WO2012132454A1 - ガラス板の製造方法及びガラス板製造装置 - Google Patents
ガラス板の製造方法及びガラス板製造装置 Download PDFInfo
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- WO2012132454A1 WO2012132454A1 PCT/JP2012/002189 JP2012002189W WO2012132454A1 WO 2012132454 A1 WO2012132454 A1 WO 2012132454A1 JP 2012002189 W JP2012002189 W JP 2012002189W WO 2012132454 A1 WO2012132454 A1 WO 2012132454A1
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- glass
- glass ribbon
- temperature
- width direction
- ribbon
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B17/00—Forming molten glass by flowing-out, pushing-out, extruding or drawing downwardly or laterally from forming slits or by overflowing over lips
- C03B17/06—Forming glass sheets
- C03B17/064—Forming glass sheets by the overflow downdraw fusion process; Isopipes therefor
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B18/00—Shaping glass in contact with the surface of a liquid
- C03B18/02—Forming sheets
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B17/00—Forming molten glass by flowing-out, pushing-out, extruding or drawing downwardly or laterally from forming slits or by overflowing over lips
- C03B17/06—Forming glass sheets
- C03B17/067—Forming glass sheets combined with thermal conditioning of the sheets
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B18/00—Shaping glass in contact with the surface of a liquid
- C03B18/02—Forming sheets
- C03B18/04—Changing or regulating the dimensions of the molten glass ribbon
- C03B18/06—Changing or regulating the dimensions of the molten glass ribbon using mechanical means, e.g. restrictor bars, edge rollers
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B18/00—Shaping glass in contact with the surface of a liquid
- C03B18/02—Forming sheets
- C03B18/18—Controlling or regulating the temperature of the float bath; Composition or purification of the float bath
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B25/00—Annealing glass products
- C03B25/04—Annealing glass products in a continuous way
- C03B25/10—Annealing glass products in a continuous way with vertical displacement of the glass products
- C03B25/12—Annealing glass products in a continuous way with vertical displacement of the glass products of glass sheets
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B35/00—Transporting of glass products during their manufacture, e.g. hot glass lenses, prisms
- C03B35/14—Transporting hot glass sheets or ribbons, e.g. by heat-resistant conveyor belts or bands
- C03B35/16—Transporting hot glass sheets or ribbons, e.g. by heat-resistant conveyor belts or bands by roller conveyors
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P40/00—Technologies relating to the processing of minerals
- Y02P40/50—Glass production, e.g. reusing waste heat during processing or shaping
- Y02P40/57—Improving the yield, e-g- reduction of reject rates
Definitions
- the present invention relates to a glass plate manufacturing method and a glass plate manufacturing apparatus.
- the glass plate manufacturing method using the downdraw method first, in the forming step, molten glass overflows from the formed body to form a glass ribbon.
- the glass ribbon is drawn downward while being held between the pair of conveying rollers, so that the glass ribbon is stretched to a desired thickness and the glass ribbon is not warped.
- the glass ribbon is cooled so that it does not occur.
- the glass ribbon is cut into a predetermined size and stacked on each other with an interleaf or the like interposed therebetween, or further conveyed and processed in the next process (for example, shape processing, chemical strengthening treatment by ion exchange). .
- the peripheral speed of a cooling roller pair provided immediately below a formed body is pulled downward from a glass ribbon provided below the conveying roller pair. It is known that the warp of the glass plate is reduced by making it smaller than the peripheral speed of the pair of conveying rollers for this purpose (Patent Document 1). Further, in the plurality of transport roller pairs arranged below the molded body, the peripheral speed of the transport roller pair disposed below is made faster than the peripheral speed of the transport roller pair disposed above, thereby allowing the glass plate to It is known to reduce the warpage (Patent Document 2).
- both end portions in the width direction of the glass ribbon in the slow cooling step are called “ears” or “ears”, and are cut from the glass ribbon and removed without being used as a glass substrate product.
- the ear is 2 to 5 times thicker than a region (hereinafter also referred to as a center region in the width direction) that can be used as a product (glass substrate).
- the thickness of the ear portion does not change so much even if the thickness of the product changes, the difference between the thickness of the central region in the width direction used as the product is thin. It gets bigger.
- the plurality of conveyance roller pairs conveys the glass ribbon while sandwiching a portion on the inner side in the width direction from the ear portion.
- the tension is applied in the width direction of the glass ribbon by cooling the ear portion immediately below the center region in the width direction of the glass ribbon immediately below the molded body.
- the shaft of the transport roller is maintained at a temperature lower than that of the glass ribbon in order to prevent deformation at a high temperature, and the transport roller itself is also cooler than the temperature of the glass in contact.
- region pinched by the conveyance roller pair is cooled earlier than the surrounding area.
- an adjacent region region indicated by symbol S in FIG. 7 that is inward in the width direction and closer to the conveyance roller than the region sandwiched between the ears and the conveyance roller pair is also faster. To be cooled.
- FIG. 7 shows the conventional glass plate manufacturing apparatus, and the other reference numerals in the figure are the same as the reference numerals of the elements described in the embodiments described later.
- the peripheral speed of the transport roller provided below is made faster than the transport roller provided above, and the peripheral speed of the transport roller is sequentially increased from the upstream side to the downstream side in the transport direction. This is based on the idea of always applying tension to the glass ribbon in the transport direction by increasing the speed.
- the peripheral speed of the downstream transport roller is simply increased with respect to the upstream, not only will the effect be produced, but for example, when a thin glass plate having a plate thickness of 0.5 mm or less is manufactured. For example, if a difference in peripheral speed as described in the embodiment [0045] is applied, the glass ribbon may be broken, which is very dangerous.
- the present invention provides a glass that suppresses the occurrence of wave-like deformation in an adjacent region adjacent to a portion sandwiched by a plurality of conveyance rollers of a glass ribbon during cooling in a slow cooling furnace when manufacturing a glass plate. It aims at providing the manufacturing method of a board, and a glass plate manufacturing apparatus.
- One embodiment of the present invention is a method for manufacturing a glass plate.
- the manufacturing method is Melting process for melting glass raw material to make molten glass; Molding a molten glass using an overflow downdraw method to form a glass ribbon; The glass ribbon is pulled down while sandwiching a neighboring region adjacent in the width direction with respect to both ends of the glass ribbon in the width direction with a plurality of transport roller pairs provided in the transport direction of the glass ribbon. And a slow cooling step of performing slow cooling.
- the forming step after forming the glass ribbon by laminating molten glass that overflows from the formed body and flows down the side wall of the formed body at the lower end of the formed body, the both ends in the width direction of the glass ribbon are formed.
- the portion is cooled faster than the central portion in the width direction of the glass ribbon.
- the glass ribbon is tensioned in the transport direction in the temperature region where the temperature of the glass ribbon is not less than the glass transition point and not more than the glass softening point so that plastic deformation does not occur in the glass ribbon.
- the peripheral speed of the transport roller of the transport roller pair provided on the downstream side of the position where the temperature of the glass ribbon becomes the glass slow cooling point in the transport roller pair is set as the transport speed. It is preferable that the temperature of the glass ribbon of the pair of rollers is higher than the peripheral speed of the pair of transport rollers provided in a temperature region where the glass transition point is equal to or higher than the glass softening point.
- the glass plate can have a thickness of 0.5 mm or less, for example.
- the temperature of the adjacent region is a glass transition point so that plastic deformation does not occur in the adjacent region adjacent to the inner side in the width direction of the glass ribbon with respect to the portion held by the transport roller. It is preferable that the tension in the transport direction is applied to the glass ribbon in the temperature range that is not higher than the glass softening point.
- the temperature of the adjacent region adjacent to the inner side in the width direction of the glass ribbon with respect to the portion of the transport roller pair sandwiched by the transport roller of the glass ribbon is a glass slow cooling point.
- the peripheral speed of the transport roller pair of the transport roller pair provided on the downstream side of the position is provided in a temperature region in the transport roller pair in which the temperature of the adjacent region is not less than the glass transition point and not more than the glass softening point. It is preferable to make it faster than the peripheral speed of the conveyance rollers of the conveyance roller pair.
- the manufacturing method of a glass plate includes the process in which the cooling rate of the said both ends is faster than the cooling rate of the center part of the width direction of the said glass ribbon.
- At least the temperature of the central portion in the width direction of the glass ribbon is equal to the glass annealing point plus 150 ° C. so that tension acts in the transport direction of the glass ribbon in the central portion in the width direction of the glass ribbon.
- the strain point is 200 ° C.
- the temperature of the glass ribbon is controlled so that the temperature becomes uniform.
- the temperature of the glass ribbon is controlled so that the temperature distribution becomes lower from the central portion toward the both end portions.
- the temperature of the glass ribbon is controlled so that there is no temperature gradient between the both end portions in the width direction of the glass ribbon and the central portion in a temperature region where the temperature of the central portion of the glass ribbon becomes a glass strain point.
- the temperature of the central portion of the glass ribbon in the width direction, in the region where the temperature of the central portion of the glass ribbon is less than the vicinity of the glass strain point so that the tension in the glass ribbon transport direction works, from the both end portions of the glass ribbon It is preferable to control the temperature of the glass ribbon so as to decrease toward the center.
- the peripheral speed of the transport roller of the transport roller pair provided downstream of the position where the temperature of the glass ribbon becomes the glass slow cooling point in the transport roller pair it is preferable that the temperature of the glass ribbon is 0.03 to 2% faster than the peripheral speed of the transport roller of the transport roller pair provided in the temperature region where the glass transition point is not lower than the glass softening point.
- the length of the glass plate in the width direction is, for example, 1000 mm or more.
- the glass ribbon is drawn downward at a transport speed of 200 m / hour or more to cool slowly.
- the manufacturing method of the glass plate of the other aspect of this invention is as follows. Melting process for melting glass raw material to make molten glass; Molding a molten glass using a downdraw method to form a glass ribbon; The glass ribbon is pulled down and gradually cooled while sandwiching a region adjacent in the width direction at both ends in the width direction of the glass ribbon with a plurality of pairs of transport rollers provided in the transport direction of the glass ribbon. And a slow cooling step of forming a glass ribbon having a thickness of 0.5 mm or less.
- the circumferential speed of the conveyance roller of the conveyance roller pair provided in the temperature region which is as follows is made faster.
- mode of this invention is a glass plate manufacturing apparatus.
- the device is A molding apparatus for molding a glass ribbon from molten glass using a downdraw method; The glass ribbon having a thickness of 0.5 mm is drawn by slowly pulling the glass ribbon downward while sandwiching a neighboring region adjacent to the width direction at both ends in the width direction of the glass ribbon with a plurality of conveying roller pairs.
- a slow cooling device for forming, The slow cooling device includes the plurality of conveyance roller pairs and a drive unit, One of the plurality of transport roller pairs is in a first temperature region where the temperature of the glass ribbon is not less than the glass transition point and not more than the softening point, and the other one of the plurality of transport roller pairs is the temperature of the glass ribbon.
- the drive unit is configured such that the transport roller of the pair of transport rollers provided in the second temperature region is determined such that the peripheral speed of the transport roller provided in the first temperature region is higher than the peripheral speed of the transport roller provided in the first temperature region.
- the conveyance roller is driven to rotate based on the peripheral speed.
- the glass plate manufacturing method and glass plate manufacturing apparatus described above can effectively apply tension to the glass ribbon transported in the slow cooling furnace in the transport direction, and is sandwiched between the pair of glass ribbon transport rollers. It can suppress that a waveform deformation
- FIG. 3 is a cross-sectional view taken along line III in FIG. 2. It is a block diagram explaining the structure of the control system which controls the rotational drive of the conveyance roller pair of 1st Embodiment of this invention. It is a block diagram explaining the structure of the control system which controls the rotational drive of the conveyance roller pair of 2nd Embodiment of this invention. It is a block diagram explaining the structure of the control system which controls the rotational drive of the conveyance roller pair of 3rd Embodiment of this invention. It is a top view explaining the inside of the conventional glass plate manufacturing apparatus.
- the center part of a glass ribbon means the center of the width direction of a glass ribbon among the widths of the width direction of a glass ribbon.
- the central region of the glass ribbon refers to a range within 85% of the width from the center in the width direction of the glass ribbon in the width in the width direction of the glass ribbon.
- the both ends of the glass ribbon refer to a range within 200 mm from the edge in the width direction of the glass ribbon.
- the adjacent region in the width direction with respect to both ends of the glass ribbon in the width direction is the width within 20% of the width of the glass ribbon from the inner edge in the width direction of the both ends. An area included up to a certain range.
- the adjacent area adjacent to the inner side in the width direction of the glass ribbon with respect to the portion sandwiched by the transport roller is within 6% of the width of the glass ribbon from the inner edge in the width direction of the portion sandwiched by the transport roller This is the area included in the range that is inside the width direction by the length of.
- the temperature of the glass ribbon is a value converted from the ambient temperature around the glass ribbon when the glass ribbon has a temperature distribution.
- the temperature of the glass ribbon ranges from ⁇ 25 to ⁇ 5 ° C. The temperature obtained by adding a specified temperature.
- FIG. 1 is a figure explaining an example of the flow of the manufacturing method of the glass plate of this embodiment.
- the glass plate manufacturing method includes a melting step (step S10), a clarification step (step S20), a stirring step (step S30), a forming step (step S40), a slow cooling step (step S50), It mainly includes a process (step S60) and a shape processing process (step S70).
- step S10 in a melting furnace (not shown), the glass raw material is heated to a high temperature by indirect heating from above and direct heating by passing an electric current through the glass to produce molten glass.
- the melting of the glass may be performed by other methods.
- a clarification process is performed (step S20).
- the defoaming of bubbles in the molten glass is promoted by increasing the temperature of the molten glass in a state where the molten glass is stored in a liquid tank (not shown), for example, compared with the heating in the melting step. . Thereby, the bubble content rate in the glass plate finally obtained can be reduced, and a yield can be improved.
- the clarification step may be performed by other methods.
- the bubbles in the molten glass may be removed using a clarifier.
- the fining agent is not particularly limited, and for example, metal oxides such as tin oxide and iron oxide are used.
- the clarification step in this case is performed by a redox reaction of a metal oxide whose valence fluctuates in the molten glass.
- the metal oxide releases oxygen by a reduction reaction, and this oxygen becomes a gas, and bubbles in the molten glass grow and float on the liquid surface. Thereby, bubbles in the molten glass are defoamed.
- a molding process is performed (step S40).
- a downdraw method is used.
- the down-draw method including overflow down-draw and slot down-draw is a known method using, for example, Japanese Patent No. 3586142 and the apparatus shown in FIGS.
