Methods for forming thin glass sheets
According to one or more embodiments disclosed herein, a glass sheet may be formed by a method which includes supplying a feed of molten glass to an upper surface of a pair of forming rolls, and rotating the pair of forming wheels to continuously form a glass sheet from the molten glass. The pair of forming rolls may be spaced apart by a forming gap, and the forming gap may have a width of less than or equal to about 800 microns. The molten glass may have a viscosity of less than or equal to about 200 poise. The glass sheet may have a thickness of less than or equal to about 800 microns immediately upon passing though the forming gap.
1. A method for forming a glass sheet, the method comprising:
supplying a feed of molten glass from a molten glass delivery device to an upper surface of a pair of forming rolls, the molten glass forming a puddle over upper surfaces of the pair of forming rolls, the pair of forming rolls spaced apart by a forming gap, the forming gap having a width of less than or equal to about 800 microns, wherein the molten glass of the puddle has a viscosity of less than about 25 poise;
rotating the pair of forming rolls at a rate to continuously form at least about 10 meters per minute of a glass sheet from the molten glass, the glass sheet having a thickness of less than or equal to about 800 microns immediately upon passing though the forming gap such that the thickness of the glass sheet varies by about 30 microns or less; and
directing the glass sheet to a heater using pressurized air from an air-bearing device controlling a direction of the glass sheet toward one or more air-bearing supports for heating the glass sheet by the heater, the heater configured to operate at a temperature greater than 100° C. and less than 500° C. such that the glass sheet has a viscosity less than 10 10 poise at a distance of at least 0.75 m from the forming gap,
wherein:
the glass sheet comprises a glass composition with a refractive index of about 1.7 or greater,
the molten glass comprises a liquidus viscosity of about 50 poise or less, and
when supplied from the molten glass delivery device, the viscosity of the molten glass of the puddle is less than the liquidus viscosity of the molten glass of the puddle.
2. The method of claim 1 , wherein the glass sheet has a width measured in a direction perpendicular to the forming gap width, and wherein a ratio of the width of the glass sheet to the thickness of the glass sheet is about 100 or greater.
3. The method of claim 1 , wherein the forming rolls are positioned horizontally relative to one another.
4. The method of claim 1 , wherein no portion of the forming rolls contact one another.
5. The method of claim 1 , wherein the molten glass is supplied from a single point source.
6. The method of claim 5 , wherein the single point source is a pipe.
7. The method of claim 1 , wherein the molten glass is supplied from a plurality of point sources.
8. The method of claim 7 , wherein the plurality of point sources are positioned along a major length of the forming gap.
9. The method of claim 1 , further comprising cutting the glass sheet.
10. The method of claim 9 , wherein the glass sheet is cut into a 100 mm diameter wafer.
11. The method of claim 1 , wherein at least one of the pair of forming rolls comprises a non-constant roll diameter.
12. The method of claim 1 , wherein the forming gap has a width less than about 100 microns.
13. The method of claim 1 , wherein the thickness of the glass sheet varies by about 10 microns or less.
14. A method for forming a high refractive index glass sheet, the method comprising:
supplying a feed of molten glass from a molten glass delivery device to an upper surface of a pair of forming rolls, the molten glass forming a puddle over upper surfaces of the pair of forming rolls, the pair of forming rolls spaced apart by a forming gap, the forming gap having a width of less than or equal to about 800 microns, wherein the molten glass of the puddle has a viscosity of less than about 25 poise;
rotating the pair of forming rolls at a rate to continuously form at least about 10 meters per minute of a glass sheet from the molten glass, the glass sheet having a thickness of less than or equal to about 800 microns immediately upon passing though the forming gap such that the thickness of the glass sheet varies by about 30 microns or less; and
directing the glass sheet to a heater using pressurized air from an air-bearing device controlling a direction of the glass sheet toward one or more air-bearing supports for heating the glass sheet by the heater, the heater configured to operate at a temperature greater than 100° C. and less than 500° C. such that the glass sheet has a viscosity less than 10 10 poise at a distance of at least 0.75 m from the forming gap,
wherein:
a glass composition of the glass sheet has a refractive index of about 1.7 or greater and the molten glass has a liquidus viscosity of about 50 poise or less,
the glass sheet has an aspect ratio defined as a width of the glass sheet divided by the thickness, wherein the aspect ratio is greater than or equal to 200, and
when supplied from the molten glass delivery device, the viscosity of the molten glass of the puddle is less than the liquidus viscosity of the molten glass of the puddle.
15. A method for forming a glass sheet, the method comprising:
supplying a feed of molten glass from a molten glass delivery device to an upper surface of a pair of forming rolls, the molten glass forming a puddle over upper surfaces of the pair of forming rolls, the pair of forming rolls spaced apart by a forming gap, wherein the molten glass of the puddle has a viscosity of less than about 25 poise;
rotating the pair of forming rolls at a rate to continuously form at least about 10 meters per minute of a glass sheet from the molten glass, the glass sheet having a thickness of less than or equal to about 1000 microns immediately upon passing though the forming gap such that the thickness of the glass sheet varies by about 30 microns or less; and
directing the glass sheet to a heater using pressurized air from an air-bearing device controlling a direction of the glass sheet toward one or more air-bearing supports for heating the glass sheet by the heater, the heater configured to operate at a temperature greater than 100° C. and less than 500° C. such that the glass sheet has a viscosity less than 10 10 poise at a distance of at least 0.75 m from the forming gap,
wherein:
the glass sheet comprises a glass composition with a refractive index of about 1.7 or greater,
the molten glass comprises a liquidus viscosity of about 50 poise or less, and
when supplied from the molten glass delivery device, the viscosity of the molten glass of the puddle is less than the liquidus viscosity of the molten glass of the puddle.