JP7194301B2 - Manufacturing method of porous glass base material for optical fiber - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a porous glass base material for optical fibers using organic siloxane as a raw material.

An optical fiber preform is manufactured, for example, by externally depositing SiO ₂ fine particles by the OVD method or the like on a core base material manufactured by the VAD method or the like, and sintering the deposited SiO 2 particles. As a silicon compound raw material for externally depositing _SiO2 fine particles on a core base material, an organosilicon compound containing no Cl (chlorine) in the molecule may be used as a starting material for _SiO2 fine particles. Examples of such organosilicon compounds include octamethylcyclotetrasiloxane (OMCTS), a highly pure organosiloxane available on an industrial scale. Patent Document 1 discloses a technique of supplying OMCTS to a burner and synthesizing glass microparticles in an oxyhydrogen flame.

When OMCTS is used as a starting material, SiO ₂ fine particles are produced by the reaction represented by the following formula [Formula 1].

Thus, if a halogen-free organic siloxane represented by OMCTS is used as the silicon compound raw material supplied to the burner, hydrochloric acid is not discharged. For this reason, there is an advantage that the degree of freedom in handling manufacturing equipment materials and exhaust gas is high.

Deposition of SiO ₂ microparticles starting from organosiloxanes is carried out, for example, as follows.
First, an organic siloxane raw material liquid is introduced into a vaporizer while controlling the flow rate with a liquid mass flow controller. Subsequently, the raw material liquid injected from the raw material liquid nozzle is mixed with the carrier gas in the vaporizer, the raw material liquid is vaporized, and a gaseous raw material gas is generated. The source gas is mixed with oxygen gas downstream of the vaporizer to form a source mixed gas. The raw material mixed gas, combustible gas, and combustion supporting gas are fed to the burner, where the combustion reaction produces _SiO2 fine particles.

JP 2019-073406 A

The generated _SiO2 fine particles are deposited on the core matrix. After depositing a predetermined amount of _SiO2 fine particles, the raw material supply to the vaporizer is stopped. At this time, the material liquid is accumulated in the material liquid pipe and the material liquid nozzle downstream of the liquid mass flow controller, and polymerization occurs at the tip of the material liquid nozzle in the vaporizer heated to the boiling point or higher of the material liquid. It is easy to produce a substance and a gel-like substance.

The present invention has been made in view of the above problems, and its object is to remove the tip of the raw material liquid nozzle in the vaporizer while the raw material supply is stopped for organic siloxane raw materials represented by octamethylcyclotetrasiloxane (OMCTS). To prevent a polymerization product or a gel-like substance from being produced in a part.

That is, in order to solve the above problems, an apparatus for manufacturing a porous glass preform for an optical fiber according to the present invention includes a liquid mass flow controller for controlling the flow rate of an organic siloxane raw material liquid, and a mixture of the raw material liquid and a carrier gas. A vaporizer that vaporizes a raw material liquid into a mixed gas of a raw material gas and a carrier gas, a raw material liquid nozzle that ejects the raw material liquid into the vaporizer, and a carrier gas supply pipe that supplies the carrier gas into the vaporizer. , a raw material pipe that guides the raw material liquid supplied from the liquid mass flow controller to the raw material liquid nozzle, a burner that burns the mixed gas together with the combustible gas and the combustion supporting gas to generate _SiO2 fine particles, and the mixed gas to the burner A mixed gas supply pipe, an on-off valve provided on the flow path of the source liquid pipe, and a purge gas supply pipe for supplying the purge gas by joining the source liquid pipe between the on-off valve and the source liquid nozzle are provided.

The manufacturing apparatus according to the present invention may further include means for adjusting the flow rate of the purge gas supplied to the purge gas supply pipe. Also, means for adjusting the flow rate of the carrier gas supplied to the carrier gas supply pipe may be further provided.

The manufacturing apparatus according to the present invention may further include an oxygen gas supply pipe for joining the oxygen gas in the middle of the mixed gas pipe. In this case, when the flow rate of the purge gas supplied from the purge gas supply pipe is L _P , and the flow rate of the oxygen gas supplied from the oxygen gas supply pipe is L _O2 , the purge gas on-off valve is closed to stop the raw material supply. 3, the purge gas and the oxygen gas may be supplied from the purge gas supply pipe and the oxygen gas supply pipe so that L _O2 /L _P >14, respectively.

