JP2852558B2 - Level sensor and manufacturing method thereof - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a level sensor for electrically detecting the level of a liquid level or the like, and a method for manufacturing the same.

[Prior art] As this kind of level sensor, a PTC thermistor made of a semiconductor such as barium titanate on a ceramic substrate,
It is known that an NTC thermistor made of titania, zirconia, or the like is provided. In such a configuration, since the thermistor has a positive or negative resistance-temperature characteristic, the thermistor is heated to a temperature higher than the Curie point by self-heating or a heater. By taking advantage of the fact that it sinks in and quenches and the resistance changes significantly, by reading its voltage or current, it is possible to determine whether the liquid level is above or below a predetermined liquid level based on the position of the thermistor. You can know. This level detection can be applied not only to the liquid surface but also to the powder layer surface and the like.

[Problem to be Solved by the Invention] In the above-described level sensor, when a thermistor layer is formed on a ceramic substrate, a rough surface is formed by a sandblast method at a required portion of the ceramic substrate. A ceramic layer of barium titanate or the like will be formed on the site, but in this type of level sensor, for example, the Curie point of barium titanate is 100 ° C or more, and this is to be rapidly cooled in a liquid. As will be understood from the fact that it becomes, it is exposed to severe thermal shock. Therefore, the thermistor layer is liable to peel off due to the use over time due to the difference in the coefficient of thermal expansion between the base and the thermistor layer. In the sand blasting method, fine cracks are easily generated on the surface of the ceramic substrate by spraying sand, and the cracks are induced to further promote peeling.

An object of the present invention is to provide a level sensor having a configuration capable of withstanding the above-described temperature shock and an optimum manufacturing method thereof.

[Means for Solving the Problems] The present invention provides a method for manufacturing a ceramic substrate, comprising:
A thermistor is provided via countless ceramic fine connectors such as fibers.

In the case of using granulated particles by a spray drying method as the fine connector, the particles have a stable property as a wedge, and the particles can be connected without impairing the electrical connection between the thermistor and the conductive path during firing. It can be said that it has a good shape for proper and reliable connection.

Here, the spray-drying method is a known means of blowing mud into mist to form fine droplets, injecting them into hot air, and drying by contacting with a flow of hot air to form granules,
When spraying, a rotating disk type or centrifugal method,
The nozzle method is effective for obtaining droplets of a uniform size.

In addition, the fine connector is 80% of the main component of the ceramic base.
When the above-mentioned material is used, it has a high physical affinity with the ceramic substrate and has no difference in the coefficient of thermal expansion, so that it can be integrated with the ceramic substrate and satisfactorily bite into the thermistor side.

In the production, the fine connector is applied to a required portion of the raw ceramic substrate in the form of a paste or the like, and then fired, and then the fine connector adheres to the ceramic substrate. Means of applying a paste-like thermistor on the connector and firing the paste is proposed.

[Operation] The fine connector becomes a wedge and bites into the thermistor, and the ceramic base and the thermistor are firmly connected via the fine connector.

Further, in the above-described method, each component is integrally fired, so that stronger connection is possible.

Embodiment An example of a method for manufacturing a level sensor according to the present invention will be described with reference to FIG.

Preparation of Ceramic Substrate First, a raw material composed of α-Al ₂ O _{3 having a} purity of 92% is used and molded to form a 0.9 mm-thick raw plate-shaped ceramic substrate 1 (FIG. 1A). A conductive path 2 made of platinum and a heater 5 having a required pattern were formed thereon by screen printing (FIG. 1B).

Further, a coating layer 3 made of α-Al ₂ O _{3 is} further formed thereon.
Was formed by screen printing, and an opening 4 was formed at a required location on the conductive path 2 where the thermistor was disposed (FIG. 1C).

Preparation of fine connector On the other hand, a water-soluble binder and water were added to a raw material composed of αAl ₂ O _{3 having} a purity of 90% to form a slurry, and a fine connector x composed of granulated particles was obtained by a spray drying method. Then, the granular fine connector x was sieved to adjust the particle size to an average of about 60 μm, and heat-treated at 600 ° C. to 700 ° C. in the atmosphere. A water-soluble binder and water were added to the granulated particles to form an ink. At this time, fine particles sieved through a 500 mesh sieve were mixed with the slurry to change the average particle size.

Formation of Level Sensor The ink 6 containing the above-mentioned granular fine connector x is supplied to the opening 4 of the coating layer 3 (FIG. 1D), and the resin is removed in an atmosphere at a temperature of 300 ° C. to form a granulated particle layer. 7 was calcined at 1500 ° C. for 2 hours in the air. After the opening 4 is adhered, dried, and lightly pressed before firing, the granular fine connector x bites into the ceramic substrate 1 side, thereby improving the adhesive strength.

Next, La or Sb as a rare earth was added to barium titanate, and an organic binder was further added to form a paste. The paste 8 was applied onto the granulated particle layer 7 of the opening 4 by transfer (FIG. 1E).

Then, this was fired at 1350 ° C. for 2 hours to be integrally sintered. As a result, a PTC thermistor 10 made of barium titanate and having a thickness of about 70 μm was formed on the required conductive path 2 of the ceramic base 1 via the granulated particle layer 7, and the level sensor S was obtained.

