U.S. patent application number 15/448485 was filed with the patent office on 2017-07-27 for nano-sized silver particle ink, nano-sized silver particle sintered body, and method for producing nano-sized silver particle ink.
This patent application is currently assigned to TANAKA KIKINZOKU KOGYO K.K.. The applicant listed for this patent is TANAKA KIKINZOKU KOGYO K.K.. Invention is credited to Hitoshi Kubo, Yuichi Makita, Noriaki Nakamura, Hiroshi Noguchi, Yusuke Ohshima, Junichi Taniuchi.
Application Number | 20170215279 15/448485 |
Document ID | / |
Family ID | 50067867 |
Filed Date | 2017-07-27 |
United States Patent
Application |
20170215279 |
Kind Code |
A1 |
Kubo; Hitoshi ; et
al. |
July 27, 2017 |
NANO-SIZED SILVER PARTICLE INK, NANO-SIZED SILVER PARTICLE SINTERED
BODY, AND METHOD FOR PRODUCING NANO-SIZED SILVER PARTICLE INK
Abstract
Provided are a fine silver particle ink composed of hexylamine,
dodecylamine, oleic acid, fine silver particles and a solvent, in
which the volume resistivity of a sintered body at 100.degree. C.
obtained after the ink is applied on a substrate by spin coating is
8 to 25 .mu..OMEGA. cm, a sintered body thereof, and a method for
producing a fine silver particle ink. When a fine silver particle
ink containing coated fine silver particles is produced by a
silver-amine complex decomposition method, production can be
carried out smoothly. The fine silver particle ink can be sintered
even at a low temperature, and a sintered body thereof has a mirror
surface and low volume resistance.
Inventors: |
Kubo; Hitoshi; (Tsukuba-shi,
JP) ; Ohshima; Yusuke; (Tsukuba-shi, JP) ;
Nakamura; Noriaki; (Tsukuba-shi, JP) ; Noguchi;
Hiroshi; (Tsukuba-shi, JP) ; Taniuchi; Junichi;
(Tsukuba-shi, JP) ; Makita; Yuichi; (Tsukuba-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TANAKA KIKINZOKU KOGYO K.K. |
Tokyo |
|
JP |
|
|
Assignee: |
TANAKA KIKINZOKU KOGYO K.K.
|
Family ID: |
50067867 |
Appl. No.: |
15/448485 |
Filed: |
March 2, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
14614196 |
Feb 4, 2015 |
9674953 |
|
|
PCT/JP2013/068991 |
Jul 11, 2013 |
|
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15448485 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B22F 9/30 20130101; B22F
2001/0066 20130101; B22F 2998/10 20130101; B22F 1/0044 20130101;
H01B 1/22 20130101; H05K 3/1291 20130101; B22F 1/0062 20130101;
B22F 9/30 20130101; B22F 3/10 20130101; Y10T 428/268 20150115; B22F
2998/10 20130101; H05K 1/097 20130101; C09D 11/52 20130101 |
International
Class: |
H05K 1/09 20060101
H05K001/09; C09D 11/52 20060101 C09D011/52; B22F 1/00 20060101
B22F001/00; B22F 9/30 20060101 B22F009/30; H01B 1/22 20060101
H01B001/22; H05K 3/12 20060101 H05K003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 7, 2012 |
JP |
2012-175456 |
Claims
1. A nano-sized silver particle ink formed by dispersing silver
particles in a solvent, wherein the silver particle use a silver
oxalate that has been wetted by 30 to 200 wt % of a solvent, as a
silver raw material, a solvent was added to the silver particles
and dissolved the silver particles such that the silver
concentration after mixing was 20 to 50 wt %, when the nano-sized
silver particle ink is analyzed by a gas chromatography system
having a FID capillary column and the molar ration of hexylamine
with respect to dodecylamine finally included in the silver
particle ink is 3:1 to 60:1, and the amount of oleic acid included
in the silver particle ink is 0.02 to 0.30 mmol/g relative to the
weight of silver and when a silver film formed by applying the ink
on a substrate by spin coating is dried for 5 minutes at room
temperature and then sintered at 100.degree. C., a sintered body
has a volume resistance of 8 to 25 .mu..OMEGA.cm.
2. The nano-sized silver particle ink according to claim 1, wherein
the solvent is composed of a mixed liquid of two or more kinds
selected from any kind of alkane and any kind of alcohol, and
mixing volume ratio is 2:1 to 4:1.
3. The nano-sized silver particle ink according to claim 1, wherein
the average diameter of the silver particle included in the ink is
10 nm to 15nm.
4. The nano-sized silver particle ink according to claim 1, wherein
when the ink is stored at normal temperature and normal pressure,
silver precipitation is visually not recognized after the passage
of one month from production.
5. The nano-sized silver particle ink according to claim 2, wherein
when the ink is stored at normal temperature and normal pressure,
silver precipitation is visually not recognized after the passage
of one month from production.
6. The nano-sized silver particle ink according to claim 3, wherein
when the ink is stored at normal temperature and normal pressure,
silver precipitation is visually not recognized after the passage
of one month from production.
7. The nano-sized silver particle ink according to claim 1, wherein
when a silver film formed by applying the ink on a substrate is
dried for 5 minutes at room temperature and then sintered at
100.degree. C., the silver film has a volume resistance of 12
.mu..OMEGA.cm or less.
