JP2002265658A - Highly permeable microporous film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a microporous film comprising a polyethylene with a raised liquid or gas permeability to the utmost while maintaining film thickness. SOLUTION: This microporous film has an excellent strength and fine particle preventing performances, good handleability and a remarkably improved liquid or gas permeability while maintaining a high porosity by regulating the structural factor to >=1.5×10<7> sec<-2> .m<-1> .Pa<-2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a microporous membrane having excellent permeability, and more particularly to the production of medical separation membranes and semiconductor products for removing pathogens such as viruses and bacteria from plasma preparations and biopharmaceuticals. Filtration filters for semiconductor chemicals that remove microparticles that cause micro defects from used chemicals such as photoresists, circulating filtration filters for wet stations during LSI and liquid crystal manufacturing, oil-water separation filters, liquid gas separation filters, etc. Industrial process filters, separation membranes for water treatment for purifying water and sewage, gas purification membranes for purifying gases such as air, separators for non-aqueous electrolyte batteries such as lithium ion batteries, nickel-metal hydride batteries Precursor for alkaline electrolyte battery separators, etc., solid electrolyte support for polymer batteries, fuel cell substrate membrane It relates a microporous polyethylene film available for a wide range of applications.

[0002]

2. Description of the Related Art In recent years, a microporous membrane used for an electronic industrial process filter for removing fine particles and solid impurities from a chemical solution or treated water used for manufacturing semiconductor products has been made of various polymer materials. Has been developed. As the polymer material used for these, polyamide, polyethylene, polypropylene, cellulose acetate, polyvinylidene fluoride, and polytetrafluoroethylene are generally used. Among such polymer materials, only polyethylene and polytetrafluoroethylene are materials having high chemical resistance that can be used as an industrial process filter. Polytetrafluoroethylene is a fluorine-containing compound, and recently has problems such as waste disposal, and the prospects for the future are not very bright, whereas polyethylene has few problems with the waste, and is inexpensive. It is a useful material because of its excellent workability.

[0003] The above-mentioned semiconductor products tend to be finely patterned year by year, and are currently all over the submicron size. On the other hand, the control size of the fine particles contained in the chemical solution or the processing water used for the semiconductor product is required to be １ ／ or less of the pattern size. Therefore, the average pore size required for the microporous membrane is 0.05 to 0.5 μm depending on the size of the fine particles to be filtered, and extends to 1.0 μm or more when including the prefilter.

[0004] When administering a preparation such as a plasma preparation or a biopharmaceutical to the human body, a sense of danger to pathogens such as bacteria, viruses, and pathogenic proteins that may be contained in the preparation has been highlighted. As a technique for physically removing such pathogens, a membrane filtration method using a separation membrane is being spotlighted as a useful means. The microporous membrane used for such an application is generally called a medical separation membrane.

[0005] The type of virus is 0.02
0.03 μm parvovirus, poliovirus, EM
From very small size such as C virus and hepatitis A virus to medium size such as hepatitis B virus, SV40 virus, BVD virus, Sindbis virus and the like having a diameter of 0.04-0.07 μm. And large size such as HIV virus having a diameter of 0.08 to 0.10 μm. Such virus group,
In order to physically remove by a membrane filtration method according to the size, excellent permeability and excellent particulate blocking performance are required in the range of 0.01 to 0.1 μm in average pore size.

[0006] The protein, which is a component of the preparation, causes hydrophobic adsorption and clogs the pores of the separation membrane to reduce the throughput,
A trouble occurs in which the components of the preparation deteriorate. Therefore,
In order to prevent such protein adsorption, the medical separation membrane needs to be coated with a protein non-adsorbing substance such as a hydrophilic material. From such a demand, in many cases, it is preferable that the material of the medical separation membrane is a material that can impart hydrophilicity.

[0007] Since plasma preparations, biopharmaceuticals, and semiconductor chemicals are generally high-viscosity liquids, the filtration speed is low, and there is a problem in productivity. In order to solve such a problem, a microporous membrane having an extremely high permeation rate is useful. Further, when a liquid having a high viscosity is handled, the filtration pressure tends to increase, and a microporous membrane having high strength that does not cause breakage, rupture, damage, dimensional deformation, and the like is required.
In particular, as the pore size becomes smaller, the filtration pressure applied to the microporous membrane increases, and in order to withstand such a high filtration pressure,
There is a demand for a material having extremely high strength and having a small decrease in filtration capacity over time.

