WO2003100810A1

WO2003100810A1 - A phosphor screen of a cathode ray tube and a method of manufacturing same

Info

Publication number: WO2003100810A1
Application number: PCT/IB2003/001763
Authority: WO
Inventors: Ties Van Bommel; Nicolaas P. Willard; Paulus H. G. Offermans
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2002-05-24
Filing date: 2003-04-29
Publication date: 2003-12-04
Also published as: AU2003225496A1

Abstract

The invention relates to a phosphor screen of a cathode ray tube (CRT) which comprises on an inner surface of a CRT panel (11), in addition to a reflective metal back layer (15), an additional reflective metal layer (13), which covers a structured black matrix layer (12) providing a one-sided reflective film. Light generated by phosphor (14) located above the black matrix (12) will be reflected by the reflective layer (13) instead of being absorbed by the black matrix (12) as would occur for a conventional CRT without this reflective layer (13). Thus, the absorption of emitted light is decreased leading to an increase in the total amount of emitted light and improved luminance and contrast performance (LCP). The invention also relates to an inexpensive method of manufacturing a said phosphor screen. In addition, the invention relates to a CRT comprising said phosphor screen.

Description

A phosphor screen of a cathode ray tube and a method of manufacturing same

The present invention relates to a phosphor screen of a cathode ray tube (CRT) providing improved luminance and contrast performance, and a method of manufacturing same.

Furthermore, the invention relates to a CRT comprising said phosphor screen. Many different display devices, such as a television receiver, commonly utilize cathode ray tubes having luminescent phosphor screens. A conventional cathode ray tube (CRT) is shown in Fig. 1. In general, a CRT comprises a glass panel 1 , which on its inside has a phosphor screen 2. In front of the screen 2 is generally provided a perforated shadow mask 3, also called a color selection electrode. A tunneled part 4 is bonded to the panel 1 to form a vacuum bulb. An electron gun 5 is installed inside a neck 6 at the rear end of the tunneled part 4, and a deflection unit 7 is provided on the outside of the neck 6 and the tunneled part 4. Electron beams emitted from the electron gun 5 are deflected by the deflection unit 7 to land at precise locations on the phosphor screen 2, thus forming a pixel, a plurality of which form a picture. However, it should be noted that CRTs without shadow masks, sometimes referred to as beam indexing CRTs or intelligent tracking CRTs, are also known (not shown or further described)). Fast intelligent tracking CRTs are also referred to as FIT tubes. Principally, there are two different categories of intelligent tracking CRTs, i.e. single beam systems with only one electron gun and multi-beam systems with several electron guns. For a color CRT, the phosphor screen includes red, green and blue phosphor layers (e.g. phosphor stripes or dots).

In general, the phosphor screen comprises a structured light absorbing carbon (graphite) layer, also called a black matrix, which is formed between the respective phosphor elements, and a reflective metal back layer, typically made of aluminium. By segregating the red, blue and green light-emitting phosphor elements, the black matrix increases the contrast of the picture.

Electrons emitted from the electron gun pass through the perforations in the shadow mask (if a shadow mask is present) to selectively excite the separated phosphor elements. When the emitted electrons hit and excite the phosphor (or an activator element incorporated in the phosphor), light energy in the form of photons are emitted, which travel in various directions out of the phosphor, upwards, downwards and sideward. Light emitted in the direction of the viewing glass panel is seen by the viewer. However, some light is emitted in other directions away from the viewing panel. The reflective metal back layer then acts to redirect or reflect this light towards the viewing panel.

In current TV tubes, a flat reflective aluminium layer is often used. This flat layer reflects the light back to the openings in the black matrix, i.e. this light is seen by the viewer, and to the light-absorbing black matrix. Since the phosphor lines or dots are not optically separated when a flat metal layer is used, color contamination problems, for instance red light, may occur in a green color line, and internal light reflection may occur. Furthermore, light emitted sideward is lost with regard to luminance and contrast performance (LCP).

