EP0403010A1

EP0403010A1 - Method of producing a display tube, and display tube

Info

Publication number: EP0403010A1
Application number: EP90201495A
Authority: EP
Inventors: Theodoor Christiaan Anna Hens; Martinus Cornelis Maria Verhoeven; Paulus Hendricus Maria Verheggen
Original assignee: Philips Gloeilampenfabrieken NV; Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 1989-06-16
Filing date: 1990-06-11
Publication date: 1990-12-19
Also published as: NL8901524A; JPH0330244A

Abstract

A method of producing a display tube having a magnetic shield 19 comprising two complementary parts 15 and 16. The two parts and 16 are first positioned facing one another at a mutual distance d and are interconnected by means of elements 35 of a non-magnetic material. Thereafter the dual magnetic shield 19 is fitted in the display tube.

Description

The invention relates to a method of producing a display tube having an inner magnetic shield comprising two complementary parts.
The invention also relates to a display tube and more specifically to a display tube produced in accordance with such a method.
An inner magnetic shield, comprising two complementary parts placed at a short distance opposite each other serves to screen an electron beam generated in a display tube from exterior magnetic fields, such as for example the magnetic field of the earth. The magnetic screening depends on the value of the distance between the two parts. To avoid unwanted influences of magnetic fields on the path of the electron beam, it is important for this distance to be substantially not subjected to changes during operation and throughout the operating life of the display tube.
However, in practice it was found that, especially in display tubes of larger dimensions, it is a problem to maintain the distance between the parts constant throughout the operating life of the display tube.
It is inter alia an object of the invention to provide a method of producing a display tube having a magnetic shield comprising two complementary parts placed at a short distance facing one another, the shield being secured in the display tube in a simple manner, so that the distance between the parts is substantially not subjected to changes.
According to the invention, a method of the type defined in the opening paragraph is characterized, in that the two parts are placed facing one another while forming a non-magnetic gap therebetween, and that the two parts are interconnected by elements of a non-magnetic material which bridge the gap whereafter the magnetic shield is secured in the display tube. In practice it has been found that this ensures that the distance between the parts remains sufficiently constant throughout the operating life of the display tube. In addition, the two parts of the magnetic shield form one integral whole before they are suspended, whilst maintaining the magnetic screening function, and are therefore easy to handle, which simplifies fitting of the shield in the display tube. Also an accurate and firm connection the two parts with the desired mutual spacing is provided between in a simple manner.
It is known per se from abstracts of Japanese Patents vol. 35 (1988), p. E624, JP-88,/13238 to interconnect the two parts of a magnetic shield after each of them has separately been fitted to a carrier frame of a shadow mask, by means of sheets of glass frit or similar materials.
A preferred embodiment of a method according to the invention, whereby the two parts are interconnected firmly in a simple and fast manner, is characterized in that interconnection of the parts is effected by attaching a non-magnetic metal or metal alloy to the parts.
A further preferred embodiment of a method according to the invention in which a shadow mask provided with a large plurality of apertures is fitted in the display tube during one manufacturing step, is characterized in that the shield is fitted in the display tube whilst mechanically being uncoupled from the shadow mask. This prevents vibrations in the shadow mask being passed on to the dual shield. These vibrations might cause an unwanted change in the interspacing of the shield parts.
The invention provides a display tube having an envelope with a display window, an electrode system generating at least one electron beam and an inner magnetic shield located between the electrode system and the display window, which shield includes two complementary parts which are placed spaced apart facing each other, the display tube providing an adequately constant magnetic screening throughout its operating life when it is characterized in that the two parts are interconnected by elements of a non-magnetic metal or metal alloy.
A display tube having an envelope with a display window, a shadow mask provided with a large plurality of apertures fitted in the envelope, an electrode system for generating at least one electron beam and an inner magnetic shield fitted in the envelope and being located between the electrode system and the shadow mask, the shield comprising two interspaced opposing complementary parts, which according to the invention is preferably characterized in that the shield is fitted in the envelope without being mechanically coupled to the shadow mask and in that the two parts are interconnected by elements of a non-magnetic material, evidences an accurate colour purity of a picture to be displayed and has a magnetic shielding which is not susceptible to vibrations in the shadow mask. A simple, mechanically uncoupled connection of the shadow mask and the magnetic shield in the display tube, is obtained in a preferred embodiment of a display tube according to the invention, in that the shadow mask is provided with flexible elements which are connected to supporting means provided in the display window, and in that the parts of the shield are each provided with suspension means each connected to a relevant supporting element.
The mechanical stability of the two parts of the magnetic shield is sufficiently high in a display tube according to the invention when it is characterized in that the two parts of the magnetic shield are interconnected at least their free ends.
Preferably, the two parts of the magnetic shield are interconnected along substantially the overall length of their facing sides. This improves the mechanical stability of the connection between the two parts of the magnetic shield to a still further extent.
Some embodiments of a method of producing a display tube according to the invention will now be described with reference to the accompanying drawing, in which

