TWI629248B - Method for producing glass substrate, glass substrate and glass substrate laminate - Google Patents

Abstract

In the method for producing a glass substrate of the present invention, even if impurities of a platinum group metal are mixed in the glass substrate, strain is less likely to occur on the glass substrate, and unevenness of the main surface of the glass substrate is less likely to be formed. The method for producing a glass substrate of the present invention comprises: a molten glass treatment step of forming a gas phase space surrounded by a surface of the molten glass and a wall by introduction of molten glass, and at least a part of the wall is made of a material containing a platinum group metal When the molten glass is processed in the glass processing apparatus, the aggregate of the volatile matter of the platinum group metal which is volatilized from the wall in the gas phase space is mixed as a foreign matter; and the agglomerate processing step reduces the size of the aggregate so that In the molten glass treatment step, the ratio of the number of aggregates having a maximum length of 50 μm or less is 70% or more. The total volume of the glass substrate of the glass substrate laminate is 0.1 m ³ or more, and the ratio of the number of aggregates having a maximum length of 50 μm or less in all the platinum group metal aggregates contained in the glass substrate is 70% or more.

Description

Method for producing glass substrate, glass substrate and glass substrate laminate

The present invention relates to a method for producing a glass substrate, a glass substrate, and a glass substrate laminate.

In general, a glass substrate is produced by a step of forming a molten glass from a glass raw material, passing through a clarification step, a homogenization step, and forming a molten glass into a glass substrate. However, in order to mass-produce a high-quality glass substrate from a high-temperature molten glass, it is desirable to mix any glass processing apparatus which does not manufacture a glass substrate, such as a foreign material which is a main cause of a glass substrate, into a molten glass. Therefore, the wall of the member that is in contact with the molten glass during the production of the glass substrate must be made of a suitable material depending on the temperature of the molten glass that is in contact with the member, the quality of the desired glass substrate, and the like.

For example, since the molten glass is in an extremely high temperature state after the molten glass is produced and supplied to the molding step, the apparatus for melting, clarifying, supplying, and stirring is made of a member containing platinum as a platinum group metal having high heat resistance ( For example, Patent Document 1).

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2010-111533

However, platinum group metals tend to volatilize at high temperatures. Further, if the volatile matter of the platinum group metal is agglomerated, the molten glass is mixed as a part of the crystal of the aggregate as a foreign matter. There is a concern that the quality of the glass substrate is degraded. In particular, the clarification step is the step of the highest temperature of the molten glass from the melting step to the forming step, so that the clarification tube mainly performing the clarification step is heated to an extremely high temperature. Therefore, in the molten glass after the clarification step, a part of the aggregate obtained by agglomerating the platinum group metal volatilized from the clarification tube is likely to be mixed into the foreign matter.

If a foreign matter of a platinum group metal is mixed in the glass substrate manufacturing process, the following problem occurs: strain is generated in the glass substrate due to the difference in thermal expansion coefficient between the foreign matter of the platinum group metal and the glass, and the display may cause display failure due to the strain; Alternatively, the platinum group metal may be present in the vicinity of the main surface of the glass substrate to form irregularities on the main surface of the glass substrate, so that the formation of the thin film transistor (TFT) provided on the main surface cannot be uniformly performed, thereby causing the display to be produced. Poor display. In recent years, with the high-definition display of the image display device, it has been strongly demanded to reduce the foreign matter of the platinum group metal mixed in the glass substrate in the glass substrate used for the display.

Thus, it is preferable to reduce the amount of foreign matter (agglomerate) of the platinum group metal mixed in the glass substrate. However, the temperature of the molten glass before forming is extremely high, particularly in the clarification tube in which the clarification step is performed, the oxygen which is the cause of the volatilization of the platinum group metal cannot be excluded from the gas phase space atmosphere of the clarification tube, and the platinum cannot be completely eliminated. Volatile metal. Further, in the clarification pipe, the temperature difference of the inner wall surface of the apparatus which is a cause of aggregation of the volatile matter of the platinum group metal cannot be made zero, and the volatilization of the platinum group metal cannot be completely eliminated. Therefore, it is difficult to completely prevent the foreign matter (agglomerate) of the platinum group metal from being mixed into the molten glass during the manufacturing process.

Therefore, an object of the present invention is to provide a method for producing a glass substrate, a glass substrate, and a glass substrate laminate which are less likely to cause the above problems even if a foreign substance (aggregate) of a platinum group metal is mixed in a glass substrate.

As described above, in view of the fact that it is difficult to completely prevent the foreign matter (aggregate) of the platinum group metal from being mixed into the molten glass during the manufacturing process of the glass substrate, the inventors of the present application even In the molten glass, a foreign matter (agglomerate) in which a platinum group metal is mixed is not easily explored in the form of a foreign matter which is strained on the glass substrate and which is less likely to form irregularities on the main surface of the glass substrate. As a result, the maximum length of the platinum group metal is 50 μm or less. It is effective for not easily causing strain on the glass substrate, and it is difficult to form the unevenness of the main surface of the glass substrate, and the foreign matter of the platinum group metal mixed in the glass substrate ( In the aggregates, it is effective that the number ratio of the foreign matter (agglomerate) of the platinum group metal having a maximum length of the platinum group metal of 50 μm or less is 70% or more. In particular, it has been found that the size of the foreign matter (aggregate) of the platinum group metal mixed in the molten glass at the time of producing the glass substrate is effective for not easily causing strain on the glass substrate and making it difficult to form the unevenness of the main surface of the glass substrate. This finding cannot be easily conceived in the prior art in order to suppress the occurrence of display defects and reduce the absolute number of foreign substances (agglomerates) of the platinum group metal.

That is, one aspect of the present invention is a method of producing a glass substrate. The method for producing the glass substrate includes the following aspects.

(first form)

A method for producing a glass substrate, comprising: a melting step of melting a glass raw material to form molten glass; and a molten glass processing step of treating the molten glass in a glass processing apparatus, wherein the glass processing apparatus is formed by introduction of the molten glass a space between the surface of the molten glass and a gas phase space surrounded by the wall, wherein at least a portion of the wall is made of a material containing a platinum group metal, and when the molten glass is processed, the platinum volatilized from the wall in the gas phase space The aggregate of the volatiles of the group metal is mixed as a foreign matter into the molten glass, and includes an agglomerate treatment step of reducing the size of the agglomerates mixed into the molten glass so as to be mixed into the aggregate of the molten glass, and the largest The ratio of the number of aggregates having a length of 50 μm or less is 70% or more.

(second form)

A method for producing a glass substrate, comprising: a melting step of melting a glass raw material to form molten glass; and a molten glass processing step of treating the molten glass in a glass processing apparatus, wherein the glass processing apparatus has a liquid phase containing the molten glass, and a gas phase space formed by the liquid surface and the wall of the molten glass, at least a part of the wall surrounding the gas phase space is made of a material containing a platinum group metal, and is present in the gas phase space when the molten glass is processed. The agglomerate of the volatile matter of the platinum group metal volatilized from the wall is mixed as the foreign matter into the molten glass; and the agglomerate treatment step of reducing the size of the agglomerate mixed into the molten glass so that the molten glass treatment step is The ratio of the number of aggregates having a maximum length of 50 μm or less mixed into the aggregate of the molten glass is 70% or more.

(third form)

A method for producing a glass substrate, comprising: a melting step of melting a glass raw material to form molten glass; and a molten glass processing step of treating the molten glass in a glass processing apparatus, wherein the glass processing apparatus is formed by introduction of the molten glass a space between the surface of the molten glass and a gas phase space surrounded by the wall, wherein at least a portion of the wall is made of a material containing a platinum group metal, and when the molten glass is processed, the platinum volatilized from the wall in the gas phase space The aggregate of the volatiles of the group metal is mixed as a foreign matter into the molten glass, and includes an agglomerate treatment step of adjusting the solubility of the agglomerate in the molten glass to reduce the size of the agglomerates mixed into the molten glass.

(fourth form)

A method for producing a glass substrate includes: a melting step of melting a glass raw material to form molten glass; and a molten glass processing step of treating the molten glass in a glass processing apparatus, The glass processing apparatus includes a liquid phase including the molten glass, and a vapor phase space formed by a liquid surface and a wall of the molten glass, and at least a part of a wall surrounding the vapor phase space is made of a material containing a platinum group metal, and When the molten glass is treated, the aggregate of the volatile matter of the platinum group metal volatilized from the wall in the gas phase space is mixed as a foreign matter into the molten glass, and further includes an agglomerate treatment step, and the control is provided to the agglomeration The amount of heat of the substance is such that the amount of heat supplied to the agglomerate is less than the minimum amount of heat that can be mixed into the aggregate of the molten glass.

(fifth form)

The method for producing a glass substrate according to any one of the first aspect to the fourth aspect, wherein, in the method for producing the glass substrate, a difference between a maximum temperature and a minimum temperature of the wall in contact with the gas phase space is 5 ° C As described above, the gas phase space contains oxygen.

(6th form)

The method for producing a glass substrate according to any one of the first aspect to the fifth aspect, wherein the temperature of the molten glass containing the agglomerate is higher than the temperature of the molten glass processing step The temperature at which the agglomerates are mixed into the molten glass in the region of the molten glass. Alternatively, in the agglomerate treatment step, the temperature of the molten glass is the highest temperature.

(7th form)

The method for producing a glass substrate according to any one of the first aspect to the sixth aspect, wherein, in the agglomerate treatment step, the solubility of the aggregated material in the molten glass is higher than the aggregated material in the molten glass treatment step. The above solubility to the area of the molten glass. Or a method of producing a glass substrate according to any one of the first aspect to the sixth aspect, wherein the agglomerate processing step is performed by The agglomerates are dissolved in the solubility of the molten glass to reduce the size of the agglomerates mixed into the molten glass. In the method for producing a glass substrate according to any one of the first aspect to the sixth aspect, in the agglomerate processing step, the molten glass is controlled by heating to improve dissolution of the aggregate in the molten glass. Solubility, and the size of the agglomerates mixed into the above molten glass is reduced.

(8th form)

The method for producing a glass substrate according to any one of the first aspect to the seventh aspect, wherein the glass processing apparatus is a clarification device having a clarification tube, wherein the molten glass flows in the clarification tube, and the The gas phase space is formed along the flow direction of the molten glass, and the agglomerate treatment step is performed in the clarification pipe.

(9th form)

The method for producing a glass substrate according to any one of the first aspect to the eighth aspect, wherein, in the molten glass treatment step, clarification of reducing the number of bubbles in the molten glass by using tin oxide contained in the molten glass The molten glass flows in the glass processing apparatus, and a temperature distribution along a flow direction of the molten glass is formed on the wall in contact with the vapor phase space, and a flow direction along the molten glass is formed in the vapor phase space. Oxygen concentration distribution.

(10th form)

The method for producing a glass substrate according to any one of the first aspect to the ninth aspect, wherein the agglomerate processing step is performed in the glass processing apparatus, and the molten glass flows in the glass processing apparatus in the glass In the molten glass flowing in the processing device, in the flow direction of the molten glass in the gas phase space, The molten glass flowing at a position corresponding to the region having the highest oxygen concentration performs the above-described coagulation treatment step.