It is known in the art to use a dome-shaped reflective metal back layer to overcome said problems associated with flat metal back layer. In comparison with a planar reflective back layer, a dome-shaped metal back layer improves the display brightness and luminance since the internal reflection and absorption of light is decreased. Furthermore, the risk of color contamination is eliminated. For instance, US 5 097 175, US 5 547 411 and US 5 489 816 describe such dome-shaped reflective metal back layers forming optically separated light cavities. Color contamination might also be reduced using pigmented phosphor, i.e. blue light, for instance, will then be absorbed by the red pigment in the red light emitting phosphor.

There are also other factors affecting color contamination, such as the spot size of the electron beam, the light scattering power of the phosphor, the size of the phosphor lines or dots, and the reflectivity of the reflective metal back layer.

However, in practice the phosphor 8 is not only contained within the lines or dots formed by the black matrix 9, but some phosphor 8 is also on top of the black matrix 9 as illustrated in Fig. 2. The prior art phosphor screen 2 shown in Fig. 2 is provided on a panel 1 as disclosed above, and has a dome-shaped reflective metal back layer 10. The light generated by the phosphor above the black matrix 9 is mostly absorbed by the black matrix 9, as illustrated in Fig. 2, and consequently this light does not add to the luminance and contrast performance (LCP). Thus, the black matrix 9 provides contrast, but reduces the luminance by absorbing some of the emitted light. An object of the present invention is to alleviate the above problems and to provide a method of manufacturing a phosphor screen of a cathode ray tube having improved luminance and contrast performance (LCP). Another object of the present invention is to alleviate the above problems and to provide a phosphor screen of a cathode ray tube (CRT), in particular a color cathode ray tube, having improved luminance and contrast performance (LCP).

Still another object of the present invention is to alleviate the above problems and to provide a cathode ray tube with improved luminance and contrast performance (LCP) which comprises said phosphor screen.

According to a first aspect of the invention, these and other objects are achieved with a phosphor screen which comprises on an inner surface of a CRT panel a structured black matrix layer, a phosphor layer, and a reflective metal back layer (herein also referred to as top layer), wherein a one-sided reflective film is provided by said black matrix layer covered by an additional reflective metal layer (herein also referred to as bottom layer).

The reflective bottom layer is preferably made of aluminium. Aluminium is highly reflective, and stable in contact with phosphor. Furthermore, aluminium is in general used for the reflective back layer, which means that good compatibility will be provided between the aluminium bottom layer and the aluminium top layer. Light generated by the phosphor located above the black matrix will, in the phosphor screen according to the present invention, be reflected by the reflective bottom layer which covers the structured black matrix instead of being absorbed by the black matrix as would occur in the conventional prior art CRT described above. This reflected light is then reflected again by the top layer and is eventually emitted through the openings in the black matrix. The absoφtion of emitted light is decreased which leads to an increase in the total amount of emitted light. Thus, the luminance and contrast performance are improved for a CRT having a phosphor screen according to the present invention in comparison with a conventional CRT (both with a flat and a dome-shaped reflective metal back layer).

A CRT (with a flat top layer) comprising a phosphor screen having a reflective bottom layer as described above will provide an increase in LCP, preferably an average increase of at least about 5%, as compared to a conventional CRT (with a flat top layer). Preferably, optically separated light cavities having light-emitting phosphor are provided by said, preferably structured, one-sided reflective film, comprising a reflective metal layer (bottom layer) together with a reflective metal back layer (top layer). This reflective metal back layer is preferably dome-shaped, but might also be rectangular or any other shape. As disclosed above, the total light output is further increased using a dome-shaped reflective top layer in comparison with a flat top layer. The use of light cavities also decreases the risk of color contamination, which might otherwise occur using said reflective bottom layer. However, potential problems with color contamination might also be effectively solved using pigmented phosphor, in combination with a dome-shaped reflective top layer or alone.

A CRT having a phosphor screen which comprises a reflective bottom layer as described above and a dome-shaped top layer, instead of a flat top layer, will give a further increase in LCP, preferably an additional average increase of at least about 5%. Thus, according to a second aspect of the invention, said object and other objects are achieved with a CRT, which comprises a phosphor screen as described above.

