U.S. patent application number 10/742552 was filed with the patent office on 2005-06-23 for diffuse high reflectance film.
Invention is credited to Bohme, Wolfgang, Durell, Christopher N..
Application Number | 20050136200 10/742552 |
Document ID | / |
Family ID | 34678483 |
Filed Date | 2005-06-23 |
United States Patent
Application |
20050136200 |
Kind Code |
A1 |
Durell, Christopher N. ; et
al. |
June 23, 2005 |
Diffuse high reflectance film
Abstract
A diffuse reflective film including a bottom layer of reflective
specular material and a top layer of polytetrafluoroethylene (PTFE)
diffuser material for diffusely reflecting at least 96% of light in
the portion of the electromagnetic spectrum between about 400
nanometers and about 2500 nanometers, and wherein the diffuse
reflective film has a thickness of less than 1500 micrometers.
Inventors: |
Durell, Christopher N.; (San
Diego, CA) ; Bohme, Wolfgang; (Uhldingen,
DE) |
Correspondence
Address: |
Toby H. Kusmer
McDermott, Will & Emery
28 State Street
Boston
MA
02109
US
|
Family ID: |
34678483 |
Appl. No.: |
10/742552 |
Filed: |
December 19, 2003 |
Current U.S.
Class: |
428/35.7 |
Current CPC
Class: |
B32B 2457/202 20130101;
B32B 2307/418 20130101; G02B 5/021 20130101; B32B 27/08 20130101;
B32B 2307/416 20130101; Y10T 428/1352 20150115; B32B 27/322
20130101; G02B 5/08 20130101; G02B 5/0284 20130101; B32B 7/12
20130101 |
Class at
Publication: |
428/035.7 |
International
Class: |
B65D 001/00 |
Claims
What is claimed is:
1. A diffuse reflective film including a bottom layer of reflective
specular material and a top layer of polytetrafluoroethylene (PTFE)
diffuser material for diffusely reflecting at least 96% of light
within a portion of the electromagnetic spectrum between about 400
nanometers and about 2500 nanometers, and wherein the diffuse
reflective film has a thickness of less than 1500 micrometers.
2. A diffuse reflective film according to claim 1, wherein the top
layer of PTFE diffuser material comprises Zenith.TM. PTFE-based
diffuse reflectance film.
3. A diffuse reflective film according to claim 1, wherein the
bottom layer of reflective specular material comprises thermally
induced phase separation (TPIS) layered polymer film.
4. A diffuse reflective film according to claim 1, wherein the top
layer of PTFE diffuser material has a thickness of not more than
1000 micrometers.
5. A diffuse reflective film according to claim 1, wherein the
bottom layer of reflective specular material has a thickness of not
more than 500 micrometers.
6. A diffuse reflective film according to claim 1, wherein an
adhesive layer is provided between the top layer of PTFE diffuser
material and the bottom layer of reflective specular material.
7. A diffuse reflective film according to claim 1, wherein an
adhesive layer is provided on a bottom surface of the bottom layer
of reflective specular material.
8. A diffuse reflective film according to claim 1, wherein one of a
top and bottom surface of the bottom layer of reflective specular
material is more reflective and the top layer of PTFE diffuser
material is placed on the more reflective surface.
9. A light conduit including a diffuse reflective film according to
claim 1, and further comprising an outer shell and, wherein the
diffuse reflective film covers at least a portion of an inner
surface of the outer shell.
10. A light box including a diffuse reflective film according to
claim 1, and further comprising an outer shell and, wherein the
diffuse reflective film covers at least a portion of an inner
surface of the outer shell.
11. A liquid crystal display including a diffuse reflective film
according to claim 1, and further comprising a light guide
directing light from a light source, wherein the diffuse reflective
film covers at least a portion of an inner surface of the light
guide.
12. A light emitting diode display including a diffuse reflective
film according to claim 1, and further comprising a light guide
directing light from a light source, wherein the diffuse reflective
film covers at least a portion of an inner surface of the light
guide.
13. An optical cavity including a diffuse reflective film according
to claim 1, and further comprising a light guide directing light
from a light source, wherein the diffuse reflective film covers at
least a portion of an inner surface of the light guide.
