U.S. patent application number 14/870008 was filed with the patent office on 2016-03-10 for optical substrates having light collimating and diffusion structures.
The applicant listed for this patent is UBRIGHT OPTRONICS CORPORATION. Invention is credited to Han-Tsung PAN, Ching-An YANG.
Application Number | 20160067931 14/870008 |
Document ID | / |
Family ID | 55436709 |
Filed Date | 2016-03-10 |
United States Patent
Application |
20160067931 |
Kind Code |
A1 |
YANG; Ching-An ; et
al. |
March 10, 2016 |
Optical substrates having light collimating and diffusion
structures
Abstract
This invention discloses a method of forming an uneven structure
on a substrate. Use a hard tool to penetrate into a mold to cut a
first trench and a second trench in an order on a surface of a
mold, wherein the hard tool has a smoothly-curved shape such that
the transverse width of each of the first trench and the second
trench increases as the penetrating depth of the hard tool
increases, wherein when each of the first trench and the second
trench marches along a first direction, the penetrating depth of
the hard tool is controlled by repeating moving the hard tool up
and down to cut the mold such that the transverse width of each of
the first trench and the second trench varies according to the
controlled penetrating depth of the hard tool, wherein the first
trench and the second trench completely overlap with each other
with no space therebetween. Then, use the surface of the mold to
emboss a thin film on a substrate.
Inventors: |
YANG; Ching-An; (Dasi Town,
TW) ; PAN; Han-Tsung; (Dasi Town, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UBRIGHT OPTRONICS CORPORATION |
Dasi Town |
|
TW |
|
|
Family ID: |
55436709 |
Appl. No.: |
14/870008 |
Filed: |
September 30, 2015 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
14469572 |
Aug 26, 2014 |
9180609 |
|
|
14870008 |
|
|
|
|
14166842 |
Jan 28, 2014 |
|
|
|
14469572 |
|
|
|
|
13073859 |
Mar 28, 2011 |
8638408 |
|
|
14166842 |
|
|
|
|
61318061 |
Mar 26, 2010 |
|
|
|
61406094 |
Oct 22, 2010 |
|
|
|
Current U.S.
Class: |
428/156 ;
264/2.5; 83/875 |
Current CPC
Class: |
B29C 33/3842 20130101;
B29C 59/026 20130101; G02B 6/0053 20130101; B29D 11/00798 20130101;
B26D 3/06 20130101; B29C 33/424 20130101; B29D 11/00278 20130101;
G02B 5/0215 20130101; G02B 5/0278 20130101; B29C 2035/0827
20130101; G02B 3/0068 20130101; G02B 5/0221 20130101; B29L 2011/00
20130101; G02F 1/133504 20130101; B29L 2011/0016 20130101; G02B
3/0043 20130101; G02B 6/0058 20130101; G02F 2001/133607 20130101;
B29C 2059/023 20130101; G02B 6/0051 20130101; G02B 27/30
20130101 |
International
Class: |
B29D 11/00 20060101
B29D011/00; B26D 3/06 20060101 B26D003/06; G02F 1/1335 20060101
G02F001/1335; B29C 33/38 20060101 B29C033/38 |
Claims
1. A method of forming an uneven structure on a substrate,
comprising: using a hard tool to penetrate into a mold to cut a
first trench and a second trench in an order on a surface of a
mold, wherein the hard tool has a smoothly-curved shape such that
the transverse width of each of the first trench and the second
trench increases as the penetrating depth of the hard tool
increases, wherein when each of the first trench and the second
trench marches along a first direction, the penetrating depth of
the hard tool is controlled by repeating moving the hard tool up
and down to cut the mold such that the transverse width of each of
the first trench and the second trench varies according to the
controlled penetrating depth of the hard tool, wherein the first
trench and the second trench completely overlap with each other
with no space therebetween; and using the surface of the mold to
emboss a thin film on a substrate.
2. The method according to claim 1, wherein each of the first
trench and the second trench is cut along the first direction by
maintaining the position of the hard tool substantially along a
straight line in the first direction.
3. The method according to claim 1, wherein each of the first
trench and the second trench has a longitudinal axis between the
opposing edges thereof.
4. The method according to claim 1, wherein the substrate is an
optical substrate having a light input surface and a light output
surface, and the uneven structure is formed on the light input
surface of the substrate.
5. The method according to claim 4, wherein the smoothly-curved
shape is a lenticular shape such that the uneven structure is a
lenticular structure.
6. The method according to claim 1, wherein the substrate is an
optical substrate having a light input surface and a light output
surface, and the uneven structure is formed on the light output
surface of the substrate.
7. The method according to claim 6, wherein the smoothly-curved
shape is a lenticular shape such that the uneven structure is a
lenticular structure.
8. The method according to claim 1, wherein the surface of the
uneven structure has roughed or textured structure for
diffusion.
9. The method according to claim 1, wherein a portion of the uneven
structure corresponding to one of the first trench and the second
trench extends from a first edge of the substrate to a second edge
of the substrate.
10. The method according to claim 1, wherein a portion of the
uneven structure corresponding to one of the first trench and the
second trench extends from an edge of the substrate to a point
inside the surface area of the substrate.
11. The method according to claim 1, wherein a portion of the
uneven structure corresponding to one of the first trench and the
second trench extends from a first point inside the surface area of
the substrate to a second point inside the surface area of the
substrate.
12. An uneven structure is formed by using a structured surface
corresponding to the uneven structure of a mold to emboss a thin
film on a substrate, wherein the structured surface corresponding
to the uneven structure of the mold is formed by using a hard tool
to penetrate into the mold to cut a first trench and a second
trench in an order on the surface of the mold, wherein the hard
tool has a smoothly-curved shape such that the transverse width of
each of the first trench and the second trench increases as the
penetrating depth of the hard tool increases, wherein when each of
the first trench and the second trench marches along a first
direction, the penetrating depth of the hard tool is controlled by
repeating moving the hard tool up and down to cut the mold such
that the transverse width of each of the first trench and the
second trench varies according to the controlled penetrating depth
of the hard tool, wherein the first trench and the second trench
completely overlap with each other with no space therebetween.
13. A method of mold making, comprising using a hard tool to
penetrate into a mold to cut a first trench and a second trench in
an order on a surface of a mold, wherein the hard tool has a
smoothly-curved shape such that the transverse width of each of the
first trench and the second trench increases as the penetrating
depth of the hard tool increases, wherein when each of the first
trench and the second trench marches along a first direction, the
penetrating depth of the hard tool is controlled by repeating
moving the hard tool up and down to cut the mold such that the
transverse width of each of the first trench and the second trench
varies according to the controlled penetrating depth of the hard
tool, wherein the first trench and the second trench completely
overlap with each other with no space therebetween.
14. A method of forming an optical film, comprising: providing a
substrate having a light input surface and a light output surface;
using the method recited in claim 1 to form a uneven structure on
the light input surface of the substrate for diffusing the light
entering the optical film; and forming a prismatic structure on a
light output surface of the substrate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 14/469,572 filed on Aug. 26, 2014, which is a
continuation-in-part of U.S. patent application Ser. No. 14/166,842
filed on Jan. 28, 2014, which is a continuation-in-part of U.S.
patent application Ser. No. 13/073,859, now U.S. Pat. No.
8,638,408, which claims priority of (a) U.S. Provisional
Application Ser. No. 61/318,061 filed on Mar. 26, 2010; and (b)
U.S. Provisional Application Ser. No. 61/406,094 filed on Oct. 22,
2010. All of these applications are incorporated by referenced
herein in their entirety.
BACKGROUND
[0002] 1. Field of Invention
[0003] The present invention relates to optical substrates having a
structured surface, particularly to optical substrates for
brightness enhancement and diffusion, and more particularly to
brightness enhancement and diffusion substrates for use in flat
panel displays having a planar light source.
[0004] 2. Description of Related Art
[0005] Flat panel display technology is commonly used in television
displays, computer displays, and displays in handheld electronics
(e.g., cellular phones, personal digital assistants (PDAs), digital
cameras, tablets, etc.). Liquid crystal display (LCD) is a type of
flat panel display, which deploys a liquid crystal (LC) module
having an array of pixels to render an image.
[0006] FIG. 1 illustrates an example of an LCD display. A backlight
LCD 10 comprises a liquid crystal (LC) display module 12, a planar
light source in the form of a backlight module 14, and a number of
optical films interposed between the LC module 12 and the backlight
module 14. The LC module 12 comprises liquid crystals sandwiched
between two transparent substrates, and control circuitry defining
a two-dimensional array of pixels. The backlight module 14 provides
planar light distribution, either of the backlit type in which the
light source extends over a plane, or of the edge-lit type as shown
in FIG. 1, in which a linear light source 16 is provided at an edge
of a light guide 18. A reflector 20 is provided to direct light
from the linear light source 16 through the edge of the light guide
18 into the light guide 18. The light guide 18 is structured (e.g.,
with a tapered plate and light reflective and/or scattering
surfaces 30 defined on the bottom surface facing away from the LC
module 12) to distribute and direct light through the top planar
surface facing towards LC module 12. The optical films may include
upper and lower diffuser films 22 and 24 that diffuse light from
the planar surface of the light guide 18. The optical films further
includes upper and lower structured surface, optical substrates 26
and 28, which redistribute the light passing through such that the
distribution of the light exiting the films is directed more along
the normal to the surface of the films. The optical substrates 26
and 28 are often referred in the art as luminance or brightness
enhancement films, light redirecting films, and directional
diffusing films. The light entering the LC module 12 through such a
combination of optical films is uniform spatially over the planar
area of the LC module 12 and has relatively strong normal light
intensity.
[0007] The main function of brightness enhancement films 26 and 28
is to improve the brightness of overall backlight module. The
effect of brightness enhancement films is to increase the amount of
light emitted at small angles to the axis of the display by
reducing the amount emitted at greater angles. Thus, as one looks
at a display at increasing angles with respect to the axis, the
perceived brightness will decline. Between 35 and 45 degrees the
perceived brightness will decline very rapidly. This effect is
known as a sharp cutoff.
[0008] In the backlight LCD 10, brightness enhancement films 26 and
28 use longitudinal prismatic structures to direct light along the
viewing axes (i.e., normal to the display), which enhances the
brightness of the light viewed by the user of the display and which
allows the system to use less power to create a desired level of
on-axis illumination. The brightness enhancement films 26 and 28
have a light input surface that is smooth or glossy, through which
light enters from the backlight module. Heretofore, many LCDs used
two brightness enhancement film layers (as in the LCD in FIG. 1)
that are rotated about an axis perpendicular to the plane of the
films, relative to each other such that the longitudinal
peaks/grooves in the respective film layers are at 90 degrees
relative to each other, thereby collimating light along two planes
orthogonal to the light output surface.
[0009] When the glossy bottom surface of the brightness enhancement
film 26 above the structured surface of the other brightness
enhancement film 28, it has been experienced that the optical
interaction between the glossy surface of top brightness
enhancement film 26 and the structured surface and/or glossy
surface of the lower brightness enhancement film 28 creates
undesirable visible artifacts in the display image in the form of
interference fringes (i.e., bright and dark repeated patterns) that
are observable in the display image. These bright and dark patterns
may also be generated between the upper brightness enhancement film
26 and the adjacent surface of the LC module 12 absenting an upper
diffuser film 22 (FIG. 1). Undesirable image affecting effects
arising from flaws and non-uniformities such as interference
fringes, cutoff effects (rainbow), physical defects, flows, stains,
can be masked by using an upper diffuser film (e.g., diffuser film
22 above brightness enhancement film 26 in FIG. 1).
[0010] There is an increasing need for reducing power consumption,
thickness and weight of LCDs, without compromising display quality
of the LCDs. Accordingly, there is a need to reduce power
consumption, weight and thickness of backlight modules, as well as
thicknesses of the various optical films. In this regard, many
light directing techniques have been developed to reduce power
consumption without compromising display brightness. Some
developments are directed to the design of the backlight module
(i.e., designing structures of the components of the backlight
module 14 in FIG. 1, comprising the light source 16 and reflector
20, and light guide 18, to improve overall light output
performance. In addition, other developments are directed to
diffuser films 22 and 24, and luminance/brightness enhancement
films 26 and 28.
[0011] Heretofore, to reduce the overall thickness of the optical
films in LCDs, much effort had been directed to reducing the number
of the optical films, from four films (e.g., optical films 22, 24,
26 and 28 in FIG. 1) to three films. In this regard, one approach
is to keep the low diffuser film 24 and low brightness enhancement
film 28 as separate structures, but the functions of the top
diffuser film 22 and top brightness enhancement film 26 are
combined and merged into a single hybrid film structure. The
three-film type display has been widely adopted in handheld
electronic devices and notebooks, where it is particularly
desirable to push the envelope to reduce overall size of such
devices.
[0012] Various efforts also have been undertaken to develop hybrid
brightness enhancement films. Referring to FIG. 2, U.S. Pat. No.
5,995,288 disclosed a coating layer of particles provided on the
underside of the optical substrate, on the opposite side of the
substrate with respect to the structured surface on the top side. A
glossy surface is no longer present at the underside of the optical
substrate. The added particles achieve the effect of scattering
light for light diffusion. Referring to FIG. 3, U.S. Pat. No.
5,598,280 disclosed a method to form small projections on the
underside of the optical substrate to improve uniformity in
luminance by light diffusion. Such diffusion treatments will hide
many of the interference fringes, making them invisible to the
user. One of the disadvantages of these approaches is that light
scattering decreases on-axis gain. Moreover, the hybrid brightness
enhancement films are also less effective in directing light within
the desirable viewing angle.
[0013] Others have explored modifying the structure of prism
surface of the structured surface of the optical substrate. For
example, referring to FIGS. 4A and 4B, U.S. Pat. No. 6,798,574
provides fine protrusions on the prism surface of the structured
surface of the optical substrate, which is supposed to spread light
in a certain direction with a wider angle.
[0014] Accordingly, all the foregoing hybrid brightness enhancement
films involve weakened light output directivity. Moreover, the
overall brightness or luminance for the foregoing films is
significantly reduced. Further, all the above-mentioned hybrid
brightness enhancement films involve relatively complex structures
requiring relatively higher manufacturing costs.
[0015] Because the composite film used in the portable apparatus is
thinner, the product has a bad stiffness and some undesired
phenomenon (e.g., Newton's ring, wet-out) easily happens. Moreover,
people use the portable apparatus in a short-distance manner, and
rainbow phenomenon easily affects display quality. Conventionally,
the backside of the substrate is designed with high haze to reduce
the above optical defects, but brightness also decays.
[0016] There remains a need for an optical substrate having a
structure that both enhances brightness and provides effective
diffusion, and overcoming the shortcomings of the prior art
multifunctional optical films.
SUMMARY OF THE INVENTION
[0017] The present invention relates to a diffused prism substrate
having both light-collimating and light-diffusing functions. More
particularly, the present invention is directed to an optical
substrate that possesses a structured surface that enhances
luminance or brightness by collimating light and enhances diffusion
of light.
