JPH11106552A - Microporous hydrophilized polyolefin membrane and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high-strength high-permeability hydrophilic microporous membrane by grafting a specified amount of an acrylic monomer onto the surface and pore surfaces of a microporous membrane made from a polyolefin composition containing an at least specified amount of an ultrahigh-molecular- weight polyolefin and having a specified porosity and a specified air permeability. SOLUTION: 5-40 wt.% acrylic monomer is grafted onto the pore surfaces and surface of a microporous membrane made from a polyolefin composition containing at least 1 wt.% ultrahigh-molecular-weight polyolefin having a weight- average molecular weight of 5×10<5> or above and having a porosity of 50% or above and an air permeability of 60 Gurley sec or below. The microporous polyolefin membrane is made by extruding a solvent solution of a polyolefin composition having a specified composition to form a film, removing the solvent from the film and heat-setting it. The acrylic monomer is grafted onto its surface after the surface is treated by irradiation with an ionizing radiation. The acrylic monomer is exemplified by a (meth)acrylic acid (ester) desirably in combination with a crosslinking agent, Mohr's salt and water/alcohol.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a microporous hydrophilic polyolefin membrane containing an ultrahigh molecular weight polyolefin, and more particularly to a method for producing a microporous hydrophilic polyolefin membrane having a high water permeability.

[0002]

2. Description of the Related Art Microporous membranes are used in various applications such as battery separators, electrolytic capacitor diaphragms, separation membranes, water treatment membranes, reverse osmosis filtration membranes, ultrafiltration membranes, microfiltration membranes, and moisture-permeable waterproof clothing. Have been. Conventionally, a method of obtaining a microporous membrane by extracting an organic medium and an inorganic powder after mixing and melt-molding an organic medium and an inorganic powder such as finely divided silica with a polyolefin is known, but extracting an inorganic substance. A process was required, and the permeability of the obtained membrane largely depended on the particle size of the inorganic powder, and its control was difficult.

[0003] Also, various methods for producing a high-strength microporous membrane using an ultrahigh molecular weight polyolefin have been proposed. For example, JP-A-60-242035 and JP-A-61-1
No. 95132, JP-A-61-195133,
JP-A-63-39602, JP-A-63-2736
No. 51, etc., a gel-like sheet is formed from a solution obtained by heating and dissolving a polyolefin composition containing an ultra-high-molecular-weight polyolefin in a solvent, and the gel-like sheet is heated and stretched to produce a microporous membrane by extracting and removing the solvent. Although the method is described, the microporous polyolefin membrane made by these techniques is characterized by a small pore size and a narrow pore size distribution, and was suitable for battery separators and the like, but a microporous membrane having a pore size of submicron units. Was not obtained.

Further, since the polyethylene microporous membrane is hydrophobic, it can be used as a separator for an organic electrolyte battery, but when used as a separator for an aqueous battery or a water treatment membrane, a surfactant or the like is used. The microporous membrane had to be hydrophilized. When a surfactant-treated microporous polyethylene membrane is used as the aqueous battery separator or the water treatment membrane, if the surfactant is immersed in the electrolytic solution or the aqueous solution for a long time, the surfactant dissolves and becomes hydrophilic. There was a problem that the output of the battery or the water treatment capacity was reduced with the decrease in the number of the groups.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a large pore size, high strength, and high strength for water treatment membranes and microfiltration membranes produced from compositions containing ultrahigh molecular weight polyolefins. It is an object of the present invention to provide a permeable and hydrophilic microporous polyolefin membrane and a method for producing the same.

[0006]

Means for Solving the Problems The present inventors have made intensive studies to achieve the above object, and as a result, extruded a composition containing an ultrahigh molecular weight polyolefin from a solution mixed with a solvent at a specific concentration, and cooled the mixture. Found that a highly permeable and hydrophilic polyolefin microporous membrane can be obtained by graft-polymerizing a highly permeable microporous polyolefin membrane obtained by the solvent removal, drying and heat fixing steps with an acrylic monomer. Reached the present invention.

