METHOD OF MANUFACTURING AN ELECTRON BEAM TUBE AND ELECTRON BEAM TUBE THUS MANUFACTURED

Abstract: The invention relates to an electron beam tube for displaying colour television pictures and to a method of manufacturing same, in which a graphite suspension comprising colloidal silicon oxide is used for contacting between the colour selection electrode and the patterns on the display window. This provides a method of manufacture which is simpler than the conventional methods.

Description: The invention relates to a method of manufacturing an electron beam tube for displaying colour television pictures, which tube is provided with a glass envelope having a substantially rectangular display window on which phosphor patterns are present, and a colour selection electrode facing these patterns, a lacquer layer being provided on the patterns and an aluminium layer being provided on the lacquer layer whereafter the lacquer layer is removed and the aluminium layer is left on the patterns, an electrically conducting contact being obtained between the patterns and the colour selection electrode via a strip-shaped electrically conducting graphite layer and the aluminium layer. A method of the type described in the opening paragraph is known, for example, from US-A 4,301,041. In a method of the type described in the opening paragraph patterns of red, green and blue phosphors are provided on the display window in a conventional manner. A lacquer layer and an aluminium layer are successively provided on these patterns. The aluminium layer is used inter alia to prevent charging of the display window and for reflection of the light emitted by the phosphors. This lacquer layer is used to establish a satisfactory coating of the phosphor patterns by the aluminium layer. In a thermal treatment after the provision of the aluminium layer, for example, when the display window and the cone are sealed, the lacquer layer is removed. A conducting contact must be provided between the colour selection electrode and the aluminium layer. As is common practice a layer of a graphite suspension in the form of a strip is used for this purpose which strip is provided on the aluminium layer on the one hand and extends on the other hand as far as, for example, suspension pins of the colour selection electrodes, which pins are sealed in the wall of a raised edge of the display window. In this respect it is to be noted that the aluminium film which is provided by vapour deposition does not provide satisfactory contacts with the suspension pins. The following problem presents itself in the method described in the opening paragraph. When the lacquer layer, the aluminium layer and the graphite layer are successively provided and when subsequently the lacquer layer is removed by a thermal treatment, the graphite layer is interrupted because the underlying lacquer layer impedes the adhesion of the graphite layer to the glass wall in areas where the aluminium layer is absent. Consequently, the lacquer layer must be removed prior to providing the graphite layer. For this purpose either an additional thermal treatment is required or it is necessary to add solvents dissolving the lacquer layer to the graphite suspension, or the lacquer layer must be removed by another process, for example, a mechanical process. Providing the graphite layer prior to providing the lacquer layer is no solution because graphite layers of the conventional composition are attacked by solvents used for the lacquer layer. It is an object of the invention to obviate the described problem at least to a considerable extent. The invention is based inter alia on the recognition that a graphite layer having a suitable composition can contribute to realising this object. According to the invention the method described in the opening paragraph is therefore characterized in that the strip-shaped graphite layer is substantially free from alkali metal ions and comprises at least 5% by weight of colloidal silicon oxide and in that the lacquer layer is also provided on said strip shaped graphite layer and the aluminium layer is provided on said lacquer layer. The method according to the invention has the advantage that it does not necessitate an additional thermal treatment for the removal of the lacquer layer and that it is not necessary to add a solvent for the lacquer layer to the graphite suspension and that the lacquer layer need not be removed in another separate step. Graphite layers of the composition mentioned above are not attacked by lacquer layers. The invention also relates to an electron beam tube for displaying television pictures, which tube is provided with a glass envelope having a substantially rectangular display window on which phosphor patterns are present, and a colour selection electrode facing these patterns, the patterns and the colour selection electrode being connected together in an electrically conducting manner by an aluminium layer and a strip-shaped electrically conducting graphite layer. A tube of this type can be manufactured in a very simple manner, namely without additional steps, when the graphite layer in the tube according to the invention is substantially free from alkali metal ions and comprises at least 5% by weight of colloidal silicon oxide and is present at the area of the aluminium layer between the glass envelope and the aluminium layer. The expression "substantially free from alkali metal ions" is understood to mean that at most approximately 1% by weight of oxides of alkali metals is present in the colloidal silicon oxide. The colour selection electrode is preferably secured to a suspension pin sealed in a raised edge of the display window and the strip-shaped graphite layer extends from the suspension pins to the aluminium layer. The invention will now be described in greater detail with reference to the accompanying drawing and an embodiment. In the drawing Figure 1 is a diagrammatic cross-section of a part of an electron beam tube in a stage of manufacture by means of conventional methods, whilst Figures 2a, b and c are diagrammatic cross-sections of a part of an electron tube in parallel successive stages of manufacture by means of conventional methods, and Figure 3 is a diagrammatic cross-section of a part of an electron tube in a stage of manufacture by means of the method according to the invention. The embodiment relates to a method of manufacturing an electron beam tube for displaying television pictures, which tube is provided with a glass envelope having a substantially rectangular display window 1 (see Figure 1). Phosphor patterns 2 are present on the display window 1 and a colour selection electrode (not shown) faces these patterns 2. A lacquer layer 3 is provided on the patterns 2 and an aluminium layer 4 is provided on the lacquer layer 3 (see Figures 2a and 2c) whereafter the lacquer layer 3 is removed and the aluminium layer 4 is left on the patterns 2. An electrically conducting contact between the patterns 2 and the colour selection electrode is obtained via a strip-shaped electrically conducting graphite layer 5 (Figures 2a, b and c) and the aluminium layer 4, more specifically in this embodiment in that the graphite layer 5 at least partly covers sealed-in metal suspension pins 6 of the colour selection electrode on he one hand and contacts the aluminium layer 4 on the other hand. In conventional methods (see Figures 2a, b and c) problems present themselves in the form of necessary additional steps. The lacquer layer 3 is provided from a solution over a large surface area. The aluminium layer 4 is provided by vapour deposition on a part of the lacquer layer 3. If the graphite layer 5 on suspension pins 6 is provided partly on the lacquer layer 3, the graphite layer 5 will not satisfactorily adhere to the glass wall 7 after the lacquer layer 4 is removed. In conventional methods the lacquer layer 3 is therefore removed at the area where the graphite layer 5 is provided. This is done by a mechanical process (see Figure 2a) in which the areas which are coated with the layers 3 and 5 are separated from each other by thermal treatment (see Figure 2b) so that the layer 3 is removed before the layer 5 is provided, or by addition of a solvent for the layer 3 to the layer 5, with layer 5 and layer 3 adjoining each other temporarily (see Figure 2c). These additional steps are obviated in the method according to the invention in that the strip-shaped graphite layer 5 is substantially free from alkali metal ions and comprises at least 5% by weight of colloidal silicon oxide and in that the lacquer layer 3 is provided on the graphite layer 5 and the aluminium layer 4 is provided on the lacquer layer 3 (Figure 3). An electron beam tube of this type can be manufactured without the said additional steps, whilst the composition of the graphite layer 5 prevents the risk of attack of this layer by solvents of the lacquer layer 3. Thus, an electron beam tube for displaying television pictures is obtained which is provided with a glass envelope having a substantially rectangular display window 1 on which phosphor patterns 2 are present, and a colour selection electrode facing these patterns 2, which patterns 2 and the colour selection electrode are connected together in an electrically conducting manner by means of an aluminium layer 4 and an electrically conducting graphite layer 5. According to the invention the graphite layer 5 is substantially free from alkali metal ions and comprises at least 5% by weight of colloidal silicon oxide, whilst the graphite layer is present at the area of the aluminium layer 4 between the glass envelope 1 and the aluminium layer 4. The colour selection electrode is preferably secured to suspension pins 6 sealed in a raised edge 8 of the display window 1 and the strip-shaped graphite layer 5 extends from the suspension pins 6 to the aluminium layer 4. The patterns 2 are provided in a conventional manner. The graphite layer is 3 to 50 µm thick and is provided by brushing etc. of an aqueous suspension comprising 20% by weight of graphite, 5% by weight of a conventional bulk colloid and 10% by weight of colloidal SiO₂ having a particle size of < 25 nm and a specific surface area of > 100 m²/g. A colloid is a substance composed of particles that are extremely small, but larger than most molecules. Colloids do not actually dissolve, but remain suspended in a suitable gas, liquid or solid. (Definition of colloid in Thorndike-Dictionary, New-York 1941). The lacquer layer 3 is 0.1-1.0 µm, for example, 0.4 µm thick and comprises acrylate resin and is provided from a solution of the said resin in toluene or from and aqueous emulsion of the said resin. The aluminium layer is 0.2-0.3 µm thick and is vapour deposited. The lacquer is removed during the thermal treatment which is required for sealing the display window to associated cone, with the display window being at a peak temperature of 440°C for 45 minutes. The invention is not limited to the embodiment described, but many variations are possible within the scope of the claims.