- the molding process of the overflow down draw method is a process of overflowing the molten glass from the molded body to flow down the side wall of the molded body, and further forming the glass ribbon by laminating the molten glass at the lower end of the molded body. It is.
- the molding process in the downdraw method will be described later. Thereby, a sheet-like glass ribbon having a predetermined thickness and width is formed.
- the temperature control of the glass ribbon for example, a cooling means such as a cooling roller, a cooling means such as an air cooling tube provided in the vicinity of both ends of the glass ribbon in the width direction, and a plurality of glass ribbons in the width direction and the transport direction are provided
- a cooling means such as a cooling roller
- a cooling means such as an air cooling tube provided in the vicinity of both ends of the glass ribbon in the width direction, and a plurality of glass ribbons in the width direction and the transport direction are provided
- heating means such as a heater.
- a slow cooling process is performed (step S50).
- the glass ribbon formed into a sheet shape is cooled below the annealing point in the slow cooling furnace shown in FIGS. 2 and 3 by controlling the cooling rate so that distortion is not generated or reduced.
- the adjacent regions adjacent to each other in the width direction at both ends in the width direction of the glass ribbon are sandwiched by a plurality of pairs of transport rollers provided in the transport direction of the glass ribbon. It is gradually cooled while being drawn downward at the peripheral speed of the roller.
- a glass ribbon having a thickness of 0.5 mm or less is formed by slowly cooling the glass ribbon while transporting it at such a transport speed.
- the strain generated in the glass ribbon is reduced by controlling so that the temperature gradient between the both ends in the width direction of the glass ribbon and the central portion in the width direction is eliminated.
- the temperature profile of the glass ribbon is distributed in a single mountain in the width direction, and then the distribution of the single mountain gradually decreases as it progresses downstream in the conveyance direction.
- a heater or the like can be controlled so that the distribution of the peaks is a straight linear distribution, that is, the temperature distribution in the width direction is constant. .
- the cooling rate at the center in the width direction of the glass ribbon is higher than the cooling rate at both ends in the glass ribbon width direction.
- the temperature profile may be made constant so that the temperature in the central portion in the width direction of the glass ribbon is the same in the temperature region near the strain point from the state where the temperature is higher than both ends.
- the glass ribbon may be slowly cooled at a temperature at which the temperature of the glass ribbon is from the annealing point (strain point ⁇ 50 ° C.) as compared with other temperature ranges. Thereby, the thermal contraction rate of a glass ribbon can be reduced.
- the temperature profile of the glass ribbon becomes a valley along the width direction, and the depth of the valley is downstream in the transport direction.
- Control of a heater or the like may be performed so that the temperature of the center portion gradually increases, that is, the temperature of the central portion gradually becomes lower than that of both end portions.
- the peripheral speed of the conveying roller is high from the viewpoint of improving the productivity of the glass plate.
- the peripheral speed of the conveying roller is preferably higher than 150 m / hour, preferably 200 m / hour or more, for example, 220 m / hour or more, 240 m / hour or more, 250 m / hour or more, 270 m / hour. It may be at least 300 m / hour or more and 340 m / hour or more.
- fever retained inside the part pinched by a conveyance roller pair becomes so small that the plate
- 0.01 to 0.5 mm is more suitable for the present invention, for example, 0.01 to 0.4 mm is more suitable for the present invention, and 0.01 to 0.3 mm is further suitable. It is suitable for the present invention, and when it is from 0.01 to 0.25 mm, it is further suitable for the present invention.
- the peripheral speed of the transport roller is not limited to the above, and for example, when the amount of molten glass flowing into a molded body described later on is less than 6 t, Even in the case where the amount flowing into the molded body per day is 6 t or more, it may be 200 m / hr or less depending on the size in the width direction of the glass to be produced.
- the amount of molten glass that flows into the molded body per day may be 2 t or more, 6 t or more, 10 t or more, 16 t or more, or 20 t or more.
- the quantity (MG amount) in which a molten glass is poured into a molded object on the 1st is large from a viewpoint of improving the productivity of a glass plate.
- the peripheral speed of the transport roller of the pair of transport rollers provided downstream from the position where the temperature of the glass ribbon becomes the slow cooling point is the temperature at which the temperature of the glass ribbon is not lower than the glass transition point and not higher than the softening point. It is faster than the peripheral speed of the transport rollers of the transport roller pair provided in the region, for example, 0.03 to 2% faster.
- a plate-making process is performed (step S60). Specifically, the glass ribbon produced
- a physical means using a cutter or a laser may be used, or a chemical means such as etching may be used.
- the method for producing a glass plate includes a cleaning step and an inspection step, but description of these steps is omitted.
- the clarification step and the stirring step can be omitted.
- FIG.2 and FIG.3 is a schematic block diagram of the glass plate manufacturing apparatus 1 which is 1st Embodiment of this invention.
- the glass plate manufacturing apparatus 1 and the glass plate manufacturing method using the glass plate manufacturing apparatus 1 according to this embodiment include a glass substrate of a flat panel display such as a liquid crystal display device or an organic EL display device, and a display surface cover of a portable terminal. It is suitably applied to the production of glass. This is because liquid crystal display devices or organic EL display devices have recently been required to have high accuracy and high image quality, and the glass substrate used for them is required to have a wave form deformation of 0.2 mm or less. Because.
- the glass plate manufacturing apparatus 1 manufactures the glass plate C from the molten glass A using the downdraw method.
- the glass plate manufacturing apparatus 1 includes a furnace chamber 11, a first slow cooling furnace 12, a second slow cooling furnace 13, and a sampling chamber (not shown) that are partitioned by heat insulating plates 21, 22, and 23 arranged in three locations in the vertical direction.
- the heat insulating plates 21 to 23 are plate members made of a heat insulating material such as ceramic fiber.
- the heat insulating plates 21 to 23 are respectively formed with transport holes 16 so that a glass ribbon B, which will be described later, passes downward.
- the heat insulating plates 21 to 23 are not shown in FIG. 2 except for two places in the horizontal direction in contact with the furnace wall 15 to be described later for ease of understanding. On the back side, the two horizontal portions are connected together. 2 and 3 show an example in which partitioning is performed at three locations by a heat insulating plate, but the number and installation positions of the heat insulating plates are not particularly limited, and one or more heat insulating plates may be provided. That's fine.
- the slow cooling device 3 described later includes a plurality of heat insulating plates, It is preferable to partition into a plurality of spaces. In other words, it is sufficient that one or more annealing furnaces are provided, but three or more are more preferably provided.
- the glass plate manufacturing apparatus 1 includes a forming device 2, a slow cooling device 3, and a plate-taking device 4.
- the forming apparatus 2 is an apparatus for forming the glass ribbon B from the molten glass A using a downdraw method.
- the forming apparatus 2 has a furnace chamber 11 surrounded by a furnace wall 15 assembled with refractory bricks, block-shaped electroformed column refractories, or the like.
- a molded body 10 and a roller pair 17 are provided in the furnace chamber 11.
- the molded body 10 includes a groove 10a opened upward (see FIG. 3), and the molten glass A flows in the groove 10a.
- the molded body 10 is made of brick, for example.
- a pair of rollers 17 are provided at positions corresponding to both ends (both ends in the width direction) in the width direction of the molten glass A fused at the lower end of the molded body 10. Transport toward.
- the left-right direction in the paper surface in FIG. 2 and the direction perpendicular to the paper surface in FIG. 2 and 3 is the transport direction of the glass ribbon B. 2 and 3
- the molded body 10 and the roller pair 17 are installed without partitioning, but in order to facilitate the adjustment of the slow cooling condition (atmosphere temperature adjustment), a heat insulating plate is provided between them. May be provided for partitioning.
- Two or more pairs of rollers 17 may be installed in the transport direction.
- the slow cooling device 3 cools the glass ribbon B while pulling it downward while holding the glass ribbon B between the plurality of conveying roller pairs 18 and 19.
- the slow cooling device 3 has a first slow cooling furnace 12 and a second slow cooling furnace 13 provided adjacent to the lower part of the furnace chamber 11.
- the first slow cooling furnace 12 and the second slow cooling furnace 13 are surrounded by the furnace wall 15 that also constitutes the furnace chamber 11.
- the slow cooling device 3 is provided with heating means that are arranged in the first slow cooling furnace 12 and the second slow cooling furnace 13 along the conveying direction of the glass ribbon B and are automatically controlled by a computer to be described later.
- the heating means is not particularly limited, and for example, an electric heater is used.
- the ambient temperature around the glass ribbon B in the first slow cooling furnace 12 and the second slow cooling furnace 13 is the width of the glass ribbon B so that the glass ribbon B is not warped or distorted by being heated by the heating means.
- the temperature is controlled so that the temperature distribution in the direction and the conveyance direction has a distribution as described later.
- the glass ribbon B becomes the softening point SP sequentially from the conveyance direction upstream side of the glass ribbon B by heating with a heating means, respectively, glass transition A point that becomes the point Tg, a point that becomes the slow cooling point AP, and a point that becomes the strain point StP are generated.
- the softening point SP indicates a temperature at which the glass has a viscosity of 10 7.6 dPa ⁇ s. Further, the annealing point AP, the viscosity of the glass indicates the temperature of 10 13 dPa ⁇ s.
- the strain point StP indicates a temperature at which the viscosity of the glass is 10 14.5 dPa ⁇ s. 2 and 3, the position of the glass ribbon B at which the temperature of the glass ribbon B becomes the temperature of these points SP, Tg, AP, and StP is determined by extending the broken lead lines in the horizontal direction. It is represented by the point where it intersects with ribbon B.
- the conveyance roller pairs 18 and 19 are provided with three conveyance roller pairs 18 arranged in the conveyance direction of the glass ribbon B in the first slow cooling furnace 12. In the second slow cooling furnace 13, four transport roller pairs 19 arranged in the transport direction of the glass ribbon B are provided.
- the two most upstream conveying roller pairs 18 are disposed in the temperature region D (first temperature region) of the glass ribbon B that is not less than the glass transition point Tg and not more than the softening point SP.
- the third and fourth transport roller pairs 18 from the upstream side are arranged in the temperature region of the glass ribbon B that is higher than the slow cooling point AP and lower than the glass transition point Tg.
- the fifth to seventh transport roller pairs 19 from the upstream side are arranged in the temperature region E (second temperature region) of the glass ribbon B that is below the annealing point AP.
- the softening point SP may be in the furnace chamber 11. Information about the temperature region of the glass ribbon B that is in the temperature region D, the temperature region E, or higher than the slow cooling point AP and less than the glass transition point Tg will be described later.
- the positions of the points SP, Tg, AP, StP are estimated based on the ambient temperature around the glass ribbon B obtained by the measurement of the temperature sensor 34, and the positions of the estimated points SP, Tg, AP, StP are estimated. Determined from.
- the slow cooling device 3 includes a detection control unit 30 and a drive unit 32 (see FIG. 4).
- the conveyance roller pairs 18 and 19 convey the glass ribbon B by drawing the glass ribbon B downward.
- Each conveyance roller pair 18 has four conveyance rollers 18a arranged on both sides of the glass ribbon B so as to sandwich a neighboring region adjacent to both ends in the width direction of the glass ribbon B, and the same side with respect to the glass ribbon B. It has two drive shafts 18b disposed on both sides of the glass ribbon B, which couples two conveying rollers 18a.
- Each conveyance roller pair 19 has four conveyance rollers 19a arranged on both sides of the glass ribbon B so as to sandwich a neighboring region adjacent to both ends in the width direction of the glass ribbon B, and the same side with respect to the glass ribbon B.
- the conveyance roller pairs 18 and 19 are not limited to those described above.
- the conveyance rollers of each roller pair are not connected to each other on the same surface side with respect to the glass ribbon B by the drive shaft, and the both ends in the width direction of the glass ribbon B are the same as the rollers of the roller pair 17. It may be arranged independently in the part.
- the temperature of the center part of the width direction of a glass ribbon is slow so that a tensile stress may work in the conveyance direction of the glass ribbon B.
- the cooling rate at the center in the width direction of the glass ribbon B is It is also possible to control the temperature so that it is faster than the cooling rate.
- the both ends (ear part) of the width direction of the glass ribbon B are lower than the temperature of a center part, and the temperature of a center part is The temperature of the glass ribbon B is controlled so as to be uniform. Further, the temperature in the width direction of the glass ribbon B in the region where the temperature in the center portion in the width direction of the glass ribbon B is greater than the strain point below the softening point so that the tensile stress in the transport direction acts on the center portion in the width direction of the glass ribbon B. The temperature of the glass ribbon B is controlled so that the distribution becomes lower from the center toward both ends.
- the temperature of the glass ribbon B is adjusted so that there is no temperature gradient between both ends (ears) in the width direction of the glass ribbon and the center. Control. Thereby, the tensile stress of a conveyance direction is applied to the center part of the width direction of the glass ribbon B.
- both end portions in the width direction of the glass ribbon B (ear The temperature of the glass ribbon B can be controlled so as to decrease from the portion) toward the center in the width direction of the glass ribbon B.
- the slow cooling step includes a first cooling step of cooling at the first average cooling rate until the temperature of the central portion in the width direction of the glass ribbon B reaches the slow cooling point, and the width direction of the glass ribbon B.
- the first average cooling rate is 5.0 ° C./second or more
- the first average cooling rate is faster than the third average cooling rate
- the third average cooling rate is the second average cooling rate.
- the average cooling rate is, in descending order, the first average cooling rate, the third average cooling rate, and the second average cooling rate.
- the cooling rate in the conveyance direction of the glass ribbon B affects the thermal shrinkage of the glass plate to be manufactured.
- the cooling rate by setting the cooling rate as described above, it is possible to obtain a glass plate having a suitable heat shrinkage rate while improving the production amount of the glass plate.
- the atmosphere around the glass ribbon B is set so that the glass ribbon B has the temperature described above.
- the temperature is controlled by the heating means.
- the detection control unit 30 includes a temperature sensor 34 arranged corresponding to the pair of conveyance rollers 18 and 19 and a computer (not shown) that functions as a peripheral speed determination unit 38.
- FIG. 4 is a block diagram illustrating the configuration of a control system that controls the rotational driving of the transport roller pairs 18 and 19.
- Each temperature sensor 34 is connected to a peripheral speed determining unit 38.
- the peripheral speed determining unit 38 is connected to drive the pair of conveying rollers 18 and 19 via the driving unit 32. Details of the detection control unit 30 will be described later.
- the drive unit 32 rotationally drives the transport rollers 18a and 19a based on the peripheral speeds of the transport rollers 18a and 19a stored in the storage unit 36 described later.
