US3737703A

US3737703A - Shadow mask frame construction

Info

Publication number: US3737703A
Application number: US00166556A
Authority: US
Inventors: A Tsuneta; S Sawagata
Original assignee: Tokyo Shibaura Electric Co Ltd
Current assignee: Toshiba Corp
Priority date: 1970-07-31
Filing date: 1971-07-27
Publication date: 1973-06-05
Anticipated expiration: 1990-06-05
Also published as: DE2138274C3; DE2138274A1; GB1302510A; DE2138274B2; FR2099406A5

Abstract

In a shadow mark for use in a colour television receiving tube of the type comprising a rectangular mask plate, and a rectangular frame member including a rectangular side wall adapted to support the mask plate and a reinforcing flange, the angle between the side wall and the reinforcing flange is made larger than 90* at the corners of the rectangular frame member and to gradually increase toward the longitudinal centres of the shorter sides and the longer sides of the rectangular frame member.

Description

United States Patent Tsuneta et al. 1 51 June 5, 1973 54 SHADOW MASK FRAME 2,897,392 7 1959 Fiore ..313 92 B CONSTRUCTION 3,497,746 2/1970 Duistermaat et aL... .313/85 S 3,549,932 12/1970 Lindeman ..313/85 S [75] Inventors: Asahide Tsuneta, Kawasak1; Sh1nlch| 3,581,135 /1971 Garren I g v 4 5 Sawagata, Tokyo, both of Japan 3,601,650 8/1971 Pappadis ..3l3/85 s [73] Assignee: Tokyo Shibaura Electric Co., Ltd.,

Kawasakbshi, Japan Primary ExaminerRobert Segal AttorneyR. D. Flynn, S H. Frishauf and Leonard [22] Filed: July 27, 1971 Holtz [21] Appl. No.: 166,556

[57] ABSTRACT Foreign Application Priority Data In a shadow mark for use in a colour television receiv- Jul 31 1970 h an /7581, ing tube of the type comprising a rectangular mask i 1970 g t; plate, and a rectangular frame member including a rectangular side wall adapted to support the mask 52 US. Cl ..313/ s, 25/25.11 Plate and a'reinfereihg flange, the angle between the [51] InLC] 01 0 0 0 9 02 side wall and the reinforcing flange is made larger 58 Field 01 Search ..313/92 B, 85 s; than at the corners of the rectangular frame 29/2511 member and to gradually increase toward the longitudinal centres of the shorter sides and the. longer sides [56] References Cited of the rectangular frame member.

UNITED STATES PATENTS 8 Claims, 12 Drawing Figures 2,795,718 6/1957 Van Kekken et al ..313/85 S PATENIEUJUH 5:975

SHEET 1 BF 2 FIGS SHADOW MASK FRAME CONSTRUCTION This invention relates to a shadow mask for use in a colour television receiving tube and more particularly to an improved construction of the frame for supporting a mask plate.

A colour television receiving tube generally comprises an envelope including a funnel having an integral neck, and a face plate joined to the opening of the funnel. On the inside of the face plate is secured a mask plate provided with a plurality of small perforations for controlling the passage of electron beams from a source of electron beams contained in the neck. Usually, the mask plate has a rectangular configuration and is provided with a curved surface having at least one centre of curvature located on the side of the source of the electron beams. The radius of curvature of the curved surface is the same as that of the curved inner surface of the face plate which is coated with phospor and it is desired that the distance between the inner surface of the face plate and the curved surface of the mask plate should be uniform at all points. Furthermore, as the metal plate constituting the mask plate is extremely thin, in order to prevent deformation of the mask plate, it is mounted on a rigid rectangular frame member which is removably mounted on pins secured to the flange of the face plate.

