COMPOSITION FOR INJECTION MOLDING AND SINTERED BODY PRODUCING
PROCESS
BACKGROUND
1. Technical Field
[OOOl] The present invention relates to compositions for
injection molding, and sintered body producing processes.
2. Related Art
[00021 The powder metallurgy process that sinters a metal
powder-containing molding to produce a metallic product has
been used in a wide range of industrial fields for its ability
to produce a near-net shaped sintered body. For example, when
used with a magnetic metal powder, the powder metallurgy
process can easily produce a magnetic core of a complex shape,
and thus has been used in, for example, magnetic actuator
component applications.
[00031 Among the many molding producingprocesses (molding
methods) known in the art, a powder injection molding method
mixes and kneads ametal powder and an organic binder, and uses
the kneaded product (compound) for inj ection molding. The
molding produced by the powder injection molding method is
sub~ectedtoadegreasingprocesstoremovetheo rganic binder,
and is calcinedtoobtainametallicproductof adesired shape.
100041 The metal powder injection molding method requires
selecting a suitable organic binder for different purposes,
including imparting shape-retainability to the molding.
[00051 For example, JP-A-11-131103 discloses
poly-a-methylstyrene, paraffinwax, stearic acid, anddibutyl
phthalate as examples of the organic binder components used
in the metal powder injection molding method.
[00061 However, without sufficiently high
shape-retainability forthe molding undergoing the degreasing
process, it is difficult to maintain the shape of the as-molded
product through degreasing and sintering, particularly when
the molding has a compl-ex shape. This causes defects such as
deformation and damage, and lowers the dimensional accuracy
ofthe sinteredbody. Thedimensionalaccuracyof the sintered
body tends to decrease particularly in the powder injection
molding method, because the method requires increasing the
proportion of the organic binder relative to the metal powder
to increase compound fluidity, and thus involves a high rate
of shrinkage. Accordingly, there is a need to suppress the
rate of shrinkage as much as possible while improving
shape-retainability against degreasing.
SUMMARY
[00071 An advantage of some aspects of the invention is to
provide a composition for injection molding that can produce
a molding having high shape-retainability, and a sinteredbody
producing process that can reliably produce a high-quality
sintered body having high dimensional accuracy.
[00081 An aspect of the invention is directed to a
composition for injection molding including a magnetic metal
powder that contains any of Fe, Ni, and Co as a main component,
and that has a mass-based particle size distribution in which
a particle diameter Dl0 at 10% cumulative mass is 2 ym or more
and less than 5 pm, a particle diameter D50 at 50% cumulative
mass is from 5 pm to 10 pm, and a particle diameter D90 at 90%
cumulative mass is from 12 pm to 28 pm; and an organic binder
that contains a first resin configured from an unsaturated
glycidyl group-contaming polymer, and a second resin having
a higher softening point than the first resin, wherein the
content of the organic binder ranges from 3 parts by mass to
9partsbymasswithrespectto100partsbymass ofthemagnetic
metal powder.
[00091 In this way, the kneaded product of the magnetic
metal powder and the organic binder can have high fluidity,
andthe organicbinder content canbe reduced. It is therefore
possibletoproduce amoldingthathas asmall rate of shrinkage
against degreasing, and that has high shape-retainability,
making it possible to obtain a composition for injection
molding capable of producing a high-quality sintered body
having high dimensional accuracy.
[ O O l O I It is preferable in the composition for injection
molding of the aspect of the invention that, in the magnetic
metal powder, particles having a particle diameter less than
10 pm account for 55 mass% or more, particles having a particle
diameter of 20 pm or more and less than 30 pm account for more
than 0 mass% and less than 15 mass%, and particles having a
particle diameter of 30 pm or more account for more than
and less than 5 mass%, and the remaining part has a particle
diameter of 10 pm or more and less than 20 pm.
[OOll] In this way, the magnetic metal powder can have a
very small proportion of particles having coarse particle
diameters, and theparticle diameter variation is particularly
suppressed to particularly improve fluidity and moldability
when kneaded with the organic binder. This makes it possible
to further reduce the relative amount of the organic binder
with respect to the magnetic metal powder while maintaining
moldability, and to further suppress the rate of shrinkage
against degreasing.
[00121 It is preferable in the composition for injection
molding of the aspect of the invention that the first resin
and the second resin have a softening point difference of from
10°C to 100°C.
[ 0 0 13 I In this way, the fluidity at the time of kneading
can be further improved, and the organic binder content with
respect to the magnetic metal powder can be further reduced.
This makes it possible to further reduce the rate of shrinkage
against degreasing.
[00141 It is preferable in the composition for injection
molding of the aspect of the invention that the unsaturated
glycidylgroup-containingpolymerbe acopolymerthatcontains
an unsaturated glycidyl group-containing monomer and an
ethylenic unsaturated ester compound monomer.
[00151 This improves the affinity of the organic binder to
the magneticmetalpowderparticles, andparticularly improves
the homogeneity of the composition for injection molding.
[00161 It is preferable in the composition for injection
molding of the aspect of the invention that the unsaturated
glycidylgroup-containingpolymeris acopolymerthatcontains
an unsaturated glycidyl group-containing monomer and a
nonpolar a-olefinic monomer.
[00171 In thisway, the affinityof the unsaturatedglycidyl
group-containing polymer to the other binder components can
improve, and the unsaturated glycidyl group-containing
polymer can stably exist between the magnetic metal powder and
the other binder components. This makes it possible to obtain
a composition for injection molding that can improve the
moldability of the degreased body (molding), and that can
suppress lowering of shape-retainability.
[ 0 0 18 I It is preferable in the composition for injection
molding of the aspect of the invention that the unsaturated
glycidylgroup-containingpolymerhas asofteningpointof from
[0019] In this way, a degreased body can be produced that
can produce a sintered body having appropriate flexibility at
the time of kneading and molding, and having homogeneity and
high dimensional accuracy.
[00201 It is preferable in the composition for injection
molding of the aspect of the invention that the organic binder
further contains a wax.
COO211 In this way, appropriate fluidity can be imparted
to the composition, and the uniformity and the moldability of
the composition can be improved. This makes it possible to
obtainacompositionthat canproduce aparticularlyhomogenous
sintered body having particularly high dimensional accuracy.
100221 It is preferable in the composition for injection
molding of the aspect of the invention that the organic binder
further contains a phthalic acid ester.
[00231 In this way, appropriate fluidity can be imparted
to the composition, and the uniformity and the moldability of
the composition can be improved. This makes it possible to
obtainacompositionthatcanproduceaparticularlyhomogenous
sintered body having particularly high dimensional accuracy.
LOO241 It is preferable in the composition for injection
molding of the aspect of the invention that the mass content
of the second resin in the organic binder is from 80 mass% to
150 mass% of the first resin.
[00251 In this way, desirable affinity between the second
resin and the magnetic metal particle can be realized while
providing desirable moldability for the composition, and a
composition that can produce a particularly homogenous
sintered body having particularly high dimensional accuracy
can be obtained.
100261 It is preferable in the composition for injection
molding of the aspect of the invention that atotal of the first
resin and the second resin account for 50 mass% or more in the
organic binder.
roo271 In this way, a degreased body that can produce a
homogenous sintered body having high dimensional accuracy can
be reliably obtained.
[00281 Another aspect of the invention is directed to a
sinteredbodyproducingprocess including: kneadingamagnetic
metal powder andanorganic binder to obtaina kneadedproduct,
the magnetic metal powder containing any of Fe, Ni, and Co as
a main component, and having a mass-based particle size
distributioninwhichaparticle diameterD10 at 10% cumulative
mass is 2 pm or more and less than 5 pm, a particle diameter
D50 at 50% cumulative mass is from 5 tim to 10 pm, and a particle
diameter D90 at 90% cumulative mass is from 12 pm to 28 pm,
the organic binder containing a first resin configured from
anunsaturatedglycidylgroup-containingpolymer, anda second
resin having a higher softening point than the first resin;
molding the kneadedproducttoobtainamolding; anddegreasing
and calcining the molding to obtain a sintered body.
[00291 Inthis way, ahigh-qualitysinteredbodyhavinghigh
dimensional accuracy can be reliably produced.
BRIEF DESCRIPTION OF THE DRAWINGS
[00301 A in the figure represents a plan view illustrating
a yoke case as an application example of a sintered body
produced in the invention, and B in the figure represents a
cross sectional view along X-X.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
COO311 Preferredembodiments of acomposition for injection
molding, and a sintered body producing process according to
the invention are described below in detail.
Composition for Injection Molding
LO0321 The composition for injection molding of the
embodiment of the invention includes a magnetic metal powder
and an organic binder, and is obtained by kneading these
components.
LO0331 The magnetic metal powder contains any one of Fe,
Ni, and Co as a main component.
LOO341 On the other hand, the organic binder serves to bind
the particles of the magnetic metal powder, and includes an
unsaturated glycidyl group-containing polymer (first resin),
and a component (second resin) having a higher softening point
than the first resin.
[00351 Injection molding of the composition for injection
molding can produce a molding that has a low rate of shrinkage
and high shape-retainability against degreasing. Further,
degreasing and calcining of the molding can produce a
high-quality sintered body that has a few defects such as
deformation and damage, and has high dimensional accuracy.
roo361 The components of the composition for injection
molding ofthe embodiment of the inventionare describedbelow.