[0008] In the industrial filtration process, in order to remove fine particles, solid impurities, viruses, and the like from a chemical solution, treated water, preparations, pharmaceuticals, and the like, pre-filtration is performed instead of complete filtration in a single filtration. It is desirable. By performing the pre-filtration, the burden on the final filtration filter can be reduced. When used as a pre-filter in this way, it is necessary to increase the permeability to the limit,
Simply having permeability does not serve as a pre-filter. Use the one with the hole diameter suitable for the purpose,
It is necessary to remove fine particles, solid impurities and the like to some extent.

Further, the highly permeable membrane includes a water treatment filter for purifying water and sewage, a gas purification filter for purifying gas such as air, and a non-aqueous electrolyte system such as a lithium ion battery. Battery separators, precursors for alkaline electrolyte battery separators such as nickel-metal hydride batteries,
It can be used for a wide range of applications such as a solid electrolyte support for a polymer battery and a fuel cell substrate membrane. As a method of improving the liquid or gas permeability of the microporous membrane, a method of reducing the film thickness is generally used. Japanese Patent Application Laid-Open No. 3-80923 discloses a technique for improving the permeability of a film by reducing the film thickness, and describes that when the film thickness is increased, high permeability cannot be obtained. When the film thickness is reduced, the permeability is improved, but the mechanical strength such as pressure resistance is impaired because the filtration layer is thin. Furthermore, since the film thickness is thin, wrinkles are easily formed during processing, and handling properties are impaired.

[0010] Japanese Patent Application Laid-Open No. 4-261441 discloses a technique in which a substantial film thickness can be reduced by providing bubbles in the film, thereby increasing the permeability of the film. The presence of air bubbles improves the permeability, but does not provide sufficient particle blocking performance. Further, in this method, the pressure resistance is inferior because the filtration layer is thin, and clogging is likely to occur because of surface filtration. As a result, the filtration processing capacity decreases over time, and the filtration life is shortened. Therefore, these methods have practical limitations.

Therefore, a microporous membrane which has good handling properties, maintains the film thickness necessary for developing strength and preventing fine particles, and can exhibit more excellent permeability with respect to liquids or gases than conventional membranes has been developed. Was sought.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polyethylene made of polyethylene, which has good handling properties, and has a liquid or gas permeability as high as possible while maintaining the film thickness necessary for developing strength and preventing fine particles. It is to provide a microporous membrane.

[0013]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, a polyethylene microporous membrane having a specific pore structure was excellent while maintaining a high porosity. The inventors have found that they have strength, fine particle blocking performance, good handling properties, and excellent liquid or gas permeability, and have accomplished the present invention. That is, the first of the present invention is made of polyethylene resin and has a thickness of 25 μm
And 1 mm or less, the average pore diameter is 0.01 to 10 μm, and the structural factor F represented by the formula (1) is 1.5 × 10 ^7.
A highly permeable microporous membrane, wherein the second is ^-2 · m ^-1 · Pa ^-2 or more.

[0014]

(Equation 4)

[Where, F is a structural factor (sec− ² · m)
^-1 · Pa ^-2 ), Q _H2O is the amount of water permeation (m ³
/ (Sec · m ² · Pa)), Q _air is the air permeation amount (m ³ / (sec · m ² · Pa)] shown in equation (3)

[0016]

(Equation 5)

[0017]

(Equation 6)

(Where r is the average pore diameter (μm), ε is the porosity (%), η is the viscosity of water (Pa · sec), τ is the flexural modulus, d
Is the film thickness (μm), ν is the molecular velocity of the gas (m / sec), Ps
Is a standard pressure (101325 Pa). Preferably, the matrix piercing strength of the microporous membrane is 9.5.
× 10 ^-2 N or more, and more preferably, the porosity of the microporous membrane is more than 80% and 95% or less. A second aspect of the present invention is a filter for the electronic industry including the microporous membrane and a medical separation filter including the microporous membrane.

The thickness of the microporous membrane of the present invention is essential to be more than 25 μm and 1 mm or less, and preferably 30 μm or less.
５００500 μm, more preferably 30-300 μm. When the film thickness is 25 μm or less, the mechanical strength such as the pressure resistance of the microporous film and the ability to prevent fine particles are insufficient, wrinkles are easily formed during processing, and the handling property is lacking. On the other hand, if it exceeds 1 mm, the ratio of the continuous pores in the microporous membrane tends to decrease, which is disadvantageous in terms of permeation performance.

