U.S. patent application number 11/077598 was filed with the patent office on 2006-09-14 for polymerizable composition comprising low molecular weight organic component.
Invention is credited to Emily S. Goenner, Clinton L. Jones, Brant U. Kolb, David B. Olson.
Application Number | 20060204676 11/077598 |
Document ID | / |
Family ID | 36577526 |
Filed Date | 2006-09-14 |
United States Patent
Application |
20060204676 |
Kind Code |
A1 |
Jones; Clinton L. ; et
al. |
September 14, 2006 |
Polymerizable composition comprising low molecular weight organic
component
Abstract
Polymerizable compositions comprising particularly useful for
brightness enhancing films.
Inventors: |
Jones; Clinton L.;
(Somerset, WI) ; Goenner; Emily S.; (Shoreview,
MN) ; Olson; David B.; (Marine on St. Croix, MN)
; Kolb; Brant U.; (Afton, MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Family ID: |
36577526 |
Appl. No.: |
11/077598 |
Filed: |
March 11, 2005 |
Current U.S.
Class: |
428/1.1 ;
428/156 |
Current CPC
Class: |
G02F 1/133507 20210101;
Y10S 977/932 20130101; G02B 6/0053 20130101; Y10T 428/2982
20150115; Y10T 428/256 20150115; Y10T 428/258 20150115; G02B 6/0065
20130101; Y10T 428/31855 20150401; Y10T 428/24479 20150115; Y10T
428/257 20150115; B82Y 30/00 20130101; Y10T 428/259 20150115; G02B
1/04 20130101; Y10S 977/84 20130101; C09K 2323/00 20200801; C09K
2323/035 20200801; Y10S 977/939 20130101; G02B 1/04 20130101; C08L
33/08 20130101; G02B 1/04 20130101; C08L 33/10 20130101 |
Class at
Publication: |
428/001.1 ;
428/156 |
International
Class: |
B32B 3/00 20060101
B32B003/00; C09K 19/00 20060101 C09K019/00 |
Claims
1. A brightness enhancing film comprising: a brightness enhancing
polymerized structure comprising the reaction product of a
substantially solvent free polymerizable composition comprising an
organic component comprising one or more ethylenically unsaturated
monomers, wherein the organic phase is free of oligomeric monomer
having a number average molecular weight of greater than 450
g/mole; and at least 10 wt-% inorganic nanoparticles.
2. The brightness enhancing film of claim 1 wherein the
polymerizable composition has a refractive index of at least 1.47,
a refractive index of at least 1.52, a refractive index of at least
1.55, or a refractive index of at least 1.60.
3. The brightness enhancing film of claim 1 wherein the organic
component has a viscosity of less than 1000 cps at 180.degree. F.,
a viscosity of less than 1000 cps at 160.degree. F., a viscosity of
less than 1000 cps at 140.degree. F., a viscosity of less than 1000
cps at 120.degree. F., a viscosity of less than 800 cps at
120.degree. F., or a viscosity of less than 600 cps at 120.degree.
F.
4. The brightness enhancing film of 1 wherein the polymerizable
composition comprises photoinitiator.
5. The brightness enhancing film of claim 4 where in the
polymerizable composition is cured by means of ultraviolet
radiation.
6. The brightness enhancing film of claim 1 wherein the organic
component comprises at least one monomer having a refractive index
of at least 1.47.
7. The brightness enhancing film of claim 6 wherein the organic
component comprises a monomer selected from the group consisting of
phenoxy ethyl acrylate; phenylthio ethyl acrylate; 2-naphthylthio
ethyl acrylate; 1-naphthylthio ethyl acrylate;
2,4,6-tribromophenoxy ethyl acrylate; 2,4-dibromophenoxy ethyl
acrylate; 2-bromophenoxy ethyl acrylate; 1-naphthyloxy ethyl
acrylate; 2-naphthyloxy ethyl acrylate; phenoxy 2-methylethyl
acrylate; phenoxyethoxy ethyl acrylate; 3-phenoxy-2-hydroxy propyl
acrylate; 2-phenylphenoxy ethyl acrylate; 4-phenylphenoxy ethyl
acrylate; 2,4-dibromo-6-sec-butylphenyl acrylate;
2,4-dibromo-6-isopropylphenyl acrylate; benzyl acrylate; phenyl
acrylate; 2,4,6-tribromophenyl acrylate; and mixtures thereof.
8. The brightness enhancing film of claim 1 wherein the organic
component comprises at least one monomer having a refractive index
of at least 1.50 in combination with a second monomer having a
refractive index of less than 1.50.
9. The brightness enhancing film of claim 8 wherein the second
monomer has a refractive index of less than 1.47.
10. The brightness enhancing film of claim 1 wherein at least one
monomer of the organic component has at least two ethylenically
unsaturated groups.
11. The brightness enhancing film of claim 10 where the monomer is
selected from hexanediol diacrylate, pentaerythritol
tri(meth)acrylate, pentaerythritol tetra(meth)acrylate,
trimethylolpropane tri(meth)acrylate, dipentaerythritol
penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate,
trimethylolpropane ethoxylate tri(meth)acrylate, glyceryl
tri(meth)acrylate, pentaerythritol propoxylate tri(meth)acrylate,
ditrimethylolpropane tetra(meth)acrylate, and mixtures thereof.
12. The brightness enhancing film of claim 1, wherein the
polymerized structure has a plurality of ridges extending along a
first surface.
13. The brightness enhancing film of claim 12 wherein the ridges
have rounded apexes having a radius ranging from 4 to 15
micrometers.
14. The brightness enhancing film of claim 1, wherein the inorganic
nanoparticles have a primary particle size in a range selected from
1 nm to 100 nm, 5 nm to 75 nm, or 10 nm to 30 nm.
15. The brightness enhancing film according to claim 1, wherein the
inorganic nanoparticles comprise 10 wt-% to 60 wt-% or 10 wt-% to
40 wt-% of the polymerized structure.
16. The brightness enhancing film according to claim 1, wherein the
nanoparticles are selected from silica, zirconia, titania, antimony
oxides, alumina, tin oxides, mixed metal oxides thereof, or
mixtures thereof.
17. The brightness enhancing film according to claim 1, wherein the
nanoparticles are surface modified such that the nanoparticles are
polymerizable with the organic component.
18. The brightness enhancing film according to claim 1 wherein the
base layer is a polarizing layer.
19. The brightness enhancing film according to claim 18 wherein the
base layer is a reflective polarizing layer.
20. A device comprising: (a) a lighting device having a
light-emitting surface; and (b) the brightness enhancing film of
claim 1 placed substantially parallel to said light-emitting
surface.
21. The device according to claim 20, wherein the lighting device
is a back-lit display device or a liquid crystal display
device.
22. The device according to claim 20, wherein the device is
selected from a handheld device, a computer display and a
television.
23. The brightness enhancing film of claim 1 wherein the film is a
turning film and the refractive index of the polymerizable
composition is at least 1.44.
24. The brightness enhancing film of claim 23 wherein the film has
rounded apexes having a radius ranging from 0.5 to 10
micrometers.
25. An illumination device comprising: (a) a lighting source having
a lightguide having a light-emitting surface; and (b) the turning
film of claim 24 placed substantially parallel to said lightguide,
said turning film having a first surface and a second surface and
an array of prisms formed on the first surface, the turning film
disposed with the first surface disposed in relation to the
light-emitting surface such that light rays exiting the
light-emmiting surface of the lightguide encounter the array of
prisms and are reflected and refracted by the array of prisms such
that the light rays exit the turning film via the second surface
and substantially along a desired angular direction, wherein the
array of prisms includes a first plurality of prisms, each of the
first plurality of prisms having a first prism configuration, and a
second plurality of prisms each having a second prism
configuration, different than the first prism configuration, the
first prism configuration and the second prism configuration being
such the light rays exiting the second surface correspond to a
substantially uniform sampling of the light rays entering the
lightguide.
26. A brightness enhancing film comprising: a brightness enhancing
polymerized structure comprising the reaction product of a
substantially solvent free polymerizable composition comprising an
organic component comprising one or more ethylenically unsaturated
monomers, wherein the organic phase is free of oligomeric monomer
having a number average molecular weight of greater than 450 g/mole
and the polymerizable composition comprises at least one ingredient
that comprises at least two ethylenically unsaturated groups.
27. A microstructured article comprising the reaction product of a
substantially solvent free polymerizable composition comprising an
organic component comprising one or more ethylenically unsaturated
monomers and optionally inorganic nanoparticles, wherein the
organic component is free of oligomeric monomer having a number
average molecular weight of greater than 450 g/mole and the
polymerizable composition comprises at least one ingredient that
comprises at least two (meth)acrylate groups.
28. The microstructured article of claim 27 wherein the article is
retroreflective.
29. The microstructured article of claim 27 wherein the article is
a flexible mold suitable for making barrier ribs fro a plasma
display panel.
Description
BACKGROUND
[0001] Certain microreplicated optical products, such as described
in U.S. Pat. Nos. 5,175,030 and 5,183,597, are commonly referred to
as a "brightness enhancing films". Brightness enhancing films are
utilized in many electronic products to increase the brightness of
a backlit flat panel display such as a liquid crystal display (LCD)
including those used in electroluminescent panels, laptop computer
displays, word processors, desktop monitors, televisions, video
cameras, as well as automotive and aviation displays.
[0002] Brightness enhancing films desirably exhibit specific
optical and physical properties including the index of refraction
of a brightness enhancing film that is related to the brightness
gain (i.e. "gain") produced. Improved brightness can allow the
electronic product to operate more efficiently by using less power
to light the display, thereby reducing the power consumption,
placing a lower heat load on its components, and extending the
lifetime of the product.
[0003] Brightness enhancing films have been prepared from high
index of refraction monomers that are cured or polymerized, as
described for example in U.S. Pat. Nos. 5,908,874; 5,932,626;
6,107,364; 6,280,063; 6,355,754; as well as EP 1 014113 and WO
03/076528.
[0004] Although various polymerizable compositions that are
suitable for the manufacture of brightness enhancing films are
known, industry would find advantage in alternative
compositions.
SUMMARY OF THE INVENTION
[0005] Presently described are brightness enhancing films that
comprise a brightness enhancing polymerized structure comprising
the reaction product of a substantially solvent free polymerizable
composition comprising an organic component and optionally an
inorganic component.
[0006] The organic component comprises one or more monomers and is
free of any oligomeric ethylenically unsaturated monomer having a
molecular weight (Mn) of greater than 450 g/mole. The organic
component preferably has a viscosity of less than 1000 cps at
180.degree. F.
[0007] The polymerizable composition comprises at least one
ingredient that comprises at least two ethylenically unsaturated
groups. For embodiments wherein the organic component is the
totality of the polymerizable composition, at least one of the
monomers comprises at least two ethylenically unsaturated groups.
However, for embodiments wherein the organic component is combined
with surface modified nanoparticles, the nanoparticles may have
sufficient functionality such that the monomer(s) of the organic
component may be monofunctional.
