JPH09102266A - Indirectly heated cathode, and cathode-ray tube using this - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive cathode-ray tube which does not cause change on standing in image indication property, using an indirectly heated cathode, by manufacturing the indirectly heated cathode where the ripple on standing of cut off voltage is reduced, at low cost. SOLUTION: The section of the metallic material constituting the tubular metallic sleeve 2 arranged to surround a spiral filament 1 has crystal grain structure of at least two or more layers in its thickness direction. A cathode cap 3 is set and fixed to one end of the metallic sleeve 2, and the top of this cathode cap 3 is coated with a thermoelectron radiative matter 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an indirectly heated cathode in a cathode ray tube, and more particularly to improvement of the cathode structure.

[0002]

2. Description of the Related Art The cutoff voltage in a cathode ray tube is an important parameter that determines the amount of electron beam emission, and if this cutoff voltage fluctuates, proper image display cannot be performed. The fluctuation of the cutoff voltage can be adjusted by changing the voltage applied to the cathode when the voltage applied to the first grid (normally 0 V) and the second grid is constant. However, when the cutoff voltage fluctuates during the operation of the cathode ray tube due to the following reasons, the voltage value applied to the cathode must be changed each time in order to properly display an image. Especially in the case of a color cathode ray tube, R, G, B
Since three cathodes are used, if the cut-off voltage fluctuates in each cathode, the color balance of the displayed image is greatly disturbed, and proper image display is impossible. The cause of the change in the cutoff voltage is considered as follows. In the cathode used for a long time,
Chromium oxide is formed on the surface of the metal sleeve that houses the filament. Oxygen in the chromium oxide permeates and diffuses in the thickness direction of the metal sleeve, oxidizing the chromium in the metal sleeve to form new chromium oxide.
Such a phenomenon is called an internal oxidation phenomenon, which increases the volume of the metal sleeve and extends the total length of the metal sleeve. As a result, the distance between the metal sleeve that defines the position of the surface of the thermoelectron material of the cathode (hereinafter simply referred to as “electron emission surface”) and the electron beam passage hole of the first grid changes, and the cutoff voltage is fluctuate.

As a technique for preventing such a change in cutoff voltage with time, there is an indirectly heated cathode disclosed in Japanese Patent Laid-Open No. 51-10756. The metal sleeve of this indirectly heated cathode is made of Ni-Cr alloy, Ti, Al, M
A material containing 5% or less of an element such as n, Si, or Y that is more easily oxidized than Cr at 1000 ° C. or higher and has a high diffusion rate is used as a material for the metal sleeve. By forming a metal sleeve using such a material, the indirectly heated cathode disclosed in JP-A-51-10756 suppresses the internal oxidation phenomenon due to the blackening treatment of the metal sleeve.
It was said that the temporal change of the indirectly heated cathode was prevented.

[0004]

However, in the metal sleeve of the conventional indirectly heated cathode as described above, in order to prevent internal oxidation of the metal sleeve, expensive Ni, Cr, and Mn are added to the Ni-Cr alloy material. , Si, Y.sub.2, etc. have to be added, so the cost of the metal sleeve material has increased significantly. Further, a metal sleeve material containing a large amount of metal additives has a small elongation rate during processing, and thus cracks and the like are likely to occur during processing, which makes processing difficult. For this reason,
It is difficult to form a metal sleeve with high processing accuracy,
A special processing technique is required to cover this processing difficulty, resulting in an increase in the cost of manufacturing the cathode. There has been a demand for a structure of an indirectly heated cathode that solves the above problems and a cathode ray tube using the indirectly heated cathode. Therefore, the present invention aims at obtaining a highly accurate indirectly heated cathode that is low in cost and reliable, and further, by using this indirectly heated cathode, it is possible to reduce a change with time in display image characteristics. The object is to obtain a cathode ray tube having excellent properties that can be obtained.

[0005]

In order to achieve the above object, the indirectly heated cathode of the present invention has a substantially tubular shape in which a filament having an insulating layer and at least one end for accommodating the filament are opened. A sleeve made of a metal plate having a cross-section of the metal material forming the tubular shape having at least two or more crystal grain structures in the thickness direction thereof; And a thermionic emission part.

