U.S. patent application number 15/363815 was filed with the patent office on 2017-03-16 for graphene-ceramic hybrid coating layer, and method for preparing the same.
The applicant listed for this patent is Hyundai Motor Company, Korea Institute of Ceramic Engineering and Technology. Invention is credited to Kwang Il Chang, Seung Hun Hur, Dha Hae Kim, Chul Kyu Song.
Application Number | 20170073563 15/363815 |
Document ID | / |
Family ID | 52775207 |
Filed Date | 2017-03-16 |
United States Patent
Application |
20170073563 |
Kind Code |
A1 |
Chang; Kwang Il ; et
al. |
March 16, 2017 |
GRAPHENE-CERAMIC HYBRID COATING LAYER, AND METHOD FOR PREPARING THE
SAME
Abstract
Disclosed are a graphene-ceramic hybrid coating layer formed
from a graphene-ceramic hybrid sol solution including graphene
(RGO: reduced graphene oxide) and a ceramic sol, wherein the
graphene content in the graphene-ceramic hybrid coating layer is
about 0.001 wt % to about 1.8 wt % based on the total weight of the
graphene-ceramic hybrid coating layer, and a method for preparing
the same.
Inventors: |
Chang; Kwang Il; (Gunpo,
KR) ; Song; Chul Kyu; (Seoul, KR) ; Kim; Dha
Hae; (Chuncheon, KR) ; Hur; Seung Hun; (Seoul,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hyundai Motor Company
Korea Institute of Ceramic Engineering and Technology |
Seoul
Jinju |
|
KR
KR |
|
|
Family ID: |
52775207 |
Appl. No.: |
15/363815 |
Filed: |
November 29, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14144184 |
Dec 30, 2013 |
9527773 |
|
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15363815 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C04B 35/14 20130101;
C03C 17/22 20130101; C04B 35/62635 20130101; C04B 35/62222
20130101; C04B 2235/3418 20130101; C04B 35/6264 20130101; B05D
1/305 20130101; C04B 2235/425 20130101; C04B 2235/666 20130101;
C04B 35/64 20130101; C03C 2218/31 20130101; C04B 2235/9607
20130101; C03C 17/006 20130101; B05D 1/02 20130101; B05D 1/18
20130101; C04B 2235/3232 20130101; C04B 35/013 20130101; C03C
2218/11 20130101; C09K 5/14 20130101; B05D 1/005 20130101; C04B
35/46 20130101; C04B 35/624 20130101; B05D 1/28 20130101 |
International
Class: |
C09K 5/14 20060101
C09K005/14; C04B 35/46 20060101 C04B035/46; C04B 35/624 20060101
C04B035/624; C03C 17/22 20060101 C03C017/22; C04B 35/626 20060101
C04B035/626; C04B 35/64 20060101 C04B035/64; C03C 17/00 20060101
C03C017/00; C04B 35/14 20060101 C04B035/14; C04B 35/622 20060101
C04B035/622 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 22, 2013 |
KR |
10-2013-0125885 |
Claims
1. A graphene-ceramic hybrid sol solution for forming a
graphene-ceramic hybrid coating layer, the graphene-ceramic hybrid
sol solution including graphene in the form of reduced graphene
oxide and a ceramic sol, wherein a graphene content in the
graphene-ceramic hybrid coating layer is about 0.001 wt % to about
1.8 wt % based on the total weight of the graphene-ceramic hybrid
coating layer.
2. The graphene-ceramic hybrid sol solution of claim 1, wherein the
graphene content is about 0.01 wt % to about 1.8 wt % based on the
total weight of the solution.
3. The graphene-ceramic hybrid sol solution of claim 1, wherein the
graphene and the ceramic sol are uniformly distributed in the
graphene-ceramic hybrid sol solution.
4. The graphene-ceramic hybrid sol solution of claim 1, wherein the
ceramic is selected from the group consisting of SiO.sub.2,
Al.sub.2O.sub.3, Li.sub.4Ti.sub.5O.sub.12, TiO.sub.2, SnO.sub.2,
CeO.sub.2, ZrO.sub.2, V.sub.2O.sub.5, B.sub.2O.sub.3, BaTiO.sub.3,
Y.sub.2O.sub.3, WO.sub.3, MgO, CuO, ZnO, AlPO.sub.4, AlF,
Si.sub.3N.sub.4, AlN, TiN, WC, SiC, TiC, MoSi.sub.2,
Fe.sub.2O.sub.3, GeO.sub.2, Li.sub.2O, MnO, NiO, zeolite, and a
combination thereof.
5-17. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to and the benefit of
Korean Patent Application No. 10-2013-0125885 filed in the Korean
Intellectual Property Office on Oct. 22, 2013, the entire contents
of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] (a) Field of the Invention
[0003] The present invention relates to a graphene-ceramic hybrid
coating layer and a method for preparing the same.
[0004] (b) Description of the Related Art
[0005] Graphene oxide (or graphite oxide, hereinafter GO) is a
sheet-shaped carbon material prepared by acid treating graphite,
and has a large amount of a hydrophilic functional group, a
carboxyl group (--COOH), a hydroxyl group (--OH), and the like on
the surface. The surface oxidizing groups produced through an acid
treatment process naturally produce hydrogen-bonds with H.sub.2O.
Thus, GO is generally prepared in a form of a hydration or in a
water-containing slurry state, with the solid concentration of the
slurry generally being about 2 to 8 wt % as long as it is not
specifically treated.
[0006] When the GO is appropriately included in a film or a
structure, strength thereof may be improved and suitable thermal
conductivity may be provided. However, treatment of the contained
moisture may hinder properties.
[0007] In general, GO may be prepared in a form of graphene through
a chemical reduction method (a hydrazine treatment and the like)
and a thermal reduction method. Herein, reduced graphene is
particularly referred to as reduced graphene oxide (RGO).
