U.S. patent application number 11/641004 was filed with the patent office on 2009-09-17 for reverse micelle nethod of producing core/shell particles.
This patent application is currently assigned to FUJIFILM Corporation. Invention is credited to Takashi Koike.
Application Number | 20090232992 11/641004 |
Document ID | / |
Family ID | 41063330 |
Filed Date | 2009-09-17 |
United States Patent
Application |
20090232992 |
Kind Code |
A1 |
Koike; Takashi |
September 17, 2009 |
REVERSE MICELLE NETHOD OF PRODUCING CORE/SHELL PARTICLES
Abstract
A core/shell particle which includes a core component that
contains a metal, and a shell component that coats the core
component, the shell component including a a hydrolysate and/or a
partial condensate of a compound represented by the formula
"(R).sub.m-A(X).sub.4-m", wherein R represents a substituted or
unsubstituted alkyl group or the like, A represents Si or Ti, X
represents a hydroxyl group or the like, and m represents an
integer of 1 to 3. Furthermore, a method of producing a core/shell
particle is provided.
Inventors: |
Koike; Takashi;
(Ashigarakami-gun, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W., SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
FUJIFILM Corporation
Minato-ku
JP
|
Family ID: |
41063330 |
Appl. No.: |
11/641004 |
Filed: |
December 19, 2006 |
Current U.S.
Class: |
427/384 ;
428/403; 428/405 |
Current CPC
Class: |
B22F 2003/248 20130101;
Y10T 428/2995 20150115; B22F 2998/10 20130101; Y10T 428/2991
20150115; C22C 2202/02 20130101; H01F 1/065 20130101; H01F 1/068
20130101; B22F 1/0018 20130101; H01F 1/09 20130101; B82Y 30/00
20130101; B22F 1/0062 20130101; H01F 1/061 20130101; B22F 2998/10
20130101; B22F 9/24 20130101; B22F 1/0062 20130101; B22F 3/24
20130101 |
Class at
Publication: |
427/384 ;
428/405; 428/403 |
International
Class: |
B05D 3/02 20060101
B05D003/02; B32B 15/02 20060101 B32B015/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 19, 2005 |
JP |
2005-365301 |
Claims
1. A core/shell particle comprising a core component that contains
a metal, and a shell component that coats the core component, the
shell component including a hydrolysate and/or a partial condensate
of a compound represented by the following formula (I):
(R).sub.m-A(X).sub.4-m Formula (I) wherein in formula (I), R
represents a substituted or unsubstituted alkyl group, or a
substituted or unsubstituted aryl group; A represents Si or Ti; X
represents a hydroxyl group or a hydrolyzable group; and m
represents an integer of 1 to 3.
2. The core/shell particle according to claim 1, wherein a ratio
(A/metal) of A included in the shell component to the metal
included in the core component is in a range of 30 to 200% in terms
of the atomic percentage.
3. The core/shell particle according to claim 1, the core shell
particle being magnetic.
4. The core/shell particle according to claim 1, wherein the core
component comprises a ferromagnetic ordered alloy phase of at least
one of a CuAu type or a Cu.sub.3Au type.
5. The core/shell particle according to claim 1, wherein a ratio
(A/metal) of A included in the shell component to the metal
included in the core component is in a range of 50 to 100% in terms
of the atomic percentage.
6. The core/shell particle according to claim 1, wherein the core
component has a particle diameter of 1 to 20 nm.
7. The core/shell particle according to claim 1, wherein in formula
(I), X is an alkoxy group.
8. The core/shell particle according to claim 1, wherein in formula
(I), m is 1 or 2.
9. The core/shell particle according to claim 1, wherein in formula
(I), m is 2 or 3; and at least one R is a substituted alkyl group
or a substituted aryl group.
10. The core/shell particle according to claim 1, wherein in
formula (I), A represents Si.
11. A method of producing a core/shell particle comprising: forming
a core component by mixing a reverse micelle solution (I) including
a reducing agent with one or more reverse micelle solutions (II)
including a metal salt, and carrying out a reduction treatment at a
temperature in the range of from -5.degree. C. to 30.degree. C.;
coating the core component with a shell component by adding a
reverse micelle solution (IIIa) containing a hydrolysate and/or a
partial condensate of a compound represented by the following
formula (I) in the form of a sol composition, wherein the coating
step further includes after the addition of the reverse micelle
solution (IIIa) containing the hydrolysate and/or the partial
condensate of the compound represented by formula (I) heating at a
temperature in the range of from 30.degree. C. to 90.degree. C.;
and annealing after the coating: (R).sub.m-A(X).sub.4-m Formula (I)
wherein in formula (I), R represents a substituted or unsubstituted
alkyl group, or a substituted or unsubstituted aryl group; A
represents Si or Ti; X represents a hydroxyl group or a
hydrolyzable group; and m represents an integer of 1 to 3.
12-13. (canceled)
14. A method of producing a core/shell particle comprising: forming
a core component by mixing a reverse micelle solution (I) including
a reducing agent with one or more reverse micelle solutions (II)
including a metal salt, and carrying out a reduction treatment at a
temperature in a range of from -5.degree. C. to 30.degree. C.;
coating the core component with a shell component by adding a
reverse micelle solution (IIIb) containing a compound represented
by the following formula (I), and allowing the compound represented
by formula (I) to be hydrolyzed and/or partially condensed, wherein
the coating step further includes after the addition of the reverse
micelle solution (IIIb) containing the compound represented by
formula (I), heating at a temperature in the range of from
30.degree. C. to 90.degree. C.; and annealing after the coating:
(R).sub.m-A(X).sub.4-m Formula (I) wherein in formula (I), R
represents a substituted or unsubstituted alkyl group, or a
substituted or unsubstituted aryl group; A represents Si or Ti; X
represents a hydroxyl group or a hydrolyzable group; and m
represents an integer of 1 to 3.
15-16. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority under 35 USC 119 from
Japanese Patent Application No. 2005-365301, the disclosure of
which is incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The present invention relates to a nanoparticle and a method
of producing the nanoparticle, and in particular, relates to a
core/shell particle and a method of producing the same.
[0004] 2. Description of the Related Art
[0005] Techniques of coating a material for a core with a material
for a shell in order to protect a chemically or physically unstable
material, or give special functions thereto, are known. Particles
manufactured by such techniques are generally called core/shell
particles.
[0006] Many applications of core/shell particles are known, such as
silver halide particles for photographic photosensitive materials
and silicone elastomer particles in a thermosetting resin. In
recent years, core/shell particles as applied to magnetic
particles, especially magnetic particles in magnetic recording
media, have attracted significant attention.
[0007] Miniturization and advances in performance of magnetic
recording media for computers such as magnetic tapes and magnetic
discs have been progressing due to densification of recording
capacity. Accompanying this, reduction in particle size of magnetic
substances has also been progressing. Among ferromagnetic materials
having the same mass, ones having a smaller particle size can
achieve lower noise.
[0008] For example, CuAu type and/or Cu.sub.3Au type ferromagnetic
ordered alloys are promising materials for improving magnetic
recording density because they have great crystal magnetic
anisotropy due to distortion that occurs in ordering, and thus
exhibit ferromagnetism even when their particle size is reduced to
a state that is generally referred to as a nanoparticle.
