JPH0760081A - Production of hollow fiber membrane - Google Patents

Abstract

PURPOSE:To form a hollow fiber membrane having a composite layer consisting of a porous layer and a non-porous dense layer by stretching hollow fiber having a double-layered structure consisting of a layer composed of a homopolymer and a layer composed of a copolymer. CONSTITUTION:When a porous hollow fiber membrane is produced by a stretching method, the degree of the crystallization of raw hollow fiber largely exerts effect on the voids or shape and size of porous of the porous membrane. That is, a layer composed of a polymer high in the degree of crystallization becomes large in average pore size or voids as compared with a layer composed of a polymer low in the degree of crystallization. From this aspect, hollow fiber having a double-layered structure consisting of a layer composed of a homopolymer high in the degree of crystallization and a layer composed of a copolymer low in the degree of crystallization is obtained. When the raw hollow fiber is stretched, the layer composed of the homopolymer becomes a porous layer and the layer composed of the copolymer becomes a non-porous dense layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for easily and efficiently producing a hollow fiber membrane used for gas exchange in artificial lungs or gas separation in oxygen enrichment.

[0002]

2. Description of the Related Art A porous hollow fiber membrane in which a large number of fine pores are formed in a tubular wall of a hollow fiber made of a thermoplastic resin is, for example, a filtration membrane in water treatment or a separation membrane in plasma separation. Alternatively, it is used in various technical fields such as gas separation membranes in artificial lungs and the like. As a method for producing a porous hollow fiber membrane, for example, a resin in which an easily soluble substance is mixed and dispersed is molded into a hollow fiber, and then the easily soluble substance is dissolved and removed by a solvent to form a large number of fine pores in a tube wall. A well-known method is a method in which a hollow fiber is made of a thermoplastic crystalline resin, and the hollow fiber is heat-treated and then stretched to form a large number of fine holes in the tube wall.

Among various hollow fiber membranes, a porous hollow fiber membrane made of polypropylene is well known as a gas exchange membrane for artificial lungs. Since the fine pores of these polypropylene porous hollow fiber membranes are remarkably large as compared with the gas molecules that permeate, the gas permeates the fine pores as a volume flow. A homogeneous membrane is also well known as a gas exchange membrane for artificial lungs, and gas is transferred by dissolving and diffusing permeating gas molecules in the membrane. A typical example is a homogeneous film made of polydimethylsiloxane rubber,
It has been commercialized. Furthermore, there are also gas separation membranes that utilize the difference in the degree of separation depending on the type of gas that the membrane material has, and these are manufactured by an extremely complicated wet spinning method.

[0004]

Membrane-type artificial lungs using a porous hollow fiber membrane have been widely used as artificial lungs applied at the time of open heart surgery. Artificial lungs using these porous hollow fiber membranes have been used without any problems when used for a relatively short time such as during open-heart surgery. However, when the artificial lung is used for a long period of time as in the treatment of lung failure, there is a problem that plasma leaks from the micropores in the tube wall.

Further, in the gas separation membrane which utilizes the difference in the degree of separation depending on the kind of gas that the membrane material has, it is necessary to make the layer for gas separation as thin as possible in order to increase the gas separation efficiency, and It is also necessary to maintain mechanical strength, and a porous layer (core layer) and a dense layer (skin layer) are required. In order to manufacture such a membrane, a wet spinning method with complicated processes and complicated conditions must be adopted.

[0006]

A method for producing a hollow fiber membrane of the present invention is a method for producing a hollow fiber membrane, which comprises a step of forming a large number of fine holes in a tube wall by stretching a hollow fiber. It is characterized in that a hollow fiber having a multi-layer structure of a layer made of a united body and a layer made of a copolymer is drawn to make it porous.
By this production method, the homopolymer layer is made porous, and the copolymer layer is a layer having no pores or very few pores or a pore diameter smaller than that of the porous layer, that is, a dense layer, which is a multi-layer. A hollow fiber membrane is formed.

In the present invention, when a porous hollow fiber membrane is produced by a stretching method, the crystallinity of the raw hollow fiber strongly influences the porosity of the porous membrane or the shape and size of fine pores. It is based on the finding. That is, under the same stretching conditions, a layer made of a polymer having a high degree of crystallinity has a larger average pore diameter or porosity than a layer made of a polymer having a low degree of crystallinity. From this viewpoint, the hollow fiber has a multi-layer structure including a layer made of a homopolymer having a high crystallinity and a layer made of a copolymer having a low crystallinity. When such an original hollow fiber is stretched, the layer made of a homopolymer becomes an ordinary porous layer and the layer made of a copolymer becomes a dense layer having no pores.

In the case of the hollow fiber membrane for artificial lung, the dense layer may be non-porous, but it is not always required to be non-porous because of the balance between gas exchange capacity and plasma leakage. Further, in the case of a gas separation membrane, it is preferably non-porous. The dense layer is preferably as thin as possible when it has no pores, and is preferably in the range of 0.1 to 20 μ, more preferably 0.1 to 10 μ.

