U.S. patent application number 12/160650 was filed with the patent office on 2010-11-25 for anti-reflective coatings.
Invention is credited to Nanning Joerg Arfsten, Hermanus Adrianus Langermans, Guido Jozefina Wilhelmus Meijers, Jens Christoph Thies, Patrick Wilhelmus Antonius Vrijaldenhove.
Application Number | 20100297430 12/160650 |
Document ID | / |
Family ID | 36579831 |
Filed Date | 2010-11-25 |
United States Patent
Application |
20100297430 |
Kind Code |
A1 |
Thies; Jens Christoph ; et
al. |
November 25, 2010 |
ANTI-REFLECTIVE COATINGS
Abstract
The invention relates to a processes and compositions for
preparing anti-reflective coatings.
Inventors: |
Thies; Jens Christoph;
(Maastricht, NL) ; Meijers; Guido Jozefina Wilhelmus;
(Stein, NL) ; Vrijaldenhove; Patrick Wilhelmus
Antonius; (Stein, NL) ; Arfsten; Nanning Joerg;
(Achen, DE) ; Langermans; Hermanus Adrianus;
(Eindhoven, DE) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Family ID: |
36579831 |
Appl. No.: |
12/160650 |
Filed: |
February 12, 2007 |
PCT Filed: |
February 12, 2007 |
PCT NO: |
PCT/EP07/01179 |
371 Date: |
August 6, 2010 |
Current U.S.
Class: |
428/323 ;
106/286.1; 106/286.4; 106/286.5; 106/286.6; 106/286.7; 106/287.1;
106/287.17; 106/287.19; 106/287.23; 427/162 |
Current CPC
Class: |
C03C 2217/45 20130101;
C03C 2217/425 20130101; G02B 1/111 20130101; Y10T 428/31507
20150401; C03C 2217/475 20130101; Y10T 428/24942 20150115; G02B
2207/101 20130101; Y10T 428/31504 20150401; C03C 2217/732 20130101;
G02B 1/118 20130101; G02B 1/10 20130101; Y10T 428/24998 20150401;
Y10T 428/24355 20150115; Y10T 428/31935 20150401; Y10T 428/249978
20150401; A47G 1/06 20130101; Y10T 428/31786 20150401; Y10T 428/265
20150115; Y10T 428/25 20150115; G02B 1/11 20130101; B82Y 20/00
20130101; C03C 17/007 20130101 |
Class at
Publication: |
428/323 ;
427/162; 106/286.1; 106/286.7; 106/286.6; 106/286.4; 106/286.5;
106/287.23; 106/287.1; 106/287.19; 106/287.17 |
International
Class: |
B32B 5/16 20060101
B32B005/16; B05D 5/06 20060101 B05D005/06; C09D 1/00 20060101
C09D001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 14, 2006 |
EP |
06075305.0 |
Nov 10, 2006 |
EP |
06023433.3 |
Claims
1. A coating composition comprising (i) surface-modified
nano-particles of a metal oxide, (ii) metal oxide based binder,
wherein the weight ratio of metal oxide in (i) to (ii) is from 99:1
to 1:1.
2. A composition according to claim 1 wherein the weight ratio is
from 85:1 to 3:2.
3. A composition according to claim 1 wherein the surface-modified
nano-particles are selected from those that form a layer having a
minimum reflection of from 0.1% to 2%
4. A coating composition comprising nano-particles of a metal
oxide, metal oxide based surface-modification agent, and binder
wherein the composition comprises: (i) up to 99.8%, by weight of
the solid fraction, of the nano-particles of a metal oxide, (ii) up
to 60%, by weight of the solid fraction, of the metal oxide based
surface-modification agent, and (iii) up to 50%, by weight of the
solid fraction, of the binder.
5. A composition according to claim 4 wherein the composition
comprises from 0.1% to 85%, by weight of the solid fraction,
nano-particles; from 0.1% to 50%, by weight of the solid fraction,
of surface-modification agent; and from 0.1% to 45%, by weight of
the solid fraction, of binder.
6. A composition according to claim 1 wherein nano-particles
comprise lithium fluoride, calcium fluoride, barium fluoride,
magnesium fluoride, titanium dioxide, zirconium oxide, antimony
doped tin oxide, tin oxide, aluminum oxide, silicon dioxide, or
mixtures thereof.
7. A composition according to claim 1 wherein the surface modifying
agent is selected from metal-alkoxides.
8. A composition according to claim 1 wherein the surface modifying
agent is selected from silane tri or tetra alkoxides and mixtures
thereof.
9. A composition according to claim 1 wherein the binder is
selected from alkoxy silanes, alkoxy zirconates, alkoxy aluminates,
alkoxy titanates, alkyl silicates, sodium silicates, and mixtures
thereof.
10. Use of a composition according to claim 1 for at least
partially coating a substrate.
11. Method of producing a composition according to claim 1 wherein
the reaction of the surface modification agent and the
nano-particles is performed in the substantial absence of an acid
catalyst.
12. A method for preparing an anti-reflective coating on a
substrate comprising: (i) reacting nano-particles with an amount of
surface modifying agent; (ii) pre-hydrolysing a binder; (iii)
mixing the surface modified particles from step (i) with the
pre-hydrolysed binder from step (ii); (iv) applying the coating
composition to a substrate; and (v) optionally, curing the
coating
13. A method of producing surface modified particles, the method
comprising: (i) reacting nano-particles in an organic solvent,
comprising about 2 wt % or less water, with a surface modifying
agent comprising reactive groups, wherein the reaction is
preferably performed in the substantial absence of an acid
catalyst, (ii) thereafter adding water to the mixture in an amount
sufficient to hydrolyse the reactive groups of the surface
modifying agent, (iii) reacting the mixture for sufficient time to
hydrolyse the modifying agent.
14. A method according to claim 12 wherein the reaction of the
surface modification agent and the nano-particles is performed in
the substantial absence of an acid catalyst.
15. A method according to claim 12 wherein nano-particles comprise
lithium fluoride, calcium fluoride, barium fluoride, magnesium
fluoride, titanium dioxide, zirconium oxide, antimony doped tin
oxide, tin oxide, aluminum oxide, silicon dioxide, or mixtures
thereof.
16. A method according to claim 12 wherein the surface modifying
agent is selected from metal-alkoxides.
17. A method according to claim 12 wherein the surface modifying
agent is selected from silane tri or tetra alkoxides and mixtures
thereof.
