Float Glass Substrate

Abstract

To provide a float glass substrate that allows bubbles contained in molten glass to be easily removed and the number of metal foreign defects to be reduced.SOLUTION: The present invention relates to a float glass substrate including an alkali-free glass, the float glass substrate having a Cl content of from 0.10 to 0.50 mass%, containing substantially no SnO2, and having a Pt content of, by mass, from 0.001 to 0.30 ppm.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a float glass substrate. [Background technology]

[0002] For glass substrates for various displays, particularly those on which a thin metal or oxide film is formed on the surface, if the substrate contains an alkali metal oxide, alkali metal ions will diffuse into the thin film and deteriorate the film properties. Therefore, it is preferable to use an alkali-free glass substrate that is substantially free of alkali metal ions.

[0003] The alkali-free glass substrate used for the above purpose is obtained by heating and melting glass raw materials prepared at a predetermined compounding ratio in a melting tank to vitrify the glass melt, and then forming the resulting molten glass into a glass ribbon of a predetermined thickness in a float bath, and cutting the glass ribbon into a predetermined shape. Here, a molten glass transport pipe made of platinum (Pt) or a platinum alloy such as a platinum (Pt)-rhodium (Rh) alloy, which has excellent heat resistance and corrosion resistance against molten glass, is installed between the melting tank and the float bath.

[0004] Conventionally, in order to improve the quality of formed glass products, a fining process is used to remove bubbles generated in the molten glass obtained by melting glass raw materials in a melting tank before the molten glass is formed in a forming device. In this fining process, a method is known in which a fining agent is added to the glass raw materials in advance, and the molten glass obtained by melting the glass raw materials is stored and maintained at a predetermined temperature for a certain period of time, so that the fining agent causes the bubbles in the molten glass to grow and float to the surface for removal. Also known is a reduced pressure degassing method in which molten glass is introduced into a reduced pressure atmosphere, and under this reduced pressure atmosphere, air bubbles in a continuously flowing molten glass stream are allowed to grow large, causing the air bubbles contained in the molten glass to float up, break, and be removed, and then the molten glass is discharged from the reduced pressure atmosphere. In order to efficiently remove bubbles from molten glass, it is preferable to carry out the above two methods in combination, that is, to carry out the reduced pressure degassing method using molten glass to which a fining agent has been added.

[0005] Glass fining agents include sulfate-based fining agents such as CaSO4 and BaSO4, and oxide-based fining agents such as As2O3, Sb2O3, and SnO2. Of these, sulfate-based fining agents are the most effective for non-alkali glass with low basicity, such as SO4 2- The solubility of As2O3 is low, so the effect of removing bubbles from molten glass is insufficient. In addition, As2O3 and Sb2O3, especially As2O3, are environmentally hazardous, so there is a demand to limit their use. In addition, the use of tin compound-based fining agents such as SnO2 causes the problem of coloring of float glass substrates. Therefore, the use of tin compound-based fining agents is not appropriate for the manufacture of float glass substrates. Patent Document 1 discloses that chloride-based fining agents such as BaCl2, SrCl2, CaCl2, MgCl2, AlCl3, and NH4Cl have excellent effects as fining agents combined with reduced pressure degassing. In addition, chlorides of alkali metals such as NaCl are disclosed as chloride-based fining agents. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2011 / 078258 Summary of the Invention [Problem to be solved by the invention]

[0007] In order to efficiently remove bubbles contained in molten glass, it is preferable to increase the amount of chloride-based fining agent used. However, it has been revealed that increasing the amount of chloride-based fining agent used increases the rate of defective products due to metal-based foreign matter defects in the inspection process, and reduces the productivity of float glass substrates.

[0008] The present invention has been made in view of the above problems, and has an object to provide a float glass substrate from which bubbles contained in molten glass can be easily removed and which has few metal-based foreign matter defects. [Means for solving the problem]

[0009] The float glass substrate of the present invention is a float glass substrate made of alkali-free glass, and is characterized in that the Cl content is 0.10 to 0.50 mass %, the SnO2 content is substantially zero, and the Pt content is 0.001 to 0.30 ppm by mass. Effect of the Invention

[0010] The float glass substrate of the present invention allows bubbles contained in molten glass to be easily removed, and has few metallic foreign matter defects. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view showing an example of the configuration of a glass manufacturing apparatus used for manufacturing the float glass substrate of the present invention. [Diagram 2] FIG. 2 is a graph showing the relationship between the Cl content of the float glass substrate in Examples 1 to 3 in which the molten glass was heat-treated at 1400° C. for 1 hour, and the dissolution rates of Pt and Rh. [Diagram 3] FIG. 3 is a graph showing the relationship between the Cl content of the float glass substrate and the dissolution rates of Pt and Rh in Examples 4 to 6 in which the molten glass was heat-treated at 1500° C. for 1 hour. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] [Float glass substrate] The float glass substrate of the present invention will now be described. The float glass substrate of the present invention is made of alkali-free glass. The term "alkali-free glass" refers to glass that does not substantially contain alkali metal oxides such as Na2O and K2O. Here, "substantially does not contain alkali metal oxides" means that the total content of alkali metal oxides is 0.1 mass% or less.

