Patent Description:
There is a market demand for very thin glass sheets having, for example, a thickness of less than <NUM>. Such thin glass sheets may be utilized in consumer electronics. These glass sheets should be relatively flat with consistent thickness. However, expensive and/or time consuming steps may be necessary to produce such thin glass sheets, such as cutting and/or polishing procedures. Additionally, applications of the glass sheets may demand for special properties of the glass, such as relatively high refractive index. For example, thin glass sheets having relatively high refractive index may be incorporated into OLED lighting devices and augmented reality electronic devices. However, such high refractive index glasses may have properties which are incompatible with standard sheet forming operations. Accordingly, there is a need for processes to produce thin glass substrates more efficiently and at lower cost. <CIT> is directed to glass forming roll and method for forming glass plate using said rolls. <CIT> is directed to glass manufacturing system to produce high quality thin glass sheet. <CIT> relates to a precision glass roll forming process and corresponding apparatuses.

According to the invention, a glass sheet is formed by a method comprising supplying a feed of molten glass to an upper surface of a pair of forming rolls, and rotating the pair of forming rolls at a rate such as to continuously form at least <NUM>/min of a glass sheet from the molten glass. The pair of forming rolls is spaced apart by a forming gap, and the forming gap may have a width of less than or equal to about <NUM> microns. The molten glass has a viscosity of less than or equal to about <NUM> Pa. s (<NUM> poise). The glass sheet has a thickness of less than or equal to about <NUM> microns immediately upon passing through the forming gap.

Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understanding the nature and character of the claims. The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiments, and together with the description serve to explain principles and operation of the various embodiments.

According to embodiments described herein, glass sheets are continuously formed by a process which utilizes a pair of forming rollers to process molten glass into a thin glass sheet having a relatively constant thickness. The glass sheets may have a thickness of less than or equal to <NUM> microns, such as less than <NUM> microns, or even less than <NUM> microns. Additionally, the formed glass sheets may have a width of, for example, at least <NUM>, at least <NUM>, or even greater. Such glass sheets may be further processed into wafers by cutting. However, additional cutting or rolling operations needed to reduce the thickness of the glass sheet may not be necessary to attain the desired glass sheet dimensional specifications.

Additionally, according to some embodiments, the glass sheets described herein may be formed from glass compositions which have relatively low liquidus viscosity, such as, for example less than <NUM> Pa. s (<NUM> poise). Such liquidus viscosities may be common for glass compositions which having relatively high refractive indices (e.g., greater than <NUM> or even greater than <NUM>). Conventional glass forming procedures may not be well equipped to handle such glass and form it at such small thicknesses and high aspect ratios.

Now referring to <FIG>, a glass sheet forming apparatus <NUM> is schematically depicted, according to one or more embodiments disclosed herein. The glass sheet forming apparatus <NUM> may include at least a molten glass delivery device <NUM> and a pair of forming rolls <NUM> (i.e., first forming roll <NUM> and a second forming roll <NUM>). The first forming roll <NUM> and the second forming roll <NUM> may be arranged horizontally with respect to one another, and the molten glass delivery device <NUM> may be arranged substantially above the pair of forming rolls <NUM>. The first forming roll <NUM> may comprise a first radial axis <NUM>, and the second forming roll <NUM> may comprise a second radial axis <NUM>. The first forming roll may be operable to rotate around the first radial axis <NUM>, and the second forming roll <NUM> may be operable to rotate around the second radial axis <NUM>. In some embodiments, the first radial axis <NUM> and the second radial axis <NUM> may be horizontally aligned.

The first forming roll <NUM> and the second forming roll <NUM> may be separated by an area referred to herein as the forming gap <NUM>. The forming gap <NUM> comprises the area between the first forming roll <NUM> and the second forming roll <NUM>, at or near their closest point. The forming gap <NUM> has a width <NUM> as measured between the first forming roll <NUM> and the second forming roll <NUM>. In embodiments where the pair of forming rolls <NUM> are horizontally aligned, the width <NUM> of the forming gap <NUM> is measured in a horizontal direction. In one or more embodiments, no portion of the first forming roll <NUM> contacts any portion of the second forming roll <NUM>. In additional embodiments, the edges of the forming rolls <NUM> contact one another, but the forming rolls <NUM> are shaped such as to from a forming gap <NUM> where the molten glass <NUM> contacts the forming rolls <NUM>.

