Method for manufacturing optical fiber

Abstract

To provide a method for manufacturing an optical fiber in which viscosity variation of resin applied during wire drawing is suppressed, and occurrence of variation of a coating diameter or thickness deviation of an optical fiber is suppressed.SOLUTION: A method includes: a viscosity measuring step of housing resin into a resin tank equipped with a viscosity meter and a thermometer, and measuring the temperature and the viscosity of resin housed inside the resin tank; and a resin applying step of supplying resin to the resin applying part from the resin tank via a piping, and applying resin to the outer periphery of a glass fiber in the resin applying part, where a heating part which heats resin so as to bring the temperature of resin inside the piping to a set target temperature is provided for the outer periphery of at least a part of the piping, and the target temperature is set on the basis of measurement results of the temperature and viscosity in the viscosity measuring step.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing an optical fiber. [Background technology]

[0002] Patent Document 1 describes a method of providing pressure gauges at the upstream and downstream ends of a resin supply pipe from a resin supply tank to an application device to monitor the pressure. The method describes a method of manufacturing an optical fiber in which the output of the pressure gauge is input to a calculation device, and a command is issued to a temperature regulator of a resin heating device so that the differential pressure becomes equal to a preset reference differential pressure, thereby increasing or decreasing the temperature of the heating device so that the viscosity of the resin becomes constant at a preset value. The method also describes providing a resin viscosity detection means in the application device. The method describes a method of comparing the viscosity measured by the resin viscosity detection means with a preset reference viscosity, and controlling the temperature of the resin heating device based on the comparison. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 8-119681 Summary of the Invention [Problem to be solved by the invention]

[0004] In the manufacture of optical fibers, in order to suppress variations in the coating diameter and thickness deviation of the optical fibers, it is desirable to set the resin temperature in the die (resin application part) to a constant target viscosity that keeps the coating diameter within the standard range.

[0005] Therefore, for example, in the method described in Patent Document 1, the temperature of the resin heating device is controlled so that the differential pressure measured by pressure gauges installed at the upstream and downstream ends of the resin supply pipe is equal to a reference differential pressure, or based on a comparison of the viscosity measured by a resin viscosity detection means installed in the coating device with the target viscosity.

[0006] When controlling the heating device based on the differential pressure of the resin supply pipe or the viscosity of the resin, the time lag for the fluctuation of the resin temperature during drawing during optical fiber manufacturing becomes large, and it is difficult to control the resin temperature to always be at the target temperature during drawing. Therefore, the temperature fluctuation of the resin applied during drawing may cause the resin viscosity to fluctuate, resulting in fluctuations in the coating diameter of the optical fiber and uneven thickness.

[0007] In addition, the physical properties of the resin material supplied to the resin supply tank may differ depending on the production lot, which may result in different viscosities even for resins at the same temperature, leaving room for improvement in suppressing the fluctuations in the viscosity of the resin applied during drawing.

[0008] An object of the present disclosure is to provide a method for manufacturing an optical fiber that can suppress fluctuations in the viscosity of the resin applied during drawing, thereby suppressing fluctuations in the coating diameter of the optical fiber and the occurrence of uneven thickness. [Means for solving the problem]

[0009] A method for producing an optical fiber according to one aspect of the present disclosure includes the steps of: a viscosity measuring step of storing a resin in a resin tank equipped with a viscometer and a thermometer and measuring the temperature and viscosity of the resin stored in the resin tank; a resin applying step of supplying the resin from the resin tank through a pipe to a resin applying section and applying the resin to an outer periphery of the glass fiber in the resin applying section, a heating unit that heats the resin in the pipe so that the temperature of the resin in the pipe reaches a set target temperature, the heating unit being provided on an outer periphery of at least a part of the pipe; The target temperature is set based on the results of measuring the temperature and viscosity in the viscosity measuring step. Effect of the Invention

