JPH0644917A - Color cathode-ray tube - Google Patents

Abstract

PURPOSE:To reduce an amount of doming for chromatic aberration in a large- sized color cathode-ray tube. CONSTITUTION:Regarding a color cathode-ray tube fitted with a shadow mask having an electron beam reflecting film, and an internal magnetic shield plate 6a, an electron absorption film 9 is formed on the internal surface of the plate 6. As a result, an electron beam emitted from an electron gun 2 is reflected on the shadow mask 3, arrives at the plate 6 and, then, is absorbed by the film 9 on the plate 6. Consequently, no electron is emitted from the plate 6 and a doming amount can be reduced approximately by 15%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color cathode ray tube having an internal magnetic shield plate. More specifically, it relates to an internal magnetic shield plate for reducing color shift of an image due to thermal expansion of a shadow mask.

[0002]

2. Description of the Related Art A conventional shadow mask type color cathode ray tube is shown in FIG. In FIG. 3, 1 is an envelope for maintaining a high vacuum inside, 2 is an electron gun for emitting three electron beams, and 3 is a shadow mask forming a color selection electrode. This shadow mask is made of, for example, a thin iron plate having many slits or dots. Reference numeral 4 denotes a translucent glass panel which constitutes a part of the envelope 1, and 5 denotes a fluorescent screen. This phosphor screen is formed by sequentially applying stripes or dots of phosphors that emit red, green, and blue to the inner surface of the glass panel 4, and these stripe groups or dot groups can be electronically accurately applied to each. They are provided in a corresponding positional relationship. Reference numeral 6 is an internal magnetic shield plate. This prevents the external magnetic field from disturbing the electron beam incident on the shadow mask 3.

Next, the operation of the color cathode ray tube will be described. The three electron beams emitted from the electron gun 2 are deflected by the deflection yoke 8 so as to scan the entire surface of the phosphor screen 5 and reach the shadow mask 3. The shadow mask 3 has a color selection function that causes three electron beams to hit only phosphor stripes or dots of the corresponding colors. As described above, these positional relationships are originally set so that accurate correspondence can be made. However, about 80% of the electron beam emitted from the electron gun 2 impinges on the shadow mask 3 and is blocked, giving completely insignificant thermal energy to the shadow mask 3 to raise the temperature of the shadow mask 3. As a result, the shadow mask 3 is deformed by thermal expansion, and the positional relationship between the shadow mask 3 and the phosphor stripes or the dots that correspond exactly to each other is deviated, causing a color misregistration of an image.

As a method for solving these problems, in JP-A-55-76553, a material having a higher electron beam reflectance than the material forming the shadow mask 3 is formed on the electron beam irradiation surface of the shadow mask 3. 4 (see FIG. 4), and in Japanese Patent Publication No. 60-14459, a solution containing a heavy metal oxide (for example, Bi ₂ O ₃ ) having an atomic number of more than 70 is sprayed. It has been proposed to apply the electron beam reflecting coating 7 by coating. Such electron beam reflective coating 7
Reflects most of the electrons that have come out of the electron gun 2 and have not passed through the holes of the shadow mask 3 and have collided with the shadow mask 3, so that the temperature rise of the shadow mask 3 is significantly reduced and the heat of the shadow mask 3 is reduced. Color shift due to expansion is reduced.

[0005]

In the conventional cathode ray tube,
Since the electron beam reflection coating 7 is provided on the electron beam irradiation surface of the shadow mask 3, the electron beam reflected by the electron beam reflection coating 7 goes to the internal magnetic shield plate 6 and is further reflected there. Thus, the reflected electrons are gradually absorbed by the shadow mask 3 while being multiply reflected. As a result, the temperature rise of the shadow mask 3 cannot be sufficiently prevented, so that the thermal deformation of the shadow mask 3 cannot be sufficiently reduced.

The reflected electrons are all the electrons that come out of the collision surface of the electrons, and are based on the true reflection, the secondary electrons, and the backscattered electrons. All electrons, including things, are included.

The present invention has been made to solve the above-mentioned problems, and further facilitates the manufacture of a large-sized color cathode ray tube in which the temperature rise of the shadow mask is further reduced and color misregistration easily occurs. The purpose is to

[0008]

According to the present invention, in a large-sized color cathode ray tube having a shadow mask with an electron beam reflective coating and an internal magnetic shield plate, an electron absorbing coating is provided on the inner surface of the internal magnetic shield plate. It is characterized by that.

