U.S. patent application number 09/773892 was filed with the patent office on 2001-10-25 for low reflective films.
This patent application is currently assigned to CPFILMS INC.. Invention is credited to Barth, Steven Allen, Enniss, James P., Packer, Elizabeth Jean, Parnandi, Aravinda, Port, Anthony Brian, Porter, Simon John, Ward, Richard J..
Application Number | 20010033934 09/773892 |
Document ID | / |
Family ID | 22248574 |
Filed Date | 2001-10-25 |
United States Patent
Application |
20010033934 |
Kind Code |
A1 |
Port, Anthony Brian ; et
al. |
October 25, 2001 |
Low reflective films
Abstract
An anti-reflecting film is made from a polymeric film substrate
consisting of cellulose acetate, polyamide or polyester. The
substrate is coated with at least two polymeric layers. An outer
layer is comprised of a fluorine containing polymer. Between the
outer layer and the substrate is an intermediate layer of an
organometallic polymeric layer. The organometallic polymeric layer
is comprised of the condensation product of a metal alkoxide and a
polymer reactive with the metal oxide.
Inventors: |
Port, Anthony Brian;
(Leicestershire, GB) ; Packer, Elizabeth Jean;
(Coventry, GB) ; Parnandi, Aravinda; (Nuneaton,
GB) ; Ward, Richard J.; (Coventry, GB) ;
Barth, Steven Allen; (Martinsville, VA) ; Enniss,
James P.; (Martinsville, VA) ; Porter, Simon
John; (Martinsville, VA) |
Correspondence
Address: |
Nixon & Vanderhye P.C.
8th Floor
1100 North Glebe Road
Arlington
VA
22201
US
|
Assignee: |
CPFILMS INC.
|
Family ID: |
22248574 |
Appl. No.: |
09/773892 |
Filed: |
February 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09773892 |
Feb 2, 2001 |
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09095010 |
Jun 10, 1998 |
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6245428 |
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Current U.S.
Class: |
428/421 ;
427/412.1; 427/419.2; 428/215; 428/216; 428/329; 428/333 |
Current CPC
Class: |
Y10T 428/31786 20150401;
G02B 1/111 20130101; Y10T 428/24975 20150115; Y10T 428/24967
20150115; C08J 7/042 20130101; C08J 7/046 20200101; Y10T 428/257
20150115; Y10T 428/3154 20150401; Y10T 428/261 20150115; C08J 7/043
20200101; Y10T 428/31663 20150401 |
Class at
Publication: |
428/421 ;
427/412.1; 427/419.2; 428/333; 428/215; 428/216; 428/329 |
International
Class: |
B05D 001/36 |
Claims
1. An anti-reflective film comprising a transparent polymeric film
substrate coated with at least two polymeric layers, the two layers
being an exposed outer polymeric layer comprising a fluorine
containing polymer and immediately adjacent thereto an inner
organometallic polymeric layer adjacent the exposed outer layer
comprising the condensation product of a metal alkoxide and a
polymer reactive with the metal alkoxide.
2. Anti-reflective film as claimed in claim 1 wherein said inner
polymeric layer comprises the reaction product of a metal alkoxide
and a polymer having silane group therein.
3. Anti reflective film as claimed in claim 2 wherein the metal
alkoxide is a titanium alkoxide, preferably titanium
isopropoxide.
4. Anti reflective film as claimed in claim 2 wherein the silane
containing polymer is a silane modified polyester.
5. Anti reflective film as claimed in claim 1, wherein the exposed
outer polymeric layer is a crosslinked fluorine containing
polymer.
6. Anti reflective film as claimed in claim 1 wherein the exposed
outer polymeric layer is an acrylate modified
perfluoropolyether.
7. Anti reflective film as claimed in claim 1 wherein the film
further comprises at least one further optically active layer
between the substrate and said inner layer.
8. Anti reflective film as claimed in claim 1 wherein the film
substrate has a hard abrasion resistant coating immediately
adjacent thereto.
9. Anti-reflective film as claimed in claim 1 wherein the inner
polymer layer has a refractive index of at least 1.60 and a
thickness of about {fraction (1/4)} wavelength and the exposed
polymeric layer has a refractive index not greater than 1.45 and a
thickness of about {fraction (1/4)} wavelength.
10. Anti-reflective film as claimed in claim 2 wherein the inner
layer comprises as an additive a carbodiimide functional
silane.
