IMPACT-DAMAGE-RESISTANT GLASS SHEET

• US 20110165393A1
• Filed: 01/07/2011
• Published: 07/07/2011
• Est. Priority Date: 01/07/2010
• Status: Active Grant

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Sternquist, Daniel A., Price, James Joseph, Bayne, John Frederick, Amin, Jaymin
• Granted Patent: US 8,889,254 B2
• Time in Patent Office: Days
• US Class Current: 428/215
• CPC Class Codes: C03C 15/00 Surface treatment of glass, not in the form of fibres or filaments, by etching etching or surface-brightening compositions, in general C09K13/00
• CPC Class Codes: C03C 15/02 for making a smooth surface
• CPC Class Codes: C03C 21/002 to perform ion-exchange between alkali ions C03C21/005 takes precedence
• CPC Class Codes: Y10T 428/24967 Absolute thicknesses specified
• CPC Class Codes: Y10T 428/265 1 mil or less

Abstract

Impact-damage-resistant glass sheet comprising at least one chemically etched surface in combination with a tempering surface compression layer, the glass sheet exhibiting a high standardized ball drop failure height and a high flexural modulus of rupture strength, useful to provide damage-resistant glass cover sheets for consumer electronic video display devices, is provided by subjecting thin glass sheet to a combination of a surface tempering treatment and a surface etching treatment that improves strength while maintaining the optical glass sheet properties required for video display applications.

Claims

1. An impact-damage-resistant glass sheet comprising at least one tempered and chemically-etched surface, said sheet exhibiting a standardized 128 g ball drop failure height of least 120 cm and said surface incorporating a surface compression layer having a depth of at least 8 μ

m and a surface compressive stress level of at least 200 MPa.

2. An impact-damage-resistant glass sheet in accordance with claim 1 wherein the glass sheet is a planar sheet of a uniform thickness not exceeding 2 mm, wherein the chemically etched surface is an acid-etched surface, and wherein the surface compression layer has a depth of at least 15 μ

m and a surface compressive stress level of at least 400 MPa.

3. An impact-damage-resistant glass sheet in accordance with claim 2 wherein the glass sheet is composed of an alkali aluminosilicate glass and wherein the surface compression layer is an ion-exchanged surface layer having a layer depth of at least about 30 μ

m and a surface compressive stress level of at least about 500 MPa.

4. An impact-damage-resistant glass sheet in accordance with claim 3 having a thickness not exceeding 1 mm and an ion-exchanged surface layer having a layer depth of at least about 40 μ

m and a surface compressive stress level of at least about 650 MPa.

5. A video display cover sheet formed of alkali aluminosilicate glass, the sheet having a thickness not exceeding 1 mm, a compressively stressed surface layer of at least 40 μ

m thickness, and a peak surface compressive stress level of at least about 650 MPa.

6. A cover sheet in accordance with claim 5 having a thickness not exceeding 0.7 mm.

7. A video display device comprising an impact-damage-resistant glass cover sheet, wherein the glass cover sheet has (i) a thickness in the range of 0.2-2 mm, (ii) an alkali aluminosilicate glass composition, and (iii) at least one surface compression layer incorporating a chemically etched surface.

8. A display device in accordance with claim 7 wherein the glass cover sheet has a thickness not exceeding 1 mm, wherein the chemically etched surface is an acid-etched surface, and wherein the surface compression layer incorporating the acid-etched surface has a depth of at least 30 μ

m and a surface stress level of at least 500 MPa.

9. A method of making an impact-damage-resistant glass sheet comprising the steps of (i) subjecting at least one surface of a glass sheet to a tempering treatment to develop a compressive surface layer thereon, and (ii) contacting the at least one surface of the glass sheet with a chemical glass etching medium to remove a layer of surface glass therefrom.

10. A method in accordance with claim 9 wherein the step of subjecting at least one surface of the glass sheet to a tempering treatment comprises subjecting the glass sheet to a tempering treatment effective to provide a surface compression level of at least 400 MPa in the surface of the sheet, and wherein the step of contacting the at least one surface of the glass sheet with a chemical glass etching medium comprises contacting the surface with an acidic etching medium for a time and at a temperature effective to remove not more than 4 μ

m of surface glass from the sheet.

