Electric lamp and discharge devices – Electrode and shield structures – Cathodes containing and/or coated with electron emissive...
Reexamination Certificate
2000-01-05
2002-04-23
O'Shea, Sandra (Department: 2875)
Electric lamp and discharge devices
Electrode and shield structures
Cathodes containing and/or coated with electron emissive...
C313S043000, C313S270000, C313S440000, C427S068000, C427S077000
Reexamination Certificate
active
06376976
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a cathode ray tube having an oxide cathode and a process for preparing the same, particularly an electron emissive material layer in the cathode and a process for preparing the same.
BACKGROUND ART
In
FIG. 14
, a cross sectional view of a conventional oxide cathode is illustrated as a model which is described, for instance, in JP-A-8-77914. In the figure,
101
is a metal substrate which contains nickel as a major component and a reducer of, for instance, silicon and magnesium. The metal substrate
101
is a circular plate constituting the bottom of a long-cavity cylindrical sleeve
102
. And
103
is an electron emissive material layer mainly comprising a needle-like particle
105
of oxides of alkaline earth metal such as barium, strontium and calcium, which adheres to the metal substrate
101
. Also,
104
is a filament which is heated in order that thermoelectrons are emitted from the electron emissive material placed in the sleeve
102
. The oxide cathode is placed in an evacuated cathode ray tube (no figure). In
FIG. 14
, the size of the needle-like particle
105
is enlarged about 10 times larger than the size (diameter and thickness) of the electron emissive material layer
103
. Therefore, among the needle-like particles
105
, except the needle-like particles
105
contacted to the metal substrate
101
, the real width shows about one tenth of the total width from the surface.
A process for preparing the oxide cathode of the cathode ray tube is as follows:
At first, particles of the alkaline earth metal carbonate are dispersed in an organic solvent to prepare a dispersion solution (paste) having suitable viscosity for spraying. By repeating a process of spraying the paste onto the metal substrate
101
and drying the same, the pre-determined thickness, for instance, 40 to 100 &mgr;m is obtained. The oxide cathode is placed in the cathode ray tube, and by forming a vacuum inside the cathode ray tube, the cathode ray tube is heated from outside or by the filament
104
. The organic solvent is decomposed and evaporated up to about 600° C., and by heating up the carbonate salt to about 900 to 1000° C., the carbonate salt is decomposed to give an oxide and the electron emissive material layer
103
is formed which emits electron.
The particles of the alkaline earth metal carbonate which form the electron emissive material is usually shaped like a needle and one of them is shown in a large scale in FIG.
15
. As is shown in
FIG. 15
, the longest length of the particles of the alkaline earth metal carbonate
105
is defined as L &mgr;m and the longest axis vertical to the direction is defined as D &mgr;m, while the same definition is applied to the particles having nearly spherical shape in the followings. Usually, the particles having an average length L of about 4 to 15 &mgr;m and an average diameter D of about 0.4 to 1.5 &mgr;m are used as the particles of the carbonate. Though the oxide after decomposition process is slightly shrunk, the shape is almost kept. Due to the shape and the size of the particles and application by spraying, suitable voids are made to achieve high electron mission and a long duration. On the other hand, JP-A-8-77914, discloses an art in which a variation in the thickness of the electron emissive material layer is reduced and a long duration is achieved by partly using spherical or branched particles. JP-A-59-191226 discloses an art in which a paste of a carbonate salt is applied by printing.
The above preparation process of spraying may cause large unevenness of the surface of the electron emissive material layer as shown in
FIG. 14
, and therefore, electron beam is distributed irregularly along the uneven surface. The reason is, for example, that in case an electric field on the surface of the electron emissive material layer is not large, the electric field converges on the top of the convex and the electron emission of the convex part becomes larger than that of the concave part. A distribution of electron beam is preferably Gaussian distribution. When the distribution is irregular, there is a problem that a pitch of a shadow mask is interfered and moire easily occured.
In case unevenness of the surface of the electron emission layer was large, there was a problem that direction of electron emission tended to be easily expanded, and therefore, the beam tended to be expanded and resolution became lowered. On the other hand, in order to reduce the unevenness of the surface of the electron emissive material layer, there can be considered a process in which a paste containing the alkaline earth metal carbonate which forms the electron emissive material layer is applied on the metal substrate by printing. In the process, however, there was a problem that no suitable voids were made on the electron emissive material layer and an amount of the electron emission was smaller than that obtained by the process of spraying.
The present invention has been made in order to solve the above problems, and there is provided a process in which surface unevenness of an electron emissive material layer is reduced and a suitable voids are formed to obtain a cathode ray tube having a little moire and high resolution. In brief, the electron emissive material layer is constituted by using two particle groups having a different shape, and by applying a process in which the shape and the ratio of the particles is specified, an excellent cathode ray tube is obtained.
DISCLOSURE OF THE INVENTION
The first oxide cathode of the cathode ray tube of the present invention comprises an electron emissive material layer having an alkaline earth metal oxide on a metal substrate containing nickel as a major component, wherein the alkaline earth metal oxide comprises a mixture of needle-like particles of the first group and bulk particles of the second group which is different from the particles of the first group. An average length of the particles of the second group is at most 60% of that of the first group particles, an average diameter of the particles of the second group is at least 1.5 times larger than that of the first group particles and a ratio of the particles of the first group in the alkaline earth metal oxide constituting the electron emissive material layer is 50 to 95% based on the atomic ratio of the alkaline earth metal oxide.
The second oxide cathode of the cathode ray tube of the present invention is that in the oxide cathode of the first cathode ray tube, the particles of the second group are spherical particles having an average diameter of at most 7 &mgr;m.
The third oxide cathode of the cathode ray tube of the present invention is that in the oxide cathode of the first or second cathode ray tube, the particles of the second group comprises an oxide of at least barium and strontium, and the total amount of barium in the particles of the second group is at most 30% based on the atomic ratio of the alkaline earth metal oxide of the particles of the second group.
The fourth oxide cathode of the cathode ray tube of the present invention is that in the oxide cathode of the first, second or third cathode ray tube, the base on which an electron emissive material layer of a metal substrate is formed is a nearly circular shape having a diameter of r
1
(mm) and the planar shape of the electron emissive material layer is a nearly circular shape having a diameter of r
2
(mm), and the following equation is satisfied.
r
2
≦r
1
−0.1
The fifth oxide cathode of the cathode ray tube of the present invention further has a layer containing, as a main component, tungsten or molybdenum between the metal substrate and the electron emissive material layer of the oxide cathode of the first, second, third or forth cathode ray tube.
The first process for preparing the oxide cathode of the cathode ray tube of the present invention comprises a process for applying, by printing, the paste for printing containing particles of the alkaline earth metal carbonate forming the electron emissive material on the metal substrate wh
Ohira Takuya
Saitoh Kiyoshi
Shinjo Takashi
Suzuki Ryo
Teramoto Hiroyuki
Lee Guiyoung
Mitsubishi Denki & Kabushiki Kaisha
O'Shea Sandra
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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