Magnetic Metal Powder
100371 A powder containing any one of Fe, Ni, and Co as a
main component is used as the magnetic metal powder, as
mentioned above. The main component is the element most
abundant inthemagneticmetallicmaterial formingthemagnetic
metal powder, and that has a content of greater than 50 mass%.
Examples of the magnetic metallic material include a Fe-based
alloy, a Ni-based alloy, and a Co-based alloy. Specific
examples include pure iron, ferrite stainless steel, sendust,
permalloy, supermalloy, permendur, Fe-Si, Fe-Al, Fe-Cr,
Fe-Al-Cr, and Fe-Si-Cr.
[00381 Of these, permendur (Fe-Co-V alloy) is preferably
used. The Fe-Co-V alloy has particularly high saturated
magnetic flux density, and can realize a magnetic metal
sintered body having excellent magnetic properties.
E00391 The magnetic metal powder may be produced by using
any method, including, for example, an atomization method
(including water atomization, gas atomization, and high-speed
rotary water jet atomization) , a reduction method, a carbonyl
method, and a pulverization method. Preferably, the magnetic
metal powder is produced by atomization. Atomization can
efficiently produce a micro magnetic metal powder. Further,
a magnetic metal powder of homogenous particle diameters with
little particle diameter variation can be obtained. The
magnetic metal powder can thus reliably prevent cavity
generation in the sintered body, and improve density. As a
result, a magnetic metal sintered body having excellent
magnetic properties andmechanical properties can be obtained.
[00401 Further, because the metal powder produced by
atomization has a shape relatively close to sphere, excellent
dispersibility and fluidity can be obtained for the organic
binder. This improves the inj ectability of the granulated
powder injected into a mold for molding, and a dense sintered
body having high dimensional accuracy can be obtained.
[00411 The magnetic metal powder used in the embodiment of
the invention has a mass-based particle size distribution in
which a particle diameter Dl0 at 10% cumulative mass from the
smaller diameter side is 2 pm or more and less than 5 prn, a
particle diameter D50 at 50% cumulative mass is from 5 pm to
10 pm, and a particle diameter D90 at 90% cumulative mass is
from 12 him to 28 ILm. The magnetic metal powder having such
a particle size distribution overall has small particle
diameters and a relatively narrow distribution range, and can
provide excellent fluidity and moldability when kneaded with
the organic binder. This makes it possible to realize a
composition for injection molding (compound) that has
sufficient fluidity and moldability even with a relatively
smaller amount of the organic binder with respect to the
magnetic metal powder. The composition for injectionmolding
can thus be used to suppress the rate of shrinkage against
degreasing, and provide a molding that has high
shape-retainability against degreasing. As a result, a
homogenous, high-quality sintered body can be produced that
has a few defects such as deformation and damage, and has high
dimensional accuracy. The sintered body has excellent
magnetic properties and mechanical properties, and is useful
as a magnetic component.
[00421 The particle diameter of the magnetic metal powder
can be measured by using a laser diffraction method.
[00431 The particle diameter D l 0 preferably ranges from 2
lim to 4 pm. The particle diameter D50 preferably ranges from
6 pm to 9 pm. The particle diameter D90 preferably ranges from
15 Lim to 25 pm.
LOO441 Preferably, the magnetic metal powder used in the
embodiment of the invention has a particle size distribution
in which particles having a particle diameter less than 10 pm
account for 55 mass% or more, particles having a particle
diameter of 20 pm or more and less than 30 pm account for more
than 0 mass% and less than 15 mass%, and particles having a
particlediameter of 30 [imormore account formore than 0 mass%
and less than 5 mass%, and in which the remaining part has a
particle diameter of 10 pm or more and less than 20 pm. The
magnetic metal powder having suchaparticle size distribution
contains a very small proportion of particles having coarse
particle diameters, and very little particle diameter
variation. This particularly improves the fluidity and
moldabilitywhenkneadedwiththeorganicbinder. As aresult,
the amount of organic binder relative to the magnetic metal
powder can be further reduced while maintaining moldability,
and the rate of shrinkage against degreasing can be further
suppressed.
[00451 More preferably, the proportion of particles having
a particle diameter less than 10 [im is 60 mass% or more, the
proportion of particles having a particle diameter of 20 pm
or more and less than 30 pm is 3 mass% or more and less than
13 mass%, and the proportion of particles having a particle
diameter of 30 pm or more is from 1 mass% to 4 mass%.
100461 The magnetic metal powder used in the embodiment of
the invention has a tap density of preferably 3.5 g/cm3 or more,
more preferably 3.8 g/cm3 or more. The particle injectability
for molding can be particularly improved with the magnetic
metal powder having such a large tap density. As a result,
a very dense sintered body can be obtained. The tap density
of the magnetic metal powder can be measured, for example,
according to the tap density measurement method specified by
JIS Z 2512.
[00471 The specific surface area of the magnetic metal
powder used the embodiment the invention not
particularly limited, and is preferably from 0.15 m2/g to 0.8
m2/g, more preferably from 0.2 m2Ig to 0.7 m2/g, further
preferablyfr0m0.3m~/~to0.6m~T/h~e.m agneticmetalpowder
withsuchawide specific surface area can increase the surface
activity (surface energy), andcaneasilybe sinteredwithless
energy. Thus, the molding can be sintered in a shorter time
period, which makes it easier to improve shape-retainability.
On the other hand, a specific surface area exceeding the
foregoing upper limits unnecessarily increases the contact
areabetween the magnetic metal powder and the organic binder,
and may lower the composition stability and fluidity. The
specific surface area of the magnetic metal powder can be
measured, forexample, accordingtothepowder (solid) specific
surface area measurement method by gas adsorption specified
by JIS Z 8830.
Organic Binder
LOO481 The organic binder includes the first resin
configured from an unsaturated glycidyl group-containing
polymer, and the second resin having a higher softening point
than the first resin, as mentioned above.
[00491 The present inventors conducted intensive studies
of a kneaded product of the magnetic metal powder and the
organic binder concerning the relationship between the
magnetic metal powder particle size distribution and the
organic binder composition, inorder to suppress the shrinkage
against degreasing while maintaining moldability. The
invention was completed based on the finding that sufficient
moldability can be provided even with a reduced amount of the
organic binder with respect to the magnetic metal powder when
themagneticmetalpowderparticle sizedistributionis limited
to a specific range and when the organic binder composition
is optimized.
[OOSOI Specifically, in the embodiment of the invention,
the magnetic metal powder has the particle diameter Dl.Q, the
particle diameter D50, and the particle diameter D90 of the
foregoing ranges, and the organic binder includes the first
resin and the second resin described above. The composition
(compound) for injectionmolding, by containing these magnetic
metal powder and the organic binder, can thus have useful
properties even with the small organic binder content of from
3 parts by mass to 9 parts by mass with respect to 100 parts
by mass of the magnetic metal powder. In this way, excellent
moldability can be obtained in molding the composition for
injection molding, and the rate of shrinkage of the molding
against degreasing can be suppressed to realize high
shape-retainability. As a result, a high-quality sintered
body having high dimensional accuracy can be obtained that has
a few defects such as deformation and damage.
[0051] The first resinand the secondresinhave a softening
point difference of preferably from 10°C to 100°C, more
preferably from 10°C to 50°C, further preferably from 15°C to
40°C. The softening point difference between the first resin
and the second resin further improves fluidity at the time of
kneading, and can further suppress the organic binder content
with respect to the magnetic metal powder. As a result, the
rateof shrinkageagainstdegreasingcanbefurthersuppressed.
100521 The amount of the second resin may be larger or
smaller than the first resin. Accordingly, the mass content
in the organic binder may be the highest for the unsaturated
glycidyl group-containing polymer (first resin), and the
second highest for the resin having a higher softening point
than the first resin, or the mass content in the organic binder
maybethehighest forthe resinhavingahigher softeningpoint
than the unsaturated glycidyl group-containing polymer (first
resin), and the second highest for the first resin. It is also
possible to contain a third resin, different from the first
resin and the second resin, in a greater content. However,
the contents are not limited to these examples.
[00531 Aside from the unsaturated glycidyl
group-containingpolymerabove, the organicbindermaybeother
resins, examples of which include polyolefins such as
polyethylene, polypropylene, polybutylene, and polypentene;
polyolefln copolymers such as polyethylene-polypropylene
copolymers, and polyethylene-polybutylene copolymers;
styrene resins such as polystyrene; acrylic resins such as
polymethylmethacrylate, andpolybutylmethacrylate; polyvinyl
chloride; polyvinylidene chloride; polyamides; polyesters
such as polyethylene terephthalate, and polybutylene
terephthalate; polyethers; polyvinyl alcohol, polyacetals,
andcopolymers of these. Other examples includevariouswaxes,
higher fatty acids (e.g . , stearic acid) , higher alcohols,
higher fatty acid esters, higher fatty acid amides, and
phthalic acid esters. These may be used ether alone or as a
mixture of two or more.