[0008] Evidence shows that not all of the oxidizing groups on the
RGO are thoroughly removed. Generally, oxygen content of the
surface oxidizing groups is less than or equal to about 5% relative
to a carbon backbone.
[0009] A heterogeneous mixture of RGO and a conventional material
has recently evoked active interest, due to its potential to
improve synergic effects between materials exceeding that of
conventional materials. The heterogeneous mixture may be used in a
high strength composite material and a fuel cell. As representative
technologies, Korean Patent No. KR2011-0012479 describes a
graphene-nanowire (semiconductor) hybrid structure where light
energy is absorbed in a graphene conductive part and electron-hole
pairs are generated. Korean Patent No. KR2010-0114646 describes a
hybrid composite manufacturing method including graphene
sheet/carbon nanotube/a polymer nanoparticle. Korean Patent No.
KR2010-0097322 describes a method of manufacturing a positive
electrode graphene material for a lithium rechargeable battery that
is a hybrid material formed by adding an Fe precursor and a
PO.sub.4 precursor. U.S. Pat. No. 8,257,867 describes a method of
manufacturing a graphene composite calcinated body having an
excellent charge and discharge ratio by sintering graphene and a
metal oxide particle in air. U.S. Patent Publication No.
2012-0149554 describes a method of manufacturing a
graphene-TiO.sub.2 hybrid material by mixing a TiO.sub.2 nanopowder
with graphene at a high temperature and high pressure and reacting
them.
[0010] However, improved materials are still needed.
SUMMARY OF THE INVENTION
[0011] According to one aspect, the present invention provides a
graphene-ceramic hybrid sol solution having improved dispersion and
safety. According to another aspect, the present invention provides
a graphene-ceramic hybrid coating layer having improved uniformity,
transparency, and thermal conductivity.
[0012] In particular, according to one embodiment, a
graphene-ceramic hybrid coating layer is formed from a
graphene-ceramic hybrid sol solution including graphene (RGO:
reduced graphene oxide) and a ceramic sol. Preferably, a graphene
content in the graphene-ceramic hybrid coating layer is about 0.001
wt % to about 1.8 wt % based on the total weight of the
graphene-ceramic hybrid coating layer, and more preferably, the
graphene content is about 0.01 wt % to about 1.8 wt % based on the
total weight of the graphene-ceramic hybrid coating layer. The
graphene and ceramic sol may be uniformly distributed in the
graphene-ceramic hybrid sol solution. The ceramic may be any
conventional ceramic and, according to a preferred embodiment, the
ceramic is selected from the group consisting of SiO.sub.2,
Al.sub.2O.sub.3, Li.sub.4Ti.sub.5O.sub.12, TiO.sub.2, SnO.sub.2,
CeO.sub.2, ZrO.sub.2, V.sub.2O.sub.5, B.sub.2O.sub.3, BaTiO.sub.3,
Y.sub.2O.sub.3, WO.sub.3, MgO, CuO, ZnO, AlPO.sub.4, AlF,
Si.sub.3N.sub.4, AlN, TiN, WC, SiC, TiC, MoSi.sub.2,
Fe.sub.2O.sub.3, GeO.sub.2, Li.sub.2O, MnO, NiO, zeolite, and
combinations thereof.
[0013] According to another aspect, the present invention provides
a method for preparing the graphene-ceramic hybrid coating
layer.
[0014] According to various embodiments, the method includes:
mixing graphene and a first dispersing agent and a first
non-aqueous based solvent to prepare a dispersion including the
graphene, the first dispersing agent and the first non-aqueous
based solvent; adding a mixed solution of a second non-aqueous
based solvent and a ceramic precursor to the dispersion to prepare
a mixture; mixing a second dispersing agent and water with the
mixture to prepare a graphene-ceramic hybrid sol solution; and
coating a substrate with the graphene-ceramic hybrid sol solution.
According to various embodiments, the method further includes
performing a mechanical dispersion treatment after mixing the
graphene, first dispersing agent, and first non-aqueous based
solvent. The mechanical dispersion treatment may be performed by
any known method, such as, for example, ultrasonication, stirring,
a shear stress (shearing force) application method, a method of
using a homogenizer, or a combination thereof. According to various
embodiments, the first dispersing agent and second dispersing agent
may each independently be polyethylene glycol (PEG), glycerol,
hydrochloric acid (HCl), acetic acid, formic acid, citric acid, a
binder, or a combination thereof. According to various embodiments,
the first non-aqueous based solvent and the second non-aqueous
based solvent are each independently be an amphiphilic solvent, a
water-soluble solvent except water, a non-water-soluble solvent, a
polar solvent, a nonpolar solvent, or a combination thereof. In
particular, the first non-aqueous based solvent and the second
non-aqueous based solvent are preferably each independently
selected from isopropyl alcohol (IPA), ethanol, acetone,
methylethylketone, methyl alcohol, ethyl alcohol, isopropyl
alcohol, acetylacetone, butyl alcohol, ethylene glycol,
polyethylene glycol, tetrahydrofuran, dimethylformamide, dimethyl
acetamide, N-methyl-2-pyrrolidone, hexane, cyclohexanone, toluene,
chloroform, dichlorobenzene, dimethylbenzene, trimethylbenzene,
pyridine, methylnaphthalene, nitromethane, acrylonitrile,
octadecylamine, aniline, dimethylsulfoxide, and combinations
thereof. According to various embodiments, the dispersion further
includes an additive selected from polyethylene glycol, glycerin,
glucose, a binder, and a combination thereof. The graphene is
preferably dispersed in an amount of about 0.001 wt % to about 5 wt
% based on a solid content of a mixture including the first
graphene dispersing agent and non-aqueous based solvent. The
coating process may be performed by any known coating process such
as dip coating, spin coating, spray coating, paint coating, bar
coating, flow coating, roll coating, or a combination thereof.
