U.S. patent application number 12/160848 was filed with the patent office on 2010-07-01 for process for coating a glass plate.
Invention is credited to Nanning Joerg Arfsten, Jens C. Thies.
Application Number | 20100167046 12/160848 |
Document ID | / |
Family ID | 36579831 |
Filed Date | 2010-07-01 |
United States Patent
Application |
20100167046 |
Kind Code |
A1 |
Thies; Jens C. ; et
al. |
July 1, 2010 |
PROCESS FOR COATING A GLASS PLATE
Abstract
Process for the preparation of glass plates by applying a porous
coating to the glass through a coating slit over the required width
of the glass, such that a coating thickness of 50-400 nm is
achieved after drying and curing, and the slit is at a distance of
between 5-10,000 times the dry coating thickness.
Inventors: |
Thies; Jens C.; (Haastricht,
NL) ; Arfsten; Nanning Joerg; (Achen, DE) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Family ID: |
36579831 |
Appl. No.: |
12/160848 |
Filed: |
February 12, 2007 |
PCT Filed: |
February 12, 2007 |
PCT NO: |
PCT/EP07/01180 |
371 Date: |
July 28, 2009 |
Current U.S.
Class: |
428/336 ;
427/162; 427/299; 427/372.2 |
Current CPC
Class: |
C03C 17/007 20130101;
Y10T 428/24942 20150115; Y10T 428/31504 20150401; C03C 2217/475
20130101; G02B 2207/101 20130101; Y10T 428/31507 20150401; G02B
1/118 20130101; A47G 1/06 20130101; B82Y 20/00 20130101; G02B 1/10
20130101; Y10T 428/31935 20150401; C03C 2217/732 20130101; Y10T
428/265 20150115; Y10T 428/31786 20150401; Y10T 428/24998 20150401;
Y10T 428/249978 20150401; Y10T 428/25 20150115; C03C 2217/45
20130101; C03C 2217/425 20130101; G02B 1/11 20130101; G02B 1/111
20130101; Y10T 428/24355 20150115 |
Class at
Publication: |
428/336 ;
427/372.2; 427/299; 427/162 |
International
Class: |
C03C 17/00 20060101
C03C017/00; B05D 3/02 20060101 B05D003/02; B05D 3/00 20060101
B05D003/00; B05D 5/06 20060101 B05D005/06; B32B 17/00 20060101
B32B017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 14, 2006 |
EP |
06075305.0 |
Nov 10, 2006 |
EP |
06023433.3 |
Claims
1. Process for the preparation of coated glass by applying a porous
coating to the glass through a coating slit wherein a coating
thickness of 50-400 nm is achieved after drying and curing, and the
slit is at a distance of between 5-10,000 times the dry coating
thickness from the glass.
2. Process according to claim 1, wherein the process is used
in-line on a float-glass line.
3. Process according to claim 2, wherein the coating is applied
directly after fabrication at the side which was not in contact
with the fluid metal.
4. Process according to claim 1, wherein the glass is at an angle
relative to horizontal of about 10.degree. or greater.
5. Process for the preparation of coated glass the process
comprising: (i) cleaning the glass (ii) providing on at least a
part of at least one side of the glass a coating through a coating
slit, such that the slit is at a distance of between 5-10,000 times
the calculated coating thickness according to the equation wet
coating thickness multiplied by concentration of solids in the
coating solution, and (iii) drying and curing the coating.
6. Process for the preparation of coated glass by applying a porous
coating to the glass through a coating slit wherein the width of
the slit is from about 0.1 mm to about 2 mm.
7. The process according to claim 1 wherein the coating solution
comprises nano-particles of a metal oxide.
8. The process according to claim 1 wherein the coating solution
comprises nano-particles of a metal oxide.
9. The coated glass obtained by the process according to claim 1.
Description
[0001] The invention relates to a process for making a coated glass
plate, the glass plate having on at least a part of at least one of
its surfaces a porous coating.
