US3479546A

US3479546A - Self-supporting shadow mask for colored tv picture tubes

Info

Publication number: US3479546A
Application number: US736192A
Authority: US
Inventors: Norman B Mears
Original assignee: Buckbee Mears Co
Current assignee: Buckbee Mears Co
Priority date: 1968-06-11
Filing date: 1968-06-11
Publication date: 1969-11-18
Anticipated expiration: 1986-11-18
Also published as: FR2010697A1; GB1227544A; NL6813155A; GB1227545A; DE1800216A1

Description

N. B. MEARS Nov. 18, 1969 SELF-SUPPORTING sHADow MASK FOR COLORED Tv PICTURE TUBES Filed June 11, 1968 INVENTOR NORMAN B. MEA/R9 AT RNEYS UnitedStates Patent O 3,479,546 SELF-SUPPORTING SHADOW MASK FOR COLORED TV PICTURE TUBES Norman B. Mears, St. Paul, Minn., assignor to Buckbee- Mears Company, St. Paul, Minn., a corporation of Minnesota Filed June 11, 1968, Ser. No. 736,192 Int. Cl. H01j 29/46 U.S. Cl. 313-85 8 Claims ABSTRACT F THE DISCLOSURE A shadow mask for colored TV picture tubes is constructed with the conventional translucent area formed by a multiude of tiny apertures in a slightly bowed-out metal sheet through which the electron beams pass from the electron guns at the rear of the tube to the viewing face at the front of the tube. Integrally `formed with the translucent area is a circumambient imperforate rim which has a strengthening bead to make it quite rigid. An inward flaring flange extends around the edge of the rim to form a haze shield. The mask is mounted to the glass bulb of the picture tube by metal spring-like members which are attached at one end to the outside of the rim and at the other end are secured to the envelope of the tube.

BACKGROUND OF THE INVENTION Field of the invention This invention is directed toward use specically in the construction of color TV picture tubes containing aperture or shadow masks.

Description of the prior art In the past the aperture masks have been made out of flat sheets of thin metal such as stainless steel, with the translucent area surrounded by an imperforate marginal area. The mask was then bowed or made somewhat concave to conform to the contour of the front face of the picture tube. It is then mounted on a fairly massive mounting ring which in turn is fastened to the inside of the picture tube bulb by suitable attachments. Not only are masks made in this manner somewhat more costly, but the mounting hardware adds considerable weight and cost. Because of its mass, the mounting hardware usually produces some fairly substantial temperature gradients over the breadth of the mask during normal use. This results in some warping or twisting of the mask within the tube and adversely affects registration of the dot-like apertures to the phosphor dots and the definition of the picture viewed on the face of the tube, at least until the entire mask reaches a uniform constant temperature. Furthermore the mounting ring technique is time consuming since the mask must be assembled to the ring before being mounted within the tube envelope. A recent innovation is a self-supporting mask which eliminates the massive mounting ring and the hardware associated therewith. This innovation is described in U.S. Patent 3,376,45'1.

SUMMARY The present invention, sometimes referred to as a uniframe mask, is somewhat of a variation of the selfsupporting mask described in the aforementioned patent. It contains the conventional bowed-out or concave translucent area but the circumambient 90 rim is strengthened with a continuous bead or rib and the metal sheet is terminated with an inward flaring ange around the edge of the rib, all to provide self supporting strengthening features to eliminate the need for additional supporting structure. The uniframe mask is mounted to the inside of the picture tube bulb by elongated, spring-like members attached at one end to the rim and at the other end to the inside of the picture tube bulb. Not only is the mask then easily removable and reinsertable at the exact same location, but this type of construction is of considerable less weight. Even more important is that the entire mask area warms up at the same rate so that there is virtually no temperature differential across the mask, at least not enough to cause any twisting or warping which would impair the quality of the picture being projected on the viewing face. Furthermore, the basic cost of the mask is reduced as well as the cost of assembly of the picture tube, at least that part allocated to assembly and mounting of the aperture or shadow mask.

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

FIG. 2 is a front View of the same shadow mask;

FIG. 3 is a top view of the same shadow mask;

FIG. 4 is a side view of the same shadow mask;

FIG. 5 is a sectional view along viewing line 5 5; and

FIG. 6` illustrates in greater detail some of the features of the construction of the spring mounts for the shadow mask.

DESCRIPTION OF THE PREFERRED EMBODIMENT The conventional shadow mask or aperture mask for a colored TV picture tube contains a transducent area 10 formed by a myriad of tiny dot-like apertures which are usually etched through a sheet of metal such as stainless steel. The aperture mask may be circular or rectangular depending on the tube type. The electron beams pass through the openings in the translucent area as they are ejected from electron guns located at the rear of the tube and travel towards the phosphor particles on the inside of the viewing face of the tube. As seen most clearly in FIGS. 3 and 4, the mask, principally the translucent area, is bowed or concave to generally follow the contour of the inside face of the picture tube. The most popular way of mounting the shadow mask within the picture tube has been with a heavy mounting ring and associated hardware with the mask being attached to the ring along the imperforate marginal area 11. In this invention this mounting ring, and its associated disadvantages, is eliminated.