14. A sign cabinet including a diffuse reflective film according to
claim 1, and further comprising walls directing light from a light
source, wherein the diffuse reflective film covers at least
portions of inner surfaces of the walls.
15. A method of forming a diffuse reflective film, comprising:
attaching a bottom layer of reflective specular material to a top
layer of polytetrafluoroethylene (PTFE) diffuser material for
diffusely reflecting at least 96% of light within the portion of
the electromagnetic spectrum between about 400 and about 800
nanometers (nm); and providing the diffuse reflective film with a
thickness of less than 1500 micrometers.
16. A method according to claim 15, wherein the top layer of PTFE
diffuser material comprises Zenith.TM. PTFE-based diffuse
reflectance film.
17. A method according to claim 15, wherein the bottom layer of
reflective specular material comprises thermally induced phase
separation (TPIS) layered polymer film.
18. A method according to claim 15, wherein the top layer of PTFE
diffuser material has a thickness of not more than 500
micrometers.
19. A method according to claim 15, wherein the bottom layer of
reflective specular material has a thickness of not more than 500
micrometers.
20. A method according to claim 15, wherein an adhesive layer is
provided between the top layer of PTFE diffuser material and the
bottom layer of reflective specular material.
21. A method according to claim 15, wherein the bottom layer of
reflective specular material comprises Vikuiti.TM. Enhanced
Specular Reflector (ESR) layered polymer film.
22. A method according to claim 15, wherein the bottom layer of
reflective specular material comprises a metal film.
23. A diffuse reflective film according to claim 1, wherein the
bottom layer of reflective specular material comprises Vikuiti.TM.
Enhanced Specular Reflector (ESR) layered polymer film.
24. A diffuse reflective film according to claim 1, wherein the
bottom layer of reflective specular material comprises a metal
film.
Description
TECHNICAL FIELD OF THE DISCLOSURE
[0001] The present disclosure relates to an improved high
reflectance material and, in particular, to the creation of a
composite material combining polytetrafluoroethylene (PTFE)
diffuser material with thermally induced phase separation (TPIS)
thin films or thin, highly reflective and specular metal films or
substrates resulting in a highly lambertian, highly reflective
diffuse material having significant optical benefits over currently
available products.
BACKGROUND OF THE DISCLOSURE
[0002] Diffuse reflection provides reflective light luminance at
many angles, in contrast to specular or mirror reflection in which
light is reflected back only at an angle equal to that of the
incident radiation. Typical diffuse reflectors, used for example as
white standards for various light measuring test instruments, are
made of white inorganic compounds (such as barium sulfate or
magnesium oxide) in the form of pressed cake or ceramic tile, all
of which are expensive, stiff, and brittle. Other existing diffuse
reflectors include (1) microvoided particle-filled articles that
depend on a difference in index of refraction of the particles, the
surrounding matrix and optional air-filled voids created from
stretching, and (2) microporous materials made from a sintered
polytetrafluoroethylene suspension. Another useful technology for
producing microporous films is thermally induced phase separation
(TIPS). Vikuiti.TM. Enhanced Specular Reflector (ESR) is an example
of a material made using TIPS and is an ultra-high reflectivity,
mirror-like optical enhancement film, which is available from the
Electronic Display Lighting Optical Systems Division of 3M Company
(www.3M.com).
[0003] Effective but inexpensive diffuse reflective films are still
needed for the many diverse light management applications that are
being developed. Many such applications require that diffuse
reflective films be as thin as possible, particularly when the
diffuse reflective films are used in electronic displays, such as
liquid crystal displays (LCD's) incorporated into notebook
computers, handheld computers, portable phones, and other
electronic devices. Furthermore, improved reflective films are
necessary that efficiently reflect light substantially uniformly
across the ultraviolet-visible-near infrared (UV-VIS-NIR) part of
the electromagnetic spectrum.
SUMMARY OF THE DISCLOSURE
[0004] The present disclosure provides a diffuse reflective film
including a bottom layer of reflective specular material and a top
layer of polytetrafluoroethylene (PTFE) diffuser material. The
resulting film is preferably flexible and can diffusely reflect
radiation substantially uniformly across the UV-VIS-NIR part of the
electromagnetic spectrum, e.g., UV-VIS-NIR light having a
wavelengths within the 250 to 2500 nanometer (nm) range, and more
efficiently than most other known reflectors of similar thickness,
e.g., greater than 96% reflective across the UV-VIS-NIR (250-2400
nanometers) part of the spectrum. The diffuse reflective film has a
reduced thickness of less than 1500 micrometers, while maintaining
a high absolute reflectance value. This reduced thickness allows
for creation of various products having a narrow profile, such as
liquid crystal display (LCD) illumination systems.
