WATCH COVER GLASS

• US 20100196685A1
• Filed: 09/25/2008
• Published: 08/05/2010
• Est. Priority Date: 09/26/2007
• Status: Active Grant

• Current Assignee: Citizen Watch Co Limited (Citizen Electronics Company Limited)
• Original Assignee: Citizen Holdings Co., Ltd. (Citizen Electronics Company Limited)
• Inventors: Takazaki, Koutarou, Murata, Yasushi
• Granted Patent: US 8,568,890 B2
• Time in Patent Office: Days
• US Class Current: 428/216
• CPC Class Codes: C03C 17/3435 comprising a nitride, oxynitride, boronitride or carbonitride
• CPC Class Codes: C03C 2217/734 comprising an alternation of high and low refractive indexes
• CPC Class Codes: G04B 39/002 made of glass
• CPC Class Codes: G04B 39/006 out of wear resistant material, e.g. sapphire
• CPC Class Codes: Y10T 428/2495 Thickness [relative or absolute]
• CPC Class Codes: Y10T 428/24975 No layer or component greater than 5 mils thick

Abstract

The present invention provides a watch cover glass having high hardness and excellent abrasion, and also having flaw resistance and antireflection function even after being used for a long period of time.

[Means for Solving]

The watch cover glass of the present invention comprises a transparent substrate and, provided on at least one surface of the substrate, an antireflection film having a lamination structure that a SiO₂ and Si₃N₄ mixed film (hereinafter, referred to as SiON film) and a Si₃N₄ film are laminated and the outermost layer is the SiON film. According to the lamination structure, the proper antireflection effect can be obtained, the hardness of the antireflection film is increased and the abrasion resistance is remarkably increased. As a result, the watch cover glass provided by the present invention has properties such that even after being used for a long period of time, the surface of the antireflection film is not finely flawed and is not peeled off, and it hardly occurs that the hands or dial plate are invisible due to surface mist and the antireflection function can be maintained.

Claims

1. A watch cover glass comprising a transparent substrate having a front surface and a back surface and, provided on at least one surface of the substrate, an antireflection film obtainable by laminating a SiO₂ and Si₃N₄ mixed film and a Si₃N₄ film alternately one after another in the total of 4 layers or 5 or more layers and having the SiO₂ and Si₃N₄ mixed film in the outermost layer.

2. The watch cover glass according to claim 1 wherein the antireflection film is obtainable by laminating the mixed film and the Si₃N₄ film alternately one after another in this order from the substrate toward the outermost layer.

3. The watch cover glass according to claim 1 wherein the antireflection film is obtainable by laminating the Si₃N₄ film and the mixed film alternately one after another in this order from the substrate toward the outermost layer.

4. The watch cover glass according to claim 1 wherein the mixed film has a nitrogen content of 5 to 90% by atom based on the total of oxygen and nitrogen.

5. The watch cover glass according to claim 1 wherein the number of the layers laminated alternately is 4 to 12 layers in the antireflection film.

6. The watch cover glass according to claim 1 wherein the mixed layer has a thickness per layer of 0.01 to 1.0 μ

m and the Si₃N₄ film has a thickness per layer of 0.01 to 1.2 μ

m.

7. The watch cover glass according to claim 1 wherein the antireflection film has a thickness of 0.1 to 4.0 μ

m.

8. The watch cover glass according to claim 1 wherein the antireflection film is formed on each of the front surface and the back surface of the substrate.

9. The watch cover glass according to claim 1 wherein the antireflection film is formed by a reactive sputtering method.

19. A watch comprising said watch cover glass as claimed in claim 1.

10. A process for producing a watch cover glass comprising a transparent substrate having a front surface and a back surface and, provided on at least one surface thereof, an antireflection film, which process comprises:

an antireflection film-forming step of laminating a SiO₂ and Si₃N₄ mixed film and a Si₃N₄ film alternately one after another in the total of 4 layers or 5 or more layers by a reactive sputtering method to prepare an antireflection film having the SiO₂ and Si₃N₄ -mixed film in the outermost layer.

11. The process for producing a watch cover glass according to claim 10 wherein the antireflection film is obtainable by laminating the mixed film and the Si₃N₄ film alternately one after another in this order from the substrate toward the outermost layer.

12. The process for producing a watch cover glass according to claim 10 wherein the antireflection film is obtainable by laminating the Si₃N₄ film and the mixed layer alternately one after another in this order from the substrate toward the outermost layer.

13. The process for producing a watch cover glass according to claim 10 wherein the reactive sputtering method is conducted in the presence of a mixed gas comprising at least a nitrogen-containing gas and an inert gas using a Si target as a raw material by DC pulse discharge.

14. The process for producing a watch cover glass according to claim 10 wherein the mixed film has a nitrogen content of 5 to 90% by atom based on the total of oxygen and nitrogen.

15. The process for producing a watch cover glass according to claim 10 wherein the number of the layers laminated alternately is 4 to 12 layers in the antireflection film.

16. The process for producing a watch cover glass according to claim 11 wherein the mixed layer has a thickness per layer of 0.01 to 1.0 μ

m and the Si₃N₄ film has a thickness per layer of 0.01 to 1.2 μ

m.

17. The process for producing a watch cover glass according to claim 11 wherein the antireflection film has a thickness of 0.1 to 4.0 μ

m.

18. The process for producing a watch cover glass according to claim 11 wherein the antireflection film is formed on each of the front surface and the back surface of the substrate.