US 3916243 A
A shadow mask for colored TV picture tubes contains the conventional foraminous or translucent area formed by multiple vertical rows of miniature apertures or slits with the improvement being a set of parallel elongated channels or grooves which are located between the vertical rows of slits or apertures to produce a self-supporting mask which has a smoothly curved surface.
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Description (OCR text may contain errors)
United States Patent 1 1 Brown CHANNELED SHADOW MASK  Inventor: Silas A. Brown, Lake Elmo, Minn.
 Assignee: Buckbee-Mears Company, St. Paul,
22 Filed: Sept. 20, 1974 211 Appl. No.: 507,689
 US. Cl. 313/403; 29/25.14  Int. Cl. H01J 29/07; l-lOlJ 29/08  Field of Search 313/403, 402, 407, 404,
 References Cited UNITED STATES PATENTS 3,653,900 Black 313/408 X Oct. 28, 1975 3,753,663 3/1973 Black 313/402 X Primary Examiner-Robert Segal Attorney, Agent, or FirmJacobson and Johnson [5 7] ABSTRACT A shadow mask for colored TV picture tubes contains the conventional foraminous or translucent area formed by multiple vertical rows of miniature apertures or slits with the improvement being a set of parallel elongated channels or grooves which are located between the vertical rows of slits or apertures to produce a self-supporting mask which has a smoothly curved surface.
7 Claims, 5 Drawing Figures U.S. Patent 0t.2s, 1975 Sheet 1 of2 3,916,243
CHANNELED SHADOW MASK BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to making a curved shadow mask having small openings or slots for use in colored television tubes as well as for other articles. More specifically, this is an etching process for producinga flat mask which can be bowed or curved to produce a curved shadow mask having a smooth, continuous gradual curve.
2. Description of the Prior Art In a colored television picture tube, a shadow mask or aperture mask is located between the electron guns at the rear of the tube and phosphor coated face plate at the face of the tube. Electron beams pass through the tiny openings or apertures in the shadow mask and impinge on a suitable color-producing phosphor dot on the face plate. Located in line with the openings of the shadow mask are three phosphor dots, lines or the like, one dot or line for each of the three primary colors. During operation of the picture tube, the shadow mask openings are used as a guide for the electron beams. In one style of these prior art masks the openings are relatively small and elongated. The process of making the openings in an elongated shape is shown and described in the co-pending application of John .I. Frantzen and Lee C. Barton titled Etching Process for Accurately Making Small Holes in Thick Materials, U.S. Pat. Ser. No. 487,665, filed July 11, 1974. The present invention relates to making a mask having elongated openings therein which is to be formed into a continuous rounded surface.
Recently, the shadow mask industry has begun using the types of shadow masks which have elongated slots or slits in the mask. The minimum dimension of the openings in these masks are usually less than the thickness of the mask material. Furthermore, the openings are usually located in vertical alignment on the mask. All these factors have coacted to make it difficult to etch a shadow mask and then form the mask into a curved mask suitable for use in a television picture. One of the problems encountered with these masks is that the mask material ruptures easily when the mask is formed into the required curved surface. The present invention has overcome the difficulty in forming a smoothly curved mask from a sheet of flat material by providing a set of parallel recessed grooves which allow the mask to be formed into a curved shape but do not structurally weaken the mask.
SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an enlarged rear sectional view of a portion of a television aperture mask;
FIG. 2 is an enlarged front sectional view showing the channels located in the television aperture mask;
FIG. 3 is a sectional end view of a portion ofa televi' sion aperture mask;
FIG. 4 is a sectional view taken along the lines of 44 of FIG. 1; and
FIG. 5 is a pictorial view of a curved mask as it appears in a television picture tube.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring toFIG. 1, reference numeral 9 generally designates an enlarged section of an etched flat mask which is to be formed and installed in the glass envelope ofa television picture tube. Mask 9 contains a plurality of rows of elongated openings 11 which are located in alignment on the mask. The width of the openings is denoted by reference letter a. Surrounding each of the openings 1 1 is a recess region 10. Recess region 10 has been formed in the mask in order that the openings 11 can be accurately etched into the mask 9. That is, ifthe minimum dimensions of the opening a are less than the thickness of the mask T (FIG. 3), it has been difficult if not impossible to directly and accurately etch such small openings without using some type of compensation techniques. Consequently,'a cavity or recessed region is first etched into the mask. Next, an opening is etched through the bottom of the cavity. Thus, the mask is left with the appearance of cavities or recesses in which the bottom has been removed to provide an opening therethrough. Although the mask retains its structural rigidity because of the thickness of the mask, when the mask has openings made by the process of removing extra material around the opening, it produces regions of low mass between regions of high mass that make it difficult to form or bend the mask into a smoothly rounded mask. Referring to FIG. 4, reference numeral 17 denotes a low mass region 17 which is located between the ends of the openings 10. One of the problems of forming the flat mask into a curved mask is that the low mass regions which are referred to as tie bars are easily ruptured or deformed when the mask is subjected to the forming process. One of the prior art techniques to eliminate this problem is to remove the tie bars and use a set of parallel filaments. However, the filaments must be supported in tension in order to maintain proper alignment and spacing of the filaments. Still another solution is to make the mask out of thinner material, however, this tends to destroy the structural rigidity of the mask to a point where it is wholly unacceptable as a self-supporting aperture mask.