11. An anti-reflective film comprising a transparent polymeric film
substrate, an exposed outer polymeric layer comprising
fluoro-containing polymers having a refractive index not greater
than 1.45 and a thickness of about {fraction (1/4)} wavelength and
an inner polymeric layer adjacent the exposed outer layer
containing metal oxide and having a refractive index of at least
about 1.6 and a thickness of about {fraction (1/4)} wavelength.
12. A multilayer anti-reflective film comprising a transparent
polymeric film substrate and including as one of its layers a
transparent polymeric layer containing inorganic powder particles
having a refractive index greater than 2.6.
13. An anti-reflective film as claimed in claim 12, wherein the
powder particles are coloured powders having an average equivalent
diameter of less than 100 nm (100-10.sup.-9 m).
14. An anti-reflective film as claimed in claim 12, wherein the
powder particles are metal compounds, in particular metal
oxides.
15. An anti-reflective film as claimed in claim 14, wherein the
metal compound is preferably an iron oxide, in particular
haematite.
16. A multilayer anti-reflective film comprising a transparent
polymeric film substrate and including as one of its layers a
transparent coloured polymeric layer containing inorganic powdered
particles which impart the coloration to said layer, and raise the
refractive index of said layer to at least 1.6.
17. A method of manufacture of an anti-reflective film in which
method a reaction mixture of a metal alkoxide and a silane modified
polymer is coated onto a transparent film substrate and cured to
form an inner polymeric layer, and a further layer of a fluorine
containing polymer is coated over the inner layer, and is cured to
form an exposed outer polymeric layer.
18. A method as claimed in claim 17, wherein the inner layer is a
reaction mixture of a metal alkoxide and a silane modified polymer
which is cured at 180.degree. C. for at least one minute, and the
second layer is a fluorine containing polymer coated over the first
layer directly in contact therewith.
19. A method as claimed in claim 17 wherein the silane modified
polymer is a polyester having silane groups on the polymer
chain.
20. A method as claimed in claim 17 where the first layer is
applied as a solution in a volatile solvent which is removed from
the layer prior to curing.
21. A method as claimed in claim 19 wherein up to 10% by weight of
a carbodiimide functional silane is added as a crosslinking agent
to said reaction mixture.
22. A method of manufacture of an anti-reflective film laminate in
which method particles of metal oxide are dispersed in a liquid
polymeric material, and the polymeric material is coated onto a
polymeric film substrate and cured to give a transparent inner
polymeric layer having a refractive index of at least about 1.6 and
a thickness of about {fraction (1/4)} wavelength, and the inner
polymeric layer is overcoated by a further transparent polymeric
layer of fluorine containing polymer which is cured to give an
outer polymeric layer having a refractive index of not greater than
1.45 and a thickness of about {fraction (1/4)} wavelength.
23. A method as claimed in claim 22, wherein the inner polymeric
layer is formed from a mixture of polymerisable monomers including
a triacrylate, or a tetra acrylate and acrylic acid and photo
initiators into which finely ground metal oxide is dispersed.
24. A method as claimed in claim 20, wherein the metal oxide is
preferably an iron oxide which has been ground to a particle size
having an average equivalent diameter of less than 100 nm
(100.times.10.sup.-9 m).
25. A method of making a multilayer anti-reflective film in which a
polymeric film substrate is coated with a transparent polymer layer
containing inorganic powdered material dispersed within the layer,
the powder particles having a high refractive index of greater than
2.6, the film having a haze value of less than 20%.
26. A method of making an antireflective film as claimed in claim
25 wherein the haze value of the film is less than 3%.
27. A method as claimed in claim 25 wherein the transparent layer
is also coloured by means of the powder particles to form a
transparent coloured layer.
28. A method as claimed in claim 25 wherein the transparent layer
is an inner layer which is overcoated by an outer polymeric layer,
the outer layer being coated onto the inner layer by either vacuum
deposition, or by coating the inner layer with a solution of the
second polymer, followed by removal of the solvent.
29. A method of manufacture of a multilayer anti-reflective
polymeric film having at least a two layer anti-reflective coating,
wherein the inner layer of said two layers has a refractive index
of at least 1.69 and comprises particles of iron oxide dispersed in
a curable polymeric resin to form a transparent high refractive
index layer.
30. A method as claimed in claim 29, wherein the refractive index
of said layer may be altered by varying the iron oxide content of
the polymeric layer.
