JPH0326896B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is applicable to computer terminals, electronic components such as display parts of office automation equipment, display parts of various in-vehicle meters and clocks, image displays, etc. A flat display tube used in various display devices, especially a display tube in which at least a portion of the flat envelope is made of glass and an oxide cathode is disposed inside the envelope. This invention relates to an improvement in the manufacturing method of.

Specific examples of display tubes include fluorescent display tubes, fluorescent light source tubes,
Although there are fluorescent light emitting tubes, flat CRTs, etc., the present invention will be explained below using an example of a fluorescent display tube.

[Prior art and its problems]

The first generation of fluorescent display tubes, called monotubes, contained an electrode structure for displaying a single number within a glass vacuum container in the shape of a small vacuum tube. The second generation is called a round multi-digit tube, in which a ceramic substrate is placed inside a round glass tube on its side, and an electrode structure is created on this substrate to display multi-digit numbers by emitting light. It was contained.

Sealing of these single tubes and round multi-digit tubes is usually done by extending the lead-in wire called a well, which connects the external lead, air-tight lead-in member (duplicate wire, 426 alloy, etc.) and internal lead together, or by extending the lead-in member. A light-emitting electrode structure is connected and fixed to a button-shaped stem equipped with an integrated lead-in wire, a glass tube is placed on the outside of the structure, and the ends of the stem and glass tube are heated and fused using a gas burner or the like. It formed a display tube.
Therefore, even though the sealed part becomes very high temperature (approximately 1000°C), the temperature of the electrode structure is only about 300°C at most, which can cause deterioration and damage to the cathode even in display tubes that use oxide cathodes. I stopped talking.

However, if an attempt is made to increase the area of the display pattern in order to improve the functionality of the display device, the diameter and depth of the round multi-digit tube will increase, which will worsen the space factor when mounted on the display device.

Therefore, the third generation flat fluorescent display tube was devised.

In general, a flat fluorescent display tube consists of an anode substrate, which is a part of the envelope, an anode coated with phosphor, etc., laminated on a glass plate using thick film printing technology, and a control electrode placed on the anode substrate. It consists of a glass top lid that houses the oxide cathode and forms part of the envelope.

The above-mentioned upper lid part is a molded upper lid part formed by molding a single glass plate into a flat ship's bottom shape, or an assembled box with a side plate glued to the periphery of a flat glass plate with low melting point fritted glass cement (hereinafter abbreviated as glass cement). There is an assembly top lid part formed into a shape.

In either upper lid part, an airtight introduction member or the like is sandwiched between the upper lid part and the anode substrate and sealed with glass cement to form an airtight envelope. A light emitting electrode structure is disposed inside this airtight envelope.

When sealing an envelope with such a structure, if you try to heat only the sealing part with a burner like a round tube, the glass anode substrate and the top cover will be damaged due to heating distortion. Most of the parts are damaged. Therefore, the entire envelope of the display tube must be placed in a heating furnace with good heat uniformity to melt the glass cement and seal the parts together. The sealing temperature required for this sealing step varies depending on the melting point of the glass cement, but generally a temperature of about 400°C or higher is required. Therefore, when the atmosphere in the furnace is an oxidizing atmosphere containing oxygen such as air, the electrode structure disposed in the envelope is oxidized, causing deterioration in quality.

Therefore, in the conventional manufacturing method, an inert gas such as nitrogen gas or argon gas is used as the atmospheric gas during sealing to perform heat sealing to prevent oxidation of the cathode and the like.

However, as in flat fluorescent display tubes, the cathode is made of oxides, that is, carbonates of barium, strontium, and calcium (Ba, Sr,
Decomposition activation in which the carbonate is coated with Ca) CO ₃ and converted into a solid solution of barium oxide, strontium oxide and calcium oxide (Ba, Sr, Ca)O during the exhaust process after sealing. It would be ideal to form an efficient electron-emitting material layer through a treatment process.

However, in the case of a display device equipped with an oxide cathode as described above, although oxidation of the electrode structure can be prevented in an inert gas, the carbonate in the electron emitting material layer of the oxide cathode may undergo chemical changes. If this occurs, a sintering phenomenon appears during the decomposition activation process, resulting in a significant decrease in electron emission ability, ie, emission, and a problem in that the display tube function deteriorates.

