U.S. patent application number 14/460513 was filed with the patent office on 2014-12-04 for metallic magnetic powder and manufacturing method of the same, magnetic painting, magnetic powder for magnetic therapy, and magnetic recording medium.
This patent application is currently assigned to THE ARIZONA BOARD OF REGENTS ON BEHALF OF THE UNIVERSITY OF ARIZONA. The applicant listed for this patent is THE ARIZONA BOARD OF REGENTS ON BEHALF OF THE UNIVERSITY OF ARIZONA, DOWA ELECTRONICS MATERIALS CO., LTD.. Invention is credited to Hirohisa OMOTO, Dong Chul PYUN, Heemin YOO, Takayuki YOSHIDA.
Application Number | 20140356642 14/460513 |
Document ID | / |
Family ID | 44227546 |
Filed Date | 2014-12-04 |
United States Patent
Application |
20140356642 |
Kind Code |
A1 |
PYUN; Dong Chul ; et
al. |
December 4, 2014 |
METALLIC MAGNETIC POWDER AND MANUFACTURING METHOD OF THE SAME,
MAGNETIC PAINTING, MAGNETIC POWDER FOR MAGNETIC THERAPY, AND
MAGNETIC RECORDING MEDIUM
Abstract
A metallic magnetic powder where a primary particle of each
metallic magnetic particle is a powder without forming an
aggregate, and a method of making the same that includes
manufacturing a metallic magnetic powder constituted of metallic
magnetic particles, containing a metallic magnetic phase, with Fe,
or Fe and Co as main components, rare earth elements or yttrium and
one or more non-magnetic components removing the non-magnetic
component from the metallic magnetic with a reducing agent, while
making a complexing agent exist for forming a complex with the
non-magnetic component in water; oxidizing the metallic magnetic
particle with the non-magnetic component removed; substituting
water adhered to the oxidized metallic magnetic particle with an
organic solvent; and coating the surface of the metallic magnetic
particle with an organic matter different from the organic solvent,
while maintaining a wet condition of the metallic magnetic particle
with the organic solvent adhered thereto.
Inventors: |
PYUN; Dong Chul; (Tuscon,
AZ) ; YOO; Heemin; (Tuscon, AZ) ; OMOTO;
Hirohisa; (Tokyo, JP) ; YOSHIDA; Takayuki;
(Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
THE ARIZONA BOARD OF REGENTS ON BEHALF OF THE UNIVERSITY OF
ARIZONA
DOWA ELECTRONICS MATERIALS CO., LTD. |
Tuscon
Tokyo |
AZ |
US
JP |
|
|
Assignee: |
THE ARIZONA BOARD OF REGENTS ON
BEHALF OF THE UNIVERSITY OF ARIZONA
Tuscon
AZ
DOWA ELECTRONICS MATERIALS CO., LTD.
Tokyo
|
Family ID: |
44227546 |
Appl. No.: |
14/460513 |
Filed: |
August 15, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13103410 |
May 9, 2011 |
|
|
|
14460513 |
|
|
|
|
Current U.S.
Class: |
428/570 ;
252/62.54 |
Current CPC
Class: |
B22F 1/02 20130101; G11B
5/653 20130101; Y10T 428/2982 20150115; G11B 5/70615 20130101; H01F
1/09 20130101; Y10T 428/12181 20150115; G11B 5/70621 20130101; B22F
1/0062 20130101; C09D 175/06 20130101; G11B 5/656 20130101; B22F
1/0088 20130101; C09D 133/20 20130101 |
Class at
Publication: |
428/570 ;
252/62.54 |
International
Class: |
H01F 1/09 20060101
H01F001/09; C09D 133/20 20060101 C09D133/20; G11B 5/65 20060101
G11B005/65; C09D 175/06 20060101 C09D175/06 |
Foreign Application Data
Date |
Code |
Application Number |
May 12, 2010 |
JP |
2010-110360 |
Claims
1. A metallic magnetic powder constituted of metallic magnetic
particles, comprising Fe, or Fe and Co as main components, having
an average major axis diameter of 10 to 50 nm confirmed by a
transmission electronic microscopic image, having a calculated
particle volume of 2500 nm.sup.3 or smaller, and having a value of
a peak diameter calculated by a wet-type particle size measurement
(DLS method) in a range of 10 to 200 nm.
2. The metallic magnetic powder according to claim 1, wherein a
value of a relative ratio (peak diameter/average major axis
diameter) of the average major axis diameter obtained by the
transmission electronic microscopic image, and a peak diameter
calculated by the DLS method is 5 or smaller.
3. A metallic magnetic powder constituted of metallic magnetic
particles, having a metal phase comprising Fe, or Fe and Co as main
components, having an oxide layer on the surface of the metal
phase, with the surface of the oxide layer coated with an organic
matter having a molecular weight of 100 or larger.
4. The metallic magnetic powder according to claim 3, wherein the
organic matter is a high molecule having polydispersity of 1.05 to
2.0.
5. The metallic magnetic powder according to claim 3, wherein the
organic matter has a structure containing a sulfonic acid group
and/or a phosphonic acid group.
6. A magnetic painting adopting the metallic magnetic powder
according to claim 1.
7. A magnetic powder for magnetic therapy adopting the metallic
magnetic powder according to claim 1.
8. A magnetic recording medium adopting the metallic magnetic
powder according to claim 1.
Description
CROSS-REFERENCE TO THE RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 13/103,410, filed May 9, 2011, which claims
priority to Japanese Patent Application No. 2010-110360, filed May
12, 2010, the entire contents of which are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a composite metallic
magnetic powder and a manufacturing method of the same used for
high density magnetic recording, a magnetic painting, magnetic
powder for magnetic therapy, and a magnetic recording medium.
[0004] 2. Description of Related Art
[0005] Further higher recording density is desired in accordance
with increase in capacity of the magnetic recording medium,
represented by the one used for the purpose of backup of data in a
computer. In order to achieve a high recording density, it appears
that a magnetic powder with small particle volume is requested. In
order to respond to such a request, after examination regarding
metallic magnetic powder, inventors of the present invention
disclose patent documents 1 to 3, and so forth.
[0006] Patent document 1 discloses a ferromagnetic iron alloy
powder for magnetic recording medium, comprising acicular particles
having an average major axis diameter (X) of 20 nm or larger and 80
nm or smaller, having an oxygen content of 15 wt % or larger and a
coercive force (Hc) of 0.0036X.sup.3-1.1X.sup.2+110X-1,390 (Oe) or
larger.
[0007] Patent document 2 discloses a technique of improving
magnetic characteristics per unit volume, by dissolving and
removing a non-magnetic component that exists on the surface of the
metallic magnetic powder, by using a reducing agent, etc.
[0008] As a development of the patent document 2, patent document 3
discloses a technique of forming a layer of carbon on the surface
of the metallic magnetic particle by coating the surface of the
metallic magnetic particle with an organic matter and applying
re-reduction treatment thereto.
(Patent document 1) Japanese Patent Laid Open Publication No.
2003-263720 (Patent document 2) Japanese Patent Laid Open
Publication No. 2007-294841 (Patent document 3) Japanese Patent
Laid Open Publication No. 2009-084600
OUTLINE OF THE INVENTION
Problem to be Solved by the Invention
[0009] Patent document 1 discloses a metallic magnetic particle for
a magnetic recording medium capable of exhibiting high magnetic
characteristics even in the form of a fine particle, and a
manufacturing method of the metallic magnetic powder. However, when
the metallic magnetic powder is composed of ultrafine particles, an
oxide layer made of a non-magnetic component formed on the surface
of each ultrafine particle becomes thick to thereby secure
stability of the ultrafine particle. Then, decrease of the magnetic
characteristics is observed.
