KR20120075426A - Production method of glass substrate for liquid crystal display - Google Patents

Abstract

PURPOSE: A manufacturing method of glass substrate for liquid crystal display is provided to improve clarifying effect by Na2O by adding predetermined amount of aluminum oxide to glass frit. CONSTITUTION: A manufacturing method of glass substrate for liquid crystal display comprises the following steps: manufacturing a molten glass(2) by fusing glass frit; and molding the molten glass into a glass plate(4). The glass composition of the glass substrate comprises SiO2, Al2O3 and R2O. The R is one or more selected from Li, Na and K, and at least part of R is Na. The inclusion rate of R2O is 0.01-2.0 mass%. The inclusion rate of Na2O which consists a part of R2O is 0.01-0.15 mass%. The glass frit includes aluminum oxide as raw material of Al2O3. 0.1-0.6 mass% of Na2O is contained in the aluminum oxide as impurities.

Description

Manufacturing method of glass substrate for liquid crystal display device {PRODUCTION METHOD OF GLASS SUBSTRATE FOR LIQUID CRYSTAL DISPLAY}

The present invention relates to a method for producing a glass substrate for a liquid crystal display device.

In order to use it as a board | substrate for liquid crystal display devices, it is calculated | required that air bubble is removed to a high level. In order to remove bubbles from the molten glass, the use of a clarifier containing a metal atom whose valence changes as the temperature of the molten glass rises or falls is effective. As such a clarifier, arsenic oxide and antimony oxide are known as exhibiting a high clarification effect. However, in view of the environmental impact, there is a social demand for reducing the use of arsenic oxide and antimony oxide. For this reason, the technique which removes air bubbles from a molten glass without resorting to these is calculated | required.

In order to solve the above-mentioned problems, it is possible to reduce bubbles remaining on the glass substrate by using tin oxide and iron oxide as clarifiers or by presenting a trace amount of alkali metal oxide in the molten glass that does not deteriorate the characteristics of the thin film transistor. It is proposed (Unexamined-Japanese-Patent No. 2009-203080). Conventionally, carbonate has been used as a raw material of alkali metal oxide (paragraph 0047).

In order to manufacture glass substrates for higher quality liquid crystal display devices, further research is required to remove bubbles from the molten glass. This invention aims at improving the clarification effect by an alkali metal oxide, when manufacturing the glass plate containing a trace amount of alkali metal oxide as a glass substrate for liquid crystal display devices.

The present invention

Melting the glass raw material to produce molten glass;

A step of molding the molten glass into a glass plate,

The glass plate comprises SiO ₂ , Al ₂ O ₃ and R ₂ O (wherein R is at least one selected from Li, Na and K, and at least part thereof is Na), and the content of R ₂ O is 0.01 to 2.0% by mass and the content by percentage of the R ₂ O Na ₂ O constituting at least a portion of the formed of a glass composition is 0.01 to 0.15 mass%,

Provides a process for the production of the glass material that the Al ₂ O ₃ glass substrate for a liquid crystal display device, comprising aluminum oxide containing in the range of 0.1 to 0.6 mass% Na ₂ O as impurities, as the material of.

According to the production process of the invention, it is possible to improve the refining effect of the Na ₂ O. Specifically, as is conventionally done, bubbles remaining on the glass plate serving as the glass substrate for a liquid crystal display device are reduced, compared with the case where the main source of sodium constituting Na ₂ O is a sodium compound prepared separately from the raw materials of other oxides. do.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows an example of the structure of the apparatus for implementing the manufacturing method by this invention.

In order to improve the bubble quality of the glass substrate for liquid crystal display devices, various studies are performed.

MEANS TO SOLVE THE PROBLEM This inventor paid attention to being able to reduce the bubble which remain | survives on a glass substrate by having a trace amount of alkali metal oxide exist in a molten glass, and advanced further.

More specifically, the quantity of the alkali metal oxide contained in a molten glass, and the raw material which is a supply source thereof was changed, and the difference of the bubble quality of glass was studied. As a result, even when the same amount of alkali metal oxide was present in the molten glass, it turned out that the clarification effect differs by the supply method.

In order to precisely control the content rate of alkali metal oxide, it is preferable to suppress the quantity of the alkali component contained as an impurity in a glass raw material as much as possible. However, the results showed that adding aluminum oxide containing a predetermined amount of Na ₂ O as an impurity to the glass raw material is preferable for the improvement of the clarification effect.

