Method for manufacturing glass articles

Abstract

A method for manufacturing a glass article comprises a forming step, wherein molten glass (Gm) overflowing from a groove portion (8) of a forming body (3) flows down along both side surfaces (10) of the forming body (3) by an overflow downdraw method and then fuses at the lower end portion (3a) of the forming body (3) to form a glass ribbon (Gr), wherein the forming body (3) contains an yttrium-containing oxide, and the molten glass (Gm) contains P2O5. In the forming step, a temperature difference (Tl-T2) between a temperature T1 of the molten glass (Gm) in the groove portion (8) and a temperature T2 of the molten glass (Gm) at the lower end portion (3a) is set to be below 100°C.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a glass article. Background Art

[0002] In the manufacturing process of glass products such as glass sheets and glass rolls, molten glass is continuously formed into a glass ribbon by flowing it down along the surface of a forming body, for example, using the overflow downdraw method. The formed glass ribbon is then cooled to near room temperature while being conveyed downstream. It is then cut into predetermined lengths to obtain glass sheets or wound into a roll to obtain a glass roll (see, for example, Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2018-062433 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] In order to improve the mechanical strength of the molded body, an yttrium-containing oxide (e.g., Y3Al5O4, a composite oxide of yttrium and aluminum) may be added to the constituent components of the molded body. 12 ).

[0008] The inventors of the present application have conducted extensive research and have discovered that when a glass ribbon containing PO is formed using a forming body containing yttrium oxide, yttrium oxide dissolves from the yttrium oxide contained in the forming body into the molten glass and diffuses, resulting in devitrification at the lower end of the forming body. Such devitrification from the yttrium oxide can cause defects in the glass ribbon and / or glass articles, and therefore, reducing its generation is important from the perspective of improving production efficiency and quality.

[0009] It should be noted that devitrified materials derived from yttrium-containing oxides are, for example, considered to be produced by the reaction of yttrium oxide (Y2O3) eluted from the yttrium-containing oxide into the molten glass with P2O5 in the molten glass. In other words, devitrified materials derived from yttrium-containing oxides are, for example, considered to be devitrified materials containing yttrium oxide and P2O5 (Y2O3-P2O5 crystals).

[0010] An object of the present invention is to reliably reduce the generation of devitrified materials derived from yttrium-containing oxides contained in a formed body when forming a glass ribbon using an overflow down-draw method.

[0011] Means used to solve problems

[0012] (1) The present invention, which was invented to solve the above-mentioned problems, relates to a method for manufacturing a glass article, characterized in that it comprises a forming step, wherein molten glass overflowing from a groove portion of a forming body is caused to flow down along both side surfaces of the forming body by an overflow downdraw method and then fused at the lower end portion of the forming body to form a glass ribbon, wherein the forming body contains an yttrium-containing oxide, and the molten glass contains P2O5, and in the forming step, the temperature difference between the molten glass in the groove portion and the molten glass at the lower end portion is set to 100°C or less.

[0013] In this way, even if yttrium oxide is dissolved into the molten glass from the yttrium-containing oxide contained in the formed body, the temperature difference of the molten glass between the groove portion of the formed body and its lower end portion is small, thereby suppressing the production of devitrified materials from the yttrium-containing oxide (for example, devitrified materials containing yttrium oxide and P2O5) at the lower end portion of the formed body.

[0014] (2) In the configuration of (1) above, the temperature of the molten glass in the groove portion is preferably 1300° C. or lower.

[0015] In this manner, the viscosity of the molten glass can be suppressed from being excessively lowered, and therefore, the molten glass can be easily formed into a glass ribbon.

[0016] (3) In the configuration of (1) or (2) above, the temperature of the molten glass at the lower end portion is preferably 1100° C. or higher.

[0017] In this manner, the viscosity of the molten glass can be suppressed from becoming excessively high, and therefore, the molten glass can be easily formed into a glass ribbon.

