A cathode ray tube

Abstract: A colour cathode ray tube includes an evacuated envelope including a panel having a faceplate, a rear metal plate hermetically connected to the faceplate through first connecting means, a plurality of funnel-shaped members connected to the rear plate through second connecting means, and a plurality of necks, respectively, extending from the funnels. A plurality of electron gun assemblies are received in the necks for emitting a plurality of electron beams and a phosphor screen formed on the inner surface of the faceplate emits visible light by excitation by the electron beams.

Description: This invention relates to the form of the envelope of a cathode ray tube and more particularly to an envelope for a cathode ray tube display device of a multi-neck structure. Colour cathode ray tubes for large-sized, high brightness, high resolution colour TV receivers for use in high definition TV systems, or for large-sized, high resolution graphic display units for use in computer terminals, have requirements differing from those for colour cathode ray tubes applicable to general consumer applications. Various investigations have been carried out to satisfy these requirements. A high brightness and a high resolution shadow mask colour cathode ray tube with a small-sized screen are at present commercially available. However, tubes with a large-sized screen having sufficiently high degrees of brightness and resolution have not yet been commercially realised. The main reason for this shortcoming can be attributed to the increase in the magnification factor of the electron-optics of the electron gun which would necessarily accompany any extended tube depth due to possible increases in tube dimensions. There is a reduction in the electron beam energy intensity on the screen surface as a result of any screen enlargement. In order to overcome such a drawback, a colour cathode ray tube of a multi-neck structure with a high resolution and brightness has been proposed in EP-A-0201865; EP-A-0201098 and EP-A-0226423. A multi-neck colour cathode ray tube is illustrated in Figure 1 of the accompanying drawings which is a cross-sectional view of the tube. The tube 1 has an evacuated envelope 2 which includes a panel 3 composed of a single faceplate 4 with a rectangular inner surface and a skirt 5 extending parallel to a central axis Z around the periphery of the faceplate 4, a funnel-shaped member 6 hermetically connected to the skirt 5 at one end and a plurality of necks 7a, 7b, 7c and 7d. In each neck an electron gun assembly 8a, 8b, 8c and 8d is provided for emitting three electron beams 9a, 9b, 9c and 9d. In the figure, the three electron beams are illustrated by a single line for simplification. A phosphor screen 10 is formed on the inner surface of the faceplate 4 for reproducing colour image by excitation by the electron beams 9a, 9b, 9c and 9d. A mask 11 with a plurality of apertures allowing passage of the electron beams is provided in the panel 3 and supported by a mask frame 12 so that there is a predetermined distance between the phosphor screen 10 and the mask 11. During operation of the tube, the electron beams 9a, 9b, 9c and 9d are deflected by deflection yokes 13a, 13b, 13c and 13d, respectively, so as to scan the first, second, third and fourth regions 10a, 10b, 10C and 10d of the phosphor screen 10. As can be seen from Figure 1, the envelope 2, especially the funnel-shaped member 6, has a complex configuration, it is difficult to form and, consequently, the envelope 2 is not suitable for mass production. It is necessary to have circular openings 14a, 14b, 14c and 14d for hermetically connecting to the respective necks 8a, 8b, 8c and 8d. In addition, walls 15a, 15b, 15c, 15d and 15e, which define the respective openings, should be inclined so as to allow the passage of the electron beams from the electron gun assemblies toward the phosphor screen 10. Furthermore, it is difficult to correctly and hermetically connect the necks 7a, 7b, 7c and 7d to the walls of the funnel-shaped member 6 at the openings 14a, 14b, 14c and 14d in order that the electron beams correctly land on the phosphor screen. Furthermore, as the size of the envelope 2 is increased, it is necessary to make the glass thickness of the funnel-shaped member 6 almost as thick as that of the panel 3 in order to maintain the strength against atmospheric pressure. On the other hand, the necks 7a, 7b, 7c and 7d, which are hermetically connected to the funnel-shaped member 6, are made of glass, the thickness of which is normally very thin at about 1 mm. The heat distribution from the funnel-shaped member 6 to the necks 7a, 7b, 7c and 7d changes abruptly. Consequently, the heat strain in the multiple heating processes which are undergone during the manufacturing process of the tube increases and the envelope tends to break at the connection between the necks and the funnel. Therefore, the envelope with the construction described above is unsuitable