JP3103879B2 - Glass manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a glass plate, a glass bottle,
The present invention relates to a method for producing high-quality glass or glass-ceramic used as a television cathode ray tube, an optical lens, an optical communication glass fiber, a structural material glass fiber, an electronic substrate, a disk, and the like.

[0002]

2. Description of the Related Art Glass is made of bulk materials such as window glass, bottle glass, television CRT, optical glass, etc., and thick-film glass, thin-film glass for solar cell covers, etc., and glass fibers for heat insulation and optical communication. It is used in a wide range of fields as a material or a functional material. When producing such glass, it is important to increase the transparency. That is, it is required to produce a glass having high transparency and uniformity without defects such as bubbles, streaks, and striae in order to obtain a high-quality product. Defects such as streaks and striae occur due to a difference in composition and refractive index as compared with product glass (base glass). In addition, glass ceramics is a material obtained by producing a glass from a glass melt and then crystallizing the same by a heat treatment, and is a material having a higher strength or a material having a higher functionality than glass.

[0003]

SUMMARY OF THE INVENTION In the conventional manufacturing method,
There are various problems as follows. In order to produce homogeneous glass with high transparency, it is necessary to install a stirring device on the upper surface of the tank kiln or crucible. However,
When a small tank kiln or crucible is used, it is difficult to secure a space for installing a stirrer. In addition, if a stirrer is attached to the upper surface of the crucible, the work of pumping out the melt is hindered. Glass tableware may be manufactured without installing a stirrer.In this case, low-density melt components are unevenly distributed at the top of the melt in the crucible and high-density melt components are unevenly distributed at the bottom. In addition, the melt tends to be non-uniform. Therefore, in order to homogenize the melt, a non-contact stirring device is desired.

[0004] In order to remove streaks (striae), means is used to stir the melt with a stirring rod or a stirring plate when melting the glass raw material in a tank kiln or crucible to make the composition uniform.
In this case, the melt is stirred by rotating a stirring rod or a stirring plate with a motor. However, the glass melt has a melting temperature of 600
High temperature of up to 1800 ° C. and extremely high reactivity. For this reason, materials used as stirring rods and stirring plates are required to withstand this high-temperature atmosphere, have low reactivity, and exhibit high strength. do not do. Also in this point, without using a stir bar or a stir plate to remove defects such as streaks (stria),
A method of stirring and homogenizing the melt in a non-contact manner is desired.

[0005] The transparency of glass is largely affected by not only inhomogeneous materials such as streaks and striae, but also by the amount of bubbles. In addition to stirring the melt, the amount of foam was adjusted to Na ₂ SO ₄ , NaNO ₃ ,
It can also be reduced by adding a fining agent such as As ₂ O ₃ , Sb ₂ O ₃ , fluoride, phosphate and the like. However, these fining agents are highly volatile substances and often have toxicity that cannot be ignored due to environmental problems. In particular, As ₂ O ₃
Is highly toxic, and Na ₂ SO ₄ , NaNO ₃ , fluoride and the like release highly toxic gases. Therefore, it is desired to omit the addition of the fining agent or to reduce the amount thereof. In particular, homogenization of an oxide glass melt has a problem different from that of other melts, for example, a metal melt. That is, the viscosity coefficient η of the oxide glass melt is extremely higher than the viscosity coefficient of the metal melt. The viscosity coefficient of the metal melt is η = 5 × 10 ^{−3 to} 16 × 10 ⁻³ poise for the low-temperature metal melt.
(400-900 ° C), η = 14 × 10 ^-3 to 2 for cast iron
8 × 10 ⁻³ poise (1250 to 1400 ° C.). On the other hand, in the soda-lime glass melt, the viscosity coefficient is η =
10 ² to 10 ³ poise (1000 to 1400 ° C.). That is, the soda-lime glass melt is 20,000 to 60,000 times more than the low temperature metal melt, and 7000 to 4,000 times more than the cast iron.
It has a ten-fold higher viscosity coefficient, indicating that defoaming is difficult.