[0010] In order to solve the above-described problem, patent
document 2 discloses a technique of downsizing the metallic
magnetic particle by removing the non-magnetic component formed on
the surface of the ultrafine particle by using the reducing agent.
However, when an object is coated with a painting using the
metallic magnetic particles, this involves a problem that an
aggregate of the metallic magnetic particles are formed.
[0011] Patent document 3 discloses a technique of depositing carbon
derived from the organic matter, on the surface of the downsized
metallic magnetic particle, and reducing the formation of the
aggregate. However, the metallic magnetic particle with carbon
deposited thereon is insufficient in stability in the painting, and
in addition, due to the carbon existing on the surface, there is a
problem that the kind of an applicable binder is limited.
[0012] As described above, the inventors of the present invention
achieve a point that it is important to inhibit the aggregate of
the particles and maintain the form of a primary particle of each
metallic magnetic particle that constitutes the metallic magnetic
powder, and consider it possible to achieve magnetic recording with
further high density if the aggregate of the metallic magnetic
particles can be inhibited in a coating film, etc, with which the
object is coated.
[0013] In view of the above-described circumstance, the present
invention is provided, and in order to solve the above-described
problem, an object of the present invention is to provide a
metallic magnetic powder which is formed, without forming an
aggregate of a primary particle of each metallic magnetic particle
that constitutes the metallic magnetic powder.
SUMMARY OF THE INVENTION
[0014] After strenuous examination regarding the above-described
problem, it is found that the metallic magnetic powder can be
obtained by coating the surface of each particle with an organic
matter, each particle constituting the metallic magnetic powder in
a state of maintaining a wet condition after removing a
non-magnetic component of the metallic magnetic powder, wherein
each metallic magnetic particle constituting the metallic magnetic
powder maintains the form of a primary particle of the metallic
magnetic particle. Thus, the present invention is completed.
[0015] Namely, in order to solve the above-described problem, a
first invention provides a manufacturing method of a metallic
magnetic powder, comprising the steps of:
[0016] manufacturing a metallic magnetic powder constituted of
metallic magnetic particles, containing a metallic magnetic phase
with Fe, or Fe and Co as main components, rare earth elements
(wherein yttrium is also treated as the rare earth element), one
kind or more non-magnetic components such as Al and Si;
[0017] removing the non-magnetic component from the metallic
magnetic particles, by making a reducing agent act thereon, while
making a complexing agent exist for forming a complex with the
non-magnetic component in water;
[0018] oxidizing the metallic magnetic particle with the
non-magnetic component removed;
[0019] substituting water adhered to the oxidized metallic magnetic
particle, with an organic solvent; and
[0020] coating the surface of the metallic magnetic particle with
an organic matter different from the organic solvent, in a state of
maintaining a wet condition of the metallic magnetic particle with
the organic solvent adhered thereto.
[0021] A second invention provides the manufacturing method of the
metallic magnetic powder according to the first invention, wherein
the step of oxidizing the metallic magnetic particle is performed
by using peroxide.
[0022] A third invention provides the manufacturing method of the
metallic magnetic powder according to the first or the second
invention, wherein the organic matter different from the organic
solvent covering the surface of the metallic magnetic particle, has
a molecular weight of 100 or more, which is larger than the
molecular weight of the organic solvent.
[0023] A fourth invention provides the manufacturing method of the
metallic magnetic powder according to any one of the first to third
inventions, wherein the organic matter different from the organic
solvent covering the surface of the metallic magnetic particle has
a structure containing a sulfonic acid group and/or a phosphonic
acid group.
[0024] A fifth invention provides the manufacturing method of the
metallic magnetic powder according to any one of the first to
fourth inventions, comprising the step of drying the metallic
magnetic powder after the step of covering the surface of the
metallic magnetic particle, with the organic matter different from
the organic solvent.
[0025] A sixth invention provides a metallic magnetic powder
constituted of metallic magnetic particles, comprising Fe, or Fe
and Co as main components, having an average major axis diameter of
10 to 50 nm confirmed by a transmission electronic microscopic
image, having a calculated particle volume of 2500 nm.sup.3 or
smaller, and having a value of a peak diameter calculated by a
wet-type particle size measurement (DLS method) in a range of 10 to
200 nm.
[0026] A seventh invention provides the metallic magnetic powder
according to the sixth invention, wherein a value of a relative
ratio of the average major axis diameter obtained by the
transmission electronic microscopic image, and a peak diameter
calculated by the DLS method is 5 or smaller.
[0027] An eighth invention provides a metallic magnetic powder
constituted of metallic magnetic particles, having a metal phase
comprising Fe, or Fe and Co as main components, having an oxide
layer on the surface of the metal phase, with the surface of the
oxide layer coated with an organic matter having a molecular weight
of 100 or larger.
[0028] A ninth invention provides the metallic magnetic powder
according to the eight invention, wherein the organic matter is a
high molecule having polydispersity of 1.05 to 2.0.
[0029] A tenth invention provides the metallic magnetic powder
according to the eight or ninth invention, wherein the organic
matter has a structure containing a sulfonic acid group and/or a
phosphonic acid group.
[0030] An eleventh invention provides a magnetic painting adopting
the metallic magnetic powder according to any one of the sixth to
ninth inventions.
[0031] A twelfth invention provides a magnetic powder for magnetic
therapy adopting the metallic magnetic powder according to any one
of the sixth to tenth inventions.
[0032] A thirteenth invention provides a magnetic recording medium
manufactured by using the metallic magnetic powder according to
anyone of the sixth to ninth inventions.
Advantage of the Invention
[0033] The metallic magnetic powder according to the present
invention is the metallic magnetic powder, wherein each particle
maintains the form of a primary particle, and contributes to
magnetic recording with high density.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a schematic view showing a state of a metallic
magnetic particle.
[0035] FIG. 2 shows a particle size distribution measured by DLS in
an aggregate according to an example.
DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0036] The following case can be given as an embodiment of the
present invention. First, regarding a metallic magnetic particle
and a manufacturing method of the metallic magnetic powder, the
metallic magnetic powder manufacturing step, the non-magnetic
component removing step, the wet-type stabilization step, the
solvent substituting step, and the organic matter coating step will
be described sequentially, and next, regarding physical
characteristics of the metallic magnetic particle and the metallic
magnetic powder, particle shape and volume, the form of the
particle, specific surface area of the particle, composition
analysis of powder, evaluation of powder magnetic characteristics,
and evaluation of a single layer magnetic tape will be described
sequentially.
<Metallic Magnetic Powder Manufacturing Step>
[0037] The manufacturing step of the metallic magnetic powder
according to the present invention will be described. The metallic
magnetic powder can be manufactured by a publicly-known method.
[0038] An example of a specific method of the metallic magnetic
powder manufacturing step will be described.
