JPH1057787A - Separating membrane and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart high pressure resistance to a separating membrane by an easy operation with high productivity without varying the performance by forming a film from a stock soln. contg. a vinyl alcohol polymer, washing the film and crosslinking the polymer by irradiation with electron beams. SOLUTION: A film is formed from a film forming stock soln. contg. a vinyl alcohol polymer, it is washed and the polymer is crosslinked by irradiation with electron beams to obtain the objective separating membrane. An ethylene- vinyl alcohol copolymer is suitable for use as the vinyl alcohol polymer as the material of the separating membrane used in the medical field because very little matter is leached from the polymer. At the time of irradiation with electron beams, a higher crosslinking effect is produced by irradiating the film in a wet state. It is therefore preferable that the film is washed to remove the solvent and the wet film is introduced into an irradiating device and irradiated with electron beams. The pref. water content of the film is about >=0.5wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a separation membrane and a method for producing the same, and more particularly, to a separation membrane made of a vinyl alcohol polymer having excellent pressure resistance and a method for producing the same.

[0002]

2. Description of the Related Art Membranes made of vinyl alcohol polymers have excellent hydrophilicity and are widely used for various separation membranes such as industrial and medical applications. For example, a film made of polyvinyl alcohol (hereinafter, abbreviated as a PVA film)
For filtration of sake (Japanese Patent Publication No. 2-8706), treatment of water (Japanese Patent Publication No. 58-20319), filtration of body fluids (Japanese Patent Publication No. 3-64150, Japanese Patent Publication No. 3-64150, etc.), etc. Or a membrane composed of an ethylene-vinyl alcohol copolymer (hereinafter, abbreviated as an EVA membrane) by hemodialysis (JP-B-61-30587).
Body fluid treatment (JP-B-63-11909, JP-B-3-
5208, JP-B-2-24576, JP-B-3-64150, etc.), and examples of application to various fields such as microfiltration and blood processing can be seen.

[0003] Such a PVA film or EVA film is usually subjected to a crosslinking treatment with a crosslinking agent for the purpose of imparting heat resistance, hot water resistance, dimensional stability, strength and the like. For example, JP-A-02-251231 discloses a method of cross-linking an EVA film using a silicon compound such as isocyanate trialkoxysilane, and JP-A-07-185278 discloses a method in which an EVA film is glutarized. A method of performing a crosslinking treatment with a crosslinking agent such as an aldehyde is disclosed.

[0004] In order to impart pressure resistance to various kinds of separation membranes, a crosslinking treatment by irradiation with ionizing radiation is also performed.
For example, Japanese Patent Publication No. Hei 8-29232 discloses a method of imparting pressure resistance by irradiating a microporous hollow fiber membrane made of polyethylene or a copolymer of ethylene and a halogenated olefin with cobalt 60γ ray and electron beam. ing.

[0005]

In the cross-linking of a separation membrane made of a vinyl alcohol polymer, the chemical cross-linking as described above is generally performed. However, in the cross-linking treatment using the above-mentioned cross-linking agent, the cross-linking treatment is carried out. It is necessary to add a step of removing the cross-linking agent later, and the cross-linking agent concentration and the processing temperature must be controlled during the cross-linking treatment, so that the operation is very complicated. On the other hand, it is also known to irradiate polyethylene or the like with γ-rays or electron beams. Because of the method of irradiation, continuity of production is lacking. Also, it is said that when the membrane is irradiated with an electron beam, the membrane shrinks due to cross-linking, thus causing a change in the pore size distribution and possibly causing a poor balance of the membrane performance. At present, electron beam irradiation is not applied to a separation membrane composed of a vinyl alcohol-based polymer having a large content.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and surprisingly, it is possible to control the balance of the film performance even when the vinyl alcohol polymer is irradiated with an electron beam. They have found that they have reached the present invention. That is, the present invention is a separation membrane made of a vinyl alcohol-based polymer crosslinked by electron beam irradiation. Further, another invention of the present invention comprises a vinyl alcohol-based polymer characterized by forming a film from a stock solution containing a vinyl alcohol-based polymer, washing the obtained film with water, and irradiating an electron beam. This is a method for producing a separation membrane.

The vinyl alcohol polymer used in the present invention refers to a polymer containing 30 mol% or more, preferably 50 mol% or more of a vinyl alcohol unit, such as a saponified product of a homopolymer of vinyl esters, ethylene,
Examples thereof include vinyl alcohol-based polymers (including random, block, and graft copolymers) containing vinyl monomer units such as propylene, acrylonitrile, vinyl chloride, and vinylpyrrolidone.

