JPS60216804A - Porous hollow yarn membrane comprising polyvinylidene fluoride and preparation thereof - Google Patents

Abstract

PURPOSE:To prepare a porous hollow yarn membrane comprising groups of pores resulting high void content and having superior characteristics useful for precision filtration membrane or ultra filtration membrane by blending polyvinyl pyrrolidone with polyvinylidene fluoride. CONSTITUTION:The material is a porous hollow yarn membrane comprising a polymer consisting primarily of polyvinylidene fluoride contg. 1-20wt% polyvinyl pyrrolidone blended therewith. The agglomerated body of the polymers forms a network structure having communicating pores. Further, the polyvinylidene fluoride has a II type crystal structure, and the average pore size of pores distributed on the internal and external surfaces of the hollow yarn membrane is 0.05-10mu and the void content is 60-90%. Such membrane is prepared by dissolving the polymers in a solvent to prepare feed liquid having >=100 poise viscosity at 20 deg.C and coagulating the soln. in a coagulating bath after extruding the soln. through a double tubular nozzle.

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 hollow fiber membrane.

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

For such purposes, cellulose ester-based, polycarbonate-based, and polypropylene-based porous membranes have conventionally been used. Porous membrane manufacturing methods include solvent evaporation drying method,
Microphase separation wet method, film stretching method, additive extraction method,
A post-irradiation etching method is well known. 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, polyvinylidene fluoride-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-55-69627 and JP-A-Sho. 5
No. 5-99934 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 support layer and includes macrovoids. With these methods, it is difficult to obtain a sieve with uniform pores, and since the membrane contains macrovoids inside, there is a problem in mechanical strength. Japanese Patent Publication No. 58-9
No. 1808 contains water-insoluble alcohol, JP-A-58-9
No. 3734 discloses a method of forming a membrane by adding hydrophilic inorganic fine powder and then extracting it to obtain a porous membrane, but the extraction requires special operations and the additives may not be present in the membrane. There is a risk that it may remain as a foreign substance. Japanese Patent Publication No. 58-9173
No. 2 discloses a manufacturing method in which a porous membrane having no asymmetric structure and an aqueous solution containing 20% or more of a solvent are coagulated.

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

[Object and structure of the invention]

In view of this situation, the purpose of the present invention is to utilize the excellent properties of polyvinylidene fluoride to obtain a porous membrane with a uniform structure and impart hydrophilicity to obtain a membrane useful for industrial and medical purposes. After extensive research, the first step was to invent a porous film-forming method as described in Japanese Patent Application No. 58-204960. That is, it is a porous membrane of a polymer mainly composed of polyvinylidene fluoride, and the 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 10μ. 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%. Furthermore, the invention provides a method for preparing a stock solution from a polymer mainly composed of polyvinylidene fluoride, a good solvent for the polymer, a poor solvent for the polymer, and a water-soluble polymer,
This is a method for producing a polyvinylidene fluoride porous membrane, which is characterized by casting, solidifying, and then removing the good solvent, the poor solvent, and the water-soluble polymer in a washing bath.

Next, as a second step, we conducted intensive research on a practical porous hollow fiber membrane and completed this project. That is, the present invention mainly consists of polyvinylidene fluoride, polyvinyl and lolidon, and
The porous hollow fiber membrane is made of a blended polymer containing 20 wt%, and the polymer aggregates form an m-shaped structure with connected pores, and the polyvinylidene fluoride of the aggregates has a ■-type crystal. structure, the average pore diameter of pores on the inner and outer surfaces of the hollow fiber membrane is 0.05 to 10μ, and the porosity of the continuous network structure is 60 to 90.
% polyvinylidene fluoride porous hollow fiber membrane. Furthermore, the present invention can dissolve polyvinylidene fluoride and polyvinylpyrrolidone in a mixed solvent consisting of a good solvent and a poor solvent for polyvinylidene fluoride.
Prepare a film-forming stock solution with a viscosity of 100 poise or more at 0°C, extrude it with the core liquid inside from a double pipe nozzle,
This is a method for producing a porous hollow fiber membrane based on polyvinylidene fluoride, which is characterized by passing through a gas or directly leading it to a coagulation bath to coagulate it, and then removing a portion of the solvent and polyvinylpyrrolidone in a washing bath.

