Carbon slurry regeneration

Abstract: In a method of regenerating a carbon slurry (14) used to produce a black matrix-type phosphor screen of a cathode ray tube, excess carbon slurry is collected (21) after the completion of carbon-coating of a cathode ray tube panel (11) and the collected carbon slurry is regenerated by means of an ion-exchange resin. The method can be employed in an apparatus for producing the screen, the apparatus including a nozzle (17) for coating the slurry (14) on the panel (11), a tank (13) containing the slurry, a supplying system (16) for supplying the slurry from the tank to the nozzle, a collecting system (21) for collecting the excess slurry produced from the nozzle back into the tank, and a carbon slurry regenerating device (24) using the ion-exchange resin. The regenerating device (29) can be placed in at least one of the supplying system (16), the collecting system (21) and the tank (13).

Description: This invention relates to regenerating carbon slurry used to produce a black matrix-type phosphor screen of a cathode ray tube and to apparatus for producing a black matrix-type phosphor screen of a cathode ray tube. A colour cathode ray tube (CRT) generally employs a black matrix-type phosphor screen in which a light-absorption layer (so-called black matrix) is formed among red, green and blue phosphor stripes (or dots) in order to improve the contrast thereof. The black matrix-type phosphor screen is generally formed as follows. As shown in Figure 1A of the accompanying drawings, the inner surface of a CRT panel 1 is first rinsed by an aqueous hydrofluoric acid solution. Then, a polyvinyl alcohol (PVA) type photosensitive film 2, made by adding ammonium dichromate to polyvinyl alcohol, is coated on the inner surface of the CRT panel 1 and then dried. As shown in Figure 1B of the accompanying drawings, a colour selecting mechanism, for example an aperture grill 3, is then used as an optical mask to expose the photosensitive film 2 to ultraviolet rays. In this exposing process, the photosensitive film 2 is exposed three times in the sequential order of, for example, the colours green, blue and red, use being made of exposing light sources 4R, 4G and 4B corresponding to the colours red, green and blue, respectively. Thereafter, the photosensitive film 2 is developed by some suitable process such as rinsing with water or the like to obtain a resist layer, in this example a resist layer 5 (5R, 5G, 5B) of stripe-configurations on the inner surface of the CRT panel 1 at positions corresponding to the respective red, green and blue colours as shown in Figure 1C of the accompanying drawings. After developing the film 2 with water, boric acid is dispensed onto the panel 1 including the resist layer 5, producing very straight edges on the PVA and thus eventually on the carbon stripes (see Figure 1D). They are then dried. This process will be hereinafter simply referred to as a hardening process. In the hardening process, a hardening agent used thereon may be generally a boric acid aqueous solution, though other aqueous solutions such as an aqueous tannic acid solution may be used. Then, as shown in Figure 1E of the accompanying drawings, a carbon slurry 6 is coated on the whole face of the inner surface of the panel 1 including the resist layers 5R, 5G and 5B, and then dried. At the next step, water 7 is sprayed to uniformly wet the carbon-coated surface as shown in Figure 1F of the accompanying drawings. This wetting process is carried out in order to provide a buffer against the extremely strong oxidant which, upon application, soaks through the carbon layer and dissolves the underlying PVA by breaking up the polymerised chains, thus also removing any carbon overlying it. Then, the resist layer 5 is swollen and a developing treatment is performed by means of, for example, water-spray, to remove the resist layer 5 and the carbon-coated layer formed on the resist layer 5, whereby carbon-stripes or black matrixes 8 of predetermined pattern are formed on the inner surface of the panel 1 as shown in Figure 1G of the accompanying drawings. Thereafter, a phosphor slurry of, for example, green colour is coated thereon and dried. Then, the coated green phosphor slurry is exposed by means of the aperture grill 3 (see Figure 1B) and developed so as to form a green phosphor stripe 9G on the inner surface of the panel 1 at a predetermined portion thereof where the black matrix 8 is not formed. In a like manner, a blue phosphor strip 9B and a red phosphor stripe 9R are formed on the inner surface of the panel 1 at predetermined portions thereof, whereby a colour phosphor screen 10 of black matrix-type is formed as shown in Figure 1H. In the above-described carbon coating process, though not shown in the figures, a carbon slurry from a carbon slurry tank is supplied through a supplying-system pipe to a carbon-coating means, that is a nozzle. The carbon slurry is ejected from the nozzle onto the inner surface of the panel 1. After the carbon-coating film is uniformly coated on the inner surface of the panel 1, the excess carbon slurry is collected back into the carbon