JP2020055721A - Method of manufacturing glass body for optical fiber - Google Patents

Abstract

To provide a method of manufacturing a glass body for optical fiber in which the glass body for optical fiber to which chlorine is sufficiently added can be efficiently manufactured.SOLUTION: The present invention relates to a method of manufacturing a glass body for optical fiber including: a dehydration treatment process of performing a dehydration treatment on a porous glass body in a reactor core pipe; and a sintering process of heating, with a heater, and sintering the porous glass body to obtain the glass body for optical fiber. In the dehydration treatment process, the gas in the reactor core pipe is discharged through an exhaust pipe connected to the reactor core pipe while a dehydration treatment gas including a chlorine-based gas is supplied into the reactor core pipe, and the dehydration treatment process includes a pre-dehydration treatment process of using a first chlorine-based gas as the chlorine-based gas, and a post-dehydration treatment process of using a second chlorine-based gas as the chlorine-based gas. The second chlorine-based gas has higher reactivity to the porous glass body in the post-dehydration treatment process than that of the first chlorine-based gas to the porous glass body in the pre-hydration treatment process.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for manufacturing a glass body for an optical fiber.

In general, a glass body for an optical fiber is produced by subjecting a porous glass body produced by a VAD (Vapor-phase Axial Deposition) method or the like to a dehydration treatment, followed by sintering to a transparent vitrification treatment. In order to reduce the loss of the optical fiber, it is preferable to use silica (SiO ₂ ) for the core. In this case, the outside of the core, the cladding obtained by adding fluorine is downdopant to SiO ₂ is provided, the glass body for optical fiber includes a core portion made of SiO _2, a fluorine SiO ₂ at the outside It is composed of the cladding part added. However, in this case, the viscosity of the clad portion decreases, and the viscosity difference between the core portion and the clad portion increases. For this reason, tensile stress concentrates on the core portion when drawing the glass body for an optical fiber, and Rayleigh scattering increases in the core of the obtained optical fiber. Therefore, in the optical fiber glass body, while maintaining the relative refractive index difference between the core and the cladding, the amount of fluorine added to the cladding is reduced to reduce the viscosity difference between the core and the cladding. In some cases, chlorine as an updopant is added to the core. Further, the glass body for an optical fiber may be composed of only a core portion or only a clad portion, and chlorine may be added to the core portion or the clad portion.

As a method of manufacturing a glass body for an optical fiber to which chlorine is added, a manufacturing method described in, for example, Patent Document 1 below is conventionally known. According to the document, a porous glass body is disposed in a core tube of a dehydration sintering apparatus, and a dehydration gas obtained by mixing silicon tetrachloride (SiCl ₄ ) and an inert gas is supplied into the core tube. Is exhausted through an exhaust pipe connected to a core tube, followed by a dehydration treatment, followed by a transparent vitrification treatment (sintering treatment) to produce a glass body for an optical fiber.

JP-A-10-53423

  However, the method for manufacturing a glass body for an optical fiber described in Patent Document 1 has the following problems, although chlorine can be sufficiently added to the glass body for an optical fiber.

That is, in the method for manufacturing a glass body for an optical fiber described in Patent Document 1, SiCl ₄ supplied at the time of dehydration treatment reacts with moisture adhering to the surface of the porous glass body to generate SiO ₂ powder. However, the SiO ₂ powder floats in the atmosphere and mixes with the exhaust gas, and it becomes easy to close the exhaust pipe in a short period of time. As a result, it is necessary to stop the dehydrating and sintering device for replacement and cleaning of the exhaust pipe, and the number of optical fiber glass bodies that can be continuously manufactured is reduced, and the optical fiber glass body can be manufactured efficiently. Disappears.

Here, in order to suppress the blockage of the exhaust pipe, instead of SiCl ₄ as the dehydration processing gas supplied to the core tube during the dehydration processing of the porous glass body, the reactivity with respect to the porous glass body is reduced. It is also conceivable to use a low chlorine-based gas (for example, chlorine). However, in this case, chlorine cannot be sufficiently added to the glass body for optical fibers.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing an optical fiber glass body that can efficiently manufacture an optical fiber glass body sufficiently doped with chlorine.

  In order to solve the above problems, the present invention provides a dehydration treatment step of dehydrating a porous glass body in a furnace tube, and a firing step of heating the porous glass body with a heater and sintering to obtain an optical fiber glass body. A method of manufacturing a glass body for an optical fiber, the method further comprising: supplying a dehydration processing gas containing a chlorine-based gas into the core tube in the dehydration step, while supplying the gas in the core tube to the core tube. Exhausted through an exhaust pipe connected to the chiller, wherein the dehydration step includes a pre-dehydration step using a first chlorine-based gas as the chlorine-based gas, and a post-dehydration step using a second chlorine-based gas as the chlorine-based gas In the post-dehydration step, the reactivity of the second chlorine-based gas with respect to the porous glass body is increased by the first chlorine-based gas with respect to the porous glass body in the pre-dehydration step. Higher than refractory, it is a manufacturing method for an optical fiber glass body.

