JPS62112638A - Porous membrane - Google Patents

Abstract

PURPOSE:To provide a porous membrane which has a very low water permeation pressure and excellent durability and is hydrophilic, by retaining a specified polymer on at least part of the pore surface of a porous polyolefin membrane. CONSTITUTION:0.5-50wt% monomer having an HLB value of 2-20, at least one polymerizable unsaturated groups, a hydrophilic moiety and a hydrophobic moiety, represented by formulas I-III (wherein l-n, h are each an integer; EO is ethylene oxide; R1 is H, CH3; R2 is propylene oxide, etc.; R5, R6 are each a 4-20C alkyl; M is an alkali metal), is deposited on at least part of the pore surface of a porous polyolefin membrane having a pore size of 0.01-5mu in an arbitrary form of a hollow yarn membrane, a flat membrane, a tubular membrane, etc. and graft-polymerized by thermal polymn. or photopolymerization to form a polymer layer of 0.2-30mg/m<2> of surface area of pore on the surface of pore.

Description

[Detailed description of the invention] related.

[Conventional technology]

Polyolefin porous membranes have excellent mechanical properties and chemical resistance, so their application fields are rapidly expanding. However, since the polyolefin porous membrane is hydrophobic, it is difficult to allow water to pass through it as it is, and a hydrophilic treatment is required in order to allow water and other hydrophilic liquids to pass through it.

The divine method of making polyolefins hydrophilic by surface modification is being considered, but it is difficult to make hydrophilic materials with smooth surfaces, such as film-like materials, in contrast to the hydrophilizing of porous membranes with complex surface shapes. It cannot be applied.

Known methods for making porous polyolefin membranes hydrophilic include organic solvent wetting/water displacement methods, physical adsorption methods, and chemical surface modification methods. The organic solution All wetting/water displacement method involves moistening the entire surface of the alcohol fin porous J return, including the two pores, which has good compatibility with water, and then replacing the Cm r8 agent with water for 1d. However, with this method, once the water in the pores escapes during storage or use, the area returns to hydrophobicity and becomes impermeable to water, so the area around the porous membrane must be filled with water at all times. is required and the handling is complicated. The physical adsorption method is a method in which a hydrophilic substance such as polyethylene glycol or a surfactant is adsorbed onto the pore surface of a porous membrane to impart υL aqueous properties to the porous membrane (for example, Japanese Patent Application Laid-Open No. 54-153872,
JP-A No. 59-24732, etc.), and the operation is simple, but it is not necessarily a sufficient hydrophilization method because the hydrophilic substance is desorbed during long-term use. do not have.

Chemical modification methods include a method in which 4'A aqueous monomer is held on the surface of a porous film and irradiated with radiation (Japanese Patent Application Laid-Open No. 56-38153), or a method in which a water-soluble monomer is applied to a hydrophobic resin porous structure. Methods such as plasma treatment in a state impregnated with polymers or surfactants have been proposed (Japanese Unexamined Patent Publication No. 56-157457), but these methods are insufficient to make the pore surface hydrophilic. Hydrophilic treatment cannot be achieved.

[Problem that the invention seeks to solve]

As mentioned above, in the conventional technology, there are problems such as temporary hydrophilization, which makes handling inconvenient, and pore surfaces not sufficiently hydrophilized. No effective hydrophilization method has been established.

An object of the present invention is to solve the problems of the prior art and to provide a polyolefin porous membrane which has excellent durability and hydrophilicity over almost the entire pore surface of the membrane. be.

[Failure to solve the problem]

The porous membrane of the present invention is a porous membrane formed by holding a polymer layer made of a monomer having an HLBi of 2 to 20 on the surface of some (or some) pores of a polyolefin porous membrane.

Polyolefins used in the polyolefin porous membrane of the present invention include ethylene, propylene, 4-methyl-1
Examples include polymers or copolymers selected from the group such as -pentene and 3-methyl-1-butene, and fluorinated polyolefins. Further, the porous membrane can be in any form such as a hollow fiber membrane, a flat membrane, a hollow membrane, a tubular membrane, etc., and can have various pore diameters depending on the purpose. Preferred examples are as follows. As the pore diameter is 0.01
Examples include those with a diameter of about 5 μm.