That is, the present invention relates to a method for preparing a polymer having a weight average molecular weight of 5 ×.
A microporous film comprising a polyolefin composition containing 1% by weight or more of 10 ⁵ or more ultrahigh molecular weight polyolefin, wherein the porosity is 50% or more and the air permeability is 60 Gurley seconds or less. on the surface and the membrane surface of the pores, a hydrophilic microporous polyethylene membrane obtained by 5 to 40 wt% graft polymerization of acrylic monomers, and its method of manufacture, the weight average molecular weight 5 × 10 ⁵ or more ultra-high molecular weight polyolefin 1 A solution consisting of 5 to 40% by weight of a polyolefin composition containing at least 5% by weight and a solvent of 95 to 60% by weight is prepared, and the solution is extruded from a die lip, cooled to form a film, and the remaining solvent is removed. An acrylic monomer is applied to the surface of the pores and the membrane surface of the microporous polyolefin membrane, which is characterized by being heat-set, by ionizing radiation treatment. % Is a method for producing a hydrophilic microporous polyethylene film, which is graft-polymerized.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION

1. Polyolefin Composition The microporous hydrophilic polyolefin membrane of the present invention is based on a microporous membrane made of a polyolefin composition containing an ultrahigh molecular weight component. The microporous polyolefin membrane used in the present invention is composed of a polyolefin containing 1% by weight or more of an ultrahigh molecular weight polyolefin having an average molecular weight of 5 × 10 ⁵ or more. When the content of the ultrahigh molecular weight polyolefin is less than 1% by weight, the entanglement of the molecular chain of the ultrahigh molecular weight polyolefin which contributes to the improvement of stretchability is hardly formed, and a high-strength microporous film cannot be obtained.

In particular, the polyolefin composition of the present invention
It is preferably a mixture of an ultrahigh molecular weight polyolefin (A) having a weight average molecular weight of 5 × 10 ⁵ or more and a polyolefin (B) having a weight average molecular weight of less than 5 × 10 ⁵ , and the weight ratio thereof is (B) / (A). Is 0.2 to 20, preferably 0.
A polyolefin composition of 5 to 10 is desirable. The weight ratio of (B) / (A) in the polyolefin composition is 0.2
If it is less than 3, the resulting gel-like sheet tends to shrink in the thickness direction, and the permeability is reduced, and the solution viscosity is increased, and the moldability is reduced. The weight ratio of (B) / (A) is 2
If it exceeds 0, the number of low molecular weight components increases, the gel structure becomes dense, and the permeability of the obtained microporous membrane decreases.

The ultra-high molecular weight polyolefin having a weight average molecular weight of 5 × 10 ⁵ or more preferably has a weight average molecular weight of 1 × 10 ⁶ to 15 × 10 ⁶ . The lower limit of the molecular weight of the polyolefin having a weight average molecular weight of less than 5 × 10 ⁵ is preferably 1 × 10 ⁵ or more. Use of a polyolefin of less than 1 × 10 ⁵ is not preferred because the permeability of the membrane is reduced as described above, and a desired microporous membrane cannot be obtained.

The polyolefin includes ethylene,
Propylene, 1-butene, 4-methyl-pentene-1,
Examples include a crystalline homopolymer obtained by polymerizing 1-hexene or the like, a two-stage polymer, a copolymer, and a blend thereof. Among these, polypropylene, polyethylene (particularly high-density polyethylene), and compositions thereof are preferred.

The molecular weight distribution of the polyolefin composition (weight average molecular weight (Mw) / number average molecular weight (Mn))
Is preferably 300 or less, particularly preferably 5 to 50. If the molecular weight distribution exceeds 300, the permeability of the membrane decreases due to low molecular weight components, which is not preferable. If the polyolefin composition has the above molecular weight and molecular weight distribution,
Any of multi-stage polymerization and a composition of two or more polyolefins may be used.

The polyolefin composition containing the above-mentioned ultrahigh molecular weight component may contain, if necessary, an antioxidant, an ultraviolet absorber, an antiblocking agent, a pigment,
Various additives such as dyes and inorganic fillers can be added within a range that does not impair the purpose of the present invention.

