JPS6359501B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a color cathode ray tube for use in color displays including television, industrial and other special uses.

The glasses used as face glasses for these cathode ray tubes are generally clear faces with visible light transmittance of 75% or more, gray faces with 60-75%, and taint faces with light transmittances of 60% or less. Color cathode ray tubes are classified and used according to rank, but in general, gray or clear face, which has good transmittance, is often used in color cathode ray tubes, even if it sacrifices contrast in terms of brightness. That is,
In order to absorb extraneous light and increase contrast, tainted glass with lower transmittance is suitable.
In general, the light output of the fluorescent surface of a color cathode ray tube is not strong enough to obtain sufficient light even if the transmittance of the glass is lowered. Various attempts have been made in other ways. One of these is black matrices, and more recently pigment phosphors have also come into use.

For example, in the case of a shadow mask type color picture tube, as shown in Fig. 1, there is a face glass part 1 whose inner surface is coated with a phosphor, a funnel part 2 joined to this with, for example, low melting point solder glass, and an electron gun. It is composed of a built-in network part 3, a shadow mask 4, etc. provided near the fluorescent surface inside a vacuum envelope composed of these parts. This shadow mask 4 allows electron beams 5B, 5G, and 5R, which pass through the holes of the shadow mask 4 at their own unique angles, to emit light of each color formed at their arrival points, as shown in FIG. 2, for example. Fluorescent dot 6B, 6
It has a function as a color selection electrode so as to strike corresponding to G and 6R, respectively. For the face glass portion 1 of a color picture tube having such a configuration, gray glass having a spectral transmittance as shown in the curve in Fig. 4, for example, has been widely used in the past. As shown, phosphor dots 6B, 6G, of blue, green, and red colors,
The black matrix type, in which the spaces between the 6R's and 6R's are filled with a light-absorbing material 7 made of black paint, has become the mainstream, and the face glass is now mainly clear glass with high light transmittance, as shown by the curve in Figure 4. It became. By using clear glass, more of the emitted light from the phosphor is taken out of the tube, while the black matrix film reflects external light and the surface of the face glass and directs it back toward the phosphor film. By absorbing the returning light,
This is to improve contrast. Furthermore, in recent years, pigment phosphors have been used in which pigments are added to each phosphor so that the reflectance of only the emitted color of each phosphor is selectively increased, and the contrast has been further improved.

However, although all of these improvement measures have greatly improved the performance, they are still not at a sufficient level, and furthermore, the market demand for high brightness and high contrast is quite strong. In addition, when used for displaying computer terminals, characters, symbols, graphs, etc. are often displayed on a portion of the screen, and the area ratio of the light emitting part to the effective screen area is small.
In some cases, the contrast is less than 10%, and improving contrast without compromising brightness has become a major challenge.

In order to improve this, this invention maximizes the light transmittance for the light emission energy of the phosphor by imparting wavelength selectivity to the light transmittance of the face glass, and This invention relates to a combination of glass and phosphor to significantly improve contrast by lowering the light transmittance in the wavelength range where the wavelength range is low.

The inventor found a problem in that the spectral transmittance of the face glass of conventional cathode ray tubes had flat characteristics over the visible range.

In other words, in the past, the phosphors of these color cathode ray tubes were composed of materials that had fairly wide emission spectra for blue, green, and red, but in recent years, with the remarkable development of phosphors, for example, green
For example, fluorescent substances such as Gd ₂ O ₂ S (Tb) and Y ₂ O ₂ S (Eu) for red, which exhibit almost line-spectrum emission characteristics, are produced, as shown in Figure 6. It became. In FIG. 6, E _B shows the spectrum of a blue phosphor, E _G1 a rare earth green phosphor, E _G2 a sulfide green phosphor, and E _R a red phosphor. If the emission spectrum of the phosphor becomes linear in this way, it goes without saying that there is no need for the spectral transmittance to be flat over the entire visible range as a face glass, and that it is possible to use a face glass with selective wavelength absorption characteristics. It will be advantageous. This invention provides face glass materials with optimal spectral transmittance characteristics to meet such requirements, such as 470~480, 510~530, 570~
This is an attempt to solve this problem by using a material containing neodymium oxide (Nd ₂ O ₃ ), which has light absorption characteristics in the wavelength region around 585 nm.

For example, a glass having a spectral transmittance as shown in the curve shown in FIG. 5 can be achieved by incorporating a small amount of the aforementioned Nd ₂ O ₃ .

That is, the curve contains 0.5% by weight of Nd ₂ O ₃ ,
The spectral transmittance is illustrated using the 1.0% curve as a curve. This transmittance is an actual measurement value for a glass plate thickness of 10.0 mm, which is approximately equal to the thickness of the central part of the face glass of a general color cathode ray tube, but the thickness of the face glass of a small cathode ray tube is For thin materials, the same effect can be obtained by increasing the Nd ₂ O ₃ content.