[0018] (4) In the above-mentioned structures (1) to (3), the molten glass preferably contains, in terms of mass%, SiO2 40-70%, Al2O3 10-30%, B2O3 0-3%, Na2O 5-25%, K2O 0-5.5%, Li2O 0.1-10%, MgO 0-5.5%, and P2O5 2-10%.

[0019] This makes it possible to obtain aluminosilicate glass suitable for chemical strengthening, and it is easy to achieve both high-level ion exchange performance and devitrification resistance.

[0020] (5) In the configurations of (1) to (4) above, the molten glass preferably contains 0 to 1 mass % of MgO.

[0021] When the MgO content of molten glass is high, a rich Mg layer is formed on the surface of the formed body that can suppress the dissolution of yttrium oxide from the yttrium-containing oxide. The rich Mg layer, for example, becomes a layer with spinel (MgAl2O4) as the main component when the formed body is an alumina-based refractory. Therefore, yttrium oxide is difficult to dissolve into the molten glass from the yttrium-containing oxide of the formed body. In contrast, if the MgO content of the molten glass is below 1% by mass, it is difficult to form a rich Mg layer on the surface of the formed body. Therefore, yttrium oxide is easily dissolved into the molten glass from the yttrium-containing oxide of the formed body. Therefore, when the MgO content of the molten glass is below 1% by mass, the effect of the present invention becomes significant.

[0022] (6) In the above-mentioned configurations (1) to (5), the molded body preferably contains 1% by mass or more of the yttrium-containing oxide.

[0023] In this manner, yttrium oxide is easily eluted from the yttrium-containing oxide of the formed body into the molten glass, and thus the effects of the present invention become significant.

[0024] Effects of the Invention

[0025] According to the present invention, when a glass ribbon is formed by an overflow down-draw method, the generation of devitrified materials derived from yttrium-containing oxides contained in a formed body can be reliably reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a side view of a manufacturing apparatus for carrying out the method for manufacturing a glass article according to an embodiment of the present invention.

[0027] Figure 2 It is a front view of a manufacturing apparatus for carrying out the manufacturing method of the glass article according to the embodiment of the present invention.

[0028] Figure 3 It shows Figure 1 An enlarged side view of the periphery of the formed body.

[0029] Figure 4 It is a longitudinal sectional view for explaining a heating test in an example of the present invention. DETAILED DESCRIPTION

[0030] The following describes embodiments of the present invention with reference to the accompanying drawings. It should be noted that in the orthogonal coordinate system formed by XYZ shown in the drawings, the X and Y directions are horizontal directions, and the Z direction is the vertical direction. Furthermore, the direction corresponding to the width direction of the formed glass ribbon Gr is referred to as the width direction X, and the direction corresponding to the thickness direction of the formed glass ribbon Gr is referred to as the thickness direction Y.

[0031] Figures 1 to 3This figure shows a manufacturing apparatus 1 for implementing the manufacturing method of a glass article according to the present embodiment. As shown in the figure, the manufacturing apparatus 1 is an apparatus for manufacturing a glass sheet G as a glass article by an overflow downdraw method. The apparatus 1 includes, in order from top to bottom, a forming furnace 2, an annealing lehr 4, a cooling chamber 5, and a cutting chamber 6. The forming furnace 2 and the annealing lehr 4, the annealing lehr 4 and the cooling chamber 5, and the cooling chamber 5 and the cutting chamber 6 are separated by partition members (e.g., the floor of a building) F1, F2, and F3, respectively, each having an opening (e.g., a slit) through which the glass ribbon Gr passes.

[0032] The forming furnace 2 is an area for forming molten glass Gm into a glass ribbon Gr by an overflow downdraw method. Arranged within the forming furnace 2 are a forming body 3 for forming the glass ribbon Gr from the molten glass Gm, and first conveying rollers 7 for cooling both ends of the glass ribbon Gr formed by the forming body 3 in the width direction X.

[0033] The formed body 3 is formed of a long refractory material along the width direction X. Examples of the refractory material include zircon, zirconia, alumina, magnesia, and xenotime.

