Color cathode ray tube apparatus

Abstract: In a color cathode ray tube apparatus, a shadow mask is fixed on a frame with a predetermined tension for cancelling a thermal expansion of the shadow mask during normal operation of the color cathode ray tube apparatus. The mechanical strength of the longer sides on the frame is higher than that of the shorter sides of the frame by fixing reinforcing plates or ribs on the longer sides in order that the tension of the shadow mask not become uneven. Furthermore, said frame is made of a material having a thermal expansion coefficient smaller than that of a material of said shadow mask.

Description: This invention relates to a cathode ray tube apparatus, and especially relates to a cathode ray tube, apparatus having a shadow mask which is fixed on a frame under a condition that a predetermined tension is applied to the shadow mask. In a flat type color cathode ray tube apparatus, about 80 % of electron beams which are emitted from electron guns collide with a shadow mask. The shadow mask is heated by the collision of the electron beams, and it is deformed by thermal expansion. In order to prevent the reduction of the quality of picture images displayed on a screen of the cathode ray tube apparatus caused by the deformation of the shadow mask, the shadow mask has been fixed on a frame under a condition that a predetermined tension is applied to the shadow mask in the conventional color cathode ray tube apparatus. The frame of the conventional color cathode ray tube apparatus is integrally formed from a plate by press working in order to make a cross-sectional shape of each side substantially L-shaped. Alternatively, the frame is formed by welding of four angle bars having a substantially L-shaped cross-section in order to make each angle between the sides be substantially right angle. Therefore, an electron beam through hole on the frame is formed as a substantially rectangular shape. At the same time, the manufacturing process of the frame can be made simple and the cost of the frame can be reduced. On the other hand, when the rigidity of the frame is not sufficient, the frame will be deformed by the tension applied to the shadow mask. Thereby, the surface of the shadow mask corrugates. Furthermore, the relative positions of electron beam through holes on the shadow mask against phosphor regions on the screen are discrepant. Thus, a mislanding occurs on the color cathode ray tube apparatus. For preventing the deformation of the frame, as shown in JP-A-3-187132, the cross-sectional shape of each side of the frame is made to be substantially triangular for increasing the rigidity of the frame. Furthermore, in the shadow mask which is fixed on the frame with the predetermined tension, the tension should be larger to cancel the thermal expansion of the shadow mask sufficiently, for preventing the mislanding due to the thermal expansion of the shadow mask, when the shadow mask is heated by the irradiation of the electron beams during operation of the color cathode ray tube apparatus. Therefore, the frame is made of a material having a larger thermal expansion coefficient than that of the material of the shadow mask, which is, for example, shown in JP-A-2-204943. In the flat type color cathode ray tube apparatus, the aspect ratio is, for example, 3:4 or 9:16, so that the screen or the frame is horizontally oblong. Thus, when the shadow mask is fixed on the frame by welding with the predetermined tension in the manufacturing process, quantities of the strain of the longer side and the shorter side are different from each other. Therefore, the tension which is applied to the shadow mask becomes uneven. As a result, the mislanding will occur due to the discrepancy between the electron beam through holes on the shadow mask and the phosphor regions on the screen by the thermal expansion of the shadow mask during operation of the color cathode ray tube apparatus. Furthermore, since the tension along the longer side is larger, the longer sides of the frame warp inward. At the same time, the shorter sides warp outward. For preventing the interlocking of the warp of the longer sides and the shorter sides, it is proposed that cuttings are provided on respective corners of the frame for warping the longer sides and the shorter sides independently, which is, for example, shown in JP-A- 5-290754. However, when the cross-section of each side of the frame is of triangular shape, a reinforcing plate is to be obliquely welded between a side wall perpendicular to the shadow mask face and a flange parallel to the shadow mask face. Alternatively, each side member of the frame is formed by bending a plate to provide a substantially triangular cross-section or formed by cutting a bar having a substantially triangular cross-section, and the side members are welded at four corners of the frame. By such a configuration, the frame has disadvantages in that the weight of the frame becomes heavier and the working process of the frame become complex, and the cost for manufacturing the frame becomes expensive. Furthermore, when the cuttings are provided on respective corners of the frame, the tension applied to the shadow mask will be uneven in the vicinity of the cuttings. Thus, the corrugation occurs in those parts, and the corrugation becomes the cause of the mislanding of the picture image displayed on the screen of the color cathode ray tube apparatus. Furthermore, in a heat treatment during the manufacturing process of the color cathode ray tube apparatus, plastic deformation occurs in the shadow mask. Thus, the tension which is applied to the shadow mask is reduced. Generally, a temperature of the shadow mask in a normal actuation of the color cathode ray tube apparatus is about 