[0008] Among them, ethylene-vinyl alcohol copolymer is very suitable as a material for a separation membrane used in the medical field because it has very little eluted material. In particular, as a material for a separation membrane used for blood treatment such as hemodialysis and plasma separation, usually, the degree of polymerization is 80 or more, and
An ethylene-vinyl alcohol copolymer having a saponification degree of ６０60 mol% and a degree of saponification of 95 mol% or more is used. In addition, as such an ethylene-vinyl alcohol copolymer, for example, a copolymerizable polymerizable monomer such as methacrylic acid, vinyl chloride, methyl methacrylate, and acrylonitrile is copolymerized in a range of 15 mol% or less. Is also good.

In the present invention, first, a separation membrane is formed from a stock solution comprising a vinyl alcohol polymer and a solvent thereof according to a known method. The solvent is not particularly limited as long as it dissolves the vinyl alcohol-based polymer. For example, water, methanol, ethanol, propanol, N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide, N- Examples thereof include methylpyrrolidone and the like and mixtures thereof.

[0010] The concentration of the vinyl alcohol polymer in the stock solution for film formation must be within a range in which the stock solution for film formation can be formed into a film, and is usually set in the range of 5 to 40 wt%. In particular, when a hollow fiber membrane is manufactured, it is preferable to set the concentration of the vinyl alcohol-based polymer in the stock solution to a range of 10 to 30 wt%. If the concentration of the vinyl alcohol-based polymer in the stock solution is outside the above range, it may be difficult to form a film. In addition, the film forming stock solution may appropriately contain additives such as boric acid, silicon oxide, titanium oxide, polyethylene glycol, and dextran.

The above-mentioned stock solution is spun from a nozzle into a coagulation bath and formed into a film. In spinning the membrane-forming stock solution, various shapes of nozzles can be used depending on the desired membrane shape. For example, if a slit-shaped nozzle is used, it can be spun into a flat membrane, and if an annular nozzle is used, it can be spun into a hollow fiber membrane or a tube.

The coagulation liquid used in the coagulation bath is not particularly limited as long as it is miscible with the above-mentioned solvent and has an action of coagulating the vinyl alcohol-based polymer, but an aqueous medium is usually used. . Examples of such a coagulating liquid include a mixture of water and an organic solvent soluble in water such as dimethyl sulfoxide, N, N-dimethylacetamide, N-methylpyrrolidone, and alcohol, or sodium chloride, sodium sulfate, and sodium hydroxide. And an aqueous solution containing an inorganic salt of

[0013] The temperature of the coagulation bath is usually set in the range of -20 to 40 ° C. The temperature of the coagulation bath, together with the type of coagulation liquid, is a factor that determines the structure of the obtained film, and is appropriately selected according to the desired film. If relatively slow coagulation is required, for example when producing a homogeneously structured membrane used in hemodialysis, the temperature of the coagulation bath may be -20 to 10 ° C.
It is preferable to set Further, when producing a membrane having a relatively large pore size such as a secondary membrane or a plasma component separation membrane, the temperature of the coagulation bath is preferably set to 5 to 40 ° C.

[0014] As a film forming method, a so-called dry-wet method in which a stock solution spun from a nozzle is once passed through a certain length of air and then introduced into a coagulation solution, or a stock solution spun from a nozzle Any of the so-called wet methods of directly introducing into the coagulation liquid may be adopted,
What is necessary is just to select suitably according to performance.

When a hollow fiber membrane is formed using an annular nozzle, nitrogen or nitrogen is usually introduced into the nozzle in order to maintain the shape of the stock solution spun from the nozzle into a hollow fiber shape.
A non-coagulable solvent is introduced into a gas such as air, or a film forming stock solution such as hexane as an injection liquid. Examples of the injection include not only the above non-coagulable solvent but also a mixture of water and an organic solvent soluble in water such as dimethyl sulfoxide, N, N-dimethylacetamide, N-methylpyrrolidone, alcohol, or sodium chloride. In addition, a liquid having coagulability with respect to a film forming solution such as an aqueous solution containing an inorganic salt such as sodium sulfate, sodium hydroxide and the like can also be used.

The coagulability of the coagulating liquid and the injection liquid affects the surface structure of the obtained film. If a liquid with good coagulability is used as the coagulating liquid or the infusate, a dense layer is likely to be formed on the surface of the membrane. A film having fine pores with a large pore diameter on the surface of the film can be produced. As described above, the surface structure of the obtained film can be controlled by adjusting the coagulability of the coagulating liquid or the injection liquid.