[0034] A groove (overflow groove) 8 is provided at the top of the forming body 3 along the width direction X. A supply pipe 9 is connected to one end of the groove 8 in the width direction X. Molten glass Gm is supplied into the groove 8 through the supply pipe 9. The method for supplying the molten glass Gm is not limited to this. For example, the molten glass Gm can be supplied from both ends of the groove 8 in the width direction X, or from above the groove 8.

[0035] The formed body 3 has a symmetrical shape in the thickness direction Y. The two side surfaces 10 in the thickness direction Y of the formed body 3 respectively include a vertical surface 11 that is a plane along the vertical direction, and an inclined surface 12 that is connected to the bottom of the vertical surface 11 and is a plane inclined relative to the vertical direction. The vertical surfaces 11 are planes parallel to each other. The inclined surfaces 12 are planes that are connected downward and inclined so as to approach each other in the thickness direction Y. That is, the formed body 3 becomes a wedge-shaped body with a tapered front end toward the bottom when viewed from the width direction X by forming the inclined surfaces 12, and the corner where the inclined surfaces 12 intersect forms the lower end 3a of the formed body 3. It should be noted that the shape of the vertical surface 11 can be changed to an inclined surface, a curved surface, etc., or it can be omitted.

[0036] In order to ensure mechanical strength, the molded body 3 contains 1% by mass or more of an yttrium-containing oxide (for example, Y3Al5O which is a composite oxide of yttrium and aluminum). 12). In the present embodiment, the formed body 3 is an alumina-based formed body containing yttrium oxide. Preferably, in the alumina-based formed body, the content of aluminum oxide (Al2O3) is 90 to 98% by mass, and the content of yttrium oxide is 2 to 10% by mass. It should be noted that the formed body 3 can be a zircon-based formed body or the like as described above. However, in the case of a zircon-based formed body, when the molten glass Gm of a prescribed tempered glass composition is made to flow down, zirconium oxide from the formed body 3 is mixed into the molten glass Gm, and there is a concern that it may become a defect (stripe-shaped defect, etc.) of the glass ribbon Gr and / or the glass plate G. Therefore, from the viewpoint of preventing the occurrence of such defects caused by zirconium oxide, the formed body 3 is preferably an alumina-based formed body.

[0037] The first conveyor rollers 7 are constructed as a pair of rollers that clamp the ends of the glass ribbon Gr in the width direction X in the thickness direction Y directly below the forming body 3. The first conveyor rollers 7 are single-arm rollers that are internally cooled throughout the forming process. The first conveyor rollers 7 are also called cooling rollers or edge rollers. It should be noted that the first conveyor rollers 7 can be arranged in multiple sections (e.g., two sections) in the vertical direction Z. For example, in the case of two sections, it is preferred that the first conveyor rollers 7 in the upper section be drive rollers and the first conveyor rollers 7 in the lower section be free rollers.

[0038] The annealing furnace 4 is an area for reducing the warpage and internal strain of the glass ribbon Gr. The interior space of the annealing furnace 4 has a predetermined temperature gradient toward the bottom. The temperature gradient of the interior space of the annealing furnace 4 can be adjusted by a heating device such as a heater arranged on the inner wall of the annealing furnace 4.

[0039] Second conveyor rollers 13 are arranged within the annealing furnace 4. The second conveyor rollers 13 are also referred to as annealing rollers. The second conveyor rollers 13 are configured as a pair of rollers that sandwich the ends of the glass ribbon Gr in the width direction X in the thickness direction Y. The second conveyor rollers 13 may be double-armed rollers arranged across the entire width direction X of the glass ribbon Gr. In this embodiment, they are single-armed rollers. The second conveyor rollers 13 are arranged in multiple stages in the vertical direction Z.

[0040] The cooling chamber 5 is an area for cooling the glass ribbon Gr to near room temperature. The cooling chamber 5 is open to the outside atmosphere at room temperature, and no heating device such as a heater is provided.