Further, the cathode ray tube of the present invention is formed with a face plate portion having a fluorescent surface on its inner surface, a funnel portion adhered to the rear of the face plate, and a rear portion of the funnel portion, and emits an electron beam. In a cathode ray tube comprising a neck portion having an electron gun, the indirectly heated cathode disposed inside the electron gun is substantially a filament having an insulating layer and at least one end for accommodating the filament being opened. A sleeve made of a metal plate having a tubular shape and having a cross-section of a metal material forming the tubular shape and having a crystal grain structure of at least two layers or more in the thickness direction thereof, and a thermoelectron provided at an end portion of the sleeve. And a thermionic emission part having an emissive material. In the indirectly heated cathode of the present invention, since the metal material forming the metal sleeve has a substantially two-layer or more crystal structure, the heat applied to the first layer when thermal stress is applied in the diameter direction of the metal sleeve. The stress is blocked in the second layer, crystal slippage hardly occurs, and there is substantially no change in the crystal grain structure after a long time operation. Therefore, the distance between the electron emission surface of the indirectly heated cathode and the electron beam passage hole of the first grid hardly changes with time, and the change with time of the cutoff voltage in the cathode ray tube of the present invention is significantly reduced.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. A feature of the present invention is that the relationship between the thickness of the plate material of the metal sleeve used for the indirectly heated cathode and the crystal grains is selected. FIG. 1 is a sectional view of an essential part showing a cathode structure of an indirectly heated cathode according to an embodiment of the present invention. In FIG. 1, the filament 1 has a wire diameter of 0.03 W-Re alloy.
A wire rod (one-dimensional wire) of mm is spirally twisted to form a primary spiral, and this primary spiral is further spirally formed to form a secondary spiral. An insulating film is applied to this secondary spiral, and blackening treatment is performed if necessary. As shown in FIG. 1, the filament 1 is housed by being surrounded by a cylindrical metal sleeve 2 having openings at both ends. The metal sleeve 2 has a diameter of 1.5 mm and a length of 2.8 mm, and is made of a Ni-Cr alloy having high thermal conductivity. The inner and outer surfaces of the metal sleeve 2 are blackened, and an oxide film having a thickness of 1.0 to 2.0 μm is formed thereon.

The material of the metal sleeve 2 is obtained by melting a Ni-Cr alloy in a high frequency induction furnace, hot forging it to a thickness of about 100 mm, and then hot rolling it to a thickness of about 10 mm. Further, a material rolled to a thickness of 1.5 mm by cold rolling is used as a material. This 1.
Annealing is performed at a temperature of about 900 ° C. to about 1000 ° C. for 1 to 2 minutes until a plate thickness (several tens of μm) required to manufacture the metal sleeve 2 is obtained from a metal material of a Ni—Cr alloy having a thickness of 5 mm. Repeat rolling. The metal sleeve 2 of this embodiment has a plate thickness of 30.
A metal material having a thickness of up to 60 μm is formed into a cylindrical shape by multistage drawing. The Ni-Cr alloy metal sleeve 2 used in this example was selected to have an average grain size of crystal grains in the thickness direction of the cross section of 13 to 15 μm. Therefore, the metal sleeve 2 having a plate thickness of 30 μm or more has a crystal grain structure of substantially two layers or more. The average grain size of the crystal grains of the metal sleeve material is set to a desired value by adjusting the number of repetitions, the annealing time and the annealing temperature when performing the annealing and rolling which are the final steps in the metal plate processing. be able to.

A cup-shaped cathode cap 3 is fitted and fixed to the cylindrical metal sleeve 2 thus formed so as to close the opening of the end of the filament 1 which is not led out. There is. The cathode cap 3 is Ni-
It is made of a Cr-based alloy. Cathode cap 3
Has a plate thickness of 0.1 mm, a diameter of 1.76 mm, and a cylindrical portion having a length of 0.6 mm. On the upper surface of the cathode cap 3, a thermoelectron emitting material 4 containing Ba as a main component is applied. The indirectly heated cathode of the present embodiment configured as described above has very little change in shape in the metal sleeve 2 after long-time operation, and in particular, the rate of increase in volume with time in the metal sleeve 2 is very small. For this reason,
The cathode ray tube using the indirectly heated cathode of the present example has a small variation rate of the cutoff voltage, and the reduction of the cathode current during operation, that is, the reduction of the screen brightness is suppressed, and in the case of the color cathode ray tube. The variations among the three colors R, G, B are reduced. Therefore, in the cathode ray tube using the indirectly heated cathode according to the present embodiment, for example, the color cathode ray tube, excellent image display characteristics can be obtained even after long-term use.

