JPH0373328B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a microporous hollow fiber, a method for producing the same, and a precision filtration filter (sterilization filter) using the hollow fiber. [Conventional technology] In recent years, filtration technology using microporous materials has been widely put into practical use in the fields of food, alcohol production, pharmaceuticals, biotechnology, chemistry, and electronics industries to save energy, simplify processes, and improve quality. Furthermore, the production of polypropylene hollow fibers as a microporous material has been actively proposed. For example, Japanese Patent Publication No. 56-52123 discloses a method for producing hollow fibers made of polypropylene having minute pores in the peripheral wall. According to the method, polypropylene is melt-spun, then heat-treated, stretched, and then heat-treated again to make it porous. Also, special public service in 1987-
Publication No. 20970 discloses that from a homogeneous mixed melt containing two partially compatible polymers, a film in which the two types of polymers exist in a partially compatible state is prepared, and one or the other is treated with a solvent. One of the polymers is removed, dried, and then stretched to make it porous. Furthermore, Japanese Patent Publication No. 57-49248 discloses a membrane filtration type hollow fiber composed of a three-dimensional network structure. [Problems to be Solved by the Invention] However, the porous polypropylene hollow fibers obtained from the prior art have the following practical drawbacks and problems. In other words, the said Tokko Sho
The hollow fiber shown in Publication No. 56-52123 has a flow rate of permeated water of 1.1 to 2.5 gfol (1.88 to
The permeation flow rate was low (4.2/m ² hr), which was insufficient for the purpose of precision filtration. The hollow fiber in Japanese Patent Publication No. 57-20970 also has a water permeability rate under a pressure of 60 atm.
The permeation flow rate was as low as 582/m ² day, which was insufficient for the purpose of precision filtration. In addition, special public service Sho 57-49248
The hollow fiber in the publication has a water permeability of 100 mm/Mg and 115
/m ² hr, but it is made of cellulose polymer and has poor chemical resistance, which limits its range of use. On the other hand, JP-A-55-131028 discloses that after mixing polyolefin resin inorganic fine powder and organic liquid,
A method for producing a microporous polyolefin porous material is disclosed, which involves melt-molding and then extracting an organic liquid and an inorganic fine powder from the molded product. However, the production method uses a three-component mixture as a starting material, and uses materials other than polyolefin. The two components had to be extracted and removed in two steps, which resulted in a disadvantage that the steps were complicated. Furthermore, Japanese Patent Application Laid-Open No. 59-64640 discloses that a crystalline thermoplastic polymer and a certain compound are melt-blended, and a sheet is formed from the melt-blended solution.
A method for producing a microporous sheet is disclosed in which the sheet is cooled to cause phase separation and then stretched to remove the compound. In this manufacturing method, stretching is carried out in a phase-separated state, so if the desired strength is to be obtained, the amount of the compound added is limited, and a high permeation flow rate cannot be expected. Furthermore, there is no disclosure regarding hollow fibers. The characteristics required of the filter material for the above-mentioned precision filtration (sterilization filter) are: (1) High filtration accuracy. (2) High mechanical strength. (3) Less eluate. (4) High chemical resistance. (5) Can be sterilized by autoclave. (6) High flow velocity. (8) Biochemically inert. (9) Stable supply possible. etc. Therefore, by selecting polypropylene as the thermoplastic resin, the present invention satisfies (3), (4), (5), (7), and (8) among the above characteristics, and produces a sintered body-like material. Because it has a membrane structure, it satisfies (1) and (2), and because the filter element is constructed from hollow fibers, the flow rate per unit volume of the element is much higher than that of conventional flat membrane elements. The object of the present invention is to provide a microporous polypropylene hollow fiber for precision filtration and a method for producing the same. Also,
In the present invention, a solution containing fine particles at a relatively high concentration of 10 ³
The object of the present invention is to provide a precision filtration filter (sterilization filter) suitable for filtration and purification at a processing rate of ~10 ⁵ /m ² hr. [Means for Solving the Problems] In order to achieve the above object, the first aspect of the present invention is to use a hollow fiber made of a collection of fine spherulites of polypropylene with a melt index of 11 to 39 and a crystallinity of 40% or more. In particular, the present invention relates to microporous hollow fibers in which hollow walls of the fibers are communicated through spaces formed between spherulites.