8. The nano-sized silver particle ink according to claim 2, wherein
when a silver film formed by applying the ink on a substrate is
dried for 5 minutes at room temperature and then sintered at
100.degree. C., the silver film has a volume resistance of 12
.mu..OMEGA.cm or less.
9. The nano-sized silver particle ink according to claim 3, wherein
when a silver film formed by applying the ink on a substrate is
dried for 5 minutes at room temperature and then sintered at
100.degree. C., the silver film has a volume resistance of 12
.mu..OMEGA.cm or less.
10. The nano-sized silver particle ink according to claim 4,
wherein when a silver film formed by applying the ink on a
substrate is dried for 5 minutes at room temperature and then
sintered at 100.degree. C., the silver film has a volume resistance
of 12 .mu..OMEGA.cm or less.
11. The nano-sized silver particle ink according to claim 1,
wherein when a silver film formed by applying the ink on a
substrate is dried for 5 minutes at room temperature and then
sintered at 100.degree. C., the silver particle sintered body
having a mirror surface.
12. The nano-sized silver particle ink according to claim 2,
wherein when a silver film formed by applying the ink on a
substrate is dried for 5 minutes at room temperature and then
sintered at 100.degree. C., the silver particle sintered body
having a mirror surface.
13. The nano-sized silver particle ink according to claim 3,
wherein when a silver film formed by applying the ink on a
substrate is dried for 5 minutes at room temperature and then
sintered at 100.degree. C., the silver particle sintered body
having a mirror surface.
14. The nano-sized silver particle ink according to claim 4,
wherein when a silver film formed by applying the ink on a
substrate is dried for 5 minutes at room temperature and then
sintered at 100.degree. C., the silver particle sintered body
having a mirror surface.
15. The nano-sized silver particle ink according to claim 7,
wherein when a silver film formed by applying the ink on a
substrate is dried for 5 minutes at room temperature and then
sintered at 100.degree. C., the silver particle sintered body
having a mirror surface.
16. A nano-sized silver particle sintered body, formed by applying
the fine silver particle ink according to claim 1 and then
sintering the ink at 100.degree. C., the silver particle sintered
body having a mirror surface.
17. A nano-sized silver particle sintered body, formed by applying
the fine silver particle ink according to claim 2 and then
sintering the ink at 100.degree. C., the silver particle sintered
body having a mirror surface.
18. A nano-sized silver particle sintered body, formed by applying
the fine silver particle ink according to claim 3 and then
sintering the ink at 100.degree. C., the silver particle sintered
body having a mirror surface.
19. A nano-sized silver particle sintered body, formed by applying
the fine silver particle ink according to claim 4 and then
sintering the ink at 100.degree. C., the silver particle sintered
body having a mirror surface.
20. A nano-sized silver particle sintered body, formed by applying
the fine silver particle ink according to claim 7 and then
sintering the ink at 100.degree. C., the silver particle sintered
body having a mirror surface.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of and claims priority to
co-pending United States patent application Ser. No. 14/614,196,
which was filed Feb. 4, 2015 and claimed priority to International
Patent Application Number PCT/JP2013/068991, which was filed on
Jul. 11, 2013 and claimed priority to Japanese Patent Application
Number 2012/175456, which was filed on Aug. 7, 2012. The disclosure
of the Patent Applications are herein incorporated by reference in
their entirety and for all purposes.
TECHNICAL FIELD
[0002] The present disclosure relates to a method for producing a
fine silver particle ink containing nanometer-sized coated fine
silver particles that exhibit satisfactory electrical conductivity
on a substrate or the like as a result of low temperature
sintering, a fine silver particle ink produced by the relevant
method, and a fine silver particle sintered body.
BACKGROUND ART
[0003] For example, in regard to a printed wiring board for
mounting electronic components, there has been a demand for
speeding up and density increase in the mounting of materials for
forming electroconductive wiring, along with the requests for size
reduction, thickness reduction, and weight reduction of electronic
equipment and an enhancement of productivity.
[0004] In this regard, attempts have been made to form silver
wiring at lower temperatures using an ink having nano-sized fine
silver particles dispersed therein, for example, by an inkjet
printing technology.
[0005] In this case, printing a desired circuit shape using an ink
containing fine silver particles, and binding the fine silver
particles in the coating film by sintering to obtain a thin film
may be considered; however, in view of the heat resistance of
substrates, there is a demand for a fine silver particle-containing
ink that can be sintered at a temperature close to 100.degree. C.
Furthermore, since silver wiring is used, lower volume resistance
is demanded, and in order to do so, it is demanded that the surface
be as smooth as possible.
[0006] For example, Patent Document 1 suggests an ultrafine metal
particle dispersion liquid in which fluidity is maintained even at
a high concentration, and ultrafine metal particles can be
flocculated and concentrated, and a method for production
thereof.
[0007] This is an ultrafine metal particle dispersion liquid in
which ultrafine metal particles having a particle size of 100 nm or
less are dispersed, using one or more of an alkylamine, a
carboxylic acid amide, and an aminocarboxylic acid as
dispersants.
