JP3102591B2 - Microporous membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microporous membrane suitable for separating and purifying a fluid, particularly an aqueous fluid. Specifically, a microporous membrane made of a hydrophobic polymer material is coated with a low hydrophilic material, and further coated with a water-insoluble hydrophilic polymer material, thereby significantly improving hydrophilicity, durability, heat stability, and water permeability. The present invention relates to a microporous membrane suitable for separating and purifying an aqueous fluid having excellent properties.

[0002]

2. Description of the Related Art Porous polymer membranes are used for water treatment of aqueous solutions and suspensions, filtration membranes or separation membranes used for the production of ultrapure water, or medical materials such as plasma separation membranes and artificial lungs. Or various fields such as a battery and a battery separator used for electrolysis, etc., and it is preferable that the membrane is hydrophilic in any case.

[0003] The hydrophilic porous membrane can be roughly classified into a porous membrane made of a hydrophilic polymer as a raw material, a porous membrane made of a hydrophobic polymer as a raw material, and a porous membrane obtained by hydrophilizing the surface of the through hole and the inner surface of the through-hole. . As the former porous membrane, a membrane made of a water-insoluble hydrophilic polymer material derived from cellulose, polyvinyl alcohol or the like is well known. The feature of these porous membranes is that the membrane material itself is hydrophilic, so it interacts with water greatly and is easily wetted by water, and water or an aqueous solution penetrates into the membrane without special treatment of the membrane in advance. , Filtration and separation can be easily performed. However, these hydrophilic porous membranes have a high water absorption rate of the polymer material itself forming the membrane, which not only leads to a decrease in mechanical strength due to swelling, but also decreases the membrane performance due to a decrease in pore size and porosity. It has the disadvantage of lowering. In addition, these hydrophilic porous membranes are often brittle at the time of drying, and have the disadvantage of low mechanical strength. further,
The preparation of these hydrophilic porous membranes involves forming a solution of a hydrophilic polymer as a raw material into a film, evaporating part or all of the solvent, and then immersing it in a coagulation bath to make it porous by phase inversion. Since it is often employed, the process is complicated and the management and treatment of the organic solvent are complicated, and the resulting film is often a film having irregular pores.

[0004] On the other hand, as the porous membrane obtained by subjecting the surface of the latter hydrophobic porous membrane to hydrophilic treatment, various membranes have been proposed depending on the treatment method. (1) A membrane obtained by a method in which a water-soluble organic solvent such as ethyl alcohol or acetone is permeated into the fine pores of a hydrophobic porous membrane, and then replaced with water. (2) A membrane having a polymerizable functional group Not ionic system,
Coating of nonionic surfactants, lipids, etc., or membranes obtained by coating with ionic, nonionic surfactants, lipids, etc. having a polymerizable functional group and subsequent polymerization (JP-A-47-14269) JP-A-60-11536, JP-A-61-2743, JP-A-62-114610, JP-A-63-1
(41609, etc.) (3) A film obtained by coating a water-soluble polymer having a polymerizable functional group and then insolubilizing the water-soluble polymer with water by irradiation with ionizing radiation such as ultraviolet rays or electron beams, or heat treatment ( JP-B-55-35145, JP-A-62-14904, JP-A-63-9
7634). However, the films obtained by these methods have various disadvantages. The membrane obtained in (1) is hydrophilic as long as the membrane surface and the inside of the micropores are in a wet state, but once the membrane is dried, the hydrophilic property is lost, and the water permeation phenomenon is observed unless the same operation is performed again. Absent. In the membrane obtained in (2), the coated surfactant or lipid elutes with the water permeation time, and the treatment liquid is gradually contaminated and the water permeation performance is reduced. In the film (3), the water-soluble polymer used for coating has a small interaction with the hydrophobic film, and the water-soluble polymer is coated on the surface of the hydrophobic film and inside the microporous with uniform and good adhesion. I haven't. In addition, when the water-insolubilization of the water-soluble polymer by the post-treatment has not sufficiently proceeded to the microporous portion of the porous membrane, the contamination of the processing solution due to the elution of the water-soluble polymer, and when the water-soluble polymer has sufficiently proceeded, In such a case, problems such as a decrease in the pore diameter and porosity occur. Further, post-treatments such as irradiation with ionizing radiation or heating are accompanied by deterioration of the film material itself, promote separation of the porous film from the water-soluble polymer, and often cause reduction in water permeability. Furthermore, it is practically difficult to industrially employ treatment by irradiation with ionizing radiation, which requires a large-scale facility, for hydrophilizing a polymer porous membrane.

