JP2001157826A - Anisotropic 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: An anisotropic polyethylene hollow-fiber porous membrane has a membrane interior dense type sponge-like anistotropic structure having a minimum pore size layer in its membrane cross section and having an outer surface pore size of 1 μm or more, an inner surface pore size of 1 μm or more and a mean pore size of 0.8 μm or less and the void ratio of the porous membrane is 50-below 90%.

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) an empty space having a minimum pore size layer in the membrane cross section, wherein both the outer surface pore size and the inner surface pore size are 1 μm or more and the average pore size is 0.8 μm or less. The dense hollow anisotropic sponge-structured polyethylene hollow fiber porous membrane having a porosity of 50% or more and less than 95%, (2) the dense internal anisotropic membrane according to the above (1), which has an average pore size of 0.03 μm or more Polyethylene hollow fiber-like porous membrane with sponge structure, (3) a dense hollow anisotropic sponge-structured polyethylene hollow fiber-like porous membrane according to (1) above, wherein the average pore size is 0.05 μm or more and 0.6 μm or less, (4) hollow The present invention relates to the above-mentioned (1) to (3), an outer dense anisotropic sponge-structured polyethylene hollow fiber-like porous membrane according to (1) to (3), wherein the inner diameter of the yarn is from 0.4 mm to 3 mm and the film thickness is from 0.05 mm to 1 mm.

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 a dense anisotropic structure having a minimum pore size layer (the densest layer) in a cross section of the film (inside of the film). What is within the membrane section?
Refers to the cross-sectional portion excluding the outer surface and inner surface of the membrane. The minimum pore size layer of the membrane of the present invention exists in a cross-sectional portion that is neither the outer surface nor the inner surface. The thickness of the minimum pore size layer is 5
0% or less, preferably 20% or less, more preferably 10% or less.
% Or less. The anisotropic structure refers to a structure in which the pore diameter is not uniform (uniform) but changes in the membrane cross-sectional direction. In the membrane of the present invention, the pore diameter continuously changes from the smallest pore diameter layer portion present at a position of the membrane cross section toward the outer surface and the inner surface, and the basic direction of the change is the position of the membrane cross section at a certain position. Is the direction in which the pore size increases from the minimum pore size layer portion existing on the outer surface and the inner surface.

[0010] The filtration resistance (permeability) of the membrane is governed by the thickness of the minimum pore size layer. 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 arranged only in the inside of the membrane instead of the entire membrane cross section, and the portion other than the minimum pore size layer is designed to have a larger pore size than the minimum pore size layer so as to minimize the filtration resistance. By doing so, it becomes possible to provide a polyethylene hollow fiber-like porous membrane having dense pores and high water permeability. In this case, the minimum pore size layer (dense pores) inside the membrane defines the filtration (sieving) function of the entire membrane, and the portions other than the minimum pore size layer do not contribute as much as possible to the increase in filtration resistance of the membrane. Responsible for the function of a support layer for maintaining the form and strength of the membrane.

Further, in the case of the dense membrane inside the membrane as in the present invention, external pressure filtration (the filtration direction of the membrane is from the outer surface to the inner surface)
In the above, the cross-sectional portion on the outer surface side of the smallest pore diameter layer having a larger pore diameter than the smallest pore diameter layer, and in the internal pressure filtration (the filtration direction of the membrane is from the inner surface to the outer surface), the pore diameter is larger than the smallest pore diameter layer. The cross-section on the inner surface side of a certain minimum pore size layer can be expected to serve as a pre-filter for the minimum pore size layer when filtering a turbid solution or the like.

A pre-filter is a filter having a large pore size which is placed in front of a filter having a small pore size.
By installing a pre-filter, a relatively clear liquid from which large turbidity etc. has been removed in advance by the pre-filter is sent to the subsequent small-diameter filter, stabilizing the filtration operation and lengthening the membrane. The service life can be prolonged, and an effect (pre-filter effect) of reducing the cost of the entire membrane filtration process including the former stage and the latter stage can be expected. In the case of the membrane of the present invention, the minimum pore size layer corresponds to a filter having a small pore size at the subsequent stage.In the case of external pressure filtration, the outer surface side is smaller than the minimum pore size layer, and in the case of internal pressure filtration, the inner surface side is smaller than the minimum pore size layer. Each is expected to correspond to the pre-filter in the former stage, and the above-mentioned pre-filter effect can be expected to be exhibited. Confirmation of the location of the minimum pore size layer and the anisotropic structure
It can be carried out by observing the cross section of the film with an electron microscope.

