U.S. patent application number 10/729916 was filed with the patent office on 2004-07-01 for metal powder and powder magnetic core using the same.
This patent application is currently assigned to JFE STEEL CORPORATION. Invention is credited to Maetani, Toshio, Nakamura, Naomichi, Uenosono, Satoshi, Ueta, Masateru.
Application Number | 20040126609 10/729916 |
Document ID | / |
Family ID | 30447694 |
Filed Date | 2004-07-01 |
United States Patent
Application |
20040126609 |
Kind Code |
A1 |
Ueta, Masateru ; et
al. |
July 1, 2004 |
Metal powder and powder magnetic core using the same
Abstract
This invention provides a metal powder for powder magnetic
cores, which have good insulation performance and high magnetic
flux density, and which is favorable for motor cores. Ferromagnetic
metal powder may be coated with a coating material and a phosphate
or phosphoric acid compound containing aluminum is used for the
coating material. Coating the surface of iron powder with aluminum
phosphate realizes to produce high-quality powder magnetic cores
that have good insulation performance and high magnetic flux
density and are favorable for motor cores. Further coating the
aluminum phosphate-coated metal powder with silane compound or
surfactant realizes more stable compressed shaped articles of the
powder. And the properties of the articles do not fluctuate while
stored for, so long as they are resistant to moisture. This
invention contributes to producing powder magnetic cores for
motors, and to the process for powder magnetic cores, furthermore,
to the related art field.
Inventors: |
Ueta, Masateru; (Chiba,
JP) ; Nakamura, Naomichi; (Chiba, JP) ;
Maetani, Toshio; (Chiba, JP) ; Uenosono, Satoshi;
(Chiba, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
JFE STEEL CORPORATION
Tokyo
JP
100-0011
|
Family ID: |
30447694 |
Appl. No.: |
10/729916 |
Filed: |
December 9, 2003 |
Current U.S.
Class: |
428/570 ;
428/548 |
Current CPC
Class: |
Y10T 428/12181 20150115;
H01F 1/061 20130101; Y10T 428/12028 20150115; H01F 1/1475 20130101;
H01F 1/14766 20130101; H01F 1/24 20130101; H01F 1/15308 20130101;
B22F 1/16 20220101 |
Class at
Publication: |
428/570 ;
428/548 |
International
Class: |
B22F 001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 26, 2002 |
JP |
2002-377770 |
Sep 18, 2003 |
JP |
2003-326834 |
Claims
What is claimed is:
1. Metal powder comprising: a ferromagnetic metal powder; a coating
material to coat a surface of the ferromagnetic metal powder; and,
a coated metal powder coated on the surface of the ferromagnetic
metal powder with the coating material; wherein the coating
material is a phosphoric acid compound which contains aluminum.
2. The metal powder according to claim 1, wherein the ferromagnetic
metal powder comprises at least one powder selected from the group
consisting of iron powder, Fe-Si alloyed powder, Fe-Al alloyed
powder, Fe-Ni alloyed powder, sendust powder, and iron-based
amorphous alloyed powder.
3. The metal powder according to claim 1, wherein the phosphoric
acid compound containing aluminum in the coating material satisfies
the following formula: 1.ltoreq.P/M.ltoreq.10 wherein P (mol)
indicates the phosphorus content of the coating material, and M
(mol) indicates the overall metal content of the coating
material.
4. The metal powder according to claim 3, wherein the phosphoric
acid compound containing aluminum in the coating material satisfies
the following formula: 2.ltoreq.P/M.ltoreq.3 wherein P (mol)
indicates the phosphorus content of the coating material, and M
(mol) indicates the overall metal content of the coating
material.
5. The metal powder according to claim 1, wherein the number of
moles of the phosphoric acid compound is in the range
0.3.ltoreq..alpha..ltoreq.1, and wherein the number of moles of all
the metal elements in the coating material is M, the number of
moles of the aluminum=element in the coating material is .alpha.M
(0.ltoreq..alpha..ltoreq.1), and the number of moles of the metal
component other than the elements in the operating material is
(1-.alpha.)M.
6. The metal powder according to claim 1, wherein the phosphoric
acid compound in the coating material comprises at least one
selected from the group consisting of metaphosphoric acid,
pyrophosphoric acid, orthophosphoric acid, triphosphoric acid,
tetraphosphoric acid, phosphoric acid monoesters,
monomethylphosphoric acid, monooctylphosphoric acid,
monophenylphosphoric acid, and their corresponding salts.
7. The metal powder according to claim 1, wherein the metal
compound containing aluminum in the coating material comprises at
least one compound selected from the group consisting of aluminum
oxide, aluminum nitrate, aluminum acetate, aluminum hydroxide,
aluminum phosphate, and aluminum chloride.
8. The metal powder according to claim 1, further comprising an
organic resin.
9. The metal powder according to claim 8, wherein the organic resin
comprises at least one resin selected from the group consisting of
epoxy resin, phenolic resin, silicone resin, amide resin and imide
resin.
10. The metal powder according to claim 1, further comprising an
oxide.
11. The metal powder according to claim 1, further comprising a
surfactant and a silane compound.
12. The metal powder according to claim 1, wherein the amount of
the coating material to coat the surface of the metal powder is
within a range of 0.01 to 5 mass % of the total amount of the metal
powder.
13. A powder magnetic core comprising: a ferromagnetic metal
powder; a coating material to coat the surface of the ferromagnetic
metal powder; and a coated metal powder coated on the surface of
the ferromagnetic metal powder with the coating material; and the
powder magnetic core compacted by submitting the coated metal
powder to pressure; wherein the coating material is a phosphoric
acid compound containing aluminum.
14. The powder magnetic core according to claim 13, wherein the
aluminum-containing phosphoric acid compound in the coating
material satisfies the following formula: 1.ltoreq.P/M.ltoreq.10
wherein P (mol) indicates the phosphorus content of the coating
material, and M(mol) indicates the overall metal content of the
coating material.
15. The powder magnetic core according to claim 13, wherein the
phosphoric acid compound containing aluminum compound in the
coating material the following formula: 2.ltoreq.P/M.ltoreq.3
wherein P (mol) indicates the phosphorus content of the coating
material, and M (mol) indicates the overall metal content of the
coating material.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates to a metal powder for a powder
magnetic core using the metal powder. The present invention also
relates to the powder magnetic core.
[0003] 2. Description of Related Art
[0004] In recent years, motor-driven electric controls have been
widely used, such as, for instance, in various types of housing
amenities, automobile power steering and power windows.
[0005] With regard to the above-mentioned usage, small-sized but
high-power and well-controllable motors are generally required to
be applied for these applications. This requirement is generally
dictated by the limited space available.
[0006] Consequently, since general-purpose motors are sometimes
difficult to use in these applications, there is a need to develop
small-sized, high-performance motors.
[0007] When such new technology requiring smaller-sized motors is
developed, it efficiently compressing into small size, will become
very important because it greatly influences the performance of
motors, without incurring any performance reduction.
[0008] In most of the conventional motors, a laminate core is used
that is prepared by blanking out a laminate block with an
electromagnetic steel or an iron sheet. The reason why such a
laminate core is used is that the electromagnetic steel and the
iron sheet are relatively inexpensive and possess good properties
such as saturated magnetic flux density and magnetic permeability,
which are essential for the motors.
[0009] However, a problem associated with reducing the size of the
laminate is that production costs increase. Production costs
increase because during blanking of laminate cores out of the
original laminate block, the laminate block is required to have a
specific size. Therefore, if the cores to be blanked out of the
original laminate block are small in size, then the amount of the
wasted part of the laminated block for the motor increases, after
having been blanked. In addition, blanking smaller cores increases
the probability of producing a larger number of faulty products.
For example, when smaller cores are blanked out, a considerable
portion of them is capable of exhibiting defects such as burrs. As
a result, it decreases the productivity of smaller cores.
[0010] Based on the above-mentioned problems, for the development
of small-sized and high-performance motors, it would be desirable
that a new core material, substitutable to the above-desired
laminate cores, be developed.
[0011] Powder magnetic core, which is formed by filling a mold with
ferromagnetic metal powder of iron, or the like, and molding it
under pressure, becomes a viable alternative as a fine core
material for motors.
[0012] The reason why such powder magnetic core is viable is
described below. Compared with the laminate cores, powder magnetic
cores do not generate any waste during their production. Therefore,
powder magnetic cores present much cheaper production costs. In
addition, since there is more freedom in designing the shape of the
core, the design is able to be changed readily. For example, it
would be possible to use the core in small-sized motors. Moreover,
mixing the metal powder with an insulating material such as resin
or inorganic powder increases the insulation performance of the
metal powder for powder magnetic cores. So, the eddy current losses
resulting from driving the motor are significantly reduced, and the
motor efficiency therefore significantly-increases. Such advantages
cannot be obtained with laminate cores but can be obtained with
powder magnetic cores.
[0013] Also, in case that such powder magnetic cores are actually
used in motors, the powder magnetic cores needs to also exhibit
improved properties.
[0014] First, the insulation performance of the powder magnetic
core has to be high enough. When the magnetic field varies in time,
such as may be the case inside of a motor, it is known that
electromotive forces are generated inside the cores. Therefore, if
the insulation performance of the cores is poor, then the
electromotive forces generate eddy currents, which results in
overheating the cores. The overheating of the cores is unfavorable
since it significantly lowers the energy efficiency of the device
and, in addition, may create substantial damage to the devices.
[0015] Therefore, the surface of iron powder is coated with an
insulating substance in order to increase the insulation
performance of the powder magnetic core itself.
[0016] Second, the magnetic properties of the powder magnetic core
have to be sufficient. The magnetic flux density of conventional
ordinary powder magnetic cores is lower than that of laminate
cores. Therefore, when a powder magnetic core is used in a motor,
it results in motor performance problems such as, for instance,
lower torque. Conventional powder magnetic cores do not exhibit a
much lower insulation performance, but their magnetic flux density
is generally insufficient to be used in motors.
[0017] Therefore, it is strongly desired to increase the magnetic
flux density of the powder magnetic cores.
[0018] Accordingly, when powder magnetic cores are used in motors,
the problems regarding insulation performance and magnetic flux
density have to be solved.
[0019] As such, various methods for increasing the magnetic flux
density and the insulation performance of the powder magnetic cores
have been investigated so far.
[0020] It is known that the magnetic flux density of the powder
magnetic cores increases with increasing the density of the
compressed shaped articles of the powder magnetic cores. Based on
such knowledge, various methods for increasing the magnetic flux
density of the powder magnetic cores have been proposed.
[0021] One factor that causes the magnetic flux density to lower is
the level of magnetic anisotropy of the cores, which depends on the
morphology of the metal powder used in the cores. Regarding using
the magnetic anisotropy, a method of reducing the magnetic
anisotropy of the powder magnetic cores by flattening the particles
of the magnetic powder to increase the magnetic flux density of the
cores has been proposed (e.g., see patent reference 1).
[0022] However, according to this method, the particles that make
up the metal powder inevitably develop morphological anisotropy,
therefore having a high-magnetization axis and a low magnetization
axis. Accordingly, the powder magnetic cores that are formed of
such metal powder cannot be applied to motors and other devices
where the magnetization direction varies.
