JPH08332361A - Production of vinyl alcohol copolymer hollow yarn membrane - Google Patents

Abstract

PURPOSE: To produce a vinyl alcohol copolymer hollow yarn membrane without generating thickness irregularity. CONSTITUTION: In a method for producing a vinyl alcohol copolymer hollow yarn membrane by a wet method or a dry and wet method, an external coagulation soln. is also allowed to flow to the inside of a double-pipe type spinning nozzle wherein a large number of holes are arranged in a circular form in parallel to the flow of the external coagulation soln. flowing to the outsized of the nozzle.

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 vinyl alcohol-based copolymer hollow fiber membrane. More specifically, 2
In a method for producing a vinyl alcohol-based copolymer hollow fiber membrane by a wet method or a dry-wet method using a double-tube spinning nozzle, a plurality of holes are flown outside a double-tube spinning nozzle having a circular arrangement. The present invention relates to a method for producing a vinyl alcohol-based copolymer hollow fiber membrane in which an external coagulation liquid is flown inside a nozzle in parallel with the flow of the external coagulation liquid to perform spinning.

[0002]

2. Description of the Related Art Generally, a hollow fiber membrane is manufactured by using a double-tubular spinning nozzle and injecting a gas or a liquid into the center thereof, and extruding a spinning solution into a coagulating solution to coagulate it. . For example, Japanese Examined Patent Publication No. 54-40654
Japanese Patent Laid-Open Publication No. Sho 55-55 discloses a method of spinning by defining the difference between the nozzle hole diameter and the outer diameter of the needle and the bath draft.
No. 22563 discloses a spinning method in which the ratio between the discharge amount of a spinning dope and the discharge amount of a gas introduced into a hollow fiber is defined.

When producing hollow fiber membranes on an industrial scale, double tube spinning nozzles with a plurality of holes rather than a single hole are usually used. The plurality of holes are arranged in a circle so that the hollow fibers extruded from the holes are solidified uniformly, and the coagulating liquid is supplied from around the holes.
And, when taking out the hollow fibers spun from each hole, each one is not taken out perpendicularly to the nozzle, but generally, several bundles are collected in one point while being collected, It is spun.

[0004]

By the way, when a resin, such as a vinyl alcohol-based copolymer, in which coagulation progresses slowly is used as the stock solution, the double tube nozzle should be sufficiently centered. However, when the coagulation liquid is spun in the same manner as in the prior art, that is, the method in which the coagulating liquid is supplied only from the outside of the double tube nozzle, the spun hollow fiber membrane is not completely perpendicular to the nozzle surface. Instead, the fibers are spun with a slight inclination toward the center, resulting in non-uniformity of the film thickness.

When a hollow fiber membrane is produced by a wet method, if spinning is continued for a long time, the coagulating liquid is supplied only from the outside, so that the hollow fiber membrane is sandwiched between the inside and the inside in the vicinity of the nozzle. A concentration difference occurs in the concentration of the coagulation liquid on the outer side, and uneven coagulation of the hollow fiber membrane occurs, which promotes nonuniformity of the membrane thickness. When the film thickness becomes non-uniform, a thin film part occurs,
It becomes weak against pressure and easily leaks. Therefore, an object of the present invention is to provide a method for producing a vinyl alcohol-based copolymer hollow fiber membrane that does not cause unevenness in the thickness of the hollow fiber membrane.

[0006]

[Means for Solving the Problems] The inventors of the present invention have made extensive studies in order to solve the above-mentioned problems, and a plurality of circularly arranged two
When a hollow fiber membrane is spun using a double-tube spinning nozzle, a plurality of holes are arranged inside the double-tube spinning nozzles arranged in a circular shape in parallel with the flow of an external coagulating liquid. Further, it was found that a hollow fiber membrane without unevenness in film thickness and unevenness of coagulation can be provided by flowing an external coagulation liquid, and the present invention was completed.

That is, according to the present invention, a plurality of holes are arranged in a circle in a method for producing a vinyl alcohol copolymer hollow fiber membrane by a wet method or a dry-wet method using a double tube type spinning nozzle. A method for producing a vinyl alcohol-based copolymer hollow fiber membrane, characterized in that the external coagulating liquid flows inside the nozzle in parallel with the flow of the external coagulating liquid flowing outside the double-tubular spinning nozzle. Hereinafter, the double-tubular spinning nozzle in which a plurality of holes used in the present invention are arranged in a circle is simply referred to as a double-tubular spinning nozzle.

