JP2001157827A - Polyethylene hollow-fiber porous membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an anisotropic polyethylene hollow-fiber porous membrane suitable for a filtering use adapted to the removal of turbidity or the like and having both of dense pores and high water transmitting capacity. SOLUTION: A polyethylene hollow-fiber porous membrane has an outer surface dense type sponge-like anisotropic structure having a minimum pore size layer in its outer surface portion and the outer surface pore size of the porous membrane is below 1 μm, the inner surface pore size thereof is 1 μm or more and the void ratio thereof is 50-below 95%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyethylene hollow fiber porous membrane having fine pores and high water permeability, which is suitable for filtration such as turbidity.

[0002]

2. Description of the Related Art Filtration operations using porous membranes such as microfiltration membranes and ultrafiltration membranes are carried out in the automobile industry (electrodeposition paint recovery and reuse system), the semiconductor industry (ultra pure water production), the pharmaceutical food industry (sterilization, It has been put to practical use in many fields such as enzyme purification. Particularly in recent years, it has been widely used as a method for producing drinking water and industrial water by turbidizing river water and the like. Materials for the membrane include cellulose, polyacrylonitrile,
A wide variety of materials such as polyolefins are used.
Among them, polyolefin-based polymers (polyethylene, polypropylene, polyvinylidene fluoride, etc.) are suitable as a material for aqueous filtration membranes because of their high water resistance due to their hydrophobicity and are widely used. Among these polyolefin polymers, they do not contain halogen elements, which are problematic at the time of disposal, and have a low level of highly reactive tertiary carbon. Is particularly promising in the future.

As a polyethylene film, Japanese Patent Application Laid-Open No. 3-42
A film having a uniform three-dimensional porous structure (page 3, upper right column, lines 10-11) as disclosed in Japanese Patent No. 025 is conventionally known. The uniform three-dimensional porous structure means a structure in which there is almost no change in the pore diameter in the membrane cross-sectional direction, and the pore diameters (and the pore diameter distribution) at any two points in the membrane cross-section are almost equal.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a polyethylene hollow fiber membrane having fine pores and high water permeability, which is suitable for filtration such as turbidity.

[0005]

According to the present invention, there is provided (1) a layer having a minimum pore size on an outer surface portion, wherein the outer surface pore size is less than 1 μm and the inner surface pore size is 1 μm or more, the average pore size is less than 1 μm,
An external dense anisotropic sponge structure polyethylene hollow fiber porous membrane having a porosity of 50% or more and 95% or less, (2) an outer surface pore diameter of 0.03 μm or more and 0.8 μm or less, and an average pore diameter of 0.03 μm or more and 0 μm or less. (1) an outer surface dense anisotropic sponge-structured polyethylene hollow fiber-like porous membrane according to the above (1), which has an outer surface pore diameter of 0.05 μm to 0.6.
μm or less, and the average pore diameter is 0.05 μm or more and 0.6 μm.
m or less, the outer surface dense anisotropic sponge-structured polyethylene hollow fiber porous membrane according to the above (1), and (4) the hollow fiber inner diameter is 0.4 mm or more and 3 mm or less and the film thickness is 0.05 m.
The present invention relates to the above-mentioned (1) to (3), an outer surface dense anisotropic sponge-structured polyethylene hollow fiber-like porous membrane according to the above (1) to (3).

Hereinafter, the present invention will be described in detail. The film of the present invention is made of polyethylene. As described above, polyethylene has 1) a low tertiary carbon content, which is rich in chemical reactivity, and therefore less chemical degradation due to chemical washing and the like than polypropylene and the like having a high tertiary carbon content, that is, long-term durability can be expected. It has the advantages of 2) not containing halogen element which is a problem at the time of disposal, and 3) being inexpensive. Polyethylene includes high-density polyethylene and low-density polyethylene, and high-density polyethylene is preferable from the viewpoint of film strength.
Further, polyethylene has various molecular weights, and from the viewpoint of film strength, the viscosity average molecular weight is preferably 100,000 or more, and more preferably 200,000 or more. The viscosity average molecular weight (Mv) of polyethylene can be determined from the following equation by measuring the intrinsic viscosity ([η]) of the decalin solution at 135 ° C. (J. Brandrup and E.H.Imm)
ergut (Editors), Polymer Ha
ndbook (2nd Ed.), page IV-7, Joh
n Wiley & Sons, New York, 1
975, or edited by Eitaro Oka et al., Plastic Materials Course 4 Polyethylene resin, p. 48, Table 3.4 d, Nikkan Kogyo Shimbun, 1969). [Η] = 6.8 × 10 ⁻⁴ × (Mv) ^0.67

