JP2013110095A - Production method of powder for micro wave-absorption heating unit, powder for micro wave-absorption heating unit, and micro wave-absorption heating unit with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide powder for a micro wave-absorption heating unit which is made of a substance of white color and is capable of effectively absorbing micro waves to generate heat.SOLUTION: The method comprises the step of sintering a mixture of powdered raw materials including 50 mass% or less of silicon oxide (not including 0 mass%) in terms of SiO, and 50 mass% or more of zinc oxide (not including 100 mass%) in terms of ZnO in a temperature range between 750°C and 1350°C inclusive.

Description

  The present invention relates to a special ceramic material used for a cooking dish for a microwave oven and the like, and particularly for a microwave absorption heating element that absorbs microwaves of 2.45 GHz and exhibits excellent heat generation performance and exhibits white color. The present invention relates to a powder manufacturing method, a powder for a microwave absorption heating element, and a microwave absorption heating element using the powder.

  A microwave oven is a cooking device that heats food using a phenomenon in which microwaves of 2.45 GHz are normally irradiated onto food and water molecules in the food absorb and vibrate microwaves. Here, the ability to absorb microwaves is not limited to water molecules, and it is known that if the material has a high dielectric loss or magnetic loss, it will absorb microwaves and rise in temperature like foods. ing.

In recent years, products using special ceramic materials that have the property of generating heat by absorbing microwaves of 2.45 GHz have been proposed as cooking dishes for microwave ovens (for example, “Dream Kitchen” manufactured by Tohi Ceramics) Such). Such cooking utensils for microwave ovens do not irradiate the ingredients with microwaves radiated from microwave ovens, but heat the cooking utensils with microwaves and heat the ingredients to cook To do.
Therefore, microwave absorption heat generation powder is mixed with the raw material of a cooking utensil body, or the layer containing microwave absorption heat generation powder is baked on the surface, and microwave absorption heat generation performance is expressed.

As the microwave absorption heating element, conventionally, a substance having a high dielectric loss such as silicon carbide or a substance having a high magnetic loss such as iron-based oxide has been used. Further, in recent years, there is a microwave absorption heating element using the MgCu-based ferrite powder disclosed in Patent Document 1 disclosed by the inventors.
However, since these substances are black, dark brown, gray, etc., there are restrictions on the color of the cooking utensil, and it is not suitable for producing a white or light-colored exothermic cooking utensil.

Here, ZnO, TiBaO _{3 and the} like having a high dielectric constant are known as white substances that exhibit microwave absorption heat generation performance. These oxides are compared with the above-described silicon carbide and iron-based oxides. Therefore, it was difficult to raise the temperature to over 200 ° C. by short-time microwave irradiation.
Therefore, there has been a demand for a heating element that has excellent microwave absorption heat generation performance, is white, has a high degree of freedom in color tone, and is rich in design.

Japanese Patent No. 4666305

  The present invention has been developed in view of the above-mentioned present situation, and an object thereof is to obtain a powder for a microwave absorption heating element and a microwave absorption heating element that are white-colored substances and have excellent microwave absorption heating performance. .

In order to solve the above-mentioned problems, the inventors diligently studied microwave absorption heat generation characteristics in various white powder compounds. As a result, it was found that white powder (powder for microwave absorption heating element) having excellent heat generation performance can be obtained by heat-treating a powder obtained by mixing a predetermined amount of ZnO and SiO ₂ under predetermined conditions.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. In the method for producing a powder for a microwave absorption heating element, the raw material powder is mixed to form a powder or molded body, then fired, and then pulverized or classified as necessary to adjust to a predetermined particle size. ,
As the raw material powder,
Silicon oxide of 50 mass% or less (excluding 0 mass%) in terms of SiO ₂ ;
Using a mixture containing 50 mass% or more (but not including 100 mass%) of zinc oxide in terms of ZnO,
And a method for producing a powder for a microwave-absorbing heating element, comprising firing at a temperature range of 750 ° C. or higher and lower than 1350 ° C.

