U.S. patent application number 15/384011 was filed with the patent office on 2017-04-06 for broadband reflectors, concentrated solar power systems, and methods of using the same.
This patent application is currently assigned to 3M Innovative Properties Company. The applicant listed for this patent is 3M INNOVATIVE PROPERTIES COMPANY. Invention is credited to Daniel T. Chen, Susannah C. Clear, Laurence R. Gilbert, Timothy J. Hebrink, Audrey A. Sherman, Michael F. Weber, Ta-hua Yu.
Application Number | 20170097174 15/384011 |
Document ID | / |
Family ID | 42310163 |
Filed Date | 2017-04-06 |
United States Patent
Application |
20170097174 |
Kind Code |
A1 |
Hebrink; Timothy J. ; et
al. |
April 6, 2017 |
BROADBAND REFLECTORS, CONCENTRATED SOLAR POWER SYSTEMS, AND METHODS
OF USING THE SAME
Abstract
Broadband reflectors include a UV-reflective multilayer optical
film and a VIS/IR-reflective layer. In various embodiments, the
VIS/IR reflective layer may be a reflective metal layer or a
multilayer optical film. Concentrated solar power systems and
methods of harnessing solar energy using the broadband reflectors
and optionally comprising a celestial tracking mechanism are also
disclosed.
Inventors: |
Hebrink; Timothy J.;
(Scandia, MN) ; Clear; Susannah C.; (Hastings,
MN) ; Gilbert; Laurence R.; (Marine on St. Croix,
MN) ; Weber; Michael F.; (Shoreview, MN) ; Yu;
Ta-hua; (Woodbury, MN) ; Chen; Daniel T.;
(Saint Paul, MN) ; Sherman; Audrey A.; (Woodbury,
MN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
3M INNOVATIVE PROPERTIES COMPANY |
St. Paul |
MN |
US |
|
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
42310163 |
Appl. No.: |
15/384011 |
Filed: |
December 19, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13142910 |
Oct 3, 2011 |
9523516 |
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PCT/US2009/068944 |
Dec 21, 2009 |
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15384011 |
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61178123 |
May 14, 2009 |
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61141338 |
Dec 30, 2008 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y02E 10/40 20130101;
F24S 10/00 20180501; G02B 19/0019 20130101; Y10T 428/3154 20150401;
Y10T 428/31913 20150401; B32B 27/36 20130101; B32B 2551/00
20130101; B32B 2383/00 20130101; H01L 31/0547 20141201; Y02E 10/44
20130101; B32B 15/18 20130101; B32B 2367/00 20130101; B32B 15/088
20130101; B32B 2325/00 20130101; F24S 2023/87 20180501; B32B 7/02
20130101; F24S 23/00 20180501; G02B 19/0042 20130101; B32B 2250/42
20130101; F24S 10/70 20180501; F24S 2030/136 20180501; Y10T
428/31681 20150401; B32B 15/09 20130101; B32B 27/306 20130101; F24S
23/77 20180501; B32B 7/12 20130101; B32B 27/304 20130101; F03G 6/06
20130101; F24S 20/20 20180501; B32B 2255/205 20130101; F24S 30/425
20180501; Y02E 10/52 20130101; B32B 15/082 20130101; B32B 27/308
20130101; B32B 2311/12 20130101; F24S 23/70 20180501; B32B 2311/30
20130101; F24S 2030/16 20180501; Y10T 428/31757 20150401; B32B
2255/10 20130101; F24S 50/20 20180501; F24S 2025/601 20180501; Y02E
10/47 20130101; G02B 5/0841 20130101; B32B 27/34 20130101; B32B
2333/12 20130101; B32B 2377/00 20130101; G02B 6/0011 20130101; B32B
2327/00 20130101; Y10T 428/31928 20150401; B32B 2311/24 20130101;
F24S 20/00 20180501; B32B 2323/00 20130101; Y10T 428/31909
20150401; B32B 15/08 20130101; B32B 27/302 20130101; B32B 27/283
20130101; B32B 2307/416 20130101; B32B 15/20 20130101; B32B 27/325
20130101; B32B 2551/08 20130101; B32B 15/085 20130101; Y10T
428/31786 20150401; B32B 2331/00 20130101; Y10T 428/31692 20150401;
Y10T 428/3175 20150401; G02B 17/006 20130101; Y02E 10/46 20130101;
F24S 23/74 20180501; F24S 23/82 20180501; H02S 20/00 20130101; B32B
2311/08 20130101; Y10T 428/24942 20150115 |
International
Class: |
F24J 2/10 20060101
F24J002/10; F24J 2/07 20060101 F24J002/07; F24J 2/38 20060101
F24J002/38; F24J 2/16 20060101 F24J002/16; F24J 2/24 20060101
F24J002/24; F24J 2/04 20060101 F24J002/04; F24J 2/14 20060101
F24J002/14 |
Claims
1. A broadband reflector comprising: a UV-reflective multilayer
optical film having a first major surface and comprising a
UV-reflective optical layer stack, wherein the UV-reflective
optical layer stack comprises first optical layers and second
optical layers, wherein at least a portion of the first optical
layers and at least a portion of the second optical layers are in
intimate contact and have different refractive indexes, and wherein
the UV-reflective optical layer stack is reflective to UV-light; a
VIS/IR-reflective multilayer optical film comprising a
VIS/IR-reflective optical layer stack, wherein the
VIS/IR-reflective optical layer stack comprises third optical
layers and fourth optical layers, wherein at least a portion of the
third optical layers and at least a portion of the fourth optical
layers are in intimate contact and have different refractive
indexes, and wherein the VIS/IR-reflective multilayer optical film
is reflective to VIS/IR-light; and a UV-absorbing layer disposed
between the first major surface of the UV-reflective multilayer
optical film and the VIS/IR-reflective multilayer optical film,
wherein the UV-absorbing layer comprises a polymer and a
UV-absorber.
2. The broadband reflector of claim 1, wherein the third optical
layers and fourth optical layers respectively comprise a
polyethylene terephthalate and a THV, a polyethylene terephthalate
and an OTP, a PEN and a THV, a PEN and an OTP, a PEN and a PMMA, a
polyethylene terephthalate and a coPMMA, a PEN and a coPMMA layer
pairs, a coPEN and a PMMA layer pairs, a coPEN and an OTP, a coPEN
and a THV, a sPS and an OTP, a sPS and a THV, a PMMA and a THV, a
COC and a THV, or an EVA and a THV.
3. The broadband reflector of claim 1, further comprising an
adhesive layer disposed on the VIS/IR-reflective multilayer optical
film opposite the UV-absorbing layer.
4. The broadband reflector claim 1, wherein the first optical
layers and second optical layers respectively comprise a
polyethylene terephthalate and a coPMMA, a sPS and an OTP, a sPS
and a THV, a PMMA and a THV, a COC and a THV, or an EVA and a
THV.
5. The broadband reflector claim 1, wherein the UV-reflective
multilayer optical film further comprises a tie layer that
comprises the first major surface of the UV-reflective multilayer
optical film.
6. The broadband reflector of claim 5, wherein the tie layer
comprises an inorganic tie layer.
7. The broadband reflector of claim 1, wherein the broadband
reflector has an average light reflectivity of at least 90 percent
over a wavelength range of from 300 to 2494 nanometers.
8. The broadband reflector of claim 1, wherein the UV-reflective
multilayer optical film further comprises a second major surface
opposite the first major surface, and wherein the UV-reflective
multilayer optical film further comprises an abrasion resistant
layer that forms the second major surface of the UV-reflective
multilayer optical film.
9. The broadband reflector of claim 8, wherein the abrasion
resistant layer comprises: an antisoiling component selected from
the group consisting of fluoropolymers, silicone polymers, titanium
dioxide particles, polyhedral oligomeric silsesquioxanes, and
combinations thereof.
10. A concentrated solar power system comprising: at least one
broadband reflector of claim 1 capable of being aligned to direct
solar radiation onto a hollow receiver; and a heat transfer fluid
partially disposed within the hollow receiver.
11. The concentrated solar power system of claim 10, further
comprising an electrical generator in fluid communication with the
hollow receiver.
12. The concentrated solar power system of claim 10, further
comprising a celestial tracking mechanism for the at least one
broadband reflector.
13. The concentrated solar power system of claim 12, wherein the
celestial tracking mechanism comprises a louver pivotally mounted
adjacent the hollow receiver, wherein the louver comprises the at
least one broadband reflector.
14. A method of harnessing solar energy, the method comprising
reflecting solar radiation using at least one broadband reflector
of claim 1 onto a hollow receiver containing a heat transfer fluid
to provide a heated heat transfer fluid.
15. The method of claim 14, further comprising thermally heating at
least a portion of a building with heat given off from the heated
heat transfer fluid.
16. The method of claim 14, further comprising generating
electrical power using the heated heat transfer fluid.
17. A method of using the broadband reflector of claim 1, the
method comprising: adhering the broadband reflector to an existing
solar reflector adapted for use in a concentrated solar power
system.
18. A solar collection device comprising at least one solar cell
and a broadband reflector according to claim 1 positioned in
proximity to the at least one solar cell.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 13/142,910, now U.S. Pat. No. 9,523,516, issued Dec. 20,
2016, which is a national stage filing under 35 U.S.C. 371 of
PCT/US2009/068944, filed Dec. 21, 2009, which claims priority to
U.S. Provisional Patent Application No. 61/141338, filed Dec. 30,
2008, and U.S. Provisional Patent Application No. 61/178123, filed
May 14, 2009, the disclosures of which are incorporated by
reference herein in their entirety.
TECHNICAL FIELD
[0002] The present disclosure relates to reflectors suitable for
reflecting a broad range of electromagnetic radiation, concentrated
solar power systems including the reflectors, and methods of using
the same.
BACKGROUND
[0003] Concentrated solar power (CSP, also known as "concentrating
solar power") technology uses sunlight directed at heat transfer
fluids that heat up and whose thermal energy is then transferred
(e.g., for heating) or turned into electrical power (e.g., by use
of a turbine generator). Conventional CSP reflectors are made with
silver coated glass, which currently reflect approximately 94
percent of the solar spectrum. Such CSP reflectors are relatively
expensive, heavy, and fragile.
[0004] CSP systems typically use lenses or reflectors and tracking
systems to focus a large area of sunlight into a small beam. The
concentrated sunlight is then used as a heat source for a
conventional power plant (e.g., a steam driven turbine generator).
A wide range of concentrating technologies exists; the most
developed are the solar trough, parabolic dish and solar power
tower.
[0005] Solar troughs are the most widely deployed and the most
cost-effective CSP technology. A solar trough consists of a linear
parabolic reflector that concentrates sunlight onto a receiver
positioned along the reflector's focal line. The reflector is made
to follow the sun during the daylight hours by tracking along a
single axis.
[0006] A parabolic dish system consists of a stand-alone parabolic
reflector that concentrates sunlight onto a receiver positioned at
the reflector's focal point. The reflector tracks the sun along two
axes. Parabolic dish systems give the highest efficiency among CSP
technologies. Power towers are less advanced than trough systems
but offer higher solar concentration ratios (e.g., in excess of
1000 times more) and better energy storage capability.
SUMMARY
[0007] CSP utility plants are being installed in high solar
irradiation climates around the world with investment projections
to exceed $200 million/year in the next 5 years. Advantageously,
broadband reflectors according to the present disclosure may be
fabricated with at least one of lower weight, lower cost, and/or
improved power collection capability as compared to conventional
reflectors used in CSP.
[0008] In one aspect, the present disclosure provides a broadband
reflector comprising: an ultraviolet-reflective (UV-reflective)
multilayer optical film having a first major surface and comprising
a UV-reflective optical layer stack, wherein the UV-reflective
optical layer stack comprises first optical layers and second
optical layers, wherein at least a portion of the first optical
layers and at least a portion of the second optical layers are in
intimate contact and have different refractive indexes; and a
visible/infrared-reflective (VIS/IR-reflective) metal layer
disposed on at least a portion of the first major surface.
[0009] In another aspect, the present disclosure provides a
broadband reflector comprising: a UV-reflective multilayer optical
film having a first major surface and comprising a UV-reflective
optical layer stack, wherein the UV-reflective optical layer stack
comprises first optical layers and second optical layers, wherein
at least a portion of the first optical layers and at least a
portion of the second optical layers are in intimate contact and
have different refractive indexes, and wherein the UV-reflective
optical layer stack is reflective to UV-light; a VIS/IR-reflective
multilayer optical film comprising a VIS/IR-reflective optical
layer stack, wherein the VIS/IR-reflective optical layer stack
comprises third optical layers and fourth optical layers, wherein
at least a portion of the third optical layers and at least a
portion of the fourth optical layers are in intimate contact and
have different refractive indexes, and wherein the
VIS/IR-reflective multilayer optical film is reflective to
VIS/IR-light; and a UV-absorbing layer disposed between the
UV-reflective multilayer optical film and the VIS/IR-reflective
multilayer optical film. In some embodiments, the first optical
layers and second optical layers and/or the third optical layers
and fourth optical layers respectively comprise a polyethylene
terephthalate and a THV, a polyethylene terephthalate and an OTP, a
PEN and a THV, a PEN and an OTP, a PEN and a PMMA, a polyethylene
terephthalate and a coPMMA, a PEN and a coPMMA layer pairs, a coPEN
and a PMMA layer pairs, a coPEN and an OTP, a coPEN and a THV, a
sPS and an OTP, a sPS and a THV, a PMMA and a THV, a COC and a THV,
or an EVA and a THV layer pairs.
[0010] In some embodiments, the UV-reflective multilayer optical
film further comprises a tie layer that forms the first major
surface of the UV-reflective multilayer optical film. In some of
those embodiments, the tie layer comprises an inorganic tie layer.
