[0001] The present invention relates to a magnetic ribbon and a magnetic core formed by
using said magnetic ribbon.
[0002] If a magnetic core is formed by winding or laminating a magnetic ribbon, and if insulation
between layers of the ribbon is poor, an eddy current flowing across the ribbon layers
occurs and an increase in eddy current losses results in an increase in overall core
losses (magnetic losses). This tendency is particularly noticeable in the case of
high frequencies. In addition, the frequency characteristics of permeability is poor,
and it is impossible to expect any advantageous use at 100 kHz or more.
[0003] Accordingly, in order to improve insulation between ribbon layers, an insulating
layer formed of a nonmagnetic material is conventionally provided between the ribbon
layers, and a uniform insulating film is formed on the ribbon surface as one means
thereof, so as to solve the aforementioned problem.
[0004] In cases where an amorphous magnetic ribbon is processed as a magnetic ribbon, annealing
is usually carried out at 400°C or thereabouts. However, if such annealing is carried
out, because of a difference in the coefficient of linear expansion, i.e., since the
coefficient of linear expansion of the insulating film is greater than that of the
amorphous ribbon, compressive stress occurs in the ribbon, and magnetic characteristics
deteriorate due to the adverse effect of magnetostriction.
[0005] In addition, there is another problem in that materials of such insulating films
capable of withstanding annealing at 400°C or thereabouts are limited. Furthermore,
if a magnetic core is formed by providing an insulating film, the filling factor (space
factor) declines, which disadvantageously causes the magnetic core to become large
in size.
[0006] Thus, as described above, when producing a magnetic core by using a magnetic ribbon,
an insulating film is generally interposed between ribbon layers, and the greatest
matter of concern to those skilled in the art lies in finding an insulating material
having an excellent insulating performance.
[0007] In accordance with the present invention, there is provided a magnetic ribbon on
at least one side of which particles, preferably fine particles, formed of a nonmagnetic,
preferably inorganic, substance having insulating properties are attached.
[0008] The invention also provides a magnetic core having such a ribbon wound therearound
or laminated thereon.
[0009] The particles may be attached so as to secure a layer of air so that in the absence
of a conventional insulating film, the air present between the layers can serve as
an insulating layer and prevent an eddy current, and the space factor can be made
as large as possible.
[0010] That is, particles formed of an inorganic substance are attached on at least one
surface of the magnetic ribbon, so that if the magnetic ribbon is wound or laminated
to form a magnetic core, the particles serve as a spacer, thereby forming a layer
of air between adjacent layers of the ribbon.
[0011] However, the particles may be attached uniformly and densely on at least one surface
of the ribbon. In this case, rather than particularly securing a layer of air, the
particles themselves function as an insulating layer. Nevertheless, in this case as
well, it is possible to obtain the same effect as that obtained by securing a layer
of air by means of the particles. Accordingly, the present invention includes both
the case where the particles are attached coarsely and the case where they are attached
densely.
[0012] The particles may be applied by any suitable method for example by passing the magnetic
ribbon through a suspension containing the particles. Where it is intended that the
particles should act as a spacer trapping a layer of air between layers or windings
of a core the proportion of particles in the suspension may be chosen to be suitably
low. For example where the particles are antimony pentoxide suspended in toluene they
may form 1% to 10%, preferably 2% to 5%, eg about 3%, by weight of the suspension.
[0013] Where it is intended that the particles should be attached more densely so as to
act as the insulation then a higher proportion may be used in the suspension. For
example, with the same materials as above, above 20% by weight, for example 20% to
50%, e.g. about 30% by weight.
[0014] Thus with the present invention a magnetic ribbon and a magnetic core can be provided
having excellent magnetic characteristics while securing insulating properties between
ribbon layers with the space factor reduced.
