TWI464127B - And a method for manufacturing a glass substrate for a liquid crystal display device - Google Patents

Description

Method for manufacturing glass substrate for liquid crystal display device

The present invention relates to a method of manufacturing 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 to remove bubbles until a high level. In order to remove bubbles from the molten glass, it is effective to use a clarifying agent containing metal atoms whose valence corresponds to the rise or fall of the temperature of the molten glass. As such a clarifying agent, it is known that arsenic oxide and cerium oxide exert a high clarifying effect. However, due to concerns about the environmental impact, the reduction in the use of arsenic oxide and antimony oxide has become a social requirement. Therefore, a technique of removing bubbles from molten glass without relying on such a requirement is required.

In order to solve the above problems, it has been proposed to use a small amount of an alkali metal oxide in which molten tin and iron oxide are used as a clarifying agent and the characteristics of the thin film transistor are not deteriorated, thereby reducing the residual glass. Air bubbles in the substrate (Japanese Patent Laid-Open Publication No. 2009-203080). Previously, as a raw material of an alkali metal oxide, a carbonate was used (paragraph 0047).

In order to manufacture a glass substrate for a higher quality liquid crystal display device, further research for removing bubbles from molten glass is necessary. An object of the present invention is to improve the clarifying effect by an alkali metal oxide when a glass plate containing a trace amount of an alkali metal oxide is produced as a glass substrate for a liquid crystal display device.

The present invention provides a method for producing a glass substrate for a liquid crystal display device, comprising the steps of: melting a glass raw material to form molten glass, and forming the molten glass into a glass plate comprising SiO ₂ and Al _{2 ;} O ₃ and R ₂ O, and said R ₂ O content ratio of 0.01 to 2.0% by mass, and the R configuration at least a portion of the Na ₂ O ₂ O content ratio of 0.01 to 0.15 mass% of the glass composition, the glass The raw material contains aluminum oxide containing Na ₂ O as an impurity in the range of 0.1 to 0.6% by mass, and is used as a raw material of the above Al ₂ O ₃ .

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

According to the production method of the present invention, the clarifying effect by using Na ₂ O can be improved. Specifically, as compared with the case where the main supply source of sodium constituting Na ₂ O is used as a sodium compound prepared separately from the raw materials of other oxides, it is reduced as a glass for a liquid crystal display device. Bubbles of the glass plate of the substrate.

Various studies have been conducted in order to improve the bubble quality of the glass substrate for a liquid crystal display device.

The inventors of the present invention focused on reducing the amount of bubbles remaining on the glass substrate by allowing a trace amount of the alkali metal oxide to be present in the molten glass.

More specifically, the amount of the alkali metal oxide contained in the molten glass and the raw material of the supply source thereof are changed, and the difference in the bubble quality of the glass is examined. As a result, it was found that even if the same amount of the alkali metal oxide was present in the molten glass, the clarifying effect was different depending on the method of supplying it.

In order to accurately control the content of the alkali metal oxide, it is preferred to suppress the amount of the alkali component as an impurity contained in the glass raw material as much as possible. However, as a result of the investigation, it was found that the addition of a specific amount of Na ₂ O as an impurity to the glass raw material is preferable for improving the clarifying effect.

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

Hereinafter, the expressions indicating the % of the content rate are all the mass%.

The present invention is suitable for producing a glass plate comprising a glass composition containing SiO ₂ , Al ₂ O ₃ and R ₂ O (R is selected from at least one of Li, Na and K, and contains at least an element of Na Further, if necessary, B ₂ O ₃ and MO (M is an element selected from at least one of Mg, Ca, Sr, and Ba) and the like, and the content of R ₂ O is 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%.