According to a third aspect of the invention, said object and other objects are achieved with a method for manufacturing a phosphor screen of a CRT having improved luminance and contrast performance (LCP) comprising: providing a one-sided reflective film comprising a reflective metal layer covering a black matrix layer on an inner surface of a CRT panel, and applying phosphor on said panel surface comprising said film. This method is easily performed and inexpensive, and provides a phosphor screen of a CRT having improved LCP without additional expensive processes compared to conventional techniques.

Preferably, the method comprises a step wherein structuring of the black matrix and the metal layer is performed simultaneously, before applying the phosphor. Thus, only one photolithographic lift-off step is necessary.

The reflective metal layer is preferably provided and structured by: applying a metal flake suspension comprising a binder forming a metal/binder layer on a black matrix layer applied on a patterned photoresist layer on an inner surface of a CRT panel, adding a photoresist swelling agent so that the photoresist becomes swollen and partially breaks the black matrix layer and the metal/binder layer, and removing said swollen photoresist together with portions of the black matrix layer and the metal layer overlying the swollen photoresist, wherein the remaining portions of said layers provide a structured one-sided reflective film comprising light-absorbing black matrix and reflective metal. After applying the phosphor, a reflective metal back layer is preferably applied forming a final phosphor screen, preferably an aluminium back layer.

As outlined above, the metal flake suspension preferably is an aluminium flake suspension. The metal flakes are preferably smaller than 500 μm as the stability of the metal flake suspension decreases as the flake size increases. More preferred is an aluminium flake size smaller than 100 μm.

Preferably, the binder comprises at least one polymer, or a combination of polymers, having good film-forming properties, such as a polybutyral, poly(vinyl pyrrolidone), poly(vinyl acetate), 2-hydroxyethyl cellulose, poly(vinyl alcohol), and poly(acryl amide).

Furthermore, the binder preferably comprises at least one polymer, or a combination of polymers, having acidic groups, most preferably carboxyl groups (-COOH), such as poly(tert-butylacrylate-co-ethylacrylate-co-methacrylic acid), carboxymethyl cellulose sodium salt, and cellulose acetate trimellitate.

Combined polymers having good film-forming properties and comprising acidic groups, such as poly(vinyl acetate-co-crotonic acid), poly(styrene-co-maleic acid), poly(acrylamide-co-acrylic acid), may also be used.

The amount of carboxyl groups is preferably about 0.01-80% (w/w), more preferably about 10- 15% (w/w).

The acidic groups of the binder will react with dissolved aluminium salts and form a cross-linked polymer matrix of metal complexes. This cross-linked polymer matrix provides an insoluble (e.g. in water) and mechanically stable layer.

The metal flake suspension is, for instance, spin coated on the black matrix layer. Examples of other application methods are spraying and flow coating (slow spin coating).

To improve the adhesion between the black matrix and the metal layer, an adhesion improving layer of a polymer comprising carboxyl groups, such as a poly(acrylic acid), might advantageously be applied on top of the black matrix layer before applying the metal layer.

The present invention also relates to a CRT, which comprises a phosphor screen manufactured as described herein. In addition to improved LCP, an advantage of the invention is that the structured film comprising at least said black matrix and reflective metal layer is made with only one photolithographic lift-off step.

Another additional advantage of the invention is that the film is applied by, for instance, spin coating using an easily made and inexpensive suspension, which relatively to the conventional evaporation process for application of a reflective top layer is a rather inexpensive process.

Furthermore, the method according to the invention is easy to introduce in the ordinary production process of CRTs. Other features and advantages of the present invention will become apparent from the embodiments described hereinafter and the appended claims.

Fig. 1 schematically shows the construction of a commonly used CRT. Fig. 2 schematically shows a part of a phosphor screen of a CRT according to prior art.

Fig. 3 schematically shows a part of a phosphor screen in accordance with an embodiment of the present invention.

Fig. 4 shows the method steps in accordance with an embodiment of the present invention for manufacturing a phosphor screen of a CRT shown in Fig. 3.

