JP2015024402A - Method of manufacturing hollow fiber membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a hollow fiber membrane which includes a step in which a hollow fiber membrane is continuously run in a drier device for drying the hollow fiber membrane, with a drying load on an existing drier being reduced for drying the hollow fiber membrane at a low cost.SOLUTION: A method of manufacturing a hollow fiber membrane includes a coagulation step in which a film forming stock liquid is coagulated in a coagulating liquid to form a hollow fiber membrane, a liquid phase pressure reducing step in which the hollow fiber membrane is submerged in a depressed liquid, and a drying step for drying the hollow fiber membrane. The liquid phase pressure reducing step is performed before the drying step.

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. Next, a hollow fiber membrane is formed 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).
In the porous part of the hollow fiber membrane produced by such a method, the hydrophilic polymer usually remains in a solution state. Therefore, after removing this hydrophilic polymer by washing or the like, the hollow fiber membrane is dried.

  Here, as a method for drying the hollow fiber membrane, for example, Patent Document 1 discloses a method using a hot air circulation type drying apparatus. Specifically, a method in which hot air is blown to the outer peripheral side of the hollow fiber membrane and dried by continuously running the hollow fiber membrane in a drying apparatus in which hot air is circulating at a wind speed of about several meters per second. Is disclosed.

  In addition, as a method of performing drying in a shorter time in a method of continuously running a hollow fiber membrane in a drying apparatus and drying the hollow fiber membrane, Patent Document 2 discloses a drying gas as a method of drying the hollow fiber membrane. Permeating from the outer peripheral side to the inner peripheral side, introducing into the hollow part, allowing the hollow part to pass through, and then allowing the hollow fiber membrane to pass from the inner peripheral side to the outer peripheral side to discharge, and then drying the gas press-in step A method is disclosed. This invention introduces a drying gas into the hollow fiber membrane by supplying a high-pressure drying gas into the cylindrical member while continuously introducing the hollow fiber membrane into the cylindrical member. It has the effect of discharging the remaining water by the pressure applied to the hollow part.

JP-A-2005-220202 International Publication 2012/004865

  In the method of drying by continuously running the hollow fiber membrane, the processing speed is increased, that is, the drying capacity is frequently improved in order to improve the production capacity. When the drying capacity is increased in the existing drying apparatus of the hot air circulation system as described in Patent Document 1, the residence time of the hollow fiber membrane in the drying apparatus is increased, the hot air speed is increased, or the hot air temperature is increased. Is necessary.

  When the staying time of the hollow fiber membrane in the drying device is lengthened, a measure is taken to increase the number of turns of the hollow fiber membrane by increasing the number of guides. However, when the number of guides is increased, the rotational resistance is increased by the number of guides, the torque for pulling the hollow fiber membrane from the drying device is increased, and the tension of the hollow fiber membrane in the drying device becomes excessive. When the tension of the hollow fiber membrane is increased, the hollow fiber membrane is deformed when coming into contact with the guide, and when it is severe, the surface structure of the hollow fiber membrane is damaged, which is not preferable.

  On the other hand, when the hot air speed in the drying device is increased, there is a concern that the vibration of the hollow fiber membrane in the drying device becomes large. When the vibration of the hollow fiber membrane increases, the hollow fiber membrane is detached from the guide during drying, leading to a process stop, or a portion where the guide contact portion and the hollow fiber membrane slide with each other due to the vibration occurs, and the surface of the hollow fiber membrane This causes problems such as damage. In order to avoid such a problem, if the take-up torque of the hollow fiber membrane is increased and the tension of the hollow fiber membrane is increased, the stay time of the hollow fiber membrane in the drying apparatus is increased. Problems occur.

  When the hot air temperature in the drying apparatus is increased, the temperature of the hollow fiber membrane reaches the same temperature as the hot air temperature at the end of drying, so that the temperature of the hollow fiber membrane after the drying ends up. When the temperature of the hollow fiber membrane becomes high, the pore diameter of the hollow fiber membrane becomes small due to heat shrinkage, and the original water permeation performance may be lowered. In addition, countermeasures such as increasing the speed of hot air in the drying apparatus or increasing the temperature of hot air have a problem that the load on the dryer increases.

  On the other hand, a method of continuously running the hollow fiber membrane and drying in a shorter time is also disclosed, but there is an existing drying device in particular, which can cope with a higher processing speed than the conventional processing speed. In the case of aiming at, the countermeasure which removes the existing drying apparatus and introduces a new drying apparatus is not preferable because it causes an increase in manufacturing cost due to an increase in equipment cost.

  The present invention has been made in view of the above circumstances, and in a hollow fiber membrane manufacturing method including a step of drying a hollow fiber membrane by continuously running the hollow fiber membrane in a drying apparatus, the drying load of an existing dryer An object of the present invention is to provide a method for producing a hollow fiber membrane that can reduce the cost and can dry the hollow fiber membrane at low cost.