Hereinafter, the present invention will be described in more detail.

Hereinafter, all% display which shows content rate is the mass%.

The present invention includes SiO ₂ , Al ₂ O ₃ and R ₂ O (R is at least one member selected from Li, Na, and K, and includes at least Na), and further, if necessary, further B ₂ O ₃ , MO (M is at least one element selected from Mg, Ca, Sr, and Ba) and the like, and is suitable for producing a glass plate made of a glass composition having a content of R ₂ O in the range of 0.01 to 2.0%. . The content of Na ₂ O in the glass composition is 0.01% to 0.15%.

In the industrially manufactured aluminum oxide (alumina), Na ₂ O may be mixed as an impurity. A glass plate for a liquid crystal display device, window glass, etc. In contrast to a glass plate for, in many cases, including the Al ₂ O ₃ in large amounts (e.g. 10-25%). For this reason, attention should also be paid to Na ₂ O mixed via alumina. Conventionally, in order to produce a glass composition containing alkali metal oxide, a trace amount of aluminum (Al ₂ O ₃₎ as the source, the content of Na ₂ O is very low alumina, specifically, less than about 0.05% content of Na ₂ O Alumina suppressed until now has been used. For example, as long as alumina having a content of Na ₂ O of 0.04% is used as a raw material, even if a glass plate made of a glass composition having a relatively high content of Al ₂ O ₃ and occupying 25% is produced, Na supplied from alumina ₂ O only accounts for about 0.01% in the glass composition. Therefore, even if a content of Na ₂ O in the alumina, or glass material addition amount variation of somewhat to (weighed value) of alumina in the manufacturing process of a batch of raw material, the content of Na ₂ O in the glass composition There is little concern about going beyond the allowable limit. Also, to remove the over-the Na ₂ O from the glass composition incorporated difficult, but it is to enhance the content of Na ₂ O in the glass composition it can be easily carried out by separate addition of sodium compounds to the glass raw material.

In view of the above circumstances, even when a small amount of alkali metal oxide is added to the glass raw material in anticipation of the acceleration of bubble removal, conventionally, sodium compounds such as sodium carbonate prepared separately while suppressing the amount of Na ₂ O mixed as impurities to the maximum. Was added to the glass raw material, and the content rate of the alkali metal oxide in the glass composition has been adjusted.

As far as the present inventors are aware, there have been no reports that the promoting effect of bubble removal by the presence of alkali metal oxide in the molten glass is affected by the introduction route of the alkali metal. However, according to the inventor's review, Na ₂ O added together with aluminum oxide (alumina), which is part of the glass raw material, contributes to the removal of bubbles more than Na ₂ O derived from the sodium compound added separately from alumina. Big. The detailed reason needs to wait for further analysis, but there is a high possibility that Na ₂ O present in the vicinity of alumina as an impurity assists in dissolving alumina, promotes melting of the glass raw material, and contributes to the removal of bubbles.

Considering only the clarification effect, it is preferable that the amount of Na ₂ O added is large. However, in order to use a glass substrate of a liquid crystal display device, it is not suitable for containing a large amount of Na ₂ O in the glass composition. In consideration of the appropriate content of Al ₂ O _{3 and} the acceptable content of Na ₂ O in this application, it is preferable that the content of Na ₂ O contained as impurities in the alumina does not exceed 0.6%. On the other hand, when the content of Na ₂ O contained in the alumina level to fall below 0.1%, an improvement in the refining effect is very limited.

Therefore, the content of Na ₂ O contained in the alumina is appropriately 0.1 to 0.6%, preferably 0.2% or more, more preferably 0.25% or more, still more preferably 0.27% or more, most preferably 0.3% or more. The content of Na ₂ O for inclusion in the glass composition may be 0.55% or less, and 0.5% or less, and if necessary, it may be limited to 0.45% or less.

