[0001] The present invention relates to ferrite particles suitable for a bonded magnetic
core, a process for producing the particles and a ferrite resin composite containing
the particles.
[0002] Ferrite particles and a ferrite resin composite are mainly used as a magnetic core
material of an induction coil for various electronic machines such as a computer,
communications apparatus and home appliances, and a magnetic core material of a transformer,
etc.
[0003] A bonded magnetic core which is superior to a sintered magnetic core in dimensional
stability, processability and resistance to brittleness, is advantageous in that a
small or thin core is realizable and mass production of even cores having a complicated
shape is easy. With the recent development of electronics, the demands for providing
lighter-weight, miniaturization and higher-accuracy cores which are to be produced
by making good use of these advantages has been increasing.
[0004] A bonded magnetic core is generally produced by kneading a magnetic material with
a resin such as nylon and phenol, and molding the resultant mixture by compression
molding or injection molding.
[0005] As the magnetic material, an oxide material such as Mn-Zn ferrite and Ni-Zn ferrite
is used. Such an oxide magnetic material is generally obtained by mixing a main raw
material such as Fe₂O₃, MnO, ZnO and NiO in advance by wet or dry blending so as to
have a desired composition, granulating the resultant mixture into particles having
a diameter of about several mm to several ten mm, calcining the obtained particles
and pulverizing the calcined particles into particles having an average particle diameter
of several µm to several hundred µm.
[0006] A bonded magnetic core is required to have a magnetic permeability as large as possible.
This demand has been increasing with the recent demand for a bonded magnetic core
having a higher capacity.
[0007] It is known that a bonded magnetic core is composed of a magnetic material combined
with a resin such as nylon and phenol, as described above, and that various properties,
in particular, the magnetic permeability of the bonded core has a closer relation
to and is more influenced by the properties of the magnetic material used in comparison
with a sintered core. Therefore, in order to obtain a bonded magnetic core having
a large magnetic permeability, it is advantageous to use ferrite particles having
a large magnetic permeability as a magnetic material.
[0008] With the recent tendency toward bonded magnetic cores having a higher capacity, demands
for smaller, thinner and complicated-molded products has been increasing. To satisfy
such demands, it is important that a ferrite resin composite can sufficiently fill
in all parts of the mold. For this purpose; the ferrite resin composite is required
to have an excellent fluidity.
[0009] However, in the ferrite particles produced by mixing raw materials such as Fe₂O₃,
MnO, ZnO and NiO, granulating the resultant mixture into particles having a diameter
of about several mm to several ten mm, calcining the obtained particles at a high
temperature and pulverizing the calcined particles in accordance with the above-described
conventional method, the crystal grains grow as large as several hundred µm and become
non-uniform. In addition, the crystal grain contains many pores. Due to the non-uiniform
crystal grains and the presence of many pores, the magnetic permeability is lowered.
As a result the obtained ferrite particles show a small magnetic permeability as magnetic
powder. Furthermore, since the magnetic powder itself is angular particles by pulverization,
the fluidity thereof is too poor for a suitable magnetic material for a bonded magnetic
core.
[0010] A magnetic material suitable for obtaining a bonded magnetic core having a large
magnetic permeability was conventionally proposed.
[0011] For example, in the method described in Japanese Patent Application Laid-Open (KOKAI)
No. 55-103705(1980), mixed ferrite particles consisting of particle groups having
different particle sizes of from 100 µm to 5 mm in diameter, for example, a large-particle
group having a diameter of 400 µm to 5 mm and a small-particle group having a diameter
of 100 to 350 µm are used as a magnetic material for obtaining a molded product (bonded
core) having a large initial magnetic permeability. However, since the mixed ferrite
particles contain particles having a large diameter such as 5 mm, they are not suitable
as a magnetic material for a bonded magnetic core.