100 degrees Celsius. On the other hand, the highest temperature of the shadow mask in the heat treatment is about 450 degrees Celsius. As mentioned above, the frame is made of the material having larger thermal expansion coefficient than that of the material of the shadow mask for preventing the reduction of the tension applied to the shadow mask. Since the temperature of the shadow mask and the frame in the heat treatment in the manufacturing process becomes about five times as large as the temperature in the normal operation of the cathode ray tube apparatus, the difference between the thermal expansion of the shadow mask and the thermal expansion of the frame is magnified. Thus, the tension applied to the shadow mask will be larger that that in the normal actuation of the color cathode ray tube apparatus or the ordinary temperature. As a result, a plastic deformation occurs in the shadow mask. The tension applied to the shadow mask in which the plastic deformation occurs will be reduced at the ordinary temperature, and a mislanding will occur during operation of the color cathode ray tube apparatus. An objective of this invention is to provide an improved color cathode ray tube apparatus, in which the tension applied to the shadow mask is uniform in each direction after the welding of the shadow mask on the frame. Another objective of this invention is to provide an improved cathode ray tube apparatus, in which no corrugation occurs on the shadow mask even when the shadow mask is welded on the frame with a predetermined tension, and the weight of the frame is not increased and the working process of the frame does not become complex. This object is achieved with the features of the claims. By such a configuration according to the invention, the quantity of the thermal expansion of the shadow mask becomes larger than that of the frame in the heat treatment of the manufacturing process. The shadow mask temporarily reduces the tension at a high temperature by the expansion. Thus, the plastic deformation may not occur on the shadow mask. When the heat treatment is completed, the shadow mask is contracted, so that the tension applied to the shadow mask recovers. As a result, the tension, by which the thermal expansion of the shadow mask by the irradiation of the electron beams in the normal actuation of the color cathode ray tube apparatus can be cancelled or absorbed, remains after the heat treatment. FIG.1 is a cross-sectional plan view showing a configuration of a first embodiment of a color cathode ray tube apparatus of this invention; FIG. 2 is a perspective view showing a configuration of a frame in an embodiment of a color cathode ray tube apparatus of this invention; FIG.3 is a drawing showing the temperature rise of a shadow mask during normal operation of the color cathode ray tube apparatus; FIG.4 is a drawing showing a characteristic curve of the reduction of a tension applied to the shadow mask; and FIG. 5 is a drawing showing characteristic curves of the thermal expansion of the shadow mask and the frame. As can be seen from FIG.1, the first embodiment of the color cathode ray tube apparatus of this invention comprises a funnel 1 made of glass, a panel 2 made of glass, a phosphor screen 8 disposed inside of the panel 2, a shadow mask 3 disposed in the vicinity of the phosphor screen 8, a frame 4 for supporting the shadow mask 3, and an electron gun 6 disposed in a neck part of the funnel 1. The shadow mask 3 is fixed on the frame 4 by resistance welding, laser welding working, and the like under a condition that a predetermined tension of about 10 Kg/mm 2 is applied to the shadow mask 3. The longer sides of the frame are about 333 mm, and the shorter sides are about 256 mm. The cross-sectional shapes of the respective sides are substantially L-shaped. Electron beams, which correspond to red, green and blue colors and are radiated from the electron gun 6, pass through predetermined electron beam through holes formed on the shadow mask and reach predetermined phosphor regions of the phosphor screen 8 corresponding to the colors of the electron beams. Each phosphor region, which is irradiated by the electron beam, luminates the color of red, green or blue corresponding to the electron beam. Thus, a color picture image can be displayed on the screen of the panel 2 of the color cathode ray tube apparatus. As can be seen from FIG.2, the frame 4 has a substantially rectangular shape viewed on a plane parallel to the shadow mask 3. A shadow mask welding face 41, which is parallel to the shadow mask 3, is formed at an open end of the frame 4. Flange faces 43, which are parallel to the shadow mask welding face 41, are formed at the other open end of the frame 4. Side walls 42 are integrally formed along the inner peripheries of longer sides and shorter sides of the shadow mask welding face 41. Furthermore, the side walls 42 and the flange faces 43 are respectively formed integrally. Reinforcing plates may be respectively fixed on the flange faces on the longer sides. As can be seen from FIG. 2, a shadow mask 3, which is made of an iron and has electron beam through holes arranged in a pitch of about 0.26 mm, is fixed on a frame 4 with a tension for cancelling or absorbing thermal expansion of the shadow mask 3 during normal operation of the color cathode ray tube apparatus. The frame 4 is made of an alloy containing 50%Ni and Fe. A slit 41d is formed at each corner of a shadow mask welding face 41 for providing an elasticity to the frame 4. Under a condition that side walls 42 of the frame 4 are warped to the inside of the frame 4, the shadow mask 3 is welded on the shadow mask welding face 41. Thereby, a predetermined tension can be applied to the shadow mask 3. When the shadow mask 