JP2818352B2 - Manufacturing method of hollow fiber membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a permeation method, an ultrafiltration method,
The present invention relates to a method for producing a hollow fiber membrane made of cellulose triacetate useful for fluid separation such as separation of a liquid and separation of a mixed gas by a dialysis method or the like.

[0002]

2. Description of the Related Art Conventionally, a material required for a hollow fiber membrane used for fluid separation such as separation of a liquid and separation of a mixed gas by a permeation method, an ultrafiltration method, a dialysis method, etc. It is required that the material be large and have high permselectivity. In particular, as the properties required for the hollow fiber membrane used in the ultrafiltration method and the dialysis method, it is required that the water permeation rate is large and the molecular weight fractionation property is excellent. Furthermore, in the case of a hollow fiber membrane used for artificial dialysis, the inner surface of the hollow fiber membrane should be as smooth as possible in order to reduce residual blood and hemolysis during hemodialysis, and to reduce performance degradation due to deposition of proteins in blood. Has been requested.

As a method for producing a hollow fiber membrane having a high water permeation rate and excellent molecular weight fractionation properties, for example, a spinning solution comprising cellulose esters, an organic solvent of cellulose esters and polyethylene glycols as a swelling agent ( A method has been proposed in which a dope is discharged from a spinneret and solidified to produce a hollow fiber membrane (Japanese Patent Application Laid-Open No. Sho 54-1979).
No. 88881). However, Japanese Patent Application Laid-Open No. 54-88881
In the method described in Japanese Patent Application Laid-Open Publication No. H11-260, the molecular weight of a solute that can be separated by solute is changed by changing the value of n of the number of oxyethylene groups (n = 1 to 30) in polyethylene glycols used as a swelling agent. In this method, the water permeation rate can be increased, but at the same time, it is difficult to improve the molecular weight fractionation characteristics. In order to further improve the molecular weight fractionation properties,
It is indispensable to form uniform pores in the membrane. For this purpose, a dope consisting of cellulose esters, a solvent, and a swelling agent that can easily achieve a suitable phase separation state must be used. Must be strictly selected.

[0004] As a method for smoothing the inner surface of the hollow fiber membrane, a method of lowering the liquid temperature of the core agent to a lower temperature than that of the spinning solution (Japanese Patent Application Laid-Open No. 56-96909), or a method in which the core agent and the spinning solution are incompatible. A method using a substance having low compatibility (Japanese Patent Application Laid-Open No.
No. 33211) has been proposed. However, JP-A-56
With the method described in -96909, it is difficult to completely suppress the interdiffusion between the spinning dope and the core agent. Further, even with the method proposed in JP-A-57-133211, the smoothness of the film is not sufficiently achieved.
This indicates that it is difficult to obtain a hollow fiber membrane having excellent inner surface smoothness only by using a substance which is incompatible with or less compatible with the spinning solution as a core agent.

[0005]

SUMMARY OF THE INVENTION In view of these prior arts, the present invention aims to provide a method for producing a hollow fiber membrane having a high water permeation rate, excellent molecular weight fractionation properties, and excellent internal smoothness. Is what you do.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies in view of the above-mentioned problems, and have found that the mixing ratio of N-methylpyrrolidone and propylene glycol is from 7: 1 to 5: 3 (weight ratio). A spinning solution in which 10 to 25% by weight of cellulose triacetate is uniformly dissolved in 90 to 75% by weight of the solution is extruded from an outer tube slit of a spinning nozzle having a double tube structure, and is spun as a core agent from an inner tube of the spinning nozzle. Simultaneously extruding the undiluted solution and the incompatible liquid, running the discharged material in a gaseous atmosphere, and finding that the above-mentioned problem can be solved by coagulating in a coagulation bath, the present invention has been completed. .

That is, the present invention provides a mixture of cellulose triacetate in which N-methylpyrrolidone and propylene glycol are mixed in a weight ratio of 8: 1 to 5: 3 so that the concentration of cellulose triacetate is 10 to 25% by weight. The uniformly dissolved spinning solution is extruded from the outer tube slit of a spinning nozzle having a double tube structure, and at the same time, a liquid immiscible with the spinning solution is extruded as a core agent from the inner tube of the spinning nozzle. This is a method for producing a hollow fiber membrane by running in a gaseous atmosphere and then introducing it into a coagulation bath for coagulation.

In the method of the present invention, cellulose triacetate is used as a raw material. Cellulose triacetate has been conventionally used as a material for forming a hollow fiber membrane, and the same material can be used in the method of the present invention.

In the method of the present invention, this cellulose triacetate is uniformly dissolved in a mixture of N-methylpyrrolidone and propylene glycol at a specific ratio to form a spinning dope, which is formed into a spinning nozzle having a double tube structure (a spinneret). )
It is important to extrude a liquid that is incompatible with the spinning dope as a core agent from the inner tube of the spinning nozzle while extruding through the annular outer tube slit.

