JP2572895B2 - Manufacturing method of porous hollow fiber membrane - Google Patents

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 porous hollow fiber membrane for gas exchange and gas separation.
The present invention relates to a method for producing a porous hollow fiber membrane that can be suitably used for a gas exchange membrane used for an artificial lung or the like or a gas separation membrane used for oxygen enrichment or the like.

[0002]

2. Description of the Related Art A porous hollow fiber membrane made of a thermoplastic resin having a structure in which a number of micropores are formed in a hollow fiber is, for example, a filtration membrane used for water treatment or the like or a separation membrane used for plasma separation or the like. Alternatively, it is used in various fields as a gas exchange membrane used as an artificial lung.

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

Further, a method of forming a hollow body by forming a hollow fiber from a thermoplastic crystalline polymer material, forming a hollow fiber, heat-treating the hollow fiber, and then stretching the hollow fiber. Is also becoming more common.

[0005] The porous hollow fiber membrane obtained in this manner and used as a gas exchange membrane for an artificial lung has a very large pore compared to gas molecules to be permeated. Pass through the hole. For example, various artificial lungs using a porous hollow fiber membrane such as a porous polypropylene membrane have been proposed.

[0006] A homogeneous membrane is also known as a gas exchange membrane for an artificial lung. In this case, gas is transferred by dissolving and diffusing gas molecules passing through the membrane.
A typical example is polydimethylsiloxane rubber, which has been commercialized. In addition, gas separation membranes utilizing the difference in the degree of separation depending on the type of gas (gas) of the membrane material,
It is manufactured by a complex wet spinning method.

[0007]

As an artificial lung applied at the time of open heart surgery or the like, a membrane oxygenator using a hollow fiber membrane is widely used. A conventional artificial lung using a porous hollow fiber membrane has been used without any problem in a relatively short time such as in open heart surgery. However, when the artificial lung is used for a long time as in the treatment of lung failure, a conventional artificial lung using a porous hollow fiber membrane may have a problem in that the serum (plasma) leaks from the pores. Was.

Further, in a gas separation membrane utilizing a difference in the degree of separation depending on the type of gas (gas) of the membrane material, it is necessary to reduce the thickness of the layer for gas separation as much as possible in order to increase the efficiency, and it is also necessary to use a mechanical method. In order to maintain strength, a porous layer (core layer) and a dense layer (skin layer) are required. Conventionally, such a membrane structure is manufactured by a complicated wet spinning method. Further, in order to form both a dense layer and a porous layer as a hollow fiber membrane, it is necessary to control many production conditions, and the process becomes complicated.

Accordingly, an object of the present invention is to provide a gas exchange membrane for an artificial lung in which a serum does not leak from a hole even when used for a long time, or a gas utilizing the difference in the degree of separation depending on the type of gas contained in the membrane material. An object of the present invention is to provide a porous hollow fiber membrane that can be preferably used for a separation membrane.

[0010]

According to the present invention, there is provided a method for producing a porous hollow fiber membrane comprising a step of forming a large number of micropores by stretching a thermoplastic resin hollow fiber. After the original hollow fiber is spun, the outer surface of the original hollow fiber is partially melted, cooled and then stretched, so that the outer surface of the porous hollow fiber membrane has no or very few pores, A method for producing a porous hollow fiber membrane, characterized in that a dense layer having pores having a smaller diameter than the porous layer is present.

Hereinafter, the present invention will be described in detail. The present inventor has found that, when producing a porous hollow fiber membrane, if the orientation state of the raw thermoplastic resin hollow fiber is not good, the expression of porosity is poor in the subsequent stretching step, and from this viewpoint, The original hollow fiber having a good orientation state is manufactured, and only the outer surface has a poor orientation state, or the outer surface is partially melted to eliminate it, and then the hollow fiber is stretched to maintain the orientation state. The yarn part is made porous as before, but the outer surface part that is not oriented or poorly oriented is non-porous, or the number of holes is small even if it is open, and it is small Was found to be. The present invention has been completed based on this finding.

In the present invention, after the undrawn original hollow fiber is spun, the outer surface of the original hollow fiber is partially melted, and the partial melting temperature is decomposed above the melting point of the thermoplastic resin constituting the hollow fiber. Below the temperature, preferably below the melting point of the thermoplastic resin and below its decomposition temperature, and below the melting point and below 50 ° C.

