JP2014200752A - Porous polymer membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous polymer membrane with suppressed coloration.SOLUTION: A porous polymer membrane comprises a fluoropolymer (A) having a vinylidene fluoride unit, and organic acid (B).

Description

The present invention relates to a polymer porous membrane.

In recent years, porous membranes have been used in various fields such as water treatment fields such as water purification and wastewater treatment, medical applications such as blood purification, food industry fields, etc., as well as charged membranes, battery separators, and fuel cells. Yes.

For example, in the field of water treatment such as water purification treatment and wastewater treatment, porous membranes are used to replace conventional sand filtration and coagulation sedimentation processes and improve the quality of treated water. In such a water treatment field, since the amount of treated water is large, it is required that the water permeability of the porous membrane is excellent. If the water permeation performance is excellent, the membrane area can be reduced, so the water purifier becomes compact and the equipment cost can be reduced.

Further, in the water purification treatment, the membrane may be washed with an alkaline solution or the like for chemical cleaning of the membrane, and the porous membrane is required to have chemical resistance. In recent years, porous films using fluoropolymers such as polyvinylidene fluoride resins as materials with high chemical resistance have been studied. At the same time, research to further improve the physical properties of fluoropolymers is also progressing.

For example, in a method of polymerizing vinylidene fluoride in an aqueous suspension medium with an oil-soluble free radical polymerization initiator in the presence of a suspending agent and a chain transfer agent, the chain transfer agent has 5 carbon atoms in the alkyl group. The following bis (alkyl) carbonate vinylidene fluoride polymerization method makes it possible to effectively adjust the molecular weight of the vinylidene fluoride polymer without adversely affecting the yield of the polymer. It is disclosed that a vinylidene fluoride polymer having thermal stability can be derived (see, for example, Patent Document 1).

In addition, polyvinylidene fluoride having an inherent viscosity of 0.5 to 2.0 dl / g produced by suspension polymerization is selected from among Ca, Ba, Zn, Mg hydroxide, carbonate or Sn, Al hydroxide. The composition containing 0.001 to 3% by weight of at least one selected inorganic compound does not decompose even if heated to a temperature higher than its melting point for a long time. It is disclosed that excellent products can be obtained (see, for example, Patent Document 2).

Furthermore, the object is a vinylidene fluoride resin composition having further improved thermal stability, in particular, coloring resistance in a low-temperature melting region (175 to 210 ° C.), and further excellent in low elution. Fluorination comprising 100 parts by weight of a vinylidene fluoride polymer having 55% or more of stable end groups and 0.01 to 0.1 parts by weight of at least one compound selected from hydroxides and oxides of magnesium and zinc A vinylidene resin composition is disclosed (for example, see Patent Document 3).

JP 59-174605 A Japanese Patent Publication No.44-19153 JP 2008-19377 A

When producing a porous membrane using a fluoropolymer, the fluoropolymer is added to an amine solvent such as dimethylacetamide and dimethylformamide, N-methyl-2-pyrrolidone, dimethylsulfoxide, etc. The raw material mixture may be dissolved, but at that time, the polymer solution may be colored, or the porous film made of fluoropolymer may be colored when immersed in an alkaline solvent. There was a problem of doing. And these coloring remained in the film finally obtained.

As a method for improving the physical properties of a fluoropolymer, a method of selecting an appropriate chain transfer agent as in Patent Document 1 or changing a polymer terminal to a stable terminal group as in Patent Document 3 is a polymer polymerization. Since it is necessary to change the method, it was difficult to say a simple method. In addition, as in Patent Document 2, the method of mixing an inorganic compound with a fluoropolymer has a low solubility of the inorganic compound in a polymer solution, and a porous membrane manufactured using the fluoropolymer is used for water purification. In cases where safety to the living body is to be considered, it is not very appropriate.
From these facts, there was room for further improvement in the production of a porous membrane using a fluoropolymer.

This invention is made | formed in view of the said present condition, and aims at providing the polymeric porous membrane by which coloring was suppressed.

The inventors of the present invention have found that the above-mentioned problems can be solved by making the polymer porous film composed of a fluoropolymer having a vinylidene fluoride unit and an organic acid, and have reached the present invention.
The polymer porous membrane of the present invention is obtained, for example, by adding an organic acid to a fluoropolymer, and thus can be obtained by a much simpler method than changing the polymerization method of the fluoropolymer, Moreover, it is more suitable than the method of adding an inorganic compound etc. also from a viewpoint of the safety | security to a biological body. Furthermore, the method of adding an organic acid to the fluoropolymer can be performed using a fluoropolymer whose terminal structure or chain transfer agent used at the time of polymerization is unknown. It can be said that it is a method.

That is, the present invention is a polymer porous membrane comprising a fluoropolymer (A) having a vinylidene fluoride unit and an organic acid (B).

The organic acid (B) is at least selected from the group consisting of acrylic acid, formic acid, citric acid, acetic acid, oxalic acid, lactic acid, pyruvic acid, malonic acid, propionic acid, maleic acid, citraconic acid, succinic acid and butyric acid One compound is preferable, and at least one compound selected from the group consisting of citric acid, malonic acid, maleic acid, and succinic acid is more preferable.

The fluoropolymer (A) is preferably a polyvinylidene fluoride or a copolymer containing a vinylidene fluoride unit and a tetrafluoroethylene unit and / or a chlorotrifluoroethylene unit.

The polymer porous membrane preferably further contains a hydrophilic polymer and / or a surfactant.

The polymer porous membrane is preferably a hollow fiber membrane.

The polymer porous membrane is preferably used for water treatment.

The present invention also provides a polymer porous membrane comprising a step of obtaining a mixture of a fluoropolymer (A) having a vinylidene fluoride unit and an organic acid (B), and a step of forming the mixture into a porous membrane. It is also a manufacturing method.

Since the porous polymer membrane of the present invention has the above-described configuration, coloring is suppressed.

FIG. 1 is a photograph showing the state of the polymer solution after stirring for 24 hours in Comparative Example 1 and Examples 1-5.

The present invention is described in detail below.

The porous polymer membrane of the present invention comprises a fluoropolymer (A) having a vinylidene fluoride unit and an organic acid (B). A porous polymer membrane made of a fluoropolymer having a vinylidene fluoride unit is produced by using a fluoropolymer (A) in a good solvent typified by dimethylacetamide, dimethylformamide, N-methyl-2-pyrrolidone, dimethylsulfoxide and the like. ), An alkali treatment step to be described later, or the membrane is washed with an alkaline solution for washing the membrane with a chemical solution, it will be colored brown. This is presumably because a dehydrofluorination reaction occurs in the vinylidene fluoride unit and a double bond is generated. Therefore, by using the organic acid (B) together with the fluoropolymer (A), the dehydrofluorination reaction is suppressed, and coloring of the porous film caused by the double bond can be suppressed.

The fluoropolymer (A) having a vinylidene fluoride unit has at least a constituent unit derived from vinylidene fluoride in the constituent unit, and is a polyvinylidene fluoride or a copolymer having a vinylidene fluoride unit. .

The polyvinylidene fluoride may be in a form in which all the structural units are other vinylidene fluoride units in addition to the form in which all the structural units are vinylidene fluoride units, but the proportion of the vinylidene fluoride units in the total structural units is 90 mol. % Is preferably exceeded. More preferably, it is 92 mol% or more, More preferably, it is 95 mol% or more.

