GB1566899A

GB1566899A - Method of manufacturing a colour display tube and colour display tube manufactured by said method

Info

Publication number: GB1566899A
Application number: GB129977A
Authority: GB
Original assignee: Philips Electronic and Associated Industries Ltd
Current assignee: Philips Electronics UK Ltd
Priority date: 1976-01-16
Filing date: 1977-01-13
Publication date: 1980-05-08
Also published as: CA1073517A; JPS5287971A; IT1077851B; BE850412A; FR2338569A1; NL7600421A; FR2338569B1; DE2700616A1; ES458398A1; ES455022A1; JPS588544B2

Description

(54) METHOD OF MANUFACTURING A COLOUR DISPLAY TUBE AND COLOUR DISPLAY TUBE MANUFACTURED BY SAID METHOD (71) We PHILIPS ELECTRONIC AND ASSOCIATED INDUSTRIES LI MITRED of Abacus House, 33 Gutter Lane, London, EC2V 8AH a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:: The invention relates to a method of manufacturing a colour display tube comprising in an evacuated envelope an electrode system to generate at least two electron beams, a display screen covered with a large number of regions luminescing in different colours, and colour selection means arranged at a short distance before the display screen to associate each electron beam with luminescent regions of one colour, which colour selection means comprise a first and a second system of lens electrodes, a lens electrode belonging to the first system being connected to a lens electrode belonging to the second system by means of an insulating member.

The invention furthermore relates to a colour display tube manufactured according to the method.

In colour display tubes, colour selection means are usually used in the form of a perforated plate which is arranged at a short distance before the display screen and which is usually referred to be the name of shadow mask. The drawback of such a shadow mask is that a large part, for example 80 to 85 %, of the electrons are intercepted, which imposes restrictions upon the maximum achievable brightness of the displayed picture. It is known to increase the brightness of the displayed picture by enlarging the apertures in the colour selection means and postfocusing the electron beams.

A tube in which the electron beams are subjected to a postfocusing is disclosed in United States Patent Specification 3,398,309. In this tube, a lens of the unipotential type is formed in each of the apertures of the colour selection means. For such lenses a rather great voltage difference is required between the electrodes which form the lens.

It is an object of the invention to provide a method manufacturing a colour display tube of the postfocusing type in which the colour selection means are of a simple construction. Another object of the invention is to provide such a colour display tube in which the colour selection means comprise only two systems of lens electrodes in such manner that, when a voltage difference is applied between the said two systems, a quadrupole lens is formed in each of the apertures of the colour selection means.

According to the invention, a method of manufacturing a colour display tube of the kind mentioned in the preamble is characterized in that starting material for the manufacture of colour selection means is an electrically insulating foil on which a first system of lens electrodes is formed on one side and a second system of lens electrodes is formed on the other side and the desired apertures in the colour selection means are obtained by the local etching through of the insulating foil.

The starting material for the manufacture of the colour selection means may be an insulating foil which is coated on both sides with a metal layer of which one metal layer is locally etched away to form a first system of lens electrodes and the other metal layer is locally etched away to form a second system of lens electrodes. Known photographic methods may be used for the local etching-away of the metal layers.

According to another embodiment of the method of the invention the two systems of lens electrodes are obtained directly by depositing metal on the relevant sides of the insulating foil. In order to obtain the desired pattern of the system of lens electrodes, photographic methods may be used in this case also, while for depositing the metal known methods, such as vapour deposition or sputtering, may be used.

In another embodiment the colour selection means is obtained by forming on one side of the insulating foil a system of lens electrodes resulting in a metal coating provided with apertures arranged according to rows, forming on the other side of the insulating foil a system of lens electrodes resulting in a metal grid of mutually connected strips which are positioned between the said rows of apertures, and etchingthrough the foil at least at the area of the said apertures. In the colour selection means obtained according to this embodiment a quadrupole lens, the electric field of which is at right angles to or substantially at right angles to the passing electron beams, is formed in each of the apertures of the colour selection means when a voltage difference is applied between the first and the second system of lens electrodes.The advantage of the colour selection means constructed according to the invention is that, compared with those according to the United States patent Specification, they can be operated at a lower voltage difference because a quadrupole lens is comparatively stronger than a unipotential lens. That a quadrupole lens focuses in one direction and defocuses in a direction at right angles thereto is in principle no drawback when the luminescent regions on the display screen have the shape of substantially parallel strips the longitudinal direction of which is parallel to the defocusing direction of the quadrupole lenses.

