JPH06210146A - Hollow fiber heterogeneous membrane and method for producing the same - Google Patents

Abstract

(57) [Summary] [Structure] A hollow fiber membrane obtained by melt-extruding a crystalline thermoplastic resin containing poly-4methyl-1-pentene as a main component into a hollow fiber shape, and then stretching the melt. Has an area open area ratio of 3% or less and a crystallinity of 55% only on the outer surface
After the hollow fiber heterogeneous membrane characterized by having the above dense layer and having the porous layer inside and the crystalline thermoplastic resin are melt-extruded under the conditions of a tension of 0.8 g to 6.0 g Then, the hollow fiber heterogeneous membrane is obtained by stretching. [Effect] The hollow fiber heterogeneous membrane of the present invention has excellent gas permeation characteristics and gas separation characteristics, and since a dense layer is stably formed on the outer surface of the membrane, the overall strength of the membrane is high. It is useful as a liquid contact membrane, a gas-gas separation membrane, a diaphragm for artificial lungs, a deoxygenation of ultrapure water, and a degassing membrane for dissolved gas such as deoxygenation of boiler ring water.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a crystalline thermoplastic resin produced by a melt molding method, preferably poly-4methyl-
1-Pentene has a highly crystalline dense thin film layer only on the outer surface of a hollow fiber membrane made of a crystalline thermoplastic resin, and a large number of fine particles supporting the dense layer on the surface are provided inside the membrane. The present invention relates to a hollow fiber heterogeneous membrane having a porous layer having pores and a method for producing the same.

The hollow fiber heterogeneous membrane of the present invention is used as a gas-gas separation membrane (gas separation membrane) for producing oxygen-enriched air, nitrogen-enriched air, carbon dioxide / nitrogen separation, methane / carbon dioxide. Used for gas separation, hydrogen / carbon monoxide separation, nitrogen oxide and sulfur oxide separation and removal from exhaust gas, and as a gas-liquid separation membrane (gas-liquid contact membrane) for artificial lungs. Membrane, artificial kidney dialysis membrane, removal of dissolved oxygen from water such as boiler water, ultrapure water for semiconductor production, water for power generation, etc., measures against red water by deoxidizing clean water, dissolved oxygen and dissolved carbon dioxide in pure water Removal, degassing and defoaming of organic solvents and acid alkalis, removal of chlorine odors and musty odors from tap water, volatile substances dissolved or dispersed in water, such as chloroform, trichloroethylene, methanol, acetone, toluene,
It is used in the fields of removing methylene chloride, dichloroethane, dichloromethane, etc., a device for dissolving oxygen in water, and recovering carbon dioxide from exhaust gases such as fumes, fermented methane gas and tertiary oil recovery.

[0003]

2. Description of the Related Art Conventionally, a heterogeneous membrane used as a gas separation membrane or a gas-liquid contact membrane having a property that gas is permeable but liquid is not permeable is obtained by pushing a polymer solution into a non-solvent. It was manufactured by a wet method for manufacturing or a method of coating another polymer on the surface of the porous film.

Recently, as a new film forming method different from the above,
Melting known as a method for producing a so-called microporous homogenous membrane, which is used as a MF membrane or a UF membrane having a large number of communicating pores through the membrane wall, using a conventional highly crystalline thermoplastic polymer such as polyethylene or polypropylene It has been proposed that a membrane having a heterogeneous structure, which is completely different in structure from a conventional porous membrane, can be produced by the same principle as the spinning-drawing method.

That is, Japanese Patent Publication No. 38250/1990 discloses that a thermoplastic crystalline polymer is melted at a melting temperature of Tm to Tm + 200 ° C. in a range of 1 to 30 cm below a discharge port while being cooled by a cross wind of about 1 m / sec. Melt extrusion film formation at Df ≦ 1500, heat treatment at Tg to Tm-10 ° C as required, and temperature at which Tg-50 ° C to Tm-10 ° C (however, Tg
Is a glass transition temperature) and the film is drawn at a draw ratio of 1.1 to 5.0 and then heat-set at a drawing temperature to Tm to obtain a thickness of 0.003 μm or more in which no pores are present. 01 to 1 μm non-porous layer and diameter 0.01 to 50 μm
Gas separation, gas permeation, which has a porous layer consisting of
It has been shown that a heterogeneous film having excellent mechanical properties can be efficiently produced.

[0006]

However, when a highly crystalline thermoplastic high molecular weight polymer is used as a membrane material and the above-mentioned known melt-processed hollow fiber type heterogeneous membrane is applied to actual industrial fields. It was not always satisfactory.

