JP4180194B2 - Plastic optical fiber, and plastic optical fiber manufacturing apparatus and manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a plastic optical fiber having a small diameter fluctuation in the longitudinal direction, a method of manufacturing a plastic optical fiber suitably used for stably manufacturing the plastic optical fiber, and a manufacturing apparatus used therefor.
[0002]
[Prior art]
If there is a diameter variation in the longitudinal direction in a plastic optical fiber (hereinafter abbreviated as POF), it causes a reduction in the uniformity of its optical transmission characteristics and mechanical characteristics. For example, when light is incident on the POF from its end surface and used for decoration using side leakage light that slightly leaks from the side surface due to light scattering inside the POF, if the optical fiber has a diameter variation, In the part where the diameter decreases in the traveling direction, the angle of light incident on the core-sheath interface increases, and the light propagating in the POF easily exceeds the critical angle of the core-sheath interface, resulting in an increase in the amount of light leakage and vice versa. In the portion where the diameter increases toward the traveling direction of light, the angle of light incident on the core-sheath interface becomes small, and the light propagating in the POF does not easily exceed the critical angle of the core-sheath interface, so the amount of leakage light is small. Become. Therefore, a difference in the amount of light leaking out of the POF occurs, which becomes a spot of light leakage and causes a reduction in visual quality. In a portion where the diameter variation width is large and the variation period is short, that is, a portion where a sudden diameter variation occurs, the angle formed by the core-sheath interface with respect to the POF central axis is large, and thus the light amount difference of leaked light is particularly large. If a POF with a large diameter variation in the longitudinal direction is used for optical communication and optical sensor applications, if the diameter of the end of the POF is larger than the inner diameter of the POF insertion part of the connector, insertion into the connector becomes difficult. If the inner diameter of the connector is smaller than the inner diameter of the connector, the POF will be loose and will be fixed in an eccentric manner with respect to the central axis of the connector. When joining these, the joining surface is displaced, which causes an increase in coupling loss. For these reasons, there is a strong demand for suppressing diameter fluctuation in the longitudinal direction of POF.
[0003]
POF is usually produced by a compound melt spinning method in which a plurality of thermoplastic resins as raw materials are melted, each is quantitatively supplied to a spinning nozzle using a metering pump, compound spinning is performed, and cooling and solidification are performed.
[0004]
The spun POF is usually subjected to a heat drawing treatment to improve its mechanical strength, and further subjected to a constant length heat treatment or a relaxation heat treatment to relieve the drawing stress, if necessary. The width of the diameter variation in the longitudinal direction is larger than that of the processed POF. The cause of this is that when tension is applied to POF having a diameter variation in the longitudinal direction under heating in the stretching process, higher stress acts on the narrow diameter portion than on the thick portion, and the narrow portion is more easily stretched than the thick portion. The original diameter variation is amplified. Therefore, in order to reduce the diameter fluctuation of the POF that has been subjected to the stretching treatment, it is extremely important to reduce the diameter fluctuation of the POF when the POF is spun.
[0005]
A major cause of fluctuations in diameter when spinning POF is fluctuations in the discharge amount of the metering pump. The metering pump has processing irregularities of the metering pump such as the drive shaft and drive gear eccentricity, fluctuations in the rotation speed of the drive device, fluctuations in the rotation speed of the metering unit due to misalignment of the rotation transmission unit connecting the drive device and metering pump, etc. Causes a variation in the discharge amount. The molten resin spun from the spinning nozzle is taken at a constant speed and cooled and solidified regardless of the discharge amount of the metering pump, so that the POF diameter fluctuates due to the discharge amount fluctuation.
[0006]
Conventionally, as a method for suppressing fluctuations in the discharge amount of a metering pump that causes fluctuations in the diameter of POF, JP-A-5-11127 discloses a metering pump for metering a plurality of molten thermoplastic resins as raw materials to a spinning nozzle. As an example, a gear-type metering pump having a plurality of metering units driven by a single drive motor is used, and the fluctuation phase of the discharge amount fluctuation in the same cycle generated in each metering part is shifted so as to cancel out the mutual discharge amount fluctuations. A method has been proposed in which the resin weighed in each metering unit is joined to eliminate the discharge amount fluctuation. However, this method requires a metering pump having a complicated structure, and if the period and magnitude of the discharge amount fluctuation of each metering unit are different, the discharge amount fluctuations cannot be canceled out. Further, when the discharge amount fluctuation of the metering pump is caused by the fluctuation of the rotational driving speed of the metering pump driving apparatus, the rotational speed fluctuation of the metering part caused by the misalignment of the rotation transmitting part connecting the driving apparatus and the metering pump, With this apparatus, it is not possible to suppress fluctuations in the discharge amount.
