JP4885894B2 - NiCuZn ferrite tiles for radio wave absorption - Google Patents

Description

  The present invention is mainly used for an outer wall portion of a high-rise building and used for a tile for preventing reflection of electromagnetic waves such as TV radio waves or an inner wall of an anechoic chamber and absorbing radio waves from inside and outside the anechoic chamber. The preferred NiCuZn-based ferrite tile is intended to suppress the occurrence of warp without causing deterioration of radio wave absorption characteristics.

  Traditionally, NiCuZn ferrite with excellent anti-reflection and radio wave absorption characteristics in the frequency band of several hundreds of MHz (hereinafter simply referred to as radio wave absorption characteristics) as a TV wave anti-reflection tile or an electromagnetic wave absorption tile in an anechoic chamber Is used. As for the size of one tile used for such purposes, one with a side of about 100 mm and a thickness of about 5 to 10 mm is often used. To improve the work efficiency of tile installation work, A larger one is desired.

  In general, NiCuZn ferrite is widely used as magnetic core parts such as noise filters and choke coils. The size of such applications is often a rectangular parallelepiped with a side of 1 mm or less, such as a chip inductor, and the dimensions are up to about 30 mm even in the shape of a toroid or drum, and a small core is the mainstream.

Therefore, in the size of the magnetic core component, deformation hardly occurs during firing. On the other hand, the ferrite tile is much larger than the magnetic core component and has a small thickness with respect to the tile area, so that the tile itself is easily deformed during firing.
Since ferrite tiles for radio wave absorption are used by being laid on a wall, the parallelism of the surface is particularly important, and it is necessary to minimize warping as much as possible.

Factors that cause warping of the ferrite tile include a density difference inside the molded body during molding, a temperature difference inside the molded body during firing, and a difference in heat conduction between the molded body and the floorboard.
As countermeasures for these, it is conceivable to make the molding density uniform by optimizing the molding conditions, to eliminate the temperature difference inside the molded body by adjusting the temperature of the firing furnace, and to select the optimum floorboard.
However, in a plate shape such as a ferrite tile, it is extremely difficult to completely prevent deformation such as warpage.

Therefore, in order to correct the warped surface, the tile surface is ground after firing, or, as described in Patent Document 1, the compact is preferably sandwiched between two flat air ring fluids. Measures to prevent warping such as firing in
In addition, after producing a thick block fired body, a method of cutting several tiles from the block fired body is also conceivable.
However, in any method, an increase in manufacturing cost is unavoidable, and productivity is lowered.
JP-A-5-306164

  The present invention advantageously solves the above-described problems, and an object thereof is to propose a NiCuZn ferrite tile for radio wave absorption that effectively prevents warping without causing degradation of radio wave absorption characteristics. .

First, the inventors have a preferred content range of iron, nickel, copper and zinc, which are the main components of ferrite, in order to develop excellent radio wave absorption characteristics in a frequency band of several hundreds of MHz, which is required as a radio wave absorption tile. (In terms of Fe ₂ O ₃ , NiO, ZnO, and CuO, respectively) were determined.
Next, various studies were conducted on additives that can effectively suppress deformation such as warping when firing the ferrite having the above-described preferred composition.
As a result, it has been found that warping can be effectively prevented by adding a trace amount of calcium without deteriorating electromagnetic characteristics such as radio wave absorption characteristics.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. As basic components, iron, nickel, copper and zinc,
48.0-50.0 mol% in terms of Fe ₂ O ₃
10.0-16.0 mol% in terms of NiO,
3.0-7.0 mol% in terms of CuO and
29.0-35.0 mol% in terms of ZnO
However, Fe ₂ O ₃ + NiO + CuO + ZnO = 100 mol%
NiCuZn ferrite tiles contained in the range of
The ferrite tile contains calcium as an auxiliary component in an amount of 110 to 300 ppm in terms of Ca, and the ratio (A / unit mm ² ) of the area (A: unit mm ² ) of the flat plate portion to the thickness (B: unit mm) of the ferrite tile B) is 1000 to 450000 mm, a NiCuZn ferrite tile for absorbing radio waves, characterized in that

2. 2. The NiCuZn ferrite tile for absorbing radio waves according to claim 1, wherein a warp amount of the NiCuZn ferrite tile defined below is 0.5% or less.
Warpage (%) = (x / y) x 100
Here, x is in accordance with JIS A 5209 “Ceramic Ceramic Tile”, taking a base point on the diagonal of the tile surface with a distance of 4/5 or more of the length of the diagonal, and from the midpoint of a straight line connecting both base points The vertical distance (mm) to the surface of the tile. Moreover, y is the distance (mm) between both base points.

