U.S. patent application number 13/125134 was filed with the patent office on 2011-09-29 for light guides.
Invention is credited to James Gourlay.
Application Number | 20110234941 13/125134 |
Document ID | / |
Family ID | 40097787 |
Filed Date | 2011-09-29 |
United States Patent
Application |
20110234941 |
Kind Code |
A1 |
Gourlay; James |
September 29, 2011 |
LIGHT GUIDES
Abstract
This invention relates to a light guide plate and methods of
manufacture. The light guide plate is suitable for use in a range
of applications, particularly those which require backlighting for
display units, for example, liquid crystal displays. The light
guide plate comprises a combination of light guide layers and one
or more scattering features.
Inventors: |
Gourlay; James; (Livingston,
GB) |
Family ID: |
40097787 |
Appl. No.: |
13/125134 |
Filed: |
October 20, 2009 |
PCT Filed: |
October 20, 2009 |
PCT NO: |
PCT/GB2009/051409 |
371 Date: |
May 20, 2011 |
Current U.S.
Class: |
349/64 ; 156/277;
156/60; 362/612; 362/613; 362/615 |
Current CPC
Class: |
G02B 6/0016 20130101;
G02B 6/0041 20130101; Y10T 156/10 20150115; G02B 6/0068 20130101;
G02B 6/007 20130101; G02B 6/0065 20130101; G02B 6/0076 20130101;
G02B 6/0073 20130101 |
Class at
Publication: |
349/64 ; 362/615;
362/613; 362/612; 156/277; 156/60 |
International
Class: |
G02F 1/13357 20060101
G02F001/13357; F21V 7/22 20060101 F21V007/22; B32B 38/14 20060101
B32B038/14; B32B 37/00 20060101 B32B037/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 21, 2008 |
GB |
0819308.8 |
Claims
1. A light guide plate comprising: a first layer of light guiding
material, a second layer of light guiding material which is mounted
upon a surface of the first layer of light guiding material, and
one or more light scattering features located at the interface
between the first and second layers of light guiding material.
2. The light guide plate according to claim 1, wherein the first
and second layers of light guiding material are made from
transparent polymer sheet.
3. The light guide plate according to claim 1, wherein the
refractive indices of the first and second layers of light guiding
material are the same or substantially the same.
4. The light guide plate according to claim 1, wherein the
refractive index of the first and second layers of light guiding
material are independently of each other about 1.4 to about
1.7.
5. The light guide plate according to claim 1, wherein the
thickness of the first and second layers of light guiding material
are independently of each other about 0.1 mm to about 10 mm.
6. The light guide plate according to claim 1, wherein the
refractive index of the one or more light scattering features is
greater than the refractive index of the first layer of light
guiding material.
7. The light guide plate according to claim 1, wherein the one or
more scattering features are dispersed within a transparent
ink.
8. The light guide plate according to claim 7, wherein the
refractive index of the transparent ink is equal to or
substantially equal to the refractive index of the first layer of
light guiding material.
9. The light guide plate according to claim 1, wherein the one or
more scattering features are in particulate form.
10. The light guide plate according to claim 9, wherein the
particle size of the particles is in the range of about 1 .mu.m to
about 20 .mu.m.
11. The light guide plate according to claim 9, wherein the
particles are silica particles.
12. The light guide plate according to claim 1, wherein the
refractive index of at least one of the scattering features is
about 1.6 to about 2.
13. A light guide device comprising a light guide plate according
to claim 1 and one or more light sources.
14. The light guide device according to claim 13, wherein the one
or more light sources are selected from LEDs, cold cathode
fluorescent lamps, laser diodes, organic light emitting diode
sources, and other electroluminescent devices.
15. The light guide device according to claim 14, wherein the one
or more light sources are selected from one or more LEDs.
16. The light guide device according to claim 13, wherein the light
guide device is edge-lit.
17. The light guide device according to claim 13, wherein the one
or more light sources are not encapsulated by a layer of light
guiding material.
18. The display device comprising the light guide device of claim
13.
19. The display device according to claim 18, wherein the display
device comprises a liquid crystal cell.
20. A method of producing a light guide plate comprising: (a)
applying to a surface of a first layer of light guiding material
one or more light scattering features; and (b) mounting a second
layer of light guiding material on the surface of the first layer
of light guiding material such that said one or more light
scattering features are located at the interface between the first
and second layers of light guiding material.
