JPH02174921A - Porous membrane and its production - Google Patents

Abstract

PURPOSE:To eliminate a decrease in the filtration efficiency of a porous membrane due to clogging by forming a flat porous membrane of PP having substantially elliptic pores in which the ratio of the major axis to minor axis is specified. CONSTITUTION:PP or molten PP is uniformly dispersed in a liq. extractant, and an easily soluble org. filler and a crystal nucleus forming agent are kneaded with the soln. The kneaded material is melted, and discharged from a die in the form of a flat membrane. The flat membrane is brought into contact with a cooling and solidifying liq. incompatible with the PP and org. filler and having 0.3-0.7cal/g specific heat capacity to form a porous undrawn flat membrane having <=0.001 birefringence in the forming axis direction. The membrane is then biaxially drawn by 100-1000% in the forming axis direction and by 0-200% in the direction at right angles to the forming axis, and then brought into contact with a liq. extractant not dissolving PP. The org. filler is then extracted, and a porous membrane is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field J] The present invention relates to a porous membrane made of polypropylene used in blood filtration devices, cell culture devices, bioreactors, extracorporeal circulation therapy devices, etc., and a method for manufacturing the same. Regarding.

[Prior Art] Conventionally, a stretching method, a mixed extraction method, and a phase separation method have been used to manufacture this type of porous membrane.

As for the drawing method, polypropylene was spun using a hollow fiber manufacturing nozzle at a spinning temperature of 210 to 270°C and a draft ratio (ratio of the linear velocity of the raw material H from the spinneret to the winding speed of the undrawn fiber) of 180 to 600. Melt spinning at 155°C and then at 155°C
After performing the first stage heat treatment at the following temperature, stretching is performed by 30 to 200% at less than 110°C, and then the second stage heat treatment is performed at a temperature higher than the first stage heat treatment temperature and lower than 155°C. A method for producing porous polypropylene hollow fibers (Japanese Patent Publication No. 56-52123), a method for forming a flat membrane by extruding a polymer selected from polypropylene at a predetermined temperature, and then rapidly cooling the flat membrane. Stretch it while
Thereafter, heat treatment is performed at a temperature of 5 to 100°C, and if the raw material is polypropylene, cooling and stretching is performed again at a temperature of 200°C or less, followed by heat treatment to obtain a porous flat membrane (USP 3558764). be.

In addition, in the mixed extraction method, a sheet portion obtained by molding a polyolefin composition containing 40 to 90% by weight of a filler of calcium sulfite alone or gypsum mixed therein is treated in an inorganic acid solution to elute calcium sulfite. This is a manufacturing method in which a polyolefin porous membrane is manufactured by stretching this sheet portion by 5 to 40% (Japanese Patent Publication No. 51-4
No. 0098) 6 Furthermore, as a phase separation method, a polyolefin, an organic filler that can be uniformly dispersed in Borylfin while melting the polyolefin, and is easily soluble in the extract used, and a crystal nucleating agent are kneaded. The kneaded product thus obtained is discharged from a die in a molten state, and the discharged molten film is cooled and solidified, and then brought into contact with an extract that does not dissolve the mj polyolefin to extract the organic filler. There is a method for producing a blood component separation membrane, which comprises a step of removing the polyolefin, and then a step of heat-treating the produced polyolefin membrane, which is fixed to a certain length, at a temperature 20 to 50°C lower than the melting temperature of the polyolefin. (Unexamined Japanese Patent Publication No. 6
2-148667).

In addition, as a method combining a phase separation method and a stretching method, 5 to 60% by weight of an ultra-high molecular weight polyolefin (A) having an intrinsic viscosity [η] of 5 and Odl/g or more and a boiling point higher than the melting point of (A) can be used. Hydrocarbon plasticizer (B) having 40 to 95% by weight
A mixture consisting of is extruded through a die into a film, sheet, or hollow molded article fc), and when the stretching ratio in the longitudinal direction is 1 and the stretching ratio in the lateral direction is E, a circle, >
1.5, λ5. >1. ．． 5. And E, x E, A film obtained by biaxially stretching the above molded product (C) at a temperature below the melting point of Al so as to satisfy 9.
There is a method for producing a film in which 81 components are extracted and removed (Japanese Patent Application Laid-Open No. 132943/1983).

[Problems to be Solved by the Invention] As described above, various methods for producing porous membranes have been proposed in the past. However, each of these methods has the following drawbacks. In other words, in the stretching method, the resulting porous membrane physically forms pores by stretching the polypropylene pus, so the pores are linear pores that are almost horizontal in the membrane thickness direction, and the degree of stretching is The pores are generated by cracking in the direction of film formation, so the pore size distribution is sharp, but only thin films can be formed.

There was a risk that pinholes would occur. Furthermore, since the pores are linear, the filtration efficiency decreases due to clogging, making it unsuitable as a filtration membrane. In addition, in the mixed extraction method, it is difficult to control the pore size, the pore size distribution is broad, and it is not possible to create a membrane with fine pores, so it is not suitable for precision filtration membranes. Furthermore, the phase separation method has a low porosity and is not suitable for producing membranes with large pores.

Furthermore, in a method that combines a phase separation method and a stretching method, this method uses ultra-high molecular weight polyolefin, so it is very advantageous in terms of strength, but due to the ultra-high molecular weight, phase separation is difficult. The problem was that the pore size distribution was very poor.

The present invention has been made in view of such problems, and includes:
It is a porous membrane made of polypropylene, and the pores are substantially oval, so it has a high porosity (and a sharp pore size distribution, and there is no decrease in filtration efficiency due to clogging).
Another object of the present invention is to provide a porous membrane that does not generate pinholes and is suitable for use in blood filtration devices, cell culture devices, bioreactors, extracorporeal circulation therapy devices, etc., and a method for manufacturing the same.

[Means for Solving the Problems] In order to solve the above-mentioned conventional problems, the porous membrane according to the present invention is a porous membrane made of polypropylene, the pores of which are substantially oval, and , the average of the short axis is 0.05 to 5 μm, the average value of the long axis is at least twice the average value of the short axis, and the birefringence in the direction of the molding axis is 0.002 μm. It is characterized by In addition, the method for producing a porous membrane according to the present invention includes polypropylene, an organic filler that can be uniformly dispersed in the polypropylene while the polypropylene is melted, and is easily soluble in the extract liquid used, and crystal nucleation. The kneaded material thus obtained is discharged in a molten state from a die in the form of a flat film, and the flat film is formed into a material that is incompatible with both the polypropylene and the organic filler and has a specific heat capacity of 0. The film was cooled and solidified by contacting with a cooling solidification liquid having a concentration of .3 to 0.7 cal/g to obtain a porous unstretched flat film having a birefringence index of 0.001 or less in the direction of the forming axis. 100-1000% in the direction of the forming axis of the flat membrane
Further, the process is characterized by including a step of applying biaxial stretching of 0 to 200% in a direction perpendicular to the forming axis, and then bringing the polypropylene into contact with an extraction liquid that does not dissolve the organic filler to extract and remove the organic filler. Here, it is preferable to include a step of performing heat treatment after extracting and removing the organic filler.