Therefore, in order to elucidate the cause, the present inventor used many inert gases as the atmospheric gas during sealing, such as chiso gas, helium gas, neon gas, argon gas, krypton gas, xenon gas, and carbon dioxide as a weakly oxidizing gas. Temperature conditions and sealing time for sealing gases, mixed gases of argon gas and oxygen, and weakly reducing gases such as mixed gases of argon gas and hydrogen gas, mixed gases of argon gas and carbon monoxide gas, etc. I experimented by changing the.

As a result, it was found that carbonates such as barium carbonate, strontium carbonate, and calcium carbonate decompose when the temperature is raised in an atmosphere with a low carbon dioxide concentration, such as in a vacuum or in an inert gas.

That is, if the carbonate is decomposed all at once at a sufficiently high temperature of about 800°C or higher, most of the carbonate will be decomposed according to the following reaction formula.

(Ba, Sr, Ca) CO ₃ → (Ba, Sr, Ca) O + CO ₂ Therefore, barium oxide, strontium oxide,
and solid solutions of calcium oxide (Ba, Sr, Ca)
Since O is obtained and carbon dioxide gas CO ₂ is exhausted, a good electron-emitting material layer is formed.

However, when carbonates are gradually decomposed at a temperature lower than 600°C, strotium carbonate, which has the lowest activation energy, decomposes first due to the difference in decomposition activation energy of barium carbonate, strontium carbonate, and calcium carbonate. strontium oxide (SrO), then barium carbonate (BaCO ₃ ) decomposes to barium oxide (BaO), and finally calcium carbonate (CaCO ₃ ) decomposes to calcium oxide (CaO), resulting in
It becomes a mixture of simple oxides such as BaO + SrO + CaO. This elemental oxide is a material that is extremely easy to sinter under high temperature conditions, and is a good solid solution oxide of barium, strontium, and calcium (Ba,
It is not easy to obtain Sr, Ca)O, and sintering occurs as soon as the decomposition is completed. This phenomenon is called low-temperature decomposition, and it is said that it must be avoided before activation.

Since the sealing operation is usually carried out at 450 DEG C. to 550 DEG C., if it is carried out in vacuum or in an inert gas, the above-mentioned low-temperature decomposition will occur, resulting in sintering.

However, when carbonate decomposes, carbon dioxide gas (CO ₂ ) is generated as shown in the reaction equation above, but this reaction is reversible, and the progress of decomposition depends on the carbonate reaction temperature (450°C or higher). It is controlled by the balance of carbon dioxide concentration in the atmosphere. Therefore, if a high concentration of carbon dioxide gas (CO ₂ ) is already present in the reaction system, the reaction will not proceed.
In other words, when heat sealing is performed in a carbon dioxide atmosphere during the sealing process, low-temperature decomposition does not occur because the carbon dioxide concentration is high, and the activation treatment after the sealing process and exhaust process creates a good electron-emitting material layer. It is believed that a certain oxide solid solution of barium, strontium, and calcium can be obtained.

[Purpose of the invention]

Therefore, in view of the above-mentioned circumstances, in a flat display tube having an oxide cathode, it is possible to decompose the carbonate-coated cathode without sintering and form an oxide solid solution with good electron emission characteristics. The object of the present invention is to provide a method for manufacturing a display tube.

[Structure of the invention]

In order to achieve the above object, the present invention provides that a flat envelope housing an electrode structure including an oxide cathode of a display tube is composed of a plurality of members, at least a part of which is a glass member. A method for manufacturing a display tube in which a low melting point fritted glass cement is adhered to a joint portion of the members, and the low melting point fritted glass cement is heated and melted to form a display tube, wherein a plurality of display tubes to which the low melting point fritted glass cement is adhered are provided. A step of pre-firing the members in an oxidizing atmosphere, and heating the plurality of members sandwiching the electrode structure in a carbon dioxide gas or vacuum atmosphere to a temperature at which the low melting point fritted glass cement starts to melt within a short time. a step of sealing the plurality of members sandwiching the electrode structure at the melting temperature of the low melting point frit glass cement in a carbon dioxide atmosphere; and a step of sealing the plurality of members sandwiching the electrode structure at a temperature at least at which the low melting point frit glass cement solidifies. After cooling in a carbon dioxide atmosphere until the temperature reaches 100, the exhaust operation is performed to create a vacuum inside the enclosure, and the cathode is ignited.
The method is characterized by comprising a step of decomposing carbonate attached to the cathode to form an oxide cathode, and a step of closing an exhaust hole of the envelope to form an airtight envelope.

