U.S. patent application number 13/387565 was filed with the patent office on 2013-03-21 for method for producing coatings having anti-reflection properties.
The applicant listed for this patent is Peter de Oliveira, Mohammad Jilavi, Sakthivel Shanmugasundaram, Michael Veith. Invention is credited to Peter de Oliveira, Mohammad Jilavi, Sakthivel Shanmugasundaram, Michael Veith.
Application Number | 20130068137 13/387565 |
Document ID | / |
Family ID | 42668519 |
Filed Date | 2013-03-21 |
United States Patent
Application |
20130068137 |
Kind Code |
A2 |
de Oliveira; Peter ; et
al. |
March 21, 2013 |
Method for Producing Coatings Having Anti-Reflection Properties
Abstract
A method for producing coatings having anti-reflection
properties uses a compound comprising at least one type of
nanoparticle and at least one solvent. The compound is applied to a
substrate and treated at various temperatures. Anti-reflection
coatings can be obtained on temperature-sensitive materials such as
PMMA or PET.
Inventors: |
de Oliveira; Peter;
(Saarbruecken, DE) ; Jilavi; Mohammad; (Kirkel,
DE) ; Shanmugasundaram; Sakthivel; (Hyderabad,
IN) ; Veith; Michael; (St.-Ingebert, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
de Oliveira; Peter
Jilavi; Mohammad
Shanmugasundaram; Sakthivel
Veith; Michael |
Saarbruecken
Kirkel
Hyderabad
St.-Ingebert |
|
DE
DE
IN
DE |
|
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20120125234 A1 |
May 24, 2012 |
|
|
Family ID: |
42668519 |
Appl. No.: |
13/387565 |
Filed: |
July 6, 2010 |
PCT Filed: |
July 6, 2010 |
PCT NO: |
PCT/EP2010/004076 PCKC 00 |
371 Date: |
January 27, 2012 |
Current U.S.
Class: |
106/287.17;
106/286.4; 106/287.18; 106/287.19; 106/287.24; 106/287.26; 427/162;
977/773 |
Current CPC
Class: |
G02B 27/0006 20130101;
G02B 1/105 20130101; G02B 1/14 20150115; G02B 1/118 20130101; G02B
1/18 20150115 |
Class at
Publication: |
106/287.17;
106/286.4; 106/287.19; 106/287.18; 106/287.26; 106/287.24; 427/162;
977/773 |
International
Class: |
B05D 5/06 20060101
B05D005/06; C08K 5/07 20060101 C08K005/07; B05D 3/02 20060101
B05D003/02; C09D 1/00 20060101 C09D001/00; C08K 5/05 20060101
C08K005/05 |
Claims
1. A process for producing coatings with anti-reflection
properties, comprising the following steps: a) producing a
composition from at least one kind of nanoparticles and at least
one solvent; b) applying the composition to a substrate; c)
thermally treating the coated substrate.
2. The process as claimed in claim 1, wherein the thermal treatment
is performed at below 200.degree. C.
3. The process as claimed in claim 1, wherein the thermal treatment
is performed at above 400.degree. C.
4. The process as claimed in claim 1, wherein step b) is performed
only once in the course of performance of the process.
5. The process as claimed claim 1, wherein the composition has a
total content of nanoparticles of more than 1% by weight.
6. The process as claimed in claim 1, wherein the composition
comprises at least two kinds of nanoparticles which differ in at
least one property selected from the group consisting of size,
composition, and internal structure.
7. The process as claimed in claim 6, wherein the two kinds of
nanoparticles differ in their mean particle size at least by a
factor of 2.
8. The process as claimed in claim 1, wherein at least one kind of
nanoparticles comprises nanoparticles stabilized by a carboxylic
acid.
9. The process as claimed in claim 1, wherein the nanoparticles
comprise one or more oxides of one or more metals or semimetals
selected from the group consisting of Mg, Si, Ge, Al, B, Zn, Cd,
Ti, Zr, Ce, Sn, In, La, Fe, Cu, Ta, Nb, V, Mo and W.
10. The process as claimed in claim 1, wherein the nanoparticles
comprise compounds selected from the group consisting of TiO.sub.2,
SiO.sub.2, ZrO.sub.2, SnO.sub.2, Al.sub.2O.sub.3, AlOOH,
Ta.sub.2O.sub.5, indium tin oxide (ITO), antimony tin oxide (ATO),
and fluorine-doped tin oxide (FTO).
11. The process as claimed in claim 1, wherein the composition
comprises at least SiO.sub.2 nanoparticles and a further kind of
nanoparticles.
12. The process as claimed in claim 1, wherein the composition
comprises at least SiO.sub.2 nanoparticles and TiO.sub.2 or ITO
nanoparticles.
13. The process as claimed in claim 1, wherein the at least one
solvent is selected from the group comprising
C.sub.1-C.sub.8-alcohols, C.sub.1-C.sub.8-ketones,
C.sub.1-C.sub.8-aldehydes, and water.
14. The process as claimed in claim 1, wherein the composition
comprises at least 2 solvents.
15. The process as claimed in claim 1, wherein the composition does
not comprise any further additives.
16. A coating with antireflection properties, comprising at least
one kind of nanoparticles covered homogeneously by a second kind of
nanoparticles.
17. A coating obtainable by a process as claimed in claim 1.
18. A composition for producing antireflection coatings, comprising
at least one kind of nanoparticles covered homogeneously by a
second kind of nanoparticles.
19. The process as claimed in claim 1, wherein the composition does
not comprise wetting agents and/or polymers.
Description
[0001] This patent application is a U.S. national stage application
of PCT international application PCT/EP2010/004076 filed on 6 Jul.
2010 and claims priority of German patent document 10 2009 035
797.1 filed on 31 Jul. 2009, the entirety of which is incorporated
herein by reference.
FIELD OF THE INVENTION
[0002] The invention relates to a process for producing coatings
with antireflection properties. The invention also relates to a
process for producing coatings which additionally have
condensation-reducing, superhydrophilic and/or self-cleaning
functions.
BACKGROUND OF INVENTION
[0003] Coatings with antireflection properties are produced by many
different techniques. One example of these is the sol-gel
technique. Such coatings may have a high transparency and high
mechanical stability.
