Note: Descriptions are shown in the official language in which they were submitted.
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ADHESION-ENHANCING COATINGS FOR OPTICALLY FUNCTIONAL COATINGS MATERIALS
Background of the Invention
Optically functional coatings are coatings whose primary function is to
to either enhance or reduce light reflectance from the surface of transparent
substrates, including plastic and glass substrates. When an optically
functional
coating reduces the amount of light reflected by the plastic or glass
substrate, it is
called "antireflective." On the other hand, when the optically functional
coating
enhances the amount of light reflected by the substrate, it is called
"reflective." An
optically functional coating can be formed from a wide variety of conventional
materials.
As described in Optical Thin Film User's Handbook by James D. Rancourt,
MacMillan Publishing Co., 19$7, optically functional coatings may be formed
from suitably deposited thin films of metals (including metalloids) or alloys
2o thereof, such as silver, gold, aluminum, palladium, and palladium-gold.
However,
one of the most versatile classes of materials used in the deposition of
optically
functional coatings are metal oxides. Herein, "metal oxides" includes oxides
of
single metals (including metalloids) as well as oxides of alloys thereof.
Examples
of particular metal oxides that have been used in optical coatings include
oxides of
aluminum, silicon, tin, titanium, niobium, zinc, zirconium, tantalum, yttrium,
cerium, tungsten, bismuth, indium, and mixtures thereof, such as A1203, Si02,
Sn02, Ti02, Nb205, ZnO, Zr02, Ta205, Y203, Ce02, W03, Bi205, In203, and
ITO (indium tin oxide). Metal oxides that are depleted in oxygen (that is,
where the
amount of oxygen in the oxide is less than the stoichiometric amount), such as
SiOX, where x is no greater than 2, have also been used. One method of
synthesizing such oxygen deficient oxides is by a modified sputtering
technique
called reactive sputtering. One of the reasons for the versatility of metal
oxides in
optically functional coatings is the fact that unlike other materials, they
may be
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used to deposit both reflective or antireflective coatings depending on the
configuration of the oxide coating and its chemical composition. Thus, as
discussed in International Publication Document WO 96/31343 (Bright), when a
single thin layer of metal oxide, such as TTO, having a thickness of about SO
Angstroms to about 3000 Angstroms is deposited over a transparent plastic
film,
such as polyester or polycarbonate, the amount of light reflected by the
polyester or
polycarbonate increases substantially. In this case the ITO film acts as a
"reflective" coating. On the other hand, when alternating layers of ITO and
Si02
or ITO and SiOx with a combined thickness of about 50 Angstroms to about and
l0 3000 Angstroms are deposited over the polyester or polycarbonate substrate,
the
amount of light reflected by the polyester or polycarbonate decreases
substantially.
In this case the alternating ITO/SiOx stack acts as an "antireflective"
coating.
Another reason for the versatility of metal oxide coatings, particularly ITO,
is that
they can be made electrically conductive by doping them with conductive
elements,
such as tin, aluminum, barium, boron, and antimony. When made conductive, the
metal oxides also help reduce static charge and electromagnetic emissions.
Whether an optically functional coating is "reflective" or "antireflective"
depends on its overall refractive index relative to the refractive index of
the
underlying substrate. The simplest reflective coating is a single thin layer
of a
2o transparent material, such as a metal or metal oxide, having a refractive
index
higher than the refractive index of the underlying substrate. Thus, when the
substrate is a transparent organic polymeric material, such as polyester or
polycarbonate, the simplest "reflective" coating is generally chosen to be a
single
thin layer of a material, such as a metal or metal oxide, having a refractive
index of
about 1.6 to about 2.7. This is because most organic polymeric materials have
indices of refraction of about 1.3 (for fluorinated polymers) to about 1.7
(for
aromatic polymers). Fluorinated thermoplastic polymers, such as TEFLON (1.35),
have the lowest indices of refraction among organic polymers, whereas aromatic
thermoplastic polymers, such as polystyrene (1.60), have some of the highest.
3o The simplest antireflective coating is a single layer of a transparent
material
having a refractive index lower than that of the substrate on which it is
disposed.
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Multilayer antireflective coatings include two or more layers of dielectric
material
on a substrate, wherein at least one layer has a refractive index higher than
the
refractive index of the substrate. The multilayer coatings are generally
deposited
thermal evaporation and sputtering techniques, as well as other vacuum
deposition
techniques. Such multilayer coatings are disclosed, for example, in
International
Publication No. WO 96/31343 (Southwall Technologies Inc.), U.S. Pat. Nos.
5,091,244 (Bjornard), 5,105;310 (Dickey), 5,147,125 (Austin), 5,270,858
(Dickey),
5,372,874 (Dickey et al.), 5,407,733 (Dickey), and 5,450,238 (Bjornard et al.)
Antireflective (AR) coatings, in particular, are becoming increasingly
to important in commercial applications. The transparency of plastic or glass,
in the
form of doors, windows, lenses, filters, display devices (for example, display
panels) of electronic equipment, and the like, can be impaired by glare or
reflection
of light. To reduce the amount of glare on plastic or glass, the surface
typically
includes a single layer of a metal oxide (such as silicon dioxide), or
suitably
alternating multilayers of metal oxides, such as ITO/Si02. For example, glass
surfaces have about 4% surface reflection, but with the aid of specialized
coatings,
such as multilayers of sputter deposited ITO/Si02, this surface reflection can
be
reduced to less than about 0.5% in the visible region of the spectrum (400-700
nm).
Antireflective (AR) film stacks prepared by vacuum sputtering of metal oxide
thin
2o films on substrates made of organic polymeric substrates, particularly
flexible
plastic substrates, such as polycarbonate, acrylic, polystyrene, and
polyesters have
been disclosed for example in U.S. Pat. No. 5,579,162 (Bjornard et al.) and
International Publication No. WO 96/31343 (Southwall Technologies Inc.).
While sputter deposited metal oxide thin films generally adhere very well to
glass and other inorganic surfaces, their adhesion to polymeric organic
surfaces and
especially their durability and scratch resistance when deposited directly on
these
polymeric surfaces are often inferior. This is mainly due to the fact that
organic
polymeric surfaces, such as the surface of transparent polyester or acrylic
films, are
themselves very soft and lack the cohesive strength necessary to make them
3o resistant to scratching or other forms of abrasion encountered in everyday
use.
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Methods for treating organic polymeric substrates to enhance the adhesion
of coatings applied thereto are known in the art. For example, methods such as
chemical etching, electron-beam irradiation, corona treatment, plasma etching,
and
coextrusion of adhesion promoting layers are known and discussed, for example,
in
the Handbook of Adhesion, edited by D.E. Packham, John Wiley & Sons, New
York (1992). None of these methods, however, result in a significant increase
in
the hardness or scratch resistance of the organic polymeric surface. One
method
disclosed in U.S. Pat. No. 5,639,546 (Bilkadi) involves the use of a primer
layer
containing the cured product of polyethylenically unsaturated monomers and an
to inorganic oxide sol to enhance adhesion of an organic material to an
organic
polymeric substrate. However, there is still a need for enhancing the adhesion
of
optically functional coatings, particularly antireflective coatings, to
organic
polymeric substrates, particularly flexible organic polymeric substrates.
Summary of the Invention
Thus, the present invention provides an adhesion-enhancing coating for use
on organic polymeric substrates that is sufficiently scratch resistant while
providing
an adherent surface for the application of an optically functional coating.
The
present invention provides a precursor composition curable to an adhesion-
enhancing coating for organic polymeric substrates, particularly,
thermoplastic
2o transparent substrates useful in optical applications. Once applied to a
polymeric
substrate, the precursor compositions cure (or at least partially cure) to
glass-like
materials that impart superior hardness, scratch resistance, and adhesion
properties
to optically functional coatings, such as antireflective coatings {for
example,
indium tin oxide), that are subsequently applied thereto. Advantageously, by
including an adhesion-enhancing coating on an organic polymeric substrate
formed
from the precursor composition, the coated substrate is a more durable
substrate for
use in CRT screens, television screens, corrective lenses, prisms, mirrors,
energy
control windows and windshields, and the like.
The adhesion-enhancing coating includes an organic matrix with inorganic
oxide particles dispersed therein. The adhesion-enhancing precursor
composition
includes a ceramer composition and one or more optional organic solvents. A
ceramer composition includes an organic polymeric binder material curable to
the
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organic matrix with colloidal inorganic oxide particles dispersed therein. In
one
embodiment, a ceramer composition in accordance with the present invention
includes at least one ethylenically unsaturated monomer, an optional
organofunctional silane monomer coupling agent, and inorganic colloidal
particles
s that at least include silica. An alternative ceramer composition according
to the
present invention includes an organofunctional silane monomer coupling agent
and
inorganic colloidal particles that at least include silica.
As used herein with respect to the present invention, the following shall
apply:
"Ceramer composition" refers to a coatable dispersion comprising
substantially non-aggregated, colloidal inorganic oxide particles dispersed in
a
curable organic binder composition, wherein curing of the binder is understood
to
mean in a broad sense the process of solidification (hardening) of the binder
brought about by a suitable approach such as cooling of a molten thermoplastic
is material, drying of a solvent-containing composition, chemical crosslinking
of a
thermosetting composition, radiation curing of a radiation curable
composition, or
the like;
"Ceramer coating" refers to a coating of a ceramer composition in which
the curable composition is cured to form a solid, substantially non-flowing
2o material; and
"Curable" means that a coatable material can be transformed into a solid,
substantially non-flowing material by means of cooling (to solidity hot
melts),
heating (to dry and solidify materials in a solvent), chemical crosslinking,
radiation
crosslinking, or the like.
25 During the manufacture of the coated organic polymeric substrate, the
precursor composition is applied to at least a portion of the organic
polymeric
substrate. Preferably and advantageously, this precursor composition is
directly
applied to the organic polymeric substrate. Optionally, the precursor
composition
can be applied to the organic polymeric substrate that has been primed, for
example
3o treated with a conventional primer such as an acrylic latex.
