Cathode-Ray Tube for Projector

Patentamt

JEuropâischesEuropean Patent Office ® Publication number: 0 058 415

Office européeneuroDéen des brevets B1

® Dateof publication of patent spécification: 22.05.85 (â) Int. Cl.4: H 01 J 29/02 (§) Application number: 82101062.6 ® Dateoffiling: 12.02.82

(54) Cathode-ray tube for projector.

(§) Priority: 12.02.81 JP 18047/81 (73) Proprietor: Kabushiki Kaisha Toshiba 72, Horikawa-cho Saiwai-ku Kawasaki-shi Kanagawa-ken 210 (JP) (§) Date of publication of application: 25.08.82 Bulletin 82/34 (72) Inventor: Sato,Takeo 3330-6, Uwanodai Fukaya-shi (§) Publication of the grant of the patent: Saitama-ken (JP) 22.05.85 Bulletin 85/21

74) Représentative: Patentanwâlte Henkel, (S) Designated Contracting States: Pfenning, Feiler, Hânzel & Meinig DE FR GB Môhlstrasse 37 D-8000 Munchen 80 (DE)

(M) Références cited : : US-A-2 832 911

CÛ m oo io o o Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall CL be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been LU paid. (Art. 99(1 ) European patent convention). Courier Press, Leamington Spa, England. the phosphor screen, and the heat conduction member is conductively in contact with a heater The present invention relates to a cathode-ray radiator which is secured on the outer side of the tube for a projector, the heat radiation character- effective area of the faceplate. istic of which is improved. This invention can be more fully understood In the cathode-ray tube for a projector, a phos- from the following detailed description when - phor screen formed on the inner surface of a face- taken in conjunction with the accompanying plate is scanned with an electron beam from an drawings, in which: electron gun. An image of an effective surface is Figs. 1 and 2 are views showing a cathode-ray thus obtained. The image of the effective surface tube for a projector according to one embodiment is focused on a projection screen by an optical of the present invention in which Fig. 1 is a sec- system arranged outside or inside the tube. tional view thereof and Fig. 2 is a plan view of a The cathode-ray tube for a video projector must heat radiating assembly thereof; and be activated at a final anode potential, that is, a Figs. 3 and 4 are graphs for comparing the potential of +25 kV to +30 kV on the phosphor characteristics of a conventional cathode-ray tube screen. The phosphor screen of the cathode-ray for a projector and a cathode-ray tube for a pro- tube for a video projector must be scanned with jector of one embodiment of the present inven- an electron beam of which the current density is tion, in which Fig. 3 is a graph for explaining the several ten times that of the electron beam used relation between the running period and the tem- for a cathode-ray tube for television. 90% of an perature rise at the central outer surface of a face- input power of 0.05 to 1.0 W/cm2 will be vanished plate, and Fig. 4 is a graph for explaining the as a heat loss. The heat loss causes rises in the relation between a predetermined temperature temperature of the phosphor on the effective area measuring position on the outer surface of the which is scanned with the electron beam and in faceplate and the temperature rise on the outer the temperature of the outer surface of the face- surface thereof. plate corresponding to the effective area. There- A cathode-ray tube for a projector according to fore, the following problems are presented. one embodiment of the present invention will be 1) Luminous efficiency is degraded owing to the described in detail with reference to Figs. 1 and 2. rise of temperature of the phosphor. A phosphor screen 14 and a metal back layer 15 2) The faceplate may be cracked by a stress are formed on an inner surface of a faceplate 11 of which is caused by a difference between the tem- an envelope comprising the faceplate 11, a funnel perature rise on the outer surface corresponding 12 and a neck 13. An electron gun 17 which emits to the effective area and the temperature rise on an electron beam 16 for scanning an effective sur- the peripheral outer surface which surrounds the face of the phosphor screen 14 is disposed in the outer surface corresponding to the effective area. neck 13. Deflection yoke 18 is mounted on an In order to solve the first problem, a cooling outer wall portion extending from the funnel 12 to mechanism on the inner surface of the faceplate the neck 13. The above structure is substantially may be adopted. However, such a cooling the same as that in the conventional cathode-ray mechanism is not proposed in practice. In fact, a tube. Further, in the present invention, a number cooling mechanism which cools the phosphor of thin wires 