U.S. patent application number 15/821540 was filed with the patent office on 2018-06-14 for method for producing silver nanoparticles, silver nanoparticles, and silver coating composition.
This patent application is currently assigned to NATIONAL UNIVERSITY CORPORATION YAMAGATA UNIVERSITY. The applicant listed for this patent is DAICEL CORPORATION, NATIONAL UNIVERSITY CORPORATION YAMAGATA UNIVERSITY. Invention is credited to Yuki IGUCHI, Masato KURIHARA, Kazuki OKAMOTO.
Application Number | 20180168037 15/821540 |
Document ID | / |
Family ID | 48781478 |
Filed Date | 2018-06-14 |
United States Patent
Application |
20180168037 |
Kind Code |
A1 |
KURIHARA; Masato ; et
al. |
June 14, 2018 |
METHOD FOR PRODUCING SILVER NANOPARTICLES, SILVER NANOPARTICLES,
AND SILVER COATING COMPOSITION
Abstract
The present invention provides silver nano-particles that are
excellent in stability and develop excellent conductivity by
low-temperature calcining, a producing method for same, and a
silver coating composition comprising the silver nano-particles. A
method for producing silver nano-particles comprising: preparing an
amine mixture liquid comprising: an aliphatic hydrocarbon monoamine
(A) comprising an aliphatic hydrocarbon group and one amino group,
said aliphatic hydrocarbon group having 6 or more carbon atoms in
total; an aliphatic hydrocarbon monoamine (B) comprising an
aliphatic hydrocarbon group and one amino group, said aliphatic
hydrocarbon group having 5 or less carbon atoms in total; and an
aliphatic hydrocarbon diamine (C) comprising an aliphatic
hydrocarbon group and two amino groups, said aliphatic hydrocarbon
group having 8 or less carbon atoms in total; mixing a silver
compound and the amine mixture liquid to forma complex compound
comprising the silver compound and the amines; and thermally
decomposing the complex compound by heating to form silver
nano-particles.
Inventors: |
KURIHARA; Masato;
(Yamagata-shi, JP) ; OKAMOTO; Kazuki; (Himeji-shi,
JP) ; IGUCHI; Yuki; (Himeji-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NATIONAL UNIVERSITY CORPORATION YAMAGATA UNIVERSITY
DAICEL CORPORATION |
Yamagata-shi
Osaka |
|
JP
JP |
|
|
Assignee: |
NATIONAL UNIVERSITY CORPORATION
YAMAGATA UNIVERSITY
Yamagata-shi
JP
DAICEL CORPORATION
Osaka
JP
|
Family ID: |
48781478 |
Appl. No.: |
15/821540 |
Filed: |
November 22, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14371462 |
Jul 10, 2014 |
9860983 |
|
|
PCT/JP2013/050048 |
Jan 7, 2013 |
|
|
|
15821540 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01B 1/02 20130101; B22F
2007/047 20130101; B22F 2301/255 20130101; H01B 1/22 20130101; C09D
11/52 20130101; C09D 7/67 20180101; C09D 5/24 20130101; B82Y 40/00
20130101; B22F 1/0062 20130101; H05K 1/097 20130101; B22F 1/0018
20130101; H05K 3/12 20130101; B22F 7/04 20130101; B22F 1/0074
20130101; B22F 1/0085 20130101; B82Y 30/00 20130101; B22F 9/30
20130101; B22F 1/0022 20130101 |
International
Class: |
H05K 1/09 20060101
H05K001/09; H01B 1/22 20060101 H01B001/22; B22F 1/00 20060101
B22F001/00; B22F 9/30 20060101 B22F009/30; C09D 7/40 20180101
C09D007/40; H01B 1/02 20060101 H01B001/02; C09D 11/52 20140101
C09D011/52; C09D 5/24 20060101 C09D005/24 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 11, 2012 |
JP |
2012-002895 |
Claims
1. A method for producing silver nano-particles comprising:
preparing an amine mixture liquid comprising: an aliphatic
hydrocarbon monoamine (A) comprising an aliphatic hydrocarbon group
and one amino group, said aliphatic hydrocarbon group having 6 or
more carbon atoms in total; an aliphatic hydrocarbon monoamine (B)
comprising an aliphatic hydrocarbon group and one amino group, said
aliphatic hydrocarbon group having 5 or less carbon atoms in total;
and an aliphatic hydrocarbon diamine (C) comprising an aliphatic
hydrocarbon group and two amino groups, said aliphatic hydrocarbon
group having 8 or less carbon atoms in total; mixing a silver
compound and the amine mixture liquid to form a complex compound
comprising the silver compound and the amines; and thermally
decomposing the complex compound by heating to form silver
nano-particles.
2. The method for producing silver nano-particles according to
claim 1, wherein the aliphatic hydrocarbon monoamine (A) is an
alkylmonoamine having 6 or more and 12 or less carbon atoms.
3. The method for producing silver nano-particles according to
claim 1 or 2, wherein the aliphatic hydrocarbon monoamine (B) is an
alkylmonoamine having 2 or more and 5 or less carbon atoms.
4. The method for producing silver nano-particles according to any
one of claims 1 to 3, wherein the aliphatic hydrocarbon monoamine
(B) is a butylamine.
5. The method for producing silver nano-particles according to any
one of claims 1 to 4, wherein the silver compound is silver
oxalate.
6. The method for producing silver nano-particles according to any
one of claims 1 to 5, wherein the aliphatic hydrocarbon monoamine
(A) is contained in the amine mixture liquid in an amount of 10 mol
% to 65 mol % of a total of the monoamine (A), the monoamine (B),
and the diamine (C).
7. The method for producing silver nano-particles according to any
one of claims 1 to 6, wherein the aliphatic hydrocarbon monoamine
(B) is contained in the amine mixture liquid in an amount of 5 mol
% to 50 mol % of a total of the monoamine (A), the monoamine (B),
and the diamine (C).
8. The method for producing silver nano-particles according to any
one of claims 1 to 7, wherein the aliphatic hydrocarbon diamine (C)
is contained in the amine mixture liquid in an amount of 15 mol %
to 50 mol % of a total of the monoamine (A), the monoamine (B), and
the diamine (C).
9. The method for producing silver nano-particles according to any
one of claims 1 to 8, wherein the monoamine (A), the monoamine (B),
and the diamine (C) are used in a total amount of 1 to 20 moles per
mole of silver atoms in the silver compound.
10. The method for producing silver nano-particles according to any
one of claims 1 to 9, wherein the amine mixture liquid further
contains an aliphatic carboxylic acid (D).
11. Silver nano-particles produced by the method according to any
one of claims 1 to 10.
12. A silver coating composition comprising silver nano-particles
produced by the method according to any one of claims 1 to 10, and
an organic solvent.
13. A silver conductive material comprising: a substrate, and a
silver conductive layer obtained by applying, onto the substrate, a
silver coating composition comprising silver nano-particles
produced by the method according to any one of claims 1 to 10 and
an organic solvent, and calcining the silver coating composition.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional of co-pending U.S.
application Ser. No. 14/371,462 filed on Jul. 10, 2014, which is a
National Stage of PCT/JP2013/050048 filed on Jan. 7, 2013, which
claims priority to Application No. 2012-002895 filed in Japan, on
Jan. 11, 2012. The entire contents of all of the above applications
are hereby incorporated by reference.
TECHNICAL FIELD
[0002] The present invention relates to a method for producing
silver nano-particles and silver nano-particles. The present
invention also relates to a silver coating composition containing
the silver nano-particles. The present invention is applied also to
a method for producing metal nano-particles containing a metal
other than silver and metal nano-particles.
BACKGROUND ART
[0003] Silver nano-particles can be sintered even at a low
temperature. Utilizing this property, a silver coating composition
containing silver nano-particles is used to form electrodes or
conductive circuit patterns on a substrate in production of various
electronic devices. Silver nano-particles are usually dispersed in
an organic solvent. Silver nano-particles have an average primary
particle diameter of about several nanometers to about several tens
of nanometers, and their surfaces are usually coated with an
organic stabilizer (protective agent). When the substrate is a
plastic film or sheet, silver nano-particles need to be sintered at
a low temperature (e.g., at 200.degree. C. or less) less than a
heat resistant temperature of the plastic substrate.
[0004] Particularly, attempts have been recently made to form fine
metal lines (e.g., silver lines) not only on heat-resistant
polyimide substrates that are already in use as substrates for
flexible printed circuit boards but also on substrates made of
various plastics, such as PET (polyethylene terephthalate) and
polypropylene, that have lower heat resistance than polyimide but
can be easily processed and are cheap. When plastic substrates
having low heat resistance are used, metal nano-particles (e.g.,
silver nano-particles) need to be sintered at a lower
temperature.
[0005] For example, JP-A-2008-214695 discloses a method for
producing silver ultrafine particles, comprising reacting silver
oxalate and oleylamine to form a complex compound containing at
least silver, oleylamine and an oxalate ion; and thermally
decomposing the formed complex compound to form silver ultrafine
particles (claim 1). Further, JP-A-2008-214695 discloses that in
the above method, a saturated aliphatic amine having 1 to 18 carbon
atoms in total is reacted in addition to the silver oxalate and the
oleylamine (claims 2 and 3), so that a complex compound can be
easily formed, the time required to produce silver ultrafine
particles can be reduced, and the silver ultrafine particles
protected by these amines can be formed in higher yield (paragraph
[0011]).