In the present invention, monomers with an HLB value of 2 to 20 (hereinafter referred to as surface-active momers) have a hydrophobic part and a hydrophobic part in their molecules, and ionicity or nonionicity is not a problem. . The molecular weight is not particularly limited, but it is preferably about 10,000 or less. In addition, the monomer has a polymerizable unsaturated bond and has an HLB value of 2 to 20.
As polymerizable unsaturated bonds, vinyl bonds, allyl
Examples include monomers having double bonds such as a bond or triple bonds such as diacetylene, and hydrophilic moieties such as ethylene oxide, phosphoric acid ester! and sulfonic acid group or its salt, hydroxyl group, carboxylic acid group or its salt, 4
, a methylene group, alkyl/L/a';, a phenyl group, a vinyl group,
Examples include monomers having a hydrocarbon chain such as an allyl group, an acetylene bond, and an alkylene oxide of 03 or more such as propylene oxide and butene oxide.

As a specific example, the following general formulas (1) to (b)
Examples include compounds represented by formula (6) and α4 formula.

H2c=cR1coo(Eo)t(Rz)m(EO)n
cOcRt=cHz (1) H2C=CRtC00(
R2)z(KO)01(Rz)ncocR,=cH2(
2) H2C=CRICOO(KO)L(Rz)In(E
O) nRs (3) H, C= CR4CO
O(R2)m(EO)t(R2)llDIR3(4)H
2C=CRICOO(EO)z(R2)mCOCR1=
CH2(5)H,C=CR1Coo((CH2)40)
kCOCR1=CH2(6)H,C=CRICo-0(
KO) 902 formula (7) % formula % (8) In general formula (1) ~ α, t, mSn% m', k
% h s EOz R1, R2, R3, R4, R5
, - and M are defined as follows, and the chain length of ethylene oxide or propylene oxide or the alkyl/
L'! Although compounds outside the scope of the present invention may be included depending on how the chain length is selected, in the present invention, these chain lengths are appropriately selected and compounds having an HLB value in the range of 2 to 20 are used. .

L, m, n, k%h; integer E○; ethylene oxide; hydrogen or methyl group R2; propylene oxide or a compound of propylene oxide and ethylene oxide R3, R4, R5+1 R6; having 4 to 20 carbon atoms Alkyl group M: alkali metal The HLB value of the surface active monomer in the present invention is 2 to 20
However, those in the range of 5 to 15 are particularly preferred. Note that HLB in the present invention is Dav
ies) method (Progress Second International Combination of Surface Activity 1.426. (1957)) was adopted.

The porous membrane of the present invention is a porous membrane formed by holding a polymer layer made of a monomer having an HLB value of 2 to 20 on the surface of at least some pores of a polyolefin porous membrane, and is a porous membrane that is normally used. It is sufficient that the polymer layer is held on the surface of the pores to a sufficient extent to allow water to pass through the pores of the porous membrane due to the pressure difference between the membranes, and to obtain a permeation flow rate that does not interfere with use. However, it is not necessary that the entire surface of the pores be coated with the polymer. The polymer layer may still be retained on the outer surface of the porous membrane.

In addition, "retained" means that the polymer layer is firmly bonded or adhered to the pore surface to the extent that it does not easily detach during storage or use, and the polymer layer is firmly attached to the pore surface. The polymer layer may be graft-polymerized to e.g.
, may be attached in close contact with the m-hole portion by an anchor effect, or may be attached by graft polymerization or an anchor effect.

The polymer layer of the present invention made of monomers having an HLB value of 2 to 20 is characterized by a high degree of hydrophilicity compared to polyolefins that are substantially insoluble in water, dusty, and have a rough texture. A porous membrane formed by holding the polymer layer on the surface of at least some of the pores of the porous polyolefin membrane has almost permanent hydrophilicity.

On the other hand, polymers consisting of a single oil body with an HLB value exceeding 20 have high solubility in water, and therefore, a porous membrane made by retaining these polymers on the pore surface of a porous polyolefin membrane can be submerged in water. During use, the polymer dissolves in water and is released, so there is a risk that the surface properties of the pores in which the polymer was initially retained may change from hydrophilic to hydrophobic. There is. In addition, a polymer made of monomers with an HLB value of less than 2 is insoluble in water, but has a large degree of hydrophobicity, so the pore surface of the porous scar of the polyon fin in which the polymer is retained is hydrophilic. Does not show gender.