slurry tank through a collection-system pipe. Generally, when the carbon slurry used in this coating process is collected and continuously recycled, the viscosity of the carbon slurry increases. At a certain point in time, the carbon slurry becomes unsuitable for use in the coating process because the carbon-coated film does not dry well after application to the panel 1 because of the increase in the viscosity of the carbon slurry. For example, if the viscosity of the carbon slurry is increased to four times its original viscosity, the thickness of the carbon-coated film is increased three times, making the carbon-coated film increasingly difficult to dry because it does not dry evenly and sufficiently. When the carbon-coated film that should be left in the afore-mentioned developing-process is too viscous, there is undesirable peeling. This phenomenon occurs especially on the peripheral portions of the panel. In the existing process, in order to control the viscosity of the carbon slurry so that it always falls in a constant range, each time the carbon slurry is coated on a predetermined number of panels a carbon slurry exhaust port of the carbon slurry tank is opened to dump some of the slurry to allow a predetermined liquid level to remain in the tank. Thereafter, fresh carbon slurry is added to the carbon slurry tank up to its predetermined liquid level. This purging technique increases the amount of carbon slurry consumed. The manufacturing cost of the black matrix of the colour cathode ray tube is thus inevitably increased. According to a first aspect of the invention there is provided a method of regenerating a carbon slurry used to produce a black matrix-type phosphor screen of a cathode ray tube, the method comprising collecting excess carbon slurry remaining after the completion of a carbon-coating process onto a cathode ray tube panel, and regenerating the collected carbon slurry by contacting it with an ion-exchange resin. According to a second aspect of the invention there is provided apparatus for producing a black matrix-type phosphor screen of a cathode ray tube, the apparatus comprising: carbon coating means for coating a carbon slurry on a cathode ray tube panel; a tank for containing the carbon slurry; a supplying system for supplying the carbon slurry from the tank into the carbon coating means; a collecting system for collecting excess carbon slurry produced from the carbon coating means into the tank; and carbon slurry regenerating means using an ion-exchange resin, the regenerating means being provided in at least one of said supplying system, said collecting system and said tank. A preferred embodiment of the invention described herewithin provides an improved method of regenerating carbon slurry used to produce a black matrix-type phosphor screen of a CRT and an improved apparatus for producing a black matrix-type phosphor screen of a CRT. The preferred method and apparatus can suppress an increase in the viscosity of a carbon slurry whereby collected carbon slurry can be used repeatedly and cyclically. Thus, the manufacturing cost of a black matrix-type phosphor screen can be decreased. The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings, in which like references identify like elements and parts throughout, and in which: Figures 1A and 1H are schematic diagrams of stages in a previously proposed method of producing a black matrix-type phosphor screen of a CRT and are useful for explaining an embodiment of the present invention; and Figure 2 is a schematic diagram of an apparatus embodying the invention for producing a black matrix-type phosphor screen according to a method embodying the invention. Prior to a description of a preferred embodiment of the invention, a principle underlying the embodiment will be described briefly. Although the present invention is not to be limited by the following explanation, it is our present understanding that the reason for an increased viscosity of a carbon slurry collected after its application in a method of producing a black matrix-type phosphor screen can be considered to be as follows. Material coated on the inner surface of the CRT panel before the carbon slurry is coated on the inner surface becomes dissolves in the collected slurry. The slurry is thereby aggregated so that the viscosity of the slurry is increased. The materials which become dissolved in the carbon slurry are polyvinyl alcohols (PVA), an ammonium dichromate (ADC), a boric acid and a tannic acid that act as hardening agents. In accordance with the preferred embodiment of the invention, the carbon slurry which is collected after the slurry has-been coated onto the CRT panel having a hardening-processed resist layer formed on its inner surface is passed through an ion-exchange resin so that the dissolved material contained in the slurry which contributes to its increased viscosity can be removed chemically. Thus, the viscosity of the collected carbon slurry can be decreased by chemical removal of aggregation agents and thereby regenerated to have substantially the same qualities as fresh carbon slurry. An example of an apparatus embodying