The adhesion-enhancing ceramer composition is in a flowable state, which
is subsequently exposed to conditions, preferably an energy source, that cure
the
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composition and form an adhesion-enhancing coating. The conditions that affect
curing include thermal energy, electron beam, ultraviolet light, or visible
light.
The present invention provides a composite structure comprising an organic
polymeric substrate having a first surface and a second surface; an adhesion-
enhancing coating on the first surface, wherein the coating comprises an
organic
matrix having inorganic oxide particles dispersed therein; wherein the organic
matrix comprises at least one polymerized ethylenically unsaturated monomer
and
the inorganic oxide particles comprise silica particles; and an optically
functional
coating on the adhesion-enhancing coating. Preferably, the adhesion-enhancing
coating is prepared from a ceramer composition comprising at least one
ethylenically unsaturated monomer, colloidal inorganic oxide particles that
include
at least silica particles, and an optional organofunctional silane monomer
coupling
agent.
The ethylenically unsaturated monomer is selected from the group of a
monofunctional ethylenically unsaturated monomer, a multifunctional
ethylenically
unsaturated monomer, and a combination thereof. Preferably, the monofunctional
ethylenically unsaturated monomer is selected from the group of a
monofunctional
(meth)acrylic acid ester, a (meth)acrylamide, an alpha-olefin, a vinyl ether,
a vinyl
ester, and a combination thereof. Preferably, the multifunctional monomer is a
2o multifunctional unsaturated ester of (meth)acrylic acid of the formula:
HZC= -~-Ol -R~-Y
Jm n
R4
wherein R4 is hydrogen, halogen or a (C1-C4)allcyl group; RS is a polyvalent
organic
group selected from the group of a cyclic, a branched, a linear, an aliphatic,
an
aromatic, or a heterocyclic moiety having carbon, hydrogen, nitrogen,
nonperoxidic
oxygen, sulfur, or phosphorus atom; Y is hydrogen, (C1-C4)allcyl, or a protic
functional group selected from the group consisting of -OH, -COOH, -SH, -
PO(OH)2, -S03H, and -SO(OH)2; m is an integer of at least 2; and n is an
integer
having a value of 1 to 3.
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In an alternative embodiment, the present invention provides an
antireflective composite structure comprising an organic polymeric substrate
having a first surface and a second surface; an adhesion-enhancing coating on
the
first surface, wherein the coating comprises an organic matrix and inorganic
colloidal particles that at least include silica dispersed in the organic
matrix; and an
antireflective coating on the adhesion-enhancing coating. The antireflective
coating is preferably substantially hydrocarbon free. More preferably, the
antireflective coating comprises at least one film comprising a material
selected
from the group of oxides of aluminum, silicon, tin, titanium, niobium, zinc,
Io zirconium, tantalum, yttrium, aluminum, cerium, tungsten, bismuth, indium,
and
mixtures thereof.
The present invention also provides an optically functional structure
comprising an organic polymeric substrate having a first surface and a second
surface; an adhesion-enhancing coating on the first surface wherein the
coating
comprises an organic matrix and inorganic colloidal particles that at least
include
silica dispersed in the organic matrix; wherein the organic matrix is formed
from
an adhesion-enhancing precursor composition comprising a ceramer composition
comprising an organofunctional silane monomer coupling agent, and colloidal
inorganic oxide particles that at least include silica; and an optically
functional
coating on the adhesion-enhancing coating, wherein the optically functional
coating is substantially carbon free. Methods of forming such structures are
also
provided.
Detailed Descriution of Preferred Embodiments
Preferably, transparent articles in accordance with the present invention
include coatings of one or more layers of at least one optically functional
material
deposited on a transparent (that is, light transmissive) organic polymeric
substrate.
An adhesion-enhancing coating according to the present invention is used to
enhance adhesion of an optically functional layer or stack to an organic
polymeric
substrate. Additionally, and advantageously, the adhesion-enhancing coating
for an
3o organic polymeric substrate of the present invention also imparts glass-
like
properties to the substrate, such as scratch resistance. Thus, an adhesion-
enhancing
coating should not significantly degrade the organic polymeric substrate or
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adversely affect its physical properties. An adhesion-enhancing coating should
also
adhere well to an organic polymeric substrate, particularly a thermoplastic
material.
Optically functional materials, which when deposited or coated on a
transparent substrate, alter the reflective properties of the substrate, as
discussed
above. That is, an optically functional material may provide a reflective or
mirror-
like property to the substrate or it may provide an antireflective property.
The optically functional coating can be formed from a wide variety of
conventional materials as discussed above. For certain embodiments of the
present
invention, optically functional materials are preferably substantially
hydrocarbon
1o free. As used herein, "hydrocarbon" refers to a group or moiety that
generally
contains only carbon and hydrogen and is typically classified as an aliphatic
group,
a cyclic group, or a combination of aliphatic and cyclic groups (for example,
alkaryl and aralkyl groups). This term does not refer to carbon coatings, such
as
diamond-like carbon coatings. However, for certain embodiments of the present
invention, optically functional materials are preferably substantially carbon
free.
An optically functional coating for use in the present invention can be
formed from a wide variety of conventional materials. They can include metals
or
metal alloys, such as silver, gold, aluminum, palladium, and palladium-gold,
metal
oxides such as oxides of aluminum, silicon, tin, titanium, niobium, zinc,
zirconium, tantalum, yttrium, aluminum, cerium, tungsten, bismuth, indium, and
mixtures thereof (for example, A1203, SiOx, particularly Si02, Sn02, TiOZ,
Nb205, ZnO, Zr02, Ta205, Y203, A1203, Ce02, W03, Bi205, In203, and ITO
(indium tin oxide)), or carbon as in diamond-like carbon coatings. As used
herein,
"metals," "metal alloys," and "metal oxides" include both metals and
metalloids.
Preferably, the optically functional coating is an antireflective coating,
which can be in the form of a single layer of a transparent material, or two
or more
layers of dielectric material on a substrate. More preferably, the
antireflective
coating includes one or more metal oxides in one or more layers. Most
preferably,
the metal oxides are vacuum deposited, particularly, sputter coated. A
particularly
3o preferred antireflective coating includes alternating layers of TTO and
SiOx
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(typically, Si02) or with SiOx as the outermost layer and ITO as the layer
directly
contacting the adhesion-enhancing coating.
Representative organic polymeric substrates include transparent polyesters,
such as poly(ethyleneterephthalate) "PET", polycarbonates,
poly(meth)acrylates,
polyphenyleneoxide, cellulose esters, such as cellulose acetate and cellulose
acetate-butyrate copolymer "CAB", polystyrene and styrene copolymers such as
acrylonitrile-butadiene-styrene copolymer and acrylonitrile-styrene copolymer,
polyolefms, such as polypropylene and polyethylene, polyvinyl chloride,
polyimides, and the like. Other polymers (including copolymers, terpolymers,
etc.)
to which have indices of refraction below that of an antireflective coating
may be
used. The term "poly{meth)acrylate" includes acrylates and methacrylates
commonly referred to as cast acrylic sheeting, stretched acrylic,
poly(methylmethacrylate) "PMMA," poly(methacrylate), poly(ethylacrylate), and
poly(methylmethacrylate-co-ethylacrylate), and the like. Preferably, the
thermoplastic substrates to which the coatings of the present invention adhere
the
most effectively are made from optically transmissive thermoplastic materials
(that
is, plastic sheets, films, or bodies having integrated transmissions over the
visible
wavelengths of at least 25% to about 90% without marked absorption or
reflection
peaks in this range) such as polyethylene terephthalate, "PET", polymethyl
2o methacrylate, polycarbonate, polystyrene, and cellulose acetate. The
substrate
thickness can vary, however, it typically ranges from about 0.1 mm to about
1000
mm, and more typically from about 10 mm to about 200 mm. Flexible organic
film substrates, however, are typically no greater than about 1 mm thick.
Additionally, the organic polymeric substrate can be a laminate of two or more
different thermoplastic materials adhered together, either with or without an
adhesive layer therebetween. The organic polymeric substrate can be made by a
variety of different methods. For example, the thermoplastic material can be
extruded and then cut to the desired dimension. It can be molded to form the
desired shape and dimension. Also, it can be cell cast and subsequently heated
and
3o stretched to form the organic polymeric substrate.
The organic polymeric substrate on which the optically functional coating is
applied may include a primed surface, which can be provided by a chemical
primer
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layer or by other methods such as chemical etching, electron-beam irradiation,
corona treatment, plasma etching, or coextrusion of adhesion promoting layers.
Flexible organic polymeric substrates that contain primed surfaces are
commercially available. An example of such a material is a polyethylene
terephthalate film primed with an aqueous acrylic latex, which is available
from
Imperial Chemical Industries, Hopewell, VA, under the trade designation ICI
617.
Preferably, the organic polymeric substrate is primed for enhanced adhesion of
the
adhesion-enhancing coating to the substrate.
During manufacture, an adhesion-enhancing precursor composition is
applied to at least one surface of the organic polymeric substrate and at
least
partially cured to form the adhesion-enhancing coating. The curing process can
be
carried out at room temperature (typically, about 20°C to about
25°C) with UV or
e-beam radiation, for example, which is particularly advantageous for
substrates
that warp during the thermal curing of coatings. The adhesion-enhancing
coating is
applied to the outer surface of the organic polymeric substrate as a liquid,
flowable
ceramer composition. Upon curing, that is, polymerizing and/or crosslinking,
the
ceramer composition is solidified to form a coating, sometimes referred to as
a
"hard coat."
The adhesion-enhancing precursor composition includes a ceramer
2o composition and one or more optional solvents. The ceramer composition
includes
substantially non-aggregated, colloidal inorganic oxide particles dispersed in
a
curable organic binder composition. Preferably, the ceramer composition has a
refractive index of about 1.40 to about 1.65, as-measured with a conventional
refractometer using a conventional measurement procedure, such as ASTM D1747-
94 ("Standard Test Method for Refractive Index of Viscous Materials").
Preferably, the curable organic binder of the ceramer composition has a
refractive
index of about 1.40 to about 1.60. Preferably, the cured adhesion-enhancing
coating has a refractive index of about 1.45 to about 1.70, and more
preferably,
about 1.50 to about 1.65.
