U.S. patent application number 11/811585 was filed with the patent office on 2007-11-01 for differentially-cured materials and process for forming same.
Invention is credited to Patrick W. Mullen, Robert B. Nilsen, William P. Rowland.
Application Number | 20070253072 11/811585 |
Document ID | / |
Family ID | 34705374 |
Filed Date | 2007-11-01 |
United States Patent
Application |
20070253072 |
Kind Code |
A1 |
Mullen; Patrick W. ; et
al. |
November 1, 2007 |
Differentially-cured materials and process for forming same
Abstract
A light-redirecting optical structure includes a first side and
a second side, the first side including plurality of linear prisms
having a visibly random shaped surface on the prisms and a
plurality of cross-cut prisms on first side which are oriented at
an angle such that it is greater than zero degrees but less than
180 degrees. A backlight wedge includes a stepped structure on a
bottom side that decreases in size traversing the wedge away from a
light source which is positioned at an end and having a visibly
random shaped surface on said wedge.
Inventors: |
Mullen; Patrick W.;
(Barkhamsted, CT) ; Nilsen; Robert B.; (Mystic,
CT) ; Rowland; William P.; (Plattsburgh, NY) |
Correspondence
Address: |
HAMILTON, BROOK, SMITH & REYNOLDS, P.C.
530 VIRGINIA ROAD
P.O. BOX 9133
CONCORD
MA
01742-9133
US
|
Family ID: |
34705374 |
Appl. No.: |
11/811585 |
Filed: |
June 11, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11022559 |
Dec 22, 2004 |
7230764 |
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11811585 |
Jun 11, 2007 |
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10744916 |
Dec 23, 2003 |
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11022559 |
Dec 22, 2004 |
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10428318 |
May 2, 2003 |
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10744916 |
Dec 23, 2003 |
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09928247 |
Aug 10, 2001 |
7250122 |
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10428318 |
May 2, 2003 |
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60226697 |
Aug 18, 2000 |
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60256176 |
Dec 15, 2000 |
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Current U.S.
Class: |
359/641 |
Current CPC
Class: |
B29K 2105/243 20130101;
G02B 5/12 20130101; B29C 2035/0827 20130101; G02B 6/0053 20130101;
B29C 35/0894 20130101; B29C 35/10 20130101; B29L 2011/0083
20130101; G03F 7/001 20130101; B29D 11/00605 20130101; G02B 5/124
20130101; G02B 5/045 20130101; B29K 2995/003 20130101; B29D 11/00
20130101; G02B 6/0038 20130101; G02B 27/30 20130101 |
Class at
Publication: |
359/641 |
International
Class: |
G02B 27/30 20060101
G02B027/30 |
Claims
1. A light-collimating optical structure comprising a first side
and a second side, the first side including an array of
light-collimating prisms formed of a radiation-cured composition,
wherein the array of light-collimating prisms includes a first
portion and a second portion, the first portion has a first index
of refraction and the second portion has a second index of
refraction, the first portion and the second portion are both
formed of the radiation-cured composition, and the first index of
refraction is different from the second index of refraction.
2. The light-collimating optical structure of claim 1 wherein the
array of light-collimating prisms includes a light-collimating
prism, the light-collimating prism includes the first portion and
the second portion, the first portion has the first index of
refraction and the second portion has the second index of
refraction, the first portion and the second portion are the same
radiation-cured composition, and the first index of refraction is
different from the second index of refraction.
3. The light-collimating optical structure of claim 1 wherein the
first index of refraction is sufficiently different from the second
index of refraction so as to result in a discontinuity in the
light-collimating optical structure.
4. The light-collimating optical structure of claim 3 wherein the
discontinuity is a visible discontinuity.
5. The light-collimating optical structure of claim 1 wherein the
first index of refraction is sufficiently different from the second
index of refraction so as to visibly alter a path of light
transmitted through the light-collimating optical structure as
compared to a light-collimating optical structure wherein the first
index of refraction is the same as the second index of
refraction.
6. The light-collimating optical structure of claim 1 wherein the
light-collimating prisms include a differentially-cured pattern on
the prisms.
7. The light-collimating optical structure of claim 1 wherein the
light-collimating prisms include visibly random shaped
surfaces.
8. The light-collimating optical structure of claim 1 wherein the
light-collimating prisms are generally linear, light-collimating
prisms.
9. The light-collimating optical structure of claim 1 wherein a
plurality of the light-collimating prisms include substantially
linear peaks.
10. The light-collimating optical structure of claim 1 wherein a
plurality of the light-collimating prisms include curved peaks.
11. The light-collimating optical structure of claim 1 wherein the
light-collimating prisms include apexes having an included angle of
about ninety degrees.
12. The light-collimating optical structure of claim 1 wherein the
first side includes a plurality of cross-cut prisms which are
oriented at an angle greater than zero degrees but less than 180
degrees with respect to the light-collimating prisms.
13. The light-collimating optical structure of claim 12 wherein the
light-collimating prisms have a height greater than the height of
the cross-cut prisms.
14. The light-collimating optical structure of claim 12 wherein the
light-collimating prisms have a height less than the height of the
cross-cut prisms.
15. The light-collimating optical structure of claim 12 wherein the
cross-cut prisms include apexes having an included angle of about
ninety degrees.
16. The light-collimating optical structure of claim 12 wherein the
cross-cut prisms include apexes having an included angle of less
than about ninety degrees.
17. The light-collimating optical structure of claim 12 wherein the
cross-cut prisms include apexes having an included angle of greater
than about ninety degrees.
18. The light-collimating optical structure of claim 1 wherein the
light-collimating prisms include bumps, pips, or differential
heights.
19. The light-collimating optical structure of claim 1 wherein the
array of light-collimating prisms includes a pattern of elevated
prism peak portions.
20. The light-collimating optical structure of claim 1 wherein the
array of light-collimating prisms includes a pattern of depressed
prism peak portions.
21. The structure of claim 1 wherein the light-collimating prisms
include a sufficient portion of prism apexes that have sufficient
curvature to reduce Lloyd's mirror fringe effects as compared to
light-collimating prisms without curvature.
22. A light-collimating optical structure comprising a first side
and a second side, the first side including an array of
light-collimating prisms formed of a radiation-cured composition,
wherein the array of light-collimating prisms includes a first
portion and a second portion, the first portion has a first density
and the second portion has a second density, the first portion and
the second portion are both formed of the radiation-cured
composition, and the first density is different from the second
density.
23. The light-collimating optical structure of claim 22 wherein the
first density is sufficiently different from the second density so
as to result in a discontinuity in the light-collimating optical
structure.
24. The light-collimating optical structure of claim 22 wherein the
light-collimating prisms include a differentially-cured pattern on
the prisms.
25. The light-collimating optical structure of claim 22 wherein the
light-collimating prisms include visibly random shaped surfaces.
Description
RELATED APPLICATIONS
[0001] This application is a Continuation Application of U.S.
patent application Ser. No. 11/022,559, filed on Dec. 22, 2004,
which is a Continuation-in-Part of U.S. patent application Ser. No.
10/744,916, filed on Dec. 23, 2003, which is a Continuation-in-Part
of U.S. patent application Ser. No. 10/428,318, filed on May 2,
2003 and now abandoned, which is a Continuation-in-Part of U.S.
patent application Ser. No. 09/928,247, filed on Aug. 10, 2001,
which claims the benefit of U.S. Provisional Application No.
60/226,697, filed on Aug. 18, 2000, and U.S. Provisional
Application No. 60/256,176, filed on Dec. 15, 2000. The entire
teachings of the above applications are incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] Many retroreflective sheeting, collimating films, etc. are
made to exacting dimensions in metal molds that are difficult and
expensive to make. The metal molds can represent a significant
barrier of entry into a high quality market for optical sheeting
and films. However, knock-off manufacturers of retroreflective
sheeting and collimating film can form inexpensive, low quality
molds from the high quality optical sheeting and film. As a means
to deter such copying, the metal molds are often engraved with a
company logo or trademark, which can cause the logo or trademark to
appear on the knock-off end product. A disadvantage of the added
logo is that it can be more difficult to engrave at the tolerances
required.
[0003] Therefore, a need exists for better marked products and a
method of marking products better.
SUMMARY OF THE INVENTION
[0004] A structure includes a microstructured layer that includes a
first cured portion and a second cured portion that are formed from
a same light or radiation-curable material. The first cured portion
is cured to a first amount of time or at a first rate, and the
second cured portion is cured to a second amount of time or at a
second rate. The first amount of time or rate is sufficiently
different than the second amount of time or rate to result in a
discontinuity on the surface of the structure. The layer can be
connected to a base. The layer and the base can be formed of the
same material. The first amount of curing can be sufficiently
different than the second amount of curing to result in a
difference between the thickness of the first portion and the
thickness of the second portion. The difference in particular
embodiments can be in a range of between about 0.02 and 2.0
micrometers. In particular embodiments, the microstructured layer
includes linear prisms, prisms, pyramids, truncated pyramids,
lenticulars, cones, moth-eye structured surfaces, diffractive
structures, diffractive structured surfaces, textured surfaces,
lenses, and/or lens arrays. In other embodiments, the cross-section
of the microstructures can include any polygonal or curved
cross-sectional shape.