[0004] For instance, document US 2008/0268229 A1 describes such
coatings, but these can be produced only by the multiple
application of several different coating compositions. In addition,
the achievement of sufficient stability requires a thermal
treatment at 550.degree. C. As a result, these coatings are
unsuitable for thermally sensitive substrates.
[0005] As a result of the number of steps required and different
coating compositions, these processes are costly and inconvenient
and are also unsuitable for large areas.
[0006] Thermally sensitive substrates are usually coated with the
aid of gas phase deposition, which is likewise a costly and
inconvenient process.
PROBLEM
[0007] The problem addressed by the invention is that of specifying
a process which allows the production of coatings of antireflection
coating in a simple manner, and also to thermally sensitive
substrates. In addition, the process is to enable generation of
surfaces with superhydrophilic and anticondensation properties in
the same way.
SUMMARY OF INVENTION
[0008] This problem is solved by the inventions having the features
of the independent claims. Advantageous developments of the
inventions are characterized in the dependent claims. The wording
of all claims is hereby incorporated into this description by
reference. The invention also comprises all viable and especially
all mentioned combinations of independent and/or dependent
claims.
[0009] Individual process steps are described in detail
hereinafter. The steps need not necessarily be performed in the
sequence specified, and the process to be outlined may also have
further unspecified steps.
[0010] The invention relates to a process for producing coatings
with antireflection properties. In a first step, a composition is
produced from at least one kind of nanoparticles and at least one
solvent. "Kind of nanoparticles" is understood in the context of
the invention to mean an amount of nanoparticles which correspond
in terms of their characteristic parameters such as size (mean
diameter, size distribution), chemical composition, internal
structure (porosity, crystallinity), any surface modification.
Typically, such parameters can be established unambiguously via the
production process for the nanoparticles.
[0011] Nanoparticles are understood in the context of the invention
to mean particles which have a mean particle diameter of less than
1 .mu.m but more than 1 nm (mean particle size measured by HTEM),
preferably of less than 250 nm, more preferably less than 100 nm.
The particles preferably have a diameter between 1 and 50 nm.
[0012] The composition can be accomplished, for example, by
dispersing the nanoparticles in an appropriate solvent or solvent
mixture. The composition preferably has a total content of
nanoparticles of more than 1% by weight, preferably more than 2% by
weight, more preferably between 1% by weight and 10% by weight,
especially between 2% by weight and 5% by weight.
[0013] The composition more preferably comprises at least two kinds
of nanoparticles which differ in at least one property selected
from size (mean diameter, size distribution), chemical composition,
internal structure (porosity, crystallinity), zeta potential.
[0014] In a preferred embodiment of the invention, the at least two
kinds of nanoparticles differ in their mean particle size at least
by a factor of 2, preferably by a factor of 2 to 10 (measured with
an ultrafine particle analyzer).
[0015] At least one kind of nanoparticles preferably comprises
nanoparticles stabilized by a carboxylic acid. The stabilization of
nanoparticles prevents the formation of agglomerates, which can
lead to cloudiness in the coating. At the same time, the charge of
the nanoparticles also determines the interaction thereof with one
another or, in the case of use of several kinds of nanoparticles,
also the interaction between the different kinds of nanoparticles.
In the case of stabilization by a carboxylic acid, it is assumed
that the carboxylic acid adds on to the surface of the
nanoparticles. As a result, the particles receive a relatively
inert surface. Suitable carboxylic acids are all mono- and
polybasic carboxylic acids having 2-8 carbon atoms, i.e., for
example, acetic acid, propionic acid, oxalic acid, glutaric acid,
maleic acid, succinic acid, phthalic acid, adipic acid, suberic
acid. Preferentially suitable are the hydroxycarboxylic acids and
fruit acids, for example glycolic acid, lactic acid, citric acid,
malic acid, tartaric acid and gluconic acid. Particular preference
is given to acids which can be removed in the course of treatment
at low temperatures, for example acetic acid, propionic acid or
oxalic acid. The carboxylic acid also alters the surface charge of
the particles.
[0016] In a further embodiment of the invention, the nanoparticles
comprise one or more oxides of one or more metals or semimetals
selected from Mg, Si, Ge, Al, B, Zn, Cd, Ti, Zr, Ce, Sn, In, La,
Fe, Cu, Ta, Nb, V, Mo or W. The nanoparticles preferably comprise
compounds selected from TiO.sub.2, SiO.sub.2, ZrO.sub.2, SnO.sub.2,
Al.sub.2O.sub.3, AlOOH, Ta.sub.2O.sub.5, indium tin oxide (ITO),
antimony tin oxide (ATO), fluorine-doped tin oxide (FTO).
[0017] In a further preferred embodiment, the composition comprises
at least nanoparticles composed of SiO.sub.2 and at least one
further kind of nanoparticles which preferably do not consist of
SiO.sub.2. Particular preference is given to compositions
comprising SiO.sub.2 nanoparticles with TiO.sub.2 nanoparticles
and/or ITO nanoparticles.
[0018] In a preferred embodiment, the ratio of SiO.sub.2
nanoparticles to the further kinds or the further kind of
nanoparticles in % by weight is between 1:1 and 20:1, preferably
between 4:1 and 10:1, more preferably between 5:1 and 7:1.
[0019] In the above preferred embodiment, it is particularly
advantageous when the SiO.sub.2 nanoparticles are much larger than
the further kind(s) of nanoparticles. Advantageously, they are of
at least twice the mean particle size, preferably even 2 to 10
times larger.
[0020] In a further embodiment of the invention, the composition
comprises at least two solvents. These are advantageously solvents
having a boiling point of below 200.degree. C., preferably of below
150.degree. C. (under standard conditions). Preference is given to
polar solvents.
[0021] Advantageously, the composition comprises at least one
solvent selected from the group comprising C.sub.1-C.sub.8-alcohols
(such as methanol, ethanol, propanol, 2-propanol,
1-methyl-2-propanol, butanol, 2-butanol, ethylene glycol),
C.sub.1-C.sub.8-ketones (such as acetone, 2-butanone, 2-pentanone,
3-pentanone, 2-methyl-2-butanone), C.sub.1-C.sub.8-aldehydes
(ethanal, propanal, butanal, pentanal), water. It is also possible
to use other polar solvents, such as tetrahydrofuran or ethers. It
is also possible to use mixtures of these solvents.
