JPH11235521A - Method for producing vinyl alcohol polymer separation membrane by stretching two-stage solidification - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for obtaining a vinyl alcohol copolymer separation membrane having a good balance by improving water permeability and dialysis without using a new membrane material and a new apparatus. To provide. The present invention uses at least two coagulation baths, and reduces the solvent content in the membrane wall at the outlet of the first coagulation bath to 20%.
８０80% by weight in an incomplete state, stretched in the range of 5-50% before reaching the second coagulation bath, then completely coagulated in the process after the second coagulation bath while relaxing, and separated A method for producing a separation membrane, characterized by producing a membrane.

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 separation membrane for blood treatment using a vinyl alcohol polymer. More specifically, the present invention relates to a well-balanced separation membrane for blood treatment having improved water permeability and dialysis properties, and more particularly to a wet production method of a separation membrane useful for artificial kidneys.

[0002]

2. Description of the Related Art In a wet production method for a separation membrane, a polymer of a membrane material is dissolved in an appropriate solvent, and this spinning solution is extruded into a coagulation solvent from an annular nozzle in the case of a hollow fiber separation membrane, for example, to polymerize the polymer. It is based on developing a film structure by precipitation and solidification. Therefore, the conventional coagulation bath examines various conditions such as composition, concentration, temperature, circulation amount, coagulation temperature, bath draft, etc. with the aim of precipitating and coagulating the polymer in the spinning solution as completely as possible. A separation membrane having the structure and performance described above is obtained. For example, JP-A-55-110132, JP-A-55-11
No. 0124 and JP-A-55-35969. An attempt to obtain an excellent hemodialysis membrane by adding a solvent of the polymer of the membrane material to a coagulation bath and adjusting the coagulation rate, ie, the rate of replacement of the solvent in the membrane wall, is disclosed in JP-A-51-70698. And so on. Further, Japanese Patent Laid-Open No. 57-199808
In JP-A No. 11-139, there is disclosed a wet method of a separation membrane in which a spinning solution is extruded into a non-coagulable liquid, cooled, uniformly gelled, and then guided to a coagulation bath to uniformly coagulate as it is. Also,
JP-A-59-160507 discloses that at least two coagulation baths are used, the substitution of the solvent in the membrane wall of the separation membrane in the first coagulation bath is interrupted, and an incomplete separation membrane is once obtained. A method of obtaining a separation membrane by substantially completely coagulating in a coagulation bath is disclosed.

[0003]

However, in recent years, with the advancement of medical treatment, the required performance of blood treatment membranes has been increasing, but the price of blood treatment membranes used has continued to decrease. ing. Accordingly, an object of the present invention is to provide a method for obtaining a vinyl alcohol-based polymer separation membrane with improved balance and improved water permeability and dialysis without using a new membrane material and a new device.

[0004]

Means for Solving the Problems The present inventors have intensively studied a method of increasing the porosity of a vinyl alcohol polymer separation membrane which has been conventionally well known, using a conventionally used apparatus. As a result, when a separation membrane in an incompletely coagulated state is created in the first coagulation bath, stretching is performed, and when the solidification is completely coagulated after the second coagulation bath while relaxing, the porosity of the separation membrane is improved, The inventors have found that the performance is improved, and have reached the present invention. That is, the present invention provides a method for producing a vinyl alcohol-based polymer separation membrane by a wet spinning method using at least two coagulation baths, wherein the solvent content in the membrane wall at the outlet of the first coagulation bath is 20 to 80% by weight. After stretching in the range of 5 to 50% before the two-coagulation bath, relax to almost the length before stretching and then lead to the second coagulation bath, or partially extend to a part of the length before stretching It is led to the second coagulation while relaxing, and in the process from the second coagulation bath to the final coagulation bath, it is further relaxed to almost the length before stretching, or 5 to 5
A vinyl alcohol-based polymer separation membrane characterized in that it is guided to a second coagulation bath while being stretched in a range of 0%, and is relaxed to a length almost before stretching in a process from the second coagulation bath to a final coagulation bath. It is a manufacturing method. Hereinafter, the present invention will be described in detail.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The term "solvent content in the membrane wall" as used herein means the ratio of the solvent weight to the total volatile matter weight in the separation membrane wall leaving the first coagulation bath. Here, the solvent in the present invention means the following. That is, in order for component (a) in all volatile components to be determined as a solvent, (a)
If necessary, it must have the ability to dissolve 15% by weight or more of a vinyl alcohol polymer alone under heating. The measurement of the solvent content in the separation membrane wall is performed in the following procedure. At the outlet of the first coagulation bath, a separation membrane is collected, and after chopping, the adhering liquid is removed by a centrifuge to obtain a wet separation membrane, and its weight is weighed. Next, the mixture is repeatedly extracted with water, and the amount of the solvent in the extract is determined by gas chromatography or the like. After the extraction, the separation membrane is dried, and the weight of the polymer is measured. From the obtained results, the solvent content relative to the total volatile content in the film wall is calculated.

