Magnetic powder and magnetic molded article

The present invention relates to a magnetic powder that contains resin-coated magnetic particles. The resin-coated magnetic particles include magnetic particles A and B that are formed in non-spherical shapes, with the magnetic particles A and B coated with a resin C. The resin-coated magnetic particles make it possible to increase the filling quantity of the magnetic particles A and B when the magnetic powder is employed to constitute a magnetic molded article, to ultimately improve the electromagnetic characteristics of the magnetic molded article.

TECHNICAL FIELD 
The present invention relates to a magnetic powder and a magnetic molded 
article constituted by molding the magnetic powder. 
BACKGROUND ART 
A resin containing magnetic material that achieves its electromagnetic 
characteristics by dispersing magnetic powder in a resin is used to 
constitute the mold core material employed in electronic parts in which 
specific electromagnetic characteristics are required, such as choke 
coils, inductors, rotary transformers, EMI elements and the like in the 
known art. Magnetic particles constituting such a magnetic powder are 
formed in an almost spherical shape to assure a sufficient degree of 
fluidity during injection molding. 
The resin containing magnetic material described above achieves outstanding 
advantages such as superior dimensional accuracy and a greater degree of 
freedom afforded in shape since it is achieved without undergoing a 
sintering process, compared to magnetic oxide materials that are achieved 
as sintered bodies through molding and sintering. However, the 
electromagnetic characteristics achieved in a magnetic molded article 
constituted of a resin containing magnetic material obtained through the 
prior art technology are inferior. 
For instance, if a ferrite resin achieving good injection moldability and a 
high degree of magnetic permeability, which is obtained by selecting an 
appropriate particle size distribution and an appropriate content of the 
ferrite powder in the ferrite resin as disclosed in Japanese Unexamined 
Patent Publication No. 163236/1994, is employed to constitute a magnetic 
molded article, a low initial magnetic permeability .mu.i of approximately 
22 is achieved. 
In Japanese Unexamined Patent Publication No. 204027/1994, an approach in 
which a heat treatment is implemented at varying temperatures for 
different particle sizes of magnetic particles mixed in a magnetic oxide 
material, is disclosed. However, the resulting magnetic molded article 
only achieves an initial magnetic permeability .mu.i of approximately 35 
at best. 
While other prior art technologies such as those disclosed in Japanese 
Unexamined Patent Publication No. 185540/1990, Japanese Unexamined Patent 
Publication No. 226799/1990, Japanese Unexamined Patent Publication No. 
96202/1991, Japanese Unexamined Patent Publication No. 12029/1992, 
Japanese Examined Patent Publication No. 52422/1991, Japanese Unexamined 
Patent Publication No. 84648/1994 and the like are known, a sufficient 
initial magnetic permeability cannot be achieved in any of the resulting 
magnetic molded articles, since the dimensions of the particles mixed in 
the magnetic oxide material are too small, the ratio at which they are 
mixed is too low. 
DISCLOSURE OF THE INVENTION 
It is an object of the present invention to provide a magnetic powder and a 
magnetic molded article constituted by molding the magnetic powder, with 
which the quantity of the magnetic particles filled in a magnetic molded 
article can be increased, to improve the electromagnetic characteristics. 
In order to achieve the object described above, the magnetic powder 
according to the present invention is constituted of an aggregation of 
resin-coated magnetic particles. The resin-coated magnetic particles 
include non-spherical magnetic particles which are coated with resin. 
According to the present invention, the term "non-spherical" covers a 
large variety of shapes including scale shapes, flat shapes, shapes with a 
portion of a sphere or ovoid missing, and shapes with indentations and 
projections formed on the surface. 
In order to improve the electromagnetic characteristics in a resulting 
magnetic molded article, the weight (filling quantity) of the magnetic 
powder relative to the entire volume must be increased as much as 
possible. However, in the prior art, it has been recommended that 
spherical or nearly spherical magnetic particles be used in consideration 
of achieving a sufficient degree of fluidity of the resin when dispersing 
the particles in the resin and, in particular, when performing injection 
molding. 
As explained earlier, with the spherical magnetic particles in the prior 
art, the initial magnetic permeability that is achieved in a resulting 
magnetic molded article is approximately 35 at best, and it is difficult 
to assure an initial magnetic permeability higher than this. The reason 
for this is deduced to be that in the prior art, with almost spherical 
magnetic particles employed, point contact occurs among the spherical 
magnetic particles on their spherical surfaces in a magnetic molded 
article, increasing the gaps between the individual magnetic particles and 
therefore limiting the degree to which the filling quantity of the 
magnetic particles can be increased. 
