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(11) | EP 0 795 192 B1 |
| (12) | EUROPEAN PATENT SPECIFICATION |
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| (54) |
METALLIZATION OF PHOSPHOR SCREENS METALLISIERUNG VON PHOSPHOR-SCHIRMEN METALLISATION D'ECRANS FLUORESCENTS |
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| Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). |
[0001] The present invention relates to a process of metallizing phosphor screens, in particular for cathode ray tubes (CRTs).
[0002] The electron permeable, light reflecting aluminium film on the target side of the phosphor screen of a CRT is formed by the evaporation of aluminium onto a smooth film of an organic material formed over the surface of a phosphor screen. This smooth film is subsequently burnt out to leave a mirror-like film of aluminium "tenting" across the top of the phosphor screen.
[0003] Various processes for metallizing phosphor screens have been proposed in the prior art and these can generally be classified as solvent based systems and aqueous based systems.
[0004] In the solvent based system, the phosphor layer is first wetted with an aqueous based pre-wet and a solvent based lacquer, comprising an approximately 2% solution of a polymer such as poly(iso-butylmethacrylate) in a solvent such as toluene, is floated on the top of the pre-wet. The water and solvent are removed by heating leaving a film of the polymeric material approximately 1µm in thickness.
[0005] The major disadvantage of this approach is that it involves the use of large quantities of volatile organic solvents, such as toluene, with all the associated environmental concerns.
[0006] Aqueous based systems are described in US-A-3067055, US-A-3582389 and US-A-3582390 in which a water-based emulsion of a water insoluble, film forming resin such as an acrylate resin copolymer is coated onto the phosphor screen, the coating is dried, the coated layer is metallized, and the coating of the resin film volatilized by heating at a temperature of up to about 450°C. The emulsion contains about 5 to 20 weight percent of the resin. In the latter patent specification hydrogen peroxide is added to the emulsion, whereby it is stated that the tendency of the metal layer to blister over the phosphor screen area during the baking-out step is reduced.
[0007] One disadvantage of the aqueous based system is that the dispersion fills all of the spaces between the phosphor strips or dots and is thus a thicker layer than in the solvent based system. Accordingly, the amount of polymer left on the screen is greater than utilized in solvent based processes and is therefore more difficult to remove. Consequently, increased energy requirements may result from the application of extended or even multiple burn out steps.
[0008] In the solvent based system as described generally above the polymer film solution and the aluminium are applied to the phosphor screen and then the funnel of a CRT is attached to the screen with a glass frit in an organic binder. It is possible to remove both the polymer film and the organic binder in one heating cycle.
[0009] In the aqueous based systems the quantities of polymer to be removed are such as to generally necessitate the bake out of the polymer film before the addition of the funnel of a CRT. Therefore two heating cycles are required with increased energy costs, and greater investment required in the number of ovens and thus also the space required on the manufacturing site. Alternatively, an oxygen rich environment may be used to bake out the polymer in one heating cycle. This approach involves increased equipment costs and the requirement of oxygen.
[0010] Another approach described in the prior art for metallizing phosphor screens is described in US-A-3910806. In the method as disclosed a thin layer of a metal such as aluminium is applied to the phosphor screen of a cathode ray tube by the transfer of a metal layer formed on a substrate directly to the phosphor layer on the phosphor screen. The metal layer is adhered to the phosphor layer by means of a pressure sensitive adhesive and the substrate which is releasably attached to the metal layer is then removed.
[0011] DE-A-3321396 discloses the application of an organic layer to a phosphor screen followed by an aluminium layer with removal of the organic layer by heating.
[0012] EP-A-0382554 discloses a method for forming a metal backed layer using a metal film transferring sheet. The method involves forming a metal film on a mold-releasable sheet and either transferring the metal film to a phosphor screen, or forming a phosphor screen on the metal film and then transferring the composite onto a face plate with subsequent removal of the mold-releasable sheet.
[0013] We have now developed a process of metallizing phosphor screens which is more energy efficient than the aqueous based systems of the prior art which does not involve the use of organic solvents, as in the solvent lacquers, and which does not involve the use of a pressure sensitive adhesive and the complicated transfer mechanism described in the prior art.