One example of the method of manufacturing the rectangular frame member is as follows. First, a metal strip having a suitable thickness, 2.6mm for example, is prepared and the metal strip is bent longitudinally by 90 to have a cross-section of a letter L. The L shaped metal strip is then bent transversely at four spaced apart points into a rectangular configuration and the opposite end of the strip is welded together to form a flat rectangular frame member. To securely support the curved mask plate, the rectangular frame member is then bent by means of a press or the like to have the same curvature as that of the periphery of the mask plate. Due to the mechanical working operations described above, internal strain is created in the frame member so that it is necessary to subject the frame member to a suitable heat treatment. However, some strain often remains unremoved.

During the evacuation step of the envelope following the incorporation of the shadow mask assembly comprising the mask platesecured to the frame member into the envelope of the receiving tube, the shadow mask is heated to a temperature of about 450C. Due to the residual strain'not removed even by this heat treatment the frame member has a tendency to twist about its axis. Such twisting causes the mask plate to deform after completion of the receiving tube so that the chance of creating the so-called misslanding increases in which the electron beams fail to correctly irradiate the phosphor dots of red, blue and green, for example, applied on the inner surface of the face plate, thus causing colour break-up of the picture image. For this reason, it is highly desirable to provide an improved rectangular frame member capable of decreasing the strain created by the mechanical working operations.

In the colour television receiving tube including a plurality of phosphor dots formed on the inner surface of the face plate, the so-called black matrix type tube has been developed in which the diameter of the perforations of the mask plate for controlling the passage of the electron beams is made larger than that of the dots. For this purpose, after forming the phosphor dots, the shadow mask is removed from the face plate and is then dipped in an etching solution to enlarge the diameter of the perforations so as to be larger than that of the phosphor dots. The etching solution remaining at the bent portions and corners of the rectangular frame member after the etching treatment tends to corrode, oxidize and rust the frame member and fine particles formed by such chemical reactions tend to close the perforations. In this manner, it is desirable to provide an improved rectangular frame member capable of preventing the retention of residual etching solution.

Accordingly, it is an object of this invention to provide an improved shadow mask for colour television receiving tubes having a rectangular frame member of a configuration capable of giving lesser tendency of preserving the strain created by a mechanical working operation and preventing the etching solution from remaining.

Another object of this invention is to provide a shadow mask including a new and improved rectangular frame member for supporting the mask plate, which is not necessary to be annealed to remove the strain created therein by the mechanical working thereof.

SUMMARY OF THE INVENTION These and further objects of the invention can be ac complished by providing a shadow mask of a colour television receiving tube of the class comprising a rectangular mask plate including a curved rectangular face having at least one centre of curvature on the side of a source of electron beams contained in the envelope of the tube, and a peripheral flange surrounding the curved rectangular face and bent toward the source of electron beams; the curved rectangular face being provided with a plurality of small perforations for controlling the passage of the electron beam; and a rectangular frame member including a rectangular side wall adapted to receive the peripheral flange and a reinforcing flange bent inwardly of the rectangular frame member away from the side wall, the side wall having a curved free edge having the same radius of curvature as the periphery of the mask plate, characterized in that the angle between the side wall and the reinforcing flange of the rectangular frame member is made larger than at the corners of the rectangular frame member and gradually increases towards the longitudinal centre of each side of the rectangular frame member.

Selection of the angle between the rectangular side wall and the reinforcing flange of the rectangular frame member to be larger than 90 not only decreases the strain created therein by the mechanical working but also prevents the etching solution utilized to etch the shadow mask from remaining on the rectangular frame member. This design further increases the area of the mask plate through which the electron beam passes or the effective area of the mask plate. However, the angle should be selected to a suitable value not to decrease the mechanical strength of the frame member. The angle is decreased gradually from the longitudinal centre of each side toward the corners of the frame member for the purpose of easy working.

Where said angle at the longitudinal centre of the longer side of the rectangular frame member is made larger than that at the longitudinal centre of the shorter side it is possible to work more easily the frame member so as to decrease internal'strain, and where at least one perforation is provided for the reinforcing flange at each corner of the rectangular frame member, the strain due to mechanical working can be reduced further and the etching solution can be more readily drained. The advantageous merit of the frame member can be enhanced by increasing the width of the side wall at the longitudinal centre of each side than that at the corners. Longitudinal grooves having a semicircular cross-section may be provided for the reinforcing flange.