[0005]

As described above, each of the conventionally known hydrophilic porous membranes has various drawbacks, is excellent in water permeability, does not reduce water permeability due to heat treatment, and can separate water-based fluids. From the viewpoint of a microporous membrane suitable for purification,
Neither is enough.

Accordingly, an object of the present invention is to provide a filtration membrane or a separation membrane used for water treatment of an aqueous solution or an aqueous suspension without the above-mentioned disadvantages, production of ultrapure water, a plasma separation membrane, an artificial lung, etc. Medical materials, or batteries, having a large number of uniform fine pores that can be suitably used in fields requiring hydrophilicity such as battery separators used for electrolysis,
An object of the present invention is to provide a hydrophilic microporous membrane having excellent durability and thermal stability.

[0007]

Means for Solving the Problems The inventors of the present invention have carefully studied the drawbacks of the conventionally provided hydrophilic porous membrane from various angles, such as materials, molding conditions, and hydrophilicity techniques. The surface of the hydrophilic polymer porous membrane is coated with a low hydrophilic material, and the microporous membrane further coated with a water-insoluble hydrophilic polymer material achieves the above object, and has reached the present invention. .

Hereinafter, the microporous membrane of the present invention will be described in detail. The hydrophobic polymer porous membrane having through micropores in the present invention is a porous membrane having uniform and fine through-pores made of a hydrophobic polymer material, and as the polymer material, for example, polyethylene , Polypropylene, poly (4
-Methyl-pentene-1), ethylene-propylene copolymer, polytetrafluoroethylene, poly (trifluorochloroethylene), polyvinylidene fluoride, polyvinylidene chloride, polyvinyl fluoride, polyvinyl chloride, polysulfone and the like.

The shape of the hydrophobic polymer porous membrane in the present invention is not particularly limited, and any of a hollow fiber-like hollow fiber membrane and a film-like flat membrane is suitably employed.

The physical properties such as the film thickness, the average pore diameter and the porosity of the hydrophobic polymer porous membrane in the present invention are not particularly limited, but the film thickness is preferably 1 to 2000 μm, particularly preferably 10 to 1000 μm. And the average pore size is preferably 0.1.
005 to 20 μm, particularly preferably 0.01 to 10 μm, and the porosity is preferably 20 to 90%, particularly preferably 30 to 80%.

In the present invention, the surface of the hydrophobic polymer porous membrane having the through micropores does not refer to the surface of the membrane, but
This is the surface of the polymer material forming the hydrophobic polymer porous membrane. That is, the film surface and the through-hole surface. In the case of a hollow fiber membrane, it refers to the outer surface, the inner surface, and the surface of the polymer material present in the through holes.

The low hydrophilic material in the present invention is a material having the same level of interaction with a polymer material forming a hydrophobic polymer porous membrane and a water-insoluble hydrophilic polymer material. The water-insoluble hydrophilic polymer material plays a role of a primer for coating the surface of the hydrophobic polymer porous membrane uniformly and with good adhesiveness. Therefore, the microporous membrane of the present invention has excellent durability and thermal stability, maintains stable water permeability for a long time, and is heat-treated, as compared with a porous membrane in which only a hydrophilic polymer material is coated on a hydrophobic polymer porous membrane. No decrease in water permeability due to water is observed. The material that satisfies these properties is not particularly limited as long as it has a good interaction with both the hydrophobic polymer material and the hydrophilic polymer material. Judging from the above, a polymer material is suitably adopted.

