JPH0250580B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to improve the internal conductive film and the external conductive film of cathode ray tubes, which are caused by the frit sealing part which is relatively prone to insulation defects due to the formation of air bubbles inside or residual surface contamination. This invention relates to a method for easily and reliably detecting insulation defects between surfaces.

Cathode ray tubes, especially color tubes that require a process of exposure using a large mask to form a fluorescent surface, are manufactured by flitting the panel (which has undergone the process of forming a fluorescent surface onto the inner surface of the bulb panel) into the large-diameter opening end of the funnel. (melting point glass powder) must be used for sealing. Air bubbles may form inside the frit sealing part.
Contaminants may remain on the end faces of panels and funnels, and contaminants may be mixed in during the process of applying the frit as a paste. When a high DC voltage that accelerates cathode rays is applied, this frit seal becomes a weak point in the electrical insulation, resulting in a relatively high number of defects where the insulation is broken or a considerable amount of current flows through it. occurs at a certain rate. For this reason, conventionally, as shown in FIG. The anode of the power source 7 is connected, while the current detection electrode 6 is closely attached to the outer periphery of the frit sealing part 1, and the value of the current i _f flowing through the frit sealing part is detected by the current detector 6.
The insulation of the frit-sealed part was tested by measuring the temperature at a. However, in the inspection method shown in FIG. 1, if the outer surface of the funnel glass wall 2 is contaminated, a relatively large leakage current i _l flows directly from the contact 5 to the detection electrode 6 on this outer surface. In addition to contamination, if a moving coil type galvanometer with a large moment of inertia is used, it will not be possible to measure the charging current waveform immediately after voltage application, or any disturbances in the current waveform due to insulation defects in the frit sealing area, which may cause problems with the frit sealing of the product. There was a problem in that it was difficult to accurately determine whether there was an insulation defect in the bonded area.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for simply and reliably detecting the presence or absence of an insulation defect in a frit sealing portion without the above-mentioned problems.

In order to achieve the above object, in the present invention,
A high voltage pulse is repeatedly applied between the internal conductive film of a cathode ray tube and an electrode that is in close contact with the outer periphery of the frit seal, and the accumulated values of the current waveform that flows in response to the applied voltage are repeatedly measured and analyzed. In this way, insulation defects in the frit sealing part are detected. When the present inventor observed the current waveform immediately after applying voltage to the frit sealing part using an electronic measuring device, it was found that if there is a defect in the frit sealing part, the capacitance using the conductive film as an electrode It has been found that even in the process where the peak of the charging current becomes high and then decreases exponentially from that peak, the exponential process may be disrupted and a transient protrusion may occur, and furthermore, this initial peak The small peaks due to irregular fluctuations observed in the process of lowering the voltage are more likely to appear immediately after voltage application, and are more noticeable when high voltage pulses are repeatedly applied than when high voltage is applied continuously for a relatively long time. This is because it was observed in The insulation defect detection device was made electronic to enable high-speed observation, and the observation results were converted into digital data, making it easy to accumulate repeated observation values and perform calculations for analysis. In order to obtain accurate and accurate observation results, we also used a guard electrode to prevent leakage current on the outer surface of the cathode ray tube from mixing with the insulation current of the frit seal.

First, with reference to Fig. 2, we will explain the outline of the conventional detection circuit (which is basically the same in the case of the present invention), including the frit sealing part that is the object of measurement and the leakage current path that causes errors. do. As you can see from the figure,
The current between the contact electrode 5 and the current detection electrode 6 flows through the _frit sealing part 1.
The leakage current i _l flows through r _s ). The internal conductive film 4 having a capacitance C _f is included in the path of i _f . i _l and i _f
Separation from the frit can be easily achieved by using the long-known guard electrode as described above, but there are some points in the insulation properties of the frit sealing part that are not always clear, and it is difficult to accurately determine whether the frit is good or bad in the mass production process. It was not easy to do so. The path of i _f has a capacity
Since C _f exists, the following equations (1), (2), and (3) hold true.
Here, t is time, q is the charge accumulated in C _f , and r _f is the resistance of the frit welded portion 1 .

E ₀ = r _f dq/dt+q/C _f (1) q(t)=C _f・E ₀ (1-e ^-t/rfCf ) (2) i _f (t)=dq/dt=E ₀ /r _f e ^-t/rfCf (3) The i _f value i _f1 when voltage is applied (t = 0) is i _f1 = E ₀ / r _f (5) Also, the time constant t ₁ = r _f C _f after elapse of i _f The value i _f2 is i _f2 =E ₀ /e·r _f (6). In these equations, r _f and C _f are assumed to be constants, but in reality, if there is an insulation defect in the frit sealing portion 1, r _f fluctuates and decreases irregularly, and C _f becomes large. Conventionally, a movable ring galvanometer 6a with a large moment of inertia was used, making it difficult to observe the current waveform. Note that the value of the total current I ₀ flowing through the galvanometer is, of course, I ₀ = _if + i _l .

