JPWO2012063669A1 - Manufacturing method of separation membrane - Google Patents

Abstract

The present invention relates to a method for producing a separation membrane in which a separation membrane including a layer mainly composed of a polyvinylidene fluoride resin is brought into contact with water at 60 ° C. to 132 ° C. or water vapor at 60 ° C. to 132 ° C. According to the present invention, in addition to the excellent physical strength and chemical strength that are the characteristics of a separation membrane made of a polyvinylidene fluoride resin, it is possible to provide a separation membrane having excellent stain resistance and heat resistance. Furthermore, since the separation membrane manufacturing method of the present invention is simple in the treatment method for improving the stain resistance, the cost for manufacturing the separation membrane can be reduced.

Description

  The present invention relates to a method for producing a separation membrane used in the fields of water treatment such as drinking water production, water purification treatment and wastewater treatment, pharmaceutical production field, food industry field and the like.

  In recent years, separation membranes have been used in various fields such as water treatment fields such as drinking water production, water purification, and wastewater treatment, and food industry. In the water treatment field such as drinking water production, water purification treatment, wastewater treatment, etc., separation membranes are used to remove impurities in water as an alternative to conventional sand filtration and coagulation sedimentation processes. In the food industry field, separation membranes are used for the purpose of separating and removing yeasts used for fermentation and concentrating liquids.

  In order to be used in these applications, the separation membrane is required to have excellent separation characteristics, chemical strength (chemical resistance), physical strength, and permeation performance. Therefore, a separation membrane using a fluorine-based resin having both chemical strength (chemical resistance) and physical strength has been used.

  However, since the fluororesin film is hydrophobic, if the processing stock solution contains a hydrophobic clogging substance, the clogging substance tends to accumulate on the film surface due to the hydrophobic interaction, and it is easy to get dirty. It was. In particular, when used for food industry or for separation / purification of physiologically active substances such as proteins, the amount of clogging substances is much larger than in the case of drinking water production. At this time, the adsorption of the clogging substance on the membrane surface is a serious problem because it causes a reduction in the recovery rate and causes a rapid reduction in the filtration rate due to the clogging of the membrane pores. Therefore, improvement of the stain resistance of the separation membrane using a fluororesin has been an important issue.

  As a method of improving the stain resistance of separation membranes using fluororesins, clogging substances can be applied by hydrophilizing the fluororesin membrane, smoothing the membrane surface, controlling the pore size of the membrane, etc. in order to weaken hydrophobic interactions. There is a method of forming a film structure that hardly adheres. However, these are not effective when implemented alone or are less effective. Therefore, a separation membrane is disclosed in which a hydrophilic polymer is mixed with a fluororesin to impart hydrophilicity, and the surface is smoothed and the pore size of the membrane is controlled (Patent Document 1). However, although this separation membrane is suitable for continuous long-term operation in water treatment applications, the ease of clogging of the separation membrane is somewhat improved when filtering liquids containing a large amount of clogging substances in the food industry. However, there is still room for improvement.

  In addition, when the food industry and physiologically active substances are repeatedly filtered, there is a method to prevent contamination by introducing sterilization before filtration in order to avoid degradation of product quality and productivity due to contamination. is there. Examples of the sterilization include heat sterilization such as flame sterilization, dry heat sterilization, steam sterilization, electromagnetic wave treatment such as gamma ray sterilization, and chemical sterilization treatment using ethylene oxide gas. Among these sterilization treatments, steam sterilization is particularly preferably used from the viewpoint of simplicity of the apparatus and safety to the living body (especially from the viewpoint of safety for humans performing sterilization work). For this reason, the separation membrane is also required to have heat resistance that does not deteriorate even when repeated steam sterilization is performed. Although the fluororesin film is excellent in heat resistance, it is not preferable that the heat resistance is lowered in conjunction with the improvement in the above-mentioned stain resistance.

  In order to achieve both the physical strength of the fluororesin membrane and the separation performance of the polysulfone resin membrane, a three-dimensional network structure layer made of polysulfone resin is laminated on the spherical structure layer made of fluororesin, and the temperature is 110 ° C. or higher. A method of heat treatment with pressurized steam is also disclosed (Patent Document 2). The fluororesin layer and the polysulfone resin layer are easily delaminated, but it is considered that delamination is prevented by heat treatment with pressurized steam at 110 ° C. or higher.

JP 2006-239680 A JP 2010-110893 A

  Until now, there has been no separation membrane having durability against steam sterilization while having stain resistance. Therefore, the present invention provides a method for producing a separation membrane excellent in any of separation performance, permeation performance, physical strength, chemical strength, stain resistance and heat resistance. In particular, the present invention provides a method for producing a separation membrane in which the stain resistance required when the liquid to be separated is highly turbid is improved as compared with a conventional separation membrane.

  In the method for producing a separation membrane of the present invention that achieves the above-described object, a separation membrane including a layer mainly composed of a polyvinylidene fluoride resin is applied to water at 60 ° C. to 132 ° C. or water vapor at 60 ° C. to 132 ° C. It is a manufacturing method made to contact.

Further, the method for producing a separation membrane of the present invention forms a separation membrane by laminating a layer containing a hydrophilic polymer on a layer mainly composed of polyvinylidene fluoride resin.
The hydrophilic polymer is at least one selected from the group consisting of cellulose ester, fatty acid vinyl ester, ethylene-vinyl alcohol copolymer, vinyl pyrrolidone, ethylene oxide, propylene oxide, and copolymers of two or more thereof. Contains
In the production method, the separation membrane is contacted with water at 60 ° C. or higher and 132 ° C. or lower or water vapor at 60 ° C. or higher and 132 ° C. or lower.

  According to the present invention, in addition to the excellent physical strength and chemical strength characteristic of a separation membrane made of a polyvinylidene fluoride resin, it is possible to provide a separation membrane excellent in dirt resistance and heat resistance. The separation membrane of the present invention is particularly suitable for high-turbidity processing stock solutions because it has higher stain resistance than conventional ones. Furthermore, since the treatment method for improving the stain resistance is simple, the cost for manufacturing the separation membrane can be reduced.

