U.S. patent application number 11/965394 was filed with the patent office on 2009-07-02 for carbon nanotube-based curable coating composition providing antistatic abrasion-resistant coated articles.
This patent application is currently assigned to Essilor International (Compagnie Generale d'Optique). Invention is credited to Haipeng Zheng.
Application Number | 20090169870 11/965394 |
Document ID | / |
Family ID | 40612799 |
Filed Date | 2009-07-02 |
United States Patent
Application |
20090169870 |
Kind Code |
A1 |
Zheng; Haipeng |
July 2, 2009 |
Carbon Nanotube-Based Curable Coating Composition Providing
Antistatic Abrasion-Resistant Coated Articles
Abstract
The present invention relates to a curable composition,
providing, upon curing, an abrasion-resistant, transparent,
antistatic coating, comprising carbon nanotubes and a binder
comprising at least one epoxysilane compound, preferably an
epoxyalkoxysilane, and optionally fillers such as nanoparticles of
non electrically conductive oxides and/or additional binder
components such as tetraethoxysilane. The invention further relates
to optical articles comprising a substrate, and, starting from the
substrate, an abrasion- and/or scratch-resistant coating, and an
antistatic coating formed by depositing directly onto said
abrasion- and/or scratch-resistant coating the above referred
curable composition. The obtained optical articles exhibit
antistatic properties, high optical transparency with about 91-92%
of transmittance, low haze and improved abrasion resistance.
Inventors: |
Zheng; Haipeng; (St.
Petersburg, FL) |
Correspondence
Address: |
FULBRIGHT & JAWORSKI L.L.P.
600 CONGRESS AVE., SUITE 2400
AUSTIN
TX
78701
US
|
Assignee: |
Essilor International (Compagnie
Generale d'Optique)
Charenton-Le-Pont
FR
|
Family ID: |
40612799 |
Appl. No.: |
11/965394 |
Filed: |
December 27, 2007 |
Current U.S.
Class: |
428/332 ;
106/287.14; 264/1.7; 428/446; 977/742 |
Current CPC
Class: |
C03C 2217/78 20130101;
C03C 2217/475 20130101; C09D 7/70 20180101; C03C 17/007 20130101;
G02B 1/14 20150115; Y10T 428/24975 20150115; C03C 17/008 20130101;
C09D 5/00 20130101; C09D 7/61 20180101; Y10T 428/26 20150115; C08K
3/041 20170501; G02B 1/105 20130101; G02B 1/16 20150115 |
Class at
Publication: |
428/332 ;
428/446; 264/1.7; 106/287.14; 977/742 |
International
Class: |
G02B 1/00 20060101
G02B001/00; B29D 11/00 20060101 B29D011/00; G02B 1/10 20060101
G02B001/10; C09D 5/00 20060101 C09D005/00; G02B 1/04 20060101
G02B001/04 |
Claims
1-21. (canceled)
22. A curable composition, providing, upon curing, an
abrasion-resistant, transparent, low haze, antistatic coating,
comprising: a) carbon nanotubes, and b) a binder comprising at
least one compound of formula: R.sub.n'Y.sub.mSi(X).sub.4-n'-m (I)
or a hydrolyzate thereof, in which the R groups are identical or
different and represent monovalent organic groups linked to the
silicon atom through a carbon atom, the Y groups are identical or
different and represent monovalent organic groups linked to the
silicon atom through a carbon atom and containing at least one
epoxy function, the X groups are identical or different and
represent hydrolyzable groups or hydrogen atoms, m and n' are
integers such that m is equal to 1 or 2 and n'+m=1 or 2.
23. The curable composition of claim 22, wherein the Y groups are
independently groups of formulae III and/or IV: ##STR00003## in
which R.sup.2 is an alkyl group or a hydrogen atom, a and c are
integers ranging from 1 to 6, and b is 0, 1, or 2.
24. The curable composition of claim 22, wherein the compound of
formula I is an epoxytrialkoxysilane of formula V or VI:
##STR00004## in which R.sup.1 is an alkyl group having 1 to 6
carbon atoms, a and c are integers ranging from 1 to 6, and b is 0,
1 or 2.
25. The curable composition of claim 22, wherein the binder further
comprises at least one compound of formula: R.sub.nSi(Z).sub.4-n
(II) or a hydrolyzate thereof, in which the R groups are identical
or different and represent monovalent alkyl groups, the Z groups
are identical or different and represent hydrolyzable groups or
hydrogen atoms, and n is an integer equal to 0, 1, or 2.
26. The curable composition of claim 22, further comprising a
filler.
27. The curable composition of claim 26, wherein the filler
comprises nanoparticles.
28. The curable composition of claim 27, wherein the nanoparticles
have a diameter ranging from 2 to 100 nm.
29. The curable composition of claim 28, wherein the nanoparticles
have a diameter ranging from 5 to 50 nm.
30. The curable composition of claim 27, wherein the nanoparticles
comprise at least one of Al.sub.2O.sub.3, TiO.sub.2, SiO.sub.2,
ZrO.sub.2, Sb.sub.2O.sub.5, Ta.sub.2O.sub.5, SnO.sub.2, zinc oxide,
indium Si.sub.3N.sub.4, and/or MgF.sub.2.
31. The curable composition of claim 26, wherein the ratio of
(theoretical dry extract weight of fillers)/(theoretical dry
extract weight of the composition) is from 25 to 80%.
32. The curable composition of claim 22, wherein the ratio of
(theoretical dry extract weight of compound of formula
I)/(theoretical dry extract weight of the composition) is from 20
to 100%.
33. The curable composition of claim 22, wherein the ratio of
(theoretical dry extract weight of compound of formula
II)/(theoretical dry extract weight of the composition) is from 15
to 60%.
34. The curable composition of claim 22, wherein the ratio of
(weight of carbon nanotubes)/(theoretical dry extract weight of
binder) is from 0.00025 to 0.01.
35. The curable composition of claim 22, wherein the carbon
nanotubes are present in an amount ranging from 0.002 to 0.015%
based on the total weight of the composition.
36. The curable composition of claim 22, wherein the composition
comprises less than 1% by weight electrically conductive fillers
based on the total weight of the composition.
37. The curable composition of claim 36, wherein the composition
comprises 0% by weight electrically conductive fillers based on the
total weight of the composition.
38. An optical article comprising a substrate, and, starting from
the substrate: an abrasion- and/or scratch-resistant coating; and
an antistatic coating formed by depositing directly onto said
abrasion- and/or scratch-resistant coating a curable composition of
claim 22.
39. The optical article of claim 38, wherein the thickness of the
antistatic coating is from 50 nm to 2 .mu.m.
40. The optical article of claim 38, wherein the abrasion- and/or
scratch-resistant coating is a (meth)acrylate based coating or
silicon-containing coating.
41. The optical article of claim 38, wherein the abrasion- and/or
scratch-resistant coating has a thickness of at least 1 .mu.m.
42. The optical article of claim 38, further defined as a lens or
lens blank.
43. The optical article of claim 38, further defined as having a
charge decay time .ltoreq.500 milliseconds.
44. The optical article of claim 38, further defined as having a
relative light transmission factor in the visible spectrum Tv
higher than 90%.
45. A process for preparing the optical article of claim 38,
comprising: providing an optical article comprising a substrate;
applying onto the surface of the substrate an abrasion- and/or
scratch-resistant coating; depositing directly onto said abrasion-
and/or scratch-resistant coating a curable composition of claim 22;
and curing said composition.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to curable compositions for
preparing transparent antistatic abrasion-resistant coatings,
articles exhibiting antistatic and abrasion-resistance properties
coated therewith, in particular optical and ophthalmic lenses for
eyeglasses, and a process to prepare such articles.
[0003] 2. Description of Related Art
[0004] It is well known that optical articles, which are
essentially composed of insulating materials, have a tendency to
get charged with static electricity, especially when they are
cleaned in dry conditions by rubbing their surface with a cloth or
synthetic piece, for example a polyester piece (triboelectricity).
The charges which are present at the surface of said optical
articles create an electrostatic field capable of attracting and
fixing, as long as the charge remains on optical articles, objects
lying in the vicinity thereof (a few centimeters) that have a very
little weight, generally small size particles such as dusts.