Fig. 1 is a schematical cross-sectional view of a display tube according to the invention, comprising a dual magnetic shield,
Fig. 2 is a schematical cross-sectional view of a dual magnetic shield according to the invention,
Fig. 3 is a schematical, perspective view of an alternative embodiment of a magnetic shield according to the invention,
Fig. 4 is a schematical, cross-sectional view of a display tube according to the invention in which a shadow mask is connected to the shield whilst being mechanically uncoupled therefrom, and
Fig. 5 is a schematical, cross-sectional view of an alternative embodiment of a display tube according to the invention, in which the shadow mask is connected to the shield without being mechanically coupled thereto.

The colour picture tube shown in a cross-sectional view in Fig. 1 has an envelope with a substantially rectangular display window 1, a cone 2, and a neck 3. The neck 3 contains an electrode system 4 having three electron guns for generating three electron beams 5, 6 and 7. The electron beams are generated in one plane (in this case the plane of drawing), and are directed to an internal display screen 8 which is applied on the display window 1 and consists of a large number of phosphor elements which are coated with an aluminium layer 20 and luminesce in red, green and blue. The phosphor elements are, for example, in the form of strips and the longitudinal direction of the strip-like elements is perpendicular to the plane through the electron gun (the plane of drawing here). On their path to the display screen 8, the electron beams 5, 6 and are deflected on to the picture screen 8 with the aid of a plurality of deflection coils 9 arranged coaxially around the tube axis, and pass through a shadow mask 10 constituted by a thin metal plate 11, whose longitudinal direction extends parallel to the phosphor elements of the display screen 8. The three electron beams 5, 6 and 7 pass through the apertures 11 at a slight angle to each other and consequently each impinge on only phosphor elements of one colour. A dual internal magnetic shield 19 which in this embodiment is in the form of a truncated cone and has a substantially rectangular end is provided with a flange 21. The dual internal shield 19 reduces the detrimental effects of external magnetic fields, such as, for example, the magnetic field of the earth, on the electron beam path. In this embodiment, the internal shield 19 is fastened by means of its flange 21 in each of its corners to a supporting strip 12 of the shadow mask supporting arrangement. The inner shield 19 comprises two complementary parts 15, 16 which are placed facing each other spaced apart by a distance d. The magnetic shielding depends on the value of this distance d. In practice it was found that it is possible to ensure in a simple manner that this distance d remains constant during the operating life of the display tube, when during manufacture of the display tube the parts 15 and 16 are first interconnected by means of elements 17 of a non-magnetic material so that the magnetic shield 19 is formed (as is shown schematically in Fig. 2), whereafter the magnetic shield 19 is secured in the display tube. Before the two parts 15 and 16 are interconnected, they are accurately positioned at the distance d (which, for example, is 5 mm) necessary for the desired magnetic shielding. In addition, securing the two complementary parts in the display tube is simplified by the fact that the two parts can be handled as one integral whole. The mechanical stability of the shield 19 in the display tube is also improved thereby. On the occurrence of shocks and/or vibrations the two parts 15, 16 move together in a similar manner so that the distance d between the two parts 15, 16 does not change. The magnetic shielding consequently remains constant. A curable synthetic resin material can, for example, be used as the material of which the elements 17 are produced.
Preferably, elements of a non-magnetic metal or metal alloy are used which are secured to the two parts of the shield, for example by welding, which in a simple way provides an adequate mechanical stability of the dual shield. An alloy of Cr, Ni and Fe is particularly suitable because of its non-magnetic properties and the fact that it can be worked in a simple manner.
It will be obvious for a person skilled in the art that the non-magnetic materials to be used and the compositions of the metal alloys can be of many different types and that consequently the invention is not limited to the examples given.
The elements 17 can, for example, be plates in the form of strips or small circles which can be connected to both the interior side and the exterior side of the parts 15 and 16.
An adequate mechanical stability of the connection between the two parts 15 and 16 is preferably obtained by using four elements 35 which interconnect the free ends of the parts 15 and 16, as shown schematically in Fig. 3. The mechanical stability of the connection is still further improved when the two parts of the magnetic shield are interconnected substantially along the overall length of their facing sides. This connection can be realised by one adequately large or several smaller elements of a non-magnetic material.
Since the shadow mask 10 and also the shield 19 are generally made of thin metal sheets, they are both very susceptible to vibrations and shocks. To prevent the shadow mask 10 from passing unwanted vibrations on to the shield, or vice versa, the shadow mask 10 is preferably, in accordance with the invention, fitted in the display tube without being mechanically coupled to the shield 19, which is shown schematically in Fig. 4. The shadow mask 10 is fitted in the display tube by means of flexible elements 22 applied in the corners of the shadow mask 10. Each flexible element 22 is connected to a supporting element 23 applied in the corresponding corner of the display window 1. The dual shield 19 is connected in the display tube by means of the flange 21 and supporting elements 24 which are applied in, for example, the corners of the display window 1. The flange 21 may directly be connected to the supporting elements 24 or, in a different embodiment, with the aid of a suspension means, for example a flat resilient element.
The mechanical stability of the dual shield 19 is indeed ensured, in accordance with the invention, by connecting the two parts and 16 of the shield 19 to elements 17 made of a non-magnetic material.
The supporting elements 23 and 24 may be different supporting elements, but preferably the shield 19 and the shadow mask are fitted in the display tube with the aid of the same supporting elements 25 as is shown schematically in Fig. 5. Each supporting element 25 is, for example, provided with a cone-shaped free end 26 to which the flexible elements 22 are connected. In this embodiment the shadow mask 10 is connected to a carrier frame 29, which carrier frame 29 is provided in its corners with the flexible elements 22. However, in an alternative embodiment, it is possible to suspend the shadow mask without a carrier frame in the display tube.
The shield 19 is provided with a flange 28 to which suspension means 27 (for example flexible elements) are connected, the supporting means themselves being connected to the free end 26 of the relevant supporting element 25. Thus, the shadow mask 10 is suspended in a simple manner separately from the shield 19.
It will be obvious that within the scope of the invention many variations are possible for a person skilled in the art. Thus, it is, for example, possible to use different types of suspensions of the shadow mask and the shield than the examples given in the description.
The invention is described with reference to a colour picture tube having a shadow mask. The invention however also relates to a display tube without shadow mask for the display of monochrome images.