[0007] The polyethylene may contain a small amount of a stabilizer such as an antioxidant or an ultraviolet absorber, if necessary. The cross-sectional structure of the film of the present invention is a sponge structure. The sponge structure refers to a structure having substantially no coarse pores (macrovoids) having a diameter (circular approximate diameter) exceeding 10% of the film thickness in the film cross section. When macrovoids exist in the cross section of the film, the film strength is undesirably reduced.

[0008] The shape of the membrane of the present invention is a hollow fiber. When the hollow fiber membrane is formed into a form (module) that is actually used for filtration, the packed membrane area per unit volume can be increased as compared with a flat membrane (sheet membrane), and the filtration capacity per volume can be increased. Is advantageous. If the inner diameter of the hollow fiber membrane is too small, it is disadvantageous because the resistance of the liquid flowing through the hollow fiber tube (thickness loss in the pipe) increases, and if it is too large, the packed membrane area per unit volume decreases, which is disadvantageous. is there. The inner diameter of the hollow fiber membrane is preferably 0.4 mm or more and 3 mm or less. On the other hand, if the thickness of the hollow fiber membrane is too small, the membrane strength is reduced, which is disadvantageous. On the other hand, if it is too large, the filtration resistance is increased, and the water permeability is reduced, which is disadvantageous. The thickness of the hollow fiber membrane is preferably 0.05 mm or more and 1 mm or less.

The film of the present invention is characterized in that it has an external dense anisotropic structure having a minimum pore size layer on the external surface. The anisotropic structure refers to a structure in which the pore diameter changes rather than being uniform (uniform) in the film cross-sectional direction (film thickness direction).
In the membrane of the present invention, the pore diameter changes continuously from the outer surface to the inner surface, and the fundamental direction of the change is the direction in which the pore diameter increases from the outer surface to the inner surface. The filtration resistance (permeability) of the membrane is the smallest pore size layer (the most dense layer)
Is governed by the thickness of the As the minimum pore diameter layer is thicker, the filtration resistance of the entire membrane increases, and the water permeability decreases. JP-A-3-
In a uniform three-dimensional porous structure as disclosed in Japanese Patent No. 42025, the whole membrane cross section is equivalent to the minimum pore diameter layer, and filtration resistance is increased (water permeability is reduced), which is disadvantageous.

On the other hand, as in the case of the membrane of the present invention, the minimum pore size layer is disposed only in the outer surface portion, not in the entire membrane cross section, and the membrane cross section other than the minimum pore size layer has a larger pore size than the minimum pore size layer to reduce the filtration resistance. By minimizing the increase as much as possible, it becomes possible to provide a polyethylene hollow fiber porous membrane having dense pores and high water permeability. In this case, the filtration (sieving) function of the membrane is performed by the smallest pore diameter layer (dense pores) in the outer surface portion,
The layer on the inner surface side from the minimum pore size layer does not contribute as much as possible to increase the filtration resistance of the membrane, and functions as a support layer for maintaining the form and strength of the membrane. In the case of a dense outer surface membrane as in the present invention, its performance is particularly exhibited in external pressure filtration (the filtration direction of the membrane is from the outer surface to the inner surface).

The outer surface portion referred to in the present invention refers to the outer surface itself and a film cross-sectional portion from the outer surface to one-tenth of the film thickness. Confirmation of the existence position and the anisotropic structure of the minimum pore size layer can be performed by observing the cross section of the membrane with an electron microscope. The pore diameter of the outer surface of the membrane of the present invention is less than 1 μm, preferably 0.03 μm or more and 0.8 μm or less, more preferably 0.05 μm or more and 0.6 μm or less. The average pore size of the membrane is less than 1 μm, preferably 0.03 μm or more and 0.8
μm or less, more preferably 0.05 μm or more and 0.6 μm
It is as follows. The average pore size of the membrane is ASTM: F316-8
6 (also called the half-dry method). What is determined by the half-dry method is the average pore size of the minimum pore size layer of the membrane. In the present invention, the measurement of the average pore diameter by the half-dry method is performed by using ethanol as a liquid to be used for a hollow fiber membrane having a length of about 10 cm,
The measurement at a temperature of ° C. and a pressure increase rate of 0.01 atm / sec was set as a standard measurement condition. The average pore diameter [μm] is determined by the following equation.