[0039] First, iron oxyhydroxide, with a ratio of Co to Fe in atomic
ratio (called "Co/Fe atomic ratio" hereafter) set in a range of 0
to 50 at %, is manufactured as a precursor substance. As a
manufacturing method of the iron oxyhydroxide, a method of adding
an aqueous ferrous salt solution to a carbonate solution, thereby
generating iron carbonate (caustic alkali may be added as needed),
then adding oxygen-containing gas to generate a nucleus crystal,
and thereafter growing a particle to form iron oxyhydroxide, and a
method of adding the caustic alkali singularly to the aqueous
ferrous salt solution to form iron oxyhydroxide, can be used.
[0040] At this time, a precursor of the metallic magnetic powder
applied to the present invention is formed by adjusting the growth
of the iron oxyhydroxide, being a raw material. Specifically, the
major axis diameter of the iron oxyhydroxide is set to 10 to 100
nm.
[0041] The manufactured iron oxyhydroxide is filtered and washed by
a publicly-known method, uniform heat treatment is applied thereto,
and further at least one kind of rare earth elements (including
yttrium), aluminium, and silicone are added thereto as a sintering
preventive agent, which is then dried in an inert gas or in the air
for 6 hours or more under condition of 80 to 300.degree. C., to
thereby obtain an iron oxyhydroxide dried solid material. By
heating and dehydrating this solid material at 250 to 700.degree.
C. by a publicly-known method, an iron-based oxide such as
.alpha.-Fe.sub.2O.sub.3 is obtained.
[0042] Subsequently, the obtained iron oxide is reduced by
vapor-phase reduction. Carbon monoxide, acethylene, and hydrogen,
etc, can be given as reducing gases. Such a reducing operation can
be performed by multi-step reduction wherein reduction is divided
into first-step reduction and second-step reduction, at different
temperatures in both steps. Specifically, the iron oxyhydroxide is
reduced while maintaining a relatively low temperature in the first
step, and is reduced while maintaining a high temperature in the
second step, with a temperature increasing step interposed between
the first step and the second step.
[0043] The metallic magnetic powder obtained after reduction has
extremely high activity, and therefore there is a possibility of
ignition if being handled in the atmosphere. Therefore, preferably
a dense oxide layer is formed on the surface of the metallic
magnetic particle by the oxidization step, so that the metallic
magnetic particle can withstand handling in the atmosphere. In
order to form a dense layer on the surface of the metallic magnetic
particle, the metallic magnetic particle is cooled to a temperature
in a range of 50 to 200.degree. C. after the aforementioned
reducing step, then weak oxidizing gas is introduced, and a stable
oxide layer is formed on the surface of the metallic magnetic
particle. If required, after the oxide layer is formed, the
metallic magnetic particles may be exposed to a reduction
atmosphere, and after a surface oxide layer modifying operation is
performed, stabilization treatment may be applied to the surface
again.
<Non-Magnetic Component Removing Step>
[0044] The non-magnetic component removing step is the step of
removing a non-magnetic component such as aluminium and rare earth
elements contained in the metallic magnetic powders manufactured by
the aforementioned step, and obtaining the metallic magnetic
powder, with particle volume reduced.
[0045] The non-magnetic component removing step is the step of
removing a non-magnetic component such as aluminium and rare earth
elements contained in the metallic magnetic powders manufactured by
the aforementioned step, and obtaining the metallic magnetic
powder, with particle volume reduced.
[0046] A specific method of the non-magnetic component removing
step will be described.
[0047] A solution dissolving a compound (complexing agent) capable
of forming a complex with at least one kind or more of the rare
earth elements, aluminium, and silicone contained in the metallic
magnetic powder obtained as described above, is prepared as a
treatment liquid. As the complexing agent, ordinarily used
chemicals in the electroless plating such as a citrate, a tartrate,
a lactate, and a malate, can be used. The concentration of the
complexing agent is preferably set to about 0.01 to 10 mol/L.
Further, a substance having a pH buffer effect such as ammonium
salt may be added as needed.
[0048] Next, the metallic magnetic powder is added to the treatment
liquid. An amount of addition of the metallic magnetic powder is
preferably about 1 to 100 g per 1 L of treatment liquid. Further,
in order to maintain uniformity of the reaction in the liquid,
stirring or forcible dispersion (for example, ultrasonic
dispersion) is preferably performed.
[0049] The reducing agent is added after the metallic magnetic
powder is uniformly dispersed into the treatment liquid. As such a
reducing agent, a strong reducing agent such as hydrazine
(N.sub.2H.sub.2), lithium aluminium hydride (LiAlH.sub.4), and
sodium boron hydride (NaBH.sub.4) can be used. The concentration of
the reducing agent is preferably set to 0.01 to 10 mol/L.
[0050] After this reducing agent is added, leaching operation is
performed for 10 to 300 minutes while maintaining a liquid
temperature at 10 to 50.degree. C. The non-magnetic component is
eluted into the treatment liquid by this leaching operation, thus
relatively increasing an amount of magnetic elements in the
particle of the metallic magnetic powder. Note that this reaction
is preferably performed in an inert gas atmosphere.
[0051] Thus, the metallic magnetic particle comprising Fe, or Fe
and Co as main components, having an average major axis diameter of
10 to 50 nm confirmed by a transmission electronic microscopic
image, and having a calculated particle volume of 2500 nm.sup.3 or
smaller, can be obtained.
<Wet-Type Stabilization Step>
[0052] The wet-type stabilization step is the step of forming the
oxide layer once, on the surface of the metallic magnetic particle
with the non-magnetic component removed, under a wet condition
without undergoing the drying step after the aforementioned
non-magnetic component removing step.
[0053] Then, without undergoing the drying step, aggregation of the
metallic magnetic particles can be inhibited by forming the oxide
layer on the surface of the metallic magnetic powder with the
non-magnetic component removed, by a wet-type method. In this
wet-type stabilizing operation, the oxide layer is formed on the
surface of the metallic magnetic powder. Wherein, in order to form
a further suitable uniform layer on the surface of the metallic
magnetic powder, peroxide, etc, is preferably used. Specifically,
oxidizing agents such as inorganic peroxide and potassium chromate,
and organic peroxide can be given. Wherein, the inorganic peroxide
and particularly hydrogen peroxide is preferable in consideration
of easiness of handling.
[0054] Here, when the metallic magnetic powder and the treatment
liquid in the non-magnetic component removing step are separated
and dried and thereafter the oxide layer is formed to thereby
manufacture the magnetic powder, characteristics of a medium are
less improved than expected in some cases, in spite of a remarkable
reduction of the volume of the metallic magnetic particle.
Regarding such a phenomenon, after examination by the inventors of
the present invention, it is found that when the metallic magnetic
powder and the treatment liquid are separated and dried and the
oxide layer is thereafter formed to thereby manufacture the
metallic magnetic powder, dispersability and compatibility with
resin are deteriorated on the surface of the metallic magnetic
particle, and further the metallic magnetic particles are
aggregated again in the process of drying. As a result, when the
metallic magnetic powder is turned into a form of coating, the
metallic magnetic particles can not be sufficiently dispersed, and
the volume of the metallic magnetic powder becomes greater than the
volume of individual particle (increase of a so-called activation
volume), and consequently an improvement effect can not be
obtained, which is expected to be obtained by reduction effect of
the volume of the metallic magnetic particle.
[0055] As an amount of addition of oxide in the wet-type
stabilization step, peroxide of 0.001 mol or more, preferably 0.005
mol or more, and further preferably 0.01 mol or more, with respect
to 1 g of the metallic magnetic powder to be treated, is added. By
adding such an amount of oxide, preferably a suitable oxide layer
can be formed, which is stabilized as the magnetic powder and
improved in preservation stability.