(11th form)

The method for producing a glass substrate according to any one of the first aspect to the tenth aspect, wherein the oxygen concentration in the gas phase space is more than 0% and 1.0% or less, and the gas phase is brought into contact with the vapor phase space. The difference between the highest temperature and the lowest temperature of the wall is 5 ° C or more and 100 ° C or less.

(12th form)

The method for producing a glass substrate according to any one of the first aspect to the eleventh aspect, wherein the temperature of the molten glass is controlled such that the temperature of the molten glass in the agglomerate treatment step is between 1670 ° C and 1730 ° C Within the scope.

(13th form)

The method for producing a glass substrate according to any one of the first aspect to the twelfth aspect, wherein the temperature of the molten glass is controlled so that the aggregated material is mixed into the molten glass in the molten glass treatment step The temperature is in the range of 1580 ° C ~ 1660 ° C.

(14th form)

The method for producing a glass substrate according to any one of the first aspect to the thirteenth aspect, wherein the molten glass treatment step includes the agglomerate treatment step.

(15th form)

The method for producing a glass substrate according to any one of the first aspect to the fourteenth aspect, The glass substrate is a glass substrate for a display.

(16th form)

The method for producing a glass substrate according to any one of the first aspect to the first aspect, wherein the concentration of the platinum group metal dissolved in the molten glass at the start of the agglomerate treatment step is 0.05 to 20 ppm.

(17th form)

The method for producing a glass substrate according to any one of the first aspect to the sixth aspect, wherein in the agglomerate processing step, [Fe ³⁺ ]/([Fe ²⁺ ]+[Fe ³ in the glass substrate ⁺ ]) The saturation solubility of the above-mentioned platinum group metal of the above molten glass is adjusted within the range of 0.2 to 0.5.

(18th form)

In the method for producing a glass substrate according to any one of the first aspect to the seventeenth aspect, the content of the alkali metal oxide in the glass substrate is 0 to 0.5% by mass.

(19th form)

A method for producing a glass substrate, comprising: a melting step of melting a glass raw material to form a molten glass; and a molten glass processing step of treating the molten glass in a glass processing apparatus having the molten glass Introducing to form a space of the gas phase space surrounded by the surface of the molten glass and the wall, at least a part of the wall being composed of a material containing a platinum group metal, and being present in the gas phase space when the molten glass is processed The aggregate of the volatile matter of the platinum group metal volatilized by the wall is mixed into the molten glass as a foreign matter; and the agglomerate treatment step is mixed in the molten glass treatment step to the above At least a part of the aggregate of the molten glass is dissolved in the molten glass, and the concentration of the platinum group metal dissolved in the molten glass at the start of the agglomerate treatment step is 0.05 to 20 ppm.

(20th form)

A method for producing a glass substrate, comprising: a melting step of melting a glass raw material to produce molten glass; and a molten glass processing step of treating the molten glass with a glass processing apparatus, wherein the glass processing apparatus is introduced by the molten glass Forming a gas phase space surrounded by the surface of the molten glass and the wall, at least a portion of the wall in contact with the gas phase space is made of a material containing a platinum group metal, and is present in the gas phase space when the molten glass is processed. The agglomerate of the volatile matter of the platinum group metal volatilized from the wall is mixed into the molten glass; and the agglomerate treatment step of dissolving at least a part of the agglomerate mixed in the molten glass in the molten glass treatment step The molten glass is adjusted in the agglomerate processing step by adjusting the temperature of the molten glass based on the number of defects of the agglomerate detected in the glass substrate produced by using the glass processing apparatus, and adjusting the agglomerate platinum group metal Saturated solubility to make a newly made glass substrate The number of defects was condensed in the above-described allowable level.

Here, in the agglomerate treatment step, in order to adjust the saturated solubility of the aggregate, it is preferred to adjust the temperature of the molten glass in the range of 1660 to 1750 °C.

(21st form)

A method for producing a glass substrate, comprising: a melting step of melting a glass raw material to produce molten glass; and a molten glass processing step of treating the molten glass with a glass processing apparatus, wherein the glass processing apparatus is introduced by the molten glass Forming a gas phase space surrounded by the surface of the molten glass and the wall, at least a portion of the wall in contact with the gas phase space is made of a material containing a platinum group metal, and is present in the gas phase space when the molten glass is processed. The agglomerate of the volatile matter of the platinum group metal volatilized from the wall is mixed into the molten glass; and the agglomerate treatment step of dissolving at least a part of the agglomerate mixed in the molten glass in the molten glass treatment step In the molten glass treatment, the platinum of the molten glass is adjusted by adjusting [Fe ³⁺ ]/([Fe ²⁺ ]+[Fe ³⁺ ]) of the glass substrate in the range of 0.2 to 0.5. The saturated solubility of the group metal is such that the number of defects of the above-mentioned agglomerates contained in the glass substrate is at an allowable level.

Here, the above [Fe ³⁺ ]/([Fe ²⁺ ]+[Fe ³⁺ ]) is preferably adjusted by adjusting the content of tin oxide contained in the glass substrate and the content of the oxide contained in the glass raw material. At least either of them to make adjustments.

Further, another aspect of the present invention is to laminate a glass substrate laminate having a plurality of glass substrates. In this case, the following twenty-first aspect is included.

(22nd form)

A glass substrate laminate in which the total volume of the glass substrate in the glass substrate laminate is 0.1 m ³ or more, and the aggregate of all platinum group metals contained in the glass substrate has a maximum length of 50 μm or less. The ratio of the number of objects is 70% or more.

Further, another aspect of the present invention is a glass substrate comprising the following twenty-third aspect.

(23rd form)

A glass substrate characterized in that the ratio of the number of aggregates having a maximum length of 50 μm or less is 70% or more in the aggregate of the platinum group metal contained in the glass substrate.

Further, another aspect of the present invention is a glass substrate manufacturing apparatus. This glass substrate manufacturing apparatus contains the following aspects.

(24th form)

A glass substrate manufacturing apparatus comprising: a melting device that melts a glass raw material to form molten glass; a glass processing device that processes the molten glass and has a surface formed by the molten glass introduced by the molten glass a space surrounding the gas phase space surrounded by the wall, wherein at least a portion of the wall is composed of a material containing a platinum group metal, and when the molten glass is treated, a volatile matter of a platinum group metal volatilized from the wall in the gas phase space The aggregate is mixed as a foreign matter into the molten glass; and the treatment unit reduces the size of the aggregate mixed into the molten glass, and is mixed into the aggregate of the molten glass in the molten glass treatment step, and the maximum length is 50 μm or less. The ratio of the number of aggregates is 70% or more.

Furthermore, another aspect of the present invention is also a glass substrate manufacturing apparatus. This glass substrate manufacturing apparatus includes the following aspects.

(25th form)

A glass substrate manufacturing apparatus comprising: a melting device that melts a glass raw material to form molten glass; and a glass processing device having a gas phase space surrounded by a surface and a wall of the molten glass by introduction of the molten glass a space in which at least a part of the wall is made of a material containing a platinum group metal, and when the molten glass is treated, an aggregate of a volatile matter of a platinum group metal volatilized from the wall in the gas phase space is mixed as a foreign matter to the above The molten glass includes an adjusting unit for adjusting the solubility of the agglomerate in the molten glass to reduce the size of the agglomerate mixed into the molten glass.

(26th form)

Further, the method for producing a glass substrate according to the first aspect to the twenty-first aspect, the glass substrate laminate of the twenty-second aspect, the glass substrate of the twenty-third aspect, and the above The glass substrate of any one of the glass substrate manufacturing apparatuses of the 24th and 25th aspect is a glass substrate which has a strain point of 650 ° C or more.

The method of producing the glass substrate of the first aspect to the twenty-first aspect, the glass substrate laminate of the twenty-second aspect, the glass substrate of the twenty-third aspect, and the glass substrate manufacturing apparatus of the twenty-fifth and twenty-fifth aspects The glass substrate is used as a glass substrate for a liquid crystal display, a glass substrate for an organic EL (Electro-Luminescence) display, or a glass substrate for a display using an LTPS (Low Temperature Poly-silicon) thin film semiconductor.

According to the method for producing a glass substrate, the glass substrate, the glass substrate laminate, and the glass substrate manufacturing apparatus, even if a foreign substance (aggregate) of a platinum group metal is mixed into the glass substrate, strain can be prevented from occurring on the glass substrate, and formation can be prevented. Concavities and convexities on the main surface of the glass substrate. Thereby, the yield at the time of manufacturing a glass substrate is improved.

40‧‧‧melting tank

41‧‧‧clarification tube

41a‧‧‧ snorkel

41b‧‧‧heating electrode

41c‧‧‧ gas phase space

42‧‧‧Forming device

52‧‧‧ Shaped body

43a, 43b, 43c‧‧‧ delivery tube

100‧‧‧Agitator

200‧‧‧Glass substrate manufacturing equipment

Fig. 1 is a flow chart showing the procedure of a method for producing a glass substrate of an embodiment.

Fig. 2 is a schematic view showing the configuration of a glass substrate manufacturing apparatus of the embodiment.

Fig. 3 is a perspective view mainly showing the clarification pipe of the embodiment.

Fig. 4 is a view showing an example of a cross section of the inside of the clarification pipe of the embodiment and a temperature distribution of the clarification pipe.

Fig. 5 is a graph showing the relationship between the maximum temperature of molten glass and the ratio of foreign matter.

The method for producing a glass substrate according to the present embodiment processes a molten glass (a molten glass treatment step) in a glass processing apparatus, and the glass processing apparatus has a space in which a vapor phase space surrounded by a surface and a wall of the molten glass is formed by introduction of molten glass. At least a part of the wall is made of a material containing a platinum group metal. For example, the glass processing apparatus has a liquid phase containing molten glass, and a gas phase space formed by a liquid surface and a wall of the molten glass. At least a portion of the wall surrounding the gas phase space is comprised of a material comprising a platinum group metal. At the time of the treatment of the molten glass, the aggregate of the volatile matter of the platinum group metal volatilized from the wall in the gas phase space is mixed as a foreign matter into the molten glass. The treatment for reducing the size of the agglomerates mixed into the molten glass is carried out so that the ratio of the number of aggregates having a maximum length of 50 μm or less to the aggregates of the molten glass is 70% or more (agglomerate treatment step) . Alternatively, the solubility of the foreign matter (agglomerate) in the molten glass is adjusted to reduce the size of the agglomerates mixed into the molten glass. For example, the amount of heat supplied to the foreign matter (aggregate) is controlled so that the amount of heat supplied to the foreign matter (agglomerate) is less than the minimum amount of heat (the agglomerate treatment step) that can reduce the size of the foreign matter (aggregate) mixed into the molten glass.

By reducing the size of the foreign matter (aggregate) of the platinum group metal mixed in the glass substrate, it is possible to prevent strain on the glass substrate from being easily formed, and it is difficult to form irregularities on the main surface of the glass substrate. Therefore, the previous problems are improved and the manufacturing yield of the glass substrate is improved.