[0005] According to one aspect of the present disclosure, the top
layer of PTFE diffuser material comprises Zenith.TM. PTFE-based
diffuse reflectance film, which is available from
SphereOptics-Hoffman LLC (www.sphereoptics.com).
[0006] According to another aspect of the present disclosure, the
bottom layer of reflective specular material comprises a thermally
induced phase separation (TPIS) layered polymer film. An example of
a suitable TPIS layer polymer film is Vikuiti.TM. Enhanced Specular
Reflector (ESR) layered polymer film, which is available from the
Electronic Display Lighting Optical Systems Division of 3M Company
(www.3M.com).
[0007] According to another aspect, the Zenith.TM. diffuse
reflectance film has a thickness of not more than 1000 micrometers,
while the bottom layer of reflective specular material has a
thickness of not more than 500 micrometers. According to an
additional aspect, an adhesive layer is provided between the
Zenith.TM. diffuse reflectance film and the bottom layer of
reflective specular material, and an adhesive layer is provided on
a bottom surface of the bottom layer of reflective specular
material. According to a further aspect, the Zenith.TM. diffuse
reflectance film is placed on the more reflective surface of the
bottom layer of reflective specular material (the top and bottom
surfaces of the bottom layer of reflective specular material may be
different in that one surface is slightly more reflective than the
other surface).
[0008] The bottom layer of reflective specular material can
comprise other thin, highly reflective and specular metal films or
substrates, and the Zenith.TM. diffuse material applied to other
films and substrates also has enhanced reflectivity and will yield
similar results.
[0009] The present disclosure also provides an optical cavity
including a light source in combination with a housing that further
contains a diffuse reflector film constructed in accordance with
the present disclosure (as described above) lining a portion of the
cavity and partially wrapping around the light source so as to
direct light from the light source into the optical cavity. The
diffuse reflector film reflects light from the light source into
the optical cavity, and also reflects light, including recycled
light, in the optical cavity toward an open space, such as a room,
or toward a viewer.
[0010] The present disclosure also provides a lamp cavity including
a light source, such as a cold cathode fluorescent lamp, in
combination with a housing that further contains a diffuse
reflector film constructed in accordance with the present
disclosure (as described above) lining a portion of the cavity
facing the light source and partially wrapping around the light
source.
[0011] Exemplary embodiments of the diffuse reflective film of the
present disclosure have been found to be useful in a variety of
structures for light management applications. For example, they
have been used as a back reflector in display products, such as
liquid crystal displays (LCD), flat panels, organic light emitting
diodes (OLED) and architectural backlight panels. The diffuse
reflective film of the present disclosure may also be used to
increase the brightness of sign cabinets, light fibers,
instrumentation enclosures, and light conduits. Such articles
containing the diffuse reflective films of the present disclosure
are further aspects of the present disclosure.
[0012] Other features and advantages of the present disclosure will
be apparent from the following detailed description of the
disclosure and the claims. The above summary of principles of the
disclosure is not intended to describe each illustrated embodiment
or every implementation of the present disclosure. The drawings and
the detailed description that follow more particularly exemplify
certain preferred embodiments utilizing the principles disclosed
herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is an enlarged side elevation view of a diffuse
reflective film constructed in accordance with the present
disclosure and including a bottom layer of reflective specular
material, a top layer of polytetrafluoroethylene (PTFE) diffuser
material, and a removable protective liner;
[0014] FIGS. 2-6 are schematic diagrams of exemplary embodiments of
liquid crystal display devices incorporating diffuse reflective
films constructed in accordance with the present disclosure;
and
[0015] FIG. 7 schematically depicts a cross-section of a light
conduit using a diffuse reflective film constructed in accordance
with the present disclosure.
