JPH0439371B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION Technical Field The present invention relates to hollow fiber membranes. More specifically, the invention relates to hollow fiber membranes used in artificial lungs, plasma separation, and the like. In particular, the present invention relates to a porous hollow fiber membrane that does not cause plasma outflow during long-term use, has a high gas exchange capacity, and is suitable for use in an oxygenator. Prior Art In general, in cardiac surgery and the like, a hollow fiber membrane oxygenator is used in an extracorporeal circulation circuit to lead a patient's blood outside the body, add oxygen to it, and remove carbon dioxide. There are two types of hollow fiber membranes used in such oxygenators: homogeneous membranes and porous membranes. In a homogeneous membrane, gas movement occurs when the molecules of the gas that permeates dissolve in the membrane and diffuse. A typical example of this is silicone rubber, which has been commercialized as the Korobo membrane lung. However, from the point of view of gas permeability, only silicone rubber is currently known as a homogeneous membrane that can be used, and the thickness of the silicone rubber membrane cannot be reduced to less than 100 μm due to its strength. For this reason, gas permeation is limited, and carbon dioxide gas permeation is particularly poor. Furthermore, the silicone rubber has the drawbacks of being expensive and having poor processability. On the other hand, in a porous membrane, the fine pores of the membrane are significantly larger than the gas molecules to be passed through, so that the gas passes through the pores as a volumetric flow. For example, various artificial lungs using porous membranes such as microporous polypropylene membranes have been proposed. For example, polypropylene is spun using a hollow fiber manufacturing nozzle at a spinning temperature of 210~210°C.
After melt spinning at 270℃ and draft ratio of 180 to 600, and then first heat treatment at 155℃ or less,
It has been proposed to produce porous polypropylene hollow fibers by stretching 30 to 200% at a temperature below 150°C, followed by a second heat treatment at a temperature above the first heat treatment temperature and below 155°C (Japanese Patent Publication No. 56-52123). issue). However, in the porous hollow fibers obtained in this way, pores are physically formed by stretching the polypropylene hollow fibers, so the pores are linear pores that are approximately horizontal in the film thickness direction, and Since the pores are generated by cracking in the axial direction of the hollow fiber depending on the degree of stretching, the cross section is approximately square or rectangular. In addition, the pores are continuous and penetrate almost linearly, and the porosity is high. For this reason, the porous hollow fibers have a high permeability to water vapor, and not only do their performance deteriorate due to condensed water, but they also have the disadvantage that plasma leaks when used with blood circulating for a long period of time. OBJECT OF THE INVENTION Therefore, an object of the present invention is to provide a novel hollow fiber membrane. Another object of the present invention is to provide a porous hollow fiber membrane having high gas exchange capacity. Still another object of the present invention is to provide a porous hollow fiber membrane that does not cause plasma outflow during long-term use, has a high gas exchange capacity, and is suitable for use in an artificial lung. These objectives are to provide a hollow fiber membrane made of polyolefin having an almost perfect circular shape with an inner diameter of 150 to 300 μm and a wall thickness of 10 to 150 μm, the inner surface of the hollow fiber membrane exhibiting a relatively dense layer, and the outer surface of the hollow fiber membrane having a relatively dense layer. Average particle size on the side is 0.1-10μm
The hollow fiber membrane has an aggregate shape of independent fine particles, forming fine communicating pores from the inner surface to the outer surface, and the space between the outer surface and the inner surface of the hollow fiber membrane is dense with the distance between the fine particles becoming smaller as it progresses toward the inner surface. This is achieved by a porous hollow fiber membrane characterized by having an anisotropic membrane structure consisting of continuous layers. Furthermore, the present invention is a porous hollow fiber membrane having a porosity of 5 to 60%. In the present invention, the O ₂ gas flux is 1.0×10 ^-5 to 2.0×10 ³ ml/min・cm ²・atm,
Preferably 1.0×10 ^-3 to 1.0×10 ³ ml/min・cm ²・
It is a hydrophobic porous hollow fiber membrane that is ATM. Also,
In the present invention, the average particle diameter of independent fine particles on the outer surface side is 1 to 1.
It is a porous hollow fiber membrane with a diameter of 7 μm. Furthermore, the present invention is a porous hollow fiber membrane having an inner diameter of 180 to 250 μm and a wall thickness of 20 to 100 μm. The present invention also provides a hydrophobic porous hollow fiber membrane in which the polyolefin is polyethylene or polypropylene, preferably polypropylene. Specific Configuration of the Invention Next, the present invention will be specifically explained with reference to the drawings. That is, FIG. 1 is a schematic drawing of the hollow fiber membrane according to the present invention, and as is clear from the figure, the inner diameter D is 150 to 300 μm, preferably
180 to 250 μm, wall thickness T is 10 to 150 μm, preferably
This is a hollow fiber membrane 1 made of polyolefin and having a substantially perfect circular shape with a diameter of 20 to 100 μm. A relatively dense layer 2 is formed on the inner surface of the hollow fiber membrane 1, while the average particle diameter d is 10 μm or less, preferably 1 to 7 μm on the outer surface.