The inventor of the present invention has conducted extensive research to 
address the problem of the prior art discussed above, and has discovered 
that by using non-spherical magnetic particles, it becomes possible to 
increase the filling quantity of the magnetic particles in a magnetic 
molded article due to reduced gaps between individual magnetic particles, 
to improve the electromagnetic characteristics. 
In addition, since the surface area per non-spherical magnetic particle is 
larger than that of an almost spherical particle, the force with which it 
adheres to the resin increases, and thus, there is another advantage that 
we may expect in that the bonding strength between the magnetic particles 
and the resin increases. 
It is desirable that the magnetic particles be constituted of a plurality 
of types of particles having different particle diameters, all of which 
are commonly coated with resin. In this case, as long as at least one of 
the plurality of types of magnetic particles is non-spherical, the other 
types of magnetic particles may be either spherical or non-spherical. In 
other words, combinations in which all the magnetic particles are 
spherical must be excluded. The particle diameter of a magnetic particle 
may be defined as the maximum diameter of the particle. 
If, among the resin-coated magnetic particles, those particles having large 
particle diameters are formed in a non-spherical shape, the gaps formed 
between the magnetic particles with the large particle diameters can be 
filled with magnetic particles having small particle diameters that are 
formed in spherical or non-spherical shapes. Thus, when a magnetic molded 
article constituted of such resin-coated magnetic particles is formed, the 
weight of the magnetic particles relative to the entire volume of the 
resin-coated magnetic particles can be further increased, thereby making 
it possible to assure even better electromagnetic characteristics. 
If magnetic particles with a large particle diameter are formed in a 
spherical shape, too, the area surrounding these magnetic particles will 
be filled by magnetic particles with small particle diameters formed in 
non-spherical shapes, thereby further increasing the weight of the 
magnetic particles relative to the entire volume of the resin-coated 
magnetic particles in a magnetic molded article, to assure further 
improvement in the electromagnetic characteristics. 
In addition, since a degradation in the electromagnetic characteristics 
occurs when the resin present between the magnetic particles presents 
magnetic resistance, it is desirable that the particle diameters of the 
magnetic particles be as large as possible. In the preferred mode 
described above, since the gaps formed between the magnetic particles with 
large particle diameters are filled by magnetic particles having smaller 
particle diameters, the magnetic resistance presented by the resin between 
the magnetic particles is reduced. Thus, the electromagnetic 
characteristics are further improved. 
Through a synergy of the advantages described above, with the magnetic 
powder according to the present invention, a magnetic molded article that 
achieves an improved initial magnetic permeability of 40 or more compared 
to the initial magnetic permeability in the 30's in the prior art is 
obtained. 
In addition, since the resin-coated magnetic particles contained in the 
magnetic powder according to the present invention are constituted by 
coating magnetic particles with resin, an improvement in the fluidity is 
achieved to enable injection molding. 
A number of different methods may be employed to form the resin coating 
film, including vapor phase methods such as gassification, liquid phase 
methods such as various composite methods implemented in a solvent and 
solid phase methods such as the method in which a resin layer is formed 
through a mechano-chemical effect while agitating a mixture containing a 
resin and the method in which a portion of the resin is caused to adhere 
through impact with the resin. 
Either a thermosetting resin or a thermoplastic resin may be employed in 
the present invention, as long as no stress occurs in the magnetic powder 
due to expansion associated with its softening and hardening. 
The magnetic powder according to the present invention does not impose any 
restrictions whatsoever on various types of surface treatments on the 
magnetic powder that are implemented as a regular practice or the addition 
of various additives that may be employed to improve various 
characteristics. 
The magnetic powder according to the present invention is employed to mold 
a magnetic molded article. Examples of such magnetic molded articles 
include the cores of choke coils, inductors, rotary transformers, EMI 
elements or the like. 
Since a resin coating film is formed on the surfaces of non-spherical 
magnetic particles in the magnetic powder according to the present 
invention, a magnetic molded article containing a great quantity of 
magnetic particles can be achieved by filling the magnetic powder into a 
metal mold and applying heat and pressure to cause the resin to melt and 
harden. The molding itself is implemented by filling the magnetic powder 
in a mold that can be heated to the temperature at which the coated resin 
becomes soft or to the temperature at which the softening starts and 
applying heat and pressure. 
In order to achieve high density filling at this point, it is effective to 
apply vibration. After the application of heat and pressure, the molded 
article is cooled and then taken out. However, depending upon the type of 
resin used, it is sometimes desirable not to apply pressure, since if 
pressure is applied, the magnetic powder becomes subject to stress during 
the cooling, resulting in a degradation in the electromagnetic 
characteristics. Depending upon the required characteristics and the 
required form, the molded article may be taken out without performing heat 
application during pressurized molding and then be heated in an oven to 
harden the resin. 
