JP6332612B2 - Method for producing alkali-free glass - Google Patents

Description

The present invention relates to a method for producing alkali-free glass, and more specifically to a method for producing alkali-free glass suitable as a display substrate for liquid crystal displays, organic EL (OLED) displays and the like. An alkali-free glass substrate used for a high-definition display has many required characteristics. As one of them, a high strain point is required. The display manufacturing process includes processes such as film formation and annealing. In these processes, the glass substrate is heat-treated at several hundred degrees Celsius. Therefore, when the glass substrate is thermally contracted during the heat treatment, pattern deviation or the like is likely to occur. Therefore, the glass substrate is required to be resistant to thermal contraction, and in particular to have a high strain point. Various glass compositions and manufacturing methods thereof have been proposed to meet such demands (for example, Patent Document 1).

JP 2012-121738 A

  In general, the higher the strain point of glass, the higher the high temperature viscosity. In particular, alkali-free glass substantially free of alkali metal components has a very high high temperature viscosity and is known as a hardly soluble glass. For this reason, the alkali-free glass is usually melted at a high temperature. However, when it melts at a high temperature, the refractory constituting the glass melting furnace is easily eroded by the glass melt, and the life of the furnace is shortened. Moreover, since energy efficiency also worsens, there is a problem both economically and environmentally.

Therefore, it is required to melt the alkali-free glass at the lowest possible temperature. However, when the melting temperature is lowered, the homogeneity of the glass deteriorates, and there is a tendency that streaks and bubbles remain in the product and the productivity deteriorates. The striae can be improved by passing the stirring step, but it is difficult to improve the foam. This is because bubbles are less likely to rise due to the high viscosity of glass. Moreover, when the melting temperature of the alkali-free glass is lowered, a layer having a high SiO ₂ concentration is likely to be formed on the melt surface. Since this layer has a high viscosity, bubbles in the glass melt are more difficult to escape and remain in the glass product.

  The subject of this invention is providing the manufacturing method of the alkali free glass which can obtain the alkali free glass which is homogeneous without a striae, and was excellent in foam quality, even if it reduced melting temperature.

The process in which a layer having a high SiO ₂ concentration is generated on the melt surface is as follows. First, among the glass components, alkaline earth metal components such as MgO and SrO dissolve at a relatively low temperature, react with a plurality of substances to form a melt, and sink below the undissolved raw material. Conversely, a hardly soluble component such as SiO ₂ remains undissolved and easily floats on the upper part of the melt, and the component is separated (melted and separated). When the alkali-free glass is melted at a low temperature, the SiO ₂ component tends to remain undissolved, and this phenomenon becomes more remarkable.

  As a result of various experiments, the present inventors have found that the above problems can be solved by using magnesium oxide having a small particle size as a magnesium raw material, and propose the present invention.

That is, the method for producing an alkali-free glass of the present invention is a method for producing an alkali-free glass substrate in which a mixed raw material containing a silica source and a magnesium source is melted and molded, and magnesium oxide having a D ₉₀ of less than 150 μm as the magnesium source It is characterized by using raw materials. In the present invention, “non-alkali glass” means a glass having an alkali metal oxide content of 0.5% or less.

According to the said structure, when a magnesium oxide raw material melt | dissolves, it reacts easily with the silica raw material etc. which exist around, a melt containing a silica component and a magnesium component is formed, and it settles to a melting furnace bottom part. Thus, melt remaining silica raw material is reduced, a high SiO ₂ concentration layer is less likely to be formed on the melt surface. As a result, bubbles contained in the melt are easily removed. In addition, since the silica component is melted together with the magnesium component and the like, and melt separation hardly occurs, the obtained glass tends to be homogeneous.

  Moreover, since defoaming and homogenization are possible without increasing the melting temperature, it is possible to reduce energy required for glass production. It is also effective in extending the life of the glass melting furnace.

  In this invention, it is preferable to adjust the usage-amount of a magnesium oxide raw material so that content of MgO in a glass composition may be 0.5-5 mass%.

In the present invention, as the silica _source, it is preferable to use a silica material _{D 50} is 10 to 150 m.

  According to the said structure, a silica raw material becomes easier to melt | dissolve.