[0016] While principles of the disclosure are amenable to various
modifications and alternative forms, specifics thereof have been
shown by way of example in the drawings and will be described in
detail. It should be understood, however, that the intention is not
to limit the disclosure to the particular embodiments described. On
the contrary, the intention is to cover all modifications,
equivalents, and alternatives falling within the spirit and scope
of the disclosure.
DETAILED DESCRIPTION
[0017] Referring to FIG. 1, the present disclosure provides a
diffuse reflective film 10 including a bottom or back layer of
reflective specular material 12 and a top or front layer 14 of
polytetrafluoroethylene (PTFE) diffuser material. The resulting
film 10 is preferably flexible such that it can be easily conformed
to many different useful configurations, and can diffusely
uniformly reflect radiation in the ultraviolet-visible-near
infrared (UV-VIS-NIR) range of the electromagnetic spectrum, i.e.
between 250 and 2500 nanometers (nm), efficiently. By "efficiently"
it is meant, for example, greater than 96% reflective across this
portion of the spectrum, than most other known reflectors of
similar thickness. The diffuse reflective film 10 has a reduced
thickness of less than 1000 micrometers, while maintaining a high
absolute reflectance value (it should be noted that the drawing in
FIG. 1 is not to scale or proportion and is greatly enlarged to
more easily illustrate the different layers). This reduced
thickness allows for creation of various products having a narrowed
profile, including LCD illumination systems.
[0018] In the exemplary embodiment of the present disclosure shown
in FIG. 2, the top layer 14 of PTFE diffuser material comprises
Zenith.TM. PTFE-based diffuse reflectance film, which is available
from SphereOptics-Hoffman LLC (www.sphereoptics.com), while the
bottom layer 12 of reflective specular material comprises a
thermally induced phase separation (TPIS) layered polymer film. An
example of a suitable TPIS layer polymer film is Vikuiti.TM.
Enhanced Specular Reflector (ESR) layered polymer film, which is
available from the Electronic Display Lighting Optical Systems
Division of 3M Company (www.3M.com). Although it should be
understood that the bottom layer of reflective specular material
can alternatively comprise thin, highly reflective and specular
metal films or substrates, and the Zenith.TM. diffuse material
applied to other metal films and substrates also has enhanced
reflectivity and will yield similar results.
[0019] An adhesive layer is provided between the Zenith.TM. diffuse
reflectance film 14 and the Vikuiti.TM. ESR layered polymer film
12, and an adhesive layer is provided on a bottom surface of the
Vikuiti.TM. ESR layered polymer film 12. A removably protective
layer 16 covers bottom surface of the Vikuiti.TM. ESR layered
polymer film 12 prior to applying the film to a desired surface for
reflecting light.
[0020] The Zenith.TM. diffuse reflectance film 14 has a thickness
of not more than 1000 micrometers, while the Vikuiti.TM. ESR
layered polymer film 12 has a thickness of not more than 500
micrometers. The Zenith.TM. diffuse reflectance film 14 is placed
on the more reflective surface of the Vikuiti.TM. ESR layered
polymer film 12 (the Vikuiti.TM. ESR layered polymer film's top and
bottom surfaces are different in that one surface is slightly more
reflective than the other surface).
[0021] The diffuse reflective film 10 of the present disclosure has
a wide variety of light management applications. The diffuse
reflective film 10 of the present disclosure may be used to
partially line an optical cavity to increase the efficient use of
light to illuminate such things as, for example, a partially
transparent image that may be either static (such as a graphics
film or a transparency) or switchable (such as a liquid crystal
display). Thus, optical cavities that are partially lined with a
diffuse reflector film 10 of the present disclosure may be used in
such devices as backlight units including as liquid crystal display
constructions (LCDs), lights, copying machines, projection system
displays, OLED display constructions, facsimile apparatus,
electronic blackboards, diffuse light standards, and photographic
lights. They may also be part of a sign cabinet system, a light
conduit or units containing light emitting diodes (LEDs).
[0022] The diffuse reflective film 10 of the present disclosure has
been found to be especially beneficial as a back reflector in back
lighting structures used for liquid crystal displays. In this type
of application, the article is placed directly behind the light
source which is illuminating a display. The film 10 acts to reflect
back light which is not directed toward the display and ultimately
a viewer. The scattering or diffuse reflection characteristics of
the film back reflector also helps provide a more overall diffuse
light source and more evenly lit display structure.