[0022] In a further embodiment, the composition comprises at least
two solvents. In a preferred embodiment, the main constituent of
the composition is nonaqueous solvents, especially alcohols.
[0023] In a further embodiment, the composition does not comprise
any further additives, such as wetting agents or polymers. This
means that the composition is substantially free of organic
substances which cannot be removed by a thermal treatment above
50.degree. C., preferably above 80.degree. C.
[0024] Normally, the composition can be obtained by mixing one or
more suspensions of the nanoparticles with one or more solvents. An
establishment of a particular pH is unnecessary.
[0025] In the next step, the composition is applied to a substrate.
The substrate used may be any desired surface suitable for
coatings. Preference is given to transparent substrates such as
glass, polycarbonates (PC), polymethyl methacrylates (PMMA),
polyethylene (PE), polystyrene, polyvinyl chloride or similar
transparent polymers.
[0026] For application of the composition, it is possible to use
any desired techniques for application of liquid or viscous
compositions, for example spraying, dipping, bar coating,
rolling.
[0027] The thickness of the composition applied is preferably
between 20 and 600 nm, depending on the desired wavelength.
Preference is given to a multiple of one quarter of the desired
wavelength, i.e., for example, 125 nm for a wavelength of 500 nm.
The thermal treatment can also alter the thickness.
[0028] In a further preferred embodiment, the composition is
applied only once. This means that an inventive coating can be
obtained after only one performance of the process.
[0029] After the application, the coated substrate is subjected to
a thermal treatment.
[0030] In a further embodiment, the thermal treatment is performed
below 200.degree. C. (low-temperature treatment), preferably
between 50.degree. C. and 150.degree. C., more preferably between
80.degree. C. and 120.degree. C. The treatment may take between 5
minutes and 5 hours, preferably between 30 minutes and 2 hours.
This embodiment enables the production of antireflection coatings
on thermally sensitive substrates, such as polymers.
[0031] The coatings produced have high mechanical stability, high
transmission (>97%), low reflection in the visible region
(<2%).
[0032] In a further embodiment, the thermal treatment is performed
at above 400.degree. C. (high-temperature treatment), more
preferably between 400.degree. C. and 700.degree. C., more
preferably between 450.degree. C. and 600.degree. C. The treatment
may take from 1 minute to 2 hours. The heating rate used may be 1
to 10.degree. C./min, preferably 5.degree. C./minute. The treatment
at high temperature leads not only to the formation of
antireflection coatings, but the layers may also additionally have
anticondensation and superhydrophilic properties. These can be
promoted by better bonding of the nanoparticles of the coating at
the high temperatures, and the formation of cavities and pores. The
two thermal treatments can also be employed in succession.
[0033] The process is especially suitable for industrial
manufacture. Thus, it is necessary to produce only one composition
and, in a preferred embodiment, the coatings can be obtained in
only one coating step. As a result, it is also possible to coat
large areas in a simple manner. The thermal treatment at low
temperature also enables the coating of thermally sensitive
substrates.
[0034] The inventive coatings can also be applied to coated
substrates. In addition, it is also possible to apply further
coatings.
[0035] The invention also relates to an antireflection coating
obtained by the process according to the invention. Advantageously,
it is a coating comprising SiO.sub.2 nanoparticles and at least one
further kind of nanoparticles, preferably TiO.sub.2 or ITO
nanoparticles.
[0036] In a preferred embodiment of the invention, the coating
comprises at least two kinds of nanoparticles which differ in their
mean particle size at least by a factor of 2, preferably by a
factor of 2 to 10.
[0037] In a further embodiment of the invention, the coating
comprises a homogeneous distribution of the at least 2 kinds of
nanoparticles. This is promoted especially by virtue of the at
least 2 kinds of nanoparticles already being present as a mixture
in the composition before application to the substrate. As a
result, the two kinds of particles can agglomerate with one
another. They advantageously agglomerate in such a way that one
kind of nanoparticles homogeneously covers the other kind of
nanoparticles. In the presence of a difference in size, there is
homogeneous coverage of the larger nanoparticles by the smaller
nanoparticles. This enables the production of a homogeneous
coating. Such an agglomeration of the nanoparticles can also
already be detected in the composition.
[0038] The invention also relates to a composition which has at
least one first kind of nanoparticles homogeneously covered by a
second kind of nanoparticles; more particularly, this is a
composition as described for the process.
[0039] In a preferred embodiment, the composition comprises at
least two kinds of nanoparticles which differ in their mean
particle size at least by a factor of 2, preferably by a factor of
2 to 10, the smaller particles homogeneously covering the larger
particles, i.e. having agglomerated homogeneously on the surface
thereof.
[0040] The invention also relates to the use of a coating or
coating produced by the process described for antireflection
coatings, especially for transparent substrates, optical elements,
lenses, spectacle glass, visual display units, mobile phone
displays, smartphones, touchscreens.
[0041] Further details and features are evident from the
description of preferred working examples which follows, in
conjunction with the dependent claims. In this context, the
respective features can be implemented alone, or several in
combination with one another. The ways of solving the problem are
not restricted to the working examples. For example, stated ranges
always include all--unspecified--intermediate values and all
conceivable sub-intervals.
[0042] The working examples are shown schematically in the figures.