[0015] The invention will be further described by way of non-limitative example with reference
to the accompanying drawings, in which :-
Figs. 1 to 3 are graphs illustrating magnetic characteristics in accordance with a
first embodiment of the present invention, in which
Fig. 1 illustrates B-H characteristics;
Fig. 2 illustrates the frequency characteristics of core loss; and
Fig. 3 illustrates the frequency characteristics of permeability;
Figs. 4 to 6 are graphs illustrating the magnetic characteristics in accordance with
a second embodiment of the present invention, in which
Fig. 4 illustrates B-H characteristics;
Fig. 5 illustrates the frequency characteristics of core loss; and
Fig. 6 illustrates the frequency characteristics of permeability; and
Fig. 7 illustrates the outline of apparatus for attaching fine articles; and
Fig. 8 is a diagram schematically illustrating means for producing a toroidal type
magnetic core.
[0016] Referring now to the accompanying drawings, a description will be given of the preferred
embodiments of the present invention.
[0017] The magnetic ribbon referred to in the present invention is a thin magnetic strip,
and, as magnetic materials, it is possible to cite the following: ferromagnetic elements
such as Fe, Co, and Ni among transition metals, alloys of ferromagnetic elements,
alloys of ferromagnetic elements and nonferromagnetic elements which are added to
improve characteristics, ferrite, permalloy, amorphous alloys, etc. As amorphous alloys,
it is possible to cite Fe-based alloys such as Fe-B, Fe-B-C, Fe-B-Si, Fe-B-Si-C, Fe-B-Si-Cr,
Fe-Co-B-Si, and Fe-Ni-Mo-B, Co-based alloys such as Co-B, Co-Fe-Si-B, Co-Fe-Ni-Mo-B-Si,
Co-Fe-Ni-B-Si, Co-Fe-Mn-B-Si, Co-Fe-Mn-Ni, Co-Mn-Ni-B-Si, and Co-Fe-Mn-Ni-B, and other
similar alloys.
[0018] The conditions of inorganic fine particles that are attached to such a magnetic ribbon
are that it is nonmagnetic, and that it has insulating properties. If the fine particles
are magnetic and conductive, an adverse effect is exerted on magnetic characteristics,
and an eddy current is liable to flow.
[0019] As inorganic substances used in the present invention, it is possible to cite the
following: (1) inorganic substances which are stable in a natural condition, including
glass (sodium silicate), mica (aluminosilicate alkali salt and phyllosilicate alkali
salt), silicon carbide, calcium sulfate semi-water salt, potassium carbonate, magnesium
carbonate, calcium carbonate, barium sulfate, and the like; (2) metal oxides such
as aluminum oxide, boron oxide, magnesium oxide, silicon dioxide, tin dioxide, zinc
oxide, zirconium dioxide, antimony pentoxide, and the like; and (3) ceramics formed
of the materials cited in (2) above and double oxides such as perovskite, silicate
glass, phosphate, titanic acid salt, niobium, tantalum, and tungstate; ceramics formed
singly or in a combination by using such ceramic materials as nitrides, including
aluminum nitride, a sintered body of aluminum oxide and nitride, boron nitride, boron
nitride magnesium, boron nitride complexes, silicon nitride, silicon nitride lanthanum,
and SIALON, carbides, including boron carbide, silicon carbide, boron carbide aluminum,
and titanium carbide, and borides, including titanium diboride, calcium hexaboride,
and lanthanum hexaboride. Among these substances, antimony pentoxide is preferably
used.
[0020] As for the size of the fine particles of the inorganic substance, if consideration
is paid to the fact that the fine particles are attached to the ribbon uniformly so
as to form an insulating layer, the size of the fine particles may be small. However,
if the particle size is made too small, it constitutes a factor making manufacture
difficult. Meanwhile, if the particle size is too large, when the magnetic core is
formed by a ribbon, the gap between the adjacent layers of the ribbon becomes too
large, so that the space factor of the magnetic material becomes small. For this reason,
it is preferred that the size of the fine particles is set in the range of 10 nm to
2 µm.