31. A method of making an anti-reflective film in which a polymeric
film substrate is coated with a transparent polymer layer
containing inorganic powdered material dispersed within the layer
to form a coloured transparent film, having a refractive index of
at least 1.6.
32. A multilayer antireflection film as claimed in claim 16 wherein
the coloration of the transparent coloured polymeric layer is
neutralised by including a suitable dye in the polymeric film
substrate, or other layer of said layers.
Description
[0001] This invention relates to low reflective transparent
polymeric films.
[0002] The transparency of windows, show cases, glass, viewers or
video screens can be effected by glare, reflective light sources,
or the reflection of surrounding scenery. In order to ameliorate
the problem with glare and reflections, anti-reflective coatings
have been developed which are typically applied to a surface by
vapour deposition or sputtering methods.
[0003] Another method for depositing anti reflective coatings is
disclosed in U.S. Pat. No. 4,687,707 in which the coating is formed
from a thin layer of a reaction product containing a metal oxide
e.g. SiO.sub.2 or TiO.sub.2. Such a product results from the
condensation of titanium tetra-alkoxides, titanium chelates or
tetraalkoxy silanes. To this layer, is added a second layer of a
condensation product containing a fluorine compound such as
fluorine containing silane compounds. This multi layer construction
bringing about an improvement in the reduction of reflectance.
[0004] U.S. Pat. No. 4,966,812 discloses the deposition of a low
refractive index anti-reflective coating on plastics material using
sol-gel techniques. U.S. Pat. No. 5,109,080 discloses a high
refractive index ceramic/polymer material which is made from a
sol-gel synthesis of a metal alkoxide with an alkoxysilane-capped
poly(arylene ether) polymeric component.
[0005] EP 0166363 discloses the use of at least two thin layers as
a low reflective coating, a first layer containing metal oxide and
having a refractive index in the range of 1.65-2.10, and a second
over layer comprising a fluorine-containing silicon compound making
a low refractive index having a refractive index of about 1.4.
[0006] The present invention provides a transparent polymeric film
having an anti-reflective coating, the coating being a novel
coating.
[0007] According to the invention there is provided an
anti-reflective film comprising a transparent polymeric film
substrate coated with at least two polymeric layers, the two layers
being an exposed outer polymeric layer comprising a fluorine
containing polymer and an inner organometallic reflective layer
adjacent the exposed layer and comprising the condensation product
of a metal alkoxide and a polymer reactive with the metal
alkoxide.
[0008] Preferably the inner organometallic polymeric layer has a
refractive index of at least 1.6, more preferably 1.7 and the outer
layer has a refractive index not greater than 1.45, and preferably
not greater than 1.4.
[0009] Additional optically active layers of a desired refractive
index may be coated onto the film substrate between said substrate
and said inner layer and said additional layer or layers may be the
same as the inner and outer layers, or different as is
required.
[0010] Also according to the invention there is provided an
anti-reflective film comprising a transparent polymeric film
substrate, an exposed outer polymeric layer comprising fluorine
containing polymers having a refractive index not greater than 1.45
and a thickness in the order of {fraction (1/4)} wavelength, and an
inner polymeric layer adjacent the exposed outer layer containing
metal oxide and having a refractive index of at least about 1.6 and
a thickness of about {fraction (1/4)} wavelength.
[0011] The polymeric film may comprise at least one of cellulose
acetate, polyamide, acrylic, polyester, and polycarbonate
films.
[0012] For the purpose of the present invention the wave length of
light is taken as substantially the middle of the visible range
that is about 550 nm in air, and the wave length in a particular
layer is related to the refractive index of the material of that
layer by the formula= 1 mat = air material
[0013] where .mu.=wavelength and .eta.=refraction index
[0014] Preferably the inner polymeric layer comprises the reaction
product of a titanium alkoxide, preferably titanium isopropoxide,
and a silane containing polymer which can undergo the sol-gel
reaction. Suitable polymers are .alpha..omega.
dihydroxypolysiloxanes poly(methyl phenyl siloxane), poly
(dimethylsiloxane), and silane modified polyesters.
[0015] Preferably the second layer is a fluorine containing polymer
which is crosslinkable, preferably using one of the known curing
techniques for example ultra violet light, thermal cure, electron
beam, free radical and cationic initiation. Preferably the fluorine
containing polymer is an acrylate, conveniently an acrylate
modified perfluoropolyether. Alternatively the fluorine containing
polymer may be a vinyl ether which is crosslinked by a cationic
initiator.