18. A method for adjusting properties of an anti-reflective coating
having nano-particles and a reactive binder comprising the steps
of: (i) regularly monitoring the optical and mechanical properties
of cured coated articles. (ii) if the optical and mechanical
properties have changed beyond those acceptable in terms of quality
control, adding pre-hydrolysed binder in such an amount to the
coating composition that the chosen balance of optical and
mechanical properties is regained.
19. A substrate coated with a composition according to claim 1.
20. A composition obtainable by the methods according to claim 12.
Description
[0001] The invention relates to coating compositions and process,
uses, and methods thereof. In particular, the present invention
relates to anti-reflective coatings based on nano-particles and
oxidised metal compound forming a binder for the particles.
[0002] The use of nano-particles to make an anti-reflective coating
has been known since the 1940's (U.S. Pat. No. 2,432,484). The
optical function is achieved by the effective refractive index of
the coating being lower than that of the substrate leading to a
gradient of refractive index from that of air to that of the
substrate. This leads to a reduction in the amount of light
reflected. U.S. Pat. No. 6,921,578 describes a method for preparing
anti-reflective coating systems in which a binder (e.g.
tetra-ortho-silicate TEOS) is hydrolyzed in the presence of the
nano-particles while using an acid catalyst. While this approach
can lead to a coating with anti-reflective properties it suffers
from a number of draw backs. For example, the process is difficult
to implement on an industrial scale as it is not easy to make
stable compositions with reproducible properties such as optical
performance and mechanical durability.
[0003] It has surprisingly being found that coatings with good,
reproducible anti-reflective and mechanical properties may be
achieved by the use of surface-modified nano-particles with a metal
oxide based binder. While not wishing to be bound by theory it is
thought that the surface-modification of the nano-particles enables
them to form a more stable coating composition with the binder
which stability is, surprisingly, further conferred upon the
coating when applied to a substrate.
SUMMARY OF THE INVENTION
[0004] The present invention relates to coating compositions
comprising: [0005] (i) surface-modified nano-particles of a metal
oxide, [0006] (ii) metal oxide based binder, wherein the dry-weight
ratio of metal oxide in (i) to (ii) is from 99:1 to 1:1.
[0007] The present invention further relates to coating
compositions comprising nano-particles of a metal oxide, metal
oxide based surface-modification agent, and binder wherein the
composition comprises: [0008] (i) up to 99.8%, by weight of the
solid fraction, of the nano-particles of a metal oxide, [0009] (ii)
up to 60%, by weight of the solid fraction, of the metal oxide
based surface-modification agent, [0010] (iii) up to 50%, by weight
of the solid fraction, of the binder.
[0011] The present invention further relates to processes for
producing such compositions and uses of such compositions.
[0012] The present invention further relates to a process for
preparing an anti-reflective coating on a substrate comprising:
[0013] (i) reacting nano-particles with an amount of surface
modifying agent; [0014] (ii) pre-hydrolysing a binder; [0015] (iii)
mixing the surface modified particles from step (i) with the
pre-hydrolysed binder from step (ii); [0016] (iv) applying the
coating composition to a substrate; and [0017] (v) optionally,
curing the coating.
[0018] The invention further relates to a method of making surface
modified particles by: [0019] (i) reacting nano-particles in an
organic solvent, comprising about 2 wt % or less water, with [0020]
(ii) a surface modifying agent comprising reactive groups, [0021]
(iii) thereafter adding water to the mixture in an amount
sufficient to hydrolyse the reactive groups of the surface
modifying agent, [0022] (iv) reacting the mixture for sufficient
time to hydrolyse the modifying agent and preferably at least
partly grafting the surface modifying agent to the surface of the
nano-particles, [0023] (v) preferably in the substantial absence of
an acid catalyst.
[0024] The present invention further relates to a process for
adjusting properties of an anti-reflective coating having
nano-particles and a reactive binder comprising the steps of:
[0025] (a) regularly monitoring the optical and mechanical
properties of cured coated articles [0026] (b) if the optical and
mechanical properties have changed beyond those acceptable in terms
of quality control adding pre-hydrolysed binder in such an amount
to the coating composition that the chosen balance of optical and
mechanical properties is regained.
[0027] As used herein, the term "nano-particles" refers to
colloidal particles whose primary particle size is less then 1
.mu.m, preferably of less than 500 nm, more preferably of less than
350 nm.
[0028] As used herein, the term "binder" refers to a substance that
can chemically cross-link the particles and preferably also between
the particles and a substrate.
[0029] As used herein, the term "pre-hydrolysing" refers to
hydrolysing the metal alkoxide binder precursor to the point that
oligomeric species are produced via partial condensation but not to
the point that gelation occurs.
[0030] As used herein, the term "acid catalyst" refers to acidic
species capable of catalysing the hydrolysis of the metal alkoxide
binder precursor.
[0031] As used herein, the term "by weight of the solid fraction"
refers to the weight percentage after removal of all solvent
including water.
[0032] Unless otherwise stated all references herein are hereby
incorporated by reference.
DETAILED DESCRIPTION OF THE INVENTION
[0033] The present invention relates to coating compositions,
processes for making an anti-reflective coating, and coated
substrates. The coatings of the present invention comprise
surface-modified nano-particles and binder.
[0034] The coatings of the present invention preferably have an
arithmetic average roughness of about 2 to about 50 nm. The
arithmetic average roughness can be measured by Atomic Force
Microscopy (AFM) and is preferably about 2 nm or larger, more
preferably about 5 nm or larger, even more preferably about 10 nm
or larger, even more preferably about 20 nm or larger. The
arithmetic average roughness preferably be about 50 nm or lower,
more preferably 45 nm or lower.
[0035] When in use the coatings of the present invention preferably
exhibit voids in the coating thereby having a porous structure. The
voids aid in obtaining anti-reflective properties. Void volume is
herewith defined as the space between the particle/binder which,
depending on the environmental circumstances, is in principle
filled with ambient air. Preferably the voids represent about 15%
or more, by volume, of the coating. Preferably the voids represent
about 20% or more, by volume, of the coating. Even more preferably
the voids represent about 30% or more, by volume of the coating.
Preferably the voids represent about 90% or less, by volume, of the
coating. More preferably the voids represent about 80% or less,
even more preferably 70% or less, by volume, of the coating.
[0036] The present coatings may be applied to various substrates.
Preferred are substrates that may benefit from an anti-reflective
coating.
[0037] The substrate herein may be organic. For example, the
substrate may be an organic polymeric such as polyethylene
naphthalate (PEN), polycarbonate or polymethylmethacrylate (PMMA),
polyester, or polymeric material with similar optical properties.