In addition, the second invention provides for 100 parts by weight of polypropylene (A) having a melt index of 11 to 39 and a crystallinity of 40% or more, which is compatible with (A) at a molding temperature of (A) or higher, and is substantially Mix and knead 50 to 150 parts by weight of organic liquid (B) that does not exhibit the desired properties to a uniform melt, and transfer the melt to a constant temperature in a cooling tank from a melt-spinning device having a double-tubular spinneret. Extrusion into a controlled organic liquid (B) to create an intermediate structure in which the organic liquid (B) exists in the interstices where polypropylene (A) spherulites are connected in the shape of grape spheres, and then (B) is extruded. Hollow fibers are produced by continuously introducing the intermediate structure into a solvent that is a good solvent and is unnecessary for (A), removing (B) from the intermediate structure, and then heat-treating it under constant tension. Furthermore, a third invention is a precision filtration device characterized in that the filter body module is a hollow fiber having a porous structure formed by an aggregation of polypropylene spherulites, a wall thickness of 30 to 70 μm, and an outer diameter of 500 μm or less. Regarding filters (sterilizing filters). The microporous polypropylene hollow fiber according to the present invention is manufactured by the following steps. (1) The crystallinity of melt index MI11-39 is
40% or more per 100 parts by weight of polypropylene (A),
Mix 50 to 150 parts by weight of an organic liquid (B) that is compatible with (A) and does not substantially volatilize at the molding temperature of (A) or higher.
Knead to make a homogeneous melt. (2) This melt is formed into hollow fibers using a melt spinning device having a double-tubular spinneret. The outer shape and wall thickness of the hollow fibers are determined by adjusting the distance from the spinneret to the cooling tank and the winding speed of the melt coming out of the spinneret. At this time, the melt is once cooled and made into pellets using a known method.
It may also be fed to a separate melting device. (3) The formed hollow fibers are cooled while passing through a cooling tank filled with an organic liquid (B) controlled at a constant temperature, thereby crystallizing the polypropylene (A). As the crystallization of polypropylene (A) progresses, the organic liquid (B) is repelled from the melt, and polypropylene (A) forms spherulites of a size corresponding to the temperature, and polypropylene (A) spherulites form. An organic body (B) is located in the gap where the grape spheres are connected.
Create an intermediate structure in which . (4) The spherical aggregate of fine spherulites of polypropylene containing an organic liquid in the interstices is cooled and solidified in the cooling tank at a lower temperature than that in cooling tank 1, so that the structure is firmly fixed. (5) Hollow fibers with a fixed structure are created by passing through an extraction tank filled with a good solvent for organic liquid (B), fixing and separating the organic liquid into micropores made of polypropylene spherulite aggregates. (6) This microporous hollow fiber is subjected to constant tension in order to maintain the external shape and wall thickness determined in (2) and the microporous structure determined in (5). Heat treated below. Polypropylene suitable for producing the microporous hollow fibers of the present invention exhibits a melt flowability of MI: 11 to MI: 39, preferably MI: 15 to MI: 30, and has a crystallinity of at least about 40%. Substantially isotactic polypropylene. MI
If it is less than 11, a uniform melt containing 30 parts by weight or more of the organic liquid cannot be produced. Also, MI
If it exceeds 39, a melt containing 30 parts by weight of polyptene or liquid paraffin cannot be melt-molded into a hollow fiber shape. When the degree of crystallinity is less than 40%, no spherical crystals are formed. Organic liquids suitable for mixing with polypropylene to produce the microporous medium fibers of the present invention include:
It is necessary that it exhibits fluidity at room temperature, does not substantially volatilize during melt molding, and is compatible with polypropylene at temperatures higher than the molding temperature of polypropylene. In order to be compatible with polypropylene, a nonpolar liquid hydrocarbon is desirable.
