JP5780024B2 - Optical fiber manufacturing method - Google Patents

Description

  The present invention relates to a method of manufacturing an optical fiber in which a glass fiber is drawn from an optical fiber preform and the outer surface of the glass fiber is coated with a resin.

  An optical fiber is obtained by heating and melting an optical fiber preform to draw a glass fiber having an outer diameter of about 125 μm, and forming a coating layer of an ultraviolet curable resin having an outer diameter of about 250 μm on the outer surface of the drawn glass fiber (also referred to as a bare fiber). Formed. The glass fiber having one or two coating layers on the outer surface is also called an optical fiber. This optical fiber is further provided with a reinforcing layer or a fiber identifying colored layer is called an optical fiber core.

  The above-described optical fiber may be continuously subjected to relatively small stress over a long period of time. Even with such a relatively small stress, if the stress is applied for a certain period of time, it may break suddenly. It is known that the dynamic fatigue coefficient (Nd) should be improved in order to avoid such a breakage of the optical fiber and ensure a breakage life. Nd is used as an index representing the growth rate of scratches on the surface of the glass fiber. If Nd is large, the growth of scratches on the glass surface is slow, and the optical fiber is said to be difficult to break for a long time.

  In order to increase Nd of this optical fiber, for example, a method for increasing the adhesion between the glass fiber and the coating layer is known. The adhesion between the glass fiber and the coating layer is determined by the silane coupling agent in the resin forming the coating layer and its reaction process. The silane coupling agent added to the resin of the coating layer first undergoes a hydrolysis reaction with moisture in the resin, and then undergoes a dehydration condensation reaction for bonding to the glass fiber, so that the glass fiber and the coating layer are brought into close contact with each other. . For this, it is necessary for the resin of the coating layer to contain moisture for hydrolysis.

  The optical fiber immediately after applying the coating layer to the drawn glass fiber is wound up by the bobbin, but the portion wound on the winding drum side (inner winding layer portion) after the winding is finished is the surface side. It will be covered with the part wound by (outer winding layer part), and will be in the state which is hard to be exposed to air | atmosphere. For this reason, it is difficult to take in sufficient moisture necessary for the hydrolysis reaction with the above-mentioned silane coupling agent, and even if the hydrolysis reaction is caused by a small amount of moisture originally present in the resin, the subsequent dehydration condensation It becomes difficult to discharge a gas mainly composed of alcohol produced by the reaction. As a result, the Nd of the optical fiber in the inner winding layer of the bobbin is not improved with respect to the Nd of the optical fiber in the outer winding of the bobbin, and it is difficult to obtain an optical fiber of uniform quality. there were.

  Therefore, in order to improve this, it is conceivable to add moisture to the resin before curing in advance, but there is a problem that the hydrolysis reaction occurs during the storage of the resin and changes in quality. Further, when the drawing speed of the optical fiber is increased to 1500 m / min or more, the time for exposure to the atmosphere after the coating resin is applied to the glass fiber to form an optical fiber strand and wound on the bobbin. Very short. For this reason, it is difficult for the optical fiber of the inner winding layer portion (also referred to as the lower opening side) of the bobbin to take in sufficient moisture into the coating resin layer.

On the other hand, for example, Patent Document 1 discloses that moisture is supplied to the surface of the glass fiber immediately before the coating resin is applied to the glass fiber to improve the adhesion between the glass fiber and the coating resin layer. Has been.
Patent Document 2 discloses a coating resin composition that simultaneously improves the dynamic fatigue characteristics and lateral pressure characteristics of an optical fiber, and discloses that the dynamic fatigue coefficient (Nd) is 20 or more. Patent Document 3 also discloses that the dynamic fatigue coefficient (Nd) is set to 20 or more by defining the moisture permeability of the coating layer outside the coating layer formed of two layers of optical fibers. Yes.