Another embodiment of the colour selection means is obtained by forming on one side of the insulating foil a system of lens electrodes resulting in a first metal grid of strips which are connected together electrically, forming on the other side of the insulating foil a system of lens electrodes resulting in a second metal grid of strips which are connected together electrically, which second grid crosses the first grid, and then etching-through the foil between the strips belonging to the same grid. In the colour selection means thus obtained, a quadrupole lens is also formed in each of the apertureswhen a voltage difference is applied between the first and the second grid.

In the colour selection means obtained according to this latter method, the insulating foil does not contribute or contributes hardly to the rigidity of the colour selection means. In particular when parts of the insulating foil remain only on the crossings of the strips, the mechanical rigidity of the colour selection means is fullv determined by the rigidity of the strips forming the grids. In that case it is recommendable to reinforce at least one of the grids by providing thereon an extra metal layer. This may be done by electroplating or chemically.

Suitable insulating foils are glass foil and synthetic foil. Polyimide foils may be used, for example the polyimide of 1-2-4-5 benzenetetracarbonic acid dianhydride and 4-4' diaminodiplenyl ether.

Embodiments of the invention will be described in greater detail by way of example with reference to the diagrammatic drawings in which: Figure 1 is a horizontal sectional view of a colour display tube embodying the invention, Figure 2 shows the principle of the postfocusing effect of a quadrupole lens, Figures 3a, b, c and d illustrate a method embodying the invention, Figure 4 shows a detail of the colour selection means shown in Figure 3d, and Figure 5 shows a detail of another embodiment of the colour selection means.

The tube shown in Figure 1 comprises a glass envelope 1, means 2 to generate three electron beams 3, 4 and 5, a display screen 6. colour selection means 7 and deflection coils 8. The electron beams 3, 4 and 5 are generated in one plane, the plane of the drawing of Figure 1, and are deflected over the display screen 6 comprising a large number of phosphor strips luminescing red, green and blue and the longitudinal direction of which is at right angles to the plane of the drawing of Figure 1. During normal operation of the tube the phosphor strips are vertical and Figure 1 hence is a horizontal sectional view of the tube. The colour selection means 7 comprise a large number of apertures 9 which are shown diagrammatically only in Figure 1.The three electron beams 3. 4 and 5 pass through the apertures 9 at a small angle with each other and consequently each impinge only upon phosphor strips of one colour. The apertures 9 in the colour selection means 7 are thus very accurately positioned relative to the phosphor strips of the display screen 6.

Figure 2 shows the principle of the postfocusing effect of a quadrupole lens. Shown is a part of the colour selection means 7 and one of the apertures 9. The potential variation along the edge of the apertures 9 is denoted by +, -, +, - in such manner that a quadrupole lens is formed. The electron beam which passes through the aperture 9 is focused in the horizontally drawn plane and is defocused in the vertically drawn plane so that, when the display screen is exactly in the horizontal focus, the electron spot 10 is formed. As will be explained hereinafter it is recommedable not to focus exactly on the display screen 6 so that a slightly wider electron spot is obtained. It is only of minor influence to the focusing when the electron beam passes through the aperture 9 at a small angle.The colour selection of the three electron beams 3, 4 and 5 takes place in a manner quite analogous to that of the known shadow mask tube. As a result of the strong focusing, however, the aperture 9 may be much larger than in the known shadow mask tube so that a far greater number of electrons impinges on the display screen 6 and a brighter picture is obtained.

The defocusing in a vertical direction need not be a drawback when phosphor strips are used which are parallel to the longitudinal direction of the spot 10.

A first embodiment of the colour selection means 7 is explained in detail with reference to Figures 3a to 3d. A polyimide foil 20 of 125 microns thickness is coated on two sides with metal layers 21 and 22, respectively. The foil consists of the polyimide of 1-2-4-5 benzenetetracarbonic acid dianhydride and 4-4' diaminodiphenyl ether. Such a foil is commercially available as Kapton. The metal layers are provided on the foil by vapour deposition or sputtering and may consist, for example, of copper, nickel, cobalt, aluminium, iron, gold or a double layer of two of these metals. At least one of the said layers preferably consists of a ferromagnetic material so as to screen the electron beam generated in the tube from the earth's magnetic field. A double layer is also possible, for example a first layer of copper on which a second layer of nickel is provided.The nickel layer may be provided by electro-plating or according to a process known as electroless nickel plating. After a thickness of approximately 30 llm of the metal layers 21 and 22 has been obtained, the laminated plate as shown in Figure 3a is obtained. A layer of photoresist material is then provided on the two surfaces of said laminated plate, which layers are each converted by photographic exposure and development into a pattern of parallel rods.