[0023] In addition, the powder magnetic cores, formed by flattened
particles alone, readily peel away in the machining direction of
the flattened particles. Therefore, for increasing the strength of
the compressed shaped articles of the powder, some amount of resin
must be added. However, the resin added to the powder tends to
lower the magnetic flux density of the powder magnetic cores and
the fact that the additive resin decreases the magnetic flux
density of the powder magnetic cores is an additional problem.
[0024] In addition, various methods have also been investigated to
increase the insulation performance of the compressed shaped
articles.
[0025] For example, methods to coat an iron powder with a resin
binder, such as, for example, epoxy resin or fluororesin to
increase the strength of the powder magnetic cores formed of the
thus-coated powder (e.g., see patent reference 2) have been
proposed.
[0026] The additive binder increases the insulation performance of
the compressed shaped articles of powdery magnetic cores, but a
problem arises in that it may significantly lower the magnetic flux
density and the magnetic permeability of the cores, since the
volume ratio of the iron to the powder magnetic cores decreases.
Therefore, this method is not applicable to the motor cores that
require high magnetic flux density.
[0027] In addition to the method of using a resin as mentioned
above, methods of coating the surface of soft magnetic powder with
a glassy insulating material that comprises indispensable elements
of P, Mg, B and Fe to thereby increase the insulation performance
of the thus-coated powder (e.g., see patent reference 5) have been
proposed.
[0028] However, when the soft magnetic powder obtained according to
the method is shaped under a high pressure equal to or greater than
588 MPa, then the glassy insulating material is broken and the
insulation performance of the thus-shaped article becomes thereby
significantly lowered. Therefore, the proposed method shows that
increasing the density of the shaped article does not necessarily
bring about an increase in the magnetic flux density thereof.
[0029] For increasing the insulation performance of metal powder
without lowering the magnetic flux density thereof, another method
comprises processing the surface of the metal powder with acid.
[0030] For example, P. Lefebver, et al. have reported that, when
metal powder is processed on its surface with sulfuric acid to
increase the surface roughness thereof, then the insulation
performance of the thus-processed metal powder increases (e.g., see
non-patent reference 1).
[0031] Further disclosed is a technology to use the iron powder
coated with phosphoric acid on the surface to obtain powder
magnetic cores which has an increased insulation performance (e.g.,
see patent reference 3 and patent reference 4).
[0032] The method for using sulfuric acid or phosphoric acid as
mentioned above is effective for preventing any reduction of the
density of the compressed shaped articles, since no resin is added
to the articles. In this method, however, since acid is used for
the surface treatment, a problem arises in that the acid that
remains on the metal and that has not reacted with the metal
gradually corrodes the metal. As a result, the magnetic properties
and the insulation performance of the powder magnetic cores formed
by this method deteriorate with time. In addition, another problem
arises in that the insulation performance of the powder magnetic
cores, which is formed of the metal, is not enough.
[0033] [Patent Reference 1] JP-A 2-153003 (claims),
[0034] [Patent Reference 2] JP-A 59-50138 (claims),
[0035] [Non-patent Reference 1] P. Lefebver et al.; Powder Met,
1999, 42, pp. 325-330,
[0036] [Patent Reference 3] JP-A 7-245209 (claims),
[0037] [Patent Reference 4] JP-T 2000-504785 (claims) (the term
"JP-T" as used herein means a published Japanese translation of a
PCT patent application),
[0038] [Patent Reference 5] JP-A 6-260319 (claims).
SUMMARY OF THE INVENTION
[0039] One of the advantages of the present invention is that it
solves the above-described problems and one of its objects is to
provide metal powder for powder magnetic cores which has the
advantages of good insulation performance and high magnetic flux
density, and which is usable in motor cores. Another object of this
invention to provide a powder magnetic core formed by the metal
powder.
[0040] In order to attain the objects mentioned above, the surface
treatment of metal and metal powder was carefully studied.
[0041] As a result, it is found that, when the surface of a metal
powder is processed with an aluminum-containing phosphate or
phosphoric acid compound, a chemical reaction occurs on the surface
of the thus-processed metal powder to form an insulating layer of
improved adhesiveness. This insulating layer has the advantages,
for instance, of improved impact resistance, pressure resistance
and improved corrosion resistance.
[0042] In addition, it was further found that, even when the powder
is shaped under a high pressure equal to or greater than 686 MPa,
the insulating layer does not break and retains its good insulating
performance.
[0043] On the basis of these findings, the present invention was
conceived.
[0044] Some of the characteristics of this invention are as
follows:
[0045] (1) Metal powder comprising:
[0046] a ferromagnetic metal powder;
[0047] a coating material to coat a surface of the ferromagnetic
metal powder; and
[0048] a coated metal powder coated on the surface of the
ferromagnetic metal powder with the coating material;
[0049] wherein the coating material is a phosphoric acid compound
which contains aluminum.
[0050] (2) The metal powder according to (1), wherein the
ferromagnetic metal powder comprises at least one powder selected
from the group consisting of iron powder, Fe-Si alloyed powder,
Fe-Al alloyed powder, Fe-Ni alloyed powder, sendust powder and
iron-based amorphous alloyed powder.
[0051] (3) The metal powder according to (1), wherein the
phosphoric acid compound containing aluminum in the coating
material satisfies the following formula:
1.ltoreq.P/M.ltoreq.10
[0052] wherein P (mol) indicates the phosphorus content of the
coating material, and M (mol) indicates the overall metal content
of the coating material.
[0053] (4) The metal powder according to (3), wherein the
phosphoric acid compound containing aluminum in the coating
material satisfies the following formula:
2.ltoreq.P/M.ltoreq.3
[0054] wherein P (mol) indicates the phosphorus content of the
coating material, and M (mol) indicates the overall metal content
of the coating material.
[0055] (5) The metal powder according to (1), wherein the number of
moles of the phosphoric acid compound is in the range
0.3.ltoreq..alpha..ltoreq- .1,
[0056] wherein the number of moles of all the metal elements in the
coating material is M, the number of moles of the aluminum element
in the coating material is by .alpha.M (0.ltoreq..alpha..ltoreq.1),
and the number of moles of the metal component other than the
aluminum elements in the coating material is (1-.alpha.)M.
[0057] (6) The metal powder according to (1), wherein the
phosphoric acid compound in the coating material comprises at least
one selected from the group consisting of metaphosphoric acid,
pyrophosphoric acid, orthophosphoric acid, triphosphoric acid,
tetraphosphoric acid, phosphoric acid monoesters,
monomethylphosphoric acid, monooctylphosphoric acid,
monophenylphosphoric acid, and their corresponding salts.
[0058] (7) The metal powder according to (1), wherein the metal
compound containing aluminum in the coating material comprises at
least one compound selected from the group consisting of aluminum
oxide, aluminum nitrate, aluminum acetate, aluminum hydroxide,
aluminum phosphate, and aluminum chloride.
[0059] (8) The metal powder according to (1), further comprising an
organic resin.
[0060] (9) The metal powder according to (8), wherein the organic
resin comprises at least one resin selected from the group
consisting of epoxy resin, phenolic resin, silicone resin, amide
resin and amide resin.
[0061] (10) The metal powder according to (1), further comprising
an oxide.
[0062] (11) The metal powder according to (1), further comprising a
surfactant and a silane compound.
[0063] (12) The metal powder according to (1), wherein the amount
of the coating material to coat the surface of the metal powder is
within a range of 0.01 to 5 mass % of the total amount of the metal
powder.
[0064] (13) A powder magnetic core comprising:
[0065] a ferromagnetic metal powder;
[0066] a coating material to coat the surface of the ferromagnetic
metal powder; and,
[0067] a coated metal powder coated on the surface of the
ferromagnetic metal powder with the coating material; and,
[0068] a powder magnetic core compacted by submitting the coated
metal powder to pressure;
[0069] wherein the coating material is a phosphoric acid compound
containing aluminum.
[0070] (14) The powdery magnetic core according to (13), wherein
the phosphoric acid compound, which contains aluminum in the
coating material, satisfies the following:
1.ltoreq.P/M.ltoreq.10
[0071] wherein P (mol) indicates the phosphorus content of the
coating material, and M (mol) indicates the overall metal content
of the coating material.
[0072] (15) The powder magnetic core according to (13), wherein the
phosphoric acid compound containing aluminum in the coating
material satisfies the following:
2.ltoreq.P/M.ltoreq.3
[0073] wherein P (mol) indicates the phosphorus content of the
coating material, and M (mol) indicates the overall metal content
of the coating material.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0074] The invention is described in detail as follows.
[0075] The invention discloses a metal powder characterized by the
fact that it is prepared by coating the surface of a starting
powder of an essentially ferromagnetic metal such as iron
(hereinafter referred to as "starting powder") with a phosphate or
phosphoric acid compound containing aluminum, in which the material
to coat the surface of the starting powder is prepared, for
example, from a phosphoric acid compound and a metal compound
containing aluminum.
[0076] In various exemplary embodiments, the term "phosphoric" acid
compound used in the starting material for the coating material is
a generic term for phosphoric acids which have at least 2 hydroxyl
groups bonding to a phosphorus atom and which are obtained through
hydration of diphosphorus pentoxide and their salts. Concretely, it
may include metaphosphoric acid, pyrophosphoric acid,
orthophosphoric acid, triphosphoric acid, tetraphosphoric acid and
their salts. Apart from the above-mentioned acid, any other
phosphoric acid compound is also employed in the invention,
including, for example, phosphoric monoesters such as
monomethylphosphoric acid, monooctylphosphoric acid,
monophenylphosphoric acid, and still other phosphoric acids and
their salts. In various exemplary embodiments, the phosphoric acid
compounds are soluble in solvents such as water.
[0077] In various exemplary embodiments, the metal compound
containing aluminum for the other starting material for the coating
material may be any one that contains aluminum. In other exemplary
embodiments, the aluminum-containing compounds can be aluminum
oxides, phosphates, nitrates, acetates, hydroxides and
chlorides.
[0078] In various exemplary embodiments, a metal compound that does
not contain aluminum may be combined with a metal compound
containing aluminum. For example, oxides, phosphates, carbonates,
nitrates, acetates, hydroxides and chlorides of any of Mg, Mn, Zn,
Co, Ti, Sn, Ni, Fe, Zr, Sr, Cu, Ca, V, Ba, etc. Additionally, in
the invention, a non-metal element-containing compound may be
combined with a metal compound. For example, oxides, phosphates,
carbonates, nitrates, acetates, hydroxides and chlorides of any of
Y, B, etc.
[0079] In various exemplary embodiments, these metal compounds are
also soluble in solvents such as water for practicality.
