TW201328991A - Process and device for manufacturing glass ribbon - Google Patents

Abstract

The present invention relates to a process for manufacturing flat ribbons of a glass-based material and to an apparatus therefor. The process comprises providing a glass preform, heating the glass preform in a furnace, forming a gob and a pre-ribbon, removing the gob and drawing the glass pre-ribbon into a flat glass ribbon. Also provided is an apparatus for drawing a glass preform into a glass ribbon, the apparatus comprising a draw furnace, stretching arms for stretching and drawing the pre-ribbon into a glass ribbon, and opposing edge rollers for applying a downward force on the glass ribbon. The draw furnace may include a plurality of individual heating elements, the temperature of each heating element capable of being separately controlled. The apparatus may further include an annealing furnace for annealing the glass ribbon.

Description

Process and apparatus for manufacturing glass ribbon Cross-reference to related applications

The present application is based on the priority of the U.S. Provisional Application No. 61/557521, filed on Nov. 9, 2011, which is hereby incorporated by reference in its entirety in its entirety in Into this article.

The present invention relates generally to methods and apparatus for forming glass ribbons, and more particularly to drawing thin, thin glass ribbons from glass preforms.

There is an increasing demand for flat glass ribbons, particularly for precision flat glass ribbons having high surface quality and consistent thickness, made of glass-based materials or glass ceramic materials. Flat panel displays incorporating such flat glass ribbons have received great attention. Most of the focus is on small units such as those for laptops and very large units such as flat panel displays (i.e., televisions). However, flexible displays are now being considered, and the demand for extremely thin flexible glass substrates has become apparent.

Two common methods for fabricating display substrates are the float process and the melt process. Both of these processes require a fire-resistant glass melter to deliver The molten glass forming material flows to the glass ribbon forming device. In the case of a high strain point glass composition, a relatively large high temperature glass melter is required to transfer the high quality flow of the molten glass forming material to the glass ribbon forming apparatus. This is because the high strain point glass has a high melting temperature, which typically exceeds 1700 °C.

In the float process, a stream of molten glass forming material is discharged from the melting furnace into a float furnace containing a liquid metal medium. Generally, the metal is tin. Control the atmosphere in the float furnace to prevent oxidation of the tin. The molten glass floats in the form of a flat continuous glass ribbon and diffuses on the liquid tin. The glass ribbon is transferred to an annealing kiln or cooling tunnel where the glass ribbon is cooled to ambient temperature at a controlled rate. The cooled glass has a flat, smooth surface which in some cases may need to be further trimmed by processes such as grinding and polishing.

However, it is very difficult to form a glass system having a high strain point in a casing containing molten tin. This is because tin has a high vapor pressure at temperatures in excess of 1050 ° C to 1100 ° C. At the high formation temperatures required for high strain point glass, the molten tin will evaporate inside the float furnace and subsequently condense in the cooler portion of the furnace. In some cases, condensation may be high enough to produce the so-called "fin rain," a condition in which tin falls on the glass as if it were raining and bonded to the surface of the glass.

In the melt process, the glass forms a melt that flows into the refractory tank and then overflows from both sides of the tank in a controlled manner. A key advantage of this process is that the surface of the resulting glass ribbon does not contact any refractory or other forming equipment. Another benefit of this process is that the process produces a very flat and uniform thickness glass ribbon. Therefore, no secondary processing is required to obtain a smooth, flat, and uniform glass ribbon for display applications. However, this method cannot handle glass having a high strain point due to the required high temperature because such temperatures greatly accelerate the deterioration of the glass forming component, and there is a possibility of increasing the contamination of the molten glass. In general, it is desirable to form a glass having a viscosity in the range of 10 ⁵ poise to 10 ⁶ poise to obtain optimum flatness and uniform thickness.

Unfortunately, both the fused draw process and the float glass process are inefficient in producing a flat, extremely thin glass ribbon from a glass composition having a high strain point (e.g., a strain point that can exceed 900 °C).

For roll-to-roll processing of flexible electronic devices and displays, the focus is on the ability to produce thin flexible glass substrates. As used herein, a reel type refers to the supply of a glass ribbon from a first reel or source reel to a second reel or take-up reel, where the pair occurs when the glass ribbon travels from the source reel to the take-up reel Glass belt treatment. Current processes for making thin glass sheets, such as slot drawing, melt forming, and floating, produce a thin glass ribbon (such as having a thickness of about 200 μιη or less than about 200 μιη (eg, 50 microns to 100 microns). There are limitations in the glass ribbon). Re-drawing or pulling down the glass pre-forms enables the fabrication of glass ribbons having a thickness of less than 100 μm with good geometric properties and strength properties. Even if the re-drawing is not a new forming process and has been used for fibers, tubes and other glass products, the ability to draw flat glass ribbons is thin enough to achieve a substrate It is flexible enough to allow the substrate to be wound and used in the unique technology of the reel process. The roll-to-roll process is capable of printing a coating on a thin substrate using existing industrial techniques. For example, thin film electronics can be stored on a moving glass ribbon in a roll-to-roll process.

