JPH0511383B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a color cathode ray tube used in television receivers and the like, and more particularly to a color cathode ray tube that takes measures against leakage of X-rays. [Prior Art] Regarding the manufacturing process of the shadow mask, that is, the color selection electrode, which is a component of a color cathode ray tube,
"Electronic Science" (published by Sanpo Co., Ltd.) 1964,
VOL. 14 (No. 9), pages 36, 39, and 40. FIG. 4 is a schematic exploded perspective view of a color cathode ray tube, in which a shadow mask 13 includes a panel 10 that is a dish-shaped glass container, and a funnel-shaped funnel 12 that houses an electron gun 11 that emits an electron beam.
It is supported by a support part 14 and built into the panel 10. This shadow mask 13 has a plate thickness of 0.15 to 0.30 mm.
It is manufactured using a thin iron plate or, in recent years, a low-expansion material of 36% Ni-Fe, and has a round or rectangular electron beam passage hole with a diameter of approximately 0.15 mm drilled in a dome shape by etching. In the initial process, it has a flat shape, and then it is made into panel 10.
In order to obtain a curved surface close to the spherical shape of the inner surface, for example, heat treatment is performed at 600 to 900°C in a hydrogen stream, press molding is performed into a predetermined shape, and then, to obtain black rust (Fe ₃ O ₄ ) on the surface. Surface treatment is performed. The process to obtain this black rust is called surface blackening.
is called. The above surface treatments include completely removing the oil that adhered during pressing, and then immersing the surface in alkaline molten salt and heating to obtain black rust, or blackening with water vapor or carbon dioxide gas. The resulting black rust film is produced by heat treatment at approximately 400 to 450°C in air during the process of manufacturing color cathode ray tubes, which oxidizes the iron that is the base material of the shadow mask 13 and generates red rust (Fe ₂ O ₃ ). Its role is to prevent this from happening. Further, while the color cathode ray tube is in operation, approximately 80% of the electron beam emitted from the electron gun impinges on the shadow mask 13. Therefore, the kinetic energy of this electron beam is converted into thermal energy, and the temperature of the shadow mask 13 increases by approximately 40 to 80 degrees Celsius, causing thermal expansion.
distortion occurs. However, the above-mentioned black rust treatment
Emissivity of shadow mask 13 from 0.15 to 0.38
0.75, improves heat dissipation, and also serves to reduce distortion caused by heat. [Problems to be Solved by the Invention] In recent years, color cathode ray tubes have been used more frequently to stare at a screen, and color cathode ray tubes with a flat shape have come to be used. Ta. This type of color cathode ray tube exhibits a color shift phenomenon on the screen due to thermal distortion of the shadow mask _13. As a countermeasure for this, thermal radiation, elastic scattering of _electron beams, or It is conceivable to form an oxide film such as PbO or Bi ₂ O ₃ on the surface of the shadow mask 13, which has excellent properties such as thermal expansion coefficient. However, as mentioned above, Shadow Mask 1
There is PbO on the side of the surface of 3 where the electron beam hits
It has been found that when an oxide film of heavy metals such as Bi ₂ O ₃ is formed, X-rays are generated by the impact of the electron beam on the heavy metals, and these X-rays leak to the outside from the panel 10 or the funnel 12. . It has also been found that a larger amount of leaked X-rays can be detected than in the case of conventional iron-composed shadow masks. This will be explained in detail below. During operation of a color cathode ray tube, 25KV (20
As mentioned above, approximately 80% of the electron beam accelerated by the inch size (in the case of inch size) collides with the shadow mask. These colliding electrons generate X-rays when their paths are bent or braked by the Coulomb field of the atomic nucleus. The ratio is shown by the following formula. (-dE/dx) _rpd = 4NZ ² ro/137
E (log2E/μ-1/3) = aNZ ² where E is the energy of the electron, μ is 1 in the case of an electron, N is the number of atoms per unit volume of the material on the surface that the electron collides with, and Z is the atom The number, ro, is the classical radius of the electron. Now, regarding how much metal is contained in the oxide film on the surface of the shadow mask mentioned above,
It is expressed as the PB ratio (Pilling-Bedworth ratio). P.B.
The ratio is given by: PB ratio = volume of oxide per metal ion / metal atom 1
Volume of metal per piece This PB ratio is 2.1 for conventional black rust and lead oxide (β
type) and 1.17 for bismuth oxide α type (Bi ₂ O ₃ ).
It is. The above conditions and the generation of back shadow X-rays are as follows: Fe ₃ O ₄
A comparison using Bi ₂ O ₃ is shown in the following table.

