U.S. patent application number 14/652084 was filed with the patent office on 2015-11-12 for method for manufacturing silver nanowires using ionic liquid.
The applicant listed for this patent is INSCON TECH CO., LTD., SOLOE TECH CO., LTD.. Invention is credited to Jong Eun KIM, Tae Young KIM, Kwang Suck SUH.
Application Number | 20150321257 14/652084 |
Document ID | / |
Family ID | 50934496 |
Filed Date | 2015-11-12 |
United States Patent
Application |
20150321257 |
Kind Code |
A1 |
SUH; Kwang Suck ; et
al. |
November 12, 2015 |
METHOD FOR MANUFACTURING SILVER NANOWIRES USING IONIC LIQUID
Abstract
The present invention relates to a method of preparing silver
nanowires having a diameter of less than 100 nm and a length of 10
.mu.m or more, and, more particularly, to a method of uniformly
preparing silver nanowires having a high aspect ratio using an
ionic liquid as an additive in addition to a silver salt precursor,
a reducing solvent and a capping agent in a polyol process. When
the technology of the present invention is used, silver nanowires
having a diameter of less than 100 nm and a length of 10 .mu.m or
more can be uniformly prepared. Further, when a transparent
conductive film is formed by applying a silver nanowire-dispersed
solution onto a base film, the transparent conductive film has a
surface resistivity of 10.sup.1.about.10.sup.3.OMEGA./.quadrature.
and a light transmittance of 90% or more to the base film.
Inventors: |
SUH; Kwang Suck;
(Gyeonggi-do, KR) ; KIM; Jong Eun; (US) ;
KIM; Tae Young; (US) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SOLOE TECH CO., LTD.
INSCON TECH CO., LTD. |
Anseong-si, Gyeonggi-do
Hwaseong-si, Gyeonggi-do |
|
KR
KR |
|
|
Family ID: |
50934496 |
Appl. No.: |
14/652084 |
Filed: |
December 14, 2012 |
PCT Filed: |
December 14, 2012 |
PCT NO: |
PCT/KR2012/010921 |
371 Date: |
June 12, 2015 |
Current U.S.
Class: |
252/514 ;
75/370 |
Current CPC
Class: |
C22B 11/04 20130101;
B22F 9/24 20130101; B22F 1/004 20130101; B82Y 30/00 20130101; B22F
1/0025 20130101; C22C 5/06 20130101 |
International
Class: |
B22F 9/24 20060101
B22F009/24; C22B 3/00 20060101 C22B003/00; C22C 5/06 20060101
C22C005/06; B22F 1/00 20060101 B22F001/00 |
Claims
1. A method of preparing silver nanowires by a polyol reduction
reaction of a mixed solution including a silver salt precursor, a
reducing solvent and a capping agent, wherein the polyol reduction
reaction of the mixed solution is performed by adding an ionic
liquid to the mixed solution as an additive, wherein the ionic
liquid is a compound comprising an organic cation having an
imidazolium group and an organic or inorganic anion, the compound
being represented by Formula 1 below in the form of a monomer or
being represented by Formula 2 below in the form of a polymer:
##STR00002## where R1, R2 and R3 are identical to or different from
each other, each of which is hydrogen or a hydrocarbon group of 1
to 16 carbon atoms, and each of which includes at least one
heteroatom selected from the group consisting of oxygen, sulfur,
nitrogen, phosphorus, fluorine, chlorine, bromine, iodine and
silicon; X-- is an anion, and is an organic or inorganic compound
including a halogen ion such as a chlorine ion (Cl.sup.-) or a
bromine ion (Br.sup.-); and n is a repetitive unit, and is a
natural number.
2. (canceled)
3. The method of claim 1, wherein, in the ionic liquid, the
monomeric cationic compound is selected from the group consisting
of 1,3-dimethylimidazolium, 1,3-diethylimidazolium,
1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium,
1-hexyl-3-methylimidazolium, 1-octyl-3-methylimidazolium,
1-decyl-3-methylimidazolium, 1-dodecyl-3-methylimidazolium and
1-tetradecyl-3-imidazolium, and the polymeric cationic compound is
selected from the group consisting of
poly(1-vinyl-3-alkylimidazolium), poly(1-allyl-3-alkylimidazolium)
and poly(1-(meth)acryloyloxy-3-alkylimidazolium).