3. 3. The NiCuZn ferrite tile for wave absorption as described in 1 or 2 above, wherein the complex magnetic permeability at 100 MHz of the NiCuZn ferrite tile satisfies μ ′: 7.5 to 9.5 and μ ″: 75 to 90.

According to the present invention, the occurrence of warpage during firing can be effectively prevented, and there is no need to grind the warped portion as in the prior art, so there is no extra cost such as processing costs. In addition, a decrease in material yield due to grinding can be suppressed.
Furthermore, CaCO ₃ and CaO added as a Ca source for adjusting the Ca content are inexpensive, and in the present invention, since the addition amount is very small, the raw material cost is not increased.

Hereinafter, the present invention will be specifically described.
First, the reason why the composition range of the basic component is limited to the above range in the present invention will be described. The contents of the basic components Fe ₂ O ₃ , NiO, CuO and ZnO are expressed in mol%. Moreover, the total of these contents is 100 mol%.
Fe ₂ O ₃ : 48.0 to 50.0 mol%
Fe ₂ O ₃ is an element useful for improving the complex magnetic permeability μ ′ and μ ″, which is an index of radio wave absorption characteristics. However, if the content is less than 48.0 mol%, μ ′ and μ ″ are considered to be frequencies. On the other hand, there is a problem of overall decrease, while if it exceeds 50.0 mol%, the sinterability is reduced, and accordingly, μ ′ and μ ″ are also reduced overall with respect to the frequency. Fe ₂ O ₃ is limited to the range of 48.0 to 50.0 mol%, preferably Fe ₂ O ₃ : 48.5 to 49.8 mol%.

NiO: 10.0-16.0 mol%
NiO is an element useful for adjusting the frequency characteristics of the complex magnetic permeability μ ′ and μ ″. However, if the content is less than 10.0 mol%, μ ′ and μ ″ in a frequency band lower than several hundred MHz are Although improved, there is a problem that μ ′ and μ ″ at several hundred MHz, which is an object of the present invention, is reduced. On the other hand, when it exceeds 16.0 mol%, μ ′ and μ ″ at a frequency band higher than several hundred MHz However, NiO is limited to the range of 10.0 to 16.0 mol%, more preferably NiO: in the range of 11.0 to 13.0 mol%. is there.

CuO: 3.0-7.0 mol%
CuO contributes effectively to the improvement of sinterability, but when the content exceeds 7.0 mol%, the complex permeability μ ′ and μ ″ decreases as a whole with respect to the frequency, whereas it is less than 3.0 mol%. Since sinterability deteriorates and μ ′ and μ ″ decrease with respect to the frequency as a whole, CuO is limited to the range of 3.0 to 7.0 mol%. More preferably, it is CuO: It is the range of 4.0-6.0 mol%.

ZnO: 29.0-35.0 mol%
ZnO is an element useful for adjusting the frequency characteristics of the complex magnetic permeability μ ′ and μ ″, similar to NiO. However, if the content is less than 29.0 mol%, μO in a frequency band higher than several hundred MHz And μ ″ improve, but there is a problem that μ ′ and μ ″ at several hundred MHz decrease. On the other hand, if it exceeds 35.0 mol%, μ ′ and μ ″ at a frequency band lower than several hundred MHz improve. However, since μ ′ and μ ″ at several hundred MHz cause a disadvantage that it decreases, ZnO is limited to the range of 29.0 to 35.0 mol%. More preferably, ZnO is in the range of 30.0 to 33.0 mol%.

In the present invention, the NiCuZn-based ferrite tile having the basic composition described above contains a trace amount of Ca of 110 to 300 ppm as an accessory component, so that deformation such as warping can be effectively performed without deterioration of radio wave absorption characteristics. To prevent. The reason why the Ca content is limited to the above range is as follows.
Ca: 110-300 ppm
When the Ca content is less than 110 ppm, warpage is unavoidable. On the other hand, when the Ca content is more than 300 ppm, the warpage can be suppressed, but the radio wave absorption characteristics are degraded. Was limited to the range of 110-300 ppm. More preferably, the range of Ca is 140 to 240 ppm.

Further, in the present invention, as shown in FIG. 1, the shape of the ferrite tile is such that the thickness of the ferrite tile is B (mm) and the area of the flat plate portion is A (mm ² ). The area ratio (A / B) is limited to a range of 1000 to 450,000 mm.
The reason is as follows. This is because when A / B is smaller than 1000 mm, the tile thickness is relatively large with respect to the tile area, and thus there is little concern about the occurrence of warping. On the other hand, in the case of a ferrite tile having a shape in which A / B is larger than 450,000 mm, warpage is unavoidable regardless of the Ca content.