In the following description, as a condition for controlling the solubility adjustment so that the solubility of the aggregate with respect to the molten glass is an example in which the aggregate can be dissolved in the molten glass and can be reduced in the minimum solubility of the size, the heat supplied to the aggregate is controlled. The heat supplied to the aggregate is described as an example in which the minimum amount of heat which is mixed into the aggregate of the molten glass can be reduced.

(Method for Producing Glass Substrate and Glass Substrate Manufacturing Apparatus)

Fig. 1 is a flow chart showing an example of the procedure of the method for producing a glass substrate of the present embodiment. As shown in FIG. 1, the manufacturing method of the glass substrate mainly includes a melting step S1, a clarification step S2, a stirring step S3, a forming step S4, a slow cooling step S5, and a cutting step S6.

FIG. 2 is a schematic view showing an example of the configuration of the glass substrate manufacturing apparatus 200 of the present embodiment. The glass substrate manufacturing apparatus 200 includes a melting tank 40, a clarification pipe 41, a stirring device 100, a molding device 42, and transfer pipes 43a, 43b, and 43c. The conveying pipe 43a connects the melting tank 40 and the clarification pipe 41. The conveying pipe 43b is connected to the clarification pipe 41 and the stirring device 100. delivery The tube 43c connects the stirring device 100 and the forming device 42.

In the melting step S1, the raw material of the glass is melted to form molten glass. The molten glass is stored in the melting tank 40 and heated to have a desired temperature. The molten glass contains a clarifying agent. From the viewpoint of reducing the environmental burden, tin oxide is suitably used as a fining agent.

In the melting tank 40, the glass raw material is heated to a temperature corresponding to its composition and the like to be melted. Thereby, in the melting tank 40, for example, a molten glass G having a high temperature of 1500 ° C to 1620 ° C is obtained. Further, in the melting tank 40, the molten glass G between the electrodes may be energized by a current flowing between at least one pair of electrodes, and in addition to the electric heating, the flame of the burner may be additionally provided to heat the glass. raw material.

The clarification step S2 is carried out inside the conveying pipe 43a and the clarification pipe 41 through which the molten glass flows. First, the temperature of the molten glass is raised. The clarifying agent causes a reduction reaction due to the temperature rise and releases oxygen. The bubbles contained in the molten glass absorb the released oxygen and expand, and float up to the surface where the molten glass is in contact with the gas phase space, and rupture and disappear. That is, the defoaming process step S2A is performed. Further, after the middle of the defoaming treatment step S2A or after the completion of the defoaming treatment step S2A, the agglomerate treatment step S2B is performed to increase the temperature of the molten glass and reduce the aggregation of the platinum group metal mixed in the defoaming treatment. The size of the object. Then, the temperature of the molten glass is lowered. Thereby, the reduced clarifying agent causes an oxidation reaction to absorb a gas component such as oxygen remaining in the molten glass. That is, the absorption processing step S2C is performed.

Specifically, the molten glass G obtained in the melting tank 40 flows from the melting tank 40 into the clarification pipe 41 through the conveying pipe 43a. The clarification pipe 41 has a space in which a vapor phase space surrounded by the surface of the molten glass G and the wall is formed by introduction of the molten glass G, and at least a part of the wall is made of a material containing a platinum group metal. For example, a liquid phase having a molten glass flow and a gas phase space formed by a liquid surface and a wall of the molten glass, at least a portion of the wall surrounding the gas phase space is composed of a material containing a platinum group metal. The transfer pipes 43a, 43b, and 43c are pipes made of a platinum group metal. Further, the platinum group metal means a metal containing a single platinum group element and an alloy containing a metal of a platinum group element. Platinum group elements are platinum (Pt), palladium (Pd), rhodium (Rh), rhodium (Ru), rhodium (Os) and 铱 (Ir) these six elements. In the present embodiment, for example, an alloy of platinum and rhodium having a platinum content of 70% or more is suitably used. The platinum group metal has a high melting point and is excellent in corrosion resistance to molten glass. A heating unit is provided in the same manner as the melting tank 40 in the clarification pipe 41. Further, a heating unit is also provided at least in the conveying pipe 43a.

In the clarification step S2, the following steps are performed: a defoaming treatment step of defoaming by heating the molten glass G; and an agglomerate treatment step of adjusting foreign matter (aggregate) to the platinum group metal mixed into the molten glass Providing heat, breaking or melting a foreign matter (agglomerate) of the platinum group metal to reduce the size of the foreign matter (agglomerate) of the platinum group metal; and an absorption treatment step of cooling the glass by cooling the molten glass Absorbs bubbles in the molten glass. In the agglomerate treatment step, in order to reduce or melt the foreign matter (aggregate) mixed in the molten glass and reduce the size of the foreign matter (aggregate) of the platinum group metal, it is necessary to make the heat supplied to the foreign matter (agglomerate) specific. Heat (minimum heat) or more. In this case, the heat of the foreign matter (aggregate) supplied to the molten glass is controlled so that the amount of heat supplied to the foreign matter (agglomerate) is equal to or higher than the minimum amount of heat. The above minimum heat can be studied in advance by performing experiments or the like in advance. In the case where the minimum heat is controlled by the temperature of the molten glass G, for example, the temperature of the molten glass G in the clarification pipe 41 is controlled to be in the range of 1580 ° C to 1730 ° C, preferably in the range of 1670 ° C to 1730 ° C.

In the clarification step S2, from the viewpoint of sufficiently clarifying the molten glass G, it is preferred that the temperature of the molten glass G flowing inside the transfer pipe 43a is not lowered, but is gradually increased. It is preferred that after the melting step S1, the molten glass G is heated to a temperature of 16 ° C or higher at a rate of 3 ° C / min or more.

The maximum temperature of the molten glass G flowing through the conveying pipe 43a is 1620 ° C to 1690 ° C, preferably 1640 ° C to 1670 ° C. Further, the temperature of the molten glass G at the inlet of the clarification pipe which is a region connecting the transfer pipe 43a and the clarification pipe 41 is 1610 ° C to 1680 ° C, preferably 1630 ° C to 1660 ° C. Further, the temperature of the molten glass G at the exit of the clarification pipe which is a region connecting the clarification pipe 41 and the transfer pipe 43b is 1530 ° C to 1600 ° C, preferably 1540 ° C. ~1580 °C.

The molten glass G clarified in the clarification pipe 41 flows from the clarification pipe 41 through the transfer pipe 43b to the stirring device 100. The molten glass G is cooled while passing through the conveying pipe 43b.

In the stirring step S3, the clarified molten glass is stirred to homogenize the components of the molten glass. Thereby, the composition irregularity of the molten glass which causes the pulse of a glass substrate etc. is reduced. The homogenized molten glass is sent to a forming step S4.

Specifically, in the stirring device 100, the molten glass G is stirred at a temperature lower than the temperature of the molten glass G passing through the clarification pipe 41. For example, in the stirring device 100, the temperature of the molten glass G is 1250 ° C to 1450 ° C. For example, in the stirring device 100, the viscosity of the molten glass G is 500 poise to 1300 poise. The molten glass G is stirred and homogenized in the stirring device 100.

The molten glass G homogenized in the stirring device 100 flows from the stirring device 100 to the forming device 42 through the conveying pipe 43c. When the molten glass G passes through the transfer pipe 43c, it is cooled to a viscosity suitable for the formation of the molten glass G. For example, the molten glass G is cooled to 1100 to 1300 °C.

Further, the stirring step S3 of the present embodiment is performed after the clarification step S2, but the stirring step S3 may be performed before the clarification step S2. In this case, the temperature of the molten glass G at the time of stirring step S3 may be equal to or higher than the temperature of the molten glass G in the clarification pipe 41.

In the forming step S4, the molten glass is continuously formed into a flat glass by an overflow down-draw method or a floating method.

Specifically, the molten glass G that has flowed into the molding device 42 is supplied to the molded body 52 provided inside the forming furnace (not shown). A groove is formed on the upper surface of the formed body 52 along the longitudinal direction of the formed body 52. The molten glass G is supplied to the groove of the upper surface of the formed body 52. The molten glass G overflowing from the groove passes through one of the side faces of the molded body 52 and flows downward. One pair of molten glass G flowing down the side of the formed body 52 merges at the lower end of the formed body 52, and is continuously formed into a flat glass GR.

In the slow cooling step S5, the flat glass continuously formed in the forming step S4 has a desired thickness and is gradually cooled so as not to cause strain and warpage.

In the cutting step S6, the slowly cooled flat glass in the slow cooling step S5 is cut to a specific length to obtain a glass plate. The glass plate was further cut to a specific size to obtain a glass substrate.

(glass substrate laminate and glass substrate)

This embodiment provides a glass substrate laminate and a glass substrate formed by laminating a plurality of glass substrates.

The glass substrate laminate of the present embodiment has a total volume of 0.1 m ³ or more, and the ratio of the number of aggregates having a maximum length of 50 μm or less in the aggregate of all platinum group metals contained in the glass substrate laminate. It is 70% or more. As described later, such a glass substrate laminate can easily form strain on the glass substrate, and it is difficult to form irregularities on the main surface of the glass substrate. Therefore, each of the glass substrates of the above laminated body is suitably used for a glass substrate for a display, and in particular, it is effective for a glass substrate for a display panel which requires high definition for screen display.

Further, the glass substrate of the present embodiment is characterized in that the ratio of the number of aggregates having a maximum length of 50 μm or less in the aggregate of the platinum group metal contained in the glass substrate is 70% or more. According to the glass substrate having such a configuration, as described later, strain can be prevented from occurring on the glass substrate, and irregularities on the main surface of the glass substrate can be more difficult to be formed.

Further, the glass substrate laminate and the glass substrate are more preferably contained in the aggregate of the platinum group metal, and the ratio of the number of aggregates having a maximum length of 50 μm or less is 90% or more. Further, the glass substrate laminate and the glass substrate are more preferably contained in the aggregate of the platinum group metal, and the ratio of the number of aggregates having a maximum length of 30 μm or less is 90% or more.

Regarding the glass used for the glass substrate, the glass having a strain point of 600 ° C or higher is suitable for a method of producing a glass substrate to be described later. The strain point is more preferably 650 ° C or higher, particularly preferably 690 ° C or higher, and particularly preferably 730 ° C or higher.

(Application example of glass substrate)

The glass substrate manufactured by the method for producing a glass substrate of the present embodiment is particularly suitably used as a glass substrate for a display such as a liquid crystal display, a plasma display, or an organic EL display, or a cover glass for a protective display. A display using a glass substrate for a display includes a flat panel display having a flat display surface, and an organic EL display, a liquid crystal display, and a curved display having a curved display surface. As a glass substrate for a high-definition display, the glass substrate is preferably used as, for example, a glass substrate for a liquid crystal display, a glass substrate for an organic EL (Electro-Luminescence) display, or a thin film poly-silicon semiconductor film using LTPS (Low Temperature Poly-silicon). Or a glass substrate for an oxide semiconductor display such as IGZO (Indium, Gallium, Zinc, Oxide).

