U.S. patent application number 11/391279 was filed with the patent office on 2006-10-19 for plating solution, conductive material, and surface treatment method of conductive material.
This patent application is currently assigned to TDK Corporation. Invention is credited to Keiichi Fukuda, Hiroyasu Morikawa, Takeshi Sakamoto, Yasuyuki Yamamoto.
Application Number | 20060231409 11/391279 |
Document ID | / |
Family ID | 37107446 |
Filed Date | 2006-10-19 |
United States Patent
Application |
20060231409 |
Kind Code |
A1 |
Sakamoto; Takeshi ; et
al. |
October 19, 2006 |
Plating solution, conductive material, and surface treatment method
of conductive material
Abstract
A plating solution including a copper salt, an organic
phosphonic acid compound, and at least one compound or ions
selected from an amine, .alpha.-amino acid, ammonium ions, carbonic
acid ions, carboxylic acid ions, dicarboxylic acid ions, sulfuric
acid ions, and thiosulfuric acid ions and a method of treating the
surface of a conductive material using this plating solution.
Inventors: |
Sakamoto; Takeshi; (Tokyo,
JP) ; Morikawa; Hiroyasu; (Tokyo, JP) ;
Yamamoto; Yasuyuki; (Tokyo, JP) ; Fukuda;
Keiichi; (Tokyo, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
TDK Corporation
Tokyo
JP
|
Family ID: |
37107446 |
Appl. No.: |
11/391279 |
Filed: |
March 29, 2006 |
Current U.S.
Class: |
205/292 |
Current CPC
Class: |
H01F 41/026 20130101;
C25D 3/38 20130101; C25D 7/001 20130101; H01F 41/26 20130101 |
Class at
Publication: |
205/292 |
International
Class: |
C25D 3/38 20060101
C25D003/38 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2005 |
JP |
2005-103537 |
Mar 15, 2006 |
JP |
2006-071010 |
Claims
1. A plating solution including: a copper salt, an organic
phosphonic acid compound, and at least one compound or ions
selected from an amine, .alpha.-amino acid, ammonium ions, carbonic
acid ions, carboxylic acid ions, dicarboxylic acid ions, sulfuric
acid ions, and thiosulfuric acid ions.
2. The plating solution as set forth in claim 1, wherein the
content of said compound or ions is, converted to said compound or
ions, 0.01 to 2 mol/liter.
3. The plating solution as set forth in claim 1, wherein said
plating solution has a pH of 8 to 12 in range.
4. The plating solution as set forth in claim 1, wherein said
plating solution further includes at least one type of compound
selected from a phosphoric acid compound and hydroxide.
5. A method of treating the surface of a conductive material
comprising using a plating solution as set forth in claim 1 and an
anode containing copper for electrolytic plating to form a
protective film comprised of copper on the surface of the
conductive material.
6. The method of treating the surface of a conductive material as
set forth in claim 5 wherein said conductive material is a rare
earth magnet.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a plating solution, a
method of treating the surface of a conductive material using this
plating solution, and a conductive material treated on its surface
by this surface treatment method.
[0003] 2. Description of the Related Art
[0004] Permanent magnets, which is one type of conductive material,
are being widely used for motors and actuators of various types of
equipment. As such permanent magnets, Sm--Co-based rare earth
permanent magnets obtained by powder metallurgy are being mass
produced due to their relatively high performance. However, such
Sm--Co-based rare earth permanent magnets have the problem of using
as materials the expensive Sm and Co, so end up becoming high in
cost.
[0005] Among the rare earth, the smaller atomic weight rare earth
elements such as cerium (Ce), praseodymium (Pr), and neodymium (Nd)
are present more abundantly than samarium (Sm) and are relatively
low in price. Further, iron (Fe) is also inexpensive.
[0006] Therefore, in recent years, relatively inexpensive materials
have been used to develop and commercialize Nd--Fe--B-based rare
earth permanent magnets having magnetic performances equal to or
better than Sm--Co-based rare earth permanent magnets.
[0007] However, such permanent magnets include as main ingredients
easily oxidizable rare earth elements and iron, so have relatively
low corrosion resistances, are degraded in performance, and have
problems in production variance. For this reason, various methods
have been proposed for coating the magnet bodies with copper
plating films (for example, Japanese Patent Publication (A) No.
60-54406, Japanese Patent Publication (A) No. 1-286407, and
Japanese Patent Publication (A) No. 8-3763).
[0008] For example, Japanese Patent Publication (A) No. 60-54406
discloses to plate the surface of an R--Fe--B-based permanent
magnet (where, R is a Y element or a rare earth element) with a
oxidation resistant plating film so as to suppress the formation of
oxides on the surface. Specifically, a Cu+Ni plating is used. By
using a copper cyanide solution as the copper base, a superior
oxidation resistant permanent magnet is obtained. However, this
publication uses copper cyanide for the plating bath, so has the
problems of a weak adhesion between the magnet body and the plating
film and a lack of reliability.
