U.S. patent application number 13/984239 was filed with the patent office on 2015-11-19 for front-lit reflective display device.
This patent application is currently assigned to 3M INNOVATIVE PROPERTIES COMPANY. The applicant listed for this patent is William J. Bryan, Encai Hao, Michael A. Meis, Mikhail L. Pekurovsky, Kevin R. Schaffer, Audrey A. Sherman, Steven D. Solomonson, Matthew S. Stay, David Scott Thompson, John A. Wheatley, Joseph W. Woody, V, Zhaohui Yang. Invention is credited to William J. Bryan, Encai Hao, Michael A. Meis, Mikhail L. Pekurovsky, Kevin R. Schaffer, Audrey A. Sherman, Steven D. Solomonson, Matthew S. Stay, David Scott Thompson, John A. Wheatley, Joseph W. Woody, V, Zhaohui Yang.
Application Number | 20150330597 13/984239 |
Document ID | / |
Family ID | 45809687 |
Filed Date | 2015-11-19 |
United States Patent
Application |
20150330597 |
Kind Code |
A2 |
Schaffer; Kevin R. ; et
al. |
November 19, 2015 |
FRONT-LIT REFLECTIVE DISPLAY DEVICE
Abstract
This application describes a front-lit reflective display
assembly including a reflective display and an illumination article
for front-lighting the display when the article is optically
coupled to a light source. The illumination article includes a
variable index light extraction layer optically coupled to a
lightguide. The variable index light extraction layer has first and
second regions, the first region comprising nanovoided polymeric
material, the second region comprising the nanovoided polymeric
material and an additional material, the first and second regions
being disposed such that for light being transported at a
supercritical angle in the lightguide, the variable index light
extraction layer selectively extracts the light in a predetermined
way based on the geometric arrangement of the first and second
regions. Front-lit reflective display devices including the
front-lit reflective display assembly optically coupled to a light
source are also described.
Inventors: |
Schaffer; Kevin R.;
(Woodbury, MN) ; Thompson; David Scott; (West
Lakeland, MN) ; Yang; Zhaohui; (North Oaks, MN)
; Hao; Encai; (Woodbury, MN) ; Sherman; Audrey
A.; (St. Paul, MN) ; Meis; Michael A.;
(Stillwater, MN) ; Bryan; William J.; (Mahtomedi,
MN) ; Wheatley; John A.; (Lake Elmo, MN) ;
Woody, V; Joseph W.; (St. Paul, MN) ; Solomonson;
Steven D.; (Shoreview, MN) ; Stay; Matthew S.;
(Minneapolis, MN) ; Pekurovsky; Mikhail L.;
(Bloomington, MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Schaffer; Kevin R.
Thompson; David Scott
Yang; Zhaohui
Hao; Encai
Sherman; Audrey A.
Meis; Michael A.
Bryan; William J.
Wheatley; John A.
Woody, V; Joseph W.
Solomonson; Steven D.
Stay; Matthew S.
Pekurovsky; Mikhail L. |
St. Paul
St. Paul
St. Paul
St. Paul
St. Paul
St. Paul
St. Paul
St. Paul
St. Paul
St. Paul
St. Paul
St. Paul |
MN
MN
MN
MN
MN
MN
MN
MN
MN
MN
MN
MN |
US
US
US
US
US
US
US
US
US
US
US
US |
|
|
Assignee: |
3M INNOVATIVE PROPERTIES
COMPANY
St. Paul
MN
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20140003086 A1 |
January 2, 2014 |
|
|
Family ID: |
45809687 |
Appl. No.: |
13/984239 |
Filed: |
February 23, 2012 |
PCT Filed: |
February 23, 2012 |
PCT NO: |
PCT/US2012/026237 PCKC 00 |
371 Date: |
September 9, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61446740 |
Feb 25, 2011 |
|
|
|
Current U.S.
Class: |
362/603 ;
362/326; 977/834 |
Current CPC
Class: |
G02F 2001/133616
20130101; B82Y 30/00 20130101; Y10S 977/834 20130101; B82Y 20/00
20130101; G02B 6/005 20130101; G02F 1/133553 20130101; F21V 5/00
20130101; G02B 6/0051 20130101 |
International
Class: |
F21V 5/00 20060101
F21V005/00; F21V 8/00 20060101 F21V008/00 |
Claims
1-20. (canceled)
21. A variable index light extraction layer having first and second
regions, the first region comprising nanovoided polymeric material,
the second region comprising the nanovoided polymeric material and
an additional material, the first and second regions being disposed
such that for light being transported at a supercritical angle in
an adjacent layer, the variable index light extraction layer
selectively extracts the light in a predetermined way based on the
geometric arrangement of the first and second regions.
22. An illumination article comprising a lightguide optically
coupled to the variable index light extraction layer of claim 21,
wherein the light guide is the adjacent layer.
23. A front-lit reflective display assembly comprising the
illumination article of claim 22 and a reflective scattering
substrate, wherein the reflective scattering substrate is optically
coupled to the variable index light extraction layer and the
lightguide.
24. A front-lit reflective display assembly of claim 23, wherein
the reflective scattering substrate comprises a reflective
display.
25. A variable index light extraction layer of claim 21, wherein
the first region has a first refractive index, the second region
has a second refractive index, and the difference between the first
and second refractive indices is about 0.03 to about 0.5.
26. A variable index light extraction layer assembly of claim 21,
wherein the nanovoided polymeric material comprises interconnected
nanovoids.
27. A variable index light extraction layer of claim 21, wherein
the first region has a first refractive index less than about
1.4.
28. A variable index light extraction layer of claim 21, wherein
the first region has a void volume of about 20 to about 60%.
29. A variable index light extraction layer of claim 21, wherein
the first region has a haze less than about 5% and a clarity
greater than about 90%.
30. A variable index light extraction layer of claim 21, wherein
the second region has a void volume of less than about 20%.
31. A variable index light extraction layer of claim 21, wherein
the variable index light extraction layer has a light transmittance
of greater than about 90%.
32. A variable index light extraction layer of claim 21, wherein
the second region comprises a plurality of second regions arranged
in a pattern across a transverse plane of the layer.
33. A variable index light extraction layer of claim 21, wherein
the second region comprises a plurality of second regions disposed
randomly across a transverse plane of the layer.
34. A variable index light extraction layer of claim 21, wherein
the first region is continuous across a transverse plane of the
layer.
35. A variable index light extraction layer of claim 21, wherein
the second region is continuous across a transverse plane of the
layer.
36. A variable index light extraction layer of claim 21, wherein
the second region comprises a plurality of second regions, and the
density of the second regions varies in one dimension across a
transverse plane of the layer.
37. A variable index light extraction layer of claim 21, wherein
the second region comprises a plurality of second regions, and the
density of the second regions varies in two dimensions across a
transverse plane of the layer.
38. A variable index light extraction layer of claim 21, wherein
the first and second regions transmit light of different
wavelengths.
39. An illumination article of claim 22, wherein the first region
has a first refractive index, the second region has a second
refractive index, and the refractive index of the lightguide is
greater than the first refractive index and less than or equal to
the second refractive index.
40. An illumination article of claim 22, wherein there is no air
gap between the lightguide and the variable index light extraction
layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is related to the following U.S.
Provisional Patent Applications, which were filed on even date
herewith and incorporated by reference: "Illumination Article And
Device For Front-Lighting Reflective Scattering Element" (U.S.
Provisional Application No. 61/446,712) and "Variable Index Light
Extraction Layer and Method of Illuminating With Same" (U.S.
Provisional Application No. 61/446,642).
FIELD
[0002] This application relates generally to illuminated display
devices, particularly display devices that are front-lit with an
illumination device.
BACKGROUND
[0003] Illumination systems or devices, such as those used to
illuminate objects or provide illumination in an electronic display
system, utilize one or more optical layers for managing light
emitted by one or more light sources. Often, the optical layers are
required to have a desired optical transmittance, optical haze,
optical clarity, or index of refraction. In many applications, the
optical layers include a lightguide used in combination with an air
layer and a light extraction layer such that light emitted by the
light source(s) is transported within the lightguide, and the air
layer and the extraction layer manage the light by supporting total
internal reflection (TIR) and extraction of the light from the
lightguide. A continuing need exists for optical films which are
capable of managing light and are suitable for use in thin,
flexible systems as well as in bulky systems.
SUMMARY
[0004] This application generally relates to front-lit reflective
display devices and methods for illuminating reflective displays.
Reflective display devices are front-lit using an illumination
device comprising a light source used in conjunction with an
illumination article. The illumination article includes, in
particular, a variable index light extraction layer having regions
of different properties such as refractive index, haze,
transmission, clarity, or a combination thereof. The illumination
article also includes a lightguide which delivers light from a
light source to the variable index light extraction layer. The
illumination article manages light emitted by the light source,
thus increasing the spatial uniformity of the light, which is then
delivered to the reflective display. This light is reflected by the
reflective display toward a viewer such that images provided by the
reflective display are illuminated.
[0005] In one aspect, this application describes a front-lit
reflective display assembly including a reflective display and an
illumination article. The illumination article includes a
lightguide and a variable index light extraction layer, where the
variable index light extraction layer is optically coupled to the
lightguide and the reflective display. The variable index light
extraction layer has first and second regions, where the first
region includes nanovoided polymeric material, and the second
region includes the nanovoided polymeric material and an additional
material. The first and second regions are disposed such that for
light emitted by a light source and injected into the lightguide,
the variable index light extraction layer selectively extracts the
light in a predetermined way based on the geometric arrangement of
the first and second regions.
[0006] The illumination article can function as a high performance
optical article having optical properties tailored for different
applications. For example, the first region can have a haze less
than about 5% and a clarity greater than about 90%, and/or the
layer can have a light transmittance of greater than about 90%. For
another example, the layer can have a haze less than about 10% and
a clarity greater than about 90%. The first and second regions can
be continuous across a transverse plane of the layer, or they can
be discontinuous, arranged in a pattern or randomly disposed. The
variable index light extraction layer can be tailored to exhibit
particular optical properties varying the relative areas of the
first and second regions. For example, the second regions can
comprise from about 5 to about 60% of an area across a transverse
plane of the layer.
[0007] In another aspect, this application describes a front-lit
reflective display device including the front-lit reflective
display assembly optically coupled to a light source.
[0008] In yet another aspect, this application describes a
front-lit reflective display including the illumination article,
light source, and reflective display. Reflective displays include
those which do not comprise a backlight. Reflective displays also
include those comprising an LCD panel, polymer dispersed liquid
crystal display panel, electrophoretic display panel,
electrofluidic display, electrowetting display or interferometric
display.
[0009] The above summary is not intended to describe each disclosed
embodiment or every implementation of this disclosure. The figures
and the detailed description below more particularly exemplify
illustrative embodiments.
BRIEF DESCRIPTION OF DRAWINGS
[0010] In the following description, reference is made to the
accompanying set of drawings that form a part of this disclosure
and in which are shown various general and specific embodiments. It
is to be understood that other embodiments are contemplated and may
be made without departing from the scope or spirit of the
invention. The following detailed description, therefore, is not to
be taken in a limiting sense. The figures are schematic drawings
and are not necessarily to scale.
[0011] FIG. 1a shows a schematic cross section of an exemplary
variable index light extraction layer.
[0012] FIGS. 1b-1c show schematic cross sections of an exemplary
variable index light extraction layer disposed on a transparent
adjacent layer.
[0013] FIG. 2 illustrates the variable index light extraction layer
having refractive indices that can vary across a transverse plane
of the layer.
[0014] FIG. 3 is a schematic cross-sectional view of a first region
of the variable index light extraction layer.
[0015] FIG. 4a is a plan view of a variable index light extraction
layer showing an exemplary geometric arrangement of the first and
second regions.
[0016] FIG. 4b illustrates the refractive index profile for the
variable index light extraction layer shown in FIG. 4a.
[0017] FIGS. 4c and 4d show profiles for selected optical
properties % transmission and % clarity, respectively, for the
variable light extraction layer shown in FIG. 4a.
[0018] FIGS. 5a and 5b show plan views of variable index light
extraction layers showing exemplary geometric arrangements of the
first and second regions.
[0019] FIG. 6 shows a schematic of an exemplary illumination device
comprising the variable index light extraction layer in combination
with a light source and a reflective scattering element.
[0020] FIG. 7 shows a schematic of an exemplary illumination
assembly comprising the variable light extraction layer in
combination with a reflective scattering element.
[0021] FIGS. 8, 9, 10a-10d and 11 show schematic cross-sectional
views of exemplary illumination assemblies comprising the variable
index light extraction layer optically coupled to a lightguide and
a reflective scattering element.
[0022] FIG. 12 shows a schematic cross-sectional view of an
exemplary optical film comprising the variable index light
extraction layer.
[0023] FIG. 13a shows a schematic cross-sectional view of an
exemplary optical film and illumination article comprising the
variable index light extraction layer optically coupled to a
lightguide.
[0024] FIG. 13b shows a schematic of an exemplary illumination
device comprising the illumination article shown in FIG. 13a in
combination with a light source and reflective scattering
element.
[0025] FIGS. 14a and 14b show reflective display devices with a
front light, with and without the variable index extraction layer,
respectively.
[0026] FIG. 15a shows a random gradient dot pattern for an
exemplary flexographic tool.
[0027] FIG. 15b shows a roll of an optical film comprising a
variable index light extraction layer disposed on a transparent
substrate.
[0028] FIGS. 16a and 16b show reflective display devices with a
front light having the variable index extraction layer, wherein the
light is off and on, respectively.
[0029] FIGS. 17a and 17b show prometric images and corresponding
plots of axial luminance as a function of position for reflective
display devices that are front-lit with and without the variable
index extraction layer, respectively.
DETAILED DESCRIPTION
[0030] In general, the variable index light extraction layer
disclosed herein comprises at least two different areas or regions,
wherein light of any angle incident upon the layer can be managed
differently because the regions have different refractive indices.
The variable index light extraction layer can be used in a variety
of optical film constructions, assemblies and devices as described
herein.
[0031] The variable index light extraction layer is an optical
layer that acts to extract light traveling in an adjacent layer at
supercritical angles, while at the same time has little to no light
scattering for subcritical angle light incident on the extraction
layer. The variable index light extraction layer extracts light
from an adjacent layer such as a transparent layer, and can deliver
the extracted light to an article or element such that the article
or element is illuminated. The variable index light extraction
layer does not have features that significantly or functionally
scatter light. Thus, when looking through the layer, as shown in
FIG. 15b, there is little distortion of images and objects on the
opposite side of the layer. Ideally, the materials in first and
second regions have different refractive indices, and both are
highly transmissive with very low haze. The first and second
regions in the variable index light extraction layer can be shaped
and arranged to yield a layer with high clarity, low haze and high
transmission when the layer is physically attached and optically
coupled to a lightguide, reflective scattering element or
reflective display.
[0032] The variable index light extraction layer allows the
lightguide to be transparent exhibiting little to no haze and high
clarity with and without illumination. This allows for viewing of
images on a reflective display or of a graphic without significant
reduction in resolution and contrast, and without visible optical
artifacts generated by light scattered or diffracted by different
regions. In traditional lightguides, extraction layers have light
scattering features in order for light being transported within the
lightguide by TIR (at angles equal to or greater than the critical
angles) in a lightguide to be directed out of the lightguide. These
light scattering features typically comprise diffuse reflective
printed extraction dots or structures that are disposed on or are
etched into the surface of the lightguide which cause significant
reduction in the viewing quality when looking through the
lightguide.
[0033] In addition to optical benefits, the variable index light
extraction layer can be produced by relatively simple coating and
printing techniques amenable to high speed, low cost
manufacturing.
