JPS628473B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a projection cathode ray tube.

In television receivers that use shadow-mask color cathode ray tubes, which are currently in widespread use, the screen size that can be obtained is thought to be limited to about 30 inches, mainly due to structural constraints. Therefore, as a means for receiving television images and the like on a screen larger than this, a projection type television receiver 1 as shown in FIG. 1 has been developed and is now becoming popular.

In this projection television receiver 1, small monochrome cathode ray tubes 2, 3, and 4 each have a screen size of about 5 to 8 inches and are for monochrome images of B (blue), G (green), and R (red). That is, a monochromatic image from a projection type cathode ray tube is enlarged and projected onto the screen 6 by the projection lens unit 5, and a large color image can be obtained on the screen 6. Since the size of this screen 6 is generally about 40 to 70 inches, the images from the small monochrome cathode ray tubes 2, 3, and 4 are projected on the screen 6 with an area enlarged approximately 50 to 100 times. .

These monochrome cathode ray tubes 2, 3, and 4 are structurally almost the same except for the type of phosphor coated inside. The structure will be briefly explained with reference to FIG. A phosphor layer 8 is formed on the inner surface of the face plate glass 7 constituting a part of the vacuum envelope 12 by a precipitation coating method using potassium silicate (K ₂ SiO ₃ ) or the like as a binder. On this phosphor layer 8, a high voltage electrode and a metal back film 9 made of a vapor-deposited film of aluminum (AL) as a light reflecting film are formed, forming a phosphor surface 10. In addition, this vacuum envelope 12
An electron gun 11 is enclosed inside the electron gun 11, and the energy of the electron beam emitted from the electron gun 11 excites the phosphor layer 8 to extract light output. In the case of such a G monochromatic cathode ray tube 3, the phosphor layer 8 has conventionally been designed to have excellent luminescent color tone and to have γ characteristics (indicating the ratio of increase in light output to increase in phosphor surface stimulation current). Sulfide is widely used as a G phosphor in ordinary shadow-mask color cathode ray tubes, etc., although it has inferior temperature characteristics (characteristics that indicate changes in the luminous efficiency of the phosphor surface due to increases in temperature of the phosphor surface). Manganese-activated zinc silicate (Zn ₂ SiO ₄ :Mn) phosphors are used because they are superior to physical phosphors.

On the other hand, in the case of such a projection type cathode ray tube, since the image is enlarged and projected onto the screen 6, it is necessary to reproduce the image with sufficient brightness on the screen 6. It is essential that the light output of the device itself be sufficiently large.
For this reason, the excitation energy density per unit area (mW cm
^-2 ) is significantly larger than that of the fluorescent surface of a conventional shadow mask type color cathode tube.

However, when operating a projection cathode ray tube for long periods of time while applying a large load to the phosphor surface, the phenomenon of deterioration of the light output from the phosphor surface over time becomes a serious problem. . The curve in Figure 3 shows Zn ₂ SiO ₄ :Mn phosphor with an average particle size of 3 μm applied by the precipitation coating method at a coating density of 4 mg cm ^-2 on the inner surface of a conventionally widely used face plate glass. This shows the relative deterioration over time of the light output from the fluorescent surface when the resulting projection cathode ray tube is operated under a constant fluorescent surface load of high voltage 27 KV current density 3 μA cm ^-2 . It is. For such a conventional fluorescent surface, after 10,000 hours, the initial light output will be reduced by 40%.
%. This optical output degradation phenomenon depends on the input load to the phosphor surface. In other words, since the load increases as the excitation energy density per unit area increases, in conventional projection cathode ray tubes, it is difficult to apply too much load to the phosphor surface from the viewpoint of the lifespan of the phosphor surface. It was hot.