[0002] Coated glass plates are known. For example, anti-reflective
coated plates are used in picture frames for framing photos,
aquarelle or watercolour paintings, drawings, etches, posters and
the like. Untreated glass plates show a strong light reflection
generally of about 8% when looking at the glass at normal angle
(90.degree.). The reflection increases sharply at sharper angles.
This reduces the clarity of the picture and is therefore
unwanted.
[0003] The coatings are commonly applied in a dip-coating process:
the glass plate is dipped in a container with a coating fluid, and
withdrawn at a certain speed. Although this method is satisfactory
in some cases it requires relatively stable coating fluids as the
fluid in the container is used in only a very small percentage. In
addition, the process is inefficient as the glass plates must be
manipulated into the container and can only be coated a few at a
time. Furthermore, the coating is applied to both sides of the
glass which may be unnecessary.
[0004] The aim of the present invention is to provide a process for
the preparation of a coated glass plate.
[0005] The present invention provides a process for the preparation
of coated plates by applying a coating to the glass through a
coating slit over the required width of the glass, such that a
coating thickness of 50-400 nm is achieved after drying and curing,
and the slit is at a distance of between 5-10,000 times the dry
coating thickness.
[0006] In a preferred embodiment, the process present process
relates to coating a glass plate with a porous coating, and in
particular an anti-reflective coating.
[0007] A further preferred embodiment relates to a coating process
used in-line on a float-glass line.
[0008] One of the problems encountered is that float glass can
become contaminated during the fabrication process especially on
the side that is contacted by the float bath. In one embodiment of
the invention, the anti-reflective coating is applied directly
after fabrication to the side which was not in contact with the
float bath.
[0009] In another embodiment of the invention, the invention
provides for a process of making a coated glass plate, the process
comprises the steps of [0010] (1) cleaning the glass, preferably
only the side to be coated [0011] (2) providing on at least a part
of at least one side of the glass plate a coating through a coating
slit over the required width of the plate, such that a coating
thickness of 50-400 nm is achieved after drying and curing, and the
slit is at a distance of between 5-10,000 times the dry coating
thickness; the coating comprising nano size particles, a binder and
a solvent [0012] (3) drying the coating
[0013] Preferably, the coating layer has an arithmetic average
roughness of 2-50 nm, and having per reflective coated side a
minimum reflection at a wavelength between 425 and 675 nm of about
2% or less.
[0014] In an alternative embodiment, the present invention provides
a process for the preparation of anti-reflective glass plates by
applying a coating to the glass through a gravure coating process
over the required width of the glass, such that a coating thickness
of 50-400 nm is achieved after drying, and the gravure roll applies
1-8 .mu.m wet coating thickness, while the coating chamber is
designed to preclude substantial solvent evaporation.
[0015] It was unexpected that, with such gravure coating technique,
thin coatings with very even thickness could be applied at
relatively high speed. This technique is preferred for applications
that require higher production rates but can accept a less even
coating. An example of such an application is glass for
mass-produced solar cells. It should be noted, however, that
coating through a slit might also be used for solar cell production
as it produces a very even coating thickness even if it is not as
fast as the gravure technique.
[0016] In a preferred embodiment of the invention, the process for
coating a glass plate with an anti-reflective layer in which the
coating is applied through a gravure coating role is used in-line
at a glass plant, preferably for glass for solar cells.
[0017] The embodiments as described herein for the coating through
a slit can also be applicable to coating with a gravure role.
[0018] In one embodiment the thickness of the coating after curing
is estimated by multiplying the wet thickness by the concentration
of solids in the coating solution.
[0019] The transparency of the anti-reflective glass plate is
preferably high. For common float glass, which has an absorbance of
1 to 1.5% at 2 mm thickness, the transparency is generally about
94% or higher at 2 mm thickness at wavelength between 425 and 675
nm, preferably about 96% or higher, more preferably about 97% or
higher, even more preferably about 98% or higher.
[0020] The coated glass plates obtained with the process of the
present invention are preferably used in framing such as frames for
photo's, paintings, posters, etches, drawings, presentation cases,
and the like.