FIG. 3 is a block diagram of one embodiment of the present invention.
When a pulse signal 20 is given from the processing device 18, the switch 8 is actuated accordingly, and a high voltage pulse with a voltage value _E0 is repeatedly applied to the measuring circuit, for example, 20 m.
A total of 10 seconds is applied, with s on and 20ms off. Since the current value to be measured is minute, it is first converted to an appropriate level by the level conversion circuit 14 and input to the current extraction circuit 15. The current extraction circuit receives an i _f1 extraction signal (pulse) 9 from the processing device shortly after voltage application.
When a is given, the peak value of the current during the signal period is determined, and after the time constant t ₁ has elapsed since the voltage is applied, i _f2 When the extraction signal 9b is given, the peak value of the current during that period is determined. When the i _l extraction signal 9c is applied at a time point t when e ^-t/t1 becomes sufficiently small, the peak value of the current during that period is extracted. In this embodiment, the current flowing into the electrode 6 is I ₀ = i _f + i _l , of which i _f changes exponentially with time and decreases as described above if the frit sealing part is normal. If there is an insulation defect in the attachment part, it will fluctuate irregularly and become larger than in the main hall. This situation is shown in FIG. The line marked E ₀ indicates the voltage application state (period switch 8 marked 20).
is closed and high voltage pulse E ₀ (e.g. constant anode voltage 28kv
(approximately 35 kV) is repeatedly applied to the pipe. The next line labeled I ₀ indicates I ₀ = _if + i _l , and 10a shows an example where there is no defect in the frit sealing portion. next i _f1
The line shown indicates the peak value 11a of I ₀ during the period of the signal 9a extracted by the extraction circuit 15 using the extraction signal 9a, and includes I _l although it is prefixed with _if .
The next line labeled i _f2 indicates the peak value of I ₀ (the maximum value during the period of the pulsed i _f2 extraction signal 9b) 12a after the time constant t ₁ = r _f・C _f has elapsed, and I _l Contains. The next line marked i _l is I ₀ when the I _l extraction signal 9c is given.
It shows the extracted value 13a of , etc., and also includes i _f which is labeled I _l but has been greatly reduced. If there is a defect in the frit sealing part, I ₀ , i _f1 , i _f2 , i _l etc. become 10b, 1, respectively.
1b, 12b, 13b, etc. That is, irregular disturbances and small peaks may appear in the process of exponentially decreasing I ₀ . Furthermore, such small peaks often appear shortly after voltage application. This means that applying high voltage pulses repeatedly is better than simply applying the same high voltage continuously.
This is the reason why defects can be easily detected. For convenience, in Figure 4, the first voltage application shows the current when the sealed part is normal, and the second time shows the current when there is a defect in the sealed part. Generally, the current becomes as shown by 10b from the first application of the high voltage pulse. Note that in the case of a defect, the first peak, ie, 11b, is generally higher than 11a in the normal state, even if no small peak appears during the drop. Now, returning to FIG. 3, the current value extracted by the extraction circuit 15 as described above is digitized by the A/D converter 16 and digitized by the memory 17.
and used for analysis and calculation by the processing device 18. The calculation results are displayed on the display 19. Distinguishing between those with normal sealing parts and those with defects is as follows:
The values of I _f1 and I _f2 may be compared with normal values for which a large amount of data has already been accumulated. Of course, the values of r _f and C _f can also be calculated, and it is also possible to distinguish between normal and abnormal conditions and estimate the cause of the abnormality. In addition, to separate the surface leakage current,
The I _l value mentioned in Figure 4 above was measured directly.
Although I _f may be calculated by subtracting it from the I ₀ value, it is also possible to provide a guard electrode 21 around the contact electrode 5 as shown in FIG. Time is also generally reduced.

As described above, according to the present invention, insulation defects in the cathode ray tube frit sealing portion can be easily and reliably detected.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the conventional detection method, FIG. 2 is an explanatory diagram of a detection circuit outline, FIG. 3 is a block diagram of an embodiment of the present invention, and FIG. 4 is an explanatory diagram of extracted current of the embodiment.
FIG. 5 is an explanatory diagram of the guard electrode. DESCRIPTION OF SYMBOLS 1...Fritt sealing part, 2...Funnel glass wall, 3...Anode terminal, 4...Interior conductive film, 9a
...I _f1 extracted signal, 9b...i _f2 extracted signal, 10a,
10b... _I0 waveform, 11a, 11b...i _f1 extracted value, 12a, 12b...i _f2 extracted value, 14...Level conversion circuit, 15...Current extraction circuit, 16...
A/D converter, 17...memory, 18...processing device, 19...display device, 21...guard electrode, i _f ...
...Fritt sealing part current, i _l ...Surface leakage current,
E ₀ ...DC high voltage, r _f ...Fritt sealing part resistance,
C _f ……i Capacity in the _f path.

Claims (1)

[Claims] 1 High voltage pulses are repeatedly applied between the internal conductive film of the cathode ray tube and the electrodes that are in close contact with the outer periphery of the frit sealing part, and the accumulated values of the current waveforms that flow in response to the applied voltage are measured repeatedly. 1. A method for detecting insulation defects in a cathode ray tube frit sealing part, characterized in that insulation defects in a frit sealing part are detected by analysis.