[0080] In various exemplary embodiments, the phosphate or
phosphorus acid compound containing aluminum that coats the surface
of the starting powder in the invention is so designed that the
molar ratio P/M is within a range of about 1 to 10, in which P
(mol) indicates the phosphorus content of the coating material and
M (mol) indicates the overall metal content of the coating
material. The reason why such range is preferable in various
exemplary embodiments is, when the ratio P/M is equal to or greater
than 1, then the chemical reaction on the metal surface can take
place and the adhesiveness of the chemical film to the surface of
the metal powder increases. As a result, the strength and the
insulation performance of the compressed shaped articles of the
coated powder is further increased. In various exemplary
embodiments, when the ratio P/M is smaller than about 10, then no
free phosphoric acid remains on the coated metal powder. As a
result, the metal powder does not corrode. In various exemplary
embodiments, the ratio P/M falls within a range from about 1 to 5.
In various exemplary embodiments, the ratio P/M is controlled to
fall between about 2 and 3, so as to more effectively prevent the
specific resistivity of the coated metal powder core from
fluctuating and become unstable.
[0081] In order to control the ratio P/M, to fall within a defined
range, for example, the following method may be used. In various
exemplary embodiments, a method for suitably determining the amount
of the phosphoric acid compound, the aluminum compound and the
other metal compound to be mixed, so that the ratio P/M falls
within a desired value. In various exemplary embodiments, there is
a method of preparing the coating material with a predetermined
ratio P/M by further adding any of the phosphoric acid compound,
the aluminum compound and the other metal compound to the resulting
mixture in order to achieve the desired value of P/M. The present
invention discusses these methods, as well as other methods similar
to in methodology and scope.
[0082] The ratio P/M may be defined, for example, as follows: The
phosphorus content and the other metal content of the compound are
determined through quantitative analysis, then they are converted
into the molar ratio of the constitutive components. Alternatively,
the phosphorus content and the other metal content of the starting
materials are determined through quantitative analysis, and then
the thus-determined starting materials are mixed in the desired
molar ratio P/M.
[0083] In various exemplary embodiments, the method of quantitative
analysis used to determine the ratio P/M comprises the following
steps:
[0084] 1) P and M in the coated iron powder and the starting powder
are quantitatively determined. In this step, M is to include the
constitutive components of the coating material.
[0085] 2) The coating fraction of P and that of M are calculated as
follows: (the content of the component in the coated powder)--(the
content of the component in the starting powder).
[0086] 3) The content of each element is divided by the atomic
weight of P or M to give the molar content of each element.
[0087] 4) From the molar content of each element obtained in the
above, the ratio P/M is calculated.
[0088] In various exemplary embodiments, the coating film, or the
lower or upper layer of the coating film may contain other
substance than the aluminum-containing phosphate or phosphoric acid
compound so far as the other substance does not have any negative
influence on the magnetic flux density and other properties of the
compressed shaped articles of the coated powder. The additional
substance may include, for example, a material such as a surfactant
for improving the wettability of the metal with the coating
substance, a resin for binding the binding powder particles
together, or any other additive for controlling the pH or other
chemical or physical properties of phosphates or other coating
substances used in coating the metal powder with the coating
material. In various exemplary embodiments, the total content of
the additional substance is not larger than 5% by mass of the
coating material.
[0089] In various exemplary embodiments, when the number of moles
of all the metal elements in the coating film is indicated by M,
the number of moles of the aluminum in the coating film is
indicated by .alpha.M (0.ltoreq..alpha..ltoreq.1) and the number of
moles of the metal component other than aluminum is indicated by
(1-.alpha.) M, then .alpha. is preferably from about 0.3 to about
1. This is because, when .alpha. is greater than about 0.3, the
amount of aluminum that is highly reactive with phosphoric acid is
sufficient to eliminate any non-reacted free phosphoric acid and,
as a result, the metal powder is protected from corrosion by the
non-reacted phosphoric acid. In various exemplary embodiments, the
range of the value .alpha. is as follows: about
0.4.ltoreq..alpha..ltoreq.about 1.0. Even more preferably, about
0.8.ltoreq..alpha..ltoreq.about 1.0.
[0090] In various exemplary embodiments, the starting powder for
use in the invention may be any metal powder that is ferromagnetic
and that has a highly saturated magnetic flux density. The metal
powder may include, for example, iron powder, Fe-Si alloyed powder
such as typically Fe-3% Si alloyed powder, as well as Fe-Al alloyed
powder, Fe-Ni alloyed powder, sendust powder, and iron-based
amorphous alloyed powder. In various exemplary embodiments, one or
more different types of metal powder selected from these are used
as the starting powder. In various exemplary embodiments, the
starting powder may be pre-worked for shaping it more easily (for
example, for shaping it into spherical granules).
[0091] In various exemplary embodiments, and with regard to the
metal powder mentioned above, pure iron powder such as typically
atomized iron powder, reduced iron powder and electrolytic iron
powder are especially favorable for the starting powder of the
invention. Because the magnetic properties of iron, such as
saturated magnetic flux density and magnetic permeability, are good
and, in addition, iron is easily compressible and is inexpensive.
Examples of such pure iron powder are JFE Steel's KIP-MG270H and
KIP-304AS.
[0092] In various exemplary embodiments, the particle size of the
starting powder mentioned above is suitably determined depending on
the use and the necessary properties of the powder magnetic cores
that are formed as a result. In various exemplary embodiments, the
constituent elements of the starting powder are controlled so as
not to have any negative influence on the compressibility of the
resulting powder and on the magnetic properties of the powder
magnetic cores formed as a result.
[0093] In various exemplary embodiments, in order to form a coating
film of phosphate or phosphoric acid compound containing aluminum
for covering the surface of the starting powder, any method of
vapor phase evaporation such as CVD or PVD can be used, In various
exemplary embodiments, other dry coating treatment such as
mechanofusion, or wet coating treatment can be effected by using a
solution of the starting materials, phosphoric acid compound and
metal compound. Any of these methods may be employed in the
invention, as well as any other similar method. In various
exemplary embodiments, the method of wet coating treatment with a
solution of the starting materials, the phosphoric acid compound
and the metal compound is especially good because of its
simplicity, compared with, for instance, vapor phase evaporation.
In the wet method, in addition, the blend ratio of the phosphoric
acid compound and the aluminum compound may be readily controlled
to fall within a desired ratio P/M. Therefore, the molar ratio P/M
of phosphorus to metal elements is more accurately controlled,
compared with, for instance, the dry coating treatment. Moreover,
the wet method enables us to obtain more uniform coating of the
surface of the starting powder with the coating material.
[0094] In various exemplary embodiments, in the wet coating
treatment, it is desirable that the pH of the solution is
controlled to fall within a desired range for the purpose of
controlling the reactivity of the solution with metal. In various
exemplary embodiments, the preferred pH range of the solution is in
a range of about 1 to about 6. In various exemplary embodiments,
when the pH of the solution is greater than 1, then the reactivity
of the solution with metal is not too high, and while the starting
powder is processed with the solution, starting powder does not
react too much with the solution. As a result, the component and
the composition of the coating film is uniform, and the
adhesiveness thereof to the substrate increases. In various
exemplary embodiments, when the pH value of the solution is smaller
than about 6, then the reactivity of the solution is not too low,
and the solution forms a coating film in a good condition.
[0095] In various exemplary embodiments, for controlling the pH of
the solution in the invention, a pH-controlling agent is added to
the solution. The pH-controlling agent includes, for example,
monosodium phosphate, disodium phosphate, sodium acid
pyrophosphate, monopotassium phosphate, dipotassium phosphate,
monosodium fumarate, and boric acid, or any other material than
those mentioned above.
[0096] In various exemplary embodiments, for treating the starting
powder in a wet condition, together with the solution, any method
of stirring and mixing them in a tank stirrer such as an attritor
or Henschel mixer may be acceptable. Otherwise, in various
exemplary embodiments, there is a method of mixing them in a
fluidized condition in a rotary fluidized-bed coating apparatus.
Any of these methods or any other similar method is employed in the
invention. In various exemplary embodiments, in order to treat the
wet treatment therewith, the solution is applied to the metal
powder all at once before or just after starting mixing them. In
various exemplary embodiments, it is intermittently applied a few
times to the powder while they are mixed. In various exemplary
embodiments, the solution is continuously applied to the powder
through a dropping device or a spray while the metal powder is
mixed.
[0097] In various exemplary embodiments, spraying is favorable
since it enables to uniformly apply the solution to the powder. In
various exemplary embodiments, the spraying droplets of the
solution has a reduced size of about 10 .mu.m or so, when the
spraying condition is suitably controlled, and therefore, the
coating film is prevented from becoming too thick. As a result, the
metal powder is entirely coated with a uniform and thin coating
film.
[0098] In various exemplary embodiments, when a fluidized-bed
stirrer such as fluidized-bed granulator or rotary granulator or a
stirring mixer such as Henschel mixer is used, an advantage is that
the particles of the metal powder are prevented from aggregating.
Accordingly, when the solution is sprayed onto the metal powder by
using such a fluidized-bed stirrer or Henschel mixer, it allows the
metal powder to be coated more uniformly. This is owing to the
synergistic effect of the spraying operation and the action of the
fluidized bed or the Henschel mixer. In various exemplary
embodiments, in order to remove the solvent more rapidly and in
order to promote the reaction further, it is advantageous to heat
the system during or after mixing it.
[0099] In various exemplary embodiments, the amount of coating
material to be applied to the metal powder is within a range from
about 0.01 to about 5% by mass of the metal powder. This is
because, if the additive-coated amount is smaller than about 0.01%
by mass, then the metal powder may be unevenly coated because the
amount of the coating material is too small and, as a result, the
insulation performance of the coated powder becomes poor. In
various exemplary embodiments, if the amount of coating material is
larger than about 5% by mass, then the proportion of the metal
powder in the powder magnetic core decreases and the magnetic flux
density of the core is thereby significantly lowered.
[0100] In various exemplary embodiments, when the starting powder
is coated with the coating material to prepare the coated powder of
the invention, the temperature of the starting powder and the
coated powder is preferably lower than 110.degree. C. During the
coating process, if the temperature of the starting powder and the
coated powder is greater than 110.degree. C., then the insulation
performance of the powder magnetic core formed of the coated powder
becomes poor. In various exemplary embodiments, the temperature of
the starting powder and the coated powder is lower than 100.degree.
C. In various exemplary embodiments, the temperature of the
starting powder and the coated powder are not higher than
90.degree. C. In order to ensure that the temperature of the
starting powder and for the coated powder is lower than 110.degree.
C. in the coating process, it is desirable that the temperature of
the coating material and the atmosphere for the coating operation
are also kept under 110.degree. C.
[0101] In various exemplary embodiments, the lowermost limit of the
temperature of the starting powder and the coated powder are not
specifically defined, but they are set to be no lower than room
temperature. In various exemplary embodiments, when the coating
treatment is effected in a wet condition, for an example with water
solvent, it takes a lot of time to remove the solvent if the
working temperature is too low. And if so, the productivity of the
coated powder may decrease significantly. Therefore, the
temperature is preferably not lower than 60.degree. C., and in
various exemplary embodiments not lower than 80.degree. C. In
various exemplary embodiments, not only the temperature of the
starting powder and the coated powder, but also that of the coating
operation atmosphere are preferably higher by at least 20.degree.