[0013] The float glass substrate of the present invention has a Cl content of 0.10 to 0.50 mass%. Cl in glass is a component derived from a chloride-based fining agent. If the Cl content is less than 0.10 mass%, the fining action of the chloride-based fining agent is likely to be insufficient. Therefore, there is a risk that bubbles contained in the molten glass will not be sufficiently removed. If the Cl content exceeds 0.50 mass%, Pt is likely to dissolve from the molten glass transport pipe into the molten glass, and the Pt ion content of the molten glass increases. The present inventors analyzed the metallic foreign matter defects of float glass substrates and found that the main component is Pt. Pt dissolved from a molten glass transport pipe into molten glass exists as Pt ions in the molten glass. The molten glass is formed into a glass ribbon in a float bath. Then, in a reducing atmosphere in the float bath, the Pt ions present in the glass ribbon are reduced, and Pt precipitates on the surface of the glass ribbon, resulting in the metallic foreign matter defects of the float glass substrate. If the Cl content is 0.10 to 0.50 mass %, bubbles contained in the molten glass can be sufficiently removed, and the elution of Pt from the molten glass transport pipe into the molten glass can be suppressed.

[0014] The float glass substrate of the present invention does not substantially contain SnO2. SnO2 is a tin compound-based fining agent. The manufacturing method of the float glass substrate of the present invention does not use a tin compound-based fining agent. Therefore, the float glass substrate is not colored. Here, "substantially does not contain SnO2" means that the content of SnO2 is less than 0.05 mass%.

[0015] The float glass substrate of the present invention has a Pt content of 0.001 to 0.30 ppm by mass. As described above, a molten glass transport pipe made of platinum or a platinum alloy is installed between the melting tank and the float bath. Therefore, it is inevitable that Pt will dissolve from the molten glass transport pipe into the molten glass, and the float glass substrate contains Pt at a mass of 0.001 ppm or more. When the Pt content of the float glass substrate increases, the number of metallic foreign matter defects increases, and the ratio of defective products caused by metallic foreign matter defects increases in the inspection process. If the Pt content is 0.30 ppm or less by mass, the ratio of defective products caused by metallic foreign matter defects does not increase in the inspection process. The float glass substrate of the present invention preferably has a Pt content of 0.001 to 0.25 ppm by mass, more preferably 0.001 to 0.20 ppm, and even more preferably 0.001 to 0.15 ppm.

[0016] The float glass substrate of the present invention preferably has an Rh content of 0.001 to 0.50 ppm by mass. When the molten glass transport pipe installed between the melting tank and the float bath is made of platinum alloy, Pt-Rh alloy is usually used. In this case, Pt and Rh are dissolved from the molten glass transport pipe into the molten glass, and the float glass substrate contains Rh at a mass of 0.001 ppm or more. If the Rh content of the float glass substrate is high, the number of metallic foreign matter defects increases, and the ratio of defective products caused by metallic foreign matter defects may increase in the inspection process. If the Rh content is 0.50 ppm or less by mass, the ratio of defective products caused by metallic foreign matter defects does not increase in the inspection process. The Rh content of the float glass substrate of the present invention is more preferably 0.001 to 0.40 ppm by mass, further preferably 0.001 to 0.30 ppm, and particularly preferably 0.001 to 0.25 ppm.

[0017] In the float glass substrate of the present invention, the total content of Pt and Rh is preferably 0.002 to 0.80 ppm by mass, more preferably 0.002 to 0.65 ppm, further preferably 0.002 to 0.50 ppm, and particularly preferably 0.002 to 0.25 ppm.

