JP5668625B2 - Optical fiber manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing an optical fiber in which a glass fiber is drawn from an optical fiber preform and an ultraviolet curable resin is applied to the surface of the glass fiber.

  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.

  However, when water is added to the resin before curing, there is a problem that the hydrolysis reaction occurs during the storage of the resin and the quality is changed. In recent years, the drawing speed of optical fibers has been increased. However, when the speed is increased to 1500 m / min or more, the coating resin is applied to the optical fibers and then the time for exposure to the atmosphere is cured. It was very short and it was difficult to incorporate moisture into the resin before the coating resin was cured.

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, Nd values of about 25 to 30 have 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 only 20 or more, and there is no disclosure about specific data and Nd being 25 or more. Moreover, considerable development costs are required to develop a new coating resin material.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a method for manufacturing an optical fiber having a dynamic fatigue coefficient Nd of 25 or more and having a predetermined value early after drawing.

An optical fiber manufacturing method according to the present invention is a method of manufacturing an optical fiber in which a glass fiber is drawn from an optical fiber preform and then an ultraviolet curable coating resin to which a silane coupling agent is added is applied to the surface of the glass fiber. After the coating resin is applied to the surface of the glass fiber by a die to form an uncured coating resin layer, the coating resin layer is sprayed in the form of a mist before the coating resin layer is cured. Contact with water droplets. In addition, it is preferable that the humidity on the exit side of the die is maintained at 70% or more by spraying mist-like water droplets.
Moreover, it is preferable that the maximum particle diameter of the said mist-like water droplet is 45 micrometers-110 micrometers.

  According to the present invention, moisture can be imparted to the surface of the coating resin layer before the coating resin layer of the optical fiber is cured, effectively promoting hydrolysis of the silane coupling agent in the coating resin. The dynamic fatigue coefficient Nd is 25 or more, and it becomes possible to make it a predetermined value early after drawing.

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 relationship between the spraying state (humidity) of the water droplet in this invention, and the dynamic fatigue coefficient Nd. It is a figure which shows the relationship between the spraying state (humidity) of the water droplet in this invention, and the breaking strength of an optical fiber. It is a figure which shows an example of the water droplet distribution sprayed on the surface of a coating resin layer by this invention. It is a figure which shows the change state of elapsed days and a dynamic fatigue coefficient (Nd) in manufacture of the optical fiber by this invention.

  An embodiment of the present invention will be described with reference to FIG. In FIG. 1, 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 in which the coating resin layer is uncured, 13b is an optical fiber in which the coating resin is cured, 14 Is a cooling device, 15 is a coating resin application die, 16 is a coating resin, 16a is an uncured coating resin layer, 16b is a cured coating resin layer, 17 is a coating resin supply device, 18 is a spray nozzle, 19 is a water droplet , 20 indicates an ultraviolet irradiation device.

As shown in FIG. 1, the basic configuration 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 application die 15 so that the coating resin 16 supplied from the coating resin supply device 17 is applied to the surface of the glass fiber 13. For example, an ultraviolet curable urethane acrylate resin to which a silane coupling agent is added is used as the coating resin 16 that protects the glass fiber 13, and the outer diameter of the cured resin layer 16b is about 250 ± 15 μm. Then, it is coated and molded. Further, the coating resin layer 16b is formed of one or two layers, and in the case of two layers, the inner layer is soft and has cushioning properties, and the outer layer is hard and resistant to external forces and the like. It is made to have.

  In the present invention, an ultraviolet curable coating resin 16 is applied to the outer periphery of the glass fiber 13 to form an uncured coating resin layer 16a, and the coating resin layer 16a is in a state before being cured by the ultraviolet irradiation device 20. The optical fiber 13a is configured to pass through a high humidity environment in which water droplets 19 sprayed in a mist form float. Thereby, the water droplet of the micro diameter sprayed in the shape of a mist contacts and adheres to the surface of the uncured coating resin layer 16a. The particle size of the water droplet 19 will be described later.

  In order to form a high-humidity environment in which water droplets 19 sprayed in a mist form float, for example, a portable spray-type humidifier is disposed near the outlet side of the die 15 and can be easily realized. be able to. The mist-like water droplet sprayed from the spray nozzle 18 of the humidifier floats in the mist state near the exit of the die 15 to form a high humidity environment. The optical fiber 13a in which the UV curable coating resin 16 is applied to the outer surface of the glass fiber 13 by the die 15 is in an uncured state before the coated resin layer 16a is cured. What is necessary is just to pass through the high humidity environment in a state. As a result, water droplets of microspheres adhere to the surface of the uncured coating resin layer 16a.

  Thereafter, the uncured coating resin layer 16 a is cured by the ultraviolet irradiation device 20 to form a coating resin layer 16 b that protects the glass fiber 13. The optical fiber 13b coated with the cured coating resin layer 16b is wound up by a winding device (not shown) as an optical fiber through a guide roller, a capstan, a dancer roller, and the like.

  A part of the water adhering to the surface of the uncured coating resin layer 16a is evaporated in the subsequent manufacturing process, but a part of the moisture is absorbed into the cured coating resin layer 16b. The moisture absorbed in the coating resin layer accelerates the hydrolysis reaction of the silane coupling agent added in the coating resin, and then undergoes a dehydration condensation reaction for bonding with the glass fiber, The coating resin layer 16b is firmly adhered.