[00541 Preferably, the organic binder contains an
unsaturatedglycidylgroup-containingpolymer, styrene resin,
waxes, and phthalic acid esters. It is believed that, with
a combination of these components, the unsaturated glycidyl
group-containing polymer imparts sufficient fluidity and
moldabilitytothe compositionwhile the styrene resin imparts
sufficient shape-retainability to the composition. The waxes
and phthalic acid esters impart fluidity to the composition
even at lower temperatures, and can be degreased by degreasing
atlowertemperatures, makingitpossibletopromotedegreasing
of the unsaturated glycidyl group-containing polymer and the
styrene resin that are degreased by higher temperatures. AS
a result, a high-quality sintered body can be obtained that
has a few defects such as deformation and damage, and excellent
mechanical properties and magnetic properties. The
components are described below. In the following, the
unsaturated glycidyl group-containing polymer will be
described as the first resin, and the styrene resin as the
second resin.
Unsaturated Glycidyl Group-Containing Polymer
[00551 The unsaturated glycidyl group-containing polymer
(first resin) is a polymer that contains an unsaturated
glycidyl group-containing monomer as a repeating unit.
Examples of the unsaturated glycidyl group-containing monomer
include glycidyl (meth)acrylate, ally1 glycidyl ether,
a-ethyl glycidyl ether, crotonyl glycidyl ether, glycidyl
crotonate, itaconic acid monoalkyl ester monoglycidyl ester,
fumaric acid monoalkyl ester monoglycidyl ester, rnaleic acid
monoalkyl ester monoglycidyl ester, and alicyclic epoxy
group-containing (meth)acrylate. One or more of these
unsaturated glycidyl group-containing monomers are contained
in the unsaturated glycidyl group-containing polymer used in
the embodiment of the invention. Particularly preferable is
glycidyl (rneth) acrylate.
[00561 The ring of the glycidyl group opens in processes
such as kneading and molding, and binds to the hydroxyl group
on the particle surface of the magnetic metal powder. As a
result, the magnetic metal powder particle strongly adheres
to the unsaturated glycidyl group-containing polymer, and by
using this as a driving force, the magnetic metal powder and
the organic binder are uniformly kneaded throughout. This
provides fluidity for the kneaded product, and can thus lower
the proportion of the organic binder.
[00571 Preferably, the unsaturated glycidyl
group-containing polymer is a copolymer of the unsaturated
glycidyl group-containing monomer and an ethylenic
unsaturatedester compoundmonomer. The copolymer containing
the ethylenic unsaturated ester compound monomer contributes
to realizing a uniform molding and degreased body having high
injectability. The ethylenic unsaturated ester compound
monomer particularly improves homogeneity, because the
ethylenic unsaturated ester compound monomer, with the
unsaturatedglycidylgroup-containingmonomer, contributes to
the affinity to the magnetic metal powder particles.
[00581 Examples oftheethylenicunsaturatedestercompound
monomer include carboxylic acid vinyl esters such as vinyl
acetate, vinyl propionate, methyl acrylate, ethyl acrylate,
butyl acrylate, methyl methacrylate, ethyl methacrylate, and
butyl methacrylate; and a-, P-unsaturated carboxylic acid
alkyl esters. These may be used either alone or as a mixture
of two or more.
LO0591 Of these ethylenic unsaturated ester compound
monomers, those containing at least one of vinyl acetate and
methyl acrylate are particularly preferable.
[00601 Examples of the unsaturated glycidyl
group-containingpolymer include Rexpearl (Japan Polyolefin) ,
Modiper (NOF Corporation) , Umex ( Sanyokasei Co . , Ltd. ) ,
Bondine (SumikaAtofina), andBondfast (Sumitomo Chemical Co.,
Ltd. )
[00611 Aside from the unsaturated glycidyl
group-containing monomers above, the unsaturated glycidyl
group-containing polymer preferably contains a nonpolar
a-olefinic monomer. By containing a nonpolar a-olefinic
monomer as a repeating unit, the unsaturated glycidyl
group-containing polymer can have strong affinity to olefinic
resins suchas the styrene resin. In this way, the unsaturated
glycidyl group-containing polymer can have affinity not only
to the magnetic metal powder particle but to the other binder
components, and can thus stably exist between the magnetic
metal powder and the other binder components. This makes it
possible to improve the moldability of the degreased body
(molding), and to particularly suppress lowering of the
shape-retainability.
[0062] Examples of the nonpolar a-olefinic monomer include
ethylene, propylene, butene-1, hexene-1, octene-1, and
4-methylpentene-1, of which ethylene, propylene, butene-1,
hexene-1, and octene-1 are preferred.
[00631 The unsaturated glycidyl group-containing polymer
used in the embodiment of the invention has a softening point
of preferably from 65°C to 105°C, more preferably from 70°C to
100°C. The unsaturated glycidyl group-containing polymer
having sucha softeningpointexhibits appropriate flexibility
duringthe kneading and molding, and contributes to producing
a degreased body that can produce a homogenous sintered body
having high dimensional accuracy.
roo641 The unsaturated glycidyl group-containing polymer
used in the embodiment of the invention has a melt mass flow
rate (190°C) of preferably from about 2 [g/10 minl to about
10 [g/10 min] , more preferably from about 3 [g/10 minl to about
8 [g/10 min]. The unsaturated glycidyl group-containing
polymer having such a melt mass flow rate excels in mold
in j ectability, and contributes to producing a degreased body
that can produce a homogenous sintered body having high
dimensional accuracy. The melt flow rate can be measured at
a measurement temperature of 190°C under a measurement load
of 2.16 kg according to the method specified by JIS K 6922-2.
[00651 Note that, aside from the unsaturated glycidyl
group-containing monomer as the repeating unit of the
unsaturated glycidyl group-containing polymer as mentioned
above, other monomers such as an ethylenic unsaturated ester
compoundmonomerandanonpolara-olefinicmonomermaybe added,
as needed.
[00661 The monomer ratio is not particularly limited. As
an example, the nonpolar a-olefinic monomer is preferably from
300 parts by mass to 2,000 parts by mass, more preferably from
400 parts by mass to 1,500 parts,by mass with respect to 100
parts by mass of the unsaturated glycidyl group-containing
monomer. In this way, the nonpolar a-olefinic monomer can
provide compatibility to the styrene resin in good balance
while the unsaturated glycidyl group-containing monomer
provides affinity to the magnetic metal particles, and
shape-retainabilityandmoldabilitycanberealizedatthe same
time. As a result, a degreased body can be obtained that can
I
produce a homogenous sintered body having high dimensional
accuracy.
[00671 The ethylenic unsaturated ester compound monomer is
preferably from 20 parts by mass to 80 parts by mass, more
preferablyfrom25partsbymassto75partsbymasswithrespect
to 100 parts by mass of the unsaturated glycidyl
group-containing monomer.
[00681 The unsaturated glycidyl group-containing polymer
has a tensile strength of from about 4 MPa to about 25 MPa,
more preferably from about 5 MPa to about 20 MPa.
[00691 The weight-average molecular weight of the
unsaturated glycidyl group-containing polymer is
appropriately set taking into account factors suchas the melt
flow rate as mentioned above, and is, for example, preferably
from10,000to400,000,m orepreferablyfrom3O1OOOto3OO,OOO.
[00701 The unsaturated glycidyl group-containing polymer
content in the organic binder is preferably from about15 mass%
to about 40 mass%, more preferably from about 20 mass% to about
35 mass%. With the unsaturated glycidyl group-containing
polymer content set in these ranges, the composition
moldability can be improved while improving the affinity
between the styrene resin and the magnetic metal particle. As
a result, a degreased body can be produced that can produce
a homogenous sintered body having high dimensional accuracy.
Styrene Resin
[00711 The second resin may be any resin, as long as it has
a softening point that satisfies the predetermined
relationship with the first resin. In the following, the
second resin will be described as being a styrene resin, as
noted above.
[00721 The styrene resin imparts an appropriate mechanical
strength to the organic binder to improve the
shape-retainability of the molding. The styrene resin thus
particularly contributes to producing a degreased body that
can produce a sintered body having high dimensional accuracy.
[00731 The styrene resin may be, for example, a polymer or
acopolymerthatcontains astyrenemonomerasarepeatingunit,
and the homopolymer polystyrene is preferably used.
COO741 The weight-average molecular weight of the styrene
resin is notparticularlylimited, andis preferably fromabout
5,OOOtoabout7O,OOO,morepreferablyfromabout7,OOOtoabout
50,000. By containing the styrene resin having such a
molecular weight, a degreased body can be produced that can
produce a homogenous sintered body having high dimensional
accuracy.
100751 Preferably, the styrene resin has a softening point
higher than the softening point of the unsaturated glycidyl
group-containingpolymer, and that fallswithinarange of from
90°C to 150°C, more preferably from 100°C to 140°C. With the
styrene resinhaving a weight-average molecular weight in the
foregoing range, the magnetic metal powder and the organic
binder can be mixed more uniformly, and the composition
moldability can be further improved. As a result, a degreased
body can be produced that can produce a homogenous sintered
body having high dimensional accuracy.
[00761 The styrene resin (second resin) content in the
organic binder is preferably from about 10 mass% to about 50
mass%, more preferably from about 15 mass% to 40 mass%. With
the styrene resin content set in these ranges, an appropriate
mechanical strength can be imparted to the organic binder, and
the homogeneity of the molding can be provided while improving
the shape-retainability of the molding. As a result, a
degreased body can be produced that can produce a homogenous
sintered body having high dimensional accuracy.