[0005] A discontinuity is considered a rise or depression in the
surface of a structure that causes incident light to display a
different shade of light than when incident light strikes a portion
of the surface not having a rise or depression. In a particular
embodiment, the discontinuity can be discerned with the naked eye.
The layer can be a prism array, such as linear prisms or
cube-corner prisms, a lenticular structure, or a sub-wavelength
structure, or a non-structured layer, such as a coating.
[0006] A method for forming a pattern in a radiation-curable
material includes providing, between a radiation source and the
radiation-curable material, a blocking pattern that can block a
portion of the radiation from the radiation source. The material is
cured with radiation from the radiation source through the blocking
pattern to form a pattern in the radiation-curable material.
[0007] A pattern transfer structure includes a radiation source for
emitting radiation, a radiation-curable material that can be cured
by the radiation, and a pattern for blocking a portion of the
radiation. The pattern is disposed between the radiation source and
the radiation-curable material during the curing of the material
such that a pattern is formed in the material.
[0008] A method for forming a prism structure includes providing a
prism mold and placing a radiation-curable material in the mold. A
pattern is provided between a radiation source and the
radiation-curable material that can block a portion of the
radiation-curable material. The radiation-curable material is cured
with radiation from the radiation source to form a pattern in the
radiation-curable material.
[0009] A prism structure includes a base and a prism array
connected to the base. The prism array includes a first cured
portion and a second cured portion that are formed from a same
radiation-curable material. The first cured portion has a first
index of refraction value and the second cured portion has a second
index of refraction value. It is believed that the index of
refraction is sufficiently different from the first index of
refraction value to result with a discontinuity, which can be
visible in particular embodiments, on the surface of the structure.
In particular embodiments, the prism array includes a random
differentially-cured pattern on the facets of the array to minimize
wet-out when the array is positioned adjacent to a surface or
layer. In alternative embodiments, the window side of the prism
array includes a regular or uniform differentially-cured pattern
formed on and/or therein. The differentially-cured pattern can
cause the contour of the surface of the prism and/or window side to
change shape, such as continuous concave-convex surface non-smooth
surface. In further embodiments, the window side of the prism array
can include a series of base planes and a series of plateaus, with
the base planes and the plateaus running along a first axis. The
plateaus and base planes alternate along a second axis, the
plateaus not being coplanar with the base planes.
[0010] A backlighting system includes a light source, a first
light-redirecting film, a second light-redirecting film, a
differentially-cured pattern, and a waveguide. The first
light-redirecting film includes a plurality of linear prisms with
the differentially-cured pattern on and/or therein. The second
light-redirecting film includes a plurality of linear prisms on a
first side and a differentially-cured pattern formed on and/or in a
second side that faces the linear prisms of the first
light-redirecting film. The waveguide is for receiving light from
the light source and redirecting the light toward the first
light-redirecting film.
[0011] In other embodiments, an optical structure comprising a
microstructured layer can be provided on a non-smooth surface. The
non-smooth surface can include an undulating pattern. In a
particular embodiment, the microstructured layer includes a
moth-eye structure formed on an excess resin layer on a substrate
film, which can be differentially-cured to form the non-smooth
surface.
[0012] A method for forming a microstructured layer provided on a
non-smooth surface, comprising dispensing a resin layer between a
substrate film and tool used to form a microstructured surface in
the resin layer, and curing the resin layer through a mask to form
a differentially-cured structure that is non-smooth with the
microstructured layer being formed on the non-smooth surface.
[0013] A light-redirecting optical structure includes a first side
and a second side. The first side includes a plurality of linear
prisms having a visibly random shaped surface on the prisms. A
plurality of cross-cut prisms on first side are oriented at an
angle such that it is greater than zero degrees but less than 180
degrees. In one embodiment, the cross-cut prisms are oriented at an
angle such that it is greater than zero degrees but less than 180
degrees, but the angle is not ninety degrees. In another
embodiment, the light-redirecting optical has a first side that
includes a plurality of first cured portions and a plurality of
second cured portions that are formed from a same radiation-curable
material. The first plurality of cured portions are cured to a
first amount of time or at a first rate. The plurality of second
cured portions are cured to a second amount of time or at a second
rate. The first amount of time or rate is sufficiently different
than the second amount of time or rate to result with
discontinuities on and/or within the surface of the structure.
[0014] A backlight wedge includes a stepped structure on a bottom
side that decreases in size traversing the wedge away from a light
source which is positioned at an end and having a visibly random
shaped surface on said wedge. In one embodiment, the tapered prisms
of the wedge include a plurality of first cured portions and a
plurality of second cured portions that are formed from a same
radiation-curable material. The first plurality of cured portions
are cured to a first amount of time or at a first rate. The
plurality of second cured portions are cured to a second amount of
time or at a second rate. The first amount of time or rate is
sufficiently different than the second amount of time or rate to
result with discontinuities on and/or within the surface of the
structure.
[0015] The invention has many advantages including forming a
permanent pattern in materials that is transparent and does not
significantly detract from other functions while adding the
benefits described below. The material can have the pattern act
similar to a watermark in paper to provide a means of
identification for a product's source that is difficult to forge.
Also, the pattern can serve as a function of light management by
altering the path of light that is transmitted through such a
structure having the pattern.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a perspective view of a radiation-curable material
and a pattern layer positioned thereover for forming a pattern in
the curable material.
[0017] FIG. 2 is a perspective view of the radiation-curable
material having a pattern formed therein.
[0018] FIG. 3 is a perspective view of a light-redirecting
structure having moth-eye structures formed thereon, the moth-eye
structures having a pattern formed therein in accordance with
another embodiment of the invention.
[0019] FIG. 4 is a perspective view of a microstructured layer
being formed on a substrate and cured through a pattern layer
positioned on the substrate.
[0020] FIG. 5 is a perspective view of a light-redirecting film
that includes a microstructured layer disposed on each side of a
substrate.
[0021] FIG. 6 is a perspective view of a standard light-redirecting
film.
[0022] FIG. 7 is a cross-sectional view of a system used to
illustrate how wet-out can occur, for example, between prism peaks
and adjacent surfaces.
[0023] FIG. 8 is a diagram illustrating a first fringe area that
can occur at the interface between a prism tip and an adjacent
surface.
[0024] FIG. 9 is a diagram illustrating a second fringe area that
can occur at the interface between a prism tip and an adjacent
surface.
[0025] FIG. 10 is a diagram illustrating a third fringe area that
can occur at the interface between a prism tip and an adjacent
surface.
[0026] FIG. 11 is a diagram illustrating a fourth fringe area that
can occur at the interface between a prism tip and an adjacent
surface.
[0027] FIG. 12 is a perspective view of a differentially-cured
light-redirecting film.
[0028] FIG. 13 is a perspective view of a differentially-cured
linear prism.
[0029] FIG. 14 illustrates a pattern used to form
differentially-cured optical structures in accordance with an
embodiment of the invention.
[0030] FIG. 15 illustrates an embodiment of a pattern used to form
differentially-cured optical structures in accordance with an
alternative embodiment of the invention.
[0031] FIG. 16 is a schematic view of a method for forming the
differentially-cured light-redirecting film.
[0032] FIG. 17 is a cross-sectional view of another embodiment of a
differentially-cured optical structure.
[0033] FIG. 18 is a perspective view of the embodiment illustrated
in FIG. 17.
[0034] FIG. 19 is a perspective view of an embodiment of a logo
pattern used to form a differentially-cured pattern.
[0035] FIG. 20 is a cross-sectional view of a backlighting system
in accordance with an embodiment of the present invention.
[0036] FIG. 21 is a perspective view of a backlighting system in
accordance with an alternative embodiment of the present
invention.
[0037] FIG. 22 is a perspective view of two films in accordance
with alternative embodiments of the present invention.
[0038] FIG. 23 is a schematic view of a method for forming a
microstructured layer on a non-smooth layer.
[0039] FIG. 24 is an enlarged view of area A of FIG. 23.
[0040] FIG. 25 shows a plot of a surface profile with an
interference microscope trace that was made across the surface of a
film made with the pattern transfer process.
[0041] FIG. 26 is a perspective view of a differentially-cured
linear prism in accordance with another embodiment of the present
invention.
[0042] FIG. 27 is a partial perspective view of a light-redirecting
optical structure in accordance with an embodiment of the present
invention.
[0043] FIG. 28 is a partial perspective view of a light-redirecting
optical structure in accordance with another embodiment of the
present invention.
[0044] FIG. 29 is a partial perspective view of a light-redirecting
optical structure in accordance with a further embodiment of the
present invention.
[0045] FIG. 30 is a perspective view of an elevated portion in
accordance with an embodiment of the present invention.
[0046] FIG. 31 is similar to the structure of FIG. 29, but further
including elevated portions.
[0047] FIG. 32 is a perspective view of a backlight wedge that
includes a stepped structure on a bottom side thereof.
[0048] FIG. 33 is a perspective view of a backlight wedge that
includes tapered prisms on the output surface.
[0049] FIG. 34 is a perspective view of a backlight wedge similar
to that shown in FIG. 33, but further includes a
differentially-cured pattern on the tapered prisms.
[0050] FIG. 35 is a perspective view of a backlight wedge similar
to that shown in FIG. 33, but further includes cross-cut
prisms.