4. The method of claim 3, wherein, in a mixing ratio of a silver
salt precursor, a capping agent and an ionic liquid, the capping
agent is included in an amount of 1 to 2 mol based on 1 mol of the
silver salt precursor, and the ionic liquid is included in an
amount of 0.001 to 0.2 mol based on 1 mol of the silver salt
precursor.
5. The method of claim 4, wherein a reaction temperature for
synthesizing silver nanowires is 50.about.180.degree. C.
6. The method of claim 5 wherein the silver salt precursor includes
a silver cation and an organic or inorganic anion, and includes at
least one selected from the group consisting of AgNO.sub.3,
AgClO.sub.4, AgBF.sub.4, AgPF.sub.6, CH.sub.3COOAg,
AgCF.sub.3SO.sub.3, Ag.sub.2SO.sub.4,
CH.sub.3COCH.dbd.COCH.sub.3Ag.
7. The method of claim 1, wherein the reducing solvent is a solvent
including diol, polyol or glycol having two or more hydroxy groups
in a molecule thereof.
8. The method of claim 5, wherein the capping agent is
polyvinylpyrrolidone (PVP) or polyvinylalcohol (PVA).
9. (canceled)
10. A silver nanowire-dispersed solution prepared by dispersing
0.1.about.5 wt % of the silver nanowires having an aspect ratio of
100 or more, prepared by the method of claim 1 in 95.about.99.9 wt
% of a solvent.
11. The silver nanowire-dispersed solution of claim 10, wherein the
solvent includes at least one selected from the group consisting of
water, methanol, ethanol, n-propyl alcohol, iso-propyl alcohol,
n-butanol, iso-butanol, hexanol, benzyl alcohol, diacetone alcohol,
ethyleneglycol, propyleneglycol, glycerol, 1,4-dioxane,
tetrahydrofuran (THF), ethyleneglycol monomethyl ether,
ethylenglycol monoethyl ether, ethyleneglycol dimethyl ether,
propyleneglycol monomethyl ether, propyleneglycol monoethyl ether,
propyleneglycol dimethyl ether, N,N-dimethylformamide,
N-methylformamide, N,N-dimethylacetamide (DMA), acetonitrile,
acetaldehyde, N-methyl-2-pyrrolidone, 2-pyrrolidone,
N-vinyl-2-pyrrolidone, dimethylsulfoxide, n-butyrolactone,
nitromethane, and ethyl lactate.
12. The silver nanowire-dispersed solution of claim 11, further
comprising 0.01 to 10 parts by weight of a dispersant and 0.01 to
10 parts by weight of a thickener based on 100 parts by weight of
the silver nanowire-dispersed solution.
13. The silver nanowire-dispersed solution of claim 12, wherein the
dispersant includes at least one selected from the group consisting
of polyoxyethylene aliphatic ether, polyoxyethylene phenyl ether,
polyimine, alkyl phosphate, an alkylammonium salt, a polyester
alkylolammonium salt, a polyacrylic alkylolammonium salt,
polydimethylsilane, polyacrylic acid, polysulfonic acid and
polyvinylpyrrolidone, and the thickener includes at least one
selected from the group consisting of a urethane-modified
thickener, an acrylic thickener, methylcellulose, ethylcellulose,
hydroxyethylcellulose, hydroxymethylcellulose,
hydroxypropylcellulose and hydroxypropylmethylcellulose.
14. A transparent conductive film formed by applying the silver
nanowire-dispersed solution including the silver nanowires prepared
by the method of claim 1 onto a base film.
15. The transparent conductive film of claim 14, wherein the
transparent conductive film has a surface resistivity of
10.sup.1.about.10.OMEGA./.quadrature. and a light transmittance of
90% or more to the base film.
16. The method of claim 3, wherein the reducing solvent is a
solvent including diol, polyol or glycol having two or more hydroxy
groups in a molecule thereof.
17. The method of claim 4, wherein the reducing solvent is a
solvent including diol, polyol or glycol having two or more hydroxy
groups in a molecule thereof.
18. The method of claim 5, wherein the reducing solvent is a
solvent including diol, polyol or glycol having two or more hydroxy
groups in a molecule thereof.