C. than room temperature. In various exemplary embodiments, they
are not lower than 60.degree. C., and not lower than 80.degree.
C.
[0102] In various exemplary embodiments, during the process of
coating the starting powder with the coating material for preparing
the coated powder of the invention, the temperature of the starting
powder and the coated powder may be controlled, for example, as
follows: Hot air/cold air is directly applied to the starting
powder and the coated powder to control the temperature of the
powder; or the tank that contains the coated powder therein is
heated/cooled at the intended temperatures. Any of these methods
may be employed in the invention. The temperature of the starting
powder and the coated powder may be controlled with any other
similar method than those described herein. In various exemplary
embodiments, in order to measure the powder temperature, for
example any method for directly contacting the powder with a
temperature sensor such as thermocouple can be used. In various
exemplary embodiments, a method for monitoring the IR rays from the
powder can also be used. In various exemplary embodiments, a method
for monitoring the peripheral equipment and atmosphere, and for
deriving the powder temperature by taking the related factors into
consideration, such as thermal conductivity and convection can be
used. Any of these methods or any other temperature measurement
method can be used.
[0103] In various exemplary embodiments, in the metal powder of
this invention, coated with a phosphate or phosphoric acid compound
containing aluminum, unreacted free phosphoric acid remains
present, although in a small amount, in the phosphate or the
phosphoric acid compound. In various exemplary embodiments, the
remaining free phosphoric acid makes the powder
moisture-absorptive, and if the powder absorbs moisture, the
phosphate or the phosphoric acid compound in the surface of the
coating film may become denatured. As a result, the coating film
shrinks, peels or softens. The specific resistivity of the powder
magnetic core of this invention, formed by pressing the metal
powder fluctuates and becomes unstable. Therefore, in various
exemplary embodiments of this invention, it is desirable to process
the coated powder for resistance to moisture absorption.
[0104] In various exemplary embodiments, the methods for making the
coated powder resistant to moisture absorption may be any method of
heating the metal powder being coated or the coated powder to
thereby promote the crosslinking reaction between free phosphoric
acid and aluminum, so as to remove the free phosphoric acid, or a
method of coating the surface of the metal powder with a
non-absorptive material to thereby make the thus-coated metal
powder resistant to moisture absorption. Any other similar method
may also be employed in this invention.
[0105] In various exemplary embodiments, in case that the metal
powder is heated for making it resistant to moisture absorption,
the heating temperature is preferably set in the range of
50.degree. C. to about 500.degree. C. This is because, if the
heating temperature is lower than about 50.degree. C., it is too
low to generate any crosslinking reaction. Additionally, the metal
powder is not completely resistant to moisture absorption. On the
other hand, if the heating temperature is higher than about
500.degree. C., the thermal stress caused by the difference in the
thermal expansion coefficient between the metal and the coating
material increases and the coating material may be broken or may
peel. The heating time is suitably determined depending on the used
heating device and the amount of the powder to be processed. From
the standpoint, of the production costs, in various exemplary
embodiments, it is desirable that the temperature is from about 70
to 350.degree. C. and the heating time from about 10.about.60
minutes. In various exemplary embodiments, air is preferred as the
atmosphere for the heating treatment, since it is easy to prepare
and handle, and since heating does not significantly increase the
production costs. In various exemplary embodiments, the atmosphere
is preferably so conditioned that its relative humidity is at most
about 40% in order for the powder to be treated without absorbing
any moisture from the atmosphere. In various exemplary embodiments,
a method of heating the powder in a drier can be used because it is
simple. Any other device and method such as rotary kiln,
fluidized-bed drier can also be used.
[0106] In various exemplary embodiments, when the powder is
subjected to treating for moisture absorption resistance as above,
it is desirable that the ratio P/M is controlled to fall between
about 2 and 3 because not only it can be done at low cost, but also
the specific resistivity of the processed powder core becomes more
effective because it becomes more stable.
[0107] In various exemplary embodiments, in order to coat the
powder with a non-absorptive material for making it resistant to
moisture absorption, for example, any method of coating the powder
with an organic substance such as resin can be used. In various
exemplary embodiments, a method of coating the powder with an oxide
such as silica, or a method of coating the powder with a
monomolecular film of surfactant or silane compound can be
used.
[0108] In various exemplary embodiments, when the powder is coated
with an organic substance, for example, the organic substance can
be any substance capable of forming a water-resistant film, such as
a resin or any other organic substance. The resin may be, for
example, epoxy resin, phenolic resin, silicone resin, amide resin,
and imide resin or any other material.
[0109] In various exemplary embodiments, when the powder is coated
with an oxide, for example, the oxide is selected from oxides of
Ti, Zr, Si, Al, Y, or can be used in the invention so far as it is
effective for moisture absorption resistance. In various exemplary
embodiments, in order to coat the metal powder with the oxide, for
example, any method of dipping the metal powder in an oxide
precursor such as alcoxide compound, or coating the metal powder
with such an oxide precursor, or a method of coating it with a
colloidal oxide, or a method of coating it with plasma of oxide
molecules can be used. Any other similar method to those described
herein may also be employed in the invention.
[0110] In various exemplary embodiments, the alcoxide compound can
be, for example, a metal alcoxide compound such as titanium
alcoxide, zirconium alcoxide, aluminum alcoxide, silicon alcoxide.
Of those alcoxide compounds, in various exemplary embodiments,
silicon alcoxide is preferred, as it is easy to handle and is
inexpensive. In various exemplary embodiments, for the alcoxide
compound, allyl silicates such as ethyl silicate and methyl
silicate, and silane compounds are also preferred.
[0111] In various exemplary embodiments, the colloidal oxide
includes, for example, alumina sol, silica sol, titania sol and
zirconia sol. The solvent for dispersing the colloid may be any
solvent, but water is preferred as it is easy to handle. In various
exemplary embodiments, the particle size of the colloidal oxide may
be any one as long as the oxide is dispersible. In various
exemplary embodiments, in view of its influence on the
compressibility of the coated powder into powder magnetic cores,
the mean particle size of the oxide is preferably at most 0.1
.mu.m.
[0112] In various exemplary embodiments, when the powder is coated
with a monomolecular film, a surfactant or a silane compound may be
used for it. Any other similar material may also be used in the
invention in order to attain the above-mentioned object.
[0113] In various exemplary embodiments, the surfactant includes,
for example, nonionic surfactants such as polyoxyethylene alkyl
ethers, polyoxyalkylene alkyl ethers, polyoxyethylene derivatives,
sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid
esters, glycerin fatty acid esters, polyoxyethylene fatty acid
esters, polyoxyethylene hardened castor oil, polyoxyethylene
alkylamines, alkylalkanolamides, polyoxyethylene-polyoxypropylene
condensates, polyoxyethylene-polyoxyprop- ylene block polymers and
ionic surfactants such as alkylsulfate ester salts, polyoxyethylene
alkyl ether sulfate ester salts, sulfonic acid salts such as
alkylbenzenesulfonic acid salts, fatty acid salts, alkylamine
salts, and quaternary ammonium salts may also be used in this
invention.
[0114] In various exemplary embodiments, the silane compound
includes, for example, alkoxysilanes of which the silicon atom is
terminated with a methyl group, methoxysilane, or with an ethyl
group, ethoxysilane; alkylsilanes prepared by adding an alkyl group
such as methyl or phenyl group to alkoxysilanes; and silane
coupling agents prepared by adding an organic functional group such
as amino, methacryl, vinyl, epoxy or mercapto group to the terminal
of alkylsilanes. Any of these may be used in the invention, but, in
various exemplary embodiments, silane-coupling agents are
preferred. In various exemplary embodiments, aminosilane coupling
agents having an amino group at the terminal thereof are preferred,
since the amino group moiety may selectively react with free
phosphoric acid, and therefore the ability of the agents to block
free phosphoric acid is high, and, in addition, since the agent
molecules themselves are highly repellent to water, the ability of
the agents to resist moisture absorption is higher than that of the
other alkyl group-having silane coupling agents.
[0115] In various exemplary embodiments, the above-mentioned
materials may be mixed with the aluminum-containing phosphate or
phosphoric acid compound or its aqueous solution, or they may be
applied to the powder coated with the phosphate or phosphoric acid
compound. When they are mixed with the aluminum-containing
phosphate or phosphoric acid compound, they may react with the
phosphate or phosphoric acid compound and the phosphate or
phosphoric acid compound may become denatured. In particular, ionic
surfactants and aminosilane coupling agents capable of forming ions
in their aqueous solution may readily denature the phosphate or
phosphoric acid compound owing to the action of the ions in the
additives. Accordingly, in various exemplary embodiments, when such
materials are used, it is desirable that the powder is first coated
with the phosphate or phosphoric acid compound and then it is
further coated with the additive in a separate step. When the
powder coated with the phosphate or phosphoric acid compound is
further coated with the moisture-resistant material in a separate
step, then the material separately added to the powder for moisture
absorption resistance may more effectively cover the whole of the
metal powder. Therefore, the method is more favorable as it is more
effective for water absorption resistance.
[0116] In various exemplary embodiments, the amount of the moisture
absorbing material to be added to the metal powder is at least
about 0.01% by mass but at most about 2.0% by mass of the metal
powder. This is because if it is smaller than about 0.01% by mass,
the material cannot fully perform its moisture absorbing
properties; but if the amount of moisture-absorbing material is
larger than about 2.0% by mass, it may lower the compressibility of
the metal powder and, as a result, the magnetic flux density of the
powder magnetic core formed of the powder and the strength of the
part may decrease. In various exemplary embodiments, the amount of
the material to be added is from about 0.01% by mass to about 1.5%
by mass, and, in various exemplary embodiments from about 0.01% by
mass to about 1.0% by mass.
[0117] In various exemplary embodiments, to add the
moisture-resistant material to the metal powder, any method can be
used. However, in various exemplary embodiments, a wet treatment
with a solution of the moisture-resistant material like that for
the case of coating the powder with the aluminum-containing
phosphate or phosphoric acid compound is preferred, since the
powder may be uniformly applied to the entirety of the powder in
such wet treatment. In particular, is, in various exemplary
embodiments, a method of spraying the material on the powder, is
preferred since the coating material may be more uniformly applied
to the powder in the method and since controlling the spraying
condition controls the film condition. Any other similar method for
adding the moisture-resistant material to the metal powder can be
used.
[0118] In various exemplary embodiments, during or after coating
with the moisture-resistant material, the metal powder may be
heated for removing the solvent and for thermally curing and
stabilizing the moisture-resistant material. The heating condition
may be suitably determined depending on the material used.
[0119] In various exemplary embodiments, the surface-coated metal
powder may be molded under pressure in a mold.
[0120] In various exemplary embodiments, the molding pressure may
be suitably determined depending on the use of the molded articles.
In various exemplary embodiments, increasing the molding pressure
is preferred since it may increase the green density of the molded
articles, therefore bettering the magnetic properties such as
magnetic flux density thereof and further increasing the mechanical
strength of the molded articles. In various exemplary embodiments,
the molding pressure is at least about 490 MPa, and, in various
exemplary embodiments, at least about 980 MPa.
