JPH08332359A - Production of hollow yarn porous membrane - Google Patents

Abstract

PURPOSE: To produce a porous membrane not locally having parts reduced in the number of pores and having high fluid transmission velocity by bringing gas into contact with the inner and outer surfaces of a hollow yarn precursor in a molten state extruded from a hollow yarn nozzle using the gas as a core agent. CONSTITUTION: At first, according to a known melt spinning method, gas is used as a core agent to extrude a crystalline thermoplastic polymer, for example, poly-4-methylpentene-1 from a hollow nozzle in a hollow yarn shape. Next, the gas is brought into contact with the inner and outer surfaces of the hollow yarn precursor in a molten state immediately after extruded from the hollow yarn nozzle by emitting gas (a) from the gas emitting orifice 1 provided to the inside of a thermoplastic polymer emitting orifice 2. By bringing the gas into contact with the outer surface of the hollow yarn, gas (b) is emitted from the gas emitting orifice 3 provided to the outside of the thermoplastic polymer emitting orifice 2. At this time, the gases (a), (b) are composed of gases not reacting with the thermoplastic polymer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hollow fiber porous membrane by melt-spinning a crystalline thermoplastic polymer into a hollow fiber and then stretching (hereinafter referred to as a melting method). The hollow fiber porous membrane produced by the present invention is a dissolved oxygen from the medical field such as microfiltration membrane, ultrafiltration membrane, membrane oxygenator, dialysis membrane for artificial kidney, boiler water, ultrapure water for semiconductor production, etc. It is used in the fields of degassing from liquids such as the removal of substances, dissolving gas in liquids, and supporting composite membranes.

[0002]

2. Description of the Related Art As a method for manufacturing a hollow fiber porous membrane by a melting method, for example, JP-A-59-199808 is known. In the melt spinning step of these methods, air is usually used as a cooling gas when cooling and solidifying the molten resin extruded from the nozzle, and the cooling gas is
It simply blows air around the molten resin. Further, the hollow fiber shape is stably maintained by melting and extruding a gas as a core agent from a nozzle, and air or nitrogen has been used as the core agent gas. In the prior art, the selection of these gases is arbitrary, and there is no mention of the effect of the type of gas on the membrane structure.

[0003]

A hollow fiber porous membrane is a membrane having a large number of pores communicating from one surface of the hollow fiber to the other surface, and in order to obtain a high fluid permeation rate, Must be formed uniformly so that there are no locally small numbers of pores. However, when observing the porous membrane manufactured under the conditions that have been earnestly studied in the prior art with an electron microscope, it was insufficient in terms of manufacturing technology such as the confirmation of a portion having a small number of pores. Therefore, the problem to be solved by the present invention is to produce a porous membrane having a high fluid permeation rate without locally having a small number of pores.

[0004]

Means for Solving the Problems As a result of intensive investigations by the present inventors on the formation mechanism of a hollow fiber porous membrane by the melting method, it was found that a hollow fiber precursor in a molten state immediately after being extruded from a nozzle was melted. It has been found that when the surface comes into contact with an oxidizing gas such as oxygen, it is oxidized to form a portion having a small number of pores, and the present invention has been completed.

That is, the essence of the present invention is to bring the hollow fiber precursor in a molten state into a uniform and stable contact with the inner and outer surfaces of the hollow fiber precursor and a non-reactive gas. The gist of the present invention is a method for producing a hollow fiber porous membrane by melt spinning, in which a crystalline thermoplastic polymer is extruded into a hollow fiber shape from a hollow fiber nozzle using a gas as a core agent, and then stretched to form a hollow fiber porous membrane. Gas (a) from a gas discharge port (A) provided inside the discharge port of the crystalline thermoplastic polymer, and a gas discharge port (B) provided outside the discharge port of the crystalline thermoplastic polymer
The gas (b) is discharged from the above, the gas (a) is brought into contact with the inner surface and the gas (b) is brought into contact with the outer surface of the extruded hollow fiber precursor in a molten state, and the gas (a) and the gas ( A method for producing a hollow fiber porous membrane is characterized in that b) is a gas that is non-reactive with the crystalline thermoplastic polymer.

The present invention will be described in more detail below. The hollow fiber porous membrane obtained by the production method of the present invention is a hollow fiber membrane having pores communicating from one surface of the hollow fiber to the other surface.

The crystalline thermoplastic polymer used in the present invention preferably has an ultimate crystallinity of 30% or more in order to produce a porous film having excellent performance. Further, in the case where the crystalline thermoplastic polymer used in the present invention has a high crystal melting point or shows oxidative decomposition by oxygen,
The present invention is more effective.

