A method for manufacturing glass plates that reduces overall thickness variation.

Abstract

A method for producing a glass sheet includes: (a) forming a glass ribbon in a vertical orientation that descends as a function of time, the glass ribbon having first and second major surfaces facing generally opposite directions and a core disposed between the first and second major surfaces; (b) passing the glass ribbon as it descends proximate a first heating zone that induces liquefaction at the first major surface while maintaining a temperature of the core below a softening temperature; and (c) slicing the glass sheet from the glass ribbon after it has moved below the first heating zone. Passing the glass ribbon proximate the first heating zone reduces overall thickness variation and surface defects such as surface roughness in the glass ribbon.

Description

Cross-reference of related applications

[0001] This application claims priority under Section 119 of U.S. Patent Act to U.S. Provisional Patent Application No. 63 / 127330 filed on 18 December 2020, and all disclosures of this provisional application are incorporated herein by reference and rely upon. [Technical Field]

[0002] This disclosure relates to a glass plate having an acceptable overall thickness variation, and more particularly to a method for manufacturing a glass plate having an acceptable overall thickness variation by cutting a glass plate from a glass ribbon whose thickness variation has been reduced by passing the glass ribbon in the immediate vicinity of one or more heating zones. [Background technology]

[0003] An augmented reality system adds computer-generated images to the real-world visual scene that the user is focusing on. Typically, an augmented reality system can include an optical system configured to allow the user to view computer-generated images on real objects or scenes that are directly visible, while simultaneously displaying these objects or scenes. The optical system can project the computer-generated images into the user's field of view using light guides, which can be made of high-refractive-index glass. Variations in the shape of the light guides can degrade the quality of the images displayed to the user. For example, to output high-quality images, it is necessary to minimize the total thickness variation of the light guides.

[0004] One process for achieving light guides with acceptable overall thickness variation involves casting a boule of high refractive index glass, sawing the boule into numerous wafers, and then planarizing the wafers by lapping and polishing or reheating. However, this process is costly and time-consuming. Furthermore, reheating the wafers can cause devitrification of the glass.

[0005] Furthermore, because the liquid-phase viscosity of high refractive index glass compositions is very low (e.g., 1 to 100 poise), the fusion process cannot be applied to high refractive index glass compositions.

[0006] Prior to this disclosure, attempts had been made to form high refractive index glass plates using a down-draw ribbon forming process. In the down-draw ribbon forming process, molten glass is fed into a molded body (such as a nip between opposing rollers). Next, the molten glass is stretched downwards to form a glass ribbon. Then, by stretching this glass ribbon downwards, the glass ribbon is attenuated (i.e., the thickness of the glass ribbon is reduced). As the glass ribbon cools, glass plates are continuously cut from the ribbon. The down-draw ribbon forming process is less expensive than the above-mentioned process of forming wafers from boules and then performing rough polishing and polishing.

[0007] However, a problem was discovered. The molded body caused variations in the thickness of the glass ribbon, and this variation in thickness was not reduced by subsequent thinning of the glass ribbon. For example, in the upper region of the molded body where the molten material spreads, the molded body cools the main surface of the glass preferentially over the glass core, resulting in undulations on the main surface called "chill wrinkles." It had been thought that this variation in thickness would be reduced by thinning the glass ribbon. However, modeling and experiments demonstrated that thinning did not reduce the variation in thickness, and in some cases even worsened it. [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] This disclosure addresses this problem by heat-treating the glass ribbon so that liquefaction occurs on one or more main surfaces of the glass ribbon before cutting the glass sheet from the ribbon. By causing liquefaction on one or more main surfaces of the glass ribbon, variations in thickness are reduced. This improvement makes it possible to form high refractive index glass sheets more economically using a form-and-draw process. [Means for solving the problem]

[0009] According to a first aspect of the present disclosure, a method for manufacturing a glass plate includes: (a) forming a glass ribbon descending as a function of time in a vertical orientation, wherein the glass ribbon has a first principal surface and a second principal surface facing generally opposite directions, and a core positioned between the first principal surface and the second principal surface; (b) passing the glass ribbon in the immediate vicinity of a first heating zone as the glass ribbon descends, the first heating zone raising the temperature of the first principal surface to a temperature sufficient to cause liquefaction at the first principal surface while keeping the temperature of the core below the softening temperature; and (c) cutting a glass plate from the glass ribbon after the glass ribbon has moved below the first heating zone.

[0010] According to a second aspect of the present disclosure, in step (b) of the first aspect, the viscosity of the first main surface is reduced, and the overall thickness variation of the glass ribbon is reduced.

[0011] According to a third aspect of the present disclosure, in the second aspect, between step (b) and step (c), after the overall thickness variation has been reduced, the temperature of the first main surface and the core approach equilibrium, the effective viscosity of the glass ribbon decreases, and the thickness of the glass ribbon decreases.

[0012] According to a fourth aspect of the present disclosure, the method according to any one of the first to third aspects further includes, before step (a), a step of sending molten glass to a nip between a pair of facing forming rollers. Further, the step of forming the glass ribbon in a vertical orientation includes a step of rotating a pair of forming rollers to roll the molten glass sent to the nip into a glass ribbon.

[0013] According to a fifth aspect of the present disclosure, the method according to any one of the first to fourth aspects further includes, after step (b) and before step (c), a step of pulling the glass ribbon downward with a pulling roller.

[0014] According to a sixth aspect of the present disclosure, in the fifth aspect, the step of pulling the glass ribbon with a pulling roller reduces the thickness of the glass ribbon between the first major surface and the second major surface.

[0015] According to a seventh aspect of the present disclosure, the method according to any one of the first to sixth aspects further includes, after step (b) and before step (c), a step of measuring the thickness of the glass ribbon between the first major surface and the second major surface.

[0016] According to an eighth aspect of the present disclosure, in any one of the first to seventh aspects, the surface roughness (R a ) of the first major surface of the cut glass plate is less than 500 nm.

[0017] According to a ninth aspect of the present disclosure, in any one of the first to eighth aspects, the overall thickness variation of the glass plate cut from the glass ribbon is less than 5 μm.

[0018] According to a tenth aspect of the present disclosure, in any one of the first to ninth aspects, the overall thickness variation of the glass plate cut from the glass ribbon is 50% or less of the overall thickness variation of the glass ribbon before step (b).

[0019] According to the eleventh aspect of this disclosure, in any one of the first to tenth aspects, the thickness of the glass ribbon between the first main surface and the second main surface after step (a) and before step (b) is 3 mm to 5 mm.

[0020] According to a twelfth aspect of the present disclosure, in any one of the first to eleventh aspects, the thickness of the glass ribbon between the first main surface and the second main surface after step (b) is at least 1.5 mm.

[0021] According to a thirteenth aspect of the present disclosure, in any one of the first to twelfth aspects, the thickness of the glass ribbon between the first principal surface and the second principal surface is reduced between step (b) and step (c).

[0022] According to a fourteenth aspect of the present disclosure, in any one of the first to thirteenth aspects, the step of raising the temperature of the first main surface includes the step of directing a flame towards the first main surface.

[0023] According to a 15th aspect of the present disclosure, in a 14th aspect, the step of directing a flame to a first main surface is performed by a horizontally oriented line burner, wherein the horizontal width of the horizontally oriented line burner is narrower than the horizontal width of the glass ribbon facing the horizontally oriented line burner.

[0024] According to a sixteenth aspect of the present disclosure, in any one of the first to fifteenth aspects, the step of raising the temperature of the first main surface includes bringing the first main surface into contact with a high-temperature body that primarily transfers heat to the first main surface by thermal radiation.

[0025] According to the 17th aspect of this disclosure, in any one of the 1st to 16th aspects, step (b) reduces devitrification in the glass ribbon.

[0026] According to the eighteenth aspect of this disclosure, in any one of the first to seventeenth aspects, (i) prior to step (b), the viscosity of the glass ribbon is 10 10 Poise ~ 10 12 (ii) In step (b), the viscosity on the first main surface of the glass ribbon, to a depth of at least 100 μm from the first main surface in the thickness direction of the glass ribbon, is 10 5 (iii) Before step (c), the viscosity of the glass ribbon bulk is reduced to below Poise, 6 Poise ~ 10 8 It rises to Poise.