In this embodiment, it is preferred to use a coating that can be
cured at temperatures sufficiently low that the organic material
remains substantially in its shape and does not suffer
substantially due to thermal degradation. One preferred method is
to use a catalyst as described in EP-A-1591804. Another preferred
method of cure is described in WO 2005/049757.
[0038] The substrate herein may be inorganic preferably glass or
quartz. Preferred is float glass. Generally, a glass plate has a
thickness of 0.5 mm or more, preferable 1 mm or more, most
preferably, about 1.8 mm or more. Generally, the glass plate has a
thickness of about 20 mm or less, preferably about 10 mm or less,
more preferably about 6 mm or less, more preferable about 4 mm or
less, and most preferred, about 3 mm or less.
[0039] The substrate preferably has a high transparency. Preferably
the transparency is about 94% or higher at 2 mm thickness and at
wavelength between 425 and 675 nm, more preferably about 96% or
higher, even more preferably about 97% or higher, even more
preferably about 98% or higher.
[0040] The substrate is preferably has a size of 10 cm or more by
10 cm or more, more preferably about 20 cm or more by 20 cm or
more. The maximum size is somewhat dictated by practical
considerations and will generally be 2 by 3 meter or less.
[0041] In one embodiment, the anti reflective glass plate has a
size of about 20 by 30 cm or multiples thereof, such as preferably
about 30 by 40 cm. Another preferred size is about 90 by 130 cm or
180 by 130 cm or multiples thereof. In another embodiment, the anti
reflective glass plate preferably has a size of about 30 by 40 inch
(about 72 by 96 cm) or multiple thereof, such as for example about
60 by 40 inch (about 144 by 96 cm).
[0042] The coating compositions herein preferably comprise
nano-particles, binder and preferably solvent.
[0043] The nano-particles are reacted with a surface modifying
agent so that particles are obtained which are reactive with the
binder. Examples of suitable particles include particles comprising
lithium fluoride, calcium fluoride, barium fluoride, magnesium
fluoride, titanium dioxide, zirconium oxide, antimony doped tin
oxide, tin oxide, aluminum oxide, silicon dioxide, and mixtures
thereof. Preferably the particles comprise silicon dioxide. More
preferably the particles comprise at least 90% by weight of silicon
dioxide.
[0044] Preferably the particles are nano-particles. Preferably the
nano-particles have a length of less than 1000 nm, more preferably
of less than 500 nm, even more preferably of less than 350 nm.
[0045] In one embodiment the particles preferably have an average
aspect ratio at least 1.5. Preferably the average aspect ratio of
the particles is at least 2, more preferably at least 4, even more
preferably at least 6, still more preferably at least 8, even more
preferably at least 10. Preferably the aspect ratio will be about
100 or lower, preferably about 50 or lower.
[0046] The sizes of the particles may be determined by spreading a
dilute suspension of the particles over a surface and measuring the
sizes of individual particles by using microscopic techniques,
preferably scanning electronic microscopy (SEM) or atomic force
microscopy (AFM). Preferably the average sizes are determined by
measuring the sizes of at least 100 individual particles. The
aspect ratio is the ratio between the length and the width of a
particle. In case of rods and worm-like particles the length is the
largest distance between two points in the particle and the width
is the largest diameter as measured perpendicular to the central
axis of the particle. Both length and width are measured from the
projection of the particles as observed under the microscope.
[0047] The coating compositions herein may comprise a mixture of
different types sizes and shapes of particles.
[0048] In one embodiment the particles used herein are
non-spherical such as, preferably, rod-like or worm-like particles,
preferably worm-like particles. Worm-like particles are particles
having a central axis that deviates from a straight line. Examples
of worm-like particles are known by the tradename Snowtex
(IPA-ST-UP, particles have a diameter of 9-15 nm with a length of
40-300 nm), available from Nissan Chemical. Hereinafter, rod-like
and worm-like particles are also denoted as elongated
particles.
[0049] In a preferred embodiment the particles used herein are
substantially spherical. Preferably the spherical particles have an
average aspect ratio of about 1.2 or lower, preferably of about 1.1
or lower. Preferably the particles have an average size of about 10
nm or larger, preferably 20 nm or larger. Preferably the particles
will have an average size of 200 nm or smaller, preferably 150 nm
or smaller, even more preferably about 100 nm or smaller.
Substantially spherical particles have the advantage that they form
coatings where the volume of nano-pores resulting from the space
between the particles is small relative to the volume formed by
non-spherical-particles. Thus the coatings suffer less from filling
of the nano-pores via capillary forces which can cause a loss in
anti-reflective performance. These particles may have a narrow or
broad particle size distribution, preferably a broad particle size
distribution.
[0050] The particles herein are generally provided in a solvent.
For example, the solvent may be water or an alcohol such as
methanol, ethanol or isopropanol (IPA).
[0051] In the case where the particles are dispersed in an organic
solvent the amount of water is preferably about 2%, by weight, or
less, more preferably about 1%, by weight, or less.
[0052] The surface modifying agent(s) react with the nano-particle
to cause the particle to be activated so that it is more
effectively able to react with the binder. The surface modifying
agent is preferably one that is able to form oxides. Preferably,
the surface modifying agent is a hydrolysable compound such as, for
example, metal-alkoxides. Suitable examples include, but are not
limited to, alkoxy silanes, alkoxy zirconates, alkoxy aluminates,
alkoxy titanates, alkyl silicates, sodium silicates, and mixtures
thereof. Preferably alkoxy silanes, more preferably tri and tetra
alkoxy silanes, are used. Tetra alkoxy silane is more
preferred.
[0053] The compositions preferably comprise between about 0.1% and
about 99.8%, by weight of the solid fraction, of surface-modified
nano-particles, relative to the final coating composition. More
preferably the compositions herein comprise from about 6% to about
85%, by weight of the solid fraction, of surface-modified
nano-particles. Even more preferably the compositions herein
comprise from about 10% to about 65%, by weight of the solid
fraction, of surface-modified nano-particles.
[0054] In one embodiment of the invention, the reaction between the
surface modifying agent and the particles is substantially
complete. That is, virtually no free surface modifying agent is
present in solution. The amount of agent is preferably at least
about 1%, by weight, relative to the particles plus surface
activating agent. More preferably the amount of agent is at least
about 2%, by weight. The amount will generally be less than about
80%, by weight, preferably less than about 60%, by weight. A stable
process and dispersion can be achieved with, for example, from 10
to 60%, by weight, of surface modifying agent relative to the
particles plus surface modifying agent. With a higher amount of
surface activating agent, the particles can be made 5, 10, or 20 nm
larger in size, which may be advantageous.