[0012] The magnetic permeability and the fluidity of the ferrite resin composite for producing
a bonded magnetic core are mainly dependent on the properties of the ferrite particles
which are mixed with base materials of a resin composite. The magnetic permeability
of the ferrite resin composite has a tendency to be enlarged with the increase in
the magnetic permeability of the ferrite particles mixed. The fluidity of the ferrite
resin composite has a tendency to become more excellent as the average particle diameter
of the ferrite particles mixed becomes smaller and the surfaces of the particles become
smoother. The magnetic permeability of the ferrite particles has a close relation
to the average particle diameter and, hence, the magnetic permeability of the ferrite
resin composite is enlarged with the increase in the average particle diameter. On
the other hand, when the average particle of the ferrite particles increases, the
fluidity of the ferrite resin composite is deteriorated.
[0013] As to the relationship between the magnetic permeability and the average particle
diameter of the ferrite particles obtained by the conventional method, when the average
particle diameter is about 100 µm, the magnetic permeability is about 18, and when
the average particle diameter is about 200 µm, the magnetic permeability is about
23.
[0014] Therefore, in order to obtain a ferrite resin composite having a large magnetic permeability
and an excellent fluidity, the ferrite particles mixed are required to have an appropriate
average particle diameter which produces a large magnetic permeability and does not
obstruct the fluidity, in particular, an average particle diameter of not more than
200 µm, and to have as smooth a surface as possible.
[0015] In the researches undertaken so as to provide ferrite particles which have a large
magnetic permeability, an appropriate particle diameter and an excellent smoothness,
the present inventors have noticed that in order to produce ferrite particles having
a large magnetic permeability, it is necessary to obtain ferrite particle having uniform
crystal grains and an appropriate grain size and containing no pore, and that in order
to obtain such ferrite particles, it is important to use spherical granules for calcination
which satisfy all the following conditions: (1) pores are easy to difluse in the ferrite
particles, (2) the ferrite particles are easy to balance with the calcination atmosphere,
and (3) the ferrite particles easily receive heat uniformly. The present inventors
have also paid attention to spray drying which is capable of granulation substantially
in the form of a sphere. As a result, it has been found that by dispersing and mixing
a mixed powder for producing ferrite particles consisting essentially of 47 to 55
mol%, calculated as Fe₂O₃, of iron oxide or iron oxide hydroxide powder, 10 to 23
mol%, calculated as NiO, of nickel oxide powder and 25 to 40 mol%, calculated as ZnO,
of zinc oxide powder into and with water containing 0.2 to 1.0 wt% of a surfactant
based on the weight of the mixed powder for producing ferrite particles so as to prepare
a water-dispersed slurry having a slurry concentration of 40 to 60 wt%, spray-drying
the resultant slurry so as to obtain the granules having an average particle diameter
of 25 to 180 µm, and calcining the obtained granules at a temperature of 1100 to 1350°C,
the obtained nickel zinc ferrite spherical particles comprises crystal grains of 5
to 15 µm in average diameter, and have an average particle diameter of 20 to 150µm
and a magnetic permeability of not less than 25. The present invention has been achieved
on the basis of this finding.
[0016] In a first aspect of the present invention, there are provided ferrite particles
for a bonded magnetic core, comprising crystal grains of 5 to 15µm in average diameter,
and having an average particle diameter of 20 to 150µm and a magnetic permeability
of not less than 25.
[0017] In a second aspect of the present invention, there is provided a ferrite resin composite
which comprises nickel zinc ferrite spherical particles comprising crystal grains
of 5 to 15µm in average diameter and having an average particle diameter of 20 to
150µm, and base materials of a resin composite and which has a magnetic permeability
of not less than 25 and an excellent fluidity.
[0018] In a third aspect of the present invention, there is provided a process for producing
ferrite particles for a bonded magnetic core, comprising crystal grains of 5 to 15µm
in average diameter, and having an average particle diameter of 20 to 150µm and a
magnetic permeability of not less than 25, the process comprising the steps of dispersing
and mixing a powder for producing ferrite particles consisting essentially of 47 to
55 mol%, calculated as Fe₂O₃, of an iron oxide or iron oxide hydroxide powder, 10
to 23 mol%, calculated as NiO, of a nickel oxide powder and 25 to 40 mol%, calculated
as ZnO, of an zinc oxide powder as a starting material into and with water containing
0.2 to 1.0 wt% of a surfactant based on the weight of the powder for producing ferrite
particles so as to prepare a water-dispersed slurry having a slurry concentration
of 40 to 60 wt%, spray-drying the resultant slurry so as to obtain granules having
an average particle diameter of 25 to 180µm, and calcining the obtained granules at
a temperature of 1100 to 1350°C.
