Television – Special applications – Flaw detector
Reexamination Certificate
1998-12-24
2003-06-24
Kelley, Chris (Department: 2613)
Television
Special applications
Flaw detector
Reexamination Certificate
active
06583812
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a cathode ray tube phosphor screen inspecting method and apparatus for inspecting defects on a phosphor screen formed on the face inner surface of a panel of a cathode ray tube in the steps of manufacturing the cathode ray tube.
Conventionally, as shown in
FIGS. 1A and 1B
, a black film
12
having a predetermined pattern is formed on a face inner surface
11
b
of a curved glass face
11
a
forming a panel
11
of a cathode ray tube such as a display tube. As shown in
FIGS. 2A
to
2
C, in the pattern of this black film
12
a large number of holes
13
having a predetermined shape such as a circular shape are regularly formed. In the steps of manufacturing a cathode ray tube, this pattern is formed on the face inner surface
11
b
through a resist coating step, an exposure step using a shadow mask, a development step using no shadow mask, and a dag coating step.
In this black film pattern formation process, as shown in
FIGS. 2A
to
2
C, small-diameter holes P
1
, a deformed hole P
2
, no-aperture portions P
3
, and large-diameter holes (not shown) sometimes form as defects in the black film
12
. That is, the small-diameter holes P
1
shown in
FIG. 2A
are smaller than other holes
13
having a predetermined shape. The deformed hole P
2
shown in
FIG. 2B
is different in shape from the circular holes
13
. In the no-aperture portions P
3
shown in
FIG. 2C
, no holes
13
are formed in portions where the apertures
13
are to be formed. The large-diameter holes are larger than other holes
13
having a predetermined shape.
Many of these small-diameter holes P
1
, deformed hole P
2
, and no-aperture portions P
3
form in the exposure step. That is, exposure is performed via a shadow mask in the exposure step. Therefore, if the diameters of some holes in the shadow mask are smaller than the diameter of other normal holes, small-diameter holes P
1
form as shown in FIG.
2
A. Also, a fine dust particle sticking to the film surface forms a deformed hole P
2
in which a part of an aperture hole
13
is missing, as shown in FIG.
2
B. Furthermore, if the shadow mask is locally devoid of holes, no-aperture portions P
3
form as shown in FIG.
2
C. Since one of three dots of blue, green, and red phosphors is formed in each hole of the shadow mask, a defect involves a set of three holes as indicated by the alternate long and two dashed lines in
FIGS. 2A and 2B
.
After a defect-free black film
12
is formed, the film
12
is sequentially coated with blue, green, and red phosphors to form phosphor films, thereby finally forming a phosphor screen. The phosphor films are formed as follows. First, a phosphor is charged into the panel inner surface, and a phosphor film of the first color is formed through spin coating, drying, an exposure step using a shadow mask, and a development step using no shadow mask. After that, phosphor films of the second and third colors are formed through the same process.
In this phosphor film formation process, as shown in
FIGS. 3A and 3B
, phosphor films
14
of blue B, green G, and red R are sometimes not well formed to produce defects. A representative defect is called dot missing e.g. phosphor peeling. In
FIG. 3A
, a part of the phosphor film
14
of blue B is missing in the aperture
13
in the black film
12
. In
FIG. 3B
, the phosphor film
14
of green G is entirely missing in the aperture
13
in the black film
12
. In either case, phosphors failed to adhere in a desired pattern. Furthermore, in the phosphor film coating process, where dust adheres to the inner surface of the panel, the portions of which the phosphors are to be formed, are occupied with the dust. These portions are defect called dust.
Although either dot missing: described above is a defect, whether dot missing is non-defective (non-defective product) or defective (defective product) is in many instances determined in accordance with the position or pattern (defect pattern) on the phosphor screen. For example, it is very difficult to form a defect-free phosphor film in a display tube for use in a monitor display; some defects are practically no problem depending on the position or pattern on the phosphor screen.
Patterns of dot missing as a defect and a method of determining whether dot missing is non-defective or defective in accordance with the pattern will be described below with reference to
FIGS. 4A
to
7
B.
FIGS. 4A and 4B
show missing of a set of three dots of blue B, green G, and red R forming one pixel. In
FIG. 4A
, three dots of blue B, green G, and red R horizontally arranged in a line are missing. In
FIG. 4B
, three dots of blue B, green G, and red R adjacent to each other in the form of a triangle are missing. In either case, it is determined that the dot missing is non-defective if only one set of dots are missing and defective if two or more sets of dots are missing.
FIGS. 5A and 5B
show missing of two adjacent dots of the same color. In
FIG. 5A
, two dots of blue B horizontally adjacent to each other are missing. In
FIG. 5B
, two dots of blue B adjacent to each other in different rows are missing. In either case, it is determined that the dot missing is defective.
FIGS. 6A and 6B
show missing of two adjacent dots of two different colors. In
FIG. 6A
, two adjacent dots of blue B and green G are missing, and it is, for example, determined that this dot missing is defective. In
FIG. 6B
, two dots of blue B and green G at a distance d
1
are missing. It is determined that this dot missing is non-defective if, for example, the distance d
1
is 50 mm or more and defective if the distance d
1
is 50 mm or less. Also, even when two dots of the same color are missing, it is determined that this dot missing is non-defective if the distance d
1
is 50 mm or more.
FIGS. 7A and 7B
show missing of one set of dots and another dot at a distance d
2
. It is determined that this dot missing is non-defective if, for example, the distance d
2
is 50 mm or more and defective if the distance d
2
is 50 mm or less.
FIG. 8
shows a method of determining whether dot missing is non-defective or defective in accordance with the position of the dot missing on an effective surface (phosphor screen) of the panel
11
. Assume, for example, that a central circle on the effective surface of the panel
11
is a region A
1
and its outside portion is a region A
2
. If this is the case, the region A
1
is required to be defect-free, and the above defect standards are applied to the region A
2
.
These non-defective·defective determination standards are sometimes changed in accordance with the type and size of display tube.
The quality of a phosphor screen on which a black film
12
and phosphor films
14
are thus formed is usually inspected at the exit of a black film coating machine or a phosphor screen coating machine. This inspection is manually performed by placing the panel
11
on a panel conveyor or unloading the panel
11
from the panel conveyor and placing the panel
11
on a light table.
In this inspection of the phosphor screen on which the black film
13
and the phosphor films
14
are formed, e.g., in inspection of the phosphor screen of a common display tube, however, searching for defects is time-consuming and difficult because the diameter of the apertures
13
in the black film
12
is 90 to 150 &mgr;m and the aperture pitch of the apertures
13
for, e.g., green and green phosphors is 200 to 280 &mgr;m, a very small value. Hence, inspecting display tubes that are becoming increasingly finer is a heavy burden on inspectors, so some improvements are being demanded.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a cathode ray tube phosphor screen inspecting method capable of automatically and accurately inspecting defects on the phosphor screen of a cathode ray tube.
It is another object of the present invention to provide a cathode ray tube phosphor screen inspecting apparatus capable of automatically and accurately inspecting defects on the phosphor screen of a cat
Hirayama Kazumasa
Imaizumi Toshiyuki
Omote Katsumi
Yamazaki Tatsuya
Bugg, Jr. George A
Kabushiki Kaisha Toshiba
Kelley Chris
Pillsbury & Winthrop LLP
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