[0010] According to the present disclosure, it is possible to provide a method for manufacturing an optical fiber in which the viscosity fluctuation of the resin applied during drawing is suppressed, thereby suppressing the occurrence of fluctuations in the coating diameter of the optical fiber and uneven thickness. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 illustrates an apparatus for manufacturing an optical fiber. [Diagram 2] FIG. 2 is a flow chart of the resin application process. [Diagram 3] FIG. 3 illustrates an approximation formula for the temperature dependency of viscosity and the calculation of the target temperature. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Description of the embodiments of the present disclosure First, the embodiments of the present disclosure will be listed and described. (1) A method for producing an optical fiber according to one embodiment of the present disclosure includes the steps of: a viscosity measuring step of storing a resin in a resin tank equipped with a viscometer and a thermometer and measuring the temperature and viscosity of the resin stored in the resin tank; a resin coating step of supplying the resin from the resin tank through a pipe to a resin coating section and coating the resin on an outer periphery of the glass fiber in the resin coating section; Including, a heating unit that heats the resin in the pipe so that the temperature of the resin in the pipe reaches a set target temperature, the heating unit being provided on an outer periphery of at least a part of the pipe; The target temperature is set based on the results of measuring the temperature and viscosity in the viscosity measuring step. According to the above-mentioned optical fiber manufacturing method, the resin in the pipe is heated so that the temperature of the resin reaches a set target temperature, so that the resin temperature can be controlled with good follow-up to the fluctuation of the resin temperature. The target temperature is set based on the temperature and viscosity measurement results in the viscosity measurement process, so that the target temperature can be estimated for each production lot. This makes it possible to effectively suppress the viscosity fluctuation of the resin applied during drawing, and to suppress the occurrence of fluctuations in the coating diameter and uneven thickness of the optical fiber.

[0013] (2) In the method for producing an optical fiber according to (1) above, The viscosity measuring step is carried out before the resin applying step, The viscosity measuring step may include measuring the viscosity of the resin at a plurality of temperatures. According to the above-described method for manufacturing an optical fiber, the viscosity of the resin is measured at a plurality of temperatures, so that the temperature dependency of the resin viscosity can be calculated for each manufacturing lot, making it easier to more accurately derive the target temperature.

[0014] (3) In the method for producing an optical fiber according to (1) or (2) above, The viscosity measuring step may include measuring the viscosity of the resin at three or more different temperatures. According to the above-described method for manufacturing an optical fiber, the temperature dependency of the viscosity of the resin is calculated for each manufacturing lot, making it easier to derive the target temperature more accurately.

[0015] (4) In a method for producing an optical fiber according to any one of (1) to (3) above, The target temperature is recorded in a memory unit; The viscosity measuring step may include measuring the viscosity of the resin when the temperature of the resin is within ±3° C. of the target temperature recorded in the memory unit. According to the above-mentioned optical fiber manufacturing method, by measuring the temperature viscosity near the target temperature during the previous manufacturing process, the time required for temperature adjustment in the resin tank can be reduced, and the temperature dependence of the resin viscosity near the target temperature can be calculated more accurately.

[0016] (5) In a method for producing an optical fiber according to any one of (1) to (4) above, The viscosity measuring step may include measuring the viscosity of the resin when the resin is not supplied from the resin tank to the resin applying unit. According to the above-mentioned method for manufacturing an optical fiber, the viscosity measurement is performed in a static environment, so that the measured viscosity at each temperature is more accurate.

[0017] (6) In a method for producing an optical fiber according to any one of (1) to (5) above, The resin inside the resin tank may be temperature-regulated by flowing a temperature-regulated liquid around the outer periphery of the resin tank. According to the above-described method for manufacturing an optical fiber, it is easy to accurately adjust the temperature of the resin inside the resin tank.

[0018] (7) In a method for producing an optical fiber according to any one of (1) to (6) above, The viscometer may be provided more centrally in the resin tank than the thermometer. According to the above-described method for manufacturing an optical fiber, it is possible to suppress the influence of the wall surface of the resin tank on the measured viscosity value in viscosity measurement using a viscometer.

