JPH0362448B2 - - Google Patents

Description

Detailed Description of the Invention Background of the Invention (Technical Field) The present invention relates to a flat membrane polypropylene film used for plasma separation to separate blood into blood cell components and plasma components, removal of bacteria in blood, etc. The present invention relates to a porous membrane and a method for manufacturing the same. More specifically, the present invention relates to a polypropylene porous membrane that has high porosity and high water permeability and causes little damage to separated blood cells and plasma components when used for plasma separation, and a method for producing the same. (Prior Art) Various permeable membranes have been used in the past to separate blood into blood cell and plasma components. These permeable membranes can be used, for example, for systemic lupus erythematosus,
Abnormal proteins in diseases caused by immune abnormalities such as rheumatoid arthritis, glomerulonephritis, and myasthenia gravis,
Plasma separation permeable membranes are used for plasma purification for the purpose of removing antigens, antibodies, immune complexes, etc., as well as for preparation of plasma preparations for blood component transfusions, pretreatment of artificial kidneys, and the like. As such membranes for plasma separation, cellulose acetate membranes (Japanese Patent Application Laid-Open No. 1989-1999-1) are used.
15476), polyvinyl alcohol film, polyester film, polycarbonate film, polymethyl methacrylate film, polyethylene film (JP-A-57-84702)
etc. have been used. However, these membranes for plasma separation not only have insufficient mechanical strength, porosity, and plasma separation ability, but when used for plasma separation, red blood cells are damaged due to clogging, and plasma components are Certain complements were activated and the separated plasma was severely damaged. In addition, polymers that are poorly soluble in solvents and have stretchability, such as crystalline polyolefins and polyamides, and compounds that are partially compatible with the polymers and easily soluble in solvents. A permeable membrane has been proposed, which is obtained by forming a mixture with a film, sheet, or hollow body into a film, sheet, or hollow body, treating the molded body with a solvent, and stretching it 50 to 1500% in one or two axial directions after drying ( Special Publication No. 57-20970). However, since such membranes are stretched to increase the pore size, they undergo significant heat shrinkage and cannot be sterilized in an autoclave when used for medical purposes. Furthermore, the pore structure on both surfaces and inside the membrane is almost uniform. Therefore, when used for plasma separation, clogging with proteins and blood cells was likely to occur. In addition, a molten mixture of 10 to 80% by weight of paraffin and 90 to 20% by weight of polypropylene resin is extruded through a die into a film, sheet, or hollow fiber, and the molten mixture is introduced into water maintained at 50°C or less for rapid cooling and solidification. A method for producing a porous membrane for extracting and separating paraffin from the obtained molded product is disclosed (Japanese Patent Application Laid-open No. 60537/1983). However, the porous membrane obtained by this method has low porosity and water permeability, and although it can be used for gas separation, the filtration rate is extremely low and cannot be used for plasma separation. Purpose of the Invention Therefore, the present invention provides a flat membrane type polypropylene porous membrane that has high porosity and water permeability, has a high plasma separation rate, and can perform stable plasma separation with less clogging of proteins and blood cells, and a method for producing the same. The purpose is to provide A membrane that achieves these objectives has a superficial porous layer with a network structure on both sides of the membrane, and a core layer with a denser network structure than the superficial porous layer is formed between the superficial porous layers. , the average pore size is 0.1-5.0μm,
Bubble point is 1.8Kgf/ ^cm2 or less, porosity is 60
85%, water permeability of 100 ml/min·mmHg·m ² or more, and a film thickness of 30 to 300 μmw. The proportion of the surface porous layer in the entire membrane is 5 to 5.
Preferably it is 30%. bubble point is
It is preferably 1.1 Kgf/cm ² or less. moreover,
It is preferable that the water permeation amount is 140 ml/min·mmHg·m ² or more. Further, the porous membrane is heated at 121°C.
It is preferable that the shrinkage rate after 120 minutes of heat treatment is 6.0% or less. Furthermore, what achieves the object of the present invention is 200 to 600 parts by weight of an organic filler and a crystal nucleating agent that can be uniformly dispersed in the polypropylene while the polypropylene is melted, per 100 parts by weight of the polypropylene.
