CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Japanese Patent Application No. 2017-187171, filed Sep. 27, 2017, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a core-shell particle, a calcinated product of a core-shell particle, a manufacturing method of a core-shell particle, an epsilon type iron oxide-based compound particle, a manufacturing method of an epsilon type iron oxide-based compound particle, a magnetic recording medium, and a manufacturing method of a magnetic recording medium.

2. Description of the Related Art

Epsilon type iron oxide (ε-Fe2O3) is drawing an attention as an excellent magnetic material due to coercivity which is three times the coercivity of a ferrite magnet.

As a method of synthesizing epsilon type iron oxide, a method of calcinating FeCo alloy powder included in a matrix formed of SiO2has been known (for example, see JP2015-153918A).

In addition, a method of synthesizing epsilon type iron oxide by a reverse micelle method performed by using a raw material micelle including iron (III) nitrate nonahydrate and a neutralizer micelle including ammonia water has been known (for example, see JP5347146B).

Further, a method of synthesizing single-phase epsilon type iron oxide from sol of iron (III) oxide hydroxide nano fine particles (β-FeO(OH)) having an average particle diameter of approximately 6 nm has been known (for example, see JP2014-224027A).

SUMMARY OF THE INVENTION

In a case of using epsilon type iron oxide as a magnetic material, characteristics such as a small primary particle diameter of epsilon type iron oxide particles and a small coefficient of variation of the primary particle diameter (that is, a small variation in primary particle diameter) are important, from viewpoints of magnetic recording density and a signal-to-noise ratio (SNR) of a magnetic recording medium, for example.

However, according to the synthesis methods of epsilon type iron oxide of the related art, calcinating is performed in a state where the unsettled number of epsilon type iron oxide precursors are included in silica present in a matrix shape. Thus, the calcinated epsilon type iron oxide is aggregated, and a primary particle diameter of the epsilon type iron oxide particles and a coefficient of variation of the particle diameter tend to increase. In a case where the primary particle diameter of the epsilon type iron oxide particles and the coefficient of variation of the particle diameter are great, an SNR and running durability of a magnetic recording medium (for example, a magnetic tape) using the epsilon type iron oxide particles are deteriorated.

In addition, even in a case where an average primary particle diameter of the epsilon type iron oxide particles of the related art is comparatively small (for example, equal to or smaller than 15 nm), it cannot be said that a coefficient of variation of the primary particle diameter is sufficiently small, and thus, in a case of using the epsilon type iron oxide particles in a magnetic recording medium (for example, a magnetic tape), an SNR and running durability are deteriorated.

In these circumstances, an object of one embodiment of the invention is to provide core-shell particles which can provide, by being calcinated, epsilon type iron oxide-based compound particles having a small coefficient of variation of primary particle diameter and showing excellent SNR and running durability when employed in a magnetic recording medium.

Another object of the embodiment of the invention is to provide a method of manufacturing core-shell particles capable of being obtained from epsilon type iron oxide-based compound particles having a small coefficient of variation of primary particle diameter and showing excellent SNR and running durability when employed in a magnetic recording medium is obtained.

Still another object of the embodiment of the invention is to provide calcinated products of core-shell particles, including epsilon type iron oxide-based compound particles having a small coefficient of variation of primary particle diameter and showing excellent SNR and running durability when employed in a magnetic recording medium.

Still another object of the embodiment of the invention is to provide epsilon type iron oxide-based compound particles having a small coefficient of variation of primary particle diameter and showing excellent SNR and running durability when employed in a magnetic recording medium.

Still another object of the embodiment of the invention is to provide a manufacturing method of epsilon type iron oxide-based compound particles having a small coefficient of variation of primary particle diameter and showing excellent SNR and running durability when employed in a magnetic recording medium.

Still another object of the embodiment of the invention is to provide a magnetic recording medium which includes epsilon type iron oxide-based compound particles having a small coefficient of variation of primary particle diameter, and shows excellent SNR and running durability.

Still another object of the embodiment of the invention is to provide a manufacturing method of a magnetic recording medium which includes epsilon type iron oxide-based compound particles having a small coefficient of variation of primary particle diameter, and shows excellent SNR and running durability.

Specific means for achieving the aforementioned objects include the following aspects.

<1> A core-shell particle comprising:

a core including at least one iron oxide selected from the group consisting of Fe2O3and Fe3O4, or iron oxyhydroxide; and

a shell that coats the core, the shell including a polycondensate of a metal alkoxide and including a metal element other than iron.

<2> The core-shell particle according to <1>, wherein one core-shell particle comprises one core.

<3> The core-shell particle according to <1> or <2>, wherein the metal element is at least one metal element selected from the group consisting of Ga, Al, In, Nb, Co, Zn, Ni, Mn, Ti and Sn.

<4> The core-shell particle according to any one of <1> to <3>, wherein the at least one iron oxide selected from the group consisting of Fe2O3and Fe3O4comprises a spinel type structure.

<5> The core-shell particle according to any one of <1> to <3>, wherein the iron oxyhydroxide comprises β-iron oxyhydroxide.

<6> The core-shell particle according to any one of <1> to <5>, wherein the metal alkoxide comprises silicon.