2. Method for Producing Microporous Membrane In the method for producing a microporous film of the present invention, a solution is prepared by heating and dissolving the above-described polyolefin composition in a solvent. Examples of the solvent include nonane, decane, decalin, p
Aliphatic or cyclic hydrocarbons such as xylene, undecane, dodecane and liquid paraffin, or mineral oil fractions whose boiling points correspond to these; The viscosity of the solvent at 25 ° C. is 30 to
It is preferably 500 cSt, particularly preferably 50 to 200 cSt. If the viscosity at 25 ° C. is less than 30 cSt, non-uniform ejection occurs, and kneading is difficult. On the other hand, if the viscosity exceeds 500 cSt, solvent removal in a subsequent step becomes difficult.

The heat dissolution is carried out with stirring at a temperature at which the polyolefin composition is completely dissolved in the solvent, or by a method in which the polyolefin composition is uniformly mixed and dissolved in an extruder. In the case of dissolving with stirring in a solvent, the temperature varies depending on the polymer and the solvent to be used. For example, in the case of a polyethylene composition, the temperature is in the range of 140 to 250C. When producing a microporous membrane from a high-concentration solution of the polyolefin composition, it is preferable to dissolve it in an extruder.

When dissolving in an extruder, first, the above-mentioned polyolefin composition is supplied to the extruder and melted. The melting temperature varies depending on the type of the polyolefin used, but is preferably the melting point of the polyolefin + 30 to 100 ° C. For example, in the case of polyethylene, 160 to 230 ° C,
It is particularly preferably 170 to 200 ° C, and in the case of polypropylene, 190 to 270 ° C, particularly 190 to 250 ° C.
It is preferred that Next, a liquid solvent is supplied to the molten polyolefin composition in the middle of the extruder.

The mixing ratio of the polyolefin composition and the solvent is such that the total of the polyolefin composition and the solvent is 100% by weight.
The polyolefin composition is 5 to 40% by weight, preferably 10 to 30% by weight, and the solvent is 95 to 60% by weight, preferably 90 to 70% by weight. When the polyolefin composition is less than 5% by weight (when the solvent exceeds 95% by weight), when forming into a sheet, the swell and neck-in are large at the die exit, making the sheet moldability and self-supporting difficult. . On the other hand, the polyolefin composition is 40% by weight.
If it exceeds (when the solvent is less than 60% by weight), shrinkage in the thickness direction increases, the porosity decreases, a microporous film having a large pore diameter cannot be obtained, and the moldability decreases. By changing the concentration in this range, the permeability of the membrane can be controlled.

Next, the heated solution of the polyolefin composition melt-kneaded in this manner is directly or through another extruder, or once cooled and pelletized, and then again through the extruder. It is extruded from a die and molded. As the die, a sheet die having a rectangular base shape is usually used, but a double cylindrical hollow fiber die, an inflation die, or the like can also be used. When a sheet die is used, the die gap is usually 0.1 to 5 mm. At the time of extrusion molding, it is heated to 140 to 250 ° C. and extruded.

The solution extruded from the die is formed into a gel-like sheet by cooling. The cooling is performed by cooling the die or cooling the gel-like sheet. As a method of cooling the gel-like sheet, a method of directly contacting with cold air, cooling water, or another cooling medium, a method of contacting with a cooling roll, or the like can be used. When cooling using a cooling roll, the distance between the die and the cooling roll is 5 mm to
It is preferably 100 mm, especially 5 mm to 50 mm. In the case where the viscosity of the resin solution is low, if the distance between the die and the cooling roll is long, the obtained sheet is liable to cause neck-in, and is preferably short. Cooling roll temperature is 30 ° C
The crystallization temperature is preferably set to a polyolefin crystallization temperature, particularly preferably 40 to 90 ° C. If the temperature of the cooling roll is too high, the gel-like sheet is gradually cooled, the walls constituting the lamellar structure of the polyolefin forming the gel structure become thicker, and the microporous tends to become a closed cell, so that the solvent is reduced and the permeation is reduced. Is reduced. If the cooling roll temperature is too low, the gel-like sheet is quenched and the gel structure becomes too dense, so the pore size becomes small,
The permeability decreases. The take-up speed is 1 to 20 m / min,
Particularly, it is preferably 3 to 10 m / min. If the take-up speed is too fast, the sheet will neck-in, and the slower is preferred.