[0009] Metal nanoparticles can be produced by a liquid phase
method. As the liquid phase method, various methods which have been
conventionally known can be employed. Examples of the liquid phase
method include, according to classification by the precipitation
method, (1) alcohol reduction methods in which a primary alcohol is
used, (2) polyol reduction methods in which a secondary, tertiary,
dihydric or trihydric alcohol is used, (3) thermal decomposition
methods, (4) ultrasonic decomposition methods, (5) reduction
methods with a potent reducing agent, and the like. Furthermore,
according to classification based on reaction systems, examples of
the liquid phase method include (6) polymer existence methods, (7)
high-boiling point solvent methods, (8) regular micelle methods,
(9) reverse micelle methods and the like. As the liquid phase
method, a reduction method established by improvement of these
methods is preferably employed, and among the reduction methods,
the reverse micelle method which is capable of readily controlling
the particle diameter is particularly preferred.
[0010] The metal nanoparticles produced by the liquid phase method
may be subjected to the annealing treatment as necessary. For
example, in the case of Cu/Au type or Cu.sub.3Au type ferromagnetic
ordered alloy, the alloy nanoparticle synthesized according to the
aforementioned method has a face centered cubic crystal structure.
The face centered cubic crystal usually exhibits soft magnetism or
paramagnetism, and those exhibiting soft magnetism or paramagnetism
are not suited for recording media. In order to obtain a
ferromagnetic ordered alloy having a coercive force of 95.5 kA/m
(1200 Oe) or greater, which is required for magnetic recording
media, an annealing treatment must be carried out at a temperature
equal to or higher than the transformation temperature at which the
alloy is transformed from its disordered phase to the ordered
phase. However, when the alloy nanoparticles produced according to
the above method are applied on a support and subjected to the
annealing treatment to produce a magnetic recording medium, the
alloy nanoparticles tend to flocculate easily with each other
leading to reduced coatability and deteriorated magnetic
properties. In addition, due to uneven particle diameter of the
resulting alloy nanoparticles, it has been difficult to form a
perfect ordered phase even if a heat treatment is executed.
Accordingly, there have been cases in which the desired
ferromagnetism is not achieved.
[0011] As methods of preventing fusion of the metal nanoparticles
resulting from annealing, those described in Japanese Patent
Application Laid-Open (JP-A) Nos. 2003-132519 and 2003-217108, and
Japanese National Phase Publication No. 2003-533363 and the like
are known. However, according to these methods, condensation of the
metal alkoxide compound used as the shell may proceed excessively,
which may cause flocculation of the core/shell particles and
generation of particles of the metal alkoxide compound alone as a
byproduct.
SUMMARY OF THE INVENTION
[0012] The present invention was accomplished in view of the
foregoing circumstances. Accordingly, the invention provides a
core/shell particle and a method of producing the same.
[0013] According to an aspect of the invention, there is provided a
core/shell particle including a core component that contains a
metal, and a shell component that coats the core component, the
shell component including a hydrolysate and/or a partial condensate
of a compound represented by the following formula (I).
(R).sub.m-A(X).sub.4-m Formula (I)
[0014] In formula (I), R represents a substituted or unsubstituted
alkyl group, or a substituted or unsubstituted aryl group; A
represents Si or Ti; X represents a hydroxyl group or a
hydrolyzable group; and m represents an integer of 1 to 3.
[0015] According to another aspect of the invention, there is
provided a method of producing a core/shell particle including:
forming a core component by mixing a reverse micelle solution
including a reducing agent with one or more reverse micelle
solutions including a metal salt, and carrying out a reduction
treatment; and coating the core component with a shell component by
adding a reverse micelle solution containing a hydrolysate and/or a
partial condensate of a compound represented by the following
formula (I) in the form of a sol composition.
(R).sub.m-A(X).sub.4-m Formula (I)
[0016] In formula (I), R represents a substituted or unsubstituted
alkyl group, or a substituted or unsubstituted aryl group; A
represents Si or Ai; X represents a hydroxyl group or a
hydrolyzable group; and m represents an integer of 1 to 3.
[0017] According to another aspect of the invention, there is
provided a method of producing a core/shell particle including:
forming a core component by mixing a reverse micelle solution
including a reducing agent with one or more reverse micelle
solutions including a metal salt, and carrying out a reduction
treatment; and coating the core component with a shell component by
adding a reverse micelle solution containing a compound represented
by the following formula (I), and allowing the compound represented
by formula (I) to be hydrolyzed and/or partially condensed.
(R).sub.m-A(X).sub.4-m Formula (I)
[0018] In formula (I), R represents a substituted or unsubstituted
alkyl group, or a substituted or unsubstituted aryl group; A
represents Si or Ai; X represents a hydroxyl group or a
hydrolyzable group; and m represents an integer of 1 to 3.
DETAILED DESCRIPTION OF THE INVENTION
Core/Shell Particle
[0019] The core/shell particle of the present invention is a
particle including a core component that contains a metal, and a
shell component that coats the core component. The shell component
includes a hydrolysate and/or a partial condensate of a compound
represented by the following formula (I).
(R).sub.m-A(X).sub.4-m Formula (I)
[0020] In formula (I), R represents a substituted or unsubstituted
alkyl group, or a substituted or unsubstituted aryl group. A
represents Si or Ti. X represents a hydroxyl group or a
hydrolyzable group. m represents an integer of 1 to 3. Details of R
and X are referred to in the section of Method of Producing
Core/shell Particles.
[0021] The core component of the core/shell particles of the
invention may be, for example, Au, Ag, Cu, Pd, Pt, CuO, FeS,
Ag.sub.2S, CuS, BaTiO.sub.3, SrTiO.sub.3, ZnO, ZnS, FePt, FePd,
CoPt, CoAu, FeNi, FeCo, Fe.sub.2O.sub.3 or the like. Among these,
FePt, FePd, CoPt, CoAu, FeNi, FeCo, Fe.sub.2O.sub.3, and the like
are preferable as magnetic materials.
[0022] The ratio (A/metal) of A included in the shell component to
the metal included in the core component is preferably in the range
of 30 to 200%, and more preferably 50 to 100% as represented by the
atomic percentage. The ratio falling within the range to be not
less than 30% permits the metal nanoparticle surface to be
uniformly coated. Also, the ratio to fall within the range to be
not greater than 200% can prevent generation of flocculated
particles of the shell component compound that are the
byproduct.
[0023] The above-described ratio of "A/metal" (A represents Si or
Ti) can be determined by carrying out element mapping of the
particles with an FE-TEM capable of finely contracting electron
beams equipped with an EDAX. Moreover, for the evaluation of the
particle diameter of the core/shell particles, a transmission
electron microscope (TEM) may be used. In order to determine the
crystal type of the core/shell particle ferromagnetized by the
annealing treatment, electron diffraction by TEM may be used, but
X-ray diffraction is preferably used for performing with high
accuracy. For analysis of the composition of the ferromagnetized
core component, the evaluation may be made with the FE-TEM equipped
with an EDAX in a similar manner described above. Evaluation of
magnetic property of the ferromagnetized core/shell particle may be
made using a vibrating sample magnetometer (VSM).
[0024] The presence/absence of the core/shell structure can be
ascertained by a TEM. The core component preferably has a particle
diameter of 1 to 20 nm. The shell layer including the shell
component preferably has a thickness of 1 to 5 nm.