As a result of analyzing the causes of such deterioration of the light output of the phosphor surface, we found that the main causes of deterioration are a decrease in the light output of the phosphor, that is, a decrease in luminous efficiency and a decrease in the light output of the phosphor.
It has become clear that this is due to the coloring of the plate/glass by the electron beam (electron beam browning). FIG. 4 shows the results of analyzing the fluorescent surface after 10,000 hours as indicated by the curve in FIG. 3. According to this, the luminous efficiency of the phosphor decreased to 0.72 (initial value is 1.0) after 10,000 hours, and the transmission ratio of the face, plate, and glass decreased to 0.56 from the initial value of 1.0. It can be seen that the optical output decreased from the initial value of 1.0 to 0.40 as a result of the combination (0.72×0.56=0.40).

The mechanism by which the luminous efficiency of phosphors decreases has not been clearly elucidated, but when the phosphor surface is operated for long periods of time under extremely harsh excitation conditions, as in projection cathode ray tubes, it may be affected by collisions with electron beams. Due to movement energy and accompanying heat energy,
In addition to gradually destroying the phosphor's light-emitting mechanism itself, these energies also destroy the alkali contained in potassium silicate (K ₂ SiO ₃ ) used as a binder when depositing the phosphor. - It is thought that the decrease is due to ions (K ^+, etc.) diffusing into the phosphor and having an adverse effect on the light-emitting mechanism.

Further, the mechanism of coloring of the face plate glass, that is, electron beam browning, can be roughly considered as follows. FIG. 5 shows an example of the composition of a conventional face plate glass. As raw materials for glass, sodium oxide (Na ₂ O) and potassium oxide (K ₂ O) are essential materials in order to provide the characteristics of face plate glass. These exist in the form of Na ⁺ (sodium ions) and K ⁺ (potassium ions) in the formed glass (called decorative ions).
However, it plays an important role in imparting the characteristics of glass. On the other hand, as shown in FIG. 2, the phosphor layer 8 of the projection cathode ray tube is made by coating the inner surface of the face plate glass 7 with a thin particulate phosphor having an average particle diameter of about 3 μm by a precipitation coating method. It is porously deposited (at most two or three layers of particles), with considerable gaps between the phosphor particles.
Therefore, when the phosphor layer 8 is excited by the electron beam from the electron gun 11, a part of the electron beam passes through the gaps between the phosphor particles and reaches the surface of the face plate glass 7. It reaches directly, collides with the surface and loses energy. Since the energy of the electron beam at this time is strong, the charge enters from the surface of the face plate glass 7 to a depth of several μm. When negative charges are stored on the face, plate, or glass surface for a long time, surrounding alkali ions such as Na ⁺ and K ⁺ are attracted to the charged parts and move, and these charges are removed. Neutralize to form colloidal Na
and K metal particles. For this reason, the surface of the originally transparent face plate glass 7 is colored.
In other words, it is considered that browning occurs.

One way to improve the phenomenon of deterioration of the light output of a projection cathode ray tube over time is to reduce the electron beam browning of the face plate glass. As mentioned above, this electron beam browning is a decorative ion in the glass.
It is thought that this phenomenon occurs because alkali ions such as Na ⁺ and K ⁺ easily move within the glass, so it is possible to reduce electron beam browning by creating a glass structure in which this movement is less likely to occur.
Whether or not alkali metal cations such as Na ⁺ and K ⁺ are difficult to move in glass can be determined by its electrical resistance. It is thought that the larger the electrical resistance, that is, the volume resistance ratio ρ (Ω·cm), the more difficult the alkali metal cations will move.

As a specific means to increase the electrical resistance of glass,
A method in which lithium ions (Li ⁺ ) are added to conventional alkali ions such as Na ⁺ and K ⁺ and the mixing ratio of these is appropriately selected is known as the mixed alkali effect. Figure 6 shows various amounts of lithium oxide (Li ₂ O) in barium oxide (BaO) of a conventional face plate glass having the composition shown in Figure 5.
The volume resistivity ratio ρ of the glass made by replacing with
It is expressed as log ρ. By adding about 1.0% by weight of Li ₂ O, the volume resistivity ρ can be significantly increased compared to conventional face plate glass (0% Li ₂ O). This effect is due to Li ₂ O
is noticeable up to about 0.3 to 3.0% by weight,
If the amount of Li ₂ O exceeds 3.0% by weight, the glass itself will suffer from a devitrification phenomenon, which is undesirable. In this way, the glass with significantly improved electrical resistance has a
Alkaline cations such as Na ⁺ and K ⁺ are difficult to move and are thought to be less likely to cause electron beam browning.