[0018] β-OH is used as an index of the amount of moisture in glass. In the float glass substrate of the present invention, when the Cl content is more than 0.35 mass % and not more than 0.50 mass %, β-OH is 0.05 to 0.20 mm -1It is preferable that β-OH is 0.05 mm. -1 If the thickness is more than this, the moisture in the glass will flow into the bubbles contained in the molten glass under reduced pressure, making the bubbles easier to grow. -1 More preferably, 0.09 mm or more -1 More preferably, β-OH is 0.20 mm or more. -1 If the thickness is less than 0.18 mm, the bubbles can be prevented from growing too large, and therefore the bubbles can be prevented from slipping through due to the enlargement of the bubble layer during the reduced pressure degassing process. -1 Less than 0.16mm is more preferable. -1 The following is even more preferred: In addition, the β-OH of the float glass substrate is 0.05 to 0.20 mm. -1 In this case, the water content in the glass is low, so the strain point of the glass substrate can be increased, and the thermal shrinkage rate of the float glass substrate can be reduced. To reduce β-OH, there are methods such as selecting glass raw materials with a low water content and melting the glass raw materials by applying electrical current and heating with electrodes.

[0019] In the float glass substrate of the present invention, when the Cl content is 0.10 to 0.35 mass %, β-OH is 0.20 to 0.50 mm -1 It is preferable that β-OH is 0.20 mm -1 If the thickness is more than this, the moisture in the glass will flow into the bubbles contained in the molten glass under reduced pressure, making the bubbles easier to grow. -1 More preferably, β-OH is 0.50 mm or more. -1 If the thickness is less than 0.45 mm, the bubbles can be prevented from growing too large, and therefore, the bubbles can be prevented from slipping through due to the enlargement of the bubble layer during the reduced pressure degassing process. -1 Less than 0.40mm is more preferable. -1 The following is even more preferred:

[0020] The β-OH can be calculated by measuring the transmittance of a float glass substrate using a Fourier transform infrared spectrophotometer (FT-IR) and using the following formula. β-OH = (1 / X)log 10(T1 / T2) X: Thickness of float glass substrate (mm) T1: Reference wave number 4000 cm -1 Transmittance (%) T2: Hydroxyl group absorption wave number 3570cm -1 Minimum transmittance (%) near

[0021] The float glass substrate of the present invention is made of alkali-free glass, does not substantially contain SnO2, and can be appropriately selected from a wide range of compositions as long as the Cl content and Pt content satisfy the above ranges. Specific examples of the composition of the float glass substrate of the present invention are shown below.

[0022] A specific example of the composition of the float glass substrate of the present invention contains, in mass % on an oxide basis, SiO2: 54-73%, Al2O3: 10.5-24%, B2O3: 0.1-12%, MgO: 0-8%, CaO: 0-14.5%, SrO: 0-24%, BaO: 0-13.5%, ZrO2: 0-5%, and MgO+CaO+SrO+BaO: 8-29.5%. Hereinafter, in this specification, mass % based on oxide will simply be referred to as "%".

[0023] In another specific example of the float glass substrate of the present invention, when both a high strain point and high solubility are to be achieved, the glass preferably contains, in mass % on an oxide basis, 58-66% SiO2, 15-22% Al2O3, 5-12% B2O3, 0-8% MgO, 0-9% CaO, 0-12.5% ​​SrO, and 0-2% BaO, i.e., MgO+CaO+SrO+BaO: 9-18%.

[0024] In another specific example of the float glass substrate of the present invention, when a particularly high strain point is desired, the compositions are preferably, in mass % on an oxide basis, SiO2: 54 to 73%, Al2O3: 10.5 to 22.5%, B2O3: 0.1 to 5.5%, MgO: 0 to 8%, CaO: 0 to 9%, SrO: 0 to 16%, BaO: 0 to 9%, and MgO+CaO+SrO+BaO: 8 to 26%.

[0025] The float glass substrate of the present invention can reduce the thermal shrinkage of the float glass substrate when the float glass substrate of the present invention has a strain point of 650°C or higher. This is preferable because it can suppress thermal shrinkage when the float glass substrate of the present invention is used as a glass substrate for a liquid crystal display (LCD) to manufacture a liquid crystal panel. A strain point of 670°C or higher is more preferable, and 680°C or higher is even more preferable. Although the upper limit of the strain point is not particularly limited, if it is 700°C or less, it is not necessary to make the temperature inside the float bath and at the outlet of the float bath very high, so that it is easy to form a glass ribbon in the float bath. In addition, it is preferable because it has little effect on the life of metal members in the float bath.

[0026] The float glass substrate of the present invention preferably has a short side of 2100 mm or more and a long side of 2400 mm or more, more preferably has a short side of 2800 mm or more and a long side of 3000 mm or more, and further preferably has a short side of 2900 mm or more and a long side of 3200 mm or more.

[0027] The float glass substrate of the present invention, for use as a glass substrate for flat panel displays (FPDs), a glass substrate for magnetic disks, a support substrate for semiconductor packages, etc., preferably has a plate thickness of 0.75 mm or less, more preferably 0.55 mm or less, and even more preferably 0.45 mm or less.