The manufacturing method of the hollow fiber membrane of this invention has the following aspects.
<1> A coagulation step of coagulating a membrane-forming stock solution in a coagulation solution to form a hollow fiber membrane, a liquid phase decompression step of immersing the hollow fiber membrane in a liquid with reduced pressure, and the hollow A method for producing a hollow fiber membrane, comprising: a drying step of drying the yarn membrane, wherein the liquid phase decompression step is performed before the drying step;
<2> The liquid phase decompression step uses the flow path member formed so that the hollow fiber membrane traveling channel penetrates the inside, and the openings at both ends of the hollow fiber membrane traveling channel are disposed in the liquid. Then, the inside of the hollow fiber membrane running channel is filled with the liquid, and the hollow fiber membrane is continuously run so as to pass through the liquid in the hollow fiber membrane running channel. The method for producing a hollow fiber membrane according to <1>, which is a step of reducing the pressure of the liquid by flowing the liquid;
<3> The flow path member further includes a branch flow path that branches from the hollow fiber membrane travel flow path and communicates with one wall surface, and the liquid phase decompression step is performed by the hollow fiber membrane travel of the flow path member. The hollow fiber membrane is formed by arranging openings at both ends of the flow channel in the liquid to fill the flow channel with the liquid, and causing the liquid in the hollow fiber membrane running flow channel to flow through the branch flow channel. The method for producing a hollow fiber membrane according to <2>, wherein the method is a step of reducing the pressure of the liquid in the traveling flow path;
<4> The method for producing a hollow fiber membrane according to any one of <1> to <3>, wherein the liquid is water;
<5> The drying step includes a pressurizing step of pressurizing a hollow portion of the hollow fiber membrane by injecting pressurized gas from an outer peripheral side of the hollow fiber membrane, <1> to <4> The manufacturing method of the hollow fiber membrane as described in any one of 4;
<6> The pressurizing step is formed such that the hollow fiber membrane traveling channel passes through the inside, and further using a channel member having a branch channel branched from the hollow fiber membrane traveling channel, The method for producing a hollow fiber membrane according to <5>, which is a step of pressurizing a hollow portion of the hollow fiber membrane by supplying the pressurized gas from a branch channel.

  According to the present invention, in the method for producing a hollow fiber membrane including the step of continuously running the hollow fiber membrane in a drying device and drying the hollow fiber membrane, the drying load of the existing dryer is reduced and the cost is reduced. A method for producing a hollow fiber membrane that can dry the hollow fiber membrane can be provided.

It is sectional drawing which shows an example of the flow-path member for liquid phase pressure reduction processes. It is a schematic block diagram which shows an example of a liquid phase pressure reduction process. It is a schematic block diagram which shows an example of a pressurization process. 2 is a schematic configuration diagram of a process of Example 1. FIG. 5 is a schematic configuration diagram of a process of Example 2. FIG.

  Hereinafter, regarding the present invention, 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 the remaining in the hollow fiber membrane formed in the coagulation step. A hydrophilic polymer removing step for removing the hydrophilic polymer by washing or the like, a liquid phase depressurizing step for immersing the hollow fiber membrane in a liquid with reduced pressure, and drying the hollow fiber membrane after the liquid phase depressurizing step A method for producing a hollow fiber membrane having a drying process will be described in detail as an embodiment.

(Coagulation process)
In the method for producing a hollow fiber membrane of the present embodiment, first, a membrane forming stock solution containing a hydrophobic polymer and a hydrophilic polymer is prepared. Then, usually, this membrane-forming stock solution is discharged into a coagulating liquid from a nozzle having an annular discharge port, and the membrane-forming stock solution is solidified in the coagulating solution, thereby forming a hollow fiber membrane.
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. Further, the structure of the hollow fiber membrane produced here is not particularly limited as long as it has the effects of the present invention. For example, the structure may include a porous substrate, may have a multilayer structure, and may be handled. The structure which has durability with respect to the rubbing etc. may be sufficient.
Examples of the porous substrate are not particularly limited as long as they have the effects of the present invention, and examples thereof include hollow knitted cords and braids made of various fibers. These materials can be used alone or in combination. Examples of fibers used for the hollow knitted string and braided string include synthetic fibers, semi-synthetic fibers, regenerated fibers, and natural fibers. The form of the fiber may be any of monofilament, multifilament, and spun yarn.

<Hydrophobic polymer>
As long as the hydrophobic polymer can form a hollow fiber membrane by a coagulation step, it can be used without particular limitation as long as it has the effect of the present invention, such as polysulfone resins such as polysulfone and polyethersulfone, and polyvinylidene fluoride. Fluorine resin, polyacrylonitrile, cellulose derivatives, polyamide, polyester, polymethacrylate, polyacrylate, and the like are preferably used. Moreover, a copolymer of these resins may be used, and a resin in which a substituent is introduced into a part of these resins or copolymers may 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. Of these, fluororesins, in particular, polyvinylidene fluoride and copolymers composed of vinylidene fluoride alone and other monomers are preferred because of their excellent durability against oxidizing agents such as hypochlorous acid. Therefore, for example, when the treatment is performed with an oxidizing agent such as hypochlorous acid in the hydrophilic polymer removing step described later, it is preferable to select a fluororesin as the hydrophobic polymer.

<Hydrophilic 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 resin having a higher molecular weight, that is, a mass average molecular weight of 500,000 to 600,000 is used as the hydrophilic polymer, a hollow fiber membrane having a good membrane structure tends to be easily formed. On the other hand, a hydrophilic polymer having a low molecular weight, that is, a mass average molecular weight of 200,000 to 300,000 can be suitably used because it is 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 (mass average molecular weights) may be appropriately blended and used according to the purpose.

