U.S. patent application number 09/026271 was filed with the patent office on 2002-10-24 for antireflection film.
Invention is credited to CHIA, YEE HO, CHOI, HYUNG-CHUL, JONES, ROBERT L., NAGARKAR, PRADNYA V, SMYTH, WILLIAM K, WANG, XIAOJIA Z.
Application Number | 20020155265 09/026271 |
Document ID | / |
Family ID | 21830842 |
Filed Date | 2002-10-24 |
United States Patent
Application |
20020155265 |
Kind Code |
A1 |
CHOI, HYUNG-CHUL ; et
al. |
October 24, 2002 |
ANTIREFLECTION FILM
Abstract
An antireflection coating comprises one or more inorganic
antireflection layers (typically metal oxide or silica layers) and
a polymer layer cured in situ, the polymer layer having a
refractive index not greater than about 1.53 over the wavelength
range of 400 to 700 nm and a thickness of from about 20 to about
200 nm. The polymer layer provides good scratch and fingerprint
protection, and also enables the thicknesses of the inorganic
antireflection layers to be reduced, thereby reducing the cost of
the coating.
Inventors: |
CHOI, HYUNG-CHUL;
(LEXINGTON, MA) ; JONES, ROBERT L.; (ANDOVER,
MA) ; NAGARKAR, PRADNYA V; (NEWTON, MA) ;
SMYTH, WILLIAM K; (SUDBURY, MA) ; WANG, XIAOJIA
Z; (ACTON, MA) ; CHIA, YEE HO; (TROY,
MI) |
Correspondence
Address: |
KIRKPATRICK & LOCKHART LLP
75 STATE STREET
BOSTON
MA
02109-1808
US
|
Family ID: |
21830842 |
Appl. No.: |
09/026271 |
Filed: |
February 19, 1998 |
Current U.S.
Class: |
428/212 |
Current CPC
Class: |
Y10T 428/269 20150115;
G02B 27/0006 20130101; Y10T 428/24942 20150115; G06F 3/041
20130101; G02B 1/04 20130101; G02B 1/14 20150115; G02B 1/113
20130101; G02B 1/105 20130101; G02B 1/04 20130101; C08L 27/12
20130101; G02B 1/04 20130101; C08L 33/08 20130101; G02B 1/04
20130101; C08L 33/10 20130101 |
Class at
Publication: |
428/212 |
International
Class: |
B32B 031/26 |
Claims
1. An article having an antireflection film, the article comprising
a substrate carrying an inorganic antireflection layer and, in
contact with the inorganic antireflection layer and forming the
outer surface of the antireflection film, a polymer layer formed by
curing a curable composition in situ on the inorganic
antireflection layer, the polymer layer having a refractive index
not greater than about 1.53 over the wavelength range of 400 to 700
nm and a thickness of from about 20 to about 200 nm.
2. An article according to claim 1 wherein the inorganic
antireflection layer is formed from a metal oxide.
3. An article according to claim 2 wherein the metal oxide layer
comprises at least one of indium oxide, titanium dioxide, cadmium
oxide, gallium indium oxide, niobium pentoxide, indium tin oxide
and tin dioxide.
4. An article according to claim 3 wherein a single layer of metal
oxide, having a thickness of from about 10 to about 30 nm is
carried by the substrate and the polymer layer, having a thickness
of from about 80 to about 150 nm is carried by the single metal
oxide layer.
5. An article according to claim 4 wherein the metal oxide layer
has a thickness of from about 17 to about 23 nm and the polymer
layer has a thickness of from about 110 to about 130 nm.
6. An article according to claim 2 comprising a first metal oxide
layer carried by the substrate; a silica layer superposed on the
first metal oxide layer; and a second metal oxide layer superposed
on the silica layer, the polymer layer being superposed on the
second metal oxide layer.
7. An article according to claim 6 wherein the first metal oxide
layer has a thickness of from about 20 to about 35 nm, the silica
layer has a thickness of from about 10 to about 25 nm, the second
metal oxide layer has a thickness of from about 50 to about 100 nm
and the polymer layer has a thickness of from about 70 to about 120
nm.