The average pore size of the microporous membrane of the present invention is 0.01
To 10 μm is essential, preferably 0.0 to 10 μm.
It is 15 to 5 μm, more preferably 0.020 to 1 μm. Even if the average pore size is less than 0.01 μm, there is no serious problem, but if the pore size is too small, the permeability will be reduced. On the other hand, if the average pore size exceeds 10 μm, the film strength will be impaired. Here, the average pore size is
It refers to the pore size obtained according to the half-dry method.

The structure factor of the microporous membrane of the present invention is as follows:
It is essential that there be 1.5 × 10 ⁷ seconds− ² · m ⁻¹ · Pa ⁻² or more, and preferably 2.5 × 10 ⁷ seconds− ² · m ⁻¹ · Pa
^-2 or more, more preferably 3.0 × 10 ⁷ seconds ^-2 · m ^-1 · P
a ^-2 or more. The fluid inside the microporous membrane capillary is
It is known that when the mean free path of a fluid is smaller than the pore diameter of the capillary, it follows the flow of Poiseuille, and when it is larger, it follows the flow of Knudsen. Here, JISP-8
Assuming that the flow of air in the air permeability measurement according to H.117 follows the flow of Knudsen and the flow of water in the measurement of water permeability at room temperature follows the flow of Poiseuille, the pore diameter r (μ
m), flexural modulus τ, water viscosity η (Pa · sec), standard pressure Ps
(101325 Pa), the porosity ε (%), the film thickness d (μm), and the molecular velocity ν (m / sec) of the gas, the water permeation amount Q _H2O (m ³ / (sec · m ² · Pa)) can be expressed by the following equation: It is represented by 2).

[0022]

(Equation 7)

On the other hand, the air permeation speed Q _air (m ³ / (sec · m ²
Pa)) is represented by equation (3).

[0024]

(Equation 8)

Therefore, the product of the air permeation amount Q _air and the water permeation amount Q _H2O is represented by the following equation (4).

[0026]

(Equation 9)

Here, when F is expressed by Expression (5), F is expressed by Expression (1).

[0028]

(Equation 10)

[0029]

[Equation 11]

That is, F is a factor determined by the porosity ε, the bending rate τ, and the film thickness d, and is a structural factor unique to the film. In conventional polyethylene microporous membranes, it was essential to reduce the film thickness in order to obtain excellent permeation performance. On the other hand, in the present invention, the structure factor F is made appropriate and the permeability of liquid or gas is improved. For this purpose, the structural factor F defined from the porosity, the bending rate, and the film thickness is set to 1.5 × 10 ⁷ seconds− ² · m ⁻¹
-It is essential to make it Pa- ² or more.

The film thickness is preferably more than 25 μm and 1 mm or less.
30 to 500 μm, more preferably 30 to 300 μm
m, and the structure factor F is set to 1.5 × 10⁷ Second^-2
・ M ^-1・ Pa^-2With the above, the microporous membrane has a high
Excellent strength, fine particle rejection, and good porosity
It has good handling properties and also has extremely excellent liquid
Or it has gas permeability. Structure factor F is 1.5
× 10⁷ Second^-2・ M^-1・ Pa^-2Less than, liquid
Or the gas permeability decreases, and the filtration throughput is not satisfied.
No.

The matrix piercing strength of the microporous membrane of the present invention is preferably at least 9.5 × 10 ^-2 N. More preferably, it is 1.0 × 10 ⁻¹ N or more, most preferably 1.
1 × 10 ⁻¹ N or more. The piercing strength determined as the maximum load in the piercing test is essentially a value that depends on the thickness and porosity of the microporous membrane, and the strength of the microporous membrane having an extremely high porosity as in the present invention. Not suitable as an indicator.

Therefore, the matrix piercing strength as an index for evaluating the true strength of the microporous membrane in the present invention is defined as the maximum load in the piercing test as the strength per 1 μm thickness of the polymer matrix based on the film thickness and porosity. It is a thing. When the matrix piercing strength is less than 9.5 × 10 ^-2 N, the mechanical durability of the microporous membrane is insufficient. For example, when the microporous membrane is used for a filter for a semiconductor chemical solution, the filtration pressure is reduced. It is not preferable because it cannot withstand and the film breaks.