[0014] Accordingly, the present invention provides a process for the metallization of a phosphor screen which process comprises the steps of:
either
a) applying to a phosphor screen a preformed film of a polymeric material which volatilizes at a temperature of below 450°C, the preformed film having a layer of metal deposited on one side thereof, to form a composite;
orb) applying to a phosphor screen a preformed sandwich of aluminium between two layers of a polymeric material;
andc) heating the composite formed in step (a) or step (b) to a temperature above the decomposition temperature of the polymeric film in order to decompose and/or volatilise the polymeric film coating.
[0015] The films described in (a) above can be applied with the aluminium layer directly in contact with the phosphors on the TV screen, or, with the polymer layer directly in contact with the phosphors on the TV screen. The advantage of the first approach is that there is no polymer layer between the aluminium layer and the phosphors. As a result, the aluminium layer is directly in contact with the phosphors and there is a much reduced chance of the aluminium film blistering during the burn out step. Additionally, since the polymer burns out above the aluminium layer a thicker and hence mechanically stronger polymer backing layer can be used to transfer the delicate aluminium layer to the phosphor screen. This facilitates the ease of application of the pre-formed aluminised film to the phosphor screen.
[0016] The advantage of using the sandwich approach (b) is that the important aluminium layer is fully protected. In step (b) the polymeric material used on either side of the aluminium layer may be the same or different.
[0017] The film of the polymeric material which is used in the process of the invention preferably has a thickness in the range of from 0.1 to 10µm, or a film area density of from 0.1 to 10 mg/cm2 or more preferably 0.1 to 3.0 mg/cm2.
[0018] A conventional solvent based lacquer will give a film in the order of one micrometre thickness.
[0019] The polymeric film is a film which decomposes and/or volatilizes at a temperature of below 450°C. Suitable polymeric films comprise poly(acrylate), poly(methacrylate) poly(hydroxyalkanoate) poly(carbonate), poly(ethyleneoxide)-poly(propyleneoxide) block copolymer, poly(alpha-methylstyrene), hydroxypropyl cellulose, methylcellulose, hydroxypropyl methyl cellulose, alginic acid or an associative thickener, such as Rheox (Registered Trade Mark) from Rohm and Haas and Rheovis from Allied Colloids.
[0020] The preferred polymeric film material for use in the present invention comprises a film of a poly(hydroxyalkanoate), preferably poly(3-hydroxybutyrate), poly(3-hydroxyvalerate), or a copolymer of 3-hydroxybutyric acid and 3-hydroxyvaleric acid. Suitable copolymers may comprise, for example 60 to 90% by weight of 3-hydroxybutyric acid and 40 to 10% by weight of 3-hydroxyvaleric acid. Suitable poly(hydroxyalkanoates) for use in the present invention are supplied in granular form or in the form of a latex under the Trade Name Biopol (Zeneca Specialities).
[0021] Biopol films are available from Goodfellow Limited, or can be prepared from Biopol in granular form such as by the methods as disclosed in WO94/00163, EP-A-0226439, WO91/13207 and DE-A-4040158. They can also be formed from a Biopol latex.
[0022] Optionally the following materials can be formulated into the polymeric film; hydrogen peroxide, ammonium oxalate or the boric acid complex of poly(vinyl alcohol). These materials are used to prevent blisters on the metal film caused by the evaporation of the polymer during the burn out cycle. Additionally, appropriate plasticisers such as phthalates and glycolates may be incorporated to reduce the brittleness of the polymer film.
[0023] A metal layer may be deposited onto the film coated screen according to techniques known in the art. For the production of CRTs the metal layer is aluminium which is preferably deposited onto the phosphor screen by vacuum evaporation. The aluminium layer preferably has a thickness in the range of from 0.1 to 0.3µm.
[0024] Alternatively, the film of the polymeric material may be metallized on one side thereof to form a laminate which is applied to the phosphor screen to form a composite, or the film of the polymeric material may be metallised on one side and an additional polymeric film applied to form a three layered laminate which is applied to the phosphor screen in the form of a composite.