8. An article according to claim 7 wherein the first metal oxide
layer has a thickness of from about 25 to about 30 nm, the silica
layer has a thickness of from about 15 to about 20 nm, the second
metal oxide layer has a thickness of from about 65 to about 80 nm
and the polymer layer has a thickness of from about 85 to about 100
nm.
9. An article according to claim 1 wherein the inorganic
antireflection layer is formed from silica.
10. An article according to claim 9 comprising a metal oxide layer
carried by the substrate; and a silica layer superposed on the
metal oxide layer, the polymer layer being superposed on the silica
layer.
11. An article according to claim 10 wherein the metal oxide layer
has a thickness of from about 10 to about 30 nm, the silica layer
has a thickness of from about 10 to about 120 nm, and the polymer
layer has a thickness of from about 50 to about 130 nm.
12. An article according to claim 11 wherein the metal oxide layer
has a thickness of from about 10 to about 20 nm, the silica layer
has a thickness of from about 10 to about 50 nm, and the polymer
layer has a thickness of from about 60 to about 100 nm.
13. An article according to claim 1 wherein the polymer layer has a
refractive index not greater than about 1.50 over the wavelength
range of 400 to 700 nm.
14. An article according to claim 1 wherein the polymer layer
comprises repeating units derived from a fluoroalkene.
15. An article according to claim 1 wherein the polymer layer
comprises repeating units derived from an alkyl acrylate or
methacrylate.
16. An article according to claim 1 wherein the polymer layer
comprises repeating units derived from a polyfunctional acrylate
monomer.
17. An article according to claim 14 wherein the polymer layer
comprises repeating units derived from a fluoroalkene and repeating
units derived from an alkyl acrylate or methacrylate, the polymer
layer having an outer portion enriched in the alkyl acrylate or
methacrylate and an inner portion enriched in the fluoroalkene.
18. An article according to claim 1 further comprising a hard coat
disposed between the substrate and the inorganic antireflection
layer.
19. A process for providing an antireflection film on a substrate,
the process comprising: depositing an inorganic antireflection
layer on the substrate; depositing a layer of a curable composition
on the inorganic antireflection layer; and effecting free radical
curing of the deposited curable composition to form a polymer layer
having a thickness of from about 20 to about 200 nm and a
refractive index not greater than about 1.53 over the wavelength
range of 400 to 700 nm.
20. A process according to claim 19 wherein the inorganic
antireflection layer is formed from a metal oxide.
21. A process according to claim 20 wherein the metal oxide
comprises at least one of indium oxide, titanium dioxide, cadmium
oxide, gallium indium oxide, niobium pentoxide, indium tin oxide
and tin dioxide.
22. A process according to claim 20 wherein a single layer of the
metal oxide having a thickness of from about 10 to about 30 nm is
deposited on the substrate and a polymer layer having a thickness
of from about 80 to about 150 nm is formed on this single metal
oxide layer.
23. A process according to claim 22 wherein the metal oxide layer
has a thickness in the range of from about 17 to about 23 nm and
the polymer layer has a thickness of from about 110 to about 130
nm.
24. A process according to claim 20 wherein a first metal oxide is
deposited on the substrate; a silica layer is deposited on the
first metal oxide layer; a second metal oxide layer is deposited on
the silica layer, and the polymer layer is formed on the second
metal oxide layer.
25. A process according to claim 24 wherein the first metal oxide
layer has a thickness of from about 20 to about 35 nm, the silica
layer has a thickness of from about 10 to about 25 nm, the second
metal oxide layer has a thickness of from about 50 to about 100 nm
and the polymer layer has a thickness of from about 70 to about 120
nm.
26. A process according to claim 25 wherein the first metal oxide
layer has a thickness of from about 25 to about 30 nm, the silica
layer has a thickness of from about 15 to about 20 nm, the second
metal oxide layer has a thickness of from about 65 to about 80 nm
and the polymer layer has a thickness of from about 85 to about 100
nm.
