JP4269576B2 - Method for producing microporous membrane - Google Patents

Description

【００４３】
【表２】

【００４４】
【発明の効果】
本発明により、十分な機械的強度、流体の透過特性、耐薬品性を併せもち、かつ優れた分離性能をもつ微多孔膜が得られるようになった。
【図面の簡単な説明】
【図１】 液−液型相分離を示す場合の相図を示す。
【図２】 固−液型相分離を示す場合の相図を示す。
【図３】 ＤＳＣ曲線中のＴｃ、Ｔｍを示す。
【図４】 中空糸膜モジュールの例を示す。
【図５】 平膜モジュールの例を示す。
【図６】 膜濾過装置の例を示す。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a polyvinylidene fluoride resin microporous membrane. More specifically, it can be suitably used for separation membranes for water treatment such as microfiltration membranes, ultrafiltration membranes, nanofiltration membrane support bases, reverse osmosis membrane support groups used for turbidity, various filters, and diaphragms. The present invention relates to a method for producing a microporous membrane.
[0002]
[Prior art]
Microporous membranes are used in various filter applications such as microfiltration membranes, ultrafiltration membranes, nanofiltration membrane support substrates, reverse osmosis membrane support substrates, and ion exchange membrane carriers. Among them, microfiltration membranes, ultrafiltration membranes, and nanofiltration membranes are used in various fields including water purification, seawater desalination pretreatment, wastewater treatment, medical use, food industry, and water production. Is widely used in ultrapure water processes such as seawater desalination, semiconductor industry and pharmaceutical industry, and electrodeposition paint reuse processes such as automobile industry. The performance required for membranes in these water treatment applications is generally high water permeability, excellent separation properties, chemical strength and physical strength.
[0003]
In these fields, if the water permeability of the membrane is excellent, the membrane area and operating pressure can be reduced. As a result, the membrane module and raw water supply pump can be miniaturized with the same amount of treated water, and the membrane filtration device can be miniaturized, so that the cost of the device can be saved and the membrane replacement cost and the device installation area are advantageous. If the separation characteristics of the membrane are excellent, not only high-quality treated water can be obtained, but also the pretreatment and posttreatment steps can be simplified in process design. In addition, for example, in water purification treatment, a bactericidal agent such as sodium hypochlorite is added to the membrane module part for the purpose of sterilizing permeate and preventing biofouling of the membrane, or as chemical cleaning of the membrane, acid, alkali, chlorine, The membrane may be washed with a surfactant or the like. Therefore, chemical resistance is required for the separation membrane. In the field of water purification treatment, there is a problem that pathogenic microorganisms that are resistant to chlorine such as cryptosporidium derived from livestock excreta cannot be treated at the water purification plant and are mixed into the treated water. There is a need for sufficient separation properties and high strength so that the membrane is broken and raw water is not mixed. In response to these demands, a separation membrane using a polyvinylidene fluoride resin having high chemical resistance and mechanical strength has been developed and used in recent years.
[0004]
As a method for producing a separation membrane using a polyvinylidene fluoride resin as a raw material, a method of developing a porous property using phase separation is widely used. As the phase separation method, a non-solvent induced phase separation method (Japanese Patent Publication No. 1-2003) is used in which a polymer solution is brought into contact with a non-solvent for the polymer, and phase separation is performed through solvent extraction into the non-solvent. However, since the film obtained by this method becomes an asymmetric film containing macrovoids, there is a problem that the mechanical strength is not sufficient. Further, there are many film forming condition factors given to the film structure and film performance, and there are drawbacks that the film forming process is difficult to control and the reproducibility is poor.
[0005]
Further, in recent years, a melt extraction method (Japanese Patent No. 2899903) has been used as a method for obtaining a symmetrical structure film not containing macrovoids. In this method, inorganic fine particles and an organic liquid are melt-kneaded in a polyvinylidene fluoride resin, extruded from a die at a temperature equal to or higher than the melting point of the polyvinylidene fluoride resin, molded by pressing with a press, and then solidified by cooling. Thereafter, an organic liquid and inorganic fine particles are extracted to form a porous structure. In the case of the melt extraction method, the porosity can be easily controlled, a macrovoid is not formed, and a relatively homogeneous and high-strength membrane is obtained. Although the separation performance and water permeability are easy to control, the dispersibility of the inorganic fine particles is excellent. If it is bad, defects such as pinholes may occur. Furthermore, the melt extraction method is a production method having a drawback that the production cost is extremely high.
[0006]
[Problems to be solved by the invention]
An object of the present invention is to provide a method for producing a microporous membrane having sufficient mechanical strength, fluid permeation characteristics, and chemical resistance, and having excellent separation performance.