In preparing a spinning dope, when a system other than a mixture of N-methylpyrrolidone and propylene glycol is used as a system for dissolving cellulose acetate, the object of the present invention is to achieve a high water permeation rate and a high molecular weight. A hollow fiber membrane having excellent fractionation properties and excellent inner surface smoothness cannot be obtained. That is, instead of propylene glycol,
For example, when polyethylene glycol or a polyethylene glycol derivative is used, a hollow fiber membrane having excellent inner surface smoothness cannot be obtained. Further, in the case of using polypropylene glycol such as dipropylene glycol and tripropylene glycol instead of propylene glycol, or a polypropylene glycol derivative such as dipropylene glycol monomethyl ether,
It is difficult to obtain a hollow fiber membrane having a high water permeation rate and excellent molecular weight fractionation characteristics.

[0011] Further, when a liquid incompatible with the spinning solution is not used as the core material, mutual diffusion of the spinning solution and the core material solution occurs,
The interface between the core solution and the spinning solution is disturbed, and the inner surface of the hollow fiber becomes rough. As the core agent used in the method of the present invention, any liquid may be used as long as it is incompatible with the spinning dope, and liquid paraffin is particularly preferred.

In order to produce a hollow fiber membrane having a high water permeation rate and excellent molecular weight fractionation properties, the ratio of N-methylpyrrolidone to propylene glycol is important.
It is necessary that the weight ratio between the two be from 8: 1 to 5: 3, with 5: 1 to 2: 1 being preferred. When the ratio of N-methylpyrrolidone is more than 8: 1 with respect to propylene glycol, the water permeation rate is reduced. On the other hand, when the ratio is less than 5: 3, it is difficult to uniformly dissolve the spinning dope, and as a result, the spinnability deteriorates and the It is difficult to manufacture a hollow fiber membrane.

Further, the cellulose triacetate concentration (content) in the spinning dope needs to be 10 to 25% by weight, preferably 15 to 23% by weight. When the concentration of cellulose triacetate exceeds 25% by weight, it is difficult to obtain a hollow fiber membrane having a high water permeation rate. On the other hand, when the concentration is less than 10% by weight, spinning becomes unstable. It becomes difficult, and the strength of the hollow fiber is reduced, and the yarn leaks easily.

Therefore, according to the method of the present invention, the undiluted spinning solution is prepared by mixing 90 to 75% by weight of a mixture of N-methylpyrrolidone and propylene glycol at a predetermined ratio and 10 to 25% by weight of cellulose triacetate to form a uniform solution. Need to be prepared.

[0015] In the method of the present invention, the viscosity of the spinning solution during spinning is 100 to 2000 poise, particularly 300 to 1 poise.
It is preferable to control the temperature of the spinning solution so as to be 000 poise. When the viscosity is less than 100 poise, it is difficult to obtain a hollow fiber having a uniform inner diameter. On the other hand, when the viscosity exceeds 2,000 poise, the spinnability deteriorates, so that it is difficult to obtain a uniform and thin hollow fiber membrane. Becomes

In the method of the present invention, the spinning solution and the core agent as described above are simultaneously discharged from the outer annular slit and the core agent from the central inner tube by using a spinning nozzle (die) having a double tube structure. And a sheath-core thread and none,
After running this in a gas atmosphere, it is introduced into a coagulation bath. Such a spinning method is known as a semi-dry semi-wet method. In the method of the present invention, the distance traveled in a gas atmosphere after discharge differs depending on the spinning speed.
In the case of minutes, 1 to 50 cm is appropriate. Further, as the coagulation bath, water or an organic solvent aqueous solution is preferable, but any coagulation bath can be arbitrarily selected as long as it can coagulate the discharged material.

In the coagulation bath, the solvent and propylene glycol elute and coagulate as hollow fibers to form the hollow fiber membrane of the present invention.

The above coagulation bath temperature is preferably from 10 to 50 ° C. If the coagulation bath temperature is less than 10 ° C., it is difficult to obtain a hollow fiber membrane having a high water permeation rate. When the temperature exceeds 50 ° C, the water permeability is large,
The molecular weight fractionation characteristics are reduced, the water permeation rate is high, and a hollow fiber membrane having excellent molecular weight fractionation characteristics cannot be obtained. When the coagulation bath temperature exceeds 50 ° C., it tends to be difficult to obtain a hollow fiber membrane having excellent inner surface smoothness.

The hollow fiber that has exited the coagulation bath may be further used, if necessary.
Water washing, drying, glycerin treatment, washing of the core, and the like are performed.

[0020]

According to the method of the present invention as described above, it is possible to easily produce a hollow fiber membrane having a high water permeation rate, excellent molecular weight fractionation properties, and good internal smoothness. The membrane can be effectively used not only for filtration and separation of liquids such as a permeation method, ultrafiltration method, and dialysis method, but also for separation of a mixed gas.