[0041] A third transport roller 14 is disposed within the cooling chamber 5. The third transport roller 14 is configured as a pair of rollers that sandwich the ends of the glass ribbon Gr in the width direction X in the thickness direction Y. The third transport rollers 14 may be double-armed rollers disposed across the entire width direction X of the glass ribbon Gr. In this embodiment, they are single-armed rollers. The third transport rollers 14 are arranged in multiple stages in the vertical direction Z.

[0042] Here, the second conveyor rollers 13 and / or the third conveyor rollers 14 may include conveyor rollers that do not clamp the end portions of the glass ribbon Gr in the width direction X. In other words, the opposing interval between the roller pairs constituting the second conveyor rollers 13 and / or the third conveyor rollers 14 may be larger than the thickness of the end portions of the glass ribbon Gr in the width direction X, allowing the glass ribbon Gr to pass between the roller pairs. It should be noted that in this embodiment, the end portions of the glass ribbon Gr in the width direction X obtained by the manufacturing apparatus 1 include ear portions that are thicker than the central portion in the width direction X due to shrinkage during the forming process.

[0043] The cutting chamber 6 is an area for cutting the glass ribbon Gr into predetermined sizes to obtain glass sheets G as glass articles. A cutting device (not shown) is disposed within the cutting chamber 6 to cut the glass ribbon Gr. In this embodiment, the glass ribbon Gr is cut by the cutting device using a scoring method, wherein the glass ribbon Gr is broken along the scoring line after a score line is formed on the glass ribbon Gr. However, this is not limited to this method. The cutting method of the cutting device may include, for example, laser cutting or laser melting.

[0044] The glass plate G is a glass substrate (mother glass plate) made from one or more product glass plates. The thickness of the product glass plate ranges from 0.05 mm to 10 mm, and the dimensions range from 700 mm x 700 mm to 3500 mm x 3500 mm. The product glass plate is used, for example, as a substrate or cover glass for a display. It should be noted that display substrates and cover glasses are not limited to flat panels and can also be curved or foldable.

[0045] like Figure 3 As shown, the manufacturing apparatus 1 further includes, outside the forming furnace 2, a first side heater 15 for heating the upper side portions of the formed body 3, a second side heater 16 for heating the lower side portions of the formed body 3, and a ceiling heater 17 for heating the top portion of the formed body 3. The first side heater 15 is disposed on the upper outer wall of the side wall portion 2a of the forming furnace 2. The second side heater 16 is disposed on the lower outer wall of the side wall portion 2a of the forming furnace 2. The ceiling heater 17 is disposed on the outer wall of the ceiling portion 2b of the forming furnace 2.

[0046] Furthermore, the manufacturing apparatus 1 is further equipped outside the forming furnace 2 with a first side thermometer 18 for measuring the temperature of the side wall 2a at a position corresponding to the first side heater 15, a second side thermometer 19 for measuring the temperature of the side wall 2a at a position corresponding to the second side heater 16, and a ceiling thermometer 20 for measuring the temperature of the ceiling 2b at a position corresponding to the ceiling heater 17. It should be noted that the heaters 15, 16, and 17 may be divided into a plurality of sections in the width direction X, thereby forming a plurality of partial heaters. In this case, the thermometers 18, 19, and 20 may be provided for each partial heater.

[0047] Next, a method for producing the glass article according to the present embodiment will be described.

[0048] like Figures 1 to 3 As shown in FIG, the present manufacturing method includes a forming step, an annealing step, and a cutting step. Each of the steps is performed using the manufacturing apparatus 1 described above.

[0049] In the forming process, molten glass Gm is supplied to the groove portion 8 of the forming body 3 in the forming furnace 2. The molten glass Gm overflowing from the groove portion 8 flows down along the vertical surface portion 11 and the inclined surface portion 12, and then rejoins at the lower end portion 3a. In this way, the molten glass Gm is continuously formed into a ribbon-shaped glass ribbon Gr.