Claims: A method of manufacturing an electron beam tube for displaying colour television pictures, which tube is provided with a glass envelope having a substantially rectangular display window on which phosphor patterns are present, and a colour selection electrode facing these patterns, a lacquer layer being provided on the patterns and an aluminium layer being provided on the lacquer layer whereafter the lacquer layer is removed and the aluminium layer is left on the patterns, an electrically conducting contact being obtained between the patterns and the colour selection electrode via a strip-shaped electrically conducting graphite layer and the aluminium layer, characterized in that the strip-shaped graphite layer is substantially free from alkali metal ions and comprises at least 5% by weight of colloidal silicon oxide and in that the lacquer layer is also provided on said strip shaped graphite layer and the aluminium layer is provided on said lacquer layer. An electron beam tube for displaying television pictures. which tube is provided with a glass envelope having a substantially rectangular display window on which phosphor patterns are present, and a colour selection electrode facing these patterns, the patterns and the colour selection electrode being connected together in an electrically conducting manner by an aluminium layer and a strip-shaped electrically conducting graphite layer, characterized in that the graphite layer is substantially free from alkali metal ions and comprises at least 5% by weight of colloidal silicon oxide and is present at the area of the aluminium layer between the glass envelope and the aluminium layer. An electron beam tube as claimed in Claim 2, characterized in that the colour selection electrode is secured to suspension pins sealed in a raised edge of the display window, and the strip-shaped graphite layer extends from the suspension pins to the aluminium layer.

Inventors: COMPEN, JOHANNES MARIA AZALINA ANTONIUS, VAN KEMENADE, WILHELMUS MARIA PETRUS
Applicants: N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1987
Main classification: H01J29
IPC codes: H01J29, H01J9