US3652895A

US3652895A - Shadow-mask having graduated rectangular apertures

Info

Publication number: US3652895A
Application number: US39382A
Authority: US
Inventors: Asahide Tsuneta; Hiroshi Tanaka; Yoshifumi Kiriake
Original assignee: Tokyo Shibaura Electric Co Ltd
Current assignee: Toshiba Corp
Priority date: 1969-05-23
Filing date: 1970-05-21
Publication date: 1972-03-28
Anticipated expiration: 1989-03-28
Also published as: DE2025128A1

Abstract

A shadow-mask for color television cathode-ray tubes, which has rectangular electron-beam-passing openings graduated in size and pitch from the center to the peripheral portion of the mask plate so that the ratio of the area occupied by the openings over the entire area of the plate is greater in the central portion than in the peripheral portion.

Description

United States Patent Tsuneta et a1.

[54] SHADOW-MASK HAVING GRADUATED RECTANGULAR APERTURES [72] Inventors: Asahide Tsuneta, Kawasaki; Hiroshi Tanaka, Fukaya; Yoshifuml Kiriake, Morioka, all of Japan [73] Assignee: Tokyo Shibaura Electric Co., Ltd.,

Kawasaki-shi, Japan [22] Filed: May21, 1970 [21] Appl. No.: 39,382

[30] Foreign Application Priority Data May 23, 1969 Japan ..44/47l36 Sept. 2, 1969 Japan ..44/83080 [52] US. Cl. ..3l3/85 S, 313/92, 96/36.l [51] Int. Cl. ....H0lj 29/06, HOlj 31/20 [58] Field of Search ..313/85 S, 92 B, 92 PD;

[451 Mar. 28, 1972 [56] References Cited UNITED STATES PATENTS 2,755,402 7/1956 Morrell ..313/85 S X 2,888,603 5/1959 Lafferty... .....313/92 PD 2/1969 Kushner... .....3l3/85S 4/1971 Maeda ..313/86 Primary Examiner-Robert Sega] Attorney-Flynn & F rishauf 57 ABSTRACT A shadow-mask for color television cathode-ray tubes, which has rectangular electron-beam-passing openings graduated in size and pitch from the center to the peripheral portion of the mask plate so that the ratio of the area occupied by the openings over the entire area of the plate is greater in the central portion than in the peripheral portion.

6 Claims, 15 Drawing Figures PATENTEOMAR28 I972 3,652,895

sum 1 OF 3 FIG. 2;. W 1 1 Q 20 21 C 220* p- 22 g x u 10 2 1: 0: .L l

DISTANCE FROM THE CENTER OF THE FILTER(mm) PATENTED MAR 28 I972 sum 2 UF 3 FIG? FIG.

SHADOW-MASK HAVING GRADUATE!) RECTANGULAR APERTURES BACKGROUND OF THE INVENTION This invention relates to improvements in shadow-masks for color television cathode-ray tubes and the method of manufacturing the same, and more particularly to a shadow-mask having rectangular openings gradated in such a manner that the ratio of the area occupied by the openings to the over-all area of the mask plate is different between the central and peripheral portions.

The shadow-mask used in the color television cathode-ray tube usually has a plurality of circular openings to pass the scanning electron beams therethrough. Such circular openings in the mask plate are substantially equal in diameter and uniformly spaced in a predetermined pattern over the entire area of the plate.

with the shadow-mask of the above type, the picture reproduced on the screen is subject to color shear in the peripheral portion due to increased deflection angle of the electron beams reaching the peripheral portion of the'shadowmask. To prevent such color shear, there have been developed so-called gradated shadow-masks. An example of such gradated shadowmask is shown in FIG. 1 of the accompanying drawings. It comprises a mask plate 1 formed with a plurality of-gradated circular openings 2 with successively smaller diameters for openings successively positioned away from the center of the plate. The center-to-center distance between adjacent two openings in a vertical or horizontal row is constant, so that distance between adjacent openings 2 is greater the further are located these openings from the center of the mask plate.