[0015] According to another aspect, the present invention provides
a graphene-ceramic hybrid coating layer prepared by the method for
preparing the graphene-ceramic hybrid coating layer.
[0016] According to various embodiments the graphene-ceramic hybrid
coating layer thus prepared has a graphene content in the
graphene-ceramic hybrid coating layer of about 0.001 wt % to about
1.8 wt % based on the total weight of the graphene-ceramic hybrid
coating layer.
[0017] According to another aspect, the present invention provides
an automobile headlamp including the graphene-ceramic hybrid
coating layer.
[0018] The present invention thus provides a graphene-ceramic
hybrid sol solution having improved dispersion and safety, a
graphene-ceramic hybrid coating layer including the same and having
improved uniformity, transparency, and thermal conductivity, and a
method for preparing the same, and an automobile headlamp including
the graphene-ceramic hybrid coating layer, wherein improved
properties are provided.
[0019] Other features and aspects of the present invention will be
apparent from the following detailed description, drawings and
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The above and other features of the present invention will
now be described in detail with reference to certain exemplary
embodiments thereof illustrated the accompanying drawings which are
given hereinbelow by way of illustration only, and thus are not
limitative of the present invention, and wherein:
[0021] FIG. 1 schematically shows differences between methods for
preparing a graphene-ceramic hybrid sol solution according to the
conventional art and one embodiment of the present invention.
[0022] FIG. 2 schematically shows a graphene-ceramic hybrid sol
solution preparation method according to one embodiment of the
present invention.
[0023] FIG. 3 shows a photograph exhibiting stability and
uniformity of graphene-ceramic hybrid sol solutions for forming the
coating layer according to one embodiment of the present invention
and Comparative Examples 1 and 2.
[0024] FIG. 4 shows a photograph exhibiting uniformity of the
graphene-ceramic hybrid coating layers according to one embodiment
of the present invention and Comparative Example 2.
[0025] FIG. 5 shows a photograph exhibiting storage stability of a
graphene-ceramic hybrid sol solution for forming the coating layer
according to one embodiment of the present invention.
[0026] FIG. 6 is a graph showing stability of graphene-ceramic
hybrid sol solutions according to Example 1 and Comparative Example
2.
[0027] FIG. 7 is a graph showing transparency of the
graphene-ceramic hybrid coating layer according to one embodiment
of the present invention.
[0028] FIG. 8 shows photographs and a diagram illustrating an
apparatus and a method for evaluating thermal conductivity of a
graphene-ceramic hybrid coating layer according to one embodiment
of the present invention.
[0029] FIG. 9 is a photograph showing a principle of forming a
graphene-ceramic hybrid coating layer using spray coating according
to one embodiment of the present invention.
DESCRIPTION OF SYMBOLS
[0030] 100: PC (polycarbonate) substrate [0031] 101: measurement
point of substrate edge temperature [0032] 102: thermocouple
(center of PC substrate) [0033] 103: heating shape by heating
source
[0034] It should be understood that the appended drawings are not
necessarily to scale, presenting a somewhat simplified
representation of various preferred features illustrative of the
basic principles of the invention.
[0035] In the figures, reference numbers refer to the same or
equivalent parts of the present invention throughout the several
figures of the drawing.
DETAILED DESCRIPTION
[0036] Hereinafter, embodiments of the present invention are
described in further detail. However, these embodiments are
exemplary, and this disclosure is not limited thereto.
[0037] The terms and words used in the specification and claims are
not supposed to be construed in a conventional manner or on a
dictionary basis, and the inventors are supposed to use the terms
and words well matching with the technical concepts based on the
principles that the concepts of the terms and words can be properly
construed in order to describe the present invention in the best
way.
[0038] It is understood that the term "vehicle" or "vehicular" or
other similar term as used herein is inclusive of motor vehicles in
general such as passenger automobiles including sports utility
vehicles (SUV), buses, trucks, various commercial vehicles,
watercraft including a variety of boats and ships, aircraft, and
the like, and includes hybrid vehicles, electric vehicles, plug-in
hybrid electric vehicles, hydrogen-powered vehicles and other
alternative fuel vehicles (e.g. fuels derived from resources other
than petroleum). As referred to herein, a hybrid vehicle is a
vehicle that has two or more sources of power, for example both
gasoline-powered and electric-powered vehicles.
[0039] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the invention. As used herein, the singular forms "a," "an" and
"the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises" and/or "comprising," when used in this
specification, specify the presence of stated features, integers,
steps, operations, elements, and/or components, but do not preclude
the presence or addition of one or more other features, integers,
steps, operations, elements, components, and/or groups thereof. As
used herein, the term "and/or" includes any and all combinations of
one or more of the associated listed items.
[0040] Unless specifically stated or obvious from context, as used
herein, the term "about" is understood as within a range of normal
tolerance in the art, for example within 2 standard deviations of
the mean. "About" can be understood as within 10%, 9%, 8%, 7%, 6%,
5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated
value. Unless otherwise clear from the context, all numerical
values provided herein are modified by the term "about".
[0041] A graphene-ceramic hybrid coating layer according to one
embodiment of the present invention is a coating layer formed from
graphene (RGO: reduced graphene oxide) and a ceramic sol solution.