Hereinafter, using the indirectly heated cathode of the above embodiment,
The experimental results of the life test that verified the effect will be explained. FIG. 2 is a side view showing a test sphere of a 51 cm color cathode ray tube which was experimentally manufactured and used in this experiment. In FIG. 2, 51
The test sphere of the cm color cathode ray tube includes a face plate portion 5 having a fluorescent surface on the inner surface, and the face plate portion 5
The funnel portion 6 which is attached and bonded to the rear of the
It has a neck portion 7 disposed in the rear of the funnel portion 6 and formed in a thin cylindrical shape. The indirectly heated cathode described above is used in the electron gun 8 which is disposed inside the neck portion 7 and emits an electron beam, and three R, G and B are provided. In this experiment, a life test was conducted by forcibly applying a load stronger than the normal cathode load condition to the indirectly heated cathode. The diameter of the electron beam passage hole of the first grid in the electron gun 8 is 0.7 mm, and the distance between the electron beam passage hole and the surface (electron emission surface) of the thermionic emission material which is an oxide emitter is about. It was set to 0.12 mm.

In this experiment, the metal sleeve of Ni-Cr alloy was made of three kinds of metal materials having plate thicknesses of 20, 30, and 40 μm. The size of the crystal grains in the cross-sectional direction of the metal material forming the cylindrical metal sleeve was about 15 μm as a result of observation by an optical microscope photograph. Therefore, the metal sleeve having a plate thickness of 20 μm was recognized to have a substantially single-layer structure. The metal sleeve having a plate thickness of 30 μm was recognized to have a substantially two-layer structure, and the metal sleeve having a plate thickness of 40 μm was recognized to have a substantially three-layer structure. The total number of cathode ray tubes used in this experiment was 15, and the three R, G, and B cathodes of one cathode ray tube were each equipped with a metal sleeve of the same thickness. That is, the plate thickness is 20 μm for all of R, G and B.
5 cathode ray tubes with metal sleeves, 5 R, G, B cathode ray tubes with 30 μm plate thickness, and R, G, B with 40 μm plate sleeves Five cathode ray tubes were manufactured.

In order to make the operating conditions in this life test the same, the cathode operating temperature was set to 860 to 880 ° C. by observing with a radiation thermometer and adjusting the electric power of the heater. The cathode operating current at this time is about 2 on average.
It was 50 μA. In addition, in order to keep the cut-off condition constant, the cathode voltage is set to 160 before the start of the life test.
The voltage of the second grid corresponding to each cathode was adjusted so that the cathode current was cut off at V (standard voltage), and the adjusted voltage was set as the set voltage. At each evaluation after a lapse of a predetermined time in the life test, each second grid was applied with a set voltage, and the cathode voltage at which the cathode current was cut off was measured. The measured cathode voltage was compared with a standard voltage (160 V) to calculate the variation rate of the cutoff voltage, and the variation rate of the cutoff voltage with time in each cathode ray tube was obtained.

FIG. 3 is a graph showing the experimental results of the above-mentioned life test, in which the horizontal axis shows the life time (h) and the vertical axis shows the change rate of cutoff voltage with time (ΔVkco:%). In FIG. 3, the solid line shows the case of a cathode ray tube using a metal sleeve having a plate thickness of 20 μm, and the long broken line shows the plate thickness of 30 μm.
The figure shows the case of a metal sleeve of m.
The case of a metal sleeve of m is shown. As shown in FIG.
In a life test after 1,000 hours have passed, the variation rate of the cutoff voltage of each cathode ray tube using a metal sleeve having a plate thickness of 20, 30, 40 μm with time was +3 to + 30%,
It had widths of -5 to + 2% and -4 to -2%, respectively. In addition, the center value of the change rate of the cutoff voltage with time was about + 12%, -2%, and -3%. The standard deviations (σ) indicating these variations are 9.
It was 3, 2.0 and 0.7.