[0021] In another embodiment of the invention, the glass plate is
used in an architectural setting such as for a window, partition,
or other glass structure. In one embodiment, the glass is curved
and can be multi-layered to improve strength.
[0022] In another embodiment, the glass is used for solar cells.
The anti-reflective properties allow for a substantial higher
efficiency, not only at around normal angle, but also at acute
angles. The latter is an advantage in comparison to multi-layer
anti-reflective coatings.
[0023] 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.
[0024] Generally, the glass plate has a thickness of 0.5 mm or
more, preferable 1 mm or more, most preferably, about 1.8 mm or
more. In general, the glass plate has a thickness of about 10 mm or
less, preferably 6 mm or less, more preferable about 4 mm or less,
and most preferred, about 3 mm or less. However, the thickness of
the glass is not critical, and could be 10 cm or less.
[0025] In another embodiment, the substrate is inorganic. More in
particular ordinary glass or quartz. Ordinary float glass is most
preferred, as it is a cheap and widely available material
[0026] An anti-reflective glass plate is meant to be a glass plate
(as defined) with a light reflection reducing coating on at least
part of at least one side of the glass.
[0027] The anti reflective glass plate will generally have a size
of 10 cm by 10 cm or larger, preferably about 20 cm by 20 cm or
larger. The maximum size is mainly dictated by practical
considerations, and will generally be 2 by 3 meter or less. In one
embodiment, the anti reflective glass plate preferably has a size
of about 20 by 30 cm or multiples thereof, such as preferably 30 by
40 and most preferably 90 by 130 cm or the multiple 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).
[0028] In one embodiment of the invention the coated glass is
coated and then tempered. This embodiment offers the advantage that
the tempering step also cures the coating hence saving energy.
[0029] Preferably at least part of the surface is coated with an
anti-reflective coating. Generally about 20% or more of the width
of a surface will be coated, preferably about 50% or more, even
more preferably, about 90% or more of the width of the surface is
coated with the anti-reflective coating.
[0030] Preferably the anti-reflective coating is such,
that--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, and most preferably
about 1% or less. The average reflection at one side, over the
region of 425 to 675 nm generally will be about 2.5% or less,
preferably about 2% or less, more preferred, about 1.5% or less,
and , even more preferably about 1% or less. Generally, the minimum
in the reflection will be at a wavelength between 425 and 675 nm,
preferably at a wavelength of 450 nm or higher, and more preferred
at 500 nm or higher. Preferably, minimum is at a wavelength of 650
nm or lower, more preferred at 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.
[0031] Generally, at least one side of the glass plate needs to be
coated e.g. in case a picture or a solar-cell substrate is glued to
the other side of the glass. However, in one embodiment of the
invention, the glass plate 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 the glass plate in use has on both
outermost sides an anti-reflective coating. It is, however, also
possible to combine different techniques to obtain various
functionalities. Other useful functionalities include anti-fogging,
anti-fouling, anti-stick, easy-clean, lubricious, antistatic,
low-emission coatings (such as low-heat emission), and the
like.
[0032] Preferably, the reflection of the glass plate (with a
coating on two sides) at the wavelength exhibiting a minimum is
about 3% or less, preferably about 2% or less, and more preferred
about 1% or less. The average reflection over a 425-675 nm
wavelength range is generally about 4% or less, preferably about 3%
or less, and even more preferably about 2% or less.
[0033] A 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. Measurements are carried out on the coated
and uncoated article. Preferably the reduction in reflection is
about 30% or more, preferably 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).
[0034] 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 still about 20 nm or larger. The
arithmetic average roughness generally will be about 50 nm or
lower, preferably 45 nm or lower.
[0035] The coating of the present invention can exhibits voids in
the coating thereby having a nano-porous structure. The voids aid
in obtaining anti-reflective properties. Generally, the coating
comprises about 20 volume% or more of void volume. Void volume is
herewith defined as open space between the particle/binder in
principle filled with ambient air. Preferably the voids represent
about 30 volume% or more, even more preferably the voids represent
about 40 volume% or more; still more preferably, the voids
represent about 50 vol. % or more. Generally, the coating exhibits
voids in the coating of about 90% or less, in another embodiment
about 80 volume% or less; and in a further embodiment about 70 vol.
