EP0170130B1 - Fluorescent screen for display units and method for its manufacture - Google Patents

Description

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

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.

From DE-A 2804127 it is known to apply phosphor to a substrate using mask screen printing. A basic mask is required for this mask screen printing and several coating masks are necessary, depending on the number of types of phosphor. It can be seen from FIG. 6 that a black border is present on the substrate. It is not described what type it is.

An electrostatic screen printing method for applying phosphor powder to a plate (16) is known from the English-language abstract of Japanese Patent Application No. 54-3463. The screen 7 produced in a special way has barrier walls 15, while the plate 16 to be printed is completely flat.

From DE-A 2540 132, a printing process is known to be 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 that are selectively “tacky” by exposure (see, for example, GB Patent 2111233A, DE-A 2934929 or US Patent 4263385).

From DE-A 1 537483 a method for producing a fluorescent screen for color picture tubes is known, in which the screen of fluorescent screen elements glowing in the primary colors are applied in a printing process. To further simplify the manufacturing process, it is proposed that the individual screens are printed on a flexible film and then this film is inserted into the tube. Various printing methods are given, e.g. also the screen printing process.

However, each of the methods mentioned has disadvantages.

The present invention is based on a fluorescent screen for image display devices known from DE-A 2806436 and 2855142. Such a fluorescent screen has a screen glass plate which has raised contrast borders or depressions for the phosphors, the contrast borders lying on the boundaries of the depressions. The phosphor is present in the depressions formed by the contrasting borders.

The invention is therefore based on the object of creating a method for producing a high-resolution multicolor fluorescent screen which satisfies the following conditions: 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 (side exposed to the electron beam) is to be avoided. In addition, the color areas should 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).

According to the invention, this object is achieved by the method specified in claim 1.

Further advantageous refinements or developments of the invention are the subject of additional claims 2 to 5.

With the application of the fluorescent colors, preferably the colors red, green and blue, to the fluorescent screen by screen printing, further photo-technical processes are not required for the phosphor coating and all of 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 technique 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 (<10 keV), 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! Jm to 30! Jm) depending on the type, the lowest possible layer thickness, i.e. 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 with the known “slurry” photo technology is obviously not feasible.

At the same time, a very high level of color purity is required, especially on the surface of the phosphor layer applied, and all the more so more imperative, the lower the cathode ray excitation energy, that is, the penetration depth of electrons into the phosphor layer. For this reason, processes in which the following colors are layered, 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 "inaccurate zones" are necessary to avoid incorrect colors due to the adjustment inaccuracies of different display components, or if the contrast needs to be increased, the color areas must be separated by black colored areas (black border, «black matrix») required. For the use of fluorescent screens based on the principle of the flat plasma screen, these conditions are met and are met by the proposed screen printing. In contrast to DE-OS 2806436, 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 solder paste or black-colored during sintering 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 is required, in particular also for the black border. 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 onto a glass plate (screen plate) of any size and thickness (flat or cylindrically curved), preferably in a layer sequence Al ₂ O ₃ -Ni-Al ₂ O ₃ -Ni (approx. One to twenty sequences of different thicknesses between 2 nm and 100 nm and a Ni final layer between 20 nm and 1000 nm).

After loading with photoresist, exposure with a defined 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).

• H₂0: 20 Vol.-% bis 90 Vol-%
• konz. H_zS0₄: 5 Vol.-% bis 40 Vol.-%
• konz. HF: 5 Vol.-% bis 30 Vol.-%

gesättigte Ammoniumfluorid-Lsg.: 0 Vol.-% bis 12 Vol.-%.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, such as, for example, B. with an etching solution of the following composition:

• H ₂ 0: 20% by volume to 90% by volume
• conc. H _z S0 ₄ : 5 vol.% To 40 vol.%
• conc. HF: 5 vol.% To 30 vol.%

saturated ammonium fluoride solution: 0 vol.% to 12 vol.%.

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; the depression is preferably set such that it approximately corresponds to the phosphor layer thickness which is subsequently targeted, so that the surface which is as smooth as possible (field strength load) is present as the basis for the aluminization of the phosphor screen to be applied later.

• Leuchtstoff: 40 Vol-% bis 90 Vol-% (z. B. 71 Vol.-%)
• Haftvermittler: 0,1 Vol.-% bis 5 Vol.-% (z. B. 0,4 Vol.-%)
• Binder: 0 vol.-% bis 20 Vol.-% (z. B. 7 Vol.-%)
• Verdünner: 10 Vol.-% bis 50 Vol.-% (z.B. 21,6 Vol.-%, z. B. Terpinöl).