[0018] In one aspect of the present invention, the optical
substrate is in the form of a film, sheet, plate, and the like,
which may be flexible or rigid, having a structured prismatic
surface and an opposing structured lenticular surface. In one
embodiment, the structured lenticular surface includes
shallow-curved lens structure (e.g., convex lens). Adjacent
shallow-curved lens structure may be continuous or contiguous, or
separated by a constant or variable spacing. The lens structure may
have a longitudinal structure with a uniform or varying cross
section. The lenticular lenses may have a laterally meandering
structure. Sections of adjacent straight or meandering lenticular
lenses may intersect or partially or completely overlap each other.
In a further embodiment, the lenticular lenses may be in the form
of lenticular segments instead of a continuous structure between
opposing edges of an optical substrate. The lenticular segments may
have regular, symmetrical shapes, or irregular, asymmetrical
shapes, which may be intersecting or overlapping. The surfaces of
lenticular lenses, including lenticular segments, may be textured
to further effect diffusion.
[0019] In a further aspect of the present invention, the
shallow-curved lens structure is provided with isolated ripples, in
the form of a single knot, or a series of knots.
[0020] In accordance with the present invention, the structured
surfaces provide both light collimation and light diffusion
characteristics, which may reduce certain undesired optical effects
such as wet-out, Newton's rings, interference fringes and
cutoff-effect (rainbow) without significantly reducing overall
brightness.
[0021] In another aspect of the present invention, the primary
objective of the invention is to provide a brightness enhancement
film having a structured underside surface, which avoids the glossy
underside surface to effectively prevent the absorption (wet-out)
between the underside of the film and the surface of optical
elements in contact with the underside. A further objective of the
invention is to provide a brightness enhancement film having the
characteristic of improved brightness enhancement effect with
minimum diffusion effect.
[0022] In one embodiment, a structured prismatic surface is
provided on one major surface and a structured lenticular surface
is provided on an opposite major surface of a substrate, wherein
the included angle .alpha. between the longitudinal axes of the
prisms and the lenticular lenses are substantially 0.degree..
[0023] The lenticular surface has a structure comprising a
plurality of convex curved surfaces, each being a cylindrical
surface formed with a large radius to render the lenticular surface
close to a flat surface, but with surface features having a slight
convex curvature. The lenticular surface structures therefore have
very little or minimal light diffusion characteristics, so that
overall brightness of the light transmitted through the lenticular
surface would not be reduced by the lenticular surface. By using
low refractive index resin material for the structure that defines
the lenticular surface features, the overall brightness of LCD can
be further increased effectively.
[0024] Another objective of the invention is to provide a
brightness enhancement film having the characteristics of reduced
distortion and/or warpage. By controlling the shrinkage rate of the
resin material used for the structure (e.g., a layer of material)
that defines the prismatic surface features to be substantially
similar or approximately to the shrinkage rate of the resin
material used for the structure (e.g., a layer of material) that
defines the lenticular surface features, the two structured
surfaces of the brightness enhancement film can reduce distortion
or warpage of the film. In one embodiment, the lenticular surface
and the prismatic surface are defined by separate layers bonded
together to form the brightness enhancement film. An intermediate
support substrate may be provided, wherein the separate lenticular
layer and the prismatic layer are bonded to two opposite major
surfaces of the support substrate. In another embodiment, the
lenticular surface and the prismatic surface are defined by the
same layer structure (e.g., a monolithic or unitary layer).
[0025] Another objective of the invention is to provide a
brightness enhancement film having the characteristics of reducing
the moire interference pattern between the structured prismatic
surface and an opposite lenticular structured surface. In one
embodiment, the width and/or pitch or the centerline spacing of the
lenticular lenses at the lenticular surface is significantly
greater than the width and/or pitch or centerline spacing of the
prismatic structures at the prismatic surface. The radius of the
lenticular lens structure is large, so as to render the underside
surface of the brightness enhancement film close to a flat surface,
but with surface features having a slight convex curvature. As a
result of the larger pitch/centerline spacing and large radius of
curvature, the moire interference pattern between the prismatic
surface and the opposite lenticular surface are significantly
reduced to a minimum.
[0026] Another objective of the invention is to provide a method of
forming an uneven structure on a substrate. The method comprises:
using a hard tool to penetrate into a mold to cut a first trench
and a second trench in an order on a surface of a mold, wherein the
hard tool has a smoothly-curved shape such that the transverse
width of each of the first trench and the second trench increases
as the penetrating depth of the hard tool increases, wherein when
each of the first trench and the second trench marches along a
first direction, the penetrating depth of the hard tool is
controlled by repeating moving the hard tool up and down to cut the
mold such that the transverse width of each of the first trench and
the second trench varies according to the controlled penetrating
depth of the hard tool, wherein the first trench and the second
trench completely overlap with each other with no space
therebetween; and using the surface of the mold to emboss a thin
film on a substrate. The uneven structure has the following
advantages: a. back light can effectively penetrate the uneven
structure without decaying to achieve the optimized brightness
gain; b. it can avoid moire resulting from more regular prismatic
structure; c. it is changed from one-dimensional lenticular
structure to two-dimensional curved structure to effectively
increase diffusion range of the optical film and screening
property.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] For a fuller understanding of the nature and advantages of
the invention, as well as the preferred mode of use, reference
should be made to the following detailed description read in
conjunction with the accompanying drawings. In the following
drawings, like reference numerals designate like or similar parts
throughout the drawings.
[0028] FIG. 1 schematically illustrates the structure of a prior
art LCD.
[0029] FIGS. 2, 3, 4a and 4b illustrate prior art hybrid brightness
enhancement optical and diffusion substrates.
[0030] FIG. 5 schematically illustrates the structure of a LCD,
which incorporate the optical substrate in accordance with one
embodiment of the present invention.
[0031] FIG. 6a is a schematic perspective view of an optical
substrate having structured light input and output surfaces, in
accordance with one embodiment of the present invention. FIGS. 6b
to 6d are sectional views of the optical substrate in FIG. 6a.
[0032] FIG. 7 shows comparative parametric study of candela
distribution curves for a Lambertian light source incident at
optical substrates having different light input and output
surfaces.
[0033] FIG. 8 is a schematic sectional view illustrating the
lenticular surface structure.
[0034] FIGS. 9a and 9b schematically illustrate a lenticular
surface structure in accordance with an embodiment of the present
invention.
[0035] FIGS. 10a and 10b schematically illustrate a lenticular
surface structure in accordance with another embodiment of the
present invention.
[0036] FIGS. 11a and 11b schematically illustrate a lenticular
surface structure in accordance with yet another embodiment of the
present invention.
[0037] FIGS. 12a and 12b schematically illustrate a lenticular
surface structure in accordance with still yet another embodiment
of the present invention.
[0038] FIGS. 13a and 13b schematically illustrate a lenticular
surface structure in accordance with a further embodiment of the
present invention.
[0039] FIGS. 14a to 14f schematically illustrate a lenticular
surface structure in accordance with another further embodiment of
the present invention.
[0040] FIGS. 15a to 15f schematically illustrate a lenticular
surface structure in accordance with still a further embodiment of
the present invention.
[0041] FIGS. 16a and 16b schematically illustrate a lenticular
surface structure in accordance with yet another embodiment of the
present invention.
[0042] FIG. 17 are schematic views of a lenticular segment in
accordance with one embodiment of the present invention.
[0043] FIGS. 18a to 18d are schematic views of a lenticular segment
in accordance with another embodiment of the present invention.
[0044] FIGS. 19a to 19d are schematic views of a lenticular segment
in accordance with a further embodiment of the present
invention.
[0045] FIGS. 20a to 20d are schematic views of a lenticular segment
in accordance with yet another embodiment of the present
invention.
[0046] FIG. 21a is a schematic view of a lenticular segment in
accordance with a still further embodiment of the present
invention; FIG. 21b is an SEM photograph of the lenticular segments
in FIG. 21a.
[0047] FIGS. 22a to 22d illustrate a knotted lenticular structure
in accordance with one embodiment of the present invention.
[0048] FIG. 23a to FIG. 23c illustrate a rippled lenticular
structure in accordance with one embodiment of the present
invention.
[0049] FIGS. 24a and 24b are photographs of optical substrates
comparing cutoff effect.
[0050] FIG. 25 illustrates an electronic device comprising an LCD
panel that incorporates the inventive optical substrate of the
present invention, in accordance with one embodiment of the present
invention.
[0051] FIG. 26 is a schematic top view of a lenticular surface
structure comprising lenticular segments in accordance with a
further embodiment of the present invention.
[0052] FIG. 27 is a schematic underside perspective view of a
brightness enhancement film, in accordance with a further
embodiment of the present invention.
[0053] FIG. 28. is a schematic top perspective view of a variation
of the brightness enhancement film of FIG. 27, in accordance with a
further embodiment of the present invention.
[0054] FIG. 29 is a schematic sectional view illustrating the
parallel relationship of the lenticular surface structure and the
prismatic surface structure.
[0055] FIG. 30 is a schematic underside perspective view of a
brightness enhancement film, in accordance with a further
embodiment of the present invention.
[0056] FIG. 31 is a schematic top view of the lenticular surface
structure of the brightness enhancement film of FIG. 30.
[0057] FIG. 31 is a schematic top view of the lenticular surface
structure of the brightness enhancement film of FIG. 30.
[0058] FIG. 32 is a schematic sectional view of a brightness
enhancement film, in accordance with another embodiment of the
present invention, illustrating a staggered relationship between
the prism and lenticular lenses
[0059] FIG. 33 to FIG. 37 illustrate a top view of a portion of
trenches formed on the surface of the mold in various embodiments
of the present invention, wherein opposing edges of each trench is
shown for convenience.
[0060] FIG. 38a illustrates a top view of the trench having a first
longitudinal axis not located between the opposing edges thereof in
FIG. 33 to FIG. 36.
[0061] FIG. 38b illustrates a top view of the trench having a first
longitudinal axis located between the opposing edges thereof in
FIG. 37.
[0062] FIG. 39a is a schematic three-dimensional view of the mold
having a plurality of trenches distributed across the surface
thereof.
[0063] FIG. 39b is a schematic top view of FIG. 39a.
[0064] FIG. 39c is a schematic three-dimensional view of the
substrate having an uneven structure (e.g., segments) formed
thereon by embossing a thin film on the substrate.
[0065] FIG. 39d is a schematic top view of FIG. 39c.
DETAIL DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0066] The present description is of the best presently
contemplated mode of carrying out the invention. This invention has
been described herein in reference to various embodiments and
drawings. This description is made for the purpose of illustrating
the general principles of the invention and should not be taken in
a limiting sense. It will be appreciated by those skilled in the
art that variations and improvements may be accomplished in view of
these teachings without deviating from the scope and spirit of the
invention. The scope of the invention is best determined by
referenced to the appended claims.
[0067] The present invention relates to a diffused prism substrate
having both light-collimating and light-diffusing functions. More
particularly, the present invention is directed to an optical
substrate that possesses a structured surface that enhances
luminance or brightness by collimating light and enhances diffusion
of light. In one aspect of the present invention, the optical
substrate is in the form of a film, sheet, plate, and the like,
which may be flexible or rigid, having a prismatic structured
surface and an opposing lenticular structured surface. In
accordance with the present invention, the structured surfaces
provide light diffusion characteristics, which may reduce certain
undesired optical effects such as wet-out, Newton's rings or
interference fringes without significantly reducing overall
brightness.
[0068] In the context of the present invention, the inventive
optical substrate may be adopted in display devices having display
panels that may be flat or curved, and rigid or flexible, which
comprise an array of display pixels. Planar light source refers to
a light source that provides illumination to cover an area of the
array of display pixels. Accordingly, for display panels having a
curved image plane of display pixels (such panels may be rigid or
flexible), the backlight would cover the array of display pixels in
the curved plane, to effectively provide illumination coverage to
the curved image plane.
[0069] The present invention will be further described below in
connection with the illustrated embodiments.
[0070] FIG. 5 schematically illustrates an example of a flat panel
display. A backlight LCD 110, in accordance with one embodiment of
the present invention, comprises a liquid crystal (LC) display
module 112, a planar light source in the form of a backlight module
114, and a number of optical films interposed between the LC module
112 and the backlight module 114. The LC module 112 comprises
liquid crystals sandwiched between two transparent substrates, and
control circuitry defining a two-dimensional array of pixels. The
backlight module 114 provides planar light distribution, either of
the backlit type in which the light source extends over a plane, or
of the edge-lit type as shown in FIG. 5, in which a linear light
source 116 is provided at an edge of a light guide 118. A reflector
is provided to direct light from the linear light source 116
through the edge of the light guide 118 into the light guide 118.
The light guide is structured (e.g., with a tapered or flat plate
and light reflective and/or scattering surfaces defined on the
bottom surface facing away from the LC module 112) to distribute
and direct light through the top planar surface facing towards LC
module 112. A reflector 120 may be provided to facilitate trapping
light escaping through the underside of the light guide 118 and
redirecting towards back to the light guide 118.
[0071] In the illustrated embodiment, there are two structured
optical substrates 126 and 128 (which may be similar in structure)
in accordance with the present invention, which are arranged with
the longitudinal prism structures generally orthogonal between the
two substrates. In FIG. 5, the two substrates 126 and 128 are
schematically illustrated, which shows the prism structures on the
substrates appearing parallel to one another (i.e., included angle
.alpha.=0.degree.; see also FIG. 6a). Typically, prism structures
are rotated with an include angle greater than 0.degree., which can
be visualized without requiring further illustration. The
structured optical substrates 126 and 128 are structured to diffuse
light as well as enhance luminance or brightness, redirecting light
out of the display. The light entering the LC module 112 through
such a combination of optical films is uniform spatially over the
planar area of the LC module 112 and has relatively strong normal
light intensity. The structured optical substrate 126 and 128
obviate the need for a separate diffuser sheet between the LC
module 112 and the upper structured optical substrate 126. This
would reduce the overall thickness of the LCD 110. Further, the
structured optical substrates 126 and 128 in accordance with the
present invention would reduce interference fringe from being
created between the substrates, and between the upper substrate and
the adjacent LC module 112. Alternatively, only one of the optical
substrates 126 and 128 need to be structured in accordance with the
present invention (e.g., only the upper optical substrate 126), to
provide acceptable interference fringe level and optical diffusion
effect. Alternatively, only one of the optical substrates 126 and
128 is provided in the LCD 110.
[0072] While the backlight module 114 is shown with a light source
116 placed at an edge of the light guide plate 118, the backlight
module may be of another light source configuration, such as an
array of LEDs positioned at an edge of a light guide, or a planar
array of LEDs in place of the light guide, without departing from
the scope and spirit of the present invention.