JP 2000-34137 A JP 2003-241032 A JP 2004-341104 A

  In recent years, optical fibers have been increasingly used in a state of being bent to a small diameter due to expansion of their applications. In order to guarantee the mechanical fracture life in such a state, the above Nd can be improved. It is requested. Conventionally, Nd of about 18 to 20 has been a global standard, but in recent years, a higher value than this has been required. Nd is affected by the state of cracks on the surface of the glass fiber and the adhesion between the coating resin layer. This adhesion force gradually increases after drawing the optical fiber (after production), but since the reaction period of the silane coupling agent is about 40 days, it reaches a predetermined value as early as possible (within 40 days). Is also needed.

  In Patent Document 1 described above, it is disclosed that the adhesion between the glass fiber and the coating resin layer is increased by applying moisture to the glass fiber surface before coating with the coating resin. There is no disclosure of how much the thickness of the glass fiber is, and cracks are generated when moisture directly adheres to the surface of the glass fiber, which may reduce the breaking strength. Further, Patent Documents 2 and 3 disclose Nd improvement by a coating resin material, but Nd is set to 20 or more, there is no disclosure of specific data thereof, and a new coating resin is disclosed. To develop materials, considerable development costs are required.

  The present invention has been made in view of the above-described situation, and an object of the present invention is to provide an optical fiber manufacturing method that improves the dynamic fatigue coefficient Nd of an optical fiber strand of an inner winding layer wound around a bobbin. And

In the method of manufacturing an optical fiber according to the present invention, after drawing a glass fiber from an optical fiber preform, the surface of the glass fiber is coated with a coating resin to which a silane coupling agent is added, and then wound on a bobbin. A manufacturing method in which an optical fiber wound in a bobbin is housed in a sealed container, and after the inside of the sealed container is depressurized, a plurality of cycles in which a gas containing moisture is introduced and the pressure is increased to atmospheric pressure or more It is characterized by repeated times.
In addition, the pressure at the time of pressure reduction in an airtight container is a pressure 30 kPa-70 kPa lower than atmospheric pressure, and it is preferable that the gas containing the water | moisture content introduce | transduced when pressurizing more than atmospheric pressure has 50% or more of humidity. Moreover, it is preferable to repeat the cycle which pressurizes more than atmospheric pressure after decompressing 3 times or more.

  According to the present invention, moisture necessary for the hydrolysis reaction with the silane coupling agent is applied to the optical fiber of the inner winding layer wound on the bobbin in the drawing process by pressurization and decompression. Since it is possible to easily discharge the alcohol generated by the dehydration condensation reaction by reducing the pressure, it is possible to improve the dynamic fatigue coefficient Nd of the inner wound layer portion.

It is a figure explaining the outline of the manufacturing method of the optical fiber by this invention. It is a figure which shows the test result which investigated the relationship between elapsed days and the optical fiber Nd of an inner layer winding layer part by manufacture of the optical fiber by this invention.

  An embodiment of the present invention will be described with reference to FIG. In the figure, 10 is an optical fiber preform, 11 is a drawing furnace, 12 is a heater, 13 is a glass fiber, 13a is an optical fiber (optical fiber) in which a coating resin is cured, 14 is a cooling device, and 15 is a coating. Dies for resin application, 16 is a coating resin, 17 is an ultraviolet irradiation device, 18 is a guide roller, 19 is a capstan, 20 is a dancer roller, 21 is a guide roller, 22 is a bobbin, 23 is a sealed container, 23a is a gas supply port , 23b are decompression ports.

As shown in FIG. 1A, the basic configuration itself of the optical fiber manufacturing method in the present invention is almost the same as the conventional one. That is, after the optical fiber preform 10 is set in the drawing furnace 11, the glass fiber 13 is drawn by being sequentially heated and melted by the heater 12. The optical fiber preform 10 is made of, for example, a core portion added with GeO ₂ and a clad made of high-purity quartz glass provided on the outer periphery of the core portion so that the optical transmission characteristics of the optical fiber to be manufactured can be obtained. Part. And the glass fiber 13 is normally drawn so that it may become a standard outer diameter of 125 micrometers.

