JP2018144005A - Porous hollow fiber membrane and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous hollow fiber membrane with excellent chemical resistance and mechanical strength, and provide a manufacturing method of the same.SOLUTION: A porous hollow fiber membrane 10 contains an ethylene-tetrafluoroethylene copolymer. The porous hollow fiber membrane 10 contains a first solvent. The first solvent is at least one kind selected from sebacic acid ester, citric acid ester, acetylcitric acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphate ester, 6-30C aliphatic acid, and epoxidized vegetable oil. The porous hollow fiber membrane 10 has a three-dimensional network structure.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a porous hollow fiber membrane and a method for producing the same.

  Membrane filtration methods using hollow fiber membranes are becoming widespread for turbidity operations of liquids to be treated, such as water treatment and sewage treatment. As a method for producing a hollow fiber membrane used for membrane filtration, a heat-induced phase separation method is known.

In the thermally induced phase separation method, a thermoplastic resin and an organic liquid are used. As an organic liquid, a thermoplastic resin does not dissolve at room temperature, but a solvent that dissolves at high temperatures, that is, a latent solvent (poor solvent), is a heat-induced phase separation method in which a thermoplastic resin and an organic liquid are kneaded at a high temperature and heated. This is a method for producing a porous body by dissolving a plastic resin in an organic liquid and then inducing phase separation by cooling to room temperature and further removing the organic liquid. This method has the following advantages.
(A) Film formation is possible even with a polymer such as polyethylene without an appropriate solvent that can be dissolved at room temperature.
(B) Since the film is melted at a high temperature and then cooled and solidified to form a film, particularly when the thermoplastic resin is a crystalline resin, crystallization is promoted during film formation, and a high-strength film is easily obtained.

From the above advantages, the thermally induced phase separation method is frequently used as a method for producing a porous membrane. However, certain crystalline resins have a problem in practical durability because the film structure tends to be spherulite and the strength is high but the elongation is low.
Conventionally, a technique for forming a film using a poor solvent of a thermoplastic resin selected from citrate esters has been disclosed (see Patent Document 1).

JP 2011-168741 A

However, the film manufactured by the method described in Patent Document 1 also has a problem of having a spherulite structure.
The present invention has been made in view of the above circumstances, and provides a porous hollow fiber membrane having a three-dimensional network structure and excellent in chemical resistance and mechanical strength, and a method for producing the same.

  In a known technique, when a porous hollow fiber membrane is produced, a poor solvent is used as a raw material containing a thermoplastic resin for heat-induced phase separation. -It has been found that a film having a three-dimensional network structure excellent in chemical resistance and mechanical strength can be produced by mixing at least one non-solvent into a solution using a tetrafluoroethylene copolymer. Invented.

The present invention provides the following inventions.
The porous hollow fiber membrane of the present invention (hereinafter referred to as the first porous hollow fiber membrane for convenience) is a porous hollow fiber membrane containing an ethylene-tetrafluoroethylene copolymer,
The porous hollow fiber membrane comprises a first solvent;
The first solvent is selected from sebacic acid ester, citric acid ester, acetyl citrate ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, fatty acid having 6 to 30 carbon atoms, and epoxidized vegetable oil At least one kind
The porous hollow fiber membrane has a three-dimensional network structure.

The first porous hollow fiber membrane of the present invention further includes a second solvent different from the first solvent,
The second solvent is sebacic acid ester, citric acid ester, acetyl citrate ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, 6 to 30 carbon atoms And at least one selected from epoxidized vegetable oils.

The porous hollow fiber membrane of the present invention (hereinafter referred to as a second porous hollow fiber membrane for convenience) is a porous hollow fiber membrane containing an ethylene-tetrafluoroethylene copolymer,
The porous hollow fiber membrane includes a first solvent and a second solvent,
The first solvent is sebacic acid ester, citric acid ester, acetyl citrate ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, 6 to 30 carbon atoms A fatty acid, and at least one selected from epoxidized vegetable oils,
Unlike the first solvent, the second solvent is sebacic acid ester, citrate ester, acetyl citrate ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester , A fatty acid having 6 to 30 carbon atoms, and at least one selected from epoxidized vegetable oils.

  In the second porous hollow fiber membrane of the present invention, the first solvent is the first solvent in the first mixed liquid in which the ratio of the ethylene-tetrafluoroethylene copolymer and the first solvent is 20:80. Even if the temperature of the mixed solution is raised to the boiling point of the first solvent, it is preferably a non-solvent in which the ethylene-tetrafluoroethylene copolymer does not dissolve uniformly in the first solvent.

  In the second porous hollow fiber membrane of the present invention, the second solvent is a second mixture in which the ratio of the ethylene-tetrafluoroethylene copolymer and the second solvent is 20:80. The solvent is preferably a solvent in which the ethylene-tetrafluoroethylene copolymer is uniformly dissolved in the second solvent at any temperature higher than 25 ° C. and lower than the boiling point of the second solvent.

  Here, “dissolves uniformly in the second solvent” means that the solution is not visually separated into two layers and the solution becomes transparent.

  The second solvent is an ethylene-tetrafluoroethylene in a second mixed liquid in which the ratio of the ethylene-tetrafluoroethylene copolymer and the second solvent is 20:80 and the temperature of the second mixed liquid is 25 ° C. The copolymer is not uniformly dissolved in the second solvent, and the ethylene-tetrafluoroethylene copolymer is not dissolved in the second mixture at a temperature higher than 100 ° C. and lower than the boiling point of the second solvent. More preferably, it is a poor solvent that dissolves uniformly in the second solvent.