As distance between adjacent openings is greater for portions of the mask plate nearer to the periphery of the plate, the percentage of electrons in the beam permitted through the prior-art gradated shadow-mask having circular openings is lower in peripheral portions than in the central portion, so that a bright color television picture can not be obtained to the disadvantage.

SUMMARY OF THE INVENTION According, an object of the invention is to provide a shadow-mask for color television cathode-ray tube, which enables improving the coefficient for beam transmittivity for the peripheral portions of the mask plate to prevent the color shading so as to obtain bright television pictures.

Another object of the invention is to provide a method of manufacturing such shadow-mask.

According to the invention, these objects are achieved by forming rectangular openings, for instance, gradated in size and/or pitch from the center toward the peripheral portion of the mask plate, so that the ratio of the area occupied by the openings to the over-all area of the mask plate is gradated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a fragmentary plan view of a conventional gradated-type shadow-mask;

FIG. 2 is a fragmentary plan view of an embodiment of the shadow-mask according to the invention;

FIG. 3 is a fragmentary schematic view of a striped screen involved in the manufacture of the embodiment of FIG. 2;

FIG. 4 schematically shows an exposing equipment involved in the manufacture of the embodiment of FIG. 2;

FIG. 5 is a plot of a filter characteristic of the striped filter shown in FIG. 4;

FIG. 6 is a fragmentary plan view of a first pattern plate involved in the manufacture of the embodiment of FIG. 2;

FIG. 7 is a fragmentary plan view of a second pattern plate involved in the manufacture of the embodiment of FIG. 2;

FIG. 8 is a fragmentary plan view of a third pattern plate involved in the manufacture of the embodiment of FIG. 2;

- FIG. 9 shows superimposed two third pattern plates of FIG.

FIG. 10 shows a final fourth pattern plate involved in the manufacture of the embodiment of FIG. 2;

FIG. 11 is a fragmentary plan view of another embodiment of the shadow-mask according to the invention;

FIG. 12 is a fragmentary sectional view of the shadow-mask according to the invention illustrating the mask opening formed;

FIG. 13 shows a further embodiment of the shadow-mask according to the invention;

FIG. 14 shows an exposing apparatus involved in the manufacture of the shadow-mask shown in FIG. 13; and

FIG. 15 shows a still further embodiment of the shadowmask according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will now be described in conjunction with preferred embodiments thereof.

Referring now to FIG. 2, an embodiment of shadow-mask 11 comprises a mask plate 12 fonned with a plurality of rectangular openings 13. The lateral dimension or width of the openings 13 is successively smaller for openings successively away from the center of the plate, but the center-to-center distance A between adjacent openings in a horizontal row and the distance B between adjacent openings in a vertical row are constant. Thus, only the lateral or horizontal width of the openings is gradated from the central portion toward the peripheral portions of the plate 12.

In case of use for a 19-inch color television receiving set, the width of the openings 13 may be about 0. l 3 mm. in the central portion of the shadow-mask and about 0.10 mm. in the peripheral portion with respect to a row pitch of 0.60 mm. being successively narrower from 0.l3 mm. (maximum) at the center to 0.10 mm. (minimum) adjacent the corners.

As is apparent from the Figure, the openings 13 are uniformly spaced in vertical rows. Accordingly, by so depositing the fluorescent material on the face plate of the color television cathode-ray tube using the shadow-mask of the above construction that three (red-, greenand blue-glowing) dots of the fluorescent material are aligned in respective horizontal rows, with dots in each triplet corresponding to each of the openings 13 aligned in the longitudinal or vertical direction of the opening, the phenomenon of color shear in the television picture may be difficult to take place.

Thus with this construction, the beam transmittivity may be increased at least by several percent as compared to the conventional gradated-type shadow-mask having circular openings as shown in FIG. 1 because there is no need for a longitudinal gradation. Particularly, the .color shading in the peripheral portions may be completely prevened and bright color picture images may be reproduced.

An example of the method of manufacturing the shadowmask of FIG. 2 embodying the invention will now be described with reference to FIGS. 3 to 10.

