JPH04265132A - Manufacturing method of porous hollow fiber membrane - Google Patents

Abstract

PURPOSE:To produce a porous hollow fiber membrane preferably usable as a gas exchange membrane for an artificial lung preventing a leak of serum even after use for a long time and a gas separation membrane for oxygen enrichment. CONSTITUTION:A double-layered structure composed of thermoplastic resins of the same kind different from each other in mol.wt. is used to undrawn hollow fibers, and these fibers are drawn to produce a porous hollow fiber membrane having a double-layered structure composed of porous and dense layers.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for producing porous hollow fiber membranes for gas exchange and gas separation, and more specifically to gas exchange membranes used in oxygenators, gas separation membranes used in oxygen enrichment, etc. The present invention relates to a method for producing a porous hollow fiber membrane that can be suitably used for membranes.

0002

[Prior Art] A porous hollow fiber membrane made of thermoplastic resin having a structure in which a large number of micropores are formed in a hollow fiber is, for example, a filtration membrane used for water treatment, or a separation membrane used for plasma separation, etc. It is also used in various fields as gas exchange membranes used as artificial lungs.

[0003] As a method for producing such a porous hollow fiber membrane made of thermoplastic resin, for example, a thermoplastic resin material in which an easily soluble substance is mixed and dispersed is formed into hollow fibers, and then this easily soluble substance is mixed and dispersed in a solvent. A method is known in which a large number of micropores are formed in a hollow fiber by dissolving and removing it.

[0004] Furthermore, after forming a thermoplastic crystalline polymer material into hollow fibers, this is heat-treated and then stretched to create a porous body using a method of generating micropores in the hollow fibers. The method is also becoming popular.

The porous hollow fiber membrane obtained in this way and used as a gas exchange membrane for oxygenators has fine pores that are significantly larger than the gas molecules to be permeated, so that the volume flow is fine. pass through the hole. For example, various artificial lungs using porous hollow fiber membranes such as porous polypropylene membranes have been proposed.

[0006] Homogeneous membranes are also known as gas exchange membranes for oxygenators, and in this case, gas molecules passing through the membrane dissolve in the membrane and diffuse, thereby causing gas movement. A typical example of this is polydimethylsiloxane rubber, which has been commercialized. In addition, the gas contained in the membrane material
Gas separation membranes that take advantage of the differences in the degree of separation depending on the type of gas separation membrane are manufactured using a complicated wet spinning method.

[0007]

[Problems to be Solved by the Invention] Membrane type oxygenators using hollow fiber membranes are widely used as oxygenators used in open heart surgery and the like. Artificial lungs using conventional porous hollow fiber membranes have been used without problems for relatively short periods of time, such as during open heart surgery. However, when the oxygenator is used for a long period of time, such as in the treatment of lung failure, conventional oxygenators using porous hollow fiber membranes may have the problem of leakage of serum (plasma) from the pores. Ta.

[0008] In addition, gas separation membranes that utilize the difference in separation degree depending on the type of gas possessed by the membrane material require the layer for gas separation to be as thin as possible in order to increase its efficiency, and mechanical Porous layer (
A core layer) and a dense layer (skin layer) are required.
Traditionally, such membrane structures have been produced by complex wet spinning methods. Furthermore, in order to form both a porous layer and a dense layer as a hollow fiber membrane, it is necessary to control many manufacturing conditions, making the process complicated.

Therefore, the object of the present invention is to provide a gas exchange membrane for an oxygenator in which serum (plasma) does not leak from the pores even after long-term use, or to eliminate the difference in separation degree depending on the type of gas contained in the membrane material. It is an object of the present invention to provide a method for producing a porous hollow fiber membrane that can be preferably used in the gas separation membrane.

