US3484638A - Shadow mask mounted in glass envelope of color tv picture tube - Google Patents

Description

Dec. 16, 196.9 N. B. MEA'RS 3,484,638

SHADOW MASK MOUNTED IN GLASS ENVELOPE OF COLOR TV PICTURE TUBE Filed July 1, 1968 INVENTOR I NORMAN B. MEAES ATTO NEYS United States Patent O 3,484,638 SHADOW MASK MOUNTED IN GLASS ENVELOPE OF COLOR TV PICTURE TUBE Norman B. Mears, St. Paul, Minn., assignor to Buckbee- Mears Company, St. Paul, Minn., a corporation of Minnesota Filed July 1, 1968, Ser. No. 741,362

Int. Cl. H01 29/06 US. Cl. 313-85 2 Claims ABSTRACT OF THE DISCLOSURE An aperture mask or shadow mask for a colored TV picture tube is constructed so that it is mounted and held securely at its outer edge by the picture tube glass bulb or envelope.

CROSS-REFERENCES TO RELATED APPLICATIONS This application is related somewhat to co-pending US. application Ser. No. 736,192, filed June 11, 1968 by the same applicant as the instant application and to US. Patent 3,376,451 dated Apr. 2, 1968.

BACKGROUND OF THE INVENTION Field of the invention This invention is directed toward use specifically in the construction of colored TV picture tubes containing shadow masks.

Description of the prior art Ordinarily shadow masks are made out of flat sheets of thin metal, such as stainless steel, containing a translucent area defined by a multitude of tiny, closely spaced apertures surrounded or enclosed by an imperforate marginal area. The translucent area is ordinarily bowed out or made somewhat concave to conform to the partial spherical shape of the front viewing face of the picture tube enevlope. In the past the mask was mounted on a fairly heavy mounting ring which, in turn, was fastened to the inside of the picture tube bulb by suitable spring-like attachments. To overcome some of the drawbacks of this method of supporting and mounting the mask, a number of more recent developments and innovations have been made. Among these are the invention such as described in the aforementioned US. patent and the aforementioned patent application. Although these most recent developments have been found quite satisfactory and have eliminated a number of the difficulties encountered with the old mounting systems, the industry is constantly on the alert and searching for still further improvements. For example, the shadow mask not only serves the normal operation function in the picture tube of ensuring that the electron beams strike the proper dots of phosphor inside the front face of the tube, but it is also used during the assembly of the picture when the phosphor dot pattern is being formed. For that purpose, the shadow mask is mounted in place temporarily and removed three times while the three sets of colored phosphor dots are being formed. It is critical that each time the mask is placed back in position, including the final time for permanent attachment, it be accurately positioned at the same location to ensure that the openings or apertures are correctly located with respect to the phosphor dots. Yet at the same time in order to expedite assembly of the picture tube, the mask must be removed easily and replaced easily when forming the phosphor dots.

SUMMARY The picture tube comprises the usual glass front piece 3,484,638 Patented Dec. 16, 1969 or face plate containing the viewing face, and a back piece which when attached to the face plate, closes up the tube and holds the electron guns, etc. These two pieces are joined together in the usual manner after the phosphor dots have been formed and after the shadow mask has been mounted to the face plate. The shadow mask is constructed with the usual translucent area surrounded by an imperforate section and shaped to conform to the contour of the viewing face of the picture tube. However, the outer edge of the mask is bent forward to form a skirt which engages a groove in the rear edge of the front section of the glass envelope which holds the mask in place but makes it easy to remove while the phosphor dots are being formed. When the two sections of the glass envelope are joined together, the back section is welded to the edge of the face plate section and holds the mask is held securely completely around its outer edge so that any temperature change-s which might tend to expand or contract the metal mask will now only make it flex forward or rearward with respect to the face of the tube. This would have little or no effect on the quality, brightness or brilliance of the picture being presented on the front face of the picture tube.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a rear view of a shadow mask constructed according to the teachings of this invention;

FIG. 2 is a rear view of the glass face plate of a picture tube in which the shadow mask would be mounted; and

FIG. 3 is a sectional view showing the shadow mask mounted in the pitcure tube face plate.