Further, as a polymer material satisfying these properties, a solubility parameter δh (J ^1/2 cm ^−3/2 ) based on a hydrogen bonding force in a solubility parameter proposed by Hildebrand is 2-1.
A polymer material having a value of 0 is particularly preferably employed. For example,
Chlorsulfonated polyethylene, chlorinated polyethylene,
Chlorinated polypropylene, ethylene-vinyl chloride copolymer, polyvinyl formal, polyvinyl ethyl ether, styrene-N-vinyl-2-pyrrolidone copolymer,
Styrene-2-vinylpyridine copolymer, styrene-maleic anhydride copolymer, N-vinyl-2-pyrrolidone-
Examples include a styrene graft copolymer, a styrene-acrylonitrile copolymer, a styrene-acrylic acid copolymer, and a styrene-acrylamide copolymer.

The water-insoluble hydrophilic polymer material in the present invention is insoluble in water, but has a large interaction with water and is easily wetted by water. A polymer material having the property that water easily penetrates into the micropores of the membrane. For example, nylon, cellulose derivatives, polyvinyl alcohol derivatives and the like are preferably employed, and nylon is particularly preferably employed.

The nylon in the present invention is not particularly limited as long as it is a linear polymer having an amide bond in the main chain. For example, dicarboxylic acids such as oxalic acid, adipic acid, sebacic acid, dodecanedioic acid, terephthalic acid, isophthalic acid, 1,4-cyclohexyldicarboxylic acid, and ethylenediamine, tetramethylenediamine, hexamethylenediamine, decamethylenediamine, 4,4-cyclohexyldiamine, 1,3-cyclohexanebismethyldiamine, trimethylhexamethylenediamine, 4,
Nylon obtained by polycondensation of a nylon salt obtained from diamines such as 4'-diaminodicyclohexylmethane, para-xylylenediamine and meta-xylylenediamine. Cyclic amide compounds such as pyrrolidone, caprolactam, dodecalactam or ε-aminocaproic acid;
Nylon obtained by polycondensing amino acids such as ω-aminoundecanoic acid and ω-aminododecanoic acid. Alternatively, a mixture or copolymer of these nylons may be used. Preferably, nylon 6, nylon 66, nylon 4, nylon 46, nylon 610, nylon 11, nylon 12, nylon MXD6, nylon 4,4'-diaminodicyclohexylmethane 6, nylon 6T, nylon 6I or a mixture of these nylons Alternatively, copolymers and the like can be mentioned. Particularly preferred are nylon 6, nylon 66, nylon 610, nylon 11,
Nylon 12, Nylon MXD6, Nylon 4,4'-
Examples thereof include diaminodicyclohexylmethane 6 or a mixture or copolymer of these nylons.

The coating in the present invention means that the surface of the hydrophobic polymer porous membrane is made of the above-mentioned low hydrophilic material and the water-insoluble hydrophilic polymer without closing the through-holes of the hydrophobic polymer porous membrane. The state covered by the material. Therefore,
Physical properties of the porous film such as film thickness, average pore size, and porosity are essentially unchanged before and after coating, and the surface state of the polymer material forming the porous film changes from hydrophobic to hydrophilic. It is.

Hereinafter, a method for producing the microporous membrane of the present invention will be described. The step of producing the microporous membrane of the present invention comprises a step of coating the surface of the hydrophobic polymer porous membrane with a low hydrophilic material and a water-insoluble hydrophilic polymer material, which comprises applying a low hydrophilic material solution. It consists of a process and a drying process, followed by a coating process and a drying process of a water-insoluble hydrophilic polymer material solution.

When a low hydrophilic polymer material is used as the low hydrophilic material, a solvent constituting the low hydrophilic polymer material solution can be appropriately selected depending on the low hydrophilic polymer material used. For example, methylene chloride, chloroform, benzene, toluene, dioxane, acetone, ethyl methyl ketone, ethyl acetate, N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide and the like can be mentioned.