The same reference numerals in the individual figures refer to
identical elements or elements of identical function or elements
which correspond to one another in terms of their function. The
individual figures show:
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] FIG. 1-1 Reflection spectrum of the coatings on
polycarbonate (PC);
[0044] FIG. 1-2 Reflection spectrum of the coatings on PMMA;
[0045] FIG. 1-3 Reflection spectrum of the coatings on glass;
[0046] FIG. 2-1 Transmission spectrum of the coatings on
polycarbonate;
[0047] FIG. 2-2 Transmission spectra of the coatings on PMMA;
[0048] FIG. 2-3 Transmission spectrum of the coatings on glass;
[0049] FIG. 3-1a Reflection spectrum of coatings comprising ITO
(visible light region) on polycarbonate;
[0050] FIG. 3-1b Reflection spectrum of coatings comprising ITO (IR
region) on polycarbonate;
[0051] FIG. 3-2a Reflection spectrum of coatings comprising ITO
(visible light region) on PMMA;
[0052] FIG. 3-2b Reflection spectrum of coatings comprising ITO (IR
region) on PMMA;
[0053] FIG. 3-3a Reflection spectrum of coatings comprising ITO
(visible light region) on glass;
[0054] FIG. 3-3b Reflection spectrum of coatings comprising ITO (IR
region) on glass;
[0055] FIG. 4-1a Transmission spectrum of coatings comprising ITO
(visible light region) on polycarbonate;
[0056] FIG. 4-1b Transmission spectrum of coatings comprising ITO
(IR region) on polycarbonate;
[0057] FIG. 4-2a Transmission spectrum of coatings comprising ITO
(visible light region) on PMMA;
[0058] FIG. 4-2b Transmission spectrum of coatings comprising ITO
(IR region) on PMMA;
[0059] FIG. 4-3a Transmission spectrum of coatings comprising ITO
(visible light region) on glass;
[0060] FIG. 4-3b Transmission spectrum of coatings comprising ITO
(IR region) on glass;
[0061] FIG. 5-1 EDX spectrum of composition S1;
[0062] FIG. 6-1 TEM image of composition S1;
[0063] FIG. 6-2 TEM image of composition S2;
[0064] FIG. 6-3 TEM image of composition S3;
[0065] FIG. 6-4a TEM image of composition S4 (ITO);
[0066] FIG. 6-4b TEM image of composition S4 (ITO);
[0067] FIG. 7-1 Measurement of photocatalytic activity;
[0068] FIG. 8-1 Comparison of the anticondensation capacity of
different samples a) glass b) S1 c) S2 d) S3;
[0069] FIG. 9-1 AFM analysis of the coating with composition L on
PMMA;
[0070] FIG. 9-2 AFM analysis of the coating with composition H-2 on
PMMA;
[0071] FIG. 9-3 AFM analysis of the coating with composition S2 on
PMMA;
[0072] FIG. 9-4 AFM analysis of the coating with composition L on
polycarbonate;
[0073] FIG. 9-5 AFM analysis of the coating with composition H on
polycarbonate;
[0074] FIG. 9-6 AFM analysis of the coating with composition S2 on
polycarbonate;
[0075] FIG. 9-7 AFM analysis of the coating with composition L on
glass;
[0076] FIG. 9-8 AFM analysis of the coating with composition H on
glass;
[0077] FIG. 9-9 AFM analysis of the coating with composition S2 on
glass;
[0078] FIG. 10-1 Microscope image (SEM) of a coating with
composition S2 (20 000.times., scale 1.3 .mu.m);
[0079] FIG. 10-2 Microscope image (SEM) of a coating with
composition S2 (50 000.times., scale 0.5 .mu.m);
[0080] FIG. 10-3 Microscope image (SEM) of a coating with
composition S2 (60.times., scale 500 .mu.m);
[0081] FIG. 10-4 Microscope image (SEM) of a coating with
composition S2 (5000.times., scale 5 .mu.m);
[0082] FIG. 10-5 Microscope image (SEM) of a coating with
composition S2 (1000.times., scale 25 .mu.m);
[0083] FIG. 10-6 Microscope image of a coating with composition S2
(2000.times., scale 13 .mu.m);
[0084] FIG. 10-7 Microscope image (SEM) of a coating with
composition S2 (10 000.times., scale 2.5 .mu.m);
[0085] FIG. 10-8 Microscope image (SEM) of a coating with
composition S2 (20 000.times., scale 1.3 .mu.m);
[0086] FIG. 11-1 EDX analysis of a coating with composition S2;
[0087] FIG. 11-2 EDX analysis of a coating with composition S2
after scratching the site with a pencil;
[0088] FIG. 12-1 Reflection spectrum of a coating with composition
S5 on glass;
[0089] FIG. 12-2 Transmission spectra of a coating with composition
S5 on glass;
[0090] FIG. 12-3 Reflection spectra of a coating with composition
S5 on polycarbonate;
[0091] FIG. 12-4 Reflection spectrum of a coating with composition
S5 on polyethylene (PE), produced by a roll-to-roll coating
process;
[0092] FIG. 12-5 Reflection spectra of coatings of different
modifications of composition S5 on glass;
[0093] FIG. 12-6 Reflection spectra of coatings with composition S5
and S6 on glass;
[0094] FIG. 12-7 Reflection spectra of coatings with compositions
S5 and S7 on glass;
[0095] FIG. 12-8 Reflection spectra of coatings with compositions
S5 and S8 on glass;
[0096] FIG. 12-9 Transmission spectra of coatings with compositions
S5 and S8 on glass;
[0097] FIG. 12-10 Reflection spectra of a glass substrate coated
with S2 on one side (A) and on both sides (B);
[0098] FIG. 13-1 Schematic diagram of the coating;
[0099] FIG. 13-2a TEM image of a sol of composition (S1);
[0100] FIG. 13-2b HTEM detail of a sol of composition (S1);
[0101] FIG. 13-3 TEM image of a sol of composition (S1).
DETAILED DESCRIPTION OF INVENTION
[0102] The compositions for production of the coatings comprise, in
a preferred embodiment, SiO.sub.2 nanoparticles with a further kind
of nanoparticles of different composition, preferably ITO or
TiO.sub.2. In order to increase the porosity, the two particles do
not have the same mean particle size. Advantageously, the SiO.sub.2
nanoparticles are 2-10 times larger than the other
nanoparticles.
[0103] A suspension of SiO.sub.2 nanoparticles preferably
stabilized with a carboxylic acid and having a proportion of 20% to
50% by weight is dispersed in at least one solvent. The solvent is
preferably ethanol, propanol, 2-propanol, or a mixture of two of
these alcohols in a ratio of 1:3 to 3:1, preferably 1:1 (by
volume).
[0104] Added to this mixture is a suspension of the second kind of
nanoparticles with a proportion of approx. 5% by weight, which are
dispersed in an alcohol or an alcohol-water mixture in a ratio of
1:1 (volume).
[0105] The total proportion of nanoparticles in the composition is
at least 0.5% by weight, preferably between 0.8 and 5% by weight,
preferably between 2 and 4% by weight. The ratio between SiO.sub.2
and the other kind of nanoparticles is between 10:1 and 5:1 in % by
weight. The other kind of nanoparticles can also influence the
absorption of the coating, for example ITO particles in the IR
region. The other kind of nanoparticles are preferably TiO.sub.2 or
ITO.