Furthermore, the method for producing a porous membrane according to the present invention includes polypropylene, an organic filler that can be uniformly dispersed in the polypropylene when the polypropylene is melted, and is easily soluble in the extract liquid used, and a crystal nucleating agent. The kneaded product thus obtained is discharged in a molten state from a die in the form of a flat film, and the flat film is incompatible with both the polypropylene and the organic filler and has a specific heat capacity of 0. 3~0.7cal/
A porous unstretched flat film having a birefringence of o, ooi or less in the direction of the forming axis is obtained by contacting with a cooling solidification liquid of 100
After applying l-axis stretching of ~1000%, the organic filler is extracted and removed by contacting with an extraction liquid that does not dissolve the polypropylene, and further adding l-axis stretching of 0 to 200% in the direction perpendicular to the forming axis. It is characterized by Here, it is preferable to include a step of applying heat treatment after applying l-axis stretching in the direction of the forming axis, and the temperature of the heat treatment is 100 to 100°C.
Preferably, the temperature is in the range of 150°C and the treatment time is between 1 second and 120 minutes.

Further, the porous hollow fiber membrane according to the present invention is a porous hollow fiber membrane made of polypropylene, the pores of which are substantially oval shaped, and whose average short axis is 0.05 to 5.
μm, the average value of the major axis is at least twice the average value of the minor axis, and the birefringence index in the fiber axis direction is O2old or more. Furthermore, the method for producing a porous hollow fiber membrane according to the present invention includes polypropylene, an organic filler that can be uniformly dispersed in the polypropylene while the polypropylene is melted, and is easily soluble in the extract liquid used, and crystals. kneading a nucleating agent, discharging the thus obtained kneaded material in a molten state from an annular spinning hole in a hollow shape, and making the hollow material incompatible with both the polypropylene and the organic filler;
And the organic filler is extracted by contacting with a cooling solidification liquid having a specific heat capacity of 0.3 to 0.7 cal/g to cool and solidify, and then bringing the cooled and solidified hollow object into contact with an extraction liquid that does not dissolve polypropylene. was removed to obtain a porous undrawn yarn with a birefringence index of 0.005 or less in the fiber axis direction, and in this way l4
．． The hollow fiber membrane obtained in step 5 is characterized by a step of stretching the hollow fiber membrane by 3 (ltl to 1000%). Here, it is preferable to include a step of heat treatment after the stretching, and the spinning draft is The temperature of the heat treatment is preferably in the range of 80 to 150°C, and the treatment time is preferably in the range of 1 second to 120 minutes.

In addition, the method for producing a porous membrane according to the present invention includes polypropylene, an organic filler that can be uniformly dispersed in the polypropylene while the polypropylene is melted, and is easily soluble in the extract liquid used, and crystals. A nucleating agent is used as a raw material and kneaded, and the kneaded product thus obtained is discharged in a molten state from a die in the form of a flat film. and specific heat capacity is 0
．． A porous unstretched flat film having a birefringence of o, ooi or less in the direction of the forming axis is obtained by cooling and solidifying by contacting with a cooling solidifying liquid having a concentration of 3 to 0.7 cal/g. 70℃
After applying biaxial stretching of 1.00 to 2000% in the direction of the forming axis and 0 to 500% in the direction perpendicular to the forming axis within the range of above and below (the melting point of the raw material - 15"c;), the polypropylene is dissolved. It is characterized by including a step of extracting and removing the organic filler by bringing it into contact with an extraction liquid that does not contain the organic filler.Here, after extracting and removing the organic filler, the temperature is higher than (stretching temperature + 10°C) and (melting point of polypropylene - - It is preferred that the method for producing a porous membrane according to the present invention includes a step of performing heat treatment at a temperature of 15° C. or lower. An organic filler that is easily soluble in the extract used and a crystal nucleating agent are mixed together, and the kneaded product thus obtained is discharged in a molten state from a die in the form of a flat film,
The flat film is cooled and solidified by contacting with a cooling solidification liquid that is incompatible with both the polypropylene and the organic filler and has a specific heat capacity of 0.3 to 0.7 cal/g, and the birefringence in the molding axis direction is A porous unstretched flat film with a ratio of 0.001 or less, the stretching temperature of which is 70°C or higher (melting point of raw material -15°C)
After applying uniaxial stretching of 100 to 2000% in the forming axis direction in the following range, the organic filler is extracted and removed by contacting with an extract that does not dissolve Bolib [1 pyrene, and then the stretching temperature is 0 to 10% in the direction perpendicular to the forming axis within the range of above the first drawing temperature and below (the melting point of polypropylene -15°C)
The method is characterized in that it includes a step of applying uniaxial stretching of 5001. Here, after stretching in the direction perpendicular to the forming axis, it is preferable to include a step of performing heat treatment at a temperature equal to or less than the second-stage stretching temperature amount F and (melting point of polypropylene - 15 ° C.), Further, the heat treatment time is from 1 second to 120 seconds.
Further, the blood filtration device according to the present invention is characterized in that the porous membrane is used as a filtration membrane.

[Function] Since the pores of the porous membrane according to the present invention are substantially oval, the membrane has a high porosity and a sharp pore size distribution, and there is no decrease in filtration efficiency due to clogging. It can be prevented. Further, according to the method for producing a porous membrane according to the present invention, the formation of pores is substantially performed by a phase separation method, so that the generation of bottle balls is almost eliminated and the pores are three-dimensionally complex. 2. Therefore, it is possible to prevent a decrease in filtration efficiency due to clogging.

Furthermore, since the pores are deformed by the drawing method, the effective pore diameter can be set arbitrarily. In addition, stretching at room temperature is advantageous in terms of cost, while stretching while heating allows the stretching speed to be increased and eliminates the risk of the membrane breaking during stretching. . In addition, even thick membranes can be made porous, making it possible to create deep-type precision filtration membranes, which can be used in blood filtration devices, cell culture devices, bioreactors, extracorporeal circulation treatment devices, etc. suitable.

[Example] Hereinafter, Examples of the present invention will be specifically described with reference to the drawings.8 The porous membrane according to the first embodiment of the present invention is a flat membrane-like porous membrane made of polypropylene. , the pores are substantially oval, and the average short diameter is 0.
．． 05 to 5μ ruled, the average value of the major axis is at least twice the average value of the minor axis, and the birefringence in the molding axis direction is 0.
002 or more, the pores are substantially oval, so the porosity is high, and the filtration efficiency does not decrease due to clogging. The reason why the major axis is made to be at least twice the minor axis is that by doing so, the actual filtration aperture can be made sharp. Further, the reason why the birefringence index is set to 0.002 or more is that birefringence occurs due to the difference in stretching ratio, and therefore, if it is less than 0.002, the major axis will not be twice the minor axis.

