Patent Publication Number: US-3876425-A

Title: Method of and device for the manufacture of a cathode-ray tube for displaying coloured pictures, as well as cathode-ray tube manufactured by said method

Description:
United States Patent Geenen et a1.  
 METHOD OF AND DEVICE FOR THE MANUFACTURE OF A CATHODE-RAY TUBE FOR DISPLAYING COLOURED PICTURES, AS WELL AS CATI-IODE-RAY TUBE MANUFACTURED BY SAID METHOD Inventors: Constant Joseph Maria Geenen;  
 Johannes Cornelis Adrianus Van Nes, both of Emmasingel.  
 Eindl&#39;ioven Netherlands U.S. Philips Corporation, New York. NY.  
 Filed: Aug. 9, 1973 Appl. No.: 387,141  
 Assignee:  
 Foreign Application Priority Data Sept. 6. 1972 Netherlands o. 7212105 US. Cl 96/36.I; 96/27 E; 354/1;  
  313/92 B Int. Cl G03c 5/00 Field of Search 96/361, 27 E; 313/92 PD. 313/92 B. 114; 95/1; 354/1 Apr. 8, 1975 [561 References Cited UNITED STATES PATENTS 3.21 1.067 10/1965 Kaplan t. 95/1 3.667.947 6/1972 McKee 96/361 3.689.267 5/1972 Little et a1. 96/36.] 1725.106 4/1973 Hosokoshi 96/36.] 3.783.754 1/1974 Takemoto et al 96/361 Primary Exuminer-Norman G. Torchin Assistant E.\&#39;amt&#39;rterEdward C. Kimlin Attorney. Agent, or Firm-Frank R. Trifari; George B. Berka [57] ABSTRACT A method of manufacturing a cathode-ray tube for displaying color pictures, comprising exposing a photosensitive layer on a support for the display screen to a narrow light beam the origin of which is situated in a plane corresponding to the deflection plane of the tube and moving the orign of the beam in the plane in accordance with the movement and deflection of the scanning electron beam in the working tube.  
 4 Claims. 3 Drawing Figures PATENTEDAPR 81975 SHEET 2 UF 2 METHOD OF AND DEVICE FOR THE MANUFACTURE OF A CATl-IODE-RAY TUBE FOR DISPLAYING COLOURED PICTURES, AS WELL AS CATHODE-RAY TUBE MANUFACTURED BY SAID METHOD The invention relates to a method of manufacturing a cathode-ray tube for displaying coloured pictures. in which a photosensitive layer is provided on a support for the display screen of the tube. a mask comprising a pattern of light-transmitting regions is placed at a short distance before the photosensitive layer, the mask is scanned by a narrow light beam to form a pattern of exposed and unexposed regions on the photosensitive layer, and the photosensitive layer is then developed. The invention also relates to a device for carrying out such a method and to a cathode-ray tube manufactured by such a method.  
  A method of the type mentioned in the preamble is known from British Pat. No. 1.257.933. Moreover it is known that the direction of the light rays which impinge upon the photosensitive layer via apertures in the mask must correspond accurately with the direction of the electron rays which in the operating tube impinge upon the display screen via the same apertures in the mask. Only then does the place of the luminescent regions ofthe display screen which are obtained after development of the photosensitive layer correspond accurately with the place of the electron spots. Differences generally cause serious colour defects. It is therefore usual to use a correction lens which brings the virtual place of the light source as readily as possible in agreement with the deflection point of the relevant electron beam in the deflection coil of the cathode-ray tube.  
  However. with such a correction lens it proves in principle not possible to obtain full agreement of the luminescent regions with the electron spots throughout the display screen. It is the object of the invention to mitigate this drawback.  
  According to the invention, a method of the type mentioned in the preamble is characterized in that the scanning light beam starts from a point which during the scanning is moved in a predetermined manner which corresponds substantially to the scanning pattern ofthe electron beam in the working tube. The scanning light beam may describe a large number of parallel lines or a spiral-like track on the mask. A spiral-like track may have the advantage that the displacement of the starting point of the scanning light beam occurs more gradually in the case in which only comparatively small corrections are necessary along a circle having the center of the display screen as center.  