[0006] JP-A-2010-265543 discloses a method for producing coated
silver ultrafine particles, comprising the first step of mixing a
silver compound that is decomposed by heating to generate metallic
silver, a mid- to short-chain alkylamine having a boiling point of
100.degree. C. to 250.degree. C., and a mid- to short-chain
alkyldiamine having a boiling point of 100.degree. C. to
250.degree. C. to prepare a complex compound containing the silver
compound, the alkylamine and the alkyldiamine; and the second step
of thermally decomposing the complex compound (claim 3, paragraphs
[0061] and [0062]).
PRIOR ART DOCUMENTS
Patent Documents
[0007] Patent Document 1: JP-A-2008-214695
[0008] Patent Document 2: JP-A-2010-265543
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0009] Silver nano-particles have an average primary particle
diameter of about several nanometers to about several tens of
nanometers, and are more likely to agglomerate than micron
(.mu.m)-size particles. Therefore, the reduction reaction of a
silver compound (thermal decomposition reaction in the above patent
documents) is performed in the presence of an organic stabilizer
(protective agent such as an aliphatic amine or an aliphatic
carboxylic acid) so that the surfaces of resulting silver
nano-particles are coated with the organic stabilizer.
[0010] Meanwhile, silver nano-particles are used in a silver
coating composition (silver ink or silver paste) in which the
particles are contained in an organic solvent. In order to
development conductivity, an organic stabilizer coating the silver
nano-particles needs to be removed during calcining performed after
application of the silver coating composition onto a substrate to
sinter the silver particles. When the temperature of the calcining
is low, the organic stabilizer is poorly removed. When the silver
particles are not sufficiently sintered, a low resistance value
cannot be achieved. That is, the organic stabilizer present on the
surfaces of the silver nano-particles contributes to the
stabilization of the silver nano-particles, but on the other hand,
interferes with the sintering of the silver nano-particles
(especially, sintering by low-temperature calcining).
[0011] The use of an aliphatic amine compound and/or an aliphatic
carboxylic acid compound each having a relatively long chain (e.g.,
8 or more carbon atoms) as an organic stabilizer makes it easy to
stabilize silver nano-particles because it is easy to ensure space
between the silver nano-particles. On the other hand, the
long-chain aliphatic amine compound and/or the long-chain aliphatic
carboxylic acid compound are/is poorly removed when the temperature
of calcining is low.
[0012] As described above, the relationship between the
stabilization of silver nano-particles and the development of a low
resistance value by low-temperature calcining is a trade-off.
[0013] As described above, in JP-A-2008-214695, oleylamine having
18 carbon atoms and a saturated aliphatic amine having 1 to 18
carbon atoms are used in combination as aliphatic amine compounds.
However, the use of oleylamine as a main ingredient of a protective
agent inhibits sintering of silver nano-particles during
low-temperature calcining. Further, the reaction rate of forming a
complex compound of oleylamine and silver oxalate is not
satisfactory.
[0014] As described above, in JP-A-2010-265543, a mid- to
short-chain alkylamine having a boiling point of 100.degree. C. to
250.degree. C. (paragraph [0061]) and a mid- to short-chain
alkyldiamine having a boiling point of 100.degree. C. to
250.degree. C. (paragraph [0062]) are used in combination as
aliphatic amine compounds. This method improves the problem
resulting from the use of oleylamine as a main ingredient of a
protective agent. However, it is desired that the production
process of silver nano-particles or the performance of resulting
silver nano-particles (development of a low resistance value by
low-temperature calcining) is further improved.
[0015] It is therefore an object of the present invention to
provide silver nano-particles that are excellent in stability and
develop excellent conductivity (low resistance value) by
low-temperature calcining, especially silver nano-particles that
develop conductivity (low resistance value) even when a calcined
silver film having a thickness of, for example, 1 .mu.m or more is
formed by low-temperature calcining, and a method for producing the
silver nano-particles. It is also an object of the present
invention to provide a silver coating composition comprising the
silver nano-particles.
Means for Solving the Problems
[0016] The present inventors have studied aliphatic amine compounds
that function as a complex-forming agent and/or a protective agent,
and have found a method capable of obtaining silver nano-particles
that are excellent in stability and develop excellent conductivity
(low resistance value) even when a silver coating film having a
relatively large thickness of, for example, 1 .mu.m or more is
formed by calcining at a low temperature of 200.degree. C. or less
(e.g., 150.degree. C. or less, preferably 120.degree. C. or less)
and for a short time of 2 hours or less (e.g., 1 hour or less,
preferably 30 minutes or less).
[0017] The present invention includes the following aspects.
[0018] (1) A method for producing silver nano-particles
comprising:
[0019] preparing an amine mixture liquid comprising:
[0020] an aliphatic hydrocarbon monoamine (A) comprising an
aliphatic hydrocarbon group and one amino group, said aliphatic
hydrocarbon group having 6 or more carbon atoms in total;
[0021] an aliphatic hydrocarbon monoamine (B) comprising an
aliphatic hydrocarbon group and one amino group, said aliphatic
hydrocarbon group having 5 or less carbon atoms in total; and
[0022] an aliphatic hydrocarbon diamine (C) comprising an aliphatic
hydrocarbon group and two amino groups, said aliphatic hydrocarbon
group having 8 or less carbon atoms in total;
[0023] mixing a silver compound and the amine mixture liquid to
form a complex compound comprising the silver compound and the
amines; and
[0024] thermally decomposing the complex compound by heating to
form silver nano-particles.
[0025] (2) The method for producing silver nano-particles according
to the above (1), wherein the aliphatic hydrocarbon monoamine (A)
is an alkylmonoamine having 6 or more and 12 or less carbon
atoms.
[0026] (3) The method for producing silver nano-particles according
to the above (1) or (2), wherein the aliphatic hydrocarbon
monoamine (B) is an alkylmonoamine having 2 or more and 5 or less
carbon atoms.
[0027] (4) The method for producing silver nano-particles according
to any one of the above (1) to (3), wherein the aliphatic
hydrocarbon monoamine (B) is a butylamine.
[0028] (5) The method for producing silver nano-particles according
to any one of the above (1) to (4), wherein the silver compound is
silver oxalate.
[0029] (6) The method for producing silver nano-particles according
to any one of the above (1) to (5), wherein the aliphatic
hydrocarbon monoamine (A) is contained in the amine mixture liquid
in an amount of 10 mol % to 65 mol % of a total of the monoamine
(A), the monoamine (B), and the diamine (C).
[0030] (7) The method for producing silver nano-particles according
to any one of the above (1) to (6), wherein the aliphatic
hydrocarbon monoamine (B) is contained in the amine mixture liquid
in an amount of 5 mol % to 50 mol % of a total of the monoamine
(A), the monoamine (B), and the diamine (C).
[0031] (8) The method for producing silver nano-particles according
to any one of the above (1) to (7), wherein the aliphatic
hydrocarbon diamine (C) is contained in the amine mixture liquid in
an amount of 15 mol % to 50 mol % of a total of the monoamine (A),
the monoamine (B), and the diamine (C).
[0032] (9) The method for producing silver nano-particles according
to any one of the above (1) to (8), wherein the monoamine (A), the
monoamine (B), and the diamine (C) are used in a total amount of 1
to 20 moles per mole of silver atoms in the silver compound.
[0033] (10) The method for producing silver nano-particles
according to any one of the above (1) to (9), wherein the amine
mixture liquid further contains an aliphatic carboxylic acid
(D).
[0034] (11) Silver nano-particles produced by the method according
to any one of the above (1) to (10).
[0035] Coated silver nano-particles whose surfaces are coated with
a protective agent, wherein the protective agent comprises the
aliphatic hydrocarbon monoamine (A) having 6 or more carbon atoms
in total, the aliphatic hydrocarbon monoamine (B) having 5 or less
carbon atoms in total, and the aliphatic hydrocarbon diamine (C)
having 8 or less carbon atoms in total.
[0036] Coated silver nano-particles whose surfaces are coated with
a protective agent, wherein the protective agent comprises the
aliphatic hydrocarbon monoamine (A) having 6 or more carbon atoms
in total, the aliphatic hydrocarbon monoamine (B) having 5 or less
carbon atoms in total, the aliphatic hydrocarbon diamine (C) having
8 or less carbon atoms in total, and the aliphatic carboxylic acid
(D).
[0037] (12) A silver coating composition comprising silver
nano-particles produced by the method according to any one of the
above (1) to (10), and an organic solvent. The silver coating
composition may take any form without any limitation. For example,
a silver coating composition in which the silver nano-particles are
dispersed in suspension state in the organic solvent, or a silver
coating composition in which the silver nano-particles are
dispersed in kneaded state in the organic solvent.