The present invention will be explained in detail below. Mainly polyvinylidene fluoride and 1 to 20w of polyvinylpyrrolidone
In the blended polymer containing t%, polyvinylidene fluoride may be a homopolymer or a copolymer, but the vinylidene fluoride monomer occupies the majority. The molecular weight of the polyvinylidene fluoride is:
For example, about 100,000 to 1,000,000 is used.

Polyvinylpyrrolidone coexists with polyvinylidene fluoride from the membrane-forming stock solution, and a portion of it coexists as a constituent of the membrane even after coagulation and washing. The amount is within a range that allows the network structure and crystal structure of polyvinylidene fluoride, which is the main component, to be characterized as described below as a component of the present invention.

That is, firstly, the crystal structure of polyvinylidene fluoride should not be exposed. Polyvinylidene fluoride has three crystal modifications, and the film of the present invention has the thermodynamically most stable modification.
It has a type crystal structure. 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.

(1) R. Hasegawaetal, Polym
er J, 3゜(5), 591 (1972).

(2J R, Hasegawa et al., Poly
Mer J, 3°(5), 600 (1972).

(3) Y, Takahashi and H, Ta
dokoro.

Macromolecules, 13. 1317(
(1980) The present invention also has substantially no orientation. 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 type 1, which is thermally unstable.

Second, the content of polyvinylpyrrolidone is 1 to 20 wt%
is preferred. When it is less than 1 wt%, it is difficult to develop a porous membrane structure, and the membrane has poor hydrophilicity. If it exceeds 20 wt%, the porous membrane structure becomes vague, the membrane is weak, and as a constituent, it is easily washed away and becomes unstable.

The porous hollow fiber membrane of the present invention is used in membrane separation technology and has an inner diameter of 20 to 2000μ and a membrane thickness of 10 to 300μ. Preferably, the inner diameter is 40 to 1000μ and the film thickness is 10 to 300μ.

The average pore diameter of pores on the inner and outer surfaces of the hollow fiber membrane is 0.05.
~10μ. The average pore size is the average pore size determined by a scanning electron microscope. The average pore diameter is 0.05μ (
-500 people), the characteristics of the porous membrane that are the object of the present invention cannot be exhibited. Furthermore, if the average pore diameter exceeds 10 μm, this corresponds to a pinhole defect in the membrane, and naturally the membrane function and morphology cannot be maintained. The membrane of the present invention has a group of pores within its interconnected network structure, and the total porosity thereof is 60 to 90%.

The porosity was calculated using the following formula.

Here is the measured density of polyvinylidene fluoride ■ type crystal sample 1
．． Although 8 g/cd was used, it is 1.958 g/cd 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.

The content of polyvinylpyrrolidone in the film can be determined by the absorption spectrum of polyvinylpyrrolidone (1680cI) by infrared analysis.
The absorbance of m-') was compared with the absorbance of the absorption spectrum (1402α-1) of polyvinylidene fluoride.

In the calculation of the porosity, polyvinylpyrrolidone was also included in the weight of the membrane.

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 hollow fiber membrane. Even if any of the quaternary components is missing, surface pores and tissue pores with sufficient characteristics described above cannot be obtained.

That is, polyvinylidene fluoride and polyvinylpyrrolidone are dissolved in a mixed solvent consisting of a good solvent and a poor solvent for polyvinylidene fluoride to prepare a film forming stock solution.

The action of polyvinylpyrrolidone is first to contribute to the structure formation of this porous hollow fiber membrane. The second purpose is to impart hydrophilicity to the membrane. Thirdly, in producing hollow fiber membranes, it imparts high viscosity and stability to the membrane forming solution, ie, the spinning solution (dope), which has a remarkable effect. Generally, the viscosity of a single solution of polyvinylidene fluoride is very low, for example, even a 20% solution is about 50p.

ise (20° C.), and it is difficult to spin it as it is. The viscosity of the spinning dope in the present invention is preferably in the range of 100 poise or more and about 1000 poise or less when measured at 20°C.