[0055] In another embodiment, the reaction between the particles
and surface modifying agent is not `complete`, but some binder is
left in the solution. If this is the case, no or less binder has to
be added during formulating the coating composition.
[0056] Generally, the reaction is performed in a solvent. Depending
on the chemistry of the binder, many solvents are useful. Suitable
examples of solvents include water, non-protic organic solvents,
and alcohols. Examples of suitable solvents include, but are not
limited to, isopropanol, ethanol, acetone, ethylcellosolve,
methanol, propanol, butanol, ethyleneglycol, propyleneglycol,
methyl-ethyl-ether, methyl-butyl-ether, 1-methoxy propan-2-ol,
toluene, methyl-ethylketone, and mixtures thereof. Preferred are
isopropanol, ethanol, methanol, propanol, and mixtures thereof.
[0057] In one embodiment of the invention, the reaction is
performed in an organic solvent. Preferably, the amount of water
will be about 5% or less, by weight, relative to the solvent. This
is preferred because when the nano-particles have some acidity on
their surface. If the acid groups are concentrated in sufficiently
low amount of water, no catalyst is needed for the reaction between
the surface modifying agent and the particles. In addition, the
reaction preferentially takes place on or near the surface of the
particles. Furthermore when the amount of acid catalyst in the
coating composition is very low it can have benefits such as
greater stability. More preferably, the amount of water is about 20
wt % or less, for example about 10%, 5% or less. Some water may
necessary in order to cause hydrolysis of the surface modifying
compound. Preferably, the amount of water will be about 1% by
weight or more, preferably about 2% by weight or more.
[0058] In a preferred embodiment of the invention about equal or
more molar amounts of water is used relative to the molar amounts
of hydrolysable groups. It is more preferred to use about 3 times
or more of water than hydrolysable groups, even more preferred
about 5 times or more. Preferably the relative molar amount of
water is about 20 times or less than the molar amount of
hydrolysable groups, more preferred about 15 times or less.
[0059] The reaction of the modifying compound and the particles is
preferably such that the reaction is about 80% or more complete,
more preferably about 90% or more. This appears to give an
advantage with respect to the stability of the properties of the
composition. It may be useful--in order to achieve a substantially
complete reaction--to heat the reaction mixture. Suitable reaction
temperatures include about 50.degree. C. or higher, preferably
55.degree. C. or higher, more preferably 65.degree. C. or higher.
Preferably, the temperature is about 100.degree. C. or less,
preferably about 80.degree. C. or less.
[0060] It is possible to measure the extent of the reaction with GC
and Karl-Fisher titration by measuring the amount of alkanol and
water that has been liberated.
[0061] It is preferred that the reaction is performed in the
absence of substantial amounts of acid catalyst. It is preferred
that the reaction is preformed in the absence of substantial
amounts of catalyst. It is thought that the absence of catalyst
improves the stability of the ultimate coating composition.
[0062] The time for the reaction generally will be about 1 hour or
more. Generally, the time will be 24 hrs or less.
[0063] In one embodiment of the invention, the invention relates to
a method of making surface modified particles by: [0064] (1)
reacting nano-particles in an organic solvent, comprising about 2%
or less, preferably 1% or less, even more preferably 0.5%, by
weight, or less water, with [0065] (2) a surface modifying agent
comprising reactive groups, [0066] (3) thereafter adding water to
the mixture in an amount sufficient to hydrolyse the reactive
groups of the surface modifying agent, [0067] (4) reacting the
mixture for sufficient time to hydrolyse the modifying agent and
preferably at least partly condensate the surface modifying agent,
[0068] (5) preferably in the substantial absence of an acid
catalyst
[0069] In one embodiment the present coating compositions comprise:
[0070] (i) surface-modified nano-particles of a metal oxide, [0071]
(ii) metal oxide based binder, wherein the surface-modified
nano-particles are selected from those that form a layer having a
minimum reflection of from 0.1% to 2%, preferably 0.2% to 1.25%.
The reflectivity of the layer of surface-modified nano-particles is
measured by dip coating a 10 cm.times.10 cm piece of float glass
substrate in a 500 ml sample of surface-modified nano-particles
solution to an appropriate quarter wavelength thickness (90 nm-130
nm dry thickness) such that the wavelength of minimum reflection
lies between 500 nm and 650 nm, and after being cured at
450.degree. C. for 4 hours. The reflection being measured using a
Minolta CM-2600D spectrophotometer under standard conditions.
[0072] The coating composition as applied to substrate comprises a
binder, which has the primary function of keeping the surface
activated particles attached to each other the substrate.
Preferably the binder forms covalent bonds with the particles and
the substrate. For this purpose, the binder--before
curing--preferably comprises inorganic compounds with alkyl or
alkoxy groups. Further, the binder preferably polymerises itself to
form a substantially continuous polymeric network.
[0073] In one embodiment of the invention the binder of the coating
consists substantially of an inorganic binder. It has been found
that such a coating shows very good mechanical properties and good
adhesion to the substrate resulting in for example high puncture
resistance, high scratch resistance and good wear resistance.
[0074] The inorganic binder is preferably derived from one or more
inorganic oxides. Preferably the binder is a hydrolysable compound
such as metal-alkoxides. Preferably the binder is selected from
alkoxy silanes, alkoxy zirconates, alkoxy aluminates, alkoxy
titanates, alkyl silicates, sodium silicates, and mixtures thereof.
Preferred are alkoxy silanes, preferably tri and tetra alkoxy
silanes. Preferably, ethyl silicate, aluminate, zirconate, and/or
titanate binders are used. Tetra alkoxy silane is most
preferred.
[0075] The amount of binder in the coating composition is
preferably 1% or more, more preferably 2% or more, by weight of the
solid fraction. Preferably the amount will be about 40% or less,
more preferably 25% or less, by weight of the solid fraction. The
percentage is calculated as the amount of metal oxide in the binder
relative to the amount of metal oxide in the surface-modified
nano-particles. Thus the percentage metal oxide of particles plus
surface activating compound is used.
[0076] The pre-reaction of the binder composition may be performed
with a compound to catalyze the conversion of the precursor into
the oligomers. In case of alkoxy silane or ethyl silicate binders
as the precursor preferably an acid, for example acetic acid is
used as the catalyst. The amount of catalyst can be relatively low,
as only the binder has to react.
[0077] Preferably a catalyst is used which brings the pH of the
solution at about 2 or higher, more preferred about 3 or higher.