A film-forming stock solution can be prepared by mixing and dissolving the above-described hydrophobic polymer and hydrophilic polymer in a solvent (good solvent) in which they are soluble. Other additive components may be added to the film-forming stock solution as necessary.
The type of the solvent is not particularly limited as long as it has the effect of the present invention, but when performing the coagulation step 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 portion. Therefore, it is preferable to select a solvent that is easily mixed with water uniformly. 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. You may use independently and may use 2 or more types together. Moreover, you may mix and use the poor solvent of a hydrophobic polymer or a hydrophilic polymer for the said solvent in the range which does not impair the solubility of a hydrophobic polymer or a hydrophilic polymer.
10-100 degreeC is preferable and, as for the temperature of film forming undiluted | stock solution, 20-80 degreeC is more preferable. The higher the temperature of the membrane-forming stock solution, the higher the content of the poor solvent component necessary for the membrane-forming stock solution having the same composition to start phase separation. Therefore, when the membrane-forming stock solution is immersed in a coagulating solution having the same composition and the same temperature, the phase separation speed of the membrane-forming stock solution is reduced, the formed phase separation structure is roughened, and the resulting hollow fiber membrane membrane Increases water permeability.
By the way, when the film-forming stock solution is kept at a high temperature for a long time, there is a problem that the film-forming stock solution is gelled or altered depending on the type or composition of the film-forming stock solution. In addition, when a polymer component having a high molecular weight is used as the polymer component in the film-forming stock solution, or when the concentration of the polymer component in the film-forming stock solution is high, the viscosity of the film-forming stock solution increases if the temperature of the film-forming stock solution is too low , It may be difficult to form a film stably. Therefore, from these viewpoints, the temperature of the film-forming stock solution is preferably 10 to 100 ° C, and more preferably 20 to 80 ° C.

If the concentration of the hydrophobic polymer in the membrane forming stock solution is too low or too high, the stability during film formation tends to be low, and a suitable hollow fiber membrane structure tends to be difficult to form. 10 mass% is preferable with respect to the total mass of the film forming stock solution, and 15 mass% is more preferable. Further, the upper limit is preferably 30% by mass and more preferably 25% by mass with respect to the total mass of the film-forming stock solution. That is, the concentration of the hydrophobic polymer in the film-forming stock solution is preferably 10 to 30% by mass and more preferably 15 to 25% by mass with respect to the total mass of the film-forming stock solution.
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 with respect to the total mass of the membrane-forming stock solution in order to make it easier to form a hollow fiber membrane. The upper limit of the concentration of the hydrophilic polymer is preferably 20% by mass, and more preferably 12% by mass with respect to the total mass of the film-forming stock solution from the viewpoint of the handleability of the film-forming stock solution. That is, the concentration of the hydrophilic polymer in the film-forming stock solution is preferably 1 to 20% by mass and more preferably 5 to 12% by mass with respect to the total mass 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. Although there is no restriction | limiting in particular in the temperature of coagulation liquid, Usually, 40-90 degreeC is preferable and 50-80 degreeC is more preferable.
The lower the temperature of the coagulation liquid, the higher the phase separation rate of the film-forming stock solution immersed in the coagulation liquid, and the resulting phase separation structure tends to become dense. On the other hand, the mutual diffusion rate between the good solvent in the hollow porous membrane after the phase separation structure is formed and the poor solvent in the coagulation liquid is slowed down, and the hollow porous membrane expresses mechanical strength. Therefore, there is a problem that the time required for coagulation becomes long. Conversely, when the temperature of the coagulation liquid is high, the phase separation speed of the membrane-forming stock solution immersed in the coagulation liquid decreases, the formed phase separation structure becomes rough, and the membrane permeability of the hollow porous membrane increases. Since the mutual diffusion rate between the good solvent remaining in the hollow porous membrane after the phase separation structure is formed and the poor solvent in the coagulation liquid is increased, the hollow porous membrane exhibits mechanical strength. The time required for coagulation is shortened.
However, it is necessary to strengthen heating means and heat insulation means for keeping the temperature of the coagulating liquid constant as the temperature of the coagulating liquid increases. Moreover, the good solvent and the poor solvent in the coagulation liquid are likely to evaporate from the coagulation liquid surface, and dew condensation is likely to occur in the low temperature part. When the coagulating liquid temperature is equal to or higher than the boiling point of the coagulating liquid, the coagulating liquid surface fluctuates due to boiling of the coagulating liquid, making it difficult to form a stable film.
From such a viewpoint, the temperature of the coagulation liquid is preferably 40 to 90 ° C, more preferably 50 to 80 ° C.

(Hydrophilic polymer removal step)
In the manufacturing method of the hollow fiber membrane of this embodiment, it is preferable to have a hydrophilic polymer removing step.
The hollow fiber membrane formed by the above-described coagulation process generally has a large pore diameter and potentially has high water permeability, but a large amount of hydrophilic polymer is in solution in the porous portion of the hollow fiber membrane. If it remains, sufficient high water permeability cannot be exhibited. Therefore, it is preferable to perform the hydrophilic polymer removal process which removes the hydrophilic polymer which remains in the porous part of a hollow fiber membrane after a coagulation process.

  In the porous portion of the hollow fiber membrane obtained in the coagulation step, the hydrophilic polymer remains in a high concentration solution state. Such a high-concentration hydrophilic polymer is relatively easily removed to some extent by immersing the hollow fiber membrane in a cleaning solution. Therefore, as the hydrophilic polymer removal step, first, the hollow fiber membrane is washed by immersing it in a cleaning liquid. (I) The hollow fiber membrane is washed, and (ii) the hydrophilic polymer using an oxidizing agent. (Iii) The method of performing the washing | cleaning process of the hydrophilic polymer made into low molecular weight one by one in order is preferable.

