GB2303735A

GB2303735A - Shadow mask frame assembly

Info

Publication number: GB2303735A
Application number: GB9615554A
Authority: GB
Inventors: Bongkwon Jeong
Original assignee: Samsung Display Devices Co Ltd
Current assignee: Samsung SDI Co Ltd
Priority date: 1995-07-24
Filing date: 1996-07-24
Publication date: 1997-02-26
Also published as: KR200147271Y1; JPH0935654A; CN1147686A; DE19629927A1; KR970007204U; GB9615554D0

Abstract

A shadow mask frame assembly for use in a color picture tube includes a shadow mask 14, having a plurality of perforations and a skirt 13, a frame 16 and corner springs 17 for hanging the frame 16 on the inside of the panel of a color picture tube. The frame 16 has a flange 15 with thermal expansion parts 18 formed by cutting the short sides of the flange 15 at points on both sides of the central line of the short sides. The cuts are parallel to the central axis of the color picture tube. The thermal expansion parts 18 have metal sections 19 mounted thereon, which sections 19 have a lower thermal expansion rate than the frame 16. The parts 18 and sections 19 together act as bimetals to reduce doming of the shadow mask when hot.

Description

DESCRIPTION SHADOW MASK FRAME ASSEMBLY The present invention relates to a shadow mask frame assembly for use in a color picture tube.

Generally, a color picture tube comprises a bulb integrating a panel, a funnel and a neck, an electron gun system mounted in the neck, and a screen having a plurality of three different phosphors arranged on the inside of the panel to produce the three primary colors red (R), green (G), and blue (B). A metal shadow mask is placed directly behind the screen, in the plane of intersection of the electron beams emitted from the electron gun system, to ensure that each beam hits the correct phosphor. The mask acute as a physical barrier to the beams as they progress from one location to the next and minimizes the generation of spurious color caused by excitation of the wrong phosphor.The mask is associated with a frame to form a mask asse:bly, which is mounted on the inside of the panel.

Referring to Fig. 3, of the accompanying drawings a conventional mask assembly comprises a shadow mesk 4 having an effective part 1, a reinforcing bead 2 bordering the effective part 1, and a skirt 3 depending almost vertically relative to the effective part: and a frame 6 having a vertical connection part 5 with curved corner portions, and a corner spring 7 attached to each of the curved anner portions for banging tbe shadow mask assembly cn corner pins arranged on the inside of the panel.

In such a conventional shadow mask, only 15-25% of the electron beams that pass through the apertures of the shadow mask 4 land on the phosphors of the screen, and the remaining electron beams impinge upon the solid part of the shadow mask 4, thus increasing its temperature about 30 to 80 OC. As a result, there occurs a doming phenomenon in which the shadow mask is expanded towards the screen, so that the electron beams are incorrectly landed on wrong phosphors thereby resulting in so-called purity drift representing degradation of color purity.

Zn order to prevent the damping phenomenon, Rorean Patent No. 92-6232, granted to the RCA Licensing Corporation on August 1, 1992, shows a mask frame structure herein the corner parts of the shadow mask and the are cut at the ends. A part of the skirt in the corners of the mask and the flange in the corners of the frame are level and form an acute angle with the main and the subordinate axis. However, such a structure does not sufficiently resolve the doming problem, so that the difference in thermal expansion between the mask and the frame cannot be reduced, thus increasing the time required to compensate for the thermal compensation.

It is an aim of the present invention to provide a means for improving the responsiveness to the initial doing phenomenon caused by the difference in thermal expansion between the shadow mask and the frame in a color picture tube, whereby the thermal compensation may be obtained in a short time to improve the color purity of the screen.

According to the present invention, a shadow mask frame structure used in a color picture tube comprises a shadow mask having a plurality of perforations and a skirt, and corner springs for hanging the shadow mask to the inside of the panel of the color picture tube. The frame has a flange with expansion parts formed by cutting the short sides of the flange at a point in both sides of the central line of the ebort sides. The cutting line is parallel to the central axis of the color picture tube. Low expansion metal is mounted to the thermal expansion part and this metal has a lower thermal expansion rate than the frame.

