JPH0559850B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing a quartz glass pipe with a low water content and a smooth inner wall. The quartz glass pipe obtained according to the present invention can be suitably used as a glass for cladding of an optical fiber base material. Furthermore, it can be suitably used as a cladding glass for a single mode fiber, which requires an extremely low water content. (Prior Art) Conventionally, as a method for manufacturing a base material for a quartz-based glass tube or an optical fiber, there is a so-called external method as disclosed in Japanese Patent Application Laid-open No. 73522/1983. This method uses a rotating refractory starting material (called a mandrel) such as carbon, quartz glass, or alumina.
Fine particulate glass (hereinafter referred to as soot) such as SiO ₂ produced by flame hydrolysis reaction of raw materials such as SiCl ₄ is deposited on the outside of the mandrel, and after a predetermined amount has been deposited, the deposition is stopped and the mandrel is pulled out. The obtained pipe-shaped soot body is sintered in a high-temperature electric furnace to melt and vitrify it to obtain pipe-shaped glass. (Problems to be Solved by the Invention) However, the above method has the disadvantage that the inner wall of the soot is easily scratched after the mandrel is pulled out, and it is difficult to obtain a smooth inner wall of the sintered glass tube. . In addition, in order to prevent the soot internal wall from being scratched, the temperature of the flame is set high during the soot deposition process, increasing the bulk density of the soot body and depositing soot on the mandrel, which makes it difficult to pull out the mandrel. Moreover, subsequent dehydration treatment becomes difficult. The present invention relates to an improvement of the above-mentioned method, and aims to overcome the above-mentioned drawbacks and provide a method for producing a quartz-based glass tube having a smooth inner wall and an extremely low water content. (Means for Solving the Problems) The present invention involves depositing fine particulate glass produced by a flame hydrolysis reaction of a vapor phase glass forming raw material on a starting material to form a deposit, and then depositing the starting material from the deposit. In the method of obtaining a transparent glass tube by drawing out a pipe-shaped deposited body and heat-treating the pipe-shaped deposited body, a lubricant containing boron nitride as a main component is applied to the surface of the starting material before depositing the fine-grained glass. This is a method for manufacturing a glass tube whose main component is quartz, which is characterized by applying a coating. In a particularly preferred embodiment of the present invention, about 1
The above method in which the bulk density of the cm-thick part is deposited in the range of 0.2 to 0.7 g/ ^cm3 , the above method in which the deposited body (soot body) is substantially pure silica glass fine particles, and the heating of the pipe-shaped soot body Examples include the above-mentioned method for obtaining a transparent quartz glass tube containing F by carrying out the treatment in an atmosphere containing fluorine. Furthermore, the present invention involves depositing fine particulate glass produced by flame hydrolysis reaction of vapor phase glass forming raw materials onto a starting material whose surface has been previously coated with a lubricant containing boron nitride as a main component, and then forming a deposit. After drawing out the starting material from the deposit and forming it into a pipe, the pipe-shaped deposit is heat-treated to form a transparent glass tube mainly composed of quartz, and the inside of the glass tube has a higher refractive index than that of the glass tube. The present invention relates to a method for producing glass containing quartz as a main component for an optical fiber base material, which is characterized by inserting and integrating a transparent glass rod. The present invention makes it easier to pull out the mandrel after soot deposition by applying a lubricant containing boron nitride as a main component to the surface of the mandrel before depositing soot on the mandrel, which is a starting material, in the so-called external deposition method. Its purpose is to smooth the internal walls of the body. The lubricant used in the present invention is preferably one containing an inorganic compound as a main component because it is stable even under high temperature conditions caused by the flame during soot deposition. This is because even if an organic compound is applied, the mandrel is heated to 500 to 700° C. or higher by the flame during soot deposition, so the organic compound is decomposed and volatilized. In the present invention, a lubricant containing boron nitride as a main component is used for the following reasons. As lubricants containing inorganic compounds as a main component, for example, boron nitride-based, graphite-based, molybdenum sulfide-based lubricants, etc. are relatively easily available. Among them, boron nitride
