JPH02164428A - Polysulfone hollow fiber separation membrane - Google Patents

Abstract

PURPOSE:To obtain a membrane of high fraction molecular weight having inner and outer dense layers of highly reliable fraction by providing pores with an average diameter of 100Angstrom -0.5mum on both inner and outer surfaces and forming a cross section relative to the longitudinal direction of a hollow fiber into a five-layer construction. CONSTITUTION:A hollow dense membrane of polysulfone resin which has pores with an average pore diameter of 100Angstrom -0.5mum on both the inner and outer surfaces and a cores section, relative to the longitudinal direction of hollow fiber, of which is comprised of a five-layer construction comprising an inner- surface dense layer, inner side void layer, intermediate sponge layer, outer side void layer, and outer-surface dense layer is obtained. Since the hollow fiber membrane has the most dense construction in which pores are formed on both the inner and outer surfaces, while strength of the membrane is maintained by the intermediate sponge layer and water permeability of the membrane is improved by both the inner and outer void layers, a membrane of high fractional molecular weight having inner and outer dense layers of highly reliable fraction can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a hollow fiber separation membrane made of polysulfone resin.

(Prior Art) Polysulfone resins are excellent in heat resistance, chemical resistance, and safety, and various hollow fiber membranes made from them have been proposed in the past.

For example, JP-A-58-156018 discloses a hollow fiber ultrafiltration membrane having a five-layer structure consisting of an inner surface dense layer, an inner void layer, an intermediate layer, an outer void layer, and an outer surface dense layer. . Here, the dense layer means, in the cross section of the membrane,
Refers to the place where polymers are most densely assembled. The membrane disclosed in the publication has dense layers of comparable density on both the inner and outer surfaces.

That is, it has the characteristic that two layers having an ultrafiltration function exist in the cross section of one hollow fiber membrane.

In particular, the dense layer disclosed in the same publication consists of a collection of small polymer particles of about 0.01 μm, and the gaps between the particles are very narrow and densely packed near the inner and outer surfaces, and as the distance from the surface increases, the gap between the particles increases. At the same time, the particle size becomes thicker.Both the inner and outer surfaces are smooth, and in a scanning electron microscope,
It is stated that the existence of such pores is not recognized, and that the pore size is estimated to be 10 to 100 people.

The film disclosed in the publication has the same degree of density in both the inner and outer surface dense layers, so even if a defect occurs on the inner surface,
Since the dense layer on the outer surface prevents the permeation of solutes, the molecular weight fraction remains unchanged and the reliability of the fractionation is high.

For example, even if the inner or outer surface of this membrane is scratched or rubbed with something like a needle, the permeation inhibition rate of solutes such as dextran and proteins often remains unchanged. In a membrane having a dense layer only on the inner surface, as seen in Japanese Patent Publication No. 50-22508, if the inner surface is scratched, the solute permeation rejection rate will be greatly reduced, so it is especially difficult to use for pharmaceutical water. The double-sided dense layer is an extremely important feature in the field of producing water using membranes, such as water for injection, which must never be contaminated with bacteria, pyrogene, etc.

Furthermore, it provides the advantage of sharp fractionation even in general applications.

On the other hand, membranes with dense layers on the inner and outer surfaces so dense that no pores are observed under an electron microscope have the drawback that not only do they not have high water permeability, but they also cannot provide membranes with a high molecular weight cut-off. There is.

(Problems to be Solved by the Present Invention) The present invention provides a membrane having dense layers on both inner and outer surfaces with high reliability in fractionation and having a high molecular weight cut-off.

(Means for Solving the Problems) The hollow fiber membrane made of the polysulfone resin of the present invention has pores with an average pore diameter of 100 Å to 0.5 μm on the inner and outer surfaces, and has pores in the longitudinal direction of the hollow fibers. The cross section of the membrane has a five-layer structure consisting of (a) inner surface dense layer, (b) inner void layer, (c) intermediate sponge layer, (d) outer void layer, and (e) outer surface dense layer. It is characterized by the fact that

FIG. 1 is an electron microscope cross-sectional photograph of the membrane of Example 2 of the present invention. It can be seen that the cross section of the membrane shows a five-layer structure consisting of an inner surface dense layer, an inner void layer, an intermediate sponge layer, an outer void layer, and an outer surface dense layer.

Figure 2 is an electron micrograph of the outer surface of the same membrane.
It was observed that there were about 1000 holes in diameter.

Figure 3 is an electron micrograph of the inner surface of the same membrane.
It is observed that there are approximately 1000 holes with an equivalent circle diameter.

As shown in Figures 2 and 3, both the inner and outer surfaces of the membrane are
They have pores of similar size.

Furthermore, the pores are sufficiently smaller than those in the inner and outer void layers and the sponge part of the intermediate layer shown in Figure 1, so both the inner and outer surfaces have the most dense structure in the entire membrane cross section. Similar to the membrane disclosed in Japanese Patent No. 58-156018, it provides fractionation reliability to the membrane.