[0025] The application of the preformed film or the metallized polymeric film to the phosphor screen may be carried out by any suitable technique. It may be advantageous to pre-wet the phosphor screen, for example with a sodium silicate based aqueous solution, in order to assist in the even and uniform application of the film on the phosphor screen.
[0026] The composite formed either in step (a) or step (b) of the method of the invention is then heated to a temperature above the decomposition and/or volatilization temperature of the polymeric film to burn out the polymeric film. The preferred polymeric films for use in the present invention will decompose on heating to leave no residue, preferably at a temperature of below 350°C.
[0027] In putting the process of the present invention into practice, the heating of the composite in step (c) may be combined with the step of sealing the funnel of a cathode ray tube to the phosphor screen, i.e. a separate baking step to volatilise the polymeric film coating becomes unnecessary. The sealing of a cathode ray tube funnel to a metallized phosphor screen is well known in the art, the seal generally being effected by using a frit sealing process in which a glass frit in an organic binder is used to seal the components together. The oxygen which is present in the cathode ray tube is generally sufficient to assist in the burn out of the polymeric film coating, although it will be understood that additional air or oxygen-enriched air may be introduced into the cathode ray tube, as necessary. The frit sealing of the metallized phosphor screen to the cathode ray tube will generally occur at a temperature of about 450°C. The conventional temperature profile for the sealing cycle is termed a Lehr cycle.
[0028] The present invention also includes within its scope a phosphor screen which has been metallized by the process of the invention and a cathode ray tube which includes at least one phosphor screen which has been metallized by the process of the invention.
[0029] The present invention will be further described with reference to the following Examples in which the following definitions are used.
Lehr Cycle
[0030] The Lehr cycle used in the following Examples is as follows: heat from room temperature to 450°C at 10°C/min, hold at 450°C for 45 minutes and then cool to room temperature.
Aluminised
[0031] Aluminised refers to the vapour deposition of a 1 inch piece of 99.99% pure aluminium wire (0.58 mm diameter) at 1.5 x 10-5 mbar using an Edwards coating system E306A (Registered Trade Mark) to produce an aluminium coating on the substrate.
EXAMPLE 1
The preparation of pre-formed aluminised from 1µm mean particle size Biopol latex
[0032] A 7.6cm x 7.6cm (3" x 3") square piece of glass plate was spun horizontally on its axis at a rate of 160 rpm for 20 seconds. During this time, ca 10 ml of 29% solids containing Biopol latex (supplied by Zeneca Specialities, Batch Number: BPL No. 505/1001) was slurried directly onto the spinning glass slide. The glass slide was spun again for a further 20 seconds at 160 rpm to remove any excess latex and to leave a thin even thickness wet latex coat on the glass slide. The slide was dried at room temperature to leave a translucent plastic coating on the slide (film area density = 0.34 mg/cm2). The plastic film was aluminised and then peeled off the slide ready for further use.
The aluminisation of TV screens using pre-formed aluminised and non-aluminised Biopol films made from 1µm mean particle size Biopol latex
EXAMPLE 2
[0033] A piece of colour TV screen was pre-wetted using an aqueous sodium silicate based pre-wet. Whilst the screen was still wet, a piece of pre-formed aluminised film as made in Example 1 was placed onto the phosphor screen with the aluminised side of the film facing away from the phosphors. The screen was dried at room temperature and heated under the conditions of the Lehr cycle to leave an aluminium film adhering to the phosphors.
EXAMPLE 3
[0034] A piece of colour TV screen was pre-wetted using an aqueous sodium silicate based pre-wet. Whilst the screen was still wet, a piece of pre-formed aluminised film as made in Example 1 was placed onto the phosphor screen with the aluminised side of the film facing towards the phosphors. The screen was dried at room temperature and heated under the conditions of the Lehr cycle to leave an aluminium film adhering to the phosphors.