Phase separation is also induced by contact with water vapor, and a network structure as a porous membrane is developed. Polyvinylpyrrolidone having a molecular weight of 10,000 to 360,000 can be used. A high molecular weight of 40,000 to 360,000 is preferable from the viewpoint of adjusting the viscosity of the spinning dope and film properties. These may be used alone or in combination.

Polyvinylidene fluoride 10-30wt% as spinning stock solution
It is prepared by dissolving 2 to 30 wt% of polyvinylpyrrolidone and polyvinylpyrrolidone in the following mixed solvent. If the polyvinylidene fluoride concentration is less than 10 wt%, the viscosity of the stock solution is too low, making spinning difficult and making the film weak. If it exceeds 30W%, it will be difficult to dissolve, and the stock solution will be non-uniform and unstable, easily gelling. Furthermore, the undiluted solution,
The preferred range from viscosity, spinnability, and membrane properties is 15 to 2.
set%. When the polyvinylpyrrolidone concentration is less than 2%, no effect of increasing the viscosity of the stock solution or developing the film structure is observed. If it exceeds 3wt%, the viscosity of the stock solution will be 1ooopoi.
If the temperature exceeds se (20°C), the viscosity becomes high and difficult to handle, and the film becomes unstable. Further, from the viewpoint of stock solution viscosity, spinnability and membrane properties, the preferable range is 3 to 20 wt%.

As a good solvent for polyvinylidene fluoride used in the mixed solvent, N-methyl-2-pyrrolidone, diethylace I amide, diethylborumamide, hexamethylphosphoramide, tetramethylurea, hexamethylphosphoramide, and dimethyl sulfoxide are preferable. . At least one kind, and if necessary, two or more kinds, are used from among these solvent groups. N-Methyl-2-, which has a large dissolving power and is water-soluble
Pyrrolidone is a particularly preferred good solvent.

The poor solvent used in the mixed solvent must be one that can be mixed with a good solvent and the water-soluble polymer described below and phase-separated 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 for dissolving polyvinylidene fluoride at high temperatures, so it can be presumed 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, acetone, methyl ethyl ketone, cyclohexanone, triethyl phosphate, dimethyl succinate, γ-butyrolactone, and ε-caprolactone are preferred, and acetone, methyl ethyl ketone, and cyclohexanone are particularly preferred from the viewpoint of stock solution, spinning, and membrane properties.

Predetermined amounts of polyvinylidene fluoride and polyvinylpyrrolidone are mixed and dissolved to prepare a spinning stock solution.

The stock solution, which has been dissolved and defoamed by heating, is extruded from the outer ring part of the double tube nozzle, and at the same time, the core liquid is discharged from the inner ring part to spin into hollow fibers. The discharged thread is passed through a gas or directly introduced into a coagulation bath, where it is coagulated to form a hollow fiber membrane. Next, the solvent, polyvinylpyrrolidone, and in some cases the core liquid are removed in a washing bath to obtain the hollow fiber membrane of the present invention. Furthermore, the core liquid can be removed and the hollow fiber membranes can be dried with glycerin by known methods.

Although water or alcohol can be used in the spinning coagulation bath, it is particularly preferable to use an aqueous solution containing 20% or more of a polyvinylidene fluoride solvent as disclosed in JP-A-58-91732. 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 membrane-constituting polymer are removed in a washing bath. Large pores and voids appear that slow the progress of phase separation of the stock solution, but when the discharged thread is substantial, for example, use a bath solution containing a solvent with a slippage of 50 to 80% that solidifies within 1 minute. It is preferable.

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.

〔Effect of the invention〕

The structure of the porous hollow fiber 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 and solution flux for high molecular weight solutes 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.

In particular, the water-soluble polymer contained in the membrane makes the membrane highly hydrophilic, making it extremely suitable for aqueous separation. Furthermore, it can be applied as a cell culture diaphragm (separation and can also serve as a carrier). It can also be used for gas separation and filtration and cleaning.

The present invention will be explained below using Examples, but the present invention is not limited to these Examples.