[00771 The proportion of the styrene resin (second resin)
with respect to the unsaturated glycidyl group-containing
polymer is preferably from 80 mass% to 150 mass%, more
preferably from 90 mass% to 140 mass%, further preferablymore
than 100 mass% and 130 mass% or less. With the styrene resin
proportion set in these ranges, the affinity between the
styrene resin (second resin) and the magnetic metal particle
can be desirably provided while providing composition
moldability, and a degreased body can be produced that can
produce a particularly homogenous sintered body having
particularly high dimensional accuracy.
[00781 The total of the unsaturated glycidyl
group-containing polymer and the styrene resin preferably
accounts for at least 50 mass%, more preferably at least 55
mass% in the organic binder. In this way, a degreased body
can be produced that can produce a homogenous sintered body
having high dimensional accuracy.
Waxes
COO791 Waxes impart appropriate fluiditytothe composition,
and improve the compositionuniformityandmoldability. Waxes
thus contribute to producing a degreased body that can produce
a particularly homogenous sintered body having particularly
high dimensional accuracy.
[00801 Examples of the waxes include plant waxes such as
Candelilla wax, carnauba wax, rice wax, Japan wax, and jojoba
oil, animal waxes such as bee wax, lanolin, and whale wax,
mineral waxes such as montan wax, ozokerite, and ceresin,
natural waxes such as paraffin wax, microcrystalline wax, and
petroleum wax (including petrolatum), synthetic hydrocarbons
such as polyethylene wax, modified waxes such as montan wax
derivatives, paraffin wax derivatives, and microcrystalline
wax derivatives, hydrogenated waxes such as hydrogenated
castor oil, and hydrogenated castor oil derivatives, fatty
acids such as 12-hydroxystearic acid, acid amides such as
stearic acid amide, and synthetic waxes, including esters such
as phthalic imide anhydride. These are used either alone or
in a combination of two or more.
[00811 Particularly preferred are petroleum waxes, and
modified products thereof. Paraffin wax, microcrystalline
wax, carnaubawax, andderivatives of these aremore preferred,
andparaffinwaxandcarnaubawaxare furtherpreferred. These
waxes have excellent compatibility to the styrene resin, and
enable production of a homogenous binder.
LOO821 The welght-average molecular weight of the waxes is
preferably 100 or more and less than 10,000, more preferably
from 200 to 5,000. With the waxes having weight-average
molecular weights falling in these ranges, the magnetic metal
powder and the organic binder can be mixed more uniformly, and
the composition moldability can be further improved.
100831 Waxes havlny a softening point lower than the
softening point of the unsaturated glycidyl group-containing
polymer, and that falls within the range of from 30°C to 100°C,
more preferably from 50°C to 95°C are preferably used.
COO841 When containing wax, a plurality of waxes having
different softening points may be contained. In this way, the
composition moldablllty can be improved. In this case, the
softening point dlf ference between the wax having the highest
softening point and the wax having the lowest softening point
is not particularly limited, and is preferably from about 3°C
to about 40°C, more preferably from about 5°C to about 30°C.
Examples of specific combinations include a combination of
paraffin wax and carnauba wax.
[00851 The wax content in the organic binder is preferably
from about 10 mass% to about 45 mass%, more preferably from
about 15 mass% to about 40 mass%. With the wax content set
in these ranges, it is possible to suppress lowering of
shape-retainability while imparting appropriate fluidity to
the organic binder. As a result, a degreased body can be
produced that can produce a particularly homogenous sintered
body having particularly high dimensional accuracy.
[00861 The proportion of the waxes with respect to the
unsaturated glycidyl group-containing polymer is preferably
from 80 mass% to 150 mass%, more preferably from 90 mass% to
140 mass%, furtherpreferablymore than100 mass% and130 mass%
or less. With the wax proportion set in these ranges, it is
possible to suppress lowering of shape-retainability while
imparting appropriate fluidity to the composition.
Phthalic Acid Esters
roo871 Thephthalic acidesters impart appropriate fluidity
to the composition, and improve the compositionuniformity and
moldability. The phthalic acid esters thus contribute to
producing a degreased body that can produce a particularly
homogenous sinteredbodyhavingparticularlyhigh dimensional
accuracy.
[00881 Examples of the phthalic acid esters include
dimethyl phthalate, diethyl phthalate, butyl phthalate,
dibutyl phthalate, diisobutyl phthalate, and dioctyl
phthalate. These are used either alone or in a combination
of two or more.
[00891 T h e p h t h a l i c a c i d e s t e r c o n t e n t i n t h e o r g a n i c b i n d e r
2 8
is preferably from about 5 mass% to about 30 mass%, more
preferably from about 10 mass% to about 25 mass%. With the
proportion of phthalic acid ester set in these ranges, it is
possible to impart appropriate fluidity to the composition,
and suppress lowering of shape-retainability.
[00901 The proportion of the phthalic acid ester with
respect to the unsaturated glycidyl group-containing polymer
is preferably from about 30 mass% to about 80 mass%, more
preferably from about 40 mass% to about 70 mass%. With the
proportion of phthalic acid ester set in these ranges, it is
possible to suppress lowering of shape-retainability while
imparting appropriate fluidity to the composition.
Other Components
[00911 The organic binder may contain other components, in
addition to the foregoing four components.
[00921 The number of carbon atoms in the saturated fatty
acid is preferably from about 12 to about 20. In this way,
moldability can be particularly improved.
[00931 Examples of the higher fatty acid include stearic
acid, oleic acid, and linoleic acid. Particularly preferred
foruse are saturated fattyacids suchas lauric acid, myristic
acid, palmitic acid, stearic acid, and arachidic acid.
E00941 Examples of the alcohol include polyalcohol,
polyglycol, andpolyglycerol. Particularlypreferred for use
are, forexample, cetylalcohol, stearylalcohol, oleylalcohol,
and mannitol.
Examples of the fatty acid metal include compounds
that contain higher fatty acids (such as lauric acid, stearic
acid, succinicacid, stearyllacticacid, lacticacid, phthalic
acid, benzoic acid, hydroxystearic acid, ricinoleic acid,
naphthenic acid, oleic acid, palmitic acid, and erucic acid)
and metals (such as Li, Na, Mg, Ca, Sr, Ba, Zn, Cd, Al, Sn,
Pb, and Cd) . Particularly preferred for use are, for example,
magnesium stearate, calcium stearate, sodium stearate, zinc
stearate, calcium oleate, zinc oleate, and magnesium oleate.
[00961 Examples of the non-ionic surfactant lubricant
include Electrostripper TS-2, and Electrostripper TS-3 (Kao
Corporation) .
[00971 Examples of the silicone-based lubricant include
dimethylpolysiloxane and modified products thereof,
carboxyl-modified silicone, a-methylstyrene-modified
silicone, a-olefin-modified silicone, polyether-modified
silicone, fluorine-modified silicone, hydrophilic specially
modified silicone, olefin polyether-modified silicone,
epoxy-modified silicone, amino-modified silicone,
amide-modified silicone, and alcohol-modified silicone.
[00981 Examples of yet other components include fatty acid
esters (such as palm oil), adipic acid esters (such as dibutyl
adipate) , sebacic acid esters (such as dibutyl sebacate) ,
polyvinylpyrrolidone, polyether, polypropylene carbonate,
ethylene bis stearamide, sodium alginate, agar, gum arabic,
resin, sucrose, and ethylene-vinyl acetate copolymer (EVA).
These may be used either alone or in a combination of two or
more.
[0099] The content of suchacomponent in the organic binder
preferably from 0.1 mass% to 10 mass%, more preferably from
[OlOOl The mass ratio of the other components with respect
to the unsaturated glycidyl group-containing polymer is
preferably from 0.005to 0.3, morepreferablyfrom 0.0lto 0.2.
[OlOlI The composition for injection molding may also
include, for example, antioxidants, degreasing promoting
agents, and surfactants, in addition to the foregoing
components.
[0102] The organic binder content in the composition for
injection molding is from 3 parts by mass to 9 parts by mass
with respect to 100 parts by mass of the magnetic metal powder,
as notedabove. Preferably, the organic binder content is from
about 4 parts by mass to about 9 parts by mass, more preferably
from about 5 parts by mass to about 8 parts by mass.
Sintered Body Producing Process
[01031 The sintered body producing process of the
embodiment of the invention is described below.
[01041 The sintered body producing process of the
embodiment of the invention includes a kneading step of
kneadingtheabove-mentionedmagneticmetalpowderandorganic
binder to obtain a kneaded product, a molding step of molding
the kneaded product into a desired shape, a degreasing step
of subjecting the molding to a degreasing process, and a
calcining step of calcining the degreased body. Each step is
described below in order.
kneading Step
[01051 The kneaded product is prepared by kneading the
materials, including the above-mentioned magnetic metal
powder and organic binder. ~ n e a d i n ~ m a ~pebref ormedbyusing
various types of kneaders, for example, such as a pressurized
or double-arm kneader, a roller kneader, a Banbury kneader,
and a one-axis or two-axis extruder.
[01061 The total kneading time is preferably from about 15
min to about 210 min.
[01071 The viscosity of the kneaded product is preferably
from 500 P to 7,000 P (from 50 Pass to 700 Paes) , more preferably
from 1,000 P to 6,000 P (from 100 Pa.s to 600 Pa.s). In this
way, the moldability canbe particularly improved. Viscosity
can be measured with a Capillograph at a maintained kneaded
product temperature of 190°C.