[0025] The shell component of the core/shell particle of the
invention is highly heat resistant, therefore, the particles hardly
fuse even though a heating treatment is carried out. Furthermore,
because of having the alkyl group included in the composition of
the shell component, it has high affinity to the solvent, and thus
dispersibility in the solvent is also favorable.
[0026] Hereinafter, the method of producing the core/shell particle
of the invention will be explained in detail. Various explanations
described below are made based on typical embodiments of the
invention, but the invention is not limited to such
embodiments.
Method of Producing Core/Shell Particles
[0027] The method of producing a core/shell particle of the present
invention may be the following method (a) or (b).
[0028] Method (a) includes: forming a core component by mixing a
reverse micelle solution (1) including a reducing agent with one or
more reverse micelle solutions (2) including a metal salt, and
carrying out a reduction treatment; and coating the core component
with a shell component by adding a reverse micelle solution (3A)
containing a hydrolysate and/or a partial condensate of a compound
represented by formula (I) described above in the form of a sol
composition, following the core forming.
[0029] Method (b) includes: forming a core component by mixing a
reverse micelle solution (1) including a reducing agent with one or
more reverse micelle solutions (2) including a metal salt, and
carrying out a reduction treatment; and coating the core component
with a shell component by adding a reverse micelle solution (3B)
containing a compound represented by formula (I) described above,
and allowing the compound represented by formula (I) to be
hydrolyzed and/or partially condensed, following the core
forming.
[0030] Hereinbelow, each process will be explained.
Core Formation
[0031] First, the reverse micelle solution (1) is prepared by
mixing a water-insoluble organic solvent containing a surfactant
with an aqueous reducing agent solution.
[0032] An oil-soluble surfactant may be used as the surfactant.
Specific examples thereof include sulfonates (e.g., AEROSOL OT
produced by Tokyo Chemical Industries, Ltd.), quaternary ammonium
salts (e.g., cetyltrimethylammonium bromide), and ethers (e.g.,
pentaethylene glycol dodecyl ether).
[0033] Preferable examples of the water-insoluble organic solvent
dissolving the surfactant include alkanes and ethers. An alkane
having 7 to 12 carbon atoms is preferable as the water-insoluble
organic solvent. Specifically, heptane, octane, nonane, decane,
undecane and dodecane are preferable. Diethyl ether, dipropyl
ether, and dibutyl ether are included in preferable examples of
ethers usable as the water-insoluble organic solvent. The amount of
the surfactant in the water-insoluble organic solvent is preferably
20 to 200 g/l.
[0034] As the reducing agent in the aqueous reducing agent
solution, it is preferable to use one or more selected from
alcohols; polyalcohols; H.sub.2; HCHO; and compounds containing
S.sub.2O.sub.6.sup.2-, H.sub.2PO.sub.2.sup.-, BH.sub.4.sup.-,
N.sub.2H.sub.5.sup.+, H.sub.2PO.sub.3.sup.- and the like. The
amount of the reducing agent in the aqueous solution is preferably
3 to 50 mol relative to 1 mol of metal salt.
[0035] The mass ratio of water to the surfactant (water/surfactant)
in the reverse micelle solution (1) is preferably 20 or lower. When
the mass ratio exceeds 20, precipitation easily occurs and the
particles tend to be uneven. The mass ratio is preferably 15 or
lower and more preferably 0.5 to 10.
[0036] Besides the above micelle solution (1), a reverse micelle
solution (2) is prepared by mixing a water-insoluble organic
solvent containing a surfactant with an aqueous metal salt
solution. The conditions of the surfactant and the water-insoluble
organic solvent (e.g., materials to be used, concentrations, and
the like) are the same as in the case of the reverse micelle
solution (1). The conditions similar to or different from the
reverse micelle solution (1) may be used.
[0037] The components of the reverse micelle solution (2) may be
similar to or different from, the components of the reverse micelle
solution (1). Further, the mass ratio range of water to the
surfactant in the reverse micelle solution (2) may be the same as
that in the reverse micelle solution (1), and the mass ratio may be
the same as or different from that in the case of the reverse
micelle solution (1).
[0038] Specific examples of the metal salt contained in the aqueous
metal salt solution include HAuCl.sub.4, AgNO.sub.3, CH.sub.3COOAg,
(CH.sub.3COO).sub.2Cu, TiCl.sub.4, BaCO.sub.3, BaCl.sub.2,
SrCO.sub.3, SrCl.sub.2, (CH.sub.3COO).sub.2Zn, ZnSO.sub.4,
H.sub.2PtCl.sub.6, K.sub.2PtCl.sub.4,
Pt(CH.sub.3COCHCOCH.sub.3).sub.2, Na.sub.2PdCl.sub.4,
Pd(OCOCH.sub.3).sub.2, PdCl.sub.2,
Pd(CH.sub.3COCHCOCH.sub.3).sub.2, Fe.sub.2(SO.sub.4).sub.3,
Fe(NO.sub.3).sub.3, (NH.sub.4).sub.3Fe(C.sub.2O.sub.4).sub.3,
Fe(CH.sub.3COCHCOCH.sub.3).sub.3, (CH.sub.3COO).sub.2Fe,
NiSO.sub.4, CoCl.sub.2, Co(OCOCH.sub.3).sub.2. However, the metal
salt which may be used in the invention is not limited to these
examples.
[0039] The concentration of the aqueous metal salt solution (as the
metal salt concentration) is preferably 0.1 to 1000 .mu.mol/ml, and
more preferably 1 to 100 .mu.mol/ml.
[0040] The reverse micelle solutions (1) and (2) prepared as
described above are mixed. Although the mixing method is not
particularly limited, in view of uniformity of reduction, mixing is
preferably carried out by adding the reverse micelle solution (2)
to the reverse micelle solution (1) while stirring the reverse
micelle solution (1). A reductive reaction is carried out after the
completion of the mixing to form metal-containing cores. The
temperature during the reduction is preferably a constant
temperature within a range of -5 to 30.degree. C.
[0041] When the reduction temperature is lower than -5.degree. C.,
a problem may arise in that the water phase freezes, thereby
resulting in an uneven reductive reaction. When the reduction
temperature exceeds 30.degree. C., flocculation or precipitation
may easily occur, thereby making the system unstable in some cases.
The reduction temperature is more preferably 0 to 25.degree. C. and
still more preferably 5 to 25.degree. C.
[0042] The foregoing term "constant temperature" means that, when
the preset temperature is T(.degree. C.), the real temperature
falls in a range of T.+-.3.degree. C. The upper limit and the lower
limit of the real reduction temperature have to be within the
above-mentioned range of the temperature (-5 to 30.degree. C.).
Further, the reverse micelle solution (1) may be added after the
mixing.
[0043] Although the duration of the core forming process should be
properly set depending on the amounts or the like of the reverse
micelle solutions, the duration is preferably 1 to 30 minutes and
more preferably 5 to 20 minutes.
