JP2007076985A - LOW LOSS Ni-Cu-Zn-BASED FERRITE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sintered article of a low loss Ni-Cu-Zn-based ferrite which is smaller in the core loss than conventional without being accompanied by the marked decrease of the saturated magnetic flux density. <P>SOLUTION: In Ni-Cu-Zn-based ferrites having a chemical composition of (Ni<SB>(1-a)</SB>Cu<SB>a</SB>)O-yZnO-zFe<SB>2</SB>O<SB>3</SB>, a low loss Ni-Cu-Zn-based ferrite for which x+y+z=100, 47.0≤z≤49.7, 18.0≤y≤28.0, 0.05≤a≤0.40, and which is formed by firing a raw material containing 0.02-0.50 wt.% of V<SB>2</SB>O<SB>5</SB>and 0.02-0.60 wt.% of TiO<SB>2</SB>as sub-components, can be reduced in core loss by about 10-20% as compared with the case of no addition of V<SB>2</SB>O<SB>5</SB>and TiO<SB>2</SB>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a low-loss Ni—Cu—Zn ferrite suitable for a transformer and choke coil used in a power supply circuit of a small electronic device.

  In portable electronic devices such as mobile phones, notebook PCs, and small game machines, in addition to increasing functions, the need to maintain and improve the power supply duration has been increasing. As a result, the demand for low power supply circuit elements has been increasing in recent years. . In order to improve the efficiency and miniaturization of the entire power supply circuit, it is extremely important to improve the characteristics of the ferrite material used as the core material of the coil in the power supply circuit. The technical requirements for the ferrite material used for the coil in the power supply circuit include the following items.

  First, a ferrite material having a high saturation magnetic flux density is required. This is because a magnetic core material having a higher saturation magnetic flux density is less likely to cause magnetic saturation even with a small core, and thus a small coil shape can be realized.

  Next, a low-loss ferrite material is required. In a coil core such as a transformer or a choke coil on a power supply circuit, the magnetic flux density changes at a frequency of several tens of kHz to several MHz. At this time, a loss (core loss) occurs due to irreversibility of the magnetization process. As the coil shape becomes smaller, the magnetic flux concentrates in a narrow region, and as a result, the amount of change in the magnetic flux density in the coil core increases. Since the loss in the ferrite material generally increases in proportion to the 2.5-3rd power of the change width of the magnetic flux density, in order to reduce the size of the coil without increasing the loss of the coil, the loss of the coil core material is low. Loss is necessary.

  Finally, a ferrite material having a large specific resistance is required. In particular, in the power supply circuits of portable electronic devices, it is considered that the degree of surface mounting integration will increase. In this case, a Ni—Cu—Zn ferrite material having a high electrical resistance that enables a series winding and a laminated structure is an optimal material as a coil core material at present.

  Here, as a Ni-Cu-Zn ferrite material for a coil core used for a power supply circuit of a portable electronic device, a core loss is 2000 mW / cc (excitation condition: frequency 500 kHz, with a material having a saturation magnetic flux density of 4400 G or more. For materials having a total excitation amplitude of 1000 G) or less and a saturation magnetic flux density of 4000 G or more and less than 4400 G, a material having a core loss of 1200 mW / cc (excitation conditions: frequency 500 kHz, excitation total amplitude 1000 G) or less is used. In response to conflicting demands for functional integration and extended power supply duration, there are now cases where these existing materials cannot respond. In order to reduce the cross-sectional area of the coil core by 20% while maintaining the same coil loss, the core loss is 1200 mW / cc (excitation condition: frequency 500 kHz, excitation total amplitude 1000 G) or less when the saturation magnetic flux density is 4400 G or more. A material having a magnetic flux density of 4000 G or more and less than 4400 G requires a material having a core loss of 800 mW / cc or less (excitation conditions: frequency 500 kHz, excitation total amplitude 1000 G).

Thus, in order to have a high saturation magnetic flux density, a low loss and a large specific resistance, in addition to the adjustment of the main component of the Ni—Cu—Zn ferrite material, V ₂ O ₅ which has a sintering promoting effect as a subsidiary component, core loss Due to the composite addition of TiO _{2 having} a reduction effect, a ferrite material satisfying the above requirements is expected.