[0073] While the illustrated embodiment of the LCD 110 does not
include additional pure, the optical films in the LCD 110 may
include optional upper and/or lower diffuser films, without
departing from the scope and spirit of the present invention. In
other words, it is well within the scope of the present invention
to replace the brightness enhancement films 26 and/or 28 in the LCD
10 shown in FIG. 1, to achieve the benefits of the present
invention. It is noted that a diffuser film or layer is
distinguishable from an optical substrate for brightness
enhancement (i.e., brightness or luminance enhancement film
discussed below), in that the diffuser film does not have prismatic
structures. Diffuser film primarily scatters and spreads light,
instead of primarily directing light to enhance luminance in a
direction out of the display as in the case of a luminance
enhancement film.
[0074] The optical substrate of the present invention has prismatic
structures and lenticular structures on opposing sides, which are
configured to both enhance luminance and diffuse light.
Specifically, the optical substrate shown in FIG. 5 includes
opposing structured surfaces in accordance with the present
invention, which diffuse light as well as redistribute the light
passing through such that the distribution of the light exiting the
films is directed more along the normal to the surface of the
films.
[0075] FIG. 6a illustrates an optical substrate that combines
prismatic and lenticular structures on opposing sides of the
substrate, in accordance with one embodiment of the present
invention, which can be used as the structured optical substrate
126 and/or 128 in the LCD 110 in FIG. 5. The optical substrate 50
has a structured lenticular surface 52 and a structured prismatic
surface 54. In this illustrated embodiment, the structured
prismatic surface 54 is a light output surface and the structured
lenticular surface 52 is a light input surface.
[0076] The prismatic surface 54 includes parallel rows of
contiguous or continuous longitudinal prisms 58, extending between
two opposing edges of the substrate 50. In the embodiment of FIG.
6a, the rows of longitudinal prisms 58 are arranged in parallel
laterally (side-by-side), defining parallel peaks 60 and valleys
62. The sectional profile of the peak 60 is symmetrical about peak
in this embodiment (viewed in the x-z plane). The peak vertex angle
may be right angled, and the peaks are of constant or similar
height and/or the valleys are of constant or similar depth, across
the plane of the prismatic surface 54. The distance or pitch
between adjacent peaks/valleys is constant in the illustrated
embodiment of FIG. 6a.
[0077] For ease of reference, the following orthogonal x, y, z
coordinate system will be adopted in explaining the various
directions. For the embodiment shown in FIG. 6a, the x-axis is in
the direction across the peaks 60 and valleys 62, also referred to
as the lateral or transverse direction of the prisms 58. The y-axis
is orthogonal to the x-axis, in a generally the longitudinal axis
or direction of the prisms 58. The longitudinal direction of prisms
58 would be in reference to the general direction in which the
peaks 60 proceed from one end to another end of the prisms 58. The
prismatic surface 54 lies in an x-y plane. For a rectangular piece
of the optical substrate, the x and y-axes would be along the
orthogonal edges of the substrate. The z-axis is orthogonal to the
x and y-axes. The edge showing the ends of the laterally arranged
15 rows of prisms 58 lies in the x-z plane, such as shown in FIG.
6a, which also represents a sectional view in the x-z plane. The
prisms 58 each has a constant sectional profile in the x-z plane.
References to cross sections of prisms 58 would be sections taken
in x-z planes, at various locations along the y-axis. Further,
references to a horizontal direction would be in an x-y plane, and
references to a vertical direction would be along the
z-direction.
[0078] The lenticular structured surface 52 comprises a
shallow-curved lens structure (e.g., a convex or concave lens
structure, or a combination of convex and concave). Particularly,
the lenticular structured surface 52 includes parallel, contiguous
or continuous rows of lenticular lenses 56, each extending in the
x-direction continuously between two opposing edges of the
substrate 50. The curved surfaces of adjacent lenticular lenses
intersect, defining parallel grooves 51 and crowns 59. For the
lenticular lenses 56, the y-axis is in the direction across the
grooves 51 and crowns 59, also referred to as the lateral or
transverse direction of the lenticular lenses 56. The x-axis
represents the longitudinal axis or direction of the lenticular
lenses 56. The longitudinal direction of lenticular lenses would be
in reference to the general direction in which the crowns 59
proceed from one end to another end of the lenticular lenses 56.
The edge showing the ends of the laterally arranged rows of
lenticular lenses 56 lies in the y-z plane, such as shown in FIG.
6a, which also represents a sectional view in the y-z plane. The
lenticular lenses 56 each has a constant sectional profile in the
y-z plane. References to cross sections of lenticular lenses 56
would be sections taken in y-z planes, at various locations along
the x-axis. Further, references to a horizontal direction would be
in an x-y plane, and references to a vertical direction would be
along the z-direction.
[0079] Referring also to FIG. 6b to FIG. 6d, which illustrate
sectional views taken along the x-axis, the y-axis, and at an angle
45 degrees to the x and y axes. In the illustrated embodiment, the
structured prismatic surface 54 and the structured lenticular
surface 52 are generally parallel to each other in the overall
optical substrate structure (i.e., do not form an overall substrate
structure that is generally tapered like a light guide plate in a
backlight module, or that is concave or convex). In the illustrated
embodiment, the substrate 50 comprises three separate layers,
including a first structured layer 57 bearing the prismatic surface
of prisms 58, a second structured layer 55 bearing the lenticular
surface of lenticular lenses 56, and an intermediate planar base
layer 53 supporting the layers 55 and 57. The two structured layers
55 and 57 are adhered to the base layer 53 to form the overall
optical substrate 50. It can be appreciated that the optical
substrate may be formed from a single integrated physical layer of
material, instead of three separate physical layers, without
departing from the scope and spirit of the present invention. The
optical substrate 50 may be a unitary or monolithic body, including
a base portion bearing the surface structures of prisms and
lenticular lenses.
[0080] The structured prism surface 54 has a plurality of
triangular prisms 58 in the sectional view of FIG. 6b taken along
the x-z plane. The structured lenticular surface 52 has a plurality
of curved convex lenses 56 in the sectional view of FIG. 6c taken
along the y-z plane. The triangular prisms 58 lean next to each
other defining a contiguous or continuous prismatic structured
surface 54, while the lenticular lenses 56 also leans next to each
other defining a contiguous or continuous lenticular structured
surface 52. The lenticular structured surface 52 contributes to
diffusion function and may reduce certain undesired optical defects
such as wet-out, Newton's rings, and interference fringes.
[0081] In the illustrated embodiment of FIG. 6a, the longitudinal
direction of the lenticular lenses and the longitudinal direction
of the prisms are orthogonal. The longitudinal directions of the
lenticular lenses and the prisms may be configured at different
included angles .alpha.. The included angle .alpha. may range from
0.degree. to 90.degree., preferably 45.degree. to 90.degree., in
order to provide an optical substrate having satisfactory ability
to diffuse light while not significantly reducing the overall
brightness. The included angle .alpha. may be substantially
90.degree. to provide preferable performance. Alternatively, the
included angle .alpha. may be substantially 0.degree., as
illustrated in the embodiments illustrated in FIGS. 27-31, which
will be discussed in detail later below.
[0082] In the illustrated embodiment, the lenticular layer 55 and
the prism layer 57 may be made of the same or different material,
and the base layer 53 may be made of a same or different material.
The lenticular layer 55 and the prism layer 57 may be formed using
an optically transparent material, preferably a polymerizable
resin, such an ultraviolet or visible radiation-curable resin, such
as UV curable adhesive. Generally, the structured prismatic surface
54 and lenticular surface 52 are formed by applying a coatable
composition comprising a polymerizable and crosslinkable resin onto
a master mold or master drum and undergoing a hardening process.
For example, the prismatic and lenticular structures are formed on
the base layer 53 by die assemblies, press rolling machines, mold
pressing assemblies or other equivalent apparatuses. The base layer
53 may be made of a transparent material, such as
polyethylene-terephthalate (PET), polyethylene (PE), polyethylene
napthalate (PEN), polycarbonate (PC), polyvinyl alcohol (PVA), or
polyvinyl chloride (PVC). The base layer 53 may instead be made
from the same transparent material as the structured layers 55 and
57. The base layer 53 provides the necessary thickness to provide
structural integrity to the final film of optical substrate 50.
[0083] In another embodiment, the prismatic structured surface 54
can be integrately-formed by molding, pressing, embossing,
calendaring or extrusion onto the transparent base film, while the
structured lenticular surface 52 is manufactured separately on to
the transparent base layer 53 by UV curing with resin.
[0084] Further discussions of processes for forming a substrate
having structured surfaces may be referenced to U.S. Pat. No.
7,618,164, which had been incorporated by reference herein.
[0085] In still another embodiment, the structured lenticular
surface 52 can be integrally-formed by molding, pressing,
embossing, calendaring or extrusion onto the transparent base layer
53, while the prismatic structured surface 54 is manufactured
separately on to the transparent base layer 53 by UV curing with
resin.
[0086] In a further embodiment, the prismatic structured surface 54
may be formed integrally or separately onto a base film, while the
structured lenticular surface may also be formed integrally or
separately onto another base film. The two base films is combined
back to back by simply stacking or applying adhesives such as
pressure sensitive adhesive (PSA) to the films to form a structure
equivalent to the base layer 53. It is apparent that many
techniques and combinations of manufacture methods may be applied
to obtain the combination of the structured prismatic surface, the
structured lenticular surface and the base layer, or equivalent
thereof.
[0087] The dimensions of the optical substrate are generally as
follows, for example:
Thickness of base layer 53=tens of micrometers to several
millimeters Peak height of prism (as measured from the adjacent
surface of the base layer, or if a base layer is integral to the
prisms, as measured from the valley between adjacent
non-intersecting prisms)=tens to hundreds of micrometers Distance
of prism valley bottom from top of base layer=about 0.5 to hundreds
of micrometers Vertex angle of prism peaks=about 70 to 110 degrees
Pitch between adjacent prism peaks=tens to hundreds of micrometers
Crown height of lenticular lens (as measured from the adjacent
surface of the base layer, or if a base layer is integral to the
lenticular lens, as measured from the valley between
non-intersecting adjacent lenses)=1 to 300 micrometers Pitch
between adjacent crown heights=10 to several hundred
micrometers
[0088] The optical substrates in accordance with the present
invention may be used with LCDs to be deployed for displays, for
example, for televisions, notebook computers, monitors, portable
devices such as cell phones, digital cameras, PDAs and the like, to
make the displays brighter.
[0089] The effects of the lenticular surface 52 and the prismatic
surface 54 and their interactions for various optical substrate
configurations can be observed in reference to FIG. 7 shows
comparative parametric study of candela distribution curves for a
Lambertian light source incident at optical substrates having
different light input and output surfaces. The curves in solid
lines represent candela distributions in the X-direction, and the
curves in dotted line represent candela distributions in the Y
direction. For the examples illustrated in FIG. 7, the X-direction
is horizontal, and the Y-direction is into the page.
[0090] The candela distribution curve 201 in FIG. 7 shows the
candela distribution curve for a Lambertian light source, in the
absence of any optical substrate. The distributions in the X and Y
directions are same.
[0091] The candela distribution curve 202 in FIG. 7 shows the
result for a Lambertian light source incident on a planar PET film.
The candela distribution curves 202 are substantially similar to
the candela distribution curve 201.
[0092] The candela distribution curve 203 in FIG. 7 shows the
result for a Lambertian light source incident on an optical
substrate having a light output surface in the form of a
one-dimensional structured prismatic film with the longitudinal
axis of the prisms in the Y-direction, without any lenticular
structure. The candela distribution curve indicates an obvious
enhancement in distribution in primarily X-direction. This improves
the brightness by collimating light from a light input surface to a
light output surface in the on-axis direction. With the triangular
structure of the prismatic output surface of the optical substrate,
light is redirected in X-direction when passing through the optical
film.
[0093] The candela distribution curve 204 in FIG. 7 shows the
result for a Lambertian light source incident on an optical
substrate having a one-dimensional lenticular structured film, in
which the longitudinal axis of the lenticular lenses is in the
Y-direction. The candela distribution curve indicates light is
diverged in X-direction while passing through the lenticular
film.
[0094] The candela distribution curve 205 in FIG. 7 shows the
result of a Lambertian light source incident on an optical
substrate having a structured lenticular light input surface and a
structured prismatic light output surface. The longitudinal axes of
the two structured surfaces are rotated with respect to one another
by 90.degree., with the longitudinal axis of the prisms in the
Y-direction. The result indicates more enhanced light in the
X-direction and more diverged light (i.e., diffusion) in the
Y-direction.
[0095] The candela distribution curve 206 in FIG. 7 shows the
result of a Lambertian light source incident on another optical
substrate having a structured lenticular light input surface and a
structured prismatic light output surface. The longitudinal axes of
the two structured surfaces are rotated with respect to one another
by 0.degree., both in the Y-direction. The result indicates
enhanced light as well as diverged/diffused light in the same
direction.
[0096] In accordance with the above comparative study, it is
observed that a lenticular light input surface diverges light to
effect diffusion, and a prismatic light output surface enhances
light in the on-axis direction, in a scattering and refracting
manner.
[0097] In another embodiment of the invention, at least some
lenticular lenses do not intersect each other, leaving the adjacent
convex curved lens surfaces discontiguous or discontinuous. While
the embodiments discussed below are in reference to prisms having
longitudinal axis normal to the longitudinal axis of the lenticular
lenses (i.e., included angle .alpha.=90 degrees), the lenticular
surface discussed below are equally applicable to included angles
.alpha. that are within the range of 0 to 90 degrees (such as the
embodiment of .alpha.=0 degree discussed later below). FIG. 8 is a
cross-sectional view of an optical substrate 550 view in the y-z
plane (same plane as in FIG. 6b). The optical substrate 550
includes a base layer 510 and a plurality of lenticular lens 520
having convex curved surfaces 524 formed on the top surface of the
base layer 510, and longitudinal prisms 512 (similar to the prisms
58) formed on the bottom surface of the base layer 510. The surface
524 of each of the lenticular lenses 520 corresponds substantially
to a section of the surface of a circular cylinders 522 having a
radius "r" with center "O" in cross-section, which surface section
corresponds to a subtended angle .theta., and a subtended arc
between point "a" and "b" in cross-section. In the sectional view
shown in FIG. 8, the lens 520 corresponds to a segment of the
circle 522, which is bounded by the chord a-b and the arc a-b. As
shown in FIG. 8, adjacent arcuate surfaces 524 of lenticular lenses
520 do not contact one another to form a contiguous or continuous
lens surface, as compared to FIG. 6b. In this embodiment, the
surface 524 of each lens 520 "bottoms" onto the top of the base
layer 510, with a flat spacing between adjacent lenses. In this
embodiment, the lens width pitch 1 is the same for the
discontinuous lenses 520. The spacing pitch 2 may be the same or
different between adjacent discontinuous lenses.