0.1 to 5.0 parts by weight is added and melt-kneaded, the mixture thus obtained is discharged in a molten state from a die in the form of a flat film, and the discharged molten film is filled with the organic filler or its similar compound or the organic filler. The resulting polypropylene membrane is plunged into a cooling solidification liquid made of a solvent that is compatible with the filler, and then brought into contact with an extraction liquid that does not dissolve the polypropylene to remove the organic filler contained therein. This is a method for producing a flat polypropylene porous membrane, which is fixed and heat-treated at a temperature of 110 to 150°C. Further, the crystal nucleating agent is preferably an organic heat-resistant substance having a melting point of 150°C or higher and a gelling point higher than the crystallization initiation temperature of polypropylene.
Furthermore, it is preferable that the extract is a halogenated hydrocarbon. Specific Structure of the Invention The present invention will be specifically explained below. The flat membrane type porous polypropylene membrane of the present invention is a porous membrane consisting essentially of polypropylene, and has a superficial porous layer having a network structure on both sides of the membrane, and a superficial porous layer between the superficial porous layers. A core layer with a denser network structure is formed, and the average pore size is
0.1-5.0μm preferably 0.2-3.0μm, ASTMF316
The bubble point measured using isopropyl alcohol according to the modified method is 1.8 Kgf/cm ² or less, preferably 1.1 Kgf/cm ² or less, the porosity is 60 to 85%, preferably 65 to 85%, and the water permeability is 100 ml/cm 2 or less. min・mm
Hg・m ² or more, preferably 140ml/min・mmHg・
m ² or more, and the film thickness is 30 to 300 μm, preferably
It is 60 to 200 μm. Furthermore, it is preferable that the surface porous layer accounts for 5 to 30% of the entire membrane. The above-mentioned network structure has a state in which thread-like bodies in the form of a number of threads are intertwined. Surprisingly, when the polypropylene porous membrane of the present invention having such characteristics is used to perform plasma separation, the surface porous layer acts as a prefilter, resulting in less clogging of proteins and blood cells and a stable result. It has been found that plasma separation can be carried out using this method, and damage to the separated plasma, particularly activation of complement components, can be kept to an extremely low level. Activation of complement components in plasma is thought to occur through two routes: the so-called classical pathway and the so-called alternative pathway. This will determine whether activation is induced. For example, cellulose acetate membranes and polyvinyl alcohol membranes conventionally used as membranes for plasma separation cause complement activation through a different route. Polymethyl methacrylate membrane, which has been considered to be an excellent material in terms of complement activity,
It has been found that plasma separated through the pores of a membrane significantly induces activation of alternative pathways. In contrast, with the porous membrane of the present invention, activation of complement was extremely low even in plasma separated after passing through the pores of the membrane. In the porous membrane of the present invention, the average pore diameter is from 0.1 to
5.0 μm is a diameter that allows plasma components to pass through without passing through blood cell components (red blood cells, white blood cells, platelets), and within the above range, without passing through blood cell components, It can permeate more than 95% of total protein, which is a plasma component. Further, it is preferable that the average pore diameter is 0.2 to 3.0 μm. Note that the average pore diameter referred to here is the average pore diameter of the entire membrane as measured using a mercury porosimeter, and does not refer to the pore diameter of only the surface porous layer. Furthermore, the bubble point of 1.8Kgf/ ^cm2 or less is to define the maximum pore diameter of the membrane; if this value is exceeded, blood cell components such as red blood cells may enter the pores, causing hemolysis or clogging. They do things like that. In addition, the porosity must be between 60 and 85%.
If it is less than 60%, performance may deteriorate or a sufficient plasma separation rate may not be obtained, while if it exceeds 85%, it may not be strong enough to withstand use. Further, the amount of water permeation is required to be at least 100 ml/min·mmHg·m ² , and if it is less than this, there is a risk that a sufficient plasma separation rate may not be obtained. Furthermore, the film thickness must be between 30 and 300 μm.