It is preferred that the content of graphene in the coating layer
is about 0.001 wt % to about 1.8 wt % based on the total weight of
the coating layer. When the graphene content in the
graphene-ceramic hybrid coating layer is less than about 0.001 wt
%, a coating layer having excellent thermal conductivity and high
strength is not provided, and when the graphene content in the
coating layer is more than about 1.8 wt %, uniformity of the
graphene-ceramic hybrid sol solution for forming the coating layer
is not secured, and uniformity and transparency of the coating
layer is not secured. In particular, in order to provide a
graphene-ceramic hybrid coating layer having excellent uniformity
and transparency, uniformity of the graphene-ceramic hybrid sol
solution for forming the coating layer is required. When the
graphene content in the coating layer is maintained within the
above ranges, such an effect may be expected. The graphene content
ensuring uniformity and transparency of the graphene-ceramic hybrid
coating layer is about 0.001 wt % to about 1.8 wt % based on the
total weight of the coating layer. In addition, while thickness of
graphene is a molecular unit, the diameter of graphene is only
several micrometers. As such, graphene may have a problem of
becoming wrinkled. Further, an excess of the graphene may be
impurities, since a general ceramic sol has a high specific gravity
and viscosity, and thus is mixed with a relatively soft graphene
and ceramic. Accordingly, it is important to adjust the content of
the graphene. When the graphene content is within the above range,
the graphene and ceramic sol may be uniformly distributed in the
graphene-ceramic hybrid sol solution. These facts may be expected
without being bound to a specific theory. The ceramic may be any
conventional ceramic material and, preferably, is selected from the
group consisting of SiO.sub.2, Al.sub.2O.sub.3,
Li.sub.4Ti.sub.5O.sub.12, TiO.sub.2, SnO.sub.2, CeO.sub.2,
ZrO.sub.2, V.sub.2O.sub.5, B.sub.2O.sub.3, BaTiO.sub.3,
Y.sub.2O.sub.3, WO.sub.3, MgO, CuO, ZnO, AlPO.sub.4, AlF,
Si.sub.3N.sub.4, AlN, TiN, WC, SiC, TiC, MoSi.sub.2,
Fe.sub.2O.sub.3, GeO.sub.2, Li.sub.2O, MnO, NiO, zeolite, and
combinations thereof. For example, one example includes one or more
of TiO.sub.2, SiO.sub.2, CeO.sub.2, ZnO, Al.sub.2O.sub.3, and
SnO.sub.2.
[0042] According to another embodiment, a method for preparing a
graphene-ceramic hybrid coating layer includes: mixing graphene, a
first dispersing agent and a first non-aqueous based solvent to
prepare a dispersion including the graphene, the first dispersing
agent and the first non-aqueous based solvent; adding a mixed
solution of a second non-aqueous based solvent and a ceramic
precursor to the dispersion to prepare a mixture; mixing a second
dispersing agent and water with the mixture to prepare a
graphene-ceramic hybrid sol solution; and coating a substrate with
the graphene-ceramic hybrid sol solution. According to various
embodiments, the graphene may be formed by reducing graphene oxide,
graphite oxide, or a mixture thereof by a reduction method. The
reduction method may be selected from conventional reduction
methods and, for example, may be a chemical reduction method, a
thermal reduction method, or a combination thereof. For example,
the chemical reduction method may be performed under a strong base
such as hydrazine, and the thermal reduction method may be
performed under an inert gas atmosphere at a high temperature.
However, RGO prepared by reducing graphene oxide, graphite oxide,
and the like is reported to not completely remove a part of the
oxidizing groups on the surface. As such, since oxygen content (due
to oxidizing groups on the surface) is generally less than or equal
to about 5% relative to a carbon backbone, graphene (RGO) of the
present invention includes less than or equal to about 5 wt % of
oxygen content relative to the carbon backbone.
[0043] According to various embodiments, the process of mixing
graphene, a first dispersing agent and a first non-aqueous based
solvent to prepare the dispersion (also referred to herein as
"first process") is a process in which graphene is dispersed alone
before mixing the graphene dispersion with the ceramic sol
solution. This is beneficial in order to remove water that is
hydrogen-bonded with a hydrophilic functional group, for example a
carboxyl group (--COOH) or a hydroxyl group (--OH), and in order to
maximize graphene dispersion. According to various embodiments,
while forming a ceramic sol, the sol may function as a first
dispersing agent. In particular, after mixing the graphene, first
dispersing agent, and first non-aqueous based solvent, the process
of preparing the dispersion may further include a process of
washing the resultant with a non-aqueous based solvent, and
mechanical-dispersion process for treating the same. Further, after
mixing the first dispersing agent and the first non-aqueous based
solvent, the method may include washing the resultant with a
non-aqueous based solvent before the mechanical dispersion
treatment. When the washing is performed with the first non-aqueous
based solvent, the resultant may be in a form more suitable for a
subsequent process. In particularly, considering a subsequent
process, the same kinds of non-aqueous based solvent as the first
non-aqueous based solvent may be preferably used in the washing
process. According to various embodiments, the process of washing
the first non-aqueous based solvent is performed to thoroughly
remove moisture (H.sub.2O) adsorbed on the surface of the graphene.
This process may be a simple washing process, or may be performed
through more complex procedures such as an ultrasonication
dispersion treatment or after an ultrasonication dispersion
treatment. The washing process may be performed as many times as
needed. By carrying out the washing process with the non-aqueous
based solvent, a degree of moisture removal at the surface of the
graphene may have a beneficial effect on long-time stability of the
sol solution. Therefore, inclusion of a method of performing
washing and/or a washing degree may control moisture and, thus, may
improve resultant properties. Specifically, when moisture is
removed, a sol stability effect may be maximized.