[0006] According to Stokes' law, the rise of bubbles is inversely proportional to the viscosity coefficient. In this regard, in order to promote defoaming from the melt, the melt is heated to lower the viscosity coefficient,
Alternatively, it is important to introduce an efficient stirring method. The glass melt has a strong reactivity and reacts with a tank kiln or a platinum crucible to erode. Foreign matter eluted from the refractory brick of the tank kiln into the melt causes defects in the glass. Platinum dissolved in the melt causes light scattering and fluorescence. In either case,
It is not preferable in producing high quality glass. Also,
Platinum crucibles are disadvantageous in that they are extremely expensive, soften at high temperatures, and are easily embrittled in a reducing atmosphere. Therefore, melting at a high temperature for a long time is not preferable, and it is required to melt the glass at a lower temperature in a shorter time. In order to impart properties corresponding to various uses to the glass, it is desirable to widen the composition range. However, even if it is known that a composition having a high refractive index exists, there are composition regions that cannot be put to practical use by the prior art because it is difficult to remove bubbles, remove streaks, striae, and the like. This means that if bubbles, streaks, striae and the like can be easily removed, the composition range can be expanded.
As described above, in order to obtain various characteristics, the composition range must be expanded.

[0007] Glass production is a typical energy-intensive industry, and new technologies corresponding to prevention of depletion of energy resources, reduction of burden on living environment, reduction of CO ₂ amount causing global warming, and the like. Is required. In this regard, in the prior art, in order to remove defects such as bubbles, streaks, and striae in glass production, the temperature is raised to a high temperature during melting to lower the viscosity, and the tank kiln is operated for a long time. The homogenization and transparency of the glass are maintained by the high-temperature and long-time melting treatment. However, such a situation prevents the depletion of energy resources,
This is contrary to the reduction of the burden on the living environment, and the development of a technology capable of melting at lower temperature and shortening the operation time is desired. The present invention has been devised to meet such a demand, and promotes the stirring of the melt by devising the application of a magnetic field to produce a homogeneous and highly transparent glass and glass ceramic regardless of the composition. The purpose is to:

[0008]

SUMMARY OF THE INVENTION The present invention provides an oxide, sulfide, halide, nitride,
By applying a vertical magnetic field to a melt such as an oxynitride, a spiral convection is generated in the melt. Defects such as bubbles, streaks, and striae are removed from the melt by the spiral convection. The melt after the magnetic field treatment is poured into a plate, a mold, a roll, or the like, or quenched by pulling with a traction machine. This produces a homogeneous and transparent glass, a homogeneous amorphous material and a metastable crystal. Further, when a transverse magnetic field that generates a forced flow from the bottom surface to the molten metal surface and from the molten metal surface to the bottom surface is applied to the glass melt, the melt is further homogenized. Furthermore, homogenization of the melt is promoted by applying a pulsed vertical magnetic field or a horizontal magnetic field. The transverse magnetic field is particularly effective when melting glass having a composition containing a component having a large specific gravity difference. Segregation low density component in the vicinity of the molten metal surface by the effect of gravity, the crucible bottom easily gathered dense component, for example in the vicinity of the molten metal surface component of SiO ₂ rich in PbO-SiO ₂ system, components of the PbO-rich in the vicinity of the bottom I do. This segregation is eliminated by forcibly flowing the melt in the vertical direction, and the density of the melt is made more uniform.

As the magnetic field generating means, a normal magnet, a superconducting metal magnet, a superconducting oxide magnet or the like is used. The applied magnetic field is not particularly limited, but is 0.01 to
The magnetic field strength is set to about 100 Tesla. Necessary stirring is performed by adjusting the magnetic field strength according to the viscosity of the melt and appropriately controlling the rotation speed or the flow speed. In the case of producing bulk glass, the glass can be rapidly cooled by a casting method, a roll method, a method of pouring a melt into water, ice water, or liquid nitrogen.