A glass ribbon that does not have warpage, wrinkles, or other significant deformations beyond the outermost edges of the glass ribbon can be achieved by controlling the viscosity of the drawn glass and maintaining a particular heat distribution within the draw furnace. The glass ribbon can be expanded by using a second furnace that thermally adjusts the drawn shape. The deformation can be further reduced by applying a low draw tension to the glass belt. A protective coating can be applied to the drawn glass ribbon to maintain the strength properties of the glass ribbon and enable the glass ribbon to be wound.

Accordingly, in one embodiment, a method for making a glass ribbon is disclosed, the method comprising the steps of: heating a glass preform in a draw furnace to form a glass ribbon, the glass preform comprising a central portion, a For the opposite edge portions and the thickness of the glass preform is greater than 200 μm, but preferably less than 1.5 mm, the heating step comprises the step of heating the glass preform to center the glass ribbon in the viscoelastic region of the glass ribbon The temperature of the portion is greater than the temperature of the edge portion of the glass ribbon. The glass ribbon is drawn to a predetermined thickness such that the central portion of the glass ribbon is less than 200 μm and the central portion is heat treated in a thermal conditioning furnace at a temperature greater than the annealing temperature of the glass ribbon but less than the softening point of the glass ribbon. The first coating can be applied to a glass ribbon, and after coating the first coating, the glass ribbon can be wound onto a take-up reel having a bend radius of less than about 10 cm.

The draw furnace can include edge heating elements that are vertically positioned to the side heating elements. The method may further comprise the step of heating the glass preform in the preheat furnace prior to heating of the draw furnace.

The step of drawing the glass ribbon preferably includes the step of contacting the glass ribbon with a tractor assembly that pulls down the glass ribbon between the two counter-rotating conveyor belts. Preferably, the central portion of the glass ribbon has a thickness of less than about 200 μm. The edge portion of the glass ribbon can also be less than 200 μm.

The strain point of the glass preform is preferably greater than about 600 ° C, and in some embodiments the strain point is greater than about 900 ° C.

A protective coating can be applied to the glass ribbon before the tractor assembly contacts the glass ribbon such that the coating is between the glass ribbon and the counter-rotating conveyor belt. For example, the protective coating can be applied as a solid film derived from a roll of coating material unrolled from a source roll and can be applied to a glass ribbon. Once formed, the glass ribbon can be rolled onto a reel.

In another embodiment, an apparatus for drawing a glass ribbon is described, the apparatus comprising a draw furnace configured to heat a solid glass preform, the draw furnace comprising horizontally aligned in a direction of a width of the draw furnace a plurality of heating elements and a second plurality of heating elements arranged horizontally in a direction perpendicular to the width of the drawing furnace.

The apparatus can further comprise a thermal conditioning furnace comprising a plurality of heating elements arranged vertically along the length of the thermal conditioning furnace. Opposing counter-rotating conveyor belts are rotatably mounted below the draw furnace and are preferably configured to extend toward and retract away from the glass ribbon, respectively, the opposing counter-rotating belts are designed to engage the glass ribbon and Apply a downward force to Glass belt. The apparatus preferably includes a first coating applicator for coating the film material between the glass ribbon and the counter-rotating conveyor belt. In some embodiments, the apparatus includes a second coating applicator downstream of the counter-rotating conveyor belt.

Preferably, the first plurality of heating elements are independently controlled (i.e., the temperature of the heating elements are independently controlled). The second plurality of heating elements can also be independently controlled.

The apparatus may further comprise a preheating furnace located upstream of the draw furnace.

Other objects, features, details and advantages of the present invention will become more apparent from the description of the appended claims.

In the following detailed description, exemplary embodiments of the present invention It will be apparent, however, that the invention may be practiced in other embodiments of the specific embodiments disclosed herein. In addition, descriptions of well-known devices, methods, and materials may be omitted to avoid obscuring the description of the invention. Finally, in any applicable case, the same component symbols refer to the same components.

Embodiments of the invention include, inter alia, the steps of providing a glass preform; heating the glass preform in a furnace; forming a glass paste ball and drawing the preform into a glass ribbon. Forming the glass paste ball means heating the glass preform to at least the softening point of the glass preform, at which time the thickened portion of the preform (glass paste ball) is pulled away from the body of the preform, thereby using the glass paste The ball draws a wide flow of glass. The softening point is generally considered to be the temperature at which the glass will deform under its own weight, and the glass viscosity at the softening point is about 10 ^7.6 poise.

In one embodiment of the invention, the glass preform is formed by conventional glass forming techniques. These techniques include chemical vapor deposition and casting methods, including the use of a sol gel process. Chemical vapor deposition (CVD) techniques are well known in the art of fiber optics, and such techniques include external vapor deposition (OVD), vapor deposition (VAD), and modified chemical vapor deposition (MCVD), to name a few. An example. Both OVD and VAD must hydrolyze the glass precursor chemicals in the flame to form soot and deposit the soot on the target to form a porous glass soot preform. The preform can then be cleaned by first heating the preform in the presence of a cleaning gas, such as a chlorine-containing gas, and then further heating the preform to a temperature sufficient to combine the soot particles into a clear solid glass preform. Dewatering and combining porous soot preforms. However, it should be noted that the available glass deposition methods are not limited to the examples described above.