[0012]

(Equation 1)

The surface tension of ethanol at 25 ° C. is 2
1.97 dynes / cm (Chemical Handbook Basic Edition, 3rd revised edition, edited by The Chemical Society of Japan, page II-82, Maruzen Co., Ltd., 19)
1984), the average pore diameter [μm] = 62834 / (half dry air pressure [Pa]) in the case of the standard measurement conditions in the present invention. If the average pore size of the membrane determined by the half-dry method (the average pore size of the minimum pore size layer of the membrane) is large, the ability to prevent permeation of a substance to be prevented from permeating, for example, a turbid substance, is reduced, so that effective filtration and separation cannot be performed. . Conversely, if the average pore size of the membrane is too small, the water permeability will decrease and the filtration rate will decrease, and in this case also, effective filtration and separation will not be possible. The average pore size of the membrane is less than 1 μm, preferably 0.03 μm or more and 0.8 μm or less, more preferably 0.1 μm or less.
The thickness is preferably from 05 μm to 0.6 μm.

The pore size of the outer surface is represented by a pore size corresponding to a pore area specific gravity of 50% of pores observed (existing) on the outer surface in an electron microscope observation image of the outer surface. The pore diameter corresponding to the pore area specific gravity of 50% is defined as the sum of the pore areas of the pores observed (existing) on the surface in order from the smaller pore diameter or the larger pore diameter in order from the larger pore. The obtained value indicates the hole diameter of the hole at which 50% of the total of the hole area of each hole is reached. When the hole to be observed is not circular (such as an elliptical shape), the diameter in the case of circular approximation (diameter of a circle having the same area as the hole area of the hole) is used.

The pore diameter on the inner surface of the film of the present invention is 1 μm or more. If it is less than 1 μm, the filtration resistance on the inner surface side having no minimum pore size layer becomes unnecessarily large, and the filtration resistance of the whole membrane increases, and the water permeability is undesirably reduced. The pore diameter of the inner surface is represented by a pore diameter corresponding to a pore area specific gravity of 50% of pores observed (existing) on the inner surface in an electron microscope observation image of the inner surface, as in the case of the outer surface. If the hole to be observed is not circular (e.g., elliptical), the diameter in the case of circular approximation is used. If the pore diameter of the inner surface is too large, the film strength tends to be reduced.

The porosity of the film of the present invention is 50% or more and 95% or less, preferably 60% or more and 90% or less. If the porosity is small, the water permeability is low, which is disadvantageous. If the porosity is too large, the film strength is low, which is disadvantageous. The porosity can be determined by the following equation.

[0017]

(Equation 2)

Here, the term “wet membrane” refers to a membrane in which water is filled in the pores but not in the hollow part.
Specifically, a sample membrane having a length of 10 to 20 cm is immersed in ethanol to fill the hole with ethanol, and then repeatedly immersed in water 4 to 5 times to sufficiently replace the inside of the hole with water. Can be obtained by holding one end of the hand and shaking it about five times, holding the other end of the hand and shaking it about five times again to remove water in the hollow portion. The dry film can be obtained by drying the wet film in an oven at, for example, 80 ° C. until the weight becomes constant after measuring the weight of the wet film. The film volume can be determined from the film volume [cm ³ ] = π {(outer diameter [cm] / 2) ² − (inner diameter [cm] / 2) ² } (film length [cm]). If the weight of one film is too small and the error in weight measurement is large, a plurality of films can be used.