According to the method for manufacturing a glass body for an optical fiber of the present invention, in the pre-dehydration treatment step of the dehydration treatment step, the reactivity of the first chlorine-based gas with respect to the porous glass body is different from the reactivity of the porous glass body in the post-dehydration treatment step. Since the reactivity is lower than the reactivity of the second chlorine-based gas, the concentration of SiCl ₄ generated by the reaction between the porous glass body and the first chlorine-based gas decreases. Therefore, even if the generated SiCl ₄ reacts with moisture adhering to the surface of the porous glass body in the pre-dehydration process, the concentration of the generated SiO ₂ powder also decreases. Therefore, even if the gas in the furnace tube is exhausted through the exhaust tube, the blockage of the exhaust tube is sufficiently suppressed. In the post-dehydration treatment step, the reactivity of the second chlorine-based gas with respect to the porous glass body is higher than the reactivity of the first chlorine-based gas with the porous glass body. Chlorine can be sufficiently added. At this time, SiCl ₄ is generated by the reaction between the porous glass body and the second chlorine-based gas. At this time, the moisture attached to the surface of the porous glass body in the pre-dehydration treatment step has been sufficiently removed. . For this reason, the concentration of the SiO ₂ powder generated by the reaction between SiCl ₄ and the moisture attached to the surface of the porous glass body becomes sufficiently low. Therefore, even if the gas in the furnace tube is exhausted through the exhaust tube, the blockage of the exhaust tube is sufficiently suppressed. As described above, according to the glass body for an optical fiber of the present invention, a glass body for an optical fiber to which chlorine is sufficiently added can be efficiently produced.

  In the method for producing a glass body for an optical fiber, the second chlorine-based gas is different from the first chlorine-based gas, and the second chlorine-based gas includes a temperature of the heater and a partial pressure ratio to the dehydration gas. A gas having a higher reactivity with the porous glass body than the first chlorine-based gas when the same conditions are applied to the first chlorine-based gas and the second chlorine-based gas. Preferably, there is.

  In this case, chlorine can be effectively added to the glass body for optical fibers.

  In the method of manufacturing a glass body for an optical fiber, the second chlorine-based gas is preferably the same as the first chlorine-based gas.

  In this case, since the second chlorine-based gas is the same as the first chlorine-based gas, it is not necessary to switch the chlorine-based gas from the first chlorine-based gas to the second chlorine-based gas in the dehydration process. Therefore, the trouble of switching the chlorine-based gas can be omitted, and the glass body for optical fiber can be easily manufactured.

  In the method for producing a glass body for an optical fiber, in the case where the second chlorine-based gas is the same as the first chlorine-based gas, the pre-dehydration treatment step and the post-dehydration treatment step include: It is preferable that a partial pressure ratio of the chlorine-based gas is different, and a partial pressure ratio of the second chlorine-based gas to the dehydration processing gas is larger than a partial pressure ratio of the first chlorine-based gas to the dehydration processing gas.

In this case, in the post-dehydration treatment step, the concentration of the chlorine-based gas in the dehydration treatment gas increases, so that the reactivity of the chlorine-based gas with respect to the porous glass body is made higher than the reactivity of the chlorine-based gas in the pre-dehydration treatment step. Can be. In addition, since the increase in the relative refractive index difference with respect to SiO ₂ is generally proportional to the increase in the 1 / 4th power of the partial pressure ratio of the chlorine-based gas, the partial pressure ratio of the chlorine-based gas in the post-dehydration process is determined by the pre-dehydration process. By making the partial pressure ratio higher than the chlorine-based gas partial pressure ratio in the process, the refractive index of the obtained optical fiber glass body can be easily adjusted.

  In the method for manufacturing a glass body for an optical fiber, when the second chlorine-based gas is the same as the first chlorine-based gas, the temperature of the heater is reduced in the pre-dehydration process and the post-dehydration process. Differently, it is preferable that the temperature of the heater in the post-dehydration process is higher than the temperature of the heater in the pre-dehydration process.

  In this case, in the post-dehydration treatment step, the chlorine-based gas in the dehydration treatment gas is heated to a higher temperature, so that the activity of the chlorine-based gas is further increased. For this reason, the reactivity of the chlorine-based gas with respect to the porous glass body can be made higher than the reactivity of the chlorine-based gas in the pre-dehydration treatment step.

  In the method for manufacturing a glass body for an optical fiber, the first chlorine-based gas is preferably chlorine.