The dense layers on both the inner and outer surfaces of the membrane of the present invention preferably have a certain thickness for this purpose. In order to further improve the reliability of the fractionation, it is preferable that the void layer has a thickness of 1 to 20%, preferably 3 to 10%, of the entire film thickness for both the inside and outside, even at its thinnest point from the tip to the surface. However, if it exceeds 15%, water permeability may be impaired.

In addition, in this application, the strength of the membrane is maintained by the intermediate sponge layer, and the water permeability of the membrane is improved by both the inner and outer void layers, and pores are formed on both the inner and outer surfaces, so it has a high molecular weight fraction and good water permeability. A film with properties can be obtained. The thickness of the intermediate sponge layer is preferably 1 to 20% of the total thickness from the viewpoint of strength and water permeability. More preferably, it is 3 to 10%.

The pores on both the inner and outer surfaces of the membrane with an average pore diameter of 100 Å to 0.5 μm refer to pores in which the average diameter of a circle having the same area as the pore observed with a scanning electron microscope is larger than 100 and 0.5 μm or less. Mainly, the presence of pores larger than 0.5 μm on the inner and outer surfaces is unfavorable in terms of strength.

The average pore diameter is preferably in the range of 500 Å or more and 0.5 μm from the viewpoint of high molecular weight cut-off and reliability.

The polysulfone resin has a repeating unit given by any of the following formulas (1) to (III).

υ These polymers have excellent heat resistance and PH resistance, and have the characteristics of being compatible with steam sterilization, which is essential in the medical field.

Next, an example of the method for manufacturing the polysulfone hollow fiber membrane of the present invention will be described.

In the present invention, a dry-wet spinning method is preferably used in which a spinning solution in which a polymer is dissolved is discharged from an annular nozzle, travels through the air, and is then coagulated in a coagulation bath to produce a hollow fiber membrane. In this dry-wet spinning membrane manufacturing method, in the process of extruding a spinning dope consisting of a polysulfone resin, a solvent, and a nonsolvent from an annular nozzle into a coagulation bath to form a hollow fiber membrane, (i) the polymer concentration is 10 to 30 (ii) The weight ratio of nonsolvent/(solvent/nonsolvent) is 50 to 90% of the weight ratio at the compatibility limit, and (in) 40 to 90% by weight as the internal coagulation liquid. It is characterized by using an aqueous solution of glycols.

As the solvent in the stock solution in this method, aprotic polar organic solvents such as N-methyl 2-pyrrolidone, dimethylacetoacetamide, and dimethylformamide are preferably used. In addition, as non-solvents in the stock solution, glycols such as polyethylene glycol and polypropylene glycol,
Although electrolytes, polyvinylpyrrolidone, etc. can be used, glycols are preferred from the viewpoint of spinnability and provide a good membrane.

The polymer concentration in the stock solution is 10-30% by weight, preferably 15-25% by weight. This value is particularly related to the strength of the hollow fiber membrane obtained.

The weight ratio of solvent/nonsolvent is set so that the weight ratio of nonsolvent/(solvent+nonsolvent) takes a value within the range of 50 to 90% of the weight ratio at the compatibility limit.

The compatibility limit is the point at which a polymer solution can become a homogeneous solution.
Refers to the point of phase separation. Since it is generally a function of temperature, it is necessary to find the compatibility limit at the spinning temperature.

If it is less than 50%, the viscosity of the stock solution will be low and the spinnability will be poor, or the cross section of the resulting hollow fiber membrane will not have a five-layer structure. When it is more than 90%, the cross section of the hollow fiber membrane obtained often does not have a five-layer structure.

Glycols used in the internal coagulation liquid include ethylene glycol, diethylene glycol, triethylene glycol,
Tetraethylene glycol, average molecular weight 200-600
It is preferable to use at least one type of polyethylene glycol, propylene glycol, dipropylene glycol, and tripropylene glycol. High molecular weight glycols have high melting points and water solubility decreases as the molecular weight increases, so it may be difficult to obtain spinning stability, especially when the glycol concentration in the internal coagulation solution increases. .

Among these, tetraethylene glycol has excellent spinning stability and
Most preferred due to the variability of membrane performance.

The composition of the internal coagulation liquid is 40 to 90% by weight of glycols.
It is preferable that it is an aqueous solution of.

If it is less than 40% by weight, it is difficult to maintain a balance between the pore sizes on the inner and outer surfaces of the hollow membrane, and the pores on the inner surface tend to become smaller.

On the other hand, at 90% or more, the water permeability may disappear. Moreover, the pores on the inner surface may become significantly larger than those on the outer surface, which is not preferable.

(Effects of the Invention) The hollow membrane of the present invention provides the reliability of fractionation, which is an essential requirement for a separation membrane, by providing dense layers with the same degree of density on both the inner and outer surfaces, compared to the conventional five-layer structure membrane. It is possible to significantly improve the low water permeability and small fractionated molecular weight, which had been disadvantageous, while taking advantage of the characteristics of It can be expected to make a significant contribution to water production and the purification of medically valuable substances.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples.

