JPS6097001A - Polyvinylidene fluoride porous membrane and its preparation - Google Patents

Abstract

PURPOSE:To obtain a membrane useful for industrial and medical purposes in uniform constitution, by using a polymer based on polyvinilidene fluoride having a fine open cell reticulated structure formed thereto. CONSTITUTION:A film forming stock solution consists of 5-35wt% of polyvinyliden fluoride, good and poor solvents therefor and 2-30wt% of a water soluble polymer. As the good solvent, N-methyl-2-pyrrolidone, DMA and DMF are pref. used and, as the poor solvent, there are acetone, MEK or cyclohexanone and, as the water soluble polymer, polyether and polyvinyl pyrrolidone are pref. This film forming stock solution is cast while the separation of a coagulated phase is allowed to advance in the open air or steam-containing gas and the formed film is immersed in a washing bath comprising a liquid capable of dissolving and removing three components other than polyvinylidene fluoride such as water for 5min or less to prepare a membrane. By this method, II-type crystal constitution as shown by the drawing is formed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applicable to industrial operations such as precision filtration, ultrafiltration, concentration of aqueous solutions, substance separation, etc., and medical applications such as filtration type artificial kidneys and plasma separation. The present invention relates to a suitable polyvinylidene fluoride porous membrane.

[Prior art]

In recent years, porous membranes have been used in the production of ultrapure water for the electronics industry, etc., industrial wastewater treatment such as paper pulp wastewater, separation and purification in the sugar manufacturing industry, blood purification and removal such as filtration-type artificial kidneys, plasma separation, and plasma albumin recovery. It has been used in industrial and medical separation and purification techniques such as precision filtration for bacteria and depyrogenization.

For such purposes, cellulose ester-based, polycarbonate-based, and polypropylene-based porous membranes have conventionally been used. Known methods for producing porous membranes include a solvent evaporation dry method, a microphase separation wet method, a film stretching method, an additive extraction method, and a knitting method after irradiation. However, the polymer material, porous membrane structure, and stability thereof, particularly in terms of permeability, mechanical strength, heat resistance, and solvent resistance, are not always satisfied.

From this point of view, polydifluoride-based resins, which have excellent properties in terms of mechanical strength, heat resistance, and solvent resistance, have attracted attention, and several techniques have been disclosed regarding porous membranes thereof. JP-A-54-16383 discloses a wet film forming method using a single solvent solution. Japanese Unexamined Patent Publication 1973-
No. 66935, JP-A No. 55-69267 and JP-A No. 5
No. 5-99304 discloses a method of adding a surfactant to a membrane forming stock solution, but in both cases a non-solvent is used for coagulation, so the unconfined porous membrane has a skin layer. Japanese Patent Publication No. 56-5
No. 6202 is a hollow porous membrane having a skin layer and a capo-3-layer and includes macrovoids.

With these methods, it is difficult to obtain a membrane with uniform pores, and since the membrane contains macrovoids inside, there is a problem in mechanical strength. JP-A No. 58-91808 discloses a method of forming a membrane by adding water-insoluble alcohol, JP-A No. 58-93734 or hydrophilic inorganic fine powder, and then extracting them to obtain a porous membrane. However, special operations are required for extraction, and there is a risk that additives may remain in the membrane as foreign matter. JP-A-58-91731 discloses a manufacturing method in which a porous membrane having no asymmetric structure is coagulated in an aqueous solution containing 20% or more of a solvent.

Polyvinylidene fluoride is rapidly converted into plasma due to its regular molecular structure and cohesive force, and even with these conventional techniques, it is quite difficult to obtain a uniform porous membrane without an asymmetric structure. Furthermore, since polynylidene fluoride is extremely hydrophobic, it has the disadvantage that the membrane is difficult to wet during separation operations of aqueous solutions.

[Object and structure of the invention]

4- In view of this situation, we have made use of the excellent properties of polyvinylidene fluoride to create a porous membrane with a uniform structure and impart hydrophilicity to obtain a membrane useful for industrial and medical purposes. As a result of intensive research, we have completed the present invention.