[0027] According to the 19th aspect of this disclosure, in any one embodiment of the 1st to 18th aspects, step (b) is performed within a time of less than 10 seconds.

[0028] According to the 20th aspect of this disclosure, in any one of the first to 19 aspects, the refractive index of the glass plate for wavelengths of 589 nm to 633 nm at a temperature of 20 °C to 25 °C is 1.75 to 2.5.

[0029] According to a 21st aspect of the present disclosure, a method for manufacturing a glass plate includes (a) forming a glass ribbon descending as a function of time in a vertical orientation, wherein the glass ribbon has a first principal surface and a second principal surface facing generally opposite directions, and a core positioned between the first principal surface and the second principal surface; (b) passing the glass ribbon in the vicinity of a first heating zone, (i) raising the temperature of the first principal surface to a temperature sufficient for liquefaction to occur at the first principal surface while keeping the temperature of the core below the softening temperature, and (ii) raising the temperature of the second principal surface to the liquidus temperature while keeping the temperature of the core below the softening temperature; and (c) cutting a glass plate from the glass ribbon after the glass ribbon has moved below the first heating zone and the second heating zone.

[0030] According to a 22nd aspect of this disclosure, in a 21st aspect, the first heating zone and the second heating zone are arranged with a vertical offset from each other.

[0031] According to the 23rd aspect of this disclosure, in the 21st aspect, the horizontal planes of the first heating zone and the second heating zone overlap each other.

[0032] According to a 24th aspect of the present disclosure, in a 21st or 22nd aspect, in step (b), the viscosity of the first main surface is reduced, the viscosity of the second main surface is reduced, and the overall thickness variation of the glass ribbon is reduced.

[0033] According to a 25th aspect of the present disclosure, in any one of the 21st to 23rd aspects, between step (b) and step (c), after the overall thickness variation of the glass ribbon has been reduced, the temperatures of the first main surface, the second main surface, and the core approach equilibrium, the effective viscosity of the glass ribbon decreases, and the thickness of the glass ribbon decreases. [Brief explanation of the drawing]

[0034] [Figure 1] Flowchart illustrating a method for manufacturing a glass plate according to an embodiment of this disclosure [Figure 2] Figure 1 shows a perspective view illustrating how molten glass is fed into a mold in the form of a pair of forming rollers, forming a glass ribbon in a vertical direction, and the glass plates cut from the glass ribbon. [Figure 3A] This is an elevation view showing the state in Figure 2. With the temperature of the glass ribbon core below the softening temperature, the temperature of the first and second main surfaces of the glass ribbon is raised to a temperature sufficient to cause liquefaction of the glass ribbon on the first and second main surfaces. The diagram shows the glass ribbon being passed in the immediate vicinity of the first and second heating zones, which are positioned vertically offset from each other, in order to reduce variations in the overall thickness of the glass ribbon and surface defects due to surface tension before thinning the glass ribbon. [Figure 3B]The figure is the same as Figure 3A, except that the glass ribbon passes in the immediate vicinity of the first and second heating zones, which are positioned without vertical displacement (i.e., the horizontal plane extending through the glass ribbon overlaps with the first and second heating zones). [Figure 4A] This is a side view showing the state in Figure 2, illustrating the first and second heating zones positioned at vertically offset locations. [Figure 4B] This is a side view showing the state in Figure 2, illustrating the first and second heating zones, which are positioned so that their horizontal planes do not shift vertically and overlap each other. [Figure 5] Figures 4A and 4B show enlarged views of region V, illustrating the thickness between the first and second main surfaces and the surface roughness of the first main surface. [Figure 6] This is an enlarged view of region VI in Figure 2, showing a state where the first main surface of the glass ribbon has cold wrinkles, which are one of the causes of the variation in the overall thickness of the glass ribbon. [Figure 7A] Figures 3A and 3B are perspective views of one embodiment of the first and second heating zones, showing a first line burner oriented horizontally to direct the flame towards the first main surface of the glass ribbon in order to cause liquefaction on the first main surface, and a second line burner oriented horizontally to direct the flame towards the second main surface of the glass ribbon in order to cause liquefaction on the second main surface. [Figure 7B] Figures 3A and 3B are perspective views of other embodiments of the first and second heating zones, showing a first high-temperature body that transfers heat to the first main surface mainly by thermal radiation throughout the entire first heating zone, causing liquefaction on the first main surface, and a second high-temperature body that transfers heat to the second main surface mainly by thermal radiation throughout the entire second heating zone, causing liquefaction on the second main surface. [Figure 8] This figure relates to Example 1, showing that when a quartz crucible containing a cubic glass cube is heated with a flame, the cubic glass cube inside is heated by thermal radiation from the crucible, and as a result, the cold wrinkles on the surface of the cubic glass cube that were present at the start of the experiment ("t=0 seconds") are removed within 90 seconds ("t=90 seconds"). [Figure 9] This figure relates to Example 2 and is an infrared image of a glass ribbon passing in the immediate vicinity of the first heating zone by a horizontally oriented line burner, according to one embodiment of the method in Figure 1. The figure shows how the glass ribbon becomes thinner as it descends, as the temperature of the first main surface and the temperature of the glass ribbon core equilibrium and the effective viscosity of the glass ribbon decreases. [Figure 10] This figure, also relating to Example 2, is a graph showing the surface properties measurement results of glass plates cut from the glass ribbon in Figure 9. It shows that the first main surface of the glass plate that passed very close to the first heating zone while it was part of the glass ribbon had a surface property with a smaller height difference than the second main surface of the glass plate that did not pass very close to the heating zone while it was part of the glass ribbon. [Figure 11] This graph relates to the computer model of Example 3 and illustrates the principle that, a few seconds before the thinning coefficient of the glass ribbon begins to decrease, the temperature of the first main surface of the glass ribbon can rise to a temperature sufficient to cause liquefaction at least on the first main surface. This illustrates that, before the effective viscosity of the glass ribbon decreases to a degree sufficient to cause thinning, there is sufficient time during liquefaction on the first main surface for surface defects and overall thickness variations to be reduced by surface tension. [Figure 12] This figure, also relating to Example 3, shows that before a decrease in the thickness of the glass ribbon is observed due to a decrease in the effective viscosity of the entire glass ribbon, the viscosity of the first main surface decreases to less than 1000 poise (i.e., 10³ poise) due to the heat flux, which is low enough to reduce surface defects and overall thickness variation due to surface tension. [Figure 13A] This figure relates to Comparative Example 4A and shows the measured surface roughness (Ra) and surface properties of a glass plate cut from a glass ribbon that did not pass immediately in the vicinity of the first heating zone before cutting. [Figure 13B]This figure relates to Example 4B and shows the measured surface roughness (Ra) and surface properties of a glass plate cut from a glass ribbon that has passed very close to a first heating zone where the glass ribbon was heated to a temperature sufficient to cause liquefaction on its first main surface before cutting. [Modes for carrying out the invention]

[0035] Next, with reference to Figures 1 to 7B, a method 10 for manufacturing the glass plate 12 will be described. Method 10 includes a step 14 for forming a glass ribbon 16 in a vertical orientation. The glass ribbon 16 has a first main surface 18 and a second main surface 20. The first main surface 18 and the second main surface 20 are oriented in generally opposite directions. The glass ribbon 16 further has a first side edge 22 and a second side edge 24. The first side edge 22 and the second side edge 24 define the generally opposite sides of the glass ribbon 16. "Vertically oriented" means that the first main surface 18 and the second main surface 20 form a plane that is approximately vertical. The glass ribbon 16 also has a thickness 26, which is the horizontal distance between the first main surface 18 and the second main surface 20. Furthermore, the glass ribbon 16 has a width 28, which is the horizontal distance between the first side edge 22 and the second side edge 24. The thickness 26 and width 28 of the glass ribbon 16 can vary as a function of the vertical position along the glass ribbon 16. The glass ribbon 16 has a composition.

