JP5611572B2 - Stress control area - Google Patents

Description

  The present disclosure relates to the manufacture of display devices, such as glass sheets used as substrates in liquid crystal displays (LCDs). More specifically, the present disclosure relates to a glass formed of a glass ribbon in addition to the stress and shape in the glass ribbon in which the sheet is manufactured by a downdraw glass manufacturing method (for example, a fusion downdraw method). The present invention relates to a method and apparatus for controlling a stress in a sheet and its shape.

  Display devices are used in various applications. For example, thin film transistor liquid crystal displays (TFT-LCDs) are used in notebook computers, flat panel desktop monitors, LCD televisions, and the Internet and communication devices, to name a few.

  Many display devices such as TFT-LCD panels and organic light emitting diode (OLED) panels are formed directly on a flat glass sheet (glass substrate). In order to increase the production speed and reduce the cost, in a general panel manufacturing process, a large number of panels are simultaneously formed on a single substrate or a sub-piece of the substrate. At various points in the process, the substrate is divided into small portions along the cutting line.

  Such cutting changes the stress distribution within the glass, particularly the in-plane stress distribution seen when the glass is flattened in a vacuum. In particular, the cutting relieves stress at the cutting line in such a way that the cut edge is not pulled. Such stress relief generally results in a change in shape of the vacuum flattened glass subpiece, a phenomenon that display manufacturers call “strain”. Although the amount of shape change is generally very small, from the point of view of the pixel structure used in modern displays, the distortion caused by the cutting is so great that it produces a significant number of defective (failed) displays. Thus, distortion issues are an important concern for display manufacturers, and specifications regarding acceptable distortion as a result of cutting are required.

  In addition to causing distortion when the glass sheet is cut into sub-pieces, stresses, including residual stresses frozen in the distorting glass and temporary stresses that disappear as a temperature equilibrium of the glass, are also Affects the shape of the glass ribbon used in the manufacture of The shape of the glass ribbon in turn affects processes such as sheet separation. In particular, the shape of the ribbon affects the movement of the ribbon during scoring in addition to affecting scoring and the substantial separation of individual sheets from the ribbon.

  In the context of the above description, considerable efforts have been made to control the stress and shape within the glass ribbon used to produce glass sheets in the downdraw glass making process. The present disclosure provides a method and apparatus that reduces the unintentional effects of these undesired stresses and shapes on the glass ribbon and the final sheet formed from the glass ribbon.

According to a first aspect, an apparatus for producing a glass sheet (13) by a downdraw method for producing a glass ribbon (15) is disclosed. This device
(A) a first set of pulling rolls (60) in contact with the glass ribbon (15) during use of the device;
(B) a second set of traction rolls (70) in contact with the glass ribbon (15) during use of the device, the second set of traction rolls positioned below the first set of traction rolls (60) ( 70)
(C) A stress control region (50) that passes through the glass ribbon (15) during use of the device and is positioned between the first set of traction rolls (60) and the second set of traction rolls (70). And a stress control region (50) having an across-the-draw spatial temperature resolution of 150 mm or less in the glass ribbon (15)
Including.

  According to a second aspect, in an apparatus comprising heating elements (51) arranged in two rows and having openings (55) between the two rows for receiving a glass ribbon (15), the device Discloses a device characterized in that the glass ribbon (15) has a transverse transverse spatial temperature resolution of 150 mm or less.

According to the third aspect,
(A) producing a glass ribbon (15) using the downdraw method, and
(B) including each step of cutting the sheet (13) from the glass ribbon (15),
Disclosed is a method of forming a glass sheet, wherein the glass ribbon (15) passes through a stress control region (50) having a transverse transverse spatial temperature resolution of 150 mm or less in the glass ribbon (15).

  The reference signs used in the above summary of various aspects of the disclosure are for the convenience of the reader and are not to be construed as limiting the scope of the invention. More generally, the summary of the invention described above and the detailed description set forth below are merely illustrative of the invention and are intended to provide an overview and framework for understanding the nature and nature of the invention. Please understand that.

  Additional features and advantages of the invention will be set forth in the detailed description that follows, and in part will be apparent to those skilled in the art from the description or by carrying out the invention as described herein. It will be clear immediately. The accompanying drawings are included to enhance the understanding of the present invention and are incorporated in and constitute a part of this specification. It should be understood that the various features of the invention disclosed in this specification and the drawings can be used in any combination.