2. As raw material powder,
Silicon oxide of 50 mass% or less (excluding 0 mass%) in terms of SiO ₂ ;
A powder for microwave-absorbing heating element obtained by firing a mixture containing zinc oxide at 50 mass% or more (excluding 100 mass%) in terms of ZnO,
When the complex dielectric constant ε at 2.45 GHz of the resin sheet formed by mixing and molding the above powder for microwave absorption heating element: silicone resin at a ratio of 75:25 (mass%) is expressed by the following formula (1): A powder for a microwave absorption heating element, wherein ε ′ ≧ 3 and ε ″ ≧ 0.5.
Record
ε = ε ′ + ε ″ i (1)
However, i is an imaginary unit.

3. A microwave-absorbing heating element comprising the powder described in 2 above at least in part.

Further, in the present invention, the microwave absorbing heating element powder described in 2 above is mixed with a heat-resistant resin and molded, or a mixed liquid in which a glaze is mixed is applied to the surface of the ceramic substrate and then fired. Alternatively, a microwave absorption heating element can be obtained.
Furthermore, a ceramic raw material powder may be mixed with the above-mentioned powder for microwave absorption heating element, molded and fired to obtain a microwave absorption heating element.

  According to the present invention, a powder for a microwave-absorbing heating element exhibiting excellent heat generation performance by absorbing a microwave of 2.45 GHz and exhibiting white color and excellent color tone adjustment, and microwave absorption using the powder A heating element can be obtained.

Is a graph showing the relationship between the content of SiO ₂ and the sample surface temperature. It is the graph which showed the relationship between a calcination temperature and a sample surface temperature.

Hereinafter, the present invention will be specifically described.
In the present invention, the raw material powder is mixed to form a powder or molded body, then fired, and then pulverized or classified as necessary to adjust to a predetermined particle size to obtain a powder for microwave absorption heating element In particular, the present invention relates to a powder for a microwave absorption heating element obtained at that time, and a microwave absorption heating element using the powder.

First, the basic composition of the raw material powder used in the present invention will be described. In addition, the% display showing the component composition of the powder for microwave absorption heating elements (hereinafter also referred to as heating powder) and the microwave absorption heating element shown below means mass% unless otherwise specified.
Silicon oxide: 50% or less (excluding 0%) in terms of SiO ₂
Zinc oxide: 50% or more in terms of ZnO (not including 100%)
ZnO is a substance that absorbs microwaves and generates heat alone, and generates heat up to about 150 ° C. by microwave irradiation at 500 W for 1 minute. Therefore, 50% or more of zinc oxide is added in terms of ZnO.
By adding SiO ₂ to this and performing heat treatment, the heat generation performance is further improved, and the temperature can be raised to 200 ° C. or higher. However, since SiO ₂ itself is a substance that does not generate heat, if the silicon oxide exceeds 50% in terms of SiO ₂ , the heat generation performance is reduced and the effect of addition is lost. Accordingly, the silicon oxide must be 50% or less in terms of SiO ₂ . Preferably it is 5 to 40%, More preferably, it is 7 to 35% of range.
In addition to silicon oxide and zinc oxide, various ceramic powders such as Al ₂ O ₃ , MgO, TiO ₂ and BaTiO ₃ can be mixed. Since it becomes difficult to generate heat up to a high temperature exceeding ℃, the content of components other than ZnO and SiO ₂ is less than 50%.

Further, there is no particular limitation on the predetermined particle size of the above-described zinc oxide or silicon oxide, but zinc oxide has an average particle size of about 0.1 to 10 μm, and silicon oxide has an average particle size of 0. It is preferable to be about 0.05 to 10 μm.
Other ceramic powders preferably have an average particle size of about 0.1 to 10 μm.