3o The curable organic binder of the ceramer composition can include a
variety of monomers, oligomers, and/or polymers that can form a cured matrix
for
inorganic oxide particles. Preferably, ceramer compositions in accordance with
the
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present invention include an ethylenically unsaturated monomer, an optional
organofunctional silane monomer coupling agent, and inorganic colloidal
particles
that at least include silica. An alternative ceramer composition in accordance
with
the present invention is made from an organofunctional silane monomer coupling
agent and inorganic colloidal particles that at least include silica.
Ethvlenicallv Unsaturated Monomer
Preferably, the ethylenically unsaturated is a monofunctional ethylenically
unsaturated monomer or a multifunctional ethylenically unsaturated monomer, or
a
combination thereof. Preferably, each of the monomers has a refractive index
of
to about 1.40 to about 1.65.
The multifunctional ethylenically unsaturated monomer is preferably an
ester of (meth)acrylic acid. It is more preferably selected from the group
consisting
of a difunctional ethylenically unsaturated ester of acrylic or methacrylic
acid, a
trifunctional ethylenically unsaturated ester of acrylic or methacrylic acid,
a
tetrafunctional ethylenically unsaturated ester of acrylic or methacrylic
acid, and a
combination thereof. Of these, trifunctional and tetrafunctional ethylenically
unsaturated esters of (meth)acrylic acid are more preferred.
Preferred multifunctional ethylenically unsaturated esters of (meth)acrylic
acid have a refractive index of about 1.40 to about 1.65 and can be described
by the
2o formula:
H2C= ~-O -R5-Y
~m n
~4
R
wherein R4 is hydrogen, halogen or a (C,-C4)alkyl group (preferably R4 is
hydrogen
or a methyl group); RS is a polyvalent organic group, which can be cyclic,
branched, or linear, aliphatic, aromatic, or heterocyclic, having carbon,
hydrogen,
nitrogen, nonperoxidic oxygen, sulfur, or phosphorus atoms; Y is hydrogen, (C1-
C4)alkyl, or a protic functional group; m is an integer designating the number
of
acrylic or methacrylic groups in the ester and has a value of at least 2; and
n has a
value of the valence of RS - m. Referring to this formula, preferably, RS has
a
molecular weight of about 14-100, m has a value of 2-6 (more preferably m has
a
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value of 2-5, most preferably m has a value of 3-4, or where a mixture of
multifunctional acrylates and/or methacrylates are used, m has an average
value of
about 2.05-S), and n is an integer having a value of 1 to 3. Preferred protic
functional groups are selected from the group consisting of -OH, -COOH, -SH,
PO{OH)2, -S03H, and -SO(OH)2.
Examples of suitable multifunctional ethylenically unsaturated esters of
(meth)acrylic acid are the polyacrylic acid or polymethacrylic acid esters of
polyhydric alcohols including, for example, the diacrylic acid and
dimethylacrylic
acid ester of aliphatic diols such as ethyleneglycol, triethyleneglycol, 2,2-
dimethyl-
1,3-propanediol, 1,3-cyclopentanediol, 1-ethoxy-2,3-propanediol, 2-methyl-2,4-
pentanediol, 1,4-cyclohexanediol, 1,6-hexamethylenediol, 1,2-cyclohexanediol,
1,6-cyclohexanedimethanol; the tliacrylic acid and trimethacrylic acid esters
of
aliphatic triols such as glycerin, 1,2,3-propanetrimethanol, 1,2,4-
butanetriol, 1,2,5-
pentanetriol, 1,3,6-hexanetriol, and 1,5,10-decanetriol; the triacrylic acid
and
trimethacrylic acid esters of tris(hydroxyethyl) isocyanurate; the
tetraacrylic and
tetramethacrylic acid esters of aliphatic triols, such as 1,2,3,4-
butanetetrol, 1,1,2,2,-
tetramethylolethane, 1,1,3,3-tetramethylolpropane, and pentaerythlitol
tetraacrylate; the pentaacrylic acid and pentamethacrylic acid esters of
aliphatic
pentols such as adonitol; the hexaacrylic acid and hexamethacrylic acid esters
of
2o hexanols such as sorbitol and dipentaerythritol; the diacrylic acid and
dimethacrylic
acid esters of aromatic diols such as resorcinol, pyrocatechol, bisphenol A,
and
bis(2-hydroxyethyl) phthalate; the trimethacrylic acid ester of aromatic
triols such
as pyrogallol, phloroglucinol, and 2-phenyl-2,2-methylolethanol; and the
hexaacrylic acid and hexamethacrylic acid esters of dihydroxy ethyl hydantoin;
and
mixtures thereof.
Preferably, the multifunctional ethylenically unsaturated ester of
(meth)acrylic acid is a nonpolyethereal multifunctional ethylenically
unsaturated
ester of (meth)acrylic acid. More preferably, the multifunctional
ethylenically
unsaturated ester of (meth)acrylic acid is selected from the group consisting
of
3o pentaerythritol triacrylate (PETA), pentaerythritol ~ trimethacrylate, and
a
combination thereof. Most preferably, the multifunctional ethylenically
unsaturated ester of (meth)acrylic acid is pentaerythritol triacrylate.
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In addition to the multifunctional ethylenically unsaturated esters of acrylic
acid, the ceramer composition can include a monofunctional ethylenically
unsaturated esters of (meth)acrylic acid (that is, an alkyl and/or aryl
acrylate or
methacrylate). Preferably, the alkyl group of the (meth)acrylate has about 4
to
about 14 carbon atoms (on average). The alkyl group can optionally contain
oxygen atoms in the chain thereby forming ethers, for example. Preferably, the
aryl
group of the (meth)acrylate has about 6 to about 20 carbon atoms (on average).
Examples include, but are not limited to, 2-hydroxyethyl acrylate, 2-
hydroxymethyl acrylate, 2-methylbutyl acrylate, isooctyl acrylate, lauryl
acrylate, 4-
1o methyl-2-pentyl acrylate, isoamyl acrylate, sec-butyl acrylate, n-butyl
acrylate, n-
hexyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, n-decyl acrylate,
isodecyl
acrylate, isodecyl methacrylate, and isononyl acrylate. Other examples
include, but
are not limited to, poly-ethoxylated or -propoxylated methoxy (meth)acrylate
{that
is, poly(ethylene/propylene oxide) mono-(meth)acrylate) macromers (that is,
~ 5 macromolecular monomers), polymethylvinyl ether tnono(meth)acrylate
macromers, and ethoxylated or propoxylated nonyl-phenol acrylate macromers.
The molecular weight of such macromers (that is, macromolecular monomers) is
typically about 100 grams/mole to about 600 grams/mole, and preferably, about
300 grams/mole to about 600 grams/mole. Preferred monofunctional
20 {meth)acrylates that can be used include 2-methylbutyl acrylate, isooctyl
acrylate,
lauryl acrylate, and methoxy-capped poly{ethylene glycol) mono-methacrylate.
The monofunctional ethylenically unsaturated monomer may also be
selected from the group of a (meth)acrylamide, an alpha-olefin, a vinyl ether,
a
vinyl ester, and a combination thereof. Examples include, but are not limited
to,
25 acrylamides, such as acrylamide, methacrylamide, N-methyl acrylamide, N-
ethyl
acrylamide, N-methylol acrylamide, N-hydroxyethyl acrylamide, diacetone
acrylamide, N,N-dimethyl acrylamide, N,N-diethyl acrylamide, N-ethyl-N-
aminoethyl acrylamide, N-ethyl-N-hydroxyethyl acrylamide, N,N-dimethylol
acrylamide, N,N-dihydroxyethyl acrylamide, t-butyl acrylamide,
3o dimethylaminoethyl acrylamide, N-octyl acrylamide (normal and branched),
and
1,1,3,3-tetramethylbutyl acrylamide. Other examples include acrylic acid,
methacrylic acid, itaconic acid, crotonic acid, malefic acid, fumaric acid,
2,2'-
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(ethoxyethoxy)ethyl acrylate, 2-hydroxyethyl acrylate or methacrylate, 2-
hydroxypropyl acrylate or methacrylate, 3-hydroxypropyl acrylate or
methacrylate,
t-butyl acrylate, n-butyl methacrylate, isobornyl acrylate, 2-(phenoxy)ethyl
acrylate
or methacrylate, biphenylyl acrylate, t-butylphenyl acrylate, , cyclohexyl
acrylate,
dimethyladamantyl acrylate, 2-naphthyl acrylate, phenyl acrylate, N-vinyl
pyrrolidone, and N-vinyl caprolactam. Preferred reinforcing monofunctional
acrylic monomers include acrylic acid, t-butyl acrylate, N,N-dimethyl
acrylamide,
1,1,3,3-tetramethylbutyl acrylamide, N-octyl acrylamide, 2-(phenoxy) ethyl
acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, isobornyl
acrylate,
to and 2-(phenoxy)ethyl acrylate.
In general, the acrylamide compounds have the following formula:
R3 O R1
I II I
H2C=C-C-N
R2
wherein: R1 and R2 are each independently hydrogen, a (C~-C8)alkyl group
optionally having hydroxy, halide, carbonyl, and amido functionalities, a (C1-
C8)alkylene group optionally having carbonyl and amido functionalities, a (C1-
C4)alkoxymethyl group, a (C4-C18)aryl group, a (C~-C3)alk(C4-C~8)aryl group,
and
a (C4-C1$)heteroaryl group; with the proviso that only one of R' and R2 is
hydrogen; and R3 is hydrogen, a halogen, or a methyl group. Preferably, R1 is
a
(C1-C4)alkyl group; R2 is a (C,-C4)alkyl group; and R3 is hydrogen, a halogen,
or a
2o methyl group. R~ and R2 can be the same or different. More preferably, each
of
Rl and R2 is CH3, and R3 is hydrogen.
