JPH10212115A - Production of high purity quartz glass powder and production of quartz glass molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high purity quartz glass powder remarkably low in a metallic impurity content by using a high polymer material having ash content of a specific value or below for a part in contact with a process powder. SOLUTION: The high polymer material is used for a packing or the like in an equipment in contact with the process powder such as the quartz glass powder, a silica gel powder or the like. In the production process, the material is worn by the process powder and a trace of the worn particle is stuck to the process powder. The material itself does not become a contaminant of the high purity quartz glass powder because of being burnt and gasified in the succeeding firing process. However, the particle of an inorganic material blended in the material except silica remains on the surface of the high purity quartz glass powder as the contaminated material to degrade the quality of a quartz glass molding article. Then, the use of the material having <=10wt.% ash for a part in contact with the process powder is essential. As the material, poly-tetrafluoroethylene(PTFE) or a nylon is particularly preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-purity quartz glass powder and a quartz glass molded body.

[0002]

2. Description of the Related Art In recent years, glass products used in the optical communication field, the semiconductor industry, and the like have been subjected to very strict control on trace impurities. For example, when the glass product is an optical fiber, ZrO ₂ that does not assimilate into glass,
When heat-resistant fine particles such as TiO ₂ and Cr ₂ O ₃ are contained, they remain as particles even when drawing the fiber from the preform, and serve as nuclei for damage. The particle size is 2
Even with a thickness of μm, breakage occurs (JP-A-7-10585). When the impurity level in this region is reached, it is lower than the lower limit of analysis by a commonly used analysis method, and impurities cannot be detected by so-called bulk analysis.

Further, when a glass product is a jig for manufacturing a semiconductor used at a high temperature, if impurities such as alkali metals and alkaline earth metals are present, not only the contamination of the semiconductor due to the diffusion thereof but also the glass treatment is performed. It is also known that problems such as causing local crystallization of the tool and reducing the strength of the glass occur. Such high-quality glass is mainly produced by (1) a method of purifying natural quartz, (2) a method of adhering and growing fumes generated by decomposition of silicon tetrachloride in an oxyhydrogen flame to a substrate, (3) ) It is produced by, for example, baking silica gel obtained by hydrolyzing and gelling silicon alkoxide. However, it cannot be said that any of the methods always satisfies the required quality level.

[0004]

SUMMARY OF THE INVENTION In view of the above circumstances, the present inventors have conducted intensive studies on a method for producing high-purity quartz glass powder and a quartz glass molded body from which contamination by impurity fine particles has been removed. The present inventors have found that the main cause is a polymer material used at a site where the process powder comes into contact, and arrived at the present invention.

[0005]

That is, the present invention is characterized in that, in the production of high-purity quartz glass powder, a polymer material having an ash content of 10% by weight or less is used in a portion where the process powder contacts. Manufacturing method of high-purity quartz glass powder,
And so on.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The high-purity quartz glass powder targeted in the present invention is not limited to any of natural products and synthetic products, but as ultra-high-purity quartz glass, there is a demand for removal of contamination by impurity fine particles below the lower limit of analysis. A method for producing a high-purity quartz glass powder and a quartz glass molded body derived from a sol-gel method using strong tetraalkoxysilane as a raw material will be described. The hydrolysis of alkoxyxylan by the sol-gel method is performed by reacting alkoxyxylan with water according to a known method.

The alkoxysilane used as a raw material is preferably a C1 to C4 lower alkoxysilane such as tetramethoxysilane or tetraethoxysilane or an oligomer thereof. The amount of water used is usually selected from the range of 1 to 10 equivalents of the alkoxy group in the alkoxysilane. At this time, if necessary, an organic solvent such as an alcohol or an ether which is compatible with water may be mixed and used. Representative examples of the alcohol used include lower aliphatic alcohols such as methanol and ethanol.

In this hydrolysis reaction, hydrochloric acid is used as a catalyst.
An acid such as acetic acid or an alkali such as ammonia may be added as a catalyst. It is needless to say that all substances to be introduced into the reaction system, such as water and catalyst used here, need to be of high purity. Gelation of the hydrolysis product is performed under heating or at room temperature. Since the rate of gelation can be improved by heating, the gelation time can be controlled by adjusting the degree of heating. The obtained gel may be dried after fragmentation, or may be fragmented after drying. In any case,
The particle size after drying is 10-1000 μm, preferably 1
It is preferable to perform subdivision so as to have a thickness of 00 to 600 μm.