When nylon is used as the water-insoluble polymer material, the solvent constituting the nylon solution can be appropriately selected depending on the nylon used. Nylon 6,
For crystalline nylon such as nylon 66 and nylon MXD6, formic acid, calcium chloride / methanol, calcium chloride / ethanol, metacresol, phenol / methanol, phenol / ethanol, trifluoroethanol, hexafluoroisopropanol, trifluoroacetic acid Such a solvent having an action of breaking a hydrogen bond between amide groups of nylon is preferably used, and formic acid, calcium chloride / methanol, and calcium chloride / ethanol, which are low in boiling point and inexpensive, are particularly preferably used. Further, for example, nylon 6-nylon 66-nylon 12 (weight fraction of 0.
46-0.32-0.22), nylon 6-nylon 6
6-nylon 610 (weight fraction 0.44-0.35-
0.21), nylon 6-nylon 66-nylon 61
0-Nylon 12 (weight fraction 0.40-0.25-
0.20-0.15), nylon 6-nylon 66-nylon 4,4'-diaminodicyclohexylmethane 6
Hydrogen bonds between amide groups are reduced as in the above-mentioned multi-component copolymer of nylon such as (weight fraction 0.40-0.30-0.30), and methanol is used for nylon having reduced crystallinity. A solvent in which a lower aliphatic alcohol occupies 80% by volume or more such as ethanol, isopropanol and butanol is preferably employed, and methanol and ethanol are particularly preferably employed. All of the above solvents do not need to be anhydrous, and even if they contain water as long as they do not inhibit the solubility of nylon, they do not hinder the coating.

The concentrations of the low hydrophilic polymer material solution and the nylon solution can be arbitrarily selected, but are preferably 0.05 to 10% by weight / volume, and particularly preferably 0.1 to 10% by weight.
1 to 5% by weight / volume. The coating may be completed by a single application, but it is also possible to repeatedly apply the solution with a low concentration.

The temperature of the coating step is appropriately selected depending on the boiling point of the solvent used or the viscosity of the low hydrophilic polymer material solution and the nylon solution, and is not particularly limited, but is preferably room temperature to 100 ° C., particularly preferably room temperature. ６０60 ° C.

The application time is determined by the viscosity of the low hydrophilic polymer material solution and the nylon solution, the average pore diameter of the hydrophobic polymer porous membrane, the porosity, the hydrophobic polymer porous membrane and the low hydrophilic polymer material solution and the nylon solution. It is arbitrarily selected depending on the interaction with and the like, but is preferably 1 second to several tens of minutes, and particularly preferably 1 second to several ten minutes.
0 seconds to several minutes.

The coating method is not limited at all, and various methods are appropriately adopted. For example, a method of dipping a hydrophobic polymer porous membrane into a low hydrophilic polymer material solution and a nylon solution, supplying the low hydrophilic polymer material solution and a nylon solution to one side of the hydrophobic polymer porous membrane, and applying a pressure difference Examples include a method of permeating the inside of the fine pores of the polymer porous membrane, a method of supplying a low hydrophilic polymer material solution and a nylon solution to the hydrophobic polymer porous membrane in a spray form, and the like, which is simple in equipment and operation. In consideration of the properties and reproducibility of the coating state, a method of dipping a hydrophobic polymer porous membrane is preferably employed.

Dipping can be carried out in a batch system using a hydrophobic polymer porous membrane cut into various shapes, or a polymer porous membrane (hollow fiber membrane or flat membrane) wound into a roll can be continuously formed. Both can be performed by a continuous method of dipping.

The drying step following the coating step is a step of evaporating and removing the solvent constituting the low hydrophilic polymer material solution and the nylon solution, and a usual drying method is employed. For example, natural air drying, hot air drying, vacuum drying and the like are employed, and these are employed alone or in appropriate combination. Of course, a batch system and a continuous system are appropriately adopted according to the coating method,
Both are possible.

The drying temperature and the drying time are appropriately selected depending on the vapor pressure of the solvent, the concentration of the solution, etc., but are preferably room temperature to 150 ° C. for several minutes to several hundred hours, and particularly preferably room temperature to 10 hours.
It is tens of minutes to tens of hours at 0 ° C. The atmosphere in the drying step is not particularly limited, and an air atmosphere is sufficient.