[0007]
On the other hand, in order to suppress fluctuations in the discharge amount from the metering pump, there is a method of detecting a change in the discharge pressure of the metering pump and changing the rotation speed of the metering pump so as to reduce it. However, with this method, it is not possible to distinguish between a change in discharge pressure and a change in discharge amount due to a change in viscosity due to temperature, molecular weight fluctuation, etc. of the raw material fluid, and even if the discharge amount does not change, the discharge caused by other causes Since the rotation speed of the metering pump is corrected by the pressure fluctuation, there is a problem that the average discharge amount per unit time of the metering pump changes. As a method for solving this problem, Japanese Patent No. 2816962 discloses that only the discharge pressure fluctuation signal in a specific frequency band corresponding to the discharge amount fluctuation of the metering pump is detected, and the metering pump is rotated so as to eliminate the fluctuation. A method is disclosed in which the speed is changed, the rotational speed per unit time of the metering pump drive motor is detected, and when a deviation occurs between the detected rotational speed and the set rotational speed, the deviation is corrected.
[0008]
[Problems to be solved by the invention]
However, the method described in Japanese Patent No. 2816962 discloses a very gentle discharge other than a specific frequency band corresponding to the discharge amount fluctuation caused by the rotation of the metering pump among the discharge pressure changes caused by the discharge amount change of the metering pump. For example, a change in the discharge amount caused by a change in pump efficiency indicating the actual discharge amount with respect to the theoretical discharge amount in one rotation of the metering pump cannot be corrected, and such a discharge amount variation occurs. In this case, there was still a problem that the average diameter of the POF would change.
[0009]
SUMMARY OF THE INVENTION An object of the present invention is to provide a POF that has very little longitudinal diameter variation and average diameter unevenness and excellent optical characteristics and uniformity in mechanical characteristics, a method for stably manufacturing such POF, and a POF manufacturing apparatus used therefor Is to provide.
[0010]
[Means for Solving the Problems]
The gist of the present invention is a plastic optical fiber that has been subjected to a heat-stretching treatment, and for an optical fiber having a length of 1000 m, the diameter change amplitude-wavelength period characteristic obtained by Fourier transform of the diameter change in the longitudinal direction of the optical fiber. The maximum amplitude at the wavelength period of 0.1 m to 20 m in the evaluation is 3 μm or less, and the maximum and minimum values of the average diameter value of the optical fiber represented by (maximum diameter−minimum diameter) / 2 for each measurement length of 20 m. The difference is 2 μm or less in the plastic optical fiber.
[0011]
Also, the gist of the present invention is to provide a plurality of metering pumps that supply the spinning nozzle while metering a resin that is a raw material of the plastic optical fiber, a spinning nozzle that compositely spins the plurality of supplied resins, and a discharge of the metering pump. Pressure conversion means that converts pressure fluctuations into electrical pressure signals, a signal filter that receives pressure signals output from the pressure conversion means and passes only signals in a specific frequency band, and fluctuations in pressure signals that have passed through the signal filter A means for changing the rotational speed of the metering pump drive motor so as to reduce the rotational speed of the metering pump and the rotational speed per unit time of the metering pump drive motor, and the detected rotational speed and a preset rotational speed per unit time Means to correct the deviation and continuously measure the diameter of the plastic optical fiber discharged from the spinning nozzle and taken at a constant speed From the measured value, the average diameter of the plastic optical fiber represented by (maximum diameter−minimum diameter) / 2 in the range of the predetermined length is calculated, and the average diameter is deviated from the preset optical fiber diameter. Is generated in a plastic optical fiber manufacturing apparatus provided with a spinning device having means for changing the rotational setting speed of the drive motor of the metering pump so as to correct the deviation.