[0007]
[Means for Solving the Problems]
  The object of the present invention is to make polyvinylidene fluoride.HomopolymerYoAnd a composition comprising only γ-butyrolactone or propylene carbonate dissolved at 120 ° C to 170 ° C.A method for producing a microporous film by discharging a limer solution from a discharge port having a temperature Ts and cooling the polymer solution, wherein the crystallization temperature Tc of the polymer solution is 40 ° C. or more and 105 ° C. or less, and the polymer is cooled. The average cooling rate when the solution passes through Tc is 2 × 10³10 ° C / min or more⁶° C / min or less and Ts isTc <TsThis is achieved by a method for producing a microporous membrane that satisfies the relationship ≦ Tc + 90.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0011]
  In the present invention, the solvent is polyvinylidene fluoride.HomopolymerA solvent that can be dissolved by 30% by weight or more below the boiling point of the solvent.Yes, γ-ButyrolactoNLopyrene CarbonateThis is true.
[0012]
  The film-forming stock solution used in the present invention is mainly polyvinylidene fluoride.HomopolymerAnd meltOnly in the mediumIt is a polymer solution comprised from. However, non-solvents, nucleating agents, antioxidants, plasticizers, molding aids, lubricants, and the like can be added as necessary, as long as the effects of the present invention are not significantly impaired. A film-forming stock solution is obtained by heating and dissolving these blends.
[0013]
When producing a porous membrane by a thermally induced phase separation method, two types of thermally induced phase separation mechanisms are mainly used. One is a liquid-liquid phase separation method in which a polymer solution that is uniformly dissolved at a high temperature is separated into a polymer rich phase and a dilute phase due to a decrease in the dissolution ability of the solution when the temperature is lowered, and the other is a polymer solution that is uniformly dissolved at a high temperature. However, this is a solid-liquid phase separation method in which crystallization of a polymer occurs during cooling and phase separation into a polymer solid phase and a polymer dilute solution phase (Journal of Membrane Science 117 (1996) 1-31). Whether it is the former or the latter is determined by the phase diagram of the polymer and the solution.
[0014]
FIG. 1 shows a phase diagram when a typical liquid-liquid phase separation is shown. The melting point Tm (° C.) and the crystallization temperature Tc (° C.) of the film-forming stock solution can be obtained by the method described later. For Tm and Tc, unless otherwise specified, in the present invention, a value measured at a DSC heating / cooling rate of 10 ° C./min in differential scanning calorimetry (DSC measurement) is adopted. The binodal curve is obtained by plotting the cloud point obtained from the cloud point measurement. In this case, the binodal curve is on the higher temperature side than the crystallization curve, and when the polymer solution is cooled down, when the solution is gradually cooled down from Tm, the one that is uniformly dissolved by the residual heat reaches the binodal curve The binodal decomposition occurs in the polymer, phase separation into a polymer rich phase and a dilute phase occurs until the crystallization temperature is reached. The porous structure from which the solvent is finally removed is a sea-island structure, although it depends on the polymer solution composition and the cooling rate.
[0015]
FIG. 2 shows a phase diagram when a typical solid-liquid phase separation is shown. In this case, the crystallization curve is on the higher temperature side than the binodal curve. In this case, when the temperature of the polymer solution is lowered, the polymer is crystallized when the crystallization temperature is reached. When the temperature is further lowered, crystal growth occurs. The porous structure from which the solvent is finally removed often has a spherulite structure, although it depends on the polymer solution composition and the temperature lowering rate.
[0016]
  For example, polyvinylidene fluorideHomopolymer /All of the solvent phase diagrams are solid-liquid types that are hidden behind the crystallization temperature curve and no binodal curve is observed. The relative position of the binodal curve shifts to a higher temperature as the solvent has a lower affinity for the polymer, but no solvent that exhibits a liquid-liquid type has been reported yet.
[0017]
  In the present invention, Tc is defined as follows. Polyvinyl fluorideHomopolymer andMeltingMade of medium onlyA mixture having the same composition as the membrane stock solution is sealed in a sealed DSC vessel, heated to a dissolution temperature at a heating rate of 10 ° C./min using a DSC apparatus, and held for 5 minutes to dissolve uniformly, and then the temperature is lowered. The rising temperature of the crystallization peak observed in the process of lowering the temperature at a rate of 10 ° C./min is defined as Tc (FIG. 3).
[0018]
  As a result of extensive studies, we have found that there is a close relationship between the crystallization temperature of this polymer solution and the membrane structure obtained by thermally induced phase separation. In the present invention, the crystallization temperature Tc (° C.) is 40 ° C. or higher.105 ° CThe following polymer solution is used. That is, film forming factorTieBy controlling the crystallization temperature to be high, the film structure, that is, the spherulite particle size can be miniaturized. That the membrane structure is minute means that a membrane having excellent separation performance can be obtained.