0010

[Means for Solving the Problems] That is, according to the present invention,
In a method for producing a porous hollow fiber membrane that includes a step of forming a large number of micropores by drawing hollow fibers made of thermoplastic resin, undrawn raw hollow fibers are mixed with a plurality of thermoplastic resins of the same type having different molecular weights. By creating a layered structure and then stretching this raw hollow fiber, the porous hollow fiber membrane has no pores, very few pores, or a layer in which pores with a smaller pore size than other porous layers exist. Provided is a method for producing a porous hollow fiber membrane characterized by the presence of at least one (dense layer).

The present invention will be explained in detail below. The inventors have discovered that when manufacturing porous hollow fiber membranes, porous membranes with different average pore diameters can be obtained in the subsequent stretching process even under the same stretching conditions, depending on the molecular weight of the raw hollow fibers. Heading: Previously filed (Japanese Unexamined Patent Publication No. 79806/1983). In other words, thermoplastic resins with larger molecular weights are made porous by stretching, compared to thermoplastic resins with smaller molecular weights.
This results in a porous membrane with a smaller average pore size.

[0012] In addition, in the method for producing a porous hollow fiber membrane, the inventors have discovered that the pore diameter changes depending on the stretching strain rate or stretching ratio when the stretching step is carried out at a predetermined temperature range (110°C to 155°C). Heading: Previously filed (Japanese Patent Application No. 59-268410).

[0013] Based on these findings, the present inventor conducted further experiments and studies, and found that the undrawn raw hollow fiber was multilayered with the same type of thermoplastic resin with different molecular weights, and the By controlling the stretching strain rate and stretching ratio during the stretching process within a predetermined temperature range (110°C to 155°C), the layer made of a thermoplastic resin with a small molecular weight becomes porous (porous layer). We discovered that a layer made of a thermoplastic resin with a large molecular weight is either non-porous or has small pores (dense layer) with only a small number of pores.
The present invention has been achieved.

The thermoplastic resin used in the present invention is not particularly limited, but includes, for example, polypropylene,
Examples include polyolefins such as polyethylene and poly(4-methyl-pentene-1), and thermoplastic resins such as polyvinylidene fluoride and ethylenetetrafluoroethylene copolymers.

Furthermore, when the molecular weight of the thermoplastic resin used is expressed in terms of melt viscosity, its melt viscosity {melt flow index (MFI) or melt index (MI
)} does not need to be particularly limited as long as it is within a range that allows spinning of hollow fibers. For example, when polypropylene is used, it is preferable to use polypropylene of 0.5 to 40 g/10 min in consideration of spinning efficiency and productivity of raw hollow fibers.

Among thermoplastic resins having such melt viscosities, thermoplastic resins having different melt viscosities (that is, different molecular weights) are used in combination in the present invention. In this case, the desired purpose cannot be achieved with a combination of materials with similar molecular weights (melt viscosity), so for example, when using polypropylene as the thermoplastic resin, MFI
It is preferable to use a combination with a difference of 1 to 35.

In the present invention, first, the above thermoplastic resin is spun using a multilayer hollow fiber nozzle to obtain an undrawn thermoplastic resin hollow fiber having a multilayer structure. A multilayer structure is a structure consisting of two or more layers, and the number of layers can be determined depending on the purpose and field of application. The layer ratio (ratio of layer thickness) can also be determined depending on the purpose, field of application, etc., and all combinations can be used, except when at least one layer is so thin that it cannot be molded. can.

In the present invention, as described above, since the multilayer structure can be completely controlled in advance at the stage of the hollow fiber, the multilayer structure of the hollow fiber membrane obtained after stretching can be completely controlled. Can be done.

When polypropylene hollow fibers are used in the present invention, the above-mentioned polypropylene is first spun into undrawn polypropylene hollow fibers according to a known method for producing hollow fibers. For example, the spinning temperature may be higher than the temperature at which the thermoplastic resin used can be discharged and lower than the thermal decomposition temperature of the thermoplastic resin. When polypropylene is used as the thermoplastic resin, the spinning temperature may be, for example, higher than the temperature at which polypropylene can be discharged and lower than the thermal decomposition temperature of polypropylene, and is usually 170 to 300°C.
Preferably it is 190-270°C.