FIG. 1 is a schematic view of an apparatus used for determining the value of the irreversible filtration resistance increase rate α of the separation membrane. FIG. 2 is an explanatory diagram showing a method of obtaining the irreversible filtration resistance increase rate α from the graph of total permeation amount−filtration resistance.

[Layer composed mainly of polyvinylidene fluoride resin (base material layer)]
The separation membrane in the present invention is a separation membrane having a layer mainly composed of polyvinylidene fluoride resin. The separation membrane may be composed only of a layer mainly composed of polyvinylidene fluoride resin, or may be a laminate with other layers. The layers other than the layer mainly composed of polyvinylidene fluoride resin will be described later. The layer mainly composed of the polyvinylidene fluoride resin is an indispensable layer for the separation membrane in the present invention. Hereinafter, the layer mainly composed of the polyvinylidene fluoride resin is referred to as a “base material layer”.

  The layer having a polyvinylidene fluoride resin as a main component is a layer having a polyvinylidene fluoride resin content of 50% by mass or more based on the entire layer. The base material layer may contain additives other than the polyvinylidene fluoride resin in order to further improve the stain resistance which is the object of the present invention. In addition, other components such as organic substances, inorganic substances, and polymers may be included as long as the object of the present invention is not impaired. The additive for improving the stain resistance and the content thereof will be described later.

  The polyvinylidene fluoride resin in the present invention is a resin containing a homopolymer of vinylidene fluoride or a co-polymer of vinylidene fluoride and tetrafluoroethylene, hexafluoropropylene, ethylene trifluoride chloride, vinyl fluoride or the like. It is a resin containing a polymer. The polyvinylidene fluoride resin may contain a plurality of types of copolymers.

  Further, the weight average molecular weight of the polyvinylidene fluoride resin may be appropriately selected depending on the required strength and water permeability of the separation membrane. In general, when the weight average molecular weight increases, the water permeability performance decreases, and when the weight average molecular weight decreases, the strength decreases. For this reason, the weight average molecular weight is preferably from 50,000 to 1,000,000. In particular, when the treatment stock solution is highly turbid and clogging substances adhering to the separation membrane need to be removed by chemical cleaning and the high turbidity treatment stock solution needs to be repeatedly filtered, the weight average molecular weight is 100,000 to 700,000. Is preferred. Further, when the chemical cleaning is performed a plurality of times, the weight average molecular weight is preferably 150,000 or more and 600,000 or less.

  Examples of the shape of the base material layer include a flat plate shape, a hollow fiber shape, and a tubular shape, and an appropriate shape can be selected and used in accordance with the form of the filtration device to be used and the properties of the processing stock solution.

  The structure of the base material layer is preferably porous because it is required to maintain the permeation performance as a separation membrane.

  Although there is no restriction | limiting in particular in the temperature which forms a base material layer, For example, the formation temperature of 135 degrees C or less is mentioned. “Forming temperature” as used herein refers to the process of obtaining a film-forming solution by dissolving a raw material polymer in a solvent at the beginning of the process of forming a base material layer used as a separation membrane, and kneading the film-forming solution. It is not the temperature in the process in which it is present, but the temperature in the process in which the base material layer forms the structure and the subsequent processes. Specifically, if the base material layer is a hollow fiber membrane, it is the temperature in the step after the membrane-forming solution is discharged from the die. If the base material layer is a flat film, it is the temperature of the step after coating the film forming solution on a glass substrate or the like.

[Heat treatment]
In the present invention, after the separation membrane having the base material layer is formed, in order to improve the stain resistance of the separation membrane, a heat treatment is performed by bringing the separation membrane into contact with a heat medium of 60 ° C. or higher and 132 ° C. or lower. When the temperature of the heat medium is 60 ° C. or higher, the membrane structure on the surface of the separation membrane changes to the extent that stain resistance is exhibited. Since the film structure further changes as the temperature of the heat source becomes higher, the temperature of the heat medium is preferably 75 ° C. or higher. On the other hand, if the temperature of the heat medium becomes too high, the film structure is significantly deteriorated and, on the contrary, the stain resistance is lowered. In order to prevent deterioration of the film structure, the temperature of the heat medium is preferably 125 ° C. or lower.

  Examples of the heat medium include hot air, water, and water vapor. Among these, if hot air is used, a high-temperature heat source of 60 ° C. or more and 132 ° C. or less can be easily obtained, but it is not preferable because the separation performance may be impaired due to drying of the separation membrane. Therefore, water or water vapor is used as a heating medium in order to heat while preventing drying.

  In order to obtain water or water vapor exceeding 100 ° C., the pressure of the atmosphere in which water or water vapor exists is increased and water or water vapor is pressurized. Furthermore, by using water or water vapor in a pressurized state, the water or water vapor easily penetrates into the details of the separation membrane, so that the stain resistance of the separation membrane is further improved. In addition, when using the water vapor | steam of a pressurized state, it is preferable to use saturated water vapor | steam. This is because the saturated steam having the specified temperature is preferable in terms of production management because the pressure is uniquely determined. In addition, when using the water vapor | steam of a pressurization state, it is preferable that the partial pressure of water vapor | steam is 1.1 atm or more, and temperature is 110 degreeC or more.

  Alternatively, the separation membrane and water may be housed in a sealed container, and the inside of the container may be decompressed to vaporize the water. In such a reduced pressure state, boiling water or saturated water vapor of less than 100 ° C. can be used as a heat medium. As described above, the temperature and pressure of the saturated steam treatment are uniquely determined. Therefore, when it is desired to use steam having a temperature of less than 100 ° C. as a heat medium, this reduced pressure method is preferable in terms of production management.

  Examples of the method of performing the treatment with water or steam include a batch method and a continuous method, and either means may be used.