In some embodiments, the inorganic tie layer comprises titanium
dioxide or aluminum oxide. In some embodiments, the
VIS/IR-reflective metal layer comprises at least one of silver,
copper, stainless steel, or aluminum (i.e., comprises silver,
copper, stainless steel, aluminum, or any combination thereof).
[0011] In another aspect, the present disclosure provides a
broadband reflector comprising: a UV-reflective multilayer optical
film having a first major surface and comprising a UV-reflective
optical layer stack, wherein the UV-reflective optical layer stack
comprises first optical layers and second optical layers, wherein
at least a portion of the first optical layers and at least a
portion of the second optical layers are in intimate contact and
have different refractive indexes, and wherein the UV-reflective
optical layer stack is reflective to UV-light; a VIS/IR-reflective
multilayer optical film comprising a VIS/IR-reflective optical
layer stack, wherein the VIS/IR-reflective optical layer stack
comprises third optical layers and fourth optical layers, wherein
at least a portion of the third optical layers and at least a
portion of the fourth optical layers are in intimate contact and
have different refractive indexes, and wherein the
VIS/IR-reflective multilayer optical film is reflective to
VIS/IR-light; and a UV-absorbing layer disposed between the
UV-reflective multilayer optical film and the VIS/IR-reflective
multilayer optical film.
[0012] In some embodiments, the broadband reflector has an average
light reflectivity of at least 95 percent over a wavelength range
of 350 to 400 nanometers. In some embodiments, the broadband
reflector has an average light reflectivity of at least 90 percent
over a wavelength range of from 300 to 2494 nanometers.
[0013] In some embodiments, the UV-reflective multilayer optical
film further comprises a second major surface opposite the first
major surface, and wherein the UV-reflective multilayer optical
film further comprises an abrasion resistant layer that forms the
second major surface of the UV-reflective multilayer optical film.
In some of those embodiments, the abrasion resistant layer
comprises: an antisoiling component selected from the group
consisting of fluoropolymers, silicone polymers, titanium dioxide
particles, polyhedral oligomeric silsesquioxanes, and combinations
thereof. In some embodiments, the abrasion resistant layer
comprises a conductive filler; for example, to facilitate static
charge dissipation.
[0014] In some embodiments, the broadband reflector is
thermoformable. In some embodiments, the broadband reflector has a
parabolic or curved surface.
[0015] In yet another aspect, the present disclosure provides a
concentrated solar power system comprising: at least one broadband
reflector according to the present disclosure and capable of being
aligned to direct solar radiation onto a hollow receiver; and a
heat transfer fluid partially disposed within the hollow
receiver.
[0016] In some embodiments, the concentrated solar power system
further comprises an electrical generator in fluid communication
with the hollow receiver.
[0017] In some embodiments, the concentrated solar power system
further comprises a celestial tracking mechanism for the at least
one broadband reflector. The at least one broadband reflector may,
for example, be pivotally mounted on a frame. In some embodiments,
both the hollow receiver and the at least one broadband reflector
are pivotally mounted on a frame. The pivotally mounted components
may pivot, for example, in one direction or in two directions. In
some embodiments, the hollow receiver is stationary.
[0018] In yet another aspect, the present disclosure provides a
method of harnessing solar energy, the method comprising reflecting
solar radiation using at least one broadband reflector according to
the present disclosure onto a hollow receiver containing a heat
transfer fluid to provide a heated heat transfer fluid.
[0019] In some embodiments, the method further comprises thermally
heating at least a portion of a building with heat given off from
the heated heat transfer fluid. In some embodiments, the method
further comprises generating electrical power using the heated heat
transfer fluid.
[0020] In yet another aspect, the present disclosure provides a
broadband reflector comprising:
[0021] a UV-reflective multilayer optical film having a first major
surface and comprising a UV-reflective optical layer stack, wherein
the UV-reflective optical layer stack comprises first optical
layers and second optical layers, wherein at least a portion of the
first optical layers and at least a portion of the second optical
layers are in intimate contact and have different refractive
indexes;
[0022] an adhesive layer disposed on at least a portion of the
first major surface; and
[0023] a VIS/IR-reflective metallic substrate disposed on at least
a portion of the adhesive layer.
[0024] In some embodiments, the adhesive layer comprises a
pressure-sensitive adhesive layer.
[0025] In this application:
[0026] "light" refers to electromagnetic radiation, whether visible
to the unaided human eye or not;
[0027] "optical layer" means having a layer of a material having a
thickness in a range of about one quarter of a wavelength or
wavelengths of light to be reflected (e.g., optical layer in the
context of a UV-reflective optical layer stack means a layer of
material having a thickness of about one quarter of a wavelength of
UV-light, while optical layer in the context of a VIS/IR-reflective
optical layer stack means a layer of material having a thickness of
about one quarter of a wavelength of VIS/IR-light;
[0028] "polymer" refers to a macromolecular compound consisting
essentially of one or more repeated monomeric units, or a mixture
of macromolecular compounds that consist essentially of one or more
like repeated monomeric units;
[0029] "UV-absorber" means a material capable of absorbing or
blocking electromagnetic radiation at wavelengths less than 380
nanometers (nm), while remaining substantially transparent at
wavelengths greater than 400 nm;
[0030] "UV-light" means electromagnetic radiation having a
wavelength in a range of from greater than 350 to 400 nm;
[0031] "UV-reflective" means substantially reflective to UV-light
(for example, at least 30, 40, 50, 60, 70, 80, 90, or 95 percent
reflective to at least a portion of UV-light at a 90 degree angle
of incidence);
[0032] "UV-absorbing" means substantially absorbing at normal
incidence (90 degree angle of incidence) of light at least some
wavelengths in a range of from 300 to 400 nanometers (for example,
at least 30, 40, 50, 60, 70, 80, 90, or 95 percent absorbing of
light at wavelengths in a range of from 300 to 400 nm);
[0033] "VIS/IR-light" means electromagnetic radiation having a
wavelength in a range of from greater than 400 to 2494 nm; and
[0034] VIS/IR-reflective" means substantially reflective to
VIS/IR-light (for example, at least 30, 40, 50, 60, 70, 80, 90, or
95 percent reflective at normal incidence to light at wavelengths
in a range of from greater than 400 to 2494 nm).
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] The disclosure may be more completely understood in
consideration of the following detailed description of various
embodiments of the disclosure in connection with the accompanying
drawings, in which:
[0036] FIG. 1A is a schematic side view of a broadband reflector
100 according to one embodiment of the present disclosure;
[0037] FIG. 1B is a schematic side view of a UV-reflective optical
layer stack 140 included in broadband reflector 100;
[0038] FIG. 2A is a schematic side view of a broadband reflector
200 according to another embodiment of the present disclosure;
[0039] FIG. 2B is a schematic side view of a VIS/IR-reflective
optical layer stack 240 included in broadband reflector 200;
[0040] FIG. 3 is a schematic plan view of concentrated solar power
system according to one embodiment of the present disclosure;
[0041] FIG. 4 is a schematic plan view of concentrated solar power
system according to one embodiment of the present disclosure;
[0042] FIG. 5 is a plot of percent reflection versus wavelength for
the broadband reflector of Example 1;
[0043] FIG. 6 is a plot of percent reflection versus wavelength for
the broadband reflector of Example 2;
[0044] FIG. 7 is a schematic diagram of an embodiment of a tracker
device for moving linear parabolic broadband reflectors disclosed
herein mounted in a frame;
[0045] FIG. 8a is a diagram showing an embodiment of an array of
hollow receivers with louvers comprising the broadband reflectors
disclosed herein, wherein the louvers are oriented to enhance
capture of rays from the morning sun;
[0046] FIG. 8b is a diagram showing an embodiment of an array of
hollow receivers with louvers comprising the broadband reflectors
disclosed herein, wherein the louvers are oriented to enhance
capture of rays from the mid-day sun; and
[0047] FIG. 8c is a diagram showing an embodiment of an array of
hollow receivers with louvers comprising the broadband reflectors
disclosed herein, wherein the louvers are oriented to enhance
capture of rays from the evening sun.
DETAILED DESCRIPTION
[0048] Referring now to FIG. 1A, broadband reflector 100 according
to one exemplary embodiment of the present disclosure has
UV-reflective multilayer optical film 110 with first major surface
115 and UV-reflective optical layer stack 140. VIS/IR-reflective
metal layer 130 is disposed on at least a portion of first major
surface 115. UV-reflective multilayer optical film 110 may contain
additional layers such as, for example, optional tie layer 120 and
optional abrasive resistant hardcoat 150. UV-reflective multilayer
optical film 110 reflects UV-light while VIS/IR-light that is
transmitted through UV-reflective multilayer optical film 110 is
reflected by VIS/IR-reflective metal layer 130. Optional adhesive
layer 125 is disposed on metal layer 130 opposite UV-reflective
multilayer optical film 110.
[0049] UV-reflective optical layer stack 140 will be better
understood with reference to FIG. 1B. UV-reflective optical layer
stack 140 comprises first optical layers 160a, 160b, . . . , 160n
(collectively first optical layers 160) in intimate contact with
second optical layers 162a, 162b, . . . , 162n (collectively second
optical layers 162). First optical layers 160 and second optical
layers 162 have respective refractive indexes that are different.
Accordingly, a reflection is generated at each interface between
the adjacent optical layers. Light that is not reflected at the
interface between adjacent optical layers typically passes through
successive layers and is either reflected at a subsequent interface
or passes through the UV-reflective optical layer stack
altogether.
[0050] The normal reflectivity for a particular layer pair is
primarily dependent on the optical thickness of the individual
layers, where optical thickness is defined as the product of the
actual thickness of the layer times its refractive index. The
intensity of light reflected from the optical layer stack is a
function of its number of layer pairs and the differences in
refractive indices of optical layers in each layer pair. The ratio
n.sub.1d.sub.1/(n.sub.1d.sub.1+n.sub.2d.sub.2) (commonly termed the
"f-ratio") correlates with reflectivity of a given layer pair at a
specified wavelength. In the f-ratio, n.sub.1 and n.sub.2 are the
respective refractive indexes at the specified wavelength of the
first and second optical layers in a layer pair, and d.sub.1 and
d.sub.2 are the respective thicknesses of the first and second
optical layers in the layer pair. By proper selection of the
refractive indexes, optical layer thicknesses, and f-ratio one can
exercise some degree of control over the intensity of first order
reflection. For example, first order visible reflections of violet
(400 nanometers wavelength) to red (700 nanometers wavelength) can
be obtained with layer optical thicknesses between about 0.05 and
0.3 nanometers. In general, deviation from an f-ratio of 0.5
results in a lesser degree of reflectivity.
[0051] The equation .lamda./2=n.sub.1d.sub.1+n.sub.2d.sub.2 can be
used to tune the optical layers to reflect light of wavelength
.lamda. at a normal angle of incidence. At other angles, the
optical thickness of the layer pair depends on the distance
traveled through the component optical layers (which is larger than
the thickness of the layers) and the indices of refraction for at
least two of the three optical axes of the optical layer. The
optical layers can each be a quarter-wavelength thick or the
optical thin layers can have different optical thicknesses, as long
as the sum of the optical thicknesses is half of a wavelength (or a
multiple thereof). An optical stack having more than two layer
pairs can include optical layers with different optical thicknesses
to provide reflectivity over a range of wavelengths. For example,
an optical stack can include layer pairs that are individually
tuned to achieve optimal reflection of normally incident light
having particular wavelengths or may include a gradient of layer
pair thicknesses to reflect light over a larger bandwidth.
[0052] A typical approach is to use all or mostly quarter-wave film
stacks. In this case, control of the spectrum requires control of
the layer thickness profile in the film stack. A broadband
spectrum, such as one required to reflect visible light over a
large range of angles in air, still requires a large number of
layers if the layers are polymeric, due to the relatively small
index differences achievable with polymer films compared to
inorganic films. Layer thickness profiles of such films can be
adjusted to provide for improved spectral characteristics using the
axial rod apparatus taught in U.S. Pat. No. 6,783,349 (Neavin et
al.) combined with layer profile information obtained with
microscopic techniques.
[0053] Desirable techniques for providing a multilayer optical film
with a controlled spectrum include: [0054] 1) The use of an axial
rod heater control of the layer thickness values of coextruded
polymer layers as taught in U.S. Pat. No. 6,783,349 (Neavin et
al.). [0055] 2) Timely layer thickness profile feedback during
production from a layer thickness measurement tool such as e.g. an
atomic force microscope (AFM), a transmission electron microscope,
or a scanning electron microscope. [0056] 3) Optical modeling to
generate the desired layer thickness profile. [0057] 4) Repeating
axial rod adjustments based on the difference between the measured
layer profile and the desired layer profile.
[0058] The basic process for layer thickness profile control
involves adjustment of axial rod zone power settings based on the
difference of the target layer thickness profile and the measured
layer profile. The axial rod power increase needed to adjust the
layer thickness values in a given feedblock zone may first be
calibrated in terms of watts of heat input per nanometer of
resulting thickness change of the layers generated in that heater
zone. Fine control of the spectrum is possible using 24 axial rod
zones for 275 layers. Once calibrated, the necessary power
adjustments can be calculated once given a target profile and a
measured profile. The procedure is repeated until the two profiles
converge.
[0059] The layer thickness profile (layer thickness values) of this
UV reflector can be adjusted to be approximately a linear profile
with the first (thinnest) optical layers adjusted to have about a
1/4 wave optical thickness (index times physical thickness) for 340
nm light and progressing to the thickest layers which can be
adjusted to be about 1/4 wave thick optical thickness for 420 nm
light.