[0012]
Furthermore, the gist of the present invention resides in an optical fiber manufacturing method characterized in that an optical fiber is manufactured using the manufacturing apparatus.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
By performing Fourier transform on data obtained by continuously measuring the POF diameter (referred to as data measured at intervals of 10 mm or less in the present invention), the amplitude and wavelength of the periodic fluctuation of the POF diameter can be known. . The POF of the present invention has a maximum amplitude of 3 μm or less at a wavelength period of 0.1 m to 20 m in the evaluation of wavelength period amplitude-wavelength period characteristics obtained by Fourier transform of the diameter change in the longitudinal direction of the POF measured between 1000 m. The difference between the maximum value and the minimum value of the average diameter represented by (maximum diameter−minimum diameter) / 2 measured every 20 m between 1000 m and preferably every 10 m is 1 μm or less. That is, the POF of the present invention has excellent uniformity in optical transmission characteristics and mechanical characteristics by reducing the periodic diameter fluctuation amplitude, lengthening the fluctuation period, and reducing the average diameter fluctuation. In the application utilizing side light leakage, light leakage spots are small, and even when inserted into a connector or the like, POF can be easily inserted into the connector without causing problems such as eccentricity.
[0014]
When the diameter variation is Fourier transformed, the entire diameter variation formed by synthesizing various diameter variation components each having a specific variation period can be decomposed into each diameter variation component. The fluctuation amplitude can be obtained. In the evaluation of the amplitude-wavelength period characteristic of the diameter change obtained by Fourier transform of the diameter change in the POF longitudinal direction of the present invention, the diameter variation component for each wavelength period of 0.01 m, for example, is converted by the Fourier transform. And the fluctuation amplitude of the diameter fluctuation component of each wavelength period is obtained, and the wavelength period of each diameter fluctuation component and the amplitude of the diameter fluctuation in the wavelength period are obtained. The data plotted with the wavelength period on the horizontal axis and the fluctuation amplitude of the wavelength period on the vertical axis is a diagram showing the amplitude-wavelength period characteristics of the diameter change of the POF as illustrated in FIGS. 1 and 2 show the measurement results for the conventional POF, and FIGS. 3 and 4 show the measurement results for the POF of the present invention.
[0015]
In the present invention, the structure of the POF is not particularly limited. For example, an SI-type POF having a core-sheath structure and a refractive index that changes rapidly at the interface thereof, the refractive index continuously changes from the central portion toward the outer peripheral portion. GI-type POF, multi-layer POF in which a plurality of (co) polymers having different refractive indexes are laminated in a concentric manner, and the refractive index changes stepwise from the center toward the outer periphery, a sea material having a plurality of island portions in common And a multi-core POF that is focused in a state of being separated from each other.
[0016]
The POF of the present invention can be produced, for example, as follows.
FIG. 5 is a diagram showing an outline of the POF manufacturing apparatus of the present embodiment. The POF manufacturing apparatus of this embodiment is an apparatus for manufacturing a POF having a core-sheath structure. The core material is extruded from the core material extruder 11a, quantified by the metering pump 12a, and supplied to the spinning nozzle 13. The sheath material is extruded from the sheath material extruder 11b, and is similarly quantified by the metering pump 12b and supplied to the spinning nozzle 13. At that time, the rotation speeds of the metering pumps 12a and 12b are controlled as described later. A sheath material is concentrically laminated on the outer peripheral portion of the core material by the spinning nozzle 13, and unstretched POF is spun from the spinning nozzle.
[0017]
As the core material extruder 11a and the sheath material extruder 11b, known extruders such as a vent type devolatilizing extruder are used.
