Glass with a high strain point and high Young's modulus

Abstract

To provide glass compositions with a high Young's modulus and high dimensional stability while having other advantageous properties and characteristics.SOLUTION: Substantially alkali free glasses are disclosed which can be used to produce substrates for flat panel display devices, e.g., active-matrix liquid crystal displays (AMLCDs). The glasses have high annealing temperatures and Young's modulus. Methods for producing substantially alkali free glasses using a downdraw process (e.g., a fusion process) are also disclosed.SELECTED DRAWING: Figure 5

Description

Description of Related Applications

[0001] This application claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Patent Application No. 62 / 686,850, filed June 19, 2018, the contents of which are relied upon and incorporated herein by reference in their entirety. [Technical Field]

[0002] FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate to display glass, and more particularly, to display glass for active matrix liquid crystal displays. [Background technology]

[0003] The manufacture of liquid crystal displays, such as active matrix liquid crystal display (AMLCD) devices, is complex, and the properties of the substrate glass are important. First and foremost, the glass substrates used in the manufacture of AMLCD devices must have tightly controlled physical dimensions. Downdraw sheet stretching methods, and in particular the fusion process described in U.S. Patent Nos. 5,629,997 and 5,729,297, both to Dockerty, can produce glass sheets that can be used as substrates without the need for costly post-forming finishing operations such as lapping and polishing. Unfortunately, the fusion process imposes fairly severe limitations on the glass properties, which require a relatively high liquidus viscosity.

[0004] In the field of liquid crystal displays, thin film transistors (TFTs) based on polycrystalline silicon are preferred due to their ability to transport electrons more efficiently. Polycrystalline silicon transistors (p-Si) are characterized as having higher mobility than those based on amorphous silicon transistors (a-Si). This allows for the production of smaller, faster transistors, which ultimately leads to brighter, faster displays.

[0005] One problem with p-Si-based transistors is that their fabrication requires higher process temperatures than those used to fabricate a-Si transistors. These temperatures range from 450°C to 600°C, compared to the peak temperature of 350°C used in a-Si transistor fabrication. At these temperatures, most AMLCD glass substrates undergo a process known as consolidation. Consolidation, also known as thermal stability or dimensional change, is an irreversible dimensional change (shrinkage) in the glass substrate due to a change in the fictive temperature of the glass. "Fictive temperature" is a concept used to describe the structural state of glass. Glass that is rapidly cooled from a high temperature is said to have a higher fictive temperature due to the "frozen in" higher temperature structure. Glass that is cooled more slowly, or annealed by being held near the anneal point for a period of time, is said to have a lower fictive temperature.

[0006] The amount of compaction depends on both the process for making the glass and the viscoelastic properties of the glass. In the float process for producing sheet products from glass, the glass sheet cools relatively slowly from the melt and therefore "freezes" into a relatively low-temperature structure. In contrast, in the fusion process, the glass sheet cools very rapidly from the melt and freezes into a relatively high-temperature structure. As a result, glass produced by the float process will experience less compaction than glass produced by the fusion process, since the driving force for compaction is the difference between the fictive temperature and the process temperature experienced by the glass during compaction. Therefore, it would be desirable to minimize the level of compaction in glass substrates produced by the fusion process as well as other forming processes (e.g., the float process).

[0007] There are two approaches to minimize compaction in the glass. The first approach is to thermally pretreat the glass to create a fictive temperature similar to that experienced by the glass during p-Si TFT fabrication. This approach has several drawbacks. First, the multiple heating steps utilized during p-Si TFT fabrication create slightly different fictive temperatures in the glass that the pretreatment cannot fully compensate for. Second, the thermal stability of the glass becomes closely tied to the details of its p-Si TFT fabrication, which could mean different pretreatments for different end users. Finally, pretreatments add cost and complexity to the process.

[0008] Another approach is to slow the strain rate at the process temperature by increasing the viscosity of the glass. This can be achieved by increasing the viscosity of the glass. The anneal point represents the temperature corresponding to the fixed viscosity of the glass, so increasing the anneal point is equivalent to increasing the viscosity at the fixed temperature. However, the challenge with this approach is cost-effectively producing high-anneal-point glasses. The primary factors affecting cost are defects and asset life. In modern melters coupled to fusion draw systems, four types of defects are commonly encountered: (1) gaseous inclusions (bubbles or blisters), (2) solid inclusions due to the inability to properly melt the refractory or batch, (3) metallic defects consisting primarily of platinum, and (4) devitrification products resulting from low liquidus viscosity or excessive devitrification at both ends of the isopipe. Glass composition has a disproportionate effect on the melting rate and, therefore, the tendency of the glass to form gaseous or solid defects, and the oxidation state of the glass affects its tendency to contain platinum defects. Devitrification of the glass on the forming mandrel, or isopipe, can best be controlled by selecting a composition with a high liquidus viscosity.

[0009] The useful life of an asset is determined primarily by the rate of wear or deformation of the various refractory and precious metal components of the melting and forming system. Recent advances in refractory materials, platinum system design, and isopipe refractories offer the potential to significantly extend the useful operating life of melters coupled to fusion draw machines. As a result, the life-limiting components of modern fusion draw melting and forming platforms are the electrodes used to heat the glass. Tin oxide electrodes corrode slowly over time, with the corrosion rate being a strong function of both temperature and glass composition. To maximize the useful life of an asset, it is desirable to identify compositions that reduce the corrosion rate of the electrodes while maintaining the defect-limiting attributes described above.

[0010] As long as the compaction of the glass is below a threshold level, a critical attribute determining the suitability of glass as a substrate is the lack or variability in the overall pitch of the substrate during TFT fabrication, which can result in misalignment of TFT components and defective pixels in the final display. This variability is most pronounced due to variations in the compaction of the glass, variations in the elastic strain of the glass under stresses imposed by films deposited during TFT fabrication, and variations in the relaxation of those same stresses during TFT fabrication. Glasses with high dimensional stability have reduced compaction variability as well as reduced stress relaxation, and glasses with high Young's modulus help reduce distortion due to film stress. As a result, glasses with both high Young's modulus and high dimensional stability minimize overall pitch variability during TFT processing, making them advantageous substrates for these applications.

[0011] Additionally, glasses with high strain points and high Young's modulus may also find application as carriers for flexible organic light-emitting diodes (OLEDs) and as substrates for hard disk drives manufactured from heat-assisted magnetic recording (HAMR) technology. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] U.S. Patent No. 3,338,696 [Patent Document 2] U.S. Patent No. 3,682,609 Summary of the Invention [Problem to be solved by the invention]

[0013] Therefore, there is a need in the art for glass compositions that have a high Young's modulus and high dimensional stability, while also having other advantageous properties and characteristics. [Means for solving the problem]

[0014] One or more embodiments of the present disclosure relate to glasses comprising, in mole percent on an oxide basis, the following ranges: 65-75% SiO, 12-14% AlO, 0-3% BO, 4-8% MgO, 5-10% CaO, 0-5% SrO, and 0-2% other oxides including YO, ZrO, and ZnO. In additional embodiments, the glass comprises, in mole percent on an oxide basis, in the ranges: 69-73% SiO, 12-14% AlO, 0-3% BO, 4-7% MgO, 5-6% CaO, 3-4% SrO, and 0-1% other oxides including YO, ZrO, ZnO, and has a strain point greater than 760°C, a 200 poise temperature less than 1650°C, a liquidus temperature less than 1300°C, a liquidus viscosity greater than 20,000 poise, a Young's modulus greater than 85 GPa, and / or a viscosity greater than 33 GPa / g / cm. 3 It has a specific elastic modulus of greater than .

[0015] Exemplary glasses may be in the MgO·CaO·SrO·Al2O3·SiO2 system, with the addition of small amounts of Y2O3, ZrO2, and ZnO, providing a strain point of 780°C, a liquidus viscosity of greater than 68,000 poise, and a 200 poise temperature (or typical melting temperature) of 1650°C, offering higher strain points, energy savings during melting, and extended melting bath life, all of which contribute to significant cost savings. Additional glasses may be in the MgO·CaO·SrO·BaO·B2O3·Al2O3·SiO2 system, providing strain points of 757°C or higher, liquidus viscosities of greater than 62,400 poise, specific moduli of greater than 32.18, and Young's moduli of greater than 83.56 GPa.

[0016] One or more embodiments of the present disclosure relate to a glass comprising, in mole percent on an oxide basis, the following ranges: 69-74% SiO, 11-14% AlO, 0-3% BO, 4-7% MgO, 5-7% CaO, 0-3% SrO, and 1-5% BaO. Additional embodiments of the present disclosure relate to a glass having a strain point greater than 752°C, a liquidus temperature less than 1300°C, a liquidus viscosity greater than 20,000 poise, a Young's modulus greater than 83.56 GPa, and / or a Young's modulus greater than 32 GPa / g / cm. 3 The present invention relates to a glass having a specific elastic modulus of greater than 1000 kJ / cm2 and containing, in mole percent on an oxide basis, the following ranges: 70-73% SiO2, 11-13% Al2O3, 0-1% B2O3, 4-7% MgO, 5-7% CaO, 0-3% SrO, and 1-5% BaO.