The porous hollow fiber membrane of the present invention (hereinafter referred to as a third porous hollow fiber membrane for convenience) is a porous hollow fiber membrane containing an ethylene-tetrafluoroethylene copolymer,
The porous hollow fiber membrane includes a first solvent,
The first solvent is sebacic acid ester, citric acid ester, acetyl citrate ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, 6 to 30 carbon atoms Of the first mixed liquid in the first mixed liquid in which the ratio of the ethylene-tetrafluoroethylene copolymer and the first solvent is 20:80. Even if the temperature is raised to the boiling point of the first solvent, the ethylene-tetrafluoroethylene copolymer is a non-solvent that does not uniformly dissolve in the first solvent.

The third porous hollow fiber membrane of the present invention may contain a second solvent different from the first solvent,
The second solvent is sebacic acid ester, citric acid ester, acetyl citrate ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, 6 to 30 carbon atoms And at least one selected from epoxidized vegetable oils,
In the second mixed liquid in which the ratio of the ethylene-tetrafluoroethylene copolymer and the second solvent is 20:80, the ethylene-tetrafluoroethylene copolymer is second when the temperature of the second mixed liquid is 25 ° C. The ethylene-tetrafluoroethylene copolymer is uniformly dissolved in the second solvent at a temperature higher than 100 ° C. and lower than the boiling point of the second solvent. A poor solvent that dissolves is preferred.

  The porous hollow fiber membrane of the present invention may contain an inorganic substance.

  The inorganic substance is preferably at least one selected from silica, lithium chloride, and titanium oxide.

The method for producing the porous hollow fiber membrane of the present invention comprises:
A method for producing a porous hollow fiber membrane comprising an ethylene-tetrafluoroethylene copolymer,
Dissolving an ethylene-tetrafluoroethylene copolymer in a solvent containing at least a first solvent and a second solvent;
Separating the solution containing the dissolved ethylene-tetrafluoroethylene copolymer,
The first solvent is sebacic acid ester, citric acid ester, acetyl citrate ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, 6 to 30 carbon atoms In the first liquid mixture, the ratio of the ethylene-tetrafluoroethylene copolymer and the first solvent is 20:80, and the first liquid mixture is at least one selected from: A non-solvent in which the ethylene-tetrafluoroethylene copolymer is not uniformly dissolved in the first solvent even if the temperature of the first solvent is raised to the boiling point of the first solvent,
The second solvent is sebacic acid ester, citric acid ester, acetyl citrate ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, 6 to 30 carbon atoms In the second mixed liquid, the ratio of the ethylene-tetrafluoroethylene copolymer and the second solvent is 20:80, and the second mixed liquid. Is a solvent in which the ethylene-tetrafluoroethylene copolymer is uniformly dissolved in the second solvent at any temperature higher than 25 ° C. and lower than the boiling point of the second solvent.

  In the method for producing a porous hollow fiber membrane of the present invention, the second solvent is a second mixed liquid in a second liquid mixture in which the ratio of the ethylene-tetrafluoroethylene copolymer and the second solvent is 20:80. When the temperature of the liquid is 25 ° C., the ethylene-tetrafluoroethylene copolymer is not uniformly dissolved in the second solvent, and the temperature of the second mixed liquid is higher than 100 ° C. and any of the boiling points of the second solvent and lower. It is preferable that the ethylene-tetrafluoroethylene copolymer is a poor solvent in which the ethylene-tetrafluoroethylene copolymer is uniformly dissolved in the second solvent at a temperature.

  The step of phase separation is preferably liquid-liquid phase separation.

  According to the present invention, there is provided a porous hollow fiber membrane in which the membrane structure forms a three-dimensional network structure, the pores are good, the chemical resistance and the mechanical strength are high.

It is a schematic diagram which shows the outer surface of one Embodiment of the porous hollow fiber membrane of this invention. It is a schematic diagram which shows the outer surface of the porous hollow fiber membrane of a comparative example.

  Embodiments of the present invention will be described in detail. In addition, this invention is not limited to the following embodiment.

<Porous hollow fiber membrane>
Hereinafter, the porous hollow fiber membrane of the present invention will be described.
FIG. 1 schematically shows the outer surface of a porous hollow fiber membrane according to the present invention.
The porous hollow fiber membrane of the present invention comprises an ethylene-tetrafluoroethylene copolymer as a thermoplastic resin. The outer surface of the porous hollow fiber membrane 10 shown in FIG. 1 is not a spherulite structure but a three-dimensional network structure. By adopting a three-dimensional network structure, the tensile elongation at break is increased, and resistance to alkalis (such as aqueous sodium hydroxide) frequently used as a film cleaning agent is increased.

  The porous hollow fiber membrane 10 can contain up to about 5 mass% of components (impurities and the like) other than the ethylene-tetrafluoroethylene copolymer. For example, the porous hollow fiber membrane contains a solvent used at the time of production, and as described later, the porous hollow fiber membrane 10 contains at least a non-solvent (first solvent) used as a solvent at the time of production, A solvent or a poor solvent (second solvent) may be included. These solvents can be detected by pyrolysis GC-MS (gas chromatography mass spectrometry).