[0098] In a preferred embodiment, the angle .theta. of lenticular
structure is in the range of 5 degrees to 90 degrees, more
preferably in the range of 20 degrees to 65 degrees. The height (H)
of the lenticular lens structure (measured from the top of the base
layer 510, or if the base layer is integral to the lenticular lens
structure, measured from the valley between adjacent
non-intesecting or non-overlapping lenticular lenses) is identical,
preferably in the range of 1 .mu.m to 100 .mu.m, more preferably in
the range of 2 .mu.m to 50 .mu.m. The curvature of the lenticular
lenses is the same. Prism 512 peak height=5 .mu.m to 100 .mu.m;
pitch of adjacent prism peaks=10 .mu.m to 500 .mu.m; thickness of
base layer 510=5 .mu.m to 1000 .mu.m; Pitch 1=5 .mu.m to 500 .mu.m;
Pitch 2=1 .mu.m to 100 .mu.m, preferably 0 .mu.m; distance between
centers O of adjacent lenses=5 .mu.m to 500 .mu.m.
[0099] In a preferred embodiment, the vertex angle of prisms 512 is
in the range of 70 degrees to 110 degrees, more preferably in the
range of 80 degrees to 100 degrees. In another preferred
embodiment, the vertical height (H) of the prism unit is in the
range of 10 .mu.m to 100 .mu.m, more preferably in the range of 20
.mu.m to 75 .mu.m. Alternatively, the prism unit may or may not
have the same vertical heights. In another preferred embodiment,
the horizontal pitch of the prisms 512 is in the range of 10 .mu.m
to 250 .mu.m, more preferably in the range of 15 .mu.m to 80
.mu.m.
[0100] FIG. 9a is a top perspective view and FIG. 9b is a sectional
view (in the y-z plane) of another embodiment of an optical
substrate 551. In this embodiment, the curvature and height of the
lenticular lenses 520' are respectively the same, and the distance
pitch 2 between two discontinuous lenticular lenses 520' of the
structured lenticular surface is the same. In this embodiment, the
surface 524' of each lens 520' does not bottom onto the top of the
base layer 510. The vertical height (H) of the lenticular lens
structures (measured from the top of the base layer 510, or if the
base layer is integral to the lenticular lenses, measured from the
valley between adjacent lenticular lenses) is identical, preferably
in the range of 1 .mu.m to 300 .mu.m, more preferably in the range
of 2 .mu.m to 50 .mu.m. The curvature of the lenticular lenses is
the same. Pitch 1=5 .mu.m to 500 .mu.m; Pitch 2=1 .mu.m to 100
.mu.m.
[0101] FIG. 10a and FIG. 10b illustrates another embodiment of an
optical substrate 552. In this embodiment, the distance pitch 2
between two discontinuous lenticular lenses 520'' of the structured
lenticular surface 524'' is variable or different across the
section. The height of the lenticular lenses (measured from the top
of the base layer 510, or if the base is integral to the lenticular
lenses, measured from the valley between non-intersecting adjacent
lenticular lens) is identical, preferably in the range of 1 .mu.m
to 100 .mu.m, more preferably in the range of 2 .mu.m to 50 .mu.m.
The curvature of the lenticular lenses is the same. Pitch 1=5 .mu.m
to 500 .mu.m; Pitch 2 varies between 1 .mu.m to 100 .mu.m.
[0102] FIGS. 11a and 11b illustrate still another embodiment of an
optical substrate 553. In this embodiment, the vertical height (H)
of the structures of the lenticular lenses 525 is variable.
Further, the radius of curvature of different lenticular lenses 525
may also vary and/or different lenticular surfaces may conform to
cylinders of different cross-sections other than a circle (e.g., an
ellipse or other cross-sections of regular or irregular geometries)
and further of varying sizes. Longitudinal lenticular structures
having a uniform cross-section defining other convex curve surface
profiles are also contemplated (e.g., same profile or different
profiles for different lenticular lenses). Pitch 1=5 .mu.m to 500
.mu.m; Pitch 2=1 .mu.m to 100 .mu.m; height varies 0.5 .mu.m to 300
.mu.m.
[0103] FIGS. 12a and 12b illustrate yet still another embodiment of
an optical substrate 554. In this embodiment, some of the adjacent
lenticular lenses intersect or partially overlap each other, thus
defining a contiguous or continuous lenticular structured surface
with some of the lenticular lenses 526 having an asymmetrical
cross-section (as viewed in the y-z plane shown in FIG. 12b). The
vertical height and curvature of the lenticular lenses 526 are
respectively the same between the lenses. Pitch 1=5 to 500 .mu.m;
the extent of intersection may be between 1 .mu.m to 50 .mu.m
overlap of the edges of adjacent lenticular lenses.
[0104] FIGS. 13a and 13b illustrate a further embodiment of an
optical substrate 555. In this embodiment, the lenticular lenses
527 are discontinuous across in the y-direction (as shown in the
illustrated sectional view). Portions of adjacent lenticular lenses
527 may be adjoining or contiguous. The lenticular lenses 527 swing
laterally (in the y-direction), along the longitudinal direction
(x-direction) of the lenses. In one embodiment, the lenticular
structure may be viewed as comprising rows of laterally meandering
longitudinal lenticular lenses and/or sections of continuous curved
segments (i.e., sections with a curve in a particular direction, or
generally C-shaped or S-shaped curve sections) coupled end-to-end
to form the overall meandering longitudinal lenticular lens
structure. In one embodiment, the laterally meandering rows of
longitudinal lenticular structures are arranged in parallel
laterally (side-by-side in the y-direction). In one embodiment, the
lateral waviness is regular with a constant or variable wavelength
and/or wave amplitude (or extent of lateral deformation). The
lateral waviness may generally follow a sinusoidal profile, or
other curved profile. In another embodiment, the lateral waviness
may be of random wavelength and/or wave amplitude. In one
embodiment, the vertical height, curvature, surface profile, and/or
width of the lenticular lenses 527 respectively may be the same for
adjacent lenses across a particular cross-sectional plane, and may
be constant or varying for different cross-sectional plane along
the longitudinal x-direction. Pitch 1=5 .mu.m to 500 .mu.m; Pitch
2=0 .mu.m to 100 .mu.m.
[0105] FIGS. 14a and 14b illustrate a modification of the
embodiment of FIGS. 13a and 13b. In this embodiment of an optical
substrate 556, some of the adjacent laterally meandering lenticular
lenses intersect or partially overlap each other, thus defining a
contiguous or continuous lenticular surface at some locations along
the length of each lenticular lens 528. Those adjacent lenticular
lenses 528 that intersect would have an asymmetrical cross-section
(as viewed in the y-z plane shown in FIG. 14b; see also FIG. 12b).
The lenticular lenses 528 have the same height. Other structures
may be similar to those in the embodiment of FIG. 13.
[0106] FIGS. 14c to 14f illustrate a variation of the laterally
meandering lenticular lenses 528 shown in FIGS. 14a and 14b. As
illustrated, part of the lenticular lenses 528' in FIGS. 14c to 14f
intersect or partially or completely overlap each other, thus
defining a contiguous or continuous lenticular structured surface
on the optical substrate 556'. Essentially, the lenticular lenses
528' combine the height varying feature of the lenticular lenses
528 in FIGS. 14a and 14b, and the intersecting feature of the
lenticular lenses 526 in FIGS. 12a and 12b. As shown in the x-y
plane of FIG. 14d, the lenticular lenses 528' are not all
longitudinally continuous from one edge to an opposing edge of the
optical substrate 556'. Some of the lenticular lens 528' appear as
longitudinal segments that are shorter, having a terminating end at
a place (e.g., 580 and 581), where one section of a lenticular lens
528' completely overlaps another lenticular lens 528'. There are
spaces or flats (e.g., at 582 and 583) between the lenticular
lenses 528'.
[0107] U.S. Pat. No. 7,618,164 incorporated in the present
invention by reference hereafter describes "Hard tools can be used
to cut the surface of the mold to form above-described the
structured surface (e.g., even structure) of the optical surface.
The hard tools may be diamond tools of very small size mounted on a
CNC (Computer Numeric Control) machine (e.g., turning, milling and
ruling/shaping machines)." The even structure in FIG. 14c to FIG.
14f can be formed by cutting trenches on the surface of the mold
through a control system (e.g., CNC system) and using the surface
of the molding to emboss a thin film on the substrate.
[0108] A portion of lenticular lenses 528' in FIG. 14c to FIG. 14f
result from overlap of the lenticular lenses 528 in FIG. 14a to
FIG. 14b; that is, a plurality of trenches are cut in an order on
the surface of the mold, each trench is cut in a first direction,
(if the trenches do not overlap, the lenticular lenses 528 can be
formed), then a portion of lenticular lenses 528' in FIG. 14c to
FIG. 14 can be formed by overlap of the trenches. From what FIG.
14c to FIG. 14f illustrate previously, the lenticular lenses 528'
are not all longitudinally continuous from one edge to an opposing
edge of the optical substrate 556'; that is, a portion of trenches
are cut off by the other trench(es) such that a portion of
lenticular lenses 528'(segments) of the uneven structure correspond
to the portion of a portion of trenches that is not cut off.
[0109] FIGS. 15a and 15b illustrate a further embodiment of an
optical substrate 557. In this embodiment, adjacent lenticular
lenses 529 are separated by a spacing, and the height varies along
the length of each lenticular lens in the x-direction. In this
illustrated embodiment, as the height varies along a lens, the
sectional surface profile varies in the x direction. The height
variation may generally follow a sinusoidal profile, or other
curved profile, in regular, constant, varying or random wavelength
and/or wave amplitude. The width of the lenses (e.g., pitch 1
between point "a" to point "b" as shown in FIG. 8) is the same for
adjacent lenses, and constant along each lens in the x-direction.
In an alternate embodiment, the width may also vary between
adjacent lenses or along the x-direction for one or more of the
lenses. The spacing (e.g., pitch 2 as shown in FIG. 8) between
lenses may be constant across a section as shown in FIG. 14b (also
shown in FIG. 9b) or may be varying across a section (e.g., as
shown in FIG. 10b). Pitch 1=5 .mu.m to 500 .mu.m; Pitch 2=0 .mu.m
to 100 .mu.m; range of height variations=1 .mu.m to 50 .mu.m.
[0110] FIGS. 15c to 15f illustrate a variation of the height
varying lenticular lenses 529 shown in FIGS. 15a and 15b. As
illustrated, the longitudinal lenticular lenses 529' in FIGS. 15c
to 15f intersect or partially overlap each other, thus defining a
contiguous or continuous lenticular structured surface on the
optical substrate 557'. Essentially, the longitudinal lenticular
lenses 529' combine the height varying feature of the lenticular
lenses 529 in FIGS. 15a and 15b, and the intersecting feature of
the longitudinal lenticular lenses 526 in FIGS. 12a and 12b. The
structure in FIGS. 15c to 15f can be formed by the following way:
(a) using a hard tool to penetrate into a mold to cut a plurality
of trenches in an order on a surface of a mold (maybe through a
control system), wherein the hard tool has a shape such that the
transverse width of each trench increases as the penetrating depth
of the hard tool increases, wherein when each of the plurality of
trenches marches along a first direction, the penetrating depth of
the hard tool is controlled by repeating moving the hard tool up
and down to cut the mold such that the transverse width of each of
the plurality of trenches varies according to the controlled
penetrating depth of the hard tool, wherein each adjacent two
trenches completely overlap with each other with no space
therebetween; (b) using the surface of the mold to emboss a thin
film on a substrate. When a trench marches along the first
direction, the transverse width of the trench has the maximum value
and the minimum value alternating with each other by repeating
moving the hard tool up and down such that the trench has a
structure in the form of the annelid; comparing with the trench
having the constant transverse width controlled by the constant
penetrating depth, it changes one-dimensional cylindrical structure
to two-dimensional structure in the form of the annelid so as to
increase the diffusion of the optical film. When two trenches
marches along the first direction (preferably along a straight line
in the first direction), the present invention solves the problem
"there exists a space between the traverse width of the former
trench and the traverse width of the latter trench having the
minimum at the same time" which guarantees that there is no flat
portion on the film embossed by the mold so as to increase the
diffusion performance. Preferably, use the hard tool to cut a
plurality of trenches in an order on the surface of the roll
through a CNC (Computer Numeric Control) system, wherein when each
trench is cut, the hard tool is not pulled away from the roll (when
the hard tool does not penetrate into the mold/roll, the mold/roll
has a unstructured surface; however, when the hard tool penetrates
into the mold/roll, the front end of the hard tool is kept below
the unstructured surface until the trench is completely formed); it
changes one-dimensional cylindrical structure to two-dimensional
structure in the form of the annelid such that there exists no
space between adjacent two trenches so as to increase the diffusion
of the optical film. Preferably, (the front end of) the hard tool
has a lenticular shape (as illustrated in FIG. 8, the front end of
the hard tool has an arc shape); comparing with the film embossed
by the mold cut by the hard tool having a prismatic shape, the film
embossed by the mold cut by the hard tool having a lenticular shape
has a better diffusion performance. However, the hard tool of the
present invention is not limited to have an arc shape, the hard
tool having a smoothly-curved shape to get a better diffusion
performance can be applied in the present invention. Preferably,
comparing with cutting each trench meandering along the first
direction, cutting each trench by maintaining the hard tool
substantially along a straight line in the first direction not only
shortens the time of the mold-making but also enhances the
precision of the mold to reduce the error of the mold-making (the
front end of the hard tool has an arc shape so as to guarantee that
each trench cut on the mold has a smooth arc shape and the film
embossed by the mold has a better diffusion performance).
[0111] FIGS. 16a to 16b illustrate still another embodiment of an
optical substrate 558. In this embodiment, instead of the
continuous longitudinal lenticular structure extending across the
entire optical substrate as in the prior embodiments, it is broken
into lenticular segments. Referring also to FIG. 17, each
lenticular segment 530 is generally in an elongated, slender
structure having rounded ends. The overall structure of the
lenticular segment 530 is symmetrical in the x-y plane, resembling
a segment of an ellipsoid. The top view of the structure of the
lenticular segment 530 shown in FIG. 17c is generally a
symmetrical, slender, elongated or flat elliptic-like structure.
The longitudinal sectional profile of the lenticular segment 530
shown in FIG. 17a is generally slender and elongated curved
surface, resembling the top of an ellipse. In the illustrated
embodiment of FIG. 16a, the lenticular segments 530 are arranged in
straight longitudinal rows in the X-direction, with the
longitudinal (or major) axis of the lenticular segments 530 aligned
with the longitudinal direction (i.e., X-direction) of the rows. In
an alternate embodiment, the planar geometry of the lenticular
segments may be asymmetric. The lenticular segments 530 are
isolated or separated from each other in this embodiment. The
transverse sectional profile of the lenticular segment 530 shown in
FIG. 17b is generally cylindrical surface, resembling the sectional
profiles in the earlier embodiments. In this embodiment, the
vertical height (H) along each lenticular segment may be viewed to
vary a great degree along the longitudinal x-direction. The overall
height of the lenticular segments 530 is the same. By controlling
the surface curvature, the ratio of the pitch (L) and height (H),
the lenticular segment 530 can effect light diffusion in the x-y
plane (i.e., along the x and y directions). The dimensions of the
segment 530: length L1=1 .mu.m to 5000 .mu.m; pitch L2=0.5 .mu.m to
2000 .mu.m; H=0.1 .mu.m to 500 .mu.m. The distribution of the
segments 530 is from about 30% to 100% coverage of the area of the
optical substrate. It is noted that 100% coverage means the
lenticular segments are overlapping (see, for example, FIG. 19 and
discussion below).