There is first prepared a striped screen 22 having transparent portions 20 and non-transparent portions 21, as shown in FIG. 3. This striped screen 22 is placed in front of a lightsensitive film 24 in an exposing apparatus 23, as shown in FIG. 4. Ahead of the striped screen 22 is disposed a lens system 25 with-an iris 26. The striped screen 22 is required to be exposed to uniform external light through the lens system 25 with the iris 26. This is achieved by, for instance, a dispersing plate 28 such as opal glass to disperse light from a lamp 27 into light of uniform intensity.

Between the lamp 27 and the dispersing plate 28 is interposed a filter 29 having a transmittivity characteristic as shown in FIG. 5 which gradually decreases the transmittivity with distance from the center to impart a gradated characteristic to the uniform light from the dispersing plate 28. The gradated characteristic of the light from the dispersing plate 28 is transferred to the light-sensitive film 24, when the film 24 is exposed through the striped screen 22 provided with uniformly spaced stripes having equal width throughout its area as shown in FIG. 3. The intensity of the exposure light, because of the use of the iris 26, is not uniformly distributed over the film 24, but light incident on the portion corresponding to the central part of the transparent portion 20 of the striped screen 22 is more intense on account of the perfect shadow of the iris 26 than light incident on the portion corresponding to the peripheral part of the transparent portion on account of the partial shadow of the iris 26 in addition to the intensity distribution characteristic of FIG. 5, if introduced. Thus, when the exposed light-sensitive film 24 is developed for a predetermined time, the images of the stripes on the developed film 24 are not of a uniform width throughout the length thereof, but the developed film 24, constituting a first pattern 32 as shown in FIG. 6, has transparent portions 30 tapering from the center toward the ends.

A second pattern 33 having a transparent portion 34 and non-transparent stripes 35 is shown in FIG. 7. It is prepared in the manner similar to the previous first pattern by using a required pattern to expose a light-sensitive film in the exposing apparatus, with one exception that the filter having the transmittivity characteristic of FIG. is used only in the preparation of the first pattern.

The first and

second pattern carriers

32 and 33 are then superimposed upon each other such that the stripes of the first pattern are perpendicular to the stripes of the second pattern so as to develop a third pattern carrier 41, by contact printing as shown in FIG. 8. The third pattern carrier 41 carries a plurality of rectangular non-transparent spots 40 arranged in columns and rows at predetermined center-to-center pitches. Only the width of the spots 40 is gradated from the central portion toward the peripheral portions of the carrier 41.

Two pattern carriers carrying the identical third pattern shown in FIG. 8, namely

pattern carriers

41 and 42 in FIG. 9, are superimposed upon each other in a staggered fashion such that the columns of the rectangular spots 40 of the pattern carrier 41 come mid-way between adjacent columns of the spots 43 of the other pattern carrier 42 and the center of the vertical distance between adjacent spots 40 of the carrier 41 is substantially in horizontal alignment with the center of the length of the corresponding spot 43 of the other carrier 42.

The resultant pattern of the combination of the two

third pattern carriers

41 and 42 is used to develop and fix a fourth negative pattern on a light-sensitive film, by contact printing as indicated at 45 in FIG. 10, which corresponds to the shadow-mask pattern of the embodiment of FIG. 2.

The fourth pattern thus formed on the forth pattern carrier 45 is then transferred onto a mask plate by the known photoetching technique. By way of example, on a thin soft steel plate not shown, constituting the mask plate, is coated a lightsensitive liquid agent, on which is closely applied the pattern carrier 45 having the fourth pattern for exposing to light rays. After the exposure, the plate is washed with water to remove that part of the light-sensitive agent which remains uncured without receiving the light rays, and the developed mask plate is dried and then sujbected to heat treatment. Then, exposed portions of the steel plate free from the light-sensitive agent are etched, thus obtaining the shadow-mask having gradated rectangular beam-passing openings 13 as shown in FIG. 2. With the above etching process, the shape of the formed openings 13 is not exactly rectangular as is illustrated but somewhat inclined to be eliptic. However, there is no appreciable influence on the effects featured by the invention.