[0021] In addition, as for the amount of the fine particles attached, the fine particles
may preferably be attached in such a manner that they are attached by 10⁻⁷cm³ to 2
x 10⁻⁴cm³, more preferably 3 x 10⁻⁶cm³ - 10⁻⁵cm³, per unit area (1 cm²). If this
amount attached is calculated into the weight of fine particles per unit area, although
its value changes depending on the specific weight of the material of the fine particles,
in the case of antimony pentoxide, the weight is 3.8 x 10⁻⁷g/cm² - 7.6 x 10⁻⁴g/cm²,
preferably 1.1 x 10⁻⁵g/cm² - 3.8 x 10⁻⁵g/cm².
[0022] Means for attaching the fine particles is so arranged that these fine particles are
dispersed in water or a volatile organic solvent such as toluene, and, after this
solution is applied to the ribbon surface, force or natural drying is carried out,
thereby allowing the fine particles to be attached to the ribbon. The concentration
of this solution determines the amount of fine particles to be attached to the ribbon.
In other words, in the case of antimony pentoxide, this inorganic substance may be
dispersed in toluene in a colloidal state at a rate of from 0.1 to 30 wt% with respect
to toluene. 3 wt% or thereabouts in this range is also effective, a decline in the
space factor is practically nil, and the magnetic characteristics do not deteriorate.
The thickness of the film of the solution applied is preferably 10 µm or less in determining
the aforementioned amount of fine particles to be attached. In addition, a drying
furnace may be used for evaporation of the solvent depending on the solvent, and drying
may be carried out at 100°C or above.
[0023] With respect to the magnetic ribbon, or an amorphous ribbon, in particular, annealing
may be carried out for 0.5 - 5 hours at the temperature of 300 - 500°C in an inert
gas atmosphere such as nitrogen so as to eliminate strain, as required. This annealing
may be effected after the ribbon is wound or laminated into a magnetic core, or may
be effected in the state of the ribbon. In particular, when annealing is effected
at a temperature 10 to 50°C higher than the Curie point, a magnetic core exhibiting
excellent characteristics with respect to high frequencies can be obtained. Incidentally,
annealing may be effected in a magnetic field or in a nonmagnetic field.
[0024] In addition, when the amorphous magnetic core with the ribbon wound therearound or
laminated thereon is annealed since the fine particles disposed between adjacent ribbon
layers are powders, the magnetic core is not subjected to linear expansion. The fine
particles rather exhibit the action of absorbing the stress accompanying the shrinkage
of the amorphous ribbon.
[0025] On the basis of the foregoing, a description will now be given of a method of producing
a magnetic core in accordance with the present invention.
[0026] First, a magnetic ribbon and a solution containing fine particles are prepared. The
solution containing the fine particles is applied to at lest one surface of the magnetic
ribbon by any of the various methods of application, and the solvent is allowed to
dry. The resultant magnetic ribbon with the fine particles attached thereto is wound
under tension, thereby obtaining a toroidal-type magnetic core. Finally, annealing
for eliminating strain is carried out, as necessary. Incidentally, tension applied
at the time of winding is preferably 0.05 o 2 kg.
[0027] Meanwhile, when a laminated type magnetic core is produced, the ribbon with fine
particles attached thereto is cut into a predetermined configuration, and the cut
pieces are laminated so as to form the magnetic core. Annealing which is carried out
as necessary may be effected prior to the lamination or after the magnetic core has
been formed subsequent to the lamination.
[0028] Examples of the present invention will be described hereafter.
[0029] By using the apparatus shown in Fig. 7, an amorphous ribbon 1a (2605S-2, Fe₇₈-B₁₃-Si₉,
10 mm width) made by Allied Corp. is fed forward into a colloidal solution 2 of antimony
pentoxide. When the amorphous ribbon 1a is lifted up, the amorphous ribbon 1a is clamped
by a pair of bar coaters 3 so as to allow excess solution to drop. Then, while the
ribbon 1a is being dried with hot air by means of a hot air drier 4, the ribbon 1a
was taken up. As for the colloidal solution 2 of antimony pentoxide, toluene was used
as the solvent, and 3 wt% of antimony was dispersed with respect to toluene 97 wt%.