With a magnetic molded article constituted by molding the magnetic powder 
according to the present invention, good electromagnetic characteristic 
values and, in particular, an initial magnetic permeability , .mu.i of 40 
or more, can be achieved. These are the characteristics that are the 
minimum requirements that must be achieved in the cores in parts such as 
choke coils, inductors and EMI elements whose cores have been constituted 
of sintered bodies in the prior art. Thus, the magnetic powder according 
to the present invention can be used as a high accuracy material for 
constituting various cores that demonstrate superior dimensional accuracy 
compared to sintered cores while achieving characteristics comparable to 
those achieved with sintered cores. The magnetic molded article according 
to the present invention may be used by itself or it may be used in 
combination with other molded articles constituted of sintered magnetic 
material, a magnetic oxide material, a metallic magnetic material, a 
non-magnetic material or the like.

BEST MODE FOR CARRYING OUT THE INVENTION 
In FIG. 1, a resin-coated magnetic particle includes a non-spherical 
magnetic particle A which is thinly coated with resin C. The magnetic 
powder according to the present invention is an aggregation of the 
magnetic particles A, one of which is shown in FIG. 1. The non-spherical 
magnetic particles A may be obtained in the form of pulverized ferrite 
pieces. The maximum value for the particle diameter D1 of the magnetic 
particles A is determined in correspondence to the thickness of the 
magnetic molded article. For instance, if the minimum thickness of the 
magnetic molded article is 5000 .mu.m, the maximum particle diameter D1 of 
the magnetic particles A is 5000 .mu.m. 
When a magnetic molded article is formed by magnetic powder that contains a 
great number of non-spherical magnetic particles A as shown in FIG. 1, a 
phenomenon in which a projecting portion of another magnetic particle A 
fits in an indented portion of a magnetic particle A occurs, thereby 
reducing the gaps between the magnetic particles. Thus, the filling 
quantity of the magnetic particles A can be increased to improve the 
electromagnetic characteristics. 
In addition, since the surface area per non-spherical magnetic particle A 
is larger than that of an almost spherical particle, there is an added 
advantage of an increase in the strength achieved through an increased 
adhesion to the resin C. 
Next, in FIG. 2, the combined resin-coated magnetic particles are 
constituted of a first magnetic particle A having a particle diameter D1 
and second magnetic particles B having a particle diameter D2, with the 
first magnetic particle A and the second magnetic particles B commonly 
coated by resin C. Both the first magnetic particle A having the particle 
diameter D1 and the second magnetic particles B having the particle 
diameter D2 are formed in a non-spherical shape. The particle diameter D2 
of the second magnetic particles B is much smaller than the particle 
diameter D1 of the first magnetic particle A. The particle diameters D1 
and D2 of the first magnetic particle A and the second magnetic particles 
B are defined as the maximum diameters of the individual particles. It is 
desirable to set the maximum and minimum particle diameters of the first 
magnetic particle A at 5000 .mu.m and 355 .mu.m respectively. It is 
desirable to set the particle diameter D2 of the second magnetic particles 
B at less than 355 .mu.m if the particle diameter D1 of the first magnetic 
particle A is set as described above. 
When a magnetic molded article is formed using a magnetic powder 
constituted of resin-coated magnetic particles such as illustrated in FIG. 
2, the gaps formed between the first magnetic particles A having the large 
particle diameter D1 are filled with second magnetic particles B having 
the small particle diameter D2, thereby further increasing the weight of 
the magnetic particles A and B relative to the entire volume of the 
resin-coated magnetic particles to assure even more improved 
electromagnetic characteristics. 
In addition, since the gaps formed between the first magnetic particles A 
having the large particle diameter D1 are filled with the second magnetic 
particles B having the small particle diameter D2, the quantity of the 
resin C present between the magnetic particles can be reduced to lower its 
magnetic resistance. As a result, the electromagnetic characteristics can 
be further improved. 
Through a synergy of the advantages described above, it is possible to 
obtain a magnetic molded article that achieves an initial magnetic 
permeability of 40 or more compared to the initial magnetic permeability 
in the 30's achieved in the prior art through the magnetic powder 
according to the present invention. 
While both the first magnetic particle A and the second magnetic particles 
B are formed in non-spherical shapes in FIG. 2, it is only required that 
at least either the first magnetic particles A or the second magnetic 
particles B be non-spherical. In other words, the first magnetic particles 
A may be formed in a spherical shape with the second magnetic particles B 
formed in non-spherical shapes, or the first magnetic particles A may be 
formed in non-spherical shapes with the second magnetic particles B formed 
in a spherical shape. 