After the operation time of 1,000 hours in the above-mentioned life test, the cathode ray tube having the largest variation in the variation rate with time of the three cathode voltages in the same cathode ray tube is
In the case of using a metal sleeve having a plate thickness of 20 μm, the temporal change rate of each of the R, G, and B indirectly heated cathodes in the cathode ray tube had a width of 23% of +7 to + 30%. In addition,
In the cathode ray tube using the metal sleeve having a plate thickness of 30 μm, the temporal variation of each of the R, G, and B indirectly heated cathodes was 2% at the maximum, 0 to + 2%. Further, in a cathode ray tube using a metal sleeve having a plate thickness of 40 μm, R,
The temporal change rate of each of the G and B indirectly heated cathodes is -3 to -4 at maximum.
It was a 1% width of%. As a result, when the plate thickness of the metal sleeve is 20 μm, that is, when the metal sleeve has a substantially single-layer crystal grain structure, the change rate of the cutoff voltage of the cathode in all the cathode ray tubes over time and the variation in the same cathode ray tube. It can be understood that the variations among the R, G, and B3 colors are very large. On the other hand, when the plate thickness of the metal sleeve is 30 μm or 40 μm, that is, when the metal sleeve is formed to have a substantially two-layer or three-layer crystal grain structure, the cut-off voltage of each cathode changes with time and the same cathode ray tube. The variation among the R, G, and B three colors was at a very low level with no practical problems. In the metal sleeve, the single-layer crystal grain structure is a structure in which each of the main crystal grains is exposed on both front and back surfaces of the metal sleeve. Further, the two-layer or three-layer crystal grain structure means a structure in which the main crystal grains in the thickness direction of the metal sleeve are substantially two-stage or three-stage.

After completing the above life test experiment,
Cross-sectional micrographs of metal sleeves with three different plate thicknesses (400
4) is shown in FIGS. 4, 5 and 6. 4 shows a metal sleeve having a thickness of 20 μm, and FIG. 5 shows a metal sleeve having a thickness of 3 μm.
In the case of 0 μm, FIG. 6 shows the case where the plate thickness of the metal sleeve is 40 μm. As can be understood from these photographs, the crystalline state in the cross section of the metal sleeve after the end of the life test experiment is that, in a metal sleeve with a plate thickness of 20 μm, thermal stress is applied due to long-term use, and crystal slip occurs, and as a result, , The metal sleeve is locally deformed. Also,
In the metal sleeve having a plate thickness of 20 μm, in addition to such local deformation, the cylindrical metal sleeve was deformed as a whole into a tall shape. Further, in the metal sleeve, the end portion of the metal sleeve near the cathode cap has a particularly high temperature, so that the metal sleeve having a plate thickness of 20 μm bulges outward by about 40 μm in the thickness direction. On the other hand, plate thickness 30μ
m and the thickness of the metal sleeve 40 μm, the thickness 20
Almost no deformation like a metal sleeve of μm was seen. This is considered to be because even if thermal stress is applied in the plate thickness direction of the metal sleeve, the thermal stress applied to the first layer is blocked in the second layer, and crystal slip does not occur as a whole. Further, in the case of a metal sleeve having a plate thickness of 30 μm or 40 μm, the metal sleeve is deformed into a tal type as a whole when the plate thickness is 20 μm, or the vicinity of the cathode cap is expanded. There wasn't.

As described above, since the crystal grain structure in the cross section of the metal sleeve used for the indirectly heated cathode is substantially two layers or more, the shape of the metal sleeve after a long time operation (1,000 hours) has passed. The change is prevented, and in particular, the rate of increase in volume of the metal sleeve over time is greatly reduced. Therefore, in the cathode ray tube using such an indirectly heated cathode, the variation rate of the cutoff voltage with time becomes extremely small. By using such an indirectly heated cathode as a color cathode ray tube, R, The variation in cutoff voltage between the G and B3 colors is greatly reduced. As described above, in order to prevent the deformation of the metal sleeve, it is necessary that the crystal grain structure of the metal sleeve cross section has at least two layers. However, if the plate thickness of the metal sleeve is too large, The heat capacity of the cathode becomes too large, and it takes time for the heat of the filament to be transferred to the electron emitting material, which causes a problem that the output time of the cathode ray tube (the time until the image is displayed after switching on) becomes long. Therefore, it is desirable that the plate thickness of the metal sleeve is set to 60 μm or less in consideration of its heat capacity. Incidentally, in the present invention, the size of the crystal in the rolling direction of the metal sleeve is not referred to because it is considered that long crystal grains are formed in the rolling direction of the rolled metal sleeve. This is because they are very different. In addition, that the average grain size of the crystal grains in the cross-sectional direction of the metal material forming the metal sleeve in the present invention is 13 to 15 μm does not mean that the numerically strict average value is 13 to 15 μm.
This means that the metal material is mainly composed of particles having a particle size of 3 to 15 μm.