[0017] One or more embodiments of the present disclosure relate to a glass comprising, in mole percent on an oxide basis, the following ranges: 68.84-74.07% SiO, 10.41-14.87% AlO, 0-2% BO, 3.44-7.45% MgO, 4.19-8.23% CaO, 0-3.36% SrO, 0.91-5.59% BaO, and 0.09-0.2% SnO. Additional embodiments of the present disclosure relate to glasses comprising, in mole percent on an oxide basis, the following ranges: 69.86-72.13% SiO2, 11.58-13.01% Al2O3, 0-1% B2O3, 4.44-6.45% MgO, 5.53-7.23% CaO, 0.09-1.67% SrO, 2.92-4.57% BaO, and 0.09-0.1% SnO2.

[0018] Additional embodiments of the present disclosure relate to objects comprising glass produced by a downdraw sheet manufacturing process. Further embodiments relate to glass produced by a fusion process or variations thereof.

[0019] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments described below. [Brief explanation of the drawings]

[0020] [Figure 1] Schematic of a forming mandrel used to produce precision sheet in the fusion draw process [Figure 2] Cross-sectional view of the forming mandrel of Figure 1 taken along location 6 [Figure 3] Graph of the blackbody spectrum at 1200°C and 1140°C and the transmission spectrum of a 0.7mm thick Eagle XG® amorphous thin film transistor substrate. [Figure 4] Graph of the boundary of the convex hull of some embodiments [Figure 5] A graph of the convex hull of FIG. 4 with a group of example compositions contained within it. [Figure 6] Graph of equation (2) for randomly selected compositions within the convex hull of Figure 4 [Figure 7] Graph of equation (3) for randomly selected compositions within the convex hull of Figure 4 [Figure 8] Graph of the MgO·CaO·SiO2·Al2O3 (20% by mass Al2O3) system DETAILED DESCRIPTION OF THE INVENTION

[0021] Described herein are alkali-free glasses and methods for their manufacture that have high annealing points and / or strain points and high Young's moduli, which can have excellent dimensional stability (i.e., low compaction) during TFT fabrication and reduce variability during the TFT process. Glasses with high annealing points and / or strain points can help prevent panel distortion due to compaction / shrinkage during post-glass fabrication heat treatments. In addition, some embodiments of the present disclosure have high liquidus viscosities, thus reducing or eliminating the possibility of devitrification on relatively cold forming mandrels. As a result of the specific details of their composition, the exemplary glasses melt to good quality with very low levels of gaseous inclusions and minimal corrosion to precious metals, refractories, and tin oxide electrode materials.

[0022] In one embodiment, the substantially alkali-free glass can have a high anneal point. In some embodiments, the anneal point is greater than about 790° C., 795° C., 800° C., or 805° C. While not being bound by any particular theory of operation, it is believed that such a high anneal point results in a slow relaxation rate—and therefore a relatively small amount of compaction—allowing the exemplary glass to be used as a backplane substrate in low temperature polysilicon processes.

[0023] The liquidus temperature of glass (T liq ) is the temperature above which crystalline phases cannot coexist in equilibrium with the glass. In various embodiments, the glass article can be heated to a T within the range of about 1200°C to about 1350°C, or within the range of about 1220°C to about 1325°C. liqIn another embodiment, the viscosity corresponding to the liquidus temperature of the glass is about 150,000 poise or greater. In some embodiments, the viscosity corresponding to the liquidus temperature of the glass is about 175,000 poise or greater, 200,000 poise or greater, 225,000 poise or greater, or 250,000 poise or greater.

[0024] In another embodiment, the exemplary glass is T 35k -T liq >0.25T 35k A temperature of -225°C may be provided to ensure that there is minimal tendency for devitrification on the forming mandrel of the fusion process.

[0025] In one embodiment, the glass includes a chemical fining agent. Such fining agents include, but are not limited to, SnO2, As2O3, Sb2O3, F, Cl, and Br, and the concentration of the chemical fining agent is maintained at a level of 0.5 mol% or less. In some embodiments, the chemical fining agent includes one or more of SnO2, As2O3, Sb2O3, F, Cl, or Br at a concentration of about 0.5 mol% or less, 0.45 mol% or less, 0.4 mol% or less, 0.35 mol% or less, 0.3 mol% or less, or 0.25 mol% or less. Chemical fining agents may also include other oxides of transition metals, such as CeO2, Fe2O3, and MnO2. These oxides may impart color to the glass due to visible absorption in the final valence state in the glass; therefore, their concentration may be at a level of 0.2 mol% or less. In one or more embodiments, the glass composition includes one or more oxides of transition metals at a concentration of about 0.2 mol%, 0.15 mol%, 0.1 mol%, or 0.05 mol% or less. In some embodiments, the glass composition includes any one or combination of SnO2, As2O3, Sb2O3, F, Cl, and / or Br in the range of about 0.01 mol% to about 0.4 mol%. In specific embodiments, the glass composition includes any one or combination of Fe2O3, CeO2, and / or MnO2 in the range of about 0.005 mol% to about 0.2 mol%. In some embodiments, As2O3 and Sb2O3 comprise about 0.005 mol% or less of the glass composition.

[0026] In one embodiment, the exemplary glass is fabricated into sheets by a fusion process. This fusion draw process can result in a pristine, fire-polished glass surface that reduces surface-mediated distortion for high-resolution TFT backplanes and color filters. Figure 1 is a schematic diagram of a forming mandrel, or isopipe, in a non-limiting fusion draw process. Figure 2 is a schematic cross-sectional view of the isopipe near location 6 in Figure 1. Glass is introduced at inlet 1 and flows along the bottom 4 of a trough formed by weir walls 9 to the compression end 2. The glass overflows the weir walls 9 on both sides of the isopipe (see Figure 2), and the two streams of glass join or fuse at base 10. Edge directors 3 at both ends of the isopipe serve to cool the glass and create thicker pieces at the edges, called beads. The beads are pulled down by pulling rolls, allowing for sheet formation at high viscosities. By controlling the speed at which the sheet is drawn from the isopipe, the fusion draw process can be used to produce a wide range of thicknesses at a constant melt rate.

[0027] Downdraw sheet stretching methods, and in particular the fusion method described in U.S. Patent Nos. 5,999,949 and 5,999,962 (both to Dockerty), both of which are incorporated herein by reference, can be used herein. While not bound by any particular theory of operation, it is believed that the fusion method can produce glass substrates that do not require polishing. Current glass substrate polishing can produce glass substrates with an average surface roughness (Ra) of greater than about 0.5 nm, as measured by atomic force microscopy. Glass substrates produced by the fusion method have an average surface roughness, as measured by atomic force microscopy, of less than 0.5 nm. The substrates also have an average internal stress, as measured by optical retardation, of 150 psi (about 1.03 MPa) or less. Of course, the embodiments described herein are equally applicable to other forming processes, such as, but not limited to, float forming, and the claims appended hereto should not be limited to the fusion method.

[0028] In one embodiment, the exemplary glasses are manufactured into sheets using a fusion process. While the exemplary glasses are compatible with the fusion process, they may also be manufactured into sheets or other articles by different manufacturing processes. Such processes include slot draw, float, rolling, and other sheet forming methods known to those skilled in the art.

[0029] In contrast to these alternative methods of forming glass sheets, the fusion process, as described above, can produce very thin, very flat, highly uniform sheets with pristine surfaces. While the slot draw process can produce pristine surfaces, the dimensional uniformity and surface quality of glass produced by the slot draw process are generally inferior to glass produced by the fusion draw process due to changes in orifice shape over time, the accumulation of volatile debris at the orifice-glass interface, and the challenges of creating orifices that deliver truly flat glass. The float process can deliver very large, uniform sheets, but their surfaces are substantially damaged by contact with the float bath on one side and exposure to condensation products from the float bath on the other side. This means that float glass must be polished for use in high-performance display applications.

[0030] The fusion method involves rapid cooling of the glass from a high temperature, which may result in a high fictive temperature Tf. This fictive temperature can be considered to represent the difference between the structural state of the glass and the state if it were fully relaxed at the temperature of interest. The process of reheating a glass with a glass transition temperature Tg to a processing temperature Tp such that Tp < Tg ≤ Tf will be affected by the viscosity of the glass. Since Tp < Tf, the structural state of the glass is out of equilibrium at Tp, and the glass will spontaneously relax to an equilibrium structural state at Tp. This relaxation rate is inversely proportional to the effective viscosity of the glass at Tp, and thus, a high viscosity results in a slow relaxation rate and a low viscosity results in a fast relaxation rate. The effective viscosity varies inversely with the fictive temperature of the glass, and thus, a low fictive temperature results in a high viscosity and a high fictive temperature results in a relatively low viscosity. Therefore, the relaxation rate at Tp is directly related to the fictive temperature of the glass. The process of introducing a high fictive temperature results in a relatively high relaxation rate when the glass is reheated at Tp.

