JP2003041450A - Method for producing hollow fiber membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a hollow fiber membrane, which enables the downsizing of an installation for improving the order of crystal orientation, the improvement of production efficiency, and the reduction of production cost, and the stable production of the hollow fiber membrane having desired membrane characteristics. SOLUTION: This method for producing the hollow fiber membrane, having a spinning process for spinning a melted crystalline polymer to produce the hollow fiber and a drawing process for drawing the hollow fiber to form the porous hollow fiber membrane, is characterized by having a process for stretching and relaxing the hollow fiber between the spinning process and the drawing process.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a microfiltration hollow fiber membrane.

[0002]

2. Description of the Related Art In recent years, a large amount of high-purity water has been required in various applications such as electronic industry, medical / medical use, household use, and boiler use. The method of producing a large amount of high-purity water has been studied. As one of the methods, a method of purifying water using a microfiltration membrane capable of removing bacteria and the like is known. As a microfiltration membrane used for such an application, a hollow fiber-shaped microfiltration membrane (hereinafter referred to as "hollow fiber membrane") having a large separation performance per unit area is known.

[0003] Regarding a conventional method for producing a hollow fiber membrane, Japanese Patent Laid-Open No. Sho 5
It is disclosed in JP-A-7-66114 and JP-A-5-49878. That is, a hollow fiber is obtained by spinning a molten resin into a hollow fiber as a method of producing a hollow fiber membrane excellent in water permeability while being able to highly prevent unnecessary components such as bacteria in the water to be treated. After that, the hollow fiber is annealed (heat-treated), and then stretched to form a large number of pores in the yarn, thereby producing a hollow fiber membrane having a large number of pores. . Further, as a resin used in the method for producing a hollow fiber membrane, a crystalline polymer such as polyethylene having a relatively high molecular weight is widely used because of its excellent chemical stability and durability.

[0004] In the manufacturing process described above, it is the annealing process that most affects the characteristics of the hollow fiber membrane. The quality of the vacancy is determined by the skill of the annealing process. JP-A-57-6
6114, Japanese Patent Application Laid-Open No. 5-49878, and the like disclose techniques relating to various annealing treatments. Specifically, the treatment atmosphere, temperature, tension during annealing, etc. have been studied.

[0005]

However, in the conventional method for producing a hollow fiber membrane, when a crystalline polymer having a relatively high molecular weight is used, even if the crystalline polymer is oriented and crystallized by spinning, the lamella is The molecular chains inside are inclined with respect to the fiber axis (in this case, the longitudinal direction of the hollow fiber),
In order to orient this molecular chain in the fiber axis direction, it is necessary to carry out annealing for a long time, and as a typical example, it is necessary to carry out annealing for 5 hours or more. As a result, there is a problem that the heating equipment for annealing (manufacturing equipment) needs to be increased in size, the production efficiency is lowered, and the energy cost is increased.

[0006] Further, when the annealing treatment is insufficient, pore formation during the stretching treatment becomes non-uniform, and as a result, desired membrane characteristics (separation characteristics, fractionation characteristics, pore diameter, porosity, etc.) are obtained. )
In some cases, it was not possible to stably obtain a hollow fiber membrane having

[0007] Therefore, the present invention aims to reduce the size of equipment for improving the orientation of crystal molecular chains in the fiber axis direction, improve production efficiency, reduce manufacturing cost, and stabilize a hollow fiber membrane having desired membrane characteristics. It is an object of the present invention to provide a method for producing a hollow fiber membrane that can be obtained by

[0008]