Drying is performed while heating under normal pressure or reduced pressure. The heating temperature varies depending on the conditions, but is usually 50 to 200 ° C. The operation can be performed either batchwise or continuously. The degree of drying is
Usually, it is performed up to a liquid content of 1 to 30% by weight. continue,
Particles outside the standard size are separated by classification. The classification method is not particularly limited, but usually a classification method using a vibrating sieve is employed. Since the hardness of the powder is greatly increased by drying, in the production of high-purity quartz glass powder, attention must be paid to the selection of materials after the drying step. That is, the gel in the wet state before drying has a Vickers hardness of almost 0, but the gel after drying has a hardness of 30 or more, and the quartz glass powder has a hardness of 800 or more.

[0010] The material of the main equipment with which the process powder comes into contact is devised such as using quartz glass in order to prevent contamination by impurity fine particles. However, there are many portions where quartz glass cannot be used in processing. . For example, a polymer material is generally used as a material such as a net, a tapping ball, and a packing used for a sieve. Normally, the polymer material is burned and gasified in the firing step described below, and thus does not become a contaminant of the high-purity quartz glass powder. However, the present inventors have found that, depending on the amount, inorganic substances other than silica mixed with the polymer material become unexpectedly contaminants of high-purity silica glass powder and greatly impair the quality of the quartz glass molded body. .

The process powder referred to here is a silica glass powder having a liquid content of 30% by weight or less, which is a quartz glass powder and a precursor thereof. The liquid content refers to a weight reduction rate (ratio of a phenomenon weight value to an initial weight) when a constant weight is reached by heating with an infrared heater or the like. Silica gel having a liquid content of more than 30% by weight has a low hardness and hardly wears the polymer material. However, the process powder referred to in the present invention has a higher hardness than the polymer material as described above. The material is worn, and the wear is mixed into the process powder.

Although the mechanism of the contamination is not always clear, the polymer material is worn by the process powder, a small amount of the abrasion powder adheres to the powder, and after firing, the inorganic substance particles are converted into high-purity quartz. It seems to remain on the glass powder surface. As a result, particles of inorganic substances that remain in the form of fine particles in the quartz glass molded body obtained by melt molding and are not assimilated into quartz glass may cause disconnection,
Alkaline earth metals are considered to be nuclei for crystallization of glass and reduce the quality. The mixing amount of these fine particles is equal to or lower than the lower limit of analysis by a commonly used analysis method, and is a level of a region where the amount of impurities cannot be determined by so-called bulk analysis. The content of the inorganic substance particles blended in the polymer material has a correlation with the ash content.
The ash referred to here is the residual amount when the polymer material is heated in an air atmosphere at 600 ° C. for 5 minutes in an infrared heating furnace or the like.

In the present invention, it is an essential requirement that a polymer material having an ash content of 10% by weight or less be used in a portion where the process powder contacts. Preferably 5% by weight ash
The following is assumed. As the polymer material, polytetrafluoroethylene (PTFE), polytrifluoroethylene chloride (PCTF)
E), polytetrafluoroethylene / propylene hexafluoride (F
EP) and other fluororesins (trademark: "Teflon"), hard vinyl chloride, soft vinyl chloride, polypropylene, polyethylene, polyester, EVA, phenol, epoxy,
Nylon, urea, acryl and the like can be mentioned, of which “Teflon” or nylon is particularly preferred. In any of these cases, the ash content must not exceed 10% by weight. If the ash content exceeds 10% by weight, the level of contamination cannot be detected by commonly used analytical methods, but the quality of the quartz glass molded article is greatly impaired.