EXAMPLE 4
The preparation of pre-formed aluminised films from 0.5µm mean particle size Biopol latex
[0035] A 7.6cm x 7.6cm (3" x 3") square piece of glass plate was spun horizontally on its axis at a rate of 160 rpm for 20 seconds. During this time, ca 10 ml of 41% solids containing Biopol latex (supplied by Zeneca Specialities, Batch Number: BPL No. 510/0301) was slurried directly onto the spinning glass slide. The glass slide was spun again for a further 20 seconds at 160 rpm to remove any excess latex and to give a thin even thickness wet latex coat on the glass slide. The slide was dried at room temperature to leave a translucent polymeric coating on the slide (film area density = 2.83 mg/cm2). The polymeric film was then aluminised and peeled off the glass backing slide ready for further use.
The aluminisation of TV screens using pre-formed aluminised Biopol films made from 0.5µm mean particle size Biopol latex
EXAMPLE 5
[0036] A piece of colour TV screen was pre-wetted using an aqueous sodium silicate based pre-wet. Whilst the screen was still wet, a piece of pre-formed aluminised film as made in Example 4 was placed onto the phosphor screen with the aluminised side of the film facing towards the phosphors. The screen was dried at room temperature and heated under the conditions of the Lehr cycle to leave an aluminium film adhering to the phosphors.
EXAMPLE 6
The preparation of pre-formed aluminised films from poly(propylene carbonate)
[0037] A 7.6cm x 7.6cm(3" x 3") square piece of glass plate was spun horizontally on its axis at a rate of 160 rpm for 20 seconds. During this time, ca 10 ml of a 5% w/w solution of poly(propylene carbonate) (supplied by PAC Polymers Inc., grade 40 M, lot number 20507-72-21) in dichloromethane was slurried directly onto the spinning glass slide. The glass slide was spun again for a further 20 seconds at 160 rpm to remove any excess liquid and to leave a thin even thickness wet polymeric coat on the glass slide. The slide was dried in an oven at 55°C for 1 hour, aluminised and peeled off the glass backing slide ready for further use. (Film area density = 0.65mg/cm2).
The aluminisation of TV screens using pre-formed aluminised poly(propylene carbonate) films
EXAMPLE 7
[0038] A piece of colour TV screen was pre-wetted using an aqueous sodium silicate based pre-wet. Whilst the screen was still wet, a piece of pre-aluminised poly(propylene carbonate) film as made in Example 6 was placed onto the phosphor screen with the aluminised side of the film facing towards the phosphors. The screen was dried at room temperature and heated under the conditions of the Lehr cycle to leave an aluminium film adhering to the phosphors.
The preparation of pre-formed aluminised films made from poly(isobutyl methacrylate)(PIBMA)
EXAMPLE 8
[0039] A stock solution was made by dissolving 5g of poly(isobutyl methacrylate) [PIBMA] (supplied by ICI Acrylics, under the trade name Elvacite, grade 2045) in 45g of toluene. To this stock solution was added 10 drops of di-n-butylphthalate as plasticizer and 10 drops of Disperbyk 164 as wetting agent (supplied by BYK). 2ml of this stock solution was coated onto a Teflon tile covering ca. 40 cm2 of the Teflon. The tile was left to dry in an oven at 45°C for 3 hours, then, ca. 30 cm2 of the resulting plastic film was peeled off the Teflon backing tile, placed flat onto a glass slide and aluminised. (Film area density = 5.2mg/cm2).
The preparation of pre-formed aluminised films made from hydroxypropylcelluose
EXAMPLE 9
[0040] A 7.6cm x 7.6cm(3" x 3") piece of Mylar sheet was spin coated with 10 ml of the following aqueous stock solution: 40g of 5wt% hydroxypropylcellulose (supplied by Hercules Ltd, Aqualon division under the trade name Klucel (viscosity type L) in water containing 5 drops of BYK024 wetting agent, supplied by BYK). The sheet was dried in an oven for 2 days at 45°C, aluminised and peeled off its Mylar backing sheet ready for further use. (Film area density = 1.7mg/cm2).
EXAMPLE 10
[0041] A piece of colour TV screen was pre-wetted using an aqueous sodium silicate based pre-wet. Whilst the screen was still wet, a piece of pre-aluminised cellulose film as made in Example 9 was placed onto the phosphor screen with the aluminium side of the film facing away from the phosphors. The screen was dried at room temperature and heated under the conditions of the Lehr cycle to leave in the main part an aluminium film adhering to the phosphors.