That is, in a conventional heterogeneous film of a high crystallinity thermoplastic polymer produced by the melting method, the position of the dense layer is not fixed stably, and in some cases, the dense layer is formed inside the hollow fiber. ,
Some of them were formed in the cross section of the membrane, and some of them were formed inside and outside the hollow fiber, and there were various heterogeneous structures in the same hollow fiber. Furthermore, the density and thickness of the dense layer are not stable, and in the extreme case, it has the same homogeneous structure as a so-called microporous membrane in which a large number of large pores completely penetrate the membrane wall. On the contrary, a part having a homogeneous structure without any porous layer was recognized, and the film was a heterogeneous film with large unevenness in characteristics. These drawbacks were extremely inconvenient when the membrane was to be industrially applied.

[0008] For example, when such a hollow fiber heterogeneous membrane is applied as an air separation membrane, the membrane will be modularized by using several kilometers to several tens of kilometers. The fluctuation of the dense layer density is large,
The performance of the entire membrane module may be extremely deteriorated due to the part of the low oxygen / nitrogen separation coefficient α existing in part.

Further, the conventional hollow fiber heterogeneous membrane is used as a so-called next-generation artificial lung membrane by an external reflux system in which blood is flown outside the hollow fiber, for example, as a gas (oxygen) -liquid (blood) contact membrane. If you try to apply it, the gas exchange capacity (removing carbon dioxide in the blood and enriching oxygen) is greatly increased, and there is no deterioration in performance even after long-term use, and there is no leakage of blood components. In that respect, it was not always satisfactory. That is, in the conventional hollow fiber heterogeneous membrane, even in one hollow fiber, the dense layer does not exist stably on the outer surface of the membrane, and the outer surface is often porous. This is a phenomenon in which water in the blood gradually condenses in the porous portion during long-term use, causing a large decrease in gas exchange performance as in the case of the conventional polypropylene (PP) microporous membrane, a so-called wet rung phenomenon. There has occurred. Furthermore, in the worst case, leakage of blood plasma components may occur.

According to the present invention, the dense layer is stably formed only on the outer surface of the hollow fiber membrane, the total strength of the membrane is high, and the dense layer is suitable for each industrial application as a gas-liquid contact membrane. It has thickness and compactness, and as a gas-gas separation membrane,
In particular, it is an object of the present invention to provide an excellent hollow fiber heterogeneous membrane having a high oxygen / nitrogen separation ability as an air separation membrane and a method capable of stably producing such a heterogeneous membrane at a level of industrialization without fluctuation in characteristics. To do.

[0011]

The present inventor has completed the present invention as a result of earnest research on the above-mentioned problems.

That is, according to the present invention, a crystalline thermoplastic resin, preferably a crystalline thermoplastic resin containing poly-4-methyl-1-pentene as a main component (hereinafter referred to as PMP polymer) is melt-extruded into a hollow fiber shape. In the hollow fiber membrane obtained by stretching, the hollow fiber membrane has a dense layer having an area porosity of 3% or less only on the outer surface, and has a porous layer inside the membrane. After melt-extruding the hollow fiber heterogeneous membrane and the take-up tension of 0.8 g to 6.0 g,
The present invention relates to a method for producing a hollow fiber heterogeneous membrane, which comprises stretching.

The present invention will be described in more detail below. Examples of the crystalline thermoplastic resin referred to in the present invention include poly-4-methyl-1-pentene, polypropylene, polyethylene, polyoxymethylene and the like, among which poly-4-methyl-1-pentene is preferable.

The PMP polymer of the present invention is a 4-methyl-1-pentene homopolymer or 4-methyl-1-pentene.
A copolymer or mixture containing 85% or more of pentene, and other α-olefins such as ethylene, propylene, 1-butene, 1-hexene, 1-octene, 1-octadecene as a monomer to be copolymerized, Examples thereof include α-olefins having 2 to 20 carbon atoms such as 1-tetradecene, vinyl-based monomers, vinylidene-based monomers, acrylic-based monomers, halogen-containing monomers and silicon-containing monomers.

Examples of the mixture include organic polymers, oligomers, plasticizers, inorganic fillers and the like. The heterogeneous membrane of the present invention is a membrane in which the hollow fiber membrane cross section is made of the same material in the thickness direction of the membrane and is composed of a porous portion and a dense layer portion which are substantially in communication with each other, and the dense layer has a hollow fiber outer surface. It exists only in the stable state. Such an inhomogeneous structure can be easily confirmed by a high resolution scanning electron microscope observation image of the cross section of the outer surface, the inner surface of the hollow fiber membrane and the membrane wall in the thread direction. Further, the fact that the porous parts of the heterogeneous membrane of the present invention are substantially in communication with each other can be easily confirmed by the increase in weight when the membrane is impregnated with ethanol.