[0008] However, this Patent Document 1 has no disclosure on the
sintering temperature, and when the inventors of the present
disclosure conducted an experiment, it was found that a sintering
temperature far higher than 100.degree. C. was needed.
[0009] Furthermore, Patent Document 2 discloses a method for
producing an ultrafine silver particle colloid by mixing a silver
salt, a reducing agent that does not exhibit a reducing ability in
an organic solvent, and an alkylamine in an organic solvent.
[0010] It is said that this ultrafine silver particle colloid has
an average particle size of 1 to 20 nm and is monodisperse, the
particles are polygonal and have a uniform shape, and the colloid
is suitable as a material for a low temperature sinterable saline
paste or the like. However, there is no disclosure on a specific
sintering temperature, and according to an experiment of the
inventors of the present disclosure, the sintering temperature was
definitely far higher than 100.degree. C. as expected.
[0011] Furthermore, there is no disclosure on the surface roughness
of the sintered bodies of Patent Documents 1 and 2, and it has been
confirmed that both have matt surfaces, and the volume resistance
of the sintered bodies are more than 30 .mu..OMEGA.cm at a film
thickness of about 500 nm in terms of weight.
CITATION LIST
Patent Document
[0012] Patent Document 1: JP 2002-121606 A
[0013] Patent Document 2: JP 2005-36309 A
[0014] Patent Document 3: JP 2010-265543 A
SUMMARY OF DESCRIPTION
[0015] In some embodiments, a fine silver particle ink can be
sintered at a low temperature of about 100.degree. C. and also
gives a sintered body having a smooth surface, a fine silver
particle sintered body, and a method for producing a fine silver
particle ink are disclosed. For example, in accordance with one
embodiment of the disclosure, a fine silver particle ink composed
of hexylamine, dodecylamine, oleic acid, fine silver particles, and
a solvent, which is characterized in that after the fine silver
particle ink is applied on a substrate by spin coating, the volume
resistivity of a sintered body at 100.degree. C. is 8 to 25
.mu..OMEGA.cm.
[0016] In some embodiments, a fine silver particle sintered body
having a mirror surface is formed by applying a fine silver
particle ink such as described above, and then sintering the ink at
100.degree. C.
[0017] Furthermore, in some embodiments, a method for producing a
fine silver particle ink comprises a first step of kneading silver
oxalate and N,N-dimethyl-1,3-diaminopropane; a second step of
kneading the kneading product obtained in the first step with
hexylamine, dodecylamine, and oleic acid, and thereby forming a
silver complex; a third step of heating and stirring the silver
complex, and thereby producing fine silver particles; and a
dispersion step of dispersing the fine silver particles obtained in
the third step in a solvent, and thereby forming an ink.
[0018] In another embodiment, a fine silver particle ink can have a
mirror surface by forming a film by spin coating at room
temperature, and sintering the film at a low temperature.
Furthermore, the sintered body has low volume resistivity, and the
fine silver particle ink enables the formation of an
electroconductive film or an electroconductive wiring even on a
substrate having low heat resistance.
[0019] In yet another embodiment, a method for producing a fine
silver particle ink which can be sintered at a low temperature
while setting the room temperature retention time for a coating
film to zero or for 5 minutes, is disclosed.
BRIEF DESCRIPTION OF DRAWINGS
[0020] FIG. 1 is a transmission electron microscopic (TEM) image of
coated fine silver particles produced by one embodiment of the
present disclosure;
[0021] FIG. 2 is a scanning electron microscopic (SEM) image of a
cross-section of a sintered film (sintered body) of coated fine
silver particles produced by an embodiment of the present
disclosure;
[0022] FIG. 3 is a line diagram illustrating the relationship
between the sintering time and the volume resistance in a sintered
film (sintered body) of coated fine silver particles produced by an
embodiment of the present disclosure;
[0023] FIG. 4 is a photograph showing a mirror image at the mirror
surface of the same sintered film shown in FIG. 3;
[0024] FIG. 5 is a gas chromatographic chart diagram at the time of
amine quantification of a coated fine silver particle ink produced
by an embodiment of the present disclosure; and
[0025] FIG. 6 is a gas chromatographic chart diagram at the time of
oleic acid quantification of a coated fine silver particle ink
produced by an embodiment of the present disclosure.
DETAILED DESCRIPTION
[0026] Hereinafter, the method for producing coated fine silver
particles according to the present disclosure, a fine silver
particle ink produced by the method according to the present
disclosure, and a sintered body of these fine silver particles will
be described.
[0027] It is known that an ink containing fine silver particles
protected by a protective film of an alkylamine is produced by
heating a complex compound formed from a silver compound such as
silver oxalate and an alkylamine in the presence of an alkylamine,
and aggregating atomic silver that is generated by decomposing the
silver compound of oxalic acid ion contained in the relevant
complex compound.
[0028] In the first step according to an exemplary embodiment of
the present disclosure, silver oxalate that has been wetted in
advance by 30 to 200 wt % of a solvent such as decane or methanol,
and an alkyldiamine including N, N-dimethyl-1, 3-diaminopropane are
kneaded. Completion of this kneading is determined based on whether
the complex compound (silver complex) to be purified exhibits a
color corresponding to the constituent component thereof.
[0029] In the second step, hexylamine, dodecylamine and oleic acid
are added to the kneading product obtained in the first step.