[Explanation of Examples]

The present invention will be explained below based on the illustrated embodiments.

FIG. 1 is an exploded perspective view of a fluorescent display tube, and FIG. 2 is a longitudinal sectional view of FIG. 1. FIG. 3 is a flowchart showing the manufacturing method of the present invention.

In FIG. 1, A is an anode substrate which is one of the plurality of members constituting the envelope H, B is an upper lid part which is one of the same members, and C is an electrode structure. A fluorescent display tube is formed by joining the parts in a sealing process.

The anode substrate A is a glass substrate 1 which is an insulating substrate.
On one side of each anode segment 2, a wiring conductor 3 corresponding to a lead wire is printed with a conductive material such as silver paste using a thick film printing method, and then fired to evaporate the binder and solvent in the paste.

Next, an insulating layer 4 is applied to the surface of the wiring conductor 3 by printing. The insulating layer 4 is made of lead borosilicate glass as a main component, mixed with a vehicle, a solvent, a pigment, etc. to form a paste. The insulating layer 4 is
Instead of coating the entire surface, as shown in Fig. 2, it is deposited by thick film printing except for the through hole 6 for connecting the wiring conductor 3 and the anode conductor 5, which will be described later, and then baked. do.

Further, glass cement 7 is applied to the peripheral edge of the anode substrate 1. The glass cement is made of lead borosilicate glass as a main material, and may be formed into a paste by mixing it with a vehicle, an organic solvent, etc., and may be applied by a printing method or by other known methods. After application, the binder and contaminants on each member may be fired or evaporated by pre-baking in an oxidizing atmosphere. Next, the anode conductor 5 is also formed by a printing method and connected to the wiring via the through hole.

Next, a phosphor 8 is deposited on the anode conductor 5. The anode substrate A is formed by depositing the phosphor 8 by a known method such as a printing method, an electrodeposition method, a precipitation method, or a slurry method.

The upper lid part B includes a molded upper lid part formed by molding a piece of glass with a mold, and an assembled upper lid part formed by adhesively assembling a plane plate and a side plate.Hereinafter, the present invention will be described with respect to the assembled upper lid part.

A step of applying a transparent conductive film 9a such as tin oxide to a glass flat plate 9 having insulating and translucent properties by a spraying method, and then applying adhesive to the periphery of the glass flat plate 9 on which the transparent conductive film has been formed. Glass cement with 1
0 is printed as a thick film, and the side plate 11 is adhered and erected thereon, and the exhaust pipe is also arranged on the side plate 11 using glass cement. Next, the upper lid part B is formed by a step of applying glass cement 10 to the end part 13 of the side plate and preliminarily baking it.

The electrode structure C is formed by forming the electrode support frame 14 by etching or pressing 426 alloy,
The electrode support frame 14 is placed in a furnace and subjected to oxidation treatment to form an oxide layer on the surface to improve compatibility with the glass cement 10, and a mesh-shaped control electrode 15 is placed on the electrode support frame 14. Welding process;
Next, a step of welding and attaching a cathode support 16 consisting of an anchor and a support near the left and right ends of the electrode support frame 14, and adding Ba, Sr, Ca, etc. to this cathode support.
The electrode structure C is formed by arranging the linear cathode 17 coated with carbonate and further arranging the getter 18.

Next, the assembly step is a step of assembling and pressing members A, B, and C from above and below in order to embed the electrode structure C on the anode substrate A and seal the upper cover B. Next, in the sealing step, the pressed member is placed in a sealing furnace and sealed by heating as shown in the temperature curve of FIG. 4. Furthermore, there are two types of sealing furnaces: batch type and in-line type, but both types are equipped with an air supply and exhaust system that allows the atmosphere inside the sealing furnace to be changed. First, the batch type case will be explained.

