JP7056407B2 - How to dry ruthenium oxide powder - Google Patents

Description

The present invention relates to a method for drying ruthenium oxide powder.

Generally, a resistor provided in a chip resistor, a hybrid IC, a resistance network, or the like is formed by printing a resistor paste on a ceramic substrate and firing it. As the resistor paste, those containing ruthenium oxide powder and glass powder as main components as conductive particles are widely used.

As a method for producing the ruthenium oxide powder, for example, atypical ruthenium oxide hydrate is dispersed in water or an organic solvent to loosen agglomerates, dried and fired, so that there are no fine and coarse particles of 10 μm or less. A method for producing a Ru oxide powder or a Ru composite oxide powder is disclosed (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 11-157845

By the way, when the ruthenium oxide powder is produced in a wet manner, the ruthenium oxide powder is obtained in a state where water is attached to the surface by washing or the like, so it is necessary to dry the water. This drying is generally performed using a drying oven.

From the viewpoint of shortening the drying time, it is preferable to raise the temperature (atmospheric temperature) in the drying furnace, but the higher the atmospheric temperature, the more easily the ruthenium oxide powder is oxidized and deteriorated. Therefore, it is necessary to set the atmospheric temperature low so as not to cause deterioration, and the time required for drying tends to be long. Specifically, the drying temperature is limited to about 150 ° C., and it takes 20 hours to dry at this temperature.

In addition, since the ruthenium oxide powders aggregate and solidify in the process of drying the wet ruthenium oxide powder, the ruthenium oxide powder does not form a powder, but forms a wafer-like dried body in which particles are fixed to each other. .. Since this dried product needs to be repulverized using, for example, a pulverizer, the number of steps is increased.

When the ruthenium oxide powder is produced in a wet manner as described above, the drying time is long and it is necessary to repulverize the powder, so that the ruthenium oxide powder may not be produced with high productivity.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique for efficiently drying ruthenium oxide powder.

According to one aspect of the invention
By irradiating the moist powder containing ruthenium oxide and water with microwaves and heating and volatilizing the water, the moist powder is dried into a dry body having a porous structure in which the ruthenium oxide powder is aggregated. A method for drying the ruthenium oxide powder is provided.

According to the present invention, the ruthenium oxide powder can be efficiently dried.

FIG. 1 is a schematic configuration diagram showing an outline of a drying device for drying ruthenium oxide powder.

In order to solve the above problems, the present inventor has studied a case where a ruthenium oxide powder (wet powder) to which moisture is attached is dried in a high temperature atmosphere. As a result, it was found that in this drying method, not only the water content but also the ruthenium oxide powder and the container for containing the wet powder are heated, so that the thermal efficiency is lowered. Further, in this drying method, by heating the wet powder from the surface side exposed to the outside air, the drying gradually progresses from the surface of the wet powder toward the inside, so that the particles aggregate and stick to each other in the process of drying the moisture. It was found that the powder that was finally obtained was easy to form a wafer-like dried body in which the particles were firmly adhered to each other.

For this reason, the present inventor investigated a drying method with high thermal efficiency and focused on microwaves. According to the microwave, only the water adhering to the surface of the ruthenium oxide powder can be directly heated, so that the thermal efficiency can be improved. Moreover, since the surface of the wet powder and the inside thereof can be uniformly heated, the finally obtained dried product can be formed in a porous shape by volatilizing the water to form bubbles. As a result, it is possible to prevent the particles from aggregating and firmly fixing in the drying process. The present invention has been made based on the above findings.

<One Embodiment of the present invention>
Hereinafter, an embodiment of the present invention will be described. FIG. 1 is a block diagram showing an outline of a drying device for drying ruthenium oxide powder.

(Drying device)
First, the drying device 10 used in the drying method of the present embodiment will be described.

In this embodiment, a drying device 10 capable of irradiating microwaves is used in order to directly heat the moisture adhering to the surface of the ruthenium oxide powder. Specifically, as shown in FIG. 1, the drying apparatus 10 includes a drying furnace main body 11, a microwave transmitting unit 12, and a waveguide 13. The drying oven main body 11 is configured to accommodate the wet powder 1 which is the object to be dried. A waveguide 13 is connected to the drying furnace main body 11, and a microwave transmission unit 12 is provided at one end of the waveguide 13. The microwave transmitting unit 12 generates microwaves, and the waveguide 13 propagates the generated microwaves into the drying furnace main body 11 and introduces them.