[0034] This disclosure generally relates to polymeric optical films
or layers that exhibit regions of high index-like optical
properties and low index-like optical properties, or otherwise
interact with the transmission, scattering, absorption, refraction
or reflection of light. The regions of high index-like optical
properties and low index-like optical properties vary across a
transverse plane of the optical layer, that is, the optical layer
is a variable index optical layer. Throughout this disclosure, the
term "index" is often used in place of index of refraction or
refractive index. The transverse plane of a variable index light
extraction layer disclosed herein can be described as a plane that
is parallel to at least one major surface of the layer.
[0035] FIG. 1a shows a schematic cross section of an exemplary
variable index light extraction layer 100. The extraction layer
comprises first regions 140a and 140b, both regions comprising a
nanovoided polymeric material. In some embodiments, the nanovoided
polymeric material comprises a plurality of interconnected
nanovoids as described in WO 2010/120422 A1 (Kolb et al.) and WO
2010/120468 A1 (Kolb et al.). The plurality of interconnected
nanovoids is a network of nanovoids dispersed in a binder wherein
at least some of the nanovoids are connected to one another via
hollow tunnels or hollow tunnel-like passages. Nanovoided polymeric
material comprising interconnected nanovoids have nanovoids or
pores that can extend to one or more surfaces of the material.
[0036] The variable index light extraction layer comprises second
region 130 disposed between first regions 140a and 140b. The second
region comprises the nanovoided polymeric material and an
additional material. In some embodiments, this additional material
occupies at least a portion of the void volume of the nanovoided
polymeric material. Throughout this disclosure, dashed lines in
cross section and plan views are used to indicate general location
of the first and second regions, however, these dashed lines are
not meant to describe any sort of boundary between the regions.
[0037] FIG. 1b shows a schematic cross section of an exemplary
variable index light extraction layer disposed on a transparent
adjacent layer. Optical film 105 comprises variable index light
extraction layer 100 disposed on adjacent layer 120 which is a
transparent substrate. Variable index light extraction layer 100
comprises first regions 140a and 140b, and second region 130
disposed between the first regions.
[0038] In general, an area or region is identified by the material
it comprises in combination with the refractive index of the
region. The first region comprises a nanovoided polymeric material
and has a first refractive index. A first region is identified if
substantially all of the region comprises the nanovoided polymeric
material and if the region has a refractive index within .+-.0.02
across a continuous transverse plane of the layer. Methods for
determining the refractive index across a transverse plane of the
layer are described below.
[0039] The second region comprises the nanovoided polymeric
material and an additional material, and has a second refractive
index that is different from the first refractive index by at least
about 0.03. The nanovoided polymeric material is the same material
in both the first and second regions. A material is considered an
additional material if it is incorporated substantially within the
variable index light extraction layer and causes a change in
refractive index of the first region by at least about 0.03, for
example, from about 0.03 to about 0.5, from about 0.05 to about
0.5, or from about 0.05 to about 0.25.
[0040] In some embodiments, the additional material is different
from the binder used to form the nanovoided polymeric material. In
some embodiments, the additional material is the same as the binder
used to form the nanovoided polymeric material. A second region is
identified if (i) all of the region comprises the nanovoided
polymeric material, (ii) the region has a refractive index within
.+-.0.02 across a continuous transverse plane of the variable index
light extraction layer, and (iii) the region has a refractive index
that is different from that of the first region by at least about
0.03.
[0041] In some embodiments, the variable index light extraction
layer can be made by combining an additional material with portions
of the nanovoided polymeric material that has been formed into some
desirable shape such as a layer. Enough of the additional material
is combined with the nanovoided polymeric material such that the
desired change in refractive index results, and which is at least
about 0.03, for example, from about 0.03 to about 0.5, from about
0.05 to about 0.5, or from about 0.05 to about 0.25.
[0042] The variable index light extraction layer comprises the
first and second regions disposed relative to each other such that
for light being transported at supercritical angles in an adjacent
layer, the variable index light extraction layer selectively
extracts the light in a predetermined way based on the geometric
arrangement of the first and second regions. As used herein,
supercritical angles are angles that are equal to or greater than
the critical angle for a given interface formed by the first region
of the variable index light extraction layer and the adjacent
layer, is determined by the refractive index difference between the
first region and the adjacent layer. The critical angle is the
smallest angle of incidence at which a light ray passing from one
medium to another less refractive medium can be totally reflected
from the boundary between the two.
[0043] Referring to FIG. 1b, which is a simplified view of FIG. 1a,
light represented by rays 150 and 160 are being transported within
adjacent layer 120 by TIR. In this embodiment, the refractive index
of first regions 140a and 140b are that much less than that of the
adjacent layer which defines critical angle .theta..sub.c as shown.
Light traveling at a supercritical angle represented by ray 150
strikes an interface between adjacent layer 120 and first region
140b, and this angle of incidence for ray 150 is greater than
.theta..sub.c, which results in substantially all of the light
being reflected at the interface.
[0044] Also in this embodiment, the refractive index of second
region 130 is approximately equal to or greater than that of
adjacent layer 120. In this circumstance there is no critical angle
at the interface and the light represented by ray 160 passes
through the interface between adjacent layer 120 and second region
130, thus being extracted from the adjacent layer into the second
region 130.
[0045] Thus, for the embodiment shown in FIG. 1a and FIG. 1b, the
first and second regions are disposed relative to each other such
that light being transported at supercritical angles in an adjacent
layer can be extracted selectively by the variable index light
extraction layer in a predetermined way based on the geometric
arrangement of the first and second regions.
[0046] FIG. 1c shows the schematic cross section of optical film
105 with light at subcritical angles impinging on the adjacent
layer. Light represented by rays 180 and 190 impinges at
subcritical angles on surface 170 of adjacent layer 120, and the
light travels essentially undeviated through layers 120 and 100.
Light represented by ray 190 travels through first region 140b, and
light represented by ray 180 travels through second region 130.
There is little to no deviation of light travelling through the
different regions of variable index light extraction layer 100.
This results in an optical film, such as exemplary optical film
105, that has low haze and high clarity, such that when one looks
through the optical film there is little to no distortion of images
on the opposite side. The variable index light extraction layer can
have any geometric arrangement of first and second regions to
produce the desired extracted light pattern.
[0047] In general, the refractive index profile of the variable
index light extraction layer may vary in any way, as long as the
desired optical performance of the layer is obtained. FIG. 2
illustrates the variable index light extraction layer having
refractive indices that can vary across a transverse plane of the
layer. The refractive index profile shows a plot of distance d,
which corresponds to a distance across a transverse plane of the
layer, for the layer in plan view. FIG. 2 shows that at some
initial position on the layer corresponding to d.sub.0, the layer
has first refractive index n.sub.1 corresponding to the first
region. Moving across the transverse plane of the layer, first
refractive index n.sub.1 is observed until reaching d.sub.1 where
the refractive index of the layer abruptly increases to n.sub.2
which corresponds to the second refractive index of the second
region. Continuing to move across the transverse plane of the
layer, the second refractive index n.sub.2 is observed until
reaching d.sub.2 where the refractive index of the layer abruptly
decreases to n.sub.1 indicating a second first region.
[0048] The change in refractive index between two adjacent first
and second regions having low and high indices, respectively, can
vary in a number of ways. For example, the change in refractive
index can be abrupt, as in a step function, between two adjacent
regions. For another example, the change in refractive index can be
monotonic, with the refractive index continuously increasing or
decreasing (depending on whether the change is observed as a
function of moving from the first region to the second region, or
the second region to the first region, respectively). In some
cases, the first and second refractive indices of the adjacent
first and second regions vary as some combination of step and
monotonic functions.
[0049] The first region of the variable light extraction layer has
a refractive index less than that of the second region. For
example, the first refractive index may be less than about 1.4,
less than about 1.3 or less than about 1.2. The first refractive
index may be from about 1.15 to about 1.45, from about 1.2 to about
1.42, from about 1.2 to about 1.40 or from about 1.2 to about 1.35.
In general, the particular first and second refractive indices, as
well as the particular difference between the two, depends on the
desired optical performance of the variable index light extraction
layer as described below. The difference in refractive index
between the first and second regions is greater about 0.03. In some
embodiments, the difference in refractive index between the first
and second regions is greater than 0.05, greater than 0.1, greater
than 0.2 or greater than 0.25.
[0050] The nanovoided polymeric material typically comprises a
plurality of interconnected nanovoids or a network of nanovoids
dispersed in a binder. At least some of the nanovoids in the
plurality or network are connected to one another via hollow
tunnels or hollow tunnel-like passages. The nanovoids are not
necessarily free of all matter and/or particulates. For example, in
some cases, a nanovoid may include one or more small fiber- or
string-like objects that include, for example, a binder and/or
nano-particles. Some disclosed first regions include multiple
pluralities of interconnected nanovoids or multiple networks of
nanovoids where the nanovoids in each plurality or network are
interconnected. In some cases, in addition to multiple pluralities
of interconnected nanovoids, the disclosed first regions may
include a fraction of closed or unconnected nanovoids meaning that
the nanovoids are not connected to other nanovoids via tunnels.
[0051] The nanovoided polymeric material is designed to support TIR
by virtue of including a plurality of nanovoids. When light that
travels in an optically transparent (clear and non-porous) adjacent
layer and that light is incident on a stratum possessing high
porosity, the reflectivity of the incident light is much higher at
oblique angles than at normal incidence. In the case of nanovoided
first regions having little to no haze, the reflectivity at oblique
angles greater than the critical angle is close to about 100%. In
such cases, the incident light undergoes TIR.
[0052] The nanovoids in the disclosed first region have an index of
refraction n.sub.v and a permittivity .di-elect cons..sub.v, where
n.sub.v.sup.2=.di-elect cons..sub.v, and the binder has an index of
refraction n.sub.b and a permittivity .di-elect cons..sub.b, where
n.sub.b.sup.2=.di-elect cons..sub.b. In general, the interaction of
a layer of nanovoided polymeric material with light, such as light
that is incident on, or propagates in, the layer, depends on a
number of characteristics of the layer such as, for example, the
layer thickness, the binder index, the nanovoid or pore index, the
pore shape and size, the spatial distribution of the pores, and the
wavelength of light. In some cases, light that is incident on or
propagates within the layer of nanovoided polymeric material "sees"
or "experiences" an effective permittivity .di-elect cons..sub.eff
and an effective index n.sub.eff, where n.sub.eff can be expressed
in terms of the nanovoid index n.sub.v, the binder index n.sub.b,
and the nanovoid porosity or volume fraction "f". In such cases,
the layer is sufficiently thick and the nanovoids are sufficiently
small so that light cannot resolve the shape and features of a
single or isolated nanovoid. In such cases, the size of at least a
majority of the nanovoids, such as at least 60% or 70% or 80% or
90% of the nanovoids, is not greater than about .lamda./5, or not
greater than about .lamda./6, or not greater than about .lamda./8,
or not greater than about .lamda./10, or not greater than about
.lamda./20, where .lamda. is the wavelength of light.
[0053] In some embodiments, light that is incident on a disclosed
first region of the variable light extraction layer is visible
light which can be in a range of from about 380 nm to about 750 nm,
or from about 400 nm to about 700 nm, or from about 420 nm to about
680 nm. In such cases, the first region of the variable light
extraction layer has an effective index of refraction and includes
a plurality of nanovoids if the size of at least a majority of the
nanovoids, such as at least 60% or 70% or 80% or 90% of the
nanovoids, is not greater than about 70 nm, or not greater than
about 60 nm, or not greater than about 50 nm, or not greater than
about 40 nm, or not greater than about 30 nm, or not greater than
about 20 nm, or not greater than about 10 nm.
[0054] In some cases, the disclosed first region of the variable
index light extraction layer is sufficiently thick so that the
region can reasonably have an effective index that can be expressed
in terms of the indices of refraction of the nanovoids and the
binder, and the nanovoid or pore volume fraction or porosity. In
such cases, the thickness of the first region is not less than
about 100 nm, or not less than about 200 nm, or not less than about
500 nm, or not less than about 700 nm, or not less than about 1,000
nm.
[0055] When the nanovoids in a disclosed first region are
sufficiently small and the region is sufficiently thick, the first
region has an effective permittivity .di-elect cons..sub.eff that
can be expressed as:
.di-elect cons..sub.eff=f.di-elect cons..sub.v+(1-f).di-elect
cons..sub.b (1)
In such cases, the effective index n.sub.eff of the first region
can be expressed as:
n.sub.eff.sup.2=fn.sub.v.sup.2+(1-f)n.sub.b.sup.2 (2)
In some cases, such as when the difference between the indices of
refraction of the pores and the binder is sufficiently small, the
effective index of the first region can be approximated by the
following expression:
n.sub.eff=fn.sub.v+(1-f)n.sub.b (3)
In such cases, the effective index of the first region is the
volume weighted average of the indices of refraction of the
nanovoids and the binder. For example, a first region that has a
void volume fraction of about 50% and a binder that has an index of
refraction of about 1.5, has an effective index of about 1.25.
[0056] FIG. 3 is a schematic cross-sectional view of a first region
of the variable index light extraction layer that includes a
network of nanovoids or plurality of interconnected nanovoids and a
plurality of particles dispersed substantially uniformly within a
binder. First region 300 comprises plurality of interconnected
nanovoids 320 dispersed in binder 310. Nanovoids 320 includes
interconnected nanovoids 320A-320C. First and second major surfaces
330 and 332, respectively, are porous as indicated by surface pores
320D-G which may or may not provide a tunnel that extends from one
surface to another or through the thickness of the region. Some of
the nanovoids, such as nanovoids 320B and 320C, are within the
interior of the first region and may or may not tunnel to a
surface.
[0057] Voids 320 have a size d.sub.1 that can generally be
controlled by choosing suitable composition and fabrication, such
as coating, drying and curing conditions. In general, d.sub.1 can
be any desired value in any desired range of values. For example,
in some cases, at least a majority of the nanovoids, such as at
least 60% or 70% or 80% or 90% or 95% of the nanovoids, have a size
that is in a desired range. For example, in some cases, at least a
majority of the nanovoids, such as at least 60% or 70% or 80% or
90% or 95% of the nanovoids, have a size that is not greater than
about 500 nm, not greater than 400 nm, not greater than about 300
nm, not greater than about 200 nm, not greater than about 100 nm,
not greater than about 70 nm, or not greater than about 50 nm. In
some cases, some of the nanovoids can be sufficiently small such
that the refractive index of the region is changed, with little or
no scattering of light.
[0058] Binder 310 can comprise any material such as a polymer. The
binder may be a polymer formed from a polymerizable composition
comprising monomers, wherein the monomers are cured using actinic
radiation, e.g., visible light, ultraviolet radiation, electron
beam radiation, heat and combinations thereof, or any of a variety
of conventional anionic, cationic, free radical or other
polymerization techniques, which can be chemically or thermally
initiated. Polymerization may be carried out using solvent
polymerization, emulsion polymerization, suspension polymerization,
bulk polymerization, and the like. Useful monomers include small
molecules having a molecular weight less than about 500 g/mole,
oligomers having a molecular weight of greater than 500 to about
10,000 g/mole, and polymers having a molecular weight of greater
than 10,000 to about 100,000 g/mole.
[0059] Representative examples of curable groups suitable in the
practice of the present disclosure include epoxy groups,
ethylenically unsaturated groups, olefinic carbon-carbon double
bonds, allyloxy groups, (meth)acrylate groups, (meth)acrylamide
groups, cyanoester groups, vinyl ethers groups, combinations of
these, and the like. The monomers may be mono- or multifunctional
and capable of forming a crosslinked network upon polymerization.
As used herein, (meth)acrylate refers to acrylate and methacrylate,
and (meth)acrylamide refers to acrylamide and methacrylamide.