[01081 The organic binder used in this step is preferably
powdery. The organic binder may be prepared into a powder by
using a common pulverization method, particularly preferably
freeze pulverization. The binder powder obtained by freeze
pulverization is particularly fine and uniform, and exhibits
the original binder characteristics without being strongly
affected by the heat of pulverization.
[01091 The average particle diameter of the binder powder
is preferably from about 10 pm to about 500 pm, more preferably
from about 15 pm to about 400 pm. By pulverizing the binder
to these particle diameters by freeze pulverization, the
effects due to the specific gravity difference in the nixture
can be minimized, and the binder powder and the magnetic metal
powder can be uniformly mixed.
[OllO] The average particle diameter is determined as the
particle diameter of when the cumulative amount is 50% in terms
of mass, by using a laser diffraction method.
[Olll] The kneading of the composition increases the
compositiontemperatureby externalheat orby the self-heating
associated with the kneading. As a result, in the kneaded
product, an inner layer of primarily the unsaturated glycidyl
group-containing polymer is formed over the magnetic metal
powder particle, and an outer layer of primarily the other
components is formed thereon. The unsaturated glycidyl
group-containing polymer does not easily cause sudden
degradationeven incontact withthemetallic element, andthus
the formation of the inner layer suppresses the catalytic
activity due to the contact of the other components and the
metallic element. Here, the catalytic activity means the
sudden degradation caused by the contact of the other
components and the metallic element, and suppressing the
catalytic activity is effective in suppressing cracking and
other defects in the degreased body. This makes it possible
to suppress the sudden degradation of the organic binder, and
to avoid lowering of shape-retainability.
Molding Step
[0112] In the molding step, the kneaded product is molded
to produce a molding of desired shape and dimensions.
[01131 The molding may be performed by using methods such
as injection molding, compression molding, and extrusion
molding. The shape and the dimensions of the product molding
are decided taking into account the shrinkage that occurs in
the subsequent degreasing and sintering.
[01141 The molding may be subjected to post-processes such
as machining, and laser processes, as needed.
[01151 The molding used in the embodiment of the invention
is not limited to the product obtained after the kneading step
and the molding step, and may be a product obtained by using
any method.
Degreasing Step
1101161 Then, the molding is subjected to a degreasing
process. This removes (degrease) the binder contained in the
molding, and yields a degreased body.
[0117] The molding is heated in the degreasing step.
Preferably, the heating procedure includes three degreasing
temperature increasing procedures. The heating temperature
in each degreasing temperature increasing procedure is set
according to the degradation temperature TH [OC] of the
high-temperature binder component in the organic binder under
one atmosphere, and the degradation temperature TL [OC] of the
low-temperature binder component under one atmosphere. When
the organic binder contains three or more components, two of
the components having higher contents represent the
high-temperature binder component and the low-temperature
binder component in order of decreasing degradation
temperatures under one atmosphere.
[01181 The degreasing process in the embodiment of the
invention includes a first degreasing temperature increasing
procedure that heats the molding at a temperature below
(TL-30°C), a second degreasing temperature increasing
procedure that heats the molding at a temperature at or above
(TL-30°C) and less than (TL+50°C) after the first degreasing
temperature increasing procedure, and a third degreasing
temperature increasing procedure that heats the molding at a
temperature at or above (TL+50°C) and less than (TH+200°C) after
the seconddegreasingtemperature increasing procedure. Each
degreasing temperature increasing procedure is described
below.
First Degreasing Temperature Increasing Procedure
[01191 In the first degreasing temperature increasing
procedure, the molding is heated at a temperature below
(TL-30°C). It is considered that, in this temperature range,
the temperature heats the organic binder, but does not cause
large degradation. The molding can thus have uniform
temperature while suppressing the organic binder from being
denatured.
[01201 The heatingtimeinthe firstdegreasingtemperature
increasing procedure is not particularly limited, and is
preferably from about 0.5 hours to about 15 ho,urs, more
preferably from about 1 hour to about 10 hours. In this
degreasing temperature increasing procedure, the foregoing
temperature is the maximum temperature, and heating may be
continuedatthis maximum temperature throughout the foregoing
heating time, orheatingmaybeperformedatlowertemperatures
throughout except for using the maximum temperature only
partially in the heating time. The same is the case for the
other temperature increasing procedures described below.
[01211 The heating atmosphere in the first degreasing
temperature increasing procedure is not particularly limited,
and may be, for example, an inert gas-containing atmosphere
(such as in nitrogen gas, and argon gas), an oxidizing
gas-containing atmosphere (such as in air), a reducing
gas-containing atmosphere (such as in hydrogen), or a reduced
pressure atmosphere of these atmospheres. The inert
gas-containing atmosphere is preferred, and the nitrogen
gas-containinyatmosphere is more preferred. In this way, the
molding can have uniform temperature while suppressing
undesirable effects such as the unintendedvaporization of the
organic binder, the oxidation of the magnetic metal powder,
and denaturing. This contributes to producing a degreased
body that can produce a homogenous sintered body having high
dimensional accuracy.
[01221 In this case, the atmosphere pressure is preferably
about the atmospheric pressure (for example, from about 50 kPa
to about 200 kPa) or higher.
[01231 As described above, the heating temperature in this
degreasing temperature increasing procedure is appropriately
set according to the component composition of the organic
binder. As an example, the heating temperature is set to 100°C
or less.
Second Degreasing Temperature Increasing Procedure
LO1241 In the second degreasing temperature increasing
procedure, the molding is heated at a temperature at or above
(TL-30°C) and below (TL+50°C) . It is considered that, in this
temperature range, the low- temperature binder component
starts to degrade, whereas little degradation occurs in the
high- temperature binder component. This creates a difference
in the extent of degradationbetween these two components, and
the low-temperature binder component is preferentially
removed. Degreasing thus takes place by gradually degrading
and removing the binder components in small amounts, rather
than suddenly degrading large amounts of binder component
As a result, defects such as the deformation and cracking of
t
the molding (degreased body) due to sudden degradation are
unlikely to occur. Specifically, the preferential removal of
the low-temperature binder component leaves micro channels of
the low-temperature binder component in the molding, and thus
the high-temperature binder component can smoothly discharge
through these channels in the subsequent temperature
increasing procedure. Thus, by the provision of the second
degreasingtemperature increasing procedure, a degreasedbody
can be obtained that can produce a sintered body having high
dimensional accuracy.
[01251 The heating time in the second degreasing
temperature increasing procedure is not particularly limited,
and is preferably from about 1 hour to about 20 hours, more
preferably from about 2 hours to 15 hours. In this way,
channels of sufficient length and diameter can be formed for
the smooth discharge of the high-temperature binder component
in the subsequent temperature increasing procedure
[01261 The. heating atmosphere in the second degreasing
temperature increasing procedure is not limited either, and
maybe any of the foregoing atmospheres. The reducedpressure
atmosphere is preferred, and the reduced pressure atmosphere
of inert gas-containing atmosphere is more preferred. In this
way, the degradation of the low-temperature binder component
can be promoted, and the heating temperature can be lowered
eveninthe foregoingranges. This canreduce the time required
forthe degreasing step. Further, the low-temperature binder
component does not easily soften, and defects such as the
deformation and cracking of the degreased body can be
suppressed.
[01271 The pressure of the reduced pressure atmosphere is
not particularly limited, and is preferably from about Pa
to about 10 kPa, more preferably from about Pa to about
1 kPa. In this way, the low-temperature binder component can
be selectively degraded and removed in a relatively short time
perlod. As a result, shape-retainability can be desirably
provided while desirably reducing the degreasing step time.
[01281 Further, as describedabove, the heating temperature
in this degreasing temperature increasing procedure is
appropriately set according to the component composition of
the organic binder. As an example, the heating temperature
is higher than the heatingtemperature of the first degreasing
temperature increasing procedure, and ranges from 5 0°C to
35O0C.
Third Deyreasiny Temperature Increasing Procedure
[01291 In the third degreasing temperature increasing
procedure, the molding is heated at a temperature at or above
(TL+50°C) and less than (TH+200°C). It is considered that, in
this temperature range, the high-temperature binder component
starts to degrade. As described above, the second resin
discharges through the channels formed in the molding
(degreasedbody), andcanthus be evenlyremoved. As aresult,
a degreased body can be obtained that can produce a homogenous
sintered body having high dimensional accuracy.
[01301 Theheatingtime inthethirddegreasingtemperature
increasing procedure is not particularly limited, and is
preferably from about 0.5 hours to about 15 hours, more
preferably from about 1 hour to about 10 hours. In this way,
the organic binder components can be sufficiently removed.
[01311 The heating atmosphere in the third degreasing
temperature increasing procedure is not particularly limited
either, andmaybe any of the foregoing atmospheres. The inert
gas-containing atmosphere is preferred, and the nitrogen
gas-containing atmosphere ismore preferred. In this way, the
degraded component3 i n the organic binder can be efficiently
discharged by the gas exchange around the molding (degreaaed
body) while suppressingoxidationordenaturingofthemagnetic
metal powdex, From the standpoint of efficient vas exchange,
it is preferable to continuously supply (flow) inert gas into
the space where the molding is disposed, instead of confining
the inert gas.
[01321 In this case, the atmosphere pressure is preferably
about the atmospheric pressure (for example, from about 50 kPa
to about 200 kPa) or higher.