27. A process according to claim 19 wherein the inorganic
antireflection layer is formed from silica.
28. A process according to claim 27 wherein a metal oxide layer is
deposited upon the substrate, a silica layer is deposited on the
metal oxide layer and the polymer layer is formed on the silica
layer.
29. A process according to claim 28 wherein the metal oxide layer
has a thickness of from about 10 to about 30 nm, the silica layer
has a thickness of from about 10 to about 120 nm and the polymer
layer has a thickness of from about 50 to about 130 nm.
30. A process according to claim 29 wherein the metal oxide layer
has a thickness of from about 10 to about 20 nm, the silica layer
has a thickness of from about 10 to about 50 nm and the polymer
layer has a thickness of from about 60 to about 100 nm.
31. A process according to claim 19 wherein the polymer layer has a
refractive index not greater than about 1.50 over the wavelength
range of 400 to 700 nm.
32. A process according to claim 19 wherein the curable composition
comprises a polymer of a fluoroalkene.
33. A process according to claim 19 wherein the curable composition
comprises a polymer of an alkyl acrylate or methacrylate.
34. A process according to claim 19 wherein the curable composition
comprises a polyfunctional acrylate monomer.
35. A process according to claim 32 wherein the curable composition
comprises both a polymer of a fluoroalkene and a polymer of an
alkyl acrylate or methacrylate, and wherein the curing causes
segregation of material within the polymer layer, thereby producing
a polymer layer having an outer portion enriched in the alkyl
acrylate or methacrylate and an inner portion enriched in the
fluoroalkene.
36. A process according to claim 19 further comprising depositing a
hard coat on the substrate before the inorganic antireflection
layer is deposited thereon.
37. A process according to claim 19 wherein the curing of the
curable composition is conducted in air.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a process for providing an
antireflection film on a substrate, and to the article formed by
this process.
[0002] It has long been known that it is advantageous to provide
various articles, for example lenses, cathode ray tubes, flat panel
displays, window films and windshields, with antireflection films
which reduce the amount of light reflected from the surface of the
article and thus reduce or eliminate "ghost" images formed by such
reflected light. For example, U.S. Pat. Nos. 5,106,671; 5,171,414
and 5,234,748 describe antireflection films which are placed on the
inside surface of automobile windshields to reduce the intensity of
the image of the instrument panel caused by light reflected from
the inside surface of the windshield.
[0003] Antireflection coatings on a substrate typically comprise a
plurality of inorganic layers, for example a metal or metal oxide
layer and a silica layer. (The term "silica" is used herein in
accordance with its normal meaning in the antireflection art to
mean a material of the formula SiO.sub.x where x is not necessarily
equal to two. As those skilled in the art are aware, such silica
layers are often deposited by chemical vacuum deposition or
sputtering of silicon in an oxygen atmosphere, so that the material
deposited does not precisely conform to the stoichiometric formula
SiO.sub.2 of pure silica.) Typically, one surface of a silica layer
is exposed, and this exposed surface, which has a high surface
energy, as shown by its low contact angle with water, is highly
susceptible to fingerprints and other marks. Such marks are
extremely difficult to clean, often requiring the use of chemical
cleaners.
[0004] U.S. Pat. No. 4,765,729 (Taniguchi) describes an
anti-reflection optical article, which comprises a substrate
bearing a single-layer or multi-layer anti-reflection film having a
surface film composed of an inorganic substance, and a coating of
an organic substance containing a curing material formed on the
surface of the anti-reflection film, wherein the surface
reflectance of the optical article is lower than 3% and the
stationary contact angle to water is at least 60.degree.. The
inorganic substance is preferably silica and the preferred curing
material is a silanol-terminated polysiloxane. According to this
patent, the thickness of the organic substance should be in the
range of 0.0005 to 0.5 .mu.m (0.5 to 500 nm), especially 0.001 to
0.3 .mu.m (1 to 300 nm). The provision of the layer of organic
substance is stated to increase the scratch and stain resistance of
the optical article.
