EP0170130A1 - Fluorescent screen for display units and method for its manufacture - Google Patents

Abstract

The invention relates to a fluorescent screen for image display devices with a screen glass plate (1) and a phosphor layer (6) located thereon, which is introduced into depressions (4) which are surrounded by a contrasting border layer (5), in particular colored black. With this fluorescent screen, the highest color purity is to be achieved and, in particular, a combination of false colors on the surface of the layer of the respective color is to be avoided. For this purpose, the invention provides that the fluorescent colors of the phosphor layer (6), preferably the fluorescent colors red (R), green (G) and blue (B), in a grid or line-shaped systematic arrangement by a screen printing process on the screen glass plate (1) are upset. A fluorescent screen according to the invention is used as a flat plasma screen.

Description

The invention relates to a fluorescent screen according to the preamble of claim 1. The invention further relates to a method for producing such a fluorescent screen.

Multi-color fluorescent screens are usually produced in a known manner with the aid of an elaborate “slurry” photo technology process. Other proposals have also been made for applications with flat image display devices. A spraying method is known from DE-OS 28 04 127, which, however, can only be used up to certain resolution limits with regard to detent roughness.

DE-OS 23 06 436 and DE-OS 25 55 172 describe processes for the production of conductive, mechanically stable, in particular black, color point borders, which have proven themselves and which are assumed here.

From DE-AS 25 40 132 a printing process emerges as known which, in addition to the printing of phosphors, also requires a photo process for precise positioning.

Finally, methods are known, the basis of which is dusting or "brushing" on adhesive layers made selectively by exposure to light (see, for example, GB-PS 2 111 233A, DE-PS 29 34 929 or US-PS 4 263 385).

However, each of the methods mentioned has disadvantages.

The invention is therefore based on the object of creating a high-resolution multi-color fluorescent screen, the Rb 1 Lk / 30.7.1984 the following conditions are sufficient: the thickness of the phosphor layer should be as small as possible while at the same time having a high surface coverage density (high transparency). The highest color purity is to be achieved and in particular a combination of false colors on the surface of the layer of the respective color (electron beam - exposed side) is to be avoided. In addition, the color areas are to be separated by areas colored black to increase the contrast and to sharply separate the light-exciting electron beams for the individual colors (color purity in electron beam mode).

This object is achieved according to the invention by means of a fluorescent screen with the features of claim 1.

Further advantageous refinements or developments of the invention are the subject of additional claims 2 to 6.

With the application of the fluorescent colors, preferably the colors red, green and blue, to the fluorescent screen by screen printing, further phototechnical processes in the phosphor coating are not required and all the requirements mentioned are met.

In order to enable the successive screen printing of the different colors without damaging the previous print by the subsequent one, it is intended to protect the color areas by a mechanically stable raised (black) border. Nevertheless, it was not obvious to apply the fluorescent areas with screen printing if the black border was raised, since screen printing normally only works with direct contact on a surface. A modification of the printing technology with much smaller printing areas on the screen (stencil) than on the substrate, high squeegee printing and special flow properties of the phosphor paste made screen printing possible.

In contrast to the known shielding methods, the invention has significant advantages that can only be achieved together with the new screen printing method.

Especially for low-energy cathode ray excitation of phosphors (<10keV), but also conceivable for other applications, a phosphor layer texture is required which, with a very high surface coverage density with phosphor "bodies", optimally set size and light efficiency (grain 0.1 µm to 30 µm) depending on the type at the same time, the lowest possible layer thickness, that is, high light transparency. This is achieved by the method according to the invention by adjusting the flow properties of the phosphor paste and by precisely metering the amount per area during printing. For example, such a layer production is obviously not feasible with the known “slurry” photo technology.

At the same time, a very high level of color purity is required, especially on the surface of the applied phosphor layer, and the more imperative the lower the cathode ray excitation energy, ie the depth of penetration of electrons into the phosphor layer. For this reason, processes in which the following colors are layered on top of one another, exposed and partially removed again after application of a first color are not very suitable for producing the required color-pure layer surface.

If a sharp separation of color points is not guaranteed by a given electron beam geometry, or if "security zones" are necessary for the impinging electron beam due to the adjustment novelties of different display components to avoid false colors, or if the contrast needs to be increased, then the color areas must be separated by black colored areas (black border, "black matrix") required. For the application of fluorescent screens after the principle of the flat plasma screen, these conditions are set and are met by the proposed screen printing. In contrast to DE-OS 28 06 436, in which a black border with good adhesion is built up with the help of photo-technical measures, it is part of the shielding concept proposed here to also apply the black border made of black-colored or, during sintering, black-colored glass solder paste by means of screen printing .

As an essential point - especially when using the fluorescent screen according to the invention in display systems with exposure to high electrical field strengths - good adhesion to the substrate, in particular also for the black border, is required. The two black border variants with vapor-deposited and etched structures and according to the concept proposed here with screen printing are ideally suited for this.

This fluorescent screen is manufactured, for example, as follows: A layer is vapor-deposited on a glass plate (screen plate) of any size and thickness (flat or cylindrically curved), preferably in a layer sequence Al203-Ni-Al203-Ni (approx. One to twenty sequences of different thicknesses between 2 nm and 100nm and a Ni final layer between 20nm and 1000nm).

After loading with photoresist, exposure with a fixed structure of the black border including fixed alignment marks and development in the usual way, the vapor-deposited structure is etched off where the coating with fluorescent material is intended (creation of "windows" of any structure).