That is, the present invention is a porous membrane made of a polymer mainly composed of polyvinylidene fluoride, in which the aggregates of the polymer form a network structure having interconnected pores, and the aggregates are The porous membrane has a crystal structure and is substantially non-oriented, and the pores on the surface of the porous membrane form a repeating pore group or a planar network structure, and the average pore diameter is 0.05 to 1.
0 μ, and the pores in the continuous mesh structure are polyhedral and communicate with each other, and the porosity is 60 to 9.
5% polyvinylidene fluoride porous membrane. Furthermore, the present invention provides a polymer mainly composed of polyvinylidene fluoride, a membrane forming stock solution prepared from the polymer, cast, solidified, and then the good solvent, the poor solvent, and the water-soluble polymer removed in a cleaning bath. This is a method for producing a porous polyvinylidene fluoride membrane.

The present invention will be explained in detail below. The polymer aggregate mainly composed of polyvinylidene fluoride may be only polyvinylidene fluoride, or may be a copolymer in which polyvinylidene fluoride substantially accounts for the majority, or a blend.

Further, a part of the water-soluble polymer added during production may remain in the mixture or on the surface. The hydrophilicity of the membrane is improved by the residual trace amount of water-soluble polymer. There are three crystal modifications of polyvinylidene fluoride, and the film of the present invention has the -type crystal structure, which is thermodynamically the most stable. This is one condition for imparting heat resistance, especially heat resistance to film properties.

Regarding the crystal structure and stability, there are the following documents.

fil R9Haseoawa etai,,Poly
u+er J, 3°(5), 591 (1972).

[2J R, Haseoawa etai;, Poly
mer' J, β-2(5), 600 (1972
).

[3) ・Y, Takahashi and H,
Tadokoro.

Macromolecules, 13. 1317
(1980) The membranes of the present invention are also substantially unoriented.

When a water film is stretched, its pores and network structure are deformed, so that it does not function as a porous film, and its crystal form transforms into a thermally unstable (2) type.

In the membrane of the present invention, the pores on the surface form (a>repetitive pore group (Fig. 1 (a)) or (b) a planar network structure [Fig. 1 (b)]). The pore diameter is 0.05 to 10μ. Figure 1 (ce) shows typical scanning electron micrographs of the membrane surface of the present invention. The average pore diameter is the average diameter determined by a scanning electron microscope. The average pore size is 0.
．． If the number of porous membranes is less than 0.05μ-500, the characteristics of the porous membrane targeted by the present invention cannot be exhibited. Further, when the average pore diameter is 10 μm or more, this corresponds to a pinhole defect in the membrane, and naturally the membrane function and formation cannot be maintained. In the membrane of the present invention, the pores in the communicating network structure are polyhedral and communicate with each other [Scheme 2 (a>). This polyhedron is formed by the growth of a dilute polymer layer when the membrane-forming stock solution unique to the present invention undergoes solidification phase separation after casting, and is replaced with water in the coagulation bath and water washing bath, and the vacancies in the membrane are It became a hole.

On the other hand, the thick polymer phase is concentrated on the faces and twills of these polyhedra, and finally forms polymer aggregates at the interfaces and twills of the polyhedra. It is necessary that at least communicating pores exist at the interface, and this allows the membrane to function as a porous membrane for molecular purposes and precision filtration. Depending on the film forming conditions, if most of the boundary surfaces of the polyhedron become communicating pores, the polymer aggregates will concentrate on the twills and form a network structure within the bone tracts. Typical scanning electron micrographs of the membrane of the invention are shown in FIG. 2(b)(C). In addition, the porosity of the entire pores in the continuous network structure is 60
~95%. The porosity was calculated using the following formula (1).

Here is the measured density of polyvinylidene fluoride ■ type crystal sample 1
．． 89/crI was used, but it is 1,958 g/cif for an ideal crystal with 100% crystallinity (Reference 2).