21. The method according to claim 20, wherein (a) comprises
applying to the surface a transparent ink comprising the scattering
features, and curing the ink.
22. The method according to claim 20, wherein an additive printing
method is used to apply the one or more light scattering
features.
23. The method according to claim 22, wherein the additive printing
method is a screen printing method.
24. The method according to claim 20, wherein (b) comprises
applying a liquid polymer on the surface, and curing the liquid
polymer.
25. The method according to claim 20, wherein the second light
guide layer is a polymer sheet and (b) comprises laminating the
polymer sheet to the first light guide layer.
Description
FIELD OF THE INVENTION
[0001] This invention relates to a light guide plate and a light
guide device comprising said light guide plate and methods of
manufacture thereof. The light guide device is suitable for use in
a range of applications, particularly in connection with the
backlighting of displays, for example, liquid crystal displays.
BACKGROUND OF THE INVENTION
[0002] Light guide devices are known in the art and are utilised,
by way of example, for illumination, backlighting, signage and
display purposes. Typically, a light guiding device comprises a
light source such as a fluorescent lamp or a plurality of light
emitting diodes (LEDs) and a light guide plate which is constructed
from a standard injection-moulded or machined transparent plastic
component.
[0003] The light guide plate will often comprise suitable
structural surface modifications which disturb the total internal
reflection of the light from the light source such that the light
is guided through the transparent light guide in a controlled
manner and emitted in a substantially perpendicular direction to
that of the direction of propagation of light within the
transparent guide.
[0004] However, there are a number of problems associated with the
manufacture of such a light guide plate. For instance, an
injection-moulded light guide comprising these surface features
requires a suitable mould to be micro-machined or laser cut, often
at great cost.
[0005] Other techniques useful for preparing light guide plates
include micro-stamping or hot embossing of suitable polymer sheets.
However, the optical quality of the end light guide is restricted
by the stamp quality and associated manufacturing process.
[0006] Furthermore, the micro-mechanical surface features described
may easily be damaged during production of the light guide plate,
or during assembly of a light guide device. In addition, stringent
dust-free production and assembly processes are required to ensure
that no dust particles are collected on the surface features, which
may have an adverse effect on light propagation through the light
guide. Consequently, production costs and assembly process costs
are high.
[0007] Due to the increasing size of display units and therefore
increasing size of backlights required for use in these units, the
physical limitations of the manufacturing and assembly processes
become more critical and the associated costs increase. There is
therefore an ongoing need for alternative and/or improved light
guide plates and devices and methods of formation thereof for use
in, inter alia, backlighting applications.
[0008] It is an object of the present invention to provide a light
guide plate that addresses one or more of the aforesaid
disadvantages.
SUMMARY OF THE INVENTION
[0009] According to a first aspect of the invention, there is
provided a light guide plate comprising a first layer of light
guiding material upon a first surface of which is mounted a second
layer of light guiding material and one or more light scattering
features located at the interface between the first and second
layers of light guiding material.
[0010] According to a second aspect of the invention, there is
provided a light guide device comprising a light guide plate
according to the first aspect of the invention and one or more
light sources. The one or more light sources may be coupled
externally to the light guide plate. Preferably the device is
edge-lit. Optionally, the one or more light sources may not be
encapsulated by a layer of light guiding material.
[0011] Light from the one or more light sources may be guided
within both the first layer of light guiding material and the
second layer of light guiding material by total internal
reflection. The one or more light scattering features may disturb
or break the total internal reflection of the guided light and the
disturbed light may be emitted in a direction which is
perpendicular or substantially perpendicular to the direction of
guided light. As such, there is provided a light guide device
comprising one or more light sources coupled to a light guide plate
wherein said light guide plate comprises a first layer of light
guiding material upon a first surface of which is mounted a second
layer of light guiding material and one or more light scattering
features located at the interface between the first and second
layers of light guiding material, wherein light from the one or
more light sources is guided within both the first layer of light
guiding material and the second layer of light guiding material by
total internal reflection and said one or more light scattering
features disturb the total internal reflection of the guided light
and the disturbed light is emitted in a direction which is
perpendicular or substantially perpendicular to the direction of
guided light.
[0012] According to a third aspect of the invention, there is
provided a display device comprising a light guide device according
to the second aspect of the invention. The display device may be a
liquid crystal display device and may therefore comprise a liquid
crystal cell which may also be referred to as a liquid crystal
panel.