11. A method in accordance with claim 9 wherein the step of subjecting the glass surface to a tempering treatment precedes the step of subjecting the glass surface to the etching medium.

12. A method in accordance with claim 9 wherein the glass sheet is of alkali aluminosilicate composition, and wherein the surface of the glass sheet subjected to the tempering treatment is substantially free of surface flaws of a depth greater than about 2 μ

m.

13. A method in accordance with claim 9 wherein the tempering treatment is selected from the group consisting of thermal tempering and chemical tempering.

14. A method in accordance with claim 13 wherein the tempering treatment comprises chemical tempering and includes a step of contacting at least one surface of the glass with an ion-exchange strengthening medium.

15. A method in accordance with claim 9 wherein the etching medium is an aqueous solution comprising a fluoride compound.

16. A method in accordance with claim 15 wherein the etching efficiency of an etching bath containing the etching medium is maintained by:

removing a volume of the medium from the bath that (i) contains HF at a concentration below a predetermined minimum level and/or (ii) contains dissolved glass at a concentration above a predetermined maximum level, and

replacing the volume with an equivalent volume of an HF solution containing a concentration of HF exceeding the predetermined minimum level.

17. A method of making a display cover sheet for a video display device comprising the steps of selecting an alkali aluminosilicate glass sheet of a thickness not exceeding 1 mm, contacting at least one surface of the glass sheet with an ion-exchange strengthening medium to develop a compressive surface layer thereon, and contacting the at least one surface of the glass sheet with a chemical glass etching medium to remove a layer of surface glass therefrom.

18. A method in accordance with claim 17 wherein the step of contacting the at least one surface of the glass sheet with the glass etching medium comprises contacting the surface with an acidic fluoride-containing glass etching medium and is carried out at a temperature and for a time not exceeding a time effective to remove a layer of surface glass not exceeding 4 μ

m in thickness from the glass sheet.

19. A method in accordance with claim 17 wherein the step of contacting the at least one surface of the glass sheet with the acidic glass etching medium is carried out at a temperature and for a time effective to remove a layer of glass not exceeding about 2 μ

m in thickness from the surface of the glass sheet.

20. A method in accordance with claim 17 wherein the step of contacting the at least one surface of the glass sheet with the acidic glass etching medium is carried out for a time not exceeding a time effective to reduce the compressive stress level in the glass sheet surface by 3%.

21. A method in accordance with claim 17 wherein the step of contacting at least one surface of the glass sheet with an ion-exchange strengthening medium comprises contacting the surface with a source of alkali metal ions of larger ionic diameter than at least one alkali metal ion component present in the glass.

22. A method in accordance with claim 21 wherein the step of contacting the at least one surface of the glass sheet with an ion-exchange strengthening medium is carried out at a temperature below the strain point of the glass, and for a time at least sufficient to develop a compressive stress layer with a depth in excess of 40 μ

m and a peak compressive stress level in excess of 650 MPa in the at least one surface.

23. A method in accordance with claim 17 wherein the step of contacting the at least one surface of the glass sheet with the glass etching medium is carried out for a time and at a temperature such that (i) not more than a 2 μ

m thickness of surface glass is removed from the sheet surface;

(ii) a compressive stress of at least 650 MPa glass is retained in the sheet surface;

(iii) the glass sheet retains a final haze level not exceeding 0.1%; and

(iv) the glass sheet retains a final light transmission level and a final surface gloss level that differ by less than 1% from, respectively, an initial light transmission level and an initial surface gloss level for the glass sheet.

24. A method in accordance with claim 17 which comprises a further step, prior to the step of contacting at least one surface of the glass sheet with an ion-exchange strengthening medium, of treating at least one surface of the glass sheet to provide an anti-glare surface thereon.

25. A method in accordance with claim 17 which comprises a further step, prior to the step of contacting at least one surface of the glass sheet with an ion-exchange strengthening medium, of pre-treating the at least one surface of the glass sheet to reduce the population and/or size of surface flaws thereon.

26. A method in accordance with claim 25 wherein the step of pre-treating comprises contacting the at least one surface of the glass with an etching solution to remove surface glass therefrom.