[0050] The molten glass Gm is an aluminosilicate glass containing P2O5. Specifically, the molten glass Gm preferably contains, by mass%, 40-70% SiO2, 10-30% Al2O3, 0-3% B2O3, 5-25% Na2O, 0-5.5% K2O, 0.1-10% Li2O, 0-5.5% MgO, and 2-10% P2O5. By defining the glass composition range in this manner, it is easy to achieve both high levels of ion exchange performance and devitrification resistance in the glass ribbon Gr. Consequently, a glass ribbon Gr (glass sheet G) suitable for chemically strengthened glass sheets used as cover glasses for mobile phones, digital cameras, PDAs (mobile terminals), touch panel displays, and the like can be obtained.

[0051] MgO is a component that reduces high-temperature viscosity, improves meltability and formability, or increases the strain point and Young's modulus. Among alkaline earth metal oxides, it is the most effective component in improving ion exchange performance. However, if the MgO content is too high, the density and thermal expansion coefficient tend to increase, and the glass becomes more susceptible to devitrification. Therefore, the preferred upper limit range for MgO is 5.5% by mass or less and 4% by mass or less. When the MgO content is 0% to 1% by mass, it is difficult for the Mg-rich layer, which functions as a diffusion-suppressing layer containing yttrium oxide, to form on the surface of the forming body 3. Therefore, temperature management of the molten glass Gm, described later, becomes particularly important.

[0052] When chemically strengthening glass, P2O5 improves ion exchange performance, particularly increasing the stress depth of the compressive stress layer. Furthermore, increasing the P2O5 content facilitates phase separation in the glass. The lower limit of P2O5 is preferably 2% by mass or greater, more preferably 4% by mass or greater. On the other hand, the upper limit of P2O5 is preferably 10% by mass or less, more preferably 9.5% by mass or less, and even more preferably 9% by mass or less.

[0053] Li₂O is an ion exchange component that reduces high-temperature viscosity, improving meltability and formability. It also increases Young's modulus. Furthermore, Li₂O dissolves during ion exchange treatment, degrading the ion exchange solution. Therefore, the preferred lower limit of the Li₂O content, in mass %, is 0.1% or greater, 0.5% or greater, 1.0% or greater, 1.5% or greater, 2.0% or greater, and particularly 2.5% or greater. The preferred upper limit is 10% or less, 8% or less, 5% or less, 4.5% or less, 4.0% or less, and particularly less than 3.5%.

[0054] During the forming process, the temperature difference (T1-T2) between the temperature T1 of the molten glass Gm in the groove portion 8 of the forming body 3 and the temperature T2 of the molten glass Gm at the lower end portion 3a of the forming body 3 is controlled to be 100°C or less. The temperature difference (T1-T2) is preferably 90°C or less, 80°C or less, and particularly 70°C or less. This allows yttrium oxide to elute from the yttrium-containing oxide contained in the forming body 3 into the molten glass Gm. The small temperature difference (T1-T2) of the molten glass Gm can suppress the formation of devitrified materials (e.g., Y2O3-P2O5 crystals) derived from the yttrium-containing oxide at the lower end portion 3a of the forming body 3. In other words, defects caused by devitrified materials derived from the yttrium-containing oxide can be suppressed in the glass ribbon Gr and glass sheet G, thereby improving production efficiency and quality. The lower limit of the temperature difference (T1-T2) of the molten glass Gm can be, for example, 0°C or greater.

[0055] The temperature T1 of the molten glass Gm in the groove portion 8 of the forming body 3 is preferably 1300°C or lower, 1250°C or lower, and particularly 1220°C or lower. This prevents the viscosity of the molten glass Gm from becoming excessively low, making it easier to form the glass ribbon Gr from the molten glass Gm. Furthermore, when the temperature T1 is 1220°C or lower, the amount of yttrium oxide dissolution from the yttrium-containing oxide in the forming body 3 can be significantly reduced, thereby more reliably suppressing the formation of devitrified materials from the yttrium-containing oxide.