  An example of batch-type heat treatment will be described. In the case of the hot water treatment, hot water that can sufficiently immerse the separation membrane and the separation membrane in the container may be added. When pressurizing the hot water, the hot water and the separation membrane may be placed in a pressure vessel that can be sealed, and the inside of the vessel may be pressurized. In the case of steam treatment, a separation membrane may be placed in a commercially available autoclave, and steam at a predetermined temperature may be supplied for a predetermined time. Water vapor can be supplied in either normal pressure or pressurized state. The decompression process can be performed using a device such as a commercially available evaporator.

  An example of continuous heat treatment will be described. In the case of hot water treatment, the separation membrane may be continuously supplied into the warm bath. In the case of water vapor treatment, a room for supplying water vapor is provided regardless of the pressure state, and the entrance / exit is made as small as possible with a labyrinth seal or the like to minimize the dissipation of water vapor. Separation membranes may be continuously supplied into the room and processed at a predetermined temperature for a predetermined time. The treatment time can be controlled by the separation membrane moving time (supply speed and separation membrane moving distance).

  The treatment time is not particularly limited, but if the treatment time is too short, the effect of improving stain resistance may not be sufficiently exhibited. Further, since the stain resistance is not improved after a certain processing time, it is only economically disadvantageous to perform the processing for a longer time. A preferable treatment time is 40 minutes or more and 120 minutes or less, and an optimum treatment time may be determined in consideration of the treatment temperature, the effect of improving stain resistance, and the economy. In order to perform the process with the optimum process temperature and time with good reproducibility, for example, when performing the steam process, it is preferable to use an autoclave capable of controlling the process temperature and time by a program.

  In the present invention, the processing time indicates the time during which the separation membrane is in contact with the heat medium having a predetermined temperature. For this reason, it is assumed that the time during which the inside of the apparatus is in the heating or cooling process in the batch processing is not included in the processing time.

[Separation membrane of laminate]
[Layer containing hydrophilic polymer (functional layer)]
In order to further improve the stain resistance of the separation membrane, a layer containing a hydrophilic polymer is laminated on the base material layer to form a separation membrane of the laminate, and the separation membrane is subjected to water at 60 ° C. or higher and 132 ° C. or lower, Alternatively, it is preferable to perform a heat treatment in contact with water vapor at 60 ° C. to 132 ° C. Hereinafter, the layer containing the hydrophilic polymer is referred to as “functional layer”.

  The hydrophilic polymer in the functional layer may contain at least one of cellulose ester, fatty acid vinyl ester, ethylene-vinyl alcohol copolymer, vinyl pyrrolidone, ethylene oxide, and propylene oxide. Moreover, what copolymerized these 2 or more types may be used.

  The resin constituting the functional layer is a copolymer of a hydrophilic polymer and an alkene such as ethylene or propylene, an alkyne such as acetylene, a monomer such as vinyl halide, vinylidene halide, methyl methacrylate, or methyl acrylate. There may be. In particular, ethylene, methyl methacrylate, and methyl acrylate are preferably used because they are available at low cost and easily obtain a copolymer. As a method for obtaining the hydrophilic polymer or copolymer, known polymerization techniques such as radical polymerization, anionic polymerization, and cationic polymerization can be used.

  Since the functional layer structure is required to maintain the permeation performance as a separation membrane, it is preferably porous.

  In the separation membrane of the laminate, the part responsible for stain resistance is the outermost layer of the separation membrane, so that when the functional layer is laminated on the base material layer, the functional layer is arranged on the primary side of the separation membrane. It is preferable to form a separation membrane in order to exhibit stain resistance. Here, the primary side of the separation membrane is the surface on the side through which the processing stock solution is passed when the separation membrane module is configured using the separation membrane. Conversely, the surface on the side through which the filtrate is passed becomes the secondary side of the separation membrane.

  The number of functional layers to be stacked is not particularly limited. However, if the number of stacked layers increases, the interface between layers becomes easy to peel off, and the stacking process becomes complicated, which increases the cost. Therefore, a separation membrane having a total of two layers composed of one functional layer and one base layer is preferably used.

  The details of the heat treatment for bringing the separation membrane of the laminate into contact with water at 60 ° C. to 132 ° C. or water vapor at 60 ° C. to 132 ° C. are the same as the heat treatment described above. In addition, even if it heat-processes after forming a base material layer, a functional layer is laminated | stacked on the base material layer which performed this heat processing, and also it heat-processes to the separation film of the laminated body on which this functional layer was laminated | stacked. Good. However, depending on the composition of the base material layer and the functional layer, the heat treatment may cause irreversible shrinkage. Therefore, when only the base material layer is preliminarily heat-treated and contracted, only the functional layer contracts when the last heat treatment is performed, and the base material layer and the functional layer may be peeled off. Accordingly, it is preferable that the heat treatment is not performed during the formation of the separation film of the stacked body, and the heat treatment is performed after the formation of the separation film of the stacked body.

  Furthermore, in order to improve the chemical resistance of the separation membrane, it is preferable that the functional layer further contains a polyvinylidene fluoride resin. Since the hydrophilic polymer or copolymer forms a dense structure with the polyvinylidene fluoride resin, it is preferably mixed with the polyvinylidene fluoride resin under appropriate conditions. Furthermore, when the hydrophilic polymer or copolymer and the polyvinylidene fluoride resin are mixed and dissolved in a good solvent for the polyvinylidene fluoride resin, it is particularly preferable because the handling becomes easy.

  When the resin constituting the functional layer is a polymer containing a hydrophilic polymer and a polyvinylidene fluoride resin, the content of the hydrophilic polymer with respect to the entire resin constituting the functional layer is 0.5% by mass or more and 50% It is preferable that it is below mass%. When the content of the hydrophilic polymer is less than 0.5% by mass, the hydrophilicity of the functional layer may be insufficient. When the content of the hydrophilic polymer exceeds 50% by mass, the amount of polyvinylidene fluoride resin is relatively decreased, and the chemical resistance and heat resistance of the polyvinylidene fluoride resin may be insufficient.