The pore size of the outer surface and the inner surface of the membrane of the present invention is 1
μm or more. Larger pores on the inner surface and outer surface are more advantageous in terms of water permeability, but too large ones are disadvantageous in terms of membrane strength. The pore diameter of the outer surface and the inner surface is represented by a pore diameter corresponding to a pore area specific gravity of 50% of the pores observed on the outer surface or the inner surface in an electron microscope observation image of the outer surface or the inner 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 average pore size of the membrane is 0.8 μm or less, preferably 0.03 μm or more and 0.8 μm or less, and more preferably 0.05 μm or more and 0.6 μm or less. The average pore size of the membrane can be determined according to the method described in ASTM: F316-86 (also known as 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 carried out by using ethanol as a liquid to be used and measuring the hollow fiber membrane having a length of about 10 cm at 25 ° C. and a pressure increase rate of 0.01 at
The measurement at m / sec was set as a standard measurement condition. Average pore size [μ
m] is obtained from the following equation.

[0015]

(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 preferably 0.8 μm or less, preferably 0.03 μm or more and 0.8 μm or less, and more preferably 0.05 μm or more and 0.6 μm or less.

The porosity of the film of the present invention is from 50% to 95%, preferably from 60% to 90%. 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.

[0018]

(Equation 2)

Here, the term “wet membrane” refers to a membrane in which the pores are filled with water but the hollow portions are not filled with water.
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. Extruded into a liquid bath through the air in a thread form and cooled, causing liquid-liquid phase separation in the compatible material to generate a pore structure, solidifying and fixing the structure, and then extracting and removing the organic liquid to remove polyethylene. In a method for obtaining a hollow fiber-like porous membrane,
1) The hollow part forming fluid is a liquid capable of liquid-liquid phase separation with polyethylene at a high temperature, and 2) At least the upper part of the liquid bath is composed of a liquid capable of liquid-liquid phase separation with polyethylene at a high temperature. There is a method characterized by the following.

The organic liquid used here is in a liquid-liquid phase separated state at a certain temperature and in a polyethylene concentration range when mixed with polyethylene (two phases of polyethylene rich phase droplets / polyethylene dilute phase, that is, organic liquid rich phase droplets coexist). 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, when the temperature is raised to a temperature higher than or equal to an upper limit temperature at which a liquid-liquid phase separation state in the mixed composition is obtained, 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. 1 shows an example of this phase diagram. In FIG. 1, 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 include phthalic acid esters such as dibutyl phthalate, diheptyl phthalate, dioctyl phthalate, di (2-ethylhexyl) phthalate, diisodecyl phthalate, ditridecyl phthalate, and sebacin such as dibutyl sebacate. Acid esters, adipates such as dioctyl adipate, maleates such as dioctyl maleate, trimellitates such as trioctyl trimellitate, phosphates such as tributyl phosphate and trioctyl phosphate, 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.

Furthermore, a liquid that is incompatible with polyethylene alone at high temperatures even when used alone, or a liquid such as liquid paraffin that is compatible with polyethylene at high temperatures alone is too high in compatibility to capture the phase separation state of liquid-liquid two phases. 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 from polyethylene at a high temperature, that is, a liquid-liquid phase separated state (polyethylene dense phase droplets) 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-portion forming fluid when discharged from the spinning nozzle for forming a hollow fiber is not necessarily required to be a temperature at which the liquid-liquid phase separation state occurs with polyethylene, 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.

The extrudate which has been extruded into the air is then led to a liquid bath and cooled to a temperature at which the polyethylene in the extrudate solidifies. The compatibilized material extruded from the spinneret is cooled while passing through the liquid bath from the spinneret outlet, causing liquid-liquid phase separation to occur, and a pore structure is generated, and then solidified, and the pore structure is fixed. Is done. The composition of the liquid bath is at least
The upper part of the liquid bath, which is the part that the extrudate extruded from the spinner first touches, is a liquid capable of liquid-liquid phase separation with polyethylene at high temperature, that is, a certain temperature and polyethylene concentration when mixed with polyethylene. It is preferable to use a liquid capable of forming a liquid-liquid phase separated state (polyethylene concentrated phase droplet / polyethylene diluted phase, that is, a two-phase coexistence state of organic liquid concentrated phase droplet) in the range of the present invention on the outer surface side. It is necessary to make a simple structure. However, the temperature of the liquid bath needs to be lower than the temperature at which the liquid and the liquid phase separate from the polyethylene (that is, the solidification temperature of the polyethylene or lower). Examples of such a composition forming at least the upper layer portion of the liquid bath include the same ones as the examples of the organic liquid described above. The boiling point of the liquid bath composition may be lower than the upper limit of the liquid-liquid phase separation temperature range, unlike the above-mentioned organic liquid.