for mass-production. EP-A-0356823 falling within the terms of Article 54(3)EPC is in the name of the same Applicant as the present application and it has an earlier priority date than, but it was not published until after, the priority date of the present application. The publication discloses a colour cathode ray tube in which the hermetically sealed envelope includes a glass screen section having phosphor material on the inner surface thereof and a rear section including a metal plate, carrying a plurality of glass funnel-shaped members each having a neck and an electron gun assembly in each neck. The metal plate is hermetically connected to the screen section through a first annular metal connecting member which has a first flat portion contacting the metal plate and bonded to the screen section and a second flat annular portion contacting and secured to the metal plate. Each funnel-shaped member is hermetically connected to the metal plate, through a second annular metal connecting member. According to a first aspect of the present invention, a display device having an evacuated envelope includes a glass screen section having phosphor material on the inner surface thereof and a rear section carrying a source of electrons whereby the phosphor material emits visible light when excited by a beam of electrons from the source, said rear section including an apertured metal plate hermetically sealed to the periphery of the glass screen section by an annular metal connecting member which has a first flat annular portion contacting the metal plate and bonded to the glass screen section and a second flat annular portion contacting and secured to the metal plate, characterised in that the first and second portions of the connecting member are separated by a further annular portion which includes a projection which projects away from the plate and constitutes a deformable portion capable of absorbing strain caused by differential thermal expansion between the metal plate and the screen section. According to a second aspect of the present invention, a cathode ray tube device having an evacuated envelope includes a glass screen section having phosphor material on the inner surface thereof; an apertured metal plate hermetically sealed to the periphery of the glass screen section by a first annular metal connecting member which has a first flat annular portion contacting the metal plate and bonded to the glass screen section and a second flat annular portion contacting and secured to the metal plate; a plurality of glass funnel-shaped members each having a neck and an electron gun assembly in the neck; each of said funnel shaped members being hermetically connected to the plate around an aperture therein by a second annular metal connecting member which has a first flat annular portion contacting the metal plate and bonded to the funnel shaped member and a second flat annular portion contacting and secured to the metal plate, characterised in that the first and second portions of the first connecting member and optionally the first and second portions of each second connecting member are separated by a further annular portion which includes a projection which projects away from the plate and constitutes a deformable portion capable of absorbing strain caused by differential thermal expansion between the metal plate and the screen section and between the metal plate and the funnel shaped member respectively. Since the first and second connecting members, which can each stabilise strain caused by difference between thermal expansion of the panel and that of the rear plate and difference between thermal expansion of the rear plate and that of the necks, respectively, are used for connecting the rear plate and the necks through the funnels, the cathode ray tube can be prevented from destruction when differential thermal expansion of the glass panel and that of the rear metal plate occurs during a heating process. Therefore, accidental destruction of the tubes during tube manufacturing process has been remarkably decreased. Furthermore, since the tube includes the first and second connecting members, the rear plate, which bridges the panel and the necks made of glass through the funnels, can be made of mild steel which is cheaper than a sealing alloy. As the result, the price of the tube can be reduced. In order that the invention may be more readily understood, it will now be described, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 is a cross-sectional view of a conventional multi-neck colour cathode ray tube; Figure 2 is a perspective view of a colour cathode ray tube in accordance with a preferred embodiment of the invention, having the cross-section of Figure 3; Figure 3 is a cross-sectional view of the colour cathode ray tube shown in Figure 2; Figure 4 is a cross-sectional view of an enlargement of first and second connecting members; Figure 5 is a cross-sectional view of the first connecting member during manufacture; Figure 