19. The method of claim 6, wherein the reducing solvent is a
solvent including diol, polyol or glycol having two or more hydroxy
groups in a molecule thereof.
20. A silver nanowire-dispersed solution prepared by dispersing
0.1.about.5 wt % of the silver nanowires having an aspect ratio of
100 or more, prepared by the method of claim 7 in 95.about.99.9 wt
% of a solvent.
21. The silver nanowire-dispersed solution of claim 20, further
comprising 0.01 to 10 parts by weight of a dispersant and 0.01 to
10 parts by weight of a thickener based on 100 parts by weight of
the silver nanowire-dispersed solution.
22. The silver nanowire-dispersed solution of claim 21, wherein the
dispersant includes at least one selected from the group consisting
of polyoxyethylene aliphatic ether, polyoxyethylene phenyl ether,
polyimine, alkyl phosphate, an alkylammonium salt, a polyester
alkylolammonium salt, a polyacrylic alkylolammonium salt,
polydimethylsilane, polyacrylic acid, polysulfonic acid and
polyvinylpyrrolidone, and the thickener includes at least one
selected from the group consisting of a urethane-modified
thickener, an acrylic thickener, methylcellulose, ethylcellulose,
hydroxyethylcellulose, hydroxymethylcellulose,
hydroxypropylcellulose and hydroxypropylmethylcellulose.
Description
TECHNICAL FIELD
[0001] The present invention relates to a method of preparing
silver nanowires and, more particularly, to a method of uniformly
preparing silver nanowires having an aspect ratio of 100 or more
(for example, having a diameter of less than 100 nm and a length of
10 .mu.m or more) using a silver salt precursor, a reducing
solvent, a capping agent and an ionic liquid.
BACKGROUND ART
[0002] Recently, touch screen panels have been used as important
components of various types of electric, electronic and
communication appliances, such as smart phones, tablet computers,
etc.
[0003] A transparent electrode film is used as a main component of
a touch screen panel. As the transparent electrode film, a film
having a surface resistivity of 500.OMEGA./.quadrature. and a light
transmittance of 90% or more to a base film is used. Currently,
indium tin oxide (ITO) is generally used as a transparent electrode
material. A transparent electrode film having a surface resistivity
of 50.about.500.OMEGA./.quadrature. and a light transmittance of
90% or more to a base film can be fabricated by forming an ITO thin
film on a glass substrate or a transparent polymer film using
sputtering.
[0004] However, the ITO thin film is problematic in that its
production cost is very high and it is easily damaged due to the
difference in thermal expansibility or thermal shrinkability
between the ITO thin film and a base film. Particularly, since the
brittleness of the ITO thin film formed on a polymer film is very
high, when this ITO thin film is used as a transparent electrode
film of a touch screen panel, there is a problem of the ITO thin
film being cracked by mechanical or physical deformation.
[0005] Therefore, novel raw materials for transparent electrode
films, which can overcome the above problems of ITO, have lately
attracted considerable attention. For this purpose, there have been
many efforts made to fabricate a transparent electrode film using a
novel raw material such as a conducting polymer, a carbon nanotube,
graphene or a metal nanowire. Particularly, metal nanowire, such as
silver nanowire, has lately been in the spotlight as a transparent
electrode material that can be used in place of ITO due to the
metal wire having very high electroconductvity and a high aspect
ratio.
[0006] Silver nanowires, as reported in US 2005/0056118, Science
298, 2176, 2002, Chem. Mater. 14, 4736, 2002, can be prepared by a
so-called polyol process. Further, there is disclosed a method of
synthesizing silver nanowires having a one-dimensional shape in a
solution phase using a silver salt precursor (metal precursor), a
reducing solvent such as ethyleneglycol (EG) and a capping agent
such as polyvinylpyrrolidone (PVP). Further, there was reported a
method of synthesizing silver nanowires using an ionic liquid as a
capping agent instead of PVP in the polyol process (Angewandte
Chemie, 121, 3864, 2009).