  For example, the porous hollow fiber membrane of the present invention (first porous hollow fiber membrane) is a porous hollow fiber membrane containing an ethylene-tetrafluoroethylene copolymer, and the porous hollow fiber membrane is a non-solvent. The first solvent includes a sebacic acid ester, a citric acid ester, an acetyl citric acid ester, an oleic acid ester, a palmitic acid ester, a stearic acid ester, a phosphoric acid ester, and a fatty acid having 6 to 30 carbon atoms. And at least one selected from epoxidized vegetable oils, and the porous hollow fiber membrane has a three-dimensional network structure.

Examples of fatty acids having 6 to 30 carbon atoms include capric acid, lauric acid, and oleic acid.
Examples of the epoxidized vegetable oil include epoxy soybean oil and epoxidized linseed oil.

  Moreover, the first porous hollow fiber membrane may further include a second solvent different from the first solvent. Examples of the second solvent include sebacic acid ester, citric acid ester, acetyl citrate ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, 6 to 30 carbon atoms. It is preferably at least one selected from the following fatty acids and epoxidized vegetable oils.

The porous hollow fiber membrane of the present invention (second porous hollow fiber membrane)
A porous hollow fiber membrane comprising an ethylene-tetrafluoroethylene copolymer,
The porous hollow fiber membrane includes a first solvent and a second solvent,
The first solvent is sebacic acid ester, citric acid ester, acetyl citrate ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, 6 to 30 carbon atoms A fatty acid, and at least one selected from epoxidized vegetable oils,
Unlike the first solvent, the second solvent is sebacic acid ester, citrate ester, acetyl citrate ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester , A fatty acid having 6 to 30 carbon atoms, and at least one selected from epoxidized vegetable oils.

  The first solvent is a first mixed liquid in which the ratio of the ethylene-tetrafluoroethylene copolymer and the first solvent is 20:80, and the temperature of the first mixed liquid is raised to the boiling point of the first solvent. However, it is preferable that the ethylene-tetrafluoroethylene copolymer is a non-solvent that does not uniformly dissolve in the first solvent.

  The second solvent is a second solvent in which the ratio of the ethylene-tetrafluoroethylene copolymer and the second solvent is 20:80 and the temperature of the second mixture is higher than 25 ° C. It is preferable that the ethylene-tetrafluoroethylene copolymer is a solvent in which the ethylene-tetrafluoroethylene copolymer is uniformly dissolved in the second solvent at any temperature below the boiling point.

  The second solvent is an ethylene-tetrafluoroethylene in a second mixed liquid in which the ratio of the ethylene-tetrafluoroethylene copolymer and the second solvent is 20:80 and the temperature of the second mixed liquid is 25 ° C. The copolymer is not uniformly dissolved in the second solvent, and the ethylene-tetrafluoroethylene copolymer is not dissolved in the second mixture at a temperature higher than 100 ° C. and lower than the boiling point of the second solvent. More preferably, it is a poor solvent that dissolves uniformly in the second solvent.

  The determination method of the non-solvent, the solvent, and the poor solvent in the present invention will be described in the method for producing a porous hollow fiber membrane described later.

The porous hollow fiber membrane of the present invention (third porous hollow fiber membrane) is a porous hollow fiber membrane containing an ethylene-tetrafluoroethylene copolymer,
The porous hollow fiber membrane includes a first solvent,
The first solvent is sebacic acid ester, citric acid ester, acetyl citrate ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, 6 to 30 carbon atoms Of the first mixed liquid in the first mixed liquid in which the ratio of the ethylene-tetrafluoroethylene copolymer and the first solvent is 20:80. Even if the temperature is raised to the boiling point of the first solvent, the ethylene-tetrafluoroethylene copolymer is a non-solvent that does not uniformly dissolve in the first solvent.

Furthermore, the third porous hollow fiber membrane may contain a second solvent different from the first solvent. The second solvent is sebacic acid ester, citric acid ester, acetyl citrate ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, 6 to 30 carbon atoms And at least one selected from epoxidized vegetable oils,
In the second mixed liquid in which the ratio of the ethylene-tetrafluoroethylene copolymer and the second solvent is 20:80, the ethylene-tetrafluoroethylene copolymer is second when the temperature of the second mixed liquid is 25 ° C. The ethylene-tetrafluoroethylene copolymer is uniformly dissolved in the second solvent at a temperature higher than 100 ° C. and lower than the boiling point of the second solvent. A poor solvent that dissolves is preferred.

(Physical properties of porous hollow fiber membrane)
Next, physical properties of the porous hollow fiber membrane of the present invention will be described.
The initial value of the tensile elongation at break of the porous hollow fiber membrane is preferably 60% or more, more preferably 80% or more, still more preferably 100% or more, and particularly preferably 120% or more. The tensile elongation at break can be measured by the measuring method in the examples described later.

  The alkali resistance can be measured by the elongation at break before and after immersion in alkali, and the tensile elongation at break after being immersed in a 4% NaOH aqueous solution for 10 days is preferably maintained at 60% or more with respect to the initial value. . More preferably, it is 65% or more, More preferably, it is 70% or more.

  From a practical viewpoint, the compressive strength of the porous hollow fiber membrane 10 is 0.2 MPa or more, preferably 0.3 to 1.0 MPa, more preferably 0.4 to 1.0 MPa.