This invention can be more fully understood from the following detailed description when taken in connection with the accompanying drawings, in which:

FIG. 1 is a side view, partly broken away, of a colour television receiving tube employing a shadow mask embodying the invention;

FIG. 2 is a perspective view, partly broken away, of the shadow mask shown in FIG. 1;

FIG. 3 is a perspective view of the rectangular frame member of the shadow mask shown in FIG. 2;

FIGS. 4, and 6 show coss-sections at a corner, centre of the shorter side and centre of the longer side of the rectangular frame member shown in FIG. 3 taken along lines 4-4, 5-S and 66, respectively;

FIG. '7 is an enlarged perspective view of a corner of the rectangular frame member shown in FIG. 3;

FIG. is a perspective view of a modified rectangular frame member;

FIG. 9 is an enlarged perspective view of a corner of the frame member shown in FIG. 8; and

FIGS. 10, 11 and 12 show cross-sections at a corner, centre of the shorter side and centre of the longer side of the rectangular frame member shown in FIG. 8, taken along lines l010, IIl1 and 12-12, respectively.

The envelope of a colour television receiving tube shown in FIG. 1 comprises a funnel 2 having an integral neck which contains a source of electron beams I and a face plate 9. The shadow mask 8 embodying the invention is removably mounted in the peripheral flange 3 of the face plate by means of pins 7 secured thereto. The outer edge of the flange 3 is sealed to the opening of the funnel 2 at 14 by means of a low melting glass for example. On the inner surface 15 of the face plate 9 are formed, such as by coating, a plurality of phosphor dots, not shown, adapted to emanate red, blue and green colours, for example, when impinged upon by the electron beams in a manner well known in the art. The face plate 9 is substantially rectangular and its inner surface 15 is a curved surface having at least one centre of curvature located on the side of the source of electron beams 1.

As shown in FIG. 2, the shadow mask 8 comprises a rectangular mask plate 18, and a rectangular frame member 19 supporting the mask plate 18. The mask plate 18 has a curved surface having a plurality of fine perforations 16 for controlling the passage of the electron beams impinging upon the phosphor dots and the same radius of curvature as the inner surface 15 of the face plate. The periphery of the mask plate is bent at right angles towards the source of electron beams to form a peripheral flange 17 used to mount the mask plate on the frame member.

The rectangular frame member 19 comprises a vertical side wall 20 adapted to receive the peripheral flange 17 of the musk plate 18 and a reinforcing flange 22a projecting inwardly from the side wall and is bent at varying angles as will be described later with respect to the vertical side wall 20. The free edge 23 of side wall 20 is curved with the same radius of curvature as'the periphery of the mask plate 18. The peripheral flange 17 of the mask plate is fitted on the vertical side wall 20 and welded thereto as by welding whereby the mask plate is securely fixed to the rectangular frame member The cross-sectional configurations at a corner, longitudinal centre of a shorter side 24 and at the longitudinal centre of a longer side 25 of the rectangular frame member 19 are shown by FIGS. 4, 5 and 6, respectively. More particularly, the angle between the vertical side wall 20 and the reinforcing flange 22a equals +a,, 90+e and 90+a respectively, at these sections. The cross-sectional configuration of the reinforcing flange 22a is straight at any point of respective sides. Desirably, the above described angles have a relation a, a a but the angular relation may also be a a and a, a Angles a and a gradually decrease from the longitudinal centres of respective sides toward the corners of the rectangular frame member. As shown in FIGS. 4-6, the surface of the reinforcing flange is inclined toward the source of electron beams. The inclined angle is selectively determined within (1,, a and a The widths of the vertical side wall 20 at various sections equal 1,, l and 1 as shown in FIGS. 4, 5 and 6 and it is desirable that they satisfy a relation l, l l As shown in FIG. 3, each side wall has a free edge 23 and a stationary edge opposite the free edge, the radius of curvature of the stationary edge being different from thatof the free edge. The widths of the side walls (or the distance) between the free edge and the corresponding stationary edge are 1 1 and 1 respectively at the corner along line 4-4, the longitudinal center of the shorter side wall along line 5-5 and the longitudinal center of the longer side wall along line 6-6. However, if desired, the relation may be l, l and l, l The widths l and 1 at the longitudinal centres of the shorter and longer sides gradually decrease toward the corners of the rectangle. In this manner, by making the width of the side wall 20 larger at the centres of respective sides than at the corners of the rectangular frame member, it is possible to increase the mechanical strength of the frame member.