The vinyl alcohol copolymer used in the present invention is a polymer containing a vinyl alcohol unit in an amount of 30 mol% or more, preferably 50 mol% or more, and specifically, a homopolymer of vinyl ester. And saponified products of vinyl alcohol-based copolymers containing vinyl monomers such as ethylene, propylene, acrylonitrile, vinyl chloride, and vinylpyrrolidone (including random, block, and graft copolymers), and the like. .

Among them, the ethylene-vinyl alcohol type copolymer is suitable as a material for a separation membrane used in the medical field because it has a very small amount of eluate. In particular, as a material of a separation membrane used for blood treatment such as hemodialysis and plasma separation, an ethylene-vinyl alcohol-based copolymer having a polymerization degree of 800 or more, an ethylene content of 10 to 60 mol% and a saponification degree of 96 mol% or more is usually used. Polymers are used. In addition,
As the ethylene-vinyl alcohol-based copolymer, for example, a copolymerizable polymerizable monomer such as methacrylic acid, vinyl chloride, methyl methacrylate, acrylonitrile may be copolymerized within the range of 15 mol% or less. Good.

The stock solution for spinning comprises a vinyl alcohol copolymer and its solvent. The solvent is not particularly limited as long as it dissolves the vinyl alcohol copolymer, and examples thereof include methanol, ethanol, propanol, N, N.
Examples thereof include dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide, N-methylpyrrolidone, water and the like, and mixtures thereof. In addition, boric acid, silicon oxide, titanium oxide, ethylene glycol, polyethylene glycol, polypropylene glycol, tetraethylene glycol, triethylene glycol, glycerin, polyhydric alcohols such as butanediol, dextran and the like are added to the spinning dope. The agent may be contained if necessary.

The concentration of the vinyl alcohol copolymer in the spinning dope needs to be within the range in which the film forming dope can form a film, and is usually set in the range of 5 to 40% by weight. In particular, when producing a hollow fiber membrane, the concentration of the vinyl alcohol-based copolymer in the spinning solution is 10 to 30 mol%.
It is preferable to set in the range of. If the concentration of the vinyl alcohol copolymer in the spinning dope is out of the above range, it may be difficult to form a film.

The temperature of the spinning dope is adjusted in the range of 10 to 100 ° C, preferably 30 to 80 ° C. If the temperature of the spinning solution is higher than the above range, the vinyl alcohol-based copolymer itself may be denatured, and if the temperature is lower than the above range, the viscosity of the film-forming solution becomes too high to form a film. It can be difficult.

The coagulating liquid used in the coagulating bath is not particularly limited as long as it is miscible with the stock solution solvent and has an action of coagulating the vinyl alcohol copolymer, but an aqueous medium is usually used. To be done. Examples of the 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 hydroxide, sodium chloride, magnesium chloride, sodium sulfate. Examples thereof include aqueous solutions containing inorganic salts such as ammonium sulfate and ammonia water.

The temperature of the coagulation bath is usually set in the range of -20 to 40 ° C. The temperature of the coagulation bath is a factor that determines the structure of the obtained film in combination with the type of the coagulation liquid. When relatively slow coagulation is required, for example, when producing a membrane having a homogeneous structure used for hemodialysis, the temperature of the coagulation bath may be set low, for example, −20 to 10 ° C. preferable. Further, when a slow coagulation is not required as in the case of producing a porous membrane used for plasma separation, the temperature of the coagulation bath is, for example, 10 to 40.
It is preferable to set it higher, such as ℃.

In the present invention, a nozzle having a plurality of holes arranged in a circle is used as the double-tubular spinning nozzle. The circular shape includes not only a circular shape but also a substantially circular shape. A plurality means two or more, but a larger number is preferable because the effects of the present invention are well expressed. Usually 10 holes
It is carried out by one or more.

The external coagulation liquid flowing outside the double-tubular spinning nozzle is an external coagulation liquid introduced from the outside of the nozzle in which a plurality of holes are arranged in a circle, as shown in FIG. The external coagulation liquid flowing inside the double-tubular spinning nozzle is an external coagulation liquid flowing inside the nozzle in which a plurality of holes are arranged in a circle, as shown in FIG. It is necessary that these flows flow in parallel.

In the case of the wet method, the spinning dope is spun directly from the spinning nozzle into the coagulation bath. Further, in the case of the dry-wet method, the spinning dope is spun out from the spinning nozzle, once run in the atmosphere, and then introduced into the coagulation bath. In the present invention, a wet method is preferred in which the nozzle is fixed vertically upward and the spun spinning solution is spun directly into the coagulation bath.

