JPH05270941A - Microwave absorbing heating element and its production - Google Patents

Abstract

PURPOSE:To provide a microwave absorbing heating element capable of generating heat with a high exothermic efficiency by efficiently absorbing microwaves with hardly any penetration thereof through the interior of the heating element. CONSTITUTION:The microwave absorbing heating element is composed of a silicon carbide-containing porous body, having 30-80% porosity and containing 70-95wt.% silicon carbide and 5-30wt.% inorganic binder. Silicon carbide fine powder having <=5mum grain diameter is contained in an amount of 3-20wt.% based on the silicon carbide raw material. The microwave absorbing heating element of this invention contains the prescribed amount of the silicon carbide as a heating element. Since the heating element is a porous body having the porosity as high as 30-80%, the gas diffusivity is excellent and the heat convection and thermal shock resistance are good. Furthermore, since the silicon carbide fine powder is contained in the prescribed proportion, the microwave absorbing exothermic efficiency is remarkably high.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a microwave absorbing heating element, and more particularly to a microwave absorbing heating element which absorbs microwaves and self-heats due to a dielectric phenomenon. The present invention relates to a method for manufacturing a microwave absorption heating element whose absorption and heating characteristics are significantly improved.

[0002]

2. Description of the Related Art Conventionally, timber, cloth, plastic, etc. are dried and processed by utilizing the phenomenon that a substance is heated by absorbing microwaves. These utilize dielectric heating in which dipoles mainly present in a substance are oscillated by an alternating electric field caused by microwaves and heat is generated by friction between molecules.

Most of the use of such microwave heating is based on the heat generation of water molecules having an electric dipole function existing in an object to be heated. It is used for heating and drying substances containing water.

However, with such heating by water molecules, it is impossible to heat the object to be heated to 100 ° C. or higher due to latent heat of vaporization, and when water in the object to be heated disappears due to evaporation, a heat source Since there is no water, the heating phenomenon is reduced and the temperature of the heated object does not rise. That is, heating to a temperature of 100 ° C. or higher is not possible simply by irradiating a heated object containing water with microwaves. Therefore, conventionally, a dielectric or magnetic body that absorbs microwaves and self-heats is used as a heating element, and an object to be heated is heated to a high temperature by contact with or radiation from the heating element.

Conventionally, as the heating element, lead titanate-based porcelain or ferrite-based porcelain, which is heat-resistant porcelain, or soda glass has been used.

[0006]

However, in the above-mentioned conventional heating element, since some of the irradiated microwaves pass through the heating element, the heating efficiency is poor, so that improvement of the heating characteristics is desired. There is.

The present invention has been made in view of the above-mentioned conventional circumstances, and the microwave is efficiently absorbed without being substantially transmitted through the heating element, thereby generating microwaves with high heating efficiency. An object is to provide an absorption heating element and a method for manufacturing the same.

[0008]

A microwave absorbing heating element according to claim 1 is a microwave comprising a silicon carbide-containing porous body having a porosity of 30 to 80%, which is produced by using silicon carbide powder and an inorganic binder. An absorption heating element, the porous body comprising 70 to 95% by weight of silicon carbide and an inorganic binder 30.
˜5 wt%, and 3 to 20 wt% of the silicon carbide powder is fine powder having a particle size of 5 μm or less.

In the method for manufacturing a microwave absorption heating element according to a second aspect of the present invention, the porosity is 30 to 80% by molding and firing a mixed raw material containing silicon carbide powder and an inorganic binder.
Of the silicon carbide-containing porous body, wherein the ratio of the silicon carbide powder to the inorganic binder in the mixed raw material is 70 to 95% by weight of silicon carbide and 30 parts by weight of the inorganic binder 30. ~ 5% by weight,
Further, 3 to 20% by weight of the silicon carbide powder is characterized by being a fine powder having a particle size of 5 μm or less.

The present invention will be described in detail below.

In the microwave absorbing heating element of the present invention,
When the porosity of the porous body is less than 30%, the thermal shock resistance of the porous body is insufficient and the gas diffusion is poor. Further, if the porosity exceeds 80%, the strength is insufficient and the practicality is impaired.

Further, if the silicon carbide content of the porous body is less than 70% by weight, the microwave absorption and heat generation efficiency is not sufficient.
If it exceeds 5% by weight, the amount of the inorganic binder component that solidifies the silicon carbide powder (or particles) becomes relatively small, so that it becomes difficult to sinter by the ordinary sintering method, and the practical strength of the obtained porous body is reduced. Run short.

In the present invention, examples of the inorganic binder constituting the porous body include clay, feldspar, quartz, mullite, glass, cordierite, crystallized glass, frit, aluminum titanate and silicon nitride.