EXAMPLE 11
[0042] A piece of colour TV screen was pre-wetted using an aqueous sodium silicate based pre-wet. Whilst the screen was still wet, a piece of pre-aluminised cellulose film as made in Example 9 was placed onto the phosphor screen with the aluminium side of the film facing towards the phosphors. The screen was dried at room temperature and heated under the conditions of the Lehr cycle to leave in the main part an aluminium film adhering to the phosphors.
EXAMPLE 12
The formation of pre-formed Biopol/Aluminium/PIBMA film sandwiches
[0043] A piece of pre-aluminised Biopol film as made in Example 4 whilst adhered to its glass backing slide, was spin coated (160 rpm, 20 seconds) with 10ml of a 5% w/w solution of Elvacite (PIBMA) in toluene (slurried on). The slide was re-spun (160 rpm, 20 seconds). The resulting film was dried in an oven at 55°C for 1 hour, then the whole film sandwich was peeled off the glass backing slide ready for further use. (Film area density = 3.1mg/cm2).
The aluminisation of TV screens using pre-formed Biopol/Aluminium/PIBMA film sandwiches
EXAMPLE 13
[0044] A piece of TV screen was pre-wetted using an aqueous sodium silicate based pre-wet. Whilst the screen was still wet, a piece of Biopol/Aluminium/PIBMA sandwich as made in Example 12 was placed onto the phosphors with the PIBMA side of the film facing towards the phosphors. The screen was dried at room temperature and heated under the conditions of the Lehr cycle to leave an aluminium film adhering to the phosphors.
EXAMPLE 14
The preparation of pre-formed poly(propylene carbonate) aluminium/PIBMA film sandwiches
[0045] A pre-aluminised poly(propylene carbonate) film as made in Example 6 whilst still on its glass backing side was spin coated (160 rpm, 20 seconds) with 10ml of a 5% w/w solution of Elvacite (PIBMA) in toluene (slurried on). The slide was re-spun (160 rpm, 20 seconds). The resulting film was dried in an oven at 55°C for 1 hour, then the film sandwich was peeled off the glass backing slide ready for further use. (Film area density = 1.08mg/cm2).
The aluminisation of TV screens using pre-formed poly(propylene carbonate)/Aluminium/PIBMA film sandwiches
EXAMPLE 15
[0046] A piece of colour TV screen was pre-wetted using an aqueous sodium silicate based pre-wet. Whist the screen was still wet, a piece of poly(propylene carbonate)/aluminium/PIBMA film as made in Example 14 was placed onto the phosphor screen with the PIBMA side of the film facing towards the phosphors. The screen was dried in air at room temperature and heated under the conditions of the Lehr cycle to leave in the main an aluminium film adhered to the phosphors.
1. A process for the metallization of a phosphor screen which process comprises the steps
of:
either
either
a) applying to a phosphor screen a preformed film of a polymeric material which volatilizes at a temperature of below 450°C, the preformed film having a layer of metal deposited on one side thereof, to form a composite;
orb) applying to a phosphor screen a preformed sandwich of aluminium between two layers of a polymeric material;
andc) heating the composite formed in step (a) or step (b) to a temperature above the decomposition temperature of the polymeric film in order to decompose and/or volatilise the polymeric film coating.
2. A process as claimed in claim 1 wherein the film of polymeric material has a thickness
in the range of from 0.1 to 10µm.
3. A process as claimed in claim 1 or claim 2 wherein the film of polymeric material
has a film area density of from 0.1 to 10 mg/cm2.
4. A process as claimed in any one of the preceding claims wherein the polymeric film
comprises a film of a poly(acrylate), poly(methacrylate), poly(hydroxy-alkanoate),
poly(carbonate), poly(ethyleneoxide), poly(propyleneoxide) block copolymer, poly(alpha-methylstyrene)hydroxypropyl
cellulose, methylcellulose, hydroxypropyl methylcellulose, alginic acid or an associative
thickener.