[0044] According to an embodiment for the present invention, in the
first process, sol stability may be reduced by added moisture even
if only a small amount of moisture is added. In particular, even if
only a small amount of moisture is adsorbed on the graphene,
stability of the entire graphene-ceramic hybrid mixed sol may be
dramatically reduced because there is serious interface instability
at an interface with the sol. The mechanical dispersion treatment
may be performed by any known method, such as ultrasonication,
stirring, a shear stress (shearing force) application method, a
method of using a homogenizer, or a combination thereof. Further,
because the dispersion is maximized by simultaneous dispersion with
the dispersing agent and dispersion by mechanical dispersion
treatment, it is possible to maintain dispersion stability
maintained until the graphene is included in the mixture of the
first graphene dispersing agent and non-aqueous based solvent at a
maximum amount of about 5 wt % based on a solid content. When a
network of a ceramic precursor is formed (preparation reaction of a
sol solution), ions derived from the ceramic precursor, chemical
species, and the like are aggregated on the graphene to thereby
reduce surface non-uniformity to a certain degree.
[0045] According to preferred embodiments, the first dispersing
agent is specifically polyethylene glycol (PEG), glycerol,
hydrochloric acid (HCl), acetic acid, formic acid, citric acid, a
polymer, or a combination thereof. One or more additives, such as
polyethylene glycol, glycerin, glucose, a polymer, and a mixture
thereof may be further included, in addition to the first
dispersing agent. Further, one or more other additives may be
included, such as a binder dispersing agent, a curing agent, a
polymer, an inorganic-based powder, and the like. According to
preferred embodiments, the first non-aqueous based solvent is
selected form an amphiphilic solvent, a water-soluble solvent
except water, a non-water-soluble solvent, a polar solvent, a
nonpolar solvent, or a mixed solvent, and specifically IPA
(iso-propyl alcohol), ethanol, acetone, methylethylketone, methyl
alcohol, ethyl alcohol, isopropyl alcohol, acetylacetone, butyl
alcohol, ethylene glycol, polyethylene glycol, tetrahydrofuran,
dimethylformamide, dimethyl acetamide, N-methyl-2-pyrrolidone,
hexane, cyclohexanone, toluene, chloroform, dichlorobenzene,
dimethylbenzene, trimethylbenzene, pyridine, methylnaphthalene,
nitromethane, acrylonitrile, octadecylamine, aniline,
dimethylsulfoxide, or a mixed solvent thereof.
[0046] In the subsequent process of adding a mixed solution of a
second non-aqueous based solvent and a ceramic precursor to the
dispersion to prepare a mixture, a dispersing agent and or additive
may be omitted. According to various embodiments, the second
non-aqueous based solvent may be added as a dilution solvent or a
sol stabilization solvent. Further, the second non-aqueous based
solvent may be the same as the first non-aqueous based solvent and
may be either homogeneous or heterogeneous, and may be a mixed
solvent. According to preferred embodiments, the ceramic precursor
may be selected from titanium iso-propoxide (TTIP) and tetramethyl
orthosilicate (TMOS). Preferably, the dispersion including graphene
and the mixed solution of the ceramic precursor is prepared such
that they are dispersed separately and mixed to prepare a sol
solution. This allows for the ceramic precursor molecule species to
be maximally dispersed and adsorbed on a sheet-shaped
nanostructure, graphene, to thereby form a uniform graphene-ceramic
sol solution.
[0047] In the next process of mixing a second dispersing agent and
water with the mixture to prepare a sol solution for a coating
layer of a graphene-ceramic hybrid composition, the second
dispersing agent may be the same material as the first dispersing
agent, or a different material, and may be a mixed material. For
example, when the first dispersing agent is polyethylene glycol,
the second dispersing agent may be polyethylene glycol or
hydrochloric acid.
[0048] After the sol solution for the coating layer of the
graphene-ceramic hybrid composition is prepared, a substrate is
coated with the sol solution to prepare the graphene-ceramic hybrid
coating layer. The coating process may be performed by any general
coating method, and according to various embodiments, is performed
specifically dip coating, spin coating, spray coating, paint
coating, bar coating, flow coating, roll coating, or a combination
thereof. According to preferred embodiments, the coating method is
dip coating, spin coating, or spray coating. For example, the
coating process according to one embodiment of the invention may be
performed using spray coating as shown in FIG. 9, regardless of the
kinds or shapes of the substrates to be coated (e.g., such as a
large area, a curved substrate, and the like). However, the coating
process it is not limited thereto.
[0049] According to another embodiment of the present invention, a
graphene-ceramic hybrid coating layer prepared using the above
preparation method is provided. In the graphene-ceramic hybrid
coating layer prepared according to the above preparation method,
the graphene content in the graphene-ceramic hybrid coating layer
is preferably about 0.001 wt % to about 1.8 wt % based on the total
weight of the graphene-ceramic hybrid coating layer.
[0050] In addition, the present invention includes applying the
coating layer to an automobile headlamp. Such coating, in
particular, is expected to suppress fogging due to thermal
conductivity by lamp heat due to effects of the present invention,
for example excellent thermal conductivity as described above. As
one specific industrial application of the present coating, the
coating may be applied to a lens (PC curved substrate) of an
automobile head lamp to reduce fogging problems.
[0051] Hereinafter, specific exemplary embodiments of the present
invention are described. However, the specific exemplary
embodiments are merely used to exemplarily illustrate the present
invention in more detail, and are not to be seen as limiting the
present invention. Furthermore, what is not described in this
disclosure may be sufficiently understood by those skilled in the
art who have knowledge in this field.