[0036] Method 10 further includes a step 30 of sending the molten glass 32 to a mold 34. The mold 34 forms a glass ribbon 16.

[0037] In several embodiments, the mold 34 comprises a pair of opposing forming rollers 36a, 36b. In such embodiments, the step 30 of feeding molten glass 32 into the mold 34 includes the step of feeding the molten glass 32 as a flow 38 to a nip 40 between the pair of forming rollers 36a, 36b. For example, the flow 38 of molten glass 32 can be fed from a fishtail section (slot opening) 42 to the center of the nip 40. The flow 38 is fed from above the horizontal rotation axes 44a, 44b of the pair of forming rollers 36a, 36b. The width / length and thickness of the slot opening 42 can be in a wide range. The flow 38 of molten glass 32 is fed to the nip 40 at a glass temperature of approximately 1000°C or higher. 1 It has a viscosity on the order of poise. The molten glass 32 that is fed forms a pool 46 of molten glass 32 on a pair of forming rollers 36a, 36b. The pair of forming rollers 36a, 36b can be temperature-controlled to have a surface temperature in the range of about 500°C to about 600°C or higher, depending on the composition and viscosity of the glass to be formed. Processes and devices for temperature control of the pair of forming rollers 36a, 36b are well understood in the art and will not be described in detail herein. In such embodiments using a pair of forming rollers 36a, 36b, step 14 for forming a glass ribbon 16 in a vertical orientation includes rotating the pair of forming rollers 36a, 36b to roll the molten glass 32 fed to the nip 40 into a glass ribbon 16. The pair of forming rollers 36a and 36b rotate inward toward the pool of molten glass, as indicated by the arrows in Figure 2. This flattens, thins, and smooths the molten glass 32 in the pool 46, forming a glass ribbon 16 that extends vertically downward from the rotation axes 44a and 44b of the pair of forming rollers 36a and 36b.

[0038] Although a pair of forming rollers 36a and 36b are used as the mold 34 to form the glass ribbon 16, this is merely one example of a mold 34 and is not intended to be limiting. This method 10 encompasses any type of mold 34 that can be used to form the glass ribbon 16 vertically from the mold 34.

[0039] The glass ribbon 16 descends as a function of time after molding. In other words, the mold 34 continuously molds the glass ribbon 16 until the supply source of molten glass 32 for the glass ribbon 16 is depleted. For example, a certain volume portion of the glass ribbon 16 that was at position 48a at one point in time may descend as the molding of the glass ribbon 16 continues, and at a later point in time it may be at position 48b.

[0040] The glass ribbon 16 has a core 50 (see Figure 5). The core 50 is located between the first main surface 18 and the second main surface 20 and includes, for example, a volume portion that is equidistant from the first main surface 18 and the second main surface 20, and also equidistant from the first side edge 22 and the second side edge 24. In some embodiments, the core 50 is spaced at least 40 percent of the thickness 26 from the first main surface 18 and at least 40 percent of the thickness 26 from the second main surface 20. In some embodiments, the core 50 is spaced at least 40 percent of the width 28 from the first side edge 22 and at least 40 percent of the width 28 from the second side edge 24.

[0041] After the glass ribbon 16 is formed, it solidifies. When the first main surface 18 and the second main surface 20 solidify, they solidify with surface defects such as variations in thickness 26, including cold wrinkles 52, and surface roughness imparted to the first main surface 18 and the second main surface 20 by the mold 34. The cold wrinkles 52 are undulations that occur after the glass ribbon 16 is formed because the main surfaces 18 and 20 cool preferentially to the core 50. During forming, heat is removed from the glass by rapid heat conduction, making it difficult to avoid the formation of cold wrinkles 52. Other defects such as pressure checks (i.e., cracks) and scratches may also occur.

[0042] Method 10 further includes step 54 of passing the glass ribbon 16 in the immediate vicinity of the first heating zone 56. In the first heating zone 56, the temperature of the first major surface 18 of the glass ribbon 16 is raised to a temperature sufficient to cause liquefaction of the composition of the glass ribbon 16 at the first major surface 18 by applying a heat flux to the first major surface 18 of the glass ribbon 16. This is such that the viscosity from the first major surface 18 of the glass ribbon 16 to a depth of at least 100 μm (for example, 100 μm to 500 μm, etc.) in the direction of the thickness 26 is 5 less than 10 4 poise, for example 10 3 poise or 10 5 poise to the order of 10

[0043] may correspond to. However, all of the thickness 26 of the glass ribbon 16, the descending speed of the glass ribbon 16, and the first heating zone 56 are configured such that the temperature of the core 50 of the glass ribbon 16 remains below the softening temperature of the composition of the glass ribbon 16. If the core 50 were to soften, thinning of the glass ribbon 即16 would occur before reduction or removal of surface defects. For example, assuming that the descending speed of the glass ribbon 16 and the heat flux applied in the first heating zone 56 are arbitrarily given, by increasing the thickness 26 of the glass ribbon 16, liquefaction of the first major surface 18 can be achieved in the first heating zone 56 so as not to cause loss of structural integrity due to softening of the core 50. Alternatively, regarding the heat flux applied in the first heating zone 56, the length of the glass ribbon 16 to which the heat flux is applied can be shortened or the intensity of the heat flux can be decreased to make the thickness 26 of the glass ribbon 16 liquefied at the first major surface 18 shallower so as not to cause softening in the core 50. In a plurality of embodiments, the thickness 26 of the glass ribbon 16 in the immediate vicinity of the first heating zone 56 is 3 mm to 5 mm. Note that this thickness 26 refers to any thickness 26 measured at an arbitrary position between the both side edges 22, 24.In the first heating zone 56, the temperature of the first main surface 18 is raised to a temperature sufficient to cause liquefaction on the first main surface 18 (and thereby cause a decrease in viscosity in the direction from the first main surface 18 toward the thickness 26), while keeping the temperature of the core 50 below the softening temperature. As a result, in the first heating zone 56, surface defects can be reduced or eliminated by the surface tension of the first main surface 18. In other words, cold wrinkles 52 that were present on the first main surface 18 until it reached the vicinity of the first heating zone 56 are reduced to an inconspicuous degree or eliminated while the first main surface 18 is liquefied in the vicinity of the first heating zone 56. Thus, the overall thickness variation of the glass ribbon 16 is reduced. Also, the surface roughness (R) of the first main surface 18 is reduced. a ) also becomes smaller. Even if there are pressure burrs or scratches on the glass ribbon 16 before it enters the first heating zone 56, these can be repaired or removed. Other surface defects can also be removed or made less noticeable. In this specification, "total thickness variation" means the difference between the minimum and maximum values ​​of the thickness 26. In the case of the glass ribbon 16, the minimum and maximum values ​​of the thickness 26 are the values ​​of the thickness 26 measured along the same line extending horizontally. In the case of the glass plate 12, the total thickness variation is the difference between the minimum and maximum values ​​of the thickness 26 over the entire glass plate 12 in a free state without any pressure applied.

[0044] As described above, the glass ribbon 16 solidifies before entering the first heating zone 56. This is because the viscosity of the glass ribbon 16 is 10 10 Poise ~ 10 12 Poise, for example 10 11This corresponds to a temperature on the order of Poise. It is not necessary to cool the glass ribbon 16 to a temperature below the setting zone of the composition in which the glass ribbon 16 becomes elastic. In the elastic state, the cross-sectional shape of the glass ribbon 16 is fixed, becoming the characteristic cross-sectional shape of the glass ribbon 16. The glass ribbon 16 may change from this state due to bending, but is biased by internal stress to return to its original setting cross-sectional shape. However, in several embodiments, the glass ribbon 16 is cooled to a temperature below the composition setting zone by the time it reaches the vicinity of the first heating zone 56. In practice, in several embodiments, the glass ribbon 16 is cooled to ambient temperature by the time it reaches the vicinity of the first heating zone 56. Nevertheless, in order to minimize the overall stress on the glass ribbon 16, it may be beneficial to keep the temperature of the glass ribbon 16 above the annealing temperature of the composition when it reaches the vicinity of the first heating zone 56. The annealing temperature of the composition is when the viscosity of the composition is about 10 13 This is the temperature at which pores occur.