Casting of the glass preforms can include mixing the plexiglass precursors to form the pot blank preforms as compared to OVD or VAD. Drying the preform preform by heating and/or exposing the preform preform to a suitable cleaning gas, such as a chlorine containing gas, and subsequently heating the preform preform to merge the preform preform into a transparent Solid glass preforms. An alternative to casting glass preforms involves melting the glass in a suitable crucible The glass (e.g., cullet or glass soot) and thereafter the molten glass is cast into a suitable mold to form the desired preform shape. Both casting methods are well known in the art and the two casting methods are not further described. As with the previously described method of depositing glass, it should be noted that the casting method is not limited to the examples described herein.

In other embodiments, the glass preform can be formed by other conventional glass forming techniques, such as the melt or float process previously described. Moreover, such processes are well known and do not further describe such processes.

FIG. 1 illustrates an exemplary apparatus for drawing glass ribbon 12 from glass preform 14 in accordance with an embodiment of the present invention, generally indicated by symbol number 10. The glass preform 14 is a glass sheet, as seen in the edge-on of Figure 1. The glass preform 14 can be greater than 200 μm, such as greater than 0.5 mm, greater than 0.7 mm, greater than 1.0 mm, or greater than 1.2 mm. However, the glass preform 14 is typically required to be less than 1.5 mm. Apparatus 10 in accordance with an embodiment of the present invention includes a downward feed assembly 16 for holding and moving glass preform 14 , a draw furnace 18 , an optional thermal conditioning furnace 20 , an optional preheat furnace 22 , a first coating Layer applicator 24, tractor 26, optional second coating applicator 28, and take-up reel device 30. Typically, the apparatus 10 is capable of producing a thin glass ribbon from the preform in a ratio of about 3: 1 depending on the width of the preform. That is, since the glass ribbon is necked when the glass ribbon is drawn from the glass preform, the glass ribbon typically has a total width of about one-third of the total width of the glass preform, the glass preform comprising the edge portion And a central portion disposed between the edge portions.

The glass preform 14 can be provided by any of the techniques described above or by any other known glass fabrication technique. Preferably, the glass preform 14 is rectangular in shape, the glass preform 14 having generally parallel opposing sides and a width greater than the thickness. The preformed glass is preferably substantially transparent to visible wavelengths having a transmittance of at least about 95% in the wavelength range from about 390 nm to about 750 nm. For preforms that may be formed in other shapes, such as a cylindrical shape, the preforms may be shaped into a generally rectangular shape, such as by grinding. Although the glass ribbon 12 can be drawn from a glass preform having a strain point similar to that of a conventional glass for a float or melt process (eg, between about 600 ° C and 700 ° C), A glass having a much higher strain point (such as a strain point greater than about 700 ° C, 800 ° C, or even greater than about 900 ° C) is drawn. For example, pure molten vermiculite having a strain point of about 1956 °C can be drawn into a glass ribbon using the apparatus and method of the present invention.

The glass preform 14 is typically suspended from the preform down feed assembly 16 and the preform down feed assembly 16 includes a clip 32 for holding and securely holding the glass preform 14. The down feed assembly 16 is capable of moving the glass preform up or down (along the Z axis 34) in a parallel vertical direction via a motor 36 that is coupled to the screw 38 by a nut (not shown). As used herein, the X axis, the Y axis, and the Z axis represent three vertical axes. However, other suitable drive configurations known in the art that provide precise control of the downward feed speed can be substituted. The down feed assembly 16 can also be oriented perpendicular to the Z axis (ie, at X-Y level) The pre-forms are moved in the face to allow the glass preform to be properly positioned within the draw furnace 18. For example, the glass preform 14 is preferably located at the center of the draw furnace to ensure uniform heating of the preform.

Once the glass preform 14 is suspended from the down feed assembly 16, the glass preform 14 is lowered to the high temperature zone of the draw furnace 18 by the down feed assembly, at which point the lower portion of the glass preform 14 is heated to At least the softening point of the glass preform 14. For example, the draw furnace can be heated to a temperature of at least about 1075 ° C to spheroidize the preform. The practice of gobbing of glass paste allows the glass to reduce its width under its own weight and accomplish the practice of spheroidizing the glass paste at a temperature slightly higher than the actual drawing operating temperature. The drawing furnace 18 may be: an electric resistance furnace in which heat is obtained by flowing a current through the electric resistance heating element; an induction furnace in which heat is taken by current in the microwave susceptor; or the furnace can be heated to at least glass preforming Any other heating method for the temperature of the softening point of the piece. For example, the furnace can be a gas furnace that burns gaseous fuel to form a flame. Preferably, the furnace is capable of heating the glass to a temperature of at least about 900 °C; more preferably to at least about 1500 °C; and optimally to at least about 2200 °C. Once the preform has been "glass paste spheroidized", the temperature of the draw furnace can be lowered.