[0056] Meanwhile, an upper limit of addition of the peroxide is
preferably set to 0.05 mol or less, with respect to 1 g of the
metallic magnetic powder to be treated. By setting the addition of
the peroxide to the aforementioned amount or less, it is possible
to prevent a case that oxidation reaction occurs at the same time
on the surface of the metallic magnetic particle, and as a result,
the suitable oxide layer can not be formed, and a case that the
metallic magnetic particle receives excessive oxidation and the
volume of a metal core is reduced, and as a result, such a metallic
magnetic particle is not suitable as a high density magnetic
recording material.
[0057] A reaction temperature in the wet-type stabilization step is
preferably set to 0 to 50.degree. C. and preferably set to 10 to
40.degree. C., from a viewpoint of securing appropriate
productivity, and from a viewpoint of securing formation of a
uniform oxide layer by suppressing non-uniformity of reaction and
improving the magnetic characteristics.
<Solvent Substituting Step>
[0058] The solvent substituting step is the step of substituting
moisture covering the surface of the metallic magnetic particle
once, for suppressing the aggregation of the metallic magnetic
particles, when the metallic magnetic powder is turned into a dried
powder.
[0059] A specific method of the solvent substituting step will be
described.
[0060] After the aforementioned wet-type stabilization step, the
obtained metallic magnetic powder and the treatment liquid are
separated from each other. A publicly-known general method may be
used as the separation method. Here, in order to remove a component
generated during operation of the non-magnetic component removing
step, which remains on the surface of the metallic magnetic
particle, the separated metallic magnetic powder is dispersed into
clean pure water again. At this time, the pure water is preferably
stirred, or ultrasonic washing is preferably used.
[0061] After dispersion into the pure water, the separating
operation is performed again, to separate the metallic magnetic
powder and a washing liquid from each other, and thereafter the
separated metallic magnetic powder is dispersed again into an
organic solvent, to thereby obtain an organic solvent dispersion
liquid of the metallic magnetic powder.
[0062] Note that by repeating the operation of separating the
metallic magnetic powder and the organic solvent from each other by
performing separating operation of the obtained metallic magnetic
powder into the organic solvent dispersion liquid, and thereafter
dispersing the separated metallic magnetic powder into the organic
solvent again, the moisture remained on the surface of the metallic
magnetic particle can be further substituted with the organic
matter, and this is preferable.
[0063] There is no particular limit in a temperature condition of
the solvent substituting operation. However, the operation is
preferably performed at a lower temperature than a vaporization
temperature of a used organic medium, from a viewpoint of
operability.
[0064] As preferable examples of the organic solvent used in the
solvent substituting operation, toluene, methyl ethyl ketone, and
cyclohexanone can be given.
[0065] An effect of the solvent substituting step will be
described, with reference to FIG. 1.
[0066] FIG. 1 is a schematic view showing a state of the metallic
magnetic particle, wherein FIG. 1A shows a case that the solvent
substituting step is executed, and FIG. 1B shows a case that the
solvent substituting step is not executed.
[0067] When the solvent substituting step is executed, as shown in
FIG. 1A, organic matter 2 as will be described later is coated with
metallic magnetic particle 1 in the "organic matter coating step",
without aggregation of the metallic magnetic particles. As a
result, the metallic magnetic particle 1 coated with the organic
matter, is not aggregated again from the first step to the final
step, with the subsequent prescribed step interposed, and therefore
the magnetic characteristics can be sufficiently exhibited.
[0068] Meanwhile, when the solvent substituting step is not
executed, as shown in FIG. 1B, the organic matter 2 is coated with
the metallic magnetic particle 1 in a state of aggregation. When
such a state is formed once, the aggregation is not solved from the
first step to the final step, with the subsequent prescribed step
interposed, and therefore the magnetic characteristics can not be
sufficiently exhibited.
<Organic Matter Coating Step>
[0069] The organic matter coating step is the step of further
adding the organic matter to the organic solvent dispersion liquid
of the metallic magnetic powder obtained by the solvent
substituting step, and coating the surface of the metallic magnetic
particle with the organic matter.
[0070] The organic matter used at this time is preferably a
substance different from the aforementioned organic solvent and has
a larger molecular weight than that of the organic solvent. By
adding the organic matter, the organic matter is adsorbed on the
surface of the metallic magnetic particle, and the magnetic powder
is suitably dispersed in the organic solvent by benefit of the
organic matter.
[0071] Here, as the organic matter, homopolymer, copolymer, random
polymer, block copolymer, dendrimer, isotactic polymer, straight
chain or branched polymer, star polymer, partial polymer, and graft
copolymer can be given as examples. Here, the "polymer" is made by
polymerizing two or more monomers, and includes a homopolymer,
being the monomer, and a copolymer. Further, the polymer may be
formed into various shapes, depending on the purpose of use.
[0072] Particularly, the polymer having an unsaturated structure
such as an ethylene group is preferable as the polymer of the
present invention. For example, N-functionalized polymer, (methane
phemin) acrylic acid, vinyl polymer, conjugated high molecule such
as polythiophene, styrene polymer, polyethylene glycol,
polysiloxanes, polyethylene oxide, hydroxyl ethyl (methane phemine)
acrylic acid, dimethyl amino ethyl (methane phemine) acrylic acid,
polyacrylonitrile, polystyrene, polymethyl metha acrylate (PMMA),
polypyrroles, protein, peptide, fluorescent polymer having straight
chain or branched alkyl group, and also as the polymer having
relatively low molecule, oleylamine, olein acid, and TOPO are given
as examples.
[0073] Further, the polymer having carbon numbers of 1 to 24 is
preferable as the polymer having the aforementioned structure.
Moreover, such a polymer may be used singly or may be used in
combination. Moreover, the polymer obtained by polymerizing the
high molecule having one or preferably two or more unsaturated
groups, and the monomer obtained by ethylenizing alkoxysilan, can
also be used.
[0074] Among the substances having the above-described structure,
it is preferable to use the polymer including polystyrene,
polymethacrylate, polyacrylate, polyacrylonitrile, a vinyl group,
and the polymer including polythiophene, polypyrrole,
polyaniline.
[0075] Among the above-described organic matters, the one having a
phosphonate group or a sulfonate group in its structure is
preferable. This is because by having such a functional group
adsorbed on the surface of the metallic magnetic particle,
dispersability of the metallic magnetic particle in a magnetic
painting, being a product as will be described later, can be
secured.
[0076] The molecular weight of the organic matter adsorbed on the
surface of the metallic magnetic particle is 100 or more, 100000 or
less, and preferably 1000 or more and 50000 or less. This is
because if the molecular weight is 100 or more, an effect of
securing the dispersability of the metallic magnetic particle can
be obtained, and if the molecular weight is 100000 or less, a
presence amount of the organic matter per unit volume of the
metallic magnetic particle can be secured, and an effect of
securing the dispersability of the metallic magnetic particle can
be obtained.
[0077] It is also preferable that the organic matter added to the
magnetic painting, being the product as will be described later,
namely a so-called binder component is previously adsorbed on the
surface of the metallic magnetic particle. With this structure,
when the magnetic painting is manufactured, it can be manufactured
without adding a binder again, and this is preferable from the
viewpoint of reducing the step.