[0031] One means of reducing the relaxation rate at Tp is to increase the viscosity of the glass at that temperature. The annealing point of the glass represents the temperature at which the glass has a viscosity of 10 13.2 poises. As the temperature decreases below the annealing point, the viscosity of the supercooled melt increases. At a fixed temperature below Tg, the glass with a higher annealing point has a higher viscosity than the glass with a lower annealing point. Therefore, increasing the annealing point will increase the viscosity of the substrate glass at Tp. Generally, the compositional changes necessary to increase the annealing point also increase the viscosity at all other temperatures. In non-limiting embodiments, the fictive temperature of the glass produced by the fusion method is about 10 11 ~10 12Increasing the anneal point of a glass, which corresponds to a poise viscosity and is therefore compatible with the fusion process, generally increases its fictive temperature as well. For a given glass, regardless of the glass-forming process, the higher the fictive temperature, the lower the viscosity at temperatures below Tg; therefore, increasing the fictive temperature counteracts the increase in viscosity that would otherwise be obtained by increasing the anneal point. To substantially change the relaxation rate at Tp, a relatively large change in anneal point is generally necessary. Exemplary glass embodiments are those in which the glass has an anneal point of about 790°C or higher, 795°C or higher, 800°C or higher, or 805°C or higher. While not bound by any particular theory of operation, it is believed that such a high anneal point results in an acceptably slow rate of thermal relaxation during low-temperature TFT processing, e.g., typical low-temperature polysilicon rapid thermal annealing cycles.

[0032] Increasing the anneal point, in addition to its effect on the fictive temperature, also increases the temperature of the entire melting and forming system, particularly the temperature on the isopipe. For example, "Eagle XG" glass and Lotus™ glass (Corning Incorporated, Corning, New York) have anneal points that differ by about 50°C, and their delivery temperatures to the isopipe also differ by about 50°C. The zircon refractory from which the isopipe is formed exhibits thermal creep when held at temperatures above about 1310°C for extended periods, which can be accelerated by the mass of the glass on the isopipe in addition to the mass of the isopipe itself. A second exemplary glass aspect is one whose delivery temperature is about 1350°C or less, or 1345°C or less, or 1340°C or less, or 1335°C or less, or 1330°C or less, or 1325°C or less, or 1320°C or less, or 1315°C or less, or 1310°C or less. Such delivery temperatures would allow for long production campaigns to be run without the need to replace the isopipe, or would allow for longer periods between isopipe changes.

[0033] In production trials of high-annealing point glasses and feed temperatures below 1350°C and 1310°C, the glasses were found to be more prone to devitrification at the root of the isopipe and—especially—on the edge directors than were low-annealing point glasses. Careful measurements of the temperature profile along the isopipe indicated that the edge director temperatures were much lower than expected relative to the center base temperature, likely due to radiative heat losses. The edge directors are generally maintained at a lower temperature than the center base temperature to ensure that the glass is sufficiently viscous as it moves away from the base to place the sheet between them under tension and therefore maintain a flat shape. Because the edge directors are located at both ends of the isopipe, they are difficult to heat, and therefore the temperature difference between the center of the base and the edge directors may vary by 50°C or more.

[0034] Without intending to be bound by theory, it is believed that the increased tendency toward devitrification in the fusion process can be understood in terms of the radiative heat loss of the glass as a function of temperature. The fusion process is essentially an isothermal process, so while the glass exits the inlet at a particular viscosity and the base at a much higher viscosity, the actual viscosity values ​​do not depend strongly on the process temperature or the identity of the glass. Therefore, glasses with higher annealing points generally require much higher isopipe temperatures than glasses with lower annealing points to closely match the feed and outlet viscosities. As an example, Figure 3 shows blackbody spectra corresponding to 1140°C and 1200°C, respectively, for "Eagle XG" and "Lotus" glasses, near the temperatures at the base of the isopipe (10 in Figure 2). The vertical line at approximately 2.5 μm corresponds approximately to the onset of the infrared cutoff, a region in the near infrared where optical absorption in borosilicate glasses rises steeply to a high, nearly constant value. At wavelengths shorter than its cutoff wavelength, glass is fairly transparent to wavelengths between 300 nm and 400 nm, which is its UV cutoff. Between about 300 nm and about 2.5 μm, a black body at 1200°C has more absolute energy, and a greater proportion of its total energy, than a black body at 1140°C. Because the glass is fairly transparent throughout this wavelength range, the radiative heat loss from glass at 1200°C is much greater than that of glass at 1140°C.

[0035] Again, without being bound by any particular theory of operation, it is believed that because radiative heat losses increase with temperature, and because higher anneal point glasses are formed at higher temperatures than lower anneal point glasses, the temperature difference between the central base and the edge directors generally increases with the anneal point of the glass, which will directly relate to the tendency of the glass to form devitrification products on the isopipe or edge director.

[0036] The liquidus temperature of a glass is defined as the highest temperature at which crystalline phases will appear if the glass is held at that temperature indefinitely. The liquidus viscosity is the viscosity of the glass at the liquidus temperature. To completely avoid devitrification on an isopipe, it would be helpful for the liquidus viscosity to be high enough to ensure that the glass is no longer at or near its liquidus temperature on the isopipe refractory or edge director material.

[0037] In practice, most alkali-free glasses do not have liquidus viscosities of the desired magnitude. Experience with substrate glasses suitable for amorphous silicon applications (e.g., "Eagle XG" glass) has shown that edge directors can be continuously maintained at temperatures up to 60°C below the liquidus temperature of a particular alkali-free glass. It was understood that higher annealing point glasses would require higher forming temperatures, but it was not predicted that the edge directors would be much lower relative to the central base temperature. A useful metric for tracking this effect is the ratio of the delivery temperature onto the isopipe to the glass's liquidus temperature, T liq In the fusion method, the difference between 35k ) is generally desirable. For a particular delivery temperature, T 35k -T liq It would be useful to maximize T 35k -T liq It was found that long-term production can be carried out when T is about 80°C or higher. As the temperature increases, T 35k -T liq must increase as well, so that T near 1300°C 35k About T 35k -T liq Setting the temperature above about 100°C will help. 35k -T liq The minimum useful value of varies approximately linearly with temperature from about 1200°C to about 1320°C, according to Eq. (1): Minimum T 35k -T liq =0.25T 35k -225, (1) where all temperatures are in °C. Thus, one or more embodiments of the exemplary glasses may be expressed according to T 35k -T liq >0.25T 35k It has a temperature of -225°C.

[0038] Furthermore, the forming process may require a glass with a high liquidus viscosity. This is necessary to avoid devitrification products at the interface with the glass and minimize visible devitrification products in the final glass. Therefore, for a given glass suitable for fusion of a particular sheet size and thickness, adjusting the process to produce wider or thicker sheets generally results in lower temperatures at both ends of the isopipe. Some embodiments have a higher liquidus viscosity to provide greater manufacturing versatility through the fusion process. In some embodiments, the liquidus viscosity is about 150 kP or greater.

[0039] In examining the relationship between liquidus viscosity and subsequent devitrification tendency in the fusion process, the inventors found that high feed temperatures, such as those of the exemplary glasses, generally require higher liquidus viscosities for long-term manufacturing than would be the case for typical AMLCD substrate compositions with lower anneal points. Without intending to be bound by theory, this is believed to be due to the accelerated rate of crystal growth with increasing temperature. The fusion process is essentially an isoviscosity process, so a glass with a higher viscosity at a fixed temperature will form at a higher temperature through the fusion process than a glass with a lower viscosity. While some degree of undercooling (cooling below the liquidus temperature) can be maintained for extended periods in glasses at lower temperatures, the rate of crystal growth increases with temperature, and therefore a glass with a higher viscosity will grow an equally unacceptable amount of devitrification product in a shorter period of time than a glass with a lower viscosity. Depending on where it is formed, the devitrification product can impair forming stability and introduce visible defects into the final glass.

[0040] For fusion formation, one or more embodiments of the glass compositions have a liquidus viscosity of about 150,000 poise or greater, or 175,000 poise or greater, or 200,000 poise or greater. A surprising result is that throughout the range of the exemplary glasses, it is possible to obtain a liquidus temperature low enough and a viscosity high enough that the liquidus viscosity of the glasses is unusually high compared to other compositions.

[0041] In the glass compositions described herein, SiO serves as a base glass former. In certain embodiments, the SiO concentration can be greater than 60 mole percent to provide the glass with density and chemical durability suitable for flat panel display glasses (e.g., AMLCD glasses) and a liquidus temperature (or liquidus viscosity) that allows the glass to be formed by downdraw processes (e.g., fusion processes). Regarding the upper limit, the SiO concentration can generally be about 80 mole percent or less to allow batch materials to be melted using conventional bulk melting techniques, e.g., Joule melting in a refractory melter. As the SiO concentration increases, the 200 poise temperature (melting temperature) generally increases. In various applications, the SiO concentration is adjusted so that the glass composition has a melting temperature of 1,750°C or less. In some embodiments, the concentration of SiO2 is in the range of about 65 mol% to about 75 mol%, or in the range of about 69 mol% to about 73 mol%, or in the range of about 69 mol% to about 74 mol%, or in the range of about 70 mol% to 73 mol%, or in the range of about 68.84 to 74.07 mol%, or in the range of about 69.86 mol% to about 72.13 mol%.

[0042] Al2O3 is another glass former used to produce the glasses described herein. Concentrations of Al2O3 of 10 mole percent or greater impart a low liquidus temperature and high viscosity to the glass, resulting in a high liquidus viscosity. Using at least 10 mole percent Al2O3 also improves the annealing point and Young's modulus of the glass. For the ratio (MgO + CaO + SrO + BaO) / Al2O3 to be 1.0 or greater, the concentration of Al2O3 will be less than about 15 mole percent. In some embodiments, the concentration of Al2O3 is in the range of about 12 to 14 mole percent, or in the range of about 11 to about 14 mole percent, or in the range of about 11 mole percent to about 13 mole percent, or in the range of about 10.41 mole percent to about 14.07 mole percent, or in the range of about 11.58 mole percent to about 13.01 mole percent. In some embodiments, the concentration of Al2O3 is about 10.0 mol% or greater, 10.5 mol% or greater, 11.0 mol% or greater, 11.5 mol% or greater, 12.0 mol% or greater, 12.5 mol% or greater, or 13.0 mol% or greater, while maintaining a ratio of (MgO+CaO+SrO+BaO) / Al2O3 of 1.0 or greater.

