JP2017014056A - Production method of glass plate and production device of glass plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a glass plate and a production device of the glass plate, capable of producing a glass plate having a uniform thickness, which suppress stria generation by controlling temperature of molten glass flowing into a molding device.SOLUTION: The production method of the glass plate includes: a supply step for supplying the molten glass into a supply tube, to supply it to the molding device; and a molding step for molding the glass plate from the molten glass. In the supply step, the molten glass is flown into the supply tube so that temperature of the molten glass gets lower toward a flowing direction of the molten glass, while the supply tube surrounded by heat insulator for keeping temperature of the molten glass flowing the supply tube is electrically heated. The supply tube is divided into a first tube part, a second tube part and a third tube part, toward a downstream side from an upstream side of the frow direction. An electric current flowing in the second tube part is higher than that in the first tube part. The insulator surrounding the third tube part has lower heat conductivity than that surrounding the first insulator.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a glass plate manufacturing method and a glass plate manufacturing apparatus.

  A glass plate used as a glass substrate of a flat panel display such as a liquid crystal display and a plasma display is required to have high flatness on the surface. In particular, in recent years, there has been an increasing demand for flatness of the glass plate surface. Further, a glass plate for a TFT liquid crystal display is required to have high thermal stability. For the production of such a glass plate, a glass raw material prepared so as to realize it is used.

  Such a glass plate for a flat panel display is manufactured by, for example, an overflow down draw method. In the overflow down-draw method, the molten glass that has flowed into the groove on the upper surface of the molded body flows down along both sides of the molded body, joins at the lower end of the molded body, and is then drawn downward to draw a glass ribbon. Is formed. After the glass ribbon is cooled, the glass ribbon is cut into a predetermined size to form a glass plate.

  Since the glass raw material used for manufacture of a glass plate is usually sparingly soluble, a portion called a striae having a component different from the surroundings may occur in the molten glass. When glass ribbons formed by the overflow downdraw method are drawn downward, the stretched state may be different depending on the striae in the molten glass and the difference in temperature and viscosity between the surroundings. Thereby, there exists a possibility that the flatness of the glass ribbon surface may deteriorate. In order to solve such a problem of striae, for example, in Patent Document 1 (Japanese Patent Laid-Open No. 2004-67408), silica having an average particle diameter of 30 μm to 60 μm is used as a glass raw material. A technique for suppressing the occurrence is disclosed.

  However, even if the technique disclosed in Patent Document 1 (Japanese Patent Application Laid-Open No. 2004-67408) is used, if the temperature of the molten glass supplied to the molded body is not uniform, heterogeneous melting that causes striae Glass is generated, and the striae may not be sufficiently suppressed.

  The present invention controls the temperature of the molten glass supplied to the molded body, thereby suppressing the occurrence of striae in the molten glass and producing a glass plate having a uniform thickness. It is an object of the present invention to provide a method and a glass plate manufacturing apparatus.

  The method for producing a glass plate according to the present invention includes a supply step of flowing molten glass through a supply pipe and supplying the molten glass to a forming device, and a forming step of forming the glass plate from the molten glass supplied to the forming device in the supply step. . In the supply process, the molten glass is cooled so that the temperature of the molten glass decreases in the flow direction of the molten glass while the supply tube surrounded by a heat insulating material for keeping the molten glass flowing through the supply pipe is energized and heated. Pour into supply tube. The supply pipe is divided into a first pipe section, a second pipe section, and a third pipe section from the upstream side to the downstream side in the flow direction. The current flowing through the second tube section is higher than the current flowing through the first tube section. The heat insulating material surrounding the third pipe section has a lower thermal conductivity than the heat insulating material surrounding the first pipe section.

  In this glass plate manufacturing method, the temperature of the molten glass flowing through the supply pipe is controlled by energizing and heating the supply pipe surrounded by the heat insulating material. The temperature of the molten glass flowing in the center of the cross section of the supply pipe is higher than the temperature of the molten glass flowing in the vicinity of the inner wall surface of the supply pipe. Since this temperature difference of the molten glass causes striae of the molten glass, the smaller the temperature difference, the better. The second pipe section of the supply pipe is a portion through which a higher current flows than the first pipe section, and the temperature drop of the molten glass flowing in the vicinity of the inner wall surface of the supply pipe is suppressed. As a result, the temperature difference of the molten glass is reduced. Moreover, the 3rd pipe | tube division of a supply pipe | tube is a part with high heat retention compared with a 1st pipe | tube division, and the fall of the temperature of molten glass is suppressed. Thereby, since the temperature of the molten glass supplied to a shaping | molding apparatus becomes uniform, generation | occurrence | production of the striae of molten glass is suppressed. Therefore, this glass plate manufacturing method can manufacture a glass plate having a uniform plate thickness.

  In the supplying step, in the second tube section, it is preferable to flow the molten glass so that the difference between the temperature of the supplying tube and the temperature of the molten glass flowing through the center of the cross section of the supplying tube is reduced along the flow direction.

  In the second pipe section, the inner diameter of the supply pipe is preferably smaller along the flow direction.

  The current flowing through the third tube section is preferably lower than the current flowing through the second tube section.

  The difference between the temperature of the supply pipe and the temperature of the molten glass flowing through the center of the cross section of the supply pipe is preferably 50 ° C. or less at the boundary between the second pipe section and the third pipe section.

  An apparatus for producing a glass plate according to the present invention includes a forming device for forming a glass plate from molten glass, and a supply pipe for supplying the molten glass to the forming device. The supply pipe is surrounded by a heat insulating material for holding the molten glass flowing through the supply pipe. The supply pipe flows the molten glass through the supply pipe so that the temperature of the molten glass decreases in the flow direction of the molten glass while being energized and heated. The supply pipe is divided into a first pipe section, a second pipe section, and a third pipe section from the upstream side to the downstream side in the flow direction. The current flowing through the second tube section is higher than the current flowing through the first tube section. The heat insulating material surrounding the third pipe section has a lower thermal conductivity than the heat insulating material surrounding the first pipe section.