[0060] Useful monomers include styrene, alpha-methylstyrene,
substituted styrene, vinyl esters, vinyl ethers,
N-vinyl-2-pyrrolidone, (meth)acrylamide, N-substituted
(meth)acrylamide, octyl (meth)acrylate, iso-octyl (meth)acrylate,
nonylphenol ethoxylate (meth)acrylate, isononyl (meth)acrylate,
diethylene glycol (meth)acrylate, isobornyl (meth)acrylate,
2-(2-ethoxyethoxyl)ethyl (meth)acrylate, 2-ethylhexyl
(meth)acrylate, lauryl (meth)acrylate, butanediol
mono(meth)acrylate, beta-carboxyethyl (meth)acrylate, isobutyl
(meth)acrylate, cycloaliphatic epoxide, alpha-epoxide,
2-hydroxyethyl (meth)acrylate, (meth)acrylonitrile, maleic
anhydride, itaconic acid, isodecyl (meth)acrylate, dodecyl
(meth)acrylate, n-butyl (meth)acrylate, methyl (meth)acrylate,
hexyl (meth)acrylate, (meth)acrylic acid, N-vinylcaprolactam,
stearyl (meth)acrylate, hydroxyl functional polycaprolactone ester
(meth)acrylate, hydroxyethyl (meth)acrylate, hydroxymethyl
(meth)acrylate, hydroxypropyl (meth)acrylate, hydroxyisopropyl
(meth)acrylate, hydroxybutyl (meth)acrylate, hydroxyisobutyl
(meth)acrylate, tetrahydrofurfuryl (meth)acrylate, combinations of
these, and the like.
[0061] Functional oligomers and polymers may also be collectively
referred to herein as "higher molecular weight constituents or
species." Suitable higher molecular weight constituents may be
incorporated into compositions of the present disclosure. Such
higher molecular weight constituents may provide benefits including
viscosity control, reduced shrinkage upon curing, durability,
flexibility, adhesion to porous and nonporous substrates, outdoor
weatherability, and/or the like. The amount of oligomers and/or
polymers incorporated into fluid compositions of the present
disclosure may vary within a wide range depending upon such factors
as the intended use of the resultant composition, the nature of the
reactive diluent, the nature and weight average molecular weight of
the oligomers and/or polymers, and the like. The oligomers and/or
polymers themselves may be straight-chained, branched, and/or
cyclic. Branched oligomers and/or polymers tend to have lower
viscosity than straight-chain counterparts of comparable molecular
weight.
[0062] Exemplary polymerizable oligomers or polymers include
aliphatic polyurethanes, acrylics, polyesters, polyimides,
polyamides, epoxy polymers, polystyrene (including copolymers of
styrene) and substituted styrenes, silicone containing polymers,
fluorinated polymers, combinations of these, and the like. For some
applications, polyurethane and acrylate oligomers and/or polymers
can have improved durability and weatherability characteristics.
Such materials also tend to be readily soluble in reactive diluents
formed from radiation curable, (meth)acrylate functional
monomers.
[0063] Because aromatic constituents of oligomers and/or polymers
generally tend to have poor weatherability and/or poor resistance
to sunlight, aromatic constituents can be limited to less than 5
weight percent, preferably less than 1 weight percent, and can be
substantially excluded from the oligomers and/or polymers and the
reactive diluents of the present disclosure. Accordingly,
straight-chained, branched and/or cyclic aliphatic and/or
heterocyclic ingredients are preferred for forming oligomers and/or
polymers to be used in outdoor applications.
[0064] Suitable radiation curable oligomers and/or polymers for use
in the present disclosure include, but are not limited to,
(meth)acrylated urethanes (i.e., urethane (meth)acrylates),
(meth)acrylated epoxies (i.e., epoxy (meth)acrylates),
(meth)acrylated polyesters (i.e., polyester (meth)acrylates),
(meth)acrylated (meth)acrylics, (meth)acrylated silicones,
(meth)acrylated polyethers (i.e., polyether (meth)acrylates), vinyl
(meth)acrylates, and (meth)acrylated oils.
[0065] Materials useful for toughening the nanovoided layer 300
include resins with high tensile strength and high elongation, for
example, CN9893, CN902, CN9001, CN961, and CN964 that are
commercially available from Sartomer Company; and EBECRYL 4833 and
Eb8804 that are commercially available Cytec. Suitable toughening
materials also include combinations of "hard" oligomeric acrylates
and "soft" oligomeric acrylates. Examples of "hard" acrylates
include polyurethane acrylates such as EBECRYL 4866, polyester
acrylates such as EBECRYL 838, and epoxy acrylates such as EBECRYL
600, EBECRYL 3200, and EBECRYL 1608 (commercially available from
Cytec); and CN2920, CN2261, and CN9013 (commercially available from
Sartomer Company). Examples of the "soft" acrylates include EBECRYL
8411 that is commercially available from Cytec; and CN959, CN9782,
and CN973 that are commercially available from Sartomer Company.
These materials are effective at toughening the nanovoided
structured layer when added to the coating formulation in the range
of 5-25% by weight of total solids (excluding the solvent
fraction).
[0066] The nanovoided polymeric material may or may not contain
particles. Particles 340 have a size d.sub.2 that can be any
desired value in any desired range of values. For example, in some
cases at least a majority of the particles, such as at least 60% or
70% or 80% or 90% or 95% of the particles, have a size that is in a
desired range. For example, in some cases, at least a majority of
the particles, such as at least 60% or 70% or 80% or 90% or 95% of
the particles, have a size that is not greater than about 5 um, or
not greater than about 3 um, or not greater than about 2 um, or not
greater than about 1 micron, or not greater than about 700 nm, or
not greater than about 500 nm, or not greater than about 200 nm, or
not greater than about 100 nm, or not greater than about 50 nm
[0067] In some cases, particles 340 have an average particle size
that is not greater than about 5 um, not greater than about 3 um,
not greater than about 2 um, not greater than about 1 um, not
greater than about 700 nm, not greater than about 500 nm, not
greater than about 200 nm, not greater than about 100 nm, or not
greater than about 50 nm. In some cases, some of the particles can
be sufficiently small such that the refractive index of the region
is changed, with little or no scattering of light.
[0068] In some cases, d.sub.1 and/or d.sub.2 are sufficiently small
such that the refractive index of the region is changed, with
little or no scattering of light. In such cases, for example,
d.sub.1 and/or d.sub.2 are not greater than about .lamda./5, not
greater than about .lamda./6, not greater than about .lamda./8, not
greater than about .lamda./10, not greater than about .lamda./20,
where .lamda. is the wavelength of light. As another example, in
such cases, d.sub.1 and d.sub.2 are not greater than about 70 nm,
not greater than about 60 nm, not greater than about 50 nm, not
greater than about 40 nm, not greater than about 30 nm, not greater
than about 20 nm, or not greater than about 10 nm
[0069] Other properties of particles used in the nanovoided
polymeric layer include shape. The particles can have a regular
shape such as spherical, or an irregular shape. The particles can
be elongated having an average aspect ratio that is not less than
about 1.5, not less than about 2, not less than about 3, not less
than about 4, or not less than about 5. In some cases, the
particles can be in the form or shape of a string-of-pearls (such
as SNOWTEX-PS particles available from Nissan Chemical) or
aggregated chains of spherical or amorphous particles, such as
fumed silica.
[0070] The nanoparticles can be inorganic or organic, or a
combination thereof. In some embodiments, the nanoparticles can be
porous particles, hollow particles, solid particles, or a
combination thereof. Examples of suitable inorganic nanoparticles
include silica and metal oxides such as zirconia, titania, ceria,
alumina, iron oxide, vanadia, antimony oxide, tin oxide,
alumina/silica, silica/zirconia and combinations thereof. The
nanoparticles can be surface-modified such that they bond to the
binder chemically and/or physically. In the former case, the
surface-modified nanoparticles have functionality that chemically
reacts with the binder. In general, surface modification is well
known and can be carried out with conventional materials and
techniques as described in the references cited above.
[0071] The weight ratio of binder to nanoparticles can range from
about 30:70, 40:60, 50:50, 55:45, 60:40, 70:30, 80:20 or 90:10 or
more depending on the desired properties of the nanovoided
polymeric layer. The preferred ranges of wt % of nanoparticles
range from about 10% by weight to about 60% by weight, and can
depend on the density and size of the nanoparticle used.
[0072] In cases where the primary optical effect of network of
voids 320 and particles 340 is to affect the effective index and to
minimize scattered light, the optical haze of optical layer 300
that is due to voids 320 and particles 340 is not greater than
about 5%, or not greater than about 4%, or not greater than about
3.5%, or not greater than about 4%, or not greater than about 3%,
or not greater than about 2.5%, or not greater than about 2%, or
not greater than about 1.5%, or not greater than about 1%. In such
cases, the effective index of the effective medium of the optical
layer is not greater than about 1.40, or not greater than about
1.35, or not greater than about 1.3, or not greater than about
1.25, or not greater than about 1.2, or not greater than about
1.15.
[0073] First region 300 can have other materials in addition to
binder 310 and particles 340. For example, first region 300 can
include one or more additives, such as for example, coupling
agents, to help wet the surface of a substrate, not expressly shown
in FIG. 3, on which the nanovoided polymeric material is formed.
Other exemplary materials in first region 300 include initiators,
such as one or more photo-initiators, anti-stats, UV absorbers and
release agents.
[0074] The nanovoided polymeric material is typically formed as a
layer. Methods for making a layer of the nanovoided polymeric
material are described in the Kolb et al. references cited above.
In one process, first a solution is prepared that includes a
plurality of particles, such as nano-particles, and a polymerizable
material dissolved in a solvent, where the polymerizable material
can include, for example, one or more types of monomers. Next, the
polymerizable material is polymerized, for example by applying heat
or light, to form an insoluble polymer matrix in the solvent. In
some cases, after the polymerization step, the solvent may still
include some of the polymerizable material, although at a lower
concentration. Next, the solvent is removed by drying or
evaporating the solution resulting in first region 300 that
includes a network, or a plurality, of voids 320 dispersed in
polymer binder 310. The first region further includes plurality of
particles 340 dispersed in the polymer. The particles are bound to
the binder, where the bonding can be physical or chemical.
[0075] In general, a nanovoided polymeric layer can be formed with
a desired porosity or void volume, which can depend on the desired
properties of the first region of the variable index light
extraction layer. For example, the first region may have a void
volume of about 20 to about 70%, about 30 to about 70% or about 40
to about 70%. In some cases, the void volume is not less than about
20%, not less than about 30%, not less than about 40%, not less
than about 50%, not less than about 60%, not less than about 70%,
not less than about 80%, or not less than about 90%.
[0076] In some embodiments, first region 300 has a low optical
haze. In such cases, the optical haze of the optical layer is not
greater than about 10%. Or not greater than about 7%, or not
greater than about 5%, or not greater than about 4%, or not greater
than about 3.5%, or not greater than about 4%, or not greater than
about 3%, or not greater than about 2.5%, or not greater than about
2%, or not greater than about 1.5%, or not greater than about 1%.
The haze variation across the first region can be in the range of
from about 1-5%, of from about 1-3%, of from about 1-2%, or less
than 1%. In such cases, the optical film can have a reduced
effective index that is not greater than about 1.40, or not greater
than about 1.35, or not greater than about 1.3, or not greater than
about 1.2, or not greater than about 1.15, or not greater than
about 1.1, or not greater than about 1.05. For light normally
incident on optical layer 300, optical haze, as used herein, is
defined as the ratio of the transmitted light that deviates from
the normal direction by more than 4 degrees to the total
transmitted light. Haze values disclosed herein were measured using
a Haze-Gard Plus haze meter (BYK-Gardiner, Silver Springs, Md.)
according to the procedure described in ASTM D1003.
[0077] In some embodiments, first region 300 has a high optical
clarity. For light normally incident on first region 300, optical
clarity, as used herein, refers to the ratio
(T.sub.1-T.sub.2)/(T.sub.1+T.sub.2), where T.sub.1 is the
transmitted light that deviates from the normal direction between
1.6 and 2 degrees, and T.sub.2 is the transmitted light that lies
between zero and 0.7 degrees from the normal direction. Clarity
values disclosed herein were measured using a Haze-Gard Plus haze
meter from BYK-Gardiner. In the cases where first region 300 has a
high optical clarity, the clarity is not less than about 80%, or
not less than about 85%, or not less than about 90%, or not less
than about 95%.
[0078] The nanovoided polymeric material of the first region 300,
can be made by coating the solvent containing solution described
above onto a substrate. In many cases the substrate can be formed
of any polymeric material useful in a roll to roll process. In some
embodiments the substrate layer is transparent with little to no
haze and high clarity and is formed of polymers such as
polyethylene terephthalate (PET), polycarbonates, acrylics, and
cycloolefin polymers. The substrate may also comprise transparent
substrates such as glass and other transparent inorganic materials.
The substrate may also comprise reflective scattering substrates or
materials such as diffuse white polymeric substrates, semispecular
substrates polymeric substrates such as multilayer optical films
(for example ESR available from 3M), metallic semispecular
reflectors for example brushed aluminum. In some cases the
substrate may comprise a release liner such that the nanovoided
polymeric layer 300 may be transferred to another substrate for
example to an adhesive layer.
[0079] For embodiments in which the first region comprises
nanovoided polymeric material, the additional material defines the
second region. The additional material resides within the nanovoids
of the nanovoided polymeric material and has a refractive index
high enough such that the refractive index of the second region is
greater than that of the first region. Useful additional materials
include any material that can be incorporated within the nanovoided
polymeric material such that the variable index light extraction
layer can function as desired. The additional material has a high
refractive index in the sense that it can increase the refractive
index of the nanovoided polymeric material, i.e., can increase the
first refractive index by at least about 0.03, for example, from
about 0.03 to about 0.5, from about 0.05 to about 0.5, or from
about 0.05 to about 0.25.
[0080] In general, the additional material can have a refractive
index in a range of from about 1.40 to 2.1. The exact range of
refractive indices for the additional material will depend on the
refractive index the nanovoided polymeric material and also the
refractive index of an adjacent layer from which the extraction
layer is extracting light. For the purposes of the invention
described herein, the variable index light extraction layer is
designed to extract light from an adjacent transparent layer. In
order to perform this function the first region of the variable
index light extraction layer must have a refractive index less than
that of the adjacent transparent layer, and the second region of
the variable index light extraction layer has a refractive index
approximately equal to or greater than that of the adjacent
transparent layer from which the light is being extracted.
[0081] In general, the additional material is incorporated into the
nanovoided polymeric material with little or no additional material
on a surface of the nanovoided polymeric material. In some
embodiments, the additional material substantially completely fills
the interconnected nanovoids such that little or no void volume
(less than 5% void volume) remains within the second region. In
some embodiments, the additional material partially fills the
interconnected nanovoids such that some void volume remains. The
second regions comprise a particular amount of void volume
depending upon the refractive index of the additional material and
the desired difference in refractive indices between the first and
second regions. For example, the second region may have a void
volume less than about 20%, less than about 10%, less than about 5%
or less than about 1%.
[0082] Exemplary additional materials include small molecules,
oligomers and polymers. Any of the materials described above for
making the nanovoided polymeric material may be used as the
additional material. Generally, the additional material is
deposited into voids of the nanovoided nanovoided polymeric
material, using methods such as printing which are described below.
In some cases, the additional material is a polymerizable material
that is 100% solids and has a viscosity that under the conditions
of application allows the additional material to penetrate the
nanovoided polymeric material thus forming the second region.
[0083] The particular choice of additional material may depend on
the method by which it is incorporated into the nanovoided
polymeric layer. Various methods are described below. For example,
in some embodiments, the variable index light extraction layer is
made by depositing the additional material on selected areas or
regions of a surface of a layer comprising the nanovoided polymeric
material. The additional material then penetrates the nanovoided
polymeric material such that little or no additional material
remains on a surface of the layer. This embodiment may require an
additional material having a low enough viscosity and molecular
constituents with sizes that are small enough to penetrate into and
through the nanovoids of the nanovoided polymeric material.