Therefore, Patent Documents 1 and 2 disclose examples in which V ₂ O ₅ and TiO ₂ are added in combination to Ni—Cu—Zn ferrite.

Japanese Patent Laid-Open No. 06-084622 JP 2001-093718 A

However, the technique described in Patent Document 1 intends to improve the function as a radio wave absorber in a frequency region where the loss of the ferrite material is large, and the power source having a main component ZnO amount of 32 to 35 mol%. It is an incompatible composition region for circuit elements, and is not intended to reduce the loss of ferrite material by the combined addition of V ₂ O ₅ and TiO ₂ .

Further, in the technique described in Patent Document 2, the content of carbon in the ferrite sintered body is 96 ppm by weight, and the allowable addition amounts of V ₂ O ₅ and TiO ₂ are 0.0011% by weight, 0.00%, respectively. The purpose is to increase the bending strength by limiting to 012% by weight, and the composite addition of V ₂ O ₅ and TiO ₂ is not intended to reduce the loss of the ferrite material.

  As a general property of Ni—Cu—Zn-based ferrite, it is known that the core loss tends to increase in a composition having a large saturation magnetic flux density. However, in order to meet demands for miniaturization and high efficiency of power supply circuits of small electronic devices, a ferrite material having a high saturation magnetic flux density, a small core loss, and a large specific resistance value is required.

  Accordingly, an object of the present invention is to solve the above-described problems and provide a sintered body of low-loss Ni—Cu—Zn-based ferrite having a core loss smaller than that of the prior art without significantly reducing the saturation magnetic flux density. is there.

The present invention, the table because, Ni, Cu, Zn, as a main component an oxide of Fe, the chemical composition of _{x (Ni (1-a)} Cu a) O · yZnO · zFe 2 O 3 Solve the Problems In the Ni—Cu—Zn based ferrite, x + y + z = 100, 47.0 ≦ z ≦ 49.7, 18.0 ≦ y ≦ 28.0, 0.05 ≦ a ≦ 0.40, A low-loss Ni—Cu—Zn-based ferrite obtained by firing a raw material containing 0.02 to 0.50% by weight of V ₂ O ₅ and 0.02 to 0.60% by weight of TiO ₂ is there.

More specifically, in the Ni—Cu—Zn-based ferrite, when the Fe ₂ O ₃ content z is less than 47 mol%, the saturation magnetic flux density is clearly reduced, and the Fe ₂ O ₃ content z is 49.7 mol%. In the case of exceeding the value, the specific resistance tends to decrease clearly locally, which is not desirable. Further, when the ZnO content y is less than 18.0 mol%, the core loss is large and the initial magnetic permeability tends to decrease clearly. When the ZnO content y exceeds 28.0 mol%, the saturation magnetic flux density is clearly decreased. This is not desirable because the magnetic transition temperature Tc is lowered. Further, regarding the NiO / CuO ratio, when a is less than 0.05, the sintering temperature is increased, which is undesirable because an increase in core loss occurs. When a exceeds 0.40, the core loss tends to increase obviously. This is not desirable.