[0121] In various exemplary embodiments, a lubricant may be applied
or added to the entire surface of the mold in which the coated
metal powder is molded. The lubricant is effective for reducing the
friction between the mold and the powder molded therein under
pressure, and is therefore effective for preventing the reduction
in the density of the molded articles. In addition, the lubricant
further reduces the friction of the molded articles when they are
taken out of the mold, and is therefore effective in preventing the
molded articles from being cracked or damaged while they are taken
out of the mold.
[0122] In various exemplary embodiments, the lubricant includes,
for examples, metal soap such as lithium stearate, zinc stearate or
calcium stearate, and wax such as fatty acid amides.
[0123] In various exemplary embodiments, the powder magnetic core
that is formed of the metal powder obtained according to the
invention may be subjected to heat treatment, after its formation
through pressure molding, for strain removal from it to thereby
reduce the hysteresis loss thereof. The heat treatment condition
including the heating temperature, the heating time and the heating
atmosphere may be suitably determined in accordance with the use of
the product. In various exemplary embodiments, the heating
temperature may be set between about 300 and 700.degree. C., and
the heating time may be set between about 5 and 120 minutes. In
various exemplary embodiments, the heating atmosphere may be air in
which the powder may be processed in a simple heating device, or an
inert atmosphere such as Ar or N.sub.2, or a reducing atmosphere
such as H.sub.2, or in vacuum. The dew point of the atmosphere may
be suitably determined in accordance with the use of the product.
During the heat treatment, or during the step of heating or cooling
it, the product may be kept at a constant temperature for a
predetermined period of time.
[0124] The compressed shaped articles thus formed in the manner as
described above have a high magnetic flux density and good
insulation performance, and are free from the corrosion that is
generally problematic in treatment with acid.
[0125] In various exemplary embodiments, when the temperature of
the starting powder and the coated powder of the invention is kept
under 110.degree. C. during the process of producing the coated
powder by coating the starting powder with a coating material, then
the insulation performance of the powder magnetic core formed of
the coated powder is better. It is known that, when the
aluminum-containing phosphate compound is heated, it undergoes
various physical changes and, in particular, when it is heated from
room temperature up to 110.degree. C., it undergoes phase
transformation into a readily-hydrolyzable unstable condition (*1).
The temperature control in coating the starting powder under
110.degree. C. in the present invention could prevent the phase
transformation and could therefore have some positive influence on
improving the insulation performance of the coated powder.
[0126] (*1) Mitsutomo Tsuwako, Inorganic Polymer, CMC (1985), pp.
265-266.
Examples of the invention are described below.
EXAMPLE 1
[0127] Iron powder KIP-304AS (by JFE Steel) was used for the
starting powder. For the coating material, used was a mixture of
phosphoric acid compound and metal compound that had been
conditioned to have a ratio P/M (by mole) as in Table 1 below. For
the ratio P/M, the data were rounded off at the tenth place
thereof.
[0128] The powder was coated in wet treatment. The solution for the
wet treatment had a solid concentration of 5% by mass in distilled
water.
[0129] For controlling the ratio P/M, the dissolution ratio or the
blend ratio of the phosphoric acid compound and the metal compound
was controlled, or the phosphate was dissolved in the solution so
as to have a predetermined ratio P/M. The ratio P/M was so
controlled that the molar ratio, .alpha., of the aluminum atom to
all the metal components could be 0<.alpha..ltoreq.1. To samples
26 to 30 of the invention, added was the pH-controlling agent as in
Table 1 for their pH control.
[0130] A rotary fluidized-bed coating apparatus was used for mixing
the coating material and the starting powder. While the starting
powder was fluidized in the apparatus, the coating material was
sprayed on the fluidized powder in such a controlled manner that
the solid content of the coating material could be as in Table 1.
After being sprayed, the powder was kept fluidized for 20 minutes
and dried. Through the treatment, the metal powder was coated with
the coating material on the surface of the starting power. The tank
temperature, the starting material temperature and the coated
powder temperature were all 80.degree. C. Up to 0.2% by mass of a
lubricant, zinc stearate was added to the powder, which was then
pressed in a mold into a ring sample (outer diameter, 38 mm; inner
diameter, 25 mm; height 6.2 mm). The molding pressure was between
980 and 1980 MPa. When no lubricant was added to the powder, a
lubricant dispersion solution prepared by dispersing zinc stearate
in water was applied to the inner wall of the mold for mold
lubrication. Some of the thus-molded ring samples were heated in
air at 400.degree. C. for 60 minutes. The amount of the lubricant
added to the powder, the molding pressure, and the presence or
absence of heat treatment of the ring samples is shown in Table
2.
[0131] The green density, the specific resistivity and the magnetic
flux density of the thus-molded ring samples were measured, and the
data are given in Table 2.
[0132] The size and the weight of each sample were measured, and
the green density thereof was computed from the data. The specific
resistivity was measured according to a four-terminal method in
which the current was 1 A. The magnetic flux density was measured
as follows: A formal enamelled wire of 0.6 mm in diameter was wound
around the ring sample, with 100 turns on the primary side and 20
turns on the secondary side. The resulting coil was tested for the
magnetic flux density B10 k thereof in a magnetic field H=10
kA/m.
[0133] To check the samples as to whether or not their resistivity
and magnetic properties may worsen in time, the samples were stored
at a temperature of 25.degree. C. and a humidity of 40% for 10
days, and their specific resistivity and magnetic flux density were
measured in the same manner as above.
[0134] The solid content is hereinafter defined as follows: The
solvent is evaporated away from the coating material, which is
sprayed to the metal powder, and the amount of the remaining solute
is measured.
1 TABLE 1 Phosphoric Acid Metal Compound 2 (or Compound Metal
Compound 1 pH-controlling agent) Solid No. designation designation
ratio* name ratio* P/M .alpha. pH Content Remarks 1 85% aluminum
100 -- -- 2 1 1.2 0.20 sample 1 of orthophosphoric hydroxide the
invention acid 2 85% aluminum 100 -- -- 10 1 2.0 0.50 sample 2 of
orthophosphoric hydroxide the invention acid 3 85% aluminum 100 --
-- 4 1 1.2 1.00 sample 3 of orthophosphoric hydroxide the invention
acid 4 85% aluminum 100 -- -- 2 1 1.0 0.10 sample 4 of
orthophosphoric chloride the invention acid 5 85% aluminum 100 --
-- 2 1 1.0 0.20 sample 5 of orthophosphoric chloride the invention
acid 6 85% aluminum 100 -- -- 2 1 1.0 0.20 sample 6 of
orthophosphoric chloride the invention acid 7 85% aluminum 100 --
-- 4 1 1.0 0.50 sample 7 of orthophosphoric chloride the invention
acid 8 85% aluminum 100 -- -- 6 1 1.0 1.00 sample 8 of
orthophosphoric chloride the invention acid 9 85% aluminum 100 --
-- 2 1 1.0 0.10 sample 9 of orthophosphoric acetate the invention
acid 10 85% aluminum 100 -- -- 2 1 1.2 0.20 sample 10 of
orthophosphoric acetate the invention acid 11 85% aluminum 100 --
-- 3 1 1.2 1.00 sample 11 of orthophosphoric acetate the invention
acid 12 85% aluminum 100 -- -- 3 1 1.2 3.00 sample 12 of
orthophosphoric acetate the invention acid 13 85% aluminum 100 --
-- 7 1 1.2 5.00 sample 13 of orthophosphoric acetate the invention
acid 14 -- aluminum 100 -- -- 1 1 1.2 0.05 sample 14 of phosphate
the invention 15 -- aluminum 100 -- -- 2 1 1.2 0.10 sample 15 of
phosphate the invention 16 -- aluminum 100 -- -- 3 1 1.2 0.05
sample 16 of phosphate the invention 17 -- aluminum 100 -- -- 3 1
1.2 0.10 sample 17 of phosphate the invention 18 -- aluminum 100 --
-- 3 1 1.2 0.20 sample 18 of phosphate the invention 19 -- aluminum
100 -- -- 3 1 1.2 0.50 sample 19 of phosphate the invention 20 --
aluminum 100 -- -- 4 1 1.2 1.00 sample 20 of phosphate the
invention 21 pyrophosphoric aluminum 100 -- -- 2 1 1.5 1.00 sample
21 of acid acetate the invention 22 85% aluminum 50 manganese 50 2
0.5 3.0 0.50 sample 22 of orthophosphoric hydroxide phosphate the
invention acid 23 -- aluminum 80 zinc nitrate 20 4 0.2 1.5 0.75
sample 23 of phosphate the invention 24 designation aluminum 100 --
-- 3 1 1.2 0.20 sample 24 of phosphate the invention 25 -- aluminum
100 -- -- 3 1 1.2 0.20 sample 25 of phosphate the invention 26 --
aluminum 90 monosodium 10 3 0.9 3.0 0.10 sample 26 of phosphate
fumarate the invention 27 -- aluminum 90 sodium acid 10 3 0.9 4.0
0.10 sample 27 of phosphate pyrophosphate the invention 28 --
aluminum 90 monopotassium 10 3 0.9 4.0 0.10 sample 28 of phosphate
phosphate the invention 29 -- aluminum 90 boric acid 10 3 1 4.0
0.10 sample 29 of phosphate the invention 30 -- aluminum 80 boric
acid 20 3 1 6.0 0.10 sample 30 of phosphate the invention 31 -- --
-- comparative sample 1 32 -- -- -- comparative sample 2 33 epoxy
resin -- 0.20 comparative sample 3 34 epoxy resin -- 0.50
comparative sample 4 35 epoxy resin -- 1.00 comparative sample 5 36
0.1 N sulfuric acid 0.1 0.20 comparative sample 6 37 85%
orthophosphoric acid 0.8 0.20 comparative sample 7 38 85%
orthophosphoric acid 163 g, MgO 31 g, boric acid 30 g 3.0 0.20
comparative sample 8 39 85% orthophosphoric acid 163 g, MgO 31 g,
boric acid 30 g 3.0 0.50 comparative sample 9 40 polyamide resin --
1.00 comparative sample 10 *Ratio: This is the ratio of the metal
element atom of the indicated component to the number of atoms M of
all the metal components.
[0135]
2 TABLE 2 immediately after preparation after 10 days Magnetic
Magnetic Molding Green Specific Flux Specific Flux Amount Lubricant
Pressure Heat Density resistivity Density resistivity Density No.