It exhibits an aggregate-like layer 4 of a large number of fine particles 3 of m, and the fine pores 5 in the dense layer 2 communicate with the fine pores 6 in the fine particle aggregate-like layer 4, so that the inner surface side is moved from the inner surface side to the outer surface side. This is a porous hollow fiber membrane having hydrophobic properties and having communicating pores formed therein. Such a hydrophobic porous hollow fiber membrane is manufactured, for example, as follows. That is, as shown in FIG. 2, a blend 11 of polyolefin and an organic filler is supplied from a hopper 12 to a kneader, for example, a twin-screw extruder 13, and the blend is melt-kneaded and extruded. Thereafter, it is sent to the spinning device 14 and discharged from the annular spinning hole (not shown) of the spinneret device 15 into a gaseous atmosphere, for example, air, and at the same time an inert gas supplied from the line 16 is introduced into the center of the interior. The hollow object 17 thus formed is introduced into a cooling tank 19 containing a cooling solidification liquid 18, and brought into contact with the cooling solidification liquid 18 to be cooled and solidified. In this case, as shown in FIG. 2, the hollow object 17 and the cooled solidified liquid 18 are brought into contact with each other through a cooled solidified liquid distribution pipe 20, which is provided downwardly through the bottom of the cooling tank 19, for example. It is desirable that the cooled and solidified liquid 18 is caused to flow down into the hollow body 17 and brought into cocurrent contact with the hollow body 17 along the flow. The cooled solidified liquid 18 that has flowed down is received and stored in a solidification tank 21, into which the hollow object 17 is introduced,
After the direction is changed by the direction change rod 22 and brought into sufficient contact with the cooling solidification liquid 18 to solidify it, the winding bobbin 23
Wind it up. The accumulated cooled solidified liquid is discharged from the line 24 and circulated to the cooling tank 19 by the pump 25. Note that, as described later, when the cooled and solidified liquid is highly volatile and immiscible with water, such as hydrocarbons and halogenated hydrocarbons, a layer 26 of water or the like is added as an upper layer to prevent evaporation. It may be provided. The hollow material 18 cooled and solidified in this manner is wound onto a bobbin 23, and then cut into predetermined dimensions.
Then, the cut hollow object 18 is immersed in an extraction solution.
A hollow fiber membrane is obtained by extracting and removing the organic filler from the membrane and drying if necessary. Further, by heat-treating the hollow fiber membrane thus obtained, a hollow fiber membrane with even better dimensional stability can be obtained. Polyolefins used as raw materials in the present invention include polypropylene, polyethylene, etc., and their melt index (MI) is 5 to 70.
Those having an MI of 10 to 40 are particularly preferred. Among the polyolefins, polypropylene is particularly preferred. The organic filler must be able to be uniformly dispersed in the polyolefin while the polyolefin is melting, and be easily soluble in the extract as described below. Such fillers include liquid paraffin (number average molecular weight 100~
2000), α-olefin oligomers [e.g., ethylene oligomers (number average molecular weight 100 to 2000), propylene oligomers (number average molecular weight 100 to 2000),
Ethylene-propylene oligomer (number average molecular weight
100-2000), paraffin wax (number average molecular weight 200-2500), various hydrocarbons, etc., and liquid paraffin is preferred. The blending ratio of the polyolefin and the organic filler is 35 to 150 parts by weight, preferably 50 to 100 parts by weight, per 100 parts by weight of the polyolefin. In other words, if the organic filler is less than 35 parts by weight, a porous hollow fiber membrane with sufficient gas permeability cannot be obtained, whereas if it exceeds 150 parts by weight, the viscosity becomes too low and it is difficult to form the membrane into a hollow shape. This is because the quality decreases. Such raw material formulations 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. The raw material mixture prepared in this way is further processed using an extruder such as a twin-screw extruder to