% or less.
[0036] The process for making the present coated glass plate
preferably comprises the steps of [0037] (1) producing the glass on
a float-glass line; [0038] (2) optionally cleaning the glass,
[0039] (3) providing on at least a part of at least one side of the
glass plate a coating, the coating being applied through a coating
slit over the required width of the plate such that a coating
thickness of 50-400 nm is achieved after drying and curing, and the
slit is at a distance of between 5-10,000 times the dry coating
thickness; the coating comprising nano sized particles, a binder
and a solvent, [0040] (4) drying and, if necessary, curing the
coating.
[0041] Preferably the coating layer has an arithmetic average
roughness of 2-50 nm, and having per reflective coated side a
minimum reflection at a wavelength between 425 and 675 nm of about
2% of less.
[0042] For many 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.
[0043] However, cleaning may be dispensed with where the glass is
clean enough already or where the intended application of the
coated glass does not require a high quality coating.
[0044] The coating is provided on at least a part of at least one
side of the glass plate. In the process of the present invention,
the coating is applied via a slit over the required width of the
plate such that a coating thickness of 50-400 nm is achieved after
drying and curing, and the slit is at a distance of between
5-10,000 times the dry coating thickness. With this coating
technique it is possible to use in a continuous or semi-continuous
process. Furthermore, it is an advantage that it is unnecessary to
use large amounts of coating composition. In addition, the coating
composition can be used continuously with less quality control
issues or prolonged storage times. Therefore it is possible to use
less stable coating solutions. This is a clear advantage, as normal
silica-based coatings tend to have a shelve life of 1-4 weeks.
After such time it is necessary to replace the solution which can
be difficult and can cause substantial waste problems.
[0045] The coating generally has a thickness of 1-5 .mu.m before
drying. The required wet thickness is dependant on the solid
content of the coating, and is not important as such. The coating
thickness generally is 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, the width of the slit,
the distance of the slit to the glass plate, the pressure put on
the coating while flowing through the slit, and the speed of
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 preferably 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
50 nm or more, preferable about 60 nm or more, most preferably
about 70 nm or more. Thickness is measured either spectroscopically
(reflectometery or ellipsometery) or by directly observing a
fracture surface by electron microscopy.
[0046] The slit of the coating apparatus has the length of the part
that is required to be coated. Generally, the whole length of a
plate will be coated. In one embodiment, only the outer mm. is not
coated. Generally, the slit will be straight, but it can or needs
to be curved if necessary, in order to keep that the distance to
the plate substantially the same across the coated length.
[0047] Generally, the coating will be forming a bead on top of the
slit, either by capillary forces, or by slight pressure, e.g.
because the surface of the coating material in the storage tank is
slightly above the height of the slit. The bead is than brought
into contact to the plate, and the coating adheres to the glass, as
the adhesive forces are larger than the cohesive forces within the
bead. The plate can than be drawn along the slit, or the slit can
be drawn along the plate, or both movements can be made, as to coat
the required length of the plate.
[0048] In order to increase the capillary force, for e.g. higher
flow speed, it is preferred to coat the slit with a high surface
tension material, such as for example PTFE, or other fluorinated
materials. A high surface tension causes a larger bead, and thereby
an easier coating process.
[0049] In a preferred embodiment, the substrate is at an angle
which helps a liquid coating `flow` causing a more equal coating.
The angle preferably is about 2 degrees or higher, more preferably
about 5 degrees or higher, and even more preferably 10 degrees or
higher. The angle may be as high as about 90 degrees (i.e.
vertical). In one embodiment, the plate is preferably approximately
vertical as an optimal leveling of the coating on the glass plate
may take place.
[0050] The width of the slit is preferably about 0.1 mm or larger,
more preferably about 0.25 mm or larger, even more preferably,
about 0.5 mm or larger. Preferably, the width of the slit will be
about 5 mm or smaller, even more preferably 2 mm or smaller.