[0051] FIG. 36 is a perspective view of another embodiment of a
backlight wedge in accordance with an embodiment of the present
invention.
[0052] FIG. 37 is a perspective view of a backlight wedge that
includes a stepped structure on a bottom surface.
[0053] FIG. 38 is a perspective view of the backlight wedge of FIG.
37 that further includes tapered prisms on a top surface.
[0054] FIG. 39 is a perspective view of the backlight wedge of FIG.
37 that further includes linear prisms on a top surface.
[0055] FIG. 40 is a perspective view of the backlight wedge of FIG.
39 that further includes a differentially-cured pattern on the
linear prisms.
[0056] FIG. 41 is a perspective view of the backlight wedge of FIG.
41 that further includes cross-cut prisms.
[0057] FIG. 42 is a perspective view of the backlight wedge of FIG.
37 that further includes prisms that have a varying included
angle.
[0058] FIG. 43 is a perspective view of the backlight wedge of FIG.
42 that further includes cross-cut prisms.
[0059] FIG. 44 is a perspective view of the backlight wedge of FIG.
43 that further includes a differentially-cured pattern on the
prisms.
[0060] FIG. 45 is similar to the embodiment of FIG. 44, but the
cross-cut prisms extend above the prisms having the varying
included angle.
[0061] FIG. 46 is a perspective view of the backlight wedge of FIG.
37 that further includes prisms having a varying included angle on
a top surface in accordance with another embodiment of the present
invention.
[0062] FIG. 47 is a perspective view of a prior art stepped
waveguide.
[0063] FIG. 48 is a perspective view of the waveguide of FIG. 47
that further includes linear and cross-cut prisms on the top
surface having a differentially-cured pattern thereon.
[0064] FIG. 49 is a perspective view of the waveguide of FIG. 48
that further includes a waveguide positioned below the stepped
waveguide.
[0065] FIG. 50 is a perspective view of the waveguide of FIG. 49,
but the cross-cut prisms extend above the linear prisms.
[0066] FIG. 51 is similar to the embodiment of FIG. 50, but the
prisms on top of the waveguide have a varying included angle.
[0067] FIG. 52 is similar to the embodiment of FIG. 51, but further
includes additional cross-cut prisms.
[0068] FIG. 53 is a perspective view of a waveguide that includes
tapered prisms on the bottom surface.
[0069] FIG. 54 is a perspective view of the waveguide of FIG. 53
that has been modified and another waveguide provided at the apices
of the prisms.
[0070] FIG. 55 is a perspective view of the backlight wedge of FIG.
38 shown upside down.
[0071] The foregoing and other objects, features and advantages of
the invention will be apparent from the following more particular
description of various embodiments of the invention, as illustrated
in the accompanying drawings in which like reference characters
refer to the same parts throughout the different views. The
drawings are not necessarily to scale, emphasis instead being
placed upon illustrating the principles of the invention. All parts
and percentages are by weight unless otherwise specified.
DETAILED DESCRIPTION OF THE INVENTION
[0072] A description of various embodiments of the invention
follows.
[0073] Generally, the invention is directed to forming a pattern in
a radiation-curable material. The pattern, in one embodiment, is
transparent when viewed in a direction substantially normal to the
material. However, in a particular embodiment, the pattern can be
seen more clearly at a viewing angle of about fifteen degrees from
the normal.
[0074] Often, the term optical "sheets" refers to a more rigid
substrate, for example, one that could be leaned against a wall
without folding over on itself, and the term optical "films" refers
to a substrate that is more flexible, for example, one that could
be rolled up. However, depending on the size and thickness of the
sample, a film can act as a sheet. For example, a small, thin
polyester film can be rigid enough to lean against a wall without
folding over on itself. For purposes of understanding aspects of
the present invention, the terms "sheet" and "film" can be used
interchangeably. Sheets and films of the present invention can be
formed from plastic material, such as, polyurethane, polypropylene,
acrylic, polyurea, polyvinyl chloride, polycarbonate, polyester, or
polymethylmethacrylate. Polyurea is disclosed in U.S. patent
application Ser. No. 10/634,122, filed Aug. 4, 2003, the entire
teachings of which are incorporated herein by reference.
[0075] FIG. 1 illustrates an embodiment of the present invention
for forming a pattern, such as exemplary pattern "ABC" provided by,
for example, mask or pattern layer 10 disposed between a radiation
source 14 and a radiation-curable material 12. In one embodiment,
the mask layer 10 can include polycarbonate, polyethylene,
polybutylene or the like, and may include a low-tack adhesive. The
curable material 12 can include coatings and microstructured or
patterned materials formulated from materials, such as monomers
and/or oligomers that include epoxy, polyester, urethane, polyether
and acrylic acrylates or methacrylates or cationic monomers and
oligomers. Various additives including fillers, free-radical
initiators, and cationic initiators can be included in the material
12 to improve processing or performance. See, for example, Sartomer
Company Bulletin Nos. 4018 or 4303, the entire teachings of which
are incorporated herein by reference. The radiation source 14
preferably provides actinic radiation, which causes photochemical
activity in the curable material 12. For example, typical
ultraviolet light can be used. In particular embodiments, a
silicone-based coating can be provided on the mask layer 10 to
prevent the mask from adhering to the radiation-curable material 12
after it has been cured. In other embodiments, the material that
forms the mask layer 10 and the radiation-curable material 12 can
be selected to prevent the mask from adhering to the material after
it has cured.
[0076] The pattern layer 10 can include any kind of material that
blocks at least a portion of the radiation from the radiation
source to leave a similar pattern in the cured material 12. For
example, the pattern can be formed by a colored pattern, such as
using common printing inks, printed on a transparent polymer film
or light redirection properties of the film. The pattern can also
be formed by embossing patterns that affect the transparency of the
film. In one embodiment, the pattern can be applied directly on
either side of a substrate that carries the curable material 12
and, after curing, the pattern may or may not be removed to leave
the cured pattern in the cured layer 12. In alternative
embodiments, the pattern layer 10 can include a stencil or the
like, such as a colored or semi-transparent film material or a
clear resin with ultraviolet blocking chemical therein.
[0077] As shown in FIG. 2, the pattern layer 10 has been removed
but the pattern "ABC" has been transferred to the cured material
12. It is believed that the pattern changes the curing rate of the
material 12 to form the pattern in the cured material. It is
believed that the molecules in the formed pattern are denser
because the molecules have a longer time to cross-link than the
molecules that do not have a mask thereover. These denser regions
appear to have different indices of refraction. The pattern is best
viewed at an angle of about fifteen degrees to the surface.
[0078] FIG. 3 illustrates another embodiment for forming a pattern
in a material. In this embodiment, a pattern layer 10 is positioned
over a cured light-redirecting or retroreflective structure 16 that
can contain, for example, linear or cube-corner prisms. Examples of
suitable cube-corner prisms are disclosed in U.S. Pat. No.
3,684,348, issued to Rowland on Aug. 15, 1972, the entire teachings
of which are incorporated herein by reference.
[0079] A moth-eye structured layer 18 can be formed on the opposite
side of the light-redirecting or retroreflective structure 16 as
shown in FIG. 3. Moth-eye subwavelength structures are explained in
more detail in U.S. Pat. No. 6,356,389, which issued to Nilsen et
al. on Mar. 12, 2002, which corresponds to International
Publication No. WO 01/35128, published on May 17, 2001. The entire
teachings of each are incorporated herein in their entirety. The
moth-eye structures 19 are cured by the radiation source 14 through
the pattern layer 10 and light-redirecting structure 16 such that
the pattern is formed in the resin layer just below moth-eye
structures 18 without changing the shape of the moth-eye structures
or diffusing structure or other suitable structures. The outside
surface of the layer 18 can include indentations or contours 17
that are formed adjacent to the differentially-cured pattern.
[0080] A sub-wavelength structure applied can have an amplitude of
about 0.4 microns and a period of less than about 0.3 microns. The
structure is sinusoidal in appearance and can provide a deep green
to deep blue color when viewed at grazing angles of incidence if
the period is about 200 nanometers or about 0.15 micrometers. In a
particular embodiment, the amplitude is greater than two times the
period to provide a two or greater to one aspect ratio.
[0081] To form a sub-wavelength structure, the structure is first
produced on a photo resist-covered glass substrate by a holographic
exposure using an ultraviolet laser. A suitable device is available
from Holographic Lithography Systems of Bedford, Massachusetts. An
example of a method is disclosed in U.S. Pat. No. 4,013,465, issued
to Clapham et al. on Mar. 22, 1977, the entire teachings of which
are incorporated herein by reference. This method is sensitive to
any changes in the environment, such as temperature and dust, and
care must be taken. The structure is then replicated in a nickel
shim by an electroforming process.
[0082] In other embodiments, as illustrated in FIG. 4, a pattern
layer 10 can be placed on a first side of a substrate 11 and a
microstructured layer, such as a moth-eye structured layer 18, can
be formed on a second side of the substrate 11. The moth-eye
structures 19 are cured by the radiation source 14 through the
pattern layer 10 such that the pattern is formed in the resin layer
just below moth-eye structures 19 without changing the shape of the
moth-eye structures or diffusing structure or other suitable
structures. The outside surface of the layer 18 can include
indentations or contours 17 that are formed adjacent to the
differentially-cured pattern. As illustrated in FIG. 5, the mask 10
can be removed and microstructures, such as linear prisms 32, can
be formed on the first side of the substrate 11. In particular
embodiments, the substrate 11 can be formed from a thermoset or
thermoplastic material and layers 18 and 32 can be formed from a
thermoset material.