The microporous membrane according to the present invention is not only a hydrophilic membrane in which water easily penetrates into the penetrating micropores only by contact with water, but also removes water penetrating into the penetrating micropores.
Even when the membrane is dried, it is characterized in that the water easily permeates again into the through micropores when brought into contact with water again. In addition, the water permeability continues very stably over a long period of time.

The microporous membrane of the present invention described in detail above is not limited to a polymer material constituting the porous membrane, and may be a highly hydrophobic polymer such as polyethylene, polypropylene, and polytetrafluoroethylene. Even if it is a porous membrane made of a material, its surface is coated with a water-insoluble hydrophilic polymer material typified by nylon to coat it, thereby significantly improving the hydrophilicity and making it easy to penetrate water. It is a film having. Furthermore, since the microporous membrane of the present invention has a primer layer having an interaction between the hydrophobic polymer porous membrane and the coating layer of the water-insoluble hydrophilic polymer material, the hydrophilic layer has extremely excellent water permeation stability. Porous membrane.

[0029]

EXAMPLES The present invention will be described more specifically with reference to examples, but the present invention is of course not limited to the following examples. (Example 1) Polypropylene (UBE-PP-F109)
K, trade name: Ube Industries, Ltd., MFI = 9g / 10
Min) using an inflation molding machine equipped with a die having an outer diameter of 150 mm, discharge temperature 190 ° C, take-off speed 30m
The blown film was formed under the condition of / min. The unstretched polypropylene film was obtained by subjecting the obtained polypropylene film to a heat treatment in a heated air bath at 145 ° C. for 30 minutes.

The unstretched film was treated with liquid nitrogen (-196
C.), the film was stretched by 20% with respect to the initial length, and heat-set in a heated air bath at 145 ° C. for 2 minutes while maintaining the stretched state.

This film was heated in an air atmosphere at 130 ° C. for 3 hours.
After performing the 100% heat stretching, the sheet was further heat-set in a heated air bath at 145 ° C. for 30 minutes to obtain a polypropylene microporous flat membrane.

The average pore diameter of the obtained microporous polypropylene flat membrane was 0.27 μm as measured by a half dry method using ethanol. The porosity is determined by the POROSIMETRO SERIE manufactured by CARLOERBA (Italy).
S) When measured by a mercury intrusion method using 1500, 7
2.4%.

The surface and cross section of this polypropylene microporous flat membrane were examined with a scanning electron microscope (X-60 manufactured by Hitachi, Ltd.).
Observation by 5) shows that fine fibrils are formed in the flat membrane on the surface of the membrane substantially parallel to and at equal intervals in the stretching direction of the membrane, and the fibrils and the gaps between the fibrils expand two-dimensionally in the cross-sectional direction of the membrane. It was found that a large number of fine through holes were formed.

Next, a styrene-maleic anhydride copolymer having a concentration of 1% by weight / volume (DAIRAK 232, trade name: Sekisui Chemical Co., Ltd.)
) Was immersed in a chloroform solution for 1 minute at room temperature to sufficiently spread the solution into the through-holes of the polypropylene microporous flat membrane, and then air-dried at room temperature for 2 hours.

Further, the membrane was treated with a nylon 6-nylon 66-nylon 12 (weight fraction) having a concentration of 2% by weight / volume.
0.46-0.32-0.22) Immerse in a methanol solution of the copolymer for 1 minute at room temperature, sufficiently spread the solution into the through micropores of the polypropylene microporous flat membrane, and then 24 hours at room temperature Air dried.

When the surface and cross section of the obtained microporous membrane were observed with a scanning electron microscope, a form in which essentially the same number of through micropores as the microporous flat membrane before coating was retained was observed. .

When water was brought into contact with the microporous membrane, the water easily penetrated into the micropores and permeated. Permeation rate is 24
It was 5.6 liter / mim · m ² · kgf / cm ² .

The microporous flat membrane whose water permeation rate was measured was dried at room temperature, heat-treated at 80 ° C. for 1 hour, and brought into contact with water again. As described above, water easily permeated into the micropores and permeated. Water permeation rate of 241.5 l / mim · ^m 2 · k
gf / cm ² .

