Ferrite sintered plate and ferrite sintered sheet

Abstract

The present invention relates to a ferrite sintered plate having a composition comprising 47 to 50 mol % of Fe.sub.2O.sub.3, 7 to 26 mol % of NiO, 13 to 36 mol % of ZnO, 7 to 12 mol % of CuO and 0 to 1.5 mol % of CoO, as calculated in terms of the respective oxides, in which the ferrite sintered plate has a volume resistivity of 110.sup.8 to 110.sup.12.Math.cm and a thickness of 10 to 60 m; and a ferrite sintered sheet comprising the ferrite sintered plate on a surface of which a groove or grooves are formed, and an adhesive layer and/or a protective layer formed on the ferrite sintered plate, in which the ferrite sintered sheet has a magnetic permeability at 500 kHz a real part of which is 120 to 800 and an imaginary part of which is 0 to 30, and a product (m) of the real part of the magnetic permeability at 500 kHz of the ferrite sintered sheet and a thickness of the ferrite sintered plate is 5000 to 48000. The ferrite sintered plate and the ferrite sintered sheet according to the present invention have a high volume resistivity as well as a large value and a small value of a magnetic permeability thereof, and therefore can be suitably used as a shielding plate in a digitizer system.

Claims

1. A ferrite sintered plate which has a composition comprising 47 to 50 mol % of Fe.sub.2O.sub.3, 7.0 to 15.1 mol % of NiO, 13 to 36 mol % of ZnO, 7.0 to 12 mol % of CuO and 0 to 1.5 mol % of CoO, as calculated in terms of the respective oxides, which has a volume resistivity of 110.sup.8 to 110.sup.12 cm and which has a thickness of 10 to 60 m, wherein the ferrite sintered plate has a magnetic permeability at 500 kHz a real part of which is 296 to 1200 and an imaginary part of which is 0 to 90.

2. The ferrite sintered plate according to claim 1, wherein a product (m) of the real part of the magnetic permeability at 500 kHz of the ferrite sintered plate and a thickness of the ferrite sintered plate is 7500 to 72000.

3. The ferrite sintered plate according to claim 1, wherein at least one groove is formed on at least one surface of the ferrite sintered plate and the depth of the at least one groove is 1/20 to of a thickness of the ferrite sintered plate.

4. A ferrite sintered sheet comprising the ferrite sintered plate according to claim 1, and an adhesive layer or a protective layer which is formed on at least one surface of the ferrite sintered plate.

5. A ferrite sintered sheet comprising the ferrite sintered plate according to claim 1, an adhesive layer formed on one surface of the ferrite sintered plate, and a protective layer formed on the other surface of the ferrite sintered plate.

6. A ferrite sintered sheet comprising the ferrite sintered plate according to claim 1, and adhesive layers respectively formed on opposite surfaces of the ferrite sintered plate.

7. A ferrite sintered sheet comprising the ferrite sintered plate according to claim 1, and protective layers respectively formed on opposite surfaces of the ferrite sintered plate.

8. The ferrite sintered sheet according to claim 4, wherein the ferrite sintered plate is partitioned into small pieces.

9. The ferrite sintered sheet according to claim 8, wherein the ferrite sintered sheet has a magnetic permeability at 500 kHz a real part of which is 120 to 800 and an imaginary part of which is 0 to 30, and a product of the real part of the magnetic permeability at 500 kHz of the ferrite sintered sheet and a thickness of the ferrite sintered plate is 5000 to 48000.

10. A digitizer system comprising a detector and a shielding plate disposed adjacent to the detector, in which the shielding plate is constituted of the ferrite sintered plate according to claim 1.

11. A digitizer system comprising a detector and a shielding plate disposed adjacent to the detector, in which the shielding plate is constituted of the ferrite sintered sheet according to claim 4.

Description

EXAMPLES

(1) Typical embodiments of the present invention are as follows.

(2) The composition of the ferrite sintered plate was measured using a fluorescent X-ray analyzer 3530 manufactured by Rigaku Corporation.

(3) The density of the ferrite sintered plate was calculated from an outer dimension and a weight of the ferrite sintered plate measured using calipers and a micrometer.

(4) The thickness of each of the ferrite sintered plate and the ferrite sintered sheet was measured using a micrometer.