[0045] In several embodiments, step 54 is performed within a time frame of 1 to 10 seconds. In other words, it takes only 1 to 10 seconds for a given portion of the glass ribbon 16 to pass in the immediate vicinity of the first heating zone 56. In several embodiments, step 54 is performed within a time frame of 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 seconds, or any time within the range ending at any two of these times (e.g., 2 to 9 seconds). After this time has elapsed, the given portion of the glass ribbon 16 has descended below the first heating zone 56. Furthermore, if the time is shorter than 1 second, the heat flux acting on the first main surface 18 will be insufficient, making it highly unlikely that the temperature of the first main surface 18 of the glass ribbon 16 will be raised to a temperature sufficient for liquefaction to occur on the first main surface 18. Even if it were possible, the continuous depth of the liquefied portion from the first main surface 18 in the direction of the thickness 26 will be insufficient, making it unlikely that surface defects can be removed to a visible level. On the other hand, a time exceeding 10 seconds is longer than the time required for the surface tension of the liquefied first main surface 18 to remove surface defects, so there is no need to spend more than 10 seconds. Moreover, if the time exceeds 10 seconds, the risk of softening the core 50 due to the heat flux acting on the first main surface 18 is unnecessarily increased.

[0046] In several embodiments, step 54 of method 10 reduces devitrification within the glass ribbon 16. The glass ribbon 16 may have some degree of devitrification (including devitrification continuous with the first main surface 18 of the glass ribbon 16) before it passes in the immediate vicinity of the first heating zone 56. If devitrification exists within the glass ribbon 16, it can be reduced by rapidly heating the first main surface 18 to cause sufficient liquefaction and then cooling it.

[0047] In several embodiments, step 54 of method 10, which involves raising the temperature of the first main surface 18, includes directing a flame 58 (see Figure 7A) onto the first main surface 18. For example, in one embodiment, a horizontally oriented line burner 60 directs a flame 58 from the combustion of fuel onto the first main surface 18 of the glass ribbon 16, thereby raising the temperature of the first main surface 18 and causing liquefaction on the first main surface 18. Note that "horizontally oriented" means that the line burner 60 has a horizontal width 62 and a vertical height 64, and that the horizontal width 62 is greater than the vertical height 64, for example, at least three times greater. In several embodiments, the horizontal width 62 is narrower than the width 28 of the glass ribbon 16 facing the line burner 60. In this embodiment, the line burner 60 can be positioned in the center so that it does not extend laterally beyond the side edges 22, 24 of the glass ribbon 16.

[0048] In other embodiments, the step of raising the temperature of the first main surface 18 to a temperature sufficient to cause liquefaction on the first main surface 18 includes the step of facing the first main surface 18 toward a high-temperature body 66 (see Figure 7B). The high-temperature body 66 also generates heat transfer by air convection, but mainly transfers heat to the first main surface 18 throughout the first heating zone 56 by thermal radiation 68. In other words, the high-temperature body 66 does not have a turbine that directs the heated gas toward the first main surface 18 of the glass ribbon 16. Similar to the line burner 60, the high-temperature body 66 can be oriented horizontally, with a width 70 several times greater than its height 72. The high-temperature body 66 can also be centrally positioned so that it does not extend laterally beyond the side edges 22, 24 of the glass ribbon 16.

[0049] Although a line burner 60 and a high-temperature body 66 are used to raise the temperature of the first main surface 18 to a temperature sufficient for liquefaction to occur, this is illustrative and not intended to be limiting. Method 10 encompasses any device that causes liquefaction to occur on the first main surface 18.

[0050] As the glass ribbon 16 descends and moves away from the immediate vicinity of the first heating zone 56, and after the reduction of the overall thickness variation on the first main surface 18 is complete, the temperatures of the glass ribbon 16 on both main surfaces 18, 20 and the core 50 approach equilibrium. That is, the temperature of the core 50 rises and the temperature of the first main surface 18 decreases. As a result, the effective viscosity of the glass ribbon 16 becomes 10 6 Poise ~ 10 8 Poise, or 10 7 The viscosity decreases to the order of Poise. "Effective viscosity" refers to the average viscosity across the entire horizontal cross-section of the glass ribbon 16. As the effective viscosity of the glass ribbon 16 decreases, the glass ribbon 16 is thinned downwards (by its own weight, or by tension from the tension rollers described later, or both). As a result, the thickness 26 and width 28 of the glass ribbon 16 decrease as a function of downward position. In some embodiments, the thickness 26 of the glass ribbon 16 after passing in the immediate vicinity of the first heating zone 56 is at least 1.5 mm.

[0051] Conventionally, it was believed that even without prior reduction or removal of surface defects in step 54, thinning would reduce or remove surface defects. In other words, it was thought that all parts of the glass ribbon 16, including those with surface defects, would shrink uniformly. However, modeling and experiments revealed the surprising result that if the first heating zone 56 is too strong and the temperature of the core 50 rises to a temperature exceeding the softening temperature of the glass ribbon 16 composition, the glass ribbon 16 will be thinned (i.e., stretched downwards, reducing its thickness 26 and width 28) without any reduction or removal of surface defects. Thinning of the glass ribbon 16 preferentially occurs in the thin parts of the glass ribbon 16, for example, in the valleys 74 of the cold wrinkles 52. As a result of this preferential thinning, defects such as cold wrinkles 52 worsen, and the valleys 74 of the cold wrinkles 52 move closer to the core 50, making the peaks 76 of the cold wrinkles 52 more prominent. In other words, step 54 of method 10 must be performed so that the reduction or removal of surface defects due to surface tension occurs before the glass ribbon 16 is thinned. Otherwise, the thinning of the glass ribbon 16 will only worsen the surface defects.

[0052] In several embodiments, method 10 further includes step 78 of passing the glass ribbon 16 in the immediate vicinity of a second heating zone 80. In the second heating zone 80, the temperature of the second main surface 20 is raised to a depth of at least 100 μm (e.g., 100 μm to 500 μm) in the direction of thickness 26 from the second main surface 20 to a temperature sufficient to cause liquefaction of the glass ribbon 16. As with the first heating zone 56, the thickness 26 of the glass ribbon 16, the descent rate of the glass ribbon 16, and the second heating zone 80 are all configured such that the temperature of the core 50 of the glass ribbon 16 remains below the softening temperature of the composition of the glass ribbon 16. This allows surface defects of the second main surface 20 to be repaired by surface tension before the glass ribbon 16 is thinned, further reducing the overall thickness variation of the glass ribbon 16. In addition, devitrification can also be removed in this step 78. The step of raising the temperature of the second main surface 20 to a temperature sufficient for liquefaction to occur on the second main surface 20 can be carried out in the same way as the temperature increase of the first main surface 18 described above, so it is not necessary to explain it again here. For example, in several embodiments, the step of raising the temperature of the second main surface 20 includes the step of directing a flame to the second main surface 20 using a second line burner 82 or the like that is oriented horizontally, or the step of facing the second main surface 20 to a second high-temperature body 83 or the like. The second line burner 82 and the second high-temperature body 83, oriented horizontally, are the same as the line burner 60 and the high-temperature body 66, except that they are positioned to face the second main surface 20 instead of the first main surface 18 of the glass ribbon 16. In either case, the overall thickness variation of the glass ribbon 16 is reduced, and after the glass ribbon 16 has descended below the second heating zone 80, the temperatures of the first main surface 18, the second main surface 20, and the core 50 approach equilibrium, the effective viscosity of the glass ribbon 16 decreases, the glass ribbon 16 becomes thinner, and the thickness 26 of the glass ribbon 16 decreases.

[0053] In several embodiments, the horizontal planes 85 of the first heating zone 56 and the second heating zone 80 overlap each other. The horizontal plane 85 is a conceptual plane that extends through the glass ribbon 16. In this case, the core 50 remains below its softening temperature, while the first main surface 18 and the second main surface 20 rise simultaneously to a temperature sufficient for liquefaction to occur on both surfaces.