[0009] On the other hand, Japanese Patent Publication (A) No.
1-286407 discloses electrolytic plating in a copper pyrophosphate
plating bath so as to form a copper plating film on the surface of
the R--Fe--B-based permanent magnet. However, this publication uses
a copper pyrophosphate plating bath, so has the problem that the
R--Fe--B-based permanent magnet with the greater tendency for
ionization than copper dissolves by immersion and the
R--Fe---B-based permanent magnet ends up being corroded at its
surface.
[0010] Further, Japanese Patent Publication (A) No. 8-3763
discloses successively treating the surface of a magnet by
electroless Cu plating, electrolytic Cu plating, and electrolytic
Ni and P alloy plating to form multiple plating films and thereby
improve the R--Fe--B-based permanent magnet in corrosion
resistance. However, a Nd--Fe--B-based permanent magnet suitably
used as a rare earth magnet has the property of hydrogen
embrittlement, so ends up breaking due to the hydrogen gas produced
by the electroless Cu plating and therefore a plating film with
good pore sealability cannot be obtained.
[0011] As opposed to this, the assignee previously proposed in
Japanese Patent No. 3614754 the method of using as the plating
solution for forming the Cu plating film a plating solution
containing an aliphatic phosphonic acid. With this method, by using
a plating solution containing an aliphatic phosphonic acid, it is
possible to improve the formability of the Cu plating film and
improve the adhesion, corrosion resistance, and heat
resistance.
[0012] However, in this Japanese Patent No. 3614754, there is the
problem that in the actual production process, if using the same
plating solution for repeated plating, the plating solution ends up
deteriorating and the color of the Cu changes from a skin color to
a dark brown color. For this reason, with the method disclosed in
this publication, for example, it is necessary to replace the
plating solution with a new solution (a plating solution not
previously used for plating) about once every several dozen batches
for plating. This has become a cause of higher cost,
SUMMARY OF THE INVENTION
[0013] An object of the present invention is to provide a plating
solution able to form a protective film superior in adhesion,
corrosion resistance, and heat resistance on the surface of a
magnet or other conductive material and able to stably form a
protective film having a high adhesion and a good appearance even
with repeated plating, a method of treating the surface of a
conductive material using this plating solution, and a conductive
material obtained by this method.
[0014] The inventors engaged in intensive studies to achieve the
above object and as a result discovered that by adding a
predetermined compound or ions to a plating solution including a
copper salt and organic phonic acid compound, the above object can
be achieved and thereby completed the present invention.
[0015] That is, the plating solution according to the present
invention includes a copper salt,
[0016] an organic phosphonic acid compound, and
[0017] at least one compound or ions selected from an amine,
.alpha.-amino acid, ammonium ions, carbonic acid ions, carboxylic
acid ions, dicarboxylic acid ions, sulfuric acid ions, and
thiosulfuric acid ions.
[0018] In the plating solution of the present invention, the
content of the compound or ions is, converted to the compound or
ions, preferably 0.01 to 2 mol/liter. If the content of the
compound or ions is too low, the effect of the present invention
ends up becoming small. On the other hand, if too great, uneven
plating tends to easily occur.
[0019] The plating solution of the present invention is preferably
alkaline, specifically preferably has a pH of 8 to 12 in range.
[0020] The plating solution of the present invention preferably
further includes at least one type of compound selected from a
phosphoric acid compound and a hydroxide.
[0021] The method of treating the surface of a conductive material
according to the present invention comprises using any of the above
plating solutions and an anode containing copper for electrolytic
plating to form a protective film comprised of copper on the
surface of the conductive material.
[0022] The conductive material of the present invention is a
conductive material obtained by surface treatment by the above
method.
[0023] In the present invention, the conductive material is not
particularly limited so long as it is a material comprised of a
material having conductivity, but preferably is a metal, more
preferably a metal magnet, furthermore preferably a rare earth
magnet. As the rare earth magnet, for example, an R--Fe--B-based
rare earth magnet including R (where R is a Y element or a rare
earth element), Fe, and B may be mentioned, in particular an
Nd--Fe--B-based rare earth permanent magnet may be preferably
mentioned.
[0024] The plating solution of the present invention contains a
copper salt and an organic phosphonic acid compound, so for example
when using the plating solution of the present invention and an
anode containing copper to form a protective film comprised of
copper on the surface of a conductive material, it is possible to
form a protective film superior in adhesion and improve the
corrosion resistance and heat resistance of the conductive
material.
[0025] Further, the plating solution of the present invention
contains, in addition to the copper salt and organic phosphonic
acid compound, the predetermined compound or ions. For this reason,
even if repeatedly plating, it is possible to stably form a
protective film having a high adhesion and further a good
appearance.
