JP6920834B2 - Porous hollow fiber membrane and its manufacturing method - Google Patents

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 for sterilization operations of liquids to be treated, such as clean water treatment and sewage treatment, are becoming widespread. A heat-induced phase separation method is known as a method for producing a hollow fiber membrane used for membrane filtration.

In the heat-induced phase separation method, a thermoplastic resin and an organic liquid are used. The heat-induced phase separation method using a solvent that does not dissolve the thermoplastic resin at room temperature but dissolves at high temperature as the organic liquid, that is, a latent solvent (poor solvent), kneads the thermoplastic resin and the organic liquid at high temperature and heats them. This is a method in which a plastic resin is dissolved in an organic liquid and then cooled to room temperature to induce phase separation, and the organic liquid is further removed to produce a porous body. This method has the following advantages.
(A) A film can be formed even with a polymer such as polyethylene that does not have a suitable solvent that can be dissolved at room temperature.
(B) Since the film is formed by melting at a high temperature and then cooling and solidifying, when the thermoplastic resin is a crystalline resin, crystallization is promoted during the film formation and a high-strength film can be easily obtained.

Due to the above advantages, the heat-induced phase separation method is often used as a method for producing a porous membrane. However, in some crystalline resins, the film structure tends to be spherulite, and although the strength is high, the elongation is low and brittle, so that there is a problem in practical durability.
Conventionally, a technique for forming a film using a poor solvent of a thermoplastic resin selected from citric acid esters has been disclosed (see Patent Document 1).

Japanese Unexamined Patent Publication No. 2011-168741

However, the film produced by the method described in Patent Document 1 also has a problem that it has 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 chemical resistance and mechanical strength, and a method for producing the same.

According to 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. However, as a result of diligent studies, the present inventor has made ethylene as a thermoplastic resin. -It was found that a film having a three-dimensional network structure having excellent chemical resistance and mechanical strength can be produced by mixing at least one non-solvent with a solution using a chlorotrifluoroethylene copolymer. The present invention has been reached.

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-chlorotrifluoroethylene copolymer.
The porous hollow fiber membrane contains a first solvent and contains
The first solvent is sebacic acid ester, acetylcitrate ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, fatty acid having 6 to 30 carbon atoms, and At least one selected from epoxidized vegetable oils,
The porous hollow fiber membrane has a three-dimensional network structure.

The porous hollow fiber membrane further contains a second solvent that is 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, carbon number 6 or more and 30 or less. It is preferably at least one selected from the above fatty acids and 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-chlorotrifluoroethylene copolymer.
The porous hollow fiber membrane contains 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, carbon number 6 or more and 30 or less. At least one selected from the fatty acids and epoxidized vegetable oils of
Unlike the first solvent, the second solvent is a sebacic acid ester, a citric acid ester, an acetyl citric acid ester, an adipic acid ester, a trimellitic acid ester, an oleic acid ester, a palmitic acid ester, a stearic acid ester, and a phosphoric acid ester. , At least one selected from fatty acids having 6 or more and 30 or less carbon atoms, and epoxidized vegetable oils.

In the second porous hollow yarn film of the present invention, the first solvent is the first mixed solution of the ethylene-chlorotrifluoroethylene copolymer and the first solvent in a ratio of 20:80. It is preferable that the ethylene-chlorotrifluoroethylene copolymer is a non-solvent that does not uniformly dissolve in the first solvent even if the temperature of the mixed solution is raised to the boiling point of the first solvent.