As the glass substrate for a display, an alkali-free glass or a glass containing a small amount of alkali is used. The glass substrate for display has high viscosity at high temperatures. For example, the temperature of the molten glass having a viscosity of 10 ^2.5 poise is 1500 ° C or higher. Further, the alkali-free glass is a glass which does not substantially contain a composition of an alkali metal oxide (R ₂ O). The fact that the alkali metal oxide is not contained in the raw material, and the alkali metal oxide is not added as a glass raw material, for example, the content of the alkali metal oxide is less than 0.1% by mass.

(glass composition)

In the melting tank 40, the glass raw material is melted by a heating unit (not shown) to produce molten glass G. The glass raw material is formulated into a glass that substantially achieves the desired composition. As an example of the composition of the glass, as a flat panel display (FPD) comprises a display glass substrate or the like with a preferred SiO ₂ 50 mass alkali-free glass of the glass substrate to 70% by mass%; Al ₂ O ₃ 0 mass% to 25 mass%; B ₂ O ₃ 0% by mass to 15% by mass; MgO 0% by mass to 10% by mass; CaO 0% by mass to 20% by mass; SrO 0% by mass to 20% by mass; BaO 0% by mass to 10% by mass. Further, BaO may be 0% by mass to 20% by mass, instead of BaO 0% by mass to 10% by mass. Here, the total content of MgO, CaO, SrO, and BaO is 5% by mass to 30% by mass.

Further, as the glass substrate for a display, a glass containing a trace amount of an alkali metal oxide and a small amount of alkali may be used. The glass containing a trace amount of alkali contains 0.1% by mass to 0.5% by mass of R' ₂ O as a component thereof, and preferably contains 0.2% by mass to 0.5% by mass of R' ₂ O as a component thereof. Here, R 'is selected from Li, Na and K, of at least one, R' ₂ O-based Li ₂ O, Na ₂ O, the total content of K ₂ O. Further, the total content of R' ₂ O may be less than 0.1% by mass. Therefore, in the glass substrate of the present embodiment, in addition to the alkali-free glass, a glass having an alkali metal oxide (R' ₂ O) content of 0 to 0.5% by mass is preferably used.

The glass produced according to the present embodiment may further contain 0.01% by mass to 1% by mass (preferably 0.01% by mass to 0.5% by mass) of SnO _{2 in} addition to the above components; and Fe ₂ O ₃ 0% by mass to 0.2% by mass (preferably It is 0.01% by mass to 0.08% by mass). Further, in consideration of environmental burden, it is preferred that the glass produced by the present invention does not substantially contain As ₂ O ₃ , Sb ₂ O ₃ and PbO. In order to reduce the environmental burden, tin oxide (SnO ₂ ) is preferably used as a fining agent.

In the present embodiment, the molten glass processing step is a clarification step, and the molten glass processing apparatus is a clarification device including the clarification tube 41. However, the apparatus for performing the molten glass processing step is provided in the melting tank 40 and the forming apparatus. The apparatus for specifically treating the molten glass between 42 is not particularly limited. The glass processing apparatus may be, for example, a stirring device or a conveying pipe for conveying molten glass, in addition to the clarifying device. Therefore, the treatment of the molten glass includes, in addition to the treatment for clarifying the molten glass, the treatment of homogenizing the molten glass, the treatment of transporting the molten glass, and the like. Further, although the example in which the agglomerate treatment step S2B is performed in the clarification step S2 has been described, for example, the agglomerate treatment step S2B may be performed in the step of stirring the step S3 and transporting the molten glass G by the transfer tube. Further, even in the case where the agglomerate treatment step S2B is performed in the clarification step S2, as described above, the agglomerate treatment step S2B does not need to be performed before the absorption treatment step S2C, and can be performed after the absorption treatment step S2C.

(constitution of clarification pipe)

Next, the configuration of the clarification pipe 41 of the clarification device in the present embodiment will be described in detail. Further, the clarification device includes a vent pipe 41a, a heating electrode 41b, and a refractory protective layer and a refractory brick (not shown) which surround the outer periphery of the clarification pipe 41, in addition to the clarification pipe 41. Fig. 3 is a view mainly showing the appearance of the clarification pipe 41. Fig. 4 is a cross-sectional view showing the inside of the clarification pipe 41 and a view showing an example of the temperature distribution of the clarification pipe.

A vent pipe 41a and a pair of heating electrodes 41b are attached to the clarification pipe 41. The inside of the clarification pipe 41 has a space in which the gas phase space 41c surrounded by the surface and the wall of the molten glass G is formed by the introduction of the molten glass G. For example, the inside of the clarification pipe 41 has a liquid phase in which the molten glass G flows, and a gas phase space formed by the liquid surface and the wall of the molten glass G. The gas phase space 41c is formed along the flow direction of the molten glass G. At least a portion of the wall surrounding the gas phase space 41c is composed of a material containing a platinum group metal. In the present embodiment, the entire wall surrounding the gas phase space 41c is made of a material containing a platinum group metal.

The vent pipe 41a is provided in the wall contacting the gas phase space 41c in the flow direction of the molten glass G, and connects the gas phase space 41c to the atmosphere outside the clarification pipe 41. The vent pipe 41a is preferably formed of a platinum group metal in the same manner as the clarification pipe 41. Since the vent pipe 41a has a heat dissipation function, the temperature of the vent pipe 41a is easily lowered, and a heating mechanism for heating the vent pipe 41a may be provided.

The pair of heating electrodes 41b are provided on the flange-shaped electrode plates at both ends of the clarification pipe 41a. The heating electrode 41b causes a current supplied from a power source (not shown) to flow to the clarification pipe 41, and the clarification pipe 41 is electrically heated by the current. In the case where tin oxide is used as the fining agent, for example, the wall of the clarification tube 41 is heated to a maximum temperature of 1670 ° C to 1750 ° C, more preferably 1690 ° C to 1750 ° C. The difference between the highest temperature and the lowest temperature of the wall of the clarification pipe 41 is 5 ° C or more, and the gas phase space has oxygen. The temperature of the molten glass G is heated to a temperature that promotes the reduction reaction of tin oxide. Further, the molten glass G is preferably heated to a temperature at which the foreign matter (agglomerate) of the platinum group metal is broken or melted, for example, 1670 ° C or higher, more preferably heated to 1680 ° C or higher. More specifically, it is preferably heated to 1670 ° C ~ 1730 ° C, more preferably heated to 1680 ° C ~1700 °C. When the maximum temperature of the molten glass G exceeds 1730 ° C, the tube containing the platinum group metal constituting the clarification tube 41 a is easily melted. Further, the maximum temperature of the molten glass G can be calculated from the measured value of a thermocouple (not shown) provided in the clarification pipe 41.

The temperature of the molten glass G flowing inside the clarification pipe 41 can be controlled by controlling the current flowing through the clarification pipe 41.

The pair of heating electrodes 41b are provided in the clarification pipe 41, but the number of the heating electrodes 41b is not particularly limited. By controlling the amount of current of the heating electrode 41b, the temperature of the wall of the clarification tube 41 which is in contact with the gas phase space 41c is controlled, for example, in the range of 1500 to 1750 °C.

Inside the clarification pipe 41, a bubble containing CO ₂ or SO ₂ contained in the molten glass G is removed by a redox reaction of a clarifying agent such as tin oxide contained in the molten glass G. Specifically, first, the temperature of the molten glass G is raised to reduce the clarifying agent, and oxygen bubbles are generated in the molten glass G. An oxygen bubble mixture containing bubbles of a gas component such as CO ₂ , N ₂ , and SO ₂ contained in the molten glass G and a reduction reaction by a clarifying agent. The bubble which is combined with the oxygen bubble floats up to the surface of the molten glass G which is in contact with the gas phase space to release the bubble, that is, the crack disappears (defoaming treatment). The temperature of the molten glass G in the defoaming treatment is from 1610 ° C to 1730 ° C, preferably from 1640 ° C to 1710 ° C. When it is the temperature of the above range, the platinum group metal is largely volatilized from the wall of the clarification pipe 41. Since oxygen is released into the gas phase space by defoaming, the oxygen concentration in the gas phase space where the defoaming treatment is performed is increased, and as a result, the volatilization of the platinum group metal is more active. Along with this, the concentration of the volatile matter of the platinum group metal contained in the gas phase space becomes high, and therefore, aggregation of the volatile matter of the platinum group metal contained in the gas phase space is likely to occur. In particular, the volatiles of the platinum group metal are prone to localized cooling of the walls, for example to the walls near the inlet of the clarification tube 41. Therefore, one of the aggregates of the platinum group metal adhering to the wall of the clarification pipe 41 is partially detached, and it is easy to be mixed into the molten glass G as a foreign matter. For example, after the molten glass flows into the clarification pipe 41, it is easy to cause agglomeration of the volatile matter of the platinum group metal contained in the gas phase space and the agglomerate is mixed into the molten glass in the region where the temperature of the molten glass G is from 1580 ° C to 1660 ° C. G.

Therefore, in the middle of the defoaming treatment or after the completion of the defoaming treatment, an agglomerate treatment step of reducing the size of the foreign matter (aggregate) of the platinum group metal mixed in the molten glass G is performed.

In the case where the agglomerate treatment step is performed after the completion of the defoaming treatment, it is preferred to raise the temperature of the molten glass G so that the temperature of the molten glass G containing the foreign matter (agglomerate) of the platinum group metal is higher than that of the platinum group metal ( Agglomerate) The temperature of the molten glass mixed into the region of the molten glass G.

Further, in the case where the agglomerate treatment step is carried out in the middle of the defoaming treatment step, the defoaming treatment step and the agglomerate treatment step are simultaneously performed. In the case where the agglomerate treatment step is performed in the middle of the defoaming treatment step, the defoaming treatment step and the agglomerate treatment step may be simultaneously performed. In the case where the agglomerate treatment step is carried out in the middle of the defoaming treatment step, the molten glass is at the highest temperature in the agglomerate treatment step. That is, the defoaming treatment step (melting glass treatment step) may also include a coagulum treatment step.

In the agglomerate treatment step, it is preferred to control the heat applied to the foreign matter (agglomerate) of the platinum group metal mixed in the molten glass, specifically, by setting the temperature of the molten glass G to 1670 ° C or more. Opening and melting foreign matter (agglomerate) of platinum group metals. In this case, the agglomerate treatment step is carried out so that the ratio of the number of the foreign matter having a maximum length of 50 μm or less is 70% or more among the foreign matter (aggregate) of the platinum group metal mixed in the molten glass G. The glass substrate produces less strain and less irregularities are formed on the main surface of the glass substrate. In order to form a foreign matter having such a size, it is preferable to maintain the temperature of the molten glass G at 1,670 ° C or higher for 10 minutes or longer, and more preferably for 30 minutes or longer. In other words, in the agglomerate reduction treatment for reducing the size of the foreign matter (agglomerate) of the platinum group metal, the foreign matter (aggregate) of the platinum group metal can be reduced by holding at a temperature of 1670 ° C or higher for 10 minutes or longer. size.