[0084] In some embodiments, the variable index light extraction
layer is made by depositing a polymerizable composition on selected
areas or regions of a surface of a layer comprising the nanovoided
polymeric material. The polymerizable composition then penetrates
the nanovoided material such that little or no polymerizable
composition remains on a surface of the layer. The polymerizable
composition can then be polymerized by conventional means to form
the additional material, thus forming the second region having both
the first material and the additional material. In some cases the
additional material penetrates completely through the thickness of
the layer of the nanovoided polymeric material.
[0085] The first and second regions may be disposed relative to
each other, across a transverse plane of the variable index light
extraction layer, in order to manage light in a desired way. For
example, the second region may comprise a plurality of second
regions arranged in a pattern across a transverse plane of the
layer. For another example, the second region may comprise a
plurality of second regions arranged randomly across a transverse
plane of the layer. Either the first or second region may be a
continuous region across a transverse plane of the layer. For a
first or second region that is discontinuous, i.e., is a plurality
of regions, the density can vary in any direction across a
transverse plane of the layer. For example, the density of second
regions can vary in one or two dimensions across a transverse plane
of the layer. Several of these embodiments are described in FIGS.
4a-4d, 5a and 5b.
[0086] The optimal thickness of the variable index light extraction
layer is determined by the function that the layer is designed to
perform. The layer thickness depends on the nature of the
nanovoided polymeric material. The variable index light extraction
layer should be thick enough such that the first region can provide
optical isolation of an adjacent transparent substrate, in which
supercritical light is propagating, from another layer which is
disposed on an opposing side of the variable index light extraction
layer. The thickness of the nanovoided polymeric layer should be
thin enough such that the additional material can be deposited onto
the layer and penetrate substantially into the layer, and is some
cases through the thickness of the layer, thus creating the second
region. In some cases the variable index light extraction layer has
a thickness greater than about 500 nm, or in the range of from
about 500 nm to about 100 um, from about 500 nm to about 8 um, from
about 1 micron to about 5 um, or from about 1 um to about 3 um.
[0087] The variable index light extraction layer supports or
promotes TIR, and so the layer is sufficiently thick so that the
evanescent tail of a light ray that undergoes TIR at a surface of
the variable index light extraction layer does not optically
couple, or optically couples very little, across the thickness of
the layer. In such cases, the thickness of the variable index light
extraction layer is not less than about 0.5 um, not less than about
1 um, not less than about 1.1 um, not less than about 1.2 um, not
less than about 1.3 um, not less than about 1.4 um, not less than
about 1.5 um, not less than about 1.7 um, or not less than about 2
um. A sufficiently thick variable index light extraction layer can
prevent or reduce an undesired optical coupling of the evanescent
tail of an optical mode across the thickness of the layer.
[0088] In some cases, the variable index light extraction layer has
low optical haze measured as a bulk property of the layer. In such
cases, the optical haze of the variable index light extraction
layer is not greater than about 10%, not greater than about 7%, not
greater than about 5%, not greater than about 4%, not greater than
about 3.5%, not greater than about 4%, not greater than about 3%,
not greater than about 2.5%, not greater than about 2%, not greater
than about 1.5%, or not greater than about 1%. In such cases, the
variable index light extraction layer can have a reduced effective
index that is not greater than about 1.40, not greater than about
1.35, not greater than about 1.3, not greater than about 1.2, not
greater than about 1.15, not greater than about 1.1, or not greater
than about 1.05. Optical haze, as used herein, is defined for
normally incident light on the surface of a given layer, as the
ratio of the transmitted light that deviates from the normal
direction by more than 4 degrees to the total transmitted light.
Haze values disclosed herein were measured using a Haze-Gard Plus
haze meter (BYK-Gardiner, Silver Springs, Md.) according to the
procedure described in ASTM D1003.
[0089] In some cases, the variable index light extraction layer has
high optical clarity. Optical clarity, as used herein, is defined
for light normally incident on the layer and refers to the ratio
(T.sub.1-T.sub.2)/(T.sub.1+T.sub.2), where T.sub.1 is the
transmitted light that deviates from the normal direction between
1.6 and 2 degrees, and T.sub.2 is the transmitted light that lies
between zero and 0.7 degrees from the normal direction. Clarity
values disclosed herein were measured using a Haze-Gard Plus haze
meter from BYK-Gardiner. In cases where variable index light
extraction layer has high optical clarity, the clarity is not less
than about 80%, not less than about 85%, not less than about 90%,
or not less than about 95%.
[0090] The variable index light extraction layer can comprise the
first and second regions disposed relative to each other, in some
desired geometric arrangement across a transverse plane of the
layer, so that the layer provides desired optical performance
features. FIG. 4a is a plan view of a variable index light
extraction layer showing an exemplary geometric arrangement of the
first and second regions. Variable index light extraction layer 400
comprises first region 410 that is continuous across the layer as
seen in plan view of the layer, and second regions 420 are discreet
regions enclosed by the rectangles illustrated using dashed
lines.
[0091] As stated above, dashed lines are used throughout this
disclosure to indicate general location of the first and second
regions, however, these dashed lines are not meant to describe any
sort of boundary between the regions. As described herein, the
second regions are formed by depositing additional material on
nanovoided polymeric material, typically by some printing means,
such that the penetration, wicking, etc. of the additional material
into the nanovoided polymeric material is dependent on the
chemistry of the materials used to form the regions as well as
properties such as viscosity, wetting, temperature and so
forth.
[0092] Second regions 420 are shaped as rectangles or stripes of
substantially the same length and width, extending across the width
of layer 400, and disposed from left to right with increasing
frequency. Second regions 420 have a refractive index greater than
that of first region 410 by at least about 0.03. FIG. 4b
illustrates the refractive index profile for variable index light
extraction layer 400 with the x-axis identifying positions d down
the length of the layer at some substantially single position
w.sub.1 as shown in FIG. 4a. The refractive index profile shows the
variation in the refractive index of layer 400 which comprises a
pattern between first and second refractive indices, n.sub.1 and
n.sub.z, respectively. FIGS. 4c and 4d show profiles for selected
optical properties % transmission and % clarity, respectively, and
for both properties, there is substantially little or no variation
down the length of the layer.
[0093] FIG. 5a shows a plan view of another variable index light
extraction layer showing an exemplary geometric arrangement of the
first and second regions. Variable index light extraction layer 500
comprises first region 510 that is continuous across the layer as
seen in plan view of the layer, and second regions 520 are discreet
regions enclosed by the circles illustrated using dashed lines. The
pattern also shows that the density of the second regions 520 can
vary in both the x and y dimensions.
[0094] FIG. 5b shows a plan view of another variable index light
extraction layer showing an exemplary geometric arrangement of the
first and second regions. Variable index light extraction layer 530
comprises first region 540 that is continuous across the layer as
seen in plan view of the layer, and second regions 550 are discreet
regions enclosed by the shapes, in this case hearts, as illustrated
using dashed lines. The pattern shows that the geometric
arrangement of high index regions, do not have to vary in a
gradient fashion, but that they may also be patterned to provide
image-wise extraction of supercritical light from an adjacent
transparent layer.
[0095] The geometric arrangement of the first and second regions of
the variable light extraction layer is designed to extract
supercritical light propagating in an adjacent transparent layer
and deliver that light to another layer on the opposing side of the
variable index light extraction layer in a predetermined pattern,
for example substantially uniform illumination.
[0096] The variable index light extraction layer may be disposed on
a substrate. The substrate may comprise a support used to
manufacture the layer as described in PCT Application No.
US2011/021053 (Wolk et al.). In some embodiments, an optical film
includes the variable index light extraction layer disposed on a
transparent substrate. As used herein, "transparent" means
substantially optically clear and substantially low haze and
non-scattering. Exemplary transparent substrates have requisite
optical properties depending on desired properties of the optical
film. The transparent substrate may comprise a polymeric substrate
such as a polyester, poly(meth)acrylate, polycarbonate and the
like. In some embodiments, the transparent substrate comprises a
lightguide as described below. In some embodiments, the transparent
substrate has some level of haze and can provide some light
scattering such that light can be scattered in a forward direction
toward reflective scattering element layer 650.
[0097] FIG. 6 shows a schematic of exemplary illumination device
600 comprising the variable index light extraction layer in
combination with a reflective scattering element which is
illuminated by the device. Illumination device 600 comprises
lightguide 610 disposed adjacent to variable light extraction layer
630. The lightguide is optically coupled to the top surface 625 of
the variable index light extraction layer 630 (denoted by the
dashed line between the two surfaces). Adjacent opposing surface
635 of the variable index light extraction layer is reflective
scattering element 650 shown in the form of a layer for simplicity.
The reflective scattering element is optically coupled to the
bottom surface of the variable index light extraction layer 635
(denoted by the dashed line between the two surfaces). Light source
601 is optically coupled to lightguide 610 such that light emitted
by the light source can enter the lightguide. In some embodiments,
there are no air gaps between the bottom surface 615 of lightguide
610 and the top surface 625 of the variable index light extraction
layer 630 and there are no air gaps between the bottom surface 635
of the variable index light extraction layer 630 and the reflective
scattering element 650 in order for optical coupling to occur.
[0098] In some embodiments, lightguide 610 has a refractive index
between those of the first and second regions of the variable index
light extraction layer.
[0099] According to this embodiment, a method of providing light
comprises: providing a light source, lightguide and an optical film
comprising the variable index light extraction layer; and optically
coupling the light source to the lightguide and the lightguide to
the variable index light extraction layer, such that light emitted
by the light source is transported within the lightguide by total
internal reflection and selectively extracted from the lightguide
by the variable index light extraction layer.
[0100] In some embodiments, variable light extraction layer 630 can
be disposed directly on surface 645 of reflective scattering
element 650. Lightguide 610 can be directly attached to surface 625
of the variable light extraction layer by several methods. As
described below, lightguide 610 can comprise a thermoplastic resin
material, for example, an acrylic, and in these cases, the
lightguide can be formed by either casting molten resin onto
surface 625 of the variable index extraction layer, or it can be
attached to the variable index extraction layer by an insert
injection molding process. In some cases lightguide 610 comprises
an elastomeric material such that it can be heat laminated to
surface 625 of the variable index extraction layer. In some cases
lightguide 610 comprises a pressure sensitive adhesive (PSA) such
that it can be directly laminated to surface 625 of the variable
index extraction layer. In cases where lightguide 610 is not an
adhesive, surface 625 of the variable index light extraction layer
can be adhered to surface 615 of the lightguide using an optically
clear adhesive. Optically clear adhesives are described below.
[0101] Lightguide 610 may include any suitable material or
materials. For example, the lightguide may include glass,
acrylates, including polymethylmethacrylate, polycarbonate,
polystryrene, styrene methacrylate copolymers and blends,
cycloolefin polymers (e.g. ZEONEX and ZEONOR available from ZEON
Chemicals L.P., Louisville, Ky.), fluoropolymers, polyesters
including polyethylene terephthalate (PET), polyethylene
naphthalate (PEN), and copolymers containing PET or PEN or both;
polyurethanes, epoxies, polyolefins including polyethylene,
polypropylene, polynorbornene, polyolefins in isotactic, atactic,
and syndiotactic strereoisomers, and polyolefinss produced by
metallocene polymerization. In some cases, the lightguide can be
elastomeric such as elastomeric polyurethanes materials and
silicone based polymers, including but not limited to,
polydialkylsiloxanes, silicone polyureas, and silicone
polyoxamides.
[0102] In some embodiments, the lightguide is a viscoelastic
lightguide as described in WO 2010/005655 A2 (Sherman et al.). In
general, the viscoelastic lightguide comprises one or more
viscoelastic materials which exhibit both elastic and viscous
behavior when undergoing deformation. Elastic characteristics refer
to the ability of a material to return to its original shape after
a transient load is removed. One measure of elasticity for a
material is referred to as the tensile set value which is a
function of the elongation remaining after the material has been
stretched and subsequently allowed to recover (destretch) under the
same conditions by which it was stretched. If a material has a
tensile set value of 0%, then it has returned to its original
length upon relaxation, whereas if the tensile set value is 100%,
then the material is twice its original length upon relaxation.
Tensile set values may be measured using ASTM D412. Useful
viscoelastic materials may have tensile set values of greater than
about 10%, greater than about 30%, or greater than about 50%; or
from about 5 to about 70%, from about 10 to about 70%, from about
30 to about 70%, or from about 10 to about 60%.
[0103] Viscous materials that are Newtonian liquids have viscous
characteristics that obey Newton's law which states that stress
increases linearly with shear gradient. A liquid does not recover
its shape as the shear gradient is removed. Viscous characteristics
of useful viscoelastic materials include flowability of the
material under reasonable temperatures such that the material does
not decompose.
[0104] The viscoelastic lightguide may have properties that
facilitate sufficient contact or wetting with at least a portion of
a material designed to extract light from the lightguide, e.g., an
optical article, such that the viscoelastic lightguide and the
optical article are optically coupled. Light can then be extracted
from the viscoelastic lightguide. The viscoelastic lightguide is
generally soft, compliant and flexible. Thus, the viscoelastic
lightguide may have an elastic modulus (or storage modulus G') such
that sufficient contact can be obtained, and a viscous modulus (or
loss modulus G'') such that the layer doesn't flow undesirably, and
a damping coefficient (G''/G', tan D) for the relative degree of
damping of the layer. Useful viscoelastic materials may have a
storage modulus, G', of less than about 300,000 Pa, measured at 10
rad/sec and a temperature of from about 20 to about 22.degree. C.
Viscoelastic properties of materials can be measured using Dynamic
Mechanical Analysis according to, for example, ASTM D4065, D4440,
and D5279.
[0105] In some embodiments, the viscoelastic lightguide comprises a
PSA layer as described in the Dalquist criterion line (as described
in Handbook of Pressure Sensitive Adhesive Technology, Second Ed.,
D. Satas, ed., Van Nostrand Reinhold, New York, 1989.)
[0106] The viscoelastic lightguide may have a particular peel force
or at least exhibit a peel force within a particular range. For
example, the viscoelastic lightguide may have a 90.degree. peel
force of from about 50 to about 3000 g/in, from about 300 to about
3000 g/in, or from about 500 to about 3000 g/in. Peel force may be
measured using a peel tester from IMASS.
[0107] In some embodiments, the viscoelastic lightguide comprises
an optically clear lightguide having high light transmittance of
from about 80 to about 100%, from about 90 to about 100%, from
about 95 to about 100%, or from about 98 to about 100% over at
least a portion of the visible light spectrum (about 400 to about
700 nm). In some embodiments, the viscoelastic lightguide has a
haze value of less than about 5%, less than about 3%, or less than
about 1%. In some embodiments, the viscoelastic lightguide has a
haze value of from about 0.01 to less than about 5%, from about
0.01 to less than about 3%, or from about 0.01 to less than about
1%. Haze values in transmission can be determined using a haze
meter according to ASTM D1003.
[0108] In some embodiments, the viscoelastic lightguide comprises
an optically clear lightguide having high light transmittance and a
low haze value. High light transmittance may be from about 90 to
about 100%, from about 95 to about 100%, or from about 99 to about
100% over at least a portion of the visible light spectrum (about
400 to about 700 nm), and haze values may be from about 0.01 to
less than about 5%, from about 0.01 to less than about 3%, or from
about 0.01 to less than about 1%. The viscoelastic lightguide may
also have a light transmittance of from about 50 to about 100%.