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

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

The second solvent is a second mixed solution in which the ratio of the ethylene-chlorotrifluoroethylene copolymer to the second solvent is 20:80, and the temperature of the second mixed solution is 25 ° C. The fluoroethylene copolymer does not dissolve uniformly 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. It is preferable that the polymer is a poor solvent that is uniformly dissolved 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-chlorotrifluoroethylene copolymer.
The porous hollow fiber membrane contains a first solvent and contains
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, carbon number 6 or more and 30 or less. The first mixture in the first mixture, which is at least one selected from the ester of the ester and the epoxidized vegetable oil and in which the ratio of the ethylene-chlorotrifluoroethylene copolymer to the first solvent is 20:80. It is a non-solvent in which the ethylene-chlorotrifluoroethylene copolymer does not uniformly dissolve in the first solvent even when the temperature of the liquid is raised to the boiling point of 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 citric acid ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, carbon number 6 or more and 30 or less. At least one selected from the fatty acids and epoxidized vegetable oils of
In the second mixed solution in which the ratio of the ethylene-chlorotrifluoroethylene copolymer to the second solvent is 20:80, when the temperature of the second mixed solution is 25 ° C., the ethylene-chlorotrifluoroethylene copolymer is formed. The ethylene-chlorotrifluoroethylene copolymer is the second solvent at any temperature above 100 ° C. and below the boiling point of the second solvent, which does not dissolve uniformly in the second solvent. It is preferable that the solvent is a poor solvent that dissolves uniformly in the mixture.

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 a porous hollow fiber membrane of the present invention is
A method for producing a porous hollow fiber membrane containing an ethylene-chlorotrifluoroethylene copolymer.
A step of dissolving the ethylene-chlorotrifluoroethylene copolymer in a solvent containing at least a first solvent and a second solvent, and
It has a step of phase-separating a solution containing a dissolved ethylene-chlorotrifluoroethylene 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, carbon number 6 or more and 30 or less. The first mixture in the first mixture, which is at least one selected from the ester of the ester and the epoxidized vegetable oil and in which the ratio of the ethylene-chlorotrifluoroethylene copolymer to the first solvent is 20:80. It is a non-solvent in which the ethylene-chlorotrifluoroethylene copolymer does not uniformly dissolve in the first solvent even when the temperature of the liquid is raised 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, carbon number 6 or more and 30 or less. In a second mixture of at least one selected from the ester of the ester and the epoxidized vegetable oil, the ratio of the ethylene-chlorotrifluoroethylene copolymer to the second solvent is 20:80, the second mixture. It is preferable that the temperature of the liquid is higher than 25 ° C. and the ethylene-chlorotrifluoroethylene copolymer is uniformly dissolved in the second solvent at any temperature below the boiling point of the second solvent.

In the method for producing a porous hollow yarn film of the present invention, the second solvent is a second mixed solution in which the ratio of the ethylene-chlorotrifluoroethylene copolymer to the second solvent is 20:80. When the temperature of the mixed solution is 25 ° C, the ethylene-chlorotrifluoroethylene copolymer does not dissolve uniformly in the second solvent, and the temperature of the second mixed solution is higher than 100 ° C and below the boiling point of the second solvent. It is preferable that the ethylene-chlorotrifluoroethylene copolymer is a poor solvent in which the ethylene-chlorotrifluoroethylene copolymer is uniformly dissolved in the second solvent at such 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 is high, and the mechanical strength is 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 the comparative example.

Embodiments of the present invention will be described in detail. The present invention is not limited to the following embodiments.

<Pollous hollow fiber membrane>
Hereinafter, the porous hollow fiber membrane of the present invention will be described.
FIG. 1 schematically shows the outer surface of the porous hollow fiber membrane according to the present invention.
The porous hollow fiber membrane of the present invention contains an ethylene-chlorotrifluoroethylene copolymer as a thermoplastic resin. The outer surface of the porous hollow fiber membrane 10 shown in FIG. 1 has a three-dimensional network structure rather than a spherulite structure. By adopting a three-dimensional network structure, the tensile elongation at break is increased, and the resistance to alkalis (sodium hydroxide aqueous solution, etc.), which are often used as a film cleaning agent, is increased.

The porous hollow fiber membrane 10 may contain components (impurities, etc.) other than the ethylene-chlorotrifluoroethylene copolymer up to about 5% by mass. For example, the porous hollow fiber membrane contains a solvent used during production, and as will be described later, the porous hollow fiber membrane 10 contains at least a non-solvent (first solvent) used as a solvent during production, and further. It may contain a solvent or a poor solvent (second solvent). These solvents can be detected by thermal decomposition GC-MS (gas chromatography-mass spectrometry).