[0044] Since the reduction in the core forming process greatly
affects the monodispersibility of the particle diameter
distribution, it is preferable to carry out the reduction with
stirring at a rate as high as possible. A preferable stirring
apparatus may be a stirring apparatus having high shearing force,
and may be specifically a stirring apparatus in which: the stirring
blade basically has a turbine type or paddle type structure; a
sharp edge is attached to the end of the blade or a position where
it is in contact with the blade; and the blade is rotated by a
motor. Specifically, Dissolver (manufactured by Tokushu Kika Kogyo
Co., Ltd.), Omnimixer (manufactured by Yamato Scientific Co.,
Ltd.), Homogenizer (manufactured by SMT), and the like are useful.
By using such an apparatus, monodispersed metal-containing core
particles can be produced in the form of a stable dispersion in a
liquid.
Coating
[0045] Further, separately from the above process, the reverse
micelle solution (3A) is prepared by mixing a water-insoluble
organic solvent containing a surfactant with a water soluble
organic solvent containing the compound represented by the above
formula (I) or a hydrolysate or a partial condensate of the
compound represented by the above formula (I) in the form of a sol
composition. Requirements for the surfactant and the
water-insoluble organic solvent (substance used, concentration and
the like) are similar to those in the case of the reverse micelle
solution (1). The requirements similar to or different from the
requirements for the reverse micelle solution (1) can be employed.
Alternatively, the core component may be coated with the shell
component by adding the reverse micelle solution (3B) containing a
compound represented by formula (I) instead of the reverse micelle
solution (3A), and allowing the compound represented by formula (I)
to be hydrolyzed and/or partially condensed. Hereinafter, the
reverse micelle solution (3A) and the reverse micelle solution (3B)
may be collectively referred to as "reverse micelle solution
(3)"
[0046] In formula (I), R represents a substituted or unsubstituted
alkyl group, or a substituted or unsubstituted aryl group. X
represents a hydroxyl group or a hydrolyzable group, which may be
e.g., an alkoxy group (preferably an alkoxy group having 1 to 5
carbon atoms, for example, a methoxy group, an ethoxy group or the
like), halogen (for example, chlorine, bromine, iodine or the
like), or R.sup.2COO, wherein R.sup.2 is preferably a hydrogen atom
or an alkyl group (for example, CH.sub.3COO, C.sub.2H.sub.5COO or
the like). X is preferably an alkoxy group, and particularly
preferably a methoxy group or an ethoxy group. m represents an
integer of 1 to 3. When a plurality of R.sup.5 are present, the
plurality of R.sup.5 may be the same or different. When a plurality
of Xs are present, the plurality of Xs may be the same or
different. m is preferably 1 or 2, and particularly preferably
1.
[0047] The substituent included in R is not particularly limited,
but examples thereof include halogen (fluorine, chlorine, bromine
and the like), a hydroxyl group, a mercapto group, a carboxyl
group, an amino group, an epoxy group, alkyl groups (a methyl
group, an ethyl group, an i-propyl group, a propyl group, a
tert-butyl group, an octadecyl group and the like), aryl groups (a
phenyl group, a naphthyl group and the like), aromatic heterocyclic
groups (a furyl group, a pyrazolyl group, a pyridyl group and the
like), alkoxy groups (a methoxy group, an ethoxy group, an
i-propoxy group, a hexyloxy group and the like), aryloxy groups (a
phenoxy group and the like), alkylthio groups (a methylthio group,
an ethylthio group and the like), arylthio groups (a phenylthio
group and the like), alkenyl groups (a vinyl group, a 1-propenyl
group and the like), acyloxy groups (an acetoxy group, an
acryloyloxy group, a methacryloyloxy group and the like),
alkoxycarbonyl groups (a methoxycarbonyl group, an ethoxycarbonyl
group and the like), aryloxycarbonyl groups (a phenoxycarbonyl
group and the like), carbamoyl groups (a carbamoyl group, an
N-methylcarbamoyl group, an N,N-dimethylcarbamoyl group, an
N-methyl-N-octylcarbamoyl group and the like), acylamino groups (an
acetylamino group, a benzoylamino group, an acrylamino group, a
methacrylamino group and the like), and the like. These
substituents may be further substituted.
[0048] Two or more of the compounds represented by formula (I) may
be used in combination. Specific examples of the compounds
represented by formula (I) include vinyl trichlorosilane, vinyl
triethoxysilane, vinyl tris(.beta.-methoxy)silane, amino propyl
triethoxysilane, amino propyl methoxy diethoxysilane, glycidoxy
propyl dimethoxysilane, isopropyl triisostearoyl titanate,
isopropyl tridodecyl benzene sulfonyl titanate, isopropyl
tris(dioctyl pyrophosphate)titanate, tetraisopropyl bis(dioctyl
phosphite)titanate, tetraoctyl bis(ditridecyl phosphite)titanate,
tetra(2,2-diallyloxymethyl-1-butyl)bis(ditridecyl)phosphite
titante, bis(dioctyl pyrophosphate)oxyacetate titanate, bis(dioctyl
pyrophosphate)ethylenetitanate, isopropyl tri(dioctyl
phosphate)titanate, isopropyl tricumyl phenyl titanate, isopropyl
tri(N-amidoethyl aminoethyl)titanate, and compounds (1) to (41)
illustrated below, but the compound which can be used in the
invention is not limited thereto.
##STR00001## ##STR00002## ##STR00003##
[0049] When the compound represented by formula (I) in the reverse
micelle solution (3) is included in the form of a sol composition
of its hydrolysate and/or its partial condensate, the
hydrolysis/cQndensation reaction of the compound represented by
formula (I) can be carried out without a solvent or in a solvent,
but it is preferred to use an organic solvent for homogeneously
mixing the components. For example, alcohols, aromatic
hydrocarbons, ethers, ketones, esters and the like are suited. As
the solvent, any one that dissolves the silane compound and the
catalyst is preferred. Also, the solvent is preferably used as an
application liquid or a part of the application liquid in light of
the process performance.
[0050] Among these, examples of the alcohols include e.g.,
monohydric alcohols or dihydric alcohols. Of these, as the
monohydric alcohol, saturated aliphatic alcohols having 1 to 8
carbon atoms are preferred. Specific examples of these alcohols
include methanol, ethanol, n-propyl alcohol, i-propyl alcohol,
n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, ethylene
glycol, diethylene glycol, triethylene glycol, ethylene glycol
monobutyl ether, ethylene glycol acetate monoethyl ether, and the
like.
[0051] Specific examples of the aromatic hydrocarbons include
benzene, toluene, xylene, and the like; specific examples of the
ethers include tetrahydrofuran, dioxane, and the like; specific
examples of the ketones include acetone, methyl ethyl ketone,
methyl isobutyl ketone, diisobutyl ketone, and the like; specific
examples of the esters include ethyl acetate, propyl acetate, butyl
acetate, propylene carbonate, and the like.
[0052] These organic solvents can be used one of them alone, or two
or more thereof as a mixture. The concentration of the solid
content in the reaction is not particularly limited, but is usually
in the range of 1% by mass to 90% by mass, and preferably in the
range of 20% by mass to 70% by mass.