The composition of the entire liquid bath may be at least in the upper layer of the liquid bath, and may be entirely composed of only a liquid capable of liquid-liquid phase separation with polyethylene at a high temperature. A liquid that has the ability to liquid-liquid separate from polyethylene at high temperatures that must be present in the upper layer of the bath,
If it is immiscible with water and has a lower specific gravity than water, a two-layer liquid in which the upper part of the liquid bath is a liquid capable of liquid-liquid phase separation with polyethylene at the high temperature and the lower part is water. Can be a bath. Liquids capable of liquid-liquid phase separation with polyethylene at high temperatures are usually organic compound liquids. An organic compound liquid usually has a lower cooling capacity than water because it has a lower specific heat than water. If the cooling capacity is weak, it is difficult to obtain a porous film having fine pores.

Therefore, from the viewpoint of securing the cooling capacity, which is one of the important functions of the liquid bath, the liquid bath is made up of only an organic compound liquid capable of liquid-liquid phase separation from polyethylene at a high temperature. A liquid bath having a two-layer structure in which an organic compound liquid having an ability to separate liquid and liquid phases from polyethylene at a high temperature, being immiscible with water and having a lower specific gravity than water is used as an upper layer, and water is used as a lower layer is preferable. Examples of such an organic compound liquid having the ability to separate liquid and liquid phases from polyethylene at a high temperature, being immiscible with water, and having a lower specific gravity than water include di (2-ethylhexyl) phthalate and diisodecyl phthalate. And examples of the organic liquid. By using such a liquid bath having a two-layer structure, the cooling ability in the liquid bath is ensured by the presence of the lower aqueous layer, and the preferred film structure of the present invention is provided by the presence of the upper organic compound liquid layer. Formation is also ensured.

In such a two-layer liquid bath, the thickness of the upper layer (organic compound liquid layer) is required to be 1 mm or more, preferably 5 mm or more from the viewpoint of making the film structure suitable for the present invention. Yes, at the same time, it is 30 cm or less, preferably 10 cm or less, and more preferably 2 cm or less from the viewpoint of not lowering the cooling capacity of the liquid bath. On the other hand, the thickness of the lower layer (water layer) needs to be 5 cm or more, preferably 10 cm or more, from the viewpoint of securing the cooling capacity. Such 2
FIG. 2 shows a conceptual diagram of an example of a film forming flow when a liquid bath having a layer structure is used.

In the hollow fiber-like material coming out of the liquid bath, the polyethylene thick phase portion generated during liquid-liquid phase separation during cooling is solidified by cooling to form a porous structure (porous skeleton). The polyethylene dilute phase (organic liquid rich phase) portion is a pore portion filled with the organic liquid. By removing the organic liquid clogging the pores, the porous membrane disclosed in the present invention can be obtained. The removal of the organic liquid in the film does not dissolve or degrade the polyethylene, and extracts and removes the organic liquid to be removed with a volatile liquid that dissolves, and then, after drying, volatilizes and removes the volatile liquid remaining in the film. Can be implemented. Examples of such volatile liquids for organic liquid extraction include hydrocarbons such as hexane and heptane, methylene chloride,
Chlorinated hydrocarbons such as carbon tetrachloride, methyl ethyl ketone and the like can be mentioned.

[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 diameter of the outer surface and the inner surface is 10 magnifications.
After photographing at 00x or 5000x, place the transparent sheet on top of the electron micrograph copy of the outer and inner surfaces, which were enlarged twice in length and width, respectively, and placed the holes on the surface black 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 Qua manufactured by Leica was used.
The determination was made based on the pore area value and pore diameter value (circular approximate diameter value) of each pore obtained by using nitimet 500.

