JP2013031832A - Method for manufacturing porous membrane, and microfiltration membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porous membrane excellent in chemical resistance and also excellent in filtering flow rate and a fractionation performance.SOLUTION: A method for manufacturing the porous membrane includes: a film-forming stock solution preparation process for dissolving a chlorinated polyvinyl chloride to a solvent that is a good solvent to the chlorinated polyvinyl chloride and has the compatibility to water, and desirably further dissolving a compound (A) that is soluble to both the solvent and water to obtain a film-forming stock solution; a film-forming process for forming the film-forming stock solution in membrane to obtain an uncoagulated film; a moisture absorption process for retaining the uncoagulated film in air that contains water vapor to absorb moisture; and a coagulation process for coagulating the uncoagulated film in a congealed liquid after the moisture absorption process.

Description

  The present invention relates to a method for producing a porous membrane made of chlorinated polyvinyl chloride and a microfiltration membrane made of chlorinated polyvinyl chloride.

In recent years, due to increasing interest in environmental pollution and stricter regulations, water treatment by a membrane method using a separation membrane having excellent separation completeness and compactness has attracted attention.
In the water treatment by the membrane method, the membrane is washed with an oxidizing agent such as sodium hypochlorite or hydrogen peroxide, acid or alkali, etc. in order to decompose and remove the organic and inorganic substances clogged on and inside the membrane. Therefore, the separation membrane is required to have high oxidation deterioration resistance and acid / alkali resistance.

Against this background, fluorine-based polymers such as polyvinylidene fluoride; vinyl chloride polymers (polyvinyl chloride, chlorinated polyvinyl chloride, etc.), chlorine-based polymers such as polyvinylidene chloride; etc. are used as film-forming polymers. It has been.
In particular, a vinyl chloride polymer is suitable as a separation membrane material because it is excellent in chemical resistance and inexpensive, and does not generate harmful hydrogen fluoride during incineration unlike a fluorine polymer.

As a conventional method for producing a vinyl chloride polymer separation membrane, for example, Patent Document 1 discloses that a polyvinyl chloride, a vinyl chloride-vinyl acetate-maleic anhydride copolymer, a heat stabilizer, and a pore-control agent are used as an organic solvent. A method is described in which a hollow filter membrane is produced by forming a membrane by a dry-spray wet spinning process using a slurry suspended in a coagulant and coagulating it in a coagulating liquid.
The method described in Patent Document 1 has a low solubility in a solvent used in a wet process of a vinyl chloride resin, and therefore requires long-time dissolution and stirring at a high temperature to prepare a slurry, and a heat stabilizer is used. Since it is necessary to add, there is a problem in terms of cost, which is not desirable for industrial production. In addition, coarse macrovoids of several tens of micrometers or more that cause film defects tend to be formed immediately below the surface.

Patent Document 2 discloses a non-solvent that dissolves polyvinyl chloride or chlorinated polyvinyl chloride and a hydrophilic polymer (for example, hydroxypropylmethylcellulose phthalate) in a solvent (for example, tetrahydroxyfuran) and then is compatible with the solvent. A method is described in which a solution to which (for example, isopropyl alcohol) is added is applied to a nonwoven fabric and the solvent is dried.
In Patent Document 3, as a method for producing an asymmetric membrane having a stepwise difference in pore diameter in the thickness direction, a solution obtained by dissolving chlorinated polyvinyl chloride in tetrahydroxyfuran and then adding isopropyl alcohol is used as a nonwoven fabric. A method is described in which two porous substrates are impregnated, the solvent is dried, and then the porous substrate is divided into two.
However, the methods of Patent Documents 2 and 3 require long stirring in the step of adding and mixing a non-solvent, and it takes time to dry the solvent. In addition, it is not desirable for industrial production because it is necessary to use a highly volatile solvent.
In addition, the separation membrane obtained by the method described in Patent Document 3 essentially has a small stepwise change in pore diameter in the internal direction, and in order to have an inclined structure in order to increase water permeability, the pore diameter It was necessary to superimpose different porous membrane materials. In addition, the average pore diameter on the membrane surface is 2 μm or more, and there is concern that bacteria such as Escherichia coli may permeate.

Patent Document 4 describes, for example, a method for producing a hollow fiber membrane by continuously discharging a dimethylacetamide solution containing chlorinated polyvinyl chloride and polyethylene glycol from a hollow fiber nozzle and coagulating it in a water bath. Has been.
Although this patent document 4 describes a chlorinated polyvinyl chloride ultrafiltration membrane having a molecular weight cut-off of 150,000 or less, a porous membrane having a surface pore size of 0.05 to 1 μm suitable for microfiltration is disclosed. Is not listed.