[0028] [Manufacturing method of float glass substrate] Next, the method for producing the float glass substrate of the present invention will be described with reference to the drawings. Fig. 1 is a cross-sectional view showing one example of the configuration of a glass production apparatus used for producing the float glass substrate of the present invention.

[0029] The glass manufacturing apparatus shown in FIG. 1 includes a melting tank 100 , a vacuum degassing apparatus 400 , and a forming apparatus 700 .

[0030] An upstream horizontal pipe 210 , an upstream vertical pipe 200 , and an upstream horizontal pipe 220 are provided between the dissolution tank 100 and the vacuum degassing apparatus 400 to connect the dissolution tank 100 and the vacuum degassing apparatus 400 .

[0031] A downstream horizontal pipe 510 , a downstream vertical pipe 500 , and a downstream horizontal pipe 520 are provided between the vacuum degassing apparatus 400 and the molding apparatus 700 to connect the vacuum degassing apparatus 400 and the molding apparatus 700 .

[0032] The vacuum degassing apparatus 400 includes a vacuum degassing vessel 410 , an uprising pipe 420 , a downcomer pipe 430 , and a vacuum housing 440 .

[0033] The vacuum degassing vessel 410 is housed and disposed within a vacuum housing 440 with its major axis oriented horizontally. A vertically oriented uprising pipe 420 is attached to the underside of one end of the vacuum degassing vessel 410, and a downcomer pipe 430 is attached to the underside of the other end. A portion of the uprising pipe 420 and the downcomer pipe 430 are located within the vacuum housing 440.

[0034] The upstream horizontal pipe 210 and the upstream horizontal pipe 220 are provided so that the molten glass G transported from the melting tank 100 flows into the upstream vertical pipe 200 from an upper lateral side, flows downward through the upstream vertical pipe 200, and flows out from a lower lateral side of the upstream vertical pipe 200. The upstream vertical pipe 200 is provided therein with a stirrer 300 for stirring the molten glass G. The upstream horizontal pipe 220 is connected to an uprising pipe 420, and transports the molten glass G to the vacuum degassing apparatus 400.

[0035] A downstream horizontal pipe 510 and a downstream horizontal pipe 520 are provided so that the molten glass G transported from the vacuum degassing apparatus 400 flows into the downstream vertical pipe 500 from a lower lateral side, flows upward through the downstream vertical pipe 500, and flows out from an upper lateral side of the downstream vertical pipe 500. The downstream vertical pipe 500 is provided with a stirrer 600 therein for stirring the molten glass G.

[0036] The downstream horizontal pipe 520 is connected to a lip 720 of the forming device 700 and transports the molten glass G to the forming device 700. The forming device 700 uses a float bath to obtain a float glass substrate. The float bath includes a bath 710 that contains molten metal M, a lip 720, and a twill 730 that adjusts the flow rate of the molten glass G flowing over the lip 720. The larger the gap between the lip 720 and the twill 730, the greater the flow rate of the molten glass G. The float bath is a device that continuously supplies molten glass G to the bath surface of the molten metal M in the bath 710 and forms it into a band-shaped glass ribbon. As the molten metal M, molten tin, molten tin alloy, or the like is used.

[0037] In the glass manufacturing apparatus shown in Fig. 1, molten glass G is transported in the order of an upstream horizontal pipe 210, an upstream vertical pipe 200, an upstream horizontal pipe 220, an uprising pipe 420, a reduced pressure degassing vessel 410, a downcomer pipe 430, a downstream horizontal pipe 510, a downstream vertical pipe 500, and a downstream horizontal pipe 520. These correspond to the above-mentioned molten glass transport pipes, are cylindrical, and are made of platinum (Pt) or a platinum alloy such as a Pt-Rh alloy. Moreover, the stirrers 300 and 600 are made of platinum (Pt) or a platinum alloy such as a Pt-Rh alloy. The reduced pressure degassing vessel 410 may have an elliptical cylindrical shape. The upstream horizontal pipe 210, the upstream horizontal pipe 220, the downstream horizontal pipe 510, or the downstream horizontal pipe 520 may be an inclined pipe inclined with respect to a horizontal plane.

[0038] The manufacturing method for the float glass substrate involves melting glass raw materials in a melting tank 100 to produce molten glass G, subjecting the molten glass G to a vacuum degassing process in a vacuum degassing apparatus 400, and forming the molten glass G into a band-shaped glass ribbon in a forming apparatus 700. The glass ribbon is then slowly cooled in a slow-cooling apparatus (not shown), and inspected for bubble defects and foreign matter defects, and then cut using a processing apparatus to obtain a float glass substrate. When the float glass substrate is used as a glass substrate for a flat panel display (FPD), the float glass substrate is further subjected to cutting and folding, chamfering, and polishing in this order. After the polishing process, the float glass substrate is inspected for bubble defects and foreign matter defects. In the polishing process, at least one of the two main surfaces of the float glass substrate is polished to remove minute irregularities and undulations present on the main surface of the float glass substrate.