  Next, the glass fiber 13 immediately after drawing is cooled to a predetermined temperature by the cooling device 14. Thereafter, the glass fiber 13 passes through the coating resin coating die 15 so that the coating resin 16 is applied to the surface of the glass fiber 13. For the coating resin 16 that protects the glass fiber 13, for example, an ultraviolet curable urethane acrylate resin to which a silane coupling agent is added is used, and the outer diameter of the coating resin layer after the curing is about 250 ± 15 μm. It is applied and molded as follows. In addition, the coating resin layer is formed of one or two layers, and in the case of two layers, the inner layer is soft to provide cushioning properties, and the outer layer is hard to have resistance to external forces and the like. To be allowed to.

  The optical fiber coated with a coating resin 16 such as an ultraviolet curable resin is made into an optical fiber strand 13a protected by a coating resin layer by curing the resin applied by the ultraviolet irradiation device 17. The optical fiber 13 a is taken up by a capstan roller 19 through a guide roller 18. The optical fiber 13a taken up by the capstan roller 19 is taken up by a take-up bobbin 22 through a dancer roller 20, a guide roller 21 and the like.

  In the present invention, the optical fiber 13a wound around the bobbin 22 is housed in a sealed container 23 as shown in FIG. It is characterized by repeating the cycle of introducing and pressurizing to atmospheric pressure or more a plurality of times. The sealed container 23 has a gas introduction port 23a and a gas exhaust port 23b, and has a configuration in which the inside of the container can be brought into a predetermined reduced pressure state and a pressurized state by controlling opening and closing of the valve.

  FIG. 1C is a diagram for explaining an example of a control mode of pressure reduction and pressurization, and is performed on the basis of atmospheric pressure (103.3 kPa). For example, it is preferable to exhaust (evacuate) the pressure so that the pressure becomes 30 kPa to 70 kPa lower than the atmospheric pressure over about 6 minutes. If the degree of depressurization is less than 30 kPa with respect to atmospheric pressure, the replacement efficiency of the gas in the container is poor, and if the degree of depressurization exceeds 70 kPa with respect to atmospheric pressure, the coating resin layer of the optical fiber is damaged. there is a possibility.

  After reaching a predetermined reduced pressure state, a gas containing moisture is introduced, and the pressure is increased to a level slightly higher than atmospheric pressure (several kPa). This pressurization is performed slowly over about 3 minutes from the depressurized state. The introduction gas for pressurization is a humid gas containing moisture, and may be air other than argon gas or nitrogen gas, for example. The humidity of the introduced gas is preferably 50% or more as will be described later.

When the pressure in the sealed container reaches a predetermined reduced pressure value, the pressurization may be started immediately, or the pressurization may be started after some time. In addition, when shifting from pressurization to depressurization, it is preferable to depressurize after some time (about 30 minutes) rather than immediately depressurize.
When the inside of the sealed container 23 is depressurized from the atmospheric pressure to the above-mentioned predetermined pressure, and then pressurized to the predetermined pressure and returned to the atmospheric pressure as one cycle, it is repeated three or more cycles as will be described later. Is preferred.

  By repeating this depressurization and pressurization, the gas easily penetrates into the optical fiber strand of the inner winding layer wound around the bobbin 22 by the depressurization, and water is added with a small amount of water originally present in the resin. It is possible to promote the discharge of gas mainly composed of alcohol generated by the dehydration condensation reaction after the decomposition reaction. Then, by applying pressure, wet gas is diffused into contact with the optical fiber of the inner winding layer portion in which the gas easily penetrates and the silane coupling agent is hydrolyzed in the coating resin layer. It is possible to promote the incorporation of moisture necessary for the reaction.