In this case, among the chlorine-based gases, chlorine has relatively low reactivity with the porous glass body, and the concentration of SiCl ₄ generated by the reaction between the porous glass body and the first chlorine-based gas is particularly low. Therefore, even if the generated SiCl ₄ reacts with the moisture adhered to the surface of the porous glass body in the pre-dehydration process, the concentration of the generated SiO ₂ powder also becomes lower. Therefore, even if the gas in the furnace tube is exhausted through the exhaust tube, the blockage of the exhaust tube is more sufficiently suppressed.

In the present invention, “reactivity with the porous glass body” refers to the ability of the porous glass body to increase the relative refractive index difference at a wavelength of 632.8 nm with respect to SiO _2, and the porous glass in the post-dehydration treatment step. Whether the reactivity with respect to the body is higher than the reactivity with respect to the porous glass body in the pre-dehydration treatment step depends on the relative refractive index difference of the optical fiber glass body with respect to SiO _{2 at} a wavelength of 632.8 nm after the pre-dehydration treatment step. The determination can be made based on whether or not the difference is larger than the relative refractive index difference at a wavelength of 632.8 nm of the porous glass body with respect to SiO ₂ . Here, the relative refractive index difference is defined as follows.
Relative refractive index difference ^{_{= (n 1 2 -n 2 2}} ) / 2n 1 2
(In the formula, _{n 1} is the refractive index of the porous glass body at a wavelength of 632.8 nm, _{n 2} is the refractive index of SiO ₂ at a wavelength of 632.8 nm)
The “reactivity with the porous glass body” can be changed by changing not only the type of the chlorine-based gas but also the partial pressure ratio and the temperature of the chlorine-based gas.

  In the present invention, the “chlorine gas” refers to a gas containing a chlorine atom.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the glass body for optical fibers which can manufacture efficiently the glass body for optical fibers to which chlorine was fully added is provided.

FIG. 1 is a schematic cross-sectional end view showing an example of a dehydration sintering apparatus for carrying out a method for manufacturing a glass body for optical fibers of the present invention.

  Hereinafter, an embodiment of the method for manufacturing a glass body for optical fibers of the present invention will be described in detail.

  First, prior to description of an embodiment of a method for manufacturing a glass body for optical fibers of the present invention, a dehydration sintering apparatus for performing the method for manufacturing a glass body for optical fibers of the present invention will be described with reference to FIG. FIG. 1 is a schematic cross-sectional end view showing an example of a dehydration sintering apparatus for carrying out the method for producing a glass body for optical fibers of the present invention.

  As shown in FIG. 1, the dehydration sintering apparatus 100 includes a furnace tube 1 for accommodating a porous glass body P, and a heating furnace 2 surrounding the furnace tube 1. The furnace tube 1 has a furnace tube body 1a and a lid 1c for closing an upper end opening 1b of the furnace tube body 1a. An insertion hole 1d for inserting a support rod 4 for suspending the porous glass body P is formed in the lid 1c. A connecting portion 5 for suspending the porous glass body P is attached to a lower end of the support rod 4, and the connecting portion 5 is connected to the porous glass body P. The furnace tube 1 has a gas supply port 1e for supplying a dehydration processing gas containing a chlorine-based gas and an exhaust port 1f for exhausting the gas in the furnace tube 1. An exhaust pipe 3 is connected to the exhaust port 1f, and the exhaust pipe 3 is provided with an exhaust gas treatment device (not shown).

  The heating furnace 2 includes an outer wall portion 2a, a heater chamber 2b between the outer wall portion and the furnace tube 1, and a heater 2c disposed in the heater room 2b and surrounding the furnace tube 1. I have.

  Next, an embodiment of a method of manufacturing a glass body for an optical fiber using the dehydrating and sintering apparatus 100 will be described.

  In the method for manufacturing a glass body for an optical fiber of the present embodiment, first, a porous glass body P is prepared. Here, the porous glass body P includes, for example, a soot portion and a glass rod serving as a dummy extending from both ends of the soot portion. Then, after raising the support rod 4 to a position (not shown) at which the porous glass body P can be attached, the prepared porous glass body P is hung on the support rod 4 via the connection part 5. By lowering the support rod 4 downward, the porous glass body P is accommodated in the furnace tube 1, and the lid 1 c closes the upper end opening 1 b of the furnace tube body 1 a.

  Next, the porous glass body P is subjected to a dehydration treatment in the core tube 1 (a dehydration treatment step).

  Next, the porous glass body P is sintered to obtain an optical fiber glass body (sintering step).

  In the dehydration process, the gas in the core tube 1 is discharged through an exhaust pipe 3 connected to an exhaust port 1 f of the core tube 1 while supplying a dehydration process gas containing a chlorine-based gas into the core tube 1. Exhaust to processing equipment. In the dehydration process, a pre-dehydration process using a first chlorine-based gas as a chlorine-based gas is performed, and then a post-dehydration process using a second chlorine-based gas as a chlorine-based gas is performed. Then, in the post-dehydration treatment step, the reactivity of the second chlorine-based gas with respect to the porous glass body P is made higher than the reactivity of the first chlorine-based gas with the porous glass body P.