The method for producing a hollow fiber membrane of the present invention comprises a spinning step of spinning a molten crystalline polymer into a hollow fiber, and a stretching step of stretching the hollow fiber to make it porous. In the method for producing a hollow fiber membrane having the above, it is characterized by including a step of stretching and relaxing between the spinning step and the stretching step. Further, it is preferable to perform at least a part of the steps of stretching and relaxing under heating conditions because the effect of improving the crystal orientation order is high. At this time, it is preferable to perform extension and relaxation by using a plurality of drive rollers having different peripheral speeds because continuous processing can be performed. At this time, it is preferable to heat the hollow fiber by passing it through a heating furnace, or to heat it with a driving roller, because continuous heat treatment can be performed. Also,
It is preferable to dispose a free roller having no driving force between the plurality of driving rollers because the processing time at the time of relaxation can be adjusted appropriately. The heating conditions set the melting point of the crystalline polymer to T
When m, the temperature range of (Tm-5) ° C to (Tm-50) ° C is more preferable. Further, in the step of performing the elongation and the relaxation, performing the elongation and the relaxation twice or more, and in the step of performing the elongation and the relaxation, the elongation rate is equal to or lower than the yield point elongation rate at the temperature during the elongation. The elongation and the steps of performing the elongation and the relaxation to increase the 50% elongation elastic recovery rate of the hollow fiber to 40% or more respectively improve the crystal orientational order and reduce the pores formed after the elongation. It is preferable because it can be made uniform. Further, it is preferable that the stretching step includes a cold stretching step and a hot stretching step because uniform pores can be stably obtained. Furthermore, 0
It is more preferable to carry out cold stretching at a temperature of from C to Tm-50 ° C and to carry out hot stretching at a hot stretching ratio of 2 to 10 times. Further, it is preferable to have a heat setting step after the stretching step because the dimensions of the hollow fiber membrane can be stabilized. Further, it is preferable to have a hydrophilic treatment step after the stretching step because the water permeability of the hollow fiber membrane can be improved.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing a hollow fiber membrane of the present invention will be described in detail below. The method for producing a hollow fiber membrane of the present invention is
The molten crystalline polymer is extruded to spin a hollow fiber,
The hollow fiber is characterized in that it is stretched, then relaxed, and then stretched. The manufacturing method in which pores are formed by stretching does not require a step of removing the solvent remaining in the yarn after shaping the hollow fiber, and is therefore excellent in productivity.

[0010] The hollow fiber and the hollow fiber membrane respectively mean "one having no pores before being stretched" and "one having pores formed by being stretched". Further, the stretching and the stretching respectively refer to “stretching to the extent that pores are not formed in the hollow fiber” and “stretching to such extent that pores are formed in the hollow fiber”.

First, the type of crystalline polymer suitable for use in the method for producing a hollow fiber membrane of the present invention will be described. Examples of the crystalline polymer may include various thermoplastic resins such as polyolefin, polyamide, and polyethylene terephthalate. Among these, polyolefin is chemically stable and may be eluted from the membrane into the water to be treated. In particular, it is suitable as a hollow fiber membrane for producing highly pure water. Examples of polyolefins include polyethylene, polypropylene, poly-3-methylbutene-1, poly-4-methylpentene-1, and polyvinylidene fluoride.

[0012] Further, the density of the hollow fibers obtained in the spinning step and the average molecular weight of the polymer affect the formation of pores in the subsequent drawing step. Therefore, it is preferable to control these according to the type of polymer used and the performance of the hollow fiber membrane to be produced.

When polyethylene is used as the crystalline polymer, the density of the hollow fiber after spinning according to JIS K 7112 is preferably 0.95 × 10 ³ kg / m ³ or more, and 0.96 × 10 3. It is more preferably ³ kg / m ³ or more. The weight average molecular weight of polyethylene constituting the hollow fiber after spinning is preferably 5.0 × 10 ⁴ or more. Here, the weight average molecular weight of polyethylene is obtained from the average value in terms of polystyrene when polyethylene is dissolved in o-dichlorobenzene and the molecular weight distribution is measured by the GPC method.

[0014] As the hollow fiber membrane, a single layer structure having a single pore size and a laminated structure in which layers having different pore sizes are laminated concentrically are known. In the hollow fiber membrane having a laminated structure, the constituent layers are obtained from different types of the above-mentioned crystalline polymers, or the same polymers having different properties such as molecular weight distribution.

[0015] Next, each step of the method for producing a hollow fiber membrane of the present invention using the above-mentioned crystalline polymer will be described step by step.

(A) Spinning Step First, in the spinning step (A), a molten resin composed of one or a plurality of types of crystalline polymers that compose each layer is formed in accordance with the different polymer composition of each layer of the hollow fiber membrane, The number of layers is prepared and the hollow fiber is spun by a known method.

[0017] For example, a known spinning nozzle having a discharge port formed in an annular shape is used, and a molten resin is extruded from the discharge port of the spinning nozzle using an extruder to obtain a hollow fiber having a single-layer structure or a laminated structure. After spinning, the hollow fiber can be obtained by solidifying by cooling and then winding by a winding device. When spinning a hollow fiber having a single-layer structure, one kind of molten resin is discharged from one discharge port formed in an annular shape, and when spinning a hollow fiber having a laminated structure, a plurality of kinds of molten resin are used. Hollow fibers can be spun by simultaneously discharging molten resin from a plurality of annular discharge ports arranged concentrically.

[0018] The heating temperature of the resin during spinning must be set to a temperature at which the resin does not solidify during spinning, that is, higher than the melting point of the resin, but to completely prevent the resin from solidifying during spinning. In particular, it is preferable to set the temperature 10 to 100 ° C. higher than the melting point of the resin. On the other hand, the hollow fiber after spinning is preferably quenched using a spinning tube, and the temperature of the air flowing in the spinning tube is preferably set to about 10 to 40 ° C. Further, the winding of the hollow fiber after cooling is preferably performed at a winding speed of 20 to 600 m / min. However, the present invention is not limited to these manufacturing conditions.