[0019] In the accompanying drawings:
Figs. 1 to 6 are scanning-type electron micrographs (x 6500), in which
Figs. 1, 2 and 3 show the structures of the ferrite particles for a bonded magnetic
core obtained in Examples 1, 2 and 4, respectively; and
Figs. 4, 5 and 6 show the structures of the ferrite particles obtained in Comparative
Examples 3,4, and 7, respectively.
[0020] The nickel zinc ferrite spherical particles as ferrite particles, comprising crystal
grains of 5 to 15µm in average diameter and having an average particle diameter of
20 to 150µm of the present invention are produced by using an iron oxide or iron oxide
hydroxide powder, a nickel oxide powder and a zinc oxide powder as starting materials.
More specifically, the nickel zinc ferrite spherical particles are produced by dispersing
and mixing a mixed powder for producing ferrite particles of 47 to 55 mol%, preferably
48 to 53 mol%, calculated as Fe₂O₃, of iron oxide or iron oxide hydroxide, 10 to 23
mol%, preferably 13 to 20 mol%, calculated as NiO, of nickel oxide and 25 to 40 mol%,
preferably 27 to 39, calculated as ZnO, of zinc oxide into and with water containing
0.2 to 1.0 wt% of a surfactant based on the weight of the mixed powder for producing
ferrite particles so as to prepare a water-dispersed slurry having a slurry concentration
of 40 to 60 wt%, spray-drying the resultant slurry so as to obtain the granules having
an average particle diameter of 25 to 180µm, and calcining the obtained granules at
a temperature of 1100 to 1350°C.
[0021] The reason why the nickel zinc ferrite spherical particles having a magnetic permeability
of not less than 25 are obtained according to the present invention is considered
to be that the nickel zinc ferrite spherical particles obtained by the process according
to the present invention comprises uniform crystal grains of an appropriate size containing
few pores.
[0022] Since the ferrite particles for a bonded magnetic core according to the present invention
are spherical particles having appropriate sizes unlike the irregular, the particles
of the present invention have an excellent fluidity which facilitates the production
of a molded product having a complicated shape when the ferrite particles are kneaded
with a resin and molded, especially, by injection molding.
[0023] The ferrite particles for a bonded magnetic core according to the present invention
comprises ferrite particles having a composition represented by 47 to 55 mol%, preferably
48 to 53 mol% of Fe₂O₃, 10 to 23 mol%, preferably 13 to 20 mol% of NiO and 25 to 40
mol%, preferably 27 to 39 of ZnO. The particles having a composition other than this
ranges are unfavorable for practical use because the magnetic permeability is apt
to be lowered.
[0024] The ferrite particles for a bonded magnetic core according to the present invention
comprise nickel zinc ferrite spherical particles having an average diameter of 20
to 150µm, preferably 30 to 140 µm and comprising crystal grains of 5 to 15µm, preferably
5 to 13 µm in average diameter. If the average particle diameter of the ferrite particles
is less than 20µm, the growth of the particles is unfavorably insufficient. The average
particle diameter of more than 150µm is also unfavorable because the crystal grains
abnormally grow and many pores tend to remain therein, thereby lowering the magnetic
permeability.
[0025] In order to obtain the ferrite particles for a bonded magnetic core according to
the present invention, it is necessary to control the average particle diameter of
the granules before calcination in the range of 20 to 180µm.
[0026] For this purpose, it is necessary to disperse and mix the mixed powder for producing
ferrite particles into and with water containing 0.2 to 1.0 wt%, preferably 0.2 to
0.8 wt% of a surfactant based on the weight of the mixed powder for producing ferrite
particles, thereby obtaining a water-dispersed slurry having a slurry concentration
of 40 to 60 wt%, preferably 40 to 55 wt%, and thereafter to spray-dry the resultant
slurry. If the slurry concentration is less than 40 wt%, the spray-drying efficiency
is lowered, which often leads to the reduction in the productivity. If the slurry
concentration is more than 60 wt%, it is difficult to supply and spray-dry the slurry
and, hence, it is difficult to produce the ferrite particles for a bonded core of
the present invention.