[0026] Further, the surface treatment method of the present
invention uses the plating solution of the present invention and an
anode containing copper. For this reason, the conductive material
may be stably formed on its surface with a protective film having a
high adhesion and further a good appearance.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] Below, embodiments of the present invention will be
explained. In the present embodiment, the method of treating the
surface of a permanent magnet using the plating solution of the
present invention will be explained.
[0028] Permanent Magnet
[0029] First, the permanent magnet, a type of conductive material,
will be explained.
[0030] The permanent magnet is not particularly limited, but an
R--Fe--B-based rare earth magnet including R (where, R is one or
more rare earth elements including Y), Fe, and B is preferable. In
this R--Fe--B-based rare earth magnet, the contents of R, Fe, and B
are preferably 5.5 atomic %.ltoreq.R.ltoreq.30 atomic %, 42 atomic
%.ltoreq.Fe.ltoreq.90 atomic %, 2 atomic %.ltoreq.B.ltoreq.28
atomic %.
[0031] In particular, when producing a permanent magnet by the
sintering method, the following composition is preferable.
[0032] As R, one or more of Nd, Pr, Dy, Ho, and Tb or further one
or more of La, Sm, Ce, Gd, Er, Eu, Pm, Tm, Yb, Lu, and Y is
preferably included.
[0033] Note that when using two or more elements as R, as the
material, it is preferable to use a Misch metal or other
mixture.
[0034] R has a content of preferably 5.5 to 30 atomic %.
[0035] If R is too low in content, the crystal structure of the
magnet becomes a cubic crystal structure of the same structure as
.alpha.-Fe and a high coercive force (iHc) cannot be obtained,
while if too great, a R-rich nonmagnet phase increases and the
residual magnetic flux density (Br) falls.
[0036] Fe has a content of preferably 42 to 90 atomic %.
[0037] If Fe is too low in content, Br drops, while if too great,
the iHc falls,
[0038] B has a content of preferably 2 to 28 atomic %.
[0039] If B is too low in content, the crystal structure of the
magnet becomes rhombohedral structure, so the coercive force (iHc)
becomes insufficient, while if too great, the B-rich nonmagnetic
phase increases and the residual magnetic flux density (Br)
falls.
[0040] Note that it is possible to replace part of the Fe with Co
to improve the temperature characteristic without impairing the
magnetic characteristic. In this case, if the amount of Co
substitution exceeds 50 atomic % of the Fe, the magnetic
characteristic deteriorates, so the amount of Co substitution is
preferably 50 atomic % or less.
[0041] Further, in addition to R, Fe, and B, the magnet may contain
as unavoidable impurities Ni, Si, Al, Cu, Ca, etc. of 3 atomic % of
the total or less.
[0042] Further, it is possible to substitute part of B by one or
more of C, P, S, and Cu to realize an improvement of productivity
and lower cost. In this case, the amount of substitution is
preferably 4 atomic % of the total or less. Further, for
improvement of the coercive force, improvement of the productivity,
and reduction of the cost, one or more of Al, Ti, V, Cr, Mn, Bi,
Nb, Ta, Mo, W, Sb, Ge, Sn, Zr, Ni, Si, Hf, etc. may be added. In
this case, the amount of addition is preferably made, in total, 10
atomic % or less.
[0043] The permanent magnet in the present embodiment has a
substantially cubic crystal structure main phase. This main phase
has a particle size of preferably 1 to 100 .mu.m or so. Further,
usually, it includes a nonmagnetic phase of a volume ratio of 1 to
50%.
[0044] The permanent magnet is preferably produced by the following
powder metallurgy method.
[0045] First, the metals or alloy forming the materials are mixed
to give the desired composition. Next, the mixed materials are
melted in a vacuum or inert gas atmosphere, then cast to obtain an
alloy of the desired composition. The casting method is not
particularly limited, but for example, the strip cast method etc.
may be mentioned. The "strip cast method" is the method of
supplying the melted liquid state alloy to a roll and continuously
casting it into an alloy sheet. The alloy obtained by the casting
does not necessarily have to be a single alloy having the final
Composition. For example, it may also be a mixture of several types
of alloys different in composition. Further, the alloy is not
particularly limited in shape. It does not necessarily have to be a
sheet and, for example, may also be an ingot.
[0046] Then, the obtained alloy is crushed using a jaw crusher etc.
to pieces of alloy of 5 to 100 mm square sizes. The obtained pieces
of alloy are made to store hydrogen. Next, the hydrogen-storing
pieces of alloy are roughly pulverized to obtain alloy powder. Note
that in the rough pulverization, by making the pieces of alloy
store hydrogen in advance, it is possible to cause pulverization
from the surface in a self-decay like manner. After this, the
obtained alloy powder is heat treated to remove the hydrogen.
