JP6412683B2 - Ferrite manufacturing method - Google Patents

Description

It relates to a manufacturing method of the present invention the ferrite, particularly to strength enhancement techniques of the ferrite.

  Ferrite, which is ceramic, includes manganese zinc-based ferrite (Ma—Zn-based ferrite), nickel-zinc-based ferrite (Ni—Zn-based ferrite), and the like depending on the composition of the main component including iron oxide. Ferrite is used, for example, as a ferrite core in a coil element. Generally, a ferrite core is manufactured by forming a powdery raw material constituting ferrite using a mold and firing the formed body.

  By the way, in recent years, various electronic devices have been rapidly reduced in size and weight, and the demand for downsizing of electronic components incorporated in electronic devices has been increasing. Therefore, further miniaturization is demanded for the ferrite core constituting the coil element as the electronic component.

  In order to manufacture an extremely small ferrite core, it is difficult to mold only with a mold as in the past. It is necessary to use it and grind it into a desired shape.

  However, ferrite has a problem that breakage such as chipping and cracking occurs during cutting. In coil elements intended for high-density surface mounting, a plurality of elements are simultaneously molded on a single substrate and separated into individual coil elements by subsequent dicing, so the ferrite core is damaged during the dicing process. there's a possibility that. Therefore, attempts to prevent the above-mentioned breakage during processing by improving the strength of the ferrite itself by improving the cutting and dicing processing technology, or changing the ferrite composition and ferrite manufacturing conditions, etc. Has been made. The following Patent Documents 1 to 3 describe techniques for improving the strength of ferrite.

Japanese Patent Laid-Open No. 2003-286071 JP 2005-104787 A JP-A-2005-213115

  About the method of preventing the breakage of the ferrite core by improving the cutting and dicing processing techniques, the manufacturing cost of the ferrite core increases because a complicated manufacturing process is required. In addition, since electronic devices in which small electronic components are incorporated are often mainly carried by users (cell phones, portable music players, etc.), there is a possibility that the devices may be shocked by dropping or the like. Always exists. Even if the breakage of the ferrite core at the time of manufacture is prevented by improving the processing technique, the damage cannot be prevented against an impact after processing such as dropping.

On the other hand, if the strength of the ferrite itself can be improved, it is possible to suppress an increase in cost and prevent damage due to impact after processing. As a method for improving the strength of ferrite, it is known that SiO ₂ is contained in ferrite as described in the above patent documents.

However, the effect of improving the strength of ferrite by containing SiO ₂ is based on the action of inhibiting the sinterability and suppressing the particle size of ferrite, so the particle size of SiO ₂ is controlled accurately and uniformly. In this case as well, there is a problem that process manufacturing costs increase.

In addition, there is a strength improvement technique for suppressing densification and cracking by interposing between the particles glass obtained by reacting SiO ₂ with alkali such as Na, but the reactivity of SiO ₂ and alkali is controlled. For this purpose, it is necessary to make the additive into a fine powder with a small particle size and to control the particle size with extremely high accuracy. That is, if the particle size is not uniform, a difference in reactivity occurs. As a result, a difference in strength improvement effect also occurs, and a desired strength cannot be obtained with good reproducibility.

Note in the above patent documents have been described for the particle size of the additives such as SiO _2, but there is wide in its value range, in practice, impossible to obtain the strength improving effect of the more expected. Therefore, even if there is a certain width in the range of the particle diameter, for example, even when defined by the average particle diameter, a ferrite having a uniform and high strength and a method for producing the ferrite are required.

  The present invention has been made to meet such a demand, and an object of the present invention is to provide an inexpensive and high-strength ferrite and a method for producing a high-strength ferrite at a low cost with high productivity.

In order to achieve the above object, the present invention provides a ferrite production comprising a sintered body containing, as a main component, Ni—Zn-based ferrite composed of Fe ₂ O ₃ , ZnO, CuO, and NiO, and SiO ₂ as an accessory component. A method,
A pre-firing step of pre-firing the mixture of raw materials as the main component at a temperature lower than the sintering temperature of the ferrite;
A pulverizing step for further pulverizing the powder obtained by the pre-baking step;
An addition step of adding the subcomponent having an average particle diameter B to the pulverized product obtained by the pulverization step;
A molding step for molding the pulverized product to which the subcomponent has been added in the addition step into a predetermined shape;
And sintering steps to obtain the sintered body by firing the molded body obtained by the molding step at a temperature lower than the melting point of the sub-components,
Including
In the pulverizing step, the main component in the sintered body after the sintering step is adjusted to have a predetermined average particle size A, and in the adding step, the subcomponent having a predetermined average particle size B is adjusted. By adding the above, the sintered body in which the ratio B / A of the average particle diameter A of the main component to the particle diameter B of the subcomponent is 0.5 <B / A ≦ 1 is obtained by the firing step. ,
This is a method for producing ferrite characterized by the above.

