JP2013018669A - Method of manufacturing optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing an optical fiber having dynamic a fatigue coefficient Nd of not lower than 25 and reaching a specified value of the dynamic fatigue coefficient soon after drawing.SOLUTION: In the method of manufacturing an optical fiber in which glass fiber 13 is drawn from optical fiber base material 10, and a coating resin, which is an ultraviolet-curing type and added with a silane coupling agent, is thereafter coated on the surface of the glass fiber, a gas 17 containing water having a pH of 4.0-5.5 is supplied on the surface of the glass fiber 13 right before coating the coating resin 16 with a dice 15. In this case, the water content is preferably 0.004-0.008 kg/m.

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 surface of the glass fiber is coated with a coating 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 coating the outer surface of the drawn glass fiber (also referred to as a bare fiber) with an ultraviolet curable resin having an outer diameter of about 250 μm. 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. Also, when the drawing speed of the optical fiber is higher than 1500 m / min, after the coating resin is applied to the optical fiber, the exposure time to the atmosphere is extremely short, and moisture is contained in the resin before the coating resin is cured. It was difficult to capture.

On the other hand, for example, in Patent Document 1, a gas containing 0.008 kg / m ³ or more of moisture is supplied to the surface of the glass fiber immediately before the coating resin is applied to the glass fiber. It is disclosed to improve the adhesion to the layer.
In Patent Document 2, the dynamic fatigue coefficient (Nd) is set to 18 or more by setting the pH of the coating resin layer (primary coating layer) in contact with the glass fiber surface of the optical fiber to 4.5 or less. It is disclosed. Patent Document 3 also discloses that the dynamic fatigue coefficient (Nd) is 18 or more by setting the pH of the entire coating layer of the optical fiber strand to 5.5 or less.

JP 2000-34137 A JP 2003-4993 A JP 2005-55779 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 the above Patent Document 1, before coating with a coating resin, a gas containing 0.008 kg / m ³ or more of moisture is supplied to the surface of the glass fiber, thereby increasing the adhesion between the glass fiber and the coating resin layer. However, there is no disclosure of how much Nd is thereby obtained. Further, since cracks are generated when moisture directly adheres to the surface of the glass fiber, if too much moisture is contained, the breaking strength may be lowered.

  Patent Document 2 discloses that the primary coating layer in contact with the glass fiber is acidified to make Nd 18 or more, and Patent Document 3 includes the entire primary and secondary coating layers. Although it has been disclosed that Nd is 18 or 20 or more by making the coating layer acidic, there is no disclosure of specific data, and it is quite appropriate to develop a new coating resin material. Development costs are required.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide an optical fiber manufacturing method in which the dynamic fatigue coefficient Nd is 25 or more and a predetermined dynamic fatigue coefficient value is quickly obtained 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. And the gas containing the water | moisture content of pH 4.0-5.5 is supplied to the surface of the glass fiber just before apply | coating coating resin with a die | dye, It is characterized by the above-mentioned.
Further, the water content is preferably 0.004 kg / m ^{3 to} 0.008 kg / m ³ .

  According to the present invention, before the coating resin of the optical fiber is applied, moisture that promotes hydrolysis of the silane coupling agent in the coating resin is effectively supplied to the glass fiber surface without reducing the breaking strength. In addition, the dynamic fatigue coefficient Nd can be 25 or more, and a predetermined dynamic fatigue coefficient can be obtained at an early stage 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 elapsed days and dynamic fatigue coefficient (Nd) at the time of changing the water pH and water content in this invention. It is a figure which shows the relationship between moisture content and breaking strength at the time of changing pH of the water | moisture content in 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 coating, 16 is a coating resin, 16a is an uncured coating resin layer, 16b is a cured coating resin layer, 17 is a gas containing moisture at pH 4.0 to 5.5, 18 is a spray nozzle, 19 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, when the glass fiber 13 passes through the die 15, the coating resin 16 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, the acidity of pH 4.0 to 5.5 is applied to the surface of the glass fiber 13 immediately before the UV curable coating resin 16 is applied to the outer periphery of the glass fiber 13, that is, between the cooling device 14 and the die 15. A gas containing water is supplied. In order to adjust the pH of the moisture contained in the gas to 4.0 to 5.5, it is appropriate to use carbon dioxide gas (CO ₂ ) or the like.

  A form of supplying moisture-containing gas to the glass fiber 13 may be such that the glass fiber 13 is exposed to a high-humidity environment (in a mist state) in which water droplets float in a mist form. For example, as shown in FIG. 1, a glass fiber 13 is sprayed with a water-containing gas 17 from a spray nozzle 18, or as disclosed in Patent Document 1, a glass fiber 13 is filled with a water-containing gas. You may make it pass.