[0112] FIGS. 18 to 21 illustrate variations of the lenticular
segments on the structured lenticular surface of optical
substrates, in accordance with further embodiments of the present
invention. Other than the lenticular segments, the remaining
structures in the various embodiments may be similar to those in
FIG. 16.
[0113] In the embodiment of FIG. 18, the elliptic-like lenticular
segments 532 on the optical substrate 559 are asymmetrical (not
symmetrical) in the x-y plane, as compared to the lenticular
segment 530 in the FIG. 16 embodiment.
[0114] In the embodiment of FIG. 19, the elliptical-like lenticular
segments 534 are symmetrical, but intersect or partially overlap
each other on the optical substrate 560, as compared to the
lenticular segment 530 in the FIG. 16 embodiment. The illustrated
structured surface can provide better diffusion.
[0115] In the embodiment of FIG. 20, the elliptical-like lenticular
segments 535 are asymmetrical and intersect or partially overlap
each other on the optical substrate 561, as compared to the FIG. 19
embodiment. The illustrated structured surface can also provide
better diffusion.
[0116] In the embodiment of FIG. 21, the elliptical-like lenticular
segments 536 are symmetrical and intersect or partially overlap
each other on the optical substrate 562, similar to the FIG. 19
embodiment, but the surface of the lenticular segments 536 in this
embodiment is roughened or textured with dents, lines, cracks,
pits, and/or protrusions, etc. to increase diffusion effect. FIG.
21b shows an SEM photograph of the textured surface of the
lenticular segments. The lenticular structures in the other
embodiments disclosed herein may also be similarly textured.
[0117] FIG. 26 is a schematic top view illustrating a variation of
the arrangement of the lenticular lenses in the form of lenticular
segments 530 on the structured lenticular surface of optical
substrate 1558, in accordance with an alternate embodiment of the
present invention. Compared to the straight line alignment of the
lenticular segments 530 illustrated in FIG. 16, the lenticular
segments 530 in FIG. 26 are aligned in a longitudinal wavy row
extending in the longitudinal X-direction, with their longitudinal
(or major) axis following a generally wavy profile 1550. The wavy
profile 1550 may be regular, irregular, sinusoidal, and/or random
waveform or wavy profile. FIG. 26 is merely a schematic depiction
of the alignment of the lenticular segments in a single wavy row,
in accordance with one embodiment. For simplicity, only one wavy
row is illustrated in FIG. 26. Even though not illustrated in FIG.
26, there are multiple wavy rows at the lenticular surface of the
optical substrate 1558, wherein the wavy rows are arranged in
parallel and extend in the longitudinal X-direction. In other
embodiments, the lenticular segments may be symmetrical or
non-symmetrical, may intersect or partially overlap (in either or
both the longitudinal Y-direction or the lateral X-direction),
and/or may have textured surface, similar to the embodiments
disclosed in the earlier embodiments above.
Experimental Results
[0118] Various sample optical substrates have been evaluated for
the effect of angle and Refractive Index versus haze and gain, and
the effect on interference fringes.
[0119] Haze measurement is made on sample optical substrates having
only lenticular lenses on the light input surface without prisms on
the opposing light output surface. Haze is measured by placing the
respective optical substrates in a haze meter (e.g., Haze Turbidity
Meter by Nippon Denshoku Industries Co. Ltd., Model No.
NDH-2000).
[0120] Gain of sample optical substrates is evaluated using a
colorimeter (e.g., TopCon BM7 Luminance colorimeter), to determine
the on-axis luminance emitting from backlight through optical
substrates of the present invention, which have both structured
prismatic light output surface and structured lenticular light
input surface (i.e., prism structures and lenticular structures are
present on opposing sides of the optical substrate). On-axis
luminance is the intensity of light emitting normal to the test
samples. Data was reported as the luminance in candela per square
meter (cd/m.sup.2). For the evaluation of gain, a lower diffuser
sheet is placed on the backlight, which is interposed between the
backlight and each sample optical substrate under evaluation. No
other optical films or LC module is being used for gain evaluation.
The luminance value for each sample optical substrate is measured.
The luminance value of the same backlight with only the same lower
diffuser sheet is measured. The value of on-axis luminance gain is
expressed as the ratio of the measured luminance value of a sample
optical substrate (with the intermediate lower diffuser) to the
measured luminance value of the backlight with the lower diffuser
only.
[0121] Interference fringe effect of the sample optical substrates
of the present invention are simply observed by the naked eye using
the backlight, with intermediate layers of a lower diffuser sheet
placed on the backlight, and a prismatic luminance enhancement
sheet (with no lenticular structures on the light input side)
between the sample optical substrate and the lower diffuser
sheet.
[0122] The flat ratio is the ratio of Pitch 2/(Pitch 2+Pitch 1).
For all the experiments, pitch 1 is constant for the sample optical
substrates.
Experiment A
[0123] Table 1 shows the effects of the angle .theta. of the
lenticular structure (e.g., similar to embodiment shown in FIG. 6a,
with flat ratio at 0%) on gain and diffusion/haze. It has been
observed that interference fringes are eliminated and the gain
maintained between 1.49 and 1.54 for angle .theta. in the range of
16 degrees to 66 degrees.
TABLE-US-00001 TABLE 1 Haze (single side Gain lenticular (with
prism structure structure with no on the Lenticular structure Flat
prism light Radius Angle .theta. Refractive Angle .alpha. ratio
structure) output Dark and bright (.mu.m) (deg.) Index (deg.) % %
side) fringes 600 6 1.48 90 0 2.38 1.55 Observed 600 16 1.48 90 0
20.25 1.54 Observed 600 26 1.48 90 0 42.92 1.53 Very slight 58 36
1.48 90 0 58.04 1.53 Not observed 600 46 1.48 90 0 65.6 1.51 Not
observed 600 56 1.48 90 0 70.83 1.49 Not observed 58 66 1.48 90 0
72.9 1.51 Not observed 58 82 1.48 90 0 78.24 1.42 Not observed 58
106 1.48 90 0 79.09 1.25 Not observed 58 120 1.48 90 0 81.01 1.23
Not observed 58 144 1.48 90 0 81.18 1.20 Not observed
Experiment B
[0124] Table 2 shows the effects of the refractive index of the
lenticular structure (e.g., structure shown in FIGS. 6a and 8 with
zero flat ratio). At bigger angles .theta., haze is higher but gain
is lower. Haze will increase when the refractive index of
lenticular structure increases. However, the gain of optical
substrate will decrease. It appears that the preferred refractive
index of lenticular structure is in the range of 1.45 to 1.58.
TABLE-US-00002 TABLE 2 Haze (single side Gain lenticular (with
prism structure structure with no on the Lenticular structure Flat
prism light Radius Angle .theta. Refractive Angle .alpha. ratio
structure) output Dark and bright (.mu.m) (deg.) Index (deg.) % %
side) fringes 58 82 1.56 90 0 87.2 1.34 Not observed 58 66 1.56 90
0 75.7 1.48 Not observed 58 52 1.56 90 0 71.8 1.51 Not observed 58
36 1.56 90 0 63.0 1.51 Not observed 58 82 1.48 90 0 78.2 1.42 Not
observed 58 66 1.48 90 0 72.9 1.51 Not observed 58 52 1.48 90 0
68.4 1.53 Not observed 58 36 1.48 90 0 58.0 1.53 Not observed
Experiment C
[0125] Table 3 shows there is no significant change in haze and
gain while changing lenticular radius (e.g., structure shown in
FIGS. 6a and 8 with zero flat ratio). However, angle .theta. is
significant to changes in haze and gain.
TABLE-US-00003 TABLE 3 Haze (single side Gain lenticular (with
prism structure structure with no on the Lenticular structure Flat
prism light Radius Angle .theta. Refractive Angle .alpha. ratio
structure) output Dark and bright (.mu.m) (deg.) Index (deg.) % %
side) fringes 7.8 106 1.48 90 0 77.2 1.35 Not observed 23 106 1.48
90 0 81.5 1.34 Not observed 58 106 1.48 90 0 79.1 1.25 Not observed
7.8 66 1.48 90 0 70.5 1.51 Not observed 23 66 1.48 90 0 70.0 1.51
Not observed 58 66 1.48 90 0 72.9 1.51 Not observed 7.8 36 1.48 90
0 29.3 1.55 observed 23 36 1.48 90 0 50.9 1.54 Not observed 58 36
1.48 90 0 58.0 1.53 Not observed
Experiment D
[0126] Table 4 shows the effects of the flat ratio of the optical
substrate, such as embodiment shown in FIG. 9. At low flat ratio,
the optical substrate has higher haze and interference fringes may
be eliminated. When the flat ratio of the optical substrate is
higher, the ability to eliminate the interference fringes
decreased. The preferable flat ratio of the optical film does not
exceed 10%.
TABLE-US-00004 TABLE 4 Haze Gain (single side (with lenticular
prism structure structure with no on the Lenticular structure Flat
prism light Radius Angle .theta. Refractive Angle .alpha. ratio
structure) output Dark and bright (.mu.m) (deg.) Index (deg.) % %
side) fringes 58 106 1.48 90 7.76 74.7 1.27 Not observed 58 106
1.48 90 34.70 61.4 1.34 Observed 58 106 1.48 90 61.64 50.8 1.37
Observed
Experiment E
[0127] In this experiment, the two optical substrates are rotated
with respect to one another to vary the angle .alpha. (see
embodiment of FIG. 6a). Table 5, the angle .alpha. can be
substantially 90.degree. to provide a brightness enhancement film
having acceptable diffusion that also exhibits good gain.
TABLE-US-00005 TABLE 5 Haze (single Gain side (with lenticular
prism structure structure with no on the Lenticular structure Flat
prism light Radius Angle .theta. Refractive Angle .alpha. ratio
structure) output (.mu.m) (deg.) Index (deg.) % % side) 600 6 1.48
0 0 2.4 1.55 600 16 1.48 0 0 20.3 1.52 600 26 1.48 0 0 42.9 1.48
600 6 1.48 45 0 2.4 1.55 600 16 1.48 45 0 20.3 1.52 600 26 1.48 45
0 42.9 1.49 600 6 1.48 75 0 2.4 1.55 600 16 1.48 75 0 20.3 1.53 600
26 1.48 75 0 42.9 1.49 600 6 1.48 90 0 2.4 1.55 600 16 1.48 90 0
20.4 1.54 600 26 1.48 90 0 42.9 1.53
[0128] Given the afore-described embodiments and experimental
results, one can reasonably anticipate the effects of selecting
and/or combining the different features of structured surfaces to
reduce interference fringes and increase gain, without compromising
acceptable diffusion, as well as achieve the other benefits of the
present invention noted above. For example, the level of light
scatting is controlled by parameters including refractive index
(RI) of resin, radius of curvature of the lenticular lenses,
subtended angle/height of the lenticular lens, flat ratio, etc. It
is clear that there is synergy in the combination of the structured
lenticular light input surface and the structured prismatic light
output surface to achieve the benefits of the present
invention.
[0129] While the afore-described optical substrates comprising a
prismatic structured surface and an opposite lenticular structured
surface, diffusion can be accomplished while reducing certain
undesired optical effects such as wet-out, Newton's rings or
interference fringes, without significantly reducing overall
brightness. While the lenticular structured surface reduces cutoff
effect (manifested as a rainbow at the cutoff) between perceived
dark and light regions to some extent at certain angle of view or
observation, a more gradual or soft cutoff would be desirable for
certain display applications.
[0130] According to another aspect of the present invention, the
lenticular structure surface of the optical substrate comprises a
shallow-curved lens structure having "ripples" distributed along
the lenticular structure (which may be otherwise uniform in cross
section). The ripples may resemble knots or a series of knots. The
level of light scatting would then be controlled by parameters
including density of the ripples, in addition to refractive index
(RI) of resin, radius of curvature of the lenticular lenses,
subtended angle/height of the lenticular lens, flat ratio, etc.
[0131] FIGS. 22a to 22d illustrate an optical substrate 70 having a
knotted structured lenticular surface in accordance with one
embodiment of the present invention. In this embodiment, the
structure of the optical substrate 70 is essentially similar to the
optical substrate 50 shown in FIG. 6a and described above, except
for the addition of isolated knots 86 on the structured lenticular
surface 72 as further explained below, and a structured prismatic
surface 74 having prism heights alternately varying along the
prisms 78. Both structured layers are supported by the base layer
53.
[0132] The shallow-curved convex lenses 76 are provided with
ripples in the form of pre-defined isolated knots 86 distributed in
the x-direction, along the otherwise continuous, uniform lenticular
lenses 76. The knots 86 are each in the form of a section of an
annular band around the cylindrical surface of the lenticular
lenses 76. In the sectional view of FIG. 22a, the knots 86 have a
convex curved sectional profile. The pre-defined knots 86 on the
structured lenticular surface 72 scatter light in the longitudinal
x direction parallel to the longitudinal lenticular lenses 76, and
the shallow-curved lenticular lenses can scatter light in the
lateral y direction perpendicular to longitudinal lenticular lenses
76, so the shallow-curved lens structure with pre-defined knots
surface can improve diffusion effect as compared to the earlier
embodiment of FIG. 6a, for example. Accordingly, the knots 86
contribute to diffusion and also reduce certain undesirable optical
defects such as cutoff-effect (rainbow), Newton's rings, and
interference fringes. The knots may be several micrometers to
hundreds of micrometers wide (in the x-direction, viewed in section
as shown in FIG. 22a), and one micrometer to tens of micrometers
above or below the adjacent surface of the lenticular lens. The
distance between isolated knots 86 along a lenticular lens may be
several micrometers to thousands of micrometers.
[0133] In this embodiment, the longitudinal prisms 78 have peaks
alternating between two heights (about 3 .mu.m difference in
heights) along the longitudinal y direction. The prismatic
structured surface 74 can improve brightness by collimating light
incident on the structured lenticular surface to emit light in an
on-axis direction.
[0134] The triangular prisms 78 lean next to each other defining a
continuous or contiguous prismatic structured surface, while the
shallow-curved lenses 76 also lean next to each other defining a
continuous or contiguous lenticular structured surface 72. As in
earlier embodiments, the longitudinal directions of the lenticular
lenses 76 and the prisms 78 may be configured at different included
angles .alpha.. The included angle .alpha. may range from 0.degree.
to 90.degree., preferably 45.degree. to 90.degree., to provide an
optical substrate having satisfactory ability to diffuse light
while not significantly reducing the overall brightness. The
included angle .alpha. may be substantially 90.degree. to provide
preferable performance. The fabrication of the optical substrate 70
may involve similar processes as in earlier embodiments.
