U.S. patent application number 15/903871 was filed with the patent office on 2018-06-28 for peg-assisted deposition of crack-free titania nanocrystalline coatings over ai flakes.
The applicant listed for this patent is Toyota Jidosha Kabushiki Kaisha, Toyota Motor Engineering & Manufacturing North America, Inc.. Invention is credited to Debasish Banerjee, Masahiko Ishii, Khoa Vo, Songtao Wu.
Application Number | 20180179389 15/903871 |
Document ID | / |
Family ID | 55016555 |
Filed Date | 2018-06-28 |
United States Patent
Application |
20180179389 |
Kind Code |
A1 |
Vo; Khoa ; et al. |
June 28, 2018 |
PEG-ASSISTED DEPOSITION OF CRACK-FREE TITANIA NANOCRYSTALLINE
COATINGS OVER AI FLAKES
Abstract
A multi-layered pigment includes a metal core such as
Al--SiO.sub.2. A high refractive index layer such as TiO.sub.2 is
applied by an aqueous organic two-phase process to and surrounding
the metal core. The high refractive index layer has a thickness
greater than 120 nm wherein the high refractive index layer is
uniform and crack-free.
Inventors: |
Vo; Khoa; (Ypsilanti,
MI) ; Wu; Songtao; (Ann Arbor, MI) ; Banerjee;
Debasish; (Ann Arbor, MI) ; Ishii; Masahiko;
(Okazaki City Aichi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Toyota Motor Engineering & Manufacturing North America,
Inc.
Toyota Jidosha Kabushiki Kaisha |
Plano
Toyota-shi Aichi-ken |
TX |
US
JP |
|
|
Family ID: |
55016555 |
Appl. No.: |
15/903871 |
Filed: |
February 23, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14323308 |
Jul 3, 2014 |
9932480 |
|
|
15903871 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08K 9/02 20130101; C09C
2200/302 20130101; C09C 2200/1054 20130101; C09C 1/0021 20130101;
C09C 2200/1058 20130101; C09C 2200/304 20130101; C09C 1/642
20130101 |
International
Class: |
C09C 1/00 20060101
C09C001/00; C09C 1/64 20060101 C09C001/64 |
Claims
1. A multi-layered pigment comprising: a metal core; a high
refractive index layer applied by an aqueous organic two-phase
process to and surrounding the metal core, the high refractive
index layer having a thickness greater than 120 nm wherein the high
refractive index layer is uniform and crack-free.
2. The multi-layered pigment of claim 1 wherein the core material
is selected from the group consisting of: Al, Cr and Al coated with
SiO.sub.2.
3. The multi-layered pigment of claim 1 wherein the high refractive
index layer is selected from the group consisting of: TiO.sub.2,
Fe.sub.2O.sub.4, Cr.sub.2O.sub.3, and Fe.sub.3O.sub.4
4. The multi-layered pigment of claim 3 wherein the high refractive
index layer includes TiO.sub.2.
5. The multi-layered pigment of claim 3 wherein the metal core is
Al coated with SiO.sub.2.
6. A multi-layered pigment comprising: an Al--SiO.sub.2 core; a
TiO.sub.2 layer applied by an aqueous organic two-phase process to
and surrounding the Al--SiO.sub.2 core, the TiO.sub.2 layer having
a thickness greater than 120 nm wherein the TiO.sub.2 layer is
uniform and crack-free.
7. A multi-layered pigment comprising: an Al--SiO.sub.2 core; a
TIO.sub.2 layer applied by an aqueous organic two-phase process to
and surrounding the Al--SiO.sub.2 core, the TiO.sub.2 layer having
a thickness of 160 nm wherein the TiO.sub.2 layer is uniform and
crack-free.
Description
CROSS REFERENCE TO RELATED APPLICATION(S)
[0001] This application is a continuation application of U.S.
Patent Application No. 14/323,308, filed Jul. 3, 2014, which is
incorporated in its entirety by reference.
FIELD OF THE INVENTION
[0002] The invention relates to processes for forming pigments
having metal cores and a uniform smooth crack-free layer of a high
refractive index material and materials formed by the process.
BACKGROUND OF THE INVENTION
[0003] Generally, luster and interference pigments are known in the
art for use in various applications such as automotive finishes,
coatings and other pigment applications.