It is a schematic front view of the molten glass manufacturing apparatus of exemplary embodiment. It is a schematic side view of the molten glass manufacturing apparatus of exemplary embodiment. A glass ribbon (not shown) moves down the centerline of the drawing between the pulling rolls. FIG. 3 is a schematic front view of an embodiment of a heating element in a stress control region. 1 is a perspective view of an embodiment of a heating element and related equipment in a stress control region. FIG. Figure 6 is a graph showing the measured stress of a glass sheet for four active heating elements in the stress control region. Figure 6 is a graph showing the measured stress of a glass sheet for nine active heating elements in the stress control region.

  1-3 are not measured and are not intended to show the relative sizes of the elements shown.

  The fusion downdraw method (known as the fusion method, overflow downdraw method or overflow method) is described below. It should be understood that the methods and apparatus disclosed and claimed herein can also be applied to other downdraw methods, such as the slot draw method. Melting devices are well known in the art and are not described in detail to avoid obscuring the description of the exemplary embodiments.

  As shown in FIG. 1, the conventional fusion method uses a forming structure (iso-pipe) 37 that receives molten glass (not shown) in a cavity 39. The isopipe includes a root 41 where molten glass from the two converging sidewalls of the isopipe meet to form the ribbon 15. After leaving the root, the ribbon first exceeds the edge roller 27 and then the first set of tow rolls 60. As it flows downward, the glass passes through a set area, schematically shown at 31 in FIG. As is known in the art, at a temperature above the set area, the glass becomes essentially a viscous liquid. At temperatures below the set area, the glass basically looks like an elastic solid. As the glass is cooled from the high temperature through the set region, there is no sudden change from viscous to elastic behavior. Instead, the viscosity of the glass gradually increases, via a viscoelastic state where the viscous and elastic responses are significant and ultimately behave as an elastic solid.

Glass that is cooled from high temperature to low temperature has an increase in viscosity that results in stress relaxation. Consider first a glass material that is cooled at a constant rate CR at a temperature T ₀ . The temperature as a function of time is given by

At time t = 0, let γ be the small instantaneous shear strain of the glass. Some shear stress σ is required to maintain strain. In general, unless the temperature T ₀ is very low, the stress decreases in time. For times greater than zero, the shear relaxation coefficient is defined as:

If the strain is very small, the shear stress is linearly related to the shear strain and the coefficient is independent of the strain. As time progresses during cooling, G (t; T ₀ , CR) generally decreases due to stress relaxation. When T ₀ is high and CR is small, G (t; T ₀ , CR) rapidly decays to zero. When T ₀ is low and CR is very large, G (t; T ₀ , CR) does not decay clearly. Anyway, the coefficient G (t; T ₀ , CR) approaches the asymptotic value G (∞; T ₀ , CR) over time.

The stress relaxation rate F (T ₀ , CR) is defined as follows.

At high initial temperatures or slow cooling, F approaches zero. At low initial temperatures or fast cooling, F approaches 1. The set region is defined as follows according to the definition of a certain cooling rate CR and the above-described stress relaxation rate.

Setting area is the temperature region of from _{T 95} to _{T 0.}

  While the first set of pulling rolls 60 is positioned in the setting area, the edge roller 27 contacts the ribbon 15 at a position above the setting area in FIG. Depending on the application, the second set of tow rolls 70 is positioned within or below the set area. As shown in FIG. 2, additional sets of tow rolls 80 and 90 can be used if desired. The temperature of the edge roller is below the temperature of the glass. For example, the edge roller is water cooled or air cooled. As a result of this low temperature, the edge roller locally lowers the glass temperature. This cooling reduces ribbon attenuation. That is, local cooling assistance controls the reduction in ribbon width that occurs during pulling (eg, through the action of a pulling roll). Tow rolls are also generally cooler than the glass they contact, but because they are positioned far below the pulling device, the temperature difference can be smaller than at the edge rollers.

