JP2010168243A - Method for producing glass pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a novel method capable of suppressing a decrease in ultraviolet light transmittance while maintaining high production efficiency in glass tube stretching.
SOLUTION: The pressure on the inner side 3 of the glass tubes 1 and 2 is kept higher than the pressure on the outer side 4, and in this state, the glass tube 1 is heated and softened and stretched to have a desired outer diameter, inner diameter and thickness. The glass tube 2 is formed. At least one atmosphere of the inner side 3 and the outer side 4 of the glass tubes 1 and 2 is an atmosphere mainly composed of a gas 7 that is chemically inert at a temperature at which the glass tubes 1 and 2 are heated and softened.
[Selection] Figure 1

Description

  The present invention relates to a method for manufacturing a glass tube. Specifically, for example, the present invention relates to an improvement in a drawing process when manufacturing a glass tube used as an ultraviolet light transmitting material.

In a drawing process for forming a glass tube used as an ultraviolet light transmitting material into a desired shape, the glass tube is usually heated and softened while keeping the inner pressure of the glass tube higher than the outer pressure, and the glass tube is stretched in this state. Are formed in a tubular body having an outer diameter, an inner diameter, and a thickness.
In recent years, high-purity quartz glass tends to be used as an ultraviolet light transmitting material.

Conventionally, discharge lamps that emit vacuum ultraviolet light having a wavelength of 200 nm or less have been used in photocleaning, photoetching, and the like. As a discharge lamp, a mercury lamp in which mercury or a rare gas is sealed in a glass tube made of synthetic quartz glass and emits vacuum ultraviolet light having a wavelength of 185 nm is known.
This type of mercury lamp has been promoted to increase the output in response to a request from a user, but there is a problem of countermeasures against heat accompanying the high temperature of the lamp. Furthermore, restrictions on the use of mercury have been demanded due to global environmental problems, and as a result, excimer lamps have attracted attention as ultraviolet light sources that can replace mercury lamps.

Further, as the miniaturization of semiconductor elements increases, excimer light sources are attracting attention from the viewpoint of resolution. KrF excimer light (emission center wavelength 248 nm), ArF excimer light (193 nm), ArCl excimer light (175 nm), F ₂ Development of a high-power ultraviolet light source having an emission center wavelength of 260 nm or less, such as excimer light (157 nm), is in progress.
In the optical material used for these light sources, if there is absorption in this wavelength range, a part of the light from the light source is absorbed by the optical material, and the optical material is damaged by the energy of the absorbed light. For example, there is a risk of causing a rapid decrease in light transmittance.
Under such circumstances, high-purity quartz glass is being widely used as an ultraviolet light transmitting material that is resistant to an excimer light source that is high-power vacuum ultraviolet light (for example, Patent Document 1: Japanese Patent Application Laid-Open No. 2005-306650, Patent Document 2: JP 2001-114529 A).

On the other hand, in order to efficiently manufacture a glass tube into a tubular body having a desired outer diameter, inner diameter, and thickness, it is necessary to lower the viscosity of the glass to an appropriate value. For this purpose, the heating temperature is appropriately increased. There is a need.
The same applies to the drawing processing of the quartz glass tube, and the viscosity of the glass can be increased by setting the heating temperature to 1700 ° C. or higher, specifically about 1750 to 2100 ° C., compared to 1700 ° C. or lower disclosed in Patent Document 1. Decreases, and the processing speed can be increased.

Further, in the glass tube stretching process, stretching is usually performed by pressurizing the inside of the glass tube to reduce the ratio between the outer diameter and the inner diameter of the glass tube (thinning). Conventionally, inexpensive nitrogen (N ₂ ) gas or air is used as the pressurized gas for pressurizing the inside of the glass tube (for example, Patent Document 3: Japanese Patent Laid-Open No. 62-162632, Patent Document 4: (See JP-A-02-296740, Patent Document 5: JP-A-7-109136, etc.)