For example, the porous hollow fiber membrane (first porous hollow fiber membrane) of the present invention is a porous hollow fiber membrane containing an ethylene-chlorotrifluoroethylene copolymer, and the porous hollow fiber membrane is the first. The first solvent contains sebacic acid ester, acetylcitrate ester, adipic acid ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, and 6 or more carbon atoms. It is at least one selected from 30 or less fatty acids and epoxidized vegetable oils, and the porous hollow fiber membrane has a three-dimensional network structure.

Examples of fatty acids having 6 or more and 30 or less carbon atoms include capric acid, lauric acid, and oleic acid.
Examples of the epoxidized vegetable oil include epoxidized soybean oil and epoxidized flaxseed oil.

Further, the first porous hollow fiber membrane may further contain 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, carbon number 6 or more and 30 or less. It is preferably at least one selected from the above fatty acids and epoxidized vegetable oils.

The porous hollow fiber membrane (second porous hollow fiber membrane) of the present invention is a porous hollow fiber membrane containing an ethylene-chlorotrifluoroethylene copolymer.
The porous hollow fiber membrane contains 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, carbon number 6 or more and 30 or less. At least one selected from the fatty acids and epoxidized vegetable oils of
Unlike the first solvent, the second solvent is a sebacic acid ester, a citric acid ester, an acetyl citric acid ester, an adipic acid ester, a trimellitic acid ester, an oleic acid ester, a palmitic acid ester, a stearic acid ester, and a phosphoric acid ester. , At least one selected from fatty acids having 6 or more and 30 or less carbon atoms, and epoxidized vegetable oils.

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

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

The second solvent is a second mixed solution in which the ratio of the ethylene-chlorotrifluoroethylene copolymer to the second solvent is 20:80, and the temperature of the second mixed solution is 25 ° C. The fluoroethylene copolymer does not dissolve uniformly 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. It is more preferable that the polymer is a poor solvent that is uniformly dissolved in the second solvent.

The method for determining non-solvent, solvent, and 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 (third porous hollow fiber membrane) of the present invention is a porous hollow fiber membrane containing an ethylene-chlorotrifluoroethylene copolymer.
The porous hollow fiber membrane contains a first solvent and contains
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, carbon number 6 or more and 30 or less. The first mixture in the first mixture, which is at least one selected from the ester of the ester and the epoxidized vegetable oil and in which the ratio of the ethylene-chlorotrifluoroethylene copolymer to the first solvent is 20:80. It is a non-solvent in which the ethylene-chlorotrifluoroethylene copolymer does not uniformly dissolve in the first solvent even when the temperature of the liquid is raised to the boiling point of the first solvent.

Further, the third porous hollow yarn film may contain a second solvent different from the first solvent, and the second solvent is a sebacic acid ester, a citrate ester, an acetyl citrate ester, an adipic acid ester, and the like. At least one selected from trimellitic 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.
In the second mixed solution in which the ratio of the ethylene-chlorotrifluoroethylene copolymer to the second solvent is 20:80, when the temperature of the second mixed solution is 25 ° C., the ethylene-chlorotrifluoroethylene copolymer is formed. The ethylene-chlorotrifluoroethylene copolymer is the second solvent at any temperature above 100 ° C. and below the boiling point of the second solvent, which does not dissolve uniformly in the second solvent. It is preferable that the solvent is a poor solvent that dissolves uniformly in the mixture.

(Physical characteristics of porous hollow fiber membrane)
Next, the physical characteristics 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.

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

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

The surface aperture ratio (surface aperture ratio) 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 having an aperture ratio of 20% or more on the surface on the side in contact with the liquid to be treated for filtration, both deterioration of water permeability due to clogging and deterioration of water permeability due to scratching of the membrane surface are reduced, and filtration stability is improved. be able to. However, even if the aperture ratio is high, if the hole diameter is too large, the desired 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. When 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 when the pore diameter is 10 nm or more, sufficiently high water permeability can be ensured.

