JP2012148959A - Method for producing glass substrate for liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance a clarification effect (an air bubble reduction effect) with an alkali metal oxide in producing a glass plate containing a minute amount of the alkali metal oxide as a glass substrate for a liquid crystal display device.SOLUTION: There is provided a method for producing the glass substrate for a liquid crystal display device which comprises a step for producing molten glass by melting raw materials for glass and a step for forming the molten glass into the glass plate, wherein the glass plate contains SiO, AlOand RO (R: at least one kind selected from among Li, Na and K and at least a part of them is Na) as well as comprises a glass composition having 0.01-2.0 mass% RO content and 0.01-0.15 mass% NaO content, and the raw materials for glass include aluminum oxide (alumina) containing NaO in the range of 0.1-0.6 mass% as a raw material for AlO.

Description

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

  In order to be used as a substrate for a liquid crystal display device, it is desirable that bubbles are removed to a high level. In order to remove bubbles from the molten glass, it is effective to use a fining agent containing a metal atom whose valence changes with an increase or decrease in the temperature of the molten glass. As such a fining agent, arsenic oxide and antimony oxide are known to exhibit a high fining effect. However, due to concerns about the impact on the environment, reduction of the use of arsenic oxide and antimony oxide is a social request. For this reason, the technique which removes a bubble from molten glass without relying on these is calculated | required.

  In order to solve the above-described problems, tin oxide and iron oxide are used as a clarifying agent, and a trace amount of alkali metal oxide that does not deteriorate the characteristics of the thin film transistor is present in the molten glass, thereby remaining on the glass substrate. It has been proposed to reduce bubbles (Patent Document 1). Conventionally, carbonates have been used as raw materials for alkali metal oxides (paragraph 0047).

JP 2009-203080 A

  In order to produce higher quality glass substrates for liquid crystal display devices, further research is required to remove bubbles from the molten glass. An object of the present invention is to improve the clarification effect of an alkali metal oxide when producing a glass plate containing a trace amount of an alkali metal oxide as a glass substrate for a liquid crystal display device.

The present invention
A step of melting a glass raw material to produce a molten glass;
Forming the molten glass into a glass plate,
The glass plate contains SiO ₂ , Al ₂ O ₃ and R ₂ O, and the content of R ₂ O is 0.01 to 2.0% by mass, and constitutes at least a part of the R ₂ O. A glass composition having a Na ₂ O content of 0.01 to 0.15% by mass,
The method for producing a glass substrate for a liquid crystal display device, wherein the glass raw material contains, as the Al ₂ O ₃ raw material, an aluminum oxide containing Na ₂ O as an impurity in a range of 0.1 to 0.6% by mass, I will provide a.

  Here, R is at least one selected from Li, Na and K, and at least a part thereof is Na.

According to the production method of the present invention, the clarification effect by Na ₂ O can be improved. Specifically, as has been conventionally performed, the glass substrate for a liquid crystal display device is used rather than a case where the main supply source of sodium constituting Na ₂ O is a sodium compound prepared separately from other oxide raw materials. Air bubbles remaining on the glass plate are reduced.

It is a figure which shows an example of a structure of the apparatus for enforcing the manufacturing method by this invention.

  Various studies have been conducted to improve the bubble quality of glass substrates for liquid crystal display devices.

  The inventor paid attention to the fact that bubbles remaining on the glass substrate can be reduced by allowing a small amount of alkali metal oxide to be present in the molten glass, and further researched.

  More specifically, the amount of alkali metal oxide contained in the molten glass and the raw material which is the supply source were changed to study the difference in the bubble quality of the glass. As a result, it was found that even if the same amount of alkali metal oxide is present in the molten glass, the clarification effect varies depending on the supply method.

In order to accurately control the content of the alkali metal oxide, it is preferable to suppress the amount of alkali components contained as impurities in the glass raw material as much as possible. However, as a result of research, it has been found that it is preferable to add an aluminum oxide containing a predetermined amount of Na ₂ O as an impurity to the glass raw material for improving the fining effect.