[01331 As described above, the heating temperature in this
degreasing temperature increasing procedure is appropriately
set according to the component composition of the organic
binder. As an example, the heating temperature is higher than
the heating temperature of the second degreasing temperature
increasing procedure, and ranges from 200°C to 600°C.
Degreasing Temperature Decreasing Procedure
[01341 The degreased body is cooled after the temperature
increasing procedures as described above. Cooling may be
natural cooling open to the atmosphere, or natural cooling in
a cooling gas-charged space, or may be forced cooling that
involves blowing or circulating a cooling gas.
LO1351 The cooling gas may be the same gas used in the
temperature increasing procedure. However, inert gas is
preferred, and nitrogen gas is more preferred. Use of these
gases can suppress oxidation and denaturing of the magnetic
metal powder, and oxidation and contamination in the deyreasing
apparatus.
LO1361 This completes the deyreasiny step.
LO1371 The degreased body after the degreasing process may
be subjected to post -processes for the p~Y!pb8e!J of, f OT e~ample,
burring, or formation of a microstructure such as a groove.
[ 0 13 8 I It is not necessarily required to completely remove
the binder in the molding in the degreasing process. For
example, a part of the binder may remain at the end of the
degreasing process.
LO1391 As described above, the temperature increasing
procedure in the degreasing step is performed in multiple
stages according to the degradation temperatures of the
components in the organic binder. Uniform degreasing is thus
possible while suppressing defects in the molding (degreased
body). Itisthereforepossibletoreliablyobtainadegreased
body that can produce a uniform sintered body having high
dimensional accuracy.
[01401 Further, the temperature increasing procedures
improve the degreasing efficiency, and the degreasing can be
finished in a shorter time period. This makes it possible to
produce the degreased body in a short time period.
Calcining Step
[01411 The calcining step is described below. Calcining
the degreased body sinters the magnetic metal powder and
produces the sintered body.
[01421 The degreased body is heated in the calcining step.
Preferably, the heating procedure includes three calcining
ternperatureincreasingprocedures. Specifically, theheating
procedure includes a first calcining temperature increasing
procedure that heats the degreased body at a temperature below
750°C, a second calcining temperature increasing procedure
that heats the degreased body at a temperature of 750°C or more
and less than 1,050°C after the first calcining temperature
increasing procedure, and a third calcining temperature
increasing procedure that heats the degreased body at a
temperature of 1, 050°C or more and less than 1, 600°C after the
second calcining temperature increasing procedure. Each
calcining temperature increasing procedure is described
below.
First Calcining Temperature Increasing Procedure
[01431 In the first calcining temperature increasing
procedure, the degreasedbodyis heatedat atemperature below
750°C. This temperature range is intended to remove the
remaining organic binder in the degreasedbody, and to provide
uniform temperature forthe degreasedbody. Thus, by heating
the degreased body in this temperature range for a certain time
period, the sintering in the calciningtemperature increasing
procedure (described below) can proceed in a uniform fashion.
The heating temperature is appropriately set in the foregoing
range according to the composition of the organic binder. As
anexample, the heatingtemperature is preferably 500°C or more
and less than 750°C.
101441 The heating time in the first calcining temperature
increasing procedure is not particularly limited, and is
preferablyfromabout1hourtoabout20 hours, more preferably
from about 2 hours to about 15 hours. This makes it possible
to reliably remove the organic binder, and to provide
sufficiently uniform temperature for the degreased body.
LO1451 The heating atmosphere in the first calcining
temperature increasing procedure is not particularly limited
either, and may be any of the foregoing atmospheres. The
reduced pressure atmosphere is preferred, and the reduced
pressure atmosphere of inert gas is more preferred. In this
way, the degraded components in the organic binder can be
efficiently discharged by the gas exchange and vacuum
evacuation around the degreased body while suppressing the
oxidation and denaturing of the magnetic metal powder.
Second Calcining Temperature Increasing Procedure
101461 In the second calcining temperature increasing
procedure, the deyreased body is heated at a temperature of
750°Cormore andlessthan1,050~C. In this temperature range,
the magnetic metal powder starts to sinter. The heating also
initiatesthe reactionwhereby the oxygenatoms in themagnetic
metal powder bind to the carbon atoms contained in the degraded
components of the organic binder, and causes the degraded
components to vaporize and discharge. This improves the
sintering by the reduction of the magnetic metal powder, and
at the same time causesthe discharge ofthe degradedcomponents
in the organic binder, and thus contributes to improving the
properties, including mechanical properties and magnetic
properties, of the product sintered body.
LO1471 The heatingtime in the secondcalciningtemperature
increasing procedure is not particularly limited, and is
preferablyfromabout lhourtoabout 25 hours, more preferably
from about 2 hours to about 20 hours.
[0148] The heating atmosphere in the second calcining
temperature increasing procedure is not particularly limited
either, andmaybe any ofthe foregoingatmospheres. The inert
gas-containing atmosphere is preferred, and the argon
gas-containingatmosphere ismore preferred. In this way, the
magnetic metal powder can be efficiently sintered while
suppressing oxidation and denaturing of the magnetic metal
powder.
[01491 In this calciningtemperature increasing procedure,
it is preferable to improve the gas exchange efficiency and
promote discharge of the unwanted products by continuously
supplying (flowing) inert gas into the space where the
degreased body is disposed, because the procedure involves
generation of materials, for example, such as the carbon
monoxide produced by the binding of the oxygen atom and the
carbon atom.
[01501 In this case, the atmosphere pressure may be
atmospheric pressure or higher pressure. However,
considering cost and other factors, the atmosphere pressure
ispreferablyataboutatmosphericpressure (for example, about
50 kPa to about 200 kPa) .
Third Calcining Temperature Increasing Procedure
[01511 In the third calcining temperature increasing
procedure, the degreased body is heated at a temperature of
1,050°Cormore. Inthis temperature range, themagneticmetal
powder is brought to the final sinter state to produce the
sintered body. The maximum heating temperature is
appropriately set according to the composition of the magnetic
metal powder. As an example, the maximum heating temperature
is set to from about 1,050°C to about 1,400°C.
[01521 The heating time in the third calcining temperature
increasing procedure is not particularly limited, and is
preferably from about lhourto about 25 hours, more preferably
from about 2 hours to about 20 hours.
[01531 The heating atmosphere in the third calcining
temperature increasing procedure is not particularly limited
either, andmaybe any of the foregoingatmospheres. The inert
gas-containing atmosphere is preferred, and the argon
gas-containingatmosphereismorepreferred. In this way, the
same effects described above can be obtained.
[01541 In this calciningtemperatureincreasingprocedure,
it is preferable to confine inert gas in the space where the
degreased body is disposed. In this way, the elements do not
easily undergo vaporization, and unintended changes in the
composition of the magnetic metal powder can be suppressed by
the calcining temperature increasing procedure performed in
the confined inert gas-containing atmosphere, even when, for
example, the magnetic metal powder contains elements, such as
Cr, having a relatively high vapor pressure.
[01551 In this case, the atmosphere pressure may be at
atmospheric pressure or higher pressure. However,
considering cost and other factors, the atmosphere pressure
is preferablyataboutatmosphericpressure (for example, from
about 50 kPa to about 200 kPa) . '
First Calcining Temperature Decreasing Procedure
[01561 The sintered body is cooled after the
above-mentioned temperature increasing procedures. The
temperature decreasing procedure is not particularly limited,
and preferably includes a first calcining temperature
decreasing procedure and second calcining temperature
decreasing procedure performed after the first calcining
temperature decreasing procedure.
[0157] In the first calcining temperature decreasing
procedure, the sinteredbodyisplacedunderareducedpressure
atmosphere. This prevents the sintered body and the oxygen
and nitrogen gases from contacting each other, and thus
prevents contamination of the sintered body. Contamination
in the calcining apparatus also can be prevented. Further,
by beingplace din a reducedpressure atmosphere, the sintered
body immediately after the sintering can be prevented from
rapid temperature decrease. In this way, defects such as
contamination, cracking, and deformation of the sintered body
can be suppressed. The temperature may be gradually lowered
while applying heat to the sintered body, as needed.
[01581 The reduced pressure atmosphere is preferably a
reduced pressure atmosphere of inert gas.
[01591 The pressure of the reduced pressure atmosphere is
not particularly limited either, and is preferably from about
Pa to about 10 kPa, more preferably from about Pa to
about1kPa. In this way, an appropriate temperature dropping
rate can be realized while preventing contamination of the
sinteredbody, andahigh-qualitysinteredbodycanbeproduced
48
in a short time period.
[01601 The cooling time in the first calcining temperature
decreasing procedure is not particularly limited, and is
preferably from about 1 min to about 1 hour, more preferably
from about 3 min to about 30 min.
Second Calcining Temperature Decreasing Procedure
[01611 In the second calcining temperature decreasing
procedure, the sintered body is placed in an inert gas
atmosphere. In this way, coolingofthe sinteredbodyproceeds
by theheat exchange with theatmosphere. Further, usinginert
gas prevents oxidation of the sinteredbody, and contamination
inside the calcining apparatus. Further, in this case,
heat-exchange efficiency can be improved by continuously
supplying (flowing) or circulating the inert gas in the space
where the sintered body is disposed.