Examples of the homopolymer used as a material for forming the hollow fiber membrane include polyolefins such as low density polyethylene, high density polyethylene, polypropylene, and poly (4-methyl-pentene-1). Further, as the copolymer, ethylene-propylene copolymer, ethylene-acrylic acid ester copolymer, ethylene-vinyl acetate copolymer and the like are preferable. The molecular weight of the thermoplastic resin used is not particularly limited as long as it can be spun, but in consideration of the spinning efficiency and the productivity of the raw hollow fiber, for example, in the case of polypropylene, it is represented by a melt flow index of 0.5.
It is preferably about 40 g / 10 minutes.

Homopolymers such as polyethylene and polypropylene are usually polymers having high crystallinity, and their crystallinity is lowered by means of copolymerization or the like. It is impossible to greatly change the original crystallinity of the resin in the tube wall direction of the hollow fiber to such an extent that the porous structure is largely different depending on the spinning conditions such as spinning temperature, take-up speed, and draft. In the present invention, a hollow fiber having a multi-layer structure of a layer made of a homopolymer and a layer made of a copolymer can be easily obtained to obtain a hollow fiber having greatly different crystallinity in the tube wall direction.

The raw hollow fiber can be produced by a conventionally known method. The spinning temperature for obtaining a hollow fiber membrane having a desired structure varies depending on the type of thermoplastic resin, but for polypropylene, for example, it is usually 170 to 300 ° C., preferably 190.
~ 270 ° C, usually 150 ~ 30 for high density polyethylene
0 [deg.] C., preferably 160-270 [deg.] C., in the case of poly (4-methyl-pentene-1), it is usually in the range of 260-330 [deg.] C., preferably 270-300 [deg.] C., and their copolymers have almost the same temperature range or It can be spun in a rather low temperature range.

The multi-layer structure may be a multi-layer structure having two layers or more, and the ratio of layer thickness is not particularly limited, and may be appropriately determined depending on the purpose, application field and the like.

The raw hollow fiber may be stretched by a single-stage or multi-stage stretching in a specific temperature range, for example, a temperature range of several degrees Celsius to several tens of degrees Celsius lower than the melting point of the polymer after stretching at around room temperature. , 140-150 ℃ for polypropylene
Examples include a method of further stretching at a temperature, a method of stretching at a specific temperature range and a specific stretching strain rate, and the like. The conditions may be set as appropriate in consideration of the target pore diameter, porosity, or non-porous state of the dense layer.

As the stretching strain rate decreases, the pore size and porosity of the micropores increase. In order to obtain a hollow fiber membrane having a pore size and a porosity within a preferable range, the stretching strain rate is 20% / min or less, preferably 15% / min or less, more preferably 12%.
/ Min or less is preferable. It is also preferable to heat the raw hollow fiber before stretching, for example, in the temperature range of 100 to 155 ° C. for polypropylene. Further, after stretching, for example, with polypropylene, it is also preferable to perform heat setting treatment in a temperature range of about 100 to 150 ° C. while tension is applied to the hollow fiber.

Of the hollow fiber membrane obtained by the above method,
The porosity of the porous layer is preferably large in order to realize excellent gas exchange ability or gas separation ability. The porosity increases in proportion to the draw ratio within a practical draw ratio range. The draw ratio is preferably 50 to 400%, preferably about 200 to 300%, and the porosity corresponding to these draw ratios is about 30 to 80% and about 60 to 75%. If the draw ratio is too large to exceed 400%, the resulting hollow fiber may have a small diameter or a small pore size, which is not preferable.

[0016]

EXAMPLES The present invention will be described in detail below with reference to examples. Example 1 A polypropylene homopolymer [manufactured by Ube Industries, Ltd., MFI = 9 g / 10 min, density = 0.907 g /] was used by using a two-layer nozzle for producing a hollow fiber equipped with a gas supply pipe having a diameter of 33 mm and an inner diameter of 27 mm. cm ³ ] as an inner layer, and an ethylene-propylene copolymer [manufactured by Ube Industries, Ltd., MFI = 9 g /
10 minutes, density = 0.900 g / cm ³ ] as an outer layer, and the ratio of the inner layer to the outer layer was 1: 9, spinning was carried out at a spinning temperature of 200 ° C., a take-up speed of 116 m / min, an inner diameter of 230 μ, and an outer diameter of 35.
0 μ of raw hollow fiber was obtained. This raw hollow fiber was heat-treated in an air heating tank at 135 ° C for 1 minute, then at 135 ° C, strain rate 1
300% of the initial length was stretched under the condition of 1.8% / min, and the stretched state was maintained in a heated air tank at 150 ° C for 2
Heat treated for minutes. The thickness of the obtained hollow fiber membrane on the outer surface side of 6 μm was non-porous, and the other portions were porous. The average pore diameter of the porous layer was 80 μm, and the porosity was 65%.

[0017]

According to the method for producing a hollow fiber membrane of the present invention, the raw hollow fiber has a multi-layer structure of a layer made of a homopolymer and a layer made of a copolymer, and the raw hollow fiber having this multi-layer is formed. A hollow fiber membrane having a multilayer structure of a porous layer and a dense layer having no pores can be obtained by a very simple method of stretching. The obtained multi-layer hollow fiber membrane is a gas exchange membrane or

Claims (1)

[Claims] 1. A method for producing a hollow fiber membrane, which comprises the step of forming a large number of fine holes in a tube wall by stretching the hollow fiber,
A method for producing a hollow fiber membrane, which comprises making a hollow fiber having a multi-layered structure of a layer made of a homopolymer and a layer made of a copolymer to be porous by stretching.