[0023] As used herein, the term "structure" refers to any unit or
article capable of holding or supporting the diffuse reflective
film 10 in place, such as, for example, a rigid or flexible frame,
an awning, umbrella, backlight constructions having both static or
moving images, light conduits, light boxes, LCDs, LED displays,
sub-components of LCDs, sub-components of LED displays, and
reflectors.
[0024] As used herein, the term "optical cavity" refers to an
enclosure designed to contain a light source and direct the light
from the light source toward an object benefiting from
illumination, such as a static display, a changing image or an
insufficiently illuminated object. In certain implementations, the
optical cavity includes a lightguide or waveguide.
[0025] Schematic figures of several structures including liquid
crystal displays (LCD) and incorporating the diffuse reflective
film 10 constructed in accordance with the present disclosure are
shown in FIGS. 2-6. In FIG. 2, a structure 20 is shown that has a
fluorescent light source 22 coupled to a plastic light guide 24.
Although not shown, a diffuser, a brightness enhancing film, and a
reflective polarizer film, for example, can be placed on top of the
guide 24 and act to redirect and polarize the light emitted from
the plastic light guide 24 towards the LCD and the viewer. If the
light is not at the correct range of viewing angles, nor of the
correct polarization, it is reflected back towards the light guide
24. The LCD is placed on top of the films and is typically
constructed of a liquid crystal sandwiched between two
polarizers.
[0026] The diffuse reflective film 10 acts as a light recycler by
(1) reflecting the light rejected from the reflective polarizing
film and/or from the brightness enhancement film and (2) gives that
light another opportunity to reach a viewer. This rejecting and
recycling can occur numerous times increasing the amount of light
directed towards the LCD and the viewer.
[0027] This increased optical efficiency of the diffuse reflective
film 10 can be used to reflect incident light between the
polarizing and/or brightness enhancement films and the diffuse
reflective film 10 to increase display luminance by controlling the
angles over which light is emitted. The reflected light is
scattered by the diffuse reflective film 10 into all angles. The
light within the transmission angles of the polarizing and/or
brightness enhancement films is transmitted towards the viewer.
Light in the second angular range is reflected for additional
scattering.
[0028] Additionally, the diffuse reflective film 10 may be placed
behind or around the light source 22, such as a cold cathode
fluorescent lamp to increase light coupling efficiency into the
plastic light guide 24.
[0029] In FIG. 3, another LCD display 30 is shown, containing a
light guide 34 and a light source 32. A single piece of the diffuse
reflective film 10 covers the bottom surface of the light guide 34,
but also wraps around a portion of the light source 32. In this
manner, the diffuse reflective film 10 aids in the reflection of
light from the light source 32 into the light guide 34, thereby
increasing the efficiency of the light guide 34 and also improving
the ease of manufacture of the display 30 by forming a single,
integrated diffuse reflective film 10 for the display. In addition,
the improved single diffuse reflective film 10 avoids any possible
loss of light between two separated, diffuse reflective films 10,
such as shown in FIG. 2.
[0030] The increased optical efficiency of the diffuse reflective
film 10 is used to increase the reflective efficiency of an optical
cavity and/or to mix discrete wavelengths of light to make a
uniform colored or white light source. In the schematic drawing of
portions of an LCD device 40 shown in FIG. 4, three fluorescent
lamps 42 are depicted in an optical cavity 44. All of the lamps 42
may be white or each lamp may be a selected color, such as red,
green and blue. The optical cavity 44 is lined with the diffuse
reflective film 10 of the present disclosure to both increase
reflectance and mix the discrete colors adequately to form a white
light source with good spatial light emitting uniformity to
illuminate the LCD 40.
[0031] In FIG. 5, the LCD device 50 is shown with two light
emitting diodes (LEDs) 52 as the light source that provides light
to an optical cavity 54. The diodes 52 may be colored or white. The
optical cavity 54 is lined with the diffuse reflective film 10 of
the present disclosure to both increase reflectance and mix the
discrete colors adequately to form a white light source with good
spatial light emitting uniformity to illuminate the LCD.