[0083] In various embodiments, the optical structures described by
James J. Cowan in the following references can be implemented
herein: Cowan, J.J., "The Holographic Honeycomb Microlens," Proc.
SPIE--The International Society of Optical Engineering, 523:251-259
(1985), and Cowan, J. J., "Aztec Surface-relief Volume Diffractive
Structure," J. Optical Soc. Am., Vol. 7, No. 8:1529-1544 (1990).
The entire teachings of these references are incorporated herein by
reference.
[0084] In another embodiment, a fine pattern can be formed on the
mask layer 10. For example, the pattern can be a few tenths of a
millimeter or less in width. A curable material, which can be
substantially clear when cured, is formed on the opposite side of
the mask layer 10 of the pattern and cured by a radiation source
14. The fine pattern is thus transferred to the cured material. The
mask layer 10 is removed and the cured sheet is placed in front of
a display, such as a liquid crystal display. The fine pattern
breaks up the pixel pattern in the display without as much light
loss as with diffuser sheets. The result is similar to surface
structures that are designed to apodize the wavefront.
[0085] In radiation cured casting processes where it is desirable
to produce features with multiple angles, one normally cuts
multiple angle features into the mold that is used for the
reproduction of the features. This is commonly true in the
manufacture of light-guiding or light-reflecting products where
small angle changes can strongly affect the product performance.
The cutting and replication of molds are costly and time consuming
processes.
[0086] With embodiments of this invention, one can produce a
variety of angle and pattern variations in a product from a single
mold design. One prints a "photomask" onto the surface of a carrier
sheet or film prior to formation and radiation cure of a mold
formed structure. The "photomask" can be clear or colored and be
applied to either side of the carrier. If the curing radiation is
highly collimated, it is desirable to have the "mask" be
semi-transparent to allow for slow curing in that area. In cases
where the radiation is less collimated, one can obtain cure through
totally opaque masks via scattering and reflections into the masked
area.
[0087] The resulting product then displays different optical
behavior in areas that have been masked due to the variation in
shrinkage and refractive index related to the speed of cure that is
varied by the "mask".
[0088] FIG. 6 shows a perspective view of a typical collimating
film 30 with linear prisms 32 having linear peaks 34 and valleys
36. The dihedral angle of the first side 38 and second side 39 of
the peak 34 is typically ninety degrees. However, it can be a
non-right angle. The linear prisms 32 can be formed on a base film
40.
[0089] It has been discovered that when the film 30 is positioned
adjacent to an optical element such as a diffuser or collimating
film, a portion of film 30 such as prism peaks 34 can "wet-out,"
which results in a visible defect. The wetting is believed to be a
result of both the contact point and the shape of the prism tip. A
sharp prism tip creates angles with the adjacent film and light
source that cause optical paths for the light reflection and
refraction that causes fringes that create a wetting
appearance.
[0090] FIG. 7 illustrates a concept called "Lloyd's mirror" that
explains how wet-out occurs, for example, at the interface between
prism peaks and adjacent surfaces. Lloyd's mirror is described in
the book entitled Fundamentals of Optics, F. A. Jenkins and H. E.
White (New York, McGraw-Hill), third edition, pp. 241-243 (1957),
the entire teachings of which are incorporated herein by
reference.
[0091] When light from a point source S reflects at grazing
incidence off of a flat surface 132 of a glass plate, for example,
there is a one-half wavelength phase change in the reflected light.
When the reflected beam, for example, beam 134, combines with a
beam 136 from the source S that is not reflected, interference
fringes are produced. For example, area 138 is a dark band because
beams 134 and 136 are 180 degrees out of phase. Alternating dark
and bright bands are produced along area 140. The same result
occurs if the light is traveling within the glass plate because the
total internal reflection is at an angle beyond the critical
angle.
[0092] FIGS. 8, 9, 10, and 11 illustrate four locations at which
Lloyd's mirror fringes can occur for each sharp prism tip 142 at
the interface between the tip and an adjacent surface, for example,
a diffuser 144. The diffuser surface acts as an imaging screen
making the fringes visible. The light source 146 is shown at the
bottom of each figure. FIGS. 8, 9, 10, and 11 illustrate a first
fringe area 148, a second fringe area 150, a third fringe area 152,
and a fourth fringe area 154, respectively, in which interference
fringes can occur.
[0093] The result for white light sources is a relatively wide band
of gray fringes on either side of the prism tip 142. If the prism
tip 142 is flat or slightly rounded in any way, there may also be
Newton's fringes or rings on top of the prism tips 142. One can
calculate the distance, Delta X, between the successive Lloyd's
mirror-type fringes using the following formula (although the
fringes are actually wider apart than calculated because of the
forty-five degree angle of the diffuser 144 to the tip 142):
Wavelength of a given light=[(Delta X).times.(Distance between real
and virtual images)]/Distance from source to diffuser surface. For
example, assuming that the wavelength of red light is about 0.6
micrometers, the distance between real and virtual images is about
ten micrometers, and the distance from the source to the diffuser
surface is about 150.0 micrometers. These assumptions give a Delta
X of about nine micrometers or, allowing for the forty-five degree
diffuser tilt, it is about twelve micrometers. Thus, for red light,
a dark fringe can occur just adjacent to the tip and then another
dark fringe can occur about twelve micrometers from the tip.
[0094] With white light, there is a continuum of overlapping light
and dark fringes in this area because of the continuum of
wavelengths from about 300 to 700 nanometers. It has been
discovered that by spacing the prism tip 142 away from adjacent
surfaces, such as a diffuser, Lloyd's mirror fringes can be
substantially minimized or even eliminated altogether.
[0095] FIG. 12 shows a perspective view of a prism array 52 of a
differentially-cured collimating film 50. Many of the prisms that
are not blocked by a mask, such as prism 54, have a linear peak 56.
Many of the prisms that are blocked, such as prism 58, are believed
to have a curved peak 60 that can be reduced in height. The curved
and reduced height peak is a result of curing through a mask, which
reduces or increases the cure rate with respect to the surrounding
areas. Typically, peak 60 is shaped compared to the normal apex of
linear peak 56 of prism 58. The region 62 is shaped in respect to
another region, which can result in a wider light distribution. The
shaped center line 66 of the peak in this prism can be off center
in respect to the normal center line 64 depending upon the curing
mask used. This region 62 also can have a slightly different index
of refraction in respect to other areas. The prisms can be formed
on a base film 68, such as a polyester, polycarbonate,
polyurethane, acrylic and polyvinyl chloride. In a particular
embodiment, the mask can cover up to about fifty percent of the
area of the product to be formed, such as a collimating film. The
shape of the differential cure area can be essentially any
configuration or size. This allows one to tailor the
light/distribution in specification areas of the sheet, such as to
comers or edges, instead of the center of the sheet. Also, if a
greater percentage of the area of the structure were blocked as
compared to exposed to ultraviolet light, the exposed portion can
result in raised portions or bumps. In structures where a lesser
percentage of the area of the structure were blocked as compared to
exposed to ultraviolet light, the structure can have an appearance
with recesses. The valleys of the prisms do not appear to change
the shape. If significant excess resin is present, the valley can
change shape as a result of the added volume of resin being
cured.
[0096] In alternative embodiments, one or both sides 69 of base
film 68 can have a differentially-cured pattern formed therein. By
providing a differentially-cured pattern on both sides of a film,
the film is strengthened and is more rigid. For example, the film
is more stable to temperature and humidity changes. In other
embodiments, a thermoplastic polymeric layer is extruded and
optical structures, such as micro optical structures, are applied
to both sides of the layer to form a mechanically stable composite
film.
[0097] The slight rounding of the tips or peaks 60 caused by the
differentially-cured process causes the angles between an adjacent
prism facets and the prism tips to be varied, thus reducing the
wetting effect.
[0098] FIG. 13 over-exaggerates a visible random shape surface that
can be formed on prism 58 by the differentially-cured process. In
this embodiment, about a 0.3 micrometer or one-half wavelength
depth 59 structure 61 with a continuously varying, somewhat random
slope causes the light ray path length as shown, for example, in
FIGS. 8, 9, 10, and 11, to be random in length. In reality, there
is a plurality of structures 61 on each prism 58. Therefore, the
uniform phase changes that occur from a flat reflecting surface do
not occur. Interference fringes do not occur and wet-out is not
visible. Thus, the slight curvature of the structure 61 reduces
Lloyd's mirror fringe effects. The structure 63 can have a random
oscillation of about 250 micrometers.
[0099] In the area that was blocked, the prisms can have nanometer
size striations caused by the differential cure shrinkage pattern.
These striations can perform like a vertical linear moth-eye
structure. Some striations can extend from the peak to valley. The
striation can range in width of between about 250 and 770
nanometers, depending on the mask pattern. The striations can cause
upward light tunneling.