In the actual magnetic powder, the resin-coated magnetic particles such as 
illustrated in FIG. 1, and the magnetic particles such as illustrated in 
FIG. 2 are provided together. The number of magnetic particles contained 
in the resin-coated magnetic particle shown in FIG. 2, i.e., the ratio of 
the first magnetic particles A and the second magnetic particles B, is not 
necessarily restricted to that illustrated in the figure. 
The initial magnetic permeability of a magnetic molded article is 
determined in relation to the initial magnetic permeabilities of the 
magnetic particles A and B. It is desirable to use magnetic particles A 
and B having initial magnetic permeabilities of 200 or more. 
Since the advantages of the present invention are achieved by forming 
magnetic particles in non-spherical shapes, they can be achieved in the 
same manner even with different types of magnetic particles. In other 
words, the magnetic particles according to the present invention may be 
constituted of either a magnetic oxide material or a metallic magnetic 
material. A typical example of a magnetic oxide material is ferrite, which 
includes Mn group soft ferrites, Mg group soft ferrites and Ni group soft 
ferrites. These magnetic ferrite materials may contain various additives. 
Furthermore, a magnetic oxide material or a metallic magnetic material may 
be employed by itself to constitute the resin-coated magnetic particles, 
or a magnetic particle constituted of a plurality of magnetic materials 
selected from the magnetic materials listed above may be contained within 
one resin-coated magnetic particle. 
An Mn soft ferrite, an Mg soft ferrite, an Ni soft ferrite or the like may 
be employed by itself to constitute the resin-coated magnetic particles or 
a magnetic particle constituted of a plurality of magnetic materials 
selected from the ferrite materials listed above may be contained within a 
single resin-coated magnetic particle. 
The magnetic powder according to the present invention may contain either 
resin-coated magnetic particles constituted by employing one of the 
various magnetic materials listed above or resin-coated magnetic particles 
which include magnetic particles each constituted of a plurality of 
magnetic materials selected from the magnetic materials listed above, or 
the magnetic powder according to the present invention may contain both of 
them. 
Next, an explanation is given in more specific terms in reference to test 
examples. 
TEST EXAMPLE 1 
Ferrite powder achieved by pulverizing an Mn soft ferrite was classified 
into 5 different particle size distributions 
particle diameters of 1000 .mu.m or more; 
particle diameters less than 1000 .mu.m and equal to or more than 425 
.mu.m; 
particle diameters less than 425 .mu.m and equal to or more than 300 .mu.m; 
particle diameters less than 300 .mu.m and equal to or more than 125 .mu.m; 
and 
particle diameters less than 125 .mu.m. 
Of the ferrite powders having the various particle size distributions 
achieved through this classification, the powders that belong in a 
particle size distribution of 355 .mu.m or more constitute a group of 
first magnetic particles A, whereas the ferrite powders that belong in a 
particle size distribution of less than 355 .mu.m constitute a group of 
second magnetic particles B. The maximum particle diameter of the magnetic 
particles included in the group of first magnetic particles A is 
approximately 5000 .mu.m. 
Since the group of first magnetic particles A and the group of second 
magnetic particles B are both constituted of the ferrite powder achieved 
through pulverization, they are formed in non-spherical shapes (amorphous 
shapes). 
Next, the group of first magnetic particles A, 50 wt % or more of which has 
a particle size distribution within the range of 425 .mu.m to 1000 .mu.m 
and the group of second magnetic particles B, 50 wt % or more of which has 
a particle size distribution within the range of 125 .mu.m to 300 .mu.m 
was mixed at a mixing ratio (weight ratio) A:B of 6:4. 
This mixed ferrite powder was then placed within a grinding mill and 
agitated for approximately 3 minutes with a styrene acrylic resin powder 
added. Thus, a magnetic powder achieved by coating the mixed ferrite 
powder with the styrene 25 acrylic resin was obtained. The ratio at which 
the mixed ferrite powder and the styrene acrylic resin was mixed was 10:1 
in weight ratio. With this, a magnetic powder containing the resin-coated 
magnetic particles such as illustrated in FIG. 2 was achieved. 
Next, the magnetic powder thus achieved was placed in a metal mold and was 
heated to a temperature of 140.degree. C. while applying pressure at 1 
(t/cm.sup.2) to produce a toroidal core, and its electromagnetic 
characteristics were measured. 
For purposes of comparison, after obtaining magnetic particles constituted 
of spherical Mn soft ferrite were obtained in conformance to a method in 
the prior art, they were classified by employing the method described 
above, the classified magnetic particles were mixed at the same particle 
size distributions and the same mixing ratio as above and were then coated 
with styrene acrylic resin through a process similar to that described 
above. Using a magnetic powder containing the resin-coated magnetic 
particles thus obtained, a toroidal core was produced in a manner 
identical to that described above and its electromagnetic characteristics 
were measured. 