Example 1 Polyvinylidene fluoride E (hereinafter abbreviated as PVDF): penw
alt, Kynar (registered trademark) 301F (molecular weight 6
50000)] 118wt% weight% based on the total amount,
), and polyvinylpyrrolidone [hereinafter PVP
Omitted: G, A, F, company, Ni-30 (molecular weight 40,000
)] 112wt, 60% of N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) as a good solvent and 11% of acetone as a poor solvent.
A spinning stock solution was prepared by heating and dissolving in a mixed solvent consisting of 0 wt%. The viscosity of the stock solution was 150 poise (20°C). Hollow fiber spinning is performed using polyethylene glycol as the core liquid, and NMP y is passed through 1 clR in the air.
owt%, methanol 15wt% and water 151#t%
The membrane was introduced into a coagulation bath consisting of and washed with warm water (40°C) to obtain a hollow fiber membrane. The hollow fiber membrane has an outer diameter of 500μ and an inner diameter of 300μ.
Then, using a scanning electron microscope, the outer surface was 1:1μ and the inner surface was 0.
．． A group of 5μ pores was observed. The cross section showed a network structure of communicating pores, and no macrovoids were observed.

The porosity was 88%. The PVP content in the membrane-constituting polymer was found to be 1.6% by infrared analysis, and it was confirmed by X-ray diffraction that most of the PVDF was a ■ type bond.

Comparative Example 1 A 18W% solution was prepared by dissolving PVPF in NMP, dimethylacetamide, and dimethylacetamide. In either case, it was difficult to spin hollow fibers with low viscosity (several 10 pOieS or less, 20° C.).

Comparative Example 2 PVDF 20wt%, calcium chloride dihydrate 2wt%, cyclohexanol 14wt%, and NM
Although a stock solution consisting of P64wt% was prepared, it was not sufficiently dissolved and gradually gelled, making it impossible to spin.

Comparative Example 3 PVDF 20wt%, poly(ethylene glycol/propylene glycol) 16wt%, and NM
A stock solution containing 64 wt% of P was prepared and spun in the same manner as in Example 1. Hollow fibers with an outer diameter of 640 μm and an inner diameter of 410 μm were obtained, but no pores of 0.1 μm or more were observed on the outer and inner surfaces, and the porous network structure was insufficiently developed.

Examples 2 to 4 Film forming stock solutions were prepared not shown in Table 1, and the viscosity was 200p.
oise or more in the same manner as in Example 1 to obtain a hollow fiber membrane. All exhibited porous hollow fiber membrane structures and excellent membrane performance.

Example 5 When spinning was attempted by replacing acetone with methyl-1-tyrene ketone in Example 1, a porous hollow fiber membrane could be obtained in the same manner.

(JJ, bottom margin)

[Brief explanation of drawings]

