WO2023203390A1

WO2023203390A1 - Broadband reflectors including polymeric layers, and composite cooling systems

Info

Publication number: WO2023203390A1
Application number: PCT/IB2023/050464
Authority: WO
Inventors: Timothy J. Hebrink; Tracey D. SORENSEN; Edward J. Kivel; Scott W. DEGNER
Original assignee: 3M Innovative Properties Company
Priority date: 2022-04-19
Filing date: 2023-01-19
Publication date: 2023-10-26

Abstract

The present disclosure provides a broadband reflector including a multilayer optical film comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting an average of at least 90 percent of incident light over at least a wavelength range from 400 nanometers (nm) to 2000 nm or from 350 nm to 2500 nm. The broadband reflector is essentially free of metal. Optionally, the broadband reflector is capable of sub-ambient cooling or above ambient cooling. The present disclosure further provides composite cooling systems including the broadband reflector attached to the roof and/or side(s) of a vehicle, a modular data center, or surface(s) of a building or shelter.

Description

BROADBAND REFLECTORS INCLUDING POLYMERIC LAYERS, AND COMPOSITE COOLING SYSTEMS

[0001] This invention was made with Government support under Cooperative Agreement DE- AR0001100. The Government has certain rights in this invention.

Background

[0002] Passive radiative cooling without external energy sources may be appealing for reducing electricity needed in cooling applications such as refrigeration, air conditioning, vehicles, electrical transformers, and communication antennas. Surface material properties for passive radiative cooling to occur during the day include low emittance over the solar energy wavelengths of 0.3 to 2.5 micrometers and high emittance over infrared wavelength range of 3 to 20 micrometers. For cooling surfaces below air temperature by passive radiative cooling, the surface may have high emittance in the infrared wavelength range of 8 to 13 micrometers and not in the wavelength range of 3 to 8 micrometers (or 13 to 20 micrometers). According to Kirchhoff s law of thermal radiation, high emittance correlates to high absorbance. The orientation of the radiative cooling surface relative to the sky, especially on vertical surfaces, may affect performance. Some investigation into the ability to conduct passive cooling during the day has been conducted. Some cooling panels made with fdms for passive cooling have been described. Further advancements in passive radiative cooling technologies would be desirable.

Summary

[0003] In a first aspect, a broadband reflector is provided. The broadband reflector comprises a multilayer optical film comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 90 percent of incident light over at least a wavelength range from 400 nanometers (nm) to 2000 nm or from 350 nm to 2500 nm, wherein the broadband reflector is essentially free of metal.

[0004] Optionally, the multilayer optical film comprises an ultraviolet-visible (UV-VIS) reflector and an infrared (IR) reflector. A suitable UV-VIS reflector is comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 350 nanometers (nm) to 400 nm and an average of at least 95 percent of incident light over at least a wavelength range from 400 nm to 800 nm. A suitable IR reflector is comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 90 percent of incident light over at least a wavelength range from 0.8 micrometers to 2.0 micrometers.

[0005] Optionally, the multilayer optical film comprises an ultraviolet (UV) reflector, a visible reflector, and an IR reflector. Either 1) the visible reflector is disposed between the UV reflector and the IR reflector or 2) the IR reflector is disposed between the UV reflector and the visible reflector. A suitable UV reflector is comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 350 nm to 400 nm. A suitable visible reflector is comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 400 nm to 800 nm. A suitable IR reflector is comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 90 percent of incident light over at least a wavelength range from 0.8 micrometers to 2.0 micrometers.

[0006] In a second aspect, a composite cooling system is provided. The composite cooling system includes a broadband reflector according to the first aspect attached to a roof and/or at least one side of a vehicle.

[0007] In a third aspect, another composite cooling system is provided. The composite cooling system includes a broadband reflector according to the first aspect attached to a modular data center.

[0008] In a fourth aspect, an additional composite cooling system is provided. The composite cooling system includes a broadband reflector according to the first aspect attached to at least one surface of a building or a shelter. Brief Description of the Drawings

[0009] FIG. 1A is a schematic cross-sectional view of an exemplary broadband reflector preparable according to the present disclosure.

[0010] FIG. IB is a schematic cross-sectional view of another exemplary broadband reflector preparable according to the present disclosure.

[0011] FIG. 1C is a schematic cross-sectional view of a further exemplary broadband reflector preparable according to the present disclosure.

[0012] FIG. 2 is a schematic cross-sectional view of an additional exemplary broadband reflector preparable according to the present disclosure.

[0013] FIG. 3 is a schematic side view of an exemplary multilayer optical film.

[0014] FIG. 4 is a schematic side view of a composite cooling system including a broadband reflector and a substrate.

[0015] FIG. 5 is a schematic side view of an exemplary composite cooling system including broadband reflectors on a vehicle.

[0016] FIG. 6 is a schematic perspective view of another exemplary composite cooling system including a broadband reflector on a modular data center.

[0017] FIG. 7 is a schematic perspective view of a further exemplary composite cooling system including a broadband reflector on a building.

[0018] FIG. 8 is a graph of reflection spectra of the exemplary broadband reflector of Example 5 at 0° incidence angle.

[0019] FIG. 9 is a graph of the layer design for Modeled Example 8.

[0020] FIG. 10 is a graph of reflection spectra of the exemplary broadband reflector of Modeled Example 8.

[0021] FIG. 11 is a graph of the layer design for Modeled Example 9.

[0022] FIG. 12 is a graph of reflection spectra of the exemplary broadband reflector of Modeled Example 9.

[0023] FIG. 13 is a graph of the layer design for Modeled Example 10. [0024] FIG. 14 is a graph of reflection spectra of the exemplary broadband reflector of Modeled Example 10.

[0025] FIG. 15 is a graph of the layer design for Modeled Example 11.

[0026] FIG. 16 is a graph of reflection spectra of the exemplary broadband reflector of Modeled Example 11.

Detailed Description

[0027] Glossary

[0028] As used herein, “copolymer” refers to a polymer formed of two or more different monomers.

[0029] As used herein, “fluoropolymer” refers to any organic polymer containing fluorine.

[0030] As used herein, “nonfluorinated” means not containing fluorine.

[0031] As used herein, “essentially free of metal” refers to an article (e.g., broadband reflector) containing less than 0.5 % by weight metal, based on the total weight of the article. The metal includes elemental metals, metal oxides, or any combination thereof.

[0032] As used herein, “nonplanar” refers to an article (e.g., broadband reflector) not lying or able to be confined within a single plane but rather having a three-dimensional quality.

[0033] As used herein, “adjacent” encompasses both in direct contact (e.g., directly adjacent) and having one or more intermediate layers present between the adjacent materials.

[0034] As used herein, “secured to” and “attached to” each means directly or indirectly affixed to (e.g., in direct contact with, or adhesively bonded to by a unitary layer of adhesive).

[0035] As used herein, “incident” with respect to light refers to the light falling on or striking a material.

[0036] As used herein, the “atmospheric window region” or “atmospheric window wavelength range” of the electromagnetic spectrum refers to a portion of the electromagnetic spectrum that partially or fully includes wavelengths that can be partially transmitted through the atmosphere. The atmospheric window region may include at least some infrared wavelengths of light. The atmospheric window region may be defined as wavelengths ranging from 8 to 13 micrometers, 7 to 14 micrometers, or even 6 to 14 micrometers. [0037] As used herein, “infrared” (IR) refers to infrared electromagnetic radiation having a wavelength of >700 nm to 1 mm, unless otherwise indicated.

[0038] As used herein, “visible” (VIS) refers to visible electromagnetic radiation having a wavelength to from 400 nm to 700 nm, inclusive, unless otherwise indicated.

[0039] As used herein, “ultraviolet” (UV) refers to ultraviolet electromagnetic radiation having a wavelength of at least 250 nm and up to but not including 400 nm, unless otherwise indicated.

[0040] As used herein, “radiation” refers to electromagnetic radiation unless otherwise specified.

[0041] As used herein, “absorption” refers to a material converting the energy of light radiation to internal energy.

[0042] As used herein, “absorb” with respect to wavelengths of light encompasses both absorption and scattering, as scattered light also eventually gets absorbed.

[0043] As used herein, “scattering” with respect to wavelengths of light refers to causing the light to depart from a straight path and travel in different directions with different intensities.

[0044] As used herein, “reflectance” is the measure of the proportion of light or other radiation striking a surface at normal incidence which is reflected off it. Reflectivity typically varies with wavelength and is reported as the percent of incident light that is reflected from a surface (0 percent - no reflected light, 100 - all light reflected. Reflectivity and reflectance are used interchangeably herein.

[0045] As used herein, “reflective” and “reflectivity” refer to the property of reflecting light or radiation, especially reflectance as measured independently of the thickness of a material.

[0046] As used herein, “average reflectance” refers to reflectance averaged over a specified wavelength range.

[0047] Absorbance can be measured with methods described in ASTM E903-12 “Standard Test Method for Solar Absorptance, Reflectance, and Transmittance of Materials Using Integrating Spheres”. Absorbance measurements described herein were made by making transmission measurements as previously described and then calculating absorbance using Equation 1.

[0048] As used herein, the term “absorbance” with respect to a quantitative measurement refers to the base 10 logarithm of a ratio of incident radiant power to transmitted radiant power through a material. The ratio may be described as the radiant flux received by the material divided by the radiant flux transmitted by the material. Absorbance (A) may be calculated based on transmittance (T) according to Equation 1 :

A = -log₁₀ T (1)

[0049] Emissivity can be measured using infrared imaging radiometers with methods described in ASTM E 1933- 14 (2018) “Standard Practice for Measuring and Compensating for Emissivity Using Infrared Imaging Radiometers.” According to Kirchhoff s law of thermal radiation, absorbance correlates with emittance. Absorbance, absorptivity, emissivity, and emittance are used interchangeably herein for the same purpose of emitting infrared energy to the atmosphere. Absorb and emit are also used interchangeably herein.

[0050] As used herein, the terms “transmittance” and “transmission” refer to the ratio of total transmission of a layer of a material compared to that received by the material, which may account for the effects of absorption, scattering, reflection, etc. Transmittance (T) may range from 0 to 1 or be expressed as a percentage (T%).

[0051] As used herein, “transparent” refers to a material (e.g., film or layer) that absorbs less than 20% of light having wavelengths between 350 nm and 2500 nm.

[0052] As used herein, “bandwidth” refers to a width of a contiguous band of wavelengths.

[0053] As used herein, the term “passive radiative cooling” refers to providing cooling without consuming energy from a source of energy, such as a battery or other electricity source. Passive radiative cooling may be defined in contrast to “active cooling” for which a source of energy is consumed (for example, cooling by air conditioning unit having a compressor and fan powered by electricity).

[0054] As used herein, the term “sub-ambient cooling” refers to cooling a surface below ambient air temperature. The sub-ambient cooling may occur under direct solar irradiation (e.g., sunlight).

