Treatment of glass to reduce venting during thermal treatment and a glass article made thereby

• US 4,824,712 A
• Filed: 10/08/1985
• Issued: 04/25/1989
• Est. Priority Date: 07/16/1984
• Status: Expired due to Fees

• Current Assignee: PPG Industries Incorporated (Nouryon BV)
• Original Assignee: PPG Industries Incorporated (Nouryon BV)
• Inventors: Falleroni, Charlene A., Lin, Chia-Cheng
• Primary Examiner(s): Kellogg, Arthur
• Application Number:
  US06/785,431
• Time in Patent Office: 1,295 Days
• Field of Search: 65/28, 65/36, 65/60.8, 428/137, 428/409, 428/427, 428/140, 428/410
• US Class Current: 428/137
• CPC Class Codes: C03B 27/012 by heat treatment, e.g. for crystallisation; Heat treatment of glass products before tempering by cooling C03B27/008, C03B27/016 take precedence
• CPC Class Codes: C03C 17/02 with glass C03C17/34, C03C17/44 take precedence
• CPC Class Codes: Y02P 40/57 Improving the yield, e-g- reduction of reject rates
• CPC Class Codes: Y10T 428/24322 Composite web or sheet
• CPC Class Codes: Y10T 428/24347 From both sides
• CPC Class Codes: Y10T 428/31 Surface property or characteristic of web, sheet or block
• CPC Class Codes: Y10T 428/315 Surface modified glass [e.g., tempered, strengthened, etc.]

Abstract

A method and composition for coating scored regions or holes in glass articles prior to heat treatment in order to maintain residual compressive stresses and reduce venting are disclosed. The method and composition of the present invention utilize silica-containing sols which gel and density and ultimately form glassy films during the heat treatment of the coated glass articles.

Claims

1. A method of heat treating a glass sheet having a scored region comprising the steps of:

a. coating said scored region with a sol composition prepared from an alkoxide and comprising silicon;

b. hydrolyzing said alkoxide and polymerizing to form a gel;

c. heating said glass sheet to a temperature above its strain point and below its melting point and sufficient to cause said gel to densify;

d. maintaining said temperature for a sufficient time to cause said gel to form a glassy coating; and

e. cooling said glass sheet.

2. A method according to claim 1, wherein said sol comprises silicon and at least one metal selected from the group consisting of titanium, boron and sodium.

3. A method according to claim 2, wherein said coating has a molar ratio of 75 to 80 percent SiO₂ and 10 to 25 percent Na₂ O.

4. A method according to claim 1, wherein said scored region comprises a hole, having a circumferential wall, extending through the thickness of said glass sheet, and said coating step includes coating said circumferential wall of said hole.

5. A method according to claim 4, wherein said coating step further includes coating a portion of each surface of said glass sheet immediately adjacent to said hole.

6. A method according to claim 5, further including the step of shaping said glass sheet to a desired shape between said heating and cooling steps.

7. The method as in claim 1, wherein the cooling in said cooling step is rapid enough to impart a temper in said glass sheet.

8. A method of heat treating a glass sheet having a scored region comprising the steps of:

a. coating said scored region with a sol composition prepared from an alkoxide and comprising silicon and boron;

b. hydrolzying said alkoxide and polymerizing to form a gel;

c. heating said glass sheet to a temperature above its strain point and below its melting point and sufficient to densify said gel;

d. maintaining said temperature for a sufficient time to cause said gel to form a glassy coating; and

e. cooling said glass sheet,

wherein said coating has a molar ratio of 55 to 80 percent SiO₂ and 20 to 45 percent B₂ O₃.

9. A method of heat treating a glass sheet having a scored region comprising the steps of:

a. coating said scored region with a sol composition prepared from an alkoxide and comprising silica and at least one metal selected from the group consisting of titanium, boron and sodium, which sol forms a gel;

b. heating said glass sheet to a temperature above its strain point and below its melting point and sufficient to cause said gel to densify;

c. maintaining said temperature for a sufficient time to cause said gel to form a glassy coating; and

d. cooling said glass sheet,

wherein said coating has a molar ratio of 75 to 90 percent SiO₂ and 10 to 25 percent TiO₂.

10. A tempered glass article comprising a glass sheet having at least one hole extending entirely through its thickness, and a sol-gel coating fused to the wall of said hole, wherein said coating comprises SiO₂ and B₂ O₃.

11. A tempered glass article according to claim 10, wherein said coating has molar percentage ranges of 55 to 80 percent SiO₂ and 20 to 45 percent B₂ O₃.

12. A tempered glass article comprising a glass sheet having at least one hole extending entirely through its thickness, and a sol-gel coating comprising silica fused to the wall of said hole and coating a portion of each surface of said glass sheet immediately adjacent to said hole, wherein said coating has molar percentages of 75 to 80 percent SiO₂ and 10 to 25 percent Na₂ O.

13. A tempered glass article comprising a glass sheet having at least one hole extending entirely through its thickness, and a sol-gel coating comprising silica fused to the wall of said hole and coating a portion of each surface of said glass sheet immediately adjacent to said hole, wherein said coating has molar percentages of 75 to 90 percent SiO₂ and 10 to 25 percent TiO₂.

14. A method of heat treating a glass sheet having a scored region comprising the steps of:

coating said scored region with a sol-gel composition comprised essentially of boron and silica compositions and having a viscosity lower than that of said glass sheet;

heating said glass sheet to a temperature above its strain point and below its melting point and sufficient to cause said sol-gel to flow over said coated scored region;

maintaining said temperature for a sufficient time to allow said sol-gel to flow and fill any imperfections in said coated scored region; and

cooling said glass sheet.

15. A method according to claim 14, wherein said sol-gel has a molar ratio of 55 to 80 percent SiO₂ and 20 to 45 percent B₂ O₃.

16. A tempered glass article comprising a glass sheet having at least one hole extending entirely through its thickness, and a sol-gel coating essentially containing silica and boron compositions bonded to the wall of said hole.

17. A tempered glass article according to claim 16, wherein said coating comprises 55 to 80 percent SiO₂ and 20 to 45 percent B₂ O₃.

18. A tempered glass article according to claim 17, wherein said coating comprises SiO₂ and B₂ O₃ in a molar ratio of 75 to 25.