If it is less than 30μm, there will be problems in terms of strength, while if it is 300μm
If it exceeds this, the volume will be large when incorporated into a module, which poses a practical problem. In addition, the proportion of the surface porous layer in the entire membrane is 5
~30% is preferred. If it is less than 5%, the effect of the prefilter may be insufficient when used for plasma separation, and if it exceeds 30%, there is a risk that membrane strength sufficient for use may not be obtained. The portion of the membrane other than the surface porous layer is a core layer having a denser network structure than the surface porous layer.
Further, the porous membrane of the present invention has a flat membrane shape. The porous membrane preferably has a shrinkage rate of 6.0% or less after heat treatment at 121°C. 121℃,
120 minutes of heat treatment indicates high-pressure steam sterilization according to the Japanese Pharmacopoeia. The shrinkage rate indicates the degree of change in the porous membrane before and after the heat treatment. Since the porous membrane of the present invention is a flat membrane, the change in the length of the porous membrane in the direction of the forming axis and the length in the direction perpendicular to the forming axis after the heat treatment is 6.0% or less. As described later, if the shrinkage rate exceeds 6.0%,
This is because the amount of water permeated and the plasma separation rate after heat treatment decrease, making it impossible to separate blood components sufficiently. Further, it is preferable that the shrinkage rate is 3.0% or less. The polypropylene porous membrane of the present invention having such characteristics is produced, for example, as follows. That is, as shown in FIG. 1, polypropylene, an organic filler, and a crystal nucleating agent mixture 11, which is blended as necessary, are fed from a hopper 12 to a kneader, for example, a twin-screw extruder 13. The compound is melt-kneaded and extruded, sent to a T-die 14 and discharged in the form of a flat film, which cools the cooling liquid 16 in the cooling tank 15.
It is brought into contact with the roller 17 in the cooling tank 15 to be solidified, and is completely cooled and solidified while passing through the cooling tank 15, and then wound onto a tension roll 19. Also, during this time, line 20
After being discharged from line 21, the cooling liquid 16 supplied by
2, it is cooled to a predetermined temperature and recirculated. Then, the wound film-like material is further introduced into an extraction tank (not shown) containing an extraction liquid to extract the organic filler. If this extract is volatile and immiscible with water, such as halogenated hydrocarbons, as will be described later, a layer of water or the like may be provided as an upper layer to prevent evaporation. Then, if necessary, re-extraction is performed, and in order to stabilize the structure and permeation performance, the membrane-like material is fixed to a certain length and heat-treated. The organic filler may be extracted by providing an extraction layer before winding. The polypropylene used as a raw material in the present invention is not limited to propylene homopolymer, but also other monomers containing propylene as a main component (e.g.
There are block polymers with polyethylene), random polymers, etc. A melt index (MI) of 5 to 70 is preferable, especially an MI of 5 to 70.
10 to 40 is preferred. Further, polypropylene having a large molecular weight, that is, a low MI may be blended in order to increase the strength of the membrane. Among the polypropylenes, propylene homopolymers are particularly preferred, and those with a high degree of crystallinity are more preferred. The degree of crystallinity is the weight fraction of crystalline parts relative to the total weight, and is determined by X-ray diffraction, infrared absorption spectrum, density, etc. In general, vinyl polymers (CH ₂ -CHR) n can take three three-dimensional structures depending on the arrangement of the substituents R: regular isotactic and syndiotactic structures, and disordered attack structures. . The higher the proportion of isotactic or syndiotactic in a polymer, the easier it is to crystallize. This also applies to polypropylene, and when expressed in terms of tactility, which is an index different from the crystallinity of polypropylene, it is preferable that the tactility is 97% or more. The melting point of polypropylene varies depending on the degree of polymerization, etc.
The temperature is around 160-180℃. The organic filler used in the production method of the present invention must be one that can be uniformly dispersed in the polyolefin while it is melted, and that is easily soluble in the extract as described below. is necessary. Such fillers include liquid paraffin (number average molecular weight 100-2000), α-olefin oligomers [e.g. ethylene oligomer (number average molecular weight 100-2000), propylene oligomer (number average molecular weight 100-2000), ethylene- Propylene oligomer (number average molecular weight 100-2000), etc.]