In addition, as a tile shape in this invention, it is preferable to set it as thickness B: 0.1-15mm of a ferrite tile, and area A: 10000-90000mm < ² > of a flat plate part.

  As described above, by appropriately adjusting the basic components and the tile shape and adding an appropriate amount of Ca, deformation such as warping during firing can be prevented. However, the mechanism of the warp suppressing effect at the time of firing the ferrite tile by adding Ca in the scope of the present invention has not yet been elucidated.

The target in the present invention is as follows for the warpage amount and the radio wave absorption characteristics.
Warpage amount In the present invention, the warpage amount defined by the following equation is targeted to be 0.5% or less.
Warpage (%) = (x / y) × 100
Where x: vertical distance (mm)
y: Distance between both base points (mm)
Here, as shown in FIG. 2, the vertical distance x is in accordance with JIS A 5209 “Ceramic Ceramic Tile”, with the base points separated by 4/5 or more of the length of the diagonal on the diagonal of the surface of the tile. It can be obtained by measuring the distance from the midpoint of the straight line connecting the base points to the surface of the tile. If the tile surface is square or rectangular, the base point is on the diagonal line as described above, but if the tile surface is circular, the base point is on the diameter, and if it is irregular, the base point is on the longest line on the surface. It ’s fine. A value obtained by dividing the vertical distance x by the distance y between both base points is defined as a warp (unit:%).

Radio wave absorption characteristics In the present invention, the radio wave absorption characteristics are evaluated by the complex permeability at 100 MHz. The case where μ ′ of the complex permeability is 7.5 to 9.5 and μ ″ satisfies the range of 75 to 90. It is said that it has excellent radio wave absorption characteristics.
Here, the complex permeability means that, when an alternating magnetic field H is applied to a magnetic material, when a phase lag occurs in the change of the magnetic flux density B, when a sine wave is complexly displayed, H ratio,
μ = B / H = μ′−jμ ″
Say. μ ′ and μ ″ are real numbers.

Next, the suitable manufacturing method of the ferrite tile according to this invention is demonstrated.
Fe ₂ O ₃ , NiO, ZnO, and CuO within the scope of the present invention are weighed and mixed by a wet or dry method using a mixer such as an attritor or a ball mill, and then calcined at 800 to 1000 ° C. After adding CaCO ₃ or CaO to the calcined powder so as to have a Ca content in the range of the present invention, using a mixer such as an attritor or a ball mill, wet or dry, pulverized average particle size: 1 to 2 μm Grind to the extent. A binder such as PVA is added to the pulverized powder, granulated using a spray dryer or a wire mesh, and then filled into a mold designed to have a tile shape within the scope of the present invention after firing and press molded. The obtained molded body was fired under firing conditions of a temperature increase rate of 30 to 240 ° C./h, a maximum temperature of 1000 to 1150 ° C., a maximum temperature holding time of 1 to 10 hours, and a temperature decrease rate of about 30 to 240 ° C./h. By doing so, it is possible to manufacture a ferrite tile in which warpage is suppressed. Moreover, the same effect can be acquired even if it adds Ca before calcination.
The ferrite tile of the present invention can also be applied to thin ferrites such as plate-like noise suppression ferrites used for ferrite substrates and ICs.

Example 1
Weighed so that the main components are Fe ₂ O ₃ : 49.5 mol%, NiO: 12.4 mol%, ZnO: 32.4 mol% and CuO: 5.7 mol%, and after dry mixing with a vibration ball mill, calcined at 900 ° C Then, CaCO ₃ was added so that the amount of Ca in the raw material was 40 to 600 ppm, and then wet pulverized with an attritor to obtain a raw material powder having an average particle size of 1.7 μm (air permeation method) . PVA as a binder was added to this and granulated with a spray dryer. The granulated powder is filled into a predetermined mold and press-molded, and then heated in an air atmosphere at a heating rate: 40 ° C./h, maximum temperature: 1050 ° C., maximum temperature holding time: 4 h. The temperature was increased at a rate of temperature increase of 40 ° C./h to obtain a ferrite tile of 100 mm × 100 mm × 6 mm (A = 10000 mm ² , B = 6 mm, A / B = 1667).
Table 1 shows the results of investigations on the warpage and radio wave absorption characteristics of the ferrite tile thus obtained.