The porous membrane described above can be obtained using a manufacturing apparatus as shown in FIG. That is, first, a mixture of polypropylene as a raw material, an organic filler that can be uniformly dispersed in the polypropylene when the polypropylene is melted and is easily soluble in the extract used, and a crystal nucleating agent is prepared.
is supplied from the hopper 2 to a mixer, for example, a twin-screw press ratio machine 3, and premixed in a molten state. Then, the kneaded material thus obtained is discharged in a molten state from the die 4 in the form of a flat film,
The flat film is guided to a cooling tank 5 by a cooling roller 6a, and a cooling solidification liquid 5a is introduced which is incompatible with both the polypropylene and the organic filler and has a specific heat capacity of 0.3 to 0.7 cal/g.
A porous unstretched flat film with a birefringence index of 0.001 or less in the direction of the forming axis is obtained by cooling and solidifying in contact with 0.
Next, the flat film obtained in this way is stretched biaxially by 100 to 1000% in the direction of the forming axis and 0 to 200% in the direction perpendicular to the forming axis by applying tension with the stretching roller 6b. The pores are made substantially oval, and then the organic filler is extracted and removed by contacting with an extraction solution that does not dissolve polypropylene in an extraction tank 7.

Then, after further heat treatment is performed in a heat treatment device 8 to stabilize the structure and improve dimensional stability, the film is wound up in a winding device 9.

Moreover, the above-mentioned porous membrane can also be obtained by the following method. That is, first, in the same way as in the above method, polypropylene, an organic filler that can be uniformly dispersed in the polypropylene while the polypropylene is melted, and a crystal nucleating agent that is easily soluble in the extract used, and a crystal nucleating agent are kneaded. The obtained kneaded material is discharged in a molten state from a die in the form of a flat film, and the flat film is incompatible with both the polypropylene and the organic filler and has a specific heat capacity of 0.3 to 0.7 cal/.
A porous unstretched flat film having a birefringence index of 0.001 or less in the direction of the forming axis is obtained by contacting with the cooling solidification liquid (g) and cooling and solidifying it. Subsequently, the flat membrane thus obtained was uniaxially stretched by 100 to 100% in the direction of the forming axis.
After that, the organic filler is extracted and removed by contacting with an extraction solution that does not dissolve polypropylene. Then, after further uniaxial stretching of 0 to 20 oz in a direction perpendicular to the forming axis, heat treatment is performed.

The polypropylene used as a raw material for the porous membrane is generally called polypropylene, and may be any of a polypropylene homopolymer, a block polymer, and a random polymer, but preferably a polypropylene homopolymer. More desirably, Mr (melt index) is 10 (g/1Osin) or more. Here, M■ is measured according to JIS K7210 "Flow test method for thermoplastic plastics", and the measurement conditions are a temperature of 230° C. and a load of 2.16 kg. In addition, the birefringence index (Δn) in the present invention refers to a value determined by the retardation method, and the organic filler blended into the raw material is one that is uniformly mixed into the polypropylene while it is melted. It needs to be able to be dispersed and easily soluble in the extract solution described below.

Such a filler is preferably liquid paraffin, and more preferably the amount added is 100 to 500 parts by weight per 100 parts by weight of polypropylene.
If it is less than parts by weight, the porosity is low in the unstretched membrane state;
This is because stretching has little effect, and if the amount exceeds 50 [1 part by weight, the viscosity becomes too low and moldability deteriorates. Such raw material blending is possible by melt-kneading a mixture of a predetermined composition using an extruder such as a twin-screw extruder, extruding it, and then pelletizing it (pre-blending method).

In addition, as a crystal nucleating agent to be added to the raw material, a dibenzylidene sorbitol-based crystal nucleating agent is preferable because it is less likely to elute into the blood, and the amount added is 0.1 to 1 part by weight of polypropylene lO. The amount of the crystal nucleating agent is preferably 5.0 parts by weight.If the amount is less than 0.1 parts by weight, the effect as a nucleating agent will not be sufficiently exhibited and the film strength will be very low. If the amount is larger than this, the dispersion of the nucleating agent becomes poor and fish eyes (a state in which the nucleating agent is not covered with polypropylene and is exposed on the surface) occur, resulting in a decrease in the yield rate.

As the cooling solidification liquid, a liquid that is incompatible with the organic filler and has a specific heat capacity of 0.3 to 0.7 cal/g, more preferably 0.3 to 0.6 cal/7 g is used. Specifically, for such a cooling solidified liquid and 12, the kinematic viscosity at 20°C is 2 to 50 cst, more preferably 8 to 4 cst.
Silicone oils such as 0cst dimedyl silicone oil and methylphenyl silicone oil, and an average molecular weight of 100 to 400, more preferably 180 to 3.
30 polyethylene glycols and the like. In this way, as a cooled and solidified liquid.

The organic fillers used are incompatible and have a specific heat capacity of 0.
The reason for using a liquid of 3 to 0.7 cal/g is as follows. That is, if dihalogenated hydrocarbons are used as a liquid 5 that can dissolve an organic filler in the cooling solidification liquid, for example, liquid paraffin (described later) is used as the organic filler, polypropylene and the organic filler will dissolve in the cooling solidification liquid. While the phase separation is progressing, the organic filler is dissolved and extracted, and the organic filler moves from the inside of the discharged material from the die to the surface side, and when the discharged material is completely cooled and solidified.

The proportion of the organic filler inside the discharged product becomes low, and the porosity inside the membrane after the organic filler is more completely dissolved and extracted becomes low.

It is presumed that the filtration ability of the membrane is reduced.

In addition, when the same liquid as the organic filler or its similar compound is used as the cooling solidification liquid, for example, liquid paraffin is used as the organic filler, if liquid paraffin with a number average molecular weight similar to that of the liquid paraffin is used, the discharged The organic filler (liquid paraffin) can have a predetermined pore density without significantly migrating in the discharged material, and the specific heat is not too large, so an appropriate cooling rate promotes crystallization of polypropylene and provides a stable shape. However, during the cooling process, the organic filler or the cooling solidification liquid is localized on the surface of the discharged material that has not yet been completely cooled and solidified, and the polypropylene composition fraction on the surface becomes low. The pores are large, and the solid phase has a highly uneven surface with particulate polypropylene spread in a network.Furthermore, as a cooling solidification liquid, even if it is an inert liquid that is not compatible with organic fillers. When using something with a large specific heat capacity, for example liquid paraffin as an organic filler, if water with a large specific heat capacity of about 1.0 cal 7g is used, the polypropylene will be rapidly cooled due to its high cooling effect, and the surface will become dense. There is a risk that a thin skin layer will be formed and a flat membrane with low filtration capacity will be created. On the other hand, as a cooled solidified liquid, it is not compatible with organic fillers and has a specific heat capacity of 0.
If a solution with a weight of 3 to 0.7 cal 7 g was used, the organic filler would not be localized on the surface of the flat membrane, the polypropylene cooling rate would be appropriate, and the surface would have an appropriate polypropylene composition fraction. This is because, as crystallization is promoted, the surface is formed by a large number of polypropylene lumps formed by fine polypropylene particles connected in the direction of the molding axis, similar to the inside of the film, and exhibits a smooth surface.

It is preferable that the flat film cooled and solidified by the cooling solidification liquid 5a has a birefringence index of 0.0 or less in the direction of the forming axis, and a film having a birefringence higher than this is formed using the raw material without being stretched. It is difficult.

In addition, in order to make the pores substantially oval, the cooled and solidified flat membrane is stretched in the direction of the forming axis and in the direction perpendicular to the forming axis using a stretching roller 6b. It is preferable that it is 100 to 1000% in the direction perpendicular to the forming axis, and 0 to 200X in the direction perpendicular to the forming axis.If it is more than 200%, the major axis will be less than twice the minor axis, the pore diameter will become broad, and the filtration efficiency will deteriorate. .