According to an embodiment, the stress control region 50 (stress control assembly) is incorporated into the drawing process at a position below the first set of traction rolls 60 and above the second set of traction rolls 70. As shown in FIG. 1, the stress control region is closer to the first set of traction rolls than the second set of traction rolls. In some embodiments, the stress control region is a region where the properties of the glass ribbon change from a viscous liquid to an elastic solid , eg, the region of the setting region, although it may be used at other locations if desired . Located in the lower third region .

  The stress control region provides a stretch transverse temperature control level that was not achievable with conventional drawing methods. Quantitatively, the stress control region provides a stretch transverse spatial temperature resolution of 150 mm or less (˜6 inches), for example, a spatial temperature resolution of about 75 to about 125 mm (˜3-5 inches). As used herein, the spatial temperature resolution of the stress control region is such that the temperature at two points changes substantially independently of each other, i.e., the temperature change at one point is ± 10% at maximum at the other point. The minimum horizontal distance between two points that provides a temperature change of. The two points are located in the high-quality portion of the glass ribbon, that is, the portion that eventually becomes the glass sheet (glass substrate). In particular, the level of spatial temperature resolution is used to control the stress of the glass ribbon and can reduce the distortion of the glass substrate when cut into sub-pieces (see above).

  FIG. 3 is a schematic diagram of an embodiment of a stress control region showing the use of a plurality of closely packed heating elements 51 to achieve stretch transverse spatial temperature resolution that can control stress within the glass ribbon. Although the heating element (winding) was previously used in the melter for all temperature control, the space temperature at the ribbon surface is fine enough to allow the winding to significantly control the stress in the glass ribbon. To provide resolution, the spacing was too wide in the direction transverse to the stretch. Also, the spacing between the windings and the ribbon surface was too large for this purpose.

  According to the present disclosure, both the stretch transverse spacing between heating elements (ie, the distance between the centers between adjacent elements) and the distance from the element to the glass ribbon (ie, the distance from the ribbon to the heating element). Is used to achieve a stretch transverse spatial temperature resolution of 150 mm or less. To simplify manufacturing, the physical spacing between adjacent heating elements is usually the same for all elements. However, varying intervals can be used if desired. Thus, as used herein, the spacing between heating elements is the average spacing between centers for all elements used in the stress control region.

  Similarly, the spacing from element to glass ribbon is usually the same for all elements, but can be different for some or all elements if desired. For example, to account for the characteristics of a particular device, the spacing on one side of the ribbon can be different from the spacing on the other side, or the spacing near one edge of the ribbon can be It can be different from the interval. Thus, as used herein, the element to ribbon spacing is the average spacing for all elements used within the stress control region. Adjustments in this spacing are usually made, for example, by moving all elements closer or further away from the ribbon, or by using a stress control area device having a spacing from a particular element to the ribbon to reduce the spacing from different elements to the ribbon. By changing to a different device, all intervals are changed equally. Also, if necessary, the individual spacing for some or all elements can be adjusted.

  With respect to these two spacings, namely the spacing between elements and the spacing between elements and ribbons, the spacing between elements is usually substantially smaller than the spacing between elements and ribbons. For example, in one embodiment, the distance from the glass ribbon to the element is between 50 mm and 200 mm (˜2-8 inches), while the spacing between the elements is 50 mm (˜2 inches) or less, eg, about 30 mm. (˜1 inch) or less. In other embodiments, for similar spacing between elements, the spacing from element to glass ribbon is in the range of 0.5 to 1.5 times the diameter of the nearest pulling roll. For reference, the diameter of conventional pulling rolls is in the range of 120-150 mm (~ 5-6 inches). Note that the spacing between the heating element and the glass ribbon usually has no tow roll or other types of rolls so as to locally affect the temperature of the ribbon and not interfere with the capabilities of the individual elements. I want to be.

Various combinations of spacing between elements and from element to ribbon are used for the stress control region. In some embodiments, these spacings are such that a change in power of 1 watt transmitted to the individual heating elements is at least 3.5 kilopascals ( 0.5 at least in one location in a representative glass sheet cut from the ribbon). psi) is selected to produce a stress change. In other embodiments, the spacing achieves a stress change of at least 7 kilopascals ( 1 psi).

