Mask for color picture tube

Details Mask for color picture tube Mask for color picture tube

2001-07-10

2003-09-02

Patel, Ashok (Department: 2879)

Electric lamp and discharge devices

Cathode ray tube

Shadow mask, support or shield

C313S403000

Reexamination Certificate

active

06614153

ABSTRACT:

CLAIM OF PRIORITY
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from my application
MASK FOR COLOR PICTURE TUBE
filed with the Korean Industrial Property Office on Jul. 12, 2000 and there duly assigned Ser. No. 39984/2000.
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a color picture tube, and more particularly, to a mask which is installed close to a fluorescent film at the inner side of a panel and performs a color selection function.
2. Related Art
In a color picture tube adopted in computer monitors or televisions, three electron beams are emitted from an electron gun and pass through electron beam passing holes of a mask having a color selection function. Then, the electron beams land on red, green and blue fluorescent substances on a fluorescent film formed on a screen surface of a panel to excite the fluorescent substance so that an image is formed.
In the above color picture tube for forming an image, the mask having a color selection function is divided into a dot mask used for computer monitors and a slot mask (or a slit mask) used for televisions. Since the screen surfaces are formed to have predetermined curvatures considering landing of deflected electron beams, the dot mask and slot mask are designed to have curvatures corresponding to those of the screen surfaces.
The above masks are formed of a thin plate having a thickness of 0.1 through 0.25 millimeters (mm) and a plurality of electron beam passing holes are formed therein by etching the thin plate. Then, the thin plate is formed to have a predetermined curvature. When the mask does not have a predetermined curvature or more, mechanical intensity of the mask deteriorates so a permanent plastic deformation can be generated to the mask due to impacts occurring during production of picture tubes or transfer thereof. As a result, the color selection function which is an intrinsic function of the mask may not be properly performed. Also, the mask formed to have a predetermined curvature is supported by a frame installed on an inner surface of the panel. The mask is easily heated by thermions emitted by the electron gun and thermally expands. Accordingly, a doming phenomenon occurs so that the color selection function with respect to the three electron beams cannot be performed.
As the size of a color picture tube recently increases, an image is distorted due to the curvature of a screen surface and a natural image does not get smoothly represented, so that a flat screen surface is required.
Slot type masks for preventing the doming phenomenon and enabling a flat screen surface are disclosed in U.S. Pat. No. 3,638,063 to Tachikawa et al., entitled GRID STRUCTURE FOR COLOR PICTURE TUBES, issued on Jan. 25, 1972, U.S. Pat. No. 4,942,332 to Adler et al., entitled TIED SLIT MASK FOR COLOR CATHODE RAY TUBES, issued on Jul. 17, 1990, U.S. Pat. No. 4,926,089 to Moore, entitled TIED SLIT FOIL SHADOW MASK WITH FALSE TIES, issued on May 15, 1990, and U.S. Pat. No. 4,973,283 to Adler et al., entitled METHOD OF MANUFACTURING A TIED SLIT MASK CRT, issued on Nov. 27, 1990. Of the disclosed masks, an aperture grille type mask is shown in FIG.
1
.
Referring to
FIG. 1
, the aperture grille type mask
10
includes strips
11
which are separated a predetermined distance from one another and parallel to each other and form slots. In the mask
10
, both end portions of each of the strips
11
are supported at a frame
12
to have tension. Each of strips
11
contacts damper wires
13
to prevent independent vibration of each strip. However, such a mask is difficult to handle during a manufacturing process since it has a structure in which the strips
11
are parallel to each other and only both end portions of the strips
11
are fixed.
To solve the above problem, as shown in
FIG. 2
, an example of a slot type mask has been suggested in U.S. Pat. No. 4,942,332. As shown in the drawing, in the slot type mask, a plurality of strips
22
and
22
′ forming a slit
21
are formed on a thin plate by being separated a predetermined distance and the strips
22
and
22
′ are connected by tie bars
23
. Thus, since the strips
22
and
22
′ are connected by the tie bars
23
, howling generated by vibrations due to impacts and sonic waves applied from the outside can be slightly reduced. Nevertheless, the howling reducing effect cannot be expected much since the vibrations of the tie bars
23
are transferred by the tie bars
23
through the neighboring strips.
FIG. 3
shows a mask having false ties disclosed in U.S. Pat. No. 4,926,089. As shown in the drawing, in a mask
30
, strips
31
and
31
′ installed parallel to each other is connected by a tie bar
32
for forming a slot
33
. A plurality of false ties
34
extending from the strips
31
and
31
′ and not contacting the adjacent strops
31
and
31
′ are positioned in the slot
33
between the tie bars
32
.
In the above mask
30
, visibility of an image is improved by disposing the false ties
34
between the tie bars
32
. However, since the strips
31
and
31
′ are connected by the tie bars
32
, a problem that vibrations generated by an impact applied to a portion are transferred to a neighboring strip cannot be solved.
In particular, in the above mask type, a moire phenomenon occurs because scanned electron beams and the holes of the mask are interfered with each other. The moire phenomenon becomes serious at the peripheral portion of a screen because the shape of a spot of an electron beam landing on a fluorescent film is deformed to be horizontally elongated due to a strong pincushion magnet field by a deflection yoke as a deflection angle of an electron beam increases. Accordingly, methods of selecting a mask pitch at which the moire phenomenon is minimized or reducing a vertical pitch to reduce is used to reduce the depth of modulation, are used. However, the above methods are not recommended because transmissivity at the periphery portion of the mask is lowered and the brightness of a screen is not uniform.
Also, in the mask method, a mask doming phenomenon becomes serious as the mask is heated by the electron beams. Furthermore, the doming phenomenon easily occurs at the peripheral portion of a mask. In the case of a tension mask, when a steel frame which is cheap is used, the mask including a mask bridge portion extends in a horizontal direction so that color escape in a wrinkle shape is generated on a screen.
SUMMARY OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide a tension mask for a color picture tube which can improve a vibration reduction effect by reducing transfer of vibrations between electron beam strips.
It is a further object of the present invention to provide a tension mask which can reduce a moire phenomenon due to interference between the scanned electron beam and holes of a mask and reduce a doming phenomenon of the mask, and improve brightness of an image.
Accordingly, to achieve the above objects and others, there is provided a tension mask for a color picture tube comprising a plurality of strips separated a predetermined distance from each other and parallel to each other, and a plurality of real bridges for connecting the neighboring strips and forming slots through which electron beams pass, the number of the real bridges gradually decreasing from the central portion of the tension mask to the peripheral portion thereof. The electron beams pass through the slots or penetrate the slots.
It is preferred in the present invention that the real bridge is not formed between an end strip located at the outermost portion of the tension mask in a horizontal direction and a strip adjacent thereto.
Also, it is preferred in the present invention that a plurality of dummy bridges extending from the strips in the opposite directions to face each other but not physically contacting each other, are disposed between the real bridges connecting the strips.
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