[0019] Since the steps from spinning to winding are continuously performed, the hollow fiber immediately after spinning is pulled by the winding device. As a result, tension is applied to each crystalline polymer molecule, molecular chains are oriented and oriented crystallization occurs, and a laminated structure of a stacked lamella is formed. Then, the pores are formed by destroying the laminated structure of the stacked lamella in the subsequent stretching step.

(B) Step of performing elongation and relaxation The hollow fiber obtained through the above (A) spinning step is (B)
Extend and relax. This treatment is performed in order to grow the stacked lamella formed in the hollow fiber in the spinning step and improve the crystal orientation order, and has an effect equivalent to that of the conventional annealing treatment.

[0021] As a result of earnest studies by the present inventors, the elongation and relaxation are alternately performed, and the crystal orientation order can be effectively improved, the effect of the treatment can be obtained in a short time, and the productivity can be improved. I found it to be excellent. The extension and relaxation may be performed in a batch system or continuously.

[0022] It is preferable that at least one of the stretching and the relaxation is performed under a heating condition because the crystal orientation order can be effectively improved. When the melting point of the crystalline polymer constituting the hollow fiber is Tm (° C), the lower limit of the temperature is preferably (Tm-50) ° C or higher, and (Tm).
-40) C or higher is more preferable, and (Tm-30) C or higher is further preferable. The upper limit is preferably (Tm-5) ° C or lower, more preferably (Tm-7) ° C or lower (Tm-10).
C. or lower is more preferable. For the heat treatment, known methods such as a dry hot air method, a steam (steam) heating method, a vacuum heating method, and a heating roll contact method can be used.

[0023] Table 1 shows the measurement results of the 50% elongation elastic recovery rate of the polyethylene hollow fiber when the elongation and relaxation were performed and when only the elongation was performed. The 50% elongation elastic recovery rate is an index of pore formation and is preferably as large as possible. The examination was conducted by a tensile and tensile tester with a constant temperature layer (Shimadzu AG-1
000D). The test length (distance between chucks) was set to 150 mm, hollow fibers were attached thereto, and the temperature of the thermostatic layer was set to 110 ° C. and left for 5 minutes (waiting time for heating), followed by extension treatment or extension-relaxation treatment. went. At this time, the extension speed and the relaxation speed were set to 150 mm / min.

[0024] Further, each treatment time was set to 5 minutes for the extension treatment or the extension-relaxation treatment time. That is, in the case of the extension processing, even after the extension was started up to the predetermined condition, the whole processing time from the start of the extension was set to 5 minutes by keeping the same state. In addition, the extension-relaxation process, after reaching a predetermined extension rate after the start of extension, is continuously relaxed to a predetermined extension rate, and then held in that state, so that the total processing time from the start of extension is increased. 5 minutes.

[0025] Table 1 shows the measurement results of the 50% elongation elastic recovery of the obtained hollow fibers. From this result, it is understood that the relaxation treatment is preferable to the extension treatment alone.

【table 1】

[0026] Next, Fig. 1 shows the measurement results of the 50% elongation elastic recovery rate of the polyethylene hollow fiber subjected to elongation and relaxation.
"○" indicates the hollow fiber that has not been stretched and relaxed, "□" indicates the hollow fiber that has been stretched at an extension rate of 15%, and "●" indicates that the extension rate is 15% and the relaxation rate is 66.7%. The hollow fiber which carried out the process is shown. For stretching and relaxing, a hand-held stretching machine that has a chuck that can fix hollow fibers and that can be moved manually, and a dry heat oven that has an opening on the side so that the hand-held stretching machine can be inserted. It was done using. In detail, after fixing the hollow fiber to the chuck of the hand-drawing machine, the hollow fiber fixed by the chuck was inserted from the opening of the oven, and the chuck was manually moved to perform the treatment under predetermined conditions. The processing temperature is 110 ° C.

[0027] From FIG. 1, it is found that the 50% elongation elastic recovery rate is larger when the hollow fiber is relaxed after the elongation and the number of repetition of the relaxation step after the elongation is larger than that when the hollow fiber is treated while only being elongated, and the relaxation step is 50. It can be seen that the% elongation elastic recovery rate is further increased. The lower limit of the number of steps of relaxing after stretching is one, but it is desirable that the number of times is large for effective treatment. This is because in order to orient the tilted molecular chains properly in the fiber axis direction and to change the incomplete crystal around the lamella into a complete structure, it is necessary to stretch-relax more than once to stretch-relax once. This is because it is preferable to repeat. The number of times depends on equipment restrictions.