As the above extraction liquid, any liquid can be used as long as it does not dissolve the polypropylene constituting the porous membrane and can dissolve and extract the organic filler.

- Examples include butanols, pentanols, hexanols, octatools, alcohols such as lauryl alcohol, and halogenated hydrocarbons. Hydrogens are preferred, and chlorinated fluorinated hydrocarbons are particularly preferred from the viewpoint of safety to the human body.

The heat treatment in the heat treatment equipment ra6 is performed in a gaseous atmosphere such as air, nitrogen, carbon dioxide, etc., and the temperature is IQjJ~
Preferably, the treatment time is between 1 second and 120 minutes in the range -150°C; outside these ranges: 1
01) If the temperature is lower than 150°C, the fixation will be insufficient, and if the temperature is higher than 150°C, the holes will collapse.

Note that the method for stretching the flat membrane is not particularly limited, and may be carried out continuously or batchwise.
Further, the stretching temperature may be lower than the heat treatment temperature, but from the viewpoint of cost, it is desirable to stretch at room temperature.

In the method for manufacturing a porous membrane according to the present embodiment as described above, since the phase separation method and the stretching method are combined, the pores can be made into substantially oval shapes, and therefore the porosity is high. , resulting in a membrane with a sharp pore size distribution. In addition, since the formation of pores is essentially carried out by a phase separation method, the generation of pinholes is almost eliminated, and the pores are three-dimensionally complex, which prevents a decrease in filtration efficiency due to clogging. can. Furthermore, since the pores are deformed by the stretching method, the effective pore diameter can be set arbitrarily, and the stretching can be performed at room temperature, which is advantageous in terms of cost. Furthermore, since even thick membranes can be made porous, a deep-type precision filtration membrane can be made.

The porous membrane according to this embodiment is particularly suitable for use as a blood filtration device as shown in FIG.

That is, as shown enlarged in FIG.
1, a spacer 12, and a support 13 are laminated in order to constitute a blood separation filter 14, and this filter 14 is attached to a housing 15. Blood is introduced from a blood inlet 16, and the inner surface of the porous IIJIII or Blood is filtered by flowing blood on the outer surface, and the filtered blood flows out from the blood inlet 17 and the plasma flows out from the plasma inlet 18.

In addition, a housing is produced in the same manner, a gel matrix containing cells or enzymes is encapsulated on the inner or outer surface of the porous membrane, and a circulating fluid such as a reaction liquid or body fluid is flowed on the outer or inner surface, thereby forming a cell culture device, a bioreactor, etc. It can also be used as an extracorporeal circulation treatment device. In addition, when the above porous membrane is used as a filtration membrane, it must be treated with a wood-carrying treatment, but the method is not particularly limited. (Teroyoshi).

An example in which the present invention is applied to a flat porous membrane as a first embodiment has been described above, but an example in which the present invention is applied to a hollow porous membrane as a second embodiment will now be described. That is, the porous hollow fiber membrane according to this example is a porous hollow fiber membrane made of polypropylene, the pores of which are substantially oval shaped, and whose average short axis is 0.
05 to 5 μ■, and the average value of the major axis is more than twice the average value of the minor axis, and the birefringence in the m-off axis direction is 0.0
It is 1 or more. In the case of hollow fibers, birefringence exists even in an unstretched state, but when stretched so that the major axis is twice or more the minor axis, the birefringence increases to 0.01 or more.

The porous hollow fiber membrane described above can be used in blood applications, particularly as a filter for blood separation. That is, as shown in FIG. 6, after inserting the hollow fiber bundle 2a into a housing 22 having a plurality of boats 21, both sides of the hollow fiber bundle 20 are fixed with a botting agent 23, and then the botting agent 23 is removed with a sharp knife. By cutting the hollow fiber, the cross section of the hollow fiber is exposed, and blood is allowed to flow on the inner or outer surface of the hollow fiber, thereby forming a blood filtration device. Further, as in the first embodiment, it can be used as a cell culture device, a bioreactor, and an extracorporeal circulation treatment device.

The above-mentioned porous hollow fiber membrane is manufactured, for example, as follows. That is, as shown in FIG. 7, polypropylene, an organic filler that can be uniformly dispersed in the polypropylene when the polypropylene is melted, and an organic filler and a crystal nucleating agent that are easily soluble in the extract liquid used are combined. The compound 30 is supplied from a hopper 31 to a kneading machine, for example, a single-screw extruder 32 , where the compound 30 is melt-kneaded and extruded, and then sent to a spinning device 33 where gas is passed through an annular spinning hole of a spinneret device 34 . A hollow object 35 is discharged into the air, for example, and the hollow object 35 comes out.
is introduced into a cooling tank 37 containing a cooling solidification liquid 36, and brought into contact with the cooling solidification liquid 36 to be cooled and solidified.

In this case, as shown in FIG. 7, the contact between the hollow object 35 and the cooled solidified liquid 36 is caused by, for example, a cooled solidified liquid distribution pipe 38 that penetrates the bottom of the cooling tank 37 and is provided downward.
It is desirable to allow the cooled solidified liquid 36 to flow down into the tank and bring the hollow objects 35 into parallel contact with each other along the flow.Firstly, the cooled solidified liquid 36 that has flowed down is received and stored in the solidification tank 39, and the solidified liquid 36 is received and stored therein. Introduce the hollow object 35 and change the direction of the rod 40°41.42
The cooling liquid 36 is brought into sufficient contact with the cooling solidification liquid 36 to be solidified. The accumulated cooled solidified liquid 36 is discharged from the circulation line 43 and circulated to the cooling tank 37 by the circulation pump 44. Next, the solidified hollow material 35 is guided by a drive roller 45 to a shower conveyor type extractor 47 that showers down an extract 46 that dissolves the organic filler and only polypropylene.

In the extractor 47, the hollow material 35 is brought into sufficient contact with the extraction liquid while being conveyed on the belt conveyor 48, and the residual organic filler is extracted and removed, thereby changing the birefringence in the fiber axis direction. When it is 0.005 or less, the hollow fiber membrane 35a has porosity. M, the hollow fiber membrane 35a is led out from the extractor 47 by a drive roller 49,
Thereafter, if necessary, the product is further subjected to steps (not shown) such as re-extraction and dry heat treatment, and then guided to a heat treatment device 51 by a drive roller 50.

Therefore, the drive roller 50 and the first
A tension is exerted between the roller 51a and the hollow fiber membrane 35a at a predetermined ratio, that is, 300 to 100 liters.
000% stretching is applied, and this stretching makes the birefringence index in the fiber axis direction 0.01 or more. The inside of the heat treatment device 51 is maintained at a predetermined temperature condition by heating means such as a heater 51b, and the hollow fiber membrane 35a is heat treated while moving between the rollers in the heat treatment device 51 to stabilize the membrane structure. Finally, 1 liter of hollow fiber was extracted from the heat treatment bag @51.
The i35a is wound onto a bobbin 52a by a winding device 52.