[0043] Some embodiments of the present disclosure have a Young's modulus greater than about 83 GPa, or greater than about 83.5 GPa, or greater than about 84 GPa, or greater than about 84.5 GPa, or greater than about 85 GPa.

[0044] Some embodiments of the aluminosilicate glass article have a density of less than about 2.7 g / cc, or less than about 2.65 g / cc, or less than about 2.61 g / cc. In various embodiments, the density is in the range of about 2.48 g / cc to about 2.65 g / cc.

[0045] B2O3 is both a glass former and a fluxing agent that promotes melting and lowers the melting temperature. It affects both the liquidus temperature and viscosity. Increasing B2O3 can be used to increase the liquidus viscosity of the glass. To achieve these effects, the glass composition of one or more embodiments may have a B2O3 concentration of 0.01 mole percent or greater. As noted above with respect to SiO2, glass durability is critical for LCD applications. Durability can be controlled to some extent by elevated concentrations of alkaline earth oxides, but can be significantly reduced by elevated B2O3 content. Annealing points decrease with increasing B2O3, so it may be helpful to maintain a low B2O3 content relative to typical concentrations in amorphous silicon substrates. Thus, in some embodiments, the glass composition has a B2O3 concentration in the range of about 0.0 to 3 mole percent, or greater than 0 to about 3 mole percent, or about 0.0 to about 1 mole percent, or about 0 to about 2 mole percent.

[0046] The concentrations of Al2O3 and B2O3 can be selected as a pair to increase the anneal point, increase the modulus, improve durability, lower density, and decrease the coefficient of thermal expansion (CTE) while maintaining the melting and forming properties of the glass.

[0047] For example, increasing B2O3 and correspondingly decreasing Al2O3 can help maintain lower density and CTE, while increasing Al2O3 and correspondingly decreasing B2O3 can help increase the annealing point, modulus, and durability, provided that the Al2O3 increase does not reduce the (MgO + CaO + SrO + BaO) / Al2O3 ratio below about 1.0. For (MgO + CaO + SrO + BaO) / Al2O3 ratios less than about 1.0, it may be difficult or impossible to remove gaseous inclusions from the glass due to late melting of the silica raw materials. Furthermore, when (MgO + CaO + SrO + BaO) / Al2O3 ≦1.05, mullite, an aluminosilicate crystal, may appear as a liquid phase. Once mullite is present as a liquid phase, the compositional sensitivity of the liquidus increases significantly, and mullite devitrification products grow very rapidly and are very difficult to remove once formed. Thus, in some embodiments, the glass composition has (MgO+CaO+SrO+BaO) / Al2O3 > 1.0 (i.e., about 1.0 or greater). In various embodiments, the glass has (MgO+CaO+SrO+BaO) / Al2O3 > 1.05 (i.e., about 1.05 or greater), or a ratio within the range of about 1 to about 1.25.

[0048] In one or more embodiments, the glasses used in AMLCD applications have a coefficient of thermal expansion (CTE) (over a temperature range of 22-300°C) in the range of about 3.0 ppm to about 4.0 ppm, or in the range of about 3.2 ppm to 3.9 ppm, or in the range of about 3.23 ppm to about 3.88 ppm.

[0049] The glasses described herein contain alkaline earth oxides in addition to the glass formers (SiO, AlO, and BO). In one embodiment, at least three alkaline earth oxides, e.g., MgO, CaO, and BaO, and optionally SrO, are part of the glass composition. The alkaline earth oxides impart various properties to the glass that are important for melting, fining, forming, and end use. Therefore, to improve the glass's performance in these respects, in one embodiment, the ratio of (MgO + CaO + SrO + BaO) / AlO is about 1.0 or greater. As this ratio increases, the viscosity tends to increase more strongly than the liquidus temperature, and therefore the T 35k -T liq It becomes increasingly difficult to obtain suitably high values ​​of . Therefore, in another embodiment, the ratio (MgO+CaO+SrO+BaO) / Al2O3 is about 2 or less. In some embodiments, the ratio (MgO+CaO+SrO+BaO) / Al2O3 is in the range of about 1 to about 1.2, or in the range of about 1 to about 1.16, or in the range of about 1.1 to about 1.6. In specific embodiments, the ratio of (MgO+CaO+SrO+BaO) / Al2O3 is less than about 1.7, or less than 1.6, or less than 1.5.

[0050] For certain embodiments of the present disclosure, alkaline earth oxides may be treated as effectively a single compositional component, since their effects on viscoelastic properties, liquidus temperature, and liquidus relations are qualitatively more similar to each other than to those of the glass-forming oxides SiO, AlO, and BO. However, while the alkaline earth oxides CaO, SrO, and BaO can form solid solutions with feldspar minerals, particularly anorthite (CaAlSiO) and celsian (BaAlSiO), and the same strontium, MgO does not participate significantly in these crystals. Thus, if the feldspar crystals are already in the liquid phase, the over-addition of MgO will serve to stabilize the liquid relative to the crystals and therefore lower the liquidus temperature. At the same time, the viscosity curve generally becomes steeper, lowering the melting temperature with little or no effect on the low-temperature viscosity.

[0051] The inventors have found that the addition of small amounts of MgO will favor forming by lowering the liquidus temperature and increasing the liquidus viscosity, while maintaining a high anneal point and therefore low compaction, and will favor melting by lowering the melting temperature. In various embodiments, the glass composition includes MgO in an amount ranging from about 4 mol% to about 8 mol%, or from about 4 mol% to about 7 mol%, or from about 3.44 mol% to about 7.45 mol%, or from about 4.44 mol% to about 6.45 mol%.

[0052] Surprisingly, T 35k -T liq The inventors have found that for glasses with suitably high values ​​of MgO, the ratio of MgO to other alkaline earth oxides, MgO / (MgO + CaO + SrO + BaO), falls within a relatively narrow range. As mentioned earlier, the addition of MgO can destabilize feldspar minerals, thus stabilizing the liquid and lowering the liquidus temperature. However, once MgO reaches a certain level, mullite Al6SiO 13will be stabilized, thus increasing the liquidus temperature and decreasing the liquidus viscosity. Furthermore, higher concentrations of MgO tend to decrease the viscosity of the liquid, and therefore, even if the liquidus viscosity remains unchanged with the addition of MgO, the liquidus viscosity will decrease over time. Therefore, in another embodiment, 0.20≦MgO / (MgO+CaO+SrO+BaO)≦0.40, or in some embodiments, 0.22≦MgO / (MgO+CaO+SrO+BaO)≦0.37. MgO may be used to increase the T, consistent with obtaining other desirable properties. 35k -T liq Within these ranges, the glass formers and other alkaline earth oxides may be varied to maximize the value of .

[0053] Without being bound by any particular theory of operation, it is believed that the calcium oxide present in the glass composition can produce a low liquidus temperature (high liquidus viscosity), a high anneal point and Young's modulus, and a CTE in the range most desirable for flat panel applications, particularly AMLCD applications. Its presence also favorably contributes to chemical durability, and compared to other alkaline earth oxides, it is relatively inexpensive as a batch material. However, at high concentrations, CaO increases density and CTE. Furthermore, at sufficiently low SiO concentrations, CaO can stabilize anorthite and therefore reduce liquidus viscosity. Thus, in one or more embodiments, the CaO concentration can be 4.0 mol% or greater. In various embodiments, the concentration of CaO in the glass composition is in the range of about 5 mol% to about 10 mol%, or in the range of about 5 mol% to about 6 mol%, or in the range of about 5 mol% to about 7 mol%, or in the range of about 4.19 mol% to about 8.23 ​​mol%, or in the range of about 5.53 mol% to about 7.23 mol%.

[0054] Both SrO and BaO can contribute to a low liquidus temperature (high liquidus viscosity); therefore, the glasses described herein typically contain at least both of these oxides. However, the selection and concentration of these oxides are chosen to avoid an increase in CTE and density, and a decrease in modulus and anneal point. The relative proportions of SrO and BaO can be balanced to obtain the appropriate combination of physical properties and liquidus viscosity so that the glass can be formed by downdraw processes. In various embodiments, the glasses contain SrO in the range of about 0 to about 5 mol%, or about 3 to about 4 mol%, or greater than about 0 to about 3 mol%, or about 0 mol% to about 3.36 mol%, or about 0.09 mol% to about 1.67 mol%. In one or more embodiments, the glasses contain BaO in the range of about 0 to about 5 mol%, or 1 to about 5 mol%, or about 0.91 to about 5.59 mol%, or about 2.92 mol% to about 4.57 mol%.