The molten glass delivery device <NUM> may supply a feed of molten glass <NUM> to an upper surface <NUM>, <NUM> of the pair of forming rolls <NUM>. The molten glass delivery device <NUM> may be positioned relative to the first forming roll <NUM> and the second forming roll <NUM> such that molten glass is fed directly over the forming gap <NUM>. In other embodiments, the molten glass delivery device <NUM> may not be exactly centered over the forming gap <NUM>, but may be positioned to expel molten glass into the "valley" formed by the first forming roll <NUM> and the second forming roll <NUM>.

While <FIG> depict the molten glass delivery device <NUM> as a pipe <NUM>, the molten glass <NUM> may be delivered using any suitable glass delivery method by any suitable device. For example, the molten glass <NUM> may be delivered to the pair of forming rolls <NUM> in batches from a crucible or a pre-shaped ladle. In another embodiment, the molten glass <NUM> may be continuously fed to the pair of forming rolls <NUM> as a stream of glass from a fishtail orifice, slot orifice, fusion forming isopipe, or an extrusion furnace.

As shown in <FIG> the molten glass <NUM> may be delivered through a single pipe <NUM>. As described herein, pipes, or other conduit means which deliver the molten glass substantially in a single dimension are referred to as point source delivery devices. For example, substantially cylindrical tubes, conduits, hoses, mains, ducts, lines, channels, pipelines, and drains are all considered point source delivery devices. According to one or more embodiments, a pipe <NUM> may be utilized that has a diameter of from about <NUM> to about <NUM>. However, other sizes and subranges of pipe diameter are contemplated based on desired width and thickness of the formed glass sheet <NUM>.

In other embodiments, the molten glass <NUM> may be delivered through a plurality of point sources. For example, as shown in <FIG>, the molten glass delivery device <NUM> may comprise a plurality of pipes, such as a first pipe <NUM>, a second pipe <NUM>, and a third pipe <NUM>. The plurality of pipes <NUM>, <NUM>, <NUM> may be positioned along a major length of the forming gap <NUM> (perpendicular to the width <NUM> of the forming gap <NUM>).

In additional embodiments, the molten glass <NUM> may be delivered through non-point source delivery devices. For example, <FIG> depict an elongated aperture delivery device <NUM>, such as a fishtail orifice or slot orifice. The major length of the elongated delivery device <NUM> may be positioned along a major length of the forming gap <NUM> (perpendicular to the width <NUM> of the forming gap <NUM>). According to one or more embodiments, an elongated delivery device may be utilized that has a width of from about <NUM> to about <NUM>. However, other sizes and subranges of width are contemplated based on desired width and thickness of the formed glass sheet <NUM>.

According to additional embodiments, the point at which the molten glass exits the molten glass delivery device <NUM> may be below the top edge of the first forming roll <NUM> and the second forming roll <NUM>. However, the point at which the molten glass exits the molten glass delivery device <NUM> should be high enough to remain above the level of the puddle <NUM> so that sufficient puddling can be attained so that a desired glass width <NUM> can be attained.

The molten glass <NUM> has a viscosity of less than or equal to about <NUM> Pa. s (<NUM> poise) as it exits the molten glass delivery device <NUM>. According to additional embodiments, the molten glass <NUM> may have a viscosity of less than or equal to about <NUM> Pa. s (<NUM> poise), less than or equal to about <NUM> Pa. s (<NUM> poise), less than or equal to about <NUM> Pa. s (<NUM> poise), less than or equal to about <NUM> Pa. s (<NUM> poise), less than or equal to about <NUM> Pa. s (<NUM> poise), less than or equal to about <NUM> Pa. s (<NUM> poise), less than or equal to about <NUM> Pa. s (<NUM> poise), or even less than or equal to about <NUM> Pa. s (<NUM> poise), as it exits the molten glass delivery device <NUM>. The molten glass <NUM> may have any of these disclosed viscosities as it rests on the upper surface <NUM> of the first forming roll <NUM> and the upper surface <NUM> of the second forming roll <NUM>, and as it passes through the forming gap <NUM>.