6 is a cross-sectional view of the first connecting member after connection; Figure 7 is a cross-sectional view of a part of a colour cathode ray tube in accordance with another embodiment of the invention; Figure 8 is a cross-sectional view of a part of a colour cathode ray tube in accordance with another embodiment of the invention; and Figure 9 is a cross-sectional view of part of a colour cathode ray tube in accordance with a still further embodiment of the invention. In Figures 2 and 3, a colour cathode ray tube 20 with a multi-neck structure includes an evacuated envelope 21. The envelope 21 includes a panel 22 which is composed of a single glass faceplate 23 with roughly rectangular shape and a glass skirt extending from the periphery of the faceplate 23 approximately parallel to a centre axis Z of the faceplate 23, a rear metal plate 25 is hermetically connected to the skirt 24 through a first connecting member 26 having the form of an annular ring and has a main surface approximately parallel to the faceplate 23. Twelve glass funnel-shaped members 27a, 27b, ... 27l, each of which has a conical shape, are hermetically connected to the rear plate 25 through second connecting members 28a, 28b, ... 28l having the form of an annular ring. Twelve glass necks 29a, 29b, ... 29l are hermetically connected to the respective funnels 27a, 27b, ... 27l. On the envelope 21, reinforcement plates 30a, 30b and 30c, each of which has a main surface approximately perpendicular to the main surface of the rear plate 25, are provided for reinforcement of the rear plate 25. The cathode ray tube 20 also includes twelve electron gun assemblies 31a, 31b, ... 31l, which are received in the necks 29a, 29b, ... 29l for emitting three electron beams. A phosphor screen on the inside of plate 23 is composed of a plurality of three kinds of phosphor stripes for emitting respective red, green and blue light. A shadow mask 33, which has a plurality of apertures is positioned a predetermined distance from the phosphor screen 32 and a mask frame 34 supports the shadow mask 33. During operation of the cathode ray tube 20, the electron gun assemblies emit three electron beams in response to picture signals corresponding to each colour. The electron beams scan a specified area of the phosphor screen 32. In the case of this embodiment, the phosphor screen 32 is divided into a total of twelve specified areas, three specified areas vertically and four specified areas horizontally. Since this type of colour picture tube can be regarded as similar to the case of multiple small colour picture tubes which are arranged in series, the picture quality, that is to say, the convergence and resolution (spot diameter of an electron beam on the screen), is the same as that in a small size colour picture tube and is superior to that of a normal size colour picture tube. The panel 22, which comprises the faceplate 23 and the skirt 24, is made of soft glass. The first connecting member 26 is a ring-shaped thin metal plate of width 30 mm, of which the outer periphery is roughly the same shape as that of the outer periphery of the skirt 24. The member 26 is made of a sealing alloy consisting of 50% nickel alloy with a thickness of 0.1 mm. The member 26 also has an annular deformable projection 36 with a radius approximately 4 mm inside the skirt 24 for absorbing strain caused by differential expansion between the skirt 24 and the rear plate 25 by deformation of the projection 36. The rear plate 25 with twelve openings is made of mild steel with a thickness of 2 mm and has an outer periphery which is roughly the same as that of the outer periphery of the skirt 24. The second connecting members 28a, 28b, ... 281 are ring-shaped thin metal plate of width 5 mm, respectively. Each member is made of a sealing alloy consisting of 50% nickel alloy with a thickness of 0.2 mm. Each of the funnel-shaped members 27a, 27b, ... 271 has a conical shape with a diagonal length of the wider end opening of approximately 50 mm and is hermetically connected to each neck 29a, 29b, ... 291 of an external diameter 22.5 mm. The funnels and the necks are made of soft glass. The shape of the openings in the rear plate 25, the inner periphery of the second connecting members and the inner periphery of the funnel-shaped members are roughly the same so as to be hermetically connected to each other. The reinforcement plates 30a, 30b and 30c fixed to the rear plate 25 are made of mild steel of thickness 2.0 mm and have a length of 40 mm, respectively. Next, with reference to Figure 4, the bonding method for the panel 22, the rear plate 25 and the funnel 27 through the first and second connecting members 26 and 28 is explained. In the envelope 21 of the cathode ray tube 20, frit sealing is used for glass-metal seal and seam welding is used for metal-metal seal. Namely, the end of the skirt 24 and a first flat portion 26a of the first connecting member 26 are hermetically connected to each other by a frit