  The aperture ratio (surface aperture ratio) of the surface of the porous hollow fiber membrane 10 is 20 to 60%, preferably 25 to 50%, and more preferably 25 to 45%. By using a membrane with an opening ratio of 20% or more on the surface in contact with the liquid to be treated for filtration, both the water permeability degradation due to clogging and the water permeability degradation due to membrane surface abrasion are reduced, and the filtration stability is improved. be able to. However, even if the aperture ratio is high, if the pore diameter is too large, the required separation performance may not be exhibited. Therefore, the pore diameter on the outer surface is 1,000 nm or less, preferably 10 to 800 nm, and more preferably 100 to 700 nm. If the pore diameter is 1,000 nm or less, the component to be blocked contained in the liquid to be treated can be blocked, and if it is 10 nm or more, sufficiently high water permeability can be secured.

  The thickness of the porous hollow fiber membrane 10 is preferably 80 to 1,000 μm, more preferably 100 to 300 μm. When the thickness is 80 μm or more, the strength is high, and when it is 1,000 μm or less, the pressure loss due to the membrane resistance is small.

  The porosity of the porous hollow fiber membrane 10 is preferably 50 to 80%, more preferably 55 to 65%. When the porosity is 50% or more, the water permeability is high, and when it is 80% or less, the mechanical strength is high.

  An example of the shape of the porous hollow fiber membrane 10 is an annular single layer membrane, but it may be a multilayer membrane having different pore sizes between the separation layer and the support layer supporting the separation layer. Further, the outer surface and the inner surface may have an irregular cross-sectional structure such as having protrusions.

(Process target liquid)
The liquids to be treated by the porous hollow fiber membrane 10 are suspension water and process process liquids. The porous hollow fiber membrane 10 is suitably used in a water purification method including a step of filtering suspended water.

  Suspended water includes natural water, domestic wastewater, and treated water thereof. Examples of natural water include river water, lake water, groundwater, and seawater. Natural water treated water obtained by subjecting these natural waters to sedimentation treatment, sand filtration treatment, coagulation sedimentation sand filtration treatment, ozone treatment, activated carbon treatment and the like is also included in the suspension water to be treated. An example of domestic wastewater is sewage. Sewage primary treated water subjected to screen filtration and sedimentation treatment, sewage secondary treated water subjected to biological treatment, and further processing such as coagulation sedimentation sand filtration, activated carbon treatment, and ozone treatment 3 The next treatment (advanced treatment) water is also included in the suspension water to be treated. These suspended waters include turbid substances (humus colloids, organic colloids, clays, bacteria, etc.) composed of fine organic substances, inorganic substances and organic-inorganic mixtures of the order of μm or less.

  The water quality of suspended water (such as the above-mentioned natural water, domestic wastewater, and treated water thereof) can be generally expressed by turbidity and organic substance concentration, which are representative water quality indicators, alone or in combination. When the water quality is classified by turbidity (average turbidity, not instantaneous turbidity), it is roughly divided into low turbid water with turbidity less than 1, turbid water with turbidity of 1 to less than 10, high turbidity with turbidity of 10 to less than 50, It can be classified into ultra-turbid water with turbidity of 50 or more. Moreover, when the water quality is classified by organic substance concentration (total organic carbon (TOC): mg / L) (this is not an instantaneous value but an average value), the water quality is generally less than 1, low TOC water, 1 It can be classified into medium TOC water of less than 4 or more, high TOC water of 4 or more and less than 8, and ultra-high TOC water of 8 or more. Basically, the higher the turbidity or TOC, the more easily the clogging of the filtration membrane. Therefore, the higher the turbidity or TOC, the greater the effect of using the porous hollow fiber membrane 10.

  The process process liquid refers to a liquid to be separated when separating valuables from non-valuables in foods, pharmaceuticals, and semiconductor manufacturing. In food production, the porous hollow fiber membrane 10 is used when, for example, separating alcoholic beverages such as sake and wine from yeast. In the manufacture of pharmaceuticals, for example, the porous hollow fiber membrane 10 is used for sterilization when purifying proteins. In semiconductor manufacturing, for example, the porous hollow fiber membrane 10 is used for separation of abrasive and water from polishing wastewater.

<Method for Producing Porous Hollow Fiber Membrane 10>
Next, the manufacturing method of the porous hollow fiber membrane 10 is demonstrated. A method for producing a porous hollow fiber membrane includes: (a) a step of preparing a melt-kneaded product; and (b) supplying the melt-kneaded product to a multi-structure spinning nozzle and extruding the melt-kneaded product from the spinning nozzle. A step of obtaining a membrane, and (c) a step of extracting the plasticizer from the hollow fiber membrane. When the melt-kneaded product contains an additive, the method for producing the porous hollow fiber membrane 10 includes a step (d) of extracting the additive from the hollow fiber membrane after the step (c).

  The concentration of the thermoplastic resin in the melt-kneaded product is preferably 20 to 60% by mass, more preferably 25 to 45% by mass, and still more preferably 30 to 45% by mass. When this value is 20% by mass or more, the mechanical strength is high, and when it is 60% by mass or less, the water permeability is good. The melt-kneaded product may contain an additive.

  The melt-kneaded product may be composed of two components of a thermoplastic resin and a solvent, or may be composed of three components of a thermoplastic resin, an additive and a solvent. As will be described later, the solvent contains at least a non-solvent.

  As the extractant used in the step (c), it is preferable to use a liquid that does not dissolve thermoplastic resins such as methylene chloride and various alcohols but has high affinity with the plasticizer.

  In addition, when using the melt-kneaded material which does not contain an additive, you may use the hollow fiber membrane obtained through a process (c) as the porous hollow fiber membrane 10. FIG. When the porous hollow fiber membrane 10 is produced using a melt-kneaded product containing an additive, the production method according to the present invention is performed by extracting and removing (d) the additive from the hollow fiber membrane after the step (c). It is preferable to further include a step of obtaining the porous hollow fiber membrane 10. As the extractant in the step (d), it is preferable to use a liquid which can dissolve hot water or an additive such as acid or alkali but does not dissolve the thermoplastic resin.