[0005] In order to decrease or suppress attraction of the
particles, it is necessary to decrease the intensity of the
electrostatic field, i.e. to decrease the number of static charges
which are present at the surface of the article. This may be
carried out by imparting mobility to the charges, for instance by
introducing in the optical article a layer of a material inducing a
high mobility of the charges. Materials inducing the highest
mobility are conductive materials. Thus, a material having a high
conductivity allows dissipating more rapidly charges.
[0006] It is known in the art that an optical article acquires
antistatic (AS) properties owing to the incorporation at the
surface thereof, in the stack of functional coatings, of at least
one electrically conductive layer, which is called an antistatic
layer. The presence of such a layer in the stack imparts to the
article AS properties, even if the AS coating is interleaved
between two coatings or two substrates which are not
antistatic.
[0007] By "antistatic," it is meant the property of not retaining
and/or developing an appreciable electrostatic charge. An article
is generally considered to have acceptable antistatic properties
when it does not attract or fix dust or small particles after one
of its surfaces has been rubbed with an appropriate cloth. It is
capable of quickly dissipating accumulated electrostatic
charges.
[0008] The ability of a glass to evacuate a static charge created
by rubbing with a cloth or any other electrostatic charge
generation process (charge applied by corona . . . ) can be
quantified by measuring the time required for said charge to be
dissipated (charge decay time). Thus, antistatic glasses have a
discharge time in the order of 100-200 milliseconds, while static
glasses have a discharge time in the order of several tens seconds,
sometimes even several minutes. A static glass having just been
rubbed can thus attract surrounding dusts as long as it requires
time to get discharged.
[0009] Only a limited number of materials are known in the art for
preparing electrically conductive inorganic or organic layers
having high optical transparency, i.e. a transmittance in the
visible light of at least 90%. Known optically transparent
antistatic coatings include vacuum-deposited metal or metal oxide
films, for example films based on optionally doped
(semi-)conductive metal oxides such as tin oxide doped with indium
(ITO), tin oxide doped with antimony (ATO) or vanadium pentoxyde,
spin-coated or self-assembled conductive polymer films, spin-coated
or extruded carbon nanotube-based composite films.
[0010] ITO is the industry standard antistatic agent to provide
optically transparent electrically conductive thin coatings, but
the performance of ITO suffers when it is applied to plastics.
These coatings are fragile and are readily damaged during bending
or other stress inducing conditions. Conductive polymers represent
the most investigated alternative to ITO coatings, but they still
cannot match the optical and electrical performances of ITO and
sometimes suffer from thermal and environmental stability problems
in specific applications.
[0011] Currently, nanocomposites obtained by dispersing carbon
nanotubes (CNT) into polymer matrices have brought many promising
electrical and mechanical characters in various applications.
However, they are still in their infancy and raise a lot of
challenges, such as low loading percentage in polymer systems.
[0012] Many antistatic polymeric carbon nanotube-based composites
have been explored, comprising polymeric resin and electrically
conductive carbon fiber/nanotube, or a combination of carbon
fiber/nanotube and non-conductive filler. The amount of the
electrically conductive filler system utilized is dependent upon
the desired electrical conductivity (surface and volume
conductivity or resistivity) while preferably preserving intrinsic
properties of the polymeric resin such as impact and flex modulus.
The polymeric CNT-based composites can be applied in
electromagnetic shielding, electrostatic dissipation or antistatic
purposes in packaging, electronic components, housings for
electronic components and automotive housings.
[0013] U.S. Pat. No. 5,908,585 discloses a glass substrate coated
with a transparent electrically conductive film obtained from a
coating composition containing, based on the total solid content,
0.1 wt % of CNT, 19.9 wt % of conductive nanoparticles of
antimony-doped tin oxide and 80 wt % (as SiO.sub.2) of hydrolyzed
tetraethoxysilane. After high temperature baking at 350.degree. C.,
the resulting coating is 200 nm-thick and has a surface resistivity
of 3.10.sup.9 .OMEGA./with an overall light transmittance of 92%
and a haze value of 1.9%. The rest of coatings show even higher
haze value than 2%. The abrasion-resistance properties were not
investigated.
[0014] U.S. patent application No. 2003/158323 discloses an
effective dispersion process of CNT into organic polymer matrices
such as polyimide or poly(methyl methacrylate) to achieve high
retention of optical transparency in the visible range. The final
transmittance and the relative optical transparency are still lower
than 90%.
[0015] U.S. patent application No. 2004/197546 discloses a process
to achieve an optically transparent and electrically conductive
CNT-based film disposed on a porous membrane through the filtration
on said membrane of a dispersion comprising single walled carbon
nanotubes and a surfactant or surface stabilizing polymer. However,
it is difficult to make such CNT-based film with good quality on
curved surfaces, which limits its application in ophthalmic lens
industry.
[0016] U.S. patent application No. 2005/209392 describes flexible
transparent carbon nanotube-based composites films obtained either
by first applying a polymer binder onto a transparent substrate,
following by a layer of CNT which penetrates into the binder, or by
first coating a CNT layer onto the substrate and then applying the
polymer binder which diffuses into the CNT network, or a
combination of both to form a sandwich structure. The polymer
binders can be thermoplastics or thermosets, including silicones,
organosilicon polymers, fluorosilicones and inorganic-organic
hybrid compounds such as heat-curable silanes, fluorosilanes and
metal alkoxides. Although the films having a layer of CNT exhibit
light transmittance of about 90-92% at the wavelength of 550 nm and
small changes in sheet resistance after having been subjected to an
abrasive treatment, the CNT layer show potential high haze after a
spray process, due to the absence of binders or surfactants in the
CNT dispersion, which is not investigated.
[0017] JP2007155802 describes a vacuum deposition process for
depositing a thin film using a water repellent composition
comprising a conductive material including CNT. The solution to be
evaporated comprises large amounts of CNT, typically around 8% by
weight. The purpose of this patent application is to apply a water
repellent antistatic film. The abrasion resistance is not a
specific purpose of the described technique.
[0018] The above-mentioned electrically conductive or antistatic
coatings have shown very promising performances, but still have
limitations with the process, their transparency, or haze values,
which prevent them from some specific applications, especially in
ophthalmic lens application. In addition, no antistatic coating has
been reported to increase abrasion resistance.
SUMMARY OF THE INVENTION
[0019] An object of the invention is to provide novel curable
coating compositions capable of imparting antistatic and abrasion
resistance properties to an article, especially a transparent and
low haze article, and overcoming the problems and disadvantages
associated with current CNT-based compositions.
[0020] Another object of the invention is to provide electrically
conductive coatings providing antistatic properties, having low
haze and excellent scratch and/or abrasion resistance at the same
time.
[0021] To achieve the foregoing objects, there is provided an
optical article comprising a substrate, and, starting from the
substrate:
[0022] an abrasion- and/or scratch-resistant coating,
[0023] an antistatic coating formed by depositing directly onto
said abrasion- and/or scratch-resistant coating a curable
composition comprising:
[0024] a) carbon nanotubes, and
[0025] b) a binder comprising at least one compound of formula:
R.sub.n'Y.sub.mSi(X).sub.4-n'-m (I)
or a hydrolyzate thereof, in which the R groups are identical or
different and represent monovalent organic groups linked to the
silicon atom through a carbon atom, the Y groups are identical or
different and represent monovalent organic groups linked to the
silicon atom through a carbon atom and containing at least one
epoxy function, the X groups are identical or different and
represent hydrolyzable groups or hydrogen atoms, m and n' are
integers such that m is equal to 1 or 2 and n'+m=1 or 2.
[0026] One embodiment of the invention is directed to a curable
composition which provides, upon curing, an abrasion-resistant,
transparent, antistatic coating, comprising:
[0027] a) carbon nanotubes, and
[0028] b) a binder comprising at least one compound of formula:
R.sub.n'Y.sub.mSi(X).sub.4-n'-m (I)
or a hydrolyzate thereof, wherein R, Y, X, m and n' are such as
described above.
[0029] In one embodiment of the invention the binder further
comprises at least one compound of formula:
R.sub.nSi(Z).sub.4-n (II)
or a hydrolyzate thereof, in which the R groups are identical or
different and represent monovalent alkyl groups, the Z groups are
identical or different and represent hydrolyzable groups or
hydrogen atoms, and n is an integer equal to 0 or 1, with the
proviso that the Z groups do not all represent a hydrogen atom when
n=0.