Other structural units that may be contained in the polyvinylidene fluoride include hexafluoropropylene units, chlorotrifluoroethylene units, perfluorovinyl ether units, vinyl alcohol units, vinyl ester monomer units, and unsaturated carboxylic acid ester monomers. Examples include units.

The weight average molecular weight of the polyvinylidene fluoride is preferably 50,000 to 1,000,000 from the viewpoint of mechanical strength and processability of the polymer porous membrane.
The weight average molecular weight can be determined by gel permeation chromatography (GPC).

Examples of the copolymer having a vinylidene fluoride unit include a copolymer containing a vinylidene fluoride unit and a tetrafluoroethylene unit such as a vinylidene fluoride / tetrafluoroethylene copolymer, and a vinylidene fluoride / chlorotrifluoroethylene copolymer. Copolymers containing vinylidene fluoride units and chlorotrifluoroethylene units such as polymers, copolymers containing vinylidene fluoride units and hexafluoropropylene units such as vinylidene fluoride / hexafluoropropylene copolymers, etc. Can be mentioned. From the viewpoint of mechanical strength and alkali resistance, a copolymer containing a vinylidene fluoride unit and a tetrafluoroethylene unit and / or a chlorotrifluoroethylene unit is preferable, and a vinylidene fluoride / tetrafluoroethylene copolymer is particularly preferable.

From the viewpoint of film formability and alkali resistance, the vinylidene fluoride / tetrafluoroethylene copolymer has a molar ratio of vinylidene fluoride units and tetrafluoroethylene units (vinylidene fluoride units / tetrafluoroethylene units) of 50 to 99 / It is preferable that it is 50-1. Examples of such a polymer include Neoflon VT50, VP50, VT100, VP100, VP101, and VP100X manufactured by Daikin Industries, Ltd. The vinylidene fluoride / tetrafluoroethylene copolymer preferably has a vinylidene fluoride unit / tetrafluoroethylene unit in a molar ratio of 50 to 90/50 to 10, more preferably 50 to 85/50 to 15. Further preferred. Especially preferably, it is 60-85 / 40-15. When the tetrafluoroethylene unit is 10 mol% or more, the dehydrofluorination reaction caused by the alkali treatment is easily suppressed, and when the tetrafluoroethylene unit is 15 mol% or more, the alkali resistance is drastically improved. In addition to vinylidene fluoride / tetrafluoroethylene copolymer consisting of only vinylidene fluoride units and tetrafluoroethylene units, vinylidene fluoride / tetrafluoroethylene copolymers include vinylidene fluoride units and tetrafluoroethylene units. In addition, a terpolymer having other structural units such as a hexafluoropropylene unit, a chlorotrifluoroethylene unit, a perfluorovinyl ether unit, a vinyl alcohol unit, and a vinyl ester monomer unit may be used as long as the characteristics are not impaired.
In addition, when the said vinylidene fluoride / tetrafluoroethylene copolymer further has other structural units in addition to the vinylidene fluoride units and tetrafluoroethylene units, the vinylidene fluoride units and tetrafluoroethylene units in all the structural units The total ratio is preferably 80 mol% or more, and more preferably 85 mol% or more. More preferably, it is 90 mol% or more, Most preferably, it is 97 mol% or more.

From the viewpoint of film formability and alkali resistance, the vinylidene fluoride / chlorotrifluoroethylene copolymer has a molar ratio of vinylidene fluoride units to chlorotrifluoroethylene units (vinylidene fluoride units / chlorotrifluoroethylene units) of 50. It is preferable that it is -99 / 50-1, and it is more preferable that it is 60-99 / 40-1. In addition to vinylidene fluoride / chlorotrifluoroethylene copolymer consisting only of vinylidene fluoride units and chlorotrifluoroethylene units, vinylidene fluoride / chlorotrifluoroethylene copolymers include vinylidene fluoride units and chlorotriethylene. In addition to fluoroethylene units, terpolymers having other structural units such as hexafluoropropylene units, tetrafluoroethylene units, perfluorovinyl ether units, vinyl alcohol units, vinyl ester monomer units, etc., as long as the properties are not impaired. Good.
When the vinylidene fluoride / chlorotrifluoroethylene copolymer further includes other structural units in addition to the vinylidene fluoride units and chlorotrifluoroethylene units, the vinylidene fluoride units and chlorotriethylene occupying the total structural units. The total proportion of fluoroethylene units is preferably 80 mol% or more, and more preferably 85 mol% or more.

The weight average molecular weight of the copolymer having a vinylidene fluoride unit is preferably 10,000 or more from the viewpoint of mechanical strength and film formability. More preferably, it is 50000-1 million, More preferably, it is 100000-900000.
The weight average molecular weight can be determined by gel permeation chromatography (GPC).

The fluoropolymer (A) preferably further has a unit represented by the following formula (1) (hereinafter also referred to as a unit of the formula (1)).
—CHX ¹ —CX ² (OR) — (1)
(In the formula, ^one of X ¹ and X ² is a hydrogen atom and the other is a fluorine atom, and R is either a hydrogen atom or an alkyl group having 1 to 8 carbon atoms).
When the said fluoropolymer (A) has the said Formula (1) unit, the polymeric porous membrane of this invention will be excellent by water permeability.

R in the above formula (1) may be either a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, but is preferably hydrogen, a methyl group or an ethyl group. In this case, the water permeability of the polymer porous membrane is greatly improved.
Moreover, when the said fluoropolymer (A) has two or more units of said Formula (1), R of each unit may be the same and may differ.
Hereinafter, in the present specification, the fluoropolymer (A) having the unit of the formula (1) is also referred to as a fluoropolymer (A1), and the polyvinylidene fluoride having the unit of the formula (1) is referred to as polyvinylidene fluoride ( The copolymer having a vinylidene fluoride unit having a1) and the above formula (1) unit is also referred to as a copolymer (b1) having a vinylidene fluoride unit.

In the polyvinylidene fluoride (a1), the constituent ratio of each unit of the vinylidene fluoride unit and the unit represented by the above formula (1) (vinylidene fluoride unit / formula (1) unit) is a molar ratio. 80.00 to 99.99 / 0.01 to 20.00.
In this case, the polyvinylidene fluoride (a1) has both excellent hydrophilicity and excellent mechanical strength at a high level.

In the copolymer (b1) having the vinylidene fluoride unit, the constituent ratio of each unit of the vinylidene fluoride unit, tetrafluoroethylene and chlorotrifluoroethylene units, and the unit represented by the above formula (1) Vinylidene chloride unit / tetrafluoroethylene and chlorotrifluoroethylene unit / unit of formula (1)) in a molar ratio of 30.00 to 84.99 / 15.00 to 50.00 / 0.01 to 20.00. Preferably there is.
In this case, the copolymer (b1) having the vinylidene fluoride unit has both excellent hydrophilicity and excellent mechanical strength at a high level.

The organic acid (B) is at least selected from the group consisting of acrylic acid, formic acid, citric acid, acetic acid, oxalic acid, lactic acid, pyruvic acid, malonic acid, propionic acid, maleic acid, citraconic acid, succinic acid and butyric acid A single compound is preferred. From the viewpoint of suppression of coloration of the polymer porous membrane, easy availability, and biosafety, it is more preferably at least one compound selected from the group consisting of citric acid, malonic acid, maleic acid and succinic acid. .

The content ratio of the fluoropolymer (A) and the organic acid (B) in the polymer porous membrane of the present invention is 99.99: 0.01 to 80.00: 20.00 (weight ratio). Is preferred. When the content ratio of the fluoropolymer (A) and the organic acid (B) is within such a range, coloring of the polymer porous membrane can be sufficiently suppressed, and the strength of the polymer porous membrane can be reduced. No damage. The content ratio of the fluoropolymer (A) to the organic acid (B) is more preferably 99.95: 0.05 to 85.00: 15.00, still more preferably 99.90: 0.10. 90.00: 10.00.

