COLOUR DISPLAY TUBE HAVING A MULTIPART SUSPENSION MEANS FOR A COLOUR SELECTION ELECTRODE AND METHOD OF MANUFACTURING A COLOUR DISPLAY TUBE

Abstract: A colour display tube having a display window and a colour selection electrode. The colour selection electrode is suspended from the display window by means of suspension means. These suspension means consist of a first element 33 which is connected to the colour selection electrode, and a second element 28 which is connected to the display window. This second element consists of two separately made parts, a head 30 and a base 29.

Description: The invention relates to a colour display tube comprising an envelope comprising a display window and a colour selection electrode, and suspension means for suspending the colour selection electrode from the said display window, which suspension means each comprises a first element which is secured to the colour selection electrode and a second element which is secured to the display window, the first element having an aperture and the second element having a portion which engages in the said aperture. A colour display tube of the type described in the opening paragraph, having suspension means in the vicinity of the four corners of a substantially rectangular display window is known from the published European Patent Application EP-A2-0156362. In the colour display tube described therein, the first element of each suspension means is a flat resilient element which is substantially perpendicular to the electron beams to be deflected to the relevant corner, and the second element is a metal pin which is secured on one side to the corner of an upright edge belonging to the display window and on the other (free) side has a convex portion. This pin is a metal body which is made in one piece. It is made of tinplate or moulded or turned from a rod-like metal body. From EP-A-0214689 a cathode ray tube is known, which comprises suspension means for suspending a colour selection electrode, said suspension means each comprising a metal pin with a mounting pad, connected to a (display) window by a plastically reformed metal connector. An important aspect of the suspension of the colour selection electrode is the dimensional accuracy with which the said (convex) portion of the second element of each suspension means engages in the aperture of the first element. When the display screen is provided on the display window in a photographic manner, repeatedly mounting and demounting of the colour selection electrode is necessary. In this process the insertion reproducibility, i.e. the degree of reproducibility of the location of the colour selection electrode is very important. This insertion reproducibility is co-determined by the accuracy with which the said (convex) portion and the surface of this portion of the second element of each suspension means is made. Consequently, it is an object of the invention to provide a means of increasing the insertion reproducibility of the colour selection electrode. This object is achieved by a colour display tube of the type mentioned in the opening paragraph, which is characterized according to the invention in that the second element of each suspension means comprises at least two separately made parts which are interconnected, the first part being connected to the display window and the second part containing the portion of the second element of the suspension means which engages in the aperture of the first element of the suspension means the first part forming a structural post upon which the second part is mounted. The first part of the second element of the suspension means will hereinafter be referred to as "the base", the second part will be referred to as "the head". The insight on which the invention is based is that due to the fact that the second element consists of at least two separately produced parts it is possible to manufacture the head with a very high dimensional accuracy without it being necessary to produce the entire second element with the same dimensional accuracy. In this way a very high insertion reproducibility of the colour selection electrode can be obtained in a readily conceivable way. A further aspect of the invention is that due to the fact that the said parts of the second element are manufactured separately, different requirements may be met for each of the parts. The base is connected to the display window. Dependent upon the manner of interconnecting, the demands imposed on the base and on the head are different. For example, in the case of sealing the base partly into the display window it is advantageous to roughen the surface of the base. A preferred embodiment of a colour display tube according to the invention is characterized in that the second part is an at least substantially spherical member. Spherical members having a high dimensional accuracy, a high degree of reproducibility and a very accurate surface can be made readily. The spherical shape has the highest symmetry. Consequently, the orientation of a spherical head relative to the base does not influence the dimensional accuracy with which the head engages in the aperture in the first element. Errors caused by deviations in the orientation of the head relative to the base can thus be avoided. A further preferred embodiment of the colour display tube according to the invention is characterized in that the first part consists of a material having a coefficient of expansion which is at least substantially equal to the coefficient of expansion of the material of which the display window is made. Thermal stresses which may lead to cracking may occur due to differences in the coefficients of thermal expansion of the display window and the base. Differences in the coefficients of thermal expansion may in addition lead to a change in the position of the base as a function of temperature. The position of the base may also change as a function of time due to thermal stresses present in the base or in the display window, which are caused by the difference in the coefficients of thermal expansion. Due to these effects the position of the shadow mask may change, thereby reducing picture quality. Yet another preferred embodiment of the colour display tube according to the invention is characterized in that the second part is made of a corrosion-resistant material. Due to corrosion the surface of the head may be damaged, which leads to a reduced insertion reproducibility. Within the scope of the invention both parts can advantageously be interconnected after the first part has been connected to the display