In Patent Document 5, an N-2-methylpyrrolidone solution containing chlorinated polyvinyl chloride and methylcellulose is kept under water vapor, and then immersed in a coagulation liquid, thereby microfiltration with a surface pore diameter of 0.3 to 0.5 μm. A method of manufacturing a membrane is described.
However, in the method of Patent Document 5, water permeability does not develop in a state where the oxidation treatment is not performed with hypochlorous acid after film formation.

  When an oxidizing agent such as hypochlorous acid is used, the film production equipment is corroded in addition to the cost of using the chemicals, so the production cost tends to be high, such as the need to use equipment with high corrosion resistance. It was.

Japanese Patent No. 4243293 Japanese Patent No. 4395904 Japanese Patent Publication No. 1-41653 International Publication No. 2011/004786 Pamphlet Special table 2010-527290

Separation membranes obtained by the methods described in Patent Documents 1 to 4 are not sufficient for performing advanced membrane treatment such as microfiltration, for example, improving the fractionation performance by controlling the pore size, and reducing the pore size. Even so, it is desirable to obtain a good filtration flow rate.
Further, the method described in Patent Document 1 requires dissolution at high temperature and addition of a heat stabilizer, and the method described in Patent Document 5 requires treatment with an oxidizing agent in order to develop water permeability. It is desirable to obtain a membrane having water permeability by an easier and less expensive method.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a porous membrane having excellent chemical resistance and excellent filtration flow rate and fractionation performance.

  The method for producing a porous membrane according to the present invention is a method for producing a film-forming stock solution by dissolving chlorinated polyvinyl chloride in a good solvent for chlorinated polyvinyl chloride and a solvent compatible with water. A film stock solution preparing step, a film forming step of forming the film forming stock solution into a film to obtain an uncoagulated film, a moisture absorbing step of absorbing the moisture by holding the uncoagulated film in air containing water vapor, and the moisture absorbing After the step, there is a coagulation step of coagulating the uncoagulated film in a coagulation liquid.

In the film-forming stock solution preparing step, it is preferable that the compound (A) soluble in both the solvent and water is dissolved in the film-forming stock solution.
In the moisture absorption step, when the amount of water vapor per unit volume of the air containing the water vapor is V (unit: g / m ³ ) and the moisture absorption time is t (unit: second), the value of V × t is 30 to It is preferably 600 (unit: g / m ³ · sec).
The compound (A) is preferably lithium chloride or lithium bromide.
It is preferable that the porous membrane is a microfiltration membrane.
The compound (A) is preferably polyvinyl pyrrolidone having a weight average molecular weight of 50,000 or less.
The present invention provides a microfiltration membrane having an inclined three-dimensional network structure made of chlorinated polyvinyl chloride and having a maximum pore size within the membrane of 0.1 μm to 5 μm.

According to the present invention, a porous film having moisture permeability, excellent chemical resistance, and an inclined three-dimensional network structure can be produced without performing treatment with an oxidizing agent such as sodium hypochlorite.
The three-dimensional network structure referred to in the present invention is a network structure in which the polymers forming the porous film are in the form of fibrils and communicate with each other three-dimensionally. The inclined three-dimensional network structure is a structure in which the size of the three-dimensional network structure changes continuously in the thickness direction. When it has an inclined structure in which the pore diameter gradually increases from the vicinity of the membrane surface in contact with the water to be treated toward the inner layer of the membrane, the fractionation performance and water permeability are excellent.
That is, according to the present invention, a porous membrane having excellent chemical resistance and excellent filtration flow rate and fractionation characteristics can be obtained.
For example, a chlorinated polyvinyl chloride porous membrane suitable as a microfiltration membrane can be obtained.

3 is a surface SEM observation photograph of the porous membrane obtained in Example 1. FIG. 2 is a cross-sectional SEM observation photograph of the porous film obtained in Example 1. 3 is a surface SEM observation photograph of the porous membrane obtained in Example 2. 3 is a cross-sectional SEM observation photograph of the porous membrane obtained in Example 2. 4 is a surface SEM observation photograph of the porous membrane obtained in Example 3. 4 is a cross-sectional SEM observation photograph of the porous membrane obtained in Example 3. 4 is a cross-sectional SEM observation photograph of the porous film obtained in Example 4. 6 is a surface SEM observation photograph of the porous membrane obtained in Example 6. 6 is a cross-sectional SEM observation photograph of the porous membrane obtained in Example 6. 4 is a surface SEM observation photograph of the porous membrane obtained in Example 7. FIG. 6 is a cross-sectional SEM observation photograph of the porous membrane obtained in Example 7. 4 is a surface SEM observation photograph of the porous membrane obtained in Example 8. FIG. 6 is a cross-sectional SEM observation photograph of the porous membrane obtained in Example 8. 4 is a surface SEM observation photograph of the porous membrane obtained in Example 9. 6 is a cross-sectional SEM observation photograph of the porous membrane obtained in Example 9. 4 is a surface SEM observation photograph of the porous film obtained in Example 10. FIG. 2 is a cross-sectional SEM observation photograph of the porous membrane obtained in Example 10.