In the embodiment of the draw furnace 18 illustrated in FIG. 2, the draw furnace is a resistor comprising a pair of opposing side plates 42 and a pair of opposing end plates 44 arranged in a rectangular shape defining a hollow interior space 46. Pulling furnace. The drawing furnace 18 comprises a plurality of horizontally arranged heating zones, designated as zones 2-5 in Figure 2, each heating zone comprising laterally aligned along the two major sides of the glass ribbon. One or more heating elements 48. Preferably, the heating elements of each heating zone are controlled independently of the heating elements of the other heating zones and, in some embodiments, independently of the other heating elements in the same heating zone. Each heating element 48 is preferably shaped as a strip to ensure a sufficient current carrying capacity, and each heating element 48 can be formed of, for example, molybdenum dichloride. To assist in sensing a uniform thermal gradient and reducing hot spots created by the close proximity of the glass preform to the heating element, the side panels 42 and end plates 44 may be formed and positioned by a suitable high temperature thermally conductive material such as tantalum carbide (eg, Hexoloy®). Between the glass preform and the heating element, the side plates diffuse heat provided by the heating element and provide a more uniform heat distribution at each heating zone within the draw furnace 18. The end plate 44 of the rectangular draw furnace has side plates 42 A similar configuration and heating end plate 44 is heated as a heated zone (labeled as zone 6 in Figure 3) that is isolated from zones 2-5. A separate heating element 50 in the end zone (Zone 6) provides for drawing the edge of the glass sheet at a temperature different from the viscosity of the central section of the glass ribbon by heating the edge of the glass ribbon to a temperature different from the temperature of the central section of the glass ribbon. Ability. The end heating element 50 can have the same design as the side heating element 48 but aligns the isometric heating elements 50 in an orientation generally oriented perpendicular to the orientation of the side heating elements 48, and the end heating elements 50 are positioned to heat the glass ribbon. The edge is not the lateral (main) surface of the glass ribbon. Preferably, the edge of the glass preform is heated to a temperature greater than the temperature of the interior, central portion of the glass preform. End plate 44 isolates end heating element 50 from glass ribbon 12. Side panel 42 and end panel 44 mitigate warpage and other flatness deformations that may be experienced by the drawn glass ribbon due to thermal variations and tensile stresses applied across the preform.

Most glass forming operations require isothermal conditions, but when re-drawing a wide flat glass ribbon, it may preferably have non-isothermal conditions. The isothermal conditions on the glass preform together with the tensile force applied to the tapered glass ribbon may result in uneven tensile tension across the width of the preform. Under isothermal conditions, the tensile tension at the center of the preform will be greater than the tensile tension at the edges and thus the glass draw at the center of the preform will be drawn faster than the glass at the edges. The resulting differential tensile tension across the width of the preform may result in warpage and thickness variations in the glass ribbon. For example, the curl at the edges of the glass ribbon can be revealed. In particular, heating the edge of the glass preform to the temperature above the center of the preform at the root of the preform reduces the tensile tension effect and produces a flatter drawn glass ribbon. As used herein, a preformed root refers to a point at which a glass preform forms a transition from an elastomeric solid to a viscous liquid, generally characterized by a reduced width. More simply, the root indicates the area where the glass preform is over and the glass ribbon begins. The ability to have temperature control between the center of the glass preform and the edge of the preform, particularly at the root of the preform, enables the drawing of a flat, substantially warp free glass ribbon. However, the glass ribbon exhibits a slight thickness variation at the extreme edges. Therefore, it may be necessary to remove the edge portion.

In one embodiment, the individual side heating elements 48 can be arranged linearly (i.e., in a single row) across the width of the furnace. Preferably, the individual heating elements 48 are independently controlled, for example, by a controller (not shown) such that the temperature of the individual heating elements can be independently adjusted. The use of individual heating elements that independently control the temperature provides greater flexibility to the drawing process by facilitating the application of a specific spatial temperature profile to the glass preforming The pieces, and in particular the width across the glass ribbon, are applied to the glass ribbon, thereby reducing temperature-related defects such as glass ribbon warpage due to uneven temperature distribution across the width of the glass ribbon. Where multiple independently controlled heating elements are used, the controller can also control the temperature of the individual heating elements to adjust the temperature profile applied to the glass preform.

As illustrated in FIG. 3, each of the draw furnace heating elements 48 and 50 can be formed as a "U" shaped member that extends in a longitudinal direction L that coincides with the longitudinal direction of the draw furnace 18. That is, preferably, at least a portion of each of the individual heating elements 48 and/or 50 extends vertically along the length of the draw furnace in the draw direction. The thermocouple 52 can be inserted into the draw furnace 18 at a location suitable for monitoring the temperature within the draw furnace.

In addition to the draw furnace 18, as illustrated in FIG. 4, the preheat furnace 22 can be positioned above the draw furnace 18. The draw furnace 18 can be idling between draw cycles at about 500 ° C to extend the life of the draw furnace heating element and reduce the time required to heat the furnace to the draw temperature. If the thermal expansion of the glass is sufficiently low, it is generally not a problem to immerse the glass preform into a draw furnace at 500 °C. However, for high CTE glass, or if the glass is ion exchangeable glass, care must be taken when loading the glass preform into the draw furnace. In order to prevent thermal shock to the glass preform, or thermal shock to the draw furnace component, the preheating furnace 22 can be used to preheat the glass preform to a suitable temperature before the glass preform 14 enters the draw furnace 18. temperature. The preheating furnace 22 includes one or more heating elements 53 arranged across the width of the preheating furnace 22, wherein the heating elements can be electrical resistance heating elements. For example, the heating element 53 can be a wire heating element (such as a wire Loop wire heating element). Suitable heating element materials may comprise tungsten or nichrome.