Examples of suitable acrylamides are N-{3-
bromopropionamidomethyl)acrylamide, N-tert-butylacrylamide, N,N-
dimethylacrylamide, N,N-diethylacrylamide, N-(5,5-dimethylhexyl)acrylamide, N-
(1,1-dimethyl-3-oxobutyl)acrylamide, N-(hydroxymethyl)acrylamide, N-
(isobutoxymethyl)acrylamide, N-isopropylacrylamide, N-methylacrylamide, N-
ethylacrylamide, N-methyl-N-ethylacrylamide, N-(fluoren-2-yl)acrylamide, N-(2-
fluorenyl)-2-methylacrylamide, 2,3-bis(2-furyl)acrylarnide, N,N'-methylene-bis
acrylamide. A particularly preferred acrylamide is N,N-dimethyl acrylamide.
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Optional Organofunctional Silane Monomer Counting Anent
A wide variety of organofunctional silane monomers may be used in the
practice of the present invention. The preferred organofunctional silanes are
hydrolyzable organofunctional silanes, also known in the art as "coupling
agents"
for coupling silica particles to organic materials. Representative examples
include
methyl trimethoxysilane, methyl triethoxysilane, phenyl trimethoxysilane,
phenyl
triethoxysilane, (meth)acryloxyalkyl trimethoxysilanes, such as
methacryloxypropyl trimethoxysilane, (meth)acryloxypropyl Mchlorosilane,
phenyl trichlorosilane, vinyl trimethoxysilane, vinyl triethoxysilane, propyl
1o trimethoxysilane, propyl triethoxysilane, glycidoxypropyl trimethoxysilane,
glycidoxypropyl triethoxysilane, glycidoxypropyl trichlorosilane, perfluoro
alkyl
trimethoxysilane, perfluoro alkyl triethoxysilane, perfluoromethyl alkyl
trimethoxysilanes, such as tridecafluoro-1,1,2,2 tetrahydrooctyi
trimethoxysilane,
perfluoroalkyl trichlorosilanes, trifluoromethylpropyl trimethoxysilane,
trifluoromethylpropyl trichlorosilane, and perfluorinated sulfonimido ethyl
trimethoxysilane (available from the Minnesota Mining and Manufacturing
Company, St. Paul, MN, under the trade designation FC 405), combinations of
these, and the like. Optionally, the colloidal inorganic particles may be
surface
treated with a silane coupling agent and, in such embodiments, the coupling
agent
2o may be the same or different from the silane monomers used to form the bulk
of
the organic binder of the ceramer composition.
Colloidal Inorganic Particles
In the present invention, a ceramer composition includes colloidal inorganic
particles that at least include silica. Silica sots useful for preparing
ceramer
compositions can be prepared by methods well known in the art. A used herein,
"sot" shall refer to a colloidal dispersion of substantially non-aggregated,
inorganic
oxide particles in a liquid medium. Colloidal silicas dispersed as sots in
aqueous
solutions are also available commercially under such trade names as LUDOX
(E.I.
DuPont de Nemours and Co., Wilmington, DE), NYACOL (Nyacol Co., Ashland,
3o MA), and NALCO (Nalco Chemical Co., Oak Brook, IL). Nonaqueous silica sots
(also called silica organosols) are also commercially available under the
trade
names NALCO 1057 (a silica sot in 2-propoxyethanol, Nalco Chemical Co.) and
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MA-ST, IP-ST, and EG-ST (Nissan Chemical Ind., Tokyo, Japan). The silica
particles preferably have an average particle diameter of about 5 nm to about
1000
nm, and more preferably, about 10 nm to about 50 nm. Average particle size can
be measured using transmission electron microscopy to count the number of
particles of a given diameter. Additional examples of suitable colloidal
silicas are
described in U.S. Pat. No. 5,126,394 (Bilkadi).
Preferably, the silica particles are functionalized with a coupling agent.
More preferably, the silica particles are (meth)acrylate functionalized.
Herein,
"(meth)acrylate functionalized" means the silica particles are f unctionalized
with a
l0 (meth)acrylate terminated organofunctional silane. The functionalized
particles
bond intimately and isotropically with the organic matrix. Typically, the
silica
particles are functionalized by adding a (meth)acrylate functionalized silane
to
aqueous colloidal silica. Examples of (meth)acrylate functionalized colloidal
silica
are described in U.S. Pat. Nos. 4,491,508 (Olsen et al.), 4,455,205 (Olsen et
al.),
4,478,876 (Chung), 4,486,504 (Chung), and 5,258,225 (Katsamberis).
In addition to silica, the colloidal inorganic particles may further include
colloidal particles of higher refractive index than silica. Examples of such
higher
index colloidal particles include, but are not limited to, alumina, titania,
zirconia,
ceria, and antimony oxide sols, all of which are available commercially from
suppliers such as Nyacol Co., Ashland, MA, and Nalco Chemical Co., Oak Brook,
IL.
It is highly desirable that the colloidal inorganic particles of the coating
be
derived from a sol rather than a powder, which can result in an intractable
mass
that is unsuitable for coating as an aqueous sol. The addition of additives,
such as
high molecular weight polymers, may enable compositions derived from colloidal
powder to be cast on to inorganic polymeric substrates. However, it is
believed
that the use of compositions containing colloidal powder will result in
coatings
having relatively poor optical transparency and poor flow properties for
coating.
Therefore, the use of colloidal powders is not preferable in the coatings of
the
present invention. The colloidal silica particles are employed in the coating
at 10%
to 50% by weight, and more preferably, at 25% to 40% by weight, and most
preferably, at 30% to 33% by weight.
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A ceramer composition of the present invention preferably includes an
organic matrix and colloidal inorganic particies that at least include silica.
Preferably, the organic matrix is prepared from a curable organic binder that
includes an ethylenically unsaturated monomer selected from the group of a
multifunctional ethylenically unsaturated ester of (meth)acrylic acid, a
monofunctional ethylenically unsaturated monomer (for example, an ester or
amide), and a combinations thereof; and an optional organofunctional silane
coupling agent.
The ceramer composition preferably includes no greater than about 80
to percent by weight (wt.%) of at least one ethylenically unsaturated monomer
and at
least about 20 wt.% colloidal inorganic oxide particles, based on the total
weight of
the ceramer composition. Preferably, it includes at least about 40 wt.% of at
least
one ethylenically unsaturated monomer, and no greater than about 60 wt.% of
colloidal inorganic oxide particles.
If the ethylenically unsaturated monomers used include a mixture of
multifunctional and monofunctional ethylenically unsaturated monomers, the
multifunctional monomer is preferably used in an amount of at least about 20
wt.%, and the monofunctional monomer is preferably used in an amount of at
least
about 5 wt.%. Preferably, the multifunctional monomer is used in an amount of
no
2o greater than about 60 wt.%, and the monofunctional monomer is used in an
amount
of no greater than about 20 wt.%.
If used, an organofunctional silane coupling agent is preferably used in an
amount of no greater than about 80 wt.%, more preferably, no greater than
about 70
wt.%, and most preferably, no greater than about 60 wt.%, based on the total
weight of the ceramer composition. It is preferably used in an amount of at
least
about S wt.%, more preferably, at least about 10 wt.%, and most preferably, at
least
about 20 wt.%, based on the total weight of the ceramer composition.
It is the combination of the organic matrix with the colloidal inorganic
oxide particles that at least include silica (with or without a coupling
agent) that
results in unexpected and improved properties as a adhesion-enhancing coating.
The multifunctional ethylenically unsaturated esters of (meth)acrylic acid
tend to
increase the hardness of the coating, whereas the monofunctional ethylenically
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unsaturated monomer tends to "toughen" the coating without significant loss in
abrasion resistance. This toughness property also results in the coating being
able
to be flexed.
In many instances, the adhesion-enhancing coating can adhere directly to
the organic polymeric substrate without the need for an additional primer or
adhesion promoter, which is advantageous at least because this results in a
labor
and material savings.
Initiators and Photosensitizers
During the manufacture of an abrasion resistant coating, the ceramer
1o composition is exposed to an energy source, for example, heat or UV or e-
beam
radiation, that initiates the curing process of the ceramer composition. This
curing
process typically occurs via a free radical mechanism, which can require the
use of
a free radical initiator (simply referred to herein as an initiator, for
example, a
photoinitiator or a thermal initiator). If the energy source is an electron
beam, the
electron beam generates free radicals and no initiator is required. If the
energy
source is heat, ultraviolet light, or visible light, an initiator is required.
When the
initiator is exposed to one of these energy sources, the initiator generates
free
radicals, which then initiates the polymerization and crosslinking.
Examples of suitable free radical thermal initiators include, but are not
limited to, peroxides such as benzoyl peroxide, azo compounds, benzophenones,
and quinones. Examples of photoinitiators that generate a free radical source
when
exposed to visible light radiation include, but are not limited to,
benzophenones.
Examples of photoinitiators that generate a free radical source when exposed
to
ultraviolet light include, but are not limited to, organic peroxides, azo
compounds,
quinones, benzophenones, nitroso compounds, acryl halides, hydrozones,
mercapto
compounds, pyrylium compounds, triacrylimidazvles, bisimidazoles,
chloroallcytriazines, benzoin, benzoin methyl ether, benzoin ethyl ether,
benzoin
isopropyl ether, benzoin isobutyl ethers and methylbenzoin, diketones such as
benzil and diacetyl, phenones such as acetophenone, 2,2,2-tri-bromo-1-
3o phenylethanone, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-
phenylacetophenone,
2,2,2,-tribromo-1(2-nitrophenyl) ethanone, benzophenone, and 4,4-
bis(dimethyamino)benzophenone. Examples of commercially available ultraviolet
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photoinitiators include those available under the trade designations 1RGACURE
184 (1-hydroxycyclohexyl phenyl ketone), IRGACURE 361 and DAROCUR 1173
(2-hydroxy-2-methyl-1-phenyl-propan-1-one) from Ciba-Geigy, Hawthorn, NY.
Typically, if used, an amount of an initiator is included in the precursor
composition to effect the desired level and rate of cure. Preferably, the
initiator is
used in an amount of about 0.1 wt.% to about 10 wt.%, and more preferably
about
2 wt.% to about 4 wt.%, based on the total weight of the ceramer composition
without solvent. It should be understood that combinations of different
initiators
can be used if desired.