If the porosity exceeds 95%, the membrane will be weak, and if it is less than 60%, it will become too dense and the membrane properties will be poor.

81 The membrane manufacturing method of the present invention uses the above-mentioned specific quaternary components in the membrane-forming stock solution to develop a continuous network structure characteristic of a porous membrane. Absence of any of the quaternary components does not result in surface pores and tissue pores with sufficient customization as described above.

The formation of a water film is similar to visual phase separation, and the progress of phase separation induced by contact with water vapor and the development of a network structure as a porous film can be observed using an optical microscope. can do. Furthermore, when observed with the naked eye, it is observed that the cast thin layer becomes devitrified. Therefore, we have completed a production method in which the cast membrane forming stock solution is subjected to solidification phase separation in the atmosphere or a gas containing water vapor, and then components other than the polymer are removed in a cleaning bath. In order to induce phase separation to proceed within a practical time, for example within 5 minutes, a water vapor pressure of 16IIIiF at 30°C, for example, is required.
k11, that is, relative humidity of 50% or more is required. The cleaning bath is preferably a liquid capable of dissolving and removing three components other than polyvinylidene fluoride, and can be selected from non-solvents for polyvinylidene fluoride. Specific examples include water, alcohol, etc., but water is generally preferred.

Wet film formation may be performed using the membrane forming stock solution of the present invention using a coagulation bath of a known method. In particular, it is preferable to use an aqueous solution of polyvinylidene fluoride containing 20% or more of a solvent as disclosed in JP-A-58-91731 as the coagulation bath.

The scope of the present invention also includes a production method in which a cast membrane-forming stock solution is subjected to coagulation phase separation in a coagulation bath, and then components other than the polymer are removed in a washing bath. Although it is better to slow the progress of phase separation of the stock solution to develop uniform and large pores and voids, it is important to consider the practical time, e.g., within 5 minutes for a flat membrane, and within 1 minute for a hollow fiber. The solvent content depends on the composition of the film-forming stock solution, but is generally preferably 50 to 80%.

Good solvents for polyvinylidene fluoride used in the membrane forming stock solution include N-methyl-2-pyrrolidone, diethylacetamide, diethylformamide, hexamethylphosphoramide, tetramethylurea, hexamethylphosphoramide,
Dimethyl sulfoxide is preferred. At least one solvent from these solvent groups is used, and if necessary, a mixed solvent is used. Particularly preferred good solvents are N-methyl-2-pyrrolidone, dimethylacetamide, and dimethylformamide, which have a high dissolving power and are water-soluble.

The poor solvent used in the present invention must be capable of being mixed with a good solvent and the water-soluble polymer described below, and capable of phase separation as a dilute phase of the polymer (polyvinylidene fluoride) in the membrane forming stock solution. Furthermore, since it is a poor solvent, for example, it has an affinity to dissolve polyvinylidene fluoride at high temperatures, so it can be assumed that the phase separation mechanism of the present invention proceeds smoothly and microscopically. If the poor solvent is water-soluble, it can be washed with water. Ketones, esters and cyclic esters have been found to be preferred. Among them, acetin, methylethylmutone, cyclohexanone, triethylbosphate, dimethylsuccinate, γ-butyrolactone, and ε-caprolactone are particularly preferred.

The water-soluble polymer used in the present invention must be able to be mixed with the above-mentioned good solvent and poor solvent and undergo phase separation as a dilute phase of the polymer (polyvinylidene fluoride) in the membrane forming stock solution. Also, from the perspective of water-soluble polymers, it is a pore-forming agent that forms its own dense phase and develops into pores. If it is water-soluble, it can be substantially removed from the membrane by hydrogen washing, while the trace amount of water-soluble polymer remaining in the membrane imparts hydrophilic properties to the membrane of the present invention. Preferred water-soluble polymers include polyether (polyethylene glycol, polypropylene glycol, etc.) and polyvinylpyrrolidone. At least one of these water-soluble polymers is used, but if necessary, polymers of the same type or different types having different properties may be used in combination.