The apparatus 10 can include an optional thermal conditioning furnace 20 that can be positioned below the draw furnace 18 with respect to the draw direction. The embodiment of the thermal conditioning furnace 20 is illustrated in Figures 2 and 5. Preferably, the thermal conditioning furnace 20 has a plurality of heating zones vertically aligned in the direction L along the conditioning furnace, the plurality of heating zones comprising a plurality of heating elements 54 arranged vertically downward along the length of the conditioning furnace. The thermal conditioning furnace 20 typically has a reduced temperature capability compared to the draw furnace 18, and the thermal conditioning furnace 20 can, for example, be equipped with a resistance wire heating element 54. That is, the heating element 54 preferably has a lower current carrying capacity than the drawing furnace heating elements 48 and/or 50. The thermal conditioning furnace 20 is preferably rectangular in shape with the individually controlled side heating elements and end heating elements. It should be noted that the heat regulating furnace 20 is not annealed because it is intended to make the temperature of the upper heating zone of the heat regulating furnace higher than the annealing point of the glass ribbon. The heat regulating furnace 20 is used to control the shape of the glass ribbon to reduce deformation in the glass ribbon. Additionally, the thermal conditioning furnace 20 helps reduce some of the internal stresses introduced into the glass ribbon by the tempered glass. The thermal conditioning furnace 20 can be directly coupled to the draw furnace 18, as illustrated in Figure 1, or the thermal conditioning furnace 20 can be isolated or spaced apart from the draw furnace 18.

Similar to the draw furnace 18, the thermal conditioning furnace 20 preferably includes a heat sink 39 positioned between the heating element and the drawn glass ribbon along the width of the thermal conditioning furnace. The heat regulating furnace may also include a heat sink 41 positioned between the end heating element and the edge of the glass ribbon. The heat sink 19 and the heat sink 23 may be formed of Hexoloy® or the like.

The addition of the thermal conditioning furnace 20 below the redrawn furnace can further have the ability to draw a flat glass ribbon. Although the top zone in the conditioning furnace is at a temperature just below the softening point of the glass but above the annealing point of the glass, the top zone is still hot enough to allow the viscoelastic deformation of the glass. As the glass ribbon traverses the upper portion of the thermal conditioning furnace, the edge of the drawn glass ribbon cools faster than the central region. As the draw tractor uniformly applies tensile tension at more raised portions of the glass ribbon (not confused with the underlying viscous regions of the preforms mentioned above), the glass flattens as the edges are quenched. The central zone of the conditioning furnace is at a temperature greater than the glass annealing temperature of the glass ribbon, and the lower zone is at a temperature that is approximately the strain point of the glass. This condition allows for the reduction or elimination of any residual stress in the glass ribbon since the glass ribbon is so thin that the time of the glass ribbon in such regions is sufficient. This in turn allows the glass to be wound without damage and subsequently used in a reel process.

After the drawing process has stabilized, the polymer coating 56 is preferably applied to the glass ribbon above the draw tractor 26. The coating 56 protects the glass ribbon from contact with downstream draw elements to maintain acceptable optical quality of the surface and to prevent surface damage to the glass that can reduce the strength of the glass ribbon. In addition to or in lieu of coating the coating, a system for applying the edging to the edge of the ribbon can be performed during drawing. By providing a position at which the glass ribbon can be conveyed, the rimmed edges of the glass ribbon can be reeled from the spool. That is, the roll conveyor can utilize a mechanical transfer system to clamp the edging. Alternatively, if the polymer coating is removed prior to applying the edging, the edge edging application can be performed offline. Therefore, the equipment and process can be full A portion or portion of the width of the protective coating is applied to the surface of the glass ribbon and the coating can be permanently or temporarily bonded to the glass.

Thus, FIG. 1 illustrates a first coating applicator 24 for applying a protective polymer coating 56 to the glass ribbon 12. The protective polymer coating 56 can be supplied from at least one supply roll 58 and the protective polymer coating 56 can be applied to the glass ribbon 12 by the applicator 60. For example, applicator 60 can include a roller for pressing a coating film to a glass ribbon. Preferably, the coated protective polymer coating 56 is applied to the two major surfaces of the glass ribbon. The protective polymer coating 56 provides mechanical protection to the quality zone of the glass ribbon 12 and prevents direct contact of the glass ribbon with the tractor 26. As used herein, the term quality zone refers to the portion of the glass ribbon that is ultimately sold and used for manufacture, which is in direct contrast to the edge portion of the glass ribbon that is typically removed from the glass ribbon and can be used as a cullet for further glass forming processes. . Therefore, the quality zone is the central part of the glass ribbon.