[0051] Preferably, the distance between the slit and the surface to
be coated will be about 5 times the dry coating thickness or more,
preferably about 10 times, and more preferably about 20 times the
dry coating thickness. Preferably, the distance is about 10,000
times or less, preferably about 1000 times or less.
[0052] In a preferred embodiment of the invention measures are
taken to increase the evaporation of the solvent and/or to withdraw
the evaporated solvent off after coating of the glass. For example,
a hood and/or air flow can be used to aid removal of the
solvent.
[0053] In one embodiment, the coated and dried plate is subjected
to a curing step.
[0054] In another embodiment, the process comprises a further step,
the coated glass plate being subjected to a quality control step
after coating and drying, but before curing the coating. After
coating, but before curing, the antireflective properties are
discernable although slightly different from the cured coated
plate. For example, upon cure, the coating may shrink, causing a
shift in wavelength at minimum reflection. If 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.
[0055] The coating used in this invention comprises nano sized
particles, a binder and a solvent.
[0056] Examples of suitable particles are particles comprising
lithium fluoride, calcium fluoride, barium fluoride, magnesium
fluoride, titanium dioxide, zirconium oxide, antimony doped tin
oxide, tin oxide, aluminum oxide, and silicon dioxide. Preferably
particles comprising silicon dioxide, most preferably particles
consisting for at least for 90 wt. % of silicon dioxide are
used.
[0057] In one embodiment of the invention, the coating comprises
particles having an average aspect ratio larger than 1.5, as the
glass plate shows an advantageous low reflection of light.
[0058] Preferably the aspect ratio of the particles is larger than
2, more preferably larger than 4, even more preferably larger than
6, even still more preferably larger than 8, most preferably larger
than 10. Generally, the aspect ration will be about 100 or lower,
preferably about 50 or lower.
[0059] 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 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 the length and the width are measured of the
projection of the particles as observed under the microscope.
[0060] In one embodiment, rod-like and/or worm-like particles,
preferably worm-like particles, are used. Worm-like particles are
particles having a central axis that deviates from a straight line.
Examples of worm-like particles are known by the trade name Snowtex
(IPA-ST-UP, particles have a diameter of 9-15 nm with a length of
40-300 nm), as delivered by Nissan Chemical.
[0061] 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.
[0062] In a preferred embodiment, the coating comprises particles
are largely spherical (i.e. having an aspect ratio of about 1.2 or
lower, preferably of about 1.1 or lower), and generally have a size
of about 10 nm or larger, preferably 20 nm or larger, and most
preferred 40 nm or higher. Generally, the particles will have a
size of 200 nm or smaller, preferably 150 nm or smaller, and most
preferred about 100 nm or smaller. With respect to other
characteristics, the description of the non-spherical particles
described above is equally applicable to the spherical particles.
The advantage of using largely spherical particles is that the
volume nano-pores resulting from the space between spherical
particles is small relative to the space between non-spherical
particles and thus the coatings derived from spherical particles
suffer less from filling of the nano-pores via capillary forces
leading to a loss in anti-reflective performance.
[0063] In another embodiment, the coating comprises mixtures of
above described particles.
[0064] The coating preferably comprises a binder, which has as main
function to keep the particles attached and adhered to the glass
plate. Preferably, the binder forms covalent bonds with the
particles and the substrate. For this purpose, the binder--before
curing--preferably contains inorganic compounds with alkyl or
alkoxy groups, but other compounds may be suitable as well.
Further, the binder preferably polymerises itself to form a
continuous polymeric network.
[0065] In one embodiment of the invention the binder of the coating
consists substantially of an inorganic binder, as such coating
shows good mechanical properties and good adhesion to the
substrate, resulting in, for example, high puncture resistance,
high scratch resistance and good wear resistance.
[0066] The inorganic binder preferably comprises one or more
inorganic oxides, for example silicon dioxide. The binder
preferably is a crosslinked inorganic material that covalently
links the particles and the substrate.