[0038] (13) A silver conductive material comprising:
[0039] a substrate, and
[0040] a silver conductive layer obtained by applying, onto the
substrate, a silver coating composition comprising silver
nano-particles produced by the method according to any one of the
above (1) to (10) and an organic solvent, and calcining the silver
coating composition. The calcining is performed at a temperature of
200.degree. C. or less, for example, 150.degree. C. or less,
preferably 120.degree. C. or less, for 2 hours or less, for
example, 1 hour or less, preferably 30 minutes or less.
[0041] (14) The silver conductive material according to the above
(13), wherein the silver conductive layer is patterned.
[0042] (15) A method for producing a silver conductive material
comprising:
[0043] applying, onto a substrate, a silver coating composition
comprising silver nano-particles produced by the method according
to any one of the above (1) to (10) and an organic solvent, and
then,
[0044] calcining the silver coating composition to forma silver
conductive layer. The calcining is performed at a temperature of
200.degree. C. or less, for example, 150.degree. C. or less,
preferably 120.degree. C. or less, for 2 hours or less, for
example, 1 hour or less, preferably 30 minutes or less.
[0045] (16) The method for producing a silver conductive material
according to the above (15), wherein the silver coating composition
is applied in a pattern, and is then calcined to form a patterned
silver conductive layer.
[0046] A method for producing metal nano-particles comprising:
[0047] preparing an amine mixture liquid comprising:
[0048] an aliphatic hydrocarbon monoamine (A) comprising an
aliphatic hydrocarbon group and one amino group, said aliphatic
hydrocarbon group having 6 or more carbon atoms in total;
[0049] an aliphatic hydrocarbon monoamine (B) comprising an
aliphatic hydrocarbon group and one amino group, said aliphatic
hydrocarbon group having 5 or less carbon atoms in total; and
[0050] an aliphatic hydrocarbon diamine (C) comprising an aliphatic
hydrocarbon group and two amino groups, said aliphatic hydrocarbon
group having 8 or less carbon atoms in total;
[0051] mixing a metal compound and the amine mixture liquid to form
a complex compound comprising the metal compound and the amines;
and
[0052] thermally decomposing the complex compound by heating to
form metal nano-particles.
[0053] Coated metal nano-particles whose surfaces are coated with a
protective agent, wherein the protective agent comprises the
aliphatic hydrocarbon monoamine (A) having 6 or more carbon atoms
in total, the aliphatic hydrocarbon monoamine (B) having 5 or less
carbon atoms in total, and the aliphatic hydrocarbon diamine (C)
having 8 or less carbon atoms in total.
[0054] Coated metal nano-particles whose surfaces are coated with a
protective agent, wherein the protective agent comprises the
aliphatic hydrocarbon monoamine (A) having 6 or more carbon atoms
in total, the aliphatic hydrocarbon monoamine (B) having 5 or less
carbon atoms in total, the aliphatic hydrocarbon diamine (C) having
8 or less carbon atoms in total, and the aliphatic carboxylic acid
(D).
[0055] A metal coating composition comprising the coated metal
nano-particles and an organic solvent. The metal coating
composition may take any form without any limitation. For example,
a metal coating composition in which the metal nano-particles are
dispersed in suspension state in the organic solvent, or a metal
coating composition in which the metal nano-particles are dispersed
in kneaded state in the organic solvent.
Effects of the Invention
[0056] In the present invention, as aliphatic amine compounds that
function as a complex-forming agent and/or a protective agent, an
aliphatic hydrocarbon monoamine (A) having 6 or more carbon atoms
in total, an aliphatic hydrocarbon monoamine (B) having 5 or less
carbon atoms in total, and an aliphatic hydrocarbon diamine (C)
having 8 or less carbon atoms in total are used.
[0057] The aliphatic hydrocarbon diamine (C) having 8 or less
carbon atoms in total has a high ability to coordinate to silver in
a silver compound, and therefore has the effect of promoting
complex formation. Further, the aliphatic hydrocarbon diamine (C)
also has the effect of promoting thermal decomposition of a
resulting complex. The aliphatic hydrocarbon monoamine (B) having 5
or less carbon atoms in total has a shorter carbon chain than the
aliphatic hydrocarbon monoamine (A) having 6 or more carbon atoms
in total, and therefore the function of the aliphatic hydrocarbon
monoamine (B) itself as a protective agent (stabilizer) is
considered to be lower. However, the aliphatic hydrocarbon
monoamine (B) has a high ability to coordinate to silver in a
silver compound due to its higher polarity than the aliphatic
hydrocarbon monoamine (A), and is therefore considered to have the
effect of promoting complex formation.
[0058] The aliphatic hydrocarbon monoamine (A) having 6 or more
carbon atoms in total has high performance as a protective agent
(stabilizer) to protect the surfaces of resulting silver particles.
Further, part of the surfaces of the silver particles, to which the
aliphatic hydrocarbon monoamine (A) is not attached, is coated with
the aliphatic hydrocarbon monoamine (B) having 5 or less carbon
atoms in total and the aliphatic hydrocarbon diamine (C) having 8
or less carbon atoms in total attached thereto. That is, the
function of the aliphatic hydrocarbon monoamine (B) and the
aliphatic hydrocarbon diamine (C) themselves as a protective agent
is considered to be low, but the aliphatic hydrocarbon monoamine
(B) and the aliphatic hydrocarbon diamine (C) are considered to
play a role in coating part of the surfaces of the silver particles
to assist the function of the aliphatic hydrocarbon monoamine (A)
as a protective agent. Therefore, silver nano-particles can be
properly stabilized even when the amount of the aliphatic
hydrocarbon monoamine (A) having 6 or more carbon atoms in total
attached to the surfaces of the silver particles is reduced.
[0059] As described above, the step of forming a complex compound
can be efficiently performed, and stabilized silver nano-particles
can be efficiently produced.
[0060] The aliphatic hydrocarbon monoamine (B) having 5 or less
carbon atoms in total and the aliphatic hydrocarbon diamine (C)
having 8 or less carbon atoms in total each have a short carbon
chain, and are therefore easily removed from the surfaces of the
silver particles in a short time of 2 hours or less, for example, 1
hour or less, preferably 30 minutes or less even by low-temperature
calcining at a temperature of 200.degree. C. or less, for example,
150.degree. C. or less, preferably 120.degree. C. or less. In
addition, the presence of the monoamine (B) and the diamine (C)
reduces the amount of the aliphatic hydrocarbon monoamine (A)
having 6 or more carbon atoms in total attached to the surfaces of
the silver particles. This makes it possible to easily remove these
aliphatic amine compounds from the surfaces of the silver particles
in such a short time as described above even by low-temperature
calcining at such a low temperature as described above, thereby
allowing the silver particles to be sufficiently sintered.
[0061] As described above, according to the present invention, it
is possible to provide silver nano-particles that have excellent
stability and can develop excellent conductivity (low resistance
value) by calcining at a low-temperature of 200.degree. C. or less,
for example, 150.degree. C. or less, preferably 120.degree. C. or
less, and a short-time of 2 hours or less, for example, 1 hour or
less, preferably 30 minutes or less even when having a silver film
formed with a relatively large film thickness of, for example, 1
.mu.m or more; and a method for producing such silver
nano-particles. In addition, according to the present invention, it
is also possible to provide a silver coating composition comprising
the silver nano-particles in stable dispersion state in an organic
solvent. Further, the present invention is also applied to a method
for producing metal nano-particles containing a metal other than
silver, and said metal nano-particles. According to the present
invention, it is possible to form a conductive film or a conductive
line even on any plastic substrate having low heat resistance such
as a PET substrate or a polypropylene substrate.
BRIEF DESCRIPTION OF THE DRAWING
[0062] FIG. 1 is a transmission electron microscope (TEM)
photograph of silver nano-particles obtained in Example 1.
MODES FOR CARRYING OUT THE INVENTION
[0063] In a method for producing silver nano-particles according to
the present invention, first, an amine mixture liquid is prepared
which comprises:
[0064] an aliphatic hydrocarbon monoamine (A) comprising an
aliphatic hydrocarbon group and one amino group, said aliphatic
hydrocarbon group having 6 or more carbon atoms in total;
[0065] an aliphatic hydrocarbon monoamine (B) comprising an
aliphatic hydrocarbon group and one amino group, said aliphatic
hydrocarbon group having 5 or less carbon atoms in total; and
[0066] an aliphatic hydrocarbon diamine (C) comprising an aliphatic
hydrocarbon group and two amino groups, said aliphatic hydrocarbon
group having 8 or less carbon atoms in total. Then, a silver
compound and the amine mixture liquid are mixed with each other to
forma complex compound comprising the silver compound and the
amines. Then, the complex compound is thermally decomposed by
heating to form silver nano-particles. Thus, the method for
producing silver nano-particles according to the present invention
mainly includes a preparation step for an amine mixture liquid, a
forming step of a complex compound, and a thermal-decomposition
step of the complex compound.