As the organic filler used in the second manufacturing process, liquid paraffin is preferred as in the first example, but the amount added is preferably 50 to 200 parts by weight per 100 parts by weight of polypropylene. From the viewpoint of spinnability and pore size controllability, 100 to 150 parts by weight is particularly preferable, and 200 parts by weight is particularly preferable.
This is because if it is more than 50 parts by weight, it cannot be processed into a hollow shape, and if it is less than 50 parts by weight, the porosity will not increase even if it is stretched.

Other than that, the polypropylene used as the raw material, the crystal nucleating agent, the cooling solidification liquid, the extraction liquid, the heat treatment temperature, etc. are the same as in the first example. That is, as the Bob 1 cobylene, a polypropylene homopolymer or the like is used, preferably a polypropylene homopolymer, more preferably a polypropylene homopolymer, and more preferably a polypropylene homopolymer.
Use 0 or more. In addition, as the crystal nucleating agent, a dibenzylidene sorbitol type crystal nucleating agent is preferable, and the amount added is 0.1 to 100 parts by weight of polypropylene.
Preferably it is 5.0 parts by weight, particularly preferably 0.
．． 2 to 1.0 weight. Further, as the cooling solidification liquid, it is preferable to use silicone oil or polyethylene glycol having a specific heat capacity of 0.3 to 0.7 cal/g, and the temperature of the heat treatment in the heat treatment device 51 is in the range of 80 to 150 °C. The processing time is from 1 second to 120 seconds.
Preferably between minutes.

If the temperature is higher than 150°C, the pores will be crushed by heat, and if the temperature is lower than 80°C, the heat treatment will have no effect.

Furthermore, in this embodiment, the ratio (draft ratio) between the linear velocity of the raw material discharged from the nozzle device 34 and the winding speed of the undrawn yarn is preferably in the range of 100 to 300. However, there is a risk that the phase separation between polypropylene and organic filler may not occur properly, resulting in insufficient porosity. Further, the birefringence index in the fiber axis direction of the hollow fiber membrane 35a from which the organic filler has been extracted and removed in the extractor 47 is 0.005.
The reason for the following is that if the birefringence becomes high, phase separation will not be successful and it will not be sufficiently porous. Furthermore, in order to make the pores substantially oval, the hollow fiber membrane 35a has a diameter of 300 mm.
A stretching of ~1000% is applied, but if the stretching ratio is less than 300, the pores will not become elliptical (do not become twice the short diameter), and stretching exceeding 1000% will result in poor membrane strength. It is possible.

Note that the stretching method is not particularly limited (it may be carried out continuously or batchwise; furthermore, the stretching temperature may be lower than or equal to the heat treatment temperature; When using a membrane as a filtration membrane or a mass transfer membrane, it may be necessary to perform hydrophilic treatment, but the method is not particularly limited. You can.

Similar to the first embodiment, the porous hollow fiber membrane according to this embodiment combines the phase separation method and the stretching method, so the pores are substantially oval, the porosity is high, and the pore size is The membrane has a sharp distribution, and since the pores are oval, there is no reduction in filtration efficiency due to clogging. In addition, since the formation of pores is essentially carried out by a phase separation method, the generation of pinholes is almost eliminated, and the pores are three-dimensionally complex, which prevents a decrease in filtration efficiency due to clogging. be able to. Furthermore, since the pores are deformed by the stretching method, the effective pore diameter can be set arbitrarily, and stretching can be performed at room temperature.
It is advantageous in terms of cost. Further, even thick films can be made porous.

Next, the inventor conducted the following experiment in order to demonstrate the effects of the present invention.

(Experimental Example I) fII 1 , polypropylene containing dibenzylidene sorbitol crystal nucleating agent (Mitsui Noblen J3) 1-NG.

1115) was extruded using a twin-screw extruder (PCM-30, Ikegai Tekko), and at this time liquid paraffin (liquid paraffin 70S) was added to 100 parts by weight of polypropylene through a vent.

200 parts of Chuo Kasei) were added dropwise to form mixed wire pellets.

This pellet was extruded into a flat film from a T-die at 160°C using a twin-screw extruder, and then cooled and solidified using a cooling roll at 35°C. After biaxial stretching in the direction perpendicular to the axis, chlorofluorinated hydrocarbon (Daiflon Solvent S-3, Daikin Industries)
A porous flat membrane was obtained by extracting and removing liquid paraffin.

The above film was heat treated at 100 to 110°C for 20 seconds.

The birefringence (△n) and porosity of this porous flat membrane are shown in Table 1, with a conventional example without prolonged stretching as Comparative Example 1, and Fig. 4 shows a conventional unstretched porous membrane. An StJ (scanning electron microscope) photograph of the porous membrane according to Example 1, which was stretched by 500% in the direction of the forming axis, is shown in FIG. 5 as an SEW photograph.

Table 1 (Experiment example rr) Polypropylene containing dibenzylidene sorbitol crystal nucleating agent (Mitsui Noblen J3H-NG).

141:15) was extruded using a twin-screw extruder (PCM-30, Ikegai Tekko), and at this time, polypropylene 10
0 parts by weight of liquid paraffin (liquid paraffin 70S
, Chuo Kasei) was dropped into mixed wire pellets, and the pellets were passed through a single-screw extruder (No. 30° Kasamatsu Processing).
Polyethylene glycol (PEG-200,
Daiichi Kogyo Seiyaku) is used to cool and solidify chlorinated fluorohydrocarbons (
A porous undrawn yarn was obtained by extracting and removing liquid paraffin using Tyflon Solvent S-3 (Daikin Industries). This undrawn yarn was drawn to each drawing ratio at room temperature.

Heat treatment was performed at 100 to 110°C for 20 seconds to obtain a porous membrane.

! ”j Shishie A top z [! 300.400.5 porous undrawn yarns, respectively.
Table 2 shows the birefringence and porosity of the 00% stretched film.

The ratio of the above porous undrawn yarn is 0.50 and 100.20, respectively.
Table 2 shows the birefringence and porosity of the film after 0% stretching.

Table 2 shows the birefringence and porosity of the material made porous by the stretching method described in Hidandan Japanese Patent Publication No. 5G-52123.

In addition, FIG. 8 shows the SE of the outer surface of the conventional unstretched porous hollow fiber.
! , l photograph, and FIG. 9 show SEM photographs of the outer surface of the porous hollow fiber according to Example 2, which was stretched by 500%.

Table 2 Next, a third embodiment of the present invention will be described. In the first embodiment described above, the stretching process was carried out at room temperature when producing a flat porous membrane, but in this embodiment, the stretching process was carried out in a heated state. As a result, the stretching processing time can be shortened, and the production line can also be shortened. In the following description, only the parts that are different from the first embodiment will be described. That is, in the manufacturing apparatus shown in FIG.
Similar to the embodiment, the birefringence in the molding axis direction is 0.00.
A porous unstretched flat film with a diameter of 1 or less is obtained, and while applying heat to this flat film at 70°C or higher and lower than (the melting point of the raw material -15°C), tension is applied to the flat film by a stretching roller 6b and the film is stretched 100° in the direction of the forming axis.
By applying biaxial stretching of ~2000% and 0 to 500% in a direction perpendicular to the forming axis, the pores are made substantially oval, and then brought into contact with an extraction liquid that does not dissolve polypropylene in an extraction tank 7. The organic filler is extracted and removed.