Further, in the present embodiment, in the agglomerate treatment step, it is also preferred to control the solubility so that the foreign matter (aggregate) of the platinum group metal mixed in the molten glass is dissolved. The solubility of the molten glass is higher than the solubility of the foreign matter (agglomerate) of the platinum group metal in the region of the molten glass in the molten glass treatment step. When the solubility of the foreign matter (aggregate) to the molten glass G is increased, the solubility of the aggregate to the molten glass can be increased by increasing the temperature of the molten glass G, or by increasing the temperature of the molten glass G and / or to extend the treatment time, and to increase the amount of dissolution of foreign matter (agglomerate) into the molten glass G.

Further, the foreign matter (agglomerate) of the platinum group metal is a linear elongated line in one direction. Therefore, the maximum length of the aggregate of the platinum group metal (foreign matter) means the length of the long side of the rectangle which is externally connected (externally cut) to the image of the foreign object when the foreign matter (aggregate) of the platinum group metal is photographed.

Before the agglomerate treatment step, the ratio of the foreign matter (agglomerate) of the platinum group metal having a maximum length of 100 μm or more exceeds 80%. Further, in the present embodiment, the foreign matter (aggregate) of the platinum group metal before the agglomerate treatment step means a ratio of the maximum length to the minimum length, that is, a foreign matter of a platinum group metal having an aspect ratio of more than 100. For example, the foreign matter (agglomerate) of the platinum group metal has a maximum length of 50 μm to 300 μm and a minimum length of 0.5 μm to 2 μm.

Then, the temperature of the molten glass G is lowered to oxidize the reduced fining agent. Thereby, the oxygen of the bubble remaining in the molten glass G is absorbed by the molten glass G (absorption treatment). As a result, the remaining bubbles become smaller and disappear. Thus, the bubbles contained in the molten glass G are removed by the redox reaction of the clarifying agent. Further, in the absorption treatment step S2C, the temperature of the molten glass G and the temperature of the wall of the clarification pipe 41 are lowered to 1,580 ° C or lower, and the oxygen concentration in the gas phase space is lowered as compared with the defoaming treatment step S2A, so that it is difficult to carry out Volatilization and agglomeration of platinum group metals. Therefore, in the absorption treatment step S2C, compared with the defoaming treatment step S2A, the possibility that the new aggregate of the platinum group metal becomes a foreign matter and is mixed into the molten glass G is extremely low.

Although not shown, a refractory protective layer is provided on the outer wall surface of the clarification pipe 41. A refractory brick is further provided on the outer side of the refractory protective layer. The refractory bricks are placed on abutment (not shown). Further, the temperature of the wall of the clarification pipe 41 contacting the gas phase space 41c may be adjusted by the refractory protective layer and/or the refractory brick to adjust the amount of heat released from the clarification pipe 41 and/or flow in the clarification pipe 41. Molten glass temperature.

4 shows an example of the temperature distribution of the clarification pipe 41 corresponding to the position of the clarification pipe 41 in the X direction (the temperature distribution in the X direction of the wall of the clarification pipe 41 which is in contact with the gas phase space 41c). In the temperature distribution, the temperature becomes the highest temperature T _max between the end portion 41d (inlet) of the molten glass G inflow side of the clarification pipe 41 and the vent pipe 41a. A temperature gradient from the position P of the highest temperature T _{max to} the temperature drop toward the end portion 41d of the clarification pipe 41 is formed. Similarly, a temperature gradient from the position P of the highest temperature T _{max from} the position in the X direction of the vent pipe 41a is formed. Further, although not shown, in addition to the above, a temperature gradient region is formed between the position of the vent pipe 41a in the X direction and the end portion 41e (outlet) of the molten glass G outflow side of the clarification pipe 41. In such a temperature gradient region, in any of the temperature gradient regions, the temperature difference between the highest temperature and the lowest temperature in the temperature gradient region exceeds 0 ° C and is 150 ° C or less, more preferably exceeds 0 ° C and is 100 ° C or less. As shown in FIG. 4, the defoaming process is started in the first half of the temperature rise section until the temperature of the wall becomes the highest temperature _Tmax , at least until the maximum temperature _Tmax . In addition, the agglomerate treatment step is started in the second half of the temperature rise interval including the highest temperature T _max , at least to the highest temperature T _max . The agglomerate treatment step starts, for example, at a temperature at which the temperature of the molten glass G is 1670 °C or higher. Further, the time point at which the defoaming treatment step ends and the agglomerate treatment step are completed may be either first, but the foreign matter of all the platinum group metals mixed in the molten glass is used as the object of the agglomerate treatment step. Preferably, the end of the agglomerate treatment step is coincident with or after the end of the defoaming treatment step.

As described above, in the present embodiment, the bubbles in the molten glass G are subjected to the defoaming treatment. However, at this time, the aggregate of the volatile matter of the platinum group metal volatilized from the wall is mixed into the molten glass G as a foreign matter. The amount of the agglomerates mixed in the molten glass G is reduced, and the ratio of the number of foreign substances (agglomerates) having a maximum length of 50 μm or less is 70% or more in the foreign matter (agglomerate) of the molten glass G. Alternatively, the amount of heat applied to the foreign matter of the platinum group metal is controlled to reduce the size of the foreign matter of the platinum group metal mixed therein. Thereby, even if a foreign matter of a platinum group metal is mixed into the glass substrate, strain on the glass substrate can be prevented, and the glass substrate can be easily formed. The unevenness of the main surface.

Further, the difference between the highest temperature and the lowest temperature of the temperature of the wall in contact with the gas phase space in the above-mentioned clarification pipe 41 is 5 ° C or more, even if the gas phase space is an oxygen-containing atmosphere, that is, even if it is easy to generate a platinum group metal The condition of the agglomerate can also reduce the size of the foreign matter of the platinum group metal contained in the molten glass, or the ratio of the number of foreign matters of the platinum group metal having a maximum length of 50 μm or less is 70% or more. Therefore, even if a foreign matter of a platinum group metal is mixed into the glass substrate, strain on the glass substrate can be prevented from occurring, and irregularities on the main surface of the glass substrate can be prevented from being easily formed.

Further, in the step of performing the agglomerate treatment, it is preferred to raise the temperature so that the temperature of the molten glass G containing the aggregate is higher than the foreign matter (aggregate) of the platinum group metal in the molten glass treatment step, and is mixed into the region of the molten glass G. The temperature of the molten glass. Thereby, the foreign matter (aggregate) of the platinum group metal can be reliably broken or melted, and the size of the foreign matter (aggregate) of the platinum group metal can be reliably reduced.

Further, the glass processing apparatus has a clarification device for the clarification pipe 41, and the gas phase space in the clarification pipe 41 is formed along the flow direction of the molten glass, and the agglomerate treatment step is preferably performed on the clarification pipe 41. The temperature of the molten glass G in the clarification pipe 41 is the highest temperature until the forming step, so that the foreign matter (agglomerate) of the platinum group metal can be easily broken or melted by heat.

In the glass treatment step of the present embodiment, the tin oxide contained in the molten glass G is used to reduce the number of bubbles in the molten glass G, and the wall in the glass processing apparatus which is in contact with the gas phase space is formed along the molten glass. The temperature distribution in the flow direction causes the gas phase space to form an oxygen concentration distribution along the flow direction of the molten glass G. In such an apparatus, since there is an oxygen concentration distribution which affects the volatilization of the platinum group metal, aggregation of volatile matter of the platinum group metal is likely to occur, and the aggregate is easily mixed as a foreign matter into the molten glass. That is, in this case, the size of the foreign matter (agglomerate) of the platinum group metal can be easily reduced, and the strain on the glass substrate can be prevented from being easily formed, and the glass substrate can be easily formed. The unevenness of the main surface.

Preferably, the agglomerate treatment step is carried out in a glass processing apparatus, and the molten glass flowing in the flow direction of the molten glass flowing in the glass processing apparatus at a position corresponding to a flow direction corresponding to a region having the highest oxygen concentration in the gas phase space The condensate treatment step is carried out in a manner included. In the temperature distribution shown in Fig. 4, the defoaming treatment of the molten glass G is most actively performed at the highest temperature T _max . Thereby, the oxygen concentration becomes the highest in the region in the gas phase space near the highest temperature T _max due to the oxygen released from the bubble. For example, the agglomeration treatment step is performed on the molten glass passing through the position in the flow direction corresponding to the region in the gas phase space having the highest oxygen concentration. Therefore, even if the platinum group metal is active in the volatilization of the platinum group metal due to the maximum oxygen concentration, the aggregate of the platinum group metal is likely to be generated, and the aggregate of the platinum group metal can be efficiently mixed as a foreign matter to the molten glass. Reduce the size of the foreign object.

It is preferable that the oxygen concentration in the gas phase space of the clarification pipe 41 exceeds 0% and is 1.0% or less, and the difference between the highest temperature and the lowest temperature of the wall of the clarification pipe 41 is 5 ° C or more and 100 ° C or less. Thereby, the volatilization of the platinum group metal can be suppressed, and the foreign matter of the platinum group metal mixed in the molten glass G can be suppressed. However, even in this case, the foreign matter of the platinum group metal cannot be completely made zero. Therefore, the effect of the present embodiment in which the size of the foreign matter of the platinum group metal is reduced, the strain on the glass substrate is less likely to occur, and the unevenness of the main surface of the glass substrate is less likely to be formed is more remarkable. Further, since the volatilization of the platinum group metal can be suppressed, the life of the device made of the platinum group metal such as the clarification pipe 41 can be improved.

Further, in at least a part of the molten glass treatment step, the temperature of the molten glass G is controlled to a temperature range of 1580 ° C to 1660 ° C, and the temperature of the molten glass G at the agglomerate treatment step is controlled at 1670 ° C to 1730 ° C, and The defoaming treatment is reliably performed, and the size of the foreign matter (agglomerate) of the platinum group metal can be reliably reduced. In other words, it is possible to achieve a reduction in the number of bubbles included in the glass substrate and a reduction in foreign matter of the platinum group metal having a maximum length of 50 μm or more. Further, when the oxygen concentration in the gas phase space of the clarification pipe 41 has a distribution depending on the place, in the region where the oxygen concentration is higher than a specific value, it is easy to mix the platinum group into the molten glass G. Since the foreign matter (aggregate) of the metal is adjusted, the temperature of the molten glass G is preferably adjusted to a level that reduces the size of the foreign matter (aggregate) of the platinum group metal even if the foreign matter (aggregate) of the platinum group metal is mixed. Temperature, for example, a temperature above 1680 °C. More preferably, the temperature of the molten glass is controlled to form a temperature distribution of the molten glass along the oxygen concentration distribution in the gas phase space.

In the above embodiment, as an example of the condition for controlling the solubility of the aggregate in the molten glass, an example of controlling the amount of heat supplied to the aggregate is exemplified. However, the condition for adjusting the solubility is such that the solubility is equal to or higher than the above minimum solubility, and the following conditions including the above-described heat control can be exemplified. The solubility can be adjusted by controlling the conditions or controlling the conditions in combination.