- the drive unit 32 has a motor (not shown) provided corresponding to each of the conveyance roller pairs 18 and 19.
- the motor may not be provided corresponding to each conveyance roller pair 18, 19, and the number thereof may be smaller than the number of each conveyance roller pair 18, 19, for example.
- the driving force from the motor is transmitted to the transport rollers 18a and 19a via, for example, a universal joint.
- the temperature sensor 34 detects the atmospheric temperature at the arrangement position in the first slow cooling furnace 12 and the second slow cooling furnace 13, respectively.
- the peripheral speed determining unit 38 determines the peripheral speeds of the plurality of transport rollers 18a and 19a based on the thickness of the glass plate to be manufactured.
- the peripheral speeds of the transport rollers 18a and 19a are preferably glass ribbons so that all the transport rollers 19a provided in the temperature region E are faster than all the transport rollers 18a provided in the temperature region D.
- the conveying roller 19a provided downstream is determined to be faster than the position where the temperature of B becomes the strain point StP. That is, in the slow cooling process, in the temperature region where the temperature of the glass ribbon B is not less than the glass transition point and not more than the softening point so that the glass ribbon B does not undergo corrugated plastic deformation,
- the plurality of transport rollers 18a and 19a are controlled so as to apply tension.
- the peripheral speed determination unit 38 first refers to the softening point SP, glass transition point Tg, annealing point AP, and strain point StP of the glass ribbon B stored in the storage unit 36 to be described later, and the temperature sensor 34. The positions of these points SP, Tg, AP, and StP in the slow cooling furnaces 12 and 13 are estimated based on the atmospheric temperature detected by the above. Next, the peripheral speed determination unit 38 increases the peripheral speed of the three transport rollers 19 a provided in the temperature region E as compared with the peripheral speed of the two transport rollers 18 a provided in the temperature region D.
- the upper limit of the ratio of the fast peripheral speed to the slow peripheral speed is preferably 1.02, for example, from the viewpoint of suppressing cracking of the glass ribbon B, and prevents plastic deformation.
- the lower limit of the ratio is preferably set to 1.0003. That is, the peripheral speed of the three transport rollers 19a in the temperature region E is preferably 0.03 to 2% faster than the peripheral speed of the two transport rollers 18a in the temperature region D, and 0.05 to 1 0.7% faster, more preferably 0.1-1.5% faster, more preferably 0.2-1.0% faster, and more preferably 0.3-0.8% faster.
- the peripheral speed of the transport rollers 18a and 19a that is higher than the slow cooling point AP and less than the glass transition point Tg, and the peripheral speed of the transport roller 18a when the transport roller 18a is further located on the upstream side of the temperature region D are
- the peripheral speed of the conveying roller 18a in the temperature region D may be the same or different, and is particularly preferably different. If they are different, the transport roller 18a on the upstream side from the temperature region D, the transport roller 18a in the temperature region D, and the transport roller 19a that is higher than the slow cooling point AP and less than the glass transition point Tg, in that order, are faster. Is preferred.
- the peripheral speed of the most upstream transport roller 18a and the peripheral speed of the second transport roller 18a from the upstream side may be the same or different, and are preferably different. If they are different, it is preferable that the circumferential speed of the second conveying roller 18a from the upstream side is faster than the circumferential speed of the most upstream conveying roller 18a.
- the peripheral speeds of the three transport rollers 19a from the downstream side may be all the same, partly the same or all different, and particularly preferably all different. When all are different, it is preferable that the peripheral speed of the transport roller 19a on the most downstream side is the fastest and the peripheral speed of the third transport roller 19a from the downstream side is the slowest.
- the temperature of the adjacent region is equal to or higher than the glass transition point Tg so that a wave-shaped plastic deformation does not occur in the adjacent region adjacent to the inner side in the width direction of the glass ribbon B with respect to the portion sandwiched by the transport rollers 18a and 19a. It is preferable to apply a tensile stress in the transport direction to the glass ribbon B in a temperature range that is equal to or lower than the softening point SP.
- the temperature of the adjacent region adjacent to the inner side in the width direction of the glass ribbon with respect to the portion sandwiched by the transport roller of the glass ribbon is downstream of the position where the glass annealing point AP is set.
- the peripheral speed of the transport roller pair of the provided transport roller pair is set so that the temperature of the adjacent roller of the transport roller pairs 18 and 19 is equal to or lower than the glass transition point Tg and the softening point SP. It is preferable to make it faster than the peripheral speed of the conveying roller 18a in terms of exerting tensile stress.
- the peripheral speeds of the transport rollers 18a and 19a are determined so that the transport roller 19a provided in the temperature region E is faster than the transport roller 18a provided in the temperature region D, and rotated accordingly.
- the driving it is possible to prevent the deformation of the wave shape generated in the inner region in the width direction of the transport rollers 18a and 19a, which can effectively apply tension in the transport direction of the glass ribbon B.
- the peripheral speed determination unit 38 includes a storage unit 36.
- the storage unit 36 stores the peripheral speeds of the plurality of transport rollers 18a and 19a determined as described above.
- the storage unit 36 stores the softening point SP, the glass transition point Tg, the annealing point AP, and the strain point StP of the glass ribbon B for each glass composition.
- the computer uses heating means in the slow cooling furnaces 12 and 13 so that the atmospheric temperature in the slow cooling furnaces 12 and 13 is maintained within a predetermined temperature range based on the ambient temperature detected by the temperature sensor 34. Automatic control.
- the predetermined temperature range of the first slow cooling furnace 12 is set to, for example, 500 to 800 degrees.
- the predetermined temperature range of the second slow cooling furnace 13 is set to 200 to 500 degrees, for example.
- the sampling apparatus 4 has a sampling chamber (not shown) arranged on the downstream side of the second slow cooling furnace 13.
- the glass ribbon B is cut at regular intervals, and the glass plate C is sampled.
- the thickness of the glass plate C is 0.5 mm or less, for example.
- the size of the glass plate C is not particularly limited, and for example, the length in the width direction is 500 to 3500 mm ⁇ the length in the longitudinal direction is 500 to 3500 mm.
- the length in the width direction of the glass plate C may be 1000 mm or more, 1500 mm or more, 2000 mm or more, 2500 mm or more
- the length in the longitudinal direction may be 1000 mm or more, 1500 mm or more, 2000 mm or more, 2500 mm or more.
- the larger the glass plate C is the larger the distance from the conveyance roller at the center in the width direction of the glass ribbon B and the outer wall of the slow cooling furnace, so that the glass ribbon B is near the conveyance roller and in the width direction. There is a tendency that a temperature difference is likely to occur between adjacent regions which are regions of the inner glass ribbon B.
- the length in the width direction of the glass plate C is 1000 mm or more
- the shape of the glass ribbon B in the vicinity of the transport roller and the inner side in the width direction tends to be easily deformed. Become prominent.
- the effect of this invention becomes so useful that the length of the width direction of the glass plate C is 1500 mm or more, 2000 mm or more, 2500 mm or more.
- the glass plate manufacturing apparatus 1 further includes an input unit (not shown) that receives an operator's input operation, and this input unit receives the peripheral speed or rotational speed of the transport rollers 18a and 19a input by the operator.
- the storage unit 36 may not store the softening point SP, the glass transition point Tg, the annealing point AP, the strain point StP, and the like of the glass ribbon B.
- the softening point SP and glass transition of the glass ribbon B may be determined by an operator.
- the input unit may be directly connected to the drive unit, and the peripheral speed or rotation speed of the transport roller may be directly input to the drive unit.
- the glass plate manufacturing apparatus 1 configured as described above, in the temperature region where the temperature of the glass ribbon B is not less than the glass transition point Tg and not more than the glass softening point SP, a tensile stress is applied to the glass ribbon B in the transport direction.
- the peripheral speed of the conveying roller 19a of the conveying roller pair 19 provided in the temperature region where the temperature of the glass ribbon B is equal to or lower than the glass annealing point AP is such that the temperature of the glass ribbon B is equal to or higher than the glass transition point Tg.
- the rotational driving of the transport rollers 18a and 19a is controlled so as to be faster than the peripheral speed of the transport roller 18a provided in the temperature region D that is equal to or lower than the softening point SP.
- the above-described generation is performed. Due to the compressive stress, plastic deformation (waveform deformation) easily occurs in the adjacent region of the glass ribbon in the vicinity of the transport rollers 18a and 18b and in the width direction, and the flatness of the glass plate is deteriorated. More specifically, for example, when temperature control of the glass ribbon is performed so that a tensile stress (tension) in the conveyance direction is applied to the central portion in the width direction of the glass ribbon B, compression is applied to the adjacent region, and waves are applied to the adjacent region. The plastic deformation with the shape tends to occur.
- the problem of such plastic deformation is that the difference between the thickness of the both ends of the glass ribbon B in the width direction and the thickness of the adjacent region is likely to be large, and the thickness is 0.5 mm or less that is easy to deform even with small stress due to the thin thickness. It becomes remarkable when manufacturing the glass plate of this. That is, when only the manufacturing method of Patent Document 1 described above is used, when a glass plate having a thickness of 0.5 mm or less is manufactured, the adjacent region that is the inner region in the width direction of the transport roller is more easily deformed, and the glass plate This will worsen the flatness.
- the peripheral speed of the transport roller provided below is higher than that of the transport roller provided above.
- 0049] is considered to be premised on a relatively thick glass with a thickness of about 0.7 to 1 mm, and the peripheral speed of the transport roller is increased in order from the upstream side to the downstream side in the transport direction. This is based on the idea that tension is always applied to the glass ribbon in the transport direction.
- plastic deformation occurs in the adjacent region of the glass ribbon as a phenomenon in a limited temperature region of the glass ribbon, and it is necessary to provide a peripheral speed difference between the conveyance rollers in an appropriate temperature region. It is.
- tension is applied to the glass ribbon B in the transport direction in a temperature region where the temperature of the glass ribbon B is not less than the glass transition point Tg and not more than the glass softening point SP. For this reason, it can suppress that a waveform deformation
- the pair of transport rollers 19 provided in a temperature region where the temperature of the glass ribbon B is equal to or lower than the glass annealing point AP.
- the transport rollers 18a, 19a are set so that the peripheral speed of the transport roller 19a is faster than the peripheral speed of the transport roller 18a provided in the temperature region D where the temperature of the glass ribbon B is not less than the glass transition point Tg and not more than the softening point SP. Rotational drive of is controlled.
- the plurality of transport roller pairs 18 and 19 may be provided at least in the temperature region D and the temperature region E. Further, the number of the plurality of transport roller pairs is not particularly limited as long as it is at least two. Note that the positions of the softening point SP, the glass transition point Tg, the annealing point AP, and the strain point StP, and the number of transport roller pairs located in each region formed with these points as boundaries are not particularly limited.
- FIG. 5 is a block diagram illustrating the configuration of a control system that controls the rotational drive of the transport roller pairs 18 and 19.
- elements indicated by the same reference numerals as those referred to in the first embodiment are the same as the elements described in the first embodiment.
- the detection unit 47 is connected to the temperature sensor 44.
- the temperature sensor 44 detects the temperatures of the transport rollers 18a and 19a.
- detecting the temperatures of the transport rollers 18a and 19a includes calculating the temperatures of the transport rollers 18a and 19a.
- the temperature difference data stored in the storage unit 46 at the atmospheric temperature detected by each temperature sensor 44 is referred to, and the temperatures of the transport rollers 18a and 19a are calculated.
- the detection unit 47 calculates the thermal expansion amount of the transport rollers 18a and 19a as a change in diameter, as will be described later.
- the storage unit 46 of the peripheral speed determination unit 48 stores temperature difference data.
- the temperature difference data includes data on the difference between the atmospheric temperature of the slow cooling furnaces 12 and 13 and the temperature (surface temperature) of the transport rollers 18a and 19a at each atmospheric temperature, which is measured in advance when the slow cooling furnaces 12 and 13 are installed.
- the temperature difference data is stored differently depending on the structure of the slow cooling furnaces 12 and 13.
- the storage unit 46 further stores thermal expansion coefficients (hereinafter also referred to as roller thermal expansion coefficients) of the transport rollers 18a and 19a.
- the roller thermal expansion coefficient is determined from the material of the transport rollers 18a and 19a.
- the storage unit 46 also includes a rotational speed of each of the transport rollers 18a and 19a determined by the peripheral speed determination unit 48, a reference peripheral speed distribution set between the plurality of transport roller pairs 18 and 19, and each transport roller.
- a reference value of the diameters 18a and 19a is further stored.
- the reference value of the diameter of each of the transport rollers 18a and 19a is a diameter at the time of a new article at normal temperature (for example, 25 degrees).
- the storage unit 46 has conditions for achieving a reference peripheral velocity distribution (the temperature of the transport roller, the temperature of the glass ribbon B, the thermal expansion coefficient of the glass ribbon, the thickness, the width of the glass ribbon B, the glass ribbon B Memory).
- the peripheral speed determining unit 48 includes a plurality of transport roller pairs 18 and 19 when the relative speed between the peripheral speeds of the transport rollers 18 a and 19 a and the transport speed of the glass ribbon B is constant between the transport roller pairs 18 and 19.
- Set the peripheral speed ratio peripheral speed distribution.
- the peripheral speed of the transport roller 19a of the transport roller pair 19 provided in the temperature region E is higher than the peripheral speed of the transport roller 18a of the transport roller pair 18 provided in the temperature region D. Is set.
- the peripheral speed determining unit 48 maintains the magnitude relationship of the peripheral speeds of the transport rollers 18a and 19a in the temperature regions D and E determined in the first embodiment, and the transport rollers 18a and 18a calculated by the detection unit 47 are maintained. Based on the change of the diameter of 19a, the rotational speed of each conveyance roller 18a, 19a is determined so that the peripheral speed ratio between the some conveyance roller pair 18,19 may be maintained.
- the peripheral speeds of the transport rollers 18a and 19a may be calculated by an operator instead of the peripheral speed determining unit 48.
- the glass plate manufacturing apparatus 1 further includes an input unit similar to that described in the first embodiment.
- the storage unit 46 does not store temperature difference data, roller thermal expansion coefficient, peripheral speed distribution, reference values of the diameters of the respective transport rollers 18a and 19a, conditions for achieving the reference peripheral speed distribution, and the like.
- it is calculated by the operator based on temperature difference data, roller thermal expansion coefficient, peripheral speed distribution, reference value of the diameter of each of the transport rollers 18a and 19a, conditions for achieving the reference peripheral speed distribution, and the like. What is necessary is just to memorize
- the peripheral speed ratio between the plurality of transport roller pairs 18 and 19 is, for example, that of the most upstream transport roller 18a in order from the immediately downstream transport roller 18a with the peripheral speed of the most upstream transport roller 18a as a reference.