By selecting respective angles in ranges 041 5 15, a 10 5 and 15 55, more particularly, a, 5, a l0 and a 30 it is possible to minimize the strain created by the mechanical working operations of the frame member as well as the thermal deformation caused by the heat treatment of the frame member. thus effectively preventing decrease in the mechanical strength of the frame member.

At four corners of the frame member, since the reinforcing flange 22a and the side wall 20 are bent together at substantially right angles, maximum strains are created at these corners. Accordingly, in order to absorb or eliminate the strains at the corners, it is advantageous to form at least one perforation 26 through the reinforcing flange 22a at each corner as shown in FIG. 7. In the case shown therein, there are provided six such perforations 26.

One method of fabricating the rectangular frame member 19 is as follows. First, a metal strip having a desired thickness, 2.6mm for example, width and 7 points and the opposite ends of the strip are welded together to obtain a rectangular frame member. The frame member is then deformed by means of a press such that its free edge (the upper edge as viewed in FIG. 3) will have the same curvature as the periphery as the mask plate 18. Then, if desired,'the frame member may be subjected to a heat treatment to remove the strain caused by the working operations. Thereafter, the mask plate 18 is mounted on the rectangular frame member. Fixtures provided on respective sides of the frame member for receiving the pins shown in FIG. 1 are not shown.

A modified rectangular frame member 27 shown in FIGS. 8 to 12 also comprises a vertical side wall 20 and a reinforcing flange 22b, and the free edge 23 (upper edge as viewed in FIG. 8) of the vertical side wall 20 is curved with the same radius of curvature as the periphery of the mask plate in the same manner as, in the first embodiment. However, the cross-sections at the corner, at the longitudinal centre of the shorter side 24 and at the longitudinal centre of the longer side 25 taken along lines l10, 11-11 and 12-12 in FIG. 8 have configurations as shown in FIGS. 10, 11 and 12, respectively. More particularly, the reinforcing flange 22b is not bent sharply at right angles with respect to the vertical side wall 20 but instead flange 22b and side wall 20 are interconnected by a rounded connection of a radius of curvature R which is selected to be equal to one to three times the thickness of the metal strip constituting the frame member. The inner edge of the flange 22b is curved in the opposite direction with a radius of curvature of R The angle between a tangent line 28 to the inner curved edge of flange 22b and the inner side of the vertical side wall 20 equals 90+a at the corner, 90"+ct at the longitudinal centre of the shorter side 24 and 90+oz at the longitudinal centre of the longer side 25 of the rectangular frame member. As above described, these angles have a relationa (1 04 Where these angles are selected within ranges a 7, 01 4 30 and a 45 it is pos sible to minimize the strain in the frame member and prevent decrease in the mechanical strength thereof. Angles a and a; decrease gradually toward the corners from their maximum values at the centre of the sides as in the first embodiment. As shown in FIG. 9, a groove 29 is formed in each side of the reinforcing flange 22b. Each groove 29 extends in the direction of each side of the rectangular frame member and the depth of the groove 29 decreases gradually from the centre toward the corners of the rectangular frame member. The grooves 29 form curved surfaces having radius of curvature R as shown in FIGS. 10, 11 and 12. The crosssectional configuration of respective grooves is semicircular and their radius of curvature R is substantially equal to 15R,. Thus, the depth and width of each groove are the maximum at the centre of each side of the frame member and gradually decrease toward the corner. Considering a shorter side 24, for example, the width of the groove equals l3 to 15mm, the depth about 2 mm, whereas at the centre of the longer side 25, the depth of groove equals about 3mm. Although the strain in the frame member produced therein by the working operations reduces with the radius of curvature R the mechanical strength of the frame member is also reduced so that it is necessary to select R to a proper value.