  The film-forming factors that affect the crystallization temperature of the raw film-forming solution include, for example, the polymer concentration in the polymer solution, polymer grade (molecular weight, branched shape, type of copolymer), solvent type, and crystal formation. There are additives. For example, for the polymer concentration, the higher the polymer concentration, the higher the Tc and the smaller the spherulite particle size. The relationship between Tc itself and the spherulite particle size was also found, and the relationship was found that the spherulite particle size becomes smaller as Tc shifts to a higher temperature. In addition, regarding the influence of the molecular weight of the polymer, it was found that the higher the molecular weight, the smaller the spherulite particle size. There is little correlation between molecular weight and Tc, and it is a homopolymer or copolymer, or a difference in branching shape affects Tc. When the molecular weight is close, if a polymer grade having a high Tc is used due to the difference in branching or copolymer, the spherulite particle size tends to be small.
[0019]
  It is preferred for the present invention to select the polymer grade so that the polymer concentration of the polymer solution is increased or the Tc of the polymer solution is increased.That's right.
[0020]
  It can be seen that the spherulite structure formation process is a crystal formation process from the results of X-ray diffraction. The crystal formation process is an exothermic process. Generally polyvinylidene fluorideHomopolymerThe first crystal produced when any crystalline polymer crystallizes is called the primary nucleus. This primary nucleus grows into one spherulite. When the primary nucleation rate is slow, the primary nucleation generated at the beginning causes heat generation, so that new primary nucleation around the primary nucleation is suppressed, and the initially generated crystal grows into a large crystal. Since the growth of spherulites continues until the spherulites collide with each other, and the growth stops due to the collisions, the final spherulite grain size depends on the number of primary nuclei generated first. That is, in order to obtain a small microspherulite structure, it is necessary to generate a large number of primary nuclei. A polymer solution having a high Tc is a stock solution that easily undergoes crystallization, and it is considered that primary nuclei are instantly generated at a number of locations at the time of primary nucleation, and a fine spherulite structure is obtained. Conversely, a polymer solution having a low Tc is a stock solution in which crystallization hardly occurs, and the primary nucleation generated during the primary nucleation at the time of primary nucleation suppresses the primary nucleation, resulting in a small and large spherulite number. It is considered that a spherulite structure is obtained.
[0021]
  Tc of the polymer solution used in the present invention is 40 ° C. or higher105 ° CIt is as follows. More preferably, it is 45 degreeC or more and 105 degrees C or less, More preferably, it is 48 degreeC or more and 95 degrees C or less. If Tc is lower than 40 ° C., a microstructure film cannot be obtained. Tc105 ° CIf it is higher, the crystallization of the polymer solution is likely to occur easily, and it is necessary to control the film forming conditions such as the dissolution tank, the film forming raw material piping, and the temperature lowering condition at a high temperature, resulting in a lot of energy loss. Further, it is necessary to increase the polymer concentration, and it is difficult to obtain a film having a high porosity.
[0022]
  Polyvinyl fluoride in polymer solution used in the present inventionHomopolymer thickThe degree is preferably 30% by weight or more and 60% by weight or less. More preferably, it is 33 to 55 weight%, More preferably, it is 35 to 50 weight%. If the resin concentration is less than 30% by weight, the Tc of the polymer solution becomes low and it is difficult to obtain a microstructure. In addition, since the polymer solution viscosity is lowered, when it is molded into a hollow fiber shape, the strength of the hollow fiber after discharging the die is weakened, and the structure is liable to collapse during winding, which may cause a problem in film formation stability. When the resin concentration is higher than 60% by weight, the porosity of the obtained film is lowered and the permeability is deteriorated. Polyvinyl fluorideHomopolymer thickBy controlling the degree to 30% by weight or more and 60% by weight or less, a film having high permeability, a fine structure can be obtained, and film forming stability is also improved.
[0023]
  Here, polyvinylidene fluoride in the film-forming stock solutionHomopolymericThe weight average molecular weight is 2 × 10^FiveThe above is preferable. Molecular weight 2 × 10^FiveIf it is less than 1, the solution viscosity will be low, the film-forming stability will be poor, and the resulting film strength will tend to be weak. Also, when the polymer has a high molecular weight, the solution viscosity of the polymer solution is high, so the movement of the polymer chain is suppressed, the crystal growth rate is slow, and a large number of spherulite nuclei are formed, so that a film having a microstructure can be obtained. easy. Polyvinylidene fluoride in the present inventionHomopolymericThe weight average molecular weight is preferably 3 × 10^Five~ 3x10⁶It is.