Preparation Example 1
Preparation of Graphene Oxide
[0052] 10 g of natural graphite and 7.5 g of sodium nitrate were
put in a reactor and 621 g of 96% sulfuric acid was slowly added
while stirring. After the three materials were sufficiently mixed,
45 g of manganese peroxide was added. Because the manganese
peroxide has a potential for explosion and generates heat and gases
when reacting with strong sulfuric acid, it is gradually added over
the course of 1 hour little by little. After adding the manganese
peroxide, the resultant was stirred at room temperature and reacted
for 4 to 6 days. Then, 1 L of 5% sulfuric acid was added. Because a
large amount of heat and gases may be generated by this process,
the reactor was suitably cooled and the sulfuric acid was added
slowly over 1 hour, and then the resultant was held at room
temperature for one day while being stirred. After one day, 30 g of
30% hydrogen peroxide was slowly added and reacted for 2 hours. In
order to remove a large amount of sulfuric acid and hydrogen
peroxide in the resulting product, washing and centrifugation were
performed repeatedly. The process was performed as follows:
centrifugation was performed to remove a supernatant, a mixed
solution including 3% sulfuric acid and 0.5% hydrogen peroxide at a
ratio of 1:1 was added to the remaining precipitate, and the
resultant was sufficiently agitated and centrifuged and a
supernatant was removed. Then, the mixed solution was added to the
remaining precipitate and mixed. These processes were repeated 15
times, and then the mixed solution was replaced by water 5-6 times
to obtain an aqueous graphene-oxide (GO) slurry.
[0053] A GO slurry is generally a material that is produced by acid
treatment of graphite and purification processes, and thus the GO
slurry in the present invention may be a generally-known
sheet-shaped graphene oxide or graphite oxide without limitation.
In general, an aqueous GO slurry has a solid content of 2 to 8 wt %
based on the total weight of the centrifuged slurry.
Preparation Example 2
Preparation of Thermally Reduced Graphene
[0054] Reduced graphene oxide (RGO) was prepared by vacuum-drying
the aqueous graphene-oxide slurry obtained according to Preparation
Example 1 at 100.degree. C. for 24 hours and heat-treating it at
600.degree. C. under a N.sub.2 atmosphere for 30 minutes.
Preparation Example 3
Preparation of Chemically Reduced Graphene
[0055] Reduced graphene oxide powder was prepared by adding
hydrazine to the aqueous graphene oxide slurry prepared according
to Preparation Example 1, reacting the mixture for 24 hours, and
centrifuging/washing/drying a precipitate obtained therefrom.
Example 1
Preparation of Graphene-TiO.sub.2 Hybrid Sol Solution
[0056] 10 mg of the thermally reduced graphene prepared according
to Preparation Example 2 was put in a 500 mL plastic bottle, 200 ml
of IPA was added thereto, 20 g of PEG was added thereto, and the
mixture was ultrasonication-dispersed for 10 minutes. 50 ml of
acetylacetone was added to the IPA-dispersed graphene (GP)
dispersion, and 50 ml of a TiO.sub.2 ceramic precursor reagent
(titanium iso-propoxide (TTIP)) was added thereto, and the mixture
was agitated for greater than or equal to 30 minutes to prepare
"reactant A". The agitation made the TTIP ion species and chemical
species sufficiently uniformly contact the surface of a GP
sheet-shaped structure, and provided uniformity of a sol prepared
in the next step. 150 ml of water, 10 g of PEG (polyethylene
glycol), and 1 ml of HCl were added to the reactant A, and the
mixture was uniformly agitated for 90 minutes, to prepare a
GP-TiO.sub.2 hybrid sol solution.
Preparation of Graphene-TiO.sub.2 Hybrid Coating Layer
[0057] The GP-TiO.sub.2 hybrid sol solution was spin-coated on a
glass substrate that was plasma-treated on the surface (800 rpm).
The spin-coated layer was vacuum-dried at room temperature and
heat-treated at 180.degree. C. for 1 hour, forming a GO-TiO.sub.2
hybrid coating layer. Herein, the graphene content (or content of
carbon) of the coating layer was about 0.01-0.03 wt %.
Example 2
Preparation of Graphene-TiO.sub.2 Hybrid Sol Solution
[0058] 10 mg of the thermally reduced graphene according to
Preparation Example 2 was put in a 500 mL plastic bottle, 150 ml of
DMF was added thereto, 15 g of PEG was added thereto, and the
mixture was ultrasonication-dispersed for 10 minutes. 50 ml of
acetylacetone was added to the GP dispersion dispersed in DMF, 50
ml of titanium iso-propoxide (TTIP) as a TiO.sub.2 ceramic
precursor reagent was added thereto, and the mixture was agitated
for greater than or equal to 30 minutes (a reactant A). This
process made the TTIP ion species and chemical species sufficiently
uniformly contact the surface of a GP sheet-shaped structure and
provided uniformity of a sol prepared in the next step. 150 ml of
water, 20 g of PEG (polyethylene glycol), and 1 ml of HCl were
added to the reactant A, and the mixture was uniformly reacted
(agitated) for 90 minutes, thereby preparing a GP-TiO.sub.2 hybrid
sol solution. This hybrid sol was not precipitated but was
uniformly coated without a stain.
Preparation of Graphene-TiO.sub.2 Hybrid Coating Layer
[0059] The GP-TiO.sub.2 hybrid sol solution was spin-coated on a
glass substrate that was plasma-treated on the surface (800 rpm).
The spin-coating layer was vacuum-dried at room temperature and
then heat-treated at 180.degree. C. for 1 hour, thereby forming a
GO-TiO.sub.2 mixed layer. Herein, the graphene content (or content
of carbon) of the coating layer was about 0.01-0.03%.
Example 3
Preparation of Graphene-TiO.sub.2 Hybrid Sol Solution
[0060] 15 mg of the chemically reduced graphene preparation
according to Example 3 was put in a 500 mL plastic bottle, 150 ml
of IPA was added thereto, 20 g of PEG was added thereto, and the
mixture was ultrasonication-dispersed for 10 minutes. 70 ml of IPA,
30 ml of DMF, and 50 ml of acetylacetone were additionally added to
the GP dispersion dispersed in IPA, 50 ml of titanium iso-propoxide
(TTIP) as a TiO.sub.2 ceramic precursor reagent was added thereto,
and the mixture was agitated for greater than or equal to 30
minutes to prepare "reactant A". This process made the TTIP ion
species and chemical species sufficiently uniformly contact the
surface of a GP sheet-shaped structure and provided uniformity of a
sol prepared in the next step. 150 ml of water, 20 g of PEG
(polyethylene glycol), 0.7 ml of HCl, 0.3 ml of acetic acid, and
0.5 ml of citric acid were added to the reactant A, and the mixture
was uniformly reacted (agitated) for 90 minutes, thereby preparing
a GP-TiO.sub.2 hybrid sol solution. This hybrid sol was not
precipitated but was uniformly coated without a stain.