- the peripheral speed is set to increase by 0.1% of the peripheral speed.
- the peripheral speed of the most downstream side conveyance roller 19a is 100.6% of the most upstream side conveyance roller 18a.
- the peripheral speed set from the peripheral speed ratio is set using the peripheral speed of the transport roller 18a on the most upstream side.
- the peripheral speed ratio set as a reference in this way is the peripheral speed ratio when the conventional glass ribbon B is gradually cooled without causing problems of scratches or shape deformation.
- the reference peripheral speed distribution is stored and held in the peripheral speed determining section 48 together with conditions such as the temperature, thermal expansion coefficient, thickness, width, and glass flow rate of the glass ribbon B. As will be described later, this peripheral speed ratio is set by correcting the reference peripheral speed distribution when conditions of slow cooling such as the temperature of the glass ribbon B change.
- the peripheral speed determination unit 48 corrects and sets the reference peripheral speed ratio according to the temperature, thermal expansion coefficient, thickness, glass flow rate, and the like of the glass ribbon B. Specifically, the reference temperature in each of the transport roller pairs 18 and 19 is set as the condition at that time in the peripheral speed ratio set as the reference peripheral speed distribution. Therefore, when the current temperature of the glass ribbon B changes with respect to this reference temperature, for example, when the temperature T 1 changes to T 2 , the difference in thermal expansion coefficient between the temperature difference between T 2 and T 1 is calculated. The peripheral speed determining unit 48 corrects the peripheral speed ratio set as the reference peripheral speed distribution. This is because the conveyance speed of the glass ribbon B changes depending on the coefficient of thermal expansion determined by the temperature of the glass ribbon B and the coefficient of thermal expansion.
- the peripheral speed ratio may be more generally corrected using the difference in the thermal expansion coefficient in consideration of the thermal expansion coefficient and the temperature of the glass ribbon B.
- Such a peripheral speed ratio is corrected and set by changes in conditions such as the thickness, width, and glass flow rate of the glass ribbon B in addition to the temperature dependency of the glass ribbon B and the thermal expansion coefficient. Therefore, the conditions for the reference peripheral speed ratio such as the temperature of the glass ribbon B, the temperature-dependent characteristics of the thermal expansion coefficient, the thickness, the width, and the glass flow rate are stored and held in advance in the peripheral speed determination unit 48.
- the glass thermal expansion coefficient is determined from the composition of the molten glass.
- the peripheral speeds of the respective transport roller pairs on the downstream side are calculated on the basis of the current peripheral speed of the transport roller pair on the most upstream side.
- the peripheral speed ratio in accordance with the change in the state including the temperature of the glass ribbon B, it is possible to determine a more appropriate rotational speed of the transport rollers 18a and 19a.
- the peripheral speed determining unit 48 determines the rotational speed of each of the transport rollers 18a and 19a according to the following formula based on the calculated peripheral speed of each of the transport rollers 18a and 19a.
- Rotational speed peripheral speed / (diameter of thermally expanded conveying roller ⁇ ⁇ )
- the ambient temperature detected at the arrangement position of each of the conveying roller pairs 18 and 19 in the slow cooling furnaces 12 and 13 changes with respect to the temperature of the conveying roller pairs 18 and 19 at the reference peripheral speed ratio described above.
- the rotational speeds of the transport rollers 18a and 19a are determined so as to maintain the above-described peripheral speed ratio.
- the detection unit 47 detects the roller thermal expansion coefficient at the temperature of the conveyance rollers 18a and 19a and the conveyance roller 18a and 19a with respect to the conveyance rollers 18a and 19a detected by the temperature sensor 44.
- the peripheral speed determination unit 48 calculates a new rotational speed from the amount of change in the diameter of the transport roller 18a calculated by the detection unit 47 according to the following formula, assuming that the amount of change in the peripheral speed is 1, and the transport roller 18a, The rotational speed of 19a is changed.
- New rotation speed (peripheral speed + change amount of peripheral speed) / ((change diameter of transport roller + change amount of transport roller diameter) ⁇ ⁇ )
- the rotation speed determined by the peripheral speed determination unit 48 is sent to the drive unit 32, and the rotation of the transport rollers 18a and 19a is controlled.
- the peripheral speed ratio is not limited to that described above.
- the peripheral speed determination unit 48 may calculate specific peripheral speeds of the transport rollers 18a and 19a as the peripheral speed distribution instead of the peripheral speed ratio.
- the reference peripheral speed distribution and the corrected peripheral speed are also set as specific speed values.
- the peripheral speed distribution in addition to adjusting the rotational speed so as to have a set peripheral speed distribution according to the temperature of the diameter of the conveying roller, the peripheral speed distribution becomes a reference peripheral speed distribution according to the temperature of the glass ribbon. Correct and set.
- the reference peripheral velocity distribution need not be corrected in accordance with the current temperature of the glass ribbon.
- the rotational speed of each of the transport rollers 18a and 19a is controlled so as to compensate for the change in consideration of the change in the state that occurs in the transport rollers 18a and 19a. Therefore, it is possible to suppress the difference in the relative speed between the peripheral speeds of the transport rollers 18a and 19a and the transport speed of the glass ribbon B in the plurality of transport roller pairs 18 and 19 with higher accuracy. . Thereby, the slip between the glass ribbon B and the conveyance rollers 18a and 19a can be prevented, and the quality of the glass plate surface can be improved.
- the peripheral speed distribution of the plurality of pairs of conveying rollers 18 and 19 used for conveying the glass ribbon B is corrected and set according to the temperature of the glass ribbon B, the glass ribbon B is excessive and the glass ribbon B is deformed. In addition, the glass ribbon B can be prevented from being pulled and broken by being faster than necessary. Such an effect is more conspicuous in the production of a thin glass sheet having a thickness of 0.5 mm or less that has a high glass conveyance speed and is easily deformed because the strength of the glass ribbon B is small.
- the temperature of the glass ribbon B and the temperatures of the transport rollers 18a and 19a change as described above.
- the correction amount is small, and the distribution of the set reference peripheral speed ratio is not greatly changed. That is, it does not change that the peripheral speed of the transport roller of the pair of transport rollers provided in the temperature region E is faster than the peripheral speed of the transport roller of the pair of transport rollers provided in the temperature region D.
- the temperature sensor detects the ambient temperature in the slow cooling furnaces 12 and 13 and calculates the transport roller temperature using this, but the transport roller temperature may be directly measured.
- a thermometer for continuously measuring the temperature of the conveyance roller may be used as the conveyance roller state detection unit.
- FIG. 6 is a block diagram illustrating the configuration of a control system that controls the rotational drive of the conveying roller pairs 18 and 19.
- the detection unit 57 is connected to the distance measurement sensor 54.
- a plurality of distance measuring sensors 54 are provided corresponding to the respective transport roller pairs 18 and 19.
- the distance measurement sensor 54 detects the drive shaft interval.
- the drive shaft spacing is such that the drive shafts 18b and 19b connect the conveying rollers 18a and 19a on the same side with respect to the glass ribbon B, and the drive shaft 18b disposed opposite to the drive shafts 18b and 19b. , 19b.
- the pair of transport rollers 18 and 19 sandwich the glass ribbon B in a state where the pair of transport rollers 18a and 19a are urged to each other.
- the amount of wear of each of the transport rollers 18a and 19a is determined based on the fact that the amount of change from the new roller radius of the roller radius calculated according to the following equation is caused by the wear of the transport rollers 18a and 19a. Is detected.
- the peripheral speed determination unit 58 of the detection control unit 50 is a peripheral speed ratio of the peripheral speeds of the transport rollers 18a and 19a caused by the change in the radius of the transport rollers 18a and 19a due to the detected wear of the transport rollers 18a and 19a.
- the rotational speeds of the transport rollers 18a and 19a are determined so as to compensate for the deviation from the above.
- the change in the radius calculated based on the wear state is used as the diameter change of the transport rollers 18a and 19a.
- the wear roller 18a and 19a used in the second embodiment use this wear state. It can also be applied together with the temperature of 19a. In this case, the diameters of the transport rollers 18a and 19a vary with the amount of wear and also with thermal expansion.
- the rotational speeds of the transport rollers 18a and 19a can be calculated so that the peripheral speeds of the transport rollers 18a and 19a changed with the change in diameter are maintained at the peripheral speed ratio. Furthermore, in addition to changes in the diameters of the transport rollers 18a and 19a, a change in the transport speed of the glass ribbon B that changes according to the temperature of the glass ribbon B due to the thermal expansion of the glass ribbon B as a state of the glass ribbon B is integrated and applied. You can also
- the distance measuring sensor 54 replaces the distance between the drive shafts 18b, 19b of the transport roller pair 18, 19 with the origin of the drive shafts 18b, 19b of the transport roller pair 18, 19 It may be configured to detect the amount of wear by reading the deviation from the position.
- the origin position is a center position where the drive shafts 18b and 19b are located when the transport rollers 18a and 19a are new, and is stored in the storage unit 56.
- the amount of wear of the transport rollers 18a and 19a is detected using the deviation of the drive shafts 18b and 19b from the origin position of the pair of transport rollers 18 and 19, and the roller diameter of the transport rollers thus worn can be calculated.
- the diameters of the transport rollers 18a and 19a are not limited to being calculated by the detection unit 57, and may be calculated by an operator based on the amount of wear, for example. In this case, based on the diameters of the transport rollers 18a and 19a calculated by the operator and input to the peripheral speed determination unit 58, the peripheral speed determination unit 58 calculates the rotation speeds of the transport rollers 18a and 19a.
- the rotational speeds of the transport rollers 18a and 19a may be further calculated based on the diameters of the transport rollers 18a and 19a calculated by the operator, and the calculation result may be input to the peripheral speed determination unit 58.
- the rotational speed calculated or input by the peripheral speed determining unit 58 is determined by the peripheral speed determining unit 58 and transmitted to the drive unit 32.
- the wear amount and the origin position of the transport rollers 18 a and 19 a may be calculated by the operator, and the calculated values may be stored in the storage unit 56.
- the rotation speeds of the transport rollers 18a and 19a are determined so as to compensate for the diameter changes of the transport rollers 18a and 19a generated in the respective rollers of the transport roller pair 18 and 19.
- the rotational speed of each roller of the roller pair 17 may be determined so as to compensate for a change in the diameter of each roller of the roller pair 17 used as the cooling roller pair in the molding process.
- each roller of the roller pair 17 detects the state of each roller of the roller pair 17 using a detection unit such as the above-described conveyance roller state detection units 47 and 57, and the roller pair based on the detection result.
- the rotational speed of each roller of the roller pair 17 is determined so as to compensate for the change in the diameter of each of the 17 rollers.
- the peripheral speed of each roller of the roller pair 17 is set to an appropriate value so that the thickness distribution of the glass plate and the unevenness of the glass surface are minimized. Distribution and unevenness of the glass surface will be deteriorated. That is, when the peripheral speed of the roller pair 17 changes, the amount of the glass ribbon B stretched between the lower end of the formed body and the roller pair 17 and the glass ribbon performed between the roller pair 17 and the conveying roller pair 18.
- the temperature distribution in the width direction of the glass ribbon B between the lower end of the formed body and the roller pair 17 and the width of the glass ribbon between the roller pair 17 and the conveying roller pairs 18 and 19 are changed.
- the thickness distribution in the width direction of the manufactured glass plate and the size of the irregularities on the glass surface change because the shape of the temperature distribution in the direction is different.
- the rotational speed of each roller of the roller pair 17 is determined so as to compensate for a change in the diameter of each roller of the roller pair 17.
- the rotational speed may be determined so as to compensate for a change in the diameter of each roller of at least one of the rollers of the conveying roller pair 18, 19 and the roller pair 17. In other words, it is not necessary to determine the rotation speed of the roller so as to compensate for the change in the diameter of the cooling roller or the conveyance roller, and it is not necessary to perform it for all rollers (cooling roller, conveyance roller), You may go.
- the glass ribbon B has a low viscosity and is less likely to slip.
- slip is likely to occur in the glass ribbon B having the softening point SP or less. For this reason, it is preferable to determine the rotation speed of the conveyance roller so as to compensate for a change in the diameter of the conveyance roller provided in the region where the central portion of the glass ribbon B is equal to or lower than the softening point SP.
- the central portion of the glass ribbon B is compensated for a change in the diameter of the conveyance roller provided in a temperature region in which the temperature of the glass ribbon B is not less than the glass transition point Tg and not more than the softening point SP.
- the rotation speed of the conveying roller it is preferable to determine the rotation speed of the conveying roller so as to compensate for a change in the diameter of the conveying roller provided in a temperature region in which at least the temperature of the central portion of the glass ribbon B is not less than the glass transition point Tg and not more than the softening point SP.
- the diameter of the conveyance roller provided in the temperature region where the temperature of the central portion of the glass ribbon B is not less than the glass transition point Tg and not more than the softening point SP is likely to change, the diameter change of the conveyance roller provided in this region is compensated. It is preferable to determine the rotation speed of the transport roller so that it does.
- the glass temperature is higher than the softening point SP, the compressive stress acting on the glass is instantly relieved, so that the glass ribbon B is less likely to be wave-shaped plastically deformed.
- the glass temperature is lower than the glass transition point Tg, since the viscosity of the glass ribbon B is sufficiently increased, the corrugated plastic deformation hardly occurs.
- the upstream roller tends to change in roller diameter due to wear or thermal expansion. That is, it is preferable to determine the rotation speed of the conveyance roller so as to compensate for a change in the diameter of the conveyance roller provided at least in the temperature region where the temperature is not less than the glass transition point Tg and not more than the softening point SP.
- the conveyance roller state detection unit 57 of the glass plate manufacturing apparatus shows changes in the diameters of the conveyance rollers 18a and 19a calculated based on the number of days of use of the conveyance rollers 18a and 19a.
- a device that counts the diameter change of the transport rollers 18a and 19a may be used.
- the device that counts the diameter change sends the usage days of the transport rollers 18 a and 19 a to the peripheral speed determination unit 58.
- the peripheral speed determining unit 58 as a past replacement record for each of the transport rollers 18a and 19a, stored in the storage unit 56 of the peripheral speed determining unit 58, shows the amount of wear from the new roller diameter when the roller roller has been replaced in the past.
- the amount of wear per day is calculated based on these and the number of days until replacement.