  The hydrophilic polymer or copolymer before being mixed with the polyvinylidene fluoride resin is a group consisting of cellulose ester, fatty acid vinyl ester, ethylene-vinyl alcohol copolymer, vinyl pyrrolidone, ethylene oxide and propylene oxide. When at least one selected from the above is contained in an amount of 50 mol% or more, the hydrophilicity of the separation membrane is increased, and as a result, the permeation performance and stain resistance are improved, which is preferable. As for the content rate of cellulose ester etc., 60 mol% or more is more preferable.

  However, in the case of vinyl pyrrolidone, ethylene oxide, and propylene oxide, water solubility is exhibited as the content increases. Since the separation membrane in the present invention is used in water, the hydrophilic polymer or copolymer needs to be substantially insoluble in water, and the hydrophilic polymer or copolymer itself is insoluble in water. There must be water insolubility imparted by appropriate treatment. In the case of a hydrophilic polymer or copolymer having vinyl pyrrolidone, ethylene oxide, or propylene oxide in the main chain and / or side chain, a method of making it water-insoluble by copolymerizing with other monomers is preferably used. For example, a random copolymer of vinyl pyrrolidone and methyl methacrylate (PMMA-co-PVP) and a graft polymer of vinyl pyrrolidone and polymethyl methacrylate (PMMA-g-PVP) set the copolymer molar ratio appropriately. As a result, a water-insoluble hydrophilic polymer or copolymer can be obtained.

  On the other hand, in the case of a cellulose ester or a fatty acid vinyl ester, even if the content rate is increased, it is generally not water-soluble, and the content rate can be adjusted in a wide range. Hydrolysis of a part of cellulose ester and fatty acid vinyl ester ester produces a hydroxyl group that is more hydrophilic than the ester. When the proportion of hydroxyl groups increases, the miscibility between the hydrophilic polymer or copolymer and the hydrophobic polyvinylidene fluoride resin decreases, but the hydrophilicity of the resulting separation membrane increases and the permeation performance. And dirt resistance is improved. Therefore, the method of hydrolyzing the ester within the range of being mixed with the polyvinylidene fluoride resin is preferable from the viewpoint of improving the membrane performance.

  When the separation membrane is a hydrophilic high molecular polymer or copolymer mainly composed of cellulose ester and / or fatty acid vinyl ester, the ester can be used even in a range that does not impair the miscibility with the polyvinylidene fluoride resin. It is preferable because the degree of hydrolysis can be adjusted over a wide range and hydrophilicity is easily imparted to the separation membrane. The hydrophilic polymer or copolymer mainly composed of cellulose ester and / or fatty acid vinyl ester means that the content of cellulose ester or fatty acid vinyl ester is 70 mol% or more, or the content of cellulose ester It is a hydrophilic polymer or copolymer in which the sum of the ratio and the fatty acid vinyl ester content is 70 mol% or more. The content is more preferably 80 mol% or more.

  In particular, the cellulose ester has three ester groups in the repeating unit, and it is easy to achieve both miscibility with the polyvinylidene fluoride resin and hydrophilicity of the separation membrane by adjusting the degree of hydrolysis thereof. Therefore, it is preferable. Examples of cellulose esters include cellulose acetate, cellulose acetate propionate, and cellulose acetate butyrate.

  Examples of fatty acid vinyl esters include homopolymers of fatty acid vinyl esters, copolymers of fatty acid vinyl esters and other monomers, and those obtained by graft polymerization of fatty acid vinyl esters onto other polymers. As the homopolymer of the fatty acid vinyl ester, polyvinyl acetate is preferable because it is inexpensive and easy to handle. As a copolymer of a fatty acid vinyl ester and another monomer, an ethylene-vinyl acetate copolymer is preferable because it is inexpensive and easy to handle.

  The characteristics of the ethylene-vinyl alcohol copolymer vary depending on the proportion of ethylene contained. The proportion of ethylene in the ethylene-vinyl alcohol copolymer is preferably 10% by mass or more and 50% by mass or less. If it is less than 10% by mass, improvement of heat resistance by ethylene may be insufficient. When the amount is more than 50% by mass, the proportion of vinyl alcohol is relatively small, and hydrophilicity is not sufficiently exhibited. Furthermore, the mechanical strength of the ethylene-vinyl alcohol copolymer is increased by saponification. In the ethylene-vinyl alcohol copolymer, the higher the proportion of the saponified vinyl alcohol moiety, the higher the mechanical strength, and it is preferable that the ethylene-vinyl alcohol copolymer be a completely saponified ethylene-vinyl alcohol copolymer. The proportion of the ethylene-vinyl alcohol copolymer in the hydrophilic polymer is preferably 70% by mass or more. More preferably, it is 80 mass% or more.

  The addition amount of the hydrophilic polymer can be selected depending on the properties of the liquid to be filtered. When the turbidity concentration is high and the decrease in filtration flux is large, in addition to imparting stain resistance to the separation membrane surface, the separation membrane is washed with a chemical solution to recover the separation membrane performance. In view of the increase in the content, the hydrophilic polymer content can be relatively reduced to maintain high chemical resistance.

[Pore on separation membrane surface]
One factor that greatly affects the separation function and dirt resistance of the separation membrane is the size of the pores on the primary surface of the separation membrane. The size of the pores is preferably controlled according to the use of the separation membrane. Regarding the average value of the pore size, the larger the pore diameter, the greater the amount of water permeation. As the pore size is smaller, the clogging of clogging substances can be suppressed, but the amount of water permeation decreases, and when clogging substances accumulate on the surface, the increase in differential pressure becomes noticeable and the operability deteriorates. There's a problem.

