JP2014024692A - MgCuZn-BASED FERRITE POWDER FOR MICROWAVE ABSORPTION HEATING ELEMENT AND MICROWAVE ABSORPTION HEATING ELEMENT USING THE SAME - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a MgCuZn-based ferrite powder for a microwave absorption heating element, excellent in heat-generating performance to the predetermined temperature and capable of arbitrarily selecting a heat-up stop temperature in a low temperature range such as 30 to 100°C, and to provide a microwave absorption heating element using the same.SOLUTION: An average particle size of a MgCuZn-based ferrite powder is in the range of 2 to 500 μm as the MgCuZn-based ferrite powder having a predetermined component composition.

Description

  The present invention relates to a ferrite powder for a microwave absorption heating element that absorbs microwaves such as a microwave oven and generates heat, and stops heating at a desired temperature, and a microwave absorption heating element using the powder, In particular, the present invention relates to a MgCuZn ferrite powder for a microwave absorption heating element that can be suitably used for a heat insulating material, a furnace, a hot compress, a thermotherapy, etc., and can be stopped at a relatively low temperature range from room temperature to about 100 ° C. Is.

  A microwave oven is a cooking device that heats food using a phenomenon in which a food is usually irradiated with microwaves of 2.45 GHz and water molecules in the food absorb the microwaves and vibrate. 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.

  However, microwave-absorbing heating elements that use dielectric loss continue to rise to very high temperatures when they absorb microwaves. Therefore, for safe use, the content of heat-generating powder must be adjusted to balance heat dissipation. There is a need to.

  Therefore, the inventors have developed technology focusing on Mg-based ferrite that generates heat only with the contribution of magnetic loss with a small dielectric loss, and as a result, absorbs microwaves and exhibits excellent heat generation performance. The MgCuZn ferrite powder for microwave absorption heating elements that stops the temperature rise at a predetermined temperature was proposed (see Patent Document 1). Here, the technique described in Patent Document 1 is an excellent technique that has excellent temperature rise characteristics and can stop the temperature rise at a desired temperature.

Japanese Patent No. 4666305

  However, since the MgCuZn ferrite powder described in the above-mentioned Patent Document 1 is mainly used for cooking utensils that are burnt with a microwave oven, the temperature rise stop temperature is limited to a range of 100 to 290 ° C. Therefore, it was extremely difficult to stop the temperature increase in a temperature range lower than 100 ° C.

Moreover, it is necessary to use a heat insulating material that may be in direct contact with the human body, such as a portable body warmer or a warm compress, in a temperature range in which there is no risk of burns. For example, the product specification of “Hokkairo (registered trademark) for neck and shoulder” manufactured by Hakugen has a maximum temperature of 60 ° C. and an average temperature of 47 ° C. Furthermore, when used as a heat insulating material for food, it is desirable to maintain the temperature at about 70 ° C. in order to suppress drying of the food material due to heat insulation.
Therefore, in order to use in these applications, a microwave absorbing exothermic powder that not only absorbs microwaves but generates heat rapidly but also stops temperature rising at a desired temperature of 100 ° C. or lower is required.

  The present invention has been developed in view of the above-described present situation, and it is needless to say that the heat generation performance up to a predetermined temperature is excellent, and a microwave that can arbitrarily select a temperature rise stop temperature in a low temperature range of 30 to 100 ° C. The object is to propose an MgCuZn ferrite powder for an absorption heating element and a microwave absorption heating element using the powder.

In order to solve the above-described problems of the MgCuZn ferrite powders for heating elements, the inventors diligently studied the relationship between the basic composition of MgCuZn ferrite and the temperature rise stop temperature. As a result, by adjusting the composition ratio of MgO, ZnO, CuO and Fe ₂ O ₃ to a predetermined range, and further selecting the particle diameter of the ferrite powder appropriately, the temperature rise is stopped in a temperature range of 30 to 100 ° C. They found that the temperature could be adjusted.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. 46～51Mol% iron oxide in terms _{of Fe} 2 _{O 3,}
The copper oxide contains 2 to 15 mol% in terms of CuO and the zinc oxide contains more than 28 mol% and less than or equal to 33 mol% in terms of ZnO, and the balance is MgCuZn ferrite powder composed of magnesium oxide and inevitable impurities, and the average of the MgCuZn ferrite powder MgCuZn ferrite powder for microwave-absorbing heating elements, wherein the particle size is 2 to 500 μm.

