JPS645739B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a cathode ray tube, and more particularly to a spotting process.

It is well known that in the manufacturing process of cathode ray tubes, a spot-knocking process is performed in one step after evacuation. This spot-knocking process applies a voltage higher than the maximum voltage used when the cathode ray tube is mounted in a set to the electrodes of the electron gun to generate sparks within the tube and improve the withstand voltage characteristics. It is something to do.

FIG. 1 is a longitudinal sectional view showing an example of a cathode ray tube, particularly a shadow mask type color picture tube. In the figure, 1 is an envelope (hereinafter referred to as a bulb), 2 is an electron gun,
3 is a getter, and 4 is a shadow mask. The getter 3 is fixed to the other end side of a getter support 3a whose one end is fixed to the electron gun 2, and in this example, it is arranged to extend to the funnel portion 1a. .

Further, FIG. 2 shows an example of the configuration of the electron gun 2, and in the figure, 21 is a _G1 electrode, 22 is a _G2 electrode,
23 is G ₃ electrode, 24 is G ₄ electrode, 25 is G ₅ electrode,
26 is the G ₆ electrode, 27 is the cathode and the G ₁ electrode 2
1, and a heater 28 is arranged in this cathode 27.

In a color picture tube having such a configuration, an anode voltage is applied to the G ₆ electrode 26 and the G ₄ electrode 24,
This anode voltage is the highest for current color picture tubes, approximately
The voltage is about 30KV, and therefore, in color picture tubes that use such high voltages, the withstand voltage characteristics of the electron gun are an important point in ensuring the reliability of the color picture tube as a product. The level of the withstand voltage characteristics is evaluated based on the frequency of spark occurrence and defects caused by dark current between the electrodes forming the electron gun. Most of these sparks and dark currents are caused by electrons generated by field emission from the low potential electrode of the electron gun.
Therefore, suppressing the electron emission is a key point in improving the withstand voltage characteristics. However, recent color picture tubes tend to be equipped with multistage focusing electron guns in order to improve focus characteristics, and this is becoming the mainstream.

A feature of this multistage focusing electron gun is that weak focusing lenses are combined in multiple stages to reduce the spherical aberration of the main lens system. However, as a result of this, the number of electrodes increases, the opposing area of electrodes with a high potential difference increases, and the electrodes themselves become more complex, so it is unlikely that the unnecessary electron emission will increase before the results are obtained. Unavoidably, it has been as difficult to improve the withstand voltage characteristics as with, or even more than, conventional color picture tube electron guns. Methods for improving withstand voltage characteristics include design methods and manufacturing methods, and spot-noting is one of the manufacturing methods. That is, a voltage higher than the applied voltage in the used set is applied to the electron gun to forcibly generate sparks within the tube, which are dissipated by the energy of the spark from the electron emission source which reduces the withstand voltage characteristics.

The wiring in Fig. ₂ shows the voltage application relationship in the spot-knocking process.
The configuration is such that a positive high voltage is applied to the _G6 electrode 26 and the other electrodes are grounded. This process is performed after the electron gun is enclosed in a valve and evacuated. Therefore, each electrode that makes up the electron gun can be regarded as a spark gap installed in a vacuum, and Figure 3 shows the electrodes in Figure 2. This is an equivalent circuit when viewed as a spark gap, and 33 to 35 indicate spark gaps.

However, as is clear from FIG. 2, since the shapes of each electrode are different, the discharge starting voltage of each spark gap is different. Therefore, even if a high voltage is applied to the electrodes using the wiring as described above, sparks will only occur at the gap with the lowest discharge starting voltage.
Others do not spark.

As a result, knocking is performed only between electrodes where the discharge starting voltage is low. To prevent this phenomenon, spark gaps are usually designed and manufactured so that the discharge starting voltage is uniform between each spark gap.

However, it is virtually impossible to completely equalize the level at this time, and even if the amount of electrons emitted is the same, the degree of influence on the withstand voltage characteristics of the picture tube varies depending on the position of the emission source. Knocking requires positional selectivity. However, due to the above-mentioned reasons, conventional spot noticing simply causes sparks only at locations where sparks are likely to occur, making it impossible to effectively suppress defective phenomena.

The present invention enables an excellent spot-noting method that overcomes these conventional drawbacks.