[0067] In this description, the term "nano-particles" means that
primary particles have a size (average primary particle diameter)
of less than 1,000 nm. The particle size refers to the size of a
particle not including a protective agent (a stabilizer) present on
(coating) the surface of the particle (i.e., refers to the size of
silver itself). In the present invention, the silver nano-particles
have an average primary particle diameter of, for example, 0.5 nm
to 100 nm, preferably 0.5 nm to 50 nm, more preferably 0.5 nm to 25
nm, even more preferably 0.5 nm to 10 nm.
[0068] The silver compound used in the present invention is one
that is easily decomposed by heating to generate metallic silver.
Examples of such a silver compound that can be used include: silver
carboxylates such as silver formate, silver acetate, silver
oxalate, silver malonate, silver benzoate, and silver phthalate;
silver halides such as silver fluoride, silver chloride, silver
bromide, and silver iodide; silver sulfate, silver nitrate, silver
carbonate, and the like. In terms of the fact that metallic silver
is easily generated by decomposition and impurities other than
silver are less likely to be generated, silver oxalate is
preferably used. Silver oxalate is advantageous in that silver
oxalate has a high silver content, and metallic silver is directly
obtained by thermal decomposition without the need for a reducing
agent, and therefore impurities derived from a reducing agent are
less likely to remain.
[0069] When metal nano-particles containing another metal other
than silver are produced, a metal compound that is easily
decomposed by heating to generate a desired metal is used instead
of the silver compound. As such a metal compound, a metal salt
corresponding to the above mentioned silver compound can be used.
Examples of such a metal compound include: metal carboxylates;
metal halides; and metal salt compounds such as metal sulfates,
metal nitrates, and metal carbonates. Among them, in terms of the
fact that a metal is easily generated by decomposition and
impurities other than a metal are less likely to be generated,
metal oxalate is preferably used. Examples of another metal include
Al, Au, Pt, Pd, Cu, Co, Cr, In, and Ni.
[0070] Further, in order to obtain a composite with silver, the
above mentioned silver compound and the above mentioned compound of
another metal other than silver may be used in combination.
Examples of another metal include Al, Au, Pt, Pd, Cu, Co, Cr, In,
and Ni. The silver composite is composed of silver and one or more
other metals, and examples thereof include Au--Ag, Ag--Cu,
Au--Ag--Cu, Au--Ag--Pd, and the like. The amount of silver occupies
at least 20 wt %, usually at least 50 wt %, for example, at least
80 wt % of the total amount of the metals.
[0071] In the present invention, as an aliphatic hydrocarbon amine
compounds that function as a complex-forming agent and/or a
protective agent, the aliphatic hydrocarbon amine (A) having 6 or
more carbon atoms in total, the aliphatic hydrocarbon amine (B)
having 5 or less carbon atoms in total, and the aliphatic
hydrocarbon diamine (C) having 8 or less carbon atoms in total are
used.
[0072] Although established, the "aliphatic hydrocarbon monoamine"
in this description refers to a compound composed of one to three
monovalent aliphatic hydrocarbon groups and one amino group. The
"hydrocarbon group" refers to a group only composed of carbon and
hydrogen. Each of the aliphatic hydrocarbon amine (A) and the
aliphatic hydrocarbon amine (B) does not have, on its hydrocarbon
group, a hetero atom (atom other than carbon and hydrogen) such as
an oxygen atom or a nitrogen atom.
[0073] Further, the "aliphatic hydrocarbon diamine" refers to a
compound composed of a bivalent aliphatic hydrocarbon group
(alkylene group), two amino groups between which said aliphatic
hydrocarbon group is interposed, and, if necessary, aliphatic
hydrocarbon group (s) (alkyl group (s)) substituted for hydrogen
atom(s) on the amino group (s). The aliphatic hydrocarbon amine (C)
does not have, on its hydrocarbon group, a hetero atom (atom other
than carbon and hydrogen) such as an oxygen atom or a nitrogen
atom.
[0074] The aliphatic hydrocarbon monoamine (A) having 6 or more
carbon atoms in total has, due to its hydrocarbon chain, high
performance as a protective agent (a stabilizer) onto the surfaces
of resulting silver particles.
[0075] The aliphatic hydrocarbon monoamine (A) includes a primary
amine, a secondary amine, and a tertiary amine. Examples of the
primary amine include saturated aliphatic hydrocarbon monoamines
(i.e., alkylmonoamines) such as hexylamine, heptylamine,
octylamine, nonylamine, decylamine, undecylamine, dodecylamine,
tridecylamine, tetradecylamine, pentadecylamine, hexadecylamine,
heptadecylamine, and octadecylamine. Examples of the saturated
aliphatic hydrocarbon monoamine other than the above-mentioned
linear aliphatic monoamines include branched aliphatic hydrocarbon
amines such as isohexylamine, 2-ethylhexylamine, and
tert-octylamine. Another example of the saturated aliphatic
hydrocarbon monoamine includes cyclohexylamine. Other examples of
the primary amine include unsaturated aliphatic hydrocarbon
monoamines (i.e., alkenylmonoamines) such as oleylamine.
[0076] Examples of the secondary amine include dialkylmonoamines
such as N,N-dipropylamine, N,N-dibutylamine, N,N-dipentylamine,
N,N-dihexylamine, N,N-dipeptylamine, N,N-dioctylamine,
N,N-dinonylamine, N,N-didecylamine, N,N-diundecylamine,
N,N-didodecylamine, N-methyl-N-propylamine, N-ethyl-N-propylamine,
and N-propyl-N-butylamine. Examples of the tertiary amine include
tributylamine, trihexylamine, and the like.
[0077] Among them, saturated aliphatic hydrocarbon monoamines
having 6 or more carbon atoms are preferred. When the number of
carbon atoms is 6 or more, space can be secured between silver
particles by adsorption of amino groups to the surfaces of the
silver particles, thereby improving the effect of preventing
agglomeration of the silver particles. The upper limit of the
number of carbon atoms is not particularly limited, but saturated
aliphatic monoamines having up to 18 carbon atoms are usually
preferred in consideration of ease of availability, ease of removal
during calcining, etc. Particularly, alkylmonoamines having 6 to 12
carbon atoms such as hexylamine, heptylamine, octylamine,
nonylamine, decylamine, undecylamine, and dodecylamine are
preferably used. The above-mentioned aliphatic hydrocarbon
monoamines (A) may be used singly or in combination of two or more
of them.
[0078] The aliphatic hydrocarbon monoamine (B) having 5 or less
carbon atoms in total has a shorter carbon chain than the aliphatic
monoamine (A) having 6 or more carbon atoms in total, and therefore
the function of the aliphatic hydrocarbon monoamine (B) itself as a
protective agent (a stabilizer) is considered to be low. However,
the aliphatic hydrocarbon monoamine (B) has a high ability to
coordinate to silver in the silver compound due to its higher
polarity than the aliphatic monoamine (A), and is therefore
considered to have the effect of promoting complex formation. In
addition, the aliphatic hydrocarbon monoamine (B) has a short
carbon chain, and therefore can be removed from the surfaces of
silver particles in a short time of 30 minutes or less, or 20
minutes or less, even by low-temperature calcining at a temperature
of, for example, 120.degree. C. or less, or about 100.degree. C. or
less, which is effective for low-temperature calcining of resulting
silver nano-particles.
[0079] Examples of the aliphatic hydrocarbon monoamine (B) include
saturated aliphatic hydrocarbon monoamines (i.e., alkylmonoamines)
having 2 to 5 carbon atoms such as ethylamine, n-propylamine,
isopropylamine, n-butylamine, isobutylamine, sec-butylamine,
tert-butylamine, pentylamine, isopentylamine, and tert-pentylamine.
Other examples of the aliphatic hydrocarbon monoamine (B) include
dialkylmonoamines such as N,N-dimethylamine and
N,N-diethylamine.
[0080] Among them, n-butylamine, isobutylamine, sec-butylamine,
tert-butylamine, pentylamine, isopentylamine, tert-pentylamine, and
the like are preferred, and the above-mentioned butylamines are
particularly preferred. The above-mentioned aliphatic hydrocarbon
monoamines (B) may be used singly or in combination of two or more
of them.
[0081] The aliphatic hydrocarbon diamine (C) having 8 or less
carbon atoms in total has a high ability to coordinate to silver in
the silver compound, and therefore has the effect of promoting
complex formation. Generally, aliphatic hydrocarbon diamines have
higher polarity than aliphatic hydrocarbon monoamines, and
therefore have a high ability to coordinate to silver in a silver
compound. Further, the aliphatic hydrocarbon diamine (C) has the
effect of promoting lower-temperature and shorter-time thermal
decomposition in the thermal-decomposition step of the complex
compound, and therefore production of silver nano-particles can be
more efficiently conducted. Further, a protective film containing
the aliphatic diamine (C) on silver particles has high polarity,
which improves the dispersion stability of the silver particles in
a dispersion medium comprising a highly-polar solvent. Furthermore,
the aliphatic diamine (C) has a short carbon chain, and therefore
can be removed from the surfaces of silver particles in a short
time of 30 minutes or less, or 20 minutes or less, even by
low-temperature calcining at a temperature of, for example,
120.degree. C. or less, or about 100.degree. C. or less, which is
effective for low-temperature and short-time calcining of resulting
silver nano-particles.