Among the aluminum oxides (alumina) manufactured industrially, there is a case where Na ₂ O as an impurity is mixed. The liquid crystal display device with a window glass with a glass plate, a glass plate of different, often contain considerable amounts (e.g. 10-25%) of Al ₂ O _3. Therefore, it is also necessary to pay attention to Na ₂ O mixed in via alumina. In the prior art, in order to produce a glass composition containing a trace amount of an alkali metal oxide, alumina having an extremely low content of Na ₂ O, specifically, alumina having a Na ₂ O content of about 0.05% or less is suppressed. It is used as a supply source of aluminum (Al ₂ O ₃ ). For example, if alumina having a Na ₂ O content of 0.04% is used as a raw material, a glass plate containing a glass composition having a relatively high content of Al ₂ O ₃ and 25% is produced from alumina. Na ₂ O is also only about 0.01% in the glass composition. Therefore, even if the content of Na ₂ O in the alumina as a raw material or the amount of alumina added in the preparation step of the glass raw material batch (weighing value) somewhat changes, Na ₂ O in the glass composition The concern that the content rate rises above the allowable limit is also small. Further, although it is difficult to be mixed with an excess of Na ₂ O were removed from the glass composition, but by the addition of sodium is added to the glass raw material compound, it can be more easily implemented to improve the glass composition of the Na ₂ O content ratio.

In the case where the amount of the alkali metal oxide is added to the glass raw material in order to promote the removal of the bubbles, the amount of Na ₂ O mixed as an impurity is suppressed as much as possible. A sodium compound such as sodium is added to the glass raw material and the content of the alkali metal oxide in the glass composition is adjusted.

As far as the inventors are aware, there has been no report on the effect of removing bubbles by the presence of an alkali metal oxide in molten glass, which is affected by the introduction route of alkali metal. However, according to the study of the present inventors, Na ₂ O added together with aluminum oxide (alumina) which is a part of the glass raw material, and Na derived from a sodium compound which is not added together with alumina Compared with ₂ O, the contribution to the removal of bubbles is large. Although the details of the reason must be awaited for future analysis, the melting of the Na ₂ O-assisted alumina which is extremely close to the alumina as an impurity promotes the melting of the glass raw material and contributes to the removal of the bubbles.

If only the clarifying effect is considered, the addition amount of Na ₂ O is more preferable. However, the glass substrate for a liquid crystal display device of used, unsuitable glass composition containing a large number of Na ₂ O. When the content ratio of Al ₂ O ₃ in the application and the content ratio of Na ₂ O are considered, it is desirable that the content of Na ₂ O contained in the alumina as an impurity does not exceed 0.6%. On the other hand, when the content of Na ₂ O contained in the alumina is less than 0.1%, the improvement of the clarifying effect is greatly restricted.

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

In the production method of the present invention, basically, it is not necessary to separately prepare a sodium compound (sodium salt) such as sodium carbonate or sodium chloride. Therefore, the manufacturing method of the present invention is more advantageous than the prior art in terms of reducing the preparation cost of raw materials. For example, when a glass having a content of Al ₂ O ₃ is suppressed to a lower level and the content of Na ₂ O is increased to a permissible limit, a sodium compound may be added to the glass raw material. It compensates for the deficiency of Na ₂ O in the glass composition. In the actual mass production step, in order to compensate for variations in the Na ₂ O impurity amount in the alumina as a raw material, it is also desirable to add a sodium compound to the glass raw material. In the present invention, as the supply source of Al ₂ O ₃ in the glass composition, if the content of Na ₂ O is used as the alumina in the above range, the addition of the sodium compound to the glass raw material is not excluded.

Among them, in order to enhance the clarifying effect, it is preferred that more than half (more than 50%) of Na ₂ O contained in the glass composition, and further 55% or more, especially 60% or more, is derived from the glass raw material as Al _{2 .} The Na ₂ O contained in the aluminum oxide (alumina) contained in the raw material of O ₃ . Even when in this case, the glass raw material, the Na ₂ O as material, material other than the oxide of a different ₂ O Na, may contain a sodium compound. However, it is preferable that the glass raw material contains substantially no sodium compound except for the case where it is contained as a raw material of an oxide other than Na ₂ O as an impurity.

That is, in the present invention, the glass composition is preferably further contained in substantially all of the Na ₂ O Na ₂ O from those contained in the glass raw material as an impurity. In this case, the sodium compound is not added to the glass raw material as a separate raw material. In the preferred embodiment, it is not excluded that the raw material other than the alumina constituting the glass raw material contains Na ₂ O as an impurity. The above-mentioned "substantially all" means that the ratio is high, for example, 90% or more, further 95% or more, and more preferably 98% or more. In addition, the above-mentioned "substantially not contained" means that the ratio is as low as, for example, less than 10%, further less than 5%, and more preferably less than 2%.