[0039] The melting tank 100 is equipped with a burner for melting the supplied frit. The burner forms a flame by mixing a fuel such as natural gas or heavy oil with gas and burning it. A burner that mainly uses air as the gas is called an air combustion burner, and a burner that mainly uses oxygen as the gas is called an oxygen combustion burner. The burner heats the frit from above by radiating a flame toward the frit. The melting tank 100 may be equipped with electrodes for heating the frit.

[0040] The glass raw materials may be, for example, silica sand, boric acid, limestone, aluminum oxide, strontium carbonate, magnesium oxide, etc., and may be mixed to obtain the desired alkali-free glass composition for the float glass substrate.

[0041] A chloride-based fining agent is added to the glass raw materials. The chloride-based fining agent is preferably BaCl2·2H2O, SrCl2·6H2O, CaCl2, MgCl2·6H2O or NH4Cl, from the viewpoint of not being likely to deliquesce.

[0042] The chloride-based fining agent is added so that the Cl content in the produced float glass substrate is 0.10 to 0.50 mass %.

[0043] In the method for producing a float glass substrate, molten glass G supplied from a melting tank 100 is degassed under reduced pressure in a reduced pressure degassing tank 410 which has been depressurized to a predetermined pressure. The molten glass G is preferably continuously supplied to and discharged from the reduced pressure degassing tank 410.

[0044] The reduced pressure degassing vessel 410 is preferably heated to an internal temperature range of 1200 to 1600° C., particularly 1350 to 1550° C., so that the fining action of the chloride-based fining agent can be sufficient.

[0045] When performing reduced pressure degassing, the atmosphere in the reduced pressure housing 440 is exhausted from the outside by a vacuum degassing means such as a vacuum pump through a suction opening provided at a predetermined position of the reduced pressure housing 440. This indirectly exhausts the atmosphere in the reduced pressure degassing tank 410 housed in the reduced pressure housing 440, and the inside of the reduced pressure degassing tank 410 is depressurized to a predetermined pressure. The pressure inside the reduced pressure degassing vessel 410 is preferably 13.33 to 53.33 kPa. The fining step in the manufacturing method of a float glass substrate is not limited to vacuum degassing, and high-temperature fining may be employed in which molten glass is heated to a high temperature (for example, above 1600° C.) to promote the fining action.

[0046] In the method for producing a float glass substrate, the following (1) to (4) can reduce the elution of Pt and Rh from the molten glass transport pipe into the molten glass. (1) As shown in Examples 1 to 6 described later, the higher the temperature of the molten glass (hereinafter also referred to as "glass temperature"), the greater the amount of eluted Pt and Rh. Therefore, the amount of eluted Pt and Rh can be reduced by lowering the temperature of the molten glass passing through the molten glass transport pipe. (2) As shown in Examples 1 to 6 described later, the amount of Pt and Rh dissolved increases as the Cl content of the float glass substrate increases. Therefore, the amount of Pt and Rh dissolved can be reduced by reducing the Cl content of the float glass substrate. (3) Increasing the flow rate of molten glass passing through the molten glass transport pipe can reduce the contact time between the molten glass and the molten glass transport pipe, thereby reducing the amount of Pt and Rh dissolved. (4) By lowering the ratio of the surface area to the volume of the molten glass transport pipe, the contact area between the molten glass and the molten glass transport pipe can be reduced, thereby reducing the amount of Pt and Rh eluted.

[0047] On the other hand, the above methods (1) to (3) for reducing the amount of Pt and Rh dissolved are all disadvantageous from the viewpoint of removing bubbles contained in the molten glass. The above method (3) is because increasing the flow rate of the molten glass shortens the residence time of the molten glass passing through the reduced pressure degassing tank. Moreover, the above methods (3) and (4) for reducing the amount of Pt and Rh dissolved are disadvantageous in the case of small-scale production of float glass substrates. The above method (4) is because lowering the ratio of the surface area to the volume of the molten glass transport pipe increases the diameter of the molten glass transport pipe. Therefore, the above methods (1) to (4) for reducing the amount of eluted Pt and Rh need to be implemented from the viewpoint of removing bubbles contained in the molten glass and taking into account the production volume of float glass substrates. The flow rate of the molten glass in the above (3) (hereinafter also referred to as the "glass flow rate") is 0.03 to 1.5 m 3 It is preferable that the ratio is / h. The ratio of the surface area to the volume of the molten glass transport pipe in the above (4) (hereinafter also referred to as "surface area / volume") is 0.03 to 0.3 cm -1 It is preferable that the thickness is 0.03 to 0.2 cm. -1 It is more preferable that: EXAMPLES