The materials to which the present invention is applied include glass, amorphous materials, metastable crystals, and the like. Examples of the glass include bulk glass such as window glass, bottle glass, and CRT glass for television, thick film glass and thin film glass for solar cell covers, glass fibers for heat insulation, and optical communication. As materials, oxide glass such as silicate, germanate, phosphate, borate, tellurate, sulfide glass containing S, Se, and halide containing F, Cl, Br, I, etc. There are glass, nitride glass, oxynitride glass, and the like.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventors have conducted various investigations and studies to overcome the above-mentioned problems, and have found that a magnetic field is applied to a melt of an oxide, sulfide, halide, nitride, oxynitride, or the like. Clarified that a spiral flow occurs in the melt. The generated convection has a very effective effect on removing glass defects. In particular, by applying a vertical magnetic field, a spiral convection having excellent central symmetry is generated, and the melt is uniformly stirred, so that a homogeneous glass is obtained. As a result, streaks and striae disappear in a short time and at a lower temperature, and high-quality glass and glass ceramics are produced. In addition, bubbles in the melt are collected near the center of the crucible by a spiral flow, and the distance between the bubbles is shortened to promote association. For this reason, the bubbles become large-diameter bubbles having a large levitation force, the rising speed of the bubbles increases, and the bubbles are easily removed. That is, since the rising velocity V is proportional to the square of the radius of the bubble when obeying Stokes' law, it is necessary to promote the association of the bubble for efficient bubble removal. The bubble-like flow promotes the association of bubbles. As a result, glass and the like without bubbles can be obtained even if the addition of harmful fining agents, which are pollution sources, is significantly reduced.

A basic composition used as a sheet glass, a bottle glass, etc., in a system of CaO—Na ₂ O—SiO ₂ —Al ₂ O ₃ in which the amount of SiO ₂ and Al ₂ O ₃ is large, is expected to have high strength. , Melt viscosity and melting temperature T _m (SiO
₂ : T _m = 1703 ° C., Al ₂ O ₃ : T _m = 2015
° C). For this reason, the foam was poorly cut and was not put to practical use. However, when the spiral convection is generated according to the present invention, the association and flotation of the bubbles are promoted, so that a sufficiently bubble-free and highly-refined glass is obtained. This means that SiO ₂ used as optical glass
_{-B 2 O 3 -BaO-La 2} O 3 -Al 2 O 3 -TiO
_{The same} is true for the ₂ system. That is, La ₂ O ₃ or TiO
A composition having a large amount of ₂ has a high refractive index and is useful as a lens, but has a too high melting point (La ₂ O ₃ : T _m = 20).
00 ° C., TiO ₂ : T _m = 1640 ° C.) When the melting temperature of this system is increased, the volatile component B ₂ O
₃ tends to evaporate, and the strength of the lens can be improved by adding Al ₂ O ₃ . However, B ₂ O ₃ and Al ₂ O
An increase of ₃ is effective for improving the quality, but has an adverse effect on the defoaming. Also in this respect, when the spiral convection is generated according to the present invention, the association and floating separation of the bubbles are promoted, so that an optical glass having a composition with a large amount of both components and high clarity can be obtained.

To homogenize the melt, it is also effective to apply a pulsed vertical magnetic field. That is, the rotation speed of the melt
When a pulse-like vertical magnetic field is applied in synchronization with (seconds / 1 rotation) , the rotation speed increases, and the homogenization of the melt is efficiently promoted. When a pulsed transverse magnetic field is applied to the melt, a forced flow from the bottom surface to the molten metal surface or from the molten metal surface to the bottom surface is generated, and the melt is similarly homogenized. When a pulsed transverse magnetic field is applied in synchronization with the flow speed of the melt, the flow speed increases, and the homogenization of the melt is efficiently promoted. For stirring the glass melt, a noncontact magnetic stirring method alone is also effective. However, when applied to a large tank kiln, there is a case where stirring is good at the center of the kiln, but insufficient at the bottom and near the inner wall. Insufficient stirring is likely to occur, especially when the melt viscosity is high. Therefore,
The use of compound agitation combined with non-magnetic agitation such as mechanical agitation (paddler method, blender method, stirrer method, rotor method, tube method), etc., ensures that the melt is sufficient even in large tank kilns. Is stirred.