  The glass plate manufacturing method and glass plate manufacturing apparatus according to the present invention manufactures a glass plate having a uniform thickness without striae by controlling the temperature of the molten glass supplied to the molded body. can do.

It is a flowchart which shows an example of the process of the manufacturing method of the glass plate which concerns on embodiment. It is a schematic diagram which shows the structure of the glass plate manufacturing apparatus which concerns on embodiment. It is a schematic diagram of an example of a 3rd supply pipe | tube. It is sectional drawing of a 3rd supply pipe | tube. It is a graph showing the temperature change of the molten glass which flows in the 3rd supply pipe | tube in the cross-sectional direction of a 3rd supply pipe | tube. It is a graph showing the temperature change of the molten glass which flows in the 3rd supply pipe | tube in the longitudinal direction of a 3rd supply pipe | tube.

(1) Outline of Glass Plate Manufacturing Method An embodiment of a glass plate manufacturing method and a glass plate manufacturing apparatus according to the present invention will be described with reference to the drawings. Drawing 1 is a flow chart which shows an example of a process of a manufacturing method of a glass plate of an embodiment.

  As shown in FIG. 1, the glass plate manufacturing method mainly includes a melting step S1, a refining step S2, a stirring step S3, a supplying step S4, a forming step S5, a slow cooling step S6, and a cutting step. S7.

In the melting step S1, molten glass is obtained by putting a glass raw material into a melting tank and heating it. The molten glass flows out from the outlet formed at the bottom of the melting tank toward the refining step S2. Heating of the molten glass in the melting tank is carried out by supplying electricity to the molten glass and directly heating the molten glass, or by indirectly heating the molten glass above the liquid surface with a burner flame. This is done by heating. A fining agent is added to the glass raw material. The fining agents are, for example, SnO ₂ , As ₂ O ₃ and Sb ₂ O ₃ . From the viewpoint of reducing the environmental load, SnO ₂ is used as a clarifying agent.

In the clarification step S2, the molten glass flowing through the pipe extending from the melting tank is heated in the clarification tank, so that bubbles containing CO ₂ , N ₂ , SO _{2 and the} like contained in the molten glass are reduced by the clarifier. Absorbs oxygen produced by the reaction. Bubbles grown by absorbing oxygen float on the liquid surface of the molten glass and disappear. In the clarification step S2, the temperature of the molten glass is further lowered to cause the reduced clarifier to undergo an oxidation reaction, and gases such as oxygen remaining in the molten glass are absorbed by the molten glass. The reduction reaction and oxidation reaction of the fining agent are performed by controlling the temperature of the molten glass in the fining tank. In the clarification step S2, a reduced pressure defoaming method may be used in which a space in a reduced pressure atmosphere is formed in the clarification tank, and bubbles in the molten glass are grown and removed in a reduced pressure atmosphere.

  In the stirring step S3, the molten glass flowing through the pipe extending from the clarification tank is stirred in the stirring tank, and the components of the molten glass are homogenized. Thereby, the composition nonuniformity of the molten glass which is the cause of striae is reduced.

  In supply process S4, the molten glass stirred with the stirring tank flows through piping, and is supplied to a shaping | molding apparatus.

  In the forming step S5, a glass ribbon is continuously formed from the molten glass supplied to the forming apparatus by the overflow down draw method.

  In the slow cooling step S <b> 6, the glass ribbon is gradually cooled so that the formed glass ribbon has a desired thickness and distortion and warpage do not occur.

  In cutting process S7, the cooled glass ribbon is cut | disconnected by predetermined length, and a glass base plate is obtained. The glass base plate is further cut into a predetermined size to obtain a product-sized glass plate. Then, the glass plate end face is ground and polished, and the glass plate is cleaned. Furthermore, the presence or absence of defects such as bubbles, striae and scratches is inspected, and a glass plate that has passed the inspection is packed and shipped as a product. The dimension of the glass plate in the width direction is, for example, 500 mm to 3500 mm. The dimension of the length direction of a glass plate is 500 mm-3500 mm, for example.

The glass raw material used in this method for producing a glass plate is prepared so that a glass having a desired composition can be substantially obtained. As an example of the glass composition, non-alkali glass suitable as a glass plate for a flat panel display is SiO ₂ : 50% by mass to 70% by mass, Al ₂ O ₃ : 0% by mass to 25% by mass, B ₂ O _3. 1% 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 To do. Here, the total content of MgO, CaO, SrO and BaO is 5% by mass to 30% by mass.

Moreover, you may use the alkali trace amount containing glass which contains a trace amount of alkali metals as a glass plate for flat panel displays. The alkali-containing glass contains 0.1% by mass to 0.5% by mass of R ′ ₂ O as a component, and preferably 0.2% by mass to 0.5% by mass of R ′ ₂ O. Here, R ′ is at least one selected from Li, Na and K. The total content of R ′ ₂ O may be less than 0.1% by mass.

The composition of the glass, in addition to the above components, SnO _2: 0.01 wt% to 1 wt% (preferably 0.01 mass% to 0.5 _{mass%), Fe 2 O 3:} 0 wt% -0.2 mass% (preferably 0.01 mass%-0.08 mass%) may be further contained. The glass composition preferably contains substantially no As ₂ O ₃ , Sb ₂ O ₃ or PbO in consideration of environmental load.

In addition, the glass plate for flat panel displays has a 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.

