JP2001190939A - Method of manufacturing polyethylene hollow fiber porous membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a polyethylene hollow fiber porous membrane simultaneously having dense microspores and high water permeability, which is suited for the use in turbidity removal by the filtration. SOLUTION: In the method for obtaining a polyethylene hollow fiber porous membrane by fusing a polyethylene and an organic liquid at a high temperature, extruding the fused liquid into a liquid into a liquid bath to solidify the fused liquid by cooling through the air to constitute hollow fibrous state and then extracting and removing said organic liquid, (1) the liquid bath is constituting of two layers wherein the upper layer part comprises a liquid immiscible with water having an activity to separatee polyethylene in liquid-liquid phase at a high temperature and the lower layer part comprises water, and (2) the hollow fibrous material is elongated so that the elongation retention becomes from 5% or more to 150% or less prior to or after the organic liquid after the solidifying by cooling procedure is extracted and removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a polyethylene hollow fiber porous membrane having fine pores and high water permeability, which is suitable for filtration applications 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 for use 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 membrane having a uniform three-dimensional porous structure (page 3, upper right column, lines 10-11) as disclosed in Japanese Patent Publication No. 025 is conventionally known. This 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 pore diameter distributions) at any two points in the membrane cross-section are almost equal. In such a film having a uniform structure in the film cross section direction, the transmission resistance of the entire film cross section is increased,
In order to obtain high water permeability, it was necessary to increase the pore diameter, and it was difficult to obtain a membrane having high water permeability while having fine pores (small pore diameter).

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a polyethylene hollow fiber porous membrane having dense pores and high water permeability, which is suitable for filtration applications such as turbidity.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, the polyethylene membrane obtained by the following production method has high water permeability while having fine pores. To accomplish the present invention. That is, the present invention provides (1) a method in which polyethylene and an organic liquid are melted at a high temperature, and then the melt is injected into a hollow portion from a spinning hole for forming a hollow fiber into a hollow portion while passing through the air into a hollow fiber shape. In a method of extruding into a liquid bath, solidifying by cooling, and then extracting and removing the organic liquid to obtain a polyethylene hollow fiber porous membrane, (a) the liquid bath separates liquid polyethylene and liquid phase at a high temperature in an upper layer portion of the liquid bath. The lower layer is a two-layer liquid bath composed of water which is immiscible with water and having a residual elongation of 5% before or after extraction and removal of the organic liquid after cooling and solidification. % To 150% or less.
A method for producing a polyethylene hollow fiber-like porous membrane, (2) a method for producing a polyethylene hollow fiber-like porous membrane according to the above (1), wherein the upper layer thickness is 1 mm or more and 30 cm or less, and (3) an upper layer thickness of 5 mm or more and 30 cm or less. (1) The method for producing a polyethylene hollow fiber-like porous membrane according to the above (1), (4) the above (2) and (3), wherein the thickness of the upper layer portion is 10 cm or less.
(5) The method for producing a polyethylene hollow fiber-like porous membrane according to the above (5).
(2) and (3) above, wherein the thickness of the upper layer portion is 2 cm or less.
(6) The method for producing a polyethylene hollow fiber-like porous membrane according to the above (6).
(1) The method for producing a polyethylene hollow fiber porous membrane according to (1) to (5), wherein the thickness of the lower layer is 5 cm or more; (7) The method according to (1) to (5), wherein the thickness of the lower layer is 10 cm or more. A method for producing a polyethylene hollow fiber-like porous membrane,

(8) The polyethylene hollow fiber porous membrane according to the above (1) to (7), wherein the residual elongation by stretching before or after extraction and removal of the organic liquid after cooling and solidification is 10% or more and 100% or less. (9) The method for producing a polyethylene hollow fiber porous membrane according to the above (1) to (8), wherein the hollow part forming fluid is a liquid having a boiling point not lower than the spinning temperature, and (10) forming the hollow part. The method for producing a polyethylene hollow fiber-like porous membrane according to the above (1) to (8), wherein the fluid is a liquid having a boiling point equal to or higher than the spinning temperature and having a capability of performing liquid-liquid phase separation with polyethylene at a high temperature. .