[0047] Next, the dehydrogenated alloy powder has added to it a
pulverization aid in an amount of 0.03 to 0.4 wt % or so. By adding
the pulverization aid, it is possible to reduce the amount of
residual carbon after sintering and possible to improve the
magnetic characteristics. Note that the pulverization aid is not
particularly limited, but for example a fatty acid-based compound
may be used.
[0048] Next, the pulverization aid-containing alloy powder is
finely pulverized using a jet mill etc. The fine pulverization is
preferably performed until for example the alloy powder is reduced
in particle size to 1 to 10 .mu.m or so, in particular 3 to 6 .mu.m
or so.
[0049] Next, the finely pulverized powder is shaped, preferably in
a magnetic field, to obtain a shaped product. In this case, a
magnetic field strength of 400 to 1600 kA/m or so and a shaping
pressure of 50 to 500 MPa or so are preferable.
[0050] The obtained shaped product is sintered at 1000 to
1200.degree. C. for 0.5 to 5 hours and rapidly cooled. After this,
it is heat treated, preferably in an inert gas atmosphere, at 500
to 900.degree. C. for 1 to 5 hours (aging treatment). Note that the
steps before this heat treatment (aging treatment) are preferably
performed in a vacuum or in an Ar gas or other nonoxidizing gas
atmosphere to prevent oxidation.
[0051] When the thus produced permanent magnet has for example an R
comprised of Nd, it is particularly superior in magnetic
characteristics, and is known to have a negative heat expansion
coefficient in a direction perpendicular to the C-axis. The thus
obtained permanent magnet is formed on its surface with a
protective film comprised of copper using the following plating
solution of the present invention.
[0052] Below, the method of forming a protective film on the
permanent magnet will be explained.
[0053] Formation of Protective Film
[0054] In the present embodiment, above the permanent magnet is
electroplated on its surface using the plating solution of the
present invention so as to form a protective film comprised of
copper.
[0055] Below, the plating solution of the present invention will be
explained.
[0056] Plating Solution
[0057] The plating solution of the present invention includes a
copper salt,
[0058] an organic phosphonic acid compound, and
[0059] at least one type of compound or ions selected from an
amine, .alpha.-amino acid, ammonium ions, carbonic acid ions,
carboxylic acid ions, dicarboxylic acid ions, sulfuric acid ions,
and thiosulfuric acid ions.
[0060] The plating solution of the present invention contains, in
addition to the copper salt and organic phosphonic acid compound,
the predetermined compound or ions, so when forming a protective
film comprised of copper on the surface of the permanent magnet,
even with repeated plating, it is possible to stably form a
protective film high in adhesion and good in appearance.
[0061] Note that the reason for this is not necessarily clear, but
is believed to be as follows.
[0062] In the past, because organic phosphonic acid forms complex
with copper ion strongly, the color of the copper ends up
deteriorating. As opposed to this, predetermined compound or ions
able to ease that phosphonic acid and copper ion form complex
exist, dissociating the copper ion is easy and plating with
excellent externals becomes possible.
[0063] As the predetermined compound (amine, .alpha.-amino acid),
for example, ethylamine, diethylamine, alanine, glycine, etc. may
be mentioned.
[0064] Further, as the compound forming the predetermined ions
(ammonium ions, carbonic acid ions, carboxylic acid ions,
dicarboxylic acid ions, sulfuric acid ions, and thiosulfuric acid
ions), for example, ammonia, carbonic acid, carboxylic acid,
dicarbonic acid, sulfuric acid, persulfuric acid, thiosulfuric acid
and also their salts may be mentioned. Specifically, sodium
carbonate, acetic acid, copper (II) acetate, formic acid, fumaric
acid, maleic acid, sodium sulfate, ammonium chloride, ammonium
sulfate, oxalic acid, sodium persulfate, etc. may be mentioned.
These may be dissolved in the plating solution to form the
predetermined ions. Note that the copper (II) acetate generates
copper ions in addition to the predetermined ions (acetic acid
ions) in the plating solution. For this reason, this copper (II)
acetate also acts as a copper salt.
[0065] The content of the compound or ions in the plating solution
is, converted to each compound and ions, preferably 0.01 to 2
mol/liter, more preferably 0.1 to 1 mol/liter. If the content of
these compounds or ions is too low, the effect of the present
invention ends up becoming small. On the other hand, if too great,
uneven plating tends to easily occur. Note that for example even
when including as the ions bivalent ions (carbonic acid ions,
dicarboxylic acid ions, sulfuric acid ions, or thiosulfuric acid
ions), the content means not the number of moles considering the
number of charges of these ions, but the number of moles of these
ions themselves.