[0006] 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. And vinyl alcohol-based polymers (including random, block, and graft copolymers) containing vinyl units such as ethylene, propylene, acrylonitrile, vinyl chloride, and vinylpyrrolidone.

[0007] Among them, ethylene-vinyl alcohol (E
The VA) -based copolymer is suitable as a material for a separation membrane used in the medical field because of very little eluate.
In particular, as a material for a separation membrane used for blood treatment such as hemodialysis and plasma separation, usually, E having a polymerization degree of 800 or more, an ethylene content of 10 to 60 mol%, and a saponification degree of 95 mol% or more is used.
A VA copolymer is used. In addition, as such an EVA-based copolymer, for example, a copolymerizable monomer such as methacrylic acid, vinyl chloride, methyl methacrylate, and acrylonitrile may be copolymerized within a range of 15 mol% or less.

Next, as a solvent for dissolving these vinyl alcohol polymers, dimethyl sulfoxide (DMS) is used.
O), N, N dimethylacetamide (DMAc), dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), N-methylmorpholine-n-oxide (N-MMO) hydrate, N-propanols And hydrates thereof and the like, or a mixed solvent containing these as components. In order to obtain a blood treatment membrane having a desirable balance between water permeability and dialysis, which is the object of the present invention, the polymer In particular, DMSO is particularly desirable because it has high solubility and is easy to control the film-forming conditions, and does not have a concern that highly toxic substances remain in the film.

The vinyl alcohol polymer is dissolved in these solvents, and the concentration of the vinyl alcohol polymer in the stock solution is 5 to 50% by weight, preferably 10 to 30% by weight. If the concentration is lower than this, the film strength after film formation becomes weak, and if the concentration is higher, the viscosity becomes high, making film formation difficult, which is not preferable. The stock solution may appropriately contain additives such as boric acid, silicon oxide, titanium oxide, polyethylene glycol, dextran and the like.

[0010] The temperature of the spinning solution is usually 0 to 120 ° C, preferably 40 to 90 ° C. At higher temperatures, the vinyl alcohol polymer may be decomposed or deteriorated,
If the temperature is lower than this, the viscosity of the stock solution becomes too high, and film formation is difficult.

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 a function of coagulating the vinyl alcohol-based polymer, but an aqueous medium is usually used. Examples of such a coagulating solution include a mixture of water and an organic solvent soluble in water such as DMSO, DMAc, NMP, DMF, and alcohol, or an aqueous solution containing an inorganic salt such as sodium chloride, calcium chloride, sodium sulfate, and sodium hydroxide. And the like.

The above-mentioned stock solution is spun from a nozzle into a coagulation bath to form a film. In spinning the film forming stock solution, various shapes of nozzles can be used depending on the desired film shape. For example, when a slit-shaped nozzle is used, the fiber can be spun into a flat membrane, and when an annular nozzle is used, the fiber can be spun into a hollow fiber or a tube. Above all, a hollow fiber membrane that can take a large effective membrane area per occupied volume is preferable, and such a hollow fiber usually has an outer diameter of 40 to 3000 μm and a film thickness of 10 to 1000 μm.
Some are used.