In addition to the initiator, the ceramer composition of the present invention
can include a photosensitizer. The photosensitizer aids in the formation of
free
radicals that initiate curing of the precursor composition, especially in an
air
atmosphere. Suitable photosensitizers include, but are not limited to,
aromatic
ketones and tertiary amines. Suitable aromatic ketones include, but are not
limited
to, benzophenone, acetophenone, benzil, benzaldehyde, and o-
chlorobenzaldehyde,
xanthone, tioxanthone, 9,10-anthraquinone, and many other aromatic ketones.
Suitable tertiary amines include, but are not limited to,
methyldiethanolamine,
ethyldiethanolamine, triethanolamine, phenylmethyl-ethanolamine,
dimethylaminoethylbenzoate, and the like. Typically, if used, an amount of
initiator is included in the precursor compositions to effect the desired
level and
rate of cure. Preferably, the amount of photosensitizer used in the
compositions of
the present invention is about 0.01 wt.% to about 10 wt.%, more preferably
about
0.05 wt.% to about 5 wt.%, and most preferably, about 0.25 wt.% to about 3
wt.%,
based on the total weight of the ceramer composition (that is, the adhesion-
coating
precursor composition without solvent). It should be understood that
combinations
of different photosensitizers can be used if desired.
Other O»tional Additives
The ceramer composition can also preferably include a leveling agent to
improve the flow or wetting of the ceramer composition on the transparent
thermoplastic substrate. If the ceramer composition does not properly wet the
thermoplastic substrate, this can lead to visual imperfections (for example,
pin
holes and/or ridges) in the coating. Examples of leveling agents include, but
are
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not limited to, alkoxy terminated polysilicones such as that available under
the
trade designation DOW 57 (a mixture of dimethyl-, methyl-, and (polyethylene
oxide acetate)-capped siloxane) from Dow Coming, Midland, MI; and
fluorochemical surfactants such as those available under the trade
designations
FC430, FC431, and FX313 from Minnesota Mining and Manufacturing Company,
St. Paul, MN. The ceramer composition can include an amount of a leveling
agent
to impart the desired result. Preferably, the leveling agent is present in an
amount
up to about 3 wt.%, and more preferably, about 0.5 wt.% to about 1 wt.%, based
on
the total weight of the ceramer composition. It should be understood that
to combinations of different leveling agents can be used if desired.
Additionally, if organofunctional silane monomers are used, it may be
desirable in some instances to add about 1 wt.% to about 3 wt.% glacial acetic
acid
or similar carboxylic acids as a catalyst for hydrolysis of the
organofunctional
silane.
Polymeric materials are known to degrade by a variety of mechanisms.
Common additives that can offset this are known as stabilizers, absorbers,
antioxidants, and the like. The ceramer compositions of the present invention
can
include one or more of the following: ultraviolet stabilizer, ultraviolet
absorber,
ozone stabilizer, and thermal stabilizer/antioxidant.
2o An ultraviolet stabilizer and/or ultraviolet absorber for improving
weatherability and reducing the "yellowing" of the adhesion-enhancing coating
with time. An example of an ultraviolet stabilizer includes that available
under the
trade designation TIIVZJVIN 292 (bis(1,2,2,6,6-pentamethyl-4-
piperidinyl)sebacate)
and an example of an ultraviolet absorber includes that available under the
trade
designation TINUVIN 1130 (hydroxyphenyl benzotriazole), both of which are
available from Ciba-Geigy. The ceramer composition can include an amount of
either an ultraviolet stabilizer and/or an ultraviolet absorber to impart the
desired
result. Preferably, the ultraviolet stabilizer or absorber is present in an
amount up
to about 10 wt.%, and more preferably, about 1 wt.% to about 5 wt.%, based on
the
3o total weight of the ceramer composition. It should be understood that
combinations of different ultraviolet stabilizers and absorbers can be used if
desired.
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An ozone stabilizer protects against degradation resulting from reaction
with ozone. Examples of ozone stabilizers include, but are not limited to,
hindered
amines such as that available under the trade designation IRGONOX 1010
available from Ciba-Geigy and phenoltriazine commercially available from
Aldrich
Chemical Company, Inc., Milwaukee, WI. The ceramer composition can include
an amount of an ozone stabilizer to impart the desired result. Preferably, the
ozone
stabilizer is present in an amount up to about 1 wt.%, more preferably about
0.1
wt.% to about 1.0 wt.%, and most preferably about 0.3 wt.% to about 0.5 wt.%,
based on the total weight of the ceramer composition.
1o Method of Preuaring the Adhesion-Enhancine COatinE
The ceramer composition is typically coated out of an organic solvent.
Thus, the adhesion-enhancing coating composition typically includes the
ceramer
composition with one or more organic solvents to reduce the viscosity of the
composition and adjust the percent solids content, and thereby enhance the
flow
characteristics. The desired viscosity depends on various conditions such as
the
coating thickness, application technique, and the type of substrate. In
general, the
viscosity of the ceramer composition at 25°C is about 1-200 centipoise,
preferably
about 3-75 centipoise, more preferably about 4-50 centipoise, and most
preferably
about 5-20 centipoise. In general, the solids content of the ceramer
composition is
2o about 5-99%, preferably about 10-70%, more preferably about 15-30%, and
most
preferably about 17-26% solids.
The organic solvent should be selected such that it is compatible with the
components in the ceramer composition. As used in this context, "compatible"
means that there is minimal phase separation between the solvent and the
curable
organic binder of the ceramer composition. Additionally, the solvent or
solvents
should be selected such that they do not adversely affect the cured adhesion-
enhancing coating properties or attack the thermoplastic material.
Furthermore, the
solvents) should be selected such that they have an appropriate drying rate.
That
is, the solvents) should not dry too slowly, which would slow down the process
of
3o making a coated organic polymeric substrate, nor too quickly, which could
cause
defects such as pin holes or craters in the coating. Examples of suitable
solvents
include alcohols, preferably the lower alcohols such as isopropyl alcohol, n-
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butanol, methanol, ethanol, ketones such as methyl ethyl ketone, glycols, and
combinations thereof.
To make the adhesion-enhancing ceramer composition of the invention, all
the components are mixed together including the colloidal inorganic particles
and
the optional organofunctional coupling agent. The mixture is then heated to
about
55°C and the solvents {including water) are removed under mild vacuum
(about 90
mm Hg) to obtain the ceramer. Additionally, it is preferred to filter the
ceramer
composition prior to application to a substrate in an effort to remove gel
particles
or other agglomerated materials. This can be done by filtering the ceramer
to composition through a ten-, five-, or one-micron filter that is made of a
material
that is unreactive with the solvent or any of the components of the
composition.
The coating can be applied by any technique such as spray coating, knife
coating, dip coating, flow coating, roll coating, and the like. In spray
coating, the
ceramer is atomized and then applied to the outer surface of the substrate. In
dip
is coating, the substrate is immersed into the ceramer and then the excess
coating
drips off of the substrate. In flow coating, the thermoplastic substrate is
held in a
vertical position and the ceramer is applied across the top of the substrate.
The
ceramer then flows down the substrate. In roll coating, the ceramer is applied
to
the substrate by a roll coater.
20 A particularly preferred method of coating involves a continuous process.
This process includes the steps of placing an organic polymeric substrate
having
outer surface on a conveyor belt. This substrate is conveyed to a coating
station
where a ceramer composition is applied to the outer surface. Next, the
solvent, if
used, is flashed off in a flashing unit, at a temperature suitable for the
solvent used.
25 This is typically accomplished at a temperature of about 15-75°C,
preferably at a
temperature of about 40-65°C. Although a flashing unit is shown, which
can be a
forced-air oven or an infrared heat source, for example, the solvent can be
removed
simply by evaporation under ambient conditions. Once the solvent is removed,
if it
is used, the layer of ceramer composition is exposed to an energy source to
initiate
3o curing the ceramer composition to form a adhesion-enhancing coating on the
organic polymeric substrate. It should be understood that this is meant to be
an
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illustration of one process of the invention; it is within the scope of this
invention
to have many variations on this process.
The ceramer composition should be applied to the organic polymeric
substrate in a manner to eliminate or minimize any optical imperfections. If
the
coating contains defects, such as dust particles or ridges, this can detract
from the
optical clarity of the transparency or create distortion in the transparency.
Some
defects can be created during the flashing step; these defects are typically
either pin
holes or surface roughness caused by uneven drying. To minimize the formation
of
these defects, the temperature and humidity are often controlled in the clean
room
i o or at the coating station. The actual temperature and humidity conditions
are
dependent upon the chemistry of the ceramer composition. Preferably, the
ceramer
composition is applied at a temperature of about 15-35°C, and more
preferably
' about 20-25°C. The humidity is preferably about 30-50% relative
humidity.
After flashing off the solvent, if used, the ceramer composition is exposed
i5 to an energy source to cure the composition and form an adhesion-enhancing
(or a
hard) coating. This energy source can be thermal energy, electron beam,
ultraviolet
light, or visible light. The amount of energy required is primarily dependent
on the
chemistry of the precursor composition, as well as its thickness and density.
For
thermal energy, the oven temperature will typically range from about
50°C to about
20 250°C (preferably about 90°C to about 110°C) for about
15 minutes to about 16
hours. It should be noted that care should be taken during thermal curing not
to
degrade the thermoplastic material. Electron beam radiation can be used at an
energy level of about 0.1 megarad to about 10 megarad (Mrad), preferably at an
energy level of about 1 Mrad to about 10 Mrad. Ultraviolet radiation refers to
25 nonparticulate radiation having a wavelength within the range of about 200
to
about 400 nanometers, preferably within the range of about 250 to 400
nanometers.