(conditions for adjusting the solubility of condensate)

As conditions for adjusting the solubility of the aggregate, for example, (a) the concentration of the platinum group metal dissolved in the molten glass; (b) the temperature or temperature distribution of the molten glass (the heat supplied to the aggregate); c) pressure in the gas phase space; (d) oxygen activity of the molten glass.

(a) Concentration of platinum group metals dissolved in molten glass

The lower the concentration of the platinum group metal dissolved in the molten glass at the beginning of the coagulation treatment step, the higher the solubility of the foreign matter of the platinum group metal dissolved in the molten glass in the platinum treatment step. The concentration of the platinum group metal of the molten glass can be determined, for example, by sampling the molten glass in the clarification tube, cooling, pulverizing, and measuring by ICP quantitative analysis.

When the concentration of the platinum group metal is too low, the solubility of the aggregate of the platinum group metal becomes large, and conversely, the platinum group metal is eluted from the wall of the clarification tube which is in contact with the molten glass to the molten glass, and the clarification tube is melted.

The concentration of the platinum group metal is adjusted in view of suppressing the occurrence of such defects.

Further, the platinum group metal dissolved in the molten glass at the beginning of the agglomerate treatment step in the clarification tube 41 is mainly derived from the contact with the molten glass from the clarification tube 41, or the delivery tube 43a or the like. The platinum group metal dissolved on the wall surface. The amount of the platinum group metal eluted from the wall depends on the temperature of the molten glass in the defoaming treatment step before the start of the agglomeration treatment step or the wall surface of the clarification tube 41 which is in contact with the molten glass. Therefore, by adjusting the temperature or temperature distribution of the wall surface of the conveying pipe 43a and the clarification pipe 41, the concentration of the platinum group metal of the molten glass at the start of the coagulating treatment step can be adjusted. For example, the current can be adjusted by adjusting the current flowing through the clarification pipe 41, adjusting the current supplied to the heater disposed around the clarification pipe 41, or by a combination of the above. By reducing the concentration of the platinum group metal dissolved in the molten glass at the beginning of the agglomerate treatment step, the solubility of the foreign matter of the platinum group metal dissolved in the molten glass at the beginning of the agglomerate treatment step increases. In this respect, it is preferred to adjust the concentration of the platinum group metal dissolved in the molten glass at the beginning of the agglomerate treatment step to 0.05 to 20 ppm.

Thereby, even in the manufacturing process of a glass substrate, even if the aggregate of a platinum group metal mixes in a molten glass, the glass substrate which the number of defects of the platinum group metal aggregates is the tolerance level can be manufactured.

(b) Temperature or temperature distribution of molten glass

In the clarification pipe 41, the solubility of the aggregate of the platinum group metal mixed into the molten glass can be increased by increasing the temperature of the molten glass. The temperature or temperature distribution of the molten glass has been described above, and the description thereof is omitted.

When the temperature of the molten glass is too high, the amount of dissolution of the aggregate of the platinum group metal increases, and the following defects occur.

‧ increase in reboiled bubbles

When the temperature of the molten glass in the clarification pipe 41 is too high, excessive defoaming is performed in the defoaming treatment step, so that the oxygen activity of the molten glass is lowered, and as a result, the molten glass is in a reduced state. When the absorption treatment step is carried out in this state, there is a case where excessively re-boiled bubbles are generated in the molten glass due to the following mechanism, and bubbles of the reboiled bubbles remain in the glass substrate. The reboiled gas bubbles specifically include bubbles of SO ₂ or CO ₂ generated by sulfur or carbon contained as impurities in the molten glass. When the reduction state of the molten glass becomes long, SO ₃ and CO ₃ dissolved in the molten glass are easily reduced, and SO ₂ and CO _{2 are} easily formed. Since SO ₂ and CO ₂ are less soluble in molten glass than SO ₃ and CO ₃ , they are likely to become bubbles. When such a heavy boiling bubble is generated in a large amount, it may remain as a bubble defect in a glass substrate, and the quality of a glass substrate may fall. Further, the bubbles remaining on the glass substrate are detected by, for example, a laser microscope or visual inspection.

‧ increase in the amount of volatilization of glass components

When the temperature of the molten glass in the clarification pipe 41 is too high, a component of the molten glass such as B ₂ O ₃ is volatilized to a large amount in the gas phase space. As a result, the glass composition changes locally, and the glass characteristics such as the thermal expansion coefficient or the viscosity of the glass locally change, and a pulse line is generated on the glass substrate.

‧ increase in the amount of platinum group metal

When the temperature of the molten glass in the clarification pipe 41 is too high, the temperature of the gas phase space in contact with the molten glass is also increased, and the amount of oxygen released into the gas phase space by the defoaming treatment of the molten glass is increased. The platinum group metal is easily volatilized from the wall of the clarification tube surrounding the gas phase space. When the amount of volatilization of the platinum group metal increases, the concentration of the platinum group metal in the gas phase space becomes high, and aggregation and aggregates are likely to be mixed into the molten glass.

‧Clarification of the melt loss of the tube

If the temperature of the molten glass in the clarification pipe 41 is too high, the wall of the clarification pipe 41 which is in contact with the molten glass may be melted.

The adjustment of the temperature or temperature distribution of the molten glass in the clarification pipe 41 is performed from the viewpoint of suppressing the occurrence of such a disadvantage.

(c) Pressure in the gas phase space

The solubility of the agglomerates of the platinum group metal can be increased by increasing the pressure of the gas phase space 41c of the clarification tube 41. The pressure in the gas phase space means the total pressure of the gas contained in the gas phase space.

For example, it is possible to adjust the amount (suction amount) of the gas in the gas phase space 41c to the outside of the clarification pipe 41 through the vent pipe 41a, or the supply amount of the gas in the clarification pipe 41 such as an inert gas, self-melting. The amount of gas released by the glass is adjusted to adjust the pressure of the gas phase space 41c. For example, by adjusting the pressure difference between the gas phase space 41c and the atmosphere outside the clarification pipe 41 by connecting the outlet of the vent pipe 41a of the clarification pipe 41 to the suction device or narrowing the outlet, the suction can be adjusted. the amount. For example, by adjusting the amount of the clarifying agent contained in the molten glass and the blending ratio of the glass component, the amount of gas released from the molten glass can be adjusted. Further, for example, the pressure of the gas phase space 41c can be determined to be higher or lower than the atmospheric pressure on the outer side of the clarification pipe 41 based on the amount of gas discharged from the vent pipe 41a.

The method of increasing the pressure of the gas phase space 41c in order to dissolve the foreign matter in the molten glass in the molten glass, as described above, by adjusting the supply amount of the gas in the clarification pipe 41, for example, the supply amount of the inert gas, or self-melting The amount of gas released by the glass is released. The pressure in the gas phase space 41c is preferably adjusted within a range of, for example, 0.8 to 1.2 atm.

When the pressure in the gas phase space 41c is too high, the amount of dissolution of the aggregate of the platinum group metal increases, which in turn causes the following disadvantages.

‧Clarification

If the pressure in the gas phase space 41c is too high, there is a possibility that bubbles generated in the molten glass are hardly released from the surface of the molten glass in the defoaming treatment step, resulting in poor clarification.

‧ increase in the amount of platinum group metal

When the pressure in the gas phase space 41c is too high, the pressure difference from the atmosphere outside the clarification pipe 41 becomes large, and the flow velocity of the gas flow in the gas phase space 41 rises. Therefore, the concentration of the platinum group metal in the gas phase space 41c cannot be increased, and it is difficult to be saturated, so that the amount of volatilization of the platinum group metal from the wall of the clarification pipe 41 is increased.

In view of suppressing the occurrence of such a disadvantage, pressure adjustment in the gas phase space is performed.

(d) Oxygen activity of molten glass

In the clarification pipe 41, the solubility of the aggregate of the platinum group metal can be increased by increasing the oxygen activity of the molten glass. The oxygen activity of the molten glass means the amount of oxygen dissolved in the molten glass (the amount of oxygen present in the molten glass as bubbles) is removed. In the present embodiment, [Fe ³⁺ ]/([Fe ²⁺ ]+[Fe ³⁺ ]) is used as an index of oxygen activity. Here, the activity of Fe ²⁺ and Fe ³⁺ contained in the [Fe ²⁺ ] and [Fe ³⁺ ]-based molten glass, specifically, the content expressed by mass percentage can be measured by spectrophotometry.

For example, in the defoaming treatment step in the clarification step, the temperature of the molten glass becomes high, and the oxygen dissolved in the molten glass becomes bubbles and is defoamed, so that the oxygen activity of the molten glass is lowered. On the other hand, in the clarification step, if the temperature of the molten glass becomes low, the clarifying agent absorbs oxygen, and thus the oxygen activity increases.

For example, in addition to adjusting the amount of the clarifying agent and the oxide contained in the molten glass in the melting step, in addition to adjusting the amount of the clarifying agent or the glass raw material oxide contained in the molten glass, it is also possible to adjust the condensation by the clarification step. The oxygen activity of the molten glass is adjusted by foaming the oxygen-containing gas in the molten glass before the start of the agglomeration treatment step or before the start of the agglomeration treatment step.

The adjustment of the oxygen activity in the molten glass can also be carried out in conjunction with the adjustment of the temperature or temperature distribution of the molten glass. Further, adjusting the oxygen activity in the molten glass can also be performed together with the pressure adjustment of the gas phase space 41c. As described above, in addition to adjusting the amount of the clarifying agent or the glass raw material oxide contained in the molten glass, it is also possible to adjust the temperature of the molten glass before the start of the agglomerating treatment step in the clarification step, or to treat the agglomerate The oxygen-containing gas is bubbled in the molten glass before the start of the step to adjust the oxygen activity in the molten glass. In the agglomerate treatment step, it is preferred to adjust [Fe ³⁺ ]/([Fe ²⁺ ]+[Fe ³⁺ ]) as an index of oxygen activity, for example, in the range of 0.2 to 0.5.

When the oxygen activity of the molten glass is adjusted too high in the oxygen activity of the molten glass, the amount of the aggregate of the platinum group metal is increased, and the following disadvantages are caused.

‧ Increased volatilization of platinum group metals

When the oxygen activity of the molten glass is excessively large, the amount of oxygen released from the molten glass to the gas phase space increases in the defoaming treatment step, and the oxygen concentration in the gas phase space increases, so that the platinum group metal is easily oxidized and is easily volatilized. If the platinum group metal is easily volatilized, it is easy to form agglomerates of the platinum group metal and is easily incorporated into the molten glass.

‧Residual oxygen bubbles in molten glass

When the oxygen activity of the molten glass is too large, in the absorption treatment step, the reduced clarifying agent does not absorb oxygen, and oxygen-containing bubbles (oxygen bubbles) are formed in the molten glass, which remain as bubbles in the glass substrate. Therefore, the quality of the glass substrate is easily lowered.

From the viewpoint of suppressing the occurrence of such a disadvantage, it is preferred to increase the amount of dissolution of the aggregate of the platinum group metal by adjusting the oxygen activity of the molten glass, and to combine the appropriate condition parameters (temperature of the molten glass, etc.). Adjustment.