The method for producing the porous membrane of the present invention will be described in detail. The porous membrane in the present invention is preferably a microfiltration membrane. The microfiltration membrane is a porous membrane having an average pore diameter of the fractionation layer of 0.05 μm or more and 1 μm or less.
When the average pore size is larger than 1 μm, harmful bacteria such as Escherichia coli may flow out, which is not preferable. On the other hand, when the average pore diameter is 0.05 μm or more, good water permeability is easily obtained. More preferably, it is the range of 0.05-0.4 micrometer.
When the porous membrane has the above-described inclined three-dimensional network structure, the pore size of the fractionation layer is represented by the pore size at the surface in contact with the water to be treated.
In the present invention, the value of the average pore diameter on the surface of the membrane is calculated by obtaining the average diameter of the pores with image processing software or the like for an image obtained by photographing the membrane surface with an electron microscope.

In the present invention, the maximum pore diameter inside the membrane is preferably 0.1 μm to 5 μm. When the maximum pore size inside the membrane is 0.1 μm or more, good water permeability is easily obtained. More preferably, it is 0.2 μm or more. When the maximum pore size inside the membrane is larger than 5 μm, the mechanical strength of the membrane tends to decrease, which is not preferable. The maximum pore diameter inside the membrane is calculated by obtaining the maximum diameter of the pores with image processing software or the like on a screen obtained by photographing a cross section perpendicular to the membrane surface with an electron microscope.
The value of the maximum pore diameter inside the membrane in the present invention is determined by using image processing software or the like for an image obtained by continuously photographing a cross section perpendicular to the membrane surface with an electron microscope at a magnification of 300 times or more along the cross section. This is a value obtained by a method in which the maximum diameter of each of the holes is determined and the largest value among the obtained maximum diameters of the holes is defined as the “maximum hole diameter inside the membrane”.

In the present invention, the form of the porous membrane is not particularly limited, and may be, for example, a flat membrane or a hollow shape. In order to increase the film strength, it may be in the form of a composite film in which a multi-membrane film is laminated on a support.
Although the thickness of a porous membrane is not specifically limited, For example, the range of 10-1000 micrometers is preferable and the range of 20-500 micrometers is more preferable.

The chlorinated polyvinyl chloride used in the present invention is a polymer in which some of hydrogen atoms of polyvinyl chloride are chlorinated. A polymer obtained by polymerizing a chlorinated vinyl chloride monomer by a known method may be used, or a polymer obtained by chlorinating polyvinyl chloride by a known method may be used. It is also available from commercial products.
The degree of polymerization of vinyl chloride in the chlorinated polyvinyl chloride used in the present invention is not particularly limited, but it is in the range of 500 to 1500 because the viscosity of the stock solution is easy to adjust and the strength and elongation of the resulting film tend to increase. Preferably, the range of 600-1200 is more preferable.
The degree of chlorination of the chlorinated vinyl chloride resin is not particularly limited, but is preferably 62% by mass or more, and more preferably 65% by mass or more because the solubility in a solvent used for film formation is increased.
In this specification, the degree of chlorination refers to the mass fraction of chlorine added to the chlorinated vinyl chloride resin per unit mass of the chlorinated vinyl chloride resin.

In the present invention, first, chlorinated polyvinyl chloride is dissolved in a good solvent for chlorinated polyvinyl chloride and compatible with water, or chlorinated polyvinyl chloride is chlorinated. A film-forming stock solution is prepared by dissolving a compound (A) soluble in both the solvent and water in a film-forming stock solution dissolved in a solvent that is a good solvent for polyvinyl chloride and compatible with water. Prepare (film-forming stock solution preparation step).
Examples of such a solvent include N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide and the like. In particular, N-methyl-2-pyrrolidone, N, N-dimethylacetamide, and N, N-dimethylformamide, which have high solubility of chlorinated polyvinyl chloride even at low temperatures, are preferable.
These solvents may be used alone or in combination of two or more.

10-30 mass% is preferable and, as for content of chlorinated polyvinyl chloride in a film-forming stock solution, 12-25 mass% is more preferable. When it is at least the lower limit of the above range, a three-dimensional network structure excellent in permeability is likely to be formed, and when it is at most the upper limit of the above range, gelation of the film forming stock solution is difficult to occur.
The film-forming stock solution is preferably heated in order to dissolve the chlorinated vinyl chloride resin satisfactorily. The heating temperature of the film-forming stock solution may be in a temperature range where the components contained in the film-forming stock solution are not thermally decomposed. For example, 10-60 degreeC is preferable and 20-50 degreeC is more preferable.