In the production method of the present invention, there is no need to separately prepare sodium compounds (sodium salts) such as sodium carbonate and sodium chloride. For this reason, also from the viewpoint of reducing the procurement cost of raw materials, the manufacturing method of the present invention may be advantageous over the prior art. However, for example, when it is necessary to produce a glass in which the content of Na ₂ O is raised to an acceptable limit while suppressing the content of Al ₂ O ₃ low, a sodium compound is added to the glass raw material to give Na ₂ O in the glass composition. It can also compensate for the lack of. In the mass production process of reality, in order to compensate the variation of the Na ₂ O impurities in the alumina as a raw material, which may be desirable to add a sodium compound in a glass material. In the present invention, as long as alumina having a content of Na ₂ O in the above-described range is used as the source of Al ₂ O _{3 in} the glass composition, auxiliary addition of the sodium compound to the glass raw material is not excluded.

However, in order to enhance the refining effect, the (amount exceeding 50%), a majority of the Na ₂ O, also more than 55%, in particular more than 60% contained in the glass composition, it is included as a material of Al ₂ O ₃ in the glass raw material it is derived from the Na ₂ O contained in the aluminum oxide (alumina), it is preferred. Also in this case, glass materials may comprise a sodium compound separately from the raw material of the oxide other than as a material of Na ₂ O, Na ₂ O. However, glass materials are preferably, except when contained as impurities in the raw material of the oxide other than the Na ₂ O, and that is substantially free of sodium compounds.

That is, in the present invention, Na ₂ O is substantially all contained in the glass composition, and more preferably it is derived from the Na ₂ O contained as impurities in a glass raw material. In this case, the sodium compound is not added to the glass raw material as an independent raw material. However, even in this preferred embodiment, it is not excluded until Na ₂ O is included as an impurity in the raw materials other than the alumina constituting the glass raw material. "Substantially all" in the above means that a ratio is high so that it may occupy 90% or more, 95% or more, more preferably 98% or more, for example. In addition, said "substantially free" mentioned above means that a ratio is low, for example less than 10%, and also less than 5%, More preferably, less than 2%.

Surprisingly, for glass compositions comprising K ₂ O with Na ₂ O as alkali metal oxide (R ₂ O), the effect of the present invention is remarkable. In order to acquire this remarkable effect, it is preferable to add potassium compounds, such as potassium carbonate, potassium nitrate, and potassium chloride, to a glass raw material. Glass composition constituting the glass plate according to the present invention, it is preferable that contains K ₂ O. In this case, R requires K together with Na.

Hereinafter, the content rate of each component of the glass composition suitable for application of this invention is illustrated below. In addition, below, about a each component, a more preferable content rate is shown in (), a more preferable content rate is in {}, and a particularly preferable content rate is shown in [].

Glass composition, as R ₂ O, it is preferred to include in the scope of the following Li ₂ O, Na ₂ O and K ₂ O, respectively.

Li ₂ O: 0 to 0.1%, (0 to 0.05%), {0 to 0.02%}

Na ₂ O: 0.01 to 0.15%, (0.01 to 0.13%), {0.02 to 0.12%}, [0.03 to 0.10%]

K ₂ O: 0 to 1.9%, (0.1 to 1.5%), {0.15 to 1.2%}, [0.2 to 1.0%]

It shows a preferred content of R ₂ O in the following.

R ₂ O: 0.01 to 2.0%, (0.12 to 1.6%), {0.17 to 1.3%}, [more than 0.2% to 1.1% or less]

It is preferable that a glass composition contains each of the following components with each said component.

SiO ₂ : 50 to 70%, (55 to 65%), {57 to 62%}

B ₂ O ₃ : 1 to 18%, (5 to 18%), {7 to 14%}, [10 to 13%]

Al ₂ O ₃ : 10 to 25%, (15 to 19%), {16 to 18%}

MgO: 0 to 10%, (0.5 to 4%), {1 to 3%}

CaO: 0 to 20%, (2 to 9%), {3 to 8%}, [4 to 7%]

SrO: 0 to 20%, (0.5 to 9%), {1 to 5%}, [2 to 3%]

BaO: 0 to 10%, (0 to 6.5%), {0 to 2%}, [0.5 to 1%]

Here, the preferable content rate of MO (total content rate of MgO, CaO, SrO, and BaO) is as follows.

MO: 5 to 30%, (5 to 20%), {5 to 16%}, [8 to 13%]

The example of the preferable range of the content rate of each glass component mentioned above may need to be changed suitably according to the content rate of another component. For example, the content of B ₂ O ₃ is in some cases from 1 to 6% preferred. The content of Al ₂ O ₃ is in some cases is 18.5 to 22% preferred. 8 to 11% of a content rate of CaO may be preferable. When content rate of CaO exists in 8 to 11% of range, content rate of MgO, SrO, and BaO is 0 to 3%, respectively, and 0 to 1% is especially preferable.