Added (mas. %) (MPa) Treatment (Mg/m.sup.3) (.mu..OMEGA.m) B10k (T)
(.mu..OMEGA.m) B10k (T) Remarks 1 0.20 0.20 980 yes 7.54 95 1.50
100 1.50 sample 1 of the invention 2 0.50 0.20 980 yes 7.50 240
1.51 212 1.47 sample 2 of the invention 3 1.00 mold 980 no 7.35
4550 1.41 4479 1.41 sample 3 of lubrication the invention 4 0.10
mold 980 no 7.62 132 1.52 130 1.54 sample 4 of lubrication the
invention 5 0.20 mold 980 no 7.59 242 1.50 244 1.51 sample 5 of
lubrication the invention 6 0.20 mold 980 no 7.58 253 1.50 261 1.50
sample 6 of lubrication the invention 7 0.50 mold 1470 no 7.67 343
1.57 341 1.59 sample 7 of lubrication the invention 8 1.00 mold
1470 no 7.56 323 1.49 301 1.46 sample 8 of lubrication the
invention 9 0.10 mold 1470 yes 7.73 98 1.69 101 1.70 sample 9 of
lubrication the invention 10 0.20 mold 980 yes 7.64 103 1.57 105
1.58 sample 10 of lubrication the invention 11 1.00 mold 980 yes
7.45 1304 1.48 1381 1.48 sample 11 of lubrication the invention 12
3.00 mold 980 yes 7.23 8750 1.32 8749 1.34 sample 12 of lubrication
the invention 13 5.00 mold 980 yes 7.01 12353 1.30 10579 1.27
sample 13 of lubrication the invention 14 0.05 0.20 980 no 7.64 85
1.63 89 1.64 sample 14 of the invention 15 0.10 0.20 980 no 7.62
120 1.60 119 1.61 sample 15 of the invention 16 0.05 mold 980 no
7.62 108 1.62 110 1.66 sample 16 of lubrication the invention 17
0.10 mold 980 no 7.61 160 1.65 161 1.65 sample 17 of lubrication
the invention 18 0.20 mold 980 yes 7.62 200 1.63 203 1.64 sample 18
of lubrication the invention 19 0.50 mold 1470 yes 7.65 398 1.58
401 1.59 sample 19 of lubrication the invention 20 1.00 mold 1470
yes 7.54 1574 1.54 1575 1.53 sample 20 of lubrication the invention
21 1.00 mold 1470 no 7.55 1245 1.55 1246 1.55 sample 21 of
lubrication the invention 22 0.50 mold 1980 no 7.75 308 1.73 310
1.73 sample 22 of lubrication the invention 23 0.75 mold 980 yes
7.56 340 1.51 342 1.51 sample 23 of lubrication the invention 24
0.20 mold 1980 yes 7.74 120 1.74 122 1.73 sample 24 of lubrication
the invention 25 0.20 mold 980 no 7.60 320 1.60 321 1.61 sample 25
of lubrication the invention 26 0.20 mold 980 no 7.60 520 1.60 520
1.61 sample 26 of lubrication the invention 27 0.20 mold
lubrication 980 no 7.61 542 1.59 542 1.60 sample 27 of the
invention 28 0.20 mold lubrication 980 no 7.60 453 1.59 454 1.60
sample 28 of the invention 29 0.20 mold lubrication 980 no 7.62 592
1.61 593 1.61 sample 29 of the invention 30 0.20 mold lubrication
980 no 7.62 493 1.61 495 1.62 sample 30 of the invention 31 0.00
mold lubrication 980 no 7.66 8.5 1.67 8.0 1.68 comparative sample 1
32 0.00 mold lubrication 1470 no 7.71 4.2 1.72 4.2 1.71 comparative
sample 2 33 0.20 mold lubrication 980 no 7.57 2310 1.54 2308 1.54
comparative sample 3 34 0.50 mold lubrication 980 no 7.45 8710 1.48
8709 1.48 comparative sample 4 35 1.00 mold lubrication 980 no 7.32
23600 1.35 23590 1.36 comparative sample 5 36 0.20 mold lubrication
980 no 7.58 67 1.55 31 1.32 comparative sample 6 37 0.20 mold
lubrication 980 no 7.57 45 1.56 17 1.24 comparative sample 7 38
0.20 mold lubrication 980 yes 7.62 24 1.59 16 1.60 comparative
sample 8 39 0.50 mold lubrication 1470 yes 7.60 35 1.56 19 1.57
comparative sample 9 40 2.00 mold lubrication 1470 * 6.80 14210
1.01 14200 1.00 comparative sample 10 *Heat treatment at
200.degree. C. for 2 hours.
[0136] As is obvious from Table 2, the samples of the invention all
have high green density, high specific resistivity and high
magnetic flux density, and their resistivity and magnetic
properties did not lower at all in time. When sample 25 of the
invention is compared with samples 26 to 30 of the invention, it is
understood that the pH control with the pH-controlling agent is
effective for improving the properties of the powder magnetic core,
especially for increasing the specific resistance thereof.
[0137] Pressing only the starting powder formed comparative samples
1 and 2. Not coated with the coating material, the specific
resistivity of these comparative samples was extremely low.
[0138] For comparative samples 3 to 5, the starting powder was
coated with water-dispersible epoxy resin (resin concentration, 5
mass %) but not with the coating material of the invention. These
comparative samples were fabricated and evaluated in the same
manner as that for the samples of the invention. The magnetic flux
density of the epoxy resin-coated samples was much lower than that
of the samples of the invention that had been fabricated by coating
the starting powder with the same amount of the coating material
followed by pressing the coated powder under the same pressure.
[0139] For comparative sample 6, the starting powder was mixed with
a predetermined amount of 0.1 N sulfuric acid; and for comparative
sample 7, it was mixed with a predetermined amount 85%
orthophosphoric acid. The resulting metal powder was dried and
evaluated in the same manner as that for the samples of the
invention. It is understood that the insulation performance and the
magnetic properties of these comparative samples worsened in
time.
[0140] For comparative samples 8 and 9, the starting powder was
processed with an aqueous solution that had been prepared by
dissolving 163 g of 85% orthophosphoric acid, 31 g of MgO and 30 g
of boric acid in one liter of distilled water followed by further
adding distilled water thereto to make it have a solid
concentration of 5% by mass, in the same manner as that for the
samples of the invention, and the resulting samples were evaluated
also in the same manner as the samples of the invention. It is
understood that the specific resistivity of these comparative
samples is much lower than that of samples 18 and 19 of the
invention for which the starting powder was coated with the same
amount of the coating material of the invention and was pressed
under the same molding pressure.
[0141] For comparative sample 10, the starting powder was coated
with water-dispersible amide resin (solid concentration, 5 mass %).
The coated powder was pressed and then heated at 200.degree. C. for
2 hours, and the thus-pressed sample was evaluated. It is
understood that the specific resistivity of the sample is high but
the magnetic flux density thereof is extremely low.
EXAMPLE 2
[0142] Ring samples (outer diameter, 38 mm; inner diameter, 25 mm;
height, 6.2 mm) were fabricated in the same manner as in Example 1,
for which, however, the ratio P/M and the value .alpha. of the
coating material were changed as in Table 3 below.
[0143] The green density, the specific resistivity and the magnetic
flux density of these samples were measured, and the data are given
in Table 4.
3 TABLE 3 Coating Molding Coating Material Condition Condition
Phosphoric Solid Molding Acid Metal Compound I Metal Compound II
Content Pressure No. Compound designation ratio* designation ratio*
P/M .alpha. pH (mas. %) (MPa) Remarks 41 orthophosphoric aluminum 0
1 1 1.3 1.0 980 sample 31 of the acid phosphate invention 42
orthophosphoric aluminum 100 -- 0 2 1 1.2 1.0 980 sample 32 of the
acid phosphate invention 43 orthophosphoric aluminum 100 -- 0 3 1
1.2 1.0 980 sample 33 of the acid phosphate invention 44
orthophosphoric aluminum 100 -- 0 4 1 1.0 1.0 980 sample 34 of the
acid phosphate invention 45 orthophosphoric aluminum 100 -- 0 10 1
1.0 1.0 980 sample 35 of the acid phosphate invention 46
orthophosphoric aluminum 30 zinc 70 3 0.3 1.2 0.5 1470 sample 36 of
the acid (85%) hydroxide phosphate invention 47 orthophosphoric
aluminum 50 zinc 50 3 0.5 1.2 0.5 1470 sample 37 of the acid (85%)
hydroxide phosphate invention 48 orthophosphoric aluminum 80
manganese 20 3 0.8 1.2 0.5 1470 sample 38 of the acid (85%)
hydroxide phosphate invention 49 orthophosphoric aluminum 90
manganese 10 3 0.9 1.2 0.5 1470 sample 39 of the acid (85%)
hydroxide phosphate invention 50 orthophosphoric aluminum 100 -- 0
3 1 1.2 0.5 1470 sample 40 of the acid (85%) hydroxide invention
*Ratio: This is the ratio of the metal element atom of the
indicated component to the number of atoms M of all the metal
components.
[0144]
4 TABLE 4 after 10 days Condition in Sample Preparation immediately
after preparation Magnetic solid Molding Green Specific Magnetic
Specific Flux content Pressure Heat Density resistivity Flux
Density resistivity Density No. .alpha. P/M (mas. %) (MPa)
Treatment (Mg/m.sup.3) (.mu..OMEGA.m) B10k (T) (.mu..OMEGA.m) B10k
(T) Remarks 41 1 1 1 980 yes 7.45 120 1.49 120 1.49 sample 31 of
the invention 42 1 2 1 980 yes 7.46 898 1.48 899 1.49 sample 32 of
the invention 43 1 3 1 980 yes 7.44 1251 1.47 1249 1.48 sample 33
of the invention 44 1 4 1 980 yes 7.45 450 1.47 451 1.44 sample 34
of the invention 45 1 10 1 980 yes 7.45 232 1.48 210 1.43 sample 35
of the invention 46 0.3 3 0.5 1470 yes 7.59 120 1.56 121 1.45
sample 36 of the invention 47 0.5 3 0.5 1470 yes 7.62 232 1.54 235
1.49 sample 37 of the invention 48 0.8 3 0.5 1470 yes 7.64 380 1.59
382 1.59 sample 38 of the invention 49 0.9 3 0.5 1470 yes 7.64 376
1.59 394 1.60 sample 39 of the invention 50 1 3 0.5 1470 yes 7.65
385 1.59 384 1.60 sample 40 of the invention
[0145] Table 4 confirms the following. Comparing samples 31 to 35
of the invention with each other, it is understood that, when the
ratio P/M falls between 2 and 3, then the insulation performance of
the samples is good and, in addition, the properties of the samples
stored for 10 days fluctuate little and are stable. Comparing
samples 36 to 40 of the invention with each other, it is understood
that, when the molar fraction, .alpha., of aluminum is closer to 1,
then the insulation performance of the samples is better and, in
addition, the properties of the samples stored for 10 days
fluctuate little and are stable.
EXAMPLE 3
[0146] Iron powder KIP-304AS (by JFE Steel) was used for the
starting powder. For the coating material, the phosphoric acid
compound that had been conditioned to have a ratio P/M and a value
a as in Table 5 below was used. For the ratio P/M, the data were
rounded off.
[0147] The powder was coated in wet treatment. The solution for the
wet treatment had a solid concentration of 5% by mass in distilled
water.
[0148] The ratio P/M was controlled in the same manner as in
Example 1.
[0149] For coating the starting iron powder with the coating
material, the powder was stirred in a Henschel mixer and a solution
of the coating material was sprayed on the powder being stirred in
the mixer. The amount of the coating material sprayed on the powder
was as in Table 5, in terms of the solid content of the coating
material. During the coating treatment, the temperature of the
starting powder and the coated powder was 80.degree. C. The coated
powder was dried in air at room temperature for 24 hours.