In the present invention, in order to improve the porosity, the film-forming stock solution may contain a compound (A) that is soluble in both the solvent and water in the film-forming stock solution as a pore-forming agent.
Examples of the compound (A) (pore forming agent) include lithium salts such as lithium chloride and lithium bromide; water-soluble polymers such as polyvinylpyrrolidone and polyethylene glycol.
When the compound (A) (pore-forming agent) remains in the membrane after coagulation, there is a risk that water permeability will decrease due to elution into the filtered water or pore clogging. Therefore, the compound (A) after the coagulation step may occur. The (pore forming agent) is washed away with water.
When the compound (A) is a polymer, the weight average molecular weight of the compound (A) is a polyoxyethylene equivalent molecular weight measured by gel permeation chromatography (GPC) using polyoxyethylene as a standard substance.

In particular, as the compound (A), lithium bromide, lithium chloride, or polyvinylpyrrolidone having a weight average molecular weight of 50,000 or less, more preferably 40,000 or less is preferably used from the viewpoint of pore-forming properties and detergency. In particular, lithium bromide or lithium chloride is preferable from the viewpoints of ease of preparation of a film forming stock solution, ease of washing and removal after film formation, and suppression of macrovoid generation.
1-30 mass% is preferable and, as for content of the compound (A) in a film forming undiluted | stock solution, 2-20 mass% is more preferable. It is preferable that the surface opening rate tends to be higher than the lower limit of the above range, and it is preferable from the upper limit of the above range in terms of ease of washing and removing after film formation.

Macrovoids are coarse pores formed inside the film, and are particularly easily formed in films manufactured by wet or dry wet methods. Such macrovoids are connected to defects on the film surface and tend to cause leaks or cause a decrease in film strength. The macro void in the present invention indicates a pore having a maximum diameter larger than 5 μm.
The maximum diameter of the pores inside the membrane is the same as the method for obtaining the maximum pore diameter inside the membrane. It is obtained by the method of obtaining the diameter.

Next, a film-forming stock solution is formed into a film to form an uncoagulated film (film-forming step). That is, film formation is performed according to the form of the porous film to be obtained.
The method for forming the film can be performed by appropriately using a known film forming method. In the case of a flat film, for example, a method of applying a film-forming stock solution at a desired thickness on a smooth substrate such as a glass plate may be used.

Subsequently, the unsolidified film is held in air containing water vapor to absorb moisture (moisture absorption step).
The moisture absorption step can be performed, for example, by a method in which an uncoagulated film is allowed to stand in an environment including air containing water vapor and held for a predetermined time (moisture absorption time). Or when manufacturing a hollow fiber membrane continuously, after spinning a membrane-forming stock solution continuously, it can carry out by the method of running in the air containing water vapor at a predetermined speed.
When the amount of water vapor per unit volume of air containing water vapor is V (unit: g / m ³ ) and the moisture absorption time (retention time) is t (unit: seconds), the value of V × t is 30 to 600 ( unit: preferably g / ^m is ^{3-sec), 35~300 (g / m 3} · sec) is more preferred.
When the value of V × t is within the above range, a surface pore size suitable for microfiltration is easily obtained.
The water vapor amount (V) is determined from the temperature and relative humidity of air containing water vapor.
Although the temperature of the air containing water vapor | steam is not specifically limited, Since it is necessary to lengthen moisture absorption time when there are few amounts of water vapor | steam, 10-100 degreeC is preferable from the point of productivity and 20-100 degreeC is more preferable.
The moisture absorption time (holding time) is preferably 0.01 to 60 seconds, more preferably 0.01 to 30 seconds from the viewpoint of productivity.

Next, a porous film is obtained by immersing the uncoagulated film after the moisture absorption process in a coagulating liquid and coagulating it (coagulating process).
The coagulation liquid is preferably water or a mixture of water and a solvent used for the preparation of the film forming solution (an aqueous solution of the solvent). In the mixture of the solvent and water, the concentration of the solvent is not particularly limited. However, when the ratio of the solvent is increased, the time required for coagulation tends to be long, and therefore 50% by mass or less is preferable, and 30% by mass or less is more preferable. .

  The porous membrane after the coagulation step is washed with water to remove the remaining solvent and the added compound (A). Cleaning can be performed by a method of immersing in water. When the cleaning of the compound (A) is insufficient, it tends to remain on the membrane surface, block the pores and not obtain water permeability.

According to the present invention, as shown in the examples below, a film-forming stock solution in which chlorinated polyvinyl chloride is dissolved in a good solvent for chlorinated polyvinyl chloride and a solvent compatible with water. Or chlorinated polyvinyl chloride is dissolved in a good solvent for chlorinated polyvinyl chloride and a solvent compatible with water, and further a compound (A Water to be treated by producing a porous film by a method in which the film-forming stock solution in which the solution is dissolved is solidified through a moisture absorption step and the solvent and the added pore-forming agent (compound (A)) are washed with water. A porous membrane having an inclined three-dimensional network structure in which the pore diameter gradually increases from the vicinity of the membrane surface in contact with the inner layer toward the inner membrane layer is obtained.
In the method for producing a porous membrane of the present invention, a porous membrane having moisture permeability can be obtained simply by coagulating the membrane and washing with water. That is, for example, treatment using an oxidizing agent such as sodium hypochlorite is not performed.
Since the porous membrane of the present invention is made of chlorinated polyvinyl chloride, it has excellent chemical resistance.
In the present invention, “consisting of chlorinated polyvinyl chloride” means that the polymer compound (compound having a molecular weight of 10,000 or more) contained in the porous film is only chlorinated polyvinyl chloride.

Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to these examples.
[Example 1]
Commercially available chlorinated polyvinyl chloride (manufactured by Tokuyama Sekisui Industry Co., Ltd., product name: HA-53K, chlorination degree: 67% by mass, polymerization degree of vinyl chloride: 1000) was used.
N-methyl-2-pyrrolidone (manufactured by Wako Pure Chemical Industries, reagent special grade, hereinafter sometimes referred to as NMP) was used as a solvent for the film-forming stock solution, and lithium bromide (Wako Pure Chemical Industries, Ltd.) was used as the compound (A). A reagent special grade) was used.
A film-forming stock solution was prepared by dissolving chlorinated polyvinyl chloride and lithium bromide in NMP as a solvent in a water bath at 40 ° C. with the following composition.
Chlorinated polyvinyl chloride: 20% by mass,
Lithium bromide: 4% by mass
NMP: 76% by mass.

Next, the film-forming stock solution obtained above was uniformly applied to a glass plate with a thickness of about 75 μm to form an uncoagulated film, and then in an air at a temperature of 19.3 ° C. and a relative humidity of 30.4%. The moisture absorption process was performed under the condition of standing still for 2 seconds.
Then, it was immersed in the coagulation liquid for 1 minute with the glass plate, and the porous film was obtained. As the coagulation liquid, an NMP aqueous solution having a concentration of 8% by mass (a mixture of 8% by mass of NMP and 92% by mass of water) was used.
The saturated water vapor amount at 19.3 ° C. is 16.6 g / m ³ , and the value of V × t in this example is 40.4 g / m ³ · sec.

After removing the obtained porous membrane from the glass plate, it was immersed in water at 20 ° C. for 1 hour and washed to remove the remaining solvent and compound (A).
The surface structure of the washed porous membrane was observed at a magnification of 10,000 times with a scanning electron microscope (manufactured by Hitachi High-Technology Corporation, product name: S-3400N, hereinafter referred to as SEM). The obtained image is shown in FIG. The average pore diameter of the surface determined from the obtained image was 0.11 μm.
The cross-sectional structure of the washed porous membrane was observed with the SEM at a magnification of 5,000 times. That is, the washed porous membrane was immersed in liquid nitrogen for about 1 minute and frozen, and then observed with a razor in a cross section cut in a direction perpendicular to the surface. The obtained image is shown in FIG.
From the results of FIG. 2, it can be seen that the obtained porous film has an inclined three-dimensional network structure in which the pore diameter gradually increases from the surface in the thickness direction. Moreover, it turns out that the coarse macrovoid was not formed from the result of FIGS. The maximum pore size inside the membrane was 0.3 μm.

[Measurement of water permeability]
The obtained porous membrane is dried and then cut into a circle having a diameter of 25 mm, set in a filter holder (product name: Swinex 25, adaptive filter size 25 mm) manufactured by Millipore, and ultrapure water is filtered under a pressure of 30 kPa. The water permeability (m ³ / m ² / hr / MPa) was determined from the flow rate for 1 minute.
The water permeability of the obtained membrane was 21 m ³ / m ² / hr / MPa.

[Example 2]
In Example 1, a porous film was produced and observed in the same manner as in Example 1 except that the conditions of the moisture absorption process were changed as follows.
That is, the unsolidified film was allowed to stand for 14 seconds in air at a temperature of 19.2 ° C. and a relative humidity of 29.0%. The saturated water vapor amount at 19.2 ° C. is 16.5 g / m ³ , and the value of V × t in this example is 67.0 g / m ³ · sec.
In the same manner as in Example 1, an image obtained by observing the surface structure of the porous membrane is shown in FIG. 3, and an image of the cross-sectional structure is shown in FIG. The average pore diameter on the surface determined from the image of FIG. 3 was 0.14 μm.
From the results of FIG. 4, it can be seen that the obtained porous film has an inclined three-dimensional network structure in which the pore diameter gradually increases from the surface in the thickness direction. 3 and 4, it can be seen that coarse macrovoids were not formed. The maximum pore size inside the membrane was 0.4 μm.

The amount of water permeation (m ³ / m ² / hr / MPa) of the obtained porous membrane was determined in the same manner as in Example 1. The water permeability of the obtained membrane was 30 m ³ / m ² / hr / MPa.