[0053] When the compound represented by formula (I) in the reverse
micelle solution (3) is included in the form of a sol composition
of its hydrolysate and/or its partial condensate, it is preferred
that the hydrolysis/condensation reaction of the compound
represented by formula (I) be carried out in the presence of a
catalyst. Examples of the catalyst include inorganic acids such as
hydrochloric acid, sulfuric acid and nitric acid; organic acids
such as oxalic acid, acetic acid, formic acid, methanesulfonic acid
and toluenesulfonic acid; inorganic bases such as sodium hydroxide,
potassium hydroxide and ammonia; organic bases such as
triethylamine and pyridine; metal alkoxides such as triisopropoxy
aluminum and tetrabutoxy zirconium, and the like. In light of
production stability of the sol liquid and storage stability of the
sol liquid, acid catalysts (inorganic acids, organic acids) are
preferred. As the inorganic acid, hydrochloric acid and sulfuric
acid are preferred, while as the organic acid one having an acid
dissociation constant (pKa value at 25.degree. C.) in water of 4.5
or less is preferred. Hydrochloric acid, sulfuric acid, and organic
acids having an acid dissociation constant in water of 3.0 or less
are more preferred. Hydrochloric acid, sulfuric acid, and organic
acids having an acid dissociation constant in water of 2.5 or less
are more preferred, and organic acids having an acid dissociation
constant in water of 2.5 or less are more preferred.
Methanesulfonic acid, oxalic acid, phthalic acid and malonic acid
are still more preferred, and oxalic acid is particularly
preferred.
[0054] Hydrolysis/condensation reaction is usually carried out by
adding 0.3 to 2 mol, preferably 0.5 to 1 mol of water per 1 mol of
the hydrolyzable group of the compound represented by formula (I),
and then stirring in the presence or absence of the solvent and
preferably in the presence of the catalyst at 25 to 100.degree.
C.
[0055] When the hydrolyzable group is alkoxide and the catalyst is
an organic acid, the amount of added water can be reduced because
proton is supplied from the carboxyl group or sulfo group of the
organic acid. The amount of added water per 1 mol of the alkoxide
group of the compound represented by formula (I) is usually 0 to 2
mol, preferably 0 to 1.5 mol, more preferably 0 to 1 mol, and
particularly preferably 0 to 0.5 mol. When the alcohol is used as
the solvent, the case in which water is not substantially added is
also suitable.
[0056] The amount of the catalyst to be used is usually 0.01 to 10
mol % and preferably 0.1 to 5 mol % based on the hydrolyzable group
when the catalyst is an inorganic acid. When the catalyst is an
organic acid, the amount of the catalyst to be used varies
depending on the amount of added water. More specifically, when
water is added, the amount is usually 0.01 to 10 mol %, preferably
0.1 to 5 mol % based on the hydrolyzable group, while when water is
not substantially added, the amount is usually 1 to 500 mol %,
preferably 10 to 200 mol %, more preferably 20 to 200 mol %, still
more preferably 50 to 150 mol %, and particularly preferably 50 to
120 mol % based on the hydrolyzable group. The reaction is carried
out usually by stirring at 25 to 100.degree. C., but the reaction
is preferably controlled ad libitum depending on the reactivity of
the compound represented by formula (I).
[0057] The sol composition of the hydrolysate and/or the partial
condensate of the compound represented by formula (I) is gelled by
adsorption on the surface of the metal core formed in the core
forming process, and coats the metal core in the form of a gel
film.
[0058] To a mixture of the reverse micelle solutions (1) and (2)
after the completion of the core forming process is added the
reverse micelle solution (3) while keep stirring at a high rate in
the core forming process. By carrying out the stirring at a high
rate, collision frequency between the reverse micelle containing
the metal nanoparticles and the reverse micelle containing the
compound for forming the shell component is increased, whereby
uniform coating is enabled. Insufficient stirring is not preferred
because particles may be generated through flocculation of the
compound for forming the shell component alone.
[0059] It is preferred that after adding the reverse micelle
solution (3), at least one dispersant having 1 to 3 amino groups or
carboxy groups is added in an amount of 0.001 to 10 mol per 1 mol
of the alloy nanoparticle to be produced.
[0060] By adding such a dispersant, the core/shell particles that
are in a more monodisperse state without flocculation may be
obtained. When the amount of addition is less than 0.001 mol, there
may be a case in which monodispersibility of the core/shell
particles cannot be further improved, while the amount of greater
than 10 mol may cause flocculation.
[0061] As the aforementioned dispersant, an organic compound having
a group adsorbable to the surface of the core/shell particle is
preferable. Specific examples of the dispersant include organic
compounds having 1 to 3 groups selected from amino groups, carboxyl
groups, sulfonic acid groups and sulfinic acid groups. Only a
single dispersant may be used, or two or more dispersants may be
used in combination.
[0062] The dispersant may be, for example, a compound having a
structural formula represented by R--NH.sub.2,
NH.sub.2--R--NH.sub.2, NH.sub.2--R(NH.sub.2)--NH.sub.2, R--COOOH,
COOH--R--COOH, COOH--R(COOH)--COOH, R--SO.sub.3H,
SO.sub.3H--R--SO.sub.3H, SO.sub.3H--R(SO.sub.3H)--SO.sub.3H,
R--SO.sub.2H, SO.sub.2H--R--SO.sub.2H, or
SO.sub.2H--R(SO.sub.2H)--SO.sub.2H, wherein R is a linear, branched
or cyclic, saturated or unsaturated hydrocarbon.
Heat Treatment
[0063] The coating process preferably includes, after the addition
of the reverse micelle solution (3), heating at a temperature
higher than the temperature at the core forming process (heat
treatment process). The shell component that coats the particles
can become harder by the heat treatment. The heat treatment
temperature is preferably maintained at a constant temperature
which is in a range of 30 to 90.degree. C. The heat treatment time
is preferably 5 to 180 minutes. When the heat treatment temperature
is higher than the above range or the heat treatment time is longer
than the above range, flocculation or precipitation easily occurs.
On the contrary, when the temperature is lower than the above range
or the time is shorter than the above range, the reaction may not
be completed, leading to a change in the composition. The heat
treatment temperature is more preferably 40 to 80.degree. C. and
still more preferably 40 to 70.degree. C. The heat treatment time
is more preferably 10 to 150 minutes and still more preferably 20
to 120 minutes.
[0064] The aforementioned term "constant temperature" means that,
when the preset temperature is T(.degree. C.), the real temperature
falls in a range of T.+-.3.degree. C. Particularly, the heat
treatment temperature is higher than the temperature at the core
forming process by preferably 5.degree. C. or larger, and more
preferably 10.degree. C. or larger provided the heat treatment
temperature is within the aforementioned teat treatment temperature
range (30 to 90.degree. C.). When the difference between the core
forming temperature and the heat treatment temperature is smaller
than 5.degree. C., a composition according to the formulation may
not be obtained.
[0065] After the completion of the coating process, it is preferred
to eliminate unreacted metal ion by adding a chelating agent. The
state in which the metal ion is left may lead to possibility of
producing impurities through reduction of the unreacted metal ion
in the washing and dispersion process described later. Specific
examples of the chelating agent used in this procedure include
ethylenediaminetetraacetic acid, nitrilotriacetic acid,
hydroxyethyliminodiacetic acid,
hydroxyethylethylenediaminetriacetic acid,
diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic
acid, dicarboxymethylglutamic acid tetrasodium salt,
N,N-bis(2-hydroxyethyl)glycine, 1,3-propanediaminetetraacetic acid,
1,3-diamino-2-hydroxypropanetetraacetic acid, L-aspartic
acid-N,N-diacetic acid, hydroxyethylidenediphosphonic acid,
nitrilotris(methylenephosphonic acid), phosphonobutanetriacetic
acid, N,N,N',N'-tetrakis(phosphonomethyl)ethylene diamine, and the
like.