Examples of crystalline thermoplastic polymers include polyolefins such as polyethylene, polypropylene, poly-4-methylpentene-1 and poly-3-methylbutene-1, chlorine-containing polymers such as polyvinylidene chloride, and polyfluorinated polymers. Fluorine-containing polymers such as vinylidene, polyacetators
, Polyoxyethylene, polyphenylene oxide and other polyethers, polymethylene sulfide, polyethylene sulfide and other polythioethers, nylon 6,
Examples thereof include polyamide such as nylon 66, polyester such as polyethylene terephthalate, polystyrene, and the like. Of course, these copolymers may be used.

Among these, poly-4-methylpentene-
Homopolymer of 1 and poly-4-methylpentene-such as a copolymer containing 50% by weight or more of 4-methylpentene-1.
The 1-based polymer is preferable because it has a high ultimate crystallinity and is more easily oxidized than oxygen. Examples of preferred copolymerization components of the copolymer containing 50% by weight or more of 4-methylpentene-1 include ethylene, propylene, butene-1, isobutylene, pentenes, hexenes, and other α-olefins.

In the method for producing a hollow fiber porous membrane of the present invention, first, a crystalline thermoplastic polymer as described above is extruded into a hollow fiber form from a hollow fiber nozzle by using a gas as a core agent according to a known melt spinning method. . Next, gas is brought into contact with the inner surface and outer surface of the molten hollow fiber precursor immediately after being extruded from the hollow fiber nozzle. In the present invention, contacting the gas on the inner surface of the hollow fiber means that the gas (a) is discharged from the gas discharge port (A) provided inside the discharge port of the crystalline thermoplastic polymer.
Is discharged. The contact of the gas with the outer surface of the hollow fiber is performed by discharging the gas (b) from the gas discharge port (B) provided outside the discharge port of the crystalline thermoplastic polymer. At this time, the gas (a) and the gas (b) need to be gases that are non-reactive with the crystalline thermoplastic polymer.

The position of the gas discharge port (A) is not limited as long as it is provided inside the discharge port of the crystalline thermoplastic polymer, and the shape is not limited. A slit-like shape along a concentric circle may be mentioned inside the polymer discharge port. Further, the gas (a) discharged from the gas discharge port (A) can also serve as the core agent in the melt spinning, and in this case, the core agent gas discharge port of the hollow fiber nozzle is the gas discharge port ( It is more preferable because it becomes A) and the structure of the hollow fiber nozzle can be simplified.

The gas discharge port (B) is installed outside the discharge port of the crystalline thermoplastic polymer, and is located on the outer surface of the hollow fiber precursor in a molten state with respect to the fiber direction of the hollow fiber. The position is not particularly limited as long as the gas (b) is brought into uniform contact with the entire melted portion, but the gas (b)
In consideration of economic efficiency such as the amount of use of the gas, it is installed at a point where the hollow fiber precursor in a molten state solidifies, that is, a position where the gas (b) is brought into contact only with the molten portion between the nozzle and the solidification point. Is preferred.

Further, the gas discharge port (B) is preferably provided in the vicinity of the discharge port of the crystalline thermoplastic polymer in the circumferential direction of the hollow fiber, so that the gas (b) can be more uniformly and surely supplied. In order to bring it into contact with the outer surface of the body, the position within 50 mm from the outermost discharge port of the crystalline thermoplastic polymer is preferable, and more preferably within 10 mm.
The gas outlet (B) may or may not be integrated with the hollow fiber nozzle as long as the gas (b) can be brought into uniform contact with the outer surface of the hollow fiber precursor. As an example which is not integrated with the nozzle, a gas discharge part having a discharge port toward the outer surface of the hollow fiber precursor is provided on the concentric circle of the discharge port of the crystalline thermoplastic polymer provided in a circular shape (see FIG. 1). ) Is installed directly below the hollow fiber nozzle, and its discharge port is a gas discharge port (B).
As an example, an example in which the gas (b) is discharged is given. Here, the shape of the gas discharge port (B) is, for example, a slit shape,
It may be porous or the like and is not particularly limited.

In order to install the gas discharge port (B) close to the discharge port of the crystalline thermoplastic polymer in the circumferential direction of the hollow fiber, the gas discharge port (B) is integrated with the hollow fiber nozzle. Preferably. When a plurality of crystalline thermoplastic polymer discharge ports are provided in one hollow fiber nozzle, use of a hollow fiber nozzle integrated with a gas discharge port (B) that does not require alignment or the like. Is preferred. As the gas discharge port (B) integrated with the hollow fiber nozzle, for example,
In the hollow fiber nozzle in which the gas discharge port (A) (also serving as the core discharge port) and the discharge port of the crystalline thermoplastic polymer are circular, the outside of the discharge port of the crystalline thermoplastic polymer (the crystalline thermoplastic polymer) is used. In the case where the combined ejection ports have a plurality of layers of two or more layers, a circular slit provided on a concentric circle of the outermost ejection port) can be used as the gas ejection port (B). Hereinafter, such a nozzle will be referred to as a triple or more multi-annular nozzle.