This operation was repeated five times, but there was no change in the phenomenon of water permeation into the microporous membrane, and the water permeation rate was 219.
It was 3 liters / mim · m ² · kgf / cm ² .

(Comparative Example) The polypropylene microporous flat membrane described in Example 1 was treated with nylon 6-nylon 66-nylon 12 having a concentration of 2% by weight / volume (weight fraction 0.46-0.
32-0.22) Add 1 part of the copolymer to a methanol solution at room temperature.
After immersing for a minute, the solution was sufficiently spread to the inside of the through micropores of the microporous polypropylene flat membrane, and then air-dried at room temperature for 24 hours.

When this microporous flat membrane was brought into contact with water,
Water readily penetrated and permeated into the pores. Permeability is 17
It was 7.9 liters / mim · m ² · kgf / cm ² .

After drying the microporous flat membrane whose water permeability was measured at room temperature, the water permeability was measured again and found no change.
However, when this membrane was heat-treated at 80 ° C. for 1 hour, the water permeation rate was 23.1 liter / mim · m ² · kgf / cm.
Dropped to ² . When this operation was repeated again, the water permeation rate was reduced to 3.1 liter / mim · m ² · kgf / cm ² . This is considered to be due to the fact that the nylon coating layer covering the surface of the polypropylene microporous flat membrane was peeled off from the polypropylene surface by the heat treatment, the polypropylene surface was exposed, and the water permeability was reduced.

(Example 2) The polypropylene microporous flat membrane described in Example 1 was treated with styrene-N having a concentration of 1% by weight / volume.
-Vinyl-2-pyrrolidone (molar fraction 0.5-0.
The solution was immersed in the chloroform solution of 5) at room temperature for 1 minute to sufficiently spread the solution into the through-holes of the microporous flat polypropylene membrane, and then air-dried at room temperature for 2 hours.

Further, the membrane was treated with nylon 6-nylon 66-nylon 12 (weight fraction) at a concentration of 2% by weight / volume.
0.46-0.32-0.22) Immerse in a methanol solution of the copolymer for 1 minute at room temperature, sufficiently spread the solution into the through micropores of the polypropylene microporous flat membrane, and then 24 hours at room temperature Air dried.

When the surface and the cross section of the obtained microporous membrane were observed with a scanning electron microscope, a form in which essentially the same number of through micropores as the microporous flat membrane before coating was retained was observed. .

When this microporous flat membrane was brought into contact with water,
Water readily penetrated and permeated into the pores. Permeability is 22
It was 8.3 liter / mim · m ² · kgf / cm ² .

The microporous flat membrane whose water permeation rate was measured was dried at room temperature, heat-treated at 80 ° C. for 1 hour, and brought into contact with water again. As described above, water easily permeated and permeated into the micropores. Water permeation rate of 219.5 l / mim · ^m 2 · k
gf / cm ² .

This operation was repeated five times, but there was no change in the phenomenon of water permeation into the microporous membrane, and the water permeation rate was 193.
It was 1 liter / mim · m ² · kgf / cm ² .

[0049]

The microporous membrane of the present invention covers the surface of the hydrophobic polymer porous membrane and the inner surface of the through pores with a primer layer made of a low hydrophilic material, and further with a water-insoluble hydrophilic polymer material. By doing so, the hydrophilicity is remarkably improved, and the microporous membrane is excellent in durability, heat stability, and water permeability. Therefore, it is of course used as a separation membrane that is extremely suitable for separation and purification of aqueous fluids, but also has a hydrophilicity of the coating layer,
Utilizing its insulation and durability, it has become possible to apply it to batteries, battery separators used for electrolysis, and the like.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) B01D 69/02

Claims (1)

(57) [Claims] 1. The surface of a hydrophobic polymer porous membrane having through micropores has a solubility parameter δh based on hydrogen bonding force of 2
-10 (J ^1/2 cm ^-3/2 ), and the surface of the low hydrophilic material is further coated with a water-insoluble hydrophilic polymer material. Microporous membrane.