[0054] In other embodiments, the first heating zone 56 and the second heating zone 80 are positioned vertically offset from each other. That is, the first heating zone 56 is positioned higher or lower than the second heating zone 80, and the horizontal planes 85 do not overlap. By offsetting the zones 56 and 80 in this way, it is possible to prevent the glass ribbon 16 from softening to the point where the core 50 of the glass ribbon 16 begins to thin down before the surface defects of the first main surface 18 and the second main surface 20 can be removed during the liquefaction of the first main surface 18 and the second main surface 20. However, if the thickness 26 of the glass ribbon 16 is sufficiently thick, it is not necessary to offset them in this way, and both main surfaces 18 and 20 can be heated simultaneously. In this case, even if both main surfaces 18 and 20 are heated simultaneously, the core 50 will not soften while the liquefaction of both main surfaces 18 and 20 is occurring and surface defects are being removed.

[0055] In several embodiments, Method 10 further includes a step 84 for measuring the thickness 26 of the glass ribbon 16. The thickness 26 can be measured with any measuring device 86, such as a device that measures thickness by the transmittance of light 88. For example, the measuring device 86 can be a confocal chromatic imager. By measuring the thickness 26 of the glass ribbon 16, feedback can be obtained in near real time, making it possible to adjust the thickness 26 of the glass ribbon 16 by changing the size of the gap 90 between a pair of molding rollers 36a, 36b, changing the flow rate of the molten glass 32 flow 38, or changing the rotation speed of the pair of molding rollers 36a, 36b. If the surface roughness of the first main surface 18 of the glass ribbon 16 is too high, surface scattering of transmitted light may occur, but by step 54 of Method 10, for example, such surface scattering of transmitted light can be minimized, thereby improving the reliability of the measurement in step 84.

[0056] In several embodiments, method 10 further includes step 92 of pulling the glass ribbon 16 downward with tension rollers 94. The tension rollers 94 are positioned below the first heating zone 56. The tension rollers 94 may comprise a pair of tension rollers 94 adjacent to the first side edge 22. The tension rollers 94 are provided such that tension roller 94a contacts the first main surface 18 of the glass ribbon 16 and tension roller 94b contacts the second main surface 20. Similarly, the tension rollers 94 may comprise a pair of tension rollers 94 adjacent to the second side edge 24. This pair of tension rollers 94 are also provided such that one contacts the first main surface 18 and the other contacts the second main surface 20. In other embodiments, only a pair of tension rollers 94 may be positioned in the center between the first side edge 22 and the second side edge 24. This pair of tension rollers 94 is also provided such that one roller contacts the first main surface 18 and the other roller contacts the second main surface 20. The tension rollers 94 generate a slight tension in the glass ribbon 16 in order to stabilize it and thin it. In some embodiments, the tension rollers 94 pull the glass ribbon 16, further reducing the thickness 26 of the glass ribbon 16. The surface material and surface properties of the tension rollers 94 must be selected so as not to adversely affect the overall thickness variation of the glass ribbon 16.

[0057] Method 10 further includes a step 96 of cutting the glass plate 12 from the glass ribbon 16. This step 96 is performed after the glass ribbon 16 has moved below the first heating zone 56 and the second heating zone 80 (if included). As described above, the glass ribbon 16 is formed continuously until the source of molten glass 32 is depleted. Thus, the glass plate 12 can be one of a plurality of 98 glass plates 12 sequentially cut from the glass ribbon 16. Step 96 encompasses any process used to cut the glass plate 12. In some embodiments, the step of cutting the glass plate 12 includes first drawing a cleavage line in the glass ribbon 16, applying tensile stress across the cleavage line to create a crack, and then propagating the crack so that it penetrates the thickness 26 of the glass ribbon 16. The cleavage line can be formed by conventional methods. For example, a cleavage line can be created by bringing the glass ribbon 16 into contact with a cleavage-drawing member 100, such as a cleavage-drawing wheel, scribe, or polishing member, which forms damage on the first main surface 18 or the second main surface 20. Then, tensile stress is applied to the side of the glass ribbon 16 on which the cleavage line has been made, by bending the glass ribbon 16 in a direction that applies tension across the cleavage line. This tension causes the crack formed in the cleavage line to propagate and penetrate the thickness 26 of the glass ribbon 16. It is preferable to form the cleavage line over the quality region of the glass ribbon 16, that is, over the ribbon width 28 between the side edges 22 and 24. The first main surface 18 and the second main surface 20 of the glass ribbon 16 become the first main surface 18 and the second main surface 20 of the glass plate 12.

[0058] In other embodiments, the cleavage member 100 is a laser, and optionally, a laser and a cooling device. The cooling device brings a cooling fluid, such as a cooled gas, liquid, or a combination thereof (mist), into contact with the glass ribbon 16. The laser heats the glass ribbon 16 by striking a narrow area of ​​the glass ribbon 16 and heating that area with a laser beam that travels across the intended cleavage path. Subsequently, by cooling the heated path with the cooling fluid, a large tension is generated in the glass ribbon 16, creating a cleavage line.

[0059] In several embodiments, the surface roughness (R) of the first main surface 18 before step 54 of method 10 (or when step 54 is not performed) a ) is greater than 1000 nm, for example, 1000 nm to 5000 nm. On the other hand, the surface roughness (R) of the first main surface 18 of the glass plate 12 after step 54 of method 10 a The surface roughness (R) is less than 500 nm, for example, 50 nm to 500 nm, 50 nm to 250 nm, or 100 nm to 200 nm. a ) refers to the height deviation 102 from the average height line 104 of the cross-sectional shape recorded at multiple locations along the length 106 to be evaluated, and the arithmetic mean of the absolute values ​​of these records is taken (see Figure 5). In practice, the surface roughness (R) of the first main surface 18 before step 54 (or if step 54 is not performed) is measured. a ) prevents a portion of the glass ribbon 16 from passing in the immediate vicinity of the first heating zone 56 (for example, by passing it with the heat flux stopped), and then the surface roughness (R) of the glass plate 12 cut from this portion is determined. a This can be confirmed by measuring the surface roughness (R) of the first main surface 18 after step 54. a ) passes a portion of the glass ribbon 16 very close to the first heating zone 56, and then the surface roughness (R) of the glass plate 12 cut from this portion is measured. a This can be confirmed by measuring ).

[0060] In several embodiments, the overall thickness variation of the glass ribbon 16 and / or the glass plate 12 cut from the glass ribbon 16 before step 54 of Method 10 (or when steps 54 and 78 are not performed) is 5 μm or more, for example, 5 μm to 20 μm. In several embodiments, by performing steps 54 and 78, the overall thickness variation of the glass ribbon 16 and the glass plate 12 cut from the glass ribbon 16 becomes less than 5 μm, for example, 0.5 μm to 4.9 μm. As described above, the overall thickness variation of the glass ribbon 16 is kept below the desired level even after passing through the mold 34 and through the cooling wrinkles 52, so the glass ribbon 16 can be molded with an overall thickness variation smaller than the desired level. In method 10, the steps of passing the glass ribbon 16 immediately in the vicinity of the first heating zone 56 in step 54 and passing the glass ribbon 16 immediately in the vicinity of the second heating zone 80 in step 78 (if step 78 is included) reduce the overall thickness variation of the glass ribbon 16. Subsequently, as the temperature of the core 50 rises and equilibrium with the temperature of the main surfaces 18 and 20, the glass ribbon 16 becomes thinner, further reducing the overall thickness variation of the glass ribbon 16. Therefore, the glass plates 12 cut from the glass ribbon 16 in step 96 have a desirable overall thickness variation of less than 5 μm.

[0061] In several embodiments, the overall thickness variation of the glass plate 12 formed by Method 10 is 50% or less (e.g., 10% to 50%) of the overall thickness variation of the glass ribbon 16 before step 54 (and, if included, step 78) of Method 10. In several embodiments, the overall thickness variation of the glass plate 12 formed by Method 10 is 50% or less (e.g., 10% to 50%) of the overall thickness variation of the glass plate 12 formed by a method that does not include steps 54 and 78. For example, the overall thickness variation of the glass ribbon 16 before step 54 (and, if included, step 78) may be 8 μm, in which case the overall thickness variation of the glass plate 12 cut from this glass ribbon 16 after step 54 and optionally step 78 will be 4 μm or less.