[0030] The antistatic coatings of the present invention can be used
in different stacks and still provide antistatic properties to an
optical article, even if other functional coatings, especially
antireflective coatings made of dielectric materials, are deposited
over said coatings.
[0031] The invention also relates to a process for preparing a
transparent antistatic optical article having improved abrasion
resistance, comprising: [0032] providing an optical article
comprising a substrate, [0033] applying onto the surface of the
substrate an abrasion- and/or scratch-resistant coating, and [0034]
depositing directly onto said abrasion- and/or scratch-resistant
coating the above described curable composition, and curing said
composition.
[0035] Other objects, features and advantages of the present
invention will become apparent from the following detailed
description. It should be understood, however, that the detailed
description and the specific examples, while indicating specific
embodiments of the invention, are given by way of illustration
only, since various changes and modifications within the spirit and
scope of the invention will become apparent to those skilled in the
art from this detailed description.
DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
[0036] The terms "comprise" (and any grammatical variation thereof,
such as "comprises" and "comprising"), "have" (and any grammatical
variation thereof, such as "has" and "having"), "contain" (and any
grammatical variation thereof, such as "contains" and
"containing"), and "include" (and any grammatical variation
thereof, such as "includes" and "including") are open-ended linking
verbs. They are used to specify the presence of stated features,
integers, steps or components or groups thereof, but do not
preclude the presence or addition of one or more other features,
integers, steps or components or groups thereof. As a result, a
method, or a step in a method, that "comprises," "has," "contains,"
or "includes" one or more steps or elements possesses those one or
more steps or elements, but is not limited to possessing only those
one or more steps or elements.
[0037] Unless otherwise indicated, all numbers or expressions
referring to quantities of ingredients, ranges, reaction
conditions, etc. used herein are to be understood as modified in
all instances by the term "about."
[0038] When an optical article comprises one or more surface
coatings, the phrase "to deposit a coating or layer onto the
optical article" means that a coating or layer is deposited onto
the outermost coating of the optical article, i.e. the coating
which is the closest to the air.
[0039] A coating that is "on" a side of a lens is defined as a
coating that (a) is positioned over that side, (b) need not be in
contact with that side, i.e., one or more intervening coatings may
be disposed between that side and said coating and (c) need not
cover that side completely.
[0040] As used herein, a coating "A" that has been deposited
"directly onto" a coating "B" means that (a) coatings "A" and "B"
are in contact with each other in the final optical article, i.e.
no intervening coating may be disposed between them; and (b)
coating "A" has been deposited using any means of depositing (such
as spin coating, dip coating, or vacuum deposition) and need not
cover coating "B" completely.
[0041] The optical article prepared according to the present
invention is a transparent optical article, preferably a lens or
lens blank, and more preferably an ophthalmic lens or lens blank.
The optical articles may be coated on their convex main side (front
side), concave main side (back side), or both sides with the stack
abrasion- and/or scratch-resistant coating/antistatic coating
according to the invention.
[0042] Herein, the term "lens" means an organic or inorganic glass
lens, comprising a lens substrate which may be coated with one or
more coatings of various natures.
[0043] The lens substrate may be made of mineral glass or organic
glass, preferably organic glass. The organic glasses can be either
thermoplastic materials such as polycarbonates and thermoplastic
polyurethanes or thermosetting (cross-linked) materials such as
diethylene glycol bis(allylcarbonate) polymers and copolymers (in
particular CR-39.RTM. from PPG Industries), thermosetting
polyurethanes, polythiourethanes, polyepoxides, polyepisulfides,
poly(meth)acrylates and copolymers based substrates, such as
substrates comprising(meth)acrylic polymers and copolymers derived
from bisphenol-A, polythio(meth)acrylates, as well as copolymers
thereof and blends thereof. Preferred materials for the lens
substrate are polycarbonates and diethylene glycol
bis(allylcarbonate) copolymers, in particular substrates made of
polycarbonate.
[0044] The optical article comprising a substrate used herein may
also be a carrier onto which the abrasion- and/or scratch-resistant
coating and the antistatic coating are stored. They can be
transferred later from the carrier onto the substrate of e.g. an
optical lens. The carrier which may be coated according to the
present process may optionally bear at least one functional
coating. Obviously, the coatings are applied on the surface of the
carrier in the reverse order with regard to the desired order of
the coating stack on the lens substrate.
[0045] The surface of the article onto which the abrasion- and/or
scratch-resistant coating will be deposited may optionally be
subjected to a pre-treatment step intended to improve adhesion, for
example a high-frequency discharge plasma treatment, a glow
discharge plasma treatment, a corona treatment, an electron beam
treatment, an ion beam treatment, an acid or base treatment.
[0046] The abrasion- and/or scratch-resistant coating according to
the invention may be deposited onto a naked substrate or onto the
outermost coating layer of the substrate if the substrate is coated
with surface coatings.
[0047] According to the invention, the optical article may comprise
a substrate coated with various coating layers, chosen from,
without limitation, an impact-resistant coating (impact resistant
primer), a polarized coating, a photochromic coating, a dyeing
coating, or several of those coatings.
[0048] The abrasion- and/or scratch-resistant coating for use in
the present invention is defined as a coating which improves the
abrasion- and/or scratch-resistance of the finished optical article
as compared to a same optical article but without the abrasion-
and/or scratch-resistant coating. According to the invention, any
known optical abrasion- and/or scratch-resistant coating
composition may be used herein.
[0049] Preferred abrasion- and/or scratch-resistant coatings are
(meth)acrylate based coatings and silicon-containing coatings.
[0050] (Meth)acrylate based coatings are typically UV-curable. The
term (meth)acrylate means either methacrylate or acrylate.
[0051] The main component of the (meth)acrylate based curable
coating composition may be chosen from monofunctional
(meth)acrylates and multifunctional (meth)acrylates such as
difunctional (meth)acrylates; trifunctional (meth)acrylates;
tetrafunctional (meth)acrylates, pentafunctional (meth)acrylates,
hexafunctional (meth)acrylates.
[0052] Examples of monomers which may be used as main components of
(meth)acrylate based coating compositions are:
[0053] monofunctional (meth)acrylates: Allyl methacrylate,
2-ethoxyethyl acrylate, 2-ethoxyethyl methacrylate, caprolactone
acrylate, isobornyl methacrylate, lauryl methacrylate,
polypropylene glycol monomethacrylate.
[0054] difunctional (meth)acrylates: 1,4-butanediol diacrylate,
1,4-butanediol dimethacrylate, 1,6-hexanediol diacrylate,
1,6-hexanediol dimethacrylate, ethoxylated bisphenol A diacrylate,
polyethylene glycol di(meth)acrylates such as polyethylene glycol
diacrylate, tetraethylene glycol diacrylate, polyethylene glycol
dimethacrylate, polyethylene glycol diacrylate, tetraethylene
glycol diacrylate, tripropylene glycol diacrylate, neopentyl glycol
diacrylate, tetraethylene glycol dimethacrylate, diethylene glycol
diacrylate.
[0055] trifunctional (meth)acrylates: Trimethylolpropane
trimethacrylate, Trimethylolpropane triacrylate, pentaerythritol
triacrylate, ethoxylated trimethylolpropane triacrylate,
trimethylolpropane trimethacrylate.
[0056] tetra to hexa(meth)acrylates: Dipentaerythritol
pentaacrylate, pentaerythritol tetraacrylate, ethoxylated
pentaerythritol tetraacrylate, pentaacrylate esters.
[0057] Silicon-containing abrasion- and/or scratch-resistant
coatings are preferably sol-gel coatings, which may be obtained by
curing a precursor composition containing silanes or hydrolyzates
thereof. The sol-gel silicon based coating compositions which may
be used are homogeneous mixtures of a solvent, a silane and/or an
organosilane, optionally a surfactant, and optionally a catalyst
which are processed to form a coating suitable for optical
application. The term "homogeneous" as used herein refers to a form
which has a uniform or similar structure throughout and is given
the ordinary meaning known to persons skilled in the art.
[0058] The preferred abrasion- and/or scratch-resistant coatings
are epoxytrialkoxysilane-based hard coatings, more preferably
.gamma.-glycidoxypropyl-trimethoxysilane-based hard coatings.