Broadband Reflectors

[0055] In a first aspect, the present disclosure provides a broadband reflector. The broadband reflector comprises:

[0056] a multilayer optical film comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 90 percent of incident light over at least a wavelength range from 400 nanometers (nm) to 2000 nm or from 350 nm to 2500 nm, wherein the broadband reflector is essentially free of metal. [0057] Providing a broadband reflector that is essentially free of metal can be advantageous for various reasons. Commercially available passive radiative cooling films are typically metal vapor coated to reflect infrared light. A metal vapor coating, however, blocks cellular communication and can be prone to corrosion in hot and humid environments. Broadband reflectors according to at least certain embodiments of the present disclosure lacking a significant amount of metal can be used in applications where cellular communication is needed to pass through the layers of the broadband reflector. Metal layers also limit the extent that passive radiative cooling films can be thermoformed into useful form factors. In contrast, broadband reflectors according to at least certain embodiments of the present disclosure may have a nonplanar shape, for instance imparted to the broadband reflector by thermoforming.

[0058] Referring to the schematic cross-sectional view of FIG. 1A, a broadband reflector 100a is provided, comprising a multilayer optical film 102 comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 90 percent of incident light over at least a wavelength range from 400 nanometers (nm) to 2000 nm or from 350 nm to 2500 nm, wherein the broadband reflector is essentially free of metal.

[0059] Advantageously, in some embodiments of the broadband reflector, at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, the multilayer optical film provides a 1^st order reflection band, a 2^nd order reflection band, and optionally a 3^rd order reflection band, wherein the 2^nd order reflection band substantially overlaps at least one of the 1^st and 3^rd order reflection bands to form a single wide reflection band. Particularly efficient use of multilayer optical film stacks, especially in applications that call for high or at least substantial reflectivity over a wide spectral range that spans both visible and infrared wavelengths, can be made by overlapping multiple harmonic reflection bands from a given multilayer stack or packet in an optical article, including at least one 2^nd order reflection band. Efficiency can be enhanced by making use of not only 1^st order reflections but also 2^nd order reflections in the functional operation of the article, and by tailoring the stack so that the 2^nd order reflection band overlaps, or substantially overlaps, the 1^st order reflection band and/or a 3^rd order reflection band to produce a widened and combined, continuous reflection band. The reader should understand that in some cases the stack of microlayers may produce at least one other reflection band that is spectrally separated from, and not a part of, the single continuous reflection band. For example, the 2^nd, 3^rd, and 4^th order reflection bands may overlap with each other to form a single, widened, continuous reflection band, but the stack of microlayers may also produce a 1^st order reflection band that is spaced apart from, and not a part of, such widened reflection band. [0060] If the 2^nd order reflection band does not actually overlap but is sufficiently close to substantially overlap, for example, the 1^st order reflection band, then the 2^nd order reflection band may have a long wavelength band edge whose wavelength X 2nd differs from a wavelength Xsist of a short wavelength band edge of the 1^st order reflection band by no more than 5% of Xsist- Similarly, if the 2^nd order reflection band does not actually overlap but is sufficiently close to substantially overlap the 3^rd order reflection band, then the 2^nd order reflection band may have a short wavelength band edge whose wavelength Xs2nd differs from a wavelength Z rd of a long wavelength band edge of the 3^rd order reflection band by no more than 5% of Xs2nd- We use the term “substantially overlap” and the like to encompass both the situation where the two reflection bands at issue actually overlap, i.e., wherein the long or short wavelength band edge of one band falls between the long and short band edges of the other band, and the situation where the two bands (as determined by their respective band edges) do not actually overlap but are within the 5% tolerances mentioned above.

[0061] In order to produce significant 2^nd order reflections, the relative thicknesses of the “A” and “B” microlayers in a given stack are tailored so that the f-ratio of the optical repeat units is significantly different from 0.5 (50%), and this design feature can also provide significant benefits to the film manufacturer. In particular, to the extent material “A” of the “A” microlayers is more expensive than material “B” of the “B” microlayers (or vice versa), one can select an f-ratio that reduces the amount of material “A”, and increases the amount of material “B”, in the stack (or vice versa), relative to a stack design whose f-ratio is 0.5. By selecting the “thinner” microlayer in the ORU to be the more expensive material and the “thicker” microlayer in the ORU to be the less expensive material, the overall raw material cost of the finished film can be significantly reduced. For example, optical quality polyethylene naphthalate (PEN) is currently more expensive than optical quality polyethylene terephthalate (PET); therefore, to achieve a target f-ratio other than 50% that produces a significant 2^nd order reflection, the thickness of a PEN microlayer in each optical repeat unit can be reduced while the thickness of a PET microlayer in each optical repeat unit can be increased, thereby reducing the overall material cost of the film.

[0062] Additional details regarding providing such overlapping harmonics (e.g., 1^st order reflection band, a 2^nd order reflection band, and optionally a 3^rd order reflection band) are described in U.S. Patent No. 9,678,252 (Kivel et al.), incorporated herein by reference in its entirety. Further, specific examples of broadband reflectors exhibiting such reflection bands are described in the Examples below.

[0063] In some cases, the multilayer optical film comprises: [0064] a) an ultraviolet-visible (UV-VIS) reflector comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 350 nanometers (nm) to 400 nm and an average of at least 95 percent of incident light over at least a wavelength range from 400 nm to 800 nm; and

[0065] b) an infrared (IR) reflector comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 90 percent of incident light over at least a wavelength range from 0.8 micrometers to 2.0 micrometers.

[0066] Referring to the schematic cross-sectional view of FIG. IB, the present disclosure provides a broadband reflector 100b comprising a multilayer optical film 102 by combining at least an IR reflector 104 and a UV-VIS reflector 106.

[0067] In some cases, the multilayer optical film comprises:

[0068] a) an ultraviolet (UV) reflector comprising a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 350 nanometers (nm) to 400 nm;

[0069] b) a visible reflector comprising a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 400 nm to 800 nm;

[0070] c) an infrared (IR) reflector comprising a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 90 percent of incident light over at least a wavelength range from 0.8 micrometers to 2.0 micrometers,

[0071] wherein either 1) the visible reflector is disposed between the UV reflector and the IR reflector or 2) the IR reflector is disposed between the UV reflector and the visible reflector.

[0072] Referring to the schematic cross-sectional view of FIG. 1C, the present disclosure provides a broadband reflector 100c comprising a multilayer optical film 102 by combining at least each of a UV reflector 130, a visible reflector 120, and an IR reflector 110. The present disclosure also provides a broadband reflector 100c comprising a multilayer optical film 102 by combining each of a UV reflector 130, an IR reflector 120, and a visible reflector 110. As such, in some cases the visible reflector is disposed between the UV reflector and the IR reflector, whereas in other cases the IR reflector is disposed between the UV reflector and the visible reflector.

[0073] In certain embodiments, broadband reflectors according to the present disclosure absorb an average of at least 60, 70, 80, 90, or 95 percent of incident light over at least a wavelength range from 3.0 micrometers to 20 micrometers or 8 micrometers to 13 micrometers. It is to be understood that the percent of incident light absorbed refers to the amount absorbed integrated over a particular wavelength range (as opposed to the amount of a single wavelength that is absorbed).

[0074] In certain embodiments, broadband reflectors according to the present disclosure absorb an average of at least 60, 70, 80, 90, or 95 percent of incident light over at least a wavelength range from 8.0 micrometers to 13 micrometers. Preferably, broadband reflectors according to at least certain embodiments of the present disclosure are capable of sub-ambient cooling, such as exhibiting passive radiative cooling to below ambient temperature under direct solar irradiation (e.g., sunlight).

[0075] In certain embodiments, broadband reflectors according to the present disclosure absorb an average of at least 60, 70, 80, 90, or 95 percent of incident light over at least a wavelength range from 4.0 micrometers to 20 micrometers. Preferably, broadband reflectors according to at least certain embodiments of the present disclosure are capable of above ambient cooling under direct solar irradiation (e.g., sunlight).

Ultraviolet Reflector

[0076] As mentioned above, the UV reflector is comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 350 nanometers (nm) to 400 nm, such as at least 96%, 97%, 98%, or even at least 99% of incident light. The UV reflector preferably reflects over a wider wavelength range than 350 nm to 400 nm; in some cases the UV reflector reflects an average of at least 95 percent of incident light over at least a wavelength range from 300 nm to 400 nm, such as at least 96%, 97%, 98%, or even at least 99% of incident light.

[0077] The use of multilayer reflective films comprising alternating layers of two or more polymers to reflect light is known and is described, for example, in U.S. Pat. No. 3,711,176 (Alfirey, Jr. et al.), U.S. Pat. No. 5,103,337 (Schrenk et al.), WO 96/19347 (Jonza et al.), and WO 95/17303 (Ouderkirk et al.). The reflection and transmission spectra of a particular multilayer film depends primarily on the optical thickness of the individual layers, which is defined as the product of the actual thickness of a layer times its refractive index. Accordingly, fdms can be designed to reflect infrared, visible, or ultraviolet wavelengths XM of light by choice of the appropriate optical thickness of the layers in accordance with the following formula:

[0078] X_M =(2/M)*D_r

[0079] wherein M is an integer representing the particular order of the reflected light and D_r is the optical thickness of an optical repeating unit (also called a multilayer stack) comprising two or more polymeric layers. Accordingly, D_r is the sum of the optical thicknesses of the individual polymer layers that make up the optical repeating unit. D_r is always one half lambda (X) in thickness, where lambda is the wavelength of the first order reflection peak. By varying the optical thickness of an optical repeating unit along the thickness of the multilayer film, a multilayer film can be designed that reflects light over a broad band of wavelengths. This band is commonly referred to as the reflection band or stop band. In some embodiments, a reflection band has a sharp spectral edge at the long wavelength (red) and/or short wavelength (blue) side. It may be desirable to design a reflective film or other optical body that reflects light over a selected range in the visible region of the spectrum, e.g., a reflective film that reflects only green light. In such a case, it may be desirable to have sharp edges at both the red and blue sides of the reflection band. Multilayer optical films exhibiting sharpened reflective bandedge(s) are described in detail, for instance, in U.S. Patent No. 6,967,778 (Wheatley et al.), incorporated herein by reference in its entirety.

[0080] In one embodiment, an optical polymer film or a layered optical polymer film having a first and second major surface is provided. “Film” is used to refer to planar forms of plastic that are thick enough to be self-supporting but thin enough to be flexed, folded, conformed or creased without cracking. Film thickness depends upon desired applications and manufacturing methods.

[0081] “Optical Film” is used herein to refer to any reflective or partially reflective polymer film designed to exhibit desired reflection, transmission, absorption, or refraction of light upon exposure to a specific band of wavelengths of electromagnetic energy. Thus, conventional normally transparent polymeric films, such as polyester and polypropylene, are not considered “optical films” for the purposes of the present disclosure, even though such films may exhibit some degree of reflectance, or glare, when viewed from some angles. Films that exhibit both reflective and transmissive properties, however, such as those that are partially transmissive, are considered within the scope of this disclosure. Preferred optical polymer films generally absorb less than 25 percent of the radiant energy that impacts the film’s surface. Preferably, the radiating energy absorbed is less than 10 percent and most preferably less than 5 percent. The radiant energy, typically expressed as the energy in a range of wavelengths, may be reflected either specularly or diffusely. The reflectance may be isotropic, i.e., the fdm has the same reflective properties along both in-plane axes, or may be anisotropic, i.e., the film has different reflective properties along the orthogonal in-plane axes. The difference in reflective properties along the inplane axes can be varied by controlling the relationship between the indices of refraction along each axis for each of the component materials.