((I) Cleaning process of hollow fiber membrane)
(I) The hollow fiber membrane washing step is a step of washing the hollow fiber membrane obtained in the coagulation step by immersing it in a washing solution. The washing liquid used in the washing process of the hollow fiber membrane is not particularly limited as long as it has a clear and hydrophilic polymer dispersion or dissolution, as long as it has the effects of the present invention, but has a high washing effect. Water is preferred. 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. As the cleaning liquid, a good solvent of a hydrophobic polymer, for example, a mixed liquid of N, N-dimethylformamide, N, N-dimethylacetamide and the like and water can be used.
The washing temperature is preferably high, 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 molecular weight of hydrophilic polymer using oxidizing agent)
(I) Although the hydrophilic polymer remaining in the hollow fiber membrane can be removed to some extent by the washing step of the hollow fiber membrane, the hydrophilic polymer is still present in the porous portion of the hollow fiber membrane at a constant concentration. Remains. In such a case, in order to obtain a higher cleaning effect, it is preferable to perform (ii) a step of lowering the molecular weight of the hydrophilic polymer using an oxidizing agent.
Specifically, the hollow fiber membrane is immersed in a chemical solution containing an oxidizing agent to hold the chemical solution in the hollow fiber membrane, and then the hollow fiber membrane holding the chemical solution is placed in the gas phase, for example, saturated water vapor, saturated air The method of heating in the atmosphere of these etc. is mentioned. As the oxidizing agent, ozone, hydrogen peroxide, permanganate, dichromate, persulfate, or the like can be used. Of these, hypochlorite is particularly preferably used from the viewpoints of strong oxidizing power, excellent decomposing performance of the hydrophilic polymer, ease of handling, and low cost. Examples of hypochlorite include sodium hypochlorite and calcium hypochlorite, with sodium hypochlorite being particularly preferred.

  The temperature of the chemical solution when immersing the hollow fiber membrane is preferably 50 ° C. or lower, and more preferably 30 ° C. or lower. When the temperature of the chemical solution is higher than 50 ° C., oxidative decomposition is promoted during the immersion of the hollow fiber membrane, and the hydrophilic polymer dropped into the chemical solution is further oxidatively decomposed, leading to waste of the oxidant. On the other hand, although the oxidative decomposition is suppressed when the temperature is excessively low, the cost for controlling the temperature to a low temperature tends to increase as compared with the case of carrying out at normal temperature (25 ° C.). Therefore, from these viewpoints, the temperature of the chemical solution is preferably 0 ° C. or higher, and more preferably 10 ° C. or higher. That is, the temperature of the chemical solution when immersing the hollow fiber membrane is preferably 0 to 50 ° C, more preferably 10 to 30 ° C. The immersion time of the hollow fiber membrane is preferably 1 to 300 seconds, preferably 10 to 120 seconds, from the viewpoint of suppressing the waste of the oxidizing agent due to the hydrophilic polymer falling off in the chemical solution. Is more preferable.

  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 (1 atm). It is preferable to use a fluid having a high relative humidity as the heating fluid, that is, heating under humid heat conditions, because drying of an oxidizing agent such as hypochlorite is prevented and efficient decomposition treatment is possible. 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. That is, in this embodiment, it is preferable to heat the hollow fiber membrane under wet heat conditions of 50 ° C./80% RH to 100 ° C./100% RH, and wet heat of 80 ° C./90% RH to 100 ° C./100% RH. It is more preferable that the conditions are satisfied.

((Iii) Low molecular weight hydrophilic polymer washing step)
Thus, (ii) after carrying out the step of reducing the molecular weight of the hydrophilic polymer using an oxidizing agent, the hollow fiber membrane is again formed under the same conditions as in the above-described (i) hollow fiber membrane washing step. It is preferable to perform a washing step of the hydrophilic polymer reduced in molecular weight by removing the hydrophilic polymer reduced in molecular weight to some extent (iii) by immersing in a cleaning liquid and washing.

(Liquid phase decompression process)
After performing the hydrophilic polymer removing step as necessary as described above, it is preferable to perform the liquid phase decompression step before performing the drying step. By performing the liquid phase decompression step, the hydrophilic polymer still remaining in the hollow fiber membrane can be effectively removed even if the hydrophilic polymer removal step is performed.
The liquid phase depressurization step is a step of immersing the hollow fiber membrane in a liquid whose pressure has been reduced. By immersing the hollow fiber membrane in a liquid with reduced pressure, the outer peripheral side of the hollow fiber membrane is decompressed, and the hydrophilic polymer remaining in the porous portion of the hollow fiber membrane is transferred to the outer peripheral side of the hollow fiber membrane. It can be discharged. That is, the liquid phase decompression step is such that the pressure on the outer peripheral side of the hollow fiber membrane is lower than the inner peripheral side (hollow part), and the hydrophilic polymer is moved to the outer peripheral side of the hollow fiber membrane by the pressure difference at that time. It is the process of moving and removing.
Depressurization in the liquid phase has the advantage of requiring less pump power because, for example, the capacity of suction by the pump is smaller than in the case of depressurization in the gas phase. In addition, it is possible to reduce moisture retained by the hollow fiber membrane (hereinafter sometimes referred to as “membrane retained moisture”) in addition to ensuring the effect of removing the hydrophilic polymer in the previous stage. There is also.