In the embodiment shown in FIGS. 10, 11 and 12 the width of the vertical side wall 20 is selected to satisfy a relation l l l in order to prevent decrease in the mechanical strength of the frame member. Similar to the embodiment shown in FIG. 3, the widths l and 1 decrease toward the corners. However, these widths may be selected to satisfy the conditions l l and l, I

Again, it is advantageous to form at least one perforation 26 at each corner to decrease strain and to provide good drainage of the etching solution used to etch the mask plate.

The steps of manufacturing the modified frame member are substantially identical to those described in connection with the first embodiment except that grooves 29 and perforations 26 are formed before the metal strip is bent into the L shaped cross-section.

In the frame member of the shadow mask, since the angle between the vertical side wall and the reinforcing flange is made larger than the tendency of the width of the reinforcing flange for obstructing the passage of the electron beams is decreased. In other words, it is possible to increase the effective area of the mask plate in which perforations 16 are provided. Further more, according to this invention it is possible to decrease the residual strain. The construction of the frame member is suitable for the black matrix type shadow mask in which the diameter of the perforations 16 is enlarged by dipping the shadow mask in an etching solution. Where the reinforcing flange 22b is constructed to have two oppositely curved surfaces of radii of curvatures R and R as shown in FIG. 8, the advantageous effect described above can be enhanced. Perforations 26 at the corners not only decreases the residual strain but also improves drainage of the residual etching solution. Further, the fact that the angle between the vertical side wall and reinforcing flange of the rectangular frame member increases toward the corner also contributes to the decrease of the residual strain.

What we claim is:

1. A shadow mask of a color television receiving tube of the class comprisingi a rectangular mask plate including' a curved rectangular face having at least one centre of curvature on the-side of a source of electron beams contained in the envelope of said tube, and a pcripheral flange surrounding said curved rectangular face and bent toward said source of electron beams, said curved rectangular face being provided with a plurality of small perforations therein for controlling the passage of said electron beams; and a rectangular frame member having two shorter side walls and two longer side walls adapted to receive said peripheral flange inclined toward said source of electron beams and a reinforcing flange bent inwardly of said rectangular frame and away from said side walls, each of said side walls having a curved free edge and a stationary edge opposite said curved free edge, said curved free edge having the same radius of curvature as the periphery of said mask plate,

the radius of curvature of said stationary edge opposite to said free edge of each side wall differing from that of said free edge, the angle between said side wall and said reinforcing flange equaling 90+a 90+or and 9O+a at the corner, at the longitudinal centre of said shorter side wall and at the longitudinal centre of the longer side wall, respectively, and said angles 04,, a and a having a relation a a the angles and a gradually decreasing from the longitudinal centres of said shorter and longer side walls toward the corner of said rectangular frame member wherein a =5 to l5,-a =l0 to 45, and a =l5 to 55.

2. The shadow mask according to claim 1 wherein said side walls have widths l l and I at the corners, at the longitudinal centre of the shorter side and at the longitudinal centre of the longer side, respectively, of said rectangular frame member, said widths being measured between said stationary and free edges of said side walls and having a relation l l l and said widths l and I gradually decreasing from said centres toward said corners.

3. The shadow mask according to claim 1 wherein said reinforcing flange is formed with at least one perforation at each corner of said rectangular frame member.

4. The shadow mask according to claim 1 wherein the transverse cross-section of said reinforcing flange of said rectangular frame member is substantially linear at any side thereof.