[0027] As the iron oxide, which is one of the starting materials of the present invention,
α-Fe₂O₃, γ-Fe₂O₃ and Fe₃O₄ are usable. As the ion oxide hydroxide, α-FeOOH, β-FeOOH
and γ-FeOOH are usable.
[0028] As the surfactant, surfactants generally used as a dispersant for a water-dispersed
slurry, for example, alkali salts, amine salts and ammonium salts of anionic surfactants,
lower fatty acid salts and hydrochlorides of cationic surfactants are usable. The
amount of surfactant used is preferably 0.2 to 1.0 wt% based on the weight of the
mixed powder for producing ferrite particles in consideration of sphericity of the
ferrite particles obtained.
[0029] The calcining temperature is in the range of 1100 to 1350°C. If the temperature is
lower than 1100°C, it is difficult to obtain large crystal grains. If it exceeds 1350°C,
the abnormal growth of the crystal grains is accelerated, so that the crystal grains
become unfavorably non-uniform and contain many pores.
[0030] The ferrite resin composite according to the present invention is a mixture of the
above-described nickel zinc ferrite spherical particles comprising crystal grains
of 5 to 15µm in average diameter and having an average particle diameter of 20 to
150µm and a resin, and has a magnetic permeability of not less than 25 and an excellent
fluidity.
[0031] The nickel zinc ferrite spherical particles of the present invention may be coated
in advance with a coupling agent which is generally used as a surface treating agent,
for example, a silane coupling agent, titanium coupling agent, aluminum coupling agent
and zircoaluminate coupling agent, or a cationic, anionic or nonionic surfactant in
order to enhance various properties such as the dispersibility.
[0032] The mixing ratio (wt%) of the nickel zinc ferrite spherical particles to the base
materials of a resin composite according to the present invention is 90 to 95/5 to
10, preferably 92 to 9416 to 8 in consideration of the magnetic permeability and the
fluidity of the ferrite resin composite.
[0033] The base materials of a resin composite in the present invention is a resin with
a plasticizer, lubricant, antioxidant, etc., added thereto, if necessary.
[0034] As the resin, those generally used for a resin component are usable. Concrete examples
thereof are a thermoplastic resin such as a polystyrene resin, polyethylene resin,
AS resin (acrylonitrile-styrene copolymer), ABS resin (acrylonitrile-butadiene-styrene
copolymer), vinyl chloride resin, EVA resin (ethylene-vinylacetate copolymer), PMMA
resin (polymethylmethacrylate), polyamide resin, polypropylene resin, EEA resin (ethylene-ethylacrylate
copolymer) and PPS resin (polyphenylene sulfide), and a thermosetting resin such as
a phenol resin, urea resin, melamine resin, alkyd resin, epoxy resin and polyurethane
resin.
[0035] Although the ferrite resin composite of the present invention is usable both for
compression molding and for injection molding, since the fluidity thereof is excellent,
it is preferably used for injection molding.
[0036] The nickel zinc ferrite spherical particles of the present invention, which have
an average particle diameter of 20 to 150µm and a magnetic permeability of not less
than 25, are suitable as ferrite particles for a bonded magnetic core.
[0037] A ferrite resin composite of the present invention has a large magnetic permeability
such as not less than 25 due to the large magnetic permeability of the ferrite particles
which are mixed with the base materials of a resin composite, and an excellent fluidity
due to the ferrite particles having appropriate size and smooth spherical surfaces.
The ferrite resin composite of the present invention is thereof suitable as a ferrite
resin composite which is now demanded.
[0038] In addition, the application of the ferrite resin composite of the present invention,
which has a large magnetic permeability, to an electromagnetic wave absorber and an
electromagnetic wave insulator is expected.
[Examples]
[0039] The present invention will be more precisely explained while referring to Examples
as follows.
[0040] However, the present invention is not restricted to Examples under mentioned. From
the foregoing description, one skilled in the art can easily ascertain the essential
characteristics of the present invention, and without departing from the spirit and
scope thereof, can make various changes and modifications of the invention to adapt
it to various usages and conditions.