In addition, in order to reduce the solubility in water of a polymer layer consisting of a monomer with an HLB value of more than 20, it is possible to introduce a crosslinked structure into the polymer layer, but in that case, the polymer layer ()Δ The disadvantage is that the pores of the porous membrane swell and the pore diameter of the porous membrane becomes smaller.

The amount of the polymer layer held on the surface of at least a part of the pores of the polyolefin porous ff J'' of the present invention is approximately 15 to 50 lbf based on the weight of the polyolefin porous membrane.
It is preferable that it is about 1 to 5, more preferably 1 to 5.
0% by weight, particularly preferably 2 to 15% by weight, and approximately 1% by weight relative to the pore surface area of the porous polyolefin membrane.
It is 0■/m2.

Various methods can be employed to obtain the porous membrane of the present invention, but usually the surfactant is attached to the pore surface of the polyolefin porous membrane. - can be employed.

A method for attaching a surface-active monomer to a porous membrane is to add a surface-active monomer to a suitable solvent such as an organic solvent or water.
And if necessary, prepare a solution in which a polymerization catalyst is dissolved,
A method of immersing a polyolefin porous membrane in the solution,
Alternatively, a method can be adopted in which a membrane module μ is manufactured using a porous polyolefin membrane and then this solution is press-fitted into the porous membrane.

The surface active monomer thus retained on the pore surface of the porous polyolefin membrane is polymerized by thermal polymerization, photopolymerization, radiation polymerization, etc. to form a hydrophilic polymer layer on the pore surface of the porous membrane. can be formed.

When preparing the above solution, water or an organic solvent that can dissolve the surfactant is used, but when adding a polymerization catalyst, a solvent that can also dissolve the polymerization catalyst should be used. is desirable. However, when using water as a solvent, if the surface-active monomer is dissolved in water in advance, even if the polymerization catalyst is not originally soluble in water, it will be microdispersed in water due to the surface activity of the surface-active monomer, and it will essentially dissolve. Since it acts as if it were dissolved, water can be used as a solvent even when adding a polymerization catalyst that does not dissolve in water.

Since the surface of a polyolefin porous membrane is hydrophobic, especially when water is used as a solvent, when an aqueous solution containing a surface-active monomer permeates into the pores, the surface-active monomer binds its hydrophilic groups on the pore surface. Since it is easily adsorbed toward the outside, if this state is fixed through polymerization, it is possible to impart waterway properties more efficiently. Note that it is preferable to use water as a solvent from the viewpoint of workability, working environment, etc.

Further, when an organic solvent is used as the f4 medium, there are advantages such that the solution permeates into the pores of the polyolefin porous membrane in a short time and that the solvent can be easily removed from the pores.

Furthermore, even when polymerization is carried out in a state in which the surfactant polymers are randomly oriented on the pore surface without using the above-mentioned oriented adsorption, the formed polymer layer has a lower degree of hydrophilicity than polyolefin. Because of their large size, the pore surfaces on which the polymer layer is retained are relatively hydrophilic compared to the pore surfaces on which the polymer is not retained.

In the case of thermal polymerization, various peroxides, azo compounds, redox initiators, etc. known as radical polymerization initiators can be used as the polymerization catalyst used in polymerizing the surfactant. Examples include benzoyl peroxide, dicumyl peroxide, azobisisobutyronitrile, azomethane, and combinations of metal salts and hydrogen peroxide.

In the case of photopolymerization, diacetyl, benzyl, benzaldehyde, cyclohexanone, and other calpho-/” compounds, benzophenone, per-7 chloropenzophenone,
2. Ketone compounds such as 4-dichlorobenzophenone, anobenzophenone, penzophenone μphyto, and acetophenone; anthragynone thread compounds such as anthraquinone and 2-ethylanthraquinone; azo compounds such as azobisisobutyronitrile and azomethane; Photopolymerization catalysts such as benzoyl peroxide, biacetyl nitrate, benzyl dimethyl ketal, dibenzothiazolyl sulfide, eosin, erythrosin, neutral red, and pictolyab μ- can be used.