According to the method for manufacturing a glass body for an optical fiber of the present embodiment, in the pre-dehydration treatment step of the dehydration treatment step, the reactivity of the first chlorine-based gas with respect to the porous glass body P is equal to the second reactivity with respect to the porous glass body P. Since the reactivity is lower than the chlorine-based gas, the concentration of SiCl ₄ generated by the reaction between the porous glass body P and the first chlorine-based gas is reduced. Therefore, even if the generated SiCl ₄ reacts with the moisture in the atmosphere in the pre-dehydration process, the concentration of the generated SiO ₂ powder also decreases. Therefore, even if the gas in the furnace core tube 1 is exhausted through the exhaust pipe 3, the blockage of the exhaust pipe 3 is sufficiently suppressed. In the post-dehydration process, the reactivity of the second chlorine-based gas with respect to the porous glass body P is higher than the reactivity of the first chlorine-based gas with the porous glass body P. Chlorine can be sufficiently added to the body. At this time, SiCl ₄ is generated by the reaction between the porous glass body P and the second chlorine-based gas. At this time, in the pre-dehydration treatment step, water adhered to the surface of the porous glass body P is sufficiently removed. Have been. For this reason, the concentration of the SiO ₂ powder generated by the reaction between SiCl ₄ and the moisture attached to the surface of the porous glass body P is sufficiently low. Therefore, even if the gas in the furnace core tube 1 is exhausted through the exhaust pipe 3, the blockage of the exhaust pipe 3 is sufficiently suppressed. As described above, according to the glass body for an optical fiber of the present invention, a glass body for an optical fiber to which chlorine is sufficiently added can be efficiently produced.

  Next, the dehydration step and the sintering step will be described in detail.

(A) Dehydration Step The dehydration step is a step of dehydrating the porous glass body P in the core tube 1. The dehydration process includes the pre-dehydration process and the post-dehydration process, as described above.

The dehydration processing gas further includes an inert gas as a carrier gas in addition to the chlorine-based gas. The inert gas may be used, for example He, Ne, Ar, etc. _{N 2.}

(Porous glass body)
The porous glass body P can be obtained by a soot method such as a VAD method or an external method. In the soot method, a porous glass body P is obtained as follows. That is, first, a dummy rod having a shape connectable to the connection portion 5 at the lower end of the support rod 4 and a glass rod on which glass fine particles are deposited are welded in advance. Then, a burner is installed, and a glass raw material gas such as SiCl ₄ is supplied into a flame reacted by flowing an oxygen gas, a hydrogen gas, and an inert gas through the burner, and glass particles are generated on a rotating glass rod. . Thus, a porous glass body P is obtained.

  The porous glass body P may be constituted by a core portion and a clad portion outside the core portion, may be constituted only by the core portion, or may be constituted only by the clad portion.

The porous glass body P contains, for example, SiO ₂ .

(Pre-dehydration treatment step)
In the pre-dehydration treatment step, a first chlorine-based gas is used as the chlorine-based gas. As the first chlorine-based gas, for example, chlorine, thionyl chloride (SOCl ₂ ), SiCl ₄ , carbon tetrachloride (CCl ₄ ), or the like can be used.

Among them, chlorine is preferable as the first chlorine-based gas. In this case, OH groups on the surface of the porous glass body P and moisture attached to the surface are removed by the following equations (1) and (2).

2SiOH (porous glass body P) + Cl ₂ → 2Si—Cl + 2HCl + O ₂ (1)
2H ₂ O + 2Cl ₂ → 4HCl + O ₂ (2)

On the other hand, chlorine causes the following reaction (3) with the porous glass body P.

SiO ₂ (porous glass body P) + 2Cl ₂ → SiCl ₄ + O ₂ (3)

The SiCl ₄ generated at this time reacts with H ₂ O in the atmosphere by the following formula (4) to generate SiO ₂ powder.

SiCl ₄ + 2H ₂ O → SiO ₂ (powder) + 4HCl (4)

However, among the chlorine-based gases, chlorine has low reactivity with the porous glass body P, and the concentration of SiCl ₄ generated by the reaction between the porous glass body P and the first chlorine-based gas (reaction of the formula (3)). Is particularly low. Therefore, even if the generated SiCl ₄ reacts with moisture adhering to the surface of the porous glass body P in the pre-dehydration process, the concentration of the generated SiO ₂ powder also becomes lower (Equation (4)). )reference). Therefore, even if the gas in the furnace core tube 1 is exhausted through the exhaust pipe 3, the blockage of the exhaust pipe 3 is more sufficiently suppressed.