Parafine wax (number average molecular weight 200-2500),
There are various hydrocarbons, and liquid paraffin is preferred. The blending ratio of polypropylene and the organic filler is 200 to 600 parts by weight, preferably 300 to 500 parts by weight, per 100 parts by weight of polypropylene. If the organic filler is less than 200 parts by weight,
This is because the porosity and water permeability are too low to obtain sufficient filtration performance, and if it exceeds 600 parts by weight, the viscosity becomes too low and the moldability into a membrane material decreases. Such raw material mixtures are prepared (designed) by a pre-kneading method in which a mixture of a predetermined composition is melt-kneaded using an extruder such as a twin-screw extruder, extruded, and then pelletized. do. In the present invention, the crystal nucleating agent blended into the raw material has a melting point of 150°C or higher, preferably 200°C or higher.
It is an organic heat-resistant material with a gelling point of 250°C or higher than the crystallization initiation temperature of the polypropylene used. The reason for blending such a crystal nucleation agent is
The aim is to reduce the size of polypropylene particles and control the pore size of the pores formed by the organic filler that is kneaded and later extracted. For example, 1,3,2,4-dibenzylidene sorbitol, 1,3,2,4-bis(P-methylbenzylidene) sorbitol, 1,3,2,4-
(P-ethylbenzylidene) sorbitol, and the like. Generally, crystal nucleation molding agents are used to improve the transparency of molded resins. However, by using the above-mentioned crystal nucleating agent in the present invention, the polypropylene particles are reduced to the extent that the pore diameter formed in the membrane is not regulated by the polypropylene particle diameter, so that the polypropylene particles can be extracted after kneading. The pore size formed by the organic filler can be controlled to suit the purpose. When the crystal nucleating agent is blended with polypropylene, the ratio of the crystal nucleating agent to 100 parts by weight of polypropylene is 0.1 to 5 parts by weight, preferably 0.1 to 1.0 parts by weight. The raw material mixture thus prepared is further processed using an extruder such as a twin-screw extruder, for example.
The mixture is melted and kneaded at a temperature of 160 to 250°C, preferably 180 to 230°C, and discharged from a T-die in the form of a flat film, and the molten discharged material is allowed to fall and come into contact with the cooled solidified liquid in a cooling tank. As the cooling solidification liquid, a solvent having compatibility with the organic filler, its analogous compound, or the organic filler is used. For example, when liquid paraffin with a number average molecular weight of 324 is used as the organic filler or its similar compound, liquid paraffin,
For example, liquid paraffin with a number average molecular weight of 324, liquid paraffin with a number average molecular weight of 299, and liquid paraffin with a number average molecular weight of 420.
It is preferable to use liquid paraffin having a relatively similar number average molecular weight. Furthermore, examples of solvents that are compatible with the organic filler include tetrachloromethane, 1,1,2,2-tetrachloro-1,2difluoroethane, 1,2,2-trichloro-1,
Examples include halogenated hydrocarbons such as 2,2-trifluoroethane, trichloroethylene, and perchlorethylene. In the present invention, by using an organic filler, a similar compound thereof, or a solvent that is compatible with the organic filler in the cooling liquid, a surface porous layer having a relatively loose network structure is formed on both sides of the membrane, and a surface porous layer is formed inside the layer. We were able to obtain a highly permeable porous membrane with a sandwich structure consisting of a core layer with a denser network structure than the core layer. It is preferable to use an organic filler or its analog as the cooling liquid. The reason for this is that by being compatible with the organic filler in the raw material, a surface porous layer having a relatively loose network structure can be reliably formed on the membrane surface. The film-like material completely cooled and solidified in the cooling solidification tank is sent to an extraction tank or the like, where the organic filler is dissolved and extracted. Methods for dissolving and extracting the organic filler include an extraction tank method, a shower method in which the extract liquid is showered onto a film-like material on a belt conveyor, and a method in which a film-like material that has been rolled up once is rolled back into another skein. Any method may be used as long as the film-like material can come into contact with the extract, such as a rolling method in which a skein is immersed in the extract, and it is also possible to combine two or more of these methods. As the 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. For example, tetrachloromethane, 1,1,
2-Trichloro-1,2,2-trifluoroethane, 1,1,2-trichloro-1,2,2-trifluoroethane, trichlorofluoromethane, dichlorofluoromethane, 1,1,2,2-tetrachloro There are halogenated hydrocarbons such as -1,2-difluoroethane, trichlorethylene, perchlorethylene, etc. Among these, chlorofluorinated hydrocarbons are preferred from the viewpoint of extraction ability against organic fillers and safety for the human body. preferable. The porous membrane thus obtained is then further heat treated. Heat treatment is performed in a gaseous atmosphere such as air, nitrogen, carbon dioxide, etc. at a temperature of 10% below the melting temperature of polypropylene.