[0008] In a preferred embodiment, the polymerizable composition
comprises the organic component and at least 10 wt-% inorganic
nanoparticles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The invention may be more completely understood in
consideration of the following detailed description of various
embodiments of the invention in connection with the accompanying
drawings, in which:
[0010] FIG. 1 is a schematic view of an illustrative
micro-structured article of the present invention in a backlit
liquid crystal display;
[0011] FIG. 2 is a perspective view of an illustrative polymerized
structure bearing a micro-structured surface;
[0012] FIG. 3 is a cross-sectional view of an illustrative
micro-structured article that has prism elements of varying
height;
[0013] FIG. 4 is a cross-sectional view of an illustrative
micro-structured article that has prism elements of varying
height;
[0014] FIG. 5 is a cross-sectional view of an illustrative
micro-structured article;
[0015] FIG. 6 is a cross-sectional view of an illustrative
micro-structured article in which the prism elements are of
different heights and have their bases in different planes;
[0016] FIG. 7 is a cross-sectional view of an illustrative
micro-structured article;
[0017] FIG. 8 is a cross-sectional view of an illustrative
micro-structured article;
[0018] FIG. 9 is a cross-sectional view of an illustrative
micro-structured article;
[0019] FIG. 10 is a schematic view of an illumination device
including a turning film;
[0020] FIG. 11 is a cross-sectional view of a turning film;
[0021] FIG. 12 is a cross-sectional view of another turning
film.
[0022] While the invention is amenable to various modifications and
alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the
invention.
DETAILED DESCRIPTION
[0023] Brightness enhancing films generally enhance on-axis
luminance (referred herein as "brightness") of a lighting device.
Brightness enhancing films can be light transmissible,
microstructured films. The microstructured topography can be a
plurality of prisms on the film surface such that the films can be
used to redirect light through reflection and refraction. The
heights of the prisms typically range from about 1 to 75 microns.
When used in an optical display such as that found in laptop
computers, watches, etc., the microstructured optical film can
increase brightness of an optical display by limiting light
escaping from the display to within a pair of planes disposed at
desired angles from a normal axis running through the optical
display. As a result, light that would exit the display outside of
the allowable range is reflected back into the display where a
portion of it can be "recycled" and returned back to the
microstructured film at an angle that allows it to escape from the
display. The recycling is useful because it can reduce power
consumption needed to provide a display with a desired level of
brightness.
[0024] As described in Lu and Lu et al., a microstructure-bearing
article (e.g. brightness enhancing film) can be prepared by a
method including the steps of (a) preparing a polymerizable
composition (i.e. the polymerizable composition of the invention);
(b) depositing the polymerizable composition onto a master negative
microstructured molding surface in an amount barely sufficient to
fill the cavities of the master; (c) filling the cavities by moving
a bead of the polymerizable composition between a preformed base
and the master, at least one of which is flexible; and (d) curing
the composition. The master can be metallic, such as nickel,
nickel-plated copper or brass, or can be a thermoplastic material
that is stable under the polymerization conditions, and that
preferably has a surface energy that allows clean removal of the
polymerized material from the master. One or more the surfaces of
the base film can optionally be primed or otherwise be treated to
promote adhesion of the optical layer to the base.
[0025] The brightness enhancing or other microstructured articles
comprise a polymerized structure comprising the reaction product of
an organic component optionally comprising a plurality of (e.g.
surface modified colloidal) nanoparticles. The polymerized
structure can be an optical element or optical product constructed
of a base layer and an optical layer. The base layer and optical
layer can be formed from the same or different polymer
material.
[0026] As used herein "polymerizable composition" refers to the
total composition including the organic component that comprises at
least one polymerizable monomer and the optional inorganic
nanoparticles. The "organic component" refers to all of the
components of the composition except for the inorganic
nanoparticles. For embodiments wherein the polymerizable
composition is free of inorganic nanoparticles, the organic
component and polymerizable composition are one in the same. The
composition is particularly amenable to the method of forming
microstructured articles that is described in Lu and Lu et al., as
previously described.
[0027] The organic component as well as the polymerizable
composition is preferably substantially solvent free.
"Substantially solvent free" refer to the polymerizable composition
having less than 5 wt-%, 4 wt-%, 3 wt-%, 2 wt-%, 1 wt-% and 0.5
wt-% of (e.g. organic) solvent. The concentration of solvent can be
determined by known methods, such as gas chromatography. Solvent
concentrations of less than 0.5 wt-% are preferred.
[0028] The components of the organic component are preferably
chosen such that the organic component has a low viscosity.
Typically the viscosity of the organic component is substantially
lower than the organic component of compositions previously
employed. The viscosity of the organic component is less than 1000
cps and typically less than 900 cps. The viscosity of the organic
component may be less than 800 cps, less than 450 cps, less than
600 cps, or less than 500 cps at the coating temperature. As used
herein, viscosity is measured (at a shear rate up to 1000 sec-1)
with 25 mm parallel plates using a Dynamic Stress Rheometer.
Further, the viscosity of the organic component is typically at
least 10 cps, more typically at least 50 cps, even more typically
at least 100 cps, and most typically at least 200 cps at the
coating temperature.
[0029] The coating temperature typically ranges from ambient
temperature, (i.e. 25.degree. C.) to 180.degree. F. (82.degree.
C.). The coating temperature may be less than 170.degree. F.
(77.degree. C.), less than 160.degree. F. (71.degree. C.), less
than 150.degree. F. (66.degree. C.), less than 140.degree. F.
(60.degree. C.), less than 130.degree. F. (54.degree. C.), or less
than 120.degree. F. (49.degree. C.). The organic component can be a
solid or comprise a solid component provided that the melting point
in the polymerizable composition is less than the coating
temperature. The organic component can be a liquid at ambient
temperature.
[0030] The organic component as well as the polymerizable
composition has refractive index of at least 1.47, for most product
applications; whereas the polymerizable resin composition of a
turning film may have a refractive index as low as 1.44. The
refractive index of the organic component or the polymerizable
composition may be at least 1.48, 1.49, 1.50, 1.51, 1.52, 1.53,
1.54, 1.55, 1.56, 1.57, 1.58, 1.59, or 1.60. The polymerizable
composition including the nanoparticles can have a refractive index
as high as 1.70. (e.g. at least 1.61, 1.62, 1.63, 164, 1.65, 1.66,
1.67, 1.68, or 1.69) High transmittance in the visible light
spectrum is also typically preferred.
[0031] The polymerizable composition is energy curable in time
scales preferably less than five minutes such as for a brightness
enhancing film having a 75 micron thickness. The polymerizable
composition is preferably sufficiently crosslinked to provide a
glass transition temperature that is typically greater than
45.degree. C. The glass transition temperature can be measured by
methods known in the art, such as Differential Scanning Calorimetry
(DSC), modulated DSC, or Dynamic Mechanical Analysis. The
polymerizable composition can be polymerized by conventional free
radical polymerization methods.
[0032] Various kinds and amounts of monomers alone or in
combination with each other can be employed to provide compositions
meeting the viscosity and/or refractive index criteria just
described.
[0033] Suitable monomers having a high refractive index and a
number average molecular weight no greater than 450 g/mole include
for example phenoxy ethyl acrylate;
phenoxy-2-methylethyl(meth)acrylate;
phenoxyethoxyethyl(meth)acrylate;
3-hydroxy-2-hydroxypropyl(meth)acrylate; benzyl(meth)acrylate,
4-(1-methyl-1-phenethyl)phenoxyethyl(meth)acrylate; phenylthio
ethyl acrylate; 2-naphthylthio ethyl acrylate; 1-naphthylthio ethyl
acrylate; 2,4,6-tribromophenoxy ethyl acrylate; 2,4-dibromophenoxy
ethyl acrylate; 2-bromophenoxy ethyl acrylate; 1-naphthyloxy ethyl
acrylate; 2-naphthyloxy ethyl acrylate; phenoxy 2-methylethyl
acrylate; 3-phenoxy-2-hydroxy propyl acrylate; 2-phenylphenoxy
ethyl acrylate; 4-phenylphenoxy ethyl acrylate;
2,4-dibromo-6-sec-butylphenyl acrylate;
2,4-dibromo-6-isopropylphenyl acrylate; benzyl acrylate; phenyl
acrylate; 2,4,6-tribromophenyl acrylate.
[0034] At least one of the ingredients of the polymerizable
composition comprises at least two ethylenically unsaturated
groups. It is preferred that the polymerizable ingredient comprises
at least one ingredient that comprises two or more (meth)acrylate
groups. If surface modified nanoparticles are employed that
comprise sufficient polymerizable (meth)acrylate groups, all the
monomers of the organic component may be monofunctional.
[0035] Monomers that comprise at least two (meth)acrylate groups
are also described as crosslinkers. Suitable crosslinkers include
for example hexanediol diacrylate, pentaerythritol
tri(meth)acrylate, pentaerythritol tetra(meth)acrylate,
trimethylolpropane tri(meth)acrylate, dipentaerythritol
penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate,
trimethylolpropane ethoxylate tri(meth)acrylate, glyceryl
tri(meth)acrylate, pentaerythritol propoxylate tri(meth)acrylate,
and ditrimethylolpropane tetra(meth)acrylate. Any one or
combination of crosslinkers may be employed. Since methacrylate
groups tend to be less reactive than acrylate groups, the
crosslinker(s) are preferably free of methacrylate
functionality.
[0036] When a crosslinker is present, it is preferably present in
the organic component of the polymerizable composition in an amount
of at least about 2 wt-%. Typically, the amount of crosslinker is
not greater than about 25 wt-%.
[0037] Various crosslinkers are commercially available. For
example, pentaerythritol triacrylate (PETA) and dipentaerythritol
pentaacrylate are commercially available from Sartomer Company,
Exton, PA under the trade designations "SR444"and "SR399LV"
respectively; from Osaka Organic Chemical Industry, Ltd. Osaka,
Japan under the trade designation "Viscoat #300"; from Toagosei Co.
Ltd., Tokyo, Japan under the trade designation "Aronix M-305"; and
from Eternal Chemical Co., Ltd., Kaohsiung, Taiwan under the trade
designation "Etermer 235". Trimethylol propane triacrylate (TMPTA)
and ditrimethylol propane tetraacrylate (di-TMPTA) are commercially
available from Sartomer Company under the trade designations
"SR351"and "SR355". TMPTA is also available from Toagosei Co. Ltd.
under the trade designation "Aronix M-309". Further, ethoxylated
trimethylolpropane triacrylate and ethoxylated pentaerythritol
triacrylate are commercially available from Sartomer under the
trade designations "SR454"and "SR494"respectively.
[0038] Provided that the organic component and polymerizable
composition as a whole has the desired refractive index, the
organic component can comprise other (e.g. lower refractive index)
monomers. Suitable monomers may provide other beneficial
characteristics such as improved adhesion or reduced viscosity.
Suitable monomers include mono- or di-functional ethylenically
unsaturated monomers such as (meth)acrylates or monomeric
N-substituted or N,N-disubstituted (meth)acrylamides, especially
acrylamide. These include N-alkylacrylamides and
N,N-dialkylacrylamides, especially those containing C.sub.1-4 alkyl
groups. Examples are N-isopropylacrylamide, N-t-butylacrylamide,
N,N-dimethylacrylamide, N,N-diethylacrylamide, N-vinyl pyrrolidone,
N-vinyl caprolactam.
[0039] The polymerizable compositions described herein preferably
comprise inorganic particles. In general, the viscosity of the
organic component is generally within the lower target ranges as
previously described when relatively high concentrations (e.g. 40
wt-% to 70 wt-%) of inorganic nanoparticles as employed. When lower
concentrations of nanoparticles are employed (e.g. 10 wt-% to 40
wt-%), the organic component may fall within the higher viscosity
target ranges.