[0024]
In the present invention, a polymer solution which is a film-forming stock solution is discharged from a discharge port. The discharge port can be selected as appropriate, and a T die, a double tubular discharge port, or the like can be used. The solution discharged from the discharge port is cooled to become a gel-like molded body.
[0025]
  In the present invention, the discharge port temperature Ts (° C.) is the temperature at the discharge port of a base that discharges a polymer solution that is a raw film forming solution. In the present invention,Tc <TsTs is controlled so as to satisfy the relationship of ≦ Tc + 90. Tc + 10 ≦ Ts ≦ Tc + 85 is preferable, and Tc + 20 ≦ Ts ≦ Tc + 80 is more preferable. It is advantageous that the Ts is as low as possible from the viewpoint of the cooling effect, but if the temperature is too low, there is a problem in film formation stability. When Ts is lower than Tc, gelation accompanying crystallization occurs at the discharge port, and discharge stability is lowered, leading to clogging of the discharge port. When Ts is larger than Tc + 90, a sufficient cooling effect cannot be obtained due to the residual heat of the film itself in the cooling process, and a microstructure cannot be obtained. The discharge port temperature and the melting temperature may be different. The melting temperature can be preferably set to a temperature higher than the discharge port temperature from the viewpoint of performing the melting uniformly in a short time.
[0026]
As a cooling method, cooling with air, cooling with a roll, or a method of immersing directly in a liquid cooling bath can be used. When extruding with a T-die or the like to obtain a flat film, any of air cooling, roll cooling, and cooling bath cooling can be suitably used. In the case of a flat membrane, a method of coating on a substrate such as a nonwoven fabric as a molding method is also preferably used. In order to obtain a hollow fiber-like membrane, the most preferable method is to discharge from a hollow outlet in order to stabilize the cross-sectional shape of the hollow fiber and then immerse in a liquid cooling bath in the same manner as dry and wet spinning. In this case, the dry part has a role of stabilizing the hollow shape and preventing the coolant from entering the discharge port. However, when the effect as a cooling bath is expected, the dry length is preferably within 10 cm. Air cooling is also possible. However, roll cooling is not suitable for hollow fiber membranes because the cooling rate is uneven.
[0027]
In the cooling bath, it is preferable to use a liquid containing the above-described solvent in a concentration range of 65 wt% to 99 wt%, more preferably 75 wt% to 95 wt%. A plurality of solvents may be mixed and used. The same solvent as that used for the film-forming stock solution is preferably used from the viewpoint of waste liquid recovery. Moreover, a non-solvent may be mixed as long as it does not deviate from the concentration range. In many cases, water is used as the non-solvent. The cooling bath temperature is preferably not higher than Tc of the film forming stock solution. When the cooling bath is in this temperature range, the solid-liquid phase separation induced by temperature becomes dominant in the gelation step. By applying a large temperature difference from the discharge temperature and quenching, the phase separation structure becomes fine, and a membrane structure having excellent separation performance and high strength and elongation is exhibited. Further, by allowing the cooling liquid to contain a solvent having the above concentration range, non-solvent-induced phase separation can be suppressed and molding can be performed without forming a dense layer on the film surface. When the concentration of the solvent in the cooling liquid is low and a non-solvent such as water is contained at a high concentration, a dense layer is formed on the surface of the membrane, and even if it is stretched, the water permeability is lowered. The form of the cooling bath is not particularly limited as long as the cooling liquid and the polymer solution formed into a film can be sufficiently brought into contact with each other and can be cooled, and the cooling liquid is literally stored. The liquid tank may be in the form of a liquid tank, and if necessary, the liquid tank may be circulated or updated with a liquid whose temperature and composition are adjusted. The liquid tank form is most suitable, but in some cases, the cooling liquid may flow in the pipe, or the cooling liquid may be jetted onto a film running in the air. May be.
[0028]
In the present invention, when the polymer solution is cooled, 2 × 10 2 when the polymer solution passes the crystallization temperature Tc.^Three10 ° C / min or more⁶It is characterized by cooling at an average temperature decrease rate Vt of not more than ° C / min. The average cooling rate Vt is preferably 5 × 10^Three℃ / min or more 6 × 10^Five° C / min or less, more preferably 10^Four℃ / min or more 3 × 10^FiveIt is below ℃ / min. By performing cooling phase separation at an average temperature drop rate Vt in this range, it becomes possible to produce a microporous membrane having a further microstructure.