[0082] Optical films come in a variety of forms and are selected according to a desired application. Some suitable examples include multilayer polarizers, visible and infrared mirrors, and color films such as those described in Patent Publications WO 95/17303, WO 96/19347, and WO 97/01440; U.S. Pat. No. 6,045,894 (Jonza et al.) U.S. Pat. No. 6,531,230 (Weber et al.); U.S. Pat. No. 5,103,337 (Schrenk et al.), U.S. Pat. No. 5,122,905 (Wheatley et al.), U.S. Pat. No. 5,122,906 (Wheatley), U.S. Pat. No. 5,126,880 (Wheatley et al.), U.S. Pat. No. 5,217,794 (Schrenk), U.S. Pat. No. 5,233,465 (Schrenk et al.), U.S. Pat. No. 5,262,894 (Wheatley et al.), U.S. Pat. No. 5,278,694 (Wheatley et al.), U.S. Pat. No. 5,339,198 (Wheatley et al.), U.S. Pat. No. 5,360,659 (Arends et al.), U.S. Pat. No. 5,448,404 (Schrenk et al.), U.S. Pat. No. 5,486,949 (Schrenk et al.) U.S. Pat. No. 4,162,343 (Wilcox et al.), U.S. Pat. No. 5,089,318 (Shetty et al.), U.S. Pat. No. 5,154,765 (Armanini), and U.S. Pat. No. 3,711,176 (Alfirey, Jr. et al.); and Reissued U.S. Pat. No. RE 31,780 (Cooper et al.) and U.S. Pat. No. RE 34,605 (Schrenk et al.), all contents of which are incorporated herein by reference.

[0083] Examples of optical fdms comprising immiscible blends of two or more polymeric materials include blend constructions wherein the reflective and transmissive properties are obtained from the presence of discontinuous polymeric regions having a cross-sectional diameter perpendicular to the major axis that is on the order of a fraction of the distance corresponding to a wavelength of light, and may also obtain the desired optical properties through orientation, such as the blend mirrors and polarizers as described in Patent Publications WO 97/32224 (Ouderkirk et al.), U.S. Pat. No. 6,179,948 (Merrill et al.), and U.S. Pat. No. 5,751,388 (Earson), the contents of which are all herein incorporated by reference.

[0084] In some embodiments, the polymeric optical layers of the UV reflector comprise a fluoropolymer, a polymethyl methacrylate (PMMA), a copolymer of ethyl acrylate and methyl methacrylate (CoPMMA), or combinations thereof. When the UV reflector comprises a fluoropolymer, the polymeric optical layers preferably comprise a fluoropolymer independently selected from the group consisting of a copolymer of tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and vinylidene fluoride; a copolymer of TFE, HFP, vinylidene fluoride, and perfluoropropyl vinyl ether (PPVE); a polyvinylidene fluoride (PVDF); an ethylene chlorotrifluoroethylene (ECTFE) polymer; an ethylene tetrafluoroethylene (ETFE); a perfluoroalkoxy alkane (PF A) polymer; a fluorinated ethylene propylene (FEP) polymer; a polytetrafluoroethylene (PTFE); a copolymer of TFE, HFP, and ethylene; and combinations thereof. In some embodiments, the polymeric optical layers of the UV reflector comprise alternating layers of CoPMMA and THV.

[0085] In select embodiments, a suitable THV comprises a copolymer comprising 24 to 47 mole % of tetrafluoroethylene monomers, 5 to 23 mole % of hexafluoropropylene monomers, and 35 to 70 mole % of vinylidene fluoride monomers. The copolymer comprises end groups and at least a portion of the end groups on the copolymer are nonacidic. This THV tends to have reduced HF content as compared to some other THV copolymers. Such a THV copolymer may be made, for instance, by combining the tetrafluoroethylene monomers, hexafluoropropylene monomers, and vinylidene fluoride monomers in an aqueous emulsion comprising ammonium 4,8-dioxa-3-H- perfluorononanoate, and polymerizing the monomers in the presence of oxidizing manganese ions and dialkyl ether to create a polymer dispersion, wherein the polymer dispersion contains at least 10 wt.% solids and a particle size distribution of 80 nm to 150 nm. In preferred embodiments, a source of the oxidizing manganese ion is potassium permanganate and the dialkyl ether is dimethyl ether.

[0086] In some embodiments, the THV copolymer comprises at least 24 mole %, at least 30 mole %, at least 35 mole %, or at least 40 mole % TFE monomers. In some embodiments, the copolymer comprises up to 47 mole %, up to 40 mole %, up to 35 mole %, or up to 30 mole % TFE monomers. In some embodiments, the copolymer comprises 24 to 47 mole %, more particularly 30 to 47 mole % TFE monomers. In some embodiments, the copolymer comprises 39 mole % TFE monomers.

[0087] In some embodiments, the THV copolymer comprises at least 5 mole %, at least 7 mole %, at least 9 mole %, at least 11 mole %, at least 13 mole %, at least 15 mole %, at least 17 mole %, at least 19 mole %, or at least 21 mole % HFP monomers. In some embodiments, the copolymer comprises up to 23 mole %, up to 21 mole %, up to 19 mole %, up to 17 mole %, up to 15 mole %, up to 13 mole %, up to 11 mole %, up to 9 mole %, or up to 7 mole % HFP monomers. In some embodiments, the copolymer comprises 5 to 23 mol %, more particularly 5 to 13 mole % HFP monomers. In some embodiments, the copolymer comprises 11 mole % HFP monomers.

[0088] In some embodiments, the THV copolymer comprises at least 35 mole %, at least 40 mole %, at least 45 mole %, at least 50 mole %, at least 55 mole %, at least 60 mole %, or at least 65 mole % VDF monomers. In some embodiments, the copolymer comprises up to 70 mole %, up to 65 mole %, up to 60 mole %, up to 55 mole %, up to 50 mole %, up to 45 mole %, or up to 40 mole % VDF monomers. In some embodiments, the copolymer comprises 35 to 70 mole %, more particularly 35 to 60 mole %, even more particularly 35 to 50 mole % VDF monomers. In some embodiments, the copolymer comprises 50 mole % VDF monomers.

[0089] The nonacidic end groups derive from the choice of chain transfer agent and initiator used to make the THV copolymer. The chain transfer agent typically includes a dialkyl ether, such as dimethyl ether or methyl t-butyl ether. In preferred embodiments, the dialkyl ether is dimethyl ether. Although the dialkyl ethers may be expected to react similarly as chain transfer agents, in practice, some dialkyl ethers (e.g., diethyl ether) are less favorable due to handling difficulties. The initiator typically includes oxidizing manganese ions, such as those deriving from potassium permanganate, sodium permanganate, or Mn³⁺ salts (like manganese triacetate, manganese oxalate, etc.). The preferred metal salt is KMnO4.

[0090] Optionally, the THV copolymer comprises a calcium carbonate additive, which advantageously acts as a scavenger in the THV to minimize degradation of the copolymer and/or generation of HF. A suitable calcium carbonate includes for instance and without limitation, nanocalcium carbonate particles having an average diameter that is less than 100 nm, 90 nm, 80 nm, 70 nm, 60 nm, or less than 50 nm; and 1 nm or greater. The average diameter of nanosized calcium carbonate particles can be determined using transmission electron microscopy (TEM). One suitable nanocalcium carbonate is commercially available under the trade name “SOCAL 31” from Imerys (Paris, France).

[0091] FIG. 3 shows one suitable UV reflector 320, which may also be used as a visible reflector, a UV-VIS reflector, or an IR reflector, depending on the configuration of the optical layers. UV reflector 320 includes one or more first optical layers 312, one or more second optical layers 314, and optionally one or more UV/VIS transparent additional skin layers 318.

[0092] UV reflector 320 includes a multilayer optical stack 308 having alternating layers 312, 314 of at least two materials, typically comprising different polymers. An in-plane index of refraction nl in one in-plane direction of high refractive index layer 312 is higher than the in-plane index of refraction n2 of low refractive index layer 314 in the same in-plane direction. The difference in refractive index at each boundary between layers 312, 314 causes part of the incident light to be reflected. The transmission and reflection characteristics of multilayer optical fdm 308 is based on coherent interference of light caused by the refractive index difference between layers 312, 314 and the thicknesses of layers 312, 314. When the effective indices of refraction (or in-plane indices of refraction for normal incidence) differ between layers 312, 314, the interface between adjacent layers 312, 314 forms a reflecting surface. The reflective power of the reflecting surface depends on the square of the difference between the effective indexes of refraction of the layers 312, 314 (e.g., (nl - n2)²). By increasing the difference in the indices of refraction between the layers 312, 314, improved optical power (higher reflectivity), thinner films (thinner or fewer layers), and broader bandwidth performance can be achieved. The refractive index difference in one in-plane direction in an exemplary embodiment is at least about 0.05, preferably greater than about 0.10, more preferably greater than about 0.15 and even more preferably greater than about 0.20.

[0093] In some embodiments, the materials of layers 312, 314 inherently have differing indices of refraction. In another embodiment, at least one of the materials of the layers 312, 314 has the property of stress induced birefringence, such that the index of refraction (n) of the material is affected by the stretching process. By stretching multilayer optical film 320 over a range of uniaxial to biaxial orientations, films can be created with a range of reflectivities for differently oriented plane -polarized incident light.

[0094] The number of layers in the UV reflector 320 is selected to achieve the desired optical properties using the minimum number of layers for reasons of film thickness, flexibility and economy. In the case of reflective films such as mirrors, the number of layers is preferably less than about 2,000, more preferably less than about 1,000, and even more preferably less than about 750. In some embodiments, the number of layers is at least 150 or 200. In other embodiments, the number of layers is at least 250. Optionally, each of the UV reflector, the visible reflector, and the IR reflector independently comprises between 300 and 2000, inclusive, alternating first and second polymeric optical layers.

[0095] In some embodiments, the UV reflector 320 further comprises optional additional non- optical or optical skin layers. Optional skin layers 318 may protect the optical layers 312, 314 from damage, aid in the co-extrusion processing, and/or enhance post-processing mechanical properties. The additional skin layers 318 are often thicker than the optical layers 312, 314. The thickness of the skin layers 318 is usually at least two times, preferably at least four times, and more preferably at least ten times, the thickness of the individual optical layers 312, 314. The thickness of the skin layers 318 may be varied to make a UV reflector having a particular thickness. A tie layer (not shown) may optionally be present between the skin layer(s) and the optical layers. Typically, one or more of the additional layers 318 are placed so that at least a portion of the light to be transmitted, polarized, and/or reflected by the optical layers 312, 314, also travels through the additional layers (i.e., the additional layers are placed in the path of light which travels through or is reflected by optical layers 312, 314). To provide a degree of antisoiling properties, one or both of the skin layers (preferably at least the outermost skin layer) comprises fluoropolymer.

[0096] UV reflector 320 comprises multiple low/high index pairs of film layers, wherein each low/high index pair of layers 312,314 has a combined optical thickness of 1/2 the center wavelength of the band it is designed to reflect. Stacks of such films are commonly referred to as quarter-wave stacks. In some embodiments, different low/high index pairs of layers may have different combined optical thicknesses, such as where a broadband reflective optical film is desired.