Hereinafter, each said component is demonstrated.

SiO ₂ is a component constituting the skeleton of the glass, and has a function of increasing chemical durability and heat resistance of the glass. If the content of SiO ₂ is too low, the effect is not sufficiently obtained. On the other hand, when the content of SiO ₂ is too high, loss of transparency, the temperature increases, as well as be a meltable lowering elevated the viscosity of the glass melt.

B ₂ O ₃ is a component that lowers the viscosity of the glass and promotes dissolution and clarification of the glass. If the content of B ₂ O ₃ is too low, the melting property is deteriorated. On the other hand, when the content of B ₂ O ₃ is too high, volatilization becomes large amount of B ₂ O ₃ from the molten glass surface, it is difficult to homogenize the glass.

Al ₂ O ₃ has the effect of increasing the strain point of the glass. If the content of Al ₂ O ₃ is too low, the effect is not sufficiently obtained. On the other hand, when the content of Al ₂ O ₃ is too high, there is a case to increase the viscosity of the glass become difficult, the dissolution of the glass.

MO is a component that lowers the viscosity of the glass and promotes dissolution and clarification of the glass. When the content rate of MO is too low, the effect is not fully acquired. On the other hand, when the content rate of MO is too high, the chemical durability of glass may fall.

Each of MgO, CaO, SrO and BaO is an optional component, and all of these need not be included in the glass. However, to reduce the weight of glass, the addition of MgO and CaO is relatively advantageous compared to the addition of SrO and BaO. However, when the content rate of MgO is too high, the powder phase property may increase, and durability to an acid may fall. In addition, excessively large content of CaO causes a loss of transparency of the glass. On the other hand, SrO and BaO are also components which raise the oxidizing property of a glass raw material and raise clarity. Moreover, BaO has an effect which suppresses powder phase of glass and improves solubility. However, BaO has a problem that the load on the environment is slightly large. In consideration of these comprehensively, it is preferable that the content rates of MgO, CaO, SrO, and BaO be in the ranges exemplified above.

Alkali metal oxides R ₂ O is, in a large effect of lowering the viscosity of the glass component, and is an important component for enhancing the fining of the glass. If the content of R ₂ O is too low, the effect is not sufficiently obtained. On the other hand, when the content of R ₂ O is too high, alkali metal ions elute from the glass to deteriorate the characteristics of the TFT (Thin Film Transistor), or the coefficient of thermal expansion of the glass is too high, which may cause breakage of the substrate during heat treatment. . It is also most preferred example of the content of R ₂ O to obtain a suitable thermal expansion coefficient of the liquid crystal display device is 0.22 to 0.5%, preferably from 0.22% to 0.35%.

Na ₂ O is included in the glass composition constituting the glass plate produced by the present invention, but Li ₂ O and K ₂ O are optional components. However, K ₂ O is preferably included as a part of the alkali metal oxides. Potassium ion (K ⁺ ) has a relatively small mobility because the ion radius is larger than lithium ions (Li ⁺ ) and sodium ions (Na ⁺ ). For this reason, K ₂ O is unlikely to cause a problem caused by the movement of the alkaline component as compared with Li ₂ O and Na ₂ O. Problems arising due to the movement of the alkaline component include the generation of stria in addition to the deterioration of the characteristics of the TFT described above. In some cases from the glass melt, if the alkali metal ions in combination with B ₂ O ₃ volatilization from the surface of the glass melt as boric acid, alkali, and forming a concentration gradient of these components in the glass melt, causing the striae in the glass being formed.

Accordingly, the content of K ₂ O is preferably higher than the content of the Li ₂ O content and Na ₂ O of, and more preferably that exceeds the sum of the content of Li ₂ O and Na in ₂ O content, Na It may exceed two times the content of O _2. The content of K ₂ O is preferably in excess of 0.2%.