As for the heating conditions, as shown in FIG. 4, the built-in electrode structure C is heated in an oxidizing atmosphere to about 350 DEG C., which is a temperature range in which significant oxidation does not occur, for pre-baking. In this pre-firing process, the binder in the glass cement and the contaminants attached to each member are burned or evaporated. Further, when each member is preliminarily fired as described above, the temperature may be increased as shown by the chain line in FIG.

Next, the atmosphere in the sealing furnace is changed from an oxidizing atmosphere to a vacuum or carbon dioxide gas. When the atmosphere in the sealing furnace is a vacuum atmosphere, the oxidizing atmosphere is evacuated and the glass cement is maintained in a vacuum state to a temperature at which it starts to melt, and the temperature is increased by heating. Then, as the gas contained in the glass cement is exhausted, the glass cement begins to melt, so there is very little gas in the glass cement. Therefore, in the next sealing process, there are no air bubbles in the molten glass cement.
Since a sealed portion with a high density of glass is formed, the bonding strength is strong and a sealed state in which slow leakage does not occur is achieved.

If the atmosphere in the sealing furnace is a carbon dioxide gas atmosphere, the oxidizing atmosphere is evacuated to create a vacuum state before the heating and temperature increase. The temperature inside the furnace at this time is 300 to 350℃
Because the glass cement has become so hot, the gas in the glass cement is easily released. Therefore, by extending the evacuation time to some extent, the gas in the glass cement can be evacuated. The temperature inside the furnace in a vacuum state is approximately
Since the temperature is below 300℃, the life of seal parts is extended. When the temperature is then heated, a carbon dioxide atmosphere is created, so that the next sealing step can be carried out in the same atmosphere. Therefore, gas replacement at a high temperature of 400 to 450° C. is no longer required, which simplifies the gas replacement device of the sealing furnace and extends the life of the vacuum equipment.
As described above, in the temperature raising step, there are two types of furnace atmospheres, but in either case, the furnace temperature is raised to 400° C. or higher, preferably until the glass cement begins to melt. The temperature increase rate varies depending on the size of the fluorescent display tube, the thickness of the glass plate, etc., and ranges from 2°C/min to 50°C/min.

Next, the inside of the furnace is made into an atmosphere of carbon dioxide gas at almost atmospheric pressure, and the temperature is adjusted to a temperature suitable for sealing, for example, 450 to 550℃.
The glass cement is melted and sealed by keeping it for a predetermined period of time (5 to 30 minutes, determined by temperature conditions).

Next, the temperature inside the furnace is slowly cooled to below the temperature at which glass cement solidifies (300 to 380°C). At this time, the atmosphere is carbon dioxide gas.

Fluorescent display tubes having an exhaust pipe that have undergone the slow cooling process are transferred from the sealing furnace to an exhaust machine, where they are subjected to exhaust and cathode decomposition activation processes. When the degree of vacuum inside the envelope exceeds a specified level, the linear cathode is heated by passing electricity through it, and carbonates of barium, strontium, and calcium (Ba, Sr, Ca) are heated.
When CO ₃ is decomposed, a solid solution of barium, strontium, and calcium oxides (Ba, Sr, Ca)O and carbon dioxide gas are generated. The carbon dioxide gas is exhausted by the exhaust system, and the decomposition activation of the cathode is completed.

Next, the exhaust pipe is heated and melted to seal the envelope to form a sealed envelope, and the inside of the envelope is maintained in a vacuum.

The sealed envelope is coated with a getter film by heating and evaporating the getter, which has been placed in advance, using high-frequency heating to increase the degree of vacuum inside the envelope and to adsorb the gas generated after sealing. to form.

Next, by aging the fluorescent display tube, it is possible to obtain good electron emission and stable light emission characteristics.

Further, the following method will be explained as an application example of the previous embodiment.

First, the product is placed in a sealing furnace, followed by a preliminary firing process in the air, a temperature raising process in vacuum or a carbon dioxide atmosphere until the sealing temperature is reached, and a sealing process in which the sealing temperature is maintained at the sealing temperature in a carbon dioxide atmosphere. The steps up to the next slow cooling step are the same as in the previous example, but in this example, after slow cooling, the inside of the furnace is evacuated and evacuated using the vacuum exhaust system installed in the furnace. If the inside of the enclosure is also kept in a vacuum state, and once the specified degree of vacuum is reached, the linear cathode is ignited to decompose and activate the carbonate, and the exhaust pipe is sealed, the cathode and phosphor will not be exposed to the atmosphere after sealing. Since it is no longer exposed to moisture, it is not contaminated by moisture in the atmosphere, and a fluorescent display tube with even better characteristics can be obtained.