FIG. 2 is a graph showing the relationship between the number of days elapsed after the above-described treatment is performed on the optical fiber wound on the bobbin and the dynamic fatigue coefficient (Nd) of the optical fiber in the inner winding layer portion. The dynamic fatigue coefficient (Nd) was measured by a test method defined in IEC 60793-1-33 established by IEC (International Electrotechnical Commission).
FIG. 2 (A) shows a case where the cycle of pressure reduction to pressurization was not performed (0 cycle), and the cycle of pressure reduction to pressurization was repeated three times with the humidity of the introduced gas at the time of pressurization being 50% and 70%. It is a test result in the case. From this test result, Nd did not increase regardless of the number of days elapsed when the cycle of reduced pressure to pressurization was not performed.

  On the other hand, it can be seen that Nd increases with the number of days elapsed when the pressure reduction and the gas pressurization treatment are performed. In addition, the higher the humidity of the gas containing moisture, the greater the effect. Compared to the treatment at a humidity of 50%, the treatment at a humidity of 70% has the same decompression to pressurization cycle. Even if the number of times is N, the final value of Nd can be increased.

  FIG. 2 (B) shows the case where the cycle of reduced pressure to increased pressure is not performed (0 cycle), the humidity of the introduced gas at the time of pressurization is 50%, and the cycle of reduced pressure to increased pressure is 3 times or more (3 cycles). , 10 cycles, 30 cycles). From this test result, it was found that Nd can be further increased by increasing the number of cycles of reduced pressure to increased pressure even when the humidity is the same. However, when the cycle of decompression to pressurization is changed from 3 times to 10 times, the final Nd value can be increased (in this case, “23” → “26”), whereas the decompression to pressurization is increased. Even if the number of cycles is further increased to 30 times, the final value of Nd does not change much (in this case, “26” → “27”).

  However, when the cycle of decompression to pressurization is 10 times, it takes about 30 days for Nd to reach the saturation value, whereas when the cycle of decompression to pressurization is 30 times. , Nd has reached the saturation value in about 10 days. That is, even if the saturation value is finally reached, the predetermined Nd value can be reached early by increasing the number of cycles of pressure reduction to pressurization. As a result, even when the number of days from manufacture to shipment of the optical fiber is short, the dynamic fatigue coefficient can be set to a value in a favorable range at an early stage.

DESCRIPTION OF SYMBOLS 10 ... Optical fiber base material, 11 ... Drawing furnace, 12 ... Heater, 13 ... Glass fiber, 13a ... Optical fiber (optical fiber strand) by which coating resin was hardened, 14 ... Cooling device, 15 ... For coating resin coating 16 ... coating resin, 17 ... ultraviolet irradiation device, 18 ... guide roller, 19 ... capstan, 20 ... dancer roller, 21 ... guide roller, 22 ... bobbin, 23 ... sealed container, 23a ... gas supply port, 23b ... Decompression port.

Claims (4)

An optical fiber manufacturing method in which a glass fiber is drawn from an optical fiber preform, and then the surface of the glass fiber is coated with a coating resin to which a silane coupling agent is added, and then wound on a bobbin.
The optical fiber wound around the bobbin is housed in a sealed container, and after the inside of the sealed container is depressurized, a cycle of introducing a gas containing moisture and pressurizing to a pressure higher than atmospheric pressure is repeated a plurality of times. An optical fiber manufacturing method.   2. The method of manufacturing an optical fiber according to claim 1, wherein the pressure in the sealed container at the time of decompression is a pressure 30 kPa to 70 kPa lower than the atmospheric pressure.   The method for producing an optical fiber according to claim 1 or 2, wherein the gas containing moisture introduced when the pressure is increased to the atmospheric pressure or more has a humidity of 50% or more.   The method of manufacturing an optical fiber according to any one of claims 1 to 3, wherein the cycle of pressurizing to atmospheric pressure or higher after the pressure reduction is repeated three or more times.

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