Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
  • H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
  • H01J29/10—Screens on or from which an image or pattern is formed, picked up, converted or stored
  • H01J29/18—Luminescent screens
  • H01J29/28—Luminescent screens with protective, conductive or reflective layers

Definitions

• the present invention relates to a process of metallizing phosphor screens, in particular for cathode ray tubes (CRTs) .
• CRTs cathode ray tubes
• 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-
• 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.
• 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-butylmeth- acrylate) in a solvent such as toluene, is floated on the top of the pre-wet.
• a solvent based lacquer comprising an approximately 2% solution of a polymer such as poly(iso-butylmeth- acrylate) in a solvent such as toluene
• 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.
• 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.
• aqueous based system 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.
• 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.
• 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.
• 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.
• the present invention provides a process for the metallization of a phosphor screen which process comprises the steps of: either a(i) applying to a phosphor screen a preformed film of a polymeric material which volatilizes at a temperature of below 450°C; a(ii) depositing a layer of metal upon the film coated screen to form a composite; or b) 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; or c) applying to a phosphor screen a preformed sandwich of aluminium between two layers of a polymeric material; and d) heating the composite formed in step a(ii) , step (b) or step (c) to a temperature above the decomposition temperature of the polymeric film in order to decompose and/or volatilise the polymeric film coating.
• the films described in (b) 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.
• step (c) the polymeric material used on either side of the aluminium layer may be the same or di ferent.
• 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 lO ⁇ m, or a film area density of from 0.1 to 10 mg/cm 2 or more preferably 0.1 to 3.0 mg/cm 2 .
• a conventional solvent based lacquer will give a film in the order of one micrometre thickness.
• 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) , hydroxy- propyl cellulose, methylcellulose, hydroxypropyl methyl cellulose, alginic acid or an associative thickener, such as Rheox from Rohm and Haas and Rheovis from Allied Colloids.
• the preferred polymeric film material for use in the present invention comprises a film of a poly- (hydroxyalkanoate) , preferably poly(3-hydroxy- butyrate) , 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) .
• Biopol films are available from Goodfellow Limited, or can be prepared from Biopol in granular form such as by the methods as disclosed in W094/00163, EP-A-0226 39, W091/13207 and DE-A-4040158. They can also be formed from a Biopol latex.
• 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.
• a metal layer may be deposited onto the film coated screen according to techniques known in the art.
• 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 0.3 ⁇ m.
• 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.
• 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.
• step (d) The composite formed either in step (a) (ii) , step (b) or step (c) 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.
• the heating of the composite in step (d) 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.
• 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.
• 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.
• Alu inised 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 to produce an aluminium coating on the substrate.
• a 3" x 3" square piece of glass plate was spun horizontally on its axis at a rate of 160 rpm for 20 seconds.
• ca 10 ml of 29% solids containing Biopol latex supplied by Zeneca Specialities, Batch Number: BPL No. 505/1001
• 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 plastic film was then peeled off the glass backing slide ready for further use.
• the film was aluminised then peeled off the slide ready for further use.
• 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.
• 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
• 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 non- aluminised film as made in Example 1 was placed onto the phosphor screen. The latter was aluminised and heated under the conditions of the Lehr cycle to leave an aluminium film adhering to the phosphors.
• a 3" x 3" square piece of glass plate was spun horizontally on its axis at a rate of 160 rpm for 20 seconds.
• ca 10 ml of 41% solids containing Biopol latex supplied by Zeneca Specialities, Batch Number: BPL No. 510/0301
• 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 polymeric film was then aluminised and peeled off the glass backing slide ready for further use.
• 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 5 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.
• a 3" x 3" square piece of glass plate was spun horizontally on its axis at a rate of 160 rpm for 20 seconds.
• 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.
• 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 7 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.
• a 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) .
• 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 10 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.
• 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 10 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.
• 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 13 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.
• 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 15 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.

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• Formation Of Various Coating Films On Cathode Ray Tubes And Lamps (AREA)
• Manufacture Of Electron Tubes, Discharge Lamp Vessels, Lead-In Wires, And The Like (AREA)

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• 1994
  • 1994-11-30 GB GB9424162A patent/GB9424162D0/en active Pending
• 1995
  • 1995-11-27 WO PCT/GB1995/002769 patent/WO1996017371A1/en not_active Ceased
  • 1995-11-27 AU AU39331/95A patent/AU3933195A/en not_active Abandoned
  • 1995-11-27 JP JP8518418A patent/JPH10510092A/ja active Pending
  • 1995-11-27 DE DE69503804T patent/DE69503804T2/de not_active Expired - Fee Related
  • 1995-11-27 EP EP95937127A patent/EP0795192B1/de not_active Expired - Lifetime

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