Process for metallizing phosphor screens

Details Process for metallizing phosphor screens Process for metallizing phosphor screens

1997-12-03

1999-02-23

Bell, Janyce

Coating processes

Electrical product produced

Fluorescent or phosphorescent base coating

427 68, 427108, 427226, 427404, 4274071, 4274072, 427379, 4273855, 4273897, B05D 512

Patent

active

058741240

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process of metallizing phosphor screens, in particular for cathode ray tubes (CRTs).
The electron permeable, light reflecting aluminium film on the target side of the phosphor screen of a CRT is formed by the evaporation of aluminium onto a smooth film of an organic material formed over the surface of a phosphor screen. This smooth film is subsequently burnt out to leave a mirror-like film of aluminium "tenting" across the top of the phosphor screen.
Various processes for metallizing phosphor screens have been proposed in the prior art and these can generally be classified as solvent based systems and aqueous based systems.
In the solvent based system, the phosphor layer is first wetted with an aqueous based prewet and a solvent based lacquer, comprising an approximately 2% solution of a polymer such as poly(iso-butylmethacrylate) in a solvent such as toluene, is floated on the top of the prewet. The water and solvent are removed by heating leaving a film of the polymeric material approximately 1 .mu.m in thickness.
The major disadvantage of this approach is that it involves the use of large quantities of volatile organic solvents, such as toluene, with all the associated environmental concerns.
Aqueous based systems are described in U.S. Pat. Nos. 3,067,055, 3,582,389 and 3,582,390 in which a water-based emulsion of a water insoluble, film forming resin such as an acrylate resin copolymer is coated onto the phosphor screen, the coating is dried, the coated layer is metallized, and the coating of the resin film volatilized by heating at a temperature of up to about 450.degree. C. The emulsion contains about 5 to 20 weight percent of the resin. In U.S. Pat. No. 3,582,389, the addition of materials to the dispersion is described. A neutralising agent is added to adjust the pH of the dispersion to the range of 4.0 to 8.0. A boric acid complex of poly(vinylalcohol) in an amount of up to 1.0% is added to reduce the blistering of the metal film over bare glass during the baking out step. Colloidal silica, in amounts of up to 25% and soluble silicates, in amounts of up to 2% are added to improve the adherence of the metallized layer to the glass and thereby reduce peeling of the metallized layer subsequent to the baking out step. In U.S. Pat. No. 4,123,563, the addition of ammonium oxalate is described to regulate the porosity of the polymer film and the metal layer. This prevents blisters on the metal film caused by the evaporation of the polymer layer. Similarly, U.S. Pat. No. 3,582,390 describes the use of hydrogen peroxide for the same purpose.
One disadvantage of the aqueous based system is that the dispersion fills all of the spaces between the phosphor strips or dots and is thus a thicker layer than in the solvent based system. Accordingly, the amount of polymer left on the screen is greater than that utilized in solvent based processes and is therefore more difficult to remove. Consequently, increased energy requirements may result from the application of extended or even multiple burn out steps. An alternative approach is to introduce oxygen into the funnel to assist burn out. This involves increased equipment costs and the hazards associated with using oxygen.
In the solvent based system as described generally above the polymer film solution and the aluminium are applied to the phosphor screen and then the funnel of a CRT is attached to the screen with a glass frit in an organic binder. It is possible to remove both the polymer film and the organic binder in one heating cycle.
In the aqueous based systems the quantities of polymer to be removed are such as to generally necessitate the bake out of the polymer film before the addition of the funnel of a CRT. Therefore two heating cycles are required with increased energy costs, and greater investment required in the number of ovens and thus also the space required on the manufacturing site.
We have now developed a process of metallizing phosphor screens which is more energy efficient than the prior art methods by utilizi

REFERENCES:
patent: 556664 (1896-09-01), Sasa et al.

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