[0066] The copper salt is not particularly limited so long as it
dissolves in the plating solution and generates copper ions when
the plating solution is completed. As the compound forming this
copper salt, in addition to copper salt itself, an oxide of copper,
a hydroxide of copper, etc. may be mentioned. Specifically, copper
sulfate, copper phosphate, copper chloride, copper phosphonate, or
another copper salt or an oxide of copper or hydroxide of copper
etc. may be mentioned. The content of the copper salt in the
plating solution is, converted to copper ions, preferably 0.1 to
2.0 mol/liter, more preferably 0.2 to 1.0 mol/liter. If the copper
salt is too low in content, the protective film tends to become
difficult to form. On the other hand, it the cop salt is too great
in content, the ratio of the copper ions not formed into complexes
in the plating solution tends to become higher. Note that the
content of the copper salt means the content of the copper salt in
the plating solution as a whole. That is, for example, when using
the copper (II) acetate as the compound forming the acetic acid
ions, not only acetic acid ions, but also copper ions are generated
in the plating solution. In this case, the content of the copper
salt is the content including the copper (II) acetate,
[0067] The organic phosphonic acid compound is not particularly
limited, but for example, DL-1-aminoethyl phosphonic acid,
2-aminoethyl phosphonic acid, aminomethyl phosphonic acid,
tert-butyl phosphonic acid, diethyl cyanophosphonate, dimethyl
phosphonic acid, diethylene triamine pentamethylene phosphonic
acid, hydroxyl iminobismethylene phosphonic acid, hexamethylene
diamine tetramethylene phosphonic acid, phenyl phosphonic acid,
diethyl cyanomethyl-phosphonate, nitrilotris(methylene)
triphosphonic acid, diethyl phenyl-phosphonate, diethyl
vinyl-phosphonate, tetraethyl ethylene-diphosphonate,
ethylenediamine tetramethylene phosphonic acid, dimethyl
(2-oxoheptyl)-phosphonate, dimethyl (2-oxopropyl)-phosphonate,
dimethyl allyl-phosphonate, 1,4-butane diphosphonic acid, dimethyl
2-acetoxyethylphosphonate, diethyl 3,3-dimethyl
cyclohex-1-enyl-phosphonate, methylene diphosphonic acid,
1-hydroxyethane-1,1-diphosphonic acid, diethyl
3,3-dimethyl-cyclopent-1-enyl-phosphonate, diethyl
3-methylcyclohex-1-enyl-phosphonate, diethyl
3-methylcyclopent-1-enyl-phosphonate, aminotrimethylene phosphonic
acid, (1-aminopropyl)phosphonic acid, (1-aminobutyl)phosphonic
acid, (1-aminopentyl)phosphonic acid, (1-aminohexyl) phosphonic
acid, (1-amino-2-methylpropyl)phosphonic acid,
(1-amino-3-methylbutyl)phosphonic acid,
(1-amino-2-methylbutyl)phosphonic acid, (1-aminooctyl)phosphonic
acid, (1-amino-2,2-dimethylpropyl)phosphonic acid,
(1-amino-1-methylethyl)phosphonic acid,
(1-amino-1-methylpropyl)phosphonic acid,
(1-amino-1-methylbutyl)phosphonic acid,
(1-amino-1,2-dimethylpropyl) phosphonic acid,
(1-amino-1,3-dimethylbutyl)phosphonic acid,
(1-amino-1-phenylmethyl)phosphonate,
(1-amino-1-cyclopentyl)phosphonic acid,
(1-amino-1-cyclohexyl)phosphonic acid, 3-aminopropyl phosphonic
acid, dimethyl (2-oxo-4-phenylbutyl)-phosphonate, diethyl
3,3-diethoxypropyl-phosphonate, etc. may be mentioned.
[0068] The content of the organic phosphonic acid compound in the
plating solution is preferably 0.1 to 1.0 ml/liter, more preferably
0.3 to 0.6 mol/liter. If the organic phosphonic acid compound is
too low in content, the protective film which is formed tends to
deteriorate in adhesion. On the other hand, if too great, the
plating solution ends up becoming expensive and the production cost
ends up increasing as a general trend.
[0069] The plating solution of the present invention may contain,
in addition to the above, a phosphoric acid compound or
hydroxide.
[0070] The phosphoric acid compound is not particularly limited,
but for example potassium pyrophosphate, sodium phosphate, calcium
phosphate, etc. may be mentioned.
[0071] The hydroxide is not particularly limited, but for example
potassium hydroxide, sodium hydroxide, calcium hydroxide, etc. may
be mentioned
[0072] The content of the phosphoric acid compound, converted to
phosphoric acid ions, is preferably 0.03 to 1.0 mol/liter, more
preferably 0.1 to 0.5 mol/liter. Further, the content of the
hydroxide is preferably 0.5 to 7.0 mol/liter, =ore preferably 1.0
to 5.0 mol/liter. Note that the above content of the phosphoric
acid compound means the content of the phosphoric acid compound in
the plating solution. That is, for example, when using copper
phosphate as the copper salt, not only copper ions, but also
phosphoric acid ions are generated in the plating solution. In this
case, the content of the phosphoric acid compound is the content
including the copper phosphate.