[0060] The UV-reflective optical layer stack comprises first
optical layers and second optical layers, which have an average
individual layer thickness of about one quarter the wavelength of
UV-light, and a layer pair thickness of about one half the
wavelength of UV-light. For example, at 400 nanometers (nm) the
average individual layer thickness would be about 100 nm, and the
average layer pair thickness would be about 200 nm. Similarly, at
350 nm the average individual layer thickness would about 87 nm,
and the average layer pair thickness would be about 175 nm. Of
course, true thickness will typically vary such that a range of
thickness (and hence reflective response) will be obtained.
Further, the thickness of individual first and/or second optical
layers may be varied, for example, according to a thickness
gradient in which the first and/or second layers gradually become
thicker (or thinner) with respect to the first major surface,
thereby achieving a broadband reflective response (i.e., UV-light
and VIS/IR-light).
[0061] Since reflectivity at a given interface is typically
relatively low, the number of the optical layers is typically large
(e.g., at least 100, 250, 500, or even at least 1000 optical
layers) such that the total light reflectivity is high.
[0062] In order for an optical layer stack to function efficiently,
the first and second optical layers (or, as described hereinbelow,
third and fourth optical layers in the case of a UV/IR optical
layer stack) at least a portion, typically all or substantially
all, of any two optical layers that are in intimate contact (i.e.,
a layer pair) have a refractive index difference that results in
reflection of a portion of any light traversing the interface
between the optical layers.
[0063] An exemplary layer pair 164a is shown in FIG. 1B. Typically,
the optical layers of a given layer pair are selected such as to be
substantially transparent to those light wavelengths at which
reflectivity is desired. Light that is not reflected at a layer
pair interface passes to the next layer pair interface where a
portion of the light is reflected and unreflected light continues
on, and so on. In this way, an optical layer stack (e.g., a
UV-reflective optical layer stack or a VIS/IR-reflective optical
layer stack) with many optical layers (e.g., more than 100 optical
layers) is capable of generating a high degree of reflectivity,
which may be broadband. The difference in refractive index, with
respect to at least one dimension, between layers of the layer pair
is typically 0.05 or larger, more typically at least 0.1, although
lesser differences may also be used if desired.
[0064] Birefringence (e.g., caused by stretching) of optical layers
is an effective method for increasing the difference in refractive
index of the optical layers in a layer pair. Multilayer reflective
optical films that include layer pairs are oriented in two mutually
perpendicular in-plane axes are capable of reflecting an
extraordinarily high percentage of incident light depending on the
number of optical layers, f-ratio, indices of refraction, etc., and
are highly efficient reflectors. Reflectors can also be made using
a combination of uniaxially-oriented layers with in-plane indices
of refraction that differ significantly.
[0065] As shown in FIG. 1B, the layer pairs may be arranged as
alternating layer pairs (e.g., ABABAB.). In other embodiments, they
may also be arranged with intermediate layers such as, for example,
a third optical layer (e.g., ABCABC . . . ) or in non-alternating
fashion (e.g., ABABABCAB . . . , ABABCABDAB . . . or ABABBAABAB . .
. , etc.). Typically, the layer pairs are arranged as alternating
layer pairs.
[0066] The optional abrasion resistant layer may comprise any
abrasion resistant material that is transparent to the wavelengths
of UV-light and VIS/IR-light reflected by the broadband reflector.
Examples of scratch resistant coatings include: a thermoplastic
urethane available as TECOFLEX from Lubrizol Advanced Materials,
Inc, Cleveland, Ohio, ??containing 5 weight percent of a UV
absorber available as TINUVIN 405 from Ciba Specialty Chemicals
Corp., 2 weight percent of a hindered amine light stabilizer
available as TINUVIN 123, and 3 weight percent of a UV-absorber
available as TINUVIN 1577 from Ciba Specialty Chemicals Corp. and a
scratch resistant coating preparable by curing a curable siliceous
polymer composition available as PERMA-NEW 6000 (or PERMA-NEW
6000B) CLEAR HARD COATING SOLUTION from California Hardcoating Co.
of Chula Vista, Calif.
[0067] The abrasion resistant layer may have any suitable
thickness, typically depending on the choice of abrasion resistant
material used. Typical abrasion resistant layer thicknesses are on
the order of 1 to 10 micrometers, more typically 3 to 6
micrometers, although other thicknesses may be used.
[0068] The optional abrasion resistant layer may optionally include
at least one antisoiling component. Examples of antisoiling
components include fluoropolymers, silicone polymers, and titanium
dioxide particles, fluoropolymers, silicone polymers, titanium
dioxide particles, polyhedral oligomeric silsesquioxanes (e.g., as
available as POSS from Hybrid Plastics of Hattiesburg, Miss.), and
combinations thereof. The abrasion resistant layer may also
comprise a conductive filler, typically a transparent conductive
filler. The abrasion resistant layer may also comprise an
inherently static dissipative polymer such as those available as
STATRITE X5091 or STATRITE M809 from Lubrizol Corp.
[0069] If present, the optional tie layer facilitates adhesion of
the VIS/IR-reflective metal layer to the UV-reflective multilayer
optical film. The tie layer may be organic (e.g., a polymeric layer
or adhesive), inorganic, or other. Exemplary inorganic tie layers
include amorphous silica, silicon monoxide, and metal oxides (e.g.,
tantalum pentoxide, titanium dioxide, and aluminum oxide). The tie
layer may be provided by any suitable means, including vapor
coating, solvent casting, and powder coating techniques. In order
that it does not degrade performance of the broadband reflector,
the optional tie layer is typically substantially not absorptive of
light (e.g., having an absorbance of less than 0.1, less than 0.01,
less than 0.001, or less than 0.0001) over the wavelength range of
from greater than 400 to 2494 nm.
[0070] The VIS/IR-reflective metal layer may comprise any metal or
metals that reflects VIS/IR light, typically efficiently. In
general, the VIS/IR-reflective metal layer should be at least about
100 nm thick to ensure high reflectivity. Exemplary metals include
silver, copper, aluminum, copper on silver, nichrome, stainless
steel, and nickel. The metal layer may be secured to the
UV-reflective multilayer optical film by any suitable technique
including lamination, sputtering, and vapor coating. For example,
the metal layer may be provided by laminating the UV-reflective
multilayer optical film to polished aluminum stock, silver coated
aluminum stock, polished stainless steel stock, and silver coated
glass (including retro-fitting existing silver coated glass CSP
troughs). In some embodiments, the metal layer includes a
VIS/IR-reflective foil, a vapor coated metal surface (e.g., front
surface VIS/IR-reflective metal layers on a glass or polymeric
backing), or metallic sheet stock.
[0071] Referring now to FIG. 2A, a broadband reflector 200
according to another exemplary embodiment of the present disclosure
has UV-reflective multilayer optical film 110 with first major
surface 115, UV-reflective optical layer stack 140, optional tie
layer 120, and optional abrasive resistant hardcoat 150.
VIS/IR-reflective multilayer optical film 280 comprises
VIS/IR-reflective optical layer stack 240. Optional adhesive layer
225 is disposed on at least a portion of VIS/IR-reflective
multilayer optical film 280 opposite UV-reflective multilayer
optical film 110.
[0072] Referring now to FIG. 2B, VIS/IR-reflective optical layer
stack 240 comprises third optical layers 260a, 260b, . . . , 260n
(collectively third optical layers 260) and fourth optical layers
262a, 262b, . . . , 262n (collectively fourth optical layers 262)
analogous to the first and second optical layers 160, 162, but of
different thickness and optionally composition. VIS/IR-reflective
optical layer stack 240 may be constructed generally as in
UV-reflective optical layer stack 140 except for optical layer
thicknesses that will differ due to the wavelength difference.
Materials selection for third and fourth optical layers may be the
same or different as the first and second optical layers of
UV-reflective optical layer stack 140 as desired.
[0073] Referring again to FIG. 2A, UV-absorbing layer 290 is
disposed (e.g., sandwiched) between UV-reflective multilayer
optical film 110 and VIS/IR-reflective multilayer optical film 280,
which is reflective to VIS/IR-light.
[0074] The UV-absorbing layer is disposed between the UV-reflective
multilayer optical film and the VIS/IR multilayer optical film, and
serves to absorb UV-light that would otherwise impinge on the
VIS/IR-reflective multilayer optical film and could lead to
degradation over time. Solar light, in particular the ultraviolet
radiation from 280 to 400 nm, can induce degradation of plastics,
which in turn results in color change and deterioration of optical
and mechanical properties. Inhibition of photo-oxidative
degradation is important for outdoor applications wherein long term
durability is mandatory. The absorption of UV-light by polyethylene
terephthalates, for example, starts at around 360 nm, increases
markedly below 320 nm, and is very pronounced at below 300 nm.
Polyethylene naphthalates strongly absorb UV-light in the 310-370
nm range, with an absorption tail extending to about 410 nm, and
with absorption maxima occurring at 352 nm and 337 nm. Chain
cleavage occurs in the presence of oxygen, and the predominant
photooxidation products are carbon monoxide, carbon dioxide, and
carboxylic acids. Besides the direct photolysis of the ester
groups, consideration has to be given to oxidation reactions, which
likewise form carbon dioxide via peroxide radicals.
[0075] The UV-absorbing layer comprises a polymer and a
UV-absorber. Typically, the polymer is a thermoplastic polymer, but
this is not a requirement. Examples of suitable polymers include
polyesters (e.g., polyethylene terephthalate), fluoropolymers,
acrylics (e.g., polymethyl methacrylate), silicone polymers (e.g.,
thermoplastic silicone polymers), styrenic polymers, polyolefins,
olefinic copolymers (e.g., copolymers of ethylene and norbornene
available as TOPAS COC from Topas Advanced Polymers of Florence ,
Ky.), silicone copolymers, fluoropolymers, and combinations thereof
(e.g., a blend of polymethyl methacrylate and polyvinylidene
fluoride).
[0076] The UV-absorbing layer protects the VIS/IR-reflective
optical layer stack from UV-light caused damage by absorbing any
UV-light that may pass through the UV-reflective optical layer
stack. In general, the UV-absorbing layer may include any polymeric
composition (i.e., polymer plus additives), including
pressure-sensitive adhesive compositions, that is capable of
withstanding UV-light for an extended period of time.
[0077] A variety of ultraviolet light absorbing and stabilizing
additives are typically incorporated into the UV-absorbing layer to
assist in its function of protecting the VIS/IR-reflective
multilayer optical film. Non-limiting examples of the additives
include one or more compounds selected from ultraviolet light
absorbers, hindered amine light stabilizers, antioxidants, and
combinations thereof
[0078] UV stabilizers such as UV-absorbers are chemical compounds
that can intervene in the physical and chemical processes of
photoinduced degradation. The photooxidation of polymers from
ultraviolet radiation can therefore be prevented by use of a
UV-absorbing layer that contains at least one UV-absorber to
effectively absorb light at wavelengths less than about 400 nm.
UV-absorbers are typically included in the UV-absorbing layer in an
amount that absorb at least 70 percent, typically 80 percent, more
typically greater than 90 percent, or even greater than 99 percent
of incident light in a wavelength region from 180 to 400 nm.
[0079] Typical UV-absorbing layer thicknesses are from 10 to 500
micrometers, although thinner and thicker UV-absorbing layers may
also be used. Typically, the UV-absorber is present in the
UV-absorbing layer in an amount of from 2 to 20 percent by weight,
but lesser and greater levels may also be used.
[0080] One exemplary UV-absorber is a benzotriazole compound,
5-trifluoromethyl-2-(2-hydroxy-3-alpha-cumyl-5-tert-octylphenyl)-2H-benzo-
triazole. Other exemplary benzotriazoles include
2-(2-hydroxy-3,5-di-alpha-cumylphehyl)-2H-benzotriazole,
5-chloro-2-(2-hydroxy-3-tert-butyl-5-methylphenyl)-2H-benzotiazole,
5-chloro-2-(2-hydroxy-3,5-di-tert-butylphenyl)-2H-benzotriazole,
2-(2-hydroxy-3,5-di-tert-amylphenyl)-2H-benzotriazole,
2-(2-hydroxy-3-alpha-cumyl-5-tert-octylphenyl)-2H-benzotriazole,
2-(3-tert-butyl-2-hydroxy-5-methylphenyl)-5-chloro-2H-benzotriazole.
Additional exemplary UV-absorbers include
2(-4,6-diphenyl-1-3,5-triazin-2-yl)-5-hexcyloxy-phenol, and those
available from Ciba Specialty Chemicals Corp. as TINUVIN 1577 and
TINUVIN 900. In addition, UV-absorber(s) can be used in combination
with hindered amine light stabilizer(s) (HALS) and/or antioxidants.
Exemplary HALSs include those available from Ciba Specialty
Chemicals Corp. as CHIMASSORB 944 and TINUVIN 123. Exemplary
antioxidants include those available as IRGANOX 1010 and ULTRANOX
626 from Ciba Specialty Chemicals Corp.
[0081] In addition to adding UVA, HALS, and antioxidants to the
UV-absorbing layer, the UVA, HALS, and antioxidants can be added to
other layers present in broadband reflectors according to the
present disclosure.
[0082] Other additives may be included in the UV-absorbing layer.
Small particle non-pigmentary zinc oxide and titanium oxide can
also be used as blocking or scattering additives in the
UV-absorbing layer. For example, nanoscale (i.e., nanometer-scale)
particles can be dispersed in polymer or coating substrates to
minimize ultraviolet radiation degradation. The nanoscale particles
are transparent to visible light while either scattering or
absorbing harmful UV radiation thereby reducing damage to
thermoplastics. U.S. Pat. No. 5,504,134 (Palmer et al.) describes
attenuation of polymer substrate degradation due to ultraviolet
radiation through the use of metal oxide particles in a size range
of about 0.001 micrometer to about 0.20 micrometer in diameter, and
more preferably from about 0.01 to about 0.15 micrometers in
diameter. U.S. Pat. No. 5,876,688 (Laundon) teaches a method for
producing micronized zinc oxide that are small enough to be
transparent when incorporated as ultraviolet light (UV) blocking
and/or scattering agents in paints, coatings, finishes, plastic
articles, and cosmetics, which are well suited for use in the
present invention. These fine particles such as zinc oxide and
titanium oxide with particle size ranged from 10-100 nm that can
attenuate UV radiation are commercially available from Kobo
Products, Inc., South Plainfield, N.J. Flame retardants may also be
incorporated as an additive in the UV-absorbing layer.