The parts of the metal layers 21 and 22 exposed after development are removed by means of a suitable etching liquid. After removing the remaining photoresist material, a foil 20 is obtained which is coated on both sides with metal strips 23 and 24, respectively, as is shown in Figure 3b. In said foil the strips 23 form a first system of lens electrodes and the strips 24 form a second system of lens electrodes. The mutual connection of the conductors belonging to the same system is obtained by leaving a connection strip at the ends of the conductors (not shown in the Figure). In the following phase of the method, shown in Figure 3c, the parts of the foil 20 present between the conductors 23 are etched away without attacking the conductors.An etchant suitable for this purpose consists of hydrazinehydrate or a diluted lye, preferably KOH, which is sprayed against the side of the foil 20 coated with the conductors 23.

After removing the said parts of the foil a matrix of rectangular apertures 9 is also obtained with which in principle the colour selection means are completed.

Although in Figure 3c the side faces of the rods 27 remaining on the foil 20 are shown to be straight, in fact some underetching occurs. This is no drawback because as a result of this the rods 27 are better protected against the electron beams by the lens electrodes. The possibility of charging, if any, of the insulation material by the electron beams can further be reduced by removing the part of the rods 27 situated between the conductors 24. As is shown in Figure 3d only blocks 26 remain of the original foil, which blocks are situated at the area where the conductors 23 cross the conductors 24.

Numerous variations of the abovedescribed method are possible. Instead of first providing the metal layers 21 and 22 on the foil and etching the conductors out of said layers, it is also possible to provide the conductors directly on the foil according to the desired pattern. For that purpose the foil is coated on two sides with a layer of photoresist material in which a pattern of rods is provided photographically. A metal layer is then provided across said pattern, which layer does not adhere to the parts of the foil which are not coated with photoresist material. The remaining photoresist material of the foil is finally removed and only the metal adhering directly on the foil remains on the foil according to the desired pattern.

It is furthermore possible first to etch the conductors from the metal layer vapourdeposited on the foil and then to give the conductors the desired thickness, for example, electrolytically.

Instead of vapour-depositing or sputtering, it is furthermore possible to obtain the laminated plate shown in Figure 3a by coating the foil 20 on two sides with a metal foil. For that purpose, the metal foils are wetted on one side with an adhesive consisting of the polyamide of 1-2-4-5 benzenetetracarbonic acid dianhydride and 4-4' diaminodiphenyl ether. The two metal foils are then pressed against the polyimide foil 20 and the resulting assembly is heated in a furnace under a non-oxidizing atmosphere to a temperature of 350"C for approximately 30 minutes. The polyamide is converted into the polyimide while expelling water and the metal foils rigidly adhere to the foil 20. For the rest the method may be continued as is described with reference to Figures 3b c and d.

Although the invention has been explained with reference to an insulating foil of a polyimide, it is alternatively possible to use foils of another insulating material, for example glass. The advantage of a synthetic foil, however, is that it is not fragile and can readilv be handled.

Figure 4 shows on an enlarged scale t part of the colour selection means shown in Figure 3t1 situated around an aperture 9.

The strips 23 and 24 have a width of ().24 mm and each of the apertures 9 forms a square of 0.56 x (),56 mm so that the transmission of the colour selection means is approximntely 50 'X,. For postfocusing the electron beams, of which Figure 4 shows only the beam directed on the phosphor strip (;, the colour selection means can be operated at the following voltages.

At a potential of the display screen 6 of 25 kV and a potential of the horizoiitil conductors 23 of 25.45 kV and of the vertical conductors 24 of 24.55 kV, the focal dis tance of the quadrupole lenses is 18.0 mm in the centre of the display screen with perpendicular incidence and is 12.7 mm at the edge of the curved display screen where the electron beams are incident at in angle of approximitely 37 to the normal of the display screen. The distance ol the colour selection means 7 to the display screen 6 is 50 mm in the centre and 10 mm at the edge, so that the focus of the quadrupole lenses lies everywhere just slightly beyond the display screen.As a result of this it is prevented that a so-called focus ring becomes visible on the display screen. The electron spots in the centre of the display screen are then (1.10 mm wide and in the corners they are ().09 mm wide. A suitable width of the phosphor strips R. G and B then is 0.13 mm.

The remainder of the surface of the display screen may eventually be coated with a light-absorbing material.

In the colour selection means 7 shown in Figure 5. one system of lens electrodes consists of an aluminium raster 31 formed on a polyimide foil 30 and provided with rectangular apertures 9 of 0.54 x 0.54 mm.