In some embodiments, the relatively low viscosities disclosed herein may be utilized because the glass composition which is formed may have a relatively low liquidus viscosity. The temperature where crystal phases start to develop is known as the liquidus temperature. The crystallization point may also be cast in terms of the liquidus viscosity, which is the viscosity of the particular glass composition at the liquidus temperature. In general, the viscosity of the molten glass <NUM> when delivered out of the molten glass delivery device <NUM> and in the puddle <NUM> may be less than the liquidus viscosity of the molten glass <NUM> such that crystallization is prevented. As described herein, the liquidus viscosity of the molten glass <NUM> and/or the formed glass sheet <NUM> may be less than or equal to about <NUM> Pa. s (<NUM> poise), less than or equal to about <NUM> Pa. s (<NUM> poise), less than or equal to about <NUM> Pa. s (<NUM> poise), less than or equal to about <NUM> Pa. s (<NUM> poise), less than or equal to about <NUM> Pa. s (<NUM> poise), less than or equal to about <NUM> Pa. s (<NUM> poise), less than or equal to about <NUM> Pa. s (<NUM> poise), or even less than or equal to about <NUM> Pa. s (<NUM> poise). Such relatively low liquidus viscosities may be common in some glasses having relatively high refractive indices.

According to the presently disclosed processes, the molten glass <NUM> may form a puddle <NUM> (sometimes referred to as a pool herein) over the upper surface <NUM> of the first forming roll <NUM> and the upper surface <NUM> of the second forming roll <NUM>. The formation of the puddle <NUM> may allow for glass to run past the perimeter of the molten glass delivery device <NUM> and extend the length of the puddle (i.e., in the direction perpendicular to the width <NUM> of the forming gap <NUM>. That is, the length of the puddle may be determinative of the width <NUM> of the formed glass sheet <NUM>. Therefore, increased pooling allows for wider glass sheets <NUM>. Additionally, puddling may allow for the consistent and continued forming of the glass sheet <NUM> even while an irregular stream of molten glass <NUM> is delivered from the molten glass delivery device <NUM>. For example, the glass sheet <NUM> can continue to be formed even when the mass flowrate of molten glass <NUM> varies.

According to the embodiments described herein, the pair of forming rolls <NUM> may rotate to continuously form the glass sheet <NUM> from the molten glass <NUM>. As depicted in <FIG>, the first forming roll <NUM> and the second forming roll <NUM> rotate in opposite directions with respect to one another to facilitate the forming of the glass sheet <NUM>. The molten glass <NUM> may pass through the forming gap <NUM> and exit below the forming gap <NUM> in a somewhat viscous condition. Following the passing of the molten glass <NUM> through the forming gap <NUM>, the glass may be cooled to a solid state.

The pair of forming rolls <NUM> rotate at rotational speeds suitable for forming a desired rate of glass sheet <NUM>. For example, the glass forming process disclosed herein may be run at a mass flow rate per unit width in a range of from about <NUM>/hour-meter (<NUM> lb/hr-inch) to about <NUM>/hour-meter (<NUM> lb/hr-inch). The forming rolls <NUM> rotate at a rate such as to produce at least about <NUM>/min, such as at least about <NUM>/min, at least about <NUM>/min, at least about <NUM>/min, at least about <NUM>/min, at least about <NUM>/min, at least about <NUM>/min, at least about <NUM>/min, at least about <NUM>/min, at least about <NUM>/min, or even at least about <NUM>/min.

The cooling of the molten glass <NUM> below the forming gap <NUM> may be enabled by the contacting of the molten glass <NUM> with the pair of forming rolls <NUM> at the forming gap <NUM>. The pair of forming rolls <NUM> may have a temperature that is less than that of the pooled molten glass <NUM>, but still greater than ambient temperatures. For example, the first forming roll <NUM> and/or the second forming roll <NUM> may have a temperature of about <NUM> to about <NUM>. Heaters, heat exchangers, etc. may be utilized to accurately control the temperature of the pair of forming rolls <NUM>. In some embodiments, the forming rolls <NUM> may be heated only by contact with the molten glass <NUM>. In additional embodiments, the forming rolls <NUM> may be maintained at a temperature below that of the molten glass <NUM> by cooling fluid or other cooling means.