[0073] The plating solution of the present invention may further
contain a brightening agent in an amount of 0 to 10 ml/liter in
range. The brightening agent is not particularly limited, but for
example various types of organic compound, etc. may be
mentioned.
[0074] The plating solution of the present invention is preferably
alkaline, specifically has a pH of 8 to 12 in range, more
preferably 9.5 to 10.5 in range. By adjusting the plating solution
in pH to this range, it is possible to improve the stability of the
permanent magnet in the plating solution.
[0075] Electrolytic Plating
[0076] Next, the above plating solution of the present invention
and an anode containing copper are used to form a protective film
on the surface of the permanent magnet by the barrel plating method
or rack plating method etc.
[0077] The anode containing copper is not particularly limited. A
copper anode usually used in electrolytic plating may be used. Due
to the ease of dissolution of the copper ions, oxygen-free copper,
electrolytic copper, phosphorus copper, etc. are preferable.
[0078] Further, as specific plating conditions, the temperature of
the plating bath is preferably made 55 to 65.degree. C. and the
current density at the time of plating is preferably made 0 to 5
A/dm.sup.2. Further, the thickness of the protective film formed by
this copper plating is preferably 1 to 50 .mu.m, more preferably 5
to 20 .mu.m.
[0079] The protective film formed using the plating solution of the
present invention is resistant to substitution reactions with the
magnet material at the time of plating and good in adhesion.
[0080] Note that in the present invention, the above-mentioned
protective film (hereinafter, in the present embodiment, suitably
referred to as the "first protective film") may if necessary be
formed with a second protective film. The second protective film is
not particularly limited, but in the present embodiment, it is
comprised of an electrolytic nickel plating film or a multilayer
film of a copper pyrophosphate plating film and electrolytic nickel
plating film.
[0081] When forming an electrolytic nickel plating film, the barrel
plating method is preferably used. As the plating bath, the usual
watt bath or nickel sulfamate bath is preferably used. The plating
bath has a pH of preferably 3.5 to 6.0, more preferably 4.0 to 5.0,
and has a temperature of preferably 40 to 50.degree. C.
[0082] When forming a copper pyrophosphate plating film, the barrel
plating method is preferably used. As the plating bath, the
following composition of plating bath is preferably used. This
plating bath preferably contains copper pyrophosphate 3 hydrate in
an amount of 60 to 110 g/liter, potassium pyrophosphate in 200 to
500 g/liter, ammonia in 1 to 7 g/liter, and a brightening agent in
0 to 5 ml/liter. The plating bath has a pH of preferably 8.0 to
11.0, more preferably 8.5 to 9.5, and has a temperature of
preferably 50 to 60.degree. C.
[0083] The second protective film has a thickness or preferably 0.1
to 15 times the thickness of the first protective film.
[0084] The thus surface treated permanent magnet may be suitably
used as a part requiring heat resistance and resistance to
temperature changes as conditions of use in, for example,
automobiles, industrial machinery, etc. or parts requiring heat
resistance in the process of production of the parts (for example,
resin molding of magnets etc.). Further, this permanent magnet has
superior magnetic characteristics even when particularly thin in
shape or large in specific area with regard to weight.
[0085] Note that the present invention is not limited to the above
embodiment and may be modified in various ways within the scope of
the present invention.
[0086] For example, in the above embodiment, as the conductive
material of the present invention, a rare earth magnet was
illustrated, but the conductive material of the present invention
is not limited to a rare earth magnet and may be any conductive
material able to be treated on the surface by the plating solution
of the present invention.
EXAMPLES
[0087] Below, the present invention will be explained further with
reference to detailed examples, but the present invention is not
limited to these Examples.
Example 1
[0088] A sintered body having the composition of 14Nd-1Dy-7B-78Fe
(numerals indicate atomic ratio) produced by the powder metallurgy
method was heat treated in the Ar atmosphere at 600.degree. C. for
2 hours, worked to a size of 50.times.50.times.5 (mm), and barrel
polished to round the edges and obtain a permanent magnet body.
[0089] Next, a sample of this permanent magnet body was washed by
an alkaline degreasing solution, then activated at its surface by a
3% nitric acid solution, then washed well by pure water. The sample
of this permanent magnet body was then formed on its surface with a
protective film by the method explained below.
[0090] First, as the plating bath for forming the protective film,
copper sulfate in an amount of 0.2 mol/liter, aminotrimethylene
phosphonic acid in 0.6 mol/liter, ammonium sulfate in 0.01
mol/liter, potassium hydroxide in 2 mol/liter, and brightening
agents were used to construct a pH 8.0 1-liter plating bath at
60.degree. C.