℃, preferably at a temperature of 180 to 220℃, and discharged into the gas atmosphere from the annular hole of the spinning device, and at the same time, an inert gas such as nitrogen, carbon dioxide, helium, argon, air, etc. is added to the center of the spinning device. A hollow object is formed by introducing gas, and this hollow object is allowed to fall and is then brought into contact with the cooled solidified liquid in the cooling tank. This falling distance is preferably 5 to 1000 mm, particularly preferably 10 to 500 mm. That is, if the falling distance is less than 5 mm, pulsation may occur and the hollow object may be crushed when it enters the cooled and solidified liquid. The hollow object has not yet solidified sufficiently in this cooling tank, and since the central part is filled with inert gas, it is easily deformed by external force. The cooled solidified liquid 18 is allowed to flow down into a cooled solidified liquid distribution pipe 20 provided downwardly through the bottom of the cooling solidified liquid 18,
By bringing the hollow objects into co-current contact with the flow, the hollow objects can be forcibly moved downward and deformation of the hollow objects due to external forces (such as fluid pressure) can be prevented. At this time, the flow rate of the cooled and solidified liquid is sufficient under natural flow. Further, the cooling temperature at this time is 10 to 60°C, preferably 20 to 50°C. That is, if the temperature is less than 10°C, the cooling solidification rate is too fast and most of the thick wall portion becomes a dense layer, resulting in a low gas exchange ability. On the other hand, if the temperature exceeds 60°C, the crystallization rate of the polyolefin will slow down, the particle size of the fine particles on the outer surface will become too large, and the microscopic pores will not only become too large, but also the dense layer will become extremely thin or even worse. This is because it disappears completely at high temperatures, which may cause clogging or plasma outflow when used in an artificial lung, for example. However, even with such a film,
The inner side or the outer side can be used as a hollow fiber membrane in plasma separation by a hydrophilic treatment (for example, alcohol treatment). As the cooling solidification liquid, any liquid can be used as long as it does not dissolve the polyolefin, has a relatively high boiling point, and can dissolve the organic filler.
Examples include alcohols such as methanol, ethanol, propanols, butanols, hexanols, octanols, and lauryl alcohol; liquid fatty acids such as oleic acid, palmitic acid, myristic acid, and stearic acid; and alkyl esters thereof. (e.g. esters such as methyl, ethyl, isopropyl, butyl), octane, nonane, decane, kerosene, light oil, liquid hydrocarbons such as toluene, xylene, methylnaphthalene, 1,1,2-trichloro-1,2 , 2-trifluoroethane, trichlorofluoromethane,
There are halogenated hydrocarbons such as dichlorofluoromethane and 1,1,2,2-tetrachloro-1,2-difluoroethane, especially chlorofluorinated hydrocarbons, among which, as described below, the organic filler Particularly preferred are those that can dissolve the agent, such as halogenated hydrocarbons. In other words, when halogenated hydrocarbons are used, not only is the organic filler extracted to some extent while the hollow material is solidified in the solidification tank, but also the extraction liquid used in the subsequent extraction process is If the same material is used, there is no need to wash and remove the cooled and solidified liquid, and there is no risk of contaminating the extract. Furthermore, if halogenated hydrocarbons are used, there is no risk of fire. Among these halogenated hydrocarbons, chlorofluorinated hydrocarbons are particularly preferred because they are safe for the human body. The cooled solidified liquid flowing through the cooled solidified liquid distribution pipe is received and stored in a solidification tank provided at the bottom, and the hollow object is completely solidified by passing through the cooled solidified liquid in this solidification tank. The solidified hollow material is then rolled up. The rolled hollow object has a predetermined dimension, e.g.
After being cut into ~50cm pieces, it was placed in the extract solution at 0~50℃.
A hollow fiber membrane is obtained by immersing the membrane preferably at a temperature of 20 to 40°C for 1 to 30 minutes, preferably 3 to 20 minutes. In this case, so-called constant length extraction is most preferable, in which the length is kept constant throughout the extraction process. Any extract can be used as long as it does not dissolve the polyolefin constituting the hollow fiber membrane and can dissolve and extract the organic filler. For example, hydrocarbons, 1,1,2-trichloro-1,2,2-trifluoroethane, trichlorofluoromethane, dichlorofluoromethane,
There are halogenated hydrocarbons such as 1,1,2,2-tetrachloro-1,2-difluoroethane,
Among these, halogenated hydrocarbons are preferred from the viewpoint of extraction ability for organic fillers, and chlorofluorocarbons are particularly preferred from the viewpoint of safety to the human body. The hollow fiber membrane thus obtained is further subjected to heat treatment if necessary. Heat treatment is performed at 50 to 160℃ in a gaseous atmosphere such as air, nitrogen, or carbon dioxide.