As for the additive as an accessory component, V ₂ O ₅ has a sintering promoting effect. By adding 0.02% by weight or more based on the total weight of the main component, the sintering temperature is lowered by about 50 ° C. Sintering at 980 ° C. or lower becomes possible, and at the same time, the core loss is reduced. TiO ₂ has the effect of expanding the sintering temperature range as well as the effect of reducing the core loss. By adding 0.02% by weight or more with respect to the total weight of the main component, the core loss is reduced by 10% or more, and V ₂ O _{5 is} added. Only by sintering at 1080 ° C. where a significant increase in core loss is observed, the core loss can be reduced by 10% or more compared to the composition containing no additive. On the other hand, when the amount of V ₂ O ₅ added exceeds 0.50% by weight, the core permeability is significantly increased along with the decrease in the initial magnetic permeability. When the added amount of TiO ₂ exceeds 0.60% by weight, the increase in core loss accompanying the decrease in initial permeability and the increase in sintering temperature is remarkable. As described above, the addition amounts of V ₂ O ₅ and TiO ₂ are respectively limited to 0.02 wt% or more and 0.5 wt% or less and 0.02 wt% or more and 0.60 wt% or less. Within this range, V ₂ O ₅ and TiO ₂ are simultaneously added and adjusted, that is, V ₂ O ₅ is limited to 0.15 to 0.40 wt% and TiO ₂ is limited to 0.05 to 0.40 wt%. Therefore, the core loss is 1200 mW / cc or less for materials with a saturation magnetic flux density of 4400 G or more (excitation conditions: frequency 500 kHz, excitation total amplitude 1000 G), and the core loss is 800 mW / cc for materials with a saturation magnetic flux density of 4000 G or more and less than 4400 G (excitation conditions: It was found that a spinel-type Ni—Cu—Zn-based ferrite sintered body having a frequency of 500 kHz and an excitation total amplitude of 1000 G) or less was obtained, and the fluctuation of the core loss value became smaller with respect to the fluctuation of the sintering temperature.

  Furthermore, it is also a low-loss Ni—Cu—Zn-based ferrite that is fired at a sintering temperature of 980 to 1060 ° C. so that the average crystal grain size of the fired body is 1.5 to 10 μm.

  Therefore, according to the present invention, it is a ferrite material having a higher saturation magnetic flux density, a smaller core loss, and a higher specific resistance value than the conventional composition without causing a significant decrease in the saturation magnetic flux density. Since the increase in the core loss accompanying the increase in the sintering temperature is suppressed, the labor for controlling the sintering temperature is reduced, and the low-loss Ni—Cu—Zn ferrite sintered body that can reduce the manufacturing cost and increase the yield rate. Can be provided.

  Next, embodiments of the low-loss Ni—Cu—Zn-based ferrite according to the present invention will be described with specific examples.

In a Ni—Cu—Zn based ferrite whose main component is an oxide of Ni, Cu, Zn, and Fe and whose chemical composition is represented by x (Ni _(1-a) Cu _a ) O · yZnO · zFe ₂ O ₃ , x + y + z = 100, 47.0 ≦ z ≦ 49.7, 18.0 ≦ y ≦ 28.0, 0.05 ≦ a ≦ 0.40, and V ₂ O ₅ as a subcomponent is 0.02 to 0. In the low-loss Ni—Cu—Zn-based ferrite characterized by containing 50 wt% and TiO ₂ in an amount of 0.02 to 0.60 wt%, the raw material powder is weighed so as to have the above-described composition, After wet mixing and dehydration treatment, calcination is performed at 700 to 850 ° C. for 2 to 10 hours. Thereafter, it is pulverized and granulated, formed into a required shape, and debindered. This is sintered in a sintering atmosphere having an oxygen concentration of 21% (in the air) at a temperature range of 900 ° C. to 1180 ° C. for 1 to 10 hours.

  In the present invention, it is desirable to select a sintering temperature range of 980 to 1060 ° C. so that the average crystal grain size is 1.5 to 10 μm as the sintering temperature. This is because it becomes difficult to increase the sintering density to obtain a large saturation magnetic flux density at a sintering temperature lower than this, and the irreversibility in the AC magnetization process increases at a sintering temperature higher than this. As a result, the increase in core loss becomes remarkable.

  Next, specific examples will be given to describe the low-loss Ni—Cu—Zn-based ferrite of the present invention in more detail.