[0007] The polyethylene hollow fiber-like porous membrane produced by the above-mentioned production method does not have a uniform three-dimensional structure in cross section, but has an anisotropic structure. The anisotropic structure refers to a structure in which the pore diameter changes rather than being uniform (uniform) in the membrane cross-sectional direction. In the anisotropic structure, the minimum pore size layer (the densest layer) that determines the separation function (blocking ability in filtration) of the membrane and causes a decrease in water permeability due to high permeation resistance
Occupies only one portion of the membrane cross section. In other words, the cross-sectional structure of the anisotropic structure membrane has a minimum pore diameter layer that has dense pores (pores with small pore diameters) that determine the separation function of the membrane and has a high permeation resistance but occupies only one part of the membrane cross-section. It consists of portions other than the minimum pore size layer which are not directly involved in the separation function and are formed of communication holes having a larger pore size than the minimum pore size layer, and therefore do not contribute much to the increase in the permeation resistance of the membrane.

By forming such an anisotropic structure, it is possible to form a porous polyethylene membrane which can achieve both the existence of dense pores and the development of high water permeability. In particular, when the hollow part forming fluid is a liquid having a boiling point not lower than the spinning temperature and a liquid capable of liquid-liquid phase separation with polyethylene at a high temperature, large pores are opened on both the inner and outer surfaces, and the minimum pore diameter layer is formed. However, a dense anisotropic structure inside the film, which is present in the cross-sectional portion of the film that is neither the outer surface nor the inner surface, is formed. In the case of a membrane having such a structure, the liquid to be filtered first passes through pores on the outer surface or inner surface having a larger pore size than the smallest pore size layer before passing through the smallest pore size layer.

At this time, coarse particles and turbid components are removed on the outer surface or inner surface before filtration and separation in the minimum pore size layer, and the liquid is clarified to some extent (coarse separation is performed). Is sent to the smallest pore diameter layer, where the originally required dense separation (separation by small pores) is performed. 1
Two-stage filtration (pre-filtration, that is, coarse separation and main filtration) can be performed by two times of membrane filtration, and efficient filtration can be performed. In a conventional uniform (non-anisotropic) three-dimensional porous structure as disclosed in Japanese Patent Application Laid-Open No. 3-42025, the entire membrane cross section is equivalent to the minimum pore diameter layer. It is difficult to achieve both the presence of dense pores and the development of high water permeability. Whether the film cross-sectional structure is anisotropic or uniform can be determined by observing the film cross section with an electron microscope.

The details of the manufacturing method of the present invention will be described below. Polyethylene is (1) inexpensive and has good mechanical strength properties, and (2) has a small amount of tertiary carbon, which is rich in chemical reactivity. It has the advantages of being able to expect long-term durability with little chemical deterioration due to chemical cleaning and the like, and (3) not containing a halogen element which is a problem at the time of disposal. Polyethylene includes high-density polyethylene and low-density polyethylene, and high-density polyethylene is preferable in view of the strength of the obtained film. Further, polyethylene has various molecular weights, and from the viewpoint of the strength of the obtained film, the viscosity average molecular weight is preferably 100,000 or more, preferably 200,000 or more. Further, from the viewpoint of moldability, the viscosity average molecular weight is preferably 1,000,000 or less. The viscosity average molecular weight (Mv) of polyethylene can be determined from the following equation by measuring the intrinsic viscosity ([η]) of a decalin solution at 135 ° C. ((J. Brandrup and EHI)
mergut (Editors), Polymer
Handbook (2nd Ed.), Page IV-7, J.
ohn & Sons, New York, 1975). [Η] = 6.8 × 10 ⁻⁴ × (Mv) ^{0.67 The} polyethylene may contain a small amount of a stabilizer such as an antioxidant or an ultraviolet absorber, if necessary.

The organic liquid used in the present invention, when mixed with polyethylene, is in a liquid-liquid phase separated state (polyethylene concentrated phase droplet /
The liquid is a liquid which can take a polyethylene dilute phase, that is, a two-phase coexistence state of an organic liquid concentrated phase droplet, and has a boiling point not lower than the upper limit temperature of the liquid-liquid phase separation temperature range. Instead of a single liquid, it may be a mixed 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. It is possible to obtain a uniformly dissolved molten phase. When the melt 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 a temperature at which the polyethylene solidifies. The pore structure is fixed by cooling to (usually 100 to 150 ° C.), and a porous body is obtained by removing the organic liquid. 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)
The portion becomes the hole 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.