The specific method of the liquid phase decompression step is not particularly limited as long as it has the effect of the present invention. For example, as shown in FIG. It is preferably carried out using the “member 11”. The flow path member 11 includes a hollow fiber membrane travel flow path 12 that allows the hollow fiber membrane to pass therethrough, and a branch flow path 13 that is formed so as to branch from the hollow fiber membrane travel flow path 12 and communicate with one wall surface. It is formed so as to penetrate the inside of the member 11, and openings 12 a and 12 b are provided at both ends of the hollow fiber membrane running flow path 12. Here, the branch flow path 13 has a connection port 13a for connecting a pressure reducing means such as a pressure reducing pump.
Such a flow path member 11 is disposed in the liquid, and the hollow fiber membrane 10 that has undergone the coagulation step and, if necessary, the hydrophilic polymer removal step is continuously introduced into the flow path member 11 from its opening 12a. While being introduced, by reducing the pressure of the liquid in the hollow fiber membrane running flow path 12, the outer peripheral side of the hollow fiber membrane 10 is decompressed in the flow path member 11 and remains in the porous portion of the hollow fiber membrane 10. The hydrophilic polymer is sucked and removed to the outer peripheral side of the hollow fiber membrane 10 along with the liquid.

In the liquid phase decompression step in the present embodiment, as shown in FIG. 2, a cleaning tank 20 containing a liquid is prepared, the flow path member 11 is immersed in the cleaning tank 20, and the hollow fiber membrane traveling flow path 12 is The openings 12a and 12b at both ends are arranged in the liquid so that the hollow fiber membrane running channel 12 is filled with the liquid and the hollow fiber membrane 10 is passed through the liquid in the hollow fiber membrane running channel 12. It is preferable that the liquid flow in the hollow fiber membrane running flow path 12 is caused to flow by continuously running, thereby reducing the pressure of the liquid. Further, in the liquid phase decompression step, the openings 12a and 12b at both ends of the hollow fiber membrane running channel 12 of the channel member 11 are disposed in the liquid, and the hollow fiber membrane running channel 12 is filled with the liquid. More preferably, it is a step of causing the liquid in the hollow fiber membrane traveling channel 12 to flow through the branch channel 13 to reduce the pressure of the liquid in the hollow fiber membrane traveling channel 12. By such a process, the hollow fiber membrane running flow is caused by the flow pressure loss of the liquid flowing between the outer peripheral side of the hollow fiber membrane 10 and the wall surface of the hollow fiber membrane running flow channel 12 in the hollow fiber membrane running flow channel 12. The pressure of the liquid inside the passage 12 can be reduced.
When the above-described liquid phase decompression step is performed, if the pressure difference between the inner peripheral side and the outer peripheral side of the hollow fiber membrane 10 is large, the hollow fiber membrane 10 is immersed in the liquid and the flow path member 11 In the portion existing outside the liquid, the liquid in the cleaning tank 20 passes through the membrane and is introduced into the inner peripheral side of the hollow fiber membrane 10. The introduced liquid then passes through the membrane again and is discharged to the outer peripheral side by the operation of the decompression means. As a result, the hydrophilic polymer remaining in the porous portion of the hollow fiber membrane 10 is removed from the connection port 13a together with the liquid.
According to such a liquid phase decompression step, according to the method of passing liquid from the inner peripheral side to the outer peripheral side of the hollow fiber membrane 10, the hydrophilic polymer pulled away from the hollow fiber membrane 10 is dispersed or dissolved in the liquid. Since it is sucked and removed together with the liquid, the concern of re-adhering to the hollow fiber membrane 10 is reduced, and a high removal effect is obtained.

The depressurization conditions for such a liquid phase depressurization step are as follows: type of hollow fiber membrane 10 (material of hollow fiber membrane 10 or membrane structure), concentration of hydrophilic polymer remaining in hollow fiber membrane 10, flow path member It is necessary to consider the equipment cost to make the pressure resistance 11 and the pressure resistance performance of the hollow fiber membrane 10 itself, and make the hollow fiber membrane 10 difficult to shake in the liquid phase decompression step and the cleaning liquid supply step described later. There is. From such a viewpoint, the pressure in the liquid phase 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 lower the gauge pressure, the higher the effect of reducing the film retention moisture.
In the present embodiment, in order to wash the hydrophilic polymer, high-pressure washing water is supplied to the hollow portion of the hollow fiber membrane 10 in the cleaning liquid supply step described later, so that the hollow portion of the hollow fiber membrane 10 is press-fitted. From the viewpoint of preventing the washed water from propagating through the hollow portion and moving to the subsequent drying step, the pressure in the liquid phase decompression step is preferably -0.08 to -0.1 MPa.
In addition, the residence time of the hollow fiber membrane 10 in the liquid phase decompression step (the residence time in the flow path member 11) is preferably 2 to 10 seconds. If the residence time of the hollow fiber membrane 10 is 2 to 10 seconds, a sufficient hydrophilic polymer removal effect can be obtained efficiently.
In addition, as a liquid in the washing tank 20, it is preferable to use the washing | cleaning liquid illustrated by the washing | cleaning process of the above-mentioned (i) hollow fiber membrane.
The temperature of the liquid in the cleaning tank 20 is not particularly limited as long as it has the effects of the present invention, but is preferably 30 to 80 ° C. When the temperature of the liquid is higher than 80 ° C., the heating energy of the hollow fiber membrane in the drying process described later can be somewhat reduced. However, since the saturated vapor pressure of the liquid becomes high, a high degree of reduced pressure cannot be secured, and there is a concern that the effect of reducing the moisture retained in the film before the drying process will be reduced. Conversely, if the temperature of the liquid is less than 30 ° C., a high degree of vacuum can be secured, and it becomes easier to ensure the effect of reducing the moisture retained in the film before the drying process, but the hollowness in the drying process is higher than when the temperature is high There is a concern that the heating energy of the yarn film is required.