As the shape of the separation membrane, various shapes such as a flat membrane, a tubular membrane, and a hollow fiber membrane have been known.
In the present invention, any shape can be used. From a practical point of view, a hollow fiber membrane that can take a large effective membrane area per occupied volume is preferable,
Such hollow fiber membranes usually have an outer shape of 40 to 3,000 μm.
m, a film thickness of about 10 to 1,000 μm is used.

The structure of the separation membrane includes various structures such as a homogenous sponge structure, a non-uniform structure having a dense layer on the surface, and a finger-like structure having large voids inside the membrane. May be used.

The separation membrane formed by the above method is irradiated with an electron beam. In the case of irradiation with an electron beam, if the separation membrane in a dry state is irradiated with the electron beam, depolymerization takes precedence. Irradiation to a wet separation membrane is less effective, and the crosslinking effect is greater. Therefore, it is preferable that after the film is formed, the film is appropriately washed to remove the solvent, and then guided into an electron beam irradiation apparatus in a wet state, and irradiated with an electron beam.
The moisture content of the separation membrane is preferably in a wet state of 0.5 wt% or more, and more preferably in a wet state of 5 wt% or more. The electron beam may be irradiated while the separation membrane is immersed in water, but the electron beam is also consumed by water, so that the irradiation efficiency deteriorates. Irradiation with an electron beam in a state where the film is kept at a constant length is more preferable because shrinkage of the film is suppressed and deterioration of the film performance is small. The state where the membrane is held at a certain length means
In the case of continuous production, it refers to a state where the film sending speed and the take-up speed are almost equal.
A state where both ends are fixed.

If the irradiation dose is too small, the effect of the present invention is small. If the irradiation dose is too large, discoloration of the separation membrane or remarkable decrease in water permeability of the membrane occurs.
d, preferably from 10 Mrad to 50 Mrad. By irradiating such a dose, the vinyl alcohol-based polymer is crosslinked.

The thickness of the separation film bundle irradiated with the electron beam depends on the acceleration voltage of the electron accelerator, but is preferably 5 cm or less. In order to give an effective range of 5 cm or more to the electron beam, a high accelerating voltage is required, and it becomes difficult to irradiate the electron beam during the film forming process, which is not preferable. Note that the acceleration voltage of the electron accelerator is preferably 300 KeV to 5 MeV. Here, if the acceleration voltage is lower than 300 KeV, the effective range of the electron beam becomes short, which is not preferable. On the other hand, if it is higher than 5 MeV, operation becomes difficult as described above, which is not preferable.

Since the irradiation time of the electron beam is proportional to the irradiation dose of the electron beam, the set time may be appropriately changed depending on the intended irradiation dose. However, electron beam irradiation involves a rise in the temperature of the substance to be irradiated, and the rise in temperature is proportional to the irradiation dose. That is, short-time irradiation is preferably repeated several times.

The atmosphere in which the cross-linking treatment is carried out with an electron beam is usually air, but in order to carry out the cross-linking treatment more efficiently, it is preferable to carry out the treatment in an inert gas such as nitrogen. More preferably, the washing water for the separation membrane is degassed. In the present invention, a separation membrane composed of a vinyl alcohol-based polymer crosslinked by electron beam irradiation is obtained, but other known crosslinking methods such as chemical crosslinking may be used in combination.

The membrane cross-linked in this way is used in a wet state or after being dried. From the viewpoint of easy handling, it is preferable that the membrane be in a dry state. As a method for drying the film, a method of drying under normal pressure or reduced pressure at a temperature lower than the glass transition point of the vinyl alcohol polymer, preferably around room temperature, freezing the wet film with liquid nitrogen, and sublimating the water under reduced pressure. Examples of the method include a freeze-drying method, an organic solvent replacement method in which water is replaced with an organic solvent miscible with water such as methanol, ethanol, and acetone, followed by evaporating and drying the organic solvent. The film in a dry state is subjected to a heat treatment according to a known method, if desired.

The thus obtained hollow fiber membrane is appropriately formed into a module or the like by a known method, and is used for medical applications such as hemodialysis and plasma separation, desalting, fractionation, concentration, and the like of an aqueous protein solution.
It is used for various purposes such as food use such as fruit juice concentration and industrial use such as wastewater treatment.

According to the present invention, a membrane-forming stock solution containing a vinyl alcohol-based polymer is formed into a membrane, and the membrane after the membrane formation is irradiated with an electron beam to crosslink the separation membrane composed of the vinyl alcohol-based polymer. Is obtained, but the operation is simple because it is only performed by irradiating an electron beam. Further, since the step of irradiating an electron beam is incorporated in the step of film formation, the crosslinking treatment can be continuously performed. Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto.

