JP5831709B2 - Melt spinning apparatus and method for producing hollow fiber - Google Patents

Description

  The present invention relates to a melt spinning apparatus and a method for producing hollow fibers, and more particularly to a melt spinning apparatus used for producing a polyolefin porous hollow fiber membrane and a method for producing such hollow fibers.

  Conventionally, polyolefin porous hollow fiber membranes have been used in a wide range of fields such as wastewater treatment, production of ultrapure water, and air purification because they are excellent in chemical stability, strength characteristics, flexibility, etc. Yes. Such a method for producing a polyolefin porous hollow fiber membrane includes a spinning process in which polyolefins such as polyethylene and polypropylene are melt-spun to obtain hollow fibers, and the hollow fibers obtained in the spinning process are stretched to be porous. It consists of a stretching process. The spinning process usually includes a cooling process in which when the molten polyolefin resin is discharged from the nozzle, cooling air is continuously blown to the resin with a blower or the like to cool and solidify to form hollow fibers. . In the stretching step, if a uniform hollow fiber having a constant diameter and film thickness is used, thread breakage in the stretching step hardly occurs and a homogeneous porous hollow fiber membrane can be stably obtained. It is desirable to produce a uniform hollow fiber having a constant film thickness.

  Conditions such as the amount and direction of cooling air when cooling air is blown to the molten resin to solidify it affect the homogeneity of the film thickness and diameter of the resulting hollow fiber. This is important because it affects the performance of the hollow fiber membrane obtained by stretching. And what was described in patent document 1 is known as an apparatus for cooling and solidifying molten resin.

  FIG. 5 is a cross-sectional view showing a conventionally used melt spinning apparatus 101. In the melt spinning apparatus 101 as shown in FIG. 5, the molten resin is discharged downward from the nozzle 107 of the head 105 disposed above the cooling apparatus 103 and dropped. At this time, since the periphery of the nozzle 107 of the head 105 becomes high temperature due to the heat of the molten resin, thermal buoyancy occurs in the vicinity of the head 105 due to the difference between the ambient temperature of the nozzle 107 and the temperature of the cooling air flowing from the cooling device 103. . When thermal buoyancy is generated in the vicinity of the head 105, warm air around the nozzle 107 flows in a direction away from the nozzle 107, and an airflow in which cooling air flows in the vicinity of the nozzle 107 is generated. When cooling air flows near the nozzle 107, the temperature around the nozzle 107 decreases, and the molten resin is partially cooled. As a result, there is a problem that cooling spots are generated in the molten resin.

  Further, when the cooling air flows in the vicinity of the nozzle 107, a complicated air flow is generated in the vicinity of the nozzle 107, and the air temperature in the vicinity of the nozzle 107 is lowered, so that the nozzle discharge resin temperature and the surface temperature of the falling resin are changed in the circumferential direction and time The fiber diameter of the hollow fiber and the film thickness become non-uniform due to unevenness of the resin viscosity and elongation characteristics during dropping. In the stretching process, when hollow fibers having a non-uniform yarn diameter and film thickness are stretched, the cross-sectional stress value generated by the tensile force acting on the hollow fibers at the time of stretching with respect to the cross-section of the hollow fibers Changed, the shape and size of the holes formed on the side surfaces became non-uniform, and there was a problem that a highly accurate hollow fiber membrane could not be formed.

  Therefore, the present invention has been made to solve the above-described problems, and when producing hollow fibers such as hollow fibers used for hollow fiber membranes, the diameter and thickness of the hollow fibers are reduced. It is an object of the present invention to provide a melt spinning apparatus and a method for producing hollow fibers that can be made uniform.