[0082] The aliphatic hydrocarbon diamine (C) is not particularly
limited, and examples thereof include ethylenediamine,
N,N-dimethylethylenediamine, N,N'-dimethylethylenediamine,
N,N-diethylethylenediamine, N,N'-diethylethylenediamine,
1,3-propanediamine, 2,2-dimethyl-1,3-propanediamine,
N,N-dimethyl-1,3-propanediamine, N,N'-dimethyl-1,3-propanediamine,
N,N-diethyl-1,3-propanediamine, N,N'-diethyl-1,3-propanediamine,
1,4-butanediamine, N,N-dimethyl-1,4-butanediamine,
N,N'-dimethyl-1,4-butanediamine, N,N-diethyl-1,4-butanediamine,
N,N'-diethyl-1,4-butanediamine, 1,5-pentanediamine,
1,5-diamino-2-methylpentane, 1,6-hexanediamine,
N,N-dimethyl-1,6-hexanediamine, N,N'-dimethyl-1,6-hexanediamine,
1,7-heptanediamine, 1,8-octanediamine, and the like. They are all
alkylenediamines having 8 or less carbon atoms in total in which at
least one of the two amino groups is a primary amino group or a
secondary amino group, and have a high ability to coordinate to
silver in the silver compound, and therefore have the effect of
promoting complex formation.
[0083] Among them, N,N-dimethylethylenediamine,
N,N-diethylethylenediamine, N,N-dimethyl-1,3-propanediamine,
N,N-diethyl-1,3-propanediamine, N,N-dimethyl-1,4-butanediamine,
N,N-diethyl-1,4-butanediamine, N,N-dimethyl-1,6-hexanediamine, and
the like are preferred, which are alkylenediamines having 8 or less
carbon atoms in total in which one of the two amino groups is a
primary amino group (--NH.sub.2) and the other is a tertiary amino
group (--NR.sup.1R.sup.2). Such preferred alkylenediamines are
represented by the following structural formula:
R.sup.1R.sup.2N--R--NH.sub.2
[0084] wherein R represents a bivalent alkylene group, R.sup.1 and
R.sup.2 may be the same or different from each other and each
represent an alkyl group, and the total number of carbon atoms of
R, R.sup.1, and R.sup.2 is 8 or less. The alkylene group does not
contain a hetero atom such as an oxygen atom or a nitrogen atom.
Further, the alkyl group does not contain a hetero atom such as an
oxygen atom or a nitrogen atom.
[0085] When one of the two amino groups is a primary amino group,
the ability to coordinate to silver in the silver compound is high,
which is advantageous for complex formation, and when the other is
a tertiary amino group, a resulting complex is prevented from
having a complicated network structure because a tertiary amino
group has a poor ability to coordinate to a silver atom. If a
complex has a complicated network structure, there is a case where
the thermal-decomposition step of the complex requires a high
temperature. Among these diamines, those having 6 or less carbon
atoms in total are preferred, and those having 5 or less carbon
atoms in total are more preferred in terms of the fact that they
can be removed from the surfaces of silver particles in a short
time even by low-temperature calcining. The above-mentioned
aliphatic hydrocarbon diamines (C) may be used singly or in
combination of two or more of them.
[0086] The ratio among the aliphatic hydrocarbon monoamine (A)
having 6 or more carbon atoms in total, the aliphatic hydrocarbon
monoamine (B) having 5 or less carbon atoms in total, and the
aliphatic hydrocarbon diamine (C) having 8 or less carbon atoms in
total used in the present invention is not particularly limited.
For example,
the amount of the aliphatic monoamine (A) may be 10 mol % to 65 mol
%; the amount of the aliphatic monoamine (B) may be 5 mol % to 50
mol %, and the amount of the aliphatic diamine (C) may be 15 mol %
to 50 mol %, on the basis of the total amount [(A)+(B)+(C)] of the
monoamine (A), the monoamine (B) and the diamine (C) in the amine
mixture liquid.
[0087] By setting the content of the aliphatic monoamine (A) to 10
mol % to 65 mol %, the carbon chain of the component (A) can easily
fulfill its function of protecting and stabilizing the surfaces of
resulting silver particles. If the content of the component (A) is
less than 10 mol %, there is a case where the protective and
stabilization function is poorly developed. On the other hand, if
the content of the component (A) exceeds 65 mol %, the protective
and stabilization function is sufficient, but the component (A) is
poorly removed by low-temperature calcining. The lower limit of the
content of the component (A) is preferably 10 mol % or more, more
preferably 20 mol % or more. The upper limit of the content of the
component (A) is preferably 65 mol % or less, more preferably 60
mol % or less.
[0088] By setting the content of the aliphatic monoamine (B) to 5
mol % to 50 mol %, the effect of promoting complex formation is
easily obtained, the aliphatic monoamine (B) itself can contribute
to low-temperature and short-time calcining, and the effect of
facilitating the removal of the aliphatic diamine (C) from the
surfaces of silver particles during calcining is easily obtained.
If the content of the component (B) is less than 5 mol %, there is
a case where the effect of promoting complex formation is poor, or
the component (C) is poorly removed from the surfaces of silver
particles during calcining. On the other hand, if the content of
the component (B) exceeds 50 mol %, the effect of promoting complex
formation is obtained, but the content of the aliphatic monoamine
(A) is relatively reduced so that the surfaces of resulting silver
particles are poorly protected and stabilized. The lower limit of
the content of the component (B) is preferably 10 mol % or more,
more preferably 15 mol % or more. The upper limit of the content of
the component (B) is preferably 45 mol % or less, more preferably
40 mol % or less.
[0089] By setting the content of the aliphatic diamine (C) to 15
mol % to 50 mol %, the effect of promoting complex formation and
the effect of promoting the thermal-decomposition of the complex
are easily obtained, and further, the dispersion stability of
silver particles in a dispersion medium containing a highly-polar
solvent is improved because a protective film containing the
aliphatic diamine (C) on silver particles has high polarity. If the
content of the component (C) is less than 15 mol %, there is a case
where the effect of promoting complex formation and the effect of
promoting the thermal-decomposition of the complex are poor. On the
other hand, if the content of the component (C) exceeds 50 mol %,
the effect of promoting complex formation and the effect of
promoting the thermal-decomposition of the complex are obtained,
but the content of the aliphatic monoamine (A) is relatively
reduced so that the surfaces of resulting silver particles are
poorly protected and stabilized. The lower limit of the content of
the component (C) is preferably 15 mol % or more, more preferably
20 mol % or more. The upper limit of the content of the component
(C) is preferably 45 mol % or less, more preferably 40 mol % or
less.
[0090] In the present invention, the use of the aliphatic monoamine
(B) and the aliphatic diamine (C) each having a high ability to
coordinate to silver in the silver compound makes it possible,
depending on their contents, to reduce the amount of the aliphatic
monoamine (A) having 6 or more carbon atoms in total adhered to the
surfaces of silver particles. Therefore, these aliphatic amine
compounds are easily removed from the surfaces of silver particles
even by the above-described low-temperature and short-time
calcining so that the silver particles are sufficiently
sintered.
[0091] In the present invention, the total amount of the monoamine
(A), the monoamine (B) and the diamine (C) is not particularly
limited, but may be about 1 to 20 moles as represented by the total
amount of the amine components [(A)+(B)+(C)], per 1 mole of silver
atoms in the silver compound as a starting material. If the total
amount of the amine components [(A)+(B)+(C)] is less than 1 mole
per 1 mole of the silver atoms, there is a possibility that part of
the silver compound remains without being converted to a complex
compound in the complex compound-forming step so that, in the
subsequent thermal decomposition step, silver particles have poor
uniformity and become enlarged or the silver compound remains
without being thermally decomposed. On the other hand, it is
considered that even when the total amount of the amine components
[(A)+(B)+(C)] exceeds about 20 moles per 1 mole of the silver
atoms, there are few advantages. In order to produce a dispersion
liquid of silver nano-particles in substantial non-solvent reaction
system, the total amount of the amine components [(A)+(B)+(C)] may
be, for example, about 2 moles or more per 1 mole of the silver
atoms. By setting the total amount of the amine components to about
2 to 20 moles, the complex compound-forming step and the
thermal-decomposition step of the complex compound can be
successfully performed. The lower limit of the total amount of the
amine components is preferably 2 moles or more, more preferably 6
moles or more per 1 mole of silver atoms in the silver
compound.
[0092] In the present invention, an aliphatic carboxylic acid (D)
may further be used as a stabilizer to further improve the
dispersibility of silver nano-particles in a dispersion medium. The
aliphatic carboxylic acid (D) may be used by adding to the liquid
amine mixture. The use of the aliphatic carboxylic acid (D) may
improve the stability of silver nano-particles, especially the
stability of silver nano-particles in a coating material state
where the silver nano-particles are dispersed in an organic
solvent.