[0004] Such pigments may be formed by deposition of titanium oxide
over highly reflective platelet-like aluminum flakes in a water
system. TiO.sub.2, may he deposited to the Al flake under highly
acidic conditions such as at a pH of less than 2.0 such that a
hydrolysis reaction for TiO.sub.2 may be achieved. However, such a
process results in unsatisfactory coatings due to the diffusion of
aqueous solution through the SiO.sub.2 layer.
[0005] Problems associated with the above deposition include both
etching of the Al core and a change in pH near the SiO.sub.2--Al
surface which are undesired for TiO.sub.2 deposition. At such low
pH, the protons in the aqueous solution can still diffuse through
the SO.sub.2 layer and react with the Al core during the typical
long deposition period. This side reaction between the proton and
Al as well as the resultant pH increase at the core surface renders
the deposition of TiO.sub.2 difficult. Diffusion of protons through
the SiO.sub.2layer may cause a reaction with Al such that hydrogen
gas is released causing weak adhesion of the TiO.sub.2 particles
and the formation of channels or cracks in the SiO.sub.2 and
TiO.sub.2 layers. Additionally, an increase in the pH may cause
rapid deposition of the TiO.sub.2 layer and formation of large
particles of TiO.sub.2 which would adversely affect the pigment's
properties.
[0006] Additionally, problems associated with using a sol-gel
process includes the formation of cracks and other imperfections
for high refractive index layers that are greater than 120 nm.
There is therefore a need in the art for an improved process and
pigment that solves the problems identified above and produces a
pigment that has a crack-free and uniform high refractive index or
TiO.sub.2 layer. There is also a creed in the art for a an improved
process and pigment that includes high refractive index layers that
have a thickness of greater than 120 nm and is crack-free and
uniform.
SUMMARY OF THE INVENTION
[0007] In one aspect there is disclosed, a multi-layered pigment
that includes a metal core. A high refractive index layer is
applied by an aqueous organic two-phase process to and surrounding
the metal core. The high refractive index layer has a thickness
greater than 120 nm wherein the high refractive index layer is
uniform and crack-free.
[0008] In a further aspect there is disclosed, a multi-layered
pigment that includes an Al--SiO core A TiO.sub.2 layer is applied
by an aqueous organic two-phase process to and surrounding the
Al--SiO.sub.2 core. The TiO.sub.2 layer has a thickness greater
than 120 m wherein the TiO.sub.2 layer is uniform and
crack-free.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1a is a SEM image of a coated particle having a
TiO.sub.2 coating without the addition of an organic binder;
[0010] FIG. 1b are SEM image of a coated particle having a
TiO.sub.2 coating without the addition of an organic binder;
[0011] FIG. 1c are SEM image of a coated particle having a
TiO.sub.2 coating without the addition of an organic binder;
[0012] FIG. 1d is a SEM image of a coated particle having a
TiO.sub.2 coating with the addition of an organic binder;
[0013] FIG. 1e is a SEM image of a coated particle having a
TiO.sub.2 coating with the addition of an organic binder;
[0014] FIG. 1f is a SEM image of a coated particle having a
TiO.sub.2 coating with the addition of an organic binder;
[0015] FIG. 2a is a SEM image of a coated particle having a
TiO.sub.2 coating without the addition of an organic binder
following sintering;
[0016] FIG. 2b is a SEM image of a coated particle having a
TiO.sub.2 coating without the addition of an organic binder
following sintering;
[0017] FIG. 2c is a SEM image of a coated particle having a
TiO.sub.2 coating with addition of an organic binder following
sintering;
[0018] FIG. 2d is a SEM image of a coated particle having a
TiO.sub.2 coating with the addition of an organic binder following
sintering;
[0019] FIG. 3a are images of TiO.sub.2 layers of varying thickness
over an Al core;
[0020] FIG. 3b are SEM images of FIG. 3a in cross section;
[0021] FIG. 3c are SEM images of FIG. 3a of the surface;
[0022] FIG. 4 is an EDX image of a pigment having a TiO.sub.2 layer
160 nm thick.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] There is disclosed a process of forming a multi-layered
pigment and a multi layered pigment that has a uniform surface
coating for use in high chroma and other pigment systems. The
process provides a low cost process using a two-phase system to
produce pigments in an economical manner. The multi-layered pigment
includes a uniform coating of a high refractive index material that
does not include cracks or other imperfections.