[0106] In a preferred embodiment, the TiO.sub.2 particles are
produced by a hydrothermal method. For this purpose, a titanium
alkoxide, preferably titanium isopropoxide, is added to an alcohol,
preferably ethanol, n-propanol, isopropanol, and hydrolyzed under
acidic conditions with a substoichiometric amount of water.
Advantageously, the addition of the water is preceded by addition
of an alcohol or polyalcohol, especially ethylene glycol. The
hydrolysis is effected thereafter with heating and under pressure
(hydrothermal reaction), for example by heating in a closed vessel.
Preferred temperatures are above 100.degree. C., preferably between
150.degree. C. and 300.degree. C. The resulting particles are then
washed with aprotic solvents and dried at temperatures below
100.degree. C., preferably between 40.degree. C. and 100.degree. C.
The resulting powders (type 2) are notable for good dispersibility
and particularly advantageous properties for production of the
antireflection coatings.
[0107] The following compositions were produced:
TABLE-US-00001 Composition Particles 1 Particles 2 S1 SiO.sub.2, 15
nm, acid- TiO.sub.2, 5 nm, produced by stabilized reflux method
(type 1) S2 SiO.sub.2, 15 nm, acid- TiO.sub.2, 5 nm, produced by
stabilized hydrothermal method (type 2) S3 SiO.sub.2, 15 nm, acid-
TiO.sub.2, 3-4 nm, produced stabilized by hydrothermal method (type
3) H1 TiO.sub.2 as S1 -- H2 TiO.sub.2 as S2 -- H3 TiO.sub.2 as S3
-- L SiO.sub.2, 15 nm, acid- -- stabilized S4 SiO.sub.2, 15 nm,
acid- ITO, produced from stabilized Nano-ITO c5000 S1N paste ITO
ITO, produced from -- Nano-ITO c5000 S1N paste S5 SiO.sub.2, 15 nm,
acid- TiO.sub.2, type 2 stabilized S6 SiO.sub.2, 30 nm, acid-
TiO.sub.2 as S5 stabilized S7 SiO.sub.2, 30 nm, base- -- stabilized
S8 SiO.sub.2 as S5 TiO.sub.2 (type 2)
[0108] The compositions were applied to different substrates, such
as glass, polycarbonate (PC), PMMA or PET.
[0109] The coated substrates were then subjected to a thermal
treatment. The influence of a treatment at low temperature and of a
treatment at high temperature was studied. Unless stated otherwise,
the coated substrates hereinafter have been treated at low
temperature.
[0110] FIG. 1-1 shows reflection spectra of the coatings of
compositions S1, S2, S3, H1, H2, H3 and L on polycarbonate (PC).
Compositions H1, H2 and H3 gave very similar spectra.
[0111] FIG. 1-2 shows reflection spectra of the coatings of
compositions S1, S2, S3, H1, H2, H3 and L on PMMA. Compositions H1,
H2 and H3 gave very similar spectra.
[0112] FIG. 1-3 shows reflection spectra of the coatings of
compositions S1, S2, S3, H1, H2, H3 and L on glass. Compositions
H1, H2 and H3 gave very similar spectra.
[0113] In all analyses, it is clearly evident that the coating
produced with composition S2 has particularly advantageous
properties.
[0114] FIGS. 2-1 to 2-3 show the transmission properties of the
same samples.
[0115] FIGS. 3-1a and 3-1b show the reflection spectrum of the
coating of composition S4 in the region of visible light and in the
infrared region (IR region) on polycarbonate compared to the
uncoated substrate (polycarbonate: PC), of the coating with
composition L and of a coating only of composition ITO. FIGS. 3-2a,
b and 3-3a,b show the same analyses for coatings on PMMA and
glass.
[0116] FIGS. 4-1a,b, 4-2a,b and 4-3a,b show the corresponding
transmission spectra of the samples from 3-1a,b, 3-2a,b and
3-3a,b.
[0117] The coatings also have a high porosity. This has been
confirmed by ellipsometry. The samples also have a very low contact
angle with respect to water, especially of below 40.degree. on
glass.
[0118] The roughness of the surfaces was also confirmed by AFM
analyses. For instance, with the aid of AFM analyses, the mean
roughness (R.sub.a) and the root mean square roughness (R.sub.RMS)
of different coatings (produced by the low-temperature method) was
determined. The roughness of the coating with S2 is much higher in
almost all cases than the roughness of the corresponding coatings
composed of compositions H-2 and L. The roughness of the coating
with composition L on polycarbonate is higher, but the AFM image
(FIG. 9-4) shows an inhomogeneous coating and the coating can also
be detached easily. For all other coatings, a homogeneous surface
is evident. The pores are distributed homogeneously.
TABLE-US-00002 Composition Substrate FIG. R.sub.a R.sub.RMS L PMMA
9-1 2.2272 3.1044 H2 PMMA 9-2 0.6473 0.8989 S2 PMMA 9-3 2.5585
3.3252 L PC 9-4 8.3599 10.4023 H2 PC 9-5 0.9590 1.2367 S2 PC 9-6
2.1416 2.7637 L glass 9-7 1.3493 1.7218 H2 glass 9-8 0.9537 1.2872
S2 glass 9-9 2.4477 3.1326
[0119] The properties of the coatings can be improved once again by
the treatment at high temperature. The individual nanoparticles of
the coating can probably form even more advantageous pores at this
temperature.
[0120] For instance, the coatings with S1, S2 or S3 have a
photocatalytic activity which leads to the decomposition of organic
substances on the surface. This is also referred to as a
self-cleaning property. FIG. 7-1 shows the measurement of the
photocatalytic activity of coatings on glass treated at a high
temperature. All coatings have a similar activity, even though the
coatings with S1, S2 and S3 have a much lower content of TiO.sub.2
compared to the coating composed of pure TiO.sub.2 (H).
[0121] At the same time, these coatings, probably due to the
exceptional porosity thereof, are also superhydrophilic (contact
angle 0.degree.). The coatings with compositions S2 and S3 do not
lose this property even after repeated wetting or after prolonged
storage (several months). The coatings composed of composition H2
lose this property with time.