[0083] The thickness of the UV-absorbing layer is dependent upon an
optical density target at specific wavelengths as calculated by the
Beer-Lambert Law. In typical embodiments, the UV-absorbing layer
has an optical density greater than 3.5 at 380 nm; greater than 1.7
at 390; and greater than 0.5 at 400 nm. Those of ordinary skill in
the art will recognize that the optical densities must remain
fairly constant over the extended life of the article in order to
provide the intended protective function.
[0084] In general, UV-reflective multilayer optical films and
VIS/IR-reflective multilayer optical films are specular reflectors,
although this is not a requirement. Both multilayer reflective
optical films rely on index of refraction differences between at
least two different materials (typically polymeric materials (e.g.,
polymers or combinations of polymers)).
[0085] The first and third optical layers are typically
birefringent layers that comprise respective first and third
polymers, which may be single polymers or combinations of polymers,
which are uniaxially-oriented or biaxially-oriented to create a
sufficiently high refractive index difference between the first and
second optical layers or third and fourth optical layers, although
this is not a requirement. High reflectivity can also be achieved
by increasing the number of layers for optical pairs with less
refractive difference between first and second optical layers. In
those embodiments wherein the first optical layer is birefringent,
the first polymer is typically capable of developing a large
birefringence when stretched. Depending on the application, the
birefringence may be developed between two orthogonal directions in
the plane of the film, between one or more in-plane directions and
the direction perpendicular to the film plane, or a combination of
these. The first polymer should maintain birefringence after
stretching, so that the desired optical properties are imparted to
the finished film.
[0086] The second and fourth optical layers can be layers
comprising respective second and fourth polymers, which may be
single polymers or combinations of polymers, that are birefringent
and uniaxially- or biaxially-oriented or the second optical layers
can have an isotropic index of refraction that is different from at
least one of the indices of refraction of the respective first and
third optical layers after orientation. The second and fourth
polymers advantageously develop little or no birefringence when
stretched, or develops birefringence of the opposite sense
(positive-negative or negative-positive), such that its film-plane
refractive indices differ as much as possible from those of the
first (or third) polymers in the finished film. For most
applications, it is advantageous that neither the first polymer nor
the second polymer absorbance incident light within the bandwidth
of interest for the film in question, resulting in all incident
light within the bandwidth being either reflected or transmitted.
However, some level of absorbance may be acceptable for some
applications.
[0087] The first, second, third, and fourth optical layers may
comprise one or more polymers (including miscible polymer blends).
Useful classes of polymers include polyesters and
polycarbonates.
[0088] Polyesters may be derived, for example, from ring-opening
addition polymerization of a lactone, or by condensation of a
dicarboxylic acid (or derivative thereof such as, for example, a
diacid halide or a diester) with a diol. Exemplary dicarboxylic
acids include: 2,6-naphthalenedicarboxylic acid; terephthalic acid;
isophthalic acid; phthalic acid; azelaic acid; adipic acid; sebacic
acid; norbornenedicarboxylic acid; bicyclooctanedicarboxylic acid;
1,6-cyclohexanedicarboxylic acid; t-butyl isophthalic acid,
trimellitic acid, sodium sulfonated isophthalic acid;
4,4'-biphenyldicarboxylic acid. Acid halides and lower alkyl esters
of these acids, such as methyl or ethyl esters may also be used as
functional equivalents. The term "lower alkyl" refers, in this
context, to alkyl groups having from one to ten carbon atoms.
Exemplary diols include: ethylene glycol; propylene glycol;
1,4-butanediol; 1,6-hexanediol; neopentyl glycol; polyethylene
glycol; diethylene glycol; tricyclodecanediol;
1,4-cyclohexanedimethanol; norbornanediol; bicyclooctanediol;
trimethylolpropane; pentaerythritol; 1,4-benzenedimethanol;
bisphenol A; 1,8-dihydroxybiphenyl; and 1,3-bis
(2-hydroxyethoxy)benzene.
[0089] Exemplary polymers useful for forming birefringent optical
layers include, for example: polyethylene terephthalates (PETs)
(e.g., a PET having an inherent viscosity of 0.74 dL/g, available
from Eastman Chemical Company (Kingsport, Tenn.)); polyethylene
2,6-naphthalates (PENs); copolyesters derived from
naphthalenedicarboxylic acid, an additional dicarboxylic acid, and
a diol (coPENs) (e.g., a polyester derived through co-condensation
of 90 equivalents of dimethyl naphthalenedicarboxylate, 10
equivalents of dimethyl terephthalate, and 100 equivalents of
ethylene glycol, and having an intrinsic viscosity (IV) of 0.48
dL/g, and an index of refraction is approximately 1.63); polyether
imides; and polyester/non-polyester combinations; polybutylene
2,6-naphthalates (PBNs); modified polyolefin elastomers, e.g., as
available as ADMER (e.g., ADMER SE810) thermoplastic elastomers
from Mitsui Chemicals America, Inc. of Rye Brook, N.Y.; and
copolyesters derived from terephthalic acid such as those described
in U.S. Pat. No. 6,449,093 B2 (Hebrink et al.) or U.S. Pat. App.
Publ. No. 2006/0084780 A1 (Hebrink et al.); thermoplastic
polyurethanes (TPUs) (e.g., as available as ELASTOLLAN TPUs from
BASF Corp. of Florham Park, N.J. and as TECOFLEX or STATRITE TPUs
(e.g., STATRITE X5091 or STATRITE M809) from The Lubrizol Corp. of
Wickliffe, Ohio); and syndiotactic polystyrenes (sPSs), which is
particularly useful due to its low UV-light absorbance; and
combinations thereof.
[0090] PEN has a large positive stress optical coefficient, retains
birefringence effectively after stretching, and has little or no
absorbance within the visible range. PEN also has a large index of
refraction in the isotropic state. Its refractive index for
polarized incident light of 550 nm wavelength increases when the
plane of polarization is parallel to the stretch direction from
about 1.64 to as high as about 1.9. Increasing molecular
orientation increases the birefringence of PEN. The molecular
orientation may be increased by stretching the material to greater
stretch ratios and holding other stretching conditions fixed.
coPENs such as those described in U.S. Pat. Nos. 6,352,761 B1 and
6,449,093 B2 (both to Hebrink et al.) are particularly useful for
their low temperature melt processing capability.
[0091] Exemplary melt-processible polymers useful in
non-birefringent optical layers include: polyesters (e.g.,
polycyclohexanedimethylene terephthalate commercially available
from Eastman Chemical Co, Kingsport, Tenn.); polysulfones;
polyurethanes; polyamides; polyimides; polycarbonates;
polydimethylsiloxanes; polydiorganosiloxane polyoxamide block
copolymers (OTPs) such as, e.g., those described in U.S. Publ. Pat.
Appln. Nos. 2007/0148474 A1 (Leir et al.) and 2007/0177272 A1
(Benson et al.); fluoropolymers including, e.g., homopolymers such
as polyvinylidene difluoride (PVDFs), copolymers such as copolymers
of tetrafluoroethylene, hexafluoropropylene, and vinylidene
fluoride (THVs), copolymers of hexafluoropropylene,
tetrafluoroethylene, and ethylene (HTEs); copolymers of
tetrafluoroethylene and norbornene; copolymers of ethylene and
tetrafluoroethylene (ETFEs); copolymers of ethylene and vinyl
acetate (EVAs); copolymers of ethylene and chlorotrifluoroethylene
(ECTFEs), and fluoroelastomers; acrylics such as polymethyl
methacrylate (PMMA, e.g., as available as CP71 and CP80 from Ineos
Acrylics, Inc. of Wilmington, Del.) and copolymers of methyl
methacrylate (coPMMAs) such as, e.g., a coPMMA made from 75 weight
percent methyl methacrylate and 25 weight percent ethyl acrylate
(available from Ineos Acrylics, Inc., as PERSPEX CP63) and a coPMMA
formed from methyl methacrylate and n-butyl methacrylate; styrenic
polymers; vinyl acetate copolymers (e.g., ethylene vinyl acetate
copolymers); copolymers of ethylene and a cyclic olefin (COCs);
blend of PMMA and PVDF (e.g., as available from Solvay Polymers,
Inc., Houston, Tex., as SOLEF); polyolefin copolymers such as poly
(ethylene-co-octene) (PE-POs) available from Dow Chemical Co.,
Midland, Mich. as ENGAGE 8200, poly (propylene-co-ethylene) (PPPE)
available from Fina Oil and Chemical Co., Dallas, Tex. as Z9470,
and a copolymer of atactic polypropylene (aPPs) and isotactic
polypropylene (iPPs) available from Huntsman Chemical Corp., Salt
Lake City, Utah as REXFLEX W111; and combinations thereof. Second
optical layers can also be made from a functionalized polyolefin,
such as linear low density polyethylene-g-maleic anhydride
(LLDPE-g-MA) such as that available from E. I. du Pont de Nemours
& Co., Inc., Wilmington, Del. as BYNEL 4105; and combinations
thereof.
[0092] In some embodiments, the melt-processible copolymers of
tetrafluoroethylene and other monomer(s), described above, include
additional monomers such as, e.g., propylene, ethylene, norbornene,
and/or perfluorinated vinyl ethers represented by the formula:
CF.sub.2.dbd.CF(OCF.sub.2CF(R.sub.f)).sub.aOR'.sub.f
wherein R.sub.f is a perfluoroalkyl group having from 1 to 8
(typically 1 to 3 carbon atoms), and R'.sub.f is a
perfluoroaliphatic group, typically a perfluoroalkyl or
perfluoroalkoxy group having from 1 to 8 (typically 1 to 3 carbon
atoms), and a is 0, 1, 2, or 3. Exemplary perfluorinated vinyl
ethers having this formula include: CF.sub.2.dbd.CFOCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2CF.sub.2OCF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2CF.sub.3,
CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)OCF.sub.2CF.sub.2CF.sub.3, and
CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)OCF.sub.2CF(CF.sub.3)OCF.sub.2CF.sub.-
2CF.sub.3. Exemplary melt-processible copolymers of
tetrafluoroethylene and other monomer(s) discussed above include
those available as DYNEON THV 220, DYNEON THV 230, DYNEON THV 500,
DYNEON THV 500G, DYNEON THV 510, DYNEON THV 510D, DYNEON THV 610,
DYNEON THV 815, and DYNEON THVP 2030G from Dyneon LLC of Oakdale,
Minn. Additional useful polymers are disclosed in U.S. Pat. No.
6,498,683 B2 (Condo et al.) and U.S. Pat. No. 6,352,761 B1 (Hebrink
et al.).
[0093] Polymers used for forming optical layers of the
UV-reflective optical layer stack typically have little or no
absorbance at wavelengths above 350 nm, and desirably above 300
nm.
[0094] In general, at least the second and fourth polymers should
be chosen so that in the respective optical layer stack, the
refractive indexes of the second and fourth optical layers, in at
least one direction, differ significantly from the index of
refraction of the respective first and third optical layers in the
same direction. Because polymeric materials are typically
dispersive, that is, the refractive indices vary with wavelength,
these conditions must be considered in terms of a particular
spectral bandwidth of interest. It will be understood from the
foregoing discussion that the choice of a second polymer is
dependent not only on the intended application of the optical layer
stack in question, but also on the choice made for the first
polymer, as well as processing conditions.
[0095] The UV-reflective and/or VIS/IR multilayer optical films may
optionally include one or more non-optical layers such as, for
example, one or more skin layers or one or more interior
non-optical layers, such as, for example, protective boundary
layers between packets of optical layers. Non-optical layers can be
used to give the multilayer optical film structure or to protect it
from harm or damage during or after processing. For some
applications, it may be desirable to include sacrificial protective
skins, wherein the interfacial adhesion between the skin layer(s)
and the optical layer stack is controlled so that the skin layers
can be stripped from the optical layer stack before use.
[0096] Materials may be chosen for the non-optical layers that
impart or improve properties such as, for example, tear resistance,
puncture resistance, toughness, weatherability, and solvent
resistance of the multilayer optical body. Typically, one or more
of the non-optical layers are placed so that at least a portion of
the light to be transmitted or reflected by optical layers also
travels through these layers (i.e., these layers are placed in the
path of light that travels through or is reflected by the first and
second optical layers). The non-optical layers typically do not
substantially affect the reflective properties of the broadband
reflectors over the wavelength region of interest. Properties of
the non-optical layers such as thermal expansion and shrinkage
characteristics need to be considered along with the properties of
the optical layers to give the film of the present invention that
does not crack or wrinkle when laminated to severely curved
substrates.
[0097] The non-optical layers may be of any appropriate material
and can be the same as one of the materials used in the optical
layer stack. Of course, it is important that the material chosen
not have optical properties deleterious to those of the optical
layer stack(s). For example, the non-optical layers should
typically have little or no absorbance that would interfere with
optical layer stack. The non-optical layers may be formed from a
variety of polymers, such as polyesters, including any of the
polymers used in the first and second optical layers. In some
embodiments, the material selected for the non-optical layers is
similar to or the same as the material selected for the second
optical layers. The use of coPEN, coPET, or other copolymer
material for skin layers reduces the breaking apart of multilayer
optical film(s) due to strain-induced crystallinity and alignment
of a majority of the polymer molecules in the direction of
orientation.