Next, an example of a preferred method for producing the film of the present invention will be described. As a preferred example of the production method of the membrane of the present invention, after the polyethylene and the organic liquid are compatible at a high temperature, the compatible material is hollowed out by injecting a hollow fiber forming fluid into the hollow portion from a hollow fiber forming spout. By extruding into a water bath through the air in a thread form and cooling, a liquid-liquid phase separation occurs in the compatible substance to generate a pore structure, solidify and fix the structure, and then the organic liquid is extracted and removed to remove polyethylene hollow. In a method for obtaining a fibrous porous membrane,
1) The hollow part forming fluid is a liquid capable of separating liquid and liquid phases from polyethylene at a high temperature, and 2) The time required for the extrudate to travel in air is between 0 and 1 second (however, 0 is not included). ). A conceptual diagram of an example of such a film forming flow is shown in FIG.

The organic liquid used here is in a liquid-liquid phase separation state at a certain temperature and in a range of polyethylene concentration when mixed with polyethylene (two-phase coexistence of polyethylene concentrated phase droplet / polyethylene diluted phase, ie, organic liquid concentrated phase droplet). Is a liquid whose boiling point is not lower than the upper limit temperature of the liquid-liquid phase separation temperature range. It may be a mixed liquid instead of a single liquid. When such an organic liquid and polyethylene are mixed in a concentration range in which liquid-liquid phase separation occurs, if the temperature is raised to a temperature higher than the upper limit temperature at which a liquid-liquid phase separation state is obtained in the mixed composition, polyethylene and the organic liquid are mixed. A homogeneously dissolved compatible substance can be obtained. When the compatibilized material is cooled, a coexistence state (liquid-liquid phase separation state) of two liquid-liquid phases (polyethylene concentrated phase droplets and organic liquid concentrated phase droplets) appears, a pore structure is generated, and the polyethylene is further solidified. The pore structure is fixed by cooling to a temperature (usually 100 to 150 ° C.).

FIG. 2 shows an example of this phase diagram. In FIG. 2, the polyethylene concentration is a ratio of the weight of the polyethylene to the sum of the weight of the polyethylene and the weight of the organic liquid. The liquid 1 phase region is a region where polyethylene and an organic liquid are compatible, the liquid and liquid 2 phase region is a region where a polyethylene rich phase (liquid) and a polyethylene dilute phase (liquid) coexist, and the solidified region is where polyethylene is solidified. The region (region where solid polyethylene and organic liquid coexist) is shown. After the pore structure is fixed, a hollow fiber-like porous body is obtained by removing the organic liquid from the membrane. At this time, the polyethylene rich phase portion at the time of liquid-liquid phase separation is cooled and solidified to form a porous structure (porous skeleton), and the polyethylene dilute phase (organic liquid rich phase) portion becomes a pore portion.

Examples of such organic liquids are dibutyl phthalate, diheptyl phthalate, dioctyl phthalate,
Phthalic acid esters such as di (2-ethylhexyl) phthalate, diisodecyl phthalate, ditridecyl phthalate,
Sebacic esters such as dibutyl sebacate, adipic esters such as dioctyl adipate, maleic esters such as dioctyl maleate, trimellitic esters such as trioctyl trimellitate, tributyl phosphate, trioctyl phosphate and the like Phosphoric esters,
Examples thereof include propylene glycol dicaprate, glycol esters such as propylene glycol dioleate, glycerin esters such as glycerin trioleate, and the like, alone or in combination of two or more.

Further, a liquid which is incompatible with polyethylene at high temperature alone or a liquid such as liquid paraffin which is compatible with polyethylene at high temperature alone is too high in compatibility to obtain a liquid-liquid two phase separation state. The definition of an organic liquid (a liquid that can take a liquid-liquid phase separation state at a certain temperature and polyethylene concentration range when mixed with polyethylene and has a boiling point higher than the upper limit of the liquid-liquid phase separation temperature range) A mixed liquid mixed with the above-mentioned organic liquid examples (phthalates and the like) within a range not to be missed can also be mentioned as an example of the organic liquid.

Polyethylene and the above-mentioned organic liquid can be mixed and dissolved at a predetermined mixing ratio at a temperature not lower than the upper limit temperature of the liquid-liquid phase separation temperature range at the mixing ratio by using, for example, a twin screw extruder. it can. The mixing ratio of polyethylene and the organic liquid is disadvantageous because if the ratio of polyethylene is too small, the strength of the obtained membrane is too low, and conversely, if the ratio of polyethylene is too large, the water permeability of the obtained membrane is too low. Disadvantageous. The mixing ratio of the polyethylene and the organic liquid is 10/90 to 40/60, preferably 15/85 to 30/70, by weight of the polyethylene / organic liquid.