Once the drawing has begun, the glass preform is lowered into the furnace at a precise feed rate, which is controlled based on the downward feed motor speed and the temperature profile formed within the draw furnace 18. For example, a typical downward feed rate for a glass preform is about 10 mm/min to 12 mm/min. As previously stated, once the glass paste ball has dripped and the glass ribbon has engaged the tractor 26, the draw furnace is lowered from the initial glass paste spheroidization temperature (e.g., about 1075 ° C) to a suitable draw temperature. The main parameter driving factors for the re-drawing process are: the feed rate down, the furnace temperature that controls the viscosity of the glass, and the drag rate, also known as the draw speed. The draw viscosity is generally in the range of from about 10 ⁶ poise to about 10 ⁷ poise. The suitable draw tension is measured by the force in the down feed system, and the satisfactory draw tension can range from about 2 pounds to 3 pounds. A difficulty in drawing a sheet glass ribbon from a glass preform is that the preform may have a thickness of, for example, about 0.70 mm and a width of about 300 mm, which is equivalent to an aspect ratio of about 1:400 or greater. . Therefore, in order to maintain proper flatness of the drawn glass ribbon, it is necessary to carefully monitor the glass preform down feed rate, the draw furnace temperature, and the draw rate applied by the tractor 26.

In an alternative embodiment, the polymeric coating can be applied, for example, by drawing a glass ribbon through a liquid coating bath. Alternatively, the liquid coating can be sprayed onto the glass surface. The liquid coating can be applied to one or more surfaces of the glass. The liquid coating can then be cured by suitable curing equipment required by the type of coating. For example, the curing device may be an oven that cures the coating by heat (thermal curing), or the curing device may cure the coating (photocuring) by exposing the coating to ultraviolet light. The coating or coating applied to the glass ribbon can be permanently or temporarily bonded to the glass.

Once the glass paste balls have dripped through the thermal conditioning furnace 20 and are located below the thermal conditioning furnace 20, the glass paste balls are typically manually pulled down via a coating applicator and the glass paste balls are placed into the drawn tractor assembly 26. The draw tractor 26 includes two counter-rotating conveyor belts 62 driven by a plurality of drive wheels 64 such that the motion between the two counter-rotating conveyor belts 62 is downward. The counter-rotating conveyor belt 62 can move inward toward the glass ribbon or outward away from the glass ribbon. When the conveyor belts are brought together, the glass ribbon 12 is pinched between the conveyor belts. The conveyor belt can be opened and closed by a pneumatic actuator and can be lost The pinch force applied by the conveyor belt is adjusted when the belt is closed. For thin glass ribbons having a central portion of thickness (eg, average thickness) equal to or less than about 200 μm (such as equal to or less than about 150 μm, equal to or less than about 100 μm, and in some cases equal to or less than about 50 μm) The pinch force is maintained to a minimum to avoid crushing the glass ribbon between the conveyor belts, but the pinching force is sufficient to allow the conveyor belt to open and close smoothly. The tractor unit speed is servo controlled and sets the speed of the tractor unit to a speed sufficient to maintain a slight tension on the ribbon. A load cell on the clamping device (not shown) provides measurement feedback to the controller such that the draw tension applied to the preform can be controlled. A typical draw speed or drag rate is about 0.30 m/min.

The conveyor belt 62 pulls down the glass ribbon 12 from the glass preform 14. Conveyor belt 62 is preferably formed from a high temperature resistant elastomeric material. It has been found that a softer, more flexible conveyor belt is superior to a hard conveyor belt surface. Preferably, the conveyor belt 62 extends across the entire width of the glass ribbon and the conveyor belt 62 can be, for example, wider than the glass ribbon. The coating as previously described can be positioned between the glass ribbon and the conveyor belt, such as by coating the coating on the glass ribbon, to protect the major surface of the glass ribbon from direct contact with the conveyor belt.

Alternatively, the tractor 26 can include a plurality of narrow conveyor belts that can be independently vertically positioned, and wherein each conveyor belt can travel open or closed. For example, six conveyor belts can be used, with three conveyor belts on one side of the glass ribbon and the other three conveyor belts on the other side of the glass ribbon. The tractor system is capable of drawing a glass ribbon only by the edges of the glass ribbon or only by the center of the glass ribbon or a combination of such edges and center. Traction conveyor belt This configuration allows a substantially uniform draw force to be applied to the entire much wider glass ribbon (e.g., a glass ribbon having a width of up to 500 mm). The previously described "single" tractor is limited to a belt width of less than about 150 mm.

When the glass ribbon 12 is pulled down by the tractor 26, the thickness of the glass ribbon is reduced until the central portion of the glass ribbon reaches a predetermined thickness. That is, the glass ribbon will typically include a central portion and a thickened edge portion. The edge portion can be removed, wherein the center portion can be further processed. The thickness of the glass ribbon, and in particular the thickness of the central portion, is (especially) the speed at which the glass ribbon is drawn from the preform, the rate at which the preform is fed into the draw furnace 18 (downward feed rate), and the draw furnace The factor of temperature. The upper limit of the thickness of the glass ribbon that can be drawn is generally determined by the thickness of the preform. Preferably, the drawn glass ribbon has a maximum thickness of less than about 1.5 mm, less than about 1.0 mm, and more preferably less than about 0.7 mm, but is typically greater than 200 μm. The glass ribbon drawn according to an embodiment of the present invention may be drawn such that the central portion of the glass ribbon has a thickness equal to or less than about 200 μm, equal to or less than about 150 μm, equal to or less than about 100 μm, or equal to or less than about 50. Mm. The thickness of the edge portion of the glass ribbon can also be drawn to less than 200 μm.