[0122] Superhydrophilicity also leads to anticondensation
properties of the coatings. For instance, coatings composed of
compositions S1, S2 and S3 (treated by high-temperature methods)
clearly exhibit an anticondensation property (FIG. 8-1a-d).
[0123] In a further preferred embodiment, the composition is
produced using a mixture of two alcohols, preferably of ethanol and
2-propanol, SiO.sub.2 nanoparticles and TiO.sub.2 nanoparticles,
preferably TiO.sub.2 nanoparticles of type 2 (composition S5).
[0124] FIG. 12-1 shows the reflection spectra of coatings with
composition S5 on glass with different thermal treatment. It is
found that very good properties are obtained even in the case of
treatment at low temperature. The same also applies to the
transmission properties (FIG. 12-2). In that case too, a clearly
comparable transmission is achieved even at low temperatures.
[0125] The same also applies to coating on polymers such as
polycarbonate (FIG. 12-3), where an average reflection of only
1.68% is achieved for the range of 400-780 nm. On PET too, such a
coating exhibits very good properties (FIG. 12-4).
[0126] This composition is quite insensitive to slight alteration
of its constituents. For instance, coating S5 was modified as
follows, and the respective reflection spectra were measured (FIG.
12-5):
TABLE-US-00003 Reflection spectrum Average 380-780 nm S5A 5% more
SiO.sub.2 than S5 1.54 S5B 5% less SiO.sub.2 than S5 1.54 S5C 5%
more ethanol than S5 1.54 S5D 5% less ethanol than S5 1.72 S5E 5%
more 2-propanol than S5 1.79 S5F 5% less 2-propanol than S5 1.49
S5G 5% more TiO.sub.2 than S5 1.48 S5H 5% less TiO.sub.2 than S5
1.46 S5 -- 1.58
[0127] Only the decrease in ethanol or an increase in the content
of 2-propanol led to slightly poorer properties.
[0128] In addition, the influence of the size difference of the
nanoparticles was studied. For instance, composition S6 was
produced with SiO.sub.2 nanoparticles of twice the size. FIG. 12-6
shows the reflection spectra on glass. Again, a slight improvement
in the properties is found. The larger SiO.sub.2 particles probably
lead to the formation of larger cavities and nanopores.
[0129] The influence of the stabilization of the SiO.sub.2
particles was studied in composition S7. This composition was
produced analogously to composition S6, but with ammonia-stabilized
SiO.sub.2 nanoparticles. The reflection spectrum (FIG. 12-7) shows
much poorer properties. The acid of the composition probably
under-protects the formation of nanopores and cavities during the
thermal treatment.
[0130] In order to study the influence of the TiO.sub.2
nanoparticles, composition S8 was produced with lyothermally
produced TiO.sub.2 nanoparticles. FIG. 12-8 shows the reflection
spectra measured. An average value of 1.47% (400-800 nm) was
measured for S5, and an average value of 1.77% (400-800 nm) for S8.
In transmission too (FIG. 12-9), the coating with composition S5 is
superior to the coating with composition S8.
[0131] FIG. 12-10 shows reflection spectra of glass substrates
coated on one side (A) and two sides (B) (S2-450.degree. C.). It is
clearly evident that the coating on one side shows a much better
result. In addition, the haze of the coatings was studied, and very
low values (0.06-0.1) were measured.
[0132] An important effect of the invention appears to lie in the
interactions between the different nanoparticles in the
composition. FIG. 13-1 shows a schematic diagram of a coating. The
large circles show the SiO.sub.2 particles covered homogeneously by
the smaller TiO.sub.2 particles (small circles). The elliptical
elements exhibit cavities and nanopores (these are pores within the
order of magnitude of nanometers, i.e. between 1 and 1000 nm,
preferably between 50 and 800 nm).
[0133] This interaction is already formed in the inventive
composition. For instance, FIGS. 13-2a,b and 13-3 show TEM images
of a composition. These clearly show the large SiO.sub.2 particles
with a diameter of approx. 30 nm, which are covered homogeneously
with the TiO.sub.2 particles of size approx. 2-6 nm.
[0134] Production of the Compositions
[0135] Composition S1
[0136] 3 ml of commercially available nanoparticles (Levasil 200S
30%, 15 nm, stabilized with acetic acid) were dispersed in 24 ml of
ethanol and mixed for 5 minutes. Thereafter, 3 ml of TiO.sub.2
suspension (type 1; reflux method, 5 nm, 5% by weight of TiO.sub.2
dispersed in 1:1 ethanol:water by volume) were added and the
mixture was stirred for 2 hours. The composition has an
SiO.sub.2:TiO.sub.2 ratio of 6:1. This was also confirmed by
energy-dispersive X-ray spectroscopy (EDX) (FIG. 5-1). Analysis by
transmission electron microscopy shows that the particles are
present in good dispersion (FIG. 6-1).
[0137] Composition S2
[0138] Same preparation as composition S1, but with a TiO.sub.2
suspension comprising type 2 TiO.sub.2 particles (5 nm, see later
description). Analysis by transmission electron microscopy shows
that the particles are present in very good dispersion (FIG.
6-2).
[0139] Composition S3
[0140] Same preparation as composition S1, but with a TiO.sub.2
suspension with type 3 TiO.sub.2 particles (3-4 nm) produced by the
lyothermal process. Analysis with transmission electron microscopy
shows that the particles are present in very good dispersion (FIG.
6-3).
[0141] Compositions H1, H2, H3 (TiO.sub.2 Sols)
[0142] For TiO.sub.2 sols containing 3% by weight, 18 ml of the
type 1, 2 or 3 TiO.sub.2 suspension were dispersed in 12 ml of
ethanol and the mixture was stirred for 2 hours. H1 consists of
type 1, H2 of type 2 and H3 of type 3.
[0143] Composition L
[0144] For a 3% by weight SiO.sub.2 sol, 3 ml of SiO.sub.2
suspension (Levasil 200S, 30%, 15 nm, stabilized with acetic acid)
were dispersed in a mixture of 24 ml of ethanol and 3 ml of water
and mixed for 2 hours.