[0018]
In this embodiment, gear type metering pumps are used as metering pumps 12a and 12b. The gear-type metering pump is preferably used for manufacturing POF with a small diameter fluctuation in the longitudinal direction because the discharge quantity fluctuation is relatively small. This gear type metering pump is composed of a pair of gears (drive gear, driven gear) that rotate in mesh with each other, a casing, and a pair of side plates (front plate, back plate) that sandwich the casing. Yes. The casing has a bowl-shaped inner wall, and a pair of gears is housed in a space formed by the inner wall, and the gear tooth tip is configured to rotate in contact with the inner wall. When the gear is rotated, a suction port for the liquid transported to the back plate that contacts the portion where the meshing of the gear is released is formed, and a discharge port is formed on the back plate that contacts the portion where the meshing starts. Yes. In such a gear-type metering pump, a gear drive shaft (a gear rotational driving force transmitting portion) having one end coupled to the drive gear and the other end protruding outside the metering pump is coupled to a known drive motor 25 by a coupling or the like. By being connected and rotating the drive motor 25, a pair of meshed gears rotate and liquid feeding is performed. At that time, the liquid to be transported is filled from the suction port into a space formed by the tooth groove portion of the gear and the casing that are not meshed with each other, and is transported as the gear rotates, and the gear meshes with the gear tooth space. When the volume of the liquid is reduced, it is pushed out and discharged from the discharge port. In this case, a liquid feeding system including a gear, a casing, a discharge port, and a suction port is referred to as a measuring unit. That is, in this case, one measuring unit is driven by one drive motor 25. In the present invention, it is possible to use a gear-type metering pump having a plurality of measuring units for one drive shaft. However, for the reason described later, a metering driven by a single drive motor. Those having one part are preferred.
[0019]
As the spinning nozzle 13, a composite spinning nozzle suitable for the structure of the POF to be manufactured is selected and used. As the spinning nozzle 13, a nozzle having only one spinning hole may be used, and a structure having a plurality of spinning holes and distributing the resin supplied from the metering pumps 12a and 12b to the plurality of spinning holes. May be used.
[0020]
In the present invention, when spinning, the number of rotations of one or a plurality of metering pumps 12a and 12b is controlled by three control methods to be described later, and the amount of resin discharged from the metering pumps 12a and 12b is kept constant. As a result, the diameter fluctuation of the POF spun from the spinning nozzle 13 is reduced.
[0021]
In the present invention, by detecting the pressure of the resin discharged from the metering pumps 12a and 12b, the number of revolutions of the metering pumps 12a and 12b is controlled to reduce the variation in the amount of resin discharged (first Control method). In the present embodiment, the core material metering pump 12a and the sheath material metering pump 12b are controlled using the same mechanism, and therefore only the core material metering pump control mechanism will be described below.
[0022]
By the way, normally, discharge pressure fluctuations caused by the metering pump, such as machining spots of the metering pump and eccentricity of the connecting shaft of the gear drive and the drive motor, appear as periodic fluctuations of 1 times or less of the pump rotation speed. On the other hand, the discharge pressure fluctuation that does not affect the POF diameter fluctuation because the discharge amount does not change due to other than the metering pump, such as the viscosity change due to the molten resin temperature or molecular weight change, compared with the discharge pressure fluctuation caused by the metering pump. Appears as a gradual periodic or aperiodic change. Therefore, in the first control, using the frequency characteristics and periodicity of the discharge pressure fluctuation, the discharge pressure fluctuation of the metering pump is separated into the fluctuation caused by the metering pump and the fluctuation caused by something other than the metering pump, and quantified. The rotational speed of the metering pump is controlled so as to reduce fluctuations in the discharge pressure caused by the pump. It should be noted that non-periodic metering pump discharge rate fluctuations that affect the POF diameter variation due to other than the metering pump are reduced by a third control method to be described later.
[0023]
Hereinafter, the contents of the first control will be specifically described. First, the discharge pressure fluctuation of the metering pump 12a is detected by the pressure converter 20 as an electrical pressure signal. The response frequency of the pressure transducer 20 is preferably as high as possible from the viewpoint of control accuracy, and is preferably 50 Hz or more, and more preferably 100 Hz or more.
[0024]
The pressure signal is sent to a discharge amount fluctuation control device composed of a signal filter 22a and a rotation speed control / comparison / correction unit 22b, and only the pressure signal corresponding to the frequency band corresponding to the pressure fluctuation caused by the metering pump 12a. Are separated by the signal filter 22a and input to the rotational speed control / comparison / correction unit 22b. The frequency band corresponding to the pressure signal resulting from the metering pump 12a is preset in the signal filter 22a. The set frequency band of the signal filter 22a is preferably set to a range equal to or higher than the frequency of one rotation of the metering pump 12a. When electric noise enters the pressure signal from the power supply of the pressure transducer 20, the noise is discharged. It is preferable to set the power supply frequency or less in a range not to detect it as a fluctuation.