It is preferred that UV light have an energy level of at least 300 Watts/inch
(120
Watts/cm), preferably at least 600 Watts/inch {240 Watts/cm). Visible
radiation
refers to nonparticulate radiation having a wavelength within the range of
about
30 400 nanometers (nm) to about 800 nm, preferably in the range of about 400
nm to
about, 550 nm. In general, it is preferred to cure in an inert atmosphere
{that is,
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minimal oxygen present) such as a nitrogen atmosphere. UV and visible light
curing is preferred because there tends to be very little, if any, damage of
the
thermoplastic material when they are used as the energy source for curing the
composition. There is a concern with thermal energy, that if the thermoplastic
is
either exposed too long and/or at too high of a temperature, this excessive
thermal
exposure may cause degradation of the thermoplastic material.
The ceramer composition can be applied over the entire substrate surface or
a portion thereof. The coating thickness of the ceramer composition will
depend
upon the formulation and the amount of solvent. Typically, the cured coating
has a
1o thickness of at least about 1 micron, and preferably, at least about 2
microns.
Typically, the cured coating has a thickness of no greater than about 50
microns,
preferably, no greater than about 25 microns, more preferably, no greater than
about 10 microns, and most preferably, no greater than about 4 microns. The
amount of the ceramer composition applied to the substrate is adjusted to
provide
this coating thickness.
Once the ceramer composition has formed an adhesion-enhancing coating
on the organic polymeric substrate, an optically functional coating can be
formed
on at least a portion of the adhesion-enhancing coating. As previously
mentioned,
preferred optically functional coatings are substantially hydrocarbon free and
can
2o be formed from one or more thin metal, or metal oxide films. More
preferably, the
optically functional coating is formed from a material selected from the group
of
oxides of aluminum, silicon, tin, titanium, niobium, zinc, zirconium,
tantalum,
yttrium, aluminum, cerium, tungsten, bismuth, indium, and mixtures thereof.
Objects and advantages of this invention will now be illustrated by the
following Examples, but the particular materials and amounts thereof recited
in
these examples, as well as other conditions and details, should not be
construed to
unduly limit this invention.
Exaerimental Examples
Advantages of the invention are illustrated by the following examples.
3o However, the particular materials and amounts thereof recited in these
examples, as
well as other conditions and details, are to be interpreted to apply broadly
in the art
and should not be construed to unduly limit the invention.
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Test Procedure 1- Drv Adhesion:
This test was run according to ASTM Test Procedure D3359-95 (Standard
Test Methods for Measuring Adhesion by Tape Test). This adhesion test was used
to determines how well the sputter-deposited metal oxide antireflective film
coating adheres to the underlying substrate. The test was carned out using a
multiblade cutter commercially available from BYK/Gardner, Inc. of Silver
Spring,
MD. The cutter had six parallel blades spaced 1.5 mm (0.06 inch) apart. The
test
specimen was cut in a cross-hatch pattern according to Fig. 1 of ASTM D3359-
95.
After the cuts were made, the surface was brushed lightly to remove any
surface
debris.
The adhesion of the coating was tested by gently placing the center of a 2.5
cm wide piece of adhesive tape (SCOTCH Brand Transparent Tape No. 850,
commercially available from Minnesota Mining and Manufacturing Company, St.
Paul, MN) on the grid, pressing the tape onto the grid by passing a rubber
roller
weighing 5 pounds (2.3 kg) once over the tape,. and then removing the tape at
180
angle at a rapid rate. The grid was examined using an illuminated magnifier
and
rated according to the classification set forth in ASTM D3359-93. To provide
an
effective antireflective film for a particular substrate, the sputter
deposited metal
oxide antireflective coating of this invention must exhibit an adhesion value
of SB
on the Gardner scale, which represents no delamination. That is, the edges of
the
cuts are completely smooth with none of the grid squares detached. A value of
5B
is needed to pass this test.
Test Procedure 2 - KnoOp Indentation Hardness:
This test was run according to ASTM Test Procedure D 1474-85 (Standard
Test Methods for Indentation Hardness of Organic Coatings). This method
(Method A in ASTM D1474-85) consists of applying a 25-gram load to the surface
of a coating by means of a pyramidal shaped diamond having specified face
angles,
and converting the measurements of the resultant permanent impression to a
hardness number expressed as KHN (Knoop Hardness Number). All measurements
of KHN were carried out on a Micromet-4 Microhardness Tester (manufactured by
Buehler LTD, Lake Bluff, 1L). Prior to testing all samples were coated with an
extremely thin layer of Palladium/Gold metal for the purpose of enhancing the
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contrast between the microindented area and the rest of the flat film. The
Palladium/Gold thin film was deposited by sputtering in the vacuum chamber of
a
Denton Vacuum Model Desk II Cold Sputter/Etch Unit (manufactured by Denton
Vacuum, Moorestown, NJ) under the following operating conditions: 50 mTorr
vacuum pressure, 30-40 milliamps sputtering current, and 45 seconds sputtering
time. In all cases the thickness of the sputter-deposited Palladium/Gold film
was
found to be in the range 20-30 nanometer and therefore of negligible effect on
the
indentation hardness of the underlying sample.
Test Procedure 3 - Pencil Hardness:
1o This test was run according to ASTM D3363-92a (Standard Test Method
for Film Hardness by Pencil Test). This test method covers a procedure for
rapid
determination of the film hardness of an organic coating on a substrate in
terms of
drawing leads or pencils leads of known hardness. In this test method all test
samples were placed on a 1/8 inch (0.3 cm) horizontal glass sheet and the
carefully
planarized tip (see section 6.1 ) of a lead pencil of specified hardness held
firmly
against the film at 45 angle and pushed away from the operator in a 1/4-inch
(6.5
mm) stroke. The process is started with the hardest pencil and continued down
the
scale of hardness to the pencil that will not cut into or gouge the film. Uni
Hardness Pencils (manufactured by Mitsubishi, Japan) were used throughout this
test.
Test Procedure 4 - Determination of the Outical Clarity:
The relative optical clarity of all samples in the following examples were
determined by measuring their haze according to the procedure of ASTM Standard
D-1003-95 "Standard Test Method for Haze and Luminous Transmittance of
Transparent Plastics," wherein the method recommended in paragraph X2
"Alternative Haze (Short-cut) Procedure" was followed. In this short-cut
procedure
the observed haze of a sample (that is, the percent of transmitted light that
is
scattered so that its direction deviates more than a specified angle from the
direction of the incident beam) was determined at 23°C using a Pacific
Instruments
3o Model XL211 Hazemeter (Gardner Neotec Instrument Division, Silver Springs,
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MD) equipped with an integrating sphere. The lower the percent haze value, the
higher the optical clarity of the sample under consideration.
Preparation of cer~mer composition (A):
In a round-bottomed flask were mixed 1195 grams (g) of NALCO 2327
s silica sol (an ammonium ion-stabilized dispersion (40% solids) of colloidal
silica
particles having a pH of 9.3 and average particle diameter of 20 nanometers,
available from Nalco Chemical Co., Chicago, 1L), 118 g of N,N-dimethyl
acrylamide (Aldrich Chemical Company, Inc.), 120 g of 3-
(trimethoxysilyl)propyl
methacrylate coupling agent (Aldrich Chemical Company, Inc.) and 761 g of
to pentaerythritol triacrylate (Aldrich Chemical Company, Inc.).
The round-bottomed flask was then mounted on the vacuum line of a Buchi
8152 Rotavapor (Buchi Laboratory AG, Flanil, Switzerland) with the bath
temperature set at SSoC. A refrigerated mixture of 50% deionized water/50%
antifreeze (Texaco) recirculated through the cooling coils. Volatile
components
15 were removed at a reduced pressure of 25 mm Hg until the distillation rate
was
reduced to less than 5 drops per minute (approximately 2 hours). The resulting
material (1464 g) was a clear liquid dispersion of acrylated silica particles
in a
mixture of N,N-dimethyl acrylamide and pentaerythritol acrylate monomers (a
ceramer). The refractive index of this dispersion was 1.5024.
2o Preuaration of ceramer composition (B):
In a glass round-bottom flask were mixed 67.15 g of NALCO 1042 silica
sol (an acidic silica sol (34% solids) having a pH = 2.8 and average particle
diameter of 20 nanometers, available from Nalco. Chemical Co., Chicago, IL),
11.2
g of 2-hydroxyethyl acrylate, 5.6 g of 3-{trimethoxysilyl)propyl methacrylate
25 coupling agent, and 7.9 g of pentaerythritol triacrylate. Water was
extracted using a
Buchi 121 Rotavapor exactly as in preparation (A). The resulting anhydrous
dispersion was crystal clear and almost water-thin.
Preparation of ceramer comDOSition (C):
In a 500 ml round bottom flask were mixed 100 g of NALCO 1042 silica
30 sol (34% solids, pH 3.2, mean particle size 20 nanometer), 2 g of glacial
acetic
acid catalyst, and 21 g of methyl triethoxysilane (Aldrich Chemical Company,
Inc.)
and 65 g of reagent grade ethanol. This mixture was stirred vigorously at room
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temperature for 24 hours, ai~er which the round bottom flask was attached to a
rotovap and the water/alcohol mixture evaporated at 42°C using a Buchi
121
Rotavapor. The viscous, clear, residue in the round bottom flask was then
completely redispersed in 65 g of ethanol to give a clear suspension.
Preparation of ceramer comuosition lD):
In a 500 ml round bottom flask were mixed 100 g of NALCO 1042 silica
sol, 3 g of glacial acetic acid and 35 g of Nyacol 50/20 zirconia sol (20%
Zr02
solids, nitrate stabilized, obtained from Nyacol Corporation, Philadelphia,
PA). To
this mixed oxide suspension were added dropwise and with vigorous mixing 25 g
to of phenyl triethoxysilane (Aldrich Chemical Company, Inc.) dissolved in 65
g of
ethanol. After mixing for 2 hours at room temperature, the round bottom flask
was
attached to the rotoevaporator and the water ethanol diluent removed under
vacuum at 35°C. The viscous residue in the round bottom flask was then
redispersed in 85 g of ethanol to give a stable, bluish-tint suspension.
~ 5 Preuaration of ceramer comuosition (El:
Ceramer composition (E) is obtained in exactly the same manner as
ceramer composition (B) except that no 3-(trimethoxysilyl)propyl methacrylate
coupling agent was used.