In the heterogeneous film of the present invention, the dense layer has high crystallinity, and the crystallinity thereof is preferably 55% or more, more preferably 60% or more. The fact that the dense layer has high crystallinity can be confirmed by carefully cutting off only the dense layer in the surface layer portion of the heterogeneous film with a microtome, and by a highly crystalline diffraction pattern by electron diffraction of the thin film. Further, the crystallinity of the dense layer can be easily known by a formula by measuring the heat of fusion of the dense layer in the surface layer portion removed by a microtome.

[0017] However, Wc: Crystallinity of heterogeneous film made of PMP-based resin ΔH _f : Heat of fusion of heterogeneous film made of PMP-based resin (cal
・ G ⁻¹ ) ΔH _fcry : Heat of fusion of 100% crystal of PMP resin (14.8
When the cal · g ⁻¹ ) film is applied to various industrial fields, it is desired that the film has excellent mechanical strength, chemical resistance, and heat resistance. These characteristics are improved as the crystallinity increases, and the higher the crystallinity, the more preferable. In particular, the dense layer, which is the material separation active layer, preferably has a higher crystallinity.

The permeation mechanism of the non-aggregating gas that permeates the membrane is
There are the following three types depending on the size of the pore size (for example,
For example, Tsutomu Nakagawa: High-pressure gas, 18 (9), 471, (198
1)). (1) When the membrane has extremely small pores
(The extremely small pores referred to here mean the high
It can be thought of as a free volume that occurs between child chains with a certain probability:
It is generally said that the pore size is 0.001 μm or less.
In this case, the mechanism of gas permeation through the membrane is
It becomes]. Gas permeability coefficient P [cm³． (STP) c
m²/ Cm²． sec. cmHg] is a value peculiar to the polymer and
Permeation rate Q = P / L [cm]
³(STP) / cm²． sec. cmHg] has a small film thickness L
How big it gets! Also the ratio of the velocities of the gas passing through the membrane,
For example P _O2/ P_N2= Q_O2/ Q_N2(P_O2: Oxygen permeation staff
Number, P_N2: Nitrogen permeability coefficient, Q_O2: Oxygen transmission rate, Q_N2:
Nitrogen permeation rate is shown for each polymer regardless of film thickness.
It has a unique value. (2) Even if the film is large, it has only holes with a mean free path of gas.
If not present (273K if the gas is oxygen or nitrogen, 1
(Atm is about 0.06 μm) Rate-determining mechanism of gas permeation mechanism
Becomes Knudsen flow.

In this case, the gas permeation is inversely proportional to the square root of the gas molecular weight. Moreover, even in the case of mixed gas of several kinds, each molecule passes through the pore independently of other molecules. Therefore, for example, the separation coefficient α when a mixed gas of oxygen and nitrogen permeates through the membrane at the same time is always (M _N2 / M _O2 = 28
/ 32) ^0.5 = 0.935. However, M _N2 and M _O2 represent the molecular weight of nitrogen and the molecular weight of oxygen, respectively. (3) When the radius of the pores communicating with the membrane becomes about 5 times or more the mean free path of gas, the rate of the gas permeation mechanism becomes Poiseuille flow. In this case, the gas permeation amount is inversely proportional to the gas viscosity. Under such conditions, when the gas mixture is simultaneously passed through the membrane, the gas mixture is no longer separated. However, when each pure gas is permeated separately, the permeation amount is inversely proportional to the ratio of the viscosity of the gas. For example, when pure gases of oxygen and nitrogen are used as gases, the ratio of the amount of permeation at 25 ° C. is 0.866 within the error range.

Strictly speaking, the gas permeation mechanism of the membrane is 3 above.
It is a mixture of different types of mechanisms. The heterogeneous membrane of the present invention does not have any large communication hole that penetrates the membrane wall such that the gas permeation mechanism becomes viscous flow rate controlling, and preferably in a standard state of non-aggregated gas represented by oxygen or nitrogen, There are only communicating holes having a pore diameter equal to or smaller than the Knudsen flow rate controlling, and most preferably the gas permeation mechanism is dissolution / diffusion controlling, and there are no physical communicating holes anymore.

The pore size of the communication hole penetrating the hollow fiber membrane through the membrane wall can be determined from the ratio of the speeds of the pure gases permeating the membrane. For example, when oxygen and nitrogen are used as pure gases, if there are many large communication holes in the hollow fiber membrane that cause viscous flow that communicates with the membrane wall, the ratio of the oxygen permeation rate through the membrane and the nitrogen permeation rate will be incorrect. Within the range of 0.935 or less.

For example, in the case of porous hollow fiber membranes such as polyethylene and polypropylene that have been widely used in household water purifiers in recent years, the ratio of oxygen and nitrogen permeation rates (separation coefficient) is 0, regardless of the type of membrane. 935 or less is shown.