JP 2005-306650 A JP 2001-114529 A Japanese Patent Laid-Open No. 62-162632 Japanese Patent Laid-Open No. 02-296740 JP-A-7-109136

However, when the glass is in a high temperature environment, nitrogen gas exhibits a reducing property with respect to the glass, and a reaction for extracting oxygen (O ₂ ) from the SiO ₂ network in the glass proceeds. For this reason, after the drawing process, an oxygen deficiency defect having an absorption peak at a wavelength of 163 nm is formed near the surface of the glass tube, resulting in a problem that the ultraviolet light transmittance is lowered. When air is used as the pressurized gas, nitrogen in the air causes a similar reaction, and oxygen deficiency defects are formed.

  In order to suppress the occurrence of oxygen-deficient defects, it may be possible to lower the heating temperature (for example, 1700 ° C. or lower) in the stretching process. However, in that case, since the glass is stretched with a high viscosity, a new problem arises that the processing speed is slowed and the production efficiency is lowered.

  The present invention has been made in view of such conventional circumstances, and the object of the process is to suppress a decrease in ultraviolet light transmittance while maintaining high manufacturing efficiency in the glass tube drawing process. It is to provide a novel method capable of

In order to achieve the above object, the present inventors have continued intensive research, and the reaction in which nitrogen gas contained in the atmosphere in the conventional drawing process extracts oxygen atoms from SiO ₂ on the glass surface is greatly activated. Focused on the existence of energy. And since the energy for exceeding the barrier of activation energy is supplied as thermal energy, it came to the conclusion that generation | occurrence | production of an oxygen excess defect becomes remarkable, so that heating temperature rises.
In other words, as long as the glass tube as the ultraviolet light transmitting material is stretched in an atmosphere containing nitrogen as in the prior art, it is difficult to increase the heating temperature and efficiently manufacture. Then, it has been found that it is useful for solving the problems of the present invention that the atmosphere of at least one of the inside and outside of the glass tube is a chemically inert atmosphere at a temperature at which the glass tube is heated and softened. The invention has been completed.

That is, in the method for producing a glass tube according to the present invention, the inner pressure of the glass tube is kept higher than the outer pressure, and in this state, the glass tube is heated and softened and stretched to form a tubular body having a desired shape. In the stretching process,
At least one of the inside and outside of the glass tube is characterized in that it is an atmosphere mainly composed of a chemically inert gas at a temperature at which the glass tube is heated and softened.
Here, the “chemically inert gas at the temperature at which the glass tube is heated and softened” does not contain nitrogen.

As the inert gas, for example, any one of He, Ne, and Ar, or two or more of them, or one or more of them Examples thereof include a mixed gas in which an inert gas and oxygen (O ₂ ) are mixed.

In the conventional drawing process, the inside of the glass tube is often pressurized with nitrogen gas or air, and the outside of the glass tube is often nitrogen gas. However, as mentioned above, when subjected to a heat process to a quartz glass or the like, when a high temperature atmosphere, the nitrogen is a reduced resistance to SiO _2, pull the oxygen atoms from SiO _2, a chemical reaction that produces the nitrogen oxides Is easy to progress. When such a chemical reaction proceeds, a Si—Si type oxygen deficiency defect having an absorption peak at a wavelength of 163 nm is formed on the surface of the glass.
On the other hand, as in the present invention, an atmosphere mainly containing a chemically inert gas at a temperature at which the glass tube is heated and softened, for example, any one of inert gases of He, Ne, and Ar, Alternatively, when two or more of these inert gases are used as the atmosphere, the above-described chemical reaction is suppressed, and formation of Si—Si type oxygen deficiency defects can be suppressed.

Further, when a mixed gas of any one of He, Ne, and Ar and oxygen (O ₂ ) is used as the inert gas, the mixing ratio of the oxygen is 0.01 mol% in terms of a molar ratio. When it is above, a preferable result can be obtained as compared with the case where the ratio is less than 0.01 mol%.
Moreover, even if the mixing ratio of the oxygen (O ₂ ) exceeds 10 mol% in terms of molar ratio, there is no significant difference in effect compared to the case where the mixing ratio is 10 mol% or less.
Therefore, when a mixed gas of any one of He, Ne, and Ar and oxygen (O ₂ ) is used as the inert gas, a preferable mixing ratio of the oxygen is 0.01 to It is in the range of 10 mol%.

  The present invention can be preferably used for producing a quartz glass tube as an ultraviolet light transmitting material. In order to obtain a quartz glass tube having a wide ultraviolet light transmission wavelength range, it is more preferable to use fluorine-added quartz glass.