[0091] Next, this plating bath was used with an electrolyte copper
plate as an anode and the above obtained permanent magnet body
facing it for plating under a condition of a current density of 1
A/dm.sup.2 to form a protective film of a thickness of 10 .mu.m.
Next, the same plating bath and anode were used under same
conditions to plate 100 batches and fabricate 100 samples.
[0092] Among the obtained samples, the first batch sample, and
100th batch sample were subjected to a pressure cooker test (P.C.T.
test) under conditions of 120.degree. C., 100% RH, 2 atm, and 24
hours to evaluate the corrosion resistance. As a result of the
P.C.T. test, in both the first batch sample and 100th batch sample,
no points of rust or blisters could be observed, i.e., the results
were good.
[0093] Further, a first batch sample and 100th batch sample
prepared by a method same to the above were used to evaluate the
heat resistance, Specifically, first, this first batch sample and
100th batch sample were allowed to stand in a 300.degree. C.
thermostatic chamber for 1 hour or more for heating, then were
allowed to naturally cool to room temperature. Next, such once
heated samples and completely unheated samples were magnetized
until the saturated state and measured for overall magnetic flux
density to investigate the rate of drop in the overall magnetic
flux density (the rate in drop of characteristics). The rate in
drop of characteristics, in both the first batch sample and 100th
batch sample, was 0.01%, i.e., the results were good.
[0094] Further, a first batch sample and 100th batch sample
prepared by a method same to the above were used to measure the
peeling force to evaluate the protective film adhesion.
Specifically, first, each of this first batch sample and 100th
batch sample was cut on its surface with two parallel cuts of
widths of 10 mm to depths of 30 to 40 .mu.m and lengths of 20 to 30
mm. Further, one ends of these cuts were joined by a cut of a same
depth. The peeling force when peeling off only the plating film
perpendicular from that part was measured. The peeling force, in
both the first batch sample and 100th batch sample, was 50 MPa or
more and the adhesion was high, i.e., the results were good.
Example 2
[0095] Except for using a plating bath (pH=9.0) containing copper
phosphate in an amount of 0.3 mol/liter, diethylene triamine
pentamethylene phosphonic acid in 1.0 mol/liter, sodium carbonate
in 0.5 mol/liter, sodium hydroxide in 2 mol/liter, and brightening
agents, the same procedure was followed as in Example 1 to plate
100 batches and obtain 100 samples. For each of the obtained
samples, the same procedure was followed as in Example 1 to
evaluate the corrosion resistance, heat resistance and protective
film adhesion. As a result, in both the first batch sample and
100th batch sample, no points of rust or blisters could be
observed. Further, the rate an drop of characteristics was 0.01% in
each case and, further, the peeling force was 50 MPa or more in
each case, i.e., the results were good.
Example 3
[0096] Except for using a plating bath (pH=12) containing copper
(II) acetate in an amount of 0.5 mol/liter, diethylene triamine
pentamethylene phosphonic acid in 0.1 mol/liter, alanine in 0.5
mol/liter potassium hydroxide in 2 mol/liter, and brightening
agents, the same procedure was followed as in Example 1 to plate
100 batches and obtain 100 samples. For each of the obtained
samples, the same procedure was followed as in Example 1 to
evaluate the corrosion resistance, heat resistance and protective
film adhesion. As a result, in both the first batch sample and
100th batch sample, no points of rust or blisters could be
observed, Further, the rate in drop of characteristics was 0.01% in
each case and, further, the peeling force was 50 MPa or more in
each case, i.e., the results were good.
Example 4
[0097] Except for using a plating bath (pH=10) containing copper
hydroxide in an amount of 2.0 mol/liter, diethylene triamine
pentamethylene phosphonic acid in 1.0 mol/liter, ammonium sulfate
in 1.0 mol/liter, potassium hydroxide in 2.0 mol/liter, and
brightening agents, the same procedure was followed as in Example 1
to plate 100 batches and obtain 100 samples. For each of the
obtained samples, the same procedure was followed as in Example 1
to evaluate the corrosion resistance, heat resistance and
protective film adhesion. As a result, in both the first batch
sample and 100th batch sample, no points of rust or blisters could
be observed, Further, the rate in drop of characteristics was 0.01%
in each case and further, the peeling force was 50 MPa or more in
each case, i.e., the results were good.
Example 5
[0098] Except for using a plating bath (pH=12) containing copper
oxide in an amount of 2.0 mol/liter, diethylene triamine
pentamethylene phosphonic acid in 1.0 mol/liter, ammonium sulfate
in 2.0 mol/liter, potassium hydroxide in 2.0 mol/liter, and
brightening agents, the same procedure was followed as in Example 1
to plate 100 batches and obtain 100 samples. For each of the
obtained samples, the same procedure was followed as in Example 1
to evaluate the corrosion resistance, heat resistance and
protective film adhesion. As a result, in both the first batch
sample and 100th batch sample, no points of rust or blisters could
be observed, Further, the rate in drop of characteristics was 0.01%
in each case and, further, the peeling force was 50 MPa or m=re in
each case, i.e., the results were good.