Table I presents the moldability, the electromagnetic characteristics and 
the volume weight indices achieved by the toroidal cores thus obtained. In 
Table I, the volume weight index refers to the value calculated through 
the following formula when the volume of the toroidal core is expressed as 
V (cc) and the weight of the ferrite within it is expressed as W (g). 
EQU Volume weight index=W/V 
The volume V (cc) of the toroidal core represents the total volume of the 
group of first magnetic particles A, the group of second magnetic 
particles B and the styrene acrylic resin, and the weight W (g) of the 
ferrite filling represents the weight of the mixture constituted of the 
group of first magnetic particles A and the group of second magnetic 
particles B. 
TABLE I 
______________________________________ 
Resin 
content Initial Volume 
ratio magnetic weight 
magnetic Ferrite: permeability index 
No. particle shape resin moldability (1 kHz) (g/cc) 
______________________________________ 
11 Non-spherical 
10:1 good 40 3.31 
12 Spherical 10:1 good 35 3.15 
______________________________________ 
Thermosetting resin powder (epoxy resin): 
Product name; Ararudite AT1, manufactured by Ciba Geigy 
In Table I, the volume weight index in test piece No. 12 (example for 
comparison) achieved by coating the spherical magnetic particles 
constituted of an Mn soft ferrite, with the resin being low, at 3.15, and 
consequently, a sufficient degree of magnetic particle filling could not 
be achieved, resulting in a low initial magnetic permeability of 35. In 
contrast, the volume weight index in test piece No. 11 achieved by coating 
non-spherical magnetic particles constituted of pulverized pieces of an Mn 
soft ferrite with the resin being high, at 3.31, achieving an initial 
magnetic permeability of 40 and demonstrating a significant improvement in 
the electromagnetic characteristics over test piece No. 12. 
The electromagnetic characteristics, the moldability and the like of a 
magnetic molded article constituted of the magnetic powder according to 
the present invention can be controlled at desirable values by controlling 
the particle size distribution of the magnetic particles that are to be 
included in the resin-coated magnetic particles, the mixing ratio at which 
a plurality of types of magnetic particles having different particle 
diameters are mixed, the mixing ratio at which the magnetic particles and 
the resin are mixed, the initial magnetic permeability of the magnetic 
particles and the like. Examples of control of these factors are explained 
below in reference to test examples. 
TEST EXAMPLE 2 
Particle Size Distribution 
The mixing ratios (weight ratios) in the group of first magnetic particles 
A and the group of second magnetic particles B obtained through a 
classification process similar to that employed in test example 1 were 
varied within the particle size distribution ranges given in reference to 
test example 1. Both the group of first magnetic particles A and the group 
of second magnetic particles B are constituted of pulverized pieces of Mn 
soft ferrite, and are non-spherical. The group of first magnetic particles 
A and the group of second magnetic particles B were mixed at a mixing 
ratio (weight ratio) A:B of 6:4. This mixed ferrite powder was then placed 
in a grinding mill and agitated for approximately 3 minutes with a styrene 
acrylic resin powder added. Thus, a magnetic powder achieved by coating 
the mixed ferrite powder with the styrene acrylic resin was obtained. The 
mixed ferrite powder and the styrene acrylic resin were mixed at a weight 
ratio of 10:1. 
Next, using the magnetic powders thus obtained, toroidal cores were 
produced through a molding process similar to that employed in test 
example 1 and their electromagnetic characteristics were measured. 
Table II presents particle size distributions, mixing ratios, moldability, 
electromagnetic characteristics and volume weight indices of core test 
pieces Nos. 21 to 28 thus obtained. 