- the new roller diameter stored in the storage unit 56 is referred to, and the roller diameter is calculated according to the following equation.
- the product of the amount of wear per day ⁇ the number of days of use corresponds to the amount of wear of the transport rollers 18a and 19a, as shown in the following formula using the number of days of use sent from the device for counting the diameter change. Detected.
- roller diameter new diameter-(amount of wear per day x number of days used)
- the peripheral speed determination unit 58 stores past replacement results and roller diameters when new, for each of the transport rollers 18a and 19a.
- the amount of wear per day can be calculated by an operator and stored in the storage unit 56.
- the diameter change of the transport rollers 18a and 19a due to the wear amount may be calculated by the operator and transmitted to the detection control unit 50 or the drive unit 32. Further, the wear amount of the roller diameter when it was replaced in the past and the number of days used until the replacement may be calculated by the operator, and the calculated value may be stored in the storage unit 56.
- the second embodiment and the modified example of the third embodiment can be combined.
- the deviation from the peripheral speed ratio can be compensated more accurately than when the second embodiment or the third embodiment is applied alone. it can.
- the problem of plastic deformation is likely to occur when both ends (ear portions) in the width direction of the glass ribbon are rapidly cooled by the roller pair 17.
- the glass liquid phase temperature is as high as 1050 ° C. to 1250 ° C.
- the adjacent region when both ends (ears) in the width direction of the glass ribbon are rapidly cooled by the roller pair 17 and the center position of the glass ribbon B
- the production method of the present invention that hardly causes plastic deformation is suitable for production of a glass plate using glass having a liquidus temperature of 1100 ° C. to 1250 ° C. Production of a glass plate using a glass having a liquidus temperature of 1150 ° C.
- a glass plate for a flat panel display such as a liquid crystal display or an organic EL display having a small liquidus viscosity of 150,000 dPa ⁇ s or less is in a state where devitrification is likely to occur during the molding process. For this reason, it is necessary to raise the temperature of the molten glass at the time of a shaping
- the present invention is suitable for the production of a glass plate using a glass having a liquidus viscosity of 150,000 dPa ⁇ s or less, and the production method of the present invention is more suitable for the production of a glass plate using 35,000 to 150,000 dPa glass.
- the production method of the present invention is more suitable for the production of a glass plate using glass of 50,000 to 100,000 dPa ⁇ s, and the production method of the present invention is more suitable for the production of a glass plate of glass using 50,000 to 80,000 dPa ⁇ s. .
- the production method of the present invention is suitable for producing a glass plate using glass having a thermal expansion coefficient (100 to 300 ° C.) [ ⁇ 10 ⁇ 7 ° C.] of 30 or more.
- a thermal expansion coefficient 100 to 300 ° C.
- thermal shock and thermal shrinkage tend to increase in the heat treatment process during the production of the flat panel display.
- the production method of the present invention is suitable for producing a glass plate having a thermal expansion coefficient (100 to 300 ° C.) [ ⁇ 10 ⁇ 7 ° C.] of less than 30 to 40, and the thermal expansion coefficient is less than 32 to 40
- the production method of the present invention is more suitable for the production of glass plates, and the production method of the present invention is more suitable for the production of glass plates of 34 to 40.
- the glass substrate for liquid crystal displays is mentioned suitably, for example.
- the following glass composition is illustrated as a glass composition of the glass substrate for liquid crystal displays. 50 to 70% by mass of SiO 2 B 2 O 3 0-15% by mass, Al 2 O 3 5 to 25% by mass, MgO 0-10% by mass, CaO 0-20% by mass, SrO 0-20% by mass, BaO 0-10% by mass, RO 5-20% by mass (provided that R is all components contained in the glass plate selected from Mg, Ca, Sr and Ba, and is at least one). It is preferable to contain.
- non-alkali glass glass containing substantially no alkali component
- a small amount of an alkali component may be included.
- R ′ 2 O is more than 0.05% by mass and 2.0% by mass or less, more preferably R ′ 2 O is more than 0.1% by mass and 2.0% by mass or less (provided that R ′ is Li, Na And all components contained in the glass plate selected from K and K, which are at least one kind).
- a glass ribbon was manufactured according to the following method using a conventional glass plate manufacturing apparatus and the glass plate manufacturing apparatus of the present embodiment, and the wavy deformation generated in the glass ribbon was measured. .
- the glass plate manufacturing apparatus is the glass plate manufacturing apparatus 1 by the downdraw method shown in FIG.3 and FIG.4, and the glass used the aluminosilicate glass containing the component shown below. SiO 2 60% by mass Al 2 O 3 19.5 mass% B 2 O 3 10% by mass CaO 5% by mass SrO 5% by mass SnO 2 0.5% by mass
- the peripheral speed determining unit 38 provided the temperature of the glass ribbon B conveyed in the slow cooling furnace in the temperature region D where the glass transition point Tg or more and the softening point SP or less.
- the peripheral speed of the transport roller 19a provided in the temperature region E downstream of the position where the temperature of the glass ribbon B becomes the annealing point AP is 0.6% faster than the peripheral speed of the transport roller 18a.
- the peripheral speed of the transport roller 19a is determined, and the rotational drive of each of the transport rollers 18a and 19a is controlled based on the determined peripheral speed, so that the width is 0.5 mm and the length in the width direction is 2000 mm ⁇ the length in the length direction is 2500 mm.
- a glass substrate for liquid crystal display was prepared.
- Example 2 the peripheral speed of each of the transport rollers 18a and 19a is determined so as to maintain the peripheral speed distribution, and based on the determined peripheral speed of the transport roller, the transport roller 18a is determined. , 19a except that the glass substrate for liquid crystal display with a thickness of 0.5 mm was manufactured under the same conditions as in Example 1.
- the peripheral speed determining unit 38 provided the temperature of the glass ribbon B conveyed in the slow cooling furnace in the temperature region D in which the glass transition point Tg or more and the softening point SP or less.
- the peripheral speed of the transport roller 19a provided in the temperature region E downstream of the position where the temperature of the glass ribbon B becomes the annealing point AP is 0.6% faster than the peripheral speed of the transport roller 18a.
- the peripheral speed of the transport roller 19a is determined, and the rotational drive of each of the transport rollers 18a and 19a is controlled based on the determined peripheral speed, and is 0.7 mm thick and has a width direction length of 2000 mm ⁇ a length direction length of 2500 mm.
- a glass substrate for liquid crystal display was prepared.