Polyvinylpyrrolidone is particularly preferred in view of its properties, viscosity, etc.

The composition of the membrane-forming stock solution varies depending on the structure and form of the intended porous membrane and the membrane-forming method, but is generally preferably in the following range. The polyvinylidene fluoride content is 5 to 35 wt%, and the water-soluble polymer content is 2 to 3 wt%. These concentrations are determined from the use, dark conversion properties, and viscosity of the film-forming stock solution. If polyvinylidene fluoride is less than 5 wt%, the resulting film will be weak (,
If it exceeds 35 wt%, the solubility of the raw material 12 will be impaired, but the viscosity will be too high and it will be difficult to form a film. The effect of adding poor solvents and water-soluble polymers is 2.
wt% or more, and if it is added in excess, the stock solution will undergo phase separation or gelation. Furthermore, if necessary, non-solvents such as water and alcohol, fine powder additives such as silica and alumina, etc. may be added to adjust the viscosity and membrane pore diameter of the membrane forming stock solution of the present invention.

The membrane of the present invention can be molded into any shape, such as a flat membrane, a cylindrical membrane, or a hollow fiber membrane. Further, the film may be formed on a support such as a nonwoven fabric, or may be formed as another thin porous film for a support.

〔Effect of the invention〕

The structure of the porous membrane of the present invention has pore groups with high porosity on the surface and within the structure, and has excellent characteristics as a microfiltration membrane or an ultrafiltration membrane.

That is, the permeability of high molecular weight solutes and the solution flow rate are high.

It is composed of polyvinylidene fluoride type crystals, is thermally stable, can be heat sterilized, and is useful in the food industry, pharmaceutical industry, and medicine. The water-soluble polymer makes it a hydrophilic membrane, making it suitable for hydrogen separation operations. In addition to the fluid separation membrane, it may also be used as a diaphragm. For example, it can be applied to diaphragms for electrolysis and protective membranes for wound surfaces (human skin).

Furthermore, it can be applied as a cell culture diaphragm (separation and can also serve as a carrier).

Although the present invention is described above using Examples, the present invention is not limited to these Examples.

Example 1 Polyhynylidene fluoride (hereinafter abbreviated as PVDF)
Wal wo company, Kynar (o registered trademark) 30
1F) 16% by weight (hereinafter abbreviated as %), N-methyl-2-
Pyrrolidone (hereinafter abbreviated as NMP) 64%, cyclohexanone 10%, and polyvinylpyrrolidone [hereinafter PVP]
Abbreviated as: Company G, A, F, K-30 (molecular weight 40,000
)] A film-forming stock solution consisting of 10% was prepared and cast onto a glass plate using a doctor knife having an original size of 150μ.

(a) 5M in atmosphere 30℃, 60%RH (relative humidity)
The cast membrane was left to stand until it became sufficiently cloudy, and then immersed in a water washing bath to obtain a P V D F membrane (Example 1a). (b) NMP 70%, methanol 15% and water 15% immediately after casting.
2 m after the cast film becomes cloudy.
After tn, the membrane was immersed in a water washing bath to obtain a PVDF membrane (Example 1b). Using a 0.05% aqueous solution of live serum globulin, the ultrafiltration rate of water (UFR (ρ/77f-hr)) and solute permeability (SC (%)) were measured as membrane performance. The film properties are shown in Table 1. Also, the X-ray diffraction photograph is shown in Figure 3 (a), which shows a ■-type crystal [Figure (b)]
and was substantially non-oriented.

(The following is a blank space) 15- Table 1 17- 16- Comparative Example 1 A film-forming stock solution consisting of 16% PVDF and 84% NMP was cast in the same manner as in Example 1, and (a) washing with water after film-forming in the air, and (b) ) PVDF membranes [Ratio 1a and Ratio IB] were obtained by coagulation bath membrane forming and washing with water. The results are shown in Table 1, and a uniform structure as a porous membrane was not formed, and the membrane performance was also poor.