[0029]
The average temperature-decreasing rate Vt during film formation in the present invention is determined by the following method a or b.
a. When the polymer solution is in the air when the crystallization temperature Tc is reached
Vt = (Ts−Tc) / t (sc)
Ts: discharge port temperature (° C.), Tc: crystallization temperature (° C.),
t (sc): Elapsed time (min) from reaching the Tc after the film-forming stock solution is discharged
In the measurement of t (sc), it is possible to determine at which point the film temperature in the air reaches Tc by thermography or the like. T (sc) can be calculated from the distance from the discharge port to the Tc arrival point and the film forming speed.
b. When the polymer solution is in the cooling bath when the crystallization temperature Tc is reached
Vt = (Ts−Ta) / t (sa)
Ts: discharge port temperature (° C.), Ta: cooling bath temperature (° C.),
t (sa): Elapsed time (min) from discharge of the film-forming stock solution to arrival of the cooling bath
In the measurement of t (sa), the temperature of the polymer solution is considered to be instantaneously equal to the temperature of the cooling bath when immersed in the cooling bath. Therefore, t (sa) can be calculated from the distance from the discharge port to the liquid level of the cooling bath and the film forming speed.
[0030]
Average cooling rate is 2 × 10^ThreeWhen the temperature is less than ° C./min, the porous structure is enlarged and a membrane having good separation performance cannot be obtained. On the other hand, the average cooling rate is 10⁶In order to make it larger than ° C./min, it is necessary to cool at a very high rate. For example, in the case of using a cooling system with a cooling bath, it is necessary to discharge at a very high discharge speed and immerse in the cooling bath, and there is a problem of uneven discharge and uneven cooling. I can't get it.
[0031]
The reason why the microstructure can be obtained by increasing the cooling rate when passing through the crystallization temperature Tc is that heat generation during primary nucleation due to the temperature drop, which is the cause of crystal growth, is removed by rapid cooling. This is considered to be due to the generation of the microstructure.
[0032]
The microporous membrane of the present invention obtained by the manufacturing method as described above has a strength compared to that of a conventional microporous membrane due to a structure in which microscopic spherulite structures are connected and voids are formed in the gaps. It is possible to increase the water permeability and the separation performance.
[0033]
  In the case of obtaining a hollow fiber-like microporous membrane, it is preferable to discharge the polymer solution from a tube outside the double tubular discharge port and inject an injection solution or an injection gas into the hollow portion. In this case, the injection solution or the injection gas is preferably one that does not dissolve or soften the polymer solution in the film forming process from the viewpoint of moldability. The injection gas is preferably an inert gas such as nitrogen or air, and may contain solvent vapor or water vapor in order to control the aggregation of the polymer. However, in order to obtain a high degree of freedom in the polymer solution composition that can be selected to form a hollow fiber membrane and an efficient cooling effect, a method of forming a hollow portion using an injection solution is more preferably employed. In the case of using an injection solution, the aforementioned polyvinylidene fluoride is used.HomopolymerOn the other hand, it is preferable to use a liquid containing a solvent having solubility in a concentration range of 70% by weight or more, more preferably 80% by weight or more. A plurality of solvents may be used as a mixture. Use of the same solvent as that used for the polymer solution that is the film-forming stock solution is preferable from the viewpoint of waste liquid recovery. Moreover, a non-solvent may be mixed as long as it does not deviate from the concentration range. In many cases, water is used as the non-solvent. When the injection composition for forming the hollow portion is within this concentration range, non-solvent-induced phase separation is suppressed, and a membrane having excellent permeability can be formed without forming a dense layer on the inner surface of the membrane. Is possible. The temperature of the hollow portion forming gas or the hollow portion forming liquid is preferably Ts or less so as not to dissolve or soften the polymer solution in the film forming step.
[0034]
  The cooled and gelled membrane is then immersed in an extraction solvent, or the solvent is extracted by membrane drying to obtain a porous membrane. In addition to the above manufacturing process, uniaxial or biaxial stretching is performed to improve membrane permeability for the purpose of improving porosity and pore diameter by stretching or tearing the contact portion between spherulites, and strengthening membrane strength by stretching orientation. It can also be preferably adopted. Stretching may be performed at any time before and after the solvent extraction process as long as it is gelled and the film is phase-separated. The stretching temperature is preferably in the temperature range of 50 ° C. to 140 ° C., and the stretching ratio is preferably in the range of 1 to 5.0 times, more preferably in the range of 1.1 to 3.0 times. The stretching ratio here is the ratio of the sample length after stretching to the sample length before stretching in the case of uniaxial stretching, and the ratio of the film area after stretching to the film area before stretching in the case of biaxial stretching. is there. When it is stretched in a low temperature atmosphere of less than 50 ° C., it is difficult to stably and uniformly stretch, and there is a possibility that only a structurally weak portion is broken. When stretched at a temperature exceeding 140 ° C, polyvinylidene fluorideHomopolymericSince it is close to the melting point, the porous structure is melted and stretched without forming too many pores, so that the water permeation performance does not increase. The stretching is preferably performed in a liquid because temperature control is easy, but it may be performed in a gas such as steam. Alternatively, temperature control may be performed at the rolling part as in the rolling method. As the drawing bath liquid, polyvinylidene fluorideHomopolymerThose that do not substantially dissolve are used. Water is convenient and preferable, but when stretching at about 90 ° C. or higher, it is also preferable to use low molecular weight polyethylene glycol or the like. Also preferred is a mixture of water and polyethylene glycol.