[0016] The invention also provides a method of manufacture of an
anti reflective film in which method fine particles of metal oxide
are dispersed in a liquid polymeric material, and the liquid
polymeric material is coated onto a polymeric film substrate and
cured to give a transparent inner polymeric layer having a
refractive index of at least about 1.60 and a thickness of about
{fraction (1/4)} wavelength, and the inner polymeric layer is
overcoated by an outer polymeric layer of fluorine containing
polymer which is cured to give an exposed outer polymeric layer
having a refractive index no greater than 1.45 and a thickness of
substantially {fraction (1/4)} wavelength.
[0017] The invention also provides a further method of manufacture
of an anti-reflective film in which method a reaction mixture of a
metal alkoxide and a silane modified polymer is coated onto a
transparent film substrate and cured to form an inner polymeric
layer, and a second layer of a fluorine containing polymer is
coated over the inner layer, and is cured to form an exposed outer
polymeric layer.
[0018] The outer layer can be coated onto the inner layer by either
vacuum deposition, or by overcoating the inner layer with a
solution of the fluorine containing polymer, followed by removal of
the solvent.
[0019] Preferably the first layer is a reaction mixture of a metal
alkoxide and a silane modified polyester, and the mixture is cured
at 180.degree. C. for at least one minute to form said inner layer,
and the outer layer is a fluorine containing polymer which is
coated over the inner layer directly in contact therewith.
Preferably the outer layer is curable on exposure to ultra violet
light.
[0020] Preferably the metal alkoxide is a titanium or zirconium
alkoxide.
[0021] Preferably up to 10% by weight of a silane coupling agent,
preferably a carbodiimide functional silane, is added as a
crosslinking agent to the sol-gel reaction mixture, more preferably
about 4% carbodiimide.
[0022] Alternatively the inner polymeric layer may be formed from
polymerisable monomers such as acrylates, methacrylates, vinyl
ether, epoxies, or other monomers containing unsaturated bonds, or
from a mixture of polymerisable monomers preferably a triacrylate,
or a tetraacrylate and acrylic acid and photo initiators into which
fine metal mineral powder is dispersed. Preferably the mineral
powder is a colour imparting powder such as a metal oxide, and the
particles are sufficiently small that the layer is transparent.
Preferably the metal oxide is an iron oxide, preferably haematite
which has been ground to a particle size having an average
equivalent diameter of less than 100 nm (100.times.10.sup.-9m) and
preferably less than 50 nm (50.times.10.sup.-9m).
[0023] The invention also relates to a method of making a multi
layer anti reflective polymeric film comprising a polymer film
substrate and having as one of its layers a layer comprising
particles of metal oxide, preferably iron oxide, dispersed in a
curable polymeric resin, the particles having an average equivalent
diameter of less than 100.times.10.sup.-9 m. The presence of the
metal oxide powder especially coloured powder, such as iron oxide,
colours the polymer film layer which absorbs some light and thereby
reduces reflection to give an improved anti-reflectance.
[0024] If it is desired to reduce the coloration due to the pigment
a dye may be added to the film substrate or other layer to produce
an overall neutral colour e.g. grey by the addition of blue and red
dyes to the polyester substrate.
[0025] The refractive index may be varied by varying the content of
iron oxide present in the polymeric coating. The iron oxide may
comprise up to 85% by weight of the coating but preferably
comprises 25-70% by weight of the coating and more preferably
40-55% by weight.
[0026] Also, according to the invention there is provided a further
method of making a multi-layer anti-reflective film in which a
polymeric film substrate is coated with a transparent polymer layer
containing inorganic powdered material dispersed within the layer,
the powder particles have a high refractive index of greater than
2.6, the film having a haze value of less than 20%.
[0027] The haze value will be dependant upon several features
including particle size. Preferably the particle size does not
exceed 50 nm.
[0028] The film haze is measured in accordance with ASTMS D1003-61
using a HazeGard Plus hazemeter catalogue number 4725 available
from BYK Gardner Inc. of Silver Spring, Md.
[0029] Preferably the haze value does not exceed 5%, and more
preferably does not exceed 3%.
[0030] Also, according to yet another aspect of the invention there
is provided a further method of making an anti-reflective film in
which a polymeric film substrate is coated with at least one
transparent polymer layer containing inorganic powdered material
dispersed within the layer and forming a coloured film, having a
refractive index of at least 1.6.