From the viewpoint of uniformly irradiating the object to be dried with microwaves, the drying furnace main body 11 may be provided with a turntable 14 on which the wet powder 1 or the container 2 containing the wet powder 1 is placed and rotated. preferable. Further, it is preferable that a stirrer fan 15 (stirring blade) for diffusing microwaves is provided inside the drying furnace main body 11 in the vicinity of the opening of the waveguide 13.

From the viewpoint of improving the drying efficiency of the drying device 10, it is preferable that the drying furnace main body 11 is configured to be ventilable. In the drying oven main body 11, water is heated and volatilized by microwave irradiation to generate water vapor, while the inner surface of the container 2 and the drying oven main body 11 is not heated so much by microwaves and remains at a low temperature. Therefore, steam may come into contact with the inner surface of the container 2 or the drying furnace main body 11 to cause dew condensation, which may lower the drying efficiency. In this respect, by configuring the drying furnace main body 11 so that it can be ventilated, the drying efficiency can be improved and the drying time can be shortened.

Specifically, the drying furnace main body 11 is provided with a supply port 16 for supplying gas to the inside thereof and a discharge port 17 for discharging water vapor generated by volatilization of the gas and water inside the drying furnace main body 11. It is preferable that the supply port 16 is provided with the gas supply device 20. From the viewpoint of further improving the drying efficiency, the gas supply device 20 is preferably configured to supply warm air as a gas. For example, the gas supply device 20 may be a heater heating type and may be configured to include a fan 22 for sending gas (air) and a heater 21 for heating air. The temperature of the warm air is preferably 50 ° C. or higher because the amount of saturated water vapor increases as the temperature of the hot air increases and the ventilation efficiency of the water vapor increases. On the other hand, the temperature is preferably 70 ° C. or lower in order to suppress the deterioration of the ruthenium oxide powder.

Further, if the irradiation amount of the microwave of the microwave transmitting unit 12 is constant, the excessive microwave may cause sparks when the drying progresses and the content of the water contained in the wet powder 1 decreases. Therefore, from the viewpoint of safety, it is preferable that the microwave transmitting unit 12 is configured to reduce the amount of microwave irradiation according to the decrease in the content of water contained in the wet powder 1. Specifically, it is preferable to provide a detecting means for detecting the water content and to control the microwave irradiation amount according to the detected water content. As the detection means, for example, one capable of measuring the weight of the wet powder 1 or the amount of water (water vapor amount) exhausted from the drying oven main body 11 can be used. Specifically, if it is the weight of the wet powder 1, it is preferable to use a load meter, and it is preferable to install the load meter on the turntable 14 and measure the amount of decrease in water content from the amount of decrease in the amount of wet powder 1 due to the volatilization of water. .. If it is the amount of water vapor, it is preferable to use a hygrometer as a detection means. A hygrometer is installed in the discharge port 17 to measure the amount of water vapor contained in the air exhausted from the discharge port 17, and the amount of decrease thereof. It is advisable to measure the amount of decrease in water content contained in the wet powder 1. The water content may be determined by the drying time.

(Drying method of ruthenium oxide powder)
Subsequently, a method of drying the ruthenium oxide powder using the above-mentioned drying device 10 will be described.

First, a ruthenium oxide powder and a wet powder containing water, which are to be dried, are prepared. This wet powder is obtained, for example, by preparing a ruthenium oxide powder in a wet manner, washing it with water, and then performing solid-liquid separation, in which water adheres to the surface of the ruthenium oxide powder. The powder means a collection of a plurality of particles, and the wet powder means a collection of wet particles with water attached to the surface.

Subsequently, the wet powder is placed in a container. The container is preferably made of a material having excellent heat resistance and transmitting microwaves, and for example, a container made of glass, Teflon, FRP (reinforced fiber plastic), PP (polypropylene) or the like can be used.

Subsequently, as shown in FIG. 1, the container 2 containing the wet powder 1 is placed on the turntable 14 of the drying oven main body 11. The position on which the powder is placed is not particularly limited, but from the viewpoint of uniformly irradiating the wet powder 1 with microwaves, a position off the center of the turntable 14 is preferable.

Next, before irradiating with microwaves, preheating is performed to adjust the temperature inside the drying oven main body 11 (atmosphere of the wet powder 1) to 50 ° C. to 70 ° C. By preheating, dew condensation when irradiated with microwaves can be suppressed. The preheating method is not particularly limited, but it is preferable to supply warm air from the gas supply device 20 to the inside of the drying furnace main body 11 to raise the atmospheric temperature.