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 can be increased, while when the thickness is 1,000 μm or less, the pressure loss due to the film resistance can be reduced.

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, while when it is 80% or less, the mechanical strength is high.

As the shape of the porous hollow fiber membrane 10, an annular single-layer membrane can be mentioned, but a multilayer film having different pore diameters between the separation layer and the support layer that supports the separation layer may be used. Further, the outer surface and the inner surface may have an irregular cross-sectional structure such as having protrusions.

(Liquid to be treated)
The liquids to be treated by the porous hollow fiber membrane 10 are suspended water and process liquid. 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. The suspended water to be treated also includes treated water of natural water obtained by subjecting these natural waters to a sedimentation treatment, a sand filtration treatment, a coagulation sedimentation sand filtration treatment, an ozone treatment, an activated carbon treatment, or the like. An example of domestic wastewater is sewage. Sewage primary treated sewage that has been screen-filtered or settled, biologically treated sewage secondary treated water, and coagulated sedimentation sand filtration, activated carbon treatment, ozone treatment, etc. 3 Next-treated (highly treated) water is also included in the suspended water to be treated. These suspended waters contain turbid substances (such as rot colloids, organic colloids, clays, and bacteria) composed of fine organic substances, inorganic substances, and organic-inorganic mixtures on 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 generally be expressed by turbidity and organic matter concentration, which are typical water quality indicators, alone or in combination. When the water quality is classified by turbidity (average turbidity, not instantaneous turbidity), the major ones are low turbidity with turbidity of less than 1, medium turbidity with turbidity of 1 or more and less than 10, and highly turbid water with turbidity of 10 or more and less than 50. It can be classified into ultra-high turbid water with a turbidity of 50 or more. In addition, when the water quality is classified by organic matter concentration (total organic carbon concentration (Total Organic Carbon (TOC)): mg / L) (also an average value, not an instantaneous value), the water quality is largely low TOC water less than 1, 1. It can be classified into medium TOC water of 4 or more and less than 4, 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 of water, the easier it is to clog the filtration membrane. Therefore, the higher the turbidity or TOC of water, the greater the effect of using the porous hollow fiber membrane 10.

Process process liquid refers to the liquid to be separated when separating valuable and non-valuable resources in food, pharmaceutical, semiconductor manufacturing, and the like. In food production, for example, when separating alcoholic beverages such as sake and wine from yeast, the porous hollow fiber membrane 10 is used. In the production 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 separating the abrasive and water from the polishing wastewater.

<Manufacturing method of porous hollow fiber membrane 10>
Next, a method for producing the porous hollow fiber membrane 10 will be described. The method for producing a porous hollow fiber membrane consists of (a) a step of preparing a melt-kneaded product and (b) supplying the melt-kneaded product to a spinning nozzle having a multi-layer structure and extruding the melt-kneaded product from the spinning nozzle to extrude the hollow fiber. It includes a step of obtaining a film and (c) a step of extracting a 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 further preferably 30 to 45% by mass. When this value is 20% by mass or more, the mechanical strength is high, while when it is 60% by mass or less, the water permeability is high. The melt-kneaded product may contain additives.

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. Solvents include at least non-solvents, as described below.

As the extractant used in the step (c), it is preferable to use a liquid such as methylene chloride or various alcohols, which is insoluble in thermoplastic resins but has a high affinity with the plasticizer.

When a melt-kneaded product containing no additive is used, the hollow fiber membrane obtained through the step (c) may be used as the porous hollow fiber membrane 10. 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 that after step (c), (d) the additive is extracted and removed from the hollow fiber membrane to be porous. It is preferable to further include a step of obtaining the property hollow fiber membrane 10. As the extractant in the step (d), it is preferable to use hot water or a liquid that can dissolve the added additives such as acid and alkali but does not dissolve the thermoplastic resin.

Inorganic substances may be used as additives. The inorganic substance is preferably an 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, organic clay and the like, and 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 the analysis of electron micrographs. That is, first, a group of inorganic fine powders is pretreated by the method of ASTM D3849. Then, the diameters of 3000 to 5000 particles transferred to the transmission electron micrograph are measured, and these values are arithmetically averaged to calculate the primary particle size of the inorganic fine powder.