[0097] The various constituent layers of UV reflector 320, whether as skin layers or optical layers, are preferably resistant to ultraviolet radiation. Many fluoropolymers are resistant to UV- radiation. Examples of fluoropolymers that may be used include copolymers of tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and vinylidene fluoride (e.g., available from 3M Company under the trade designation 3M DYNEON THV); a copolymer of TFE, HFP, vinylidene fluoride, and perfluoropropyl vinyl ether (PPVE) (e.g., available from 3M Company under the trade designation 3M DYNEON THVP); a polyvinylidene fluoride (PVDF) (e.g., 3M DYNEON PVDF 6008 from 3M Company); ethylene chlorotrifluoroethylene polymer (ECTFE) (e.g., available as HALAR 350LC ECTFE from Solvay, Brussels, Belgium); an ethylene tetrafluoroethylene copolymer (ETFE) (e.g., available as 3M DYNEON ETFE 6235 from 3M Company); perfluoroalkoxyalkane polymers (PFA); fluorinated ethylene propylene copolymer (FEP); a polytetrafluoroethylene (PTFE); copolymers of TFE, HFP, and ethylene (HTE) (e.g., available as 3M DYNEON HTE1705 from 3M Company). Combinations of fluoropolymers can also be used. In some embodiments, the fluoropolymer includes FEP. In some embodiments, the fluoropolymer includes PFA.

[0098] Examples of non-fluorinated polymers that may be used in at least one layer of UV reflector 320 include at least one of: polypropylene, polyethylene, polyethylene copolymers, polyethylene methacrylate copolymers, ethylene vinyl acetate copolymers, polymethyl methacrylate, methyl methacrylate copolymers (e.g., copolymers of ethyl acrylate and methyl methacrylate), polyurethanes, extended chain polyethylene polymers (ECPEs), or a combinations thereof. In general, combinations of non-fluorinated polymers can be used. Exemplary nonfluorinated polymers, especially for use in high refractive index optical layers, may include homopolymers of polymethyl methacrylate (PMMA), such as those available as CP71 and CP80 from Ineos Acrylics, Inc., Wilmington, DE; and polyethyl methacrylate (PEMA), which has a lower glass transition temperature than PMMA. Additional useful polymers include: copolymers of methyl methacrylate such as, for example, a copolymer made from 75 wt.% methyl methacrylate and 25 wt.% ethyl acrylate, for example, as available from Ineos Acrylics, Inc. as PERSPEX CP63, or as available from Arkema, Philadelphia, PA as ALTUGLAS 510, and copolymers of methyl methacrylate monomer units and n-butyl methacrylate monomer units. Blends of PMMA and PVDF may also be used.

[0099] Suitable triblock acrylic copolymers are available, for example, as KURARITY LA4285 from Kuraray America Inc., Houston, TX. Additional suitable polymers for the optical layers, especially for use in the refractive index optical layers, may include at least one of: polyolefin copolymers such as poly(ethylene-co-octene) (e.g., available as ENGAGE 8200 from Dow Elastomers, Midland, MI), polyethylene methacrylate (e.g., available as ELVALOY from Dow Elastomers), poly (propylene-co-ethylene) (e.g., available as Z9470 from Atofina Petrochemicals, Inc., Houston, TX); and a copolymer of atactic polypropylene and isotactic polypropylene. Materials may be selected based on absorbance or transmittance properties described herein, as well as on refractive index. In general, the greater the refractive index between two materials, the thinner the film can be, which may be desirable for efficient heat transfer.

[00100] Multilayer optical films (including reflectors) can be made by coextrusion of alternating polymer layers having different refractive indices, for example, as described in U.S Pat. Nos. 5,882,774 (Jonza et al.); 6,045,894 (Jonza et al.); 6,368,699 (Gilbert et al.); 6,531,230 (Weber et al.); 6,667,095 (Wheatley et al.); 6,783,349 (Neavin et al.); 7,271,951 B2 (Weber et al); 7,632,568 (Padiyath et al.); 7,652,736 (Padiyath et al.); and 7,952,805 (McGurran et al.); and PCT Publications WO 95/17303 (Ouderkirk et al.) and WO 99/39224 (Ouderkirk et al.).

[00101] Optionally, the polymeric optical layers of the UV reflector comprise a PMMA or CoPMMA high refractive index first optical layer in the plurality of first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 350 nm to 400 nm.

[00102] In one preferred embodiment, the UV reflector reflects a wavelength range from 340 to 400 nanometers made with 150 high refractive index layers comprising a methyl methacrylate copolymer (CoPMMA) (e.g., available as PERSPEX CP63 from Lucite International, Cordova, Tennessee) alternating with 150 low refractive index layers comprising a fluoropolymer (e.g., available as 3M DYNEON THV221 from 3M Company).

[00103] Typically, the UV reflector has an average thickness of 15 micrometers to 50 micrometers, such as 15 micrometers or greater, 16 micrometers, 17 micrometers, 18 micrometers, 19 micrometers, 20 micrometers, 21 micrometers, 22 micrometers, 23 micrometers or 24 micrometers or greater; and 50 micrometers or less, 47 micrometers, 45 micrometers, 42 micrometers, 40 micrometers, 37 micrometers, 35 micrometers, 32 micrometers, 30 micrometers, 27 micrometers, or 25 micrometers or less.

Ultraviolet-Visible Reflector

[00104] As mentioned above, the UV-VIS reflector is comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 350 nanometers (nm) to 400 nm (e.g., wavelengths generally in the UV range) and an average of at least 95 percent of incident light over at least a wavelength range from 400 nm to 800 nm (e.g., wavelengths generally in the VIS range). The UV-VIS reflector preferably reflects over a wider UV wavelength range than 350 nm to 400 nm; in some cases the UV-VIS reflector reflects an average of at least 95 percent of incident light over at least a wavelength range from 300 nm to 800 nm, such as at least 96%, 97%, 98%, or even at least 99% of incident light.

[00105] The same principles as described in detail above with respect to multilayer reflective films for the UV reflector comprising alternating layers of two or more polymers to reflect light apply to the UV-VIS reflector. Exemplary UV-VIS reflectors include multilayer optical films, for example, as described in the section on UV reflectors hereinabove, except tuned to reflect both UV and visible wavelengths. For multilayer optical films concerned with the UV and visible wavelengths, a quarterwave stack design results in each of the layers 312, 314 (see FIG. 3) in the multilayer stack having an average thickness of not more than about 1.0 micrometer.

[00106] Suitable polymers for the polymeric optical layers include those described above with respect to the ultraviolet reflector, as well as those described below with respect to a visible reflector. In some cases, the polymeric optical layers of the UV-VIS reflector comprise alternating layers of a polyethylene terephthalate (PET) and a blend of a polyvinylidene fluoride (PVDF) and a polymethyl methacrylate (PMMA).

Visible Reflectors

[00107] As mentioned above, the visible reflector comprising a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 400 nm to 800 nm, such as at least 96%, 97%, 98%, or even at least 99% of incident light. [00108] The same principles as described in detail above with respect to multilayer reflective films for the UV reflector comprising alternating layers of two or more polymers to reflect light apply to the visible reflector. Exemplary visible reflectors include multilayer optical films, for example, as described in the section on UV reflectors hereinabove, except tuned to visible wavelengths. For multilayer optical films concerned with the visible and the near infrared wavelengths, a quarterwave stack design results in each of the layers 312, 314 (see FIG. 3) in the multilayer stack having an average thickness of not more than about 0.7 micrometers.

[00109] In some cases, the polymeric optical layers of the visible reflector comprise a fluoropolymer, a polyethylene terephthalate (PET), CoPMMA, a polypropylene (PP), a polyethylene (PE), a polyethylene copolymer, PMMA, an acrylate copolymer, a polyurethane, or combinations thereof. In some cases, the polymeric optical layers of the visible reflector comprise a fluoropolymer independently selected from the group consisting of a copolymer of tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and vinylidene fluoride; a copolymer of TFE, HFP, vinylidene fluoride, and perfluoropropyl vinyl ether (PPVE); a polyvinylidene fluoride (PVDF); an ethylene chlorotrifluoroethylene (ECTFE) polymer; an ethylene tetrafluoroethylene (ETFE); a perfluoroalkoxy alkane (PF A) polymer; a fluorinated ethylene propylene (FEP) polymer; a polytetrafluoroethylene (PTFE); a copolymer of TFE, HFP, and ethylene; and combinations thereof.

[00110] Optionally, the polymeric optical layers of the visible reflector comprise a PET high refractive index first optical layer in a plurality of first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 400 nm to 600 nm.

[00111] In select embodiments, the polymeric optical layers of the visible reflector comprise alternating layers of PET and THV. A particularly suitable THV copolymer is the THV described above comprising 24 to 47 mole % of tetrafluoroethylene monomers, 5 to 23 mole % of hexafluoropropylene monomers, and 35 to 70 mole % of vinylidene fluoride monomers, in which at least a portion of the end groups on the copolymer are nonacidic.

[00112] Typically, the visible reflector has an average thickness of 25 micrometers to 75 micrometers, such as 25 micrometers or greater, 27 micrometers, 30 micrometers, 32 micrometers, 35 micrometers, 37 micrometers, 40 micrometers, 42 micrometers, 45 micrometers or 47 micrometers or greater; and 75 micrometers or less, 72 micrometers, 70 micrometers, 67 micrometers, 65 micrometers, 62 micrometers, 60 micrometers, 57 micrometers, 55 micrometers, 52 micrometers, or 50 micrometers or less.

Infrared Reflectors

[00113] As mentioned above, the IR reflector comprises a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 90 percent of incident light over at least a wavelength range from 0.8 micrometers to 2.0 micrometers, such as at least 91%, 92%, 93%, 94%, 95%, 96%, 97%, or even at least 98% of incident light. Preferably, the IR reflector reflects an average of at least 90 percent of incident light over at least a wavelength range from 0.8 micrometers to 2.3 or 2.5 micrometers.

[00114] The same principles as described in detail above with respect to multilayer reflective films for the UV reflector comprising alternating layers of two or more polymers to reflect light apply to the IR reflector. Exemplary IR reflectors include multilayer optical films, for example, as described in the section on UV reflectors hereinabove, except tuned to infrared wavelengths. For multilayer optical films concerned with the visible and the near infrared wavelengths, a quarterwave stack design results in each of the layers 312, 314 (see FIG. 3) in the multilayer stack having an average thickness of not more than about 0.7 micrometers.

[00115] In some cases, the polymeric optical layers of the infrared reflector comprise a fluoropolymer, a polyethylene naphthalate (PEN), a polyethylene terephthalate (PET), CoPMMA, a polypropylene (PP), a polyethylene (PE), a polyethylene copolymer, PMMA, an acrylate copolymer, a polyurethane, or combinations thereof. In some cases, the polymeric optical layers of the infrared reflector comprise a fluoropolymer independently selected from the group consisting of a copolymer of tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and vinylidene fluoride; a copolymer of TFE, HFP, vinylidene fluoride, and perfluoropropyl vinyl ether (PPVE); a poly vinylidene fluoride (PVDF); an ethylene chlorotrifluoroethylene (ECTFE) polymer; an ethylene tetrafluoroethylene (ETFE); a perfluoroalkoxy alkane (PF A) polymer; a fluorinated ethylene propylene (FEP) polymer; a polytetrafluoroethylene (PTFE); a copolymer of TFE, HFP, and ethylene; and combinations thereof.

