For many applications it is desirable to have a dark glass faceplate to enhance the contrast of an image displayed on the tube; however, such faceplates are expensive. A colored, high gloss coating, formulated from materials having anti-static properties, and deposited on an exterior surface of a CRT faceplate panel is a cost-effective alternative to a dark glass faceplate. Additionally, these materials also provide the desirable anti-static properties which have become a standard requirement in many applications.

Gloss is a measure of the surface reflectivity of the faceplate panel at 60° from the vertical using a glossmeter. Gloss values range from 1 to 100, and indicate the percent of reflected light not scattered by the coating on the exterior surface of the faceplate panel.

The incorporation of anti-static properties into a faceplate coating is well known in the art and is described, for example, in U. S. Pat. No.

4,563,612, issued to Deal et al. on Jan. 7,1986. The anti-static properties of a coating relate the elapsed time required to discharge the electrostatic voltage on the coated faceplate. In U. S. Pat. No. 4,563,612, operative concentrations of an inorganic metallic compound are introduced into the coating composition for imparting the anti-static characteristics to the coating. A baking step, at a temperature of at least 120°C, and preferably in the range of 150° to 300°C, is required in order to develop the final electrical, optical and physical properties of the coating. That patent also

states that some additive materials, such as carbon, are known to impart an anti-static characteristic to a silicate coating; however, such a large concentration of carbon must be added to achieve the anti-static characteristics that it degrades the image-transmitting characteristic of the tube to an unacceptable level.

U. S. Pat. No. 5,717,282, issued to Oomen et al. on Feb. 10,1998 describes a light absorbing coating comprising at least two dyes and one or more organic solvents; however the coating is not anti-static. A coating film including an alcohol solution of silicon alkoxide, translucent and conductive particles and a plurality of types of dyes and pigments is described in U. S. 5,200,667, issued to Iwasaki et al. The inherent electrical conductivity of the coating is increased by combining metallic atoms with the alkoxide structure. U. S. 5,315,209, issued to Iwasaki on May 24,1994 describes a light absorbing film or coating on an external surface of the faceplate of the CRT formed by applying a selective light absorbing liquid. The liquid consists of a transparent base coating formed of an alcoholic solution of silicon alkoxide having either an-OH or an-OR group.

The problem to which the present invention is directed to is to formulate a colored, anti-static, high gloss, high contrast coating, utilizing an environmentally safe, aqueous solution consisting of a minimum number of inexpensive materials, and a simplified application process.

According to the present invention, a cathode ray tube (CRT) having a colored, anti-static, CRT faceplate coating, with high gloss and high contrast on an external surface of a faceplate panel of the CRT, is characterized by an organic silicate in a water-based solvent and a colorant selected from the group consisting of a Xanthene dye, a cationic thiazine dye, a sulfonephtalein indicator, an acridine dye and a cationic triphenylmethane dye. A process of manufacturing the coating also is described.

In the drawings: Fig. 1 is a partially broken-away longitudinal view of a CRT made according to the process of the present invention; and Fig. 2 is an enlarged sectional view through a fragment of the faceplate of the tube illustrated in Fig. 1, along section lines 2-2.

As illustrated in Fig. 1, a cathode-ray tube 21 includes an evacuated glass envelope having a neck section 23 integral with a funnel section 25.

A glass faceplate panel 27 is joined to the funnel section 25 by a devitrified glass frit seal 29. A luminescent screen 31 of phosphor materials is applied to an interior surface of the faceplate panel 27. A light-reflecting metal film 33 of, for example, aluminum, is deposited on the luminescent screen 31, as shown in detail in Fig. 2. The luminescent screen 31, when scanned by an electron beam from a gun 35, is capable of producing a luminescent image which may be viewed through the faceplate panel 27. A novel colored, anti-static, coating 37 having high gloss and high contrast is formed on an exterior surface 39 of the faceplate panel 27, to prevent an electrostatic charge build-up, and improve the contrast of the image, when viewed through the panel. The coating is water-based and, thus, avoids the environmental problems inherent in using an organic-based solution to form the coating.

The novel coating has anti-static characteristics, that is, when grounded, the coating does not store electrostatic charge when the tube is operated in a normal manner. The novel coating also is colored to improve image contrast.

EXAMPLE 1 The exterior surface 39 of the faceplate panel 27 of an evacuated CRT 21, is cleaned by any of the known scouring and washing procedures and, then, lightly etched with a 5 wt. % ammonium bifluoride solution and rinsed in deionized water. Next, an aqueous solution is applied to the faceplate panel 27 by spraying, spin coating, or dipping. The solution is obtained by initially forming a silica-sol. The silica-sol consists of an

organic silicate, such as tetraethoxysilane (Si (OC, HS),), having a concentration within the range of 1-10 wt. %, acidified water formed by mixing hydrochloric acid in deionized water to a pH within the range of 0-4. The mixing is continued for about 2 hours at room temperature.

An example of the silica-sol formulation is: deionized water 1395 g HC1 (37%) 42 g Si (OC, H5) 4 60 g The aqueous solution of the coating is formed by combining silica-sol 499 g Rhodamine B 0.6 g Methylene Blue 0.4 g.

The coating 37 formed by applied the coating solution of EXAMPLE 1 to the exterior surface 39 of the faceplate panel 27 has the characteristics listed in TABLE 1.

TABLE 1 CHARACTERISTIC COATED vs UNCOATED Brightness-10% Tube Face Reflectivity-28% Ambient Chromaticity x = unchanged; y =-0. 041 Gloss 9 5 Surface ResistivitylO'/D* * @ T = 18-25°C, and R. H. = 25-70% EXAMPLE 2 Starting with the silica-sol solution of EXAMPLE 1, a second aqueous solution is obtained by combining silica-sol 199.76 g Rhodamine B 0.24 g -The coating 37 formed by applied the coating solution of EXAMPLE 2 to the exterior surface 39 of the faceplate panel 27 has the characteristics listed in TABLE 2.

TABLE 2

CHARACTERISTIC COATED vs UNCOATED Brightness-2% Tube Face Reflectivity-11 % Ambient Chromaticity x = unchanged; y =-0. 013 Gloss 9 5 Surface Resistivity10'°n/D* * @ T = 18-25°C and R. H. = 25-70%

EXAMPLE 3 Starting with the silica-sol solution of EXAMPLE 1, a second aqueous solution if obtained by combining <BR> <BR> <BR> <BR> silica-sol 199.75 g<BR> <BR> <BR> <BR> <BR> Rhodamine B 0.24 g Methylene Blue 0.01 g The coating 37 formed by applied the coating solution of EXAMPLE 3 to the exterior surface 39 of the faceplate panel 27 has the characteristics listed in TABLE 3.

TABLE 3 CHARACTERISTIC COATED vs UNCOATED Brightness-6% Tube Face Reflectivity-15% Ambient Chromaticity x = unchanged; y =-0.024 Gloss 95 Surface Resistivity I 10° S2/0 * * @ T = 18-25°C and R. H. = 25-70% The coatings of the above EXAMPLES are dried by baking the coated faceplate at 65 °C. for at least 30 seconds.