~50℃ lower temperature, e.g. 110-150℃, preferably
It is carried out for 60 seconds to 180 seconds at a temperature of 130-140 ° C. When performing the above-mentioned heat treatment, it is necessary to fix the obtained porous membrane to a certain length in advance. The above-mentioned fixation of a certain length may be carried out by cutting to a certain length. The method of measuring physical properties used in the present invention is as follows. (1) Bubble Point Measurement was performed according to the modified ASTM F316 method using isopropyl alcohol as the liquid phase using a stainless steel holder with a diameter of 47 mm. The pressure was then increased, and the pressure at which a series of nitrogen bubbles began to rise uniformly and without interruption from the center of the filter in the isopropyl alcohol was defined as the bubble point. (2) Film thickness Measured using a micrometer. (3) Porosity (P) After the porous membrane is immersed in ethanol, it is replaced with water to become hydrated, and the weight (Wp) when hydrated is measured. The dry weight is Ww, and the density of the polymer is
Assuming Pg/cm ² , the porosity (P) is calculated using the following formula. P=(Wp-Ww)/(Ww/P)+(Wp-Ww)×100(%
) (4) Water permeation rate Water at 25°C was permeated through a membrane with a membrane area of 1.45×10 ^-3 m ² under a pressure of 0.7 Kgf/cm ² , and the time required for 100 ml to permeate was measured. (5) Maximum plasma separation rate (Qfmax) Measured using the circuit shown in Figure 2. In the measurement, heparinized fresh bovine blood (5000 U/) with a hematocrit of 40% was used, and a module 30 with a membrane area of 0.4 ^m2 had a blood flow rate of 100 ml/min and a pressure loss of 300 mmHg.
Increase the filtrate pump flow rate from 10ml/min to 10 → 15 → 20 → 25 → 30 → 40 → 42 every 3 minutes.
The amount of filtration immediately before TMP (total membrane pressure) increases by 20 mmHg or more within 30 minutes.
Let it be Qfmax. However, TMP=Pin+Pout/2-Pfil. G1, G2, and G3 in FIG. 2 are pressure meters, and the pressure of G1 is Pin, the pressure of G2 is Pfil, and the pressure of G3 is Pout. P each indicates a pump. (6) Average pore diameter Measured using a mercury porosimeter. (7) Complement activity (C3a, C4a) Blood collected from healthy individuals was transferred to a glass test tube and heated at 37°C for 15 minutes to completely coagulate the blood, and then serum was separated. Centrifugation was performed in a refrigerated centrifuge at 4°C, 3000 rpm, and 20 minutes.
The separated serum was immediately transferred to ice water. A mini module 30 with a membrane area of 24 cm ² provided with a porous membrane 35 is set in the circuit shown in Fig. 3, and serum is circulated at a flow rate of 5 ml/min, and the serum coming out from the filtrate side outlet 40 is distributed every 1.5 ml. sample,
C3a and C4a concentrations were measured by RIA method. C3a,
C4a is generated during the complement activation process, and it can be said that the less C4a is present, the less complement activation occurs. In the figure, 42 is a heating tank at 37°C, and 44 is a cooling tank containing ice water. Examples 1 to 3, Comparative Examples 1 to 3 Per 100 parts by weight of polypropylene (mixture) with a melt flow index of 30 and 0.3, flow rate paraffin (number average molecular weight:
324) and as a crystal nucleating agent, 1, 3, 2, 4
Bis(paraethylbenzylidene) sorbitol was melt-kneaded and pelletized using a twin-screw extruder (manufactured by Ikegai Iron Works).
