JPS642482B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a ceramic tube for a metal vapor discharge lamp, and the metal vapor discharge lamp herein refers to a metal halide lamp, a high pressure sodium lamp, etc.

As the ceramic tube for the arc tube used in these discharge lamps, the recently developed translucent polycrystalline alumina ceramic is resistant to corrosion by sodium gas and metal halogen gas, which are discharge luminous substances. The practical application of metal vapor discharge lamps using this alumina ceramic and their high lamp efficiency are attracting attention from the viewpoint of energy saving.

However, when enclosing a luminescent substance in a translucent alumina ceramic arc tube and sealing it hermetically, the alumina ceramic cannot be welded and sealed only by high-temperature heating, such as the quartz glass arc tube used in mercury lamps. Due to the lack of thermal malleability, the following sealing methods have traditionally been used.

An example of this is shown in FIG. 1, where a translucent alumina ceramic arc tube (hereinafter referred to as alumina tube) 1 is formed and fired with both ends open, and a heat-resistant metal whose thermal expansion is approximately equal to that of the alumina tube is used.
For example, a cap 2 made of a metal material such as niobium, or an alumina ceramic that is the same as or similar to the alumina tube, is fitted and sealed using a glass frit, and then the cap 2's central hole also serves as the introduction of the luminescent substance enclosed. Heat-resistant metal electrode 3
This is a sealing method in which the step of sealing the glass frit 4 with the same glass frit 4 is performed under high temperature vacuum.

This sealing method requires vacuum conditions in addition to a high temperature of 1300°C to 1400°C, which not only makes the sealing operation difficult, but also the entire inner periphery of the alumina tube 1 and the inner periphery of the center hole of the cap 2. Because the area covered by the glass seal is large, if the sealed part is exposed to thermal shock due to repeated lighting and extinguishing of the lamp and the high temperature during lighting, there is a risk that the luminescent material of the lamp may leak from the sealed part. In particular, high-efficiency and high-color-rendering lamps require mechanical strength and corrosion resistance against high temperatures and pressures, so arc tubes obtained by this method lack reliability.

Furthermore, since the cap is made of metal or ceramic, the number of parts is large, and high dimensional accuracy is required, making it uneconomical.

In addition, one method to solve the above-mentioned drawbacks is to create an arc tube (commonly known as a semi-closed type alumina tube) in which ceramic caps are sintered and integrated at both ends of the alumina tube at the same time as the alumina tube is fired. ) is known. In this method, a tube with both ends open is formed using alumina molding clay whose firing shrinkage rate is strictly controlled, and a cap is formed from an alumina raw material whose firing shrinkage rate is smaller than that of the tube. This is a method in which the molded products are fitted together and then fired in a vacuum or hydrogen atmosphere to integrate the cap and the tube at the end.

This method requires the molded tube and cap to be fitted together in their green state, which can easily cause damage to the molded product.Furthermore, it is difficult to control firing shrinkage of the tube and cap, resulting in cracks at the ends. There are also disadvantages in that the sintering seal between the tube and the cap is insufficient, causing leakage of the encapsulated luminescent material.

Furthermore, we developed a method for manufacturing arc tubes in which the alumina tube and cap are integrally molded from the same material.
As described in Publication No. 50-14171, etc., a mold with a predetermined external shape and a core of a low melting point metal or organic material is used, and a ceramic molding raw material is filled around the core. A method has been proposed in which the alumina tube and cap are then molded into an integrated shape by applying pressure from an outer mold, and then the molded body is heated to melt and remove the core to obtain an arc tube. However, in this method, the ceramic molding raw material is pressed onto the core, so the molded body may be dyed with mud, and when the core is melted, it may seep into the molded body, or it may leave traces when it flows out. Therefore, there are technical difficulties in actual application.

Further, since the conventional industrial method for manufacturing arc tubes is based on extrusion molding, the wall thickness of the arc tube is the same as that of the light emitting portion and the end portion, that is, the portion holding the discharge electrode. Therefore, if the wall thickness is reduced in order to improve the translucency, the mechanical strength of the end portion deteriorates, so there is a limit to the improvement of the translucency.

This invention makes it easy, simple, and reliable to airtightly seal the ends when producing an alumina ceramic tube as an arc tube as described above, and is particularly useful for an integrally molded structure with few sealing points that can cause leaks. This was developed in order to avoid the disadvantages of the method using a core, and to provide a technology that can improve the luminous efficiency of the lamp without deteriorating the mechanical strength of the discharge electrode support, and can be manufactured at low cost. In the manufacturing method of alumina ceramic tubes used for light bulbs, a molding clay made by adding sintering aids, plasticizers, and mixing aids to fine alumina powder is used to create translucent alumina porcelain in the final firing. a step of conditioning, a step of press-forming the tube-shaped material, and a step of press-forming the tube-shaped material into a predetermined shape by applying fluid pressure to the inside of the material within a cavity of an outer mold having a bell-shaped inner surface. a step of expanding the tube diameter at the center of the material tube with a length corresponding to the arc tube than at the ends; and a step of removing the material tube from the outer mold after this shaping step and then subjecting it to firing. This is a method for manufacturing ceramic tubes for metal vapor discharge lamps, which consists of the sequential combination of