- Comparative Example 1 a 0.5 mm thick glass substrate for a liquid crystal display was produced under the same conditions as in Example 1 except that the peripheral speeds of all the transport rollers 18a and 19a were the same. Further, as Comparative Example 2, a 0.7 mm thick glass substrate for a liquid crystal display was produced under the same conditions as in Example 3 except that the peripheral speeds of all the transport rollers 18a and 19a were the same. With respect to the glass substrates for liquid crystal displays of Examples 1 to 3 and Comparative Examples 1 and 2 thus obtained, a wave shape deformation (unevenness in the plate thickness direction) generated in an adjacent region of the glass substrate for liquid crystal displays was obtained using a thickness gauge. Measured.
- Example 1 the wave shape deformation (the height of the unevenness) was 0.05 mm or less.
- Example 2 the waveform deformation was 0.04 mm or less.
- Example 3 the waveform deformation was 0.05 mm.
- Comparative Example 1 the waveform deformation was 0.4 mm.
- Comparative Example 2 the waveform deformation was 0.25 mm.
- the glass substrate for a liquid crystal display having a thickness of 0.5 mm and a thickness of 0.7 mm
- the wave shape was assumed to satisfy the surface quality if it was within 0.2 mm in the thickness direction.
- the glass substrate for a liquid crystal display of Comparative Example 1 obtained using a conventional manufacturing apparatus had a step due to deformation of the wave shape of 0.4 mm, and did not satisfy the above surface quality.
- the glass substrate for a liquid crystal display of Comparative Example 2 obtained using a conventional manufacturing apparatus had a step due to deformation of the wave shape of 0.25 mm, and did not satisfy the above surface quality.
- the glass substrates for liquid crystal displays of Examples 1 to 3 obtained using the manufacturing apparatus 1 of the present embodiment have a step difference of 0.05 mm or less due to the deformation of the wave shape, and satisfy the above-described surface quality. It was.
- the height of the corrugated irregularities of Example 1 was improved to 1/8.
- the height of the corrugated irregularities of Example 2 was improved to 1/10.
- the height of the corrugated irregularities of Example 3 was improved to 1/5.
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Abstract
Description
また、成形体の下方に配された複数の搬送ローラ対において、上方に配置された搬送ローラ対の周速度よりも、下方に設置された搬送ローラ対の周速度を速くすることで、ガラス板の反りを低減することが知られている(特許文献2)。
しかしながら、特許文献2のように単に上流に対し、下流の搬送ローラの周速度を速くしても、効果が出ないばかりか、例えば板厚が0.5mm以下などの薄いガラス板を製造する場合に、例えば、実施例[0045]に記載されるような周速度差をつけると、ガラスリボンが割れてしまう虞があり、非常に危険である。
当該製造方法は、
ガラス原料を熔解して溶融ガラスをつくる熔解工程と、
溶融ガラスを、オーバーフローダウンドロー法を用いて成形し、ガラスリボンを形成する成形工程と、
前記ガラスリボンの幅方向の両端部に対して前記幅方向に隣接する近傍領域を、前記ガラスリボンの搬送方向に設けられた複数の搬送ローラ対で挟持しつつ、前記ガラスリボンを下方向に引き抜いて徐冷を行う徐冷工程と、を有する。
前記成形工程では、成形体からオーバーフローさせて前記成形体の側壁を流下する熔融ガラスを、前記成形体の下端で張り合わせることで前記ガラスリボンを形成した後に、前記ガラスリボンの幅方向の前記両端部を前記ガラスリボンの幅方向の中央部よりも速く冷却する。
前記徐冷工程では、前記ガラスリボンに塑性変形が生じないように、前記ガラスリボンの温度がガラス転移点以上ガラス軟化点以下となる温度領域において、前記ガラスリボンに対して前記搬送方向に張力を働かせる。
前記ガラス板は、例えば、板厚0.5mm以下とするこができる。
前記ガラスリボンの幅方向の中央部において、ガラスリボンの搬送方向に張力が働くように、少なくとも、前記ガラスリボンの幅方向の中央部の温度がガラス徐冷点に150℃を足した温度からガラス歪点から200℃引いた温度となる温度領域において、
前記ガラスリボンの幅方向の中央部の冷却速度が前記幅方向の両端部の冷却速度よりも速くなるように温度制御する、ことが好ましい。
前記ガラスリボンの幅方向の中央部の温度がガラス軟化点以上の領域において、前記ガラスリボンの幅方向の両端部が前記両端部に挟まれた中央部の温度より低く、且つ、前記中央部の温度が均一になるように前記ガラスリボンの温度を制御する。
前記ガラスリボンの幅方向の中央部において、ガラスリボン搬送方向の張力が働くように前記ガラスリボンの前記中央部の温度がガラス軟化点未満ガラス歪点以上の領域において、前記ガラスリボンの幅方向の温度分布が前記中央部から前記両端部に向かって低くなるように前記ガラスリボンの温度を制御する。
前記ガラスリボンの前記中央部の温度がガラス歪点となる温度領域において、前記ガラスリボンの幅方向の前記両端部と前記中央部との温度勾配がなくなるよう前記ガラスリボンの温度を制御する。
前記徐冷工程は、200m/時以上の搬送速度で前記ガラスリボンを下方向に引き抜いて徐冷する、ことが好ましい。
ガラス原料を熔解して溶融ガラスをつくる熔解工程と、
溶融ガラスをダウンドロー法を用いて成形し、ガラスリボンを形成する成形工程と、
前記ガラスリボンの幅方向の両端部に幅方向に隣接する近傍領域を、前記ガラスリボンの搬送方向に設けられた複数の搬送ローラ対で挟持しつつ、前記ガラスリボンを下方向に引き抜いて徐冷を行い、板厚0.5mm以下のガラスリボンを形成する徐冷工程と、を有する。
前記徐冷工程では、前記ガラスリボンの温度が徐冷点となる位置よりも下流側に設けられた前記搬送ローラ対の搬送ローラの周速度を、前記ガラスリボンの温度がガラス転移点以上軟化点以下となる温度領域に設けられた前記搬送ローラ対の前記搬送ローラの周速度よりも速くする。
当該装置は、
ダウンドロー法を用いて溶融ガラスからガラスリボンを成形する成形装置と、
前記ガラスリボンの幅方向の両端部に幅方向に隣接する近傍領域を複数の搬送ローラ対で挟持しつつ、前記ガラスリボンを下方向に引き抜いて徐冷し、板厚0.5mmの前記ガラスリボンを形成する徐冷装置と、を有し、
前記徐冷装置は、前記複数の搬送ローラ対と、駆動部とを含み、
前記複数の搬送ローラ対の1つは、前記ガラスリボンの温度がガラス転移点以上軟化点以下となる第1温度領域に、前記複数の搬送ローラ対の他の1つは、前記ガラスリボンの温度がガラス徐冷点以下となる第2温度領域に設けられて前記ガラスリボンを下方向に引き込むことで前記ガラスリボンを搬送し、
前記駆動部は、前記第2温度領域に設けられた搬送ローラ対の搬送ローラの周速度が、前記第1温度領域に設けられた搬送ローラの周速度よりも速くなるように決定された搬送ローラの周速度に基づいて、前記搬送ローラを回転駆動させる。
ガラスリボンの中央部とは、ガラスリボンの幅方向の幅のうちガラスリボンの幅方向の中心をいう。
ガラスリボンの中央領域とは、ガラスリボンの幅方向の幅のうちガラスリボンの幅方向の中心から幅の85%以内の範囲をいう。
ガラスリボンの両端部とは、ガラスリボンの幅方向の縁から200mm以内の範囲をいう。
ガラスリボンの幅方向の両端部に対して幅方向に隣接する近傍領域とは、上記両端部の幅方向内側の縁から、ガラスリボンの幅の20%以内の長さ分、幅方向内側に入った範囲までに含まれる領域をいう。
搬送ローラで狭持される部分に対してガラスリボンの幅方向内側に隣接する隣接領域とは、搬送ローラで狭持される部分の幅方向の内側の縁から、ガラスリボンの幅の6%以内の長さ分、幅方向内側に入った範囲までに含まれる領域をいう。
ガラスリボンの温度とは、後述するように、ガラスリボンに温度分布がある場合、ガラスリボンの周りの雰囲気温度から換算される値であり、例えば、雰囲気温度に-25~-5℃の範囲で定められた温度を加算した温度をいう。
図1は、本実施形態のガラス板の製造方法のフローの一例を説明する図である。ガラス板の製造方法は、熔解工程(ステップS10)と、清澄工程(ステップS20)と、攪拌工程(ステップS30)と、成形工程(ステップS40)と、徐冷工程(ステップS50)と、採板工程(ステップS60)と、形状加工工程(ステップS70)と、を主に有する。
次に、清澄工程が行われる(ステップS20)。清澄工程では、溶融ガラスが図示されない液槽に貯留された状態で、例えば、熔解工程での加熱時よりも溶融ガラスの温度を上昇させることで、溶融ガラス中の気泡の脱泡が促進される。これにより、最終的に得られるガラス板中の気泡含有率を低減することができ、歩留まりを向上させることができる。
清澄工程は、他の方法によって行われてよく、例えば、溶融ガラスが液槽に貯留された状態で、溶融ガラス中の気泡が清澄剤を用いて取り除かれてもよい。清澄剤としては、特に制限されず、例えば、酸化スズ、酸化鉄等の金属酸化物が用いられる。この場合の清澄工程は、具体的には、溶融ガラス中で価数変動する金属酸化物の酸化還元反応によって行われる。高温時の溶融ガラスにおいて、金属酸化物は還元反応により酸素を放出し、この酸素がガスとなって、溶融ガラス中の気泡を成長させて液面に浮上させる。これにより、溶融ガラス中の気泡は脱泡される。あるいは、酸素ガスの気泡は、溶融ガラス中の他の気泡中のガスを取り込んで成長し、溶融ガラスの液面に浮上する。これにより、溶融ガラス中の気泡は脱泡される。さらに、金属酸化物は、溶融ガラスの温度が低下すると、酸化反応により溶融ガラス中に残存した酸素を吸収し、溶融ガラス中の気泡を減少させる。
次に、攪拌工程が行われる(ステップS30)。攪拌工程では、ガラスの化学的および熱的均一性を保つために、攪拌装置により、溶融ガラスが機械的に攪拌される。これによって、脈理等のガラスの不均一性を抑制することができる。
成形工程では、形成されたガラスリボンの耳部(幅方向の両端部)を冷却する。より詳細には、両端部に向かって張力を加えながらガラスリボンの耳部(幅方向の両端部)の粘度についてlogη=9以上となるまでガラスリボンの耳部(幅方向の両端部)を冷却することができる。このとき、ガラスリボンの耳部(幅方向の両端部)の冷却速度は、ガラスリボンの幅方向の中央部の冷却速度よりも速い。なお、ガラスリボンの温度制御は、例えば、冷却ローラ、ガラスリボンの幅方向の両端部の近傍に設けられた風冷管などの冷却手段や、ガラスリボンの幅方向及び搬送方向に複数設けられたヒータなどの加熱手段を制御することにより実現することができる。
より詳細には、徐冷工程では、ガラスリボンの温度プロファイルを幅方向で一山の分布とし、その後一山の分布が搬送方向下流側に進むにつれて徐々に小さくなるように、ガラスリボンの周りに配置されるヒータ等の制御を行ってもよい。その際、ガラスリボンの歪点近傍の温度領域において、一山の分布が平坦な直線状の分布、すなわち幅方向の温度分布が一定となるように、図示されないヒータ等の制御を行うことができる。言い換えると、ガラスリボンの徐冷点に150℃を足した温度から歪点までの温度領域において、ガラスリボンの幅方向における中央部の冷却速度を、ガラスリボン幅方向の両端部の冷却速度よりも速くし、ガラスリボンの幅方向における中央部の温度が両端部よりも高い状態から歪点近傍の温度領域で同じになるように、温度プロファイルが一定になるようにしてもよい。
さらに、ガラスリボンの温度が徐冷点から(歪点-50℃)となる温度において、他の温度域に比べてゆっくりガラスリボンを徐冷してもよい。これにより、ガラスリボンの熱収縮率を低減することができる。
さらに、ガラスリボンの温度が、歪点から、歪点から200℃引いた温度になる温度領域において、ガラスリボンの温度プロファイルを幅方向に沿って谷になり、その谷の深さが搬送方向下流側に進むにつれて大きくなるように、すなわち、中央部の温度が両端部に比べて次第に低くなるように、図示されないヒータ等の制御を行ってもよい。このように、温度プロファイルにおいて徐々に谷を深くすることで、ガラスエッジに常にコンプレッションが加えることができるので、ガラスリボンが割れてしまうことを抑制できる。
ここで、搬送ローラの周速度は、ガラス板の生産性を向上させる観点からは、速いことが好ましい。具体的に、搬送ローラの周速度は、150m/時よりも速いことが好ましく、200m/時以上であることが好ましく、例えば、220m/時以上、240m/時以上、250m/時以上、270m/時以上、300m/時以上、340m/時以上であってもよい。また、ガラスリボンの板厚は、薄いほど搬送ローラ対で挟持される部分の内側の保有熱が小さくなるので、0.5mm以下であるとより本発明に好適となり、例えば、0.4mm以下であるとさらに本発明に好適となり、0.3mm以下であるとさらに本発明に好適となり、0.25mm以下であるとさらに本発明に好適となる。言い換えると、0.01~0.5mmであるとより本発明に好適となり、例えば、0.01~0.4mmであるとさらに本発明に好適となり、0.01~0.3mmであるとさらに本発明に好適となり、0.01~0.25mmであるとさらに本発明に好適となる。なお、搬送ローラの周速度は、上記のものに限定されるものではなく、例えば、溶融ガラスが1日に後述する成形体に流入される量が6t未満である場合は、あるいは、溶融ガラスが1日に成形体に流入される量が6t以上である場合であっても製造するガラスの幅方向の大きさによっては、200m/時以下となることもある。溶融ガラスが1日に成形体に流入される量は、2t以上であってもよく、6t以上、10t以上、16t以上、20t以上であってもよい。なお、溶融ガラスが1日に成形体に流入される量(MG量)は、ガラス板の生産性を向上させる観点から、多いほど好ましい。
徐冷工程の後、採板工程が行われる(ステップS60)。具体的に、連続的に生成されるガラスリボンは一定の長さ毎に切断され、ガラス板が採板される。
この後、形状加工工程が行われる(ステップS70)。形状加工工程では、所定のガラス板のサイズや形状に切り出す他、ガラス端面の研削・研磨が行われる。形状加工は、カッターやレーザを用いた物理的手段を用いても、エッチングなどの化学的手段を用いてもよい。
ガラス板の製造方法は、この他に、洗浄工程及び検査工程を有するが、これらの工程の説明は省略する。なお、清澄工程及び攪拌工程はそれぞれ省略できる。
図2及び図3は、本発明の第1実施形態であるガラス板製造装置1の概略構成図である。本実施形態のガラス板製造装置1およびガラス板製造装置1を用いたガラス板の製造方法は、液晶表示装置あるいは有機EL表示装置等のフラットパネルディスプレイのガラス基板や携帯端末器の表示面のカバーガラスの製造に好適に適用される。これは、液晶表示装置あるいは有機EL表示装置等は近年、高精度、高画質が要求されており、それに使用されるガラス基板には波形状変形が0.2mm以下であることが要求されているためである。また、カバーガラスは、装置の表示面などに適用されることから、それに使用されるガラス基板には極めて高い平滑性が要求されているためである。