The material of the inorganic fine powder in the porous hollow fiber membrane can be determined 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 polyvinylpyrrolidone or polyethylene glycol. Further, the viscosity of the melt-kneaded product can be controlled by using a highly viscous additive such as glycerin or ethylene glycol.

Next, the details of (a) the step 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-chlorotrifluoroethylene copolymer.
A step of dissolving the ethylene-chlorotrifluoroethylene copolymer in a solvent containing at least a first solvent and a second solvent, and
It has a step of phase-separating a solution containing a dissolved ethylene-chlorotrifluoroethylene 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, carbon number 6 or more and 30 or less. The first mixture in the first mixture, which is at least one selected from the ester of the ester and the epoxidized vegetable oil and in which the ratio of the ethylene-chlorotrifluoroethylene copolymer to the first solvent is 20:80. It is a non-solvent in which the ethylene-chlorotrifluoroethylene copolymer does not uniformly dissolve in the first solvent even when the temperature of the liquid is raised 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, carbon number 6 or more and 30 or less. In a second mixture of at least one selected from the ester of the ester and the epoxidized vegetable oil, the ratio of the ethylene-chlorotrifluoroethylene copolymer to the second solvent is 20:80, the second mixture. It is preferable that the temperature of the liquid is higher than 25 ° C. and the ethylene-chlorotrifluoroethylene 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 mixed solution in which the ratio of the ethylene-chlorotrifluoroethylene copolymer to the second solvent is 20:80, and the temperature of the second mixed solution is 25 ° C. The fluoroethylene copolymer does not dissolve uniformly 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. It is preferable that the coalescence is a poor solvent that is uniformly dissolved in the second solvent.

The method for producing a porous hollow fiber membrane of the present invention uses a non-solvent of an ethylene-chlorotrifluoroethylene copolymer as a raw material. When a non-solvent is used as the raw material of the membrane in this way, a porous hollow fiber membrane having a three-dimensional network structure can be obtained. Although the mechanism of action is not always clear, it is considered that polymer crystallization is moderately inhibited and a three-dimensional network structure is likely to be formed by using a solvent in which a non-solvent is mixed and the solubility is lowered. .. For example, non-solvents, poor solvents, and solvents 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, etc. It is selected from fatty acids having 6 to 30 carbon atoms and epoxidized vegetable oils. More preferably, sebacic acid ester, acetylcitrate ester, adipate ester, trimellitic acid ester, oleic acid ester, palmitic acid ester, stearic acid ester, phosphoric acid ester, fatty acid having 6 to 30 carbon atoms, and epoxidation. At least one selected from vegetable oils.

A solvent that can dissolve an ethylene-chlorotrifluoroethylene copolymer at room temperature is a solvent, and a solvent that cannot be dissolved at room temperature but can be dissolved at a high temperature is a poor solvent for the ethylene-chlorotrifluoroethylene copolymer. A solvent that cannot be dissolved even at a high temperature is called a non-solvent, but in the present invention, a poor solvent and a non-solvent can be determined as follows.

The non-solvent raises the temperature of the first mixed solution to the boiling point of the first solvent in the first mixed solution in which the ratio of the ethylene-chlorotrifluoroethylene copolymer to the first solvent is 20:80. Is also a solvent in which the ethylene-chlorotrifluoroethylene copolymer is not uniformly dissolved in the first solvent.

Further, as the solvent, in the second mixed solution in which the ratio of the ethylene-chlorotrifluoroethylene copolymer to the second solvent is 20:80, the temperature of the second mixed solution is higher than 25 ° C. and the second solvent is used. It is a solvent in which the ethylene-chlorotrifluoroethylene copolymer is uniformly dissolved in the second solvent at any temperature below the boiling point of.