The time of the treatment at the above-mentioned temperature depends on the balance with the treatment temperature, the thickness of the dense layer (skin layer), whether the dense layer is non-porous, the state in which the presence of pores is extremely small, the state of the porous layer ( Although it depends on whether or not the pore size is smaller than that of the core layer, it is preferably 0.5 seconds or more and 10 minutes or less. More preferably, it is 0.5 seconds or more and 5 minutes or less. When the treatment time is 0.5 seconds or less, the outer surface of the original hollow fiber is not preferable because the outer surface of the original hollow fiber is not partially melted and only nonporous or a small amount of pores can be formed. Are not preferred because they melt and melt.

In the stretching step of the present invention, a known method may be used. One or more stages of stretching in a specific temperature range, for example, after stretching near room temperature, 140 to 15
A method of further stretching in a temperature range of 0 ° C., a method of stretching at a specific stretching strain rate in a specific temperature range, or a stretching temperature in a medium selected from the group consisting of nitrogen, oxygen, argon, carbon monoxide, methane and ethane. Is a temperature of −100 ° C. or lower and a temperature of 50 ° C. or higher than the boiling point of the medium, such as a method of stretching, in a specific temperature range and / or in a specific medium, or in a specific temperature range and / or A method of stretching at a stretching strain rate to obtain a porous hollow fiber membrane made of a thermoplastic resin having a multilayer structure (a porous layer and a dense layer) is appropriately adopted.

It is important to increase the porosity of the porous layer (core layer) in order to improve the efficiency of gas exchange and gas separation. As the stretching ratio, the porosity becomes larger as the stretching ratio increases within a certain range, and is 50 to 400%, preferably 200 to 300%, with respect to the initial value.
The porosity is 30 to 80%, preferably 60 to 75%
%. Stretching at a draw ratio of more than 400% is not preferred because the hollow fiber diameter becomes thinner and the pore diameter becomes rather small.

When the porous hollow fiber membrane obtained by the present invention is used for an artificial lung, the dense layer may be made non-porous. Therefore, it is not always necessary to make the pores non-porous, and it may be in a state in which the number of pores is extremely small or in a state in which pores having a pore diameter smaller than that of the porous layer are present. When the hollow fiber membrane is used for gas separation, the dense layer is preferably non-porous.

The thickness of the dense layer of the porous hollow fiber membrane is desirably as thin as possible in the case of no pores, and is in the range of 0.1 μm to 20 μm, preferably in the range of 0.1 μm to 10 μm. Although the thermoplastic resin used in the present invention is not particularly limited, for example, polypropylene, polyethylene, polyolefin such as poly (4-methyl-pentene-1), polyvinylidene fluoride, ethylene tetrafluoroethylene copolymer and the like. Thermoplastic resins are exemplified.

When the molecular weight of the thermoplastic resin used is represented by the melt viscosity, the melt viscosity divided by the melt flow index (MFI) or the melt index (MFI)
I)｝ is not particularly limited as long as the hollow fiber can be spun. For example, in the case of using polypropylene, it is preferable to use a raw material of 0.5 to 40 g / 10 minutes in consideration of spinning efficiency and productivity of the original hollow fiber.

When a polypropylene hollow fiber is used in the present invention, a polypropylene having a predetermined melt viscosity as described above is spun in accordance with a known hollow fiber production method to obtain an undrawn polypropylene hollow fiber. For example, the spinning temperature may be higher than the temperature at which the thermoplastic resin to be used can be discharged and lower than the thermal decomposition temperature of the resin. When using polypropylene as the thermoplastic resin, the spinning temperature may be, for example, not less than a temperature at which the polypropylene can be discharged and not more than the thermal decomposition temperature of the polypropylene, and is usually 170 to
The temperature is 300 ° C, preferably 190 to 270 ° C.

When high-density polyethylene is used, it is usually 150 to 300 ° C., preferably 160 to 27 ° C.
0 ° C. When poly (4-methyl-pentene-1) is used, it is usually 260 to 330 ° C., preferably 27 to 330 ° C.
0-300 ° C. When using polyvinylidene fluoride, usually at 190 to 300 ° C., preferably 190 to 300 ° C.
280 ° C. When an ethylene tetrafluoroethylene copolymer is used, the temperature is usually 290 to 350 ° C, preferably 190 to 280 ° C.