  FIG. 2 is a schematic diagram showing an example of the configuration of the glass plate manufacturing apparatus 100 that performs the melting step S1 to the cutting step S7. The glass plate manufacturing apparatus 100 includes a melting tank 101, a clarification tank 102, a stirring tank 103, a forming apparatus 104, a first supply pipe 105a, a second supply pipe 105b, and a third supply pipe 105c. The first supply pipe 105 a connects the melting tank 101 and the clarification tank 102. The second supply pipe 105 b connects the clarification tank 102 and the stirring tank 103. The third supply pipe 105 c connects the stirring tank 103 and the molding device 104.

  In the melting step S1, the glass raw material is charged into the melting tank 101 using a screw feeder or the like. The glass raw material is heated and melted in the melting tank 101 to obtain molten glass. In the melting tank 101, for example, molten glass at 1500 ° C. to 1600 ° C. is obtained. The molten glass in the melting tank 101 flows through the first supply pipe 105 a and is supplied to the clarification tank 102.

  In the clarification step S <b> 2, the molten glass is clarified in the clarification tank 102. In the clarification tank 102, the temperature of the molten glass is adjusted, and the gas component contained in the molten glass is removed. In the clarification tank 102, the molten glass is heated to, for example, 1500 ° C. to 1700 ° C. The clarified molten glass flows through the second supply pipe 105 b and is supplied to the stirring tank 103.

  In the stirring step S3, the molten glass is stirred in the stirring tank 103, and the components of the molten glass are homogenized. The temperature of the molten glass supplied to the stirring vessel 103 is adjusted to be within a predetermined range. The temperature of the molten glass in the stirring vessel 103 is, for example, 1250 ° C to 1450 ° C. The viscosity of the molten glass in the stirring vessel 103 is, for example, 500 poise to 1300 poise. The molten glass homogenized in the stirring vessel 103 flows into the third supply pipe 105c.

  In the supply step S4, the molten glass is cooled to a temperature suitable for forming the glass ribbon in the next forming step S5 while flowing through the third supply pipe 105c. For example, the molten glass is cooled to around 1200 ° C. in the process of flowing through the third supply pipe 105c. In the supply step S4, the molten glass flowing through the third supply pipe 105c is cooled while the temperature is controlled. The temperature control of the molten glass in the supply step S4 will be described later. The molten glass cooled by the third supply pipe 105 c is supplied to the molding apparatus 104.

  In the forming step S5, the glass ribbon is continuously formed from the molten glass in the forming apparatus 104 by the overflow down draw method.

  In the slow cooling step S6, the glass ribbon molded in the molding step S5 is gradually cooled to near room temperature in the molding apparatus 104.

  In the cutting step S7, the slowly cooled glass ribbon is cut into a predetermined size by a cutting device (not shown), and a glass plate is manufactured.

(2) Outline of Supply Process Next, the supply process S4 will be described in detail. As described above, the supply step S4 is a step of cooling the molten glass flowing in the third supply pipe 105c to a temperature suitable for the forming step S5. For example, in supply process S4, it is preferable that the temperature of molten glass falls at least 150 degreeC. The temperature of the molten glass cooled in the supply step S4 is higher than at least the devitrification temperature of the glass. The devitrification temperature of the glass is about 1200 ° C. In order to maintain the homogeneity of the molten glass realized in the stirring step S3, the molten glass is cooled in the supply step S4 at a predetermined speed. Therefore, the third supply pipe 105c preferably has a mechanism for finely controlling the temperature and viscosity of the molten glass flowing in the third supply pipe 105c. Moreover, since the 3rd supply pipe | tube 105c contacts with high temperature molten glass, it is preferable to shape | mold with the refractory metal. Specifically, the third supply pipe 105c is more preferably formed from platinum or a platinum alloy.

  FIG. 3 is a schematic diagram of an example of the third supply pipe 105c. The lower arrow in FIG. 3 represents the flow direction of the molten glass. As shown in FIG. 3, the third supply pipe 105 c has a plurality of power supply terminals 111. Each power supply terminal 111 includes a flange attached to the outer peripheral surface of the third supply pipe 105c and an electrode extending from the flange. The plurality of power supply terminals 111 are attached at intervals from each other along the longitudinal direction of the third supply pipe 105c. Two adjacent power supply terminals 111 constitute one energization heating device 112. Two adjacent energization heating devices 112 share one power supply terminal 111. That is, the n + 1 power supply terminals 111 constitute n current heating devices 112. In this case, the third supply pipe 105c is divided into n sections along the longitudinal direction of the third supply pipe 105c with the n + 1 power supply terminals 111 as a boundary. For example, when the third supply pipe 105c has ten power supply terminals 111, the third supply pipe 105c is divided into nine sections. Each energization heating device 112 includes two power supply terminals 111 located at both ends of each section. Therefore, each section is provided with one current heating device 112.

  In the following, it is assumed that the third supply pipe 105c is divided into nine sections SC1 to SC9 by ten power supply terminals 111. The nine sections SC1 to SC9 are referred to as a first section SC1, a second section SC2,..., A ninth section SC9 from the upstream side to the downstream side of the third supply pipe 105c. The upstream side is the side on which the molten glass flows into the third supply pipe 105c. The downstream side is the side from which the molten glass flows out from the third supply pipe 105c.

  The third supply pipe 105c is divided into three regions, ie, a first pipe section PP1, a second pipe section PP2, and a third pipe section PP3 from the upstream side toward the downstream side. Pipe sections PP1 to PP3 are sections different from sections SC1 to SC9. The first pipe section PP1 corresponds to a region from the first section SC1 to the fifth section SC5, and its length is about 6000 mm. The second pipe section PP2 corresponds to the region from the sixth section SC6 to the seventh section SC7, and its length is about 2000 mm. The third pipe section PP3 corresponds to the region from the eighth section SC8 to the ninth section SC9, and its length is about 2000 mm. Each pipe segment PP1-PP3 is preferably composed of at least one section. The number of sections constituting each of the pipe sections PP1 to PP3 is arbitrary, but a larger number is preferable. This is because as the number of sections increases, the temperature of the molten glass flowing in the third supply pipe 105c can be controlled more finely. Moreover, the length of each section SC1-SC9 can be set arbitrarily. For example, the lengths of the sections SC1 to SC9 may all be the same or may gradually shorten from the upstream side toward the downstream side. In a region where it is desired to control the temperature of the molten glass flowing in the third supply pipe 105c more finely, it is preferable to shorten the length of the section.

