GB2052148A - Colour cathode ray tubes - Google Patents

Abstract

A flat panel type colour cathode ray tube has a flat panel 4, on which a colour phosphor screen 6 is formed, and which includes a recess 10 and guide grooves 11a, 11b for the receipt of engaging projections 12, 13a, 13b on the shadow-mask 7, which is urged towards the faceplate by springs 14. The accuracy with which the flat faceplate may be manufactured, and the avoidance of positioning projections on the faceplate, permit simplified manufacture of the phosphor pattern by printing. <IMAGE>

Description

SPECIFICATION Colour cathode ray tubes This invention relates to colour cathode ray tubes, and more particularly to so-called flat panel type colour cathode ray tubes, in which the front panel having a colour phosphor screen thereon is substantially flat.

In a prior art colour cathode ray tube, the front panel, which carries a colour phosphor screen, is of a part-spherical or part-cylindrical shape. Such a panel is generally made by pressing, and the consequent relatively low mechanical accuracy and variations in shape and dimensions, means that an electron beam landing or impinging position determining device (grid structure) such as a shadow mask or aperture grill having slits, which is provided in facing relation to the colour phosphor screen adjacent to the inner surface of the panel, must be provided using the so-called marriage or pairing system to determine the combination with a respective panel.In this system, the electron beam impinging position determining devices to be used with the respective panels, are set at the same positions as in a completed tube, and with the respective device used as a mask, respective colour phosphors are optically printed to provide the colour phosphor screen with a desired pattern.

Recently, a flat panel type colour cathode ray tube with a panel made of flat glass plate has been widely used for small size cathode ray tubes.

Figure 1 of the accompanying drawings shows diagrammatically an example of a flat panel type colour cathode ray tube. A tube or envelope 1 is formed of a neck portion 2, a funnel portion 3 and a panel 4 which is sealed to the open end of the funnel portion 3 by frit. Within the neck portion 2 is provided an electron gun 5 which will emit electron beams corresponding to, for example, red, green and blue colours, respectively. On the inner surface ofthe panel 4 there is provided a colour phosphor screen 6 made of respective colour phosphors which are coated with a predetermined pattern. In facing relation to the colour phosphor screen 6 is located an electron beam impinging position determining device 7 such as an aperture grill for registering the electron beams emitted from the electron gun 5 to land on the corresponding colour phosphors.

Since the panel of such a colour cathode ray tube is made of flat glass plate, the flatness and accordingly the shape and dimensions thereof can be very accurate. Moreover, the mechanical accuracy of the electron beam impinging position determining device is relatively high, so that when the colour phosphors are coated on the panel there is no need previously to determine the combination or pairing of the panel and the device, and hence a non-marriage system can be used.

A printing method can also be used for forming the colour phosphor screen of this kind of flat panel colour cathode ray tube, so that the process of forming the colour phosphor screen can be simplified.

In general, the electron beam inpinging position determining device is attached to the panel with a projection or stud pin provided on the panel, and a leaf spring associated with the device is engaged with the stud pin to fix the device in place.

However, the provision of such a projection or stud pin on the inner surface of the panel makes the printing method difficult or even impossible to use.

According to the present invention there is provided a flat panel type colour cathode ray tube comprising: a flat panel on which a colour phosphor screen is formed; first means located in facing relation to said flat panel for determining the impinging position of an electron beam on said colour phosphor screen; second means provided on the inner surface of said flat panel for setting a reference position of said first means for said flat panel; and third means provided on said first means for engaging with said second means.

The invention will now be described by way of example with reference to the accompanying drawings, throughout which like references designate like elements, and in which: Figure 1 is a schematic diagram showing a prior art flat panel type colour cathode ray tube; Figure 2 is a cross-sectional view showing part of an embodiment of flat panel type colour cathode ray tube according to the invention; Figure 3 is a perspective view of the part shown in Figure 2; Figure 4 is a plan view of the panel of the embodiment of Figures 2 and 3; and Figure 5 is a side view used to expain the assembling method of another embodiment of the invention.