[0040] The viscosity of the (i.e. nanoparticle-containing)
polymerizable composition is generally within the ranges previously
described for the organic component alone. In general, as the
concentration of inorganic nanoparticles of the polymerizable
composition increases, the viscosity can increase. There is
generally a substantial increase in viscosity as a function of
concentration for inorganic nanoparticles lacking a suitable
surface treatment as will subsequently be described.
[0041] The size of the particles is generally chosen to avoid
significant visible light scattering. The inorganic oxide particle
selected can impart refractive index or scratch resistance increase
or both. It may be desirable to use a mix of inorganic oxide
particle types to optimize an optical or material property and to
lower total composition cost.
[0042] The inclusion of the inorganic nanoparticles can improve the
durability. Preferably, the polymerized microstructured surface has
a scratch contrast ratio value in a range of 1.0 to 1.15, or 1.0 to
1.12, or 1.0 to 1.10, or 1.0 to 1.05 as determined according to the
test method described in U.S. patent application Ser. No. 10/938006
filed Sep. 10, 2004; incorporated herein by reference. In the case
of rounded prism apexes, e.g. having a radius ranging from about
0.5 to 15 micrometers, the scratch contrast ratio value can range
from 1.0 to 1.65, or 1.0 to 1.4, or 1.0 to 1.10.
[0043] Although inorganic nanoparticles lacking polymerizable
surface modification can usefully be employed, the inorganic
nanoparticles are preferably surface modified such that the
nanoparticles are polymerizable with the organic component. Surface
modified (e.g. colloidal) nanoparticles can be present in the
polymerized structure in an amount effective to enhance the
durability and/or refractive index of the article or optical
element. The surface modified colloidal nanoparticles described
herein can have a variety of desirable attributes, including for
example; nanoparticle compatibility with resin systems such that
the nanoparticles form stable dispersions within the resin systems,
surface modification can provide reactivity of the nanoparticle
with the resin system making the composite more durable, properly
surface modified nanoparticles added to resin systems provide a low
impact on uncured composition viscosity. A combination of surface
modifiers can be used to manipulate the uncured and cured
properties of the composition. Appropriately surface modified
nanoparticles can improve the optical and physical properties of
the optical element such as, for example, improve resin mechanical
strength, minimize viscosity changes while increasing solid volume
loading in the resin system and maintain optical clarity while
increasing solid volume loading in the resin system.
[0044] The surface modified colloidal nanoparticles can be oxide
particles having a primary particle size or associated particle
size of greater than 1 nm and less than 100 nm. It is preferred
that the nanoparticles are unassociated. Their measurements can be
based on transmission electron miscroscopy (TEM). The nanoparticles
can include metal oxides such as, for example, alumina, tin oxides,
antimony oxides, silica, zirconia, titania, mixtures thereof, or
mixed oxides thereof. Surface modified colloidal nanoparticles can
be substantially fully condensed.
[0045] Fully condensed nanoparticles, such as the collidal silica
used herein, typically have substantially no hydroxyls in their
interiors.
[0046] Non-silica containing fully condensed nanoparticles
typically have a degree of crystallinity (measured as isolated
metal oxide particles) greater than 55%, preferably greater than
60%, and more preferably greater than 70%. For example, the degree
of crystallinity can range up to about 86% or greater. The degree
of crystallinity can be determined by X-ray defraction techniques.
Condensed crystalline (e.g. zirconia) nanoparticles have a high
refractive index whereas amorphous nanoparticles typically have a
lower refractive index.
[0047] Silica nanoparticles can have a particle size from 5 to 75
nm or 10 to 30 nm or 20 nm. Silica nanoparticles are typically in
an amount from 10 to 60 wt-%. Typically the amount of silica is
less than 40 wt-%.
[0048] Suitable silicas are commercially available from Nalco
Chemical Co. (Naperville, Ill.) under the trade designation NALCO
COLLOIDAL SILICAS. For example, silicas include NALCO trade
designations 1040, 1042, 1050, 1060, 2327 and 2329. Suitable fumed
silicas include for example, products sold under the tradename,
AEROSIL series OX-50, -130, -150, and -200 available from DeGussa
AG, (Hanau, Germany), and CAB-O-SPERSE 2095, CAB-O-SPERSE A105,
CAB-O-SIL M5 available from Cabot Corp. (Tuscola, Ill.).
[0049] Zirconia nanoparticles can have a particle size from
approximately 5 to 50 nm, or 5 to 15 nm, or 10 nm. Zirconia
nanoparticles can be present in the durable article or optical
element in an amount from 10 to 70 wt %, or 30 to 50 wt %.
Zirconias for use in materials of the invention are commercially
available from Nalco Chemical Co. (Naperville, Ill.) under the
product designation NALCO OOSSOO8 and from Buhler AG Uzwil,
Switzerland under the trade designation "Buhler zirconia Z-WO sol".
Zirconia nanoparticle can also be prepared such as described in
U.S. patent application Ser. No. 11/027426 filed Dec. 30, 2004 and
U.S. Pat. No. 6,376,590.
[0050] Titania, antimony oxides, alumina, tin oxides, and/or mixed
metal oxide nanoparticles can have a particle size or associated
particle size from 5 to 50 nm, or 5 to 15 nm, or 10 nm. Titania,
antimony oxides, alumina, tin oxides, and/or mixed metal oxide
nanoparticles can be present in the durable article or optical
element in an amount from 10 to 70 wt %, or 30 to 50 wt %. Mixed
metal oxide for use in materials of the invention are commercially
available from Catalysts & Chemical Industries Corp.,
(Kawasaki, Japan) under the product designation Optolake.
[0051] Surface-treating the nano-sized particles can provide a
stable dispersion in the polymeric resin. Preferably, the
surface-treatment stabilizes the nanoparticles so that the
particles will be well dispersed in the polymerizable resin and
result in a substantially homogeneous composition. Furthermore, the
nanoparticles can be modified over at least a portion of its
surface with a surface treatment agent so that the stabilized
particle can copolymerize or react with the polymerizable resin
during curing.
[0052] The nanoparticles are preferably treated with a surface
treatment agent. In general. a surface treatment agent has a first
end that will attach to the particle surface (covalently, ionically
or through strong physisorption) and a second end that imparts
compatibility of the particle with the resin and/or reacts with
resin during curing. Examples of surface treatment agents include
alcohols, amines, carboxylic acids, sulfonic acids, phospohonic
acids, silanes and titanates. The preferred type of treatment agent
is determined, in part, by the chemical nature of the metal oxide
surface. Silanes are preferred for silica and other for siliceous
fillers. Silanes and carboxylic acids are preferred for metal
oxides such as zirconia. The surface modification can be done
either subsequent to mixing with the monomers or after mixing. It
is preferred in the case of silanes to react the silanes with the
particle or nanoparticle surface before incorporation into the
resin. The required amount of surface modifier is dependant upon
several factors such particle size, particle type, modifier
molecular wt, and modifier type. In general it is preferred that
approximately a monolayer of modifier is attached to the surface of
the particle. The attachment procedure or reaction conditions
required also depend on the surface modifier used. For silanes it
is preferred to surface treat at elevated temperatures under acidic
or basic conditions for from 1-24 hr approximately. Surface
treatment agents such as carboxylic acids may not require elevated
temperatures or extended time.
[0053] Representative embodiments of surface treatment agents
suitable for the compositions include compounds such as, for
example, isooctyl trimethoxy-silane,
N-(3-triethoxysilylpropyl)methoxyethoxyethoxyethyl carbamate
(PEG3TES), N-(3-triethoxysilylpropyl)methoxyethoxyethoxyethyl
carbamate (PEG2TES), 3-(methacryloyloxy)propyltrimethoxysilane,
3-acryloxypropyltrimethoxysilane,
3-(methacryloyloxy)propyltriethoxysilane, 3-(methacryloyloxy)
propylmethyldimethoxysilane,
3-(acryloyloxypropyl)methyldimethoxysilane,
3-(methacryloyloxy)propyldimethylethoxysilane, 3-(methacryloyloxy)
propyldimethylethoxysilane, vinyldimethylethoxysilane,
phenyltrimethoxysilane, n-octyltrimethoxysilane,
dodecyltrimethoxysilane, octadecyltrimethoxysilane,
propyltrimethoxysilane, hexyltrimethoxysilane,
vinylmethyldiacetoxysilane, vinylmethyldiethoxysilane,
vinyltriacetoxysilane, vinyltriethoxysilane,
vinyltriisopropoxysilane, vinyltrimethoxysilane,
vinyltriphenoxysilane, vinyltri-t-butoxysilane,
vinyltris-isobutoxysilane, vinyltriisopropenoxysilane,
vinyltris(2-methoxyethoxy)silane, styrylethyltrimethoxysilane,
mercaptopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane,
acrylic acid, methacrylic acid, oleic acid, stearic acid,
dodecanoic acid, 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEAA),
beta-carboxyethylacrylate, 2-(2-methoxyethoxy)acetic acid,
methoxyphenyl acetic acid, and mixtures thereof. Further, a
proprietary silane surface modifier, commercially available from
OSI Specialties, Crompton South Charleston, W.Va. under the trade
designation "Silquest A1230", has been found particularly
suitable.
[0054] The surface modification of the particles in the colloidal
dispersion can be accomplished in a variety of ways. The process
involves the mixture of an inorganic dispersion with surface
modifying agents. Optionally, a co-solvent can be added at this
point, such as for example, 1-methoxy-2-propanol, ethanol,
isopropanol, ethylene glycol, N,N-dimethylacetamide and
1-methyl-2-pyrrolidinone. The co-solvent can enhance the solubility
of the surface modifying agents as well as the surface modified
particles. The mixture comprising the inorganic sol and surface
modifying agents is subsequently reacted at room or an elevated
temperature, with or without mixing. In one method, the mixture can
be reacted at about 85 degree C. for about 24 hours, resulting in
the surface modified sol. In another method, where metal oxides are
surface modified the surface treatment of the metal oxide can
preferably involve the adsorption of acidic molecules to the
particle surface. The surface modification of the heavy metal oxide
preferably takes place at room temperature.
[0055] The surface modification of ZrO.sub.2 with silanes can be
accomplished under acidic conditions or basic conditions. In one
case the silanes are heated under acid conditions for a suitable
period of time. At which time the dispersion is combined with
aqueous ammonia (or other base). This method allows removal of the
acid counter ion from the ZrO.sub.2 surface as well as reaction
with the silane. In a one method the particles are precipitated
from the dispersion and separated from the liquid component.
[0056] A combination of surface modifying agents can be useful,
wherein at least one of the agents has a functional group
co-polymerizable with a hardenable resin. For example, the
polymerizing group can be ethylenically unsaturated or a cyclic
function subject to ring opening polymerization. An ethylenically
unsaturated polymerizing group can be, for example, an acrylate or
methacrylate, or vinyl group. A cyclic functional group subject to
ring opening polymerization generally contains a heteroatom such as
oxygen, sulfur or nitrogen, and preferably a 3-membered ring
containing oxygen such as an epoxide.
[0057] A preferred combination of surface modifying agents includes
at least one surface modifying agent having a functional group that
is co-polymerizable with the (organic component of the) hardenable
resin and a second modifying agent different than the first
modifying agent. The second modifying agent is optionally
co-polymerizable with the organic component of the polymerizable
composition. The second modifying agent may have a low refractive
index (i.e. less than 1.52 or less than 1.50). The second modifying
agent is preferably a polyalkyleneoxide containing modifying agent
that is optionally co-polymerizable with the organic component of
the polymerizable composition.