  The preferable range of the average pore diameter of the pores varies depending on the properties of the processing stock solution or the clogging substance contained in the solution, but is 0.001 μm or more from the viewpoint of achieving both stain resistance and water permeation performance required as a water treatment membrane. It is preferable that it is 5 μm or less. More preferably, it is 0.005 μm or more and 0.2 μm or less. When the average pore diameter of the pores is within this range, it is difficult for clogging with dirt substances and a continuous filtration operation for a long time can be performed. Further, even when the clogging substance is clogged in the primary side surface portion of the separation membrane, the membrane filterability can be efficiently recovered by washing.

  The average pore diameter of the pores is obtained by arithmetic averaging by taking a photograph of the separation membrane surface with a scanning electron microscope at 60,000 times, measuring the diameters of 20 or more arbitrary pores. If the pore is not circular, use an image analysis software that is generally available to obtain an equivalent circle of the pore (a circle having an area equal to the area of the pore). It is calculated by the method.

[Surface roughness of separation membrane surface]
As the primary surface of the separation membrane is as smooth as possible, the stain resistance is improved. In the case of a structure in which the primary side surface of the separation membrane has many irregularities, the area to which the clogging substance adheres increases, and the clogging substance does not easily peel off. The surface roughness of the primary side surface of the separation membrane can be determined by observing the unevenness of the surface of the separation membrane with an atomic force microscope and analyzing the image obtained. Parameters indicating the surface roughness include an arithmetic average roughness representing the overall roughness within the observation range, a maximum height representing the size of the specific irregularities on the surface, and the calculation method of each parameter is JIS B 0601-2001. From the viewpoint of the stain resistance of the separation membrane, it is preferable that the value is small regardless of which parameter is used.

[Non-solvent induced phase separation]
Examples of the method for forming the separation membrane having the pores in the pore diameter range as described above include a phase separation method, an etching method, and a stretching method. In particular, the non-solvent-induced phase separation method, which is a type of phase separation method, adjusts the composition of the membrane-forming stock solution that forms the separation membrane, the composition of the coagulation bath, etc. Can be suitably used.

  Non-solvent-induced phase separation is a method in which a membrane-forming solution in which a raw material polymer for a separation membrane is uniformly dissolved in a solvent is immersed in a coagulation bath containing the non-solvent and the solubility of the raw material polymer is lowered and precipitated. This is a method of inducing separation. The coagulation bath at this time may contain a good solvent or a poor solvent as long as it contains a non-solvent of the raw material polymer. The structure of the separation membrane before the heat treatment can be designed according to the required performance such as the water permeability and turbidity removal performance of the separation membrane. That is, in order to obtain a separation membrane that emphasizes high water permeability, the area ratio of the opening portion on the primary side surface of the separation membrane is increased, or the size of the void inside the separation membrane is increased, or the porosity is increased. The structural design such as Alternatively, in order to obtain a separation membrane that emphasizes high turbidity removal performance, a structural design such as reducing the pore diameter of the primary surface of the separation membrane may be performed. The structure of the primary surface of these separation membranes, the size of the voids inside the separation membrane, the void ratio, etc., the polyvinylidene fluoride resin and hydrophilic polymer or copolymer in the membrane-forming solution, and other additives The content can be controlled by the mixing ratio of the non-solvent, the good medium, the poor solvent in the coagulation bath, the coagulation bath temperature, and the like.

  In the present invention, a membrane obtained by coagulating a raw material polymer forming a separation membrane in a coagulation bath containing a non-solvent for the raw material polymer is a membrane obtained by a non-solvent induced phase separation method. To do.

  In addition, the non-solvent mentioned here is a solvent that does not dissolve and swell the polymer to be dissolved even when heated to the melting point of the polymer to be dissolved or the boiling point of the solvent. When the polymer to be dissolved is a polyvinylidene fluoride resin, non-solvents include water, hexane, pentane, benzene, toluene, methanol, ethanol, carbon tetrachloride, o-dichlorobenzene, trichloroethylene, and ethylene glycol. , Diethylene glycol, triethylene glycol, propylene glycol, butylene glycol, pentanediol, hexanediol, aliphatic hydrocarbon such as low molecular weight polyethylene glycol, aromatic hydrocarbon, aliphatic polyhydric alcohol, aromatic polyhydric alcohol, chlorination Hydrocarbons or other chlorinated organic liquids and mixed solvents thereof may be mentioned.

  A good solvent is a solvent that can dissolve 5% by mass or more of a polymer even in a low temperature region of 60 ° C. or lower. When the polymer to be dissolved is a polyvinylidene fluoride resin, the good solvents are N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, dimethylformamide, methyl ethyl ketone, acetone, tetrahydrofuran, tetramethylurea, trimethyl phosphate And lower alkyl ketones, esters, amides and the like, and mixed solvents thereof.

  The poor solvent means that the polymer cannot be dissolved at 5% by mass or more at a low temperature of 60 ° C. or lower, but can be dissolved at 5% by mass or more in a high temperature region of 60 ° C. or higher and below the melting point of the polymer. It is a solvent. When the polymer to be dissolved is a polyvinylidene fluoride resin, the poor solvent is cyclohexanone, isophorone, γ-butyrolactone, methyl isoamyl ketone, dimethyl phthalate, propylene glycol methyl ether, propylene carbonate, diacetone alcohol, glycerol triacetate And the like, and a mixed solvent thereof.

[Thickness of separation membrane]
The total thickness of the separation membrane is preferably determined from the balance between the physical strength of the separation membrane required for the separation membrane and the water permeability. That is, the thicker the separation membrane, the higher the physical strength but the lower the water permeability. Conversely, the thinner the separation membrane, the higher the water permeability, but the physical strength and the separation performance decrease. Considering these balances, the total thickness of the separation membrane is preferably 100 μm or more and 500 μm or less. In the case of a laminate separation membrane, the thickness of the entire laminate is not the thickness of individual layers constituting the laminate, but the total thickness of the separation membrane.

  In the laminate separation membrane, it is preferable to determine the thicknesses of the base material layer and the functional layer in consideration of the balance between water permeability and strength. The preferable thickness range of each of the base material layer and the functional layer varies depending on the strength and structure of the material used, and therefore may be determined in consideration of the performance of the target separation membrane.