[0013] According to a fourth aspect of the invention, a method of
producing a light guide plate comprises: [0014] a) applying to a
first surface of a first layer of light guiding material one or
more light scattering features; and [0015] b) mounting a second
layer of light guiding material on the first surface of the first
layer of light guiding material such that said one or more light
scattering features are located at the interface between the first
and second layers of light guiding material.
[0016] The method may further comprise combining the light guide
plate with one or more light sources to form a light guide device.
The method may also comprise forming a display device from said
light guide device.
[0017] The method of applying the one or more light scattering
features to the first surface of the first layer of light guiding
material may comprise applying to the first surface an ink
comprising the one or more light scattering features, and curing
the ink. The method of applying the ink may comprise printing or
stencilling the ink onto a first surface of the first layer of
light guiding material. The one or more scattering features may be
present on either or both of the first and second layers of light
guiding material prior to the layers being combined.
[0018] In (b), the method of combining the first and second layers
of light guiding material may comprise applying a liquid polymer to
the first surface, and curing the liquid polymer.
[0019] The second layer of light guiding material may be combined
with the first layer of light guiding material using a standard
lamination technique. Such a technique may require the use of a
transparent adhesive.
[0020] Since the one or more scattering features are located at the
interface between the first and second layers of light guiding
material and not on an external surface of a light guiding
material, a light guide plate in accordance with the present
invention is easier to clean and has a reduced risk of damage
during handling.
[0021] Furthermore, the one or more light scattering features can
be easily applied to the surface of a layer of light guiding
material by any additive printing method, such as screen printing,
for example, so as to obviate the need for expensive micromachining
equipment previously used to create surface-modified structural
scattering features, thereby reducing manufacture costs. The light
guide plate according to the present invention may be produced
using roll-to-roll production.
DETAILED DESCRIPTION OF THE INVENTION
The Layers of Light Guiding Material
[0022] The first and second layers of light guiding material which
may also be referred to herein as first and second light guide
layers are light transmissive. Preferably, the light guide layers
are transparent to the light generated by the one or more light
sources. The first light guide layer (which may be referred to as a
substrate layer) may be formed from a transparent polymer sheet
such as polyethylene terephthalate (PET), polycarbonate or acrylic.
The second light guide layer may be made from a range of suitable
polymers, including acrylics, epoxies or urethanes. The thickness
of the first and second light guide layers may, independently of
each other be about 0.1 to about 10 mm. Typically, the thickness of
the light guide layers is of the order of about 0.1 mm. The
refractive index of the light guide layers may be equal to or
greater than 1.4. The refractive index of the light guide layers
may, independently of each other, be selected from about 1.4 to
about 1.7. The refractive index of the first layer and the second
layer may be the same or may be different.
[0023] The second light guide layer may be combined with the first
guide layer using a standard lamination technique. Such a technique
may require use of a transparent adhesive. The transparent adhesive
may have a refractive index which is the same or substantially the
same as the refractive index of the first and second light guide
layers. The first and second light guide layers may be optically
joined during manufacture. Optically joined indicates that the
layers are combined in such a way that, optically, these layers are
effectively indistinguishable. The method of applying the second
guide layer to the first guide layer may comprise applying and
curing a liquid polymer. Methods of curing may comprise one or more
of thermal, UV and/or two-part curing. The method may comprise
printing, stencilling or dispensing the liquid polymer. Preferably,
when the second light guide layer is applied in the form of a
liquid polymer, the one or more scattering features will be
disposed on the first light guide layer only, prior to combining
the two light guide layers.
Scattering Features
[0024] The one or more light scattering features disturb the total
internal reflection of the guided light. The one or more light
scattering features may be referred to as light extraction
features. The application of the scattering features may be
accomplished by dispersing the features in a transparent printing
ink and applying the ink to a surface of one or more of the light
guide layers prior to the layers being combined.
[0025] Preferably, the scattering features are transparent to the
light generated by the one or more light sources. The scattering
features may be reflective, e.g. silver flakes. Preferably, the
scattering features have a higher refractive index than the
refractive index of the first light guide layer and/or second light
guide layer, for example, about 1.6 to about 2, for example,
greater than about 1.6. The one or more scattering features may be
in particulate form. The one or more scattering features may have a
particle size in the range of from about 1 .mu.m to about 20 .mu.m.
Transparent particulate material which has a refractive index
greater than the refractive index of the first light guide layer
may be suitable for use in the present invention. The particles may
be silica particles, e.g. silica spheres.