  In each of the sections SC1 to SC9 of the third supply pipe 105c, the two power supply terminals 111 constituting one current heating device 112 cause electricity to flow through the section, and the section is heated by Joule heat. Thereby, the molten glass in the 3rd supply pipe | tube 105c is heated. Each energization heating device 112 can individually control current and voltage. Thereby, the temperature of the molten glass which flows through the inside of each section SC1-SC9 of the 3rd supply pipe | tube 105c is controllable. Therefore, in the supply step S4, the temperature and viscosity of the molten glass flowing in the third supply pipe 105c can be finely controlled.

  Further, as shown in FIG. 3, a measuring device 113 is attached to each section SC1 to SC9 of the third supply pipe 105c. The measuring device 113 measures the temperature and viscosity of the molten glass that passes through the sections SC1 to SC9 of the third supply pipe 105c. The measuring device 113 includes, for example, a thin tube viscometer, a rotary viscometer, a thermometer and the like. The capillary tube viscometer passes a fluid sample to be measured through the capillary tube, and measures the viscosity of the sample from the time (flow rate) for the sample to pass through the capillary tube and the pressure difference between both ends of the capillary tube. A rotary viscometer measures the viscosity of a sample by reading a viscous resistance, which is a resistance received by a fluid sample from the rotating body, from the rotational torque of the rotating body.

  FIG. 4 is a cross-sectional view of the third supply pipe 105c cut along the longitudinal direction of the third supply pipe 105c. The lower arrow in FIG. 4 represents the flow direction of the molten glass. As shown in FIG. 4, the third supply pipe 105c is surrounded by refractories 106a to 106c. The refractories 106a to 106c are attached so as to be in contact with the outer peripheral surface of the third supply pipe 105c. In the third supply pipe 105c, the first refractory 106a is attached to the first pipe section PP1, the second refractory 106b is attached to the second pipe section PP2, and the second refractory 106b is attached to the third pipe section PP3. Three refractories 106c are attached. In FIG. 3, the refractories 106a to 106c are omitted.

  The first refractory 106a and the second refractory 106b are formed from an electroformed refractory. This electroformed refractory is, for example, SCIMOS-M manufactured by Saint-Gobain TM. This electroformed refractory has a thermal conductivity of 3.0 W / m · K at 400 ° C. The third refractory 106c is formed from a high-alumina refractory and heat-resistant brick. This fire and heat resistant brick is, for example, LAP-165 manufactured by Isolite Kogyo Co., Ltd. The thermal conductivity of the refractory and heat-resistant brick is 0.37 W / m · K at 400 ° C. The thickness of the 1st refractory 106a and the 2nd refractory 106b is 25 mm. The thickness of the third refractory 106c is 65 mm. The first refractory 106a and the second refractory 106b are refractories for promoting the heat radiation of the molten glass with a minimum heat resistance, whereas the third refractory 106c is for keeping the molten glass warm. Refractory. In addition, as long as the heat insulation performance of the 3rd refractory 106c is superior to the 1st refractory 106a and the 2nd refractory 106b, the material and dimension of the refractories 106a-106c may be set arbitrarily. In this case, the material and thickness of the second refractory 106b may be different from those of the first refractory 106a. The better the heat insulation performance of the refractories 106a to 106c, the higher the heat retaining power that maintains the temperature of the molten glass flowing in the section to which the refractory is attached.

  The refractories 106a to 106c mainly have an effect of suppressing a decrease in the temperature of the molten glass flowing in the third supply pipe 105c. Since the third supply pipe 105c made of refractory metal has high thermal conductivity, when the refractories 106a to 106c are not attached to the third supply pipe 105c, the heat of the molten glass flowing in the third supply pipe 105c is It is easy to discharge to the space around the third supply pipe 105c through the third supply pipe 105c. If the molten glass flowing through the third supply pipe 105c is easily radiated, it becomes difficult to control the temperature and viscosity of the molten glass. Therefore, the refractories 106a to 106c are necessary for finely controlling the temperature and viscosity of the molten glass flowing in the third supply pipe 105c in the supply step S4.

  Further, as shown in FIG. 4, the inner diameter of the third supply pipe 105c changes from d1 to d3 from the upstream side toward the downstream side. The inner diameter of the third supply pipe 105c is a diameter of a circle that is a cut surface when the space in which the molten glass in the third supply pipe 105c flows is cut in the cross-sectional direction of the third supply pipe 105c. On the upstream side of the first section SC1, the inner diameter of the third supply pipe 105c continuously increases from d1 (130 mm) to d2 (200 mm). In the first section SC1, the upstream portion whose inner diameter is d1 is a portion connected to the tube through which the molten glass supplied from the stirring vessel 103 flows in the stirring step S3. On the downstream side of the first section SC1 and the portion from the second section SC2 to the sixth section SC6, the inner diameter is d2. In the seventh section SC7, the inner diameter decreases continuously from d2 to d3 (145 mm). In the eighth section SC8 and the ninth section SC9, the inner diameter is d3. The inner diameters d1, d2, and d3 of the third supply pipe 105c are set so that the friction loss head at a desired flow rate of the molten glass coincides with the level difference of the liquid level of the molten glass before and after the third supply pipe 105c, or The heat dissipation amount corresponding to the temperature difference of the molten glass before and after the third supply pipe 105c is set.