[0020] When high-density polyethylene is used, the temperature is usually 150 to 300°C, preferably 160 to 300°C.
The temperature is 270°C. When poly(4-methyl-pentene-1) is used, the temperature is usually 260 to 330°C, preferably 270 to 300°C. When polyvinylidene fluoride is used, the temperature is usually 190 to 300°C, preferably 190 to 280°C. When using ethylenetetrafluoroethylene copolymer, usually 290
-350°C, preferably 190-280°C.

[0021] Next, the stretching step of the present invention may be carried out using a known method, such as a method of stretching in a specific temperature range in one stage or in multiple stages, for example, after stretching at around room temperature,
A method of further stretching in a temperature range of 0°C, a specific temperature range,
A method of stretching at a specific stretching strain rate or a stretching temperature of −100° C. or lower in a medium selected from the group consisting of nitrogen, oxygen, argon, carbon monoxide, methane and ethane,
In addition, a multilayer structure can be obtained by stretching in a specific temperature range and/or specific medium, or at a specific temperature range and/or specific stretching strain rate, such as a method of stretching at a temperature 50°C higher than the boiling point of the medium or less. A method for obtaining a thermoplastic resin is adopted as appropriate.

[0022] In this drawing step, at least one layer is non-porous, has very few pores, or has at least one layer (dense layer) in which pores have a smaller pore size than other porous layers. It is meant to encourage
Since the other layers are formed to form porous layers, it is necessary to set appropriate conditions for stretching. Therefore, for example, within a certain temperature range,
When adopting a method of stretching at a specific stretching strain rate, the stretching temperature, stretching ratio, and stretching strain rate are determined by the presence or absence of pores in one layer, the number of pores, the size of pores, and the average pore diameter and voids of other porous layers. In order to keep the rate as specified, it is necessary to set it appropriately.

For example, in the case of polypropylene, the stretching temperature is preferably 100 to 155°C. Furthermore, it is important to increase the porosity of the porous layer in order to improve the efficiency of gas exchange and gas separation. As for the stretching ratio, the porosity increases as the stretching ratio increases within a certain range, and is 50 to 400%, preferably 200 to 300% of the initial value.
It is. The porosity is 30 to 80%, preferably 6
It is 0-75%. Stretching at a stretching ratio exceeding 400% is not preferable because the hollow fiber diameter becomes thinner or the pore diameter becomes smaller.

[0024] The stretching strain rate is less than 20%/min, preferably less than 15%/min, more preferably less than 12%/min. In addition, in the present invention, for example, in the case of polypropylene, the raw hollow fiber is heated to 100 to 155
It is preferable to perform the heat treatment at a temperature in the range of 0.degree. C. in order to further grow the oriented crystallization of the original hollow fiber.

In addition, after the stretching process, for example in the case of polypropylene, the stretched hollow fibers are stretched at 100°C with tension applied.
It is preferable to perform the heat setting treatment at a temperature in the range of 155° C. to 155° C. since this prevents the drawn hollow fibers from shrinking due to heat.

In the porous hollow fiber membrane having a multilayer structure obtained as described above, the layer having a smaller molecular weight (that is, having a larger MFI or MI) becomes a porous layer, and the layer having a larger molecular weight (that is, having a larger MFI or MI) becomes a porous layer. A layer with a smaller MFI or MI is either non-porous or has very few pores, or a layer with pores smaller in diameter than other porous layers (a dense layer), and a composite layer consisting of a combination of the two. Exhibits a layered structure. Further, the layer ratio is completely controlled by the layer ratio in the multilayer structure during spinning of the unstretched thermoplastic resin. Therefore, at least one layer that is extremely thin, has no pores, has very few pores, or has pores with a smaller pore size than other porous layers can be present.