The thickness of the glass ribbon can be measured as part of the draw process and the results of this measurement can be used to control, for example, the downward feed rate of the preform and/or the draw rate of the tractor 26. The thickness of the glass ribbon can be measured by a suitable metrology device, such as a laser micrometer, indicated by reference numeral 66 in Figure 1. Such devices are readily commercially available. The error signal is developed by the metrology device 66 based on a predetermined set point of the thickness of the ribbon that has been input to the controller. The error signal is relayed to the controller (not shown). The controller can be (for example Such as) computer. The controller can then adjust the down feed rate, edge drum speed and/or torque or furnace temperature, or a combination thereof, according to predetermined instructions, such as a computer program, to reduce the error signal from the metrology device 66 and thus correct the ribbon. thickness.

In some embodiments, an optional second coating applicator 28 can be used. As illustrated in FIG. 1, a second coating applicator assembly 28 for applying a protective film 68 to the glass ribbon 12 can be included. A protective film is supplied from at least one supply reel 70 and a protective film is applied to the glass ribbon 12 by the applicator reel 72. Preferably, the coated protective film 68 is applied to both major surfaces of the glass ribbon.

The final step is to wind the coated glass ribbon. The manner in which the drawn glass ribbon is recovered from the drawing operation depends in part on the thickness of the glass ribbon and, more particularly, on the thickened edge portion. For example, if the thickened edge portion of the glass ribbon has a thickness equal to or less than about several hundred micrometers, the glass ribbon can be wound on the large reel 31 shown in Fig. 1 using a motor-mounted reel machine. The reel machine has tension control that allows the glass to be securely wound on the reel with minimal tension. The reel can be stored for a long period of time and the surface tension from the curved glass around the diameter of the reel is sensed on the glass ribbon, so having a reduced winding tension on the glass will reduce damage. The large reel 31 can then be used as a source reel in a subsequent reel process in which the glass ribbon is moved from the source reel to a subsequent take-up reel and as the ribbon travels from the source reel to the take-up reel The glass ribbon is subjected to intermediate processing. Intermediate processing may include, for example, trimming (eg, removal) of the ribbon edge, deposition of one or more film layers, or may be used to attach the ribbon to the glass ribbon Any other process for the value of the promotion of the final product. For roll processing, several spools of glass ribbon can be spliced together to provide a longer length of glass ribbon.

Alternatively, individual panels of a predetermined size may be cut from the glass ribbon later if desired. The glass ribbon having a thickness (e.g., a thickness greater than about one millimeter) that causes the glass ribbon to break during attempting to wind the ribbon to be cut into individual panels of a predetermined size or a plurality of predetermined dimensions must be cut during the drawing process. The operation of cutting the glass ribbon into individual panels can be accomplished by any of the methods known in the art, including scoring and cutting or laser cutting of the glass ribbon.

Instance

As described above, careful management of the temperature profile is required to overcome the differential draw tension experienced by the glass preform when the glass preform is drawn into a glass ribbon. To this end, the drawing furnace and the heat regulating furnace are divided into a plurality of zones, wherein the temperature in the zone can be individually controlled. Referring to, for example, Figures 2 and 3, an exemplary temperature profile for drawing a glass ribbon from a glass sheet preform can be formed to heat the zones for the draw furnace and the heat regulating furnace in accordance with Table 1.

The glass preform according to examples of the present invention can have a width in the range of from about 280 mm to about 325 mm. The length of the glass piece corresponds to the amount of glass that is intended to be drawn and the physical capabilities of the drawing equipment. The glass preforms have strain points in the range of from about 600 °C to about 1956 °C (eg, from about 600 °C to about 1000 °C, from about 600 °C to about 900 °C, or from about 600 °C to about 800 °C). In other embodiments, the glass preform has a strain point in the range of from about 700 ° C to about 1956 ° C, from about 800 ° C to about 1956 ° C, from about 900 ° C to about 1956 ° C, or from about 1000 ° C to about 1956 ° C. The thickness of the preform can range, for example, from about 0.70 mm to about 1.5 mm.

Preferably, the glass preform is driven downward by a feed down assembly 16 to feed at a feed rate ranging from about 10 mm/min to about 12 mm/min. The draw speed applied by the tractor assembly 26 is in the range of from about 0.2 meters per minute to about 0.4 meters per minute. For example, the draw speed applied by the tractor 26 can be about 0.3 meters per minute to provide a draw tension of about 2.8 pounds at the centerline of the glass ribbon.