[0067] The inorganic binder may result after the cross-linking
reaction and heating of the non-reacted binder, for example an
alkoxy silane, an alkyl silicate or a sodium silicate. As alkoxy
silanes preferably tri and tetra alkoxy silanes are used.
Preferably, ethyl silicate binders are used. Due to the heating
step these silicium compounds are converted into silicon
dioxide.
[0068] In another embodiment, the binder is an organic coating,
wherein the particles bear reactive organic groups, and optionally,
further coating material is present which has groups, reactive with
the reactive groups on the particles. This embodiment is preferred
in case the glass plate is of organic nature, and cannot withstand
baking temperatures of up to 400.degree. C. In one embodiment, the
reactive groups on the particles are (meth)acrylate, and the
reactive groups on the further coating material is of ethylenic
unsaturated, preferably (meth)acrylate. Examples of suitable
coatings are described in WO2004/104113.
[0069] Preferably, the coating 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 on the glass plates.
Preferably the viscosity of the coating is about the value of the
neat non-reactive solvent, and is the amount of solids in the
coating about 5 wt % or less, preferably, about 4% or less, more
preferred about 3% or less. To have an economic process, the amount
of solids generally will be about 0.5 wt % or more, preferably
about 1 wt % or more, more preferably about 2 wt % or more.
Preferably, the viscosity will be about 2.0 mPas or more,
preferably 2.2 mPas or more and even more preferably about 2.4 mPas
or more. Generally, the viscosity is about 20 mPas or less,
preferable about 10 mPas or less, more preferably about 6 mPas or
less, and even more preferred about 3 mPas or less. The viscosity
can be measured with a Ubbelohde PSL ASTM IP no 1 (type 27042)
[0070] Depending on the chemistry of the binder, many solvent are
useful. Suitable examples of solvents include water, non-protic
organic solvents, and alcohols.
[0071] 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. The concentration of solids in the coating
composition may be between 1 and 20 weight (wt) %, preferably
between 1 and 5 wt. %. The wt % of the particles, based on 100% of
solids is for example more than 50 wt. %, preferably more than 60
wt. % and most preferably more than 70 wt. % in the final coating.
The concentration of solids is the concentration of all components
that don't evaporate after the application of the coating
composition to the article.
[0072] The coating composition may comprise a compound to catalyze
the conversion of the precursor into the binder. 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 catalyst
preferably is added to the coating composition just prior to its
application. In case of UV curable materials, a light sensitive
initiator is generally used as catalyst.
[0073] The coating composition may also comprise a hydrophobic
inorganic binder precursor. The addition of such a precursor can
lead to hydrophobic and even super-hydrophobic properties of the
resulting coating while retaining the anti-reflective function.
Preferably a hydrophobic coating is obtained with static water
contact angles of greater than 90.degree. , more preferably with a
static water contact angles of greater than 140.degree. . An
example of such a hydrophobic binder precursor additive binder can
be, but is not limited to, 1H,1H,2H,2H-(Perfluorooctyl)
triethoxysilane (see formula I)
##STR00001##
[0074] For organic binders, a fully organic solvent system is
preferred, although some water may be present. Examples of suitable
solvents include 1,4-dioxane, acetone, chloroform, cyclohexane,
diethylacetate, propanol, ethanol, methanol, butanol, methyl ethyl
ketone, methyl propyl ketone, tetrahydrofuran, toluene and
tetrafluoroisopropanol. Preferred solvents are methanol, methyl
ethyl ketone, isopropanol or 1-methoxypropan-2-ol.
[0075] It is an advantage of the present invention that the coating
is insensitive to moisture. Thus, in contrast to the three-layer
coating, the space where the glass plates are coated need not to be
humidity controlled, and humidity between for example 30 and 80% is
acceptable. Further, the inorganic coating also is not sensitive to
time delays between coating and curing. The organic UV curable
coating is generally cured directly after application, although
this is also not critical.