[0059] A particularly preferred curable composition for an
abrasion- and/or scratch-resistant coating comprises a surfactant,
a hydrolyzate of an epoxytrialkoxysilane and dialkyldialkoxysilane,
colloidal mineral fillers and a catalytic amount of an
aluminum-based curing catalyst, the remaining of the composition
being essentially comprised of solvents typically used for
formulating abrasion- and/or scratch-resistant compositions.
Typical ingredients which may be used in such abrasion- and/or
scratch-resistant coating composition are disclosed in French
patent application FR 2702486, which is incorporated herein by
reference. Especially preferred silicon based abrasion- and/or
scratch-resistant coating compositions are those comprising as the
main constituents a surfactant, a hydrolyzate of
.gamma.-glycidoxypropyl-trimethoxysilane (GLYMO) and
dimethyl-diethoxysilane (DMDES), colloidal silica and a catalytic
amount of aluminum acetylacetonate.
[0060] The abrasion- and/or scratch-resistant coating preferably
has a thickness of at least 1 .mu.m, more preferably at least 1.5
microns, still more preferably at least 2 microns, even better at
least 3 microns, and preferably less than 10 .mu.m, more preferably
less than 5 .mu.m.
[0061] The abrasion- and/or scratch-resistant coating is preferably
deposited onto a substrate already coated with an impact-resistant
primer coating.
[0062] The impact-resistant coating which may be used in the
present invention can be any coating typically used for improving
impact resistance of a finished optical article. This coating
generally enhances adhesion of the abrasion and/or
scratch-resistant coating on the substrate of the finished optical
article. By definition, an impact-resistant primer coating is a
coating which improves the impact resistance of the finished
optical article as compared with the same optical article but
without the impact-resistant primer coating.
[0063] Typical impact-resistance primer coatings are (meth)acrylic
based coatings and polyurethane based coatings, in particular
coatings made from a latex composition such as a poly(meth)acrylic
latex, a polyurethane latex or a polyester latex.
[0064] The inventive curable coating composition directly applied
onto the above-described abrasion- and/or scratch-resistant coating
provides, upon curing, a functional transparent coating having
antistatic properties and abrasion resistance. It will be sometimes
referred to in this patent application as the "antistatic
composition".
[0065] Said curable composition comprises CNT and a binder
comprising at least one compound of formula:
R.sub.n'Y.sub.mSi(X).sub.4-n'-m (I)
or hydrolyzates thereof, in which the R groups are identical or
different and represent monovalent organic groups linked to the
silicon atom through a carbon atom, the Y groups are identical or
different and represent monovalent organic groups linked to the
silicon atom through a carbon atom and containing at least one
epoxy function, the X groups are identical or different and
represent hydrolyzable groups or hydrogen atoms, m and n' are
integers such that m is equal to 1 or 2 and n'+m=1 or 2.
[0066] The X groups may independently and without limitation
represent H, alkoxy groups --O--R.sup.1, wherein R.sup.1 preferably
represents a linear or branched alkyl or alkoxyalkyl group,
preferably a C.sub.1-C.sub.4 alkyl group, acyloxy groups
--O--C(O)R.sup.3, wherein R.sup.3 preferably represents an alkyl
group, preferably a C.sub.1-C.sub.6 alkyl group, and more
preferably a methyl or ethyl group, halogen groups such as Cl and
Br, amino groups optionally substituted with one or two functional
groups such as an alkyl or silane group, for example the
NHSiMe.sub.3 group, alkylenoxy groups such as the isopropenoxy
group, trialkylsiloxy groups, for example the trimethylsiloxy
group.
[0067] The X groups are preferably alkoxy groups, in particular
methoxy, ethoxy, propoxy or butoxy, more preferably methoxy or
ethoxy. In this case, compounds of formula I are alkoxysilanes.
[0068] The integers n and m define three groups of compounds I:
compounds of formula RYSi(X).sub.2, compounds of formula
Y.sub.2Si(X).sub.2, and compounds of formula YSi(X).sub.3. Among
these compounds, epoxysilanes having the formula YSi(X).sub.3 are
preferred.
[0069] The monovalent R groups linked to the silicon atom through a
Si--C bond are organic groups. These groups may be, without
limitation, hydrocarbon groups, either saturated or unsaturated,
preferably C.sub.1-C.sub.10 groups and better C.sub.1-C.sub.4
groups, for example an alkyl group, preferably a C.sub.1-C.sub.4
alkyl group such as methyl or ethyl, an aminoalkyl group, an
alkenyl group, such as a vinyl group, a C.sub.6-C.sub.10 aryl
group, for example an optionally substituted phenyl group, in
particular a phenyl group substituted with one or more
C.sub.1-C.sub.4 alkyl groups, a benzyl group, a (meth)acryloxyalkyl
group, or a fluorinated or perfluorinated group corresponding to
the above cited hydrocarbon groups, for example a fluoroalkyl or
perfluoroalkyl group, or a (poly)fluoro or perfluoro
alkoxy[(poly)alkyloxy]alkyl group.
[0070] Preferably The R groups do not contain fluorine. More
preferably, compounds of formula I do not contain fluorine.
[0071] The most preferred R groups are alkyl groups, in particular
C.sub.1-C.sub.4 alkyl groups, and ideally methyl groups.
[0072] The monovalent Y groups linked to the silicon atom through a
Si--C bond are organic groups since they contain at least one epoxy
function, preferably one epoxy function. By epoxy function, it is
meant a group of atoms, in which an oxygen atom is directly linked
to two adjacent carbon atoms or non adjacent carbon atoms comprised
in a carbon containing chain or a cyclic carbon containing system.
Among epoxy functions, oxirane functions are preferred, i.e.
saturated three-membered cyclic ether groups.
[0073] Epoxysilanes compounds of formula I provide a highly
cross-linked matrix. The preferred epoxysilanes have an organic
link between the Si atom and the epoxy function that provides a
certain level of flexibility.
[0074] The preferred Y groups are groups of formulae III and
IV:
##STR00001##
in which R.sup.2 is an alkyl group, preferably a methyl group, or a
hydrogen atom, ideally a hydrogen atom, a and c are integers
ranging from 1 to 6, and b is 0, 1 or 2.
[0075] The preferred group having formula III is the
.gamma.-glycidoxypropyl group (R.sup.2.dbd.H, a=3, b=0) and the
preferred (3,4-epoxycyclohexyl)alkyl group of formula IV is the
.beta.-(3,4-epoxycyclohexyl)ethyl group (c=1). The
.gamma.-glycidoxyethoxypropyl group may also be employed
(R.sup.2.dbd.H, a=3, b=1).
[0076] Preferred epoxysilanes of formula I are epoxyalkoxysilanes,
and most preferred are those having one Y group and three alkoxy X
groups. Particularly preferred epoxytrialkoxysilanes are those of
formulae V and VI:
##STR00002##
in which R.sup.1 is an alkyl group having 1 to 6 carbon atoms,
preferably a methyl or ethyl group, and a, b and c are such as
defined above.
[0077] Examples of such epoxysilanes include but are not limited to
glycidoxy methyl trimethoxysilane, glycidoxy methyl
triethoxysilane, glycidoxy methyl tripropoxysilane,
.alpha.-glycidoxy ethyl trimethoxysilane, .alpha.-glycidoxy ethyl
triethoxysilane, .beta.-glycidoxy ethyl trimethoxysilane,
.beta.-glycidoxy ethyl triethoxysilane, .beta.-glycidoxy ethyl
tripropoxysilane, .alpha.-glycidoxy propyl trimethoxysilane,
.alpha.-glycidoxy propyl triethoxysilane, .alpha.-glycidoxy propyl
tripropoxysilane, .beta.-glycidoxy propyl trimethoxysilane,
.beta.-glycidoxy propyl triethoxysilane, .beta.-glycidoxy propyl
tripropoxysilane, .gamma.-glycidoxy propyl trimethoxysilane,
.gamma.-glycidoxy propyl triethoxysilane, .gamma.-glycidoxy propyl
tripropoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,
2-(3,4-epoxycyclohexyl)ethyltriethoxysilane. Other useful
epoxytrialkoxysilanes are described in Patents U.S. Pat. No.
4,294,950, U.S. Pat. No. 4,211,823, U.S. Pat. No. 5,015,523, EP
0614957 and WO 94/10230, which are hereby incorporated by
reference. Among those silanes,
.gamma.-glycidoxypropyltrimethoxysilane (GLYMO) is preferred.
