JP2008161755A - Manufacturing method of hollow fiber membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for sufficiently removing a hydrophilic polymer remaining in a hollow fiber membrane at a low cost and in a short time without enlarging equipment. <P>SOLUTION: In the manufacturing method of the hollow fiber membrane 10 comprising a step of coagulating a film forming stock solution containing the hydrophobic polymer and the hydrophilic polymer to form the hollow fiber membrane 10, and a hydrophilic polymer removing step of removing the hydrophilic polymer remaining in the hollow fiber membrane 10, at least the pressure-reduction to discharge the hydrophilic polymer to the outer peripheral side of the hollow fiber membrane 10 is conducted by reducing pressure of the outer peripheral side of the hollow fiber membrane 10 as the hydrophilic polymer removing step. In this occasion, it is preferable that the pressure-reduction is conducted to the hollow fiber membrane 10 immersed in a washing solution. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a hollow fiber membrane suitably used for a filtration membrane or the like.

  Concentrating and collecting useful components in the fields of food industry, medical field, electronics industry, etc., removal of unnecessary components, fresh water, etc. are composed of cellulose acetate, polyacrylonitrile, polysulfone, fluororesin, etc. Porous hollow fiber membranes produced by dry and wet spinning are frequently used for microfiltration membranes, ultrafiltration membranes, reverse osmosis filtration membranes and the like.

  In the case of producing a hollow fiber membrane by wet or dry wet spinning, first, a membrane forming stock solution containing a hydrophobic polymer and a hydrophilic polymer is prepared. Here, the hydrophilic polymer is added in order to adjust the viscosity of the membrane-forming stock solution to a range suitable for the formation of the hollow fiber membrane and stabilize the membrane-forming state, such as polyethylene glycol and polyvinylpyrrolidone. Is often used. Subsequently, a hollow fiber membrane is obtained by a coagulation step in which the membrane-forming stock solution is discharged in a ring shape and coagulated in the coagulation solution. In addition, the film-forming stock solution may be introduced into the coagulating liquid through a free running portion that is in contact with air (dry wet spinning method) or directly into the coagulating liquid (wet spinning method).

  However, in the hollow fiber membrane obtained at this point, a large amount of the hydrophilic polymer usually remains in the porous portion in a solution state. If the hydrophilic polymer remains in this way, the water permeation performance, which is one of the important performances required for the hollow fiber membrane, becomes insufficient. Therefore, after the coagulation step, a step of removing the remaining hydrophilic polymer from the hollow fiber membrane is necessary for obtaining a highly permeable hollow fiber membrane.

  As a method for removing the remaining hydrophilic polymer from the hollow fiber membrane, there is a method of washing the hollow fiber membrane in a water bath. However, this method generally takes a long time because the hydrophilic polymer in the hollow fiber membrane is removed from the hollow fiber membrane by diffusing and moving in the water bath. Therefore, when such a cleaning method is adopted in the process of continuously producing hollow fiber membranes, it is necessary to extremely increase the water bath equipment for cleaning in order to ensure sufficient cleaning time, and the point of manufacturing cost There is a problem. In addition, a method for removing a hydrophilic polymer from a hollow fiber membrane using an oxidizing agent or a hydrolyzing agent is also generally known (see, for example, Patent Document 1), but this method also requires a long time. .

Patent Document 2 discloses a method in which a solidified hollow fiber membrane is held in an oxidizing agent and then heated in a gas phase. According to this method, it is considered that the hydrophilic polymer can be effectively removed by controlling the concentration of the oxidant and the temperature at the time of heating in the gas phase. After the heating, it is necessary to finally wash the hollow fiber membrane to remove the low molecular weight hydrophilic polymer. The removal of the hydrophilic polymer in this washing step is also applied to the hollow fiber membrane. This is due to the diffusion movement of the remaining hydrophilic polymer.
The speed of diffusion transfer depends on the concentration difference between the concentration of the hydrophilic polymer remaining in the hollow fiber membrane and the concentration of the hydrophilic polymer on the outer surface of the membrane, so that the cleaning with a high concentration of the remaining hydrophilic polymer is performed. In the initial stage, the diffusion transfer rate is high, and a hydrophilic polymer removal effect that is adequate for the washing time can be expected. However, when the concentration of the hydrophilic polymer remaining in the hollow fiber membrane is gradually lowered, the above-mentioned concentration difference is reduced, and accordingly, a long time is required for washing.
In order to develop higher water permeability, it is necessary to remove the hydrophilic polymer remaining in the hollow fiber membrane as much as possible. Thus, in the method relying on diffusion transfer, it still takes a long time for washing. Therefore, there is a concern about the increase in the size of the bathing facility and the accompanying increase in facility cost and running cost.

On the other hand, in Patent Document 3, the cleaning liquid is press-fitted from the outer peripheral side of the hollow fiber membrane to the inner peripheral side, that is, the hollow portion side in the pressurizing region, and the outer periphery of the hollow fiber membrane is pressed from the hollow portion in the non-pressurizing region A method is disclosed in which the cleaning liquid is discharged to the side and the hollow fiber membrane is cleaned.
Japanese Patent No. 3196029 JP-A-2005-42074 JP-A-9-57078

According to the method of Patent Document 3, it is considered that the hydrophilic polymer remaining in the hollow fiber membrane can be forcibly discharged to the outside with a cleaning liquid, compared with a cleaning method that relies on diffusion movement of the hydrophilic polymer. It can be expected that the cleaning time can be shortened.
However, in this method, even when the molecular weight of the remaining hydrophilic polymer is relatively large, even if the hydrophilic polymer dispersed in the washing liquid press-fitted in the pressurizing zone can move to the hollow portion side. In the non-pressurized region, there is a concern that the hydrophilic polymer is left behind in the hollow portion because the liquid passage resistance is not sufficiently discharged from the hollow portion side to the outer peripheral side.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method capable of sufficiently removing the hydrophilic polymer remaining in the hollow fiber membrane at low cost and in a short time without increasing the size of the equipment.