5. The shadow mask according to claim 1 wherein said reinforcing flange at each side of said rectangular frame member is provided with a groove extending in the longitudinal direction of said side, the depth and width of said groove gradually decreasing from the centre of said side toward the corners of said rectangular frame member, and said groove being convexed toward the free edge of said side wall.

6. The shadow mask according to claim 5 wherein said side walls have widths l l and 1 at the corners, at the longitudinal centre of the the shorter side and at the longitudinal centre of the longer side, respectively, of said rectangular frame member, said widths being measured between said stationary and free edges of said side walls and having a relation l, l l and .said

widths l and I gradually decreasing from said centres toward said corners.

7. The shadow mask accordingto claim 5 wherein said reinforcing member is provided with at least one perforation at each corner of said rectangular frame member.

8. The shadow mask according to claim 6 wherein said reinforcing member is provided with at least one perforation at each corner of said rectangular frame member. a, a a the angles a and a gradually decreasing from the longitudinal centres of said shorter and longer side walls toward the corner of said rectanular frame member, wherein (1 5 to 15, 0: 32 10 to 45,

Claims

1. A shadow mask of a color television receiving tube of the class comprising: a rectangular mask plate including a curved rectangular face having at least one centre of curvature on the side of a source of electron beams contained in the envelope of said tube, and a peripheral flange surrounding said curved rectangular face and bent toward said source of electron beams, said curved rectangular face being provided with a plurality of small perforations therein for controlling the passage of said electron beams; and a rectangular frame member having two shorter side walls and two longer side walls adapted to receive said peripheral flange inclined toward said source of electron beams and a reinforcing flange bent inwardly of said rectangular frame and away from said side walls, each of said side walls having a curved free edge and a stationary edge opposite said curved free edge, said curved free edge having the same radius of curvature as the periphery of said mask plate, the radius of curvature of said stationary edge opposite to said free edge of each side wall differing from that of said free edge, the angle between said side wall and said reinforcing flange equaling 90*+ Alpha 1, 90*+ Alpha 2 and 90*+ Alpha 3 at the corner, at the longitudinal centre of said shorter side wall and at the longitudinal centre of the longer side wall, respectively, and said angles Alpha 1, Alpha 2 and Alpha 3 having a relation Alpha 1< Alpha 2<3, the angles Alpha 2 and Alpha 3 gradually decreasing from the longitudinal centres of said shorter and longer side walls toward the corner of said rectangular frame member wherein Alpha 1 5 to 15*, Alpha 2 10 to 45*, and Alpha 3 15 to 55*.

2. The shadow mask according to claim 1 wherein said side walls have widths l1, l2 and l3 at the corners, at the longitudinal centre of tHe shorter side and at the longitudinal centre of the longer side, respectively, of said rectangular frame member, said widths being measured between said stationary and free edges of said side walls and having a relation l1< l2< l3, and said widths l2 and l3 gradually decreasing from said centres toward said corners.

6. The shadow mask according to claim 5 wherein said side walls have widths l1, l2 and l3 at the corners, at the longitudinal centre of the the shorter side and at the longitudinal centre of the longer side, respectively, of said rectangular frame member, said widths being measured between said stationary and free edges of said side walls and having a relation l1<l2<l3, and said widths l2 and l3 gradually decreasing from said centres toward said corners.

7. The shadow mask according to claim 5 wherein said reinforcing member is provided with at least one perforation at each corner of said rectangular frame member.

8. The shadow mask according to claim 6 wherein said reinforcing member is provided with at least one perforation at each corner of said rectangular frame member. Alpha 1< Alpha 2< Alpha 3, the angles Alpha 2 and Alpha 3 gradually decreasing from the longitudinal centres of said shorter and longer side walls toward the corner of said rectanular frame member, wherein Alpha 1 5 to 15*, Alpha 232 10 to 45*, and Alpha 3to 55*.