[0078] Preferred epoxysilanes of formula I having one Y group and
two X groups include, but are not limited to, epoxydialkoxysilanes
such as .gamma.-glycidoxypropyl-methyl-dimethoxysilane,
.gamma.-glycidoxypropyl bis(trimethylsiloxy)methylsilane,
.gamma.-glycidoxypropyl-methyl-diethoxysilane,
.gamma.-glycidoxypropyl-methyl-diisopropenoxysilane, and
.gamma.-glycidoxyethoxypropyl-methyl-dimethoxysilane. When epoxy
dialkoxysilanes are used, they are preferably combined with
epoxytrialkoxysilanes such as those described above, and are
preferably employed in lower amounts than said
epoxytrialkoxysilanes.
[0079] In one embodiment of the invention, the binder of the
antistatic composition further comprises at least one compound of
formula:
R.sub.nSi(Z).sub.4-n (II)
or a hydrolyzate thereof, in which the R groups are identical or
different and represent monovalent alkyl groups, the Z groups are
identical or different and represent hydrolyzable groups or
hydrogen atoms, and n is an integer equal to 0, 1 or 2, preferably
0 or 1, with the proviso that the Z groups do not all represent a
hydrogen atom when n=0, and preferably do not all represent a
hydrogen atom.
[0080] Compounds of formula II or their hydrolyzates may be used to
improve the cross-linking of the coating obtained from the curable
composition of the invention, thereby providing higher hardness and
abrasion-resistance.
[0081] Silanes of formula II bear three to four Z groups directly
linked to the silicon atom, each leading to an OH group upon
hydrolysis and one or two monovalent organic R groups linked to the
silicon atom. It is worth noting that SiOH bonds may be initially
present in the compounds of formula II, which are considered in
this case as hydrolyzates. Hydrolyzates also encompass siloxane
salts.
[0082] The Z groups may represent hydrolyzable groups independently
chosen from the hydrolyzable groups which have been previously
cited when describing the X groups. Preferably, the Z groups are
hydrolyzable groups which are identical or different.
[0083] The most preferred R groups are C.sub.1-C.sub.4 alkyl
groups, such as methyl, ethyl, n-propyl, i-propyl, n-butyl,
i-butyl, preferably methyl groups.
[0084] Most preferred compounds of formula II are those having
formula Si(Z).sub.4. Examples of such compounds are
tetraalkoxysilanes such as tetraethoxysilane
Si(OC.sub.2H.sub.5).sub.4 (TEOS), tetramethoxysilane
Si(OCH.sub.3).sub.4 (TMOS), tetra(n-propoxy)silane,
tetra(i-propoxy)silane, tetra(n-butoxy)silane,
tetra(sec-butoxy)silane or tetra(t-butoxy)silane, preferably
TEOS.
[0085] Compounds of formula II may also be chosen from compounds of
formula RSi(Z).sub.3, for example methyl triethoxysilane
(MTEOS).
[0086] Silanes present in the curable antistatic composition may be
hydrolyzed partially or totally, preferably totally. Hydrolyzates
can be prepared in a known manner, e.g. such as disclosed in FR
2702486 and U.S. Pat. No. 4,211,823. Hydrolysis catalysts such as
hydrochloric acid or acetic acid may be used to promote the
hydrolysis reaction over the condensation reaction.
[0087] The binder, which includes compounds of formula I and II but
not fillers, is generally comprised in the antistatic coating
composition in an amount ranging from 1 to 20% by weight based on
the total weight of the antistatic composition, preferably from 2
to 15%. When the antistatic composition does not comprise fillers
such as nanoparticles, it preferably comprises from 5 to 15% of
binder by weight based on the total weight of the antistatic
composition.
[0088] Compounds of formula I are generally used in an amount
ranging from 1 to 10% by weight based on the total weight of the
antistatic composition, preferably from 2 to 8%. The ratio of
(theoretical dry extract weight of compounds of formula
1)/(theoretical dry extract weight of the composition) preferably
ranges from 20 to 100%, more preferably from 25 to 80%, even better
from 30 to 70%.
[0089] When compounds of formula II are present, they are generally
used in an amount ranging from 1 to 10% by weight based on the
total weight of the antistatic composition, preferably from 2 to
8%. When compounds of formula II are present, the ratio of
(theoretical dry extract weight of compounds of formula
II)/(theoretical dry extract weight of the composition) preferably
ranges from 15 to 60%, more preferably from 20 to 55%, even better
from 25 to 50%.
[0090] In some embodiments, the antistatic composition does not
comprise any compound of formula II. Preferably, the antistatic
composition does not comprise any compounds of formula II when
fillers are present in said composition.
[0091] In preferred embodiments, the antistatic composition does
not comprise any fluorinated compound, except usual surfactants
used in very low amounts (Typically less than 0.5% by weight in the
liquid coating composition).
[0092] Carbon nanotubes (CNT) contained in the antistatic
composition refer to tubular structures grown with a single wall or
multi-wall, which can be thought of as a rolled up sheet formed of
a plurality of hexagons, the sheet formed by combining each carbon
atom thereof with three neighboring carbon atoms. The carbon
nanotubes used in the invention have preferably a diameter on the
order of half nanometer to less than 10 nanometers. Carbon
nanotubes can function as either an electrical conductor, similar
to a metal, or a semiconductor, according to the orientation of the
hexagonal carbon atom lattice relative to the tube axis and the
diameter of the tubes. Within the scope of the present invention,
the term CNT(s) designates both single wall carbon nanotubes and
multi-wall carbon nanotubes such as double wall carbon nanotubes.
CNT are preferably single wall carbon nanotubes.
[0093] Preferably, commercially available CNT used are purified to
remove the large catalyst particles which are utilized in their
formation.
[0094] Incorporation of CNT into the present coating composition so
as to form optically transparent films which exhibit uniform
optical density across their area can be carried out according to
methods well known to those skilled in the art. Typically, CNT
dispersions are prepared by placing CNT into a solvent containing a
sufficient concentration of stabilizing agent to suspend the CNT.
The solvent is preferably a polar solvent, like water, alcohol, or
a mixture of water and alcohol. The CNT concentration in the
dispersion is preferably less than 1 weight percent (wt %) and
preferably mono-dispersed CNT coatings having high optical
transparency and low haze are achieved. The CNT dispersion is
generally mixed mechanically with a homogenizer for 10 min to 1 h,
followed by ultrasonic treatment for 10 min to 30 min. The
combination of high shear mixing and ultrasonic treatment gives
dispersions of higher quality than those obtained using a single
mixing tool. The dispersed CNT solutions are generally then
centrifuged or placed under sedimentation for over one day. CNT
agglomerates or bundles are preferably removed to get a uniform
dispersion, allowing obtaining dispersions in the range of
0.001-0.02 wt % of CNT.
[0095] The stabilizing agents which may be used to prepare CNT
dispersions are not particularly limited and can comprise a variety
of synthetic or naturally occurring surfactants include, without
limitation, sodium dodecyl sulfate (SDS), octylphenol ethylene
oxide condensates (octyl-phenoxypolyethoxyethanol compounds) such
as Nonidet P-40 (NP-40) or Triton.RTM. surfactants manufactured by
the Dow Chemical Corporation such as TRITON X-100.RTM., TRITON
X-305.RTM. or TRITON X-405.RTM., poloxamers (e.g., the
Pluronic.RTM. series of detergents and Poloxamer 188.RTM., which is
defined as
HO(C.sub.2H.sub.4O).sub.a(C.sub.3H.sub.6O).sub.b(C.sub.2H.sub.4O).sub.aH,
with the ratio of a to b being 80 to 27 and the molecular weight
being in the range of 7680 to 9510), ammonium bromides and
chlorides (e.g., cetyltrimethylammonium bromide, tetradecylammonium
bromide and dodecylpyrimidinium chloride), polyoxyethylene sorbitol
esters (e.g., TWEEN.RTM. and EMASOL.RTM. series detergents), and
naturally occurring emulsifying agents such as cyclodextrins.
[0096] Production of stable aqueous dispersions of carbon nanotubes
is described in more detail in U.S. Pat. Appl. No. 6,878,361.
[0097] In general, CNT are used in the composition in an amount
ranging from 0.002 to 0.015%, preferably from 0.004 to 0.012% by
weight based on the total weight of the antistatic composition.