The method for producing a hollow fiber membrane of the present invention comprises a coagulation step in which a membrane-forming stock solution containing a hydrophobic polymer and a hydrophilic polymer is coagulated in a coagulation liquid to form a hollow fiber membrane, and the hollow fiber membrane remains in the hollow fiber membrane. In the method for producing a hollow fiber membrane having a hydrophilic polymer removal step for removing the hydrophilic polymer, the hydrophilic polymer removal step includes reducing the outer peripheral side of the hollow fiber membrane and removing the hydrophilic polymer from the hollow fiber. It has the pressure reduction process discharged | emitted to the outer peripheral side of a film | membrane, It is characterized by the above-mentioned.
At this time, it is preferable to perform the pressure reducing step on the hollow fiber membrane immersed in the cleaning liquid, and further, in the pressure reducing step, the cleaning liquid is passed from the inner peripheral side to the outer peripheral side of the hollow fiber membrane. It is preferable.
It is preferable that the hydrophilic polymer removing step further includes a cleaning liquid supply step for supplying the cleaning liquid from the outer peripheral side to the inner peripheral side of the hollow fiber membrane after the decompression step.
The hydrophilic polymer removing step preferably further includes the pressure reducing step after the cleaning liquid supplying step.
When the depressurization step is performed on the hollow fiber membrane immersed in the cleaning liquid, the hydrophilic polymer removal step includes a post-process for depressurizing the outer peripheral side of the hollow fiber membrane in the gas phase. It is preferable.

  According to the present invention, the hydrophilic polymer remaining in the hollow fiber membrane can be sufficiently removed at a low cost and in a short time without increasing the size of the equipment.

  The method for producing a hollow fiber membrane of the present invention comprises a coagulation step in which a membrane forming stock solution containing a hydrophobic polymer and a hydrophilic polymer is coagulated in a coagulation solution to form a hollow fiber membrane, and after this coagulation step, a hollow fiber is formed. A hydrophilic polymer removing step of removing the hydrophilic polymer remaining in the film. Moreover, after a hydrophilic polymer removal process, it usually has a drying process which dries a hollow fiber membrane. Hereinafter, the production method of the present invention will be described in detail.

[Coagulation process]
The method for producing a hollow fiber membrane of the present invention includes a coagulation step in which a membrane-forming stock solution containing a hydrophobic polymer and a hydrophilic polymer is coagulated in a coagulation solution to form a hollow fiber membrane.
There is no restriction | limiting in particular in the structure of the hollow fiber membrane to manufacture, The thing provided with the porous base material can also be manufactured. For example, when manufacturing a hollow fiber membrane having a braid as a porous substrate, for example, a nozzle having a hollow portion formed at the center and an annular discharge port formed outside thereof is used. A braid is introduced, and after the film forming stock solution from the discharge port is applied to the outer periphery of the braid, it is introduced into the coagulation liquid to perform the coagulation step. The hollow fiber membrane provided with the porous substrate has higher strength than the hollow fiber membrane not provided with the porous substrate. On the other hand, in the case of a normal hollow fiber membrane that does not include a porous substrate, the membrane-forming stock solution may be discharged from a nozzle in which an annular discharge port is formed. Alternatively, a membrane-forming solution may be applied to the outside of the membrane thus formed to form a multilayered membrane to produce a hollow fiber membrane that is durable against rubbing during handling.
Further, the coagulation step may be performed by either a dry-wet spinning method in which the film-forming stock solution is introduced into the coagulating solution through an idle running portion in contact with air or a wet spinning method that is directly guided to the coagulating solution.

  The hydrophobic polymer is not particularly limited as long as it can form a hollow fiber membrane by a coagulation step, and can be used without particular limitation as long as it is such as polysulfone resin such as polysulfone or polyethersulfone, polyvinylidene fluoride, etc. And fluororesin, polyacrylonitrile, cellulose derivatives, polyamide, polyester, polymethacrylate, polyacrylate, and the like. Further, copolymers of these resins may be used, and those having a substituent introduced into a part of these resins and copolymers can also be used. Further, the same type of polymers having different molecular weights may be blended and used, or two or more different types of resins may be mixed and used. Among these, fluororesins, especially polyvinylidene fluoride and copolymers made of vinylidene fluoride and other monomers have excellent durability against oxidizing agents such as hypochlorous acid. Therefore, when producing a hollow fiber membrane that is treated with an oxidizing agent, it is preferable to select a fluororesin as the hydrophobic polymer.

The hydrophilic polymer is added to adjust the viscosity of the membrane-forming stock solution to a range suitable for the formation of the hollow fiber membrane and stabilize the membrane-forming state. Polyethylene glycol, polyvinyl pyrrolidone, etc. are preferable. used. Among these, polyvinylpyrrolidone and a copolymer obtained by copolymerizing other monomers with polyvinylpyrrolidone are preferable from the viewpoint of controlling the pore diameter of the hollow fiber membrane and the strength of the hollow fiber membrane.
Moreover, 2 or more types of resin can also be mixed and used for a hydrophilic polymer. For example, when a higher molecular weight hydrophilic polymer is used, a hollow fiber membrane having a good membrane structure tends to be formed. On the other hand, the low molecular weight hydrophilic polymer is suitable in that it is more easily removed from the hollow fiber membrane in the hydrophilic polymer removing step described later. Therefore, the same kind of hydrophilic polymers having different molecular weights may be appropriately blended depending on the purpose.

A film-forming stock solution can be prepared by mixing the above-described hydrophobic polymer and hydrophilic polymer in a solvent in which they are soluble (good solvent). Other additive components may be added to the film-forming stock solution as necessary.
There is no particular limitation on the type of solvent, but when performing the coagulation process by dry and wet spinning, the pore diameter of the hollow fiber membrane is adjusted by absorbing the membrane forming stock solution in the idle running section, so that it is mixed uniformly with water. It is preferable to select a solvent that can be easily treated. Examples of such a solvent include N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, N-methyl-2-pyrrolidone, N-methylmorpholine-N-oxide, and the like. Can be used. Moreover, you may mix and use the poor solvent of a hydrophobic polymer or a hydrophilic polymer in the range which does not impair the solubility of the hydrophobic polymer or hydrophilic polymer to a solvent.