When applied to a quartz glass tube of ultraviolet light transmitting material, it is preferable that the light transmittance of the glass tube after stretching is from 60% or more to a wavelength of 170 nm to 400 nm. In particular, it is preferable that the light transmittance at a wavelength of 163 nm is 75% or more, more desirably 80% or more, and particularly desirably that there is substantially no absorption peak at a wavelength of 163 nm. Furthermore, it is preferable that the average concentration in the thickness direction of the Si—Si type oxygen-deficient defect having an absorption peak at a wavelength of 163 nm of the glass tube after the stretching is 1 × 10 ¹⁶ cm ⁻³ or less.

The absorption cross section of absorption at a wavelength of 163 nm is σ = 6.0 × 10 ⁻¹⁷ cm ² (refer to the literature K. Awazu, et al., J. Appl. Phys., 69 (1991) 4183). The concentration can be calculated.

By forming a chemically inert atmosphere at the temperature at which the glass tube is heated and softened, the heating temperature can be set to 1700 ° C. or higher. Therefore, the viscosity of the glass is lowered and the processing speed can be increased.
That is, it is preferable that the heating temperature in the stretching step is 1700 ° C. or higher because high production efficiency is maintained. Furthermore, the heating temperature is preferably 1750 ° C. or higher, more preferably 1800 ° C. or higher. However, if the heating temperature is 2200 ° C. or higher, stretching proceeds due to the weight of the glass, making it difficult to perform stretching in an internally pressurized state. For this reason, it is preferable that heating temperature shall be 2100 degrees C or less.

The cross-sectional area of the glass tube before stretching is preferably 30 cm ² or more. Here, the cross-sectional area is a cross-sectional area when the glass tube is cut perpendicularly to the axial direction (when cut into a circle).
The larger the cross-sectional area of the glass tube as a starting material before stretching, the higher the temperature applied to the glass, and therefore it is more susceptible to the influence of the environmental atmosphere. The relationship between the glass cross-sectional area, glass viscosity (glass temperature), and tension when the glass tube is stretched is expressed by a viscous body uniaxial viscous deformation formula. Therefore, the heating temperature can be set higher as the cross-sectional area of the glass tube increases.
Therefore, the larger the cross-sectional area of the glass tube, the more remarkable the effect that at least one of the atmosphere inside and outside the glass tube is chemically inert at the temperature at which the glass tube is heated and softened.

If the cross-sectional area of the glass tube before stretching is less than 30 cm ² , the above-described advantages cannot be obtained, which is not preferable.

As described above, the present invention is excellent in ultraviolet light transmittance because the glass tube is stretched in an atmosphere mainly composed of a chemically inert gas at a temperature at which the glass tube is heated and softened. A glass tube can be manufactured efficiently.
In particular, when used for manufacturing a glass tube made of quartz glass, an excellent ultraviolet light transmitting material can be manufactured at low cost.
Furthermore, since the ultraviolet absorption edge of fluorinated quartz glass has a shorter wavelength shift compared to quartz glass without fluorine addition, it can provide many effects such as providing a quartz glass tube with a wide ultraviolet light transmission wavelength range. Have.

The simplified diagram which shows an example of embodiment of this invention.

Hereinafter, exemplary embodiments will be described.
In FIG. 1, the outline of the extending | stretching process in the manufacturing method of the glass tube which concerns on this invention is shown.
In the figure, 1 is a glass tube before stretching (starting material before stretching), and 2 is a glass tube after stretching formed in a tubular body having a desired outer diameter, inner diameter, and thickness. These glass tubes 1 and 2 are heated and softened by heating means 5 and 5 such as heaters while keeping the pressure of the inner side 3 higher than the pressure of the outer side 4, and are stretched by the stretching rolls 6 and 6 in this state.