  A device for carrying out a method according to the invention preferably comprises reflection means for reflecting a primary light beam. rotation means for rotating the reflection means about an axis of rotation. and translation means for translating rotation means in at least two mutually perpendicular directions, which reflection means are furthermore tiltable relative to the rotation means about an axis which extends at right angles to a plane through the said axis of rotation and the axis of the said primary light beam. The operation of such a device will be described hereinafter with reference to an embodiment.  
  The invention will be described in greater detail with reference to the accompanying drawing, of which FIG. 1 shows an exposure device for carrying out a method according to the invention,  
  FIG. 2 shows a part of the device shown in FIG. 1 on an enlarged scale. and  
  FIG. 3 is a diagrammatic representation to explain the invention.  
  FIG. 1 shows an exposure device which comprises a housing I on which a window part 2 of a cathode-ray tube to be manufactured is provided. The inside of the window part 2 comprises a photosensitive layer 2. A shadow mask 4 having apertures 5 is mounted in the window part 2 in exactly the same position as that in which the said shadow mask will afterwards be present in the operating cathode-ray tube. The photosensitive layer 3 is exposed via the apertures 5 in the shadow mask 4. In the present case the apertures 5 are circular, which, however, does not mean a restriction for the more general application of the invention, so that a pattern of exposed circular regions is formed on the photosensitive layer 3. After the exposure, the photosensitive layer 3 is developed as a result of which in the present case a pattern of luminescent regions (phosphor dots) is formed on the window part 2. The exposure is totally carried out three times. namely once from the deflec tion point of each electron beam. After the last development, the window part comprises three patterns of phosphor dots, namely in the present case a hexagonal pattern of green. red and blue luminescent phosphor dots. The photosensitive layer 3 may consist ofan inorganic photosensitive layer. which becomes insoluble by exposure to light. The phosphor may already be present in said layer. in which case development is carried out by dissolving the unexposed parts ofthe layer and rats ing them away. The photosensitive layer 3 may also consist of a photoconductive layer on a conductive substratum. In that case the photoconductive layer is provided with an electric surface charge which leaks away from the exposed parts of the layer. Phosphor particles charged with the same sign are then deposited on the photoconductive layer 3, which particles adhere only to the exposed parts of the layer since they are repelled by the charge on the unexposed parts. Similar methods and all kinds of variations are generally known and need not be further explained. They may also be used for applying a non-reflecting layer between the phosphor dots so as to reduce the reflection of ambient light.  
  The exposure which forms the subject matter of the present invention is carried out by means of a light beam 6 which is formed by reflection of a primary light beam 7 in the center of a mirror 8. The plane of the mirror 8 is at right angles to the plane of the drawing of FIG. 1. The mirror 8 can be tilted about an axis 10 at right angles to the plane of the drawing. When the mirror 8 is tilted about the axis 10, the light beam 6 describes a line on the photosensitive layer 3. The mirror 8 with the axis 10 are rotatable about the axis of rotation 9. When the mirror 8 is rotated about the axis 9, the light beam 6 describes a circle on the photosensitive layer 3. By the combination of a slow tilting about the axis I0 and a rapid rotation about the axis 9, the light beam 6 describes a spiral on the photosensitive layer 3. The pitch of said spiral must be of the order of magnitude of the diameter of the light beam 6 so that each place of the photosensitive layer is exposed. The rotation and tilting of the mirror in such manner that the primary light beam 7 remains always directed on the center of the mirror 8 is carried out by means of the device 11 which will be described with reference to FIG. 2.  
  FIG. 2 shows the device denoted in FIG. 1 by I] for the rotation and tilting of the mirror 8 and for the movement of the center of the mirror 8. The light beam 6 is formed by reflection of a primary light beam 7 on the mirror 8. The mirror 8 can be tilted about the axis 10 which in the position shown is at right angles to the plane of the drawing. The tilting of the mirror 8 is obtained by means of the device 12. The mirror 8 with the axis 10 and the device 12 are mounted on rotation means 13 which are rotatable about the axis 9. The primary light beam 7 is obtained by reflection of a light beam 14 on a mirror [5. The mirror 15 is rigidly mounted relative to the rotation means 13 so that the light beam 7 always remains directed on the center of the mirror 8 during the rotation ofmirror l5 and mirror 8 about the axis 9. since the light beam 14 is parallel to the axis 9. The light beam I4 is formed by reflection of a light beam 16 on a mirror 17. The mirror 17 can be swung relative to the mirror 15 about the axis 18 which is parallel to the axis 9. As a result ofthis the mirror 17 during rotation of the axis 9 can always remain directed on the light beam 16. The light beam 16 is formed by reflection of a light beam 19 from a mirror 20 which can be swung about an axis 21. The telescopic connection 22 ensures that the mirrors [7 and 2t) always re main directed to each other. The light beam [9 finally is produced by the lamp 23 in the reflector l4 and collimated by the lens 25. It is also possible to produce the light beam by means of a laser device.  