[0058] The surface modified particles can then be incorporated into
the curable resin in various methods. In a preferred aspect, a
solvent exchange procedure is utilized whereby the resin is added
to the surface modified sol, followed by removal of the water and
co-solvent (if used) via evaporation, thus leaving the particles
dispersed in the polyerizable resin. The evaporation step can be
accomplished for example, via distillation, rotary evaporation or
oven drying.
[0059] In another aspect, the surface modified particles can be
extracted into a water immiscible solvent followed by solvent
exchange, if so desired.
[0060] Alternatively, another method for incorporating the surface
modified nanoparticles in the polymerizable resin involves the
drying of the modified particles into a powder, followed by the
addition of the resin material into which the particles are
dispersed. The drying step in this method can be accomplished by
conventional means suitable for the system, such as, for example,
oven drying or spray drying.
[0061] The polymerizable compositions described herein can also
contain one or more other useful additives as known in art
including but not limited to surfactants, pigments, fillers,
polymerization inhibitors, antioxidants, anti-static agents, and
other possible ingredients.
[0062] The radiation curable articles of this invention may be
prepared by simply blending the components thereof, with efficient
mixing to produce a homogeneous mixture, and then removing any
solvent employed in preparation of said components. Air bubbles can
be removed by application of vacuum or the like, with gentle
heating if the mixture is viscous, and casting or otherwise
creating a film of the resulting blend on a desired surface. The
film can then be charged to a mold bearing the microstructure to be
replicated and polymerized by exposure to ultraviolet radiation,
producing cured optical resinous articles of the invention having
the aforementioned properties. If polymerized on a surface other
than the one on which it is to be used, the optical resinous
article can be transferred to another surface.
[0063] Such a polymerization process lends itself to rapid, mass
production of articles with no adverse environmental impact because
no or only a minor amount of solvent or other volatiles are
evolved. The process also lends itself to replication of articles
with microstructure comprising utilitarian discontinuities, such as
projections and depressions, which are readily released from the
mold without loss of the detail of the mold and with retention of
the replication of such detail under a wide variety of conditions
during use. The articles can be formed with a wide variety of
desired properties, such as toughness, flexibility, optical clarity
and homogeneity, and resistance to common solvents, the
microstructure of such articles having high thermal dimensional
stability, resistance to abrasion and impact, and integrity even
when the articles are bent.
[0064] Suitable methods of polymerization include solution
polymerization, suspension polymerization, emulsion polymerization,
and bulk polymerization, as are known in the art. Suitable methods
include heating in the presence of a free-radical initiator as well
as irradiation with electromagnetic radiation such as ultraviolet
or visible light in the presence of a photoinitiator. Inhibitors
are frequently used in the synthesis of the polymerizable
composition to prevent premature polymerization of the resin during
synthesis, transportation and storage. Suitable inhibitors include
hydroquinone, 4-methoxy phenol, and hindered amine nitroxide
inhibitors at levels of 50-1000 ppm. Other kinds and/or amounts of
inhibitors may be employed as known to those skilled in the
art.
[0065] The radiation (e.g. UV) curable compositions comprise a
least one photoinitiator. A single photoinitiator or blends thereof
may be employed in the brightness enhancement film of the
invention. In general the photoinitiator(s) are at least partially
soluble (e.g. at the processing temperature of the resin) and
substantially colorless after being polymerized. The photoinitiator
may be (e.g. yellow) colored, provided that the photoinitiator is
rendered substantially colorless after exposure to the UV light
source.
[0066] Suitable photoinitiators include monoacylphosphine oxide and
bisacylphosphine oxide. Commercially available mono or
bisacylphosphine oxide photoinitiators include
2,4,6-trimethylbenzoydiphenylphosphine oxide, commercially
available from BASF (Charlotte, N.C.) under the trade designation
"Lucirin TPO"; ethyl-2,4,6-trimethylbenzoylphenyl phosphinate, also
commercially available from BASF under the trade designation
"Lucirin TPO-L"; and bis(2,4,6-trimethylbenzoyl)-phenylphosphine
oxide commercially available from Ciba Specialty Chemicals under
the trade designation "Irgacure 819". Other suitable
photoinitiators include 2-hydroxy-2-methyl-1-phenyl-propan-1-one,
commercially available from Ciba Specialty Chemicals under the
trade designation "Darocur 1173" as well as other photoinitiators
commercially available from Ciba Specialty Chemicals under the
trade designations "Darocur 4265", "Irgacure 651", "Irgacure 1800",
"Irgacure 369", "Irgacure 1700", and "Irgacure 907".
[0067] The photoinitiator can be used at a concentration of about
0.1 to about 10 weight percent. More preferably, the photoinitiator
is used at a concentration of about 0.5 to about 5 wt-%. Greater
than 5 wt-% is generally disadvantageous in view of the tendency to
cause yellow discoloration of the brightness enhancing film. Other
photoinitiators and photoinitiator may also suitably be employed as
may be determined by one of ordinary skill in the art.
[0068] Surfactants such as fluorosurfactants and silicone based
surfactants can optionally be included in the polymerizable
composition to reduce surface tension, improve wetting, allow
smoother coating and fewer defects of the coating, etc.
[0069] Composition that are too high in viscosity to be used in the
process just described can optionally be prepared into brightness
enhancing film with extrusion processes as are known in the
art.
[0070] The optical layer can directly contact the base layer or be
optically aligned to the base layer, and can be of a size, shape
and thickness allowing the optical layer to direct or concentrate
the flow of light. The optical layer can have a structured or
micro-structured surface that can have any of a number of useful
patterns such as described and shown in the FIGURES. The
micro-structured surface can be a plurality of parallel
longitudinal ridges extending along a length or width of the film.
These ridges can be formed from a plurality of prism apexes. These
apexes can be sharp, rounded or flattened or truncated. For
example, the ridges can be rounded to a radius in a range of 4 to 7
to 15 micrometers.
[0071] These include regular or irregular prismatic patterns can be
an annular prismatic pattern, a cube-corner pattern or any other
lenticular microstructure. A useful microstructure is a regular
prismatic pattern that can act as a totally internal reflecting
film for use as a brightness enhancement film. Another useful
microstructure is a corner-cube prismatic pattern that can act as a
retro-reflecting film or element for use as reflecting film.
Another useful microstructure is a prismatic pattern that can act
as an optical element for use in an optical display. Another useful
microstructure is a prismatic pattern that can act as an optical
turning film or element for use in an optical display.
[0072] The base layer can be of a nature and composition suitable
for use in an optical product, i.e. a product designed to control
the flow of light. Almost any material can be used as a base
material as long as the material is sufficiently optically clear
and is structurally strong enough to be assembled into or used
within a particular optical product. A base material can be chosen
that has sufficient resistance to temperature and aging that
performance of the optical product is not compromised over
time.
[0073] The particular chemical composition and thickness of the
base material for any optical product can depend on the
requirements of the particular optical product that is being
constructed. That is, balancing the needs for strength, clarity,
temperature resistance, surface energy, adherence to the optical
layer, among others.
[0074] Useful base materials include, for example,
styrene-acrylonitrile, cellulose acetate butyrate, cellulose
acetate propionate, cellulose triacetate, polyether sulfone,
polymethyl methacrylate, polyurethane, polyester, polycarbonate,
polyvinyl chloride, polystyrene, polyethylene naphthalate,
copolymers or blends based on naphthalene dicarboxylic acids,
polycyclo-olefins, polyimides, and glass. Optionally, the base
material can contain mixtures or combinations of these materials.
In an embodiment, the base may be multi-layered or may contain a
dispersed component suspended or dispersed in a continuous
phase.
[0075] For some optical products such as microstructure-bearing
products such as, for example, brightness enhancement films,
examples of preferred base materials include polyethylene
terephthalate (PET) and polycarbonate. Examples of useful PET films
include photograde polyethylene terephthalate and MELINEX.TM. PET
available from DuPont Films of Wilmington, Del.
[0076] Some base materials can be optically active, and can act as
polarizing materials. A number of bases, also referred to herein as
films or substrates, are known in the optical product art to be
useful as polarizing materials. Polarization of light through a
film can be accomplished, for example, by the inclusion of dichroic
polarizers in a film material that selectively absorbs passing
light. Light polarization can also be achieved by including
inorganic materials such as aligned mica chips or by a
discontinuous phase dispersed within a continuous film, such as
droplets of light modulating liquid crystals dispersed within a
continuous film. As an alternative, a film can be prepared from
microfine layers of different materials. The polarizing materials
within the film can be aligned into a polarizing orientation, for
example, by employing methods such as stretching the film, applying
electric or magnetic fields, and coating techniques.
[0077] Examples of polarizing films include those described in U.S.
Pat. Nos. 5,825,543 and 5,783,120, each of which are incorporated
herein by reference. The use of these polarizer films in
combination with a brightness enhancement film has been described
in U.S. Pat. No. 6,111,696, incorporated by reference herein.
[0078] A second example of a polarizing film that can be used as a
base are those films described in U.S. Pat. No. 5,882,774, also
incorporated herein by reference. Films available commercially are
the multilayer films sold under the trade designation DBEF (Dual
Brightness Enhancement Film) from 3M. The use of such multilayer
polarizing optical film in a brightness enhancement film has been
described in U.S. Pat. No. 5,828,488, incorporated herein by
reference.
[0079] This list of base materials is not exclusive, and as will be
appreciated by those of skill in the art, other polarizing and
non-polarizing films can also be useful as the base for the optical
products of the invention. These base materials can be combined
with any number of other films including, for example, polarizing
films to form multilayer structures. A short list of additional
base materials can include those films described in U.S. Pat. Nos.
5,612,820 and 5,486,949, among others. The thickness of a
particular base can also depend on the above-described requirements
of the optical product.
[0080] Durable microstructure-bearing articles can be constructed
in a variety of forms, including those having a series of
alternating tips and grooves sufficient to produce a totally
internal reflecting film. An example of such a film is a brightness
enhancing film having a regular repeating pattern of symmetrical
tips and grooves, while other examples have patterns in which the
tips and grooves are not symmetrical. Examples of microstructure
bearing articles useful as brightness enhancing films are described
by U.S. Pat. Nos. 5,175,030 and 5,183,597, which are both
incorporated herein by reference.
[0081] According to these patents, a microstructure-bearing article
can be prepared by a method including the steps of (a) preparing a
polymerizable composition; (b) depositing the polymerizable
composition onto a master negative microstructured molding surface
in an amount barely sufficient to fill the cavities of the master;
(c) filling the cavities by moving a bead of the polymerizable
composition between a preformed base and the master, at least one
of which is flexible; and (d) curing the composition. The master
can be metallic, such as nickel, nickel-plated copper or brass, or
can be a thermoplastic material that is stable under polymerization
conditions and that preferably has a surface energy that permits
clean removal of the polymerized material from the master. The
particular method used to create the microstructure topography
described herein can be similar to the molding process described in
U.S. Pat. No. 5,691,846 which is incorporated by reference herein.
The microstructure article according to the invention can be formed
from a continuous process at any desired length such as, for
example, 5, 10, 100, 1000 meters or more.