Comuarative Example A
20 The hardness and optical properties of the substrate, as described above,
were determined as follows:
A - Indentation hardness: a 25 mm x 75 mm sample of a substrate (a polyester
film having a thickness of about 4-7 mils (0.10-0.18 mm) which included an
acrylate-based primer layer commercially available under the trade designation
ICI
25 617 or ICI SOSP, from Imperial Chemical Industries, Hopewell, VA) was
attached
by means of two thin segments of 3M Scotch Double Stick Tape to a 25 x 75 x 2
mm glass microscope slide (VWR Scientific) in such a way that at least 95% of
the
polyester film rested in direct contact with the hard glass surface. The
microscope
glass was then placed in the vacuum chamber of a Denton Vacuum Model Desk II
3o Cold Sputter/Etch Unit (Demon Vacuum, Moorestown, NJ 08057) and the
polyester side coated with a thin layer of Palladium/Gold according to Test
Procedure 2. I~.noop hardness at ambient conditions (27% relative humidity,
23°C)
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was measured according to Test Procedure 2. The observed average indentation
hardness over 3 successive determinations was 19.1 ICHN. This result is
reported in
Table I.
B - Pencil hardness: Samples of the substrate were placed on 1/8 inch {0.3 cm)
thick glass plate and their pencil hardness measured as in Test Procedure 3.
As
reported in Table 1, the average pencil hardness of the polyester film was
found to
be 2H.
C - Optical clarity: Sheets of uncoated substrate were subjected to Test
Procedures 4 above. As seen in Table 1, the percent haze of these film samples
to was found to be 0.6, indicating excellent optical clarity.
Comparative Example B
A thin film of TTO having a thickness of 130 nanometer was vacuum
deposited on the substrate, as described above, using a DC magnetron
sputtering
apparatus equipped with a 90/10% In2O3/Sn02 target. Throughout the deposition
process the vacuum pressure was held at 8.0 mTorr with an oxygen gas flow of
1.6
SCCM (standard cubic centimeter per minute) and an argon gas flow of 30 SCCM.
The apparatus was operated at a power setting of 285 watts, a voltage of 349
volts
and a current of 0.8 amperes. The polyester substrate was supported on a
coating
web moving at a constant speed of 4 inches per minute (10.2 cm/minute).
Samples of the ITO-coated substrate were conditioned for 24 hours at the
ambient environment (53% relative humidity and 23°C) and then subjected
to Test
Procedures 1, 2, 3, and 4 above. It is seen from Table 1 that the sputter-
deposited
ITO thin film did not adhere to the underlying polyester substrate as it
completely
failed the cross-hatch adhesion test. On the other hand, the indentation
hardness,
pencil hardness and optical clarity of the ITO coated polyester were
indistinguishable from those of bare polyester observed in Comparative Example
A.
Example 1
An improved substrate obtained by overcoating the substrate, as described
3o above, with a ceramer composition was prepared as follows: 4 parts of
Ceramer
composition (A) were added to 21 parts isopropanol and 0.14 part of IRGACURE
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184 photoinitiator to form a 16 wt.% clear, crosslinkable ceramer dispersion
in
isopropanol. This 16 wt.% dispersion was coated onto polyester substrate (as
described in Comparative Example A) using a #21 wire-bound coating bar
(available from RD Specialties, Rochester, NY). Immediately after coating, the
coated sheets were placed in a forced air convection oven for 2.5 minutes at
67°C
to flash off the isopropanol. Next, the coated sheets were placed onto the
conveyor
belt of a UV Curing Station {Model MC-6RQN, Fusion W curing Inc., Rockville,
MD) equipped with a Fusion "H" lamp, and running at a belt speed of 30
feet/minute (9 meters/minute). The resulting cured coatings on the substrate
were
perfectly clear to the eye. They were about 3.0-3.5 microns thick. The average
percent haze of the coated sheets, measured according to Test Procedure 4 was
0.7%.
Samples of the cured coating were additionally subjected to Test
Procedures 2 and 3. It is seen from Table 1 that the Knoop hardness of the
ceramer
is at least twice the value for bare polyester observed in Comparative Example
A.
Similarly, the pencil hardness of the ceramer is five fold higher than that of
the
bare polyester of Comparative Example A.
Example 2
Sheet samples {7.5 cm x 7.5 cm) of ceramer-coated substrate prepared in
2o Example 1 were introduced into the vacuum chamber of the sputter-deposition
apparatus and an ITO thin film 130 nanometer thick was deposited on the
ceramer
surface under exactly the same conditions as described in Comparative Example
B.
The resulting ITO coated samples were conditioned for 24 hours at the
ambient environment (53% relative humidity and 23°C) and then subjected
to Test
Procedures 1, 2, 3, and 4 above. It is seen from Table 1 that the sputter-
deposited
ITO thin film exhibited 100 percent cross-hatch adhesion to the ceramer coated
polyester, unlike the case of the ITO film deposited directly on polyester in
Example 2. Moreover, it is seen from Table 1 that both the Knoop indentation
hardness and pencil hardness are several folds higher than those of Example 2,
indicating that the ceramer interlayer derived from composition (A) between
the
polyester film substrate and the Tf0 thin film has a profound effect on the
durability of the sputter-deposited metal oxide thin film.
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Comparative Examune C
The hardness and optical properties of a typical acrylic substrate used as the
organic substrate in antireflective film constructions were determined as
follows:
A - Indentation hardness: Square samples of 3 mm thick unprimed acrylic
substrates (commercially available under the trade designation ACRYLITE, from
Cyro Industries, Woodcliff Lake, NJ) were coated with Palladium/Gold and their
Knoop indentation hardness determined as in Test Procedure 2. The average
Knoop hardness observed over three samples was found to be 19.0 as shown in
Table 1.
1o B - Pencil hardness: Samples of the above acrylic sheets were tested for
their
pencil hardness according to Test Procedure 3. As reported in Table 1, the
average
pencil hardness of the acrylic sheets was found to be 1H.
C - Optical clarity: Samples of the above acrylic sheets were subjected to
Test
Procedure 4 above. As seen in Table 1, the percent haze of these sheets was
found
to be 0.6, indicating excellent optical clarity.
Comparative Examine D
A thin film of ITO having a thickness of 130 nanometer was vacuum
deposited on the acrylic sheets of Comparative Example C using exactly the
same
conditions as in Comparative Example B.
2o Samples of the ITO-coated acrylic sheets were conditioned for 24 hours at
the ambient environment and then subjected to Test Procedures 1,2,3 and 4
above.
The results are reported in Table 1. It is seen from the Table that the
sputter-
deposited ITO thin film exhibited 0% adhesion to the acrylic substrate. The
Knoop
indentation hardness, pencil hardness and optical clarity of the ITO coated
acrylic
were indistinguishable from those of the bare polyester sheets in Comparative
Example A.
Examone 3
Sheets of unprimed acrylic from Comparative Example C (ACRYLITE,
obtained from Cyro Industries, Woodcliff Lake, NJ) were overcoated with a
ceramer coating prepared and cured exactly as in Example 1. The surface and
optical properties of the ceramer coated acrylic sheets were then determined
according to Test Procedures 2, 3, and 4. The results are reported in Table 1.
It is
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seen from this Table that the Knoop indentation hardness of the ceramer coated
acrylic (50) is more than twice as high as the ICnoop hardness of the bare
acrylic
substrate (19.0) of Example 5. Moreover, the pencil hardness of the ceramer
coated
acrylic is five fold greater than the pencil hardness of the bare acrylic of
Comparative Example C, while the optical clarity for both the ceramer coated
acrylic and the bare acrylic sheets are virtually identical.
Example 4
Square samples (7.5 cm x 7.5 cm) of ceramer-coated acrylic sheets prepared
in Example 3 were introduced into the vacuum chamber of the sputter-deposition
1o apparatus and an ITO thin film, 130 manometer thick, was deposited on the
ceramer
surface under exactly the same conditions as described in Comparative Example
B.
Samples of the ITO-coated acrylic substrate were conditioned for 24 hours
at the ambient environment (53% relative humidity and 23°C} and then
subjected
to Test Procedures 1, 2, 3, and 4 above. It is seen from Table 1 that the
sputter-
deposited ITO thin film exhibited 100 percent cross-hatch adhesion to the
ceramer
coated acrylic, unlike the case of the ITO film deposited directly on acrylic
in
Comparative Example D. Moreover, it is seen from Table 1 that both the Knoop
indentation hardness and pencil hardness are several folds higher than those
of
Comparative Example D, indicating that the ceramer interlayer between the
acrylic
2o film substrate and the ITO thin film has a profound effect on the
durability of the
sputter-deposited metal oxide thin film.
Comuarative Example E
Comparative Example A was repeated, except that instead of a polyester
film a polycarbonate film (175 microns thick, obtained from Tekra Corporation,
New Berlin, WI) was used as the organic substrate. The observed Knoop hardness
of this polycarbonate was 17.1. Its pencil hardness was 1H and its percent
haze was
0.9.
Comparative Examine F
A thin film of ITO having a thickness of 130 manometer was vacuum
3o deposited on the polycarbonate film of Comparative Example E using exactly
the
same procedure as in Comparative Example B.
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Samples of the TTO-coated polycarbonate film were conditioned for 24
hours at the ambient environment and then subjected to Test Procedures l, 2,
3,
and 4 above. It was found that the sputter-deposited ITO thin film did not
adhere to
the underlying polycarbonate substrate as it completely failed the cross-hatch
adhesion test (see Table 1). The Knoop indentation hardness, pencil hardness
and
optical clarity of the ITO coated polycarbonate were indistinguishable from
those
of bare polycarbonate observed in Comparative Example E.
Examule 5
An improved substrate obtained by overcoating the polycarbonate substrate
I o of Comparative Example E with a ceramer coating was prepared as follows: 4
parts
of Ceramer composition (A) were added to 21 parts isopropanol and 0.14 part of
IRGACURE 184 photoinitiator to form a 16 wt.% clear, crosslinkable ceramer
dispersion in isopropanol. This 16 wt.% dispersion was coated, dried and cured
onto samples of the polycarbonate film of Comparative Example E in exactly the
IS same manner described in Example 1. The resulting cured coatings on the
polycarbonate substrate were perfectly clear to the eye. The average percent
haze of
the coated sheets, measured according to Test Procedure 4 was 1.1, indicating
excellent optical clarity.