In the present invention, before the drawing step, for example, in the case of polypropylene, the original hollow fiber is
It is preferable to perform the heat treatment at a temperature in the range of 好 ま し い 155 ° C. to further grow the oriented crystallization of the original hollow fiber. In addition, for example, in the case of polypropylene, it is preferable to perform a heat setting treatment at a temperature in the range of 100 to 155 ° C. while applying tension to the stretched hollow fiber after the stretching process, in order to prevent the heat shrinkage of the stretched hollow fiber.

In the porous hollow fiber membrane obtained as described above, the partially unmelted layer of the undrawn hollow fiber becomes a porous layer, and the partially melted layer of the undrawn hollow fiber is a dense layer. It has a multi-layered structure in which holes or extremely few holes are present, or a combination of layers in which holes having a smaller diameter than the porous layer are present. The layer ratio is controlled by the layer ratio in the multilayer structure due to the difference in the orientation of the undrawn hollow fiber due to the partial melting when the undrawn thermoplastic resin hollow fiber is partially melted.

In the present invention, the range of partial melting of the undrawn hollow fiber can be completely controlled, and layers having different orientations can be set as desired in advance at the stage of the original hollow fiber. The multilayer structure of the hollow fiber membrane obtained after stretching is also completely controlled.

[0024]

EXAMPLES The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.

(Example 1) Polypropylene (trade name: U
BE-PP-F109, manufactured by Ube Industries, Ltd., MFI = 9
g / 10 minutes) using a hollow fiber production nozzle equipped with a gas supply pipe having a diameter of 33 mm and an inner diameter of 27 mm, and a spinning temperature of 200
At a take-off speed of 116 m / min.
An original hollow fiber having an outer diameter of 350 μm was obtained. Next, the raw hollow fiber is treated in an air heating tank at 185 ° C. for 30 seconds to partially melt the outer surface of the raw hollow fiber, and after cooling, at a temperature of 135 ° C., a draw ratio of 300 to the initial length. %, Strain rate 8.
The film was stretched at 33% / 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 is completely nonporous, and the surface of the inner diameter portion of the hollow fiber has the same pore diameter as that produced when the outer surface of the original hollow fiber was not partially melted. Was. The porosity was 60%.

(Example 2) Polypropylene (trade name: U
BE-PP-F109, manufactured by Ube Industries, Ltd., MFI = 9
g / 10 min) using a hollow fiber production nozzle equipped with a gas supply pipe having a diameter of 33 mm and an inner diameter of 27 mm, and a spinning temperature of 200
At a take-off speed of 116 m / min.
An original hollow fiber having an outer diameter of 350 μm was obtained. Next, the raw hollow fiber is treated in an air heating tank at 170 ° C. for 30 seconds to partially melt the outer surface of the raw hollow fiber, and after cooling, at a temperature of 135 ° C., a draw ratio of 400 to the initial length. %, Strain rate 8.
The film was stretched at 33% / 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 number of pores on the outer surface of the obtained hollow fiber membrane was also reduced, and the pore diameter was considerably smaller than the pore diameter on the surface of the hollow fiber inner diameter portion (pore diameter before treatment). The surface of the hollow fiber inner diameter portion kept the state before the treatment. The porosity is 68
%Met.

[0029]

As described above, according to the present invention,
Even after prolonged use, the serum does not leak from the hole,
Further, a porous hollow fiber membrane having a multilayer structure of a porous layer and a dense layer and having a small layer thickness and excellent mechanical strength can be efficiently produced.

Claims (1)

(57) [Claims] In a method for producing a porous hollow fiber membrane comprising a step of forming a large number of micropores by stretching a hollow fiber made of a thermoplastic resin, an undrawn original hollow fiber is spun and then spun. By partially melting the outer surface of the hollow fiber and stretching it after cooling, the outer surface of the porous hollow fiber membrane has few or no pores on the outer surface, or pores having a smaller diameter than the porous layer are formed. A method for producing a porous hollow fiber membrane, wherein an existing dense layer is present.