[0109] The viscoelastic lightguide may have a refractive index in
the range of from about 1.3 to about 2.6, 1.4 to about 1.7, or from
about 1.5 to about 1.7. The particular refractive index or range of
refractive indices selected for the viscoelastic lightguide may
depend on the overall design of the illumination device and the
particular application in which the device may be used.
[0110] The viscoelastic lightguide material may comprise
nanoparticles that can modify the refractive index of the
viscoelastic lightguide material or to affect the mechanical
properties of the viscoelastic lightguide material. Suitable
nanoparticles have sizes such that the particles produce the
desired effect without introducing significant amount of scattering
into lightguide material.
[0111] The viscoelastic lightguide generally comprises at least one
polymer. The viscoelastic lightguide may comprise at least one PSA.
PSAs are useful for adhering together adherends and exhibit
properties such as: (1) aggressive and permanent tack, (2)
adherence with no more than finger pressure, (3) sufficient ability
to hold onto an adherend, and (4) sufficient cohesive strength to
be cleanly removable from the adherend. Materials that have been
found to function well as pressure sensitive adhesives are polymers
designed and formulated to exhibit the requisite viscoelastic
properties resulting in a desired balance of tack, peel adhesion,
and shear holding power. Obtaining the proper balance of properties
is not a simple process. A quantitative description of PSAs can be
found in the Dahlquist reference cited above.
[0112] Useful PSAs are described in detailed in the Sherman et al.
references cited above. Useful PSAs include poly(meth)acrylate PSAs
derived from: monomer A comprising at least one monoethylenically
unsaturated alkyl (meth)acrylate monomer, wherein a homopolymer of
the monomer has a Tg of no greater than about 0.degree. C.; and
monomer B comprising at least one monoethylenically unsaturated
free-radically copolymerizable reinforcing monomer, wherein a
homopolymer of the monomer has a Tg higher than that of monomer A,
for example, at least about 10.degree. C. As used herein,
(meth)acrylic refers to both acrylic and methacrylic species and
likewise for (meth)acrylate.
[0113] In some embodiments, the viscoelastic lightguide comprises
natural rubber-based and synthetic rubber-based PSAs, thermoplastic
elastomers, tackified thermoplastic-epoxy derivatives, polyurethane
derivatives, polyurethane acrylate derivatives, silicone PSAs such
as polydiorganosiloxanes, polydiorganosiloxane polyoxamides and
silicone urea block copolymers.
[0114] In some embodiments, the viscoelastic lightguide comprises a
clear acrylic PSA, for example, those available as transfer tapes
such as VHB.TM. Acrylic Tape 4910F or 4918 from 3M Company and
3M.TM. Optically Clear Laminating Adhesives (8140 and 8180
series).
[0115] In some embodiments, the viscoelastic lightguide comprises a
block copolymer dispersed in an adhesive matrix to form a Lewis
acid-base pair. In some embodiments, the viscoelastic lightguide
comprises a stretch releasable PSA that can be removed from a
substrate when stretched at or nearly at a zero degree angle.
[0116] In some embodiments the lightguide 610 may comprise an
additional coating or a top film having a coating on the outer
surface 605. The extra coating or film may be designed to any
desirable property to the surface of the lightguide. Examples of
coatings include, for example, hardcoats, anti-reflective coatings,
anti-soiling coatings, matte coatings, anti-fog coatings,
anti-scratch coatings, privacy coatings or a combination thereof.
Coatings such as hardcoats, anti-fog coatings, and anti-scratch
coatings that provide enhanced durability, are desirable in
applications such as, for example, touch screen sensors, display
screens, graphics applications and the like. Examples of privacy
coatings include, for example, blurry or hazy coatings to give
obscured viewing or louvered films to limit the viewing angle. In
some cases where the coating is provided as a film it is desirable
to adhere the film to the surface 605 of the lightguide 610 with an
adhesive having a refractive index that is less than the refractive
index of the lightguide. Alternatively, a nanovoided layer may be
disposed between the top surface 605 of the light guide 610 and the
bottom of the additional top film.
[0117] As described above, lightguide 610 can be adhered to
variable index light extraction layer 630 using an optically clear
adhesive (OCA). In some embodiments, the OCA comprises a PSA having
high light transmittance of from about 80 to about 100%, from about
90 to about 100%, from about 95 to about 100%, or from about 98 to
about 100% over at least a portion of the visible light spectrum
(about 400 to about 700 nm), and/or a haze value of from about 0.01
to less than about 5%, from about 0.01 to less than about 3%, or
from about 0.01 to less than about 1%.
[0118] In some embodiments, useful PSAs include those described in
the Dalquist criterion line (as described in Handbook of Pressure
Sensitive Adhesive Technology, Second Ed., D. Satas, ed., Van
Nostrand Reinhold, New York, 1989.) The PSA may have a particular
peel force or at least exhibit a peel force within a particular
range. For example, the PSA may have a 90.degree. peel force of
from about 10 to about 3000 g/in, from about 300 to about 3000
g/in, or from about 500 to about 3000 g/in. Peel force may be
measured using a peel tester from IMASS.
[0119] The OCA may have a refractive index in the range of from
about 1.3 to about 2.6, 1.4 to about 1.7, or from about 1.5 to
about 1.7. The particular refractive index or range of refractive
indices selected for the OCA may depend on the overall design of an
optical film comprising the lightguide and the variable index light
extraction layer. In general the OCA should have a refractive index
approximately equal to or greater than that of the lightguide, and
between that of the first and second regions of variable index
light extraction layer 630.
[0120] The PSA used as the OCA may comprise any of the materials
described above for the viscoelastic lightguide. Additional
exemplary OCAs that are PSAs include tackified thermoplastic
epoxies as described in U.S. Pat. No. 7,005,394 (Ylitalo et al.),
polyurethanes as described in U.S. Pat. No. 3,718,712 (Tushaus),
polyurethane acrylates as described in US 2006/0216523 (Shusuke).
In some embodiments, the adhesive comprises a clear acrylic PSA,
for example, those available as transfer tapes such as VHB.TM.
Acrylic Tape 4910F and 4918 from 3M Company, 3M.TM. Optically Clear
Laminating Adhesives (8140 and 8180 series) and 3M.TM. Optically
Clear Laminating Adhesives 8171 CL and 8172 CL) described in WO
2004/0202879. Useful OCAs are also described in US 2011/0039099
(Sherman et al.). In some embodiments, the OCA may comprise a PSA
having a microstructured adhesive surface to allow for air bleed
upon application to the surface of the lightguide as described, for
example, in US 2007/0212535 (Sherman et al.).
[0121] The adhesive may comprise a stretch releasable PSA. Stretch
releasable PSAs are PSAs that can be removed from a substrate if
they are stretched at or nearly at a zero degree angle. In some
embodiments, the adhesive or a stretch release PSA used as in the
optical tape has a shear storage modulus of less than about 10 MPa
when measured at 1 rad/sec and -17.degree. C., or from about 0.03
to about 10 MPa when measured at 1 rad/sec and -17.degree. C.
Stretch releasable PSAs may be used if disassembling, reworking, or
recycling is desired.
[0122] In some embodiments, the stretch releasable PSA may comprise
a silicone-based PSA as described in U.S. Pat. No. 6,569,521 B1
(Sheridan et al.) or U.S. Provisional Application Nos. 61/020,423
(63934US002, Sherman et al.) and 61/036,501 (64151US002, Determan
et al.). Such silicone-based PSAs include compositions of an MQ
tackifying resin and a silicone polymer. For example, the stretch
releasable PSA may comprise an MQ tackifying resin and an
elastomeric silicone polymer selected from the group consisting of
urea-based silicone copolymers, oxamide-based silicone copolymers,
amide-based silicone copolymers, urethane-based silicone
copolymers, and mixtures thereof.
[0123] In some embodiments, the stretch releasable PSA may comprise
an acrylate-based PSA as described in WO 2010/078346 (Yamanaka et
al.) and WO 2010/077541 (Tran et al.) Such acrylate-based PSAs
include compositions of an acrylate, an inorganic particle and a
crosslinker. These PSAs can be a single or multilayer.
[0124] In some embodiments the adhesive layer may comprise the
cured reaction product of a multifunctional ethylenically
unsaturated siloxane polymer and one or more vinyl monomers as
described in U.S. Pat. No. 7,862,898 (Sherman et al.) and U.S. Pat.
No. 7,892,649 (Sherman et al.).
[0125] In some embodiments the use of self-wetting adhesives as
described in WO 2010/132176 (Sherman et al.) and WO 2009/085662
(Sherman et al.) is beneficial in placement of the illumination
device 600 onto a reflective scattering element.
[0126] An exemplary PSA comprises a polymer derived from an
oligomer and/or monomer comprising polyether segments, wherein from
35 to 85% by weight of the polymer comprises the segments. These
adhesives are described in US 2007/0082969 A1 (Malik et al.).
Another exemplary PSA comprises the reaction product of a free
radically polymerizable urethane-based or urea-based oligomer and a
free radically polymerizable segmented siloxane-based copolymer;
these adhesives are described in U.S. Provisional Application
61/410,510 (Tapio et al.).
[0127] The PSA can optionally include one or more additives such as
nanoparticles, plasticizers, chain transfer agents, initiators,
antioxidants, stabilizers, viscosity modifying agents, and
antistats.
[0128] In some embodiments, a seal layer is disposed on the
variable index light extraction layer in order to minimize
penetration of contaminants into the latter. For example, a seal
layer may be disposed on the variable index light extraction layer
such that it is in between the variable index light extraction
layer and an adhesive layer. For another example, a seal layer may
be disposed on the variable index light extraction layer such that
it is in between the variable index light extraction layer and the
lightguide, and the seal layer has a refractive index that is
approximately equal to or greater than that of the lightguide.
[0129] Suitable seal layers include pressure sensitive adhesive
polymers and copolymers which can be acrylic or acrylate based,
styrene butadiene, or styrene isoprene type copolymer thermoplastic
resins and similar polymers so long as they do not contain a
significant fraction of low molecular weight species capable of
penetration into the nanovoided first region. Other polymer seal
layers can be heat activated adhesive polymers including acrylics,
acrylic-vinyl acetate, copolymers, block copolymers, EVA
copolymers, polyamides, polyesters, polyethylene polymers and
copolymers, polyisobutylene, polypropylene polymers and copolymers,
polyurethane polymers and copolymers and other polymers including
Surlyn plastic, vinyl acetate, and polyvinylidene fluoride
polymers, their alloys, copolymers and derivatives with acid salt
groups. These materials can be laminated with a direct film
lamination, applied by melt coating or coated from an aqueous or
solvent borne emulsion or dispersion of the polymer by any suitable
coating method. Two example of suitable polymeric dispersions
useful as seal layers are NEOCRYL A-614 and NEOPAC R-9699
(available from DSM (6401 JH Heerlen, Netherlands).
[0130] The light source is optically coupled to the lightguide such
that at least some of the light from the light source can enter the
lightguide. For example, a light source may be optically coupled to
the lightguide such that greater than 1, greater than 10, greater
than 20, greater than 30, greater than 40, greater than 50, greater
than 90%, or about 100% of light emitted by the light source enters
the lightguide. For another example, a light source may be
optically coupled to the lightguide such that from about 1 to about
10%, from about 1 to about 20%, from about 1 to about 30%, from
about 1 to about 40%, from about 1 to about 50%, from about 1 to
about 100%, from about 1 to about 100%, from about 50 to about
100%, or from about 1 to about 100% of light emitted by the light
source enters the lightguide. The light source may emit light
having a random or a particular angular distribution.
[0131] The light source may comprise any suitable light source.
Exemplary light sources include linear light sources such as cold
cathode fluorescent lamps and point light sources such as light
emitting diode (LEDs). Exemplary light sources also include organic
light-emitting devices (OLEDs), incandescent bulbs, fluorescent
bulbs, halogen lamps, UV bulbs, infrared sources, near-infrared
sources, lasers, or chemical light sources. In general, the light
emitted by the light source may be visible or invisible. At least
one light source may be used. For example, from 1 to about 10,000
light sources may be used. The light source may comprise a row of
LEDs positioned at or near an edge of the lightguide. The light
source may comprise LEDs arranged on a circuit such that light
emitted from the LEDs lights up continuously or uniformly the
lightguide throughout a desired area. The light source may comprise
LEDs that emit light of different colors such that the colors can
mix within the lightguide.
[0132] "LED" refers to a diode that emits light, whether visible,
ultraviolet, or infrared. It includes incoherent encased or
encapsulated semiconductor devices marketed as "LEDs," whether of
the conventional or super radiant variety. If the LED emits
non-visible light such as ultraviolet light, and in some cases
where it emits visible light, it is packaged to include a phosphor
(or it may illuminate a remotely disposed phosphor) to convert
short wavelength light to longer wavelength visible light, in some
cases yielding a device that emits white light.
[0133] An "LED die" is an LED in its most basic form, i.e., in the
form of an individual component or chip made by semiconductor
processing procedures. The component or chip can include electrical
contacts suitable for application of power to energize the device.
The individual layers and other functional elements of the
component or chip are typically formed on the wafer scale, and the
finished wafer can then be diced into individual piece parts to
yield a multiplicity of LED dies.
[0134] Multicolored light sources, whether or not used to create
white light, can take many forms in a light assembly, with
different effects on color and brightness uniformity of the light
guide output area or surface. In one approach, multiple LED dies
(e.g., a red, a green, and a blue light emitting die) are all
mounted in close proximity to each other on a lead frame or other
substrate, and then encased together in a single encapsulant
material to form a single package, which may also include a single
lens component. Such a source can be controlled to emit any one of
the individual colors, or all colors simultaneously. In another
approach, individually packaged LEDs, with only one LED die and one
emitted color per package, can be clustered together for a given
recycling cavity, the cluster containing a combination of packaged
LEDs emitting different colors such as blue/yellow, red/green/blue,
red/green/blue/white, or red/green/blue/cyan/yellow. Amber LEDs can
also be used. In still another approach, such individually packaged
multicolored LEDs can be positioned in one or more lines, arrays,
or other patterns.
[0135] If desired, other visible light emitters such as linear cold
cathode fluorescent lamps (CCFLs) or hot cathode fluorescent lamps
(HCFLs) can be used instead of or in addition to discrete LED
sources as illumination sources for the disclosed backlights. In
addition, hybrid systems such as, for example, (CCFL/LED),
including cool white and warm white, CCFL/HCFL, such as those that
emit different spectra, may be used. The combinations of light
emitters may vary widely, and include LEDs and CCFLs, and
pluralities such as, for example, multiple CCFLs, multiple CCFLs of
different colors, and LEDs and CCFLs. The light sources may also
include lasers, laser diodes, plasma light sources, or organic
light emitting diodes, either alone or in combination with other
types of light sources, e.g., LEDs.
[0136] For example, in some applications it may be desirable to
replace the row of discrete light sources with a different light
source such as a long cylindrical CCFL, or with a linear surface
emitting light guide emitting light along its length and coupled to
a remote active component (such as an LED die or halogen bulb), and
to do likewise with other rows of sources. Examples of such linear
surface emitting light guides are disclosed in U.S. Pat. No.
5,845,038 (Lundin et al.) and U.S. Pat. No. 6,367,941 (Lea et al.).
Fiber-coupled laser diode and other semiconductor emitters are also
known, and in those cases the output end of the fiber optic
waveguide can be considered to be a light source with respect to
its placement in the disclosed recycling cavities or otherwise
behind the output area of the backlight. The same is also true of
other passive optical components having small emitting areas such
as lenses, deflectors, narrow light guides, and the like that give
off light received from an active component such as a bulb or LED
die. One example of such a passive component is a molded
encapsulant or lens of a side-emitting packaged LED. Any suitable
side-emitting LED can be used for one or more light sources, e.g.,
Luxeon.TM. LEDs (available from Lumileds, San Jose, Calif.), or the
LEDs described, e.g., in U.S. Pat. No. 7,525,126 (Leatherdale et
al.) and US 2007/0257270 (Lu et al.).