[Example 3]
In Example 1, a porous film was produced and observed in the same manner as in Example 1 except that the conditions of the moisture absorption process were changed as follows.
That is, the unsolidified film was allowed to stand for 5 seconds in air having a temperature of 19.3 ° C. and a relative humidity of 33.0%. The saturated water vapor amount at 19.3 ° C. is 16.6 g / m ³ , and the value of V × t in this example is 27.4 g / m ³ · sec.
The image obtained by observing the surface structure of the porous membrane in the same manner as in Example 1 is shown in FIG. 5, and the image of the cross-sectional structure is shown in FIG. The average pore diameter of the surface determined from the image of FIG. 5 was less than 0.05 μm.
From the results of FIG. 6, it can be seen that the obtained porous film has an inclined three-dimensional network structure in which the pore diameter gradually increases from the surface in the thickness direction. Also, from the results of FIGS. 5 and 6, it can be seen that coarse macrovoids were not formed. The maximum pore size inside the membrane was 0.5 μm.

[Example 4]
This example is a comparative example in which a porous film was manufactured by a dry manufacturing method without performing a moisture absorption step and without using a coagulating liquid.
The same NMP as the solvent for the chlorinated polyvinyl chloride and the film forming stock solution was used.
First, in the following composition, chlorinated polyvinyl chloride was dissolved in NMP in a 30 ° C. water bath, and isopropyl alcohol was further added and mixed to prepare a film forming stock solution.
Chlorinated polyvinyl chloride: 9% by mass,
Isopropyl alcohol: 27% by mass
NMP: 64% by mass.
Next, the film-forming stock solution obtained above was uniformly applied to a glass plate with a thickness of about 75 μm to form an unsolidified film, and then allowed to stand in air at a temperature of 30 ° C. and a relative humidity of 60% for 30 minutes. Then, NMP and isopropyl alcohol were removed by drying to obtain a porous membrane.
The cross-sectional structure of the obtained porous membrane was observed with a SEM at a magnification of 5,000 times in the same manner as in Example 1. The obtained image is shown in FIG.
As shown in the results of FIG. 7, the obtained porous membrane had a network structure with a uniform pore diameter in cross section. That is, the hole diameter was uniform in the thickness direction, and an inclined three-dimensional network structure was not formed.

[Example 5]
This example is a comparative example using a non-chlorinated vinyl chloride resin (manufactured by Tokuyama Sekisui Chemical Co., Ltd., product name: TS-1000) instead of chlorinated polyvinyl chloride.
Preparation of a film forming stock solution was attempted in the same manner as in Example 1 except that a vinyl chloride resin was used. However, the liquid was gelled, and film formation could not be performed.

[Example 6]
In this example, a porous membrane was produced without using lithium bromide (compound (A)).
First, in this example, a film-forming stock solution was prepared in the same manner as in Example 1 except that the stock solution composition was changed to the following ratio.
Chlorinated polyvinyl chloride: 21% by mass,
NMP: 79% by mass.

Next, the film-forming stock solution obtained above was uniformly applied to a glass plate with a thickness of about 75 μm to form an unsolidified film, and then 10% in air at a temperature of 19.6 ° C. and a relative humidity of 60.6%. The moisture absorption process was performed under the condition of standing still for 2 seconds.
Then, it was immersed in the coagulation liquid for 1 minute with the glass plate, and the porous film was obtained. As the coagulation liquid, an NMP aqueous solution having a concentration of 8% by mass (a mixture of 8% by mass of NMP and 92% by mass of water) was used.
The saturated water vapor amount at 19.6 ° C. is 16.9 g / m ³ , and the value of V × t in this example is 102 g / m ³ · sec.
After removing the obtained porous membrane from the glass plate, it was washed by immersion in water at 20 ° C. for 1 hour to remove the remaining solvent.
In the same manner as in Example 1, an image obtained by observing the surface structure of the porous film at 20000 times is shown in FIG. 8, and an image of the cross-sectional structure is shown in FIG. The average pore diameter on the surface determined from the image of FIG. 8 was 0.06 μm.
From the results of FIG. 9, it can be seen that the obtained porous film has an inclined three-dimensional network structure in which the pore diameter gradually increases from the surface in the thickness direction. 8 and 9, it can be seen that coarse macrovoids were not formed. The maximum pore size inside the membrane was 0.3 μm.

The amount of water permeation (m ³ / m ² / hr / MPa) of the obtained porous membrane was determined in the same manner as in Example 1.
The water permeability of the obtained membrane was 8 m ³ / m ² / hr / MPa.

[Example 7]
In this example, a porous membrane was produced using lithium chloride as the compound (A).
First, in this example, a film-forming stock solution was prepared in the same manner as in Example 1 except that the stock solution composition was changed to the following ratio.
Chlorinated polyvinyl chloride: 20% by mass,
Lithium chloride: 4% by mass
NMP: 76% by mass.