  The partial pressure ratio (R1) of the first chlorine-based gas to the dehydration processing gas is not particularly limited, but is preferably 0.01 or more. In this case, the porous glass body P can be more efficiently dehydrated than when the partial pressure ratio R1 is less than 0.01.

  The partial pressure ratio R1 is more preferably 0.25 or more.

  The temperature of the heater 2c is not particularly limited as long as it is a temperature lower than the sintering temperature of the porous glass body P and a temperature capable of dehydrating OH groups on the surface of the porous glass body P and moisture attached to the surface. However, from the viewpoint of promoting the diffusion of the first chlorine-based gas into the porous glass body P, the temperature is preferably 1000 ° C. or higher. However, the temperature of the heater 2c is preferably 1200 ° C. or lower from the viewpoint of promoting the diffusion of the first chlorine-based gas into the porous glass body P and sufficiently suppressing the softening of the porous glass body P.

(Post-dehydration treatment step)
In the post-dehydration treatment step, a second chlorine-based gas is used as the chlorine-based gas. As the second chlorine-based gas, for example, SOCl ₂ , SiCl ₄ , CCl ₄ or the like can be used. In the present embodiment, a gas different from the first chlorine-based gas is used as the second chlorine-based gas. In this case, when the temperature of the heater 2c and the partial pressure ratio with respect to the dehydration processing gas are the same as those of the first chlorine-based gas and the second chlorine-based gas, the second chlorine-based gas is used for the first chlorine-based gas. It is preferable that the gas has a higher reactivity with the porous glass body P than the system gas. In this case, chlorine can be effectively added to the glass body for optical fibers. For example, when using chlorine as the first chlorine-based gas, SOCl ₂ , SiCl ₄ , CCl ₄ or the like can be used as the second chlorine-based gas. When the temperature of the heater 2c and the partial pressure ratio with respect to the dehydration processing gas are the same, the reactivity of the chlorine-based gas with the porous glass body P is １ ／ of the partial pressure ratio of the chlorine-based gas. The slope of a straight line indicating the relationship between the power and the relative refractive index difference of the optical fiber glass body with respect to SiO ₂ can be used as an index.

  Although the partial pressure ratio (R2) of the second chlorine-based gas to the dehydration treatment gas depends on the type of the second chlorine-based gas, it cannot be specified unconditionally. For example, when the second chlorine-based gas is thionyl chloride, It is preferably 0.03 or more. In this case, chlorine can be more efficiently added to the porous glass body P than when the partial pressure ratio R2 is less than 0.03.

  For example, when the second chlorine-based gas is thionyl chloride, the partial pressure ratio R2 is more preferably 0.05 or more.

  However, the partial pressure ratio R2 is a partial pressure ratio at which the partial pressure of the second chlorine-based gas is the same as the saturated vapor pressure of the second chlorine-based gas at the temperature of the pipe for supplying the second chlorine-based gas into the reactor core tube 1. It is preferably smaller than Ra. In this case, unlike the case where the partial pressure ratio R2 is equal to or higher than Ra, when the second chlorine-based gas is supplied into the reactor core tube 1 through the pipe, dew condensation of the second chlorine-based gas can be suppressed in the pipe, Corrosion and deterioration of the piping due to condensation can be sufficiently suppressed. When the partial pressure ratio R2 is smaller than Ra, a predetermined amount of the second chlorine-based gas can be supplied into the reactor core tube 1.

  The temperature of the heater 2c is not particularly limited, but is preferably 1100 ° C. or higher from the viewpoint of more sufficiently adding chlorine to the porous glass body P. However, the temperature of the heater 2c is preferably 1200 ° C. or less from the viewpoint of promoting the diffusion of the second chlorine-based gas into the porous glass body P and sufficiently suppressing the softening of the porous glass body P. .

(B) Sintering Step The sintering step is a step of sintering the porous glass body P to obtain an optical fiber glass body. In the sintering step, a sintering gas is supplied from the gas supply port 1 e into the furnace tube 1, and the gas in the furnace tube 1 is discharged through an exhaust pipe 3 connected to an exhaust port 1 f of the furnace tube 1. Exhaust to processing equipment. In the sintering step, after the porous glass body P having undergone the dehydration processing step is moved above the heater 2c, the lower end of the porous glass body P is arranged inside the heater 2c, and the porous glass body P is heated by the heater 2c. This can be performed by lowering while heating, or by heating the porous glass body P by the heater 2c without moving the porous glass body P that has undergone the dehydration process.

  In the sintering step, the temperature of the heater 2c is set to be equal to or higher than the sintering temperature of the porous glass body P. Here, the sintering temperature of the porous glass body P is a minimum value of the temperature of the heater 2c that can make the porous glass body P transparent vitrified. The sintering gas contains an inert gas.