The second system of lens electrodes consists of a grid of nickel strips 32 shown horizontally in the drawing and having a width of 0.26 mm.The transmission of the colour selection means thus is again approximately 50 %. The postfocusing effect of this embodiment of the colour selection means is analogous to that described with reference to Figure 4 if during operation of the tube the raster 31 has a potential of approximately 23 kV and the strips 32 convey a potential of approximatley 25 kV at a potential of the display screen 6 of approximately 25 kV. An advantage of the colour selection means shown in Figure 5 with respect to those of Figure 4 is that the foil 30 contributes essentially to the mechanical rigidity of the colour selection means.

An extra reinforcing layer on the strips 32 or the raster 31 is then not strictly necessary.

Reference is mate to our copending British Patent Applications No. 1286177 (Serial No. 15668to7) and 1287/77 (Serial No. 1566898) which describe other display tubes.

WIlAT WE CLAIM IS: A method of manufacturing i colour display tube comprising in an evacuated envelope an electrode system to generate at least two electron beams, a display screen covered with a large number of regions luminescing in different colours, and colour selection means arranged at a short distance before the display screen to associate each electron beam with luminescent regions of one colour, which colour selection means comprise a first and a second system of lens electl-o(les, a lens electrode belonging to the first system being connected to a lens electrode belonging to the second system by means of an insulating member, characterized in that starting material for the manufacture of the colour selection means is an electrically insulating foil on which a first system of lens electrodes is formed on one side and a second system of lens electrodes is formed on the other side. and the desired apertures in the colour selection means are obtained by locally etching-through the insulating foil.

2. A method as claimed in Claim 1, characterized in that starting material for the manufacture of the colour selection means is an insulating foil which is coated on two sides with a metal layer of which one metal layer is locally etched away to form a first system of lens electrodes and the other metal layer is locally etched away to form a second system of lens electrodes.

3. A method as claimed in Claim 1, characterized in that at least one of the systems of lens electrodes is provided directly on the foil by depositing metal.

4. A method as claimed in Claim 1, 2 or 3, characterized in that at least one of the systems of lens electrodes is reinforced mechanically by providing thereon an extra metal layer.

5. A method as claimed in Claim 1, 2, 3 or 4, characterized in that on one side of the insulating foil a system of lens electrodes is formed resulting in a metal coating provided with apertures arranged according to rows, on the other side of the insulating foil a system of lens electrodes is formed resulting in a metal grid of strips which are connected together, which strips are positioned between the said rows of apertures and the foil is etched through at least at the area of the said apertures.

6. A method as claimed in Claim 1, 2, 3

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

Although the invention has been explained with reference to an insulating foil of a polyimide, it is alternatively possible to use foils of another insulating material, for example glass. The advantage of a synthetic foil, however, is that it is not fragile and can readilv be handled.

Figure 4 shows on an enlarged scale t part of the colour selection means shown in Figure 3t1 situated around an aperture 9.

The strips 23 and 24 have a width of ().24 mm and each of the apertures 9 forms a square of 0.56 x (),56 mm so that the transmission of the colour selection means is approximntely 50 'X,. For postfocusing the electron beams, of which Figure 4 shows only the beam directed on the phosphor strip (;, the colour selection means can be operated at the following voltages.

At a potential of the display screen 6 of 25 kV and a potential of the horizoiitil conductors 23 of 25.45 kV and of the vertical conductors 24 of 24.55 kV, the focal dis tance of the quadrupole lenses is 18.0 mm in the centre of the display screen with perpendicular incidence and is 12.7 mm at the edge of the curved display screen where the electron beams are incident at in angle of approximitely 37 to the normal of the display screen. The distance ol the colour selection means 7 to the display screen 6 is 50 mm in the centre and 10 mm at the edge, so that the focus of the quadrupole lenses lies everywhere just slightly beyond the display screen.As a result of this it is prevented that a so-called focus ring becomes visible on the display screen. The electron spots in the centre of the display screen are then (1.10 mm wide and in the corners they are ().09 mm wide. A suitable width of the phosphor strips R. G and B then is 0.13 mm.

The remainder of the surface of the display screen may eventually be coated with a light-absorbing material.

In the colour selection means 7 shown in Figure 5. one system of lens electrodes consists of an aluminium raster 31 formed on a polyimide foil 30 and provided with rectangular apertures 9 of 0.54 x 0.54 mm.