[0030] Next, in the third step, the silver complex is heated and
stirred at 110.degree. C. During this heating and stirring, when
the cream colored silver complex gradually turns brown and further
changes to black, purification of the fine silver particles can be
confirmed. In this third step, gas bubbles are generated from the
reaction system, and the time point at which these gas bubbles are
no longer generated is considered as the end point of the reaction
induced by heating and stirring.
[0031] In a centrifugation process, an alcohol such as methanol is
added to the reaction system of the third step (matrix containing
fine silver particles), the mixture is sufficiently stirred, and
this mixture is supplied to a centrifuge.
[0032] Since fine silver particles do not dissolve in methanol, the
fine silver particles are precipitated by centrifugation and
separated from the methanol solution. At this time, since the
diamine that has not adsorbed to the fine silver particles as a
protective agent, hexylamine, dodecylamine and oleic acid are
dissolved in methanol, when the supernatant generated by
centrifugation is removed, any excess amounts of these organic
protective agents that are not dissolved can be separated.
[0033] Purification of fine silver particles by this addition of
methanol and centrifugation is carried out at least two times, and
thus fine silver particles are obtained as a precipitate.
[0034] The dispersion step involves dispersing the fine silver
particles that have been obtained from the centrifugation process,
in a solvent to form an ink. For example, a silver ink is obtained
by dissolving the fine silver particles in a mixed solvent of
octane and butanol (4:1) to be a silver concentration of 20 to 50
wt %. The mixed solvent may include trace amounts of hexylamine,
dodecylamine, and oleic acid.
[0035] When silver oxalate is wetted in advance with a solvent, a
rapid decomposition reaction of the silver compound or evaporation
of the constituent components of the alkylamine can be suppressed
at the time of kneading of the silver oxalate and alkylamine. When
the amount of the solvent is less than 30 wt %, the suppressive
effect is insufficient, and when the amount of the solvent is more
than 200 wt %, excessive suppression occurs.
[0036] In addition, if kneading is possible in the first step, it
is not essential to wet the silver oxalate. However, in this case,
precise control is required for the kneading, such as by kneading
small amounts of silver oxalate and the alkylamine several
times.
[0037] When coated fine silver particles are produced, silver
carboxylate, silver chloride, silver nitrate or the like can be
used as the silver compound; however, from the viewpoint that
metallic silver is easily purified by decomposition, and impurities
other than silver are not easily generated, silver oxalate is
preferred.
[0038] As described above, the silver concentration in the coated
fine silver particles is determined by subjecting the silver
precipitate obtained after methanol washing in the centrifugation
process, to a TG-DTA analysis (thermogravimetry-differential,
thermal analysis). Furthermore, in regard to the composition of the
protective agent present in a fine silver particle ink, an analysis
of the amine component can be carried out by directly feeding a
fine silver particle ink obtained as a final product, to a gas
chromatography system having a FID (hydrogen flame ionization
detector) capillary column.
[0039] The molar ratio of hexylamine with respect to dodecylamine
finally included in the fine silver particle ink is 3:1 to 60:1,
and is preferably in the range of 3:1 to 9:1. Furthermore, the
amount of oleic acid included in the fine silver particle ink is
0.02 to 0.30 mmol/g relative to the weight of silver. If the ratio
exceeds the range described above, film formation may be achieved
incompletely, the volume resistance of the sintered body may be
large, or an ink having poor uniformity of fine silver particles
may be obtained.
[0040] Film formation using the fine silver particle ink obtained
after the various processes described above can be achieved by, for
example, rotating a base material (substrate) such as a PET
(polyethylene terephthalate) film, and then spin coating the fine
silver particle ink by dropping the ink onto the base material. The
silver film thus formed is dried, together with the base material,
in air at room temperature for about 5 minutes, and then is
sintered by heating at 100.degree. C. using a dryer.
[0041] At this time, an optimal sintering time can be determined by
measuring the volume resistance of the film at every hour. Also,
the film thickness of the sintered silver can be calculated by SEM
observation.
[0042] Regarding the solvent in the dispersion step, for example, a
mixed solution of n-octane and n-butanol is preferred for the
dispersion of coated fine silver particles.
[0043] According to the present disclosure, since silver oxalate is
wetted by a solvent before being mixed with an alkylamine, when
silver oxalate is mixed with N,N-dimethyl-1,3-diaminopropane, the
decomposition reaction of silver oxalate and evaporation of the
constituent components of the alkylamine can be sufficiently
suppressed, and the reaction proceeds uniformly. Thus, a
N,N-dimethyl-1,3-diaminopropane-coordinated silver complex is
produced.
[0044] Furthermore, also in the second step of adding hexylamine,
dodecylamine and oleic acid to the
N,N-dimethyl-1,3-diaminopropane-coordinated silver complex, the
composition of the protective agent on the surface of the silver
particles thus produced is made uniform by the presence of the
solvent.