The physical properties of the membrane were shown in terms of water permeability, bursting strength, and dextran permeation rejection rate (representing the size of the molecular weight fraction).

In addition, the cross section, inner surface, and outer surface of the membrane were observed using a scanning electron microscope.

The measurement method for each physical property is shown below.

Water permeation 1 Cut the hollow fiber membrane into a length of 20 cm and cut it into pieces at a temperature of 25 cm from one end.
Inject pure water at ℃, remove air from the other end, and then seal.
Internal pressure filtration was performed at an average pressure of 1 atm, and the amount of filtrate was measured.
Calculate the water permeation amount per unit time and unit membrane inner surface area.

Cut the bifurcated hollow fiber membrane to 20CI, and add 1 liter of nitrogen from the openings at both ends.
kg/cd/5ecO pressure increase rate, and the pressure at which the hollow fiber membrane ruptures is defined as the bursting strength.

Dextran - Prepare a 5% by weight aqueous solution of dextran with a molecular weight of approximately 70,000 (Dextran T-70 manufactured by Pharmacia) in pure water at 25°C.

The hollow fiber membrane was cut into a length of 20 cm, and the aqueous solution was supplied into the hollow part so that the flow rate inside the hollow fiber membrane was 111 l/sec and the average filtration pressure was 1 arm.

The dextran concentration of the filtrate is read over time using a digital refractometer (■ Atago DBX-50).

From the maximum dextran concentration Cpmax of the filtrate and the raw aqueous solution concentration Co, the rejection rate R is determined by the following formula.

The smaller R is, the higher the molecular weight cutoff is.

Examples 1 to 4, Comparative Examples 1 and 2 Polysulfone (Udel-P3500 manufactured by U, C, C,
), 53 parts by weight of N-methyl-2-pyrrolidone (manufactured by Mitsubishi Kasei Ltd.), and 28 parts by weight of tetraethylene glycol (manufactured by Tokyo Kasei Ltd.) was obtained.

This spinning dope was extruded from an annular nozzle for manufacturing hollow fibers, passed through the air for 3c+a, and then coagulated in a coagulation bath to obtain a hollow fiber membrane.

At this time, water or a 30 to 90% by weight aqueous solution of tetraethylene glycol was used as the internal coagulation liquid, and water was used as the coagulation bath.

The spinning temperature was 30°C.

The results are shown in Table 1.

The compatibility limit of the polysulfone/N-methyl-2-pyrrolidone/tetraethylene glycol system at 30°C is 0.50 in terms of nonsolvent/(solvent+nonsolvent) when 20 parts by weight of polysulfone is used. The value in the stock solutions of Examples 1 to 4 was 0.35, which was 70% of the compatibility limit.

The inner surface of the membrane of Example 2 was injected with a 24G injection needle to a length of 1 cm.
When the throat was injured and evaluated, the dextran inhibition rate was 35%.

On the other hand, when similar evaluation was performed on the membrane of Comparative Example 1, the dextran rejection rate was reduced to 41%.

Margin Comparative Example 3: Polysulfone (U, C, C, 11def-P350)
0) A homogeneous polymer solution containing 17 parts by weight of N-methyl-2-pyrrolidone (manufactured by Mitsubishi Kasei ■), and 25 parts by weight of tetraethylene glycol (manufactured by Tokyo Kasei ■) was obtained.

This spinning stock solution was extruded from an annular nozzle for manufacturing hollow fibers, traveled 3 cm in the air, and then coagulated in a coagulation bath to obtain a hollow fiber membrane with an outer diameter of 1080 μm and an inner diameter of 59.0 μm.

At this time, water was used as the internal coagulation liquid and water as the coagulation bath.

The spinning temperature was 50°C.

This membrane has a water permeability of 0.65 (rrf/hr −rd
・atl++) is as high as that of Example 1.2, but the inhibition rate of dextran T-70 is as high as 65%, and the molecular weight cutoff is considered to be small.

Electron microscopic observation of this membrane revealed that the inner and outer surfaces of the membrane contained 100%
There were no holes that could reach humans, and the cross section had a five-layer structure, which is the membrane disclosed in Japanese Patent Application Laid-open No. 156018/1983.

[Brief explanation of the drawing]

FIG. 1 shows the cross-sectional structure of the hollow fiber of Example 2.
This is a double photo. FIG. 2 shows the structure of the outer surface of the hollow fiber of Example 2.
This is a 1,000x photo. FIG. 3 shows the structure of the inner surface of the hollow fiber of Example 2.
This is a 1,000x photo. Patent applicant: Asahi Kasei Industries, Ltd.

Claims (1)

[Claims] A hollow fiber membrane made of polysulfone resin, having pores with an average pore diameter of 100 Å to 0.5 μm on the inner and outer surfaces, and a cross section of the membrane in the longitudinal direction of the hollow fibers.
It is characterized by having a five-layer structure consisting of (a) inner surface dense layer, (b) inner void layer, (c) intermediate sponge layer, (d) outer void layer, and (e) outer surface dense layer. Polysulfone-based hollow fiber separation membrane