[0007] However, in such methods of synthesizing silver nanowires,
different shapes of silver nanoparticles as well as silver
nanowires are simultaneously prepared, so it is not suitable for
using these silver nanoparticles as a transparent electrode
material. For instance, granular silver nanostructures are prepared
together with silver nanowires. In this case, there are problems in
that granular silver nanostructures must be separated from silver
nanostructures after the preparation of silver nanostructures, and
in that the yield of silver nanowires is low.
[0008] Further, Korean Unexamined Patent Application Publication
No. 10-2010-0055983 discloses a method of preparing metal nanowires
by a polyol reduction reaction in which a metal salt is mixed and
reacted with a reducing solvent in the presence of an ionic
liquid.
[0009] However, in order to fabricate a transparent electrode film
having excellent light transmittance and surface resistance
characteristics using silver nanowires, it is required to develop a
method of more uniformly synthesizing silver nanowires having a
higher aspect ratio.
DISCLOSURE
Technical Problem
[0010] An object of the present invention is to provide a
technology of uniformly and reproducibly preparing silver nanowires
having an aspect ratio of 100 or more (for example, having a
diameter of less than 100 nm and a length of 10 .mu.m or more)
without preparing different shapes of silver nanostructures by a
polyol reduction reaction using a metal salt as a precursor.
[0011] Other objects of the present invention are not limited to
the above-mentioned object, and will be clearly understood from the
following descriptions by those skilled in the art.
Technical Solution
[0012] The present invention relates to a method of preparing
silver nanowires having a high aspect ratio (for example, having a
diameter of less than 100 nm and a length of 10 .mu.m or more)
using an imidazolium-based ionic liquid as an additive in a polyol
process.
[0013] In order to accomplish the above object, silver nanowires
were prepared by a polyol reaction in which an imidazolium-based
ionic liquid (additive) was mixed and reacted with a mixed solution
including a silver salt precursor, a reducing solvent and a capping
agent.
[0014] From the research results of the present inventors, it was
found that, in the process of preparing silver nanowires by the
polyol reduction reaction of a mixed solution including a silver
salt precursor (for example, AgNO.sub.3), a reducing solvent (for
example, ethyleneglycol), a capping agent (for example,
polyvinylpyrrolidone) and the like, when a small amount of an
imidazolium-based ionic liquid was added to the mixed solution as
an additive, silver nanowires having a diameter of less than 100 nm
and a length of 10 .mu.m or more were uniformly prepared. The
silver salt precursor is a compound including a silver cation and
an organic or inorganic anion. For example, AgNO.sub.3,
AgClO.sub.4, AgBF.sub.4, AgPF.sub.6, CH.sub.3COOAg,
AgCF.sub.3SO.sub.3, Ag.sub.2SO.sub.4, CH.sub.3COCH.dbd.COCH.sub.3Ag
or the like may be used as the silver salt precursor. The silver
salt is dissociated in a solvent, and is then converted into metal
silver by a reduction reaction.
[0015] The reducing solvent is a polar solvent that can dissolve a
silver salt. The reducing solvent is referred to as a solvent
having two or more hydroxy groups in a molecule thereof, such as
diol, polyol or glycol. Specific examples of the reducing solvent
may include ethyleneglycol, 1,2-propyleneglycol,
1,3-propyleneglycol, glycerin, glycerol, diethylglycol, and the
like. The reducing solvent serves to produce metal silver by
inducing the reduction reaction of silver cations at a
predetermined temperature or more as well as serves as a solvent
for dissolving a silver salt.
[0016] The capping agent serves to one-dimensionally grow silver
nanoparticles because it is adsorbed (hereinafter, capped) only on
a specific crystal plane by the interaction between the capping
agent and the silver nanoparticles formed in the initial stage of a
synthesis reaction. The capping agent is polyvinylpyrrolidone (PVP)
or polyvinylalcohol (PVA).
[0017] The imidazolium-based ionic liquid, as represented by
Formulas 1 and 2 below, is a monomeric or polymeric compound
including an organic cation having an imidazolium group and an
organic or inorganic anion. Particularly, in the case where the
imidazolium-based ionic liquid including a chlorine ion (Cl.sup.-)
or a bromine ion (Br.sup.-) as an anion is used as an additive,
when a silver salt is converted into metal silver by a polyol
reduction reaction, the metal silver nanoparticles are
one-dimensionally and uniformly grown by the chemical interaction
between the imidazolium-based ionic liquid and a silver ion or
metal silver, thus finally forming silver nanowires having a high
aspect ratio, that is, having a diameter of less than 100 nm and a
length of 10 .mu.m or more.