[Application field]
The separation membrane according to the present invention can be used for water purification treatment, clean water treatment, waste water treatment, industrial water production, etc. in the field of water treatment, and can use river water, lake water, ground water, sea water, sewage, waste water, etc. as a treatment stock solution. . Further, since the stain resistance is high, it is suitably used particularly when the processing stock solution contains a lot of turbidity. In the pharmaceutical manufacturing field, the food industry field, etc., the processing stock solution is particularly suitable because it is clogged and contains a large amount of substances. Further, when the separation membrane according to the present invention is used as a blood purification membrane, it can be expected to improve the removability of blood waste products and the durability of the blood purification membrane due to its high breaking strength.

  EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

The stain resistance of the separation membrane was evaluated by the value of the irreversible filtration resistance increase rate α of the separation membrane. The calculation of α was evaluated as follows using the apparatus shown in FIG. The separation membrane module 1 was prepared so that the effective membrane area of the separation membrane was about 20 cm ² . A stainless steel pressure tank (ADVANTEC PRESURE VESSEL DV-10, capacity 10 L) was used as the stock solution tank 10. The stock solution tank 10 contains Lake Biwa water (turbidity 1.0 NTU or less, TOC (total organic carbon) 1.2 mg / L, calcium concentration 15 mg / L, silicon concentration 0.5, manganese concentration 0.01 mg / L or less) as a stock solution. , Iron concentration 0.01 mg / less). A stainless steel pressure tank (ADVANTEC PRESURE VESSEL DV-40, capacity 40 L) was used as the distilled water tank 11. The distilled water tank 11 was filled with distilled water from a pure water production device Auto Still (manufactured by Yamato Kagaku).

  The primary side of the separation membrane module 1 and the stock solution tank 10 were connected to form a stock solution supply line 18. The stock solution supply line 18 is provided with a stock solution supply line valve 14. The secondary side of the separation membrane module 1 and the distilled water tank 11 were connected to form a distilled water supply line 19. The distilled water supply line 19 is provided with a distilled water supply line valve 15. Further, a filtrate tank 13 for storing the filtrate was provided, and the secondary side of the separation membrane module 1 and the filtrate tank 13 were connected by a filtrate line 21. The filtrate line valve 17 is provided in the filtrate line 21. Furthermore, a waste liquid tank 12 for receiving waste liquid generated by cleaning the separation membrane module 1 was provided, and the primary side of the separation membrane module 1 and the waste liquid tank 12 were connected by a waste liquid line 20. The waste liquid line 20 is provided with a waste liquid line valve 16.

  The stock solution supply line valve 14 and the filtrate solution line valve 17 are opened, the distilled water supply line valve 15 and the waste solution line valve 16 are closed, and compressed air adjusted to 100 kPa is supplied into the stock solution tank 10, and the separation membrane is supplied from the raw water tank 10. The stock solution (lake water) was supplied into the module 1 for total filtration. This was designated as a filtration step. While storing the filtrate in the filtrate tank 13, the mass of the filtrate was continuously measured, and the time when 50 g was filtered was regarded as the end of one set. After the completion of one set of filtration, the raw solution supply line valve 14 and the filtrate line valve 17 are closed, the distilled water supply line valve 15 and the waste liquid line valve 16 are opened, and the compressed water adjusted to 150 kPa in the distilled water tank 11. Air was supplied, distilled water was supplied from the distilled water tank 11 to the secondary side of the separation membrane module 1, and permeated to the primary side to perform backwashing. This was made into the backwash process. While storing the backwashed waste liquid in the waste liquid tank 12, the mass of the waste liquid was continuously measured, and the point in time when 10 g of the waste liquid was discharged was regarded as the end of one set. This filtration step and backwashing step were repeated 30 cycles alternately.

  The total filtered water amount (g) and the filtration resistance (1 / m) in each cycle were determined, and plotted on a graph with the total filtered water amount (g) on the horizontal axis and the filtration resistance (1 / m) on the vertical axis. FIG. 2 shows an example of the plot. From the graph of FIG. 2, it can be read that during the filtration process of each cycle, the filtration resistance gradually increases as the amount of filtered water increases, and then the filtration resistance decreases all at once when the backwash process is performed.

Filtration resistance can be calculated by the following formula.
Filtration resistance (1 / m) = (filtration pressure (Pa) × membrane area (m ² ) × filtrate density (g · m ⁻³ )) / (filtrate viscosity (Pa · s) × (per second) Permeated water mass (g · s ⁻¹ ))).

  In the graph of total filtered water amount-filtration resistance, a least square approximation line of 21 filtration resistance values at the start of each filtration process from the 10th set to the 30th set was drawn. The slope of this least square approximation line (Δ filtration resistance / Δtotal filtered water amount) was α. The lower the value of α, the slower the irreversible increase in the filtration differential pressure, so it can be said that the separation membrane is excellent in dirt resistance.

  However, the absolute value of α varies depending on factors such as the performance of the separation membrane and the properties of Lake Biwa water used for measuring filtration resistance. Therefore, using the same Lake Biwa water, α of the separation membranes of Examples and Comparative Examples and α (αB of the separation membranes prepared by the same method as the Examples and Comparative Examples except that no heat treatment is performed. ) Were measured to determine (α / αB). This (α / αB) is used as an index for evaluating the stain resistance of the separation membranes of Examples and Comparative Examples. If (α / αB) is less than 1, the increase in irreversible filtration resistance is suppressed by the heat treatment, that is, the antifouling performance of the separation membrane is improved. Furthermore, it shows that the smaller the (α / αB), the better the antifouling performance of the separation membrane.