The importance of obtaining a smoothly curved aperture mask is that the spacing between the openings must be accurately aligned in order to produce a television picture of good quality.
Referring to FIGS. 2 and 3, reference numerals l5 and 16 designate a set of parallel elongated channels which are located on each side of opening 1 1. Although FIGS. 2 and 3 reveal only two channels, the channels are located between all the rows of vertical openings.
Channels 15 and 16 are identical in size and shape and have a width designated by W and an unetched depth designated by reference letter S. The channels are etched in the face of the mask which is opposite the side of the mask containing the recess region 10. It has been found that by etching a set of parallel continuous channels produces a mask which can be formed with a curved surface without rupturing the tie bars or deforming the surface of the mask.
As can be seen in FIG. 3, the cross section of the mask becomes more uniform without regions of high mass adjacent to regions of low mass. It is this feature which is believed to allow the mask to be accurately 3 formed into a self-supporting shadow mask.
Referring to FIG. 5, reference numeral 20 designates how a mask may appear in its formed or bowed shape. That is, the surface of the mask has a spherical curvature thereto. In order to illustrate the position of the line of openings 22 and the position of the channels 21, three rows of openings and channels are shown in mask 20. The channels extend parallel to the rows of openings and extend from the top side of the mask to the bottom side of the mask. It should be understood that the rows of openings and channels extend completely across the face of the mask but for purposes of illustration, only three rows of openings and channels have been shown.
The openings and the thicknesses of a typical mask are pointed out by the following example.
EXAMPLE A sheet of material having a thickness T of 0.0056 inches was etched until the cavities had a dimension b of 0.0142 inside, with an opening a of 0.0045. The depth of unetched portion of the opening c was 0.0023 inches. The channels which run parallel to the rows of elongated openings had an etched width W of 0.0ll inches and an unetched depth S of 0.0017 inches. The mask was formed into a curved shadow mask without any rupturing of the tie bars occurring during the forming process.
From the above example and test work performed on the present invention, it has been found that the present invention has its greatest utility where the mask thickness exceeds the minimum dimension of the opening in the mask. [t is these particular masks which are extremely difficult to form into a properly curved surface without rupturing the tie bars between the openings.
1. An aperture mask having a plurality of openings therein for the projection of an electron beam therethrough comprising:
a sheet of metal having a topside and a bottomside,
said sheet of metal having an aperture region defined by a plurality of openings therein, said plurality of openings comprising a plurality of rows of openings located in substantial alignment to thereby form a plurality of spaced rows of openings, each of said plurality of openings having a cavity surrounding the opening in said mask;
a plurality of channels substantially symmetrically located between the rows of said openings and extending from the topside of said mask to the bottomside of said mask with at least one channel located between adjacent rows of openings; said plurality of channels and cavities having related depths to effect uniformity of mask shaping without rupturing of the mask material.
2. The mask of claim 1 wherein said sheet of metal having openings therein are elongated.
3. The mask of claim 2 wherein said plurality of channels are located on the one side of said mask and the cavities are located on the opposite side of the mask.
4. The mask of claim 3 wherein the openings have a minimum dimension less than the thickness t of said mask.
5. The mask of claim 4 wherein the plurality of channels are spaced equidistant between the rows of said openings.
6. The mask of claim 5 wherein the plurality of channels have an etched depth which is at least half the thickness t of said mask.
7. The mask of claim 6 wherein the mask has a cross sectional area which is characterized by substantially uniform thickness.