[0025]
The rotation speed control / comparison / correction unit 22b processes the rotation command signal issued from the metering pump drive motor rotation speed setting device 24 so as to reduce the pressure fluctuation caused by the metering pump, and outputs the processed rotation command signal. It outputs to the metering pump drive motor drive device 23 and changes the rotation speed of the metering pump drive motor 25.
[0026]
In the present embodiment, as a control method for controlling the rotation speed of the metering pump drive motor 25, a predetermined control rotation speed larger than the set rotation speed and a small predetermined control rotation speed (for example, 10 times the set rotation speed and 0.1 times), one of the control rotational speeds that suppresses the change with respect to the change in the discharge pressure is selected, and the rotational speed of the metering pump 12a is instantaneously switched to the control rotational speed. Is adopted. When this method is adopted, since the resin used as the raw material for POF exhibits an elastic behavior in the molten state, the rotation speed of the metering pump 12a is instantaneously and rapidly changed, and the discharge pressure from the metering pump 12a is changed to several tens. Even if the pressure fluctuates by about Hz, the pressure fluctuation is absorbed by the resin existing in the resin flow path downstream of the metering pump 12a, so that the fluctuation range of the discharge pressure of the resin discharged from the spinning nozzle 13 is reduced, and spinning. The diameter variation of the formed POF is reduced. In the present invention, the control method for controlling the rotation speed of the metering pump drive motor 25 is not limited to this. For example, the discharge pressure fluctuation is suppressed in conjunction with the discharge pressure fluctuation of the metering pump 12a. In addition, a method of continuously changing the rotation speed of the metering pump drive motor 25 can be used.
[0027]
As the drive motor 25 for driving the metering pump 12a, a motor having excellent resolution and responsiveness is preferable, and a servo motor is particularly preferable. The signal filter 22a and the rotation speed control / comparison / correction unit 22b of the present invention can be configured by, for example, a combination of known electronic components, but are not limited thereto.
[0028]
As described above, when the rotation speed of the metering pump 12a is changed so as to reduce the discharge pressure fluctuation of the metering pump 12a, the time required for one rotation of the metering pump 12a changes, and the unit time per unit time is changed. The discharge amount may change. In order to prevent this, in the present invention, the rotational speed of the metering pump 12a is constantly monitored by a rotational speed sensor or the like (for example, when a servo motor is used as the metering pump drive motor, the encoder built in the motor). When the metering pump rotation amount deviates from the set rotation speed, the control rotation speed larger than the set rotation speed selected to suppress the discharge pressure fluctuation of the metering pump 12a by the rotation speed control / comparison / correction unit 22b. Alternatively, by gradually changing the small control rotation speed by a small amount, the amount of metering pump rotation per unit time is made to coincide with the set rotation speed, and the time required for one rotation of the metering pump 12a is kept constant. (Second control method)
[0029]
The discharge pressure fluctuation of the metering pump 12a is a fluctuation in the rotational speed of the output shaft of the metering pump driving device among the discharge amount fluctuations reduced by the first and second control methods, and the driving device and the metering pump are connected. In the case of the discharge amount fluctuation generated due to a cause other than the processing spot of the metering section of the metering pump 12a such as the rotational speed fluctuation of the metering section due to the misalignment or the like of the rotation transmitting section, for example, a plurality of driving shafts with a plurality of Even if a metering pump 12a of a type having a metering unit is used to detect and control the discharge pressure fluctuation of one metering unit, a sufficient discharge pressure fluctuation reducing effect can be obtained. In this case, the POF raw material discharged from each metering section can be supplied to each spinning hole of the spinning nozzle 13 having a plurality of spinning holes, and a plurality of POFs can be spun simultaneously.
[0030]
On the other hand, when a metering pump 12a having one metering unit for one drive shaft is used and is driven by one independent drive motor 25, and each drive motor 25 is controlled separately, for example, a gear as a metering pump is used. When the metering pump is used, the amount of discharge changes due to eccentric rotation of the drive gear, gear tooth gap volume irregularity, gear tooth thickness irregularity, etc., or when the gear is engaged and the liquid filled in the gear tooth gap is pushed out In addition, the discharge amount fluctuation caused by the processing spots of the metering unit of the metering pump 12a such as the discharge amount fluctuation (pulsation) caused by the change in the volume reduction amount per unit time of the space formed between the gear tooth grooves Is more preferable because it can be suppressed. Thus, the POF material discharged from the metering pump 12a is spun by having a plurality of spinning holes and distributing the material supplied from the metering pump 12a to a plurality of the spinning holes. Is preferably supplied to the spinning nozzle 13 so that a large number of POFs having extremely small diameter fluctuations in the longitudinal direction can be obtained simultaneously.