[0009]

Since the electron absorption coating provided by the present invention absorbs most of the electrons reflected from the shadow mask, the electrons are not returned to the shadow mask again, and the temperature rise of the shadow mask is further reduced. The thermal expansion of the shadow mask is reduced, and the color shift of the image is reduced even in a large-sized color cathode ray tube.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to FIGS. FIG. 1 is a sectional view showing a cathode ray tube of the present invention.
FIG. 2 is an enlarged cross-sectional view showing the main part of FIG. In these figures, 1 is an envelope, 2 is an electron gun, 3 is a shadow mask, 4 is a glass panel, 5 is a fluorescent screen, 6 is an internal magnetic shield plate, 8 is a deflection yoke, and 9 is an internal magnetic shield plate 6.
Is an electron absorption coating formed on the inner surface (surface facing the shadow mask). An electron beam reflecting film is formed on the inner surface of the shadow mask 3 (the surface facing the electron gun 2).
This is the same bismuth oxide (Bi
It is a film of ₂ O ₃ ).

Next, the operation will be described. The electron beam emitted from the electron gun 2 is reciprocally deflected left and right and up and down by the deflection yoke 8 and passes through each hole of the shadow mask 3 to pass through the fluorescent screen 5.
And emits visible light to produce an image on the glass panel 4. However, most of the electron beam does not pass through the hole of the shadow mask 3 and collides with the shadow mask 3 and is reflected by the electron beam reflection coating 7 (see FIG. 4) to travel backward. The backscattered electrons that have traveled backward reach the inner surface (the surface facing the shadow mask 3) of the internal magnetic shield plate 6 and are absorbed by the electron absorption coating 9 provided there. Conventionally, the electrons are reflected on the inner surface of the inner magnetic shield plate 6 and travel toward the shadow mask 3 again, but according to the present invention, they are almost absorbed there. Therefore, almost no electrons are absorbed in the shadow mask 3,
The rise of the shadow mask 3 is suppressed.

Below, an electron of the present invention is formed by spraying a mixture of titanium (Ti) or titanium oxide (TiO), potassium (K) adhesive water glass and pure water on the inner surface of the inner magnetic shield plate 6. An example of the absorption coating 9 will be described.

Embodiment 1. Titanium (Ti) powder 3Kg
In pure water 1900Cc, ammonia water after the average particle diameter of the powder was added (concentration 0.26%) 15 cc was pulverized to 1μm or less, the adhesive potassium-based water glass (SiO ₂ solid thereto as a dispersant 20% by weight)
Add 0.75 Kg and stir well to evenly disperse. The coating liquid thus prepared is applied to the inner surface of the blackened inner magnetic shield plate 6 for a 25-inch color cathode ray tube by a conventionally used spraying method such as an air spray method to obtain a coating film having a thickness of about The electron absorption coating 9 is formed by applying the coating to a thickness of 1 μm. After that, the internal magnetic shield plate 6 with the electron absorption coating 9 and the shadow mask 3 with the electron beam reflection coating 7 made of bismuth oxide are put into a normal cathode ray tube manufacturing process, and the cathode ray tube of the present invention,
A cathode ray tube with a 5-inch electron absorption coating 9 is prepared. The doming suppression effect D ₂ of the coating 9 is about 45%.

Example 2. The manufacturing method of the electron absorption coating 9 made of titanium oxide (TiO) is the same as in the first embodiment.
The same method is used except that titanium oxide (TiO) powder is used instead of powder. The method for measuring the doming suppression effect D ₂ of the coating film 9 (which will be described in detail below) is the same as in Example 1, and the result of the suppression effect is titanium (Ti).
Is about the same value as about 45%.

Now, the measuring method for the local doming (color shift) amount in the 25-inch color cathode ray tube will be described below. The measurement conditions are single color (normally green) no signal, electron beam current (1 cathode) of 0.15 mA, electron beam accelerating pressure of 29 KV, heater voltage of 6.3 V, and the raster has two symmetrical positions in the center of the screen. The size is the same, 120 * 120 (mm), and the measurement positions are the center of the raster size, and there are two positions (± 180, 0). The measuring method is a method using an ordinary landing measuring device, a pattern generation device, an electromagnetic purity coil and the like.

Under these conditions, the doming suppression effects (D ₁ , D ₂ ) in the conventional cathode ray tube and the cathode ray tube of the present invention are calculated by the following equations.