[0018] In the present invention, the aspect ratio of silver
nanowires is 100 or more, but the upper limit thereof is not
predetermined and can be adjusted to the maximum aspect ratio to
such a degree that they can exist as silver nanowires by
controlling the content of the ionic liquid. When the aspect ratio
of silver nanowires is excessively large, they do not exist in the
form of wire, and they may be entangled as yarn. Therefore, if
necessary, uniform silver nanowires having a high aspect ratio can
be prepared by controlling the content of the ionic liquid.
##STR00001##
[0019] In the Formulas 1 and 2, R1, R2 and R3 are identical to or
different from each other, each of which is hydrogen or a
hydrocarbon group of 1 to 16 carbon atoms, and each of which
includes at least one heteroatom selected from the group consisting
of oxygen, sulfur, nitrogen, phosphorus, fluorine, chlorine,
bromine, iodine and silicon. Further, X.sup.- is an anion, and is
an organic or inorganic compound including a halogen ion such as a
chlorine ion (Cl.sup.-) or a bromine ion (Br.sup.-). n is a
repetitive unit, and is a natural number.
[0020] Specific examples of the monomeric cationic compound
represented by Formula 1 above may include 1,3-dimethylimidazolium,
1,3-diethylimidazolium, 1-ethyl-3-methylimidazolium (EMIM),
1-butyl-3-methylimidazolium (BMIM), 1-hexyl-3-methylimidazolium
(HMIM), 1-octyl-3-methylimidazolium (OMIM),
1-decyl-3-methylimidazolium, 1-dodecyl-3-methylimidazolium and
1-tetradecyl-3-imidazolium, and specific examples of the polymeric
cationic compound represented by Formula 2 above may include
poly(1-vinyl-3-alkylimidazolium), poly(1-allyl-3-alkylimidazolium)
and poly(1-(meth)acryloyloxy-3-alkylimidazolium). In order to
synthesize silver nanowires, it is preferred that a chlorine ion
(Cl.sup.-) or a bromine ion (Br.sup.-) be used as the anion of the
ionic liquid of Formula 1 or 2.
[0021] Hereinafter, the method of preparing silver nanowires
according to the present invention will be described in detail.
[0022] First, a silver salt precursor, a reducing agent, a capping
agent and an ionic liquid are mixed at an appropriate ratio and
then stirred at room temperature for a predetermined amount of
time. Subsequently, the mixture is reacted at a temperature of
50.about.180.degree. C. for 30 minutes.about.7 days to form silver
nanowires. When the reaction temperature is low, reaction time is
long because it takes more time to grow silver nanowires, but on
the other hand, when the reaction temperature is high, silver
nanowires are formed relatively rapidly.
[0023] In the present invention, in order to uniformly prepare
silver nanowires, the content ratio of each of the components of
the mixture is important. It is preferred that the capping agent is
included in an amount of 1 to 2 mol based on 1 mol of the silver
salt precursor, and the ionic liquid is included in an amount of
0.001 to 0.2 mol based on 1 mol of the silver salt precursor. In
this case, when the amount of the capping agent is less than 1 mol
and the amount of the ionic liquid is less than 0.001 mol, each of
which being an excessively low amount, there is a problem in that
silver nanowires are not uniformly formed and exist in a mixture of
nanowires and nanoparticles. Further, when the amount of the
capping agent is more than 2 mol and the amount of the ionic liquid
is more than 0.2 mol, each of which being an excessively high
amount, there is a problem in that the diameter of silver nanowires
increases to 100 nm or more, or three-dimensional silver
nanoparticles are formed, and thus it is difficult to form uniform
silver nanowires. Particularly, when the ionic liquid is used in an
amount of 0.005 to 0.02 mol, it is advantageous to form uniform
silver nanowires.
