METHOD OF MANUFACTURING A COLOUR DISPLAY TUBE

Abstract: A method of manufacturing a colour display tube comprising an envelope having a display window and a colour selection electrode and suspension means for suspending the colour selection electrode, which suspension means each contain a member which is fused into the envelope, these members being heated by means of a laser. In this way, a simplification of the fusing arrangement and a higher efficiency can be obtained. The members may be provided with bores on which the laser beam is incident.

Description: The invention relates to a method of manufacturing a colour display tube comprising an envelope having a display window and, in the envelope, a colour selection electrode having a large number of apertures, and a plurality of suspension means for suspending the colour selection electrode opposite the display window, a member of each suspension means being fused, at least in part, into the envelope. Such a method is known from DE-A1-1 920 068. Said publication discloses a method in which a pin-shaped member of each suspension means is fused into the display window by means of a heating element which comprises an infrared radiation source. The infra-red radiation shines through the envelope to heat the member. For each member a separate heating element comprising an infrared lamp is used, each heating element being positioned close to the member on the opposite side of the envelope. The known method requires relatively much space and complicated equipment is necessary. It is an object of the invention to provide a method which requires less space and a simpler set-up. To this end in the method according to the invention as claimed in claim 1 during fusing the said member is heated by means of a laser beam generated by a laser and one common laser is used for heating a plurality of said members. The known method uses for each member to be fused a separate heating element. Four heating elements are necessary which take in relatively much space. In the method according to the invention a laser beam is generated in one common laser. The laser beam can be led to fusing arrangements by means of e.g. reflectors, optical fibres or an optical divider. The total amount of space needed is less and the set-up is simplified. Furthermore, using a laser beam for heating the members to be fused permits an accurately localized supply of the energy needed to fuse a member into the envelope, namely into the member to be fused. The amount of heat supplied can be accurately adjusted so that no more energy than necessary is used. Moreover this reduces the spread in properties of the connections formed between the fused members and the envelope amongst individual tubes. A preferred embodiment of the method according to the invention is characterized in that more than one member is fused substantially simultaneously. This accelerates the fusion process. A further improved embodiment is characterized in that the laser beam passes through the envelope. This may be advantageous if the members are fused in places which are not readily accessible. A further preferred embodiment of the method according to the invention is characterized in that said members are provided with a respective bore which is closed on one side, the laser beam being incident on the open side of said bore. Energy is supplied to the inside of the members by providing the member to be fused with a bore on which the laser beam is incident. In this way the loss of energy is reduced so that the member is heated more quickly and in a more controlled manner. A further embodiment of the method according to the invention is characterized in that a member having a base is fused and that the bore extends into the base. The energy is supplied to the base. Since this is the part of the member which is fused, this results in an increased fusing rate. A still further embodiment of the method according to the invention is characterized in that a member is fused the bore of which extends conically from the open side to the interior. In this way the energy of the laser beam is concentrated in the tip of the bore, thus increasing the efficiency with which the member is heated. A still further embodiment of the method according to the invention is characterized in that a member is fused the bore of which is blackened on the inside. In this way, the absorption of the laser beam in the bore is increased. Another embodiment of the method according to the invention is characterized in that a member is fused, such that the member-glass contact area extends substantially in one plane. The member is fused to a very small depth. The temperature distribution is more homogeneous in a flat base than in a pointed base, resulting in faster fusion. It is remarked that European patent application EP-A-0 332 262, which is part of the state of the art according to art 54(3) EPC describes a method of manufacturing a colour display tube comprising an envelope having a display window and, in the envelope, a colour selection electrode having a large number of apertures, and suspension means for suspending the colour selection electrode opposite the display window, a member of each suspension means by means of a fusing arrangement being fused, at least partly, into the envelope, wherein during fusing the said member is heated by means of a laser beam generated by a laser; the member-glass contact area extends substantially in one plane. The invention will now be described in more detail by means of a few embodiments and with reference to the drawing, in which Fig. 1 is a schematic, sectional view of a colour display tube which can be manufactured according to the invention; Fig. 2 is a detailed sectional view of a colour display tube which can be manufactured according to the invention which detail represents, inter alia , the suspension means; Fig. 3 shows an arrangement which can suitably be used for the method according to the invention; Figs. 4 a , 4 b and 4 c are illustrations of the method according to the invention. The Figures are schematic representations and are not drawn to scale, corresponding parts in the different embodiments bearing the same reference numerals. Fig. 1 is a sectional view of a colour display tube which can be manufactured according to the invention. The colour display tube comprises an envelope 1 having, in the present example, a substantially rectangular display window 2 having an upright edge 3. The envelope further comprises a cone 4 and a neck 5. A pattern of phosphors 6 luminescing in red, green and blue is provided on the display window 2. An electron gun 9 for generating three electron beams 10, 11 and 12 is mounted in the neck 5 of the colour display tube. These beams are deflected by a coil system 13 and intersect substantially at the location of the colour selection electrode 7, after which each of the electron beams is incident on one of the three phosphors provided on the screen. Each suspension means 8 comprises a member, which is fused into the envelope with its base, in this example, near the corner of the upright edge 3 of the display window 2, and a second member connected to the colour selection electrode, which in the present example is a plate-shaped resilient element which extends transversely to the electron beams 10, 11 and 12 which are deflected to the relevant corner. Fig. 2 is a detailed sectional view of a colour display tube which can be manufactured according to the invention as shown in Fig. 1. The member 13 of a suspension means is fused into the upright edge 3 of the display window 2 by means of a base 14 and, in the present example, extends transversely to the edge 3 of the display window 2. The colour selection electrode 7 is formed by a thin mask sheet 16 having a large number of apertures and which is provided with an upright edge 17. A mask edge 18 is secured to the upright edge 17. A support strip 19 is secured to the corner of the mask edge 18. The second member of the suspension means, a flat resilient element 20, is secured to said support strip 19. The flat resilient element 20 is at an angle to the longitudinal axis of the colour display tube, such that it extends substantially perpendicularly to the electron beams 10, 11 and 12 which are deflected to the relevant corner of the display window 2. In the present example, the flat resilient element contains a part 21 which has partly the shape of a hollow cone, and which is secured to a substantially flat part 22. Part 21 comprises aperture 23 in which engages head 24 of the member 13. The shape of the members shown herein is nob to be regarded as limitative. Fig. 3 shows an arrangement which can suitably be used in the method according to the invention. One common laser is used for a group of fusing arrangements. In this way, the total space needed for the group of fusing arrangements is reduced. Such an arrangement is schematically shown in Fig. 3. A laser beam is generated by laser 40. This laser beam is divided into n -sub-beams, in the present example four, 42 up to and including 45, in the optical divider 41. These sub-beams are led to arrangements 46 up to and including 49. These sub-beams may be divided further in an arrangement, as shown, for example, in Fig. 3, in which sub-beam 45 is sub-divided into four beams 50 to 53 in the fusing arrangement 49, by means of which beams 50 up to and including 53, for example, four members, can be fused simultaneously. The latter division has the advantage that the four members can be fused simultaneously, which is much quicker and reduces the possibility of errors in the positioning relative to one another. Fig. 4 is an illustration of the method according to the invention. Member 38 is heated by means of a laser beam 37. Member 38 is provided with a bore 39. Member 38, hereinafter called "pin", is subsequently pressed into the envelope 36 by means of a pressure system 400. This can be carried out in any place and at any angle desired because it does not require complicated equipment. In the present example, the pin 38 is provided with a conical bore 39 which extends into the part to be fused. Owing to this, energy is supplied to where it is necessary. The least possible energy is lost. In the present example, laser beam 37 and pin 38 are on the same side of the envelope. In order to increase the absorption of the laser beam the bores may have been blackened, that is, provided with a substance or being treated such that a very high absorption of the laser beam is obtained at the inner surface of the bores. It is alternatively possible to heat pin 38 by means of a laser beam which passes through the envelope, as is shown in Fig. 4 b . This may have advantages, for example if it is difficult or even impossible to subject the pins directly to the laser beam because of the presence of objects around the pins. Figure 4 c shows a pin 38 having a flat base. The advantage of this embodiment of the method according to the invention is that the laser beam does not have to be focussed, less glass has to be displaced, and the temperature of the base is more homogeneous during the fusion process. An inhomogeneous temperature distribution in the base, i.e., the portion of the pin 38 to be fused, induces, after cooling, thermal stresses in the glass. Besides, when the temperature distribution is inhomogeneous there is a greater risk that the glass is locally overheated. It will be clear that within the scope of the present invention many variations are possible to those skilled in the art.