Next, while rotating the container 2 by the turntable 14, microwaves are generated from the microwave transmitting unit 12, and the microwave is micron with respect to the wet powder 1 placed inside the drying furnace main body 11 from the waveguide 13. Irradiate the waves. Moisture contained in the wet powder 1 is directly heated by irradiation with microwaves. That is, in the aggregate of the wet powder 1, the moisture existing on the surface side exposed to the outside air and the moisture existing inside are uniformly heated. As a result, water is volatilized from the wet powder 1 to obtain a dried product.

The obtained dried product is in a state where the ruthenium oxide particles are aggregated and the particles are fixed to each other. In the present embodiment, since the water is uniformly heated and volatilized, the dried body has bubbles formed by the volatilization of the water and has a porous structure.

In the present embodiment, it is preferable that the drying by irradiation with microwaves is performed while ventilating the atmosphere of the wet powder 1 (inside the drying oven main body 11). Further, it is preferable that the ventilation is performed by supplying warm air having a temperature of 50 ° C. to 70 ° C. to the drying oven main body 11.

Further, in the present embodiment, it is preferable to reduce the amount of microwave irradiation according to the amount of decrease in the amount of water contained in the wet powder 1. The amount of decrease in water can be grasped by using the drying time as a guide, but it is preferable to measure it with a load meter installed on the turntable 14. Then, it is preferable to control so as to reduce the amount of microwave irradiation according to the amount of decrease in the measured water content.

The microwave output is not particularly limited, but from the viewpoint of efficient drying, 1 kg of wet powder 1 and a drying time of 1 hour should be 600 W / kg hour or more and 1250 W / kg hour or less. Is preferable.

Subsequently, the dried product obtained by drying is crushed. Specifically, the dried product is taken out from the container 2 and crushed with a spoon or the like to obtain a dried ruthenium oxide powder.

<Effects of this embodiment>
According to this embodiment, one or more of the following effects are exhibited.

As a comparative form, when ruthenium oxide powder having moisture adhered to the surface is heated and dried in a high temperature atmosphere, the wet powder is dried because the drying gradually progresses from the surface side exposed to the outside air to the inside. It takes a long time.
On the other hand, in the present embodiment, the wet powder 1 is irradiated with microwaves to selectively heat the water contained in the wet powder 1. That is, not only the surface of the wet powder 1 but also the water existing inside is uniformly heated. As a result, the time required for drying can be shortened as compared with the case of gradually drying from the surface side as in the comparative form. Further, since the water is directly heated, the energy can be reduced without heating the ruthenium oxide powder, the container 2, or the like as in the comparative form.

Further, in the comparative form, since the wet powder 1 gradually dries from the surface side exposed to the outside air toward the inside, in the obtained dried body, the particles are densely aggregated and firmly fixed in the process of drying. It ends up. Therefore, it is necessary to repulverize the dried product by a pulverizer.
On the other hand, in the present embodiment, the moisture contained in the wet powder 1 is volatilized by irradiation with microwaves to form bubbles, so that dense aggregation of particles during the drying process is suppressed. , The obtained dried product can be formed in a porous shape. According to the porous dry body, bubbles are formed and the particles do not adhere firmly to each other, so that it can be easily crushed using a spoon or the like, and repulverization by a crushing device is required. do not. Further, since the dried body does not firmly adhere to the container 2, the dried body can be easily separated from the container 2. Therefore, the ruthenium oxide powder can be produced with high productivity.

Further, in the present embodiment, it is preferable to perform drying by irradiation with microwaves while ventilating the atmosphere of the wet powder 1. Ventilation allows the water vapor produced during the drying process to be discharged. As a result, it is possible to prevent water vapor from coming into contact with ruthenium oxide powder having a low temperature without being heated and causing dew condensation, and it is possible to improve the drying efficiency.

Further, in the present embodiment, it is preferable to supply warm air having a temperature of 50 ° C. to 70 ° C. to the drying oven main body 11 for ventilation. According to the warm air, the decrease in the atmospheric temperature can be suppressed, so that the drying efficiency can be maintained high.

Further, in the present embodiment, it is preferable to reduce the amount of microwave irradiation according to the amount of decrease in the amount of water contained in the wet powder 1. As a result, it is possible to efficiently dry the product without causing sparks when the water content is low.

Hereinafter, description will be given based on examples.