The dried silica gel thus obtained can be directly heated in a temperature range of 1000 to 1300 ° C. to make it nonporous to obtain synthetic quartz powder.
It is preferable to make a synthetic quartz powder after performing a heat treatment at a temperature of 0 to 500 ° C. The reason is described below. In the dried silica gel obtained by the above method, an unreacted alkoxy group and a part of the by-produced alcohol remain even when the by-produced alcohol is removed by drying. Actually, when the carbon concentration in the dried silica gel powder is measured, it is 1 to 3% by weight although it varies depending on the drying conditions. This silica gel powder is placed in an oxygen-containing gas at 1000 to 1300 ° C.
When heating and baking are performed in the temperature range described above, most of the carbon is burned and removed during the temperature rise process, but a part of the carbon is sometimes trapped as unburned carbon in the synthetic quartz powder. If synthetic quartz powder containing this unburned carbon is used, CO or CO ₂ gas is generated during melt molding, which causes the generation of bubbles. Therefore, it is necessary to remove substantially all of the unburned carbon before sealing the silica gel, and the rate of temperature increase during the temperature increase process is important.

However, when synthetic quartz powder is industrially manufactured, a large-diameter quartz crucible is used, and the temperature in the crucible during the heating process becomes non-uniform. It is difficult to raise the temperature of the part in a predetermined temperature pattern. As a result, when directly heated in a temperature range of 1000 to 1300 ° C. and made nonporous to obtain synthetic quartz powder, in some cases, synthetic quartz powder in which carbon remains is partially generated and the synthetic quartz powder is used. The phenomenon that minute bubbles are generated in the molded article is observed. On the other hand, according to the study of the present inventors, when the residual carbon in the dried silica gel is brought into contact with an oxygen-containing gas in a temperature range of 300 ° C. or higher, the residual carbon decreases while generating CO and CO ₂ , and decreases as the treatment temperature is increased. It was found that the rate increased and that the non-porous silica gel proceeded rapidly in the temperature range of 600 ° C. or higher. Therefore, once 300-500
Heat treatment in a temperature range of 5 ° C.
After the content is reduced to 000 ppm or less, preferably 1000 ppm or less, it is heated in a temperature range of 1000 to 1300 ° C. to make it non-porous to obtain a synthetic quartz powder.

The processing time in this temperature range depends on the processing temperature, but is usually about 1 to 10 hours. In addition, the operation method can be performed in either a batch system or a continuous system. A method using a rotary kiln is an example of a continuous method. That is, the heating process is performed in the furnace core tube while continuously supplying the dried silica gel powder from one end of the furnace tube of the rotary kiln, and the powder after the treatment is continuously discharged from the furnace tube. In this case, as the material of the furnace tube, it is necessary to select a material that does not cause contamination of the processed powder with the material, and is preferably made of quartz. In the case of quartz, there is a limit to the size of the furnace tube due to manufacturing, so
Depending on the conditions, the heat treatment may be performed by arranging multiple stages of rotary kilns in series.

Next, the silica gel thus obtained is heated in a temperature range of 1000 to 1300 ° C. to make it nonporous, thereby obtaining a synthetic quartz powder. The operation is generally performed in a batch method. The container used must be made of a material that does not cause contamination of the synthetic quartz powder with impurities, for example, quartz. A specific example is a quartz crucible. In the present invention, an outlet for the dry gas is provided in the silica gel powder, and the heat treatment is performed while flowing the dry gas.
Examples of the drying gas include an inert gas such as nitrogen and argon, oxygen, air, and a mixed gas thereof, but air is preferred from the viewpoint of economy. Dust is removed from a gas to be used by a filter or the like in advance.

Further, moisture contained by a method such as adsorption is sufficiently removed, and the dew point is -20 ° C. or lower, preferably −20 ° C.
It is necessary to keep the temperature below 40 ° C. If the dew point is higher than this range, the residual silanol concentration of the obtained synthetic quartz powder is undesirably high. The drying gas is supplied from an insertion tube inserted into the powder. The material is preferably a material that does not cause contamination of impurities, for example, quartz. The position of the drying gas outlet is not particularly limited, but is preferably provided between the bottom of the container and half the height of the powder. If you set it higher than that,
The rate of silanol reduction decreases. The flow rate of the drying gas is selected from a region where the bubbling phenomenon does not occur.

When the bubbling phenomenon occurs, although the reason is not clear, the rate of reduction of silanol decreases, and further, powder overflows from the container. The bubbling phenomenon is
This is manifested when a gas at a specific flow rate or higher flows. That is, as the flow rate of the dry gas supplied into the powder is increased, the discharge pressure of the dry gas increases, and when a specific flow rate is reached, soaring of the powder on the powder surface is observed, and the discharge pressure increases rapidly. descend. The specific flow rate value varies depending on the position of the outlet of the drying gas and the particle size of the powder. That is, this specific flow rate value is linearly proportional to the distance between the position of the outlet of the dry gas and the upper end of the powder layer,
Further, it was confirmed by experiments of the present inventors that the particle diameter was dependent on the 1.8th power.