<7> The core-shell particle according to <6>, wherein an element mass ratio of iron with respect to silicon is from 1/2 to 1/15.

<8>

A method of manufacturing a core-shell particle, the method comprising:

emulsifying, in an organic solvent including a surfactant, a core component including at least one iron oxide selected from the group consisting of Fe2O3and Fe3O4, or iron oxyhydroxide; and

coating the core formed by the emulsifying with a shell comprising a polycondensate of a metal alkoxide and comprising a metal element other than iron.

<9> The method of manufacturing a core-shell particle according to <8>, wherein the surfactant comprises a nonionic surfactant.

<10> The method of a manufacturing core-shell particle according to <8> or <9>, wherein one core-shell particle is formed with respect to one core.

<11> The method of manufacturing a core-shell particle according to any one of <8> to <10>, wherein the metal element is at least one kind of metal element selected from the group consisting of Ga, Al, In, Nb, Co, Zn, Ni, Mn, Ti and Sn.

<12> The method of manufacturing a core-shell particle according to <8> to <11>, wherein the at least one iron oxide selected from the group consisting of Fe2O3and Fe3O4comprises a spinel type structure.

<13> The method of manufacturing a core-shell particle according to any one of <8> to <11>, wherein the iron oxyhydroxide comprises β-iron oxyhydroxide.

<14> The method of manufacturing a core-shell particle according to any one of <8> to <13>, wherein the metal alkoxide comprises silicon.

<15> The method of manufacturing a core-shell particle according to <14>, wherein an element mass ratio of iron with respect to silicon in the core-shell particle is from 1/2 to 1/15.

<16> A method of manufacturing an epsilon type iron oxide-based compound particle, the method comprising: forming the core-shell particle according to any one of <1> to <7>; calcinating the core-shell particle; and removing a shell of the core-shell particle.

<17> A method of manufacturing an epsilon type iron oxide-based compound particle, the method comprising: forming a core-shell particle according to the method of manufacturing a core-shell particle according to any one of <8> to <15>; calcinating the core-shell particle; and removing a shell of the core-shell particle.

<18> A method of manufacturing a magnetic recording medium, the method comprising: forming an epsilon type iron oxide-based compound particle according to the method of <16>; preparing a composition for forming a magnetic layer, the composition comprising the epsilon type iron oxide-based compound particle; applying the composition for forming a magnetic layer onto a non-magnetic support; and drying the composition for forming a magnetic layer on the non-magnetic support to form a magnetic layer.

<19> A method of manufacturing a magnetic recording medium, the method comprising:

forming an epsilon type iron oxide-based compound particle according to the method of <17>; preparing a composition for forming a magnetic layer, the composition comprising the epsilon type iron oxide-based compound particle; applying the composition for forming a magnetic layer onto a non-magnetic support; and drying the composition for forming a magnetic layer on the non-magnetic support to form a magnetic layer.

<20> An epsilon type iron oxide-based compound particle, in which an average primary particle diameter is 6.0 nm to 20 nm, and a coefficient of variation of primary particle diameter is smaller than 0.4.

<21> The epsilon type iron oxide-based compound particle according to <18>, which is a core of a calcinated product of the core-shell particle according to any one of <1> to <7>.

<22> A magnetic recording medium comprising: the epsilon type iron oxide-based compound particle according to <18> or <19>.

<23> A method of manufacturing a magnetic recording medium, the method comprising: preparing a magnetic layer forming composition including the epsilon type iron oxide-based compound particle according to <18> or <19>; applying the magnetic layer forming composition onto a non-magnetic support; and drying the magnetic layer forming composition on the non-magnetic support to form a magnetic layer.

<24> A calcinated product of the core-shell particle according to any one of <1> to <7>.

According to this disclosure, it is possible to provide a core-shell particle which can provide, by being calcinated, epsilon type iron oxide-based compound particles having a small coefficient of variation of primary particle diameter and showing excellent SNR and running durability when employed in a magnetic recording medium.

According to this disclosure, it is possible to provide a method of manufacturing core-shell particles which can provide, by being calcinated, epsilon type iron oxide-based compound particles having a small coefficient of variation of primary particle diameter and showing excellent SNR and running durability when employed in a magnetic recording medium.

According to this disclosure, it is possible to provide a calcinated product of the core-shell particle including epsilon type iron oxide-based compound particles having a small coefficient of variation of primary particle diameter and showing excellent SNR and running durability when employed in a magnetic recording medium.

According to this disclosure, it is possible to provide epsilon type iron oxide-based compound particles having a small coefficient of variation of primary particle diameter and showing excellent SNR and running durability when employed in a magnetic recording medium.

According to this disclosure, it is possible to provide a method of manufacturing epsilon type iron oxide-based compound particles having a small coefficient of variation of primary particle diameter and showing excellent SNR and running durability when employed in a magnetic recording medium.

According to this disclosure, it is possible to provide a magnetic recording medium which includes epsilon type iron oxide-based compound particles having a small coefficient of variation of primary particle diameter, and shows excellent SNR and running durability.

According to this disclosure, it is possible to provide a method of manufacturing a magnetic recording medium which includes epsilon type iron oxide-based compound particles having a small coefficient of variation of primary particle diameter, and shows excellent SNR and running durability.