[0026] The scattering features, e.g. particles, may be loaded into
an ink. The ink is light transmissive and preferably transparent to
the light generated by the one or more light sources. The ink,
which may be a polymeric material and may comprise the scattering
features, may be applied to a light guide layer to form a thin
pattern of features, according to any of a number of methods which
may be referred to in general terms as additive printing processes.
For example, conventional screen printing incorporates the use of a
mesh screen with openings corresponding to the pattern required to
be printed. This pattern may facilitate the accurate delivery of a
volume of ink to the required areas of the light guide layer. Other
suitable examples of additive printing methods include stencil
printing, ink jet printing, flexographic printing and other known
lithographic techniques.
[0027] Suitable inks for use in the present invention include those
which are transparent to light generated from the one or more light
sources, have a low refractive index, for example about 1.4 to
about 1.5, and which may be UV or solvent cured. The refractive
index of the ink may be the same or substantially the same as the
refractive index of the first and/or second light guide layer. For
example, a suitable UV curing ink is Windowtex Gloss which is an
acrylic based, transparent UV curing polymer screen printable ink
and is commercially available from MacDermid Autotype.
[0028] The ink may be applied in varying amounts and shapes which
may depend on how close to the one or more light sources the ink is
being deposited. The intensity of the light becomes less as the
distance from the light source increases if light is scattered out
of the light-guide. Therefore, smaller sized ink dots which are
more widely spaced may be deposited closer to the position of the
light source, whereas larger sized ink dots which are more closely
spaced may be deposited as the distance from the light source
increases. The ink dots may have a height of from about 0.01 mm to
about 0.1 mm and may have a spacing and/or diameter of from about
0.1 mm to about 10 mm. The distribution of ink may be tailored to
achieve a uniform or substantially uniform overall extraction of
light. The printing pattern of the ink may determine the pattern of
the particles on the surface of the light guide layer and therefore
the location of the light scattering features.
[0029] An additional reflective element, e.g. a reflective sheet
may, optionally, be located below the lower external surface of the
first light guide layer in order to re-direct light which would
otherwise be directed in a direction significantly away from the
direction in which the device is intended to be viewed, for
example, when used as a backlight.
[0030] In the present invention, particle size distribution
measurements are measured using a Malvern Particle Size Analyzer,
Model Mastersizer, from Malvern Instruments. A helium-neon gas
laser beam is projected through a transparent cell which contains
the particles suspended in an aqueous solution. Light rays which
strike the particles are scattered through angles which are
inversely proportional to the particle size. The photodetector
array measures the quantity of light at several predetermined
angles. Electrical signals proportional to the measured light flux
values are then processed by a microcomputer system, against a
scatter pattern predicted from theoretical particles as defined by
the refractive indices of the sample and aqueous dispersant to
determine the particle size distribution.
Light Guide Devices
[0031] Light guide devices are employed for a range of functions
including illumination, backlighting, signage and display purposes.
Typically, known light guide devices are constructed from an
injection moulded or machined transparent plastic component, onto
which a light source is integrated by means of mechanical
attachment at the edge of the transparent plastic component.
Examples of such devices are described in WO 2005/101070, the
contents of which are incorporated herein in their entirety by
reference.
[0032] Common to all of these devices is the fact that light from
the light source is guided through a transparent guide plate,
typically made of plastic, by total internal reflection. For
edge-lit backlighting applications, light is emitted in a
substantially perpendicular direction to that of the direction of
propagation of the light within the transparent guide plate. This
may be achieved through the light being directed so as to interact
with scattering structures located on an external surface of the
light guide plate, thus providing a non-flat surface, and which
disturb the total internal reflection.
[0033] Light guide devices according to the present invention may
be made using roll-to-roll production and screen printing
techniques. The external surfaces of the light guide plate and
light guide device according to the present invention are typically
smoother than conventional light guide plates and preferably
flat.
[0034] The integration of one or more light sources to the edge of
the light guide plate according to the present invention may be
achieved according to a range of techniques. A light source may be
integrated by means of mechanical attachment at the edge of the
light guide plate. The integration of one or more light sources to
the edge of the light guide plate may be achieved by a butt
coupling process where the one or more light sources are attached
to the end of the light guide plate by UV curing with a high
refractive index photonic adhesive that acts to reduce reflections
from the ends of the light guide layer. The light guide plate may
be hot cleaved or polished to provide a suitable optical surface at
the end of the light guide plate which facilitates good coupling of
light from the one or more light sources into the light guide
layers.