When a hollow fiber is formed into a film using an annular nozzle, nitrogen, air or the like is usually provided inside the nozzle in order to maintain the shape of the stock solution spun from the nozzle into the hollow fiber. A non-coagulable solvent is introduced as a gas or a stock solution such as hexane as an injection liquid. As the injection solution, not only the above non-coagulating solvent but also DMSO, DMAc,
NMP, a mixture of water and an organic solvent soluble in water such as alcohol, or a liquid having a solidifying property with respect to a film forming stock solution such as an aqueous solution containing an inorganic salt such as sodium chloride, calcium chloride, sodium sulfate, and sodium hydroxide. Can also be used.

The coagulability of the above-mentioned coagulation liquid and injection liquid affects the surface structure of the obtained film. When a liquid with good coagulability is used as a coagulating liquid or an injecting liquid, a dense layer is easily formed on the surface of the film, and when a liquid with low coagulability is used, a film having a large pore diameter is produced on the surface of the film. be able to. Thus, the surface structure of the obtained film can be controlled by adjusting the coagulation properties of the coagulation liquid and the injection liquid.

The solvent content in the membrane wall at the outlet of the first coagulation bath must be in the range of 20 to 80% by weight. More preferably, it is 30 to 50% by weight. If the content of the solvent is more than 80% by weight, the solvent exchange rate in the membrane wall is too low and the expression of the membrane structure in the first coagulation bath is weak, and even if the film is stretched in this state, the membrane structure does not change. The membrane structure is determined by the conditions after the two-coagulation bath, and an excellent separation membrane aimed at by the present invention cannot be obtained.

If the content of the solvent in the membrane wall at the outlet of the first coagulation bath is smaller than 20% by weight, the solvent exchange rate in the membrane wall is excessively advanced and the membrane structure is substantially determined in the first coagulation bath. Therefore, even if the film is stretched in this state, the effect is no longer exhibited, and a membrane having an excellent balance between water permeability and dialysis, which is the object of the present invention, cannot be obtained.

Methods for controlling the solvent content in the membrane wall include a method of adjusting the solvent concentration of the first coagulation bath, a method of adjusting the residence time by changing the size of the first coagulation bath, and a method of controlling the residence time. There is a method of adjusting the residence time by changing the membrane moving time in the above, but it is simpler and easier to control by changing the solvent concentration, changing the membrane moving time, or combining them.

As described above, the solvent content in the membrane wall is adjusted to 20 to 80.
When stretched in the range of 5 to 50% with incomplete coagulation between weight%, it is assumed that the stretching stimulus induces the formation of new pores in the membrane wall. The micropores already formed in the first coagulation bath are temporarily expanded by stretching,
It is considered that the pores are relaxed in the next relaxation step and return to the original size, so that a large number of fine pores having a uniform pore diameter are formed, the aperture ratio is increased, and the performance is improved.

The film thus solidified in an incomplete state in the first coagulation bath is 5 to 50 cm between the first coagulation bath and the second coagulation bath.
%. Preferably it is 10 to 30%. If the stretching is less than 5%, the development of micropores is insufficient and sufficient performance cannot be obtained. On the other hand, if it is more than 50%, the size of the micropores becomes too large, and the balance between water permeability and dialysis properties is unfavorably deteriorated.

Further, when stretching is performed in the present invention, it is more effective to provide a gas phase between the first coagulation bath and the second coagulation bath, and if the gas phase is higher than the first coagulation bath temperature. It is more effective.