Specifically, the boiling point is 180°C or higher, and in the case of a mixed substance, the initial boiling point is 180°C or higher. Preferably, the boiling point or initial boiling point is 200°C or higher. The liquid hydrocarbon exhibiting the above characteristics is a single substance or a mixture of carbon atoms in the range of 11 to 40. Among them, polybutene or liquid paraffin is most suitable. An organic liquid having a polar group will completely separate from the polypropylene at the outlet of the spinneret of the melt spinning device, resulting in the organic liquid spewing out and making it impossible to take off the hollow fibers. When the number of carbon atoms is 40 or more, fluidity is lost in the early stage of cooling, which impedes the growth of polypropylene spherulites and prevents the formation of uniform gaps. Furthermore, if the number of carbon atoms is 11 or less, it will partially volatilize before entering the cooling tank, and it will not become uniformly microporous. The melt is polypropylene with a crystallinity of 50% or more.
It is produced by mixing 50 to 150 parts by weight of an organic liquid to 100 parts by weight and heating the mixture to 170°C or higher. At this time, 0 to 1 part by weight of a nucleating agent consisting of a sorbitol derivative may be added for the purpose of adjusting the size of the popipropylene spherulites. For mixing the melt, a known kneader such as a single screw extruder,
This can be done using a twin-screw extruder, Banbury mixer, router kneader, etc. When the melt is kneaded in an extruder having a kneading function, it is directly supplied to a gear pump and a spinneret. Alternatively, the melt may be cooled and pelletized using known methods and equipment, and then fed to a melt spinning apparatus consisting of an extruder, gear pump, and spinneret. Cooling for processing into pellets is preferably carried out by rapid cooling such as water cooling. The temperature of the extruder and die of the melt spinning equipment is 170
It is best to adjust the melt viscosity to 2000-7000P at a temperature of ~230°C. The melt is quantitatively pumped through a gear pump, discharged from a double-tubular spinneret, and shaped into hollow fibers. The shape of the hollow fiber is determined by the diameter of the double tube (), the discharge amount of the melt (), and the distance from the mouthpiece to the cooling tank (Fig.
It can be determined based on the relationship between the distance () to the cooling tank 6) and the winding speed (). As in the present invention,
When containing a large amount of organic liquid, the melt viscosity is low compared to the case of polypropylene units.
It is preferable to shorten the distance from the cap ( ) to the cooling tank. Generally, in melt spinning polypropylene fibers, the melt viscosity and crystallization can be controlled.
Affects physical properties. In the case of polypropylene, the crystallization rate is extremely fast, so cooling conditions are very important. In the case of conventional production of polypropylene porous hollow fibers in which stretching effects are expected, it is generally desirable to suppress crystallization and orientation as much as possible during the cooling stage. However, in the case of the present invention, instead of forming holes in the drawing process, polypropylene spherulites are formed and the gaps and holes are formed between them, so crystallization occurs actively and quickly during the cooling step. It is a weight to do. Therefore, the cooling bath should be controlled at a temperature where the crystallization rate is critical.
Polypropylene is said to have the fastest crystallization rate at about 110°C to 120°C. When an organic liquid is contained, the temperature at which the crystallization rate is fastest shifts to the lower temperature side. The cooling temperature suitable for the present invention varies depending on the content of the organic liquid, the content of the nucleating agent, the intended filtration precision, etc.; ±5℃ around center
It is best to control the temperature within the range of A good pore shape distribution cannot be obtained. Further, as the cooling medium, in order to maintain the shape of the hollow fibers during the cooling process, it is desirable to use a cooling medium that is the same as or similar to the organic liquid mixed with polypropylene. In the extraction tank, the organic liquid present in the gaps between the polypropylene spherulites is extracted and removed using a good solvent of the organic liquid mixed with polypropylene, thereby obtaining porous hollow fibers made essentially of polypropylene. Good solvents for organic liquids include aliphatic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbon solvents, and ethers.