5. A process as claimed in claim 4 wherein the poly(hydroxyalkanoate) is a poly(3-hydroxybutyrate),
a poly(3-hydroxyvalerate) or a copolymer of 3-hydroxybutyric acid and 3-hydroxyvaleric
acid.
6. A process as claimed in any one of the preceding claims wherein the phosphor screen
is pre-wetted before step (a) or (b).
7. A process as claimed in any one of the preceding claims wherein the metal which is
deposited upon the film coated screen or upon the polymeric film is aluminium.
8. A process as claimed in claim 7 wherein the layer of aluminium is deposited by vacuum
evaporation.
9. A process as claimed in claim 8 wherein the layer of aluminium has a thickness in
the range of from 0.1 to 0.3µm.
10. A process as claimed in any one of the preceding claims wherein the decomposition
and/or volatilisation of the polymeric film is effected at a temperature of below
350°C.
11. A process claimed in any one of the preceding claims wherein the heating of the composite
in step (c) is effected during the sealing of the funnel of a cathode ray tube to
the phosphor screen.
12. A process as claimed in claim 11 wherein the maximum temperature reached during the
sealing step is about 450°C.
13. A phosphor screen which has been metallized by a process as claimed in any one of
the preceding claims.
14. A cathode ray tube which includes at least one phosphor screen which has been metallized
by a process as claimed in any one of claims 1 to 12.
1. Verfahren zur Metallisierung eines Bildschirms, wobei das Verfahren folgende Schritte
aufweist: entweder
a) Aufbringen einer vorgefertigten Schicht eines Polymermaterials auf den Bildschirm, dass sich unterhalb einer Temperatur von 450°C verflüchtigt, wobei auf eine Seite der Schicht Metall aufgebracht ist, um ein Verbundmaterial zu bilden;
oderb) Aufbringen einer Sandwich-Verbundjschicht aus Aluminium zwischen zwei Schichten Polymermaterials auf einen Bildschirm;
undc) Aufheizen des in Schritt (a) oder Schritt (b) gebildeten Verbands auf eine Temperatur oberhalb der Zersetzungstemperatur der Polymerschicht, um die Polymerbeschichtung zu zersetzen und/oder zu verflüchtigen.
2. Verfahren nach Anspruch 1, bei dem das Polymermaterial eine Schichtdicke in dem Bereich
von 0,1 µm bis 10µm aufweist.
3. Verfahren nach Anspruch 1 oder 2, bei dem das Polymermaterial eine flächenbezogene
Schichtdichte (Flächengewicht) von 0,1 mg/cm2 bis 10 mg/cm2 aufweist.
4. Verfahren nach einem der vorhergehenden Ansprüche, bei dem die Polymerschicht eine
Schicht aus einem Polyacrylat, Polymethacrylat, Polyhydroxyalkanoat, Polycarbonat,
Polyethylenoxid, Polypropylenoxid-Blockcopolymer, Poly(alphamethylstyren) hydroxypropylzellulose,
Methylzellulose, Hydroxypropylmethylzellulose, Alginsäure oder ein assoziatives Verdickungsmittel
ist.
5. Verfahren nach Anspruch 4, bei dem das Polyhydroxyalkanoat ein Poly-3-Hydroxybutyrat,
ein Poly-3-Hydroxyvalerat oder ein Copolymer aus 3-Hydroxybuttersäure und 3-Hydroxyvaleriansäure
ist.
6. Verfahren nach einem der vorausgehenden Ansprüche, bei dem der Bildschirm vor Schritt
(a) oder (b) vorbefeuchtet ist.
7. Verfahren nach einem der vorausgehenden Ansprüche, bei dem das Metall, das auf dem
beschichteten Schirm oder auf der Polymerschicht abgelagert wird, Aluminium ist.
8. Verfahren nach Anspruch 7, bei dem das Aluminium durch Vakuumverdampfung abgelagert
wird.
9. Verfahren nach Anspruch 8, bei dem die Aluminiumschicht eine Dicke in dem Bereich
von 0,1 bis 0,3 µm aufweist.