A part of a phosphor screen comprising a reflective bottom layer according to an embodiment of the invention is shown in Fig. 3. The phosphor screen in Fig. 3 is present on an inner surface of a glass panel

1 1 , and comprises a structured, one-sided reflective, double-layered film of a structured black matrix layer 12 located on the panel 11 and a similarly structured reflective metal layer 13 constituting a reflective bottom layer, preferably made of aluminium. Phosphor 14 is provided in the openings of the double-layered film. A reflective dome-shaped metal back layer 15, which constitutes a reflective top layer, covers the phosphor 14 and is in contact with at least a part of the double-layered film.

The term "film" as used herein means a continuous or discontinuous coating. By a discontinuous film is meant that the film is broken in accordance with a pattern, i.e. a structured film which provides lines or dots without film. A film may comprise one or more layers. Consequently, a layer may also be structured.

The one-sided reflective film disclosed herein comprises preferably at least two layers, i.e. black matrix and metal, but could also comprise any additional layer(s) between these two layers.

As illustrated in Fig. 3, the light generated by the phosphor 14 located above the black matrix 12 will be reflected by the reflective bottom layer 13 instead of being absorbed by the black matrix 12 as would occur for the conventional prior art phosphor screen described above. This reflected light is then reflected again by the top layer 15 and is eventually emitted through the openings in the black matrix 12. The absorption of emitted light is decreased which leads to an increase in the total amount of emitted light. Thus, the luminance and contrast performance are on average improved by at least about 10%, such as 14%, for a CRT according to the embodiment of the present invention described herein in comparison with a conventional CRT having a flat metal back layer (top layer). The phosphor screen shown in Fig. 3 is preferably made in a process implementing a method according to an embodiment of the invention, which steps are shown in Fig. 4 and outlined below.

First, a standard, water-based photosensitised resist 16, for instance comprising poly(vinyl pyrrolidone) (PVP) and photosensitive bisazide, is applied on an inner surface of CRT glass panel 11 (step A in Fig. 4). This layer 16 is thereafter exposed to UV light through a shadow mask as a result of which the exposed areas are cured. The unexposed and unhardened areas are washed away with water and the remaining pattern 16 is dried. Thus, a resist pattern 16 is formed (step B in Fig. 4).

On top of the entire surface including both the photocured pattern 16 and the uncovered areas of the panel 1 1 , a graphite suspension is applied and dried, thus forming a black matrix layer 12 (step C in Fig. 4).

On top of the non-structured black matrix 12, a layer 13 of metal flakes suspended in water or any other solvent, such as ethanol, together with a binder is applied by slow spin coating (step D in Fig. 4). The photoresist pattern 16 is then swollen by a photoresist swelling agent, such as sulfamic acid or nitric acid. 5% sulfamic acid is preferred when an ethanol suspension is used and 5% nitric acid is preferred when an aqueous suspension is used. During this step, the graphite layer 12 and the metal/binder layer 13 become strongly interlinked and form an insoluble film, i.e. insoluble in, for instance, water or 5% nitric acid. At the same time, the double-layered film is partially and broken open in accordance with a pattern by the swollen resist dots 16' (step E in Fig. 4).

The swollen resist dots 16' and the black matrix 12' and the metal flakes 13' overlying the swollen resist 16' are then jointly removed by a high pressure water jet. A structured, one-sided reflective, double-layered film having dots or stripes corresponding to the perforations of the shadow mask is obtained (step F in Fig. 4).

These dots or stripes are then filled with phosphor 14 of said three colors in a manner known to persons skilled in the art. It may be noted that the phosphor 14 has a better adhesion to the aluminium layer 13 than to the black matrix 12. A reflective metal back layer 15, preferably dome-shaped, is then provided using any suitable process.