  The temperature and viscosity of the molten glass flowing through the third supply pipe 105c vary depending on the sections SC1 to SC9. In the same section, the temperature and viscosity of the molten glass differ between the vicinity of the upper surface side and the vicinity of the bottom surface side of the third supply pipe 105c. Here, the upper surface side of the third supply pipe 105c is a portion above the radial center of the third supply pipe 105c, and the bottom surface side of the third supply pipe 105c is lower than the radial center of the third supply pipe 105c. It is a part of.

  Differences in the temperature and viscosity of the molten glass flowing in the third supply pipe 105c cause striae of the molten glass. In supply process S4, the temperature of the molten glass which flows through the 3rd supply pipe | tube 105c falls, and a viscosity rises. For this reason, if there is a portion in the third supply pipe 105c where the flow rate of the molten glass is smaller than the surroundings, the sensible heat of the molten glass brought into the portion from the upstream side is lowered, so the temperature of the molten glass is lowered. As a result, since the viscosity of the molten glass increases, the flow rate of the molten glass further decreases. In order to prevent this vicious cycle, it is important to control the temperature and viscosity of the molten glass flowing in the third supply pipe 105c so as not to generate stagnation with a flow velocity smaller than that of the surroundings. When stagnation of molten glass occurs in the third supply pipe 105c, a foreign molten glass is generated. If the foreign molten glass enters the glass ribbon formed in the forming step S5, it causes defects such as striae formed on the glass plate as the final product. The striae of the glass plate is a kind of distortion in which the thickness of the glass plate varies within a predetermined width. The striae are continuously generated in a streak along the glass ribbon conveyance direction in the forming step S5.

Of the components contained in the molten glass, SiO ₂ is a light component and ZrO ₂ is a heavy component. Therefore, SiO ₂ tends to stay on the upper surface side of the third supply pipe 105c, and ZrO ₂ tends to stay on the bottom surface side of the third supply pipe 105c. As described above, when the components of the molten glass are unevenly dispersed in the third supply pipe 105c, it causes striae.

  Further, when the molten glass flows through the third supply pipe 105c, heat transfer occurs from the molten glass to the third supply pipe 105c, so that the temperature of the molten glass decreases. In this case, in the cross-sectional direction of the third supply pipe 105c, the closer the molten glass is to the inner peripheral surface of the third supply pipe 105c, the easier the heat exchange with the third supply pipe 105c occurs, and thus the temperature tends to decrease. On the other hand, in the cross-sectional direction of the third supply pipe 105c, as the molten glass is farther from the inner peripheral surface of the third supply pipe 105c, heat exchange with the third supply pipe 105c is less likely to occur, and thus the temperature is less likely to decrease. That is, the temperature of the molten glass flowing through a place far from the inner peripheral surface of the third supply pipe 105c is less likely to decrease.

  As a result, the temperature of the molten glass flowing in the third supply pipe 105c is closest to the temperature of the third supply pipe 105c on the inner peripheral surface of the third supply pipe 105c. Further, the difference between the temperature of the molten glass and the temperature of the third supply pipe 105c increases from the inner peripheral surface of the third supply pipe 105c toward the center of the cross section of the third supply pipe 105c. FIG. 5 is a graph showing a temperature change of the molten glass flowing in the third supply pipe 105c in the cross-sectional direction of the third supply pipe 105c. In FIG. 5, the horizontal axis represents the distance from the center of the cross section of the third supply pipe 105c, and the vertical axis represents the temperature of the molten glass. As shown in FIG. 5, the temperature of the molten glass continuously decreases from the center of the cross section of the third supply pipe 105 c toward the inner peripheral surface. Therefore, the temperature of the molten glass is not uniform in the cross-sectional direction of the third supply pipe 105c. The non-uniformity of the temperature of the molten glass in the cross-sectional direction of the third supply pipe 105c causes striae. This is because if molten glass having a non-uniform temperature in the cross-sectional direction of the third supply pipe 105c is supplied to the forming step S5, the formation of a homogeneous glass ribbon is hindered. Therefore, it is preferable that the temperature of the molten glass flowing in the third supply pipe 105c is as uniform as possible in the cross-sectional direction of the third supply pipe 105c. In particular, the temperature of the molten glass is preferably uniform in the third pipe section PP3 on the downstream side of the third supply pipe 105c. Specifically, the temperature difference of the molten glass in the cross-sectional direction of the third supply pipe 105c is preferably 50 ° C. or less at the boundary between the second pipe section PP2 and the third pipe section PP3.

  The method of reducing the temperature difference of the molten glass in the cross-sectional direction of the third supply pipe 105c includes a method of passing a large current through the third supply pipe 105c to increase the amount of generated heat and canceling the heat dissipation, and a method of reducing the refractories 106a to 106c. There is a method of increasing heat resistance to reduce heat dissipation. In the method of flowing a large current, the performance of controlling the flow rate of the molten glass is excellent, but the temperature distribution of the molten glass may become uneven depending on the position of the electrode. On the other hand, the method of increasing the thermal resistance of the refractories 106a to 106c is excellent in temperature uniformity of the molten glass and energy saving. Therefore, in this embodiment, a large current is passed through the second pipe section PP2 to reduce the temperature difference, and at the same time, the flow control performance of the entire third supply pipe 105c is improved, and particularly high-precision temperature control is required. A method of increasing the thermal resistance of the third refractory 106c in the three-pipe section PP3 is employed.