It is preferably carried out at a temperature of 70 to 140°C for 1 to 120 minutes, preferably 2 to 60 minutes. This heat treatment stabilizes the structure of the hollow fiber membrane and increases its dimensional stability. Further, in this case, stretching may be performed before or during the heat treatment. The hollow fiber membrane obtained in this way has an inner diameter of
150-300μm, preferably 180-250μm, wall thickness
It has a perfect circular shape of 10 to 150 μm, preferably 20 to 100 μm. The cross-sectional structure changes depending on the manufacturing conditions of the hollow fiber membrane, but as mentioned above, by using a liquid that can dissolve organic fillers such as alcohols and halogenated hydrocarbons as a cooling solidification liquid, the magnification can be increased. As is clear from Figures 3 to 6, which are 1000x scanning electron micrographs, polyolefin fine particles are formed independently from the inner surface to the outer surface, with a dense layer near the inner surface. The result is a porous layer near the outer surface. This cross-sectional structure varies depending on the temperature of the cooled and solidified liquid, and as the temperature increases, the formation of fine particles of polyolefin progresses toward the inner surface. However, in either case, the fine particles near the interior are dense, whereas the fine particles near the outer surface form an aggregate that exists independently. Therefore, the temperature of the cooled and solidified liquid is -1 to 0°C in the case of Fig. 3, 8°C in the case of Fig. 4, 17 to 20°C in the case of Fig. 5, and 24 to 0°C in the case of Fig. 6. It is 27℃. Figures 7 to 10 are scanning electron micrographs of the inner surface at a magnification of 3,000 times, and the inner surface has a hexagonal shape in which polyolefin particles are partially fused, and the surface is relatively smooth. . Note that the temperature of the cooled and solidified liquid is
-1 to 0℃ in the case of figure 8, 8℃ in case of figure 9, 17 to 20℃ in case of figure 9, 24 to 27 in case of figure 10
It is ℃. On the other hand, Figures 11 to 14 are scanning electron micrographs of the outer surface at a magnification of 3000 times, showing that the outer surface has polyolefin fine particles formed independently, with many gaps between the fine particles. There is. Note that the temperature of the cooled solidified liquid is -1 in the case of Fig. 11.
-0°C, 8°C in the case of Fig. 12, 17 - 20°C in the case of Fig. 13, and 24 - 27°C in the case of Fig. 14.
The average particle size of the polyolefin fine particles formed on the outer surface in this way is 0.1 to 10 μm, preferably 1 to 7 μm, and the degree of distribution of these fine particles varies depending on the hollow fiber membrane manufacturing conditions. Membrane structures with different sizes and ratios of micropores between the membranes can be obtained. Also, the draft ratio is 20-1000,
Preferably it is 50 to 500, and the gas flux is 1.0×10 ^-5 to 2.0×10 ³ ml/min・cm ²・atm, preferably 1.0×10 ⁻³ to 1.0×10 ³ ml/min・cm ²・atm
It is. Next, the present invention will be explained in more detail by giving examples. Examples 1 to 8 40 wt.
-30-25), extruded and pelletized. The pellets were processed using a twin-screw extruder (Ikegai Iron Works Co., Ltd.) using the device shown in Figure 2.
PCM-30-25) 13 is melted at 200-210℃, core diameter 1.0mm, inner diameter 2.9mm, outer diameter 3.7mm, land length.
The molten hollow material 17 was discharged into the air at a rate of 14.8 g/min from the 15.0 mm annular spinning hole 15, and nitrogen gas was introduced into the center of the interior at a rate of 8.5 ml/min to cause the molten hollow material 17 to fall. 1,1,2-trichloro-1,2,2 in the cooling tank 19 at a falling distance of 355 mm.
- After contacting with trifluoroethane (hereinafter referred to as Freon 113), the cooling solidified liquid distribution pipe 20
It was cooled by bringing it into co-current contact with Furion 113 flowing down inside. At this time, the liquid temperature of Furion 113 is the first
It was as shown in the table. Next, the hollow object 17 is introduced into the Freon 113 in the solidification tank 18, and then the direction is changed by the change-of-direction rod 22, and the object is run almost horizontally for about 3 m to completely solidify it, and then the bobbin 2
3. The winding speed and draft ratio at this time were as shown in Table 1. After cutting the hollow material wound on a bobbin to a length of 30 cm, it was immersed in Freon 113 at a liquid temperature of 23°C twice for 5 minutes to perform constant length extraction, and then placed in air at 140°C for 20 minutes.