Surprisingly, the effect of the present invention is remarkably exhibited in a glass composition containing K ₂ O as an alkali metal oxide (R ₂ O) together with Na ₂ O. In order to obtain such a remarkable effect, it is preferred 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 of the present invention contains K ₂ O. In this case, R is composed of Na and K as essential components.

Hereinafter, the content of each component of the preferred glass composition suitable for use in the present invention is exemplified below. Further, in the following, for each component, a more preferable content ratio is shown in (), and a preferred content ratio is shown in {}, and a particularly preferable content ratio is shown 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 ratio of R ₂ O is shown below.

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

The glass composition preferably contains the above components and the respective components below.

‧SiO ₂ : 50~70%, (55~65%), {57~62%}

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

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

‧MgO: 0~10%, (0.5~4%), {1~3%}

‧CaO: 0~20%, (2~9%), {3~8%}, [4~7%]

‧SrO: 0~20%, (0.5~9%), {1~5%}, [2~3%]

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

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

‧MO: 5~30%, (5~20)%, {5~16%}, [8~13%]

The preferred range of the content ratio of each of the above-mentioned glass components is appropriately changed depending on the content ratio of the other components. For example, there is a case where the content of B ₂ O ₃ is preferably from 1 to 6%. The content of Al ₂ O ₃ is preferably 18.5 to 22%. The content of CaO is preferably 8 to 11%. When the content of CaO is in the range of 8 to 11%, the content of MgO, SrO, and BaO is preferably 0 to 3%, particularly preferably 0 to 1%.

Hereinafter, each component described above will be described.

SiO ₂ forms a component of the skeleton of the glass and has an effect of improving the chemical durability and heat resistance of the glass. If the content of SiO ₂ is too low, the effect cannot be sufficiently obtained. On the other hand, when the content ratio of SiO ₂ is too high, the devitrification temperature rises, the meltability falls, and the viscosity of the glass melt increases.

B ₂ O ₃ system reduces the viscosity of glass and promotes the melting and clarification of glass. If the content of B ₂ O ₃ is too low, the meltability is lowered. On the other hand, when the content ratio of B ₂ O ₃ is too high, the amount of volatilization of B ₂ O ₃ from the surface of the glass melt increases, and it is difficult to achieve homogenization of the glass.

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

MO is a component that reduces the viscosity of glass and promotes the melting and clarification of glass. If the content of MO is too low, the effect cannot be fully obtained. On the other hand, if the content ratio of MO is too high, the chemical durability of the glass is lowered.

Each of MgO, CaO, SrO, and BaO is an optional component, and it is not necessary to include all of them in the glass. Among them, after lightening the glass, it is relatively advantageous to add MgO and CaO as compared with the addition of SrO and BaO. However, if the content ratio of MgO is too high, the phase separation property of the glass increases and the durability against the acid decreases. Moreover, if the content rate of CaO becomes too large, it will become a cause of devitrification of a glass. On the other hand, SrO and BaO are also components which improve the oxidizability of a glass raw material and improve clarification. Further, BaO has an effect of suppressing the phase separation of the glass and improving the meltability. However, BaO has a problem of a heavy load on the environment. In consideration of these, it is preferable to set the content ratio of MgO, CaO, SrO, and BaO to the above-exemplified range.

The alkali metal oxide R ₂ O is a component which has a large effect of lowering the viscosity of the glass, and is an important component for improving the clarity of the glass. If the content of R ₂ O is too low, the effect cannot be sufficiently obtained. On the other hand, when the content ratio of R ₂ O is too high, the 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 excessively high, and the heat treatment is performed. The cause of damage to the substrate. Further, in order to obtain a thermal expansion coefficient suitable for a liquid crystal display device, an optimum content ratio of R ₂ O is 0.22 to 0.5%, preferably 0.22 to 0.35%.