As is clear from the curves in Figure 5, these glasses have a large absorption band in the wavelength range of 570 to 585 nm, while the visual sensitivity of the naked eye is maximum around 555 nm. By using a combination of phosphors with emission spectra such as the following, it is possible to improve contrast without sacrificing output.

However, among the phosphors shown in FIG.
For example, Gd ₂ O ₂ S:Tb is exemplified as a rare earth phosphor that emits green light and has a linear emission dominant wavelength of 540 to 550 nm, but other rare earth phosphors that emit green light include, for example, Y In general, this type of phosphor, including ₂ SiO ₅ :Tb, Y ₂ O ₂ S:Tb, etc., has little brightness saturation and is very bright at high stimulation current density. On the other hand, it has the characteristic of being darker at low current densities than the sulfide phosphors currently used in general televisions and the like.

Figure 7 shows the current density vs. brightness characteristics of Gd ₂ O ₂ S:Tb as a rare earth phosphor and ZnS:Cu, Au, and Al as a sulfide phosphor. % Ad ₂ O ₃ added is used. Considering the example of a CRT for a color television, which is generally about 20 inches in size, the effective fluorescent surface area is about 1200 parallel centimeters, and the monochromatic average electron beam current to form an image is about 300 to 500 μA, with a peak value of 2 to 500 μA. Reaches 3mA. That is, the current density is 0.25 to 0.42μA/cm ² on average and 1.7 to 0.42μA/cm 2 at the peak.
2.5μA/cm Used in ^second place. For this reason, when a rare earth phosphor is used, a phenomenon occurs in which the highlight portion of the screen is bright, but on the average screen, the sulfide phosphor is brighter.

On the other hand, when looking at the body color of these rare earth and sulfide-based phosphors, most rare earth phosphors are white, and sulfide-based phosphors generally have a yellowish body color. When these are combined with a phase glass containing Nd ₂ O ₃ , the optical absorption band of the phase glass extends from 570 to 590 nm. In addition to the large reflection of external light on the body surface itself, the face glass body color (slightly reddish-purple body color) is emphasized, so there is a risk that viewers will be extremely picky about it.
However, the spectrum of sulfide-based yellow body color is 550.
The energy is large at ~600 nm, and this is close to the absorption band of the phase glass, and the result is complementary to the energy of this absorption band. Therefore, when a sulfide-based phosphor is mixed, it is possible to reduce the incidence from the outer surface of the phase glass. The reflection of incoming light is small, which improves the contrast of the screen, and also works to soften the color of the face glass, shifting the color of the glass to a safe one.

In experiments conducted by the inventors, we have found that effects can be obtained by using a mixture of sulfide phosphors and rare earth phosphors to achieve both properties, considering both brightness and body color. Therefore, this mixing ratio is 0.5 to 1 part sulfide phosphor to 1 part rare earth phosphor by weight.
It was found that using a range of 2.0 is more advantageous than using each phosphor alone.

Figure 8 shows an example of ZnS: Cu, Au, Al.
The emission spectrum of a green phosphor produced by mixing Y ₂ O ₂ S:Tb at a weight ratio of 1:1 per 10 mm of glass plate thickness.
Data actually measured through a phase glass containing 1.0 Nd ₂ O ₃ is shown.

In this way, a sulfide phosphor and a rare earth phosphor are mixed in an appropriate mixing ratio to produce a green phosphor for a cathode ray tube, which contains Nd ₂ O ₃ in the face glass and has wavelength selectivity in light transmittance. By using a mixture of materials, it has become possible to construct a cathode ray tube that takes full advantage of the characteristics of the phase glass, which has good brightness and contrast, and has wavelength selectivity.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional view of a shadow mask type color picture tube, Fig. 2 is a diagram of the relationship between phosphor dots, a shadow mask, and an electron beam, Fig. 3 is an explanatory diagram of a black matrix phosphor surface, and Fig. 4 is a conventional one. FIG. 5 is a diagram showing an example of the spectral transmittance characteristics of the face glass for a color cathode ray tube of the present invention, and FIG. 6 is a diagram showing the light emission of a typical phosphor. It is a figure showing a spectrum.
FIG. 7 shows a comparison of the brightness characteristics of a green-emitting sulfide phosphor and a rare earth phosphor, and FIG. 8 shows an example of the emission spectrum when the mixed phosphor of the present invention is used. In the figure, 1 is face glass, 6B, 6G, 6R
is a fluorescent dot. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. In a cathode ray tube containing neodymium oxide in the face glass and having a fluorescent surface composed of phosphors of a plurality of emission colors on the inner surface, sulfide is used as the green phosphor of the fluorescent surface. A color cathode ray tube characterized by using a mixture of a rare earth phosphor and a rare earth phosphor at a weight ratio of 1:0.5 to 2.0.