2. A microwave absorption heating element that generates heat by absorbing microwaves,
2. A microwave-absorbing heating element comprising the MgCuZn ferrite powder according to 1 described above at least partially.

  According to the present invention, microwaves in a microwave oven at 2.45 GHz are effectively absorbed, heated and heated rapidly, and at a desired temperature in a low temperature range of 30 to 100 ° C., the temperature rise A microwave absorbing heating element that stops can be obtained.

It is the graph which showed the temperature rising characteristic at the time of irradiating the 500 W microwave to the ferrite resin sheet according to this invention compared with the temperature rising characteristic of the conventional (outside of this invention) ferrite resin sheet. It is the graph which showed the temperature rising characteristic when 500 W of microwaves were irradiated to the ferrite resin sheet according to this invention compared with the temperature rising characteristic of the resin sheet containing silicon carbide powder.

Hereinafter, the present invention will be specifically described.
First, the temperature rise stop temperature: Ts in the present invention is a plate-like sintered body (heating element) having a vertical and horizontal size of 40 mm × 40 mm and a thickness of about 5 mm after compression molding of ferrite powder and firing. ) And using a commercially available microwave oven, the surface temperature of the plate-like sintered body after being irradiated with 500 W microwave is considered to be constant with almost no temperature change for 60 to 90 seconds. And The surface temperature of the plate-like sintered body is measured with a radiation thermometer.
Further, the temperature rise stop temperature: Tsr in the present invention means that the ferrite powder is kneaded in a medium such as a resin, molded and then compression molded, and then the vertical and horizontal dimensions are 40 mm × 40 mm and the thickness is about 5 mm. When the surface temperature of the plate-like sintered body after being irradiated with 500 W microwave using a commercially available microwave oven is considered to be constant with almost no temperature change for 60 to 90 seconds. Let it be temperature.

Next, the basic composition of the MgCuZn ferrite powder in the present invention will be described. In addition, unless otherwise indicated, the% display showing the component composition of the MgCuZn ferrite powder shown below means mol%.
Iron oxide: 46-51% in terms of Fe ₂ O ₃
Iron affects the stability and specific resistance of the ferrite phase, and greatly affects the rate of temperature rise due to microwave application. If the amount of iron oxide is less than 46% in terms of Fe ₂ O ₃ , a phase other than ferrite is generated and it is difficult to obtain a ferrite single phase, and the heating rate of the heating element decreases. On the other hand, when the amount of iron oxide exceeds 51% in terms of Fe ₂ O ₃ , the specific resistance of the heating element is lowered, and the heat generation performance is reduced by reflecting the microwave like metal, or when the microwave is irradiated There is a risk of sparking.
Therefore, the amount of iron oxide is limited to the range of 46 to 51% in terms of Fe ₂ O ₃ . Preferably it is 48 to 49.8% of range.

Copper oxide: 2 to 15% in terms of CuO
Copper affects the temperature rise stop behavior at a high temperature in the temperature rise characteristics of the heating element by microwave application. When the amount of copper oxide is less than 2% or more than 15% in terms of CuO, in any case, the temperature of the heating element rises with microwave irradiation without stopping the heating of the heating element Will continue to do. Therefore, the amount of copper oxide is limited to a range of 2 to 15% in terms of CuO. Preferably it is 3 to 12%, More preferably, it is 4 to 9% of range.

Zinc oxide: more than 28% and not more than 33% in terms of ZnO Zinc is an element that affects Ts (or Tsr) in the temperature rise characteristics of the heating element by applying microwaves. In the present invention, Ts (or Tsr) can be arbitrarily set over a low temperature range of 30 to 100 ° C. by adjusting the amount of zinc oxide to more than 28% and 33% or less in terms of ZnO. Here, according to experiments by the inventors, the relationship between Ts (or Tsr) and the ZnO compounding ratio is approximated by the following equation (1).
Ts (or Tsr) (° C.) = − 10.5 × ZnO (%) + 374 (1)
As apparent from the above formula (1), Ts (or Tsr) decreases as the amount of zinc oxide increases, and when it exceeds 33% in terms of ZnO, Ts (or Tsr) becomes less than 30 ° C. Use is lost. On the other hand, Ts increases as the amount of zinc oxide decreases, and when the amount of zinc oxide becomes 28.0% or less in terms of ZnO, Ts increases.
Therefore, the amount of zinc oxide is limited to a range of more than 28.0% and not more than 33% in terms of ZnO. Preferably it is 29 to 32%, more preferably 30.5% or more and 32% or less.