BN is preferable because it has a sublimation point of 3000°C or higher and is sufficiently stable even at high temperatures. On the other hand, graphite-based lubricants tend to oxidize due to the oxygen and heat generated by the flame during soot deposition and become CO or CO ₂ and easily volatilize, and may not be effective. Molybdenum sulfide lubricants are thermally stable and are effective when used solely for the purpose of making it easier to pull out the mandrel. However, the contamination of metal impurities into the resulting pipe-shaped soot or transparent quartz pipe may pose a problem. Boron nitride does not suffer from the above problems and is a preferred lubricant. The present invention will be specifically explained using figures. FIG. 2 is a diagram showing an example of a method for depositing soot on a mandrel, in which 1 is a chuck of a rotary lifting device;
2 is a mandrel. Reference numeral 3 denotes a quartz glass sleeve which is used to hold the soot body during subsequent drawing of the mandrel or heat treatment of the pipe-shaped soot body. 4 is a reaction vessel, 6 is an oxyhydrogen burner, and gas phase raw materials for glass synthesis are stored in this burner 6.
SiCl ₄ , O ₂ , H ₂ , etc. are introduced. Soot 8 is generated within the flame 7 and is deposited on the mandrel 2. 9 is a soot deposit body, and the mandrel 2 is gradually pulled up while being rotated by the chuck 1. A soot deposit 9 is formed in the axial direction from the upper part. In the present invention, a lubricant is applied on the mandrel 2 in advance. The material of the mandrel is
quartz glass, silicon carbide, carbon, alumina,
Any heat-resistant material such as zirconia may be used. As mentioned above, a boron nitride-based lubricant is preferable because it is thermally stable and does not introduce metal impurities into the product. Among these, the lubricant can be easily applied by spraying a fine powder of boron nitride dispersed with Freon gas to form a chip on the mandrel. It is effective when the thickness of the lubricant layer is about 0.1 mm or less. When soot is deposited on a mandrel coated with this lubricant, the bulk density of the soot body is
It is desirable that it be 0.2 g/cm ³ or more. Here. The bulk density refers to the average value of a layer approximately 1 cm thick near the mandle. This is because if it is less than 0.2 g/cm ³ , cracks are likely to occur during the soot deposition process. By using a lubricant, the mandrel can be easily pulled out as long as the bulk density of the soot body is set to 0.2 g/cm ³ or more and the occurrence of cracks during soot deposition is suppressed. However, in order to sufficiently remove the OH groups or moisture remaining in the pipe-shaped soot body during the subsequent heat treatment, the bulk density must be 0.7 g/cm ³
The following is desirable. Note that FIG. 1 shows the cross-sectional structure of the soot body formed in this manner. 2 is a mandrel 9 is a soot body, and 10 is a thin layer of lubricant. The soot body is then dehydrated and further sintered to obtain a transparent glass tube. The lubricant layer on the inner wall of the transparent glass tube is washed away, for example, by immersing it in an HF solution and removing the inner glass layer. Note that if the heat treatment for dehydration and sintering of the soot body is performed in a fluorine atmosphere, a glass tube whose main component is fluorine-doped quartz can be obtained. Alternatively, by heating from the outside while flowing a fluorine compound gas into the hollow part, the inner wall of the tube is polished by the fluorine in the gas phase, and the viscosity is reduced by the heat, making it smooth. As the fluorine compound gas, for example, CCl ₂ F ₂ , CF ₄ , SF ₆ etc. are used, among which
SF ₆ is desirable because of its high etching speed. A specific method is, for example, inserting the obtained sintered body into a furnace at 1700° C. and treating it with SF ₆ at 500 c.c./min for 15 minutes. (Example) Example 1 A quartz rod with an outer diameter of 20 mm and a length of 600 mm was prepared as a mandrel, and boron nitride fine particles were applied to this by a thickness of approximately 50 μm by spraying using Freon gas, and then a second It was held in chuck 1 of the device shown in the figure. A quartz glass tube with a length of 150 mm, an outer diameter of 23 mm, and a wall thickness of 1.45 mm was fixed to the upper end of the mandrel 2 as a sleeve 3, and soot was deposited using a burner for soot synthesis installed on the side of the sleeve tube 3. I started. mandrel 2
By rotating at 30 rpm and pulling upward at a speed of 40 mm/hr, the outer diameter of the mandrel 2 is 110 mm.
A soot body 9 having a diameter of φ was formed. At this time, the raw materials shown in Table 1 were charged into the soot synthesis burner 6.