Before the phosphors are printed on, the glass is etched onto the coating surface in a manner known per se, in such a way that depressions of between 1 μm and 50 μm are formed and at the same time an etching which is as smooth as possible is achieved, for example with an etching solution of the following

Advantageous are the good anti-reflective treatment of the phosphor-coated side and the increased adhesion of the phosphor to be applied later on the roughened surface and its mechanical protection through the specified recess; Preferably, the depression sc is set so that it approximately corresponds to the later targeted luminous layer thickness, so that the surface that is as smooth as possible (field strength load) is present as the basis for the aluminization of the fluorescent screen to be applied later.

The fluorescent structure (preferably three colors: red, green, blue and, in the case of a very fine grid (<0.3 mm step), preferably a line arrangement (inline) is produced by printing the individual colors in succession, adjusted at the positions provided for this within the black border It is important that the passage of the amount of phosphor is in a precise relationship to the targeted layer thickness, the stencil area and the flow properties of the phosphor paste. An essential component of the phosphor paste is an adhesion promoter which remains in the tempered state (after the binder components have been "driven out"). An SiO ₂ coating liquid can be used, for example .. In principle, all systems are suitable as binders as long as they neither chemically damage the luminescent material nor leave annoying "residues" after the layers have been tempered, it being important to ensure that luminescent-specific maximum temperatures (in the range 380 ° C to 500 ° C) have to. Binders based on acrylate or nitrocellulose are preferably used. A preferred composition is, for example:

The thickness of the phosphor layers is set between 1 µm and 70 µm, preferably about 20 µm in the above phosphor examples. It is essential for this that the printing area on the stencil (screen) has only about 20% to 70%, preferably 40%, area opening compared to the area to be printed. The screens suitable for printing are between 165mesh and 600mesh (preferably 400mesh), depending on the resolution of the grid required.

At the end of the layer production, annealing ensures that all binder fractions are evaporated, a major advantage of the proposed screen printing process being that a very low binder fraction can be used in order to achieve a high areal density of the phosphor coating.

The fluorescent screen can also be produced in the following way: A glass solder layer with the desired structure of the black border is printed on a glass plate of any size and thickness (flat or cylindrically curved). For reasons of anti-reflective coating on the inside of the screen (to which the phosphor layer is applied), it is advisable to use the glass sets listed in the first example to produce a relatively smooth anti-reflective layer after the glass has been mechanically lapped with fine-grained silicon carbide (preferably 500 - 1000 ) was matted very evenly. This The method has the advantage that an antireflection coating on the glass side covered with phosphorus, combined with an increase in adhesive strength for applied layers, is carried out.

The desired thickness of the black border after sintering the glass solder print is between 2 µm and 60 µm. In order to achieve a black coloring of the glass solder paste, any "black dye" addition is permitted which ensures the constancy of the thermal expansion and the strength of the glass solder application after sintering. All types are generally suitable as binder systems if a complete burn-out is guaranteed at the temperature required or maximum permissible for a particular type of glass solder; a suitable glass solder mixture:

A blackening can also be supported by reducing tempering or generated alone (without "black dye").

After the completion of the black border structure, the procedure is analogous to that of the first exemplary embodiment.

The invention is further explained on the basis of the exemplary embodiments shown in the figures. Corresponding parts are provided with the same reference symbols in the figures.

• Fig. 1 den erfindungsgemäßen Leuchtschirm schematisch im Schnitt und
• Fig. 2 eine weitere Ausführungsform des erfindungsgemäßen Leuchtschirmes schematisch im Schnitt.

Show it

• Fig. 1 shows the fluorescent screen according to the invention schematically in section and
• Fig. 2 shows a further embodiment of the fluorescent screen according to the invention schematically in section.

The fluorescent screen glass 1 shown in FIG. 1 has depressions 4. The depressions 4 are approximately 10 μm to 20 μm etched into the fluorescent screen glass 1 and are preferably provided with the colors red (R), green (G) and blue (B) as the phosphor layer 6, which are screen-printed through the film 2, which has screen openings 3 is provided, applied. In this exemplary embodiment, the black border 5 is applied using photo technology (thin layer).

In the embodiment shown in FIG. 2, the black border 5 is applied in screen printing as black glass solder through the screen openings 3 in the film 2 onto the fluorescent screen glass 1, so that depressions 4 are formed which, depending on the glass solder thickness, are approximately 20 μm and for receiving the phosphor layer 6 (fluorescent screen colors).

Claims (6)

1. fluorescent screen for image display devices with a screen glass plate and a phosphor layer thereon, which is introduced into depressions which are surrounded by a black-colored contrasting border layer, characterized in that the fluorescent colors of the fluorescent layer (6), preferably the fluorescent colors red (R), Green (G) and blue (B) are applied to the screen glass plate (1) in a grid or line systematic arrangement by a screen printing process. 2. Illuminated screen according to claim 1, characterized in that the contrast border layer (5) of black colored or black sintering glass solder paste is applied by means of screen printing on the screen glass plate (1). 3. fluorescent screen according to claim 1 or 2, characterized in that the thickness of the phosphor layer (6) is between 1µm and 70µm. 4. A method for producing a fluorescent screen according to one of claims 1 to 3, characterized in that a metallic multilayer sequence is evaporated onto the screen glass plate (1), and that the evaporated structure is etched off where the coating with the phosphor layer (6) by means of a Screen printing process is carried out in recesses (4) which have previously been etched into the screen glass plate (1). 5. The method according to claim 4, characterized in that the recesses (4) of the layer thickness of the phosphor layer to be subsequently applied (6) almost correspond. 6. The method according to claim 4 or 5, characterized in that on the screen glass plate (1) a glass solder layer in the structure of the contrast border layer (5) is printed.

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