(5) The value and the value of the ferrite sintered sheet subjected to partitioning treatment were measured as follows. That is, both the values of a ring member formed by punching the ferrite sintered sheet into a ring shape having an outer diameter of 20 mm and an inner diameter of 10 mm were measured at a frequency of 500 kHz using an impedance analyzer 4294A manufactured by Agilent Technologies.

(6) The value and the value of the ferrite sintered plate or the ferrite sintered sheet subjected to no partitioning treatment were measured as follows. That is, the ferrite sintered plate or the ferrite sintered sheet was cut into a ring shape having an outer diameter of 20 mm and an inner diameter of 10 mm by an ultrasonic processor to obtain a ring member, and both the and values of the thus obtained ring member were measured at a frequency of 500 kHz using an impedance analyzer 4294A manufactured by Agilent Technologies.

(7) The volume resistivity of the ferrite sintered plate was measured using any of a high resistance meter 4339B manufactured by Agilent Technologies and a resistance meter 3541 manufactured by Hioki E. E. Corp., according to the magnitude of the resistivity to be measured.

Example 1

(8) The respective raw material oxides were weighed such that a ferrite material obtained therefrom had a predetermined composition, and wet-mixed with each other for 20 hr using a ball mill. Thereafter, the resulting mixed slurry was subjected to filtration and then drying to obtain mixed particles as a raw material. The thus obtained mixed particles were calcined at 730 C. for 2 hr, and the resulting pre-calcined product was pulverized using a ball mill, thereby obtaining NiZnCu ferrite particles according to the present invention.

(9) Eight parts by weight of polyvinyl butyral as a binder material, 3 parts by weight of benzyl-n-butyl phthalate as a plasticizer and 50 parts by weight of 3-methyl-3-methoxy-1-butanol as a solvent were added to 100 parts by weight of the thus obtained NiZnCu ferrite particles, and then the resulting mixture was fully mixed to obtain a slurry. The thus obtained slurry was applied onto a PET film using a doctor blade-type coater to form a coating film thereon. The coating film was then dried to obtain a green sheet having a thickness of 43 m. Using a blade mold, grid-like grooves were formed on one surface of the green sheet.

(10) The resulting green sheet was degreased at 400 C., and then sintered at 960 C. for 2 hr, thereby obtaining a ferrite sintered plate. The thus obtained ferrite sintered plate had a composition comprising 47.1 mol % of Fe.sub.2O.sub.3, 9.9 mol % of NiO, 33.8 mol % of ZnO and 9.2 mol % of CuO, a volume resistivity of 310.sup.11.Math.cm, a thickness of 35 m, a density of 5.23 g/cm.sup.3, of 849 and of 34. In addition, the product (m) of the real part of the permeability and the thickness of the ferrite sintered plate was 29722.

(11) A PET film having a thickness of 5 m was attached onto one surface of the resulting ferrite sintered plate, and a double-sided tape having a thickness of 5 m was attached onto the other surface of the ferrite sintered plate, thereby obtaining a ferrite sintered sheet having a thickness of 45 m.

(12) The resulting ferrite sintered sheet was partitioned into small pieces using a roller, and the ferrite sintered sheet after being subjected to the partitioning treatment had of 535 and of 7. In addition, the product (m) of the real part of the magnetic permeability and the thickness of the ferrite sintered plate was 18725.

Examples 2 to 4

(13) Respective ferrite sintered plates and ferrite sintered sheets were produced by the same method as in Example 1. The production conditions used in the Examples and various properties of the thus obtained ferrite sintered plates and ferrite sintered sheets are shown in Table 1.