Although the glass composition constituting the glass plate produced according to the present invention contains Na ₂ O, Li ₂ O and K ₂ O are optional components. Among them, it is preferred that the K ₂ O system is contained as a part of the alkali metal oxide. Compared with lithium ion (Li ⁺ ) and sodium ion (Na ⁺ ), the potassium ion (K ⁺ ) ion has a large radius, so the mobility is relatively small. Therefore, when K ₂ O is compared with Li ₂ O and Na ₂ O, it is difficult to cause a problem caused by the movement of the alkali component. Among the problems associated with the movement of the alkali component, in addition to the deterioration of the characteristics of the TFT described above, the occurrence of streaks is also included. In the glass melt, if the alkali metal ion is combined with B ₂ O ₃ and volatilized from the surface of the glass melt in the form of boric acid, a concentration gradient of the components is formed in the glass melt to produce on the formed glass. stripe.

Therefore, the content of K ₂ O is preferably higher than the content ratio of Li ₂ O and the content of Na ₂ O, and more preferably more than the total content of Li ₂ O and the content of Na ₂ O, and may exceed The content of Na ₂ O is twice as high. The content of K ₂ O is preferably more than 0.2%.

The glass composition may also contain ingredients other than the above. Examples of such a component 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 , and La ₂ O _{3 .} , SnO ₂ , Fe ₂ O ₃ , CeO ₂ , F, Cl, Br, As ₂ O ₃ and Sb ₂ O ₃ . Among them, As ₂ O ₃ and Sb ₂ O ₃ have a large environmental load, so the respective content ratios 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 enumerated from the above P ₂ O ₅ to Br is preferably 0 to 3%, more preferably 0 to 2%, still more preferably 0 to 1.5%.

Among the oxides exemplified above, in addition to As ₂ O ₃ and Sb ₂ O ₃ , metal oxides having different valences may be contained. For example, it is known that Fe exists in the form of FeO or Fe ₂ O ₃ in glass. Examples of such an oxide which is expected to have a clarifying effect include SnO ₂ , Fe ₂ O ₃ and CeO ₂ , in particular, SnO ₂ and Fe ₂ O ₃ . The glass composition preferably further contains SnO ₂ , more preferably further contains Fe ₂ O ₃ . However, if the content of the oxides is too large, problems such as devitrification of the glass and coloring may occur. A preferred range of the content of SnO ₂ , Fe ₂ O ₃ and CeO ₂ is as follows.

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

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

‧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%, still more preferably 0.1 to 1%.

Although SO ₃ is a component which can be expected to have a clarifying effect, if it coexists with SnO ₂ , the bubble remaining on the contrary will increase. The content of SO ₃ is preferably from 0 to 0.01%, more preferably from 0 to 0.005%.

Although a halogen element such as F, Cl, or Br is a component which can be expected to have a clarifying effect, when a platinum stirrer is used in a glass manufacturing apparatus, bubbles are 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%.

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

The glass composition constituting the glass plate of the present invention may be substantially composed of SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ , MO, R ₂ O and the above-mentioned components of P ₂ O ₅ to Sb ₂ O ₃ , or 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 , or substantially 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 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 and ZrO _{2 are} formed.

Here, the above-mentioned "substantial composition" means 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.

Further, in the present specification, the oxide having a change in the valence is exemplified as long as the metal element is the same, but it is not intended to exclude the oxide other than the valence (for example, it may contain Fe _{2 )} of O ₃ in the glass composition also allow FeO). Wherein, the metal oxides of different valences can be obtained by converting the oxides into the valences of the indicated valences (for example, in the glass composition containing Fe ₂ O ₃ and FeO, the total of the analytical values of Fe) It is expressed as Fe ₂ O ₃ ).

The raw material to be supplied to each component may be any material that has been used in addition to alumina. As described above, as a raw material of each component, a high-purity raw material having a low content ratio which excludes an alkali metal oxide is used. In the present invention, the content of the alkali metal oxide in each of the raw materials other than alumina is suppressed to less than 0.1%, preferably less than 0.05%, more preferably less than 0.03%.

Fig. 1 is a view showing an example of a manufacturing apparatus for carrying out the production method of the present invention. Hereinafter, an example of the manufacturing method of the present invention which is carried out using the apparatus 100 will be described. The following is an illustration of a method for continuously producing a glass sheet and suitable for mass production.

First, each raw material was mixed to prepare a glass raw material batch 1. The prepared batch 1 is placed in the melting tank 10, heated and melted, and is, for example, molten glass 2 of 1500 ° C or higher.