  In the supply step S4, the temperature of the molten glass flowing in the third supply pipe 105c is controlled in order to prevent striae due to the above-described causes. Specifically, the third supply pipe 105c is energized and heated, the molten glass flowing in the third supply pipe 105c is heated, and the third supply pipe 105c is surrounded by the refractories 106a to 106c. 3 Heat dissipation of the molten glass flowing in the supply pipe 105c is suppressed. In the supply step S4, the temperature of the molten glass is controlled so that the temperature of the molten glass flowing through the third supply pipe 105c gradually decreases from the upstream side toward the downstream side. In each section SC1 to SC9 of the third supply pipe 105c, the temperature of the molten glass is individually controlled. The energization heating device 112 of the third supply pipe 105c controls the current and voltage flowing through the sections SC1 to SC9 based on the measurement data of the measurement device 113 so that the temperature of the molten glass shows a change described later. In the third supply pipe 105c, the current flowing through the second pipe section PP2 (sections SC6 to SC7) is higher than the current flowing through the first pipe section PP1 (sections SC1 to SC5). Specifically, the current flowing through the second pipe section PP2 is 2000A, and the current flowing through the first pipe section PP1 is 1000A. Note that the current flowing through the third pipe section PP3 (sections SC8 to SC9) is preferably lower than the current flowing through the second pipe section PP2. Here, the current flowing through the third tube section PP3 is 1000A. The higher the current flowing through the pipe sections PP1 to PP3, the more easily the pipe section is heated. The appropriate current value strongly depends on the inner diameter and thickness of the third supply pipe 105c.

  FIG. 6 is a graph showing a temperature change of the molten glass flowing in the third supply pipe 105c in the longitudinal direction of the third supply pipe 105c. In FIG. 6, the horizontal axis represents the distance from the upstream end of the third supply pipe 105c, and the vertical axis represents the temperature of the molten glass. FIG. 6 shows the ranges of sections SC1 to SC9 and pipe sections PP1 to PP3. In FIG. 6, the solid line L1 represents the temperature of the molten glass in contact with the inner peripheral surface of the third supply pipe 105c, that is, the change of the “tube temperature” that is the temperature of the third supply pipe 105c, and the dotted line L2 represents the first line L2 3 represents a change in “center temperature” which is the temperature of the molten glass at the center of the cross section of the supply pipe 105c. In FIG. 6, a chain line L3 represents the glass average temperature obtained by weighted averaging with the mass flow rate of the molten glass per unit cross-sectional area.

  Next, the temperature change of the molten glass shown in FIG. 6 will be described. Since the molten glass flowing into the third supply pipe 105c is the molten glass homogenized in the stirring step S3, the tube temperature and the center temperature of the molten glass flowing into the first pipe section PP1 (sections SC1 to SC5) The difference is zero. The 1st pipe division PP1 is an area | region for cooling a molten glass to such an extent that it does not fall below the devitrification temperature of glass. In the first tube section PP1, the tube temperature and the center temperature gradually decrease, and the difference between the tube temperature and the center temperature tends to gradually increase due to heat radiation from the third supply tube 105c. The difference between the tube temperature and the center temperature is preferably 100 ° C. or less at the boundary between the first tube section PP1 and the second tube section PP2. In FIG. 6, in the first pipe section PP1, the glass average temperature decreases from 1470 ° C. to 1260 ° C.

  In the second pipe section PP2, a decrease in pipe temperature is suppressed. The current flowing through the second pipe section PP2 is higher than the current flowing through the first pipe section PP1. Therefore, the amount of heat applied to the second pipe section PP2 by energization heating is larger than the amount of heat applied to the first pipe section PP1 by energization heating. Therefore, in the second pipe section PP2, heat radiation from the third supply pipe 105c is suppressed, and the temperature of the third supply pipe 105c is maintained almost constant. At this time, in the second pipe section PP2, heat moves from the molten glass at the center of the cross section of the third supply pipe 105c toward the molten glass in contact with the inner peripheral surface of the third supply pipe 105c. Decrease gradually. As a result, in the second pipe section PP2, the difference between the pipe temperature and the center temperature tends to gradually decrease. The difference between the tube temperature and the center temperature at the boundary between the second tube section PP2 and the third tube section PP3 is preferably 50 ° C. or less. In FIG. 6, in the second pipe section PP2, the glass average temperature decreases from 1260 ° C. to 1250 ° C.

  In the seventh section SC7 of the second pipe section PP2, the inner diameter of the third supply pipe 105c decreases. For this reason, in the second pipe section PP2, the area of the outer peripheral surface of the third supply pipe 105c gradually decreases, so that the heat radiation of the molten glass through the third supply pipe 105c is suppressed. That is, in the second tube section PP2, the difference between the tube temperature and the center temperature is gradually decreased due to two factors, that is, application of high current and decrease in inner diameter.

  In the third pipe section PP3, the temperature of the molten glass becomes substantially uniform. The heat insulation performance of the third refractory 106c surrounding the third pipe section PP3 is superior to the first refractory 106a and the second refractory 106b. Therefore, in the 3rd pipe division PP3, compared with 1st pipe division PP1 and 2nd pipe division PP2, the thermal radiation of the molten glass via the 3rd supply pipe | tube 105c is suppressed more. The current flowing through the third pipe section PP3 is lower than the current flowing through the second pipe section PP2, and the amount of heat applied to the third pipe section PP3 by energization heating is applied to the second pipe section PP2 by energization heating. Less than the amount of heat Therefore, the temperature rise of the molten glass flowing in the third pipe section PP3 is suppressed. As a result, in the third tube section PP3, the difference between the tube temperature and the center temperature is further reduced by heat transfer in the molten glass in a state where the glass average temperature is substantially constant. In FIG. 6, the glass average temperature is maintained at 1250 ° C. in the third pipe section PP3.