The uniframe aperture mask of the present invention contains the conventional translucent area 10 surrounded by the marginal imperforate area 11. Extending rearward at about from a planar projection of the translucent area is an integral continuation of the imperforate section forming a deep drawn rim 12 completely around the aperture mask. The rim 12 is formed with an elongated continuous inner bead or outer groove 13 which serves to strengthen the rim area 12. The rim 12 terminates with an integral continuation of the imperforate section aring inward to form a flange 14 extending around the entire rear edge of the rim. The latter provides what is commonly referred to as a haze shield which eliminates or minimizes the hazy eifect that might otherwise be present because of the dispersal of the electron beam pattern. The haze shield area 14 is terminated by a tiny upturned lip 15 which denes the 'outer dimensions of the opening through which the electron beams travel from the electron guns, not shown, through the translucent area 10. An aperture mask constructed in this manner has a degree of rigidity and a substantial degree of resiliency so during normal handling prior to being permanently installed inside the envelope of the colored TV picture tube, even though it may be twisted somewhat or otherwise subjected to various forces, it returns to its original shape when the force is removed. Therefore it can be handled with a great deal less care than has been the case with the shallow drawn aperture mask of the past before it was mounted on and supported by the heavy -mounting ring. Attached to the outside of rim 12, preferably at three points as illustrated in the drawings, are mounts 16 for attaching the self supporting shadow mask to the envelope of the picture tube. Preferably the mounts 16 are attached to the rim by spot welding the at plate portion 16a to the rim 12, but, of course, other methods of attachment can be utilized. The mounts 16 are made out of a strip of metal, such as 301 stainless steel. In the center area of the strip a section is punched out to form tongue member 17 which protrudes angularly outward from 16a and remains joined thereto at one end 18. At its other end the tongue member 17 is bent to form tab 19 for resting against the inner surface of the picture tube envelope. A hole 20 is pierced through the tab area 19 for engaging mounting pins or studs suitably located and jutting inward from the picture tube envelope. The tongues 17 on the mounts 16 are characterized by a degree of resiliency which, when the mask assembly is temporarily mounted in the tube envelope, removed and then later reinstalled, will make the translucent area of the shadow mask return to its original location with respect to the front face of the picture tube which is necessary to maintain register between the miniature apertures in the translucent area and their respectively associated phosphor dots on the inner front face of the tube.

Although in the embodiment described herein only a single strengthening bead 13 is shown in rim 12, it is contemplated that the mask can be formed with a number of similar strengthening beads or ribs in the rim to provide the desired rigidity and resiliency. It is also contemplated that if necessary, strengthening ribs or beads can be formed in the iiange 14 which serves as the haze shield. The additional strengthening ribs may take the form of continuous elongated beads or may be discontinuous, such as parallel elongated ribs in the upper and lower portions of liange 14 or in the left and right side portions.

Although not shown in the drawings, ordinarily when the aperture mask or shadow mask is inserted in the picture tube envelope, it is provided with a lbeam shield which is an annular ange which extends outward around the outer rear edge of the mask, usually from the area where flange 14 meets the rear edge of the rim 12. The beam shield extends outward to the glass envelope and serves to cut down spurious reflections which might otherwise interfere with the view of the picture at the front of the tube. It is contemplated that a beam shield may be incorporated in the present invention as an integral part of the mask by being a continuation of the imperforate section of the rnetal sheet where lip is shown in the drawing. In other words, a beam shield may be formed by a ange flaring outward at a sharp angle to the edge of flange 14 so that its outer edge rests against the inside surface of the tube envelope. A flange of this nature not only will perform the necessary function of a beam shield but also provides additional strengthening to the overall construction of the uniframe mask- It is also contemplated that a funnel-shaped magnetic shield may be made a part of the uniframe mask assembly by being attached at the rear of the mask in a manner similar to that illustrated and described in U.S. Patent 3,376,451.