[0024] The process of the present invention allows for an
economical procedure to produce pigments having varying thicknesses
of high refractive layers of thicknesses up to 200 nm. The process
eliminates side reactions and processing problems in prior art
applications. The process solves the problems of both etching of
the Al core and a change in pH near the SiO.sub.2--Al surface which
are undesired for TiO.sub.2 deposition. The process eliminates
cracks and other imperfections in a high refractive index layer for
various thicknesses.
[0025] The process of forming a multi layered pigment includes the
steps of: providing a metal core material; dispersing the metal
core material in a first solvent and organic binder mixture;
depositing a high refractive index material onto the metal core
material; drying the deposited high refractive index and metal core
material wherein the high refractive index layer is uniform and
crack-free.
[0026] The metal core material may include various metals including
Al, Cr and coated Al such as Al coated with a layer of SiO.sub.2.
in one aspect, the high refractive index layer includes TiO.sub.2.
Additional high refractive index materials may include
Fe.sub.2O.sub.4, Cr.sub.2O.sub.3, and Fe.sub.3O.sub.4. The high
refractive index layer may have a thickness of from 50-200 nm. In
another aspect the high refractive index layer may have a thickness
greater than 120 nm.
[0027] The step of dispersing the metal core material may include
suspending the metal core material in, a solution of a first
solvent such as ethanol and an organic binder. The organic binder
may include anionic, cationic, zwitterionic and non-ionic binders.
Various examples of binders include: ammonium lauryl sulfate,
sodium lauryl sulfate, sodium dodecyl sulfate (SDS), sodium lauryl
ether sulfate (SLES), sodium lauroyl sarcosinate cetyl
trimethylammonium bromide (CDB), hexadecyl trimethyl ammonium
bromide, cetyl trimethylammonium chloride (CTAC), Cocamidopropyl
betaine, Polyethylene glycol; Polyoxypropylene glycol alkyl ethers;
Polyoxyethylene glycol, alkylphenol ethers (Triton X-100);
Polyoxyethylene glycol sorbitan alkyl esters; Block copolymers of
polyethylene glycol and polypropylene glycol; Glycerol alkyl
esters; and Glucoside alkyl ethers. In one aspect, the organic
binder is present in an amount of from 0.5% to 10% by weight in
relation to the core metal particle and first solvent.
[0028] The step of depositing a high refractive index material onto
the metal core material may include dissolving a high refractive
material precursor in a second solvent and adding the dissolved
metal precursor and water to the dispersed core material in the
first solvent and organic binder mixture. The second solvent may
include ethanol. In one aspect water may be added to the mixture at
the same time as the dissolved metal precursor with another
subsequent amount of water added following addition of the
dissolved metal precursor. The metal precursor may include
tetraethyl orthotitanate (TEOT) or other metal compounds that
dissolve in art organic solvent. The resulting particles may then
be washed with a solvent and filtered and then dried at room
temperature for a specified period of time such as for example 24
hours. The resulting dried particles have a layer of high
refractive index material deposited thereon and the layer is
uniform and crack-free.
[0029] Following the step of dying, the particles may be sintered
removing the organic binder. In one aspect, the particles may be
sintered at a temperature of less than or equal to 400.degree. C.
for a specified time. The resulting sintered particles have a layer
of high refractive index material deposited thereon and the layer
is uniform and crack-free.
[0030] In another aspect, there is disclosed a multi-layered
pigment that includes a metal core. A high refractive index layer
is applied to and surrounds the passivation layer wherein the high
refractive index layer is uniform and crack-free. The high
refractive index layer may have a thickness of from 50-200 another
aspect the high refractive index layer may have a thickness greater
than 120 nm.
[0031] In one aspect the metal core material may include an
Al--SiO.sub.2 core and the high refractive index material may
include a TiO.sub.2 layer applied by an aqueous organic two-phase
process to and surrounding the Al--SiO.sub.2 core. The TiO.sub.2
layer having a thickness greater than 120 nm wherein the TiO.sub.2
layer is uniform and crack-free.
EXAMPLES
Materials
[0032] Aluminum flakes were obtained from Silberline Manufacturing
Co coated with a thin SiO.sub.2 layer. Titanium (IV) ethoxide,
polyethylene glycol (PEG, average molecular weight 1000 Da), and
ethanol (99%) were purchased from Sigma-Aldrich Chemical Co, (St.
Louis. Mo.). Unless mentioned, all reagents and solvents used in
the expert erns were of the highest grade commercially
available.
