Methods for forming thin glass sheets

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 1010 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.

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 1010 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.