The bubbling phenomenon referred to herein means that a mixed portion of solid and gas is continuously generated in the powder layer. By firing while supplying a gas having a flow rate equal to or less than the specific value into the powder, quartz powder with low silanol can be efficiently obtained. Also, since no overflow from the container occurs, the product can be obtained substantially quantitatively. However,
If the flow rate of the flowing dehumidifying gas is extremely small, the effect is reduced. Therefore, it is preferable to perform firing while supplying a dehumidifying gas having a flow rate of at least 10% of a specific value, preferably 20% or more of a specific value. desirable. In addition, if the operation is performed in the vicinity of a specific value, there is a risk that a bubbling phenomenon may occur due to a change in silica gel particle size. Therefore, 95% of the specific value, preferably
It is preferable to set 90% as the upper limit of the gas flow rate.

The firing temperature is usually 1100-1300 ° C.
It is. If it is lower than this range, it takes a long time for sintering, and if it is too high, sintering between particles occurs, and crushing is required after firing, which is not preferable. The firing time depends on the firing temperature, but is usually 10 to 100 hours, and is continued until the silanol concentration in the synthetic quartz powder becomes 100 ppm or less, preferably 60 ppm or less. Since the above-mentioned heat treatment equipment and non-porous treatment equipment are at high temperatures, polymer materials cannot be used, but for example, a scoop used for charging / removing process powder into a stock tank or crucible It is necessary to consider materials such as. because,
This is because, depending on the amount, the inorganic substance mixed in the polymer material used for such a fixture becomes a contaminant of high-purity quartz glass powder and greatly impairs the quality of the quartz glass molded article. In the present invention, also in this case, a polymer material having an ash content other than silica of 10% by weight or less, preferably 5% by weight or less is used.

The synthetic quartz powder thus obtained is formed into a compact. The molding method differs depending on the use of the molded body. For example, when the use is a crucible, the arc melt method is used.
Examples include a method of forming an ingot by the Bernoulli method using an acid / hydrogen flame, and a fusion method of heating and melting under vacuum using a carbon mold. When the application is an optical fiber, there is a method in which a quartz glass powder is melted in a crucible, the tube is continuously pulled out from a lower part through a molding device to produce a tube, and then a fiber is formed. In any case, when the synthetic quartz powder obtained by the method of the present invention is used, a quartz glass molded article having excellent quality can be obtained.

[0023]

[Example 1]

(Hydrolysis to drying) High-purity tetramethoxysilane was reacted with water to obtain a lump wet gel. Subsequently, the lump-shaped wet gel was pulverized by a net pulverizer and dried by heating under reduced pressure to obtain powdery dry silica gel (liquid content: 30% by weight or less). This powdery dry silica gel was classified with a vibration sieving machine to obtain particles of 500 μm or less and 100 μm or more. The screen of the sieve and the tapping balls attached to the sieve contained the main components, ash and metal components shown in Table 1.

[0024]

[Table 1] The metal components are those detected by qualitative analysis using fluorescent X-rays.

(Heat treatment) Using dry silica gel, heat treatment was carried out by a rotary kiln shown in FIG.
The furnace tube is made of quartz, length (heating zone): 2 m, inner diameter: 200 mm, supply port donut weir opening diameter: 40 mm,
The diameter of the outlet donut-shaped weir opening is 40 mm.
The core tube was adjusted so that the inclination angle was 0.5 °. First, each heating heater was heated to 500 ° C., and while the furnace tube was rotated at 4 rpm, powdery dry silica gel was supplied from the supply port at 6.2 kg / H and air at 4500 L / H. The powder discharged from the discharge port,
Using the same rotary kiln, a heat treatment was performed again under the following conditions. First heater: 600 ° C, second heater: 700 ° C, third heater: 850 ° C, fourth heater: 1000 ° C, fifth heater: 1060
° C, while rotating the furnace tube at 4 rpm,
Air was supplied at a rate of 6.5 kg / H from the supply port at a rate of 1000 L / H to obtain a powder used for firing.