In the present invention, when the flow rate of the purge gas supplied from the purge gas supply pipe is L _P and the flow rate of the carrier gas supplied from the carrier gas supply pipe is L _C , the on-off valve is closed to stop the raw material supply. , the purge gas and the carrier gas may be supplied from the purge gas supply pipe and the carrier gas supply pipe so that L _C /L _P >10, respectively.

Further, the method for producing a porous glass preform for an optical fiber according to the present invention includes the step of controlling the flow rate of the raw material liquid of organic siloxane by means of a liquid mass flow controller; a step of leading the raw material liquid to the nozzle of the vaporizer; a step of ejecting the raw material liquid from the raw material liquid nozzle into the vaporizer; and a carrier gas, supplying the mixed gas to a burner, burning the mixed gas with the combustible gas and the supporting gas in the burner to generate _SiO2 fine particles, A step of depositing _SiO2 fine particles on the starting core preform to form a porous glass preform for optical fiber, and closing an on-off valve provided on the flow path of the raw material liquid pipe to stop the supply of the raw material liquid from the liquid mass flow controller. and a step of supplying the purge gas to the source liquid pipe from the purge gas supply pipe that merges between the on-off valve of the source liquid pipe and the source liquid nozzle.

The manufacturing method according to the present invention preferably further includes a step of additionally mixing oxygen gas into the mixed gas and supplying the mixed gas to the burner. In this case, when the flow rate of the purge gas supplied from the purge gas supply pipe is L _P and the flow rate of the oxygen gas to be additionally mixed is L _O2 , in the step of supplying the purge gas to the raw material liquid pipe, L _O2 /L _P > 14, the purge gas and the oxygen gas may be supplied respectively.

In the production method according to the present invention, the purge gas is supplied to the raw material liquid pipe, where L _P is the flow rate of the purge gas supplied from the purge gas supply pipe, and L _C is the flow rate of the carrier gas supplied into the vaporizer. , preferably the purge gas and the carrier gas are supplied such that L _C /L _P >10.

In the present invention, the carrier gas may be nitrogen, argon, or helium. Also, the organic siloxane is preferably octamethylcyclotetrasiloxane (OMCTS).

According to the present invention, it is possible to prevent the formation of a polymerization product or a gel-like substance at the tip of the raw material liquid nozzle for an organic siloxane raw material represented by octamethylcyclotetrasiloxane (OMCTS).

FIG. 2 is a supply flow diagram around a vaporizer in the apparatus for manufacturing a porous glass preform for optical fibers according to the present embodiment.

Embodiments of the present invention will be described in detail below, but the present invention is not limited to these.
FIG. 1 is a supply flow diagram around a vaporizer in an apparatus for manufacturing an optical fiber porous glass preform according to the present embodiment. A raw material liquid 101 stored in a raw material tank 100 is flow-controlled by a liquid mass flow controller 1 and supplied to a vaporizer 2 through raw material liquid pipes 101a and 101b. A raw material liquid 101 is ejected from the tip of the raw material liquid nozzle 3 in the vaporizer 2, and is made into fine droplets by a carrier gas 102 also introduced into the vaporizer 2 and heated. As a result, the raw material liquid 101 is vaporized into a mixed gas 103 in which the raw material gas and the carrier gas 102 are mixed. The mixed gas 103 is supplied to the burner 4 through a mixed gas pipe 103a. The mixed gas 103 is combusted with combustible gas 104 and combustion supporting gas 105 to produce _SiO2 fine particles. At this time, in order to promote the combustion of the raw material gas, the oxygen gas 106 supplied from the oxygen gas supply pipe 106a is joined in the middle of the mixed gas pipe 103a, and the oxygen gas 106 is mixed with the mixed gas and then supplied to the burner 4. may While generating the SiO ₂ fine particles in this manner, the burner 4 is relatively reciprocated along the starting core base material by a reciprocating means (not shown), thereby performing external deposition on the starting core base material.