[0062] Steps 54 and 78 not only reduce the overall thickness variation of the glass plate 12 compared to the case where steps 54 and 78 are not performed, but also improve the strength of the glass plate 12. If steps 54 and 56 of Method 10 are not performed, it is thought that surface defects such as scratches and pressure punctures that were present in the molded glass ribbon 16 would remain in the glass plate 12 cut from the glass ribbon 16. Steps 54 and 78 reduce or remove such surface defects, resulting in a glass plate 12 with optimal strength.

[0063] The glass plate 12 has a width of 108 between its side edges 22 and 24. This width 108 is the same as the width of the glass ribbon 16. The glass plate 12 also has a length 110. This length 110 is roughly perpendicular to the side edges 22 and 24 and parallel to the vertical portion of the glass ribbon 16 from which the cut glass plate 12 originates. It is not necessary for all glass plates 12 cut from the glass ribbon 16 to have the same width 108 or the same length 110. In several embodiments, the width 108 of the glass plate 12 is 5 mm to 500 mm, and the length 110 is 5 mm to 500 mm. In other embodiments, the width 108 is wider than 500 mm, and the length 110 is longer than 500 mm.

[0064] As described above, the composition of the glass ribbon 16 is directly transferred to the glass plate 12. Method 10 can be used with any glass composition. In several embodiments, the composition is such that the refractive index of the glass plate 12 cut from the glass ribbon 16 (refractive index for wavelengths of 589 nm to 633 nm at a temperature of 20 °C to 25 °C) is 1.75 to 2.5. In other embodiments, the refractive index of the glass plate 12 is 1.45 to 1.75. For example, a composition containing 40.1 mol% SiO2, 11.3 mol% Li2O, 3.8 mol% ZrO2, 4.8 mol% Nb2O5, 2.4 mol% B2O3, 22.9 mol% CaO, 5.4 mol% La2O3, and 9.3 mol% TiO2 has a refractive index of 1.8 (at a wavelength of 633 nm). In mass%, this composition contains 28.5 mass% SiO2, 4.00 mass% Li2O, 5.5 mass% ZrO2, 15 mass% Nb2O5, 2.0 mass% B2O3, 15.2 mass% CaO, 21 mass% La2O3, and 8.8 mass% TiO2.

[0065] In some embodiments, the glass composition is (in terms of oxide-based mass percentage, with total mass percentage being 100%) 5-55% by mass of SiO2, 5-10 mass% of ZrO2, 3.5-18 mass% CaO and 0.2-30 mass% of La2O3, 0.5-20% by mass of Nb2O5, 5-20 mass% TiO2, 0-0.2 mass% As2O3, It comprises 0.05 to 0.9 mass% (preferably 0.1 to 0.9 mass%, for example 0.1 to 0.8 mass%) of Er2O3, and / or 0.05 to 1 mass% of Pr2O3, or 0.05 to 1 mass% of Nd2O3, or 0.05 to 1 mass% of Ho2O3, or 0.05 to 1 mass% of Ce oxide (CeO2).

[0066] In several embodiments, the glass composition is (in terms of oxide-based mass percentage, with total mass percentage being 100%) 5-60% by mass of SiO2, 5-10 mass% of ZrO2, 3.5-18 mass% CaO and 0.2-30 mass% of La2O3, 0.5-20% by mass of Nb2O5, 5-20 mass% TiO2, 0-0.2 mass% As2O3, 0.01-0.5 mass% (for example, 0.05-0.5 mass%, or 0.1-0.5 mass%) of Er2O3, 2-5% by mass of Na2O, 0-9 mass% K2O5 and SrO of 1 mass% or less, 0-20 mass% BaO and F at 0-1 mass%, It contains 0-20% by mass of B2O3.

[0067] Since the refractive index of pure silica is approximately 1.5, by keeping the amount of SiO2 below 55% by mass (for example, 7-45% by mass) and adding a dopant with a higher refractive index, it is possible to produce a highly transparent, non-colored, high-refractive-index glass. However, if the amount of SiO2 is increased to over 60%, it becomes necessary to add dopants or components with a higher refractive index, potentially resulting in colored glass rather than transparent glass. According to some embodiments, the total amount of Er2O3, Nd2O3, Ho2O3, Ce oxide, and Pr2O3 in the glass is less than 1.5% by mass. This contributes to maintaining the transparency of the glass and high transmittance at the desired wavelength. As mentioned above, the liquid-phase viscosity of glass compositions forming relatively high-refractive-index glass is very low, so a fusion process cannot be used to form a glass plate 12 from such a composition.

[0068] In several embodiments, Method 10 is a continuous process that includes the steps of feeding molten glass 32 into a mold 34, forming a glass ribbon 16 and passing it in the immediate vicinity of a first heating zone 56 and a second heating zone 80 (if included), and cutting a plurality of glass plates 12 from the glass ribbon 16, without interruption over a period of several days, months, or even years. In other embodiments, Method 10 is a non-continuous batch process in which a predetermined amount of molten glass 32 is fed into a mold 34, thereby forming a glass ribbon 16 of a limited length, from which a limited number of glass plates 12 can be cut.

[0069] Steps 54 and 78 (if included) of Method 10 are performed to reduce or remove surface defects, thereby providing a glass ribbon 16 that can cut glass plates 12 with acceptable overall thickness variation and surface roughness. If these steps are not performed, it is considered necessary to reduce the thickness variation of glass plates 12 by acid etching, mechanical grinding and polishing, or both. However, the latter Method 10 is more expensive than steps 54 and 78 (if included) of Method 10. Also, mechanical grinding and polishing may not be optimal for reducing surface defects and thickness variation of glass plates 12 because it may generate glass dust or cause damage to the interior of the glass plates 12 beyond the main surfaces 18 and 20. On the other hand, in the case of steps 54 and 78 (if included) of this process, the generation of such glass dust is avoided, and no damage occurs to the interior of the thickness 26 beyond the main surfaces 18 and 20. Furthermore, steps 54 and 56 of Method 10 (if included) are performed as an inline process before separating the glass plate 12 from the glass ribbon 16. Acid etching and mechanical grinding / polishing, on the other hand, are not typically inline processes and require moving the glass plate 12 to a separate station. Also, steps 54 and 78 of Method 10 (if included) are both performed in less than 10 seconds, while acid etching can take several hours. Moreover, as mentioned above, the glass plate 12 can be manufactured in a wide variety of sizes, including lengths 110 of 500 mm or more. Mechanical grinding / polishing wheels are not suitable for grinding / polishing glass plates 12 of such sizes. [Examples]

[0070] Example 1 - In Example 1, as shown in Figure 8, a quartz crucible 112 was placed upside down on top of a cubic glass 114. The cubic glass 114 had cold wrinkles 52 on its top surface. The cubic glass 114 had the same composition as described above, containing 28.5 mass percent of SiO2. The refractive index of this glass composition was 1.8. At time t=0, no flame was directed at the quartz crucible 112. However, from after t=0 until 90 seconds later (t=90 seconds), the flame of an oxygen gas torch was directed at the quartz crucible 112, resulting in an increase in the temperature of the quartz crucible. The heat from the quartz crucible 112 was then radiated to the glass 114. During these 90 seconds, the heat radiated from the quartz crucible 112 raised the temperature of the top surface of the cubic glass 114 to a level sufficient for liquefaction to occur to a certain depth. The resulting surface tension removed the previously present cooling wrinkles 52. The cooling wrinkles 52 are visible in the diagrams of the cubic glass 114 at t=0 and t=55. On the other hand, in the diagram of the cubic glass 114 at t=90, not only are the cooling wrinkles 52 absent, but a smooth surface is also visible. Furthermore, the overall cubic shape of the cubic glass 114 remained intact. This indicates that a heat flux could be applied to the top surface of the cubic glass 114 by radiant heating that was sufficient to raise the temperature of the top surface of the cubic glass 114 to a temperature sufficient to cause liquefaction on the top surface for a sufficient amount of time to remove the cold wrinkles 52, but without heating the core of the cubic glass 114 to a temperature higher than the softening point of the composition.

