JP5780005B2 - Ultraviolet irradiation furnace for optical fiber and optical fiber manufacturing method - Google Patents

Description

  The present invention relates to an ultraviolet irradiation furnace for an optical fiber in which a coating of an ultraviolet curable resin is formed on the outer periphery of a drawn optical fiber, and an optical fiber manufacturing method.

  A conventional ultraviolet irradiation furnace is a curing device for curing an ultraviolet curable resin applied to the outer periphery of an optical fiber, and a cylindrical quartz tube is disposed in the passage of the optical fiber. An ultraviolet lamp for irradiating ultraviolet rays is disposed outside the quartz tube. By irradiating the ultraviolet ray from the ultraviolet lamp toward the quartz tube, the ultraviolet curable resin applied to the optical fiber passing through the quartz tube is cured (for example, see FIG. 4 of Patent Document 1).

  Further, in the conventional ultraviolet irradiation furnace, if there is oxygen inside the quartz tube, curing of the ultraviolet curable resin is hindered. For this reason, an oxygen-free chamber is provided at the upper end and the lower end of the quartz tube so that outside air does not mix inside the quartz tube and the oxygen concentration does not increase. Nitrogen gas, which is a purge gas, is introduced into the upper oxygen-free chamber, and nitrogen gas is allowed to flow from the oxygen-free chamber into the quartz tube. Thereby, the oxygen concentration in the quartz tube is lowered, and the ultraviolet curable resin of the optical fiber is cured (for example, see Patent Document 2).

JP 2005-350310 A JP 2004-189540 A

By the way, in the ultraviolet irradiation furnace, a volatile component is generated when the ultraviolet curable resin is cured. However, since the inside of the quartz tube has a sealed structure, the volatile component hardly flows out to the outside. If the volatile component stays in the quartz tube, the quartz tube becomes cloudy and the ultraviolet curable resin is not sufficiently irradiated with ultraviolet rays.
In order to prevent such fogging of the quartz tube, the purge amount of nitrogen gas flowing inside the quartz tube may be increased, and the volatile component may be forced to be discharged to the outside, but when the nitrogen purge gas is increased in this way, This leads to the cause of optical fiber runout and increased manufacturing costs.

  The object of the present invention has been made in view of the above-described circumstances, and further reduces the oxygen concentration in the quartz tube and smoothly discharges volatile components staying in the quartz tube to the outside to suppress fogging in the quartz tube. An object of the present invention is to provide an ultraviolet irradiation furnace for an optical fiber and a method for manufacturing the optical fiber.

  An ultraviolet irradiation furnace for an optical fiber according to the present invention that can solve the above-mentioned problems includes a cylindrical quartz tube that passes an optical fiber coated with an ultraviolet curable resin on the outer periphery, and an upstream end of the quartz tube. An ultraviolet for an optical fiber, comprising: an inert gas supply port for supplying an inert gas; and an ultraviolet irradiation unit that cures the ultraviolet curable resin applied to the optical fiber by irradiating the ultraviolet from the radial outside of the quartz tube. An irradiation furnace, wherein the opening diameter of the optical fiber entrance side at the upper end of the ultraviolet irradiation furnace is within a range of 3 mm to 10 mm, and the opening diameter of the optical fiber exit side of the lower end of the ultraviolet irradiation furnace is within a range of 4 mm to 20 mm. The outgoing wire side opening diameter is larger than the incoming wire side opening diameter.

  According to the ultraviolet irradiation furnace for an optical fiber thus configured, the oxygen concentration in the quartz tube can be reduced from the current level by setting the optimum diameter of the incoming side opening diameter and the outgoing side opening diameter larger than the incoming side opening diameter. In addition to the reduction, the volatile components staying in the quartz tube can be smoothly discharged to the outside to suppress fogging in the quartz tube.

  Moreover, the ultraviolet irradiation furnace for optical fibers which concerns on this invention is an ultraviolet irradiation furnace for optical fibers as described above, Comprising: It is preferable that the said outgoing wire side opening diameter is smaller than the internal diameter of the said quartz tube.

  According to the ultraviolet irradiation furnace for an optical fiber having the above-described configuration, since the outgoing-side opening diameter is set smaller than the inner diameter of the quartz tube, the oxygen concentration in the quartz tube can be further reduced.

  An ultraviolet irradiation furnace for an optical fiber according to the present invention is the ultraviolet irradiation furnace for an optical fiber described above, which is provided on an incoming line side provided between the inert gas supply port and the outer peripheral upper portion of the quartz tube. It is preferable that the airtight packing has a two-stage configuration.