The shape of the gas outlets (B) in the triple or more multi-annular nozzles is not particularly limited, but for example, a shape in which all the outlets are installed flush with the nozzle surface (second) (Fig.) A shape in which the outer peripheral portion of the discharge port is projected from the nozzle surface to cover all or part of the hollow fiber precursor in a molten state (Fig. 3), and the gas discharge port (B) is a crystalline thermoplastic resin rigid body discharge. The shape installed discontinuously around the exit (4th
(Fig. 5) and the like.

In the present invention, the gas (a) discharged from the gas discharge port (A) and the gas (b) discharged from the gas discharge port (B) are gases that are non-reactive with the crystalline thermoplastic polymer. Must be The gas that is non-reactive with the crystalline thermoplastic polymer may be any substance that does not oxidize the crystalline thermoplastic polymer, such as oxygen and ozone, unless it is an oxidizing gas, for example, nitrogen, Non-oxygen gas such as carbon dioxide and argon can be used. It may be a mixture of these gases. The non-oxygen gas as used herein may be any one that does not oxidize the crystalline thermoplastic polymer under melt spinning conditions, and varies depending on the polymer, the type of oxidizing gas, and the like.
It is preferable that the concentration of the oxidizing gas such as oxygen is 1 mol% or less. In the present invention, nitrogen is the most preferable non-oxygen gas from the viewpoint of cost.

In the melt spinning step in the present invention, the gas discharge port (A) provided inside the discharge port of the crystalline thermoplastic polymer.
(A) and the gas (b) from the gas discharge port (B) provided outside the discharge port of the crystalline thermoplastic polymer, and the inner surface of the extruded hollow fiber precursor in a molten state. To a gas (a), the outer surface is contacted with the gas (b), and the gases (a) and (b) are gases that are non-reactive with the crystalline thermoplastic polymer. This is the same as the melt spinning step of the method for producing a hollow fiber porous membrane, and the optimum conditions suitable for the purpose can be selected.

As melt spinning conditions, the temperature of melt extrusion is not lower than the crystal melting point (Tm) of the crystalline thermoplastic polymer, preferably (Tm + 20) ° C. to (Tm + 200) ° C.
And the draft is 50 to 10,000, preferably 20.
It is 0-1500. At this time, melt spinning is performed while flowing the gas (a) inside the hollow fiber.

The hollow fiber after melt spinning is cooled in a gas. Cooling of the molten hollow fiber precursor until reaching the solidification point is performed by the gas (b) discharged from the gas discharge port (B) provided outside the discharge port of the crystalline thermoplastic polymer. Cooling after solidification is performed by applying cooling air in the same manner as the known melt spinning method. The cooling condition is that the solidification point of the extruded hollow fiber is 5 to 200 mm from the nozzle,
It is preferably adjusted to 10 to 50 mm. From the economical viewpoint, it is most preferable to use air as the cooling air.

The discharge rates of the gas (a) and the gas (b) are
It may be appropriately prepared depending on the type of gas used, the size of the hollow fiber membrane to be produced, the type of polymer used, and the like. The process for producing a porous membrane after melt spinning in the present invention is the same as in the case of a known method for producing a melt-processed porous membrane.

The melt-spun hollow fiber is optionally heat-treated in order to increase the crystallinity of the crystalline thermoplastic polymer and reduce crystal defects. The heat treatment temperature is not less than the glass transition point (Tg) of the crystalline thermoplastic polymer and not more than the crystalline melting point (Tm) of the crystalline thermoplastic polymer.

The melt-spun hollow fibers or the melt-spun and heat-treated hollow fibers are stretched to make them porous.
Plate crystals grown by melt spinning at right angles to the fiber direction of the hollow fiber are regularly stacked. By stretching this, the laminated plate crystals are cleaved to form a porous body.

The stretching conditions are not particularly limited, and optimum conditions suitable for the purpose can be selected. For example, if the stretching temperature is (Tm-10) ° C or lower, it can be arbitrarily set according to the purpose, and the stretching ratio is preferably 1.3 to 6 times,
4 times is more preferable. Further, the stretching may be multi-stage stretching. In this case, the stretching ratio in each stage is preferably 1.1 times or more, and the stretching ratio in total is 1.3 to 6. It is preferably double and more preferably 2 to 4 times.