The heterogeneous membrane of the present invention has a separation coefficient of oxygen and nitrogen of 0.935 or more, preferably 1.0 or more, and more preferably 4.0 or more. The porosity of the communication holes of the heterogeneous membrane of the present invention is preferably 3% or less, more preferably 0.
%. If the porosity is 3% or more, the applicable practical fields are limited, which is not preferable. For example, when a heterogeneous membrane having a porosity of 3% or more is applied as an air separation membrane, a high oxygen / nitrogen separation coefficient cannot be expected no matter how small the pore size is. Further, when it is applied as a diaphragm for artificial lungs, the gas exchange capacity decreases with time and it becomes difficult to use it for a long time.

It is extremely difficult to know the porosity of the membrane, but it can be determined by the following method. 1974, Journal of Applied Polymer Science (JOURNAL.O
F.APPLIED.POLYMER.SCIENCE VOL.18, PP.805-819) No. 18, page 805, YASUDA et al. "Pore size of microporous polymer membranes" (PORE.SIZE.OF) .MICROPOROUS.POLYMER.MEMBRENE
By the method of (S), the average pore diameter of the communication holes penetrating the membrane wall is calculated,
Next, the permeation amount of ethanol that permeates the heterogeneous membrane as a liquid can be measured and calculated by the following formula.

[0025] However, V _Et-oH : Ethanol permeation rate of the membrane [cm ³ /sec.cm ² ] L: Film thickness [cm] η: Ethanol viscosity 1.78 × 10 ^-8 [kgf.sec / cm ² ] ΔP: Inside the membrane wall -Outside pressure difference (driving force for ethanol permeation) [kgf
/ cm ² ] r: Average pore diameter (radius) of communicating pores [cm] ε _s : Area of membrane Porosity Of course, a membrane having a porosity of 0% does not permeate ethanol at all.

The thickness of the dense layer of the heterogeneous membrane of the present invention is not particularly limited, but even when it is used for a gas separation membrane or a gas-liquid contact membrane, it is preferably as thin as possible in order to increase the permeation rate of the substance.

Although it is extremely difficult to accurately and directly measure the average thickness of the dense layer of the heterogeneous membrane, it can be approximated by an equation from the measured values of the permeation rates of oxygen and nitrogen that permeate the membrane. The formula is a very small number of pinholes that can be detected only in the gas permeation test, which is the most precise and most sensitive.
It is also applicable to the case where there is a gas that passes through the membrane, which is very small up to the mean free path of the gas or less). The thickness of the dense layer was calculated from the oxygen permeation rate of the completely non-porous layer by removing the minute pinhole permeation portion from the ratio of the permeation rates of oxygen and nitrogen.

[0028] However, L: dense layer thickness [μm] P _O2 : oxygen permeability coefficient of membrane material [cm ³ (STP) .cm / cm ² .se
c.cmHg] Q _O2 : Oxygen permeation rate of the membrane [cm ³ (STP) / cm ² .sec.cm
Hg] α: Separation coefficient of oxygen / nitrogen of membrane [−] α ₁ : Separation coefficient of oxygen / nitrogen of membrane material α ₂ = 0.935: Separation coefficient of oxygen / nitrogen of Knu-Sen flow.

In the case of the PMP polymer, the oxygen / nitrogen separation coefficient α ₁ = 3.8 and the oxygen permeability coefficient P _o2 = 1.8 of the spun yarn having a homogeneous structure before the drawing operation. × 10 ^-9 [cm
³ (STP) .cm / cm ² .sec.cmHg] is used.

The heterogeneous film of the present invention can be provided with a property having optimum characteristics (dense layer density and thickness) for the required performance in each industrial application field. For example, when used as a gas-liquid contacting diaphragm for degassing a dissolved gas in water or as an air-supplying membrane for a gas into water, only the gas permeability of a heterogeneous membrane is important, rather than the denseness of a dense layer. Rather, it is important how to reduce the film thickness and increase the gas permeability. Of course, its compactness must completely prevent liquid leakage. Poly-4-methyl-1-pentene is a highly hydrophobic material by nature, and even if it is large, liquid leakage does not occur at all as long as it allows a minute pinhole such that the Knudsen flow is rate-determining. The present invention has a film thickness of about 2 while maintaining the dense layer optimum for such applications.
It is possible to provide a heterogeneous film that achieves an ultrathin film thickness of less than or equal to μm, and more preferably about 0.1 μm.

On the other hand, when the heterogeneous membrane of the present invention is applied as an air separation membrane, the dense layer is thinned to increase the gas permeation rate and, at the same time, the oxygen / nitrogen separation ability makes the membrane practical. Will be important above. That is, it is important to increase the density of the dense layer, which is the separation active layer of the heterogeneous membrane, to the limit. The thickness of the dense layer is 2 μm or less, more preferably 0.5 μm, while maintaining the denseness of the high dense layer that is the dissolution / diffusion-controlling gas membrane permeation mechanism, which is optimal for such use according to the present invention. Heterogeneous films thinned to a degree can be provided.