[0055] To summarize the effects / roles of the core components of the glass of the present disclosure, SiO is the base glass former. AlO and BO are also glass formers and can be selected as pairs. For example, increasing BO and correspondingly decreasing AlO can be used to obtain lower density and CTE, while increasing AlO and correspondingly decreasing BO can be used to increase the annealing point, Young's modulus, and durability, provided that the ratio of RO / AlO is not reduced below about 1.0 (RO = (MgO + CaO + SrO + BaO)). If this ratio becomes too low, meltability is impaired, i.e., the melting temperature becomes too high. BO can be used to lower the melting temperature, but high levels of BO impair the annealing point.

[0056] In addition to meltability and annealing point considerations, for AMLCD applications, the CTE of the glass should match that of silicon. To achieve such a CTE value, exemplary glasses can control the RO content of the glass. For a given Al2O3 content, controlling the RO content corresponds to controlling the RO / Al2O3 ratio. In practice, glasses with suitable CTEs can be produced when the RO / Al2O3 ratio is less than about 1.6.

[0057] In addition to these considerations, the glasses preferably are formable by downdraw processes, e.g., fusion processes. This means that the liquidus viscosity of the glass must be relatively high. Individual alkaline earths play an important role in this regard, as they can destabilize crystalline phases that would otherwise form. BaO and SrO are particularly effective in controlling liquidus viscosity and are included in exemplary glasses at least for this purpose. As shown in the examples presented below, various combinations of alkaline earths produce glasses with high liquidus viscosity, whose total alkaline earth content satisfies the constraints of a low melting temperature, a high anneal point, and the R0 / Al2O3 ratio necessary to achieve an adequate CTE. In some embodiments, the liquidus viscosity is about 150 kP or greater.

[0058] In addition to the above components, the glass compositions described herein may contain various other oxides to adjust various physical, melting, fining, and forming properties of the glass. Examples of such other oxides include, but are not limited to, TiO2, MnO, Fe2O3, ZnO, Nb2O5, MoO3, Ta2O5, WO3, YO3, La2O3, and CeO2, as well as other rare earth oxides and phosphates. In one embodiment, the amount of each of these oxides may be 2.0 mole percent or less, and their total concentration may be 5.0 mole percent or less. In some embodiments, the glass compositions include ZnO, YO3, and / or ZrO2 in an amount ranging from about 0 to about 2 mole percent, or from about 0 to about 1 mole percent. The glass compositions described herein may also contain various contaminants, particularly Fe2O3 and ZrO2, associated with batch materials and / or introduced into the glass by the melting, fining, and / or forming equipment used to produce the glass. The glass may also contain SnO2 as a result of Joule melting using tin oxide electrodes and / or through batch incorporation of tin-containing materials such as SnO2, SnO, SnCO3, SnC2O2, and the like.

[0059] The glass compositions are generally alkali-free; however, the glass may contain some alkali contaminants. For AMLCD applications, it is desirable to maintain alkali levels below 0.1 mole percent to avoid adverse effects on thin film transistor (TFT) performance due to diffusion of alkali ions from the glass into the silicon of the TFT. As used herein, an "alkali-free glass" is a glass having a total alkali concentration of 0.1 mole percent or less, where the total alkali concentration is the sum of the concentrations of Na2O, KO, and Li2O. In one embodiment, the total alkali concentration is 0.1 mole percent or less.

[0060] As previously mentioned, a (MgO+CaO+SrO+BaO) / Al2O3 ratio of 1.0 or greater improves fining, i.e., the removal of gaseous inclusions from molten batch materials. This improvement allows for the use of more environmentally friendly fining packages. For example, on an oxide basis, the glass compositions described herein may have one or more or all of the following compositional characteristics: (i) an As2O3 concentration of at most 0.05 mole percent, (ii) an Sb2O3 concentration of at most 0.05 mole percent, and (iii) an SnO2 concentration of at most 0.25 mole percent.

[0061] As2O3 is an effective high-temperature fining agent for AMLCD glasses, and in some embodiments described herein, As2O3 is used in fining due to its excellent fining properties. However, As2O3 is hazardous and requires special handling during the glassmaking process. Therefore, in certain embodiments, fining is performed without the use of significant amounts of As2O3, i.e., the finished glass contains at most 0.05 mole percent As2O3. In one embodiment, As2O3 is not intentionally used in fining the glass. In such cases, the finished glass typically has at most 0.005 mole percent As2O3 as a result of contaminants present in the batch materials and / or the equipment used to melt the batch materials.

[0062] Although less toxic than As2O3, Sb2O3 is also hazardous and requires special handling. Furthermore, Sb2O3 increases density, increases CTE, and decreases annealing point compared to glasses using As2O3 or SnO2 as a fining agent. Therefore, in certain embodiments, fining is performed without significant amounts of Sb2O3, i.e., the finished glass has at most 0.05 mole percent Sb2O3. In other embodiments, no Sb2O3 is intentionally used in fining the glass. In such cases, the finished glass typically has at most 0.005 mole percent Sb2O3 as a result of contaminants present in the batch materials and / or the equipment used to melt the batch materials.

[0063] Compared to As2O3 and Sb2O3 fining, tin fining (i.e., SnO2 fining) is less effective, but SnO2 is a ubiquitous material with no known detrimental properties. Also, for many years, SnO2 has been a component of AMLCD glasses due to the use of tin oxide electrodes in the Joule melting of batch materials for such glasses. The presence of SnO2 in AMLCD glasses has not caused any known adverse effects on the use of these glasses in the manufacture of liquid crystal displays. However, high concentrations of SnO2 are undesirable because they can cause the formation of crystalline defects in AMLCD glasses. In one embodiment, the concentration of SnO2 in the finished glass is 0.25 mole percent or less.

[0064] In some embodiments, it has been unexpectedly discovered that the higher viscosity glasses described herein can contain higher concentrations of SnO2 without any detrimental effects to the glass. For example, conventional wisdom would dictate that glasses with high annealing points result in high melting temperatures. Such high melting temperatures can result in poor inclusion quality in the respective glasses. To address such inclusion quality, fining agents can be added; however, glasses with low viscosities generally cannot accommodate the addition of SnO2 due to its crystallization in the glass. However, exemplary glasses as described herein can have higher viscosities, resulting in higher forming temperatures, and therefore, higher concentrations of fining agents can be added to the glass, thereby resulting in fewer inclusions. Simply put, it has been discovered that by changing the composition of the exemplary glasses to result in higher processing temperatures, a greater amount of fining agent can be added to remove inclusions before crystallization occurs. Thus, exemplary glasses include SnO2 at a concentration between 0.001 mol % and 0.5 mol % and have a T of about 1270° C. or greater, about 1280° C. or greater, or about 1290° C. or greater. 35kP Another exemplary glass may include SnO2 at a concentration between 0.001 mol % and 0.5 mol %, and have a T of about 1650° C. or greater, about 1660° C. or greater, or about 1670° C. or greater. 200P Another exemplary glass may include SnO2 at a concentration between 0.001 mol % and 0.5 mol %, and have a T of about 1270° C. or greater, about 1280° C. or greater, or about 1290° C. or greater. 35kP and T of about 1650°C or more, about 1660°C or more, or about 1670°C or more 200P Further exemplary glasses may include SnO2 in a concentration between 0.001 mol % and 0.5 mol % and have a liquidus temperature greater than about 1150°C, greater than about 1165°C or greater, or greater than about 1170°C. Such glasses may have a T 35kP and / or T 200POf course, SnO2 can be provided to the glass as a result of Joule melting using a tin oxide electrode and / or by batching with tin-containing materials such as SnO2, SnO, SnCO3, SnCO2, and the like.

[0065] Tin fining can be used alone or in combination with other fining techniques, if desired. For example, tin fining can be combined with halide fining, e.g., bromine fining. Other possible combinations include, but are not limited to, tin fining plus sulfate, sulfide, cerium oxide, mechanical frothing, and / or vacuum fining. It is believed that these other fining techniques can be used alone. In certain embodiments, maintaining the (MgO + CaO + SrO + BaO) / Al2O3 ratio and the individual alkaline earth concentrations within the ranges previously described makes the fining process easier and more effective.

[0066] The glasses described herein can be produced using a variety of techniques known in the art. In one embodiment, the glasses are produced using a downdraw process, such as a fusion downdraw process. In other embodiments, the glasses are produced using a float process. In one embodiment, a method for producing an alkali-free glass sheet is described, comprising the steps of selecting, melting, and fining batch materials such that the glass comprising the sheet contains SiO, AlO, BO, MgO, CaO, and BaO, and has a (MgO + CaO + SrO + BaO) / AlO ratio, on an oxide basis, of 1.0 or greater.

[0067] U.S. Patent Nos. 5,785,726 (Dorfeld et al.), 6,128,924 (Bange et al.), 5,824,127 (Bange et al.), and 7,628,038 and 7,628,039 (De Angelis et al.) disclose processes for producing arsenic-free glass. U.S. Patent No. 7,696,113 (Ellison) discloses a process for producing arsenic- and antimony-free glass using iron and tin to minimize gaseous inclusions.