[0082] The durable article can be used in applications needing
durable micro-structured film including, for example, brightness
enhancing films. The structure of these durable brightness
enhancing films can include a wide variety of micro-structured
films such as, for example, U.S. Pat. No. 5,771,328, U.S. Pat. No.
5,917,664, U.S. Pat. No. 5,919,551, U.S. Pat. No. 6,280,063, and
U.S. Pat. No. 6,356,391, all incorporated by reference herein.
[0083] A backlit liquid crystal display generally indicated at 10
in FIG. 1 includes a brightness enhancement film 11 of the present
invention that can be positioned between a diffuser 12 and a liquid
crystal display panel 14. The backlit liquid crystal display can
also include a light source 16 such as a fluorescent lamp, a light
guide 18 for transporting light for reflection toward the liquid
crystal display panel 14, and a white reflector 20 for reflecting
light also toward the liquid crystal display panel. The brightness
enhancement film 11 collimates light emitted from the light guide
18 thereby increasing the brightness of the liquid crystal display
panel 14. The increased brightness enables a sharper image to be
produced by the liquid crystal display panel and allows the power
of the light source 16 to be reduced to produce a selected
brightness. The brightness enhancement film 11 in the backlit
liquid crystal display is useful in equipment such as computer
displays (laptop displays and computer monitors), televisions,
video recorders, mobile communication devices, handheld devices
(i.e. cellphone, PDA), automobile and avionic instrument displays,
and the like, represented by reference character 21.
[0084] The brightness enhancement film 11 includes an array of
prisms typified by prisms 22, 24, 26, and 28, as illustrated in
FIG. 2. Each prism, for example, such as prism 22, has a first
facet 30 and a second facet 32. The prisms 22, 24, 26, and 28 can
be formed on a body portion 34 that has a first surface 36 on which
the prisms are formed and a second surface 38 that is substantially
flat or planar and opposite the first surface.
[0085] A linear array of regular right prisms can provide both
optical performance and ease of manufacture. By right prisms, it is
meant that the apex angle .theta. is approximately 90.degree., but
can also range from approximately 70.degree. to 120.degree. or from
approximately 80.degree. to 100.degree.. The prism facets need not
be identical, and the prisms may be tilted with respect to each
other. Furthermore, the relationship between the thickness 40 of
the film and the height 42 of the prisms is not critical, but it is
desirable to use thinner films with well defined prism facets. The
angle that the facets can form with the surface 38 if the facets
were to be projected can be 45.degree.. However, this angle would
vary depending on the pitch of the facet or the angle .theta. of
the apex.
[0086] FIGS. 3-9 illustrate representative embodiments of a
construction for an optical element. It should be noted that these
drawings are not to scale and that, in particular, the size of the
structured surface is greatly exaggerated for illustrative
purposes. The construction of the optical element can include
combinations or two or more of the described embodiments below.
[0087] Referring to FIG. 3, there is illustrated a representative
cross-section of a portion of one embodiment of an optical element
or light directing film. The film 130 includes a first surface 132
and an opposing structured surface 134 which includes a plurality
of substantially linearly extending prism elements 136. Each prism
element 136 has a first side surface 138 and a second side surface
138', the top edges of which intersect to define the peak, or apex
142 of the prism element 136. The bottom edges of side surfaces
138, 138' of adjacent prism elements 136 intersect to form a
linearly extending groove 144 between prism elements. In the
embodiment illustrated in FIG. 3, the dihedral angle defined by the
prism apex 142 measures approximately 90 degrees, however it will
be appreciated that the exact measure of the dihedral angle in this
and other embodiments may be varied in accordance with desired
optical parameters.
[0088] The structured surface 134 of film 130 may be described as
having a plurality of alternating zones of prism elements having
peaks which are spaced at different distances from a common
reference plane. The common reference plane may be arbitrarily
selected. One convenient example of a common reference plane is the
plane which contains first surface 132; another is the plane
defined by the bottom of the lower most grooves of the structured
surface, indicated by dashed line 139. In the embodiment
illustrated in FIG. 3, the shorter prism elements measure
approximately 50 microns in width and approximately 25 microns in
height, measured from dashed line 139, while the taller prism
elements measure approximately 50 microns in width and
approximately 26 microns in height. The width of the zone which
includes the taller prism elements can measure between about 1
micron and 300 microns. The width of the zone that includes the
shorter prism elements is not critical and can measures between 200
microns and 4000 microns. In any given embodiment the zone of
shorter prism elements can be at least as wide as the zone of
taller prism elements. It will be appreciated by one of ordinary
skill in the art that the article depicted in FIG. 3 is merely
exemplary and is not intended to limit the scope of the present
invention. For example, the height or width of the prism elements
may be changed within practicable limits--it is practicable to
machine precise prisms in ranges extending from about 1 micron to
about 200 microns. Additionally, the dihedral angles may be changed
or the prism axis may be tilted to achieve a desired optical
effect.
[0089] The width of the first zone can be less than about 200 to
300 microns. Under normal viewing conditions, the human eye has
difficulty resolving small variations in the intensity of light
that occur in regions less than about 200 to 300 microns in width.
Thus, when the width of the first zone is reduced to less than
about 200 to 300 microns, any optical coupling that may occur in
this zone is not detectable to the human eye under normal viewing
conditions.
[0090] A variable height structured surface may also be implemented
by varying the height of one or more prism elements along its
linear extent to create alternating zones which include portions of
prism elements having peaks disposed at varying heights above a
common reference plane.
[0091] FIG. 4 illustrates another embodiment of the optical element
similar to FIG. 3 except that the film 150 includes a structured
surface 152 which has a zone of relatively shorter prism elements
154 separated by a zone including a single taller prism element
156. Much like the embodiment depicted in FIG. 3, the taller prism
element limits the physical proximity of a second sheet of film to
structured surface 152, thereby reducing the likelihood of a
visible wet-out condition. It has been determined that the human
eye is sensitive to changes in facet heights in light directing
films and that relatively wide zones of taller prism elements will
appear as visible lines on the surface of a film. While this does
not materially affect the optical performance of the film, the
lines may be undesirable in certain commercial circumstances.
Reducing the width of a zone of taller prism elements
correspondingly reduces the ability of a human eye to detect the
lines in the film caused by the taller prism elements.
[0092] FIG. 5 is a representative example of another embodiment of
an optical element in which the prism elements are approximately
the same size but are arranged in a repeating stair step or ramp
pattern. The film 160 depicted in FIG. 5 includes a first surface
162 and an opposing structured surface 164 including a plurality of
substantially linear prism elements 166. Each prism element has
opposing lateral faces 168, 168' which intersect at their upper
edge to define the prism peaks 170. The dihedral angle defined by
opposing lateral faces 168, 168' measures approximately 90 degrees.
In this embodiment the highest prisms may be considered a first
zone and adjacent prisms may be considered a second zone. Again,
the first zone can measure less than about 200 to 300 microns.
[0093] FIG. 6 illustrates a further embodiment of an optical
element. The film 180 disclosed in FIG. 6 includes a first surface
182 and an opposing structured surface 184. This film may be
characterized in that the second zone which includes relatively
shorter prism elements contains prism elements of varying height.
The structured surface depicted in FIG. 6 has the additional
advantage of substantially reducing the visibility to the human eye
of lines on the surface of the film caused by the variations in the
height of the prism elements.
[0094] FIG. 7 shows another embodiment of an optical element for
providing a soft cutoff. FIG. 7 shows a brightness enhancement
film, designated generally as 240, according to the invention.
Brightness enhancement film 240 includes a substrate 242 and a
structured surface material 244. Substrate 242 is can generally be
a polyester material and structured surface material 244 can be an
ultraviolet-cured acrylic or other polymeric material discussed
herein. The exterior surface of substrate 242 is preferably flat,
but could have structures as well. Furthermore, other alternative
substrates could be used.
[0095] Structured surface material 244 has a plurality of prisms
such as prisms 246, 248, and 250, formed thereon. Prisms 246, 248,
and 250 have peaks 252, 254, and 256, respectively. All of peaks
252, 254, and 256 have peak or prism angles of preferably 90
degrees, although included angles in the range 60 degrees to 120
degrees. Between prisms 246 and 248 is a valley 258. Between prisms
248 and 250 is a valley 260. Valley 258 may be considered to have
the valley associated with prism 246 and has a valley angle of 70
degrees and valley 260 may be considered the valley associated with
prism 248 and has a valley angle of 110 degrees, although other
values could be used. Effectively, brightness enhancement film 240
increases the apparent on axis brightness of a backlight by
reflecting and recycling some of the light and refracting the
remainder like prior art brightness enhancement film, but with the
prisms canted in alternating directions. The effect of canting the
prisms is to increase the size of the output light cone.
[0096] FIG. 8 shows another embodiment of an optical element having
rounded prism apexes. The brightness enhancement article 330
features a flexible, base layer 332 having a pair of opposed
surfaces 334, 336, both of which are integrally formed with base
layer 332. Surface 334 features a series of protruding
light-diffusing elements 338. These elements may be in the form of
"bumps" in the surface made of the same material as layer 332.
Surface 336 features an array of linear prisms having blunted or
rounded peaks 340 integrally formed with base layer 332. These
peaks are characterized by a chord width 342, cross-sectional pitch
width 344, radius of curvature 346, and root angle 348 in which the
chord width is equal to about 20-40% of the cross-sectional pitch
width and the radius of curvature is equal to about 20-50% of the
cross-sectional pitch width. The root angle ranges from about
70-110 degrees, or from about 85-95 degrees, with root angles of
about 90 degrees being preferred. The placement of the prisms
within the array is selected to maximize the desired optical
performance.
[0097] Rounded prism apex brightness enhancement articles usually
suffer from decreased gain. However, the addition of high
refractive index surface modified nanoparticles can offset the lost
gain from the rounded prism apex brightness enhancement
articles.
[0098] FIG. 9 shows another embodiment of an optical element having
flat or planar prism apexes. The brightness enhancement article 430
features a flexible, base layer 432 having a pair of opposed
surfaces 434, 436, both of which are integrally formed with base
layer 432. Surface 434 features a series of protruding
light-diffusing elements 438. These elements may be in the form of
"flat bumps" in the surface made of the same material as layer 432.
Surface 436 features an array of linear prisms having flattened or
planar peaks 440 integrally formed with base layer 432. These peaks
are characterized by a flattened width 442 and cross-sectional
pitch width 444, in which the flattened width can be equal to about
0-30% of the cross-sectional pitch width.
[0099] Another method of extracting light from a lightguide is by
use of frustrated total internal reflection (TIR). In one type of
frustrated TIR the lightguide has a wedge shape, and light rays
incident on a thick edge of the lightguide are totally internally
reflected until achieving critical angle relative to the top and
bottom surfaces of the lightguide. These sub-critical angle light
rays are then extracted, or more succinctly refract from the
lightguide, at a glancing angle to the output surface. To be useful
for illuminating a display device, these light rays must then be
turned substantially parallel to a viewing, or output, axis of the
display device. This turning is usually accomplished using a
turning lens or turning film.
[0100] FIGS. 10-12 illustrate an illumination device including a
turning film. The turning film can include the inventive material
disclosed herein for form a durable turning film. A turning lens or
turning film typically includes prism structures formed on an input
surface, and the input surface is disposed adjacent the lightguide.