Spark generation in a vacuum does not occur unless the degree of vacuum deteriorates when a potential difference is applied between the electrodes, even if it is localized. The cause of the deterioration of the vacuum level is
Either a substance with a high vapor pressure attached to or contained in the electrode evaporates, a substance constituting the electrode itself evaporates, or the thermal velocity of the residual gas increases due to an increase in the surrounding temperature. . but,
For example, in a color picture tube, since it affects the performance and lifespan of the display,
Since the materials and heat treatment are used to suppress this as much as possible, deterioration due to this cause cannot be exploited. However, in a normal color picture tube, for example, residual gas is always present, albeit in a very small amount, so it can be used to lower the degree of vacuum. The present invention skillfully applies this phenomenon to spotting. below,
The present invention will be explained in detail.

FIG. 4 is an example diagram for explaining the method of the present invention. In this figure, parts having the same functions as those in FIG. 2 are designated by the same numbers as in FIG. 2. In FIG. 4, 40 is an electrode burning coil for passing high frequency current, and the magnetic flux generated when the coil 40 is energized generates an eddy current in the _G5 electrode 25.
A portion of the electrode 25 near the G ₆ electrode 26 is heated.
In this state, the degree of vacuum in the area between the G ₅ electrode 25 and the G ₆ electrode 26 deteriorates due to the above-mentioned reason, and sparks are likely to occur, so an anode is formed.
Even if a high voltage is applied to the G ₆ electrode 26 and the G ₄ electrode 24, sparks can be selectively generated between the G ₅ electrode 25 and the G ₆ electrode 26.
Therefore, by adjusting the position and shape of the electrode burning coil 40 and the high-frequency current value, it is possible to cause local vacuum deterioration and perform the necessary selective knocking.

Furthermore, in actual color picture tubes, etc., an evaporative getter is used to maintain the degree of vacuum inside the tube. Evaporative getters are usually made of materials such as Ba and Al, and have a very low work function, so that when these evaporated substances adhere to the electrodes of the electron gun, the electron emission is likely to occur.

For this reason, the getter source is installed away from the electron gun body as explained in FIG. 1 above. However, when the getter is evaporated, the degree of vacuum inside the picture tube is temporarily degraded, and as a result, the getter material scatters and adheres to the electron gun. This phenomenon is called backflash, and it is currently difficult to completely suppress it.

Therefore, when spot-knotting is performed, a very thin film of Ba, Al, etc. is usually attached to the entire electrode surface. Therefore, if the temperature of the electrode is further increased during the electrode heating shown in FIG. When collides with the high potential side electrode,
The high potential side electrode is heated and sparks are likely to be generated for the above-mentioned reasons.

Furthermore, for the above reasons, the electrode surface is covered with a thin film of Ba, Al, etc., but if this film could be prevented from adhering from the beginning, the work function of the electrode surface would increase and electron emission due to the electric field would be prevented during the operation. This can reduce the spot-knocking work itself. Based on this idea, it is more efficient to prevent adhesion from the beginning than to remove it once it has adhered to the electrode surface. For this purpose, a method is usually adopted in which the electrode is heated with high frequency when the getter is evaporated.
This alone is not sufficient, and the purpose can be achieved by using spot notching in addition to this.

That is, this is a method in which high-frequency heating for the getter flash, high-frequency heating for the electrode, and spot-knocking are performed simultaneously.

The above has described an electron gun having six grids from the _G1 electrode to the _G6 electrode in a color picture tube as an example, but the method of the present invention can be similarly applied to other cathode ray tubes. The electrode heating method may be a method other than high frequency heating.

As described above, according to the method of the present invention, it is possible to improve the withstand voltage characteristics, and it is also possible to improve the voltage resistance characteristics even when the distance between the electrodes is the same and only a specific part requires efficient knocking, which was a problem in the past. The method of the invention enables an excellent method such as selective processing.

[Brief explanation of drawings]

Figure 1 is a sectional view showing an example of a color picture tube, Figure 2 is a diagram showing the electron gun structure and wiring during spot knocking, Figure 3 is an equivalent circuit diagram of Figure 2, and Figure 4 is the invention of the present invention. FIG. 2 is a diagram for explaining a spot finding method according to the method of FIG. 1...Envelope, 2...Electron gun, 3...Getsuta,
21-27...electrode, 40...electrode firing coil.

Claims (1)

[Scope of Claims] 1. A method for manufacturing a cathode ray tube, characterized in that, in manufacturing a cathode ray tube, a spot-knocking process is performed while heating electrodes other than the cathode among the electrodes constituting the electron gun. 2. A method for manufacturing a cathode ray tube, which comprises performing a getter flash during the spot-knocking process while heating the electrodes constituting the electron gun, except for the cathode. .