  In order to solve the above-described problems, the present invention is a hollow fiber melt spinning apparatus having a nozzle having a nozzle for continuously discharging a molten resin, and a direction facing the molten resin discharged from the nozzle. A cooling device configured to flow a fluid having a temperature lower than that of the molten resin, and an upper end thereof is disposed in close contact with the head so as to surround the nozzle and between the head and the cooling device. A heat retaining cylinder for maintaining the ambient temperature of the molten resin discharged from the nozzle, and an exhaust port formed below the lower end of the heat retaining cylinder to prevent fluid flowing upward from entering the heat retaining cylinder. It is characterized by having.

  According to the present invention configured as described above, by maintaining the ambient temperature of the hollow fiber discharged from the nozzle, the ambient temperature of the molten resin in the heat retaining cylinder is rapidly changed by the cooling air flowing upward. And the change in the heat transfer behavior of the molten resin can be prevented. At the same time, by providing an exhaust port below the lower end of the heat retaining cylinder, even if the cooling air rises, this cooling air can be prevented from entering the heat retaining cylinder. Thereby, the cooling spot of molten resin can be eliminated. Further, by preventing the cooling air from entering the heat insulation cylinder, the air flow in the heat insulation cylinder can be stabilized. Thereby, the fluctuation | variation in the circumferential direction and time of the surface temperature of the resin which is discharged from the nozzle can be prevented.

  In the present invention, preferably, a shutter configured to cover the lower end of the heat retaining cylinder, having an opening with a predetermined diameter immediately below the nozzle of the head, and preventing fluid from flowing into the heat retaining cylinder. I have.

  According to the present invention configured as described above, by providing the shutter, it is possible to more reliably prevent the cooling air from entering the heat insulating cylinder while flowing the molten resin downward from the opening.

  In the present invention, preferably, the temperature of the heat insulation cylinder is controlled, and a sensor for detecting at least one of the surface temperature or the internal temperature of the heat insulation cylinder, or the outer surface temperature of the molten resin discharged from the nozzle. And a temperature control device for heating or cooling the heat insulation cylinder based on the detection result of the sensor.

  Thereby, the temperature in a heat insulation cylinder can be maintained appropriately, and the cooling spot of molten resin can be suppressed more reliably.

  In order to solve the above-described problems, the present invention is a method for producing hollow fibers using a melt spinning apparatus, and a step of continuously discharging a molten resin from a nozzle head of the melt spinning apparatus; The melt resin is disposed between the head and the cooling device and surrounding the nozzle so that the upper end thereof is in close contact with the head, and melt spinning for maintaining the ambient temperature of the melt resin discharged from the nozzle Cooling by passing through a cooling device of a melt spinning apparatus configured to pass a fluid having a temperature lower than the temperature of the molten resin in a direction opposite to the molten resin flowing from the heat insulating cylinder, and a step of passing the apparatus through the heat insulating cylinder The melt spinning apparatus is formed below the lower end of the heat insulation cylinder, and has an exhaust port that prevents upwardly flowing fluid from entering the heat insulation cylinder. And

  As described above, according to the present invention, when producing hollow fibers such as hollow fibers used in the hollow fiber membrane, the yarn diameter and film thickness of the hollow fibers can be made uniform.

It is the schematic which shows the melt spinning apparatus by embodiment of this invention. It is sectional drawing which shows the spinning head, heat insulation cylinder, and cooling device by embodiment of this invention. It is sectional drawing which shows the melt spinning apparatus by the 1st modification of embodiment of this invention. It is sectional drawing which shows the melt spinning apparatus by the 2nd modification of embodiment of this invention. It is sectional drawing which shows the melt spinning apparatus used conventionally.

The method for producing a hollow fiber membrane according to an embodiment of the present invention is mainly performed by discharging a molten resin in which a polyolefin resin such as polyethylene or polypropylene is heated to a melting point or more from an annular nozzle to obtain hollow fibers. A spinning step to obtain, and a drawing step of drawing the hollow fiber. And a spinning process has a cooling process which blows cooling gas to the outer peripheral surface of the hollow molten resin discharged from the annular nozzle, and cools and solidifies.
Hereinafter, a melt spinning apparatus used for carrying out the spinning process will be described in detail with reference to the drawings.