The light rays exiting the lightguide at the glancing angle,
usually less than 30 degrees to the output surface, encounter the
prism structures. The light rays are refracted by a first surface
of the prism structures and are reflected by a second surface of
the prism structures such that they are directed by the turning
lens or film in the desired direction, e.g., substantially parallel
to a viewing axis of the display. Turning films may have rounded
apexes, having a radius for example of at least 0.5 micrometers and
typically no greater than 10 micrometers.
[0101] Referring to FIG. 10, an illumination system 510 includes
optically coupled a light source 512; a light source reflector 514;
a lightguide 516 with an output surface 518, a back surface 520, an
input surface 521 and an end surface 522; a reflector 524 adjacent
the back surface 520; a first light redirecting element 526 with an
input surface 528 and an output surface 530; a second light
redirecting element 532; and a reflective polarizer 534. The
lightguide 516 may be a wedge or a modification thereof. As is well
known, the purpose of the lightguide is to provide for the uniform
distribution of light from the light source 512 over an area much
larger than the light source 512, and more particularly,
substantially over an entire area formed by output surface 518. The
lightguide 516 further preferably accomplishes these tasks in a
compact, thin package.
[0102] The light source 512 may be a CCFL that is edge coupled to
the input surface 521 of the lightguide 516, and the lamp reflector
514 may be a reflective film that wraps around the light source 512
forming a lamp cavity. The reflector 524 backs the lightguide 516
and may be an efficient back reflector, e.g., a lambertian or a
specular film or a combination.
[0103] The edge-coupled light propagates from the input surface 521
toward the end surface 522, confined by TIR. The light is extracted
from the lightguide 516 by frustration of the TIR. A ray confined
within the lightguide 516 increases its angle of incidence relative
to the plane of the top and bottom walls, due to the wedge angle,
with each TIR bounce. Thus, the light eventually refracts out of
each of the output surface 518 and the back surface 520 because it
is no longer contained by TIR. The light refracting out of the back
surface 520 is either specularly or diffusely reflected by the
reflector 524 back toward and largely through the lightguide 516.
The first light redirecting element 526 is arranged to redirect the
light rays exiting the output surface 518 along a direction
substantially parallel to a preferred viewing direction. The
preferred viewing direction may be normal to the output surface
518, but will more typically be at some angle to the output surface
518.
[0104] As shown in FIG. 11, the first light redirecting element 526
is a light transmissive optical film where the output surface 530
is substantially planar and the input surface 528 is formed with an
array 536 of prisms 538, 540 and 542. The second light redirecting
element 532 may also be a light transmissive film, for example a
brightness enhancing film such as the 3M Brightness Enhancement
Film product (sold as BEFIII) available from Minnesota Mining and
Manufacturing Company, St. Paul, Minn. The reflective polarizer 534
may be an inorganic, polymeric, cholesteric liquid crystal
reflective polarizer or film. A suitable film is the 3M Diffuse
Reflective Polarizer film product (sold as DRPF) or the Specular
Reflective Polarizer film product (sold as DBEF), both of which are
available from Minnesota Mining and Manufacturing Company.
[0105] Within array 536, each prism 538, 540 and 542 may be formed
with differing side angles as compared to its respective neighbor
prisms. That is, prism 540 may be formed with different side angles
(angles C and D) than prism 538 (angles A and B), and prism 542
(angles E and F). As shown, prisms 538 have a prism angle, i.e.,
the included angle, equal to the sum of the angles A and B.
Similarly, prisms 540 have a prism angle equal to the sum of the
angles C and D, while prisms 542 have a prism angle equal to the
sum of the angles E and F. While array 536 is shown to include
three different prism structures based upon different prism angle,
it should be appreciated that virtually any number of different
prisms may be used.
[0106] Prisms 538, 540 and 542 may also be formed with a common
prism angle but with a varied prism orientation. A prism axis "1"
is illustrated in FIG. 11 for prism 538. The prism axis 1 may be
arranged normal to the output surface 530, as shown for prism 538,
or at an angle to the output surface either toward or away from the
light source as illustrated by phantom axes "1.sup.+" and
"1.sup.-", respectively, for prisms 540 and 542.
[0107] Prisms 538, 540 and 542 may be arranged within array 536 as
shown in FIG. 11 in a regular repeating pattern or clusters 543 of
prisms, and while the array 536 is not shown to have like prisms
adjacent like prisms, such a configuration may also be used.
Moreover, within the array 536, the prisms 538, 540 and 542 may
change continuously from a first prism configuration, such as prism
configuration 538, to a second prism configuration, such as prism
configuration 540, and so on. For example, the prism configuration
may change in a gradient manner from the first prism configuration
to the second prism configuration. Alternatively, the prisms may
change in a step-wise manner, similar to the configuration shown in
FIG. 11. Within each cluster 543, the prisms have a prism pitch,
which is selected to be smaller than the spatial ripple frequency.
Likewise, the clusters may have a regular cluster pitch. The prism
array can be symmetrical as shown in FIG. 11 or the prism array can
be non-symmetrical.
[0108] While the array 536 shown in FIG. 11 has prisms having a
symmetric configuration, an array of prisms, such as array 536'
shown in FIG. 12 formed in light redirecting element 526', may be
used. Referring then to FIG. 12, in the array 536', prisms 538',
for example, has angle A' unequal to angle B'. Similarly for prisms
540' and 542', angle C' is unequal to angle A' and angle D', and
angle E' is unequal to either of angle A', angle C' or angle F'.
The array 536' may be advantageously formed using a single diamond
cutting tool of a predetermined angle, and tilting the tool for
each cut producing prisms of differing prism angle and symmetry.
However, it will be appreciated that with the use of a single
cutting tool, the prism angles will be the same, i.e.,
A+B=C+D=E+F.
[0109] It is contemplated that as few as two different prism
configurations may be used and arranged in clusters within the
array 536, although as many prism sizes as necessary to accomplish
a modification of the output profile from the lightguide 516 may be
used. One purpose of the prism side angle variation is to spread
and add variable amounts of optical power into the first light
redirecting element 526. The varying configuration of prisms 538,
540 and 542 serves to provide substantially uniform sampling of the
input aperture of the lightguide, which minimizes non-uniformities
in the light extracted from the lightguide 516. The net result is
an effective minimization of the ripple effect particularly near
the entrance end 521 of the lightguide 516.
[0110] For the following defined terms, these definitions shall be
applied, unless a different definition is given in the claims or
elsewhere in this specification.
[0111] The term "microstructure" is used herein as defined and
explained in U.S. Pat. No. 4,576,850, the disclosure of which is
incorporated by reference herein. Thus, it means the configuration
of a surface that depicts or characterizes the predetermined
desired utilitarian purpose or function of the article having the
microstructure. Discontinuities such as projections and
indentations in the surface of said article will deviate in profile
from the average center line drawn through the microstructure such
that the sum of the areas embraced by the surface profile above the
center line is equal to the sum of the areas below the line, said
line being essentially parallel to the nominal surface (bearing the
microstructure) of the article. The heights of said deviations will
typically be about +/-0.005 to +/-750 microns, as measured by an
optical or electron microscope, through a representative
characteristic length of the surface, e.g., 1-30 cm. Said average
center line can be piano, concave, convex, aspheric or combinations
thereof. Articles where said deviations are of low order, e.g.,
from +/-0.005+/-0.1 or, preferably, +/-0.05 microns, and said
deviations are of infrequent or minimal occurrence, i.e., the
surface is free of any significant discontinuities, are those where
the microstructure-bearing surface is an essentially "flat" or
"smooth" surface, such articles being useful, for example, as
precision optical elements or elements with a precision optical
interface, such as ophthalmic lenses. Articles where said
deviations are of low order and of frequent occurrence include
those having anti-reflective microstructure. Articles where said
deviations are of high-order, e.g., from +/-0.1 to +/-750 microns,
and attributable to microstructure comprising a plurality of
utilitarian discontinuities which are the same or different and
spaced apart or contiguous in a random or ordered manner, are
articles such as retroreflective cube-corner sheeting, linear
Fresnel lenses, video discs and brightness enhancing films. The
microstructure-bearing surface can contain utilitarian
discontinuities of both said low and high orders. The
microstructure-bearing surface may contain extraneous or
non-utilitarian discontinuities so long as the amounts or types
thereof do not significantly interfere with or adversely affect the
predetermined desired utilities of said articles.
[0112] Retro-reflective films generally are capable of returning a
significant percentage of incident light at relatively high
entrance angles regardless of the rotational orientation of the
sheeting about an axis perpendicular to its major surface. Cube
corner retro-reflective film can include a body portion typically
having a substantially planar base surface and a structured surface
comprising a plurality of cube corner elements opposite the base
surface. Each cube corner element can include three mutually
substantially perpendicular optical faces that typically intersect
at a single reference point, or apex. The base of the cube corner
element acts as an aperture through which light is transmitted into
the cube corner element. In use, light incident on the base surface
of the sheeting is refracted at the base surface of the sheeting,
transmitted through the respective bases of the cube corner
elements disposed on the sheeting, reflected from each of the three
perpendicular cube corner optical faces, and redirected toward the
light source, as described in U.S. Pat. No. 5,898,523, which is
incorporated by reference herein.
[0113] The term "polymer" will be understood to include polymers,
copolymers (e.g., polymers formed using two or more different
monomers), oligomers and combinations thereof, as well as polymers,
oligomers, or copolymers that can be formed in a miscible blend by,
for example, coextrusion or reaction, including
transesterification. Both block and random copolymers are included,
unless indicated otherwise.
[0114] The term "(meth)acrylate" refers to both acrylate and
methacrylate compounds.
[0115] The term "refractive index" is defined herein as the
absolute refractive index of a material that is understood to be
the ratio of the speed of electromagnetic radiation in free space
to the speed of the radiation in that material. The refractive
index can be measured using known methods and is generally measured
using an Abbe Refractometer in the visible light region.
[0116] The term "nanoparticles" is defined herein to mean particles
(primary particles or associated primary particles) with a diameter
less than about 100 nm.
[0117] The term "associated particles" as used herein refers to a
grouping of two or more primary particles that are aggregated
and/or agglomerated.
[0118] The term "aggregation" as used herein is descriptive of a
strong association between primary particles that may be chemically
bound to one another. The breakdown of aggregates into smaller
particles is difficult to achieve.
[0119] The term "agglomeration" as used herein is descriptive of a
weak association of primary particles that may be held together by
charge or polarity and can be broken down into smaller
entities.
[0120] The term "primary particle size" is defined herein as the
size of a non-associated single particle.
[0121] The term "sol" is defined herein as a dispersion or
suspension of colloidal particles in a liquid phase.
[0122] The term "stable dispersion" is defined herein as a
dispersion in which the colloidal nanoparticles do not agglomerate
after standing for a period of time, such as about 24 hours, under
ambient conditions--e.g. room temperature (about 20-22.degree. C.),
atmospheric pressure, and no extreme electromagnetic forces.
[0123] The term "gain" is defined herein as a measure of the
improvement in brightness of a display due to a brightness
enhancing film, and is a property of the optical material, and also
of the geometry of the brightness enhancing film. Typically, the
viewing angle decreases as the gain increases. A high gain is
desired for a brightness enhancing film because improved gain
provides an effective increase in the brightness of the backlight
display.
[0124] The recitation of numerical ranges by endpoints includes all
numbers subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2,
2.75, 3, 3.80, 4, and 5).