Fig. 5 Y shows a face plate that has been improved by adding 1.0% by weight of Li ₂ O so that electron beam browning is less likely to occur.
This is an example of the composition of plate glass. (Glass with this composition is hereinafter referred to as browning-resistant glass.) An improved face plate glass was manufactured using such browning-resistant glass, and Zn ₂ SiO ₄ with an average grain size of 3 μm was prepared as before. : A projection type cathode ray tube is manufactured by coating Mn phosphor on the inner surface of the face plate glass mentioned above at a coating density of 4 mg cm ^-2 by a precipitation coating method. The curve in FIG. 3 shows the relative aging characteristics of the light output from the phosphor surface when this projection cathode ray tube is operated at a high voltage of 27 KV and a constant phosphor surface load of 3 .mu.A.cm ^-2 at a current density.
The light output (initial ratio) after 10,000 hours is 0.40 using the curved conventional face plate glass, compared to 0.40 when using the curved conventional face plate glass.
0.42, and despite the use of Browning-resistant glass, the phenomenon of optical output deterioration was not significantly improved. As a result of various investigations into the reasons why this deterioration phenomenon cannot be improved, it has become clear that there is a problem in the interaction between the browning-resistant glass and the phosphor.

This invention was made in view of the problems that arise when such browning-resistant glass is used as the face plate glass of a projection type cathode ray tube, and the present invention provides advantages of the face plate glass of the browning-resistant glass. be able to fully demonstrate
It is an object of the present invention to provide a projection type cathode ray tube in which the optical output of a fluorescent surface is less likely to deteriorate over time.

An embodiment of the present invention will be described below with reference to the drawings. Figure 4 shows the analysis results of the cause of light output deterioration after 10,000 hours of the phosphor surface created by the combination of the browning-resistant glass face plate glass described in Figure 3 and the Zn ₂ SiO ₄ :Mn phosphor. This shows that. What is clear from this result is that
By using browning resistant glass,
The coloring phenomenon of faces, plates, and glass is GL _ASS.
Although the transmission ratio of 0.56 is now 0.70, which is a significant improvement as intended, conversely, when this new face plate glass is used, the luminous efficiency of the phosphor increases from 0.72 to the light output ratio. It has decreased to 0.60, and as a result of combining both, the phenomenon of deterioration of the optical output of the fluorescent surface has not been significantly improved. As a result of various investigations into the cause of this, it became clear that Li ₂ O added to the new face plate glass accelerated the deterioration of the luminous efficiency of the Zn ₂ SiO ₄ :Mn phosphor. . Although the mechanism of accelerated deterioration in this case cannot be clearly determined, it is generally considered as follows. In other words, the Li ⁺ ions themselves in the glass are very mobile, so in the area where the face/plate glass and the Zn ₂ SiO ₄ :Mn phosphor are in contact, the Li + ions themselves are easily moved due to the impact caused by the electron beam and the temperature rise caused by the electron beam. Li ⁺ ions become very active and move and diffuse from the glass surface into the phosphor, resulting in
It is thought that the light emitting mechanism itself of the Zn ₂ SiO ₄ :Mn phosphor is affected in some way, accelerating the phenomenon of deterioration of the optical output. We also investigated various measures to _{prevent accelerated} deterioration _.
It has become clear that this is unavoidable as long as fluorophores are used in combination.

For this reason, face plate glass made of Li ₂ O-added Browning-resistant glass and various G
(Green) An analytical study was conducted on the deterioration of the light output of the phosphor surface in combination with a phosphor. At this time, the initial light output of the G phosphor under consideration was
Zn ₂ SiO ₄ : Not only is it not much different from Mn phosphor, _but it also has γ characteristics and temperature characteristics _that are particularly required for the performance of phosphor for projection cathode ray tubes.
Those that were equal to or higher than Mn were selected.

