Electric lamp and discharge devices – Cathode ray tube – Envelope
Reexamination Certificate
2002-12-24
2004-11-16
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Envelope
C220S00230A, C445S008000, C348S818000, C348S825000, C348S836000, C348S821000
Reexamination Certificate
active
06819039
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Japanese application ser. no. 2001-391668, filed on Dec. 25, 2001
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to a glass funnel for projection in which pad portions for fixing a cooling means are integrally formed to be protruded on outer surfaces of a sidewall portion.
2. Description of Related Art
Conventionally, as a cathode ray tube (CRT) being a major constituting part of a television set and the like, so-called a direct-view type cathode ray tube and a projection cathode ray tube are known. The cathode ray tube comprises a panel having a face portion with a substantially rectangular shape to display an image, and a funnel having substantially funnel-shaped sidewall portion extending from a large opening portion with a substantially rectangular shape to a small opening portion with a substantially circular shape. A neck portion in which an electron gun is inserted is connected to the small opening portion. The panel and the funnel can be made by press molding a molten glass using molds that comprise a female mold and a male mold.
Compared with the direct-view type cathode ray tube having a structure to display an image by arranging three primary colors of light in R, G, B on a display screen, the projection cathode ray tube uses three cathode ray tubes to irradiate R, G, B lights respectively, and then to display an image by focusing these lights to enlargely project onto a screen. For the projection cathode ray tube, because the light on the display screen has to be enlarged and projected, display characteristics of the high brightness and the high fineness are required than the direct-view type cathode ray tube. Accordingly, the panel of the projection cathode ray tube is usually at a very high temperature, so that a cooling means is usually attached onto the surface of the panel.
The cooling means has to be properly arranged to a position separated by a prescribed distance to a fluorescent face formed on the face portion of the panel. For example, as disclosed in Japanese publication No. 5-27209, pad portions, which serve as positioning portions of an instrument to fix the cooling means, are integrally formed on the sidewall portions of the funnel to which the panel is sealed. The pad portion has an end face that is substantially perpendicular to a central axis line of the funnel, and the end face is used as a reference end face for positioning the cooling means. Furthermore, the pad portion has a side face extending towards the large opening portion side from the reference end face to an outer surface of the sidewall portion.
In the conventional art, as conditions required by the pad portion mentioned above, because only positioning the cooling means properly by the reference end face is regarded as important, the planarity of the reference end face is the only thing to be noticed. However, the shape of the reference end face or the shape of a joining portion between the pad portion and the outer surface of the sidewall portion of the funnel is not particularly concerned.
Accordingly, the pad portion, which is tried to design or manufacture, has a shape as shown in
FIGS. 4A
to
4
C That is, as shown in
FIG. 4A
, a ridgeline of the reference end face
7
′ of the pad portion
6
′ are shaped such that it has a straight line portion on a top portion, and rising portions
9
′,
9
′ from the outer surface
4
a
′ of the sidewall portion
4
′ are connected in bending form to the both sides of the straight line portion
8
′. In addition, joining portions between the outer surface
4
a
′ of the sidewall portion
4
′ and the rising portions
9
′,
9
′ are formed with small circular arcs each of which, for example, has a curvature radius less than 10 mm.
Furthermore, as shown in
FIG. 4B
, as viewing from a direction perpendicular to an imaginary plane including the central axis line Z′ of the funnel and passing the top portion
8
′, a gradient of a first side face
10
′ extending toward the large opening portion side (the arrow A side) from the top portion
8
′ of the reference end face
7
′ to the outer surface
4
a
′ of the sidewall portion
4
′, i.e., an inclination angle &agr;′ of the first side face
10
′ with respect to the central axis line Z′ of the funnel, is set less than 10°. Moreover, the curvature radius of the joining portion
12
′ between the first side face
10
′ and the outer surface
4
a
′ of the sidewall portion
4
′ is set, for example, less than 3 mm. Furthermore, the curvature radius of the joining portion
11
′ between the outer surface
4
a
′ of the sidewall portion
4
′ and the edge of the reference end face
7
′ at the side of the central axis line Z′ of the funnel is set, for example, less than 3 mm.
As shown in
FIG. 4B
i.e., a vertically cross-sectional view cut along the line y—y in FIG.
4
B and along the line x—x in
FIG. 4A
, as viewing from a direction along an imaginary line directing toward an adjacent portion between the top portion
8
′ of the reference end face
7
′ and the rising portion
9
′ from the central axis line Z′ of the funnel in the direction perpendicular to the central axis line Z′, the gradient of the second side face
13
′ extending towards the large opening portion side from the adjacent portion of the reference end face
7
′ to the outer surface
4
a
′ of the sidewall portion
4
′, i.e., the expanding angle (the inclination angle) &bgr;′ with respect to the central axis line Z′ of the funnel is set less than 10°. In addition, the curvature radius of a joining portion
14
′ between the second side face
13
′ and the outer surface
4
a
′ of the sidewall portion
4
′ is set less than 3 mm, and the curvature radius of a joining portion
15
′ between the reference end face
7
′ and an entire side face including the first side face
10
′ and the second side face
13
′ is set less than 2 mm.
After the above pad portion structure is proposed, to improve the efficiency related to the press molding of the glass funnel for projection is pursued. As a result, a property of taking the glass funnel out of the mold (female mold) or moldability is pursued.
For example, as described above, the top portion of the pad portion has the straight line portion and the bending portions formed at the both sides thereof, the curvature radius of the joining portions between each portion of the pad portion and the outer surfaces of the sidewall portion is small, the gradient of the side face of the pad portion is small, which cause following problems. Namely, during the press molding for the funnel, it is very difficult to fill a sufficient amount of glass to molding faces corresponding to the pad portions of the mold, so that defects due to the insufficient filling will occur, the property of taking the funnel out of the mold gets worse, and scratches or minute cracks may occur on the pad portions.
In order to eliminate such problems, lubricant is tried to provide to the molding faces corresponding to the pad portions of the mold. However, this solution causes new problems, such as the occurrence of oil stain or wrinkle caused by the lubricant. Theoretically, it is possible to provide a good property of taking the funnel out of the mold by reducing the temperature of the mold, but it is very difficult to maintain an optimum temperature. Therefore, even though the extent of the temperature lowering is slightly excessive, disadvantages such as occurrence of cracks might be caused.
Moreover, to change the molding method or the molding condition to attempt to solve the above problem, not only requires considerable time and labor, but also requires delicate temperature adjustment, and therefore, experience is required. However, in spi
Fujihara Shigeo
Odani Osamu
Harper Holly
J.C. Patents
Nippon Electric Glass Co. Ltd.
Patel Nimeshkumar D.
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