[0019] DETAILED DESCRIPTION OF EMBODIMENTS OF THE DISCLOSURE Specific examples of the method for producing an optical fiber according to the embodiment of the present disclosure will be described below with reference to the drawings. Note that the present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0020] 1 illustrates an apparatus 1 for manufacturing an optical fiber G. The apparatus 1 for manufacturing an optical fiber G is an apparatus for applying a resin that will become a coating layer to a glass fiber G0 that has been drawn by a drawing furnace. The apparatus 1 for manufacturing an optical fiber G includes a resin application unit 10, a resin tank 20, a pipe 30, a heating unit 40, a temperature measurement unit 50, a control unit 60, and a resin temperature adjustment unit 70.

[0021] The resin coating unit 10 is configured to store liquid resin R. The resin coating unit 10 is configured to coat the outer periphery of the glass fiber G0 with resin R by passing the glass fiber G0 fed from an upstream portion of the resin coating unit 10 (upper portion in FIG. 1) through the inside of the resin coating unit 10. The glass fiber G0 then passes through a resin curing device (not shown), whereby the resin R coated around the glass fiber G0 is cured. As a result, a coating layer is formed around the glass fiber G0, and the optical fiber G is manufactured.

[0022] Two or more coating layers may be formed around the glass fiber G0. For example, when the coating layer is two layers, both the primary resin and the secondary resin may be applied. When both the primary resin and the secondary resin are applied, in addition to the example of FIG. 1, another set of the resin application unit 10, the resin tank 20, the piping 30, the heating unit 40, the temperature measurement unit 50, the control unit 60, and the resin temperature adjustment unit 70 is provided. Alternatively, in addition to the example of FIG. 1, another set of the resin tank 20, the piping 30, the heating unit 40, the temperature measurement unit 50, the control unit 60, and the resin temperature adjustment unit 70 may be provided, so that both the primary resin and the secondary resin may be applied by the resin application unit 10.

[0023] The resin tank 20 contains the resin R to be applied around the glass fiber G0. The resin tank 20 includes a thermometer 21 and a viscometer 22. The thermometer 21 is configured to measure the temperature of the resin R stored inside the resin tank 20. The viscometer 22 is configured to measure the viscosity of the resin R stored inside the resin tank 20. The viscometer 22 may be, for example, a rotational viscometer. It is desirable that the viscometer 22 be provided closer to the center of the resin tank 20 than the thermometer 21.

[0024] The piping 30 supplies the resin R from the resin tank 20 to the resin coating unit 10. A heating unit 40 is provided on at least a portion of the outer periphery of the piping 30. The heating unit 40 heats the resin R in the piping 30 so that the temperature of the resin R becomes a set target temperature. Setting of the target temperature will be described later.

[0025] The temperature measuring unit 50 is provided in a part of the piping 30 from the resin tank 20 to the resin coating unit 10. The temperature measuring unit 50 is configured to measure the temperature of the resin R flowing inside the piping 30. The temperature measuring unit 50 may be provided so as to be connected to the piping 30 on the resin coating unit 10 side rather than the heating unit 40.

[0026] The control unit 60 is configured to be able to acquire the temperature of the resin R in the resin tank 20 from the thermometer 21. The control unit 60 is configured to be able to acquire the viscosity of the resin R in the resin tank 20 from the viscometer 22. The control unit 60 is configured to be able to acquire the temperature of the resin R in the piping 30 from the temperature measurement unit 50. The control unit 60 is configured to calculate and set a target temperature from the temperature and viscosity of the resin R in the resin tank 20 such that the resin application unit 10 has a target viscosity.

[0027] The control unit 60 controls the heating unit 40 so that the temperature of the resin R in the pipe 30 becomes the set target temperature. The control unit 60 determines whether the temperature of the resin R in the pipe 30 becomes the set target temperature based on the temperature of the resin R measured by the temperature measurement unit 50.

[0028] The control unit 60 may include a storage unit for recording the target temperature and the like at the time of the previous manufacturing. The target temperature will be described later.