window. During connecting the second element of the suspension means to the display window the head may be damaged when both parts of the second element are interconnected. It is also possible that the position of the second element deviates from the desired position such that it exceeds the limits of accuracy. Both deviations may lead to a reduction of the insertion reproducibility of the colour selection electrode and even to rejects. The risk that the head is damaged can be reduced by interconnecting the head to the base after the base has been connected to the display window; moreover, even when the position of the base connected to the display window deviates from the desired position this can be compensated to a certain extent when the head is connected to the base. The insertion reproducibility can thus be improved and the number of rejects decreased. For this reason, the invention also relates to a method of manufacturing a colour display tube of the type described hereinbefore, which method is characterized in that the first and the second part of each suspension means are connected to each other after the first part has been connected to the display window. The invention will now be explained in more detail by means of a few embodiments and with reference to a drawing, in which Figure 1 is a sectional schematic view of a colour display tube according to the invention; Figure 2 is a sectional detailed view of a colour display tube according to the invention, which detail depicts, amongst others, the suspension means; Figure 3 is a sectional view of a second element of the suspension means, which can suitably be used in a colour display tube according to the present state of the art; Figure 4 is a sectional view of a second element of the suspension means, which can suitably be used in a colour display tube according to the invention; Figures 5, 6, 7, 8 and 9 are sectional views of further examples of a second element of the suspension means, which can suitably be used in a colour display tube according to the invention. Figure 1 is a sectional view of a colour display tube according to the invention. The colour display tube comprises an envelope 1 having, in this example, a substantially rectangular display window 2 having an upright edge 3, and further comprising 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. A substantially rectangular colour selection electrode 7 having a great number of apertures is suspended by means of suspension means 8 at a short distance from the display window 2 near the corners of the said upright edge 3. 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 impinges on one of the three phosphors provided on the screen. Each suspension means 8 comprises a first element which is secured to the colour selection electrode and which, in the present example, is a plate-shaped resilient element which extends perpendicularly to the electron beams 10, 11 and 12 which are deflected to the relevant corner, and a second element which, in the present example, is secured near the corner of the upright edge 3 of the display window 2. Figure 2 is a sectional detailed view of a colour display tube according to the invention as shown in Figure 1. In the present example, the second element 13 of the suspension means is sealed to the upright edge 3 of the display window 2 and extends perpendicularly to the edge 3 of the display window 2. This second element 13 comprises a head 14, a base 15 interconnected by a connection 16. The colour selection electrode 7 consists of a thin mask blank 17 in which many apertures are provided, and which has an upright edge 18. A mask edge 19 is secured to the upright edge 18. A support strip 20 is secured to the corner of the mask edge 19. The first element of the suspension means, being a flat resilient element 21, is secured to this support strip 20. The flat resilient element 21 is at an angle with the longitudinal axis of the colour display tube, such that it extends substantially perpendicularly to the electron beams 10, 11 and 12 which are to be deflected to the relevant corner of the display window 2. In this example, the flat resilient element contains a part 22 which is partly formed as a hollow cone, and which is secured to a mainly flat part 23. The part 22 comprises an aperture 24 in which the head 14 of the second element 13 engages. The shape of the first element shown is not to be considered as limitative. It will be clear that within the scope of the invention many variations of the shape of the first element shown are possible, for example a first element as shown and described in GB 2,097,996 A. In this specification the first element consists of two parts which are interconnected by means of a spring construction. To illustrate the present state of the art, Figure 3 shows a second element 25 of the suspension means, as known from EP-A2-0156362. This element consists of a bottom portion 26, a convex portion 27 which engages in an aperture in a first element of the suspension means, which first element is not shown, and a neck 28. This second element 25 is a metal member which is manufactured in one piece. It consists of tinplate or it is turned or moulded from a rod-like metal body. The left-hand half of this drawing is a sectional view of a second element which is made of tinplate, the right-hand half is a sectional view of a second element which is turned from a rod-like metal body. To attain a high dimensional accuracy of the convex portion 27 and the surface of this portion 27 both methods of manufacturing are less suitable. Deviations which may adversely affect the insertion reproducibility of the colour selection electrode comprise deviations in the shape of the convex portion 27, for example deviations from the spherical shape, as well as irregularities in the surface of the convex portion 27, for example corrugations which may be formed during the turning of a rod-like body to form the second element 25. Figure 4 is a sectional view of a second element 28 of the suspension means which is suitable for use in a colour display tube according to the invention. In this example, the second element 28 consists of a base 29, a convex head 30, interconnected by a connection 31. The head 30 engages in the aperture 32 of the first element 33 of the suspension means. This first element 33 is connected to a colour selection electrode which is not shown in the drawing. The parts 29 and 30 of the second element 28 of the suspension means may be made of different materials. They may also be made of the same material. One or both parts