[0078] The value of polydispersability of the high molecule used in
the present invention falls within a range of 1 to 2, and more
preferably within a range of 1.05 to 1.20. The value of the
polydispersability is approximately 1, thereby showing an ideal
polymer and this is preferable. When the polydispersability shows a
value smaller than 2, uniform particle coating can be obtained, and
such an organic matter can be used in the present invention.
[0079] The constituent ratio (weight ratio) of [metal]/[coating
material (organic matter)] in the metallic magnetic particle of the
present invention is preferably 10/90 to 90/10. Particularly, the
ratio of a metal portion is set to be high for the purpose of use
for the magnetic recording in which high magnetic characteristics
are required, and the ratio of a coating material (organic matter)
portion is set to be high for the purpose of use for DDS (Drug
Delivery System) as will be described later in which not so high
magnetic characteristics are required.
[0080] As the purpose of use other than the magnetic painting,
being the product as will be described later wherein the metallic
magnetic particle of the present invention is used, the purpose of
use for a magnetic induction therapy (DDS) can be considered. In
the magnetic induction therapy, the polymer is used in the painting
and a medicine is contained in this polymer portion, so that the
medicine can reach an affected part effectively by being guided by
magnetism from outside. At this time, if there is less metal
portion, such a portion is hardly recognized as a foreign matter by
a living body, and it is expected that rejection hardly occurs
preferably in this case. Namely, mixture of a medicine component
into a polymer structure portion, being the painting, is also one
of the preferable embodiments of the present invention.
[0081] It is also preferable that after the operation of the
organic matter coating step is ended, the metallic magnetic powder
is dried to be a dry powder. This is because according to this
structure, the aggregation is hardly generated by the effect that
the surface of the metallic magnetic particle is coated with the
organic matter, unlike a case that it is coated with water. Namely,
this is because even if undergoing the drying step, the aggregation
of the metallic magnetic powder hardly occurs, and relatively soft
dry powder can be obtained. This is preferably suitable in
handling.
[0082] Note that the drying step is preferably performed for a long
time at a low temperature. Specifically, the temperature is set to
100.degree. C. or less and preferably 80.degree. C. or less.
(Physical Characteristics of the Metallic Magnetic Particle and
Metallic Magnetic Powder)
[0083] Physical characteristics of the metallic magnetic particle
and the metallic magnetic powder according to the present invention
will be described.
<Particle Shape and Weight>
[0084] The metallic magnetic particle of the present invention is
formed into a acicular, fusiform, or flat acicular shape. Here, the
flat acicular particle is one of the embodiments of the acicular
particles, wherein the shape of the particle obtained by being cut
by the short axis is not a circle but an elliptical shape.
Discrimination can be made by TEM images. Specifically, there are a
method of inclining the particle and confirming the degree of the
separation of a cross-section from the circle, and a method of
confirming the ratio of the cross-section by using shadowing. Note
that the particle whose cross-section is determined to be a circle,
is the fusiform particle.
[0085] The metallic magnetic particle of the present invention is
set to have a size of 10 to 50 nm, preferably 10 to 45 nm, and
further preferably 10 to 30 nm in a major axis diameter when the
particle has the acicular shape or the shape similar to the
acicular shape. By setting the size of the metallic magnetic
particle within this range, such a metallic magnetic particle can
contribute to high density magnetic recording.
[0086] When the major axis diameter is 50 nm or less, the size of
the particle itself is not excessively large, and preferably the
metallic magnetic powder constituted of such particles can be
applied to the high density magnetic recording. Further, when the
major axis diameter is 10 nm or more, a problem of super para of
the magnetism can be preferably prevented. Moreover, in the high
density magnetic recording, an axial ratio is also an important
factor in a case of the metallic magnetic particle that exhibits
magnetism by using magnetic shape anisotropy. However, in this
case, the axial ratio may be 2 or more.
[0087] Further, in the metallic magnetic particle according to the
present invention, when the particle, being approximately a
cylindrical shape, is calculated, (namely, when obtaining a value
calculated by (average short axis
diameter/2).sup.2.times.circumference ratio.times.average major
axis diameter), the particle has a volume of 2500 nm.sup.3 or less,
and further fine particle has a volume of 2250 nm.sup.3 or less,
and more further fine particle has a volume of 2000 nm.sup.3 or
less. The finer particle with small volume, being approximately the
cylindrical, contributes to reducing a particle-like noise.
Accordingly, the fine particle with small volume, being
approximately the cylindrical, is preferable. However, as described
above, from the viewpoint of preventing the deterioration of the
magnetic characteristics due to super para, the particle volume of
500 nm.sup.3 or more is preferable.
[0088] In the metallic magnetic powder according to the present
invention, components such as aluminium, silicone, and rare earth
elements, are reduced. Specifically, the atomic ratio of
[non-magnetic component (R+Si+Al)])/[magnetic component (Fe+Co)] is
20% or less, and when the aforementioned components are further
reduced, the atomic ratio is 15% or less, and when the
aforementioned components are more further reduced, the atomic
ratio is 12% or less.
[0089] Note that in the present invention, the rare earth element
containing yttrium is described as "R" in some cases.
[0090] When the metallic magnetic powder is manufactured, in order
to prevent sintering of the metallic magnetic particle, the
non-magnetic component exists outside of a metal core. Accordingly,
by removing the non-magnetic component, the effect of reducing the
volume of the metallic magnetic particle can be obtained. Further,
by removing the non-magnetic component, higher magnetic
characteristics per unit volume of the metallic magnetic particle
can be obtained.
<Form of the Particle>
[0091] The average major axis diameter of the metallic magnetic
particle according to the present invention, was measured by
photographing an image obtained by observing the magnetic powder in
a bright field under accelerated voltage of 100 kV by using a
through electron microscope (Model: JEM-100CXMark-II by JEOL Ltd.
About 300 particles were measured during this measurement.
[0092] A diameter of the aggregate of the metallic magnetic
particles of the present invention was calculated by particle size
measurement using DLS method. Specifically, the diameter was
calculated by using a DLS apparatus produced by OTSUKA ELECTRONICS
Co, Ltd.
<Specific Surface Area of the Particle>
[0093] The specific surface area of the metallic magnetic particle
of the present invention was measured by using a BET one point
method. Specifically, the specific surface area was measured by
using "4 SORB US" produced by YUASA-IONICS COMPANY, LIMITED., as a
measurement apparatus.
<Composition Analysis of the Powder>
[0094] The composition of the metallic magnetic powder of the
present invention was obtained by mass analysis of an entire body
of the metallic magnetic particle containing a metallic magnetic
phase and an oxide layer. Specifically, determinate quantities of
Co, Al, and rare earth elements were measured by using a
high-frequency inductive plasma emission analyzer ICP (IRIS/AP)
produced by Nippon Jarrell-Ash Co. Ltd., and the determinate
quantity of Fe was measured by using a HIRANUMA automatic titrator
(COMTIME-980) produced by HIRANUMA SANGYO KK. The result of the
determinate quantity is given by mass, and therefore by suitably
converting it to the atomic ratio (at %), Co/Fe atomic ratio,
Al/(Fe+Co) atomic ratio, Y/(Fe+Co) atomic ratio, (R+Al+Si)/(Fe+Co)
atomic ratio were obtained. Note that in each comparative example
and each example, Si/(Fe+Co) is a measurement limit or smaller.