[0066] In an embodiment, after the coating process, the solution
after the coating process is washed with a mixed solution of water
and a primary alcohol and then precipitation treatment is carried
out using a primary alcohol to produce a precipitate, which is then
dispersed in an organic solvent. Impurities are removed by
providing the washing and dispersing in this embodiment, thereby
improving the coatability at the time of forming a layer containing
the core/shell particles of the invention by coating. The above
washing and the dispersing are respectively carried out at least
once and preferably twice or more.
[0067] Although there is no particular limitation on the primary
alcohol used in the washing step, methanol, ethanol, or the like is
preferable. The mixing ratio by volume (water/primary alcohol) is
preferably in a range of 10/1 to 2/1 and more preferably in a range
of 5/1 to 3/1. If the proportion of water is high, it may be
difficult to remove the surfactant. On the contrary, if the
proportion of the primary alcohol is high, flocculation may
occur.
[0068] As in the foregoing, core/shell particles dispersed in the
solution can be obtained. The core/shell particles exhibit
excellent monodispersibility, hardly flocculate, and may keep the
state in which they are uniformly dispersed.
[0069] The core/shell particles before annealing have a particle
diameter of preferably 1 to 20 nm, and more preferably 3 to 10 nm.
The coefficient of variation of the particle diameter of the
core/shell particle of the invention is preferably less than 10%,
and more preferably 5% or less.
Annealing Treatment
[0070] In the method of producing a core/shell particle of the
invention, it is preferable to subject to the annealing treatment
after the coating process. The method for heating in the annealing
treatment is not particularly limited. The annealing can be carried
out by any of a method of heating after applying on the support, a
method of heating by an autoclave in the state of a dispersion, a
method of treating in a heating furnace following evaporation of
the solvent to give the powder, and the like, but the invention is
not limited thereto.
[0071] The core/shell particle of the invention after subjecting to
the annealing treatment is preferably magnetic. In this case, the
core/shell particle preferably has a coercive force of preferably
95.5 to 636.8 kA/m (1200 to 8000 Oe), and more preferably 95.5 to
398 kA/m (1200 to 5000 Oe) when applied to a magnetic recording
medium in light of possible adapting to the recording head.
EXAMPLES
[0072] The present invention will now be described with reference
to Examples. However, the Examples should not be construed as
limiting the invention.
Synthesis of Sol Composition
Preparation of Organosilane Sol Composition A
[0073] To a reactor equipped with a stirrer and a reflux condenser,
48 g of acryloyloxypropyltrimethoxysilane (Compound (14)), 37 g of
oxalic acid, and 124 g of ethanol were added and mixed. After the
mixing, hydrolysis was conducted by allowing the reaction at
70.degree. C. for 5 hrs, followed by cooling to room temperature.
Accordingly, a sol composition A in which the silane compound was
partially condensed was obtained.
Preparation of Organosilane Sol Composition B
[0074] To a reactor equipped with a stirrer and a reflux condenser,
48 g of acryloyloxypropyltrimethoxysilane, 0.84 g of aluminum
diisopropoxide ethylacetoacetate, 60 g of methyl ethyl ketone, 0.06
g of hydroquinonemonomethyl ether, and 11.1 g of water were added
and mixed. After the mixing, hydrolysis was conducted by allowing a
reaction at 60.degree. C. for 4 hrs, followed by cooling to room
temperature. Accordingly, a transparent sol composition B in which
the silane compound was partially condensed was obtained.
Preparation of Organosilane Sol Composition C
[0075] A transparent sol composition C in which the silane compound
was partially condensed was obtained by a similar manipulation to
the preparation of the sol composition B except that
acryloyloxypropyltrimethoxysilane was replaced with
methacryloyloxypropyltrimethoxysilane (Compound (15)) in the
preparation of the sol composition B.
Preparation of Organosilane Sol Composition D
[0076] A transparent sol composition D in which the silane compound
was partially condensed was obtained by a similar manipulation to
the preparation of the sol composition B except that
acryloyloxypropyltrimethoxysilane was replaced with
tetraethoxysilane in the preparation of the sol composition B.
Example 1
Synthesis of Core/Shell Particle
[0077] The following operation was performed in a highly purified
N.sub.2 gas.
[0078] To an aqueous reducing agent solution in which 0.48 g of
NaBH.sub.4 (produced by Wako Pure Chemical Industries, Ltd.) is
dissolved in 18 ml of H.sub.2O (deoxygenated) was added an alkane
solution prepared by dissolving 12.4 g of AEROSOL OT (produced by
Tokyo Chemical Industries, Ltd.) in 120 ml of decane (produced by
Wako Pure Chemical Industries, Ltd.), which was mixed to prepare a
reverse micelle solution (1).
[0079] To an aqueous metal salt solution prepared by dissolving
0.44 g of ammonium ferric trioxalate
(Fe(NH.sub.4).sub.3(C.sub.2O.sub.4).sub.3 (produced by Wako Pure
Chemical Industries, Ltd.) and 0.41 g of potassium chloroplatinate
(K.sub.2PtCl.sub.4) (produced by Wako Pure Chemical Industries,
Ltd.) in 18 ml of H.sub.2O (deoxygenated) was added an alkane
solution prepared by dissolving 12.4 g of AEROSOL OT in 120 ml of
decane, which was mixed to prepare a reverse micelle solution
(2).
[0080] To an aqueous reducing agent solution in which 0.12 g of
NaBH.sub.4 (produced by Wako Pure Chemical Industries, Ltd.) is
dissolved in 4.5 ml of H.sub.2O (deoxygenated) was added an alkane
solution prepared by dissolving 3.1 g of AEROSOL OT in 30 ml of
decane, which was mixed to prepare a reverse micelle solution
(2)'.
[0081] To a solution prepared by dissolving 0.77 ml of a 22.9%
methyl ethyl ketone dispersion of the sol composition A in 3.73 ml
of ethoxyethanol was added an alkane solution prepared by
dissolving 3.1 g of AEROSOL OT in 30 ml of decane, which was mixed
to prepare a reverse micelle solution (3).
[0082] To an aqueous solution prepared by dissolving 0.01 g of
BICINE (N,N-bis(2-hydroxyethyl)glycine; produced by Dojindo
Laboratories) in 4.5 ml of H.sub.2O (deoxygenated) was added the
alkane solution prepared by dissolving 3.1 g of AEROSOL OT in 30 ml
of decane, which was mixed to prepare a reverse micelle solution
(4).
[0083] The reverse micelle solution (2) was added at once to the
reverse micelle solution (1) at 22.degree. C. while stirring at a
high rate using an Omnimixer (manufactured by Yamato Scientific
Co., Ltd.) (core forming process). Four minutes later, the reverse
micelle solution (2)' was added at once. In additional 6 minutes,
the reverse micelle solution (3) was added at once (coating
process). In additional 2 minutes, 3 ml of oleylamine was added at
once. Two minutes thereafter, stirring apparatus was changed to a
magnetic stirrer, and the temperature was elevated to 40.degree. C.
and kept for 110 minutes (heat treatment process), and thereto was
added the reverse micelle solution (4) at once, followed by further
stirring for 10 min.