The separation membrane once stretched needs to be relaxed to almost its original length. That is, after the film is stretched in the range of 5 to 50%, the film is relaxed to almost the length before stretching and then guided to the second coagulation bath, or the resin is partially relaxed to a part of the length before stretching, and In the process from the second coagulation bath to the final coagulation bath, it is further relaxed to almost the length before stretching, or it is guided to the second coagulation bath while being stretched in the range of 5 to 50%, and the second coagulation is performed. From the bath to the final coagulation bath, it is necessary to relax the length almost to the length before stretching. Considering the performance of the membrane, it is preferable that the stretching is returned to the original length. However, if the stretching is left in a range of several percent, that is, about 5%, the hollow fiber is stretched and the processability in the subsequent process is reduced. It is preferable to leave a little stretching since it improves. When the coagulation in the second coagulation bath is completed in a state where the relaxation is excessively longer than the original length, large pores remain in the membrane wall, and the balance between water permeability and dialyzability is deteriorated. Conversely, if it is desired to relax the length to be shorter than the original length, it is not preferable because the passability of the subsequent process is deteriorated.
As described above, the relaxation of the film may be performed before entering the second coagulation bath, or may be performed simultaneously with the washing after entering the second coagulation bath. Considering the simplification of the process, it is better to perform the relaxation and the cleaning at the same time.

The temperature of the first coagulation bath also affects the appearance of the membrane structure, and the temperature of the first coagulation bath changes the gelation (cloudiness) of the spinning stock solution.
The effect of the present invention is remarkably exhibited when the temperature is equal to or lower than the temperature and the temperature after the second coagulation bath is equal to or higher than the gelling temperature. The gelation temperature mentioned here is a temperature at which the stock solution starts to become cloudy when the stock solution is gradually cooled at a rate of 1 ° C. per minute. When the temperature of the first coagulation bath is higher than the gelling temperature, the pores of the membrane become large as a whole, and the balance between water permeability and permeability deteriorates.
On the other hand, when the temperature of the second coagulation bath is lower than the gelation temperature, the development of micropores generated by stretching is poor, and the balance between water permeability and permeability is also poor.

After completion of the solidification, a wet heat treatment is performed. In the present invention, the wet heat treatment temperature is 40 to 80 ° C., preferably 55 to 80 ° C.
７０70 ° C. If the time for the wet heat treatment is insufficient, the passability in the subsequent step is impaired, and the storage stability of dimensions and performance after drying is reduced. If the wet heat treatment is excessive, the film structure changes, and the desired performance of the present invention cannot be obtained. The wet heat treatment is usually performed by a method in which the hollow fiber is passed through warm and hot water also for washing, but the wet heat treatment and the water washing need not necessarily be performed simultaneously,
After passing the hollow fiber through a saturated steam atmosphere and performing a wet heat treatment, it is possible to perform necessary water washing, and conversely, it is also possible to perform a wet heat treatment after water washing. However,
In a continuous process, from the viewpoint of simplification of the process, it is preferable to perform the wet heat treatment and the water washing simultaneously.

The film in a wet state is immersed in a water-miscible volatile organic solvent to replace water present on the surface or inside of the film.
Dry under normal pressure or reduced pressure. As the organic solvent in this case, a lower aliphatic alcohol or ketone having 1 to 5 carbon atoms is preferable, and for example, methanol, ethanol, amyl alcohol, acetone, methyl ethyl ketone, diethyl ketone and the like are used. Of these, acetone is particularly preferred. The drying is performed under normal pressure or reduced pressure, and the temperature and the steam pressure are 55 ° C. or less, preferably 50 ° C. or less, and the steam pressure is 20 mmHg or less. The water vapor pressure is preferably 10 mmHg or less. By performing solvent replacement and drying under such conditions, drying can be performed while maintaining wet performance.

The dried hollow fiber membrane is subjected to a dry heat treatment mainly for the purpose of improving the storage stability of dimensions and performance. Dry heat treatment temperature is 40-70 ° C, preferably 55-65 ° C
It is. Above this, the film structure changes and the performance decreases. Below this, sufficient heat fixation is not possible, and shrinkage proceeds with time, resulting in a change in the performance of the film. The water vapor pressure in the dry heat treatment atmosphere must be 60 mmHg or less. Above this value, water molecules are adsorbed on the vinyl alcohol polymer, and when released into a room temperature atmosphere after the dry heat treatment, the water molecules are desorbed. The film structure changes with the separation, and the performance is reduced.

The separation membrane thus obtained has excellent dimensional stability in a dry state and does not change with time, so that it is advantageous for storage. Moreover, since it is dried, it is convenient for transportation and the like. The dry separation membrane can reproduce the performance before drying by re-wetting with water or physiological saline before use.