[Table] When the length of the soot body 9 reached 550 mm, the raw material was stopped and left at room temperature for about 1 hour, and then the mandrel was pulled out by applying force between the mandrel 2 and the quartz glass sleeve tube 3. The average bulk density of this soot body was 0.3 g/cm ³ .
The obtained pipe-shaped soot body was dehydrated in an electric furnace under the atmospheric conditions shown in Table 2 and further sintered to obtain a transparent glass tube.

[Table] This glass tube was measured at 2.7 μm using an infrared spectrophotometer.
When the amount of residual OH was measured by measuring the absorbance of OH, the amount was less than 0.1 ppm, which was below the detection sensitivity of the device. The resulting glass tube is immersed in a 25% HF solution for about 3 hours, removing about 10 μm of the glass layer on the inner surface and washing off the lubricant on the inner surface, resulting in an outer diameter of 48 mmφ, inner diameter of 10 mmφ, and length with no scratches on the inner surface.
A 20 cm pure quartz glass tube was obtained. A 3 mmφ quartz glass rod containing 4% by weight of GeO ₂ prepared separately by the VAD method was inserted into the pure quartz glass tube, and when heated and melted to coalesce, a refractive index distribution as shown in FIG. 3 was obtained. A preform for single mode fiber was obtained. n ₀ is the refractive index of pure silica glass, n ₁
The relative refractive index difference between and n ₀ was 0.3%, and the lengths of a and b were 3 mm and 45 mm, respectively. The preform was drawn to have an outer diameter of 125 mmφ, and the increase in OH absorption loss at a wavelength of 1.38 μm was 5 dB/Km.
Transmission loss at 1.3μm and 1.55μm is 0.55dB/Km,
The loss was relatively low at 0.28dB/Km. Example 2 A pipe-shaped soot body was prepared in the same manner as in Example 1, dehydrated under the conditions shown in Table 3, and further made transparent.

[Table] At this time, SF ₆ is the residual OH in the pipe-shaped soot.
In addition to the effect of removing groups, F is added to the glass and has the effect of lowering the refractive index. Under the conditions in Table 2, approximately 1% by weight of F is added, and the refractive index is 0.3 compared to pure quartz.
%descend. The residual OH groups in the glass tube thus obtained were measured using an infrared spectrophotometer and were found to be 0.1 ppm or less, which was below the detection limit, as in Example 1.
The size of the glass tube obtained was the same as in Example 1. This glass tube was subjected to the same HF treatment as in Example 1, and then a pure silica glass rod was inserted into the glass tube, which was separately produced by the VAD method, and then heated and melted to form a single mode fiber preform having the refractive index distribution shown in Figure 4. I got it. The relative refractive index difference between n ₂ and n ₀ was 0.3%, and a was 3 mm and b was 45 mm. The preform was drawn to have an outer diameter of 125 mmφ, and the increase in OH loss at 1.38 μm was measured to be 4.5 dB/Km, and the transmission loss at 1.3 μm and 1.55 μm was 0.48 dB/Km and 0.24 dB/Km, respectively. It was something. (Effects of the Invention) In the present invention, by applying a lubricant containing boron nitride as a main component to the mandrel surface before soot deposition, the mandrel can be easily pulled out after soot deposition, which improves productivity. Since the resulting glass tube inner wall is smooth and has a low moisture content, a high-quality glass tube can be obtained, and if used for manufacturing a glass fiber preform, an excellent optical fiber or single mode optical fiber can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a soot body obtained by the method of the present invention, Fig. 2 is a diagram illustrating an embodiment of the present invention, and Fig. 3 is a cross-sectional view of a soot body obtained by the method of the present invention. A diagram showing the refractive index distribution of the preform,
FIG. 4 is a diagram showing the refractive index distribution of the single mode fiber preform obtained in Example 2 of the present invention.

Claims (1)

[Scope of Claims] 1. Particulate glass produced by flame hydrolysis reaction of a raw material for forming a vapor phase glass is deposited on a starting material to form a deposit, and then the starting material is drawn from the deposit to form a pipe shape. Later, in the method of heat-treating the pipe-shaped deposit to obtain a transparent glass tube, it is preferable to apply a lubricant containing boron nitride as a main component to the surface of the starting material before depositing the particulate glass. A method for manufacturing glass tubes whose main component is quartz. 2 The deposition of fine particulate glass has a bulk density of 0.2 g/cm ³ in the approximately 1 cm thick part of the deposit near the starting material.
The method for manufacturing a glass tube containing quartz as a main component according to claim 1, wherein the amount is in the range of 0.7 g/cm ³ or less. 3. A method for producing a glass tube containing quartz as a main component according to claim 1 or 2, wherein the deposited body is made of substantially pure particulate quartz glass. 4. The pipe-shaped deposit is heated in an atmosphere containing fluorine to obtain a transparent quartz glass tube containing fluorine, the main component of which is quartz according to any one of claims 1 to 3. Method of manufacturing glass tubes. 5 Fine particulate glass produced by a flame hydrolysis reaction of a vapor phase glass forming raw material is deposited on a starting material whose surface has been previously coated with a lubricant containing boron nitride as a main component to form a deposit, and then the deposit is After drawing out the above starting material and making it into a pipe shape, the pipe-shaped deposit is heat-treated to form a transparent glass tube mainly composed of quartz, and a transparent glass rod having a higher refractive index than the glass tube is placed inside the glass tube. 1. A method for producing glass containing quartz as a main component for use as a base material of optical fiber, which comprises inserting and integrating glass.