Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
1999-04-22
2001-07-03
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S403000, C313S404000, C313S407000, C313S408000
Reexamination Certificate
active
06255765
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a shadow mask type color cathode ray tube, and more particularly to a color cathode ray tube having a shadow mask provided with press-formed embossments in a skirt portion thereof of such dimensions that concentration of stress in an apertured portion of the shadow mask is prevented in the operation of fitting the skirt portion of the shadow mask into a support frame.
In general, a shadow mask for use in a color cathode ray tube is press-formed and it has an apertured portion having a multiplicity of electron-transmissive apertures, an imperforate portion surrounding and integral with the aperture portion and a skirt portion bent back from a periphery of the imperforate portion. The skirt portion of the shadow mask is fitted in a support frame, is spot-welded to the support frame and fixed in a panel portion of the color cathode ray tube such that the imperforate portion of the shadow mask faces a phosphor screen coated on an inner surface of a faceplate of a panel portion.
FIGS. 4A
to
4
C are respectively structural views showing an example of the shadow mask used in a conventional color cathode ray tube.
FIG. 4A
is a front view of the shadow mask,
FIG. 4B
is a side view of a short side of the shadow mask, and
FIG. 4C
is a fragmentary sectional view of a region extending from the imperforate portion to the skirt portion.
In
FIGS. 4A
to
4
C, reference numeral
40
designates a shadow mask,
41
is an apertured portion,
42
is an imperforate portion,
43
is a skirt portion, and x marks are weld points.
The shadow mask
40
has a curved apertured portion
41
having a multiplicity of electron-transmissive apertures (not shown), a curved imperforate portion
42
surrounding and integral with the apertured portion
41
and a skirt portion
43
bent back from a periphery of the curved imperforate portion
42
, and is usually integrally formed by press-forming a multi-apertured thin sheet-like metal blank.
The multi-apertured thin sheet-like metal blank is very thin and therefore the press-formed shadow mask
41
is not always good in forming characteristics. The strength of the thin sheet-like metal blank is relatively weak and the shape of the shadow mask
40
obtainable by press-forming is limited. The corners of the shadow mask
40
are bent back from the curved imperforate portion
42
to form the skirt portion
43
with a smoothly falling curve, or are bent back stepwise from the curved imperforate portion
42
to form the skirt portion
43
with at least one step. The portion between the corners of the shadow mask
40
is bent back from the curved imperforate portion
42
with a relatively small radius to form the skirt portion
43
. As a result, the skirt portion
43
of the shadow mask
40
curls outwardly by a distance AS from a straight line passing through a bend line between the imperforate portion
42
and the skirt portion
43
and parallel to the longitudinal axis of the cathode ray tube, in a region between the corners of the shadow mask
40
, as shown in FIG.
4
C.
The fixation of the press-formed shadow mask
40
to a support frame (not shown) is performed as follows: the skirt portion
43
of the shadow mask
40
is fitted inside the support frame (rarely outside the support frame), and is spot-welded to the support frame at several weld points marked with X as shown in FIG.
4
B. The number of the weld points of the skirt portion
43
and the support frame are two on each long side, two on each short side and one at each corner of the shadow mask
40
, for example.
Large curl &Dgr;S is always easily made in the skirt portion
43
in press-forming the above-explained conventional shadow mask
40
. If the size of the curl A S exceeds an acceptable limit, the problem arises in that the curl &Dgr;S is an obstacle to fitting the skirt portion
43
into the support frame and degrades workability of the fitting operation. If the skirt portion
43
having a large curl &Dgr;S is forcibly fitted into the support frame, the stress caused to the skirt portion
43
is transmitted to the imperforate portion
42
and the apertured portion
41
, distorts the curved contour of the apertured portion
41
of the shadow mask
40
, and as a result, the color selection property of the shadow mask
40
is degraded.
To solve these problems, Japanese Patent Application No. Hei 9-56286 filed (laid-open on Sep. 25, 1998) by the same applicants as the present application, which corresponds to the copending application Ser. No. 09/035,896 which issued as U.S. Pat. No. 6,111,346, proposes a color cathode ray tube which is provided with a plurality of embossments and a plurality of notches around the circumference of the long and short sides of the skirt portion
43
of the shadow mask
40
such that the embossments extend in a direction of the height of the skirt portion
43
and project arcuately toward the imperforate portion
42
, and such that the notches are disposed between two adjacent ones of the embossments
43
and extend a fraction of the height of the skirt portion
43
in the direction of the height of the skirt portion, in order to limit the size of curls &Dgr;S occurring in the skirt portion
43
, the embossments and notches being formed in the operation of press-forming the shadow mask
40
.
In the above proposal, the plural embossments and notches formed in the skirt portion
43
limit the size of the curls &Dgr;S occurring in the skirt portion
43
such that concentration of stress in an apertured portion
41
of the shadow mask
40
is prevented in the operation of fitting the skirt portion
43
of the shadow mask
40
into a support frame.
SUMMARY OF THE INVENTION
It is one of the present invention to provide a shadow mask type color cathode ray tube provided with a shadow mask structure for preventing concentration of stress in an apertured portion of the shadow mask in the operation of fitting the skirt portion of the shadow mask into a support frame, by reducing the size of the curls &Dgr;S occurring in the skirt portion of the press-formed shadow mask more effectively.
For achieving the aforesaid object, a color cathode ray tube according to an embodiment of the present invention includes a generally rectangular shadow mask having a curved apertured portion having a multiplicity of electron-transmissive apertures, a curved imperforate portion surrounding and integral with the apertured portion and a skirt portion bent back from a periphery of the curved imperforate portion, and a generally rectangular support frame for suspending the shadow mask by spot welding the skirt portion thereto, within a panel portion of the color cathode ray tube; the skirt portion being provided with a plurality of embossments extending in a direction of a height of the skirt portion, the plurality of embossments being distributed over each of central portions extending a distance PHL and a distance PVL in long and short sides of the skirt portion, respectively, the PHL and PVL satisfying following inequalities: 0.5 HL≦PHL≦0.85 HL, 0.5 VL≦PVL≦0.85 VL, and the HL and VL being longitudinal lengths of the long and short sides of the skirt portion, respectively, wherein a depth of the plurality of embossments decreases or increases with increasing distance from centerlines of the long and short sides and a maximum and minimum of the depth of said plurality of embossments satisfy a following relationship on each of the long and short sides: 0.2≦(Pmax−Pmin)/Pmax≦0.6 where Pmax is the maximum of the depth of the embossments and Pmin is the minimum of the depth of the embossments.
With the structure of the present invention, the size of the curls &Dgr;S occurring in the skirt portion of the press-formed shadow mask is reduced to a greater extent, concentration of stress caused by large-sized curls of the skirt portion in an apertured portion of the shadow mask is reduced or eliminated in the operation of fitting the skirt portion of the shadow mask into a support frame, and consequently occurrence of
Hagiwara Koji
Ito Hiroshi
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Patel Vip
Quarterman Kevin
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