10. Verfahren nach einem der vorausgehenden Ansprüche, bei dem die Zersetzung und/oder
Verflüchtigung der Polymerschicht bei einer Temperatur unterhalb 350°C bewirkt wird.
11. Verfahren nach einem der vorausgehenden Ansprüche, bei dem das Aufheizen des Verbundmaterials
in Schritt (c) während des Aufsiegelns des Trichters oder einer Kathodenstrahlröhre
auf den Bildschirm bewirkt wird.
12. Verfahren nach Anspruch 11, bei dem die bei dem Aufsiegelschritt erreichte Maximaltemperatur
ungefähr 450°C beträgt.
13. Bildschirm der durch ein Verfahren nach einem der vorausgehenden Ansprüche metallisiert
ist.
14. Kathodenstrahlröhre die wenigstens einen Bildschirm aufweist, der durch ein Verfahren
nach wenigstens einem der Ansprüche 1 bis 12 metallisiert worden ist.
1. Procédé de métallisation d'un écran phosphorescent, lequel procédé comprend les étapes
consistant à :
soit
soit
a) appliquer sur l'écran phosphorescent un film préformé en un matériau polymère qui se volatilise à une température inférieure à 450°C. le film préformé ayant une couche de métal déposée sur l'une de ses faces, de manière à former un composite ;
oub) appliquer sur l'écran phosphorescent un sandwich préformé d'aluminium compris entre deux couches de matériau polymère ;
etc) chauffer le composite formé dans l'étape (a) ou l'étape (b) à une température supérieure à la température de décomposition du film polymère de manière à décomposer et/ou volatiliser le revêtement formé par le film polymère.
2. Procédé selon la revendication 1, dans lequel le film de matériau polymère a une épaisseur
dans la gamme de 0,1 à 10 µm.
3. Procédé selon la revendication 1 ou la revendication 2 dans lequel le film de matériau
polymère a une densité surfacique de film de 0,1 à 10 mg/cm2.
4. Procédé selon l'une quelconque des revendications précédentes, dans lequel le film
polymère comprend un film de poly(acrylate), poly(méthacrylate), poly(hydroxy-alcanoate),
poly(carbonate), poly-(oxyde d'éthylène), copolymère bloc de poly(oxyde de propylène),
poly(alphaméthylstyrène)hydroxypropyl cellulose, méthylcelulose, hydroxy propyl méthylcellulose,
acide alginique ou un épaississant associatif.
5. Procédé selon la revendication 4 dans lequel le poly(hydroxyalcanoate) est un poly(3-hydroxybutyrate),
un poly(3-hydroxyvalérate) ou un copolymère d'acide 3-hydroxybutyrique et 3-hydroxyvalérique.
6. Procédé selon l'une quelconque des revendications précédentes, dans lequel l'écran
phosphorescent est prémouillé avant l'étape (a) ou l'étape (b).
7. Procédé selon l'une quelconque des revendications précédentes, dans lequel le métal
qui est déposé sur l'écran revêtu du film ou sur le film polymère est de l'aluminium.
8. Procédé selon la revendication 7 dans lequel la couche d'aluminium est déposée par
évaporation sous vide.
9. Procédé selon la revendication 8 dans lequel la couche d'aluminium a une épaisseur
dans la gamme de 0,1 à 0,3 µm.
10. Procédé selon l'une quelconque des revendications précédentes, dans lequel la décomposition
et/ou volatilisation du film polymère est effectuée à une température inférieure à
350°C.
11. Procédé selon l'une quelconque des revendications précédentes, dans lequel le chauffage
du composite dans l'étape (c) est effectué pendant le scellage de l'entonnoir du tube
à rayons cathodiques à l'écran phosphorescent.
12. Procédé selon la revendication 11 dans lequel la température maximale atteinte durant
l'étape de scellage est d'environ 450°C.
13. Ecran phosphorescent métallisé par un procédé selon l'une quelconque des revendications
précédentes.
14. Tube à rayons cathodiques comprenant au moins un écran phosphorescent qui a été métallisé
par un procédé selon l'une quelconque des revendications 1 à 12.