[0041] In the following examples and comparative examples, a cylindrical molded product
having an outer diameter of 36 mm, an inner diameter of 24 mm and a height of 10 mm
was produced by the press-molding of the granules of a mixture of ferrite particles
and polyvinyl alcohol (MABOZORUT-30 produced by Matsumoto Yushi Seiyaku Co., Ltd.)
under a pressure of 1 ton/cm² as a sample being measured. The magnetic permeability
of the ferrite particles are expressed by the values obtained by measuring the magnetic
permeability of the thus-obtained molded product which has been wound with a winding
at 40 turns, by an impedance analyzer 4194A (produced by Yokokawa Hewlet Packard,
Ltd.) at a frequency of 1 MHz.
[0042] The magnetic permeability of the ferrite resin composite of the present invention
was measured by the same method described above except for using a molded product
having an outer diameter of 36mm, an inner diameter of 24mm and a height of 10mm,
and produced by the press-molding of the granules of the ferrite resin composite.
Example 1
[0044] 33.85 kg of iron oxide (α-Fe₂O₃), 6.10 kg of nickel oxide and 10.95 kg of zinc oxide
were mixed to produce a mixed powder for producing ferrite particles which contained
50.1 mol% of Fe₂O₃, 18.7 mol% of NiO and 31.2 mol% of ZnO. The mixed powder was then
charged into 60.5ℓ of an aqueous solution of 0.3 wt% of polycarboxylic acid ammonium
salt (SN dispersant 5468: produced by Sannopco Co., Ltd.) based on the weight of the
mixed powder for producing ferrite particles. The slurry concentration in the aqueous
solution was 45.7 wt%. The slurry was spray-dried to obtain granules having an average
particle diameter of 105µm.
[0045] The granules obtained were calcined at a temperature of 1320°C for 3 hours to obtain
ferrite particles for a bonded magnetic core which was composed of nickel zinc ferrite
spherical particles.
[0046] The magnetic permeability of the ferrite particles for a bonded magnetic core obtained
was 32.7. It was confirmed from the observation of the scanning-type electron micrograph
shown in Fig. 1 that the ferrite particles were nickel zinc ferrite spherical particles
which were composed of crystal grains 12.2µm in average diameter and which had an
average particle diameter of 80µm and few pores.
Examples 2 to 6, Comparative Examples 1 to 7
[0047] Ferrite particles for a bonded magnetic core were produced in the same way as in
Example 1 except for varying the composition of the mixed powder for producing ferrite
particles, the kind and the amount of surfactant, the concentration of the mixed slurry
for producing ferrite particles, the particle size of the granules and the calcining
temperatures.
[0048] The main producing conditions and the properties of the ferrite particles for a bonded
magnetic core are shown in Table 1.
[0049] In Example 3, Fe₃O₄ was used as the iron oxide material and in Example 5, polycarboxylic
acid sodium salt (Nobcosant K: produced by Sannopco Co., Ltd.) was used as the surfactant.
[0050] In Comparative Example 7, the mixed powder for producing ferrite particles was granulated
into granules about 6 mm in diameter by the conventional method without spray-drying,
the granules were calcined at a temperature of 1250°C, and the calcined granules were
then pulverized to obtain ferrite particles for a bonded magnetic core having a particle
diameter of 39µm and containing many pores.
Example 7
[0051] 190 g (equivalent to 94.9 wt% based on the composite) of the ferrite particles obtained
in Exmaple 1, 10 g (equivalent to 5.0 wt% based on the composite) of ethylene-vinyl
acetate copolymer resin (Evaflex 250, density 0.95 g/cc, produced by Mitsui Polychemical
Co., Ltd.) and 0.2 g (equivalent to 0.1 wt% based on the composite) of zinc stearate
were kneaded at 110°C for 15 minutes by a blast mill 30C-150 (produced by Toyo Seiki
Co., Ltd.) to obtain a kneaded mixture.