[0084] After cooling to room temperature, 3 ml of oleic acid
(produced by Wako Pure Chemical Industries, Ltd.) was added, and
mixed. The mixture was removed into the ambient air. For disrupting
the reverse micelle, a mixed solution of 450 ml of H.sub.2O and 450
ml of methanol was added thereto, and the mixture was separated
into an aqueous phase and an oil phase. The core/shell particles
before subjecting to the annealing treatment were obtained in the
oil phase in a dispersed state. The oil phase was recovered, and
washed once with a mixture of 900 ml of H.sub.2O and 300 ml of
methanol. Thereafter, 300 ml of ethanol was added thereto and
centrifugal separation was carried out under a condition of 3000
rpm for 10 min with a centrifugal separator to allow the metal
nanoparticles to be precipitated. The supernatant was eliminated,
and 40 ml of heptane (produced by Wako Pure Chemical Industries,
Ltd.) was added thereto followed by redispersion. Furthermore, 40
ml of ethanol was added, and then precipitation by centrifugal
separation and dispersion in 40 ml of heptane were repeated twice.
Finally, 15 ml of heptane was added to obtain a liquid containing
the core/shell particles before subjecting to the annealing
treatment. The alloy composition was Fe/Pt=55/45% (atomic
percentage).
Example 2
[0085] A liquid containing the core/shell particles before
subjecting to the annealing treatment was obtained by a similar
manipulation to Example 1 except that the sol composition A was
replaced with the sol composition B.
Example 3
[0086] A liquid containing the core/shell particles before
subjecting to the annealing treatment was obtained by a similar
manipulation to Example 1 except that the sol composition A was
replaced with the sol composition C.
Example 4
[0087] A liquid containing the core/shell particles before
subjecting to the annealing treatment was obtained by a similar
manipulation to Example 1 except that the reverse micelle solution
(3) was changed to include 0.46 ml of the sol composition A and
3.54 ml of ethoxyethanol.
Example 5
[0088] A liquid containing the core/shell particles before
subjecting to the annealing treatment was obtained by a similar
manipulation to Example 1 except that the reverse micelle solution
(3) was changed to include 3.08 ml of the sol composition A and
0.92 ml of ethoxyethanol.
Example 6
[0089] A liquid containing the core/shell particles before
subjecting to the annealing treatment was obtained by a similar
manipulation to Example 1 except that the reverse micelle solution
(3) was changed to include 0.15 ml of the sol composition A and
3.85 ml of ethoxyethanol.
Example 7
[0090] A liquid containing the core/shell particles before
subjecting to the annealing treatment was obtained by a similar
manipulation to Example 1 except that the reverse micelle solution
(3) was changed to include 0.30 ml of the sol composition A and
3.70 ml of ethoxyethanol.
Example 8
[0091] A liquid containing the core/shell particles before
subjecting to the annealing treatment was obtained by a similar
manipulation to Example 1 except that the reverse micelle solution
(3) was changed to include 3.85 ml of the sol composition A and
0.15 ml of ethoxyethanol.
Example 9
[0092] A liquid containing the core/shell particles before
subjecting to the annealing treatment was obtained by a similar
manipulation to Example 1 except that in the reverse micelle
solution (3), sol composition A was changed to 0.75 g of octadecyl
trimethoxysilane and ethoxyethanol was changed to 4.5 ml of
hexanol.
Example 10
[0093] A liquid containing the core/shell particles before
subjecting to the annealing treatment was obtained by a similar
manipulation to Example 1 except that in the reverse micelle
solution (3), sol composition A was changed to 1.88 g of isopropyl
triisostearoyl titanate and ethoxyethanol was changed to 4.5 ml of
hexanol.
Example 11
[0094] A liquid containing the core/shell particles before
subjecting to the annealing treatment was obtained by a similar
manipulation to Example 1 except that in the reverse micelle
solution (3), sol composition A was changed to 0.36 g of
aminopropyl trimethoxysilane and ethoxyethanol was changed to 4.5
ml of hexanol.
Example 12
[0095] A liquid containing the core/shell particles before
subjecting to the annealing treatment was obtained by a similar
manipulation to Example 1 except that in the reverse micelle
solution (2) 0.41 g of potassium chloroplatinate
(K.sub.2PtCl.sub.4) (produced by Wako Pure Chemical Industries,
Ltd.) was not added, and after the temperature was elevated to
40.degree. C., 10 ml of 1N NaOH was added.
Example 13
[0096] A liquid containing the core/shell particles before
subjecting to the annealing treatment was obtained by a similar
manipulation to Example 1 except that the metal salt contained in
the reverse micelle solution (2) was changed to 0.796 g of sodium
chloroaurate (NaAu Cl.sub.4) (produced by Wako Pure Chemical
Industries, Ltd.).
Comparative Example 1
[0097] A liquid containing the core/shell particles before
subjecting to the annealing treatment was obtained by a similar
manipulation to Example 1 except that the sol composition A was
replaced with the sol composition D.
Comparative Example 2
[0098] A liquid containing the alloy particles before subjecting to
the annealing treatment was obtained by a similar manipulation to
Example 1 except that the sol composition was not added.
[0099] Each of the liquid containing the core/shell particles
before subjecting to the annealing treatment produced in Examples 1
to 13 and Comparative Examples 1 and 2 (the liquid containing the
alloy particles in Comparative Example 2) was applied on a glass
substrate as a support with spin coating. Thereafter, drying was
conducted in the air at 250.degree. C., followed by carrying out an
annealing treatment in an atmosphere of N.sub.2+H.sub.2 (5%) in an
infrared heating furnace at 500.degree. C. for 30 min to form a
layer including the core/shell particles (layer including the metal
particles in Comparative Example 2).
[0100] Moreover, ratio of the metal included in the core component
and Si or Ti included in the shell component (Si or Ti/metal) was
determined by carrying out element mapping with a transmission
electron microscope HF-2200 manufactured by Hitachi
High-Technologies Corporation. The results are shown in Table 1
below.
TABLE-US-00001 TABLE 1 Coefficient Coefficient Constituent Average
variation of variation of ratio of SI to particle particle Average
particle magnetic alloy diameter diameter particle diameter
Inclusion in reverse Core (% (atomic before before diameter after
after Sample name micell solution (3) particle percentage)
annealing (nm) annealing annealing (nm) annealing Example 1 Sol
composition A FePt 50 5.5 9.8 5.5 9.9 Example 2 Sol composition B
FePt 50 5.7 10.1 5.7 10.1 Example 3 Sol composition C FePt 50 5.5
9.7 5.6 9.8 Example 4 Sol composition A FePt 30 5.3 9.8 5.3 9.8
Example 5 Sol composition A FePt 200 7.5 10.2 7.5 10.3 Example 6
Sol composition A FePt 10 5.2 9.9 13.6 22.4 Example 7 Sol
composition A FePt 20 5.5 10.0 7.6 15.7 Example 8 Sol composition A
FePt 250 7.7 10.3 7.8 10.4 Example 9 Octadecyl FePt 50 5.5 9.9 5.6
10.0 trimethoxysilane Example 10 Isopropyl FePt 50 5.3 9.8 5.3 10.0
triisostearoyl titanate Example 11 Aminopropyl FePt 50 5.4 9.9 5.5
9.9 trimethoxy silane Example 12 Sol composition A Fe.sub.2O.sub.3
50 6.0 10.2 6.1 10.2 Example 13 Sol composition A Au 50 5.7 10.0
5.7 10.1 Comparative Sol composition D FePt 50 5.7 10.3 23.5 28.5
Example 1 Comparative None FePt 0 5.4 10.0 20.4 30.2 Example 2
[0101] The coefficient of variation of the average particle
diameter (volume average particle diameter) in the above Table 1
were determined with an image processing software KS300
manufactured by Carl Zeiss Inc., by performing image processing of
the TEM photograph for observation of the core/shell particles.