The glass composition may also contain components other than the above. Such components include P ₂ O ₅ , SO ₃ , TiO ₂ , ZrO ₂ , ZnO, MnO, Nb ₂ O ₅ , Ta ₂ O ₅ , MoO ₃ , WO ₃ , Y ₂ O ₃ , La ₂ O ₃ , SnO ₂ , Fe ₂ O ₃ , CeO ₂ , F, Cl, Br, As ₂ O ₃ and Sb ₂ O ₃ can be exemplified. However, as As ₂ O ₃ and Sb ₂ O ₃ have a large environmental load, the respective content rates are preferably less than 0.1%, and also less than 0.01%, particularly less than 0.005%. The total of the content of the listed ingredients as described by from P ₂ O ₅ to the Br is preferably 0-3%, more preferably 0 to 2%, more preferably 0 to 1.5%.

Examples of the oxides exemplified above include As ₂ O ₃ and Sb ₂ O _3. In addition, oxides of metals that can take on different valences are also included. For example, Fe, it is known that present as FeO or Fe ₂ O ₃ from the glass. Examples of such oxides that can expect a clarification effect include SnO ₂ , Fe ₂ O _3, and CeO ₂ , in particular SnO ₂ and Fe ₂ O ₃ . The glass composition, it is preferable to further include SnO _2, and more preferably further comprising Fe ₂ O _3. However, when the content rate of these oxides becomes excessive, problems, such as loss of transparency of a glass and coloring may arise. A preferable range of the content of SnO _2, Fe ₂ O ₃ and CeO ₂ is as follows.

SnO ₂ : 0 to 0.7%, (0.01 to 0.5%), {0.05 to 0.3%}, [0.1 to 0.25%]

Fe ₂ O ₃ : 0 to 0.3%, (0 to 0.2%), {0.01 to 0.15%}, [0.02 to 0.1%]

CeO ₂ : 0 to 1.5%, (0 to 1.2%), {0.01 to 1%}

SnO _2, the total of the content of Fe ₂ O ₃ and CeO ₂ is preferably 0 to 1.5%, more preferably from 0.01 to 1.2%, more preferably 0.1 to 1%.

Although SO ₃ is a component in which a clarification effect can be expected, when coexisting with SnO ₂ , bubbles remaining may increase. The content rate of SO ₃ becomes like this. Preferably it is 0 to 0.01%, More preferably, it is 0 to 0.005%.

Halogen elements, such as F, Cl, and Br, are components which can expect a clarification effect, but when a stirrer made of platinum is used for a glass manufacturing apparatus, air bubbles may be generated by contact with platinum. The sum total of content rates of F, Cl, and Br becomes like this. Preferably it is 0 to 0.05%, More preferably, it is 0 to 0.01%.

ZrO ₂ may be inevitably mixed from the refractory brick constituting the glass plate manufacturing apparatus in the mass production step. The content rate of ZrO ₂ becomes like this. Preferably it is 0 to 0.2%, More preferably, it is 0 to 0.15%.

Glass composition constituting the glass plate according to the present invention is substantially composed from ingredients described to open to _{SiO 2, B 2 O 3,} Al 2 O 3, MO, R 2 O and the P ₂ O ₅ from Sb ₂ O ₃ May be substantially composed of SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ , MO, R ₂ O, SnO ₂ , Fe ₂ O ₃ , CeO ₂ , F, Cl, Br and ZrO ₂ , May be substantially composed of SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ , MO, R ₂ O, SnO ₂ , Fe ₂ O ₃ , CeO ₂ and ZrO ₂ , and SiO ₂ , B ₂ O ₃ , Al ₂ It may also consist substantially from O ₃ , MO, R ₂ O, SnO ₂ , Fe ₂ O ₃ and ZrO ₂ .

Here, the term "substantially constituted" means 99.8% or more, preferably 99.85% or more, more preferably 99.9% or more, and particularly preferably 99.95% or more.

Further, in this present specification, with respect to the oxide valence change, but illustrates only the oxide of one kind the same by the metal element, which is not intended to exclude the oxide other than the singer (e.g., Fe ₂ O ₃ FeO is also acceptable in glass compositions that may be included). However, an oxide of a metal capable of having a different hydrolysis is, it is assumed that, in terms of an oxide of a representation mantissa count his content (for example, the glass composition comprising a Fe ₂ O ₃ and FeO, the Fe analysis value To be expressed in terms of Fe ₂ O ₃ ).