[0150] Next, the powder was processed in different methods as shown
in Table 5 for making it resistant to moisture absorption.
Concretely, the treatment for moisture absorption resistance was
effected after the coating treatment with the phosphate. This is as
follows. An aqueous solution of the moisture-resistant material
having a solid concentration of 5% by mass was sprayed on the
powder in a Henschel mixer in the same manner as that for spraying
the phosphate on it. Thus sprayed, the powder was dried in air at
room temperature for 24 hours. On the other hand, the powder was
coated with a single substance of oxide sol having a mean particle
size of 50 nm. Apart from these, the treatment with the phosphate
and the treatment with the moisture-resistant material were similar
and explained below. The moisture-resistant material was added to
the phosphate solution and was processed to have a solid
concentration of 5% by mass. The resulting solution was then
applied to the starting powder.
[0151] Thus prepared, the powder was exposed to a temperature of
20.degree. C. and a relative humidity of 30% for 1 day and for 60
days.
[0152] Each sample was molded into ring samples in the same manner
as in Example 1, and the green density, the specific resistivity
and the magnetic flux density of each ring sample was measured. The
resulting data is shown in Table 6.
[0153] Mold lubrication was used during molding of the samples.
Some of the molded samples were subjected to heat treatment as
shown in Table 6, for which the heat treatment condition was the
same as in the condition of Example 1.
[0154] HLB in Table 5 is an abbreviation of "hydrophile lipophile
balance", and indicates the degree of hydrophilicity (that is, the
solubility in water) of the nonionic surfactant.
5 TABLE 5 Phosphoric Acid Solid Treatment for Moisture Absorption
Resistance Compound P/ Content mode of amount added No. Designation
M .alpha. (mas. %) treatment condition for treatment (mas. %)
Remarks 1 aluminum 3 1 0.20 not treated -- -- sample 41 of
phosphate the invention 2 aluminum 3 1 1.00 not treated -- --
sample 42 of phosphate the invention 3 aluminum 3 1 0.20 powder
Heated in air at 150.degree. C. for 30 min. -- sample 43 of
phosphate heating the invention 4 aluminum 3 1 1.00 powder Heated
in air at 250.degree. C. for 30 min. -- sample 44 of phosphate
heating the invention 5 aluminum 3 1 0.20 coating with Coated with
aluminum phosphate 0.1 sample 45 of phosphate oxide and then
further with colloidal the invention silica. 6 aluminum 3 1 1.00
mixing with Aluminum phosphate was mixed 0.5 sample 46 of phosphate
oxide with zirconia sol, and the resulting the invention mixture
was used for simultaneous coating treatment and moisture resistance
treatment. 7 aluminum 3 1 0.20 coating with Coated with aluminum
phosphate 0.1 sample 447 of phosphate oxide and then further with
ethyl silicate. the invention 8 aluminum 3 1 1.00 coating with
Coated with aluminum phosphate 0.5 sample 48 of phosphate resin and
then further with silicone resin. the invention 9 aluminum 3 1 0.20
mixing with Aluminum phosphate was mixed with 0.05 sample 49 of
phosphate surfactant nonionic surfactant (polyoxyethylene alkyl the
invention ether with HLB of 13.6), and the resulting mixture was
used for simultaneous coating treatment and moisture resistance
treatment. 10 aluminum 3 1 0.20 coating with Coated with aluminum
phosphate 0.05 sample 50 of phosphate surfactant and then further
with ionic the invention surfactant (polyoxyethylene alkylamine).
11 aluminum 3 1 0.20 mixing with Coated with aluminum phosphate
0.02 sample 51 of phosphate silane and then further with
alkylsilane the invention (trimethylmethoxysilane). 12 aluminum 3 1
0.20 coating with Coated with aluminum phosphate 0.02 sample 52 of
phosphate silane and then further with aminosilane the invention
(aminopropyltriethoxysilane). 13 aluminum 3 1 1.00 coating with
Coated with aluminum phosphate 0.05 sample 53 of phosphate silane
and then further with alkoxysilane the invention
(trimethylmethoxysilane). 14 aluminum 3 1 0.20 coating with Coated
with aluminum phosphate 0.02 sample 54 of phosphate silane and then
further with aminosilane the invention
(aminopropyltriethoxysilane). 15 aluminum 3 0.9 0.50 coating with
Coated with aluminum phosphate 0.02 sample 55 of phosphate silane
and then further with aminosilane the invention zinc phosphate
(aminopropyltriethoxysilane). orthophosphoric acid
[0155]
6 TABLE 6 Specific Resistivity Magnetic Flux Density Molding
(.mu..OMEGA.m) Green Density (Mg/m.sup.3) B10k (T) Amount Added
Pressure Heat after 1-day after 60-day after 1-day after 60-day
after 1-day after 60-day No. P/M (mas. %) (MPa) Treatment exposure
exposure exposure exposure exposure exposure Remarks 1 3 0.20 1470
no 451 915 7.62 7.62 1.65 1.66 sample 41 of the invention 2 3 1.00
1470 no 3250 6580 7.54 7.54 1.53 1.54 sample 42 of the invention 3
3 0.20 1470 no 320 500 7.63 7.62 1.64 1.66 sample 43 of the
invention 4 3 1.00 1470 no 1754 2201 7.55 7.54 1.54 1.53 sample 44
of the invention 5 3 0.20 1470 no 870 865 7.50 7.49 1.50 1.51
sample 45 of the invention 6 3 1.00 1470 no 3545 3812 7.43 7.44
1.46 1.49 sample 46 of the invention 7 3 0.20 1470 no 890 882 7.53
7.54 1.53 1.53 sample 447 of the invention 8 3 1.00 1470 no 3545
3987 7.43 7.44 1.48 1.49 sample 48 of the invention 9 3 0.20 1470
no 556 670 7.60 7.61 1.65 1.64 sample 49 of the invention 10 3 0.20
1470 no 601 615 7.61 7.62 1.65 1.65 sample 50 of the invention 11 3
0.20 1470 no 870 910 7.62 7.62 1.66 1.65 sample 51 of the invention
12 3 0.20 1470 no 901 900 7.62 7.63 1.65 1.66 sample 52 of the
invention 13 3 1.00 1470 no 3650 3648 7.54 7.55 1.53 1.53 sample 53
of the invention 14 3 0.20 1470 yes 405 410 7.62 7.62 1.65 1.65
sample 54 of the invention 15 3 0.50 1980 yes 450 455 7.60 7.61
1.64 1.64 sample 55 of the invention
[0156] From Table 6 above, it is understood that samples 43 to 53
of the invention that had been treated for moisture absorption
resistance fluctuated little in point of the specific resistivity
thereof and were stable even after subjected to 60-day exposure.
Comparing samples 43 and 44 of the invention with samples 45 to 53
of the invention, it is understood that the moisture resistance
treatment effected by coating the powder with the
moisture-resistance material is more effective than that effected
by heating the powder in that the specific resistance of the
samples treated by the former mode is more stable than that of the
samples treated by the latter mode.
[0157] Samples 49 to 53 of the invention that had been treated with
surfactant or silane are better than samples 45 to 48 of the
invention that had been treated with oxide or resin in that the
green density and the magnetic flux density of the former are
higher than those of the latter. This confirms that surfactant and
silane are more suitable to the moisture-resistant material for use
in the invention. When sample 49 of the invention that was coated
with surfactant and phosphate compound at the same time is compared
with sample 50 of the invention that was separately coated with
them, it is understood that the specific resistivity of the latter
is more stable than that of the former. This confirms that
separately coating the powder is more effective for moisture
absorption resistance.
[0158] Samples 52 and 53 of the invention processed with
aminosilane are better than the other samples in that their
specific resistance is much more stable than that of the others.
This confirms that aminosilane is extremely effective for the
treatment for moisture absorption resistance.
[0159] Sample 54 of the invention was fabricated in the same manner
as that for sample 52 of the invention, and this was further
subjected to heat treatment. Thus processed, sample 54 also enjoyed
the same effect as that of the others.
[0160] Except samples 41 and 42 of the invention not processed for
moisture absorption resistance, all the samples of the invention
had good powder flowability even after 60-day exposure.
EXAMPLE 4
[0161] Sendust powder having a mean particle size of 80 .mu.m,
iron-based cobalt alloy amorphous powder, 4% Mo-79% Ni permalloy
powder, and Fe-3% Si alloyed powder was prepared. In the same
manner as in Example 1, these were coated with the coating material
as in Table 7, in which the ratio P/M and the value .alpha. are
given, and the coated powder were molded into ring samples (outer
diameter, 38 mm; inner diameter, 25 mm; height, 6.2 mm).
[0162] The green density, the specific resistivity and the magnetic
flux density of the thus-obtained ring samples were measured, and
the data are given in Table 8.
[0163] This confirms the effectiveness of the invention not only
for iron powder but also for other metal and alloyed powders.
7 TABLE 7 Coating Molding Condition Condition Coating Material
Solid Molding Phosphoric Acid Metal Compound I Metal Compound II
Content Pressure No. Compound designation ratio* designation ratio*
P/M .alpha. pH (mas. %) (MPa) Remarks 51 orthophosphoric aluminum
100 -- 0 3 1 1.2 1.0 980 sample 31 of the acid phosphate invention,
sendust powder used 52 orthophosphoric aluminum 100 -- 0 3 1 1.2
1.0 980 sample 32 of the acid phosphate invention, amorphous powder
used 53 orthophosphoric aluminum 100 -- 0 3 1 1.2 1.0 980 sample 33
of the acid phosphate invention, permalloyed powder used 54
orthophosphoric aluminum 100 -- 0 3 1 1.2 1.0 980 sample 34 of the
acid phosphate invention, Fe- 3% Si powder used *Ratio: This is the
ratio of the metal element atom of the indicated component to the
number of atoms M of all the metal components.
[0164]
8 TABLE 8 immediately after preparation Condition in Sample
Preparation Magnetic after 10 days solid Molding Green Specific
Flux Specific Magnetic content Pressure Heat Density resistivity
Density resistivity Flux Density No. .alpha. P/M (mas. %) (MPa)
Treatment (Mg/m.sup.3) (.mu..OMEGA.m) B10k (T) (.mu..OMEGA.m) B10k
(T) Remarks 51 1 2 1 980 yes 5.70 25467 0.89 26450 0.89 sample 41
of the invention 52 1 2 1 980 yes 7.20 12476 1.30 12456 1.31 sample
42 of the invention 53 1 2 1 980 yes 7.44 69825 0.58 70487 0.59
sample 43 of the invention 54 1 2 1 980 yes 7.21 5467 1.35 5456
1.35 sample 44 of the invention
EXAMPLE 5
[0165] Iron powder KIP-304AS (by JFE Steel) was used for the
starting powder. For the coating material, the phosphoric acid
compound and the metal compound that had been conditioned to have a
ratio P/M as in Table 9 below, were used. For the ratio P/M, the
data was rounded off. The molar ratio, .alpha., of aluminum to M is
also shown in Table 9.