Carbon disulfide etc. are suitable. The time required for extraction varies depending on the content of the organic liquid, the shape of the hollow fibers, the winding speed, etc., but the amount remaining in the finished hollow fibers should be 0.1 wt% or less, preferably 0.7% or less. You should decide. At this time, it is good to run the hollow fibers through a tank filled with the good solvent, but it is also possible to run the hollow fibers over the hollow fibers with a shower. The microporous hollow fibers produced here retain stress due to the effects of the process up to winding, making them thermally unstable and prone to shrinkage, so heat treatment is performed by constant length tensioning. The temperature of heat treatment should be between 50°C and 80°C, preferably between 70°C and 80°C. A time of around 1 minute is sufficient. Hereinafter, the present invention will be explained in more detail based on the drawings. As shown in the model in Fig. 1, the hollow fiber of the present invention has a hollow wall composed of an aggregate of spherulites g of polypropylene itself, and has a structure similar to that of a sintered body made of ultrafine particles. It shows. Therefore, although the porosity is not particularly high, the curvature ratio is high, so it is difficult to clog and can be used as a filter material with a high permeation flow rate. Furthermore, the size of the spherulites is substantially uniform when produced under the same manufacturing conditions, and therefore a filter material with a sharp pore size distribution can be obtained. FIG. 2 shows an example of a hollow fiber manufacturing apparatus. Pellets made of a homogeneous mixed melt of polypropylene and organic liquid are fed into an extruder 2 as shown in Fig. 2.
The pellets are fed through a hopper 1, and while passing through an extruder, the pellets are melted, the viscosity is adjusted to 2,000 to 7,000 P, and a gear pump 3 is used to quantitatively feed the pellets to a spinneret 4. The melt is made into hollow fibers 5 using a spinneret.
and extruded into the first cooling tank 6. Cooling tank 6
The organic liquid filled with the organic liquid is controlled by a temperature controller 7 to maintain a constant temperature. Then, it is continuously fed into the second cooling tank 8 and cooled. After cooling, the hollow fibers are subjected to extraction and removal of organic liquid in an extraction tank 9.
It is heat-set under constant length tension in a dryer 10, and then taken to a winder 1.
It is wound up at 1. The surfaces of several types of hollow fibers (300μ in diameter, 200μ in inner diameter) produced by the manufacturing method of the present invention are further made hydrophilic by corona treatment, plasma treatment, oxidizing agent treatment, surfactant treatment, etc. , the fiber bundle is assembled into a module 15 shown in FIG. 3, and the precision filtration filter is removed. Potting agents 18, 18 are attached to the top and bottom of the module 15, and the module 15 is set in the housing 16. It is fixed to the upper edge of the housing 16 via an upper potting agent rubber gasket 14. The sample liquid enters from the lower inlet 17, passes through the module 15, and is sent to the sample liquid outlet 12 from the open end 13 of the hollow fiber bundle. When we evaluated the filtration performance of the above precision filtration filter (sterilization filter), we found that the precision filter completely blocks the passage of Escherichia coli and P. aeruginosa by adjusting the organic liquid content and cooling temperature. It has been found that a precision filter can be obtained that blocks this. Also, the permeation flow rate of these modules is 10 ³ to 10 ⁵
/m ² hr. The precision filtration filter (sterilization filter) made of microporous polypropylene hollow fibers of the present invention is used in the fields of food, fermentation, pharmaceuticals, biotechnology, chemistry, and electronic industries for the purpose of completely removing trace amounts of foreign substances and microorganisms in aqueous solutions. It is useful as a precision filter (sterilization filter) for water treatment. Also,
When not subjected to hydrophilic treatment, it is useful as a filter for removing water from oil by utilizing the water-repelling properties of the material. [Effects of the Invention] The hollow fibers of the present invention are made of an aggregate of fine polypropylene spherulites, and have hollow walls with a porous structure in which spaces communicate between the spherulites, so that the filtration accuracy is improved. It has a high permeation flow rate and is suitable as a precision filtration filter. Furthermore, in the present invention, the hollow fibers are made by extruding from a double tubular spinneret into an organic liquid (B) controlled at a constant temperature in a cooling tank, followed by solvent removal and heat treatment.