  According to the ultraviolet irradiation furnace for an optical fiber having the above-described configuration, since the airtight packing on the incoming line side has a two-stage configuration, it is possible to further improve the airtightness in the quartz tube, so that the outside air can enter the quartz tube and the inside of the quartz tube. Leakage of the inert gas introduced into can be reduced.

An optical fiber manufacturing method according to the present invention capable of solving the above-mentioned problems is that an optical fiber coated with an ultraviolet curable resin on the outer periphery passes downward from above in a cylindrical quartz tube, and An inert gas is supplied into the quartz tube from an inert gas supply port provided at an upstream end, and ultraviolet rays are irradiated onto the optical fiber from an ultraviolet irradiation unit disposed outside the quartz tube, An optical fiber manufacturing method for curing an ultraviolet curable resin applied to an optical fiber,
The optical fiber enters from an entrance side opening above the quartz tube and within a range of 3 mm to 10 mm, and is below the quartz tube and within a range of 4 mm to 20 mm larger than the entrance side opening diameter. It is characterized by outgoing from the outgoing side opening.

  According to the optical fiber manufacturing method configured in this way, the oxygen concentration in the quartz tube is reduced from the current level by setting the optimum diameter of the incoming side opening diameter and the outgoing side opening diameter larger than the incoming side opening diameter. In addition, the volatile components staying in the quartz tube can be smoothly discharged to the outside, and fogging in the quartz tube can be suppressed.

  According to the ultraviolet irradiation furnace for an optical fiber and the optical fiber manufacturing method according to the present invention, by setting the opening diameter of the ultraviolet irradiation furnace to an optimum diameter, the oxygen concentration in the quartz tube can be reduced from the current state, Volatile components staying in the quartz tube can be smoothly discharged to the outside to suppress fogging in the quartz tube.

It is a schematic block diagram of the ultraviolet irradiation furnace for optical fibers which concerns on this invention.

  Hereinafter, an ultraviolet irradiation furnace for an optical fiber and an optical fiber manufacturing method according to an embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1, in the ultraviolet irradiation furnace 10 for an optical fiber of the present embodiment, a coating device for applying an ultraviolet curable resin is disposed on the upstream side, and the coating device is applied to the outer periphery of the optical fiber 11. The cured UV curable resin is cured by UV irradiation.
The main parts of the optical fiber ultraviolet irradiation furnace 10 are an irradiation furnace main body 12, a cylindrical quartz tube 13 having an inner diameter D0, and an ultraviolet lamp that is disposed outside the quartz tube 13 and irradiates ultraviolet rays. 14.

  Moreover, the ultraviolet irradiation furnace 10 for optical fibers is provided in the upper part of the irradiation furnace main body 12, and is provided in the lower end of the irradiation furnace main body 12, the inlet cover 15 which has the inlet 17 of the incoming line side opening diameter D1 in an upper end, and a lower end. And an outlet cover 16 having an outgoing line opening 18 having an outgoing line side opening diameter D2.

  An inert gas supply port 19 is provided at a side portion of the inlet cover 15, and an inert gas G such as nitrogen gas supplied from the gas introduction pipe 21 is introduced into the quartz tube 13. By introducing the inert gas G, the oxygen concentration in the quartz tube 13 can be reduced. By reducing the oxygen concentration that hinders the curing of the ultraviolet curable resin, the ultraviolet curable resin can be cured without being inhibited by oxygen. The introduced inert gas G is naturally discharged from the outgoing wire opening 18 having the lower outgoing wire side opening diameter D2.

  Since the ultraviolet lamp 14 becomes high temperature when irradiated with ultraviolet rays, the cooling air 24 is introduced from the air introduction pipe 23 and cooled. The cooling air 24 flows outside the quartz tube 13 and is then exhausted as exhaust air 26 from the air exhaust tube 25. The air discharge pipe 25 is connected to an exhaust device (not shown), and has a negative pressure of about −0.5 kPa compared to the atmospheric pressure.

  A cylindrical reflecting mirror 31 centering on the quartz tube 13 is disposed outside the ultraviolet lamp 14. Ultraviolet light irradiated from the ultraviolet lamp 14 by the reflecting mirror 31 is reflected by the reflecting mirror 31 and indirectly re-irradiated to the optical fiber 11 in the quartz tube 13.