Claims

1. A method of producing a display tube having an inner magnetic shield, comprising two complementary parts, characterized in that the two parts are placed facing one another while forming a non-magnetic gap therebetween, and that the two parts are interconnected by elements of a non-magnetic material which bridge the gap, whereafter the magnetic shield is secured in the display tube.

2. A method as claimed in Claim 1, characterized, in that connecting the parts is effected by connecting elements made of a non-magnetic metal or metal alloy to the parts.

3. A method as claimed in Claim 1 or 2, in which during a different manufacturing step a shadow mask having a large number of apertures is connected in the display tube, characterized in that the shield is fitted in the display tube without being mechanically coupled to the shadow mask.

4. A display tube produced in accordance with the method as claimed in any one of the preceding Claims.

5. A display tube having an envelope with a display window, an electrode system for generating at least one electron beam and an inner magnetic shield located between the electrode system and the display window, the shield comprising two spaced-apart facing complementary parts, characterized in that the two parts are interconnected by elements of a non-magnetic metal or metal alloy.

6. A display tube having an envelope with a display window, a shadow mask connected in the envelope and having a large number of apertures, an electrode system for generating at least one electron beam and an inner magnetic shield which is fitted in the envelope and is located between the electrode system and the shadow mask, the shield comprising two spaced-apart, facing complementary parts, characterized in that the shield is fitted in the envelope without being mechanically coupled to the shadow mask and in that the two parts are interconnected by elements of a non-magnetic material.

7. A display tube as claimed in Claim 6, characterized in that the shadow mask is provided with flexible elements which are connected to supporting elements applied in the display window, and in that the parts of the shield are each provided with suspension means which are each connected to a relevant supporting element.

8. A display tube as claimed in Claim 4, 5, 6 or 7, characterized in that the two parts of the magnetic shield are interconnected at least by means of their free ends.

9. A display tube as claimed in any one of the Claims 4 to 8, inclusive, characterized in that the two parts of the magnetic shield are interconnected substantially along the overall length of their facing sides.