Hollow fibers with hollow walls having a porous structure can be easily produced. Furthermore, the precision filtration filter made of hollow fibers of the present invention can have a filtration area approximately three times larger per unit volume than conventional pleated precision filters, making it a filter material with high throughput. is obtained. Furthermore, due to the characteristics of polypropylene material, it has chemical resistance, autoclave resistance,
A filter element is obtained that is chemically and biologically active. In addition, it is cheaper than Teflon filter elements, which have the above-mentioned excellent properties, and is stable in supply. The present invention will be explained in more detail with reference to examples below. Comparative Example 1 High-density polyethylene with density: 0.965 g/cm ³ and MI: 13 [High-Zex manufactured by Mitsui Petrochemical Industries, Ltd.]
1300J] to 100 parts by weight of liquid paraffin [Daphne Oil CP-15N manufactured by Idemitsu Kosan Co., Ltd.] with initial boiling point: 286℃, specific gravity (15/4℃): 0.9589, kinematic viscosity (37.8℃): 8.30cSt. 2 parts were mixed and kneaded in a twin-screw extruder for kneading, cooled with water, and made into pellets.The pellets were put into an extruder, melted at 170°C, and quantitatively transferred to a spinneret at 3.0 cm ³ /min using a gear pump. Although the material was fed and extruded through an annular slit with an outer diameter of 6 mm and a slit width of 1 mm, a hollow shape could not be obtained. Comparative Example 2 50 parts by weight of the high-density polyethylene used in Comparative Example 1 and polypropylene with a density of 0.91 g/cm ³ , MI: 19, and crystallinity of 52% [J- manufactured by Idemitsu Petrochemical Co., Ltd.
2000G] and 80 parts by weight of the liquid paraffin used in Comparative Example 1 were kneaded and extruded using a melt spinning device in the same manner as in Comparative Example 1, but no hollow shape was obtained. Comparative Example 3 To 100 parts by weight of the polypropylene used in Comparative Example 2,
80 parts by weight of atactic polypropylene was kneaded in the same manner as in Comparative Example 1, and the mixture was heated at 60°C ± 5°C in a melt spinning device.
It was extruded and wound up at a rate of 80 m/min in a liquid paraffin cooling tank 1 adjusted to the following conditions. The cooling tank 2 was also filled with liquid paraffin, and the extrusion tank was filled with Freon 113 [Lureon Solv R113J, manufactured by Asahi Glass].The dryer had an outer diameter of 300 μm and a wall thickness of 50 μm, but the amount of permeated water was It was small at 150/m ² hr. It is thought that the atactic polypropylene hinders the growth of polypropylene spherulites, making the pore diameter small and irregular. Comparative Example 4 100 parts by weight of the polypropylene used in Comparative Example 2,
40 parts by weight of the liquid paraffin used in Comparative Example 1 was kneaded and melt-spun in the same manner as in Comparative Example 3.
A hollow fiber with a wall thickness of 56 μm was obtained, but the amount of permeated water was 200 μm.