FIG. 1 is a scanning electron micrograph (magnification: 5000 times) of the outer surface of the polynylidene fluoride porous hollow fiber membrane of the present invention, FIG. 2 is a cross section thereof, and FIG. 3 is a scanning electron micrograph (magnification: 5000 times) of the inner surface thereof. Procedure 13 Official Document (Method) 1. Indication of the Case Patent Application No. 1987-73006 2. Name of the Invention Polyvinylidene Fluoride Porous Hollow Fiber Membrane A> and its Manufacturing Method 3. Person Making the Amendment Relationship with the Case Special E' [Applicant: 1-11 Minamihonmachi, Higashi-ku, Osaka-shi, Osaka Prefecture (300), Representative of Teijin Ltd., Sa Okamoto. In other words, Fig. 1 is corrected as ". Between the above amendments, May 1985 - Japan Patent and Trademark Agency Director General 1, Indication of Case Patent Application No. 1987-73006 2, Title of Invention Polyvinylidene Fluoride Porous Hollow Fiber Membrane and Process for Producing the Same 3. Relationship with the case of the person making the amendment Patent applicant 1-11 Minamihonmachi, Higashi-ku, Osaka-shi, Osaka Prefecture (3()0) Representative of Teijin Ltd. Sa Okamoto 4 Department 4, Agent Uchisaiwai-cho, Chiyoda-ku, Tokyo 2-chome-1-1-5, Subject of amendment (1) The scope of claims in the specification will be corrected as shown in the attached sheet. (2) Correct “conventional cellulose” in line 4 of page 3 of the same to “conventional cellulose”. (3) Correct “polycarbonate” in line 5 of page 3 of the same to “polycarbonate”. (4) Correct “porous” on page 5, line 8 of the same page to “porous.”
” he corrected. (6) “1.958J” on page 10, line 2 of the same page is “1.92J”
5,” he corrected. (Correct “95%” in line 3 of page 10 of the same document to “90%”. (8) Line 1 from the bottom of page 10 of the same document, lines 1 and 13 of page 12
Correct "adjustment" in the two lines from the bottom of the page to "preparation". (9) Lines 9 to 8 from just below No. 11, “Water vapor and...(
(omitted)...deleted. (To) Change "Standard solution, viscosity" in line 5 of page 12 to "approximately 100".
~1000poise undiluted liquid Mushimaro,” he corrected. 0v "25et%" on page 12, line 6 of the same page is changed to "25wt%".
%” and correct it. Side Correct "fusamethyl" in the 4th line from the bottom of No. 12 to "xamethyl". 03 In the same page 13, line 12, [ethyl ketone...(omitted)...triethyl] is corrected to "ethyl ketone, cyclohexanone, triethyl." En I'p rPenwaltJ on page 16, line 2
ennwalt J toiT positive m'le. 09 Correct "inner system" in the 7th line from the bottom of page 16 to read "1 inner diameter." (16) "1:1μ" in the 6th line from the bottom of page 16 is changed to "1.
1μ” is corrected. Claims (1) A porous hollow fiber membrane of a blended polymer mainly composed of polyvinylidene fluoride and containing 1 to 20 wt% of polyvinylpyrrolidone, the network having pores in which aggregates of the polymer communicate with each other. Forming a similar tissue;
The polyvinylidene fluoride of the aggregate has an H-type crystal structure, and the average pore diameter of the pores on the inner and outer surfaces of the hollow fiber membrane is 0.
．． A polyvinylidene fluoride hollow fiber membrane, characterized in that the diameter of the polyvinylidene fluoride hollow fiber membrane is 05 to 10μ, and the porosity of the continuous network structure is 60 to 90%. ('2J Polyvinylidene fluoride and polyvinylpyrrolidone are dissolved in a mixed solvent consisting of a good solvent and a poor solvent for polyvinylidene fluoride, and the viscosity at 20°C is 10 g.
Prepare a membrane forming stock solution with a poise or higher strength, extrude it with the core liquid inside through a double tube nozzle, pass through the gas or directly lead it to a coagulation bath, coagulate it, and then remove it from the solvent in a washing bath. A method for producing a porous hollow fiber membrane based on polyvinylidene fluoride, which comprises removing a portion of polyvinylpyrrolidone. (3) N-methyl-2-pyrrolidone was used as a good solvent, and acetone, methyl ethyl ketone,
At least one selected from the group consisting of cyclohexanone
The manufacturing method according to claim 2, using N.

Claims (1)

[Scope of Claims] (1) A porous hollow fiber membrane of a blended polymer mainly composed of polynylidene fluoride and containing 1 to 20 wt% of polyvinylpyrolinton, the membrane having pores in which aggregates of the polymer communicate with each other. The polyvinylidene fluoride of the aggregate has a ■-type crystal structure, and the average pore diameter of the pores on the inner and outer surfaces of the hollow fiber membrane is 0.05 to 10μ. and a polyvinylidene fluoride hollow fiber membrane, characterized in that the porosity of the continuous network structure is 60 to 90%. (Dissolve polyvinylidene difluoride and polyvinylpyrrolidone in a mixed solvent consisting of a good solvent and a poor solvent for polyvinylidene fluoride, and the viscosity at 20°C is 100 pois.)
Adjust the membrane forming stock solution above e, extrude it with the core liquid inside through a double tube nozzle, pass through the gas or directly lead it to a coagulation bath, coagulate it, and then remove it from the solvent in a washing bath. A method for producing a porous hollow fiber membrane based on polyvinylidene fluoride, which comprises removing a portion of polyvinylpyrrolidone. (3) N-methyl-2-pyrrolidone was used as a good solvent, and acetone, methyl ethyl ketone,
At least one selected from the group consisting of cyclohexanone
A manufacturing method according to the claims using seeds.