[0056] The temperature T2 of the molten glass Gm at the lower end portion 3a of the forming body 3 is preferably 1130°C or higher, 1150°C or higher, and particularly 1180°C or higher. This prevents the viscosity of the molten glass Gm from becoming excessively high, making it easier to form the glass ribbon Gr from the molten glass Gm. Furthermore, since the temperature T2 is relatively high, it is easier to control the temperature difference (T1-T2) to 100°C or lower.

[0057] The temperature T1 of the molten glass Gm in the groove portion 8 of the forming body 3, the temperature T2 of the molten glass Gm at the lower end portion 3a of the forming body 3, and the temperature difference (T1-T2) can be adjusted, for example, by the heaters 15 to 17. Furthermore, the temperatures T1 and T2 can be measured, for example, by a radiation thermometer or estimated based on the furnace wall temperature of the forming furnace 2 measured by the thermometers 18 to 20.

[0058] The time required from when the molten glass Gm overflows the groove portion 8 of the forming body 3 to when it passes through the lower end portion 3 a of the forming body 3 is, for example, 10 to 600 seconds, or more preferably 60 to 300 seconds.

[0059] In the annealing step, the glass ribbon Gr formed in the forming step is annealed in the annealing furnace 4 .

[0060] In the cooling step, the glass ribbon Gr annealed in the annealing step is cooled to near room temperature in the cooling chamber 5 .

[0061] In the cutting step, the glass ribbon Gr cooled in the cooling step is cut in the cutting chamber 6 to obtain a glass sheet G. The cutting step includes a first cutting step of cutting the glass ribbon Gr at predetermined lengths in the width direction X to obtain the glass sheet G, and a second cutting step of cutting and removing the ear portions at both ends of the glass sheet G in the width direction X.

[0062] It should be noted that the post-cutting process is not particularly limited and may include, for example, a cutting process for cutting a glass sheet G into a desired size, an end surface processing process, a cleaning process, an inspection process, a packaging process, a chemical strengthening process, etc. In the inspection process, it is preferable to inspect whether the glass sheet G contains devitrified materials derived from yttrium-containing oxides.

[0063] While the manufacturing apparatus and the manufacturing method of the glass article according to the embodiment of the present invention have been described, the embodiment of the present invention is not limited thereto, and various modifications can be made without departing from the spirit of the present invention.

[0064] In the above-described embodiment, a case where the glass article is the glass sheet G has been described. However, the glass article may be, for example, a glass roll obtained by winding a glass ribbon Gr into a roll shape.

[0065] In the above-described embodiment, the case where the molten glass Gm is aluminosilicate glass is exemplified. However, the molten glass Gm may be glass containing P 2 O 5 other than aluminosilicate glass.

[0066] Example

[0067] Hereinafter, examples of the present invention will be described, but the present invention is not limited to these examples.

[0068] like Figure 4 As shown, as a test body 101 for the comparative test of Examples 1, 2 and the comparative example, a test body was prepared in which molten glass 102 was arranged on a refractory 103 and the two 102 and 103 were in contact with each other. Molten glass 101 was an aluminosilicate glass containing P2O5 (8.7% by mass) and MgO (0.1% by mass) of the same material as the molten glass Gm, and refractory 103 was a rod-shaped alumina refractory containing yttrium oxide (3% by mass) of the same material as the forming body. In other words, the contact portion between the molten glass 102 and the refractory 103 reproduced the contact portion between the molten glass Gm flowing down from the surface of the forming body 3 and the forming body 3. It should be noted that the structure of the test body 101 is common to Examples 1, 2 and the comparative example.

[0069] A heating test was conducted on each of the test pieces 101 of Examples 1 and 2 and the comparative example, wherein the test pieces 101 were heated in an electric furnace 104 equipped with a heater 104a. In the heating test, the test pieces 101 were heated at a first temperature that reproduced the temperature of the molten glass Gm in the groove portion 8 of the forming body 3, and then heated at a second temperature that reproduced the temperature of the molten glass Gm at the lower end portion 3a of the forming body 3. It should be noted that the temperatures shown below are the ambient temperatures of the electric furnace 104, but the temperatures of the molten glass 102 can also be considered the same.