The compatible material (melt) is guided to a portion called a head at the tip of the extruder and extruded. By mounting a die for extruding the compatible material into a predetermined shape at the extrusion port in the head, the compatible material can be formed into a predetermined shape and extruded. In the case of the present invention, a spinneret for forming into a hollow fiber (hollow fiber forming spinneret) is attached to the extrusion port of the head. The hollow fiber forming spinneret has an annular hole for extruding the compatible material into a hollow shape (annular shape) and an extruded hole for preventing the hollow portion of the extruded hollow material from closing to form a column. Spouting nozzle having a hole (existing inside the above-mentioned annular hole; the shape is a circular hole) for discharging a hollow part forming fluid to be injected into the hollow part of the hollow material formed on the extrusion side surface It is. The miscible material of polyethylene and the organic liquid is injected into the hollow portion of the hollow fiber through a hole formed inside the hole through the hole inside the hole for forming the hollow fiber through the hole of the above-described hole for forming a hollow fiber. (Even in an inert gas).

The fluid forming the hollow portion is a liquid capable of liquid-liquid phase separation with polyethylene at a high temperature, that is, a liquid-liquid phase separated state (polyethylene concentrated phase droplet) at a certain temperature and polyethylene concentration range when mixed with polyethylene. /
A liquid capable of forming a polyethylene dilute phase, that is, a two-phase coexistence state of an organic liquid concentrated phase droplet is used. However, the temperature of the hollow part forming fluid when discharged from the spinning nozzle for forming a hollow fiber is not necessarily required to be a temperature at which the polyethylene and the liquid-liquid phase separation state are obtained, and is higher than a temperature range at which the liquid-liquid phase separation state is obtained. Or lower. Examples of such a fluid for forming a hollow portion include the same examples as those of the above-described organic liquid. The boiling point of the hollow part forming fluid is different from the above-mentioned organic liquid, and may be equal to or lower than the upper limit temperature of the liquid-liquid phase separation temperature range as long as it is equal to or higher than the spinning temperature. By using a liquid capable of forming a liquid-liquid phase separation state with polyethylene as the hollow portion forming fluid, the inner surface side can have a suitable structure of the present invention.

[0027] The compatible material extruded into the air is then led to a water bath (a liquid bath consisting essentially of water) and cooled to a temperature at which the polyethylene in the extrudate solidifies. The temperature of the water bath is set below the solidification temperature of the polyethylene in the extrudate. The compatibilized material extruded from the spinneret is cooled while passing through the water bath from the spinneret outlet, thereby causing a liquid-liquid phase separation to occur, a pore structure is generated, and then solidified, and the pore structure is fixed. You. The time required for the compatible material extruded from the spinneret into the air to enter the water bath, that is, the air travel time, is from zero to one second (but not including zero). When the air traveling time is zero, the extruded surface of the spinneret comes into contact with the water surface of the water bath.

The spinning temperature is set to a temperature higher than the temperature at which the polyethylene and the organic liquid are compatible with each other, that is, the liquid-liquid phase separation temperature range in the mixing ratio (usually about 150 to 300 ° C.).
The temperature is always higher than the water bath temperature set below the temperature at which the polyethylene in the extrudate solidifies. Therefore, when the air traveling time is zero, the spinneret is constantly cooled by the water in the water bath, and the temperature control of the spinneret becomes unstable, which is not suitable. On the other hand, if the air traveling time is too long, the porosity of the outer surface decreases, and the water permeability of the membrane decreases, which is not preferable.

The air travel time is preferably between zero and 0.5.
It is between 5 seconds (but not including 0), and more preferably between 0 and 0.25 seconds (but not including 0).
In the measurement of the aerial traveling time, when the hollow fiber is wound without tension at the outlet of the water bath, it is obtained from the winding speed and the aerial traveling distance (the distance between the spout surface and the water bath surface) according to the following formula. be able to.