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

  Hereinafter, all the percentage displays indicating the content are mass%.

The present invention contains SiO ₂ , Al ₂ O ₃ and R ₂ O (R is at least one selected from Li, Na and K, and an element containing at least Na), and if necessary, further B ₂ O. ₃ and MO (M is an element which is at least one element selected from Mg, Ca, Sr and Ba) and the like, and the glass composition has a R ₂ O content of 0.01 to 2.0%. Suitable for manufacturing glass plates made of objects. The content of Na ₂ O in this glass composition is 0.01 to 0.15%.

Industrially produced aluminum oxide (alumina) may contain Na ₂ O as an impurity. Unlike a glass plate for window glass or the like, a glass plate for a liquid crystal display device often contains a considerable amount (for example, 10 to 25%) of Al ₂ O ₃ . For this reason, it is necessary to pay attention to Na ₂ O mixed via alumina. Conventionally, in order to produce a glass composition containing a trace amount of an alkali metal oxide, as an aluminum (Al ₂ O ₃ ) supply source, alumina having a very low content of Na ₂ O, specifically, Na ₂ O Alumina whose content is suppressed to about 0.05% or less has been used. For example, as long as alumina having a Na ₂ O content of 0.04% is used as a raw material, a glass plate made of a glass composition having a relatively high Al ₂ O ₃ content of 25% may be manufactured. Na ₂ O supplied from alumina accounts for only about 0.01% in the glass composition. Therefore, even if there is some variation in the content of Na ₂ O in the alumina used as a raw material or the amount of alumina added (weighed value) in the glass raw material batch preparation step, the content of Na ₂ O in the glass composition Is unlikely to rise above acceptable limits. Further, it is difficult to remove excessively mixed Na ₂ O from the glass composition, but it is easy to increase the content of Na ₂ O in the glass composition by separately adding a sodium compound to the glass raw material. Can be implemented.

From the above circumstances, even if a small amount of alkali metal oxide is added to the glass raw material in the hope of promoting the removal of bubbles, conventionally, while suppressing the amount of Na ₂ O mixed as an impurity as much as possible, A separately prepared sodium compound such as sodium carbonate has been added to the glass raw material to adjust the content of the alkali metal oxide in the glass composition.

As far as the present inventor is aware, there has been no report that the effect of promoting the removal of bubbles due to the presence of the alkali metal oxide in the molten glass is affected by the introduction route of the alkali metal. However, according to the study of the present inventor, Na ₂ O added together with aluminum oxide (alumina) which is a part of the glass raw material is more than Na ₂ O derived from a sodium compound added separately from alumina. Greatly contributes to the removal of bubbles. Details of the reason for this need to be waited for further analysis, but Na ₂ O, which is present in the very vicinity of alumina as an impurity, assists in the melting of alumina and contributes to the removal of bubbles by promoting melting of the glass raw material. The possibility is high.

If only the clarification effect is considered, it is better that the amount of Na ₂ O added is large. However, in order to use as a glass substrate of a liquid crystal display device, it is not appropriate to contain a large amount of Na ₂ O in the glass composition. Considering the acceptable content suitable content of Al ₂ O ₃ in this application and Na ₂ O, content of Na ₂ O contained as impurities in the alumina is desirably not exceed 0.6% . On the other hand, when the content of Na ₂ O contained in alumina is less than 0.1%, the improvement of the clarification effect is extremely limited.

Accordingly, the content of Na ₂ O contained in alumina is suitably 0.1 to 0.6%, preferably 0.2% or more, more preferably 0.25% or more, and still more preferably 0.27. % Or more, most preferably 0.3% or more, and depending on the content of Na ₂ O to be included in the glass composition, it may be 0.55% or less, and even 0.5% or less. For example, it may be limited to 0.45% or less.