[0027]

Example 1 Ethylene content 33 mol%, degree of polymerization 130
0, an ethylene-vinyl alcohol (EVA) copolymer having a saponification degree of 99.9 mol% was converted to dimethyl sulfoxide (D
MSSO) to obtain a spinning dope. The gelation temperature of this stock solution was 20 ° C. Using a double-ring nozzle, while injecting nitrogen gas as an internal injection liquid, a nozzle draft 2.0 was used at 0 ° C. and 22% by weight of DM.
The undiluted solution was extruded into a first coagulation bath composed of an aqueous solution containing SO, and was coagulated. At this time, the solvent exchange rate in the hollow fiber membrane wall discharged from the first coagulation bath was 40% by weight. The space between the first coagulation bath and the second coagulation bath was provided as a 2 m empty feeding section, and the film was stretched by 20% in a 25 ° C. atmosphere. The stretched hollow fiber membrane was guided to a second coagulation bath at 55 ° C. as it was, and relaxed to the original length while washing with water. After relaxation, wash and dry as before,
Dry heat treatment was performed to obtain a dry hollow fiber membrane having an inner diameter of 175 microns and an outer diameter of 225 microns. Table 1 shows spinning conditions for producing the hollow fiber membrane. The bundle of dried hollow fiber membranes was assembled into a module having an effective area of 1.2 m ² , and the water permeability, urea clearance, and albumin rejection of the aqueous system were measured according to the dialyzer performance evaluation criteria. Table 2 shows the results.

Examples 2 to 7 and Comparative Examples 1 to 5 The same spinning dope as in Example 1 was used.
An EVA copolymer film was produced in the same manner as in Example 1 except that the first coagulation bath temperature and the second coagulation bath temperature were variously changed as shown in Table 1. Table 2 shows the performance of the obtained EVA-based copolymer film.

Example 8 Spinning was carried out under exactly the same conditions as in Example 4 except that the temperature of the empty feeding section was set at 5 ° C. to obtain a hollow fiber membrane, and the membrane performance was measured. The results are shown in the table. Since the development of pores was weaker than in Example 4, the dialyzability was slightly insufficient, but the performance was such that it could be used as a dialysis membrane.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

The vinyl alcohol polymer separation membrane according to the present invention is obtained by using a conventional membrane material, particularly an EVA copolymer, by using a conventional apparatus to obtain a well-balanced separation membrane having improved water permeability and dialysis. Since it can be manufactured, it is a useful method as a method for manufacturing a hemodialysis membrane for an artificial kidney because a water-permeable and dialysis property is improved without increasing the manufacturing cost of the hollow fiber membrane and a balanced membrane is obtained. .

Claims (3)

[Claims] 1. A method for producing a vinyl alcohol-based polymer separation membrane by a wet spinning method using at least two coagulation baths, wherein the solvent content in the membrane wall at the outlet of the first coagulation bath is 20 to 80% by weight. After stretching in the range of 5 to 50% before reaching the second coagulation bath, the film is relaxed to almost the length before stretching, and then guided to the second coagulation bath, or the length before stretching is almost equal to one. To the second coagulation while partially relaxing up to the portion, and in the steps from the second coagulation bath to the final coagulation bath, it is further relaxed to a length almost before stretching, or 5 to 5
A vinyl alcohol-based polymer separation membrane characterized in that it is guided to a second coagulation bath while being stretched in a range of 0%, and is relaxed to a length almost before stretching in a process from the second coagulation bath to a final coagulation bath. Production method. 2. The method for producing a vinyl alcohol-based polymer separation membrane according to claim 1, wherein the temperature of the first coagulation bath is equal to or lower than the gelling temperature of the spinning dope and the temperature of the second coagulation bath is equal to or higher than the gelation temperature. 3. The method for producing a vinyl alcohol polymer separation membrane according to claim 1, wherein the vinyl alcohol polymer separation membrane by a wet spinning method using at least two coagulation baths is a dialysis membrane for blood treatment.