式中、Ａ、Ｂ、およびＣは原料種に応じて求められた係数である。 The temperature of the vaporizer 2 is set from the viewpoint of efficiently vaporizing the raw material liquid 101 and preventing polymerization of the raw material liquid 101 . When using OMCTS as the organic siloxane raw material, it is preferable to set the temperature of the vaporizer 2 at a temperature of 160° C. or more and 220° C. or less. When the temperature is low, the vapor pressure of the raw material liquid is lowered, and when the temperature is lower than 160°C, the vaporization efficiency is significantly lowered. If the temperature exceeds 220° C., there is a possibility that the polymer originating from the raw material liquid 101 will precipitate especially in the vicinity of the raw material liquid nozzle 3 . Also, the mixed gas pipe 103a to the burner 4 arranged downstream of the vaporizer 2 is preferably heated to a temperature higher than the liquefying temperature of the raw material gas so that the raw material gas in the mixed gas 103 is not liquefied. The liquefaction temperature of the raw material gas can be obtained by experiments, or it can be calculated backward from the Antoine equation (equation (1)) using the raw material gas partial pressure Ps obtained from the pressure inside the pipe and the molar ratio of the raw material components in the mixed gas 103. , the liquefaction temperature T can be easily obtained.

In the formula, A, B, and C are coefficients determined according to the raw material species.

For example, when organic siloxane OMCTS is used as a raw material, the coefficients A = 8.8828, B = 1358.7, and C = 175.06 are known. T becomes 133°C. Note that the formula (1) is merely an empirical formula obtained by fitting data, and there is a possibility that the piping temperature may drop instantaneously or locally by several degrees Celsius under the influence of changes in the flow rate of the mixed gas 103 or the like. Therefore, in order to prevent reliquefaction of the raw material gas with a margin, the mixed gas pipe 103a is actually heated to a temperature higher than the liquefaction temperature T obtained by using the equation (1) by at least 20°C. is preferred. Further, when the temperature of the mixed gas pipe 103a exceeds 220°C, the polymer originating from the raw material tends to precipitate on the inner wall of the mixed gas pipe 103a. .

When the external deposition amount reaches a predetermined amount, the on-off valve 5 installed between the source liquid pipes 101a and 101b is closed to stop the supply of the source liquid. After that, the purge gas 107 is supplied from the purge gas supply pipe 107a that merges with the raw material pipe 101b on the downstream side of the on-off valve 5, and the raw material solution 101 accumulated in the raw material pipe 101b and the raw material solution nozzle 3 is purged to the vaporizer 2. . As the purge gas, it is preferable to use an inert gas that hardly reacts with the raw material liquid, such as nitrogen, argon, or helium.

It is preferable to continue supplying the carrier gas 102 into the vaporizer 2 even after the raw material liquid 101 is purged. By doing so, the purged raw material liquid evaporates in the vaporizer 2 to become raw material gas, which is accompanied by the carrier gas 102 and discharged to the burner 4 through the mixed gas pipe 103a. At this time, it is preferable to continue the combustion reaction by supplying the combustible gas 104 and the combustion supporting gas 105 to the burner 4 until all the purged raw material liquid evaporates. In this way, unreacted source gas can be prevented from condensing and fouling the inner wall of the deposition vessel. At this time, SiO ₂ fine particles ejected from the burner 4 due to the purged raw material liquid may be further deposited on the outer circumference of the porous glass base material.

After the supply of the raw material liquid 101 is temporarily stopped to complete the production of the base material, the on-off valve 5 is opened to produce the next base material and the supply of the raw material liquid 101 is restarted. It takes time to completely replace the purge gas remaining in the pipe 101b and the raw material liquid nozzle 3 . Therefore, it is preferable to minimize the volumes of the portions of the raw material pipe 101b and the raw material nozzle 3 that are purged with the purge gas. When OMCTS is used as a raw material, when the volume of the raw material liquid pipe 101b to be purged and the raw material liquid nozzle 3 is V ₁ [ml], and the full range flow rate of the raw material liquid mass flow controller is F [g/min], (0 .95×60×V ₁ )/F<10. More preferably, (0.95×60×V ₁ )/F<5. More preferably, (0.95×60×V ₁ )/F<1. 0.95 [g/ml] is the specific gravity of OMCTS at room temperature.

When generalized to raw materials other than OMCTS (where the specific gravity is S), it is preferable that (S × 60 × V ₁ )/F < 10, and (S × 60 × V ₁ )/F < 5. is more preferable, and (S×60×V ₁ )/F<1 is even more preferable.

In order to reduce the volume of the piping, the inner diameter of the raw material liquid piping may be narrowed, and the length of the raw material liquid piping may be shortened. When the inner diameter of the raw material liquid pipe is narrowed, the pressure loss increases and the raw material liquid supply during manufacturing is not affected. It is preferable to adjust the inner diameter and length of the raw material liquid pipe so that the pressure loss is 10 kPa or less. More preferably, the pressure loss is 5 kPa or less, and more preferably 1 kPa or less.