[0125] As used in this specification and the appended claims, the
singular forms "a", an and "the" include plural referents unless
the content clearly dictates otherwise. Thus, for example,
reference to a composition containing "a compound" includes a
mixture of two or more compounds. As used in this specification and
the appended claims, the term "or" is generally employed in its
sense including "and/or" unless the content clearly dictates
otherwise.
[0126] Unless otherwise indicated, all numbers expressing
quantities of ingredients, measurement of properties and so forth
used in the specification and claims are to be understood as being
modified in all instances by the term "about."
[0127] The present invention should not be considered limited to
the particular examples described herein, but rather should be
understood to cover all aspects of the invention as fairly set out
in the attached claims. Various modifications, equivalent
processes, as well as numerous structures to which the present
invention can be applicable will be readily apparent to those of
skill in the art to which the present invention is directed upon
review of the instant specification.
[0128] The following ingredients of Table I were used in the
preparation of the organic component of the examples.
TABLE-US-00001 TABLE I Generic Chemical Description Supplier
(Location) Trimethylolpropane SR-351 Sartomer Co. triacrylate
(Exton, PA) Tribromophenoxyethyl BR-31 DAI-ICHI KOGYO acrylate
SEIYAKU CO., LTD (Kyoto, Japan) Phenoxyethyl acrylate SR-339
Sartomer Co. (Methoxyethoxy) ethoxy Sigma-Aldrich acetic acid
(Milwaukee, WI) (trimethyoxysilyl)propyl Silquest A174 OSI
Specialties methacrylate (South Charleston, WV) proprietary silane
Silquest A1230 OSI Specialties Lucirin TPO-L LR 8893 BASF
(Charlotte, NC) Hexanedioldiacrylate SR 238 Sartomer Co.
Beta-carboxyethyl acrylate BCEA Surface Specialties (Smyrna, Ga)
napthyloxyethylacrylate NOEA As described in U.S. Pat. No.
6,541,591 napthylthiolethylacrylate NSEA As described in Ex. 4-10
of U.S. patent application Ser. No. 11/026573 filed Dec. 30,
2004.
[0129] Three ZrO.sub.2 sols were prepared as described in U.S.
patent application Ser. No. 11/027426 filed Dec. 30, 2004.
ZrO.sub.2 Sol 1
[0130] 38.58 g Yttrium Acetate Hydrate (Aldrich) was dissolved in
1500 g Zirconium Acetate Solution (MEI Corp) and the solution was
dried at room temperature overnight then in a forced air oven at
90.degree. C. for 4 hrs. The solid was dissolved in sufficient
deionized water to give a 12.5% solution. This was pumped at a rate
of 80 mL/min through 100 feet of 1/4'' outside-diameter stainless
steel tubing that was immersed in a bath of oil heated to
206.degree. C. The flow then passed to an additional 40-foot length
of tubing immersed in an ice/water bath to cool the stream. A
backpressure regulator was placed at the end of the tubing to
maintain an exit pressure of 260-290 psig. The product of this step
was a liquid suspension of fine particles of a white solid.
[0131] The liquid suspension was concentrated to 14.5% solids using
a rotovap. This concentrate was pumped at a rate of 10 mL/min
through 100 feet of 1/4'' outside diameter stainless steel tubing
that was immersed in a bath of oil heated to 206.degree. C. The
flow then passed to an additional 40-foot length of tubing immersed
in an ice/water bath to cool the stream. A backpressure regulator
was placed at the end of the tubing to maintain an exit pressure of
260-270 psig. The product of this step was a liquid sol (10.5%
solids).
ZrO.sub.2 Sol 2
[0132] 79.5 g Yttrium Acetate Hydrate (Aldrich) was dissolved in
3000 g Zirconium Acetate Solution (MEI Corp) and the solution was
dried at room temperature overnight then in a forced air oven at
90.degree. C. for 4 hrs. The solid was dissolved in sufficient
deionized water to give a 12.5% solution. This was pumped at a rate
of 80 mL/min through 100 feet of 1/4'' outside-diameter stainless
steel tubing that was immersed in a bath of oil heated to
206.degree. C. The flow then passed to an additional 40-foot length
of tubing immersed in an ice/water bath to cool the stream. A
backpressure regulator was placed at the end of the tubing to
maintain an exit pressure of 250-310 psig. The product of this step
was a liquid suspension of fine particles of a white solid.
[0133] The liquid suspension was concentrated to about 18.5% solids
using a rotovap. This concentrate was pumped at a rate of 15 mL/min
through 100 feet of 1/4'' outside diameter stainless steel tubing
that was immersed in a bath of oil heated to 206.degree. C. The
flow then passed to an additional 40-foot length of tubing immersed
in an ice/water bath to cool the stream. A backpressure regulator
was placed at the end of the tubing to maintain an exit pressure of
230-340 psig. The product of this step was a liquid sol. The sol
was further concentrated via rotary evaoporation to yield a final
of 40.47% solids.
[0134] ZrO.sub.2 Sol 3 can be produced in the same manner yielding
a sol with 45.78% solids.
[0135] The three ZrO.sub.2 sols were tested according to the
following ZrO.sub.2 Test Methods:
Photon Correlation Spectroscopy (PCS)
[0136] The volume-average particle size was determined by Photon
Correlation Spectroscopy (PCS) using a Malvern Series 4700 particle
size analyzer (available from Malvern Instruments Inc.,
Southborough, Mass.). Dilute zirconia sol samples were filtered
through a 0.2 .mu.m filter using syringe-applied pressure into a
glass cuvette that was then covered. Prior to starting data
acquisition the temperature of the sample chamber was allowed to
equilibrate at 25 .degree. C. The supplied software was used to do
a CONTIN analysis with an angle of 90 degrees. CONTIN is a widely
used mathematical method for analyzing general inverse
transformation problems that is further described in S. W.
Provencher, Comput. Phys. Commun. 27, 229 (1982). The analysis was
performed using 24 data bins. The following values were used in the
calculations: refractive index of water equal to 1.333, viscosity
of water equal to 0.890 centipoise, and refractive index of the
zirconia particles equal to 1.9.
[0137] Two particle size measurements were calculated based on the
PCS data. The intensity-average particle size, reported in
nanometers, was equal to the size of a particle corresponding to
the mean value of the scattered light intensity distribution. The
scattered light intensity was proportional to the sixth power of
the particle diameter. The volume-average particle size, also
reported in nanometers, was derived from a volume distribution that
was calculated from the scattered light intensity distribution
taking into account both the refractive index of the zirconia
particles and the refractive index of the dispersing medium (i.e.,
water). The volume-average particle size was equal to the particle
size corresponding to the mean of the volume distribution.
[0138] The intensity-average particle size was divided by the
volume-average particle size to provide a ratio that is indicative
of the particle size distribution.
Crystalline Structure and Size (XRD Analysis)
[0139] The particle size of a dried zirconia sample was reduced by
hand grinding using an agate mortar and pestle. A liberal amount of
the sample was applied by spatula to a glass microscope slide on
which a section of double coated tape had been adhered. The sample
was pressed into the adhesive on the tape by forcing the sample
against the tape with the spatula blade. Excess sample was removed
by scraping the sample area with the edge of the spatula blade,
leaving a thin layer of particles adhered to the adhesive. Loosely
adhered materials remaining after the scraping were remove by
forcefully tapping the microscope slide against a hard surface. In
a similar manner, corundum (Linde 1.0 .mu.m alumina polishing
powder, Lot Number C062, Union Carbide, Indianapolis, Ind.) was
prepared and used to calibrate the diffractometer for instrumental
broadening.
[0140] X-ray diffraction scans were obtained using a Philips
vertical diffractometer having a reflection geometry, copper
K.sub..alpha. radiation, and proportional detector registry of the
scattered radiation. The diffractometer was fitted with variable
incident beam slits, fixed diffracted beam slits, and graphite
diffracted beam monochromator. The survey scan was conducted from
25 to 55 degrees two theta (2.theta.) using a 0.04 degree step size
and 8 second dwell time. X-ray generator settings of 45 kV and 35
mA were employed. Data collections for the corundum standard were
conducted on three separate areas of several individual corundum
mounts. Data was collected on three separate areas of the thin
layer sample mount.
[0141] The observed diffraction peaks were identified by comparison
to the reference diffraction patterns contained within the
International Center for Diffraction Data (ICDD) powder diffraction
database (sets 1-47, ICDD, Newton Square, Pa.) and attributed to
either cubic/tetragonal (C/T) or monoclinic (M) forms of zirconia.
The (111) peak for the cubic phase and (101) peak for the
tetragonal phase could not be separated so these phases were
reported together. The amounts of each zirconia form were evaluated
on a relative basis and the form of zirconia having the most
intense diffraction peak was assigned the relative intensity value
of 100. The strongest line of the remaining crystalline zirconia
form was scaled relative to the most intense line and given a value
between 1 and 100.
[0142] Peak widths for the observed diffraction maxima due to
corundum were measured by profile fitting. The relationship between
mean corundum peak widths and corundum peak position (2.theta.) was
determined by fitting a polynomial to these data to produce a
continuous function used to evaluate the instrumental breadth at
any peak position within the corundum testing range. Peak widths
for the observed diffraction maxima due to zirconia were measured
by profile fitting observed diffraction peaks. The following peak
widths were evaluated depending on the zirconia phase found to be
present: Cubic/Tetragonal (C/T): (1 1 1) Monoclinic (M): (-1 1 1),
and (1 1 1) A Pearson VII peak shape model with K.sub..alpha.1 and
K.sub..alpha.2 wavelength components accounted for, and linear
background model were employed in all cases. Widths were found as
the peak full width at half maximum (FWHM) having units of degrees.
The profile fitting was accomplished by use of the capabilities of
the JADE diffraction software suite. Sample peak widths were
evaluated for the three separate data collections obtained for the
same thin layer sample mount.
[0143] Sample peaks were corrected for instrumental broadening by
interpolation of instrumental breadth values from corundum
instrument calibration and corrected peak widths converted to units
of radians. The Scherrer equation was used to calculate the primary
crystal size. Crystallite Size (/D)=K.lamda./.beta. (cos .theta.)
In the Scherrer equation, [0144] K=form factor (here 0.9); [0145]
.lamda.=wavelength (1.540598 .ANG.); [0146] .beta.=calculated peak
width after correction for instrumental broadening (in
radians)=[calculated peak FWHM-instrumental breadth](converted to
radians) where FWHM is full width at half maximum; and [0147]
.theta.=1/2 the peak position (scattering angle). The
cubic/tetragonal crystallite size was measured as the average of
three measurements using (1 1 1) peak. Cubic/Tetragonal Mean
Crystallite Size=[D(1 1 1).sub.area 1+D(1 1 1).sub.area 2+D(1 1
1).sub.area 3]/3 The monoclinic crystallite size was measured as
the average of three measurement using the (-1 1 1) peak and three
measurements using the (1 1 1) peak. Monoclinic Mean Crystallite
Size=[D(-1 1 1).sub.area 1+D(-1 1 1).sub.area 2+D(-1 1 1).sub.area
3+D(1 1 1).sub.area 1+D(1 1 1).sub.area 2+D(1 1 1).sub.area 3]/6
The weighted average of the cubic/tetragonal (C/T) and monoclininc
phases (M) were calculated. Weighted average=[(% C/T)(C/T size)+(%
M)(M size)]/100 In this equation, [0148] % C/T=the percent
crystallinity contributed by the cubic and tetragonal crystallite
content of the ZrO.sub.2 particles; [0149] C/T size=the size of the
cubic and tetragonal crystallites; [0150] % M=the percent
crystallinity contributed by the monoclinic crystallite content of
the ZrO.sub.2 particles; and [0151] M size=the size of the
monoclinic crystallites. Dispersion Index
[0152] The Dispersion Index is equal to the volume-average size
measured by PCS divided by the weighted average crystallite size
measured by XRD.