[0035]
A membrane module using a porous membrane manufactured by the manufacturing method of the present invention, a membrane filtration device using the membrane module, and a method for producing permeated water from raw water using the membrane filtration device include wastewater treatment. It can contribute to the advancement of water treatment technologies such as water purification and industrial water production. Here, the module refers to a module in which a plurality of hollow fiber membranes are bundled and placed in a cylindrical container, and both ends or ends are fixed with polyurethane, epoxy resin, etc., and permeate can be collected. Or by fixing both ends of the hollow fiber membrane in a flat plate shape so that the permeated water can be collected. Examples are shown in FIGS. The membrane filtration device is a device for performing membrane filtration of raw water by providing a pressure means such as a pump or a water level difference on the raw water side of the membrane module or a suction means such as a pump or siphon on the permeate side, and an example is shown in FIG. Raw water includes river water, lake water, ground water, seawater, sewage, drainage, and treated water thereof.
[0036]
【Example】
The present invention will be described below with reference to specific examples, but the present invention is not limited to these examples.
[0037]
  Here, parameters related to the present invention were measured by the following method.
(1) Melting temperature Tm (° C), crystallization temperature Tc (° C)
Vinylidide fluorideHomopolymer andMeltingMade of medium onlyA mixture having the same composition as the membrane stock solution is sealed in a sealed DSC container and heated at a rate of temperature increase of 10 ° C./min using a DSC-6200 manufactured by Seiko Denshi.SolveThe starting temperature of the melting peak observed during the heating process was defined as the uniform melting temperature Tm. Furthermore, after melting for 5 minutes, the rising temperature of the crystallization peak observed in the process of lowering the temperature at a temperature lowering rate of 10 ° C./min was defined as the crystallization temperature Tc (FIG. 3).
(2) Cloud point (° C)
Vinylidide fluorideHomopolymer andMeltingMade of medium onlyA mixture of the same composition as the membrane stock solution is sealed with a preparation, cover glass, and grease, heated to a melting temperature with a microscope cooling / heating device (LK-600 manufactured by Japan High-Tech), and held for 5 minutes for dissolution. After that, the cloud point observed in the process of lowering the temperature at a temperature lowering rate of 10 ° C./min was taken as the cloud point temperature.
(3) Average cooling rate Vt
Unless otherwise stated, b. The following method was used for calculation.
[0038]
Vt = (Ts−Ta) / (dry length / extrusion speed of polymer solution)
Ts: discharge port temperature (° C.), Ta: cooling bath temperature (° C.),
(4) Transmission characteristics
The reverse osmosis membrane treated water at 25 ° C is fed to a hollow fiber membrane small module (length is about 20cm, number of hollow fiber membranes is about 1 to 10) using a water level difference of 1.5m as driving force, and permeated for a certain time The value obtained by measuring the amount of water was calculated by converting per 100 kPa.
(5) Polystyrene latex blocking performance
A stock solution in which uniform latex particles made of Seradyn having a particle size of 0.309 μm are dispersed in reverse osmosis membrane treated water is used as feed water, and a permeation water is obtained by cross flow filtration with a feed pressure of 3 kPa and an average membrane surface velocity of 20 cm / s. It was. The polystyrene latex concentration of the feed water and the permeated water was determined from an ultraviolet-visible spectrophotometer, and the rejection was determined from the following equation. The permeated water concentration was determined by sampling the solution 30 minutes after the start of filtration.
[0039]
  Rej. = (1-Cb / Ca) × 100
Rej. : Rejection (%), Ca: feed water concentration (ppm), Cb: permeate concentration (ppm)
(5) Breaking strength and elongation of the hollow fiber membrane
Using a tensile tester, a membrane having a test length of 50 mm in a wet state was measured at a crosshead speed of 50 mm / min under a load of 2000 g full scale.