Preferably, the weight ratio defined as weight of carbon
nanotubes/weight of binder ranges from 0.00025 to 0.01, more
preferably from 0.0005 to 0.008, even better from 0.0008 to 0.006,
the best ranging from 0.0008 to 0.0045.
[0098] By weight of binder, it is meant the theoretical dry extract
weight of binder in the composition.
[0099] Preferably, the ratio weight of carbon nanotubes/theoretical
dry extract weight of the antistatic composition ranges from 0.0002
to 0.008, more preferably from 0.0005 to 0.005.
[0100] By "theoretical dry extract weight of a component in a
composition," it is meant the theoretical weight of solid matter of
this component in said composition, i.e. its weight contribution to
the theoretical dry extract weight of said composition.
[0101] The theoretical dry extract weight of a composition is
defined as the sum of the theoretical dry extract weights of each
of its components. As used herein, the theoretical dry extract
weight of compounds of formula I or II is the calculated weight in
R.sub.n'Y.sub.mSi(O).sub.(4-n'-m)/2 or R.sub.nSi(O).sub.(4-n)/2
units, wherein R, Y, n, n' and m are such as defined
previously.
[0102] In some embodiments, the antistatic composition comprises
fillers, generally nanoparticles (or nanocrystals), for increasing
the hardness and/or the refractive index of the cured coating. The
nanoparticles may be organic or inorganic. A mixture of both can
also be used. Preferably, inorganic nanoparticles are used,
especially metallic or metalloid oxide, nitride or fluoride
nanoparticles, or mixtures thereof.
[0103] By "nanoparticles", it is meant particles which diameter (or
longest dimension) is lower than 1 .mu.m, preferably lower than 150
nm and still better lower than 100 nm. In the present invention,
fillers or nanoparticles preferably have a diameter ranging from 2
to 100 nm, more preferably from 2 to 50 nm, and even better from 5
to 50 nm.
[0104] Suitable inorganic nanoparticles are for example
nanoparticles of aluminum oxide Al.sub.2O.sub.3, silicon oxide
SiO.sub.2, zirconium oxide ZrO.sub.2, titanium oxide TiO.sub.2,
antimony oxide Sb.sub.2O.sub.5, tantalum oxide Ta.sub.2O.sub.5,
zinc oxide, tin oxide SnO.sub.2, indium oxide, cerium oxide,
Si.sub.3N.sub.4, MgF.sub.2 or their mixtures.
[0105] It is also possible to use particles of mixed oxides or
composite particles, for example those having a core/shell
structure. Using different types of nanoparticles allows making
hetero-structured nanoparticles layers.
[0106] Preferably, the nanoparticles are particles of aluminum
oxide, tin oxide, zirconium oxide or silicon oxide SiO.sub.2, more
preferably SiO.sub.2 nanoparticles. Mineral fillers are preferably
used under colloidal form, i.e. under the form of fine particles
dispersed in a dispersing medium such as water, an alcohol, a
ketone, an ester or mixtures thereof, preferably an alcohol.
[0107] When fillers are present, they are generally used in an
amount ranging from 0.5 to 10% by weight based on the total weight
of the antistatic composition, preferably from 1 to 8%. When
fillers are present, the ratio of (theoretical dry extract weight
of fillers)/(theoretical dry extract weight of the composition)
preferably ranges from 25 to 80%, more preferably from 30 to 75%,
even better from 40 to 70%. The theoretical dry extract weight of
fillers is generally equal to the weight of solid fillers.
[0108] In some embodiments, the antistatic composition does not
comprise any filler such as nanoparticles. Preferably, the
antistatic composition does not comprise any filler when compounds
of formula II are present in said composition.
[0109] One of the difficulties in the preparation of a composition
exhibiting at the same time electric conductivity properties along
with hardness and/or abrasion-resistance properties is to get a
homogeneous dispersion having small size particles capable of being
used in the optic field, especially in the ophthalmic field, that
is to say exhibiting a level of haze which does not prevent it from
being used in this field. This means that the fillers must not be
substantially agglomerated with the CNT.
[0110] The antistatic composition optionally comprises a catalytic
amount of at least one curing catalyst, so as to accelerate the
curing step. Examples of curing catalysts are photo-initiators that
generate free radicals upon exposure to ultraviolet light or heat
such as organic peroxides, azo compounds, quinones, nitroso
compounds, acyl halides, hydrazones, mercapto compounds, pyrylium
compounds, imidazoles, chlorotriazines, benzoin, benzoin alkyl
ethers, diketones, phenones, and mixtures thereof.
[0111] The antistatic composition may also comprise a curing
catalyst such as aluminum acetylacetonate, a hydrolyzate thereof or
carboxylates of metals such as zinc, titanium, zirconium, tin or
magnesium. Condensation catalysts such as saturated or unsaturated
polyfunctional acids or acid anhydrides may also be used, in
particular maleic acid, itaconic acid, trimellitic acid or
trimellitic anhydride. Numerous examples of curing and/or
condensation catalysts are given in "Chemistry and Technology of
the Epoxy Resins", B. Ellis (Ed.) Chapman Hall, New York, 1993 and
"Epoxy Resins Chemistry and Technology" 2.sup.eme edition, C. A.
May (Ed.), Marcel Dekker, New York, 1988.
[0112] In general, the catalysts described above are used according
to the invention in an amount ranging from 0.01 to 10%, preferably
from 0.1 to 5% by weight based on the total weight of the curable
antistatic composition.
[0113] The antistatic composition according to the invention may
also contain various additives conventionally used in polymerizable
compositions, in conventional proportions. These additives include
stabilizers such as antioxidants, UV light absorbers, light
stabilizers, anti-yellowing agents, adhesion promoters, dyes,
photochromic agents, pigments, rheology modifiers, lubricants,
cross-linking agents, photo-initiators fragrances, deodorants and
additional surfactants.
[0114] The remaining of the antistatic composition is essentially
comprised of solvents, which may be chosen from water or
water-miscible alcohols, e.g. methanol, ethanol, 2-butanol, or
mixtures of water and water-miscible alcohols.
[0115] The ratio of theoretical dry extract weight of the
composition/total weight of the composition according to the
invention is generally lower than 30%, and preferably ranges from 1
to 20%, more preferably from 1.5 to 15%, even better from 2 to
10%.
[0116] The coating compositions of the invention allow to achieve a
sufficient electrical conduction, so that it is not necessary to
add additional conductive compounds.
[0117] In a preferred embodiment, the antistatic composition
according to the invention does not contain conductive polymers,
such as, without limitation, polyanilines, polypyrroles,
polythiophenes, polyselenophenes, polyethylene-imines,
poly(allylamine) or polyvinylphenylene.
[0118] In another preferred embodiment, the antistatic composition
according to the invention comprises less than 1% by weight based
on the total weight of the antistatic composition, of electrically
conductive fillers, which are generally oxides such as ITO, ATO,
zinc antimonate (ZnSb.sub.2O.sub.6), indium antimonate
(InSbO.sub.4), or SrTiO.sub.3, preferably less than 0.5% by weight
and even better 0%. Within the meaning of the invention, oxides
such as SiO.sub.2, Al.sub.2O.sub.3, ZrO.sub.2, SnO.sub.2 and
mixtures thereof are not considered to be electrically conductive
oxides (fillers).
[0119] Once the antistatic composition according to the invention
has been prepared, it is deposited onto the above described
abrasion- and/or scratch-resistant coating by any of the methods
used in liquid coating technology such as, for example, spray
coating, spin coating, flow coating brush coating, dip coating or
roll-coating. Spin coating and dip coating are the preferred
methods. The composition can be applied by a series of successive
layers or thin coats onto the substrate to achieve the desired
thickness. The antistatic composition is then cured according to
known methods.
[0120] In the final optical article, the thickness of the inventive
antistatic coating preferably ranges from 50 nm to 2 .mu.m, more
preferably from 100 nm to 1.5 .mu.m, even better from 100 nm to 1
.mu.m.
[0121] It is possible to apply other coatings onto the antistatic
coating, such as an antireflection coating and/or an anti-fouling
top coat. Other coatings such as a polarized coating, a
photochromic coating, a dyeing coating or an adhesive layer, for
example an adhesive polyurethane layer, may also be applied onto
said antistatic coating.
[0122] Articles obtained according to the invention will be now
described in more details.
