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
  • H01J29/86—Vessels; Containers; Vacuum locks
  • H01J29/867—Means associated with the outside of the vessel for shielding, e.g. magnetic shields
  • H01J29/868—Screens covering the input or output face of the vessel, e.g. transparent anti-static coatings, X-ray absorbing layers
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05F—STATIC ELECTRICITY; NATURALLY-OCCURRING ELECTRICITY
  • H05F3/00—Carrying-off electrostatic charges
  • H05F3/02—Carrying-off electrostatic charges by means of earthing connections
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
  • H01J2229/00—Details of cathode ray tubes or electron beam tubes
  • H01J2229/863—Passive shielding means associated with the vessel
  • H01J2229/8633—Meshes and patterns

Definitions

• This invention concerns visual display units or VDU's as they are commonly referred to.
• Such devices normally incorporate a television tube for displaying information derived from a processor unit or computer unit associated therewith.
• a visual display unit having an electroconductive material located in front of the visual display unit cathode ray tube screen, the electroconductive material being connected to charge dissipating means and being arranged relative to the screen so that electrical charge appearing on the screen is conducted to the dissipating means.
• the charge can be dissipated through an electrical connection made between the conductive material and an actual or effective earth.
• a corona discharge electrode pointing away from where the operator would normally be situated may be provided and the electroconductive material connected thereto so that the charge is dissipated using the known principle of electrical discharge using a point discharge electrode.
• a separate conductive screen may be required between it and the operator to prevent any air flow between the discharging point and the operator.
• the conductive material may be applied directly to the surface of the cathode ray tube of the V D U.
• the material may be a film, and a suitable film is one manufactured by National Adhesives Limited and marketed by them under trade names such as TL121, TL125 and T L126. It is to be understood that reference to these specific products is not intended to limit the invention to the use of these particular materials which are specified by way of example only.
• the materials concerned are water- based polymers which when cured (dried) do not depend on the atmospheric humidity for their conductive properties.
• such materials are intrinsically electroconductive and it is advantageous if the film is of such material or possesses such properties so that the conductive nature of the film is not affected by the prevailing humidity of the environment in which the VDU is located.
• Electrical connection to such a film is established either by creating a conductive region in electrical contact with the remainder of the film to which an electrical lead is attached for dissipating any charge built up on the surface of the VDU; or the coated region is surrounded by a conductive frame which is connected through a suitable conductor for charge dissipation purposes.
• the conductive material forms part of a separate self- supporting mask which is adapted to be placed in front of the cathode ray tube either in toto or around its boundary region or may be simply stretched across in front of the cathode ray tube in a suitable bounding frame or supporting structure or may be stuck to a frame which normally surrounds the glass CRT screen.
• a suitable conductive terminal is provided such as a metal eyelet or solder tag to which an electrical connection can be made.
• the conductive material may be in the form of a fine grid of lines which may be all parallel one to the other or may intersect for example at right angles to form a rectilinear array.
• a grid of lines at a pitch of 20 to the inch and each line having a width of approximately 0.010 inches may be used. If not transparent, there will be a reduction of light from the surface of the CRT in use by by appropriate choice of pitch and line width, the light loss can be kept to a minimum, where it is not significant.
• each line will additionally act as a discharge corona wire and less of the conductive material would in practice be necessary.
• the charge may of course be dissipated as described earlier by electrical connection to an appropriate earth or discharging electrode.
• the grid may be formed as a mesh which is then mounted on a transparent carrier sheet member, desirably a flexible sheet.
• Metal mesh of typical size 100 micron aperture and .05mm dia. wire is necessary to achieve the optical properties required.
• the kinds of metals which can be used commercially to make mesh of this fineness is limited by the ability to draw the metal to the small diameter required; the metals commonly used are brass and stainless steel.
• some form of blacking process is required so that the mesh is rendered as non-reflective as possible in order to enhance the optical properties.
• a possible method is to electroplate a brass mesh, with, for example, black chrome. The problem with this is that the deposit of chrome (or other plating material) in effect tends to weld or bond together the wire mesh at the points where one wire crosses another.
• a solution to this problem is to form the mesh, after electroplating, using a male and female press tool, thereby to give the mesh a permanent dished shape which substantially coincides with the contours of the VDU screen.
• a method of blacking metal mesh without causing it to become inflexible, comprises an oxidising process which can be applied to stainless steel mesh (which is also more robust than brass mesh).