Example 1
Weight average molecular weight (Mw) is 4.17 × 10^FiveA homogeneous solution was obtained by dissolving 40% by weight of the vinylidene fluoride homopolymer and 60% by weight of γ-butyrolactone at 150 ° C. The Tc of this solution was 57 ° C. Accordingly, the discharge temperature Ts is 57.℃ <Ts≦ 147° C.This polymer solution was allowed to stand at 110 ° C., defoamed, and discharged from the tube outside the double tubular die for hollow fiber molding at Ts = 100 ° C. A 100 wt% γ-butyrolactone injection solution was injected into the hollow portion from the tube inside the double tubular die. A cooling bath comprising 80% by weight of γ-butyrolactone and 20% by weight of water having a dry length of 4 cm and a liquid temperature of 5 ° C. was discharged at an extrusion speed of 6.0 m / min and a film forming average temperature reduction rate of 14250 ° C./min. The solution was gelled in the membrane and stretched 1.5 times in a hot water bath at 80 ° C. to obtain a hollow fiber membrane.
[0040]
  The performance of this hollow fiber membrane is shown in Table 2. Mechanical strength, permeation characteristics and separation performance were all high. The film structure had a structure in which spherulites having a particle size of 1.8 μm were stacked and pores were connected to the gaps between the spherulites.
Example 2
Weight average molecular weight (Mw) is 4.17 × 10^FiveA homogeneous solution was obtained by dissolving 33% by weight of vinylidene fluoride homopolymer and 67% by weight of γ-butyrolactone at 120 ° C. The Tc of this solution was 41 ° C. Accordingly, the discharge temperature Ts is 41.℃ <Ts≦ 131° C.Using this polymer solution, a hollow fiber membrane was obtained in the same manner as in Example 1 except that the membrane formation conditions were changed as shown in Table 1. As an injection solution into the hollow part, an injection solution consisting of 90% by weight of γ-butyrolactone and 10% by weight of water was used. The performance of this hollow fiber membrane is shown in Table 2. Both transmission characteristics and separation performance were high. The film structure had a structure in which spherulites having a particle diameter of 3.2 μm were stacked and pores were connected to the gaps between the spherulites.
Example 3
Weight average molecular weight (Mw) is 3.58 × 10^FiveA homogeneous solution was obtained by dissolving 55% by weight of vinylidene fluoride homopolymer and 45% by weight of propylene carbonate at 170 ° C. The Tc of this solution was 78 ° C. Accordingly, the discharge temperature Ts is 78.℃ <Ts≦ 168° C.Using this polymer solution, a hollow fiber membrane was obtained in the same manner as in Example 1 except that the membrane formation conditions were changed as shown in Table 1. Propylene carbonate was also used as a solvent for the injection solution and the cooling bath. The performance of this hollow fiber membrane is shown in Table 2. Mechanical strength, permeation characteristics and separation performance were all high. The film structure had a structure in which spherulites having a particle size of 1.9 μm were laminated and pores were connected to the gaps between the spherulites.
Example 4
Weight average molecular weight (Mw) is 4.17 × 10^FiveA homogeneous solution was obtained by dissolving 55% by weight of vinylidene fluoride homopolymer and 45% by weight of propylene carbonate at 170 ° C. The Tc of this solution was 79 ° C. Accordingly, the discharge temperature Ts is 79.C <Ts ≦ 169 ° C.Using this polymer solution, a hollow fiber membrane was obtained in the same manner as in Example 3 except that the membrane formation conditions were changed as shown in Table 1. In observation by thermography, the temperature of the hollow fiber was lowered to 79 ° C. or less at 3 cm below the base, and the average film forming temperature drop rate Vt was a. Using this method, it was calculated as 3500 ° C./min.
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  The performance of this hollow fiber membrane is shown in Table 2. Both transmission characteristics and separation performance were high. The film structure had a structure in which spherulites having a particle size of 2.2 μm were laminated and vacancies were connected to gaps between the spherulites.
Example 5
Weight average molecular weight (Mw) is 3.58 × 10^FiveA homogeneous solution was obtained by dissolving 50% by weight of vinylidene fluoride homopolymer and 50% by weight of propylene carbonate at 170 ° C. The Tc of this solution was 73 ° C. Accordingly, the discharge temperature Ts is 73.℃ <Ts≦ 163° C.This polymer solution was produced from a T-die having a dry length of 7 cm and a 120 ° C. T-die to a winding roll having a winding speed of 10.0 m / min in a cooling bath composed of 85% by weight of propylene carbonate and 15% by weight of water at a liquid temperature of 5 ° C. The film was cast at an average film temperature drop rate of 16429 ° C./min and gelled in a cooling bath to obtain a flat film. The performance of this membrane is shown in Table 2. Mechanical strength, permeation characteristics and separation performance were all high. The film structure had a structure in which spherulites having a particle diameter of 3.2 μm were stacked and pores were connected to the gaps between the spherulites.