Even if the polymer porous membrane of the present invention is partially composed of the fluoropolymer (A) and the organic acid (B), the whole is composed of the fluoropolymer (A) and the organic acid (B). It may be.
The polymer porous membrane may be composed of a fluoropolymer (A) containing a fluoropolymer (A1) and an organic acid (B), and the surface thereof is composed of the fluoropolymer (A1) and an organic acid. (B) is preferable.
This is because in this case, the polymer porous membrane is extremely excellent in water permeability.

As will be described later, the porous polymer membrane of the present invention may be subjected to a specific alkali treatment step from the viewpoint of improving hydrophilicity.

When a part of the polymer porous membrane is made of the fluoropolymer (A1), the ratio of the fluoropolymer (A1) to the whole fluoropolymer (A) is 0.01 to 99% by weight. preferable.

The porous polymer membrane of the present invention may be substantially composed only of the fluoropolymer (A) and the organic acid (B), or in addition to the fluoropolymer (A) and the organic acid (B). Further, it may contain other resins.

However, even when the polymer porous membrane of the present invention contains other resins, from the viewpoint of mechanical strength and alkali resistance, the fluoropolymer (A) and the organic acid (B) are added to the entire polymer porous membrane. The content is preferably 40% by weight or more, more preferably 60% by weight or more, and still more preferably 80% by weight or more.

As said other resin, a thermoplastic resin is mentioned, for example. A thermoplastic resin is a resin that deforms or flows by an external force when heated.
Examples of the thermoplastic resin include polyethylene resin, polypropylene resin, acrylic resin, polyacrylonitrile, acrylonitrile-butadiene-styrene (ABS) resin, polystyrene resin, acrylonitrile-styrene (AS) resin, vinyl chloride resin, polyethylene terephthalate. , Polyamide resin, polyacetal resin, polycarbonate resin, modified polyphenylene ether resin, polyphenylene sulfide resin, polyamideimide resin, polyetherimide resin, polysulfone resin, polyethersulfone resin, and mixtures and copolymers thereof. Other resins miscible with these may be mixed.

The thermoplastic resin is preferably at least one selected from the group consisting of polyethylene resins, polypropylene resins, and acrylic resins because of its high chemical resistance.

The polyethylene resin is a resin made of an ethylene homopolymer or an ethylene copolymer. The polyethylene resin may be composed of a plurality of types of ethylene copolymers. Examples of the ethylene copolymer include a copolymer of ethylene and one or more selected from linear unsaturated hydrocarbons such as propylene, butene and pentene.

The polypropylene resin is a resin made of a propylene homopolymer or a propylene copolymer. The polypropylene resin may be composed of a plurality of types of propylene copolymers. Examples of the propylene copolymer include a copolymer of propylene and one or more selected from linear unsaturated hydrocarbons such as ethylene, butene, and pentene.

The acrylic resin is a polymer compound mainly including a polymer such as acrylic acid, methacrylic acid and derivatives thereof such as acrylamide and acrylonitrile. Particularly preferred are acrylic ester resins and methacrylic ester resins.

When the polymer porous membrane of the present invention is composed of the fluoropolymer (A), the organic acid (B) and the other resin, the polymer porous membrane is adjusted by adjusting the type and amount of the other resin. Strength, water permeability, blocking performance, etc. can be adjusted.

From the viewpoint of hydrophilization, the viewpoint of phase separation control, and the viewpoint of improving mechanical strength, the polymer porous membrane of the present invention is further composed of polyvinylpyrrolidone, polymethyl methacrylate resin, polyethylene oxide, polyvinyl alcohol, polyacetic acid. Hydrophilic polymers such as vinyl, polyethylene vinyl alcohol, polypropylene glycol, polyacrylic acid; inorganic components such as silica fine particles, titanium oxide fine particles, activated carbon fine particles, calcium carbonate, montmorillonite; glycerin, polyoxyethylene sorbitan fatty acid ester (for example, monostearin) Acid polyoxyethylene sorbitan, polyoxyethylene coconut oil fatty acid sorbitan, monooleic acid polyoxyethylene sorbitan, monolauric acid polyoxyethylene sorbitan, monopalmitic acid polyoxyethylene sol It may contain additives such as; Tan, etc.), polyoxyethylene fatty acid esters (e.g. polyethylene glycol monostearate, surfactants such as monooleate polyethylene glycol monolaurate polyethylene glycol phosphate, etc.); polytetrafluoroethylene.
Among them, it is also one of preferred embodiments of the present invention that the porous polymer membrane of the present invention further contains a hydrophilic polymer and / or a surfactant.

The porous polymer membrane of the present invention preferably has a pore size of 2 nm to 1.0 μm, and more preferably 5 nm to 0.5 μm. If the pore diameter is too small, the gas or liquid permeability may be insufficient, and if the pore diameter is too large, the blocking performance may be lowered, or the mechanical strength may be lowered and the glass may be easily damaged.
The pore diameter is measured by taking a photograph of the surface of the porous polymer membrane at a magnification at which the pores can be clearly confirmed using an SEM or the like, and measuring the diameter of the pores. In the case of an elliptical hole, the diameter of the pore can be obtained by (a × b) ^0.5, where a is the minor axis and b is the major axis. Further, a rough pore diameter can be obtained from the fine particle rejection rate. That is, for example, a polymer porous film that blocks 95% or more of polystyrene fine particles of 50 nm or more is considered to have a pore diameter of 50 nm or less.

The porous polymer membrane of the present invention preferably has a pure water permeability coefficient of 1.0 × 10 ⁻¹⁰ m ³ / m ² / s / Pa or more, and 2.0 × 10 ⁻¹⁰ m ³ / m ^2. / S / Pa or more is more preferable. The upper limit of the pure water permeability coefficient is not particularly limited, but a higher value is desirable as long as the target solid substance removal rate and strength are maintained.
The pure water permeability coefficient can be determined by pressurizing ion-exchanged water to 0.01 MPa or more with a pump or nitrogen at a temperature of 25 ° C., and filtering the produced porous polymer membrane. Specifically, it is a value obtained from the following formula.
Pure water permeability coefficient = (permeated water amount) / (membrane area) / (permeation time) / (evaluation pressure)

The polymer porous membrane of the present invention preferably has a fine particle rejection of 100 nm or 50 nm of 90% or more, and more preferably 95% or more. The porous polymer membrane of the present invention can further control the pore size according to the size of the substance to be blocked. For example, when a 200 nm substance is to be removed, the 200 nm fine particles are 95%. What is necessary is just to be able to remove above.
The fine particle blocking rate is a value obtained by filtering a dispersion solution obtained by diluting polystyrene latex fine particles having a controlled particle size to about 100 ppm with ion-exchanged water as an evaluation stock solution, and calculating the following formula.
Fine particle rejection (%) = {((Evaluation stock solution absorbance) − (Transmission solution absorbance)) / (Evaluation stock solution absorbance)} × 100

From the viewpoint of mechanical strength, the polymer porous membrane of the present invention preferably has a maximum point breaking strength of 0.5 MPa or more, and more preferably 0.6 MPa or more.
The maximum point breaking strength is a value obtained by measuring the breaking strength of a test piece under the conditions of a distance between chucks of 20 mm and a tensile speed of 20 mm / min and using a cross-sectional area before a tensile test as a unit measurement area.