Preparation of Graphene-TiO.sub.2 Hybrid Coating Layer
[0061] The GP-TiO.sub.2 hybrid sol solution was spray-coated on a
PC (polycarbonate) substrate that was plasma-treated on the
surface, and the spray coating layer was vacuum-dried at 50.degree.
C. and heat-treated on the surface by repeatedly applying instant
thermal impacts with an IR lamp. The heat treatment was performed
at 300.degree. C. and the exposure time was 3 seconds, and the
treatment was repeatedly performed. The treatment repetitions were
performed when the temperature of the substrate dropped
sufficiently to room temperature. Herein, the lower part of the
substrate was water-cooled (or air cooled), so that the temperature
of the substrate was less than 100.degree. C.
Example 4
Preparation of Graphene-SiO.sub.2 Hybrid Sol Solution
[0062] 15 mg of the chemically reduced graphene prepared according
to Preparation Example 3 was put in a 500 mL plastic bottle, 150 ml
of IPA was added thereto, 10 g of PEG was added thereto, and the
mixture was ultrasonication-dispersed for 10 minutes. 100 ml of
ethanol was added thereto, then 10 ml of TMOS (tetramethyl
orthosilicate) was added thereto, and the resulting mixture was
agitated for greater than or equal to 30 minutes. At this time, the
TMOS did not yet become a sol and uniformly contacted the interface
of the GP. 50 mL of water and 3 g of PEG were added to the
solution, and the mixture was agitated for one hour, preparing a
GP-SiO.sub.2 hybrid sol solution.
Preparation of Graphene-SiO.sub.2 Hybrid Coating Layer
[0063] The GP-SiO.sub.2 hybrid sol solution was spray-coated on a
glass substrate that was plasma-treated on the surface, and the
spray coating layer was vacuum-dried at 80.degree. C. under a
nitrogen atmosphere and heat-treated at 300.degree. C. for 3 hours.
Herein, a GP content (content of carbon) of the obtained hybrid
layer was about 1.8%.
Comparative Example 1
Ceramic Sol
[0064] A TiO.sub.2 sol solution was prepared by using 50 mL of IPA,
adding 50 mL of titanium iso-propoxide (TTIP) as a TiO.sub.2
ceramic precursor reagent thereto, agitating the mixture for
greater than or equal to 30 minutes, adding 10 mL of water, 10 g of
PEG (polyethylene glycol), and 1 mL of HCl thereto, and then
uniformly reacting (agitating) the resulting mixture for 90
minutes.
Comparative Example 2
Simple Mixing
[0065] A TiO.sub.2 sol solution was prepared by using 50 mL of
acetylacetone, adding 50 mL of titanium iso-propoxide (TTIP) as a
TiO.sub.2 ceramic precursor reagent thereto, agitating the mixture
for greater than or equal to 30 minutes, adding 10 mL of water, 10
g of PEG (polyethylene glycol), and 1 mL of HCl thereto, and
uniformly reacting (agitating) the resulting mixture for 90
minutes. 10 mg of the graphene prepared according to Preparation
Example 2 was added to the TiO.sub.2 sol solution to obtain a
physically simple mixture.
Evaluation 1: Uniformity (Stability) of Sol Solution for
Graphene-Ceramic Hybrid Coating Layer
[0066] Uniformity (stability) of a sol solution for a
graphene-ceramic hybrid coating layer of (C) according to one
embodiment of the present invention and a sol solution for a
graphene-ceramic hybrid coating layer (B) prepared by simply mixing
a graphene dispersion and a ceramic sol solution according to
Comparative Example 2 was evaluated by examining photographs of
each sol solution shown in FIG. 3.
[0067] In particular, FIG. 3 shows a photograph exhibiting
stability and uniformity of sol solutions for a graphene-ceramic
hybrid coating layer according to one embodiment as compared with
the sol solutions according to Comparative Examples 1 and 2. FIG. 3
(A) shows the sol solution for the graphene-ceramic hybrid coating
layer according to Comparative Example 1, and FIG. 3 (B) shows the
sol solution for the graphene-ceramic hybrid coating layer
according to Comparative Example 2. FIG. 3 (C) shows the sol
solution for a graphene-ceramic hybrid coating layer according to
one embodiment of the present invention.
[0068] Referring to FIG. 3 (B), the sol solution prepared as a
simple mixture according to Comparative Example 2 exhibits two
serious problems. (1) The graphene dispersion is hydrophobic and is
not well mixed with a sol solution and, thus, mostly floats on top
of the sol solution, resulting in non-uniformly dispersion in the
sol solution. (2) In an ultrasonication step for dispersing a mixed
solution of the graphene dispersion and the sol solution, moisture
adsorbed on the surface of the graphene had an interface reaction
with the sol (the moisture showed a maximized concentration on the
interface) and extremely deteriorated interface properties, the
mixed solution of the graphene dispersion and the sol solution
became cloudy, and a precipitate was produced therein. The
cloudiness was examined with the naked eye to compare it with the
pure sol solution (A). On the other hand, the sol solution for a
graphene-TiO.sub.2 hybrid coating layer according to one embodiment
of the present invention was uniform, as shown in FIG. 3 (C), and
this uniform solution had a positive influence on uniformity and
stability of a coating layer thus formed. The uniformity and
stability were inherent effects of the present invention that could
not be obtained from a conventional simply-mixed solution.