Here, the inventors consider as follows the mechanism by which excellent microwave absorption heat generation performance can be obtained by satisfying the above component composition amounts.
That is, when a predetermined amount of ZnO and SiO ₂ coexist, Zn ₂ SiO ₄ which is an olivine compound is generated in a specific temperature range, so that the dielectric properties of the heating element are improved and good heat generation properties can be obtained. I guess.

Next, the reason for limiting the firing temperature will be described.
Firing temperature: 750 to 1350 ° C.
The firing temperature greatly affects the reactivity between ZnO and SiO ₂ . That is, when the firing temperature is less than 750 ° C., the olivine compound generating reaction that improves the heat generation characteristics does not proceed sufficiently, so that the heating element cannot be heated to a high temperature exceeding 200 ° C. On the other hand, if the firing temperature exceeds 1350 ° C., it is affected by the evaporation of ZnO and the structural change of SiO ₂ , so that the heat generation characteristics of the heating element deteriorate. Therefore, the firing temperature is limited to the range of 750 to 1350 ° C. Preferably, it is the range of 850-1200 degreeC. The firing time is not particularly limited, but is preferably about 0.5 to 10 hours.

  Steps for producing other powders for microwave-absorbing heating elements, that is, a mixing step, a step to form a powder or a molded body, and a step of adjusting to a predetermined particle size by performing pulverization or classification, etc. Just follow the usual method.

The powder for a microwave absorption heating element obtained by the above-described manufacturing method is a resin sheet formed by mixing a powder for a microwave absorption heating element: silicone resin at a ratio of 75:25 (mass%) at 2.45 GHz. When the complex permittivity: ε is expressed by the following formula (1), it is important that ε ′ (real part) and ε ″ (imaginary part) indicate predetermined values. In addition, the said mixing and shaping | molding are based on a conventional method.
Record
ε = ε ′ + ε ″ i (1)
However, i is an imaginary unit.

ε ′ ≧ 3 and ε ″ ≧ 0.5
The predetermined value mentioned above is that ε ′ is 3 or more and ε ″ is 0.5 or more. This is because if either ε ′ or ε ″ is out of the above range, the dielectric loss for the microwave of 2.45 GHz is too small to generate heat up to a high temperature of 200 ° C. or higher. .
In addition, as for a preferable range, (epsilon) 'is 3.6 or more, and (epsilon)''is 0.8 or more. Further, although there are no particular limitations on the upper limits of ε ′ and ε ″, it is industrially advantageous that ε ′ is about 30 and ε ″ is about 15.

Measurement method of complex dielectric constant Powder and silicon resin (solvent: toluene) (YSR3022 made by Momentive Performance Materials Japan GK) and curing catalyst (YC6843 made by Momentive Performance Materials Japan GK) Were mixed and formed into a sheet, and then the solvent was volatilized. The ratio of powder: silicone resin in the molded product was set to 75:25 (maas%). The curing catalyst was mixed so as to be 10 parts by mass with respect to 100 parts by mass of the silicon resin in the molded product.
A ring shape having an outer diameter of 7 mm, an inner diameter of 3 mm, and a thickness of 1 mm is cut out from the sheet, placed on an APC7 type coaxial sample holder, and a complex dielectric of 2.45 GHz by a S-parameter method using a network analyzer. The rate was measured. In the examples described later, the values of ε ′ and ε ″ were measured by the above method.

Next, the case where a cooking device for microwave oven (microwave absorption heating element), for example, a cooking dish is manufactured using the above powder for microwave absorption heating element will be described.
First, zinc oxide and silicon oxide adjusted to the preferred component composition as described above are mixed, heat-treated at a temperature of 750 to 1350 ° C. in an air atmosphere as a powder or molded body, and then pulverized as necessary Then, classification is performed to adjust to a predetermined particle size, and a powder for a microwave absorption heating element is obtained in which the values of ε ′ and ε ″ are set to the predetermined values. In that case, special raw material manufacturing methods, such as a wet synthesis method and a hydrothermal synthesis method, can also be used.