If the concentration of the hydrophobic polymer in the membrane forming stock solution is too thin or too thick, the stability at the time of membrane formation tends to be reduced, and it is difficult to form a suitable hollow fiber membrane structure. % By mass is preferable, and 15% by mass is more preferable. Further, the upper limit is preferably 30% by mass, and more preferably 25% by mass.
On the other hand, the lower limit of the concentration of the hydrophilic polymer is preferably 1% by mass and more preferably 5% by mass in order to make the hollow fiber membrane easier to form. The upper limit of the concentration of the hydrophilic polymer is preferably 20% by mass, and more preferably 12% by mass from the viewpoint of the handleability of the film-forming stock solution.

  As the coagulation liquid, water, alcohols, glycerin, ethylene glycol or the like can be used alone or in combination.

[Hydrophilic polymer removal step]
The hollow fiber membrane formed by the above-mentioned coagulation process generally has a large pore diameter and potentially has high water permeability, but a large amount of hydrophilic polymer remains in the hollow fiber membrane in a solution state. Therefore, sufficient high water permeability cannot be exhibited as it is. Therefore, after the coagulation step, a hydrophilic polymer removal step for removing the hydrophilic polymer remaining in the hollow fiber membrane is performed.

  In the present invention, as the hydrophilic polymer removing step, it is necessary to perform at least a pressure reducing step described later, but before that, as a preliminary step, (i) a hollow fiber membrane washing step described below, and (ii) The step of reducing the molecular weight of the hydrophilic polymer using an oxidizing agent and the step of washing the hydrophilic polymer having the reduced molecular weight may be sequentially performed. Whether or not to perform such a preliminary process may be appropriately determined mainly depending on the structure of the hollow fiber membrane. For example, when the hollow fiber membrane has a multilayer structure or when the pore diameter is dense, it is preferable to carry out the preliminary steps (i) to (iii), and this preliminary step is repeated a plurality of times as necessary. It is preferable to carry out in order to further enhance the effect of the subsequent decompression step.

(Preliminary process)
(I) Hollow fiber membrane washing step In the hollow fiber membrane obtained in the coagulation step, the hydrophilic polymer remains in the membrane (porous portion) in a high-concentration solution state. Such a high concentration of the hydrophilic polymer is relatively easily removed to some extent by immersing the hollow fiber membrane in a cleaning solution. Therefore, it is preferable to first perform the step of immersing and cleaning the hollow fiber membrane in a cleaning solution as a preliminary step.
The cleaning liquid is not particularly limited as long as it is a clear liquid in which the hydrophilic polymer is dispersed or dissolved, but water is preferable because of its high cleaning effect. Examples of water to be used include tap water, industrial water, river water, well water, and the like, and alcohols, inorganic salts, oxidizing agents, surfactants, and the like may be mixed and used. In addition, as the cleaning liquid, a mixed liquid of a good solvent for the hydrophobic polymer and water can be used. When such a mixture is used, the hydrophobic polymer constituting the hollow fiber membrane can be appropriately swollen, and as a result, the hydrophilic polymer remaining in the hollow fiber membrane can be easily eluted. When such a mixed solution is used, the higher the proportion of the good solvent in the mixed solution, the greater the effect.However, if the proportion is too high, the hollow fiber membrane will dissolve, so the proportion of the good solvent in the mixed solution The upper limit is preferably 85% by mass, and more preferably 70% by mass.

When the hollow fiber membrane is immersed and washed in the cleaning liquid, the hydrophilic polymer is mainly removed by diffusion movement, and therefore, treatment for enhancing the effect of diffusion movement may be performed together. For example, bubbling or cascade processing may be performed to increase the concentration gradient, or the cleaning solution may be forced to flow. Further, the temperature of the cleaning liquid may be increased, or degassed water may be used as the cleaning liquid. These treatments are effective even when used alone, but it is more preferable to carry out these treatments in combination.
For example, the washing temperature is preferably higher, preferably 50 ° C. or higher, more preferably 80 ° C. or higher, in order to keep the viscosity of the hydrophilic polymer solution low and prevent a decrease in diffusion transfer rate. Further, when cleaning is performed while boiling the cleaning liquid, the outer surface of the hollow fiber membrane can be scraped off by bubbling due to boiling, so that efficient cleaning is possible.

(Ii) Step of lowering the molecular weight of the hydrophilic polymer using an oxidizing agent The hydrophilic polymer remaining in the hollow fiber membrane is in a relatively low concentration state due to the above-described (i) washing step of the hollow fiber membrane. . In order to obtain a higher cleaning effect at such a low concentration, it is preferable to reduce the molecular weight by oxidizing and decomposing the hydrophilic polymer using an oxidizing agent.
Specifically, it is preferable to first hold a chemical solution containing an oxidizing agent in the hollow fiber membrane, and then heat the hollow fiber membrane holding the chemical solution in a gas phase. In order to retain a chemical solution containing an oxidant in the hollow fiber membrane, a method of infiltrating the oxidant into the membrane (porous portion) of the hollow fiber membrane or an oxidant to the hydrophilic polymer remaining on the surface of the hollow fiber membrane It is conceivable to absorb and swell, and as a specific method for that purpose, an oxidizing agent is attached to the roller surface, the hollow fiber membrane is wound around the roller and brought into contact with the oxidizing agent, and is slightly larger than the outer diameter of the hollow fiber membrane. There is also a method of directly applying an oxidizing agent to the hollow fiber membrane surface by supplying an oxidizing agent to the inner surface of the ring through a hollow fiber membrane through the inner diameter ring hole, but the hollow fiber membrane is immersed in a chemical solution containing the oxidizing agent. The method is preferably the method.

  As the oxidizing agent, ozone, hydrogen peroxide, permanganate, dichromate, persulfate, etc. can be used, but it has strong oxidizing power and excellent decomposition performance, excellent handling properties, and low cost. Of these, hypochlorite is particularly preferable. Examples of hypochlorite include sodium hypochlorite and calcium hypochlorite, with sodium hypochlorite being particularly preferred.