The porosity of the microporous membrane of the present invention is preferably more than 80% and 95% or less. More preferably 8
It is 1-94%, most preferably 82-93%. If the porosity is less than 80%, the structural factor value will not be appropriate, and sufficient permeability tends not to be exhibited. On the other hand, if it exceeds 95%, the strength of the microporous membrane and the particle blocking performance Tends to be insufficient.

The polyethylene used in the present invention is a high-density polyethylene which is a crystalline polymer mainly composed of ethylene, or a unit of an α-olefin such as propylene, butene, pentene, hexene and octene with respect to the ethylene unit. A copolymer (linear copolymer polyethylene) containing 4 mol% or less may be used. Polyolefins such as polypropylene, medium-density polyethylene, linear low-density polyethylene, low-density polyethylene, and EPR may be blended with these at a ratio of 30% or less. preferable.

The weight average molecular weight of the polyethylene used in the present invention is not particularly limited, but is preferably less than 380,000.
More preferably less than 350,000, most preferably less than 300,000. The average molecular weight refers to a weight average molecular weight obtained by GPC (gel permeation chromatography) measurement or the like.
Since accurate GPC measurement is difficult for a resin having more than 10,000, the viscosity average molecular weight by a viscosity method can be applied as a substitute. Weight average molecular weight of 3
If it is 80,000 or more, it tends to be difficult to uniformly melt and knead.

Next, a method for producing the microporous polyethylene membrane of the present invention will be described. Polyethylene is dissolved in a solvent called a plasticizer at a temperature higher than its melting point to prepare a polymer solution. Here, the polymer solution preferably has a low polymer concentration in order to make the structure factor value appropriate. After preparing the polyethylene polymer solution, the polymer solution is cooled to a temperature lower than the crystallization temperature to form a polymer gel, and a plasticizer is extracted from the polymer gel to obtain a polyethylene molded body. Thereafter, the polyethylene molded body is stretched at an appropriate magnification after extraction of the plasticizer to produce a polyethylene microporous membrane. After stretching the polyethylene molded body, heat treatment such as heat fixing or thermal relaxation may be performed.

As the plasticizer, an organic compound capable of forming a uniform solution with polyethylene at a temperature lower than its boiling point is used. Specific examples include decalin, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decyl alcohol, nonyl alcohol, diphenyl ether, n-decane, n-dodecane, liquid paraffin, paraffin wax and the like. Of these, liquid paraffin, dioctyl phthalate, and decalin are preferred. The weight fraction of the plasticizer in the polymer solution is not particularly limited. However, in order to make the structure factor value of the polymer solution appropriate, the polymer concentration is a dilute concentration with a weight fraction of 10 to 45%. Is preferred.

In the present invention, the weight fraction of the plasticizer is 90 to
It is preferably 55%, more preferably 80 to 6%.
0%, most preferably 75-65%. If it is less than 55%, it tends to be difficult to obtain a microporous membrane having an appropriate structural factor value. On the other hand, if it exceeds 90%, the viscosity of the hot solution decreases and molding becomes difficult. This results in a decrease in strength and a decrease in the ability to prevent fine particles. In order to produce the microporous membrane of the present invention, first, a membrane is formed using the polyethylene solution thus obtained.

Although there is no particular limitation on the film forming method, for example, polyethylene powder and a plasticizer are supplied to an extruder, melt-kneaded, and then cast from a coat hanger die onto a cooling roll to obtain a film having a thickness of several tens μm to several m.
m can be formed continuously. In the present invention, since ultra-high molecular weight polyethylene is not an essential component, a special heating and melting equipment is not required, and adjustment of a homogeneous gel-like sheet can be extremely easily performed only by adding polyethylene and a plasticizer to an extruder. Can be.

Next, a porous film is produced by extracting and removing the plasticizer from the obtained gel-like molded product. Examples of the extraction solvent include hydrocarbons such as n-hexane and cyclohexane, halogenated hydrocarbons such as methylene chloride and 1,1,1, -trichloroethane, alcohols such as ethanol and isopropanol, diethyl ether and tetrahydrofuran. And ketones such as acetone and 2-butanone. In addition, environmental adaptability,
In consideration of safety and hygiene, alcohols and ketones are preferable among the solvents.