In the production method of the present invention, basically, it is not necessary to separately prepare sodium compounds (sodium salts) such as sodium carbonate and sodium chloride. For this reason, the production method of the present invention can be more advantageous than the conventional method from the viewpoint of reducing raw material procurement costs. However, for example, in the case where a glass in which the content of Na ₂ O is increased to an allowable limit while keeping the content of Al ₂ O ₃ low is to be produced, a sodium compound is added to the glass raw material, and the glass composition The shortage of Na ₂ O may be compensated. In an actual mass production process, it may be desirable to add a sodium compound to the glass raw material in order to compensate for fluctuations in the amount of Na ₂ O impurities in the alumina used as the raw material. In the present invention, as long as alumina having a Na ₂ O content in the above range is used as a source of Al ₂ O ₃ in the glass composition, auxiliary addition of a sodium compound to the glass raw material is eliminated. Is not to be done.

However, in order to enhance the clarification effect, a majority of Na ₂ O contained in the glass composition (an amount exceeding 50%), more than 55%, especially 60% or more is the raw material of Al ₂ O _{3 in} the glass raw material. It is preferable to be derived from Na ₂ O contained in the aluminum oxide (alumina) contained. Even in this case, the glass raw material, as a raw material for Na ₂ O, separately from the raw material of the oxide other than Na ₂ O, may contain sodium compounds. However, it is preferable that the glass raw material does not substantially contain a sodium compound except when it is contained as an impurity in an oxide raw material other than Na ₂ O.

That is, in the present invention, it is more preferable that substantially all of Na ₂ O contained in the glass composition is derived from Na ₂ O contained as an impurity in the 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 form, it is not excluded that Na ₂ O is contained as an impurity in raw materials other than alumina constituting the glass raw material. “Substantially all” in the above description means that the ratio is high enough to occupy, for example, 90% or more, further 95% or more, more preferably 98% or more. Further, “substantially free” in the above means that the ratio is low to some extent, for example, less than 10%, further less than 5%, more preferably less than 2%.

Surprisingly, in the glass composition containing K ₂ O together with Na ₂ O as an alkali metal oxide (R ₂ O), the effect of the present invention is remarkably exhibited. In order to obtain this remarkable effect, it is preferable to add a potassium compound such as potassium carbonate, potassium nitrate, or potassium chloride to the glass raw material. It is preferred that the glass composition constituting the glass plate according to the present invention contains K ₂ O. In this case, R requires K as well as Na.

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

The glass composition preferably contains Li ₂ O, Na ₂ O and K ₂ O as R ₂ O in the following ranges.
_{· Li 2 O: 0~0.1%,} (0~0.05%), {0~0.02%}
_{· Na 2 O: 0.01~0.15%,} (0.01~0.13%), {0.02~0.12%}, [0.03~0.10%]
_{· K 2 O: 0~1.9%,} (0.1~1.5%), {0.15~1.2%}, [0.2~1.0%]

The preferred content of R ₂ O is shown below.
R ₂ O: 0.01 to 2.0%, (0.12 to 1.6%), {0.17 to 1.3%}, [over 0.2% and 1.1% or less]

It is preferable that a glass composition contains the following each components with said each component.
・ SiO ₂ : 50 to 70%, (55 to 65%), {57 to 62%}
_{· B 2 O 3: 1~18%} , (5~18%), {7~14%}, [10~13%]
_{· Al 2 O 3: 10~25%} , (15~19%), {16~18%}
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 of MO (total content of MgO, CaO, SrO and BaO) is as follows.
MO: 5-30%, (5-20)%, {5-16%}, [8-13%]

The illustration of the preferable range of the content rate of each said glass component may be suitably changed according to the content rate of another component. For example, the content of B ₂ O ₃ may be preferably 1 to 6%. In some cases, the content of Al ₂ O ₃ is preferably 18.5 to 22%. In some cases, the CaO content is preferably 8 to 11%. When the CaO content is in the range of 8 to 11%, the MgO, SrO, and BaO content is preferably 0 to 3%, particularly preferably 0 to 1%.

