GB2226695A

GB2226695A - Shadow mask for colour cathode ray tube

Info

Publication number: GB2226695A
Application number: GB8926462A
Authority: GB
Inventors: Min-Ho An
Original assignee: Samsung Electron Devices Co Ltd
Current assignee: Samsung SDI Co Ltd
Priority date: 1988-11-26
Filing date: 1989-11-23
Publication date: 1990-07-04
Anticipated expiration: 2009-11-23
Also published as: GB2226695B; NL190825B; NL8902852A; GB8926462D0; NL190825C

Abstract

A shadow mask 1, having a mixture of different aperture shapes is disclosed, wherein at least either pin cushion type apertures 3 or drum type apertures 4 are mixed with slit type apertures 2. When the shadow mask is used as an exposing mask for screen manufacture, the pin cushion type apertures are formed at the portions where decreased amounts of light beams are required, and the drum type apertures are formed at the portions where increased amounts of light beams are required. Further, the maximum width of the pin cushion type apertures is almost the same as the width of the slit type apertures, while the minimum width of the drum type apertures is almost the same as the width of the slit type apertures. By this arrangement the photo sensitivity differences between the exposed portions of the whole panel are reduced, and so, black matrix formation becomes uniform. <IMAGE>

Description

SHADOW MASK FOR COLOR CATHODE RAY TUBE Field of the Invention The present invention relates to a shadow mask for color cathode ray tube, and particularly to a shadow mask which is used as an exposing mask.

Field of the Invention In a color cathode ray tube which is provided with an inline type electron gun, the phosphor which constitutes the phosphor screen should be formed in the form of stripes while a black matrix made of a light absorbing material such as graphite is provided between the phosphor stripes in order to prevent the lowering of the luminance due to the external light rays.

The phosphor stripes and the black matrix are formed through the use of a photo sensitive synthetic resin based on the photo etching method, i.e., based on the exposure and development. Here, as the exposing mask, a shadow mask which guides the electron beams in a completed color cathode ray tube is usually used. Such a conventional shadow mask is shown in Figure 1, and the shadow mask 1' is provided with numerously large number of slit type apertures 2 having a width h respectively.

Meanwhile, Figure 2 illustrates an exposing device which is for showing the method of exposing the inner face of the panel using the shadow mask 1' as the exposing mask.

This exposing device is constituted such that the shadow mask 1' as the exposing mask is installed in the interior of a panel 5 coated with a photo sensitive material, and a shutter having a slit 7a is moved in the direction of the shorter side of the panel 5, so that the inner face of the panel 5 should be exposed in a stepwise manner through the use of the light rays radiated from a light source 6, thereby forming continuous black matrices and phosphor stripes.

However, the distances from the light source 6 to the respective points on the panel 5 are different one another, and therefore, the illuminances at the different points on the panel become different one another, with the result that the levels of the exposure also become different one another.

Accordingly, the state of the black matrices and the phosphor stripes formed on the inner face of the panel 5 becomes defective. For example, the black matrices which -are usually formed before the phosphor stripes creates peelings at the exposed portions, and therefore, in the case where the exposure is insufficient, the widths of the black matrices B are irregularly expanded relative to the standard widths as shown in Figure 3A, while, in the case where the exposure is excessive, the widths of the black matrices B are irregularly narrowed as shown in Figure 3B, so that the linearity of the black matrices B is aggravated. If the linearity of the black matrices B is aggravated, then the phosphor stripes formed between the black matrices are also correspondingly aggravated.

conventional attempt for overcoming such a disadvantage is disclosed in Japanese Utility Model Publication No. 58-41633, in which efforts are made mainly for modifying the shape of the slit of the shutter, but this could not give a proper solution to the above described problem.

Summarv of the Invention The present invention is intended to overcome the above described disadvantage.

Therefore it is the object of the present invention to provide a shadow mask for color cathode ray tube, in which the exposures can be made uniform over the whole surface of the panel when performing exposures using an exposing mask.

In achieving the above object, the shadow mask for color cathode ray tube according to the present invention comprises a shadow mask provided with numerous of apertures for guiding the electron beams, characterized in that the shadow mask is provided with apertures which consist of at least either pin cushion type apertures or drum type apertures mixed with slit type apertures.

Brief descriotion of the drawings The above object and other advantages of the present invention wi4ll become more apparent by describing the preferred embodiment of the present invention with reference to the attached drawings in which:: Figure 1 is a perspective view showing the structure of the conventional shadow mask frame, with a portion of it enlarged; Figure 2 is a schematical sectional view of the usual exposing device; Figure 3A is an enlarged plan view of the inner face of the panel showing a defective formation of the black matrices in the case where the exposure is insufficient; Figure 3B is an enlarged plan view of the inner face of the panel corresponding to Figure 3A but in the case where the exposure is excessive; Figure 4A is a schematical view of a pin cushion type apertures formed on the shadow mask according to the present invention; Figure 4B is a schematical view of a drum type apertures formed on the shadow mask according to the present invention;; Figures 5A and 5B respectively illustrate the embodiments for the shadow mask according to the present invention.

Description of the Dreferred embodiment Figure 4 illustrates the shape of the apertures provided on the . shadow mask according to the present invention, in which Figure 4A shows pin cushion type apertures and Figure 4B shows drum type apertures. A pin cus-hion type aperture 3 has a minimum width hi and a maximum width h2, while a drum type aperture 4 has a maximum width h3 and a maximum wi-dth h4. Here, the maximum width h2 of the pin cushion type aperture 3 and the minimum width h3 of the drum type aperture 4 .6-suld be desirably formed in almost the same size as the width h of a usual slit type aperture 2.Accordingly, the area of the opening portion of the pin cushion type aperture 3 becomes smaller than that of the slit type aperture 2, while the area of the opening portion of the drum type aperture 4 becomes larger than that of the slit type aperture 2.