TABLE II 
__________________________________________________________________________ 
Particle size distribution of 
Particle size distribution of 
Resin 
magnetic particles A (.mu.m) magnetic particles B (.mu.m) content 
Initial volume 
1000 or 425 or 
300 or 125 or 
mixing 
ratio magnetic 
weight 
more 1000.about.425 less more 300.about.125 less ratio ferrite: 
permeability index 
No. (wt. %) (wt. %) 
(wt. %) (wt. %) (wt. %) 
(wt. %) A:B resin 
moldability (1 kHz) 
(g/cc) 
__________________________________________________________________________ 
21 40 60 0 0 50 50 60:40 
10:1 
good 42 3.33 
22 50 50 0 0 50 50 60:40 10:1 good 40 3.31 
23 60 40 0 0 50 50 60:40 10:1 bad 39 3.27 
24 50 50 0 0 60 40 60:40 10:1 good 42 3.34 
25 50 50 0 0 40 60 60:40 10:1 not good 39 3.27 
26 0 50 50 50 50 0 60:40 10:1 good 47 3.49 
27 0 50 50 0 50 50 60:40 10:1 good 40 3.30 
28 50 50 0 50 50 0 60:40 10:1 good 53 3.66 
__________________________________________________________________________ 
As indicated in Table II, initial magnetic permeabilities of 40 or more as 
well as outstanding moldability are achieved in test Pieces Nos. 21, 22, 
24 and 26 to 28, in all of which, 50 wt % or more of the group of first 
magnetic particles A have a particle size distribution within the range of 
425 .mu.m or more and less than 1000 .mu.m and 50 wt % or more of the 
group of second magnetic particles B have a particle size distribution 
within the range of 125 .mu.m or more and less than 300 .mu.m. 
In contrast, with the test piece No. 23, in which 50 wt % or more of the 
group of first magnetic particles A have a particle diameter of 1000 .mu.m 
or more, the moldability tends to be inferior compared to that in the 
other test pieces, whereas in the case of the test piece No. 25, in which 
50 wt % or more of the group of second magnetic particles B have a 
particle diameter of 125 .mu.m or less, the electromagnetic 
characteristics tend to be inferior compared to those achieved by the 
other test pieces. 
Consequently, 50 wt % or more of the group of first magnetic particles A 
should have a particle size distribution within the range of 425 .mu.m or 
more, and less than 100 .mu.m and that 50 wt % or more of the group of 
second magnetic particles B should have a particle size distribution 
within the range of 125 .mu.m or more and less than 300 .mu.m. 
In addition, it is learned from Table II that the optimal mixing ratio of 
the mixed ferrite powder and the resin is within the range over which the 
volume weight index is at 3.3 or more. 
TEST EXAMPLE 3 
Mixing ratio of the group of first magnetic particles A and the group of 
second magnetic particles B. 
The group of first magnetic particles A and the group of second magnetic 
particles B were obtained through a method identical to that employed in 
test example 1. An adjustment was made on the group of first magnetic 
particles A so that 97 wt % of the group of first magnetic particles A 
would have a particle size distribution of 425 .mu.m or more and less than 
1000 .mu.m while achieving an average particle diameter of approximately 
600 .mu.m. In addition, an adjustment was made on the group of second 
magnetic particles B so that 97 wt % of the group of second magnetic 
particles B would have a particle size distribution of 125 .mu.m or more 
and less than 300 .mu.m while achieving an average particle diameter of 
approximately 180 .mu.m. The group of first magnetic particles A and the 
group of second magnetic particles B were mixed, toroidal cores were 
produced through a method similar to that employed in test example 1 and 
their electromagnetic characteristics were measured. 
Table III presents the particle size distributions in the group of first 
magnetic particles A and the group of second magnetic particles B, the 
mixing ratios, the resin content ratios, the moldability, the initial 
magnetic permeabilities and the volume weight indices of test pieces Nos. 
31 to 39 thus obtained. 
TABLE III 
__________________________________________________________________________ 
Particle size distribution of 
Particle size distribution of 
Resin 
magnetic particles A (.mu.m) magnetic particles B (.mu.m) content 
Initial volume 
1000 or 425 or 
300 or 125 or 
mixing 
ratio magnetic 
weight 
more 1000.about.425 less more 300.about.125 less ratio ferrite: 
permeability index 
No. (wt. %) (wt. %) 
(wt. %) (wt. %) (wt. %) 
(wt. %) A:B resin 
moldability (1 kHz) 
(g/cc) 
__________________________________________________________________________ 
31 1.5 97 1.5 1.5 97 1.5 40:60 
10:1 
good 49 3.55 
32 1.5 97 1.5 1.5 97 1.5 50:50 10:1 good 54 3.69 
33 1.5 97 1.5 1.5 97 1.5 60:40 10:1 good 53 3.67 
34 1.5 97 1.5 1.5 97 1.5 70:30 10:1 good 49 3.57 
35 1.5 97 1.5 1.5 97 1.5 80:20 10:1 good 42 3.35 
36 1.5 97 1.5 1.5 97 1.5 90:10 10:1 good 45 3.45 
37 1.5 97 1.5 1.5 97 1.5 95:5 10:1 good 49 3.55 
38 1.5 97 1.5 1.5 97 1.5 99:1 10:1 good 53 3.66 
39 1.5 97 1.5 1.5 97 1.5 100:0 10:1 bad 37 3.21 
__________________________________________________________________________ 
By referring to table III, it is learned that test pieces Nos. 31 to 38 
that satisfy 99.gtoreq.A.gtoreq.40 or 60.gtoreq.B.gtoreq.1 on a premise 
that A+B=100 with A representing the weight of the group of first magnetic 
particles A, and B representing the weight of the group of second magnetic 
particles B achieve good electromagnetic characteristics and superior 
moldability. In the case of test piece No. 39 which does not fall into 
either of the ranges above with A=100 and B=0, both the moldability and 
the initial magnetic permeability are inferior. Thus, it is concluded that 
it is desirable to mix the group of first magnetic particles A and the 
group of second magnetic particles B. 