In one of the last steps in the production of the CRT, the CRT, including said double-layered film, is annealed at about 450°C to pyrolyse all organic compounds. The binder in the metal/binder layer is then pyrolysed leaving a structured pure metal layer 13. The essence of the process described herein is the use of the right binder. The binder is a polymer, or a combination of polymers, which is soluble in alkaline water or in the solvent used, for instance ethanol, and which does not form insoluble metal complexes and which becomes insoluble when exposed to acidic water. The polymer should also have good film-forming properties, and such a film should in addition be permeable to water. Furthermore, the film should be mechanically stable during the removal of the resist dots by a pressurized water jet, and it should leave no residue after a final anneal step at about 450°C.

The solvent of the metal flake suspension is preferably water, since water is more environmentally desirable and more inexpensive to use than other solvents, such as ethanol. A preferred binder composition is a combination of a good film-forming polymer, such as polybutyral, and a polymer having acidic groups, such as carboxyl (- COOH), sulfonic acid (-SO₃H), phosphor containing acidic groups, e.g. phosphinic acid groups (-PO(OH)₂), or phenol (-C₆H₄OH) groups. These acidic groups will interact with the metal flakes and react with dissolved aluminium salts forming a cross-linked polymer matrix of metal complexes during the addition of the photoresist swelling agent, thus providing the closely interlinked double-layered film.

The acidic groups are preferably carboxyl groups, since polymers comprising carboxyl groups are less inclined ton form insoluble metal complexes in comparison to other acidic polymers. Furthermore, films formed of polymers comprising carboxyl groups are often more mechanically stable than films formed of other acidic polymers. In addition, sulfonic and phosphinic acid groups are often not completely removed during the annealing step.

Examples of polymers having good film-forming properties and which may be used in ethanol suspensions are polybutyral, poly( vinyl pyrrolidone), poly(vinyl acetate), and 2-hydroxyethyl cellulose.

Examples of polymers having good film-forming properties and which may be used in aqueous suspensions are poly(vinyl pyrrolidone), poly(vinyl alcohol), and poly(acryl amide). Examples of polymers having acidic groups and which may be used in an ethanol suspension are co-polymers comprising methacrylic acid, such as poly(tert- butylacrylate-co-ethylacrylate-co-methacrylic acid).

Examples of polymers having acidic groups and which may be used in aqueous suspensions are carboxymethyl cellulose sodium salt and cellulose acetate trimellitate.

Examples of polymers having good film-forming properties and comprising acidic groups, and which may be used in ethanol suspensions, are poly(vinyl acetate-co- crotonic acid) and poly(styrene-co-maleic acid).

An example of a polymer having good film-forming properties and comprising acidic groups, and which may be used in an aqueous suspension, is poly(acrylamide-co- acrylic acid).

The amount of acidic groups is also important. A polymer with a high degree of carboxyl groups, such as poly(acrylic acid), often gives insoluble metal complexes and an unstable suspension. The concentration of carboxyl groups should be about 0.01-80% (w/w), preferably about 10-15% (w/w).

The adhesion of the metal flakes on the graphite layer may be further improved by applying a thin layer of a polymer containing carboxyl groups on top of the graphite layer before applying the metal layer. This polymer could either be the same as the one used in the binder composition or it could be a different one. For instance, poly(acrylic acid) may be used in the formation of this adhesion improving film.

The invention will now be further illustrated by means of the following non- limiting examples. Example 1 : An ethanol suspension

2.00 g of a 20%o (w/w) suspension of aluminium flakes (Metalure W-2002, article no 50635) in ethanol was mixed with 0.67 g of a 4% (w/w) solution of poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) (Aldrich, article no 41843-9) in ethanol and 1.33 g of a 2% (w/w) solution of poly(tert-butyl acrylate-co-ethyl acrylate-co-methacrylic acid) (Aldrich, article no 44479-0). This suspension was stirred over night.

The ratio of aluminium to polymers in this suspension is about 7,5:1. For a CRT, it is desirable to obtain the thinnest possible but still optically dense aluminium flake layer 13. The mass average molecular weight of the poly(vinyl-butyral-co-vinylalcohol- co-vinylacetate) used is about 70-100 000 g/mol, the vinyl butyral content is about 80% (w/w), the vinyl alcohol content is about 18-20% (w/w), and the vinyl acetate content is about 0-1.5% (w/w).