The molten glass 2 flows 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 a heating mechanism (not shown). In the clarification tank 11, the molten glass 2 is heated to, for example, 1550 ° C or higher, and heated to 1600 ° C or higher as the case may be. By raising the temperature, the viscosity of the molten glass 2 is lowered to promote the removal of bubbles.

Further, the molten glass 2 flows from the clarification tank 11 through the conduit 22 to the stirring device 12. The molten glass 2 is homogenized by stirring in a stirring agitator 12b in the stirring tank 12a.

The homogenized molten glass 2 flows from the stirring device 12 through the conduit 23 into the forming device 13. The molten glass 2 is cooled while passing through the conduit 23 and cooled to a temperature suitable for forming (for example, 1200 ° C). The forming device 13 shown is a device of the type in which the molten glass 2 is formed into a glass ribbon 3 by a so-called lower pulling method. The molten glass 2 overflows from the upper portion of the forming device 13, and two branch flows flow down the side wall to the lower side, and the two branches at the lower end of the forming device 13 merge to form the glass ribbon 3. The glass ribbon 3 is slowly cooled while traveling downward, and is cut into a glass plate 4 of a specific size in a cutting device (not shown).

(Example)

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples.

Each of the raw materials was mixed to prepare a glass raw material batch in such a manner that the molten glass became the composition shown in Table 1. The glass raw batch was blended into 50 g of the resulting glass. As a raw material, cerium oxide (refined cerium), boron oxide, aluminum oxide (alumina), basic magnesium carbonate, calcium carbonate, cerium nitrate, cerium nitrate, potassium carbonate, tin oxide, and oxidation are used. Iron, regarding the samples 1, 3, 5, and 7 further use sodium carbonate. For each raw material other than alumina and sodium carbonate, the content of the sodium compound contained as an impurity is converted to Na ₂ O and is less than 0.03%. As described in more detail, each of the raw materials other than boron oxide, aluminum oxide, and sodium carbonate is used as a material in which the content of the sodium compound contained as an impurity is converted to Na ₂ O and is less than 0.01%.

As the alumina, the content of Na ₂ O contained as an impurity is used as the value described in Table 2. The meltability is affected by the size (particle size) of the raw material. Therefore, the center diameter of the alumina used is uniform: sample 1 to 4 is about 60 μm, and sample 5 to 8 is 1 to 2.5 μm. The sodium oxide in each glass is derived only from impurities of the raw material and mainly derived from impurities of alumina (samples 2, 4, 6, and 8), or impurities derived from raw materials such as alumina and sodium carbonate and mainly derived from carbonic acid. Any of sodium (samples 1, 3, 5, 7). In Samples 1, 3, 5, and 7, the amount of sodium carbonate added was defined so that the content of each component containing Na ₂ O was the same as that of the corresponding sample (samples 2, 4, 6, and 8). 1,3,5,7 in the sample, the amount of Na ₂ O of the glass composition is supplied via an impurity of the alumina is generally about 1 of Na ₂ O / 12 ~ 1/5.

The glass raw material batch was put into platinum crucible, and the platinum crucible was kept in an oven maintained at an ambient temperature of 1500 ° C or 1520 ° C for 2 hours to melt the glass raw material batch. Then, the platinum crucible taken out from the furnace was placed on an iron plate to be rapidly cooled, and then slowly cooled at 730 ° C for 1 hour.

With regard to the glass sample in the thus obtained platinum crucible, the number of bubbles was counted using an optical microscope, and the clarification was evaluated. Specifically, the marker is placed on the circumference of the glass sample with a radius of 10 mm at equal intervals to make 16 minute points so that the point coincides with the center of the field of view of the optical microscope, and the calculation can be confirmed in the field of view. Bubbles in the glass. The number of bubbles is converted to the number of glass per 1 g. The results are shown in Table 2.

* % other than the column of bubble density means mass%.

* The value in the brackets of the bubble density is the rate of decrease in the bubble density at the same temperature with respect to the sample having the same composition of the carbonate as the main additive source.

* The particle diameter (central particle diameter) is a value R50 at which the cumulative particle size of the laser diffraction method reaches 50% by mass.