In addition, the measurement of curvature was performed by the method mentioned above, and the acceptance standard of curvature was made into <= 0.5%.
Regarding the radio wave absorption characteristics, a toroidal core having an outer diameter of 10 mm, an inner diameter of 6 mm, and a height of 2 mm is cut out from the same tile, and the complex permeability μ at 100 MHz is measured using an impedance analyzer (Agilent Technology 4291A). Evaluation was made by measuring the electromagnetic characteristics of ', µ ". Acceptance criteria for µ' and µ" were 7.5 to 9.5 and 75 to 90, respectively.

  As is clear from the table, all of Invention Examples 1 to 8 containing an appropriate amount of Ca in the ferrite tile had a warp amount of 0.5% or less and excellent radio wave absorption characteristics.

Example 2
As the main components, Fe ₂ O ₃ , NiO, ZnO and CuO are weighed so as to have the composition shown in Table 2, and after dry mixing with a vibration ball mill, calcined at 870 ° C., then CaCO ₃ is added to the raw material. After adding Ca so that it might become 220 ppm, it wet-grinded with the attritor and obtained the raw material powder of average particle diameter: 1.5micrometer (air permeation method). PVA as a binder was added to this and granulated with a spray dryer. Next, the same tile and toroidal core as in Example 1 were manufactured under the same firing conditions as in Example 1, and the amount of warpage and complex permeability μ ′ and μ ″ at 100 MHz were measured.
The results obtained are shown in Table 2.

  As is clear from the table, all of Invention Examples 9 to 12 in which the basic components satisfy the appropriate range have a warp amount of 0.5% or less and excellent radio wave absorption characteristics.

Example 3
Weighed so that the main components are Fe ₂ O ₃ : 49.2 mol%, NiO: 12.7 mol%, ZnO: 32.6 mol%, and CuO: 5.5 mol%, and after dry mixing with a vibration ball mill, calcined at 910 ° C Then, CaCO ₃ was added so that the amount of Ca in the raw material was 230 ppm, and then wet pulverized with an attritor to obtain a raw material powder having an average particle size of 1.8 μm (air permeation method). PVA as a binder was added to this and granulated with a spray dryer. Next, tiles having the shapes shown in Table 3 were produced under the same firing conditions as in Example 1, and the warpage was measured. In addition, a toroidal core similar to that in Example 1 was produced, and complex magnetic permeability μ ′ and μ ″ at 100 MHz were measured.
The results obtained are shown in Table 3.

  As is clear from the table, each of Invention Examples 13 to 20 had a warpage amount of 0.5% or less and excellent radio wave absorption characteristics, but A / B was outside the proper range. In all 15, the amount of warpage exceeded 0.5%, and the tile shape was forced to deteriorate.

It is the figure which showed the relationship between thickness B (mm) of a ferrite tile, and the area of a flat plate part A (mm < ² >). It is the figure which showed the measuring point of the curvature amount of a ferrite tile.

Claims (3)

As basic components, iron, nickel, copper and zinc,
48.0-50.0 mol% in terms of Fe ₂ O ₃
10.0-16.0 mol% in terms of NiO,
3.0-7.0 mol% in terms of CuO and
29.0-35.0 mol% in terms of ZnO
However, Fe ₂ O ₃ + NiO + CuO + ZnO = 100 mol%
NiCuZn ferrite tiles contained in the range of
The ferrite tile contains calcium as an auxiliary component in an amount of 110 to 300 ppm in terms of Ca, and the ratio (A / unit mm ² ) of the area (A: unit mm ² ) of the flat plate portion to the thickness (B: unit mm) of the ferrite tile B) is 1000 to 450000 mm, a NiCuZn ferrite tile for absorbing radio waves, characterized in that 2. The NiCuZn ferrite tile for absorbing radio waves according to claim 1, wherein a warp amount of the NiCuZn ferrite tile defined below is 0.5% or less.
Warpage (%) = (x / y) x 100
Here, x is in accordance with JIS A 5209 “Ceramic Ceramic Tile”, taking a base point on the diagonal of the tile surface with a distance of 4/5 or more of the length of the diagonal, and from the midpoint of a straight line connecting both base points The vertical distance (mm) to the surface of the tile. Moreover, y is the distance (mm) between both base points.   The NiCuZn ferrite tile for wave absorption according to claim 1 or 2, wherein the complex permeability at 100 MHz of the NiCuZn ferrite tile satisfies μ ': 7.5 to 9.5 and µ ": 75 to 90. .

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