[0027]

【Example】

Example 1 Ethylene content 32 mol%, degree of polymerization 1300, degree of saponification 9
16 parts by weight of a 9% ethylene-vinyl alcohol copolymer (manufactured by Kuraray Co., Ltd., EVAL ECF100A) and dimethyl sulfoxide (hereinafter abbreviated as DMSO)
84 parts by weight were mixed and dissolved to prepare a uniform solution, which was used as a stock solution.

The stock solution was kept at 55.degree.
Directly extruding into a −2 ° C. DMSO aqueous solution containing 30% by weight of DMSO while introducing nitrogen gas into the inside from a double annular nozzle of 385 mm in inner diameter of 0.185 mm 1.2
It was taken out at m / min and solidified to form a hollow fiber membrane.

After the coagulated hollow fiber membrane passes through the washing tank,
It was guided into an electron accelerator, passed once at an acceleration voltage of 750 KeV, an electron beam current of 4.9 mA, and a hollow fiber passage speed of 1.2 m / min, and irradiated with an electron beam. CT irradiation dose
It was 5 Mrad when measured with an A film dosimeter. The hollow fiber membrane after the electron beam irradiation was replaced with acetone, dried at 25 ° C., and then subjected to a dry heat treatment to obtain a dry hollow fiber membrane having an inner diameter of 180 μm and a film thickness of 15 μm.

The dried hollow fiber membrane obtained above was
Swelled with water at 37 ° C, immersed in water at 37 ° C, sealed one end of each hollow fiber membrane, gradually applied air pressure from the opposite end, and measured the air pressure when the hollow fiber membrane burst. This was taken as the burst strength. The results are shown in Table 1.

Examples 2 to 4 In Example 1, the hollow fiber membrane washed with water was introduced into an electron accelerator, and the acceleration voltage was 750 Kev and the electron beam current was 4.9 m.
A, twice and four times at a hollow fiber passage speed of 1.2 m / min,
The same operation as in Example 1 was performed except that the passage was repeated 10 times, to obtain a dry hollow fiber membrane having an inner diameter of 180 μm and a film thickness of 15 μm. The electron beam irradiation dose was 10 Mrad,
The values were 20 Mrad and 50 Mrad. In Examples 2 to 4, the burst strength was measured for each hollow fiber membrane in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 1 A dry hollow fiber membrane having an inner diameter of 180 μm and a film thickness of 15 μm was obtained in the same manner as in Example 1, except that the irradiation of the electron beam was omitted. The burst strength of Comparative Example 1 was measured for each hollow fiber membrane in the same manner as in Example 1.
The results are shown in Table 1.

Using the hollow fiber membranes obtained in Examples 1 to 4 and Comparative Example 1, modules for an artificial kidney having an effective membrane area of 1.2 m ² were produced. Using this module, water permeability and urea permeability were measured based on the dialysis performance evaluation standard of the Japanese Society for Artificial Organs. The literature ("Kidney and dialysis",
The inhibition rate of albumin was measured according to the method described in Supplement 27, p. 169, 1989). Further, the burst strength at 37 ° C. was also measured. The moisture content of the hollow fiber was determined from the difference between the weight of the wet hollow fiber and the weight of the dry hollow fiber. The results are shown in Table 1.

Example 5 In Example 4, 30% by weight DM used as a coagulation bath was used.
The same operation as in Example 4 was performed except that the temperature of the SO aqueous solution was set to 8 ° C, to obtain a dry hollow fiber membrane having an inner diameter of 179 µm and a film thickness of 15 µm. The irradiation amount of electron beam is 50 Mrad
Met. Effective membrane area 1.
A 2 m ² module for an artificial kidney was prepared, and its water permeability, urea permeability, albumin rejection, burst strength at 37 ° C., and water content were measured. The results are shown in Table 1.

Comparative Example 2 The same operation as in Example 5 was performed except that the step of irradiating the electron beam with 50 Mrad was omitted.
A dry hollow fiber membrane having a thickness of 80 μm and a thickness of 15 μm was obtained.
Using the obtained hollow fiber membrane, a module for an artificial kidney having an effective membrane area of 1.2 m ² was prepared, and the water permeability, urea permeability, albumin rejection, burst strength at 37 ° C., and water content were measured. The results are shown in Table 1. From Table 1, it can be seen that the hollow fiber membrane irradiated with the electron beam has a higher burst strength than the hollow fiber membrane not irradiated with the electron beam, and the burst strength increases with an increase in the irradiation dose.