(Margin below) Table 2 [Note 1] Examples 2 to 8 where no pores are observed under scanning microscope observation at a magnification of 50,000 PVDFi 6%, NMP 64%, poor solvent 1 shown in Table 3
0% and PVP (K-30>10% color) film forming stock solutions were cast in the same manner as in Example 1, (a) film forming in the air and washing with water, and (b) film forming in a coagulation bath with water washing. Example 2
~8 PVDF 16%, NMP 64%, poor solvent 1 shown in Table 3
A film forming stock solution consisting of 0% and 10% PVP (K-30) was cast in the same manner as in Example 1, and the PVDF
Films [Examples 2 (a), (b) to 8 (a), (b) were obtained. All exhibited uniform porous structures and excellent membrane performance.

Examples 9 to 15 A membrane forming stock solution consisting of 16% PVDF, 64% good solvent, 10% poor solvent and 10% water-soluble polymer shown in Table 4 was cast in the same manner as in Example 1, and contained 65% good solvent. A film was formed in a coagulation bath and washed with water to obtain a PVDF film (Examples 9 to 5).

All exhibited uniform porous structures and excellent membrane performance.

Comparative Example 2 The same film-forming stock solution as in Example 1 was heated in the atmosphere at elevated temperature (45°C, 30%
PH) and left for 51n. The cast membrane remained transparent and became translucent after being placed in a water washing bath. 5th result
As shown in the table, a uniform membrane structure as a porous membrane could not be obtained. Furthermore, the cast membrane remains transparent even under a dehumidified atmosphere (30°C, 40% PH).
It was shown that water vapor with a pH of 0% or more is required.

(The following is a blank space) 23- Table 5 Example 16.17 The membrane of Example 1b and the membrane of Example 8b were subjected to moist heat treatment at 121°C for 301n in a high-pressure steam sterilizer. The membrane was slightly colored (brown) and shrunk by several percent in the in-plane longitudinal direction, but no other abnormalities were observed.

Table 6 shows the membrane performance of raw serum albumin (molecular weight 60,000), Serum Globin (molecular group 160,000), and Propxrane (2 million) using an aqueous solution of Propxrane (2 million) K, and no change in performance was observed. Ta.

(Margin below) 25-

[Brief explanation of drawings]