In this way, after stopping the supply of the raw material, the volume to be gas-purged becomes small. After controlling the flow rate by the liquid mass flow controller 1, the raw material is supplied to the burner 4 in a short time. Immediately after the raw material supply is started, the replacement time can be further shortened by temporarily increasing the flow rate supplied by the liquid mass flow controller (for example, by setting it to the full range).

When the source liquid 101 remaining in the source liquid pipe 101b and the source liquid nozzle 3 is purged after the deposition is finished and the source liquid supply is stopped, if the flow rate of the purge gas 107 is too large relative to the flow rate of the carrier gas 102, Liquefaction and incomplete combustion are likely to occur at the outlet of the burner 4. If liquefaction or incomplete combustion occurs, and unreacted raw material droplets adhere to the surface of the porous glass base material being manufactured, or if the density of the deposited soot layer locally decreases, this will be the starting point. It causes cracks in the base material. In liquefaction, the purged raw material liquid is not sufficiently vaporized in the vaporizer 2 and is discharged as droplets toward the burner 4, or the raw material components in the mixed gas are discharged to the burner 4 in a state of high concentration. It is produced by being condensed at a low temperature part near the burner 4 by being supplied. Incomplete combustion occurs when the flow rate of the oxygen gas 106 and the combustion support gas 105 supplied to the burner 4 is insufficient with respect to the raw material components in the mixed gas.

The source liquid 101 remaining in the source liquid pipe 101b and the source liquid nozzle 3 is pushed out by the purge gas 107 and ejected into the vaporizer 2, where it is vaporized. Since the volume of the raw material gas vaporized in the vaporizer 2 is approximately 100 times the volume of the supplied raw material liquid, the flow rate of the purge gas is adjusted so that the flow rate of the purge gas does not become excessively large relative to the flow rate of the carrier gas. It is preferable to flow by adjusting the flow rate. When the purge gas flow rate is L _P [SLM], the raw material liquid remaining in the raw material liquid pipe 101b and the raw material liquid nozzle 3 is pushed out by the purge gas at a flow rate of Q ₁ [g/min] according to Equation (2).
Q ₁ = 0.95 x 1000 x L _P (2)

Further, Lc [SLM] is the carrier gas flow rate, Ps [atm] is the saturated vapor pressure of the source gas (for example, vaporized _OMCTS ) at the vaporizer temperature TV [°C], P [atm] is the total pressure in the vaporizer, When the molecular weight of the raw material is M [g/mol], the raw material flow rate Q ₂ [g/min] is represented by the formula (3).

Assuming that the volumes of the raw material pipe 101b and the raw material nozzle 3 to be purged are V ₁ [ml], the raw material pushed out by the purge gas is at least during the period from when the purge gas starts to flow until 1000 V ₁ /L _P elapses. The purge gas flow rate Lp and the carrier gas flow rate Lc should be adjusted so as to satisfy the relationship Q ₁ <3×Q ₂ so that the vaporization of the gas does not become insufficient. Also, the saturated vapor pressure Ps [atm] of the raw material (for example, OMCTS) at the temperature T _V [° C.] in the vaporizer 2 can be obtained from Equation (1). As shown in FIG. 1, flow control means 6 may be provided in the source liquid pipe 101b and the purge gas supply pipe 107a for purging the source liquid nozzle 3. FIG. A regulating valve such as a needle valve may be used as the flow rate adjusting means 6, or a gas mass flow controller may be used. A pressure drop, such as an orifice, may be provided to regulate the front and back pressure. Assuming that the flow rate of the carrier gas is L _{C and} the volume of the source liquid pipe 101b and the source liquid nozzle 3 to be purged is V ₁ , at least the period from when the purge gas starts to flow until the time V ₁ /L _P elapses is L Preferably, _C is adjusted such that L _C /L _P >10, more preferably L _C /L _P ≧20. Moreover, it is preferable to further mix oxygen gas with the mixed gas discharged from the vaporizer 2 toward the burner 4 . Assuming that the flow rate of the oxygen gas to be mixed is L _O2 and the volume of the vaporizer 2 is V ₂ , at least the period from when the purge gas starts to flow until the time V ₂ /(L _C +L _P ) elapses is L Preferably, the flow rate is adjusted such that _O2 /L _P >14, more preferably L _O2 /L _P ≧23.