Comparative Example 1

(14) The respective raw material oxides were weighed such that ferrite obtained therefrom had a predetermined composition, and wet-mixed with each other for 20 hr using a ball mill. Thereafter, the resulting mixed slurry was subjected to filtration and drying to obtain mixed particles as a raw material. The thus obtained mixed particles were calcined at 1000 C. for 2 hr, and the resulting pre-calcined product was pulverized using a dry-type vibration mill, thereby obtaining NiZnCu ferrite particles. The thus obtained NiZnCu ferrite particles had a composition comprising 49.5 mol % of Fe.sub.2O.sub.3, 8.3 mol % of NiO, 35.0 mol % of ZnO and 7.2 mol % of CuO. The resulting NiZnCu ferrite particles were mixed with an ethylene-vinyl acetate copolymer such that the proportion of the NiZnCu ferrite particles in the obtained mixture was 60 vol %, and the resulting mixture was kneaded at 80 C. using a plastomill. The thus obtained kneaded material was formed into a sheet having a thickness of 50 m at 60 C. using a twin hot roll press. The thus obtained sheet had a volume resistivity of 710.sup.10.Math.cm, and of 16 and of 0 as measured at 500 kHz. In addition, the product (m) of and the thickness of the sheet was 800.

Comparative Example 2

(15) Flat iron-aluminum-silicon alloy particles (weight ratio of iron/aluminum/silicon: 85:6:9; aspect ratio: 20 to 30; average particle diameter: 40 m) were fully mixed in a solution prepared by dissolving 20% by weight of a styrene-based elastomer in cyclohexanone, in amounts calculated such that volume ratios of the alloy particles and the styrene-based elastomer after removing the solvent from the resulting mixture were 55% by volume and 45% by volume, respectively, thereby obtaining a slurry. At that time, ethyl cyclohexanone was added to the slurry in order to suitably control a viscosity of the slurry. The thus obtained slurry was applied onto a PET film using a doctor blade-type coater, and then dried. The resulting coated film was press-molded at a temperature of 130 C. and a pressure of 90 MPa for 5 min, thereby obtaining a sheet comprising the flat iron-aluminum-silicon alloy particles and having a thickness of 60 m. The resulting sheet had a volume resistivity of 310.sup.5.Math.cm, and of 110 and of 0 as measured at 500 kHz. In addition, the product (m) of and the thickness of the sheet was 6600.

Comparative Example 3

(16) A ferrite sintered plate and a ferrite sintered sheet were produced by the same method as in Example 1. The production conditions used in Comparative Example 3 and various properties of the thus obtained ferrite sintered plate and ferrite sintered sheet are shown in Table 1.

(17) TABLE-US-00001 TABLE 1 Fe.sub.2O.sub.3 NiO ZnO CuO CoO No. [mol %] [mol %] [mol %] [mol %] [mol %] Example 1 47.1 9.9 33.8 9.2 0.0 Example 2 49.9 7.8 35.2 7.1 0.0 Example 3 49.2 15.1 23.9 11.8 0.0 Example 4 48.8 25.8 14.0 11.4 0.0 Example 5 48.4 11.4 28.0 10.9 1.3 Comp. 49.5 8.3 35.0 7.2 0.0 Example 1 Comp. Example 2 Comp. 51.8 12.7 31.2 4.3 0.0 Example 3 Sintering Sintered Volume temperature density Thickness resistivity No. [ C.] [g/cc] [m] [.Math.cm] Example 1 960 5.23 35 .sup.3 10.sup.11 Example 2 920 5.16 15 3 10.sup.8 Example 3 880 5.13 60 2 10.sup.8 Example 4 860 5.08 50 4 10.sup.9 Example 5 905 5.15 45 .sup.8 10.sup.10 Comp. 50 .sup.7 10.sup.10 Example 1 Comp. 60 3 10.sup.5 Example 2 Comp. 1150 5.16 53 5 10.sup.3 Example 3 Before partitioning After partitioning thickness thickness No. at 500 kHz [m] at 500 kHz [m] Example 1 849 34 29772 535 7 18725 Example 2 1197 75 17950 718 20 10770 Example 3 296 0 17735 201 0 12060 Example 4 174 0 8681 125 0 6250 Example 5 511 0 22985 332 0 14940 Comp. 16 0 800 Example 1 Comp. 110 0 6600 Example 2 Comp. 456 0 24181 292 0 15476 Example 3

INDUSTRIAL APPLICABILITY

(18) The ferrite sintered plate and the ferrite sintered sheet according to the present invention have a high electric resistivity as well as a magnetic permeability having a large real part and a small imaginary part . Therefore, the ferrite sintered plate and the ferrite sintered sheet can be suitably used as a shielding plate for improving read sensitivity or positional accuracy in a digitizer system.