  An inorganic substance may be used as an additive. The inorganic substance is preferably inorganic fine powder. The primary particle size of the inorganic fine powder contained in the melt-kneaded product is preferably 50 nm or less, more preferably 5 nm or more and less than 30 nm. Specific examples of the inorganic fine powder include silica, fine powder silica, titanium oxide, lithium chloride, calcium chloride, and organic clay. Among these, fine powder silica is preferable from the viewpoint of cost. The above-mentioned “primary particle size of inorganic fine powder” means a value obtained from analysis of an electron micrograph. That is, a group of inorganic fine powder is first pretreated by the method of ASTM D3849. Thereafter, the diameter of 3000 to 5000 particles copied in the transmission electron micrograph is measured, and the primary particle diameter of the inorganic fine powder is calculated by arithmetically averaging these values.

  The inorganic fine powder in the porous hollow fiber membrane can determine the material of the inorganic fine powder by identifying the element present by fluorescent X-rays or the like.

  When an organic substance is used as an additive, hydrophilicity can be imparted to the hollow fiber membrane by using a hydrophilic polymer such as polyvinyl pyrrolidone or polyethylene glycol. Moreover, the viscosity of the melt-kneaded product can be controlled by using an additive having a high viscosity such as glycerin or ethylene glycol.

Next, details of the step (a) of preparing the melt-kneaded product in the method for producing a porous hollow fiber membrane, that is, the production method of the present invention will be described.
The method for producing a porous hollow fiber membrane of the present invention is a method for producing a porous hollow fiber membrane containing an ethylene-tetrafluoroethylene copolymer,
Dissolving an ethylene-tetrafluoroethylene copolymer in a solvent containing at least a first solvent and a second solvent;
Separating the solution containing the dissolved ethylene-tetrafluoroethylene copolymer,
The first solvent is sebacic acid ester, citric acid ester, acetyl citrate ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, 6 to 30 carbon atoms In the first liquid mixture, the ratio of the ethylene-tetrafluoroethylene copolymer and the first solvent is 20:80, and the first liquid mixture is at least one selected from: A non-solvent in which the ethylene-tetrafluoroethylene copolymer is not uniformly dissolved in the first solvent even if the temperature of the first solvent is raised to the boiling point of the first solvent,
The second solvent is sebacic acid ester, citric acid ester, acetyl citrate ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, 6 to 30 carbon atoms In the second liquid mixture, the ratio of the ethylene-tetrafluoroethylene copolymer and the second solvent is 20:80. This is a solvent in which the ethylene-tetrafluoroethylene copolymer is uniformly dissolved in the second solvent at any temperature higher than 25 ° C. and lower than the boiling point of the second solvent.

  The second solvent is an ethylene-tetrafluoroethylene in a second mixed liquid in which the ratio of the ethylene-tetrafluoroethylene copolymer and the second solvent is 20:80 and the temperature of the second mixed liquid is 25 ° C. The copolymer is not uniformly dissolved in the second solvent, and the ethylene-tetrafluoroethylene copolymer is not dissolved in the second mixture at a temperature higher than 100 ° C. and lower than the boiling point of the second solvent. The poor solvent which melt | dissolves uniformly in 2 solvents may be sufficient.

  The method for producing a porous hollow fiber membrane of the present invention uses a non-solvent of an ethylene-tetrafluoroethylene copolymer as a raw material. Thus, when a non-solvent is used for the raw material of the membrane, a porous hollow fiber membrane having a three-dimensional network structure is obtained. The mechanism of action is not necessarily clear, but it is considered that the use of a solvent with a lower solubility by mixing a non-solvent moderately inhibits the crystallization of the polymer and tends to form a three-dimensional network structure. . For example, non-solvents, poor solvents, and solvents include sebacic acid ester, citrate ester, acetyl citrate ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, It is selected from fatty acids having 6 to 30 carbon atoms and epoxidized vegetable oil. More preferably, at least selected from sebacic acid ester, citric acid ester, acetyl citrate ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, fatty acid having 6 to 30 carbon atoms, and epoxidized vegetable oil One type.

  Solvent that can dissolve ethylene-tetrafluoroethylene copolymer at normal temperature, solvent that cannot be dissolved at normal temperature but can be dissolved at high temperature, poor solvent of ethylene-tetrafluoroethylene copolymer, high temperature A solvent that cannot be dissolved even though is called a non-solvent, in the present invention, a poor solvent and a non-solvent can be determined as follows.

  The non-solvent, even if the temperature of the first mixed solution is raised to the boiling point of the first solvent in the first mixed solution in which the ratio of the ethylene-tetrafluoroethylene copolymer and the first solvent is 20:80, The ethylene-tetrafluoroethylene copolymer is not uniformly dissolved in the first solvent.

  Further, the solvent is a boiling point of the second solvent having a temperature of the second mixed liquid higher than 25 ° C. in the second mixed liquid in which the ratio of the ethylene-tetrafluoroethylene copolymer and the second solvent is 20:80. It is a solvent in which the ethylene-tetrafluoroethylene copolymer is uniformly dissolved in the second solvent at any of the following temperatures.