glass layer 40. Also, the end of the funnel 27h and one surface of the second connecting member 28h are hermetically connected to each other by a frit glass layer 41. The bonding by the frit glass layer is completed by heating at a temperature of about 450°C for one hour. For increasing the bonding strength of the bond between the frit glass layers 40 and 41 and the first and second connecting members 26 and 28h, respectively, oxide layers are formed on the surface portions of the first and second members 26 and 28h to which the frit glass layers 40 and 41 are bonded. After bonding as mentioned above, since thermal expansion coefficient of the first and second connecting member 26 and 28h are 99.0 x 10⁻⁷/°C and that of the panel 22 and funnel 27h are 100 x 10⁻⁷/°C, residual strain is negligibly small. The second member 28h and a second flat portion 26b of the first connecting member 26 which is substantially coplanar with the portion 26a are bonded to the rear plate 25 by seam welding. For the welding, it is preferable to space the positions where welding is carried out as far as possible from the bonding position where the frit sealing is carried out in order to prevent peeling of the frit glass layer due to thermal deformation caused by the heat during the welding. Although resistance welding is used for the welding of the rear plate 25 to the first and second connecting members 26 and 28h in this embodiment, any welding can be applicable, such as plasma welding, laser welding, ultrasonic welding. The first connecting member 26 has a third flat portion 26c which is substantially coplanar with the first and second flat portions and which isolates the projection 36 from the first flat portion 26a. The third flat portion 26c is difficult to deform by strain caused by differential thermal expansion between the rear plate 25 and the panel 21, as compared with the deformability of the projection 36. If the thermal expansion coefficient of all parts of the envelope of the tube is the same and the thermal capacity of the parts are also equal, no strain would remain in any part after connection and, thus, there would be spontaneous breakage. In the case of bonding the glass member to the metal member, the strength of glass to resist the strain due to bonding is weaker than that of metal, in particular, tensile strength of glass is very weak. On the other hand, since the strength of the metal to resist the strain is much stronger than that of the glass, the metal member is hardly broken under the strain. It can be considered that there are two main causes of the breakage of the glass member due to the bonding. One cause is a difference between thermal expansion coefficient of glass and that of the metal. Another cause is a difference between thermal expansion amount (or thermal contraction amount) of the glass member and that of the metal member. In other words, latter cause depends on difference of thermal capacity of the members. The breakage due to the former does not depend on the size of the member. On the other hand, the breakage due to the latter is determined by the sizes of the members, the ratio of material with different thermal expansions included in the whole of the tube. In general, the larger the tube size, the greater the influence. In the embodiment, the first connecting member 26 mentioned above can stabilise such strain caused by difference of thermal expansion amount by deformation of the projection 36. This mechanism is explained, in detail, with reference to Figures 5 and 6. As shown in Figure 5 showing the condition of bonding by frit sealing, the projection 36 is not deformed when the first connecting member 26, which has been previously welded to the rear plate 25 at the point S, is bonded to the end of the skirt 24 by frit glass, since the frit glass is melted at high temperature. As shown in Figure 6, when these members have reached normal temperature, since thermal expansion amount of the rear plate 25 is greater than that of the panel 22, the rear plate 25 thermally contracts inwards (in the direction of arrow). As the thermal contraction, the projection 36 is deformed, as shown in Figure 6, and absorbs the difference in thermal expansion of the panel 22 and the rear plate 25. When the projection 36 is deformed, the third flat portion 26c which isolates the projection 36 from the frit sealing portion is hardly deformed. The strain due to the thermal contraction is not transferred to the frit sealing portion. In consequence, the breakage of the panel by the thermal contraction of the rear plate 25 can be prevented. As shown in Figure 6, the skirt 24 is not directly sealed to the rear plate 25. However, since the skirt 24 is pressed against the rear plate 25 due to atmospheric pressure, the position of the skirt end is hard to shift on the rear plate 25. In the embodiment mentioned above, the projection 36, which absorbs the strain caused by the difference in thermal expansion, is only provided on the first