[00116] Optionally, the polymeric optical layers of the visible reflector comprise alternating layers of PET and THV. A particularly suitable THV copolymer is the THV described above comprising 24 to 47 mole % of tetrafluoroethylene monomers, 5 to 23 mole % of hexafluoropropylene monomers, and 35 to 70 mole % of vinylidene fluoride monomers, in which at least a portion of the end groups on the copolymer are nonacidic. [00117] In select embodiments, the visible reflector is disposed between the UV reflector and the IR reflector. In such embodiments, optionally the polymeric optical layers of the IR reflector comprise a PEN high refractive index first optical layer in a plurality of first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 600 nm to 2000 nm (i.e., 2 micrometers) In some cases, the polymeric optical layers of the IR reflector comprise alternating layers of PEN and PMMA. The PMMA may be blended with PVDF, although this is not required.

[00118] Typically, the IR reflector has an average thickness of 75 micrometers to 150 micrometers, such as 75 micrometers or greater, 80 micrometers, 85 micrometers, 90 micrometers, 95 micrometers, 100 micrometers, 105 micrometers, 110 micrometers, 115 micrometers or 120 micrometers or greater; and 150 micrometers or less, 145 micrometers, 140 micrometers, 135 micrometers, 130 micrometers, 125 micrometers, 120 micrometers, 115 micrometers, 110 micrometers, 105 micrometers, or 100 micrometers or less.

Composite Cooling Systems

[00119] Referring now to FIG. 4, in use a broadband reflector article (e.g., a radiative cooling article) 400 may be secured to a substrate 410 such that the article 400 is in thermal communication with substrate 410, and together form a composite cooling system 450. The article 400 may be generally planar in shape; however it does not need to be planar and may be flexible to conform to substrate 410 and thus be nonplanar. Composite cooling system 450 may reflect sunlight 404 to cool substrate 410, which may be particularly effective in daytime environment. Without radiative cooling by the article 400, sunlight 404 may be absorbed by the substrate 410 and converted into heat. Reflected sunlight 405 may be directed into atmosphere 408. The article 400 may radiate light 406 in the atmospheric window region of the electromagnetic spectrum into atmosphere 408 to cool substrate 410, which may be particularly effective in the nighttime environment. The article 400 may allow heat to be converted into light 406 (e.g., infrared light) capable of escaping atmosphere 408 through the atmospheric window. The radiation of light 406 may be a property of article 400 that does not require additional energy and may be described as passive radiation, which may cool article 400 and substrate 410, which is thermally coupled to a (e.g., radiative cooling) article 400. During the day, the reflective properties allow article 400 to emit more energy than is absorbed. The radiative properties in combination with the reflective properties, to reflect sunlight during the day, the article 400 may provide more cooling than an article that only radiates energy through the atmosphere and into space. [00120] The broadband reflector article 400 may be suitable for outdoor environments and have, for example, a suitable operating temperature range, water resistance, and ultraviolet (UV) stability. Resistance to photo-oxidation can be measured by changes in reflectivity or changes in color. The broadband reflector articles described herein may not have a change in reflectivity of greater than 5% over at least 5 years. The articles described herein may not have a change in color, described as b* per ASTM G-155-13 (2013), of greater than 5 after exposure to 18,700 kJ/m² at 340 nanometers. One mechanism for detecting the change in physical characteristics is the use of the weathering cycle described in ASTM G155-05a (October 2005) using a D65 light source in the reflected mode. Under the noted test, the article should withstand an exposure of at least 18,700 kJ/m² at 340 nanometers without change in reflectivity, color, onset of cracking, or surface pitting.

[00121] Exemplary substrates for substrate 410 include vehicles (e.g., the roof, body panels, and/or windows), buildings (e.g., roofs, walls), and modular data centers. Exemplary substrates may be part of a larger article, apparatus, or system (e.g., a window of building).

[00122] In a second aspect, the present disclosure provides a composite cooling system. The composite cooling system includes a broadband reflector according to the first aspect attached to a roof and/or at least one side of a vehicle. For example, passive radiation cooling could be used to cool the sides of refrigerated semi-truck trailers, trains, and buses with less energy than currently required. Additionally, electric vehicles would advantageously have longer driving ranges in hot climates if the need for air conditioning was reduced by incorporating metal free radiative cooling film that can be thermoformed into the shape of 3 -dimensional vehicle roofs and/or sides. Referring to FIG. 5, a schematic side view of an exemplary composite cooling system 520 is provided including a broadband reflector 522 attached to a roof 521 of a vehicle 526 and a broadband reflector 524 attached to a side door 523 of the vehicle 526. It can be seen that the broadband reflectors 522 and 524 each have a nonplanar shape due to conforming to the shape of the roof 521 and door 523, respectively.

[00123] In a third aspect, another composite cooling system is provided. The composite cooling system includes a broadband reflector according to the first aspect attached to a modular data center. Modular data centers are data centers that are typically assembled from modular components and can be prepared at various convenient locations. In some cases, modular data centers are portable. Data centers in particular are a high growth market which is creating great demand for cooling systems and new cooling methods. Referring to FIG. 6, a schematic perspective view of a composite cooling system 630 is provided including a broadband reflector 632 atached to a side wall 631 of a modular data center 636 and a broadband reflector 634 atached to a top wall 633 of the modular data center 636.

[00124] In a fourth aspect, an additional composite cooling system is provided. The composite cooling system includes a broadband reflector according to the first aspect attached to at least one surface of a building or a shelter. Referring to FIG. 7, a schematic perspective view of a composite cooling system 740 is provided including a broadband reflector 742 on a roof 741 of a building 744 (a shelter is not shown). FIG. 7 further illustrates the broadband reflector 742 being exposed to solar energy 118 (from the sun). The broadband reflector 742 may radiate light in the atmospheric infrared region of the electromagnetic spectrum into atmosphere through the sky 745 to cool the building 744, which may be particularly effective in a nightime environment.

[00125] For each of the composite cooling systems described herein, the one or more (e.g., radiative cooling) articles are in thermal communication with a substrate and together form a composite cooling system. Radiative cooling may be achieved with these composite cooling systems as described above with respect to FIG. 4.

[00126] Among other parameters, the amount of cooling and temperature reduction may depend on the reflective and absorptive properties of the broadband reflector article. The cooling effect of the broadband reflector article 400 may be described with reference to a first temperature of the ambient air proximate or adjacent to the substrate and a second temperature of the portion of substrate proximate or adjacent to the article. In some embodiments, the first temperature is greater than the second temperature by at least 0.5 degrees Celsius (in some embodiments, at least 1, 1.5, 1.7, 2, 2.5, 2.7, 3, 3.5, 4, 4.5, 5, 5.5, 8.3, or even at least 11.1) degrees Celsius (e.g., at least 0.9, 1.8, 3.6, 5, 10, 15, or even at least 20 degrees Fahrenheit) and 12 degrees Celsius or less.

[00127] Optional Layers

[00128] Referring to FIG. 2, a schematic side view of an exemplary broadband reflector 200 is shown. The broadband reflector 200 comprises a UV reflector 210 (e.g., indirectly) adjacent to a visible reflector 220, which is (e.g., indirectly) adjacent to an IR reflector 230. The broadband reflector 200 further includes several optional layers: an optional outer layer 240 (e.g., indirectly) adjacent to the UV reflector 210, an optional polymeric sheet 250 atached to the IR reflector 230, an optional transparent adhesive layer or hot melt THV layer 260 attached to the optional polymeric sheet 250, and one or more optional transparent adhesive tie layers 272, 274, 276, and/or 278, which may adhere various layers together as shown in FIG. 2. For instance, transparent adhesive tie layer(s) 274 and/or 276 may be disposed between the three reflectors such that the broadband reflector article comprises a transparent adhesive layer or hot melt THV layer atached to at least one of the UV reflector, the visible reflector, or the IR reflector. When the outer layer 240 is present, there could be an optional transparent adhesive tie layer 272 located between the outer layer 240 and the UV reflector 210. As discussed above, alternatively the visible reflector and IR reflector may be switched such that the visible reflector is layer 230 and the IR reflector is layer 220. Also as discussed above, a multilayer optical fdm may comprise a UV-VIS reflector and an IR reflector, and the various optional layers discussed herein may also be used in combination with these two reflectors.

[00129] In some embodiments, the optional transparent adhesive layer 260 is an air bleed adhesive disposed adjacent to the optional polymeric sheet 250 or the IR reflector (or visible reflector) 230. Further optionally, a release liner may be provided directly adjacent to the air bleed adhesive layer 260 (not shown). Optional releasable liners used with an optional adhesive layer may comprise, for example, a polyolefin film, a fluoropolymer film, a coated PET film, or a siliconized film or paper.

[00130] In some embodiments, the broadband reflector 200 comprises an optional outer layer 240 that is a protective layer, a hard coat layer, or an antisoiling layer. The outer layer 240 is disposed adjacent to the UV reflector 210. An outer layer is typically configured to protect the UV reflector 210 from degradation due to issues such as corrosion, weathering, dirt, scratches, and the like.

[00131] Each of the above-mentioned optional layers is described below in detail.

[00132] Protective Layer

[00133] In some embodiments, the broadband reflector optionally further comprises a protective layer comprising a fluoropolymer, the protective layer disposed adjacent to a major surface of the UV reflector or the UV-VIS reflector. The protective layer is an outer layer. In some embodiments, an outer surface of the protective layer is paterned and/or is textured, e.g., including a light mate finish. In certain embodiments, a textured surface is provided for aesthetic purposes, for instance, texturing could be employed to provide the layer with an appearance of a natural wood grain.

[00134] Any suitable fluoropolymer material may be used in the protective layer. Non-limiting examples of fluoropolymers that may be used include: a polymer of tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and vinylidene fluoride (for example, available under the trade designation “3M DYNEON THV” from 3M Company), a polymer of TFE, HFP, vinylidene fluoride, and perfluoropropyl vinyl ether (PPVE) (for example, available under the trade designation “3M DYNEON THVP” from 3M Company), a polyvinylidene fluoride (PVDF) (for example, “3M DYNEON PVDF 6008” available from 3M Company), an ethylene chlorotrifluoroethylene (ECTFE) polymer (for example, available under the trade designation “HALAR 350LC ECTFE” from Solvay, Brussels, Belgium), an ethylene tetrafluoroethylene (ETFE) (for example, available under the trade designation “3M DYNEON ETFE 6235” from 3M Company), a perfluoroalkoxy alkane (PF A) polymer, a fluorinated ethylene propylene (FEP) polymer, a polytetrafluoroethylene (PTFE), a polymer of TFE, HFP, and ethylene (for example, available under the trade designation “3M DYNEON HTE1705” from 3M Company), or various combinations thereof. In general, various combinations of fluoropolymers can be used. In some embodiments, the fluoropolymer includes FEP. In some embodiments, the fluoropolymer includes PFA.