  The heating element in the stress control region can be composed of various materials and can have various shapes. For example, wire or rod-shaped refractory materials are used for this purpose. FIG. 4 shows an embodiment that uses iron / chromium / aluminum hot wire to form the heating element 51. The elements are supplied with current via individual elements or lead wires 52 which in turn supply the element groups (compare the central heating elements supplied individually and the elements supplied in groups at the ends). Is done. Adjacent or non-adjacent heating elements can be supplied in sequence, depending on the installation specifications. The element is attached to a heat-resistant frame 53 that is fixed to a predetermined position of the fusion draw device via a bolt 54, for example. Insulation (eg, alumina insulation; not shown) is used to control heat loss from the stress control region. During use, the glass ribbon passes through the opening 55, for example, through the center of the opening.

  The length of the frame 53 depends on the ribbon width. Usually, the length of the frame is slightly longer than the width of the ribbon, although the stress control region has a length that is shorter than the width of the ribbon if necessary. In certain embodiments, the height of the frame 53 is in the range of 125-150 mm (˜5-6 inches) due to the slightly shorter heating element 51. For example, the average height of the heating element is in the range of 50-100 mm (˜2-4 inches), for example, about 75 mm (˜3 inches). The frame and, if necessary, the heating element can be made higher if necessary if a viewing window can be formed at the end of the frame 53. (Also, as shown in FIG. 2, one or more viewing windows 45 are provided as part of the tow roll assembly.) A heating element having a height shorter than 50 mm (˜2 inches) is between a very small element and a ribbon. Spacing is required and therefore may not be suitable for most applications.

  The depth of the frame depends on the spacing between the element and the ribbon. In some embodiments, the depth of the frame is about 3 times the height of the frame. Note that when the ribbon passes through the center of the opening in the stress control region, the depth of the opening is equal to twice the distance between the element and the ribbon plus the glass thickness. For thin glass, eg glass with a thickness of 0.7 mm or less, such as common LCD and OLED glass, the depth is basically twice the distance between the element and the ribbon, eg 100 mm and 400 mm. Between (˜4-16 inches).

  As is apparent from the above, the overall dimensions of the stress control region are appropriate in terms of the overall size of the fusion draw device that simplifies the structure and attachment of the region.

An important advantage of using a stress control region is that the stress control region reduces the need for other parts of the fusion draw device to perform stress control and eliminates it in some embodiments. In particular, it is possible to substantially reduce the need to care for portions on the stress control region by this aspect of the glass manufacturing method. Other parts are not well positioned to control stress. That is, more energy (heat) must be applied to the ribbon as compared to the stress control region. More energy in turn reduces the stretch transverse tension of the ribbon and the ribbon resembles stretch transverse warp, in particular the lateral relief of a curtain with the ribbon surface suspended vertically. It is more susceptible to curtain warp that creates shape. A large amount of energy is introduced into the ribbon by providing a stress control area in the setting area where the properties of the glass ribbon change from viscous liquid to elastic solid , for example, in the lower third of the setting area. The stress can be controlled without reducing the chance that the ribbon will create a transverse transverse warp, for example a curtain warp.

  In addition to being able to reduce the possibility of warping in the cross-stretch direction, again, a relatively small amount of energy is introduced into the ribbon in the stress control region, so that the stress control region is also down-the- draw) Does not adversely affect the temperature distribution. This further reduces the possibility of warping. This is because the temperature distribution in the drawing direction also produces warping, but by leaving them unaltered, a system whose warpage was controlled prior to the introduction of the stress control region would result in its introduction as a result of this region. This is because the possibility of losing control is low.

  The following non-limiting examples illustrate particular applications of the stress control region of the present disclosure.

This example demonstrates the ability of the stress control region to reduce the residual stress of a glass sheet prepared using a fusion draw apparatus. In particular, the examples show the stress level provided with four active heating elements (FIG. 5; comparative example) and the stress level provided with nine active heating elements (FIG. 6; example). Compare The stress control region is configured as described above in connection with FIG. 4 and is below the first set of traction rolls and above the second set of traction rolls of the fusion draw device, ie, FIG. It is located in the lower third of the setting area between the pulling rolls 60 and 70.