[0005] However, this patent gives no directions for controlling the
thickness of the organic substance within the very broad range
which it suggests for such thickness, and all of the worked
examples use a dip coating technique which would lead to very thin
coatings the thickness of which would be expected to vary
significantly over the surface of the coated substrate, since the
coating solution will accumulate at the lowest point on the
substrate. Furthermore, in these worked examples, a substrate such
as a lens is first provided with antireflection layers of metal
oxide and silica to a total thickness of .lambda./4 and then the
organic substance is applied by dip coating. In these
circumstances, proper antireflection properties will be obtained
only if the organic substance is very thin, less than 10 nm, so
that it has essentially no effect on the optical properties of the
antireflection coating, and as already indicated, it is difficult
to achieve uniformity in such very thin coatings.
[0006] Perhaps the most effective antireflection film available
commercially is that sold by Southwall Technologies, 1029
Corporation Way, Palo Alto, Calif. 94303. This material comprises a
180 .mu.m poly(ethylene terephthalate) substrate provided with an
abrasion-resistant hard coat, and then successively with a 17 nm
indium tin oxide (ITO) layer, a 23 nm silica layer, a 95 nm ITO
layer, an 84 nm silica layer and finally a thin "lubrication"
layer, which is formed from a fluoropolymer and is stated to
improve the scratch resistance and the susceptibility of the
surface to marking.
[0007] This complex film possesses excellent antireflection
characteristics, but is so expensive (approximately US$10 per
square foot, US$100 m.sup.-2) as to preclude its use in many
applications where antireflection films are desirable. Much of the
high cost of this film can be attributed to the 95 nm ITO layer and
84 nm silica layer; since these layers are typically formed by
sputtering, and the cost of a sputtered layer is directly
proportional to its thickness. Furthermore, if it is desired to
produce large quantities of such a complex film on a production
line basis, the need for four separate sputtering stations, all of
which must be maintained under high vacuum, results in a complex
and costly apparatus.
[0008] It has now been found that providing a "thick" (i.e.,
optically active) polymer layer of carefully controlled refractive
index above an inorganic antireflection layer or layers, the
thickness(es) of the inorganic layer(s) can be greatly reduced,
thereby reducing the overall cost of the antireflection coating,
especially when the inorganic layer(s) is/are applied by a process
such as sputtering or chemical vapor deposition in which the
residence time of the substrate within the coating apparatus is
directly proportional to the thickness of the required layer. Also,
an antireflection coating using such a thick polymer layer, which
can readily be applied with good uniformity by solution or other
coating techniques, has good scratch and stain resistance.
SUMMARY OF THE INVENTION
[0009] Accordingly, this invention provides an article having an
antireflection film. This article comprises a substrate carrying an
inorganic antireflection layer, and in contact with the
antireflection film and forming the outer surface of the
antireflection film, a polymer layer formed by curing a curable
composition in situ on the inorganic antireflection layer, the
polymer layer having a refractive index not greater than about 1.53
over the wavelength range of 400 to 700 nm and a thickness of from
about 20 to about 200 nm.
[0010] This invention also provides a process for providing an
antireflection film on a substrate. This process comprises
depositing an inorganic antireflection layer on the substrate;
depositing a layer of a curable composition on the inorganic
antireflection layer; and effecting free radical curing of the
deposited curable composition to form a polymer layer having a
thickness of from about 20 to about 200 nm and a refractive index
not greater than about 1.53 over the wavelength range of 400 to 700
nm.
[0011] In the present process, the curing of the curable
composition may be effected by cross-linking of one or more
polymers or oligomers, or by polymerization of one or more monomers
or oligomers, or by a combination of both cross-linking and
polymerization. Such curing techniques are familiar to those
skilled in polymer technology.
BRIEF DESCRIPTION OF THE DRAWING
[0012] The accompanying drawing shows reflectance curves for two
preferred antireflection films of the present invention prepared in
the Example below.