  In the ultraviolet irradiation furnace 10 for an optical fiber of the present embodiment, the outgoing line side opening diameter D2 is set to be larger than the incoming line side opening diameter D1 and smaller than the inner diameter D0 of the quartz tube 13 (D1 <D2 <D0). Specifically, the incoming wire side opening diameter D1 of the incoming wire port 17 is in the range of 3 mm to 10 mm. Moreover, the outgoing wire side opening diameter D2 of the outgoing wire port 18 is in the range of 4 mm to 20 mm.

In addition to setting the incoming wire side opening diameter D1 of the incoming wire port 17, the optimum diameter of the outgoing wire side opening diameter D2 of the outgoing wire port 18 is set so as to be larger than the incoming wire side opening diameter D1 and smaller than the inner diameter D0 of the quartz tube 13. To do.
By making the outgoing line side opening diameter D2 larger than the incoming line side opening diameter D1, the inert gas G can be easily discharged, and the volatile components staying in the quartz tube 13 are smoothly discharged to the outside. Can suppress fogging. Moreover, the oxygen concentration can be reduced by making the outgoing wire side opening diameter D2 smaller than the inner diameter D0 of the quartz tube 13. By setting the optimum diameter in this way, the oxygen concentration in the quartz tube 13 can be reduced to 1000 ppm or less, and the volatile components staying in the quartz tube 13 can be discharged smoothly to the outside.

  The optical fiber ultraviolet irradiation furnace 10 is provided with two-stage inlet-side airtight packings 27 and 28 made of rubber between the inert gas supply port 19 and the outer periphery of the quartz tube 13. The first airtight packing 27 on the upstream side is in contact with the inert gas G whose upper surface is pressurized with the positive pressure P1, and the second airtight packing 28 on the downstream side is sucked with the negative pressure P2 on the lower surface. Is in contact with the cooled cooling air 24 (P2 <P1).

The airtight packings 27 and 28 prevent the cooling air 24 that cools the ultraviolet lamp 14 from sucking the inert gas G, and the supply of the inert gas G into the quartz tube 13 is reduced. This prevents the oxygen concentration in the tube 13 from increasing. The packing may be one-stage, but in particular, by using the two-stage inlet-side airtight packings 27 and 28, intrusion of outside air into the quartz tube 13 and leakage of the inert gas G introduced into the quartz tube 13 Can be minimized.
Further, between the lower outer periphery of the quartz tube 13 and the air introduction tube 23 and the air discharge tube 25, a rubber outgoing wire side airtight packing 29 is provided.

  As described above, according to the ultraviolet irradiation furnace 10 for an optical fiber of the present embodiment, the incoming wire side opening diameter D1 of the upper incoming wire port 17 is within the range of 3 mm to 10 mm, and the outgoing wire side opening diameter of the lower outgoing wire port 18. The optimum diameter is set so that D2 is in the range of 4 mm to 20 mm, and the outgoing wire side opening diameter D2 is larger than the incoming wire side opening diameter D1. Thereby, while reducing the oxygen concentration in the quartz tube 13 from the present condition, the volatile component which stays in the quartz tube 13 can be discharged | emitted smoothly outside, and the fogging in the quartz tube 13 can be suppressed.

  Moreover, according to the ultraviolet irradiation furnace 10 for optical fibers, since the outgoing wire opening diameter D2 is set smaller than the inner diameter D0 of the quartz tube 13, the oxygen concentration in the quartz tube 13 can be further reduced.

  Moreover, according to the ultraviolet irradiation furnace 10 for optical fibers, the airtight packings 27 and 28 on the incoming line side provided between the inert gas supply port 19 and the upper outer periphery of the quartz tube 13 are configured in two stages. Further, the airtightness in the quartz tube 13 can be further improved, and the intrusion of outside air into the quartz tube 13 and the leakage of the inert gas G introduced into the quartz tube 13 can be reduced.

  Moreover, according to the manufacturing method of the optical fiber of this embodiment, first, the incoming side opening diameter D1 is set within a range of 3 mm to 10 mm, and the outgoing side is within a range of 4 mm to 20 mm larger than the incoming side opening diameter. The optimum diameter of the opening diameter D2 is set. Next, the optical fiber 11 coated with an ultraviolet curable resin on the outer periphery enters from the incoming side opening diameter D1 above the cylindrical quartz tube 13 and from the outgoing side opening diameter D2 below the quartz tube 13. Let it come out.