  When the hollow fiber membrane is immersed in a chemical solution containing an oxidizing agent, at least a part of the hydrophilic polymer remaining in the hollow fiber membrane starts oxidative decomposition and is eluted into the chemical solution, consuming the oxidizing agent. Therefore, during immersion, it is preferable to add an oxidant as appropriate to the chemical solution in order to maintain the oxidant concentration of the chemical solution within a certain range. However, at the time of such immersion, the chemical solution is simply immersed in the hollow fiber membrane, and the hydrophilic polymer is not oxidatively decomposed as much as possible. It is preferable that the oxidative decomposition is performed in that the amount of the oxidizing agent to be used is minimized. For this purpose, the temperature of the chemical solution is preferably 50 ° C. or lower, and more preferably 30 ° C. or lower. When the temperature is higher than 50 ° C., oxidative decomposition is promoted during the immersion of the hollow fiber membrane, and the hydrophilic polymer that has fallen into the chemical solution is further oxidatively decomposed, leading to waste of the oxidant. Such waste of the oxidizing agent tends to increase the labor and cost of the work and also increase the load of waste liquid treatment. On the other hand, when the temperature is excessively low, the oxidative decomposition is suppressed, but the cost for controlling the temperature to a low temperature tends to increase as compared with the case of carrying out at normal temperature. Therefore, from this point, the temperature of the chemical solution is preferably 0 ° C. or higher, and more preferably 10 ° C. or higher.

  Moreover, when using hypochlorite as an oxidizing agent, in order to suppress decomposition | disassembly of a hypochlorite as much as possible, it is preferable that the pH of the chemical | medical solution containing an oxidizing agent shall be 11 or more. Furthermore, the concentration of the oxidant in the chemical solution needs to be in a suitable range because the oxidant is consumed as little as possible by oxidative decomposition treatment with a small amount of pickup, and when using hypochlorite, The lower limit of the effective chlorine concentration is preferably 2000 mg / L, more preferably 5000 mg / L or more. The upper limit is preferably 120,000 mg / L or less, more preferably 100000 mg / L or less.

  After the chemical solution is held in the hollow fiber membrane, the hydrophilic polymer is oxidatively decomposed by heating the hollow fiber membrane in the gas phase. By heating in the gas phase, the chemical liquid retained in the hollow fiber membrane is hardly diluted and the chemical liquid is hardly dropped and eluted into the heating medium, so that the oxidizing agent in the chemical liquid is the hollow fiber membrane. It is preferable because it is efficiently used for decomposing the hydrophilic polymer remaining therein.

As a specific heating method, it is preferable to heat the hollow fiber membrane using a heating fluid under atmospheric pressure. By performing under atmospheric pressure, even if continuous processing is performed, there is no need to provide a special sealing device at the entrance and exit of the hollow fiber membrane or use a pressure-resistant structure device, so the device merit is great, The operability is also very good.
In addition, using a fluid with high relative humidity as the heating fluid, that is, heating under humid heat conditions, prevents drying of oxidants such as hypochlorite and enables efficient decomposition treatment. preferable. At that time, the relative humidity of the fluid is preferably 80% or more, more preferably 90% or more, and most preferably in the vicinity of 100%.
The lower limit of the heating temperature is preferably 50 ° C., more preferably 80 ° C., because the treatment time can be shortened when continuous treatment is performed. The upper limit of the temperature is preferably 100 ° C. in the atmospheric pressure state.

(Iii) Washing step of hydrophilic polymer with reduced molecular weight Thus, after carrying out the step of lowering the molecular weight of hydrophilic polymer using an oxidizing agent as described above, (i) Washing the hollow fiber membrane described above It is preferable to remove the hydrophilic polymer having a reduced molecular weight to some extent by again immersing the hollow fiber membrane in a washing solution and washing under the same conditions as in the step.

(Decompression process and cleaning liquid supply process)
After performing a preliminary process as needed as mentioned above, a pressure reduction process is performed. According to such a decompression step, even a hydrophilic polymer that remains even after the preliminary step can be effectively removed.
The depressurization step is a step of depressurizing the outer peripheral side of the hollow fiber membrane and discharging the hydrophilic polymer remaining in the hollow fiber membrane to the outer peripheral side of the hollow fiber membrane. The hydrophilic polymer is moved to the outer peripheral side of the hollow fiber membrane and removed by the pressure difference at that time so as to be lower than the peripheral side (hollow part).

Although there is no restriction | limiting in particular in the specific method of a pressure reduction process, For example, the method of using the pressure-resistant cylinder member 11 as shown in FIG. 1 is mentioned.
The cylindrical member 11 is formed with a connection port 11a for connecting a decompression means such as a decompression pump on the side surface, and at both ends, the tubular member 11 has a clearance that allows the hollow fiber membrane 10 to pass therethrough. A seal mechanism (not shown) made of, for example, a labyrinth seal or the like, which can keep the inside of 11 at a reduced pressure state or a pressurized state from the outside, is provided. Such a cylindrical member 11 is disposed in a gas phase such as the atmosphere, and the hollow fiber membrane 10 that has undergone a solidification step and a preliminary step as necessary is continuously introduced into the cylindrical member 11 from its one end 11b. By operating the decompression means, the outer peripheral side of the hollow fiber membrane 10 is decompressed in the cylindrical member 11, and the hydrophilic polymer remaining in the hollow fiber membrane 10 is entrained in the gas phase to the outer peripheral side of the hollow fiber membrane 10. And sucked and removed.