[0031]
In addition, conditions such as the supply pressure, temperature, and viscosity of the resin supplied to the metering pump 12a may fluctuate greatly. For example, a part of the resin transported as the metering pump 12a may be placed on a sliding part such as a gear or a gear shaft. When a gear-type metering pump or the like that is supplied to a small gap of about several μm and used as a lubricant for the sliding part is used, the leakage of the transport liquid from the sliding part to the outside of the pump or the transport liquid The backflow (back flow) to the suction port may increase due to a decrease in the viscosity of the transport liquid or a decrease in the supply pressure of the transport liquid from the supply port. At this time, the pump efficiency indicating the actual discharge amount with respect to the theoretical discharge amount in one rotation of the metering pump changes, and the diameter of the spun POF may fluctuate even at the same rotation speed. Since the POF spinning device of the present embodiment also reduces the variation in the diameter of POF caused by such a cause, as shown in FIG. 5, the POF spinning device 30 provided downstream of the first take-up device 16 is used. The diameter is continuously measured to calculate the average diameter of the POF for each predetermined length, the diameter difference detector 40 compares the average diameter with a preset set diameter, and there is a difference between the two. In this case, the diameter difference detector 40 is configured to output a control signal for changing the rotational speed setting value of the metering pump drive motor rotational speed setting device 24 (third control method). For example, when the average diameter is larger than the set diameter, the diameter difference detector 40 outputs a control signal that decreases the rotational speed set value and increases the rotational speed set value when the average diameter is smaller than the set diameter. Therefore, the diameter of the spun POF can be maintained at a constant value even if the discharge efficiency of the metering pump 12a fluctuates due to external factors such as the resin supply conditions to the metering pump 12a.
[0032]
The POF diameter can be measured after stretching if the set diameter is set to the diameter of the POF after stretching. In this case, the wire diameter measuring device 30 is installed before or after the second take-up device 18. . Further, when changing the rotational speed set value of the metering pump drive motor rotational speed setting device 24 according to the difference between the average diameter and the set diameter of the POF, the metering pump drive motor rotation for the core material and the sheath material is performed. Although it is most preferable to change the rotational speed setting value of the speed setting device 24 at the same ratio in order to keep the POF structure the same, the diameter fluctuation rate generated due to the discharge efficiency fluctuation of the metering pump 12a is usually Since it is about several percent of the average diameter, the POF core material occupancy ratio, that is, the discharge rate ratio of the core material to the total material of the POF is the same as the POF of the normal core-sheath structure or the core-sheath protective layer structure. In POF occupying 90% or more, even if only the rotational speed setting value of the metering pump drive motor rotational speed setting device 24 for the core material is changed, a sufficient effect is obtained.
[0033]
As described above, in the POF manufacturing method of the present invention, it is possible to reduce the fluctuation in the diameter of the unstretched POF by reducing the fluctuation in the discharge amount of the resin from the metering pump 12a. In this case, it is possible to reduce the variation in the diameter of the POF.
[0034]
The POF spun from the spinning nozzle 13 passes through the first take-up device 16, the heating drawing furnace 17, and the second take-up device 18 via the air-cooled quench device 14 and the guide 15. At that time, since the take-up speed of the second take-up device 18 is set higher than the take-up speed of the first take-up device 16, the POF heated in the heating and drawing furnace 17 is drawn. A known roller or the like is used as the first take-up device 16 and the second take-up device 18. In the heating and drawing furnace 17, the POF is heated by a heating medium such as hot air. The stretching ratio is not particularly limited, but the POF diameter spots tend to be amplified by stretching, so in order to obtain a POF with small diameter spots, it is preferably 3 times or less. In order to reduce the thermal shrinkage of POF, it is preferable that the stretched POF is further subjected to a heat relaxation treatment. The heating relaxation process is performed, for example, by arranging a heating furnace between two take-up devices and making the take-up speed of the front-stage take-up device higher than the take-up speed of the rear-stage take-up device. The POF thus stretched is taken up by the take-up device 19.