[0030]

(Equation 3)

As described above, the outer surface side can be made to have a preferable structure of the present invention by guiding the compatible substance discharged from the spinneret to the water bath after a specific idle running time. Thus, by using a liquid capable of forming a liquid-liquid phase separation state with polyethylene as the hollow part forming fluid, and guiding the compatible substance discharged from the spout to a water bath after a specific idle running time, the membrane is formed. The entire structure can be a suitable external dense anisotropic structure disclosed in the present invention. In the hollow fiber-like material coming out of the water bath, the polyethylene thick phase portion generated during the liquid-liquid phase separation generated during cooling is solidified by cooling to form a porous structure (porous skeleton),
Polyethylene dilute phase during liquid-liquid phase separation (organic liquid rich phase)
The portion is a hole filled with organic liquid. By removing the organic liquid clogging the pores, the porous membrane disclosed in the present invention can be obtained.

The organic liquid in the film is removed by extracting and removing the organic liquid to be removed without dissolving or deteriorating the polyethylene with a volatile liquid that dissolves the polyethylene, and then drying and evaporating the volatile liquid remaining in the film. It can be implemented by removing.
Examples of such volatile liquids for organic liquid extraction include:
Examples thereof include hydrocarbons such as hexane and heptane, chlorinated hydrocarbons such as methylene chloride and carbon tetrachloride, and methyl ethyl ketone.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
The present invention is not limited to this. The pure water permeability, breaking strength and breaking elongation were determined by the following measuring methods. Further, the pore diameters of the outer surface and the inner surface are 50 magnifications.
After photographing at 00x or 10000x, the transparent sheet is placed on the electron micrograph copy of the outer and inner surfaces, which is enlarged twice in length and width, respectively, and the transparent sheet is placed on the transparent sheet. After black-and-white binarization by painting (holes are black), the images were taken into a computer using a CCD camera, and image analysis software Qu manufactured by Leica was used.
It was determined based on the pore area value and pore diameter value (circular approximate diameter value) of each pore obtained by using antimet500.

Pure water permeability: One end of a wet hollow fiber membrane having a length of about 10 cm, which was immersed in ethanol and then immersed in pure water several times, was sealed at one end, and an injection needle was inserted into the hollow at the other end. Under the injection needle, pure water at 25 ° C. is injected into the hollow portion at a pressure of 0.1 MPa, and the amount of pure water permeating from the outer surface is measured, and the pure water permeability is calculated from the following equation. Were determined.

[0035]

(Equation 4)

Here, the effective membrane length refers to the net membrane length excluding the portion where the injection needle is inserted. Breaking strength and breaking elongation: Using a tensile tester (Autograph AG-A type manufactured by Shimadzu Corporation), the hollow fiber was pulled at a distance between chucks of 50 mm and a pulling speed of 200 mm / min. The breaking strength and the breaking elongation were determined by the following equations.

[0037]

(Equation 5)

Here, the film cross-sectional area [cm ² ] = π {(outer diameter [cm] / 2) ² − (inner diameter [cm] / 2) ² }. Elongation at break [%] = 100 (displacement at break [mm]) / 50

[0039]

Example 1 High-density polyethylene (manufactured by Mitsui Chemicals, Hyzex Million 030S, viscosity average molecular weight: 450,000) 2
0 parts by weight and 80 parts by weight of a mixed organic liquid having a weight ratio of diisodecyl phthalate (DIDP) to di (2-ethylhexyl) phthalate (DOP) of 3 to 1 (DIDP / DOP = 3/1). , Twin screw extruder (TE manufactured by Toshiba Machine Co., Ltd.)
(M-35B-10 / 1V) and mixed by heating.
30 ° C.), a ring for extruding a compatible material with an outer diameter of 1.58 mm / inner diameter of 0.83 mm on the extrusion surface of the spinning hole for hollow fiber molding attached to the extrusion opening in the head (230 ° C.) at the tip of the extruder. The above-mentioned compatible material is extruded from the hole, and DOP is formed as a hollow-portion forming fluid from the circular hole for discharging the hollow-portion forming fluid having a diameter of 0.6 mm inside the annular hole for extruding the compatible material.
Was discharged and injected into the hollow portion of the hollow fiber extrudate.

The hollow fiber extruded material extruded from the spinneret into the air is placed in a 39 ° C. water bath through an air traveling distance of 1.5 cm, passed through about 2 m of water, solidified by cooling, and then cooled. Was wound out of the water bath at a speed of 16 m / min without applying tension. The air travel time at this time is determined as 0.06 seconds based on the air travel distance and the winding speed.