Next, the film-forming stock solution obtained above was uniformly applied to a glass plate with a thickness of about 75 μm to form an uncoagulated film, and then 14% in air at a temperature of 19.8 ° C. and a relative humidity of 60.3%. The moisture absorption process was performed under the condition of standing still for 2 seconds.
Then, it was immersed in the coagulation liquid for 1 minute with the glass plate, and the porous film was obtained. As the coagulation liquid, an NMP aqueous solution having a concentration of 8% by mass (a mixture of 8% by mass of NMP and 92% by mass of water) was used.
The saturated water vapor amount at 19.8 ° C. is 17.1 g / m ³ , and the value of V × t in this example is 144 g / m ³ · sec.
After removing the obtained porous membrane from the glass plate, it was immersed in water at 20 ° C. for 1 hour and washed to remove the remaining solvent and compound (A).
In the same manner as in Example 1, an image obtained by observing the surface structure of the porous film at 20000 times is shown in FIG. 10, and an image of the cross-sectional structure is shown in FIG. The average pore diameter of the surface determined from the image of FIG. 10 was 0.10 μm.
From the results of FIG. 11, it can be seen that the obtained porous film has an inclined three-dimensional network structure in which the pore diameter gradually increases from the surface in the thickness direction. Moreover, it turns out that the coarse macrovoid was not formed from the result of FIG. The maximum pore size inside the membrane was 1.0 μm.

The amount of water permeation (m ³ / m ² / hr / MPa) of the obtained porous membrane was determined in the same manner as in Example 1.
The water permeability of the obtained membrane was 31 m ³ / m ² / hr / MPa.

[Example 8]
In this example, a porous membrane was produced using polyvinyl pyrrolidone (Sigma-Aldrich Polyvinyl pyrrolidone K16-18: weight average molecular weight 4000) as the compound (A).
First, in this example, a film-forming stock solution was prepared in the same manner as in Example 1 except that the stock solution composition was changed to the following ratio.
Chlorinated polyvinyl chloride: 20% by mass,
Polyvinylpyrrolidone K16-18: 4% by mass
NMP: 76% by mass.

Next, the film-forming stock solution obtained above was uniformly applied to a glass plate with a thickness of about 75 μm to form an unsolidified film, and then 30% in air at a temperature of 19.5 ° C. and a relative humidity of 59.6%. The moisture absorption process was performed under the condition of standing still for 2 seconds.
Then, it was immersed in the coagulation liquid for 1 minute with the glass plate, and the porous film was obtained. As the coagulation liquid, an NMP aqueous solution having a concentration of 8% by mass (a mixture of 8% by mass of NMP and 92% by mass of water) was used.
Saturated water vapor amount at 19.5 ° C. is 16.8 g / ^{m 3,} values of V × t in this example is 300 g / ^{m 3} · sec.
After removing the obtained porous membrane from the glass plate, it was immersed and washed in 20 ° C. water for 8 hours to remove the remaining solvent and compound (A).
In the same manner as in Example 1, an image obtained by observing the surface structure of the porous film at 20000 times is shown in FIG. 12, and an image of the cross-sectional structure is shown in FIG. The average pore diameter on the surface determined from the image of FIG. 12 was 0.05 μm. From the results of FIG. 13, it can be seen that the obtained porous film has an inclined three-dimensional network structure in which the pore diameter gradually increases in the thickness direction from the surface. From the result of FIG. 13, it can be seen that macrovoids having a maximum diameter exceeding 5 μm are formed several tens of μm below the surface.

The amount of water permeation (m ³ / m ² / hr / MPa) of the obtained porous membrane was determined in the same manner as in Example 1.
The water permeability of the obtained membrane was 11 m ³ / m ² / hr / MPa.

[Example 9]
In this example, a high molecular weight polyvinyl pyrrolidone (polyvinyl pyrrolidone K79 manufactured by Nippon Shokubai Co., Ltd .: weight average molecular weight 400,000), which is difficult to be washed with water as the compound (A), was used to produce a porous membrane, and then washed sufficiently. This is a comparative example that was not performed.
First, in this example, a film-forming stock solution was prepared in the same manner as in Example 1 except that the stock solution composition was changed to the following ratio.
Chlorinated polyvinyl chloride: 20% by mass,
Polyvinylpyrrolidone K79: 4% by mass
NMP: 76% by mass.

Next, the film-forming stock solution obtained above was uniformly applied to a glass plate with a thickness of about 75 μm to form an uncoagulated film, and then 14% in air at a temperature of 19.5 ° C. and a relative humidity of 59.8%. The moisture absorption process was performed under the condition of standing still for 2 seconds.
Then, it was immersed in the coagulation liquid for 1 minute with the glass plate, and the porous film was obtained. As the coagulation liquid, an NMP aqueous solution having a concentration of 8% by mass (a mixture of 8% by mass of NMP and 92% by mass of water) was used.
Saturated water vapor amount at 19.5 ° C. is 16.8 g / ^{m 3,} values of V × t in this example is 140 g / ^{m 3} · sec.
After removing the obtained porous membrane from the glass plate, it was immersed in water at 20 ° C. for 24 hours for cleaning.