From the viewpoint of mechanical strength, the polymer porous membrane of the present invention preferably has a maximum point elongation of 120% or more, and more preferably 150% or more.
The maximum point elongation is a value obtained by measuring the breaking strength of a test piece under the conditions of a distance between chucks of 20 mm and a tensile speed of 20 mm / min, and from the elongation of the maximum point with reference to 20 mm between the chucks.

The structure of the polymer porous membrane of the present invention is not particularly limited. For example, a three-dimensional network structure in which the solid content spreads in a three-dimensional network, or a spherical structure in which a large number of spherical or nearly spherical solid components are connected directly or via a streaky solid content. Etc. Moreover, you may have both these structures.

The polymer porous membrane of the present invention is preferably a flat membrane or a hollow fiber membrane, and more preferably a hollow fiber membrane from the viewpoint of the unit area and the amount of treated water per unit volume.

When the polymer porous membrane of the present invention is a flat membrane, the thickness of the polymer porous membrane is preferably 10 μm to 1 mm, and more preferably 30 μm to 500 μm.

When the polymer porous membrane of the present invention is a hollow fiber membrane, the inner diameter of the hollow fiber membrane is preferably 100 μm to 10 mm, more preferably 150 μm to 8 mm. The outer diameter of the hollow fiber membrane is preferably 120 μm to 15 mm, more preferably 200 μm to 12 mm.
The film thickness of the porous polymer membrane of the present invention is preferably 20 μm to 3 mm, more preferably 50 μm to 2 mm. Moreover, although the hole diameter of the inner and outer surfaces of the hollow fiber membrane can be freely selected depending on the application, it is preferably in the range of 2 nm to 1.0 μm, more preferably 5 nm to 0.5 μm.

The polymer porous membrane of the present invention is suitable as a microfiltration membrane or ultrafiltration membrane used for water treatment such as drinking water production, water purification treatment, wastewater treatment in the form of a hollow fiber membrane, a flat membrane, a membrane filter, etc. Can be used. Moreover, in the ultrapure water production field, it can also be used as a charged porous membrane for enhancing ion exclusion and increasing the purity of the obtained pure water. The polymer porous membrane of the present invention is preferably a polymer porous membrane for water treatment because of its high permeation performance of the treatment liquid.

The porous polymer membrane of the present invention is also suitably used in the medical field, food field, battery field and the like.

In the medical field, the membrane of the present invention is used as a blood purification membrane for the purpose of removing blood waste, particularly blood dialysis to substitute for renal function, blood filtration, blood filtration dialysis, etc. A molecular porous membrane can be used.

In the food field, the polymer porous membrane of the present invention can be used for the purpose of separating and removing yeasts used for fermentation and concentrating liquids.

In the battery field, the polymer porous membrane of the present invention can be used as a separator for a battery so that the electrolytic solution can permeate but a product generated by a battery reaction cannot permeate, or as a base material of a polymer solid electrolyte. it can.

In addition, it can be suitably used as an oil absorbing material, a porous bearing, a filter and the like.

The polymer porous membrane of the present invention can of course be used as it is as a porous membrane for the above-mentioned applications, but it is integrated with other porous substrates and porous resin members made of other resins. (Composite membrane) may be used.
Here, examples of the other resin include the thermoplastic resins described above.

Specifically, for example, when used as a flat membrane, the surface of the porous substrate may be coated with the polymer porous membrane of the present invention, or the porous substrate and the polymer porous membrane of the present invention may be used. It may be a laminate of layers made of a porous film. Further, a porous substrate, a layer made of the polymer porous membrane of the present invention, and the porous resin member may be laminated in any order.
Also, when used in a hollow fiber membrane, a porous coating layer made of the above-mentioned other resin is formed on the surface (inner surface and / or outer surface) of the porous polymer membrane of the present invention which is a hollow fiber membrane. May be integrated.

Examples of the porous substrate include woven fabrics, knitted fabrics, and nonwoven fabrics made of organic fibers such as polyester fibers, nylon fibers, polyurethane fibers, acrylic fibers, rayon fibers, cotton, and silk. Moreover, the textile fabric, knitted fabric, or nonwoven fabric which consists of inorganic fibers, such as glass fiber and a metal fiber, is also mentioned. From the viewpoint of stretchability and cost, a porous substrate made of organic fibers is preferable.
The pore diameter on the surface of the porous substrate can be freely selected depending on the application, but is preferably 5 nm to 1.0 μm, more preferably 8 nm to 0.5 μm.

Next, the manufacturing method of the polymeric porous membrane of this invention is demonstrated.
The porous polymer membrane of the present invention is manufactured by performing at least a step of forming a porous membrane on a mixture of a fluoropolymer (A) having a vinylidene fluoride unit and an organic acid (B). Can do. Thus, the production of a polymer porous membrane comprising the steps of obtaining a mixture of a fluoropolymer (A) having a vinylidene fluoride unit and an organic acid (B), and molding the mixture into a porous membrane. The method is also one aspect of the present invention.

First, a method for producing a fluoropolymer (A) having a vinylidene fluoride unit will be described.
The fluoropolymer (A) can be produced by a conventionally known method. For example, it can be produced by a polymerization method such as solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization or the like, but it is preferably produced by emulsion polymerization or suspension polymerization in terms of industrial implementation.

In the above polymerization, a polymerization initiator, a surfactant, a chain transfer agent, and a solvent can be used, and conventionally known ones can be used.

The solvent may be appropriately determined depending on the polymerization method, and examples thereof include water, a mixed solvent of water and alcohol, and a fluorine-containing solvent.

As said polymerization initiator, an oil-soluble radical polymerization initiator, a water-soluble radical polymerization initiator, etc. can be used, for example.

As the surfactant, a known surfactant can be used. For example, a nonionic surfactant, an anionic surfactant, a cationic surfactant, or the like can be used. Among these, a fluorine-containing anionic surfactant is preferable, and ether-bonded oxygen may be contained (that is, an oxygen atom may be inserted between carbon atoms). A linear or branched fluorine-containing anionic surfactant having 4 to 20 carbon atoms is more preferred.

Examples of the chain transfer agent include hydrocarbons such as ethane, isopentane, n-hexane and cyclohexane; aromatics such as toluene and xylene; ketones such as acetone; acetates such as ethyl acetate and butyl acetate; Examples include alcohols such as methanol and ethanol; mercaptans such as methyl mercaptan; halogenated hydrocarbons such as carbon tetrachloride, chloroform, methylene chloride, and methyl chloride. The amount added may vary depending on the size of the chain transfer constant of the compound used, but is usually used in the range of 0.001 to 10% by mass with respect to the polymerization solvent.

It does not specifically limit as polymerization temperature, It may be 0-100 degreeC. The polymerization pressure is appropriately determined according to other polymerization conditions such as the type, amount and vapor pressure of the solvent to be used, the polymerization temperature, etc., but may usually be 0 to 9.8 MPaG.

Although the said fluoropolymer (A) can be manufactured by such a method, the said fluoropolymer (A) may be a commercial item.
Examples of the commercially available fluoropolymer (A) include, for example, Kureha Corporation KF1000 series, KF7000 series, Solvay Solef6000 series, Solef1000 series, Daikin Kogyo Neoflon VP800 series, VT50, VP50, VT100, VP100, VP101, VP100X, etc. are mentioned.