D ₁ = {1- (doming amount in a conventional cathode ray tube) / (doming amount in a standard cathode ray tube) * 100 (%) -------- (1) D ₂ = {1- (Doming amount in the cathode ray tube of the present invention) / (Doming amount in the standard cathode ray tube) * 100 (%) -------- (2)

However, the cathode ray tube of the present invention means a cathode ray tube provided with the internal magnetic shield plate 6 with the electron absorption coating 9 and the shadow mask 3 with the electron beam reflection coating 7 made of bismuth oxide. The conventional cathode ray tube refers to a cathode ray tube including the internal magnetic shield plate 6 without the electron absorption coating 9 and the shadow mask 3 with the electron beam reflection coating 7.
The standard cathode ray tube is a cathode ray tube in which the shadow mask 3 and the internal magnetic shield plate 6 do not have the coatings 7 and 9, respectively. The two types of 25-inch cathode ray tubes manufactured by the above-described manufacturing method, that is, the doming (color shift) amount of the product of the present invention and the conventional product are set to the above measurement conditions, and the normal measurement method is used. Respectively, and D ₁ = 30
%, D ₂ = 45%. Thus, the electron absorption coating 9
The effect of suppressing the doming was increased by about 15% as compared with the conventional cathode ray tube.

The film thickness is determined by the penetration depth of the electron beam into the film 9, and this penetration depth depends on the density of the film 9, the atomic number and the energy of the electron beam. Since the energy of the electron beam reflected from the electron beam reflection coating 7 of the shadow mask 3 is distributed in a wide range of several + eV to 30 KeV, when the thickness of the electron absorption coating 9 made of titanium is less than 0.5 μm. The beam penetrates the coating film 9 and cannot absorb the energy of the beam sufficiently. On the other hand, when the film thickness exceeds 3 μm, the absorption rate of the energy is saturated and the adhesive force of the film decreases. As a result, the cathode ray tube is clogged and the withstand voltage characteristics deteriorate. Therefore, the thickness of the electron absorption coating is 0.5 to 3 μm.

In general, the electron beam absorptivity of a substance is higher in a substance having a lower density, so that the electron absorption coating 9 is a substance whose density is smaller than that of the main component iron of the low carbon steel plate constituting the inner magnetic shield plate 6, Alternatively, it is suitable to be composed of an element having an atomic number smaller than that of iron or an inorganic compound containing those elements. For example, there are metal elements such as titanium, manganese, magnesium, beryllium, and aluminum, and oxides, nitrides, and carbides thereof. The iron density and atomic number are 7.9 and 2, respectively.
6, those of titanium are 4.5, 22 and those of titanium oxide (TiO) are 4.9, 18.5 (equivalent atomic number). (See Metal Data Book, edited by The Japan Institute of Metals, Maruzen 1974, p. 9 and Dictionary of Physical and Chemistry, 3rd edition, Iwanami Shoten, p. 514). The calculation method of the equivalent atomic number is described in J.
J. Appl. Phys. Vol. 27, No. 7, (1
988), pp. See 1210-1215.

Incidentally, in the case of operating a high resolution, large size, flattened or high brightness cathode ray tube in which the amount of color misregistration (dorming) of an image becomes larger, a conventional cathode ray tube using the electron beam reflection coating 7 is used. The effect of suppressing the doming (color misregistration) (D ₁ ) is insufficient at about 30%, and the improvement of the suppressing effect has been demanded.

[0022]

As described above, the electron absorption coating 9 provided on the inner surface of the internal magnetic shield plate 6 absorbs most of the electrons reflected from the shadow mask 3 (the amount of electrons returned to the shadow mask 3 is changed again). The temperature rise of the shadow mask 3 is reduced, the thermal expansion of the shadow mask 3 is reduced, and the color shift of the image is also reduced. The doming (color shift) suppressing effect D ₂ of the cathode ray tube of the present invention was about 45%, which was larger than that of the standard product. Therefore,
The doming suppression effect of the product of the present invention is about 1 times that of the conventional product.
It is possible to increase by 5%, and it becomes easy to easily manufacture a cathode ray tube of a high resolution, large size, flattened or high luminance cathode ray tube in which color shift easily occurs.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a cathode ray tube according to the present invention.

FIG. 2 is a partially enlarged sectional view of an internal magnetic shield plate which is a main part of FIG.

FIG. 3 is a cross-sectional view showing a conventional cathode ray tube.

FIG. 4 is a partially enlarged cross-sectional view of the shadow mask of FIG.

[Explanation of symbols]

 1 envelope 2 electron gun 3 shadow mask 4 glass panel 5 fluorescent screen 6 internal magnetic shield plate 8 deflection yoke 9 electron absorption coating

Claims (1)

[Claims] 1. A color cathode ray tube comprising a shadow mask with an electron beam reflection coating and an internal magnetic shield plate, wherein an electron absorption coating is provided on the inner surface of the internal magnetic shield plate.