[0123] The present invention provides optical articles having
charge decay times .ltoreq.500 milliseconds, preferably .ltoreq.200
milliseconds and better .ltoreq.150 milliseconds.
[0124] Surface resistivity of optical articles provided by the
present invention is lower than or equal to
10.sup.12.OMEGA./.quadrature., preferably lower than or equal to
5.10.sup.11.OMEGA./.quadrature., still better lower than or equal
to 10.sup.11.OMEGA./.quadrature., and generally higher than or
equal to 10.sup.6.OMEGA./.quadrature..
[0125] It is generally considered that an article exhibits
antistatic properties when its surface resistivity is lower than or
equal to 10.sup.12.OMEGA./.quadrature.. By surface resistivity of
the optical article, it is meant the surface resistivity which is
measured at the surface of the final optical article on its main
face coated with both the abrasion- and/or scratch-resistant
coating and the antistatic coating described above.
[0126] The final optical articles preferably do not absorb light in
the visible range (or little), which means herein that when coated
on one side with the abrasion- and/or scratch-resistant coating and
the antistatic coating according to the invention, the optical
article has a luminous absorption in the visible range due to both
coatings of preferably 1% or less, more preferably less than 1%,
and/or a relative light transmission factor in the visible
spectrum, Tv (or .zeta.v), preferably higher than 90%, more
preferably higher than 91%, and even better higher than 92%.
Preferably, both features are simultaneously satisfied and can be
reached by carefully controlling thicknesses of the coatings.
[0127] As used herein, the Tv factor is such as defined in the
standard NF EN 1836 and corresponds to the 380-780 nm wavelength
range.
[0128] In an alternative embodiment, the optical article may be
tinted or dyed and absorb light in the visible range.
[0129] The final optical articles prepared according to the
invention preferably have low haze characteristics. Haze is a
measurement of the transmitted light scattered more than
2.5.degree. from the axis of the incident light. The smaller the
haze value, the lower the degree of cloudiness. The haze value of
the present optical articles is preferably less than 0.8%, more
preferably less than 0.5%, still more preferably less than 0.3% and
even better less than 0.2%.
[0130] Optical articles according to the invention also have
improved abrasion resistance, compared to substrates which do not
comprise the inventive antistatic abrasion-resistant coating.
[0131] Whatever the embodiment of the present invention, the
antistatic abrasion resistant coating of the invention shows many
advantages compared to other antistatic coating systems, including
applicability to most substrates with excellent adhesion, in
particular plastic substrates, and high electrical
conductivity.
[0132] The invention also relates to a process for preparing an
abrasion- and/or scratch-resistant antistatic optical article,
comprising: [0133] providing an optical article comprising a
substrate, [0134] applying onto the surface of the substrate an
abrasion- and/or scratch-resistant coating, and [0135] depositing
directly onto said abrasion- and/or scratch-resistant coating the
above described curable composition, and curing said
composition.
[0136] The present optical articles can be processed simply and at
low temperature (.ltoreq.100.degree. C.), using environment
friendly solvents (alcohol or water/alcohol co-solvent). The
present process is flexible and allows incorporation of other
functional coatings onto the substrate. It is more convenient than
the process disclosed in U.S. pat. appl. No. 2005/209392, in which
two steps are necessary to form the antistatic coating.
[0137] The present invention can be used in the ophthalmic field to
prepare antistatic lenses, but also for general antistatic purpose
in photographic films, electronics or food packaging, and imaging
materials.
[0138] Now, the present invention will be described in more detail
with reference to the following examples. These examples are
provided only for illustrating the present invention and should not
be construed as limiting the scope and spirit of the present
invention.
EXAMPLES
1. Testing Methods
[0139] The following test procedures were used to evaluate the
optical articles prepared according to the present invention. Three
samples for each system were prepared for measurements and the
reported data were calculated in the average of three data.
[0140] a) Charge Decay Time
[0141] In the present patent application, charge decay times of
optical articles which have been beforehand subjected to a corona
discharge at 9000 volts were measured using JCI 155v5 Charge Decay
Test Unit from John Chubb Instrumentation at 25.4.degree. C. and
50% relative humidity.
[0142] The unit was set up with JCI 176 Charge Measuring Sample
Support, JCI 191 Controlled Humidity Test Chamber, JCI 192 Dry Air
Supply Unit and Calibration of voltage sensitivity and decay time
measurement performance of JCI 155 to the methods specified in
British Standard and Calibration voltage measurements and resistor
and capacitor values traceable to National Standards.
[0143] b) Surface Resistivity
[0144] Surface resistivity of optical articles coated according to
the invention was measured at 23.degree. C. and 55% relative
humidity using modified concentric ring probe Model 863 (2.5'') for
curve lens substrate with variable diopters and 6487 Laboratory
Digital Resistance/Current Meter (100V was applied) from
Electro-Tech Systems.
[0145] c) Dry Adhesion Test
[0146] Dry adhesion of the coatings was measured using the
cross-hatch adhesion test according to ASTM D3359-93, by cutting
through the coatings a series of 5 lines, spaced 1 mm apart with a
razor, followed by a second series of 5 lines, spaced 1 mm apart,
at right angles to the first series, forming a crosshatch pattern
comprising 25 squares. After blowing off the crosshatch pattern
with an air stream to remove any dust formed during scribing, clear
cellophane tape (3M SCOTCH.RTM. n.degree. 600) was then applied
over the crosshatch pattern, pressed down firmly, and then rapidly
pulled away from coating in a direction perpendicular to the
coating surface. Application and removal of fresh tape was then
repeated two additional times. Adhesion is rated as follows (0 is
the best adhesion, 1-4 is in the middle, and 5 is the poorest
adhesion):
TABLE-US-00001 Adhesion score Squares removed Area % left intact 0
0 100 1 <1 >96 2 1 to 4 96-84 3 >4 to 9 83-64 4 >9 to
16 63-36 5 >16 <36
[0147] d) Determination of the Abrasion Resistance ("ISTM Bayer
Test" or "Bayer Alumina")
[0148] The Bayer abrasion test is a standard test used to determine
the abrasion resistance of curved/lens surfaces. Determination of
the Bayer value was performed in accordance with the standards ASTM
F735-81 (Standard Test Method for Abrasion Resistance of
Transparent Plastics and Coatings Using Oscillating Sand
Method).
[0149] Per this test, a coated lens and an uncoated lens (reference
lens of similar curvature, diameter, thickness and diopter) were
subjected to an oscillating abrasive sand box (approximately 500 g
of aluminum oxide ZF 152412 supplied by Specialty Ceramic Grains,
former Norton Materials) for 300 cycles of abrasion in 2 minutes.
Only fresh sand is used for each measurement.
[0150] The haze H of both the reference and coated sample were then
measured with a Haze Guard Plus meter, in accordance with ASTM
D1003-00, before and after the test has been performed. The results
are expressed as a calculated ratio of the reference lens to the
coated lens (Bayer value=H.sub.standard/H.sub.sample). The Bayer
value is a measure of the performance of the coating, with a higher
value meaning a higher abrasion resistance.
[0151] e) Haze Value, Tv and Thickness
[0152] The haze value of the final optical article was measured by
light transmission utilizing the Haze-Guard Plus haze meter from
BYK-Gardner (a color difference meter) according to the method of
ASTM D1003-00, which is incorporated herein in its entirety by
reference. All references to "haze" values in this application are
by this standard. The instrument was first calibrated according to
the manufacturer's directions. Next, the sample was placed on the
transmission light beam of the pre-calibrated meter and the haze
value was recorded from three different specimen locations and
averaged. Tv was measured using the same device.
[0153] Thickness of the films was evaluated by ellipsometer
(thickness <1 .mu.m) equipped with M-44.TM., EC-270 and LPS-400
with 75 W Xenon Light Source from J. A. Woollam Co. Inc. or with a
Metricon Model 2010 Prism Coupler apparatus (thickness >1 .mu.m)
from Metricon Corporation.
2. Experimental Details
[0154] a) General Procedure for Preparation of Antistatic Coating
Compositions
[0155] 5 g of surfactant Triton X-305.RTM. were dissolved in 495 g
of deionized water, in which 300 mg of CNT powder (Purified HiPco)
were subsequently introduced. A homogenizer was then used to mix
the CNT dispersion for 20 minutes, and a high power sonic horn
(500-watt) operated at 20 kHz was applied for 15 minutes of
ultrasonic treatment. The dispersion was subjected to sedimentation
for two days and contained about 0.01 wt % of CNT after removal of
the precipitates. It was stable for more than 1 month without any
precipitates or agglomerates.
