weight of the substrate, and then the thickness of the film substrate was determined. Weight per unit area [g/m ² /μm] per 1 μm thick.

(14) Falling strength and elongation at break of the film substrate

The drop strength and the elongation at break of the film substrate were measured using a Tensilon tensile tester. The calculation was performed in the same manner as (11) except that the film substrate was used instead of the film.

(15) Solid liquid test (degree of fouling)

The fouling characteristics of the membrane were investigated using actual sludge fluid. The apparatus was an impregnated membrane separation activated sludge method test apparatus (Model IMF-5) manufactured by Miyamoto Seisakusho Co., Ltd. The activated sludge liquid was adjusted so that the MLSS concentration in the apparatus tank was about 10,000 mg/L, and the 匣 type filter which attached the film to the both surfaces was provided. The filtration filtration operation was performed with a peristaltic pump at a filtration rate of a membrane area of 0.6 m ³ /day per 1 m ² . Continuous operation is performed without setting the operation stop time during the filtration operation, and continuous aeration is performed from the lower portion of the 匣 type filter membrane. The operation was continued for 2 weeks, and the degree of fouling was determined by monitoring the rise in the pressure difference between the membranes. It is based on whether the pressure difference rise within 2 weeks exceeds 25 kPa.

(Examples 1 to 4 and Comparative Examples 1 to 4)

After the film substrate is first cut to a specific size, it is fixed to the film forming frame while being careful not to be wound into the wrinkles. Next, the film substrate was immersed in a solution (film-forming material liquid) composed of a polymer, a solvent, and a non-solvent which form a film, and left for 1 minute. Thereafter, the substrate impregnated with the film forming raw material liquid was slowly pulled up, and then placed in a drying zone (in a constant temperature and humidity chamber) adjusted to a specific temperature and humidity for 10 minutes to form a film. Next, the film thus produced was applied with hydroxypropylcellulose (HPC).

(Examples 5 and 6)

The film roll was placed on the unwinding free roll, and the film was formed by passing through the impregnation bath in which the film forming material liquid was placed, and passing through the drying zone to a continuous film forming apparatus which was taken up by a winder. It took time for the film substrate to pass through the impregnation bath to 1 minute, and it was slowly taken up. At this time, the drying zone is also prepared at a specific temperature and humidity. The film thus produced was subjected to HPC coating treatment.

HPC coating is carried out according to the following methods. First, in a mixed solution of ethanol:RO water=60/40 (weight ratio), in order to make HPC 0.6% by weight The solution was dissolved to prepare a HPC solution, and the film prepared above was slowly immersed in the HPC solution (starting from the end in such a manner that bubbles were not mixed). After immersing for 30 minutes at room temperature, the film was taken out, and the remaining adhering liquid was removed, and washed gently with water. Thereafter, the RO water at 60 ° C was slowly immersed and allowed to stand for 30 minutes. The film was taken out and air-dried to finish the treatment. Moreover, the temperature and humidity during air drying are in the range of 20 to 30 ° C and a humidity of 40 to 70%.

(Comparative Example 5)

After the solution of the polymer, the solvent, and the non-solvent having the same composition as in Example 2 was prepared, sucrose fatty acid ester (the first industrial drug manufactured by DK ESTER) was added so as to be 10% by weight based on the dissolved polymer concentration. SS), stir until a homogeneous solution. The substrate was immersed in this liquid to prepare a film. The film was produced in the same manner as in Example 2 except that the coating was not performed by HPC.

The details of the film substrate, the production method, and the evaluation results of Examples 1 to 6 and Comparative Examples 1 to 5 are shown in Tables 1 to 3, respectively.