[0035]
FIG. 4 shows a POF manufactured under exactly the same manufacturing conditions as the POF in FIG. 2 except that the fiber was spun by the above method, and the diameter was measured over a length of 1000 m. The results of the Fourier transform of the change in diameter are plotted with the wavelength period on the horizontal axis and the amplitude on the vertical axis. FIGS. 1 and 3 are plots of POFs obtained by stretching the POFs of FIGS. 2 and 4 twice as in the case of FIG.
[0036]
As shown in FIGS. 3 and 4, the POF manufactured by the method of the present invention has a greatly reduced diameter variation compared to the conventional POF shown in FIGS. 1 and 2, and over a length of 1000 m, The maximum amplitude in the wavelength period of 0.1 m to 20 m in the amplitude-wavelength period characteristic evaluation of the diameter change obtained by performing Fourier transform on the diameter change in the longitudinal direction of the POF is 3 μm or less.
[0037]
【Example】
(Example 1)
Polymethylmethacrylate as the core material, vinylidene fluoride / tetrafluoroethylene = 80/20 (mol%) copolymer as the sheath material, gear-type metering pump as metering pump for the core material and sheath material, metering pump drive motor Using a 100W AC servo motor with a 1/100 speed reducer, and a high-temperature strain gauge pressure detector manufactured by Dinisco Co., Ltd. as the pressure transducer. It supplied to the POF manufacturing apparatus of the structure as shown in FIG. 5 in which the pass frequency band of the signal filter of the control device was set in the range of each gear type metering pump rotational frequency to 30 Hz. Then, the POF continuously discharged from the spinning nozzle is cooled and solidified while being drawn at 25 m / min, and the diameter variation of the unstretched POF is measured using a Keyence Co., Ltd. laser outer diameter measuring device (resolution: 0.1 μm). Measure continuously, calculate the difference between the average diameter and the set diameter every minute (25m), and correct the set speed of the metering pump drive motor rotation speed setting device based on the difference between the average diameter and the set diameter While spinning the POF, the hot POF was subjected to a hot-air heating stretching process at a stretch ratio of 2 times continuously to the spun POF, and the POF diameter fluctuation after the stretching process was continuously measured using the same laser outer diameter measuring device at 50 m / By winding at a speed of minutes, POF having an average diameter of about 750 μm and a sheath thickness of about 60 μm was obtained.
[0038]
The diameter fluctuation width between 1000 m of unstretched POF is about 2 μm, and the diameter fluctuation width between 1000 m of POF after 2 times stretching treatment is about 9 μm, and the difference between the maximum value and the minimum value of the average diameter every 10 m Was as small as about 1 μm. Moreover, when the amplitude-wavelength period characteristic of the diameter change obtained by Fourier transform of the diameter change in the longitudinal direction of the POF between 1000 m was evaluated, the maximum amplitude in the wavelength period of 0.1 m to 20 m was about before the stretching process. It was very small, about 0.5 μm and about 1.2 μm after the stretching treatment.
[0039]
(Comparative Example 1)
Same as in Example 1 except that the core and sheath metering pump discharge amount fluctuation control device was removed and the AC servo motor was rotated at a constant rotation speed, and the draw ratio was doubled with an average diameter of about 750 μm and a sheath thickness of about 60 μm. Obtained POF. The diameter variation of the POF measured by the same method as in Example 1 was about 7 μm for the unstretched POF, and the diameter variation between 1000 m of the POF after the stretching treatment was about 20 μm. In addition, when the amplitude-wavelength period characteristic of the diameter change obtained by Fourier transform of the diameter change in the POF longitudinal direction was evaluated, the maximum amplitude in the wavelength period from 0.1 m to 20 m was about 4 μm before the stretching process, and after the stretching process. It was as large as about 11 μm. Further, regarding the POF after the stretching treatment, the difference between the maximum value and the minimum value of the average diameter measured every 20 m between 1000 m was about 4 μm.
[0040]
(Comparative Example 2)
The difference between the average diameter and the set diameter is obtained, and the same control as that in Example 1 is performed except that the control for correcting the set rotation speed of the metering pump drive motor rotation speed setting device based on the difference between the average diameter and the set diameter is stopped. A POF that had been subjected to hot-air heat drawing treatment with an average diameter of about 750 μm and a sheath thickness of about 60 μm and a draw ratio of 2 was obtained.