  In the present invention, it is preferable to prepare the mixed raw material so that the glass has a strain point of 680 ° C. or higher.

  Since the glass having a strain point of 680 ° C. or higher has high temperature viscosity and is hardly meltable, the effect of the present invention can be enjoyed accurately.

In the present invention, _SiO 2 55 to _70% by mass percent in terms of oxide as a glass _{composition, Al 2 O 3 16~25%,} B 2 O 3 0~10%, 0.5~5% MgO, CaO 3 -13%, SrO 0 to 10%, BaO 0 to 10%, ZrO ₂ 0 to 5%, and mixed raw material so as to be a glass having an alkali metal oxide content of 0.5% or less Is preferably prepared.

  Since the glass having the above composition has a high-temperature viscosity and is hardly meltable, the effect of the present invention can be enjoyed accurately.

  Hereinafter, the manufacturing method of the glass substrate of embodiment of this invention is demonstrated. In addition, in description of the containing range of each component,% display points out the mass%.

  First, glass raw materials are prepared and mixed so as to obtain a target glass composition. As a glass raw material, for example, a glass raw material that becomes a silica source, a boron source, an alumina source, an alkaline earth metal source, or the like is mixed to prepare a batch. The method for mixing the raw materials is not particularly limited. For example, a bread mixer, a rotary mixer, or the like can be used, and an optimum mixing method may be appropriately determined according to the mixing weight per one time.

As a target glass composition, for example, SiO ₂ 55 to 70%, Al ₂ O ₃ 16 to 25%, B ₂ O ₃ 0 to 10%, MgO 0.5 to 5%, and CaO 3 in mass% based on oxide. The glass raw material is prepared so that the content of ˜13%, SrO 0-10%, BaO 0-10%, ZrO ₂ 0-5% and the content of alkali metal oxide is 0.5% or less. By setting it as such a target glass composition, the various characteristics requested | required of the glass substrate for a display can be satisfied. The reason why the composition range is as described above will be described later.

Hereafter, the glass raw material used in this invention is demonstrated.
(Silica source)
As the silica source, natural silica sand (SiO ₂ ) or silica powder can be used. Silica raw _{material, D 50} is 10~300μm, 20~150μm, 10~150μm, it is particularly preferred to use those of 30 to 150 [mu] m. When the particle size of the silica raw material is too coarse, reaction with the magnesium oxide raw material is difficult to occur, melt separation occurs, and a layer having a high SiO ₂ concentration is likely to be formed on the melt surface. Further, if the melting temperature is increased to avoid this, the life of the melting furnace is shortened and the energy efficiency is deteriorated. When the particle size of the silica raw material is too fine, agglomeration occurs and coarse secondary particles are formed, which may cause problems such as undissolved particles of SiO ₂ and melting separation.
(Boron source)
Examples of the boron source include hydroborates such as orthoboric acid (H ₃ BO ₃ ), metaboric acid (H ₃ BO ₃ ), and tetraboric acid (H ₂ B ₄ O ₇ ), and boron oxide (B ₂ O _3). ) Etc. can be used. A total amount of orthoboric acid, metaboric acid, and tetraboric acid containing 80 to 95% by mass of the total boron source is used as the boron source. If it is less than 80%, the amount of water in the molten glass is insufficient and the high-temperature viscosity increases, making it difficult to obtain a homogeneous molten glass. If it is more than 95%, the amount of water in the glass raw material batch becomes excessive, and the glass raw material tends to aggregate.
(Alumina source)
As the alumina source, alumina (Al ₂ O ₃ ) and aluminum hydroxide (Al (OH) ₃ ) can be used. As the aluminum source, it is preferable to use aluminum hydroxide containing 5 to 100% by mass of the total aluminum source. If it is less than 5%, the amount of water in the molten glass is insufficient and the high-temperature viscosity increases, making it difficult to obtain a homogeneous molten glass.
(Alkaline earth metal source)
Calcium carbonate (CaCO ₃ ) or the like as a calcium source, magnesium oxide (MgO) or the like as a magnesium source, barium nitrate (Ba (NO ₃ ) ₂ ) or the like as a barium source, strontium nitrate (Sr (NO ₃ ) ₂ ) or the like as a strontium source Can be used.