The generation of fine holes penetrating the hollow fiber membrane wall is suppressed,
In addition, it is not easy to industrially stably produce a heterogeneous membrane in which only the outer surface layer of the hollow fiber membrane is made into a dense thin film.

The present inventors have earnestly studied a method for producing a heterogeneous membrane having a dense layer on the outer surface of a hollow fiber membrane made of a PMP polymer by a melting method, and as a result, surprisingly, It was discovered that industrial production is possible only by controlling the take-up tension of the spun yarn.

Here, the take-up tension of the spun yarn refers to the tension (grams) applied to one hollow fiber 5 m below the spinning nozzle surface. The take-up tension of spun yarn is from 0.8g to 6.0g.
Is preferable, and more preferably 2.0 g to 3.5.
It is g.

As the take-up tension is reduced, a dense layer is clearly formed on the outer surface of the hollow fiber membrane, but the dense layer tends to be thick. When the tension is 0.8 g or less, not only a practical thin dense layer can no longer be formed, but also the porosity of the porous layer of the heterogeneous film becomes extremely low. As a result, the permeation resistance of the gas to be separated and separated increases, which is extremely unpractical as a gas separation membrane.

On the other hand, as the tension is increased, the dense layer becomes thinner, but a large number of communicating holes are formed in the dense layer, and the hole diameter also becomes large and the denseness decreases. In addition, the location where the dense layer is formed tends to change. Further tension is 6.
If the amount exceeds 0 g, not only a large number of communication holes are formed through the dense layer, but also the drawability of the spun yarn is extremely reduced, and many yarn breakages occur during the drawing process, making industrial production difficult. .

The optimum heterogeneous film properties naturally vary depending on the industrial application field. For example, for gas-gas separation represented by a separation membrane for oxygen and nitrogen from air, a heterogeneous membrane having no communication holes in a dense layer is most suitable, and when producing this heterogeneous membrane, The take-up tension may be adjusted to a lower value within the range of the present invention. Also, in the diaphragm for degassing from an aqueous liquid and the diaphragm for supplying air to a liquid typified by an artificial lung, it is sufficient that the density of the dense layer is such that the liquid does not leak, and rather the thickness of the dense layer. It is important to make the gas as thin as possible to reduce the gas permeation resistance. In this case, the take-up tension of the spun yarn may be adjusted higher within the scope of the present invention.

The take-up tension of the spun yarn can be easily adjusted by balancing the spinning temperature, the resin extrusion speed, the take-up speed and the like. For example, in order to adjust the take-up tension to a large extent, it can be easily adjusted by lowering the spinning temperature, increasing the resin extrusion speed, or increasing the take-up speed.

What is even more surprising is that we have obtained that the cooling conditions of the melt-extruded hollow strands stabilize the desired heterogeneous membrane properties without fluctuation, and the industrial production is stable without yarn breakage. It has been found to be one of the most important factors to do. That is, the cooling air velocity is strictly controlled, vibration of the strand in a molten state having an extremely low elastic modulus extruded from the hollow fiber manufacturing nozzle is suppressed as much as possible, and the cooling point of the molten resin is fixed to stabilize the industrial properties. It is extremely important for producing hollow fiber membranes.

The optimum cooling air velocity for producing the hollow fiber heterogeneous membrane of the present invention is the dimension of the hollow fiber (inner diameter, outer diameter, wall thickness).
Needless to say, it slightly varies depending on the spinning speed, but it is preferable to apply a wind of 0.1 m / sec to 0.9 m / sec directly under the nozzle. When the wind is 0.1 m / sec or less and 1.0 m / sec or more, the drawing unevenness in the direction of the hollow fiber in the subsequent drawing operation (this yarn unevenness easily occurs due to the formation of a transparent part and an opaque part during the drawing). It is possible to distinguish: A uniform thing becomes a white and opaque thread due to diffuse reflection of the porous layer). In an extreme case, the yarn diameter varies greatly depending on the location, and not only the yarn unevenness but also the yarn breakage frequently occurs during the drawing.

There is no limitation on the method of uniformly applying the cooling air to the outer surface of the hollow fiber, but the hollow fiber is taken out for cooling uniformity of the molten hollow strand extruded from the nozzle, cooling effect, and vibration suppression. Directional and countercurrent are preferred. When there is a difference in how to apply cooling air to the outer surface of the hollow fiber, for example, when wind is applied from only one side of the hollow fiber due to cross wind, there is unevenness in the characteristics in the circumferential direction of the hollow fiber. Becomes

The temperature of the cooling air may be about the ambient temperature of the room, and no special temperature adjustment is required. When the heterogeneous membrane of the present invention is applied as, for example, an air separation membrane, it is most important to increase the oxygen permeation rate and the oxygen / nitrogen separation coefficient α.