  Next, a preferable range of the temperature of the molten glass passing through the third supply pipe 105c will be described. At the upstream end of the third supply pipe 105c, the pipe temperature and the center temperature are preferably 1420 ° C. to 1470 ° C. At the boundary between the first tube section PP1 and the second tube section PP2, the tube temperature is preferably 1210 ° C to 1260 ° C, and the center temperature is preferably 1300 ° C to 1350 ° C. At the boundary between the second tube section PP2 and the third tube section PP3, the tube temperature is preferably 1210 ° C to 1260 ° C, and the center temperature is preferably 1250 ° C to 1300 ° C. At the downstream end of the third supply pipe 105c, the pipe temperature and the center temperature are preferably 1240 ° C to 1280 ° C.

(3) Features The glass plate manufacturing method of the embodiment is cooled while passing through the third supply pipe 105c by supplying and heating the third supply pipe 105c surrounded by the refractories 106a to 106c in the supply step S4. The temperature of the molten glass to be produced can be finely controlled. The third supply pipe 105c is divided into three pipe sections PP1 to PP3. In the first pipe section PP1, the molten glass is cooled to a temperature close to a temperature suitable for the forming step S5. The second pipe section PP2 is a portion where a higher current flows than the first pipe section PP1 on the upstream side, and a decrease in the temperature of the molten glass flowing in the vicinity of the inner wall surface of the third supply pipe 105c is suppressed. As a result, in the second pipe section PP2, the temperature difference of the molten glass in the cross-sectional direction of the third supply pipe 105c is reduced. The third pipe section PP3 is surrounded by a third refractory 106c having higher heat insulation performance than the first refractory 106a and the second refractory 106b. The third pipe section PP3 is a portion where the heat retention of the molten glass is higher than that of the first pipe section PP1 and the second pipe section PP2, and is reduced in the second pipe section PP2 while maintaining the temperature of the molten glass. The temperature difference of the molten glass is further reduced. Thereby, at the downstream end of the third supply pipe 105c, the temperature of the molten glass becomes substantially uniform in the cross-sectional direction of the third supply pipe 105c. As a result, the molten glass having a uniform temperature is supplied to the forming step S5, so that occurrence of striae of the molten glass is suppressed. Therefore, this glass plate manufacturing method can suppress the occurrence of striae in the molten glass and can manufacture a glass plate having a uniform plate thickness.

  In the glass plate manufacturing method, the second pipe section PP2 has a portion where the inner diameter of the third supply pipe 105c gradually decreases. For this reason, in the second pipe section PP2, the area of the outer peripheral surface of the third supply pipe 105c gradually decreases, so that the heat radiation of the molten glass through the third supply pipe 105c is suppressed. Thereby, in the 2nd pipe division PP2, the fall of the temperature of the molten glass which flows in the vicinity of the inner wall face of the 3rd supply pipe | tube 105c is suppressed. Therefore, in the second pipe section PP2, the temperature difference of the molten glass in the cross-sectional direction of the third supply pipe 105c is reduced.

  Moreover, in this glass plate manufacturing method, the current flowing through the third tube section PP3 is smaller than the current flowing through the second tube section PP2. Therefore, in the third pipe section PP3, the temperature of the third supply pipe 105c is less likely to rise compared to the second pipe section PP2. Thereby, in the 3rd pipe division PP3, the temperature of molten glass is maintained substantially constant by the 3rd refractory 106c which has high heat insulation performance. Therefore, in the third pipe section PP3, the temperature difference of the molten glass in the cross-sectional direction of the third supply pipe 105c is reduced.

(4) Modified Examples The glass plate manufacturing method and the glass plate manufacturing apparatus 100 according to the embodiment have been described above. However, the present invention is not limited to the above-described embodiment, and various types of the glass plate can be used without departing from the spirit of the present invention. Changes may be made. For example, the modifications described below may be applied to the present invention.

(4-1) Modification A
In the glass plate manufacturing method of the embodiment, the second pipe section PP2 has a portion where the inner diameter of the third supply pipe 105c gradually decreases. However, the second pipe section PP2 may not have a portion where the inner diameter of the third supply pipe 105c gradually decreases. In that case, in order to suppress the heat radiation of the molten glass in the second tube section PP2, the current flowing through the second tube section PP2 may be higher than 2000A of the embodiment, and the second refractory surrounding the second tube section PP2 A refractory having higher heat insulation performance than the second refractory 106b of the embodiment may be used as 106b. For example, the third refractory 106c of the embodiment may be used as such a refractory.

(4-2) Modification BA
In the glass plate manufacturing method of the embodiment, the current flowing through the third tube section PP3 is smaller than the current flowing through the second tube section PP2. However, the current flowing through the third pipe section PP3 may not be smaller than the current flowing through the second pipe section PP2 depending on the inner diameter of the third supply pipe 105c and the target value of the temperature of the molten glass. For example, the current flowing through the third tube section PP3 may be the same as the current flowing through the second tube section PP2. In this case, you may use the refractory which has the heat insulation performance higher than the 3rd refractory 106c of embodiment as a refractory surrounding 3rd pipe division PP3.

(4-3) Modification C
In the glass plate manufacturing method of the embodiment, the third supply pipe 105c is formed of platinum or a platinum alloy, but may be formed of other platinum group metals. The “platinum group metal” is a metal composed of a single platinum group element and a metal alloy composed of a platinum group element. The platinum group elements are six elements of platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), osmium (Os) and iridium (Ir). Platinum group metals are expensive, but have a high melting point and excellent corrosion resistance against molten glass. Therefore, the platinum group metal is suitable as a material for the third supply pipe 105c.

(4-4) Modification D
In the manufacturing method of the glass plate of embodiment, the glass raw material prepared for manufacture of the alkali free glass suitable for a glass plate for flat panel displays or alkali trace content glass is used.