The poor solvent is a second mixed solution in which the ratio of the ethylene-chlorotrifluoroethylene copolymer to the second solvent is 20:80, and the temperature of the second mixed solution is 25 ° C. The fluoroethylene copolymer does not dissolve uniformly 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. A solvent in which the polymer is uniformly dissolved in the second solvent.

To determine whether it is a solvent, a poor solvent, or a non-solvent, specifically, about 2 g of an ethylene-chlorotrifluoroethylene copolymer and about 8 g of a solvent are put in a test tube, and the test tube block heater is used for 10 Warm the solvent to the boiling point in increments of ° C, mix the inside of the test tube with a spatula or the like, and judge by the solubility in the above temperature range.

The boiling points of specific examples of the above esters are as follows. Tributyl acetylcitrate has a boiling point of 343 ° C, dibutyl sebacate at 345 ° C, dibutyl adipate at 305 ° C, diisobutyl adipate at 293 ° C, and bis2-ethylhexyl adipate at 335 ° C. , Diisononyl adipate is 250 ° C. or higher, diethyl adipate is 251 ° C., triethyl citrate is 294 ° C., and triphenyl sulfite is 360 ° C.

For example, when an ethylene-chlorotrifluoroethylene copolymer is used as a thermoplastic resin and triethyl citrate is used as a solvent, it dissolves uniformly at about 200 ° C., and when triphenylphosphorous acid or oleic acid is used, it does not dissolve.

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

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto.

[Example 1]
The melt-kneaded product was extruded using a spinning nozzle having a double tube structure to obtain a porous hollow fiber membrane of Example 1. Ethylene-chlorotrifluoroethylene copolymer (ECTFE) resin (manufactured by Solvay Specialty Polymers, Hall 901) 40% by mass as thermoplastic resin, fine silica (primary particle size: 16 nm) 23% by mass, bis2-adipate as solvent A melt-kneaded product was prepared using ethylhexyl (DOA, boiling point 335 ° C.) of 4.1% by mass and triphenyl sulfic acid (TPP, boiling point of 360 ° C.) of 32.9% by mass .

The extruded hollow fiber-like molded product was allowed to pass through an idle distance of 120 mm and then solidified in water at 30 ° C. to prepare a porous hollow fiber membrane by a heat-induced phase separation method. It was picked up at a speed of 5 m / min and wound up in a skein. The obtained two-layer hollow filamentous extruded product was immersed in isopropyl alcohol to extract and remove the solvent. Subsequently, the hollow fiber membrane was replaced with water by immersing it in water for 30 minutes. Subsequently, the mixture 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 silica powder. The film structure showed a three-dimensional network structure as shown in FIG.

[Example 2]
A melt-kneaded product was prepared using diisononyl adipate (DINA, boiling point 250 ° C. or higher) 4.1% by mass instead of 4.1% by mass of bis2-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 membrane structure of the porous hollow fiber membrane showed a three-dimensional network structure as shown in FIG.

[Example 3]
Example 1 and Example 1 except that a melt-kneaded product was prepared using 32.9% by mass of oleic acid (boiling point 285 ° C.) instead of 32.9% by mass of triphenylphosphorous acid (TPP, boiling point 360 ° C.) as a solvent. Similarly, a porous hollow fiber membrane was produced.

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

[Comparative Example 1]
A hollow fiber membrane of Comparative Example 1 was obtained in the same manner as in Example 1 except that the solvent was only DOA. The membrane structure showed a spherulite structure as shown in FIG.

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

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

(2) Observation of Surface Aperture Ratio, Pore Diameter, and Pore Structure 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 at an acceleration voltage of 3 kV. The cross-section 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 by the numerical value "6", and further by binarization by a single threshold value, by "threshold value: 105". Thresholded. The aperture ratio of the film surface was determined by determining the occupied area of the pores in the binarized image thus obtained.

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

As for the film structure, the state of the film surface and the cross section photographed at 5000 times was observed, and the one without spherulites and the polymer stem expressing the network structure three-dimensionally was determined to be a three-dimensional network structure.