(Example 1)
First, a wet powder containing water, which was prepared by a wet method and separated into solid and liquid through washing, was prepared. 1.0 kg of this wet powder was dried under the conditions shown in Table 1 below in the drying apparatus shown in FIG. 1 and crushed to obtain a dried ruthenium oxide powder.

(Examples 2 to 4)
In Examples 2 to 4, ruthenium acid acid powder was produced in the same manner as in Example 1 except that the weight of the wet powder and the microwave output were appropriately changed as shown in Table 1.

(Comparative Example 1)
In Comparative Example 1, ruthenium oxide powder was produced in the same manner as in Example 1 except that the wet powder was left to dry in a drying oven having a temperature of 150 ° C.

In Comparative Example 1, drying was performed by setting the atmospheric temperature to 150 ° C. so as not to deteriorate the ruthenium oxide powder, but it was confirmed that it took 20 hours to complete the drying. Further, it was confirmed that the dried product obtained by drying had particles firmly adhered to each other to form a wafer, and it was necessary to re-powder using a pulverizer.

On the other hand, in Examples 1 to 4 in which drying was performed by irradiation with microwaves, it was confirmed that the time required to complete the drying was less than 1 hour, which was significantly shorter than that in Comparative Example 1. It was also confirmed that the obtained dried product had a porous shape due to the volatilization of water and the formation of bubbles, and could be easily crushed with a spoon or the like.

<Preferable Aspect of the Present Invention>
Hereinafter, preferred embodiments of the present invention will be described.

(Appendix 1)
According to one aspect of the invention
By irradiating the moist powder containing ruthenium oxide and water with microwaves and heating and volatilizing the water, the moist powder is dried into a dry body having a porous structure in which the ruthenium oxide powder is aggregated. A method for drying the ruthenium oxide powder is provided.

(Appendix 2)
In the method for producing ruthenium oxide powder in Appendix 1, preferably.
The wet powder is dried while ventilating the atmosphere of the wet powder.

(Appendix 3)
In the method for producing ruthenium oxide powder in Appendix 2, preferably.
Ventilation is performed by supplying warm air having a temperature of 50 ° C. or higher and 70 ° C. or lower to the atmosphere of the wet powder.

(Appendix 4)
In the method for producing ruthenium oxide powder according to any one of Supplementary note 1 to 3, preferably.
After adjusting the atmospheric temperature of the wet powder to 50 ° C. or higher and 70 ° C. or lower, the wet powder is dried.

(Appendix 5)
In the method for producing ruthenium oxide powder according to any one of Supplementary note 1 to 4, preferably.
The irradiation amount of the microwave is reduced according to the decrease in the content of the water contained in the wet powder.

(Appendix 6)
In the method for producing ruthenium oxide powder according to any one of Supplementary note 1 to 5, preferably.
The output of the microwave is set to 600 W / kg · hour or more and 1250 W / kg · hour or less per 1 kg of the wet powder and 1 hour of drying time.

1 Wet powder 2 Container 10 Drying device 11 Drying furnace body 12 Microwave transmitter 13 Waveguide 14 Turntable 15 Star Rafan (stirring blade)
16 Supply port 17 Discharge port 20 Gas supply device 21 Heater 22 Fan

Claims (6)

By irradiating the wet powder containing ruthenium oxide and water with microwaves while diffusing them with a stirring blade and heating the water to volatilize the wet powder, the moist powder has a porous structure in which the ruthenium oxide powder is aggregated. A method for drying ruthenium oxide powder to be dried on a dry body having. The method for drying ruthenium oxide powder according to claim 1, wherein the wet powder is dried while ventilating the atmosphere of the wet powder. The method for drying ruthenium oxide powder according to claim 2, wherein the atmosphere of the wet powder is ventilated by supplying warm air having a temperature of 50 ° C. or higher and 70 ° C. or lower. The method for drying ruthenium oxide powder according to any one of claims 1 to 3, wherein the wet powder is dried after adjusting the atmospheric temperature of the wet powder to 50 ° C. or higher and 70 ° C. or lower. The method for drying ruthenium oxide powder according to any one of claims 1 to 4, wherein the irradiation amount of the microwave is reduced according to the decrease in the content of the water contained in the wet powder. The ruthenium oxide powder according to any one of claims 1 to 5, wherein the output of the microwave is 600 W / kg · hour or more and 1250 W / kg · hour or less per 1 kg of the wet powder and 1 hour of drying time. Drying method.

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