[0135] FIGS. 23a to 23c illustrate still another embodiment of
structured lenticular surface having ripples 185 resembling a
series of adjoining knots 186 on the structure lenticular light
input surface 172 of the optical substrate 170, as compared to the
previous embodiment shown in FIG. 22. Other than the ripples 185,
the remaining structure of the optical substrate 170 may be similar
to those in the optical substrate 70 in the FIG. 22 embodiment. In
particular, the shallow-curved convex lenses 176 are provided with
isolated predefined ripples 185 in the form of a series of knots
186 distributed in the x-direction, along the otherwise continuous,
uniform lenticular lenses 176. In this embodiment, the series of
knots 186 form ripples 185 on the otherwise uniform longitudinal
lenticular lenses 176, including connected knots 186 of different
widths and/or thicknesses/heights (viewed in a sectional view in
the x-z plane). There may be a series of two to tens of knots in
each ripple 185. The distance between isolated ripples 185 (series
of knots 186) along a lenticular lens may be several micrometers to
thousands of micrometers. The ripples 185 on the structured
lenticular surface 172 scatter light in the longitudinal x
direction parallel to the longitudinal lenticular lenses 176, and
the shallow-curved lenticular lenses can scatter light in the
lateral y direction perpendicular to longitudinal lenticular lenses
176, so the shallow-curved lens structure with pre-defined rippled
surface can improve diffusion effect as compared to the earlier
embodiment of FIG. 6a, for example. Accordingly, the ripples 185
contribute to diffusion and also reduce certain undesirable optical
defects such as cutoff-effect (rainbow), Newton's rings, and
interference fringes.
[0136] As shown in the embodiment of FIG. 23, the knots 186 in each
ripple 185 (i.e., a series of knots) are not at the same height. As
more clearly shown in FIG. 23b, the ripples 185 of each lenticular
lens 176 have heights varying along a sine curve or any other
defined curve, or a curve varying in a randomed/pseudo-randomed
manner. However, some or all the knots in a ripple can be of the
same height. Further, some or all of the ripples may be similar or
different viewed in x-z section (i.e. viewed in FIG. 23b).
[0137] It is well within the scope and spirit of the present
invention to provide ripples on the other embodiments of lenticular
structures disclosed herein, to improve diffusion
characteristics.
Experimental Results
[0138] The effects, namely cutoff effect (rainbow) achieved by
knotted lenticular lens structure as light input surface may be
judged by the naked eye. FIG. 24a is a photograph showing visual
perception of two optical substrates at certain view angle, each
having only structured prismatic output surface (no structured
lenticular light input surface), on a back light (e.g., a light
guide and a bottom diffuser) background. FIG. 24b is a photograph
showing visual perception of two optical substrates at certain view
angle, each having a light input surface having a rippled
lenticular lens structure and a light output surface having a
prismatic structure, on a back light. Comparing FIG. 24a to FIG.
24b, the transitions (circled area) between perceived darkness and
brightness exhibit a sharper cutoff, which is accompanied by a
rainbow at the transitions in FIG. 24a, but the transitions between
perceived darkness and brightness are more gradual without any
obvious rainbow in FIG. 24b. According to these results, it is
clear that the shallow-curved lens structure with pre-defined knots
can effectively reduce rainbow.
[0139] Given the ability for the shallow-curved lens structure with
pre-defined knots to provide better diffusion effects, there would
be more parameters to control diffusion over a two dimensional
plane (i.e., across the x-y plane) of the optical substrate. The
diffusion characteristics in the x direct of the optical substrate
may be varied by selecting the height and density of the knots. The
diffusion characteristics in the y-direction may be varied by
selecting the curvature radius, and subtended angle .theta. of the
shallow-curved lens. Accordingly, optical substrates can be
designed to provide the appropriate gain and haze for different
backlit modules to achieve the desired display quality in different
LCD applications. Further examples of underside lenticular surface
to provide desired diffusion characteristics are discussed
below.
[0140] In another aspect of the present invention, the primary
objective of the invention is to provide a brightness enhancement
film having a structured underside surface, which replaces the
glossy underside surface to effectively prevent the absorption
(wet-out) between the underside of the film and the surface of
optical elements in contact with it. A further objective of the
invention is to provide a brightness enhancement film having the
characteristic of improved brightness enhancement effect.
[0141] FIGS. 27 to 31 illustrate embodiments of brightness
enhancement films having a structured prismatic surface provided on
one major surface and a structured lenticular surface provided on
an opposite major surface of a substrate, wherein the included
angle .alpha. between the longitudinal axes of the prisms and the
lenticular lenses is substantially 0.degree., as noted earlier
above. Further, in this Referring to FIG. 27, as in the previous
embodiments, the lenticular surface has a structure comprising a
plurality of convex curved surfaces, each being a cylindrical
surface formed with a large radius to render the lenticular surface
close to a flat surface, but with surface features having a slight
convex curvature.
[0142] FIG. 27 illustrates the structure of an optical substrate
that functions well as a brightness enhancement film, which
combines prismatic and lenticular structures on opposing sides of
the substrate, in accordance with one embodiment of the present
invention, which can be used as the structured optical substrate
126 and/or 128 in the LCD 110 in FIG. 5, instead of embodiments of
the optical substrates discussed above. Generally, the optical
substrate 1050 has a structured lenticular surface 1052 and a
structured prismatic surface 1054. In this illustrated embodiment,
the structured prismatic surface 1054 is a light output surface and
the structured lenticular surface 1052 is a light input surface.
FIG. 28 illustrates a variation of the structure shown in FIG. 27,
in that there are less prisms that corresponds to the width of a
lenticular lens. Otherwise, the structures of FIG. 27 and FIG. 28
are quite similar, as described below. The relationship of the
number of prisms corresponding to the width of a lenticular lens
will be discussed later below.
[0143] Adopting the same coordinate system, for the embodiment
shown in FIG. 27, given the parallel relationship of the lenticular
lenses and the prisms, the y-axis is in the direction across the
peaks 1060 and valleys 1062, also referred to as the lateral or
transverse direction of the prisms 1058. The x-axis is orthogonal
to the y-axis, in a generally longitudinal axis or direction of the
prisms 1058. The longitudinal direction of prisms 1058 would be in
reference to the general direction in which the peaks 1060 proceed
from one end to another end of the prisms 1058. The prismatic
surface 1054 lies in an x-y plane. For a rectangular piece of the
optical substrate, the x and y-axes would be along the orthogonal
edges of the substrate 1050. The z-axis is orthogonal to the x and
y-axes (and the x-y plane). The edge showing the ends of the
laterally arranged rows of prisms 1058 lies in the y-z plane, such
as shown in FIG. 27, which also represents a sectional view in the
y-z plane. The prisms 1058 each has a constant sectional profile in
the y-z plane. References to cross sections of prisms 1058 would be
sections taken in y-z planes, at various locations along the
x-axis. Further, references to a horizontal direction would be in
an x-y plane, and references to a vertical direction would be along
the z-direction.
[0144] The prismatic surface 1054 includes parallel rows of
contiguous or continuous longitudinal prisms 1058 of similar peak
pitch and width (i.e., the width of the widest section or base of a
prism), protruding at the light output surface (e.g., from a common
base plane P-P shown in FIGS. 27 and 28, where the valleys 1062
lie) and extending between two opposing edges of the substrate
1050. The structure of the prisms 1058 is similar to the prisms in
the earlier embodiments, and further disclosed above. However, in
the current embodiment, the included angle between the axes of the
prisms 1058 and the lenticular lenses 1056 is 0 degree. That is,
the longitudinal axes of the prisms 1058 and the lenticular lenses
are parallel. Specifically, in the embodiment of FIG. 27 the rows
of longitudinal prisms 1058 are arranged in parallel laterally
(side-by-side), defining parallel peaks 1060 and valleys 1062. The
sectional profile of the peak 1060 is symmetrical about peak in
this embodiment (viewed in the y-z plane). As in the earlier
embodiments, the peak vertex angle may be right angled, and the
peaks are of constant or similar height and/or the valleys are of
constant or similar depth, across the plane of the prismatic
surface 1054. The distance or pitch between adjacent peaks/valleys
is constant in the illustrated embodiment of FIG. 27.
[0145] The lenticular structured surface 1052 is quite similar to
the lenticular structured surface 52 discussed in connection with
the embodiment of FIG. 6a, except the radius of curvature of the
shallow-curved lens structure (e.g., a convex or concave lens
structure, or a combination of convex and concave) in this
embodiment is quite large in comparison to the widths of the
lenticular lenses 1056 and prisms 1058. Particularly, as in the
earlier described embodiments, the lenticular structured surface
1052 includes parallel, contiguous or continuous rows of lenticular
lenses 1056 of similar width and/or pitch of crowns 1059), each
protruding at the light input surface (e.g., from a common base
plane L-L shown in FIGS. 27 and 28, where the valleys 1051 lie; see
also distance a-b shown in FIG. 29) and extending in the
x-direction continuously between two opposing edges of the
substrate 1050. The curved surfaces of adjacent lenticular lenses
intersect, defining parallel grooves or valleys 1051 and crowns
1059. For the lenticular lenses 1056, the y-axis is in the
direction across the grooves or valleys 1051 and crowns 1059, also
referred to as the lateral or transverse direction of the
lenticular lenses 1056. The x-axis represents the longitudinal axis
or direction of the lenticular lenses 1056. The longitudinal
direction of lenticular lenses would be in reference to the general
direction in which the crowns 1059 proceed from one end to another
end of the lenticular lenses 1056. The edge showing the ends of the
laterally arranged rows of lenticular lenses 1056 lies in the y-z
plane, such as shown in FIG. 27, which also represents a sectional
view in the y-z plane. The lenticular lenses 1056 each has a
constant sectional profile in the y-z plane. References to cross
sections of lenticular lenses 1056 would be sections taken in y-z
planes, at various locations along the x-axis. Further, references
to a horizontal direction would be in an x-y plane, and references
to a vertical direction would be along the z-direction.
[0146] As in the earlier embodiments, in the illustrated embodiment
of FIG. 27, the structured prismatic surface 1054 and the
structured lenticular surface 1052 are generally parallel to each
other in the overall optical substrate structure (i.e., do not form
an overall substrate structure that is generally tapered like a
light guide plate in a backlight module, or that is concave or
convex). The prisms 1058 and the lenticular lenses 1056 on opposite
major surfaces of the brightness enhancement film 1050 are
horizontally staggered across the film. In the illustrated
embodiments of FIGS. 27 and 28, the pitch or the centerline spacing
of the lenticular lenses 1056 at the lenticular surface 1052 is not
the same as (in the illustrated embodiment, is significantly
greater than) the pitch or centerline spacing of the prisms 1058 at
the prismatic surface 1054. Further, in the illustrated embodiments
of FIGS. 27 and 28, the width (i.e., the width of the base, or base
width) of the lenticular lenses 1056 along the base plane L-L and
the width (i.e., the width of the base, or base width) of the
triangular prisms 1058 along a base plane P-P are not the same.
Alternatively, the peak-to-peak distance between adjacent prism
peaks are not the same as the crown-to-crown distance between
adjacent lenticular lens crowns. In the embodiment of FIGS. 27 and
28, in the lateral y-direction, the lenticular lenses 1056 and the
prisms 1058 are not aligned in a one-to-one (i.e., one prism, one
lenticular lens) relationship. For example, in the illustrated
embodiment of FIG. 27, the width of about ten prisms 1058
corresponds to the width of about four lenticular lenses 1056
(i.e., the width of about 2.5 prisms 1058 corresponds to the width
of one lenticular lens 1056; see, vertical lines A perpendicular to
the major surface of the support base layer 1053 in FIG. 27). In
the illustrated embodiment of FIG. 28, the width of about five
prisms 1058 corresponds to the width of about three lenticular
lenses 1056 (i.e., the width of about 1.67 prisms 1058 corresponds
to the width of one lenticular lens 1056; see, lines B
perpendicular to the major surface of the base layer 1053 in FIG.
28). In other words, the ratio of the width of the lenticular lens
1056 to the width of the prisms 1058 is about 1.67 and 2.5 in the
illustrated embodiments. Most (substantially all) of the valleys
1062 of the prisms 1058 are not vertically aligned with the valleys
1051 of the lenticular lenses 1056 across the base layer 1053, with
the exception at the two lateral ends (in y-direction) in FIGS. 27
and 28. In addition, most (or substantially all) of the peaks 1060
of the prisms 1058 are not vertically aligned with the crowns 1059
of the lenticular lenses 1056 across the base layer 1053 (or the
brightness enhancement film 1050) (for the portion of the
brightness enhancement film 1050 shown in FIGS. 27 and 28, no
vertical alignment of the crowns 1059 and peaks 1060). Furthermore,
while some of the valleys and/or peaks of the prisms 1058 and some
of the valleys and/or crowns of the lenticular lenses 1056 are
vertically aligned (e.g., at the two lateral ends (in y-direction)
in FIGS. 27 and 28), given the pitch of the peaks of the prisms
1058 is different from the pitch of the crowns of the lenticular
lenses 1056, no two adjacent (i.e., a pair of) prisms 1058 are
vertically aligned with no adjacent (i.e., a pair of) lenticular
lenses 1056, as clearly shown in FIGS. 27 and 28 (i.e., not in a
one pair-to-one pair relationship).
[0147] Other than these specific illustrated examples, the ratios
of the width and/or pitch of the lenticular lens and prism may
range from ratio=0.1 to 10, or 0.2 to 4, or 1 to 4, or 1.67 to 2.5.
While the illustrated embodiments shown have the width/pitch of the
lenticular lenses greater than the width of the prisms, it is
contemplated that the width/pitch of the lenticular lenses may be
less than or equal the width/pitch of the prisms without departing
from the scope and spirit of the present invention.
[0148] In the alternate embodiment of a brightness enhancement film
2050 shown in FIG. 32, the pitch P of the peaks 1060 (or the width)
of the prisms 1058 is equal to the pitch P of the crowns 1059 (or
the width) of the lenticular lens 1056. However, the prisms 1058
and the lenticular lenses 1056 are horizontally staggered (e.g.,
offset) in the y-direction. In the illustrated embodiment of FIG.