[0166] Using a Henschel mixer and a spray, the starting powder was
coated with the phosphoric acid compound in the same manner as in
Example 3. The temperature of the starting powder and the coated
powder is shown in Table 9. The coated powder was dried in air at
room temperature for 24 hours.
[0167] Next, some samples were treated for moisture absorption
resistance according to the method shown in Table 9. Concretely,
the treatment for moisture absorption resistance was effected after
the coating treatment with the phosphate compound. This is as
follows. An aqueous solution of the moisture-resistant material
having a solid concentration of 5% by mass was sprayed on the
powder in a Henschel mixer in the same manner as that for spraying
the phosphate compound on it. Thus sprayed, the powder was dried in
air at room temperature for 24 hours. Apart from it, the treatment
with the phosphate compound and the treatment with the
moisture-resistant material were effected at the same. This is as
follows. The moisture-resistant material was added to the phosphate
solution and this was processed to have a solid concentration of 5%
by mass. The resulting solution was applied to the starting
powder.
[0168] Thus prepared, the powder was exposed to a temperature of
20.degree. C. and a relative humidity of 30% for 1 day and for 60
days. Each sample was molded in a mold into ring samples (outer
diameter, 38 mm; inner diameter, 25 mm; height, 6.2 mm). The
molding pressure fell between 686 and 1980 MPa. Applying a
lubricant dispersion, which had been prepared by dispersing zinc
stearate in water, to the inner wall thereof, lubricated the mold.
The molded samples were heated in air at 400.degree. C. for 60
minutes. The molding pressure is shown in Table 9.
[0169] The green density, the specific resistivity and the magnetic
flux density of the thus-molded ring samples were measured, and the
data are given in Table 10. The size and the weight of each sample
were measured, and the green density thereof was computed from the
data. The specific resistivity was measured according to a
four-terminal method in which the current was 1 A. The magnetic
flux density was measured as follows. A formal wire of 0.6 mm in
diameter was wound around the ring sample, with 100 turns on the
primary side and 20 turns on the secondary side. The resulting coil
was tested for the magnetic flux density B10 k thereof in a
magnetic field H=10 kA/m.
[0170] Comparing samples 45 to 64 of the invention with samples 65
to 67 of the invention, it is obvious that the insulation
performance of the molded samples is extremely good when the
coating temperature is lower than 110.degree. C. Comparing samples
47 to 49 of the invention with each other, it is understood that
the insulation performance of the samples is good when the coating
temperature is not higher than 100.degree. C., and the insulation
performance thereof is better when the coating temperature is not
higher than 90.degree. C. From samples 63 and 64 of the invention,
it is understood that, when the coating temperature of lower than
110.degree. C. is combined with the treatment for moisture
absorption resistance, then the samples are more stable with no
fluctuation of their properties even after being stored for 60
days. Comparing samples 51 to 53 with each other, it is understood
that, when the ratio P/M is set between 2 and 3, then the specific
resistivity and the magnetic flux density of the samples are more
stable with little fluctuation thereof even after 60-day exposure.
Comparing samples 59 to 62 with each other, it is understood that,
when the molar fraction, .alpha., of aluminum is nearer to 1, then
the properties of the samples are more stable with littler
fluctuation thereof even after 60-day exposure. 0.5% by mass of
zinc stearate powder was added to the powder for sample 48 of the
invention, and the resulting mixture was pressed to prepare a
sample, and this was evaluated. In molding the mixture therein, the
mold was not lubricated. The sample of this case was also good,
like sample 48 of the invention.
9 TABLE 9 Treatment for Coating Material Coating Condition Moisture
Absorption Resistance Molding metal coating condition Condition
metal com- solid temper- for amount molding phosphoric acid
compound pound P/ content ature mode of treat- added pressure No.
compound I II .alpha. M pH (mas. %) (.degree. C.) treatment ment
(mas. %) (MPa) Remarks 55 orthophosphoric aluminum -- 1 3 1.2 0.01
60 not treated -- -- 980 sample 45 acid (85%) acetate of the
invention 56 orthophosphoric aluminum -- 1 3 1.2 0.05 90 not
treated -- -- 1980 sample 46 acid (85%) acetate of the invention 57
-- aluminum -- 1 3 1.2 0.2 105 not treated -- -- 980 sample 47
phosphate of the invention 58 -- aluminum -- 1 3 1.2 0.2 95 not
treated -- -- 980 sample 48 phosphate of the invention 59 --
aluminum -- 1 3 1.2 0.2 90 not treated -- -- 980 sample 49
phosphate of the invention 60 -- aluminum -- 1 3 1.2 0.5 105 not
treated -- -- 1470 sample 50 phosphate of the invention 61 --
aluminum -- 1 1 1.2 1.0 100 not treated -- -- 1980 sample 51
phosphate of the invention 62 orthophosphoric aluminum -- 1 3 1.2
1.0 100 not treated -- -- 1980 sample 52 acid (85%) phosphate of
the invention 63 orthophosphoric aluminum -- 1 5 1.2 1.0 100 not
treated -- -- 1980 sample 53 acid (85%) phosphate of the invention
64 orthophosphoric aluminum -- 1 3 1.2 2.0 90 not treated -- --
1176 sample 54 acid (85%) phosphate of the invention 65
orthophosphoric aluminum -- 1 3 1.2 0.5 80 not treated -- -- 1470
sample 55 acid (85%) hydroxide of the invention 66 orthophosphoric
aluminum -- 1 4 1.2 0.5 100 not treated -- -- 1470 sample 56 acid
(85%) hydroxide of the invention 67 orthophosphoric aluminum -- 1 1
1.2 2.0 60 not treated -- -- 1176 sample 57 acid (85%) acetate of
the invention 68 orthophosphoric aluminum boric 1 6 1.0 5.0 90 not
treated -- -- 686 sample 58 acid (85%) hydroxide acid of the
invention 69 orthophosphoric aluminum manga- 0.1 10 1.0 3.0 80 not
treated -- -- 686 sample 59 acid (85%) hydroxide nese of the phos-
invention phate 70 orthophosphoric aluminum manga- 0.4 10 1.0 3.0
80 not treated -- -- 686 sample 60 acid (85%) hydroxide nese of the
phos- invention phate 71 orthophosphoric aluminum manga- 0.8 10 1.0
3.0 80 not treated -- -- 686 sample 61 acid (85%) hydroxide nese of
the phos- invention phate 72 orthophosphoric aluminum -- 1 10 1.0
3.0 80 not treated -- -- 686 sample 62 acid (85%) hydroxide of the
invention 73 -- aluminum -- 1 3 1.2 0.1 80 surfactant Phosphoric
0.05 980 sample 63 phosphate added acid of the compound II
invention was mixed with nonionic surfactant (polyoxyethylene alkyl
ether with HLB of 13.6), and the resulting mixture was used for
simultaneous coating treatment and moisture resistance treatment.
74 -- aluminum -- 1 3 1.2 0.5 80 coated Coated with 0.05 980 sample
64 phosphate with phosphoric acid of the silane compound and
invention then further with aminosilane (aminopropyl-
triethoxysilane). Treatment for Coating Material Coating Condition
Moisture Absorption Resistance Molding metal condi- condi-
Condition metal com- mode of tion for tion for amount molding
phosphoric acid compound pound P/ treat- treat- mode of treat-
added pressure No. compound I II .alpha. M pH ment ment treatment
ment (mas. %) (MPa) Remarks 75 orthophosphoric aluminum -- 1 4 1.2
0.5 150 not treated -- -- 1470 sample 65 acid (85%) hydroxide of
the invention 76 orthophosphoric aluminum manga- 0.8 10 1.0 3.0 180
not treated -- -- 686 sample 66 acid (85%) hydroxide nese of the
phos- invention phate 77 -- aluminum -- 1 3 1.2 0.5 110 coated
Coated with 0.05 980 sample 67 phosphate with phosphoric acid of
the silane compound and invention then further with aminosilane
(aminopropyl- triethoxysilane)
[0171]
10 TABLE 10 Properties of Properties of Sample after 60-day
exposure Condition for Sample Preparation Sample after 1-day
exposure magnetic solid coating molding green specific magnetic
flux green specific flux P/ content temperature pressure density
resistivity density B10k density resistivity density B10k No.
.alpha. M (mas. %) (.degree. C.) (MPa) (Mg/m.sup.3) (.mu..OMEGA.m)
(T) (Mg/m.sup.3) (.mu..OMEGA.m) (T) Remarks 55 1 3 0.01 60 980 7.65
21 1.70 7.65 35 1.71 sample 45 of the invention 56 1 3 0.05 90 1980
7.70 41 1.74 7.69 68 1.74 sample 46 of the invention 57 1 3 0.2 105
980 7.62 200 1.64 7.63 268 1.64 sample 47 of the invention 58 1 3
0.2 95 980 7.63 312 1.65 7.62 452 1.64 sample 48 of the invention
59 1 3 0.2 90 980 7.62 1214 1.64 7.62 1542 1.63 sample 49 of the
invention 60 1 3 0.5 105 1470 7.60 540 1.61 7.60 701 1.61 sample 50
of the invention 61 1 1 1.0 100 1980 7.63 1420 1.62 7.63 1790 1.58
sample 51 of the invention 62 1 3 1.0 100 1980 7.64 2543 1.61 7.64
3521 1.60 sample 52 of the invention 63 1 5 1.0 100 1980 7.64 850
1.63 7.62 1250 1.58 sample 53 of the invention 64 1 3 2.0 90 1176
7.50 3545 1.50 7.51 4554 1.52 sample 54 of the invention 65 1 3 0.5
80 1470 7.60 1350 1.66 7.61 1875 1.65 sample 55 of the invention 66
1 4 0.5 100 1470 7.58 102 1.60 7.57 125 1.61 sample 56 of the
invention 67 1 1 2.0 60 1176 7.51 1545 1.51 7.52 1875 1.50 sample
57 of the invention 68 1 6 5.0 90 686 7.20 15424 1.21 7.20 16584
1.21 sample 58 of the invention 69 0.1 10 3.0 80 686 7.12 8542 1.15
7.10 15487 1.10 sample 59 of the invention 70 0.4 10 3.0 80 686
7.12 9781 1.16 7.11 14871 1.15 sample 60 of the invention 71 0.8 10
3.0 80 686 7.12 10541 1.15 7.12 13540 1.15 sample 61 of the
invention 72 1 10 3.0 80 686 7.12 12455 1.15 7.11 13154 1.16 sample
62 of the invention 73 1 3 0.1 80 980 7.64 1542 1.65 7.64 1610 1.65
sample 63 of the invention 74 1 3 0.5 80 980 7.61 3546 1.60 7.61
3601 1.61 sample 64 of the invention 75 1 4 0.5 150 1470 7.61 62
1.61 7.61 54 1.51 sample 65 of the invention 76 0.8 10 3.0 180 686
7.11 2130 1.21 7.10 2100 1.15 sample 66 of the invention 77 1 3 0.5
110 980 7.61 1570 1.60 7.60 1210 1.51 sample 67 of the
invention
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