When producing a hollow fiber membrane, a fluid is introduced into the inside of a double-tubular spinning nozzle for the purpose of maintaining the shape of the spun polymer in a hollow fiber shape. As such a fluid, in general, a gas such as nitrogen or air, a solvent that is non-coagulating to a spinning stock solution such as hexane is used as an internal coagulating liquid, but not only the above non-coagulating solvent, Dimethyl sulfoxide, N, N-dimethylacetamide, N-methylpyrrolidone, a mixture of water and a water-soluble organic solvent such as alcohol, or an aqueous solution containing an inorganic salt such as sodium chloride, calcium chloride or sodium sulfate,
It is also possible to use a liquid having coagulability with respect to the stock solution for film formation.

The coagulability of the coagulation liquid and the injection liquid described above affects the structure of the surface of the obtained film. When a liquid having a good coagulability is used as the coagulating liquid or the injecting liquid, a dense layer is easily formed on the surface of the film, and conversely, when a liquid having a low coagulating property is used as the coagulating liquid or the injecting liquid, It is possible to produce a membrane having micropores with a large pore size on the surface. By adjusting the coagulability of the coagulating liquid or the injecting liquid in this manner, the structure of the surface of the obtained film can be controlled.

In the present invention, it is important that the external coagulating liquid also flows inside along with the flow of the external coagulating liquid flowing outside the double tube spinning nozzle. As an example of the method of supplying the external coagulating liquid, while flowing the external coagulating liquid from the outer peripheral portion of the nozzle, fixing the cylindrical pipe in the central portion, and supplying the coagulating liquid from the upper portion and reversing the nozzle, A method of running the external coagulation liquid in parallel with the inside (Fig. 1),
Examples of the method include a method of using an Natsu type nozzle to flow the external coagulation liquid in parallel with the outside and inside of the nozzle, and a method of combining these. In the above method, a weir as shown in FIG. 1 may be provided in order to make the flow of the liquid effective.

The flow velocity of the external coagulating liquid (inner coagulating liquid) flowing inside the double-tubular spinning nozzle is Vin, the flow velocity of the external coagulating liquid (outer coagulating liquid) flowing outside is Vout,
When the take-up speed of the hollow fiber membrane is Vf, if the speed Vout of the outer coagulating liquid is faster than the speed Vin of the inner coagulating liquid, the hollow fiber membrane will incline from the outer side to the inner central part, so that the inner film thickness Tends to be a thin film with uneven thickness. Further, the inside of the slower speed has a relatively higher concentration of the coagulation liquid than the outside, and the inside coagulation becomes slower, so that the unevenness of coagulation easily occurs. On the contrary, when the inner speed Vin becomes faster than twice the outer speed Vout, the hollow fiber membrane is pushed from the inner side to the outer side and is inclined so as to spread, so that the outer layer becomes thin and has uneven thickness. In addition, the concentration of the coagulating liquid on the outer side, which has a low velocity, becomes relatively thick and coagulation plaques are also likely to occur. Further, it is preferable that the speed Vin of the coagulating liquid is somewhat higher than the speed Vf of the hollow fiber membrane, which serves to prevent the hollow fiber membrane from tilting inward. When Vin is faster than 5 times the take-up speed Vf of the hollow fiber membrane, the hollow fiber membrane is violently pulled by the flow of the coagulating liquid, and the fiber breaks easily.

From this point of view, Vout <Vin <
It is preferable that the spinning is performed while satisfying 2 × Vout and Vf <Vin <5 × Vf, because the effect of the present invention is remarkable. Vin
And Vout are values obtained by calculation from the cross-sectional area of the spinning tube and the flow rate, and Vf is directly obtained from the take-up speed of the hollow fiber membrane.

As the structure of the hollow fiber membrane, there are various structures such as a homogeneous sponge structure, a heterogeneous structure having a dense layer on the surface, and a finger-like structure having a large void inside the membrane. It may have a structure. The thickness of the hollow fiber membrane is usually 40 to 3000 μ in outer diameter.
m, and a film thickness of about 10 to 1000 μm is used.

The hollow fiber membrane thus obtained is washed with water or warm water. Moreover, stretching, heat treatment, etc. are performed as needed. The membrane thus obtained is kept in a wet state or dried, but it is preferable to keep the membrane in a dry state from the viewpoint of handling convenience. As a method for drying the film, a method of drying at a temperature not higher than the glass transition point of the vinyl alcohol-based copolymer, preferably atmospheric pressure or reduced pressure at around room temperature, freezing the wet film with liquid nitrogen and sublimating water under reduced pressure Freezing It is possible to use an organic solvent replacement method in which water is replaced with an organic solvent that is miscible with water, such as drying, methanol, ethanol, or acetone, and then the organic solvent is evaporated to dryness. The dried film is optionally heat treated according to known methods.