The raw material which supplies each component can use the material conventionally used except alumina. As described above, conventionally, as a raw material of each component, a high-purity raw material having low alkali metal oxide content and low content thereof has been used. Also in this invention, it is preferable to suppress the content rate of the alkali metal oxide in each raw material except alumina to less than 0.1%, Preferably it is less than 0.05%, More preferably, it is less than 0.03%.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows an example of the manufacturing apparatus for implementing the manufacturing method of this invention. An example of the manufacturing method of this invention implemented using this apparatus 100 is demonstrated below. The following is an example of the method suitable for mass production which continuously manufactures a glass plate.

First, each raw material is mixed and the glass raw material batch 1 is manufactured. The manufactured batch 1 is thrown into the dissolution tank 10, heated and melt | dissolved, and it becomes the molten glass 2 of 1500 degreeC or more, for example.

The molten glass 2 flows into the clarification tank 11 through the conduit 21 from the melting tank 10. Similarly to the dissolution tank 10, the clarification tank 11 is provided with the heating means which abbreviate | omits illustration. In the clarification tank 11, the molten glass 2 is heated to 1550 degreeC or more, if necessary, to 1600 degreeC or more, for example. By heating up, the viscosity of the molten glass 2 falls, and removal of air bubbles is accelerated.

In addition, the molten glass 2 flows into the stirring apparatus 12 from the clarification tank 11 through the conduit 22. The molten glass 2 is stirred and homogenized by the stirrer 12b which rotates in the stirring tank 12a.

The homogenized molten glass 2 flows into the shaping | molding apparatus 13 from the stirring apparatus 12 through the conduit 23. When the molten glass 2 passes through the conduit 23, it is cooled and cooled to the temperature (for example, 1200 degreeC) suitable for shaping | molding. The molding apparatus 13 shown is an apparatus of the type which shape | molds the molten glass 2 into the glass ribbon 3 by what is called a downdraw method. The molten glass 2 overflows from the upper part of the shaping | molding apparatus 13, becomes two flows, and flows downward along a side wall, and the two flows of the glass ribbon 3 join at the lower end of the shaping | molding apparatus 13, do. The glass ribbon 3 is slow cooled while advancing downward, and is cut | disconnected by the glass plate 4 of a predetermined | prescribed magnitude | size by the cutting device not shown.

(Example)

Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to a following example.

Each raw material was mixed and the glass raw material batch was manufactured so that the glass obtained by melting may become the composition shown in following Table 1. The glass raw material batch was combined so that the glass obtained might be 50 g. Examples of the raw materials include silicon oxide (purified silica sand), boron oxide, aluminum oxide (alumina), basic magnesium carbonate, calcium carbonate, strontium nitrate, barium nitrate, potassium carbonate, tin oxide and iron oxide. , Carbonate was further used sodium carbonate. Each raw material other than the sodium carbonate and alumina, the content of sodium compounds contained as impurities are converted into Na ₂ O was used as the material less than 0.03%. In more detailed description, respective raw materials other than the boron oxide, alumina, and sodium carbonate, the content of sodium compounds contained as impurities are converted into Na ₂ O was used as the material of less than 0.01%.

Alumina include, to the content of Na ₂ O contained as an impurity was used to be the value shown in Table 2. Since solubility was influenced by the size (particle diameter) of the raw material, the center diameter of the used alumina was unified to about 60 µm for Samples 1 to 4 and 1 to 2.5 µm for Samples 5 to 8. Sodium oxide in each glass is derived not only from the impurities of the raw material, but mainly from the impurities of alumina (Samples 2, 4, 6, 8), or from the impurities of the raw materials such as alumina and sodium carbonate, and mainly from sodium carbonate. It was either derived (samples 1, 3, 5, 7). In samples 1, 3, 5, and 7, the addition amount of sodium carbonate was determined so that the content rate of each component containing Na ₂ O was the same as that of the corresponding sample (samples 2, 4, 6, 8). In Samples 1, 3, 5, and 7, the amount of Na ₂ O in the glass composition supplied via the impurity of alumina is about 1/12 to 1/5 of the entire Na ₂ O.

The glass raw material batch was put into a platinum crucible, the platinum crucible was kept in a furnace kept at an ambient temperature of 1500 ° C or 1520 ° C for 2 hours, and the glass raw material batch was melted. Subsequently, the platinum crucible taken out in the furnace was placed on an iron plate and quenched, followed by slow cooling under conditions of 730 ° C for 1 hour.