(Firing) 130 k of powder obtained by heat treatment
g was placed in a quartz glass crucible of 550 mmφ × 600 mmH. Subsequently, as shown in FIG.
A quartz glass tube was inserted, and dehumidified air having a dew point of -45 ° C was supplied at a rate of 6 L / Hr per kg of the powder. At this time,
No bubbling of the powder was observed. It was kept at 1200 ° C. for 60 hours while supplying dehumidified air at the same flow rate. After completion of the firing, the powder was cooled to room temperature while supplying dehumidified air, and the powder was recovered. At this time, no overflow of powder from the crucible was observed. After mixing the recovered powder with a rotary blender, the silanol concentration was measured by infrared absorption method and found to be 36 ppm. Analysis of metal impurities showed the values shown in Table 2.

[0027]

[Table 2]

(Melting Molding) 50 g of the synthetic quartz glass powder obtained by firing was crushed into a carbon crucible (inner diameter: 40 mm, height: 6 mm).
0 mm) and melted at 1780 ° C. using a vacuum melting furnace (“FVPHP-R-5” manufactured by Fuji Denki Kogyo Co., Ltd.) to obtain a cylindrical quartz glass molded body. In the molded body,
No foaming was observed. (Heating test) The quartz glass molded body obtained by the melt molding was charged into a carbon crucible again, and was subjected to normal pressure and argon gas flow in a vacuum melting furnace ("FVPPHP-R-5" manufactured by Fuji Denpa Kogyo KK). The temperature was maintained at 1630 ° C. for 5 hours. After cooling, no opaque portion was observed in the quartz glass molded body taken out.

Comparative Example The same operation as in the example was performed except that the tapping balls used in the vibration sieving machine were changed to those shown in Table 3.

[Table 3] When the silanol concentration of the obtained synthetic quartz glass powder was measured, it was 40 ppm. Analysis of the metal impurities showed the values shown in Table 4.

[0030]

[Table 4] This synthetic quartz glass powder was melt-molded to obtain a cylindrical quartz glass molded body. A heating test was performed under the same conditions as in Example 1. After cooling, it was observed that opaque spots were scattered on the quartz glass molded body taken out. When the opaque spot was analyzed using microscopic X-rays, it was cristobalite and the quartz glass was locally crystallized.

[0031]

According to the present invention, it is possible to obtain a high-purity quartz glass powder and a quartz glass compact having extremely few metal impurities.

[Brief description of the drawings]

FIG. 1 is a diagram showing a rotary kiln used in a heat treatment in Example 1.

FIG. 2 is a conceptual diagram showing firing in Example 1.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Masaki Yasuda 1-1 Kurosaki Castle Stone, Yawatanishi-ku, Kitakyushu City Inside Mitsubishi Chemical Corporation Kurosaki Office

Claims (10)

[Claims] 1. A method for producing a high-purity quartz glass powder, comprising using a polymer material having an ash content of 10% by weight or less in a portion where the process powder contacts in the production of the high-purity quartz glass powder. 2. The method for producing high-purity quartz glass powder according to claim 1, wherein the high-purity quartz glass powder is synthetic quartz glass powder. 3. The method for producing high-purity quartz glass powder according to claim 2, wherein the synthetic quartz glass powder is obtained by a sol-gel method. 4. The method according to claim 3, wherein tetraalkoxysilane is used as a raw material for the sol-gel method. 5. The method for producing high-purity quartz glass powder according to claim 4, wherein the tetraalkoxysilane is tetramethoxysilane. 6. The method according to claim 1, wherein the contact portion of the process powder is a tapping ball of a vibrating sieve.
5. The method for producing a high-purity quartz glass powder according to any one of 5. 7. The method for producing a high-purity quartz glass powder according to claim 1, wherein a portion where the process powder comes into contact is a mesh of a vibrating sieve. 8. The method for producing a high-purity quartz glass powder according to claim 1, wherein a portion in contact with the process powder is a packing. 9. The method for producing high-purity quartz glass powder according to claim 1, wherein the liquid content of the process powder is 30% by weight or less. 10. A method for producing a quartz glass molded body, comprising melting and molding a high-purity quartz powder obtained by the production method according to claim 1.