The gel sheet extruded from the die and cooled is washed with a solution to remove residual solvent. Examples of the washing solvent include hydrocarbons such as pentane, hexane, and heptane; chlorinated hydrocarbons such as methylene chloride and tetrachlorocarbon; fluorinated hydrocarbons such as ethane trifluoride; and ethers such as diethyl ether and dioxane. Volatile ones can be used. These solvents are appropriately selected according to the solvent used for dissolving the polyolefin composition, and used alone or as a mixture. The washing method can be performed by a method of immersing in a solvent for extraction, a method of showering the solvent, a method of a combination thereof, or the like.

The washing as described above is performed until the residual solvent in the molded product becomes less than 1% by weight. Thereafter, the washing solvent is dried, and the washing solvent can be dried by a method such as heat drying or air drying. The dried molded product is desirably heat-set at a temperature in the range from the crystal dispersion temperature to the melting point. If the heat setting temperature exceeds the melting point, the resin will melt. Although the time of the heat setting varies depending on the heat setting temperature, it is preferably performed for 10 seconds to 10 minutes.

The wall of the gel structure is composed of one to several layers of polyolefin lamella, and the crystal is stabilized by heat setting, and the lamella layer is made uniform. For this reason, the small pore diameter portion is reduced, the average pore diameter is slightly increased, and the permeability is further increased. In addition, the pore size distribution becomes broad and gentle, but becomes sharp by heat fixing. The microporous polyolefin membrane obtained as described above has an air permeability of 5 to 60.
It is a highly permeable membrane having a large pore diameter of 50 sec / 100 cc, a porosity of 50 to 95%, and an average pore diameter of 0.05 to 1.0 μm.

3. Graft polymerization treatment The hydrophilic polyolefin microporous film of the present invention is obtained by irradiating the above-mentioned polyolefin microporous film with ionizing radiation or plasma to generate radicals inside the microporous film, and converting the acrylic monomer into a gas phase or liquid. It is produced by contacting a microporous membrane with a phase and graft polymerizing an acrylic monomer. Since the ionizing radiation penetrates into the polyolefin microporous membrane, the graft polymer is formed almost uniformly on the surface of the pores of the membrane and on the membrane surface according to the ionizing radiation polymerization method. Ionizing radiation includes α-rays, β-rays, γ-rays and X-rays.
An electron beam graft polymerization method using β rays (electron beam) is preferably used from the viewpoint of handling.

The electron beam irradiation graft polymerization method includes a simultaneous irradiation method in which the microporous film and the acrylic monomer coexist and the electron beam is simultaneously irradiated, and an acrylic monomer method after the microporous film is irradiated with the electron beam in advance. Is pre-irradiation method. It is preferable to use the pre-irradiation method because homopolymerization of the acrylic monomer can be suppressed.

In the pre-irradiation method, an acceleration voltage of 100 to
5000 keV is preferred, and more preferably 200-8.
Irradiate with 00 keV electron beam. Irradiation with an electron beam does not require an inert gas atmosphere unlike the plasma method, and can be performed in an air atmosphere. The irradiation dose is 10 to 50
0 kGy is suitable, preferably 50 to 200 kGy.
It is. If it is less than 10 kGy, grafting of the acrylic monomer is not sufficiently performed, and if it exceeds 500 kGy, the microporous membrane may be deteriorated. Next, the polyolefin microporous film irradiated with an electron beam is immersed in an acrylic monomer solution to form a graft polymer.

As the plasma irradiation graft polymerization method, argon, helium, and the like having a pressure of 10 ⁻² to 10 mbar are used.
Under an atmosphere of nitrogen, air, etc., usually at a frequency of 1 to 30 MH
z, plasma treatment for 1 to 1000 seconds at an output of 1 to 1000 W is performed on the microporous membrane to generate radicals on the surface of the microporous membrane, and then immersion treatment in an acrylic monomer solution to obtain a graft polymer To form

Specific examples of the acrylic monomer to be graft-polymerized include acrylic acid, methacrylic acid, acrylate, methacrylate, acrylamide, acrylonitrile, styrene and derivatives thereof. One or more of these can be selected and used. In addition, it is preferable that a cross-linking agent is present when the acrylic monomer is graft-polymerized, if necessary. Examples of the crosslinking agent include those having two or more double bonds in the molecule. Acrylate and tetraethylene glycol acrylate. Among the above-mentioned monomers, it is preferable to use a monomer composed of acrylic acid, methacrylic acid, or an ester thereof, or an acrylic monomer composed of acrylamide or a derivative thereof.