The pH is preferably about 5.5 or lower, more preferred about 4.5
or lower. Suitable catalysts include, but are not limited to,
organic acids like acetic acid, formic acid, nitric acid, citric
acid, tartaric acid, inorganic acids like phosphoric acid,
hydrochloric acid, sulphuric acid, and mixtures thereof, although
acid with buffer capacity are preferred.
[0078] The pre-reaction is preferably performed in a solvent, which
is preferably a mixture of water and an organic solvent. Depending
on the chemistry of the binder, many solvents are useful. Suitable
solvents include, but are not limited to, water, non-protic organic
solvents, alcohols, and combinations thereof. Examples of suitable
solvents include, but are not limited to, isopropanol, ethanol,
acetone, ethylcellosolve, methanol, propanol, butanol,
ethyleneglycol, propyleneglycol, methyl-ethyl-ether,
methyl-butyl-ether, toluene, methyl-ethylketone, and combinations
thereof.
[0079] In one embodiment of the invention, the reaction is
performed in an organic solvent. Preferably, the amount of water
will be about 30%, by weight relative to the solvent or less, more
preferably about 20%, by weight, or less.
[0080] In a preferred embodiment of the invention about equal or
more molar amounts of water is used relative to the molar amounts
of hydrolysable groups. It is more preferred to use about 3 times
or more of water than hydrolysable groups, even more preferred
about 5 times or more. Preferably the relative molar amount of
water is about 30 times or less than the molar amount of
hydrolysable groups, more preferred about 20 times or less.
[0081] The reaction is preferably performed at temperatures of
about 25.degree. C. or higher. Generally, the temperature will be
about 100.degree. C. or lower.
[0082] The reaction generally takes about 4 hr to 7 days. The
extent of the reaction can be determined by testing the steel wool
properties of the coating.
[0083] The surface-modified particles and the binder are preferably
mixed in such a ratio that chosen optical and mechanical properties
are obtained. In addition to the particles and binder other
components may be added, such as further solvent, catalyst,
hydrophobic agent, levelling agent, and the like. The formulation
so obtained is named the coating composition.
[0084] In one embodiment the present coating compositions comprise:
[0085] (i) surface-modified nano-particles of a metal oxide, [0086]
(ii) metal oxide based binder, wherein the weight ratio of metal
oxide in (i) to (ii) is from 99:1 to 1:1.
[0087] Preferably the weight ratio of metal oxide is from 85:1 to
3:2, more preferably from 65:1 to 2:1.
[0088] A further embodiment of the present coating compositions
comprises nano-particles of a metal oxide, metal oxide based
surface-modification agent, and binder wherein the composition
comprises: [0089] (i) up to 99.8%, by weight of the solid fraction,
of the nano-particles of a metal oxide, [0090] (ii) up to 60%, by
weight of the solid fraction, of the metal oxide based
surface-modification agent, and [0091] (iii) up to 50%, by weight
of the solid fraction, of the binder.
[0092] Preferably the composition comprises up to 85%, more
preferably up to 75%, even more preferably up to 65%, by weight of
the solid fraction, of nano-particles of a metal oxide. Preferably
the composition comprises at least 0.1%, more preferably at least
5%, even more preferably at least 10%, by weight of the solid
fraction, of nano-particles of a metal oxide.
[0093] Preferably the composition comprises up to 50%, more
preferably up to 40%, by weight of the solid fraction, of metal
oxide based surface-modification agent. Preferably the composition
comprises at least 0.1%, more preferably at least 5%, even more
preferably at least 10%, by weight of the solid fraction, of metal
oxide based surface-modification agent.
[0094] Preferably the composition comprises up to 45%, more
preferably up to 40%, by weight of the solid fraction, of binder.
Preferably the composition comprises at least 0.1%, more preferably
at least 5%, by weight of the solid fraction, of binder.
[0095] Generally, the coating composition comprises an amount of
non-reactive solvent to adjust the viscosity of the particles and
binder to such a value that thin layers can be applied to the
substrate. Preferably, the viscosity will be about 2.0 mPas or
more, preferably 2.2 mPas or more, even more preferably about 2.4
mPas or more. Preferably, the viscosity is about 20 mPas or less,
preferably about 10 mPas or less, more preferably about 6 mPas or
less, and even more preferably about 3 mPas or less. The viscosity
can be measured with a Ubbelohde PSL ASTM IP no 1 (type 27042).
[0096] Preferably the amount of solids in the coating compositions
herein is about 5% by weight or less, more preferably about 4%, by
weight, or less, even more preferred about 3%, by weight, or less.
Preferably the amount of solids is about 0.5%, by weight, or more,
more preferably about 1%, by weight, or more, more preferably about
1.5%, by weight, or more.
[0097] Any suitable solvent may be used herein. Examples include
water, non-protic organic solvents, and alcohols. In one
embodiment, with an inorganic binder an organic solvent is used,
more preferably a mixture of water and alcohol is used as the
solvent.
[0098] The weight percentage of the particles (the amount as
originally added to the composition) based on 100% of solids of the
coating composition is preferably 20% or more, more preferably 30%
or more, even more preferably 40% or more in the final coating. The
weight percentage of particles, based on 100% solids, will
preferably be about 96% or lower, more preferably 95% or lower,
even more preferably 90% or lower. The concentration of solids is
the concentration of all components that don't evaporate after the
application of the coating composition to the article.
[0099] The present coating is preferably such that, when measured
for one coated side at a wavelength between 425 and 675 nm (the
visible light region), the minimum reflection is about 2% or less,
preferably about 1.5% or less, more preferably about 1% or less.
The average reflection at one side, over the region of 425 to 675
nm preferably will be about 2.5% or less, more preferably about 2%
or less, even more preferably about 1.5% or less, still more
preferably about 1% or less. Generally, the minimum in the
reflection will be at a wavelength between 425 and 650 nm,
preferably at a wavelength of 450 nm or higher, and more preferably
at 500 nm or higher. Preferably, minimum is at a wavelength of 600
nm or lower. The optimal wavelength for the human eye is a minimum
reflection around 550 nm as this is the wavelength (colour) at
which the human eye is most sensitive. In case a colour shade is
required, a minimum at lower or higher wavelength can be chosen.
The reflection can be measured with any suitable reflectometer or
colorimeter as known to the skilled artisan. Generally, the
reflection will show a slope or a curve over the 425-675 nm
wavelength. The minimum is defined as either a minimum in a curve,
or the lower end of the slope, being at 675 or at 425 nm.