[0070] (1) Example 1

[0071] In Example 1, the test piece 101 was heated in an electric furnace 104 at 1250°C for 72 hours and then at 1180°C for 48 hours. 1250°C is the first temperature that reproduces the temperature of the molten glass Gm in the groove portion 8 of the forming body 3, and 1180°C is the second temperature that reproduces the temperature of the molten glass Gm at the lower end portion 3a of the forming body 3. That is, in Example 1, the temperature difference (T1-T2) is 70°C, which is obtained by subtracting the second temperature from the first temperature. It should be noted that the reason for heating at the first temperature (1250°C) longer than that at the second temperature (1180°C) is to ensure sufficient time for yttrium oxide to dissolve from the yttrium-containing oxide in the refractory (forming body) 103. In Example 2 and the comparative example, the heating time at the first temperature is longer than that at the second temperature for the same reason.

[0072] (2) Example 2

[0073] In Example 2, the test piece 101 was heated at 1220°C for 72 hours and then at 1150°C for 48 hours in the electric furnace 104. 1220°C is the first temperature that reproduces the temperature of the molten glass Gm in the groove portion 8 of the forming body 3, and 1150°C is the second temperature that reproduces the temperature of the molten glass Gm at the lower end portion 3a of the forming body 3. That is, in Example 2, the temperature difference (T1-T2) is 70°C.

[0074] (3) Comparative Example

[0075] In the comparative example, the test piece 101 was heated at 1250°C for 72 hours and then at 1120°C for 48 hours in the electric furnace 104. 1250°C is the first temperature that reproduces the temperature of the molten glass Gm in the groove portion 8 of the forming body 3, and 1120°C is the second temperature that reproduces the temperature of the molten glass Gm at the lower end portion 3a of the forming body 3. That is, in the comparative example, the temperature difference (T1-T2) is 130°C.

[0076] Each molten glass 102 that had undergone the above heating test was then cooled to room temperature. SEM images were then used to identify pitting in each cooled glass. EPMA was then used to determine whether the observed pitting was devitrified material (Y2O3-P2O5 crystals) derived from yttrium oxide. The results showed that in Examples 1 and 2, where the temperature difference (T1-T2) was 100°C or less, no devitrified material derived from yttrium oxide was observed in the glasses obtained by cooling molten glass 102. On the other hand, in the comparative example, where the temperature difference (T1-T2) exceeded 100°C, devitrified material derived from yttrium oxide was observed in the glasses obtained by cooling molten glass 102.

[0077] Based on the test results of Example 1, the glass ribbon Gr was formed in the forming step by setting the temperature of the molten glass Gm in the groove portion 8 of the forming body 3 to 1220°C and the temperature of the molten glass Gm at the lower end portion 3a of the forming body 3 to 1150°C. In this case, the time required for the molten glass Gm to overflow the groove portion 8 of the forming body 3 and pass through the lower end portion 3a of the forming body 3 was approximately 300 seconds. As a result, no devitrified materials derived from yttrium oxide were observed in the resulting glass sheet G.

[0078] Based on the test results of Example 2, the glass ribbon Gr was formed in the forming step by setting the temperature of the molten glass Gm in the groove portion 8 of the forming body 3 to 1250°C and the temperature of the molten glass Gm at the lower end portion 3a of the forming body 3 to 1180°C. In this case, the time required for the molten glass Gm to overflow the groove portion 8 of the forming body 3 and pass through the lower end portion 3a of the forming body 3 was approximately 300 seconds. As a result, no devitrified materials derived from yttrium oxide were observed in the resulting glass sheet G.

[0079] Based on the test results of the comparative example, during the forming process, the temperature of the molten glass Gm in the groove portion 8 of the forming body 3 was set to 1250°C, and the temperature of the molten glass Gm at the lower end portion 3a of the forming body 3 was set to 1120°C, and the glass ribbon Gr was formed. In this case, the time required for the molten glass Gm to overflow the groove portion 8 of the forming body 3 and pass through the lower end portion 3a of the forming body 3 was approximately 300 seconds. As a result, devitrified materials derived from yttrium oxide were confirmed in a portion of the resulting glass sheet G.