  As the inert gas, for example, He, Ar, or the like can be used. The inert gas may be the same as or different from the inert gas used in the dehydration process.

The present invention is not limited to the above embodiment. For example, in the above embodiment, in the post-dehydration treatment step, a gas different from the first chlorine-based gas is used as the second chlorine-based gas, but the second chlorine-based gas may be the same as the first chlorine-based gas. In this case, in the post-dehydration treatment step, the partial pressure ratio (R2) of the second chlorine-based gas to the dehydration treatment gas needs to be larger than the partial pressure ratio R1 of the first chlorine-based gas. That is, the ratio of R2 to R1 must be greater than one. In this case, in the post-dehydration treatment step, the concentration of the chlorine-based gas in the dehydration treatment gas increases, so that the reactivity of the chlorine-based gas with respect to the porous glass body P is made higher than the reactivity of the chlorine-based gas in the pre-dehydration treatment step. be able to. In general, the increase in the relative refractive index difference with respect to SiO ₂ glass is proportional to the increase in the 1 / 4th power of the partial pressure ratio of the chlorine-based gas. By making the partial pressure ratio higher than the chlorine-based gas partial pressure ratio in the treatment step, the refractive index of the obtained optical fiber glass body can be easily adjusted.

  The ratio (R2 / R1) is not particularly limited as long as it is larger than 1, but is preferably 1.5 or more. In this case, chlorine can be more efficiently added to the porous glass body P than when the above ratio is less than 1.5. The ratio (R2 / R1) is more preferably 2.5 or more, and even more preferably 16.5 or more.

  Alternatively, when the second chlorine-based gas is the same as the first chlorine-based gas, in the post-dehydration process, the temperature (T2) of the heater 2c is set higher than the temperature (T1) of the heater 2c in the pre-dehydration process. You may. That is, the temperature ratio of T2 to T1 (T2 / T1) must be greater than one. In this case, in the post-dehydration treatment step, the chlorine-based gas in the dehydration treatment gas is heated to a higher temperature, so that the activity of the chlorine-based gas is further increased. For this reason, the reactivity of the chlorine-based gas with respect to the porous glass body can be made higher than the reactivity of the chlorine-based gas in the pre-dehydration treatment step.

  The temperature ratio is not particularly limited as long as it is larger than 1, but is preferably 1.08 or more. In this case, chlorine can be more efficiently added to the porous glass body P than when the temperature ratio is less than 1.08. In the temperature ratio (T2 / T1), T1 and T2 are absolute temperatures.

  However, the temperature ratio is preferably 1.16 or less. In this case, the blockage of the exhaust pipe 3 can be more sufficiently suppressed as compared with the case where the temperature ratio exceeds 1.16.

  Hereinafter, the content of the present invention will be described more specifically with reference to examples, but the present invention is not limited to the following examples.

(Examples 1 to 11)
First, a porous glass body P was produced as follows. That is, first, a dummy rod having a shape connectable to the connection portion 5 at the lower end of the support rod 4 and a glass rod on which glass fine particles were deposited were prepared in advance, and these were welded. Then, a burner is installed, and oxygen gas, hydrogen gas, and Ar gas, which is an inert gas, are flowed through the burner to supply SiCl ₄ as a glass raw material into the flame and react with the flame. A soot part was formed. At this time, the glass rod was made of SiO ₂ . Thus, a porous glass body P was obtained. The obtained porous glass body P was composed of a soot portion and a glass rod serving as a dummy extending from both ends of the soot portion.

  As for the obtained porous glass body P, the total length of the soot portion was 300 mm and the diameter was 30 mm. Then, after raising the support rod 4 to a position (not shown) where the porous glass body P can be attached, the prepared porous glass body P was hung on the support rod 4 via the connection part 5. By lowering the support rod 4 downward, the porous glass body P was accommodated in the furnace tube 1, and the upper end opening 1b of the furnace tube body 1a was closed by the lid 1c (see FIG. 1).

  Next, a dehydration step and a sintering step were sequentially performed on the porous glass body P by the dehydration and sintering apparatus 100.

  In the dehydration step, first, a pre-dehydration step was performed on the porous glass body P. Specifically, the porous glass body P was inserted inside the heater 2c by lowering the support rod 4. Then, a dehydration processing gas composed of the first chlorine-based gas shown in Table 1 and He as an inert gas is supplied into the furnace tube 1 at a flow rate of 3 L / min from the gas supply port 1e, while the inside of the furnace tube 1 is supplied. Was exhausted to the exhaust gas treatment device through the exhaust pipe 3 connected to the exhaust port 1f. At this time, the partial pressure ratio R1 of the first chlorine-based gas to the dehydration treatment gas was as shown in Table 1 as the partial pressure ratio of the first chlorine-based gas in the pre-dehydration treatment step. The partial pressure ratio R1 is a ratio of the partial pressure of the first chlorine-based gas when the pressure of the dehydration processing gas is set to 1. The temperature T1 of the heater 2c in the pre-dehydration process was as shown in Table 1.