In the present invention, the following _{D 90} of 150μm magnesium oxide used as the magnesium source, preferably 120～150Myuemu, particularly using those 130～150Myuemu. The _{D 50} of the magnesium oxide is 50 to 120 [mu] m, it is particularly preferably 70-100. If the particle size of the magnesium oxide raw material is too coarse, the reactivity with the silica raw material becomes low, and a layer having a high SiO ₂ concentration is likely to be formed on the melt surface when the raw material is dissolved, making it difficult to remove bubbles in the melt. Further, if the melting temperature is increased in order to avoid this, problems such as shortening the life of the melting furnace and deteriorating energy efficiency occur. In addition, when the particle size of a magnesium oxide raw material is too fine, there exists a possibility that malfunctions, such as a segregation occurring at the time of mixing of a raw material, may arise.
(Zirconia source)
As the zirconia source, zircon (ZrO ₂ · SiO ₂ ), zirconia (ZrO ₂ ), or the like can be used.

  Next, the reason why the ratio of each component in the target composition is limited as described above will be described.

  Glass substrates used for high-definition displays have many required characteristics. In particular, the following characteristics (1) to (7) are required. According to the said glass composition, these characteristics can be satisfy | filled simultaneously.

  (1) When the alkali component in the glass is large, alkali ions are diffused into the semiconductor material on which the film is formed during the heat treatment, and the characteristics of the film are deteriorated. Therefore, the content of alkali components (particularly, Li component and Na component) should be small, and desirably not substantially contained.

  (2) Various chemicals such as acid and alkali are used in the photolithography etching step. Therefore, it has excellent chemical resistance.

  (3) The glass substrate is heat-treated at several hundred degrees Celsius in steps such as film formation and annealing. When the glass substrate is thermally contracted during the heat treatment, pattern deviation or the like is likely to occur. Therefore, heat shrinkage is difficult, especially the strain point is high.

(4) The thermal expansion coefficient is close to a member (for example, a-Si, p-Si) formed on the glass substrate. For example, the thermal expansion coefficient is 30 to 45 × 10 ⁻⁷ / ° C. When the thermal expansion coefficient is 45 × 10 ⁻⁷ / ° C. or less, the thermal shock resistance is also improved.

  (5) The Young's modulus (or specific Young's modulus) is high in order to suppress problems caused by the bending of the glass substrate.

  (6) Excellent meltability in order to prevent melting defects such as bubbles, blisters and striae.

  (7) Excellent devitrification resistance to avoid generation of foreign matter in the glass substrate.

  Hereinafter, each component of the glass composition will be described.

The content of SiO ₂ is preferably 55 to 70%, more preferably 58 to 65%. When the content of SiO ₂ is less than 55%, the strain point of the glass is lowered, and the glass substrate is cracked or heat deformation or heat shrinkage easily occurs in the heat treatment process when manufacturing the display device. In addition, the thermal expansion coefficient becomes too large, making it difficult to achieve consistency with the thermal expansion coefficient of the surrounding materials, and the thermal shock resistance is likely to decrease. Furthermore, acid resistance also deteriorates. On the other hand, when the content of SiO ₂ is more than 70%, the high temperature viscosity of the glass becomes high, and it becomes difficult to melt or mold the glass. In addition, the thermal expansion coefficient becomes too small, making it difficult to match the thermal expansion coefficient of the surrounding material.

When the content of Al ₂ O ₃ is too large, the strain point of the glass is lowered, the heat treatment step in manufacturing the display, or cracked glass substrate, thermal deformation or thermal shrinkage may become likely to occur. On the other hand, when the content of Al ₂ O ₃ is too small, or decreased resistance to buffered hydrofluoric acid for glass, the liquidus temperature of the glass and becomes difficult to mold the glass substrate increases. A suitable range for the Al ₂ O ₃ content is 16 to 25%, more preferably 16 to 20%.