The face of the polycarbonate film bearing the cured ceramer coating was
2o additionally subjected to Test Procedures 2 and 3. It is seen from Table 1
that the
Knoop hardness of the ceramer is more than twice the value for bare
polycarbonate
observed in Comparative Example E. Similarly, the pencil hardness of the
ceramer
is five fold higher than that of the bare polycarbonate of Comparative Example
E.
Examule 6
2S A thin film of TTO having a thickness of 130 nanometer was vacuum
deposited on the polycarbonate film of Example S using exactly the same
procedure as in Comparative Example B.
Samples of the ITO-coated polycarbonate film were conditioned for 24
hours at the ambient environment (S3% relative humidity and 23°C) and
then
30 subjected to Test Procedures 1, 2, 3, and 4 above. The results, displayed
in Table 1,
indicate that the sputter-deposited ITO thin film exhibited 100 percent cross-
hatch
adhesion to the ceramer coated polycarbonate, unlike the case of the ITO film
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WO 99/38034 PCT/US98/11135
deposited directly onto polycarbonate as in Comparative Example F. Moreover,
it
is seen from Table 1 that both the ICnoop indentation hardness and pencil
hardness
are several folds higher than those of Comparative Example F, indicating that
the
ceramer interlayer between the polycarbonate film substrate and the ITO thin
film
has a profound effect on the durability of the sputter-deposited metal oxide
thin
film.
Examule 7
An improved substrate obtained by overcoating the polyester film of
Comparative Example A with a ceramer coating was prepared as follows: 4 g of
to Ceramer composition (B) were added to 21 g of isopropyl alcohol and 0.14 g
of
IRGACURE 184 photoinitiator to give a 16 wt.% dispersion in the solvent. This
16 wt.% dispersion was coated on the polyester substrate of Comparative
Example
A and subsequently cured in exactly the same fashion as in Example 1. The
resulting cured coating on the polyester sheets was optically clear to the
naked eye.
The average percent haze of the coated sheets was 0.7.
Samples of the cured coating were additionally subjected to Test
Procedures 2 and 3. It is seen from Table 1 that the Knoop hardness of the
ceramer
is at least twice the value for bare polyester observed in Comparative Example
A.
Similarly, the pencil hardness of the ceramer is five fold higher than that of
the
2o bare polyester of Comparative Example A.
Examine 8
Sheet samples (7.5 cm x 7.5 cm) of ceramer-coated polyester film prepared
in Example 7 were introduced into the vacuum chamber of the sputter-deposition
apparatus and an ITO thin film 130 nanometer thick was deposited on the
ceramer
surface under exactly the same conditions as described in Comparative Example
B.
The resulting ITO coated samples were conditioned at the ambient environment
for
at least 24 hours and then subjected to Test Procedures 1, 2, 3, and 4. The
sputter-
deposited ITO thin film exhibited 100 percent cross-hatch adhesion to the
ceramer
coated polyester, unlike the case of the ITO film deposited directly onto
polyester
3o in Comparative Example B. Furthermore, it is seen from Table 1 that both
the
Knoop indentation hardness and pencil hardness are several folds higher than
those
of Comparative Example B, indicating that the ceramer interlayer derived from
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composition (B) between the polyester film substrate and the ITO thin film has
a
profound effect on the durability of the sputter-deposited metal oxide thin
film.
Comparative Example G
This example evaluates a crosslinked organic polymer filled with colloidal
silica powder (fumed silica) that has been surface treated with a coupling
agent.
A mixture containing 50 parts fumed silica powder (AEROSIL 8972,
available from DeGussa Corp., Teterboro, NJ), 2.5 parts 3-
(trimethoxysilyl)propyl
methacrylate coupling agent (Aldrich Chemical Company, Inc., Milwaukee, WIJ,
7.5 parts deionized water and 50 parts pentaerythritol triacrylate was
homogenized
in a high shear mixer for 30 minutes. Four grams of this homogenized
composition
were added to 21 g of isopropyl alcohol and 0.14 g of IRGACURE 184
photoinitiator to give a 16 wt.% dispersion in the water/alcohol mixture. This
16
wt.% dispersion was coated on the polyester substrate of Comparative Example A
and subsequently cured in exactly the same fashion as in Example 1. The
resulting
cured coating. on the polyester sheets was not optically clear. The average
percent
haze of the coated sheets was 40, rendering this coating unsuitable as a
substrate
for antireflective constructions.
Example 9
An improved antireflective construction using a ceramer coating derived
from composition (C) was obtained as follows: In a first step, square samples
of
acrylic sheets as in Comparative Example C were flow-coated with ceramer
composition (C) using a disposable polyethylene syringe fitted with a Gelman
Acrodisc disposable filter (0.45 micron nominal porosity). The coated sheets
were
left at room temperature for 12 minutes and then baked at 95°C for 2
hours to
effectuate cure of the ceramer coating. The resulting coat was crystal clear.
In a second step, a thin film of ITO having a thickness of 130 nanometers
was vacuum deposited on the ceramer coated acrylic sheets using exactly the
same
conditions as in Comparative Example B. Samples of the ITO-coated acrylic were
conditioned for 24 hours at the ambient environment (53% relative humidity and
23°C) and then subjected to Test Procedures 1, 2, 3, and.4 above.
It is seen from Table 1 that the sputter-deposited ITO thin film exhibited
100 percent cross-hatch adhesion to the ceramer coated acrylic, unlike the
case of
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the TTO film deposited directly on acrylic in Comparative Example D. Moreover,
it is seen from Table 1 that both the Knoop hardness and pencil hardness are
several folds higher than those of Comparative Example D, indicating that the
ceramer interlayer between the acrylic substrate and the ITO thin film has a
profound effect on the durability of the sputter-deposited metal oxide thin
film.
Examule 10
An improved antireflective construction using a ceramer hardcoat derived
from composition (D) was obtained as follows: The two-step procedure in
Example 9 was repeated except that in the first step the acrylic sheets were
coated
to with composition (D) instead of composition (C). Here again, it is seen
from Table
1 that the sputter-deposited TTO thin f lm exhibited 100 percent cross-hatch
adhesion to the ceramer coated acrylic, unlike the case of the ITO film
deposited
directly on acrylic in Comparative Example D. Moreover, it is seen from Table
1
that both the Knoop hardness and pencil hardness are several folds higher than
those of Comparative Example D, indicating that the ceramer interlayer
containing
both Si02 and Zr02 between the acrylic substrate and the ITO thin film
enhances
by several folds the scratch resistance and overall durability of the sputter-
deposited metal oxide thin film.
Example 11
2o An improved substrate obtained by overcoating the polyester film of
Comparative Example A with a ceramer coating was prepared as follows: 4 g of
Ceramer composition (E) were added to 21 g of isopropyl alcohol and 0.14 g of
IRGACURE 184 photoinitiator to give a 16 wt.% dispersion in the solvent. This
16 wt.% dispersion was coated on the polyester substrate of Comparative
Example
A and subsequently cured in exactly the same fashion as in Example 1. The
resulting cured coating on the polyester sheets was optically clear to the
naked eye.
The average percent haze of the coated sheets was 0.7.
Samples of the cured coating were additionally subjected to Test
Procedures 2 and 3. It is seen from Table 1 that the Knoop hardness of the
ceramer
is at least twice the value for bare polyester observed in. Comparative
Example A.
Similarly, the pencil hardness of the ceramer is five fold higher than that of
the
bare polyester of Comparative Example A.
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Example 12
Sheet samples ( 7.5 cm x 7.5 cm) of ceramer-coated polyester film prepared
in Example 11 were introduced into the vacuum chamber of the sputter-
deposition
apparatus and an ITO thin film 130 nanometer thick was deposited on the
ceramer
surface under exactly the same conditions as described in Comparative Example
B.
The resulting ITO coated samples were conditioned at the ambient environment
for
at least 24 hours and then subjected to Test Procedures 1, 2, 3, and 4. The
sputter-
deposited ITO thin film exhibited 100 percent cross-hatch adhesion to the
ceramer
coated polyester, unlike the case of the ITO film deposited directly onto
polyester
to in Comparative Example B. Furthermore, it is seen from Table 1 that both
the
Knoop indentation hardness and pencil hardness are several folds higher than
those
of Comparative Example B, indicating that the ceramer interlayer derived from
composition (E) between the polyester film substrate and the ITO thin film has
a
profound effect on the durability of the sputter-deposited metal oxide thin
film.
Table 1
Example Dry Knoop Pencil Optical
Adhesio Hardness Hardness Clarity
n x~tv
Comp. Ex. - 19.1 1 H 0.6
A
Comp. Ex. OB 19.1 1 H 0.6
B
1 49.9 SH 0.7
2 SB 49.9 SH 0.7
Comp. Ex. - 19 1 H 0.5
C
Comp. Ex. OB 19 1H 0.5
D
3 - 50.0 SH 0.5
4 5B 50.0 SH 0.5
Comp. Ex. - 17.1 1H 0.9
E
Comp. Ex. OB 17.1 1H 0.9
F
- 50.1 SH 1.1
6 SB 50.1 5H 0.9
7 44.4 SH 0.7
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WO 99/38034 PCT/US98/11135
Example Dry Knoop Pencil Optical
Adhesio Hardness Hardness Clarity
n xiilv
8 SB 44.6 SH 0.7
Comp. Ex. - - - 40
G
9 SB 41 SH 0.6
SB 45 SH 0.9
11 - 45 SH 0.7
12 SB 45 5H 0.8
The foregoing detailed description and examples have been given for clarity
of understanding only. No unnecessary limitations are to be understood
therefrom.
5 The invention is not limited to the exact details shown and described, for
variations obvious to one skilled in the art will be included within the
invention
defined by the claims.
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