It will be apparent to those skilled in the art that various other modifications and changes can be made in the present invention without departing from the spirit and scope of the invention. Chemical. Thus, it is intended that the present invention cover the modifications and modifications of the invention

10‧‧‧ Equipment

12‧‧‧glass ribbon

14‧‧‧Glass preforms

16‧‧‧ Down feed component

18‧‧‧ Pulling furnace

20‧‧‧heat adjustment furnace

19‧‧‧Dissipation plate

23‧‧‧Dissipation plate

22‧‧‧Preheating furnace

24‧‧‧First coating applicator

26‧‧‧ traction machine

28‧‧‧Second coating applicator

30‧‧‧Winding reel device

31‧‧‧ large scroll

34‧‧‧Z axis

L‧‧‧ portrait

32‧‧‧Clamping parts

36‧‧‧Motor

38‧‧‧ screw

39‧‧‧Dissipation plate

42‧‧‧ side panels

41‧‧‧heat plate

44‧‧‧End board

46‧‧‧Internal space

48‧‧‧ heating elements

52‧‧‧ thermocouple

50‧‧‧ heating element

53‧‧‧ heating element

54‧‧‧ heating element

56‧‧‧Coating

58‧‧‧ Supply reel

60‧‧‧applicator

62‧‧‧Reverse rotation conveyor belt

64‧‧‧Drive wheel

66‧‧‧Measuring device

68‧‧‧Protective film

70‧‧‧ Supply reel

X‧‧‧ axis

72‧‧‧applicator reel

Z‧‧‧ axis

Y‧‧‧ axis

Figure 1 is a side cross-sectional view of an apparatus for re-drawing a glass sheet into a thinner glass sheet; and Figure 2 is a side cross-sectional view of the drawing furnace for the apparatus of Figure 1, the drawing furnace Including an optional preheating furnace and a thermal conditioning furnace; Fig. 3 is a top cross-sectional view of the drawing furnace of Fig. 2, showing a horizontally arranged heating element comprising independently controlled heating zones; Fig. 4 is for A perspective view of the individual heating elements of the drawing furnace of Figure 2; and Figure 5 is a top cross-sectional view of the thermal conditioning furnace of Figure 2, the heating furnace comprising vertically arranged heating elements, the heating elements comprising independent Controlled heating zone.

10‧‧‧ Equipment

12‧‧‧glass ribbon

14‧‧‧Glass preforms

16‧‧‧ Down feed component

18‧‧‧ Pulling furnace

20‧‧‧heat adjustment furnace

22‧‧‧Preheating furnace

24‧‧‧First coating applicator

26‧‧‧ traction machine

28‧‧‧Second coating applicator

30‧‧‧Winding reel device

31‧‧‧ large scroll

32‧‧‧Clamping parts

36‧‧‧Motor

38‧‧‧ screw

56‧‧‧Coating

58‧‧‧ Supply reel

60‧‧‧applicator

62‧‧‧Reverse rotation conveyor belt

64‧‧‧Drive wheel

66‧‧‧Measuring device

68‧‧‧Protective film

70‧‧‧ Supply reel

72‧‧‧applicator reel

X‧‧‧ axis

Y‧‧‧ axis

Z‧‧‧ axis

Claims (10)

A method for making a glass ribbon, the method comprising the steps of: heating a glass preform in a draw furnace to form a glass ribbon, the glass preform comprising a central portion, a pair of opposing edge portions, and a thickness greater than 200 μm, the heating step comprising the step of heating the glass preform such that a temperature of one of the central portions of the glass ribbon is greater than the edge of the glass ribbon in a viscoelastic region of the glass ribbon a temperature of the portion; drawing the glass ribbon such that a central portion of the glass ribbon has a thickness equal to or less than 200 μm; and a thickness greater than an annealing temperature of the glass ribbon but less than a softening point of the glass ribbon Temperature to heat the drawn glass ribbon in a thermal conditioning furnace; applying a first coating to the glass ribbon; and winding the glass ribbon onto a take-up reel, wherein the wrapped glass One of the belts has a bending radius of less than about 10 cm. The method of claim 1, the method further comprising the step of heating the glass preform in a preheating furnace prior to the heating step of the draw furnace. The method of claim 1 wherein the step of heating the glass preform comprises the step of positioning the edge heating element perpendicular to the side heating element. The method of claim 1, wherein the drawing step comprises the step of contacting the glass ribbon with a tractor assembly that pulls down the ribbon between two counter-rotating conveyor belts. . The method of claim 1 wherein the glass preform has a strain point greater than about 600 °C. The method of claim 4, wherein a first coating is applied to the glass ribbon before the tractor assembly contacts the glass ribbon such that the first coating is located in the glass ribbon and the counter-rotating Between the conveyor belts. The method of claim 1, the method further comprising the step of winding the glass ribbon on a reel. An apparatus for drawing a glass ribbon, the apparatus comprising: a draw furnace configured to heat a solid glass preform, the draw furnace comprising a first plurality of heating elements and a second a plurality of heating elements, wherein the first plurality of heating elements are horizontally aligned along a direction of a width of the drawing furnace and the second plurality of heating elements are horizontally aligned in a direction perpendicular to the width of the drawing furnace a heat regulating furnace comprising a plurality of heating elements vertically arranged along a length of the heat regulating furnace; Opposing counter-rotating conveyor belts rotatably mounted below the draw furnace and configured to extend toward and retract from the glass ribbon, respectively, wherein the extending step An equal conveyor belt is engaged with the glass ribbon to apply a downward force to the glass ribbon; and a first coating applicator for rotating the glass ribbon with the counter-rotating A film material is applied between the conveyor belts. The apparatus of claim 8 wherein the heating elements of the first plurality of heating elements are independently controlled. The apparatus of claim 8 further comprising a preheating furnace upstream of the draw furnace.