Remainder: Magnesium oxide and inevitable impurities The amount of magnesium oxide which is the main component of the remainder is in the range of about 1 to 25% in terms of MgO. If the amount of magnesium oxide is less than 1% in terms of MgO, the compounding ratio of CuO or the like increases, and the raw material cost becomes expensive. On the other hand, if the amount of magnesium oxide exceeds 25% in terms of MgO, a foreign phase other than the ferrite phase tends to remain and the temperature rise characteristics deteriorate, which is not preferable. A more preferable range of the amount of magnesium oxide is 6 to 22% in terms of MgO.
Note that in the ferrite powder, the raw material composition and manufacturing process, SiO ₂ and Mn, Ca, but as Al and P in some cases be mixed as inevitable impurities, these are a total amount of 0.5% or less If there is no particular problem.

The component composition of the MgCuZn ferrite powder of the present invention has been described above. However, in the present invention, it is not sufficient that the component composition satisfies the above range, and it is important to keep the particle size of the ferrite powder within a predetermined range. is there.
Average particle size of ferrite powder: 2 to 500 μm
The particle size of the ferrite powder greatly affects the microwave absorption efficiency. When kneading the ferrite powder with the resin, in order to obtain a desired calorific value, it is desirable to add about 10-80 mass% ferrite powder with respect to the total amount with the resin, but when the particle size is finer than 2 μm, The microwave absorption efficiency of the microwave absorption heating element is lowered, and the heating rate and the reaching temperature of the heating element are lowered. On the other hand, if the particle size exceeds 500 μm, a heating element with a smooth surface cannot be obtained when used by adding to the resin.
Therefore, the average particle size of the ferrite powder according to the present invention is limited to the range of 2 to 500 μm. A preferred average particle size is in the range of 3 to 250 μm, more preferably 5 to 100 μm.
The average particle size in the present invention means a 50% particle size value (D ₅₀ ) obtained when measured with a laser diffraction particle size distribution meter. In the examples described below, it was sampled from the MgCuZn ferrite powder the prototype was measured D _50.

Next, the case where the heat generating body using the said ferrite powder is manufactured is demonstrated.
In the present invention, the above-described MgCuZn ferrite powder is contained in at least a part of the heating element or is included in the surface, whereby the microwave absorption heating element according to the present invention can be obtained. Of course, there is no problem even if the whole heating element is contained uniformly or appropriately segregated.
Accordingly, at least a part of the heating element in the present invention may be any of the above-mentioned inclusion forms.

First, Fe ₂ O ₃ , CuO, ZnO and MgO adjusted to the above preferred component composition are mixed as a starting material, pulverized or molded, and then heat-treated (fired) in the range of 850 to 1200 ° C. Ferrite is formed and then further pulverized or classified as necessary to adjust to a predetermined particle size. For the pulverization, a dry pulverizer such as an atomizer or a vibration mill is preferably used, but a wet pulverizer such as an attritor or a rotating ball mill may be used. For classification, a general classifier such as sieving or air classifier can be used.

At that time, the firing temperature described above has a great influence on the ferrite formation reaction and the crystal grain growth. If the firing temperature is less than 850 ° C., the ferrite formation reaction does not proceed sufficiently, unreacted Fe ₂ O ₃ , MgO, etc. may remain, which may reduce the microwave absorption heat generation performance, which is not preferable. . On the other hand, when the firing temperature exceeds 1200 ° C., a Cu ₂ O phase, which is a different phase, precipitates and the dielectric properties of the heating element change, which makes it impossible to obtain a temperature rise stop behavior, which is also not preferable.
Therefore, the firing temperature in the present invention is preferably in the range of 850 to 1200 ° C. More preferably, it is the range of 900-1150 degreeC. The firing time is not particularly limited but is preferably about 0.5 to 10 hours.
The MgCuZn ferrite powder of the present invention can also use a special ferrite raw material manufacturing method such as a mixed roasting method or a coprecipitation method.