In such a configuration, as shown in FIG. 2, when the thermistor 10 is connected, as shown in FIG. 2, since each of the particulate microconnectors x of the granulated particle layer 7 is made of the same ceramic material, it is integrated with the ceramic base 1 side. The granular micro connector x acts as a wedge and cuts into the thermistor 10 side. Therefore, the thermistor 10 is firmly connected to the ceramic base 1.

-Strength test In order to check the connection strength of the thermistor 10, a level sensor S was prepared by changing only the average particle size of the granular fine connector x, and was placed in a dryer at 200 ° C for 10 minutes, and then taken out. Repeat the cooling and heating cycle of placing in ice water for 10 minutes 1000 times,
The state of adhesion of the thermistor 10 was observed. At this time, the average particle diameter of the fine connector x was 20 μ, 40 μ, 60 μ, 80 μ, 100 μm.
μ. In addition, a sample was not observed on which the ink 6 containing the particulate fine connector x was not applied.

As a result, in the level sensor S in which the granular micro connector x of 20 μm to 80 μ was interposed, no crack or the like was generated even by the cooling / heating cycle. However, in the case of 100 μm, the thermistor 10 partially cracked. In addition, the thermistor 10 was peeled off without the granular fine connector x.

In this way, it was found that the connection strength of the thermistor 10 was dramatically improved by applying the micro connector x of 80 μ or less. It was also found that the use of a micro connector x of 100 μ improves the structure compared to the conventional configuration.

Thus, it has been found that the level sensor S according to the present invention has high thermal shock resistance.

-Consideration of the forming means In the above-mentioned manufacturing means, in the case of the fine connector x obtained by the spray drying method or the like, the fine connector x is spherical, the constricted portion is reliably formed, a good wedge can be formed, and the primary wedge before firing is formed. The particles are not easily condensed and have good sinterability. Further, when the particles are coated and baked on the ceramic substrate 1, the particles are kept in contact with each other, the bonding force is strong, and the connection between the thermistor 10 and the conductive path 2 can be secured as shown in FIG.

As a means for increasing the adhesive strength between the ceramic base 1 and the fine connector x, it is conceivable to bond the ceramic base 1 with glass or the like, but the contact between the thermistor 10 and the conductive path 2 becomes poor. For this reason, as described above, it is considered that the best method is to apply the fine connector x on the ceramic base 1 and then to fire it integrally.

It is preferable that the main component of the fine connector x be the same as the material of the ceramic base 1 or a material containing 80% or more. It foreign material or, if it is the compounding ratio of less than the content fee, it increases the matrix components after sintering by SiO ₂ being contained (glass component), contact between the thermistor 10 and the conductive path 2 in the same manner as described above In addition, since the matrix component has a low melting point, the bonding strength is reduced in a high-temperature atmosphere, and the thermistor 10 is easily peeled off due to a difference in thermal expansion between the ceramic substrate 1 and the micro connector x. It is because it is expected to become.

The ceramic substrate 1 is desirably formed of Al ₂ O ₃ for applying a voltage to the thermistor 10 or providing a heater for heating on the ceramic substrate 1. In this case, the ceramic base 1 may be formed of another material, and its surface may be coated with an Al ₂ O ₃ layer.

As described above, a PTC thermistor obtained by adding a rare earth element such as La or Sb to barium titanate as described above has excellent heat resistance, low electric resistance at room temperature, and good characteristics.

The heater 5 can be formed on the ceramic base 1 or the like as described above for the purpose of further expanding the operating temperature range.

In addition, when the liquid or gas to be brought into contact with the level sensor S is corrosive to the thermistor 10, a pinel layer may be added to the surface of the level sensor S by a known method such as a protective layer such as glass or thermal spraying. Thereby, the durability can be improved.

Further, the shape of the fine connector x is not only spherical,
Various shapes such as a square shape and a fiber shape can be proposed.

Further, the present invention can also be used for forming a TNC thermistor made of zirconia or the like on the ceramic substrate 1.

[Effects of the Invention] As described above, in the present invention, the thermistors are arranged on the required conductive paths of the ceramic base via innumerable ceramic microconnectors, so that the microconnectors bite into the thermistors as wedges, The ceramic substrate and the thermistor are firmly connected to each other through the fine connector. Therefore, the level sensor S used in an intense temperature environment has an excellent effect of significantly improving the durability. is there.

[Brief description of the drawings]

The accompanying drawings show an embodiment of the present invention, FIG. 1 is a manufacturing process diagram, and FIG. 2 is an enlarged vertical sectional side view showing a bonding state between the ceramic base 1 and the thermistor 10. S: Level sensor x: Fine connector 1: Ceramic base 2: Conductive path 4: Opening 10: Thermistor

Continuation of front page (72) Inventor Kanehisa Tachibana 14-18, Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi Prefecture Inside of Japan Special Ceramics Co., Ltd. (56) References JP-A-60-39510 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) G01F 23/22

Claims (4)

(57) [Claims] 1. The method according to claim 1, wherein the particles are formed on required conductive paths of the ceramic substrate.
A level sensor comprising a thermistor disposed via countless ceramic fine connectors such as fibers. 2. The method according to claim 1, wherein said fine connector is granulated by a spray drying method.
Level sensor according to the item. 3. The level sensor according to claim 1, wherein said fine connector is made of a material containing at least 80% of a main component of a ceramic base. 4. A ceramic fine connector is coated on a required portion of a raw ceramic substrate, then fired, and a paste-like thermistor is coated on the fine connector attached to the ceramic substrate. A method for manufacturing a level sensor, characterized in that the level sensor is fired.