• This process for example available under licence from the company Inco, is a non- electrolytic oxidising process, whereby the stainless steel mesh is immersed in a bath of acids and additives.
• it is necessary to roughen the inherent polished surface of the wire; this may be done by chemical etching, or by electrolytic action, or by ion bombardment of the kind which is normally used to etch a metal surface prior to bonding with paint, rubber, adhesive or the like.
• blasting with a ceramic, aluminium oxide, or ferrous grit imparts a uniform matt surface to the wire.
• a grit size smaller than the aperture size of the mesh should be used, typically 50-75 microns.
• Masks may be constructed from a conductive fabric mesh such as dark or black nylon. This material has an inherent sheen on the surface of each fibre and overall there is a certain amount of light reflectivity.
• the fine mesh is formed from a metallic material which is chemically treated or electroplated to give a matt black surface to all of the metal content of the mesh so as to reduce overall light reflectivity of the mask.
• the conductive mesh in contact with the cathode ray tube face.
• the mask may be secured to the VDU screen using transparent adhesive material located at least in the corner regions of the mask and adapted to adhere to the mask material and to glass.
• the transparent adhesive material may be transparent adhesive double-sided tape.
• the transparent sheet member may be formed from a plastics material of the type which adheres to glass without the use of an adhesive.
• one corner which may contain an earth wire, is fixed first.
• the diagonally opposite corner is then fixed, the slack being taken out.
• the other two diagonally opposite corners are then stretched and fixed simultaneously to eliminate wrinkles.
• such a grid of lines or conductive film may be applied directly to the glass of the cathode ray tube in the visual display unit with appropriate electrical connection if required for dissipating the charge.
• the transparent sheet member which is used may be formed from a material haivng filtering characteristics to reduce any ultra violet or other radiation which may escape from the cathode ray tube under normal use of the tube. In this way a visual display unit can be rendered even more acceptable to operators having particularly sensitive skins.
• the improved mask is formed oversize and is adapted to be cut down to just fit the CRT screen to which it is to be applied.
• a kit for fitting a mask to a cathode ray tube screen comprises a mask as set forth above, of overall dimensions as large as the largest screen for which the kit is intended, and a template having printing and indicia thereon and capable of being offered up to the cathode ray tube to which the mask is to be fitted so that two adjoining edges are aligned with the edges of the aperture containing the cathode ray tube screen (for example, one bottom edge and one side edge) and the template material is such that after it has been smoothed over the CRT screen, the two other bounding edges of the screen can be felt through the template and marked therein by means of a sharp edge or point to provide cutting lines to allow the template to be cut down exactly to the size of the cathode ray tube screen.
• the template can then be used to trace around the mask or to allow the mask to be cut directly to the correct size.
• the mask is convenient to pack and transport, in that it can be rolled up with the template and packed in the centre of a cardboard tube along with the earth wire and adhesive pieces, if used.
• the finished VDU shield may be supplied as a universal fitting; ie a large rectangle which the customer cuts to fit a particular VDU screen, it could alternatively be supplied as a pre-cut device, the customer giving the size or the model of his VDU so that the mesh can be cut to fit this size, typically by die cutting, by the VDU shield manufacturer.
• the VDU shield is to be connected by a conductive lead to a convenient earthpoint, thereby to dissipate the static from the VDU screen and to alternate the radiation therefrom.
• a wire may be used for this purpose, but as a retrofit device and fitting externally to an existing VDU, may be considered untidy.
• a further feature of this invention concerns the use of a self-adhesive metal strip.
• a self-adhesive metal strip typically this would be 50 microns thick aluminium approx. 10mm wide, having an adhesive backing, eg acrylic, which would be protected before use with a silicon paper backing strip.
• an adhesive backing eg acrylic
• Such a material is available from companies such as Sellotape, 3 M and Barrier. This material is attached at one end to a convenient edge or corner of the VDU screen, before fitting the shield, and thence led and stuck to the contours of the screen frame, around the cabinet, to the back of the VDU, where it is stuck to a convenient earthpoint, eg chassis, co-axial, or power earth connection. This results in a neat appearance for the the earth connection, more acceptable than a wire.
• a convenient earthpoint eg chassis, co-axial, or power earth connection.
• a readily detachable plastics shield may be preferred.
• the television may be used for normal viewing without the shield, or with the shield when using the computer.
• the shield has to be fitted onto the screen and then removed many times, so that the shield material has to be robust and have an easy fitting method.
• a suitable material is transparent PVC of a grade known as "self-cling" or “window-cling”. This is typically about .010 inch thick, and is commonly used for stickers on windows as notices and signs, as for example as a wallet to retain and fix the motor vehicle licence to the windscreen of the car.