Here, if the minimum width hl of ttse pin cushion type aperture 3 and the maximum width h4 of the drum type aperture 4 are made to be approximately same as the width h of the slit type aperture 2, then the relationship between the areas of the opening portions becomes contrary to the case of the preferred embodiment of the present invention described above, but it will not be a desirable form because the arrangement into an in-line state becomes difficult when using a combination with the slit type apertures 2.

Thus, as shown in Figures 5A and 5B, the various kinds of the apertures according to the present invention are mixedly provided to the shadow mask 1. For example, if the exposure at the outer -middle portion of the longer side of the panel exceeds the reference value, and if the exposure at the outer middle portion of the shorter side of the panel falls below the reference value1 then the pin cushion type apertures 3 are provided to the outer middle portion of the longer side of the panel where the exposure is excessive, wh-ile the drum type apertures 4 are provided to the outer middle portion of the shorter side where the exposure is insufficient (a reverse case is illustrated in Figure 5B.) Under this condition, it is desirable that the maximum with h2 of the pin cushion type aperture 3 is designed .n almost the same size as the width of the slit type apertures 2 as described above, and in accordance with the degree of insufficiency of the exposures, the minimum width hl is gradually increased until the shape of the aperture is made to be almost same as the slit type aperture 2 upon reaching the portion where to exposure becomes equivalent to the reference value. Further, the drum type apertures 4 should also be desirably provided in a manner of gradually decreasing the maximum width h4.

The shadow mask of the present invention constituted as above will now be described as to its operations.

The shadow mask according to the present invention is used as an exposing mask for exposing the inner face of the panel after it is installed. As a matter of describing convenience, descrrptions will be made referring to the formation process of the black matrices, but the circumstance will be same also in the case of the formation process of the phosphor stripes.

If light rays are irradiated from the light source 6, then the light beams will expose the inner face of the panel 5 in a stepwise manner through the slit 7a of the moving shutter 7, and this will produce the same effect as that the respective apertures 2,3,4 are let to be moved over the inner face of the panel in the lengthwise direction thereof.

Accordingly, the exposure levels for the different positions of the stripes formed on the panel 5 will be controlled, and in the case of the pin cushion type aperture 3 in which the area of its opening portion is smaller than that of the usual slit type aperture 2, the average passing amount of the light beams is reduced, while, in the drum type apertures 4, the case becomes contrary. As a result, the intensities of the light beams arriving to the respective portions of the inner face of the panel 5 become almost uniform, thereby making the overall exposure for the whole panel uniform.

Accordingly, the photo sensitivity differences between the exposed portions of the whole panel are reduced, and therefore, the formation state of the black matrices, and particularly the linearity and the density of the black matrices become uniform.

Thus, thetadopt-ion of the shadow mask according to the present invention enables to form good quality phosphor layers, thereby making it possible to produce high quality color cathode ray tubes capable of giving improved images.

Claims

CLAIMS:

1. A shadow mask for color cathode ray tube, comprising a shadow mask provided with numerous apertures for guiding electron beams, characterized in that said shadow mask is provided with at least either pin cushion type apertures or drum type apertures mixed with slit type apertures.

2. The shadow mask for color cathode ray tube as claimed in claim 1, wherein, when said shadow mask is used as an exposing -mask, said pin cushion type apertures are formed at the portions where decreased amounts of light beams are required.

3. 7he shadow mask for color cathode ray tube as claimed in claim 1, wherein, when said shadow ma-sk is used as an exposing mask, said drum type apertures are formed at the portions where increased amounts of light beams are required.

4. The shadow mask for color cathode ray tube as c l-a imed in any one of claims 1 and 2, wherein the maximum width of said pin cushion type apertures is almost same as the width of said slit type apertures.

5. The shadow mask for color cathode ray tube as claimed in any one of claims 1 to 3, wherein the minimum width of said drum type apertures is almost same as the width of said slit type apertures.

6. A shadow mask for use in a process for forming a phosphor and matrix coating in a color cathode ray tube, said mask comprising an array of apertures for transmitting light to predetermined portions of a photosensitive layer on the panel of a said tube in an exposure step of said process, wherein the size and/or shape of said apertures in said array are adapted so as to regulate the exposure level of said portions over the exposed area of said panel.

7. A shadow mask in or for a color cathode ray tube, the apertures of said shadow mask forming a nonuniform pattern which serves to compensate for variation in the distance between different parts of the tube panel and a fixed light source so as to regulate the exposure level across the tube panel during an exposure step of a process for forming the phosphor screen of the tube.

8. A shadow mask according to claim 7 wherein the non-uniformity of the pattern is in the shape of the apertures.

9. A shadow mask according to claim 8 wherein said pattern includes first substantially straightsided slit apertures, second elongate apertures of larger opening area than the first apertures and having generally convex sides, and third elongate apertures of smaller opening area than the first apertures and having generally concave sides.

10. A shadow mask substantially as hereinbefore described with reference to Figure 5A of the accompanying drawings.

11. A shadow mask substantially as hereinbefore described with reference to Figure 5B of the accompagying drawings.

12. A method of forming a phosphor screen on the panel of a color cathode ray tube by an exposure technique using a shadow mask according to any preceding claim.

13. A color cathode ray tube including a shadow mask according to any of claims 1 to 11.

14. A color cathode ray tube including a phosphor screen formed by a method according to claim 12.