may be made of, for example, metal, metal alloys, synthetic resin, glass or ceramics. The connection 31 may be made in any way suitable for interconnecting the parts 29 and 30. This may be, for example, resistance welding, laser welding, ultrasonic welding, thermocompression, bonding by means of an adhesive, cementing or bonding using an enamel. In this example, the base 29 is secured to the display window 2 by sealing it into the upright edge 3 of the display window. This method of connecting the base to the display window as well as the shape of the base should not be considered as limitative. Many other methods of connecting the base to the display window may suitably be used, for example, by means of thermocompression or ultrasonic welding. The spherical head 30 and the surface of this head 30 can be manufactured with a much greater accuracy than the spherical end 27 shown in Figure 3. The degree of accuracy with which the head 30 engages in aperture 32 of the first element 33 has thus been increased and, consequently, the insertion reproducibility of the selection electrode connected to this first element has also been increased. The base 29 may be manufactured with a much smaller degree of accuracy. Other shapes may be used for the head 30, for example a conical shape. The advantage of the spherical shape relative to other shapes is that the location of the head 30 relative to the base 29 cannot be influenced by the orientation of this head 30 relative to the base 29. This may occur, for example, when the head is cone-shaped. For this reason, the head 30 is preferably spherical. Preferably, the base 29 consists of a material whose coefficient of expansion is at least substantially equal to the coefficient of expansion of the material used for the display window. Problems, such as those described above, which may occur due to differences in the coefficients of thermal expansion of the base and the display window are then avoided as much as possible. Preferably, the head 30 consists of a corrosion-resistant material. Corrosion may damage the surface of the head 30, which leads to a reduced insertion reproducibility of the colour selection electrode. The base may be made of, for example, steel of the type N 1048 or of the type N 691. The head may be made of, for example, steel of the type N 1201. Figures 5, 6, 7, 8 and 9 are sectional views of further examples of a second element of the suspension means which is suitable for use in a colour display tube according to the invention. In Figure 5 a hollow base 34 is connected to the head 35 by means of connection 36. This head 35 engages in the aperture 38 of the first element 37 of the suspension means. In Figure 6 the base 38 is sealed into the upright edge 3 of the display window 2 at a predetermined angle. The base 38 is connected to the head 39 by means of connection 40. This head 39 engages in the aperture 42 of the first element 41 of the suspension means. In Figure 7 the base 43 is connected to the upright edge 3 of the display window 2 by means of thermocompression using a metal connection layer 44. Thermocompression is a method in which the metal of the connection layer is plastically deformed in contact with the glass, at an elevated temperature, but below the softening temperature of the glass. This method is described, inter alia , in American Ceramics Society Bulletin, volume 51, No. 9, page 683 (1972). In Figure 7 the base 43 consists of a solid cylinder 49 having a flange 50 which forms an acute angle with this cylinder. The base 43 is connected to the head 46 by means of connection 45. The head 46 engages in the aperture 47 of the first element 48 of the suspension means. Figure 8 is a sectional view of a second element of the suspension means 51, consisting of a base 52 and a head 55. The base 52 consists of a support 53 and a neck 54. The head 55 lies against the surface 56 of the neck 54 and is connected to the base 52 by means of the connection 57. Figure 9 shows a second element of the suspension means 58, consisting of a base 59 and a head 60, which are interconnected by means of a connection 61. In this example, the base consists of a bracket. The connections 36, 40 and 45 shown in the Figures 5, 6, 7, 8 and 9 may be formed in any suitable way, for example in the ways described hereinbefore. It will be clear that within the scope of the invention many variations are possible to those skilled in the art. For example, the base of the second element does not have to be connected to the upright edge of the display window, but instead may be connected to the front face of the display window. Within the scope of the invention other shapes for the base are alternatively possible.

Claims: 1. A colour display tube comprising an envelope comprising a display window and a colour selection electrode and suspension means for suspending the colour selection electrode from the said display window, which suspension means each comprises a first element which is secured to the colour selection electrode and a second element which is secured to the display window, the first element having an aperture, and the second element having a portion which engages in the said aperture, characterized in that the second element of each suspension means comprises at least two separately made parts, which are interconnected, the first part being connected to the display window, the second part containing the portion of the second element which engages in the aperture of the first element, the first part forming a structural post upon which the second part is mounted . 2. A colour display tube as claimed in Claim 1, characterized in that the second part is an at least substantially spherical member. 3. A colour display tube as claimed in Claim 1 or 2, characterized in that the first part consists of a material whose coefficient of expansion is at least substantially equal to the coefficient of expansion of the material of which the display window is made. 4. A colour display tube as claimed in Claim 1, 2 or 3, characterized in that the second part is made of a corrosion-resistant material. 5. A method of manufacturing a colour display tube according to any one of the preceding Claims, characterized in that the first and the second part of each suspension means are connected to each other after the first part has been connected to the display window.

Inventors: KIESCHKE, HANS GERHARD, VAN DER AVOORT, HENRICUS JOZEF MARIA, VAN RENS, PIET CHRISTIAAN JOZEF
Applicants: N.V. PHILIPS' GLOEILAMPENFABRIEKEN
Application year: 1988
Main classification: H01J29
IPC codes: H01J29