According to one or more embodiments, the forming rolls <NUM> may be designed to maintain a uniform forming gap <NUM>. For example, the forming rolls <NUM> may be accurately machined to have a radial uniformity of within <NUM> microns, within <NUM> microns, or even better.

In additional embodiments, the forming rolls <NUM> may be shaped such that thermal expansion to portions of the forming rolls <NUM> are accounted for. Without being bound by theory, when forming rolls <NUM> contact the molten glass <NUM>, they are heated up relative to their normal non-contacted temperature, and thermal expansion occurs. This thermal expansion is usually not constant over the whole forming roll <NUM>. For example, the expansion may be larger in the central portion of the forming rolls <NUM>. Therefore, the forming rolls <NUM> may have a slightly smaller diameter at some regions (such as those in the central portion of the forming rolls <NUM>) at ambient temperature conditions to account for the increased thermal expansion. If no shape compensation is utilized, a glass sheet that is thicker near the edges of the glass sheet <NUM>, thinner in the central portion, may be formed. By having a non-constant roll diameter of at least one of the forming rolls <NUM>, this can be compensated.

The forming gap <NUM> has a width <NUM> of less than or equal to about <NUM> microns. In additional embodiments, the forming gap <NUM> has a width <NUM> of less than or equal to about <NUM> microns, less than or equal to about <NUM> microns, less than or equal to about <NUM> microns, less than or equal to about <NUM> microns, less than or equal to about <NUM> microns, less than or equal to about <NUM> microns, or even less than or equal to about <NUM> microns. In additional embodiments, the forming gap <NUM> has a width <NUM> of greater than or equal to about <NUM> microns, greater than or equal to about <NUM> microns, greater than or equal to about <NUM> microns greater than or equal to about <NUM> microns, greater than or equal to about <NUM> microns, greater than or equal to about <NUM> microns, greater than or equal to about <NUM> microns, or even greater than or equal to about <NUM> microns. As described herein, the width <NUM> of the forming gap <NUM> is measured during glass forming to account for any thermal expansion that may occur due to the heating of the rolls.

Upon the passing of the molten glass <NUM> through the forming gap <NUM>, the glass sheet <NUM> is formed. The glass sheet <NUM> has a width <NUM> measured in a direction perpendicular to the forming gap width <NUM>, an edge <NUM>, and a surface <NUM>. Additionally, the glass sheet <NUM> has a thickness <NUM> measured in the same direction as the forming gap width <NUM>.

The glass sheet <NUM> has a thickness <NUM> immediately upon passing through the forming gap <NUM> of less than or equal to <NUM> micron. For example, in one or more embodiments, the glass sheet <NUM> has a thickness <NUM> of less than or equal to about <NUM> microns, less than or equal to about <NUM> microns, less than or equal to about <NUM> microns, less than or equal to about <NUM> microns, less than or equal to about <NUM> microns, less than or equal to about <NUM> microns, or even less than or equal to about <NUM> microns immediately upon passing through the forming gap <NUM>. In additional embodiments, the glass sheet <NUM> has a thickness <NUM> of greater than or equal to about <NUM> microns, greater than or equal to about <NUM> microns, greater than or equal to about <NUM> microns greater than or equal to about <NUM> microns, greater than or equal to about <NUM> microns, greater than or equal to about <NUM> microns, greater than or equal to about <NUM> microns, or even greater than or equal to about <NUM> microns immediately upon passing through the forming gap <NUM>.

In one or more embodiments, the thickness <NUM> of the glass sheet <NUM> varies by about <NUM> microns or less. For example, the thickness <NUM> of the formed glass sheet <NUM> varies by about <NUM> microns or less, or even by about <NUM> microns or less. As described herein, the variance of the thickness <NUM> of the glass sheet <NUM> refers to the difference in thickness of the glass sheet <NUM> at two distinct points of thickness measurement.