In the present invention, the raw material silicon carbide powder contains silicon carbide fine powder having a particle size of 5 μm or less in a proportion of 3 to 20% by weight. Here, the particle size of the silicon carbide powder is 5
If the proportion of the silicon carbide fine powder having a particle size of less than or equal to μm exceeds 20% by weight, the porosity of the obtained porous body decreases, and the gas diffusibility becomes insufficient. If this ratio is less than 3% by weight, part of the microwaves passes through the heating element, and the heating efficiency decreases.

The average particle size of the raw material silicon carbide powder other than the silicon carbide fine powder having a particle size of 5 μm or less is preferably about 50 to 500 μm.

Such a microwave absorbing heating element of the present invention can be manufactured according to the method of the present invention, for example, by the following method.

That is, the particle size is 5 μ at a ratio of 3 to 20% by weight.
Silicon carbide powder containing m or less of silicon carbide fine powder and the inorganic binder, a pore-forming material, and if necessary, an organic binder and water are mixed and molded, and then 800 to
Baking is performed at about 1500 ° C.

In the above method, foamed styrene beads, acrylic beads, carbon beads and the like can be used as the pore-forming material, and these are blended and used in an appropriate amount according to the desired porosity. Further, as the organic binder, methyl cellulose, polyvinyl alcohol, paraffin, etc. can be used, and the usage amount of these organic binders and the usage amount of water are also appropriately determined according to the raw material component ratio, molding conditions and the like.

[0019]

The microwave absorbing heating element of the present invention uses a predetermined amount of silicon carbide as a heating element and has a porosity of 30 to 80.
%, The gas diffusivity is extremely good, and the heat convection and thermal shock resistance are good.
Further, since the raw material contains fine silicon carbide powder in a predetermined ratio, the microwave absorption heat generation efficiency is remarkably high.

[0020]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples below.

Comparative Example 1 75% by weight of silicon carbide powder (average particle size 200 μm), 20.5% by weight of glass frit as an inorganic binder, 4% by weight of expanded styrene beads as a pore-forming material and 0.5% by weight of organic binder (methylcellulose). % Was thoroughly mixed, and then 10% by weight of water was added to this mixed raw material and mixed. The obtained mixed powder is press-molded at 100 kg / cm ² , dried, heated to 400 ° C. at 50 ° C./Hr and held at 400 ° C. for 1 hour, and then 1200 ° C. to 200 ° C.
/ Hr to raise the temperature, hold at 1200 ° C. for 1 hour, and bake,
After that, the temperature was lowered.

The characteristics of the obtained silicon carbide-containing porous body are shown in Table 1.
Shown in. Here, the absorption and exothermic properties were evaluated by the temperature of the porous body when irradiated with a microwave having an output of 500 W for 2 minutes and the temperature of 100 ml of water placed on the opposite side of the porous body.
It can be said that the less the microwave is transmitted, the less the water temperature rises.

Examples 1 to 4 The same as Comparative Example 1 except that silicon carbide fine powder having a particle size shown in Table 1 was used so that a part of the raw material silicon carbide powder had a ratio shown in Table 1. Then, a silicon carbide-containing porous body was produced, and its characteristics are shown in Table 1. From Table 1, it is clear that the microwave absorption heating element of the present invention has a low microwave transmission rate and a remarkably high microwave absorption heating efficiency.

[0024]

[Table 1]

[0025]

As described in detail above, according to the microwave absorption heating element and the method of manufacturing the same of the present invention, the microwave absorption heating element is made of silicon carbide and has extremely excellent gas diffusibility and thermal shock resistance. A microwave absorbing heat generating element which is excellent in heat transmission efficiency, has substantially no microwave transmission, and is extremely excellent in microwave absorbing heat generating efficiency.

Claims (2)

[Claims] 1. A microwave absorption heating element comprising a silicon carbide-containing porous body having a porosity of 30 to 80%, which is produced by using silicon carbide powder and an inorganic binder, and the porous body comprises silicon carbide 70 to 95% by weight and inorganic binder 3
A microwave absorption heating element comprising 0 to 5% by weight, and 3 to 20% by weight of the silicon carbide powder is a fine powder having a particle size of 5 μm or less. 2. A porosity of 30 is obtained by molding and firing a mixed raw material containing silicon carbide powder and an inorganic binder.
A method for producing a microwave absorption heating element comprising a porous body containing silicon carbide of 80% to 80%, wherein the ratio of the silicon carbide powder to the inorganic binder in the mixed raw material is silicon carbide 70.
~ 95 wt%, inorganic binder 30-5 wt%
And 3 to 20% by weight of the silicon carbide powder
Is a fine powder having a particle diameter of 5 μm or less.