[0076] Preferably the coating composition is applied to the article
in a thickness eventually resulting in a thickness after cure of
about 50 nm or larger, preferably of about 70 nm or larger, more
preferably about 90 nm or higher. Preferably, the thickness after
cure will be about 300 nm or less, preferably of about 200 nm or
less, more preferably about 160 nm or less, and most preferred
about 140 nm or less.
[0077] 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
fragments in small pieces when the glass plate breaks. The
tempering step is usually carried out as known to those skilled in
the art and involves heating 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 be cured during the
tempering process. In that case the curing and tempering process
are thus carried out in one step.
[0078] In one embodiment of the invention, the coating is applied
(semi-) continuous in line of a glass-plate manufacturer, and
thereafter, the coating cured while the glass is subjected to a
tempering step.
[0079] The invention will be further elucidated by the following
examples, without being limited thereto.
EXAMPLES
[0080] The preparation of inorganic coatings systems based on
particles both with a high and low aspect ratio is described in
section A. Preparation of organic/inorganic hybrid coatings using
UV curing are described in section B. The properties of the anti
reflective coating systems are described in Section C.
[0081] The silica particles were delivered by Nissan Chemical and a
summary of their properties is given in Table 1.
TABLE-US-00001 TABLE 1 Types and properties of silica particles.
particle SiO.sub.2 H.sub.2O Viscosity Specific Particle Particle
Size (nm) (wt %) (%) (mPa s.) Gravity pH Shape Solvent MT-ST 10-15
30-31 <2.0 <5 0.98-1.02 2-4 Spherical Methanol IPA-ST-UP 9-15
15-16 <1.0 <20 0.85-0.90 2-4 Worm-like* Iso- propanol
*worm-like particles have a high aspect ratio: a diameter of 9-15
nm and a length of 40-300 nm
Section A:
[0082] Coating formulations were prepared either by grafting
reactive inorganic binder (alkoxy silanes) onto the surface of the
silica particles (type IPA-ST-UP) and then mixing with a
pre-hydrolysed binder (mixture B, see table 2) or by directly
mixing the particles (type MT-ST) with the pre-hydrolysed
binder.
[0083] 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 diluted with solvent to the
desired concentration and hydrochloric acid was added to get a pH
of 1 (mixture B). Table 2 shows the amounts of chemicals used.
TABLE-US-00002 TABLE 2 Material Mixture B Tetraethylorthosilicate
11.9 wt-% Water (hydrolysis agent) 10.9 wt-% Acetic acid 1.2 wt-%
Isopropanol 75.8 wt-% Hydrochloric acid 0.2 wt-% Total 100 wt-%
[0084] Reactive inorganic binder precursor groups were grafted onto
the worm like silica nano-particles by adding an alkoxy silane to a
suspension of the oxide particles in solvent. Table 3 shows the
amounts of chemicals used. After stirring, water was added to the
mixture and the mixture was heated to 80.degree. C. and kept there
for 4 hours. After cooling down the mixture was diluted with
solvent to the desired concentration. At this point a certain
amount of mixture B is added to the reaction mixture to get the
desired final formulation suited for the dipping process (example
formulation 1).
[0085] Example formulation 2 based on spherical nano-silica
particles was prepared by adding pre-hydrolysed binder (mixture B)
and water to a suspension of the spherical oxide particles in
solvent. At this point the resultant mixture was diluted with
solvent to the desired concentration for application to the
substrate. Table 3 shows the amounts used.
TABLE-US-00003 TABLE 3 Compounds in weight percentage used for
inorganic AR liquid coating formulations. Weight percentages of
silica particles are given in equivalent dry weight, i.e. weight
percentage solids. Material Formulation 1 Formulation 2 Isopropanol
(solvent) 85.8 wt-% 75.9 wt-% ST-UP particles 1.6 wt-% MT-ST
particles 2.6 wt-% Tetraethylorthosilicate 3.8 wt-% Water
(hydrolysis agent) 5.0 wt-% 8.3 wt % Mixture B 3.9 wt-% 13.2 wt-%
Total 100 wt-% 100 wt-%
A2: Preparation of an Inorganic AR Coating or Film on a
Substrate
[0086] Thin films of the formulations 1 and 2 are prepared on glass
slides by the following procedure. A glass plate is washed and
dried thoroughly to prepare it for the coating process. The glass
slide is then coated with either formulation 1 or 2. The coating is
applied through a slit of 2 mm which is drawn along the glass plate
at a distance of 400 .mu.m. The glass plate is kept at a 80.degree.