[0024] The silver nanowires formed in this way are filtered and
then washed with a solvent such as water or alcohol. These filtered
silver nanowires are dispersed in a solvent to prepare a silver
nanowire-dispersed solution. In this case, it is preferred that
water or a water-based solvent be used as the solvent for
dispersing the silver nanowires. Specific examples of the solvent
for dispersing the silver nanowires may include water, methanol,
ethanol, n-propyl alcohol, iso-propyl alcohol, n-butanol,
iso-butanol, hexanol, benzyl alcohol, diacetone alcohol,
ethyleneglycol, propyleneglycol, glycerol, 1,4-dioxane,
tetrahydrofuran (THF), ethyleneglycol monomethyl ether,
ethylenglycol monoethyl ether, ethyleneglycol dimethyl ether,
propyleneglycol monomethyl ether, propyleneglycol monoethyl ether,
propyleneglycol dimethyl ether, N,N-dimethylformamide,
N-methylformamide, N,N-dimethylacetamide (DMA), acetonitrile,
acetaldehyde, N-methyl-2-pyrrolidone, 2-pyrrolidone,
N-vinyl-2-pyrrolidone, dimethylsulfoxide, n-butyrolactone,
nitromethane, and ethyl lactate. These solvents may be used
independently or in a combination thereof.
[0025] The silver nanowire-dispersed solution is prepared by
dispersing 0.1.about.5 wt % of the silver nanowires of the present
invention in 95.about.99.9 wt % of the solvent. The silver
nanowire-dispersed solution may further include a dispersant and a
thickener in order to improve the dispersibility of silver
nanowires.
[0026] Here, when the content of silver nanowires in the silver
nanowire-dispersed solution is less than 0.1 wt %, there are
disadvantages in that surface resistivity becomes high because the
amount of nanowires is excessively small, and in that coatability
becomes poor because wet-coating thickness must be increased.
Further, when the content of silver nanowires in the silver
nanowire-dispersed solution is more than 5 wt %, there are
disadvantages in that it is difficult to coat the silver
nanowire-dispersed solution because the amount of nanowires is
excessively large, and in that light transmittance becomes low
because an excessive amount of silver nanowires is used.
[0027] The dispersant serves to allow silver nanowires to be stably
dispersed in a solvent by electrostatic repulsion or steric barrier
because the dispersant is adsorbed on the surface of silver
nanowires. The thickener serves to adjust the fluidity of the
silver nanowire-dispersed solution. It is effective that each of
the dispersant and the thickener be included in an amount of 0.01
to 10 parts by weight based on 100 parts by weight of the silver
nanowire-dispersed solution. Here, when the amount of the
dispersant is less than 0.01 wt %, there is a disadvantage in that
a dispersion effect is barely exhibited. Further, when the amount
thereof is more than 10 wt %, there is a disadvantage in that the
amount of the dispersant is excessively large, and thus this
dispersant leak out from the surface of the silver
nanowire-dispersed solution to decrease the surface resistivity
thereof or the surface thereof becomes excessively slippery.
[0028] The dispersant may include at least one selected from the
group consisting of polyoxyethylene aliphatic ether,
polyoxyethylene phenyl ether, polyimine, alkyl phosphate, an
alkylammonium salt, a polyester alkylolammonium salt, a polyacrylic
alkylolammonium salt, polydimethylsilane, polyacrylic acid,
polysulfonic acid and polyvinylpyrrolidone. More specifically, the
dispersant may include at least one selected from the group
consisting of Triton X-100, Triton X-200, Pluronic P123, F127, F68,
L64, BYK-181, 184, 191, 192, 194, Disperbyk-181, 184, 190, Tego
710, 720W, 730W, Zonyl FSN, FSO, FSP, cetyltrimethylammonium
bromide (CTAB), cetyltrimethylammonium chloride (CTAC),
tetrabutylammonium bromide (TBAB), tetrabutylammonium chloride
(TBAC), sodium dodecylsulfate (SDS), sodium dodecylbenzenesulfonate
(SDBS), polystyrene sulfonate (PSSA),
poly(sodium-4-styrenesulfonate) (PSSNa), and
dodecylbenzenesulfonate (DBSA). Examples of the thickener may
include, but are not limited to, a urethane-modified thickener, an
acrylic thickener, methylcellulose, ethylcellulose,
hydroxyethylcellulose, hydroxymethylcellulose,
hydroxypropylcellulose and hydroxypropylmethylcellulose. These
thickeners may be used independently or in a combination
thereof.