It was small at /m ² hr. Comparative Example 5 Comparative Example: 100 parts by weight of polypropylene [Polypro, J740 manufactured by Mitsui Petrochemical Co., Ltd.] with a density of 0.91 g/cm ² , MI: 25, and crystallinity of 44 g and 80 parts by weight of the liquid paraffin used in Comparative Example 1. The fibers were kneaded and melt-spun in the same manner as in 3 to obtain hollow fibers with an outer diameter of 290 μm and a wall thickness of 53 μm, but the amount of permeated water was as small as 300/m ² hr. Comparative Example 6 100 parts by weight of the polypropylene used in Comparative Example 2 and 80 parts by weight of solid paraffin [Paraffin Wax manufactured by NOF Co., Ltd.] were kneaded and melt-spun in the same manner as in Comparative Example 3 to obtain an outer diameter of 300μ and a wall thickness of 50μ. Hollow fibers were obtained, but the amount of permeated water was as small as 180/m ² . Comparative Example 7 Polypropylene with a density of 0.91 g/cm ³ and MI: 10 [Polypro J640 manufactured by Mitsui Petrochemicals Co., Ltd.] and 40 parts by weight of the liquid paraffin used in Comparative Example 1 were kneaded in the same manner as in Comparative Example 1, but pellets were mixed. It could not be processed into a shape. Comparative Example 8 100 parts by weight of polypropylene [Polypro J900 manufactured by Mitsui Petrochemicals Co., Ltd.] with a density of 0.91 g/cm ³ and MI: 40 and 40 parts by weight of the liquid paraffin used in Comparative Example 1 were kneaded in the same manner as in Comparative Example 1. The material was then extruded using a melt spinning device, but a hollow shape could not be obtained. Comparative Example 9 100 parts by weight of the polypropylene used in Comparative Example 2,
160 parts by weight of the liquid paraffin used in Comparative Example 1 was kneaded in the same manner as in Comparative Example 1, but it could not be processed into pellets. Example 1 100 parts by weight of polypropylene with MI: 19 or more [Idemitsu Petrochemical Co., Ltd. J-2000G] and 50 parts by weight of polybutene with an initial boiling point of 286°C [Idemitsu Polybutene OH],
The mixture was kneaded using a twin-screw extruder, cooled with water, and pelletized. The pellets were put into an extruder, melted at 170°C, fed quantitatively into a spinneret at a rate of 3.0 cm ³ /min using a gear pump, and extruded through an annular slit with an outer diameter of 6 mm and a slit width of 1 mm. This was extruded into a polybutene or cooling tank 1 controlled at 60°C±5°C, and wound up at 80 m/min. Cooling tank 2 contains the same liquid paraffin as cooling tank 6, and extrusion tank contains Freon.
113 [Asahi Glass Freonsolve 113] has been filled. In addition, the dryer was adjusted to 75°C. The hollow fibers produced here have an outer diameter of 300μ and a wall thickness of 50μ.
Permeated water amount is 2000/m ² hr, porosity is 38%
The curve ratio was 111%. Examples 2 to 9 The blending amounts of polypropylene, organic liquid, and nucleating agent as shown in Table 1 were combined and kneaded, and melt spinning was performed in the same manner as in Example 1. Table 2 shows the performance of the obtained hollow fibers. Examples 10 to 11 Melt spinning was performed on pellets prepared by kneading the same formulation as in Example 2 under varying temperature conditions of cooling bath 1 as shown in Table 3. Table 4 shows the performance of the obtained hollow fibers. Examples 12 to 13 Pellets prepared by kneading with the same composition as in Example 2 were melt-spun by varying the heat treatment temperature as shown in Table 5. Table 6 shows the performance of the obtained hollow fibers. Example 16 16,000 hollow fibers obtained in Example 2 were bundled,
A cylindrical filter element with an outer diameter of 70 mm in width and 250 mm in length was made. When this was assembled into AMF Incorporated's cartridge housing (IZMP) and water at 20°C was flowed from the outside of the hollow fiber at a pressure of 0.3 kg/ ^cm2 , the amount of water permeation was
It was heated at 30/min. This amount of water permeation is thought to be due to the fact that the filtration area per unit volume of the conventional filter element that can be attached to the housing (IZMP) is approximately three times greater. Example 14 The hollow fiber obtained in Example 2 had a filtration area of
Make a module so that it is 0.10m ² and attach it to this
Water containing Eschinia coli at a concentration of 10 ² cells/ml was pressurized to 1 kg/cm ² and filtered 5 times. The secondary filtrate remaining in the Houfing was heated in TSB medium at 37°C.