22 made of a good heat conduction indirectly from the outer surface of the faceplate material such as copper are meshed or arranged is currently used. Further, in order to solve the in a stripe pattern. The thin wires 22 are arranged second problem, it is very effective to reduce the in contact with the outer surface of the faceplate temperature difference between the outer surface 11 corresponding to the effective area of the corresponding to the effective area and the peri- phosphor screen 14. Further, the ends of the thin pheral outer surface by conducting heat on the wires 22 are conductively in contact with a frame- outer surface of the faceplate corresponding to like heat plate 21 extending outward from the the effective area to the peripheral outer surface edge portion of the faceplate 11. The thin wires 22 and the peripheral part of the faceplate. For this are sealed in a transparent sealing member layer purpose, conventionally, various structures have 23 of a thin film. Further, a transparent plate 24 for been proposed. However, these cooling devices mechanically reinforcing and preventing damage are large in size, resulting in low relative lumi- of the transparent sealing member layer 23 is nance. Thus, the satisfactory cathode-ray tube for formed. a projector cannot be obtained. After the heat radiating plate 21 is formed, a It is an object of the present invention to pro- copper wire of 0.1 to 0.2 mm in diameter is wound vide a cathode-ray tube for a projector which is around the plate 21 at a pitch of 1 to 3 mm. relatively simple in construction and low in cost Alternatively, a heat conductive member may be and which eliminates or reduces the above prob- printed on a portion of the transparent plate 24 lems. corresponding to the faceplate 11. In this case, the In order to achieve the above and other objects heat radiation plate 21 preferably extends from of the present invention, there is provided a the periphery of the transparent plate 24 in con- cathode-ray tube for a projector characterized in sideration of heat radiation. The connection be- that a mesh-like or striped heat conduction tween the thin wires 22 and the heat radiating member is disposed on the outer surface of the plate 21 may be preferably established by adhe- faceplate corresponding to the effective area of sion under pressure, soldering or welding. Fur- ther, it is effective to increase heat absorption and 60% the temperature rise of the conventional radiation by subjecting the heat radiating plate 21 faceplate. Further, the cooling effect of the face- and the thin wires 22 to the blackening treatment. plate according to the present invention is im- A transparent synthetic resin, especially, an addi- proved by about 34%. tion reaction type transparent silicone is prefer- The above comparison is performed when the able as the transparent sealing member layer 23. thin copper wires 22 are not blackened. Further, According to a method for manufacturing a the above embodiment of the present invention cathode-ray tube for a projector of the present does not provide a tight contact between the heat invention, a heat radiating assembly comprising radiating plate 21 and the copper wires 22. When the heat radiating plate 21 and the thin wires 22 is these procedures are completely performed, the placed on the outer surface of the faceplate 11. effects shown in Fig. 3 are further improved. Transparent silicone which is hardened by the When the effects indicated by the curves 31 and addition reaction is poured. Further, the trans- 32 of Fig. 3 are applied to a case wherein an input parent plate 24 is placed on poured transparent power per unit area on the phosphor screen is silicone. The heat radiating assembly is sand- 0.08 W/cm2, the temperature rise is reduced by wiched between the transparent plate 24 and the about 15 to 17°C under natural convection on the outer surface of the faceplate 11 and adhered outer surface of the faceplate. For example, when under pressure. a phosphor screen made of a phosphor P43 Various characteristics of a conventional (Gd20lS:Tb) is used, luminance is increased by cathode-ray tube for a projector and a cathode- 13% as compared with the conventional sample. ray tube of one embodiment of the present inven- However, in consideration of the size of an open- tion will be described with reference to Figs. 3 and ing which may be determined by the diameter of 4. the copper wire and the pitch of the turns, and Fig. 3 shows a curve 31 indicating the relation transmission loss of the transparent sealing between the temperature rise at the central outer member layer composed of transparent silicone surface of the faceplate corresponding to