[0156] Coating solutions were prepared by mixing GLYMO, TEOS (when
present), HCl and SiO.sub.2 or SnO.sub.2 nanoparticle aqueous
dispersion (when present) in methanol under agitation for 12 h,
followed by dispersing with 2-butanol, Al(AcAc).sub.3, a surfactant
(FC-430), and the above described CNT dispersion.
[0157] CNT powder was purchased from Carbon Nanotechnologies, Inc.,
which comprises purified carbon nanotubes of less than 15 wt % ash
content, grown by the HiPCO method (High Pressure catalytic
decomposition of Carbon monOxide) and prepared from laser ablation.
Triton X-305.RTM. was purchased from Dow Chemical Corporation; the
SnO.sub.2 nanoparticles aqueous dispersion (SN15ES, 15 wt % of
nanoparticles, 10-15 nm diameter) was purchased from NYACOL
Nanotechnologies, Inc.; the SiO.sub.2 nanoparticles aqueous
dispersions (NH-1530, 2540, 4030, 30 or 40 wt % of nanoparticles,
diameter of 15, 25 or 40 nm) were purchased from Silco
International Inc. FC-430 surfactant was purchased from 3M.
[0158] b) Preparation of Coated Optical Articles
[0159] The optical articles used in the examples were round lenses
(piano or -2.00 with 68 mm of diameter) comprising either an
ORMA.RTM. substrate (obtained by polymerizing CR-39.RTM. diethylene
glycol bis(allyl carbonate) monomer), or Airwear.RTM. ESSILOR
production lenses comprising a polycarbonate substrate.
[0160] In examples 1' to 5' and 6 to 12, ORMA.RTM. lenses were
spin-coated on their convex side with an impact-resistant primer
coating based on a polyurethane latex comprising polyester
moieties, cured at 75.degree. C. for 15 min (Witcobond.RTM. 234
purchased from BAXENDEN CHEMICALS, modified by dilution so as to
obtain an adequate viscosity, spin coating at 1500 rpm for 10 to 15
seconds). After cooling for 16 min, the primer coating was coated
with a polysiloxane-type abrasion- and scratch-resistant coating
("Hard coat"; thickness: 1.8 .mu.m) obtained by curing for 15 min
at 75.degree. C. a composition comprising GLYMO (224 parts by
weight), DMDES (120 parts by weight), 0.1 N HCl (80.5 parts by
weight), colloidal SiO.sub.2 (718 parts by weight, containing 30%
by weight of nanoparticles in methanol), Al(AcAc).sub.3 (15 parts
by weight) as a curing catalyst, a surfactant (0.1 parts by weight
of EFKA.RTM. 3034 from Ciba Specialty Chemicals) and
ethylcellosolve (44 parts by weight). The composition was fast
cured for 25 min at 135.degree. C. and let cooled down. The surface
of the deposited hard coat was then corona treated and spin-coated
at 500/1000 rpm with an antistatic composition, which was pre-cured
at 80.degree. C. for 5 minutes and post-cured at 100.degree. C. for
3 hours.
[0161] In examples 1 to 5, Airwear.RTM. lenses (already provided
with a GLYMO-based abrasion- and scratch-resistant coating
(.about.5 microns) but no primer coating) were directly subjected
to corona treatment and antistatic coating deposition under the
same conditions.
[0162] In comparative example C1, no antistatic coating was formed
onto the Airwear.RTM. lens. In comparative example C2, no
antistatic coating was formed onto the coated ORMA.RTM. lens, which
only contains the same impact-resistant primer coating and the same
abrasion- and scratch-resistant coating as in examples 1' to 5' and
6 to 12.
[0163] c) Details of Coating Formulations
[0164] The coating formulations used in the examples are described
in Tables 1 and 2. The figures in the tables are weight
percentages.
TABLE-US-00002 TABLE 1 Example 1 and 1' 2 and 2' 3 and 3' 4 and 4'
5 and 5' GLYMO 3.200 4.000 2.400 4.000 5.200 TEOS 4.800 4.000 5.600
5.600 5.600 0.1N HCl 2.392 2.300 2.484 2.852 3.128 Methanol 8.832
8.730 8.934 10.578 11.811 CNT dispersion 80.000 80.000 80.000
76.000 73.000 2-Butanol 0.544 0.680 0.408 0.680 0.884
Al(AcAc).sub.3 0.216 0.270 0.162 0.270 0.351 Surfactant FC-430
0.016 0.020 0.012 0.020 0.026
TABLE-US-00003 TABLE 2 Example 6 7 8 9 10* 11** 12*** GLYMO 4.000
3.200 2.400 3.200 3.200 3.200 3.200 0.1N HCl 0.920 0.736 0.552
0.736 0.736 0.736 0.736 SnO.sub.2 nanoparticles 14.000 16.000
18.000 12.000 0 0 0 SiO.sub.2 nanoparticles 0 0 0 0 12.000 12.000
12.000 Methanol 4.110 3.288 2.466 3.288 3.288 3.288 3.288 CNT
dispersion 76.000 76.000 76.000 80.000 80.000 80.000 80.000
2-Butanol 0.680 0.544 0.408 0.544 0.544 0.544 0.544 Al(AcAc).sub.3
0.270 0.216 0.162 0.216 0.216 0.216 0.216 Surfactant FC-430 0.020
0.016 0.012 0.016 0.016 0.016 0.016 *15 nm SiO.sub.2 nanoparticles
were used. **25 nm SiO.sub.2 nanoparticles were used. ***40 nm
SiO.sub.2 nanoparticles were used.
[0165] d) Coating Characteristics and Performances
[0166] The thickness of the antistatic coating and performance test
data of the prepared optical articles are collected in Tables 3 and
4.
TABLE-US-00004 TABLE 3 Film performance tests of coatings (Airwear
.RTM. lenses) Thick- Decay Exam- ness time Dry ple (nm) T (%) Haze
(ms) R (.OMEGA./.quadrature.) Bayer adhesion 1 691 91.2 0.13 74.1
8.01E+10 5.83 0 2 674 91.2 0.18 58.2 4.72E+10 5.54 0 3 745 91.4
0.15 63.5 6.54E+10 6.38 0 4 923 91.2 0.12 61.7 5.67E+10 5.98 0 5
1046 91.3 0.08 78.2 8.97E+10 5.30 0 C1 -- 91.5 0.13 1,450 1.38E+13
4.65 0
TABLE-US-00005 TABLE 4 Film performance tests of coatings (ORMA
.RTM. lenses) Thick- Decay Dry ness time adhe- Example (nm) T %
Haze (ms) R (.OMEGA./.quadrature.) Bayer sion 1' 685 92.6 0.14 107
3.27E+11 5.09 0 2' 692 92.6 0.15 93.7 1.76E+11 5.02 0 3' 731 92.5
0.17 133 4.05E+11 5.35 0 4' 944 92.5 0.16 89.6 1.67E+11 5.21 0 5'
1024 92.4 0.17 93.7 2.62E+11 5.33 0 6 294 92.1 0.18 135 1.25E+11
4.62 0 7 272 91.9 0.20 137 1.56E+11 4.55 0 8 235 91.9 0.28 166
4.67E+11 4.52 0 9 251 91.9 0.32 98.3 4.32E+10 4.54 0 10 342 92.2
0.26 146 1.51E+11 4.94 0 11 411 92.0 0.34 105 8.82E+10 5.21 0 12
385 91.9 0.39 131 1.30E+11 5.09 0 C2 -- 92.8 0.11 181,00 3.45E+14
3.14 0
[0167] As can be seen from Tables 3 and 4, optical articles coated
according to the invention exhibit antistatic properties (surface
resistivity <5.10.sup.11 .OMEGA./.quadrature. and short decay
time, <150 ms), high optical transparency with about 91-92% of
transmittance, low haze (<0.5%), excellent abrasion resistance
(ISTM Bayer generally >5) and maintain excellent adhesion to the
underlying coating (crosshatch test 0). It is particularly
important to note that the bi-layer abrasion-resistant
coating/antistatic coating provides better abrasion resistance
properties than the sole abrasion-resistant coating.
* * * * *