As a more preferable method, as shown in FIG. 2, a cleaning tank 12 containing a cleaning liquid is prepared, the hollow fiber membrane 10 is immersed in the cleaning tank 12, and the hollow fiber membrane 10 immersed in the cleaning liquid is used. Then, the method of performing the pressure reduction process similarly to the case of FIG.
When the pressure reducing step is performed in this manner, if the pressure difference between the inner peripheral side and the outer peripheral side of the hollow fiber membrane 10 is large, it is possible to cause a flow of cleaning liquid mainly as indicated by arrows in FIG. As a result, in the hollow fiber membrane 10 exposed from the cylindrical member 11 and immersed in the cleaning liquid, the cleaning liquid in the cleaning tank 12 passes through the membrane (porous portion), and the inside of the hollow fiber membrane 10 Introduced on the circumferential side. The introduced cleaning liquid then passes through the membrane (porous part) again by the operation of the decompression means and is discharged to the outer peripheral side. As a result, the hydrophilic polymer remaining in the hollow fiber membrane 10 is removed from the connection port 11a together with the cleaning liquid.
As described above, according to the method in which the cleaning liquid is passed from the inner peripheral side to the outer peripheral side of the hollow fiber membrane 10 by the decompression step, the hydrophilic polymer separated from the hollow fiber membrane 10 is dispersed or dissolved in the cleaning liquid and sucked together with the cleaning liquid Therefore, the concern of adhering to the hollow fiber membrane 10 is reduced, and a high removal effect is obtained.
In addition, when the decompression step is performed on the hollow fiber membrane 10 immersed in the cleaning liquid, the hollow fiber membrane 10 depends on the operating pressure (gauge pressure) of the decompression means, the structure of the hollow fiber membrane 10, and the like. In some cases, the pressure difference between the inner peripheral side and the outer peripheral side does not increase. In that case, due to the flow resistance, the cleaning liquid in the cleaning tank 12 cannot pass from the outer peripheral side to the inner peripheral side through the membrane (porous portion), and as a result, air is not supplied to the inner peripheral side. In some cases, the cleaning liquid may not be introduced to the inner peripheral side while it is full. However, even in that case, since the cleaning liquid in the cleaning tank 12 is absorbed to some extent at least by the membrane (porous portion) of the hollow fiber membrane 10, the flow of the cleaning liquid mainly as indicated by the arrows in FIG. The flow of the outer periphery side of the thread membrane 10 → the membrane (porous portion (shown in the cross section in the figure)) 10a → the outer periphery side occurs, and the absorbed cleaning liquid is discharged to the outer periphery side of the hollow fiber membrane 10 by the operation of the decompression means. Is done. As a result, even in this case, the hydrophilic polymer remaining in the hollow fiber membrane 10 is removed together with the cleaning liquid to the outer peripheral side of the hollow fiber membrane 10 and discharged from the connection port 11a.

As a more effective method, there may be mentioned a method of providing a cleaning liquid supply process for forcibly supplying the cleaning liquid from the outer peripheral side to the inner peripheral side of the hollow fiber membrane 10 after the decompression process.
Specifically, as shown in FIG. 5, two cylindrical members 11, 11 are installed in series in the cleaning tank 12 with a space therebetween, and are connected to the connection port 11 a of the cylindrical member 11 on the front stage side (left side in the figure). Is connected to a pressure reducing means (not shown), and a supply means (not shown) such as a pressure supply pump for supplying a cleaning liquid is connected to the connection port 11a of the cylindrical member 11 on the rear side (right side in the figure).
Then, the hollow fiber membrane 10 is sequentially introduced into the cylindrical members 11 and 11 from the front side, and the decompression means and the supply means are operated. Then, the flow of the cleaning liquid mainly as indicated by the arrow in FIG. 6 occurs, and the cleaning liquid is supplied from the outer peripheral side of the hollow fiber membrane 10 to the inner peripheral side in the cylindrical member 11 on the rear stage (cleaning liquid supplying step). In the cylindrical member 11 on the front side, the cleaning liquid can be passed from the inner peripheral side of the hollow fiber membrane 10 to the outer peripheral side (decompression step).
Thus, when the cleaning liquid supply process is provided after the pressure reducing process, the amount of the cleaning liquid flowing from the inner peripheral side to the outer peripheral side of the hollow fiber membrane 10 in the pressure reducing process is increased as compared with the case of FIG. The removal effect of the polymer is increased.

The conditions for the decompression step and the cleaning liquid supply step may be set as appropriate according to the membrane structure of the hollow fiber membrane 10 and the concentration of the hydrophilic polymer remaining in the hollow fiber membrane 10. If the pressure is reduced or the supply pressure is excessively increased in the cleaning liquid supply process, the equipment cost for making the cylinder members 11 and 11 pressure resistant increases. In particular, when the supply pressure is high, the cleaning liquid supply process is performed. There is also a concern that a large amount of the cleaning liquid flows out from the sealing mechanism at both ends of the subsequent cylindrical member 11 and the hollow fiber membrane 10 shakes. It is also necessary to consider the pressure resistance performance of the hollow fiber membrane 10 itself. From these points, the pressure in the decompression step is preferably -0.05 to -0.1 MPa, more preferably -0.08 to -0.1 MPa as the gauge pressure of the decompression means, and the supply pressure in the cleaning liquid supply step Is preferably more than 0 and not more than 0.4 MPa, more preferably more than 0 and not more than 0.3 MPa. Further, within such a range, the higher the difference in gauge pressure between the decompression step and the cleaning liquid supply step, the higher the hydrophilic polymer removal effect tends to be obtained.
If each staying time of the hollow fiber membrane 10 in the decompression process and the cleaning liquid supply process (staying time in the cylindrical members 11, 11) is 2 to 10 seconds, respectively, a sufficient hydrophilic polymer removing effect can be obtained efficiently. be able to.

  The cleaning liquid in the cleaning tank 12 can be selected from those exemplified in the above (i) hollow fiber membrane cleaning step, and it is preferable to use water since it has a high cleaning effect. In the cleaning liquid supply step, the cleaning liquid may be supplied in the form of pressurized steam to the outer peripheral side of the hollow fiber membrane. Since the pressurized steam is reduced in pressure after being supplied and is pressed into the hollow fiber membrane 10 as a high-temperature cleaning liquid, the hydrophilic polymer can be more effectively captured and removed in the cleaning liquid.