the and of the transparent plate, the total luminous effective area of the phosphor screen when a con- efficacy is improved by 5%. ventional cathode-ray tube which has a rec- Therefore, in order to minimize the decrease in tangular faceplate of 10 mm thickness is activated luminous efficacy due to the temperature rise of at an input power per unit area of the phosphor the phosphor, the size of the opening must be screen of 0.18 W/cm2. This temperature rise is further enlarged and heat conductivity of the thin given by a difference between the measured tem- wires 22 must be increased. perature and room temperature. In this condition, The distribution of heat on the outer surface of the temperature rise at the central outer surface of the faceplate will be described with reference to the faceplate reaches 75 to 77°C. Fig. 4. On the other hand, according to the present In the same conditions as described above, the invention, a non-coated copper wire 22 of 0.2 mm conventional cathode-ray tube for a projector and in diameter is wound around the heat radiating the cathode-ray tube of the present invention are plate 21 of the framelike shape which is made of activated. Temperatures at the central portion of an aluminum plate of 0.5 mm thickness, 180 mm the faceplate, a portion corresponding to the edge length and 145 mm width and which has a rec- of the outer surface corresponding to the effective tangular opening of 120 mm length and 75 mm area, a peripheral portion of the faceplate have width at the center of the aluminum plate. The been measured. Further, the temperature of the heat radiating plate 21 is wrapped by the copper heat plate of the present invention has been also wire at a pitch of about 2.5 mm. This heat measured. The results are shown by a curve 33 radiating plate is placed on the rectangular face- for the conventional cathode-ray tube for a pro- plate of 10 mm thickness of the cathode-ray tube jector and by a curve 34 for the cathode-ray tube for a projector so as to align the opening with the for a projector of the embodiment of the present outer surface corresponding to the effective area. invention. Compositions A and B of the addition reaction The temperature of the outer surface of the type transparent silicone YE5822 manufactured faceplate corresponding to the central portion of by Toshiba Silicone KK are mixed in a ratio of the phosphor screen in the conventional cathode- 10:1. The mixture is filled in the opening. The ray tube for a projector is measured to be at a transparent plate 24 of glass of 2 mm thickness is temperature of about 76°C. The temperature at placed on the mixture. The mixture is then cured the peripheral portion of the faceplate is about under proper pressure at a temperature of about 20°C, resulting in a temperature difference of 50°C for 30 minutes to 1 hour. When cathode-ray 56°C. On the other hand, according to the tube thus prepared is used under substantially the cathode-ray tube for a projector of the present same conditions as in the conventional one, the invention, the temperature of the outer surface of temperature rise at the central portion of the face- the faceplate corresponding to the central portion plate 11 is indicated by a curve 32. The tempera- of the phosphor screen is measured to be about ture rise saturates at 50°C. 50°C. The temperature at the peripheral portion of The temperature rise at the central portion of the heat radiating plate is about 23°C. Thus, the the faceplate according to the present invention is temperature difference is only about 27°C. Stress acting on the peripheral portion of the faceplate is comprised in the range from 0.1 mm to 0.2 mm. thus reduced to about 1/2 to 1/3, facilitating the 3. A cathode-ray tube for a projector according prevention of cracking of the faceplate. to claim 1, wherein said heat conduction member In the above embodiment, the frame-like heat is embedded in a transparent sealing member radiating plate and the metal wires of a stripe layer. pattern are used. However, the present invention 4. A cathode-ray tube for a projector according is not limited to this combination. A heat conduc- to claim 3, wherein a transparent protecting plate tion member of a mesh-like pattern (including is further secured on said transparent sealing lattice and net-like patterns) may be used. Further, member layer. the mesh-like or striped heat conduction member 5. A cathode-ray tube for a projector according may be printed on the transparent plate or on the to claim 4, wherein said heat radiator extends faceplate. It is apparent that the transparent plate from a peripheral portion of said transparent pro- and the transparent sealing member layer may be