ガラス板製造装置1は、ダウンドロー法を用いて溶融ガラスAからガラス板Cを製造する。ガラス板製造装置1は、上下方向の3箇所に配された断熱板21,22,23によって間仕切りされてなる、炉室11、第1の徐冷炉12、第2の徐冷炉13、図示しない採板室を有している。断熱板21~23は、セラミックファイバ等の断熱材からなる板状部材である。断熱板21~23には、後述するガラスリボンBが下方に向かって通過するように、それぞれ搬送孔16が形成されている。断熱板21~23はそれぞれ、図2において、理解の容易さのため、後述する炉壁15に接する水平方向の2個所を除いて図示を省略しているが、ガラスリボンBに対し紙面前面側及び背面側において、水平方向の2個所同士は一体に繋がっている。なお、図2及び図3では、断熱板により3箇所で間仕切りがされている例が示されているが、断熱板の個数及び設置位置は特に限定されず、断熱板は1以上設けられていればよい。なお、断熱板の数が多いほど、独立して雰囲気温度を制御できる空間が多くなり、徐冷条件の調整が容易になるので、後述する徐冷装置3には、断熱板が複数設けられ、複数の空間に間仕切りされていることが好ましい。言い換えると、徐冷炉は1以上設けられていてればよいが、3以上設けられていることがさらに好ましい。
成形装置2は、溶融ガラスAからダウンドロー法を用いてガラスリボンBを成形する装置である。成形装置2は、耐火物レンガやブロック状の電鋳柱耐火物等により組み立てられた炉壁15で囲まれた炉室11を有している。炉室11内には、成形体10と、ローラ対17とが設けられている。成形体10は、上方に向かって開放された溝10aを含み(図3参照)、溝10a内を溶融ガラスAが流れる。成形体10は、例えば煉瓦により構成されている。ローラ対17は、成形体10の下端で融合した溶融ガラスAの幅方向両側の端部(幅方向の両端部)に対応する位置にそれぞれ1対設けられ、溶融ガラスAを狭持し下方に向けて搬送する。なお、図2中紙面内の左右方向及び図3中の紙面に垂直方向が、ガラスリボンBの幅方向である。図2及び図3中紙面内の上下方向が、ガラスリボンBの搬送方向である。なお、図2及び図3では、成形体10とローラ対17が、間仕切りされずに設置されているが、徐冷条件の調整(雰囲気温度調整)を容易にするため、これらの間に断熱板を設けて間仕切りしてもよい。また、ローラ対17は、搬送方向に2対以上設置されても良い。
徐冷装置3は、ガラスリボンBを複数の搬送ローラ対18,19で挟持しつつ下方に向けて引き抜きながら徐冷する。徐冷装置3は、炉室11の下方に隣接して設けられた第1の徐冷炉12及び第2の徐冷炉13を有している。第1の徐冷炉12及び第2の徐冷炉13は、炉室11をも構成する上述の炉壁15で囲まれてなる。徐冷装置3は、第1の徐冷炉12及び第2の徐冷炉13内に、ガラスリボンBの搬送方向に沿って配された、後述するコンピュータに自動制御される加熱手段が設けられている。加熱手段は、特に制限されず、例えば電気ヒータが用いられる。第1の徐冷炉12及び第2の徐冷炉13内のガラスリボンBの周りの雰囲気温度は、加熱手段で加熱されることにより、ガラスリボンBに反りや歪が発生しないように、ガラスリボンBの幅方向及び搬送方向の温度分布が後述するような分布を持つように温度制御されている。第1の徐冷炉12及び第2の徐冷炉13内には、加熱手段で加熱されることにより、ガラスリボンBの搬送方向上流側から順に、ガラスリボンBがそれぞれ、軟化点SPとなる点、ガラス転移点Tgとなる点、徐冷点APとなる点、歪点StPとなる点が生じる。軟化点SPとは、ガラスの粘度が107.6dPa・sの温度を示す。また、徐冷点APとは、ガラスの粘度が1013dPa・sの温度を示している。歪点StPとは、ガラスの粘度が1014.5dPa・sの温度を示している。なお、図2及び図3において、ガラスリボンBの温度がこれらの点SP,Tg,AP,StPの温度となるガラスリボンBの位置は、破線の各引き出し線を水平方向に延長したときにガラスリボンBと交わる点で表される。なお、徐冷炉12,13内の搬送ローラ対18,19の設置数に制約は無く、少なくとも1以上設けられていればよい。
さらに、徐冷装置3は、検出制御部30と、駆動部32とを有している(図4参照)。
すなわち、成形体の下端で熔融ガラスAを張り合わせてガラスリボンBを形成した後に、ガラスリボンBの幅方向の両端部(耳部)の粘度をηとしたときlogη=9以上、好ましくはlogη=9以上14.5以下となるまで両端部が冷却され、かつ、両端部の冷却速度がガラスリボンBの幅方向の中央部の冷却速度よりも速くなるように、温度制御される。
駆動部32は、後述する記憶部36に記憶された搬送ローラ18a,19aの周速度に基づいて、搬送ローラ18a,19aを回転駆動させる。駆動部32は、各搬送ローラ対18,19に対応して設けられた、図示されないモータを有している。なお、モータは、各搬送ローラ対18,19に対応して設けられていなくてもよく、その数は、例えば、各搬送ローラ対18,19の数より少なくてもよい。この場合、複数の搬送ローラ18a,19aが1台のモータで駆動されるように、各搬送ローラ18a,19a間で速度比を変更できるギアを備えたものを用いることができる。この場合、モータからの駆動力は、例えば、ユニバーサルジョイントなどを介して搬送ローラ18a,19aに伝達される。
ここで、検出制御部30について、より詳細に説明する。
温度センサ34は、第1の徐冷炉12及び第2の徐冷炉13内での配置位置における雰囲気温度をそれぞれ検出する。
温度領域Dにおいて、最も上流側の搬送ローラ18aの周速度と、上流側から2番目の搬送ローラ18aの周速度は、同一又は異なってよく、特に異なっているのが好ましい。異なる場合は、上流側から2番目の搬送ローラ18aの周速度が、最も上流側の搬送ローラ18aの周速度より速いことが好ましい。また、温度領域Eにおいて、下流側から3つの搬送ローラ19aの周速度は、全て同一、一部同一又は全て異なってよく、特に全て異なっているのが好ましい。全て異なる場合は、最も下流側の搬送ローラ19aの周速度が最も速く、下流側から3番目の搬送ローラ19aの周速度が最も遅いことが好ましい。
搬送ローラ対18,19のうち、ガラスリボンの搬送ローラで狭持される部分に対してガラスリボンの幅方向内側に隣接する隣接領域の温度がガラス徐冷点APとなる位置よりも下流側に設けられた搬送ローラ対の搬送ローラの周速度を、搬送ローラ対18,19のうち、隣接領域の温度がガラス転移点Tg以上軟化点SP以下となる温度領域に設けられた搬送ローラ対18の搬送ローラ18aの周速度よりも速くすることが、引っ張り応力を働かせる点で好ましい。
また、図示されないコンピュータは、温度センサ34で検出された雰囲気温度に基づいて、徐冷炉12,13内の雰囲気温度がそれぞれ所定の温度範囲内で維持されるよう、徐冷炉12,13内の加熱手段を自動制御する。第1の徐冷炉12の所定の温度範囲は、例えば、500~800度に設定されている。第2の徐冷炉13の所定の温度範囲は、例えば、200~500度に設定されている。
従来のように、図7に示す搬送ローラ対18,19に挟持される領域が冷却されてガラスが収縮する場合、図7において符号Sで示す領域(隣接領域)には、圧縮応力が働く。この時、搬送ローラの近傍でかつ搬送ローラより幅方向内側の隣接領域のガラス温度が軟化点(粘度ηがlogη=7.65となる温度)より高温である場合には、搬送ローラ対18,19に狭持される領域よりも幅方向内側であって搬送ローラ近傍の領域である隣接領域に働く圧縮応力が瞬時に緩和されるため、波形状の塑性変形は生じ難い。他方、同じ隣接領域のガラス温度がガラス転移点よりも低温である場合には、粘度が十分に上昇しているため、波形状の塑性変形は生じ難い。
しかしながら、ガラスリボンの上記隣接領域に塑性変形が生じるのは、上述の通り、限られたガラスリボンの温度領域における現象であり、適切な温度領域の搬送ローラ間で周速度差をつけることが必要である。このため、特許文献2のように単に上流に対し、下流の搬送ローラの周速度を速くしても、効果が出ないばかりか、ガラスリボンに塑性変形が生じたり、板厚が0.5mm以下のガラス板を製造する場合に、例えば、実施例[0045]に記載されるような周速度差をつけると、ガラスリボンが割れるおそれがある。
本実施形態では、具体的に、ガラスリボンBに対して搬送方向に引っ張り応力を働かせるために、ガラスリボンBの温度がガラス徐冷点AP以下となる温度領域に設けられた搬送ローラ対19の搬送ローラ19aの周速度が、ガラスリボンBの温度がガラス転移点Tg以上軟化点SP以下となる温度領域Dに設けられた搬送ローラ18aの周速度よりも速くなるように、搬送ローラ18a,19aの回転駆動が制御される。
次に、本発明の第2実施形態であるガラス板製造装置について説明する。
ここでは、上述の第1実施形態との相違に注目して説明する。
第2実施形態では、検出制御部40のコンピュータは、周速度決定部48として機能するほか、図5に示すように、搬送ローラ状態検出部(以下、単に検出部ともいう)47のうち温度センサ44を除く部分としてさらに機能する。図5は、搬送ローラ対18,19の回転駆動を制御する制御系の構成を説明するブロック図である。図5において、第1実施形態で参照した符号と同じ符号で示す要素は、第1実施形態で説明した要素と同じである。検出部47は、温度センサ44と接続されている。温度センサ44は、搬送ローラ18a,19aの温度を検出する。ここで、搬送ローラ18a,19aの温度を検出することには、搬送ローラ18a,19aの温度を算出することも含まれる。この場合は、各温度センサ44により検出された雰囲気温度における、記憶部46に記憶された温度差データが参照されて、搬送ローラ18a,19aの温度が算出される。検出部47は、検出された搬送ローラ18a,19aの温度に基づいて、後述するように、搬送ローラ18a,19aの熱膨張量を直径の変化として算出する。
記憶部46には、また、周速度決定部48で決定された各搬送ローラ18a,19aの回転速度、複数の搬送ローラ対18,19間で設定された基準となる周速度分布、各搬送ローラ18a,19aの直径の基準値がさらに記憶される。各搬送ローラ18a,19aの直径の基準値は、それぞれ常温(例えば、25度)での新品時の直径である。また、記憶部46は、基準となる周速度分布を達成するときの条件(搬送ローラの温度、ガラスリボンBの温度、ガラスリボンの熱膨張係数、ガラスリボンBの厚さ、幅、ガラスリボンの流量等)を記憶する。
複数の搬送ローラ対18,19間の周速度比は、例えば、最上流側の搬送ローラ18aの周速度を基準として、その直ぐ下流側の搬送ローラ18aから順に、最上流側の搬送ローラ18aの周速度の0.1%ずつ周速度が速くなるよう設定される。本実施形態で、最下流側の搬送ローラ19aの周速度は、最上流側の搬送ローラ18aの100.6%である。このような周速度比に従って複数の搬送ローラ対18,19が制御されることで、ガラスリボンBが搬送ローラ対18,19の上方で変形することなく、かつ、ガラスリボンBの表面に微細なキズが生じるのを抑えることができる。この場合、周速度比から設定される周速度は、最上流側の搬送ローラ18aの周速度を用いて値が設定される。このように基準として設定される周速度比は、従来ガラスリボンBがキズや形状変形の問題が生じることなく徐冷されたときの周速度比である。この基準となる周速度分布は、ガラスリボンBの温度、熱膨張係数、厚み、幅、ガラス流量等の条件とともに、周速度決定部48に記憶保持されている。この周速度比は、後述するように、ガラスリボンBの温度が変化するなどの徐冷時の条件が変化する場合に、基準となる周速度分布が修正されて設定される。
具体的には、基準の周速度分布として設定される周速度比には、そのときの条件として各搬送ローラ対18,19における基準となる温度が設定されている。したがって、この基準となる温度に対して現在のガラスリボンBの温度が変化した場合、例えば、温度T1がT2に変化した場合、T2とT1の温度差における熱膨張率の差を用いて、周速度決定部48は基準の周速度分布として設定されている周速度比を修正する。ガラスリボンBの搬送速度は、ガラスリボンBの温度と熱膨張係数によって定まる熱膨張率によって変化するからである。この場合、ガラスリボンBの種類によって熱膨張係数は異なるので、ガラスリボンBの熱膨張係数と温度を考慮した熱膨張率の違いを用いてより一般的に周速度比を修正してもよい。このような周速度比は、ガラスリボンBの温度および熱膨張係数の温度依存性のほかに、ガラスリボンBの厚み、幅、ガラス流量等の条件の変化によっても修正されて設定される。したがって、ガラスリボンBの温度、熱膨張係数の温度依存性の特性、厚み、幅、ガラス流量等の基準の周速度比における条件は、周速度決定部48に予め記憶保持されている。ガラス熱膨張係数は、溶融ガラスの組成から決定される。設定された周速度比から、最上流側の搬送ローラ対の現在の周速度を基準として、下流側の各搬送ローラ対の周速度が算出される。
このように、周速度比をガラスリボンBの温度を含む状態の変化に応じて修正することにより、より適切な搬送ローラ18a,19aの回転速度を決定できる。
周速度決定部48は、算出したあるいはオペレータにより入力された各搬送ローラ18a,19aの周速度に基づいて、下記式に従って各搬送ローラ18a,19aの回転速度を決定する。
回転速度=周速度/(熱膨張した搬送ローラの直径×π)
ここで、徐冷炉12,13内の各搬送ローラ対18,19の配置位置において検出された雰囲気温度が、上述した基準となる周速度比における搬送ローラ対18,19の温度に対して変化していた場合は、上述の周速度比を保つように、搬送ローラ18a,19aの回転速度を決定する。
具体的に、検出部47は、温度センサ44により検知された温度が変化していた搬送ローラ18a,19aについて、搬送ローラ18a,19aの温度におけるローラ熱膨張係数と、各搬送ローラ18a,19aの直径の基準値とを参照し、下記式に従ってこの搬送ローラ18aの膨張量(直径の変化量)を算出する。
dD=β・D・ΔT
dD:膨張量
β:熱膨張係数
D:搬送ローラの直径の基準値
ΔT:基準の周速度比において設定される搬送ローラの温度との温度差
新たな回転速度=(周速度+周速度の変化量)/((搬送ローラの直径+搬送ローラの直径の変化量)×π)
周速度比は、上述のものに制限されない。また、周速度決定部48は、周速度分布として、周速度比に代えて、各搬送ローラ18a,19aの具体的な周速度を算出してもよい。この場合、基準となる周速度分布および修正後の周速度も具体的な速度の値として設定される。
第2実施形態では、搬送ローラの直径の温度に応じて、設定された周速度分布に成るように回転速度を調整する他、周速度分布をガラスリボンの温度に応じて基準となる周速度分布を修正して設定する。しかし、基準となる周速度分布をガラスリボンの現在の温度に応じて修正しなくてもよい。しかし、表面品質に優れたガラス板を製造する点で、基準となる周速度分布をガラスリボンの現在の温度に応じて修正することが好ましい。
また、ガラスリボンBを搬送するために用いる複数の搬送ローラ対18,19の周速度分布をガラスリボンBの温度に応じて修正して設定するので、ガラスリボンBが余り、ガラスリボンBが変形してしまうのを防ぐことができ、また、必要以上に速くなることで、ガラスリボンBが引っ張られ、ガラスリボンBが割れるのを防ぐことができる。このような効果は、ガラスの搬送速度が速く、且つ、ガラスリボンBの強度が小さくて変形し易い厚さ0.5mm以下の薄板ガラスの製造において、より顕著である。
上述の例では、温度センサにおいて、徐冷炉12,13内の雰囲気温度が検出され、これを用いて搬送ローラ温度が算出されたが、搬送ローラ温度は直接測定されてもよい。そのために、例えば、搬送ローラ状態検出部として、搬送ローラの温度を連続的に測定するための温度計が用いられてよい。
次に、本発明の第3実施形態であるガラス板製造装置について説明する。
ここでは、上述の第1及び第2実施形態との相違に注目して説明する。
第2実施形態では、搬送ローラ状態検出部47として、搬送ローラ18a,19aの温度を検出する温度センサ44及びコンピュータが用いられたが、ここでは、図6に示すように、搬送ローラ状態検出部(以下、単に検出部ともいう)57として、搬送ローラ18a,19aの磨耗量を検出するための距離測定センサ54及び図示しないコンピュータが用いられる。なお、図6は、搬送ローラ対18,19の回転駆動を制御する制御系の構成を説明するブロック図である。図6において、第1及び第2実施形態で参照した符号と同じ符号で示す要素は、第1及び第2実施形態で説明した要素と同じである。検出部57は、距離測定センサ54と接続されている。
ローラ半径=(駆動用シャフト間隔-ガラスリボン厚み)/2
なお、第3実施形態では、搬送ローラ18a,19aの径変化として、磨耗の状態に基いて算出された半径の変化を用いるが、この磨耗の状態を第2実施形態で用いた搬送ローラ18a,19aの温度とともに統合して適用することもできる。この場合、搬送ローラ18a,19aの径は、磨耗量によって変化すると共に、熱膨張により変化する。この径を用いて、径の変化に伴って変化した搬送ローラ18a,19aの周速度が周速度比に維持されるように、搬送ローラ18a,19aの回転速度を算出することができる。
さらに、搬送ローラ18a,19aの径変化に加え、ガラスリボンの状態として、ガラスリボンBの熱膨張に起因しガラスリボンBの温度に応じて変化するガラスリボンBの搬送速度変化を統合して適用することもできる。