Further, in the method for producing ferrite, in the adding step, the subcomponent having an average particle size of 6 μm or more may be added. In the pulverizing step, the ferrite may be produced by adjusting the average particle size of the main component to 12 μm.

Ferrite manufactured by the manufacturing method of the present invention has a cutting or dicing, and the like cracking or chipping by the impact or the like after molding does not occur excellent strength characteristics when formed into a predetermined shape . Therefore, various electronic components using ferrite can be reduced in size and weight, and as a result, the electronic device in which the electronic component is incorporated contributes to reduction in size and weight.

It is a figure which shows an example of the manufacturing method of a ferrite. It is a figure which shows the intensity | strength characteristic of a ferrite. It is a figure which shows schematic structure of the ferrite which concerns on the Example of this invention.

=== Technical thought of the present invention ===
As described above, there is known a ferrite containing SiO ₂ as an additive in order to improve the strength of the ferrite. In the conventional method for improving the strength of ferrite, a fine powder additive is added to the main component of ferrite. However, there is a problem that it is necessary to control the particle diameter with high accuracy and it is difficult to obtain a uniform strength. Therefore, the present inventor combines the ferrites with SiO ₂ to improve the strength by the so-called “anchor effect”, and because SiO ₂ is a very hard substance, the particle diameter of SiO ₂ varies. In addition, it was considered that the strength of the ferrite particles was improved by inhibiting the propagation of cracks generated by impact or the like with SiO ₂ . The present invention has been made as a result of intensive studies with such a technical idea as a starting point.

=== Example ===
The ferrite according to the embodiment of the present invention is a sintered body containing Ni—Zn-based ferrite as a main component and SiO ₂ as an auxiliary component, and has a general composition. However, in the ferrite according to the example, for the purpose of improving the strength, the ratio of the average particle diameter (hereinafter also referred to as the particle size ratio) of SiO ₂ and Ni—Zn-based ferrite (hereinafter also referred to as the main component) is optimized. And has excellent strength characteristics.

=== Sample ===
In order to evaluate the characteristics of the ferrite according to the example of the present invention, various ferrites having different particle size ratios of SiO ₂ and main components were prepared as samples, and the strength of each sample was measured. FIG. 1 shows a sample preparation procedure, and the sample preparation procedure adopted here is a general one as described in, for example, Patent Document 1 described above.

Specifically, first, Ni—Zn ferrite raw materials, which are main components, are weighed and mixed (s1, s2). Here, the iron oxide is 49 mol% in terms of Fe ₂ O ₃ , the zinc oxide is 30 mol% in terms of ZnO, the copper oxide serving as a sintering aid is 6 mol% in terms of CuO, and the rest is NiO. Weighed out. Next, the raw material mixture of the main components is temporarily calcined in the atmosphere at 850 ° C. for 2 hours (s3), and the powder obtained by the calcining is pulverized with a ball mill (s4). The sub-component SiO ₂ is added to the pulverized powder (hereinafter also referred to as pulverized product) according to the sample (s5 → s6). The added amount of the auxiliary component is 0.01 wt% to 0.5 wt%, but 0.1 wt% was added here. If SiO ₂ and the above pulverized product are mixed, a binder (PVA aqueous solution or the like) is added to the mixture and granulated so as to form particles of an appropriate size (s7). Further, the granulated product is formed into a desired shape (s8). Here, it is formed into a rod shape having a width of 4 mm, a height of 3 mm, and a length of 45 mm. Then, the compact was fired at a temperature of 1070 ° C. for 1.5 hours to complete a ferrite made of a sintered body (s9). This ferrite was used as a sample (s8).

In the sample preparation procedure, the conditions of the pulverization step (s4) and the molding step (s8) are set so that the average particle diameter of the Ni—Zn-based ferrite crystals as the main component is 12 μm for all samples. It is adjusted. Depending on the sample, the SiO ₂ addition step (s6) is omitted (s5 → s7). With respect to the sample the addition of SiO _2, and changing the average particle diameter of SiO ₂ added to each sample type.

=== Characteristic evaluation ===
The firing density and the bending strength by a three-point bending strength test were measured for the samples prepared by the above-described procedure. Specifically, production conditions (presence of SiO ₂ added or added particles size of SiO _2,) was produced with seven different samples. In addition, five samples were prepared, and the bending strength (MPa) was measured according to the three-point bending strength test method based on JIS R1601, after measuring the firing density for five samples of each sample. . And the average value of the measured value with respect to the five individuals was taken as the characteristic of each sample.

  Table 1 below shows the bending strength and firing density of each sample.

Table 1 shows the average particle diameter, bending strength, and density of SiO ₂ added to each sample. Sample 1 is a ferrite to which no SiO ₂ is added, and is a Ni—Zn ferrite itself as a main component. Sample 2-7 is SiO ₂ added, the average particle diameter of SiO ₂ are different for each type of sample.