The hollow fiber porous membrane after stretching is preferably heat-set in order to impart dimensional stability and heat resistance.
The heat setting temperature is preferably Tg or more and Tm or less of the crystalline thermoplastic polymer and higher than the stretching temperature, and the relaxation ratio is preferably lower than 1 time, and 0.7
It is more preferably 5 to 0.95 times.

The dimension of the formed hollow fiber porous membrane is not particularly limited, but it is preferable that the outer diameter is 0.1 to 3 mm and the thickness is 0.01 to 1 mm. In any of the porous membranes, the average pore diameter is 0.01 to 10 μm.
It is preferred that

[0026]

The present invention will be described in more detail with reference to the following examples. However, this does not limit the present invention. [Example 1] As a crystalline thermoplastic polymer, poly-4-methylpentene-1 (TP manufactured by Mitsui Petrochemical Industry Co., Ltd., TP)
X) is used, and a core agent discharge port (gas discharge port (A)) having a diameter of 1 mm is provided at the center, and an outer diameter of 6 mm is provided on the outer concentric circle.
It has a slit-shaped crystalline thermoplastic polymer outlet having an inner diameter of 3 mm, and further has an outer diameter of 10 mm on the outer concentric circle.
It has a slit shape with an inner diameter of 8 mm, the outer peripheral portion of which protrudes 20 mm from the nozzle surface, and has a gas discharge port (B) through which gas can be discharged and brought into contact with the outer surface of the molten hollow fiber precursor. Using a triple annular nozzle (Fig. 3),
Melt spinning was performed in a draft 700 at a spinning temperature of 270 ° C. At this time, nitrogen having a purity of 99.99% or more was introduced at 1 ml / min from the core agent discharge port, and nitrogen having a purity of 99.99% or more was supplied from the gas discharge port (B) at a flow rate of 0.1 m / sec. The air is discharged as a cooling air below this by 0.1
It was supplied by an air flow of m / sec. This melt-spun hollow fiber was continuously heat-treated in an air atmosphere at 200 ° C. for about 5 seconds, then drawn at a draw ratio of 2 times, and then relaxed to 0.8 times in an air atmosphere at 200 ° C. A hollow fiber porous membrane was produced by heat setting for about 2 seconds.

The obtained hollow fiber heterogeneous membrane has an outer diameter of about 25.
The inner diameter was 0 μm and the inner diameter was about 200 μm. Observation with a scanning electron microscope (hereinafter referred to as SEM) revealed that the inner and outer surfaces had a major axis of about 0.1 μm and a minor axis of about 0.04 μm.
m pores were opened on the entire surface, and pores with a diameter of 0.05 μm were densely present on the entire cross section of the hollow fiber cut obliquely. In addition, the peak of the pore size distribution measured by mercury porosimetry
The thickness was 0.041 μm. The nitrogen permeation rate of this hollow fiber membrane was 3 at a temperature difference of 25 ° C. and a pressure difference of 1 kgf / cm ² .
It was 8.5 [Nm ³ / m ² (external surface area), Hr].

[Example 2] Poly-4-methylpentene-1 (TPX, manufactured by Mitsui Petrochemical Co., Ltd.) was used as a crystalline thermoplastic polymer, and a core agent discharge port (gas) having a diameter of 1 mm was used at the center. A circular ring nozzle having a discharge port (A)) and a slit-shaped discharge port of the crystalline thermoplastic polymer having an outer diameter of 6 mm and an inner diameter of 3 mm is formed on the outer concentric circle. A gas discharge part (FIG. 1) having a cylindrical gas discharge port (B) having a diameter of 5.5 cm toward the surface and a thickness in the fiber direction of 10 cm is formed so that the slit of the annular nozzle and the discharge port are concentric. Was installed directly under the nozzle, and melt spinning was performed at a spinning temperature of 270 ° C. and a draft 700.
At this time, nitrogen having a purity of 99.99% or more was introduced at a rate of 1 ml / min from the core agent discharge port. Purity 9 from gas discharge port (B)
Discharge 9.99% or more of nitrogen with an air flow of 0.1 m / sec.
It was supplied by an air flow of m / sec. This melt-spun hollow fiber was continuously heat-treated in an air atmosphere at 200 ° C. for about 5 seconds, then drawn at a draw ratio of 2 times, and then relaxed to 0.8 times in an air atmosphere at 200 ° C. A hollow fiber porous membrane was produced by heat setting for about 2 seconds.