Further, in order to prevent homopolymerization of the above monomers, a polymerization inhibitor such as Mohr's salt (ammonium iron (II) sulfate hexahydrate), hydroquinone monomethyl ether, isopropyl alcohol (IPA), ethylene dichloride Etc. can be used in combination.

The acrylic monomer to be graft-polymerized is
Water and an organic solvent, preferably a lower alcohol, more preferably isopropyl alcohol, are dissolved or suspended in a mixed solvent of 10 to 50% by volume of water / alcohol to prepare a homogeneous solution or emulsion of an acrylic monomer. In this case, a surfactant may be used if necessary. This surfactant is added in water or an organic solvent at a concentration of 0.1%.
Preferably, it contains about 50% by volume.

The acrylic monomer is used in an amount of 0.1 to 5
The volume of water and the organic solvent is preferably 99.9 to 50% by volume, more preferably 99.5 to 80% by volume, more preferably 0 to 20% by volume. If the acrylic monomer is less than 0.1 part by weight,
When a sufficient amount of the graft polymer cannot be formed inside the microporous membrane, on the other hand, when the amount of the acrylic monomer exceeds 50% by volume, it becomes difficult to control the polymerization amount.

Further, the crosslinking agent is preferably used in an amount of 0.1 to 10% by volume based on the volume of the acrylic monomer.
And more preferably 1 to 5% by volume thereof.
0.1% by weight of crosslinking agent based on acrylic monomer
If the amount is less than 10%, the effect of the present invention will not be exhibited, but rather, the polymerization of the monomer will be unfavorably performed.

As described above, the inside of the microporous polyolefin membrane is irradiated with an electron beam or plasma to generate radicals, and this polyolefin microporous membrane is converted into a uniform solution or emulsion of an acrylic monomer in the presence of the above-mentioned crosslinking agent. Make contact. Specifically, it is preferable to immerse the microporous polyethylene membrane in which radicals have been generated in a homogeneous solution or emulsion of an acrylic monomer in the presence of the above-mentioned crosslinking agent. This operation is performed while bubbling nitrogen gas, argon gas or the like into a uniform solution or emulsion of an acrylic monomer. At this time, the temperature of the homogeneous solution or emulsion of the acrylic monomer is preferably 0.
To 90 ° C, more preferably 20 to 60 ° C.

The above treatment is carried out until the graft ratio of the acrylic monomer becomes 5 to 40% by weight. The graft ratio is preferably 9 to 30% by weight, more preferably 15 to 3% by weight.
0% by weight. When the graft ratio is less than 5% by weight,
If the hydrophilicity is not sufficient and the graft ratio exceeds 40% by weight, the permeability of the membrane is lost, which is not preferable. The treatment time varies depending on the temperature of the homogeneous solution or emulsion of the acrylic monomer, but is, for example, about 10 to 40 minutes at 40 ° C. Next, the obtained graft microporous membrane is washed with water, toluene, xylene and the like all day and night and dried under vacuum.

By the above electron beam graft polymerization method, an intended hydrophilic microporous membrane having a graft polymer of an acrylic monomer formed almost uniformly on the microporous membrane on the surface of the pores of the membrane and on the membrane surface is obtained. Can be.

The microporous polyolefin membrane produced by the method of the present invention comprises a polyolefin composition having an ultrahigh molecular weight polyolefin component of 1% by weight or more, Mw / Mn of 5 to 300, has a high porosity and an average pore diameter. The graft polymer is used as a base material by grafting the acrylic monomer in the presence of a cross-linking agent using an ionizing radiation graft polymerization using a microporous membrane that is large and has a sufficient mechanical strength. Since the polymer is uniformly formed on the surface of the pores and on the membrane surface and the polymer is crosslinked, the hydrophilicity is further improved and the water permeability is high, which is suitable as a water treatment filter.