Weight Percent Solids
[0153] The weight percent solids were determined by drying a sample
weighing 3 to 6 grams at 120.degree. C. for 30 minutes. The percent
solids can be calculated from the weight of the wet sample (i.e.,
weight before drying, weight.sub.wet) and the weight of the dry
sample (i.e., weight after drying, weight.sub.dry) using the
following equation. wt-%
solids=100(weight.sub.dry)/weight.sub.wet
[0154] The results were as shown in Table 2 and 3 as follows:
TABLE-US-00002 TABLE 2 Intensity- Intensity-average Volume-average
average:Volume- Size (nm) Size (nm) average Ratio ZrO.sub.2 Sol 1
21.0 12.9 1.62 ZrO.sub.2 Sol 2 33.8 16.4 2.06 ZrO.sub.2 Sol 3 42.1
17.5 2.41
[0155] TABLE-US-00003 TABLE 3 M M Size C/T C/T Size XRD Average
Dispersion Intensity (nm) Intensity (nm) % C/T Size (nm) Index
ZrO.sub.2 Sol 1 18 4.0 100 8.0 85 7.4 1.74 ZrO.sub.2 Sol 1 NA NA NA
NA NA NA NA ZrO.sub.2 Sol 3 9 6.5 100 8.0 92 7.9 2.21
EXAMPLE 1
[0156] ZrO.sub.2 Sol 1 was dialyzed for approximately 12 hr (Sigma
250-7U MWCO>12,000 available from Aldrich) to yield a stable sol
at 10.93% solids. The dialyzed ZrO.sub.2 Sol 1 (435.01 g) and MEEAA
(9.85 g) were charged to a 1 liter round bottom flask and were
concentrated via rotary evaporation. Isopropanol (30 g) and NSEA
(35.00 g) were then added to the concentrated sol. The dispersion
was then concentrated via rotary evaporation. The ZrO.sub.2 filled
NSEA had a refractive index of 1.674 and was 48.83% ZrO.sub.2. 0.39
g of TPO-L was added to 40.09 g of the concentrated dispersion. To
10.03 g of this mixture, 0.98 g of SR 351 was added.
EXAMPLE 2
[0157] ZrO.sub.2 Sol 1 was dialyzed for approximately 12 hr (Sigma
250-7U MWCO>12,000 available from Aldrich) to yield a stable sol
at 10.93% solids. The dialyzed ZrO.sub.2 Sol 1 (437.02 g) and MEEAA
(10 g) were charged to a 1 L round bottom flask. The water and
acetic acid were removed via rotary evaporation. The powder thus
obtained was redispersed in D.I water. The dispersion was 21.45 wt
% ZrO.sub.2. The aqueous ZrO.sub.2 sol (206.5 g) was charged to a
jar to which was added, with stirring, 300 g 1-methoxy-2-propanol,
9.89 g A174, 6.64 g Silquest A-1230. This mixture was then poured
into a IL jar, sealed and heated to 90.degree. C. for 3 hours. The
contents of the jar were removed and concentrated to approximately
25.4 wt % ZrO.sub.2 via rotary evaporation. Deionized water (450 g)
and concentrated aqueous ammonia (29% NH4OH) (13.9 g) were charged
to a IL beaker. The concentrated ZrO.sub.2 dispersion was added
slowly to the beaker with stirring. The white precipitate thus
obtained was isolated via vacuum filtration and washed with
additional D.I. water. The damp solids were dispersed in
1-methoxy-2-propanol. The resultant silane modified zirconia sol
contained 20.53 wt % solids and 17.44 wt % ZrO.sub.2.
[0158] The silane modified ZrO.sub.2 sol (117.03 g), PEA (15.12 g),
HDDA (1.68 g) and a 5% solution of Prostab 5198 in water (0.13 g)
were added to a round bottom flask. The water and
1-methoxy-2-propanol were removed via rotary evaporation. The
ZrO.sub.2 filled resin had a refractive index of 1.584 and was 47%
ZrO.sub.2.
EXAMPLE 3
[0159] ZrO.sub.2 Sol 2 was dialyzed for approximately 4.5 hr
(Spetra/Por Membrane MWCO 12-14,000 available from VWR) to yield a
stable sol at 33.85% solids. The dialyzed ZrO.sub.2 Sol 2 (53.13
g), MEEAA (1.59 g), BCEA (1.14 g), 1-methoxy-2-propanol (133 g),
NSEA (7.09 g) and TMPTA (0.97 g) were charged to a round bottom
flask and concentrated via rotary evaporation. The ZrO.sub.2
containing resin was 58.57% ZrO.sub.2 and had a refractive index of
1.682. The ZrO.sub.2 containing resin (21.94 g) and TPO-L (0.09 g)
were mixed together.
EXAMPLE 4
[0160] ZrO.sub.2 Sol 2 was dialyzed for approximately 4.5 hr
(Spetra/Por Membrane MWCO 12-14,000 available from VWR) to yield a
stable sol at 33.85% solids. The dialyzed ZrO.sub.2 Sol 2 (109.90
g), MEEAA (3.28 g), BCEA (2.36 g), 1-methoxy-2-propanol (200 g),
NOEA (14.68 g) and TMPTA (2.00 g) were charged to a round bottom
flask and concentrated via rotary evaporation. The ZrO.sub.2
containing resin was 57.22% ZrO.sub.2 and had a refractive index of
1.661. The ZrO.sub.2 containing resin (29.47 g) and TPO-L (0.13 g)
were mixed together.
EXAMPLE 5
[0161] ZrO.sub.2 Sol 2 was dialyzed for approximately 4.5 hr
(Spetra/Por Membrane MWCO 12-14,000 available from VWR) to yield a
stable sol at 33.85% solids. The dialyzed ZrO.sub.2 Sol 2 (144.02
g), MEEAA (4.30 g), BCEA (3.09 g), 1-methoxy-2-propanol (300 g),
NOEA (10.22 g), TMPTA (4.38 g), BR31 (21.89 g) and a 5% solution of
Prostab 5198 in water (0.3 g) were charged to a round bottom flask
and the alcohol and water were removed via rotary evaporation. The
ZrO.sub.2 containing resin was 46.97% ZrO.sub.2 and had a
refractive index of 1.636. The ZrO.sub.2 containing resin (49.03 g)
and TPO-L (0.26 g) were mixed together.
EXAMPLE 6
[0162] ZrO.sub.2 Sol 3 (100.00 g), MEEAA (4.44 g), BCEA (2.13 g),
1-methoxy-2-propanol (115 g), a 50/50 mix of PEA/BR31 (29.78 g) and
a 5% solution of Prostab 5198 in water (0.12 g) were charged to a
round bottom flask and the alcohol and water were removed via
rotary evaporation. The ZrO.sub.2 containing resin was
approximately 53.3% ZrO.sub.2 and had a refractive index of 1.642.
0.47 pph of TPO-L was added to the above mixture.
EXAMPLE 7
[0163] ZrO.sub.2 Sol 3 (200 g), MEEAA (8.81 g), BCEA (4.22 g),
1-methoxy-2-propanol (230 g), a 38/50/12 mix of BR31/PEA/TMPTA
(59.1 g), and a 5% solution of Prostab 5198 in water (0.24 g) were
charged to a round bottom flask and the alcohol and water were
removed via rotary evaporation. The ZrO.sub.2 containing resin was
52.31% ZrO.sub.2 and had a refractive index of 1.638. The ZrO.sub.2
filled resin (116 g) and TPO-L (0.55 g) were mixed together.
[0164] The organic component of all the examples as well as the
polymerizable compositions of all the examples have a solvent
content of less than 2 wt-%. All of the organic components employed
in the examples have a viscosity of less than 100 cps at 50.degree.
C. All of the organic components employed in the examples have a
viscosity of less than 1000 cps at 25.degree. C. provided that the
organic component is a homogeneous mixture at 25.degree. C. All the
polymerizable compositions of the examples (i.e. including the
nanoparticles) have a viscosity of less than 1000 cps at 50.degree.
C.
[0165] In three sets of experiments, polymerizable resin
compositions were prepared into brightness enhancing films using a
master tool that had a 90.degree. apex angles as defined by the
slope of the sides of the prisms.
[0166] In the first set of experiments, the mean distance between
adjacent apices was about 50 micrometers, the apexes of the prism
are sharp, and the prisms varied in height along their length
similar to that of a brightness enhancing film sold by 3M Company
under the trade designation "Vikuiti BEF 11190/50 Film".
[0167] In the second and third set of experiments, the mean
distance between adjacent apices was about 24 micrometers and the
apex of the prism vertices was sharp.
[0168] For each experiment polymerizable resin compositions were
heated to a temperature of about 50.degree. C. and poured onto the
master tool in a sufficient volume to create a continuous film. The
master tool and polymerizable resin were pulled through a coating
bar device to create a thickness of polymerizable resin of
approximately 25 microns in the first set of experiments and
approximately 13 microns in the second and third set of
experiments. After coating, a 5 mil PET film was laminated onto the
polymerizable resin for Experiment 1; a 2 mil PET film was used for
Experiment two; and a reflective polarizer substantially the same
as commercially available from 3M Company under the trade
designation "Vikuiti DBEF-P" was used for Experiment 3. The master
tool, polymerizable resin, and PET or reflective polarizer film
were then placed into UV curing machine and exposed at 3000
millijoules/cm.sup.2. After curing, the polymerized resin and PET
were peeled from the master tool.
[0169] The gain of the resulting brightness enhancing films were
was measured on a SpectraScan.TM. PR-650 SpectraColorimeter
available from Photo Research, Inc, Chatsworth, Calif. Results of
this method for each example formed below are reported in the
RESULTS section below. In order to measure the single sheet gain
(i.e. "SS") film samples were cut and placed on a Teflon light cube
that is illuminated via a light-pipe using a Foster DCR II light
source such that the grooves of the prisms are parallel to the
front face of the Teflon light cube. For crossed sheet gain (i.e.
"XS") a second sheet of the same material is placed underneath the
first sheet and orientated such that the grooves of the second
sheet are normal to the front face of the Teflon light cube.
[0170] The results are reported in Table IV as follows:
TABLE-US-00004 TABLE IV SS Gain XS Gain SS Gain XS Gain of BEF of
BEF of BEF of BEF Uncured Film of Film of Film of Film of Example
Resin RI Exp. 1 Exp. 1 Exp. 2 Exp. 2 1 1.674 1.799 2.361 2 1.584
1.766 2.434 3 1.682 1.955 2.606 4 1.901 2.568 1.89 2.595 5 1.854
2.573 6 1.642 7 1.638 1.889 2.684
EXAMPLE 8
[0171] The brightness enhancing film commercially available from 3M
Company under the trade designation "Vikuiti T-BEF" was placed
underneath a brightness enhancing film having the same composition
as Example 6 prepared according to Experiment 3 such that the
grooves of the second sheet are normal to the front face of the
Teflon light cube. The single sheet gain of Example 6 prepared
according to Experiment 3 was 2.519. The gain of this sheet
combined with "Vikuiti T-BEF" was 3.143.
* * * * *