  At this time, the optical fiber 11 passes from the upper side to the lower side in the quartz tube 13, and the inert gas G is supplied into the quartz tube 13 from the inert gas supply port 19 provided at the upper end of the quartz tube 13. By irradiating the optical fiber 11 with ultraviolet rays from the lamp 14, the ultraviolet curable resin applied to the optical fiber 11 is cured. By setting the inlet-side opening diameter D1 and the outgoing-side opening diameter D2 to the optimum diameters described above, the oxygen concentration in the quartz tube 13 can be reduced and the volatile components that remain can be discharged smoothly to the outside. Can suppress fogging.

  Next, an embodiment of an ultraviolet irradiation furnace for an optical fiber and an optical fiber manufacturing method according to the present invention will be described.

(Measuring method)
In the embodiment, the entrance-side opening diameter D1 of the ultraviolet irradiation furnace for optical fibers is 3 mm to 10 mm, the exit-side opening diameter D2 is 4 mm to 20 mm, and D1 and D2 are appropriately changed under the condition of D1 <D2. . On the other hand, the comparative example is an example in the case where D1 and D2 are appropriately changed without departing from the conditions of the example.
In addition, in both the examples and the comparative examples, the airtight packing on the incoming line side is selected in one or two stages, and the flow rate of the inert gas (N ₂ ) is selected as either 30 or 50 liters / minute.
In both the examples and comparative examples, the quartz tube having an inner diameter D0 of 21 mm is used, and the linear velocity of the optical fiber is set to be the same.

(Measurement item)
In both Examples and Comparative Examples, the oxygen concentration in the quartz tube and the UV light power attenuation ratio (measured power / initial power) due to the fogging of the quartz tube after drawing the optical fiber by 1000 (km) are measured.
(Evaluation criteria)
The oxygen concentration is 1000 (ppm) or less, and the UV light power attenuation rate is 70 (%) or more as a pass line.

  As a result, the results shown in Table 1 are obtained.

As is clear from Table 1, in Examples 1 to 3, the oxygen concentration is reduced from 1000 (ppm) to 10 (ppm) by decreasing only the outgoing wire side opening diameter D2 from 20 mm to 10 mm in a stepwise manner. It can be seen that it decreases well. However, the UV light power attenuation rate decreases from 75 (%) to 70 (%).
Further, from the results of Example 3 and Example 4, under the conditions of D1 = 8 mm and D2 = 10 mm, the oxygen concentration and the UV light power attenuation rate do not change even if the nitrogen gas is reduced from 50 liters / minute to 30 liters / minute. It turns out that there is no problem even if nitrogen gas is reduced. This is considered to be because the relationship between D1 and D2 is optimal, and the air is smoothly exhausted while ensuring the airtightness in the quartz tube.

In Example 5, D1 and D2 were further lowered, the oxygen concentration was almost zero, and the UV light power attenuation rate also cleared the standard.
In Example 6, conversely, D1 and D2 were raised, and the oxygen concentration and UV light power attenuation rate also cleared the standards.
Example 7 shows that the oxygen concentration is even better than that of Example 4 when the airtight packing on the incoming line side has a two-stage configuration under the same conditions as in Example 4.

On the other hand, Comparative Example 1 is a case where the outgoing wire side opening diameter D2 is larger than that of Example 1, and the oxygen concentration is 3000 (ppm), which is worse than that of Example 1. This is considered to be because outside air is caught from the outlet.
The comparative example 2 is a case where the nitrogen gas of the comparative example 1 is reduced from 50 liters / minute to 30 liters / minute, and the oxygen concentration is further deteriorated compared with the comparative example 1.
Comparative Example 3 is a case where D2 is smaller than Comparative Example 1 and the incoming wire side opening diameter D1 and the outgoing wire side opening diameter D2 are the same 8 mm. In this case, the quartz tube is likely to be fogged. Compared to Example 1, the UV light power attenuation rate is reduced to 60 (%).
The comparative example 4 is a case where the outgoing-side opening diameter D2 is made smaller than that of the comparative example 3 so that D1> D2, and the UV light power attenuation rate is further lower than that of the comparative example 3.

The comparative example 5 is a case where the incoming line side opening diameter D1 is further reduced from the conditions of the comparative example 1, and in this case, the optical fiber is brought into contact with the incoming line port due to line runout, resulting in disconnection.
Comparative Example 6 is a case where the incoming line side opening diameter D1 is slightly larger than the condition of Comparative Example 5, and in this case, there was no disconnection, but the oxygen concentration was 2000 (ppm), and the standard was cleared. could not.
Comparative Example 7 is a case where the outgoing wire side opening diameter D2 is reduced from the conditions of Comparative Example 6, and although the oxygen concentration is good, the quartz tube is clouded and the UV light power attenuation rate is reduced to 60 (%). doing.