  Further, the poor solvent is ethylene-tetrafluoroethylene in a second mixed liquid in which the ratio of the ethylene-tetrafluoroethylene copolymer and the second solvent is 20:80 and the temperature of the second mixed liquid is 25 ° C. The copolymer is not uniformly dissolved in the second solvent, and the ethylene-tetrafluoroethylene copolymer is not dissolved in the second mixture at a temperature higher than 100 ° C. and lower than the boiling point of the second solvent. It dissolves uniformly in the second solvent.

  To determine whether the solvent, poor solvent, or non-solvent, specifically, about 2 g of ethylene-tetrafluoroethylene copolymer and about 8 g of solvent are put in a test tube, and the test tube block heater is used. Then, heat up to the boiling point of the solvent in steps of 10 ° C., mix the inside of the test tube with a spatula or the like, and judge the solubility in the above temperature range.

  In addition, the specific example of the said ester and its boiling point are as follows. The boiling point of acetyl tributyl citrate is 343 ° C., dibutyl sebacate is 345 ° C., dibutyl adipate is 305 ° C., diisobutyl adipate is 293 ° C., and bis-2-ethylhexyl adipate is 335 ° C. Diisononyl adipate is 250 ° C or higher, diethyl adipate is 251 ° C, triethyl citrate is 294 ° C, and triphenylphosphorous acid is 360 ° C.

  For example, when diethyl adipate is used as the solvent, the ethylene-tetrafluoroethylene copolymer is uniformly mixed and dissolved at about 200 ° C. On the other hand, when bis-2-ethylhexyl adipate is used as the solvent, it does not dissolve.

  Filtration can be performed with high efficiency by filtering the liquid to be treated using the porous hollow fiber membrane of the present invention.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

[Example 1]
The melt-kneaded product was extruded using a spinning nozzle having a double-pipe structure to obtain a porous hollow fiber membrane of Example 1. 40% by mass of ethylene-tetrafluoroethylene copolymer (ETFE) resin (manufactured by Asahi Glass Co., Ltd., TL-081), 23% by mass of fine silica (primary particle size: 16 nm) as a thermoplastic resin, and bis-2-ethylhexyl adipate as a solvent A melt-kneaded product was prepared using 32.9% by weight (DOA, boiling point 335 ° C.) and 4.1% by weight of diisobutyl adipate (DIBA, boiling point 293 ° C.).

The extruded hollow fiber-shaped molded article passed through an idle running distance of 120 mm, and then solidified in water at 30 ° C. to produce a porous hollow fiber membrane by a heat-induced phase separation method. It was taken up at a speed of 5 m / min and wound up in a skein. The obtained two-layer hollow fiber extrudate was immersed in isopropyl alcohol to extract and remove the solvent. Subsequently, the hollow fiber membrane was replaced with water by immersing in water for 30 minutes. Subsequently, it was immersed in a 20 mass% NaOH aqueous solution at 70 ° C. for 1 hour, and further washed with water to extract and remove fine powder silica. The porous hollow fiber membrane had a three-dimensional network structure as shown in FIG.
[Example 2]
Except for preparing a melt-kneaded material using 32.9% by mass of diisononyl adipate (DINA, boiling point of 250 ° C. or higher) instead of 32.9% by mass of bis-2-ethylhexyl adipate (DOA, boiling point: 335 ° C.) as a solvent. A porous hollow fiber membrane was produced in the same manner as in Example 1.

The porous hollow fiber membrane has a three-dimensional network structure as shown in FIG.
[Example 3]
Example 1 except that a melt kneaded material was prepared using 4.1% by mass of diethyl adipate (DEA, boiling point 251 ° C.) instead of 4.1% by mass of diisobutyl adipate (DIBA, boiling point 293 ° C.) as a solvent. A porous hollow fiber membrane was prepared in the same manner as described above.

  The porous hollow fiber membrane has a three-dimensional network structure as shown in FIG.

[Comparative Example 1]
A porous hollow fiber membrane of Comparative Example 1 was obtained in the same manner as in Example 1 except that the solvent was only DIBA and fine silica was removed. The film structure showed a spherulite structure as shown in FIG.

  Each physical property value in Examples and Comparative Examples was determined by the following methods.

(1) Outer diameter and inner diameter of membrane The hollow fiber membrane was sliced thinly with a razor, and the outer diameter and inner diameter were measured with a 100 × magnifier. One sample was measured at 60 points at intervals of 30 mm. At this time, a standard deviation and an average value were calculated, and (standard deviation) / (average value) was used as a coefficient of variation.

(2) Surface aperture ratio, pore diameter, pore structure observation Using an electron microscope SU8000 series manufactured by HITACHI, an electron microscope (SEM) image of the surface and cross section of the film was taken at 5000 times with an acceleration voltage of 3 kV. A cross-sectional electron microscope sample was obtained by cutting a membrane sample frozen in ethanol into round slices. Next, using the image analysis software Winroof 6.1.3, “noise removal” of the SEM image is performed with a numerical value “6”, and further binarized with a single threshold value, and then with a “threshold value: 105” Pricing was performed. The aperture ratio of the film surface was determined by determining the occupied area of the holes in the binarized image thus obtained.

  The hole diameter was determined by adding the hole area of each hole in order from the smallest hole diameter to each hole existing on the surface, and the sum of the holes reached 50% of the total hole area of each hole. .

  By observing the film surface and cross-sectional state photographed at a magnification of 5000 times, the film structure was determined to be a three-dimensional network structure without a spherulite and having a three-dimensional network structure.