B ₂ O ₃ is a component that lowers the viscosity of the glass and increases the meltability of the glass. However, if it is excessively contained, the strain point of the glass is lowered, and a glass substrate is used in the heat treatment step when manufacturing the display. Cracks and heat deformation and shrinkage are likely to occur. B ₂ O ₃ suitable range of content from 0.1 to 10%, more preferably 0.1 to 7.5%, more preferably 0.1 to 6%.

  MgO is a component that improves the meltability of the glass by lowering the high temperature viscosity without lowering the strain point of the glass. When there is too much content of MgO, it exists in the tendency for the devitrification bumps of cristobalite and enstatite to occur easily. Further, the resistance to buffered hydrofluoric acid is lowered, the glass substrate is eroded in the photoetching process, the reaction product adheres to the surface of the glass substrate, and the glass substrate tends to become cloudy. If the content of MgO is too small, the above effect cannot be obtained. A suitable range of the MgO content is 0.5 to 5%, more preferably 0.5 to 3%, and still more preferably 0.5 to 2.5%.

  CaO improves the meltability of the glass by reducing only the high temperature viscosity without reducing the strain point of the glass. When there is too much content of CaO, while resistance to buffered hydrofluoric acid will fall, the density and thermal expansion coefficient of glass will rise. When there is too little content of CaO, high temperature viscosity will rise and meltability will deteriorate easily. The suitable range of CaO content is 3 to 13%, more preferably 2.5 to 8%.

  SrO is a component that improves the chemical resistance and devitrification resistance of glass. When there is too much content of SrO, the density and thermal expansion coefficient of glass will rise. The suitable range of SrO content is 0 to 10%, more preferably 1.5 to 4.5%.

  BaO is a component that improves the chemical resistance and devitrification resistance of glass. When there is too much content of BaO, the density and thermal expansion coefficient of glass will rise. The suitable range of BaO content is 0 to 10%, more preferably 1 to 10%.

ZrO ₂ is a component that improves the chemical resistance of glass, particularly acid resistance, and improves the Young's modulus. When the content of ZrO ₂ is too large, the liquidus temperature of the glass rises, devitrification stones of zircon is readily released. A suitable range of the ZrO ₂ content is 0 to 5%, more preferably 0.1 to 1%.

Further, in the target glass composition, ZnO, TiO ₂ , P ₂ O ₅ or the like may be added in addition to the above components.

  ZnO is a component that improves the buffered hydrofluoric acid resistance of glass and improves the meltability of glass. When there is too much content of ZnO, it will become easy to devitrify glass, or a strain point will fall. The suitable range of ZnO content is 0 to 5%.

TiO ₂ has the effect of lowering the high-temperature viscosity to increase the meltability and the chemical durability. However, when the introduction amount is excessive, the ultraviolet transmittance tends to decrease. The content of TiO ₂ is preferably 0 to 5% or less. When a very small amount of TiO ₂ is introduced (for example, 0.001% or more), an effect of suppressing coloring due to ultraviolet rays can be obtained.

P ₂ O ₅ is a component that increases the strain point and is a component that can suppress precipitation of devitrified crystals of alkaline earth aluminosilicates such as anorthite. However, when P ₂ O ₅ is contained in a large amount, the glass is likely to be phase-separated. The content of P ₂ O ₅ is preferably 0 to 5%.

As a clarifier, As ₂ O ₃ , Sb ₂ O ₃ , SnO ₂ , SO ₃ , CeO ₂ , F ₂ , Cl ₂ or the like can be used. The total content is preferably 3% or less. Further it is preferred to use SnO ₂ Among these fining agents, the content thereof is preferably 0.01 to 2%.

When the glass substrate produced by the method of the present invention is used for a liquid crystal display substrate or the like, an alkali metal oxide (Li ₂ O, Na ₂ O, K ₂ O, particularly Li ₂ O, Na ₂ O) is contained in the glass. It is preferable not to contain substantially. “Containing substantially no alkali metal oxide” means that the content is suppressed to 0.5% or less. When the total content of the alkali metal oxide exceeds 0.5%, the alkali metal is diffused into the TFT semiconductor material on which the TFT is formed on the substrate, and the film characteristics are reduced. to degrade.

In addition to the above, various components can be added as long as the glass properties are not impaired. For example, Y ₂ O ₃ , La ₂ O ₃ , Nd ₂ O ₃ or the like may be added.