Although the extraction method is not particularly limited, when liquid paraffin or dioctyl phthalate is used as the plasticizer, after extracting the plasticizer with the above-mentioned extraction solvent, the extraction is performed at a temperature not higher than the temperature at which the pores of the obtained porous membrane are closed. The extraction solvent can be removed by heating and drying. When a low boiling point compound such as decalin is used as the plasticizer, the extraction solvent can be removed only by heating and drying at a temperature lower than the temperature at which the pores of the microporous membrane are closed.

Next, the porous membrane obtained by extracting the plasticizer is stretched in at least one direction. The stretching method is not particularly limited, but it is preferable to perform simultaneous biaxial stretching or sequential biaxial stretching at an appropriate magnification in order to make the structural factor value appropriate. The stretching temperature is 20 to 140 ° C., preferably 30 to 135 in both the longitudinal and transverse directions.
° C, more preferably 50 to 125 ° C. The stretching ratio is preferably 2 to 4 times in both the longitudinal and transverse directions, more preferably 2.5 to 4 times, and most preferably 3 to 4 times.
4 times. If the stretching ratio is less than 2 times, the improvement of the structural factor value F is insufficient, and if it exceeds 4 times, the pore structure becomes unnecessarily coarse, resulting in poor particle blocking performance. At the same time, if the stretching ratio exceeds 4 times, the strength of the microporous membrane decreases, which is not desirable.

[0044]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. The test method shown in the examples is as follows. (1) Dial gauge (peacock No.25 manufactured by Ozaki Seisakusho)
Measure with. (2) Porosity The volume V (cm ³ ) and the mass W (g) of the microporous membrane were measured,
The porosity ε (%) is calculated from the following equation. In the formula, ρ is the density of the resin (g / cm ³ ). ε = 100 × (1-W / (ρ × V))

(3) Average Pore Size According to the half-dry method, using fluorocarbon having a surface tension γ of 9 to 16 mN / m as a wetting liquid, the application pressure and the amount of air permeation were measured for the drying curve and the wetting curve. ,
From the pressure P _HD (Pa) at which the half of the obtained dry curve and the wet curve intersect, the average pore diameter r (μm) is determined by the following equation. r = 2860 × γ / P _HD (4) Weight average molecular weight and molecular weight distribution WATERS / 150-GPC as a device, Shodex / GPCAT-807 / S (1) as a column and Tosoh / TSK-GELGMH ₆ -HT (2) ),
Using 1,2,4-trichlorobenzene as a solvent, 1
The sample is dissolved at 60 ° C. for 2.5 hours to adjust the sample concentration to 0.05% (injection amount: 500 μl). GPC (gel permeation chromatography) measurement was performed at a measurement temperature of 140 ° C., and a weight average molecular weight (Mw) and a number average were obtained from a third-order calibration curve using a polyethylene conversion constant of 0.48 with respect to a polystyrene standard sample. The molecular weight (Mn) is determined, and the molecular weight distribution is determined from the ratio (Mw / Mn) between the weight average molecular weight and the number average molecular weight.

(5) Water Permeation A microporous membrane previously immersed in alcohol was set in a PP liquid permeation cell having a diameter of 20 mm, and the membrane was washed with pure water. .81 x 1
0 ⁴ is transmitted through pure water in Pa, the transmission amount of time has elapsed 30 seconds, the time unit, unit pressure, and calculates the permeation amount per unit area, which water permeation rate (m ³ / (s · m ² · Pa)). (6) Air Permeation Rate Air permeability is measured with a Gurley-type air permeability meter based on JISP-8117. Calculate the amount of permeation per unit time, unit pressure, and unit area from the value of air permeability, and calculate the permeation rate Q
_air (m ³ / (second · m ² · Pa)).