As a result of earnest studies on this point, the inventors of the present invention have found that the oxygen / oxygen permeation rate is not substantially reduced, and
It has been discovered that it is preferable to further sufficiently heat-treat the cooled and solidified heterogeneous film in order to improve the separation coefficient α of nitrogen. That is, heat treatment is performed at a temperature of 80 ° C to 210 ° C. There is no particular limitation on the heating atmosphere, and there is no limitation on heat treatment in heated air, hot water, or a suitable heat medium such as silicon oil. The treatment may be carried out in any of the free length, the fixed length and the stretched state of the hollow fiber heterogeneous membrane, but in order to suppress the decrease in gas permeation rate of the membrane and improve α, the heat treatment under the fixed length is preferable. Most preferably,
At a processing temperature of 140 ° C to 170 ° C and for 15 minutes in a fixed length state while applying tension that antagonizes the contraction force of the hollow fiber heterogeneous membrane
Heat treatment is performed for 90 minutes.

[0044]

【Example】

Example 1 A poly-4-methyl-1-pentene polymer having a melting point (Tm) of 231 ° C. (trade name: TPX, manufactured by Mitsui Petrochemical Co., Ltd.) having a diameter of 7 mm, a slit width of 1.5 mm, and gas can be forcibly supplied inside the hollow fiber. Using a double circular tube nozzle with such a structure, at a spinning temperature of 286 ° C, cooling air is blown directly under the nozzle at a wind speed of 0.42 m / sec in the hollow fiber winding direction and countercurrent, and the molten resin discharge speed is set to 93 g / hr. The take-off speed is 77m / min
And the take-up tension was adjusted to 1.6 g. The inner diameter of the hollow fiber is 190μm and the inner diameter is 1 by controlling the flow rate of nitrogen.
20 μm spun yarn was obtained. At this time, substantial cooling and solidification was completed about 15 cm below the nozzle. This spun yarn was continuously drawn between the rollers at a draw ratio of 2 times, and further heat-set for about 1 second while relaxing at 0.8 times in an atmosphere of 210 ° C. to give a hollow fiber heterogeneous membrane. It was manufactured. About 120
Continuous production was carried out for an hour to produce a hollow fiber heterogeneous membrane of about 900 km. No yarn breakage occurred during continuous production.
Electron microscopic (hereinafter referred to as SEM) photograph has a dense layer with no pinholes on the outer surface of the hollow fiber, and a large number of pores with pore diameters of 0.01 μm to 0.5 μm inside the membrane wall. It was confirmed to have a structure.

The SEM photograph of the inner surface of the obtained heterogeneous hollow fiber membrane is shown in FIG. 1, the SEM photograph of the longitudinal section of the hollow fiber in the direction of the hollow fiber near the outer surface of the hollow fiber, and the hollow fiber membrane of FIG. The SEM photograph of the outer surface of is shown.

It was confirmed that the obtained heterogeneous membrane did not permeate ethanol as a liquid at all, and therefore there were no communicating pores in the dense layer of the membrane. It was also confirmed that the porous layers were almost in communication with each other due to the increase in weight after ethanol impregnation.

The outer surface of the obtained heterogeneous hollow fiber membrane was removed by a microtome to remove a dense layer with a thickness of about 0.08 μm. The crystallinity of the dense layer of the obtained heterogeneous film was 64% as measured by the crystallinity by DSC.

From the obtained heterogeneous membrane, 210 hollow fibers were randomly sampled at a length of 5 m per sample, and the average hollow fiber outer diameter was 19
At 0 μm, the coefficient of variation was 1.2%, the average value of the wall thickness was 35 μm, and the coefficient of variation was 3.7%. The average value of the ratio of oxygen permeation rate and nitrogen permeation rate (separation coefficient: α) was 3.8, and the coefficient of variation was 0.8%. The average value of the oxygen transmission rate was 3.1 × 10 ⁻⁵ [cm ³ / cm ² .sec.cmHg], and the coefficient of variation was 6%. The average thickness of the dense layer was 0.6 μm and the coefficient of variation was 4%.