Example 6
[0099] Except for using a plating bath (pH=8.5) containing copper
sulfate in an amount of 1.0 mol/liter, diethylene triamine
pentamethylene phosphonic acid in 1.0 mol/liter, potassium
phosphate in 1.5 mol/liter, potassium hydroxide in 0.1 mol/liter,
and brightening agents, the same procedure was followed as in
Example 1 to plate 100 batches and obtain 100 samples. For each of
the obtained samples, the same procedure was followed as in Example
1 to evaluate the corrosion resistance, heat resistance and
protective film adhesion. As a result, in both the first batch
sample and 100th batch sample, no points of rust or blisters could
be observed, Further, the rate in drop of characteristics was 0.01%
in each case and, further, the peeling force was 50 MPa or more in
each case, i.e., the results were good.
Example 7
[0100] Except for using a plating bath (pH=9.0) containing copper
pyrophosphate in an amount of 0.5 mol/liter, diethylene triamine
pentamethylene phosphonic acid in 0.5 mol/liter, sodium thiosulfate
in 0.5 mol/liter, fumaric acid in 0.5 mol/liter, potassium
hydroxide in 2.0 mol/liter, and brightening agents, the same
procedure was followed as in Example 1 to plate 100 batches and
obtain 100 samples. For each of the obtained samples, the same
procedure was followed as in Example 1 to evaluate the corrosion
resistance, heat resistance and protective film adhesion. As a
result, in both the first batch sample and 100th batch sample, no
points of rust or blisters could be observed, Further, the rate in
drop of characteristics was 0.01% in each case and, further, the
peeling force was 50 MPa or more in each case, i.e., the results
were good.
Comparative Example 1
[0101] Except for using a copper pyrophosphate plating bath (pH=8.5
plating bath containing copper pyrophosphate 3 hydrate in an amount
of 85 g/liter, potassium pyrophosphate in 300 g/liter, ammonia in 3
ml/liter, and brightening agents), the same procedure was followed
as in Example 1 to plate 100 batches and obtain 100 samples. For
each of the obtained samples, the same procedure was followed as in
Example 1 to evaluate the corrosion resistance. As a result, in
both the first batch sample and 100th batch sample, points of rust
were observed.
Comparative Example 2
[0102] Except for using a plating bath (pH=7.0) containing copper
phosphate in an amount of 0.3 mol/liter, diethylene triamine
pentamethylene phosphonic acid in 0.5 mol/liter, potassium
hydroxide in 2 mol/liter, and brightening agents, the same
procedure was followed as in Example 1 to plate 100 batches and
obtain 100 samples. For each of the obtained samples, the same
procedure was followed as in Example 1 to evaluate the corrosion
resistance. As a result, in the first batch sample, no points of
rust or blisters could be observed, but in the 100th batch sample,
points of rust were observed.
Comparative Example 3
[0103] Except for using a plating bath (pH=9) containing copper
phosphate in an amount of 1.0 mol/liter, diethylene triamine
pentamethylene phosphonic acid in 1.0 mol/liter, ammonia in 2.1
mol/liter, potassium hydroxide in 2 mol/liter, and brightening
agents, the same procedure was followed as in Example 1 to plate
100 batches and obtain 100 samples. For each of the obtained
samples, the same procedure was followed as in Example 1 to
evaluate the corrosion resistance. As a result, in both the first
batch sample and 100th batch sample, points of rust were
observed.
Comparative Example 4
[0104] Except for using a plating bath (pH=8) containing copper
phosphate in an amount of 2.0 mol/liter, diethylene triamine
pentamethylene phosphonate in 1.0 mol/liter, and brightening
agents, the same procedure was followed as in Example 1 to plate
100 batches and obtain 100 samples. For each of the obtained
samples, the same procedure was followed as in Example 1 to
evaluate the corrosion resistance. As a result, in both the first
batch sample and 100th batch sample, points of rust were
observed,
[0105] Evaluation
[0106] From the results of Examples 1 to 7, by using the plating
solution of the present invention for plating, it could be
confirmed that even with repeated plating, deterioration of the
plating solution can be effectively prevented and a protective film
with a high adhesion could be stably formed.
[0107] On the other hand, when using a copper pyrophosphate plating
bath (comparative Example 1), the first batch and 100th batch sales
were each inferior in corrosion resistance.
[0108] Further, when using a plating bath not containing the
predetermined compound or ions (Comparative Examples 2 and 4), with
repeated plating, the corrosion resistance became inferior.
[0109] Further, when the predetermined compound or ions were too
great (Comparative Example 3), uneven plating ended up occurring.
The first batch and 100th batch samples were each inferior in
corrosion resistance.
* * * * *