The raw material pipe 101b and the purge gas supply pipe 107a for purging the raw material nozzle 3 are preferably provided with an on-off valve 7 upstream of the flow control means 6, as shown in FIG. The on-off valve 7 is closed when the raw material liquid 101 is being supplied to the vaporizer 2, and is opened when the supply of the raw material is stopped and the gas is purged. By providing the on-off valve 7 upstream of the flow control means 6, when gas purging is performed, the pressure of the purge gas from the upstream starts to be applied to the flow control means 6 immediately after the on-off valve 7 is opened, and the flow rate of the purge gas gradually increases. . Therefore, it is easy to adjust L _C /L _P and L _O2 /L _P within predetermined ranges. Moreover, it is preferable to provide a check valve 8 downstream of the flow control means 6 . By providing the check valve 8, it is possible to prevent the raw material liquid 101 from flowing back into the purge gas supply pipe 107a while the raw material is being supplied. An on-off valve may be used instead of the check valve 8. In this case, the on-off valve should be opened when the raw material supply is stopped, and should be closed when the raw material is being supplied.

Since the on-off valve 5 is closed when the supply of the raw material is stopped, the raw material liquid 101 accumulated in the raw material liquid pipe 101a from the liquid mass flow controller 1 to the on-off valve 5 does not cause pressure fluctuations due to changes in the ambient temperature. In order to prevent this, it is preferable to provide a raw material liquid branch pipe 101c that branches in the middle of the raw material liquid pipe 101a. An on-off valve 9 is provided in the raw material liquid branch pipe 101c, and when the on-off valve 5 is closed to stop the raw material supply, the on-off valve 9 is opened. The end of the raw material liquid branch pipe 101c may be connected to the raw material tank 100 as shown in FIG. 1, or may be connected to a collection tank (not shown). Further, when the pressure in these tanks rises, a back pressure valve or the like may be used to release the pressure. Further, when the on-off valve 5 is opened to supply the raw material, the on-off valve 9 is closed so that the raw material liquid 101 is supplied only to the vaporizer 2 side.

[Example 1]
OMCTS was used as the organic siloxane raw material liquid 101 , nitrogen (N ₂ ) gas was used as the carrier gas 102 , hydrogen (H ₂ ) gas was used as the combustible gas 104 , and oxygen (O ₂ ) gas was used as the combustion support gas 105 . The combustion-enhancing gas 105 was supplied as a first combustion-enhancing gas and a second combustion-enhancing gas (both O ₂ gas) whose flow rates can be independently set. The first combustion-enhancing gas and the second combustion-enhancing gas were ejected from ejection ports different from each other in the burner. After finishing the external deposition, the source was flow-reduced to 0 g/min. On the other hand, gases other than the raw material continued to flow, and a plurality of burners were used to bake the deposition surface of the porous glass base material.

At this time , the flow rate Lc of the carrier gas 102 is 21 SLM, the flow rate L _O2 of the oxygen gas 106 additionally mixed with the mixed gas 103 of the raw material gas and the carrier gas 102 is 30 SLM, the combustible gas 104 is 250 SLM, and the first combustion support gas is 25 SLM and the second combustion support gas were set at 75 SLM and supplied respectively. As soon as the raw material flow rate became 0 g/min, the on-off valve 5 was closed and the on-off valve 9 was opened. After that, by opening the on-off valve 7, the raw material liquid 101 remaining in the raw material liquid pipe 101b and the raw material liquid nozzle 3 was purged from the purge gas supply pipe 107a. Nitrogen (N ₂ ) gas was used as the purge gas 107 and supplied at a flow rate L _P of 0.3 SLM. The temperature of the vaporizer 2 was set at 200°C. When purging was performed under the above conditions, incomplete combustion and liquefaction at the outlet of the burner 4 could be prevented. In addition, it was possible to prevent the formation of polymerization products and gel-like substances at the tip of the raw material liquid nozzle 3 .

[Example 2]
External deposition and quenching of the deposition surface were performed under the same conditions as in Example 1, except that the flow rate Lp of the purge gas 107 was set to 0.9 SLM. As a result, incomplete combustion and liquefaction at the outlet of the burner 4 during purging could be prevented. In addition, it was possible to prevent the formation of polymerization products and gel-like substances at the tip of the raw material liquid nozzle 3 .

[Example 3]
External deposition and quenching of the deposition surface were performed under the same conditions as in Example 1, except that the flow rate Lp of the purge gas 107 was set to 1.5 SLM. As a result, incomplete combustion occurred at the outlet of the burner 4 during purging. In addition, at the tip of the raw material liquid nozzle 3, it was possible to prevent the formation of a polymerization product and a gel-like substance.