[0031] Preferably the inorganic powders are coloured powders
particularly metal compounds.
[0032] Suitable inorganic powders include the following:
[0033] Lead oxide
[0034] Ferric oxide
[0035] Lead Sulphide
[0036] Calcium Sulphide
[0037] Mercury Sulphide
[0038] Silicon
[0039] Silicon Carbide
[0040] Germanium
[0041] Boron
[0042] Selenium
[0043] The present invention will be described by way of example
and with reference to the accompanying drawings in which:
[0044] FIG. 1 is a schematic cross-sectional drawing of a film
laminate according to the present invention, and
[0045] FIG. 2 is a schematic cross-sectional drawing of a second
film laminate according to the invention.
[0046] With reference to FIG. 1 there is shown a transparent
polymeric film 11 of the type sold for adhering to the window glass
of building, automobiles, display cases, screens etc. The preferred
polymeric film is polyester film, preferably polyethylene
tetraphthalate (PET) which is about 25 microns in thickness. PET
film 11 has a refractive index of between 1.63-1.67, generally
about 1.65. The polyester film 11 is then optionally coated with a
hard abrasion resistant coating 12. Details of the coating 12 and
its method of application are described in U.S. Pat. No. 4,557,980
the contents of which are hereby incorporated into the present
description by reference. The abrasion resistant coating 12 is a
mixture of polymerisable monomers including triacrylate or a tetra
acrylate and acrylic acid and photoinitiators, which is applied to
the film by any suitable method, preferably by direct gravure, and
polymerised by UV radiation to cure the acrylic coating. The
coating 12 is about 4 .mu.m (microns) in thickness and has a
refractive index of about 1.52.
[0047] The PET film 11 and optionally the abrasion resistant layer
12 are in turn coated in anti-reflective layers 13. The
anti-reflective layers 13 comprise a first inner high refractive
index ceromer layer 14 about 80 nm thick containing metal oxide
particles, and a second outer lower refractive index polymeric
layer 15 about 90-100 nm thick. The outer layer 15 is exposed to
the air and is formed from a fluorine containing polymer.
[0048] In the first polymeric layer 14 the metal oxide ceromer may
be formed by an condensation reaction between a metal alkoxide and
a polyester containing silane groups. The preferred metal oxides
are Titanium and Zirconium Dioxides, more preferably Titanium
Dioxide, formed from the gel reaction between titanium isopropoxide
and a polymer having silane groups. Preferably the polymer is a
polyester having silane groups, preferably at least one end of the
polymer chain. The preferred polyesters are Morton Adcote 89R3 and
Morton Adcote 89R1 and are of the type described in U.S. Pat. No.
4,408,021, and its continuation-in-part U.S. Pat. No.
4,429,005.
[0049] The titanium isopropoxide and the silane functional
polyester groups condense to form a TiO.sub.2/polymer ceramer.
[0050] The refractive index of the first polymeric layer 14
(ceramer) is determined by the relative amounts of Titanium dioxide
and polymer present. The higher refractive index values being given
by greater proportions of Titanium Dioxide being present. However,
the properties of the layer 14 are a compromise between having a
high refractive index value and good flexibility, so that the layer
14 adheres to, and flexes with the PET film 11. The ratio of
Titanium isopropoxide:silane modified polyester should be between
60:40 and 40:60 by weight respectively, preferably 50:50.
[0051] The sol-gel reaction mixture is dissolved in methyl ethyl
ketone (MEK) to give an 8% solid solution which is coated on the
film 11 or abrasive resistant coating 12 by reverse gravure
printing using a 360 QCH gravure cylinder. The film passes through
an oven at 180.degree. C. with a residence time of 1 min to
partially cure the sol-gel coating.
[0052] An 8% solid solution gave a coating about 50 nm in thickness
(50.times.10.sup.-9 m). This thickness of coating may also be
achieved by coating less concentrated solution and building up the
coats before curing. This coating thickness is less than {fraction
(1/4)} of wavelength.
[0053] Alternative silane substituted polymers may include
polydimethyl siloxane, alkoxysilanes, and polyesters having silane
groups partially substituted for the hydroxy groups.
[0054] It is advantageous to add a small percentage by weight of a
silane coupling agent, preferably a carbodiimide functional silane
(available from Zeneca) as a cross-linking agent for reaction with
the metal alkoxide. This may help promote adhesion to the film 11
and reduce the likelihood of phase separation in the sol-gel.