Now, in order to produce the ceramic tube according to the present invention, a high-purity active alumina fine powder and a necessary sintering aid are used, and a pre-baking process is required to obtain an alumina ceramic exhibiting the desired translucency in the final firing. A plasticizer whose main component is a thermoplastic organic substance that decomposes or volatilizes, and a mixing aid such as water are weighed in a predetermined proportion and thoroughly mixed in a wet manner.
Next, it is necessary to prepare a clay for molding by drying or kneading it so that it has sufficient plasticity for molding, which will be described later.

Alumina fine powder and sintering aids are conventionally known α-alumina, γ-alumina,
Light transmittance of magnesium compounds, rare earth compounds, etc.
Selection is made depending on required conditions such as firing conditions and mechanical properties.

Thermoplastic organic substances include polyvinyl alcohol,
Methyl cellulose or the like is suitable, but its selection and amount may be determined depending on the shape and size of the product and the degree of plasticity required for the molding clay during molding, and is not limited to specific conditions.
Note that thermoplastic organic substances that are difficult to thermally decompose, such as polypropylene and polyethylene, may be softened again during pre-firing to remove the organic substances and deform the molded product, so it is possible to use some of them in combination. It is important that the thermoplastic organic substance mentioned above be the main component of the additive plasticizer.

The mixing aid can be one that wets the mixture well or acts as a solvent, and can be removed in the subsequent drying and baking process.Water is generally used, but depending on the shape of the molded product, non-aqueous additives may be used. Solvents may also be selected.

In order to obtain the necessary plasticity for the molding clay in the above-mentioned main raw material composition, it is effective to use a vacuum clay kneading machine because air is not contained in the clay.

The molding clay prepared in this way is first formed into a tube-shaped material 5 using an extrusion molding machine or a wet press machine, but the ceramic tube used for the arc tube is relatively long in length compared to the tube shape. Since a long piece is required, extrusion molding is better.

At this stage, it is desirable to form the tube so that its inner diameter after final firing is approximately the same as or slightly larger than the electrode diameter of the discharge lamp. Further, the wall thickness of the tube-shaped material 5 is determined in consideration of the reduction in thickness since the diameter of the tube-shaped material pipe becomes thinner when it is expanded in a later step.

Next, as shown in FIG. 2, the tube-shaped material 5 is guided into the cavity 7 of the mold 10 having a bell-shaped inner surface, and fluid pressure is applied to the inside of the tube-shaped material 5 from one end. A pressure injection end member 12 of a pressurizing machine (not shown) is inserted into a mold 10.
At the other end, an end member 13 for closing the opening of the tube-shaped material 5 is attached to the mold 10, and then the pressurizer is activated to form a central portion of the material tube with a length corresponding to the required arc tube. After pushing the pipe system wider than the pipe system at the end, stop the operation of the pressurizer,
The molded body 6 shown in phantom lines in the figure is removed from the mold 10 by separating it from the pressure injection end member and the end member 13, and in order to facilitate this removal, the end member 13 is indicated by suffixes a and b in the figure. As mentioned above, if the material tube is divided into two at the center in a direction perpendicular to the tube axis direction or in the tube axis direction, and the fitting portion 11 is formed here, the burrs formed on the outer surface of the molded product can be reduced and removed. This is desirable because it is easy. This mold 10 is not limited to the case where it corresponds to a single molded body as shown in FIG. Of course, types having a, b, and c may also be used, and in this case, the molded form 6 may be cut into individual products immediately after molding as described above or after firing as described below. The shape of the inner cavity of the mold 10 may be any shape as long as it satisfies the lamp characteristics and makes it easy to take out the molded product, and this shape is described as bell-shaped.
It goes without saying that some modifications are included.

Air is usually convenient for applying fluid pressure;
Of course, hydraulic pressure may be used, but in this case, it is of course necessary to select a fluid that will not attack the tube-shaped material, and if there is a risk of this, make sure that the fluid does not come into direct contact with the tube-shaped material. For example, a thin elastic membrane made of rubber may be interposed therebetween.

The molded body 6 obtained as described above is pre-fired, for example, in air so as to remove the plasticizer added for molding. The pre-firing conditions may be determined depending on the type of plasticizer and the size of the product, but the firing temperature is preferably within a range that does not deteriorate the activity of the powder of the compact, that is, 1200°C or less.

Next, the pre-fired molded body is finally fired at a high temperature. The final firing conditions are determined by appropriately determining the temperature, time, and atmosphere depending on the raw material composition, the size of the product, the required light transmittance, the mechanical strength of the product, and other conditions.