  However, in recent years, in order to realize further high definition of flat panel displays, displays using p-Si (low temperature polysilicon) TFTs or oxide semiconductors instead of conventional a-Si (amorphous silicon) TFTs. Is required. In the step of forming the p-Si • TFT and the oxide semiconductor, there is a heat treatment step at a higher temperature than the step of forming the a-Si • TFT. For this reason, the glass plate on which the p-Si • TFT and the oxide semiconductor are formed is required to have a low thermal shrinkage characteristic. In order to reduce the thermal contraction rate of the glass plate, it is preferable to increase the strain point of the glass. However, glass with a high strain point tends to have a high liquidus temperature and a low liquidus viscosity. That is, the liquid phase viscosity of the glass having a high strain point approaches the appropriate viscosity of the molten glass in the molding step S5. Therefore, in order to suppress the devitrification of the glass, it is more strongly required to make the temperature of the molten glass in the cross-sectional direction as uniform as possible in the third supply pipe 105c that supplies the molten glass to the forming apparatus 104.

  The glass plate manufacturing method of the embodiment can be applied to a glass plate manufacturing method using glass having a strain point of 665 ° C. or higher, for example, because molten glass having a uniform temperature can be supplied to the forming apparatus 104. In particular, the method for manufacturing a glass plate according to the embodiment is applied to a method for manufacturing a glass plate using glass having a strain point of 655 ° C. or higher, 680 ° C. or higher, or 690 ° C. or higher, which is suitable for p-Si · TFT and oxide semiconductor can do. Moreover, the manufacturing method of the glass plate of embodiment is applicable also to the manufacturing method of the glass plate which uses glass whose liquid phase viscosity is 6000 Pa.s or less, 5000 Pa.s or less, or 4500 Pa.s or less.

The composition of the glass having a strain point of 665 ° C. or more or a liquid phase viscosity of 4500 Pa · s or less is, for example, SiO ₂ : 52 mass% to 78 mass%, Al ₂ O ₃ : 3 mass% to 25 mass%, B ₂ O ₃ : 3% by mass to 15% by mass, RO (R is at least one of Mg, Ca, Sr and Ba): 3% by mass to 20% by mass. The mass ratio (SiO ₂ + Al ₂ O ₃ ) / B ₂ O ₃ is preferably 7-20. In order to further increase the strain point, the mass ratio (SiO ₂ + Al ₂ O ₃ ) / RO is preferably 7.5 or more. To further increase the strain point, beta-OH value is preferably from 0.1mm ^-1 ~0.3mm ^-1. Moreover, in order to suppress the fall of a liquid phase viscosity, implement | achieving a high strain point, it is preferable that mass ratio CaO / RO is 0.65.

Moreover, in order to adjust various properties of the glass, the composition of the glass may contain other oxides in addition to the components described above. Examples of the oxide include SnO ₂ , TiO ₂ , MnO, ZnO, Nb ₂ O ₅ , MoO ₃ , Ta ₂ O ₅ , WO ₃ , Y ₂ O _3, and La ₂ O ₃ . Liquid crystal displays and organic EL displays have particularly strict requirements for bubble defects in glass plates. In that case, the composition of the glass preferably contains at least SnO ₂ having a particularly high refining effect among the oxides.

  Moreover, nitrate and carbonate may be used as the RO. In order to improve the oxidizability of the molten glass, it is preferable to use an oxide containing an appropriate proportion of nitrate as RO.

100 Glass plate manufacturing apparatus 104 Molding apparatus 105c Third supply pipe (supply pipe)
106a First refractory (heat insulating material)
106b Second refractory (thermal insulation)
106c 3rd refractory (heat insulation)
PP1 1st pipe section PP2 2nd pipe section PP3 3rd pipe section

JP 2004-67408 A

Claims (6)

Supplying a molten glass through a supply pipe and supplying the molten glass to a molding apparatus;
A forming step of forming a glass plate from the molten glass supplied to the forming apparatus in the supplying step;
With
In the supplying step, the temperature of the molten glass is increased in the flow direction of the molten glass while energizing and heating the supply tube surrounded by a heat insulating material for keeping the molten glass flowing through the supply tube. The molten glass is poured into the supply pipe so as to be lowered,
When the supply pipe is divided into a first pipe section, a second pipe section, and a third pipe section from the upstream side to the downstream side in the flow direction, the current flowing through the second pipe section is the first pipe section. Higher than the current flowing through the section, and the thermal insulation surrounding the third pipe section has a lower thermal conductivity than the thermal insulation surrounding the first pipe section,
Manufacturing method of glass plate. In the second pipe section, the supplying step is such that the difference between the temperature of the supply pipe and the temperature of the molten glass flowing through the center of the cross section of the supply pipe is reduced along the flow direction. Shed
The manufacturing method of the glass plate of Claim 1. In the second pipe section, an inner diameter of the supply pipe decreases along the flow direction.
The manufacturing method of the glass plate of Claim 1 or 2. The current flowing through the third tube section is lower than the current flowing through the second tube section;
The manufacturing method of the glass plate of any one of Claim 1 to 3. The difference between the temperature of the supply pipe and the temperature of the molten glass flowing through the center of the cross section of the supply pipe at the boundary between the second pipe section and the third pipe section is 50 ° C. or less.
The manufacturing method of the glass plate of any one of Claim 1 to 4. A molding device for molding a glass plate from molten glass;
A supply pipe for supplying the molten glass to the molding apparatus;
With
The supply pipe is surrounded by a heat insulating material for keeping the molten glass flowing through the supply pipe, and the temperature of the molten glass is lowered in the flow direction of the molten glass while being electrically heated. Flowing the molten glass into the supply pipe,
When the supply pipe is divided into a first pipe section, a second pipe section, and a third pipe section from the upstream side to the downstream side in the flow direction, the current flowing through the second pipe section is the first pipe section. Higher than the current flowing through the section, and the thermal insulation surrounding the third pipe section has a lower thermal conductivity than the thermal insulation surrounding the first pipe section,
Glass plate manufacturing equipment.

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