32, adjacent prisms 1058 and adjacent lenticular lenses 1056 do not
overlap or intersect, and the width of the prisms 1058 and peak
pitch P are similar, and the width and crown pitch P of the
lenticular lenses 1056 are similar. As illustrated in the
embodiment of FIG. 32, the valleys 1062 of adjacent prisms 1058 are
vertically aligned with the crowns of the lenticular lens 1056
along line A perpendicular to the surface of the base layer 1053,
and the peaks of the prisms 1058 and the valleys of the lenticular
lenses 1056 are aligned along line B perpendicular to the surface
of base layer 1053). Other than as illustrated in the embodiment of
FIG. 32, the horizontal staggered relationship may be such that the
prisms 1058 and the lenticular lenses 1056 are staggered, with the
peaks 1060 and valleys 1051 and the crowns 1059 and valleys 1062
substantially not vertically aligned. It is contemplated that
adjacent prisms 1058 and adjacent lenticular lenses 1056 can
overlap or intersect, and/or the widths of the prisms 1058 may be
different, and/or the widths of the lenticular lenses 1056 may be
different, but with the prisms 1058 and the lenticular lenses
horizontally staggered (with the most of the peaks 1060 and valleys
1051 and most of the crowns 1059 and valleys 1062 substantially not
vertically aligned). In particular, no two adjacent prisms 1058 are
vertically aligned with two adjacent lenticular lenses 1056,
similar to the embodiments of FIGS. 27 and 28.
[0149] As noted elsewhere in this disclosure, the radius of
curvature (r in FIG. 29) of the lenticular lens structure is large,
so as to render the underside surface of the brightness enhancement
film close to a flat surface, but with surface features having a
slight convex curvature. As a result of the larger width and/or
pitch/centerline spacing and large radius of curvature of the
lenticular lenses compared to the prisms, and/or the horizontally
staggered relationship between the prisms and the lenticular
lenses, the moire interference pattern between the prismatic
surface and the opposite lenticular surface are significantly
reduced to a minimum.
[0150] In the illustrated embodiments of FIGS. 30-32, the optical
substrate 1050 comprises three separate layers, including a first
structured layer 1057 bearing the prismatic surface of prisms 1058,
a second structured layer 1055 bearing the lenticular surface of
lenticular lenses 1056, and an intermediate planar base layer 1053
supporting the layers 1055 and 1057. The two structured layers 1055
and 1057 are adhered to opposite surfaces of the base layer 1053 to
form the overall optical substrate 1050. It can be appreciated that
the optical substrate may be formed from a single integrated
physical layer of material, instead of three separate physical
layers, without departing from the scope and spirit of the present
invention. The optical substrate 1050 may be a unitary or
monolithic body, including a base portion bearing the surface
structures of prisms and lenticular lenses on opposite
surfaces.
[0151] In a sectional view taken along the y-z plane, adjacent
triangular prisms 1058 lean next to each other defining a
contiguous or continuous prismatic structured surface 1054, while
adjacent lenticular lenses 1056 also lean next to each other
defining a contiguous or continuous lenticular structured surface
1052. The lenticular structured surface 1052 contributes to
diffusion function and reduces certain undesired optical defects
such as wet-out, Newton's rings, and interference fringes. However,
given the large radius of curvature of the lenticular surface 1052,
with the lenticular surface being close to a planar surface, the
diffusion function is significantly less, compared to the earlier
described embodiments. The lenticular surface structures therefore
have very little or minimal light diffusion characteristics, so
that overall brightness of the light transmitted through the
lenticular surface would not be reduced by the lenticular surface.
By using low refractive index resin material for the structure that
defines the lenticular surface features, the overall brightness of
LCD can be further increased effectively. Nevertheless, with even a
shallow or thin lenticular surface structure, the brightness
enhancement film having the lenticular surface performs well in
reducing certain undesired optical defects such as wet-out,
Newton's rings, and interference fringes. It also reduces the moire
interference pattern between the structured prismatic surface and
the opposite lenticular structured surface.
[0152] In the illustrated embodiment, the lenticular layer 1055 and
the prism layer 1057 may be made of the same or different material,
and the base layer 1053 may be made of a same or different
material. The lenticular layer 1055 and the prism layer 1057 may be
formed using an optically transparent material, preferably a
polymerizable resin, such an ultraviolet or visible
radiation-curable resin, such as UV curable adhesive. Generally,
the structured prismatic and lenticular surfaces 1056 and 1058 are
formed by applying a coatable composition comprising a
polymerizable and crosslinkable resin onto a master mold or master
drum and undergoing a hardening process. For example, the prismatic
and lenticular structures are formed on the base layer 1053 by die
assemblies, press rolling machines, mold pressing assemblies or
other equivalent apparatuses. The base layer 53 may be made of a
transparent material, such as polyethylene-terephthalate (PET),
polyethylene (PE), polyethylene napthalate (PEN), polycarbonate
(PC), polyvinyl alcohol (PVA), or polyvinyl chloride (PVC). The
base layer 1053 may instead be made from the same transparent
material as the structured layers 1055 and 1057. The base layer
1053 provides the necessary thickness to provide structural
integrity to the final film of optical substrate 1050.
[0153] It is another objective of the invention is to provide a
brightness enhancement film having the characteristics of reduced
distortion and/or warpage. By controlling the shrinkage rate of the
resin material used for the structure (e.g., a layer of material)
that defines the prismatic surface features to be substantially
similar or approximately to the shrinkage rate of the resin
material used for the structure (e.g., a layer of material) that
defines the lenticular surface features, the two structured
surfaces of the brightness enhancement film can reduce distortion
or warpage of the film.
[0154] In another embodiment, as noted above, the prismatic
structured surface 1054 can be integrally-formed by molding,
pressing, embossing, calendaring or extrusion onto the transparent
base film, while the structured lenticular surface 1052 is
manufactured separately on to the transparent base layer 1053 by UV
curing with resin.
[0155] Further discussions of processes for forming a substrate
having structured surfaces may be referenced to U.S. Pat. No.
7,618,164, which had been incorporated by reference herein.
[0156] In still another embodiment, the structured lenticular
surface 1052 can be integrally-formed by molding, pressing,
embossing, calendaring or extrusion onto the transparent base layer
1053, while the prismatic structured surface 1054 is manufactured
separately on to the transparent base layer 1053 by UV curing with
resin.
[0157] In a further embodiment, the prismatic structured surface
1054 may be formed integrally or separately onto a base film, while
the structured lenticular surface may also be formed integrally or
separately onto another base film. The two base films is combined
back to back by simply stacking or applying adhesives such as
pressure sensitive adhesive (PSA) to the films to form a structure
equivalent to the base layer 1053. It is apparent that many
techniques and combinations of manufacture methods may be applied
to obtain the combination of the structured prismatic surface, the
structured lenticular surface and the base layer, or equivalent
thereof.
[0158] FIG. 29 is a schematic sectional view of an optical
substrate 1500 viewed in the y-z plane, for purpose of
understanding the geometry of the lenticular surface of a
brightness enhancement film as disclosed above with respect to FIG.
27. The optical substrate 1500 includes a base layer 1510 and a
plurality of lenticular lens 1520 having convex curved surfaces
1524 formed on the top surface of the base layer 1510, and
longitudinal prisms 1512 (similar to the prisms 1058 in FIG. 27)
formed on the bottom surface of the base layer 1510. The surface
1524 of each of the lenticular lenses 1520 corresponds
substantially to a section of the surface of a circular cylinders
1522 having a radius "r" with center "o" in cross-section, which
surface section corresponds to a subtended angle .theta., and a
subtended arc between point "a" and "b" in cross-section. In the
sectional view shown in FIG. 29, the lens 1520 corresponds to a
segment of the circle 1522, which is bounded by the chord a-b and
the arc a-b. As schematically shown in FIG. 29, adjacent arcuate
surfaces 1524 of lenticular lenses 1520 do not contact one another
to form a contiguous or continuous lens surface, as compared to
FIG. 27, just to illustrate that the Pitch 2 could vary over a
range, including 0 (i.e., adjacent lenticular lenses 1524 join or
are touching or contiguous with no flat space or flat groove
therebetween). In this embodiment, the surface 1524 of each lens
1520 "bottoms" onto the top of the base layer 1510, with a flat
spacing between adjacent lenses. In this embodiment, the lens width
pitch 1 is the same for the discontinuous lenses 1520. The spacing
pitch 2 may be the same or different between adjacent discontinuous
lenses.
[0159] In a preferred embodiment, the subtended angle .theta. of
the protruded arc of the lenticular lens is in the range of greater
than 0 to 160 degrees, or 0.5 degree to 90 degrees, or 1 degree to
65 degrees, or preferably in the range of 1.5 degrees to 7 degrees.
Pitch 2 is preferably 0 .mu.m (or substantially 0 .mu.m, or nearly
0 .mu.m) (i.e., there is substantially no flat space or flat groove
between adjacent lenticular lenses). Distance between crown 1511
and groove 1512 is 0.01 .mu.m to 35 .mu.m (or half of pitch 1, or
half the distance between point a to point b for lenticular lens
1524 shown in FIG. 29).
[0160] In a preferred embodiment, the vertex angle of prisms 1512
is in the range of 70 degrees to 110 degrees, more preferably in
the range of 80 degrees to 100 degrees. In another preferred
embodiment, the vertical height (H) of the prism units is in the
range of 10 .mu.m to 100 .mu.m, more preferably in the range of 20
.mu.m to 75 .mu.m. Alternatively, the prism units may or may not
have the same vertical heights. In another preferred embodiment,
the horizontal pitch of the prisms 1512 is in the range of 10 .mu.m
to 250 .mu.m, more preferably in the range of 15 .mu.m to 80
.mu.m.
[0161] The lenticular surface may have the variations similar to
the embodiments illustrated in FIGS. 9 to 12. That is, the distance
pitch 2 between two discontinuous lenticular lenses is non-zero,
which may be the same or variable or different across the section,
and/or the vertical height (T) of the lenticular lenses is
variable. Further, the radius of curvature of different lenticular
lenses may also vary and/or different lenticular surfaces may
conform to cylinders of different cross-sections other than a
circle (e.g., an ellipse or other cross-sections of regular or
irregular geometries) and further of varying sizes. Longitudinal
lenticular structures having a uniform cross-section defining other
convex curve surface profiles are also contemplated (e.g., same
profile or different profiles for different lenticular lenses).
Some of the adjacent lenticular lenses intersect or partially
overlap each other, thus defining a contiguous or continuous
lenticular structured surface with some of the lenticular lenses
having an asymmetrical cross-section (as viewed in the y-z plane
shown in FIG. 29). Further, the longitudinal lenticular lenses may
swing laterally (in the y-direction), similar to the embodiments of
FIGS. 13a, 13b, 14a and 14b, along the longitudinal direction
(x-direction) of the lenses, in the form of rows of laterally
meandering longitudinal lenticular lenses and/or sections of
continuous curved segments (i.e., sections with a curve in a
particular direction, or generally C-shaped or S-shaped curve
sections) coupled end-to-end to form the overall meandering
longitudinal lenticular lens structure. In one embodiment, the
laterally meandering rows of longitudinal lenticular structures are
arranged in parallel laterally (side-by-side in the y-direction).
In one embodiment, the lateral waviness is regular with a constant
or variable wavelength and/or wave amplitude (or extent of lateral
deformation). The lateral waviness may generally follow a
sinusoidal profile, or other curved profile. In another embodiment,
the lateral waviness may be of random wavelength and/or wave
amplitude. In one embodiment, the vertical height, curvature,
surface profile, and/or width of the lenticular lenses respectively
may be the same for adjacent lenses across a particular
cross-sectional plane, and may be constant or varying for different
cross-sectional plane along the longitudinal x-direction. Some of
the adjacent laterally meandering lenticular lenses intersect or
partially overlap each other, thus defining a contiguous or
continuous lenticular surface at some locations along the length of
each lenticular lens. Those adjacent lenticular lenses that
intersect would have an asymmetrical cross-section (as viewed in
the y-z plane, similar to the structure shown in FIG. 14b; see also
FIG. 12b). The lenticular lenses have the same height.
[0162] Further, adjacent lenticular lenses are separated by a
spacing, and the height varies along the length of each lenticular
lens in the x-direction, similar to the structure illustrated in
FIGS. 15a and 15b. The height varies along a lens, the sectional
surface profile varies in the x direction. The height variation may
generally follow a sinusoidal profile, or other curved profile, in
regular, constant, varying or random wavelength and/or wave
amplitude. The width of the lenses (e.g., pitch 1 between point "a"
to point "b" as shown in FIG. 29) is the same for adjacent lenses,
and constant along each lens in the x-direction. In alternate
embodiments, similar to FIGS. 15c to 15f, the width may also vary
between adjacent lenses or along the x-direction for one or more of
the lenses. The spacing (e.g., pitch 2 as shown in FIG. 29) between
lenses may be constant across a section or may be varying across a
section. Alternatively, the longitudinal lenticular lenses
intersect or partially overlap each other, thus defining a
contiguous or continuous lenticular structured surface on the
optical substrate.
[0163] Essentially, the longitudinal lenticular lenses can combine
any of the height varying feature and intersecting feature as
disclosed in earlier embodiments, in combination with prismatic
surface on opposite major surface of the brightness enhancement
film, to achieve the objectives of a film having low diffusion
characteristics, with minimum reduction of brightness, and
preventing moire pattern between the lenticular surface and the
prismatic surface.
[0164] As a further example, FIGS. 30 and 31 illustrate a further
embodiment of a brightness enhancement film 1150 having a
structured lenticular surface 1154 defined with micro-structures
including lenticular lenses 1056 and lenticular segments 530. As
more clearly shown in FIG. 31, the lenticular segments 530 are
arranged in straight rows, in which the axis of the lenticular
segments 530 is parallel to the axis of the longitudinal lenticular
lenses 1056. One or more rows of lenticular segments 530 intersect
or overlap with one or more adjacent lenticular lenses 1056. In
addition or in the alternate, two or more of the lenticular
segments 530 intersect or overlap along a row. In the illustrated
embodiment, the height of the lenticular lenses 1056 is the same,
and the height of the lenticular segments 530 is the same, with the
height of the lenticular lenses 1056 different from the height of
the lenticular segments 530. In an alternate embodiment, the two
height of the lenticular lenses 1056 is same as the height of the
lenticular segments 530. The structures and design considerations
for the lenticular lenses 1056 and lenticular segments 530 can be
similar to those discussed above in connection with the earlier
embodiments.
[0165] Given the afore-described embodiments and experimental
results, one can reasonably anticipate the effects of selecting
and/or combining the different features of structured surfaces to
reduce interference fringes and increase gain, without compromising
acceptable diffusion, as well as achieve the other benefits of the
present invention noted above.
[0166] In a further embodiment, the structured prismatic light
output surface may include varying peak heights, and predefined
structural irregularities distributed in the structure surface. The
pre-defined irregularities introduced may be in-kind to anticipated
structural defects arising from manufacturing, such as non-facet
flat sections in the prism structure (e.g., at peaks or valleys) of
the structured surface. The structural irregularities are
distributed across the structured light output surface in at least
one of orderly, semi-orderly, random, and quasi-random manner. The
predefined irregularities introduced into the structured light
output surface could mask certain user perceivable defects caused
by structural defects that have been unintentionally included in
the structured light output surface from the manufacturing process.