Example 6 The same operation as in Example 5 was carried out except that the irradiation amount of the electron beam was changed to 75 Mrad.
A dry hollow fiber membrane having a thickness of 14 μm was obtained. Using the obtained hollow fiber membrane, a module for an artificial kidney having an effective membrane area of 1.2 m ² was prepared, and the water permeability, urea permeability, albumin rejection, burst strength at 37 ° C., and water content were measured. The results are shown in Table 1.

As shown in Table 1, the value of the burst strength was improved by the electron beam irradiation, but the water permeability and urea permeability were slightly lowered. However, such a decrease in the performance can be controlled by changing the setting conditions during film formation, in particular, the temperature of the DMSO aqueous solution as a coagulation bath.

Example 7 The hollow fiber membrane obtained in Comparative Example 1 was cut into a length of 40 cm and then swollen with water at 25 ° C. The hollow fiber membrane is guided into the electron accelerator without being fixed, and the acceleration voltage is 750K.
eV, electron beam current 4.9 mA, passing speed 1.2 m / mi
The sample was allowed to pass through the accelerator four times at n, and was irradiated with an electron beam.
It was 20 when the irradiation dose was measured with a CTA film dosimeter.
Mrad. The contraction rate of the hollow fiber membrane was about 5%. Using the obtained hollow fiber membrane, an effective membrane area of 1.2 m ²
The module for artificial kidney was prepared and water permeability, urea permeability and albumin rejection were measured in the same manner as described above. The burst strength and water content at 37 ° C. were also measured. Table 1 shows the results. Although the rejection of albumin hardly changes, the water permeability and the urea permeability slightly decrease, indicating that the balance of the membrane performance is slightly deteriorated.

[0039]

[Table 1]

Example 8 13 parts by weight of polyvinyl alcohol having a degree of polymerization of 2400 and a saponification degree of 99% (PVA124 manufactured by Kuraray Co., Ltd.), 20 parts by weight of polyethylene glycol (average molecular weight 600), 1 part by weight of boric acid, 66 parts by weight of water The parts were mixed and dissolved to prepare a uniform solution, which was used as a stock solution.

The film forming stock solution was kept at 60 ° C., and had an outer diameter of 0.
From a double annular nozzle having a diameter of 7 mm and an inner diameter of 0.3 mm, an aqueous solution containing 1.5% by weight of sodium sulfate and 3% by weight of sodium hydroxide was used as an injection solution, and the relative humidity was 70%
Extruded at 1.2 m / min into air adjusted to 40 ° C., and after traveling 5 cm through the air, containing 15% by weight of sodium sulfate and 3% by weight of sodium hydroxide 4
The mixture was introduced into an aqueous solution at 0 ° C. and solidified to form a hollow fiber membrane.

The coagulated hollow fiber membrane was guided into an electron beam accelerator, passed eight times at an acceleration voltage of 750 KeV, an electron beam current of 4.9 mA, and a hollow fiber passage speed of 1.2 m / min, and irradiated with an electron beam. When the irradiation dose was measured by a CTA film dosimeter, it was 40 Mrad. After washing the hollow fiber membrane after electron beam irradiation with water, and replacing with acetone, 25 ° C
200 μm inner diameter and 30 μm film thickness
m of the dried hollow fiber membrane was obtained.

Using the hollow fiber membrane obtained above, a module for an artificial kidney having an effective membrane area of 1.2 m ² was prepared.
Water permeability and burst strength at 37 ° C. were measured in the same manner as in Example 5. Table 2 shows the results.

[0044]

[Table 2]

[0045]

According to the present invention, a separation membrane made of a vinyl alcohol-based polymer having an improved pressure-resistant strength, which is crosslinked by an electron beam, can be obtained by a simple method. The separation membrane made of the vinyl alcohol-based polymer of the present invention is excellent in pressure resistance, and thus is suitable as various separation membranes for microfiltration, blood treatment and the like.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Keizo Michihata 1621 Sazu, Kurashiki-shi, Okayama Prefecture Kuraray Co., Ltd.

Claims (3)

[Claims] 1. A separation membrane comprising a vinyl alcohol polymer crosslinked by electron beam irradiation. 2. A method for producing a separation membrane comprising a vinyl alcohol-based polymer, comprising forming a membrane from a stock solution containing a vinyl alcohol-based polymer, washing the obtained membrane with water, and irradiating an electron beam. . 3. The separation membrane according to claim 1, wherein the separation membrane made of a vinyl alcohol-based polymer is a separation membrane made of an ethylene-vinyl alcohol copolymer.