Method of reducing the reflectance of a transparent viewing screen and viewing screen with reduced reflectance

• US 4,731,558 A
• Filed: 11/03/1986
• Issued: 03/15/1988
• Est. Priority Date: 07/11/1983
• Status: Expired due to Fees

• Current Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Original Assignee: US Philips Corporation (Koninklijke Philips N.V.)
• Inventors: Pasmans, Johannes M. M., Rombouts, Albertus J. M., Haisma, Jan, van der Werf, Pieter
• Primary Examiner(s): Boudreau, Leo H.
• Assistant Examiner(s): WIEDER, KENNETH A
• Application Number:
  US06/926,820
• Time in Patent Office: 498 Days
• Field of Search: 313/478, 313/474, 313/116, 358/250, 358/252, 427/299, 445/6, 313/479, 313/480, 313/466
• US Class Current: 313/478
• CPC Class Codes: G02B 1/113 using inorganic layer materials only
• CPC Class Codes: H01J 2229/8915 Surface treatment of vessel or device, e.g. controlled surface roughness
• CPC Class Codes: H01J 2229/8918 by using interference effects
• CPC Class Codes: H01J 29/24 Supports for luminescent material
• CPC Class Codes: H01J 29/896 Anti-reflection means, e.g. eliminating glare due to ambient light

Abstract

A viewing screen is described, in particular the screen of a display tube, which has excellent anti-reflective properties and a method of making this screen anti-reflective. In this method the outer surface of the screen is mechanically roughened in conformity with specific requirements and subsequently an anti-reflective coating of constant thickness is applied to the roughened surface.

Claims

1. A method of reducing the reflectance of a transparent viewing screen comprising first mechanically roughening the outer surface of the screen until the roughness parameters of the resultant roughened outer surface satisfies the following requirementsnm<

R_a <

200 nm

50 nm<

R_q <

250 nm

25 nm<

R_tm <

1500 nm

25 μ

m<

S_m <

100 μ

m

wherein

R_a is the arithmetic average of the absolute difference between the surface profile and the average surface level measured along a line,

R_q is the square root of the average difference squared between the surface profile and the average surface level measured along a line,

R_tm is the peak-to-valley height difference of the surface profile averaged over a number of line intervals, and

S_m is the average distance between positive crossings of the surface profile and the average surface level measured along a line and

then providing an anti-reflective coating on the roughened outer surface in such a manner that the thickness of the resultant coating is constant.

2. A method as claimed in claim 1, characterized in that the inner surface of the viewing screen is also roughened mechanically.

3. A method as claimed in claim 2, characterized in that the roughening is effected by means of loose grains on a flexible polishing base.

4. A method as claimed in claim 3, characterized in that the anti-reflective coating is formed by vapour-deposition or sputtering in a vacuum system.

5. A method as claimed in claim 4, characterized in that on the roughened outer surface of the screen a layer of magnesium-fluoride is vapour-deposited as anti-reflective coating, the vapour-deposition flow towards said outer surface being directed at an angle smaller than 15°

to the normal to said outer surface.

6. A method as claimed in claim 5, characterized in that during vapour-deposition the outer surface of the viewing screen is brought at a temperature of approximately 300°

C.

7. A method as claimed in claim 5, characterized in that prior to vapour-deposition the outer surface of the screen is chemically activated by subjecting it to a glow-discharge for at least 15 minutes and during vapour-deposition this outer surface is maintained at room temperature.

12. A method as claimed in claim 2, characterized in that the roughening is effected by means of loose grains on a flexible polishing base.

13. A method as claimed in claim 2, characterized in that the anti-reflective coating is formed by vapour-deposition or sputtering in a vacuum system.

14. A method as claimed in claim 4, characterized in that the roughening is effected by means of loose grains on a flexible polishing base.

8. A viewing screen whose outer surface is provided with an anti-reflective coating, characterized in that at least the outer surface of the viewing screen is mechanically roughened, the roughness parameters satisfying the following requirements:

25 nm>

R_a >

200 nm

50 nm<

R_q <

250 nm

250 nm<

R_tm <

1500 nm

25 μ

m<

S_m <

100 μ

m

wherein

R_a is the arithmetic average of the absolute difference between the surface profile and the average surface level measured along a line,

R_q is the square root of the average difference squared between the surface profile and the average surface level measured along a line,

R_tm is the peak-to-valley height difference of the surface profile averaged over a number of line intervals, and

S_m is the average distance between positive crossings of the surface profile and the average surface level measured along a line

the anti-reflective coating on the roughened outer surface having a constant thickness and following the surface profile after roughening.

9. A viewing screen as claimed in claim 8, characterized in that the inner surface of the screen is also mechanically roughened.

10. A picture screen as claimed in claim 8, characterized in that the anti-reflective coating comprises a single layer whose refractive index is smaller than that of the viewing-screen material and whose optical thickness is equal to a quarter of a reference wavelength for the range of wavelengths for which the reflectance must be reduced.

11. A television picture tube provided with a viewing screen as claimed in claim 8.

15. A picture screen as claimed in claim 9, characterized in that the anti-reflective coating comprises a single layer whose refractive index is smaller than that of the viewing-screen material and whose optical thickness is equal to a quarter of a reference wavelength for the range of wavelengths for which the reflectance must be reduced.

16. A television picture tube provided with a viewing screen as claimed in claim 9.

17. A television picture tube provided with a viewing screen as claimed in claim 10.