Chunghwa Picture Tubes, Ltd.

Kuo-Cheng Chen

Ching-Hsiang Tseng

Wen-Chi Chen

Chun-Hsien Yeh

Yu-Shin Hu

Der-Jyh Chang

In a shadow mask employed as a color selection electrode in a multi-electron beam color cathode ray tube (CRT), the surface area of the mask is reduced by increasing the length of the individual elongated beam passing apertures, or slots, while reducing the ratio of the width of the bridge portion of the mask between adjacent apertures to the length of the aperture. Increasing the length of the apertures while reducing the ratio of bridge width to aperture length reduces the surface area of the mask upon which energetic electrons are incident resulting in a corresponding reduction in thermal deformation, or doming, of the shadow mask. Reduction in shadow mask doming results in reduced landing shift of the electron beams incident on phosphor elements disposed on the inner surface of the CRT's display screen for improved video image brightness and color purity. More specifically, in a shadow mask having a thickness in the range of 0.12-0.18 mm with slotted apertures, the length of the slots is in the range of 0.90-10.00 mm and the ratio of bridge width to slot length is in the range of 0.001-0.110. With this invention, electron beam transmission through the shadow mask can be increased by as much as 22% resulting in a reduction in beam landing shift error by as much as 20 .mu.m. Video image brightness is increased by as much as 17% and the color purity adjustment margin is increased to over 10 .mu.m in, for example, a color CRT with a 20 inch display screen.

Shadow mask for color CRT

A shadow mask, or color selection electrode, in a color cathode ray tube (CRT) is in the form of a thin metal foil and includes a large number of apertures through which electron beams are directed onto the phosphorescent coating on the CRT's display screen for forming a video image. The apertured shadow mask is also used with a light source during CRT manufacture to form a large number of spaced phosphor elements in the phosphorescent coating. Ideally, all of the beam passing apertures and phosphor elements are circular in cross-section, but the shadow mask is stretched and maintained under high tension when mounted in the CRT causing some of the apertures, particularly those adjacent its four corners, to also become stretched and assume an oval shape. This is avoided in the present shadow mask by providing the areas in the vicinity of four corners of the shadow mask with oval apertures which are elongated in a direction generally transverse to the mechanical forming direction, or the direction of greatest tension when the mask is stretched and mounted in a color CRT. After installation in a CRT, the oval apertures assume a circular shape because of the greater tension applied along the short axis of each aperture. The remaining apertures in the center portion of the mask retain their circular shape after installation because they are under less tension than the outer apertures.

Shadow mask for color CRT and method for forming same

In a cathode ray tube (CRT) having a glass envelope with a neck portion, a funnel portion and a display screen, or front panel, an electron gun disposed in the CRT's neck portion has a plurality of aligned electrodes, including a charged shield cup. The shield cup includes a plurality of contact springs disposed about the outer periphery thereof and engaging a conductive layer on the inner surface of the CRT's neck portion for supporting the electron gun and charging the shield cup to an electron accelerating, or anode, voltage. Also disposed on the outer periphery of the shield cup and engaging the inner conductive layer is a getter support member. To provide a zero resultant force applied to the shield cup by the three contact springs and the getter support member and maintain the electron gun coaxial with the CRT's centerline, the thickness or strength of the contact springs is established such that the resultant force of the contact springs on the shield cup provides a reaction force to, and compensates for, the force exerted by the getter support member on the shield cup.

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Sanchong, Taiwan

Kuo-Cheng Chen