[0100] Preferably, the reflection of a glass plate (with a coating
on two sides) at the wavelength exhibiting a minimum is about 3% or
less, preferably about 2% or less, more preferably about 1.5% or
less. The average reflection over a 425-675 nm wavelength range is
preferably about 4% or less, more preferably about 3% or less, even
more preferred about 2.5% or less. Preferably, the reflection will
be about 0.3% or higher, such as for example 0.4, 0.5, 0.6 or 0.7%
or higher.
[0101] Preferably, the light reflection reducing (or anti
reflective) coating is a coating that reduces the reflection of
light from an article at least one wavelength between 425 and 675
nm as measured at the normal incident angle for about 30% or more.
Measurements are carried out on the coated and uncoated article.
Preferably the reduction in reflection is about 50% or more, more
preferably about 70% or more, even more preferably about 85% or
more. The reduction in reflection as expressed in a percentage is
equal to 100.times.(reflection of the uncoated article-the
reflection of the coated article)/(reflection of uncoated
article).
[0102] The mechanical properties can be tested as steel wool
resistance. Preferably, the coating has `acceptable` steel wool
resistance which is defined as less than 10 observable scratches
after 10 rubs with 0000 steel wool with a loading of 250 g. More
preferably, the steel wool resistance is `good` which is defined 3
or less observable scratches after 10 rubs with 0000 steel wool
with a loading of 250 g.
[0103] The combination of properties of good anti-reflective
characteristic and acceptable steel wool resistance can generally
be achieved with an amount of solids of the surface-modified
particulate composition of 60%, by weight of the solid fraction, or
higher, preferably about 70%, by weight of the solid fraction, or
higher. When the particles are relatively large and monodispersed,
or in case of elongated particles, it may be possible to use about
50%, by weight of the solid fraction, or more of the
surface-modified particulate composition. Generally, the weight
percentage of pre-hydrolysed binder will be about 1% or more,
preferably about 3% or more, even more preferred about 5% or more.
When the surface modifying agent is completely reacted with the
particles, the mechanical properties are mainly determined by the
amount of pre-hydrolysed binder mixed with the particles. In this
case, an amount of about 3% or more, 4% or more, 6%, by weight, or
more, relative to the particles is preferred. The amount of the
surface-modified particulate composition will preferably be about
97%, by weight, or less. Preferably, the amount of binder is about
5%, by weight, or more. Preferably the amount of binder about 50%,
by weight of the solid fraction, or less, preferably about 30% or
less, even more preferably about 20% or less.
[0104] In one embodiment of the invention, the nano-particles are
reacted with 5-20%, by weight of the solid fraction, of surface
modifying agent up to substantial completion and are preferably
mixed with 8-20%, more preferably 10-15%, by weight of the solid
fraction, of pre-hydrolysed binder.
[0105] In another embodiment of the invention, the nano-particles
are reacted with 30-60% of binder up to substantial completion and
are mixed with 3-10%, preferably about 4-6, by weight of the solid
fraction, of pre-hydrolysed binder.
[0106] The coating composition can be applied to a substrate.
[0107] Preferably the coating composition is applied to the article
so that the resultant dry coating thickness is about 50 nm or
greater, preferably about 70 nm or greater, more preferably about
90 nm or greater. Preferably the dry coating thickness is about 300
nm or less, more preferably about 200 nm or less, even more
preferably about 160 nm or less, still more preferably about 140 nm
or less.
[0108] Preferably at least part of one of the surfaces of the
substrate is coated with the present coating composition. Generally
about 20% or more, preferably about 50% or more, even more
preferably about 90% or more, of one of the surfaces of the
substrate is coated.
[0109] A number of methods are available to apply thin coatings on
substrates. Any method of applying a wet coating composition
suitable for obtaining the required thickness would be acceptable.
Preferred methods include meniscus (kiss) coating, spray coating,
roll coating, spin coating, and dip coating. Dip coating is
preferred, as it provides a coating on all sides of the substrate
that is immersed, and gives a repeatable and constant thickness.
Spin coating can easily be used if smaller glass plates are used,
such as ones with 20 cm or less in width or length. Meniscus, roll,
and spray coating is useful for continuous processes.
[0110] The coating preferably has a thickness of 1-10 .mu.m before
drying. The required wet thickness is dependant on the solid
content of the coating. The thickness is generally measured after
drying and curing, but may be measured after drying only, i.e.
after evaporation of the non-reactive solvent(s). The thickness of
the wet coating is influenced by the viscosity of the coating, and
the dip speed in case of dip coating; each technique has its own
ways to influence the thickness of a coating. The thickness of the
coating when substantially dry (i.e. with about 20 wt % or less of
non-reactive solvent relative to the solid material) is generally
about 300 nm or less, preferably about 200 nm or less, most
preferred about 170 nm or less. Generally, the dry, uncured coating
will have a thickness of about 30 nm or more, preferable about 50
nm or more, most preferably about 60 nm or more. Thickness is
measured either spectroscopically (reflectometery or ellipsometery)
or by directly observing a fracture surface by electron
microscopy.
[0111] In one embodiment the inorganic binder precursor is
cross-linked and converted into the binder. This last step is
generally carried out by heating to for example at about
150.degree. C. or more, preferably about 200.degree. C. or more.
Preferably, the temperature will be about 700.degree. C. or less,
more preferably about 500.degree. C. or less. Curing generally
takes place in 30 seconds or more. Generally, curing is performed
in 10 hours or less, preferably 4 hour or less.
[0112] In another embodiment, the binder is cured using a catalyst
with temperatures of about 20.degree. C. or more, and generally
will be 200.degree. C. or less, preferably 140.degree. C. or
less.
[0113] In one embodiment of the process, the coating application is
applied to a glass plate before a tempering step of that glass
plate. The tempering step is normally carried to introduce internal
stresses in an ordinary glass plate by virtue of which it will
fragment in small pieces when the glass breaks. The tempering step
is usually carried out at temperature of up to 600.degree. C. One
advantage of the coating according to the invention is that the
coating can withstand this tempering process and can even be cured
before or during the tempering process. In the later case the
curing and tempering process are thus carried out in one step.
[0114] Generally, in case of flat substrates such as glass plates,
at least one side of the substrate needs to be coated e.g. in case
a product is glued to the other (non-coated) side of the substrate.