In one or more embodiments, the glass sheet <NUM> has a warp of about <NUM> microns or less. For example, in one or more embodiments, the glass sheet <NUM> has a warp of about <NUM> microns or less, about <NUM> microns or less, about <NUM> microns or less, or even about <NUM> microns or less. As used herein and as described by ASTM F1390, "warp" refers to the difference between the maximum and minimum distances of the median surface from the reference plane.

According to some embodiments, the glass sheet <NUM> has a width <NUM> about equal to the length of the puddle of molten glass <NUM> above the forming rolls <NUM>. In additional embodiments, the glass sheet <NUM> has a width <NUM> that is less than the length of the puddle of molten glass <NUM> above the forming rolls <NUM>. For example, in one embodiment, the glass sheet <NUM> is held in tension as it exits the forming gap <NUM>. Optional additional rollers under the forming rolls <NUM> may pull the glass sheet <NUM> and cause it to somewhat stretch. The glass sheet <NUM> exiting the forming gap <NUM> may be guided and brought into tension by a post forming roller that drives the glass sheet <NUM> downwards, usually imposing its speed on the glass sheet <NUM>. This speed may be greater than the speed of the forming rolls <NUM>. However, in one or more embodiments, the speed of the glass sheet <NUM> is within about <NUM>%, with about <NUM>%, within about <NUM>%, within about <NUM>%, within about <NUM>%, or even within about <NUM>% of the speed of the forming rolls <NUM>. This stretching may slightly decrease the width <NUM> or the thickness <NUM> as compared with the dimensions of the forming gap <NUM>. According to one or more embodiments, the thickness <NUM> and/or the width <NUM> of the glass sheet <NUM> following processing is within about within about <NUM>%, within about <NUM>%, within about <NUM>%, or even within about <NUM>% of the corresponding dimensions of the forming gap <NUM>.

Various widths <NUM> are contemplated herein, such as, for example, from about <NUM> to about <NUM>. For example, in one or more embodiments, the glass sheet <NUM> has a width <NUM> of from about <NUM> to about <NUM>. In one or more embodiments, the glass sheet <NUM> has a width <NUM> of about <NUM> or greater, about <NUM> or greater, about <NUM> or greater, about <NUM> or greater, about <NUM> or greater, or even about <NUM> or greater, about <NUM> or less, about <NUM> or less, about <NUM> or less, or even about <NUM> or less.

The glass sheet <NUM> may have an aspect ratio defined as the width <NUM> of the glass sheet <NUM> divided by the thickness <NUM> of the glass sheet. In one or more embodiments, the glass sheet has an aspect ratio of about <NUM> or greater, about <NUM> or greater, about <NUM> or greater, about <NUM> or greater, about <NUM> or greater, about <NUM> or greater, about <NUM> or greater, about <NUM> or greater, or even about <NUM> or greater.

The glass sheet may have a relatively high refractive index. For example, in one or more embodiments, the refractive index of the glass sheet <NUM> is about <NUM> or greater, about <NUM> or greater, about <NUM> or greater, about <NUM> or greater, about <NUM> or greater, or even about <NUM> or greater.

Following the formation of the glass sheet <NUM>, one or more post-forming steps may be included in the disclosed glass forming processes. However, it should be understood that the post-forming steps may not substantially alter the thickness <NUM> of the glass sheet <NUM>. In one or more embodiments, the glass sheet <NUM> is turned from an essentially vertical direction to an essentially horizontal direction. In another embodiment the ribbon is kept essentially vertical until the point of being cooled sufficiently to be separated into discrete sheets. In additional embodiments, the glass sheet <NUM> is flattened by applying mechanical force while still slightly viscous, the glass sheet <NUM> is guided until fully-elastic conditions have been reached, and/or the glass sheet <NUM> is cooled to room temperature (either actively or passively). In one or more embodiments, non-contact supports, such as those disclosed in <CIT>, and <CIT>, are utilized.

The glass sheet <NUM> may be cut following cooling to room temperature, or while still at elevated temperatures. In one embodiment, the glass sheet <NUM> is cut into wafers. For example, in one or more embodiments, the wafers cut from the formed glass sheet <NUM> are <NUM> diameter wafers, <NUM> diameter wafers, <NUM> diameter wafers, or <NUM> diameter wafers.