[0137] Light which enters the lightguide can be collimated such
that it is incident on an interface between the lightguide and
another medium at angles less than 50 degrees, less that 40
degrees, less than 30 degree, less than 20 degree or less than 10
degrees, where the incident angles are measured in respect to the
surface normal of the lightguide injection interface. There are
many ways to produce collimated light including but not limited to:
1. provide an LED light source or sources with highly collimating
lenses; 2. provide an LED light source or sources that are disposed
inside of a reflective wedge, where the wedge has an interior angle
of less than 20 degrees, less than 15 degrees or less than 10
degrees; 3. provide an LED light source or sources where the LED
light sources are disposed at approximately the focal point of a
compound parabolic concentrator designed to collimate the light to
desired injection angles; 4. provide an LED light source or sources
where emission is perpendicular to the plane of the lightguide and
the light is incident on a half parabolic mirror which is designed
to collimate the light injected into the lightguide; and 5. provide
an LED light source or sources disposed to emit light at the
surface of the lightguide, which has a surface relief structure to
allow light to enter the lightguide only at supercritical
angles.
[0138] A method of preparing a variable index light extraction
layer comprises: providing a nanovoided polymeric layer having a
first refractive index; and printing a additional material on the
nanovoided polymeric layer such that the additional material
substantially penetrates the nanovoided polymeric layer, thereby
forming a variable index light extraction layer comprising a first
region comprising a portion of the nanovoided polymeric layer and a
second region comprising another portion of the nanovoided
polymeric layer and the additional material; wherein the first and
second regions are disposed such that for light being transported
at a supercritical angle in an adjacent layer, the variable index
light extraction layer selectively extracts the light in a
predetermined way based on the geometric arrangement of the first
and second regions.
[0139] Printing may comprise non-impact or impact printing, and
digital or analogue printing. For example, the additional material
(also referred to as the additional material or another material)
can be printed on the nanovoided polymeric layer using flexographic
printing wherein a gravure roll having pits filled with the
additional material transfers the material to a flexographic roll
having a stamp with a desired arrangement of shapes. A layer of the
nanovoided polymeric material is passed over and in contact with
the stamp which effectively stamps or prints the web with the
additional material thus transferring the additional material from
the pattern of the flexographic roll to the surface of the
nanovoided layer. The additional material then penetrates into the
nanovoided layer, in some cases penetrating the entire thickness of
the nanovoided layer. In most cases, the material is hardened by
curing such as curing with UV radiation. This process can be
carried out in a batch wise printing process or in continuous roll
to roll process where a continuous web comprising the nanovoided
polymeric layer is passed over the flexographic roll, which results
in printing a repeating pattern or continuous pattern of the
additional material onto the nanovoided layer.
[0140] Printing may also comprise other processes including but not
limited to rotogravure printing, screen printing, inkjet printing
(aqueous, solvent or solid-based inks may be used), letterpress
printing, offset printing, heat transfer methods using heat
sensitive substrates, thermal dye transfer and dye sublimation
printing, dot-matrix printing, and printing with daisy wheels.
[0141] In general, reflective scattering element 650 can include a
wide variety of materials, assemblies and/or devices. In general,
reflective scattering element 650 is designed to take light
delivered from the variable index light extraction layer 630 and
reflect it back through the extraction layer and through outer
surface 605 of lightguide 610. The reflective scattering element
650 may be chosen such that the desired light distribution is
emitted through outer surface 605 of the lightguide 610. In some
cases reflective scattering element 650 is chosen such that the
light incident on reflective scattering element 650 is transformed
into a substantially lambertian area light source.
[0142] In general, an element is considered a reflective scattering
element if exhibits diffuse or semispecular reflection. Diffuse
reflection is the reflection of light from a surface such that an
incident ray is reflected at many angles rather than at just one
angle as in the case of specular reflection. An illuminated ideal
diffuse reflecting surface will have equal luminance from all
directions in the hemisphere surrounding the surface (Lambertian
reflectance). Semi-specular is the reflection of light from a
surface such that an incident ray is reflected at multiple angles
rather than at just one angle as in the case of a specular
reflector. In many cases a semi-specular reflector has
predominantly forward scattering where the reflected light is
spread around the specular reflected angle with at least greater
than 5% of the reflected light being outside of a 2 degree come
centered around the specular angle. In some cases greater than
about 50% of light incident from any angle is reflected outside of
a 2 degree cone centered around the incident angle.
[0143] Suitable materials for reflective scattering element 650
include diffuse reflective and semispecular reflective materials
and surfaces. Reflecting scattering elements as defined herein have
either diffuse reflection or semispecular reflection. For diffuse
reflective materials, a single incident light ray having an angle
of incidence is reflected at many angles rather than at just one
angle as in the case of specular reflection. An illuminated ideal
diffuse reflecting surface will have equal luminance from all
directions in the hemisphere surrounding the surface (Lambertian
reflectance). Generally, a diffuse reflective material, reflects
light such that rays are scattered in both forward and backward
directions (backward scattering means that light is directed back
toward the direct from which it came). A semispecular reflective
material is a material that provides diffuse reflection, but for a
single incident ray of light, the reflected rays of light are
reflected within a narrow range of angles. Generally, the light
reflect from a semi-specular reflective material is forward
directed and a minority of the light is reflected backward to the
direction from which it was incident. In some cases for the
invention described herein, reflective scattering element 650
provides diffuse reflection for the light delivered from the
lightguide such that greater than 10% of the reflected light is
outside of the range of angles defined by the range of angles of
the incident light.
[0144] Suitable reflective scattering elements include any
scattering material, for example, plaster, white paper, fibrous
materials like non-woven fiber mats and cloth, inorganic filled
white reflective polymers (inorganic particle filled polymers such
as polyesters, polyolefins, and the like), ceramic materials,
crystalline surfaces (for example marble, natural quartz or stone),
and voided polymer materials (for example those made using phase
separation techniques such as solvent induced phases separation and
thermal induced phase separation). Any voided polymeric materials
may be suitable as a reflective scattering element. In some
embodiments, the reflective scattering element comprises a graphic
such as a sign, marking or picture. Examples of semi-specular
reflective scattering materials include rough reflective metal
surface, structured specularly reflective surfaces, specularly
reflective surfaces having diffuse coatings over the specularly
reflective surface (for example, an enhanced specular reflector
such as Vikuiti.TM. ESR from 3M Co. which comprises a multilayer
optical film having a diffuse coating on a surface thereof). Some
examples include brushed aluminum and chrome, metals surfaces that
have been modified by embossing, "peening", physical or chemical
etching, or any other method that imparts a surface roughness.
Alternatively, a diffusive coating could be applied on, or placed
as a free-standing element over a specular reflector. A film having
a surface structure or roughness could be placed over or laminated
to a specular material. The reflective scattering element can take
the form of inks, paint, or coatings. Printed graphics made by such
methods as digital printing, silk screen, etc. are reflective
scattering elements. A painted wall is a reflective scattering
element. In some cases the reflective scattering element comprises
a reflective display device.
[0145] As mentioned above, lightguide 610 and reflective scattering
element 650 are optically coupled with the top and bottom surfaces,
625 and 635 respectively, of the variable index light extraction
layer. This optical coupling in many cases means that there are no
air gaps between variable index light extraction layer 630,
lightguide 610 and reflective scattering element 650.
[0146] FIG. 7 shows a schematic of an exemplary illumination
assembly comprising the variable light extraction layer in
combination with a reflective scattering element. In this
embodiment, variable index light extraction layer 730 is made on
transparent substrate 740 which is incorporated into the
illumination assembly. Surface 725 of variable index light
extraction layer 730 is optically coupled to lightguide 710, and
bottom side 742 of transparent substrate 740 is optically coupled
to reflective scattering element 750. Suitable transparent
substrates are described above.
[0147] In many cases optical coupling between variable index light
extraction layer 730 and lightguide 710 and reflective scattering
element 750 means that there are no air gaps in between the
surfaces of the layers (i.e. there are no air gaps between surfaces
715 and 725 and no air gaps between surfaces 742 and 745). Surface
742 of transparent substrate 740 can be adhered to surface 745 of
reflective scattering element 750 using any means for example by
using an optically clear pressure sensitive adhesive. Transparent
substrate 740 may have some level of haze and can provide some
light scattering, as long as the scattered light is predominantly
in the forward direction toward reflective scattering element
750.
[0148] FIGS. 8, 9, 10a-10d and 11 show schematic cross-sectional
views of exemplary illumination assemblies comprising the variable
index light extraction layer optically coupled to a lightguide and
a reflective scattering element. FIG. 8 shows illumination assembly
800 where variable index light extraction layer 830 is formed
directly on the surface of reflective scattering element 850.
Lightguide 810 is adhered directly to variable light extraction
layer 830 by means of optically clear adhesive 840 which may be a
PSA. Adhesive layer 840 preferentially has low haze, high optical
clarity and high transmission.
[0149] FIG. 9 shows illumination assembly 900 where variable index
light extraction layer 930 is formed on the surface of lightguide
910. Reflective scattering element 950 is attached to variable
index light extraction layer 930 by means of optically clear
adhesive 940 which may be a PSA. Adhesive layer 940 can have low
haze, high optical clarity and high transmission. Alternatively,
adhesive layer 940 may have some level of haze and can provide some
light scattering, as long as the scattered light is predominantly
in the forward direction toward reflective scattering element layer
950.
[0150] FIG. 10a shows illumination assembly 1000 where variable
index light extraction layer 1030 is disposed on transparent
substrate 1040. Variable index light extraction layer 1030 is
adhered to lightguide 1010 by adhesive layer 1070. Adhesive layer
1070 preferentially has low haze, high optical clarity and high
transmission for the wavelength or wavelengths of light propagating
in lightguide 1010. Transparent substrate 1040 on which the
variable index extraction layer is disposed is adhered to
reflective scattering element layer 1050 by adhesive layer 1060.
Adhesive layer 1060 can have low haze, high optical clarity and
high transmission. Alternatively, adhesive layer 1060 may have some
level of haze and can provide some light scattering, as long as the
scattered light is predominantly in the forward direction toward
reflective scattering element layer 1050.
[0151] FIG. 10b shows illumination assembly 1080 where the
orientation of variable index light extraction layer 1030 disposed
on transparent substrate 1040 has been flipped as compared to
illumination assembly 1000 shown in FIG. 10a. Variable index light
extraction layer 1030 can be adhered to reflective scattering
element layer 1050 by adhesive layer 1060 which can have low haze,
high optical clarity and high transmission, or it may have some
level of haze and can provide some light scattering, as long as the
scattered light is predominantly in the forward direction toward
reflective scattering element layer 1050. Transparent substrate
1040 on which the variable index light extraction layer is disposed
is bonded to lightguide 1010 by adhesive layer 1070. Adhesive layer
1070 preferentially has low haze, high optical clarity and high
transmission for the wavelength or wavelengths of light propagating
in lightguide 1010.
[0152] FIG. 10c shows illumination assembly 1090 which is similar
to illumination assembly 1000 shown in FIG. 10a, except that
assembly 1090 comprises seal layer 1095 disposed between variable
index extraction layer 1030 and adhesive layer 1070. FIG. 10d shows
illumination assembly 1096 which is similar to illumination
assembly 1080 shown in FIG. 10b, except that assembly 1096
comprises seal layer 1095 disposed between variable index light
extraction layer 1030 and adhesive layer 1060. Seal layers can be
used to minimize contamination of the variable index light
extraction layer as described above. Suitable materials which may
be used as seal layers are described above.
[0153] In general, for the illumination assemblies shown in FIGS.
10a-10d, adhesive layer 1070 adjacent lightguide 1010 should have a
refractive index that is approximately equal to or greater than the
refractive index of the lightguide. In FIG. 10c, seal layer 1095
should also have a refractive index that is approximately equal to
or greater than the refractive index of the lightguide.
[0154] In general, any layer disposed between the variable index
extraction layer and the lightguide should have a refractive index
that is approximately equal to or greater than the refractive index
of the lightguide. Also in general, the second region of the
variable index light extraction layer should have a refractive
index approximately equal to or greater than the refractive index
of the lightguide, and the first region should have a refractive
index less than that of the lightguide.
[0155] FIG. 11 shows illumination assembly 1100 comprising
lightguide 1110 optically coupled to variable index light
extraction layer 1130, and additional layer 1190 is disposed
between the variable index light extraction layer and reflective
scattering element 1150 such that the variable index light
extraction layer and the reflective scattering element are
optically coupled. The additional layer may comprise materials such
as UV absorbers, UV stabilizers, dyes, down converting materials
such as fluorophores, nanophosphors, quantum dots, or optical
brighteners.
[0156] In general, any layer disposed between the variable index
light extraction layer and the reflective scattering element can
have low haze, high optical clarity and high transmission, or it
may have some level of haze and can provide some light scattering,
as long as the scattered light is predominantly in the forward
direction toward the reflective scattering element. In general, any
layer disposed between the variable index light extraction layer
and the reflective scattering element can include the materials
described above for the additional layer. In general, any layer
between the variable index light extraction layer and the
reflective scattering element may comprise additional materials
such as UV absorbers, UV stabilizers, dyes, down converting
materials such as fluorophores, nanophosphors, quantum dots, or
optical brighteners. The reflective scattering element may also
comprise additional materials such as UV absorbers, UV stabilizers,
dyes, down converting materials such as fluorophores,
nanophosphors, quantum dots, or optical brighteners.
[0157] FIG. 12 shows a schematic cross-sectional view of an
exemplary optical film comprising the variable index light
extraction layer. Optical film 1200 comprises variable index light
extraction layer 1230 disposed on transparent substrate 1240. First
optically clear adhesive layer 1270 is disposed on variable index
light extraction layer 1230 opposite the transparent substrate, and
first release liner 1275 is disposed on layer 1270 opposite layer
1230. Second optically clear adhesive layer 1260 is disposed on
transparent substrate 1240 opposite variable index light extraction
layer 1230, and second release liner 1265 is disposed on layer 1260
opposite transparent substrate 1240. This optical film 1200 can be
used in conjunction with a light guide and a reflective scattering
element layer to make illumination devices for applications in
general illumination (for example task lighting, room lighting,
under cabinet lighting, and automotive interior lighting) or for
backlighting applications (for example backlighting of liquid
crystal displays suitable for mobile handheld, computer monitor and
notebook, and TV and digital signage applications, backlighting of
any other transparent display types that are transmissive and
graphics made by any means, for example graphics made by printing
methods), or can be used as a front light with reflective display
devices and graphics to make front illuminated reflective display
devices or graphics.
[0158] Release liners typically have a low adhesion surface for
contact with an adhesive layer. The first and/or second release
liners may comprise paper such as Kraft paper, or polymeric films
such as poly(vinyl chloride), polyester, polyolefin, cellulose
acetate, ethylene vinyl acetate, polyurethane, and the like. The
release liner may be coated with a layer of a release agent such as
a silicone-containing material or a fluorocarbon-containing
material. The release liner may comprise paper or a polymeric film
coated with polyethylene which is coated with a silicone-containing
material. Exemplary release liners include liners commercially
available from CP Films Inc. under the trade designations "T-30"
and "T-10" that have a silicone release coating on polyethylene
terephthalate film. Exemplary release liners include structured
release liners. Exemplary release liners include any of those
referred to as microstructured release liners which are used to
impart a microstructure on the surface of an adhesive layer. The
microstructured surface can aid air egress between the adhesive
layer and a surface to which the adhesive layer is applied.