The present invention will now be further described by way@ of example, with reference to the accompanying drawings, in which: Fig. l is a perspective view for illustrating a shadow mask assembly according to the present invention; Fig. 2 is a cross-sectional view taken along line A-A of Fig. 1; Fig. 3 is a perspective view of a known conventional shadow mask assembly; and Fig. 4 is a cross-sectional view taken along the line crossing the centre of the short side of Fig.

3.

Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

Fig. 1 shows a preferred embodiment of a shadow mask assembly according to the present invention, comprising a shadow mask 14 separated from a frame 16. The shadow mask 14 includes a plurality of terforations arranged in an effective part 11 for passing electron beams therethrough and a skirt 13 depending almost perpendicularly from the boundary of the effective part 11.

The skirt 13 is attached to the inside or outside of a flange 15 of the frame 16 welded at suitable points. There are a maximum number of three welding points along the long sides of the flange 15 and one at the central portion of the shirt sides. The skirt 13 of the shadow mask 14 and the flange 15 of the frame 16 are parallel to the central axis of the color picture tube.

According to the present invention, the frame 16 has a thermal expansion part 18, which is formed by cutting the short sides of the flange 15 at a point on both sides of the centre line of the short sides, the cutting lines being parallel to the central axis of the frame 16. The maximum length of the thermal expansion part 18 is designed as nine tenths the height of the flange 15 since excessive length may cause the loss of supporting force, resulting in excessive thermal expansion.

In addition, the thermal expansion part 18 has a metal section 19 mounted thereon, said metal section 19 having a lower thermal expansion rate than the frame 16. The metal section 19 is attached to the outside of the thermal expansion part 18 when the skirt 13 of the shadow mask is attached to the inside of the flange 15 as shown in Fig. 2, or otherwise to the inside of the thermal expansion part 18. The metal section 19 may be made of an iron-nickel alloy such as Invar with the frame 16 being made of stainless steel.

The four corners of the frame are shaped to have a plane surface for attaching a corner spring 17.

Rereinafter will be described the working effect of the inventive structure with reference to Fig. 2.

In the present embodiment, the skirt 13 of the shadow mask r4 is attached to the inside of the thermal expansion part 18 of the frame 16. When the electron beams impinge upon the solid parts of the shadow mask 14 it is thermally expanded, the central part of the shadow mask 14 swelling towards the screen due to the doming phenomenon. When the thermal expansion part 18 is heated, it serves as a bimetal with the low expansion metal section 19 bending towards the outside (towards the right side of the drawing).

The thermal expansion part 18 is substantially isolated from the remaining part of the flange 1S, thus showing more improved flexibility than the prior art.

Pence, the shadow mask 14 can quickly compensate for thermal expansion by means of the thermal expansion part 18 with the low expansion metal section 19, as shown in the comparison between Figs. 2 and 4.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the present invention is not limited to the disclosed embodiments, but, on the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A mask frame assembly for use in a color picture tube comprising a shadow mask having a plurality of perforations, a skirt, a frame for supporting the shadow mask; and corner springs for hanging the assembly of the shadow mask and frame on the inside of a panel of the color picture tube, said frame having a flange with thermal expansion parts formed by cutting short sides of the flange at a point on both sides of the central line of the short sides, the cutting line when the assembly is located in a color picture tube, being parallel to a central axis of said color picture tube, and said thermal expansion parts being provided with low expansion metal sections having a lower thermal expansion rate than said frame.

2. A mask frame assembly as claimed in claim 1, wherein the length of said thermal expansion part is at maximum nine tenths the height of said flange.

3. A mask frame assembly as claimed in claim 1, wherein said low expansion metal is attached to the outside of said thermal expansion part when the skirt of the said shadow mask is attached to the inside of said flange.

4. A mask frame assembly as claimed in claim 1, wherein said low expansion metal is attached to the inside of said thermal expansion part when the skirt of the said shadow mask is attached to the outside of said flange.

5. A mask frame assembly as claimed in claim 1, wherein said low expansion metal is made of Invar.

6. A mask frame assembly for use in a color picture tube, constructed and arranged substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.