As the glass tube 1 serving as a starting material before stretching, a glass tube made of quartz glass generally used for ultraviolet light is used. The quartz glass tube 1 is manufactured by a method usually used in this kind of field.
For example, first, a glass fine particle deposit is manufactured using a soot method in which SiCl ₄ is hydrolyzed in a flame. It is also possible to use siloxane or the like as a raw material. Next, the quartz glass base material is obtained by inserting the glass particulate deposit into a sintering furnace and making it transparent. When obtaining fluorine-added quartz glass with excellent ultraviolet light transmission, fluorine addition treatment and transparent vitrification treatment are performed in a fluorine additive-containing atmosphere such as SiF ₄ , CF _4, etc. Get. The addition concentration of fluorine additives such as SiF ₄ and CF ₄ , heating conditions, and the like are appropriately adjusted so as to obtain a desired fluorine addition amount. By using such a manufacturing method, a high-purity quartz glass in which each concentration of Al, Ca, Fe, Cu, Ni, Cr, Mg, Mn, Co, Ti, Na, K, Li, and Zn is 5 wtppb or less is obtained. It is possible to obtain.
Using the quartz glass base material and the fluorine-added quartz glass base material thus obtained, a glass tube 1 as a starting material is formed, and this glass tube 1 is subjected to the above-described stretching process.

  In the stretching process, the glass tube 1 is heated and softened on the inner side 3 of both glass tubes 1 and 2 in order to keep the pressure of the inner side 3 of the glass tubes 1 and 2 before and after the stretching process higher than the pressure of the outer side 4. A gas 7 which is chemically inert at the temperature is forcibly fed. Moreover, let the atmosphere of the inner side 3 and the outer side 4 of the glass tubes 1 and 2 before and behind a drawing process be an inert gas 7 atmosphere.

As the inert gas 7, at least a gas mainly containing a chemically inert gas at a temperature at which the glass tubes 1 and 2 are heated and softened is used. For example, any one kind of inert gas of He, Ne, Ar, a mixed gas in which two or more of them are mixed, or one or more of them is mixed with oxygen (O ₂ ). A mixed gas or the like can be used.

When a mixed gas with oxygen is used, as described above, the mixing ratio of oxygen (O ₂ ) is preferably 0.01 mol% or more and 10 mol% or less in terms of a molar ratio.

  Hereinafter, more specific examples and comparative examples will be described (see Table 1).

(Examples 1-6)
A glass tube stretching process is performed using a vertical glass tube stretching machine generally used in this type of field as shown in FIG.
The glass tube used as the starting material before stretching is assumed to have an outer diameter of 110 mm and an inner diameter of 75 mm. Also the glass composition is a SiO ₂ glass fluoridation, 1 wt% fluorine content, OH content 1 wtppm or less, Cl content is less for fluorine-containing SiO ₂ glass 1 wtppm.

The target shape of the glass tube after stretching is an outer diameter of 40 mm, an inner diameter of 38 mm, and a thickness of 1 mm.
The drawing speed for stretching is 500 mm / min.

(Examples 1-6)
The atmosphere inside and outside the glass tube is an inert gas atmosphere mainly composed of Ar. Specifically, the molar ratio is Ar: 100 to 80 mol%, O ₂ : 0 to ₂₀ mol%.
The pressure on the outside of the glass tube is atmospheric pressure, and the pressure on the inside of the glass tube is adjusted as appropriate so that the outer diameter of the glass tube becomes the target outer diameter after stretching, but is generally adjusted in the range of atmospheric pressure +200 to 800 Pa. To do. The heating temperature is adjusted at 1800 ° C.

(Comparative example)
The atmosphere inside and outside the glass tube is a gas atmosphere mainly composed of nitrogen. Specifically, a molar ratio of N ₂ ; 100 mol% is used.

Stretching is performed under the above conditions. About the obtained glass tube (Examples 1-6 and comparative example),
Measurement value A: wavelength 163 nm light transmittance [%]
Measured value B: average defect concentration in 1 mm glass thickness (Si-Si type oxygen deficiency defect concentration) [pieces / cm ³ ]
To evaluate the ultraviolet light transmittance. The results are shown in Table 1.

The measured value A is preferably as large as possible. It can be said that it is good when it is 75% or more, and it is even better when it is 80% or more.
The higher the measured value A is greater, SiO ₂ is stable, extraction of oxygen atoms from SiO ₂ is suppressed at the surface of the glass tube, the generation of Si-Si type oxygen deficient defect indicating an absorption peak in a wavelength 163nm It can be said that it is suppressed.