Figure 2 shows in cross-section the main part of an embodiment of flat panel type colour cathode ray tube according to the invention. The electron beam impinging position determining device or grid structure 7 is made of an aperture grill, so that the respective colour phosphors formed on the inner surface of panel 4 are stripes extending in the vertical direction. The aperture grill 7 has a frame 8, which consists of two sets of opposing frame members 8a, 8b, 8c, and 8d as shown in Figure 3. A line-shaped grid element 9, in which a number of slits are formed therethrough in the vertical direction is stretched between one pair of frame members 8a and 8b of the frame 8.

As shown in Figure 4, at ieast one recess 10 is formed on the inner surface of the panel 4 made of a flat glass plate at a marginal portion thereof so as to be a reference point for the horizontal and vertical directions x and y of the panel 4, which are perpendicular to each other, and based upon the reference point the aperture grill 7 is positioned relative to the panel 4. Two guide grooves or recesses 1 a and 1 b are also formed on the inner surface of the panel 4 at the marginal portion thereof, which serve to prevent the rotation of the aperture grill 7 with respect to the panel 4 and to absorb the expansion of the aperture grill 7 relative to the panel 4 owing to the difference between the thermal expansion coefficients of the aperture grill 7 and the panel 4.

An engaging element, for example, a pin 12, which will engage with the recess 10 of the panel 4, is provided on, for example, the frame 8 of the aperture grill 7 at the position corresponding to the recess 10, and engaging elements, for example, pins 1 3a and 1 3b, which will engage with the recesses 1 la and 1 1 b and are guided therealong, are provided on the frame 8 at the positions corresponding to the recesses 1 a and 11 b, respectively.

It is desired that the pins, 12, 1 3a and 1 3b and also the recesses 10, 11 a and 1 b are disposed at equal angular distances with respect to the axis of the envelope 1. For example, the two pins 1 3a and 1 3b are provided on the surface of one frame member 8a, attached to the grid element 9 and facing the panel 4, at a predetermined distance, and the guide recesses 1 a and 1 b are provided on the inner surface of the panel 4 at the positions corresponding to the pins 1 3a and 1 3b, respectively.The pin 12 is provided on the surface of the other frame member 8b, attached to the grid element 9 and facing the panel 4, at the centre position of the frame member 8b, and the recess 10 is formed on the inner surface of the panel 4 at the position corresponding to the recess 10. In this case, the recess 10 is formed of coneshape or at least such that its diameter decreases as the bottom thereof is approached, and the pin 12 has a ball-point tip so that when the pin 12 is inserted into the recess 10, the centre axis of the former coincides with that of the latter.The recesses 1 a and 11 1 are both formed to have å V-shaped cross-section and to be an elongated slit substantially along the radius of the envelope 1 and the pins 1 3a and 1 3b have ball-point tips, so that when the pins 1 3a and 1 3b are engaged with the recesses 1 a and 1 b of the panel 4, respectively, the aperture grill 7 is prevented from being rotated with respect to the panel 4 and the positional relation of the aperture grill 7 to the panel 4 on the plane perpendicular to the tubular axis of the envelope 1 is set with a predetermined relation by the engagement of the recess 10 with the pin 12 which determines the reference position in the x and y directions.

In the case where the electron beam impinging position determining device is the aperture grill 7 with slits extending in the vertical direction, if the position of the aperture grill 7 relative to the panel 4 deviates rotationally due to their relative expansion and contraction due to the difference between their thermal expansion coefficients, colour misregistratisn is caused and hence the picture quality is deteriorated. To avoid this colour misregistration and also to avoid distortion of the panel 4 or the aperture grid 7, the direction of elongated the recesses 1 a and 1 b is selected to absorb this expansion and contraction and not to rotate the aperture grill 7.

Moreover, the height of the pins 12, 1 3a and 1 3b and the depth of the recesses 10, 1 a and 1 1h are so selected that a predetermined spacing is present between the aperture grill 7 and the panel 4 when they are assembled.

As shown in Figure 2, a plurality of leaf springs 14 are attached to the back surface of the frame 8 of the aperture grill 7 by, for example, spot welding or the like and the free ends of the leaf springs 14 are abutted with a step 1 5 formed on the funnel portion 3 of the envelope 1 resiliently to urge the aperture grill 7 in the direction of the panel 4, whereby the respective pins 12, 1 3a and 1 3b are firmly pressed into the corresponding recesses 10, 1 1 a and 1 1 b.