[0068] Some embodiments relate to glasses comprising, in mole percent on an oxide basis: 65-75 SiO2, 12-14 Al2O3, 0-3 B2O3, 4-8 MgO, 5-10 CaO, 0-5 SrO, and 0-2 other oxides including Y2O3, ZrO2, and ZnO. In some embodiments, the glasses comprise, in mole percent on an oxide basis: 69-73 SiO2, 12-14 Al2O3, 0-3 B2O3, 4-7 MgO, 5-6 CaO, 3-4 SrO, and 0-1% other oxides including Y2O3, ZrO2, and ZnO. In some embodiments, the glasses have a strain point greater than 760°C. In some embodiments, the glasses have a 200 poise temperature less than 1650°C. In some embodiments, the glasses have a liquidus temperature less than 1300°C. In some embodiments, the glass has a liquidus viscosity of greater than 20,000 poise. In some embodiments, the glass has a Young's modulus of greater than 85 GPa. In some embodiments, the glass has a Young's modulus of greater than 33 GPa / g / cm. 3 It has a specific elastic modulus of greater than .

[0069] Some embodiments relate to a glass comprising, in mole percent, on an oxide basis: 69-74 SiO2, 11-14 Al2O3, 0-3 B2O3, 4-7 MgO, 5-7 CaO, 0-3 SrO, and 1-5% BaO. In some embodiments, the glass comprises, in mole percent, on an oxide basis: 70-73 SiO2, 11-14 Al2O3, 0-1 B2O3, 4-7 MgO, 5-7 CaO, 0-3 SrO, and 1-5% BaO. In some embodiments, the glass has a strain point greater than 752°C. In some embodiments, the glass has a liquidus temperature less than 1300°C. In some embodiments, the glass has a liquidus viscosity greater than 20,000 poise. In some embodiments, the glass has a Young's modulus greater than 83.56 GPa. In some embodiments, the glass has a viscosity of 32 GPa / g / cm 3 It has a specific elastic modulus of greater than .

[0070] Some embodiments relate to a glass comprising, in mole percent on an oxide basis: 68.84-74.07 SiO, 10.41-14.87 AlO, 0-2 BO, 3.44-7.45 MgO, 4.19-8.23 CaO, 0-3.36 SrO, 0.91-5.59 BaO, and 0.09-0.2% SnO. In some embodiments, the glass comprises, in mole percent on an oxide basis: 69.86-72.13 SiO2, 11.58-13.01 Al2O3, 0-1 B2O3, 4.44-6.45 MgO, 5.53-7.23 CaO, 0.09-1.67 SrO, 2.92-4.57 BaO, and 0.09-0.1% SnO2. In some embodiments, the glass has a strain point greater than 760°C. In some embodiments, the glass has a 200 poise temperature less than 1650°C. In some embodiments, the glass has a liquidus temperature less than 1300°C. In some embodiments, the glass has a liquidus viscosity greater than 20,000 poise. In some embodiments, the glass has a Young's modulus greater than 85 GPa. In some embodiments, the glass has a Young's modulus greater than 33 GPa / g / cm 3 It has a specific elastic modulus of greater than .

[0071] Some embodiments relate to a glass comprising, in mole percent on an oxide basis, SiO2, Al2O3, BO3, MgO, CaO, SrO, and BaO, and having a Young's modulus defined by the relationship: 78 GPa < 69.91973399947 + 0.803977834357368 × Al2O3 - 0.906331789808018 × BO3 + 0.773177760652988 × MgO + 0.358794596568283 × CaO + 0.0167545708595792 × SrO - 0.382565908440928 × BaO < 90 GPa. Some embodiments relate to a glass comprising, in mole percent on an oxide basis, SiO2, Al2O3, BO3, MgO, CaO, SrO, and BaO, and having an annealing temperature defined by the relationship: 750°C < 854.140323860904 + 4.46948220485465 × Al2O3 − 14.4689626526177 × BO3 − 5.91884532478309 × MgO − 5.94752853843398 × CaO − 5.85611498931903 × SrO − 6.03112833503798 × BaO < 860°C.

[0072] It will be recognized that various disclosed embodiments may include the specific features, elements, or steps described with respect to that particular embodiment. It will also be recognized that certain features, elements, or steps, although described with respect to one particular embodiment, may be substituted or combined in alternative embodiments in various non-illustrated combinations or orders.

[0073] It will also be understood that as used herein, nouns refer to "at least one" object and should not be limited to "only one" object unless expressly indicated to the contrary.

[0074] Ranges may be expressed herein as from "about" one particular value, and / or to "about" another particular value. When a range is so expressed, examples include from the one particular value and / or to the other particular value. Similarly, when values ​​are expressed as approximations, by use of the antecedent "about," it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of these ranges are significant both in relation to the other endpoint, and independently of the other endpoint.

[0075] As used herein, the terms "substantially," "substantially," and variations thereof are intended to note that a described characteristic is equal to or approximately equal to a value or description. Additionally, "substantially similar" is intended to mean that two values ​​are equal or approximately equal. In some embodiments, "substantially similar" may mean values ​​within about 10% of each other, such as within about 5% of each other, or within about 2% of each other.

[0076] Unless otherwise expressly stated, it is in no way intended that any method set forth herein be considered to require that its steps be performed in a particular order. Thus, unless a method claim actually recites the order in which its steps should be followed, or unless the claim or description specifically states otherwise that the steps should be limited to a particular order, no particular order is intended to be implied.

[0077] Although various features, elements, or steps of particular embodiments may be disclosed using the transitional phrase "comprising," it should be understood that alternative embodiments are implied, including those that may be described using the transitional phrases "consisting of" or "consisting essentially of." Thus, for example, alternative embodiments implied for a device comprising A+B+C include embodiments in which the device consists of A+B+C, and embodiments in which the device consists essentially of A+B+C.

[0078] It will be apparent to those skilled in the art that various modifications and variations can be made to the present disclosure without departing from the spirit and scope of the present disclosure. Since modifications, combinations, subcombinations, and variations of the disclosed embodiments that incorporate the spirit and substance of the present disclosure will occur to those skilled in the art, the present disclosure should be construed as including all within the scope of the appended claims and equivalents thereof. [Example]

[0079] The following examples are set forth below to illustrate methods and results according to the disclosed subject matter. These examples are not intended to be inclusive of all embodiments of the procedures disclosed herein, but rather to illustrate representative methods and results. These examples are not intended to exclude equivalents and variations of the present disclosure that would be apparent to one skilled in the art.

[0080] Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperatures, etc.), but some errors and deviations should be accounted for. Unless otherwise noted, temperatures are in °C or are ambient, and pressures are at or near atmospheric. The compositions themselves are given in mole percent on an oxide basis and are normalized to 100%. There are numerous variations and combinations of reaction conditions, e.g., component concentrations, temperatures, pressures, and other reaction ranges and conditions, that can be used to optimize product purity and yields from the described processes. No more than reasonable and routine experimentation will be required to optimize such process conditions.

[0081] The glass properties listed in Table 1 were determined according to standard techniques in the glass art. Thus, the coefficient of linear thermal expansion (CTE) over the temperature range 25-300°C is expressed in ppm, and the annealing points are expressed in °C. These were determined by the fiber stretching technique (ASTM standards E228-85 and C336, respectively). The units are in grams / cm. 3Density, in °C, was measured by the Archimedes method (ASTM C693). Melting temperature, in °C (defined as the temperature at which the glass melt exhibits a viscosity of 200 poise), was calculated using the Fulcher equation fit to high-temperature viscosity data measured with a cylindrical rotational viscometer (ASTM C965-81). Strain point and anneal point were measured with a beam bending viscometer (BBV) and were calculated based on the softening point (10 7.6 High temperature viscosity (HTV) (above the temperature corresponding to the viscosity of the glass equal to poise) was measured by a cylindrical rotational viscometer according to ASTM C965 procedure (B).

[0082] The liquidus temperature of the glass, expressed in °C, was measured using the standard gradient boat liquidus method of ASTM C829-81. This method involves placing crushed glass particles in a platinum boat, placing the boat in a furnace with a temperature gradient zone, heating the boat within the appropriate temperature zone for 24 hours, and determining by microscopic examination the maximum temperature at which crystals appear within the glass. More specifically, a glass sample is removed from the platinum boat in one piece and examined using polarized light microscopy to identify the location and nature of crystals formed relative to the platinum-air interface and within the sample. Because the furnace gradient is well known, the temperature versus location can be well predicted to within 5–10 °C. The temperature at which crystals are observed within the sample is taken to represent the glass's liquidus (for the corresponding test period). Tests are sometimes run for longer periods (e.g., 72 hours) to observe slower growth stages. The liquidus viscosity, expressed in poises, was determined from the liquidus temperature and the coefficients of the Fulcher equation.

[0083] Young's modulus values, expressed in GPa, were determined using a resonant ultrasonic spectroscopy technique of the general type described in ASTM E1875-00e1.

[0084] Exemplary glasses are shown in Table 1. As can be seen from Table 1, the exemplary glasses have density, anneal point, and Young's modulus values ​​that make them suitable for AMLCD substrate applications, more particularly for display applications such as low-temperature polysilicon and oxide thin film transistor applications. Although not shown in Table 1, the glasses have durability in acidic and basic media similar to that obtained from commercially available AMLCD substrates, and are therefore suitable for AMLCD applications. The exemplary glasses can be formed using downdraw techniques and are specifically compatible with the fusion process according to the criteria described above.

[0085] The exemplary glasses in Table 1 were prepared using commercially available sand as the silica source, ground to 90% by weight to pass a standard 100-mesh U.S. sieve. Alumina was the alumina source, periclase was the MgO source, limestone was the CaO source, strontium carbonate, strontium nitrate, or a mixture thereof was the SrO source, barium carbonate was the BaO source, and tin(IV) oxide was the SnO source. The raw materials were thoroughly mixed, loaded into a platinum vessel suspended in a furnace heated by a silicon carbide glow bar, melted and stirred at temperatures between 1600°C and 1650°C for several hours to ensure homogeneity, and delivered through an orifice in the bottom of the platinum vessel. The resulting glass patty was annealed at or near the anneal point and then subjected to various experimental methods to determine its physical, viscous, and liquidus properties.