  So the scanning light beam 6 starts from the center of the mirror 10. This center can be moved in two directions which preferably are mutually at right angles by means of the slide 26 and the slide 27. The deflection point of a deflected electron beam can be defined as the point ofintersection ofthe tangent at the axis of the deflected beam at the area of the display screen with a plane which extends at right angles to the axis of the tube and may be chosen arbitrarily. This plane is generally chosen through the center of the deflection coil system and is then termed deflection plane. During the deflection. the deflection point moves in the defleo tion plane. The nature of the said movement is inter alia closely associated with the nature of the deflection coil used. The deflection angle of the electron beam is defined as the angle between the tangent at the axis of the deflected beam at the area ofthe picture screen and the axis of the tube.  
  In FIG. 3. the \&#39;J plane is the deflection plane of a given cathode&#39;ray tube for displaying coloured pictures. The tube in question has a rather flat display screen having a radius of curvature of 1.017 mm. The deflection plane is at a distance of 273 mm from the inner surface of the display screen. The deflection point of a non-deflected electron beam coincides with the origin 0 of the deflection plane. The axis of the cathode-ray tube intersects the deflection plane in A. The distance 0A corresponds to the eccentricity of the electron beam in question relative to the axis of the tube. since the relevant tube comprises three electron guns in delta arrangement. The projection on the deflection plane of the target on the display screen of an electron beam having a deflection angle 1) is denoted by P. The direction in which the electron beam is deflected is denoted by the angle ill relative to the y-axis. The place in the deflection plane of the deflection point D of said electron beam is defined by the coordinates R and T which are each functions of d) and (it. For the relevant tube with associated deflection coil it holds that:  
 R 13mb) 40 (rg /z o) rgd) 3.2 sin d) {l (cos 2111] /)}sin :11 Ttrti, lrj 3.2 sin ti: {l+ (cos 2 cbl/Hcos &#39;11.  
 in these equations R and T are expressed in mms.  
  The center of the mirror 8 should always coincide with the deflection point D. The movement of the deflection point D in the deflection plane is ensured by the slides 26 and 27 as a function of the angle (b (FIG. 2] and the angle ll! (FIG. 3). which angle d) is obtained by tilting the mirror 8 relative to the rotation means 13. and which angle ll! is obtained by the rotation of the ro tation means 13 about the axis 9.  
  Instead of the slides 26 and 27 which move the center of the mirror 8 in the deflection plane in two mutually perpendicular directions. it is also possible to use slides which move the deflection point in a radial and aximuthal direction in the deflection plane. It is also possible to define the deflection point differently and to cause the center of the mirror 8 to make. for example. a movement parallel to the axis 9 and in a direction at right angles thereto.  
 What is claimed is:  
  LA method of manufacturing a cathode-ray tube for displaying color pictures. comprising the steps of: providing a photosensitive layer on a support for the display screen of the tube. placing a mask having a pattern of light-transmitting regions at a short distance in front of the photosensitive layer. scanning mask by rotating a narrow light beam about an axis which is parallel to the main axis of the tube. tilting the light beam about an angle with respect to the axis of rotation and, at the same time. subjecting the origin of the light beam to a translational movement in two mutually perpendicular directions in a plane corresponding to the deflection plane of the working tube. the translational movement being a function of the angle of rotation and of the angle of tilting to provide a scanning pattern for the electron beam in the working tube. and developing the resulting pattern of exposed and unexposed regions on the photosensitive layer.  
  2. A method as claimed in claim 1, characterized in that the scanning light beam is formed by reflection of a primary light beam by means of reflection means and that said reflection means are moved during the scanning to provide the previously determined compound movement.  
  3. A method as claimed in claim 1 wherein the scanning light beam describes a large number of parallel lines on the mask.  
  4. A method as claimed in claim 1 wherein the scanning light beam describes a spiral-like track on the mask.