Compositions: coating or plastic – Coating or plastic compositions – Alkali metal silicate containing
Reexamination Certificate
2001-10-09
2004-09-21
Brunsman, David (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Alkali metal silicate containing
C106S618000, C106S626000, C106S634000, C106S635000, C313S479000
Reexamination Certificate
active
06793729
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a conductive material for using in interior coating of a cathode ray tube (CRT), and more particularly, to a conductive material for using in coating a conductive layer on the inner surface of the funnel of a CRT with increased adhesiveness.
CRTs have conductive layers, which serve as an electric condenser, on the outer and inner surfaces of the funnel. The conductive layers formed of a conductive material accelerate electron beams towards a phosphor screen at a high voltage, and gather secondary electrons emitted from the shadow mask, magnetic shield, and phosphor screen.
The conductive material used to form the conductive layers includes graphite, a binder, and a dispersing agent. The conductive material further include a metal oxide to increase elastic resistance. A conductive layer formed of the conductive material, and a CRT adopting the conductive layer are obtained as follows. The conductive material is coated on the inner or outer surface of a funnel by a spraying or deposition technique, or by means of a brush or sponge. The coated conductive layer is dried and sintered in the air. The funnel having the conductive layer and a panel having a phosphor screen on its inner surface are sealed at a temperature of about 450° C. using a glass having a low melting point. An electron gun which emits electron beams is equipped into the neck portion of the funnel, and the resultant structure is hot evacuated to complete a vacuum CRT.
Since the conductive layer coated on the inner surface of the funnel of a CRT adsorbs moisture and a variety of gases in the air, the adsorbed gases are removed from the conductive layer by hot evacuation before sealing of the CRT. However, although such evacuation is carried out, the adsorbed gas which still remains in the conductive layer is released during operation of the CRT, which causes undesirable reactions with the cathode of the CRT, thereby degrading the cathode.
On the other hand, the conductive layer may partially laminate from the inner surface of the funnel in the manufacture of a CRT. As a result, arc discharging of the electron gun, or current leakage occurs during operation of the CRT. Such arc discharging or current leakage damages high-voltage stability of the CRT. For this reason, there is a need to form a conductive layer such that the conductive layer remains intact on the funnel against external vibration or impact.
Japanese Patent Laid-open Publication No. sho 55-2042; hei 3-59542; and sho 63-45428 disclose use of a metal oxide formed of iron (Fe), titanium (Ti), cobalt (Co), nickel (Ni), chromium (Cr), manganese (Mn), aluminum (Al), or silicon (Si) as an additive to a conductive material for the conductive layer of a CRT. Japanese Patent Laid-open Publication No. 63-45428 discloses a method of uniformly dispersing negatively and positively charged particles in a negatively charged dispersion medium, in which negatively charged graphite particles and positively charged metal oxide particles such as titanium dioxide (TiO
2
) are agglomerated together, and negatively charged silicon dioxide (SiO
2
) particles are dispersed around the particle complex.
Japanese Patent Laid-open Publication No. sho 61-20990 discloses a method of increasing adhesiveness of the conductive layer formed on the inner side of a CRT funnel by addition of silicon carbide particles as well as graphite particles. U.S. Pat. No. 4,479,824 discloses use of a silicon monomer as well as graphite particles to suppress separation of the conductive layer from a CRT funnel.
Japanese Patent Laid-open Publication No. sho 52-52362 and sho 63-45428 disclose use of lithium silicate, potassium silicate, or sodium silicate as a binder of conductive layer. Japanese Patent Laid-open Publication No. hei 3-141539 discloses use of a cement, which less adsorbs moisture or gases, as a binder of a conductive layer. Japanese Patent Laid-open Publication No. sho 63-114025 discloses addition of a metal hydride which can adsorb and desorb gases to a conductive material of conductive layer. Japanese Patent Application No. hei 6-093079 discloses use of potassium silicate, which less adsorbs moisture or gases, as a binder of conductive layer.
The conductive layers formed by the above-described methods are unsatisfactory, and need an improvement in terms of adhesiveness to the inner surface of the funnel. In addition, in the case where the conductive layers are left in the air after sintering, there is a need to extend a period of time for which hot evacuation is performed to exhaust the adsorbed moisture or carbonic acid gas, which lowers productivity of CRTs.
SUMMARY OF THE INVENTION
An aspect of the present invention provides an adhesive composition comprising potassium silicate dissolved in water, wherein the potassium silicate comprises silicon dioxide and potassium oxide with a mole ratio of the silicon dioxide to the potassium oxide greater than about 5.0, wherein the composition is in a liquid phase, and wherein the composition has adhesiveness of 3B 5B tested under ASTM D3359. The adhesiveness is preferably 4B to 5B. The adhesive composition further comprises a dispersing agent, which comprises at least one selected from the group consisting of carboxymethylcellulose (CMC), acryl and ethylene glycol. The adhesive composition further comprises a conductor, which comprises at least one selected from the group consisting of graphite and carbon black. The conductor advantageously comprises 20 to 80 parts-by-weight of graphite with reference to 100 parts-by-weight of a total amount of the conductive referenced material. The mole ratio of the silicon dioxide to the potassium oxide preferably ranges from about 5.0 to about 6.0, more preferably from about 5.0 to about 5.3.
Another aspect of the present invention provides a method of making a cathode ray tube. The method comprises: providing the above adhesive composition; adding a conductor to the composition; and applying the composition onto an interior surface of a cathode ray tube. In the method, the application of the composition comprises spraying the composition on the interior surface of the cathode ray tube. The method further comprises sintering the cathode ray tube after applying the composition.
A further aspect of the present invention provides a method of preparing a liquid composition comprising silicon dioxide and potassium oxide. The method comprises: providing an aqueous solution of potassium silicate comprising silicon dioxide and potassium oxide; stirring the aqueous solution with a stirrer at a rotational speed ranged from about 500 rpm to about 5,000 rpm; adding hydrosilica gel to the aqueous solution while stirring so that the mole ratio increases beyond about 4.5 without resulting in gelation of the composition. The aqueous solution before adding hydrosilica gel has a mole ratio of the silicon dioxide to the potassium oxide smaller than about 4.5. Preferably, the mole ratio before adding hydrosilica gel is from about 1.0 to about 4.0, more preferably from about 2.0 to about 3.5. When adding the hydrosilica gel the aqueous solution is advantageously at a temperature from about 40° C. to about 100° C. Preferably, the temperature is from about 55° C. to about 85° C., more preferably, from about 65° C. to about 75° C. The rotational speed is from about 900 rpm to about 4,000 rpm. Preferably, the rotational speed is from about 1,100 rpm to about 3,500 rpm. The addition of the hydrosilica gel comprises continuously feeding the hydrosilica gel. The method further comprises adding a dispersing agent. The method further comprises adding a conductor, which comprises at least one selected from the group consisting of graphite and carbon black. The conductor comprises 20 to 80 parts-by-weight of graphite with reference to 100 parts-by-weight of a total amount of the conductive material. The method further comprises a metallic compound, which is selected from the group consisting of indium tin oxide(ITO), tin oxide(SnO
2
), zinc oxide (ZnO), copper oxide(CuO), coba
Brunsman David
Jeong Eui-Kyun
Knobbe Martens Olson & Bear LLP
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