As is apparent from the results of Table 2, Examples 1 to 6 were able to obtain a film having excellent tensile properties (high relief strength and small elongation at break) and having high water permeability and good foaming point. In addition, a high membrane surface opening ratio and a fine pore number and a moderately loose intermediate layer structure can be realized on the membrane structural surface, whereby the multiplication effect of the membrane structure and the HPC coating treatment on the membrane can be obtained in practice. Excellent results of the filtration test of the sludge liquid (the pressure difference rises little). On the other hand, in Comparative Example 1, since the open porosity of the film surface was low, there was a problem that the actual sludge liquid was likely to be fouled, and the bubble point of Comparative Example 2 was low, which was not sufficient as the separation ability, and was observed at the initial stage. Sludge leaking. On the other hand, the strength of Comparative Example 3 was insufficient, and the film was found to be deformed under reduced pressure filtration, and the risk of breakage and performance was high at the time of use. In Comparative Example 4, the thickness was too large and the water permeability was lowered, and the filtration efficiency was expected to deteriorate. In Comparative Example 5, since the hydrophilization formulation was changed, the pure water flux retention rate after immersion in hot water was low, and it was suspected that the hydrophilizing agent fell off, and as a result, the actual sludge liquid was easily fouled.

[Industry Utilization]

The porous polymer membrane of the present invention is excellent in membrane properties such as water permeability and fouling resistance because it has sufficient strength for long-term use, and is therefore highly suitable for drainage treatment.

Fig. 1 (a) and (b) show scanning electron micrographs at 5000 times in the vicinity of the surface of the film, and Figs. 1(a) and 1(b) show photographs of the films of Examples 2 and 3, respectively.

Claims (8)

A porous polymer membrane for immersing in an activated sludge and obtaining a flat porous membrane of a filtrate from an activated sludge liquid, which is characterized by satisfying the following conditions A) to E) : A) pure water flux is 20~50mL/cm ² /min/bar; B) foaming point in pure water is 0.08~0.3MPa; C) polymer porous membrane system is made of polyvinyl chloride and/or When chlorochlorinated polyvinyl chloride is used; D) when the surface of the porous polymer membrane is in contact with the liquid to be treated by a 5,000-fold electron microscope, the membrane surface opening ratio is 25 to 45%, and the average pore diameter is 0.2 to 1.0. Μm, the number of pores present in 1 square micron is 0.5 to 5 pores; E) when observing the membrane cross section of the porous polymer membrane with a 5000-fold electron microscope, from the surface in contact with the liquid to be treated to the inner layer The part is a gradually sparse structure, and the porosity of the polymer network of the inner layer portion is 1 to 3 times with respect to the portion near the surface in contact with the liquid to be treated. The porous polymer membrane of the first aspect of the patent application satisfies the following conditions F) to H): F) pure water flux measured after being immersed in hot water at 60 ° C for 4 weeks and then dried. The retention rate is 80% or more; G) the thickness of the film is 80 to 150 μm; H) the relief strength per 15 mm width in both the longitudinal direction and the lateral direction is 17 to 52 N, and the elongation at break is 1 to 5%. . The polymer porous membrane according to claim 1 or 2, wherein the polymer porous membrane is composed of a membrane material composed of a polymer material for forming a mesh network structure, and a non-woven fabric for supporting the same. Membrane substrate To form. The porous membrane of the polymer of claim 3, wherein the membrane substrate satisfies the following conditions I) to K): I) the fiber diameter is 5 to 12 μm; J) the thickness is 80 to 150 μm, and each 1 μm The thickness per unit area is 0.4-0.8 g/m ² ; K) the tensile strength of each 15 mm width in both the longitudinal direction and the transverse direction is 15 to 50 N, and the elongation at break is 1 to 5%. The porous polymer membrane according to any one of claims 1 to 4, wherein the surface of the porous polymer membrane is hydrophilized by hydroxypropylcellulose. A manufacturing method comprising the steps of: coating a film substrate composed of a non-woven fabric on a polymer solution containing a polymer material, a solvent, and a non-solvent, and drying the same as in the first to fifth patent claims; The method for producing a porous polymer membrane according to any one of the preceding claims, wherein the polymer material is polyvinyl chloride and/or chlorinated polyvinyl chloride, and the non-solvent comprises isopropanol and butanol, and the non-solvent The weight percentage of isopropanol/butanol is 20 to 80%. The manufacturing method of claim 6, wherein the polymer concentration in the polymer solution is 5 to 20% by weight, and the solvent/non-solvent weight ratio is 1 to 3. The manufacturing method of claim 6 or 7, wherein the drying temperature is 10 to 40 ° C and the relative humidity is 50 to 90%.