[0028] The elongation rate is determined by the following formula (1), where S ₀ is the initial yarn length and S ₁ is the length of the stretched yarn. Further, the relaxation rate is calculated by the following formula (2), where S ₂ is the length after relaxation. That is, it is the ratio of the relaxed length to the stretched length, and a relaxation rate of 0% means no relaxation at all, and a relaxation rate of 50% means that one half of the expanded length was relaxed. The relaxation rate of 100% means that all the stretched length was relaxed.

[Formula 1]

[Formula 2]

[0029] In the case where the elongation and the relaxation of the present invention are continuously performed, for example, a method of arranging a heating furnace and a driving roller as shown in Fig. 2 and controlling the peripheral speed of the driving roller to perform the elongation and the relaxation is considered. To be The method of controlling the peripheral speed of the drive roller can be controlled by changing the rotation speed of each roller when the diameter of the drive roller is the same, and when the rotation speed of the drive roller is the same, It can be controlled by changing the diameter.

In FIG. 2, 1-3 are drive rollers,
The peripheral speed of each drive roller is V₁, V_Two, V_Three(M
/ Min). 4-10 has no driving force, but can rotate freely
It is a free roller that rolls. 11 is a heating furnace,
The peripheral speed of the moving roller is V ₁<V_Two, And V_Two> V_ThreeNo
The hollow fiber indicated by 12 by adjusting
After lengthening, it is possible to process while relaxing.

[0031] By disposing the free rollers 4 to 10 between the drive roller 2 and the drive roller 3 and folding the hollow fibers back through these free rollers, the heat treatment time can be shortened without using a long heating furnace. Can be long In addition, it is possible to adjust the staying time in the heating furnace by changing the number of installed free rollers. In the example of FIG. 2, the drive roller is arranged outside the heating furnace, and the free roller is arranged inside the heating furnace. However, these positions are not particularly limited, and even if both are arranged inside the heating furnace. Alternatively, both may be arranged outside the heating furnace.

[0032] The extension rate when extending between the drive roller 1 and the drive roller 2 is the peripheral velocity of the drive roller 1 being V ₁ (m
/ Min) and the peripheral speed of the drive roller 2 is V ₂ (m / min), it is calculated by the following formula (3). Next, the relaxation rate when the roller 2 and the roller 3 are relaxed is determined by the following formula (4), where V ₃ (m / min) is the peripheral speed of the roller 3. That is, it is the ratio of the relaxed length to the stretched length, and a relaxation rate of 0% means no relaxation at all, and a relaxation rate of 50% means that one half of the expanded length was relaxed. The relaxation rate of 100% means that all the stretched length was relaxed.

[Formula 3]

[Formula 4]

Further, for example, as shown in FIG. 3, a method in which only driving rollers are arranged in multiple stages before and after the heating furnace and the peripheral speed of each driving roller is controlled to perform extension and relaxation is also possible.
In FIG. 3, 13 to 24 are drive rollers, and the peripheral speed of each drive roller is V ₁₃ (m / min) to V _24.
(M / min). Reference numeral 25 is a heating furnace, and by adjusting the peripheral speed of the driving roller, it is possible to process the hollow fiber indicated by 26 while stretching and relaxing it. Although each drive roller is arranged outside the heating furnace in FIG. 3, a part or all of the drive roller may be arranged inside the heating furnace.

[0034] For example, the drive roller 13 and the drive roller 1
4, the peripheral speed of the driving roller 15 is 1.0 (m
/ Min), 1.2 (m / min), 1.05 (m / min), the extension ratio between the drive roller 13 and the drive roller 14 is 20%, and the extension ratio between the drive roller 14 and the drive roller 15 is 20%. The relaxation rate is 75%. By changing the peripheral speed after the driving roller 16 in the same manner as the driving rollers 13 to 15, the hollow fiber can be repeatedly stretched and loosened.

[0035] In the present invention, the treatment is preferably terminated by relaxation in order to promote the effect of improving the crystal orientation order. In the case of FIG. 3, the drive roller 13 and the drive roller 14
If the stretching is repeated between the driving roller 14 and the driving roller 15 and the stretching between the driving roller 15 and the driving roller 16 is repeated, the driving roller 22 and the driving roller 23 become loose, but in such a case, It is also possible to perform the constant length processing by (peripheral speed of drive roller 23) = (peripheral speed of drive roller 24). The number of driving rollers is not limited to this. It is also possible to dispose a free roller between the drive rollers at the portion where the hollow fiber relaxes.