However, in one embodiment of the invention, the substrate is a
glass plate that has an anti-reflective coating on both sides. This
may be achieved by coating both sides of a glass plate. It is also
possible to laminate two glass plates which are coated on one side,
whereby the non-coated sides are laminated to each other. It is
preferred that a glass plate in use has on both outermost sides an
anti-reflective coating, more preferred, an anti-reflective coating
according this invention. It is, however, also possible to combine
different techniques to obtain anti-reflective or anti-glare
properties. In one embodiment one side of a glass plate is coated
with an anti-reflective coating made with a process according the
present invention, and the other side of the glass is laminated
with a transparent film with an anti-glare or anti reflective
coating, preferably a coating made according the present invention;
the coatings according the present invention may be the same or
different in chemical composition. In a further embodiment of the
invention the film used to stick two glass plates together may be a
UV absorbing film in order to lend UV shielding properties to the
picture or image.
[0115] Other useful coatings that can be applied on the substrate
are antistatic and/or low-e coatings; the low-e coatings being
coatings that have a low emission of infra-red, thereby having
low-heat emission through the glass plate.
[0116] For all coating processes, cleaning is an important step, as
small amounts of contaminant such as dust, grease and other organic
compounds cause the anti reflective coating, or other coatings to
show defects. Cleaning can be done in a number of ways, such as
firing (heating up to 600-700.degree. C.; applicable if an
inorganic substrate is used); and/or cleaning with a cleaning fluid
such as soap in demineralised water, alcohol, or acidic or basic
detergent systems. When using a cleaning fluid, generally, the
glass plate is dried at a temperature between 20.degree. C. and
400.degree. C., optionally with applying an air flow.
[0117] In one embodiment, the process for making an anti-reflective
substrate comprises the step of cleaning the substrate.
[0118] In another embodiment the process comprises the further step
of subjecting the coated substrate to a quality control step after
coating, but before any curing. After coating, but before curing,
the anti-reflective properties are well discernable although
slightly different from the cured coated substrate. For example,
upon cure, the coating may shrink, causing a shift in wavelength at
minimum reflection. If substrates like glass plates would be not
within specifications, these plates can be taken out before curing,
thereby saving the costs of curing. Furthermore, these plates can
be cleaned, and used again in the process of the invention.
[0119] In one embodiment of the present invention anti-reflective
glass obtained according to the process of the present invention
can be framed to give picture frames or other framed articles
according to the invention. The framed glass plates with the
anti-reflective coating are preferably for domestic use.
[0120] The present coatings are able to withstand normal household
cleaning processes with water, water alcohol mixtures, water
detergent mixtures, water alcohol detergent mixtures and other
common house-hold cleaning fluids. Examples of commonly used
cleaning fluids are Glassex.RTM. and Windex.RTM. (isopropanol,
water, detergent, pH.apprxeq.10-11), or fluids comprising acetone,
methyl-ethyl-ketone, alcohol and water. Generally, the first time
an anti-reflective glass plate is cleaned the reflection may change
with 0.1-0.4% but thereafter the reflection remains virtually
constant. It was unexpected that the nano porous coating does not
tear or wear from even regular use of house hold chemicals.
Preferably, the coating exhibits a change in reflectivity of about
0.4% or less after 2 hrs immersion in Glassex.RTM., more preferably
the change is about 0.3% or less. Preferably, the coating exhibits
a steel wool resistance, measured as shown in the examples, of A.
Preferably, the coating exhibits--after 2 hours immersion in
Glassex.RTM.--a steel wool rating of B or better.
[0121] In order to protect the picture from damage by UV light it
is preferred to provide a UV screening or blocking coating on the
glass plate. The UV blocking coating may be provided on the glass
before applying the anti-reflective coating. This is preferred,
because otherwise the micro porous structure and roughness
character may decrease and thereby the antireflective properties
would be negatively influenced. However, if the UV screening
coating does not substantially influence the anti-reflective layer
it may be applied on the antireflective layer. UV blocking coatings
are known to those skilled in the art, and are e.g. described in
U.S. Pat. No. 5,371,138.
[0122] In a preferred embodiment of the invention the substrate is
glass for use in a picture frame. The picture frames preferably
comprise an anti reflective glass plate of the invention, a frame
covering the 4 outer sites of the plates and a backing of card
board, wood, plastic or other suitable material. Sometimes, the
backing is also made of glass. Generally, the backing comprises
elements to fasten the glass plate, frame and backing to each
other. Such fastening means may also be separate items. Preferably,
the backing comprises one or more rings, or the like, or a cord for
hanging the picture frame onto a wall.
[0123] A frame as used in the present application is a structure to
hold the glass plate at a fixed place. In one embodiment, it
consists of clamps at least 3 places of a glass plate (e.g. two top
corners and in the middle of the bottom of a square glass plate.
Preferably, the clamps are at all corners of the glass plate. In
another embodiment, the frame consists of at least a partial
enclosure for the glass plate. Generally, at least two sites of the
glass plates are enclosed, more preferably two opposite sites.
Often all sites are enclosed by a frame. The frame can be of metal,
wood, plastic or the like. Any known frame material can be
used.
[0124] In one embodiment, the frame is a picture frame, the word
picture being broadly interpreted as comprising photo's, paintings,
posters, etches, drawings and the like.
[0125] In another embodiment, the frame is a show-case, comprising
on at least one side a glass plate according the invention.
[0126] A glass plate is contemplated by the inventors to have a
wide meaning, including quartz, polycarbonate or other plate like
materials that have a high transparency, preferably a transparency
of about 80% or more at 2 mm thickness, more preferably about 90%
or more at 2 mm thickness.
[0127] A show case according this invention preferably comprises
all glass plates to be anti-reflective according this invention.
Often, show cases have one, two or three sides which should be
transparent and anti reflective.
[0128] The present invention furthermore relates to maintaining
acceptable quality of the dipping solution according to the
following process for adjusting properties of an anti-reflective
coating having nano-particles and a reactive binder comprising the
steps of:
(a) regularly monitoring the optical and mechanical properties of
cured coated articles, (b) if the optical and mechanical properties
have changed beyond those acceptable in terms of quality control
adding pre-hydrolysed binder in such an amount to the coating
composition that the chosen balance of optical and mechanical
properties is regained.
[0129] During quality control, or in separate measurements, one can
determine whether the products obtained after curing the coating
have the chosen and/or required properties. Hence, one can
determine whether the properties have changed to such an extent
that products are outside the specifications. Where this appears to
be the case, generally, the anti-reflective properties are still
acceptable (or even relatively good), but the mechanical properties
have become unsatisfactory, it is possible to add some
pre-hydrolysed binder to the coating solution in order to achieve
again satisfactory properties. The amount of binder to add will
generally be about 1%, by weight of the solid fraction, or more,
preferably about 2% or more. Generally, about 30%, by weight of the
solid fraction, or less will be used, preferably about 20% or less.