[0036]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited to the following examples. In addition, the test method in an Example is as follows. (1) Weight average molecular weight: GPC manufactured by Waters Corporation
Using a device, GMH-6 (manufactured by Tosoh Corporation) as a column and o-dichlorobenzene as a solvent were measured by gel permeation chromatography (GPC) at a temperature of 135 ° C. and a flow rate of 1.0 ml / min. did. (2) Film thickness: The cross section was measured by a scanning electron microscope. (3) Porosity: measured by a gravimetric method. (4) Average pore size: Perm-Porometer (Po
rous Materials Inc. Manufactured by the company). (5) Graft rate: The weight difference before and after the graft polymerization reaction was measured, and the rate of weight increase was calculated to determine the graft rate. (6) Air permeability: Measured according to JIS P8117. (7) Permeability: Perm-porometer (por
ow Materials Inc. Manufactured by the company).

Example 1 20% by weight of ultra high molecular weight polyethylene (UHMWPE) having a weight average molecular weight of 2.5 × 10 ⁶ and high density polyethylene (HDPE) 80 having a weight average molecular weight of 3.0 × 10 ⁵
% By weight of the polyethylene composition and 0.375 parts by weight of an antioxidant per 100 parts by weight of the polyethylene composition to obtain a polyethylene composition. 20 parts by weight of this polyethylene composition is charged into a twin-screw extruder, and 80 parts by weight of liquid paraffin is supplied from a side feeder of the twin-screw extruder, melt-kneaded at 200 ° C. and 200 rpm, and the polyethylene solution is mixed in the extruder. Is extruded from a T-die (die gap 0.6 mm) installed at the tip of the extruder, and the gel is formed under the conditions that the distance between the die and the roll is 20 mm, the cooling roll temperature is 80 ° C., and the take-up speed is 5 m / min. The sheet was extruded. The resulting sheet was washed with methylene chloride to extract and remove the remaining liquid paraffin, dried at 40 ° C, and heat-set at 125 ° C to obtain a polyethylene microporous membrane. This polyethylene microporous membrane has a thickness of 50μ.
m, porosity 72%, pore size 0.3 μm, and transmittance 20 Gurley seconds.

Next, the film was irradiated with an electron beam at an accelerating voltage of 250 kV and an irradiation dose of 100 kGy.
ol% acrylic acid aqueous solution, and reacted for 30 minutes under nitrogen bubbling. Thereafter, ultrasonic cleaning was performed in distilled water for 2 hours, and vacuum drying was performed at 80 ° C. for 6 hours. The acrylic acid graft ratio (weight increase ratio with respect to the base) was 18% by weight.
Was obtained. Table 1 shows the results of measuring the water permeability of this membrane.

Example 2 In Example 1, the graft polymerization treatment of acrylic acid
A microporous hydrophilized polyethylene having an acrylic acid graft ratio of% by weight in the same manner as in Example 1 except that the reaction is performed in a 20 vol% aqueous acrylic acid solution for 60 minutes instead of performing the reaction in a 0 vol% aqueous acrylic acid solution for 30 minutes. A membrane was obtained. Table 1 shows the results of measuring the water permeability of this membrane.

Example 3 The procedure of Example 1 was repeated except that the acrylic acid
Instead of performing the reaction in a 0 vol% aqueous solution of acrylic acid for 30 minutes, the reaction is carried out for 30 minutes in a 10 vol% aqueous solution of acrylic acid (acrylic acid: water: isopropyl alcohol = 10: 70: 20) to which 1 part by weight of divinylbenzene is added as a crosslinking agent. A microporous hydrophilized polyethylene membrane having an acrylic acid graft ratio of 20 wt% was obtained in the same manner as in Example 1 except that this was performed. Table 1 shows the results of measuring the water permeability of this membrane.

Example 4 In Example 1, a plasma treatment (power consumption: 10 W, irradiation time: 60 seconds, internal pressure: 0.1 mba) was performed instead of the electron beam irradiation.
r, Ar atmosphere), except that a microporous hydrophilic polyethylene film having an acrylic acid graft ratio of 14 wt% was obtained in the same manner as in Example 1. Table 1 shows the results of measuring the water permeability of this membrane.

Comparative Example 1 The results of measuring the water permeability of the ungrafted polyethylene microporous membrane obtained in Example 1 are shown in Table 1.