[0159] FIG. 13a shows a schematic cross-sectional view of an
exemplary optical film and illumination article comprising the
variable index light extraction layer optically coupled to a
lightguide. Optical film 1300 comprises illumination article 1301
and release liner 1375. Illumination article 1301 comprises
lightguide 1310 disposed on transparent substrate 1340, and
protective outer layer 1330 is disposed on the lightguide opposite
the transparent substrate. The opposing side of transparent
substrate 1340 is optically coupled to lightguide 1310. Variable
index light extraction layer 1350 is disposed on transparent
substrate 1340 opposite the lightguide, and adhesive layer 1070 is
disposed on the variable index light extraction layer opposite the
transparent substrate. In this embodiment, lightguide 1310
preferably comprises a PSA as described above. Optional seal layer
1360 is disposed between variable index light extraction layer 1350
and adhesive layer 1370. Release liner 1375 is disposed on an outer
surface of adhesive layer 1370. Exemplary seal layers and release
liners are described above.
[0160] Illumination article 1301 can have a haze value of less than
about 10%, an optical clarity greater than about 85% and a light
transmittance of greater than about 90%. In some cases illumination
article 1301 can have a haze value of less than about 7%, an
optical clarity greater than about 90%, and a light transmittance
of greater than about 92%. Optical transmittance, clarity and haze
can be measured using a Haze-Gard Plus haze meter (available from
BYK-Gardiner).
[0161] FIG. 13b shows a schematic of exemplary illumination device
1390 comprising the illumination article shown in FIG. 13a in
combination with a light source and reflective scattering element.
Release liner is removed from illumination article 1301, and the
article is then applied to reflective scattering element 1380.
[0162] For any of the illumination articles or display devices
described above, the structure of the article or device need not be
flat or planar as shown in the figures. The structure of the
article or device may be curved, up to and including curved into a
tube shape and lit from the end. The structure of the article or
device may alternatively be shaped light a 1 D tunnel. In general
the structure of the articles and devices may take on the shape of
a curve including compound curvature and may have applications in
curved displays and general illumination and decorative
lighting.
[0163] The reflective display may comprise any type of display
which reflects light as an image toward a viewer. Reflective
displays rely on ambient light for information display and hence
are ideal devices for portable electronic equipment as they do not
require a backlight for illumination. Reflective displays are used
in a wide range of applications including handheld electronic
devices such as e-books, computer monitors, televisions, instrument
panels, signage, etc.
[0164] The reflective display may comprise a liquid crystal display
(LCD) which is a type of flat panel display that uses the light
modulating properties of liquid crystals. A typical reflective
display comprising an LCD comprises a pair of rigid and/or flexible
substrates with a liquid crystal material sealed in between the
substrates. The liquid crystal material is viewable through the
front side of the display which typically comprises a transparent
electrode. In the case of a reflective display, the other substrate
that forms the back of the display provides a reflective surface.
Simply stated, the LCD operates when liquid crystal molecules in
the liquid crystal material change their conformation in response
to an applied electric filed generated between electrodes which are
part of the display. The reflective display may further include an
additional member or material such as an anti-reflection film,
barrier film or brightness enhancement film. The liquid crystal
material may be dispersed as droplets in a polymer matrix; these
types of displays are known as polymer liquid crystal displays
(PDLCs).
[0165] The reflective display may comprise an electrophoretic
display panel designed to mimic the appearance of ordinary ink on
paper. In the simplest implementation of an electrophoretic
display, a mixture of titanium oxide particles dispersed in a
hydrocarbon oil with dark-colored dye and charging agents is
disposed between two conductive plates. Upon application of a
voltage, the particles migrate electrophoretically to the front
(viewing) side of the display which then appears white due to
scattering of light. When the particles are located at the rear
side of the display, it appears dark because incident light is
absorbed by the colored dye. Thus, images are created by reflecting
and absorbing regions. Electrophoretic displays are used in devices
such as Amazon Kindle, Barnes & Noble Nook and Sony Reader.
[0166] The reflective display may comprise an electrofluidic
display. One example of an electrofluidic display is an
electrowetting display, a relatively new technology, originally
described in "Video-Speed Electronic Paper Based on Electrowetting"
by R. A. Hayes and B. J. Feenstra in Nature, Vol. 425, 383-385 (25
Sep. 2003) and developed by Liquavista BV. Electrowetting displays
comprise a transparent electrode, hydrophobic insulator, a colored
oil layer and water, sandwiched between glass or polymeric
substrates. In equilibrium the colored oil naturally forms a stable
continuous film between the water and the hydrophobic insulator.
When a voltage difference is applied across the hydrophobic
insulator, the system lowers its energy by moving the water into
contact with the insulator, thereby displacing the oil and exposing
the underlying reflecting surface. The balance between
electrostatic and surface tension forces determines how far the oil
is moved to the side. In this way the optical properties of the
stack when viewed from above can be continuously tuned between a
colored off-state and a transparent on-state, provided the pixel is
sufficiently small so that the eye averages the optical
response.
[0167] Another example of an electrofluidic display are
electrofluidic displays made using "Young-Laplace Transposition of
Brilliant Pigment Dispersions" described by J. Heikenfeld et al. in
Nature Photonics, Vol. 3, 292-296 (26 Apr. 2009). The technology is
being developed by Gamma Dynamics The technology is a three
dimensional microfluidic display device that provides a direct view
of brilliantly coloured pigment dispersions. The basic
electrofluidic structure has several important geometrical
features. The first is a reservoir that will hold an aqueous
pigment dispersion in less than 5-10% of the visible area. The
second feature is a surface channel occupying 80-95% of the visible
area; this receives the pigment dispersion from the reservoir when
a suitable stimulus is applied. Third, there is a duct surrounding
the device that enables counterflow of a nonpolar fluid (oil or
gas) as the pigment dispersion leaves the reservoir. It is
important to note that all of these features are inexpensively
formed in a single photolithographic or microreplication step.
Several additional coatings and a top substrate are added to the
reservoir structure. The surface channel is first bound by two
electrowetting plates consisting of an electrode and hydrophobic
dielectric. The top electrowetting plate is composed of a
transparent In.sub.2O.sub.3:SnO.sub.2 electrode (ITO) so that the
surface channel may be viewed by the naked eye. The bottom
electrowetting plate comprises a highly reflective electrode made
from aluminium, for example. With this arrangement, when no voltage
is applied, a net Young-Laplace pressure causes the pigment
dispersion to occupy the cavity, which imparts a larger radius of
curvature on the pigment dispersion. Therefore at equilibrium, the
pigment dispersion occupies the reservoir and is largely hidden
from view. This is analogous to connecting two soap bubbles by a
straw--the larger bubble has a larger radius of curvature and a
lower Young-Laplace pressure, and will therefore consume the
smaller bubble. When a voltage is applied between the two
electrowetting plates and the pigment dispersion, an
electromechanical pressure is induced that exceeds the net
Young-Laplace pressure, and the pigment dispersion is pulled into
the surface channel. If the volume of the pigment dispersion is
slightly greater than the volume of the surface channel, then the
pigment will be simultaneously viewable in both the reservoir and
the surface channel, and nearly the entire device area will exhibit
the coloration of the pigment. If the voltage is removed the
pigment dispersion rapidly (milliseconds to tens of milliseconds)
recoils into the reservoir. Thus a switchable device is created
that can hide the pigment or reveal the pigment with a visual
brilliance that is similar to pigment printed on paper.
[0168] The reflective display may comprise an interferometric
display which can create various colors through interference of
reflected light. One type of interferometric display is the
Mirasol.RTM. display based on the iMoD.TM. element developed by
Qualcomm MEMS Technologies. This type of interferometric element is
an electrostatically actuated, bistable MEMS device built on a
transparent substrate. The element consists of a suspended
conductive membrane serving as a mirror, over a partially
reflective optical stack. Between the membrane and the stack is a
gap of a few hundred nanometers and filled with air. Interference
between light reflected from the mirror and from the partially
reflective optical stack generates color, and black is perceived
when the element is in the collapsed state. Colored pixels have
elements with different air gaps designed to reflect in the red,
green and blue wavelengths.
[0169] The reflective display may comprise an electronic paper
display panel designed to mimic the appearance of ordinary ink on
paper. The first electronic paper, called Gyricon, consists of
polyethylene spheres between 75 and 106 micrometers across. Each
sphere is a janus particle composed of negatively charged black
plastic on one side and positively charged white plastic on the
other (each bead is thus a dipole). The spheres are embedded in a
transparent silicone sheet, with each sphere suspended in a bubble
of oil so that they can rotate freely. The polarity of the voltage
applied to each pair of electrodes then determines whether the
white or black side is face-up, thus giving the pixel a white or
black appearance.
[0170] In some cases the reflective surface of the display resides
inside of a cavity defined by the reflective part of the display
and top surface of the devices. The top surfaces may comprise
glass, polymer films, coatings, or even touch active surfaces, for
example capacitive touch screens. Thus in some embodiments the
illumination articles described herein (for example illumination
article 1301) are attached to these outer surfaces and not the
directly to the reflective element of the reflective display. In
general, the illumination article must be optically coupled to the
reflective element of the reflective display device, in that the
light extracted from the light guide 1310 in FIG. 13b by the
variable index extraction layer 1350 is delivered to the reflective
surface of the reflective display device. In some cases, the top
surfaces of the reflective displays are optically coupled to the
reflective surface in the reflective display element of the display
device in the sense that there are no air gaps between the top
surface and the reflective display element of the display device.
In some embodiments, the refractive index of the top surface and
other layers of the reflective display device above the reflective
element of the display have a refractive index that is greater than
the nanovoided polymeric first region of the variable index light
extraction layer. In some cases the refractive index of the layers
in the display device that are between the reflective surface or
element of the display are equal to or higher than the index of the
lightguide of the illumination article 1301. In some cases the
layers in the display device that are between the reflective
surface or reflective element of the display have refractive
indices that are lower than the light guide but the refractive
indices are within 0.05 of the refractive index of the lightguide,
or are within 0.03 of the refractive index of the lightguide.
EXAMPLES
[0171] The following materials were used as received.
TABLE-US-00001 Component % Solid Amount (g) A-174 Silica Nalco
2327, 43.40 482.84 Ondeo Nalco Chemical Co. Aliphatic Urethane
Acrylate, available from 100.00 42.67 Sartomer Corporation as CN
9893 Pentaerythritol Triacrylate, available from 100.00 167.69
Sartomer Corporation as SR 444 Isopropanol, available from Sartomer
Corporation -- 250.03 as IPA Ethyl Acetate, available from
Sigma-Aldrich -- 250.03 Photoinitiator, available from BASF
Corporation 100.00 5.84 as IRGACURE 184 Photoinitiator, available
from BASF Corporation 100.00 1.12 as IRGACURE 819
Example 1
Preparation of Coating Formulation
[0172] The following were added in a 1-liter wide-mouth amber
bottle, according to the amounts shown in the above table: 5.70 g
of CN 9893, 22.40 g of SR 444, 5.84 g of IRGACURE 184 and 1.12 g of
IRGACURE 819. The bottle was capped and shaken for 2 hours to
dissolve CN9893 (batch is clear). This solution is referred to as
Resin Premix.
[0173] The following were added to a 2000 mL poly bottle: 482.84 g
of A-174 treated NALCO 2327 and the Resin Premix. The two
components were mixed by transferring the batch back and forth
between the two bottles. End with the batch in the 2000 mL bottle.
To the 2000 mL bottle was added IRGACURE 184 and IRGACURE 819. The
solution was shaken for 30 minutes to dissolve photoinitiators. The
resulting batch was a translucent, low-viscosity dispersion.
[0174] The batch above was diluted to .about.17.7% solids by weight
with a 50/50 blend ethyl acetate and propylene glycol methyl ether
(available from Dow Chemical as DOWANOL PM).
Preparation of Nanovoided Polymeric Layer
[0175] The above coating formulation was coated onto 50 um PET film
(MELINEX 617 available from DuPont) using a slot die at a line
speed of 3.1 m/min. The wet coating thickness was approximately 14
um. In an inert chamber (<50 ppm O.sub.2), the wet coating was
partially cured in-line at the same line speed with UV radiation at
395 nm and dose of 850 mJ/cm.sup.2 (UV radiation was provided by
UV-LEDs available from Cree, Inc.). The partially cured coating
sample was then dried at 70.degree. C. in a 9 meter oven, and under
a nitrogen-purged atmosphere, finally cured with a 236
Watt/cm.sup.2 Fusion H bulb (available from Fusion UV Systems,
Inc.). The resulting nanovoided polymeric layer had a thickness of
approximately 2.5 um. The transmission was 94.8%, the haze was
0.66% and the clarity was 99.9% as measured using a BYK Gardner
Haze Gard Plus (Columbia, Md.). The refractive index of the
nanovoided layer was between 1.20 and 1.22 as measured using a
Metricon Prism Coupler (Metricon Corporation, Pennington,
N.J.).
Formation of Variable Index Light Extraction Layer
[0176] The nanovoided polymeric layer was printed with a UV curable
clear ink (UV OP1005 GP Varnish from Nazdar, Shawnee, Kans.) using
an indirect gravure printing process. A flexographic tool having a
gradient pattern of 200 um wide lines was fabricated (by Southern
Graphics Systems, Brooklyn Park, Minn.) based on a pdf image that
defined the gradient line pattern as determined by optical modeling
and ray tracing. A gravure roll (pyramidal and 9 cubic um per
square um) was rated to give a wet coating of approximately 9.65
um. The printing was done at 10 meters per minute with high
intensity UV curing under a nitrogen-purged atmosphere with a 236
Watt/cm.sup.2 Fusion H bulb (available from Fusion UV Systems,
Inc.) after the printing. The resulting printed layer was an
optical film comprising: first regions having a first refractive
index and comprising nanovoided polymeric material, and second
regions wherein the nanovoids are filled or partially filed with
the cured clear ink, the second regions having a second refractive
index greater than that of the first regions. The variable index
light extraction layer having first and second regions was disposed
on the DuPont 617 PET substrate. The optical properties of the
variable index light extraction layer on PET was measured using a
BYK Gardner Haze Gard Plus on two sides, the side with low density
of second high index regions and the side with high density of high
index regions. For the low density side, the transmission was
94.9%, the haze was 2.88%, the clarity was 99.2%. For the high
density side, the transmission was 94.4%, the haze was 5.09%, the
clarity was 97.6% (note the transmission is not corrected for
Fresnel reflection). The refractive index of the cured ink was
measured to be approximately 1.525 as measured on a flat cured
sample using a Metricon prism coupler (wavelength of light used to
measure the refractive index was 589 nm).
Front Lit Reflective Display Device
[0177] A light guide comprising a PSA layer (VHB Acrylic Tape 4918
from 3M Company) was obtained, having an area of 90 mm.times.120 mm
and a thickness of 2 mm. On one major surface of the lightguide was
disposed a transparent protective layer of 50 um PET film. The PET
substrate on which the variable index light extraction layer was
disposed was adhered to the opposing major surface of the
lightguide directly. To the exposed face of the variable light
extraction layer was bonded a pressure sensitive adhesive (SOKEN
2147, available from Soken Chemical and Engineering Co., Ltd.,
Japan) to act as a seal layer. This assembly, with the protective
layer facing up, was adhered to the viewing panel of an
electrophoretic electronic-book (Kindle by Amazon) using a
self-wetting adhesive (see PCT US2010/031689 and WO
2009/085662).
[0178] A light engine assembly was obtained and consisted of 20
edge-emitting white LEDs (NSSW230T from Nichia) mounted in a bezel.
Two reflectors comprising multilayer polymeric mirror film
(Vikuiti.TM. ESR from 3M Co.) were also included in the bezel to
form an optical wedge to collimate the light emitted from the LEDs.