Evaluation 2: Uniformity of Graphene-Ceramic Hybrid Coating
Layer
[0069] Uniformity of a graphene-ceramic hybrid coating layer
according to one embodiment of the present invention and the
graphene-ceramic hybrid coating layer formed by the simple mixture
of a graphene dispersion and a ceramic sol solution according to
Comparative Example 2 was evaluated by respectively spin-coating
each of the sol solutions on a PC (polycarbonate) substrate as
shown in FIG. 4.
[0070] FIG. 4 shows a photograph exhibiting uniformity of the
graphene-ceramic hybrid coating layers according to one embodiment
and Comparative Example 2. FIG. 4 (A) shows the coating layer
according to Comparative Example 2, and FIG. 4 (B) shows the
coating layer according to one embodiment of the present invention.
As shown, while the coating layer was non-uniform or peeled off in
FIG. 4(A), the coating layer according to one embodiment of the
present invention showed excellent uniformity and transparency as
shown in FIG. 4(B).
Evaluation 3: Storage Stability of Sol Solution for
Graphene-Ceramic Hybrid Coating Layer
[0071] Storage stability of a sol solution for a graphene-ceramic
hybrid coating layer according to one embodiment of the present
invention was evaluated by preparing two sol solutions, and in one
case washing it and in the other case not washing it with a
non-aqueous based solvent, and storing the two solutions in a
refrigerator for 3 days.
[0072] FIG. 5 shows a photograph exhibiting storage stability of
the sol solution for a graphene-ceramic hybrid coating layer
according to one embodiment of the present invention. FIG. 5 (A)
shows a sol solution for a graphene-ceramic hybrid coating layer
prepared by dispersing and washing graphene with a non-aqueous
based solvent more than once according to one embodiment of the
present invention, and FIG. 5 (B) shows a sol solution for a
graphene-ceramic hybrid coating layer prepared by using graphene
without dispersing and washing the graphene with a non-aqueous
based solvent according to another embodiment of the present
invention. Even though the two sol solutions for the
graphene-ceramic hybrid coating layer showed no stability
difference depending on the washing treatment due to a small amount
of difference of adsorbed moisture when prepared, referring to FIG.
5, the sol solution for the graphene-ceramic hybrid coating layer
washed more than once was excellent in terms of storage stability,
as shown in FIG. 5 A. This result suggests that the present
invention may provide a sol solution for a graphene-ceramic hybrid
coating layer having improved storage stability.
[0073] FIG. 6 is a graph showing principles of the present
invention based on comparison of principles of the conventional
method and the present invention by evaluating cloudiness and
precipitation of a solution, and stability and long-term storage
stability of a coating layer. Referring to FIG. 6, the
graphene-ceramic hybrid sol solution according to Example 1
maintained safety to a degree when the graphene content included in
a graphene-ceramic hybrid layer was in a range of 0.001 wt % to 1.8
wt %. On the other hand, a graphene-ceramic hybrid sol solution
showed sharply deteriorated safety as the graphene content included
in a graphene-ceramic hybrid layer was below 0.001 wt %.
Evaluation 4: Transparency of Graphene-Ceramic Hybrid Coating
Layer
[0074] A UV-Vis spectrophotometer (JASCO, V-530) was used to
measure transparency of a graphene-SiO.sub.2 hybrid coating layer,
and the result is provided in FIG. 7. Referring to FIG. 7, the
graphene-SiO.sub.2 hybrid coating layer showed transmittance of 81%
at a wavelength of 550 nm, and herein, included graphene in an
amount of 0.5 wt % at a thickness of 1100 nm.
Evaluation 5: Thermal Conductivity of Graphene-Ceramic Hybrid
Coating Layer
[0075] Thermal conductivity of a transparent of a graphene-ceramic
hybrid coating layer prepared according to the present invention
was evaluated by using a homemade thermal conductivity measuring
apparatus.
[0076] FIG. 8 shows photographs and a diagram illustrating the
apparatus and a method for evaluating thermal conductivity of a
graphene-ceramic hybrid coating layer according to one embodiment.
In particular, the apparatus used for evaluating thermal
conductivity of a graphene-ceramic hybrid coating layer is
illustrated in FIG. 8 (A). A thermocouple (TC2) in the center 102
of a PC (polycarbonate) substrate 100 (with a size of 10
cm.times.10 cm and a thickness of 2 mm) was heated up to
120.degree. C. by using a halogen lamp as a heating source 103 (a
heating shape: a circle with a diameter of 5 cm), and
simultaneously, a temperature on the measurement point of substrate
edge temperature TC1 101 of the substrate was measured. FIG. 8 (B)
is a photograph showing the halogen lamp heating source, and FIG. 8
(C) is a photograph showing a process of attaching TC1 and TC2 to
the substrate.
[0077] As a result of comparing and examining a bare PC substrate,
a ceramic sol coating layer formed of a pure sol solution, and
graphene-ceramic hybrid coating layer according to one embodiment
of the present invention by using the apparatus in FIG. 8, a 1000
nm-thick substrate including 0.1% of graphene showed greater than
or equal to about 4 times improved surface thermal conductivity
than the substrate before being coated with a graphene-TiO.sub.2
ceramic hybrid coating layer. In addition, the 1000 nm-thick
substrate including 0.1% of graphene showed greater than or equal
to about twice improved surface thermal conductivity than a
substrate coated with a ceramic sol solution according to
Comparative Example 1.
[0078] While this invention has been described in connection with
what is presently considered to be practical exemplary embodiments,
it is to be understood that the invention is not limited to the
disclosed embodiments, but, on the contrary, is intended to cover
various modifications and equivalent arrangements included within
the spirit and scope of the appended claims.
* * * * *