(Reference Example 1)
A vinylidene fluoride homopolymer having a weight average molecular weight of 41,000 and γ-butyrolactone were dissolved at a temperature of 170 ° C. at a ratio of 38 parts by mass and 62 parts by mass, respectively. The polymer solution was discharged from the die while accompanying γ-butyrolactone as a hollow portion forming liquid, solidified in a cooling bath composed of a mixed solution of 20 parts by weight of γ-butyrolactone at a temperature of 20 ° C. and hollow. A thread-like and porous base material layer was produced. This base material layer was comprised only with the polyvinylidene fluoride resin. Further, as can be seen from the description of the process of forming the base material layer, the base material layer was formed at a temperature of 20 ° C.

(Reference Example 2)
A hollow fiber-like porous substrate layer was produced in the same manner as in Reference Example 1.
Subsequently, 14 parts by mass of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 1 part by mass of cellulose acetate (Eastman Chemical Co., CA435-75S: cellulose triacetate), and 77 of N-methyl-2-pyrrolidone A polymer solution is prepared by mixing and dissolving 5 parts by mass of polyoxyethylene coconut fatty acid sorbitan (Sanyo Kasei Co., Ltd., trade name Ionette T-20C) at a temperature of 95 ° C. at a rate of 3 parts by mass of water. did. This film-forming stock solution was uniformly applied to the outer surface of the base material layer and immediately solidified in a water bath. Thus, a hollow fiber-like laminate separation membrane was produced in which the functional layer was laminated on the outer surface of the hollow fiber-like base material layer by the non-solvent induced phase separation method. The functional layer was composed of 93.3% by mass of polyvinylidene fluoride and 6.7% by mass of cellulose acetate with respect to the entire functional layer.

(Reference Example 3)
A hollow fiber-like porous base material layer was produced in the same manner as in Reference Example 1.
Next, 12 parts by mass of vinylidene fluoride homopolymer having a weight average molecular weight of 284,000, 7.2 parts by mass of cellulose acetate (Eastman Chemical Co., CA435-75S: cellulose triacetate), N-methyl-2-pyrrolidone Was mixed and dissolved at a temperature of 95 ° C. at a rate of 80.8 parts by mass to prepare a polymer solution. This film-forming stock solution was uniformly applied to the outer surface of the base material layer, and immediately solidified in a water bath. Thus, a hollow fiber-like laminate separation membrane was produced in which the functional layer was laminated on the outer surface of the hollow fiber-like base material layer by the non-solvent induced phase separation method. The functional layer was composed of 62.5% by mass of polyvinylidene fluoride and 37.5% by mass of cellulose acetate with respect to the entire functional layer.

(Reference Example 4)
23 parts by mass of hydrophobic silica (manufactured by Nippon Aerosil Co., Ltd .; AEROSIL-R972), 30.8 parts by mass of dioctyl phthalate, and 6.2 parts by mass of dibutyl phthalate were mixed with a Henschel mixer. To this mixture, 40 parts by mass of polyvinylidene fluoride having a weight average molecular weight of 290,000 was further added and mixed again with a Henschel mixer. The obtained mixture was further melt-kneaded with a 48 mmφ twin-screw extruder into pellets.

  The pellets were continuously charged into a 30 mmφ twin screw extruder, and melt extruded at 240 ° C. while supplying air into the hollow portion from an annular nozzle attached to the tip of the extruder. The extrudate was solidified by passing through an air travel of about 20 cm through a water bath at 40 ° C. at a spinning speed of 20 m / min to obtain a hollow fiber membrane.

  This hollow fiber membrane is continuously taken up at a speed of 20 m / min with a pair of first endless track type belt take-up machines, and passed through a first heating tank (0.8 m long) controlled at a space temperature of 40 ° C. Furthermore, the second endless track type belt take-up machine similar to the first endless track type belt take-up machine was used and the take-up was doubled at a speed of 40 m / min. Further, after leaving the second heating tank (0.8 m long) controlled at a space temperature of 80 ° C., the hollow fiber membrane is taken up at a speed of 30 m / min with a third endless track belt take-off machine. After shrinking to double, it was wound up with a casserole with a circumference of about 3 m.

  Further, this hollow fiber membrane was bundled and immersed in methylene chloride at 30 ° C. for 1 hour, and this was repeated 5 times to extract dioctyl phthalate and dibutyl phthalate, followed by drying. Subsequently, the hollow fiber membrane was immersed in a 50% by mass ethanol aqueous solution for 30 minutes, further transferred to water and immersed for 30 minutes, and the hollow fiber membrane was wetted with water. Furthermore, after being immersed in an aqueous solution of 5% by mass of caustic soda at 40 ° C. for 1 hour, this was carried out twice, followed by washing with water by being immersed in warm water at 40 ° C. for 10 hours to extract hydrophobic silica, Dried. The obtained hollow fiber membrane was heated in an oven at 140 ° C. for 2 hours. Thus, a hollow fiber-like porous base material layer was produced. This base material layer was comprised only with the polyvinylidene fluoride resin. Further, as can be seen from the description of the formation process of the base material layer, the formation temperature in the process of forming the base material layer was a maximum of 140 ° C.

  The obtained hollow fiber-like base material layer was completely immersed in an ethylene-vinyl alcohol copolymer solution (68 ° C.) for 5 minutes with both ends opened. The ethylene-vinyl alcohol copolymer solution was mixed with 100 parts by mass of a mixed solvent of 50 parts by mass of water and 50 parts by mass of isopropyl alcohol, an ethylene-vinyl alcohol copolymer (manufactured by Nippon Synthetic Chemical Industry: Soarnol (registered trademark) ET3803, ethylene). (Content 23.5% by mass) 3 parts by mass was mixed by heating and dissolved. The hollow fiber membrane bundle taken out from the ethylene-vinyl alcohol copolymer solution was dried by blowing air at room temperature for 30 minutes, and then dried in an oven at 60 ° C. for 1 hour. In this way, a hollow fiber-like laminate separation membrane in which functional layers were laminated on both the outer surface and the inner surface of the hollow fiber-like base material layer was produced. The functional layer was composed only of an ethylene-vinyl alcohol copolymer.