(3) Water permeability After dipping in ethanol, one end of a wet hollow fiber membrane having a length of about 10 cm, which was dipped in pure water several times, was sealed, and an injection needle was inserted into the hollow part at the other end. Inject pure water at 25 ° C. into the hollow part from the injection needle at a pressure of 0.1 MPa, measure the amount of pure water permeating from the outer surface, determine the pure water flux by the following formula, and evaluate the water permeability did.
Pure water flux [L / m ² / h] = 60 × (permeated water amount [L]) / {π × (membrane outer diameter [m]) × (membrane effective length [m]) × (measurement time [min]) }

  Here, the effective membrane length refers to the net membrane length excluding the portion where the injection needle is inserted.

(4) Tensile elongation at break (%)
The load and displacement at the time of tensile fracture were measured under the following conditions.
According to the method of JIS K7161, a hollow fiber membrane was used as it was for the sample.
Measuring instrument: Instron type tensile testing machine (AGS-5D manufactured by Shimadzu Corporation)
Distance between chucks: 5cm
Tensile speed: 20 cm / min From the obtained results, the tensile elongation at break was calculated according to JIS K7161.

(5) Permeability performance retention during suspension water filtration This is one index for judging the degree of permeation performance deterioration due to clogging (fouling). After dipping in ethanol, the wet hollow fiber membrane that had been dipped in pure water several times was filtered by an external pressure method at an effective membrane length of 11 cm. First, pure water was filtered at a filtration pressure that permeated 10 m ³ per day per 1 m ² of the outer membrane surface area, and the permeated water was collected for 2 minutes to obtain the initial pure water permeation amount. Next, the river surface water (Fuji River surface water: turbidity 2.2, TOC concentration 0.8 ppm), which is natural suspended water, is filtered for 10 minutes at the same filtration pressure as when the initial pure water permeability was measured. The permeated water was collected for 2 minutes from the 8th to the 10th minutes of filtration, and was used as the water permeation amount during filtration of the suspension water. The water permeability retention rate during suspension water filtration was defined by the following formula. All operations were performed at 25 ° C. and a film surface linear velocity of 0.5 m / sec.
Permeability retention rate during suspension water filtration [%] = 100 × (water permeability during suspension water filtration [g]) / (initial pure water permeability [g])
Each parameter in the formula is calculated by the following formula.
Filtration pressure = {(input pressure) + (output pressure)} / 2
Surface area outside the membrane [m ² ] = π × (thread outer diameter [m]) × (membrane effective length [m])
Membrane surface linear velocity [m / s] = 4 × (circulated water amount [m ³ / s]) / {π × (tube diameter [m]) ² −π × (membrane outer diameter [m]) ² }

In this measurement, the filtration pressure of the suspended water is not the same for each membrane, but the initial pure water permeability (also the permeability at the start of suspension filtration) is 10 m ³ per day per 1 m ^{2 of} membrane surface area. Set. This is because in actual water treatment and sewage treatment, the membrane is usually used in quantitative filtration operation (a method in which the filtration pressure is adjusted so that a constant amount of filtered water is obtained within a certain period of time). Therefore, in this measurement, the deterioration of water permeability performance can be compared under conditions as close as possible to the conditions of quantitative filtration operation within the range of measurement using one hollow fiber membrane.

(6) Elongation retention after immersion in NaOH Wet porous hollow fiber membranes were cut into 10 cm, and 20 were immersed in 500 ml of 4% aqueous sodium hydroxide and held at 40 ° C. for 10 days. The tensile elongation at break of the membrane before and after immersion in an aqueous sodium hydroxide solution was measured at n20, and the average value was calculated. The elongation retention was defined as 100 × (elongation after immersion) / (elongation before immersion), and chemical resistance was evaluated.

  Table 1 shows the composition, production conditions, and various performances of the porous hollow fiber membranes of the obtained Examples and Comparative Examples.

As shown in Table 1, in Examples 1 to 3, the non-solvent is mixed with the film-forming stock solution in the film formation by thermally induced phase separation, so that the opening property is good, the chemical resistance, and the mechanical strength are high. It can be seen that a porous hollow fiber membrane is provided.
On the other hand, it can be seen that Comparative Example 1 containing no non-solvent has a spherulite pore structure and is inferior in openness, chemical resistance and mechanical strength.

  According to the present invention, since the porous hollow fiber membrane is formed containing a non-solvent, the porosity is good, and the porosity includes an ethylene-tetrafluoroethylene copolymer having good chemical resistance and high mechanical strength. A hollow fiber membrane is provided.

10 Porous hollow fiber membrane

Claims (13)