[0013] Further, a liquid which is incompatible with polyethylene alone at high temperature even at a high temperature or a liquid such as liquid paraffin which is compatible with polyethylene at a 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 are mixed and melt-melted at a temperature higher than the upper limit temperature of the liquid-liquid phase separation temperature range at a predetermined mixing ratio by using, for example, a twin screw extruder. Can be. 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 between polyethylene and organic liquid is 10/9 by weight of polyethylene / organic liquid.
0 to 40/60, preferably 15/85 to 30/7
0.

The melt is guided and extruded to a portion called a head at the extruder tip. By mounting a die for extruding the melt into a predetermined shape at the extrusion opening in the head, the melt can be formed into a predetermined shape and extruded. In the case of the present invention, a spinneret for forming into a hollow fiber shape (spinner for forming a hollow fiber) is attached to the extrusion opening of the head. The hollow fiber forming spinneret is extruded so that the melted material is extruded into a hollow shape (annular shape) and the hollow part of the extruded hollow material is not closed to form a cylindrical shape. A spout nozzle having a hole (existing inside the above-mentioned annular hole and having a circular shape) for discharging a hollow part forming fluid to be injected into the hollow part of the hollow material on the extrusion side surface. . The melt of the polyethylene and the organic liquid is injected into the hollow portion through the hole inside the annular hole from the annular hole of the above-mentioned hollow fiber forming spinneret while the hollow portion forming fluid is injected into the hollow portion. Activated gas).

As the hollow part forming fluid, a gas (nitrogen gas or the like) or a liquid which is not reactive with the extrudate (polyethylene and organic liquid) can be used. However, if the hollow part forming fluid is a gas, it is difficult to maintain the roundness of the cross-sectional shape of the hollow material after being extruded from the spinneret, so the hollow part forming fluid is preferably a liquid. Since the hollow part forming fluid is discharged from the spinneret, it is necessary that the boiling point be equal to or higher than the spinning temperature in order to ensure that the fluid is also liquid at the time of discharging.

As a characteristic of the hollow part forming fluid, the use of a liquid having a capability of liquid-liquid phase separation with polyethylene at a high temperature in addition to a boiling point not lower than the spinning temperature improves the water permeability of the obtained membrane. It is preferable in that it is performed. However, in this case, 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 liquid and liquid phase are separated from the polyethylene, but rather than a temperature range at which the liquid and liquid phase is separated. May be higher 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 melt extruded into the air is guided to a liquid bath and cooled to a temperature at which the polyethylene in the extrudate solidifies. The melt extruded from the spinneret in this way
By cooling during passage from the spinneret outlet into the liquid bath, liquid-liquid phase separation occurs to generate a pore structure, which is then solidified to fix the pore structure. The liquid bath is a two-layer liquid bath in which the upper layer is composed of a water-immiscible liquid capable of liquid-liquid phase separation with polyethylene at a high temperature, and the lower layer is composed of water. The upper layer of the liquid bath, which is the part that the extrudate extruded from the spinner touches first, should use a liquid that has the ability to separate liquid and liquid phases from polyethylene at high temperature, which improves the water permeability of the resulting membrane. Is necessary for As a matter of course, the liquid constituting the upper layer portion of the liquid bath needs to have a lower specific gravity than water forming the lower layer portion and be immiscible with water. Examples of the composition constituting such a liquid bath upper layer include the same examples as the examples of the organic liquid described above.

The lower part of the liquid bath consists of water. The liquid forming the upper layer is usually an organic compound as described above, and generally has a low specific heat and a low cooling capacity. One of the main functions of the liquid bath is to cool the extrudate. If the cooling capacity of the liquid bath is low,
It is difficult to obtain a porous membrane having dense pores. By arranging water having a large specific heat and a high cooling capacity in the lower part, the cooling capacity of the entire liquid bath is secured. In such a two-layer liquid bath, the thickness of the upper layer is determined from the viewpoint of improving water permeability.
1 mm or more, preferably 5 mm or more, and at the same time, 30 cm or less, so as not to lower the cooling capacity of the liquid bath;
It is preferably at most 10 cm, particularly preferably at most 2 cm. On the other hand, the thickness of the lower layer (water layer) is at least 5 cm, preferably at least 10 cm, from the viewpoint of securing the cooling capacity. FIG. 1 shows a schematic diagram of an example of a film forming flow when such a two-layer liquid bath 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. A porous membrane can be obtained by removing the organic liquid clogging the hole. The removal of the organic liquid in the hollow material does not dissolve or degrade the polyethylene and removes the organic liquid to be removed by extraction with a volatile liquid that dissolves, and then, after drying, volatilizes and removes the remaining volatile liquid. 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.