The second system of lens electrodes consists of a grid of nickel strips 32 shown horizontally in the drawing and having a width of 0.26 mm.The transmission of the colour selection means thus is again approximately 50 %. The postfocusing effect of this embodiment of the colour selection means is analogous to that described with reference to Figure 4 if during operation of the tube the raster 31 has a potential of approximately 23 kV and the strips 32 convey a potential of approximatley 25 kV at a potential of the display screen 6 of approximately 25 kV. An advantage of the colour selection means shown in Figure 5 with respect to those of Figure 4 is that the foil 30 contributes essentially to the mechanical rigidity of the colour selection means.

An extra reinforcing layer on the strips 32 or the raster 31 is then not strictly necessary.

Reference is mate to our copending British Patent Applications No. 1286177 (Serial No. 15668to7) and 1287/77 (Serial No. 1566898) which describe other display tubes.

WIlAT WE CLAIM IS: A method of manufacturing i colour display tube comprising in an evacuated envelope an electrode system to generate at least two electron beams, a display screen covered with a large number of regions luminescing in different colours, and colour selection means arranged at a short distance before the display screen to associate each electron beam with luminescent regions of one colour, which colour selection means comprise a first and a second system of lens electl-o(les, a lens electrode belonging to the first system being connected to a lens electrode belonging to the second system by means of an insulating member, characterized in that starting material for the manufacture of the colour selection means is an electrically insulating foil on which a first system of lens electrodes is formed on one side and a second system of lens electrodes is formed on the other side. and the desired apertures in the colour selection means are obtained by locally etching-through the insulating foil.
2. A method as claimed in Claim 1, characterized in that starting material for the manufacture of the colour selection means is an insulating foil which is coated on two sides with a metal layer of which one metal layer is locally etched away to form a first system of lens electrodes and the other metal layer is locally etched away to form a second system of lens electrodes.
3. A method as claimed in Claim 1, characterized in that at least one of the systems of lens electrodes is provided directly on the foil by depositing metal.
4. A method as claimed in Claim 1, 2 or 3, characterized in that at least one of the systems of lens electrodes is reinforced mechanically by providing thereon an extra metal layer.
5. A method as claimed in Claim 1, 2, 3 or 4, characterized in that on one side of the insulating foil a system of lens electrodes is formed resulting in a metal coating provided with apertures arranged according to rows, on the other side of the insulating foil a system of lens electrodes is formed resulting in a metal grid of strips which are connected together, which strips are positioned between the said rows of apertures and the foil is etched through at least at the area of the said apertures.
6. A method as claimed in Claim 1, 2, 3

or 4, characterized in that on one side of the insulating foil a system of lens electrodes is fonned resulting in a first metal grid of strips which are connected together electrically, that on the other side of the insulating foil a system of lens electrodes is formed resulting in a second metal grid of strips which are connected together electrically, which second grid crosses the first grid, and that the foil between the strips belonging to the same grid is then etched through.
7. A method as claimed in any of the preceding Claims, characterized in that the msulating foil is a glass foil.
8. A method as claimed in any of the Claims 1 to 6, characterized in that the insulating foil is a synthetic foil.
9. A method as claimed in any of the Claims 1 to 6, characterized in that the insulating foil is a polyimide foil.
10. A method of making a colour display tube which comprises making a colourselection electrode by a method substantially as herein described with reference to Figures 3 and 4 or Figure 5.
11. A colour display tube manufactured according to the method as claimed in any of the preceding Claims.
12. A colour display tube comprising in an evacuated envelope means to generate a number of electron beams, a display screen comprising a large number of regions luminescing in different colours, and colour selection means provided with a large number of apertures which associate each electron beam with luminescent regions of one colour, which colour selection means comprise a first and a second system of lens electrodes, a lens electrode belonging to the first system being connected to a lens electrode belonging to the second system by means of an insulating member, characterized in that the said insulating member consists of a foil of an electrically insulating material which is perforated at least at the area of the said apertures.
13. A colour display tube as claimed in Claim 12, characterized in that the first system of lens electrodes consists of a metal coating in the form of a raster which is present on one side of the foil and is provided with apertures arranged according to rows and the second system of lens electrodes consists of a metal coating in the form of strips present on the other side of the foil, which strips are connected together electrically and positioned between the rows of apertures.
14. A colour display tube as claimed in Claim 12 or 13 characterized in that the foil is a glass foil.
15. A colour display tube as claimed in Claim 12 or 13 characterized in that the foil is a synthetic foil.
16. A colour display tube as claimed in Claim 12 or 13, characterized in that the foil is a polyimide foil.
17. A colour display tube substantially as herein described with reference to the accompanying drawings.