The poly(tert-butylacrylate-co-ethylacrylate-co-methacrylic acid) comprises on average about 23% methacrylic acid, i.e. the polymer comprises about 12% carboxyl groups.

On top of a non-structured black matrix 12 (about 0.8 + 0.1 μm) having a resist pattern 16 underneath (formed as described above), a thin layer (less than 100 nm) of 100% poly(tert-butylacrylate-co-ethylacrylate-co-methacrylic acid) was applied and dried (this layer is not shown in Fig. 4).

The suspension comprising the aluminium, polybutyral and carboxyl- containing copolymer was then spin coated at about 150 rpm for about 30 s on top of said thin film on top of said non- structured black matrix 12. The applied film 13 was then dried at about 40°C in an oven for about 5 min. The aluminium flake layer 13 was about 0.5 + 0.2 μm thick. However, this thickness is reduced during the final annealing step.

To swell the resist pattern 16 use was made of 5% sulfamic acid, pH about 1, at about 45°C for about 5 min, and the swollen resist dots 16', together with the black matrix 12' and the metal flakes 13' on top of the resist 16', were then jointly removed using a high pressure water jet spray from a Spraying Systems Autojet 125AF rig. The water pressure was about 2.4 bar, the air pressure about 1.0 bar and the distance between the panel 11 and the gun was on average about 5 cm.

The lines or dots between the structured double-layered film were then filled with red, green and blue phosphor 14 in a manner known to persons skilled in the art. Subsequently, a reflective metal back layer 15 (top layer) is applied by any conventional process, such as an evaporation process, for the formation of light cavities.

The reflective back layer 15 is preferably an aluminium layer with a thickness of maximally 300 nm. In one of the last steps in the production of the CRT, the CRT, including said double-layered film, was annealed at about 450°C to pyrolyse all organic compounds. The binder in the metal/binder layer 13 was then pyrolysed leaving a structured pure metal layer 13 of reduced thickness. Example 2: An aqueous suspension 4.10 g of a 7.5% (w/w) aluminium flake suspension comprising 13.5% (w/w) polyurethane in water (Eckart Ultrastar Aqua FP-4100) was mixed with 1.49 g of a 5.2% (w/w) solution of poly(vinyl alcohol)(Merck), 0.56 g 3.0% (w/w) Rohagit SD-15 (Rohm & Haas), 0.27 g 11.0% (w/w) Tween 20 (Aldrich), 4.61 g water, and 0.21 g 5% (w/w) ammonia. This suspension was vigorously stirred for 15 min. Rohagit SD-15 is a polyacrylate comprising carboxyl groups. It both contributes to the formation of aluminium complexes and increases the viscosity of the suspension.

Tween 20 is a polysorbate acting as a surface-active agent.

The average dimension of the aluminium flakes in Eckart Ultrastar Aqua FP- 4100 is about 12-14 μm with a flake thickness of 30 nm.

The ratio of aluminium to polymers is in this suspension about 1 :2.

A too low concentration of poly( vinyl alcohol) (PVA) leads to poor film formation and a non-uniform layer. However, a too high concentration of PVA gives a flake layer, which is fragile during treatment with the water jet. The poly(vinyl alcohol) used above has a molecular weight of 72 000 g/mol and a hydrolysis grade above 88%.

The molecular weight and the hydrolysis grade of the PVA are important characteristics. If a polymer having a too low molecular weight is used, the resulting layer becomes fragile. If a polymer having a too high molecular weight is used, it becomes difficult, or even impossible, to structure the resulting layer. Thus, the molecular weight should be higher than 16 000 g/mol, but lower than 250 000 g/mol. The most preferred molecular weight range is about 70 000-80 000 g/mol.

A hydrolysis grade above 88% is preferred, and most preferred is a hydrolysis grade of about 98%. A preferred pH range for the suspension is 4-9, and most preferred is pH 7-9. The suspension is not stable above pH 10.