Examples of organic solvents that can simultaneously dissolve the surface-active monomer and the polymerization catalyst include methanol, ethanol, butanol, propatool, chloroform, acetic acid, toluene, benzene, acetone, methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, dimethylformamide, dimethylacetamide, Dimethyl sulfoxide and the like can be mentioned. Surfactant in solution
, the composition of the solvent and polymerization catalyst is surfactant Zimmer 10.
Conditions can be adopted such as 50 to 10,000 parts by weight of the solvent and 001 to 100 parts by weight of the polymerization catalyst Q, but 500 to 10,000 parts by weight of the solvent to 100 parts by weight of the surfactant. , polymerization catalyst 0,01-3
It is preferable that the amount is about 0 parts by weight.

In addition, the dipping time or press-fitting time when dipping or press-fitting the polyolefin porous membrane using the above solution is about 0.5 seconds to 30 minutes, and the wetting property for the polyolefin porous +1i is good. It can be carried out in a shorter time than when using a suitable solution. Further, after the immersion treatment, the surrounding excess liquid may be removed, and if necessary, the solvent that has penetrated into the pores may be evaporated, and then the process may proceed to the polymerization step using fire.

In the case of thermal polymerization, the polymerization temperature is preferably higher than the decomposition temperature of the polymerization catalyst and lower than the temperature that does not change the membrane structure of the polyolefin porous membrane and damage the membrane substrate, and is usually 30°C. A temperature of about 100° C. can be used. The heating time depends on the type of polymerization catalyst and the heating temperature, but is usually about 1 minute to 5 hours, preferably about 5 minutes to 60 minutes.

In the case of photopolymerization, ultraviolet rays or visible light can be used as a light source for light irradiation, but ultraviolet rays with high energy are particularly preferred. Further, as the ultraviolet light source, a low pressure mercury lamp, a high pressure mercury lamp, a xenon lamp, an arc lamp, etc. can be used.

Light irradiation conditions depend on the light irradiation intensity; low irradiation intensity makes it difficult to achieve sufficient hydrophilicity, and high irradiation intensity causes significant damage to the polyolefin porous membrane, so choose appropriate light irradiation conditions. is necessary. For example, when using a mercury lamp as a light source, the input is about 10 to 500 W/c1n, and the irradiation is performed from a distance of about 10 to 50 cnM for about 15 to 300 seconds, resulting in a light emission of 0.001 to 10 jou.
α05~1 j oule is more preferable than about le/i
It is sufficient to irradiate energy of about /α2.

In the case of radiation polymerization, for example, an electron beam irradiation device is used, and 1
This can be carried out by irradiating an electron beam at a dose of about 10 to 50 M rad at a temperature of 20° C. or lower, preferably 100° C. or lower.

The surfactant polymer retained on the pore surface of the porous membrane is graft-polymerized to the porous membrane or polymerized on the porous membrane surface by these polymerization methods.
At least a portion of the pore surfaces of the porous membrane are covered by these polymer layers.

Note that the presence of oxygen in the atmosphere during polymerization will significantly inhibit the polymerization reaction, so an inert gas atmosphere such as a nitrogen atmosphere,
Alternatively, it is desirable to carry out the polymerization in a state substantially free of oxygen, such as in a vacuum. After the polymer layer is formed,
It is desirable to remove unnecessary components such as unreacted monomers and free polymers existing around the surface of the pores of the porous membrane using a suitable solvent. When the polymer formed on the pore surface of the porous membrane is an uncrosslinked polymer, it is preferable to use a solvent that dissolves unreacted monomers but does not dissolve the polymer.

Further, when the polymer is a crosslinked polymer, a solvent capable of dissolving unreacted monomers may be used.

By employing such a method, the porous membrane of the present invention can be obtained.

〔Example〕

The present invention will be specifically explained below using Examples.

In the examples, water permeability, water permeability, and alcohol membrane area were determined by the following method using a test membrane module with an area of 163 cm2. In addition, No. 11 (the amount retained and the surface coverage of the combined layer were measured by the following method.

(1) Hydraulic pressure: 0.1 kg per minute from one side of the test mock module (in the case of a hollow fiber membrane, the inner part of the hollow fiber)
Water at 25°C is supplied while increasing the water pressure at a rate of /cm2, and the water pressure is measured when the amount of permeated water reaches 30rrLl and 50Ll. Next, the water pressure is plotted on the horizontal axis and the amount of permeated water is plotted on the vertical axis, and the pressure value at the point where the straight line connecting the two plotted points intersects with the horizontal axis is determined, and that value is taken as the permeable pressure.