[0041]
When the diameter fluctuation of this POF was measured by the same method as in the example, the fluctuation width was about 2 μm in the unstretched POF, and the diameter fluctuation width between 1000 m of the POF after the stretching treatment was about 11 μm. Further, when the POF after the stretching treatment was evaluated for the amplitude-wavelength period characteristic of the diameter change obtained by Fourier transform of the diameter change in the POF longitudinal direction, the maximum amplitude in the wavelength period of 0.1 m to 20 m was about 1. Although it was 2 μm, the difference between the maximum value and the minimum value of the average diameter measured every 20 m between 1000 m was about 4 μm.
[0042]
【The invention's effect】
The POF of the present invention has excellent uniformity in optical transmission characteristics and mechanical characteristics due to extremely small diameter fluctuation in the longitudinal direction, and is used for POF light leakage spots, sensors, or signal transmission when POF side light leakage is used. In this case, the coupling loss due to the displacement of the joint surface between the POFs or between the POF and the light emitting / receiving element is very small.
[0043]
According to the manufacturing method and the manufacturing apparatus of the present invention, a POF having a very small diameter variation in the longitudinal direction can be easily manufactured.
[0044]
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a result of evaluating an amplitude-wavelength period characteristic of a diameter change of a POF subjected to a conventional double-stretching process.
FIG. 2 is a diagram showing an example of an evaluation result of amplitude-wavelength period characteristics of a diameter change of POF before a conventional stretching process.
FIG. 3 is a diagram showing an example of an amplitude-wavelength period characteristic evaluation result of a diameter change of a POF manufactured by the method of the present invention and subjected to double-stretching treatment.
FIG. 4 is a diagram showing an example of an amplitude-wavelength period characteristic evaluation result of a diameter change of a POF produced by the method of the present invention before stretching.
FIG. 5 is a schematic view showing the configuration of an example of the POF manufacturing apparatus of the present invention.
[Explanation of symbols]
10 POF
11a Extruder for core material
11b Extruder for sheath material
12a metering pump
12b Metering pump
13 Spinning nozzle
14 Air cooling quencher
15 Guide
16 First take-up device
17 Heating and drawing furnace
18 Second pick-up device
19 Winding device
20 Pressure transducer
22 Discharge amount fluctuation control device
22a Pressure signal filter
22b Rotational speed control / comparison / correction unit
23 Metering pump drive motor drive device
24 Metering pump drive motor rotation speed setting device
30 Wire diameter measuring instrument
40 Diameter difference detector

Claims (3)

  A plurality of metering pumps that supply the spinning nozzle while metering the resin that is the raw material of the plastic optical fiber, a spinning nozzle that compositely spins the supplied resins, and the discharge pressure fluctuation of the metering pump as an electrical pressure signal A pressure converting means for converting to a pressure signal, a signal filter for inputting a pressure signal output from the pressure converting means and allowing only a signal in a specific frequency band to pass through, and a metering pump to reduce fluctuations in the pressure signal passing through the signal filter. Means for changing the rotation speed of the drive motor, means for detecting the rotation speed per unit time of the metering pump drive motor, means for correcting the deviation between the detected rotation speed and a preset rotation speed per unit time, and spinning The diameter of the plastic optical fiber discharged from the nozzle and taken out at a constant speed is continuously measured. Calculate the average diameter of the plastic optical fiber represented by (maximum diameter-minimum diameter) / 2 in the length range, and if there is a deviation between this average diameter and the preset optical fiber diameter, the deviation A device for producing a plastic optical fiber, comprising: a spinning device having means for changing a rotational setting speed of a drive motor of a metering pump so as to correct the error. As the spinning nozzle, a spinning nozzle having a structure in which a plurality of spinning holes are provided and the resin supplied from the metering pump can be distributed to the plurality of spinning holes in the spinning nozzle is used. using a metering pump having only one measuring unit to be driven, apparatus for manufacturing a plastic optical fiber according to claim 1 in which each metering pump is characterized in that it is driven by a single drive motor, respectively. Method of manufacturing an optical fiber, characterized in that for manufacturing an optical fiber using the production apparatus according to claim 1 or claim 2.

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