[0029] The resin temperature adjustment section 70 includes a tank section 71, a flow path 72, and an adjustment section 73. The tank section 71 is configured to surround the resin tank 20. The tank section 71 is filled with a temperature-adjusted liquid W such as water. By changing the temperature of the temperature-adjusted liquid W, it is possible to change the temperature of the resin R inside the resin tank 20. That is, the temperature of the resin R inside the resin tank 20 is adjusted by the temperature-adjusted liquid W flowing around the outer periphery of the resin tank 20.

[0030] The flow path 72 connects the tank portion 71 and the adjustment portion 73. The liquid W flows through the flow path 72 so as to circulate between the tank portion 71 and the adjustment portion 73.

[0031] The adjustment unit 73 is configured to adjust the temperature of the liquid W to a desired temperature. The adjustment unit 73 is, for example, a heater.

[0032] The resin temperature adjustment unit 70 may include a pump (not shown) for sending the liquid W and circulating the liquid W between the tank unit 71 and the adjustment unit 73.

[0033] Next, a method for manufacturing an optical fiber will be described. The method for manufacturing an optical fiber includes a viscosity measurement step and a resin application step. The viscosity measurement step includes measuring the temperature and viscosity of the resin R contained inside the resin tank 20.

[0034] The viscosity measuring step is preferably performed before the resin applying step. The viscosity measuring step preferably includes measuring the viscosity of the resin R at a plurality of temperatures. For example, the viscosity measuring step preferably includes measuring the viscosity of the resin R at three or more different temperatures.

[0035] The viscosity measurement process will be described with reference to Figures 2 and 3 in addition to Figure 1. Figure 2 is a flow chart of the resin application process. Figure 3 illustrates an approximation formula for the temperature dependency of viscosity and calculation of the target temperature.

[0036] When the viscosity measurement process is started, first, the viscosity is measured at a plurality of temperatures by the viscometer 22 (step S11). In step S11 of this embodiment, the viscosities η1, η2, and η3 of the resin R are measured at three different temperatures T1, T2, and T3. However, the temperature T2 is higher than the temperature T1, and the temperature T3 is higher than the temperature T2.

[0037] For example, when the temperature of the resin R in the resin tank 20 is measured by the thermometer 21 to be temperature T1, the viscometer 22 measures the viscosity η1 of the resin R in the resin tank 20.

[0038] Next, the adjustment unit 73 of the resin temperature adjustment unit 70 heats the liquid W so that the temperature of the liquid W becomes temperature T2. As a result, the temperature of the resin R contained in the resin tank 20 rises to temperature T2. When the thermometer 21 measures that the temperature of the resin R in the resin tank 20 is temperature T2, the viscometer 22 measures the viscosity η2 of the resin R in the resin tank 20.

[0039] Next, the adjustment unit 73 of the resin temperature adjustment unit 70 heats the liquid W so that the temperature of the liquid W becomes temperature T3. As a result, the temperature of the resin R contained in the resin tank 20 rises to temperature T3. When the thermometer 21 measures that the temperature of the resin R in the resin tank 20 is temperature T3, the viscometer 22 measures the viscosity η3 of the resin R in the resin tank 20.

[0040] The control unit 60 acquires viscosities η1, η2, and η3 that are measurement results of the viscosity of the resin R at the temperatures T1, T2, and T3, respectively.

[0041] The viscosity measurement step may measure the viscosity of the resin R when the temperature of the resin R is within ±3°C of the target temperature recorded in the memory unit. For example, the temperature T2 of the resin R may be the target temperature at the time of the previous production recorded in the memory unit. The temperature T1 of the resin R may be a temperature 3°C lower than the temperature T2 of the resin R. The temperature T3 of the resin R may be a temperature 3°C higher than the temperature T2 of the resin R.

[0042] Next, the control unit 60 calculates an approximation equation between viscosity and temperature based on the result of the viscosity measurement in step S11 and on the basis of equation (1) (step S12).