(7) Matrix piercing strength Using a compression tester KES-G5 manufactured by Kato Tech Co., Ltd., the radius of curvature of the needle tip is 0.5 mm, the piercing speed is 2 mm / sec,
Perform a piercing test under the test conditions of a measurement temperature of 23 ± 2 ° C.
The maximum load E (N) at the breaking point was observed. Based on the maximum load E, the porosity ε (%), and the film thickness d (μm), the matrix puncture strength S (N) is normalized by the following equation. S = 100 × E / (d × (100−ε))

[0048]

Example 1 High-density polyethylene (weight average molecular weight 25
30, molecular weight distribution 7, density 0.956) 30 parts by mass, liquid paraffin 70 parts by mass, and 0.3 parts by mass of tetrakis- [methylene-3 based on polyethylene as an antioxidant.
-(3 ', 5'-Di-tert-butyl-4'-hydroxyphenyl) propionate] methane was uniformly kneaded at 200 ° C in a nitrogen atmosphere using a Labo Plastomill. After kneading, a gel-like sheet was obtained using a press molding machine. 2-
Liquid paraffin was extracted and removed from the obtained gel-like sheet using butanone to obtain a polyethylene sheet having a thickness of 230 µm. Then, the sheet was subjected to a test biaxial stretching machine at a temperature of 80.degree.
Biaxial stretching was sequentially performed 4 × 3 times at a rate of 0% / sec to obtain a microporous membrane. Table 1 shows the physical properties of the film.

[0049]

Example 2 A microporous membrane was obtained under the same conditions as in Example 1 except that the polyethylene sheet from which the liquid paraffin had been extracted and removed was sequentially biaxially stretched at 90 ° C. using a test biaxial stretching machine. Was. Table 1 shows the physical properties of the film.

[0050]

Example 3 A microporous membrane was obtained under the same conditions as in Example 1 except that the polyethylene sheet from which the liquid paraffin had been extracted and removed was successively biaxially stretched at 100 ° C. using a test biaxial stretching machine. Was. Table 1 shows the physical properties of the film.

[0051]

Example 4 High-density polyethylene (weight average molecular weight 25
30, molecular weight distribution 7, density 0.956) 32 parts by mass, liquid paraffin 68 parts by mass and 0.3 parts by mass of tetrakis- [methylene-3 based on polyethylene as an antioxidant.
-(3 ', 5'-di-t-butyl-4'-hydroxyphenyl) propionate] methane is kneaded at 200 ° C. in a nitrogen atmosphere using a 35 mm twin screw extruder, and the kneaded material is hanger-coated with a lip distance of 200 μm. The gel-like sheet was obtained by extrusion casting from a die onto a cooling roll. Liquid paraffin was extracted and removed from the obtained gel-like sheet using 2-butanone to obtain a polyethylene sheet.

The obtained polyethylene sheet is stretched 4 times at 80 ° C. using a roll stretching machine, stretched 3 times in the width direction at 100 ° C. using a tenter, and the stretching ratio in the width direction is relaxed by 10%. Then, a heat treatment was performed at 100 ° C. to obtain a microporous film. Table 1 shows the physical properties of the film.

[0053]

Example 5 High-density polyethylene (weight average molecular weight 25
35 parts by mass, molecular weight distribution 7, density 0.956), 35 parts by mass of liquid paraffin, and 0.3 parts by mass of tetrakis- [methylene-3 based on polyethylene as an antioxidant.
-(3 ', 5'-Di-t-butyl-4'-hydroxyphenyl) propionate] Methane is dry-blended using a Henschel mixer, kneaded at 200 ° C under a nitrogen atmosphere in a 35 mm twin-screw extruder, and kneaded. Thing between lip 200
A gel sheet was obtained by extrusion casting from a μm hanger coat die onto a cooling roll. Using 2-butanone,
Liquid paraffin was extracted and removed from the obtained gel-like sheet to obtain a polyethylene sheet.

Then, the polyethylene sheet was subjected to a biaxial stretching machine at 110 ° C. for 1
Biaxial stretching was sequentially performed 3 × 3 times at a rate of 0% / sec to obtain a microporous membrane. Table 1 shows the physical properties of the film.

[0055]

Example 6 A microporous membrane was formed in the same manner as in Example 4 except that the test biaxial stretching machine was used to perform biaxial stretching four times at 120 ° C. at a rate of 10% / sec in each of longitudinal and transverse directions. Obtained. Table 1 shows the physical properties of the film.

[0056]

Comparative Example 1 High-density polyethylene (weight average molecular weight 25
10,000 parts by weight, molecular weight distribution 7, density 0.956) 40 parts by weight, liquid paraffin 60 parts by weight, and 0.3 parts by weight of 2,6-di-t-butyl-p based on polyethylene as an antioxidant.
-Cresol is dry-blended using a Henschel mixer and 200 ° C. in a 35 mm twin screw extruder under a nitrogen atmosphere.
The mixture was kneaded, and the mixture was adjusted and extruded from a hanger coat die having a lip interval of 200 μm onto a cooling roll and cast to obtain a gel-like sheet having a thickness of 200 μm.