  Hereafter, each said component is demonstrated.

SiO ₂ is a component that forms a glass skeleton, and has an effect of increasing the chemical durability and heat resistance of the glass. If the content of SiO ₂ is too low, the effect cannot be obtained sufficiently. On the other hand, if the content of SiO ₂ is too high, the devitrification temperature is increased, the meltability is lowered, and the viscosity of the glass melt is increased.

B ₂ O ₃ is a component that lowers the viscosity of the glass and promotes melting and clarification of the glass. If the content of B ₂ O ₃ is too low, the meltability is lowered. On the other hand, if the content of B ₂ O ₃ is too high, the volatilization amount of B ₂ O ₃ from the surface of the glass melt increases, making it difficult to homogenize the glass.

Al ₂ O ₃ has an effect of increasing the strain point of glass. If the content of Al ₂ O ₃ is too low, the effect cannot be obtained sufficiently. On the other hand, if the content of Al ₂ O ₃ is too high, the viscosity of the glass increases and it may be difficult to melt the glass.

  MO is a component that lowers the viscosity of the glass and promotes melting and clarification of the glass. If the MO content is too low, the effect cannot be sufficiently obtained. On the other hand, if the MO content is too high, the chemical durability of the glass may decrease.

  Each of MgO, CaO, SrO and BaO is an optional component, and all of these need not be contained in the glass. However, in reducing the weight of the glass, the addition of MgO and CaO is relatively advantageous compared to the addition of SrO and BaO. However, if the content of MgO is too high, the phase separation property of the glass may increase and the durability against acid may decrease. Moreover, when the content rate of CaO becomes large too much, it will cause devitrification of glass. On the other hand, SrO and BaO are also components that enhance the oxidizability of the glass raw material and improve the clarity. BaO also has the effect of suppressing glass phase separation and improving meltability. However, BaO has a problem that the load on the environment is slightly large. Considering these comprehensively, it is preferable that the contents of MgO, CaO, SrO and BaO be in the ranges exemplified above.

Alkali metal oxide R ₂ O is a component that has a large effect of lowering the viscosity of the glass and is an important component for enhancing the clarity of the glass. If the content of R ₂ O is too low, the effect cannot be obtained sufficiently. On the other hand, if the content of R ₂ O is too high, alkali metal ions are eluted from the glass to deteriorate the characteristics of the TFT (Thin Film Transistor), or the thermal expansion coefficient of the glass is too high, and the substrate during the heat treatment It may cause damage. An example of the most suitable content of R ₂ O for obtaining a thermal expansion coefficient suitable for a liquid crystal display device is 0.22 to 0.5%, preferably 0.22 to 0.35%.

The glass composition constituting the glass plate produced according to the present invention contains Na ₂ O, but Li ₂ O and K ₂ O are optional components. However, K ₂ O is preferably contained as part of the alkali metal oxide. Since potassium ions (K ⁺ ) have a larger ionic radius than lithium ions (Li ⁺ ) and sodium ions (Na ⁺ ), their mobility is relatively small. For this reason, K ₂ O is less likely to cause problems caused by the movement of the alkali component as compared with Li ₂ O and Na ₂ O. Problems caused by the movement of the alkali component include generation of striae in addition to the above-described deterioration of TFT characteristics. In the glass melt, when alkali metal ions are combined with B ₂ O ₃ and volatilized from the surface of the glass melt as alkali borate, a concentration gradient of these components is formed in the glass melt. May cause striae.

Accordingly, the content of K ₂ O is, exceeds the sum of the preferably higher than content and Na ₂ O content of Li ₂ O, Li ₂ O content and Na ₂ O content of the More preferably, it may exceed twice the content of Na ₂ O. The K ₂ O content is preferably more than 0.2%.

