EP0272148A2 — Plate-like magnetoplumbite type ferrite particles…

Claim 1

Independent Claim 72 words

Ba-containing plate-like magnetoplumbite-type ferrite particles suitable for magnetic recording, which particles contain ions of one metal (II) selected from Ni and Zn and ions of one metal (IV) selected from Ti, Sn and Zr, have zinc incorporated as a solid solution close to the particle surface and exhibit a change of coercive force at a temperature of from -20 to 120°C of from -39.8 to +39.8 A m⁻¹/°C (-0.5 to +0.5 Oe/°C).

Claim 2

Dependent Claim 72 words

Ba-containing plate-like magnetoplumbite-type ferrite particles suitable for magnetic recording, which particles contain ions of one metal (II) selected from Ni and Zn and ions of one metal (IV) selected from Ti, Sn and Zr, have zinc incorporated as a solid solution close to the particle surface and exhibit a change of coercive force at a temperature of from -20 to 120°C of from -39.8 to +39.8 A m⁻¹/°C (-0.5 to +0.5 Oe/°C).

Claim 3

Dependent Claim 55 words

Particles according to claim 1, which have an average diameter of from 0.08 to 0.20 µm, a coercive force of from 4.38 × 10⁴ to 7.80 × 10⁴ A m⁻¹(550 to 980 Oe), a magnetization of not less than 51.6 A m²/kg (51.6 emu/g) and an erasing characteristic value of not less than 27 dB.

Claim 4

Dependent Claim 24 words

Particles according to claim 1 or 2, wherein the amount of zinc incorporated as a solid solution is from 0.5 to 5.0% by weight.

Claim 5

Dependent Claim 51 words

Particles according to any one of the preceding claims, which contain from 5.0 to 13.0 atom % based on Fe (III) of the said metal selected from Ni and Zn and from 3.0 to 13.0 atom % based on Fe (III) of said metal (IV) selected from Ti, Sn and Zr.

Claim 6

Dependent Claim 149 words

A process for producing plate-like magnetoplumbite-type ferrite particles suitable for magnetic recording, which process comprises: (i) subjecting an alkaline iron hydroxide (III) suspension containing ions of one metal (II) selected from Ni and Zn, ions of one metal (IV) selected from Ti, Sn and Zr, and Ba or Sr ions to an autoclaving treatment at a temperature of from 150 to 330°C to produce the plate-like magnetoplumbite-type ferrite particles containing the metals (II) and (IV), (ii) suspending the said particles in a zinc ion-containing aqueous solution of pH 4.0-12.0 to obtain plate-like magnetoplumbite-type ferrite particles containing the metals (II) and (IV) and having a hydroxide of zinc deposited on the particle surface, (iii) after filtering the said particles obtained in step (ii), heating and calcining the particles at a temperature of from 600 to 900°C so that zinc is incorporated as a solid solution close to the particle surface.

Claim 7

Dependent Claim 149 words

A process for producing plate-like magnetoplumbite-type ferrite particles suitable for magnetic recording, which process comprises: (i) subjecting an alkaline iron hydroxide (III) suspension containing ions of one metal (II) selected from Ni and Zn, ions of one metal (IV) selected from Ti, Sn and Zr, and Ba or Sr ions to an autoclaving treatment at a temperature of from 150 to 330°C to produce the plate-like magnetoplumbite-type ferrite particles containing the metals (II) and (IV), (ii) suspending the said particles in a zinc ion-containing aqueous solution of pH 4.0-12.0 to obtain plate-like magnetoplumbite-type ferrite particles containing the metals (II) and (IV) and having a hydroxide of zinc deposited on the particle surface, (iii) after filtering the said particles obtained in step (ii), heating and calcining the particles at a temperature of from 600 to 900°C so that zinc is incorporated as a solid solution close to the particle surface.

Claim 8

Dependent Claim 62 words

A process according to claim 5, wherein in step (i) the said metal (II) selected from Ni and Zn is present in an amount of from 5.0 to 13.0 atom % based on Fe (III) and the said metal (IV) selected from Ti, Sn and Zr is present in an amount of from 3.0 to 13.0 atom % based on Fe (III).

Claim 9

Dependent Claim 79 words

A process according to claim 5 or 6, wherein in step (i) an alkaline iron hydroxide (III) suspension is employed which contains a chloride, nitrate or acetate of Ni or Zn; titanium tetraoxide, titanium sulfate, tin tetrachloride, sodium stannate or zirconium oxychloride; and barium hydroxide, barium chloride, barium nitrate, strontium hydroxide, strontium chloride or strontium nitrate and in step (ii) an aqueous solution of zinc chloride, zinc bromide, zinc iodide, zinc nitrate, zinc sulfate or zinc acetate is employed.

Claim 10

Dependent Claim 31 words

A process according to any one of claims 5 to 7, wherein the temperatures in steps (i) and (iii) are from 180 to 300°C and from 700 to 900 °C respectively.

Claim 11

Dependent Claim 46 words

A process according to any one of claims 5 to 8, wherein in step (iii) the heating for calcining the particles obtained in step (ii) is carried out by using at least one flux selected from halides and sulfates of alkali metals and alkali earth metals.

Claim 12

Independent Claim 56 words

A method of preparing a magnetic recording medium, which method comprises preparing the said medium using Ba-containing plate-like magnetoplumbite-type ferrite particles as claimed in any one of claims 1 to 4 or which have been produced by a process as claimed in any one of claims 5 to 9 as the magnetic particles for the medium.

Plate-like magnetoplumbite type ferrite particles for magnetic recording and process for producing the same

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