The above aluminium flake suspension was spin coated at 300 φm for 5 s followed by 55 s at 500 φm on top of a non-structured black matrix 12 (about 0.8 + 0.1 μm) having a resist pattern 16 underneath (formed as described above). The applied film 13 was then dried at about 50°C in a hot air oven for about 15 min. The aluminium flake layer 13 was about 1.0 + 0.2 μm thick. However, this thickness is reduced during the final annealing step.

To swell the resist pattern 16 use was made of 5% nitric acid at room temperature for about 5 min, and the swollen resist dots 16', together with the black matrix 12' and the aluminium flakes 13' on top of the resist 16' were then jointly removed using a high pressure water jet spray from a Spraying Systems Autojet 1250 AF rig. The water pressure was about 5 bar.

The lines or dots between the structured double-layered film were then filled with red, green and blue phosphor 14 in a manner known to persons skilled in the art.

Next, a reflective aluminium back layer 15 (top layer) is applied by any conventional process, such as an evaporation process, for the formation of light cavities.

The reflective back layer 15 is preferably an aluminium layer with a thickness of maximum 300 nm. In one of the last steps in the production of the CRT, the CRT, including said double-layered film, is annealed at about 450°C to pyrolyse all organic compounds. The binder in the metal/binder layer 13 was then pyrolysed leaving a structured pure metal layer 13 of reduced thickness.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to persons skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

The reflective bottom layer disclosed herein, i.e. the structured film comprising black matrix and reflective metal, may, for instance, also be used as a reflective layer in a FIT tube.

Claims

CLAIMS:

1. A method of manufacturing a phosphor screen of a cathode ray tube (CRT), characterized in that the method comprises: providing a one-sided reflective film comprising a reflective metal layer covering a black matrix layer on an inner surface of a CRT panel, and - applying phosphor on said panel surface comprising said film.

2. A method according to claim 1, comprising the simultaneous structuring of the black matrix and the metal layer before applying the phosphor.

3. A method according to claim 2, wherein the reflective metal layer is provided and structured by: applying a metal flake suspension comprising a binder forming a metal/binder layer on a black matrix layer applied on a patterned photoresist layer on an inner surface of a

CRT panel, - adding a photoresist swelling agent so that the photoresist becomes swollen and partially breaks the black matrix layer and the metal/binder layer, and removing said swollen photoresist together with portions of the black matrix layer and the metal layer overlying the swollen photoresist, wherein the remaining portions of said layers provide a structured, one-sided reflective film comprising light-absorbing black matrix and reflective metal.

4. A method according to claim 3, further comprising applying a reflective metal back layer after applying the phosphor.

5. A method according to claim 3 or claim 4, wherein the metal flake suspension is an aluminium flake suspension.

6. A method according to any one of claims 3-5, wherein the binder comprises at least one polymer, or a combination of polymers, having good film-forming properties.

7. A method according to claim 6, wherein the binder comprises at least one polymer, or a combination of polymers, having acidic groups.

8. A method according to claim 7, wherein said acidic groups are carboxyl groups.

9. A method according to any one of claims 2-8, wherein the metal flake suspension is spin coated on the black matrix layer.

10. A method according to any one of claims 1-9, further comprising applying an adhesion improving layer of a polymer comprising carboxyl groups on top of the black matrix layer before applying the metal layer.

1 1. A phosphor screen of a cathode ray tube (CRT) comprising on an inner surface of a CRT panel a structured black matrix layer, a phosphor layer and a reflective metal back layer characterized in that a one-sided reflective film is provided by said black matrix layer covered by an additional reflective metal layer.

12. A phosphor screen according to claim 11, wherein the metal is aluminium.

13. A phosphor screen according to claim 11 or claim 12, wherein said film and said reflective metal back layer provide optically separated light cavities having light- emitting phosphor.

14. A phosphor screen according to claim 13, wherein said reflective metal back layer is dome-shaped.

15. A cathode ray tube (CRT) characterized in that it comprises a phosphor screen according to any one of claims 11-14.

16. A cathode ray tube (CRT) characterized in that it comprises a phosphor screen manufactured according to any one of claims 1-10.