The effect of the indirectly heated cathode of the present invention is determined by the number of layers of crystal grains in the metal sleeve, and by controlling the diameter of the crystal grains of the metal sleeve material, the metal sleeve having a desired plate thickness can be obtained. In, it is possible to surely obtain a predetermined effect. In addition, in the above-mentioned embodiment, the one in which the cathode cap is provided on the upper portion of the cylindrical metal sleeve having both ends opened is used, but the metal sleeve is not limited to this shape, and for example, one end is closed. Even if a metal sleeve having an opening at one end is used, the same effect as the above-described embodiment can be obtained. Further, in the above-described embodiment, the indirectly heated cathode is used for the color cathode ray tube, but the same effect as that of the above embodiment can be obtained by using the indirectly heated cathode of the present invention in the monochrome cathode ray tube. Play.

[0018]

According to the present invention, since the metal material constituting the metal sleeve of the indirectly heated cathode has a crystal structure of substantially two layers or more, when thermal stress is applied in the diameter direction of the metal sleeve, The thermal stress applied to the first layer is blocked in the second layer, crystal slippage hardly occurs, and the thermal stress (1,0
(00 hours) There was no substantial change in the crystal grain structure after the operation. Therefore, the distance between the electron emission surface of the indirectly heated cathode and the electron beam passage hole of the first grid hardly changes with time, and the cutoff voltage in the cathode ray tube of the present invention is substantially constant even after a long time operation. Is kept constant. Also,
According to the present invention, it is possible to form a metal sleeve without using a metal material obtained by adding expensive Ti or the like to a Ni—Cr alloy as in the prior art, and thus a low-cost indirectly heated cathode is configured. In addition, since the metal sleeve can be easily processed, it is possible to obtain a highly reliable and highly accurate indirectly heated cathode. Further, according to the present invention, it is possible to significantly reduce the change over time of the cutoff voltage in a cathode ray tube using an indirectly heated cathode, and to reduce the cathode current during operation, that is, the screen brightness, and
In the case of a color cathode ray tube, it is possible to reduce variations among R, G, and B3 colors.

[Brief description of the drawings]

FIG. 1 is a sectional view of an essential part showing a cathode structure of an indirectly heated cathode according to the present invention.

FIG. 2 is a side view showing a 51 cm color cathode ray tube used in a life test.

FIG. 3 is a graph showing experimental results of a life test.

FIG. 4 is a drawing-substituting photograph showing a crystal structure of a cross section of a metal sleeve having a plate thickness of 20 μm.

FIG. 5 is a drawing-substituting photograph showing a crystal structure of a cross section of a metal sleeve having a plate thickness of 30 μm.

FIG. 6 is a drawing-substituting photograph showing a crystal structure of a cross section of a metal sleeve having a plate thickness of 40 μm.

[Explanation of symbols]

 1 filament 2 metal sleeve 3 cathode cap 4 thermionic emission material

Claims (4)

[Claims] 1. A filament having an insulating layer and a substantially cylindrical shape having at least one end for accommodating the filament opened, and a cross-section of a metal material constituting the cylindrical shape has at least two layers or more in its thickness direction. An indirectly heated cathode, comprising: a sleeve made of a metal plate having a crystal grain structure; and a thermionic emission portion disposed at an end of the sleeve and having a thermionic emission substance. 2. The indirectly heated cathode according to claim 1, wherein the average grain size of the crystal grains in the thickness direction of the metal material constituting the sleeve is 13 to 15 μm. 3. A face plate portion having a fluorescent surface on its inner surface, a funnel portion adhered to the rear side of the face plate, and a neck portion formed behind the funnel portion and having an electron gun for emitting an electron beam. In the cathode ray tube including, the indirectly heated cathode disposed inside the electron gun is a substantially tubular shape in which a filament having an insulating layer and at least one end for accommodating the filament are opened, A sleeve made of a metal plate having a cross-section of a metal material forming a shape having a crystal grain structure of at least two layers in the thickness direction thereof, and a thermionic emission having a thermionic emission substance disposed at an end of the sleeve. And a cathode ray tube. 4. The cathode ray tube according to claim 3, wherein the average grain size of the crystal grains in the cross-sectional direction of the metal material forming the sleeve is 13 to 15 μm.