  The target glass composition is preferably determined so that the strain point of the obtained glass substrate is 680 ° C. or higher, 690 ° C. or higher, particularly 700 ° C. or higher.

  Next, the prepared raw material mixture (and, if necessary, glass cullet having the same composition as the target glass) is charged from the glass raw material charging port of the melting furnace, and melted and vitrified. The raw material batch is charged into the melting furnace continuously or intermittently using a raw material feeder such as a screw charger. The raw material charged into the melting furnace is heated by a combustion atmosphere such as a burner or heat generation of the electrodes, and the individual raw materials react to melt and vitrify. The melting temperature of glass is usually about 1500 to 1700 ° C. Glass cullet is glass waste discharged in the process of manufacturing glass. The structure of the melting furnace is not particularly limited, but preferably has melting, clarification, and stirring functions.

  Next, molten glass is supplied to a molding apparatus, and the glass is molded into a plate shape so as to have a predetermined thickness and surface quality. When supplying the molten glass to the molding apparatus, the temperature of the molten glass is gradually lowered to a viscosity suitable for molding. As a molding method, it is preferable to use an overflow downdraw method. By using the overflow downdraw method, a glass substrate having a high surface quality can be easily produced continuously. In addition, it is also possible to use other conventionally well-known plate glass forming methods such as a slot down draw method, a roll-out method, and a float method.

  Thus, the produced glass substrate is used as a board | substrate of flat panel displays, such as a liquid crystal display and an OLED display, for example.

  Hereinafter, the present invention will be described in detail based on examples.

First, by mass%, SiO ₂ 59%, Al ₂ O ₃ 19%, B ₂ O ₃ 6.5%, MgO 2.5%, CaO 6%, SrO 1%, BaO 6%, alkali metal oxides. A glass batch was prepared by blending glass raw materials so as to have a glass composition of 5% or less. Silica sand having a D50 of 90 μm was used as the silica source, and magnesium oxide having a D50 of 500 μm and D90 of 710 μm was used as the magnesium source. The glass batch was prepared by putting an appropriate amount of batch into a bread mixer and mixing for a sufficient time.

  Subsequently, the prepared glass batch was put into a continuous melting furnace and melted at 1400 to 1500 ° C. Subsequently, the molten glass was supplied to an overflow downdraw apparatus, and the glass was formed into a plate shape.

  For the glass plate thus obtained, the number of bubbles contained in the glass was counted. As a result, the average number of bubbles having a diameter of 100 μm or more was 0.4 / kg.

  Next, the magnesium source was switched to magnesium oxide having D50 of 86 μm and D90 of 150 μm, and a glass plate was produced in the same manner. As a result, the average number of bubbles after switching was 0.03 / kg.

Claims (5)

Melting a raw material mixture comprising a silica source and magnesium source, a process for the preparation of an alkali-free glass substrate of molding, as the silica _{source, D 50} is a 30 to 150 [mu] m (except when it is 1 to 30 [mu] m) using silica raw material, and method for producing an alkali-free glass D ₉₀ as the magnesium source is characterized by using the following magnesium oxide feedstock 150 [mu] m.   The method for producing an alkali-free glass according to claim 1, wherein the amount of the magnesium oxide raw material used is adjusted so that the content of MgO in the glass composition is 0.5 to 5% by mass. The method for producing alkali-free glass according to claim 1 or 2, wherein a magnesium oxide raw material having a D50 of ₅₀ to 120 µm is used as the magnesium source .   The method for producing an alkali-free glass according to any one of claims 1 to 3, wherein the mixed raw material is prepared so that the glass has a strain point of 680 ° C or higher. SiO ₂ 55 to 70%, Al ₂ O ₃ 16 to 25%, B ₂ O ₃ 0 to 10%, MgO 0.5 to 5%, CaO 3 to 13%, SrO in mass% in terms of oxide as glass composition To prepare a mixed raw material so as to be a glass containing 0 to 10%, BaO 0 to 10%, ZrO ₂ 0 to 5%, and an alkali metal oxide content of 0.5% or less. The manufacturing method of the glass substrate in any one of Claims 1-4 characterized by the above-mentioned.