DESCRIPTION OF THE PREFERRED EMBODIMENT The shadow mask 10, sometimes referred to as an aper ture mask, for color TV picture tubes contains a conventional translucent area 11 formed by a myriad of tiny, dot-like apertures which are usually etched through a sheet of metal such as stainless steel. Ordinarily the shadow mask is circular or rectangular depending on the type of tube that it is used in. Electron beams pass through the openings in the translucent area when traveling toward the prosphor particles on the inside of the viewing face of the tube from electron guns usually located at the rear of the tube. The phosphor particles, not shown, are located on the inside surface of the face plate portion 12 of the picture tube. As illustrated most clearly in FIG. 3, the viewing portion of the picture tube face plate is ordinarily bowed out in the form of a portion of a spherical surface. The translucent area 11 of shadow mask 10 is correspondingly shaped concave to conform to the shape of the viewing face so that the miniature dots or apertures in the shadow mask are in proper alignment with respect to the phosphor dots on the interior of the face plate.

The shadow mask 10 has an imperforate marginal area 13 surrounding the translucent area 11. A portion of this imperforate section 13 may be a smooth continuity of the concavity of the translucent area but at a suitable dimension, compatible with the size of the glass face plate 12, it is bent outward and then forward to form a skirt or flange 14 extending completely around the periphery of the shadow mask. The rear edge 15 of glass face plate 12 contains a continuous groove or slot 16 suitabley dimensioned so that the skirt 14 on the shadow mask 10 will set snugly in the groove. During assembly of the picture tube, the shadow mask 10 can be temporarily mounted on the glass face plate 12 in this manner so that a set of phosphor dots can be photoprinted or otherwise appropriately formed in some acceptable manner through the translucent area 11. Afterwards the mask can be slipped out of the essing is necessary to form the dots. These steps can be followed a number of times until all of the sets of dots are appropriately formed. The ease with which the mask can be attached and removed and the corresponding savings in time than becomes quite apparent, Of substantial significance is that each time the mask 10 is removed and then replaced, it will be repositioned at virtually the identical location as before so that the phosphor dots are in exact alignment with their corresponding openings in the translucent area of the shadow mask.

After all of the processing steps for forming the phosphor dots have been completed, the mask 10 is inserted in groove 16 and the funnel-shaped rearmost portion of the glass tube envelope 17 is then brough into contact with the rear edge of the face plate 12 and Welded thereto in the usual fashion. This closes up the tube envelope and holds the shadow mask 10 securely in position within the groove 16. With the shadow mask 10 held in this fashion, any temperature variations during normal use which might tend to cause the metal mask to expand or contact will only make the translucent area 11 move forward or backward slightly with respect to the face plate 12 and will not cause any of the apertures from being laterally displaced with respect to their corresponding phosphor dots on the face plate. This eliminates one of the reasons for changes in the picture appearing on the viewing face during normal use of the TV set which has been a considerable concern to the industry.

The back portion 17 of the glass tube envelope which extends rearward from edge 15 of the face plate 12 is ordinarily funnel-shaped and contains the electron guns, not shown, which provide the electron beams. The manner or process by which the two glass sections are welded together is of no particular concern in the instant invention and is well known to those of ordinary skill in the tube fabrication field.

I claim: 1

1. For a color TV picture tube, a shadow mask, comprising: a thin metal sheet having a translucent area de fined by a myriad of closely spaced miniature apertures through which electron beams pass when traveling toward the viewing face of the tube, said translucent area being enclosed by an imperforate rim section and being formed concave to conform generally to the partial spherical contour of the inner face of the tube; said rim section being bent forward to terminate with a forward extending flange continuously around the mask for nestling snugly in a continuous groove in the back edge of the picture tube face plate. a

2. In a color TV picture tube, the improvement comprising, in combination:

(a) a glass envelope, comprising a frontmost face plate portion in partial spherical contour terminating in a rearward facing enclosing edge which contains a continuous groove, and a rearmost portion extending rearward from said edge of the face plate portion;

(b) a shadow mask, comprising a thin metal sheet having a translucent area defined by a myriad of closely spaced miniature apertures through which electron beams pass when traveling from electron guns located at the rear of the tube to the viewing face in the face plate of the tube, said translucent area being formed concave to conform to the contour of the face plate, and an imperforate rim section around the translucent area extending outward to the glass envelope and being bent forward to form a flange for nestling snugly in the groove in the rear edge of the face plate portion of the glass envelope;

(c) said rearmost portion of the glass envelope holding the said flange securely in said groove when said rearmost portion is joined to the edge of the face plate portion.

References Cited UNITED STATES PATENTS 2,827,584 3/1958 Olson 313-92 X JAMES W. LAWRENCE, Primary Examiner V. LAFRANCHI, Assistant Examiner US. Cl. X.R. 313283

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