The manufacturing method of this invention includes the process of obtaining the mixture of the said fluoropolymer (A) and organic acid (B). Here, the mixture may further contain another resin; inorganic fine particles; organic liquid; a solvent such as a good solvent, a poor solvent, or a non-solvent; an additive.
Examples of the other resin include resins other than the fluoropolymer (A) that can be contained in the porous polymer membrane of the present invention described above. The solvent and additive will be described later.
In addition, it is preferable that the compounding ratio of fluoropolymer (A) and organic acid (B) in the said mixture is 99.99: 0.01-80.00: 20.00 (weight ratio). When the blending ratio of the fluoropolymer (A) and the organic acid (B) is within such a range, it is possible to obtain a polymer porous membrane that is sufficiently suppressed in coloring and does not impair strength. The blending ratio of the fluoropolymer (A) and the organic acid (B) is more preferably 99.95: 0.05 to 85.00: 15.00, still more preferably 99.90: 0.10 to 90. 0.00: 10.00.

The production method of the present invention includes a step of forming the mixture into a porous membrane. The porous membrane forming step can be performed by various methods, for example, a phase separation method, a melt extraction method, a steam Solidification method, stretching method, etching method, method of forming a porous film by sintering a polymer sheet, method of obtaining a porous film by crushing a bubbled polymer sheet, a method of using electrospinning, etc. A molding method can be used.

In the melt extraction method, in addition to the fluoropolymer (A) and the organic acid (B), a mixture containing inorganic fine particles and an organic liquid is melt-kneaded, and the mixture is melted at a temperature equal to or higher than the melting point of the fluoropolymer (A). This is a method of forming a porous structure by extruding or molding with a press machine or the like and then solidifying by cooling and then extracting an organic liquid and inorganic fine particles.

In the vapor coagulation method, in addition to the fluoropolymer (A) and the organic acid (B), at least one surface of a thin film made of a mixture containing a good solvent is compatible with the good solvent and has a fluoropolymer ( This is a method of forcibly supplying a vapor containing a saturated solvent or mist of a poor solvent that does not dissolve A) and the organic acid (B).

As the molding method, a phase separation method is preferable because the pore size can be easily controlled. Examples of the phase separation method include a thermally induced phase separation method (TIPS) and a non-solvent induced phase separation method (NIPS).
Since a three-dimensional network structure is relatively easy to produce, a porous membrane produced by a non-solvent induced phase separation method has a high mechanical strength and is suitably used for producing a membrane having an asymmetric structure. Porous membranes produced by the thermally induced phase separation method tend to be excellent in water permeability since a spherical structure is relatively easy to form, and the fluoropolymer (A) in the mixture at the time of film formation and organic The mechanical strength can be improved by increasing the total concentration with the acid (B). It is preferable to select a film formation method in consideration of these.

When using the thermally induced phase separation method, a step of dissolving the fluoropolymer (A) and the organic acid (B) in a solvent that is a poor solvent or a good solvent at a relatively high temperature to obtain a mixture, and the mixture A porous film can be obtained by passing through the step of cooling and solidifying. Thus, the process of obtaining the mixture by dissolving the fluoropolymer (A) having the vinylidene fluoride unit and the organic acid (B) in a solvent that is a poor solvent or a good solvent at a relatively high temperature, and the mixture A method for producing a porous polymer membrane comprising a step of cooling and solidifying to obtain a porous membrane is also one preferred embodiment of the present invention.

In addition to the fluoropolymer (A) and the organic acid (B), the mixture containing the solvent becomes a uniform one-phase liquid when it is maintained at a temperature higher than the temperature called cloud point (cloud point). However, phase separation occurs below the cloud point, it separates into two phases, a concentrated phase of the fluoropolymer (A) and the organic acid (B) and a solvent concentrated phase, and when the temperature falls below the crystallization temperature, the polymer matrix is fixed, A porous membrane is formed.

When the thermally induced phase separation method is used, the total content of the fluoropolymer (A) and the organic acid (B) in the mixture is preferably 10 to 60% by weight. More preferably, it is 15 to 50% by weight.
By adjusting the total concentration of the fluoropolymer (A) and the organic acid (B) to an appropriate range, the viscosity of the mixture can be adjusted to an appropriate range. If the viscosity of the mixture is not within an appropriate range, there is a possibility that it cannot be formed into a porous membrane.

The poor solvent cannot dissolve the fluoropolymer (A) and the organic acid (B) at 5% by weight or more at a temperature of less than 60 ° C., but it is at least 60 ° C. and the melting point of the resin (the melting point of the fluoropolymer (A)). Or, when the above mixture contains another resin, it is a solvent that can be dissolved by 5% by weight or less below the melting point of the melting point of the fluoropolymer (A) and the other resin, whichever is lower. Say. A solvent that can dissolve 5% by weight or more of the fluoropolymer (A) and the organic acid (B) at a temperature lower than 60 ° C. with respect to the poor solvent is referred to as a good solvent. A solvent that does not dissolve or swell the fluoropolymer (A) and the organic acid (B) up to the melting point of the resin or the boiling point of the liquid is referred to as a non-solvent.

In the case of the above mixture, examples of the poor solvent include medium chains such as cyclohexanone, isophorone, γ-butyrolactone, methyl isoamyl ketone, dimethyl phthalate, diethyl phthalate, propylene glycol methyl ether, propylene carbonate, diacetone alcohol, and glycerol triacetate. Examples include long alkyl ketones, esters, glycol esters, organic carbonates, and the like, and mixed solvents thereof. Diphenyl carbonate, methyl benzoate, diethylene glycol ethyl acetate, benzophenone, and the like are also included. In addition, even if it is a mixed solvent of a non-solvent and a poor solvent, the solvent which satisfy | fills the definition of the said poor solvent is a poor solvent.
When the thermally induced phase separation method is used, a poor solvent is preferable as the solvent contained in the mixture. However, the solvent is not limited to this, and a good solvent is used in consideration of the phase separation behavior of the fluoropolymer (A) and the organic acid (B). In some cases.

Examples of the good solvent include N-methyl-2-pyrrolidone, dimethyl sulfoxide, dimethylacetamide, dimethylformamide, methyl ethyl ketone, acetone, tetrahydrofuran, tetramethylurea, trimethyl phosphate, and other lower alkyl ketones, esters, amides, and the like. A mixed solvent is mentioned.

Examples of the non-solvent include water, hexane, pentane, benzene, toluene, methanol, ethanol, propanol, carbon tetrachloride, o-dichlorobenzene, trichloroethylene, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butylene. Aliphatic hydrocarbons such as glycol, pentanediol, hexanediol, low molecular weight polyethylene glycol, aromatic hydrocarbons, aliphatic polyhydric alcohols, aromatic polyhydric alcohols, chlorinated hydrocarbons, or other chlorinated organic liquids and The mixed solvent etc. are mentioned.

When the thermally induced phase separation method is used, in the step of obtaining the above mixture, it is preferable to dissolve the fluoropolymer (A) and the organic acid (B) in a solvent that is a poor solvent or a good solvent at 20 to 220 ° C. More preferably, it is 30-200 degreeC. When dissolved at a relatively high temperature, the total concentration of the fluoropolymer (A) and the organic acid (B) can be increased, thereby increasing the mechanical porosity of the polymer porous membrane produced through a subsequent process. Strength can be imparted.
When the said density | concentration is too high, the porosity of the polymer porous membrane obtained may become small, and there exists a possibility that water permeability performance may fall. Moreover, if the viscosity of the prepared mixture is not within an appropriate range, the porous membrane may not be formed.