(Cleaning liquid supply process)
In order to further enhance the effect of removing the hydrophilic polymer, it is possible to combine 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 liquid phase decompression process. preferable.
Specifically, two flow path members 11 described above are prepared, installed in series in the cleaning tank 20 with a gap therebetween, and a decompression means is provided at the connection port 13a of the flow path member 11 on the upstream side. And a supply means such as a pressurized supply pump for supplying the cleaning liquid is connected to the connection port 13a of the flow path member 11 on the rear stage side.
Then, the hollow fiber membrane 10 is sequentially introduced into the two flow path members 11 from the front side, and the liquid phase pressure reducing means and the cleaning liquid supply means are operated. Then, the cleaning liquid is supplied from the outer peripheral side to the inner peripheral side of the hollow fiber membrane 10 in the rear-stage flow path member 11 (cleaning liquid supply step), and the inner part of the hollow fiber membrane 10 in the front-stage flow path member 11. The cleaning liquid can be passed from the peripheral side to the outer peripheral side (liquid phase decompression step).
When the cleaning liquid supply process is provided after the liquid phase decompression process as described above, 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 liquid phase decompression process is increased. The removal effect is increased.

The supply pressure of the cleaning liquid supply step needs to consider the type of the hollow fiber membrane 10, the concentration of the hydrophilic polymer remaining in the hollow fiber membrane 10 and the like, as in the liquid phase decompression step described above. The gauge pressure is preferably more than 0 and 0.4 MPa or less, more preferably more than 0 and 0.3 MPa or less. Within such a range, the higher the difference in gauge pressure between the liquid phase decompression process and the cleaning liquid supply process, the higher the hydrophilic polymer removal effect tends to be obtained.
The staying time of the hollow fiber membrane 10 in the cleaning liquid supply step (the staying time in the flow path member 11) is preferably 2 to 10 seconds. If the residence time of the hollow fiber membrane 10 is 2 to 10 seconds, a sufficient hydrophilic polymer removal effect can be obtained efficiently.

(Drying process)
Next, the hollow fiber membrane 10 thus subjected to the liquid phase decompression step is dried (drying step).
The drying device used in the drying step is not particularly limited as long as it has the effects of the present invention as long as it does not damage the hollow fiber membrane 10, but it is preferable to use a hot air circulation type drying device. The higher the hot air speed, the shorter the drying time. On the other hand, there is a higher risk that the hollow fiber membrane will flutter in the apparatus and rub at the entrance and exit of the apparatus. Therefore, it is determined appropriately depending on the device span length, the tension of the hollow fiber membrane, and the like.
The drying temperature is preferably 60 ° C. or higher in order to shorten the processing time. On the other hand, the upper limit of the drying temperature is preferably the heat distortion temperature of the hydrophobic polymer. Specifically, when a fluororesin is used as the hydrophobic polymer, the drying temperature is preferably 60 to 130 ° C, and more preferably 80 to 100 ° C.

(Pressure process)
In the present embodiment, it is preferable to perform the pressurizing step at the final stage of the drying step.
In the final stage of the drying process, since the moisture retained by the hollow fiber membrane 10 is reduced, the pressurized gas can be easily introduced into the hollow portion of the hollow fiber membrane 10 by performing the pressurization process. It becomes possible. Here, the pressurized gas introduced into the hollow portion of the hollow fiber membrane 10 is preferably pressurized air. By introducing pressurized air into the hollow portion, in addition to the drying effect by hot air, the moisture removal effect by the pressurized air can be imparted, so that the drying effect of the hollow fiber membrane 10 can be promoted.
When the hollow fiber membrane 10 is produced by wet or dry wet spinning as in the present invention, the membrane structure of the hollow fiber membrane 10 has an asymmetric structure in which the pore diameter of the porous portion gradually decreases from the inner peripheral side to the outer peripheral side. . In such a membrane structure, when a pressure is applied from the inner peripheral side in a state where the porous portion of the hollow fiber membrane 10 is filled with moisture, a portion having a large pore diameter on the inner peripheral side of the hollow fiber membrane Then, the water | moisture content of a porous part can be extruded to an outer peripheral side even with a low pressure. When a higher pressure is applied from the inner peripheral side, moisture in the porous part can be pushed out to a portion closer to the outer peripheral side of the hollow fiber membrane. Finally, when reaching the bubble point or higher with respect to the water of the hollow fiber membrane, the moisture retained by the hollow fiber membrane can be almost completely pushed out by applying pressure from the inner peripheral side.