Preferably about 1-10%, or more preferably 4% by weight of
carbodiimide are added to a 100 parts by weight mix of Titanium
isopropoxide and silane modified polyester.
[0055] Example 1 relates to the preparation of a suitable ceramer
Coating.
EXAMPLE 1
Preparation of a 50:50 Ti(iPrO).sub.4:Adcote 89R3 Ceramer
Solution
[0056] 2.5 gms of titanium isopropoxide is taken into a
polypropylene bottle. 2.5 gms of MEK is weighed into another bottle
and 0.05 ml of 10N HCL is added. This acidic MEK is added to
titanium isopropoxide slowly taking care to contain any exotherm
present.
[0057] 2.17 gms of Adcote 89R3 (original resin containing 32.9%
solids) is taken and 3 gms of MEK are added to reduce its
viscosity. This solution is added under rapid stirring to titanium
solution slowly taking care to quench any exotherm present. When
the addition is complete pH is adjusted to 2.5. The mixture is
allowed to stir for 5 minutes. 2% crosslinking agent is added to
the solution and stirred for a further 10 minute period. Then it is
diluted further with MEK to give required concentration.
[0058] This solution now can be used to coat suitable substrates.
The cured ceramer coatings have a high refractive index in the
order of 1.69 to 1.71.
[0059] Alternatively, the first polymeric layer 14 may be formed
from the same polymeric matrix as the optional abrasion resistant
coating 12 with the further addition of particles of an iron oxide
which have been reduced to an equivalent average, diameter size of
less than 50 nm (m.sup.-9). Suitable powdered iron oxide is
available from Cookson Matthey Ceramics & Materials Ltd,
England and sold under the references AC0575 and AC 1075. The
preferred iron oxide is haematite (Fe.sub.2O.sub.3), that is the
AC0575. The amount of iron oxide added to the coating will
determine the refractive index of the coating. A layer 14
containing 35-40% by weight of iron oxide will have a refractive
index of at least 1.69, and with loadings of greater than 50% it
will be possible to raise the refractive index to at least 1.8, or
higher as is desired.
[0060] The iron oxide is suspended in suitable solvent for the
polymer, typically MEK, together with a dispersant e.g. Solsperse
24000 available from Zeneca. The mixture is thoroughly mixed in a
ball mill to ensure an even dispersion of the particles in the
solvent, and the suspension is then mixed with the polymer by
mechanical mixing.
[0061] The final layer (14) may include 5-85% by weight of
haematite, 1-13% by weight of surfactant, with the balance being
the polymer matrix.
[0062] By controlling the amount of heamatite present in the
polymer it is possible to produce a layer having a desired
refractive index. For example 20-25% iron oxide content will
produce a layer having a refractive index of at least 1.74.
[0063] Example 2 relates to the preparation of a red iron oxide
dispersion and its mixing into the polymer coating.
EXAMPLE 2
[0064] Preparation of transparent red iron oxide dispersion in
methyl ethyl ketone:
[0065] By weight--
[0066] 40% transparent red iron oxide AC1075
[0067] 6.4% Solsperse 24,000 (dispersant ex Zeneca)
[0068] 53.6% MEK
[0069] Mixed in a ball mill containing 1 mm Zirconia beads and
rolled for 3 weeks.
[0070] Final dispersion mixed with MEK and hardcoat (layer 12)
formulation (48% acrylic acid, 47% pentaerythritol triacrylate, 5%
photoinitiator--Irgacure 184 ex Ciba Geigy) to give dispersion
containing:
[0071] By weight--
[0072] 5% hardcoat formulation
[0073] 5% transparent red iron oxide
[0074] 0.8% dispersant
[0075] 89.2% MEK
[0076] The dispersion was coated onto the substrate and cured using
UV radiation to give a final coating containing approximately 18%
by volume iron oxide.
[0077] The second outer polymeric layer 15 is a fluorine containing
polymer which may be selected from among many well known and ready
synthesisable fluorinated polymers. The refractive index typically
decreases with increased fluorination. Fluorinated polymers having
a respective refractive index of between 1.3-1.45 are preferred.
Preferred fluorinated polymers may include a copolymer of
vinylidene fluoride and tetrafluorethylene, copolymers of
chlorotrifluoro ethylene and vinylidene fluoride, polyvinylidene
fluoride, dehydrofluorinated polyvinylidene fluoride, copolymer of
hexafluoropropylene and vinylidene fluoride, and fluorinated
acrylics such as poly (1-1 dihydropentadecafluorooctyl acrylate) or
poly[(11dihydropentadenefluorooctyl methacrylate) which have a
refractive index of about 1.37-1.38 and other perfluoro polyesters
containing acrylate end groups. Such material can be cured by
exposure to ultra violet light.