In addition, in FIG. 5, although the method of performing a pressure reduction process and a washing | cleaning liquid supply process one by one in the state which immersed the hollow fiber membrane 10 in the washing tank 12 containing the washing | cleaning liquid was illustrated, it is not necessary to immerse in the washing tank 12 necessarily. Instead, two cylinder members are arranged in series in the gas phase such as in the atmosphere, a pressure reducing means is connected to the connection port of the front cylinder member, and cleaning liquid is supplied to the connection port of the rear cylinder member It is good also as a form which connects the supply means to perform.
However, if it is carried out in the washing tank 12 as shown in FIG. 5, the hollow fiber membrane 10 exposed between the two cylindrical members 11 and 11 is immersed in the washing liquid. The effect of washing the hydrophilic polymer can be obtained. In addition, when the cylindrical member is arranged in the gas phase, the cleaning liquid leaks out from the hollow fiber membrane exposed between the two cylindrical members, and it is necessary to perform operations such as wiping it off. On the other hand, if it is carried out in the washing tank 12 as shown in FIG. 5, there is no particular problem even if the washing liquid leaks out.
Furthermore, since the sealing mechanism at both ends of the cylindrical members 11 and 11 has a clearance that allows the hollow fiber membrane 10 to pass through as described above, the cylindrical members 11 and 11 are disposed in the gas phase. Rather than performing in a liquid phase having a higher viscosity than the gas phase as shown in FIG. 5, the purpose is to have the inside of the cylindrical members 11, 11 in a shorter time in each of the decompression process and the cleaning process. The pressure (gauge pressure) can be reached, and accordingly, the clearance of the seal mechanism can be set larger, or the installation length of the seal mechanism (the length direction of the cylindrical member) can be set shorter.

5 illustrates the case where the cleaning liquid supply process is provided in the subsequent stage of the decompression process, but the decompression process may be in the subsequent stage.
However, if the decompression step is in the latter stage, in the cleaning solution supply step, the cleaning solution is supplied to the hollow fiber membrane in which a large amount of the hydrophilic polymer remains without passing through the decompression step. As a result, the cleaning liquid containing a large amount of the hydrophilic polymer is supplied to the hollow fiber membrane in the decompression step, and the hydrophilic polymer in the supplied cleaning liquid may be reattached to the hollow fiber membrane. Therefore, it is preferable to provide the cleaning liquid supply process after the decompression process.

As a more preferable form, as shown in FIG. 7, a decompression process is provided again after the cleaning liquid supply process, and again, the cleaning liquid is allowed to flow from the inner peripheral side to the outer peripheral side of the hollow fiber membrane 10. A form is mentioned. According to such a method, since the decompression step is repeatedly provided, among the hydrophilic polymers remaining in the hollow fiber membrane 10, those attached to the wall surface of the porous portion of the hollow fiber membrane 10, etc. In particular, a high removal effect can be exhibited even for those that are difficult to remove. Also in this case, the pressure in each decompression step is preferably -0.05 to -0.1 MPa, more preferably -0.08 to -0.1 MPa as the gauge pressure of the decompression means. The pressure is preferably more than 0 and not more than 0.4 MPa, more preferably more than 0 and not more than 0.3 MPa as the gauge pressure of the supplying means.
In addition, in FIG. 7, although the case where 3 steps of a pressure reduction process-a washing | cleaning liquid supply process-a pressure reduction process are implemented from the front | former stage side is illustrated, On the rear stage side, the cleaning liquid supply step and the pressure reduction step may be repeated as appropriate.

(Post-process)
As described above, when at least the depressurization step of using the cleaning liquid and passing it from the inner peripheral side to the outer peripheral side of the hollow fiber membrane is performed, in the last stage in the hydrophilic polymer removing step, for example, FIG. As described above, it is preferable to perform a post-process in which the outer peripheral side of the hollow fiber membrane is decompressed in a gas phase such as in the air. By performing such a post-process, it is possible to mainly remove water remaining in the hollow fiber membrane, and to reduce the load of the subsequent drying process. In such a post-process, since the hydrophilic polymer in the hollow fiber membrane has already been removed and only water remains, effective water removal can be performed.

[Drying process]
There is no restriction | limiting in particular as a method of a drying process, What is necessary is just to carry out by the method of introduce | transducing a hollow fiber membrane into drying apparatuses, such as a hot air dryer.

  According to the method as described above, as the hydrophilic polymer removal step, since the outer peripheral side of the hollow fiber membrane is depressurized, and at least a depressurization step of discharging the hydrophilic polymer to the outer peripheral side of the hollow fiber membrane, The hydrophilic polymer remaining in the hollow fiber membrane can be sufficiently removed at a low cost and in a short time without increasing the size of the water bath facility as in the conventional method depending on the diffusion movement of the hydrophilic polymer.

The amount of the hydrophilic polymer remaining in the hollow fiber membrane is determined by obtaining the absorption spectrum of the hollow fiber membrane with an infrared spectrophotometer, and the absorption strength of the hydrophobic polymer and the absorption strength of the hydrophilic polymer in this absorption spectrum. Can be grasped by comparing For example, when a hollow fiber membrane is produced using polyvinylidene fluoride as a hydrophobic polymer and polyvinylpyrrolidone as a hydrophilic polymer, the absorption strength due to the carbonyl group stretching vibration (1700 cm ⁻¹ ) of polyvinylpyrrolidone and the polyvinylidene fluoride The absorption intensity by CF stretching vibration (1400 cm ⁻¹ ) is obtained. Then, when the absorption strength due to C—F stretching vibration of polyvinylidene fluoride is defined as 100%, the percentage of the absorption strength of the carbonyl group stretching vibration of polyvinylpyrrolidone is determined from the ratio of these absorption strengths. (%) Is the amount of remaining hydrophilic polymer.
Further, when the hollow fiber membrane is provided with a porous base material such as braid, for example, the hollow fiber membrane is added to a solvent (for example, N, N-dimethylacetamide or the like) and dissolved to be an insoluble component. After removing the porous substrate, the solution is evaporated to dryness on a glass plate or the like to form a film (for example, a thickness of about 20 μm), and the absorbance spectrum of this film may be measured as described above.