  FIG. 1 is a schematic view showing a melt spinning apparatus 1 according to an embodiment of the present invention. The melt spinning apparatus 1 includes a spinning head 3 that discharges molten and heated resin, and a heat retaining cylinder 5 that is provided below the spinning head 3 and that maintains the ambient temperature of the resin discharged from the spinning head 3. And a cooling device 7 for cooling the resin discharged from the spinning head 3 and a winder 9 for winding the hollow fibers of the cooled and solidified resin. In such a melt spinning apparatus 1, the molten resin discharged from the spinning head 3 is dropped according to gravity, is cooled and solidified in the process of dropping, and winds the cooled and solidified hollow fiber. The heat insulating cylinder 5 and the cooling device 7 are arranged in parallel to the molten resin dropping direction, that is, aligned in the vertical direction.

  FIG. 2 is a cross-sectional view showing the spinning head 3, the heat retaining cylinder 5, and the cooling device 7. The spinning head 3 includes four nozzles 11 for discharging molten resin. Each nozzle 11 opens downward and is disposed on the circular bottom surface of the spinning head 3. The four nozzles 11 are arranged to form a square apex. A resin reservoir 13 for accumulating molten resin is provided at the top of the nozzle 11, and a sealing lid 15 is attached to the main body of the spinning head 3 via a seal member 17 above the resin reservoir 13. ing. Each nozzle 11 has an annular shape, and the molten resin discharged from the nozzle 11 is rectified into an annular shape.

  The cooling device 7 is disposed on the lower side of the spinning head 3, and includes a cooling cylinder 19 configured to surround the molten resin flowing from the spinning head 3, and a quench blower for feeding cooling air into the cooling cylinder. 21 and an extension pipe 23 extending upward from the cooling cylinder 19.

  The cooling cylinder 19 extends in parallel with the dropping direction of the molten resin (vertically downward), and the upper end and the lower end are open. The cooling cylinder 19 is arranged on the lower side of the spinning head 3 so that the central axis thereof is coaxial with the central axis of the spinning head 3, and the melting tube 19 falls from the four nozzles 11 of the spinning head 3. The resin has such a diameter that it can pass from the upper end toward the lower end without touching the cooling cylinder 19. The cooling cylinder 19 cools and solidifies the molten resin by applying cooling air sent from the quench blower 21 to the molten resin while the molten resin passes through the cooling cylinder 19. Such a cooling cylinder 19 has a double pipe structure including an outer cylinder 25 and an inner cylinder 27 having a porous structure.

  The quench blower 21 is configured to send cooling air between the outer cylinder 25 and the inner cylinder 27 of the cooling cylinder 19 in a direction orthogonal to the extending direction of the cooling cylinder 19. And the cooling air which flowed in between the outer cylinder 25 and the inner cylinder 27 from the quench blower 21 spreads in the circumferential direction of the cooling cylinder 19 in the space between the outer cylinder 25 and the inner cylinder 27, and passes through the inner cylinder 27. Passes from the circumferential direction toward the center of the inner cylinder 27. Accordingly, the cooling device 7 performs so-called radial quenching in which the cooling air from the quench blower 21 is applied to the molten resin from the circumferential direction. Then, the cooling air flowing in the direction perpendicular to the falling direction of the molten resin and flowing into the cooling cylinder 19 changes its direction in the cooling cylinder, and flows in the upper end direction or the lower end direction of the opened inner cylinder 27 having a lower atmospheric pressure. .

  The extension pipe 23 extends to the vicinity of the lower end of the heat retaining cylinder in parallel with the dropping direction of the molten resin. The extension pipe 23 has substantially the same diameter as the inner cylinder 27, and is configured to allow the cooling air flowing upward from the cooling cylinder 19 to flow further upward. Thereby, cooling air flows in the direction which opposes the falling direction of molten resin.