The specific method of the pressurizing step is not particularly limited as long as it has the effect of the present invention. For example, the pressure-resistant pressure drying flow path member 30 (hereinafter referred to as “flow path member” as shown in FIG. 30 ”) and a pressurizing device for a hollow fiber membrane provided with a pressurized gas supply means (not shown).
Similarly to the flow path member 11 used in the above-described liquid phase decompression step, the flow path member 30 branches from a hollow fiber membrane travel flow path (not shown) that allows the hollow fiber membrane to pass therethrough, and from the hollow fiber membrane travel flow path. A branch channel (not shown) formed so as to communicate with one wall surface is formed so as to penetrate the inside, and openings 30a and 30b are provided at both ends of the hollow fiber membrane travel channel. Here, a supply port 31 for supplying pressurized gas into the flow path member 30 is formed in the branch flow path (not shown).
A hollow fiber membrane is continuously introduced from one end 30a of the flow path member 30 and allowed to pass therethrough, and a pressurized gas supply means (not shown) is connected to the supply port 31 to operate. Is supplied into the flow path member 30.
Then, since the amount of moisture retained in the hollow fiber membrane 10 in the flow path member 30 is reduced, the pressurized gas is easily supplied to the hollow portion of the hollow fiber membrane 10 as indicated by an arrow A in the figure. .
The pressurized gas thus introduced into the inner peripheral side of the hollow fiber membrane 10, that is, the hollow portion, then flows through the hollow portion of the hollow fiber membrane 10 passing through the flow path member 30, as indicated by an arrow B in the figure. Then, the openings 30a and 30b of the flow path member 30 are reached. Then, outside the flow path member 30, the pressure on the outer peripheral side of the hollow fiber membrane 10 is lower than that on the inner peripheral side. Therefore, as shown by the arrow C in FIG. It passes through the membrane 10 and is discharged from the inner peripheral side to the outer peripheral side of the hollow fiber membrane 10.
The moisture contained in the hollow fiber membrane 10 is accompanied by such a pressurized gas, and is discharged from the inner peripheral side of the hollow fiber membrane 10 to the outer peripheral side. Furthermore, the pressurized gas supplied to the hollow portion propagates to the upstream side of the drying process, and the moisture removal effect due to the pressure is added.

  The conditions of the pressurized gas used in the pressurizing step are the type of the hollow fiber membrane 10 (the material of the hollow fiber membrane 10 or the membrane structure), the amount of water remaining in the porous portion of the hollow fiber membrane 10, and the like. Accordingly, the temperature of the pressurized gas is preferably 20 to 90 ° C, more preferably 30 to 80 ° C. If it is such temperature, reduction | restoration of a film | membrane retention | holding water | moisture content can be measured effectively, without preventing the hot air drying effect in a drying apparatus. Moreover, the energy cost for heating the pressurized gas can be moderately suppressed.

  The supply pressure of the pressurized gas is preferably a range of 0.1 to 0.3 MPa, more preferably a range of 0.1 to 0.2 MPa, as a gauge pressure of the pressurized gas supply means. When the supply pressure is in the above range, the pressurized gas can be efficiently introduced into the hollow portion of the hollow fiber membrane 10, and the equipment cost for making the flow path member 30 pressure resistant can be appropriately suppressed. The problem that the yarn 10 swings is less likely to occur. Moreover, if it is such a range, the supply pressure of pressurized gas will not exceed the pressure | voltage resistant performance of hollow fiber membrane 10 itself.

  As described above, the method for producing a hollow fiber membrane of the present invention has a liquid phase decompression step in which the hollow fiber membrane is immersed in a liquid whose pressure has been reduced before the drying step. Thus, the hollow fiber membrane can be dried at a low cost.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by the following description.
[Example 1]
(Coagulation process)
Polyvinylidene fluoride A (manufactured by Atofina Japan, product name: Kyner 301F), polyvinylidene fluoride B (manufactured by Atofina Japan, product name: Kyner 9000LD), polyvinyl pyrrolidone (ISP) so as to have the mass ratio shown in Table 1. N, N-dimethylacetamide was mixed and degassed to prepare a membrane-forming stock solution (1) and a membrane-forming stock solution (2). Here, polyvinylidene fluoride A and polyvinylidene fluoride B are hydrophobic polymers, and polyvinylpyrrolidone is a hydrophilic polymer.
Next, a nozzle having a hollow portion formed at the center and an annular discharge port formed in order so that two types of film-forming stock solutions can be applied and laminated on the outside is prepared and kept at 30 ° C. In this state, a polyester multifilament single filament braid (multifilament; 420T / 180F) is introduced into the hollow portion as a reinforcing support, and a film-forming solution (2) and a film-forming solution (1) are placed on the outer periphery. And then solidified in a coagulating liquid (mixed solution of 8 parts by mass of N, N-dimethylacetamide and 92 parts by mass of water) kept at 75 ° C. 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 in which the porous portion was further coated was obtained.
Further, the spinning speed (running speed of the hollow fiber membrane) at this time was 15 m / min.

(Hydrophilic polymer removal step)
The hollow fiber membrane thus obtained was subjected to the hydrophilic polymer removal step by repeating the following steps (i) to (iii) twice.
(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 under conditions of wet heat of 85 ° C./100% RH for a period of 3 minutes to reduce 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).

(Liquid phase decompression process)
As shown in FIG. 4, a cleaning tank 20 in which water having a temperature of 50 ° C. was placed was prepared, and the flow path member 11 shown in FIG. 1 was disposed therein. And while introducing the hollow fiber membrane 10 obtained at the said process into these flow path members 11, a pressure reduction means is connected to the connection port 13a of the flow path member 11, and the gauge pressure of a pressure reduction means is -0.06 MPa. The pressure was reduced to The residence time of the hollow fiber membrane 10 in the liquid phase decompression step was about 3 seconds.