  Next, the microwave-absorbing heating element powder is mixed with a heat-resistant resin such as silicone resin to form a heating cooker, and then heated and solidified as necessary. The mixing ratio at that time is preferably selected from about 5 to 75% depending on the desired exothermic temperature. Moreover, it can mix with a glaze etc., and can be used by baking after apply | coating to the surface of the cooking tray of a ceramic base material. At this time, the thickness of the coating layer is preferably about 50 to 300 μm. Furthermore, the powder for a microwave absorption heating element according to the present invention may be mixed with the ceramic raw material powder to form a heating element. At this time, using a raw material added to approximately 10% or more, preferably 30% or less, it may be molded and fired to prepare a cooking dish.

  The use of the powder for a microwave absorption heating element according to the present invention is not limited to the above-described heating cooker for a microwave oven, and the warmer is used by heating the wall or floor material of a microwave heating device or a microwave oven. It can be used for general articles having a purpose of raising the temperature by using microwaves, such as an anchor, clothing, and adhesive.

  When using for the said article | item, it can adjust to the heat_generation | fever temperature according to a use by adjusting the mixing ratio of base materials, such as resin, and the powder for microwave absorption heat generating bodies. Moreover, since the powder for microwave absorption heat generating bodies according to this invention is white, the heat generating body of a various color tone can be easily produced by adding the pigment of another color tone.

Hereinafter, specific examples of the present invention will be described.
[Example 1]
Using ZnO, SiO ₂ , Al ₂ O ₃ , MgO, TiO ₂ and BaTiO ₃ as the raw material powder, the raw materials are weighed and mixed at the component blending ratios shown in Table 1, without heat treatment, or in the atmosphere at 1100 ° C. Baking was performed for 2 hours to obtain exothermic powder. The color of the obtained exothermic powder was visually observed. Further, the obtained exothermic powder was kneaded with silicon resin to form a sheet of exothermic powder: resin = 75: 25 (%) and cut into a shape of 40 × 40 × about 1 mm to prepare a sheet sample. These sheet samples were placed in a commercially available microwave oven (MRO-GS8 type manufactured by Hitachi, Ltd.), and the surface temperature of the sheet immediately after irradiation with 500 W microwave for 60 seconds was measured with a radiation thermometer. Further, a ring shape having an outer diameter of 7 mm, an inner diameter of 3 mm, and a thickness of 1 mm was cut out from the sheet, and the values of ε ′ and ε ″ were measured by the S parameter method described above.
Table 1 shows the measurement results obtained.

As shown in Table 1, when ZnO, SiO _{2 and the} like are mixed and fired according to the conditions of the present invention and the values of ε ′ and ε ″ are within the range of the present invention, the temperature exceeds 200 ° C. The sheet generates heat up to a high temperature. On the other hand, in the exothermic powder other than the present invention, the sheet did not generate heat at 200 ° C. or higher.

[Example 2]
As the exothermic powder, SiO ₂ powder: 0 to 100 (%) and ZnO powder were weighed and mixed in various proportions, mixed, and baked in the atmosphere at 950 ° C. for 3 hours to obtain exothermic powder. The exothermic powder was white. Further, the obtained exothermic powder was kneaded with silicon resin to form a sheet of exothermic powder: resin = 75: 25 (%) and cut into a shape of 40 × 40 × about 1 mm to prepare a sheet sample. These sheet samples were placed in a commercially available microwave oven (MRO-GS8 type manufactured by Hitachi, Ltd.), and the surface temperature of the sheet when irradiated with a 500 W microwave for 60 seconds was measured with a radiation thermometer. Further, a ring shape having an outer diameter of 7 mm, an inner diameter of 3 mm, and a thickness of 1 mm was cut out from the sheet, and the values of ε ′ and ε ″ were measured by the S parameter method described above.