[Example 4]
External deposition and quenching of the deposition surface were performed under the same conditions as in Example 1, except that the flow rate Lp of the purge gas 107 was 3.0 SLM. As a result, incomplete combustion and liquefaction occurred at the outlet of burner 4 during purging. In addition, at the tip of the raw material liquid nozzle 3, it was possible to prevent the formation of a polymerization product and a gel-like substance.

Table 1 shows the flow rate Lp of the purge gas 107, the flow rate L _O2 of the oxygen gas 106 additionally mixed with the mixed gas 103, and the flow rate Lc of the carrier gas 102 in each example and comparative example, and the incomplete combustion and liquefaction at that time. The presence or absence is shown.

As described above, in any of the embodiments, by purging the raw material liquid 101 with the purge gas 107 while the supply of the raw material is stopped, polymerization products and gelatinous substances are generated at the tip of the raw material liquid nozzle 3 in the vaporizer 2 . could be prevented from being generated. In addition, from the viewpoint of preventing liquefaction at the outlet of the burner 4, it was found that it is preferable to adjust L _C /L _P >10, and more preferably L _C /L _P ≧20. Moreover, from the viewpoint of preventing incomplete combustion, it was found that it is preferable to adjust the flow rate so that L _O2 /L _P >14, and more preferable to satisfy L _O2 /L _P ≧23.

1 Liquid mass flow controller 2 Vaporizer 3 Raw material liquid nozzle 4 Burner 5 On-off valve 6 Flow rate adjusting means 7 On-off valve 8 Check valve 9 On-off valve 10 Flow rate adjusting means 11 Flow rate adjusting means 101 Raw material liquid 102 Carrier gas 103 Mixed gas 104 Flammable Gas 105 Supporting gas 106 Oxygen gas 107 Purge gas 101a, 101b Source liquid pipe 101c Source liquid branch pipe 102a Carrier gas supply pipe 103a Mixed gas pipe 106a Oxygen gas supply pipe 107a Purge gas supply pipe

Claims (6)

a step of controlling the flow rate of the organic siloxane raw material liquid with a liquid mass flow controller;
a step of guiding the raw material liquid supplied from the liquid mass flow controller to a raw material liquid nozzle of a vaporizer through a raw material liquid pipe;
a step of ejecting the raw material liquid from the raw material liquid nozzle into the vaporizer;
a step of mixing the spouted raw material liquid and the carrier gas in the vaporizer to vaporize the raw material liquid into a mixed gas in which the raw material gas and the carrier gas are mixed;
supplying the mixed gas to a burner;
burning the mixed gas with a combustible gas and a combustion supporting gas in the burner to produce _SiO2 fine particles;
depositing the _SiO2 particulates on a starting core preform to form a porous glass preform for an optical fiber;
A step of stopping the supply of the raw material liquid from the liquid mass flow controller by closing an on-off valve provided on the flow path of the raw material liquid pipe while maintaining the supply of the carrier gas, the combustible gas, and the combustion-supporting gas. and
a step of supplying a purge gas to the source liquid pipe from a purge gas supply pipe joining between the on-off valve of the source liquid pipe and the source liquid nozzle;
A method for producing a porous glass preform for an optical fiber. 2. The manufacturing method according to claim 1 , further comprising a step of additionally mixing oxygen gas into the mixed gas and supplying the mixed gas to the burner. Let L _P be the flow rate of the purge gas supplied from the purge gas supply pipe, L _O2 be the flow rate of the oxygen gas to be additionally mixed, and in the step of supplying the purge gas to the raw material liquid pipe, L _O2 /L _P >14. 3. The manufacturing method according to claim 2 , wherein said purge gas and said oxygen gas are respectively supplied as follows. Let L _P be the flow rate of the purge gas supplied from the purge gas supply pipe, L _C be the flow rate of the carrier gas supplied into the vaporizer, and in the step of supplying the purge gas to the raw material liquid pipe, L _C /L _P 4. A method according to any one of claims 1 to 3 , characterized in that the purge gas and the carrier gas are supplied such that >10, respectively. 5. The manufacturing method according to any one of claims 1 to 4 , wherein the carrier gas is nitrogen, argon, or helium. 6. The manufacturing method according to any one of claims 1 to 5 , wherein the organic siloxane is octamethylcyclotetrasiloxane (OMCTS).

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