[0098] Typically, the polymers of the first and second optical
layers (and likewise the third and fourth optical layers), and the
optional non-optical layers are chosen to have similar rheological
properties (e.g., melt viscosities) so that they can be co-extruded
without flow disturbances. Typically, the second and fourth optical
layers, skin layers, and optional other non-optical layers have a
glass transition temperature (T.sub.g), that is either less than or
equal to about 40.degree. C. above the glass transition temperature
of the respective first and third optical layers.
[0099] The optional non-optical layers can be thicker than, thinner
than, or the same thickness as the various optical layers. The
thickness of the optional non-optical layers is generally at least
four times, typically at least 10 times, and can be at least 100
times, the thickness of at least one of the individual optical
layers. The thickness of the non-optical layers can be varied to
make a multilayer reflective film having a particular thickness.
Optional non-optical layers may include one or more UV-absorbers
and/or stabilizers. For example, they may contain extrusion
compounded UVA absorbers such as those available as TINUVIN 1557
from Ciba Specialty Chemicals Corp., and extrusion compounded
hindered amine light stabilizers (HALS) such as those available as
CHIMASSORB 944 from Ciba Specialty Chemicals Corp.
[0100] Additional coatings may also be considered non-optical
layers. Other layers include, for example, antistatic coatings or
films; flame retardants; optical coatings; anti-fogging materials,
etc.
[0101] The broadband reflectors can be fabricated by methods
well-known to those of skill in the art by techniques such as for
example, heat lamination and adhesive bonding. Exemplary useful
adhesives (e.g., adhesive layer 120) that may be used in
fabrication of broadband reflectors according to the present
disclosure may be optically transparent and reasonably UV-light
stable or not, and include: optically clear acrylic pressure
sensitive adhesives (25 .mu.m thickness) available from 3M Company
as OPTICALLY CLEAR LAMINATING ADHESIVE 8141 or as OPTICALLY CLEAR
LAMINATING ADHESIVE 8171; tackified OTP adhesives as described in
U.S. Pat. No. 7,371,464 B2 (Sherman et al.); and non-silicone
pressure-sensitive adhesives as described in PCT Pat. Appln. No.
PCT/US08/86596 entitled "Urea-Based Pressure Sensitive Adhesives",
filed Dec. 12, 2008. In those applications wherein the adhesive is
used as optional adhesive layer 125 or optional adhesive layer 225,
then optical transparency and/or stability is typically not of
significance as little if any light will reach the adhesive in
typical constructions. Accordingly, optional adhesive layer 125 or
225 may comprise any adhesive composition such as e.g., an epoxy,
urethane, silicone, or acrylic adhesive, or a combination thereof.
The adhesive composition may comprise, for example, a
pressure-sensitive adhesive, a thermosetting adhesive, a hot melt
adhesive, or a combination thereof. Advantageously, broadband
reflectors 100 and 200 may be adhesive bonded to existing solar
reflector(s). This process is useful for retrofitting existing CSP
installations.
[0102] Further considerations relating to the selection of
materials, mode of operation, and manufacturing of multilayer
optical films can be obtained with reference to U.S. Pat. No.
5,882,774 (Jonza et al.); U.S. Pat. No. 6,157,490 (Wheatley et
al.); U.S. Pat. No. 6,207,260 B1 (Wheatley et al.); 6,783,349 B2
(Neavin et al.); U.S. Pat. No. 6,827,886 B2 (Neavin et al.); U.S.
Pat. No. 6,179,948 B1 (Merrill et al.); 6,808,658 B2 (Stover); and
U.S. Pat. No. 6,830,713 B2 (Hebrink et al.).
[0103] Broadband reflectors according the present disclosure may be
planar or curved (e.g., parabolic or parabolic trough-shaped) and
are typically in the form of a compliant sheet or film, although
this is not a requirement. For example, they may be combined with a
rigid member (e.g., a backing support) that imparts and retains a
particular shape to the broadband reflector surface (e.g., a curved
reflective surface). For purposes of the present disclosure, the
term "compliant" is an indication that the broadband reflector is
dimensionally stable yet possesses a pliable characteristic that
enables subsequent molding or shaping into various forms. In some
exemplary embodiments, broadband reflectors according to the
present disclosure may be thermoformed into various shapes or
structures for specific end use applications.
[0104] Broadband reflectors according to the present disclosure may
be converted, for example, by thermoforming, vacuum forming,
shaping, rolling, or pressure forming, into shapes and/or
dimensions (e.g., curved surfaces and parabolic surfaces)
conventionally used for reflectors such as, for example, solar
concentrators used in concentrated solar power systems.
Additionally, the broadband reflectors may be reinforced, for
example, by injection cladding, corrugation, or addition of ribs,
foam spacer layers, or honeycomb structures to improve its
dimensional stability. One exemplary reinforcing material is twin
wall polycarbonate sheeting, e.g., as available as SUNLITE
MULTIWALL POLYCARBONATE SHEET from Palram Americas, Inc. of
Kutztown, Pa. Thermoforming of multilayer optical films is
generally described in U.S. Pat. No. 6,788,463 B2 (Merrill et
al.).
[0105] Advantageously, broadband reflectors according to the
present disclosure, especially if formed into solar concentrators,
are capable of concentrating high levels of sunlight at a fraction
of the weight of conventional solar concentrators.
[0106] An exemplary concentrated solar power system 300 is depicted
schematically in FIG. 3. Concentrated solar power system 300
comprises broadband reflectors 310 connected to celestial tracking
mechanism 320 that is capable of aligning direct solar radiation
from broadband reflectors 310 onto hollow receiver 330. A heat
transfer fluid 340 circulates by means of pump 360 through the
hollow receiver 330 where it is heated by concentrated solar
radiation. The heated heat transfer fluid 340 is then directed to
an electrical generator 350 (e.g., a steam turbine) when the
thermal energy is converted to electrical energy. In another
embodiment, the heat transfer fluid may be directed to a heat
exchanger instead of the electrical generator, where the heat
content is transferred to a liquid medium such as, for example,
water that is converted to steam which drives the electrical
generator.
[0107] Another exemplary concentrated solar power system 400 is
depicted schematically in FIG. 4. Concentrated solar power system
400 comprises parabolic trough-shaped broadband reflectors 410
connected to celestial tracking mechanism 420 that is capable of
aligning direct solar radiation from broadband reflectors 410 onto
hollow receiver 430. A heat transfer fluid 440 circulates by means
of pump 460 through the hollow receiver 430 where it is heated by
concentrated solar radiation. The heated heat transfer fluid 440 is
then directed to a thermal heating system 450 where the thermal
energy is converted to electrical energy.
[0108] The hollow receivers may be transparent or opaque and should
typically be made of material (e.g., metal or glass) that is
capable of withstanding the light and heat directed upon it by the
broadband reflectors. Exemplary heat transfer fluids include water,
water/glycol mixtures, brine, molten salts, and oils, with the
selected typically being dictated by application requirements and
cost. Often the hollow receivers comprise an interior pipe coated
with a solar absorbing material disposed inside an exterior
transparent (e.g., glass) pipe, although other configurations may
also be used. In some embodiments, the heated heat transfer fluid
flowing through the solar absorbing hollow receiver exchanges heat
with water to create steam that drives an electric generator.
[0109] Further enhancements in the concentrated solar polar system
output may be achieved when anti-reflective surface structured
films or coatings are applied to the front surface of the hollow
receiver. Surface structures in the films or coating typically
change the angle of incidence of light such that it enters the
polymer and hollow receiver beyond the critical angle and is
internally reflected, leading to more absorption by the hollow
receiver. Such surface structures can be in the shape, for example,
of linear prisms, pyramids, cones, or columnar structures. For
prisms, typically the apex angle of the prisms is less than 90
degrees (e.g., less than 60 degrees). The refractive index of the
surface structured film or coating is typically less than 1.55
(e.g., less than 1.50). These anti-reflective surface structured
films or coatings can be made durable and easily cleanable with the
use of inherently UV stable and hydrophobic or hydrophilic
materials. Anti-reflective coatings (e.g., nanostructured coatings
or low refractive index coatings) could also be applied to the
interior glass surface of the hollow receiver. Durability of the
anti-reflective coatings or films can be enhanced with the addition
of inorganic nano-particles.
[0110] Broadband reflectors according to the present disclosure may
also be useful, for example, for concentrated photovoltaic systems.
For example, a broadband reflector disclosed herein may be useful
when placed in proximity to a multi junction GaAs cell, which has
an absorption bandwidth from about 350 nm to about 1750 nm, or a
mono-crystalline silicon photovoltaic cell having an absorption
bandwidth of about 400 nm to about 1150 nm. In some embodiments, a
thermal management device (e.g., in the form of ribs, pins, or
fins) may be used to dissipate heat from the solar cell.
[0111] FIG. 7 shows a tracking device 700, which may be useful, for
example, in the concentrated solar power system 400 shown in FIG.
4. Tracking device 700 comprises parabolic trough-shaped broadband
reflectors 710 with hollow receiver 730 placed at the focal line.
Two rods 770 extending outside the end pieces 712 of a
trough-shaped broadband reflector 710 are used to connect the
trough to a frame 720 and a crossbar 722, respectively, at each end
of the assembly. The crossbar 722 can be connected to a driving
mechanism. With a plurality of trough-shaped broadband reflectors
710 being pivotally positioned in a pair of parallel stationary
frames, as shown in FIG. 7, the crossbars 722 to which each trough
710 is attached can, in some embodiments, simultaneously pivot all
of the troughs about their axes. Thus, the orientation of all the
trough-shaped broadband reflectors 710 can be collectively adjusted
to follow the sun movement in unison. Although FIG. 7 shows two
crossbars 722, one on each side of the trough 710, it is possible
to use only one crossbar. In some embodiments of tracking device
700 shown in FIG. 7, the trough-shaped broadband reflector 710 is
aligned in the east-west direction with a rotational freedom in the
north-south direction typically not less than 10 degrees, 15
degrees, 20 degrees, or 25 degrees, for example, for adjustments to
track the sun through seasonal variations (i.e., through the
different paths between equinox and solstice). When the hollow
receiver 730 is incorporated into a linear parabolic trough-shaped
broadband reflector 710 tilted toward the south, the incident solar
irradiance enters within the acceptance angle of the linear
parabolic reflector. The aperture of the parabola determines how
often the position of the trough-shaped broadband reflector 710
must be changed (e.g., hourly, daily, or less frequently). In some
embodiments of tracking devices 700 shown in FIG. 7, the hollow
receiver 730 is aligned in the north-south direction, and the
rotational freedom in the east-west direction is typically not less
than 90 degrees, 120 degrees, 160 degrees, or 180 degrees, for
example, for tracking adjustments following the sun as it moves
across the sky throughout the day. In some of these embodiments,
the frame can be mounted, for example, to a back board (not shown)
for the solar collection device, which back board may comprise a
mechanism for adjusting tilt to track the sun through seasonal
variations (e.g., in the north-south direction). Although
trough-shaped broadband reflectors 710 shown in FIG. 7, have
parabolic shapes, other shapes may be used (e.g., hyperbolic,
elliptical, tubular, or triangular). Additional celestial tracking
mechanisms which allow the solar concentrating mirror and/or the
solar cell to pivot in two directions and which may be useful for
solar collection devices disclosed herein are described in U.S.
Pat. App. Pub. No. 2007/0251569 (Shan et al.).
[0112] Another embodiment of a tracking device useful for the
concentrated solar power systems disclosed herein is illustrated in
FIGS. 8a, 8b, and 8c. In this embodiment, array 800 comprises
hollow receivers 830 and louvers 810 comprising the broadband
reflector according to any of the embodiments disclosed herein
pivotally mounted adjacent the hollow receivers. A louver can
comprise, for example, the broadband reflector disclosed herein
applied onto a substrate (e.g., a glass sheet, polymeric sheet, or
polymer fiber composite) or a free-standing broadband reflector. In
some embodiments, the louver comprises a broadband reflector
disclosed herein laminated to a polymer sheet (e.g., PMMA). The
louver may be directly attached to either side of the hollow
receiver (e.g., with hinges) as shown in FIG. 8a, 8b, or 8c, or the
louver may be pivotally mounted on a frame that also holds the
hollow receiver. In some embodiments, two louvers are associated
with (e.g., hinged to) each hollow receiver.
[0113] In FIGS. 8a, 8b, and 8c, the louvers 810 are oriented toward
the morning, mid-day, and evening sun, respectively. The louvers
810 track the sun and enable increased capture of sunlight 828 by
hollow receivers 830. As a result, typically fewer hollow receivers
830 are needed in an array 800. The array 800 shown in FIGS. 8a and
8c may be especially effective at increasing the capture of
sunlight in the mornings and evenings. The louvers can move
independently with rotational freedom (e.g., in the east-west
direction) typically not less than 90 degrees, 120 degrees, 160
degrees, or 180 degrees, for example, for tracking adjustments
following the sun as it moves across the sky throughout the day.
Optionally, the array 800 can be mounted, for example, to one or
more back boards (not shown), which may comprise a mechanism for
adjusting tilt to track the sun through seasonal variations (e.g.,
in the north-south direction). The louvers may be planar,
substantially planar, or curved in shape.
[0114] Solar thermal arrays 800 with louver solar trackers 810 can
be made with a lower profile and lighter weight than solar thermal
trackers. In some embodiments of array 800, hollow receivers 830
having widths of 1 inch (2.54 cm) or less can be used to minimize
the depth profile of the array. Arrays could also be designed with
larger hollow receivers (e.g., widths of 6-inch (15 cm), 12-inch
(30.5 cm), 21-inch (53 cm), or higher). Thus, the arrays 800 can be
designed to fit a number of applications including use on roof
tops. Embodiments wherein the hollow receivers 830 are stationary
and the louvers 810 are pivotally mounted may be advantageous
(e.g., in design and/or cost) over tracking systems which require
movement of the hollow receivers. Solar concentration can be
adjusted, for example, with the size of the broadband reflector
relative to the hollow receiver and the reflectors's angle relative
to the hollow receiver to optimize the solar concentration ratio
for a desired geographic location.