【table】

[Table] As is clear from the above results, between the surface on which Fe ₃ O ₄ is formed and the surface on which Bi ₂ O ₃ is formed, the latter generates about 4.9 times more X-rays than the surface on which Bi 2 O 3 is formed. Recognize. This invention was made to solve the above-mentioned problems, and an object thereof is to provide a color cathode ray tube that can effectively prevent the leakage of X-rays generated from the surface of a shadow mask on which a heavy metal layer is formed. It is said that [Means for Solving the Problems] In the color cathode ray tube according to the present invention, a heavy metal layer is formed on at least the surface of the shadow mask on the side where the electron beam strikes, and at the same time, when the electron beam strikes the color cathode ray tube, the heavy metal layer is removed from the heavy metal layer when the electron beam strikes. The present invention is characterized in that an X-ray absorbing member having a heat-shrinkable effect and made of a material containing heavy metal for absorbing generated X-rays is provided on the outer periphery of the funnel. [Function] In the color cathode ray tube of the present invention, when the electron beam emitted from the electron gun hits the surface of the shadow mask during its operation, X-rays are generated from the heavy metal layer formed on the surface of the shadow mask. The surface temperature of the color cathode ray tube itself rose to about 40°C, and the X-ray absorbing member with a heat-shrinking effect provided on the outer periphery of the funnel contracted and adhered to the funnel due to its heat-shrinking action. X-ray is
Since the radiation is absorbed by the radiation absorbing member, leakage to the outside of the color cathode ray tube is suppressed. [Example] Before describing the example of this invention, the principle of this invention will be explained first. As mentioned above, the amount of X-rays generated from the Bi ₂ O ₃ forming surface is about 4.9 times that of Fe ₃ O ₄ , so Fe ₃ O ₄ and
In order to generate the same amount of leakage X-rays Ix as Bi ₂ O ₃ , Fe ₃ O ₄ : Ix = Io・e ^- 〓 ^t1 ... Bi ₂ O ₃ : Ix = 4.9 Io・e ^- 〓 ^t2 ... As mentioned above Relational formula for X-ray absorption = Io・e ^- 〓 Leakage X at ^t
When lead is used as a shielding material and the accelerating voltage of the color cathode ray tube's electron beam is 27KV, the generated wavelength is λ=12.4/Vkv=0.459Å, and the absorption coefficient μ is 41.4. Assuming that the equations and expressions are equal, Io・e ^- 〓 ^t1 = 4.9Io・e ^- 〓 ^t2 From this, e ^(t2-t1) 〓=4.9 That is, (t2-t1)μ=1.59 Add μ=41.4 to this When substituted, t2 = t1 + 0.038 [cm]... The formula is, when the surface of the shadow mask that the electron beam collides with is changed from the conventional Fe ₃ O ₄ to Bi ₂ O ₃ ,
It has been shown that by providing a lead layer equivalent to a thickness of 0.38 mm, it is possible to provide protection against leakage X-rays at the same level as in the case of a conventional shadow mask with a surface layer of Fe _{3 O} 4. . Based on the above principle, specific embodiments of the present invention will now be described. FIG. 1 is a sectional view showing an embodiment of a color cathode ray tube according to the present invention. In the figure, 10 is a panel with a fluorescent screen 16 formed on its inner surface, 11 is an electron gun housed in a net 15, and 12 is a connection between the panel 10 and the net 15.
13 is a shadow mask placed facing the fluorescent screen 16 on the inner surface of the panel 10, and 20 is a deflection yoke for deflecting the electron beam 24 emitted from the electron gun 11. Electron beam 2 on the surface of the shadow mask 13
As shown in FIG. 2, a layer 21 of water glass mixed with Bi ₂ O ₃ , which is a heavy metal oxide, is formed by spraying or the like on the side where 4 collides. Reference numeral 22 denotes an X-ray absorbing member, which is made of an annular heat-shrinkable material containing lead in an amount equivalent to a thickness of 0.4 mm, as shown in FIG. It is located in the department. 23 is an explosion-proof band made of 2 mm thick steel. In the above configuration, the electron beam 24 emitted from the electron gun 11 has its trajectory bent by the deflection yoke 20 and impinges on the surface of the shadow mask 13 . At this time, since a layer 21 of Bi ₂ O ₃ , which is a heavy metal oxide, is formed on the surface of the shadow mask 13, X-rays are generated from this surface layer 21 when the electron beam 24 hits it. However, since an X-ray absorbing member 22 containing lead is provided around the outer periphery of the funnel 12 of the color cathode ray tube, the generated X-rays are absorbed by this X-ray absorbing member 22 and are transmitted from the funnel 12 to the outside. Leakage is suppressed. [Effects of the Invention] As described above, according to the present invention, by forming a heavy metal layer on the surface of the shadow mask, the elastic scattering characteristics of thermal radiation and electron beams are improved, the thermal distortion of the shadow mask is reduced, and the image quality is improved. In addition to this, even with the formation of a heavy metal layer, the X-ray absorbing member effectively prevents leakage of the X-rays generated when the electron beam strikes, providing a highly safe color cathode-ray tube. There is an effect that can be achieved. Also,
When attaching the above-mentioned X-ray absorbing member to the outer periphery of the funnel, when the color cathode ray tube is operated,
Since the X-ray absorbing member can be heat-shrinked and tightly attached to the outer periphery of the funnel, the attachment state of the X-ray absorbing member to the outer periphery of the funnel may be somewhat rough, and the outer periphery of the funnel of the X-ray absorbing member It also has the effect of improving the workability of attaching it to the section.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of a color cathode ray tube according to the present invention, FIG. 2 is a partially enlarged sectional view of a shadow mask, and FIG. 3 is a perspective view of an X-ray absorbing member.
FIG. 4 is a schematic exploded perspective view of a general color cathode ray tube. 13...Shadow mask, 21...Heavy metal layer,
22...X-ray absorption member, 24...electron beam. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. In a color cathode ray tube incorporating a shadow mask which is a color selection electrode, a heavy metal layer is formed on at least the surface of the shadow mask on the side where the electron beam strikes, and when the electron beam strikes, the A color cathode ray tube characterized in that an X-ray absorbing member having a heat-shrinking effect and made of a material containing a heavy metal for absorbing X-rays generated from a heavy metal layer is provided in an annular shape around the outer periphery of the funnel. 2. The color cathode ray tube according to claim 1, wherein the heavy metal contained in the material forming the X-ray absorbing member is lead.