Alternatively, the temperature adjustment of the molten glass may be feedback-adjusted based on the number of defects of the agglomerates. The temperature of the molten glass to be adjusted may be the temperature at the time of starting the agglomerate treatment step, or may be the temperature in the middle of the agglomerate treatment step.

The laser beam is incident on the surface of the glass substrate from the oblique direction of the glass substrate and receives the reflected light, and the image obtained by receiving the light is determined to be consistent with the shape of the agglomerate of the platinum group metal. The region is capable of detecting defects of the aggregate of the platinum group metal in the glass substrate. Defects in the condensate can also be visually detected instead of using the device as such. When the allowable level of the number of defects of the aggregate is expressed by the unit mass, for example, it is 0.02 pieces/kg or less. The above tolerance level varies depending on the strain required by the user of the glass substrate or the specification of the unevenness of the main surface.

For example, when the number of defects detected in the glass substrate exceeds an allowable level, the temperature of the molten glass is increased and the saturation solubility of the platinum group metal in the molten glass is increased, thereby promoting dissolution of the agglomerates mixed into the molten glass. . On the other hand, when the number of defects detected in the glass substrate is at an allowable level, it can be lowered within a range higher than the temperature of the molten glass corresponding to the upper limit of the number of defects at the allowable level. borrow By adjusting the temperature of the molten glass in this manner, the saturation solubility of the platinum group metal can be adjusted to an appropriate range, whereby the number of defects of the aggregate contained in the glass substrate can be suppressed to an allowable level, and the bubble due to reboiling can be suppressed. The quality of the glass substrate resulting from the increase or the like is lowered.

Specifically, in the case where the glass processing apparatus includes a clarification apparatus for a clarification tube, the temperature of the molten glass can be adjusted by causing a current to flow to the clarification tube to perform electric heating. The amount of current can be adjusted according to the magnitude of the voltage applied to the heating electrode. Further, in place of the electric heating or the electric heating, the temperature of the molten glass may be indirectly adjusted by a heater (not shown) disposed around the clarification pipe. The heater is disposed, for example, inside or outside the refractory protective layer or the refractory brick. Further, the temperature of the molten glass can be adjusted by adjusting the amount of heat released from the clarification tube by using a refractory protective layer or a refractory brick.

In the agglomerate treatment step, it is preferable to adjust the [Fe ³⁺ ] of the glass substrate which is an index of the oxygen activity of the molten glass in the range of 0.2 to 0.5 in place of the temperature adjustment of the molten glass or the temperature adjustment. /([Fe ²⁺ ]+[Fe ³⁺ ]), thereby adjusting the saturation solubility of the above platinum group metal so that the number of defects of the aggregate contained in the glass substrate is at an allowable level.

(Agglomerates of platinum group metals after the agglomerate treatment step)

After the coagulum treatment step, the ratio of the number of foreign matter (agglomerates) having a maximum length of more than 50 μm in the foreign matter (agglomerate) of the platinum group metal contained in the molten glass, the glass substrate or the glass substrate laminate is reduced to less than 30%.

In the present embodiment, when the temperature of the clarification pipe 41 is raised to increase the temperature of the molten glass G, the above-described effects of the embodiment can be effectively exhibited.

For example, in order to reduce the environmental burden, it is preferable to use tin oxide as a clarifying agent for molten glass, but the temperature at which tin oxide obtains a clarifying effect (oxidation reaction) is higher than that of As ₂ O ₃ or Sb ₂ O ₃ . Therefore, when tin oxide is used as the clarifying agent, it is necessary to increase the temperature of the clarification pipe 41 and increase the temperature of the molten glass G as compared with the case of using As ₂ O ₃ or Sb ₂ O ₃ as a clarifying agent. That is, since tin oxide is used as the clarifying agent, volatilization (oxidation) of the clarification pipe 41 is more likely to occur than in the prior art, and the problem of volatilization and aggregation of the platinum group metal is likely to occur. Even if the amount of the foreign matter (aggregate) of the platinum group metal mixed into the molten glass is increased by using tin oxide as a clarifying agent, the size of the foreign matter of the platinum group metal can be reduced as shown in the embodiment, so that it is not easy. The effect of strain on the glass substrate and uneven formation of the main surface of the glass substrate is remarkable. In other words, the amount of foreign matter (aggregate) causing display failure can be sufficiently reduced.

In addition, the molten glass having a higher viscosity is slower in floating speed in the clarification step, and it is difficult to clarify. Further, in the stirring step performed in the stirring device 100, it is also difficult to uniformly stir the molten glass having a high viscosity. Therefore, in order to sufficiently obtain the clarifying effect or the homogenization of the molten glass, it is necessary to increase the temperature of the molten glass. For this reason, if the temperature of the glass processing apparatus is also raised in order to obtain a molten glass having a relatively high temperature, the volatilization of the platinum group metal becomes intense in the glass treatment step, and the amount of foreign matter (agglomerate) mixed into the molten glass is easy. increase. That is, the problem of volatilization and agglomeration of the platinum group metal tends to occur.

For example, a thin film transistor is formed on a glass substrate used for a display panel, but the glass substrate is preferably an alkali-free glass or a glass containing a small amount of alkali to avoid adversely affecting the operation of the thin film transistor. The alkali-free glass or the glass containing a small amount of alkali has higher viscosity than the alkali-containing glass such as soda glass, so the bubble float speed is slow in the clarification step, and it is difficult to clarify. For this reason, in order to sufficiently obtain the clarifying effect, it is necessary to increase the temperature of the clarification pipe 41 and increase the temperature of the molten glass G. In other words, since the object to be produced is an alkali-free glass or a glass containing a small amount of alkali, the volatilization (oxidation) of the clarification tube 41 is more likely to occur than that of the alkali glass, and the problem of volatilization and aggregation of the platinum group metal tends to occur. Even if the temperature of the clarification pipe 41 is increased by using an alkali-free glass or a glass containing a small amount of alkali, and the amount of the foreign matter (agglomerate) of the platinum group metal is mixed into the molten glass, the platinum can be reduced as shown in the embodiment. Since the size of the foreign matter of the group metal is small, it is not easy to cause strain on the glass substrate, and the effect of being able to form unevenness on the main surface of the glass substrate is remarkable. That is, it can be fully reduced to cause significant The amount of foreign matter (agglomerate) showing bad.

The above alkali-free glass or glass containing a small amount of alkali is a glass having a high strain point. The glass with the higher strain point has higher viscosity than the glass with lower strain point, so the floating speed of the bubble in the clarification step is slower and difficult to clarify. For this reason, in order to sufficiently obtain the clarifying effect, it is necessary to increase the temperature of the clarification pipe 41 and increase the temperature of the molten glass G. That is, in the case of producing a glass having a higher strain point, the volatilization (oxidation) of the clarification tube is more likely to occur than in the case of producing a glass having a lower strain point, and the problem of volatilization and aggregation of the platinum group metal is liable to occur. Even if the glass having a high strain point is used, even if the temperature of the clarification pipe 41 is increased and the amount of the foreign matter (aggregate) of the platinum group metal is increased to the molten glass, the platinum group can be reduced as shown in the embodiment. Since the size of the foreign matter of the metal is small, it is not easy to cause strain on the glass substrate, and the effect of forming the unevenness of the main surface of the glass substrate is remarkable. In other words, the amount of foreign matter (aggregate) causing display failure can be sufficiently reduced.

Further, in the glass substrate for a display, the strain point of the glass substrate is required to be 600 ° C or higher, more preferably 650 ° C or higher, and when the strain point of the glass substrate is 600 ° C or higher, the present embodiment can sufficiently reduce display defects. The effect of the amount of foreign matter (aggregate) of size is remarkable. Further, for the glass substrate for a high-definition display, the strain point is required to be higher, and the strain point is preferably 690 ° C or higher, more preferably 730 ° C or higher. When the strain point is 690 ° C or higher and 730 ° C or higher, the above effects of the present embodiment are more remarkable.

Further, the viscosity of the molten glass containing tin oxide used in the present embodiment is preferably 1500 ° C or higher, for example, 1500 ° C to 1700 ° C, or 1550 ° C to 1650 ° C, and the viscosity is 10 ^2.5 poise. . In this case, the above effects of the embodiment are more remarkable.

Further, when the thickness of the glass substrate produced by the present embodiment is 0.005 mm to 0.8 mm, preferably 0.01 mm to 0.5 mm, more preferably 0.01 mm to 0.2 mm, the above-described effects of the embodiment become More significant. When such a glass substrate having a small thickness is produced, foreign matter (aggregates) tend to occur on the surface of the glass to form surface irregularities. Yu Ben In the embodiment, the above-described effects can be utilized to solve the problem caused by the thickness of the plate.

[Experimental example]

In order to confirm the effect of the present embodiment, a glass substrate (Example) was produced by a manufacturing process including the agglomerate treatment step S2B shown in Fig. 1 . In the agglomerate treatment step S2B, control of the amount of heat supplied to the agglomerates is performed.

The production conditions of the glass substrate are as follows.

The composition of the glass of the glass substrate is: SiO ₂ 60.7% by mass; Al ₂ O ₃ 17% by mass; B ₂ O ₃ 11.5% by mass; MgO 2% by mass; CaO 5.6 % by mass; SrO 3 % by mass; SnO ₂ 0.2% by mass The strain point is 660 ° C and the thickness is 0.4 mm.

Further, the agglomerate treatment step S2B shown in Fig. 1 is not performed, and the glass substrate is produced under the above-described production conditions by the previous production step of the absorption treatment step S2C after the defoaming treatment step S2A. Specifically, in Examples 1 to 5 shown in Table 1 below, the maximum temperature of the molten glass G in the clarification pipe 41 was 1670 ° C to 1720 ° C, and the temperature of the molten glass G was 1670 ° C or more. 40 minutes. On the other hand, in Examples 6 and 7, the maximum temperature of the molten glass G was less than 1670 ° C, and the temperature of the molten glass G was 1670 ° C or more for 0 minutes.

The foreign matter (aggregate) of the platinum group metal in the thus-produced 0.1 m ³ of the plurality of glass substrates was counted by an optical microscope, and the maximum length of the foreign matter (agglomerate) of the platinum group metal was measured. Then, the ratio of the number of foreign matters having a maximum length of 50 μm or less among the foreign matter (agglomerates) of all the platinum group metals mixed in the glass substrate was determined. The ratio obtained is shown together with the highest temperature in Table 1 below. Regarding the ratio of the foreign matter of Examples 1 to 5, any glass substrate was 70% or more, and the ratio of the foreign matter of Examples 6 and 7 was 35% or less of any glass substrate. Fig. 5 is a graph showing the relationship between the maximum temperature of molten glass and the ratio of foreign matter. As can be seen from Fig. 5, the ratio of the foreign matter having a maximum length of 50 μm or less is sharply increased by the maximum temperature of the molten glass from 1660 ° C to 1670 ° C or more, and is 70% or more at a temperature of 1670 ° C or higher. When the temperature is 1690 ° C or higher, the ratio of the foreign matter having a maximum length of 50 μm or less is 92% or more. In particular, when the temperature is 1700 ° C or higher, the ratio of the foreign matter having a maximum length of 50 μm or less becomes 100%. From this, it is understood that, in the case of controlling the heat supplied to the foreign matter under the conditions of the experimental examples, the maximum temperature of the molten glass is preferably 1670 ° C or higher, preferably 1690 ° C or higher, and more preferably 1700 ° C or higher. And provide heat to foreign objects. Under the conditions of this experimental example, the maximum temperature of 1670 °C is such that the ratio of the foreign matter having a maximum length of 50 μm or less is the lower limit temperature of the highest temperature of 70%, but it is not necessary to make the maximum temperature be 1670 ° C or more, by other methods. The solubility of the agglomerates (foreign substances) can also achieve a ratio of foreign matter having a maximum length of 50 μm or less of 70%.