[0052] The thus-obtained kneaded mixture was granulated into granules having an average
particle diameter of about 3 mm, and press-molded at a temperature of 75°C and a pressure
of 1.5 ton/cm² to obtain a cylindrical molded product having an outer diameter of
36 mm, an inner diameter of 24 mm and a height of 10 mm. Since the ferrite resin composite
filled in all parts of the mold including every corner, the surface of the molded
product was smooth and the circumferential portions of the upper surface and the lower
surface of the cylinder are formed into complete circles without any chipping and
deformation.
[0053] The magnetic permeability of the molded product was 31.0
Examples 8 to 11 and Comparative Examples 8 to 11
[0055] Ferrite resin composites were produced in the same way as in Example 7 except for
varying the kind and the amount of ferrite particles, the kind and amount of additive
and the kneading temperature and time.
[0056] The main producing conditions and the properties of the composites obtained are shown
in Table 2.
[0057] Since the ferrite resin composite filled in all parts of the mold including every
corner, the molded product produced from the ferrite resin composite obtained in any
of Examples 8 to 11 had a smooth surface and complete circular circumferential portions
of the upper surface and the lower surface of the cylinder without any chipping and
deformation like the molded product obtained in Example 7.
[0058] In contrast, in the molded products produced from the ferrite resin composites obtained
in Comparative Examples 8 and 10, the surfaces were uneven and chipping or deformation
was observed at a part of the circumferential portions of the upper surface and the
lower surface of the cylinder.
Table 1
Examples & Comparative Examples |
Mixing ratio of raw materials |
Amount of Surfactant (wt%) |
Slurry concentration (wt%) |
Average particle diameter of granules (µm) |
Calcining temperature (°C) |
Ferrite particles for bonded magnetic core |
|
FezO₃ (mol %) |
NiO (mol %) |
ZnO (mol %) |
|
|
|
|
Magnetic permeability |
Average particle diameter of crystal grains (µm) |
Average particle diameter (µm) |
Example 1 |
50.1 |
18.7 |
31.2 |
0.3 |
45.7 |
105 |
1320 |
32.7 |
12.2 |
80 |
Example 2 |
50.1 |
18.7 |
31.2 |
0.3 |
45.7 |
120 |
1280 |
30.2 |
9.5 |
100 |
Example 3 |
50.1 |
18.7 |
31.2 |
0.3 |
45.7 |
99 |
1150 |
28.0 |
8.2 |
79 |
Example 4 |
50.1 |
18.7 |
31.2 |
0.7 |
52.0 |
170 |
1100 |
25.3 |
5.1 |
139 |
Example 5 |
52.0 |
17.5 |
30.5 |
0.3 |
50.2 |
115 |
1300 |
31.5 |
8.3 |
85 |
Example 6 |
48.3 |
14.5 |
37.2 |
0.3 |
41.3 |
46 |
1320 |
26.2 |
9.2 |
34 |
Comparative Example 1 |
50.1 |
18.7 |
31.2 |
0.75 |
58.3 |
250 |
1250 |
20.2 |
10.0 |
200 |
Comparative Example 2 |
50.1 |
18.7 |
31.2 |
0.3 |
30.6 |
18 |
1150 |
18.3 |
2.2 |
15 |
Comparative Example 3 |
49.8 |
18.6 |
31.6 |
0.5 |
43.2 |
53 |
1000 |
12.0 |
1.5 |
45 |
Comparative Example 4 |
49.8 |
18.6 |
31.6 |
0.5 |
43.2 |
89 |
1380 |
18.6 |
20.0 |
67 |
Comparative Example 5 |
43.2 |
23.0 |
33.8 |
0.5 |
43.2 |
97 |
1250 |
7.0 |
8.5 |
75 |
Comparative Example 6 |
60.2 |
27.5 |
12.3 |
0.5 |
43.2 |
102 |
1180 |
5.0 |
5.3 |
80 |
Comparative Example 7 |
49.5 |
18.4 |
32.1 |
― |
― |
― |
1250 |
17.5 |
27.1 |
39 |
Table 2
Examples & Comparative Examples |
Manufacture of ferrite resin composite |
Ferrite resin composite |
|
Ferrite particles |
Resin |
Additive |
Kneading |
Magnetic permeability |
|