[00135] Examples of suitable fluoropolymers include those available, for example, from 3M Company under the trade designations “3M DYNEON THV221GZ” (39 mol% tetrafluoroethylene, 11 mol% hexafluoropropylene, and 50 mol% vinylidene fluoride), “3M DYNEON THV2030GZ” (46.5 mol% tetrafluoroethylene, 16.5 mol% hexafluoropropylene, 35.5 mol% vinylidene fluoride, and 1.5 mol% perfluoropropyl vinyl ether), “3M DYNEON THV610GZ” (61 mol% tetrafluoroethylene, 10.5 mol% hexafluoropropylene, and 28.5 mol% vinylidene fluoride), and “3M DYNEON THV815GZ” (72.5 mol% tetrafluoroethylene, 7 mol% hexafluoropropylene, 19 mol% vinylidene fluoride, and 1.5 mol% perfluoropropyl vinyl ether). Examples of fluoropolymers also include PVDF available, for example, under the trade designations “3M DYNEON PVDF 6008” and “3M DYNEON PVDF 11010” from 3M Company; FEP available, for example, under the trade designation “3M DYNEON FLUOROPLASTIC FEP 6303Z” from 3M Company; ECTFE available, for example, under the trade designation “HALAR 350LC ECTFE” from Solvay; “NEOFLON EFEP” from Daikin Industries, Ltd., Osaka, Japan; “AFLAS” from Asahi Glass Co., Ltd., Tokyo, Japan; and copolymers of ethylene and tetrafluoroethylene available under the trade designations “DYNEON ET 6210A” and “DYNEON ET 6235” from Dyneon LLC; “TEFZEL ETFE” from E.I. duPont de Nemours and Co., Wilmington, DE; and “FLUON ETFE” by Asahi Glass Co., Ltd.

[00136] Har Coat Layer

[00137] In some embodiments, the broadband reflector optionally further comprises a siloxane hard coat disposed adjacent to the UV reflector or the UV-VIS reflector, the hard coat containing a UV absorber having an absorption band edge below 350 nm. A UV absorption band edge is defined as 50 percent absorption along the slope from 10 percent transmission to 90 percent transmission. A suitable siloxane hard coat includes silica filled siloxanes available, for example, from California Hard Coat, San Diego, Calif., under the trade designation “PERMA-NEW”, and from Momentive, Waterford, NY, under the trade designations “AS4000” and “AS4700”. Use of hard coats can, for example, reduce or prevent premature degradation of the broadband reflector due to exposure to outdoor elements. The hard coat is generally abrasion and impact resistant and does not interfere with the primary function of reflecting a selected bandwidth of electromagnetic radiation. In addition, siloxane components used as a durable top coat are hydrophobic in nature and can provide an easy clean surface function to the broadband reflectors disclosed herein.

[00138] UV absorbers (UVAs) and Hindered Amine Light Stabilizers (HALs) can intervene in the prevention of photo-oxidation degradation of the hard coat layer, as well as other layers of the broadband reflector (e.g., polymers such as PETs, PMMAs, and CoPMMAs). UVAs for incorporation into the hard coat layer includes benzophones, benzotriazoles, and benzotriazines. Exemplary UVAs for incorporation into the hard coat layer include those available under the trade designations “TINUVIN 1577” and “TINUVIN 1600,” from BASF Corporation, Florham Park, NJ. U.S. Pat. No. 9,670,300 (Olson et al.) and U.S. Pat. App. Pub. No. 2017/0198129 (Olson et al.) describe exemplary UVA oligomers that are compatible with PVDF fluoropolymers. Typically, UVAs are incorporated in the hard coat layer at a concentration of 1-10 wt.%.

Exemplary HALs for incorporation into the hard coat layer include those available under the trade designations “CHIMMASORB 944” and “TINUVIN 123,” from BASF Corporation. Typically, the HALs are incorporated into the hard coat layer at are 0.1-1.0 wt.%. A 10: 1 ratio of UVA to HALs can be optimum.

[00139] Antisoiling Layer

[00140] In some embodiments, the broadband reflector optionally further comprises an antisoiling layer disposed adjacent to a major surface of the UV reflector or UV-VIS reflector. The antisoiling layer is an outer layer. The antisoiling layer provides a degree of protection from soil accumulation on the surface that could impede the function of the broadband reflector (e.g., by absorbing solar radiation).

[00141] In some embodiments the optional antisoiling layer is a polymer fdm, preferably comprising one or more repellent polymers such as, for example, fluoropolymers. Examples of comonomers for making fluoropolymers that may be used include TFE, HFP, THV, PPVE. Exemplary fluoropolymers for use as the antisoiling layer include PVDF, ECTFE, ETFE, PFA, FEP, PTFE, HTE, and combinations thereof. In some embodiments, the fluoropolymer includes FEP. In some embodiments, the fluoropolymer includes PFA.

[00142] In some embodiments, the antisoiling layer is applied as a coating onto the UV reflector or UV-VIS reflector. Numerous applied antisoiling compositions are known in the art including, for example, those described in U.S Pat. Appln. Pubs. 2015/0175479 (Brown et al.), 2005/0233070 (Pellerite et al.), U.S Pat. No. 6,277,485 (Invie et al.), and WO 02/12404 (Uiu et al.)

[00143] Preferably, the protective layer or the antisoiling layer comprises ceramic or glass beads, ceramic or glass bubbles, crosslinked polymer beads, or combinations thereof. For example, ceramic or glass beads and/or ceramic or glass bubbles are hard particles that can be present on the surface (e.g., outer) layer to provide scratch resistance. In some embodiments, such beads and/or bubbles may even protrude from the surface as hemispheres or even quarter spheres.

[00144] Suitable glass beads for use include those commercially available from Potters Industries include the trade designation “EMB-20”. Silica microspheres (sometimes referred to as monodispersed silica powder) of the general type available from Fiber Optic Center, Inc. (New Bedford, MA) under the trade designation AngstromSphere may also be suitable. Potentially suitable ceramic microspheres are available under the trade designations “3M CERAMIC MICROSPHERES WHITE GRADE W-210”, “3M CERAMIC MICROSPHERES WHITE GRADE W-410”, “3M CERAMIC MICROSPHERES WHITE GRADE W-610” from 3M Company, or various combinations thereof. Potentially suitable inorganic particles also include any of the products available from 3M Company under the trade designation 3M GLASS BUBBLES (K, S, or iM Series). In general, various combinations of ceramic or glass beads and/or ceramic or glass bubbles of the same or different size may be used.

[00145] Suitable exemplary crosslinked polymer beads include for instance and without limitation, crosslinked polymer microspheres, such as the products available under the trade designations “CHEMISNOW” from Soken Chemical & Engineering Co., may be added to the antisoiling layer. Potentially suitable crosslinked polymer microspheres include products available from Soken Chemical & Engineering Co. under the trade designations “MX-500” and “MZ-5HN”. In some embodiments, semi-crystalline polymer beads, available under the trade designation “PTFE micropowder TF 9207Z” from 3M Company.

[00146] Transparent Adhesive Tie Layer

[00147] Suitable transparent adhesives for the one or more tie layers include for instance, pressure sensitive adhesives and hot melt adhesives. Classes of suitable pressure sensitive adhesives include acrylics, tackified rubber, tackified synthetic rubber, ethylene vinyl acetate and the like. Suitable acrylic adhesives are disclosed, for example, in U.S. Pat. Nos. 3,239,478 (Harlan); 3,935,338 (Robertson); 5,169,727 (Boardman); 4,952,650 (Y oung et al.) and 4,181,752 (Martens et al.), incorporated herein by reference. [00148] In select embodiments, the transparent adhesive is optically clear, which means that the adhesive has both transparency and clarity (e.g., low haze). In certain embodiments, an optically clear adhesive (OCA) is selected from an acrylate, a polyurethane, a polyolefin (such as a polyisobutylene (PIB)), a silicone, or a combination thereof. Illustrative OCAs include those described in International Pub. No. WO 2008/128073 (Everaerts et al.) relating to antistatic optically clear pressure sensitive adhesives, U.S. Pat. App. Pub. Nos. US 2009/089137 (Sherman et al.) relating to stretch releasing OCA, US 2009/0087629 (Everaerts et al.) relating to indium tin oxide compatible OCA, US 2010/0028564 (Cheng et al.) relating to antistatic optical constructions having optically transmissive adhesive, US 2010/0040842 (Everaerts et al.) relating to adhesives compatible with corrosion sensitive layers, US 2011/0126968 (Dolezal et al.) relating to optically clear stretch release adhesive tape, and U.S. Pat. No. 8,557,378 (Yamanaka et al.) relating to stretch release adhesive tapes. Suitable OCAs include acrylic optically clear pressure sensitive adhesives such as, for example, 3M OCA 8146, 8211, 8212, 8213, 8214, and 8215, each available from 3M Company, St. Paul, MN.

[00149] In some embodiments, the transparent adhesive may be resistant to ultraviolet radiation damage. Exemplary adhesives which are typically resistant to ultraviolet radiation damage include silicone adhesives and acrylic adhesives containing UV-stabilizing/blocking additive(s), for example. U.S Pat. No. 5,504,134 (Palmer et al.), for instance, 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 to about 0.2 micrometers (in some embodiments, about 0.01 micrometers to about 0.15 micrometers) in diameter. U.S. Pat. No. 5,876,688 (Laundon), describes a method for producing micronized zinc oxide that are small enough to be transparent when incorporated as UV blocking and/or scattering agents in paints, coatings, finishes, plastic articles, cosmetics and the like which are well suited for use in the present disclosure. These fine particles such as zinc oxide and titanium oxide with particle sizes ranging from 10 nm to 100 nm that can attenuate UV radiation are available, for example, from Kobo Products, Inc., South Plainfield, NJ.

[00150] A suitable hot melt adhesive includes the fluoropolymer THV (e.g., THV221 available as 3M DYNEON THV221 from 3M Company) as an alternative to the transparent adhesives described above. In particular, THV221 is resistant to UV degradation and can be hot melt extruded to act as a tie layer in broadband reflectors according to the present disclosure.

[00151] Polymeric Sheet Layer

[00152] Preferably, the polymeric sheet has a thickness of 1 to 10 millimeters. Exemplary polymeric sheets may be made of a material selected from the group consisting of polycarbonate, polyethyleneterephthalate glycol (PETG), acrylonitrile butadiene styrene (ABS), thermoplastic polyolefin (TPO), polypropylene, acrylic compounds, and mixtures thereof. One suitable polymeric sheet includes polycarbonate, such as Makrofol® polycarbonate sheets, available from Bayer AG (Darmstadt, Germany). An advantage to using a thick polymeric sheet is that it may provide a good base for thermoforming the broadband reflector into a nonplanar shape.

[00153] Outer Adhesive Layer

[00154] A radiative cooling article optionally includes an outer adhesive layer disposed adjacent to the IR reflector in a two-reflector construction or either the visible reflector or the IR reflector (whichever is not the middle reflector) in a three-reflector construction. The outer adhesive layer typically is used to attach the broadband reflector to a substrate (e.g., to form a composite cooling system). Suitable outer adhesive layers include pressure sensitive adhesives, hot melt adhesives, and air bleed adhesives. Adhesives that allow for air (or other fluid) to be released from between the adhesive layer and a substrate are well known in the art.

[00155] For example, micro-structured adhesive articles have been prepared by applying a flowable pressure sensitive adhesive to the surface of a microstructured release liner or the surface of a microstructured molding tool. The process results in the creation of an adhesive having a microstructured surface. When the resulting articles are dry laminated under pressure to substrates such as glass or polymer films, the microstructural features created in the adhesive surface allow air to escape from the bonding interface, thereby minimizing or preventing the formation of bubbles and pinholes.

[00156] During lamination, the microstructural features may flatten out and wet the substrate surface. Typically, applied pressure is used to collapse the structures during lamination and form the adhesive bond. However, this process introduces stresses into the adhesive as the adhesive relaxes and tries to return to its initial microstructured state. These stresses can create defects in the adhesive that adversely affect its adhesive and optical properties.