  In the same manner as in Example 1, an image obtained by observing the surface structure of the porous film at a magnification of 5000 is shown in FIG. 14, and an image of the cross-sectional structure is shown in FIG. From the image in FIG. 14, a concave structure of about 0.6 μm was formed, but it was blocked by unwashed polyvinyl pyrrolidone, and no clear pores were observed. From the results of FIG. 15, it can be seen that the obtained porous film has an inclined three-dimensional network structure in which the pore diameter gradually increases from the surface in the thickness direction. From the results of FIG. 15, it can be seen that macrovoids having a maximum diameter exceeding 5 μm are formed several tens of μm below the surface.

The water permeability (m ³ / m ² / hr / MPa) of the obtained porous membrane was measured by the same method as in Example 1, but the water permeability was as low as 0.2 m ³ / m ² / hr / MPa. became.

[Example 10]
This example is a comparative example in which methyl cellulose (methyl cellulose manufactured by Acros Organics Co., Ltd .: 2% aqueous solution viscosity 3000-5600 cP), which is difficult to be washed with water as a compound (A), was used to produce a porous membrane and was not sufficiently washed. It is.
First, in this example, a film-forming stock solution was prepared in the same manner as in Example 1 except that the stock solution composition was changed to the following ratio.
Chlorinated polyvinyl chloride: 19% by mass
Methyl cellulose: 3% by mass
NMP: 78% by mass.

Next, the film-forming stock solution obtained above was uniformly applied to a glass plate with a thickness of about 75 μm to form an uncoagulated film, and then 14% in air at a temperature of 19.5 ° C. and a relative humidity of 59.7%. The moisture absorption process was performed under the condition of standing still for 2 seconds.
Then, it was immersed in the coagulation liquid for 1 minute with the glass plate, and the porous film was obtained. As the coagulation liquid, an NMP aqueous solution having a concentration of 8% by mass (a mixture of 8% by mass of NMP and 92% by mass of water) was used.
Saturated water vapor amount at 19.5 ° C. is 16.8 g / ^{m 3,} values of V × t in this example is 140 g / ^{m 3} · sec.
After removing the obtained porous membrane from the glass plate, it was immersed in water at 20 ° C. for 72 hours for cleaning.
The image obtained by observing the surface structure of the porous membrane in the same manner as in Example 1 is shown in FIG. 16, and the image of the cross-sectional structure is shown in FIG. From the image in FIG. 16, the membrane surface was blocked with unwashed methylcellulose, and no clear pores were observed. It can be seen that the obtained porous film has an inclined three-dimensional network structure in which the pore diameter gradually increases from the surface toward the thickness direction. Moreover, it can be seen from the results of FIG. 17 that macrovoids having a maximum diameter exceeding 5 μm are formed several tens of μm below the surface.

The water permeability (m ³ / m ² / hr / MPa) of the obtained porous membrane was measured by the same method as in Example 1, but water permeability was not confirmed.

Claims (7)

A film-forming stock solution preparing step for obtaining a film-forming stock solution by dissolving chlorinated polyvinyl chloride in a good solvent for chlorinated polyvinyl chloride and a solvent compatible with water;
A film forming step of forming the film forming stock solution into a film to obtain an uncoagulated film;
A moisture absorption step of absorbing the moisture by holding the unsolidified film in air containing water vapor;
A method for producing a porous membrane, comprising a coagulation step of coagulating the uncoagulated membrane in a coagulation liquid after the moisture absorption step.   The method for producing a porous membrane according to claim 1, wherein in the film-forming stock solution preparing step, the compound (A) soluble in both the solvent and water is dissolved in the film-forming stock solution. In the moisture absorption step, when the amount of water vapor per unit volume of the air containing the water vapor is V (unit: g / m ³ ) and the moisture absorption time is t (unit: second), the value of V × t is 30 to The manufacturing method of the porous membrane as described in any one of Claims 1-2 which is 600 (unit: g / m < ³ > * second).   The method for producing a porous film according to any one of claims 2 and 3, wherein the compound (A) is lithium chloride or lithium bromide.   The manufacturing method of the porous membrane as described in any one of Claims 1-4 whose said porous membrane is a microfiltration membrane.   The method for producing a porous membrane according to any one of claims 2 to 5, wherein the compound (A) is polyvinylpyrrolidone having a weight average molecular weight of 50,000 or less.   A microfiltration membrane made of chlorinated polyvinyl chloride and having an inclined three-dimensional network structure with a maximum pore size of 0.1 μm to 5 μm inside the membrane.