[01621 By cooling the sinteredbodytoordinarytemperature
in this calcining temperature decreasing procedure, the
sintered body will not be oxidized even in contact with the
atmosphere.
[01631 The sinteredbodyisproducedinthemannerdescribed
above.
The product sintered body expected have a
relative density of, for example, 95% or more, preferably 96%
or more. The sintered body has high sinter density, and has
excellent appearance and dimensional accuracy
[01651 The product s i n t e r e d body may be subjected to
post-processes, forexample, suchasmachining (e.g.,c utting,
pressing, polishing), discharge process, laser process, and
etching. the post-processesmaybeperformed forthe purposes
of burring, or further improving dimensional accuracy.
[01661 Further, the product sintered body may be subjected
to processes such as HIP (hot isostatic press) process, as
needed. In this way, the sint'ered body can have even higher
density.
[01671 The HIP process may be performed, for example, at
a temperature of from 850°C to 1, 100°C for from 1 hour to 10
hours.
101681 Applied pressure is preferably 50 MPa or more, more
preferably 100 MPa or more.
[01691 The sintered body obtained as above may be used in
any applications. Examples include various structural
components, and various medical structures.
[01701 The figure shows a yoke case as an application
example of the sintered body produced by the embodiment of the
invention, in which A is a plan view, and B is a cross sectional
view at X-X.
[01711 The yoke case 1 shown in the figure includes an
annular plate-like case main body 10 having a through hole 101
penetrating through a central portion in planar view, an edge
portion 11 provided at the outer edge and the inner edge of
the case main body 10, and having a thicker thickness than the
casemainbody10, atotalof twelve cores12 arrangedatregular
intervals along the inner edge between the outer edge and the
inner edge of the case main body 10, and having a thicker
thickness thanthe casemainbody10, andapluralityof through
holes 13 scattered between the outer edge and the inner edge
of the case main body 10 and penetrating through the case main
body 10.
101721 The yoke case 1 is configured from a sintered body
of a soft magnetic metal powder. Upon providing a coil for
eachcore12, the yoke case1 forms apart of amagnetic actuator.
The yoke case 1 thus requires very high dimensional accuracy.
LO1731 Though the invention has been described with
reference to the preferred embodiments, the invention is in
no way limited by the foregoing descriptions. For example,
the degreasing step may further include a degreasing
temperature increasing procedure and a degreasingtemperature
decreasing procedure as needed, and a degreasing temperature
increasing procedure may be provided after a degreasing
temperature decreasing procedure. Similarly, the calcining
step may further include a calcining temperature increasing
procedure and a calcining temperature decreasing procedure,
and a calcining temperature increasing procedure may be
provided after a calcining temperature decreasing procedure.
Examples
to1741 Specific examples of the invention are described
below.
1. Sintered Body Production
Example 1
LO1751 First, a magnetic metal powder configured from a 49
mass% Fe-49 mass% Co-2 mass% V alloy (permendur) was prepared.
The magnetic metal powder was measured for average particle
diameter using a laser diffraction particle size distribution
measurement device (Microtrack; Nikkiso Co., Ltd.;
HRA9320-X100) . The measurement result is presented in Table
1.
LO1761 Then, an unsaturated glycidyl group-containing
polymer (first resin), a styrene resin (second resin), and a
paraffinwaxwere freeze pulverizedto obtain abinderpowder.
CO1771 The magnetic metal powder, the binder powder, and
a phthalic acid ester were mixed, and kneaded with a pressure
kneader at a knead temperature of 160°C for 30 min. Kneading
was performed in a nitrogen gas atmosphere.
[01781 Then, thekneadedproduct (composition for injection
molding) was pulverized with a pelletizer to obtain a pellet
having an average particle diameter of 5 mm.
[01791 The pellet was then used for molding, which was
performed with an injection molding device under a material
temperature of 19O0C, and an injection pressure of 10.8 MPa
(110 kgf/cm2). As a result, a molding was obtained.
[01801 The molding was subjected to a degreasing process
under the following conditions to obtain a degreased body.
Degreasing Conditions
- First degreasing temperature increasing procedure:
temperature 70°C; 3 hours; nitrogen-containing atmosphere
- Second degreasing temperature increasing procedure:
temperature 260°C; 12 hours ; nitrogen reduced pressure
atmosphere
- Third degreasing temperature increasing procedure:
temperature 475°C; 5 hours; nitrogen-containing atmosphere
- Degreasing temperature decreasing procedure: forced
cooling; 8 hours; nitrogen-containing atmosphere
[01811 The resulting degreased body was subjected to a
calcining process under the following conditions to obtain a
sintered body.
Calcining Conditions
- First calcining temperature increasing procedure:
temperature 650°C; 7 hours; nitrogen reduced pressure
atmosphere
- Second calcining temperature increasing procedure:
temperature l,OOO°C; 5 hours; argon-containing atmosphere
- Third calcining temperature increasing procedure:
temperature l,lOO°C; 8 hours; argon-containing atmosphere
- First calcining temperature decreasing procedure:
temperature 700°C; 3 min; argon reduced pressure atmosphere
- Second calcining temperature decreasing procedure: forced
cooling, 1 hour; argon-containing atmosphere
[01821 The sintered body was obtained as an annular
plate-like body (yoke case) as shown in the figure, and had
an outer diameter of 35 mm, an inner diameter of 10 mm, and
a maximum thickness of 5 mm.
Examples 2 to 6
LO1831 Sintered bodies were obtained in the same manner as
in Example 1, except that the magnetic metal powders and the
organicbinders showninTablelwereused, and that the organic
bindercontentwithrespectto100partsbymass ofthemagnetic
metal powder was changed to the values presented in Table 1.
Comparative Examples 1 to 7
lo1841 Sintered bodies were obtained in the same manner as
in Example 1, except that the magnetic metal powders and the
organic binders showninTable 2 wereused, and that the organic
bindercontentwithrespectto100partsbymass ofthemagnetic
metal powder was changed to the values presented in Table 2.
[0185] In Tables 1 and 2, the following notation was used
for each component of the organic binder. Note that in the
unsaturated glycidyl group-containing polymer, E represents
a repeating unit containing ethylene, GMA represents a
repeating unit containing glycidyl methacrylate, VA
represents a repeating unit containing vinyl a c e t a t e , and MA
represents a repeating unit containing methylacrylate.
Unsaturated Glycidyl Group-Containing Polymer
- GMA-1: E-GMA-VA copolymer (degradation temperature 310°C)
- GMA-2: E-GMA copolymer
- GMA-3: E-GMA-MA copolymer (degradation temperature 280°C)
Styrene Resin
- PS: polystyrene (weight-average molecular weight 10,000;
degradation temperature 350°C)
Waxes
- PW-1: paraffin wax (degradation temperature 260°C)
- PW-2: paraffin wax (degradation temperature 230°C)
Phthalic Acid Ester
- DBP: dibutyl phthalate
[0186] The melt flow rates of the unsaturated glycidyl
group-containing polymer were 7 g/10 min for GMA-1, 3 9/10 rnin
for GMA-2, and 7 g/10 rnin for GMA-3.
2. Evaluation of Sintered Body
2.1 Evaluation of Sinter Density
[0187] The density of each sintered body obtained in
Examples and Comparative Examples was measured by using a
method according to the Archimedes method (specified by JIS
Z 2501). The relative density of the sintered body was
calculated from the measured sinter density and the true
density of the magnetic metal powder.
2.2 Appearance Evaluation
lo1881 The appearance of each sintered body (100 samples
of each sintered body) obtained in Examples and Comparative
Examples was evaluated according to the following evaluation
criteria.
Appearance Evaluation criteria
Excellent: Cracking, damage, and deformation in at most
three samples
Good: Cracking, damage, and deformation in 4 to 10
samples
Acceptable: Cracking, damage, and deformation in 11 to
50 samples
Poor: Cracking, damage, and deformation in 51 samples
or more.
2.3 Evaluation of Dimensional Accuracy
[0189] Theouter diameterof eachsinteredbody (100 samples
of each sintered body) obtained in Examples and Comparative
Examples was measured with a micrometer. The mean value of
the measured values was then evaluated using the I1Permissible
Deviations in Width without Tolerance IndicationI1 specified
in JIS B 0411 (Permissible Deviations in Dimensions without
Tolerance Indication for Metallic Sintered Products)
according to the following evaluation criteria.