[0043] It is generally known that the viscosity of resin R is temperature dependent. As an example, the temperature dependency of viscosity is expressed by the following formula (1), where η is viscosity, T is absolute temperature, and a and b are coefficients that represent the inherent physical quantities of the liquid.

number

[0044] The viscosity η1 of the resin R at temperature T1, the viscosity η2 of the resin R at temperature T2, and the viscosity η3 of the resin R at temperature T3 are obtained in step S11. The control unit 60 calculates the coefficients a and b based on the viscosities η1, η2, and η3 obtained in step S11, the temperatures T1, T2, and T3 of the resin R at the time of measurement, and formula (1) to obtain an approximation formula for the temperature dependency of the viscosity as shown in Fig. 3. A method such as the least squares method can be used to calculate the coefficients a and b.

[0045] Next, the control unit 60 calculates a target temperature T0 based on the approximation equation so as to obtain a preset target viscosity η0 (step S13). The target temperature T0 is obtained by substituting the target viscosity η0 into equation (1) in which the coefficients a and b are determined in step S12. Once the target temperature T0 is determined, the viscosity measurement process is completed.

[0046] The viscosity measurement step is desirably performed when the resin R is not supplied from the resin tank 20 to the resin coating unit 10. In particular, when measuring the viscosity of the resin R in step S11, it is desirably not supplied from the resin tank 20 to the resin coating unit 10.

[0047] The resin application step is preferably performed after the viscosity measurement step. The resin application step includes supplying the resin R from the resin tank 20 through the piping 30 to the resin application unit 10, and applying the resin R to the outer periphery of the glass fiber G0 in the resin application unit 10.

[0048] In the resin application process, the control unit 60 acquires the temperature Tm of the resin R in the pipe 30 measured by the temperature measurement unit 50. The control unit 60 controls the heating unit 40 based on the difference between the measured temperature Tm of the resin R and the target temperature T0 so that the temperature of the resin R in the pipe 30 becomes the target temperature T0.

[0049] However, even if the resin material and the type of resin material are the same, the physical properties may differ depending on the production lot. In other words, the coefficients a and b in formula (1) may differ depending on the production lot. Therefore, even if the temperature in the resin application area is always the same, the viscosity may differ depending on the resin from different production lots.

[0050] When both the primary resin and the secondary resin are applied as the coating layer, it is desirable to make the viscosities of both the primary resin and the secondary resin in the resin application part the same. However, in the manufacturing method of Patent Document 1, it was difficult to make the viscosities of both the primary resin and the secondary resin the same due to the above-mentioned differences in manufacturing lots and differences in the settings of the resin temperature adjustment depending on the season. The coating layer was prone to uneven thickness defects due to the difference in the viscosities of both the primary resin and the secondary resin.

[0051] According to the manufacturing method of the optical fiber G of this embodiment, the resin R in the pipe 30 is heated so that the temperature of the resin R reaches the set target temperature T0, so that the resin temperature can be controlled with good follow-up to the fluctuation of the resin temperature. The target temperature T0 is set based on the measurement results of the temperatures T1, T2, T3 and the viscosities η1, η2, η3 in the viscosity measurement process, so that the target temperature T0 can be estimated according to each manufacturing lot. This makes it possible to effectively suppress the viscosity fluctuation of the resin R applied during drawing.

[0052] According to the manufacturing method of the optical fiber G of this embodiment, the viscosities η1, η2, and η3 of the resin R are measured at multiple temperatures T1, T2, and T3, so that the temperature dependence of the viscosity of the resin R can be calculated for each production lot and an appropriate target temperature T0 can be set.

[0053] According to the manufacturing method of the optical fiber G of the present embodiment, by measuring the viscosities η1, η2, η3 of the resin R at three or more different temperatures T1, T2, T3, it is possible to more accurately calculate the temperature dependence of the viscosity of the resin R, and to more accurately derive the target temperature T0. Note that, in step S11, if the number of viscosity measurements is increased, the time required for step S11 increases, but the temperature dependence of the viscosity of the resin R can be more accurately calculated.