Regardless of the case of using alumina with a relatively large particle size (samples 1 to 4) or the case of alumina having a relatively small particle size (samples 5 to 8), compare samples with the same glass composition. The bubble density of the sample using alumina having a Na ₂ O content of 0.1% or more is such that, on the other hand, the alumina having a lower content of Na ₂ O is used, and sodium hydroxide is supplied to the Na ₂ O side. The sample has a low bubble density. According to the comparison between the decrease rate of the bubble density in the sample 6 and the decrease rate of the bubble density in the sample 8, it is understood that the use of alumina having a high content of Na ₂ O is advantageous for the reduction of the bubble. Further, bubble density contained in the K 4 ₂ O reduction rate of the sample containing no train reaches a reduction rate of about two times the density of air bubbles in the sample of the O 2 K _2.

Further, the particle diameter of the alumina used in the production method of the present invention is not limited, but from the viewpoint of improvement in the meltability of the glass raw material batch, the value of R ₅₀ outside the column of Table 2 indicates alumina. The particle diameter is preferably 100 μm or less, more preferably 80 μm or less, particularly preferably 70 μm or less, and may be 10 μm or less as needed.

1. . . Glass batch

2. . . Molten glass

3. . . Glass belt

4. . . glass plate

10. . . Melting tank

11. . . Clarification tank

12. . . Stirring device

12a. . . Stirring tank

12b. . . Blender

13. . . Forming device

21, 22, 23. . . catheter

100. . . Glass plate manufacturing device

Fig. 1 is a view showing an example of a configuration of an apparatus for carrying out the production method of the present invention.

Claims (14)

A method for producing a glass substrate for a liquid crystal display device, comprising the steps of: melting a glass raw material to form molten glass, and forming the molten glass into a glass plate comprising SiO ₂ , Al ₂ O ₃ and R ₂ O, and the content of the R ₂ O is 0.01 to 2.0% by mass, and the content of the Na ₂ O constituting at least a part of the R ₂ O is 0.01 to 0.15% by mass, and the glass raw material is contained in 0.1. The aluminum oxide containing Na ₂ O as an impurity in the range of 0.6% by mass is used as a raw material of the above Al ₂ O ₃ . Here, R is at least one selected from the group consisting of Li, Na, and K, and at least a part thereof is Na. The method of claim 1, wherein the amount of Na ₂ O contained in the glass composition exceeds 50% by mass based on the Na ₂ O contained in the aluminum oxide. The method of claim 2, wherein the glass raw material does not substantially contain a sodium compound except when it is contained as an impurity in a raw material of an oxide other than Na ₂ O. The method of the requested item 2, wherein the glass raw material contains a raw material other than oxides except sodium ₂ O Na Na ₂ O as the compound of the starting material. The method of claim 1, wherein the glass composition further contains SnO ₂ . The method of claim 1, wherein the glass composition further contains Fe ₂ O ₃ . The method of claim 1, wherein the glass composition contains Al ₂ O ₃ in a range of 10 to 25% by mass. The method of claim 1, wherein the glass composition contains Na ₂ O and K ₂ O as the above R ₂ O. The method of claim 8, wherein the glass raw material contains a potassium compound. The method of a requested item, where% indicates the mass of the glass composition, respectively, containing as the R ₂ O of Li within the scope ₂ O, Na ₂ O and _{K 2 O: Li 2 O:} 0 ~ 0.1% Na ₂ O: 0.01 to 0.15% K ₂ O: 0 to 1.9%. The method of claim 10, wherein the content of the above K ₂ O exceeds 0.2%. The method of claim 10, wherein the glass composition comprises SiO ₂ : 50 to 70% B ₂ O ₃ : 1 to 18% Al ₂ O ₃ : 10 to 25% MgO: 0 to 10% CaO. :0~20% SrO: 0~20% BaO: 0~10% Li ₂ O: 0~0.1% Na ₂ O: 0.01~0.15% K ₂ O: 0~1.9%, and the MO in the glass composition The content ratio is 5 to 30%. Here, M is at least one selected from the group consisting of Mg, Ca, Sr, and Ba. The method of claim 1, wherein the content of Na ₂ O in the aluminum oxide is 0.2 to 0.6% by mass. The method of claim 13, wherein the content of Na ₂ O in the aluminum oxide is 0.25 to 0.6% by mass.