  The heat insulating cylinder 5 is constituted by a tube extending in parallel with the dropping direction of the molten resin. The diameter of the heat retaining cylinder 5 is dimensioned so that the resin falling from the four nozzles 11 can pass from the upper end toward the lower end so as not to contact the heat retaining cylinder 5. The upper end of the heat insulating cylinder 5 is disposed so as to be in close contact with the bottom surface of the spinning head 3, and the lower end is disposed at a position separated from the upper end of the extension pipe 23 of the cooling device by a predetermined distance in the vertical direction. An upper flange portion 29 and a lower flange portion 31 that extend in a direction orthogonal to the heat retaining tube 5 are provided at the upper end and the lower end of the heat retaining tube 5. The upper flange portion 29 is airtightly attached to the bottom surface of the spinning head 3 via the seal member 33, and the inside of the heat insulating cylinder 5 is in a semi-sealed state in which only the lower side is opened.

Further, a discharge port 35 for discharging the cooling air from the space where the molten resin is falling is provided between the lower end of the heat insulating cylinder 5 and the extension pipe 23 of the cooling device 7. The discharge port 35 is configured by a gap between the upper end of the extension tube 23 and the lower flange portion 31 of the heat retaining cylinder 5. The exhaust port 35 prevents the cooling air that has moved up the cooling cylinder 19 of the cooling device 7 from entering the heat retaining cylinder 5.
In this embodiment, a gap is formed between the upper end of the extension pipe and the lower flange portion of the heat retaining cylinder, and this is used as the exhaust port 35. However, according to the present invention, the exhaust port is the heat retaining cylinder. As long as the cooling air can flow in the extension pipe at a sufficient distance, for example, a hole is formed near the upper end of the extension pipe. A gap may be formed and used as an exhaust port.

Next, the operation of the melt spinning apparatus according to the above-described embodiment will be described in detail.
First, when the molten and heated resin is discharged from the nozzle 11 of the spinning head 3, the molten resin is discharged downward in the form of an annular cross section according to the shape of the nozzle 11. The molten resin discharged downward takes a shape that becomes smaller in diameter as it falls, and passes through the inside of the heat insulating cylinder 5, the extension pipe 23 of the cooling device 7, and the inside of the cooling cylinder 19 to be cooled and solidified. It is wound up as a hollow fiber by a winding device 9 provided on the lower side of the device 7. The resin discharged from the heat insulating cylinder 5 has a temperature of about 150 to 170 ° C., and the high temperature inside the heat insulating cylinder 5 is 170 ° C. which is close to the spinning nozzle temperature due to the heat radiation and heat transfer from the nozzle and the resin temperature. The temperature of the portion in contact with the cooling air at the lower end has a temperature distribution in the height direction inside the heat insulating cylinder 5 such as a temperature close to the cooling air, and the temperature distribution is maintained. And the cooling air which flows into the cooling cylinder 19 from the quench blower 21 of the cooling device 7 becomes the temperature of about 15-30 degreeC, and is lower than the temperature inside the heat insulation cylinder 5. FIG.

  The cooling air that has risen up the cooling cylinder 19 tries to enter the inside of the heat insulating cylinder 5 by its kinetic energy, but the heat insulating cylinder 5 has a semi-sealed structure that is open only on the lower side, Is filled with warm air, the air flowing upward from the extension pipe 23 does not enter the heat retaining cylinder 5 but flows toward the outside of the exhaust port 35 having a lower atmospheric pressure. Thereby, it is possible to prevent the cooling air from entering the inside of the heat insulating cylinder 5, and the temperature inside the heat insulating cylinder 5 including the vicinity of the nozzle 11 can be kept relatively high. Further, since the heat insulating cylinder 5 has a semi-hermetic structure, the cooling air does not flow into the heat insulating cylinder 5 from below. Thereby, it is possible to prevent the cooling air from flowing into the heat insulating cylinder 5 and disturbing the airflow inside the heat insulating cylinder 5.