Main component material powder _{x (Ni (1-a)} Cu a) O · yZnO · zFe 2 O 3 (x, y, z are mol%, x = 25.0, y = 26.0, z = 49. 0, a = 0.2), and V ₂ O ₅ and TiO ₂ as additives are added to the total weight of the main components as shown in Table 1, and after wet mixing, dehydration is performed. Then, after calcination at 800 ° C. for 2 hours in the air, pulverization and granulation were performed. Thereafter, this powder is pressure-molded into a toroidal shape having an outer diameter of 16 mm, an inner diameter of 10 mm, and a height of 5.0 mm at a pressure of 2000 kg / cm ² , and is baked at 950 to 1050 ° C. for 4 hours in an air atmosphere after debinding. Yui was done. The obtained sintered body had a saturation magnetization of 4πMs of about 4500 to 4800 G and an initial permeability of 500 to 550. The obtained core loss values (unit: mW / cc, excitation condition: frequency 500 kHz, excitation total amplitude 1000 G) are shown in Table 1.

As shown in Table 1, when V ₂ O ₅ and TiO _{2 are} added in amounts of 0.02 wt% to 0.50 wt% and 0.02 wt% to 0.60 wt%, V ₂ O _5. Compared with the case where TiO _{2 is} not added, the core loss is reduced by about 10%. Within this range, V ₂ O ₅ : 0.15 to 0.40 wt% and TiO ₂ : 0.05 to 0.40 wt% are compared with the case where V ₂ O ₅ and TiO _{2 are} not added. As a result, the core loss was reduced by about 20%.

Main component material powder _{x (Ni (1-a)} Cu a) O · yZnO · zFe 2 O 3 (x, y, z are mol%, x = 25.0, y = 26.0, z = 49. 0, blended with a = 0.2) ratio, further main component total weight V ₂ O _5, TiO _2, respectively 0.20 wt% with respect to, formulated as 0.40% by weight additives, wet-mixed Thereafter, dehydration treatment was performed, and calcination was performed in the air at 800 ° C. for 2 hours, followed by pulverization and granulation. Thereafter, this powder is pressure-molded into a toroidal shape having an outer diameter of 16 mm, an inner diameter of 10 mm, and a height of 5.0 mm at a pressure of 2000 kg / cm ² , and after baking for 4 hours at 940 to 1050 ° C. in an air atmosphere. Yui was done. The obtained sintered body had a saturation magnetization 4πMs of about 4400 to 4800 G and an initial permeability of 450 to 550. Table 2 shows the obtained core loss values (excitation conditions: frequency 500 kHz, excitation total amplitude 1000 G), saturation magnetic flux density B ₅₀ (under the condition of magnetic field ₅₀ Oe), and average crystal grain size. Here, the crystal grain size was obtained by mirror-polishing and drawing an arbitrary straight line on the micrograph of the surface of the sintered body etched in 140 ° C. phosphoric acid, and averaging the section lengths of 30 crystal grains.

As shown in Table 2, when the saturation magnetic flux density B ₅₀ is 4400 G or more and the average crystal grain size is in the range of 1.5 to 10.0 μm, the sintering temperature is 980 to 1060 ° C., and particularly the sintering temperature is When the average grain size exceeds 10 μm, the tendency to increase the core loss becomes remarkable. The tendency for the core loss to increase was also commonly seen in the plurality of sintered bodies shown in Table 1.

Claims (3)

In a Ni—Cu—Zn based ferrite whose main component is an oxide of Ni, Cu, Zn, and Fe and whose chemical composition is represented by x (Ni _(1-a) Cu _a ) O · yZnO · zFe ₂ O ₃ , x + y + z = 100, 47.0 ≦ z ≦ 49.7, 18.0 ≦ y ≦ 28.0, 0.05 ≦ a ≦ 0.40, and V ₂ O ₅ as a subcomponent is 0.02 to 0. A low-loss Ni—Cu—Zn-based ferrite obtained by firing a raw material containing 50 wt% and TiO ₂ in an amount of 0.02 to 0.60 wt%. _2. The low-loss Ni—Cu— according to claim 1, comprising 0.15 to 0.40 wt% of V ₂ O ₅ and 0.05 to 0.40 wt% of TiO ₂ as the subcomponents. Zn-based ferrite.   The low-loss Ni—Cu—Zn according to claim 1, wherein the sintered body is fired at a sintering temperature of 980 to 1060 ° C. such that an average crystal grain size of the fired body is 1.5 to 10 μm. Ferrite.