connecting member 26, but the second connecting member 28, which is a ring-shaped plate, has no projection. Since the bonding surface of the funnel 27 and the second connecting member 28 is small, and the difference in thermal expansion is also small, the strain, which breaks the funnel 27, does not occur. When the second connecting member is required to have a deformable projection due to increased bonding surface, the same effect can be obtained when the projection is provided in this member as well. In this embodiment, the cross-sectional shape of the projection 36 was formed in a semi-circular shape. However, the projection 36 can be formed in any shape capable of expanding and contracting in order to absorb the strain caused by difference in thermal expansion amount by deformation. For example, it can be formed in an oval or triangular shape. The connecting member may have one or more projections. Also, the connecting member may be made of a sealing alloy of 52% nickel - 6% chromium alloy. It is preferable for the projection with a semi-circular shape that the radius of the projection ranges from about 3 mm to 5 mm in the case of this embodiment. If it exceeds 5 mm, the projection will be crashed due to atmospheric pressure. The suitable size of the projection will be varied in accordance with the sizes of the tube and the connecting member. It is also preferable for the projection that the projection is smoothly connected to both flat portions of the connecting member. Although, in this embodiment, the member with a cross-sectional shape of "L" letter is used as the reinforcement plates 30a, 30b and 30c which are welded to the rear plate 25 by spot resistance welding, a flat-shaped member can be used as the reinforcement plates 30a, 30b and 30c when the plates 30a, 30b and 30c are welded by arc welding or plasma welding. Also, regarding the positioning and number of the reinforcement plates, it is effective to provide the required number of the plates where the deformation of the rear plate due to atmospheric pressure is great. Further, in the cathode ray tube shown in Figures 2 and 3, a thin metal plate, which is reinforced against atmospheric pressure by the reinforcement plates 30a, 30b and 30c, is used for the rear plate 25 to reduce weight of the envelope. However, the reinforcement plates can be omitted if the rear plate has a sufficient thickness. For example, when the rear plate with a thickness of 8 mm is used, the reinforcement plate can be omitted since the deformation of the rear plate is extremely small. Another embodiment is explained with reference to Figure 7. An envelope 50 of the cathode ray tube shown in Figure 7 has a first connecting member 51. The same as the first connecting member previously explained, the connecting member 51 has a projection 53 surrounding the skirt 54 of the panel 52 and a solid portion 51a which is harder to be deformed than the projection 53 due to the strain caused by the difference betwen thermal expansion amount of the panel 52 and that of the rear plate 56. Also, the connecting member 51 is bonded to the end of the skirt 54 by a frit glass layer 55 at one end and is welded to the rear plate 56 at point S. Thus, the panel 52 of glass is hermetically connected to the rear plate 56 of metal through the first connecting member 51. The connecting member 51 can absorb the strain caused by the difference in thermal expansion amount of the panel 52 and the rear plate 56 by deformation of the projection 53. Since the first and second connecting members are part of the envelope, it is desirable for preventing the connecting members from getting rusty. Namely, as shown in Figure 8, the first connecting member 60 is covered with a layer 61 of potting material filling the space between the wall of the skirt 62 of the panel 63 and a flange portion 64 of the rear plate 65 extending parallel to the wall of the skirt 62. Of course, the connecting member 60 has the projection 66 for absorbing the strain caused by the difference in thermal expansion amount of the panel 63 and the rear plate 65. Also, the connecting member 60 is bonded to the panel 63 by the frit glass layer 66 and is welded to the rear plate 65 at line of S. Also, if the first connecting member 70 and the projection 70A is provided, mainly inside the panel 71, as shown in Figure 9, a layer 72 of potting material can be provided so as to cover a space between the skirt 73 and the rear plate 74. The connecting member 70 is isolated from atmosphere by the layer 72 and is prevented from getting rusty. For potting material, any material, which is normally used for potting, such as liquid resin and silicone rubber, may be used. The envelope of the colour cathode ray tube according to the embodiment is applicable for an envelope of monochromo cathode ray tube. This invention may be applied to the display device in which the images are reproduced due to electron beam excitation of a phosphor screen composed of phosphor material.