As a method for cooling and solidifying the mixture, for example, a method of discharging the mixture from a die into a cooling bath containing a cooling liquid is preferable. Moreover, when manufacturing a flat polymer porous membrane, the method of casting and immersing in a cooling bath is also mentioned as a preferable method.

The cooling liquid that can be used in the cooling bath has a temperature lower than that of the mixture, for example, a solvent that is a poor solvent or a good solvent having a temperature of 5 to 50 ° C. and a concentration of 60 to 100% by weight. Can be used. The cooling liquid may be a non-solvent or a non-solvent containing a poor solvent or a good solvent.

In the step of obtaining the porous film, the total concentration of the fluoropolymer (A) and the organic acid (B) in the mixture, the composition of the solvent that dissolves the fluoropolymer (A) and the organic acid (B), cooling The composition of the cooling liquid that makes up the bath is important. By adjusting these compositions, it is also possible to control the porous structure of the polymer porous membrane that is completed through a subsequent process.

For example, by changing the combination of the composition of the mixture and the composition of the cooling liquid on one side and the other side of the porous membrane, the structure of one side of the polymer porous membrane and the other side The structure can be different.

When producing by a non-solvent induced phase separation method, a step of obtaining a mixture by dissolving the fluoropolymer (A) and the organic acid (B) in a solvent, and immersing the mixture in a coagulation bath containing the non-solvent A porous film can be obtained by passing through the process of performing. Thus, a step of obtaining a mixture by dissolving the fluoropolymer (A) having vinylidene fluoride units and the organic acid (B) in a solvent, and immersing the mixture in a coagulation bath containing a non-solvent. A method for producing a porous polymer membrane including a step of obtaining a porous membrane is also one preferred embodiment of the present invention.

As a method for immersing the mixture in a coagulation bath containing a non-solvent, for example, a method of discharging the mixture from a die into a coagulation bath containing a non-solvent is preferable. By immersing the mixture in a coagulation bath containing a non-solvent, non-solvent-induced phase separation can be caused by using the concentration gradient of the mixture and the solvent in the coagulation bath and the non-solvent as a driving force. According to this method, a dense skin layer is first formed on the outer surface where phase separation occurs due to substitution between a solvent and a non-solvent, and the phase separation phenomenon proceeds toward the inside of the membrane with the passage of time. As a result, it is also possible to manufacture an asymmetric membrane in which the pore diameter continuously increases toward the inside of the membrane following the skin layer.

In the case of using the non-solvent induced phase separation method, the mixture is preferably composed of a solvent in addition to the fluoropolymer (A) and the organic acid (B). In addition to the fluoropolymer (A), the organic acid (B) and the solvent, the mixture is preferably composed of a non-solvent.
The mixture is based on the sum of fluoropolymer (A), organic acid (B), solvent and non-solvent (if the non-solvent is not included, the sum of fluoropolymer (A), organic acid (B) and solvent) The total content of the fluoropolymer (A) and the organic acid (B) is preferably 5 to 35% by weight. More preferably, it is 10 to 25% by weight.
In the mixture, the non-solvent is preferably 0.1 to 10% by weight based on the total of the fluoropolymer (A), the organic acid (B), the solvent and the non-solvent. More preferably, it is 0.5 to 8% by weight.
By adjusting the total concentration of the fluoropolymer (A) and the organic acid (B) in the mixture to an appropriate range, the viscosity of the mixture can be adjusted to an appropriate range. If the viscosity of the mixture is not within an appropriate range, there is a possibility that it cannot be formed into a porous membrane.

The above mixture may be at room temperature or heated. For example, 10-35 degreeC is preferable.

In the non-solvent induced phase separation method, the solvent exemplified in the thermally induced phase separation method can be used as the solvent. The solvent may be a poor solvent or a good solvent, but a good solvent is preferred.
As the non-solvent, the non-solvent exemplified in the thermally induced phase separation method can be used.

The coagulation liquid that can be used as the coagulation bath is preferably solidified using a liquid containing a non-solvent, and may contain a poor solvent or a good solvent. As the non-solvent, the non-solvent exemplified in the thermally induced phase separation method can be used. For example, water can be suitably used as the non-solvent.

In the step of obtaining this porous membrane, the thermally induced phase separation method and the non-solvent induced phase separation method may be used in combination.

In the non-solvent induced phase separation method and / or the thermally induced phase separation method, a porous film is formed by discharging a mixture in which a fluoropolymer (A) and an organic acid (B) are dissolved in a solvent and then solidifying the mixture. Can be obtained. As the base, for example, a slit base, a double pipe base, a triple pipe base, or the like is used.

When producing a hollow fiber membrane as the porous membrane, for example, a double tube die or a triple tube die for spinning a hollow fiber membrane is preferably used.

When using a double-tube base, discharge the above mixture from the outer pipe of the double-tube base, and solidify in a coagulation bath or cooling bath while discharging hollow part forming fluid such as ion exchange water from the inner pipe. By doing so, a hollow fiber membrane can be obtained.

As the hollow portion forming fluid, gas or liquid can be usually used. In the thermally induced phase separation method, a liquid containing a poor solvent or a good solvent having a concentration of 60 to 100% by weight similar to the cooling liquid can be preferably used, but a non-solvent or a non-solvent containing a poor solvent or a good solvent is used. May be used. In the non-solvent induced phase separation method, the above-mentioned non-solvent is preferably used as the hollow portion forming fluid, and for example, water such as ion-exchanged water is preferable. Moreover, the non-solvent mentioned above may contain a poor solvent and a good solvent.

A hollow fiber membrane having two types of structures can also be formed by changing the composition of the hollow portion forming fluid and the cooling liquid or coagulating liquid. The hollow portion forming fluid may be supplied after cooling, but if the hollow fiber membrane is solidified only by the cooling power of the cooling bath, the hollow portion forming fluid may be supplied without cooling. .

The triple tube type die is suitable when two types of resin solutions are used. For example, a hollow fiber membrane can be obtained by discharging two types of mixture from an outer tube and an intermediate tube of a triple tube die and solidifying in a coagulation bath or a cooling bath while discharging a hollow portion forming liquid from an inner tube. It can be. In addition, the above mixture is discharged from the outer tube of the triple tube type die, the resin solution made of resin other than fluoropolymer is discharged from the intermediate tube, and the solidification bath or cooling is performed while discharging the hollow portion forming fluid from the inner tube. By solidifying in a bath, a hollow fiber membrane can be obtained.

As described above, when the hollow fiber membrane is formed by the production method using the double tube type die or the triple tube type die, the amount of the solidification liquid or the cooling liquid may be less than that in the case of producing the flat membrane. It is preferable in that it can be performed.

When the polymer porous membrane to be produced is a hollow fiber membrane, the layer made of the fluoropolymer (A) or the fluoropolymer (A) is further formed on the outer surface or inner surface of the hollow fiber membrane obtained by the above method. You may form the resin layer which consists of resin other than.
When a resin layer made of a resin other than the fluoropolymer (A) is formed, the resin layer made of another resin is integrated on the surface of the polymer porous film made of the fluoropolymer (A) and the organic acid (B). A hollow fiber membrane can be obtained.

The resin layer can be formed by applying a solution of fluoropolymer (A) or a resin solution to the outer surface or inner surface of the hollow fiber membrane. As a method of applying the fluoropolymer (A) solution or the resin solution, a method of immersing the hollow fiber membrane in the solution or dropping the solution onto the hollow fiber membrane is preferably used. As a method for applying the solution to the inner surface of the hollow fiber membrane, a method of injecting the solution into the hollow fiber membrane is preferably used.
As a method for controlling the coating amount of the solution, in addition to the method for controlling the coating amount of the solution itself, the porous membrane is immersed in the solution, or after the solution is applied to the porous membrane, A method in which a part is scraped off or blown off using an air knife is also preferably used.