• the material has several manufacturers, including Hoescht.
• the equivalent of the aforementioned metal mesh is introduced to the surface of the transparent PVC in the form of a printed black, conductive gird.
• a typical grid size would be an aperture size of 100 microns with a line width of 50 microns, a matt black conductive ink of the type manufactured by Coates Bros (Industrial Finishes) Limited, or Acheson Industries, may be used. This contains a graphite or nickel powder to give the conductivity required.
• a d.p. or direct printing whereby a flat metal plate has a grid of grooves etched into it corresponding to the grid pattern required.
• the conductive ink is put into the grooves, the excess being wiped from the surface of the plate.
• the plate is then brought into contact, under pressure, with the surface of the PVC sheet, sometimes with the plate heated also.
• the ink is transferred from the grooves to the PVC sheet which is subsequently dried.
• the printed PVC may be coated, on top of the printed grid, with a transparent varnish which can act to further retain the ink, and also may be in a matt or semi-matt form in order to make the surface of the sheet less reflective.
• the invention also provides a cathode ray tube for use in visual display units and the like in which the display screen includes over some or all of the display area an optical filter for filtering out ultra violet and other harmful radiation which may be emitted from the screen during use and which is combined with a conductive film or grid of conductive elements so that any electrical charge which might build up on the surface of the screen during use can be dissipated by electrical conduction to earth or to a discharging electrode or the like.
• the material forming the lines need not be transparent provided the line spacing is such as to allow sufficient light through from the display and does not interfere with the reading of the information in the display.
• the film of transparent electroconductive material or the grid of conductive lines may be formed by metallising the surface of the CRT or a sheet of glass or plastics material to be positioned in front of the CR T .
• the metallising may be achieved using a vacuum deposition process or the like.
• the diffusing screen may be formed integrally with the glass screen forming the end of the cathode ray tube or may be a separate sheet member located in front of a conventional cathode ray tube screen.
• diffusing screen comprises a sheet of plastic or glass one side of which is slightly "frosted” by having formed thereon a large number of dimples or pyramidal projections.
• the utilisation of a diffusing screen of this type whether formed integrally with, or in front of the screen of the monitor produces a more favourable colour rendering.
• a protective screen for reducing both glare and the electrostatic field emanating from a cathode ray tube screen may be formed from an open-weave mesh of nylon or similar plastics thread coated by a suitable electrically conductive material, with electrical connection means being provided for dissipating the electrostatic field, and mounting means being provided to effect the mounting of the mesh in front of the screen.
• the screen not only possesses the necessary characteristics to dissipate an electric field in front of the CRT, but also possesses all the characteristics needed to reduce the glare from the screen and also reduces reflections from the screen due to light incident thereon.
• a nylon thread is woven into an open weave mesh and is treated with a conductive resin, or is metallised so as to render the mesh electrically conductive.
• the conductive open weave mesh is preferably supported in a frame which corresponds to the opening containing the cathode ray tube which is to be viewed and which is adapted to be secured to a housing or other member which surrounds the cathode ray tube screen.
• the frame which bounds and supports the conductive mesh is provided with impact adhesive in one or more regions around the rear face thereof so that the frame will remain in position on the housing after it has been applied thereto and lightly pressed into place.
• the impact adhesive region is preferably protected by means of a peel-off strip material until the device is ready to be applied to a television monitor.
• the moire effects can be eliminated by arranging that the parallel lines making up the grid of lines or the lines of dots or the warp or weft of the woven mesh lies at an angle in the range 10 to 80 degrees relative to the line scan direction of the scanning spot making up the raster in the cathode ray tube.
• a preferred single inclination between the lines, lines of dots or warp or weft is 30 degrees to the line scan direction.
• a plate is first prepared by etching a rectilinear array of fine grooves onto the plate surface. The plate is then inked so as to fill the grooves; the surface is wiped so that ink just remains in the grooves, and the transparent sheet (eg P VC) is pressed into contact with the plate so as to become inked.
• the transparent sheet eg P VC
• This mask can then be mounted on a backing sheet of paper.

Landscapes

• Vessels, Lead-In Wires, Accessory Apparatuses For Cathode-Ray Tubes (AREA)
• Devices For Indicating Variable Information By Combining Individual Elements (AREA)

Applications Claiming Priority (6)

Publications (1)

Family

ID=27261884

Family Applications (1)

Country Status (2)

Cited By (11)

Citations (5)

• 1983
  • 1983-12-12 GB GB838333125A patent/GB8333125D0/en active Pending
  • 1983-12-14 EP EP83307617A patent/EP0113218A1/fr not_active Withdrawn

Patent Citations (5)

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