It was melted at ~200°C, extruded into the air through a T-die with a slit width of 0.6 mm, plunged into a cooling liquid tank placed directly below the T-die, cooled, and then rolled up. The cooling liquid and its temperature are as shown in Table 1. Cut the rolled film to a certain length (approximately 200 x 200 mm),
Both length and width were fixed, and the solution was placed in 1,1,2-trichloro-1,2,2-trifluoroethane (liquid temperature 25
℃) for 10 minutes in total four times to extract liquid paraffin, and then heat-treated in air at 135℃ for 2 minutes. The obtained porous membrane had a surface porous layer having a relatively sparse network structure on both sides, and a core layer having a denser network structure than the surface porous layer inside. FIG. 4 is a scanning electron microscope photograph (magnification 1000) showing the surface of the porous membrane of Example 1, and FIG. 5 is a scanning electron microscope photograph showing a partial cross section of the porous membrane of Example 1. (magnification
3000), and from FIG. 5 it can be seen that a superficial porous layer is formed on the surface and a core layer is formed inside the surface porous layer. Figure 6 is a scanning electron microscope photograph (3000 magnification) showing the surface of the porous membrane of Comparative Example 2, and Figure 7 is a scanning electron microscope photograph showing a partial cross section of the porous membrane of Comparative Example 1. This is a photograph (3000 magnification).
It can be seen from these photographs that no surface porous layer was formed on the surface. When evaluating overperformance, membranes were laminated and assembled into modules, made hydrophilic with 50% ethanol water, and washed with water before use. The results were as shown in Table 1. Comparative Example 4 Commercially available cellulose acetate membrane (CA, manufactured by Toyo Roshi)
was designated as Comparative Example 4. Comparative Examples 5 and 6 Samples were prepared that were not subjected to the heat treatment for 2 minutes in air at 135°C as in the example. Comparative Examples 5 and 6 were porous membranes obtained by the same method as in Examples 1 and 2 except for the above. The measurement results for C3a and C4a of Example 1 and Comparative Example 4 are shown in Tables 3 and 4.

【table】

【table】

【table】

【table】

【table】

[Table] As is clear from the results, the porous membrane of the present invention has a high porosity and water permeability, and a high plasma separation rate. On the other hand, in Comparative Example 1 in which the organic filler content was less than 200 parts by weight, the porosity and
Both water permeability and plasma separation rate are low. Furthermore, in Comparative Example 2 using water cooling, no surface porous layer was formed and the plasma separation rate was low. Furthermore, the porous membrane of the present invention, which is fixed to a certain length and heat-treated, does not undergo dimensional changes due to autoclave sterilization.