[0115] Movement of reflectors 710 shown in FIG. 7 or louvers 810
shown in FIGS. 8a, 8b, and 8c can be controlled by a number of
mechanisms (e.g., piston driven levers, screw driven levers, pulley
driven cables, and cam systems). Software can also be integrated
with the tracking mechanism based on GPS coordinates to optimize
the position of the mirrors. Feedback control loops based on solar
absorber temperature can be used to maximize solar thermal energy
generation.
[0116] Objects and advantages of this disclosure are further
illustrated by the following non-limiting examples, but the
particular materials and amounts thereof recited in these examples,
as well as other conditions and details, should not be construed to
unduly limit this disclosure.
EXAMPLES
[0117] Unless otherwise noted, all parts, percentages, ratios, etc.
in the Examples and the rest of the specification are by
weight.
Preparation of Oxalylamidopropyl-terminated
Polydimethylsiloxane
[0118] Polydimethylsiloxanediamine (830.00 grams (g);14,000 g/mole)
was placed in a 2-liter, 3-neck resin flask equipped with a
mechanical stirrer, heating mantle, nitrogen inlet tube (with
stopcock), and an outlet tube. The flask was purged with nitrogen
for 15 minutes and then, with vigorous stirring, diethyl oxalate
(33.56 grams) was added dropwise. This reaction mixture was stirred
for approximately one hour at room temperature and then for 75
minutes at 80.degree. C. The reaction flask was fitted with a
distillation adaptor and receiver. The reaction mixture was heated
under vacuum (133 Pa) for 2 hours at 120.degree. C., and then 30
minutes at 130.degree. C. until no further distillate was able to
be collected. The reaction mixture was cooled to room temperature.
Gas chromatographic analysis of the clear, mobile liquid showed
that no detectable level of diethyl oxalate remained. The ester
equivalent weight was determined using .sup.1H NMR (equivalent
weight equal to 7,916 grams/equivalent) and by titration
(equivalent weight equal to 8,272 grams/equivalent).
[0119] Preparation of OTP/Into a 20.degree. C. 10-gallon
(37.85-Liter) stainless steel reaction vessel was placed 18158.4
grams of oxalylamidopropyl-terminated polydimethylsiloxane
(titrated molecular weight=14,890 g/mole) that was prepared
generally as in the Preparation of Oxalylamidopropyl-terminated
Polydimethylsiloxane (above), but with the volumes adjusted
accordingly. The vessel was subjected to agitation (75 revolutions
per minute (rpm)), and purged with nitrogen flow and vacuum for 15
minutes. The kettle was then heated to 80.degree. C. over the
course of 25 minutes. Ethylenediamine (73.29 grams, GFS Chemicals)
was vacuum charged into the kettle, followed by 73.29 grams of
toluene (also vacuum charged). The kettle was then pressurized to
one pound per square inch (7 kPa) applied pressure and heated to a
temperature of 120.degree. C. After 30 minutes, the kettle was
heated at 150.degree. C. Once a temperature of 150.degree. C. was
reached, the kettle was vented over the course of 5 minutes. The
kettle was subjected to partial vacuum (approximately 65 mm Hg,
8.67 kPa) for 40 minutes to remove the ethanol and toluene. The
kettle was then pressured to 2 pounds per square inch (14 kPa)
applied pressure and the resultant viscous molten polymer was then
drained into polytetrafluoroethylene coated trays and allowed to
cool. The cooled silicone polyoxamide product, polydiorganosiloxane
polyoxamide block copolymer OTP1, was then ground into fine
pellets.
Example 1
[0120] A UV-reflective multilayer optical film was made with first
optical layers created from polyethylene terephthalate available as
EASTAPAK 7452 from Eastman Chemical of Kingsport, Tenn. (PET1) and
second optical layers created from a copolymer of 75 weight percent
methyl methacrylate and 25 weight percent ethyl acrylate (available
from Ineos Acrylics, Inc. of Memphis, Tenn. as PERSPEX CP63)
(coPMMA1). The PET1 and CoPMMA1 were coextruded through a
multilayer polymer melt manifold to form a stack of 223 optical
layers. The layer thickness profile (layer thickness values) of
this UV reflector was adjusted to be approximately a linear profile
with the first (thinnest) optical layers adjusted to have about a
1/4 wave optical thickness (index times physical thickness) for 340
nanometers (nm) light and progressing to the thickest layers which
were adjusted to be about 1/4 wave thick optical thickness for 420
nm light. Layer thickness profiles of such films can be adjusted to
provide for improved spectral characteristics using the axial rod
apparatus taught in U.S. Pat. No. 6,783,349 (Neavin et al.)
combined with layer profile information obtained with microscopic
techniques.
[0121] In addition to these optical layers, non-optical protective
skin layers of PET1 (101 micrometers thickness each) were
coextruded on either side of the optical stack. This multilayer
coextruded melt stream was cast onto a chilled roll at 22 meters
per minute creating a multilayer cast web approximately 1400
micrometers (55 mils) thick. The multilayer cast web was then
heated in a tenter oven at 95.degree. C. for about 10 seconds prior
to being biaxially oriented to a draw ratio of 3.3.times.3.5. The
oriented multilayer film was further heated at 225.degree. C. for
10 seconds to increase crystallinity of the PET layers. The
UV-reflective multilayer optical film (FILM 1) was measured with a
spectrophotometer (LAMBDA 950 UV/VIS/NIR SPECTROPHOTOMETER from
Perkin-Elmer, Inc. of Waltham, Mass.) to have an average
reflectivity of 97.8 percent over a bandwidth of 340-420 nm. A 10
nm thick layer of alumina was vapor coated on one side of the film.
A 110 nm thick layer of silver was vapor coated onto the alumina
layer, and then a 20 nm thick layer of copper was vapor coated over
the silver layer for improved corrosion resistance.
[0122] Average solar reflectivity (for light impinging the surface
of the film opposite the copper layer) of the resultant film was
measured and is reported in FIG. 5. Then the reflectance spectrum
was weight averaged with the Standard Air Mass 1.5 Direct Normal
and Hemispherical Spectral Solar Irradiance for 37.degree.
Sun-Facing Tilted Surface (according to ASTM G 173-03, updated
March 2006 and entitled "Standard Tables for Reference Solar
Spectral Irradiances: Direct Normal and Hemispherical on 37.degree.
Tilted Surface" resulting in a calculated 96.3 percent reflectivity
over a bandwidth of from 300 nm to 2494 nm.
Example 2
[0123] A UV-reflective multilayer optical film was made with first
optical layers created from PET1 and second optical layers created
from CoPMMA1. PET1 and CoPMMA1 were coextruded through a multilayer
polymer melt manifold to form 223 optical layers. The layer
thickness profile (layer thickness values) of this UV reflector was
adjusted to be approximately a linear profile with the first
(thinnest) optical layers adjusted to have about a 1/4 wave optical
thickness (index times physical thickness) for 340 nm light and
progressing to the thickest layers which were adjusted to be about
1/4 wave thick optical thickness for 420 nm light. Layer thickness
profiles of such films can be adjusted to provide for improved
spectral characteristics using the axial rod apparatus taught in
U.S. Pat. No. 6,783,349 (Neavin et al.) combined with layer profile
information obtained with microscopic techniques.
[0124] In addition to these optical layers, non-optical protective
skin layers of PET1 with a thickness of 101 micrometers each were
coextruded on either side of the optical stack. This multilayer
coextruded melt stream was cast onto a chilled roll at 22 meters
per minute creating a multilayer cast web approximately 1400
micrometers (55 mils) thick. The multilayer cast web was then
heated in a tenter oven at 95.degree. C. for about 10 seconds prior
to being biaxially oriented to a draw ratio of 3.3.times.3.5. The
oriented multilayer film was further heated at 225.degree. C. for
10 seconds to increase crystallinity of the PET1 layers. The
resultant UV-reflective multilayer optical film (FILM 1) was
measured with a spectrophotometer (LAMBDA 950 UV/VIS/NIR
SPECTROPHOTOMETER from Perkin-Elmer, Inc. of Waltham, Mass.) to
have an average reflectivity of 97.8 percent over a bandwidth of
350-420 nm.
[0125] A VIS/IR-light reflective multilayer optical film was made
with first optical layers created from PET1 and second optical
layers created from CoPMMA1. PET1 and CoPMMA1 were coextruded
through a multilayer polymer melt manifold to form 550 optical
layers. In addition to these optical layers, non-optical protective
skin layers of PET1(?) were coextruded on either side of the
optical stack. This multilayer coextruded melt stream was cast onto
a chilled roll at 22 meters per minute creating a multilayer cast
web approximately 1400 micrometers (55 mils) thick. The multilayer
cast web was then heated in a tenter oven at 95.degree. C. for
about 10 seconds prior to being biaxially oriented to a draw ratio
of 3.8.times.3.8. The oriented multilayer film was further heated
at 225.degree. C. for 10 seconds to increase crystallinity of the
PET1 layers. The resultant Vis/IR-light reflective multilayer
optical film (FILM 2) was measured with a LAMBDA 950 UV/VIS/NIR
spectrophotometer to have an average reflectivity of 97.1 percent
over a bandwidth of 400-800 nm.
[0126] FILM 1 was laminated to FILM 2 with an acrylate-based
optically clear pressure sensitive adhesive manufactured by 3M
Company as OPTICALLY CLEAR LAMINATING ADHESIVE PSA 8141.
[0127] A 10 nm thick layer of alumina was then vacuum vapor coated
onto the exposed surface of FILM 2. A 110 nm thick layer of silver
was vacuum vapor coated onto the alumina layer, and then a 20 nm
thick layer of copper was vacuum vapor coated over the silver layer
for improved corrosion resistance.
[0128] Average solar reflectivity (for light impinging the surface
of the film opposite the copper layer) of the resultant film was
measured and is reported in FIG. 6. Then the reflectance spectrum
was weight averaged with the Standard Air Mass 1.5 Direct Normal
and Hemispherical Spectral Solar Irradiance for 37.degree.
Sun-Facing Tilted Surface (according to ASTM G 173-03, updated
March 2006 and entitled "Standard Tables for Reference Solar
Spectral Irradiances: Direct Normal and Hemispherical on 37.degree.
Tilted Surface" resulting in a calculated 96.9 percent reflectivity
over a bandwidth of from 300 nm to 2494 nm.
Example 3
[0129] A UV-reflective multilayer optical film was made with first
optical layers created from PET1 and second optical layers created
from CoPMMA1. PET1 and CoPMMA1 were coextruded through a multilayer
polymer melt manifold to form 223 optical layers. The layer
thickness profile (layer thickness values) of this UV reflector was
adjusted to be approximately a linear profile with the first
(thinnest) optical layers adjusted to have about a 1/4 wave optical
thickness (index times physical thickness) for 340 nm light and
progressing to the thickest layers which were adjusted to be about
1/4 wave thick optical thickness for 420 nm light. Layer thickness
profiles of such films can be adjusted to provide for improved
spectral characteristics using the axial rod apparatus taught in
U.S. Pat. No. 6,783,349 (Neavin et al.) combined with layer profile
information obtained with microscopic techniques.
[0130] In addition to these optical layers, non-optical protective
skin layers of PET1 of 101 micrometers thickness each were
coextruded on either side of the optical stack. This multilayer
coextruded melt stream was cast onto a chilled roll at 22 meters
per minute creating a multilayer cast web approximately 1400
micrometers (55 mils) thick. The multilayer cast web was then
heated in a tenter oven at 95.degree. C. for about 10 seconds prior
to being biaxially oriented to a draw ratio of 3.3.times.3.5. The
oriented multilayer film was further heated at 225.degree. C. for
10 seconds to increase crystallinity of the PET1 layers. The
resultant UV-reflective multilayer optical film (FILM 1) was
measured with a LAMBDA 950 UV/VIS/NIR spectrophotometer to have an
average reflectivity of 97.8 percent over a bandwidth of 340-420
nm.
[0131] A VIS/IR-reflective multilayer optical film was made with
first optical layers created from polyethylene 2,6-naphthalate
(PEN1) and second optical layers created from PMMA1 (an acrylic
resin available under the trade designation V044 Acrylic Resin from
Arkema, Inc.). PEN1 and PMMA1 were coextruded through a multilayer
polymer melt manifold to form 275 optical layers. In addition to
these optical layers, non-optical protective skin layers of PEN1
were coextruded on either side of the optical stack. This
multilayer coextruded melt stream was cast onto a chilled roll at
22 meters per minute creating a multilayer cast web approximately
1400 micrometers (55 mils) thick. The multilayer cast web was then
heated in a tenter oven at 140.degree. C. for about 10 seconds
prior to being biaxially oriented to a draw ratio of 3.8.times.3.8.
The oriented multilayer film was further heated at 235.degree. C.
for 10 seconds to increase crystallinity of the PEN1 layers. The
resultant VIS/IR-reflective multilayer optical film (FILM 3) was
measured with a LAMBDA 950 UV/VIS/NIR spectrophotometer to have an
average reflectivity of 98.6 percent over a bandwidth of 400-900
nm.
[0132] Film 1 was laminated to Film 3 with an acrylate based
optically clear pressure sensitive adhesive manufactured by 3M
Company as OPTICALLY CLEAR LAMINATING PSA 8141.
[0133] A 10 nm thick layer of alumina was then vacuum vapor coated
onto the exposed surface of FILM 3. A110 nm thick layer of silver
was vacuum vapor coated onto the alumina layer, and then a 20 nm
thick layer of copper was vacuum vapor coated over the silver layer
for improved corrosion resistance.