[0093] As the aliphatic carboxylic acid (D), a saturated or
unsaturated aliphatic carboxylic acid is used. Examples of the
aliphatic carboxylic acid include saturated aliphatic
monocarboxylic acids having 4 or more carbon atoms such as butanoic
acid, pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid,
nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid,
tridecanoic acid, tetradecanoic acid, pentadecanoic acid,
hexadecanoic acid, heptadecanoic acid, octadecanoic acid,
nonadecanoic acid, icosanoic acid, and eicosenoic acid; and
unsaturated aliphatic monocarboxylic acids having 8 or more carbon
atoms such as oleic acid, elaidic acid, linoleic acid, and
palmitoleic acid.
[0094] Among them, saturated or unsaturated aliphatic
monocarboxylic acids having 8 to 18 carbon atoms are preferred.
When the number of carbon atoms is 8 or more, space can be secured
between silver particles by adsorption of carboxylic groups to the
surfaces of the silver particles, thereby improving the effect of
preventing agglomeration of the silver particles. In consideration
of ease of availability, ease of removal during calcining, etc.,
saturated or unsaturated aliphatic monocarboxylic compounds having
up to 18 carbon atoms are usually preferred. Particularly, octanoic
acid, oleic acid, and the like are preferably used. The
above-mentioned aliphatic carboxylic acids (D) may be used singly
or in combination of two or more of them.
[0095] When the aliphatic carboxylic acid (D) is used, the amount
of the aliphatic carboxylic acid (D) used may be, for example,
about 0.05 to 10 moles, preferably 0.1 to 5 moles, more preferably
0.5 to 2 moles per 1 mole of silver atoms in the silver compound as
a starting material. If the amount of the component (D) is less
than 0.05 moles per 1 mole of the silver atoms, the effect of
improving dispersion stability obtained by adding the component (D)
is poor. On the other hand, if the amount of the component (D)
reaches 10 moles, the effect of improving dispersion stability is
saturated and the component (D) is poorly removed by
low-temperature calcining. It is to be noted that the aliphatic
carboxylic acid (D) does not necessarily need to be used.
[0096] In the present invention, first, an amine mixture liquid
containing the aliphatic hydrocarbon monoamine (A) having 6 or more
carbon atoms in total, the aliphatic hydrocarbon monoamine (B)
having 5 or less carbon atoms in total, and the aliphatic
hydrocarbon diamine (C) having 8 or less carbon atoms in total is
prepared [preparation step for amine mixture liquid].
[0097] The amine mixture liquid can be prepared by stirring the
amine component (A), the amine component (B), and the amine
component (C), and if used, the carboxylic acid component (D) in a
given ratio at a room temperature.
[0098] Then, the amine mixture liquid containing the amine
component (A), the amine component (B), and the amine component (C)
is mixed with the silver compound to form a complex compound
containing the silver compound and the amines (complex
compound-forming step). When metal nano-particles containing
another metal other than silver are produced, a metal compound
containing a desired metal is used instead of the silver
compound.
[0099] The silver compound (or the metal compound) in powder form,
and a given amount of the amine mixture liquid are mixed. At this
time, the mixing may be performed by stirring them at a room
temperature, or may be performed by stirring them while a mixture
of them is appropriately cooled to a room temperature or less
because the coordination reaction of the amines to the silver
compound (or the metal compound) is accompanied by heat generation.
The excess amines function as a reaction medium. When a complex
compound is formed, the formed complex compound generally exhibits
a color corresponding to its components, and therefore the endpoint
of a complex compound-forming reaction can be determined by
detecting the end of a change in the color of a reaction mixture by
an appropriate spectroscopic method or the like. A complex compound
formed from silver oxalate is generally colorless (appears white to
our eyes), but even in such a case, it is possible to determine the
state of formation of a complex compound based on a change in the
form of a reaction mixture such as a change in viscosity. In this
way, a silver-amine complex (or a metal-amine complex) is obtained
in a medium mainly containing the amines.
[0100] Then, the obtained complex compound is thermally decomposed
by heating to form silver nano-particles [thermal-decomposition
step of complex compound]. When a metal compound containing another
metal other than silver is used, desired metal nano-particles are
formed. The silver nano-particles (metal nano-particles) are formed
without using a reducing agent. However, if necessary, an
appropriate reducing agent may be used without impairing the
effects of the present invention.
[0101] In such a metal-amine complex decomposition method, the
amines generally play a role in controlling the mode of formation
of fine particles by agglomeration of an atomic metal generated by
decomposition of the metal compound, and in forming film on the
surfaces of the formed metal fine particles to prevent
reagglomeration of the fine particles. That is, it is considered
that when the complex compound of the metal compound and the amine
is heated, the metal compound is thermally decomposed to generate
an atomic metal while the coordination bond of the amine to a
metallic atom is maintained, and then the metallic atoms
coordinated with the amine are agglomerated to form metal
nano-particles coated with an amine protective film.
[0102] At this time, the thermal decomposition is preferably
performed by stirring the complex compound in a reaction medium
mainly containing the amines. The thermal decomposition may be
performed in a temperature range in which coated silver
nano-particles (or coated metal nano-particles) are formed, but
from the viewpoint of preventing the elimination of the amine from
the surfaces of silver particles (or from the surfaces of metal
particles), the thermal decomposition is preferably performed at a
temperature as low as possible within such a temperature range. In
case of the complex compound from silver oxalate, the thermal
decomposition temperature may be, for example, about 80.degree. C.
to 120.degree. C., preferably about 95.degree. C. to 115.degree.
C., more specifically about 100.degree. C. to 110.degree. C. In
case of the complex compound from silver oxalate, heating at about
100.degree. C. allows decomposition and reduction of silver ions to
occur so that coated silver nano-particles can be obtained.
Further, the thermal decomposition of silver oxalate itself
generally occurs at about 200.degree. C. The reason why the thermal
decomposition temperature of a silver oxalate-amine complex
compound is about 100.degree. C. lower than that of silver oxalate
itself is not clear, but it is estimated that a coordination
polymer structure formed by pure silver oxalate is broken by
forming a complex compound of silver oxalate with the amine.
[0103] Further, the thermal decomposition of the complex compound
is preferably performed in an inert gas atmosphere such as argon,
but may be performed in the atmosphere.
[0104] When the complex compound is thermally decomposed, a
suspension exhibiting a glossy blue color is obtained. Then, the
excess amines, etc. are removed from the suspension by, for
example, sedimentation of silver nano-particles (or metal
nano-particles) and decantation and washing with an appropriate
solvent (water or an organic solvent) to obtain desired stable
coated silver nano-particles (or coated metal nano-particles).
After the washing, the coated silver nano-particles are dried to
obtain a powder of the desired stable coated silver nano-particles
(or coated metal nano-particles).
[0105] The decantation and washing are performed using water or an
organic solvent. Examples of the organic solvent that may be used
include aliphatic hydrocarbon solvents such as pentane, hexane,
heptane, octane, nonane, decane, undecane, dodecane, tridecane, and
tetradecane; aromatic hydrocarbon solvents such as toluene, xylene,
and mesitylene; alcohol solvents such as methanol, ethanol,
propanol, and butanol; acetonitrile; and mixed solvents of
them.
[0106] The method according to the present invention does not
require the use of a reducing agent. Therefore, a by-product
derived from a reducing agent is not formed, coated silver
nano-particles are easily separated from a reaction system, and
high-purity coated silver nano-particles are obtained. However, if
necessary, an appropriate reducing agent may be used without
impairing the effects of the present invention.
[0107] A silver coating composition can be prepared using the
obtained silver nano-particles. The silver coating composition can
take any form without any limitation. For example, a silver coating
composition called "silver ink" can be prepared by dispersing the
silver nano-particles in suspension state in an appropriate organic
solvent (dispersion medium). Alternatively, a silver coating
composition called "silver paste" can be prepared by dispersing the
silver nano-particles in kneaded state in an organic solvent.
Examples of the organic solvent used to obtain the coating
composition include: aliphatic hydrocarbon solvents such as
pentane, hexane, heptane, octane, nonane, decane, undecane,
dodecane, tridecane, and tetradecane; aromatic hydrocarbon solvents
such as toluene, xylene, and mesitylene; and alcohol solvents such
as methanol, ethanol, propanol, n-butanol, n-pentanol, n-hexanol,
n-heptanol, n-octanol, n-nonanol, and n-decanol. The kind and
amount of organic solvent used may be appropriately determined
depending on a desired concentration or viscosity of the silver
coating composition. The same goes for the metal
nano-particles.
[0108] The silver nano-particle powder and the silver coating
composition obtained in the present invention have excellent
stability. For example, the silver nano-particle powder is stable
during storage at a room temperature for 1 month or more. The
silver coating composition is stable at a silver concentration of,
for example, 50 wt % at a room temperature for 1 month or more
without the occurrence of agglomeration and fusion.
[0109] According to the present invention, silver nano-particles
(or metal nano-particles) whose surfaces are coated with a
protective agent are obtained. The protective agent contains the
aliphatic hydrocarbon monoamine (A) having 6 or more carbon atoms
in total, the aliphatic hydrocarbon monoamine (B) having 5 or less
carbon atoms in total, and the aliphatic hydrocarbon diamine (C)
having 8 or less carbon atoms in total. Alternatively, the
protective agent contains the aliphatic hydrocarbon monoamine (A)
having 6 or more carbon atoms in total, the aliphatic hydrocarbon
monoamine (B) having 5 or less carbon atoms in total, the aliphatic
hydrocarbon diamine (C) having 8 or less carbon atoms in total, and
the aliphatic carboxylic acid (D).
