Electrically heatable transparency

• US 5,414,240 A
• Filed: 12/27/1988
• Issued: 05/09/1995
• Est. Priority Date: 12/27/1988
• Status: Expired due to Term

• Current Assignee: Vitro Flat Glass LLC (Compagnie De Saint-Gobain)
• Original Assignee: PPG Industries Incorporated (Nouryon BV)
• Inventors: Carter, Thomas M., Wolfe, Terry L., Roginski, Amy M., Gillery, Frank H., Martino, Pamela L., Finley, James J., Coleman, Charles R., Winter, John A., Criss, Russell C.
• Primary Examiner(s): Reynolds, Bruce A.
• Assistant Examiner(s): Switzer, Michael D.
• Application Number:
  US07/290,225
• Time in Patent Office: 2,324 Days
• Field of Search: 219/203, 219/522, 219/543, 219/547, 338/306, 65/30.14, 428/34.6
• US Class Current: 219/203
• CPC Class Codes: B32B 17/10036 comprising two outer glass sheets
• CPC Class Codes: B32B 17/10174 Coatings of a metallic or dielectric material on a constituent layer of glass or polymer
• CPC Class Codes: B32B 17/10293 Edge features, e.g. inserts or holes
• CPC Class Codes: B32B 17/10348 comprising an obscuration band
• CPC Class Codes: H05B 2203/013 Heaters using resistive films or coatings
• CPC Class Codes: H05B 3/86 the heating conductors being embedded in the transparent or reflecting material H05B3/845 takes precedence

Abstract

An electrically heatable windshield with a hidden bus bar configuration. A border of opaque ceramic material, preferably a lead borosilicate enamel, is bonded to an interior surface of the transparency about its periphery. Opposing electroconductive bus bars, preferably a low frit content silver-containing ceramic material, are bonded to the ceramic material so that the entire inner edge of the bus bar overlays a portion of the ceramic material and is spaced from the inner edge of the border, providing an intermediate portion of the border between the bus bars and transparency surface that is not covered by the bus bars. An electro-conductive coating is applied to the transparency to interconnect the bus bars and covers to the inner surface of the transparency, the bus bars and the intermediate portion of the ceramic material border so that electric current flowing between the bus bars must flow through the portion of the coating that covers the intermediate portion of the border.

Claims

1. An electrically heatable transparency comprising:

a rigid substrate;

a border bonded to a surface of said substrate and extending along at least a portion of the periphery of said substrate;

a pair of opposing electroconductive bus bars spaced from each other wherein at least one of said bus bars is bonded to a portion of said border such that an inner edge of said bus bar is positioned entirely on said border and an inner portion of said border is uncovered by said bus bar; and

an electroconductive coating having a predetermined surface resistance, interconnecting said bus bars such that a portion of said coating covers said substrate surface, said inner portion of said border, and said bus bars wherein the increase in surface resistance of said coating covering said inner portion of said border is in the range of about 50% or less than the surface resistance of said coating covering said surface of said substrate.

2. The transparency as in claim 1 wherein said increase in surface resistance of said coating covering said inner portion of said border is in the range of about 20% or less than the surface resistance of said coating covering said rigid substrate surface.

3. The transparency as in claim 2 wherein said inner portion of said border has a sufficient smoothness to maintain said surface resistance of said coating over said inner portion of said border area within said range.

4. The transparency as in claim 3 wherein said bus bar is a low frit content, silver containing ceramic material.

5. The transparency as in claim 3 wherein said border is a lead borosilicate enamel which minimizes discoloration of said border enamel and/or said rigid substrate by said bus bar material such that said border enamel hides said bus bar material when said border is viewed through said rigid substrate.

6. The transparency as in claim 5 wherein said border is a tempering enamel.

7. The transparency as in claim 5 wherein said inner portion of said border area has an equivalent gloss of approximately 10 gloss units or more.

8. The transparency as in claim 5 wherein said border extends around the periphery of said transparency and both of said bus bars overlay said border and further including at least one electroconductive lead extending from one of said bus bars along a side portion of said transparency and overlaying said border such that said border hides both of said bus bars and said lead when said border is viewed through said rigid substrate.

9. The transparency as in claim 8 wherein said transparency includes additional transparent substrates secured to said rigid substrate to form a laminated assembly.

10. The transparency as in claim 9 wherein said rigid substrate is a first rigid substrate and said additional substrates include at least one additional rigid substrate secured to said first rigid substrate such that said border, bus bars, and coating are between said first rigid substrate and said additional rigid substrate.

11. The transparency as in claim 10 wherein said transparency is a windshield.

12. The transparency as in claim 11 wherein said rigid substrates are glass and the strength of said glass in the vicinity of said border and overlaying bus bars is at least 12,000 psi so as to minimize cracking of said glass due to the difference in the coefficient of thermal expansion between said bus bar material and said glass coated with said border enamel.