TEST EXAMPLE 4 
Resin Content Ratio 
The group of first magnetic particles A and the group of second magnetic 
particles B were obtained through a method similar to that employed in 
test example 1. An adjustment was made on the group of first magnetic 
particles A so that 97 wt % of the group of first magnetic particles A 
would have a particle size distribution of 425 .mu.m or more and less than 
1000 .mu.m while achieving an average particle diameter of approximately 
600 .mu.m. 1.5 wt % of the group of first magnetic particles A had a 
particle size distribution of 1000 .mu.m or more and the remaining 1.5 wt 
% had a particle size distribution of less than 425 .mu.m. An adjustment 
was made on the group of second magnetic particles B so that 97 wt % of 
the group of second magnetic particles B thus obtained would have a 
particle size distribution of 125 .mu.m or more and less than 300 .mu.m 
while achieving an average particle diameter of approximately 180 .mu.m. 
1.5 wt % of the group of second magnetic particles B had a particle size 
distribution of 300 .mu.m or more and less than 425 .mu.m and the 
remaining 1.5 wt % had a particle size distribution of less than 125 
.mu.m. 
Styrene acrylic resin coating was implemented on the group of first 
magnetic particles A and the group of second magnetic particles B through 
a method similar to that employed in test example 1. The styrene acrylic 
resin was added by varying the resin content ratio (weight ratio) relative 
to the first powder A and the second powder B. 
Next, toroidal cores were produced through a process similar to that 
employed in test example 1, and their electromagnetic characteristics were 
measured. 
Table IV presents the particle size distributions in the group of first 
magnetic particles A and the group of second magnetic particles B, the 
mixing ratios, the resin content ratios, the moldability, the initial 
magnetic permeabilities and the volume weight indices of test pieces Nos. 
41 to 48 thus obtained. In table IV, the resin content ratios relative to 
the first powder A and the second powder B are presented under 
"ferrite:resin." 
TABLE IV 
__________________________________________________________________________ 
Particle size distribution of 
Particle size distribution of 
Resin 
magnetic particles A (.mu.m) magnetic particles B (.mu.m) content 
Initial volume 
1000 or 425 or 
300 or 125 or 
mixing 
ratio magnetic 
weight 
more 1000.about.425 less more 300.about.125 less ratio ferrite: 
permeability index 
No. (wt. %) (wt. %) 
(wt. %) (wt. %) (wt. %) 
(wt. %) A:B resin 
moldability (1 kHz) 
(g/cc) 
__________________________________________________________________________ 
31 1.5 97 1.5 1.5 97 1.5 60:40 
10:0.10 
bad 38 3.25 
42 1.5 97 1.5 1.5 97 1.5 60:40 10:0.25 not good 50 3.58 
43 1.5 97 1.5 1.5 97 1.5 60:40 10:0.50 good 54 3.71 
44 1.5 97 1.5 1.5 97 1.5 60:40 10:0.75 good 54 3.68 
45 1.5 97 1.5 1.5 97 1.5 60:40 10:1 good 53 3.65 
46 1.5 97 1.5 1.5 97 1.5 60:40 10:2 good 45 3.46 
47 1.5 97 1.5 1.5 97 1.5 60:40 10:2.5 good 40 3.31 
48 1.5 97 1.5 1.5 97 1.5 60:40 10:3 good 35 3.15 
__________________________________________________________________________ 
In Table IV, test piece No. 31 in which the styrene acrylic resin is mixed 
at a resin content ratio (ferrite : resin) of 10:0.10 relative to the 
group of first magnetic particles A and the group of second magnetic 
particles B demonstrates inferior moldability and a low initial magnetic 
permeability (1 kHz) of 38. In the case of test piece No. 32 achieved at a 
resin content ratio (ferrite : resin) of 10:0.25, while it demonstrates 
superior initial magnetic permeability, its moldability is inferior. 
In contrast, test cases Nos. 43 to 48 that satisfy a resin content ratio 
range of (ferrite: resin)=(10:0.5) to (10:3) achieve both superior 
moldability and good initial magnetic permeability (1 kHz). 