Light Source
[0035] The one or more light sources can be any of those known to
those skilled in the art, including those which are suitable for
use in backlighting. Such light sources include one or more LEDs,
cold cathode fluorescent lamps, laser diodes, organic light
emitting diode sources, and other electroluminescent devices. The
light may be non-directional.
[0036] The LEDs can be any of the designs known to those skilled in
the art, including edge-emitting, side emitting, top emitting or
bare die LEDs.
Uses of the Light Guide Device
[0037] The light guide device according to the present invention
may be employed for a range of functions including illumination,
backlighting, signage and display purposes.
[0038] Liquid crystal devices are well known in the art. A liquid
crystal display device operating in a transmissive mode typically
comprises a liquid crystal cell, which may also be referred to as a
liquid crystal panel, a backlight unit incorporating a light guide
device, and one or more polarisers. Liquid crystal cells are also
well known devices. In general, liquid crystal cells typically
comprise two transparent substrates between which is disposed a
layer of liquid crystal material. A liquid crystal display cell may
comprise two transparent plates which may be coated on their
internal faces respectively with transparent conducting electrodes.
An alignment layer may be introduced onto the internal faces of the
cell in order that the molecules making up the liquid crystalline
material line up in a preferred direction. The transparent plates
are separated by a spacer to a suitable distance, for example about
2 microns. The liquid crystal material is introduced between the
transparent plates by filling the space in between them by flow
filling. Polarisers may be arranged in front of and behind the
cell. The backlight unit may be positioned behind the liquid
crystal cell using conventional means. In operation, a liquid
crystal cell, operating in a transmissive mode, modulates the light
from a light source such as a backlight unit which may comprise a
light guide device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0039] Embodiments of the invention will now be described, by way
of example only and without limitation, with reference to the
accompanying drawing and the following Example, in which:
[0040] FIG. 1 illustrates a light guide device according to the
present invention and its effect on the transmission of light.
[0041] In FIG. 1, a light guide device (1) in side elevation
comprises a first light guide layer (2) made from a transparent
polymer substrate such as a polyester, polycarbonate or acrylic.
Disposed between the first light guide layer and a second light
guide layer (7) are a plurality of scattering features (4). The
second light guide layer may be mounted on the first surface of the
first light guide layer by any suitable means known in the art,
thereby effectively encapsulating the scattering features between
the first and second light guide layers. An external light source
(3), for example an LED, is mechanically attached to one edge of
the light guide layers, which together form a light guide plate, by
any suitable means. Light (5a, 5b, 5c) generated by the LED light
source is coupled into the light guide layers such that it
propagates through the light guide layers in a direction
substantially parallel to a plane defined by the light guide
layers. The light is guided through the transparent light guide
plate due to total internal reflection. When the light encounters
the scattering features (4), it interacts with these so as to be
redirected and exit the light guide device via the top surface, as
indicated at 6a and 6c, thereby providing a backlighting function.
Also shown is the optional presence of a reflective element (8),
should it be required to redirect light indicated by (5b') through
the top of the device and in the general direction indicated by
(6b).
[0042] Typically, the refractive index of the second light guide
layer (7) is substantially equal to the refractive index of the
first light guide layer (2) such that light from the light source
(3) is guided within both the first and second light guide layers
due to the effects of total internal reflection. Therefore, the
first light guide layer and second light guide layer with the
scattering features disposed there between, collectively referred
to as the light guide plate, form a composite structure that acts
as the guiding media for light generated by the light source
mounted on the edge of the light guide plate.
EXAMPLES
Example 1
[0043] A light guide plate in accordance with the present invention
is constructed as follows. A 0.3 mm thick sheet of acrylic is used
as the first light guide layer. Silica particles (particle size: 10
micron) are dispersed in Windowtex Gloss (thickness 0.025 mm), an
acrylic based, transparent UV curing polymer screen printable ink
which is commercially available from MacDermid Autotype. The
resulting dispersion is screen printed onto the acrylic substrate
and cured. A 0.1 mm thick layer of Dymax 4-20645, a UV curing,
acrylic based transparent polymer (refractive index 1.51) is then
applied to the same surface of the acrylic substrate on top of the
printed ink and cured, resulting in an optically continuous
composite structure with the light scattering silica particles
encased at the interface between the two acrylic layers. As
described above, the top and bottom surfaces of this composite
light guide plate are free from features which may become damaged
or collect dust and the light scattering features are contained
within the composite structure.
* * * * *