The analytical studies revealed that terbium-activated yttrium silicate (Y ₂ SiO ₅ :Tb) phosphor is very compatible with this new face plate glass. The curve in Figure 3 shows a Y ₂ SiO ₅ :Tb phosphor with an average particle size of 3 μm, coated by a conventional precipitation coating method at a coating density of 4 mg cm ^-2 and containing 1.0% by weight of Li ₂ O. Browning resistant
Fluorescence when coating is formed on the inner surface of a face plate made of glass and the resulting projection type cathode ray tube is operated at a constant fluorescent surface load at a high voltage of 27 KV and a current density of 3 μA cm ^-2 . This shows the relative aging characteristics of the optical output from the surface. The light output (initial ratio) after 10,000 hours was 0.42 for the combination of the new curved face plate glass and Zn ₂ SiO ₄ :Mn phosphor, while the improved face・Plate glass
In the case of the present invention in combination with Y ₂ SiO ₅ :Tb phosphor, the value is 0.54, which is an improvement of about 30%.

Figure 4 shows the browning resistance described in Figure 3.
This figure shows the results of an analysis of the cause of optical output degradation after 10,000 hours of a phosphor surface created by a combination of an improved face plate glass and a Y ₂ SiO ₅ :Tb phosphor. From this result, by using browning-resistant glass, the coloring phenomenon of the face plate glass can be reduced to 0.56 in terms of GL _ASS transmission ratio.
was 0.72, which was a significant improvement as intended. Furthermore, the luminous efficiency of the phosphor was 0.74 for the combination of conventional face plate glass and Y ₂ SiO ₅ :Tb phosphor, whereas the efficiency of the improved face plate glass was 0.74. and
It is 0.75 for the combination of Y ₂ SiO ₅ :Tb phosphor according to this invention, and it is not affected at all even when combined with the improved face plate glass for Y ₂ SiO ₅ :Tb phosphor. That is clear. In this case, as a result of both the deterioration of the phosphor and the coloring of the GL _ASS (0.75 x 0.72 = 0.54), the light output of the cathode ray tube was 0.54 compared to the initial value of 1.0, which was a significant improvement. It is.

In addition, the initial optical output of the Y ₂ SiO ₅ :Tb phosphor is almost equivalent to that of Zn ₂ SiO ₄ :Mn, and the γ characteristics and temperature characteristics, which are important for the performance of phosphors in projection cathode ray tubes, are It has also become clear that the Zn ₂ SiO ₄ :Mn phosphor is even better than the Zn 2 SiO 4 :Mn phosphor.

As described above, according to the present invention, even if Li ₂ O-added Browning-resistant glass is used as the face plate glass of a projection cathode ray tube, the phenomenon of accelerated deterioration of the luminous efficiency of the phosphor does not occur. First, it is possible to obtain a high-quality projection type cathode ray tube in which the advantages of the browning-resistant glass can be fully utilized and the deterioration of the light output of the fluorescent surface over time has been greatly improved.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram for explaining the principle of a projection television receiver, Figure 2 is a schematic sectional view of a projection cathode ray tube, and Figure 3 is a graph of the light output of the fluorescent surface of the projection cathode ray tube over time. A diagram showing the relationship between light output and time showing deterioration,
Figure 4 shows the results of analyzing the cause of the deterioration of the optical output of the fluorescent surface, Figure 5 shows the composition of the face plate glass, and Figure 6 shows the amount of Li ₂ O added and the composition of the glass. FIG. 3 is a diagram showing the relationship with volume resistance ratio ρ. 7... Face plate glass, 8... Fluorescent layer, 10... Fluorescent surface. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. On the inner surface of the face plate glass that constitutes a part of the vacuum envelope, the face plate
In a projection cathode ray tube coated with a phosphor layer that forms part of the phosphor surface together with the glass, the face plate glass of the phosphor surface contains 0.3 to 3.0% by weight of lithium oxide (Li ₂ O). 1. A projection cathode ray tube comprising a phosphor layer containing terbium-activated yttrium silicate (Y ₂ SiO ₅ :Tb).