Thus, it is concluded that the resin content ratio (ferrite:resin) of the 
styrene acrylic resin relative to the group of first magnetic particles A 
and the group of second magnetic particles B should be within the range 
within which test pieces Nos. 43 to 48 were produced. 
TEST EXAMPLE 5 
Resin 
The same particle size distributions and the same mixing ratio of the group 
of first magnetic particles A and the group of second magnetic particles B 
as those in test example 1 were used, and a thermosetting resin and a 
thermoplastic resin were employed to coat the powder to examine changes in 
the characteristics caused by the use of different resins. The powder 
employing the thermosetting resin was molded at the temperature at which 
the resin sets. The results of the test are shown in Table V. 
TABLE V 
______________________________________ 
Resin 
content Initial Volume 
ratio magnetic weight 
Ferrite: permeability index 
No. Resin type resin moldability (1 kHz) (g/cc) 
______________________________________ 
51 Thermosetting 
10:1 good 40 3.31 
resin powder 
(epoxy resin) 
52 styrene acrylic 10:1 good 53 3.66 
resin (powder) 
______________________________________ 
Thermosetting resin powder (epoxy resin): 
Product name; Ararudite AT1, manufactured by Ciba Geigy 
As the results in Table V indicate, moldability and electromagnetic 
characteristics that are almost equivalent to those achieved when a 
thermoplastic resin is used are assured when a thermosetting resin is 
used. 
TEST EXAMPLE 6 
Initial Magnetic Permeabilities of First Magnetic Particles A and Second 
Magnetic Particles B. 
By using the first magnetic particles A and the second magnetic particles B 
(both constituted of Mn soft ferrite) at varying initial magnetic 
permeabilities .mu.i, the relationship between the initial magnetic 
permeability .mu.i of the magnetic particles and the magnetic permeability 
of a magnetic molded article was examined. 
An adjustment was made on the group of first magnetic particles A so that 
97 wt % of the group of first magnetic particles A would have a particle 
size distribution of 425 .mu.m or more and less than 1000 .mu.m while 
achieving an average particle diameter of approximately 600 .mu.m. 1.5 wt 
% of the group of first magnetic particles A had a particle size 
distribution of 1000 .mu.m or more and the remaining 1.5 wt % had a 
particle size distribution of less than 425 .mu.m. 
An adjustment was made on the group of second magnetic particles B so that 
97 wt % of the group of second magnetic particles B would have a particle 
size distribution of 125 .mu.m or more and less than 300 .mu.m while 
achieving an average particle diameter of approximately 180 .mu.m. 1.5 wt 
% of the group of second magnetic particles B had a particle size 
distribution of 300 .mu.m or more and less than 425 .mu.m and the 
remaining 1.5 wt % had a particle size distribution of less than 125 
.mu.m. 
The group of first magnetic particles A and the group of second magnetic 
particles B were mixed at a weight ratio of A:B of 6:4 and the mixture was 
then placed in a grinding mill. It was then agitated for approximately 3 
minutes with styrene acrylic resin powder added for coating. The styrene 
acrylic resin was added to achieve different resin content ratios (weight 
ratios) relative to the group of first magnetic particles A and the group 
of second magnetic particles B. 
Next, toroidal cores were produced through a process similar to that 
employed in test example 1 and their initial magnetic permeabilities were 
measured. Table VI presents the relationships between the initial magnetic 
permeabilities .mu.i of the magnetic particles and the initial magnetic 
permeability of the magnetic molded article measured for test pieces Nos. 
61 to 64 which were obtained by varying the initial magnetic permeability 
.mu.i. 
TABLE VI 
______________________________________ 
.mu.i of magnetic 
Initial magnetic permeability 
Test piece No. particles A and B of magnetic molded article 
______________________________________ 
61 50 5 
62 200 43 
63 500 45 
64 2000 50 
______________________________________ 
Table VI indicates that by using the first magnetic particles A and the 
second magnetic particles B having an initial magnetic permeability .mu.i 
of 200 or more, a magnetic molded article having an initial magnetic 
permeability of 43 or more can be achieved. 
While the invention has been particularly shown and described with respect 
to preferred embodiments thereof by referring to the attached drawings, 
the present invention is not limited to these examples and it will be 
understood by those skilled in the art that various changes in form and 
detail may be made therein without departing from the spirit, scope and 
teaching of the invention. 
INDUSTRIAL APPLICABILITY 
As has been explained, according to the present invention, a magnetic 
powder through which electromagnetic characteristics may be improved by 
increasing the filling quantity of magnetic particles when it is employed 
to constitute a magnetic molded article, and a magnetic molded article 
constituted by molding this magnetic powder are provided.