After heat treatment for 1 minute, a hollow fiber membrane having the properties shown in Table 1 was obtained. Examples 9 to 14 In the same manner as in Example 1, hydrogenated poly-α-olefin type synthetic extraction (number average molecular weight 480) was used instead of liquid paraffin, and spinning was carried out under the conditions shown in Table 1. When the same method was carried out except for Natsuta, the results shown in Table 1 were obtained. Examples 15 to 16 and Comparative Example 1 Hollow fiber membranes were produced in the same manner as in Example 1 by changing the amount of liquid paraffin charged and the spinning conditions as shown in Table 2, and the results shown in Table 2 were obtained. Obtained. Comparative Example 2 The same tests as in Examples 15 to 17 were conducted on commercially available polypropylene hollow fiber membranes for artificial lungs, and the results shown in Table 2 were obtained. Comparative Example 3 A hollow fiber membrane was produced in the same manner as in Example 15, except that water was used as the cooling solidification liquid, and the results shown in Table 2 were obtained.

【table】

【table】

[Table] Specific effects of the invention As stated above, the present invention has an inner diameter of 150~
It is a hollow fiber membrane made of polyolefin having an almost perfect circular shape with a diameter of 300 μm and a wall thickness of 10 to 150 μm.The inner surface of the hollow fiber membrane has a relatively dense layer, and the outer surface has independent layers with an average particle size of 0.1 to 10 μm. The hollow fiber membrane exhibits an aggregate-like layer of fine particles, forming fine communicating pores from the inner surface to the outer surface, and the inner surface and the outer surface of the hollow fiber membrane have a dense layer in which the distance between the particles becomes smaller as the membrane progresses toward the inner surface. Since this is a hydrophobic porous hollow fiber membrane characterized by having an anisotropic membrane structure consisting of continuous layers, the microscopic communication pores do not penetrate linearly in the membrane thickness direction, but extend through the outer surface. Since it is composed of a large number of micropores that are formed between the particles and are connected to each other from the inside toward the inside, the uniformity is very high. Therefore, when the hollow fiber membrane is used, for example, in an oxygenator, there is no plasma outflow even after long-term use, and it has a high gas exchange capacity. Further, when the porosity is 30 to 60%, the plasma outflow prevention ability and gas exchange ability are high. Therefore, the hollow fiber membrane is extremely useful as a membrane for oxygenator lungs.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the hydrophobic porous hollow fiber membrane according to the present invention, FIG. 2 is a schematic cross-sectional view of the apparatus used for manufacturing the hollow fiber membrane according to the present invention, and FIGS. is an electron micrograph showing the structure of the hollow fiber membrane according to the present invention. 1...Hollow fiber membrane, 2...Dense layer, 3...Fine particles, 4...
Fine particle aggregate layer, 5, 6... Micropore, 11... Raw material pellet, 12... Hopper, 13... Extractor, 14
... Spinning device, 15... Spinneret device, 16... Inert gas supply line, 17... Hollow object, 18... Cooled solidified liquid, 19... Cooling tank, 20... Cooled solidified liquid distribution pipe, 2
1... Solidification tank, 22... Direction changing rod, 23... Bobbin, 24
...Cooled solidified liquid circulation line, 25...Circulation pump, 2
6...Evaporation spinning water tank.

Claims (1)

[Scope of Claims] 1. A polyolefin hollow fiber membrane having an almost perfect circular shape with an inner diameter of 150 to 300 μm and a wall thickness of 10 to 150 μm, the inner surface of the hollow fiber membrane exhibiting a relatively dense layer, The outer surface side exhibits an aggregate-like layer of independent fine particles with an average particle size of 0.1 to 10 μm, and fine communicating pores are formed from the inner surface side to the outer surface side, and the space between the inner surface side and the outer surface side of the hollow fiber membrane is 1. A porous hollow fiber membrane characterized by having a continuous anisotropic membrane structure exhibiting a dense layer with smaller interparticles as it progresses toward the inner surface. 2 Claim 1 in which the porosity is 5 to 60%
The porous thread membrane described in . 3 _O2 gas flux is 1.0×10 ^-5 to 2.0×10 ³ ml/
The porous hollow fiber membrane according to claim 1 or 2, which has a particle size of min·cm ² ·atm. 4 _O2 gas flux is 1.0×10 ^-3 to 1.0×10 ³ ml/
The porous hollow fiber membrane according to claim 1 or 2, which has a particle size of min·cm ² ·atm. 5 The average particle size of independent fine particles on the outer surface side is 1 to 7 μm
A porous hollow fiber membrane according to any one of claims 1 to 4. 6. The porous hollow fiber membrane according to any one of claims 1 to 5, having an inner diameter of 180 to 250 μm and a wall thickness of 20 to 100 μm. 7. The porous hollow fiber membrane according to any one of claims 1 to 5, wherein the polyolefin is polyethylene. 8. The porous hollow fiber membrane according to any one of claims 1 to 6, wherein the polyolefin is polypropylene.