  Next, the glass fiber 13 with moisture on the surface is coated with an ultraviolet curable coating resin 16 on the outer surface by passing through a die 15. Moisture applied to the surface of the glass fiber 13 is taken into the uncured coating resin layer 16a formed by coating. 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 13a covered 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.

The moisture taken into the coating resin layer promotes 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. If this adhesion is weak, the dynamic fatigue coefficient (Nd) of the optical fiber is small, and if the adhesion is strong, it becomes large.

  In the present invention, the moisture is made acidic at pH 4.0 to 5.5, but the reaction of the silane coupling material can be promoted by making it acidic. As described above, when moisture directly adheres to the surface of the glass fiber, cracks may occur and the breaking strength may be reduced. However, by making the water acidic, the amount of water for obtaining the same effect is reduced. Therefore, it is considered that the dynamic fatigue coefficient can be increased without sacrificing the breaking strength. Although carbon dioxide is taken as an example of the gas for making the water acidic, blowing carbon dioxide directly on the die also has the effect of preventing bubbles from being mixed between the glass fiber and the coating resin layer. .

FIG. 2 (A) shows that the moisture content of the moisture-containing gas supplied to the surface of the glass fiber is constant (0.005 kg / m ³ ) and the moisture pH (4.0, 5.0, 5.5) is changed. It is a figure which shows the change with respect to the elapsed days of the dynamic fatigue coefficient (Nd) at the time. Nd was measured by a test method defined in IEC 60793-1-33 established by IEC (International Electrotechnical Commission).

  Nd increased at any tested water content, and after 40 days, Nd was almost constant at about “27”, but in the case of water at pH 5.5, it reached a predetermined Nd value. The time until was slow. On the other hand, in the case of moisture at pH 4.0, the predetermined Nd value was reached relatively early. From this result, if the amount of moisture contained in the gas is the same, even if the Nd value that finally becomes constant is almost the same, the time when the moisture pH is smaller reaches the predetermined Nd value earlier. There was found.

  If the pH of the water is less than 4.0, the acidity of the water-containing gas becomes strong, and corrosion of the equipment and devices tends to occur. Therefore, in the present invention, the pH of the water is 4.0 or more. Further, when the pH exceeds 5.5, as is apparent from the test results, it takes a long time to reach the predetermined Nd value, and there is a possibility that the predetermined Nd may not be reached. .5 or less.

In FIG. 2B, the water content (0.005 kg / m ³ , 0.008 kg / m ³ ) was changed with the water pH of the water-containing gas supplied to the surface of the glass fiber being constant (5.5). It is a figure which shows the change with respect to the elapsed days of Nd at the time. For comparison, the case where gas was supplied without moisture was also tested. As a result, it was found that without water supply, the reached value of Nd was about “20”, and it was difficult to increase Nd further.

In contrast, Nd can be increased by exposing the glass fiber to a moisture-containing gas. In this case, it has been found that when the moisture content of the moisture-containing gas is larger, the time to reach the predetermined Nd is earlier and the value of Nd is also increased. However, it has also been found that even if the water content is changed from 0.005 kg / m ³ to 0.008 kg / m ³ , the Nd value that finally becomes constant is about “27”, and there is no significant difference.

  FIG. 3 is a diagram showing the results of testing the relationship between the breaking strength of the optical fiber and the moisture content of the moisture-containing gas. The pH of the moisture (4.0, 5.5, 6.0, 7.0) is shown in FIG. Tested differently. As a result, there is no significant difference in the breaking characteristics between pH 4.0 and pH 5.5, and there is not much difference between pH 6.0 and pH 7.0, but as the moisture moves from acidic to weakly acidic / neutral, it breaks. The strength tends to decrease somewhat. From this result, it can be said that the pH of the moisture-containing gas is preferably in the range of 4.0 to 5.5.

It was also found that at any pH, the breaking strength sharply decreased when the water content was around 0.009 kg / m ³ . From this result, the water content of the water-containing gas is preferably 0.008 kg / m ³ or less. Further, if the water content is too low, it will not be evaporated or bounced due to the latent heat of the optical fiber, etc., and the effect of increasing Nd will be reduced. Therefore, it is preferably specified at 0.004 kg / m ³ or more.

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, 16a ... uncured coating resin layer, 16b ... hardened coating resin layer, 17 ... gas containing water of pH 4.0-5.5, 18 ... spray nozzle, 19 ... UV Irradiation device.

Claims (2)

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,
A method for producing an optical fiber, characterized in that a gas containing water having a pH of 4.0 to 5.5 is supplied to the surface of the glass fiber immediately before the coating resin is applied by a die. 2. The method of manufacturing an optical fiber according to claim 1, wherein the moisture content is 0.004 kg / m ^{3 to} 0.008 kg / m ³ .

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