[0045] In a case in which there is no solvent, when the
N,N-dimethyl-1,3-diaminopropane-coordinated silver complex is
produced, a solid that is difficult to stir is formed. Thus, even
if hexylamine, dodecylamine, and oleic acid are added to this solid
so as to produce silver particles, since this leads to a reaction
between a solid and a liquid, the reaction proceeds only at the
interface thereof, and the system becomes non-uniform. Therefore,
fluctuation occurs in the composition of the protective agent that
adsorbs to the individual fine silver particles. For example, when
there are particles that are rich in dodecylamine having a large
carbon number on the surface, it is contemplated that at the time
of sintering, the sintering time is lengthened because dodecylamine
has a high boiling point. Furthermore, it is expected that
sintering may be achieved with difficulties because the protective
agent film is stabilized due to the hydrophobic interaction between
dodecyl groups.
[0046] As a result, although the correct reason was not clearly
understood, as soon as the fine silver particle ink was applied on
a PET substrate (about for 0 to 5 minutes), the fine silver
particle ink could be sintered at a low temperature such as
100.degree. C. Also, the sintered body had a mirror surface, and
satisfactory results such as a volume resistance of 12
.mu..OMEGA.cm or less were obtained. Furthermore, when the fine
silver particle ink was applied on a substrate and baked at
200.degree. C., the volume resistance of the baked product was 2
.mu..OMEGA.cm or less.
EXAMPLES
[0047] Hereinafter, Examples of the present disclosure will be
specifically described.
[0048] A fine silver particle ink according to the Examples was
produced as follows.
[0049] In the first step, N,N-dimethyl-1,3-diaminopropane was
kneaded together with silver oxalate that had been wetted by 30 to
200 wt % of an organic solvent, and thus a
N,N-dimethyl-1,3-diaminopropane-coordinated silver complex was
formed. In the second step, hexylamine (carbon number: 6),
dodecylamine (carbon number: 12), and oleic acid (carbon number:
19) as a fatty acid were added to the mixture of the first step,
and the resulting mixture was kneaded.
[0050] More specifically, in the first step, silver oxalate was
synthesized from silver nitrate and oxalic acid dihydrate, and an
organic solvent was added to this silver oxalate. In the present
Example, an alkylamine was added such that the total number of
moles of the alkylamine would be approximately 4 to 6 times the
molar amount of silver oxalate. Since two silver atoms are present
in a molecule of silver oxalate, the amount of the alkylamine
corresponds to 2 to 3 times the molar amount based on silver atoms.
Specifically, the amount of silver oxalate wetted with 30 wt % of
an organic solvent was 2.17 g (Ag=10.0 mmol), and the amount of
N,N-dimethyl-1,3-diaminopropane was 0.78 g (7.61 mmol). After the
introduction of silver oxalate, the mixture was kneaded until a
creamy state was obtained at room temperature, and thereby silver
oxalate was changed to a white substance. Then, kneading was
terminated at a time point at which the relevant change was
acknowledged to be seemingly completed.
[0051] In the second step, 1.16 g (11.42 mmol) of n-hexylamine and
0.18 g (0.95 mmol) of n-dodecylamine were added to the mixture of
the first step, and 0.042 g.apprxeq.44.9 .mu.L of oleic acid (1.5
mol % with respect to Ag) was further added thereto. This mixture
was kneaded until a creamy state was obtained at room temperature,
and similarly to the first step, kneading was terminated at a time
point at which the change was acknowledged to be seemingly
completed.
[0052] To a viscous white substance obtained as described above,
diethyl ether capable of dissolving an alkylamine was added, and
thereby unreacted alkylamine that was not bound to the white
substance was separated and removed. Subsequently, the IR spectrum
(infrared absorption spectrum) of the remaining white substance was
measured, and absorption attributable to the alkyl chain of the
alkylamine was observed. From this, the white substance obtained as
described above was found to be a product formed as silver oxalate
and an alkylamine were bonded, and it was speculated that the white
substance was a complex compound formed as the amino groups of the
alkylamine are coordination bonded to the silver atoms of silver
oxalate.
[0053] In the third step, the complex compound thus obtained was
transferred to an oil bath, and heating and kneading was carried
out at a temperature set to 100.degree. C. Immediately after the
initiation of kneading, a reaction accompanied by generation of
carbon dioxide was initiated, and thereafter, kneading was carried
out until the generation of carbon dioxide was completed. Thereby,
a suspension liquid in which fine silver particles exhibiting blue
gloss were suspended in an amine mixture was obtained.
[0054] Next, in the centrifugation process, in order to substitute
the dispersing medium of the suspension liquid, 4 g of methanol was
added to the suspension liquid, and the mixture was then stirred.
Subsequently, the fine silver particles were precipitated by
centrifugation, and were separated by removing the supernatant. 4 g
of methanol was added again to the separated fine silver particles,
and the mixture was subjected to stirring and centrifugation.
Thereby, fine silver particles were precipitated and separated.
[0055] In the dispersion step, a mixed solvent of n-butanol and
n-octane (volume ratio 1:4) was added to the fine silver particles
and dissolved the fine silver particles such that the silver
concentration after mixing was 1 to 50 wt %, and preferably 20 to
50 wt %. Thus, a fine silver particle ink in which dark yellow
orange-colored coated fine silver particles were independently
dispersed was obtained. This dark yellow orange color represents
that in regard to the coated fine silver particles thus produced,
the surface atoms of the fine silver particles were in a metallic
state without forming a compound or the like, and thereby the
coated fine silver particles exhibit a surface plasmon band with a
maximum wavelength of about 396 mm that is attributable to metal
silver; and that the fine silver nanoparticles are independently
dispersed in the solvent. In addition, it is also acceptable to use
a solvent other than n-butanol and n-octane, for example, pentanol
or decane.