The obtained hollow fiber heterogeneous membrane has an outer diameter of about 25.
The inner diameter was 0 μm and the inner diameter was about 200 μm. Observation with a scanning electron microscope (hereinafter referred to as SEM) revealed that the inner and outer surfaces had a major axis of about 0.1 μm and a minor axis of about 0.04 μm.
m pores were opened on the entire surface, and pores with a diameter of 0.06 μm were densely present on the whole cross section of the hollow fiber cut obliquely. In addition, the peak of the pore size distribution measured by mercury porosimetry
The thickness was 0.051 μm. The nitrogen permeation rate of this hollow fiber membrane was 4 at 25 ° C. and a pressure difference of 1 kgf / cm ² .
It was 0.3 [Nm ³ / m ² (external surface area), Hr].

[Comparative Example 1] A core material discharge port having a diameter of 1 mm is provided at the center, and an outer diameter of 6 mm and an inner diameter of 3 mm are provided on the outer concentric circles.
Nozzle having a slit-shaped crystalline thermoplastic polymer discharge port is used, nitrogen with a purity of 99.99% or more is introduced at 1 ml / min from the core agent discharge port, and air is used as cooling air for hollow fibers and hollow fibers. A hollow fiber heterogeneous membrane was produced in the same manner as in Example 1 except that air was blown around the yarn precursor.

The obtained hollow fiber heterogeneous membrane has an outer diameter of about 25.
The inner diameter was 0 μm and the inner diameter was about 200 μm. When observed by a scanning electron microscope (hereinafter referred to as SEM), pores having a major axis of about 0.1 μm and a minor axis of about 0.04 μm are opened on the entire surface, and a major axis of about 0.15 μm is formed on the outer surface. A large number of pores having a minor axis of 0.05 μm were present, but a portion where no pores were present was observed. Moreover, pores having a diameter of 0.05 μm were densely present on the entire cross section of the hollow fiber cut obliquely. The nitrogen permeation rate of this hollow fiber membrane was 25 ° C,
18.4 [Nm ³ / m at a pressure difference of 1 kgf / cm ^2
2 (outer surface area), Hr].

[0032]

EFFECTS OF THE INVENTION It is possible to prevent the formation of a portion having a small number of locally formed pores on the surface of a hollow fiber porous membrane and to stably produce a porous membrane having a high fluid permeation rate.

[Brief description of drawings]

FIG. 1 shows a gas discharge part having a cylindrical gas discharge port (B).

FIG. 2 is a triple annular nozzle in which a gas discharge port (B) is installed flush with the nozzle surface.

FIG. 3 is a triple annular nozzle in which the outer peripheral portion of the discharge port projects from the nozzle surface.

FIG. 4 shows a triple annular nozzle in which gas discharge ports (B) are discontinuously installed.

FIG. 5 shows a triple annular nozzle in which gas discharge ports (B) are discontinuously installed.

[Explanation of symbols]

 1 Gas Discharge Port (A) 2 Crystalline Thermoplastic Polymer Discharge Port 3 Gas Discharge Port (B)

Claims (6)

[Claims] 1. A melt-spinning process in which a crystalline thermoplastic polymer is extruded into a hollow fiber shape from a hollow fiber nozzle using a gas as a core agent,
A method for producing a hollow fiber porous membrane by stretching, comprising supplying a gas (a) from a gas discharge port (A) provided inside a discharge port of a crystalline thermoplastic polymer to a crystalline thermoplastic polymer. The gas (b) is discharged from the gas discharge port (B) provided outside the combined discharge port, and the gas (a) is discharged to the inner surface of the extruded hollow fiber precursor in the molten state and the gas (b) is discharged to the outer surface. b) is brought into contact, and the gas (a) and the gas (b) are gases that are non-reactive with the crystalline thermoplastic polymer. 2. The method for producing a hollow fiber porous membrane according to claim 1, wherein the gas discharge port (B) is provided at a position within 50 mm from the outermost discharge port of the crystalline thermoplastic polymer. . 3. The method for producing a hollow fiber porous membrane according to claim 2, wherein a nozzle in which the ejection port for the crystalline thermoplastic polymer and the gas ejection port (B) are integrated is used. 4. The method for producing a hollow fiber porous membrane according to claim 3, wherein the nozzle is a triple or more multi-annular nozzle. 5. The method for producing a hollow fiber porous membrane according to claim 1, wherein the gas that is non-reactive with the crystalline thermoplastic polymer is nitrogen. 6. The method for producing a hollow fiber porous membrane according to claim 1, wherein the crystalline thermoplastic polymer is a 4-methylpentene-1 type polymer.