なお、このガラス板製造装置において、距離測定センサ54は、搬送ローラ対18,19の駆動用シャフト18b,19b同士の距離に代えて、搬送ローラ対18,19の駆動用シャフト18b,19bの原点位置からのずれを読み取って、磨耗量を検出するように構成されてもよい。原点位置は、搬送ローラ18a,19aの新品時に駆動用シャフト18b,19bが位置する中心位置であり、記憶部56において記憶される。搬送ローラ対18,19の駆動用シャフト18b,19bの原点位置からのずれを用いて、搬送ローラ18a,19aの磨耗量を検出し、これによって磨耗した搬送ローラのローラ径は算出され得る。なお、搬送ローラ18a,19aの径は、検出部57が算出することに限定されず、例えば、磨耗量に基づいてオペレータが算出してもよい。この場合、オペレータにより算出され、周速度決定部58に入力された搬送ローラ18a,19aの径に基づいて、周速度決定部58により搬送ローラ18a,19aの回転速度が算出される。あるいは、オペレータが算出した搬送ローラ18a,19aの径に基づいてさらに搬送ローラ18a,19aの回転速度を算出し、この算出結果を周速度決定部58に入力してもよい。周速度決定部58において算出されあるいは入力された回転速度は、周速度決定部58により決定され、駆動部32に伝達される。また、搬送ローラ18a,19aの磨耗量、原点位置は、オペレータが算出してもよく、算出された値は記憶部56に記憶されてよい。
一般に、ローラ対17の各ローラの周速度は、ガラス板の厚み分布やガラス表面の凹凸が最も小さくなるように適切な値に設定しているので、その値からずれることは、ガラス板の厚み分布やガラス表面の凹凸を悪化させることになる。
すなわち、ローラ対17の周速度が変化すると、成形体の下端からローラ対17の間で行われるガラスリボンBの引伸ばしの量と、ローラ対17から搬送ローラ対18の間で行われるガラスリボンBの引伸ばしの量が変ることにより、(成形体の下端~ローラ対17間でのガラスリボンBの幅方向の温度分布と、ローラ対17~搬送ローラ対18,19でのガラスリボンの幅方向の温度分布の形態が異なるため)製造されたガラス板の幅方向の厚み分布やガラス表面の凹凸の大きさが変化してしまう。このため、ローラ対17の各ローラの径変化を補償するように、ローラ対17の各ローラの回転速度が決定されることが好ましい。
すなわち、冷却ローラや搬送ローラの径変化を補償するようにローラの回転速度を決定することは、全てのローラ(冷却ローラ、搬送ローラ)で行われる必要はなく、効果的なローラのみに対して行ってもよい。
ガラスが軟化点SP以上であるとガラスリボンBは粘度が低く、スリップは生じ難い。他方、軟化点SP以下のガラスリボンBではスリップが生じやすくなる。このため、ガラスリボンBの中央部が軟化点SP以下の領域に設けられた搬送ローラの径変化を補償するように搬送ローラの回転速度を決定することが好ましい。
また、ガラスリボンBの中央部の温度がガラス転移点Tg以上軟化点SP以下となる温度領域に設けた搬送ローラは、径変化が生じやいため、この領域に設けた搬送ローラの径変化を補償するように搬送ローラの回転速度を決定することが好ましい。
ガラス温度が軟化点SPより高温である場合には、ガラスに働く圧縮応力が瞬時に緩和されるため、ガラスリボンBに波形状の塑性変形は生じ難い。他方、ガラス温度がガラス転移点Tgよりも低温である場合には、ガラスリボンBの粘度が十分に上昇しているため、波形状の塑性変形は生じ難い。
また、上流側の搬送ローラほど磨耗や熱膨張によるローラ径変化が生じやすい。つまり、少なくとも温度がガラス転移点Tg以上軟化点SP以下となる温度領域に設けた搬送ローラの径変化を補償するように搬送ローラの回転速度を決定することが好ましい。
第3実施形態のガラス板製造装置の搬送ローラ状態検出部57には、距離測定センサ54の代わりに、搬送ローラ18a,19aの使用日数に基づいて算出される搬送ローラ18a,19a直径の変化を搬送ローラ18a,19aの径変化としてカウントする装置が用いられてもよい。例えば、この径変化をカウントする装置は、搬送ローラ18a,19aの使用日数を周速度決定部58に送る。周速度決定部58は、周速度決定部58の記憶部56に記憶された、各搬送ローラ18a,19aについて過去の交換実績として、過去に交換した時のローラ直径のその新品時からの磨耗量と交換までの使用日数とを参照し、これらに基づいて1日あたりの磨耗量を算出する。次いで、記憶部56に記憶された新品時のローラ直径が参照され、下記式に従ってローラ直径が算出される。このとき、上記径変化をカウントする装置から送られた使用日数を用いて下記式に示すように、1日当りの磨耗量×使用日数の積が、搬送ローラ18a,19aの磨耗量に相当するとして検出される。
ローラ直径=新品時の直径-(1日当りの磨耗量×使用日数)
周速度決定部58は、記憶部56において、各搬送ローラ18a,19aについて過去の交換実績、新品時のローラ直径を記憶する。
この変形例によれば、より簡単な方法で、搬送ローラ18a,19aの直径の変化により生じた搬送ローラ18a,19aの周速度の周速度比からのずれを補償することができる。なお、1日あたりの磨耗量は、オペレータが算出して記憶部56に記憶させることもできる。また、上記磨耗量による搬送ローラ18a,19aの直径変化も、オペレータが算出して、検出制御部50あるいは駆動部32に伝達されるようにしてもよい。さらに、過去に交換した時のローラ直径のその新品時からの磨耗量、交換までの使用日数は、オペレータによって算出されてもよく、算出された値は記憶部56に記憶されてよい。
液相粘度が150000dPa・s以下と小さい液晶ディスプレイや有機ELディスプレイなどのフラットパネルディスプレイ用ガラス板は、成形工程時に失透が生じやすい状態にある。このため、成形工程時の溶融ガラスの温度を高温にする必要があり、上記塑性変形の問題が顕著となる。このため、液相粘度が150000dPa・s以下のガラスを用いたガラス板の製造に本発明が好適となり、35000~150000dPaのガラスを用いたガラス板の製造に本発明の製造方法がより好適となる。50000~100000dPa・sのガラスを用いたガラス板の製造に本発明の製造方法がさらに好適となり、50000~80000dPa・sを用いたガラスのガラス板の製造に本発明の製造方法が一層好適となる。
本実施形態のガラス板製造方法及びガラス板製造装置で製造されるガラス板は、例えば液晶ディスプレイ用ガラス基板が好適に挙げられる。
液晶ディスプレイ用ガラス基板のガラス組成は、以下のガラス組成が例示される。
SiO2 50~70質量%、
B2O3 0~15質量%、
Al2O3 5~25質量%、
MgO 0~10質量%、
CaO 0~20質量%、
SrO 0~20質量%、
BaO 0~10質量%、
RO 5~20質量% (但し、RはMg、Ca,Sr及びBaから選ばれる、ガラス板に含有される全成分であって、少なくとも1種である)、
を含有することが好ましい。
さらに、液晶ディスプレイ用ガラス基板に形成されるTFT(Thin Film Transistor)の破壊を抑制する観点からは、無アルカリガラス(アルカリ成分を実質的に含まないガラス)であることが好ましい。他方、溶融ガラスの熔解性及び清澄性を向上させるために、あえてアルカリ成分を微量含有させるようにしてもよい。この場合、R’2O 0.05質量%を超え2.0質量%以下、より好ましくはR’2O 0.1質量%を超え2.0質量%以下(但し、R’はLi、Na及びKから選ばれる、ガラス板に含有される全成分であって、少なくとも1種である)を含むことが好ましい。
本発明の効果を調べるために、従来のガラス板製造装置と本実施形態のガラス板製造装置とを用いて、それぞれ下記方法に従ってガラスリボンを製造して、ガラスリボンに生じる波状の変形を測定した。なお、用いたガラス板製造装置は、いずれも、図3及び図4に示すダウンドロー法によるガラス板製造装置1であり、ガラスは下記に示す成分を含有するアルミノシリケートガラスを用いた。
SiO2 60質量%
Al2O3 19.5質量%
B2O3 10質量%
CaO 5質量%
SrO 5質量%
SnO2 0.5質量%
また、実施例2として、上述の第2実施形態に従って、周速度分布を保つように各搬送ローラ18a,19aの周速度を決定し、決定された搬送ローラの周速度に基づいて、搬送ローラ18a,19aを回転駆動させた点を除いて、実施例1と同様の条件で、0.5mm厚の液晶ディスプレイ用ガラス基板を作製した。
また、比較例2として、全ての搬送ローラ18a,19aの周速度を同じにした点を除いて、実施例3と同様の条件で、0.7mm厚の液晶ディスプレイ用ガラス基板を作製した。
得られた実施例1~3、比較例1~2の液晶ディスプレイ用ガラス基板について、液晶ディスプレイ用ガラス基板の隣接領域に生じた波形状の変形(板厚方向の凹凸)をシックネスゲージを用いて計測した。この結果、実施例1では、波形状の変形(凹凸の高さ)は0.05mm以下であった。実施例2では、波形状の変形は0.04mm以下であった。実施例3では、波形状の変形が0.05mmであった。比較例1では、波形状の変形が0.4mmであった。比較例2では、波形状の変形が0.25mmであった。
なお、波形状の変形は、厚み0.5mmおよび厚み0.7mmの液晶ディスプレイ用ガラス基板においては、厚み方向に0.2mm以内のものを表面品質を満たしているとした。
これに対し、本実施形態の製造装置1を用いて得られた実施例1~3の液晶ディスプレイ用ガラス基板は、波形状の変形による段差が0.05mm以下であり、上述の表面品質を満たしていた。実施例1の波形状の凹凸の高さは1/8に改善された。実施例2の波形状の凹凸の高さは、1/10に改善された。実施例3の波形状の凹凸の高さは、1/5に改善された。
2 成形装置
3 徐冷装置
18,19 搬送ローラ対
18a,19a 搬送ローラ
30,40,50 検出制御部
32 駆動部
34,44 温度センサ
47,57 搬送ローラ状態検出部
38,48,58 周速度決定部
54 距離測定センサ
A 溶融ガラス
B ガラスリボン
C ガラス板
D ガラスリボンの温度がガラス転移点以上軟化点以下となる温度領域
E ガラスリボンの温度が徐冷点以下となる温度領域
SP 軟化点
Tg ガラス転移点
AP 徐冷点
S10 熔解工程
S40 成形工程
S50 徐冷工程
Claims (14)
- ガラス原料を熔解して溶融ガラスをつくる熔解工程と、
溶融ガラスを、オーバーフローダウンドロー法を用いて成形し、ガラスリボンを形成する成形工程と、
前記ガラスリボンの幅方向の両端部に対して前記幅方向に隣接する近傍領域を、前記ガラスリボンの搬送方向に設けられた複数の搬送ローラ対で挟持しつつ、前記ガラスリボンを下方向に引き抜いて徐冷を行う徐冷工程と、を有し、
前記成形工程では、成形体からオーバーフローさせて前記成形体の側壁を流下する溶融ガラスを、前記成形体の下端で張り合わせることで前記ガラスリボンを形成した後に、前記ガラスリボンの幅方向の前記両端部を前記ガラスリボンの幅方向の中央部よりも速く冷却し、
前記徐冷工程では、前記ガラスリボンに塑性変形が生じないように、前記ガラスリボンの温度がガラス転移点以上ガラス軟化点以下となる温度領域において、前記ガラスリボンに対して前記搬送方向に張力を働かせる、ことを特徴とするガラス板の製造方法。 - 前記徐冷工程では、前記搬送ローラ対のうち、前記ガラスリボンの温度がガラス徐冷点となる位置よりも下流側に設けられた搬送ローラ対の搬送ローラの周速度を、前記搬送ローラ対のうち、前記ガラスリボンの温度がガラス転移点以上ガラス軟化点以下となる温度領域に設けられた搬送ローラ対の搬送ローラの周速度よりも速くする、請求項1に記載のガラス板の製造方法。
- 前記ガラス板は、板厚0.5mm以下である、請求項1または2に記載のガラス板の製造方法。
- 前記徐冷工程では、前記搬送ローラで狭持される部分に対して前記ガラスリボンの幅方向内側に隣接する隣接領域に塑性変形が生じないように、前記隣接領域の温度がガラス転移点以上ガラス軟化点以下となる温度領域において、前記ガラスリボンに対して搬送方向の張力を働かせる、請求項1~3のいずれか1項に記載のガラス板の製造方法。
- 前記徐冷工程では、前記搬送ローラ対のうち、前記ガラスリボンの搬送ローラで狭持される部分に対して前記ガラスリボンの幅方向内側に隣接する隣接領域の温度がガラス徐冷点となる位置よりも下流側に設けられた搬送ローラ対の搬送ローラの周速度を、前記搬送ローラ対のうち、前記隣接領域の温度がガラス転移点以上ガラス軟化点以下となる温度領域に設けられた搬送ローラ対の搬送ローラの周速度よりも速くする、請求項1~4のいずれか1項に記載のガラス板の製造方法。
- 前記成形体の下端で前記熔融ガラスを張り合わせてガラスリボンを形成した後に、前記ガラスリボンの幅方向の前記両端部の粘度をηとしたときlogη=9以上となるまで前記両端部が冷却され、かつ、前記両端部の冷却速度が前記ガラスリボンの幅方向の中央部の冷却速度よりも速い工程を含む、請求項1~5のいずれか1項に記載のガラス板の製造方法。
- 前記徐冷工程では、
前記ガラスリボンの幅方向の中央部において、ガラスリボンの搬送方向に張力が働くように、
少なくとも、前記ガラスリボンの幅方向の中央部の温度がガラス徐冷点に150℃を足した温度からガラス歪点から200℃引いた温度となる温度領域において、
前記ガラスリボンの幅方向の中央部の冷却速度が前記幅方向の両端部の冷却速度よりも速くなるように温度制御する、請求項1~6のいずれか1項に記載のガラス板の製造方法。 - 前記ガラスリボンの幅方向の中央部の温度がガラス軟化点以上の領域において、前記ガラスリボンの幅方向の両端部が前記両端部に挟まれた中央部の温度より低く、且つ、前記中央部の温度が均一になるように前記ガラスリボンの温度を制御し、
前記ガラスリボンの幅方向の中央部において、ガラスリボン搬送方向の張力が働くように前記ガラスリボンの前記中央部の温度がガラス軟化点未満ガラス歪点以上の領域において、前記ガラスリボンの幅方向の温度分布が前記中央部から前記両端部に向かって低くなるように前記ガラスリボンの温度を制御し、
前記ガラスリボンの前記中央部の温度がガラス歪点となる温度領域において、前記ガラスリボンの幅方向の前記両端部と前記中央部との温度勾配がなくなるよう前記ガラスリボンの温度を制御する、請求項1~7のいずれか1項に記載のガラス板の製造方法。 - 前記ガラスリボンの幅方向の中央部において、ガラスリボン搬送方向の張力が働くように前記ガラスリボンの前記中央部の温度がガラス歪点近傍未満の領域において、前記ガラスリボンの前記両端部から前記中央部に向かって低くなるように前記ガラスリボンの温度を制御する、請求項1~8のいずれか1項に記載のガラス板の製造方法。
- 前記徐冷工程では、前記搬送ローラ対のうち、前記ガラスリボンの温度がガラス徐冷点となる位置よりも下流側に設けられた搬送ローラ対の搬送ローラの周速度を、前記ガラスローラ対のうち、前記ガラスリボンの温度がガラス転移点以上ガラス軟化点以下となる温度領域に設けられた搬送ローラ対の搬送ローラの周速度よりも0.03~2%速くする、請求項1~9のいずれか1項に記載のガラス板の製造方法。
- 前記ガラス板の幅方向の長さが、1000mm以上である、請求項1~10のいずれか1項に記載のガラス板の製造方法。
- 前記徐冷工程は、200m/時以上の搬送速度で前記ガラスリボンを下方向に引き抜いて徐冷する、請求項1~11のいずれか1項に記載のガラス板の製造方法。
- ガラス原料を熔解して溶融ガラスをつくる熔解工程と、
溶融ガラスを、オーバーフローダウンドロー法を用いて成形し、ガラスリボンを形成する成形工程と、
前記ガラスリボンの幅方向の両端部に対して前記幅方向に隣接する近傍領域を、前記ガラスリボンの搬送方向に設けられた複数の搬送ローラ対で挟持しつつ、前記ガラスリボンを下方向に引き抜いて徐冷を行い、板厚0.5mm以下のガラスリボンを形成する徐冷工程と、を有し、
前記成形工程では、成形体からオーバーフローさせて前記成形体の側壁を流下する熔融ガラスを、前記成形体の下端で張り合わせることでガラスリボンを形成し、
前記徐冷工程では、前記搬送ローラ対のうち、前記ガラスリボンの温度が徐冷点となる位置よりも下流側に設けられた搬送ローラ対の搬送ローラの周速度を、前記搬送ローラ対のうち、前記ガラスリボンの温度がガラス転移点以上ガラス軟化点以下となる温度領域に設けられた搬送ローラ対の搬送ローラの周速度よりも速くする、ことを特徴とするガラス板の製造方法。 - ダウンドロー法を用いて溶融ガラスからガラスリボンを成形する成形装置と、
前記ガラスリボンの幅方向の両端部に対して前記幅方向に隣接する近傍領域を複数の搬送ローラ対で挟持しつつ、前記ガラスリボンを下方向に引き抜いて徐冷し、板厚0.5mm以下の前記ガラスリボンを形成する徐冷装置と、を有し、
前記徐冷装置は、前記複数の搬送ローラ対と、駆動部とを含み、
前記複数の搬送ローラ対の1つは、前記ガラスリボンの温度がガラス転移点以上ガラス軟化点以下となる第1温度領域に、前記複数の搬送ローラ対の他の1つは、前記ガラスリボンの温度がガラス徐冷点以下となる第2温度領域に設けられて、前記ガラスリボンを下方向に引き込むことで前記ガラスリボンを搬送し、
前記駆動部は、前記第2温度領域に設けられた搬送ローラ対の搬送ローラの周速度が、
前記第1温度領域に設けられた搬送ローラの周速度よりも速くなるように前記搬送ローラ
を回転駆動させる、ことを特徴とするガラス板製造装置。
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