Electric lamp or space discharge component or device manufacturi – Process – With assembly or disassembly
Reexamination Certificate
2000-06-13
2003-07-15
Ramsey, Kenneth J. (Department: 2879)
Electric lamp or space discharge component or device manufacturi
Process
With assembly or disassembly
C427S068000, C118S053000
Reexamination Certificate
active
06592420
ABSTRACT:
This application is based on an application No. 11-172072 filed in Japan, the content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a manufacturing method for a color cathode ray tube (hereafter abbreviated to CRT) and in particular to a manufacturing method for a glass substrate having a phosphor layer on its inner surface, that is used for a front panel of a CRT.
2. Description of Related Art
FIG. 1
is a perspective view of a conventional color CRT that has been partially cut away to show its interior. The color CRT shown in the drawing includes a glass envelope formed by joining together a front substrate
1
, a funnel
91
and a neck
92
, electron guns
93
that are inserted into the neck
92
, a deflection yoke
95
that deflects electron beams
94
emitted by the electron guns
93
, a phosphor layer
96
formed on the inner surface of the front substrate
1
, color-selecting electrodes
97
positioned at fixed intervals on the side of the phosphor layer
96
nearer to the electron guns
93
, and a magnetic shield
98
. Here, the edges of the front substrate
1
are surrounded by a low barrier wall, and the term ‘inner surface’ refers to the curved surface of the front substrate
1
, but does not include the surface of the barrier wall.
FIG. 2
is an enlargement in cross-section of part of the inner surface of the front substrate
1
, used to illustrate the structure of the phosphor layer
96
. As shown in the drawing, a black film
99
with a thickness of around 1 micron is formed in stripes placed at fixed intervals on the inner surface of the front substrate
1
. Then, colored phosphor stripes
3
,
4
and
5
including phosphor particles with a diameter of 7 to 8 microns in the colors red, green and blue are formed in a specified positional relationship in the intervals between the stripes of black film
99
. A reflective layer (not shown in the drawing) is placed on top of this structure, thereby forming the phosphor layer
96
. The phosphor stripes
3
,
4
and
5
emit light in their respective colors when the electron beams
94
strike the phosphor layer
96
via the color-selecting electrodes
97
.
A conventional slurry method is used to form the phosphor layer
96
. Such a method is described briefly below, with reference to
FIGS. 3A and 3B
.
A slurry
2
is formed from a photoresist in which phosphor particles have been suspended, the photoresist consisting of an aqueous solution of polyvinyl alcohol (PVA) to which an aqueous solution of ammonium dichromate (ADC) has been added. As shown in
FIG. 3A
, the front substrate
1
is positioned so that the inner surface faces upwards, and is tilted slightly at a fixed angle. Then the slurry
2
is poured onto the front substrate
1
while it is rotated slowly in the above-mentioned position, thereby gradually spreading the slurry
2
over the inner surface of the front substrate
1
. The arrow in the drawing shows the direction in which rotation is performed. Once the slurry
2
has covered the entire inner surface of the front substrate
1
, the front substrate
1
is tilted to the position shown in FIG.
3
B and then rotated at high speed, spinning off excess slurry, and thereby forming a phosphor film of an even thickness. This phosphor film is then dried using a heater or warm air. Next, the color-selecting electrodes
97
are fixed at a certain distance from the inner surface of the front substrate
1
and exposed, before being developed using warm water or similar to form a phosphor stripe pattern in a specified color. This process is repeated in turn for each of the green, blue and red phosphors, thereby forming a phosphor pattern having the three specified colors. Following this, an organic film and then an aluminum evaporation film are formed on top of the structure, completing the formation of the phosphor layer
96
for the color CRT.
One important point to consider when using a slurry method to form the phosphor layer
96
is the need to achieve a layer of a uniform thickness when using the spinning process. An uneven phosphor layer will cause disparities in the amount of light emitted by the phosphor layer, thereby generating irregularities of light and shade on the screen surface. Furthermore, if the thicknesses of the phosphor layers for the three phosphors green, blue and red on the front substrate
1
vary at different points on the front substrate
1
, the luminance for each color will be different. As a result, the brightness of the three colors will vary from place to place on the substrate
1
and white uniformity will be markedly reduced. One method for improving this situation and increasing white uniformity is described, for example, in Japanese Laid Open Patents Nos. 59-186230 and 6-203752. These documents disclose a technique for achieving an even phosphor layer by a combination of spinning the front substrate
1
with its inner surface facing upwards, and spinning the front substrate
1
with its inner surface facing downwards, once slurry
2
has been poured and spread over the surface of the front substrate
1
.
However, the above-described related art technique makes it more difficult to recycle or reuse the excess slurry, and so the method illustrated in
FIG. 3A and 3B
is generally used to drain off excess slurry, and achieve an even phosphor layer. If this method is used, excess slurry can be recycled using simple recycling equipment, and there is little deterioration in the quality of the recycled slurry.
When the front substrate
1
is positioned horizontally with its inner surface facing upwards, the tilt angle is said to be 0°. Thus, a greater amount of excess slurry will be drained off if a larger tilt angle is used in the draining process. At the same time, however, the phosphor particles deposited on the inner surface of the front substrate
1
are loosened by the force of gravity and so are more likely to drop off. This reduces the amount of friction between the inner surface of the front substrate
1
and the phosphor particles, and accordingly reduces the concentration of phosphor particles on the front substrate
1
when high-speed rotation is performed in the spinning process, as described above.
Furthermore, the centrifugal force generated during the high-speed rotation performed in the spinning process may have a detrimental effect, particularly during the formation of the phosphor pattern for the second and third colors. This effect occurs if the orientation of the centrifugal force generated on these occasions has a certain relationship with the orientation of the grooves created by the phosphor pattern(s) of the colors that have already been applied. When phosphors are applied in a stripe pattern, this occurs when the orientation of the centrifugal force is parallel with the orientation of the stripes, in other words an orientation moving out from the center of the front substrate
1
towards its top and bottom edges (FIG.
4
). Alternatively, when phosphors are applied in dot triads, this occurs when the centrifugal force has an orientation moving out diagonally towards the four corners of the front substrate
1
. In either of these cases, phosphors are forced out from the central part of the front substrate
1
towards its edges, so that the concentration of phosphor particles in the central part of the front substrate
1
is reduced.
If the front substrate
1
has a large curvature radius, that is if it is virtually flat, the above tendencies are more marked, since the friction between the phosphor particles and the inner surface is reduced, making the movement of phosphor particles from the center of the inner surface toward its edges more likely. Conversely, if the tilt angle of the front substrate
1
in the draining and spinning processes is small, excess slurry which could not be removed is likely to accumulate on the barrier wall surfaces of the front substrate
1
. This also causes irregularities in the concentration of phosphor particles to be generated on the inner surface
Iguchi Hideo
Nishimori Hikaru
Onishi Ryouji
Tani Naoyuki
Matsushita Electric - Industrial Co., Ltd.
Ramsey Kenneth J.
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