Moreover, when manufacturing a flat film as a porous film, it can also manufacture by casting the said mixture and immersing it in a cooling bath or a coagulation bath. Moreover, it can manufacture also by discharging the said mixture to a cooling bath or a coagulation bath using a slit nozzle | cap | die.

In the case of producing a composite membrane in which a porous substrate or the like is integrated as the polymer porous membrane of the present invention, a method of immersing the porous substrate in the above mixture, on at least one surface of the porous substrate. You may perform the process of apply | coating the said mixture.

Moreover, after obtaining a porous film, this film may be further stretched. Thereby, the water permeation performance and mechanical strength of the polymer porous membrane can be further improved.
In addition, when performing the alkali treatment process mentioned later, you may perform an extending | stretching process after performing an alkali treatment process.

In this step, as a method for controlling the pore size of the porous membrane, for example, an additive for controlling the pore size is added to the above mixture and added when molding the porous membrane or after molding the porous membrane. A method of controlling the pore diameter by eluting the agent can be employed. Moreover, you may make an additive remain in a porous membrane as needed from a viewpoint of a hydrophilic improvement or a mechanical strength improvement.

Examples of the additive include organic compounds and inorganic compounds. As an organic compound, it is preferable that it is what is melt | dissolved in the solvent contained in a mixture. Further, it is preferable that the non-solvent induced phase separation method dissolves in the non-solvent contained in the coagulating liquid, and the thermally induced phase separation method dissolves in the solvent contained in the cooling liquid.

Examples of the organic compound include hydrophilic polymers such as polyvinyl pyrrolidone, polyethylene glycol, polyvinyl alcohol, polyethylene imine, polyacrylic acid, and textlan, surfactants, glycerin, and saccharides.

As the inorganic compound, a water-soluble compound is preferably used, and examples thereof include calcium chloride, lithium chloride, and barium sulfate.

As a method for controlling the pore size of the porous membrane without using additives, it is also possible to adopt a method of controlling the average pore size on the surface by controlling the phase separation rate according to the type, concentration and temperature of the non-solvent in the coagulation liquid. It is. In general, when the phase separation rate is high, the average pore size on the surface is small, and when the phase separation rate is low, the average pore size is large. Moreover, adding a non-solvent to the mixture is also effective for controlling the phase separation rate.

From the viewpoint of hydrophilization, mechanical strength improvement, and phase separation control, the above mixture is further polyvinyl pyrrolidone, polymethyl methacrylate resin, polyethylene oxide, polyvinyl alcohol, polyvinyl acetate, polyethylene vinyl alcohol, Hydrophilic polymers such as polypropylene glycol and polyacrylic acid; inorganic components such as silica fine particles, titanium oxide fine particles, activated carbon fine particles, calcium carbonate and montmorillonite; glycerin, polyoxyethylene sorbitan fatty acid ester (for example, polyoxyethylene sorbitan monostearate, Polyoxyethylene coconut oil fatty acid sorbitan, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate), It may contain additives such as; polyoxyethylene fatty acid esters (e.g. polyethylene glycol monostearate, monooleate polyethylene glycol monolaurate polyethylene glycol phosphate, etc.) surfactants such as, polytetrafluoroethylene.

By passing through such a process, in the manufacturing method of the polymeric porous membrane of this invention, the porous polymeric membrane which consists of the said fluoropolymer (A) and organic acid (B) can be manufactured.

In the method for producing a porous polymer membrane of the present invention, a step of performing an alkali treatment may be further performed.
Here, the step of performing the alkali treatment may be performed after the step of forming the mixture into a porous film, or may be performed before the step of forming the mixture into a porous film.

In the step of performing the alkali treatment (hereinafter also referred to as an alkali treatment step), the porous membrane is immersed in an alkali treatment solution in which a solid or liquid alkali is dissolved in water and / or an alcohol having 1 to 8 carbon atoms. The alkaline treatment solution is applied to the porous membrane, for example, by bringing the alkaline treatment solution into contact with the porous membrane.

Examples of the alkali include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkali carbonates such as potassium carbonate, alkaline earth metal hydroxides such as magnesium hydroxide and calcium hydroxide, and alkali metals. Alternatively, alkaline earth metal alkoxides, organic amines such as trimethylamine, triethylamine, and the like can be given.

Although it will not specifically limit as said alcohol if it is C1-C8 alcohol, Ethanol or methanol is preferable.

The alkali concentration of the alkali treatment solution is not particularly limited. For example, when sodium hydroxide is used as the alkali, an alkali treatment solution of 0.01 to 8N may be used.

When the alkali treatment solution contains both water and the alcohol, the volume ratio between them is arbitrary, but is preferably about 30 to 70/70 to 30, for example.

In this step, when the porous membrane is immersed in the alkaline treatment solution, the immersion time and the immersion temperature are not particularly limited, but it is usually sufficient to immerse in a solution at 5 to 70 ° C. for several minutes to several days. .

In the method for producing a porous polymer membrane of the present invention, the porous membrane may be subjected to a wet treatment prior to the alkali treatment step. In particular, when the porous film or the fluoropolymer (A) and the organic acid (B) to be subjected to alkali treatment are difficult to wet, the wet treatment makes it easy to wet the alkali treatment solution.
The wet treatment may be performed, for example, by immersing an alkali treatment target in an alcohol such as methanol or ethanol and then substituting it with water.

Moreover, after the alkali treatment step, the alkali treatment solution may be replaced with water as necessary.

Further, in the method for producing a porous polymer membrane of the present invention, as described above, after performing the step of subjecting the mixture to the alkali treatment by the method described above, the step of forming the porous membrane may be performed. .
Furthermore, after performing the process which performs the alkali treatment with the method mentioned above with respect to the said mixture, the process shape | molded to a porous membrane may be performed, and the alkali treatment process may be performed again after that.

In the method for producing a porous polymer membrane of the present invention, through the alkali treatment step, a part of the vinylidene fluoride unit of the fluoropolymer (A) is obtained by dehydrofluorination and addition of water or alcohol. A polymer porous membrane comprising a fluoropolymer (A) containing the fluoropolymer (A1) and an organic acid (B) substituted with the unit of the formula (1) can be obtained. And since the number of double bonds in the fluoropolymer (A) is small, the solvent solubility is not impaired and the film-forming property is excellent, and deterioration after film formation hardly occurs, so that it is excellent as a polymer porous film. Become.

An example of a preferred embodiment of the method for producing a porous polymer membrane of the present invention is a fluoropolymer (A) having a vinylidene fluoride unit, an organic acid (B), a good solvent, and optionally hydrophilic. Examples include a step of obtaining a mixture by mixing a polymer and a surfactant and a step of obtaining a porous film by immersing the mixture in a coagulation bath containing a non-solvent.

EXAMPLES Hereinafter, although an Example is hung up and demonstrated in more detail about this invention, this invention is not limited only to these Examples.
In the following examples, a polymer solution and a polymer porous membrane were prepared and evaluated by the following method.

[Measurement of UV-visible absorption spectrum]
The absorbance of the polymer solution was determined from the UV-visible absorption spectrum. The ultraviolet-visible absorption spectrum was measured using an ultraviolet-visible spectrophotometer (UV-vis Spectrophotometer U-3310 (manufactured by Hitachi High-Technologies Corporation)). The cell was a 1 cm square quartz cell, and the blank measurement was performed with a dimethylacetamide (DMAc) solution.