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 3)

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 4)

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 extrudate extruded from the spinneret into the air passes through a 1.7 cm air travel distance, and the upper layer is D-shaped.
OP (1.5cm thickness, 41 ° C), lower layer is water (15cm)
(Thickness: 29 ° C.), and after passing through a liquid bath of about 2 m to solidify by cooling, the hollow fiber is moved out of the liquid bath at a speed of 16 m / min without applying tension. Wound up. The outline of the film forming flow at this time is the same as that of FIG. Then, the obtained hollow fiber was repeatedly immersed in methylene chloride at room temperature for 30 minutes five times to obtain DI in the hollow fiber.
By extracting and removing DP and DOP, and then drying at 50 ° C. for half a day to volatilize and remove residual methylene chloride,
A polyethylene hollow fiber porous membrane was obtained.

The physical properties (outer surface pore size, inner surface pore size, average pore size, porosity, yarn diameter, pure water permeability, breaking strength, breaking elongation) of the obtained membrane are shown in Table 1, and electron micrographs. As shown in FIG. From the comparative observation of the size of the pores observed in each photograph, it is observed that this film has a minimum pore diameter layer slightly inside the cross section than on the outer surface on the outer surface side of the cross section.

[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
m, a polyethylene hollow fiber porous membrane was obtained in the same manner as in Example 1 except that a liquid bath of DOP (1.0 cm thickness, 44 ° C.) for the upper layer and water (15 cm thickness, 25 ° C.) for the lower layer was used.
When the cross section of the obtained film was observed with an electron microscope, it was an anisotropic film in which the minimum pore size layer was present inside the film. Also,
Table 1 shows the physical properties (outer surface pore size, inner surface pore size, average pore size, porosity, fiber diameter, pure water permeability, breaking strength, breaking elongation) of the membrane.

[0043]

Comparative Example 1 According to Example 3 of JP-A-3-42025 (SH800 / hydrophobic silica / DBP / D)
A hollow fiber porous membrane was obtained using the same Suntech SH800 as in Example 2 as polyethylene, except that the OP volume ratio was changed to 24/14/43/19. Table 1 shows various physical properties (pore diameter of outer surface, pore diameter of inner surface, average pore diameter, porosity, yarn diameter, water permeability of pure water, breaking strength, elongation at break) of the obtained membrane.
Shown in When the cross section of the obtained film was observed with an electron microscope, it 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 of a phase diagram of polyethylene and an organic liquid.

FIG. 2 is a conceptual diagram showing an example of a film forming flow for manufacturing the film of the present invention.

FIG. 3 is an electron micrograph print of the film obtained in Example 1.

[Explanation of symbols]

 B: Compatible material at the time of spout ejection B: Cooling process in the aerial traveling section and liquid bath C: Solidified material from liquid bath 1: Polyethylene hopper 2: Polyethylene supply port DESCRIPTION OF SYMBOLS 3 ... Organic liquid supply flow path 4 ... Organic liquid supply port 5 ... Biaxial kneading extruder 6 ... Conduit 7 ... Head 8 ... Constant gear pump drive part 9 ... Constant gear pump DESCRIPTION OF SYMBOLS 10 ... Spout for hollow fiber formation 11 ... Hollow part forming fluid supply flow path 12 ... Mixed extrudate of polyethylene and organic liquid 13 ... Hollow part forming fluid 14 ... Airborne traveling part 15. .. Upper layer of liquid bath 16 ... Lower layer of liquid bath (water) 17 ... Upper layer thickness of liquid bath 18 ... Lower layer thickness of liquid bath 19 ... Roll 20 ... Winding roll

Continued on the front page F term (reference) 4D006 GA06 GA07 HA01 MA01 MA22 MA24 MB02 MB10 MC22X NA05 NA10 PB02 PB06 PB13 PC02 PC21 PC41 4L035 AA05 AA09 BB31 BB58 BB66 DD03 DD07 DD14 EE08 EE20 FF01 HH01 HH05 JJ15 KK

Claims (1)

[Claims] 1. A film having a minimum pore size layer in a cross section of the film, having an outer surface pore size and an inner surface pore size of 1 μm or more and an average pore size of 0.8 μm or less, and having a porosity of 50% or more and less than 95%. Dense anisotropic sponge structure polyethylene hollow fiber-like porous membrane.