[0145] Composition S4
[0146] 3 ml of commercially available SiO.sub.2 nanoparticles
(Levasil 200S, 30%, 15 nm, stabilized with acetic acid) were
dispersed in 24 ml of ethanol and mixed for 5 minutes. To this were
added 3 ml of a suspension of ITO nanoparticles (5% by weight
dispersed in ethanol, produced from Nano-ITO c5000 SIN paste
(71%)), and the mixture was stirred for 2 hours. Analysis by
transmission electron microscopy shows that some of the ITO
particles are present as agglomerates (FIG. 6-4a,b).
[0147] Composition ITO
[0148] For a 3% by weight ITO sol, 18 ml of a suspension of ITO
nanoparticles (5% by weight dispersed in ethanol, produced from
Nano-ITO c5000 SIN paste (71%)) were dispersed in 12 ml of ethanol
and stirred for 2 hours.
[0149] Production of the TiO.sub.2 Nanoparticles (Type 2)
[0150] 72.08 g of titanium isopropoxide were added gradually to 50
ml of n-propanol and mixed for 5 minutes. Then 11.9 g of
concentrated HCl (37%) were added to the mixture and mixed for 5
minutes. In the next step, 27.93 g of ethylene glycol were added
gradually and mixed for 20 minutes. After thorough mixing, the
mixture was transferred to a Teflon vessel and 2.36 g of water were
added dropwise and stirred for a further hour. Thereafter, the
mixture was heated in an autoclave at 200.degree. C. for 3 h. The
resulting TiO.sub.2 particles were washed once with acetone (200
ml) and once with 1-butanal (150 ml) or 2-butanone (150 ml), and
removed by centrifugation. The particles were dried at 60.degree.
C. in a vacuum oven.
[0151] Coating of the Substrates
[0152] The compositions produced were applied with a dip-coating
machine at a speed of 2 mm/sec.
[0153] The following substrates were used: [0154] glass
(7.5.times.2.5 (1.times.w) thickness 1 mm) [0155] polycarbonate
(7.5.times.2.5 (1.times.w) thickness 4 mm) [0156] PMMA
(7.5.times.2.5 (1.times.w) thickness 3 mm)
[0157] After the coating, the coatings were treated in different
ways.
[0158] Treatment at low temperature:
[0159] Coatings on PMMA were treated at 80.degree. C. for one hour.
Coatings on polycarbonate and glass were treated at 100.degree. C.
for one hour.
[0160] Treatment at high temperature:
[0161] The coatings on glass were treated at 450.degree. C. at a
heating rate of 5.degree. C./min for 30 minutes.
[0162] Measurement of Transmission and Reflection
[0163] The reflection and transmission spectra were recorded with a
Cary 5000 instrument.
[0164] Photocatalytic Activity
[0165] The tests were conducted with coatings composed of
compositions S1, S2, S3 and H (all H sols gave similar results) on
glass which had been treated at 450.degree. C. (heating rate
5.degree. C./min) for 30 minutes. For the photodegradation
experiments, the degradation of 4-chlorophenol (4-CP) as a model
substance was studied. 50 ml of a solution with a concentration of
4-CP of c.sub.0=50 .mu.mol/l were added to the respective coated
glass plate and irradiated with synthetic sunlight using an Atlas
Suntester CPS+ with a 750 W xenon lamp. The respective
concentration c.sub.t of the 4-CPS was determined by UV-Vis
spectroscopy. In FIG. 7-1, the concentrations of 4-CP normalized to
the respective starting concentration c.sub.0 are plotted against
the irradiation time.
[0166] Measurement of Porosity
[0167] The porosity of the coatings was studied with the aid of
ellipsometry. The coatings on glass were treated at 450.degree. C.,
those on PMMA and PET at 80.degree. C., and PC at 100.degree. C.
The following refractive indices were determined:
TABLE-US-00004 Coating of composition: Glass PC PMMA PET L -
SiO.sub.2 1.4001 1.5 1.3878 H - TiO.sub.2 - 1 1.8009 1.8102 1.835
S1 1.4436 1.341 1.4045 H - TiO.sub.2 - 2 1.9028 1.8885 1.8833 S2
1.3747 1.3408 1.2511 1.403 H - TiO.sub.2 - 3 2.0488 2.0472 2.0241
S3 1.4287 1.3866 1.3524
[0168] The refractive index of all coatings S1, S2 and S3
comprising SiO.sub.2 and TiO.sub.2 is less than the refractive
index of coatings L (SiO.sub.2 1.4-1.5) and H (TiO.sub.2, anatase,
2.0-2.7). This indicates that these coatings have a higher
porosity, for example as a result of the formation of nanopores. S2
exhibits a particularly low refractive index.
[0169] Measurement of the Contact Angle of the Coatings
[0170] In addition to the refractive index, the contact angle of a
surface also permits conclusions about the porosity of a surface. A
low contact angle indicates a high roughness of the surface and
hence also a high porosity. The measurement was conducted under a
microscope at room temperature. The contact angle with respect to
water was determined at three positions on the coating and the
average was formed.
TABLE-US-00005 Material Composition of the coating (low-temperature
treatment) PC L H-1 H-2 H-3 S1 S2 S3 .crclbar. [.degree.] 69 51 62
64 50 45 50 PMMA .crclbar. [.degree.] 43 82 64 67 52 30 35 Glass
.crclbar. [.degree.] 50 70 66 72 48 31 39
[0171] Coatings S1, S2, S3 likewise exhibit low contact angles,
which indicates porosity of the coatings.
[0172] The contact angle of coatings on glass with high-temperature
treatment (450.degree. C., 30 min) was also studied:
TABLE-US-00006 H2 H2 S2 S3 Fresh sample 0 0 0 0 On new wetting for
the first time 20 21 0 0 second time 32 30 0 0
[0173] Anticondensation Properties
[0174] For this purpose, coatings of compositions S1, S2, S3
(treated by high-temperature processes) were cooled to below
5.degree. C. and exposed to an atmosphere with relative air
humidity (50-55%). All coatings clearly have anticondensation
characteristics (FIG. 8-1a-d).
[0175] Measurement of Stability/Hardness of the Coating
[0176] To measure the (mechanical) stability of the coating, a
coating of composition S2 (thermal treatment at 450.degree. C., 30
minutes, on glass substrate) was scratched with a pencil of
hardness 5H and examined with an SEM microscope and EDX. The
microscope images show a homogeneous surface. Scratching with the
pencil scratched the surface only slightly. The EDX analysis of the
undamaged surface shows essentially the signals of Si and O. After
the scratching, there are additional signals from C and Al, but
these originate from the pencil.