[0102] Moreover, each shape of the core/shell particles or magnetic
particles after subjecting to the annealing treatment obtained in
Examples 1 to 13 and Comparative Examples 1 and 2 was observed with
a transmission electron microscope 1200EX manufactured by JEOL Ltd.
Accordingly, it was shown that a shell layer resulting from the
compound represented by formula (I) was formed around the core
component including a metal as for the core/shell particles of
Examples 1 to 13 and Comparative Example 1.
[0103] In Examples 1 to 13, change in the coefficient of variation
of the particle diameter was very small. This effect was
significant in Examples 1 to 5 and 9 to 13, in which the
composition ratio of Si or Ti to the metal is in a range of 30 to
200% (atomic percentage). To the contrary, fusion of the shell
layers was found in Comparative Example 1, while fusion of the
metal nanoparticles was found and thus the particle diameter could
not be satisfactorily kept in Comparative Example 2.
[0104] The core/shell particles or magnetic particles were scraped
from the layer formed on the support in Examples 1 to 11, and
evaluation on each of magnetic property was made. The evaluation of
the magnetic property (measurement of coercive force) was made
using a highly sensitive magnetization vector measuring instrument
and a DATA processing unit, both manufactured by Toei Industry Co.,
Ltd., under a condition to provide an applied magnetic field of 790
kA/m (10 kOe). The results are shown in Table 2.
TABLE-US-00002 TABLE 2 Sample name Coercive force Hc (kA/m) Example
1 223 (2800 Oe) Example 2 239 (3000 Oe) Example 3 235 (2950 Oe)
Example 4 231 (2900 Oe) Example 5 240 (3015 Oe) Example 6 227 (2850
Oe) Example 7 223 (2800 Oe) Example 8 215 (2700 Oe) Example 9 239
(3000 Oe) Example 10 220 (2750 Oe) Example 11 221 (2775 Oe)
[0105] The core/shell particles of the present invention exhibited
the magnetic property as shown in Table 2 and it was shown that the
core/shell parties of the present invention was applicable to a
magnetic recording medium.
[0106] According to the present invention, core/shell particles
hardly accompanied by fusion resulting from the annealing treatment
and hardly accompanied by flocculation even after coating of the
shell component, and a method of producing the same can be
provided.
[0107] Hereinafter, embodiments of the invention will be described.
However, the invention is not limited to these embodiments.
[0108] [1] A core/shell particle comprising a core component that
contains a metal, and a shell component that coats the core
component, the shell component including a hydrolysate and/or a
partial condensate of a compound represented by the following
formula (I):
(R).sub.m-A(X).sub.4-m Formula (I)
[0109] wherein in formula (I), R represents a substituted or
unsubstituted alkyl group, or a substituted or unsubstituted aryl
group; A represents Si or Ti; X represents a hydroxyl group or a
hydrolyzable group; and m represents an integer of 1 to 3.
[0110] [2] The core/shell particle as described in [1], wherein a
ratio (A/metal) of A included in the shell component to the metal
included in the core component is in a range of 30 to 200% in terms
of the atomic percentage.
[0111] [3] The core/shell particle as described in [1], the
core/shell particle being magnetic.
[0112] [4] The core/shell particle as described in [1], wherein the
core component comprises a ferromagnetic ordered alloy phase of at
least one of a CuAu type (CuAu form) or a Cu.sub.3Au type
(Cu.sub.3Au form).
[0113] [5] The core/shell particle as described in [1], wherein a
ratio (A/metal) of A included in the shell component to the metal
included in the core component is in a range of 50 to 100% in terms
of the atomic percentage.
[0114] [6] The core/shell particle as described in [1], wherein the
core component has a particle diameter of 1 to 20 nm.
[0115] [7] The core/shell particle as described in [1], wherein in
formula (I), X is an alkoxy group.
[0116] [8] The core/shell particle as described in [1], wherein in
formula (I), m is 1 or 2.
[0117] [9] The core/shell particle as described in [1], wherein in
formula (I), m is 2 or 3; and at least one R is a substituted alkyl
group or a substituted aryl group.
[0118] [10] The core/shell particle as described in [1], wherein in
formula (I), A represents Si.
[0119] [11] A method of producing a core/shell particle
comprising:
[0120] forming a core component by mixing a reverse micelle
solution including a reducing agent with one or more reverse
micelle solutions including a metal salt, and carrying out a
reduction treatment; and
[0121] coating the core component with a shell component by adding
a reverse micelle solution containing a hydrolysate and/or a
partial condensate of a compound represented by the following
formula (I) in the form of a sol composition:
(R).sub.m-A(X).sub.4-m Formula (I)
[0122] wherein in formula (I), R represents a substituted or
unsubstituted alkyl group, or a substituted or unsubstituted aryl
group; A represents Si or Ai; X represents a hydroxyl group or a
hydrolyzable group; and m represents an integer of 1 to 3.
[0123] [12] The method of producing a core/shell particle as
described in [11], wherein the coating includes, after the addition
of the reverse micelle solution containing the hydrolysate or the
partial condensate of the compound represented by formula (I),
heating at a temperature higher than the temperature at the core
forming.
[0124] [13] The method of producing a core/shell particle as
described in [11], further comprising annealing after the
coating.
[0125] [14] A method of producing a core/shell particle
comprising:
[0126] forming a core component by mixing a reverse micelle
solution including a reducing agent with one or more reverse
micelle solutions including a metal salt, and carrying out a
reduction treatment; and
[0127] coating the core component with a shell component by adding
a reverse micelle solution containing a compound represented by the
following formula (I), and allowing the compound represented by
formula (I) to be hydrolyzed and/or partially condensed:
(R).sub.m-A(X).sub.4-m Formula (I)
[0128] wherein in formula (I), R represents a substituted or
unsubstituted alkyl group, or a substituted or unsubstituted aryl
group; A represents Si or Ai; X represents a hydroxyl group or a
hydrolyzable group; and m represents an integer of 1 to 3.
[0129] [15] The method of producing a core/shell particle as
described in [14], wherein the coating includes, after the addition
of the reverse micelle solution containing the compound represented
by formula (I), heating at a temperature higher than the
temperature at the core forming.
[0130] [16] The method of producing a core/shell particle as
described in [14], further comprising annealing after the
coating.
[0131] All publications, patent applications, and technical
standards mentioned in this specification are herein incorporated
by reference to the same extent as if each individual publication,
patent application, or technical standard was specifically and
individually indicated to be incorporated by reference.
* * * * *