Kind |
Amount (wt%) |
Kind |
Amount (wt%) |
Kind |
Amount (wt%) |
Temperature (°C) |
Time (min.) |
|
Example 7 |
Example 1 |
95.0 |
Evaflex 250 (produced by Mitsui Polychemical Co.,Ltd.) |
4.9 |
Zn stearate |
0.1 |
110 |
15 |
31.0 |
Example 8 |
Example 1 |
93.0 |
ditto |
7.9 |
Zn stearate |
0.1 |
100 |
15 |
28.4 |
Example 9 |
Example 2 |
95.0 |
ditto |
4.9 |
Zn stearate |
0.1 |
110 |
15 |
28.7 |
Example 10 |
Example 1 |
92.0 |
12-Nylon 3014U (produced by Ube Industries,Ltd.) |
7.9 |
Ca stearate |
0.1 |
250 |
15 |
28.5 |
Example 11 |
Example 5 |
91.0 |
ditto |
8.9 |
Ca stearate |
0.1 |
250 |
15 |
27.2 |
Comparative Examples 8 |
Comparative Examples 1 |
95.0 |
Evaflex 250 (produced by Mitsui Polychemical Co.,Ltd.) |
4.9 |
Zn stearate |
0.1 |
110 |
15 |
18.6 |
Comparative Examples 9 |
Comparative Examples 2 |
95.0 |
ditto |
4.9 |
Zn stearate |
0.1 |
120 |
15 |
16.8 |
Comparative Examples 10 |
Comparative Examples 3 |
92.0 |
12-Nylon 3014U (produced by Ube Industries,Ltd.) |
7.9 |
Ca stearate |
0.1 |
250 |
15 |
10.6 |
Comparative Examples 11 |
Comparative Examples 7 |
95.0 |
Evaflex 250 (produced by Mitsui Polychemical Co.,Ltd.) |
4.9 |
Zn stearate |
0.1 |
120 |
15 |
16.5 |
1. Ferrite particles suitable for a bonded magnetic core, which particles comprise
crystal grains of from 5 to 15µm in average diameter and have an average particle
diameter of from 20 to 150µm and a magnetic permeability of not less than 25.
2. Ferrite particles according to claim 1, which comprise from 48 to 53 mol% of Fe₂O₃,
from 13 to 20 mol% of NiO and from 27 to 39 mol% of ZnO.
3. A ferrite resin composite comprising ferrite particles according to claim 1 or
2 and a base resin, said ferrite resin composite having a magnetic permeability of
not less than 25.
4. A composite according to claim 3, which comprises from 92 to 94 wt% of the particles
and from 8 to 6 wt% of the base resin.
5. A composite according to claim 3 or 4 which comprises spherical nickel zinc ferrite
particles.
6. A composite according to any one of claims 3 to 5 in the form of a magnetic core.
7. A process for producing ferrite particles as defined in claim 1 or 2 which comprises:
(i) mixing a) from 47 to 55 mol%, calculated as Fe₂O₃, of an iron oxide or iron oxide
hydroxide powder, b) from 10 to 23 mol%, calculated as NiO, of a nickel oxide powder
and c) from 25 to 40 mol%, calculated as ZnO, of a zinc oxide powder and d) water
containing from 0.2 to 1.0 wt% of a surfactant based on the total weight of the powders
a), b) and c) so as to prepare a slurry having a slurry concentration of from 40 to
60 wt%,
(ii) spray-drying the resultant slurry so as to obtain granules having an average
particle diameter of from 25 to 180µm, and
(iii) calcining the obtained granules at a temperature of from 1100 to 1350°C.
8. A process according to claim 7 in which stage (i) comprises mixing:
a) from 48 to 53 mol% of Fe₂O₃
b) from 13 to 20 mol% of NiO
c) from 27 to 39 mol% of ZnO
d) water containing from 0.2 to 0.8 wt% of a surfactant.
9. A process according to claim 7 or 8 in which the surfactant in stage (i) is an
alkali metal salt, an amine salt, an ammonium salt of an anionic surfactant, a fatty
acid salt or a hydrochloride of a cationic surfactant.
10. A process according to any one of claims 7 to 9 which comprises the additional
step of kneading the ferrite particles with the base resin and press molding the mixture
to produce a moulded product.