Further, as shown in FIG. 4, a plurality of drive rollers having different peripheral speeds may be arranged, and the peripheral speeds of the respective drive rollers may be controlled to perform extension and relaxation while being heated by the drive rollers. In FIG. 4, _{27 to 33} are drive rollers that can be heated, and the peripheral speed of each drive roller is V ₂₇ (m / min) to V ₃₃ (m / min).
₂₇ <V ₂₈ , V ₂₈ > V ₂₉ . ． ． As described above, by heating while adjusting the peripheral speed of each drive roller, it is possible to perform heat treatment while extending and relaxing the hollow fiber indicated by 35. It should be noted that all of the driving rollers may be heated, or only a part thereof may be heated. Also in this method, the final treatment is preferably finished by relaxation, but depending on the number of drive rollers, the peripheral speeds of the drive roller at the last stage and the drive roller at the immediately preceding stage may be the same as in the device of FIG. It is also possible to perform fixed length processing.

[0037] The hollow fiber may be treated while being heated only by the driving roller, but in order to avoid temperature decrease due to outside air,
The structure may be such that the inside of the processing zone can be shielded from the outside air. Further, by disposing a heating roller in the heating furnace, it is possible to keep the temperature in the processing zone uniform. The elongation rate and relaxation rate between the rollers are determined in the same manner as in the case of FIG. The number of rollers and the like are not limited to this.

[0038] Elongation rate is a synonym for elongation used in stress-strain measurement, and is a% of the length extended by elongation to the original length.
It is preferable that it is not more than the yield point elongation rate at the treatment temperature because the crystal orientation order can be improved without breaking the stack lamella.

[0039] Note that the yield point elongation rate refers to the elongation rate at the yield point, and the yield point is obtained by stress strain measurement.
It is known that the yield point appears as a clear maximum point on the stress-strain curve and as a slope change point.The former case is the maximum point, and the latter case is the tangent line drawn before and after the slope change. The yield point is defined as the yield point (for example, Japan Society of Polymer Science, Editorial Committee for Polymer Dictionary, New Edition Polymer Dictionary, Asakura Shoten, 1988, Item 152). The stress-strain measurement is preferably performed under the same conditions as the deformation rate at the time of stretching, but it is also possible to perform the analogy by performing the stress-strain measurement at different deformation rates.

[0040] In order to achieve the effect of improving the crystal orientation order, the elongation ratio is preferably 1/15 or more of the yield point elongation ratio, and more preferably 1/6 or more of the yield point elongation ratio.
More preferably, it is 1/3 or more of the yield point elongation rate.

[0041] The relaxation rate is appropriately set between 0 and 100%, but it is preferable to approach 100% as much as possible.
However, when the relaxation rate approaches 100%, the hollow fiber may be slackened, which may make it difficult to perform extension and relaxation treatment in a continuous process. Therefore, the upper limit of the relaxation rate is limited by the device.

[0042] The lower limit value of the processing time for stretching and relaxing is preferably 5 seconds or more, more preferably 30 seconds or more. The treatment time is preferably as long as possible. However, since the production apparatus may be large, it is preferably 30 minutes or less, more preferably 15 minutes or less from the viewpoint of downsizing of the apparatus which is the gist of the present invention. .

Next, the 50% elongation elastic recovery rate will be described.
Void formation by melt spinning-drawing of a crystalline polymer is performed by the hard elastic (Hardela) of the crystalline polymer.
It is known to utilize stic) mechanical properties. Hardelast represented by crystalline polymer
One of the mechanical properties characteristic of the ic material is that it exhibits a stress-strain curve as shown in FIG. That is, FIG.
As shown in (1), the Hardelastic material is characterized by increasing tensile strain by continuously increasing stress and then exhibiting high strain recovery when the stress is continuously decreased.

[0044] This is because the stacked lamellae (crystals) that have been stacked are separated from each other due to the increase in elongation strain, and voids are formed between them, but with the decrease in stress, the stack lamellae come close again. It is considered. And
The elongation elastic recovery rate is a quantitative indicator of strain recovery when stress is continuously reduced. Note that such a Har
The mechanical properties characteristic of the delastic material are described, for example, in Toshihiko Kuroda, Akira Takizawa, Mitsuru Nagasawa, “Basic Properties and Applications of Polymers” (CMC Co., Ltd., 1984). .

[0045] In the present invention, the elongation elastic recovery rate is measured and calculated as follows. That is, using the stress-strain measuring device for the measurement, between spaced by a pair of chucks, after attaching the test sample so that the test length L _0, stretched to a length at a constant pull rate is L ₁ Then, after maintaining that state for a predetermined time, the chuck is returned at the same speed as the extension until the chuck distance becomes L ₀ . The stress becomes zero at L ₂ on the way, but this continues until it returns to the original length L ₀ . The stress-strain behavior at this time is recorded on a chart paper or the like (see FIG. 5), and the elongation elastic recovery rate is calculated based on the following formula (5).