As shown in Table 1, with respect to the average density ρ _ave , sample 1 is 5.2 and the other samples 2 to 7 are 5.1, and the minimum density ρ _min of the five measured individuals is all samples. It was the same value as average density (rho) _{ave at} 1-7. That is, a sufficiently dense density of 5.0 or more could be secured, and there was no individual difference. Then, when the bending strength of each sample 1 to 7 was measured, the bending strength (average bending strength σ _ave , minimum bending strength σ _min ) increased as the particle diameter B of SiO ₂ increased. It was confirmed that However, the increasing trend is not a simple proportional relationship. Therefore, the average particle size of the main component was A, and the average particle size of SiO ₂ was B, and the relationship between the ratio of these average particle sizes (hereinafter referred to as particle size ratio) B / A and the bending strength was examined. FIG. 2 shows the relationship between the particle size ratio and the average bending strength σ _ave .

As shown in FIG. 2, the tendency of increasing the bending strength clearly changes when the particle size ratio B / A is 0.5. Since the average particle size of the main component can be appropriately changed according to the ferrite application and the intended magnetic properties, in the ferrite according to the embodiment of the present invention, the average particle size of the main component and the average of SiO ₂ The particle size ratio B / A with the particle size is greater than 0.5.

FIG. 3 schematically shows the structure of the ferrite (hereinafter also referred to as a sintered body) 1 of this example. The strength improvement effect in the sintered body 1 of the present example will be described based on FIG. 3. In the sintered body 1 according to the example, particles of Ni—Zn-based ferrite as a main component (hereinafter also referred to as ferrite particles). ) SiO ₂ particles 3 having high hardness are arranged around 2. At this time, even if the particle diameter φs of the SiO ₂ and the particle diameter φf of the ferrite particles vary, the average particle diameter B of the SiO ₂ is as large as 0.5 or more of the average particle diameter A of the ferrite, so that the adjacent ferrite There is a high probability that the SiO ₂ particles 3 are interposed between the particles (2-2).

In the sintered body 1 having such a structure, even if some of the Ni—Zn-based ferrite particles 2 are damaged by an impact or the like and a fine crack is generated, they are interposed between adjacent ferrite particles (2-2). The large and hard (high-strength) SiO ₂ particles 3 inhibit the propagation of cracks between the ferrite particles (2-2). This makes it difficult for the sintered body 1 to break.

In the above embodiment, defines the minimum value of the particle size ratio B / A, for the maximum value, greater than 1 and sintered in 1 volume of ferrite particles 2 of SiO ₂ particles 3 It can be easily imagined that it is difficult to obtain uniform magnetic characteristics by generating a portion smaller than the volume. Therefore, it is realistic that the maximum value of the particle size ratio B / A is 1. In the above embodiment, the average particle diameter of the main component is set to 12 μm in consideration of productivity. Therefore, if the average particle diameter B of SiO ₂ is larger than 6 μm, the strength is more reliably ensured while ensuring the productivity. Can be improved.

  The present invention can be used for a ferrite core constituting a coil element.

1 Ferrite (sintered body), 2 Ni-Zn ferrite particles (ferrite particles),
3 SiO ₂ particles, s1 main component raw material weighing step, s2 main component raw material mixing step,
s3 preliminary firing step, s4 grinding step, s5 SiO ₂ addition step, s7 granulation step,
s8 molding process, s9 firing process

Claims (3)

A method for producing a ferrite comprising a sintered body containing, as a main component, Ni—Zn-based ferrite composed of Fe ₂ O ₃ , ZnO, CuO, NiO and SiO ₂ as a subcomponent ,
A pre-firing step of pre-firing the mixture of raw materials as the main component at a temperature lower than the sintering temperature of the ferrite;
A pulverizing step for further pulverizing the powder obtained by the pre-baking step;
An addition step of adding the subcomponent having an average particle diameter B to the pulverized product obtained by the pulverization step;
A molding step for molding the pulverized product to which the subcomponent has been added in the addition step into a predetermined shape;
And sintering steps to obtain the sintered body by firing the molded body obtained by the molding step at a temperature lower than the melting point of the sub-components,
Including
In the pulverizing step, the main component in the sintered body after the sintering step is adjusted to have a predetermined average particle size A, and in the adding step, the subcomponent having a predetermined average particle size B is adjusted. The sintered body in which the ratio B / A of the average particle diameter A of the main component and the average particle diameter B of the subcomponent is 0.5 <B / A ≦ 1 is obtained by the baking step. obtain,
A method for producing ferrite, characterized in that 2. The method for producing ferrite according to claim 1, wherein in the adding step, the subcomponent having an average particle diameter B of 6 [mu] m or more is added. 3. The method for producing ferrite according to claim 2, wherein in the pulverizing step, an average particle diameter A of the main component is adjusted to 12 [mu] m.

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