[0078] The preferred fluorinated polymer is an acrylate modified
low molecular weight perfluoro polyether. The low molecular
perfluoropolyether is available from Ausimont (an Italian company)
under the trade name Fluorlink .beta., which then undergoes further
reaction resulting in, preferably 100%, substitution of acrylate
groups for the isocyanate and hydroxyl groups.
[0079] Example 3 relates to the preparation of two suitable
perfluoropolyether polymers.
EXAMPLE 3
Synthesis of Acrylate Tipped Perfluoropolyether Polymers
[0080] Acrylate monomers are reacted with isocyanate terminated
fluoropolymers using a suitable solvent at room temperature. When
there is no residual isocyanate, the acrylated fluoropolymer is UV
cured to give low refractive index hard coats in the order of 1.37
to 1.4.
EXAMPLE 3a
[0081] 0.00159 moles of Fluorolink B (Fomblin Z Disoc, supplied by
Ausimont, Italy) is taken into a dry flask purged with nitrogen.
The polymer is dissolved in hexafluoroxylene. Then an excess of
hydroxybutylacrylate (0.003 moles) was added and the sum stirred at
room temperature for a week. When there is no residual isocyanate,
(confirmed by Infrared analysis), the clean, viscous solution was
applied to the first layer 14 and cured.
EXAMPLE 3(b)
[0082] 0.0015 moles of Fluorolink B is taken into a clean dry flask
and purged with nitrogen. The polymer was dissolved in
hexafluoroxylene. When dissolved completely, an excess of
pentaerythritol triacrylate is added to it and stirred at room
temperature for a week. The reaction was continued until there was
no isocyanate.
[0083] The triacrylate functionalised polymer was coated on to the
first layer 14 and UV cured to give a hard low refractive index
coating.
[0084] The fluorinated polymer may be applied as a solution in
various solvents, in particular ketones, such as methylethyl
ketone, methyl isobutyl ketone, methyl propyl ketone or mixtures
thereof in concentrations of about 2-3%.
[0085] Fluorinated polymers may be used in blends, or mixtures, or
alone. The proportions of the blends may vary depending upon the
desired properties of the second layer 15, and the fluoropolymers
may be mixed with a small percentage of polymethyl methacrylate
(0-30%) Such materials are described in U.S. Pat. No. 3,925,081 and
U.S. Pat. No. 4,046,457 the contents of which are hereby
incorporated.
[0086] The fluoropolymer second layer 15 is coated onto the dried
ceramer layer 14 by any suitable process, preferably by reverse
gravure process to a thickness (when dried) of about 90 nm
(90.times.10.sup.-9 m) which is about {fraction (1/4)} of
wavelength. The presence of any groups in the first layer 14 may
promote adhesion between the two layers 14 and 15.
[0087] Alternatively a suitable fluoropolymer may be evaporated
under vacuum and deposited onto the first polymer layer, and
subsequently cured by electron beam initiator techniques.
[0088] The film laminate will preferably comprise at least a
polyester substrate having a refractive index of about 1.6, an
inner of a polymeric film (14) containing metal oxide and having a
refractive index of greater than 1.68 and preferably greater than
1.7, and a layer thickness of about {fraction (1/4)} wavelength,
with a second polymeric layer (15) in contact with the first layer
(14) to form an exposed outer layer and comprising a fluorinated
polymer having a refractive index of 1.45 or less preferably no
more than 1.4 and a thickness of about {fraction (1/4)}
wavelength.
[0089] In a further embodiment of the invention shown in FIG. 2 the
polyester substrate 11 has the optional hard coat layer 12 adjacent
thereto as described previously. The anti-reflective layers
comprise as before the outer exposed polymeric lower refractive
index layer 15 and the adjacent inner higher refractive index layer
14.
[0090] The laminate may further comprise function layers arranged
between the hard coat (12) and the two outer layers (14) (15). The
function layers may comprise a second pair of layers 24, 25 or
alternatively may further include only one further additional layer
(24) or (25). The layers (24) (25) may be optically active having a
pre-determined refractive index, or other property such as colour
to suit the end use of the film.
* * * * *