[0046] As shown in FIG. 5, the extension length is determined by the test sun.
It is the length that the pull is extended and is L ₁-L₀Equivalent to. one
On the other hand, the length when the stress drops to 0 becomes L_Two
Then, the recovery length is L₁-L_TwoIt is represented by. In the present invention
Is L₀50% of the₁= 1.5L₀As
The elongation elastic recovery rate at this time shall be "50.
% Elongation elastic recovery rate ".

[Formula 5]

The present inventor has determined that this 50% elongation elastic recovery rate is 40%.
It has been found that when the content is at least%, the formation of pores in the subsequent stretching step can be made uniform. That is, that the 50% elongation elastic recovery rate is 40% or more means that the laminated structure of the stacked lamellae is more firmly held. Such a structure prevents the weak portion of the laminated structure of the stack dramer from being destroyed before the strong portion in the subsequent stretching step. Therefore, when the 50% elongation elastic recovery rate is 40% or more, it is possible to form pores uniformly. The larger the recovery rate, the more uniform the pores.

[0048] Therefore, in the present invention, the 50% elongation elastic recovery rate is preferably 40% or more, more preferably 50% or more, and particularly preferably 55% or more by elongation and relaxation treatment. The 50% elongation elastic recovery rate of 40% or more can be achieved when the crystalline polymer is polyethylene, for example, the elongation rate and the relaxation rate are 30% and 33%, respectively, the temperature is 110 ° C., and the number of repetitions is 5 times or more. .

(C) Stretching Step After the above-mentioned (B) stretching and relaxing steps, in order to make the hollow fiber porous, a stretching treatment is carried out in the (C) stretching step, and a hollow fiber membrane having a large number of fine pores. Is obtained. By subjecting the hollow fiber after spinning to a stretching treatment, stress concentrates in the structurally weak amorphous portion, and the amorphous chains selectively extend in the stretching direction, resulting in cleavage between the stacked lamellae. At the same time, a part of the stack lamella peels off, and these are aggregated to form microfibrils. On the other hand, a portion having a strong cohesive force in the stack lamella withstands stress while maintaining its structure, and has a large number of microfibrils 15 formed along the stretching direction like the hollow fiber membrane shown in FIG. A large number of slit-shaped fine holes 17 are formed between the stack lamella 16 and the stack lamella 16 to which they are connected. 6 is an enlarged schematic view showing the internal structure of the hollow fiber membrane, and the stretching direction is as shown in the figure.

[0050] The stretching step is preferably composed of two stages, a cold stretching step of stretching at a relatively low temperature and a hot stretching step of stretching at a temperature higher than the processing temperature in the cold stretching step. The fine pores can be controlled more precisely by performing a two-stage stretching process on the. Less than,
The case where the stretching process is performed in two stages of the cold stretching process and the hot stretching process will be described as an example, but the present invention is not limited thereto.

(C-1) Cold stretching step The cold stretching step in the cold stretching step is 0 ° C to Tm-50 ° C.
It is preferable to carry out in the temperature range of. For example, when polyethylene is used as the crystalline polymer, the treatment temperature during cold stretching is preferably 0 to 80 ° C, more preferably 10 to 50 ° C. By subjecting the hollow fiber after spinning to the cold drawing treatment as described above, uniform and micro crazes (microcracks) can be generated between the stacked lamellae. The cold draw ratio (the length of the hollow fiber after cold drawing / the length of the hollow fiber before cold drawing) is preferably 1.2 to 3.0 times.

(C-2) Hot Stretching Step In the hot stretching step, the microcracks formed by the above-described cold stretching step are enlarged, microfibrils are formed between the stack lamellas, and slit-like fine holes are formed. This is a step of obtaining a hollow fiber membrane having a porous structure. The hot stretching temperature is
It is preferable to carry out at a temperature as high as possible within a range not exceeding the melting point of the crystalline polymer. In addition, the thermal draw ratio (the length of the hollow fiber membrane after hot drawing / the length of the hollow fiber before hot drawing) is
The size can be appropriately selected depending on the target pore size, but it is preferably in the range of 2 to 10 times, preferably 3 to 6 times from the viewpoint of process stability.

(D) Heat setting step The hollow fiber membrane obtained through the above-mentioned (C) stretching step may be used as the final product, but in order to stabilize the dimensions of the hollow fiber membrane,
In the heat setting step (D), it is preferable to perform the heat treatment at a temperature higher than that in the previous heat stretching step (C-2). The heat setting temperature is preferably set to be higher than the heat drawing temperature and lower than the melting point of the crystalline polymer.