DETAILED DESCRIPTION OF THE INVENTION
[0013] As already indicated, the article of the present invention
is provided with an antireflection film comprising one or more
inorganic antireflection layers and an outer polymer layer. The
polymer layer has a thickness of from about 20 to about 200 nm and
a refractive index not greater than about 1.53 over the visible
wavelength range of 400 to 700 nm, and is formed on the inorganic
antireflection layer(s) by depositing a layer of a curable
composition and then curing this layer in situ. The relatively
thick layer of curable composition required can be applied with
good uniformity by solution coating or other conventional coating
techniques. Also, the provision of the thick polymer layer enables
the thickness, and thus the cost, of the inorganic antireflection
layers to be reduced. For example, one embodiment of the invention
described below comprises a 19 nm indium tin oxide layer, a 20 nm
silica layer and an 85 nm polymer layer; as compared to the
Southwall Technology antireflection film described above, this
embodiment of the invention reduces the amount of material which
needs to be sputtered per unit area of the film by about 80
percent, thus reducing the cost of the film by more than 50
percent.
[0014] The substrate of the present article can be any material on
which an antireflection coating is desired, provided of course that
the substrate can withstand the (relatively mild) conditions needed
for deposition of the various layers and the curing of the curable
composition. The substrate may be a finished optical article, for
example a lens, the display surface of a cathode ray tube, or an
automobile windshield. However, in most cases it is preferred that
the substrate be a plastic film, typically a polyester film; the
plastic film has the antireflection coating formed thereon, and the
resultant antireflection film may be applied to, for example, a
cathode ray tube, a flat panel display, window glass or a
windshield, which it is desired to provide with antireflection
characteristics. Suitable polyester films are readily available
commercially, for example the 4 to 7 mil (101 to 177 .mu.m)
poly(ethylene terephthalate) films sold under the trademark
"MELINEX" by ICI Americas Inc., Wilmington, Del.
[0015] Especially when the substrate is a plastic film, it may be
provided with coatings on one or both surfaces to improve its
hardness and scratch resistance, to improve the adhesion of the
inorganic antireflection layer to the substrate, or to provide any
other desired properties, for example filtration of ultra-violet
radiation or provision of a gas and/or moisture barrier. A hard
coating on the substrate will typically have a thickness of about 1
to about 15 .mu.m, preferably from about 2 to about 3 .mu.m, and
such a hard coating may be provided by free radical polymerization
(initiated either thermally or by ultra-violet radiation) of an
appropriate polymerizable material. An especially preferred hard
coat for use in the present invention is the acrylic polymer
coating sold under the trademark "TERRAPIN" by Tekra Corporation,
6700 West Lincoln Avenue, New Berlin, Wis. 53151.
[0016] As already indicated, the article of the present invention
may include one or more than one inorganic antireflection layers.
These layers may be formed from any of the inorganic materials
hitherto used in antireflection coatings. The preferred materials
for forming the inorganic antireflection layer on which the curable
composition is deposited are metal oxides and silica layer.
Preferred metal oxides are indium oxide, titanium dioxide, cadmium
oxide, gallium indium oxide, niobium pentoxide, indium tin oxide
and tin dioxide, with indium tin oxide being especially
preferred.
[0017] As will be apparent to those skilled in thin film optics and
the design of antireflection coatings, the thicknesses of the
inorganic antireflection layer(s) and the polymer layer in the
present article should be correlated so that the total thickness of
these layers is approximately .lambda./4 of the center of the
wavelength range for which antireflection characteristics are
desired, e.g., the total thickness should be approximately 135-145
nm when antireflection characteristics are desired over the entire
visible range of 400 to 700 nm. Also, the thicknesses of the
inorganic antireflection layer(s) and the polymer layer can be
adjusted relative to one another to produce minimum reflectivity
from the composite film.