[0100] FIG. 14 is a mask pattern 42 used in a differentially-cured
process in accordance with embodiments of the invention. A
plurality of at least partially opaque or black dots or areas 44 is
randomly positioned on a transparent layer 46. Opaque can be
defined as capable of blocking more than about fifty percent of
incoming light. The mask pattern 42 can be positioned over the
peaks of linear prisms, in which case prism heights and prism facet
surface variations occur where the black dots 44 are located and
the height shift and facet surface variation are constant or the
same for all masked areas or zones. Where there are no black dots
44, the prism height surface shape is constant. The mask pattern 42
can be used with any geometric structures including a smooth side
of a film or sheet. In one embodiment, the opaque areas include
alphanumerics or geometric patterns having line widths of about
fifty to 500 micrometers. There are times when it is desirable to
add control to the depth or height of the structure that a common
random pattern differential cure process does not allow. Common
random print patterns combine multiple dots or pixels to build
half-tones and then the multiple dots act as one larger dot in the
cure process, thereby adding a range of depths to the finished
structure.
[0101] A process is provided that allows practitioners of the
differential curing of optical products to control the shape of the
resulting structures. Additionally, one may choose to build two,
three, or more different heights and depths into a product while
maintaining control of each in a stepwise fashion. The advantage
gained is that the pattern is truly random in one dimension while
the shape of the surface structure varies in a non-random,
predictable fashion. One way in which this is accomplished is to
make pattern mask prints in which the opaque pixels, for example,
dots, hexagons, square, etc., have borders or "halos" around
them.
[0102] As shown in FIG. 15, a halo 49 surrounds each opaque dot or
pixel 48. This allows the pixels 48 to act as independent entities
during the cure process so that the pixels 48 do not act as larger
printed spots when the individual pixels 48 are adjacent to each
other. The halo 49 needs to be large enough to allow sufficient
radiation to cure the spaces between the pixels at a normal rate.
In a particular embodiment, the opaque pixels 48 have a diameter 51
of about 152 micrometers (6 mils), and the halo 49 has a width 53
of about 76 micrometers (3 mils). These pixels 48 can be formed on
one or both sides of an optical sheet or film and can be formed on
a structured, for example, or non-structured surface.
[0103] In one method for forming the pattern illustrated in FIG.
15, a total coverage of the pattern by opaque pixels 48 is
selected, for example, a coverage of 20 percent. Based on given
pixel 48 and associated halo 49 diameters, the pixels 48 are
randomly distributed throughout the pattern. In a specific
embodiment, the pixels 48 are printed onto a transparent film that
is then placed over a radiation-curable material during the curing
process.
[0104] Many other types of prisms can be used including cube-corner
prisms. Cube-corner or prismatic retroreflectors are described in
U.S. Pat. No. 3,712,706, issued to Stamm on Jan. 23, 1973, the
entire teachings of which are incorporated herein by reference.
Generally, the prisms are made by forming a master negative die on
a flat surface of a metal plate or other suitable material. To form
the cube-corners, three series of parallel equidistance
intersecting V-shaped grooves sixty degrees apart are inscribed in
the flat plate. The die is then used to process the desired
cube-corner array into a rigid flat plastic surface. Further
details concerning the structures and operation of cube-corner
microprisms can be found in U.S. Pat. No. 3,684,348, issued to
Rowland on Aug. 15, 1972, the entire teachings of which are
incorporated herein by reference. Also, the pattern transfer
concept can include forming a structured coating onto a smooth
surface and also forming a pattern structure onto a micro optical
array of any type, including submicron to micron size surfaces.
Further, a pattern can be placed on plano surfaces, prism surfaces,
lens structures, and others. The pattern can be random, ordered, or
designed to convey a message. In alternative embodiments, the
cube-corner arrays can be oriented in two or more directions, as
disclosed in U.S. Pat. No. 6,036,322, which issued on Mar. 14,
2000, and U.S. Pat. No. 6,457,835, which issued on Oct. 1, 2002.
The entire teachings of these patents are incorporated herein by
reference.
[0105] It has been discovered that a differentially-cured pattern
formed on facets of the cube-corner prisms can improve the
resulting light distribution, for example, by spreading out light
to smooth out the diffraction patterns. Retroreflective sheeting
that includes cube-corner prisms can be cut or formed into flakes,
chips, or threads as disclosed in U.S. patent application Ser. No.
10/438,759, filed on May 15, 2003, the entire teachings of which
are incorporated herein by reference. At least a portion of at
least some of prism facets can include a differentially-cured
surface to reduce or eliminate glint or glitter.
[0106] Referring to FIG. 16, a method for forming the
differentially-cured light-redirecting or collimating film will now
be described in further detail. A mold 102 is ruled with linear
grooves 120 essentially parallel to the axis about which the mold
rotates. Although the linear grooves on the mold 102 are shown with
their longitudinal axes oriented perpendicular to the paper, the
grooves can be oriented in any direction. In a particular
embodiment, the linear grooves 120 are ruled around the
circumference of the mold 102. The linear grooves can be pitched
between about 0.05 and 0.2 mm (0.002 and 0.008 inches). A base film
104 is unrolled from roll 106. The base film 104 can be a suitable
material, such as a polyester. Mask film 108 is unrolled from
second roll 110. Mask film can be formed of a suitable material,
such as polyester, upon which a non-transparent design is printed
on the transparent mask film. The non-transparent design can be
printed on the mask film in the same manner as a design is printed
on an overhead transparency. The base film 104 and mask film 108
are laminated together by first roller 112 against mold/roller 102.
The base film 104 and mask film 108 are kept in close contact with
mold 102 until second roller 114. In another embodiment, base film
and mask film can be laminated together as a single sheet and then
unrolled from a single roll.
[0107] In yet another embodiment, a removable pattern can be
directly printed on a first side of the base film with a suitable
light-blocking material, such as a water soluble ink or the like. A
curable layer of light-curable material is placed on the second
side of the base film, and the curable layer is
differentially-cured in the presence of light directed through the
pattern and base film to the curable layer. After differentially
curing the layer, the removable pattern is removed from the base
film. For example, it can be removed with a solvent, such as water
for a water soluble ink. However, other solvents can be used, such
as alcohol, hydrocarbons, etc., depending upon the ink or other
material used to form the light-blocking pattern on the base film.
An advantage of this embodiment is that a separate mask film is not
needed.
[0108] In another embodiment, a pattern is directly printed onto a
first side of a base film with a radiation or light-blocking
pigmented or dyed ink that is colored or a clear ink that contains
ultraviolet (UV) blocking chemicals, such as those sold by Ciba
Geigy Corporation under the trade name of "Tinuvin". The pattern
need not be removed after the curing step and it remains on the
product. This negates the need for a separate masking film and can
provide for an additional decorative or functional feature if the
pattern remains on the product surface.
[0109] Prism monomer material 116 is placed at point 118 proximate
to roller 112. The monomer material, such as an acrylic, flows into
the grooves 120 of mold 102. The prism monomer material 116 is
cured differentially by the partially blocked ultraviolet light as
it passes ultraviolet lamps 122, 124 to form differentially-cured
collimating film 126. Differentially-cured collimating or
light-redirecting film 126 is wound up on wind-up roller 128. The
mask film 108 is wound up on second wind-up roller 130.
[0110] In a collimating or light-redirecting film having portions
that are differentially-cured, light is directed through the
collimating film that results in different shades of lighting.
Lighter portions include the regions with ninety degree linear
prisms. Regions with darker portions include the prisms that were
differentially-cured by blocking by the mask. In these darker
portions, the prisms are slightly distorted due to the different
cure rate and appear darker because the light is spread over a
broader range.
[0111] A light-redirecting film sheeting can be used for
collimating or redirecting light in backlighting systems. The
light-redirecting film sheeting 200, as shown in a cross-sectional
side view in FIG. 17 and in a perspective view in FIG. 18, includes
a base film 202 formed of a transparent polyester film, such as ICI
Dupont 4000 PET, or polycarbonate, such as Rowland Technologies
"Rowtec" film, having a thickness in the range of between about 50
and 250 micrometers (0.002 and 0.01 inches). In one embodiment, the
sheeting can have a thickness in the range of between about 0.1 and
0.15 mm and (0.004 and 0.006 inches) and an index of refraction in
the range of between about 1.49 and 1.59.
[0112] A series of transparent linear prisms 204 having sides 206
are formed over the base film 202. Sides 206 can be isosceles. The
linear prisms 204 extend across the sheeting. The prisms are formed
of a transparent resin, such as a mixture of polymerized CN104
polyacrylate available from Sartomer Chemical Co. and RDX51027 from
UCB Chemical. The linear prisms are pitched a distance (p) in a
range of between about 25 and 100 micrometers (0.001 and 0.004
inches), preferably about 48 micrometers (0.0019 inches) per prism.
The linear prisms have a height (h) in a range of between about 20
and 100 micrometers (0.0008 and 0.004 inches), and in a particular
embodiment about 25 micrometers (0.001 inches). The linear prisms
have pointed peaks 206 with a peak angle ( ) as desired, with
preferred values of 88 or 90 degrees in a sheeting. Base angles
.beta..sub.1 and .beta..sub.2 can be the same or different. The
linear prisms 204 can be attached to the base film 202 by an
optional prism adhesive layer 208, such as 7650TC acrylic adhesive
available from Bostik Chemical. Prism adhesive layer 208 has a
thickness (a.sub.1) in the range of between about 2.5 and 12
micrometers (0.0001 and 0.0005 inches).