[0080] From the above, it can be understood that if the temperature difference (T1-T2) between the temperature T1 of the molten glass Gm in the groove portion 8 of the forming body 3 and the temperature T2 of the molten glass Gm at the lower end portion 3a of the forming body 3 is controlled to be below 100°C, the devitrification of yttrium oxide-containing materials can be suppressed.

[0081] Note that in the comparative example, the temperature T1 of the molten glass Gm in the groove portion 8 of the forming body 3 was set to 1250°C, resulting in devitrification of yttrium oxide-containing materials in a portion of the resulting glass sheet G. Similarly to the comparative example, in Example 2, the temperature T1 of the molten glass Gm in the groove portion 8 of the forming body 3 was set to 1250°C. Therefore, it is estimated that the molten glass Gm of Example 2 dissolved yttrium oxide to the same extent as in the comparative example. In Example 2, the temperature T2 of the molten glass Gm at the lower end portion 3a of the forming body 3 was increased to 1180°C, thereby reducing the temperature difference (T1-T2), and it is estimated that this prevented devitrification of yttrium oxide.

[0082] Furthermore, in Example 1, the temperature T1 of the molten glass Gm in the groove portion 8 of the forming body 3 was lowered to 1220°C compared to the comparative example and Example 2, and thus it is estimated that the dissolution of yttrium oxide into the molten glass Gm was reduced. Therefore, in Example 1, even if the temperature T2 of the molten glass Gm at the lower end portion 3a of the forming body 3 was lowered to 1150°C compared to Example 2, it is estimated that the devitrification of yttrium oxide can be prevented if the temperature difference (T1-T2) is maintained.

[0083] Description of Reference Numerals

[0084] 1 Glass product manufacturing device

[0085] 2 Forming furnace

[0086] 3 formed body

[0087] 3a Lower end

[0088] 4 Annealing furnace

[0089] 5 Cooling Chamber

[0090] 6 Cutting Chamber

[0091] 7 First transport roller

[0092] 8 slots

[0093] 9 Supply pipe

[0094] 13 Second transport roller

[0095] 14 Third transport roller

[0096] 15. First side heater

[0097] 16 Second side heater

[0098] 17 Ceiling heater

[0099] 18 First side thermometer

[0100] 19 Second side thermometer

[0101] 20 Ceiling thermometer

[0102] G Glass Plate

[0103] Gm molten glass

[0104] Gr glass ribbon.

Claims

1. A method for manufacturing a glass article, characterized in that: The invention has a forming step in which the molten glass overflowing from the groove of the forming body flows down along both sides of the forming body by an overflow downdraw method and then fuses at the lower end of the forming body to form a glass ribbon. The formed body is an alumina-based formed body containing yttrium oxide, and the molten glass contains P2O5, In the forming step, a temperature difference between the molten glass in the groove portion and the molten glass at the lower end portion is set to 100° C. or less.

2. The method for manufacturing a glass article according to claim 1, wherein: The temperature of the molten glass in the groove portion is 1300° C. or lower.

3. The method for manufacturing a glass article according to claim 1 or 2, wherein: The temperature of the molten glass at the lower end portion is 1100° C. or higher.

4. The method for manufacturing a glass article according to claim 1 or 2, wherein: The molten glass includes, as a glass composition, SiO2 40% to 70%, Al2O3 10% to 30%, B2O3 0% to 3%, Na2O 5% to 25%, K2O 0% to 5.5%, Li2O 0.1% to 10%, MgO 0% to 5.5%, and P2O5 2% to 10% in terms of mass%.

5. The method for manufacturing a glass article according to claim 1 or 2, wherein: The molten glass contains 0% to 1% by mass of MgO.

6. The method for manufacturing a glass article according to claim 1 or 2, wherein: The molded body contains 1% by mass or more of yttrium-containing oxide.

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