[0056] A TEM photograph of the fine silver particle ink is shown in
FIG. 1. It can be seen from FIG. 1 that the fine silver particles
are satisfactorily dispersed, and the particle size is in the range
of 10 to 15 nm.
[0057] The silver concentration in the fine silver particles was
determined by subjecting the precipitate obtained after methanol
washing, to a TG-DTA analysis.
[0058] Also, an analysis of the amine component was carried out by
producing fine silver particle inks by dissolving an Ag precipitate
that had been centrifuged after adding methanol in various
solvents, and feeding the inks directly to a gas chromatographic
system (GC) having an FID capillary column. Thus, the composition
of the protective agent that was adsorbed to the fine silver
particles was investigated.
[0059] Furthermore, a film of silver was formed on PET by spin
coating the present fine silver particle ink (dropping the Ag ink
on a PET film that was rotated at 1000 to 2000). The silver-coated
PET film thus obtained was embedded in resin, and subsequently a
silver coating film cross-section was obtained by polishing. A SEM
observation of this cross-section was conducted, and the film
thickness was measured. The film thicknesses of various silver
coating films were about 500 nm (FIG. 2). The electrical
resistances of the silver films were measured at various heating
times. The electrical resistance was carried out by a four-probe
method (Loresta-GP Mitsubishi Chemical Analytech). The volume
resistance was calculated from the film thickness of the silver
coating film estimated from the SEM observation.
[0060] FIG. 3 shows the relationship between the baking time and
the measured values of volume resistance in a case in which films
of the fine silver particle inks produced in the following
Experimental Examples 2, 6 and 8 and Comparative Example 1 were
produced by spin coating and sintered (film thickness 500 nm) at a
baking temperature of 100.degree. C. The minimum value of the
volume resistance was 12 .mu..OMEGA.cm under heating at 100.degree.
C., and the minimum value was 2 .mu..OMEGA.cm under heating at
200.degree. C.
Experimental Examples
[0061] Experimental Examples 1 to 15 are described in Table 1.
Also, Comparative Examples 1 to 8 are described in Table 2.
TABLE-US-00001 TABLE 1 Amount of addition mmol Production of
Solvent for Oleic fine Stability synthesis Solvent of ink Diamine
Hexylamine Dodecylamine acid silver particles of ink Experimental
Methanol Octane butanol 7.61 11.42 0.95 0.15 .smallcircle.
.smallcircle. Example 1 4:1 Experimental n-Hexane Octane butanol
7.61 11.42 0.95 0.15 .smallcircle. .smallcircle. Example 2 4:1
Experimental Toluene Octane butanol 7.61 11.42 0.95 0.15
.smallcircle. .smallcircle. Example 3 4:1 Experimental n-Butanol
Octane butanol 7.61 11.42 0.95 0.15 .smallcircle. .smallcircle.
Example 4 4:1 Experimental n-Octane Octane butanol 7.61 11.42 0.95
0.15 .smallcircle. .smallcircle. Example 5 4:1 Experimental
n-Decane Octane butanol 7.61 11.42 0.95 0.15 .smallcircle.
.smallcircle. Example 6 4:1 Experimental n-Dodecane Octane butanol
7.61 11.42 0.95 0.15 .smallcircle. .smallcircle. Example 7 4:1
Experimental d-Terpineol Octane butanol 7.61 11.42 0.95 0.15
.smallcircle. .smallcircle. Example 8 4:1 Experimental n-Hexane
Decane butanol 7.61 11.42 0.95 0.15 .smallcircle. .smallcircle.
Example 9 2:1 Experimental n-Decane Decane hexanol 7.61 11.42 0.95
0.15 .smallcircle. .smallcircle. Example 10 4:1 Experimental
n-Dodecane Octane pentanol 7.61 11.42 0.95 0.15 .smallcircle.
.smallcircle. Example 11 3:1 Experimental n-Hexane Octane hexanol
7.61 11.42 0.95 0.15 .smallcircle. .smallcircle. Example 12 4:1
Experimental n-Decane Octane butanol 7.61 11.42 0.47 0.15
.smallcircle. .smallcircle. Example 13 4:1 Experimental n-Decane
Octane butanol 7.61 11.42 1.90 0.15 .smallcircle. .smallcircle.
Example 14 4:1 Experimental n-Decane Octane butanol 7.61 22.85 0.95
0.15 .smallcircle. .smallcircle. Example 15 4:1
TABLE-US-00002 TABLE 2 Amount of addition mmol Production of
Solvent for Oleic fine Stability synthesis Solvent of ink Diamine
Hexylamine Dodecylamine acid silver particles of ink Comparative
None Octane butanol 7.61 11.40 0.95 0.15 .smallcircle.
.smallcircle. Example 1 4:1 Comparative Chloroform -- 7.61 11.40
0.95 0.15 x -- Example 2 Comparative Water Octane butanol 7.61
11.40 0.95 0.15 .smallcircle. x Example 3 4:1 Comparative
n-Tetradecane Octane butanol 7.61 11.40 0.95 0.15 .smallcircle.