A slight angle of around 10.degree. was built into the bezel to
provide optical collimation. The light from the LED engine was
designed to emit into an air gap region such that the light was
injected at supercritical angles into the edge of the light guide
along the left side of the vertical axis of the display. This
resulted in a front-lit reflective display device where the front
light assembly does not negatively affect the image on the display
when looking through the light guide assembly having the variable
index light extraction layer (i.e. little to not distortion of the
image).
[0179] The LEDs of the illumination device were turned on,
resulting in uniform illumination of the reflective display device,
i.e., the reflective display panel as can be seen in FIG. 14a.
Comparative Example 1
Front Lit Reflective Display Device without the Variable Index
Light Extraction Layer
[0180] A front-lit reflective display device was assembled as
described above for Example 1 with the exception that the variable
index light extraction layer on PET support was not included. The
PSA lightguide was adhered to the viewing panel of the electronic
book using the self-wetting adhesive. (The self-wetting adhesive
was used in order to facilitate rework of the assembly when the
lightguide was removed from the electronic book at a later time.
FIG. 14b shows an image of the front lit device and it is
immediately apparent that the luminance uniformity across the
display is poor.
Example 2
Preparation of Coating Formulation
[0181] The following were added in a 1-liter wide-mouth amber
bottle, according to the amounts shown in the above table: 5.70 g
of CN 9893, 22.40 g of SR 444, 5.84 g of IRGACURE 184 and 1.12 g of
IRGACURE 819. The bottle was capped and shaken for 2 hours to
dissolve CN9893 (batch is clear). This solution is referred to as
Resin Premix.
[0182] The following were added to a 2000 mL poly bottle: 482.84 g
of A-174 treated NALCO 2327 and the Resin Premix. The two
components were mixed by transferring the batch back and forth
between the two bottles. End with the batch in the 2000 mL bottle.
To the 2000 mL bottle was added IRGACURE 184 and IRGACURE 819. The
solution was shaken for 30 minutes to dissolve photoinitiators. The
resulting batch was a translucent, low-viscosity dispersion.
[0183] The batch above was diluted to .about.17.7% solids by weight
with a 50/50 blend ethyl acetate and propylene glycol methyl ether
(available from Dow Chemical as DOWANOL PM).
Preparation of Nanovoided Polymeric Layer The above coating
formulation was coated onto 50 um PET film (MELINEX 617 available
from DuPont) using a slot die at a line speed of 3.1 m/min. The wet
coating thickness was approximately 8.1 um. In an inert chamber
(<50 ppm O.sub.2), the wet coating was partially cured in-line
at the same line speed with UV radiation at 395 nm and dose of 850
mJ/cm.sup.2. (UV radiation was provided by UV-LEDs available from
Cree, Inc.). The partially cured coating sample was then dried at
70.degree. C. in a 9 meter oven, and under a nitrogen-purged
atmosphere, finally cured with a 236 Watt/cm.sup.2 Fusion H bulb
(available from Fusion UV Systems, Inc.). The resulting nanovoided
polymeric layer had a thickness of 1.3 um. The transmission was
96.4%, the haze was 1.33% and the clarity was 99.7% as measured
using a BYK gardner Haze Gard Plus (Columbia, Md.). The refractive
index of the nanovoided layer was between 1.20 and 1.22 as measured
at 589 nm using a Metricon Prism Coupler (Metricon Corporation,
Pennington, N.J.).
Formation of Variable Index Light Extraction Layer
[0184] The nanovoided polymeric layer was printed with a UV curable
clear ink (UV OP1005 GP Varnish from Nazdar, Shawnee, Kans.) using
an indirect gravure printing process. A flexographic tool having a
random 100 um gradient dot pattern having a density gradient of
second regions in the x direction (left to right) and a varying
density in the y direction at the left edge of the pattern as shown
in FIG. 15a was fabricated (by Southern Graphics Systems) based on
a pdf image that defined the dot pattern determined by optical ray
tracing modeling. A gravure roll (pyramidal and 9 cubic um per
square um) was rated to give a wet coating of approximately 9.65
um. The printing was done at 10 meters per minute with high
intensity UV curing under a nitrogen-purged atmosphere with a 236
Watt/cm.sup.2 Fusion H bulb (available from Fusion UV Systems,
Inc.) after the printing. The resulting printed layer was an
optical film comprising: first regions having a first refractive
index and comprising nanovoided polymeric material, and second
regions wherein the nanovoids are filled or partially filed with
the cured clear ink, the second regions having a second refractive
index greater than that of the first regions. The variable index
light extraction layer having first and second regions was disposed
on the DuPont 617 PET substrate and is shown in FIG. 15b. The
optical properties of the variable index light extraction layer on
PET was measured using a BYK Gardner Haze Gard Plus on two sides,
the side with low density of second high index regions and the side
with high density of high index regions. For the low density side,
the transmission was 96.6%, the haze was 3.56%, the clarity was
95.6%. For the high density side, the transmission was 95.8%, the
haze was 6.82%, the clarity was 89.9% (note the transmission is not
corrected for Fresnel reflection). The refractive index of the
cured ink was measured to be approximately 1.525 as measured on a
flat cured sample using a Metricon prism coupler (wavelength of
light used to measure the refractive index was 589 nm).
Front Lit Reflective Display Device
[0185] A light guide comprising a PSA layer (VHB Acrylic Tape 4918
from 3M Company) was obtained, having an area of 90 mm.times.120 mm
and a thickness of 2 mm. On one major surface of the lightguide was
disposed a transparent protective layer of 50 um PET film. The PET
substrate on which the variable index light extraction layer was
disposed was adhered to the opposing major surface of the
lightguide directly. To the exposed face of the variable light
extraction layer was bonded a pressure sensitive adhesive (SOKEN
2147, available from Soken Chemical and Engineering Co., Ltd.,
Japan) to act as a seal layer. This assembly, with the protective
layer facing up, was adhered to the viewing panel of an
electrophoretic electronic-book (Kindle by Amazon) using a
self-wetting adhesive (see PCT US2010/031689 and WO 2009/085662). A
light engine assembly was made and consisted of 3 edge-emitting
white LEDs (NSSW230T from Nichia) mounted in a bezel. Two
reflectors comprising multilayer polymeric mirror film (Vikuiti.TM.
ESR from 3M Co.) were also included in the bezel to form an optical
wedge to collimate the light emitted from the LEDs. A slight angle
of around 10.degree. was built into the bezel to provide optical
collimation. The light from the LED engine was designed to emit
into an air gap region such that the light was injected at
supercritical angles into the edge of the light guide along the
horizontal top edge of the display. This resulted in a front-lit
reflective display device where the front light assembly does not
negatively affect the image on the display when looking through the
light guide assembly having the variable index light extraction
layer (i.e. little to not distortion of the image) with the front
light off as can be seen in FIG. 16a.
[0186] The LEDs of the illumination device were turned on,
resulting in uniform illumination of the reflective display device,
i.e., the reflective display panel as can be seen in FIG. 16b. The
luminance uniformity was measured on the illuminated device using a
Prometric camera (available from Radiant Imaging, Redmond, Wash.).
FIG. 17a shows an image of the front lit device and a plot of the
axial luminance as a function of position. The display uniformity
is greater than 75% as measured using the formula
((max-min)/max.times.100%).
Comparative Example 2
Front Lit Reflective Display Device without the Variable Index
Light Extraction Layer
[0187] A front-lit reflective display device was assembled as
described above for Example 2 with the exception that the variable
index light extraction layer on PET support was not included. The
PSA lightguide was adhered to the viewing panel of the electronic
book using the self-wetting adhesive. (The self-wetting adhesive
was used in order to facilitate rework of the assembly when the
lightguide was removed from the electronic book at a later time).
The luminance uniformity was measured on the illuminated device
using a Prometric camera (available from Radiant Imaging, Redmond,
Wash.). FIG. 17b shows an image of the front lit device and a plot
of the axial luminance as a function of position. It is immediately
apparent that the display uniformity is poor. The luminance
uniformity is less than 5% as measured using the formula
((max-min)/max.times.100%).
Example 3
Preparation of Coating Formulation
[0188] The following were added in a 1-liter wide-mouth amber
bottle, according to the amounts shown in the above table: 5.70 g
of CN 9893, 22.40 g of SR 444, 5.84 g of IRGACURE 184 and 1.12 g of
IRGACURE 819. The bottle was capped and shaken for 2 hours to
dissolve CN9893 (batch is clear). This solution is referred to as
Resin Premix.
[0189] The following were added to a 2000 mL poly bottle: 482.84 g
of A-174 treated NALCO 2327 and the Resin Premix. The two
components were mixed by transferring the batch back and forth
between the two bottles. End with the batch in the 2000 mL bottle.
To the 2000 mL bottle was added IRGACURE 184 and IRGACURE 819. The
solution was shaken for 30 minutes to dissolve photoinitiators. The
resulting batch was a translucent, low-viscosity dispersion.
[0190] The batch above was diluted to .about.17.7% solids by weight
with a 50/50 blend ethyl acetate and propylene glycol methyl ether
(available from Dow Chemical as DOWANOL PM).
Preparation of Nanovoided Polymeric Layer
[0191] The above coating formulation was coated onto 50 um PET film
(MELINEX 617 available from DuPont) using a slot die at a line
speed of 3.1 m/min. The wet coating thickness was approximately 14
um. In an inert chamber (<50 ppm O.sub.2), the wet coating was
partially cured in-line at the same line speed with UV radiation at
395 nm and dose of 850 mJ/cm.sup.2. (UV radiation was provided by
UV-LEDs available from Cree, Inc.). The partially cured coating
sample was then dried at 70.degree. C. in a 9 meter oven, and under
a nitrogen-purged atmosphere, finally cured with a 236
Watt/cm.sup.2 Fusion H bulb (available from Fusion UV Systems,
Inc.). The resulting nanovoided polymeric layer had a thickness of
2.3 um. The transmission was 95.8%, the haze was 2.49% and the
clarity was 99.9% as measured using a BYK gardner Haze Gard Plus
(Columbia, Md.). The refractive index of the nanovoided layer was
between 1.20 and 1.22 as measured at 589 nm using a Metricon Prism
Coupler (Metricon Corporation, Pennington, N.J.).
Formation of Variable Index Light Extraction Layer
[0192] The nanovoided polymeric layer was printed with a UV curable
clear ink (UV OP1005 GP Varnish from Nazdar, Shawnee, Kans.) using
an indirect gravure printing process. A flexographic tool having a
random 100 um gradient dot pattern was fabricated (by Southern
Graphics Systems) based on a pdf image that defined the dot pattern
determined by optical ray tracing modeling. A gravure roll
(pyramidal and 9 cubic um per square um) was rated to give a wet
coating of approximately 9.65 um. The printing was done at 10
meters per minute with high intensity UV curing under a
nitrogen-purged atmosphere with a 236 Watt/cm.sup.2 Fusion H bulb
(available from Fusion UV Systems, Inc.) after the printing. The
resulting printed layer was an optical film comprising: first
regions having a first refractive index and comprising nanovoided
polymeric material, and second regions wherein the nanovoids are
filled or partially filed with the cured clear ink, the second
regions having a second refractive index greater than that of the
first regions. The variable index light extraction layer having
first and second regions was disposed on the DuPont 617 PET
substrate. The optical properties of the variable index light
extraction layer on PET was measured using a BYK Gardner Haze Gard
Plus on two sides, the side with low density of second high index
regions and the side with high density of high index regions. For
the low density side, the transmission was 96.2%, the haze was
5.64%, the clarity was 97.5%. For the high density side, the
transmission was 95.8%, the haze was 9.18%, the clarity was 94.4%
(note the transmission is not corrected for Fresnel reflection).
The refractive index of the cured ink was measured to be
approximately 1.525 as measured on a flat cured sample using a
Metricon prism coupler (wavelength of light used to measure the
refractive index was 589 nm).
Example 4
[0193] Each of the optical films (the variable index light
extraction layer on PET) from Examples 1-3 were used to assemble
two different optical articles for the purposes of evaluating
optical properties.
Optical Properties for Variable Index Light Extraction Layer Having
a Seal Layer:
[0194] The first optical articles were formed by laminating a seal
layer onto the exposed surface of the variable index light
extraction layer (the side opposite the PET substrate). The seal
layer was a pressure sensitive adhesive (Soken 2147, available from
Soken Chemical and Engineering Co., Ltd., Japan). To the opposing
side of the Soken PSA seal layer was laminated a 50 micron PET
film. For each of the optical article using the variable index
light extraction layers from examples 1-3 the transmission, haze
and clarity were measured using a BYK Gardner Haze Gard Plus on the
two sides of the variable index light extraction layer, the side
with low density of second high index regions and the side with
high density of high index regions. The results of the measurements
are shown in Table 1 and Table 2 respectively.
TABLE-US-00002 TABLE 1 Optical properties of area with high density
of second regions % Haze Clarity Example Pattern Transmission (%)
(%) 1 1-D lines 91.0 1.84 98.1 y-gradient 2 2-D dots 92.0 3.35 92.1
x, y gradient 3 2-D dots 91.9 6.96 95.7 y-gradient
TABLE-US-00003 TABLE 2 Optical properties of area with low density
of second regions % Haze Clarity Example Pattern Transmission (%)
(%) 1 1-D lines 91.0 1.99 99.2 y-gradient 2 2-D dots 92.3 1.87 95.6
x, y gradient 3 2-D dots 91.7 4.38 98.2 y-gradient
Optical Properties for Lightguide Assembly with Variable Index
Light Extraction Layer:
[0195] The second optical articles were formed by laminating a
viscoelastic lightguide onto the exposed surface of the variable
index light extraction layer (the side opposite the PET substrate).
The viscoelastic lightguide was a pressure sensitive adhesive (PSA)
with a thickness of 2 mm (VHB Acrylic Tape 4918 from 3M Company).
To the opposite major surface of the lightguide was disposed a
transparent protective layer of 50 um PET film. For each of the
optical article using the variable index light extraction layers
from examples 1-3 the transmission, haze and clarity were measured
using a BYK Gardner Haze Gard Plus on the two sides of the variable
index light extraction layer, the side with low density of second
high index regions and the side with high density of high index
regions. The results of the measurements are shown in Table 3 and
Table 4 respectively. Table 5 shows reference measurements for the
PET film (DuPont 617) used in the optical constructions and for the
PSA lightguide having PET laminated to both surfaces.
TABLE-US-00004 TABLE 3 Optical properties of area with high density
of second regions % Haze Clarity Example Pattern Transmission (%)
(%) 1 1-D lines 90.3 1.91 98.5 y-gradient 2 2-D dots 91.0 3.76 91.6
x, y gradient 3 2-D dots 90.6 6.80 95.8 y-gradient
TABLE-US-00005 TABLE 4 Optical properties of area with low density
of second regions % Haze Clarity Example Pattern Transmission (%)
(%) 1 1-D lines 90.3 1.61 99.0 y-gradient 2 2-D dots 90.3 2.37 96.8
x, y gradient 3 2-D dots 90.1 4.16 98.2 y-gradient
TABLE-US-00006 TABLE 5 Reference Measurements: % Haze Clarity
Example Pattern Transmission (%) (%) Ref 1 PET film 92.8 0.67 100
Ref 2 PSA lightguide 90.9 0.59 99.4 with PET film on both sides
[0196] All references and publications cited herein are expressly
incorporated herein by reference in their entirety into this
disclosure, except to the extent they may directly contradict this
disclosure. Although specific embodiments have been illustrated and
described herein, it will be appreciated by those of ordinary skill
in the art that a variety of alternate and/or equivalent
implementations can be substituted for the specific embodiments
shown and described without departing from the scope of the present
disclosure. This application is intended to cover any adaptations
or variations of the specific embodiments discussed herein.
Therefore, it is intended that this disclosure be limited only by
the claims and the equivalents thereof.
* * * * *