Satisfactory exposing results may be obtained with the exposing apparatus 23 of FIG. 4, for instance by disposing various parts such that the dispersing plate 28 is 1,200 mm. distant from the lamp 27, the iris 26 is 800 mm. distant from the dispersing plate 28, the striped screen 22 is 3,000 mm. distant from the iris 26, and the light-sensitive film 24 is 27.5 mm. distant from the striped screen 22.

In the above method of manufacturing the shadow-mask the gradation characteristic is introduced in the step of preparing the first pattern. It is of course possible to manufacture similar gradated-type shadow-mask by preparing the fourth pattern not imparted with the gradation characteristic and exposing the soft steel plate with the fourth gradation-free pattern carrier to the light rays through a filter having the gradation characteristic as shown in FIG. 5. Alternatively, the gradation characteristic may be introduced in the step of forming the fourth pattern.

FIG. 11 shows another embodiment of the gradated-type shadow-mask according to the invention. Unlike the embodiment of FIG. 2, in which only the the width of the rectangular openings 13 is gradated from the central portion toward the peripheral portions of the mask, in this embodiment both the width and the length of the openings 13 are gradated from the center toward the peripheral portions of the mask. Thus, the rectangular openings 13 in the peripheral portions of this embodiment are longer than the corresponding openings in the embodiment of FIG. 2, to improve the beam transmittivity in the peripheral portion that much, so that still brighter color television pictures may be obtained.

The shadow-mask of FIG. 1 1 may be manufactured substantially in the same manner as for the embodiment of FIG. 2 except for that in this case a lateral or horizontal gradation characteristic is additionally introduced in the step of forming the non-gradated second pattern for the embodiment of FIG. 2. Stated specifically, the gradated first pattern shown in FIG. 6 is superimposed on a gradated second pattern not shown to form a third pattern so as to produce a fourth pattern gradated both vertically and horizontally as shown in FIG. 11, from which to produce the shadow-mask 50.

In the above process of fabricating the shadow-mask by the photo-etching technique, inconvenience is felt in that the rectangular beam-passing openings are not correctly formed. To alleviate this inconvenience, there is proposed a method of etching the soft steel plate on both sides. FIG. 12 shows the cross section of a beam-passing opening formed by such bilateral etching method. In this case, it is possible to obtain considerably exact required rectangular configuration of the beam-passing opening by etching most part of the thickness of the mask plate 12 from the upper side and then etching the remaining part from the lower side of the plate.

However, by this method of etching from both sides part as indicated at a is unnecessarily etched in the first etching step (resulting in so-called side etching). Therefore, the width of the slits of the etching pattern applied on the upper side of the soft steel plate should be made smaller than the actual width of the openings to be formed to make up for the side etching. Accordingly, as is apparent from the embodiment of FIG. 2, the width of the slits corresponding to the openings to be formed in the peripheral portion of the mask plate is extremely small. Thus the preparation of the pattern involving such minute dimensions and the uniform formation of small-width openings in the peripheral portions of the mask plate are extremely difficult, and usually result in irregular openings to degradate the quality of the color television pictures.

In the embodiments of FIGS. 2 and 11, the width and/or the length of the beam-passing openings 13 are/is gradated.

FIGS. 13 and 15 show further embodiments, where the ratio of the area occupied by the openings to the over-all area of the mask plate is gradated from the central portion toward the peripheral portion of the mask plate in order to eliminate the above inconvenience of side etching. These embodiments are principally based on the idea that the number of openings 13 per unit area is gradated from the central portion toward the peripheral portions of the mask plate.

In the embodiment of FIG. 13, the distance d between adjacent openings 13 in a horizontal row is gradated to be greater the nearer to the periphery are located the adjacent openings.