EXAMPLE 2 The same poly (4-methyl-1-pentene) polymer as in Example 1 has a diameter of 5.0 mm, a slit width of 1.0 mm, and a double circle having a structure capable of forcibly supplying gas into the hollow fiber. Using a tube nozzle, at a spinning temperature of 278 ° C, a wind speed of 0.25 m just below the nozzle.
/ Second, cooling air is blown in the hollow fiber winding direction and countercurrent, the molten resin discharge speed is set to 93 g / hr, and the take-up speed is 5
The take-up tension was adjusted to 3.8 g by adjusting to 9 m / min. Outer diameter = 29 by controlling the flow rate of nitrogen injected into the hollow fiber
A spun yarn having a diameter of 0 μm and an inner diameter of 210 μm was obtained. At this time, substantial cooling and solidification was completed about 10 cm below the nozzle. This spun yarn was subjected to the same drawing conditions and heat setting conditions as in Example 1 to obtain a hollow fiber heterogeneous membrane. Continuous production for about 150 hours was performed to produce a hollow fiber heterogeneous membrane of about 500 km. No yarn breakage or yarn unevenness occurred during continuous production. The crystallinity of the dense layer was 66%. The open area ratio of the hollow fiber is 0.7% in area ratio, and the average value (diameter) of the communication holes is 0.007μ.
It was m. In addition, it was confirmed by the measurement of the maximum pore diameter by the bubble point method using ethanol that there were no communicating pores having a pore diameter of 0.05 μm or more. On the other hand, the presence of a large number of fine pores having a pore diameter of 0.01 to 0.8 μm was recognized inside and in the cross section of the hollow fiber. This heterogeneous film was subjected to the same sampling as in Example 1 to measure the characteristics. Average value of oxygen permeation rate = 6.7 × 10 ⁻⁴ [cm ³ / cm ² .sec.cmHg], coefficient of variation = 6.3%: oxygen / nitrogen separation coefficient α = 1.07, coefficient of variation = 4. 1%: The average value of the dense layer thickness was 0.17 μm, and the variation coefficient was 9.5%.

Comparative Example 1 According to Example 1 disclosed in Japanese Examined Patent Publication No. 2-38250, poly-4-methylpentene-1 having MI of 26 was spun using a bridge type nozzle having a diameter of 5 mm and a slit width of 1 mm. Temperature 290 ° C, take-up speed 580 m / min,
Draft 420 is used for spinning.
The area of 8 cm was cooled with a cross wind at a temperature of 25 ° C. and a wind speed of 1 m / sec. At this time, the spun yarn take-up tension is 8.3 g.
Met. The obtained spun yarn had an outer diameter average value of 58 μm and a wall thickness average value of 11 μm, but the variation in the yarn diameter was large, and the outer diameter variation coefficient was 18%, and the wall thickness variation coefficient was 22%.
It was even extended. The obtained spun yarn was heat-treated at 190 ° C. for 1 second, 5 seconds, and 30 seconds under constant length conditions, respectively, and then, at room temperature, the distance between rollers was 5 cm, and the drawing speed was 50%.
40% was stretched for 10 minutes / second, and heat-fixed at 190 ° C. for 3 minutes at a constant length. At this time, no matter how the line speed was changed and the drawing speed was fixed, yarn breakage occurred frequently regardless of the heat treatment time, and continuous drawing for more than 1 hour was impossible in all cases. The barely stretched yarn had even yarn unevenness within a few meters, and the yarn had both transparent and white opaque portions. When sampling was performed from the white and opaque portion of the drawn yarn and the film was observed by SEM, a large number of micropores were formed on both the inner and outer surfaces of the hollow fiber membrane in part. FIG. 4 shows SE of the inner surface of the obtained hollow fiber.
FIG. 5 is an SEM photograph of the outer surface. It was confirmed that both the inner surface portion and the outer surface portion had a porous portion and a non-porous portion, and that portions having different structures were mixed in the same film. The oxygen permeation rate of this membrane was 3 × 10 ^-5 [cm ³ / cm ² .sec.cmHg] in a part of the hollow fiber (several tens of centimeters) regardless of the heat treatment time, and the oxygen / nitrogen separation coefficient α = 3. .6, although the presence of a location where the dense layer has a thickness of 0.7 μm, the oxygen permeation rate is 14 × in some areas.
There was also a portion showing 10 ⁻⁵ , α = 1.15, and dense layer thickness = 0.6 μm. The same sampling as in Example 1 was performed to measure the variation in the characteristics.
The variation coefficient of oxygen permeation rate was 55% or more, the variation coefficient of oxygen / nitrogen separation coefficient α was 62% or more, and the variation coefficient of dense layer thickness was 64% or more, which were very large. The degree of crystallinity of the obtained hollow fiber membrane was 51% at a small portion and 59% at a large portion.