[0113] On the non-prism side 210 of the base film 202, a pattern
structure 212 is formed, such as with a resin composition similar
to or the same as the prism side adhesive layer. The pattern
structure 212 can be attached to the base film 202 by pattern
adhesive layer 214, which is similar in material and thickness
(a.sub.2) to prism adhesive layer 208. Pattern structure 212 has a
thickness in the range of between about 2.5 and 12 micrometers
(0.0001 and 0.0005 inches). In alternative embodiments, the pattern
structure 212 has a thickness in the range of between about 0.1 and
400 micrometers (3.94.times.10.sup.-6 and 0.016 inches). In a
particular embodiment, the pattern structure 212 is formed on the
base film 202 and cured through base film 202. The linear prisms
204 can then be formed to provide the film 200 shown in FIG. 17. In
further embodiments, a mask can be provided on pattern structure
212 and a differentially-cured pattern can be formed in the prisms
204. The thin pattern structure 212 does not adversely affect the
structure formed in the prisms 204. If the prisms 204 are first
formed on film 202 and the pattern structure 212 is cured through
the prisms 204, the structure 212 can be distorted because the path
of radiation is changed by the prisms 204 as it travels
therethrough. Additionally, it can be difficult to hold the mask on
the prism tips.
[0114] As shown in FIG. 19, pattern structure 230 includes a logo
232, which is an arrangement of four obtuse scalene triangles. The
logo can be a company name, a trademark, a figure, or other desired
design. The pattern structure can be printed on sheeting such as a
polyester overhead projector sheeting by a laser printer. In the
shown embodiment, the logo is repeated in a line on a first axis
about every 13 mm. The logos in each line are off-set in the next
by a half of a logo and the lines repeat about every 7.5 mm along a
second axis in the run/web direction, which is perpendicular to the
first axis. The lines of the logo are about 0.5 mm in width. Other
types of designs include cross hatching, geometric figures,
numerals, letters, etc.
[0115] Returning to FIG. 18, the lines are depressions 216 or
recesses in the surface of the non-prism side. Depressions 216 can
have a depth (d) in the range of between about 0.3 and 2.0
micrometers, with an average depth of one micrometer. In
alternative embodiments, the depth (d) can be in the range of
between about 0.05 and 0.125 micrometers. The depressions are not
uniform in slope from edges 218 to low point 220. The depressions
can have an average slope of about 0.1 degrees to the surface of
the base film 102 with the slope being as high as one degree.
[0116] The pattern structure is formed by placing a mask film
temporarily on one side of the base film. The mask film has a logo,
geometric form (lines, circles, curves, etc.), alphanumerics, or
any other desired design formed thereon that can block a portion of
the ultraviolet light as it passes from ultraviolet light source
through the mask film to the base film. The portion of the mask
film without the logo printed thereon is more transparent to
ultraviolet light. On the other side of the base film, an adhesive
layer is deposited and an uncured radiation-curable resin is placed
on the adhesive layer. Ultraviolet light is directed from an
ultraviolet light source through the mask layer through the base
layer, through the adhesive layer, to the resin layer. The resin
layer is differentially-cured because the ultraviolet light
intensity is blocked unevenly by the printed patterned to the resin
layer, resulting in the pattern structure. The pattern structure is
uneven and segmented. The portions of the resin layer that have the
greatest blockage from the ultraviolet light have the deepest
depressions in the surface. The portions that were directly exposed
to ultraviolet light, without blocking, resulted in segments with
relatively flat surfaces. The mask film is then removed from the
base film. The linear prisms are cast on the same side of the base
film where the mask film had been placed. The linear prisms are
cured by ultraviolet light directed through the base film. The
linear prisms can be slightly differently cured in the portions
that are exposed to the ultraviolet light that passes through the
pattern structure that is uneven and segmented.
[0117] The film can be placed between a light guide and a display,
such as a liquid crystal display. The fine pattern breaks up the
pixel pattern in the display without as much light loss as with a
diffuser sheet. The pattern structure on the film can be readily
visible across the film.
[0118] The film can be used as a single sheet or as a two-sheet or
more system. A two-sheet system has the peaks pointed in the same
direction, and the length of the peaks on each sheet are often
crossed at ninety degrees.
[0119] The differentially-cured process of the present invention
can be used to form security coatings, for example, coatings on
document or currency papers, fibers, threads, films, identification
cards, or wrapping film for expensive products.
[0120] FIG. 20 illustrates an optical system in which sheets or
films having differentially-cured structures can be implemented. In
this embodiment, a back lighting system 234 includes a light source
236 and light reflector 238. Light source 236 can be a fluorescent
light, incandescent light, or other suitable light source.
Waveguide 240, which is for directing light out of a back lighting
system, can be formed of a transparent solid material and is often
wedge-shaped. On one side of waveguide 240 is waveguide reflector
242 formed of a specular material, such as aluminum or a coated
white surface, for reflecting light back to waveguide 240.
Waveguide reflector 242 can be curved or flat. Diffuser 244 is a
film that diffuses the light from the waveguide into a
substantially uniform distribution. An example of a suitable
diffuser is a randomly textured surface or gradient index film or
engineered diffractive structure.
[0121] Above diffuser 244, first light-redirecting or collimating
film 246 can have a grooved structure 248 on a first side adjacent
waveguide 240 as disclosed in U.S. patent application Ser. No.
10/046,929, filed on Jan. 15, 2002, published as U.S. Patent
Application Publication 2003/0133301 on Jul. 17, 2003, the entire
teachings of which are incorporated herein by reference. Grooved
structure 248 can have a series of base planes 250 and plateaus 252
that run along a first axis from one side of collimating film 246
to a second side of collimating film 246 to provide an unsmooth
surface opposite the prism surface 254. Linear prism surface 254
can have prism surfaces 256 and windows 258 and be formed of a
transparent polymeric material. Prisms 260 have sides 256 with
peaks 262 and valleys 264. The pitch (p) of the prisms 260 is
measured from valley 264 to next valley 264. In one embodiment, the
pitch can be in the range of between 25 and 76 micrometers (0.001
and 0.003 inches). The height (h) of the linear prisms 260 is
measured by the vertical distance from the valley 264 to peak 262.
The height (h) can be in the range of between 7.6 and 38
micrometers (0.0003 and 0.0015 inches). Included angle (.beta.) is
measured between the two sides 256 that meet at peak 262. The angle
(.beta.) can range from about sixty to 120 degrees. In one
embodiment, the angle (.beta.) is in a range of between about sixty
and eighty-five degrees or between about 95 and 120 degrees. Sides
256 on each side of peak 262 can be side length (l) from valley 264
to peak 262 to form an isosceles triangle. Alternatively, the sides
can have different lengths, such as with a scalene triangle,
thereby tilting or canting the prisms.
[0122] Base planes 250 and plateaus 252 are connected by walls 266,
which are substantially perpendicular to base planes 250 and
plateaus 252. Walls 266 can be a few degrees off perpendicular to
either base planes 250 and plateaus 252. Also, the walls 266 can be
curved. Base planes 250 and plateaus 252 are of such sizes to
reduce the visibility of Newton's rings and moire fringes while
minimizing surface-to-surface contact with films or the peaks of
prisms, thereby reducing wet-out. The width of base plane 250 can
be in the range of between about one and about 300 micrometers. In
another embodiment, the width of base plane 250 can be in the range
of between about ten and about 200 micrometers. In particular
embodiments, the width of plateaus 252 can be in the range of
between about one and fifty micrometers. In another embodiment, the
width of plateaus 252 can be between about ten and about 50
micrometers. The ratio of the width of plateau 242 to the width of
base planes 250 can be in the range of between about one and about
ten. In one embodiment, base planes have a width of about 150
micrometers (0.006 inches) and plateaus have a width of about 25
micrometers (0.001 inches). In another embodiment, base planes 250
have a width of about 185 micrometers (0.0073 inches) and plateaus
252 have a width of about 33 micrometers (0.0013 inches). Walls 266
can have a height in the range of between about 0.4 and about 0.8
micrometers, which provides a difference in elevation between base
planes 250 and plateaus 252 from a base point in the film. In one
embodiment, the height of walls 266 is in the range of between
about 0.5 and 0.8 micrometers. The difference in elevation between
the base plane and plateaus can be less than about the wavelength
of visible light. The dimensions of the width of the plateaus can
each be less than about 3.175 micrometers (1.25.times.10.sup.-4
inches).
[0123] An optional abrasion reduction layer 268 can be positioned
between first collimating film 246 and second collimating film 270.
Abrasion reduction layer 268 can have a grooved structure on one or
two surfaces to improve performance by reducing wetting or Newton's
rings. In alternative embodiments, a diffusing layer can be
positioned above first collimating film 246 in combination with or
without the abrasion reduction layer 268.
[0124] Second light-redirecting or collimating film 270 can include
second grooved structure 272 on a first side adjacent first
collimating film 246 and prism structure 274 on an opposing side.