(2) Water permeability: Water at 25°C is flowed through one side of the test membrane module (inside the hollow fiber in the case of a hollow fiber membrane), and the amount of permeated water is measured with the transmembrane pressure differential being 50 wHg. The water permeability C1/m2-hr*+mmHg) is calculated from

(3) Water permeability by alcohol/I/hydrophilization method: Ethanol from one side of the test membrane module (inside of the hollow fiber membrane in the case of a hollow fiber membrane) that has not been subjected to hydrophilization treatment. After letting ls'l,
Water was flowed for 15 minutes at a flow rate of 100 ml/miH,
The ethanol present inside the pores is replaced with water. Subsequently, water permeability is measured by the method described in (2).

(4) Retention amount of polymer layer: Measure the weight % of the polymer layer retained with respect to the unit weight of the polyolefin porous membrane.

(5) Surface coverage; JIS K6768 (1971)
The porous membrane was immersed for 1 minute in the standard HC blue for wetness test with a surface tension of 54 dYn/cr11 described in , and then air-dried.
Ten cross sections of the porous membrane were observed using an optical microscope to determine the ratio of the thickness of the colored portion to the membrane thickness, and this was taken as the surface coverage.

Example 1 Porosity: 68mm, membrane thickness: 7oμm, inner diameter: 270Am, water permeability by alcohol/l/hydrophilization method: 1.5t/@"'
A membrane module μ with an effective membrane area of 165 cM2 was prepared using a polyethylene porous hollow fiber membrane of hr-mHll, and 7.5 ml of the solution having the composition shown in Table 1 was poured from the inside of the hollow fiber membrane of the membrane module. After being press-fitted for 10 minutes at a pressure of 100 ml/min, the P. aeruginosa was taken out into nitrogen, excess liquid was removed, and the tube was air-dried for 16 hours. Next, the membrane module was heat-treated at 60° C. for 50 minutes in a nitrogen atmosphere, and then thoroughly washed with acetone to obtain a porous membrane of the present invention.

Subsequently, the amount retained in the polymer layer and the water permeability pressure before and after hydrophilization were measured.

In addition, for the purpose of evaluating the durability of the hydrophilic treatment, a test membrane module after the hydrophilic treatment was used to evaluate the membrane area of 102 60%.
After pouring out 0 d of water, drying and handling, and measuring the water permeability pressure again were repeated 5 times. The water permeability pressure after these 5 cycles of washing and drying was exactly the same as before washing and drying, confirming the durability of the product of this example.

These results are shown in Table 1.

Examples 2 to 6 Porosity: 68 cm, thickness: 60 μm, inner diameter: 270 μm, water permeability by 14J hydration method: 1.3 t/m
Polyethylene porous hollow fiber membranes of 2.hr-mn Hi were immersed in each solution having the composition shown in Table 1 for 3 seconds each, and then taken out from the solution into nitrogen to remove excess liquid. Next, after air drying for 16 hours, each porous membrane is heat-treated at 60°C for 30 minutes in a nitrogen atmosphere to retain the polymer layer on the pore surface of the porous membrane, and then thoroughly washed with acetone. A porous membrane of the present invention was obtained by this method, and the retention amount and water permeability of the polymer layer were measured.

For Examples 2 and 4, the surface coverage was further measured and the durability was evaluated in the same manner as in Example 1. The surface coverage of the porous membranes of Examples 2 and 4 was 90-100% and 95-100%, respectively, and the water permeability did not change at all even after 5 cycles of water washing and drying.

These results are shown in Table 1.

Examples 7 and 8 The same polyethylene porous hollow fiber membranes as in Example 2 were each immersed in a solution having the composition shown in Table 1 for 5 seconds each, and then taken out of the solution into nitrogen to remove excess liquid. Next, after air-drying for 16 hours, each porous membrane was placed in a nitrogen atmosphere for 2k.
2 oct W high pressure mercury lamp (input 80W/CM type)
The surfactant was polymerized by irradiating for 3 seconds from a distance of W1, and then thoroughly washed with acetone to obtain a porous membrane of the present invention.

The retention amount and water immersion pressure of the polymer layer were measured, and the durability was evaluated in the same manner as in Example 2, and good results were obtained.

These results are shown in Table 1.

Example 9 Instead of heating and polymerizing in Example 2, an electron beam irradiation device was used to irradiate the porous membrane with an electron beam at an acceleration voltage of 200 kV, an electron current of 1 mA, and a temperature of 80°C or less.
A porous membrane of the present invention was obtained in the same manner as in Example 2 except for polymerization by M rad irradiation, and the retention amount and water permeability of the polymer layer were measured.