Further reference to the defect masking effect of predefined
structural irregularities may be made to U.S. Pat. No. 7,883,647,
which had been commonly assigned to the assignee of the present
application, and which is fully incorporated by reference
herein.
[0167] In another embodiment, the structured prismatic light output
surface may include, in the alternate or in addition, irregular
prism structures, as disclosed in U.S. Pat. No. 7,618,164, which
had been commonly assigned to the assignee of the present
application, and which is fully incorporated by reference herein.
In the alternate or in addition, the structured prismatic light
output surface may include anti-chatter structures, as disclosed in
U.S. Pat. No. 7,712,944, which had been commonly assigned to the
assignee of the present application, and which is fully
incorporated by reference herein. In the alternate or in addition,
the structured prismatic light output surface may include rows of
laterally arranged snaking, wavy or meandering longitudinal prism
structures, as disclosed in U.S. patent application Ser. No.
12/854,815 filed on Aug. 11, 2010, which had been commonly assigned
to the assignee of the present application, and which is fully
incorporated by reference herein. In another embodiment, the
structured prismatic light output surface may include, in the
alternate or in addition, irregular prism structures, as disclosed
in, which had been commonly assigned to the assignee of the present
application, and which is fully incorporated by reference
herein.
[0168] The present invention also discloses a method of forming an
uneven structure on a substrate. The uneven structure can comprise
a plurality of segments. The segments do not extend from an edge of
the substrate to an opposite edge of the substrate described
previously in FIG. 14c to FIG. 14f. For example, a segment can
extend from an edge of the substrate to a point inside the surface
area of the substrate or from a first point inside the surface area
of the substrate to a second point inside the surface area of the
substrate.
[0169] The substrate can be an optical substrate having a light
input surface and a light output surface. In one embodiment, the
uneven structure can be formed on the light input surface of the
substrate; the uneven structure can comprise at least one of a
lenticalur structure and a prismatic structure, preferably, the
uneven structure is a lenticalur structure. In another embodiment,
the uneven structure can be formed on the light output surface of
the substrate; the uneven structure can comprise at least one of a
lenticalur structure and a prismatic structure, preferably, the
uneven structure is a prismatic structure.
[0170] The method includes two main steps. In step A: cut a
plurality of trenches in an order on a surface of a mold through a
control system, wherein the plurality of trenches comprise at least
one first trench, wherein for any second trench of the at least one
first trench, the second trench overlaps with at least one third
trench different from the second trench such that the second trench
is cut off by the at least one third trench. Preferably, use a hard
tool to penetrate into the roll to cut a plurality of trenches in
an order on a surface of a roll through a CNC (Computer Numeric
Control) system, wherein each of the plurality of trenches is cut
in a first direction, wherein when the plurality of trenches is
cut, the hard tool is not pulled away from the roll (when the hard
tool does not penetrate into the mold/roll, the mold/roll has a
unstructured surface; however, when the hard tool penetrates into
the mold/roll, the front end of the hard tool is kept below the
unstructured surface until the trench is completely formed); it
changes one-dimensional cylindrical structure to two-dimensional
structure in the form of the annelid such that there exists no
space adjacent two trenches so as to increase the diffusion of the
optical film. Preferably, (the front end of) the hard tool has a
lenticular shape (as illustrated in FIG. 8, the front end of the
hard tool has an arc shape); comparing with the film embossed by
the mold cut by the hard tool having a prismatic shape, the film
embossed by the mold cut by the hard tool having a lenticular shape
has a better diffusion performance. However, the hard tool of the
present invention is not limited to have an arc shape, the hard
tool having a smoothly-curved shape to get a better diffusion
performance can be applied in the present invention. In one
embodiment, a portion of the at least one first trench that is not
cut off corresponds to a plurality of segments of the uneven
structure. In step B: use the surface of the mold to emboss a thin
film on the substrate to form the uneven structure.
[0171] A plurality of trenches is cut on a surface of a mold
through a control system. Preferably, each trench is cut in a first
direction (e.g., from an edge of the mold to an opposing edge of
the mold or a tangential direction of a roll). U.S. Pat. No.
7,618,164 fully incorporated by reference herein has disclosed how
to generate the structured surface of optical substrate in
accordance with a number of process techniques, including
micromachining using hard tools to form molds or the like. The hard
tools may be very small diamond tools mounted on CNC (Computer
Numeric Control) system (e.g. turning, milling and ruling/shaping
machines). Preferably, the control system is a CNC (Computer
Numeric Control) system and the mold is a roll.
[0172] It should be noted that FIG. 33 to FIG. 37 illustrate a
portion of trenches on the surface of the mold, however, the
trenches can be distributed across the surface of the mold (see
FIG. 39a and FIG. 39d). Moreover, the segments of the uneven
structure to be formed on the substrate are complementary to (or
correspond to) the portion of the trenches that is not cut off so
that only a set of complementary figures (see FIG. 39a and FIG.
39d) are illustrated for convenience.
[0173] FIG. 33 to FIG. 37 illustrate a top view of a portion of
trenches formed on the surface of the mold in various embodiments
of the present invention, wherein opposing edges of each trench is
shown for convenience. The trenches comprise at least one first
trench (i.e. at least one first trench is cut off), wherein for any
second trench of the at least one first trench, the second trench
overlaps with at least one third trench different from the second
trench such that the second trench is cut off by the at least one
third trench. In one embodiment, see FIG. 33, the second trench is
symbolized by 2001 and the third trench is symbolized by 2002. In
one embodiment, see FIG. 34, the second trench is symbolized by
2003 and the third trenches are symbolized by 2004, 2005. In one
embodiment, see FIG. 35, the second trench is symbolized by 2006
and the third trenches are symbolized by 2007, 2008; the second
trench is symbolized by 2007 and the third trench is symbolized by
2008. In one embodiment, see FIG. 36, the second trench is
symbolized by 2009 and the third trench is symbolized by 2010; the
second trench is symbolized by 2010 and the third trench is
symbolized by 2011. In one embodiment, see FIG. 37, the second
trench is symbolized by 2013 and the third trench is symbolized by
2014. There is at least one space between trenches in FIG. 33 to
FIG. 37, however, there can be no space between trenches (i.e.
there is no space between the segments of the uneven structure).
The second trench can overlap with two third trenches (e.g., or
more) different from the second trench such that the second trench
is cut off by the two third trenches (see FIG. 34 to FIG. 35). In
one embodiment, each trench is the second trench cut off by the at
least one third trench such that the uneven structure comprises no
continuous lens or prism extending from an edge of the substrate to
an opposite edge of the substrate.
[0174] When the trench A and the trench B (maybe at least one
trench B) are formed so that the trench A has a first edge and a
second edge and the trench B has a third edge and a fourth edge
respectively correspond to a first edge and a second edge of the
trench A, cut-off (i.e. the trench A is cut off by the trench B)
can be defined as a portion of the third edge of the trench B is
located outside the first edge of the trench A when the trench A
and the trench B exaggeratively overlap with each other. There are
many ways to form the overlap, such as controlling the depth
variation of trenches (refer back to FIG. 15a to FIG. 15f),
controlling the swing of the trenches (refer back to FIG. 13a, FIG.
13b, FIG. 14a and FIG. 14b) and controlling the depth variation and
the swing of the trenches (refer back to FIG. 13a, FIG. 13b, FIG.
14a, FIG. 14b, FIG. 15a to FIG. 15f).
[0175] In one embodiment, the trenches comprise at least one first
trench (i.e. at least one first trench is cut off), wherein for any
second trench of the at least one first trench, the second trench
overlaps with at least one third trench different from the second
trench such that the second trench is cut off by the at least one
third trench, wherein the at least one third trench comprises a
fourth trench and a fifth trench, the second trench is cut off by
the fourth trench in a first location of the second trench and the
second trench is cut off by the fifth trench in a second location
of the second trench different from the first location of the
second trench. In one embodiment, refer back to FIG. 35, the second
trench is symbolized by 2006, the third trenches are symbolized by
2007, 2008, the fourth trench is symbolized by 2007, the fifth
trench is symbolized by 2008, the second trench 2006 is cut off by
the fourth trench 2007 in a first location 2006A of the second
trench 2006 and the second trench 2006 is cut off by the fifth
trench 2008 in a second location 2006B of the second trench 2006
(different from the first location 2006A of the second trench
2006).
[0176] In one embodiment, the trenches comprise at least one first
trench (i.e. at least one first trench is cut off), wherein for any
second trench of the at least one first trench, the second trench
overlaps with at least one third trench (different from the second
trench) and a fourth trench (different from the second trench and
the at least one third trench) such that the second trench is cut
off by the at least one third trench, but is not cut off by the
fourth trench. In one embodiment, refer back to FIG. 36, the second
trench is symbolized by 2009, the third trench is symbolized by
2010, the fourth trench is symbolized by 2011, the second trench
2009 is cut off by the third trench 2010 but is not cut off by the
fourth trench 2011 (see the location 2009A).
[0177] In the embodiments illustrated in FIG. 33 to FIG. 36, the
opposing edges of each trench swing along a first longitudinal axis
2051, however, the first longitudinal axis 2051 is not located
between the opposing edges of each trench (see FIG. 38a). The
embodiments illustrated in FIG. 33 to FIG. 36 can be done by
controlling swing of the trenches (refer back to FIG. 13a, FIG.
13b, FIG. 14a and FIG. 14b), preferably, by controlling less depth
variation and more swing of the trenches (refer back to FIG. 13a,
FIG. 13b, FIG. 14a, FIG. 14b, FIG. 15a to FIG. 15f). In the
embodiments illustrated in FIG. 37, the first longitudinal axis
2051 is located between the opposing edges of each trench (see FIG.
38b). The embodiments illustrated in FIG. 37 can be done by
controlling the depth variation of the trenches (refer back to FIG.
15a to FIG. 15f) (i.e. cut a first trench 2013 along a first
direction by maintaining the position of the hard tool
substantially along a first straight line in the first direction
(see the first longitudinal axis 2051 in FIG. 38b); and cut a
second trench 2014 along the first direction by maintaining the
position of the hard tool substantially along a second straight
line (see the first longitudinal axis 2051 in FIG. 38b) parallel to
the first straight line in the first direction, wherein the
transverse width of the second trench 2014 controlled by the
penetrating depth of the hard tool is increased enough to cut off
the first trench 2013 along the transverse direction of the second
trench 2014 such that the first trench 2013 is separated into a
plurality of notches by the second trench 2014; if the penetrating
depth of each of the first trench and the second trench is constant
when it is cut along the first direction by maintaining the hard
tool substantially along the first straight line in the first
direction, it is impossible that the second trench 2014 cuts the
first trench 2013 along the traverse direction thereof. In this
case, the traverse width of the second trench 2014 is controlled by
the penetrating depth of the hard tool, and the traverse width of
the second trench 2014 increases to a certain degree enough to cut
the first trench 2013 along the traverse direction thereof).
Comparing with cutting each trench meandering along the first
direction, cutting each trench by maintaining the hard tool
substantially along the first line in the first direction not only
shortens the time of the mold-making but also enhances the
precision of the mold to reduce the error of the mold-making (the
front end of the hard tool has an arc shape so as to guarantee that
each trench cut on the mold has a smooth arc shape and the film
embossed by the mold has a better diffusion performance).
Preferably, the embodiments illustrated in FIG. 37 can be done by
controlling more depth variation and less swing of trenches (refer
back to FIG. 13a, FIG. 13b, FIG. 14a, FIG. 14b, FIG. 15a to FIG.
150. The opposing edges of each trench may be symmetrical with the
first longitudinal axis 2051. The opposing edges of each edge can
be asymmetrical with the first longitudinal axis 2051, preferably,
the average distance between one edge and the first longitudinal
axis 2051 is substantially the same as the average distance between
the other edge and the first longitudinal axis 2051.
[0178] Please refer back to FIG. 39a to FIG. 39d. FIG. 39a is a
schematic three-dimensional view of the mold having a plurality of
trenches distributed across the surface thereof. FIG. 39b is a
schematic top view of FIG. 39a. FIG. 39c is a schematic
three-dimensional view of the substrate having an uneven structure
(e.g., segments) formed thereon by embossing a thin film on the
substrate. FIG. 39d is a schematic top view of FIG. 39c. In the
embodiment illustrated in FIG. 39a and FIG. 39b, a plurality of
trenches are formed and distributed across the surface of the mold
2055 by controlling the depth variation of trenches, however, it is
not limited to this case (for example, controlling the swing of the
trenches, controlling the depth variation and the swing of the
trenches). Specifically, when a trench X is cut later than a trench
Y, the trench Y is cut off by the trench X and forms a plurality of
parts 2061 substantially arranged in a first line 2063. There is a
space 2062 between the adjacent parts 2061. In one embodiment, the
width of the trench X is larger than that of the trench Y.
Optionally, the width of a portion of the trench X is smaller than
that of the trench Y. In another embodiment, the depth variation of
the trench X is larger than that of the trench Y. After embossing,
the parts 2061 across the surface of the mold 2055 are
complementary to (or correspond to) the segments 2066 of the uneven
structure formed on the substrate 2056.
[0179] It is contemplated within the scope and spirit of the
present invention, further combination of two of more of the above
described structured surface features may be implemented to be
present in a single optical substrate, to obtain the desired
optimal result for a particular application with an LC module.
[0180] The optical substrates in accordance with the present
invention may be used with LCDs to be deployed for displays, for
example, for televisions, notebook computers, monitors, portable
devices such as cell phones, digital cameras, PDAs and the like, to
make the displays brighter. In accordance with the present
invention, the optical substrate (e.g., 50 in FIGS. 6a, and 1050 in
FIG. 27) comprises a prismatic, structured light output surface and
a structure lenticular light input surface, which together enhances
brightness, reduces interference fringes, and provides acceptable
diffusion characteristics, when applied in an LCD for example. An
inventive LCD incorporating the inventive optical substrate in
accordance with the present invention may be deployed in an
electronic device. As shown in FIG. 25, an electronic 1100 (which
may be one of a PDA, mobile phone, television, display monitor,
portable computer, refrigerator, etc.) comprises the inventive LCD
110 in accordance with one embodiment of the present invention. The
LCD 110 comprises the inventive optical substrate described above.
The electronic device 1110 may further include within a suitable
housing, a user input interface such as keys and buttons
(schematically represented by the block 1116), image data control
electronics, such as a controller (schematically represented by
block 1112) for managing image data flow to the LCD 110,
electronics specific to the electronic device 1110, which may
include a processor, A/D converters, memory devices, data storage
devices, etc. (schematically collectively represented by block
1118), and a power source such as a power supply, battery or jack
for external power source (schematically represented by block
1114), which components are well known in the art.
[0181] It will be apparent to those skilled in the art that various
modifications and variations can be made to the disclosed
structures and processes of the present invention without departing
from the scope or spirit of the invention. In view of the foregoing
descriptions, it is intended that the present invention covers
modifications and variations of this invention if they fall within
the scope of the following claims and their equivalents.
* * * * *