Therefore, in these examples, (R+Al+Si)/(Fe+Co) atomic ratio is
equal to (R+Al)/(Fe+Co) atomic ratio.
<Evaluation of the Powder Magnetic Characteristics>
[0095] A plastic container of .phi.6 mm was filled with the
metallic magnetic powder of the present invention, and by using a
VSM apparatus (VSM-7P) produced by Toei Industry Co., Ltd.,
coercive force Hc(Oe, kA/m), saturation magnetization .sigma.s
(Am.sup.2/kg), squareness ratio SQ, BSFD of a powder body (SFD
value in a bulk state) were measured, in an external magnetic field
of 10 kOe (795.8 kA/m).
<Evaluation of Dispersability of the Particle>
[0096] The dispersability of the metallic magnetic particles of the
present invention can be evaluated by adding the obtained metallic
magnetic particles into an organic solvent (such as cyclohexanone)
and observing a sedimentation state.
[0097] Further, the dispersability can also be evaluated by
measuring a particle size distribution of the metallic magnetic
particles by DLS (Dynamic Light Scattering) method. By this
measurement method, the particle size is measured by utilizing a
state of the Brownian movement of the metallic magnetic particles.
Accordingly, the particle size can be accurately measured by this
method, and this means that independency of the metallic magnetic
particle can be ensured.
[0098] Then, a value of a measured peak diameter (maximum point of
a particle presence ratio (%) by weight conversion, obtained by the
DLS measurement) falls within a range of 10 nm to 200 nm.
[0099] Meanwhile, a value of a relative ratio of the average major
axis diameter and the peak diameter (peak diameter/average major
axis diameter) was 5 or less.
<Evaluation of a Single Layer Magnetic Tape>
[0100] Regarding the metallic magnetic particle of the present
invention, in order to confirm applicability to a medium, a single
magnetic layer was formed and evaluated. An outline is based on the
following formula.
[0101] Magnetic coating mother liquid is obtained by performing
dispersion operation into the obtained metallic magnetic powder,
prescribed binder, and prescribed solvent.
[0102] Thereafter, letdown solution for diluting the coating mother
liquid was added to the obtained magnetic coating mother liquid,
and the dispersion operation was performed again, to thereby
manufacture a magnetic painting.
[0103] The obtained magnetic painting was applied to the surface of
a polyethylene film. However, an undried polyethylene film was used
for manufacturing a tape with non-oriented metallic magnetic
particles, and the polyethylene film dried in a magnetic field was
used for manufacturing the tape with oriented metallic magnetic
particles, to thereby obtain the magnetic tape sample.
[0104] Magnetic measurement was performed for the magnetic tape
sample as described above by using the VSM apparatus (VSM-7P)
produced by Toei Industry Co., Ltd., and coercive force Hcx(Oe,
kA/m), coercive force distribution SFDx in a parallel direction to
the surface of the magnetic layer, greatest energy product BHmax,
squareness ratio SQx in a parallel direction to the surface of the
magnetic layer, squareness ratio SQz in a vertical direction to the
surface of the magnetic layer, and orientation ratio OR were
obtained.
EXAMPLES
Example 1
[0105] After 3000 mL of pure water was poured into a beaker of 5000
mL, the temperature was maintained to 30.degree. C. by a
thermoregulator. Meanwhile, 0.03 mol/L of cobalt sulfate
(guaranteed reagent) solution and 0.15 mol/L of ferrous sulfate
(guaranteed reagent) aqueous solution were mixed so that a mixture
ratio was Co:Fe=1:4 (molar ratio), to thereby prepare a mixed
solution. 500 mL of the mixed solution was added to the pure water
3000 mL, which were then mixed with each other, and thereafter
granular sodium carbonate was directly added thereto, with an
amount of carbonic acid corresponding to five times of total number
of moles of Fe and Co in the aforementioned added mixed solution,
to thereby prepare a suspension liquid mainly composed of iron
carbonate, while adjusting the mixed solution so that a liquid
temperature does not exceed a range of 35.+-.5.degree. C.
[0106] After the suspension liquid was aged for 90 minutes, a
nucleus crystal was formed, then the temperature was increased to
60.degree. C., and oxidation was continued for 90 minutes by
ventilating pure oxygen, at a flow rate of 30 mL/minute.
Thereafter, the pure oxygen was switched to nitrogen, and the
suspension liquid was aged for about 45 minutes.
[0107] Next, the liquid temperature was decreased to 40.degree. C.,
to stabilize the temperature of the liquid, and thereafter 1.0 mass
%, of aluminium sulfate aqueous solution was continued to be added
for 25 minutes at an addition velocity of 5.0 g/minute, to thereby
grow iron oxyhydroxide. Thereafter, the pure oxygen was flown to
the suspension liquid, at a flow rate of 50 mL/minute, to thereby
complete oxidation. Note that the end point of the oxidation was
confirmed by taking-up a small amount of a supernatant solution of
the suspension liquid, then adding a hexacyano iron potassium
solution thereto, and confirming that a liquid color was not
changed.
[0108] After oxidation of the suspension liquid was ended, 300 g of
sulfate aqueous solution of yttrium oxide (containing 2.0 mass % of
yttrium) was added to the suspension liquid, to form a solid
solution of yttrium, and obtain a powder (cake) of iron
oxyhydroxide whose surface is coated with yttrium.
[0109] The cake of the iron oxyhydroxide was filtered, collected,
and washed by water, and thereafter dried for hours at 130.degree.
C., to thereby obtain a dried solid substance of the iron
oxyhydroxide. 10 g of the dried solid substance was put in a bucket
and sintered for 30 minutes at 450.degree. C. in the atmosphere
while adding steam at 1.0 g/minute as moisture content, to thereby
obtain an iron-based oxide mainly composed of .alpha.-iron oxide
(hematite).
[0110] The iron-based oxide mainly composed of the .alpha.-iron
oxide was charged into the bucket where ventilation is possible,
and thereafter the bucket was installed in a through type reduction
furnace, then hydrogen gas was ventilated at a flow rate of 40
L/minute and sintering was performed for 30 minutes at 400.degree.
C. while adding steam at 1.0 g/minute as a moisture content.
[0111] After this reduction treatment was ended, supply of the
steam was stopped, and the temperature was increased to 600.degree.
C. at a temperature increasing velocity of 15.degree. C./minute in
a hydrogen atmosphere. Thereafter, reduction treatment was
performed at a high temperature for 60 minutes while adding steam
at 1.0 g/minute as moisture content, to thereby obtain an
iron-based alloy powder of example 1 (metallic magnetic powder as
an intermediate product).
[0112] Next, in order to remove the non-magnetic component from the
iron-based alloy powder, the treatment liquid to be used was
adjusted. Specifically, 0.05 mol/L of sodium tartrate, being a
complexing agent and 0.1 mol/L of ammonium sulfate, being a buffer
agent, were mixed into 900 mL of pure water, to thereby prepare a
treatment liquid adjusted to pH9 with NH.sub.3.
[0113] Then, 10 g of the iron-based alloy powder after reduction
treatment was charged into the treatment liquid, and the
temperature was maintained to 30.degree. C. Thereafter, 0.3 mol/L
of sodium borohydride, being the reduction agent, was added, and
the above mixture was then aged while being stirred for 30 minutes
at 30.degree. C., to thereby obtain slurry.