FIG. 1 shows the measurement results obtained. In the figure, the numerical value on the measurement point means that the numerical value of the numerator is ε ′ and the numerical value of the denominator is ε ″.
As is clear from the figure, ZnO and SiO ₂ were mixed and fired at a ratio according to the present invention, and when the values of ε ′ and ε ″ were within the scope of the present invention, the sheet was 200 ° C. Exothermic to a high temperature exceeding On the other hand, when the mixing ratio was outside the range of the present invention, the sheet did not generate heat at 200 ° C. or higher.

Example 3
As the exothermic powder, raw materials having a compounding ratio of SiO ₂ : ZnO = 17: 83 (%) were weighed and mixed, and baked in the atmosphere at 300 to 1370 ° C. for 2 hours to obtain exothermic powder. The exothermic powder was white. The obtained exothermic powder was kneaded with silicon resin to form a exothermic powder: resin = 75: 25 (%) sheet, and cut into a shape of 40 × 40 × about 1 mm to prepare a sheet sample. These sheet samples were placed in a commercially available microwave oven (MRO-GS8 type manufactured by Hitachi, Ltd.), and the surface temperature of the sheet when irradiated with a 500 W microwave for 60 seconds was measured with a radiation thermometer. Further, a ring shape having an outer diameter of 7 mm, an inner diameter of 3 mm, and a thickness of 1 mm was cut out from the sheet, and the values of ε ′ and ε ″ were measured by the S parameter method described above.

FIG. 2 shows the obtained results. In the figure, the numerical value on the measurement point means that the numerical value of the numerator is ε ′ and the numerical value of the denominator is ε ″.
As is clear from the figure, when the raw material powder mixed in the addition amount according to the present invention is fired at the firing temperature according to the present invention, and the values of ε ′ and ε ″ are within the scope of the present invention, The sheet exothermed to a high temperature exceeding 200 ° C. On the other hand, at a firing temperature outside the range of the present invention, the sheet did not generate heat at 200 ° C. or higher.

As described above, as shown in the examples, the powder for a microwave absorption heating element according to the present invention is white because ZnO and SiO ₂ are main components, and the microwave produced using the powder for a microwave absorption heating element It was confirmed that the absorption heating element was heated to 200 ° C. or higher by microwave irradiation of 500 W for 60 seconds.
In addition, the content of the powder for a microwave absorption heating element in the microwave absorption heating element in the present invention is not limited to 75 (%), and the exothermic temperature is adjusted to 50 by adjusting the content. It can be adjusted to an arbitrary temperature from a low temperature of about 0 ° C. to a high temperature exceeding 350 ° C.

Claims (3)

In the method for producing a powder for a microwave absorption heating element, the raw material powder is mixed to form a powder or molded body, then fired, and then pulverized or classified as necessary to adjust to a predetermined particle size. ,
As the raw material powder,
Silicon oxide of 50 mass% or less (excluding 0 mass%) in terms of SiO ₂ ;
Using a mixture containing 50 mass% or more (but not including 100 mass%) of zinc oxide in terms of ZnO,
And the manufacturing method of the powder for microwave absorption heat generating bodies characterized by baking in the temperature range of 750 degreeC or more and 1350 degrees C or less. As raw material powder,
Silicon oxide of 50 mass% or less (excluding 0 mass%) in terms of SiO ₂ ;
A powder for microwave-absorbing heating element obtained by firing a mixture containing zinc oxide at 50 mass% or more (excluding 100 mass%) in terms of ZnO,
When the complex dielectric constant ε at 2.45 GHz of the resin sheet formed by mixing and molding the above powder for microwave absorption heating element: silicone resin at a ratio of 75:25 (mass%) is expressed by the following formula (1): A powder for a microwave absorption heating element, wherein ε ′ ≧ 3 and ε ″ ≧ 0.5.
Record
ε = ε ′ + ε ″ i (1)
However, i is an imaginary unit.   A microwave-absorbing heating element comprising at least a part of the powder according to claim 2.

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