26. The transparency as in claim 1 wherein said inner portion of said border has an equivalent gloss of approximately 10 gloss units or more.

13. In an electrically heatable transparency of the type having a ceramic border bonded to a glass ply of said transparency, electroconductive bus bars bonded to said border and an electroconductive coating bonded to said glass ply and interconnecting said bus bars, the improvement comprising:

said bus bar being a low frit content, silver containing bus bar material containing approximately 80-90% silver and 1-3% frit, by weight to reduce stresses within said transparency resulting from the difference between the coefficient of thermal expansion of said bus bar material and said ceramic border and glass ply.

14. The transparency as in claim 13 wherein said bus bar material includes approximately 84% silver and 1.5% frit, by weight.

15. A method of fabricating a heatable transparency comprising:

cutting a rigid substrate to a desired shape;

bonding an opaque border having a first and second portions to a surface of said substrate along at least a portion of the substrate'"'"'s periphery;

bonding a first electroconductive bus bar to said first portion of said border wherein said second portion of said border is positioned between said first bus bar and said surface;

bonding a second electroconductive bus bar to said surface or said border wherein said second bus bar is spaced from said first bus bar;

coating said substrate with an electroconductive coating having a predetermined surface resistance, to electrically interconnect said bus bars, wherein a portion of said coating covers said substrate surface, said bus bars, and said second portion of said border; and

maintaining any increase in the surface resistance of said coating over said second portion of said border within a range of about 50% or less than said predetermined surface resistance of said coating covering said substrate surface.

16. The method as in claim 15 wherein said maintaining step includes providing a sufficiently smooth surface on said second portion of said border to maintain said increase in said surface resistance of said coating covering said second portion of said border within said range.

17. The method as in claim 16 wherein said maintaining step includes maintaining said surface resistance increase of said coating covering said second portion of said border within a range of about 20% or less than said predetermined surface resistance of said coating covering said substrate surface.

18. The method as in claim 16 wherein said maintaining step includes providing an equivalent surface gloss on said second portion of said border of about 10 gloss units or more.

19. The method as in claim 16 wherein said border bonding step includes applying a discoloration resistant opaque ceramic enamel to said surface about the periphery of said transparency and heating said border enamel to bond it onto said substrate surface while maintaining the optical quality of said substrate.

20. The method as in claim 19 wherein said bus bar bonding steps include applying a low frit content, silver containing ceramic material over said border enamel such that said bus bars are completely on said first portion of said border and heating said bus bar material to bond said material to said border enamel while maintaining the optical quality of said substrate.

21. The method as in claim 20 further including the step of heating said substrate and shaping said substrate to a desired configuration.

22. The method as in claim 21 further including the step of laminating additional substrates to said surface of said substrate.

23. The method as in claim 22 wherein said substrates are glass plies and further including the step of maintaining the glass strength of said glass plies in the vicinity of said border and bus bars at a level of about 12,000 psi or more.

24. An electrically heatable transparency comprising:

a rigid substrate;

a ceramic border bonded to a surface of said substrate and extending along at least a portion of the periphery of said substrate;

a pair of opposing electroconductive bus bars spaced from each other wherein at least one of said bus bars is bonded to a surface portion of said border such that an inner edge of said bus bar is positioned entirely along said border and an inner surface portion of said border is uncovered by said bus bar; and

an electroconductive coating, having a predetermined surface resistance, interconnecting said bus bars such that a portion of said coating covers said inner surface portion of said border along the length of said at least one bus bar, wherein said inner surface border portion has a gloss equivalent of approximately 10 gloss units or more so as to provide a sufficient smoothness to maintain a surface resistance of said coating portion covering said inner surface portion of said border within a range of about 50% or less than said predetermined surface resistance.

25. A method of fabricating a heatable transparency comprising:

cutting a rigid substrate to a desired shape;

applying a tempering enamel border having first and second portions to a surface of said substrate along at least opposing marginal edge portions of said substrate;

processing said substrate to bond said border to said substrate such that said border develops a surface having an equivalent surface gloss on at least said second portion of about 10 gloss units or more;

applying a first electroconductive bus bar to said first portion of said border along a first marginal edge portion of said substrate and a second electroconductive bus bar to said first portion of said border along an opposing marginal edge portion of said substrate, wherein said second portions of said border are positioned between said substrate surface and said first and second bus bars, respectively, and further wherein said bus bars are about 80-90% silver and 1-3% frit, by weight;

processing said substrate to bond said bus bars to said border; and

coating said substrate with an electroconductive coating having a predetermined surface resistance to electrically interconnect said bus bars, wherein a portion of said coating covers said substrate surface, said bus bars, and said second portions of said border and further wherein any increase in the surface resistance of said coating over said second portions of said border is within a range of about 50% or less than said predetermined surface resistance of said coating covering said substrate surface.