  As described above, according to the melt spinning apparatus 1 according to the present embodiment, the heat retaining cylinder 5 can prevent the cooling air from reaching the vicinity of the nozzle 11 of the spinning head 3, so that the resin is partially in the vicinity of the nozzle 11. It is possible to prevent the occurrence of cooling spots due to rapid cooling. Moreover, since the heat insulation cylinder 5 can prevent the airflow of the cooling air from being generated in the vicinity of the nozzle 11, it is possible to prevent the diameter and thickness of the molten resin from becoming nonuniform due to the airflow.

Next, a modification of the melt spinning apparatus according to the present invention will be described in detail.
FIG. 3 is a cross-sectional view showing a melt spinning apparatus according to a first modification.

  As shown in FIG. 3, in addition to the above-described melt spinning apparatus 1, the melt spinning apparatus 41 includes a temperature control device 43 for controlling the temperature of the heat retaining cylinder 5 and a molten resin dropped from the nozzle 11 of the spinning head 3. And a plurality of thermocouples 47 for measuring the temperature of the heat retaining cylinder 5. Each of the plurality of thermocouples 47 includes a temperature of the heat retaining cylinder 5, a central portion of the four resin flows, that is, a temperature near the central axis of the heat retaining cylinder 5, and a space between the resin flow and the heat retaining cylinder 5, that is, the heat retaining cylinder 5 The temperature near the inner side is measured.

  The temperature control device 43 is based on the temperature of the molten resin measured by the radiation temperature sensor 45 and / or the temperature of the thermal insulation cylinder 5 measured by the thermocouple 47 or the temperature in the thermal insulation cylinder 5. Is to control. Specifically, the temperature control device 43 has a cooling circuit, and heats or cools the heat insulating cylinder 5 by circulating the cooling water.

  Such a temperature control device 43 is used when the temperature of the molten resin measured by the radiation temperature sensor 45 is lower than a predetermined temperature, or the temperature of the heat retaining cylinder 5 measured by the heat transfer pair 47 or in the heat retaining cylinder 5. When the temperature is lower than the predetermined temperature, the heat retaining cylinder 5 is heated to increase the temperature inside the heat retaining cylinder 5. Furthermore, the temperature control device 43 is configured so that the temperature of the molten resin measured by the radiation temperature sensor 45 is higher than a predetermined temperature, or the temperature of the heat retaining cylinder 5 measured by the heat transfer pair 47 or the temperature in the heat retaining cylinder 5. When the temperature is higher than a predetermined temperature, the heat retaining cylinder 5 is cooled to return the interior of the heat retaining cylinder 5 to an appropriate temperature. Further, the temperature control device 43 equalizes the temperature spots when a difference of a predetermined value or more occurs between the temperature of the central portion of the heat insulating cylinder 5 measured by the heat transfer pair 47 and the temperature of the peripheral portion. The heat retaining cylinder 5 is heated.

  The melt spinning apparatus 41 according to the first modification includes a shutter 49 that covers the opening at the lower end of the heat retaining cylinder 5. The shutter 49 includes four openings 51 corresponding to the positions of the four nozzles 11. The diameter of the opening 51 of the shutter 49 is determined in consideration of the diameter of the molten resin having a tapered shape at the lower end of the heat insulating cylinder 5, and has a diameter slightly larger than the diameter of the molten resin. By providing such a shutter 49, it is possible to reliably prevent the cooling air of the cooling device 7 from flowing from the lower side of the heat insulating cylinder 5. Further, by covering the lower end of the heat insulating cylinder 5 with the shutter 49, the outflow of the atmosphere in the heat insulating cylinder due to the thermal convection caused by the atmospheric temperature difference between the inner peripheral surface of the heat insulating cylinder and the center, the accompanying inflow of the outside air, and the heat insulating cylinder 5 Heat dissipation from the inside can be suppressed.

Next, a second modification of the melt spinning apparatus according to the above-described embodiment will be described in detail.
FIG. 4 is a cross-sectional view showing a melt spinning apparatus according to a second modification.