[00157] A variety of techniques have been used to prepare adhesive articles with microstructured surfaces. Typically, the adhesive surface is contacted to a structured tool or release liner to form a structured pattern in the adhesive layer. For example, in U.S. Pat. No. 6,315,651 (Mazurek et al.) microstructured pressure sensitive adhesives are formed by molding an adhesive layer against a microstructured tool or a microstructured liner, and in U.S. Patent Publication No. 2006/0188704 (Mikami et al.) fluid egress structures are formed in an adhesive surface by contacting the adhesive to a structured release tool or a structured release liner. Japanese Utility Model Publication 7- 29569 (Kawada et al.) describes forming a tack label for a container such as a bottle. The tack label is readily removable from the bottle surface by soaking the bottle in an aqueous solution, because the adhesive contains an uneven shape to form penetration channels permitting fluid entry to the bond line. The labels are formed by contacting an adhesive to a structured release liner, the release liner having been formed by embossing, and then contacting the label material to the exposed adhesive surface. Additionally, in U.S. Patent Publication No. 2007/0212635 (Sherman et al.), a structured adhesive surface is formed by pressing a microstructured tool or release liner to a crosslinked adhesive surface.

[00158] Another example of a temporary topography formed on an adhesive surface is disclosed in U.S. Pat. No. 5,268,228 (Orr). A double-sided adhesive-coated tape has fine grooves on one or both sides of the tape to facilitate air venting to minimize non-contact areas. The grooves in the tape are fine enough that, once the two surfaces to be bonded are in position, the grooves largely or completely disappear. Example 1 describes scribing lines through a protective sheet that placed grooves 70-150 micrometers deep in the underlying adhesive surface.

[00159] In Japanese Patent Publication 7-138541 (Shimizu), an adhesion process film is prepared with an embossing process to form fine continuous concave grooves.

[00160] In addition, several applications have been described in which microstructured adhesive layers have beads or pegs that protrude from the adhesive surface to make the adhesive surface positionable or repositionable upon contact with a substrate surface. U.S. Pat. No. 5,296,277 (Wilson et al.) describes such a system. U.S. Pat. No. 7,060,351 (Hannington), describes an adhesive article that provides air egress, by providing an area of no initial adhesion for the air to flow out from under the construction. In the article, a continuous layer of adhesive is adhered to a surface that has a plurality of spaced-apart non-adhesive material, and the non-adhesive material becomes embedded in the adhesive layer.

[00161] Representative examples of patents describing how an adhesive's topography is built from the interface between the adhesive and the release liner include U.S. Pat. Nos. 5,296,277 and 5,362,516 (both Wilson et al.) and 5,141,790 (Calhoun et al.). The principal topographical features in the adhesive surface are isolated protrusions from the adhesive surface with identified contact areas.

[00162] An example of atemporary topography formed on an adhesive surface is disclosed in U.S. Pat. Nos. 5,344,681 and 5,449,540 (both Calhoun et al.). A segmented pressure-sensitive adhesive transfer tape is designed to prevent lateral flow of the adhesive prior to transfer but allows flow after transfer to form a continuous adhesive bond. The small adhesive segments have controllable thickness. An adhesive transfer tape comprises: a carrier with two opposed surfaces with one containing a series of recesses and the other being relatively smooth; a pressure sensitive adhesive being present in the recesses which are surrounded by an adhesive free area such that when the tape is wound about itself with the surfaces contacting and then unwound, adhesive transfers from the one surface to the other. Preferably, the recesses are formed by embossing and are in spacedapart relationship. Preferably, they are oval, circular, polygonal or rectangular in cross section. Preferably, the adhesive is acrylic or rubber resin, pressure sensitive.

[00163] Any of the adhesive layers described above may be suitable for use with the (e.g., radiative cooling) broadband reflector article.

Exemplary Embodiments

[00164] In a first embodiment, the present disclosure provides a broadband reflector. The broadband reflector comprises a multilayer optical film comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 90 percent of incident light over at least a wavelength range from 400 nanometers (nm) to 2000 nm or from 350 nm to 2500 nm. The broadband reflector is essentially free of metal.

[00165] In a second embodiment, the present disclosure provides a broadband reflector according to the first embodiment, wherein the multilayer optical film comprises a UV-VIS reflector and an IR reflector. The UV-VIS reflector is comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 350 nm to 400 nm and an average of at least 95 percent of incident light over at least a wavelength range from 400 nm to 800 nm. The visible reflector is comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 90 percent of incident light over at least a wavelength range from 0.8 micrometers to 2.0 micrometers.

[00166] In a third embodiment, the present disclosure provides a broadband reflector according to the second embodiment, wherein the polymeric optical layers of the UV-VIS reflector comprise alternating layers of a polyethylene terephthalate (PET) and a blend of a polyvinylidene fluoride (PVDF) and a polymethyl methacrylate (PMMA).

[00167] In a fourth embodiment, the present disclosure provides a broadband reflector according to the first embodiment, wherein the multilayer optical film comprises a UV reflector, a visible reflector, and an IR reflector. The UV reflector is comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 350 nanometers (nm) to 400 nm. The visible reflector is comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 400 nm to 800 nm. The IR reflector is comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 90 percent of incident light over at least a wavelength range from 0.8 micrometers to 2.0 micrometers.

[00168] In a fifth embodiment, the present disclosure provides a broadband reflector according to any of the second through fourth embodiments, wherein the polymeric optical layers of at least one of the UV reflector, the visible reflector, the UV-VIS reflector, or the IR reflector comprise a fluoropolymer independently selected from the group consisting of a copolymer of tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and vinylidene fluoride; a copolymer of TFE, HFP, vinylidene fluoride, and perfluoropropyl vinyl ether (PPVE); a polyvinylidene fluoride (PVDF); an ethylene chlorotrifluoroethylene (ECTFE) polymer; an ethylene tetrafluoroethylene (ETFE); a perfluoroalkoxy alkane (PF A) polymer; a fluorinated ethylene propylene (FEP) polymer; a polytetrafluoroethylene (PTFE); a copolymer of TFE, HFP, and ethylene; and combinations thereof.

[00169] In a sixth embodiment, the present disclosure provides a broadband reflector according to the fourth embodiment or the fifth embodiment, wherein the polymeric optical layers of the UV reflector comprise a PMMA or CoPMMA high refractive index first optical layer in the plurality of first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 350 nm to 400 nm.

[00170] In a seventh embodiment, the present disclosure provides a broadband reflector according to the fourth embodiment or the fifth embodiment, wherein the polymeric optical layers of the UV reflector comprise a fluoropolymer, a polymethyl methacrylate (PMMA), a copolymer of ethyl acrylate and methyl methacrylate (CoPMMA), or combinations thereof.

[00171] In an eighth embodiment, the present disclosure provides a broadband reflector according to any of the fourth through seventh embodiments, wherein the polymeric optical layers of the UV reflector comprise alternating layers of a copolymer of ethyl acrylate and methyl methacrylate (CoPMMA) and a copolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride (THV).

[00172] In a ninth embodiment, the present disclosure provides a broadband reflector according to any of the fourth through eighth embodiments, wherein the polymeric optical layers of the visible reflector comprise a PET high refractive index first optical layer in a plurality of first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 400 nm to 600 nm.

[00173] In a tenth embodiment, the present disclosure provides a broadband reflector according to the any of the fourth through ninth embodiments, wherein the polymeric optical layers of the visible reflector comprise a fluoropolymer, a polyethylene terephthalate (PET), CoPMMA, a polypropylene (PP), a polyethylene (PE), a polyethylene copolymer, PMMA, an acrylate copolymer, a polyurethane, or combinations thereof.

[00174] In an eleventh embodiment, the present disclosure provides a broadband reflector according to the any of the fourth through tenth embodiments, wherein the polymeric optical layers of the visible reflector comprise alternating layers of a PET and a THV.

[00175] In a twelfth embodiment, the present disclosure provides a broadband reflector according to the any of the fifth, seventh, eighth, tenth, or eleventh embodiments, wherein the THV comprises a copolymer comprising 24 to 47 mole % of tetrafluoroethylene monomers, 5 to 23 mole % of hexafluoropropylene monomers, and 35 to 70 mole % of vinylidene fluoride monomers, wherein at least a portion of end groups on the copolymer are nonacidic.

[00176] In a thirteenth embodiment, the present disclosure provides a broadband reflector according to the any of the eighth or tenth through twelfth embodiments, wherein the THV further comprises a calcium carbonate additive.

[00177] In a fourteenth embodiment, the present disclosure provides a broadband reflector according to the thirteenth embodiment, wherein the calcium carbonate additive comprises nanocalcium carbonate particles having an average diameter of less than 100 nm.

[00178] In a fifteenth embodiment, the present disclosure provides a broadband reflector according to any of the second through fourteenth embodiments, wherein the polymeric optical layers of the infrared reflector comprise a fluoropolymer, a polyethylene naphthalate (PEN), a polyethylene terephthalate (PET), CoPMMA, a polypropylene (PP), a polyethylene (PE), a polyethylene copolymer, PMMA, an acrylate copolymer, a polyurethane, or combinations thereof.

[00179] In a sixteenth embodiment, the present disclosure provides a broadband reflector according to any of the fourth through fifteenth embodiments, wherein the visible reflector is disposed between the UV reflector and the IR reflector and the polymeric optical layers of the IR reflector comprise a PEN high refractive index first optical layer in a plurality of first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 600 nm to 2000 nm.

[00180] In a seventeenth embodiment, the present disclosure provides a broadband reflector according to any of the fourth through sixteenth embodiments, wherein the visible reflector is disposed between the UV reflector and the IR reflector and the polymeric optical layers of the IR reflector comprise alternating layers of PEN and PMMA.

[00181] In an eighteenth embodiment, the present disclosure provides a broadband reflector according to the seventeenth embodiment, wherein the PMMA is blended with PVDF.

[00182] In a nineteenth embodiment, the present disclosure provides a broadband reflector according to any of the first through eighteenth embodiments, wherein the broadband reflector absorbs an average of at least 60, 70, 80, 90, or 95 percent of incident light over at least a wavelength range from 3.0 micrometers to 20 micrometers or 8 micrometers to 13 micrometers.

[00183] In a twentieth embodiment, the present disclosure provides a broadband reflector according to any of the second through nineteenth embodiments, wherein the UV reflector or the UV-VIS reflector reflects an average of at least 95 percent of incident light over at least a wavelength range from 300 nm to 400 nm.

[00184] In a twenty-first embodiment, the present disclosure provides a broadband reflector according to any of the second through fourteenth embodiments, further comprising a transparent adhesive layer or a hot melt THV layer attached to at least one of the UV reflector, the visible reflector, the UV-VIS reflector, or the IR reflector.

[00185] In a twenty-second embodiment, the present disclosure provides a broadband reflector according to any of the second through twenty-first embodiments, further comprising a protective layer comprising a fluoropolymer, the protective layer being an outer layer disposed adjacent to the UV reflector or the UV-VIS reflector. [00186] In a twenty-third embodiment, the present disclosure provides a broadband reflector according to any of the second through twenty-first embodiments, further comprising an antisoiling layer disposed adjacent to the UV reflector or the UV-VIS reflector, wherein the antisoiling layer is an outer layer.

[00187] In a twenty-fourth embodiment, the present disclosure provides a broadband reflector according to the twenty-second embodiment or twenty-third embodiment, wherein the protective layer or the antisoiling layer further comprises ceramic or glass beads, ceramic or glass bubbles, crosslinked polymer beads, or combinations thereof.