the invention for producing a black matrix-type phosphor screen of a CRT, which apparatus employs a method embodying the invention for regenerating a carbon slurry, will now be described with reference to a schematic diagram of the apparatus shown in Figure 2. A CRT panel 11, on which is coated carbon slurry (and other components) that are used to produce a black matrix-type phosphor screen, is rotatably supported by a rotary arm 12. On the inner surface of the panel 11 there is formed a resist layer 5 of a predetermined pattern that has undergone a hardening-treatment by means of, for example, a aqueous boric acid solution, as described above with reference to Figure 1D. A carbon slurry tank 13 accommodates a carbon slurry 14. The tank 13 incorporates therein stirring means 15 for stirring the carbon slurry 14. The carbon slurry 14 from the tank 13 is introduced through a supplying-system pipe 16 to a nozzle section 17 that serves as carbon coating means and is positioned in an opposing relation to the inner surface of the CRT panel 11. A pump 18 and a filter 19 are interposed in the supplying-system pipe 16 at its mid-region. On the side of the CRT panel 11, there is located a cover member 20 that surrounds the panel 11. Thus, of the carbon slurry 14 ejected from the nozzle section 17 towards the inner surface of the CRT panel 11, the excess carbon slurry 14 is stored in the lower portion of the cover member 20. The excess carbon slurry 14 is collected into the carbon slurry tank 13 via a collecting-system pipe 21. A pump 22 and a filter 23 are interposed in the collecting-system pipe 21 at its mid-region. The filters 19 and 23 are operative to remove materials that are aggregated in the carbon slurry 14, such as dust and so on. A pipe 24 is provided for supplying new slurry into the carbon slurry tank 13 and a pipe 26 is provided through which waste carbon slurry 14 within the tank 13 can be abandoned to the outside of the tank 13. The pipes 24 and 26 are fitted with valves 25 and 27, respectively, which can be opened and closed. In the above-described particularly preferred embodiment, a column 29 filled with a negative ion-exchange resin is located in the midst of the collecting-system pipe 21, more particularly at a position behind (downstream of) the filter 23. The column 29 serves as regenerating means for the carbon slurry because it chemically removes therefrom materials which lead to carbon aggregation and resulting viscosity increase. The carbon slurry 14 used in this embodiment is a carbon slurry made by the use of AQUADAG CARBON (trade name of carbon manufactured by Acheson Japan Limited). The compositions of carbon solution and ready-mixed carbon slurry solution are indicated in the following table. In the apparatus shown in Figure 2, the carbon slurry 14 within the tank 13 is conveyed to the supplying-system pipe 16 by the pump 18 through the filter 19 to the nozzle section 17. From the nozzle section 17, the carbon slurry 14 is ejected onto the inner surface of the rotating panel 11 and is uniformly coated thereon to a predetermined film thickness. The extra carbon slurry 14 ejected onto the panel 11 is stored in the lower portion of the cover member 20 and collected into the tank 13 through the collecting-system pipe 21 by the pump 22. At that time, the collected carbon slurry 14 is passed through the column 29 filled with the negative ion-exchange resin and located behind the filter 23 so that boric acid mixed into the collected carbon slurry can be chemically removed with the result that the viscosity of the collected carbon slurry is decreased. That is, the carbon slurry is regenerated and then returned to the tank 13. In this way, the carbon slurry 14 is regenerated and used repeatedly and cyclically without any significant increase in slurry viscosity over the course of these cycles. When the amount of the carbon slurry 14 within the tank 13 becomes less than a predetermined amount, fresh carbon slurry 14 is supplied into the carbon slurry tank 13 from the supply pipe 24. Practical examples of regenerating collected carbon slurry by the use of negative ion-exchange resin will now be set forth. Example 1 Carbon slurry whose viscosity was increased after the carbon slurry 14 was ejected onto and uniformly coated on the inner surface of the CRT panel 11 having the resist layer which underwent the hardening-treatment by the boric acid was collected and then regenerated by the column 29, which was filled with a strong base negative ion-exchange resin that was made by Rohm and Haas Co., Ltd. The collected carbon slurry before being regenerated contained boric acid at a concentration of 200 ppm. The resulting viscosity of the collected carbon slurry was increased to about four times that of fresh carbon slurry. The carbon slurry contained 0.5 ppm boric acid after the regeneration, and the viscosity of the regenerated carbon slurry was lowered back to its original value. Thus, regenerated carbon slurry could be used again in the carbon-coating process similarly to fresh carbon slurry. Example 2 A regeneration treatment similar to that described in Example 1 was