There will now be briefly described a method by which a uniframe aperture or shadow mask has been constructed according to the teachings of this invention. Initially the translucent area 10 must be formed in a sheet of metal of suitable size. Typically, stainless steel sheet, in the range of .01 inch thick, may be utilized and the size of the sheet and the translucent area is dictated by the size and shape of the picture tube in which the mask will `be used. Typically, the translucent area can be formed in the manner described briefly in U.S. Patent No. 3,313,225 of Norman B. Mears and other patents referred to therein. Briefly, this involves the steps of coating both sides of a fiat sheet of metal with a suitable light-sensitive enamel and after drying, projecting a pattern of a multitude of miniature dots, using a suitable light source, on both sides of the coated metal sheet in register so that the enamel coating hardens only where struck by light. The unhardened enamel is then removed and the coated metal is immersed or sprayed or otherwise subjected to a suitable chemical etchant which removes the metal from the unprotected areas to form the desired pattern of miniature holes which comprises the translucent area of the aperture mask. This process of photochemical etching is commonplace in the photoengraving art and other fields today.

Once the translucent area is formed in the flat Sheet of metal, a suitably sized blank is cut roughly to size out of the metal sheet. This includes the translucent area. The roughly cut blank is then annealed at a temperature in the range of 1,600 F. for a suitable period of time. Following this, after an adequate cooling time, the metal blank is roller-leveled once on each side. This is accomplished by applying pressure on the sheet with rollers. This is done to relieve some of the internal stresses and strains which might have developed in the metal sheet. After roller leveling, the blank is cut to the exact size and inserted into a die block having a male and female portion for forming. If a rectangular mask, such as illustrated in the drawing, is to be formed, notches are cut in the four corner areas. The blank is then held in suitable fashion in the die block and the rim is drawn down to the desired depth. Because of the nature of the material, the depth of the draw, the criticality of aperture locations and other factors, it may be preferable to draw the rim to prescribed depth in a step-by-step fashion. For example, an initial draw may be to :A3 inch then to inch, then to M; inch and finally to a rim of 11/2 inches. Suiable dies for forming the uniframe mask can be designed by those skilled in the art and various procedural steps are readily determinable by those skilled in the art of die forming.

After the rim 12 has been formed, the flange or haze shield 14 is formed by flaring the remainder of the imperforate sheet of metal inward along the edges of the rim. Preferably this should be done by first flaring the long sides of the rim, then the shorter sides and next pressing the corner areas inward. The mask is then clamped in a suitable fixture and the corners and gussets are spot welded. Next, while the mask is held in another suitable fixture, mounts 16 are spot welded at suitable locations to the outside of rim 12. Lastly, the strengthening rib or rib 13 is formed in the rim 12 while the mask is held securely in a fixture.

It should be understood, of course, that the foregoing brief description of the process for forming a uniframe mask is only intended to be illustrative and not limitive since it is contemplated that the forming operation can be accomplished in a variety of manners.

I claim:

1. An improved self-supporting shadow mask for a colored TV picture tube made from a thin metallic sheet, comprising: a concave translucent area defined by a myriad of miniature dot-like apertures through the metallic sheet; an imperforate section of said metallic sheet forming a rim circumambient to said translucent area extending rearward therefrom a substantially a angle to the planar projection of the translucent area; a continuous elongated strengthening bead formed on said rim; a further imperforate section of said metallic sheet forming a flange flaring inward from the rear edge of said rim; and means located on the outside of said rim for mounting the mask to the picture tube bulb.

2. The invention as described in claim 1 wherein said means for mounting the mask is attached directly to said rim.

3. The invention as described in claim 2 wherein said mounting means includes an elongated resilient metallic tongue extending angularly outward from said rim being joined at one end only to said rim and being coupled to the tube bulb near its other end.

4. The invention as described in claim 2 wherein said mounting means comprises: a relatively thin strap of stainless steel aixed to the outside of said rim; a resilient tongue member formed out of a central portion of said strap, said tongue member extending angularly outward from said strap and having a tab portion at its free end bent to rest against the inside of the tube bulb, said tab portion containing an opening for engaging a mounting pin extending inwardly from said bulb.

5. The invention as described in claim 3 further including elongated strengthening beads on -said flange.

6. For a color TV shadow mask made out of a metal sheet having a curved translucent face area surrounded by an imperforate rearward directed rim section with a continuous elongated strengthening bead on said rim, means for attaching the mask to the tube, comprising: mounting means attached to said rim on at least three sides of the mask, each of said mounting means having an elongated resilient metal tongue member extending angularly outward from said rim being attached to the rim at one end and being coupled to the tube bulb at its other end.

7. The invention as set forth in claim 6 wherein each of said mounting means comprises: a strap of metal rigidly secured to the outside of said rim; a resilient tongue member formed out of a portion of said strap and extending angularly outward from the strap, said tongue member having a tab portion at its free end bent to parallel the inside of the tube bulb and containing an opening adapted to engage a mounting pin in said bulb.

8. The invention as set forth in claim 7 wherein said strap bridges the bead on said rim.

References Cited UNITED STATES PATENTS 2,855,529 10/1958 Morrell 313-85X 3,368,098 2/1968 Demmy 313-85 I AMES W. LAWRENCE, Primary Examiner V. LAFRANCHI, Assistant Examiner