Comparative Example 2 In Example 1, the graft polymerization treatment of acrylic acid
Instead of performing the reaction in an aqueous solution of 0 vol% acrylic acid for 30 minutes, the same procedure as in Example 1 was repeated except that the reaction was performed in an aqueous solution of 30 vol% acrylic acid for 60 minutes. A porous membrane was obtained. Table 1 shows the results of measuring the water permeability of this membrane.

Comparative Example 3 The microporous polyethylene membrane obtained in Example 1 was stretched 5 × 5 times at 115 ° C., washed, dried and heat-set (115
° C), a film thickness of 25 µm, a porosity of 40%, and a pore size of 0.0
A microporous polyethylene membrane having a thickness of 3 μm and an air permeability of 300 Gurley seconds was obtained. Table 1 shows the water permeability of this membrane.

Comparative Example 4 The microporous polyethylene film obtained in Comparative Example 3 was subjected to a hydrophilic treatment in the same manner as in Example 1 to obtain a microporous hydrophilic polyethylene film having an acrylic acid graft ratio of 20 wt%. Table 1 shows the water permeability of this membrane.

[0046]

[Table 1]

As is clear from Table 1, when the acrylic acid graft polymerization treatment of an amount within the range of the present invention is performed on the microporous membrane having a large pore diameter obtained by the method of the present invention by the electron beam irradiation method, the water permeation rate becomes higher. A large amount of a hydrophilic microporous membrane can be obtained (Examples 1 to 3). Also, by the plasma processing method,
Similarly, a hydrophilic microporous membrane having a large water permeability is obtained (Example 4). On the other hand, if the graft polymerization is not performed, a sufficient water permeability cannot be obtained (Comparative Example 1), and if the graft polymerization rate is too high, the water permeability is impaired (Comparative Example 2). Also, when a stretching operation is applied during the production of the microporous membrane, the pore size of the obtained microporous membrane becomes small, and the water permeability of the non-grafted polymerization-processed microporous membrane becomes small (Comparative Example 3). It can be seen that a sufficient amount of water permeability cannot be obtained even if the above method is performed.

[0048]

The microporous hydrophilic polyolefin membrane of the present invention is obtained by graft-polymerizing a microporous membrane having a large pore diameter obtained from a composition containing an ultrahigh molecular weight polyolefin having a specific molecular weight range with an acrylic monomer. Thus, it is a microporous polyolefin membrane having a large pore size, high strength, high permeability and hydrophilicity, which is used for applications such as water treatment membranes and microfiltration membranes.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Hidehiko Funaoka 3-1, Chidoricho, Kawasaki-ku, Kawasaki-shi, Kanagawa Pref.

Claims (4)

[Claims] 1. A microporous film comprising a polyolefin composition containing 1% by weight or more of an ultrahigh molecular weight polyolefin having a weight average molecular weight of 5 × 10 ⁵ or more, and having a porosity of 50%.
A hydrophilic microporous polyolefin membrane in which an acrylic monomer is graft-polymerized on the surface of the pores and on the membrane surface of the microporous polyolefin membrane having an air permeability of 60 Gurley seconds or less. 2. The microporous membrane before the graft polymerization comprises one ultra-high molecular weight polyolefin having a weight average molecular weight of 5 × 10 ⁵ or more.
A solution consisting of 5 to 40% by weight of a polyolefin composition containing at least 5% by weight and a solvent of 95 to 60% by weight is prepared, and the solution is extruded from a die lip, cooled to form a film, and the remaining solvent is removed. The hydrophilic polyolefin microporous membrane according to claim 1, which is a thermosetting polyolefin microporous membrane. 3. A solution comprising 5 to 40% by weight of a polyolefin composition containing 1% by weight or more of an ultrahigh molecular weight polyolefin having a weight average molecular weight of 5 × 10 ⁵ or more and 95 to 60% by weight of a solvent is prepared. After extruding from a die lip, cooling and forming a film, the remaining solvent is removed and dried. 5-30% by weight of an acrylic monomer is graft-polymerized on the surface of the pores and on the surface of the microporous polyolefin membrane. A method for producing a hydrophilic polyolefin microporous membrane, characterized in that: 4. The method for producing a microporous hydrophilic polyolefin membrane according to claim 2, wherein the graft polymerization method of the acrylic monomer is an ionizing radiation treatment method.