In the above, the method of producing the glass substrate of the present invention, the glass substrate, and the glass substrate layered body are described in detail. However, the present invention is not limited to the above-described embodiments, and various modifications and changes can be made without departing from the spirit and scope of the invention.

Claims (19)

A method for producing a glass substrate, comprising: a melting step of melting a glass raw material to form molten glass; and a molten glass processing step of treating the molten glass while flowing the molten glass in a tube of a glass processing apparatus The glass processing apparatus includes a space in which a vapor phase space surrounded by a surface of the molten glass and a wall is formed by introduction of the molten glass, and at least a part of the wall is made of a material containing a platinum group metal, and the molten glass is processed. When the agglomerate of the volatile matter of the platinum group metal volatilized from the wall in the gas phase space is mixed as a foreign matter into the molten glass, and includes an agglomerate treatment step in the tube of the glass processing apparatus The temperature of the molten glass is 1670 ° C or more, and the amount of the agglomerates mixed in the molten glass is reduced so that the ratio of the number of aggregates having a maximum length of 50 μm or less to the aggregate of the molten glass is 70% or more; provided in the above tube of the above glass processing apparatus a vent pipe in which the phase space communicates with the atmosphere on the outer side of the glass processing apparatus, wherein the molten glass flowing through the tube of the glass processing apparatus has a highest temperature in the flow direction at a highest temperature position, and the molten glass is introduced into the glass treatment. The inlet of the tube of the apparatus is between the position of the flow direction of the molten glass of the vent tube. A method for producing a glass substrate, comprising: a melting step of melting a glass raw material to form a molten glass; and a molten glass treatment step of treating the molten glass while flowing the molten glass in a tube of a glass processing apparatus The above glass processing device has a package a liquid phase containing the molten glass, and a gas phase space formed by the liquid surface and the wall of the molten glass, at least a part of a wall surrounding the gas phase space being composed of a material containing a platinum group metal, and processing the molten glass When the agglomerate of the volatile matter of the platinum group metal volatilized from the wall in the gas phase space is mixed as a foreign matter into the molten glass, and the agglomerate treatment step is performed in the tube of the glass processing apparatus The temperature of the molten glass is 1670 ° C or more, and is reduced to the size of the agglomerate mixed in the molten glass in the molten glass treatment step so as to be mixed into the aggregate of the molten glass, and the aggregate having a maximum length of 50 μm or less The ratio of the number is 70% or more; and the tube of the glass processing apparatus is provided with a vent pipe that communicates the gas phase space with the atmosphere outside the glass processing apparatus, and flows through the tube of the glass processing apparatus. The molten glass has a maximum temperature position in the flow direction at which the highest temperature is located, and the molten glass is introduced Inlet of the glass tube processing apparatus, the above-described direction of the flow of the molten glass through a position between the trachea. A method for producing a glass substrate, comprising: a melting step of melting a glass raw material to form molten glass; and a molten glass processing step of treating the molten glass while flowing the molten glass in a tube of a glass processing apparatus The glass processing apparatus includes a space in which a vapor phase space surrounded by a surface of the molten glass and a wall is formed by introduction of the molten glass, and at least a part of the wall is made of a material containing a platinum group metal, and the molten glass is processed. When the agglomerate of the volatile matter of the platinum group metal volatilized from the wall in the gas phase space is mixed as a foreign matter into the molten glass, and includes an agglomerate treatment step in the tube of the glass processing apparatus The temperature of the molten glass is set to 1670 ° C or higher, and the solubility of the aggregate in the molten glass is adjusted to reduce the size of the aggregates mixed into the molten glass; and the tube is disposed in the tube of the glass processing apparatus. a vent pipe that communicates the vapor phase space with an atmosphere outside the glass processing apparatus, wherein the molten glass flowing through the tube of the glass processing apparatus has a highest temperature at a highest temperature in the flow direction, and the molten glass is located The inlet of the tube introduced into the glass processing apparatus is placed between the inlet of the fused pipe and the position of the molten glass in the flow direction. A method for producing a glass substrate, comprising: a melting step of melting a glass raw material to form molten glass; and a molten glass processing step of treating the molten glass while flowing the molten glass in a tube of a glass processing apparatus The glass processing apparatus includes a liquid phase including the molten glass, and a vapor phase space formed by a liquid surface and a wall of the molten glass, and at least a portion of a wall surrounding the vapor phase space is made of a material containing a platinum group metal. When the molten glass is processed, the aggregate of the volatile matter of the platinum group metal volatilized from the wall in the gas phase space is mixed as a foreign matter into the molten glass, and further includes an agglomerate treatment step in which the glass treatment is performed. In the tube of the apparatus, the temperature of the molten glass is set to 1670 ° C or higher, and the heat supplied to the aggregate is controlled so that the heat supplied to the aggregate is such that the agglomerate mixed into the molten glass can be reduced. The minimum amount of heat above the size; in the above tube of the above glass processing apparatus a vent pipe for connecting the gas phase space to the atmosphere outside the glass processing apparatus, wherein the molten glass flowing through the tube of the glass processing apparatus has a maximum temperature at a highest temperature in the flow direction Glass is introduced into the above glass treatment equipment The inlet of the tube is disposed between a position of a flow direction of the molten glass of the vent pipe. The method for producing a glass substrate according to any one of claims 1 to 4, wherein a difference between a maximum temperature and a minimum temperature of the wall in contact with the gas phase space is 5 ° C or more, and the gas phase space contains oxygen. The method for producing a glass substrate according to any one of claims 1 to 4, wherein, in the agglomerating step, the temperature is raised so that the temperature of the molten glass containing the agglomerate is higher than that in the molten glass processing step. The temperature of the molten glass mixed into the region of the molten glass. The method for producing a glass substrate according to any one of claims 1 to 4, wherein in the agglomerating step, the solubility of the agglomerate in the molten glass is higher than the melting of the agglomerate in the molten glass treatment step. The above solubility in the region of the glass. The method for producing a glass substrate according to any one of claims 1 to 4, wherein the glass processing apparatus is a clarification device having a clarification tube, wherein the molten glass flows in the clarification tube, and the gas phase space in the clarification tube The flow direction of the molten glass is formed, and the agglomerate treatment step is performed in the clarification tube. The method for producing a glass substrate according to any one of claims 1 to 4, wherein in the molten glass treatment step, clarification treatment for reducing the number of bubbles in the molten glass is performed using tin oxide contained in the molten glass, the melting The glass flows in the glass processing apparatus, and a temperature distribution along a flow direction of the molten glass is formed on the wall in contact with the gas phase space. An oxygen concentration distribution along the flow direction of the molten glass is formed in the gas phase space. The method for producing a glass substrate according to any one of claims 1 to 4, wherein the molten glass flows in the glass processing apparatus, and the agglomerate processing step is performed in the glass processing apparatus, and flows in the glass processing apparatus In the molten glass, the agglomerate treatment step is performed on the molten glass flowing in the gas phase space along the flow direction of the molten glass at a position corresponding to the region having the highest oxygen concentration. The method for producing a glass substrate according to any one of claims 1 to 4, wherein the highest temperature of the wall in contact with the gas phase space is made such that the oxygen concentration in the gas phase space exceeds 0% and is 1.0% or less. The difference from the lowest temperature is 5 ° C or more and 150 ° C or less. The method for producing a glass substrate according to any one of claims 1 to 4, wherein the temperature of the molten glass is controlled such that the temperature of the molten glass in the agglomerating step is in a temperature range of 1670 ° C to 1730 ° C. The method for producing a glass substrate according to any one of claims 1 to 4, wherein the temperature of the molten glass is controlled such that the temperature of the molten glass in the region of the molten glass in the molten glass treatment step is 1580 Within the temperature range of °C~1660 °C. The method for producing a glass substrate according to any one of claims 1 to 4, wherein the molten glass treatment step comprises the above-described agglomerate treatment step. The method for producing a glass substrate according to any one of claims 1 to 4, wherein the glass substrate is a glass substrate for a display. A method for producing a glass substrate, comprising: a melting step of melting a glass raw material to form molten glass; and a molten glass processing step of treating the molten glass in a glass processing apparatus In the glass processing apparatus, the glass processing apparatus has a space in which a vapor phase space surrounded by a surface of the molten glass and a wall is formed by introduction of the molten glass, and at least a part of the wall is made of a material containing a platinum group metal, and the molten material is processed. In the case of glass, the agglomerate of the volatile matter of the platinum group metal volatilized from the wall in the gas phase space is mixed as a foreign matter into the molten glass, and includes an agglomerate treatment step of adjusting the temperature of the molten glass, or Adjusting the solubility of the agglomerate in the molten glass, and reducing the size of the agglomerates mixed into the molten glass so as to be mixed into the aggregate of the molten glass, and the number of aggregates having a maximum length of 50 μm or less The ratio is 70% or more; and the concentration of the platinum group metal dissolved in the molten glass at the beginning of the agglomeration treatment step is 0.05 to 20 ppm. A method for producing a glass substrate, comprising: a melting step of melting a glass raw material to form molten glass; and a molten glass processing step of treating the molten glass in a glass processing apparatus having the melting a space for forming a vapor phase space surrounded by a surface of the molten glass and a wall, wherein at least a part of the wall is made of a material containing a platinum group metal, and is present in the gas phase space when the molten glass is processed. The agglomerate of the volatile matter of the platinum group metal volatilized from the wall is mixed as a foreign matter into the molten glass, and includes an agglomerate treatment step of adjusting the temperature of the molten glass or adjusting the agglomerate in the molten glass. The solubility is reduced to reduce the size of the agglomerates mixed into the molten glass so as to be mixed into the aggregate of the molten glass, and the ratio of the number of aggregates having a maximum length of 50 μm or less is 70% or more; was treated step, the glass substrate ^{[Fe 3+] / ([Fe} 2+] + [Fe 3+]) of 0.2 to 0.5 Above the saturation solubility of adjusting the platinum group metal within the range of the molten glass. A glass substrate laminate which is formed by laminating a plurality of glass substrates, and the total volume of the glass substrate of the glass substrate laminate is 0.1 m ³ or more, and all of the platinum group metals contained in the glass substrate laminate In the aggregate, the ratio of the number of aggregates having a maximum length of 50 μm or less is 70% or more. A glass substrate characterized in that the ratio of the number of aggregates having a maximum length of 50 μm or less is 70% or more in the aggregate of the platinum group metal contained in the glass substrate.