[0086] These methods are not unusual and the glasses in Table 1 can be prepared using standard methods known to those skilled in the art, including continuous melting processes, such as those performed in a continuous melting process where the melter used is heated by gas, electricity, or a combination thereof.

[0087] Suitable raw materials for making exemplary glasses include commercially available sand as a source of SiO; alumina, aluminum hydroxide, hydrated forms of alumina, and various aluminosilicates, nitrates, and halides as sources of AlO; boric acid, boric anhydride, and boron oxide as sources of BO; periclase, dolomite (also a source of CaO), magnesia, magnesium carbonate, magnesium hydroxide, and magnesium silicate, various forms of aluminosilicates, nitrates, and halides as sources of MgO; limestone, aragonite, dolomite (also a source of MgO), wollastonite, and various forms of calcium silicate, aluminosilicates, nitrates, and halides as sources of CaO; and strontium and barium oxides, carbonates, nitrates, and halides. If a chemical fining agent is desired, tin can be added as SnO, as a mixed oxide with another major glass component (e.g., CaSnO), or under oxidizing conditions as SnO, tin oxalate, tin halides, or other compounds of tin known to those skilled in the art.

[0088] While the glasses in Table 1 contain SnO as a fining agent, other chemical fining agents may be used to obtain glass of sufficient quality for TFT substrate applications. For example, the exemplary glasses may use any one or combination of AsO, SbO, CeO, FeO, and halides as deliberate additions to promote fining, any of which may be used with the SnO chemical fining agent shown in the examples. Of these, AsO and SbO are generally recognized as hazardous materials and are subject to regulation of waste streams such as those generated during glass manufacturing or TFT panel processing. Therefore, it is desirable to limit the concentrations of AsO and SbO, individually or in combination, to 0.005 mole percent or less.

[0089] In addition to the elements deliberately included in the exemplary glasses, nearly every stable element in the periodic table is present in the glasses at some level, either through low-level contamination in raw materials, high-temperature corrosion of refractories and precious metals during manufacturing, or deliberate introduction at low levels to fine-tune the properties of the final glass. For example, zirconium may be introduced as a contaminant through interaction with zirconium-rich refractories. As a further example, platinum and rhodium may be introduced through interaction with precious metals. As a further example, iron may be introduced as a tramp in raw materials or deliberately added to improve gaseous inclusion control. As a further example, manganese may be introduced for color control or to improve gaseous inclusion control. As a further example, alkalis may be present as tramp components at levels up to about 0.1 mole % of the total concentration of LiO, NaO, and KO.

[0090] Hydrogen forms the hydroxyl anion OH - hydroxyl ions are inevitably present in the form of hydroxyl ions, and their presence can be confirmed by standard infrared spectroscopy techniques. Dissolved hydroxyl ions significantly and nonlinearly affect the annealing point of the exemplary glass, and therefore, to obtain the desired annealing point, it may be necessary to adjust the concentration of the major oxide component to compensate. Hydroxyl ion concentration can be controlled to some extent by the choice of raw materials or the melting system. For example, boric acid is a major source of hydroxyl, and replacing boric acid with boric oxide may be a useful means to control the hydroxyl concentration in the final glass. The same rationale applies to other potential raw materials, including hydroxyl ions, hydrates, or compounds containing physisorbed or chemisorbed water molecules. If a burner is used in the melting process, hydroxyl ions may also be introduced by combustion products from the combustion of natural gas and related hydrocarbons; therefore, it may be desirable to shift the energy used in melting from the burner to the electrode to compensate. Alternatively, an iterative process of adjusting the major oxide component to compensate for the deleterious effects of dissolved hydroxyl ions may instead be utilized.

[0091] Sulfur is often present in natural gas, as well as being a tramp component in many carbonate, nitrate, halide, and oxide raw materials. Sulfur, in the form of SO2, can be a troublesome source of gaseous inclusions. The tendency to form SO2-rich defects can be managed to a significant extent by controlling the sulfur level in the raw materials and by including low levels of relatively reduced polyvalent cations in the glass matrix. Without intending to be bound by theory, it is believed that SO2-rich gaseous inclusions may be formed by the formation of sulfate radicals (SO4) dissolved in the glass. = The elevated barium concentration in the exemplary glasses appears to increase the desulfurization effect in the glass during the early stages of melting, but as noted above, barium has a low liquidus temperature and therefore a high T 35k -T liq and is required to obtain high liquidus viscosity. Carefully controlling the sulfur level in the raw materials to a low level is a useful means of reducing dissolved sulfur (possibly as sulfate) in the glass. Specifically, sulfur is preferably less than 200 ppm by weight of the batch materials, and more preferably less than 100 ppm by weight of the batch materials.

[0092] Reduced polyvalent elements can be used to control the tendency of exemplary glasses to form SO2 blisters. Without intending to be bound by theory, these elements behave as potential electron donors that suppress the electromotive force for sulfate reduction. The reduction of sulfate groups is SO4 = →SO2+O2+2e - where e - indicates an electron. The "equilibrium constant" for this half-reaction is K eq =[SO2][O2][e - ] 2 / [SO4 = ] where the square brackets indicate chemical activity. Ideally, the reaction produces SO2, O2, and e -We want to create sulfate groups from SO2. Adding nitrates, peroxides, or other oxygen-rich raw materials would be helpful, but would work against the reduction of sulfate groups in the early stages of melting, which would negate the benefit of adding them in the first place. SO2 has very low solubility in most glasses, and therefore is impractical to add to the glass melting process. Electrons will be "donated" by reduced polyvalent elements, e.g., ferrous iron (Fe 2+ The appropriate electron-donating half-reaction for 2Fe 2+ →2Fe 3+ +2e - It is expressed as:

[0093] This "activity" of electrons forces the sulfate reduction reaction to the left, forming SO4 in the glass. = Suitable reduced polyvalent elements include, but are not limited to, Fe 2+ , Mn 2+ , Sn 2+ , Sb 3+ , As 3+ , V 3+ , Ti 3+ , and others familiar to those skilled in the art. In each case, it may be important to minimize the concentration of such components to avoid deleterious effects on the color of the glass, or, in the case of As and Sb, to avoid adding such components at levels high enough to minimize waste management complications in the end-user's process.

[0094] In addition to the major oxide components of the exemplary glasses and the minor or tramp components mentioned above, halides may be present at various levels, either as contaminants introduced by raw material selection or as intentional components used to eliminate gaseous inclusions in the glass. Halides may be included as fining agents at levels of about 0.4 mol % or less, although it is generally desirable to use smaller amounts where possible to avoid corrosion of exhaust gas handling equipment. In some embodiments, the concentration of individual halide elements is less than about 200 ppm by weight for each individual halide, or less than about 800 ppm by weight for all halide elements combined.

[0095] In addition to these major oxide components, minor and trace components, polyvalent element and halide fining agents, it may be useful to include small concentrations of other colorless oxide components to achieve desired physical, optical, or viscoelastic properties. Examples of such oxides include, but are not limited to, TiO2, ZrO2, HfO2, Nb2O5, Ta2O5, MoO3, WO3, ZnO, In2O3, Ga2O3, Bi2O3, GeO2, PbO, SeO3, TeO2, YO3, La2O3, Gd2O3, and other compounds known to those skilled in the art. By an iterative process of adjusting the relative proportions of the major oxide components of an exemplary glass, such colorless oxides can be added to achieve the desired annealing point, T 35k -T liq , or can be added to levels up to about 2 mole percent without unacceptably affecting liquidus viscosity.

[0096] Table 1 shows examples of glasses according to some embodiments.

[0097] [Table 1-1]

[0098] [Table 1-2]

[0099] [Table 1-3]

[0100] [Table 1-4]

[0101] With reference to Table 1 above, Example 3 provides a confocal image of mullite, tridymite, and anorthite in the MgO·CaO·SiO2·Al2O3 (20 wt%) system (see, e.g., FIG. 8). This embodiment exhibits high strain points, high Young's moduli, and low 20 23This material provides many desirable properties, such as a 0 poise temperature, low CTE, and low density. However, Example 3 has a high liquidus temperature (1320°C) and low liquidus viscosity (17,000 poise), which presents some challenges for certain manufacturing processes. Example 17 provides an increase in Al2O3 of approximately 1 mol% relative to Example 3, which increases the strain point, Young's modulus, and further lowers the 200 poise temperature, lowers the liquidus temperature, and increases the liquidus viscosity. Example 21 further improves the liquidus by replacing a portion of the CaO in Example 17 with SrO, which successfully reduces the liquidus temperature and doubles the liquidus viscosity. The addition of Y2O3 and ZrO2 to Example 21 (Examples 9 and 20) further lowered the liquidus temperature and maintained a high strain point and high Young's modulus. The inclusion of Y2O3 and ZrO2 can be used in some embodiments to increase Young's modulus. Example 10 is a modification of Example 12 in which the concentration of Al2O3 is reduced and the alkaline earths are increased to improve liquidus viscosity. Small amounts of Y2O3, ZnO, and ZrO2 were added to lower the liquidus temperature in Example 10. Therefore, 1 mol% Y2O3 (Example 16) and 1 mol% Y2O3 + 0.5 mol% ZnO (Example 8) reduced the melting temperature (200 poise temperature) by about 50°C, while maintaining the liquidus temperature. Example 5 is a modification of Example 10 in which the concentration of SiO2 is reduced and the alkaline earths are increased to improve the melting temperature, resulting in a 40°C decrease from Example 10. Small amounts of Y2O3, ZnO, and ZrO2 were added to Example 5 to improve other properties. The remaining examples in Table 1 also provide improved Young's modulus and reduced melting temperatures.