[0021]

The embodiments of the method of the present invention will be specifically described below with reference to comparative examples. Here, the dextran transmittance SC having a molecular weight of 70000 is defined by the following equation.

SC = C ₂ ÷ C ₁ C ₁ represents the concentration of dextran having a molecular weight of 70000 in the stock solution, and C ₂ represents the concentration of dextran having a molecular weight of 70000 in the permeate.

The root mean square roughness (Rms) of the inner surface of the film is measured by an atomic force microscope (Seiko Electronics SPI-
3600, SFA-300 AFM unit)
This is the value obtained by measuring the inner surface shape under the conditions of a scan range of 5 μm and a scan force of 5 nm.

[0024]

Example 1 20 parts by weight of cellulose triacetate
56 parts by weight of N-methylpyrrolidone and 24 parts by weight of propylene glycol were mixed and dissolved, and this was used as a spinning dope, and spinning was performed using a spinning nozzle having a double tube structure. That is, the spinning solution at 100 ° C. was supplied from the outer tube of the nozzle, and liquid paraffin was discharged from the inner tube as a core agent. The hollow spinning stock solution that has exited the annular orifice is 15c
m, then guided into a coagulation bath of a 10% by weight aqueous solution of NMP kept at 35 ° C. for 1.1 seconds, coagulated, washed with a water washing bath, and wound up at a speed of 40 m / min. .

The cross-sectional shape of the obtained cellulose triacetate hollow fiber membrane is a perfect circle, and has an inner diameter of 204 μm and a thickness of 15 μm.
There was almost no variation in shape at μm. Also, the ultrafiltration rate U of the obtained cellulose triacetate hollow fiber membrane was
FR is 159 ml / hr · mmHg · 1.5 m ² , molecular weight 10,000 and dextran transmittance DA is 39 ml.
/ Min. -The hollow fiber membrane was as large as 1.5 m < ² > and had an extremely small dextran transmittance SC of 0.017 with a molecular weight of 70,000 as low as 0.017. The root mean square roughness (Rms) of the inner surface of the hollow fiber membrane was as small as 11 nm. Thus, a cellulose triacetate hollow fiber membrane having a high water permeation rate, excellent molecular weight fractionation properties, and excellent inner surface smoothness was obtained.

[0026]

Comparative Example 1 20 parts by weight of cellulose triacetate
62 parts by weight of N-methylpyrrolidone and 18 parts by weight of triethylene glycol were mixed and dissolved, and this was used as a spinning dope.
Spinning was performed using a spinning nozzle having a double tube structure. That is, the spinning solution at 110 ° C. was supplied from the outer tube, and liquid paraffin was discharged from the inner tube as a core agent. The hollow spinning solution leaving the annular orifice is run in 10 cm air, then guided into a coagulation bath of a 30% by weight aqueous solution of NMP maintained at 40 ° C., coagulated, and then washed in a water washing bath, and washed with a water bath at 30 m / m 2. Wound at a speed of minutes.

The ultrafiltration rate UFR of the obtained cellulose triacetate hollow fiber membrane is 399 ml / hr · mmHg
A dextran transmittance DA of 1.5 m ² and a molecular weight of 10,000 is 48 ml / min. -Dextran transmittance SC with a molecular weight of 70000, which is as large as 1.5 m ^2, is 0.1.
389, and the root mean square roughness (Rms) of the inner surface of the hollow fiber membrane was as large as 26 nm.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-6826 (JP, A) JP-A-54-88883 (JP, A) JP-A-54-88881 (JP, A) JP-A-57-1988 133211 (JP, A) JP-A-61-185305 (JP, A) JP-A-60-58210 (JP, A) JP-A-63-28405 (JP, A) JP-A-56-67505 (JP, A) JP-A-55-36335 (JP, A) JP-A-55-622214 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B01D 71/16 D01D 5/24 D01F 2/28

Claims (4)

(57) [Claims] 1. A cellulose triacetate is uniformly dissolved in a mixture of N-methylpyrrolidone and propylene glycol in a weight ratio of 8: 1 to 5: 3 so that the concentration of cellulose triacetate is 10 to 25% by weight. The spinning solution is extruded from the outer tube slit of a spinning nozzle having a double tube structure, and simultaneously, a liquid immiscible with the spinning solution is extruded as a core agent from the inner tube of the spinning nozzle, and the filamentous discharge is subjected to a gas atmosphere. A method for producing a hollow fiber membrane comprising cellulose triacetate, wherein the hollow fiber membrane is introduced into a coagulation bath and coagulated after running through the inside. 2. The method for producing a hollow fiber membrane according to claim 1, wherein liquid paraffin is used as the core agent. 3. A spinning dope having a viscosity of 100 to 100 during spinning.
3. The method for producing a hollow fiber membrane according to claim 1, wherein the extrusion is performed by heating to a temperature of 2000 poise. 4. The method for producing a hollow fiber membrane according to claim 1, wherein the temperature of the coagulation bath is 10 to 50 ° C.