When the porous hollow fiber membrane obtained by the present invention is used for an oxygenator, at least one layer may be made non-porous; It is not necessarily necessary to make the layer non-porous, and the layer may have very few pores or may have pores smaller in diameter than other layers.

[0028] When the hollow fiber membrane is used for gas separation, it is preferable that at least one of the multiple layers is non-porous. When at least one layer is non-porous, it is desirable that the thickness of that layer be as thin as possible, 0.1 μm.
m to 20 μm, preferably 0.1 μm to 10
It is in the μm range.

[0029]

EXAMPLES The present invention will be further explained below based on Examples, but the present invention is not limited to these Examples.

(Example 1) Diameter 33mm, inner diameter 27mm
Polypropylene (product name: UB) with MFI of 30 g/min is used.
E-PP-J130G (manufactured by Ube Industries, Ltd.) as the inner layer,
Polypropylene with MFI of 9 g/min (product name: UBE-
PP-F109 (manufactured by Ube Industries, Ltd.) was used as the outer layer, the layer ratio (layer thickness ratio) between the outer layer and the inner layer was 9:1 (controlled by the amount of resin extrusion), the spinning temperature was 200°C, and the take-up speed was 116 m. The fibers were spun under the conditions of 1/2 min to obtain raw hollow fibers with a multilayer structure having an inner diameter of 230 μm and an outer diameter of 350 μm. Next, this raw hollow fiber was treated in an air heating tank at 163°C for 1 minute to partially melt the outer surface of the raw hollow fiber, and after cooling, it was drawn at a temperature of 135°C at a stretching ratio of 200 to the initial length. %, strain rate 11
．． A hollow fiber membrane was produced by stretching at 8%/min and heat-treating in a heated air bath at 150° C. for 2 minutes while maintaining the stretched state. The outer surface of the obtained hollow fiber membrane was completely non-porous, and the entire surface of the inner diameter portion of the hollow fiber was uniformly porous.

(Example 2) Diameter 33mm, inner diameter 27mm
Polypropylene (product name: UB) with MFI of 30 g/min is used.
E-PP-J130G (manufactured by Ube Industries, Ltd.) as the inner layer,
Polypropylene with MFI of 9g/min (product name: UBE-P
P-F109 (manufactured by Ube Industries, Ltd.) was used as the outer layer, and the layer ratio between the outer layer and the inner layer was 9:1 (controlled by the amount of resin extrusion), and spinning was performed at a spinning temperature of 200°C and a take-up speed of 116 m/min. A raw hollow fiber having an inner diameter of 230 μm and an outer diameter of 350 μm was obtained. Next, this raw hollow fiber was treated in an air heating tank at 163°C for 1 minute to partially melt the outer surface of the raw hollow fiber, and after cooling, it was drawn at a temperature of 135°C at a stretching ratio of 350 to the initial length. %, and a strain rate of 10.3%/min, and heat-treated in a heated air bath at 150° C. for 2 minutes while maintaining the stretched state to produce a hollow fiber membrane. The outer surface of the obtained hollow fiber membrane had a few small pores, while the entire surface of the inner diameter portion of the hollow fiber was uniformly porous.

[0032]

[Effects of the Invention] As explained above, according to the present invention,
Serum (plasma) does not leak from the pores even after long-term use.
In addition, a porous hollow fiber membrane having a multilayer structure of a porous layer and a dense layer and having excellent mechanical strength can be efficiently produced.

Claims (1)

[Claims] Claim 1. A method for producing a porous hollow fiber membrane, which includes a step of forming a large number of micropores by drawing hollow fibers made of thermoplastic resin, in which undrawn raw hollow fibers are subjected to homogeneous heat treatment with different molecular weights. By creating a multilayer structure made of plastic resin and then stretching this raw hollow fiber, the porous hollow fiber membrane can be made to have no pores, very few pores, or a pore size smaller than that of other porous layers. 1. A method for producing a porous hollow fiber membrane, comprising at least one layer having pores.