Then, further in the heat treatment device 8, (stretching temperature + i
o”c) or higher (melting point of polypropylene -15°C)
After the structure is stabilized and the dimensional stability is enhanced by heat treatment in the following range, the film is wound up by the winding device 9.

Moreover, the -F2 porous membrane can also be obtained by the following method. That is, first, a porous unstretched flat film with a birefringence index of 0.001 or less in the forming axis direction is obtained in the same manner as in the above method, and this flat film is heated at a temperature of 70°C or higher and (melting point of the raw material -15°C).
While heating at the following temperature,
After applying 00% uniaxial stretching, the polypropylene is brought into contact with an extractant that does not dissolve the polypropylene to extract and remove the organic filler. Then, after applying 0 to 500% l-axis stretching in the direction perpendicular to the forming axis while heating at a temperature higher than the first stage stretching temperature and lower than (the melting point of polypropylene -15°C), the second stage The heat treatment is carried out within a range of not less than the hot drawing temperature and not more than -15° C. (the melting point of polypropylene).

Note that the melting point in this specification refers to a differential scanning calorimeter (D
iferential Scanning Calo
This refers to the temperature at the top of the endothermic peak when the temperature is raised by

l: By stretching while heating as described below, 5
It becomes possible to stretch at a high magnification at a high speed of ~10 .mu./min, and the stretching processing time can be significantly shortened. on the other hand,
When stretching is carried out at room temperature, it is possible to stretch to a high magnification at a low speed of about 1 mm/win.
If stretching is carried out at a high speed of ~Ioffis/win, the film will break at a stretching ratio of about 300%.

In the embodiment described above, in order to make the pores substantially oval, the cooled and solidified V-film is subjected to stretching treatment in the direction of the forming axis and in the direction perpendicular to the forming axis, respectively, by the drawing roller 6b. The stretching ratio is 10 in the direction of the forming axis.
It is preferably 0 to 2000%, and preferably 0 to 500% in the direction perpendicular to the molding axis. If it is more than 500%, the major axis becomes less than twice the minor axis and the pore diameter becomes broad, which improves filtration efficiency. becomes worse.

In addition, the stretching temperature is 70°C or higher and (
The melting point of the raw material -15℃) or lower, and in the second stage stretching, it is preferably above the first-stage stretching temperature and below (the melting point of polypropylene -15℃).If the temperature is below the lower limit, the effect of applying heat If the temperature is higher than the upper limit, the formed holes will be crushed by the heat.The heat treatment in the heat treatment device 8 is performed in a gaseous atmosphere such as air, nitrogen, carbon dioxide, etc., and the temperature is higher than the stretching temperature. In the range above and below (melting point of polypropylene -15°C).

It is preferable that the treatment time is between 1 second and 120 minutes. If the treatment time is outside this range, the fixation of the holes may become unstable or the holes may collapse.

(Experimental Example 11) After obtaining an unstretched flat film in the same manner as Experimental Example I except that the content of liquid paraffin was 400 parts by weight, biaxial stretching was performed at a stretching temperature of 80°C, and the liquid paraffin content was changed to 400 parts by weight. After extracting the paraffin, a porous membrane was obtained by heat treatment at 10 °C for 3 minutes.The measurement results of porosity and bubble point are shown in Table 3.The hot stretching speed was 5 to 1 ( 1 mm/sin. Also, the first
Figure 0 shows a 5E14 photograph of the outer surface of the porous flat membrane according to Example 5.

Example 1: After obtaining an unstretched flat film in the same manner as in Experimental Example ② except that the content of liquid paraffin was 400 parts by weight, the stretching temperature was 100°C.
After adding biaxial stretching and extracting liquid paraffin,
A porous membrane was obtained by heat treatment at 0° C. for 2 minutes. The measurement results of porosity and bubble point are shown in Table 3.
The hot stretching speed was 5 to 10 m/n+in.

Table 3 shows the measurement results of the porosity and bubble point of the comparison board that was not subjected to the stretching treatment.

Table-3 (Experimental Example IV)! After obtaining an unstretched flat film in the same manner as in Experimental Example I except that the content of liquid paraffin was 400 parts by weight, the stretching temperature was 80%.
After applying uniaxial stretching in the direction of the molding axis at °C to extract liquid paraffin, applying l-axis stretching in the direction perpendicular to the molding axis at 80 °C, and further heat treatment at 100 °C for 3 minutes,
A porous membrane was obtained. The measurement results of the porosity and bubble point are shown in Table 4, and FIG. 11 shows an SEM photograph of the outer surface of the porous membrane according to Example 8.

Table 4 shows the measurement results of porosity and bubble point for the samples that were not subjected to the stretching process.

Moreover, FIG. 12 shows a SEM photograph of the outer surface of the porous membrane.

Table 4 The above porosity was calculated by the gravimetric method using the following formula.

(0.91: specific gravity of polypropylene) In addition, bubble point is achieved by adding isopropyl alcohol to a certain area of the membrane, gradually pressurizing it with nitrogen gas from one side of the membrane, and then bubbles begin to come out uniformly from the entire membrane surface. It was the pressure of the time.

[Effects of the Invention] As described above, the porous membrane according to the present invention is a flat porous membrane made of polypropylene, the pores of which are substantially oval shaped, and whose average short diameter is Ga mouth, 05~
5 μm, or 1) the average value of the major axis is 2 of the average value of the minor axis
double the amount, and the birefringence in the direction of the molding axis is 0.00.
Since it is characterized by having a porosity of 2 or more, the membrane has a high porosity and a sharp pore size distribution, and can also prevent a decrease in filtration efficiency due to clogging.

In addition, the method for producing a porous flat membrane according to the present invention includes polypropylene, an organic filler that can be uniformly dispersed in the polypropylene while the polypropylene is melted, and is easily soluble in the extract solution used, and crystals. A nucleating agent is kneaded, and the kneaded material thus obtained is discharged in a molten state from a die in the form of a flat film, and the flat film is made of a material that is incompatible with both the polypropylene and the organic filler and is Heat capacity is 0.3~Q, 7c
A porous unstretched flat film having a birefringence of 0.001 or less in the direction of the forming axis is obtained by cooling and solidifying by contacting with a cooling solidification liquid having a temperature of al/g. 1 in direction
．． 00 to lO 3%, and 0 to 200 in the direction perpendicular to the molding axis
% of the biaxial stretching, the organic filler is extracted and removed by contacting the polypropylene with an extractant that does not dissolve the polypropylene, or the polypropylene is uniformly stretched over the polypropylene under the melting of the polypropylene [1]. Dispersible and for the extract liquid used.