[0054] According to the manufacturing method of the optical fiber G of this embodiment, by measuring the viscosity at a temperature near the target temperature at the time of the previous manufacturing, the time required for temperature adjustment in the resin tank 20 can be reduced, and the temperature dependence of the viscosity of the resin R near the target temperature T0 can be calculated more accurately.

[0055] It is generally known that the viscosity of a resin changes depending on the flow. According to the manufacturing method of the optical fiber G of this embodiment, the viscosity measurement step includes measuring the viscosities η1, η2, and η3 of the resin R when the resin R is not supplied from the resin tank 20 to the resin coating unit 10. Therefore, the viscosity measurement is performed in a static environment where the flow of the resin R in the resin tank 20 is suppressed, and the measured values ​​of the viscosities η1, η2, and η3 at the temperatures T1, T2, and T3 become more accurate.

[0056] According to the manufacturing method of the optical fiber G of this embodiment, the temperature of the resin R inside the resin tank 20 is regulated by flowing the temperature-regulated liquid W around the outer periphery of the resin tank 20, making it easy to accurately regulate the temperature of the resin R inside the resin tank 20.

[0057] According to the manufacturing method of the optical fiber G of the present embodiment, the viscometer 22 is provided at the center of the resin tank 20 relative to the thermometer 21. The results of the viscosity measurement by the viscometer 22 are easily affected by the wall surface of the resin tank depending on the position of the viscometer 22, but since the viscometer 22 of the present embodiment is provided at the center of the resin tank 20 relative to the thermometer 21, the influence of the wall surface of the resin tank 20 can be suppressed.

[0058] Although the present disclosure has been described in detail and with reference to specific embodiments, it is clear to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present disclosure. In addition, the number, position, shape, etc. of the components described above are not limited to the above embodiments, and can be changed to the number, position, shape, etc. that are suitable for implementing the present disclosure. [Explanation of symbols]

[0059] 1 Manufacturing equipment 10 Resin application section 20 Resin Tank 21 Thermometer 22 Viscometer 30 Piping 40 Heating section 50 Temperature measurement section 60 Control section 70 Resin temperature control section 71 Tank section 72 Flow Path 73 Adjustment part a,b coefficients G Optical Fiber G0 Glass Fiber T0 target temperature T1,T2,T3,Tm Temperature R resin W liquid η0 Target viscosity η1,η2,η3 Viscosity

Claims

1. a viscosity measuring step of storing a resin in a resin tank equipped with a viscometer and a thermometer and measuring the temperature and viscosity of the resin stored in the resin tank; a resin coating step of supplying the resin from the resin tank through a pipe to a resin coating section and coating the resin on an outer periphery of the glass fiber in the resin coating section; Including, a heating unit that heats the resin in the pipe so that the temperature of the resin in the pipe reaches a set target temperature, the heating unit being provided on an outer periphery of at least a part of the pipe; The target temperature is set based on the measurement results of temperature and viscosity in the viscosity measurement step. A method for manufacturing optical fiber.

2. The viscosity measuring step is carried out before the resin applying step, The viscosity measuring step includes measuring the viscosity of the resin at a plurality of temperatures. The method for producing the optical fiber according to claim 1 .

3. The viscosity measuring step includes measuring the viscosity of the resin at three or more different temperatures. The method for producing the optical fiber according to claim 2 .

4. The target temperature is recorded in a memory unit; The viscosity measuring step measures the viscosity of the resin when the temperature of the resin is within ±3° C. of the target temperature recorded in the memory unit. The method for producing an optical fiber according to any one of claims 1 to 3.

5. The viscosity measuring step includes measuring a viscosity of the resin when the resin is not supplied from the resin tank to the resin coating unit. The method for producing an optical fiber according to any one of claims 1 to 3.

6. The resin inside the resin tank is temperature-adjusted by flowing a temperature-adjusted liquid around the outer periphery of the resin tank. The method for producing an optical fiber according to any one of claims 1 to 3.

7. The viscometer is provided at a center of the resin tank relative to the thermometer. The method for producing an optical fiber according to any one of claims 1 to 3.

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