  The numbers along the horizontal axis in FIGS. 5 and 6 indicate individual heating elements in the stress control region, and the triangular data points located on the horizontal axis indicate the amount of power applied to the individual windings. . The square data points represent the measured stress in a typical glass sheet manufactured using the distribution of triangular data points. The black data points in each figure indicate the measured stress at the top edge of the sheet, while the white data points indicate the measured stress at the bottom of the sheet. The horizontal line represents zero stress with a point above the line showing positive stress values and a point below the line showing negative stress values. Stress was measured using conventional birefringence techniques.

  In FIG. 5, only heating elements 27, 28, 42 and 43 were supplied with current, elements 27 and 28 operated at ~ 90 watts / element power and elements 42 and 43 operated at ~ 35 watts / element power. . In FIG. 6, elements 24 to 30 and elements 42 and 43 are functioning, elements 42 and 43 again at ~ 35 watts / element power, elements 27 and 28 at ~ 90 watts / element power, element 24 The remaining elements were operated at ~ 50 watts / element of power.

  The effectiveness of the stress control region to reduce residual stress is immediately apparent from these figures. In FIG. 5, the maximum stress is about 900 kilopascals (˜130 psi), while in FIG. 6, the maximum stress is reduced to about 480 kilopascals (˜70 psi), ie a reduction of more than 45%. Furthermore, the stress distribution is flatter in FIG. 6 than in FIG. 5, which is advantageous for most applications. Moreover, the maximum stress in FIG. 6 occurs in the area where the heating element was not functioning. By allowing the element to function in this region, a further reduced maximum stress value and a flatter overall distribution were achieved.

  Accordingly, the present invention includes, but is not limited to, the following aspects and embodiments.

C1. An apparatus for producing a glass sheet by a downdraw method for producing a glass ribbon,
(A) a first set of pulling rolls in contact with the glass ribbon during use of the device;
(B) a second set of tow rolls in contact with the glass ribbon during use of the apparatus, the second set of tow rolls positioned below the first set of tow rolls;
(C) A stress control region through which the glass ribbon passes during use of the apparatus, and is positioned between the first set of pulling rolls and the second set of pulling rolls, and the glass ribbon has a stretching transverse direction of 150 mm or less And a stress control region having a spatial temperature resolution.

  C2. The apparatus according to C1, wherein the stress control region comprises a plurality of heating elements.

  C3. The apparatus according to C2, wherein the plurality of heating elements extend beyond the edge of the glass ribbon during use of the apparatus.

  C4. The apparatus according to C2 or C3, wherein the plurality of heating elements form openings through which the glass ribbon passes during use of the apparatus.

  C5. The apparatus according to C2, C3 or C4, characterized in that the average distance between the centers of the heating elements is 50 mm or less.

  C6. The apparatus according to C2, C3, C4 or C5, characterized in that the average distance between the heating element and the surface of the glass ribbon is between 50 mm and 200 mm during use of the apparatus.

  C7. C2 characterized in that, during use of the device, the average distance between the heating element and the surface of the glass ribbon is in the range of 0.5 to 1.5 times the diameter of the pulling roll closest to the stress control area, A device according to C3, C4, C5 or C6.

  C8. The apparatus according to C2, C3, C4, C5, C6 or C7, characterized in that the average height of the heating elements is in the range of 50 mm to 100 mm.

  C9. The apparatus according to any one of C1 to C8, wherein the stress control region is closer to the first set of traction rolls than to the second set of traction rolls.

  C10. The apparatus according to any one of C1 to C9, characterized in that the transverse transverse spatial temperature resolution of the stress control region in the glass ribbon is in the range of 75 mm to 125 mm.

  A device comprising a plurality of heating elements arranged in C11.2 rows and having openings between two rows for receiving glass ribbons, wherein the device has a stretch transverse space temperature of 150 mm or less in the glass ribbons A device characterized by having a resolution.

  C12. The apparatus according to C11, wherein the average height of the heating elements is in the range of 50 mm to 100 mm.

  C13. The apparatus according to C11 or C12, wherein an average distance between centers of the heating elements is 50 mm or less.

  C14. The apparatus according to C11, C12 or C13, wherein the depth of the opening is in the range of 100 mm to 400 mm.

  C15. A device according to C1, C12, C13 or C14, characterized in that the opening has a stretching transverse spatial temperature resolution of the stress control region in the glass ribbon in the range from 75 mm to 125 mm.