FIG. 1 is a schematic diagram and a scanning electron micrograph of the surface of the porous membrane of the present invention. (a) Repeated hole group, (b
) Schematic diagram of a planar network structure. (C) Surface of Example 1a,
(d>Photograph of the front surface of Example 2a, (e) back surface of Example 8a. FIG. 2 is a schematic diagram and a scanning electron micrograph of a cross section of the continuous network structure of the porous membrane of the present invention. a) Schematic diagram in which the pores are polyhedral and interconnected. (b) Cross section of Example 1A, (C) Photograph of the cross section of Example 8 (b). Figure 3 is a polyvinylidene fluoride type crystal. (a) X-ray diffraction photograph of the Example 1b film, and (b) crystal structure diagram (
This is the above-mentioned document 2). Patent applicant Teijin Co., Ltd. (C) 1μ m9- ('a) b = 9.64 people b) Oc OF Tate 3 diagram procedural correction layer January 7, 1985? Commissioner of the Japan Patent Office 1, Indication of Case Patent Application No. 58-204960 2, Name of Invention Porous Polyvinylidene Fluoride Membrane and Method for Producing the Same 3,
Relationship with the person making the amendment Patent applicant 1-11 Minamihonmachi, Higashi-ku, Osaka-shi, Osaka (300) Teijin Limited Representative Sa Okamoto, Department 4, Agent 2-1-1 Uchisaiwai-cho, Chiyoda-ku, Tokyo No. 5, "Claims" and "Detailed Description of the Invention" columns in the specification subject to amendment, and Drawing 6, Contents of the amendment (1) The claims of the specification are corrected as shown in the attached sheet. (2) “Boneto” on page 4, line 3 of the specification is changed to “Bone1-
” he corrected. (3) Correct "etch" in line 6 of page 4 to "etch". (4) Change l-69267J in the 5th line from the bottom of page 4 to l 69
Corrected to 627J. (5) 4 lines from the bottom of page 4 “99304J 999
Correct it to 34J. (6) In the first line from the bottom of page 4, ``kapo'' is corrected to ``zapo''. (7) On page 5, line 5, ``Goiha'' is corrected to ``Gogo ni''. (8) In the 7th line from the bottom of page 5, "plasmaization" is corrected to "crystallization." (9) On page 6, line 2, "composition" is corrected to "structure." (10) In lines 4 to 3 from the bottom of page 6, "Prepare a film-forming stock solution from" is corrected to read "Prepare a film-forming stock solution from a good solvent, a poor solvent for the polymer, and 2- a water-soluble polymer." (11) On page 7, line 5, "Oita" is corrected to "most part."・(12) "eta" in 5 lines from the bottom and 3 lines from the bottom on page 7
Correct i and J to ``et al, J, respectively. (13) Correct ``double wa'' in the 6th line from the bottom of page 8 to ``1 case wa''. (14) In the 5th line from the bottom of page 8, ``formation'' is corrected to ``1 form''. (15) In the same page 9, line 6, E's purpose is to be corrected to read 'child's purpose'. (16) On page 9, line 12, "Formula (1)?" is corrected to "Formula ga." (17) r 1,8 (gcn?) J on page 9, line 14 is 11.8g/cn? ) Correct it as J. (18) r 1.958J in the 3rd line from the bottom of page 9 [1,
Corrected to 925J. (19) On page 10, line 6, ``1 purposeful'' is corrected to ``spontaneous''. (20) In the 8th line from the bottom of page 11, change "The content is" to [It is necessary to determine the content. Furthermore, the solvent content is corrected. (21) In the 6th line from the bottom of page 12, [mutone, cyclohexanone,] heleether] is replaced with [ketone, cyclohexanone,
Triethyl,” he corrected. (22) On page 13, line 3, ``hydrogen'' is corrected to ``1 water system''. (23) In the third line from the bottom of page 13, ``Usage revision and darkening'' is corrected to ``1 Solubility and stability''. (24) In the 5th line from the bottom of page 14, "flow velocity" is corrected to "flux." (25) On the first line from the bottom of page 14, ``hydrogen'' is corrected to ``1 water system''. (26) On page 15, line 6, "more than" is corrected to "less than". (27) On page 15, line 10, “(○registration”) is corrected to “(registration”). (28) On page 15, line 7 from the bottom, rG, A, and FJ are corrected to [G. A, FJ. (29) "1 adjustment" in the 6th line from the bottom of page 15 is corrected as "adjustment". (30) "Adjustment" in the 4th line from the bottom of page 15 and the 2nd line of page 16 is corrected to [m1nJ. 31) “-hr” on page 16, line 5 and line 1 from the bottom of 26
・(Correct nttt HgJ to 1・hr-#Hg". (3, 2) "1B] was obtained on page 18, line 5. Result No. 1 was obtained. Result No. 2." (33) In row 1a of Table 2 on page 19, [<1.
Correct OJ to "1.0". (34) Delete lines 1 to 5 on page 20. (35) Correct 1PHJ in lines 8, 7, and 8 of page 25 to rRHJ. (36) “Blue dextran (200
10,000) Delete KJ. (37) Figure 3(b) of the drawings will be corrected as shown in the attached sheet. (Above) Claims (1) A porous membrane of a polymer mainly composed of polyvinylidene fluoride, in which aggregates of the polymer form a network structure having interconnected pores; The aggregate has a ■-type crystal structure and is substantially unoriented, and the pores on the surface of the porous membrane form a repeating group of pores or a planar network structure, and the average pore diameter is 0.05 to 0.05. A porous polyvinylidene fluoride membrane having a diameter of 10μ, the pores in the continuous network structure being polyhedral and communicating with each other, and having a porosity of 60 to 95%. (2) The pores in the communicating network are 0.05 to 10μ
2. The porous polyvinylidene fluoride membrane of claim 1, which has a substantially uniform average pore diameter of . (3) Polymer mainly composed of polyvinylidene fluoride,
14 tjL of a membrane-forming stock solution is cast and solidified from a good solvent for the polymer, a poor solvent for the polymer, and a water-soluble polymer, and then the good solvent, the poor solvent, and the water-soluble polymer are removed in a washing bath. A method for producing a porous polyvinylidene fluoride membrane, characterized by: 5- (4) N-methyl-2-pyrrolidone as a good solvent. Dimethylformamide, dimethylacetamide. Diethylacetamide, diethylformamide. Hexamethylphosphoramide, tetramethylurea. The manufacturing method according to claim 3, in which at least one selected from the group consisting of hexamethylphosphoramide and dimethyl sulfoxide is used. (5) Acetone and methyl ethyl ketone as poor solvents. 4. The manufacturing method according to claim 3, wherein at least one selected from the group consisting of cyclohexanone, diacetone alcohol, triethyl phosphate-1-, dimethyl succinate, γ-butalolactone, and ε-caprolactone is used. (6) The manufacturing method according to claim 3, wherein the water-soluble polymer is at least one selected from the group consisting of polyether and polyvinylpyrrolidone. [71] The production method according to claim 3, wherein the cast film-forming stock solution is subjected to solidification phase separation in the atmosphere or a gas containing water vapor, and then components other than the polymer are removed in a cleaning bath. 1-(8) The production method according to claim 3, wherein the cast stock solution is subjected to coagulation phase separation in a coagulation bath, and then components other than the polymer are removed in a washing bath.