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 of protein aqueous solution, fractionation, concentration, concentration of fruit juice, etc. It is used in various applications such as food applications and industrial applications such as wastewater treatment.

[0026]

EXAMPLES The present invention will now be specifically described with reference to examples, but the present invention is not limited thereto. [Examples 1 to 3 and Comparative Examples 1 to 3] Ethylene having an ethylene content of 33 mol%, a polymerization degree of 1300, and a saponification degree of 99 mol%.
Vinyl alcohol copolymer (EVAL manufactured by Kuraray Co., Ltd.
(Registered trademark) ECF100A) in DMSO,
A 7% by weight spinning solution was prepared. Nozzles arranged in a circle with 100 holes and a hole interval of 1.5 mm are fixed vertically upward in a cylindrical spinning cylinder, the outer coagulating liquid is blown upward from the outer peripheral portion of the nozzle, and the inner coagulating liquid is in the central portion of the nozzle. The inner cylinder was fixed, the coagulating liquid was supplied to the central portion of the nozzle, and the flow of the liquid was reversed so that the coagulating liquid flows in parallel with the outer coagulating liquid. Maintain the liquid level of the coagulation liquid at 50 cm, discharge the spinning solution while injecting nitrogen into the hollow fiber membrane, and DMSO2 at 0 ° C.
The stock solution was extruded into an aqueous solution containing 0% by weight and solidified.

The treatment was performed according to a known method to obtain a dry hollow fiber membrane having an average film thickness of 25 μm and an average inner diameter of 200 μm. Hollow fiber membranes were manufactured by changing the speeds of Vin, Vout and Vf. The thickness of all the obtained hollow fiber membranes was observed with a microscope, and the thickest part and the thinnest part were obtained. After assembling 1000 modules by bundling 100 hollow fibers into a bundle and moistening them, air pressure of 2 Kg / cm ² was applied to the inside of the hollow fibers for 10 minutes to obtain the leak rate at that time. The results are shown in Table 1.

Example 4, Comparative Example 4 As an internal coagulating liquid, a 20 wt% calcium chloride aqueous solution was injected at 20 ° C. instead of nitrogen, and the stock solution was extruded into a 10 wt% DMSO aqueous solution at 10 ° C. to coagulate. Thus, a dry hollow fiber membrane having an average thickness of 55 μm was obtained. Observing the cross-section of the film when the coagulation liquid was flown inside and outside and when the coagulation liquid was flowed only outside, the finger-like structure was generated uniformly when the coagulation liquid was flowed on both sides, whereas the outside When it was poured only into the water, the finger-like structure was generated unevenly. From this result, the effect of the present invention is clear.

[0029]

[Table 1]

[0030]

When a hollow fiber membrane is manufactured by a wet method or a dry-wet method using a double tube type spinning nozzle in which a plurality of holes are arranged in a circle, the external coagulating liquid flowing outside the nozzle is By flowing the external coagulation liquid inside along with the flow,
It is possible to obtain a hollow fiber membrane with less unevenness in coagulation and thickness of the hollow fiber membrane.

[Brief description of drawings]

FIG. 1 is a schematic view of a spinning cylinder used in Examples.

FIG. 2 is a schematic view of the double-tube nozzle used in the examples as seen from above.

[Explanation of symbols]

 1 Spinneret 2 Nozzle 3 Inner Cylinder for Supplying Inner Coagulation Liquid 4 Hollow Fiber 5 Flow of Outer Coagulation Liquid 6 Flow of Inner Coagulation Liquid 7 Weir 8 Hole

Claims (2)

[Claims] 1. A method for producing a vinyl alcohol-based copolymer hollow fiber membrane by a wet method or a dry-wet method using a double tube type spinning nozzle, wherein a plurality of holes are arranged in a double tube type. A method for producing a vinyl alcohol-based copolymer hollow fiber membrane, which comprises flowing the external coagulating liquid inside the nozzle in parallel with the flow of the external coagulating liquid flowing outside the spinning nozzle. 2. The method for producing a vinyl alcohol copolymer hollow fiber membrane according to claim 1, wherein the velocity of the external coagulating liquid flowing inside the double-tubular spinning nozzle in which a plurality of holes are arranged in a circle. Vin, and the velocity of the external coagulating liquid flowing outside is V
out, when the take-up speed of the hollow fiber is Vf, Vo
ut <Vin <2 × Vout and Vf <Vin <5 × V
A method for producing a vinyl alcohol-based copolymer hollow fiber membrane, which comprises spinning under the condition of f.