[0134] Average solar reflectivity of this film was measured and
then weight averaged with the Standard Air Mass 1.5 Direct Normal
and Hemispherical Spectral Solar Irradiance for 37.degree.
Sun-Facing Tilted Surface (according to ASTM G 173-03, updated
March 2006 and entitled "Standard Tables for Reference Solar
Spectral Irradiances: Direct Normal and Hemispherical on 37.degree.
Tilted Surface" to be 97.7 percent over a bandwidth of 300 nm to
2494 nm.
Prophetic Example 1
[0135] A UV/Vis-reflective multilayer optical film would be made
with first optical layers created from PET (polyethylene
terephthalate) available as EASTAPAK 7452 from Eastman Chemical and
second optical layers created from OTP1. PET and OTP1 would be
coextruded thru a multilayer polymer melt manifold to create a
multilayer melt stream having 550 alternating first and second
optical layers. The layer thickness profile (layer thickness
values) of this UV reflector would be adjusted to be approximately
a linear profile with the first (thinnest) optical layers adjusted
to have about a 1/4 wave optical thickness (index times physical
thickness) for 350 nm light and progressing to the thickest layers
which would be adjusted to be about 1/4 wave thick optical
thickness for 800 nm light. Layer thickness profiles of such films
can be adjusted to provide for improved spectral characteristics
using the axial rod apparatus taught in U.S. Pat. No. 6,783,349
(Neavin et al.) combined with layer profile information obtained
with microscopic techniques.
[0136] In addition to the first and second optical layers, a pair
of non-optical layers consisting of PET loaded with 2 weight
percent of a UV-absorber available as TINUVIN 1577 from Ciba
Specialty Chemicals Corp. would be coextrusion coated as a
protective skin layer on either side of the UV-reflective
multilayer optical film. This multilayer coextruded melt stream
would be cast onto a chilled roll at 22 meters per minute creating
a multilayer cast web approximately 1400 micrometers (55 mils)
thick. The multilayer cast web would be then heated in a tenter
oven at 95.degree. C. for 10 seconds prior to being biaxially
oriented to a draw ratio of 3.3.times.3.5. The oriented multilayer
film would be further heated at 225.degree. C. for 10 seconds to
increase crystallinity of the PET layers resulting in Film 4. A 10
nm thick layer of alumina would then be vacuum vapor coated onto
the exposed surface of FILM 4. A 110 nm thick layer of silver would
then be vacuum vapor coated onto the alumina layer, and then a 20
nm thick layer of copper would then be vacuum vapor coated over the
silver layer for improved corrosion resistance
[0137] An acrylic resin available under the trade designation V044
Acrylic Resin from Arkema, Inc. of Philadelphia, Pa., would be
extrusion compounded with 3 weight percent of a UV-absorber
available as TINUVIN 1577 from Ciba Specialty Chemicals Corp., and
0.15 weight percent of a hindered amine light stabilizer available
as CHIMASSORB 944 from Ciba Specialty Chemicals Corp., and an
anhydride-modified ethylene vinyl acetate polymer adhesive
available as BYNEL E418 from E.I. du Pont de Nemours and Co. of
Wilmington, Del., and then coextrusion coated as a tie layer onto
FILM 4 opposite the metallic layer and simultaneously directed into
a nip under a pressure of 893 kg/m (50 pounds per lineal inch)
against a casting tool having a reflector finish surface at a
temperature of 90 .degree. F. (32.degree. C.), at a casting line
speed of 0.38 meters per second (75 feet per minute) to produce
FILM 5. The coextrusion coated layers would have a total thickness
of 150 micrometers (6 mils) with a skin:tie layer thickness ratio
of 20:1. The same materials could also be coextrusion coated onto
the opposite surface of FILM 5.
[0138] A scratch resistant coating consisting of a thermally cured
siliceous polymer available as PERMA-NEW 6000 CLEAR HARD COATING
SOLUTION from California Hardcoating Co. of Chula Vista, Calif.
would be coated on top of the acrylic resin skin layer.
Prophetic Example 2
[0139] A multilayer reflective reflector would be made with first
optical layers created from PET and second optical layers created
from a terpolymer of tetrafluoroethylene, hexafluoropropylene and
vinylidene fluoride available as THV 2030 from Dyneon, LLC,
Oakdale, Minn. PET and THV 2030 copolymer would be coextruded thru
a multilayer polymer melt manifold to create a multilayer melt
stream having 550 alternating first and second optical layers. The
layer thickness profile (layer thickness values) of this UV-Vis
reflector would be adjusted to be approximately a linear profile
with the first (thinnest) optical layers adjusted to have about a
1/4 wave optical thickness (index times physical thickness) for 340
nm light and progressing to the thickest layers which would be
adjusted to be about 1/4 wave thick optical thickness for 1100 nm
light. Layer thickness profiles of such films can be adjusted to
provide for improved spectral characteristics using the axial rod
apparatus taught in U.S. Pat. No. 6,783,349 (Neavin et al.)
combined with layer profile information obtained with microscopic
techniques.
[0140] In addition to the first and second optical layers, a pair
of non-optical layers also comprised of PET loaded with 2 weight
percent of UV-absorber available as TINUVIN 1577 from Ciba
Specialty Chemicals Corp. would be coextruded as protective skin
layers on either side of the optical layer stack. This multilayer
coextruded melt stream would be cast onto a chilled roll at 22
meters per minute creating a multilayer cast web approximately 1400
micrometers (55 mils) in thickness. The multilayer cast web would
then be heated in a tenter oven at 95.degree. C. for 10 seconds
prior to being biaxially oriented to a draw ratio of 3.3.times.3.5.
The oriented multilayer film would then be further heated to
225.degree. C. for 10 seconds to increase crystallinity of the PET
layers resulting in FILM 6. A 10 nm thick layer of titania would
then vacuum vapor coated onto the exposed surface of FILM 6. A
silver layer having a 110 nm thickness would be vapor coated onto
the tie layer. A copper layer (20 nm thickness) would then also be
vapor coated onto the silver layer to protect it from
corrosion.
[0141] An acrylic resin available under the trade designation V044
Acrylic Resin from Arkema, Inc. of Philadelphia, Pa. would be
extrusion compounded with 3 weight percent of a UV-absorber
available as TINUVIN 1577 from Ciba Specialty Chemicals Corp., and
0.15 weight percent of a hindered amine light stabilizer available
as CHIMASSORB 944 from Ciba Specialty Chemicals Corp., and an
anhydride-modified ethylene vinyl acetate polymer adhesive
available as BYNEL E418 from E.I. du Pont de Nemours and Co. of
Wilmington, Del., and then coextrusion coated as a tie layer onto
FILM 6 opposite the metallic layer and simultaneously directed into
a nip under a pressure of 893 kg/m (50 pounds per lineal inch)
against a casting tool having a reflector finish surface at a
temperature of 90 .degree. F. (32.degree. C.), at a casting line
speed of 0.38 meters per second (75 feet per minute) to produce
FILM 7. The coextrusion coated layers would have a total thickness
of 150 micrometers (6 mils) with a skin:tie layer thickness ratio
of 20:1. The same materials would be coextrusion coated onto the
opposing surface of the multilayer visible reflector film.
Prophetic Example 3
[0142] A copper layer (150 nm thickness) would be vapor coated onto
one side of FILM 1 as described in Example 1.
[0143] An acrylic resin available under the trade designation V044
Acrylic Resin from Arkema, Inc. would be extrusion compounded with
3 weight percent of a UV-absorber available as TINUVIN 1577 from
Ciba Specialty Chemicals Corp., and 0.15 weight percent of a
hindered amine light stabilizer available as CHIMASSORB 944 from
Ciba Specialty Chemicals Corp., and an anhydride-modified ethylene
vinyl acetate polymer adhesive available as BYNEL E418 from E.I. du
Pont de Nemours and Co., Wilmington, Del., and then coextrusion
coated as a tie layer onto FILM 1 opposite the metallic layer and
simultaneously directed into a nip under a pressure of 893 kg/m (50
pounds per lineal inch) against a casting tool having a reflector
finish surface at a temperature of 90.degree. F. (32.degree. C.),
at a casting line speed of 0.38 meters per second (75 feet per
minute) resulting in FILM 8. The coextrusion coated layers would
have a total thickness of 150 micrometers (6 mils) with a skin:tie
layer thickness ratio of 20:1. The same materials would be
coextrusion coated onto the opposite surface of Film 8.
[0144] A scratch resistant coating consisting of a thermally cured
siliceous polymer available as PERMA-NEW 6000 CLEAR HARD COATING
SOLUTION from California Hardcoating Co. would be coated on top of
the acrylic resin skin layer.
Prophetic Example 4
[0145] A multilayer reflective reflector would be made with first
optical layers created from polyethylene 2,6-naphthalate (PEN1) and
second optical layers created from a terpolymer of
tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride
available as THVP 2030G from Dyneon, LLC, Oakdale, Minn. (THV1).
PEN1 and THV1 would be coextruded thru a multilayer polymer melt
manifold to create a multilayer melt stream having 550 alternating
first and second optical layers. The layer thickness profile (layer
thickness values) of this Vis-IR reflector would be adjusted to be
approximately a linear profile with the first (thinnest) optical
layers adjusted to have about a 1/4 wave optical thickness (index
times physical thickness) for 420 nm light and progressing to the
thickest layers which would be adjusted to be about 1/4 wave thick
optical thickness for 2500 nm light. Layer thickness profiles of
such films can be adjusted to provide for improved spectral
characteristics using the axial rod apparatus taught in U.S. Pat.
No. 6,783,349 (Neavin et al.) combined with layer profile
information obtained with microscopic techniques.
[0146] In addition to the first and second optical layers, a pair
of non-optical layers also comprised of PEN loaded with 2 weight
percent of UV-absorber available as TINUVIN 1577 from Ciba
Specialty Chemicals Corp. would be coextruded as protective skin
layers on either side of the optical layer stack. This multilayer
coextruded melt stream would be cast onto a chilled roll at 22
meters per minute creating a multilayer cast web approximately 1400
micrometers (55 mils) thick. The multilayer cast web would then be
heated in a tenter oven at 145.degree. C. for 10 seconds prior to
being biaxially oriented to a draw ratio of 3.8.times.3.8. The
oriented multilayer film would then be further heated to
225.degree. C. for 10 seconds to increase crystallinity of the PEN1
layers resulting in FILM 9.
[0147] The resultant VIS/IR-reflective multiplayer optical film
would be laminated to, or coextruded with, a UV-reflective
multiplayer optical film made with first optical layers created
from PMMA1 available under the trade designation V044 Acrylic Resin
from Arkema, Inc. and second optical layers created from a
copolymer of tetrafluoroethylene available as THVP 2030 (THV1) from
Dyneon, LLC. PMMA1 and THV1 would be coextruded through a
multilayer polymer melt manifold to create a multilayer melt stream
having 550 alternating first and second optical layers. The layer
thickness profile (layer thickness values) of this UV reflector
would be adjusted to be approximately a linear profile with the
first (thinnest) optical layers adjusted to have about a 1/4 wave
optical thickness (index times physical thickness) for 340 nm light
and progressing to the thickest layers which would be adjusted to
be about 1/4 wave thick optical thickness for 420 nm light. Layer
thickness profiles of such films can be adjusted to provide for
improved spectral characteristics using the axial rod apparatus
taught in U.S. Pat. No. 6,783,349 (Neavin et al.) combined with
layer profile information obtained with microscopic techniques.
[0148] In addition to the first and second optical layers, a pair
of PMMA1 non-optical layers would be coextruded as protective skin
layers on either side of the optical layer stack. These PMMA1 skin
layers would be extrusion compounded with 2 weight percent of a UV
absorber available as TINUVIN 1577 and 0.15 percent CHIMMASORB 944
from Ciba Specialty Chemicals Corp. This multilayer coextruded melt
stream would be cast onto a chilled roll at 22 meters per minute
creating a multilayer cast web approximately 300 micrometers
(12mils) thick. The multilayer cast web would then be heated in a
tenter oven at 135.degree. C. for 10 seconds prior to being
biaxially oriented to a draw ratio of 3.8.times.3.8. The resultant
UV-reflective multilayer optical FILM 10 would then be extrusion
hot melt laminated to the VIS/IR-reflective multilayer optical film
with a hot melt adhesive available as ADMER SE810 from Mitsui
Chemicals Americas, Inc. of Rye Brook, N.Y.
[0149] A scratch resistant coating consisting of a thermally cured
siliceous polymer available as PERMA-NEW 6000 CLEAR HARD COATING
SOLUTION from California Hardcoating Co. of Chula Vista, Calif.
would be coated on top of the acrylic resin skin layer.
Prophetic Example 5
[0150] A broadband reflector film would be made with first optical
layers created from PET 1 and second optical layers created from
OTP 1. PET 1 and OTP 1 would be coextruded thru a multilayer
polymer melt manifold to create a multilayer melt stream having 550
alternating first and second optical layers. The layer thickness
profile (layer thickness values) of this Vis-IR reflector would be
adjusted to be approximately a linear profile with the first
(thinnest) optical layers adjusted to have about a 1/4 wave optical
thickness (index times physical thickness) for 420 nm light and
progressing to the thickest layers which would be adjusted to be
about 1/4 wave thick optical thickness for 1100 nm light. Layer
thickness profiles of such films can be adjusted to provide for
improved spectral characteristics using the axial rod apparatus
taught in U.S. Pat. No. 6,783,349 (Neavin et al.) combined with
layer profile information obtained with microscopic techniques.