Prism structure 274 of second collimating film 270 can be oriented
in the same direction as the prisms on first collimating film 246.
Alternatively, it may be offset by rotating the prism orientation
up to about 180 degrees. In one embodiment, second collimating film
270 is rotated about ninety degrees with respect to the first
collimating film to reduce moire fringe formation and improve the
uniformity of the exiting light distribution. Also, the peaks 262
cross the grooved structure 272 with minimal contact to reduce
wet-out between films.
[0125] Above second collimating film 270 is liquid crystal display
276. A diffusing layer can be positioned above the second
collimating film 270. A collimating film that has linear prisms
designed with a tilt, size, and included angle that match the light
source, waveguide, and diffuser properties provides enhanced
performance. The advantages of employing linear prisms with
included angles that range from ninety-five degrees to 120 degrees
provide a light distribution that can be optimized for viewing
angles of a computer screen. The included angle is considered the
top angle of a triangular linear prism structure.
[0126] Another embodiment in which embodiments of optical films of
the present invention can be used is shown in FIG. 21. A back
lighting system 278 includes a light source 280 and a light
reflector 282. Waveguide 284 can be formed of a transparent solid
material and can be wedge-shaped and be formed from a thermoset or
thermoplastic material.
[0127] Adjacent to the first side 286 of waveguide 284 is waveguide
reflector 288 formed of a specular reflecting material. The
reflector 288 can be spaced slightly away from surface 286 to allow
total internal reflection at surface 286 to take place.
Alternatively, the reflector 288 can have a grooved structure on
the side facing waveguide 284. The grooved structure of the
reflector can be coated with a specular reflecting material.
Alternatively, if the reflector 288 is transparent, the reflector
can be coated on the side away from waveguide 284. First side 286
can be stepped in shape. Second side 290 of waveguide 284 is on the
opposite side away from waveguide reflector 288 and can have
grooved structures 292. In other embodiments, a moth-eye structured
layer can be superimposed on a differentially-cured structure on an
undulating surface on the second side 290, as illustrated, for
example, in FIG. 24.
[0128] Above waveguide 284, first light-redirecting or collimating
film 294 has first prism structure 296 with peaks 298 pointed
toward waveguide 284. In alternative embodiments, a diffusing layer
is positioned above waveguide 284. First collimating film 294 can
include first grooved structures 300 on the window side of first
prism structure 296. The peaks of linear prisms on first
collimating film 294 can run parallel to light source 280. First
grooved structure 300 has base planes 302 and plateaus 304 that are
parallel with peaks 298 to provide a non-smooth structured surface.
Base planes 302 and plateaus 304 are connected by walls 306. Walls
306 can be substantially perpendicular to base planes 302 and
plateaus 304, which includes walls 306 that can be a few degrees
off perpendicular to either base planes and plateaus. Also, the
walls can be curved. Base planes 302 and plateaus 304 are
substantially parallel but not coplanar.
[0129] Above first collimating film 294, second light-redirecting
or collimating film 308 can include second grooved structure 310
and second prism structure 312. Peaks 313 of second prism structure
312 point away from waveguide 284. Second grooved structure 310 has
base planes 316 and plateaus 318 that are in parallel with peaks
314 to provide a non-smooth structured surface. Base planes 316 and
plateaus 318 are connected by walls 320 and are substantially
parallel but not coplanar in a particular embodiment. The peaks 314
of second prism structure 312 can be oriented in a non-parallel
direction to peaks 298 of first prism structure 296. Another
orientation is ninety degrees. A diffusing layer can be positioned
above second collimating film 308. In alternative embodiments, the
moth-eye structures can be provided on any of the prism structures,
for example, on prism structure 296.
[0130] Differentially-cured structures or patterns and/or moth-eye
structures can be provided on one or both sides of any of the
elements or layers of any of the embodiments disclosed herein,
including the embodiments of FIGS. 20 and 21 to reduce undesirable
optical conditions, such as wet-out. For example, the linear prisms
of collimating films 246, 270, 294, and/or 308 can include random
and/or uniform differentially-cured patterns to minimize and
eliminate wet-out between adjacent structures. Also, grooved
structures 248, 272, 300, and/or 310 can include
differentially-cured patterns for the same reason.
[0131] FIG. 22 is a perspective view of an optical structure 322
that includes a first film 324 and a second film 326. In this
embodiment, each film 324, 326 includes a series of linear prisms
328, 330, which can be used to redirect or collimate light. Films
324, 326 can also include grooved structures 332, 334 to reduce
visible optical defects. Additionally, differentially-cured
patterns and/or moth-eye structures can be formed on one or both
sides of each film 324, 326 to further improve optical properties
of the optical structure 322. In a particular embodiment, a random
differentially-cured pattern is formed on linear prisms 328, 330
and a regular or uniform differentially-cured, for example, pattern
230, is formed on grooved structures 332, 334. In alternative
embodiments, the grooved structures 332, 334 are not present, i.e.,
the sides 336, 338 are substantially planar and a regular
differentially-cured pattern is formed thereon. In further
embodiments, the uniform differentially-cured patterns on side 338
and the random differentially-cured pattern on prisms 328 are
matched such that the combination of the patterns provides an air
gap of at least about 0.5 micrometers to prevent wet-out, avoid
moire problems, reduce scratch resistance, and avoid Newton's
rings. The depth of the differentially-cured patterns can be
adjusted to avoid visibilities of the patterns, which can sometimes
be a problem to the backlight manufacturers. Having the
differentially-cured patterns on both sides of a film, for example,
film 324 or film 326, improves the thermal, mechanical, and
moisture stability of the film. The differentially-cured pattern
feature size, depth, and spacing on either the prism side or the
opposing side can be matched to specific diffusers that can be used
adjacent to the prism side or the non-prism side, depending on the
application.
[0132] If a moth-eye structured surface is provided on side 338
with or without grooved structure 334, random differentially-cured
patterns formed on linear prisms 328 prevent wet-out to the
moth-eye surface. The moth-eye structured surface on side 338 can
be formed with differentially-cured patterns superimposed in the
moth-eye resin layer (see Example 1 below).
[0133] In alternative embodiments, microstructures that can include
a regular and/or random pattern can be formed on either side of
films 324, 326. For example, a drum can be faced and a negative
image of the desired pattern can be formed in the drum. The drum
can then be used to cast microstructures on the film.
[0134] The linear prisms in any of the embodiments of the present
application can include three or more planar surfaces or facets
(not including the base or window side) as disclosed in U.S. patent
application Ser. No. 10/023,204, filed on Dec. 13, 2001, published
as U.S. Patent Application Publication 2002/0097496 on Jul. 25,
2002, the entire teachings of which are incorporated herein by
reference.
[0135] If a non-prism side of a film, for example, side 336 with or
without grooved structure 332, is positioned adjacent to other
structures that are smooth, Newton's rings or fringes may appear. A
regular or random differentially-cured pattern can be provided on
either or both contacting surfaces to provide at least a 0.3
micrometer structure to prevent Newton fringes.
[0136] In other embodiments, a microstructured surface, such as a
moth-eye structure, can be provided on a non-smooth or undulating
surface to provide an anti-glare, anti-reflection surface and for
purposes, such as prevention or minimization of wet-out. A
particular method of manufacturing an undulating structure is
illustrated in FIG. 23 in which a casting drum 340 includes
moth-eye tooling 342 on an outer surface thereof. Although the
linear grooves of the moth-eye structure are shown with their
longitudinal axes oriented perpendicular to the paper, the grooves
can be oriented in any direction. In a particular embodiment, the
linear grooves of the moth-eye structure are ruled around the
circumference of the drum 340.
[0137] A resin 344, such as an ultraviolet-curable resin, can be
flowed between the tooling 342 and a substrate film 346 dispensed
from a roll 347. An excess layer of resin 348 can be provided on
film 346 as illustrated in FIG. 24, for example, by a fixed gap
provided between the film 346 and tooling 342. In other
embodiments, the running speed of the film 346 and viscosity of the
resin 344 can be used to control the excess resin 348 thickness. In
particular embodiments, the layer 348 has a thickness between about
0.0127 and 0.127 mm (0.0005 and 0.005 inches).
[0138] A film 350, such as a transparent, flexible thermoplastic
film, can include a mask 352 or pattern layer dispensed from roll
351. The film 350 can be laminated against the substrate film 346
as illustrated. Rollers 353 can be used to guide films 346, 350 and
mask 352 in this manufacturing setup. As the mask 352 passes by one
or more curing lamps 354, a differential shrinkage occurs in the
excess resin layer 348. The moth-eye structure 356 is small and
cures first and retains fidelity and is superimposed on the
differentially-cured areas of excess resin 348 that can be formed
in a non-smooth or wavy pattern that is determined by the pattern
of the mask 352. Moth-eye structure 356 and film 346 can be wound
up on take-up roll 358 and film 350 and mask 352 can be wound up on
take-up roll 360.
[0139] Optical structures and inventive concepts are disclosed in
commonly owned U.S. Patent Application No. 60/467,494, filed on May
2, 2003, the entire teachings of which are incorporated herein by
reference. The optical structures and concepts can be used with the
inventive principles disclosed herein.