[0018] In one preferred article of the present invention having a
metal oxide layer in contact with the polymer layer, this metal
oxide layer is the sole inorganic antireflection layer and has a
thickness of about 10 to about 30 nm, desirably about 17 to about
23 nm, while the accompanying polymer layer has a thickness of
about 80 to about 150 nm, desirably about 110 to about 130 nm. This
preferred article combines low production cost with good
antireflection properties.
[0019] A second preferred article of the present invention having a
metal oxide layer in contact with the polymer layer comprises a
first metal oxide layer, a silica layer superposed over the first
metal oxide layer, and a second metal oxide layer superposed on the
silica layer, the polymer layer being superposed on the second
metal oxide layer. In this structure, the first metal oxide layer
desirably has a thickness of from about 20 to about 35 nm,
preferably about 25 to 30 nm, the silica layer desirably has a
thickness of from about 10 to about 25 nm, preferably about 15 to
about 20 nm, the second metal oxide layer desirably has a thickness
of from about 50 to about 100 nm, preferably about 65 to about 80
nm, and the polymer layer desirably has a thickness of from about
70 to about 120 nm, preferably about 85 to about 100 nm. This
preferred three inorganic layer structure provides antireflection
performance substantially equal to that of the Southwall Technology
four inorganic layer structure discussed above, while still
providing a substantial reduction in production costs, since the
thick silica layer and the thin lubrication layer of the four
inorganic layer structure are eliminated.
[0020] When the inorganic layer in contact with the polymer layer
is a silica layer, a preferred article of the invention comprises a
metal oxide layer on the substrate and a silica layer superposed on
the metal oxide layer, the polymer layer being superposed on the
silica layer. In such a two inorganic layer structure, desirably
the metal oxide layer has a thickness of from about 10 to about 30
nm, preferably about 10 to about 20 nm, the silica layer desirably
has a thickness of from about 10 to about 120 nm, preferably about
10 to about 50 nm, and the polymer layer desirably has a thickness
of from about 50 to about 130 nm, preferably about 60 to about 100
nm.
[0021] Although other techniques, for example e-beam and thermal
evaporation may be employed to deposit the inorganic layers of the
present article, these layers are preferably deposited by
sputtering or by chemical vapor deposition, with dc sputtering
being especially preferred, although RF, magnetron and reactive
sputtering and low-pressure, plasma-enhanced and laser-enhanced
chemical vapor deposition may also be used. When the preferred
plastic film substrates are used, the deposition of each of these
layers should of course be effected at a temperature which does not
cause damage to the plastic substrate; this temperature limit of
course varies with the exact plastic substrate employed.
[0022] As already indicated, the polymer layer of the present
antireflection coating has a refractive index not greater than
about 1.53 over the wavelength range of 400 to 700 nm and a
thickness of from about 20 to about 200 nm. The preferred thickness
range for this layer is about 50 to about 130 nm, preferably about
60 to about 100 nm. Polymer layers having thicknesses within these
ranges are readily prepared by depositing a solution of an
appropriate curable material in an organic solvent using
conventional solution coating techniques, for example slot coating,
removing the solvent and curing the resultant layer of curable
material.
[0023] It is desirable to keep the refractive index of the polymer
layer as low as possible consistent with other acceptable
properties for this layer, especially hardness and scratch and
stain resistance. The polymer should also be resistant to cleaning
solvents which may be used on the film, for example ethyl alcohol,
aqueous ammonia, acetone, gasoline and isopropanol, and food and
cosmetic items, for example peanut butter and lipstick with which
it may come into contact. Finally, the polymer should also have
good durability, as measured, for example by its ability to
withstand rubbing with steel wool. Desirably, the polymer layer has
a refractive index below about 1.50 over the entire visible range
of 400 to 700 nm. To provide a suitably low refractive index, the
curable composition used to form the polymer layers desirably
comprises a polymer of a fluoroalkene, for example poly(vinylidene
fluoride) or a vinylidene fluoride/tetrafluoroethylene copolymer,
such as the material sold under the trademark "KYNAR" by San Diego
Plastics, Inc., 2220 McKinley Avenue, National City, Calif. 91950.