The glass composition may contain components other than those described 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, and As ₂ O ₃ and Sb ₂ O ₃ can be exemplified. However, As ₂ O ₃ and Sb ₂ O ₃ have a large environmental load, and therefore their respective contents are preferably less than 0.1%, more preferably less than 0.01%, and particularly preferably less than 0.005%. The total content of the components listed from P ₂ O ₅ to Br is preferably 0 to 3%, more preferably 0 to 2%, more preferably 0 to 1.5%.

In addition to As ₂ O ₃ and Sb ₂ O ₃ , the oxides exemplified above include oxides of metals that can have different valences. For example, Fe is known to exist as FeO or Fe ₂ O ₃ in glass. Examples of such oxides that can be expected to have a refining effect include SnO ₂ , Fe ₂ O ₃ and CeO ₂ , particularly SnO ₂ and Fe ₂ O ₃ . The glass composition preferably further contains SnO _2, and more preferably further contains Fe ₂ O ₃ . However, if the content of these oxides is excessive, problems such as devitrification and coloring of the glass may occur. Preferable ranges of the contents of SnO ₂ , Fe ₂ O ₃ and CeO ₂ are as follows.
_{· SnO 2: 0~0.7%, (} 0.01~0.5%), {0.05~0.3%}, [0.1~0.25%]
Fe ₂ O ₃ : 0 to 0.3%, (0 to 0.2%), {0.01 to 0.15%}, [0.02 to 0.1%]
_{· CeO 2: 0~1.5%, (} 0~1.2%), {0.01~1%}

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

SO ₃ is a component that can be expected to have a clarification effect, but if it coexists with SnO ₂ , the remaining bubbles may increase. The content of SO ₃ is preferably 0 to 0.01%, more preferably 0 to 0.005%.

  Halogen elements such as F, Cl, and Br are components that can be expected to have a clarification effect. However, when a platinum stirrer is used in a glass manufacturing apparatus, bubbles may be generated by contact with platinum. The total content of F, Cl and Br is preferably 0 to 0.05%, more preferably 0 to 0.01%.

ZrO ₂ may be inevitably mixed from the refractory bricks constituting the glass plate manufacturing apparatus in the mass production process. The content of ZrO ₂ is preferably 0 to 0.2%, more preferably 0 to 0.15%.

The glass composition constituting the glass plate according to the present invention is substantially composed of SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ , MO, R ₂ O and the components listed from the above P ₂ O ₅ to Sb ₂ O _3. manner may be _{formed, SiO 2, B 2 O 3} , Al 2 O 3, MO, R 2 O, SnO 2, Fe 2 O 3, CeO 2, F, Cl, substantially Br and ZrO ₂ It may be 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. , SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ , MO, R ₂ O, SnO ₂ , Fe ₂ O ₃ and ZrO ₂ may be substantially constituted.

  Here, “substantially composed” in the above is a ratio of 99.8% or more, preferably 99.85% or more, more preferably 99.9% or more, and particularly preferably 99.95% or more. Means to occupy.

In this specification, as for oxides whose valence changes, only one type of oxide is illustrated as long as the metal elements are the same, but this excludes oxides other than the valence. Not intended (for example, FeO is allowed in glass compositions that may contain Fe ₂ O ₃ ). However, the metal oxides that can have different valences are counted in terms of their content in terms of oxides with the indicated valences (for example, in glass compositions containing Fe ₂ O ₃ and FeO, The total analysis value of Fe is expressed in terms of Fe ₂ O ₃ ).

  As materials for supplying each component, materials conventionally used except for alumina may be used. As described above, conventionally, a high-purity raw material having a low content and excluding alkali metal oxides has been used as a raw material for each component. Also in the present invention, the content of alkali metal oxide in each raw material excluding alumina is preferably less than 0.1%, preferably less than 0.05%, more preferably less than 0.03%.

  FIG. 1 is a diagram showing an example of a manufacturing apparatus for carrying out the manufacturing method of the present invention. An example of the manufacturing method of the present invention implemented using this apparatus 100 will be described below. The following is an illustration of a method suitable for mass production that continuously produces glass plates.