C16. A method of forming a glass sheet,
(A) producing a glass ribbon using the downdraw method, and
(B) Cutting a sheet from a glass ribbon,
Including each process,
A method of passing a glass ribbon through a stress control region having a transverse transverse spatial temperature resolution of 150 mm or less in the glass ribbon.

  C17. The method of C16, wherein the transverse transverse spatial temperature resolution of the stress control region in the glass ribbon is in the range of 75 mm to 125 mm.

  C18. A stress control region for at least one of the heating elements, a change in stress of at least 3.5 kilopascals in at least one position in the sheet cut from the glass ribbon by a change in power of 1 watt transferred to the heating element A method according to C16 or C17, comprising a plurality of heating elements arranged such that occurs.

  C19. The method according to C16, C17, or C18, wherein the stress control region is within a glass setting region.

C20. The method of C19, wherein the stress control region is in the lower third of the glass setting region.

  Many modifications will be apparent to those skilled in the art from the foregoing description without departing from the scope and spirit of the invention. It is intended that the following claims include modifications, changes and equivalents thereof, as well as specific embodiments described in the specification.

13 Glass sheet (glass substrate)
DESCRIPTION OF SYMBOLS 15 Glass ribbon 27 Edge roller 31 Glass setting area 35 Separation line 37 Isopipe 39 Isopipe cavity 41 for receiving molten glass Isopipe root 45 Viewing window 50 Stress control area 51 Heating element 52 of stress control area Stress control area Heating element electrical lead 53 Heating element support frame 54 Mounting bolt 55 Glass ribbon opening 60 First set of pulling rolls 70 Second set of pulling rolls 80, 90 Additional set of pulling rolls

Claims (8)

An apparatus for producing a glass sheet by a downdraw method for producing a glass ribbon,
(A) a first set of pulling rolls in contact with the glass ribbon during use of the device;
(B) a second set of tow rolls in contact with the glass ribbon during use of the device, the second set of tow rolls positioned below the first set of tow rolls;
(C) during use of the device, including a stress control region through which the glass ribbon passes,
The stress control region includes (i) a plurality of heating elements, (ii) between the first set of pulling rolls and the second set of pulling rolls, and the properties of the glass ribbon vary from viscous liquid to elastic solid positioned below one-third of the area of the glass of the set area is to change the region to, and have a stretched transverse spatial temperature resolution of 150mm or less in the (iii) the glass ribbon,
The spatial temperature resolution is the minimum horizontal between two points located in the portion of the glass ribbon that will eventually become a glass sheet, where a change in temperature at one point results in a temperature change of ± 10% or less at another point. A device characterized by being defined as a distance .   The apparatus of claim 1, wherein the plurality of heating elements extend beyond an edge of the glass ribbon during use of the apparatus.   The apparatus according to claim 1 or 2, wherein an average distance between centers of the heating elements is 50 mm or less.   During use of the apparatus, the average spacing between the heating element and the surface of the glass ribbon is in the range of 0.5 to 1.5 times the diameter of the pulling roll closest to the stress control area. The apparatus according to any one of claims 1 to 3.   The apparatus according to claim 1, wherein the stress control region is closer to the first set of pulling rolls than to the second set of pulling rolls. A method of forming a glass sheet,
(A) producing a glass ribbon using the downdraw method, and
(B) Cutting a sheet from a glass ribbon,
Including each process,
The glass ribbon has a transverse transverse spatial temperature resolution of 150 mm or less in the glass ribbon, and the lower third of the glass setting region, which is a region where the properties of the glass ribbon change from a viscous liquid to an elastic solid Pass through the stress control area located in one area ,
The spatial temperature resolution is the minimum horizontal between two points located in the portion of the glass ribbon that will eventually become a glass sheet, where a change in temperature at one point results in a temperature change of ± 10% or less at another point. A method characterized by being defined as a distance .   The method according to claim 6, wherein the transverse transverse spatial temperature resolution of the stress control region in the glass ribbon is in the range of 75 mm to 125 mm.   The stress control region is at least 3.5 kilopascals in at least one position in a sheet cut from the glass ribbon by a change in power of 1 watt transferred to the heating element for at least one of the heating elements. 8. A method according to claim 6 or 7, comprising a plurality of heating elements arranged to produce a stress change.

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