However, since a polymer layer consisting only of a fluoroalkene
polymer will typically be too soft to give good scratch protection,
it is also desirable that the curable composition include an alkyl
acrylate or methacrylate polymer, such as the material sold under
the trademark "ELVACITE 2041" by ICI Acrylics, Inc., 3411
Silverside Road-McKean 2nd, Wilmington, Del. 19850-5391, or that
sold under the trademark "ACRYLOID A21" by Rohm and Haas, 100
Independence Mall West, Philadelphia, Pa. 19106-2399. To promote
cross-linking within the polymer layer, and thus increase the
hardness of this layer, it is advantageous to include a
polyfunctional acrylate monomer ("polyfunctional" being used herein
in its conventional sense to denote a material having a
functionality of 3 or higher) in the curable composition; a
specific preferred polyfunctional acrylate monomer is that sold
under the trademark "SR 399" by Sartomer, Inc., 502 Thomas Jones
Way, Exton, Pa. 19341; this material is stated by the manufacturer
to be dipentaerythritol pentaacrylate.
[0024] It is well known to those skilled in polymer science that
most polymers have a negative dispersion with the visible range,
i.e., their refractive index at 700 nm is smaller than their
refractive index at 400 nm. Calculations show that such negative
dispersion adversely affects the antireflection properties of the
film and hence it is desirable to reduce such negative dispersion
as far as possible. The aforementioned KYNAR polymer has a low
refractive index and small negative dispersion, which render it
very suitable for use in the present curable composition. While the
desirability of a fluoroalkene polymer to provide low refractive
index in the polymer layer and for an acrylate or methacrylate
cross-linker to provide hardness in the same layer might suggest
that the properties of the polymer layer must inevitably involve a
compromise between the two properties, it has been found that, if
the formulation of the curable composition is carefully chosen,
segregation of material occurs spontaneously during curing,
resulting in a polymer layer having an outer portion enriched in
the acrylate or methacrylate polymer (and thus of enhanced
hardness) and an inner portion enriched in the fluoroalkene polymer
(and thus of reduced refractive index). An additional benefit of
such segregation of acrylate or methacrylate polymer material
during curing is that it enables the cross-linking to occur in an
oxygen-containing atmosphere, such as air, thereby avoiding the
need for a nitrogen blanket as is customary during thin film
ultra-violet curing, and thus reducing the cost of manufacture of
the antireflection film.
[0025] The curable composition may be cured by any conventional
method, but is desirably cured by a free radical curing, which may
be initiated either thermally or by ultra-violet radiation,
although the latter is generally preferred. Persons skilled in
polymer technology will be familiar with appropriate initiators,
oxygen scavengers and other components useful in such free radical
curing. However, it should be noted that, because of the extreme
thinness of the polymer layer desired in the present process, the
type and proportion of initiator(s) required may differ from
typical formulations intended for production of thicker polymer
layers.
[0026] Preferred embodiments of the present invention will now be
described, though by way of illustration only, to show preferred
reagents, conditions and techniques used in the present
process.
EXAMPLE 1
[0027] In the preferred process, a 4 mil (101 .mu.m) poly(ethylene
terephthalate) film was solvent coated on one surface with the
aforementioned TERRAPIN acrylic polymer coating, the solvent was
allowed to evaporate and the film was placed under an ultra-violet
lamp to cure the polymer. The coated surface of the film was then
coated by direct current sputtering (chemical vapor deposition may
alternatively be used) with a 19 nm layer of indium tin oxide and
then with a 20 nm layer of silica.