Claims: Method of manufacturing a colour display tube comprising an envelope (1) having a display window (2) and, in the envelope, a colour selection electrode (7) having a large number of apertures, and a plurality of suspension means for suspending the colour selection electrode opposite the display window, a member (38) of each suspension means being fused, at least partly, into the envelope, wherein during fusing the said member (38) is heated by means of a laser beam (37) generated by a laser (40) and wherein one common laser is used for heating a plurality of said members (38). A method as claimed in claim 1, characterized in that more than one member (38) is fused substantially simultaneously. A method as claimed in claim 1 or 2, characterized in that the laser beam (37) passes through the envelope (1). A method as claimed in claim 1, 2 or 3, characterized in that said members (38) are provided with a respective bore which is closed on one side, the laser beam (37) being incident on the open side of said bore. A method as claimed in claim 4, characterized in that each member (38) has a base, which is fused and that the bore (39) extends into the base. A method as claimed in claim 4 or 5, characterized in that the bore (39) extends conically from the open side into the interior of the member (38). A method as claimed in claim 4, 5 or 6, characterized in that the bore (39) is blackened on the inside. A method as claimed in any one of the preceding claims, characterized in that each member-glass of the envelope contact area extends substantially in one plane.

Inventors: VAN DER AA, HERMAN HENRICUS MARIA
Applicants: N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1989
Main classification: H01J9
IPC codes: H01J9, H01J29