Claims: A display device having an evacuated envelope (21) including a glass screen section (22) having phosphor material on the inner surface thereof and a rear section (25,27,29) carrying a source of electrons (31) whereby the phosphor material emits visible light when excited by a beam of electrons from the source, said rear section including an apertured metal plate (25,56,65,74) hermetically sealed to the periphery of the glass screen section (22) by an annular metal connecting member (26,51,60,70) which has a first flat annular portion (26a) contacting the metal plate and bonded to the glass screen section and a second flat annular portion (26b) contacting and secured to the metal plate, wherein the first (26a) and second (26b) portions of the connecting member are separated by a further annular portion which includes a projection (36,53,66,70A) which projects away from the plate and constitutes a deformable portion capable of absorbing strain caused by differential thermal expansion between the metal plate and the screen section. A cathode ray tube device having an evacuated envelope (21) including a glass screen section (22) having phosphor material on the inner surface thereof; an apertured metal plate (25, 56, 65, 74) hermetically sealed to the periphery of the glass screen section (22) by a first annular metal connecting member (26, 51, 60, 70) which has a first flat annular portion (26a) contacting the metal plate and bonded to the glass screen section and a second flat annular portion (26b) contacting and secured to the metal plate; a plurality of glass funnel-shaped members (27) each having a neck and an electron gun assembly (31) in the neck; each of said funnel shaped members being hermetically connected to the plate around an aperture therein by a second annular metal connecting member (28) which has a first flat annular portion contacting the metal plate and bonded to the funnel shaped member (27) and a second flat annular portion contacting and secured to the metal plate (25, 56, 65, 74) wherein the first (26a) and second (26b) portions of the first connecting member (26, 51, 60, 70) and optionally the first and second portions of each second connecting member (28) are separated by a further annular portion which includes a projection (36, 53, 66, 70A) which projects away from the plate and constitutes a deformable portion capable of absorbing strain caused by differential thermal expansion between the metal plate and the screen section and between the metal plate and the funnel shaped member respectively. A device as claimed in claim 1 or 2, characterised in that the projection on the or each connecting member is separated from the first flat portion of the connecting member by a further flat annular portion (26c, 51a) which is less deformable than the projection. A device as claimed in any preceding claim characterised in that the periphery of the glass screen section (22) is separated from the metal plate (25, 56, 65, 74) by a distance which is less than the distance by which the projection (36, 53, 66, 70A) projects from the metal plate. A device as claimed in any preceding claim, characterised in that the projection on the connecting member between the screen and the plate is inside the envelope. A device as claimed in claim 1, 2, 3 or 4,characterised in that the projection on the connecting member between the screen and the plate is outside the envelope. A device as claimed in claim 6, characterised in that the projection is protected from the atmosphere. A device as claimed in any preceding claim, characterised in that the cross-sectional shape of the or each projection is semi-circular. A device as claimed in any preceding claim, characterised in that the or each connecting member is connected to the glass part by a layer of glass frit.

Inventors: NISHIMURA TAKASHI INTELLECTUAL, TAKENAKA SHIGEO INTELLECTUAL P, NISHIMURA, TAKASHI, INTELLECTUAL PROPERTY DIVISION, TAKENAKA, SHIGEO, INTELLECTUAL PROPERTY DIVISION
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1989
Main classification: H01J29
IPC codes: H01J31, H01J29