Next, the case of an in-line type furnace will be explained.

FIG. 5 is an explanatory diagram showing the configuration of an in-line sealing furnace. 21 is a preliminary firing furnace, 22 is an atmospheric gas exchange chamber, 23 is a sealing furnace, and 24
is an annealing chamber, 25 is an atmospheric gas replacement chamber, and 26 is a transfer device.

The assembly members to be sealed are placed on the conveyance device 26 and sent one after another at predetermined intervals, and while passing through the pre-firing furnace 21, they are pre-baked in the atmosphere at 300 to 350°C, and then exposed to atmospheric gas. The gas is sent into the replacement chamber 22, where the atmosphere is replaced with carbon dioxide gas. Further, it is sent to a sealing furnace 23, heated, and held at a sealing temperature to perform sealing.

When the sealing is completed, it is sent to an annealing chamber 24 and cooled down to a temperature below the solidification temperature of glass cement. The inside of the furnace is then returned to the atmospheric atmosphere in the atmospheric gas exchange chamber 25, and the gas is discharged from the outlet, completing the sealing.

〔Effect of the invention〕

As explained above, in the method for manufacturing a display tube, the present invention includes a sealing step in which glass cement is applied to the bonded portion of a plurality of glass members constituting the display tube and is heated and melted in an oxidizing atmosphere. A step of pre-firing, a step of heating and raising the temperature in carbon dioxide gas or vacuum, a step of melting and sealing the glass cement in carbon dioxide gas, a cooling step, and an exhaust operation to bring the inside of the envelope into a vacuum state. However, since it includes a step of decomposing and activating the cathode to form an oxide solid solution and a sealing step of closing the exhaust hole of the envelope, it has the following effects.

(1) A linear cathode in which carbonates of barium, strontium, and calcium are coated on a tungsten core wire decomposes at a low temperature during sealing, and the carbonates remain as they are without creating a mixture of oxides of each element. A display having an oxide cathode that can form a good solid solution of barium, strontium, and calcium oxides without sintering in the cathode decomposition activation process described below, and has excellent emission characteristics (electron emission characteristics). This has the effect of providing a tube.

[Brief explanation of drawings]

FIG. 1 is an exploded perspective view of a fluorescent display tube according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of the same embodiment, FIG. 3 is a flowchart showing the manufacturing method of the present invention, and FIG. 4 5 is a temperature curve diagram showing the temperature conditions of the sealing furnace, and FIG. 5 is an explanatory diagram showing the configuration of the in-line sealing furnace. A... Anode substrate, B... Container part, C... Electrode structure, H... Envelope, 10... Low melting point fritted glass cement.

Claims (1)

[Claims] 1. A flat envelope housing an electrode structure including an oxide cathode of a display tube is composed of a plurality of members, at least a part of which is a glass member, and a low melting point frit glass is attached to the joint of the glass members. A method for producing a display tube to which cement is adhered and which is formed by heating and melting the low melting point fritted glass cement includes pre-baking a plurality of members to which the low melting point fritted glass cement is adhered in an oxidizing atmosphere. a step of heating a plurality of members sandwiching the electrode structure in a carbon dioxide gas or vacuum atmosphere to a temperature at which the low melting point fritted glass cement starts to melt within a short time; and a step of sandwiching the electrode structure. A step of sealing the plurality of members by holding them at the melting temperature of the low melting point fritted glass cement in a carbon dioxide atmosphere, and cooling in the carbon dioxide atmosphere to at least a temperature at which the low melting point fritted glass cement solidifies,
The process involves performing an exhaust operation, creating a vacuum inside the envelope, igniting the cathode, decomposing the carbonate attached to the cathode, and forming an oxide cathode, and closing the exhaust hole of the envelope. A method for manufacturing a display tube, comprising the step of forming an airtight envelope.