[0151] In addition to the first and second optical layers, a pair
of non-optical layers consisting of PET1 loaded with 2 weight
percent of a UV-absorber available as TINUVIN 1577 from Ciba
Specialty Chemicals Corp. would be coextrusion coated as a
protective skin layer on either side of the UV-reflective
multilayer optical film. This multilayer coextruded melt stream
would be cast onto a chilled roll at 22 meters per minute creating
a multilayer cast web approximately 1400 micrometers (56 mils)
thick. The multilayer cast web would be then heated in a tenter
oven at 95.degree. C. for 10 seconds prior to being biaxially
oriented to a draw ratio of 3.3.times.3.5. The oriented multilayer
film would be further heated at 225.degree. C. for 10 seconds to
increase crystallinity of the PET layers resulting in Film 4.
[0152] An acrylic resin available under the trade designation V044
Acrylic Resin from Arkema, Inc. would be extrusion compounded with
5 weight percent of a UV-absorber available as TINUVIN 1577 from
Ciba Specialty Chemicals Corp., and 0.15 weight percent of a
hindered amine light stabilizer available as CHIMASSORB 944 from
Ciba Specialty Chemicals Corp., and an anhydride-modified ethylene
vinyl acetate polymer adhesive available as BYNEL E418 from E. I.
du Pont de Nemours and Co., and then coextrusion coated as a tie
layer onto FILM 4 and simultaneously directed into a nip under a
pressure of 893 kg/m (50 pounds per lineal inch) against a casting
tool having a reflector finish surface at a temperature of
90.degree. F. (32.degree. C.), at line speed of 0.38 meters per
second (75 feet per minute). The coextrusion coated layers would
have a total thickness of 150 micrometers (6 mils) with skin:tie
layer thickness ratio of 20:1. The same materials would be
coextrusion coated onto the opposing surface of FILM 4. The
resultant film would be laminated to or coextruded with a
UV-reflective multilayer optical film made with first optical
layers created from PMMA1 and second optical layers created from
THV1 coextruded thru a multilayer polymer melt manifold to create a
multilayer melt stream having 550 alternating first and second
optical layers. The layer thickness profile (layer thickness
values) of this UV reflector would be adjusted to be approximately
a linear profile with the first (thinnest) optical layers adjusted
to have about a 1/4 wave optical thickness (index times physical
thickness) for 340 nm light and progressing to the thickest layers
which would be adjusted to be about 1/4 wave thick optical
thickness for 420 nm light. Layer thickness profiles of such films
can be adjusted to provide for improved spectral characteristics
using the axial rod apparatus taught in U.S. Pat. No. 6,783,349
(Neavin et al.) combined with layer profile information obtained
with microscopic techniques.
[0153] In addition to the first and second optical layers, a pair
of non-optical layers comprised of PMMA1 would be coextruded as
protective skin layers on either side of the optical layer stack.
These PMMA1 skins layers would be extrusion compounded with 2
weight percent of a UV absorber available as TINUVIN 1577 from Ciba
Specialty Chemicals Corp. This multilayer coextruded melt stream
would be cast onto a chilled roll at 22 meters per minute creating
a multilayer cast web approximately 300 micrometers (12 mils)
thick. The multilayer cast web would then be heated in a tenter
oven at 135.degree. C. for 10 seconds prior to being biaxially
oriented to a draw ratio of 3.8.times.3.8.
[0154] A scratch resistant coating consisting of a thermally cured
siliceous polymer available as PERMA-NEW 6000 CLEAR HARD COATING
SOLUTION from California Hardcoating Co. would be coated on top of
the acrylic resin skin layer.
Prophetic Example 6
[0155] A highly reflective broadband reflector would be made as in
Prophetic Example 1, but rather than including the sequential
silver/copper vapor coated metal layer, the broadband reflector
film would be laminated to a sheet of polished anodized
aluminum.
Prophetic Example 7
[0156] A highly reflective broadband reflector would be made as in
Example 2, but rather than including the sequential silver/copper
vapor coated metal layer, the broadband reflector film would be
laminated to a sheet of polished stainless steel.
Prophetic Example 8
[0157] A multilayer optical film UV reflective reflector would be
made with first optical layers created from PMMA1 (an acrylic resin
available under the trade designation V044 Acrylic Resin from
Arkema, Inc.) and second optical layers created from a terpolymer
of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride
available as THV 2030 from Dyneon, LLC. The PMMA and THV would be
coextruded thru a multilayer polymer melt manifold to create a
multilayer melt stream having 550 alternating first and second
optical layers. The layer thickness profile (layer thickness
values) of this UV reflector would be adjusted to be approximately
a linear profile with the first (thinnest) optical layers adjusted
to have about a 1/4 wave optical thickness (index times physical
thickness) for 340 nm light and progressing to the thickest layers
which would be adjusted to be about 1/4 wave thick optical
thickness for 420 nm light. Layer thickness profiles of such films
can be adjusted to provide for improved spectral characteristics
using the axial rod apparatus taught in U.S. Pat. No. 6,783,349
(Neavin et al.) combined with layer profile information obtained
with microscopic techniques.
[0158] In addition to the first and second optical layers, a pair
of non-optical layers also comprised of PMMA1 would be coextruded
as protective skin layers on either side of the optical layer
stack. These PMMA1 skins layers would be extrusion compounded with
2 weight percent of a UV-absorber available as TINUVIN 1577 from
Ciba Specialty Chemicals Corp. This multilayer coextruded melt
stream would be cast onto a chilled roll at 22 meters per minute
creating a multilayer cast web approximately 300 micrometers (12
mils) thick. The multilayer cast web would then be heated in a
tenter oven at 135.degree. C. for 10 seconds prior to being
biaxially oriented to a draw ratio of 3.8.times.3.8 resulting in
FILM 10.
[0159] A titanium dioxide tie layer having a 10 nm thickness would
be vapor coated onto one side of FILM 10.
[0160] A silver layer having a 110 nm thickness would be vapor
coated onto the tie layer. A copper layer, 20 nm thickness, would
then also be vapor coated onto the silver to protect it from
corrosion.
[0161] A scratch resistant coating consisting of a thermally cured
siliceous polymer available as PERMA-NEW 6000 CLEAR HARD COATING
SOLUTION from California Hardcoating Co. would be coated on top of
the acrylic resin skin layer.
Prophetic Example 9
Film 11
[0162] A UV-VIS reflective multilayer optical film was made with
first optical layers created from polyethylene terephthalate
available as EASTAPAK 7452 from Eastman Chemical of Kingsport,
Tenn., (PET1) and second optical layers created from a copolymer of
75 weight percent methyl methacrylate and 25 weight percent ethyl
acrylate (available from Ineos Acrylics, Inc. of Memphis, Tenn., as
PERSPEX CP63) (coPMMA1). The PET1 and CoPMMA1 were coextruded
through a multilayer polymer melt manifold to form a stack of 550
optical layers. The layer thickness profile (layer thickness
values) of this UV reflector was adjusted to be approximately a
linear profile with the first (thinnest) optical layers adjusted to
have about a 1/4 wave optical thickness (index times physical
thickness) for 370 nm light and progressing to the thickest layers
which were adjusted to be about 1/4 wave thick optical thickness
for 800 nm light. Layer thickness profiles of such films were
adjusted to provide for improved spectral characteristics using the
axial rod apparatus taught in U.S. Pat. No. 6,783,349 (Neavin et
al.) combined with layer profile information obtained with
microscopic techniques.
[0163] In addition to these optical layers, non-optical protective
skin layers of PET1 (260 micrometers thickness each) were
coextruded on either side of the optical stack. This multilayer
coextruded melt stream was cast onto a chilled roll at 5.4 meters
per minute creating a multilayer cast web approximately 1100
micrometers (43.9 mils) thick. The multilayer cast web was then
preheated for about 10 seconds at 95.degree. C. and uniaxially
oriented in the machine directon at a draw ratio of 3.3:1. The
multilayer cast web was then heated in a tenter oven at 95.degree.
C. for about 10 seconds prior to being uniaxially oriented in the
transverse direction to a draw ratio of 3.5:1. The oriented
multilayer film was further heated at 225.degree. C. for 10 seconds
to increase crystallinity of the PET layers. The UV-reflective
multilayer optical film (Film 11) was measured with a
spectrophotometer (LAMBDA 950 UV/VIS/NIR SPECTROPHOTOMETER from
Perkin-Elmer, Inc. of Waltham, Mass.) to have an average
reflectivity of 96.8 percent over a bandwidth of 370-800 nm.
Film 12
[0164] A near infra-red reflective multilayer optical film was made
with first optical layers created from PET1 and second optical
layers created from coPMMA1. The PET1 and CoPMMA1 were coextruded
through a multilayer polymer melt manifold to form a stack of 550
optical layers. The layer thickness profile (layer thickness
values) of this near infra-red reflector was adjusted to be
approximately a linear profile with the first (thinnest) optical
layers adjusted to have about a 1/4 wave optical thickness (index
times physical thickness) for 750 nm light and progressing to the
thickest layers which were adjusted to be about 1/4 wave thick
optical thickness for 1350 nm light. Layer thickness profiles of
such films were adjusted to provide for improved spectral
characteristics using the axial rod apparatus taught in U.S. Pat.
No. 6,783,349 (Neavin et al.) combined with layer profile
information obtained with microscopic techniques.
[0165] In addition to these optical layers, non-optical protective
skin layers of PET1 (260 micrometers thickness each) were
coextruded on either side of the optical stack. This multilayer
coextruded melt stream was cast onto a chilled roll at 3.23 meters
per minute creating a multilayer cast web approximately 1800
micrometers (73 mils) thick. The multilayer cast web was then
preheated for about 10 seconds at 95.degree. C. and uniaxially
oriented in the machine directon at a draw ratio of 3.3:1. The
multilayer cast web was then heated in a tenter oven at 95.degree.
C. for about 10 seconds prior to being uniaxially oriented in the
transverse direction to a draw ratio of 3.5:1. The oriented
multilayer film was further heated at 225.degree. C. for 10 seconds
to increase crystallinity of the PET layers. The IR-reflective
multilayer optical film (Film 12) was measured with a
spectrophotometer (LAMBDA 950 UV/VIS/NIR SPECTROPHOTOMETER from
Perkin-Elmer, Inc. of Waltham, Mass.) to have an average
reflectivity of 96.1 percent over a bandwidth of 750-1350 nm.
[0166] A 10 nm thick layer of alumina would then be vacuum vapor
coated onto the exposed surface of FILM 12. A 110 nm thick layer of
silver could then be vacuum vapor coated onto the alumina layer,
and then a 20 nm thick layer of copper was vacuum vapor coated over
the silver layer for improved corrosion resistance.
[0167] Average solar reflectivity of this film would be expected to
be 97 percent over a bandwidth of 300 nm to 2494 nm when measured
and then weight averaged with the Standard Air Mass 1.5 Direct
Normal and Hemispherical Spectral Solar Irradiance for 37.degree.
Sun-Facing Tilted Surface (according to ASTM G 173-03, updated
March 2006 and entitled "Standard Tables for Reference Solar
Spectral Irradiances: Direct Normal and Hemispherical on 37.degree.
Tilted Surface".
ILLUSTRATIVE EXAMPLE
[0168] Film 11 and Film 12 were laminated together using an
optically clear adhesive obtained from 3M Company, St. Paul, Minn.,
as OPTICALLY CLEAR LAMINATING ADHESIVE PSA 8171 and then laminated
again to a 0.25'' thick sheet of PMMA obtained from Arkema, Inc.
under the trade designation PLEXIGLAS VO44. The resulting mirror
laminate plates were then attached to the sides of an 80 watt
crystalline silicon photovoltaic module (available under the trade
designation SHARP 80W) with added hinges which allowed tracking of
the sun as shown in FIGS. 8a-c.
[0169] Photovoltaic module power output was measured with a
handheld voltage/current meter and calculated by multiplying open
circuit voltage with closed loop current, and then multiplication
again by a fill factor of 0.75, with the assumption that the fill
factor was not changed by the concentrating mirrors. Temperature
measurements were made both by taping multiple thermocouples to the
backside of the PV module, and with the use of an infra-red
pyrometer. Power output increases over a non-concentrated solar
control photovoltaic module were measured as high as 400% in the
mornings when the sun was low in the sky and 40% during mid-day.
Measurements were made for several days in April of 2009 in
Scandia, Minn., USA which is in a northern latitude and has a
temperate climate. Considerable variability was observed when any
clouds or haze occurred in the sky so averaging of the data was
done. Power measurement results are shown in Table 1, below. The
temperatures of the photovoltaic modules did not exceed 85.degree.
C.
[0170] A UV-absorbing layer could be incorporated between Film 11
and Film 12 using the method of Prophetic Example 4, above, or on
top of Film 11. The trend in the power output observed in Table 1
would not be expected to substantially change with the addition of
the UV-absorbing layer.
TABLE-US-00001 TABLE 1 Control Example 11 Time of Day *Power(watts)
*Power(watts) % increase 8AM 15.4 76.3 396.1 9AM 36.9 104.9 184.4
10AM 57.8 114.8 98.7 11AM 77.2 120.8 56.6 12PM 80.4 113.2 40.8 1PM
80.9 110.0 35.9 2PM 74.2 108.4 46.1 3PM 68.2 106.6 56.3 4PM 58.0
108.1 86.4 5PM 32.3 105.0 225.6 6PM 16.9 79.8 372.9 Sum = 549 962.9
75.4 *assumes fill factor of .75
[0171] Although this Illustrative Example illustrates the increase
in power out of a photovoltaic module, it is expected that a
similar relative increase in power would occur from a solar thermal
panel.
[0172] All patents and publications referred to herein are hereby
incorporated by reference in their entirety. Various modifications
and alterations of this disclosure may be made by those skilled in
the art without departing from the scope and spirit of this
disclosure, and it should be understood that this disclosure is not
to be unduly limited to the illustrative embodiments set forth
herein.
* * * * *