Thus the position of the aperture grill 7 relative to the panel 4 can be positively determined by the engagement of the respective pins 12, 1 3a and 1 3b with corresponding recesses 10, 11 a and 11 b. Moreover, as the panel 4 is provided only with recesses 10, 1 a and 1 b and no projections, screen printing or other printing processes can be employed in forming the colour phosphor screen on the inner surface of the panel 4.

In the prior art, when the colour phosphor screen is formed on the inner surface of the panel 4, before the frit-sealing of the panel 4 to the funnel 3, a first colour phosphor slurry is coated on the panel 4 by the spinning coating method, then the electron beam impinging position determining device 7 is coupled to the panel 4, the coated slurry layer is exposed to light which corresponds to the electron beam for the first colour with the device 7 as an optical mask, then the device 7 is detached, and then the exposed slurry is developed to make the first phosphor with a predetermined stripe pattern. These processes are repeated similarly to form second and third phosphor patterns.

With the embodiment of cathode ray tube described above, with no projection on the inner surface of the flat panel 4, the coating of respective colour phosphor slurries can be achieved using a squeegee. Thus the phosphor slurries can be more uniformly or homogeneously coated. Moreover, the viscosity of the phosphor slurry can be increased as compared with that of the phosphor slurry used in the spinning coating method. Therefore, the drying time and the energy required for drying can be reduced.

Instead of using the optical printing method, the respective colour phosphors can be printed with predetermined patterns. In this case, exposing and developing processes can be omitted, with consequent simplification. Also, mass-production is facilitated and scattering and loss of phosphor slurry can be prevented.

In fact, a guard band made of black material such as a carbon layer is coated between adjacent respective colour phosphor stripes of the colour phosphor screen 6. This guard band can be formed with a desired pattern by, for example, the spinning coating method with carbon slurry and an optical printing method. Then, the respective colour phosphors are formed between adjacent guard bands by a printing method.

In the above embodiment the pins 12, 1 3a and 1 3b are directly attached to the frame 8 on which the grid element 9 is stretched. However, the pins may be attached to the frame 8 through attaching members, and also the positional arrangement and structure of the recesses 10, 1 a and 1 16 may be varied. Moreover, the structure of the frame 8 need not be as described with reference to Figure 3.

Figure 5 shows the main part of another embodiment of the invention. In this embodiment, the frame 8 is formed of a first frame member 8A with the engaging elements 12, 1 3a and 136 attached thereto and a second frame member 8B with the line-shaped grid element (not shown in Figure 5) stretched thereon. At first, the frame member 8A is secured with respect to the panel 4, on which the phosphor screen 6 is already formed by the manner set forth above, at the predetermined position by the engagement of the engaing elements 12, 1 3a and 1 3b with the recess 10 and grooves 1 a and 1 16. With this arrangement, a point light source 1 6 is located as shown in Figure 5, and while the moire pattern between the light from the light source 1 6 on the phosphor screen 6 through the line-shaped grid and the phosphor stripe pattern on the phosphor screen 6 is observed, the position of the second frame member 8B relative to the first frame member 8A is adjusted to assemble them in the correct position.

Claims (7)

1. A flat panel type colour cathode ray tube comprising: a flat panel on which a colour phosphor screen is formed; first means located in facing relation to said flat panel for determining the impinging position of an electron beam on said colour phosphor screen; second means provided on the inner surface of said flat panel for setting a reference position of said first means for said flat panel; and third means provided on said first means for engaging with said second means.

2. A cathode ray tube according to claim 1 wherein said second means are recesses and said third means are projections, said projections engaging with said recesses, respectively.

3. A cathode ray tube according to claim 1 wherein said second means are positioned at substantially equal angular distances about the axis of the cathode ray tube.

4. A cathode ray tube according to claim 2 wherein said recesses are three in number, one of which is a cone-shaped recess and two of which are elongated recesses in the radius direction of the cathode ray tube, each having a V-shaped cross-section.

5. A cathode ray tube according to claim 1 further comprising means for resiliently urging said first means against said flat panel.

6. A flat panel type colour cathode ray tube substantially as hereinbefore described with reference to Figures 2 to 4 of the accompanying drawings.

7. A flat panel type colour cathode ray tube substantially as hereinbefore described with reference to Figure 5 of the accompanying drawings.