Comparative Example 1
Weight average molecular weight (Mw) is 4.44 × 10^FiveA homogeneous solution was obtained by dissolving 35% by weight of vinylidene fluoride homopolymer and 65% by weight of γ-butyrolactone at 130 ° C. The Tc of this solution was 47 ° C. Accordingly, the discharge temperature Ts is 47.℃ <Ts≦ 137° C.Using this polymer solution, a hollow fiber membrane was obtained in the same manner as in Example 1 except that the membrane formation conditions were changed as shown in Table 1. The performance of this hollow fiber membrane is shown in Table 2. The blocking performance of polystyrene uniform latex particles having a particle size of 0.309 μm was as low as 33%. The film structure had a structure in which spherulites having a particle size of 4.3 μm were stacked and pores were connected to the gaps between the spherulites. It is presumed that the spherulite particle size was increased due to the slow average film formation temperature decreasing rate, and the pores in the gap were increased accordingly, and the exclusion performance was lowered.
Comparative Example 2
In Example 1, an attempt was made to discharge at a discharge port temperature Ts of 50 ° C., which is equal to or lower than Tc.
Comparative Example 3
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the discharge port temperature Ts was set to 150 ° C. The performance of this hollow fiber membrane is shown in Table 2. The blocking performance of polystyrene uniform latex particles having a particle size of 0.309 μm was as low as 44%. The film structure had a structure in which spherulites having a particle size of 5.1 μm were stacked and pores were connected to the gaps between the spherulites.
Comparative Example 4
Weight average molecular weight (Mw) is 4.44 × 10^Five25% by weight of the vinylidene fluoride homopolymer and 75% by weight of γ-butyrolactone were dissolved at 130 ° C. to obtain a uniform solution. The Tc of this solution was as low as 31 ° C. Using this polymer solution, a hollow fiber membrane was obtained in the same manner as in Example 1 except that the membrane formation conditions were changed as shown in Table 1. The performance of this hollow fiber membrane is shown in Table 2. The blocking performance of polystyrene uniform latex particles having a particle size of 0.309 μm was as low as 40%. The film structure had a structure in which spherulites having a particle size of 4.3 μm were stacked and pores were connected to the gaps between the spherulites.
Comparative Example 5
Weight average molecular weight (Mw) is 4.44 × 10^Five78% by weight of vinylidene fluoride homopolymer and 22% by weight of cyclohexanone were dissolved at 145 ° C. to obtain a uniform solution. The Tc of this solution was as high as 121 ° C. A hollow fiber membrane was obtained in the same manner as in Example 1 except that this polymer solution was allowed to stand at 145 ° C., defoamed, and the membrane formation conditions were changed as shown in Table 1. Cyclohexanone was also used as a solvent for the injection solution and the cooling bath. The performance of this hollow fiber membrane is shown in Table 2. Transmission performance 0m^Three/ (M²・ Water permeability was not developed at h · 100 kPa).
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[Table 1]

[0043]
[Table 2]

[0044]
【The invention's effect】
According to the present invention, a microporous membrane having sufficient mechanical strength, fluid permeation characteristics, and chemical resistance and having excellent separation performance can be obtained.
[Brief description of the drawings]
FIG. 1 shows a phase diagram in the case of showing liquid-liquid type phase separation.
FIG. 2 shows a phase diagram in the case of showing solid-liquid type phase separation.
FIG. 3 shows Tc and Tm in the DSC curve.
FIG. 4 shows an example of a hollow fiber membrane module.
FIG. 5 shows an example of a flat membrane module.
FIG. 6 shows an example of a membrane filtration device.

Claims (5)

Ejecting polyfluorinated vinylidene Nhomoporima Contact good beauty γ- butyrolactone or propylene carbonate only port Rimmer solution composition was dissolved at 120 ° C. or higher 170 ° C. or less consisting of a discharge port which is a temperature Ts, produce cooled and microporous membrane The crystallization temperature Tc of the polymer solution is 40 ° C. or more and 105 ° C. or less, and the average temperature drop rate when the polymer solution passes through Tc during cooling is 2 × 10 ³ ° C./min or more and 10 ⁶ ° C. / Min or less and Ts satisfies the relationship of Tc <Ts ≦ Tc + 90. Method for producing a microporous film according to claim 1, wherein polyfluorinated vinylidene Nhomoporima concentration of the polymer solution is 60 wt% or less than 30% by weight. The method for producing a microporous membrane according to claim 1 or 2, wherein the polymer solution is cooled using a liquid having a solvent of 65% by weight or more. The discharge port is a double tubular discharge port, a polymer solution is discharged from a tube outside the double tubular discharge port, and a liquid containing 70% by weight or more of solvent is injected into the hollow part to produce a microporous hollow fiber membrane The method for producing a microporous membrane according to any one of claims 1 to 3. The method for producing a microporous membrane according to any one of claims 1 to 4, wherein a microporous membrane for water filtration treatment is produced.

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