  First, each raw material is mixed to prepare a glass raw material batch 1. The prepared batch 1 is put into a melting tank 10 and heated to be melted, for example, into a molten glass 2 at 1500 ° C. or higher.

  The molten glass 2 passes from the melting tank 10 through the conduit 21 and flows into the clarification tank 11. Similarly to the melting tank 10, the clarification tank 11 is provided with heating means (not shown). In the clarification tank 11, the molten glass 2 is heated to, for example, 1550 ° C. or higher, and in some cases, 1600 ° C. or higher. By raising the temperature, the viscosity of the molten glass 2 decreases, and the removal of bubbles is promoted.

  Further, the molten glass 2 flows from the clarification tank 11 through the conduit 22 and flows into the stirring device 12. The molten glass 2 is stirred and homogenized by a stirrer 12b rotating in the stirring tank 12a.

  The homogenized molten glass 2 passes through the conduit 23 from the stirring device 12 and flows into the molding device 13. The molten glass 2 is cooled as it passes through the conduit 23 and is cooled to a temperature suitable for molding (for example, 1200 ° C.). The illustrated forming device 13 is a type of device that forms the molten glass 2 into a glass ribbon 3 by a so-called downdraw method. The molten glass 2 overflows from the upper part of the molding apparatus 13 and flows downward along the side wall as two flows, and becomes a glass ribbon 3 when the two flows merge at the lower end of the molding apparatus 13. The glass ribbon 3 is gradually cooled while proceeding downward, and is cut into a glass plate 4 having a predetermined size by a cutting device (not shown).

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not restrict | limited to a following example.

Each raw material was mixed so that the glass obtained by melting had the composition shown in Table 1 to prepare a glass raw material batch. The glass raw material batch was prepared so that the glass obtained was 50 g. As materials, silicon oxide (refined silica sand), boron oxide, aluminum oxide (alumina), basic magnesium carbonate, calcium carbonate, strontium nitrate, barium nitrate, potassium carbonate, tin oxide and iron oxide were used. For 5 and 7, sodium carbonate was further used. For each raw material excluding alumina and sodium carbonate, a material in which the content of sodium compounds contained as impurities was less than 0.03% in terms of Na ₂ O was used. More specifically, each raw material excluding boron oxide, alumina, and sodium carbonate was a material in which the content of sodium compounds contained as impurities was less than 0.01% in terms of Na ₂ O.

As the alumina, a material having a content of Na ₂ O contained as an impurity described in Table 2 was used. Since the meltability is affected by the size (particle size) of the raw material, the center diameter of the alumina used 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 originates only from the impurities of the raw material and mainly from the impurities of alumina (Samples 2, 4, 6, 8), or originates from the impurities of the raw materials such as alumina and sodium carbonate and mainly from the sodium carbonate. It came from either (Samples 1, 3, 5, 7). In samples 1, 3, 5, and 7, the amount of sodium carbonate added was determined so that the content of each component containing Na ₂ O was the same as the corresponding sample (samples 2, 4, 6, and 8). In Samples 1, 3, 5, and 7, the amount of Na ₂ O in the glass composition supplied via the alumina impurities is about 1/12 to 1/5 of the entire Na ₂ O.