[0114] A hydrogen peroxide solution obtained by diluting 17.8 g of
pure water with 35% of hydrogen peroxide was added to the obtained
slurry, and the above mixture was aged for 30 minutes while being
stirred. Then, particles were settled from the slurry by natural
sedimentation, and supernatant was removed by decantation. Then,
1000 mL of pure water was added and the mixture was stirred again
for 30 minutes, to thereby wash the iron-based alloy powder with
water. Then, the particles were settled by natural sedimentation
again, and further the supernatant mainly composed of the
aforementioned water was removed by decantation.
[0115] After the aforementioned supernatant was removed, 500 mL of
ethanol was added, and in the same way as the above-described water
washing, the settled particles were spread over ethanol by stirring
at a normal temperature. Thereafter, the particles were settled
again by natural sedimentation, and the supernatant mainly composed
of the ethanol was removed by decantation. Then, the ethanol was
added, and an operation of removing the supernatant mainly composed
of ethanol (in the present invention, the operation is called
"solvent substituting operation (1)" in some cases.) was repeated
five number of times.
[0116] After the solvent substituting operation (1) of five number
of times was performed, 500 mL of toluene was added to the settled
particles. Then, the above mixture was stirred in the same way as
the aforementioned solvent substituting operation (1) at a normal
temperature, to thereby make the magnetic powder spread over
toluene. Thereafter, the particles were settled again by natural
sedimentation, and the supernatant mainly composed of toluene was
removed by decantation. Then, the toluene was added, and the
operation of removing the supernatant mainly composed of toluene
(the operation is described as "solvent substituting operation (2)"
in some cases.) was repeated four number of times. However, in the
fourth solvent substituting operation (2), the supernatant was not
removed and the slurry of the metallic magnetic particles, in which
toluene was dispersed, was obtained.
[0117] The obtained toluene dispersed slurry of the metallic
magnetic particles was subjected to treatment for 10 minutes at a
rotation number of 4000 rpm by using a centrifugal machine, to
thereby forcibly settle the metallic magnetic particles. Then, the
supernatant mainly composed of toluene was removed, to thereby
separate and obtain the metallic magnetic particles.
[0118] The obtained 46.0 g of the metallic magnetic powder
(concentration of a solid portion: 11.2 mass %) was added to 1400 g
of cyclohexanone, and the above mixture was stirred and dispersed.
Then, the slurry was obtained by dispersing the dispersing object
by ultrasonic waves, while the liquid temperature was adjusted so
as not to exceed 50.degree. C.
[0119] Meanwhile, as the organic matter covering the metallic
magnetic particle, a treatment liquid obtained by diluting 2.0 g of
BIRON UR-8200 (registered trademark) produced by TOYOBO CO., LTD.,
with 140 g of cyclohexanone, was prepared.
[0120] Here, the treatment liquid thus obtained was added into the
slurry, and the above mixture was aged while being dispersed by
ultrasonic waves for 10 minutes, to thereby obtain the metallic
magnetic powder of the present invention, with UR-8200 adsorbed on
the surface of each metallic magnetic particle.
[0121] In order to evaluate the dispersability of the obtained
metallic magnetic powder, 0.5 g of the metallic magnetic powder was
added to 100 mL of cyclohexanone. Then, the above mixture was
subjected to dispersion treatment for 10 minutes by using an
ultrasonic distributor, to thereby obtain the slurry. Particle
sedimentation was not observed in this slurry, and the slurry shows
a uniform black color.
[0122] Evaluation of dispersability was performed to the slurry by
DLS method.
[0123] Specifically, the metallic magnetic powder was added to the
cyclohexanone and the concentration of the slurry was set to 0.5
mg/cc, and thereafter the above mixture was subjected to dispersion
treatment for 10 minutes by using the ultrasonic distributor. Then,
a particle size distribution was measured by using a probe for
concentrated solution and using Photal FPAR-1000. The measured
particle size distribution was plotted by .quadrature. in FIG. 2.
Note that FIG. 2 is a graph wherein a presence ratio of the
metallic magnetic particles by weight conversion is taken on the
vertical axis, and particle diameters are taken on the horizontal
axis.
[0124] From the result of FIG. 2, it is found that the metallic
magnetic particles with high dispersability can be obtained.
[0125] Namely, from the result of FIG. 2, it is found that a peak
diameter of the metallic magnetic particle in the slurry by the DLS
method was 38.7 nm. Meanwhile, the average major axis diameter of
the metallic magnetic powder obtained from the TEM image was 32.1
nm, and therefore the value of the peak diameter/average major axis
diameter was 1.21. As is clarified from this result, the average
major axis diameter obtained from the TEM image and the peak
diameter measured by the DLS method show approximately the same
values, and in the slurry, it can be said that the metallic
magnetic particles of the example 1 are set in almost a single
dispersion state.
[0126] The obtained 1.36 g of the metallic magnetic powder, 0.33 g
of UR-8200, being a binder, and 3.3 g of solvent in which methyl
ethyl ketone, toluene, cyclohexanone were mixed in a ratio of
33:33:34 (mass ratio), were charged into a pot having an inner
diameter of 45 mm and a depth of 13 mm. Further, 23 g of zirconia
ball (0.5.phi.) was added into this pot, leaving this pot at rest
for 10 minutes in a state that a lid of the pot was closed.
[0127] Then, the pot was set in a planetary ball mill, and a
coating mother liquid was obtained by performing dispersion
operation for 300 minutes at rotation number of 300 rpm.
[0128] Meanwhile, as a letdown solution added to the coating mother
liquid, a mixed solution, in which methyl ethyl ketone, toluene,
and cyclohexanone were mixed in a ratio of 44.3:44.3:11.3 (mass
ratio), was prepared.
[0129] 1.4 g of the letdown solution was added to the pot, and this
pot was installed in the planetary ball mill again, to thereby
manufacture the magnetic painting by performing dispersion
operation for 20 minutes at the rotation number of 300 rpm.
[0130] Contents of the pot were filtered by a PTFE filter (opening:
3.0 .mu.m) to separate and obtain only the magnetic painting.
[0131] The surface of a base film (polyethylene film 15C-B500
produced by Toray Industries, Inc. having a film thickness of 15
.mu.m) was coated with the obtained magnetic painting by using an
applicator with clearance of 55 .mu.m.
[0132] Here, the magnetic painting on the base film was dried as it
was, and a magnetic tape sample with non-orientation was obtained.
Meanwhile, after the surface of the base film was coated with the
magnetic painting, the base film was immediately inserted into a
magnetic field for 15 minutes, in which a magnetic intensity was
0.5 T, which was then dried, and the magnetic tape sample with
orientation was obtained.
[0133] Magnetic measurement was performed to the magnetic tape
sample with non-orientation by using the VSM apparatus (VSM-7P)
produced by Toei Industry Co., Ltd., and coercive force Hcx(Oe,
kA/m), magnetic force distribution SFDx in a parallel direction to
the surface of the magnetic layer, squareness ratio SQx in a
parallel direction to the surface of the magnetic layer, and
orientation ratio OR were obtained.
[0134] Meanwhile, regarding the oriented magnetic tape sample as
well, coercive force Hcx(Oe, kA/m), magnetic force distribution
SFDx in a parallel direction to the surface of the magnetic layer,
squareness ratio SQx in a parallel direction to the surface of the
magnetic layer, squareness ratio SQz in a vertical direction to the
surface of the magnetic layer, and orientation ratio OR were
obtained.