Hereinafter, the present invention will be described in detail based on examples.
[Example 1]
(Coagulation process)
Polyvinylidene fluoride A (manufactured by Atofina Japan, trade name Kyner 301F), polyvinylidene fluoride B (manufactured by Atofina Japan, trade name Kyner 9000LD), polyvinylpyrrolidone (manufactured by ISP, Trade name K-90) and N, N-dimethylacetamide were mixed to prepare a film-forming stock solution (1) and a film-forming stock solution (2).
Next, a hollow portion is formed at the center, and a nozzle in which an annular discharge port is sequentially formed on the outside so that two kinds of liquids can be sequentially applied (see FIG. 1 of JP-A-2005-42074). ) Is prepared, and this is kept at 30 ° C., and a polyester multifilament single filament braid (multifilament; 830T / 96F, 16 beats) is introduced into the hollow portion as a porous base material, and the outer periphery thereof is introduced. The film-forming stock solution (2) and the film-forming stock solution (1) were applied sequentially from the inside and coagulated in a coagulation liquid (mixed solution of 5 parts by mass of N, N-dimethylacetamide and 95 parts by mass of water) kept at 80 ° C. I let you. In this way, a hollow fiber membrane was obtained in which the braid was coated with a porous layer having an inclined structure having one fractional layer near the outer surface and increasing the pore diameter toward the inside. Of the applied film-forming stock solutions (1) and (2), the main stock solution forming the membrane structure of the hollow fiber membrane is the film-forming stock solution (1) applied to the outside.
In addition, a hollow portion having an inner diameter larger than the outer diameter of the hollow fiber membrane is formed in the center, and a nozzle having an annular discharge port formed in order so that two kinds of liquids can be sequentially applied to the outer side ( 1 is prepared, and the hollow fiber membrane obtained as described above is introduced into the hollow portion while keeping this at 30 ° C. Glycerin (first grade manufactured by Wako Pure Chemical Industries, Ltd.) and a film-forming stock solution (1) were sequentially applied from the inside and coagulated in the same coagulating liquid kept at 80 ° C. as previously used. In this way, a hollow fiber membrane having a braid support in a two-layer structure coated with a porous layer was obtained.
The spinning speed (running speed of the hollow fiber membrane) at this time was 7.3 m / min.

(Hydrophilic polymer removal step)
About the hollow fiber membrane obtained in this way, the hydrophilic polymer removal process was implemented as follows.
(1) Preliminary process The following processes (i) to (iii) were repeated twice as a preliminary process.
(I) Washing process of hollow fiber membrane The hollow fiber membrane was immersed in a washing tank containing boiling water at 100 ° C under the condition of staying time of 5 minutes for washing.
(Ii) Step of lowering the molecular weight of the hydrophilic polymer using an oxidizing agent Next, the hollow fiber membrane was placed in a water tank in which an aqueous solution of hypochlorite having a temperature of 30 ° C. and a concentration of 60000 mg / L was placed. Immersion was performed under the condition of minutes. Thereafter, the hydrophilic polymer was heated in a heat of 85 ° C. and a relative humidity of 100% under the condition of a residence time of 3 minutes to lower the molecular weight of the hydrophilic polymer.
(Iii) Step of washing hydrophilic polymer with reduced molecular weight Next, this hollow fiber membrane was washed again under the same conditions as in (i).
(2) Depressurization step-Decompression step As shown in FIG. 7, a cleaning tank 12 containing water at a temperature of 74 ° C. is prepared as a cleaning liquid, and the three cylindrical members 11, 11, 11 are spaced therein. Arranged in series. Then, the hollow fiber membranes 10 are sequentially introduced into the cylindrical members 11, 11, 11 from the front side, and the connection port 11 a of the frontmost cylindrical member 11 of the three and the connection of the last cylindrical member 11 of the three are connected. A pressure reducing means is connected to the mouth 11a, and the gauge pressure of the pressure reducing means is -0.06 MPa in the pressure reducing step on the front side (referred to as pressure reducing step (I) in Table 2), and the pressure reducing step on the rear side (Table 2). The pressure was reduced so that the pressure was reduced to 0.05 MPa. Moreover, the time (stay time) for which the hollow fiber membrane 10 stays in each cylindrical member 11, 11, 11 was made into about 3 second.
On the other hand, the supply means is connected to the connection port 11a of the central cylindrical member 11 among the three, and the cleaning liquid can be supplied separately. However, in the first embodiment, the supply means was not operated. The cylindrical member 11 to which the supply means was connected was filled with the cleaning liquid that had entered from the clearance of the seal mechanisms at both ends.

(Drying process)
After the hydrophilic polymer removal step, the hollow fiber membrane was passed through a drying step at 95 ° C. for 3 minutes.

The hollow fiber membrane having a braided support in a two-layer structure manufactured by such a coagulation step, hydrophilic polymer removal step, and drying step had an outer diameter of 2.8 mm and an inner diameter of 1.0 mm.
Further, when the amount (residual amount) of polyvinylpyrrolidone in the hollow fiber membrane was determined as follows, it was 1.62% by mass as shown in Table 2.

(Measurement of the amount of remaining polyvinylpyrrolidone)
A hollow fiber membrane was cut to a predetermined length and added to N, N-dimethylacetamide to dissolve the membrane. Subsequently, the solution after removing the porous substrate which is an insoluble component was evaporated to dryness on a glass plate to obtain a film having a thickness of about 20 μm. Next, using this film as a sample, an absorbance spectrum was measured with an infrared spectrophotometer.
Then, when the absorption strength due to C—F stretching vibration of polyvinylidene fluoride is defined as 100%, the percentage of the absorption strength of the carbonyl group stretching vibration of polyvinylpyrrolidone is determined from the ratio of these absorption strengths. (%) Was defined as the remaining amount of polyvinylpyrrolidone remaining.