[0048] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0049] [Experimental Example 1] (Examples 1 to 6) Glass raw materials were prepared based on alkali-free glass with a composition of SiO2: 59.8%, Al2O3: 17.2%, B2O3: 7.8%, MgO: 3.1%, CaO: 4.1%, SrO: 7.7%, BaO: 0.1%, and Cl: 0.20% in terms of mass% oxides. The glass raw materials were prepared so that only the Cl content was in the range of 0.00 to 0.30%. These were melted in an electric furnace using an alumina crucible to prepare glass samples. The obtained glass was heat-treated at 1400°C or 1500°C for 1 hour in a platinum alloy crucible with a Rh content of 10 at%. The Pt and Rh contents in the heat-treated glass were quantitatively evaluated by ICP-MS (inductively coupled plasma mass spectrometry), and the dissolution rates of Pt and Rh per unit area and unit time were calculated from the contact area between the molten glass and the crucible and the heat treatment time. The results are shown in Table 1 below and Figures 2 and 3. Figure 2 is a graph showing the relationship between the Cl content of the float glass substrate in Examples 1 to 3 in which the molten glass was heat-treated at 1400°C for 1 hour and the dissolution rates of Pt and Rh. Figure 3 is a graph showing the relationship between the Cl content of the float glass substrate in Examples 4 to 6 in which the molten glass was heat-treated at 1500°C for 1 hour and the dissolution rates of Pt and Rh. The dashed lines in Figures 2 and 3 are regression lines.

[0050] [Table 1] These results show that the dissolution rate of Pt and Rh increases as the Cl content increases. It also shows that the higher the temperature of the molten glass, the higher the dissolution rate of Pt and Rh. In particular, when the temperature of the molten glass is 1500°C, there is a significant tendency for the dissolution rate of Pt to increase as the Cl content increases.

[0051] [Experimental Example 2] (Examples 7 to 19) Based on the results of Experimental Example 1, the metal foreign matter quality and bubble quality of a float glass substrate manufactured by the glass manufacturing apparatus shown in Fig. 1 were evaluated by simulation. Examples 7, 8, and 13 are comparative examples, and Examples 9 to 12 and 14 to 19 are working examples.

[0052] In the glass manufacturing apparatus shown in Fig. 1, the upstream horizontal pipe 210, the upstream vertical pipe 200, the upstream horizontal pipe 220, the uprising pipe 420, the reduced pressure degassing vessel 410, the downcomer pipe 430, the downstream horizontal pipe 510, the downstream vertical pipe 500, the downstream horizontal pipe 520, and the stirrers 300 and 600 were made of a platinum alloy containing 10 at% Rh. The glass composition (excluding the Cl content) of the molten glass passing through the glass manufacturing apparatus was the same as in Examples 1 to 6.

[0053] The Pt contents shown in Tables 2 and 3 below are values ​​calculated using the regression equations in Figures 2 or 3 and the Cl contents, molten glass transport pipe surface areas, and glass flow rates shown in Tables 2 and 3 below. The Rh contents shown in Tables 2 and 3 below were also calculated in the same manner. The bubble growth index I shown in Tables 2 and 3 below is an index of the ease with which bubbles contained in molten glass grow under a reduced pressure atmosphere. The higher the bubble growth index I, the easier it is for bubbles contained in molten glass to grow. The bubble growth index I was calculated using the following formula (1). I=590.5×[β-OH]+874.1×[Cl]-5.7×[B2O3]-33.3 (1) In formula (1), [β-OH] is the β-OH (mm -1 ), [Cl] indicates the Cl content (% by mass) of the float glass substrate, and [B2O3] indicates the B2O3 content (% by mass) of the float glass substrate.

[0054] The metallic foreign matter quality and bubble quality shown in Tables 2 and 3 below were judged as "Good" or "Poor" based on the following criteria. If the metallic foreign matter quality and bubble quality are judged as "Good", it is expected that the rate of defective products caused by metallic foreign matter defects and bubble defects in the inspection process will decrease, and the productivity of float glass substrates will improve. If the Pt content was 0.30 ppm or less, the metal foreign matter quality was rated as "good," and if the Pt content was more than 0.30 ppm, the metal foreign matter quality was rated as "poor." In the case of Examples 7 to 9 and 12 to 18 in which the glass temperature was 1500°C, if the bubble growth index I was greater than 320, the bubble quality was rated as "good," and if the bubble growth index I was 320 or less, the bubble quality was rated as "poor." In addition, in the case of Examples 10, 11, and 19 in which the glass temperature was 1400°C, it was not as easy to remove bubbles contained in the molten glass as compared to the case in which the glass temperature was 1500°C, so if the bubble growth index I was greater than 400, the bubble quality was rated as "good."