[0014]

[Function] Oxide contained in tank kiln, crucible, etc.
When a longitudinal magnetic field of about 0.01 to 100 Tesla is applied to a melt of sulfide, halide, nitride, oxynitride, etc.
A spiral convection with good central symmetry is generated in the melt.
Due to this convection, bubbles in the melt are collected near the center and associated with each other to increase the diameter, thereby promoting the flotation separation. When a transverse magnetic field is applied, a forced flow in the vertical direction is generated, and the floating separation of bubbles and the homogenization of the melt are promoted. As a result, bubbles, streaks, and striae are removed, and a homogenized melt is prepared. The glass produced from this melt is free from defects such as bubbles, streaks and striae, and has high quality for flat glass, bottle glass, CRT glass for television, optical glass, glass for semiconductor substrates, solar cell cover, etc. It is used as film glass, thin film glass, glass fiber for heat insulation and optical communication.

[0015]

【Example】

Example 1: SiO ₂ : 70.0% by weight, Na ₂ O: 1
SiO ₂ , Na ₂ CO ₃ and C as raw materials were obtained so as to obtain a composition of 7.7% by weight and 12.3% by weight of CaO.
aCO ₃ was weighed and blended. After the mixture was calcined at 950 ° C. to remove CO ₂ , the remaining SiO ₂ —Na ₂ O
A sample having a CaO composition was placed in a platinum crucible and set in a high-frequency induction heating furnace. The melt was melted in air at 1500 ° C. for 1 hour, and a melt was stirred by applying a vertical magnetic field having a magnetic field strength of 1 Tesla. Next, the melt was poured out onto a carbon plate and rolled with an iron to produce a glass plate. The resulting glass plate is
It was colorless and transparent. When the number of bubbles in the glass plate was counted by microscopic observation, the number of bubbles was reduced to about 1/20 as compared with the case without stirring. Also, the number of bubbles was reduced to about 1/3 as compared with the case where stirring was performed using a platinum stirring rod. From this, it is confirmed that the number of bubbles is significantly reduced by the magnetic field stirring.

Example 2: SiO ₂ : 73.5% by weight, C
100 g of SiO ₂ , Na ₂ CO ₃ , and CaCO ₃ were weighed as raw materials so as to obtain a soda-lime glass having a composition of 10.0% by weight of aO and 16.5% by weight of Na ₂ O, and then crushed. Mixed. The mixture is calcined at 950 ° C.
O ₂ was desorbed. Remaining SiO ₂ —Na ₂ O—CaO
A sample of the composition was placed in a platinum crucible, placed in a high-frequency induction heating furnace, and melted at 1500 ° C. in an air atmosphere. After maintaining the molten state for a certain period of time, the melt was poured onto a carbon plate and rolled with an iron to produce a glass plate. The number of bubbles contained in the obtained glass plate was counted by microscopic observation. The remaining number of bubbles (pieces / cm ³ ) was compared for the three types of melting methods.

First, a paddle type stirrer was used as a conventional stirring method, and the melt was stirred at a rotation speed of 300 times / minute. Secondly, 1.0 wt% of As ₂ O ₃ was added as a fining agent, and the melt was stirred at 300 revolutions / minute using a paddle type stirrer. Third, agitation by a pulsed vertical magnetic field was performed. In this case, monitor the rotation speed of the melt with a TV camera from the top of the crucible and synchronize with the rotation speed of the melt.
Then , a sharp pulsed longitudinal magnetic field was applied every rotation.
The spontaneous rotation of the melt at 1500 ° C. is 1 per minute.
It is about 0 times, but was increased to about 350 / minute to 30 minutes after Ri by the pulse-like vertical magnetic field. During a period of 30 to 80 minutes, even when a pulsed vertical magnetic field was applied, the number of revolutions was saturated at approximately 30 to 400 times / minute. Table 1 showing the results of remaining bubbles according to the stirring method
As can be seen, the stirring by the pulsed longitudinal magnetic field showed a higher bubble reduction rate than the conventional stirring method and the addition of the fining agent (As ₂ O ₃ ). This confirms that fining agents that are harmful to the environment are reduced, and that higher quality glass can be obtained.