<FIG> shows a further embodiment with active heating of the glass following exit of the glass from the forming rolls. Glass sheet forming apparatus <NUM> includes molten glass deliver device <NUM>, which delivers molten glass <NUM> to a forming gap <NUM> between first forming roll <NUM> and second forming roll <NUM> to form glass sheet <NUM>. Glass sheet <NUM> is heated by heater <NUM> and directed by air-bearing device <NUM> to air-bearing supports <NUM> and rollers <NUM> for heating by heater <NUM>. Air-bearing device <NUM> and air-bearing supports <NUM> support and/or control the direction of glass sheet <NUM> through application of pressurized air. It is noted that turning of glass sheet <NUM> is optional. Exposure of glass sheet <NUM> to heater <NUM> and heater <NUM> enable control of the cooling rate of glass sheet <NUM>. Heaters <NUM> and <NUM> are operated at a temperature greater than <NUM>, or greater than <NUM>, or greater than <NUM>, or greater than <NUM>, or in the range from <NUM> to <NUM>, or in the range from <NUM> to <NUM>, or in the range from <NUM> to <NUM>. Heat provided by heaters <NUM> and <NUM> slow the rate of cooling of glass sheet <NUM> and reduce stress in glass sheet <NUM>. In one embodiment, glass sheet <NUM> is heated to maintain a viscosity less than <NUM><NUM> Pa. s (<NUM><NUM> poise) at a distance of at least <NUM> following exit of glass sheet <NUM> from forming gap <NUM>. Following controlled cooling, glass sheet <NUM> is directed to coolers <NUM> and <NUM>. Separation of glass sheet <NUM> into parts <NUM> is performed when the temperature of glass sheet is below the annealing point.

Various embodiments will be further clarified by the following examples. Glass was poured from a precious metal crucible at a viscosity of approximately <NUM> Pa. s (<NUM> poise) on top of a pair of rotating rolls. The rolls had an undercut in their central region designed to leave a <NUM> gap when closed against each other. Table <NUM> reports glass sheet thickness at different rolling speeds. The data show that when the rolling speed is properly adjusted, a desired thickness for a glass sheet can be reached. One can also extrapolate from the data that if a smaller gap were used between the rolls (e.g., <NUM>), a glass sheet with a thickness of about <NUM> thick sheet could be produced at a sufficient rolling speed. Additionally, it can be seen the data that for a given rolling speed, heated rolls led to a decrease in glass sheet thickness. In the particular example shown, the glass sheet thickness obtained from the heated roll was less than the dimension of the forming gap. The examples in Table <NUM> have a rolling speed of <NUM>/min and <NUM>/min respectively do not fall within the scope of the claims and are provided for reference purposes only.

As used herein, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to a "component" includes aspects having two or more such components, unless the context clearly indicates otherwise.

Directional terms as used herein - for example up, down, right, left, front, back, top, bottom - are made only with reference to the figures as drawn and are not intended to imply absolute orientation.

The terms "substantial," "substantially," and variations thereof as used herein are intended to note that a described feature is equal or approximately equal to a value or description. For example, a "substantially planar" surface is intended to denote a surface that is planar or approximately planar. Moreover, "substantially" is intended to denote that two values are equal or approximately equal. In some embodiments, "substantially" may denote values within about <NUM>% of each other, such as within about <NUM>% of each other, or within about <NUM>% of each other.

Claim 1:
A method for forming a glass sheet (<NUM>), the method comprising:
supplying a feed of molten glass (<NUM>) to an upper surface (<NUM>, <NUM>) of a pair of forming rolls (<NUM>), the pair of forming rolls (<NUM>) spaced apart by a forming gap (<NUM>), the forming gap (<NUM>) having a width (<NUM>) of less than or equal to about <NUM> microns, wherein the molten glass (<NUM>) has a viscosity of less than or equal to about <NUM> Pa.s (<NUM> poise);
rotating the pair of forming rolls (<NUM>) at a rate such as to continuously form at least <NUM>/min of a glass sheet (<NUM>) from the molten glass (<NUM>), the glass sheet (<NUM>) having a thickness (<NUM>) of less than or equal to about <NUM> microns immediately upon passing through the forming gap (<NUM>).