In the present invention, a stretching operation is performed such that the residual elongation is 5% or more and 150% or less before and after extraction and removal of the organic liquid, with respect to the hollow material after cooling and solidifying after leaving the liquid bath. I do. Residual elongation is determined by the following: when performing a stretching operation to release tension after stretching by applying tension in the axial direction of the hollow fiber-like material, the yarn length after tension release (after relaxation) and the yarn length before stretching. Defined by an expression. Residual elongation [%] = 100 {(yarn length after relaxation)-(yarn length before stretching)} / (yarn length before stretching) Since polyethylene has elasticity, the yarn length generally shrinks to some extent by release of tension. The residual elongation becomes smaller than the elongation under tension. However, when heat treatment or the like is performed under tension, the yarn length shrinks due to release of the tension is reduced. As described above, the hollow material after cooling and solidifying after leaving the liquid bath is subjected to a stretching operation before or after the extraction and removal of the organic liquid, whereby the water permeability of the obtained membrane can be improved. When the residual elongation is less than 5%, the effect of improving the water permeability is small, which is not preferable. Conversely, if the residual elongation exceeds 150%, the pore size of the obtained film increases, and the elongation also decreases, which is not preferable. Residual elongation is 10% or more and 100%
The following are particularly preferred.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.
The present invention is not limited to this. The average pore size, pure water permeability, breaking strength and breaking elongation were determined by the following measuring methods. The stretching operation is performed at room temperature (25
C.), the film was stretched to a predetermined length by applying tension at a speed of about 1.4 cm / sec, held for 30 seconds, and then the tension was released. Thread length after tension release (thread length after relaxation)
Was used to determine the residual elongation by using the fiber length after the tension was released and the hollow fiber membrane was allowed to stand at room temperature for about one day to sufficiently relax.

Average pore diameter: Measured according to the method described in ASTM: F316-86 (also known as half-dry method). Using ethanol as the liquid used, 25 ° C, pressure increase rate 0.01a
It was measured at tm / sec. The average pore diameter [μm] is determined by the following equation from the surface tension [dynes / cm] of the liquid used and the half dry air pressure [Pa]. Average pore diameter = 2860 (surface tension) / (half dry air pressure) The surface tension of ethanol at 25 ° C. is 21.97 dy.
nes / cm (edited by The Chemical Society of Japan, 3rd edition of Basic Handbook of Chemical Handbook, II-82, Maruzen Co., Ltd., 1984), the average pore diameter was calculated by the following equation.

Average pore size [μm] = 62834 / (half
(Dry air pressure [Pa]) The average pore size obtained by this half dry method is
This is the average pore size of the smallest pore size layer in the plane. Pure water permeability: After immersion in ethanol, immersion in pure water several times
Seal one end of the returned wet hollow fiber membrane of about 10 cm length,
Insert the injection needle into the hollow at the other end and inject at 25 ° C.
Pure water at 25 ° C at a pressure of 0.1 MPa from the shooting needle
Permeate volume of pure water injected into and permeating from the outer surface
[L] was measured, and the inner surface area [m ^Two]
Pure water permeability [L / m^Two/ H] was calculated. Pure water permeability = 60 (permeated water amount) / (membrane surface area) / (measurement
(Constant time [min]) In addition, surface area [m^Two] Was calculated from the following equation. Intramembrane surface area = π (membrane inner diameter [m]) x (membrane effective length [m]) Here, the effective membrane length excludes the part where the injection needle is inserted.
Refers to the net film length.

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.
The tensile strength at break and the elongation at break were determined from the load [kgf] and the displacement [mm] at break by the following formulas. Breaking strength [kgf / cm ^2] = (load at break) / (Makudan area [cm ^2]) elongation at break [%] = 100 (at break displacement) / 50 Here, Makudan area [cm ^2] is This is the area of the annular cross section of the membrane.