A readily soluble organic filler and a crystal nucleating agent are kneaded together, the kneaded product thus obtained is discharged in a molten state from a die in the form of a flat film, and the flat film is mixed with the polypropylene and the organic filler. are not compatible with both, and only one has a specific heat capacity of 0.3~
A porous unstretched flat film with a birefringence index of 0.001 or less in the forming axis direction is obtained by cooling and solidifying by contacting with a cooling solidification liquid having a concentration of 0.7 cal/g. After adding 1.00 to 1.000% l-axis stretching in the forming axis direction,
1ii by contacting the polypropylene with an extract that does not dissolve it.
The method is characterized by extracting and removing the organic filler described in item i and further adding 0 to 200% l-axis stretching in the direction perpendicular to the forming axis, so that the formation of pores is substantially performed by a phase separation method, and the pin The generation of holes is almost eliminated and the pores become three-dimensionally complex, so that it is possible to prevent a decrease in filtration efficiency due to clogging. In addition, since the pores are deformed by stretching, the effective pore diameter can be set arbitrarily, and the stretching can be done at room temperature, which is advantageous in terms of cost. can be used to create deep-type precision filtration membranes.

Further, by further subjecting the V membrane to heat treatment, it can be sterilized, and is therefore suitable for use in blood filtration devices, cell culture devices, bioreactors, extracorporeal circulation therapy devices, and the like. Moreover, these characteristics become more Pi-like when the heat treatment temperature is in the range of 1.00 to 150° C. and the treatment time is in the range of 1 second to 1.20 minutes in the manufacturing method W.

Furthermore, the method for producing a porous flat membrane according to the present invention includes polypropylene, an organic filler that can be uniformly dispersed in the polypropylene while the polypropylene is melted, and is easily soluble in the extract liquid used, and crystal nuclei. The forming agent is mixed as a raw material, and the kneaded product thus obtained is discharged in a molten state from a die in the form of a flat film, and the flat film is formed into a film that is incompatible with both the polypropylene and the organic filler and is Heat capacity is 0.3~
- A porous unstretched flat film having a birefringence index of 0.001 or less in the direction of the forming axis is obtained by contacting with a cooling solidification liquid having a temperature of 9.7 cal/6 and solidifying by cooling. 'Y:
100 to 2000% in the direction of the molding axis and 0 to 2000% in the direction perpendicular to the molding axis within the range above and below (the melting point of the raw material -15℃)
After applying 500% biaxial stretching, the organic filler is extracted and removed by contacting the polypropylene with an extractant that does not dissolve the polypropylene, or the polypropylene is uniformly stretched to the polypropylene while the polypropylene is melted. An organic filler that can be dispersed and is easily soluble in the extract used, and a crystal nucleating agent are mixed together, and the kneaded product thus obtained is discharged in a molten state from a die in the form of a flat film. ,
The flat film is cooled and solidified by contacting with a cooling solidification liquid that is incompatible with both the polypropylene and the organic filler and has a specific heat capacity of 0.3 to 0.7 cal/g, and the birefringence in the molding axis direction is A porous unstretched flat film having a stretching ratio of 0.001 or less is obtained, and the flat film is coated with a stretching temperature of 70°C or higher and (melting point of the raw material -15°C).
) 1.00 to 2000% 1 in the direction of the molding axis within the following range
After applying axial stretching, the organic filler is extracted and removed by contacting with an extraction solution that does not dissolve the polypropylene, and further the stretching temperature is in a range of not less than the stretching temperature of the first stage and not more than (the melting point of polypropylene - 15 ° C.) 0~ in the direction perpendicular to the molding axis.
Since it is characterized by including a step of adding 500% uniaxial stretching, the time for the stretching process can be shortened and the production line can also be shortened.

In addition, the porous hollow fiber membrane according to the present invention is a porous hollow fiber membrane made of polypropylene, the pores of which are substantially elliptical, and whose average short diameter is 0.05 to 5.
μm, the average value of the major axis is at least twice the average value of the minor axis, and the birefringence index in the fiber axis direction is 0.001 or more, so it is similar to the porous membrane described above. To,
The membrane has a high porosity and a sharp pore size distribution, and can also prevent a decrease in filtration efficiency due to clogging.

Furthermore, the method for producing a porous hollow fiber membrane according to the present invention includes polypropylene, an organic filler that can be uniformly dispersed in the polypropylene while the polypropylene is melted, and is easily soluble in the extract liquid used, and crystals. kneading a nucleating agent, discharging the thus obtained kneaded product in a molten state from an F-shaped spinning hole in a hollow shape, and forming a hollow membrane that is incompatible with both the polypropylene and the organic filler; and specific heat capacity is 0.
The organic filler is extracted and removed by contacting with a cooling solidification liquid having a concentration of 3 to 0.7 cal/g to cool and solidify, and then the cooled and solidified hollow material is brought into contact with an extraction liquid that does not dissolve polypropylene to extract and remove the organic filler. A porous undrawn fiber with a birefringence index of 0.005 or less was obtained, and the hollow fiber membrane thus obtained was
Since the method is characterized by applying stretching of 00 to 1000%, the formation of pores is substantially performed by a phase separation method, similar to the method for manufacturing the porous flat membrane, and the generation of pinholes is almost eliminated. The pores are three-dimensionally complex, and therefore a decrease in filtration efficiency due to clogging can be prevented. In addition, since the pores are deformed by stretching, the effective pore diameter can be set arbitrarily, and stretching can be done at room temperature, which is advantageous in terms of cost.Also, even thick films can be made porous. can do. Also,
By applying heat treatment, it is suitable for use in blood filtration devices, cell culture devices, bioreactors, extracorporeal circulation therapy devices, etc.

In addition, these characteristics have a spinning draft of 100 to 300.
Further, it is more excellent if the heat treatment temperature is in the range of 80 to 150°C and the treatment time is in the range of 1 second to 120 minutes. Furthermore, since the blood filtration device according to the present invention uses the porous membrane as a filtration membrane, the filtration efficiency is greatly improved.

[Brief explanation of the drawing]

FIG. 1 is a schematic partially cross-sectional view of a blood filtration device according to a first embodiment of the present invention, FIG. 2 is an enlarged cross-sectional view of the main part of FIG. 1, and FIG. Figure 1 is a schematic diagram showing the manufacturing process of the porous flat membrane used in the filtration device, Figure 4 is an SEM photograph of the unstretched porous flat membrane, and Figure 5 is 5011% in the direction of the forming axis.
SEM photograph of stretched porous flat membrane according to Example 1, No. 6
The figure is a schematic sectional view of a blood filtration device according to a second embodiment of the present invention. Figure 7 is a schematic diagram showing the manufacturing process of the porous hollow fiber membrane used in the filtration device shown in Figure 6, Figure 8 is an SEW photograph of the outer surface of the unstretched porous hollow fiber membrane, and Figure 9 is a 500% stretched membrane. Example 2
FIG. 10 is an SEM photograph of the outer surface of the porous hollow fiber membrane according to Example 5, FIG. 11 is an SEM photograph of the outer surface of the porous flat membrane according to Example 8, and FIG.
The figure is an SEM photograph of the outer surface of a porous flat membrane according to Comparative Example 8. l...Blend, 2...Hopper 3...
2-screw press ratio machine, 4...Dice 5...Cooling tank,
5a... Cooled solidified liquid 6a... Cooling roller,
6b... Stretching roller 7... Extraction tank, 8-...
・Heat treatment device 9... Winding device, 11... Porous membrane (flat membrane) 15.22-... Housing, 20-...
- Hollow fiber bundle 23... Botting agent, 32... Single screw extruder 33... Spinning device, 34... Mouth device 35... Hollow object, 36... Cooling solidification liquid 37.・・・
Cooling tank, 39... Solidification tank 47... Extractor,
51...Heat treatment equipment Figure 1 Figure 2 Figure 3 Figure 1 Indication of the case Japanese Patent Application No. 63-289894 2 Name of the invention Porous membrane and its manufacturing method 3 Person making the amendment Name related to the case