[0029] When the silver nanowire-dispersed solution including the
silver nanowires prepared by the technology of the present
invention is applied onto a base film and then dried, a transparent
electrode film including a three-dimensional network formed of
silver nanowires having a diameter of less than 100 nm and a length
of 10 .mu.m or more can be manufactured.
[0030] The base film may be a commonly-used transparent film, but
is not limited thereto. For example, the base film may be formed of
polyethylene terephthalate, polyester naphthalate, polycarbonate,
polymethylmethacrylate, polyacrylate, polyacrylonitrile,
polystyrene or the like. Meanwhile, in order to improve the
adhesivity between the base film and the silver nanowires, an
adhesion enhancing layer may be applied to the surface of the base
film or the base film may be surface-treated by corona treatment,
plasma treatment or the like.
[0031] As the method of coating a base film with silver nanowires,
all commonly-known technologies may be used. General examples of
the coating method may include, but are not limited to, dip
coating, spin coating, bar coating, gravure printing, reverse
gravure printing, offset printing, ink-jet printing, spray coating
and slot die coating.
[0032] The transparent electrode film made of the silver nanowires
has a surface resistivity of
10.sup.1.about.10.sup.3.OMEGA./.quadrature. and a light
transmittance of 90% or more to the base film.
Advantageous Effects
[0033] When the technology of the present invention is used, silver
nanowires having a diameter of less than 100 nm and a length of 10
.mu.m or more can be uniformly prepared in a solution phase.
Further, since each of the silver nanowires of the present
invention has a large aspect ratio of 100 or more, when a
three-dimensional network is formed on the surface of a base film
using the silver nanowires, low surface resistivity and high light
transmittance can be simultaneously realized.
DESCRIPTION OF DRAWINGS
[0034] FIGS. 1 and 2 are scanning electron microscope photographs
showing the silver nanowires and silver nanoparticles of
Comparative Example 1, respectively.
[0035] FIG. 3 is an electron microscope photograph showing the
silver nanowires of Example 1.
[0036] FIG. 4 is an electron microscope photograph showing the
silver nanowires of Example 2.
[0037] FIG. 5 is an electron microscope photograph showing the
silver nanowires of Example 3.
[0038] FIG. 6 is an electron microscope photograph showing the
silver nanoparticles of Comparative Example 2.
MODE FOR INVENTION
[0039] Hereinafter, the present invention will be described in more
detail with reference to the following Examples. However, these
Examples are set forth to illustrate the present invention, and the
scope of the present invention is not limited thereto.
Comparative Example 1
Preparation of Silver Nanowires Using Polyol Reaction
[0040] 0.1 mol (17 g) of AgNO.sub.3 (manufactured by Kojima Co.,
Ltd., purity: 99.99%) and 0.15 mol (16.7 g) of PVP (manufactured by
Aldrich Corporation, weight average molecular weight: 55,000 g/mol)
were put into a 2 L round-bottom flask, dissolved in 1 L of
ethyleneglycol (EG), and then stirred at room temperature for 10
minutes to obtain a transparent mixed solution. The color of the
mixed solution became gray brown as soon as the mixed solution was
reacted at 150.degree. C. for about 30 minutes. Subsequently, the
mixed solution was cooled to room temperature, filtered by a filter
having a pore size of 1 .mu.m, dried, and then observed using a
scanning electron microscope. As shown in the photographs of FIGS.
1 and 2, it was observed that silver nanowires having a diameter of
90.about.120 nm and a length of 5.about.20 .mu.m were formed, but
the diameters of the silver nanowires were somewhat large and not
uniform. Further, it was observed that silver nanoparticles having
a particle size of 0.5.about.5 .mu.m were formed together with the
silver nanowires.