Claims (1)

[Scope of Claims] (1) A porous membrane of a polymer mainly composed of polyvinylidene fluoride, wherein aggregates of the polymer form a network structure having interconnected pores; ■
It has a type crystal structure and is substantially non-oriented, and the pores on the surface of the porous membrane form a repeating pore group or a planar network structure, and the average pore diameter is 0.05 to 10 μ; and a polyvinylidene fluoride porous membrane characterized in that the pores in the continuous network structure are polyhedral and communicate with each other, and the porosity thereof is 60 to 95%. (2) The pores in the continuous network structure are 0.05 to 10μ
2. The porous polyvinylidene fluoride membrane of claim 1, which has a substantially uniform average pore diameter of . (3) Polymer mainly composed of polyvinylidene fluoride,
A membrane-forming stock solution is prepared from a good solvent for the polymer, a poor solvent for the polymer, and a water-soluble polymer, cast, and solidified, and then the good solvent, the poor solvent, and the water-soluble polymer are removed in a cleaning bath. A method for producing a porous polyvinylidene fluoride membrane, characterized by: (4) N-methyl-2-pyrrolidone as a good solvent. Dimethylformamide, dimethylacetamide. Diethylacetamide, diethylformamide. Hexamethylphosphoramide, tetramethylurea. The manufacturing method according to claim 3, in which at least one member selected from the group consisting of hexamethylphosphoramide and dimethyl sulfoxide is used. (5) Acetone and methyl ethyl ketone as poor solvents. The manufacturing method according to claim 3, in which at least one selected from the group consisting of cyclohexanone, diacetone alcohol, triethyl phosphate, dimethyl succinate, γ-butyrolactone, and ε-caprolactone is used. (6) The manufacturing method according to claim 3, wherein the water-soluble polymer is at least one species selected from the group consisting of polyether and polyvinylpyrrolidone. (The manufacturing method according to claim 3, in which the cast film-forming stock solution is allowed to undergo solidification phase separation in the atmosphere or a gas containing water vapor, and then components other than the polymer are removed in a cleaning bath. ( 8) The manufacturing method according to claim 3, wherein the cast stock solution is subjected to coagulation phase separation in a coagulation bath, and then components other than the polymer are removed in a washing bath.