[0032] The device 60 schematically shown in FIG. 6 uses a prismatic
light conduit 62 as the light source in an optical cavity 64. The
diffuse reflective film 10 of the present disclosure is used both
in the light conduit 62 as extractors to scatter light towards the
LCD and as back reflectors to reflect the light exiting around the
light conduit 64 to form an efficient optical cavity.
[0033] LEDs are useful light sources for small LCD devices such as
medical monitors and automotive displays. LEDs provide the
advantages of small size and lower energy consumption, but they
have relatively low luminance. The optical efficiency of designs
using LED or OLED illumination is increased when a diffuse
reflective film 10 of the present disclosure is used as a back
reflector in combination with brightness enhancing and reflective
polarizer films.
[0034] The diffuse reflective film 10 of the present disclosure can
also be used in OLED displays, which self-emits light under voltage
bias, to capture backscatter radiation from the OLED device,
redirect the light towards the viewer, and enhance the brightness
of the display. The diffuse reflective film 10 would be used in
these cases to envelope the OLED display to capture both
backscatter, side-scatter and wave-guided energy from the OLED
emission.
[0035] The diffuse reflective film 10 of the present disclosure can
also be used to enhance the perceived brightness of microdisplay
devices by creating more efficient illumination backlights, and
diffuse light illumination delivery structures (light guides and
light pipes). The diffuse reflective film 10 helps to uniformly
spread out the light over the surface of these microdisplays where
non-uniformity can result in severely degraded perception by the
viewer due to the magnified optical system viewing the
microdisplay.
[0036] The diffuse reflective film 10 of the present disclosure can
be used in plasma flat panel displays and in rear-projection
display consoles to develop and deliver an improved uniformity and
panel brightness by directing more of the lost backscatter light to
the viewed panel plane.
[0037] The diffuse reflective film 10 of the present disclosure can
be used in architectural lighting panels and room lighting to
develop and deliver an improved uniformity and panel brightness,
especially where there is a need to spread a light uniformly over a
very large surface or area. The principle use would be as a cavity
reflector or light guide for various types of sources and the
diffuse reflective film 10 would be applied to large areas where
the light is intended to be delivered to and efficiently reflected
from that surface to create an architectural or room lighting
effect.
[0038] The diffuse reflective film 10 can also be used to develop
low level laser cavity reflectors, since heat and radiation density
effects will not damage the materials.
[0039] LEDs can replace fluorescent lamps as the preferred
backlight source for small liquid crystal displays such as medical
monitors and automotive displays. The advantage of using LEDs is
their low price, small size and low energy consumption. The
disadvantage of LEDs is their relatively low brightness. With the
use of the diffuse reflective film 10 of the present disclosure as
a back reflector, the brightness of LED displays can be
increased.
[0040] Display sign cabinets that operate more efficiently by
improving brightness while requiring less electrical energy can be
made using the diffuse reflective film 10 of the present
disclosure. Sign cabinets are often made of aluminum backs
(generally painted white) and sides (typically unpainted) with
fluorescence lights that illuminate a front film to display an
image. The luminance that displays the image can be increased if
the back and all four sides of the interior are covered with the
diffuse reflective film 10 of the present disclosure. Conversely,
energy used to illuminate a display film can be proportionately
reduced while retaining the same luminance.
[0041] The diffuse reflective film 10 of the present disclosure is
also useful in light conduits or applications wherein light is
extracted from or emanates from at least a portion of the length of
the hollow light conduit. The source of light for a light conduit
is typically a point source such as a metal halide lamp, or in the
case of rectangular display conduit a linear light source such as a
fluorescent tube may be used. Typical applications are general
lighting or display lighting that includes such displays as colored
tubes and thin display images and signs.
[0042] Use of the diffuse reflective film 10 of the present
disclosure as extractors or back reflectors increases the lighting
efficiency of a light conduit. The diffuse reflection results in a
more uniform illumination.
[0043] One exemplary embodiment of a light conduit structure 70 is
shown in FIG. 7. The light conduit 70 is surrounded by an outer
shell 72. Inside the outer shell 72 the diffuse reflective film 10
of the present disclosure is placed to reflect any stray light back
into the light conduit 70 and out through the emitting surface
74.
[0044] The above specification is believed to provide a complete
description of the manufacture and use of particular embodiments of
the present disclosure. Many embodiments of the disclosure can be
made without departing from the spirit and scope of the
disclosure.
* * * * *