  After 3 hours, a post-dehydration step was performed. Specifically, a dehydration gas consisting of the second chlorine-based gas and He as an inert gas shown in Table 1 was supplied into the furnace tube 1 at a flow rate of 3 L / min from the gas supply port 1e. At this time, the exhaust gas treatment apparatus was kept operating, and the gas in the reactor core tube 1 was exhausted to the exhaust gas treatment apparatus through the exhaust pipe 3 connected to the exhaust port 1f. At this time, the partial pressure ratio R2 of the second chlorine-based gas to the dehydration treatment gas was set as shown in Table 1 as the partial pressure ratio of the second chlorine-based gas in the post-dehydration treatment step. The partial pressure ratio R2 is a ratio of the partial pressure of the second chlorine-based gas when the pressure of the dehydration processing gas is set to 1. The temperature T2 of the heater 2c in the post-dehydration process was as shown in Table 1.

  After the elapse of 3 hours and the completion of the dehydration treatment step, the sintering step was performed. Specifically, the porous glass body P was left as it was without moving, and the heater 2c was heated to 1450 ° C. and sintered. The sintering temperature of the porous glass body P was 1450 ° C. Thus, a glass body for an optical fiber having a total length of 150 mm was produced.

(Comparative Examples 1 to 8)
In the pre-dehydration step, the type of the first chlorine-based gas, the partial pressure ratio R1 and the temperature T1 are as shown in Table 1. In the post-dehydration step, the type of the second chlorine-based gas, the partial pressure ratio R2 and the temperature T2 of the heater 2c are set. As shown in Table 1, the same as in Example 1 except that the types of the first chlorine-based gas and the second chlorine-based gas, the partial pressure ratio R1 and the partial pressure ratio R2, and the temperature T1 and the temperature T2 were the same. Thus, a glass body for an optical fiber was produced.

[Evaluation]
The methods for producing the glass bodies for optical fibers of Examples 1 to 11 and Comparative Examples 1 to 8 were evaluated for the chlorine addition effect and the exhaust pipe blockage suppression effect as follows.

(Chlorine effect)
The refractive index at a wavelength of 632.8 nm of the optical fiber glass bodies obtained in Examples 1 to 11 and Comparative Examples 1 to 8 was measured, and the relative refractive index difference was calculated based on the following equation. Was used as an index of the chlorine addition effect. Table 1 shows the results.
Relative refractive index difference _{^{= (n 1 2 -n 2 2}} ) / 2n 1 2
(In the formula, _{n 1} is the refractive index of the optical fiber glass body at a wavelength of 632.8 nm, _{n 2} is the refractive index of SiO ₂ at a wavelength of 632.8 nm)
At this time, the acceptance criteria for the chlorine addition effect were as follows.

(Passing criteria) The relative refractive index difference of the glass body for optical fiber is 0.050% or more

The relative refractive index difference of the glass body for an optical fiber obtained in Comparative Example 3 (partial pressure ratio of chlorine as the first chlorine-based gas R1: 0.30, temperature T1: 1200 ° C.) was 0.041%. On the other hand, the relative refractive index differences of the glass bodies for optical fibers obtained in Examples 1 to 3 (partial pressure ratio of chlorine as the first chlorine-based gas R1: 0.30, temperature T1: 1200 ° C.) Since it was 0.050 to 0.080%, the reactivity of thionyl chloride (SOCl ₂ ), which is the second chlorine-based gas, was used in the pre-dehydration step in the post-dehydration steps of Examples 1 to 3. It can be seen that the reactivity is higher than the reactivity of chlorine as the first chlorine-based gas. The relative refractive index difference of the glass body for an optical fiber obtained in Comparative Example 5 (partial pressure ratio of thionyl chloride (SOCl ₂ ) as the first chlorine-based gas R1: 0.01, temperature T1: 1200 ° C.) 0.043%, whereas the light obtained in Examples 4 to 6 (partial pressure ratio of thionyl chloride (SOCl ₂ ) as the first chlorine-based gas R1: 0.01, temperature T1: 1200 ° C.). Since the relative refractive index difference of the glass body for fiber was 0.050 to 0.057%, in the post-dehydration treatment steps of Examples 4 to 6, thionyl chloride (SOCl ₂ ) as the second chlorine-based gas was used. It can be seen that the reactivity is higher than the reactivity of thionyl chloride (SOCl ₂ ), which is the first chlorine-based gas used in the pre-dehydration process. The relative refractive index difference of the optical fiber glass obtained in Comparative Example 7 (partial pressure ratio of thionyl chloride (SOCl ₂ ) as the first chlorine-based gas R1: 0.05, temperature T1: 1000 ° C.) 0.040%, whereas the optical fiber obtained in Example 7 (partial pressure ratio of thionyl chloride (SOCl ₂ ) as the first chlorine-based gas R1: 0.05, temperature T1: 1000 ° C.) Since the relative refractive index difference of the glass body was 0.057%, the reactivity of thionyl chloride (SOCl ₂ ), which is the second chlorine-based gas, in the post-dehydration treatment step It can be seen that the reactivity is higher than the reactivity of thionyl chloride (SOCl ₂ ), which is the first chlorine-based gas used in the above. Further, the relative refractive index difference of the glass body for an optical fiber obtained in Comparative Example 2 (partial pressure ratio of chlorine as the first chlorine-based gas: 0.30, temperature 1150 ° C.) was 0.040%. On the other hand, the relative refractive index difference of the glass body for optical fibers obtained in Examples 8 to 11 (partial pressure ratio of chlorine as the first chlorine-based gas R1: 0.30, temperature T1: 1150 ° C.) is 0.050. In the post-dehydration treatment steps of Examples 8 to 11, the reactivity of thionyl chloride (SOCl ₂ ), which is the second chlorine-based gas, was lower than that of the first dehydration treatment step. It can be seen that the reactivity is higher than that of chlorine, which is a chlorine-based gas.