[0054] (E) Hydrophilic treatment step Next, if necessary, hydrophilic treatment may be performed in the (E) hydrophilic treatment step. Specifically, after immersing the hollow fiber membrane in a hydrophilic polymer solution in which a hydrophilic polymer is dissolved in a solvent, the solvent is evaporated by a drying treatment to form a hollow fiber membrane coated with the hydrophilic polymer. Obtainable. By carrying out such hydrophilic treatment, the surface of the hollow fiber membrane can be made hydrophilic, water to be treated can be prevented from being repelled on the membrane surface, and the water permeability of the membrane can be improved. further,
By performing the hydrophilic treatment, as shown in FIG. 7, the microfibrils 15 are bundled into several microfibril bundles 18, and as a result, the slit-shaped micropores 17 become elliptic micropores 19, which are average. Since the hole diameter can be enlarged, the permeation flux can be improved. FIG. 7 is a schematic diagram showing the internal structure of the hollow fiber membrane shown in FIG. 6 after hydrophilic treatment, the same elements as those in FIG. 6 are designated by the same reference numerals, and the description thereof will be omitted. .

[0055] Next, examples according to the present invention and comparative examples will be described. The evaluation items and evaluation methods in Examples and Comparative Examples are as follows. As a 50% elongation elastic recovery rate measuring device, a tensile tester AG-1 manufactured by Shimadzu Corporation
000D was used. Test length (distance between chucks) is 50 mm
And stretched at a pulling speed of 100 mm / min. 25m
After being stretched by m (when the distance between the chucks reached 75 mm), it was held for 1 minute and then returned to the distance between the chucks of 50 mm again at 100 mm / min. The stress-strain behavior at this time was recorded on a chart paper, and the 50% elongation elastic recovery rate was measured. The test was performed using four hollow fibers each, and the average value was defined as the 50% elongation elastic recovery rate.

[0056] 2. Manufacturing apparatus The apparatus shown in FIG. 3 has a plurality of rollers arranged in front of and behind the heating furnace, and by adjusting the peripheral speed of these rollers, it is possible to continuously perform a process of repeating extension and relaxation. Is. In the figure, 25 has a furnace length of 0.8
m of the dry heating type heating furnace for heating the hollow fiber indicated by 26. A total of 12 rollers are arranged in front of and behind the heater, and it is possible to repeat extension and relaxation by adjusting the peripheral speed of each roller. The processing apparatus shown in FIG. 3 is an example, and the present invention is not limited to this apparatus.

[0057] 3. Stress strain measurement As a measuring device, Shimadzu tensile tester AG-1
000D equipped with a constant temperature layer for temperature control was used.
Test length (distance between chucks) 20 mm, pulling speed 5
It was measured at 0, 100 and 200% / min at a measurement temperature of 110 ° C. The measurement was carried out using four hollow fibers each to determine the yield point.

<Example 1> As the crystalline polymer, HY540 manufactured by Nippon Polychem Co., Ltd. was used, and 1% of this polyethylene was used.
Spin at 80 ° C and wind at a winding speed of 30 m / min.
A hollow fiber having an inner diameter of 0.47 mm and a film thickness of 0.1 mm was obtained. When the stress-strain measurement of this hollow fiber was performed, the elongation percentages at the yield point at tensile speeds of 50, 100, and 200% / min were 31%, 32%, and 31%, respectively.

[0059] The obtained hollow fiber was continuously stretched and relaxed using the manufacturing apparatus shown in Fig. 3. The temperature of the heating furnace 13 is
It was set to 110 ° C. Table 2 shows the peripheral speeds of the rollers 13 to 24, the elongation rate, and the processing time. As shown in FIG. 3 and Table 2, the treatment was performed by repeating the elongation and relaxation 5 times. In Table 2, the value in parentheses in the column of elongation ratio is the elongation ratio when the first trial length, that is, the peripheral speed of the roller 13 is used as a reference, and does not exceed the yield point based on the result of stress strain measurement. To 30%.

[0060]

[Table 2] As a result of measuring the 50% elongation elastic recovery rate of the obtained hollow fiber, it was found that the treatment time was 89% for the hollow fiber which was repeatedly stretched and relaxed.
Despite being as short as 0 seconds, it was 56%.

<Example 2> A hollow fiber similar to that of Example 1 was prepared as shown in FIG.
The elongation-relaxation was continuously performed using the manufacturing apparatus shown in FIG.
The temperature of the heating furnace 11 was 110 ° C. The peripheral speeds of the roller 1, the roller 2, and the roller 3 are
It was set to 0.4 m / min, 0.52 m / min, and 0.48 m / min, and the elongation rate was 30% and the relaxation rate was 33.3%. The heat treatment time is about 104 seconds required for extension,
The time required for relaxation was about 815 seconds. As a result of measuring the 50% elongation elastic recovery rate of the obtained hollow fiber, it was 56% despite the short heat treatment time of about 919 seconds.