3 is made of iron, the thermal expansion coefficient α M is 12 × 10 -6 (1/° C) and Young's modulus E M is 9800 kg/mm 2 . When the room temperature is 20 degrees Celsius, the temperature rise of the shadow mask during the normal operation of the color cathode ray tube apparatus will be about 80 degrees Celsius. The tension T for cancelling or absorbing the thermal expansion of the shadow mask during the normal operation is obtained by the equation of T ≧ α M · ▵ t o · E M . Actually, T is over 9.4 kg/mm 2 . A relation between the tension applied to the shadow mask 3 and the reduction of the tension after a heat treatment is shown in FIG. 4. When a conventional color cathode ray tube apparatus was produced with a shadow mask assembly, in which the shadow mask 3 made of iron was fixed on the frame 4 made of the same iron with a tension of 9.4 kg/mm 2 , the tension applied to the shadow mask 3 was reduced by about 70 to 80 % after the heat treatment in a temperature of about 450 degree Celsius. The reason the tension applied to the shadow mask 3 was reduced was the plastic deformation of the shadow mask. As can be seen from FIG. 4, it is preferable that the tension applied to the shadow mask 3 is zero for preventing the reduction of the tension applied to the shadow mask 3 due to the heat treatment. However, it is necessary that the tension applied to the shadow mask 3 in the assembly of the shadow mask assembly is 9.4 kg/mm 2 . Thus, it is impossible to make the tension applied to the shadow mask 3 zero. Therefore, a shadow mask assembly, in which the tension applied to the shadow mask 3 is zero at the temperature of 450 degrees Celsius in the heat treatment and the tension cancelling the thermal expansion can be applied to the shadow mask 3 during the normal operation of the color cathode ray tube apparatus, is necessary. For obtaining such a shadow mask assembly, a thermal expansion coefficient α F of the frame 4, in which the characteristic curve A of the thermal expansion of the shadow mask 3 and the characteristic curve B of the frame 4 cross at 450 degrees Celsius, is obtained from FIG.5. A relation between the thermal expansion coefficient α F of the frame 4, by which the tension applied to the shadow mask 3 becomes zero at 450 degrees Celsius, and the thermal expansion coefficient α M of the shadow mask 3 is shown by the equation of α F ≦ α M (1-(▵ t o /▵ t)) . Herein, the temperature rise of the shadow mask 3 during the normal operation of the color cathode ray tube apparatus is ▵ t o (°C) and the temperature rise of the shadow mask 3 in the heat treatment during the producing process of the color cathode ray tube apparatus is Δ t (°C). The thermal expansion coefficient can be decided by the above-mentioned equation. When the shadow mask 3 is made of iron, the thermal expansion coefficient of the frame α F is obtained by α F ≦ 12 × 10 -6 × (1-(80/430)). Namely, the value of the thermal expansion coefficient of the frame 4 is to be smaller than 9.7 × 10 -6 (1/°C). A material having a thermal expansion coefficient similar to the above-mentioned value is 50%Ni-Fe alloy. By such a configuration, the plastic deformation of the shadow mask in the heat treatment can be prevented. Thus, the reduction of the tension applied to the shadow mask 3 due to the plastic deformation of the shadow mask 3 can be prevented.

Claims: A color cathode ray tube apparatus comprising a funnel (1), a panel (2), a phosphor screen (8) disposed inside of said panel (2), a shadow mask (3) disposed in the vicinity of said phosphor screen (8), a frame (4) on which said shadow mask (3) is fixed and an electron gun (6) disposed in a neck part of said funnel (1), wherein said frame (4) has a shadow mask welding face (41) in which four sides thereof are continuously formed in a substantially rectangular shape defined by opposed pairs of longer and shorter sides, side walls (42) which are continuously formed along an inner periphery of said shadow mask welding face (41) and a flange face (43) which is formed along said side walls (42) and is substantially parallel to said shadow mask welding face (41); and said shadow mask (3) is fixed on said frame (4) under a condition that a predetermined tension is applied to said shadow mask (3); characterized in that said frame (4) is made of a material having a thermal expansion coefficient smaller than that of a material of said shadow mask (3); and when the thermal expansion coefficient of the material of said frame (4) is α F (1/°C), the temperature rise of said shadow mask (3) from the room temperature during operation of said color cathode ray tube apparatus is Δ t o (°C), the temperature rise of said shadow mask in a heat treatment during a production process of said color cathode ray tube apparatus in Δt (°C), the thermal expansion coefficient of the material of said shadow mask (3) is α M (1/°C), Young' modulus of said material of said shadow mask (3) at the room temperature is E M (kg/mm 2 ), said tension applied to said shadow mask (3) is T (kg/mm 2 ), the equations of α F ≦ α M (1- (▵ t o / ▵ t)) and T ≧ α M ·Δ t o ·E M are satisfied. The color cathode ray tube apparatus in accordance with claim 1, wherein a plurality of cuttings (41d) are formed on said shadow mask welding face (41), said side walls (42) of said frame (4) have elasticity in a direction outward and inward with respect to the frame (4), and said predetermined tension is applied to said shadow mask (3) by the elastic restoring force of said side walls (42) of said frame (4).

Inventors: ARAYA JUN, ISHIBASHI MAYUMI, MAKI HIDEAKI, OKAMOTO TAKAMI, ARAYA, JUN, ISHIBASHI, MAYUMI, MAKI, HIDEAKI, OKAMOTO, TAKAMI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1995
Main classification: H01J29
IPC codes: H01J29