The shadow-mask of this construction may be manufactured for instance by an exposing apparatus 60 shown in FIG. 14. The exposing apparatus of FIG. 14 is mostly the same in construction with the exposing apparatus of FIG. 4 so like parts are designated by like reference numerals, and their detailed description is omitted. The former is different from the latter in that between the striped screen 22 and the lightsensitive film 24 is interposed a concave lens 61, which is concave only on one direction and is flat on the other direction. Thus, light from the striped screen 22 is dispersed by the concave lens 61, and the dispersed light is forcused on the lightsensitive film 24 in such a manner that the distance between adjacent stripe images is successively increased toward the vertical edges of the film 24. In case the spacing and width of the original stripes are constant, the width of the openings increases at the same rate as the distance between adjacent openings in a row. in case it is desired to have openings of a constant width, while successively increasing the distance between adjacent openings, an additional gradation characteristic may be preliminarily imparted to compensate for the magnification factor of the concave lens 61 such that only the width of the openings is progressively narrower the nearer to the periphery are located the openings.

In the embodiment of FIG. 15, the width of the beampassing openings 13 is gradated to successively decrease from the central portion toward the peripheral portions and the distance between adjacent openings is gradated to successively increase from the central portion toward the peripheral portions of the shadow-mask 11. With this embodiment, it will be apparent that similar effects as with the preceding embodiments may be obtained.

What we claim is:

1. A shadow-mask for use in color television cathode-ray tubes comprising a thin metal plate formed with a plurality of substantially rectangular beam-passing openings therein, the length and width of said rectangular beam-passing openings being gradated such that the width of said openings is progressively narrower from the central portions of said plate to the peripheral portions of said plate, and such that the length of said openings is progressively greater from the central portions of said plate to the peripheral portions of said plate,

whereby the ratio of the area occupied by said rectangular beam-passing openings per unit area to the total effective area of said metal plate is graduated from the central portions toward the peripheral portions of said metal plate, the tube having reduced color shading and improved beam transmittivity.

2. The shadow-mask for use in color television cathode-ray tubes according to claim 1 wherein the ratio of the area occupied by said rectangular beam-passing openings per unit area to the total effective area of said metal plate is gradated from a maximum at said central portions to a minimum toward said peripheral portions of said metal plate.

3. The shadow-mask for use in color television cathode-ray tubes according to claim 1, wherein said rectangular beampassing openings are arranged in a plurality of first rows in the direction of beam-scan of the tube and are gradated such that the distance between adjacent openings in said rows is progressively greater from the central portions of said plate toward the peripheral portions of said plate.

4. The shadow-mask for use in color television cathode-ray tubes according to claim 1 wherein said rectangular beampassing openings are arranged in a plurality of second rows in a direction perpendicular to the direction of beam-scan of the tube.

5. The shadow-mask for use in color television cathode-ray tubes according to claim 4 wherein said rectangular beampassing openings in each of said second rows are uniformly spaced in the direction perpendicular to the direction of beam-scan of the tube.

6. The shadow-mask for use in color television cathode-ray tubes according to claim 4 wherein said second rows are vertically arranged spaced columns having a predetermined constant distance between the center lines of adjacent columns.

Claims

1. A shadow-mask for use in color television cathode-ray tubes comprising a thin metal plate formed with a plurality of substantially rectangular beam-passing openings therein, the length and width of said rectangular beam-passing openings being gradated such that the width of said openings is progressively narrower from the central portions of said plate to the peripheral portions of said plate, and such that the length of said openings is progressively greater from the central portions of said plate to the peripheral portions of said plate, whereby the ratio of the area occupied by said rectangular beam-passing openings per unit area to the total effective area of said metal plate is gradated from the central portions toward the peripheral portions of said metal plate, the tube having reduced color shading and improved beam transmittivity.

3. The shadow-mask for use in color television cathode-ray tubes according to claim 1, wherein said rectangular beam-passing openings are arranged in a plurality of first rows in the direction of beam-scan of the tube and are gradated such that the distance between adjacent openings in said rows is progressively greater from the central portions of said plate toward the peripheral portions of said plate.

4. The shadow-mask for use in color television cathode-ray tubes according to claim 1 wherein said rectangular beam-passing openings are arranged in a plurality of second rows in a direction perpendicular to the direction of beam-scan of the tube.

5. The shadow-mask for use in color television cathode-ray tubes according to claim 4 wherein said rectangular beam-passing openings in each of said second rows are uniformly spaced in the direction perpendicular to the direction of beam-scan of the tube.