tecting plate. eliminated. However, in this case, it is desired that the decrease in the luminous efficacy of the effective area be minimized. According to the present invention, the tem- 1. Kathodenstrahlröhre für einen Projektor, da- perature rise of the outer surface of the faceplate durch gekennzeichnet, daß ein gitterartiges oder corresponding to the effective area is minimized. streifenförmiges Wärmeleitelement an der The heat radiating body is preferably in tight con- Außenfläche eines Schirmträgers entsprechend tact with the peripheral portion of the faceplate einer Effektiv- oder Wirkfläche eines Leuchtstoff- and adhered so as to reduce loss in heat conduc- schirms angeordnet ist und das Wärmeleit- tion. Heat conducted from the central portion of element mit einem an der Außenseite des the faceplate through the heat conduction mem- Schirmträgers befestigten Wärmestrahler leitend ber is used for raising the temperature at the in Berührung steht. periphery of the faceplate so as to reduce a tem- 2. Kathodenstrahlröhre für einen Projektor nach perature difference thereby to reduce the stress Anspruch 1, dadurch gekennzeichnet, daß das acting on the peripheral portion of the faceplate. Wärmeleitelement dünne Kupferdrähte eines Thus, the cathode-ray tube of high luminance and Durchmessers im Bereich von 0,1-0,2 mm um- high reliability is achieved according to the faßt. present invention. 3. Kathodenstrahlröhre für einen Projektor nach Further, in the conventional cathode-ray tube Anspruch 1, dadurch gekennzeichnet, daß das for a projector, the outer surface of the faceplate Wärmeleitelement in eine durchsichtige Dicht- is electrically charged, thus resulting in deposi- element- oder Vergußmassenschicht eingebettet tion of dust or the like. However, since the heat ist. conduction member is made of an electrically 4. Kathodenstrahlröhre für einen Projektor nach conductive material the heat conduction member Anspruch 3, dadurch gekennzeichnet, daß weiter- may be grounded to the GND terminal of the hin eine durchsichtige Schutzscheibe oder -platte power source of the cathode-ray tube for a pro- an der durchsichtigen Vergußmassenschicht be- jector. Thus, the electrostatic attraction on the festigt ist. outer surface of the faceplate or the transparent 5. Kathodenstrahlröhre für einen Projektor nach plate becomes substantially zero, thus eliminat- Anspruch 4, dadurch gekennzeichnet, daß der ing the deposition of dust or the like thereon. Wärmestrahler über einen Umfangs(rand)teil der In summary, the cathode-ray tube for a pro- durchsichtigen Schutzscheibe oder -platte hinaus- jector according to the present invention is of ragt. high luminance and high reliability. Further, various expensive additional elements which are conventionally used for improving the luminance and image quality which may be degraded by con- tamination of the outer surface of the faceplate 1. Tube à rayons cathodiques pour projecteur, can be eliminated, thus facilitating the great caractérisé en ce qu'un élément de conduction de industrial applicability. chaleur en forme de maille ou en bandes est dis- posé sur la surface extérieure d'une dalle anté- rieure correspondant à une zone effective d'un écran luminescent, et en ce que l'élément de con- 1. A cathode-ray tube for a projector, wherein a duction de chaleur est en contact d'une manière mesh-like or striped heat conduction member is conductrice avec une plaque de refroidissement disposed on the outer surface of a faceplate corre- qui est fixée sur le côté extérieur de la dalle sponding to an effective area of a phosphor antérieure. screen, and said heat conduction member is con- 2. Tube à rayons cathodiques pour projecteur ductively in contact with a heat radiator which is selon la revendication 1, caractérisé en ce que secured on the outer side of the said faceplate. l'élément de conduction de chaleur comprend des 2. A cathode-ray tube for a projector according fils minces de cuivre ayant un diamètre compris to claim 1, wherein said heat conduction member entre 0,1 mm et 0,2 mm. comprises thin copper wires having a diameter 3. Tube à rayons cathodiques pour projecteur selon la revendication 1, caractérisé en ce que fixée sur la couche d'élément de fixation trans- l'élément de conduction de chaleur est enfoui parente. dans une couche d'élément de fixation trans- 5. Tube à rayons cathodiques pour projecteur parente. selon la revendication 4, caractérisé en ce que la 4. Tube à rayons cathodiques pour projecteur plaque de refroidissement s'étend à partir d'une selon la revendication 3, caractérisé en ce qu'une partie périphérique de la plaque de protection plaque de protection transparente est en outre transparente.