[F ^- Ion concentration measurement]
The F ⁻ ion concentration of the polymer solution was measured by using an ion analyzer (Expandable Analyzer Analyzer EA940 (manufactured by ORION)) after diluting the polymer solution 10 times with pure water and using the supernatant as a sample.

[Comparative Example 1]
In a screw tube, 0.300 g of polyvinylidene fluoride and 9.700 g of dimethylacetamide were mixed at 25 ° C. to obtain a polymer solution. After stirring for 24 hours, the polymer solution was clear and brown (FIG. 1). Further, when the UV-visible absorption spectrum of the polymer solution was measured, the absorbance at 350 nm was 0.279, and the absorbance at 450 nm was 0.100. The F ⁻ ion concentration of the polymer solution was 4.63 ppm.
The obtained polymer solution was coated on a glass plate using an applicator (250 μm), and immediately immersed in a water coagulation bath at 25 ° C. for 5 minutes to obtain a flat polymer porous membrane. The obtained polymer porous membrane was brown.

[Example 1]
A screw tube was mixed with 0.300 g of polyvinylidene fluoride, 0.012 g of maleic acid and 9.700 g of dimethylacetamide at 25 ° C. to obtain a polymer solution. After stirring for 24 hours, the polymer solution was colorless and transparent (FIG. 1). When the UV-visible absorption spectrum of the polymer solution was measured, the absorbance at 350 nm was 0.014, and the absorbance at 450 nm was 0.006, which was significantly lower than that of Comparative Example 1 and was almost zero. The F ⁻ ion concentration of the polymer solution was 0.28 ppm, which was significantly lower than that of Comparative Example 1, and it was found that desorption of F ⁻ ions (HF) was suppressed.
The obtained polymer solution was coated on a glass plate using an applicator (250 μm), and immediately immersed in a water coagulation bath at 25 ° C. for 5 minutes to obtain a flat polymer porous membrane. The resulting polymer porous membrane was colorless and was not colored.

[Example 2]
A screw tube was mixed with 0.300 g of polyvinylidene fluoride, 0.014 g of malonic acid, and 9.700 g of dimethylacetamide at 25 ° C. to obtain a polymer solution. After stirring for 24 hours, the polymer solution was colorless and transparent (FIG. 1). When the UV-visible absorption spectrum of the polymer solution was measured, the absorbance at 350 nm was 0.008, and the absorbance at 450 nm was 0.007, which was significantly lower than that of Comparative Example 1 and almost zero. The F ⁻ ion concentration of the polymer solution was 0.53 ppm, which was significantly lower than that of Comparative Example 1, and it was found that desorption of F ⁻ ions (HF) was suppressed.
The obtained polymer solution was coated on a glass plate using an applicator (250 μm), and immediately immersed in a water coagulation bath at 25 ° C. for 5 minutes to obtain a flat polymer porous membrane. The resulting polymer porous membrane was colorless and was not colored.

Example 3
A screw tube was mixed with 0.300 g of polyvinylidene fluoride, 0.016 g of succinic acid, and 9.691 g of dimethylacetamide at 25 ° C. to obtain a polymer solution. After stirring for 24 hours, the polymer solution was colorless and transparent (FIG. 1). When the UV-visible absorption spectrum of the polymer solution was measured, the absorbance at 350 nm was 0.015, and the absorbance at 450 nm was 0.006, which was significantly lower than that of Comparative Example 1 and was almost zero. F of the polymer solution ^- ion concentration is 1.43Ppm, significantly lower than in Comparative Example 1, F ^- desorption of ions (HF) was found to have been suppressed.
The obtained polymer solution was coated on a glass plate using an applicator (250 μm), and immediately immersed in a water coagulation bath at 25 ° C. for 5 minutes to obtain a flat polymer porous membrane. The resulting polymer porous membrane was colorless and was not colored.

Example 4
In a screw tube, 0.300 g of polyvinylidene fluoride, 0.014 g of citric acid, and 9.690 g of dimethylacetamide were mixed at 25 ° C. to obtain a polymer solution. After stirring for 24 hours, the polymer solution was colorless and transparent (FIG. 1). When the UV-visible absorption spectrum of the polymer solution was measured, the absorbance at 350 nm was 0.003, and the absorbance at 450 nm was 0.007, which was significantly lower than that of Comparative Example 1 and almost zero. The F ⁻ ion concentration of the polymer solution was 0.47 ppm, which was significantly lower than that of Comparative Example 1, and it was found that desorption of F ⁻ ions (HF) was suppressed.
The obtained polymer solution was coated on a glass plate using an applicator (250 μm), and immediately immersed in a water coagulation bath at 25 ° C. for 5 minutes to obtain a flat polymer porous membrane. The resulting polymer porous membrane was colorless and was not colored.

Example 5
In a screw tube, 0.300 g of polyvinylidene fluoride, 0.017 g of maleic acid, 0.379 g of Tween 40, and 9.330 g of dimethylacetamide were mixed at 25 ° C. to obtain a polymer solution. After stirring for 24 hours, the polymer solution was colorless and transparent (FIG. 1). When the UV-visible absorption spectrum of the polymer solution was measured, the absorbance at 350 nm was 0.034, and the absorbance at 450 nm was 0.008, which was significantly lower than that of Comparative Example 1 and was almost zero. The F ⁻ ion concentration of the polymer solution was 0.35 ppm, which was significantly lower than that of Comparative Example 1, and it was found that desorption of F ⁻ ions (HF) was suppressed.
The obtained polymer solution was coated on a glass plate using an applicator (250 μm), and immediately immersed in a water coagulation bath at 25 ° C. for 5 minutes to obtain a flat polymer porous membrane. The resulting polymer porous membrane was colorless and was not colored.

a: Polymer solution after stirring for 24 hours in Comparative Example 1 b: Polymer solution after stirring for 24 hours in Example 1 c: Polymer solution after stirring for 24 hours in Example 2 d: After stirring for 24 hours in Example 3 Polymer solution e: Polymer solution after stirring for 24 hours in Example 4 f: Polymer solution after stirring for 24 hours in Example 5

Claims (8)

A polymer porous film comprising a fluoropolymer (A) having a vinylidene fluoride unit and an organic acid (B). The organic acid (B) is at least one selected from the group consisting of acrylic acid, formic acid, citric acid, acetic acid, oxalic acid, lactic acid, pyruvic acid, malonic acid, propionic acid, maleic acid, citraconic acid, succinic acid and butyric acid. 2. The polymer porous membrane according to claim 1, which is a seed compound. The porous polymer membrane according to claim 1 or 2, wherein the organic acid (B) is at least one compound selected from the group consisting of citric acid, malonic acid, maleic acid and succinic acid. The fluoropolymer (A) is a polyvinylidene fluoride or a copolymer containing a vinylidene fluoride unit and a tetrafluoroethylene unit and / or a chlorotrifluoroethylene unit. Polymer porous membrane. Furthermore, the polymeric porous membrane in any one of Claims 1-4 containing a hydrophilic polymer and / or surfactant. It is a hollow fiber membrane, The polymeric porous membrane in any one of Claims 1-5. The polymer porous membrane according to any one of claims 1 to 6, which is used for water treatment. A method for producing a polymer porous membrane comprising a step of obtaining a mixture of a fluoropolymer (A) having a vinylidene fluoride unit and an organic acid (B), and a step of forming the mixture into a porous membrane.