(Exhaust pipe blockage suppression effect)
In Examples 1 to 11 and Comparative Examples 1 to 8, optical fiber glass bodies were continuously produced, and the number of optical fiber glass bodies continuously produced until the exhaust pipe was closed was measured. At this time, the number of glass bodies for optical fiber at this time was used as an index of the effect of suppressing the exhaust pipe from closing. Table 1 shows the results. At this time, the acceptance criteria of the exhaust pipe blockage suppression effect were as follows.

(Acceptance criteria) The number of glass bodies for optical fiber manufactured continuously is 20 or more.

  From the results shown in Table 1, it was found that the methods for manufacturing glass bodies for optical fibers of Examples 1 to 11 satisfied the acceptance criteria in terms of the chlorine addition effect and the exhaust pipe blockage suppression effect. On the other hand, it turned out that the manufacturing method of the glass body for optical fibers of Comparative Examples 1-8 does not satisfy the acceptance criteria in any of the chlorine addition effect and the exhaust pipe blockage suppression effect.

  From the above, it was confirmed that according to the method for producing a glass body for optical fibers of the present invention, a glass body for optical fibers to which chlorine was sufficiently added can be efficiently produced.

DESCRIPTION OF SYMBOLS 1 ... Core tube 2c ... Heater 3 ... Exhaust tube P ... Porous glass body

Claims (6)

A dehydration treatment step of dehydrating the porous glass body in the core tube;
Sintering by heating the porous glass body with a heater, a sintering step of obtaining an optical fiber glass body, a method for manufacturing an optical fiber glass body,
In the dehydration treatment step, while supplying a dehydration treatment gas containing a chlorine-based gas into the core tube, the gas in the core tube is exhausted through an exhaust pipe connected to the core tube,
The dehydration step includes a pre-dehydration step using a first chlorine-based gas as the chlorine-based gas, and a post-dehydration step using a second chlorine-based gas as the chlorine-based gas,
In the post-dehydration step, the reactivity of the second chlorine-based gas to the porous glass body is higher than the reactivity of the first chlorine-based gas to the porous glass body in the pre-dehydration step. A method for producing a glass body for an optical fiber.   The second chlorine-based gas is different from the first chlorine-based gas, and the second chlorine-based gas has a temperature of the heater and a partial pressure ratio with respect to the dehydration processing gas of the first chlorine-based gas and the second chlorine-based gas. The glass body for an optical fiber according to claim 1, wherein the glass body for an optical fiber is a gas having a higher reactivity with the porous glass body than the first chlorine-based gas when placed under the same conditions as the system gas. Manufacturing method.   The method for producing a glass body for an optical fiber according to claim 1, wherein the second chlorine-based gas is the same as the first chlorine-based gas.   In the pre-dehydration treatment step and the post-dehydration treatment step, the partial pressure ratio of the chlorine-based gas to the dehydration treatment gas is different, and the partial pressure ratio of the second chlorine-based gas to the dehydration treatment gas is The method for producing a glass body for an optical fiber according to claim 3, wherein the partial pressure ratio is higher than a partial pressure ratio of the first chlorine-based gas.   4. The temperature of the heater is different between the pre-dehydration step and the post-dehydration step, and the temperature of the heater in the post-dehydration step is higher than the temperature of the heater in the pre-dehydration step. 3. The method for producing a glass body for an optical fiber according to item 1.   The method for producing a glass body for an optical fiber according to any one of claims 1 to 5, wherein the first chlorine-based gas is chlorine.

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