  As shown in FIG. 4, the melt spinning device 61 includes a plurality of heat retaining cylinders 63 and cooling devices 65 corresponding to the respective nozzles 11 of the spinning head 3. The shutter 67 provided at the lower end of the heat retaining cylinder 63 has an iris diaphragm structure whose opening diameter can be adjusted. Thus, by providing the heat retaining cylinder 63 and the cooling device 65 corresponding to each nozzle 11, the opening diameter of the shutter 67 can be adjusted using the iris diaphragm structure, and therefore the opening diameter is made as small as possible. Therefore, it is possible to more reliably suppress the cooling air from flowing into the heat insulating cylinder.

  Further, by providing the temperature control device 69 in each heat retaining cylinder 63, the temperature can be measured and controlled for each molten resin discharged from the respective nozzles 11 and uniformly from the periphery of one resin flow. Heating and cooling can be performed. Thereby, a temperature spot can be eliminated more reliably and a uniform hollow fiber can be formed.

1, 41, 61 Melt spinning device 3 Spinning head 5 Thermal insulation cylinder 7 Cooling device 11 Nozzle 19 Cooling cylinder 21 Quench blower

Claims (9)

A hollow fiber melt spinning apparatus,
A head having a nozzle for continuously discharging a molten resin;
A cooling device configured to flow a fluid having a temperature lower than that of the molten resin in a direction opposite to the molten resin discharged from the nozzle;
A heat retaining cylinder for maintaining the ambient temperature of the molten resin discharged from the nozzle, the upper end of which is disposed between the head and the cooling device so as to surround the nozzle and in close contact with the head. When,
A melt spinning apparatus comprising: an exhaust port that is formed below a lower end of the heat retaining cylinder and prevents upwardly flowing fluid from entering the heat retaining cylinder.   The shutter is configured to cover a lower end of the heat retaining cylinder, has an opening having a predetermined diameter immediately below the nozzle of the head, and prevents the fluid from flowing into the heat retaining cylinder. The melt spinning apparatus according to 1. A sensor for detecting at least one of the surface temperature of the heat retaining cylinder, the internal temperature, or the outer surface temperature of the molten resin discharged from the nozzle;
A temperature control device for controlling the temperature of the insulation cylinder,
The melt spinning apparatus according to claim 1 or 2, wherein the temperature control device is configured to heat or cool the heat retaining cylinder based on a detection result of the sensor. The head includes a plurality of nozzles,
The melt spinning apparatus according to any one of claims 1 to 3, wherein one heat retaining cylinder and one cooling cylinder are provided for one nozzle.   The melt spinning apparatus according to claim 3, wherein the temperature control device includes a hot water circulation circuit.   The melt spinning apparatus according to claim 2, wherein the shutter has an iris diaphragm structure.   The melt spinning apparatus according to claim 3, further comprising an infrared radiation thermometer for measuring an outer surface temperature of the molten resin.   The melt spinning apparatus according to claim 5, wherein the temperature control device includes an electric heater for maintaining the temperature of the heat insulating cylinder. A method for producing a hollow fiber using a melt spinning apparatus,
A step of continuously discharging molten resin from the nozzle head of the melt spinning apparatus;
An upper end of the molten resin is disposed between the head and the cooling device so as to surround the nozzle and is in close contact with the head, and the ambient temperature of the molten resin discharged from the nozzle is maintained. Passing the heat-insulating cylinder of the melt spinning apparatus for,
Passing through a cooling device of the melt spinning apparatus configured to flow a fluid having a temperature lower than the temperature of the molten resin in a direction opposite to the molten resin flowing from the heat retaining cylinder, and solidifying by cooling.
The melt spinning apparatus is formed on the lower side of the lower end of the heat retaining cylinder, and has a hollow fiber characterized by having an exhaust port that prevents fluid flowing upward from entering the heat retaining cylinder. Manufacturing method.

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