Deposition of Crack Free Titania Nanocrystalline Coatings Over Al
Flakes
[0033] 0-2.7 g of PEG is dissolved in 50 ml of absolute ethanol. 5
g of SiO.sub.2-coated Aluminum flakes having particle sizes of
20-50 .mu.m and an average thickness of 300 nm are suspended in 50
ml of absolute ethanol containing PEG in a 250 ml round bottom
flask and heated to 40.degree. C. while constantly stirring. 2.5 g
of titanium (IV) ethoxide (TEOT) is dissolved in 50 ml of absolute
ethanol and heated to 40.degree. C. This solution is then metered
into the aluminum flake suspension while vigorously stirring. At
the same time, 1.8 ml of deionized (DI) water is metered in. A
further 4.7 ml of DI water is subsequently metered in. The mixture
is allowed to cool to room temperature in about 1 hour, and the
resultant intermediate is filtered off, washed with ethanol, and
air-dried at room temperature for 24 hours. The coated material is
then sintered at 400.degree. C. for 2 hours.
[0034] A process for producing multilayer pigment particles should
be stable and produce uniform crack-free particles. Referring to
FIG. 1, SEM images of samples before sintering for a coated
particle having a TiO.sub.2 coating with and without the addition
of an organic binder. FIGS 1a-c show crack formation in TiO.sub.2
layer over an aluminum flake having a layer of SiO.sub.2 whet no
PEG was added. FIGS. 1d-f shows the smooth crack-free TiO.sub.2
layer over aluminum flake with the addition of 3 weight % of PEG.
The thicknesses of TiO.sub.2 layers with and without PEG are
measured as the same thickness of 155.+-.10 nm as shown in FIG. 1c
and 1f.
[0035] Referring to FIGS. 2a-d SEM images of samples following
sintering for a coated particle having a TiO.sub.2 coating with and
without the addition of an organic binder are shown. As shown in
FIGS. 2a-b there are cracks of the TiO.sub.2 layer without addition
of PEG which become larger after calcination in comparison to the
cracks present in FIGS. 1a-c. Referring to FIGS. 2c-d no cracks are
present in the TiO.sub.2 layer when PEG was added.
[0036] The results in FIG. 2 clearly demonstrated the improvement
in the high refractive index layer at thicknesses that exceed 120
nm. The addition of the organic binder results in uniform TiO.sub.2
layer deposition over the SiO.sub.2--Al surface with no cracks or
defects.
[0037] The relationship between the amount of the high refractive
index precursor TEOT and the TiO.sub.2 layer thickness was also
investigated. FIG. 3a shows the image of four TiO.sub.2--Al pigment
samples synthesized with an increased amount of TEOT from 2.sup.nd
left to right. The Al flakes coated with a thin layer of SiO.sub.2
(.about.15 nm) was placed ort the 1.sup.st left for comparison.
Visibly all samples showed uniform colors which indicates a
consistent thickness of the TiO.sub.2 layer on the particles. The
color gradually shifts from original silver to purple, blue, green
and gold as the thickness of the TiO.sub.2 layer increases.
[0038] To analyze quantitatively the TiO.sub.2 layer thickness as
well as to assess such color shift, FE-SEM characterization of the
pigment cross-section was performed as shown in FIG. 3b. The cross
sectional SEM images confirm the application of a smooth TiO.sub.2
layer deposited over the Al core flakes.
[0039] The increase in the thickness of TiO.sub.2 layer from 0 to
120 nm is proportional to the amount of precursor added. SEM images
of the top surface as shown in FIG. 3c further reveal the smooth
surface of TiO.sub.2 layer for all of the pigment samples. By using
energy-dispersive X-ray microanalysis (EDX), the uniform TiO.sub.2
layer formation over the SiO.sub.2-coated Al cores is confirmed
with a thickness of 160 nm as shown in FIG. 4.
[0040] The ability to have various thicknesses of high refractive
index layer including layers that are greater than 120 nm and are
uniform and crack-free is an improvement of the prior art. Pigments
of various thicknesses may be utilized in structural, luster or
interference paint applications and will allow for additional color
and optical properties that are not capable using prior art
pigments.
[0041] The above examples and embodiments are tor illustrative
purposes only and changes, modifications, and the like will be
apparent to those skilled in the art and yet still fall within the
scope of the invention. As such, the scope of the invention is
defined by the claims.
* * * * *