angle. After evaporation of the solvent the dried inorganic coating
is cured in an oven for 4 hours at 450.degree. C. to ensure
complete curing. The coating has a thickness of about 200 nm.
B1. Modification of Silica Particles with Polymerisable-Groups
[0087] Radically polymerising groups were grafted onto worm like
silica nano-particles by adding a trimethoxy-silane compound
comprising an acrylate group (e.g., 3-(trimethoxysilyl)propyl
acrylate) together with p-methoxy-phenol, a compound that inhibits
polymerization of the acrylate groups, an acid and a catalytic
amount of water to a suspension of the silica nano-particles in an
isopropyl alcohol. After each addition the formulation was shortly
stirred. After the final addition the mixture was stirred for at
least one hour at room temperature. Table 4 shows the amounts of
chemicals used
TABLE-US-00004 TABLE 4 Compounds in weight percentage used for
modification of worm-like silica nano-particles. Weight percentage
of silica particles is given in equivalent dry weight, i.e. weight
percentage solids. Material Modified nano-particle solution 1
IPA-ST-UP particles 14.9 wt % 3-(trimethoxysilyl)propyl acrylate
1.5 wt % Hydroquinnone mono-methylether 0.004 wt % Water 0.63 wt %
Isopropanol 83.0 wt % Total 100 wt %
B2. Preparation of the Inorganic/Organic Hybrid AR Formulation
[0088] The acrylate modified silica particle solution was
formulated to the example formulation 3 by adding various binders,
photo-initiator, stabilizer and solvent. Table 5 shows the amounts
of chemicals used. After stirring at room temperature for at least
6 hours the formulation 3 was ready for use.
TABLE-US-00005 TABLE 5 Example formulation 3. Particle solution 1.
15.2 wt % Trimethylolpropane propoxylate triacrylate 0.28 wt %
Trimethylolpropane-tris(3-mercapto-propionate) 0.06 wt %
2-methyl-4'-(methylthio)-2-morpholino-propiophenone 0.06 wt %
Propylgallate 0.002 wt % 1-methoxy-2-propanol 84.4 wt % Total 100
wt %
B3. UV Curable Hard Coat
[0089] The UV curable hard coat (HC) formulation (3) comprises (52
w-t % solids) acrylate surface modified silica particles (MT-ST,
particles size 10-15 nm), Dipentaerythritol pentaacrylate (28 wt-%
solids), Ethoxylated (9) trimethylolpropane triacrylate (18 wt-%
solids), photo-initiator Irgacure 184 from Ciba (2 wt-% solids) and
an amount of methanol as a solvent such that the final
concentration of all solids is ca 50 wt-%.
B4. Preparation of a Coating or Film on a Substrate
[0090] Thin films of various mixtures are prepared on glass or
polycarbonate plates by the following procedure. The glass or
polycarbonate plates are washed and dried thoroughly to prepare it
for the coating process. If preferred a hard coat can be applied
before applying example formulation 3. The glass or polycarbonate
plate is then coated with the hard coat formulation as described in
example A2. After evaporation of the solvent the thin hard coat
layer is cured with UV radiation (Fusion UV Systems, D-bulb) at a
dose of 0.8 J/cm.sup.2 in air. To apply example formulation 3 onto
the hard coat or directly onto the glass or polycarbonate plate,
the glass or polycarbonate plate is coated with formulation 3.
After evaporation of the solvent the thin layer is cured with UV
radiation (Fusion UV Systems, D-bulb) under nitrogen at a dose of
2.0 J/cm.sup.2.
* * * * *