Next, the obtained hollow fiber was repeatedly immersed in methylene chloride at room temperature for 30 minutes five times to extract and remove DIDP and DOP from the hollow fiber.
For half a day to remove the remaining methylene chloride by volatilization to obtain a polyethylene hollow fiber-like porous membrane. When the cross section of the obtained film was observed with an electron microscope, it was an anisotropic film having a minimum pore size layer on the outer surface. In addition, various physical properties of the membrane (outer surface pore size, inner surface pore size, average pore size, porosity,
Table 1 shows the yarn diameter, pure water permeability, breaking strength, and breaking elongation.

[0042]

Example 2 18 parts by weight of high-density polyethylene (Suntech SH800, viscosity average molecular weight 250,000) manufactured by Asahi Kasei Corporation as polyethylene, and DIDP and DO as organic liquids
3: 1 in weight ratio with P (DIDP / DOP = 3/1)
Using 82 parts by weight of a mixture of
A polyethylene hollow fiber-like porous membrane was obtained in the same manner as in Example 1 except that the above conditions were used. The air travel time at this time is 0.17 seconds. Various physical properties of the obtained membrane (outer surface pore size, inner surface pore size, average pore size, porosity, yarn diameter, pure water permeability, breaking strength,
Elongation at break) is shown in Table 1, and an electron micrograph is shown in FIG.

[0043]

[Comparative Example 1] As polyethylene, according to Example 2 of JP-A-3-42025 (same as above except that the volume ratio of SH800 / hydrophobic silica / DOP was 27/14/59). Suntech SH800 same as Example 2
Was used to obtain a hollow fiber porous membrane. Various physical properties of the obtained membrane (outer surface pore size, inner surface pore size, average pore size, porosity, yarn diameter,
Pure water permeability, breaking strength, breaking elongation) are shown in Table 1, and an electron micrograph is shown in FIG. The obtained film had a uniform three-dimensional porous structure without anisotropy. Compared with the membrane of Example 2, the membrane of this comparative example has the same average pore diameter, but low pure water permeability, and low performance as a filtration membrane.

[0044]

[Table 1]

[0045]

According to the present invention, it has become possible to provide a polyethylene hollow fiber-like porous membrane having both fine pores and high water permeability, which is suitable for filtration applications such as turbidity.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an example of a film forming flow for manufacturing a film of the present invention.

FIG. 2 is a conceptual diagram of a phase diagram of polyethylene and an organic liquid.

FIG. 3 is an electron micrograph print of the film obtained in Example 2.

FIG. 4 is an electron micrograph print of the film obtained in Comparative Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Polyethylene hopper 2 ... Polyethylene supply port 3 ... Organic liquid supply flow path 4 ... Organic liquid supply port 5 ... Biaxial kneading extruder 6 ... Conduit 7 ... Head 8 ... Constant-quantity gear pump driving unit 9 ... Constant-quantity gear pump 10 ... Spout for forming hollow fiber 11 ... Hollow part forming fluid supply channel 12 ... Mixed extrudate of polyethylene and organic liquid 13 ... Hollow part forming fluid 14 ・ ・ ・ Aerial traveling part 15 ・ ・ ・ Water bath 16 ・ ・ ・ Roll 17 ・ ・ ・ Winding roll i ・ ・ ・ Compatible material at the time of spout discharge b ・ ・ ・ Air traveling part and liquid bath Cooling process inside

Continued on the front page F-term (reference) 4D006 GA06 GA07 HA19 MA01 MA22 MA24 MA25 MA33 MA34 MB02 MB16 MC22X MC88 NA21 NA23 NA54 NA68 NA75 PA01 PB04 4L035 AA05 AA09 BB31 BB57 CC20 DD03 DD07 EE08 EE20 FF01 HH05 HJ05 JJ15 KK

Claims (1)

[Claims] An outer surface portion having a minimum pore size layer, wherein the outer surface pore size is less than 1 μm and the inner surface pore size is 1 μm or more;
An external dense anisotropic sponge-structured polyethylene hollow fiber-like porous membrane having an average pore diameter of less than 1 μm and a porosity of 50% or more and less than 95%.