About the glass sample in the platinum crucible thus obtained, the number of bubbles was counted using an optical microscope, and clarity was evaluated. Specifically, 16 minute points are taken on the circumference of a radius of 10 mm on the glass sample using a marker so as to be equally spaced, and this point is aligned with the center of the field of view of the optical microscope, and the glass can be confirmed within the field of view. Bubbles were counted. The number of bubbles was converted into the number per 1 g of glass. The results are shown in Table 2.

Even when alumina having a relatively large particle size is used (samples 1 to 4), even when alumina having a relatively small particle size is used (samples 5 to 8), the content of Na ₂ O is 0.1 when comparing the samples having the same glass composition. The bubble density of the sample using% or more of alumina was smaller than the bubble density of the sample supplied with Na ₂ O using sodium salt while using alumina having a low Na ₂ O content as it is. It is understood that the use of alumina having a high content of Na ₂ O is advantageous for the reduction of bubbles from the contrast between the decrease rate of bubble density in sample 6 and the decrease rate of bubble density in sample 8. Further, the decrease rate of the cell density of the sample 4 containing K ₂ O is reached up to twice the rate of decrease of the cell density of the sample 2 does not contain a K ₂ O.

Further, although the in the alumina particle size to be used in the production method of the present invention limits, in terms of solubility improvement of a glass raw material batch, to show by the value of R ₅₀ except Table 2 is, the particle diameter of alumina is less than 100 ㎛, also 80 micrometers or less, especially 70 micrometers or less are preferable and you may be 10 micrometers or less as needed.

Claims (14)

Melting the glass raw material to produce molten glass;
A step of molding the molten glass into a glass plate,
The glass plate contains SiO ₂ , Al ₂ O ₃ and R ₂ O (wherein R is at least one selected from Li, Na, and K, and at least a portion thereof is Na), and the content of R ₂ O is and 0.01 to 2.0% by mass, R is the content of Na ₂ O constituting at least a portion of the O ₂ is made of a glass composition is 0.01 to 0.15 mass%,
Method of producing a glass substrate for the glass raw material as a material of the Al ₂ O ₃ comprising aluminum oxide containing in the range of 0.1 to 0.6 mass% Na ₂ O as an impurity, a liquid crystal display device. The method of claim 1 wherein the amount exceeding 50% by weight of Na ₂ O contained in the glass composition, which is derived from Na ₂ O contained in the aluminum oxide. The method according to claim 2, wherein the glass raw material is substantially free of a sodium compound except when the glass raw material is included as an impurity in a raw material of an oxide other than Na ₂ O. The method of claim 2, wherein said glass raw material comprises a sodium compound separately from the raw material of the oxide other than the Na ₂ O as raw materials for the Na ₂ O. The method of claim 1, wherein the glass composition further comprises SnO ₂ . The method of claim 1, wherein the glass composition further comprises Fe ₂ O ₃ . The method of claim 1 wherein the glass composition comprises Al ₂ O ₃ in the range of 10-25 mass%. The method of claim 1, wherein the glass composition comprises K ₂ O with Na ₂ O as the R ₂ O. 7. The method of claim 8, wherein the glass raw material comprises a potassium compound. The method of claim 1 wherein the indication in mass%, the method comprises as said glass composition wherein R ₂ O in the range below the Li ₂ O, Na ₂ O and K ₂ O, respectively.
Li ₂ O: 0% to 0.1%
Na ₂ O: 0.01% to 0.15%
K ₂ O: 0 to 1.9% 11. The method of claim 10, wherein to the content of the K ₂ O exceeds 0.2%. The said glass composition of Claim 10 expressed by the mass%,
SiO ₂ : 50 to 70%
B ₂ O ₃ : 1-18%
Al ₂ O ₃ : 10-25%
MgO: 0 to 10%
CaO: 0-20%
SrO: 0-20%
BaO: 0 to 10%
Li ₂ O: 0% to 0.1%
Na ₂ O: 0.01% to 0.15%
K ₂ O: 0 to 1.9%
Including,
The method in which the content rate of MO (wherein M is at least one selected from Mg, Ca, Sr and Ba) in the glass composition is 5 to 30%. The method of claim 1, wherein the content of Na ₂ O in the aluminum oxide of 0.2 to 0.6 mass%. 14. The method of claim 13, wherein the content of Na ₂ O in the aluminum oxide of 0.25 to 0.6 mass%.

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