The fluorescent structure (preferably three colors: red, green, blue and, in the case of a very fine grid (<0.3 mm step), preferably line arrangement (inline), is adjusted by printing the individual colors one after the other, adjusted at the positions provided within the black border, It is important that the passage of the amount of fluorescent material is in a precise relationship to the targeted layer thickness, the stencil area and the flow properties of the fluorescent material paste For example, an SiO _z coating liquid can be used. In principle, all systems are suitable as binders as long as they neither chemically damage the luminescent material nor leave any annoying "residues" after the layers have been tempered 380 ° C to 500 ° C) complied with n must be. Binders based on acrylate or nitrocellulose are preferably used. A preferred composition is, for example:

• Fluorescent: 40 vol% to 90 vol% (e.g. 71 vol%)
• Adhesion promoter: 0.1 vol.% To 5 vol.% (E.g. 0.4 vol.%)
• Binder: 0 vol.% To 20 vol.% (E.g. 7 vol.%)
• Thinner: 10 vol.% To 50 vol.% (E.g. 21.6 vol.%, E.g. terpin oil).

• z. B. Grüner Leuchtstoff: ZnS:Cu, Al, Au
• Grüner Leuchtstoff: Y₂O₂S: Tb
• Roter Leuchtstoff: Y₂O₃: Eu
• Roter Leuchtstoff: Y₂O₂S: Eu
• Blauer Leuchtstoff: ZnS: Ag

About the phosphor:

• e.g. B. Green phosphor: ZnS: Cu, Al, Au
• Green phosphor: Y ₂ O ₂ S: Tb
• Red phosphor: Y ₂ O ₃ : Eu
• Red phosphor: Y ₂ O ₂ S: Eu
• Blue phosphor: ZnS: Ag

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 165 and 600, preferably 400, number of wires per cm (165 and 600, preferably 400 mesh), depending on the required resolution of the grid.

At the end of the layer production, annealing ensures that all binder components are volatilized, whereby a major advantage of the proposed screen printing process is that a very low binder component can be used in order to achieve a high surface 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 appropriate 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 P500-P1000 according to DIN 69176) was matted very evenly. This method has the advantage that an antireflection coating of the glass side covered with phosphorus, combined with an increase in adhesive strength for applied layers, is carried out.

• Glaslot, vorzugsweise bei 430 °C
• kristallisierend aufschmelzbar:
• 50 Gew.-% bis 95 Gew.-% (z. B. 65 Gew.-%)
• «black dye» (z. B. Gemisch aus Chromoxid, Kobaltoxid, Nickeloxid, Bleioxid):
• 0 Gew.-% bis 40 Gew.-% (z. B. 15 Gew.-%) Binder auf Acrylatbasis:
• 0,1 Gew.-% bis 25 Gew.-% (z. B. 1,2 Gew.-%) Verdünner, (z.B. Terpinöl):
• 0,5 Gew.-% bis 40 Gew.-% (z. B. 18,8 Gew.-%).

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" additive is permitted that ensures the constant 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; an appropriate glass solder mixture:

• Glass solder, preferably at 430 ° C
• crystallizing meltable:
• 50 wt% to 95 wt% (e.g. 65 wt%)
• Black dye (e.g. mixture of chromium oxide, cobalt oxide, nickel oxide, lead oxide):
• 0% to 40% by weight (e.g. 15% by weight) of acrylate-based binder:
• 0.1% to 25% by weight (e.g. 1.2% by weight) of thinner (e.g. terpin oil):
• 0.5 wt% to 40 wt% (e.g. 18.8 wt%).

A blackening can also be supported by reducing tempering or generated alone (without «black dyey,).

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

Show it

• Fig. 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 as the phosphor layer 6 with the colors red (R), green (G) and blue (B), which are screen-printed by 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 exemplary 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 Fluorescent layer 6 (fluorescent screen colors) serve.

Claims (5)

1. Process for manufacturing a luminescent screen for a visual display unit with a glass plate screen and a contrast border layer situated on the said glass plate and surrounding hollows for a phosphor layer that consists of the luminous colour red, green and blue systematically arranged in a grid or line pattern, characterized in that the luminous colours (R, G, B) are applied one after the other by means of silk screen printing with a high squeegee pressure and a printing surface in the silk screen of 20% to 70% screen aperture with respect to the surface to be covered by printing.

2. Process according to Claim 1, characterized in that the thickness of the phosphor layer (6) amounts to between 1 micrometer (µm) and 70 micrometers.

3. Process according to Claim 1, characterized in that the contrast border layer is produced by means of the vacuum evaporation of a metallic multilayer sequence onto the glass plate screen (1) and that the structure deposited in this manner is removed by etching in all areas where the phosphor layer (6) is deposited into hollows (4) previously etched into the said glass plate screen (1).

4. Process according to Claim 3, characterized in that the hollows (4) correspond approximately to the thickness of the phosphor layer subsequently to be applied thereon.

5. Process according to Claim 3, characterized in that a glass soldering paste is applied by means of silk screen printing to the structure of the contrast border layer (5) on the glass plate screen (1) and accurately positioned thereon, the said paste being either black in colour or such as to turn black during the sintering.

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