Claims (1)

[Scope of Claims] (1) A flat porous membrane made of polypropylene, the pores of which are substantially elliptical and whose average short diameter is 0.05 to 5 μm; A porous membrane characterized in that the average value of the major axis is at least twice the average value of the minor axis, and the birefringence index in the forming axis direction is 0.002 or more. (2) Polypropylene, an organic filler that can be uniformly dispersed in the polypropylene when the polypropylene is melted and is easily soluble in the extract used, and a crystal nucleating agent are kneaded, and the thus obtained The kneaded material is discharged in a molten state from a die in the form of a flat film, and the flat film is incompatible with both the polypropylene and the organic filler and has a specific heat capacity of 0.3.
A porous unstretched flat film having a birefringence index of 0.001 or less in the direction of the forming axis is obtained by contacting with a cooling solidification liquid of ~0.7 cal/g to obtain a porous unstretched flat film. After applying biaxial stretching of 100 to 1000% in the direction of the forming axis and 0 to 200% in the direction perpendicular to the forming axis, the organic filler is extracted and removed by contacting with an extraction liquid that does not dissolve polypropylene. A method for producing a porous membrane, comprising: (3) The method for producing a porous membrane according to claim 2, comprising the step of performing heat treatment after extracting and removing the organic filler. (4) Polypropylene, an organic filler that can be uniformly dispersed in the polypropylene when the polypropylene is melted and is easily soluble in the extract liquid used, and a crystal nucleating agent are kneaded, and the thus obtained The kneaded material is discharged in a molten state from a die in the form of a flat film, and the flat film is incompatible with both the polypropylene and the organic filler and has a specific heat capacity of 0.3.
A porous unstretched flat film having a birefringence index of 0.001 or less in the direction of the forming axis is obtained by contacting with a cooling solidification liquid of ~0.7 cal/g to obtain a porous unstretched flat film. After adding 100 to 1000% uniaxial stretching in the direction of the forming axis, the organic filler is extracted and removed by contacting with an extraction solution that does not dissolve the polypropylene, and then stretching 0 to 2% in the direction perpendicular to the forming axis.
A method for producing a porous membrane, comprising the step of applying 00% uniaxial stretching. (5) The method for producing a porous membrane according to claim 4, further comprising the step of applying heat treatment after applying uniaxial stretching in the direction of the forming axis. (6) The method for producing a porous membrane according to claim 3 or 5, wherein the heat treatment temperature is in the range of 100 to 150°C and the treatment time is in the range of 1 second to 120 minutes. (7) A porous hollow fiber membrane made of polypropylene, the pores of which have a substantially oval shape, the average short axis of which is 0.05 to 5 μm, and the average long axis of which is the short axis. 1. A porous hollow fiber membrane having a birefringence of 0.01 or more in the fiber axis direction. (8) Polypropylene, an organic filler that can be uniformly dispersed in the polypropylene when the polypropylene is melted and is easily soluble in the extract used, and a crystal nucleating agent are kneaded, and the thus obtained The kneaded material in a molten state is discharged into a hollow shape from an annular spinning hole, and the hollow material is incompatible with both the polypropylene and the organic filler and has a specific heat capacity of 0.3 to 0.7 cal/g. The hollow material is cooled and solidified by being brought into contact with a cooling solidification solution, and then the organic filler is extracted and removed by contacting the cooled and solidified hollow material with an extraction fluid that does not dissolve polypropylene, so that the birefringence in the fiber axis direction is 0. 1. A method for producing a porous hollow fiber membrane, comprising the steps of obtaining a porous undrawn fiber having a diameter of 0.005 or less, and stretching the hollow fiber membrane thus obtained by 300 to 1000%. (9) The method for producing a porous membrane according to claim 8, further comprising the step of performing heat treatment after the centrifugation. (10) The method for producing a porous hollow fiber membrane according to claim 8 or 9, wherein the spinning draft is in the range of 100 to 300. (11) The method for producing a porous hollow fiber membrane according to any one of claims 8 to 10, wherein the heat treatment temperature is in the range of 80 to 150°C and the treatment time is in the range of 1 second to 120 minutes. (12) Polypropylene, an organic filler that can be uniformly dispersed in the polypropylene when the polypropylene is melted and is easily soluble in the extract used, and a crystal nucleating agent are kneaded as raw materials, and in this way, The obtained kneaded material is discharged in a molten state from a die in the form of a flat film, and the flat film is incompatible with both the polypropylene and the organic filler and has a specific heat capacity of 0.3 to 0.7 cal/g. It is cooled and solidified by contacting with a certain cooling solidification liquid, and the birefringence in the molding axis direction is 0.00.
A porous unstretched flat film of 1 or less is obtained, and the flat film is stretched by 100 to 2000% in the direction of the forming axis at a stretching temperature of 70°C or higher and below (the melting point of the raw material -15°C), and perpendicular to the forming axis. A method for producing a porous membrane, the method comprising the step of applying biaxial stretching of 0 to 500% in the direction, and then bringing the organic filler into contact with an extraction solution that does not dissolve polypropylene to extract and remove the organic filler. (13) After extracting and removing the organic filler, (stretching temperature +10°C) and (melting point of polypropylene -15°C)
The method for producing a porous membrane according to claim 12, comprising the step of performing heat treatment at a temperature below. (14) Polypropylene, an organic filler that can be uniformly dispersed in the polypropylene when the polypropylene is melted and is easily soluble in the extract used, and a crystal nucleating agent are kneaded, and the crystal nucleating agent obtained in this way is The kneaded material in a molten state is discharged from a die in the form of a flat film, and the flat film is incompatible with both the polypropylene and the organic filler and has a specific heat capacity of 0.
A porous unstretched flat film having a birefringence of 0.001 or less in the direction of the forming axis is obtained by contacting with a cooling solidification liquid having a concentration of 3 to 0.7 cal/g to obtain a porous unstretched flat film having a birefringence index of 0.001 or less in the direction of the forming axis. After applying 100 to 2000% uniaxial stretching in the forming axis direction at a temperature of 70°C or higher and lower than (the melting point of the raw material -15°C), the organic filler is extracted and removed by contacting with an extraction liquid that does not dissolve polypropylene. The method further includes the step of applying 0 to 500% uniaxial stretching in a direction perpendicular to the forming axis at a stretching temperature of at least the first stage stretching temperature and at most (the melting point of polypropylene -15°C). A method for producing a porous membrane. (15) The method according to claim 15, further comprising the step of applying heat treatment at a temperature equal to or higher than the stretching temperature of the second stage and lower than (the melting point of polypropylene -15°C) after applying the stretching in the direction perpendicular to the forming axis. Method for manufacturing porous membrane. (16) The method for producing a porous membrane according to any one of claims 12 to 14, wherein the heat treatment time is between 1 second and 120 minutes. (17) A blood filtration device characterized in that the porous membrane according to claim 1 or 7 is used as a filtration membrane.