[0071] Example 2 - In Example 2, molten glass having the same composition as the cubic glass of Example 1 was fed to the nip between a pair of forming rollers. The contact surfaces of the pair of forming rollers with the glass were heated to a high temperature. The pair of forming rollers were set to rotate at 0.25 meters per minute. After the pair of forming rollers formed a glass ribbon from the molten glass fed to the rollers, a flame burner directed horizontally was directed at the first main surface of the glass ribbon throughout the entire first heating zone. The horizontally directed flame burner was centrally positioned to cross the glass ribbon and had a width narrower than the width of the glass ribbon facing the flame burner. The second main surface of the glass ribbon was not heated; that is, a second heating zone was not provided. In addition, a pair of centrally positioned tension rollers pulled the glass ribbon downwards, further thinning the glass ribbon after it passed in the immediate vicinity of the flame burner. The results of infrared temperature measurement of the glass ribbon are shown in Figure 9.

[0072] Glass plates were cut from this glass ribbon. Using a coordinate measuring machine, the surface characteristics of the first main surface that passed in the immediate vicinity of the first heating zone and the surface characteristics of the second main surface that did not pass in the immediate vicinity of such a heating zone were measured. The measurement results are shown in the graph in Figure 10. "Downward distance of glass plate (mm)" refers to the distance along the length of the glass plate. From the results for the second main surface, it became clear that repeated undulations occurred in the surface height. This is probably due to cooling wrinkles. Some of the height peaks were close to 7 μm, but most were in the range of 3 μm to 5 μm. In contrast, the results for the first main surface that passed in the immediate vicinity of the flame burner showed a more consistent surface characteristic with a height of approximately 1 μm or slightly less. The increased surface characteristic in the range of 4 mm to 5 mm downward of the glass plate is probably due to dust adhering to the glass ribbon when the previous glass plate was cut.

[0073] Example 3 - Computer modeling was performed in Example 3. The modeling was performed under the following assumptions: (1) The flow rate is 60 pounds (approximately 27.2 kilograms) / hour, and the width of the glass ribbon is 150 mm; (2) The heat transfer coefficient of the glass ribbon is 5 W / (m 2· (1) It is lost due to convection at K) and irradiation with an emissivity of 0.4, (2) The gray body approximation is performed under conditions where there is no radiation from the participating medium, (3) The ambient temperature is set to a predetermined temperature of 650°C to 20°C, and (4) The viscosity of the glass ribbon as a function of temperature is given by the Vogel-Fulcher-Tammann-Hesse viscosity formula. The formula follows TIFF0007853037000001.tif9114, where μ is in units of Poise, A = -5.75, B = 5601.9, T0 = 312.3, and T is the temperature of the glass ribbon (°C). (6) The glass ribbon has a thermal conductivity of 1.0 W / (m·K). (6) The heat flux from the first hypothetically established heating zone follows a Gaussian distribution, and the baseline power density is 3*10. 5 W / m 2 (7) The full width at half maximum at the 1 / e level is set to 15 mm. In this model, the temperature change of the first main surface of the glass ribbon and the attenuation coefficient of the glass ribbon are considered as functions of time. The attenuation coefficient is the ratio of the thickness of the glass ribbon at a certain time to the thickness of the glass ribbon at the start. The modeling results are shown in the graphs of Figures 11 and 12. The graph in Figure 11 shows that the temperature of the first main surface can rise significantly to a temperature sufficient for liquefaction to occur on the first main surface before the thinning of the glass ribbon begins, i.e., before the attenuation coefficient begins to decrease. For a few seconds, this time allows the surface tension to reduce or remove surface defects on the first main surface before the thinning of the glass ribbon begins.

[0074] The graph in Figure 12 shows that the viscosity of the first main surface of the glass ribbon during heating is approximately 10 before the effective viscosity of the glass ribbon decreases to a degree sufficient for thinning of the glass ribbon to occur (i.e., before the thickness value begins to decrease from 5 mm). 11From Poise to 1000 Poise (10 3 It has been shown that the viscosity can be reduced to less than 1000 poise. This phenomenon makes it possible to reduce the viscosity of the first main surface before thinning begins, allowing surface defects to be removed by surface tension. The time the heat flux is applied to the first main surface is sufficient to reduce the surface viscosity to less than 1000 poise, but not long enough to cause devitrification or to heat the glass ribbon core to the point where it becomes as low-viscosity as the surface due to heat conduction or radiation.

[0075] Comparative Example 4A and Example 4B - In Example 4B, a glass plate was formed according to the method using the first heating zone described above. As described above, in the first heating zone, the temperature of the first main surface of the glass ribbon was raised to a temperature sufficient to cause liquefaction of the glass ribbon at the first main surface. Next, the glass plate was cut from the glass ribbon. Comparative Example 4A was carried out without using a configuration such as the first heating zone before cutting the glass plate. The composition of the glass in Comparative Example 4A and Example 4B was the same as the composition described above, and therefore the refractive index was 1.8. Next, the surface roughness (R) of the glass plates in Comparative Example 4A and Example 4B was measured. a The surface roughness (R) of the glass plate of Comparative Example 4A was measured. As shown in the screenshot in Figure 13A, a The surface roughness (R) of the glass plate in Example 4B was 1598 nm. On the other hand, as shown in the screenshot in Figure 13B, a The nm depth was 152 nm, representing a decrease of over 90 percent ((1598-152) / 1598=0.905*100%=90.5%). The surface roughness (rms) also decreased significantly from 2049 nm to 185 nm.

[0076] Preferred embodiments of the present invention are described below in separate sections.

[0077] Embodiment 1 A method for manufacturing glass plates, (a) A step of shaping a glass ribbon descending as a function of time in a vertical orientation, wherein the glass ribbon has a first principal surface and a second principal surface facing generally opposite directions, and a core disposed between the first principal surface and the second principal surface. (b) A step of passing the glass ribbon through the immediate vicinity of a first heating zone as the glass ribbon descends, wherein the first heating zone raises the temperature of the first main surface to a temperature sufficient to cause liquefaction on the first main surface, while keeping the temperature of the core below the softening temperature. (c) After the glass ribbon has moved below the first heating zone, the step of separating the glass plate from the glass ribbon, A method that includes this.

[0078] Embodiment 2 The method according to Embodiment 1, wherein in step (b), the viscosity of the first main surface is reduced and the overall thickness variation of the glass ribbon is reduced.

[0079] Embodiment 3 The method according to Embodiment 2, wherein between step (b) and step (c), after the overall thickness variation has been reduced, the temperature of the first main surface and the temperature of the core approach equilibrium, the effective viscosity of the glass ribbon decreases, and the thickness of the glass ribbon decreases.

[0080] Embodiment 4 The step before step (a) further includes feeding molten glass into the nip between a pair of opposing forming rollers, The method according to Embodiment 1, wherein the step of forming a glass ribbon in the vertical direction includes the step of rotating the pair of forming rollers to roll the molten glass sent to the nip into the glass ribbon.

[0081] Embodiment 5 The method according to Embodiment 1, further comprising the step of pulling the glass ribbon downward with a tension roller after step (b) and before step (c).

[0082] Embodiment 6 The method according to Embodiment 5, wherein the thickness of the glass ribbon between the first main surface and the second main surface is reduced by the step of pulling the glass ribbon with the tension roller.

[0083] Embodiment 7 The method according to Embodiment 1, further comprising the step of measuring the thickness of the glass ribbon between the first main surface and the second main surface after step (b) and before step (c).

[0084] Embodiment 8 The surface roughness (R) of the first main surface of the cut glass plate a The method according to Embodiment 1, wherein the wavelength is less than 500 nm.

[0085] Embodiment 9 The method according to Embodiment 1, wherein the overall thickness variation of the glass plates cut from the glass ribbon is less than 5 μm.

[0086] Embodiment 10 The method according to Embodiment 1, wherein the overall thickness variation of the glass plates cut from the glass ribbon is 50% or less of the overall thickness variation of the glass ribbon before step (b).