Using 2-butanone, liquid paraffin was extracted and removed from the obtained gel-like sheet, and then attached 2-butanone was dried and removed. Further, using a test biaxial stretching machine, under a temperature condition of 110 ° C., the longitudinal stretching speed and the transverse stretching speed were respectively 500% / sec and 20% / sec, and the longitudinal stretching ratio and the transverse stretching ratio were each 1.5 times. The film was successively biaxially stretched. Table 2 shows the physical properties of the film.

[0058]

Comparative Example 2 The polyethylene sheet obtained in Example 4 was uniaxially stretched at a stretching rate of 10% / sec and a magnification of 3 times at a temperature of 110 ° C. to obtain a microporous polyethylene membrane. Table 2 shows the physical properties of the film.

[0059]

Comparative Example 3 High-density polyethylene (weight average molecular weight 25
10,000, molecular weight distribution 7, density 0.956) 50 parts by weight, liquid paraffin 50 parts by weight and 0.3 parts by weight of 2,6-di-t-butyl-based on polyethylene as an antioxidant.
p-Cresol was dry-blended using a Henschel mixer, and 200 mm in a 35 mm twin-screw extruder under a nitrogen atmosphere.
The mixture was kneaded at ℃, the kneaded material was adjusted, and extruded from a hanger coat die with a lip between 200 μm onto a cooling roll and cast to obtain a gel-like sheet.

Using a test biaxial stretching machine, the obtained gel-like sheet was subjected to a longitudinal stretching speed and a transverse stretching speed of 10% / sec and a longitudinal stretching ratio and a transverse stretching ratio of 3% at 120 ° C., respectively. The film was successively biaxially stretched by a factor of two. Next, liquid paraffin was extracted and removed from the stretched film using 2-butanone, and the attached 2-butanone was dried and removed. Table 2 shows the physical properties of the film.

[0061]

[Table 1]

[0062]

[Table 2]

[0063]

Microporous polyethylene membrane of the present invention exhibits the structure factor 1.5 × 10 ⁷ seconds ^-2 · m ^- by the ¹ · Pa ^-2 or more, excellent strength properties, excellent particulate rejection It is possible to provide a microporous polyethylene membrane having excellent handling properties and at the same time as having a liquid or gas permeability as high as possible, and is suitable for various filter materials.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4C081 AC15 BB02 BB08 BC02 CA021 CB011 DA02 DB05 DB06 DB08 4D006 GA02 GA12 GA41 MA03 MA22 MA23 MA31 MB02 MB03 MB16 MC22X NA05 NA10 NA66 PB24 PC01 PC41 PC80 4F074 AA18 CC01 CC05 CC04 CC05 CC DA03 DA08 DA10 DA23 DA24 DA43 5H021 CC08 EE04 HH00 HH02 HH03

Claims (5)

[Claims] 1. A film made of polyethylene resin and having a thickness of 25
More than μm and 1 mm or less, average pore size is 0.01 to 10 μm
m, the structure factor F represented by the equation (1) is 1.5 ×
High permeability microporous membrane characterized in that it is 10 ⁷ seconds ^-2 · m ^-1 · Pa ^-2 or more. (Equation 1) [Where F is the structural factor (sec ^{- 2m} -1P
a ^-2 ), Q _H2O is the amount of water permeation (m ³ / (sec · m ² · Pa)) shown in equation (2), and Q _air is the amount of air permeation (m ³ / (sec · m) shown in equation (3). ² · Pa)] (Equation 3) (Where r is the average pore diameter (μm), ε is the porosity (%), η
Is the viscosity of water (Pa · sec), τ is the flexural modulus, d is the film thickness (μ
m), ν is the molecular velocity of the gas (m / sec), Ps is the standard pressure (101325 Pa)) 2. The matrix piercing strength is 9.5 × 10 ^−2.
2. The highly permeable microporous membrane according to claim 1, wherein the number is N or more. 3. The highly permeable microporous membrane according to claim 1, wherein the porosity is more than 80% and 95% or less. 4. A filter for the electronic industry, comprising the highly permeable microporous membrane according to claim 1. 5. A medical separation filter comprising the highly permeable microporous membrane according to claim 1, 2 or 3.