[0110] The prepared silver coating composition is applied onto a
substrate and is then calcined.
[0111] The application can be performed by a known method such as
spin coating, inkjet printing, screen printing, dispenser printing,
relief printing (flexography), dye sublimation printing, offset
printing, laser printer printing (toner printing), intaglio
printing (gravure printing), contact printing, or microcontact
printing. By using such a printing technique, a patterned silver
coating composition layer is obtained, and a patterned silver
conductive layer is obtained by calcining.
[0112] The calcining can be performed at 200.degree. C. or less,
for example, a room temperature (25.degree. C.) or more and
150.degree. C. or less, preferably a room temperature (25.degree.
C.) or more and 120.degree. C. or less. However, in order to
complete the sintering of silver by short-time calcining, the
calcining may be performed at a temperature of 60.degree. C. or
more and 200.degree. C. or less, for example, 80.degree. C. or more
and 150.degree. C. or less, preferably 90.degree. C. or more and
120.degree. C. or less. The time of calcining may be appropriately
determined in consideration of the amount of a silver ink applied,
the calcining temperature, etc., and may be, for example, several
hours (e.g., 3 hours, or 2 hours) or less, preferably 1 hour or
less, more preferably 30 minutes or less, even more preferably 10
minutes to 20 minutes, more specifically 10 minutes to 15
minutes.
[0113] The silver nano-particles have such a constitution as
described above, and are therefore sufficiently sintered even by
such low-temperature and short-time calcining. As a result,
excellent conductivity (low resistance value) is developed. A
silver conductive layer having a low resistance value (e.g., 15
.mu..OMEGA.cm or less, in the range of 7 to 15 .mu..OMEGA.cm) is
formed. The resistance value of bulk silver is 1.6
.mu..OMEGA.cm.
[0114] Since the calcining can be performed at a low temperature,
not only a glass substrate or a heat-resistant plastic substrate
such as a polyimide-based film but also a general-purpose plastic
substrate having low heat resistance, such as a polyester-based
film, e.g., a polyethylene terephthalate (PET) film and a
polyethylene naphthalate (PEN) film, or a polyolefin-based film,
e.g., polypropylene film, can be suitably used as a substrate.
Further, short-time calcining reduces the load on such a
general-purpose plastic substrate having low heat resistance, and
improves production efficiency.
[0115] The silver conductive material according to the present
invention can be applied to electromagnetic wave control materials,
circuit boards, antennas, radiator plates, liquid crystal displays,
organic EL displays, field emission displays (FEDs), IC cards, IC
tags, solar cells, LED devices, organic transistors, condensers
(capacitors), electronic paper, flexible batteries, flexible
sensors, membrane switches, touch panels, EMI shields, and the
like.
[0116] The thickness of the silver conductive layer may be
appropriately determined depending on the intended use.
Particularly, the use of the silver nano-particles according to the
present invention makes it possible, even when a silver conductive
layer having a relatively large film thickness is formed, for the
silver conductive layer to have high conductivity. The thickness of
the silver conductive layer may be selected from the range of, for
example, 5 nm to 10 .mu.m, preferably 100 nm to 5 .mu.m, more
preferably 300 nm to 2 .mu.m.
[0117] The present invention has been described above with
reference mainly to silver nano-particles, but is applied also to a
method for producing metal nano-particles containing a metal other
than silver and said metal nano-particles.
EXAMPLES
[0118] Hereinafter, the present invention will be described more
specifically with reference to examples, but is not limited to
these examples.
[Specific Resistance Value of Calcined Silver Film]
[0119] The specific resistance value of an obtained calcined silver
film was measured by a four-terminal method (Loresta GP MCP-T610).
The measuring limit of this device is 10.sup.7 .OMEGA.cm.
[0120] Reagents used in Examples and Comparative Example are as
follows:
N,N-Dimethyl-1,3-propanediamine (MW: 102.18): manufactured by Tokyo
Chemical Industry Co., Ltd.; n-Butylamine (MW: 73.14): reagent
manufactured by Tokyo Chemical Industry Co., Ltd.; Hexylamine (MW:
101.19): reagent manufactured by Tokyo Chemical Industry Co., Ltd.;
Octylamine (MW: 129.25): reagent manufactured by Tokyo Chemical
Industry Co., Ltd.; Oleic acid (MW: 282.47): reagent manufactured
by Tokyo Chemical Industry Co., Ltd.; Silver oxalate (MW: 303.78):
reagent manufactured by Tokyo Chemical Industry Co., Ltd.;
Methanol: special grade reagent manufactured by Wako Pure Chemical
Industries, Ltd.; 1-Butanol: reagent manufactured by Tokyo Chemical
Industry Co., Ltd.; and Octane: special grade reagent manufactured
by Wako Pure Chemical Industries, Ltd.
Example 1
(Preparation of Silver Nano-Particles)
[0121] 1.28 g (12.5 mmol) of N,N-dimethyl-1,3-propanediamine, 0.91
g (12.5 mmol) of n-butylamine, 3.24 g (32.0 mmol) of hexylamine,
0.39 g (3.0 mmol) of octylamine, and 0.09 g (0.33 mmol) of oleic
acid were added to a 50-mL flask and stirred at a room temperature
to prepare a homogeneous amine-carboxylic acid mixture
solution.
[0122] 3.04 g (10 mmol) of silver oxalate was added to the prepared
mixture solution and stirred at a room temperature to convert
silver oxalate to a viscous white substance. The stirring was
terminated when such conversion was seemingly completed. In this
way, a silver oxalate-amine complex was formed.
[0123] Then, the obtained reaction mixture was heated to
105.degree. C. to 110.degree. C. with stirring. Right after the
start of the stirring, a reaction accompanied by generation of
carbon dioxide was started. Then, the stirring was continued until
the generation of carbon dioxide was completed. As a result, a
suspension was obtained in which shiny blue silver nano-particles
were suspended in the amine-carboxylic acid mixture.
[0124] Then, 10 mL of methanol was added to the obtained suspension
with stirring. Then, the silver nano-particles were spun down by
centrifugation to remove a supernatant. Then, 10 mL of methanol was
again added to the silver nano-particles with stirring, and then
the silver nano-particles were spun down by centrifugation to
remove a supernatant. In this way, wet silver nano-particles were
obtained.
(Preparation and Calcining of Nano-Silver Coating Material)
[0125] Then, a 1-butanl/octane mixed solvent (volume ratio=1/4) was
added to the wet silver nano-particles with stirring so that a
silver concentration was 50 wt % to prepare a silver nano-particle
dispersion liquid. The silver nano-particle dispersion liquid was
applied onto an alkali-free glass plate by spin coating to form a
coating film whose film thickness after calcining was about 1
.mu.m.
[0126] After being formed, the coating film was immediately
calcined in a fan drying oven at 120.degree. C. for 15 minutes to
form a calcined silver film having a thickness of about 1 .mu.m.
The specific resistance value of the obtained calcined silver film
was measured by a four-terminal method and found to be 8.4
.mu..OMEGA.cm.
[0127] Further, the initial dispersibility [1] and the storage
stability [2] of the above described silver nano-particle
dispersion liquid were evaluated in the following manner.
[0128] [1] The above described silver nano-particle dispersion
liquid immediately after its preparation was filtered through a
0.2-.mu.m filter. As a result, clogging of the filter did not
occur. That is, the silver nano-particle dispersion liquid was kept
in a state where the silver nano-particles were well dispersed.
[0129] [2] The above described silver nano-particle dispersion
liquid immediately after its preparation was placed in a
transparent glass sampling bottle, and the sampling bottle was
hermetically sealed and then stored in a dark place at 25.degree.
C. for 7 days. As a result, a silver mirror was not observed.
Further, the silver nano-particle dispersion liquid after the
storage was filtered through a 0.2-.mu.m filter. As a result,
clogging of the filter did not occur. That is, the silver
nano-particle dispersion liquid after the storage was kept in a
state where the silver nano-particles were well dispersed.
(Regarding Silver Oxalate-Amine Complex)
[0130] The viscous white substance obtained in the process of
preparing silver nano-particles was analyzed by a DSC (Differential
Scanning calorimeter), and as a result, its average exothermic
onset temperature by thermal decomposition was 102.5.degree. C. On
the other hand, silver oxalate as a starting material was also
analyzed by a DSC similarly, and as a result, its average
exothermic onset temperature by thermal decomposition was
218.degree. C. That is, the viscous white substance obtained in the
process of preparing silver nano-particles had a lower thermal
decomposition temperature than silver oxalate as a starting
material. The results indicate that the viscous white substance
obtained in the process of preparing silver nano-particles was a
material obtained by bonding between silver oxalate and the
alkylamine, and the white substance was estimated to be a silver
oxalate-amine complex in which the amino group of the alkylamine
was coordinated to a silver atom in silver oxalate.