The results are shown in Table 1.

Example 10 A polyethylene porous flat membrane with a porosity of 70% and a water permeability of 55 t/rn"·hr-mHg by alcohol hydration method was immersed for 3 seconds in a solution having the composition shown in Table 1. The solution was taken out into nitrogen to remove excess liquid, and was further air-dried for 16 hours.

Next, the porous membrane was heat-treated at 70°C for 20 minutes in a nitrogen atmosphere, and then thoroughly washed with acetone to obtain the porous membrane of the present invention, and the retention amount and water permeability of the polymer layer were measured. did.

The results are shown in Table 1.

Example 11 Porosity: 45 cm, hole thickness: 22 μm, inner diameter: 200 μm, 1 V, water permeability by hydrophilization method: 0.8 t/m2.
After immersing a polypropylene porous hollow fiber membrane with hr-+mHg in the solution having the composition shown in Table 1 for 5 seconds, the membrane module P was taken out into nitrogen, excess liquid was removed, and it was further air-dried for 16 hours. Next, the membrane module was heat-treated at 80° C. for 20 minutes in a nitrogen atmosphere, and then thoroughly washed with acetone to obtain a porous membrane of the present invention.

Subsequently, evaluation was performed in the same manner as in Example 2.

These results are shown in Table 1.

Comparative Examples 1 and 2 Using solutions with the compositions shown in Table 1 and the other conditions being exactly the same as in Example 2, porous membranes retaining the polymer layers were obtained and their performance was evaluated. I got the result. The permeability pressure is &3, 9/tan2 and IQ., respectively. 7 to 9/α2, which is the same as O.7 in Example 2. 97cm'', this value is quite high, and it can be seen that these porous membranes do not have sufficient hydrophilicity.In addition, the surface coverage of Comparative Examples 1 and 2 is 4 to 8% and a It was ~2chi.

Comparative Example 3 Using a solution with the composition shown in Table 1 and keeping the other conditions exactly the same as in Example 2, a porous membrane retaining the polymer layer was obtained and its performance was evaluated. Got the results. The permeability pressure is 1 1. 5kl? /lyn2, which is a considerably higher value compared to 15 kg/cm'' for the bales of Example, and it can be seen that this porous membrane does not have sufficient water repellency.

Comparative Example 4 The same polyethylene porous hollow fiber membrane as in Example 2 was immersed in a solution having the composition shown in Table 1 for 1 minute, then taken out into the air and air-dried at room temperature for 16 hours to produce a membrane module. When the water permeability was measured using the membrane module, a value of 9/cm2 was obtained for I:L 2 ', indicating that hydrophilicity could be imparted by the Tsumar adhesion method on top of surface activity. After one test, the permeability pressure was F3. ,
[1 kg/m''. It can be seen that the adhesion method only imparts temporary hydrophilicity.

(Note 1) H2C=CHC00(EO)H2(PO)
2゜(EO)12CH3 (Note 2) H2C=CHC0
0 (EO), 4COCH=CH2 (Note 5) H2C=
CHC00 ((CH2)40), CoCH=CH.

(Note 4) H2C=CHC00(PO)50(EO)
13COCR-CH.

(Note 5) H2C-CHCoo(PO). (EO)
, C0CH=CH2 (Note 6) H2C=CHC00
(EO)t2(PO)2o(EO)tzcOcH=cH
2H2C=CHCI(2CI(3 (Note 8) H2C=CHC0O(PO)55COCH
=CH2 (Note 9) (EO) in (Note 1) to (Note 8)
and (PO) represent ethylene oxide and hyperpylene oxide, respectively.

〔Effect of the invention〕

As is clear from the results of the Examples, the permeability pressure of the porous membrane of the present invention is significantly lower than that of the untreated porous polyolefin membrane, indicating that it has sufficient hydrophilicity.

Furthermore, in the evaluation of durability by repeated washing and drying, there was almost no change in water permeability, indicating that the porous membrane of the present invention has hydrophilicity with durability = f. .

Claims (1)

[Claims] A porous membrane comprising a polymer layer made of a monomer having an HLB value of 2 to 20 held on the surface of at least some pores of a porous polyolefin membrane.