  In the present invention, the MgCuZn ferrite powder obtained by the above method is added to a resin or rubber to produce a molded product, or the powder is filled into a bag, so that the ferrite powder is microwave-absorbing heating element. It can be used as a heating element by being contained in the surface, part or all of the above. Further, only ferrite powder (that is, 100 mass% ferrite powder) can be formed into a predetermined shape, and then fired to form a lump, and then used as a heating element.

  The process for producing the other MgCuZn ferrite powder and the process for producing the microwave-absorbing heating element are not particularly limited in the conditions, and may follow a so-called ordinary method.

Hereinafter, specific examples of the present invention will be described.
[Example 1]
The component composition ratio was fixed at 49% Fe ₂ O ₃ and 6% CuO, and the remaining ZnO and MgO were weighed so as to have the composition ratio shown in Table 1 and wet-mixed with a ball mill, then 900 It fired at ° C., then crushed and classified to obtain MgCuZn ferrite powder having an average particle diameter D ₅₀ = 45 to 55 μm.
After a small amount of polyvinyl alcohol (PVA) is added to the MgCuZn ferrite powder and mixed, it is molded into a plate-like shape having a vertical and horizontal size of 40 mm × 40 mm, a thickness of about 5 mm, and a mass of 30 g at 1100 ° C. An MgCuZn ferrite plate was produced by heat treatment.
The obtained MgCuZn ferrite plate was placed in a commercially available microwave oven, and the surface temperature of the MgCuZn ferrite plate when irradiated with a 500 W microwave for 10 to 90 seconds was measured with a radiation thermometer.
Here, the case where the difference between the surface temperatures of 70 seconds, 80 seconds, and 90 seconds was within 10 ° C. was regarded as the temperature increase stop state, and the average value of the surface temperature at that time was defined as the temperature increase stop temperature: Ts.
Table 1 shows the results obtained.

  As is clear from the table, it was confirmed that the temperature increase of the MgCuZn ferrite plate having the composition ratio range of ZnO and MgO according to the present invention was stopped in the temperature range of 30 to 100 ° C. On the other hand, Comparative Example 1 in which ZnO exceeds the upper limit of the present invention does not raise the temperature to 30 ° C. or higher even when irradiated with microwaves, and Comparative Example 2 in which ZnO does not satisfy the lower limit of the present invention is The temperature rise stop temperature exceeded 100 ° C.

[Example 2]
The component composition ratio is fixed at 31.5% ZnO, the remaining Fe ₂ O ₃ , CuO and MgO are weighed so as to have the composition ratio shown in Table 2, and wet-mixed with a ball mill, and then fired at 1000 ° C. Then, it was crushed and classified to obtain MgCuZn ferrite powder having an average particle diameter D ₅₀ = 40 to ₅₀ μm.
The MgCuZn ferrite powder was kneaded with silicon resin to prepare a resin sheet having a ferrite powder content of 70 mass%. A sheet sample having a size of 40 mm x 40 mm and cut to a thickness of about 1 mm is placed in a commercially available microwave oven, and the surface temperature of the sheet sample when irradiated with 500 W microwave for 10 to 90 seconds is set. Measured with a radiation thermometer.
Here, the case where the difference between the surface temperatures of 70 seconds, 80 seconds and 90 seconds was within 10 ° C. was regarded as the temperature rise stop state, and the average value of the surface temperature at that time was defined as the temperature rise stop temperature: Tsr.
Table 2 and FIG. 1 show the obtained results, respectively.

As is clear from Table 2 and FIG. 1, it was confirmed that the temperature increase of the sheet samples in the composition ratio range of Fe ₂ O ₃ , CuO and MgO according to the present invention was stopped in the temperature range of 30 to 100 ° C. It was. In contrast, Comparative Examples 5 and 7 cannot raise the temperature above 30 ° C. even when irradiated with microwaves, and Comparative Examples 3, 4, 6, and 8 can obtain a temperature rise stop behavior. There wasn't.