EXAMPLE 1
[0140] A polycarbonate substrate was covered with a number 30LC
mask film (manufactured by Ivex Packaging Corporation) that had a
blue colored "PEEL" pattern printed on it. Moth-eye structures were
cast on the opposite side of the substrate and cured by ultraviolet
radiation at a web speed of about twelve meters per minute (forty
feet per minute) past two 157-236 watts/lineal centimeter (400-600
Watts/lineal inch) ultraviolet lamps manufactured by Eye
Ultraviolet Corporation. After removing the mask film, the cured
moth-eye structures retained the "PEEL" pattern that could not be
readily seen at a zero degree viewing angle but were pronounced at
about a fifteen degree viewing angle.
EXAMPLE 2
[0141] Alphanumeric images were handwritten onto the surface of a
mask film on a cling mask sample of polycarbonate film manufactured
by Rowland Technologies Incorporated. Commonly available felt tip
marker pens were used to form the images. An ultraviolet curable
coating of epoxy acrylate was applied to the other side of the
polycarbonate film and cured under a 236 Watts per lineal
centimeter (600 Watts per lineal inch) lamp at about 4.6 meters per
minute (fifteen feet per minute). The mask film was removed and the
cured coating was visually examined at various angles. The images
that had been on the mask film were visible at shallow viewing
angles in the cured coating.
EXAMPLE 3
[0142] FIG. 25 shows a plot of a surface profile with an
interference microscope trace that was made across the surface of a
film made with the pattern transfer process.
[0143] The height of the features is slightly less than one
wavelength of red light. Red light wavelength is 632.8 nm
(2.49.times.10.sup.-5 inches). The height of the features is
approximately 500 to 900 nm (1.9685.times.10.sup.-5 to
3.5433.times.10.sup.-5 inches). The average height is about 640 nm
(2.5197.times.10.sup.-5 inches).
[0144] The height and slope of the features caused some light
deviation as the light passes through the film. However, the effect
on LCD back light brightness appears to be positive by about a one
percent gain. Additionally, these features can act as resting
points for the prism peaks of collimating films as the films are
stacked upon each other and therefore prevent the majority of the
prism peaks from being damaged by abrasion.
[0145] FIG. 26 is similar to the embodiment of FIG. 13 and
illustrates a visible random shaped surface that can be formed on
prism 58 by a differentially-cured process. In this embodiment, the
amplitude A of the prism 58 is about 0.3 micrometers and the
differentially-cured structure 63 can have a random oscillation of
about 250 micrometers. In this embodiment, the sides 61 of the
linear prism 58 are curved as shown while the peak 362 is
substantially linear. The edges 61 of the prism 58 extend a
distance 364 of about 0.3 micrometers from an imaginary line 366
that represents a flat side of the prism 58.
[0146] FIG. 27 is a partial perspective view of a light-redirecting
optical structure 368 that includes linear prisms 370 and
"cross-cut" prisms or reverse threads 372. In a particular
embodiment, the prisms 370 have an included angle at the apex 371
of about 90 degrees. The cross-cut prisms 372 help smooth out the
optical output when used as light piping. If one set of prisms 370,
372 is taller than the other, wet-out can be reduced with respect
to adjacent optical structures. In a particular embodiment, a drum
can be ruled with a first set of grooves which will form linear
prisms 370. The drum can then be ruled at a wider pitch which will
form the cross-cut prisms 372.
[0147] FIG. 28 is similar to FIG. 27 but the included angle of the
cross-cut prisms 372 is varied to optimize optical performance. If
the included angle of the cross-cut prisms 372 is greater or less
than 90 degrees, more light is allowed to escape, i.e., less light
is reflected toward the light source.
[0148] FIG. 29 is a partial perspective view of a light-redirecting
optical structure 368 that includes linear prisms 370, cross-cut
prisms 372, and differentially-cured patterns 374 formed in the
prisms 370, 372. The differentially-cured patterns 374 can be used
to reduce wet-out and smooth out light that is collimated.
[0149] FIG. 30 illustrates an elevated portion 376, which can also
be referred to as a bump, feature, pip, or differential height
locator, provided on at least some of the peaks of the prisms 370,
cross-cut prisms 372, or both. Elevated portions are disclosed in
U.S. patent application Ser. No. 10/830,701, filed on Apr. 23,
2004, the entire teachings of which are incorporated herein by
reference. A plurality of elevated portions 376 can be used to
beneficially space the prisms 370, 372 away from adjacent optical
sheets, surfaces, films, substrates, or other layers to minimize
wet-out, Newton's rings, abrasions, moire fringes, or other
undesirable optical conditions. The slight curvature created in the
prism sides 378 reduces Lloyd's mirror fringe effects. In a
particular embodiment, the elevated portions 376 are randomly
located on the prism peaks. In another embodiment, the elevated
portions 376 are located on the peaks in a predetermined
pattern.
[0150] FIG. 31 is similar to the structure of FIG. 29 but further
includes the elevated portions 376 on the peaks of the prisms 370
and/or cross-cut prisms 372.
[0151] FIG. 32 is a perspective view of a backlight wedge 380 that
includes a stepped structure 382 on a bottom side that decreases in
size traversing the wedge away from the light source which is
positioned at end 384. The wedge 380 can be used in a backlit
system, for example, a computer display device, to redirect light
uniformly along output surface 386. In one embodiment, the
structures 382 are integrally molded to the wedge 380.
[0152] FIG. 33 is a perspective view of a backlight wedge 380 that
includes tapered prisms 388 on the output surface 386 to optimize
the light exiting the wedge. The tapered prisms 388 reduce light
piping away from the light source and collimates light exiting the
wedge 380.
[0153] FIG. 34 illustrates a backlight wedge 380 similar to that
shown in FIG. 33, but further includes a differentially-cured
pattern 390 on the tapered prisms 388. FIG. 35 illustrates a
backlight wedge 380 that also includes cross-cut prisms 392
traversing the wedge. The cross-cut prisms 392 can be elevated
above the tapered prisms 388 to prevent wet-out conditions. In
other embodiments, the cross-cut prisms 392 can be about the same
height as the tapered prisms 388.
[0154] FIG. 36 illustrates a backlight wedge 380 that includes
linear prisms 394 on the output surface 386 for collimating or
redirecting light. A plurality of cross-cut prisms can also be
provided on the output surface 386. Differentially-cured patterns
390 can be provided on the prisms 392, 394 for the reasons
discussed above.
[0155] FIG. 37 illustrates a backlight wedge 380 having a stepped
structure 382 on a bottom surface. A reflective surface 396 can be
provided on the bottom of the stepped structure 382 for redirecting
light up toward the output surface 386. Reflective surface can be a
reflective coating which can be formed of aluminum, silver or gold.
FIG. 38 is a wedge 382 similar to FIG. 37, but includes tapered
prisms 388 on the output surface 386. FIG. 39 is similar to the
embodiment of FIG. 39, but includes linear prisms 394 instead of
tapered prisms. The linear prisms 394 can include a
differentially-cured pattern 390 as illustrated in FIG. 40. One or
more cross-cut prisms 392 can further be provided as illustrated in
FIG. 41.
[0156] FIG. 42 illustrates a backlight wedge 380 that includes
prisms 398 which have a varying included angle along the apex 400.
The varying included angles can vary in a stepped fashion along the
length of the prisms. The varying included angle provides a
different degree of light collimation along the wedge 380, i.e.,
the prism 398 at the end farthest away from the light source has a
shallower [larger?] included angle thereby allowing more light to
pass therethrough. One or more cross-cut prisms 392 can further be
provided as illustrated in FIG. 43. The prisms 398, 390 can include
a differentially-cured pattern 390 as illustrated in FIG. 44. FIG.
45 is similar to the embodiment of FIG. 44 but the cross-cut prisms
390 extended above the prisms 398.
[0157] FIG. 46 illustrates a backlight wedge 380 that includes
prisms 402 which have a varying included angle along the apex 404.
In this embodiment, the included angle varies from a predetermined
angle, for example, 90 degrees, at a first end 406, to zero degrees
at a second end 408.
[0158] FIG. 47 is a perspective view of a prior art stepped
waveguide 410. The waveguide 410 can include linear prisms 412 and
cross-cut prisms 414 on the top surface as illustrated in FIG. 48.
The prisms 412, 414 can include a differentially-cured pattern 390
thereon. As illustrated in FIG. 49, a waveguide 416 can be
positioned below the stepped waveguide 410 for redirecting light
towards the waveguide 410. The cross-cut prisms 390 in FIG. 50 can
extend above the prisms 412 to prevent, for example, wet-out
conditions. FIG. 51 is similar to the embodiment of FIG. 50 but the
prisms 398 on the top surface of the waveguide 410 have varying
included angles. Additional cross-cut prisms 418 can be provided on
the top surface as illustrated in FIG. 52.
[0159] FIG. 53 is a perspective view of a waveguide 420 that
includes tapered prisms 338 on the bottom surface. The prism apices
can be truncated and a second waveguide 420 can be provided thereat
for redirecting light towards the waveguide 420. FIG. 55 is the
backlight wedge 380 of FIG. 38 shown upside down.
[0160] While this invention has been particularly shown and
described with references to various embodiments thereof, it will
be understood by those skilled in the art that various changes in
form and details may be made therein without departing from the
scope of the invention encompassed by the appended claims.
* * * * *