[0102] Table 2 provides further examples of glasses according to some embodiments.

[0103] [Table 2-1]

[0104] [Table 2-2]

[0105] [Table 2-3]

[0106] [Table 2-4]

[0107] In some embodiments, example compositions may be described by a convex hull, which can be defined as the smallest convex boundary that contains a group of points within a space of given dimensions. For example, given the space bounded by the following: 68.64-74.07 mol% SiO, 10.41-14.87 mol% AlO, 0-2 mol% BO, 3.44-7.45 mol% MgO, 4.19-8.23 mol% CaO, 0-3.36 mol% SrO, 0.91-5.59 mol% BaO, and 0.09-0.2 mol% SnO, AlO and BO can be grouped into a group named AlO_BO, and the remainder into a group named RO containing MgO, CaO, SrO, BaO, and SnO in their respective ranges. A new ternary space can then be defined with the boundaries set by the following compositions, expressed in mole percent, as shown in Table 3 and Figures 4 and 5:

[0108] [Table 3]

[0109] Compositions within the convex hull delimited by the boundaries formed by the compositions listed in Table 3 above have anneal points and Young's moduli, measured in mole percent oxide, given by Equations 2 and 3, respectively: 78GPa≦69.91973399947+0.803977834357368×Al2O3-0.906331789808018×B2O3+0.773177760652988×MgO+0.358794596568283×CaO+0.0167545708595792×SrO-0.382565908440928×BaO≦90GPa (2) 750℃≦854.140323860904+4.46948220485465×Al2O3−14.4689626526177×B2O3−5.91884532478309×MgO−5.94752853843398×CaO−5.85611498931903×SrO−6.03112833503798×BaO≦860℃ (3).

[0110] Figures 6 and 7 show the predicted Young's modulus and anneal point using equations (2) and (3), respectively, for a group of samples with compositions randomly selected from the convex hull (Figures 4 and 5) bounded by the compositional boundaries shown in Table 3, versus a global model with a much larger group of compositions. These figures demonstrate the agreement between a simple linear model from the data within the convex hull and the global model. Once 1000 random samples of data from the convex hull have been made with predictions of Young's modulus and anneal point for each, a linear model can be constructed. Equations (2) and (3) are valid representations of Young's modulus and anneal point within the convex hull.

[0111] Compositions within the convex hull bounded by the compositions listed in Table 3, within the composition expressed in mole percent, have respective Young's moduli and anneal points given by equations (2) and (3), respectively.

[0112] Preferred embodiments of the present invention will be described below in detail.

[0113] Embodiment 1 A glass containing, on an oxide basis, mole percent: 65-75% SiO2, 12-14% Al2O3, 0-3% B2O3, 4-8% MgO, 5-10% CaO, 0-5% SrO, and 0-2% other oxides including Y2O3, ZrO2, and ZnO.

[0114] Embodiment 2 10. The glass of embodiment 1 comprising, in mole percent on an oxide basis, 69-73% SiO, 12-14% AlO, 0-3% BO, 4-7% MgO, 5-6% CaO, 3-4% SrO, and 0-1% other oxides including YO, ZrO, and ZnO.

[0115] Embodiment 3 3. The glass of embodiment 1 or 2 having a strain point greater than 760°C.

[0116] Embodiment 4 4. The glass of any one of claims 1 to 3, having a 200 poise temperature of less than 1650°C.

[0117] Embodiment 5 5. The glass of any one of claims 1 to 4, having a liquidus temperature of less than 1300°C.

[0118] Embodiment 6 6. The glass of any one of claims 1 to 5, having a liquidus viscosity greater than 20,000 poise.

[0119] Embodiment 7 7. The glass of any one of claims 1 to 6, having a Young's modulus greater than 85 GPa.

[0120] Embodiment 8 33GPa / g / cm 3 8. The glass of any one of claims 1 to 7, having a specific elastic modulus of greater than

[0121] Embodiment 9 A liquid crystal display substrate made from the glass of any one of embodiments 1 to 8.

[0122] Embodiment 10 A glass containing, in mole percent on an oxide basis, 69-74% SiO2, 11-14% Al2O3, 0-3% B2O3, 4-7% MgO, 5-7% CaO, 0-3% SrO, and 1-5% BaO.

[0123] Embodiment 11 11. The glass of embodiment 10 comprising, in mole percent on an oxide basis, 70-73% SiO2, 11-14% Al2O3, 0-1% B2O3, 4-7% MgO, 5-7% CaO, 0-3% SrO, and 1-5% BaO.

[0124] Embodiment 12 12. The glass of claim 10 or 11, having a strain point greater than 752°C.

[0125] Embodiment 13 13. The glass of any one of claims 10 to 12, having a liquidus temperature of less than 1300°C.

[0126] Embodiment 14 14. The glass of any one of embodiments 10 to 13, having a liquidus viscosity greater than 20,000 poise.

[0127] Embodiment 15 15. The glass of any one of claims 10 to 14, having a Young's modulus greater than 83.56 GPa.

[0128] Embodiment 16 32GPa / g / cm 3 16. The glass of any one of claims 10 to 15, having a specific elastic modulus of greater than

[0129] Embodiment 17 A liquid crystal display substrate made from the glass of any one of embodiments 10 to 16.

[0130] Embodiment 18 A glass containing, in mole percent on an oxide basis, 68.84-74.07% SiO2, 10.41-14.87% Al2O3, 0-2% B2O3, 3.44-7.45% MgO, 4.19-8.23% CaO, 0-3.36% SrO, 0.91-5.59% BaO, and 0.09-0.2% SnO2.

[0131] Embodiment 19 19. The glass of embodiment 18 comprising, in mole percent on an oxide basis, 69.86-72.13% SiO2, 11.58-13.01% Al2O3, 0-1% B2O3, 4.44-6.45% MgO, 5.53-7.23% CaO, 0.09-1.67% SrO, 2.92-4.57% BaO, and 0.09-0.1% SnO2.

[0132] Embodiment 20 20. The glass of embodiment 18 or 19, having a strain point greater than 760°C.

[0133] Embodiment 21 21. The glass of any one of claims 18 to 20, having a 200 poise temperature of less than 1650°C.

[0134] Embodiment 22 22. The glass of any one of claims 18 to 21, having a liquidus temperature of less than 1300°C.

[0135] Embodiment 23 23. The glass of any one of embodiments 18 to 22, having a liquidus viscosity greater than 20,000 poise.

[0136] Embodiment 24 24. The glass of any one of embodiments 18 to 23, having a Young's modulus greater than 85 GPa.

[0137] Embodiment 25 33GPa / g / cm 3 25. The glass of any one of claims 18 to 24, having a specific elastic modulus of greater than

[0138] Embodiment 26 A liquid crystal display substrate made from the glass of any one of embodiments 18 to 25.

[0139] Embodiment 27 Mole percent on an oxide basis, including SiO2, Al2O3, B2O3, MgO, CaO, SrO, and BaO, according to the relationship: 78GPa≦69.91973399947+0.803977834357368×Al2O3-0.906331789808018×B2O3+0.773177760652988×MgO+0.358794596568283×CaO+0.0167545708595792×SrO-0.382565908440928×BaO≦90GPa A glass having a Young's modulus defined by:

[0140] Embodiment 28 Mole percent on an oxide basis, including SiO2, Al2O3, B2O3, MgO, CaO, SrO, and BaO, according to the relationship: 750℃≦854.140323860904+4.46948220485465×Al2O3-14.4689626526177×B2O3-5.91884532478309×MgO-5.94752853843398×CaO-5.85611498931903×SrO-6.03112833503798×BaO≦860℃ A glass having an annealing temperature defined by:

[0141] Embodiment 29 29. A liquid crystal display substrate made from the glass of embodiment 27 or 28. [Explanation of symbols]

[0142] 1 entrance 2 Compression end 3 Edge Director 4 Bottom 9 Weir Wall 10 base

Claims

1. 70-73% SiO in mole percent on an oxide basis ２ , 12-14% Al ２ O ３ , 0-1% B ２ O ３ , 4-7% MgO, 5-7% CaO, 0-3% SrO, 1-5% BaO, and 0.4-2% Y ２ O ３ , ZrO ２ and ZnO, A glass having a specific elastic modulus greater than 32 GPa / g / cm 3 .

2. 10. The glass of claim 1 having a strain point greater than 752°C.

3. 3. The glass of claim 1, having a liquidus temperature of less than 1300°C.

4. 4. The glass of claim 1 having a liquidus viscosity of greater than 20,000 poise.

5. 5. The glass of claim 1 having a Young's modulus greater than 83.56 GPa.

6. A substrate for a liquid crystal display made from the glass of any one of claims 1 to 5.

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