Example 3
Fe ₂ O ₃ , CuO, ZnO and MgO were weighed so that the component composition ratio would be the same molar ratio as in Example 6 shown in Table 2, and wet-mixed with a ball mill, and then at 950 ° C. in the atmosphere. And pulverized and classified for 2 hours to obtain MgCuZn ferrite powder with D ₅₀ = 1.5 to 549 μm as shown in Table 3.
Next, the obtained MgCuZn ferrite powder was kneaded with a silicon resin to prepare a resin sheet having a ferrite powder content of 70 mass%. Furthermore, the surface temperature of the sheet sample when a sheet sample having a size of 40 mm × 40 mm and cut to a thickness of about 1 mm is placed in a commercially available microwave oven and irradiated with 500 W microwave for 10 to 90 seconds. Was measured with a radiation thermometer.
Here, the case where the difference between the surface temperatures of 70 seconds, 80 seconds and 90 seconds was within 10 ° C. was regarded as the temperature rise stop state, and the average value of the surface temperature at that time was defined as the temperature rise stop temperature: Tsr.
Further, the surface state of the sheet was visually observed.
In Table 3, ◎ indicates that there is no unevenness, ○ indicates that there is slight unevenness, and × indicates that unevenness is apparently generated.
Table 3 shows the results obtained.

  As is clear from the table, the MgCuZn ferrite having a particle size range according to the present invention has a clear temperature rise stop behavior in the temperature range of 30 to 100 ° C. On the other hand, even if the comparative example 9 irradiated microwaves, it did not heat up exceeding 30 degreeC, and the comparative example 10 showed the unevenness | corrugation on the sheet | seat surface.

Example 4
A ferrite-containing resin sheet that stops heating at 60 ± 3 ° C. was prepared assuming a hot compress.
First, the component composition ratio was weighed so as to be Fe ₂ O ₃ : CuO: MgO: ZnO = 49: 6: 16.7: 28.3 (%), and dry-mixed with a vibration mill, then at 1000 ° C. Firing, then pulverizing and classifying to obtain an MgCuZn ferrite powder having an average particle diameter D ₅₀ = 60 μm.
Subsequently, the obtained MgCuZn ferrite powder was kneaded with a silicon resin to prepare a resin sheet having a ferrite powder content of 65 mass%. A sheet sample having a length and width of 40 mm × 40 mm and cut to a thickness of about 1.5 mm is placed in a commercially available microwave oven, and the temperature of the sheet surface when irradiated with 500 W microwave for 10 to 90 seconds is set. Measured with a radiation thermometer.
Similarly, a resin sheet having a heat generation powder content of 65 mass% is prepared using a commercially available heat generation powder (silicon carbide powder, D ₅₀ = 80 μm), and the length and width are 40 mm × 40 mm and the thickness is about 1.5 mm. The cut sheet sample was placed in a commercially available microwave oven, and the surface temperature of the sheet when irradiated with 500 W microwave for 10 to 90 seconds was measured with a radiation thermometer.

  FIG. 2 shows the obtained results. As is clear from the figure, the MgCuZn ferrite sheet according to the present invention (Invention Example 12) can be maintained at 60 ± 3 ° C. even if the temperature rises to 58 ° C. in 20 seconds and then microwave irradiation continues. . On the other hand, when the comparative example 11 is used at 60 ° C., it is necessary to stop the microwave in an extremely short time of about 12 to 15 seconds. This is because if the irradiation continues, the temperature will continue to rise above 100 ° C., which may cause burns and resin degradation.

As described above, as shown in each example, the MgCuZn ferrite powder according to the present invention is rapidly heated by microwave irradiation, and uses a plate-like sintered body of MgCuZn ferrite or a resin sheet containing MgCuZn ferrite powder. In the evaluation, the effect of the present invention was confirmed that the temperature increase stopped at a desired temperature in the temperature range of 30 to 100 ° C. In addition, in the above-mentioned Example, although the invention example which contains MgCuZn ferrite powder in the whole heat generating body was shown, if the MgCuZn ferrite powder according to the present invention is contained in a part of the heat generating body (including the surface layer), Similar to the above-described invention examples, it has been confirmed that it has good heat generation performance and temperature rise stop performance.

Claims (2)

46～51Mol% iron oxide in terms _{of Fe} 2 _{O 3,}
MgCuZn ferrite powder comprising 2 to 15 mol% copper oxide in terms of CuO and zinc oxide exceeding 28 mol% to 33 mol% in terms of ZnO, the balance being magnesium oxide and inevitable impurities,
The MgCuZn ferrite powder for microwave absorption heating elements, wherein the MgCuZn ferrite powder has an average particle size of 2 to 500 µm. A microwave absorption heating element that generates heat by absorbing microwaves,
A microwave absorption heating element comprising the MgCuZn ferrite powder according to claim 1 at least partially.

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