Electric lamp and discharge devices – Cathode ray tube – Shadow mask – support or shield
Reexamination Certificate
1999-03-17
2001-10-23
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Shadow mask, support or shield
C313S402000
Reexamination Certificate
active
06307310
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to color cathode ray tubes for use with color display devices in color television sets and computer monitors or the like, and more particularly to those color cathode ray tubes with improvements in shape of a shadow mask assembly used therein
2. Description of the Related Art
As shown in
FIG. 1
, a color cathode ray tube is configured including a glass valve comprising a panel portion
1
and a neck portion
2
as well as a funnel portion
3
, a phosphorus-coated surface or fluorescent film
4
as formed on the inner surface of the panel portion
1
, a shadow mask assembly
5
disposed at a specified location opposing and adjacent to the phosphor film, an internal magnetic shield (not shown) as formed into a shape along the inner wall of the funnel portion, and an electron gun
12
for production of three electron beams
13
toward the phosphor film
4
. There are co-provided and disposed outside of the neck portion
2
a magnet
9
for purity adjustment and a center beam static convergence adjustment magnet
10
plus a side beam static convergence adjustment magnet
11
, wherein said electron beams
13
operate exhibiting deflection in the presence of a magnetic field that is created by a deflection yoke
8
as disposed outside of the glass valve to thereby penetrate the perforated molded mask
6
letting the specified phosphor film
4
emit light.
In the color cathode ray tube, whether the accuracy of positional alignment of the shadow mask assembly
5
and the phosphor film
4
is good or bad can directly affect whether resultant display images are good or not in quality. More specifically, display images are deteriorated when deformation or the like takes place due to mechanical distortion and/or thermal distortion at the perforated molded mask
6
and the support frame
7
constituting the shadow mask assembly
5
.
FIGS. 2
to
4
show one example of the shadow mask assembly of conventional color cathode ray tube. In
FIG. 2
the reference numeral
40
designates such shadow mask assembly,
41
denotes a perforated molded mask,
44
represents a support frame,
45
indicates a frame-shaped portion,
46
shows a spring, and
47
is a projection (referred to as the “dowel” hereinafter) as formed at the frame-shaped portion. The perforated molded mask
41
comprises a curved surface portion
42
which has multiple electron beam penetration holes (not shown), and a skirt portion
43
that down goes from four peripheries of the curved surface portion
4
, wherein the support frame
44
is structured from a rectangular frame-shaped portion
45
and springs
46
attached to the outer wall of the frame-shaped portion
45
for permitting attachment of the support frame
44
to inside of the panel portion (not shown) as well as a plurality of dowels
47
attached to the inner wall of the frame-shaped portion
45
for causing the inner wall of the frame-shaped portion
45
and the skirt portion
43
to come into contact engagement with each other.
FIG. 3
is a diagram showing a cross-sectional view at a location indicated by A-A′ in FIG.
2
.
FIG. 4
is a sectional diagram at a location represented by B-B′ in FIG.
2
. The support frame
44
is of a nearly rectangle shape with nearby portions of four vertexes of such rectangle being connected by curved planes, which may resemble in shape substantially the L-shaped cross-section with the thickness t as shown in FIG.
3
and FIG.
4
.
The prior art shadow mask assembly
40
has the dowels
47
that are formed on the side wall of the frame-shaped portion
45
of the support frame
44
and extend toward inside of said substantial rectangle. Here, the height h of the dowels
47
as measured from inside of the sidewall of the frame-shaped portion
45
will be called the “embossing amount”. As shown in FIG.
3
and
FIG. 4
, the support frame
44
is of the shape which has those embossing portions of length values
1
1
,
1
2
in the inside direction thereof. While lengthening these embossing portion lengths
1
1
,
1
2
may enhance the mechanical strength of the support frame
44
, an excessive increase in length is not achievable due to limitations received from the cathode ray tubes effective screen size.
Since said prior art shadow mask assembly
40
is formed when press-machining the perforated molded mask
41
as was shown in
FIG. 2
in such a manner that respective upper edges (peripheries of the curved surface section
42
) of the skirt portion
43
are slightly curved outwardly at the center portions as compared to the corner sections thereof, the clearance with respect to a contact plane between the skit portion
43
and the frame-shaped portion
45
becomes larger at the corners of the skirt portion
43
thereby necessitating additional provision of the dowels
47
at respective corners of the frame-shaped portion
45
while at the same time suffering from a problem in that the resulting perforated area of the curved surface portion
42
with respect to the size of the support frame
44
gets narrower to the extent corresponding to an increase in clearance.
In said prior art shadow mask assembly
40
the contact surfaces between the skirt portion
43
and the frame-shaped portion
45
become only those layout portions of the dowels at the corners thus limiting the substantial contact regions between the skirt portion and the frame-shaped portion, which leads to a problem that the magnetic resistivity, which is important among magnetic shield characteristics of color cathode ray tubes, is significant disadvantageously at said corners of the perforated molded mask
41
thus letting any effective magnetic shield characteristics be hardly obtainable.
Another problem faced with said prior art shadow mask assembly
40
is that since the skirt portion
43
is designed so that respective upper edges thereof (peripheries of the curved surface portion
42
) are formed to be slightly curved outwardly at the center portion as compared to corners, the workability remains inferior when inserting for assembly the perforated molded mask
41
into the support frame
44
while simultaneously associating with the risk of deformation of the perforated molded mask
41
during assembly processes.
An object of the present invention is to provide a color cathode ray tube with a shadow mask assembly offering increased robustness against deformation due to mechanical and/or thermal distortion, which structure is high in accuracy of positional alignment with an associative fluorescent or phosphor film and also excellent in magnetic shield characteristics.
SUMMARY OF THE INVENTION
The present invention has attained said object by arranging the shadow mask assembly for use with the color cathode ray tube in a way which follows.
The shadow mask assembly used in the color cathode ray tube of the present invention is of the inward projected shape with substantially central portions of two side lines which nearly oppose each other at a skirt portion of a perforated molded mask being curved inwardly and with four corner sections of the perforated molded mask each being outwardly curved thus resembling approximately an arc-like shape of a radius R, while substantially central portions of two opposite side lines of a support frame are each curved outwardly to have an outward projected shape with four corners of the support frame each having a substantially arc-like shape of the radius R due to outward curvature and with a dowel being substantially centrally formed on each side line of the support frame. The distal end of such dowel is placed inside of a rectangle as formed by straight lines which connects together those points at which the corners of said perforated molded mask are in contact engagement with the support frame.
The shadow mask assembly used in the color cathode ray tube of the present invention is such that the corners of said support frame and the corners of said perforated molded mask are contacted together whereas the dowel of said suppo
Iwata Tsuyoshi
Maehara Mutsumi
Yoshioka Hiroshi
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Hopper Todd Reed
Patel Nimeshkumar D.
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