<Comparative Example 1> The same hollow fiber as in Example 1 was used. Leave the wound hollow fiber on the bobbin, 1
Batch annealing was performed for 60 minutes in a heating furnace at 10 ° C.
As a result of measuring the 50% elongation elastic recovery rate of these hollow fibers, the hollow fibers just wound up were 33%, and the hollow fibers subjected to batch annealing were 48%.

[0063] As is clear from the results of Examples 1 and 2 and Comparative Example 1, in the manufacturing method in which elongation and relaxation are repeated, it is possible to increase the 50% elongation elastic recovery rate in less time than batch annealing. It was

[0064]

As described in detail above, according to the method for producing a hollow fiber membrane of the present invention, the equipment for improving the crystal orientation order can be downsized, the production efficiency can be improved, and the production cost can be reduced. In addition, the hollow fiber membrane having desired membrane characteristics can be stably obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between elongation and relaxation and elongation elastic recovery rate during annealing treatment.

FIG. 2 is an example of an apparatus for carrying out the present invention in a continuous process.

FIG. 3 is another example of an apparatus for carrying out the present invention in a continuous process.

FIG. 4 is another example of an apparatus for carrying out the present invention in a continuous process.

FIG. 5 is a diagram showing an example of a stress strain curve of a crystalline polymer.

FIG. 6 is an enlarged schematic view of the internal structure of the hollow fiber membrane of the present invention.

7 is a schematic view of the hollow fiber membrane of FIG. 4 subjected to hydrophilic treatment.

[Explanation of symbols]

1-3 drive rollers 4-10 free rollers 11 heating furnace 12 hollow fiber 13-24 Drive roller 25 heating furnace 26 hollow fiber 27-33 Heatable drive roller 34 35 hollow fiber 36 Microfibril 37 Stack Dramella 38 fine holes 39 Microfibril bundle 40 fine holes

Continued front page    F-term (reference) 4D006 GA07 MA01 MB09 MB16 MC22X                       MC23X MC29X MC48 MC54                       NA18 NA36 NA58 NA69 NA70                       PA01 PB06 PC02                 4L036 MA04 MA19 PA01 PA03 PA09                       PA10 UA06 UA25

Claims (15)

[Claims] 1. A method for producing a hollow fiber membrane, comprising a spinning step of spinning a melted crystalline polymer into a hollow fiber, and a stretching step of stretching the hollow fiber to make it porous. A method for producing a hollow fiber membrane, comprising a step of stretching and relaxing between the stretching step and the stretching step. 2. The method for producing a hollow fiber membrane according to claim 1, wherein at least a part of the steps of stretching and relaxing is performed under heating conditions. 3. The method for producing a hollow fiber membrane according to claim 1, wherein the hollow fiber is stretched and relaxed by using a plurality of drive rollers having different peripheral speeds. 4. A free roller having no driving force is arranged between the plurality of driving rollers.
A method for producing the hollow fiber membrane described. 5. The method for producing a hollow fiber membrane according to claim 2, wherein at least a part of the steps of stretching and relaxing is performed in a heating furnace. 6. The method for producing a hollow fiber membrane according to claim 3, wherein at least a part of the drive roller can be heated to heat the hollow fiber. 7. The melting point of the crystalline polymer is Tm (° C.)
And the heating conditions are (Tm-5) ° C to (Tm-5).
The method for producing a hollow fiber membrane according to claim 2, wherein the temperature is in the range of 0) ° C. 8. The extension and the relaxation are performed twice or more in the step of performing the extension and the relaxation.
The method for producing a hollow fiber membrane according to any one of claims. 9. The stretching according to claim 1, wherein in the step of performing stretching and relaxation, the stretching is performed so that the stretching rate is equal to or lower than the yield point stretching rate at the temperature during stretching. Hollow fiber membrane manufacturing method. 10. The production of a hollow fiber membrane according to claim 1, wherein a 50% elongation elastic recovery rate of the hollow fiber is set to 40% or more by the step of performing the elongation and the relaxation. Method. 11. The method for producing a hollow fiber membrane according to claim 1, wherein the stretching step includes a cold stretching step and a hot stretching step. 12. The melting point of the crystalline polymer is Tm
The method for producing a hollow fiber membrane according to claim 11, wherein cold drawing is performed in a temperature range of 0 ° C to Tm-50 ° C when the temperature is (° C). 13. The method for producing a hollow fiber membrane according to claim 11 or 12, wherein the heat drawing is performed at a draw ratio of 2 to 10 times. 14. The method for producing a hollow fiber membrane according to claim 1, further comprising a heat setting step after the stretching step. 15. The method for producing a hollow fiber membrane according to claim 1, further comprising a hydrophilic treatment step after the stretching step.