[0055] [Table 2] The Cl content, Pt content and Rh content in Tables 2 and 3 are the contents in a float glass substrate. The surface area / volume in Tables 2 and 3 is the value obtained by dividing the surface area of ​​the molten glass transport tube by the volume of the molten glass transport tube. [Table 3]

[0056] In Examples 7 and 8, the glass flow rate is 0.02 m 3 / h, and the glass flow rate is low, so the contact time between the molten glass and the molten glass transport pipe increases, which makes it easier for the amount of Pt and Rh to dissolve out. Example 7, which has a Cl content of 0.00 mass% and a Pt content of 0.30 ppm or less, does not contain Cl. Therefore, the amount of Pt and Rh eluted was reduced, and the metal foreign matter quality was "good", but the bubble quality was "poor". In Example 8, in which the Cl content was 0.26 mass% and the Pt content was more than 0.30 ppm, the Cl content was 0.10 to 0.50 mass%. Therefore, the bubbles contained in the molten glass could be sufficiently removed, and the bubble quality was "good", but the influence of the increased amount of Pt and Rh eluted due to the low glass flow rate could not be eliminated, and the metal foreign matter quality was "poor".

[0057] In Examples 9 to 13, the glass flow rate was 0.04 m 3 / h, which is a larger glass flow rate than in Examples 7 and 8, the contact time between the molten glass and the molten glass transport pipe is reduced, which tends to reduce the amount of Pt and Rh eluted. Examples 9 to 12, in which the Cl content was 0.10 to 0.50 mass % and the Pt content was 0.001 to 0.30 ppm, were rated "good" for both the metal foreign matter quality and the bubble quality. Compared to Example 10, Example 9 has a lower Cl content and is a condition under which bubbles are less likely to grow in the vacuum degassing vessel. However, by increasing the glass temperature, bubble growth in the vacuum degassing vessel is promoted. Example 10 has a higher Cl content than Example 9, which is a condition that makes it easier for Pt and Rh to dissolve from the molten glass transport pipe into the molten glass. However, the dissolution of Pt and Rh is suppressed by lowering the glass temperature. In Example 11, the amount of eluted Pt and Rh is reduced by lowering the ratio of the surface area to the volume of the molten glass transport pipe (surface area / volume) compared to Example 10. Therefore, the Pt content and Rh content are lower than those of Example 10. In Example 12, the Cl content is higher than in Example 9, and the conditions are such that Pt and Rh are more likely to dissolve from the molten glass transport pipe into the molten glass, but the amount of Pt and Rh dissolved is reduced by lowering the ratio of the surface area to the volume of the molten glass transport pipe (surface area / volume). In Example 13, in which the Cl content was 0.30 mass% and the Pt content was more than 0.30 ppm, the Cl content was 0.10 to 0.50 mass%. Therefore, bubbles contained in the molten glass could be sufficiently removed, and the bubble quality was "good", but the influence of the increased amount of Pt and Rh eluted due to the low glass flow rate could not be eliminated, and the metal foreign matter quality was "poor".