An example of an alumina ceramic tube obtained by the above manufacturing method is shown in FIGS. 4 and 5, but the shape of the ceramic tube is not limited to the shape of a straight tube or an ellipse, and the shape of the light emitting part is not limited to that required. It is molded and fired according to the shape.

The alumina ceramic tube obtained by such a method has both ends 13 and 1 of the tube.
4 can be easily manufactured to a size suitable for insertion of the discharge electrode, and there is no joint between the central portion, that is, the portion 15 in which the luminescent substance is sealed and emits light, and the support portion of the discharge electrode. Since it is an integrally molded and fired body, the hermetic sealing part can be kept to a minimum, and the inner surface of the ceramic tube is not contaminated at all, so it has excellent light transmittance and also produces good results in baking performed during the manufacture of discharge lamps. It will bring about. Furthermore, the wall thickness of the light emitting portion of the ceramic tube is thin, so it has excellent translucency, while the wall thickness of the supporting portion of the discharge electrode is thick, so it has excellent mechanical strength.

Example: 0.05% by weight of magnesium oxide as an additive to fine alumina powder of 0.1 to 0.2 μ with a purity of 99.99%.
After adding 0.05% by weight of yttrium oxide, 3% by weight of methyl cellulose as an organic binder, 1% by weight of polyethylene glycol (trade name: Polynon) as a lubricant, and 25% by weight of water as a mixing aid, the mixture was thoroughly mixed in a kneader, and then vacuum kneaded. The clay for molding was prepared using a machine. Next, a tube-shaped material 5 with an outer diameter of 6.5 mm and an inner diameter of 2.5 mm is extruded using a piston type extruder, and immediately placed in a mold 10 whose inner cavity has a bell-shaped shape as shown in FIG. After sealing with end agent 13, air was inserted into the material tube from the other end to transform it into a molded body 6 having a shape along the cavity. The outer diameter of the center portion of the molded body 6 was approximately 10 mm, and the wall thickness was approximately 1.3 mm.

After pressure molding, the molded body was dried in a dielectric dryer for about 2 minutes while being housed in the outer mold to harden the tube surface, and then taken out from the outer mold.

Next, the mixture was heated in air at 800°C for 3 hours to completely remove organic matter, and then fired in a vacuum furnace at 1800°C for 6 hours.

The airtightness of the alumina ceramic tube thus obtained was tested using a helium leak tester, and the leakage was 10−10 atoms・cc/sec.
It withstands thermal shock tests from 200 degrees Celsius into water, and has a total light transmittance of 93% when measured with an integrating sphere transmittance meter.
Therefore, it satisfied all the performance requirements for a ceramic tube for a metal vapor discharge lamp.

As is clear from the above explanation, according to the method of manufacturing a ceramic tube for a metal vapor discharge lamp of the present invention, there is no need to combine the tube and the cap as in the past, and they can be integrated using the same material, resulting in excellent airtightness. Not only is the manufacturing process simple, but
It can be easily molded into a shape that can be adapted to various types of light emitting tubes, and has great utility as a method that can reduce the wall thickness of the tube in the light emitting section to improve light transmittance.

[Brief explanation of the drawing]

Fig. 1 is a partially cross-sectional front view of a conventional arc tube, Fig. 2 is a schematic diagram showing the molding procedure according to the method of the present invention, and Fig. 3 is a cross-sectional view showing the concept of the outer diameter that can be used in the present invention. FIGS. 4 and 5 are front views of main parts in cross section, illustrating a ceramic tube obtained according to the present invention. 1... Alumina ceramic tube, 2...
Cap, 3... Heat-resistant metal electrode, 4... Glass frit, 5... Tube-shaped material, 6... Molded body, 7... One end of tube-shaped material, 8... Other end of tube-shaped material, 9... Pipe diameter of central part, 1
0... Outer mold, 11... Fitting part, 12... Pressure injection end, 13... End member, 14... Electrode insertion part,
15... Part that emits light.

Claims (1)

[Claims] 1. In the manufacturing method of alumina ceramic tubes used in arc tubes of metal vapor discharge lamps, molding is performed by adding sintering aids, plasticizers, and mixing aids to alumina fine powder to create a composition that becomes translucent alumina porcelain in the final firing. A step of preparing the clay, then extrusion molding into the tube-shaped material, and then applying fluid pressure to the inside of the tube-shaped material in a cavity of an outer mold having a bell-shaped inner surface. A shaping step is performed in which the material tube of a length corresponding to a predetermined arc tube is expanded to a diameter larger than that at the ends at the center portion, and after this shaping step, the material tube is removed from the outer mold. A method for manufacturing a ceramic tube for a metal vapor discharge lamp, characterized by sequential combination of stages subjected to firing.