Comparative Example 2 A heterogeneous film obtained in the same manner as in Example 1 except that the spinning temperature was adjusted to 290 ° C., the resin discharge temperature was adjusted to 57 g / hr, and the take-up tension was adjusted to 0.6 g. The oxygen transmission rate is 0.5 × 10 ^-5 [cm ³ / cm ² · sec · cmHg], and α is 3.
7, and the dense layer crystallinity was 61%. The area open area ratio of the dense layer was substantially 0%. Example 3 The heterogeneous film obtained by the same method as in Example 1 was further heat-treated for 50 minutes in an air atmosphere at an ambient temperature of 160 ° C. under a fixed length. The oxygen transmission rate of the obtained heterogeneous membrane is 2.
5 × 10 ⁻⁵ [cm ³ / cm ² .sec.cmHg], dense layer crystallinity is 78
%, And oxygen / nitrogen separation coefficient α = 4.5. The area open area ratio of the dense layer was substantially 0%. Example 4 PHILL is a poly-4-methyl-1-pentene polymer.
The oxygen permeation rate of the heterogeneous membrane obtained by the same method as in Example 1 except that it was HBN020 manufactured by IPS 66 COMPANY was 2.1 × 10 ⁻⁵ [cm ³ / cm ² .sec.cmHg], and dense layer crystals were obtained. The degree of conversion was 72%, and the oxygen / nitrogen separation coefficient α = 4.3. The area open area ratio of the dense layer was substantially 0%.

Example 5 The hollow fiber heterogeneous membrane obtained in Example 4 was further heat-treated for 60 minutes in an air atmosphere at an ambient temperature of 180 ° C. under a fixed length. The oxygen transmission rate of the obtained heterogeneous membrane is 1.6.
2 × 10 ^{over 5 [cm 3 / cm 2 .sec.cmHg} ], α was 4.9.
The area open area ratio of the dense layer was substantially 0%.

[0053]

Industrial Applicability According to the present invention, it is possible to stably produce a PMP-based polymer heterogeneous film having optimum properties for various industrial fields on an industrial level.

The heterogeneous membrane of the present invention has excellent gas permeation characteristics, gas separation characteristics, and film-forming properties, and since a dense layer is stably formed on the outer surface of the hollow fiber, the overall strength of the membrane is high. It is useful as a contact membrane and a gas-gas separation membrane.

For example, when applied to a diaphragm for an artificial lung, it retains a high oxygen exchange capacity even when used for a long period of time, has no leakage of blood components, and is a next-generation artificial lung not only for open-heart surgery but also as a respiratory assist lung. It is extremely useful as a diaphragm for use. This has enabled the development of new and revolutionary life support devices for patients with heart failure and premature babies.

Further, the heterogeneous membrane of the present invention is used as a membrane for degassing dissolved gas, and is represented by, for example, deoxygenation of ultrapure water which is essential for cleaning semiconductors, deoxidation of boiler ring water, and trihalomethane in tap water. When it is applied to the removal of carcinogenic substances, it exhibits excellent degassing performance.

Further, it is possible to produce a hollow fiber heterogeneous membrane having a very high separation coefficient of oxygen and nitrogen, which has been heretofore unknown in the PMP polymer heterogeneous membrane, and it is extremely useful as an air separation membrane. Is.

[Brief description of drawings]

1 to 5 are photographs substituting for drawings showing the structure of a heterogeneous hollow fiber membrane.

FIG. 1 is an electron microscope (SEM) photograph showing the shape of the inner wall surface of the heterogeneous hollow fiber membrane of Example 1.

FIG. 2 is an SEM photograph showing the shape of the outer wall surface of the heterogeneous hollow fiber membrane of Example 1.

FIG. 3 is an SEM photograph showing the cross-sectional shape of the membrane wall of the heterogeneous hollow fiber membrane of Example 1.

FIG. 4 is an SEM photograph of the inner surface of the hollow fiber membrane of Comparative Example 1.

5 is an SEM photograph of the outer surface of the hollow fiber membrane of Comparative Example 1. FIG.

Claims (7)

[Claims] 1. A hollow fiber membrane obtained by melt-extruding a crystalline thermoplastic resin into a hollow fiber and then stretching the hollow fiber membrane, wherein the hollow fiber membrane has a dense layer only on the outer surface and is porous inside the membrane. A hollow fiber heterogeneous membrane having a layer. 2. The crystalline thermoplastic resin is poly-4methyl-
1-Pentene as a main component
The described hollow fiber heterogeneous membrane. 3. The hollow fiber heterogeneous membrane according to claim 1, wherein the dense layer has an area open area ratio of 3% or less. 4. The hollow fiber heterogeneous membrane according to any one of claims 1 to 3, wherein the dense layer has a crystallinity of 55% or more. 5. A take-up tension of the crystalline thermoplastic resin of 0.1.
A method for producing a hollow fiber heterogeneous membrane, which comprises melt-extruding under the conditions of 8 g to 6.0 g and then stretching. 6. A wind speed of 0.1 immediately below the discharge port after melt extrusion.
The method according to claim 5, wherein the film is melt-extruded to form a film by cooling and solidifying by applying a wind of up to 0.9 m / sec. 7. The hollow fiber heterogeneous membrane according to claim 1, which is 80 to 2
The method according to claim 5 or 6, wherein the heat treatment is performed at a temperature of 10 ° C.