While the membrane is thermally stable with no change in porosity or water permeability, the membrane in the comparative example shrinks significantly after autoclave sterilization. There is a risk of inconveniences such as tearing of the membrane, and other membrane performances are also significantly degraded. Specific Effects of the Invention The membrane has a superficially porous layer with a relatively sparse network structure on both sides, and a core layer having a denser network structure than the superficially porous layer is formed between the superficially porous layers. Pore diameter is 0.1~5.0μm, bubble point is
1.8Kgf/ ^cm2 or less, porosity 60-85%, water permeability
100ml/min・mmHg・^m2 or more, and the film thickness is 30~
Since it is a flat polypropylene porous membrane with a diameter of 300 μm, which is essentially made of polypropylene, it has a high porosity and water permeability, and when used for plasma separation, there is less clogging by proteins, blood cells, etc., and a high plasma separation rate is achieved. Furthermore, the plasma obtained and separated has extremely little damage. In particular, the activation of the complement system is extremely low, and it can be suitably used as a plasma separation membrane to separate blood into blood cell components and plasma components. It is particularly useful when used. Furthermore, the bubble point is 1.1Kgf/ ^cm2 or less,
Porosity is 65-83%, water permeability is 140ml/min・mm
If it is Hg·m ² or more and the film thickness is 60 to 200 μm, it will be more excellent. The present invention also involves melt-kneading 100 parts by weight of polypropylene, adding 200 to 600 parts by weight of an organic filler and 0.1 to 5.0 parts by weight of a crystal nucleating agent that can be uniformly dispersed in the polypropylene while the polypropylene is melted. The mixture thus obtained is discharged in a molten state from a die, and the discharged molten film is cooled and solidified using the organic filler or a similar compound thereof, or a solvent having compatibility with the organic filler. Flat film type polypropylene is produced by protruding the polypropylene into the membrane, then contacting it with an extract that does not dissolve the polypropylene to remove the organic filler, fixing the resulting polypropylene film to a certain length and heat-treating it at a temperature of 110 to 150°C. Since it is a method for manufacturing porous membranes,
As described above, a porous membrane having excellent performance can be easily produced.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of an example of a manufacturing apparatus used in the method for manufacturing a flat membrane type porous polypropylene membrane of the present invention, Figure 2 is a circuit diagram for measuring the maximum plasma separation rate, and Figure 3 is a diagram of complement A circuit diagram for measuring activity, FIGS. 4 and 5 are electron micrographs of the membrane surface and partial cross section of the porous membrane of the present invention, and FIGS. 6 and 7 are electron micrographs of the porous membrane of the comparative example. These are electron micrographs of the membrane surface and a partial cross section. 11... Compound, 12... Hopper, 13...
Twin screw extruder, 14...Dice, 15...Cooling tank,
16... Cooling liquid, 17... Roll, 18... Tension roll, 19... Winding roll.

Claims (1)

[Claims] 1. A membrane has a surface porous layer with a network structure on both sides, a core layer having a network structure denser than the surface porous layer is formed between the surface porous layers, and the average pore diameter is is 0.1 to 5.0μm, bubble point is 1.8Kgf/ ^cm2 or less, porosity is 60 to 85%, and water permeability is 100ml/min.
A ^flat polypropylene porous membrane, characterized in that it is substantially made of polypropylene, and has a film thickness of 30 to 300 μm. 2 The proportion of the surface porous layer in the entire membrane is 5
30% of the porous membrane according to claim 1. 3. The porous membrane according to claim 1 or 2, wherein the bubble point is 1.1 Kgf/cm ² or less. 4. The porous membrane according to any one of claims 1 to 3, wherein the water permeability is 140 ml/min·mmHg·m ² or more. 5. Claim 1, wherein the porous membrane has a shrinkage rate of 6.0% or less after heat treatment at 120°C for 120 minutes.
The porous membrane according to any one of Items 1 to 4. 6 To 100 parts by weight of polypropylene, add 200 to 600 parts by weight of an organic filler and 0.1 to 5.0 parts by weight of a crystal nucleating agent that can be uniformly dispersed in the polypropylene while the polypropylene is melted, and melt-knead in this manner. The resulting mixture is discharged from a die in a molten state in the form of a flat film, and the discharged molten film is cooled and solidified using the organic filler, its analogous compound, or a solvent that is compatible with the organic filler. After plunging into the solution and then contacting with an extraction solution that does not dissolve polypropylene to remove the organic filler contained, the resulting polypropylene film is fixed to a certain length and heat-treated at a temperature of 110 to 140°C. A method for producing a flat polypropylene porous membrane. 7. The method for producing a porous membrane according to claim 6, wherein the crystal nucleating agent is added in an amount of 0.1 to 1.0 parts by weight. 8. The porous membrane according to claim 6 or 7, wherein the crystal nucleating agent is an organic heat-resistant substance having a melting point of 150° C. or higher and a gelling point higher than the crystallization initiation temperature of polypropylene. manufacturing method. 9. The method for producing a porous membrane according to any one of claims 6 to 8, wherein the extract is a halogenated hydrocarbon.