A porous hollow fiber membrane comprising an ethylene-tetrafluoroethylene copolymer,
The porous hollow fiber membrane comprises a first solvent;
The first solvent is composed of sebacic acid ester, citric acid ester, acetyl citric acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, fatty acid having 6 to 30 carbon atoms, and epoxidized vegetable oil. At least one selected,
A porous hollow fiber membrane in which the porous hollow fiber membrane has a three-dimensional network structure. The porous hollow fiber membrane further includes a second solvent different from the first solvent;
The second solvent is sebacic acid ester, citric acid ester, acetyl citrate ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, 6 to 30 carbon atoms. The porous hollow fiber membrane according to claim 1, which is at least one selected from the following fatty acids and epoxidized vegetable oils. A porous hollow fiber membrane comprising an ethylene-tetrafluoroethylene copolymer,
The porous hollow fiber membrane comprises a first solvent and a second solvent;
The first solvent is sebacic acid ester, citric acid ester, acetyl citric acid ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, 6 to 30 carbon atoms. And at least one selected from the following fatty acids and epoxidized vegetable oils:
Unlike the first solvent, the second solvent is sebacic acid ester, citrate ester, acetyl citrate ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphorus A porous hollow fiber membrane which is at least one selected from an acid ester, a fatty acid having 6 to 30 carbon atoms, and an epoxidized vegetable oil.   In the first mixed solution, in which the ratio of the ethylene-tetrafluoroethylene copolymer and the first solvent is 20:80, the temperature of the first mixed solution is set to The porous hollow fiber membrane according to claim 3, which is a non-solvent that does not dissolve the ethylene-tetrafluoroethylene copolymer uniformly in the first solvent even when the boiling point of the solvent is increased.   In the second mixed solution, in which the ratio of the ethylene-tetrafluoroethylene copolymer and the second solvent is 20:80, the temperature of the second mixed solution is higher than 25 ° C. The porous hollow fiber membrane according to claim 3 or 4, wherein the ethylene-tetrafluoroethylene copolymer is a solvent in which the ethylene-tetrafluoroethylene copolymer is uniformly dissolved in the second solvent at any temperature below the boiling point of the second solvent.   The second solvent is a second liquid mixture in which the ratio of the ethylene-tetrafluoroethylene copolymer and the second solvent is 20:80, and the temperature of the second liquid mixture is 25 ° C. The ethylene-tetrafluoroethylene copolymer is not uniformly dissolved in the second solvent, and the temperature of the second mixed solution is higher than 100 ° C. and lower than the boiling point of the second solvent. The porous hollow fiber membrane according to claim 5, wherein the tetrafluoroethylene copolymer is a poor solvent that is uniformly dissolved in the second solvent. A porous hollow fiber membrane comprising an ethylene-tetrafluoroethylene copolymer,
The porous hollow fiber membrane comprises a first solvent;
The first solvent is sebacic acid ester, citric acid ester, acetyl citrate ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, 6 to 30 carbon atoms. In the first mixed liquid of at least one selected from the following fatty acids and epoxidized vegetable oil, wherein the ratio of the ethylene-tetrafluoroethylene copolymer and the first solvent is 20:80, A porous hollow fiber membrane which is a non-solvent in which the ethylene-tetrafluoroethylene copolymer is not uniformly dissolved in the first solvent even if the temperature of the mixed solution of 1 is increased to the boiling point of the first solvent. The porous hollow fiber membrane includes a second solvent different from the first solvent;
The second solvent is sebacic acid ester, citric acid ester, acetyl citric acid ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, 6 to 30 carbon atoms. At least one selected from the following fatty acids and epoxidized vegetable oils:
In the second mixed liquid in which the ratio of the ethylene-tetrafluoroethylene copolymer and the second solvent is 20:80, when the temperature of the second mixed liquid is 25 ° C., the ethylene-tetrafluoroethylene copolymer The ethylene-tetrafluoroethylene copolymer is not uniformly dissolved in the second solvent, and the temperature of the second mixed solution is higher than 100 ° C. and lower than the boiling point of the second solvent. Is a poor solvent that uniformly dissolves in the second solvent.   The porous hollow fiber membrane according to any one of claims 1 to 8, wherein the porous hollow fiber membrane contains an inorganic substance.   The porous hollow fiber membrane according to claim 9, wherein the inorganic substance is at least one selected from silica, lithium chloride, and titanium oxide. A method for producing a porous hollow fiber membrane comprising an ethylene-tetrafluoroethylene copolymer,
Dissolving the ethylene-tetrafluoroethylene copolymer in a solvent containing at least a first solvent and a second solvent;
Separating the solution containing the dissolved ethylene-tetrafluoroethylene copolymer,
The first solvent is sebacic acid ester, citric acid ester, acetyl citric acid ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, 6 to 30 carbon atoms. In the first mixed liquid of at least one selected from the following fatty acids and epoxidized vegetable oil, wherein the ratio of the ethylene-tetrafluoroethylene copolymer and the first solvent is 20:80, 1 is a non-solvent in which the ethylene-tetrafluoroethylene copolymer is not uniformly dissolved in the first solvent even when the temperature of the mixed liquid 1 is increased to the boiling point of the first solvent.
The second solvent is sebacic acid ester, citric acid ester, acetyl citric acid ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, 6 to 30 carbon atoms. In the second mixed solution of at least one selected from the following fatty acids and epoxidized vegetable oil, wherein the ratio of the ethylene-tetrafluoroethylene copolymer and the second solvent is 20:80, 2 is a porous solvent in which the ethylene-tetrafluoroethylene copolymer is uniformly dissolved in the second solvent at a temperature higher than 25 ° C. and lower than the boiling point of the second solvent. A method for producing a hollow fiber membrane.   The second solvent is a second liquid mixture in which the ratio of the ethylene-tetrafluoroethylene copolymer and the second solvent is 20:80, and the temperature of the second liquid mixture is 25 ° C. The ethylene-tetrafluoroethylene copolymer is not uniformly dissolved in the second solvent, and the temperature of the second mixed solution is higher than 100 ° C. and lower than the boiling point of the second solvent. The method for producing a porous hollow fiber membrane according to claim 11, wherein the tetrafluoroethylene copolymer is a poor solvent that is uniformly dissolved in the second solvent.   The method for producing a porous hollow fiber membrane according to claim 11 or 12, wherein the phase separation step is liquid-liquid phase separation.