(3) Permeability After soaking in ethanol, one end of a wet hollow fiber membrane with a length of about 10 cm, which was repeatedly soaked in pure water several times, was sealed, and an injection needle was inserted into the hollow part at the other end, under an environment of 25 ° C. 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. bottom.
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.
The hollow fiber membrane was used as it was for the sample according to the method of JIS K7161.
Measuring equipment: Instron type tensile tester (AGS-5D manufactured by Shimadzu Corporation)
Distance between chucks: 5 cm
Tensile rate: 20 cm / min From the obtained results, the tensile elongation at break was calculated according to JIS K 7161.

(5) Permeability retention rate during suspension water filtration This is an index for determining the degree of deterioration of permeability performance due to clogging (fouling). After soaking in ethanol, the wet hollow fiber membrane, which was repeatedly soaked in pure water several times, was filtered by an external pressure method with a membrane effective length of 11 cm. ^{First, the pure water was filtered at a filtration pressure of 10 m 3} per day per 1 ^{m 2} of the outer surface area of the membrane, and the permeated water was collected for 2 minutes to obtain the initial amount of pure water permeated. Next, the surface water of the river (Fuji River surface water: turbidity 2.2, TOC concentration 0.8 ppm), which is a natural suspended water, is filtered for 10 minutes at the same filtration pressure as when the initial amount of pure water permeation was measured. The permeated water was collected for 2 minutes from the 8th minute to the 10th minute of the filtration, and used as the amount of water permeated during the filtration of the suspended 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
Outer membrane surface area [m ² ] = π × (thread outer diameter [m]) × (effective membrane length [m])
Membrane surface linear velocity [m / s] = 4 × (circulating water volume [m ³ / s]) / {π × (tube diameter [m]) ^2- π × (membrane outer diameter [m]) ² }

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

(6) Elongation retention rate after immersion in NaOH A wet porous hollow fiber membrane was cut to 10 cm, and 20 of them were immersed in 500 ml of a 4% sodium hydroxide aqueous solution and kept at 40 ° C. for 10 days. The tensile elongation at break of the film before and after immersion in sodium hydroxide was measured at n20, and the average value was calculated. The elongation retention rate was defined as 100 × (elongation after immersion) / (elongation before immersion), and the elongation retention rate after NaOH immersion was evaluated.

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

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

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

10 Porous hollow fiber membrane

Claims (3)

A method for producing a porous hollow fiber membrane containing an ethylene-chlorotrifluoroethylene copolymer.
A step of dissolving the ethylene-chlorotrifluoroethylene copolymer in a solvent containing at least a first solvent and a second solvent, and
It comprises a step of phase-separating the dissolved solution containing the ethylene-chlorotrifluoroethylene 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, carbon number 6 or more and 30. In a first mixture of at least one selected from the following fatty acids and epoxidized vegetable oils, wherein the ratio of the ethylene-chlorotrifluoroethylene copolymer to the first solvent is 20:80. Even if the temperature of the first mixed solution is raised to the boiling point of the first solvent, the ethylene-chlorotrifluoroethylene copolymer is a non-solvent that does not uniformly dissolve in 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, carbon number 6 or more and 30. In a second mixture of at least one selected from the following fatty acids and epoxidized vegetable oils, wherein the ratio of the ethylene-chlorotrifluoroethylene copolymer to the second solvent is 20:80. A solvent in which the ethylene-chlorotrifluoroethylene 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. A method for producing a porous hollow filament film. The second solvent is a second mixed solution in which the ratio of the ethylene-chlorotrifluoroethylene copolymer to the second solvent is 20:80, and the temperature of the second mixed solution is 25 ° C. The ethylene-chlorotrifluoroethylene copolymer does not dissolve uniformly in the second solvent, and the temperature of the second mixed solution is higher than 100 ° C. and at any temperature below the boiling point of the second solvent. the ethylene - producing method of chlorotrifluoroethylene copolymer according to claim 1, wherein a poor solvent for uniformly dissolved in the second solvent the porous hollow fiber membrane. The method for producing a porous hollow fiber membrane according to claim 1 or 2 , wherein the phase separation step is liquid-liquid phase separation.

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