.smallcircle. Example 4 4:1 Comparative n-Decane Octane butanol
22.84 11.40 0.95 0.15 .smallcircle. x Example 5 4:1 Comparative
n-Decane Octane butanol 7.61 11.40 0.95 0.45 .smallcircle.
.smallcircle. Example 6 4:1 Comparative n-Decane Octane butanol
7.61 11.40 0.95 0.08 .smallcircle. x Example 7 4:1 Comparative
n-Decane Tetradecane 7.61 11.40 0.95 0.15 .smallcircle.
.smallcircle. Example 8 butanol 7:3
[0062] Experimental Examples 1 to 8 and Comparative Examples 2 to 4
are investigations on wetting by various organic solvents,
Comparative Example 1 is an investigation on the absence of
wetting, and Experimental Examples 9 to 12 and Comparative Example
8 are investigations on the kinds of the organic solvents used for
final dispersing. In Experimental Examples 13 to 15 and Comparative
Examples 5 to 7, fine silver particle inks are produced by
investigating the amounts of addition of
N,N-dimethyl-1,3-diaminopropane, hexylamine, dodecylamine, and
oleic acid with respect to silver oxalate.
[0063] In Experimental Examples 1 to 15, fine silver particle inks
can be synthesized, and stable inks that do not produce
precipitates for one month or more are obtained. On the other hand,
in Comparative Example 2, synthesis of fine silver particles cannot
be achieved, and an ink cannot be obtained. Furthermore, in
Comparative Examples 3, 5 and 7, fine silver particles can be
synthesized; however, thereafter, silver precipitates are
generated, and inks having poor stability are obtained.
[0064] Table 3 presents the following items of Experimental
Examples 1 to 15, and Table 4 presents the following items of
Comparative Examples 1 to 8: the molar ratios of hexylamine and
dodecylamine included in the fine silver particle inks produced
respectively in the Experimental Examples and Comparative Examples,
the ratios of mmol of oleic acid and g of silver weight, and the
results of volume resistance values (obtainable after heating for
20 minutes and after heating for 120 minutes) obtained when the
inks were spin coated on PET films and thereby sintered bodies were
formed at 100.degree. C. Also, evaluations made by visually
observing the surfaces of the films sintered at 100.degree. C. and
rated on the basis of three grades such as mirror surface (O),
dullness (A), and cloudiness (X), are described in Tables 3 and
4.
TABLE-US-00003 TABLE 3 Mirror Volume resistance surface Hexyl/
.mu..OMEGA. cm properties dodecyl Oleic After 120 After 20 of film
after (mol/ acid/Ag minutes at minutes at 120 minutes mol) (mmol/g)
100.degree. C. 100.degree. C. at 100.degree. C. Experimental 7
0.077 15.43 23.24 .smallcircle. Example 1 Experimental 6 0.073
11.99 17.82 .smallcircle. Example 2 Experimental 9 0.066 9.21 11.5
.smallcircle. Example 3 Experimental 6 0.055 10.04 13.13
.smallcircle. Example 4 Experimental 7 0.080 10.37 15.32
.smallcircle. Example 5 Experimental 7 0.075 22.31 12.30
.smallcircle. Example 6 Experimental 7 0.098 9.37 14.33
.smallcircle. Example 7 Experimental 6 0.092 16.63 28.71
.smallcircle. Example 8 Experimental 8 0.095 15.34 27.43
.smallcircle. Example 9 Experimental 7 0.073 18.79 32.19
.smallcircle. Example 10 Experimental 5 0.078 22.38 35.64
.smallcircle. Example 11 Experimental 7 0.085 13.49 19.27
.smallcircle. Example 12 Experimental 30 0.088 22.3 48.544
.smallcircle. Example 13 Experimental 3 0.040 16.9 50.108
.smallcircle. Example 14 Experimental 60 0.025 20.41 49.962
.smallcircle. Example 15
TABLE-US-00004 TABLE 4 Mirror Volume resistance surface Hexyl/
.mu..OMEGA. cm properties dodecyl Oleic After 120 After 20 of film
after (mol/ acid/Ag minutes at minutes at 120 minutes mol) (mmol/g)
100.degree. C. 100.degree. C. at 100.degree. C. Comparative 8 0.051
25.52 64.74 .DELTA. Example 1 Comparative -- -- -- -- -- Example 2
Comparative -- -- -- -- -- Example 3 Comparative 6 0.095 51268
3294100 x Example 4 Comparative 10.030 0.030 -- -- -- Example 5
Comparative 5 0.328 59144000 41541500 x Example 6 Comparative 6
0.020 12.59 16.773 .smallcircle. Example 7 Comparative 7 0.070
336.18 1978000 x Example 8
[0065] The ratios of hexylamine and dodecylamine for Experimental
Examples 1 to 15 in which stable fine silver particle inks could be
synthesized were 3 to 60, and the amount of oleic acid was in the
range of 0.025 to 0.098 mmol/g relative to the weight of silver.
Furthermore, in Experimental Examples 1 to 15, the volume
resistance values obtained when the fine silver particle inks were
spin coated on PET substrates and sintered at 100.degree. C. were
50.108 .mu..OMEGA.cm or less in 20 minutes. Thus, the electrical
resistance was decreased in a short time, and silver films having
mirror surfaces were obtained.