(Drying process)
The hollow fiber membrane 10 was dried using a hot air circulation dryer 40. The hot air velocity was about 4 m / s, and the hot air temperature was 90 ° C. The residence time of the hollow fiber membrane 10 in the drying process was 3 minutes.
As a result of measuring the moisture content of the hollow fiber membrane 10 after such a drying step, the moisture content was 0.5%. In this example, the acceptable moisture content was 1%, and a result that cleared the acceptable moisture content was obtained. Moreover, as a result of measuring the moisture content about the hollow fiber membrane 1 before a drying process, it was 82%.
Here, the moisture content is a value measured according to the following method.
<Measurement of moisture content>
The moisture content of the hollow fiber membrane was measured using an infrared moisture meter (“Model: FD-720” manufactured by Kett Science Laboratory Co., Ltd.).
The moisture content output by the moisture meter is defined as {(mass of hollow fiber membrane containing moisture−dry mass of hollow fiber membrane) / dry mass of hollow fiber membrane} × 100.
The hollow fiber membrane 10 having the braided string support finally obtained in this manner had an outer diameter of 2.8 mm.
The outer diameter of the hollow fiber membrane is a value measured according to the following method.
<Measurement of hollow fiber membrane outer diameter>
It measured using the outer diameter measuring device (the KEYENCE company make, model LS-3030). Specifically, two such outer diameter measuring devices are prepared, and these measuring devices are respectively attached so that the measured diameters are shifted from each other by 90 ° about the axis of the hollow fiber membrane 10, and the outer diameters in two directions are set. It was measured.

[Example 2]
After performing the coagulation step / hydrophilic polymer removal step by the same operation as in Example 1, a liquid phase decompression step and a drying step were performed as shown in FIG. The drying process was the same as in Example 1 except that the hot air circulation dryer 40 was used and the residence time of the hollow fiber membrane 10 was set to 2.5 minutes, followed by the pressurization process. The same conditions were used.
In the pressurization step, a drying flow path member (made of stainless steel, inner diameter: 4 mm, length: about 780 mm) 30 shown in FIG. 3 was prepared, and the pressurization step was performed. Pressurized air was used as the gas to be supplied, and the supply pressure was adjusted to 0.2 MPa. The temperature of the pressurized air was 30 ° C.
As a result of measuring the moisture content of the hollow fiber membrane 10 after such a drying step, the moisture content was 0.8%. Although the dwell time of the dryer was made shorter than that in Example 1, a low moisture content was obtained as in Example 1.
The hollow fiber membrane 10 having the braided string support finally obtained in this manner had an outer diameter of 2.8 mm. The moisture content measurement and the outer diameter measurement were performed in the same manner as in Example 1.

[Comparative Example 1]
In order to grasp the effect of the liquid phase decompression step before the drying step in Examples 1 and 2, the same operation as in Example 1 was performed except that the liquid phase decompression step was not performed under the conditions of Example 1, and solidification was performed. The drying process was performed from the process, and the hollow fiber membrane 10 was obtained.
As a result of measuring the moisture content of the obtained hollow fiber membrane 10, the moisture content was 21%, and it was not possible to achieve the acceptable moisture content of 1%. Moreover, as a result of measuring a moisture content about the hollow fiber membrane 10 before a drying process, it was 113%. The moisture content of the hollow fiber membrane 10 before the drying process of Example 1 was higher than 82%.
The hollow fiber membrane 10 having the braided string support finally obtained in this manner had an outer diameter of 2.8 mm. The moisture content measurement and the outer diameter measurement were performed in the same manner as in Example 1.

DESCRIPTION OF SYMBOLS 10 Hollow fiber membrane 11 Flow path member for liquid phase decompression 12 Hollow fiber membrane running flow path 12a, 12b Opening part 13 Branch flow path 13a Connection port 20 Washing tank 30 Pressure drying flow path member 30a, 30b Opening part 31 Supply port 40 Hot air circulation dryer

Claims (6)

A coagulation step of coagulating a membrane-forming stock solution in a coagulation solution to form a hollow fiber membrane;
Immersing the hollow fiber membrane in a liquid with reduced pressure, a liquid phase decompression step,
A drying step of drying the hollow fiber membrane,
The method for producing a hollow fiber membrane, wherein the liquid phase decompression step is performed before the drying step. The liquid phase decompression step uses a flow path member formed so that the hollow fiber membrane travel channel penetrates the inside, and the openings at both ends of the hollow fiber membrane travel channel are disposed in the liquid. Filling the road with the liquid,
By continuously running the hollow fiber membrane so as to pass through the liquid in the hollow fiber membrane running channel, the liquid in the hollow fiber membrane running channel is caused to flow, and the pressure of the liquid is reduced. It is a process to reduce, The manufacturing method of the hollow fiber membrane of Claim 1 characterized by the above-mentioned. The flow path member further has a branch flow path branched from the hollow fiber membrane travel flow path and leading to one wall surface;
The liquid phase decompression step, the openings at both ends of the hollow fiber membrane running flow path of the flow path member are arranged in the liquid to fill the flow path with the liquid,
3. The step of causing the liquid in the hollow fiber membrane running channel to flow through the branch channel to reduce the pressure of the liquid in the hollow fiber membrane running channel. A method for producing the hollow fiber membrane according to 1.   The said liquid is water, The manufacturing method of the hollow fiber membrane as described in any one of Claims 1-3 characterized by the above-mentioned.   The said drying process includes the pressurization process of injecting pressurized gas from the outer peripheral side of the said hollow fiber membrane, and pressurizing the hollow part of the said hollow fiber membrane, The any one of Claims 1-4 characterized by the above-mentioned. The method for producing a hollow fiber membrane according to one item. The pressurizing step is formed so that the hollow fiber membrane traveling channel passes through the inside, and further using a channel member having a branch channel branched from the hollow fiber membrane traveling channel,
6. The method for producing a hollow fiber membrane according to claim 5, wherein the method is a step of pressurizing a hollow portion of the hollow fiber membrane by supplying the pressurized gas from the branch channel.

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