FIG. 2 is a graph showing the results of testing the relationship between the humidity around the outlet side of the coating resin coating die 15 (periphery through which the optical fiber passes) and the dynamic fatigue coefficient (Nd) of the optical fiber. The water droplets sprayed in a mist form had a particle size of about several μm or more and a maximum particle size of about 100 μm, and the humidity was set by changing the spray amount of the water droplets. The dynamic fatigue coefficient (Nd) was measured by a test method defined in IEC 60793-1-33 established by IEC (International Electrotechnical Commission). Moreover, the measured value of Nd was measured when 30 days passed after the production of the optical fiber.
The optical fiber used for the measurement is a single-mode glass fiber having an outer diameter of 125 μm and is coated with two layers of an ultraviolet curable urethane acrylate resin to which a silane coupling agent is added as a coating resin material.

  According to this test result, when the humidity on the outlet side of the die 15 is less than 70%, it is difficult to make the Nd value 20 or more. To make the Nd value 25 or more, the outlet side humidity of the die 15 is 70%. It turned out that it was necessary to become above. That is, it has been found that it is preferable to spray mist-like water droplets so that the humidity on the outlet side of the die 15 is 70% or higher.

FIG. 3 shows the supply of moisture that promotes hydrolysis of the silane coupling agent in the glass fiber and the coating resin before and after the coating resin is applied (on the die inlet side). It is a figure which shows the result of having tested the breaking strength (tensile speed of 5 mm / min).
According to this test result, when moisture is supplied before the coating resin indicated by the dotted line is applied (method of Patent Document 1), the breaking strength decreases when the humidity is increased (water supply is increased). On the other hand, when moisture was supplied after applying the coating resin indicated by the solid line (the method of the present invention), it was found that the breaking strength increases when the humidity is increased.

  The reason for the above result is considered to be that when moisture is supplied on the inlet side of the die, moisture adheres directly to the glass fiber surface and cracks are likely to occur. Therefore, even if the adhesion between the glass fiber and the coating resin layer is improved, the occurrence of cracks that cause breakage increases, and breakage is likely to occur. On the other hand, when moisture is supplied on the outlet side of the die as in the present invention, the moisture does not directly adhere to the surface of the glass fiber, so that the occurrence of cracks is considered not to increase.

  FIG. 5 is a diagram showing a variation result of Nd depending on the maximum particle diameter of water droplets sprayed in a mist form. For comparison with and without water droplets, the test was performed without water droplets and in a sprayed state where the maximum particle size of water droplets was 10 μm, 50 μm, and 100 μm.

FIG. 4 is an example of the particle size distribution of the mist sprayed water droplets used in the present invention. The particle size distribution (dotted line) with the maximum particle size of the mist sprayed water droplets being 50 μm and the maximum particle size It is the figure which showed the particle size distribution (solid line) made into the diameter of 100 micrometers. The data of the water droplet size of 50 μm or less and 100 μm or less in FIG. 5 is sprayed with the particle size distribution of the water droplet shown in FIG.
If the particle size of the water droplet is too small, there is a possibility that it will not evaporate or bounce due to the latent heat of the optical fiber, and if it is too large, the particle size may be crushed and become solidly wetted .

  From this test result, when water droplets are not sprayed, the dynamic fatigue coefficient (Nd) is difficult to be 20 or more, but Nd can be improved by applying moisture to the uncured coating resin layer at the die outlet. There was found. However, it has been found that when the maximum particle size of the water droplet is 10 μm, it is difficult to make it 25 or more even if Nd can be improved somewhat. This is considered to be because when the water droplet has a particle diameter of less than 10 μm, even if the water droplet comes into contact with the coating resin layer, it is difficult to evaporate or repel and adhere, and sufficient moisture is not provided.

  When the maximum particle size of the water droplets was 50 μm or less and 100 μm or less, the final Nd could be improved to about 27. Therefore, it is possible to set Nd to 25 or more by setting at least the maximum particle size to be 50 μm to 100 μm (45 μm to 110 μm when the variation is ± 10%).

  However, when the maximum particle size of the water droplet is 50 μm, it takes about 40 days for the Nd to reach the saturation value, whereas when the maximum particle size of the water droplet is 100 μm, the Nd is saturated. The value is reached in about 20 days. That is, when the maximum particle size of the water droplet is 50 μm to 100 μm, even if the same Nd value is finally obtained, the larger water droplet maximum particle size can reach the predetermined Nd value earlier. 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 with which coating resin layer is uncured, 13b ... Optical fiber with which coating resin was hardened, 14 ... Cooling device, DESCRIPTION OF SYMBOLS 15 ... Die for coating resin application, 16 ... Coating resin, 16a ... Uncured coating resin layer, 16b ... Cured coating resin layer, 17 ... Coating resin supply apparatus, 18 ... Spray nozzle, 19 ... Water droplet, 20 ... UV irradiation device.

Claims (3)

After drawing a glass fiber from an optical fiber preform, a method for producing an optical fiber, in which a surface of the glass fiber is coated with an ultraviolet curable coating resin to which a silane coupling agent is added,
After the coating resin was applied to the surface of the glass fiber by a die to form an uncured coating resin layer, it was sprayed on the surface of the coating resin layer before the coating resin layer was cured. A method of manufacturing an optical fiber, characterized in that water droplets contact and adhere.   The optical fiber manufacturing method according to claim 1, wherein the humidity on the outlet side of the die is set to 70% or more by the water droplets sprayed in the form of mist.   The method for producing an optical fiber according to claim 2, wherein the maximum particle diameter of the water droplets sprayed in the form of mist is 45 µm to 110 µm.

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