  The glass raw material batch was put into a platinum crucible, and this platinum crucible was held in an oven maintained at an atmospheric temperature of 1500 ° C. or 1520 ° C. for 2 hours to melt the glass raw material batch. Subsequently, the platinum crucible taken out from the furnace was placed on an iron plate and rapidly cooled, and then gradually cooled at 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 the clarity was evaluated. Specifically, using a marker, 16 minute dots are placed on the circumference of a glass sample with a radius of 10 mm so as to be equally spaced, and these points are aligned with the center of the field of view of the optical microscope. The bubbles in the glass that could be confirmed in step 1 were counted. The number of bubbles was converted to 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) or when alumina having a relatively small particle size is used (samples 5 to 8), the glass composition is the same. When the sample using alumina with a Na ₂ O content of 0.1% or higher is used, the foam density of the sample is Na using a sodium salt while using alumina with a low Na ₂ O content. _It was less than the bubble density of the sample supplied with ₂ O. From the comparison between the reduction rate of the bubble density in the sample 6 and the reduction rate of the bubble density in the sample 8, it can be seen that the use of alumina having a high Na ₂ O content is advantageous in reducing the bubbles. Further, reduction rate of foam density in the sample 4 containing K ₂ O is, led up to about twice the rate of decrease in foam density in the sample 2 not containing K ₂ O.

Incidentally, there is no limitation on the particle size of the alumina for use in the manufacturing method of the present invention, from the viewpoint of improving meltability of the glass raw batch is to display the values in Table 2 margin of R _50, the particle size of the alumina 100μm Hereinafter, it is further preferably 80 μm or less, particularly preferably 70 μm or less, and may be 10 μm or less as necessary.

DESCRIPTION OF SYMBOLS 1 Glass batch 2 Molten glass 3 Glass ribbon 4 Glass plate 10 Melting tank 11 Clarification tank 12 Stirring apparatus 12a Stirring tank 12b Stirrer 13 Forming apparatus 21, 22, 23 Conduit 100 Glass plate manufacturing apparatus

Claims (14)

A step of melting a glass raw material to produce a molten glass;
Forming the molten glass into a glass plate,
The glass plate contains SiO ₂ , Al ₂ O ₃ and R ₂ O, and the content of R ₂ O is 0.01 to 2.0% by mass, and constitutes at least a part of the R ₂ O. A glass composition having a Na ₂ O content of 0.01 to 0.15% by mass,
The glass raw material, as a material of the Al ₂ O _3, containing aluminum oxide containing in the range of 0.1 to 0.6 wt% of Na ₂ O as an impurity, method of manufacturing a glass substrate for a liquid crystal display device.
Here, R is at least one selected from Li, Na and K, and at least a part thereof is Na. The method according to claim 1, wherein the amount of Na ₂ O contained in the glass composition is more than 50% by mass 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 contained as an impurity in an oxide raw material other than Na ₂ O. The glass raw material, as a raw material for the Na ₂ O, separately from the raw material of the oxide other than Na ₂ O, comprising a sodium compound, The method of claim 2. The method according to claim 1, wherein the glass composition further comprises SnO ₂ . The method according to claim 1, wherein the glass composition further comprises Fe ₂ O ₃ . The method according to claim 1, wherein the glass composition contains Al ₂ O ₃ in a range of 10 to 25% by mass. The glass composition, as the R ₂ O, including K ₂ O with Na ₂ O, The method according to any one of claims 1 to 7.   The method according to claim 8, wherein the glass raw material contains a potassium compound. Display by mass%, the glass composition, the as R ₂ O, Li include ₂ O, Na ₂ O and K ₂ O with the following ranges, according to any one of claims 1-9 the method of.
Li ₂ O: 0 to 0.1%
Na ₂ O: 0.01 to 0.15%
K ₂ O: 0 to 1.9% The method according to claim 10, wherein the content of K ₂ O exceeds 0.2%. Expressed by mass%, the glass composition is
SiO ₂ : 50 to 70%
B ₂ O ₃ : 1 to 18%
Al ₂ O ₃ : 10 to 25%
MgO: 0 to 10%
CaO: 0 to 20%
SrO: 0 to 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 according to claim 10, wherein the MO content in the glass composition is 5 to 30%.
Here, M is at least one selected from Mg, Ca, Sr and Ba. The Na ₂ O content of the aluminum oxide is 0.2 to 0.6 wt% A method according to any one of claims 1 to 12. The Na ₂ O content of the aluminum oxide is 0.25 to 0.6 wt%, The method of claim 13.

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