Example 1
Preparation of Silver Nanowires Using Ionic Liquid Containing
Chlorine Ion (Cl.sup.-) as Additive in Polyol Reaction
[0041] 0.1 mol of AgNO.sub.3, 0.15 mol of PVP and 0.001 mol of
1-ethyl-3-methylimidazolium chloride (EMIM-Cl) were dissolved in 1
L of ethyleneglycol (EG), and were then stirred at room temperature
for 10 minutes to obtain a transparent mixed solution. The color of
the mixed solution became gray as soon as the mixed solution was
reacted at 150.degree. C. for about 30 minutes. Subsequently, the
mixed solution was cooled to room temperature, filtered by a filter
having a pore size of 1 .mu.m, dried, and then observed using a
scanning electron microscope. As shown in the photograph of FIG. 3,
it was observed that silver nanowires having a diameter of
55.about.65 nm and a length of 10.about.30 .mu.m were uniformly
formed. Further, it was observed that, differently from the results
of Comparative Example 1 in which an ionic liquid was not used,
silver nanoparticles having different shapes from the silver
nanowires were not discovered.
Example 2
Preparation of Silver Nanowires Using Ionic Liquid Containing
Chlorine Ion (Cl.sup.-) as Additive in Polyol Reaction
[0042] Example 2 is the same as Example 1, except that 0.001 mol of
1-butyl-3-methylimidazolium chloride (BMIM-Cl) was used as an ionic
liquid. As shown in the photograph of FIG. 4, it was observed that
silver nanowires having a diameter of 55.about.65 nm were uniformly
formed. Further, it was observed that, similarly to the results of
Example 1, silver nanoparticles having different shapes from the
silver nanowires were not discovered. Comparing the results of
Example 2 with the results of Example 1, it was observed that the
shapes of silver nanowires were not changed or were only slightly
changed depending on the length of an alkyl group of an
imidazolium-based ionic liquid having a cation.
Example 3
Preparation of Silver Nanowires Using Ionic Liquid Containing
Bromine Ion (Br.sup.-) as Additive in Polyol Reaction
[0043] Example 3 is the same as Example 2, except that 0.001 mol of
1-butyl-3-methylimidazolium bromide (BMIM-Br) was used as an ionic
liquid. As shown in the photograph of FIG. 5, it was observed that
silver nanowires having a diameter of about 30 nm were uniformly
formed. Further, it was observed that, similarly to the results of
Example 1, silver nanoparticles having different shapes from the
silver nanowires were not discovered. Comparing the results of
Example 3 with the results of Example 2, it was observed that the
shapes and diameters of silver nanowires were changed depending on
the anion of the ionic liquid.
Comparative Example 2
Preparation of Silver Nanowires Using Ionic Liquid Containing
Bromine Ion (Br.sup.-) as Additive in Polyol Reaction
[0044] Comparative Example 2 is the same as Example 2, except that
1-butyl-3-methylimidazolium methyl sulfate (BMIM-MeSO.sub.4) was
used as an ionic liquid. When the anion of an ionic liquid was Cl--
or Br-- as in Examples 2 and 3, silver nanowires were formed. In
contrast, when the anion of an ionic liquid was
CH.sub.3SO.sub.4.sup.- as in Comparative Example 2, as shown in the
photograph of FIG. 6, it can be ascertained that three-dimensional
silver nanoparticles, not one-dimensional silver nanowires, were
formed.
Example 4
Manufacture of Transparent Conductive Film Using Silver Nanowires
Having High Aspect Ratio
[0045] 0.7 parts by weight of the silver nanowires prepared in
Example 2, 98.8 parts by weight of iso-propyl alcohol and 0.5 parts
by weight of a cellulose-based thickener were mixed, and were then
ultrasonically dispersed to prepare a silver nanowire-dispersed
solution. Subsequently, the silver nanowire-dispersed solution was
applied onto a polyethylene terephthalate film (thickness: 125
.mu.m) coated with an acrylic adhesion enhancing layer using a bar
coater, and was then dried at a temperature of about 100.degree. C.
for 1 minute to form a transparent conductive film. The surface
resistivity of the transparent conductive film was measured using a
four-probe method (AIT Corporation). As a result, the surface
resistivity thereof was about 95.OMEGA./.quadrature.. Further, the
light transmittance of the transparent conductive film was measured
using a UV-Vis-NIR spectrophotometer (Cary 5000). As a result, the
light transmittance of the transparent conductive film to the base
film was 94.7%.
INDUSTRIAL APPLICABILITY
[0046] The silver nanowires can be used as a main raw material of a
touch screen panel which is an important component of various types
of electric, electronic and communication appliances, such as smart
phones, tablet computers, televisions, etc.
* * * * *