Comparative Example 8 is a case where the incoming-side opening diameter D1 is further increased from the conditions of Example 1, and the UV light power attenuation rate is better than that of Example 1, but the oxygen concentration is 2000 (ppm), which exceeds the standard. doing.
Comparative Example 9 is a case where the airtight packing on the incoming line side has a two-stage configuration under the same conditions as Comparative Example 1, and although the oxygen concentration is better than Comparative Example 1, the oxygen concentration is 2200 (ppm), The standard is exceeded.

  From the above results, if D1 and D2 are appropriately set under the condition of D1 <D2 within the range of the incoming side opening diameter D1 of 3 mm to 10 mm and the outgoing side opening diameter D2 of 4 mm to 20 mm, it is a pass line. It can be seen that an oxygen concentration of 1000 (ppm) or less and a UV light power attenuation rate of 70 (%) or more can be achieved.

  In addition, the ultraviolet irradiation furnace for optical fibers and the manufacturing method of an optical fiber of this invention are not limited to embodiment mentioned above, A deformation | transformation, improvement, etc. are possible suitably, and there exists the same effect. In addition, the material, shape, dimension, numerical value, form, number, arrangement location, and the like of each component in the above-described embodiment are arbitrary and are not limited as long as the present invention can be achieved.

DESCRIPTION OF SYMBOLS 10 ... Ultraviolet irradiation furnace for optical fibers, 11 ... Optical fiber, 12 ... Irradiation furnace main body, 13 ... Quartz tube, 14 ... Ultraviolet lamp (ultraviolet irradiation part), 15 ... Inlet cover, 16 ... Outlet cover, 17 ... Inlet, DESCRIPTION OF SYMBOLS 18 ... Outlet port, 19 ... Inert gas supply port, 23 ... Air introduction pipe, 24 ... Cooling air, 25 ... Air discharge pipe, 26 ... Exhaust air, 27 ... 1st airtight packing, 28 ... 2nd Gas-tight packing, D0 ... quartz tube inner diameter, D1 ... incoming wire side opening diameter, D2 ... outgoing wire side opening diameter, G ... inert gas, P1 ... positive pressure (inert gas), P2 ... negative pressure (cooling air)

Claims (4)

A cylindrical quartz tube that passes an optical fiber coated with UV curable resin on the outer periphery;
An inert gas supply port for supplying an inert gas to the upstream end of the quartz tube;
An ultraviolet irradiation unit that cures the ultraviolet curable resin applied to the optical fiber by irradiating ultraviolet rays from the radially outer side of the quartz tube;
An ultraviolet irradiation furnace for an optical fiber comprising:
The ultraviolet irradiation furnace range from the incoming line side opening diameter 3mm of 10mm of incoming port of the optical fiber at the upper end, the range of the outgoing line side opening diameter 4mm of 20mm outgoing line port of the optical fiber of the ultraviolet irradiation furnace bottom Within
The outgoing line side aperture diameter is rather larger than the incoming side aperture diameter,
An ultraviolet irradiation furnace for an optical fiber, wherein the inert gas is naturally discharged from the outlet . An ultraviolet irradiation furnace for an optical fiber according to claim 1,
An ultraviolet irradiation furnace for an optical fiber, wherein the outgoing wire side opening diameter is smaller than the inner diameter of the quartz tube. An ultraviolet irradiation furnace for an optical fiber according to claim 1 or 2,
An ultraviolet irradiation furnace for an optical fiber, wherein an inlet-side airtight packing provided between the inert gas supply port and the upper outer periphery of the quartz tube has a two-stage configuration. An optical fiber coated with an ultraviolet curable resin on the outer periphery passes from the upper side to the lower side in the cylindrical quartz tube and is not introduced into the quartz tube from the inert gas supply port provided at the upstream end of the quartz tube. This is an optical fiber manufacturing method in which an active gas is supplied and ultraviolet light is irradiated to the optical fiber from an ultraviolet irradiation unit disposed outside the quartz tube, thereby curing the ultraviolet curable resin applied to the optical fiber. And
The optical fiber, and the incoming line from the incoming line port of the incoming line-side opening diameter from 3mm located above the quartz tube in the range of 10 mm,
And outgoing line from the output line port of the outgoing line side opening diameter from the incoming line side opening diameter greater than 4mm located below the quartz tube in the range of 20 mm,
A method for producing an optical fiber, wherein the inert gas is naturally discharged from the outlet .

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