(Reference Example 5)
20 parts by mass of polyethersulfone (Victrex 200), 10 parts by mass of polyvinylpyrrolidone (weight average molecular weight 360,000), 65 parts by mass of N-methyl-2-pyrrolidone, and 5 parts by mass of isopropanol are mixed and dissolved. The mixture was discharged and immediately solidified in water at a temperature of 20 ° C. to produce a hollow fiber separation membrane.

  Next, the produced hollow fiber-shaped separation membrane was immersed in ethanol and further immersed in hexane to dehydrate the separation membrane. Thereafter, heat treatment was performed in an atmosphere at 150 ° C. for 2 to 30 hours to crosslink polyvinyl pyrrolidone.

<Example 1, comparative example 1>
Only the hollow fiber-like base material layer obtained in Reference Example 1 was used as the separation membrane. This hollow fiber-shaped separation membrane was brought into contact with warm water or saturated steam under the temperature conditions shown in Table 1. When contacting with warm water, the separation membrane was brought into contact with warm water for 60 minutes while controlling the warm water at a predetermined temperature using a water bath. In order to make it contact with saturated steam, it was put into an autoclave (Tomy Seiko Autoclave ES-315), and the separation membrane was contacted with saturated steam for 60 minutes. The above-described evaluation was performed using the separation membrane after the heat treatment, and the irreversible filtration resistance increase rate α was obtained. Further, in order to obtain the irreversible filtration resistance increase rate αB, the above-described evaluation was performed using the separation membrane obtained in Reference Example 1. The value of (α / αB) was determined for each separation membrane and listed in Table 1.

  When the heat treatment temperature was 105 ° C and 132 ° C, (α / αB) was less than 1, and the heat resistance improved the stain resistance of the separation membrane. On the other hand, when the heat treatment was performed at 135 ° C., the stain resistance of the separation membrane was decreased.

<Example 2, Comparative Example 2, Comparative Example 3>
The hollow fiber-like laminate separation membrane obtained in Reference Example 2 was brought into contact with warm water or saturated steam under the temperature conditions shown in Table 2 in the same manner as in Example 1. The separation membrane after the heat treatment was used to determine the irreversible filtration resistance increase rate α, and the separation membrane obtained in Reference Example 2 was used to determine the irreversible filtration resistance increase rate αB. The value of (α / αB) was determined for each separation membrane and listed in Table 2.

  When the heat treatment temperature was 60 ° C. or higher and 132 ° C. or lower, (α / αB) was less than 1, and the heat resistance improved the stain resistance of the separation membrane. When the heat treatment temperature was 125 ° C. or lower, (α / αB) was further reduced. On the other hand, even when the heat treatment was performed at 40 ° C., no improvement in stain resistance was observed, and when the heat treatment was performed at 135 ° C., the stain resistance of the separation membrane was decreased.

<Example 3>
The hollow fiber laminate separation membrane obtained in Reference Example 3 was brought into contact with warm water in the same manner as in Example 1 under the temperature conditions shown in Table 3. The separation membrane after the heat treatment was used to determine the irreversible filtration resistance increase rate α, and the separation membrane obtained in Reference Example 3 was used to determine the irreversible filtration resistance increase rate αB. The value of (α / αB) was determined for each separation membrane and listed in Table 3.

  When the heat treatment temperature was 60 ° C., (α / αB) was less than 1, and the heat resistance improved the stain resistance of the separation membrane. When the heat treatment temperature was 80 ° C., (α / αB) was further reduced.

<Example 4>
The hollow fiber laminate separation membrane obtained in Reference Example 4 was brought into contact with saturated water vapor in the same manner as in Example 1 under the temperature conditions shown in Table 4. The separation membrane after the heat treatment was used to determine the irreversible filtration resistance increase rate α, and the separation membrane obtained in Reference Example 4 was used to determine the irreversible filtration resistance increase rate αB. The value of (α / αB) was determined and listed in Table 4.

  When the heat treatment temperature was 130 ° C., (α / αB) was less than 1, and the heat resistance improved the stain resistance of the separation membrane.

<Comparative Example 4>
The hollow fiber-like separation membrane obtained in Reference Example 5 was brought into contact with saturated water vapor in the same manner as in Example 1 under the temperature conditions shown in Table 5. The irreversible filtration resistance increase rate α was determined using the separation membrane after the heat treatment, and the irreversible filtration resistance increase rate αB was determined using the separation membrane obtained in Reference Example 5. The value of (α / αB) was determined and listed in Table 5.

  The heat treatment temperature was 120 ° C., but no improvement in the stain resistance of the separation membrane was observed by the heat treatment.

DESCRIPTION OF SYMBOLS 1 Separation membrane module 10 Stock solution tank 11 Distilled water tank 12 Waste solution tank 13 Filtrate tank 14 Stock solution supply line valve 15 Distilled water supply line valve 16 Waste solution line valve 17 Filtrate line valve 18 Stock solution supply line 19 Distilled water supply line 20 Waste solution line 21 Filtrate line PA Compressed air X Total filtration volume (g)
Y Filtration resistance (1 / m)
a 10th set b 30th set

Claims (3)

  A method for producing a separation membrane, comprising bringing a separation membrane comprising a layer mainly composed of a polyvinylidene fluoride resin into contact with water at 60 ° C to 132 ° C or water vapor at 60 ° C to 132 ° C. A separation membrane is formed by laminating a layer containing a hydrophilic polymer on a layer mainly composed of polyvinylidene fluoride resin.
The hydrophilic polymer includes at least one selected from the group consisting of cellulose ester, fatty acid vinyl ester, ethylene-vinyl alcohol copolymer, vinyl pyrrolidone, ethylene oxide propylene oxide, and copolymers of two or more thereof. Contains
A method for producing a separation membrane, wherein the separation membrane is contacted with water at 60 ° C. or higher and 132 ° C. or lower or water vapor at 60 ° C. or higher and 132 ° C. or lower.   The method for producing a separation membrane according to claim 2, wherein the layer containing the hydrophilic polymer further contains a polyvinylidene fluoride resin.

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