In case too much binder is added, the mechanical properties will be
excellent, but the anti-reflective properties will be insufficient.
In this, case it is possible to add some surface modified particles
(for example about 5%, by weight of the solid fraction, or more,
but generally less than about 20%, by weight of the solid fraction)
to achieve a good balance of properties.
[0130] The invention will be further elucidated by the following
examples, without being limited thereto.
EXAMPLES
[0131] In the following examples and comparative experiments,
silica particles were used as described in Table 1
TABLE-US-00001 TABLE 1 Particle SiO.sub.2 H.sub.2O Viscosity
Specific Particle Particle Size (nm) (wt %) (%) (mPa s.) Gravity pH
Shape Solvent IPA- 9-15 15-16 <1 <20 0.85-0.90 2-4 Worm-like*
Iso- ST-UP* propanol IPA- 40-50 30-31 <1 <15 0.96-1.02 2-4
spherical Iso- ST-L propanol IPA- 70-100 30-31 <1 <15
0.96-1.02 2-4 spherical Iso- ST-ZL propanol *worm-like particles
have a high aspect ratio: a diameter of 9-15 nm and a length of
40-300 nm
Example 1
[0132] A composition was prepared by reacting the components as
given in Table 2
TABLE-US-00002 TABLE 2 Component Amount Wt % Isopropanol (IPA)
123.7 59.3 IPA-ST-UP (15.6% SiO.sub.2) 30.93 14.8 (2.31% SiO.sub.2)
TEOS.sup.1 (28.8% SiO.sub.2) 23.2 11.1 (3.19% SiO.sub.2) Water
30.93 14.8 Isopropanol additional 570 To 1.5 wt % SiO.sub.2
.sup.1Tetraethylorthosilicate
[0133] The isopropanol was mixed with IPA-ST-UP particles and
surface-modification agent (TEOS) was added with stirring. After 5
mins the water was added. The composition was stirred and heated to
80.degree. C. for 4 hours. A sample of this composition (A) was
removed. 20 g of binder (prehydrolysed TEOS) was added to the
remaining composition (B).
[0134] Thin films of the compositions A and B were prepared on a
glass slide (20.times.20 cm) by the following procedure. A glass
plate was washed and dried thoroughly to prepare it for the dip
coating process. The glass slide was then lowered into the coating
formulation. It was drawn out of the formulation with a certain
speed thus depositing a thin liquid layer of the coating
formulation on the glass plate. After evaporation of the solvent
the dried inorganic coating was cured in an oven for 4 hours at
450.degree. C. to ensure complete curing.
[0135] Sample A gave a reflection of 0.5% and had a steel wool
resistance of B. Sample B gave a reflection of 1.3% and had a steel
wool resistance of A.
[0136] The compositions were allowed to age for 28 days and then
retested. Sample A had a reflection of 0.2% and a steel wool
resistance of E. Sample B had a reflection of 1.0% and a steel wool
resistance of A.
[0137] In a further experiment, 3 wt % (relative to the solid
content if the coating composition) of pre-hydrolysed TEOS binder
was added to aged Sample A. Upon retesting the steel wool
resistance was A and the reflection 1.2%.
Example 2
[0138] The compositions of Table 3 were prepared by mixing IPA and
IPA-ST-L and adding surface-modifying agent (TEOS). Thereafter
water was added. The compositions were stirred, and heated on a
water bath if needed. Thereafter 20%, by weight of the solid
fraction, of binder (prehydrolysed TEOS) was then added to the
compositions.
TABLE-US-00003 TABLE 3 C D E IPA-ST-L (g SiO.sub.2) 25.7 (7.79)
22.9 (6.94) 20.7 (6.27) TEOS (g SiO.sub.2) 0.278 (0.080) 2.68
(0.77) 5.47 (1.58) Isopropanol 105.3 99.7 97.8 Water 0.36 3.57 7.26
Reaction time 24 hr 25.degree. C. 2 hr 80.degree. C. 6 hr
80.degree. C. IPA dilution 132 123 130
[0139] At various time intervals coating composition D was
dip-coated in accordance with the procedure in Example 1. The
composition produce stable results for over a month (Table 7).
TABLE-US-00004 TABLE 7 Time (days) 2 6 12 19 23 28 Refection (%)
1.3 1.3 1.1 1.0 0.9 1.0
[0140] After 2 months the composition was still giving the 0.8-1.0%
reflection and steel wool resistance of A. After 3 months the steel
wool resistance was A/B while a reflection was 0.6%.
[0141] Accelerated aging is performed by heating the coating
composition E to 50.degree. C. When the composition starts to show
worse steel wool resistance, an addition of binder (oligomerized
TEOS) is sufficient to produce good properties.
Example 3
[0142] The composition of Table 4 was prepared by mixing IPA and
IPA-ST-ZL and adding surface-modifying agent (TEOS). Thereafter
water was added. The composition was stirred for 4 hours at
80.degree. C. A sample was coated in accordance with Example 1 and
its reflectivity measured at 0.5%. Pre-hydrolysed alkoxy silane
binder was made by adding an alkoxy silane, water and acetic acid
to solvent. After 72 hours at room temperature the mixture was the
binder was then added to the surface-modified particles.
TABLE-US-00005 TABLE 4 F Isopropanol (solvent) 1000.2 IPA-ST-ZL (g
SiO.sub.2) 228.5 (69.2) TEOS (g SiO.sub.2) 26.8 (7.72) Water 35.7
Binder (g SiO.sub.2) 77.5 (2.66)
Optical Properties of Coated Substrate
[0143] Reflectivity spectra were recorded using a Minolta
spectrophotometer CM-2600D. All UV-VIS transmission measurements
were performed using a Perkin Elmer Lambda 40 UV/NIS spectrometer.
The spectrometer is equipped with two irradiation sources, a
halogen lamp and a deuterium lamp. Spectra were recorded between
370 and 800 nm with a step width of 1 nm. Scan speed was 120 nm/min
and the slit width was 2 nm.
Steel Wool Abrasion Test:
[0144] A flat circular steel surface (diameter=2.1 cm) was covered
evenly with steel wool (grade: 0000) with a normal weight of 250 g.
The steel wool was then moved back and forth over the surface 5
times making for a total of 10 rubs over a distance of ca 5 to 10
cm. At this point the surface of the coating is visually inspected
and rated according to table 11 below.
TABLE-US-00006 TABLE 11 Number of visible scratches Rating 0-3 A
(A.sup.+ = 0 scratches; A.sup.- = 3 scratches) 4-10 B 11-15 C 16-30
D Coating completely removed E
* * * * *