[Example 2]
A hollow fiber membrane in the same manner as in Example 1, except that (2) Depressurization step-Decompression step in the hydrophilic polymer removal step of Example 1 was performed instead of (2) Depressurization step-Cleaning liquid supply step-Depressurization step Manufactured.
Specifically, in FIG. 7, a pressure reducing means is connected to the connection port 11a of the frontmost cylinder member 11 and the connection port 11a of the last cylinder member 11, and the gauge pressure of each pressure reduction means is shown in Table 2− The pressure was reduced to 0.06 MPa and −0.05 MPa. Moreover, 74 degreeC water was supplied as a washing | cleaning liquid from the supply means connected to the connection port 11a of the center cylinder member 11 among three so that a gauge pressure might be 0.05 MPa. The residence time of the hollow fiber membrane 10 in each cylindrical member 11, 11, 11 was set to about 3 seconds.
Table 2 shows the remaining amount of polyvinylpyrrolidone in the hollow fiber membrane. Further, the outer diameter and inner diameter of the obtained hollow fiber membrane were the same as those in Example 1.

[Example 3]
The hollow fiber membrane was formed in the same manner as in Example 2 except that (2) Depressurization step-Cleaning solution supply step-Depressurization step was performed so that the gauge pressure of each decompression unit and the cleaning solution supply unit became the values shown in Table 2. Manufactured. Table 2 shows the remaining amount of polyvinylpyrrolidone in the hollow fiber membrane. Further, the outer diameter and inner diameter of the obtained hollow fiber membrane were the same as those in Example 1.

[Example 4]
The hollow fiber membrane was formed in the same manner as in Example 2 except that (2) Depressurization step-Cleaning solution supply step-Depressurization step was performed so that the gauge pressure of each decompression unit and the cleaning solution supply unit became the values shown in Table 2. Manufactured. Table 2 shows the remaining amount of polyvinylpyrrolidone in the hollow fiber membrane. Further, the outer diameter and inner diameter of the obtained hollow fiber membrane were the same as those in Example 1.
Moreover, in this Example 4, mass measurement was implemented about 1 m of hollow fiber membranes before and behind a drying process. As a result, there was a mass difference of 2.6 g / m before and after the drying step, and it was found that 2.6 g / m of water was removed by the drying step.

[Example 5]
As the hydrophilic polymer removal step, (1) Preliminary step and (2) Depressurization step-Washing liquid supply step-Depressurization step were carried out in the same manner as in Example 4, and then the final step in the hydrophilic polymer removal step The drying process was performed after performing the post-process which decompressed the outer peripheral side of a hollow fiber membrane in it. Otherwise, a hollow fiber membrane was produced in the same manner as in Example 4. The post-process was performed in the apparatus process as shown in FIG. 1, the gauge pressure of the pressure reducing means was set to −0.06 MPa, and the staying time was 5 seconds.
A trap was provided in such a post process, and the amount of water removed from the hollow fiber membrane in the post process was measured. As a result, 7 g / min per unit time and 0.96 g / m when converted to the length of the hollow fiber membrane. Met. Considering this result together with the amount of water removed in the drying step of Example 4 being 2.6 g / m, according to the subsequent step in Example 5, it is removed in the drying step. It was shown that 36.9% by mass (= 0.96 / 2.6 × 100) of the moisture was removed, and the load of the drying process was reduced.

[Comparative Example 1]
A hollow fiber membrane was produced in the same manner as in Example 1, except that (1) only the preliminary step was performed as the hydrophilic polymer removing step, and no decompression step or cleaning liquid supply step was performed. Table 2 shows the remaining amount of polyvinylpyrrolidone in the hollow fiber membrane. Further, the outer diameter and inner diameter of the obtained hollow fiber membrane were the same as those in Example 1.

  As shown in Table 2, in each example, the remaining amount of polyvinylpyrrolidone in the produced hollow fiber membrane was low and high hydrophilicity compared with Comparative Example 1 in which only the preliminary step was performed as the hydrophilic polymer removal step (1). The effect of removing the conductive polymer was obtained. At that time, the higher the difference in gauge pressure between the decompression step and the cleaning liquid supply step, the higher the hydrophilic polymer removal effect tended to be obtained.

It is a schematic block diagram which shows an example of a pressure reduction process. It is a schematic block diagram which shows another example of a pressure reduction process. It is explanatory drawing which shows an example of the flow of the washing | cleaning liquid in the pressure reduction process of FIG. It is explanatory drawing which shows another example of the flow of the washing | cleaning liquid in the pressure reduction process of FIG. It is a schematic block diagram which shows an example which provided the washing | cleaning liquid supply process in the back | latter stage of the pressure reduction process. It is explanatory drawing which shows the flow of the washing | cleaning liquid in the pressure reduction process and washing | cleaning liquid supply process of FIG. It is a schematic block diagram which shows an example which provided the washing | cleaning-liquid supply process in the back | latter stage of the pressure reduction process, and also provided the pressure reduction process.

Explanation of symbols

10 Hollow fiber membrane

Claims (6)

A film-forming stock solution containing a hydrophobic polymer and a hydrophilic polymer is coagulated in a coagulation solution to form a hollow fiber membrane, and a hydrophilic polymer removal is performed to remove the hydrophilic polymer remaining in the hollow fiber membrane. In the method for producing a hollow fiber membrane having a step,
The said hydrophilic polymer removal process has a pressure reduction process which decompresses the outer peripheral side of the said hollow fiber membrane, and discharges | emits the said hydrophilic polymer to the outer peripheral side of a hollow fiber membrane, The manufacturing method of the hollow fiber membrane characterized by the above-mentioned.   The method for producing a hollow fiber membrane according to claim 1, wherein the depressurizing step is performed on the hollow fiber membrane immersed in the cleaning liquid.   The method for producing a hollow fiber membrane according to claim 2, wherein in the pressure reducing step, a cleaning liquid is passed from the inner peripheral side to the outer peripheral side of the hollow fiber membrane.   The hollow according to claim 3, wherein the hydrophilic polymer removing step further includes a cleaning liquid supply step of supplying the cleaning liquid from the outer peripheral side to the inner peripheral side of the hollow fiber membrane after the decompression step. Yarn membrane manufacturing method.   The method for producing a hollow fiber membrane according to claim 4, wherein the hydrophilic polymer removal step further includes the pressure reduction step after the cleaning liquid supply step.   6. The hollow fiber membrane according to any one of claims 2 to 5, wherein the hydrophilic polymer removing step includes a post-step in the last stage of decompressing the outer peripheral side of the hollow fiber membrane in a gas phase. Manufacturing method.

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