[0135] Measurement results are shown in table 3.
Examples 2, 3
[0136] The slurry of the metallic magnetic powder and the magnetic
tape sample of examples 2 and 3 were obtained, by performing the
same operation as the example 1, excluding a point that the organic
matter covering the surface of the metallic magnetic particle,
amount of the binder, composition of the solvent, and the mixing
ratio of the metallic magnetic powder and the solvent were
changed.
[0137] Here, amounts of the organic matters of examples 2 and 3 are
shown in table 1, and the solvent composition, the mixing ratio of
the metallic magnetic powder and the solvent, and the amount of the
binder are shown in table 2.
[0138] In the obtained slurry of the metallic magnetic powder of
the examples 2 and 3, the particles were not settled, and a
dispersion state was maintained for a long period of time. Further,
the particle size distribution was measured by the DLS method. The
result of measurement of the particle size distribution was plotted
by .DELTA. in FIG. 2 of the example 2, and .smallcircle. in FIG. 2
of the example 3.
[0139] From the result of FIG. 2, it was found that the peak
diameter obtained by the DLS method was 54.0 nm in the metallic
magnetic powder of the example 2, and 55.9 nm in the metallic
magnetic powder of the example 3. Meanwhile, the average major axis
diameter of the metallic magnetic powder obtained from the TEM
image was 32.1 nm, and therefore the value of the peak
diameter/average major axis diameter was 1.68 in the metallic
magnetic powder of the example 2, and 1.74 in the metallic magnetic
powder of the example 3.
[0140] Further, the same measurement as the example 1 was performed
to the magnetic tape samples of the examples 2 and 3. Measurement
results are shown in table 3.
Example 4
[0141] The slurry of the metallic magnetic powder and the magnetic
tape sample of example 4 were obtained by performing the same
operation as the example 1, excluding a point that the organic
matter covering the surface of the metallic magnetic particle was
changed from SUR-8200 to polystylene-acrylonitrile copolymer
(wherein the molecular weight was about 20000 and the ratio of
stylene/acrylonitrile was 1/1.5 in which the ratio was adjusted so
that the value of acrylonitrile was large.), and the organic matter
covering the surface of the metallic magnetic particle, the amount
of the binder, the solvent composition, and the mixing ratio of the
metallic magnetic powder and the solvent were changed.
[0142] Here, the amounts of the organic matters of the example 4
are shown in table 1, and the solvent composition and the mixing
ratio of the metallic magnetic powder and the solvent, and the
amount of the binder are shown in table 2.
[0143] In the obtained slurry of the metallic magnetic powder of
the example 4, the particles were not settled and the dispersion
state was maintained for along period of time.
[0144] Further, the same measurement as the example 1 was performed
to the magnetic tape sample of the example 4. Measurement results
are shown in table 3.
Comparative Example 1
[0145] The slurry and the magnetic tape sample of comparative
example 1 was obtained by performing the same operation as the
example 1, excluding a point that the surface of the metallic
magnetic particle was not coated with the organic matter, and the
amount of the binder, the solvent composition, and the mixing ratio
of the metallic magnetic powder and the solvent were changed.
[0146] Here, the solvent composition, the mixing ratio of the
metallic magnetic powder and the solvent, and the amount of the
binder of the comparative example 1 are shown in table 2.
[0147] In the obtained slurry of the metallic magnetic powder of
the comparative example 1, the aggregate of the metallic magnetic
particles was settled. Therefore, the particle size distribution by
the DLS method could not be measured.
[0148] Further, the same measurement as the example 1 was performed
to the magnetic tape sample of the comparative example 1.
Measurement results are shown in table 3.
[0149] From the results shown in table 3, it was found that the
magnetic tape having a high orientation ratio and a small coercive
force distribution could be obtained by the magnetic tape sample
using the metallic magnetic particles of the preset invention. Such
an effect can be understood from the fact that the coercive force
distribution (SFDx) of the magnetic tape of the examples 1 to 4,
and the coercive force distribution of the magnetic tape of the
comparative example 1 show approximately the same values in a case
of the magnetic tape with non-orientation, but the coercive force
distribution of the magnetic tape of the examples 1 to 4 shows
smaller values than the value of the coercive force distribution of
the magnetic tape of the comparative example 1 in a case of the
magnetic tape with orientation.
TABLE-US-00001 TABLE 1 Raw material slurry Metallic magnetic
Treatment liquid powder Cyclohexanone Organic matter Dispersion
liquid (g) (g) Kind (g) Kind (g) Example 1 46.0 1400 UR-8200 2.0
Cyclohexanone 140 Example 2 46.0 1400 UR-8200 1.1 Cyclohexanone 140
Example 3 46.0 1400 UR-8200 0.9 Cyclohexanone 140 Example 4 46.0
1400 (note)SAN 0.6 Cyclohexanone 140 Com.ex* 1 -- -- -- -- -- --
(Note) SAN: Polystylene-acrylonitrile *Com.ex* . . . Comparative
example 1
TABLE-US-00002 TABLE 2 Magnetic coating mother liquid Metallic
Letdown liquid magnetic Solvent Solvent powder Composition (mass
ratio) Binder Composition (mass ratio) Addition Methyl Addition
Addition Methyl Addition amount ethyl Cyclo- amount amount ethyl
Cyclo- amount (g) ketone Toluene hexanone (g) Kind (g) ketone
Toluene hexanone (g) Example 1 1.36 33.0 33.0 34.0 3.31 UR-8200
0.33 44.3 44.3 11.3 1.42 Example 2 1.26 32.0 32.0 36.0 3.30 UR-8200
0.44 44.3 44.3 11.3 1.42 Example 3 1.24 31.7 31.7 36.6 3.28 UR-8200
0.48 44.3 44.3 11.3 1.42 Example 4 1.25 32.0 32.0 36.0 3.42 UR-8200
0.33 44.3 44.3 11.3 1.42 Com ex.*1 2.40 1.0 1.0 -- 2.00 UR-8200
0.60 44.3 44.3 11.3 1.42 Com ex. * . . . Comparative example 1
TABLE-US-00003 TABLE 3 Magnetic tape (non-orientation)
characteristics Magnetic tape (orientation) characteristics Hcx Hcx
(Oe) (kA/m) SFDx SQx OR (Oe) (kA/m) SFDx SQx OR SQz Example 1 2281
181.5 0.67 0.64 1.0 2576 205.0 0.36 0.94 3.5 0.14 Example 2 2290
182.2 0.67 0.64 1.0 2634 209.6 0.37 0.94 3.6 0.14 Example 3 2317
184.4 0.65 0.64 1.0 2661 211.8 0.39 0.94 3.7 0.15 Example 4 2306
183.5 0.67 0.64 1.0 2591 206.2 0.38 0.93 3.4 0.15 Com ex.*1 2368
188.4 0.67 0.62 1.0 2653 211.1 0.47 0.88 2.6 0.21 Com ex. * . . .
Comparative example 1
[0150] If the metallic magnetic powder of the present invention is
used, a magnetic recording medium suitable for high density
magnetic recording can be provided. Further, by adjusting the
structure of the organic matter covering the surface of the
metallic magnetic particle, it can be considered that the metallic
magnetic powder can be used for the purpose of use for DDS (Drug
Delivery System), and the powder itself can action as a
medicine.
* * * * *