Electric lamp and discharge devices – Cathode ray tube – Envelope
Reexamination Certificate
1999-09-24
2001-07-31
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Cathode ray tube
Envelope
C313S112000, C348S835000, C359S614000
Reexamination Certificate
active
06268693
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a cathode ray tube for use in a television receiver, a display for a personal computer, and the like.
Referring to
FIG. 1
, a cathode ray tube comprises as an envelope a glass bulb which includes a glass panel
11
with a fluorescent film
10
formed on an inner surface thereof, a flare-shaped funnel
12
formed behind the glass panel
11
, and a neck
13
with an electron gun arranged therein, as well known in the prior art. In the inner surface of the glass panel, a shadow mask
14
is arranged to face the fluorescent film
10
. An electron beam emitted from the electron gun is irradiated through the shadow mask
14
onto the fluorescent film
10
so that an image is displayed on a front portion (hereinafter referred to as a face portion) of the glass panel
11
.
The interior of the above-mentioned cathode ray tube is kept in a high vacuum state so that the glass bulb is subjected to compressive stress and tensile stress. If mechanical shock is applied to the glass bulb, there is a risk of occurrence of implosion. In view of the above, the face portion of the glass panel generally has a thickness greater in its peripheral region than in its central region, for the purpose of maintaining the sufficient strength of the cathode ray tube.
Accordingly, the typical glass panel is liable to have a difference in light transmittance between a central region and a peripheral region of the face portion. As a result, the luminance in the peripheral region is reduced in comparison with the central region so that the image becomes nonuniform in brightness and is therefore hard to watch.
In addition, various kinds of glasses are used for the glass panel in dependence upon applications thereof. As the transmittance of the glass itself forming the glass panel is higher, the difference in transmittance resulting from the difference in thickness between the central region and the peripheral region of the face portion becomes smaller but the contrast is decreased.
From the above-mentioned background, a proposal is made of a cathode ray tube which has a reduced difference in transmittance between the central region and the peripheral region thereof by using a glass panel made of a glass having a high transmittance, and which has an improved contrast by bonding a colored glass plate to a face portion with an adhesive.
In recent years, the glass panel is required to have a flatness. Accordingly, it is tried to increase the radius of curvature of the face portion in a diagonal direction of the outer surface thereof to 10000 mm or more. However, the greater the radius of curvature of the face portion of the glass panel is, the higher the risk of the implosion becomes. Therefore, in case where the radius of curvature of the face portion of the glass panel in the diagonal direction of the outer surface thereof is equal to 10000 mm or more as described above, the face portion is designed so that the thickness (TE) of the peripheral region in the diagonal direction and the thickness (T
0
) of the central region satisfy the formula of 1.2≦TE/T
0
≦4.0.
However, when the difference in thickness of the face portion of the glass panel is too great between the central region and the peripheral region as described above, it is difficult to sufficiently reduce the difference in transmittance between the central region and the peripheral region even if the glass panel is made of the glass having a high transmittance.
Furthermore, the greater the thickness of the face portion of the glass panel is, the heavier the cathode ray tube becomes. The use of the colored glass plate adhered to the front surface thereof further increases the weight of the cathode ray tube. As a result, transportation is difficult.
In addition, when the colored glass plate is adhered, bubbles may be mixed in the adhesive or striae may be produced so that the image is difficult to watch. Furthermore, the adhesive may be deteriorated during the use over a long period of time so that the colored glass plate is detached.
SUMMARY OF THE INVENTION
Taking the above-mentioned circumstances into consideration, it is an object of this invention to provide a cathode ray tube which has a reduced difference in transmittance between a central region and a peripheral region of a panel and a high contrast even if a glass panel has a great difference in thickness between a central region and a peripheral region of a face portion thereof.
According to this invention, there is provided a cathode ray tube using a glass panel having a difference in thickness between a central region and a peripheral region of a face portion thereof, the glass panel having an outer surface with a colored film formed thereon, the colored film being thin in film thickness in an area corresponding to a thick part of the face portion of the glass panel and thick in film thickness in an area corresponding to a thin part of the face portion of the glass panel so as to reduce the difference in transmittance resulting from the difference in thickness between the central region and the peripheral region of the face portion of the glass panel.
According to another aspect of this invention, there is provided a cathode ray tube using a glass panel having a difference in thickness between a central region and a peripheral region of a face portion thereof, the glass panel having an outer surface with a colored film formed thereon, the colored film having a light color tone in an area corresponding to a thick part of the face portion of the glass panel and a dark color tone in an area corresponding to a thin part of the face portion of the glass panel so as to reduce the difference in transmittance resulting from the difference in thickness between the central region and the peripheral region of the face portion of the glass panel.
In addition, this invention is characterized in that the radius of curvature of the face portion of the glass panel in a diagonal direction of the outer surface thereof is equal to 10000 mm or more, that the formula of 1.2≦TE/T
0
≦4.0 is satisfied where TE and T
0
represent the thickness of the peripheral region of the face portion of the glass panel in the diagonal direction and the thickness of the central region, respectively, and that the glass panel with the colored film formed on the outer surface has a difference in transmittance less than 5% between the central region and the peripheral region of the face portion thereof.
In the cathode ray tube of this invention, the transparent colored film formed on the outer surface of the glass panel is thin in film thickness or light in color tone in the area corresponding to the thick part of the face portion of the glass panel and is thick in film thickness or dark in color tone in the area corresponding to the thin part of the face portion of the glass panel. Therefore, the reduction in luminance which has occurred only at the peripheral region of the face portion is avoided and the difference in transmittance between the central region and the peripheral region of the face portion is reduced (becomes small). It is therefore possible to approximate the transmittances of these regions to each other. The contrast is also improved by the colored film.
In case where the radius of curvature of the face portion of the glass panel in the diagonal direction of the outer surface thereof is selected 10000 mm or more, it is possible to suppress the difference in transmittance between the central region and the peripheral region of the face portion after the film is formed to a value within less than 5%, even if TE/T
0
is not smaller than 1.2 where TE and T
0
represent the thickness of the peripheral region of the face portion of the glass panel in the diagonal direction and the thickness of the central region, respectively, taking into consideration implosion-proof. Thus, it is possible to substantially completely suppress nonuniformity in brightness of the image. However, TE/T
0
greater than 4.0 is unfavorable because the weight of the cathode ray tube is
Imamura Tsutomu
Miwa Yoshiharu
Collard & Roe P.C.
Nippon Electric Glass Co. Ltd.
Patel Ashok
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