[0028] A liquid curable composition was then prepared having the
following composition (the proportions are by dry weight of the
solution):
1 % by weight Poly(vinylidene fluoride) (KYNAR) 46.8 Methyl
methacrylate (ACRYLOID A21) 6.9 Dipentaerythritol pentaacrylate
(Sartomer SR 399) 30.7 Multifunctional acrylate monomer (Sartomer
CD9051) 3.0 Coating additive (COATOSIL 3503.sup.1) 4.0 Adhesion
promoter (SILANE A174.sup.1) 1.0 Curing initiator (DARACURE
1173.sup.2) 2.0 Curing initiator (QUANTACURE BMS.sup.3) 4.0 Oxygen
scavenger (DIDMA.sup.4) 1.6 Notes: .sup.1Both available from OSi
Specialties, 39 Old Ridgebury Road, Danbury, Connecticut
06810-5121. .sup.2Available from Ciba-Geigy Corporation, 540 White
Plains Road, P.O. Box 2005, Tarrytown, New York 10591-9005.
.sup.3Manufactured by Great Lakes Chemical Corporation, and
available from Biddle Sawyer Corporation, 2 Penn Plaza, New York,
New York 10121. .sup.4Available from Aldrich Chemical Company, 1001
West St. Paul. Milwaukee, Wisconsin 53233.
[0029] The various components were prepared as stock solutions in
methyl ethyl ketone (MEK), at 20 percent w/w, except that the
ACRYLOID A21 and QUANTACURE BMS were prepared at 10 percent w/w,
and the DARACURE and DIDMA were prepared at 5 percent w/w. The
requisite quantities of the various stock solutions were then
mixed, together with sufficient additional MEK to give 2000 g of a
coating solution containing 2.75 percent solids w/w. This coating
solution was then coated via a slot coater on to the film bearing
the metal oxide and silica layers, the solvent allowed to evaporate
and the film placed under an ultra-violet lamp to produce a polymer
coating approximately 85 nm thick.
[0030] The resultant antireflection article of the present
invention had a low surface reflection, and exhibited good
resistance to scratching with steel wool or fingerprinting. The
article had a contact angle with water of approximately 89.degree.,
in contrast to the contact angle of 14-26.degree. for a bare silica
surface with no polymer coating.
EXAMPLE 2
[0031] Example 1 was repeated, except that only a 20 nm layer of
indium tin oxide was deposited on the substrate (provided with the
hard coat) and that the thickness of the polymer layer formed was
120 nm.
EXAMPLE 3
[0032] Example 1 was repeated, except that there were deposited
successively on the substrate (provided with the hard coat) a 27.5
nm layer of indium tin oxide, a 17.5 nm layer of silica, a 73 nm
layer of indium tin oxide, and a 94 nm layer of the same polymer as
in Example 1.
[0033] The accompanying drawing shows reflectance curves for two
preferred films of the invention:
[0034] Curve A: A two inorganic layer structure prepared in the
same manner as in Example 1 but having a 19 nm indium tin oxide
layer, a 40 nm silica layer and an 82.5 nm polymer layer.
[0035] Curve B: The film prepared in Example 3 above.
[0036] From these Curves, it will be seen that both films displayed
very good antireflection characteristics, with the more expensive
three inorganic layer film of Example 3 displaying a reflectance
below 1.5 percent over the range of 450-700 nm. (Later experiments
with similar films have produced reflectance as low as 0.8 percent
over this wavelength range.) The photopic reflectance value for
Curve A (measured according to CIE 1931, which specifies a weighted
average of the reflectance over the spectral range of 450 to 650 nm
centered at 550 nm and weighted mostly highly at this wavelength)
was 0.609 percent, while the corresponding value for Curve B was
0.085 percent. (The 40 nm silica layer used in the film which
produced Curve A minimized the photopic reflectance value of the
film. However, decreasing the thickness of the silica layer to 20
nm only increases this value only to 0.610 percent, and the cost
reduction associated with the reduced silica thickness is such that
in practice the 20 nm thickness used in Example 1 is
preferred.)
[0037] It will be apparent to those skilled in the relevant art
that numerous changes and modifications can be made in the
preferred embodiment of the invention described above without
departing from the scope of the invention. For example, the metal
oxide layer might be replaced by a layer of a different material
which can bond to and form an antireflection coating with silica.
The polymer layer described above could then be formed on the
silica surface in the manner already described.
* * * * *