[0066] On the other hand, in Comparative Example 1 produced without
wetting silver oxalate with a solvent, a stable fine silver
particle ink can be obtained, but the volume resistance value
obtained when the ink was spin coated on a PET substrate and then
sintered at 100.degree. C. is more than 60 .mu..OMEGA.cm in 20
minutes. Thus, the decrease in the volume resistance is slower than
the case of producing the fine silver particle ink by wetting.
Furthermore, even if the ink is heated for 120 minutes, a volume
resistance of less than 25 .mu..OMEGA.cm is not obtained. Also, the
silver film surface obtained after sintering was dull.
[0067] In Comparative Example 4, a film having very high volume
resistance and low electrical conductivity is obtained. In this
Example, a fine silver particle ink was synthesized by wetting
silver oxalate with tetradecane. However, it is speculated that
even though a final ink state was achieved, since a slight amount
of tetradecane was remaining in the ink, when the ink is sintered
at 100.degree. C., tetradecane having a high boiling point remains
behind and prevents a decrease in the electrical resistance. Also,
the silver film surface obtained after sintering was cloudy.
[0068] Comparative Example 5 is an ink produced using
N,N-dimethyl-1,3-diaminopropane in an amount of addition three
times the usual amount, and by decane wetting. Thus, synthesis of a
fine silver particle ink is possible, but the ink stability is
poor. This is speculated to be because a large amount of
N,N-dimethyl-1,3-diaminopropane is adsorbed as a protective agent
to the surfaces of the fine silver particles, and the amount of
adsorption of other protective agents is not sufficient.
[0069] Comparative Example 6 was produced by decane wetting and
using oleic acid in an amount of addition three times the usual
amount, and thus a fine silver particle ink having very high
stability is obtained. The amount of oleic acid in the ink is 0.3
mmol/g or more relative to the weight of silver, and the amount of
oleic acid in the ink is excessively large compared to Experimental
Examples 1 to 15. When this is used to form a film, a film having
very high volume resistance and low electrical conductivity is
obtained. Furthermore, the surface of the silver film obtained
after sintering was cloudy.
[0070] Comparative Example 7 was a fine silver particle ink
produced by decane wetting and using oleic acid in an amount of
addition 1/3 times the usual amount. Thus, when a film is formed,
the film has low volume resistance and satisfactory electrical
conductivity; however, the ink has poor long-term stability, and
precipitation occurs in about one month. This is because the amount
of oleic acid in the ink is only 0.02 mmol/g relative to the weight
of silver.
[0071] Comparative Example 8 is a fine silver particle ink produced
by decane wetting and using tetradecane/butanol (7:3) as the
solvent, and a stable silver ink is obtained. However, since the
ink contains a large amount of tetradecane having high boiling
point, when a film is formed, a film having very high volume
resistance and low electrical conductivity is obtained.
[0072] The ratio of hexylamine/dodecylamine included in a final
fine silver particle ink was calculated by analyzing the produced
fine silver particle ink by gas chromatography. The analysis method
is described below.
[0073] Column: Stabilwax-DB 30 m.times.0.25 mm ID, film thickness
0.25 .mu.m
[0074] Conditions for temperature rise: 80.degree. C. (retention 5
min) to 200.degree. C. (retention 20 min), temperature rise
20.degree. C./min, injection port temperature: 200.degree. C.,
split mode (20:1)
[0075] Detector temperature: 210.degree. C., FID
[0076] Carrier gas: Helium 160 kPa
[0077] Injection amount: 1 .mu.L
[0078] When a sample is analyzed by the above-described method, a
peak originating from hexylamine is detected at 2.45 to 2.65 min.,
a peak originating from diamine is detected at 3.10 to 3.30 min.,
and a peak originating from dodecylamine is detected at 10.40 to
10.50 min. (FIG. 5). The concentrations of the various protective
agents included in an Ag ink were determined from these peak areas
and calibration curves produced in advance.
[0079] The ratio of the moles of oleic acid and the weight of
silver included in a final fine silver particle ink was calculated
by analyzing the produced fine silver particle ink by gas
chromatography. The analysis method is described below.
[0080] Column: Stabilwax-DA 30 m.times.0.25 mm ID, film thickness
0.25 .mu.m
[0081] Column temperature: 250.degree. C.
[0082] Injection port temperature: 250.degree. C., split mode
(20:1)
[0083] Detector temperature: 230.degree. C., FID
[0084] Carrier gas: Helium 160 kPa
[0085] Injection amount: 1 .mu.L
[0086] When a sample is analyzed by the above-described method, a
peak originating from oleic acid is detected at 11.90 to 12.35 min.
(FIG. 6). The concentrations of various protective agents included
in an Ag ink were determined from this peak area and a calibration
curve produced in advance.
[0087] Advantageously, when ink is applied and sintered, the
sintered body of a coating film of the fine silver particle ink has
low volume resistance and has a mirror surface. Therefore, the fine
silver particle ink can be used for electroconductive silver wiring
in a printed wiring board. Furthermore, since the sintered body has
a mirror surface, an optically reflective surface can be easily
formed.
* * * * *