Although the cells were cultured for 24 hours, Eschinia coli was not present. Example 15 The hollow fiber obtained in Example 7 had a filtration area of 0.10.
Make a module so that it is m ² , and add 10 ² to this
1 kg/ml of water containing Pseudomonas at a concentration of Pseudomonas/ml.
It was pressurized to cm ² and filtered 5 times. The secondary filtrate remaining in the housing was cultured in TSB medium at 37°C for 24 hours, but Paeudomonas was not present.

【table】

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a diagram showing a model of the hollow wall in the hollow fiber of the present invention, FIG. 2 is a schematic side view of an apparatus for manufacturing the hollow fiber, and FIG. 3 is a sectional view of the precision filtration filter of the present invention. 2... Extruder, 3... Gear pump, 4... Spinneret, 5... Hollow fiber, 6, 8... Cooling tank, 9
...extruder, 10 ... dryer, 11 ... winder,
15...module.

Claims (1)

[Claims] 1. Melt index 11-39, crystallinity 40%
A hollow fiber consisting of a collection of fine polypropylene spherulites as described above, characterized in that the hollow walls of the fibers are microporous like a sintered body, with the hollow walls communicating through spaces created between the spherulites. hollow fiber. 2. The hollow fiber according to claim 1, which has a wall thickness of 30 to 70μ and an outer diameter of 500μ or less. 3. An organic liquid that is compatible with (A) at a molding temperature of (A) or higher and does not exhibit any substantial effect on 100 parts by weight of polypropylene (A) with a melt index of 11 to 39 and a crystallinity of 40% or higher. 50 to 150 parts by weight of (B) are mixed and kneaded to form a uniform melt, and the melt is passed through a melt spinning device having a double-tube spinneret into an organic liquid ( B) to create an intermediate structure in which the organic liquid (B) exists in the gaps where the polypropylene (A) spherulites are connected in the shape of grape spheres.
Next, the intermediate structure is continuously introduced into a solvent that is a good solvent for (B) but is insoluble in (A), and after removing (B) from the intermediate structure, heat treatment is performed under constant tension. Method for producing hollow fibers. 4. The method for producing hollow fibers according to claim 3, wherein the organic liquid is a liquid hydrocarbon having 12 to 40 carbon atoms. 5. Hollow fiber manufacturing according to claim 3, wherein the size of the spherical crystals is controlled by controlling the temperature of the organic liquid to control the size of the space formed between the crystals. Method. 6. The hollow space according to claim 3, wherein 0 to 1 part by weight of a nucleating agent consisting of a sorbitol derivative is added for the purpose of adjusting the size of the polypropylene spherulites when preparing the melt. Fiber manufacturing method. 7. The hollow fiber according to claim 1 or 5, wherein the organic liquid in the cooling tank is controlled to a temperature range of 30°C to 90°C (each ±5°C). manufacturing method. 8. The method for producing hollow fibers according to claim 3, characterized in that the heat treatment is performed under constant length tension so that there is substantially no change in length before and after the heat treatment. 9. The method for producing hollow fibers according to claim 8, wherein heat setting is carried out in a temperature range of 50°C to 80°C under constant length tension. 10 Melt index 11-39, crystallinity 40
% or more of polypropylene, and has a wall thickness of 30 to 70μ and an outer diameter of 500μ or less, and has a microporous hollow wall structure as a filter module. Precision filtration filter. 11 The filtration module has a filtration area of 0.10 to prevent E. coli from passing through when E. coli at a concentration of 10 ² cells/ml is passed through at a permeation flow rate of 10 ³ to ^{10 5} /m ² hr.
A precision filtration filter according to claim 10, wherein ^m2 . 12 The filtration body module prevents Pseudomonas from passing through to the secondary side when water containing Pseudomonas at a concentration of 10 ² particles/ml is pressurized to 1Kg/cm ² and filtered 5 times. The precision filtration filter according to claim 10, wherein the filtration area is 0.10 m ² so that the permeation flow rate is 10 ³ to ^{10 5} /m ² hr.