Further, the measured value B is preferably as small as possible, and is particularly favorable if it is 1.0 × 10 ¹⁶ or less.
The smaller this measured value B is, the more stable the SiO ₂ is, and the pulling out of oxygen atoms from the SiO _{2 on} the surface of the glass tube is suppressed, and the generation of Si—Si type oxygen-deficient defects showing an absorption peak at a wavelength of 163 nm. It can be said that it is suppressed.

From the results shown in Table 1, Example 1 in which the Ar gas atmosphere was used had excellent effects in both the wavelength 163 nm light transmittance and the average defect concentration in the 1 mm glass thickness, compared with the comparative example in which the nitrogen gas atmosphere was used. It is confirmed.
Furthermore, in Example 2 in which a small amount of oxygen (0.01 mol%) was added to Ar gas, a more excellent effect was confirmed in both the wavelength 163 nm light transmittance and the average defect concentration in 1 mm glass thickness.
From the results of Examples 2 to 6, the light transmittance at a wavelength of 163 nm was improved as the molar ratio of oxygen to Ar gas was increased, and the molar ratio of oxygen to Ar gas was 10 mol% (Example 5). ) Can be said to be maximally improved.
That is, from the comparison between Example 1 and Example 2 and later, when the mixing ratio of oxygen is 0.01 mol% or more in terms of molar ratio, a preferable result is obtained as compared with the case where the ratio is less than 0.01 mol%. It is confirmed.
Further, from the comparison between Example 5 and Example 6, even if the mixing ratio of oxygen exceeds 10 mol% in molar ratio, there is not much difference in the effect of improving the transmittance of wavelength 163 nm compared to the case where it is 10 mol% or less. That is confirmed.
Thus, the superiority of the manufacturing method according to the present invention is confirmed.

  Although the embodiments of the present invention have been described above, the present invention is not limited to these examples, and various modifications are possible within the scope of the technical idea described in the claims. Needless to say.

  In addition, according to the present embodiment, as a specific example of a gas that is chemically inert at the temperature at which the glass tube 1 is heated and softened, a specific example using only Ar (Example 1), and a mixture of Ar and oxygen Although specific examples using gas (Examples 2 to 6) have been shown, even in a configuration in which Ar is replaced with He or Ne, substantially the same effects as in the case of Ar can be obtained.

1: glass tube before drawing 2: glass tube after drawing 3: inside of glass tube 4: outside of glass tube 5: heating means 6: drawing roll 7: inert gas

Claims (9)

In the drawing process of keeping the inner pressure of the glass tube higher than the outer pressure, heating and softening the glass tube in that state, and drawing it into a tubular body of a desired shape,
A method for producing a glass tube, characterized in that an atmosphere of at least one of the inside and the outside of the glass tube is an atmosphere mainly composed of a chemically inert gas at a temperature at which the glass tube is heated and softened.   The inert gas is any one of He, Ne and Ar, or two or more of them, or one or more of them. 2. The method of manufacturing a glass tube according to claim 1, wherein the glass tube is a mixed gas in which a gas and oxygen are mixed.   The inert gas is a mixed gas of any one of He, Ne, and Ar and oxygen, and a mixing ratio of the oxygen is 0.01 mol% or more by molar ratio. Item 2. A method for producing a glass tube according to Item 1.   The method for producing a glass tube according to claim 3, wherein the mixing ratio of the oxygen is 10 mol% or less in terms of molar ratio.   The method for producing a glass tube according to any one of claims 1 to 4, wherein the glass tube is a quartz glass tube.   6. The method of manufacturing a glass tube according to claim 5, wherein the quartz glass tube is a fluorine-added quartz glass tube.   The method for producing a glass tube according to any one of claims 1 to 6, wherein the glass tube after stretching has a light transmittance of 60% or more over a wavelength of 170 nm to 400 nm. The Si-Si type oxygen-deficient defect density | concentration which shows the absorption peak in wavelength 163nm of the said glass tube after the said extending | stretching is 1 * 10 < ¹⁶ > cm < ^-3 > or less, The any one of Claim 1 thru | or 7 characterized by the above-mentioned. The manufacturing method of the glass tube of description.   The method for producing a glass tube according to any one of claims 1 to 8, wherein a heating temperature in the stretching step is 1700 ° C or higher.

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