[0030] Subsequently, as shown in Fig. 8, the ribbon 1b with the particles attached thereto
was fed forward via a roller 5, and was wound under tension in a final stage, thereby
forming an amorphous magnetic core 6. A plurality of magnetic cores having the same
dimensions were then formed, and were subjected to annealing for two hours at 435°C
in a nitrogen atmosphere.
[0031] With respect to the magnetic cores thus obtained, measurements were made of the B-H
characteristics, frequency characteristics of core loss, and frequency characteristics
of permeability. As for the B-H characteristics, measurements were made of two cases:
one in which a magnetic field of 10 oersted (Oe), and the other in which a magnetic
field of 1 oersted (Oe) was applied.
[0032] In addition, a colloidal solution in which 30 wt% of antimony pentoxide was dispersed
with respect to 70 wt% of toluene was applied to the ribbon 1a, and measurements were
similarly made. The detailed conditions in the respective examples were as follows:
(1) Example 1 (3 wt% solution)
(a) Magnetic core:
[0033] a toroidal core with the aforementioned ribbon wound therearound
Inside diameter: 23.00 mm
Outside diameter: 37.00 mm
Height: 10.00 mm
Mass: 42.00 g
Density of the material: 7.18 g/m³
Volume: 5.850 x 10⁻⁶ (m³)
Effective sectional area: 6.207 x 10⁻⁵ (m²)
Mean magnetic path length: 9.425 x 10⁻² (m)
Space factor: 88.67% (ratio of the volume of the ribbon to the total volume)
Tension during the magnetic ribbon winding: 0.8 kg
(b) Colloidal solution applied
[0034] Organic solvent: toluene, 100 wt%
Fine particles: antimony pentoxide, 3 wt%
(c) Results
[0035] * B-H characteristics are shown in Fig. 1.
* Frequency characteristics of core loss are shown in Fig. 2.
The number of turns of the primary winding around the core was 5, while the number
of turns of the secondary winding was 10.
* Frequency characteristics of permeability are shown in Fig. 3.
The number of turns of the primary winding around the core was 10.
Measured magnetic field: 5 mOe
Measured current: 2.65173 mA
(2) Example 2 (30wt% solution)
(a) Magnetic core:
[0036] a toroidal core with the aforementioned ribbon wound therearound
Inside diameter: 23.00 mm
Outside diameter: 37.00 mm
Height: 10.00 mm
Mass: 25.57 g
Density of the material: 7.18 g/m³
Volume: 3.561 x 10⁻⁶ (m³)
Effective sectional area: 3.779 x 10⁻⁵ (m²)
Mean magnetic path length: 9.425 x 10⁻² (m)
Space factor: 53.98%
Tension during the magnetic ribbon winding: 0.8 kg
(b) Colloidal solution applied
[0037] Organic solvent: toluene, 70 wt%
Fine particles: antimony pentoxide, 30 wt%
(c) Results
[0038] * B-H characteristics are shown in Fig. 4.
* Frequency characteristics of core loss are shown in Fig. 5.
The number of turns of the primary winding around the core was 5, while the number
of turns of the secondary winding was 10.
* Frequency characteristics of permeability are shown in Fig. 6.
The number of turns of the primary winding around the core was 10.
Measured magnetic field: 5 mOe
Measured current: 2.65173 mA
[0039] From the foregoing results, it can be appreciated that the magnetic cores of the
Examples display a hysteresis which is closer to a linear configuration, and that
the core loss is low as a whole, and a rise in the high-frequency component can be
reduced to a low level. A substantially fixed permeability was obtained up to 200
kHz.
[0040] As described above, in accordance with the present invention, since the above-described
arrangement is adopted, it is possible to improve the magnetic characteristics at
a frequency higher than 10 kHz, and the space factor can be made as large as possible,
thereby making contributions to making the magnetic core compact.