[0018]

EXAMPLE 3 A total of 20 g of PbO (62.5 mol%) and GeO ₂ (37.5 mol%) powder were weighed,
After grinding and mixing with a bud breaker, the mixture was compressed with a molding machine to form pellets. This was calcined at 650 ° C. for 3 hours, and the grinding and mixing were repeated again, and calcined at the same temperature and for the same time to obtain a crystal powder. This crystal powder was put in a platinum crucible 1 shown in FIG. The platinum crucible 1 has an opening formed in the bottom wall, and has a structure in which the opening is closed from above by a rod-shaped plug 2. The platinum crucible 1 was charged into a high-frequency induction heating furnace, and the charged raw material was heated and melted by the high-frequency heating coil 3. Melt 4 to 1
While maintaining the temperature at 000 ° C. for 1 hour and applying a transverse magnetic field of 1 Tesla with the ring-shaped magnetic field generator 5, the melt 4 was stirred to remove bubbles. Next, the rod-shaped plug 2 is pulled out from the opening of the bottom wall of the platinum crucible 1, the melt 4 having been subjected to the stirring treatment is naturally dropped by its own weight, and is guided between the rotating twin rolls 6 and 6.
By quenching and rolling, a glassy thick film 7 of yellowish transparent germanate (Pb ₅ Ge ₅ O ₁₁ ) was obtained. In the glass thick film 7, the number of bubbles was reduced to about 1/9 as compared with the case where the magnetic field stirring was not performed. When the stirring is not performed, the density difference between the melt at the bottom of the crucible and the melt at the surface is 3.1%.
In contrast, stirring the melt reduced the density difference to 0.3%. From this, it is understood that the obtained glass thick film 7 is a sufficiently defoamed high quality product. This glass thick film 7 was heat-treated at 650 ° C. for 3 hours to obtain a glass ceramic, thereby producing a pyroelectric sensor having high pyroelectric sensitivity.

[0020]

As described above, in the present invention, a magnetic field is applied to the melt to generate convection, thereby promoting the removal of bubbles and homogenizing the melt. Therefore, even a glass or a glass ceramic having a composition that cannot be produced due to high viscosity by the conventional method, a high-quality product having no defects such as bubbles, streaks, and striae can be produced. For example, glass is used as a bulk material and a functional material having high transparency and high performance.

[Brief description of the drawings]

Fig. 1 Apparatus for synthesizing a thick glass film from a melt that has been magnetically agitated by ultra-rapid cooling

[Explanation of symbols]

1: platinum crucible 2: rod-shaped plug 3: high-frequency heating coil 4: melt 5: magnetic field generator 6: twin roll 7: glass thick film

Claims (8)

(57) [Claims] 1. A vertical magnetic field is applied to a melt contained in a container,
Glass characterized by generating spiral convection with good centrosymmetricity and homogenizing the melt, guiding the processed melt to a mold, a rotating roll, or a traction machine to form a product. Manufacturing method. 2. A longitudinal magnetic field is applied to the melt contained in the container,
A spiral convection with good central symmetry is generated to melt
Homogenize and process the melt in water, ice water, or liquid
A method for producing glass, which is introduced into a glass. 3. The vertical magnetic field according to claim 1 or 2 ,
A manufacturing method in which a pulsed vertical magnetic field is synchronized with the rotation speed . 4. A transverse magnetic field is applied to the melt contained in the container,
The melt is homogenized by generating a forced flow from the bottom surface to the molten metal surface and from the molten metal surface to the bottom surface, and the treated melt is guided to a mold, a rotating roll, or a traction machine to form a product. Glass production method. 5. A transverse magnetic field is applied to the melt contained in the container,
Forced flow from the bottom to the surface and from the surface to the bottom
To homogenize the melt and transfer the treated melt to water, ice water,
Manufacturing glass characterized by being introduced into liquid nitrogen
Method. 6. The transverse magnetic field according to claim 4 , wherein the transverse magnetic field is a melt.
Manufacturing method in which a pulsed transverse magnetic field is synchronized with the flow velocity of a liquid . 7. The process for producing a 0.01 Tesla field strength of the magnetic field according to any one of claims 1-6. 8. The method of stirring the melt composite stirring in combination with mechanical stirring magnetic field agitation according to any one of claims 1-7.