[0087] Embodiment 11 The method according to Embodiment 1, wherein the thickness of the glass ribbon between the first main surface and the second main surface after step (a) and before step (b) is 3 mm to 5 mm.

[0088] Embodiment 12 The method according to Embodiment 1, wherein, after step (b), the thickness of the glass ribbon between the first main surface and the second main surface is at least 1.5 mm.

[0089] Embodiment 13 The method according to Embodiment 1, wherein the thickness of the glass ribbon between the first main surface and the second main surface decreases between step (b) and step (c).

[0090] Embodiment 14 The method according to Embodiment 1, wherein the step of raising the temperature of the first main surface includes the step of directing a flame towards the first main surface.

[0091] Embodiment 15 The step of directing the flame towards the first main surface is performed by a horizontally oriented line burner. The method according to Embodiment 14, wherein the horizontal width of the horizontally oriented line burner is narrower than the horizontal width of the glass ribbon facing the horizontally oriented line burner.

[0092] Embodiment 16 The method according to Embodiment 1, wherein the step of raising the temperature of the first main surface includes the step of bringing the first main surface into contact with a high-temperature body that primarily transfers heat to the first main surface by thermal radiation.

[0093] Embodiment 17 The method according to Embodiment 1, wherein step (b) reduces devitrification within the glass ribbon.

[0094] Embodiment 18 Prior to step (b), the viscosity of the glass ribbon is 10 10 Poise ~ 10 12 Poise, In step (b), the viscosity of the first main surface of the glass ribbon, from the first main surface to a depth of at least 100 μm in the thickness direction of the glass ribbon, is 10 5 It has decreased to below Poise, Prior to step (c), the viscosity of the glass ribbon is 10 6 Poise ~ 10 8 The method according to Embodiment 1, wherein the rise is to the poise.

[0095] Embodiment 19 The method according to Embodiment 1, wherein step (b) is performed within a time frame of 1 to 10 seconds.

[0096] Embodiment 20 The method according to Embodiment 1, wherein the refractive index of the glass plate for wavelengths of 589 nm to 633 nm at a temperature of 20 °C to 25 °C is 1.75 to 2.5.

[0097] Embodiment 21 A method for manufacturing glass plates, (a) A step of shaping a glass ribbon that descends as a function of time in a vertical direction, wherein the glass ribbon has a first principal surface and a second principal surface facing generally opposite directions, and a core disposed between the first principal surface and the second principal surface, (b) As the glass ribbon descends, the steps include: (i) passing the glass ribbon in the immediate vicinity of a first heating zone in which the temperature of the first main surface is raised to a temperature sufficient for liquefaction to occur on the first main surface while keeping the temperature of the core below the softening temperature, and (ii) passing the glass ribbon in the immediate vicinity of a second heating zone in which the temperature of the second main surface is raised to the liquidus temperature while keeping the temperature of the core below the softening temperature; (c) After the glass ribbon has moved below the first heating zone and the second heating zone, the step of separating the glass plate from the glass ribbon, A method that includes this.

[0098] Embodiment 22 The method according to Embodiment 21, wherein the first heating zone and the second heating zone are arranged with a vertical offset from each other.

[0099] Embodiment 23 The method according to Embodiment 21, wherein the horizontal planes of the first heating zone and the second heating zone overlap each other.

[0100] Embodiment 24 The method according to Embodiment 21, wherein in step (b), the viscosity of the first main surface is reduced, the viscosity of the second main surface is reduced, and the overall thickness variation of the glass ribbon is reduced.

[0101] Embodiment 25 The method according to Embodiment 21, wherein between step (b) and step (c), after the overall thickness variation of the glass ribbon has been reduced, the temperatures of the first main surface, the second main surface, and the core approach equilibrium, the effective viscosity of the glass ribbon decreases, and the thickness of the glass ribbon decreases. [Explanation of Symbols]

[0102] 12 glass plates 16 Glass Ribbons 18. First main surface 20 Second main surface 22 First lateral edge 24 Second lateral edge 26 Glass ribbon thickness 28 glass ribbon width 32 Molten glass 34 molds 36a, 36b Forming rollers 38 Flow 40 nip 42 slot openings 44a, 44b Rotation axis of the molding roller 46 Accumulation 50 cores 52. Cold wrinkles 56. First heating zone 58 Flames 60 Line Burner 62 Line burner width 64 Line burner height 66 High-temperature body 68 Thermal radiation 70 Width of high temperature body 72 Height of high temperature 74. The Valley of Cold-Related Wrinkles 76. A mountain of cold wrinkles 80 Second heating zone 82 Second Line Burner 83. The second high-temperature body 86 Measuring Devices 88 light 90 Gap of molding roller 94, 94a, 94b tensile rollers 98 Multiple glass plates 100 line drawing member 108 width of glass plate 110 Length of glass plate 112 Quartz crucible 114 cubic glass

Claims

1. A method for manufacturing glass plates, (a) A step of forming a glass ribbon descending as a function of time in a vertical orientation, wherein the glass ribbon has a first principal surface and a second principal surface facing generally opposite directions, and a core disposed between the first principal surface and the second principal surface. (b) A step of passing the glass ribbon in the immediate vicinity of a first heating zone as the glass ribbon descends, wherein the first heating zone raises the temperature of the first main surface to a temperature sufficient to cause liquefaction on the first main surface, while keeping the temperature of the core below the softening temperature. (c) After the glass ribbon has moved below the first heating zone, the step of separating the glass plate from the glass ribbon, A method that includes this.

2. The method according to claim 1, wherein in step (b), the viscosity of the first main surface is reduced and the overall thickness variation of the glass ribbon is reduced.

3. The method according to claim 2, wherein between step (b) and step (c), after the overall thickness variation has been reduced, the temperature of the first main surface and the temperature of the core approach equilibrium, the effective viscosity of the glass ribbon decreases, and the thickness of the glass ribbon decreases.

4. The method according to claim 1, further comprising the step of pulling the glass ribbon downward with a tension roller after step (b) and before step (c).

5. The method according to claim 4, wherein the thickness of the glass ribbon between the first main surface and the second main surface is reduced by the step of pulling the glass ribbon downward with the tension roller.

6. The method according to claim 1, wherein the overall thickness variation of the glass plates cut from the glass ribbon is 50% or less of the overall thickness variation of the glass ribbon before step (b).

7. The method according to claim 1, wherein the thickness of the glass ribbon between the first main surface and the second main surface decreases between step (b) and step (c).

8. The method according to claim 1, wherein the step of raising the temperature of the first main surface includes the step of directing a flame towards the first main surface.

9. Prior to step (b), the viscosity of the glass ribbon is 10 １０ Poise ~ 10 １２ Poise, In step (b), the viscosity of the first main surface of the glass ribbon, from the first main surface to a depth of at least 100 μm in the thickness direction of the glass ribbon, is 10 ５ It has decreased to below Poise, Prior to step (c), the viscosity of the glass ribbon is 10 ６ Poise ~ 10 ８ The method according to claim 1, wherein the rise is to Poise.

10. A method for manufacturing glass plates, (a) A step of forming a glass ribbon descending as a function of time in a vertical orientation, wherein the glass ribbon has a first principal surface and a second principal surface facing generally opposite directions, and a core disposed between the first principal surface and the second principal surface. (b) As the glass ribbon descends, the steps include: (i) passing the glass ribbon in the immediate vicinity of a first heating zone in which the temperature of the first main surface is raised to a temperature sufficient for liquefaction to occur on the first main surface while keeping the temperature of the core below the softening temperature, and (ii) passing the glass ribbon in the immediate vicinity of a second heating zone in which the temperature of the second main surface is raised to the liquidus temperature while keeping the temperature of the core below the softening temperature; (c) After the glass ribbon has moved below the first heating zone and the second heating zone, the step of cutting the glass plate from the glass ribbon, A method that includes this.

11. The method according to claim 10, wherein between step (b) and step (c), after the overall thickness variation of the glass ribbon has been reduced, the temperatures of the first main surface, the second main surface, and the core approach equilibrium, the effective viscosity of the glass ribbon decreases, and the thickness of the glass ribbon decreases.

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