Dimensional Accuracy Evaluation Criteria
Excellent: High grade (tolerance k 0.05 mm or less)
Good: Middle grade (tolerance above k 0.05 mm and * 0.1
mm or less)
Acceptable: Moderate grade (tolerance above + 0.1 mm and
+ 0.2 mm or less)
Poor: Outside of the tolerance range
[01901 The evaluation results are presented in Tables 1 and

Table 1 (Continued)
Magnetic
metal powder
Proportion
particle
diameter
/ 30 or more I 4.2 1 3.2 I
Particle
diameter of when
the cumulative
mass takes the
values on the
right
/ 20 or more and
I less than 30
Example 3
Particle diameter [pm]
3.9
8.9
23.6
Proportion [mass %I
Cumulative
mass [mass%]
10 (10D)
50 (50D)
90 (90D)
Particle
diameter rum1
Example 4
Particle diameter [pm]
3.2
8.1
20.8
Proportion [mass%]
10 or more and
less than 20
Organic
binder
29.8
I
28.5
I Less than 10
Unsaturated glycidyl
group-containing polymer
S tvrene resin
Phthalic acid ester
Binder amount with respect to 100 mass parts of
metal powder [mass parts]
Waxes I PW-1 I 60
, Sienvtaelrueadt iboond y
DBP I
1 results
I
56.4
30 I PW-2 I 55
Relative
density
Appearance
me
GMA - 2
PS
60.3
30
14
Dimensional I -
accuracy
7.9
9-
-
Softening
point [OC]
103
120
content
25
32
me
GMA- 1
PS
7.3
DBP I
Good
content
27
35
Softening
point [OC]
95
120
13
97.3
Good
Excellent
98.1
Excellent
Table 1 (Continued)
/ Magnetic 1 metal powder 1
Particle
diameterof when
the cumulative
mass takes the
values on the
Proportion by
particle
diameter
Cumulativemass
[mass%]
10 (10D)
50 (50D)
90 (90D)
Particle
diameter [p]
Particle diameter [pm]
2.0
5.8
14.3
30 or more
Particle diameter [p]
4.9
9.6
26.8
Proportion [mass%]
20 or more and
less than 30
Proportion [mass%]
1.3 I
10 or more and
less than 20
Less than 10
Organic
binder
4.8 I
4.6
I
I
11.8 I
30.0
64.1
Unsaturated qly
28.1
55.3
Softening Content
- - cidyl
group-containinq polymer
Type
Styrene resin
Waxes
Phthalic acid ester
GMA- 1
Softening
point [ O C I
PS
PW-1
DBP
Binder amount with respect to 100 mass parts of
metal powder [mass parts]
evaluation - I Appearance
results I Dimensional
I accuracy
Content
95
5.5
97.6
12 0
60
8.2
97.5 !
I
%
Sintered body
-
-
28
Relative
density
33
23
16
Good
Excellent
GMA- 3
Good
Good 1
PS
PW-2
DBP
52 28
12 0
55
32
26
14
[sqxed sseu] / xap~odp qam 20 sqxed sseu 0 0 0~2 wadsax 4 2 i ~2u now-e xapura
OZ uey3
ssaT pue
I [ % s sew]
[ud] xaqam-erp a 7 : 2 ~ q ~ e d [uri] xaqau~rp a ~ ~ r 7 x e d I

Table 2 (Continued)
Magnetic
metal powder
Organic
binder
Particle diameter of
when the cumulative
mass takes the values on
the right
[pml
Comparative Example 5
Particle diameter [pm]
3.2
8.1
19.9
Proportion [mass%]
Cumulative
mass
[mass %I
10 (10D)
50 (50D)
90 (90D)
Particle
diameter
30 or more / 2.3
Proportion by particle
diameter
Cornpara t ive Example 6
Particle diameter [pm]
2.0
5.8
14.3
Proportion [mass%]
1.3 I
10 or more
and less
than 20
Less than
10
Unsaturated glycidyl
group-containing polymer
I
20 or more
and less
than 30
Stvrene resin I P S 1 120 1 5 6 1 P S I 12 0 1 33 1
Waxes
Phthalic acid ester
Binderamountwithrespectto100massparts of metal
powder [mass parts]
7.5
29.6
60.6
PW-1
DBP
4.6
30.0
64.1
Type
-
o,
-
-
Sintered body
evaluation
results
Type
GMA- 1
60
Relative density
~ppearance
Dimensional accuracy
Softening
point
["CI
7.5
91.4
Poor
Poor
So£ tening
point
["CI
95
Content
-
2.6
97-5
Acceptable
Poor
28
16
Content
28
PW- 1
DBP
60 23
16

[0191] As is clear from Tables 1 and 2, the sintered bodies
obtainedin Examples all had high sinter densities. Further,
the sintered bodies obtained in Examples had excellent
appearance and dimensional accuracy. Specifically, the
moldings obtained in Examples had high shape-retainability
[01921 On the other hand, the sinter density was low, and
the appearance or dimensional accuracy was inferior in some
of the sintered bodies obtained in Comparative Examples.
[0193] The molding and the degreasedbodywere measured for
dimensions, and the rate of shrinkage against degreasing was
measured. It was found as a result that the rate of shrinkage
correlatedwiththe organic binder content. For example, the
rate of shrinkage was greater for larger organic binder
contents with respect to the metal powder, and was smaller for
smaller organic binder contents.
[01941 In each sintered body, a coil was attached to the
core, and current was flown through the coil to measure and
compare the magnetic properties of the cores. It was found
that themagnetic properties were higher inall of the sintered
bodies obtained in Examples than in the sintered bodies
obtainedinComparativeExamples. Specifically, theironloss
and the cohesive force were smaller, and the magnetic flux
density was larger. Sintered bodies with higher sinter
densities had higher magnetic properties.
[01951 The trend in the results for the examples that used
thepermendurwas alsoobservedwhentheperrnendurwas replaced
with pure iron, silicon steel, sendust, and permalloy.
CO1961 Further, the trend in the results obtained with the
styrene resin was also observed when sintered bodies were
produced in the same manner as in Examples and Comparative
Examples except for using polypropylene (softening point
130°C) instead of the styrene resin.
2.4 Evaluation of Sinter Uniformity
[01971 Each sintered body obtained in Examples and
Comparative Examples was measured for Vickers hardness on the
core surface of the yoke case shown in the figure. A
distribution range was calculated from twelve measurement
values for each sintered body, and these distribution ranges
were compared between the sintered bodies.
[01981 The distribution range of Vickers hardness was
narrowerinthe sinteredbodiesof Examplesthaninthe sintered
bodies of Comparative Examples. The result thus demonstrated
that the sintered bodies obtained in Examples had higher
uniformity than the sintered bodies obtained in Comparative
Examples.
[01991 A magnetic actuator was produced by using each yoke
case obtained in Examples and Comparative Examples. In the
magnetic actuator, a coil was provided for each core of the
yoke case, and current was flowed through the coil to generate
magnetic force i n the core, and to drive the pin disposed in
each core. Thus, twelve pins are disposed in the yoke case
shown in the figure.
[0200] The driving force of driving the twelve pins was
measured. The distribution range of driving force was also
narrower in the yoke cases of Examples than in the yoke cases
obtained in Comparative Examples.

What is claimed is:
1. A composition for injection molding, comprising:
a magnetic metal powder that contains any of Fe, Ni, and
Co as a main component, and that has a mass-based particle size
distribution in which a particle diameter DIO at 10% cumulative
mass is 2 |.im or more and less than 5 f.im, a particle diameter
D50 at 50% cumulative mass is from 5 fj.m to 10 ).im, and a particle
diameter D90 at 90% cumulative mass is from 12 |.im to 28 f.im;
and
an organic binder that contains a first resin configured
from an unsaturated glycidyl group-containing polymer, and a
second resin having a higher softening point than the first
resin,
wherein the content of the organic binder ranges from
3 parts by mass to 9 parts by mass with respect to 100 parts
by mass of the magnetic metal powder.
2. The composition for injection molding according to
claim 1, wherein, in the magnetic metal powder, particles
having a particle diameter less than 10 ]im account for 55 mass%
or more, particles having a particle diameter of 20 |.im or more
and less than 3 0 }im account for more than 0 raass% and less than
15 mass%, and particles having a particle diameter of 3 0 \,\.m
or more account for more than 0 mass% and less than 5 mass%,
69
and the remaining part has a particle diameter of 10 |.im or more
and less than 2 0 |.im.
3. The composition for injection molding according to
claim 1, wherein the first resin and the second resin have a
softening point difference of from 10°C to 100°C.
4. The composition for injection molding according to
claim 1, wherein the unsaturated glycidyl group-containing
polymer is a copolymer that contains an unsaturated glycidyl
group-containing monomer and an ethylenic unsaturated ester
compound monomer.
5. The composition for injection molding according to
claim 1, wherein the unsaturated glycidyl group-containing
polymer is a copolymer that contains an unsaturated glycidyl
group-containing monomer and a nonpolar a-olefinic monomer.
6. The composition for injection molding according to
claim 1, wherein the unsaturated glycidyl group-containing
polymer has a softening point of from .65°C to 105°C.
7. The composition for injection molding according to
claim 1, wherein the organic binder further contains a wax.
70
8. The composition for injection molding according to
claim 1, wherein the organic binder further contains a phthalic
acid ester.
9. The composition for injection molding according to
claim 1, wherein the mass content of the second resin in the
organic binder is from 80 mass% to 150 mass% of the first resin.
10. The composition for injection molding according to
claim 1, wherein a total of the first resin and the second resin
accounts for 50 mass% or more in the organic binder.
11. A sintered body producing process comprising:
kneading a magnetic metal powder and an organic binder
to obtain a kneaded product, the magnetic metal powder
containing any of Fe, Ni, and Co as a main component, and having
a mass-based particle size distribution in which a particle
diameter DIO at 10% cumulative mass is 2 |.im or more and less
than 5 |.im, a particle diameter D50 at 50% cumulative mass is
from 5 |,im to 10 ).im, and a particle diameter D90 at 90% cumulative
mass is from 12 |am to 28 |.im, the organic binder containing a
first resin configured from an unsaturated glycidyl
group-containing polymer, and a second resin having a higher
softening point than the first resin;
molding the kneaded product to obtain a molding; and
71
degreasing and calcining the molding to obtain a sintered
body.