[0058] In Examples 14 to 19, the glass flow rate is 0.65 m 3 / h, which is 15 times higher than in Examples 7 to 13, so the contact time between the molten glass and the molten glass transport tube is reduced. Also, in Examples 14 to 19, the ratio of the surface area to the volume of the molten glass transport tube is lower than in Examples 7 to 13, so the contact area between the molten glass and the molten glass transport tube is reduced. As a result, the amount of Pt and Rh eluted is reduced. On the other hand, in Examples 14 to 19, the time that the molten glass passes through the vacuum degassing tank is shortened, so that the bubbles contained in the molten glass tend to grow and rise to the surface and pass through the vacuum degassing tank before they break, which may increase the rate of defective products due to bubble defects in the inspection process. Examples 14 to 19, in which the Cl content was 0.10 to 0.50 mass % and the Pt content was 0.001 to 0.30 ppm, were rated "good" for both the metal foreign matter quality and the bubble quality. In Example 14, in which the Cl content was 0.28 mass% and the Pt content was 0.30 ppm or less, the Cl content was 0.1 to 0.5 mass%. Therefore, an increase in the amount of Pt and Rh eluted could be suppressed, and the metal foreign matter quality was "good," and bubbles contained in the molten glass were sufficiently removed, and the bubble quality was "good." In Example 15, in which the Cl content was 0.50 mass% and the Pt content was 0.30 ppm or less, the Cl content was 0.1 to 0.5 mass%. Therefore, an increase in the amount of Pt and Rh eluted could be suppressed, and the metal foreign matter quality was "good," and bubbles contained in the molten glass could be sufficiently removed, and the bubble quality was "good." Example 16, which had a Cl content of 0.50 mass% and a Pt content of 0.30 ppm or less, had a higher Cl content than Example 14 and a higher β-OH content than Example 15. Therefore, compared to Examples 14 and 15, Example 16 was able to sufficiently remove bubbles contained in the molten glass, and the bubble quality was evaluated as "good." Example 17, which has a Cl content of 0.35 mass% and a Pt content of 0.30 ppm or less, and Example 18, which has a Cl content of 0.30 mass% and a Pt content of 0.30 ppm or less, have a lower Cl content than Example 16. Therefore, the amount of Pt and Rh eluted is small, and the Pt content and Rh content are lower than those of Example 16. Examples 17 and 18 are under conditions that make it difficult for bubbles to grow in the reduced pressure degassing tank compared to Example 16, but by increasing β-OH, the growth of bubbles in the reduced pressure degassing tank is promoted. In Example 19, in which the Cl content is 0.30 mass % and the Pt content is 0.30 ppm or less, the elution of Pt and Rh is suppressed by lowering the glass temperature compared to Example 18. Therefore, the Pt content and Rh content are smaller than those of Example 18. [Explanation of symbols]

[0059] 100:Dissolution tank 200: Upstream vertical pipe 210: Upstream horizontal pipe 220: Upstream horizontal pipe 300: Stirrer 400: Decompression degassing device 410: Decompression degassing tank 420: Ascending pipe 430: Downcomer 440: Pressure reducing housing 500: Downstream vertical pipe 510: Downstream horizontal pipe 520: Downstream horizontal pipe 600: Stirrer 700: Molding equipment 710: Bathtub 720: Lip 730: Tweel G: Molten glass

Claims

1. A float glass substrate made of non-alkali glass, The Cl content is 0.10 to 0.50 mass %, and SnO 2 Substantially free of The Pt content is 0.001 to 0.30 ppm by mass, A float glass substrate having an Rh content of 0.001 to 0.50 ppm by mass.

2. 2. The float glass substrate according to claim 1, wherein the total content of Pt and Rh is 0.002 to 0.80 ppm by mass.

3. 3. The float glass substrate according to claim 1, wherein the substrate size is 2100 mm x 2400 mm or more.

4. The float glass substrate according to any one of claims 1 to 3, wherein the substrate size is 2900 mm x 3200 mm or more.

5. The float glass substrate according to any one of claims 1 to 4, having a thickness of 0.45 mm or less.

6. The Cl content is more than 0.35 mass% and not more than 0.50 mass%, and β-OH is 0.05 to 0.20 mm -1 The float glass substrate according to any one of claims 1 to 5,

7. The Cl content is 0.10 to 0.35 mass %, and β-OH is 0.20 to 0.50 mm -1 The float glass substrate according to any one of claims 1 to 5,

8. The float glass substrate according to any one of claims 1 to 7, having a strain point of 650°C or higher.

9. The float glass substrate according to any one of claims 1 to 8, having a strain point of 680°C or higher.

10. In terms of mass percentage based on oxide, SiO 2 54 to 73%, Al 2 O 3 10.5 to 24%, B 2 O 3 0.1-12%, MgO 0-8%, CaO 0-14.5%, SrO 0-24%, BaO 0-13.5%, ZrO 2 and a total content of MgO, CaO, SrO and BaO (MgO+CaO+SrO+BaO) is 8 to 29.5%.

11. In terms of mass percentage based on oxide, SiO 2 58 to 66%, Al 2 O 3 15 to 22%, B 2 O 3 11. The float glass substrate according to claim 10, comprising 5 to 12% of MgO, 0 to 8% of MgO, 0 to 9% of CaO, 0 to 12.5% ​​of SrO, and 0 to 2% of BaO, and the total amount of MgO, CaO, SrO, and BaO (MgO+CaO+SrO+BaO) is 9 to 18%.

12. In terms of mass percentage based on oxide, SiO 2 54 to 73%, Al 2 O 3 10.5 to 22.5%, B 2 O 3 0.1 to 5.5% of MgO, 0 to 8% of MgO, 0 to 9% of CaO, 0 to 16% of SrO, and 0 to 9% of BaO, and the total amount of MgO, CaO, SrO, and BaO (MgO+CaO+SrO+BaO) is 8 to 26%.

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