[0177] Production of Formulation S5
[0178] 3.27 g (3 ml) of an SiO.sub.2 sol (Levasil 200S, 30%, 15 nm,
acid-stabilized) were dispersed in 50:50 ethanol and 2-propanol
(11.85 g (15 ml)+11.70 g (15 ml)) and mixed for 5 minutes.
Thereafter, 1.8 ml of a suspension of TiO.sub.2 nanoparticles (5%
by weight (90 mg) dispersed in a mixture of 1 g of water and 0.78 g
of ethanol) were added and the composition was stirred for 2
hours.
[0179] Production of Formulation S5A
[0180] 3.4335 g of an SiO.sub.2 sol (Levasil 200S, 30%, 15 nm,
acid-stabilized) were dispersed in 50:50 ethanol and 2-propanol
(11.85 g (15 ml)+11.70 g (15 ml)) and mixed for 5 minutes.
Thereafter, 1.8 ml of a suspension of TiO.sub.2 nanoparticles (5%
by weight (90 mg) dispersed in a mixture of 1 g of water and 0.78 g
of ethanol) were added and the composition was stirred for 2
hours.
[0181] Production of Formulation S5B
[0182] 3.1065 g of an SiO.sub.2 sol (Levasil 200S, 30%, 15 nm,
acid-stabilized) were dispersed in 50:50 ethanol and 2-propanol
(11.85 g (15 ml)+11.70 g (15 ml)) and mixed for 5 minutes.
Thereafter, 1.8 ml of a suspension of TiO.sub.2 nanoparticles (5%
by weight (90 mg) dispersed in a mixture of 1 g of water and 0.78 g
of ethanol) were added and the composition was stirred for 2
hours.
[0183] Production of Formulation S5C
[0184] 3.27 g of an SiO.sub.2 sol (Levasil 200S, 30%, 15 nm,
acid-stabilized) were dispersed in a mixture of ethanol (12.433 g)
and 2-propanol (11.70 g) and mixed for 5 minutes. Thereafter, 1.8
ml of a suspension of TiO.sub.2 nanoparticles (5% by weight (90 mg)
dispersed in a mixture of 1 g of water and 0.78 g of ethanol) were
added and the composition was stirred for 2 hours.
[0185] Production of Formulation S5D
[0186] 3.27 g of an SiO.sub.2 sol (Levasil 200S, 30%, 15 nm,
acid-stabilized) were dispersed in a mixture of ethanol (11.258 g)
and 2-propanol (11.70 g) and mixed for 5 minutes. Thereafter, 1.8
ml of a suspension of TiO.sub.2 nanoparticles (5% by weight (90 mg)
dispersed in a mixture of 1 g of water and 0.78 g of ethanol) were
added and the composition was stirred for 2 hours.
[0187] Production of Formulation S5E
[0188] 3.27 g of an SiO.sub.2 sol (Levasil 200S, 30%, 15 nm,
acid-stabilized) were dispersed in a mixture of ethanol (11.85 g)
and 2-propanol (12.285 g) and mixed for 5 minutes. Thereafter, 1.8
ml of a suspension of TiO.sub.2 nanoparticles (5% by weight (90 mg)
dispersed in a mixture of 1 g of water and 0.78 g of ethanol) were
added and the composition was stirred for 2 hours.
[0189] Production of Formulation S5F
[0190] 3.27 g of an SiO.sub.2 sol (Levasil 200S, 30%, 15 nm,
acid-stabilized) were dispersed in a mixture of ethanol (11.85 g)
and 2-propanol (11.12 g) and mixed for 5 minutes. Thereafter, 1.8
ml of a suspension of TiO.sub.2 nanoparticles (5% by weight (90 mg)
dispersed in a mixture of 1 g of water and 0.78 g of ethanol) were
added and the composition was stirred for 2 hours.
[0191] Production of Formulation S5G
[0192] 3.27 g of an SiO.sub.2 sol (Levasil 200S, 30%, 15 nm,
acid-stabilized) were dispersed in a mixture of ethanol (11.85 g)
and 2-propanol (11.7 g) and mixed for 5 minutes. Thereafter, 1.8 ml
of a suspension of TiO.sub.2 nanoparticles (5.25% by weight (94.5
mg) dispersed in a mixture of 1 g of water and 0.78 g of ethanol)
were added and the composition was stirred for 2 hours.
[0193] Production of Formulation S5H
[0194] 3.27 g of an SiO.sub.2 sol (Levasil 200S, 30%, 15 nm,
acid-stabilized) were dispersed in a mixture of ethanol (11.85 g)
and 2-propanol (11.7 g) and mixed for 5 minutes. Thereafter, 1.8 ml
of a suspension of TiO.sub.2 nanoparticles (4.75% by weight (85.5
mg) dispersed in a mixture of 1 g of water and 0.78 g of ethanol)
were added and the composition was stirred for 2 hours.
[0195] Production of Coatings Comprising Compositions S5A-S5H
[0196] The compositions were applied by dip-coating at a speed of
1.7-1.8 mm/s. The thermal treatment was performed at 550.degree. C.
for 30 minutes (heating rate 5.degree. C./min.).
[0197] Production of Composition S6
[0198] 2.65 g (2 ml) of an SiO.sub.2 sol (Levasil 100S, 45%, 30 nm,
acid-stabilized) were dispersed in a mixture of 50:50 ethanol
(14.22 g) and 2-propanol (14.04 g) and mixed for 5 minutes.
Thereafter, 1.8 ml of a suspension of TiO.sub.2 nanoparticles (5%
by weight (90 mg) dispersed in a mixture of 1 g of water and 0.78 g
of ethanol) were added and the composition was stirred for 2
hours.
[0199] Production of Composition S7
[0200] The composition was produced analogously to composition S6,
except using base-stabilized (ammonia) SiO.sub.2 sol.
[0201] Production of Composition S8
[0202] The composition was produced analogously to composition S5,
except using lyothermally produced TiO.sub.2 nanoparticles (type
2).
[0203] Numerous modifications and developments of the working
examples described can be implemented.
[0204] List of literature cited:
[0205] US 2008/0268229 A1
* * * * *