[0131] The DSC analysis was performed under the following
conditions:
Device: DSC 6220-ASD2 (manufactured by SII Nanotechnology Inc.);
Sample container: 15-.mu.L gold-plated sealed cell (manufactured by
SII Nanotechnology Inc.); Temperature rise rate: 10.degree. C./min
(room temperature to 600.degree. C.); Atmosphere gas inside the
cell: air filled at atmospheric pressure; and Atmosphere gas
outside the cell: nitrogen stream (50 mL/min).
[0132] In addition, the IR spectrum of the viscous white substance
obtained in the process of preparing silver nano-particles was
measured, and as a result, absorption derived from the alkyl group
of the alkylamine was observed (at about 2,900 cm.sup.-1 and about
1,000 cm.sup.-1). The result also indicates that the viscous white
substance obtained in the process of preparing silver
nano-particles was a material obtained by bonding between silver
oxalate and the alkylamine, and the white substance was estimated
to be a silver oxalate-amine complex in which an amino group was
coordinated to a silver atom in silver oxalate.
[0133] FIG. 1 is a transmission electron microscope (TEM)
photograph (.times.100,000 magnifications) of the silver
nano-particles obtained in Example 1. Spherical particles each
having a particle size of about 5 to 20 nm were observed.
Example 2
[0134] A silver nano-particle dispersion liquid was prepared in the
same manner as in Example 1 except that the composition of the
amine-carboxylic acid mixture solution in preparation of silver
nano-particles was changed as follows: 1.28 g (12.5 mmol) of
N,N-dimethyl-1,3-propanediamine, 0.91 g (12.5 mmol) of
n-butylamine, 3.24 g (32.0 mmol) of hexylamine, 0.39 g (3.0 mmol)
of octylamine, and 0.13 g (0.45 mmol) of oleic acid. Then, a
coating film was formed and calcined in the same manner as in
Example 1.
[0135] The obtained calcined silver film had a film thickness of
about 1 .mu.m and a specific resistance value of 11.3
.mu..OMEGA.cm.
[0136] [1] The above described silver nano-particle dispersion
liquid immediately after its preparation was filtered through a
0.2-.mu.m filter. As a result, clogging of the filter did not
occur. That is, the silver nano-particle dispersion liquid was kept
in a state where the silver nano-particles were well dispersed.
[0137] [2] The above described silver nano-particle dispersion
liquid immediately after its preparation was placed in a
transparent glass sampling bottle, and the sampling bottle was
hermetically sealed and then stored in a dark place at 25.degree.
C. for 7 days. As a result, a silver mirror was not observed.
Further, the silver nano-particle dispersion liquid after the
storage was filtered through a 0.2-.mu.m filter. As a result,
clogging of the filter did not occur. That is, the silver
nano-particle dispersion liquid after the storage was kept in a
state where the silver nano-particles were well dispersed.
[0138] Further, the IR spectrum of the viscous white substance
obtained in the process of preparing silver nano-particles was
measured, and as a result, absorption derived from the alkyl group
of the alkylamine was observed (at about 2,900 cm.sup.-1 and about
1,000 cm.sup.-1) as in the case of Example 1.
Example 3
[0139] A silver nano-particle dispersion liquid was prepared in the
same manner as in Example 1 except that the composition of the
amine-carboxylic acid mixture solution in preparation of silver
nano-particles was changed as follows: 1.53 g (15.0 mmol) of
N,N-dimethyl-1,3-propanediamine, 0.73 g (10.0 mmol) of
n-butylamine, 3.24 g (32.0 mmol) of hexylamine, 0.39 g (3.0 mmol)
of octylamine, and 0.13 g (0.45 mmol) of oleic acid. Then, a
coating film was formed and calcined in the same manner as in
Example 1.
[0140] The obtained calcined silver film had a film thickness of
about 1 .mu.m and a specific resistance value of 14.2
.mu..OMEGA.cm.
[0141] [1] The above described silver nano-particle dispersion
liquid immediately after its preparation was filtered through a
0.2-.mu.m filter. As a result, clogging of the filter did not
occur. That is, the silver nano-particle dispersion liquid was kept
in a state where the silver nano-particles were well dispersed.
[0142] [2] The above described silver nano-particle dispersion
liquid immediately after its preparation was placed in a
transparent glass sampling bottle, and the sampling bottle was
hermetically sealed and then stored in a dark place at 25.degree.
C. for 7 days. As a result, a silver mirror was not observed.
Further, the silver nano-particle dispersion liquid after the
storage was filtered through a 0.2-.mu.m filter. As a result,
clogging of the filter did not occur. That is, the silver
nano-particle dispersion liquid after the storage was kept in a
state where the silver nano-particles were well dispersed.
[0143] Further, the IR spectrum of the viscous white substance
obtained in the process of preparing silver nano-particles was
measured, and as a result, absorption derived from the alkyl group
of the alkylamine was observed (at about 2,900 cm.sup.-1 and about
1,000 cm.sup.-1) as in the case of Example 1.
Example 4
[0144] A silver nano-particle dispersion liquid was prepared in the
same manner as in Example 1 except that the composition of the
amine-carboxylic acid mixture solution in preparation of silver
nano-particles was changed as follows: 1.02 g (10 mmol) of
N,N-dimethyl-1,3-propanediamine, 1.10 g (15.0 mmol) of
n-butylamine, 3.24 g (32.0 mmol) of hexylamine, 0.39 g (3.0 mmol)
of octylamine, and 0.13 g (0.45 mmol) of oleic acid. Then, a
coating film was formed and calcined in the same manner as in
Example 1.
[0145] The obtained calcined silver film had a film thickness of
about 1 .mu.m and a specific resistance value of 14.5
.mu..OMEGA.cm.
[0146] [1] The above described silver nano-particle dispersion
liquid immediately after its preparation was filtered through a
0.2-.mu.m filter. As a result, clogging of the filter did not
occur. That is, the silver nano-particle dispersion liquid was kept
in a state where the silver nano-particles were well dispersed.
[0147] [2] The above described silver nano-particle dispersion
liquid immediately after its preparation was placed in a
transparent glass sampling bottle, and the sampling bottle was
hermetically sealed and then stored in a dark place at 25.degree.
C. for 7 days. As a result, a silver mirror was not observed.
Further, the silver nano-particle dispersion liquid after the
storage was filtered through a 0.2-.mu.m filter. As a result,
clogging of the filter did not occur. That is, the silver
nano-particle dispersion liquid after the storage was kept in a
state where the silver nano-particles were well dispersed.
[0148] Further, the IR spectrum of the viscous white substance
obtained in the process of preparing silver nano-particles was
measured, and as a result, absorption derived from the alkyl group
of the alkylamine was observed (at about 2,900 cm.sup.-1 and about
1,000 cm.sup.-1) as in the case of Example 1.
Comparative Example 1
[0149] A silver nano-particle dispersion liquid was prepared in the
same manner as in Example 1 except that the composition of the
amine-carboxylic acid mixture solution in preparation of silver
nano-particles was changed as follows: 2.55 g (25.0 mmol) of
N,N-dimethyl-1,3-propanediamine, 3.24 g (32.0 mmol) of hexylamine,
0.39 g (3.0 mmol) of octylamine, and 0.13 g (0.45 mmol) of oleic
acid. Then, the silver nano-particle dispersion liquid was applied
to form each of coating films whose film thickness after calcining
was about 0.35 .mu.m, 0.65 .mu.m, or 1 .mu.m, and the each of
coating films was calcined.
[0150] The specific resistance value of the obtained calcined
silver film (film thickness: 0.35 .mu.m) was measured and found to
be about 200 .mu..OMEGA.cm.
[0151] The specific resistance value of the obtained calcined
silver film (film thickness: 0.65 .mu.m) was measured and found to
be about 200 .mu..OMEGA.cm.
[0152] The specific resistance value of the obtained calcined
silver film (film thickness: 1 .mu.m) was measured and found to be
about 2.0E+08 .mu..OMEGA.cm.
[0153] [1] The above described silver nano-particle dispersion
liquid immediately after its preparation was filtered through a
0.2-.mu.m filter. As a result, clogging of the filter did not
occur. That is, the silver nano-particle dispersion liquid was kept
in a state where the silver nano-particles were well dispersed.
[0154] [2] The above described silver nano-particle dispersion
liquid immediately after its preparation was placed in a
transparent glass sampling bottle, and the sampling bottle was
hermetically sealed and then stored in a dark place at 25.degree.
C. for 7 days. As a result, a silver mirror was not observed.
Further, the silver nano-particle dispersion liquid after the
storage was filtered through a 0.2-.mu.m filter. As a result,
clogging of the filter did not occur. That is, the silver
nano-particle dispersion liquid after the storage was kept in a
state where the silver nano-particles were well dispersed.
[0155] As described above, the silver nano-particles according to
the examples have excellent dispersibility and storage stability in
the dispersion liquid, and can impart excellent conductivity to a
calcined silver film even when said calcined silver film having a
relatively large thickness of, for example, 1 .mu.m or more is
formed by calcining at a low temperature.
* * * * *