[0026]

Example 1 High-density polyethylene (manufactured by Mitsui Chemicals, Hyzex Million 030S, viscosity average molecular weight 450,000) 20
Parts by weight of di (2-ethylhexyl) phthalate (DO
P) and liquid paraffin (Matsumura Petroleum Institute; Sumoil P)
80 parts by weight of a mixed organic liquid having a weight ratio of 7 to 3 (DOP / liquid paraffin = 7/3) with respect to a weight ratio of -350P) to a twin screw extruder (TEM-35B-10 / 1 manufactured by Toshiba Machine Co., Ltd.).
V), and the mixture is heated and kneaded to melt (230 ° C.), and the outer diameter is 1.58 mm and the inner diameter is 0.18 mm on the discharge surface of the spinning hole for hollow fiber molding attached to the extrusion port in the head (230 ° C.) at the tip of the extruder. The above-mentioned melt is extruded from an annular hole for extruding a melt of 83 mm, and DOP is formed as a fluid for forming a hollow portion from a circular hole for discharging a hollow portion having a diameter of 0.6 mm inside the annular hole for extruding the melt. Was discharged and injected into the hollow portion of the hollow fiber extrudate.

The hollow fiber extruded from the spinneret into the air passes through an air traveling distance of 1.3 cm, and the upper layer is DOP.
(1.5 cm thick, 35 ° C.), the lower layer is placed in a liquid bath of water (15 cm thick, 27 ° C.), passed through a liquid bath of about 2 m, solidified by cooling, and then tension is applied to the hollow fiber material. And rolled out of the water bath at a speed of 16 m / min.
Next, the obtained hollow fiber material was repeatedly immersed in methylene chloride at room temperature for 30 minutes five times to extract and remove DOP and liquid paraffin in the hollow fiber material, and then dried at 50 ° C. for half a day to remove residual methylene chloride. Was evaporated off.

After tension was applied to the thus obtained polyethylene hollow fiber-like porous membrane of 20 cm length to extend it to 60 cm length, the tension was released and a stretching operation was performed. The yarn length after releasing the tension was 38 cm, and the residual elongation was 90%. Various physical properties (average pore diameter, pure water permeability,
Table 1 shows the breaking strength, breaking elongation, and yarn diameter. When the structure of the obtained film was observed with an electron microscope, it was found that the film had a large number of coarse pores of 1 μm to 3 μm on the outer surface and the inner surface, and had a minimum pore diameter layer in the film cross section that was neither the outer surface nor the inner surface. It had an internal dense anisotropic structure.

[0029]

Comparative Example 1 A polyethylene hollow fiber porous membrane was obtained according to Example 3 of JP-A-3-42025. Various physical properties (average pore size, pure water permeability, breaking strength,
Table 1 shows the breaking elongation and the yarn diameter. When the structure of the obtained film was observed with an electron microscope, the outer surface, the center of the cross section,
Each of the inner surfaces had a uniform three-dimensional porous structure having substantially the same pore size and no anisotropy.

[0030]

[Table 1]

[0031]

According to the present invention, it has become possible to produce 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 schematic view of an example of a film forming flow using a two-layer liquid bath according to the present invention.

[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 drive 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 fiber forming fluid 14 ・ ・ ・ Aerial traveling part 15 ・ ・ ・ Liquid bath upper layer 16 ・ ・ ・ Liquid bath lower layer (water) 17 ・ ・ ・ Liquid bath upper layer thickness 18 ・ ・ ・ Liquid bath lower layer thickness 19 ・ ・ ・ Roll 20 ... Take-up roll

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 4D006 GA06 GA07 HA18 JA02C MA01 MA22 MA33 MB02 MB16 MC22 MC22X NA04 NA13 NA14 NA17 NA64 NA68 PB04 PB70 PC01 PC11 PC21 PC22 PC41 4L035 BB31 BB58 BB66 BB69 DD03 DD07 EE08 EE05 KK01 H05 LA01

Claims (1)

[Claims] 1. A molten mixture of polyethylene and an organic liquid is cooled and solidified by extruding a hollow fiber into a liquid bath through a hollow fiber molding spout through the air while injecting a hollow part forming fluid into the hollow part. Then, after that, the organic liquid is extracted and removed,
In a method for obtaining a polyethylene hollow fiber porous membrane,
(1) The liquid bath is a two-layer liquid bath in which the upper layer is made of a water-immiscible liquid having the ability to separate liquid and liquid phases from polyethylene at a high temperature, and the lower layer is made of water. 2) A method for producing a polyethylene hollow fiber-like porous membrane, wherein the hollow fiber is stretched so that the residual elongation is 5% or more and 150% or less after or after extraction and removal of the organic liquid after cooling and solidification. .