JPS6012650A - Cathode-ray tube - Google Patents

Abstract

PURPOSE:To provide a picture screen in which a halo does not stand out conspicuous and which is easy to see by reducing the diameter of the halo by installing a transparent base plate having a fluorescent layer inside a face glass. CONSTITUTION:A transparent base plate 7 made of glass is installed inside the face glass 1 of a vacuum encircling case 10 in such a manner that the base plate 7 is parallel to the face glass 1 with a given distance allowed between them. The base plate 7 is fixed to the face glass 1 by means of a supporting member 8. A fluorescent layer 2 is formed on a surface of the base plate 7 opposite to its surface facing the face glass 1. When the refractive indexes of the base plate 7 and the face glass 1 are almost equal, the critical angle at the interface 9 between the base plate 7 and a vacuum 6 almost equals to that at the interface 4 between the face glass 1 and air 5 thereby preventing the fluorescent layer 2 from being reilluminated by light reflected by the interface 4. As a result, a halo develops only from the interface 9 between the base plate 7 and the vacuum 6. Since all the base plate 7 have to do is to support the fluorescent layer 2, the thickness of the base plate 7 can be made very small thereby enabling the diameter of the halo to be minimized.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cathode ray tube with suppressed halo.

FIG. 1 is a partially enlarged sectional view of the face glass of a conventional cathode ray tube. In the figure, (1) is a face crow;
(2) is a fluorescent layer formed on the inner surface of the face glass (1), (3) is an aluminum back covering the fluorescent layer (2), (
4) is the interface between the face glass (1) and the air (5), (
6) is a vacuum. The light X emitted from the fluorescent layer (2) passes through the interface (
4), and this reflected light is re-reflected by the fluorescent layer (2) to generate a halo ray a. Here, the diameter of the halo is 2
L is given by 1, -1 2L=4Dtan(sln l/n)*e(1). However, D is the thickness of the face crow (1), n
is the refractive index of the face glass (1).

In a typical cathode ray tube, the thickness of the face glass (1) is about 10 mm and its refractive index is about 1°52, so a halo circle with a diameter of about 35 mm is formed with the center of the bright spot. arise. As shown in FIG. 2, this halo has a brightness distribution in which the brightness is higher at the outer periphery. This is because, as can be seen from the reflection characteristics at the interface (4) shown in FIG. 3, the reflectance increases rapidly near the critical angle.

As described above, conventional cathode ray tubes have a disadvantage in that the diameter of the halo is large, making the screen difficult to see.

This invention was made to eliminate the above-mentioned conventional drawbacks, and an object of the present invention is to provide a cathode ray tube that suppresses halo and makes the screen easier to see.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 4 is a partially cutaway schematic side view showing an example of a cathode ray tube according to the present invention, in which (10) is a true, indoor envelope, (1
) is a face glass, and inside the face glass (1), a transparent substrate (7) made of glass is disposed parallel to the face glass with a predetermined gap therebetween. This transparent 1 board (
7) is fixed to the face glass (1) by a holder (8), and a fluorescent layer (2) is formed on the opposite side to the surface facing the face glass (1).

FIG. 5 is an enlarged view of section A in FIG. 14.

In FIG. 5, the refractive index of the transparent substrate (7) is nl (nl
>1), and the refractive index of the face glass (1) is n2 (n2
>1) and the light X emitted by the fluorescent layer (2) has the incident angle and refraction angle as shown, then the following equation holds true.

n 1-s i n θ 1=sin o :2==n
2-sin θ 3=sin04 Therefore, n 1. Sin θ 1=n2aSin03*e ・
(2) Now, if we consider that the refractive index nl of the transparent substrate (7) and the refractive index n2 of the face glass (1) are almost equal, then at the interface (9) between the transparent substrate (7) and the vacuum (6) Critical angle (sin l/nl) and face glass (1)
The critical angle (s i
n-' 1/n2) is approximately equal.

This is because: Of the light emitted from the fluorescent layer (2), the light that is incident on the interface (9) at a critical angle is totally reflected at this interface (9), and the light that is emitted from the front face glass (1) This means that light that would be totally reflected at the interface (4) does not enter. In other words, the light reflected by the interface (4) is prevented from causing the fluorescent layer (2) to emit light again.

Note that the reflection of light incident on the interface (4) within the critical angle is considered to be negligible because the reflectance is low, as is clear from FIG.

Therefore, in the case of a cathode ray tube having the configuration shown in FIG. 4, the only halo generated is the halo caused by the interface (9) between the transparent substrate (7) and the vacuum (6). Here, since the transparent substrate (7) only needs to have the function of holding the fluorescent layer (2), its thickness can be made very thin, and the diameter of the halo can be made smaller than in equation (1) above. be able to.

Note that the cathode ray tube according to the present invention can be applied not only to television receivers but also to cathode ray tubes for oscilloscopes and displays.

As described above, according to the present invention, by disposing the transparent substrate on which the fluorescent layer is formed inside the face glass,
Since the diameter of the halo can be reduced, it is possible to provide a cathode ray tube having an easy-to-see screen with no noticeable halo.

[Brief explanation of drawings]

Figure 1 is a partially enlarged sectional view of the face glass in a conventional cathode ray tube, Figure 2 is a characteristic diagram showing the no-low brightness distribution, Figure 3 is a characteristic diagram showing the reflection characteristics at the interface between the face glass and air, and Figure 3 is a characteristic diagram showing the reflection characteristics at the interface between the face glass and air. , 4 is a partially cutaway sectional view showing an embodiment of the cathode ray tube according to the present invention, and FIG. 5 is an enlarged view of section A in FIG. 4. (1)...face glass, (2)--fluorescent layer,
(7)...Transparent substrate. Note that the same reference numerals in the figures indicate the same or corresponding parts. Agent Masuo Oiwa Figure 1 Figure 3 Figure 2, Ei Figure 3 entrance side (θO) Figure 4 Figure 5 Figure 1 Dan

Claims (2)

[Claims] (1) A transparent substrate having a refractive index greater than 1 is disposed inside a face glass with a predetermined gap from the face glass, and a fluorescent layer is formed on the side of the transparent substrate opposite to the face glass. A cathode ray tube characterized by: (2) The cathode ray tube according to claim 1, wherein the transparent substrate is fixed to the face glass by a holder.