performed. The negative ion-exchange resin filled into the column 29 was a boric acid selective, weak base negative ion-exchange resin, such as a boric acid selective chelate resin, made by Rohm and Haas Co., Ltd. After the collected carbon slurry in this example was passed through the ion exchange resin, the collected carbon slurry was regenerated. The negative ion-exchange resin in the column 29 in both Examples 1 and 2 can be repeatedly used after being treated by an aqueous caustic soda solution. While in the embodiment of the invention described above with reference to Figure 2 the column 29 filled with the negative ion-exchange resin is located in the midst of the collecting-system pipe 21, the column 29 may instead be located in the midst of the supplying-system pipe 16. The effect of the regeneration treatment may also be achieved by supplying the negative ion-exchange resin directly into the carbon slurry tank 13. Further the negative ion-exchange resin may simultaneously be provided at a plurality of places, for example two or more of the collecting-system pipe 21, the supplying-system pipe 16 and the carbon slurry tank 13. While aqueous boric acid solution is used in the above-mentioned embodiment as a hardening-treatment agent for the resist layer, and the boric acid is mainly removed from the collected carbon slurry by the ion-exchange resin, whereby the collected carbon slurry is regenerated, it is within the scope of the invention, that, even when other hardening-treatment agents (for example, a tannic acid aqueous solution) are used, the collected carbon slurry can be regenerated by means of an ion-exchange resin. According to the above-described method of regenerating carbon slurry used to produce a black matrix-type phosphor screen, the hardening-treatment agent or other aggregation causing agent contained in the collected carbon slurry can be removed by passing the collected carbon slurry through the ion-exchange resin so that the viscosity of the carbon slurry can be reduced to the viscosity of fresh carbon slurry. Therefore, the collected carbon slurry can be used again. Moreover, according to the above-described apparatus for producing a black matrix-type phosphor screen, since the carbon slurry regenerating means using the ion-exchange resin is provided in at least one of the supplying system, collecting-system of the carbon slurry and the carbon slurry tank, the collected carbon slurry can be regenerated and hence the carbon slurry can be used cyclically. Therefore, the waste consumption of the carbon slurry can be decreased and therefore, the manufacturing cost of the black matrix-type phosphor screen of a CRT can be decreased.

Claims: A method of regenerating a carbon slurry (14) used to produce a black matrix-type phosphor screen of a cathode ray tube, the method comprising collecting excess carbon slurry remaining after the completion of a carbon-coating process onto a cathode ray tube panel (11), and regenerating the collected carbon slurry by contacting it with an ion-exchange resin (29). A method according to claim 1, in which the ion-exchange resin is a negative ion-exchange resin. A method according to claim 2, in which the negative ion-exchange resin is a strong base negative ion-exchange resin. A method according to claim 2, in which the negative ion-exchange resin is a boric acid selective weak base negative ion-exchange resin. A method according to claim 4, in which the boric acid selective weak base negative ion-exchange resin is a boric acid selective chelate resin. Apparatus for producing a black matrix-type phosphor screen of a cathode ray tube, the apparatus comprising: carbon coating means (17) for coating a carbon slurry (14) on a cathode ray tube panel (11); a tank (13) for containing the carbon slurry (14); a supplying system (16) for supplying the carbon slurry (14) from the tank (13) into the carbon coating means (17); a collecting system (21) for collecting excess carbon slurry produced from the carbon coating means (17) into the tank (13); and carbon slurry regenerating means (29) using an ion-exchange resin, the regenerating means being provided in at least one of said supplying system (16), said collecting system (21) and said tank (13). Apparatus according to claim 6, in which the ion-exchange resin is a negative ion-exchange resin. Apparatus according to claim 7, in which the negative ion-exchange resin is a strong base negative ion-exchange resin. Apparatus according to claim 7, in which the negative ion-exchange resin is a boric acid selective weak base negative ion-exchange resin. Apparatus according to claim 9, in which the boric acid selective weak base negative ion-exchange resin is a boric acid selective chelate resin.

Inventors: DODDS ROBERT E C O SONY SAN DI, TSUTOMU INOSE C O PATENTS DIVI, YOSHIMITSU KATO C O PATENTS DI, DODDS, ROBERT E., TSUTOMU, INOSE, YOSHIMITSU, KATO, DODDS, ROBERT E., C/O SONY SAN DIEGO, TSUTOMU, INOSE, C/O PATENTS DIVISION, YOSHIMITSU, KATO, C/O PATENTS DIVISION
Applicants: SONY CORP, SONY CORPORATION
Application year: 1990
Main classification: H01J9
IPC codes: B01J45, H01J9, B01J41, H01J29