[00188] In a twenty-fifth embodiment, the present disclosure provides a broadband reflector according to any of the second through twenty-fourth embodiments, further comprising a polymeric sheet attached to the IR reflector, the polymeric sheet having a thickness of 1 to 10 millimeters.

[00189] In a twenty-sixth embodiment, the present disclosure provides a broadband reflector according to any of the fourth through twenty-fifth embodiments, wherein each of the UV reflector, the visible reflector, and the IR reflector comprises 300 to 2000 alternating first and second polymeric optical layers.

[00190] In a twenty-seventh embodiment, the present disclosure provides a broadband reflector according to any of the fourth through twenty-sixth embodiments, wherein the UV reflector has an average thickness of 15 micrometers to 50 micrometers, the visible reflector has an average thickness of 25 micrometers to 75 micrometers, and the IR reflector has an average thickness of 75 micrometers to 150 micrometers.

[00191] In a twenty-eighth embodiment, the present disclosure provides a broadband reflector according to any of the second through twenty-seventh embodiments, wherein the IR reflector reflects an average of at least 90 percent of incident light over at least a wavelength range from 0.8 micrometers to 2.5 micrometers.

[00192] In a twenty-ninth embodiment, the present disclosure provides a broadband reflector according to any of the second through twenty-eighth embodiments, further comprising a siloxane hard coat disposed adjacent to the UV reflector or the UV-VIS reflector, the hard coat containing a UV absorber having an absorption band edge below 350 nm.

[00193] In a thirtieth embodiment, the present disclosure provides a broadband reflector according to any of the first through twenty-ninth embodiments, having a nonplanar shape. [00194] In a thirty-first embodiment, the present disclosure provides a broadband reflector according to any of the first through thirtieth embodiments, wherein the broadband reflector absorbs an average of at least 60, 70, 80, 90, or 95 percent of incident light over at least a wavelength range from 8.0 micrometers to 13 micrometers.

[00195] In a thirty-second embodiment, the present disclosure provides a broadband reflector according to the thirty-first embodiment, wherein the broadband reflector is capable of subambient cooling under direct solar irradiation.

[00196] In a thirty-third embodiment, the present disclosure provides a broadband reflector according to any of the first through thirty-second embodiments, wherein the broadband reflector absorbs an average of at least 60, 70, 80, 90, or 95 percent of incident light over at least a wavelength range from 4.0 micrometers to 20 micrometers and is capable of above ambient cooling under direct solar irradiation.

[00197] In a thirty-fourth embodiment, the present disclosure provides a broadband reflector according to any of the first through thirty-third embodiments, wherein, at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, the multilayer optical film provides a 1^st order reflection band, a 2^nd order reflection band, and optionally a 3^rd order reflection band, wherein the 2^nd order reflection band substantially overlaps at least one of the 1^st and 3^rd order reflection bands to form a single wide reflection band.

[00198] In a thirty-fifth embodiment, the present disclosure provides a composite cooling system. The composite cooling system comprises the broadband reflector of any of the first through thirtyfourth embodiments attached to a roof and/or at least one side of a vehicle.

[00199] In a thirty-sixth embodiment, the present disclosure provides a composite cooling system. The composite cooling system comprises the broadband reflector of any of the first through thirtyfourth embodiments attached to a modular data center.

[00200] In a thirty-seventh embodiment, the present disclosure provides a composite cooling system. The composite cooling system comprises the broadband reflector of any of the first through thirty-fourth embodiments attached to at least one surface of a building or a shelter.

[00201] Advantages and embodiments of this invention are further illustrated by the following 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 invention. All parts and percentages are by weight unless otherwise indicated. Examples

[00202] Preparative Example 1 - MOF UV Mirror Film made with THV LIO

[00203] An ultra-violet (UV) light reflecting multilayer optical mirror film was made with first optical layers created from CoPMMA (available under the tradename “CA24” from Arkema) and second optical layers created from fluoropolymer (available under the tradename “THV255” from 3M Company). The CoPMMA and THV255 were coextruded through a multilayer polymer melt manifold to form a stack of 325 optical layers. The optical layer thickness profile of this UV reflecting mirror film was adjusted to be approximately a linear profile with the first (thinnest) optical layers adjusted to have about a ! wave optical thickness (refractive index times physical thickness) for 340 nm light and progressing to the thickest optical layers which were adjusted to have about a ! wave optical thickness for 400 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.

[00204] In addition to these optical layers, non-optical skin layers were formed, of PET having a thickness of 100 micrometers on one side of the optical layer stack and a 50:50 polymer blend of PVDF:PMMA also having a thickness of 100 micrometers on the other side of the optical layer stack. This multilayer coextruded polymer melt flow was cast onto a chilled roll at 22 meters per minute creating a multilayer cast film approximately 600 micrometers thick. The multilayer cast film was then preheated to a temperature of 95 °C and length oriented at a draw ratio of 3.5: 1, followed by preheating to 100 °C and transversely oriented in a tenter oven at a draw ratio of 3.8 : 1. The biaxially oriented multilayer optical film was further heated to 125 °C for 10 seconds to anneal the PET layers. The resulting UV reflecting mirror film was measured with a Lambda 1050 spectrophotometer to have an average reflectivity of 95% over a wavelength range of 340 nm to 400 nm.

[00205] Preparative Example 2 - MOF UV-VIS Mirror Film made with THV LIO

[00206] An ultraviolet (UV) and visible (VIS) light reflecting multilayer optical mirror film was made simultaneously with two multilayer polymer melt manifolds creating two optical packets each having 325 optical layers. The first optical layer packet was made with first optical layers created from CoPMMA (available under the tradename “CA24” from Arkema) and second optical layers created from a fluoropolymer (available under the tradename “THV255” from 3M Company). The second optical layer packet was made with third optical layers created from PET (available under the tradename “Eastapak 7452” available from Eastman) and fourth optical layers created from the same fluoropolymer (available under the tradename “THV255” from 3M Company). The CoPMMA, THV255, and PET were coextruded through a multilayer polymer melt manifold to form a stack of 650 optical layers. The optical layer thickness profde of this VIS and IR reflecting mirror fdm was adjusted to be approximately a linear profile with the first (thinnest) optical layers adjusted to have about a ! wave optical thickness (refractive index times physical thickness) for 350 nm light and progressing to the thickest optical layers which were adjusted to have about a ! wave 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.

[00207] In addition to these optical layers, non-optical skin layers were formed, of PET having a thickness of 100 micrometers on one side of the optical layer stack and a 50:50 polymer blend of PVDF:PMMA also having a thickness of 100 micrometers on the other side of the optical layer stack. This multilayer coextruded polymer melt flow was cast onto a chilled roll at 22 meters per minute creating a multilayer cast film approximately 1200 micrometers thick. The multilayer cast film was then preheated to a temperature of 95 °C and length oriented at a draw ratio of 3.5: 1 followed by preheating to 100 °C and transversely oriented in a tenter oven at a draw ratio of 3.8 : 1. The biaxially oriented multilayer optical film was further heated to 225 °C for 10 seconds to anneal the PET layers. The resulting VIS and IR reflecting mirror film was measured with a Lambda 1050 spectrophotometer to have an average reflectivity of 98% over a wavelength range of 350 nm to 800 nm.

[00208] Preparative Example 3 - MOF UV-VIS-near IR Mirror Film made with PVDF/PMMA LIO

[00209] An ultraviolet (UV), visible (VIS), and near infrared (IR) light reflecting multilayer optical mirror film was made with first optical layers created from PET (available under the tradename “Eastapak 7452” available from Eastman) and second optical layers created from a 50:50 polymer blend of PVDF (available under the tradename “PVDF 6008” from 3M Company) and PMMA (available under the tradename “VO44” from Arkema). The PET and 50:50 PVDF: PMMA polymer blend were coextruded through a multilayer polymer melt manifold to form a stack of 650 optical layers. The optical layer thickness profile of this VIS and IR reflecting mirror film was adjusted to be approximately a linear profile with the first (thinnest) optical layers adjusted to have about a ! wave optical thickness (refractive index times physical thickness) for 370 nm light and progressing to the thickest optical layers which were adjusted to have about a ! wave optical thickness for 950 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.

[00210] In addition to these optical layers, non-optical skin layers were formed, of PET having a thickness of 100 micrometers on one side of the optical layer stack and a 35:65 polymer blend of PVDF:PMMA also having a thickness of 100 micrometers on the other side of the optical layer stack. This multilayer coextruded polymer melt flow was cast onto a chilled roll at 22 meters per minute creating a multilayer cast film approximately 1400 micrometers thick. The multilayer cast film was then preheated to a temperature of 95 °C and length oriented at a draw ratio of 3.5: 1 followed by preheating to 100 °C and transversely oriented in a tenter oven at a draw ratio of 3.8 : 1. The biaxially oriented multilayer optical film was further heated to 225 °C for 10 seconds to anneal the PET layers. The resulting VIS and IR reflecting mirror film was measured with a Lambda 1050 spectrophotometer to have an average reflectivity of 98% over a wavelength range of 370 nm to 950 nm.

[00211] Preparative Example 4 - Broadband Infrared Mirror Film

[00212] An infrared (IR) light reflecting multilayer optical mirror film was made with first optical layers created from PEN (available from 3M Company) and second optical layers created from PMMA (available under the tradename “VO44” from Arkema). The PEN and PMMA were coextruded through a multilayer polymer melt manifold to form a stack of 650 optical layers. The optical layer thickness profile of this IR reflecting mirror film was adjusted to be approximately a linear profile with the first (thinnest) optical layers adjusted to have about a ! wave optical thickness (refractive index times physical thickness) for 700 nm light and progressing to the thickest optical layers which were adjusted to have about a ! wave optical thickness for 2200 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.

[00213] In addition to these optical layers, non-optical protective boundary layers of PEN having a thickness of 10 micrometers were coextruded on both sides of the optical layer stack. This multilayer coextruded polymer melt flow was cast onto a chilled roll at 5.56 meters per minute creating a multilayer cast film approximately 1778 micrometers thick. The multilayer cast film was then preheated to a temperature of 135 °C and length oriented at a draw ratio of 3.5: 1 followed by preheating to 140 °C and transversely oriented in a tenter oven at a draw ratio of 3.8: 1 to a final film thickness of 129.5 micrometers. The biaxially oriented multilayer optical film was further heated to 240 °C for 10 seconds to anneal the PEN layers. The resulting IR reflecting mirror film was measured with a Lambda 1050 spectrophotometer to have an average reflectivity of 96% over a wavelength range of 700 nm to 2200 nm.

[00214] Example 5 - Passive Radiative Cooling Film (PRCF)

[00215] UV-Visible light reflecting mirror film described in Preparative Example 2 was laminated to broadband infrared reflecting mirror film described in Preparative Example 4 with OCA8171 optically clear adhesive to create a broadband solar mirror film useful for passive radiative cooling of surfaces. Reflection spectrum of this broadband solar mirror film measured with a Lambda 1050 spectrophotometer is shown in FIG. 8. In FIG. 8, Films 1, 2, and 3 are repeat cross web measurements. Solar reflectivity as measured with a Surface Optics 41 Oi reflectometer was measured to be 0.98. Infrared emissivity as measured with a Surface Optics ET100 was measured to be 0.91.

[00216] Example 6 - Passive Radiative Cooling Film

[00217] UV-Visible light reflecting mirror film described in Preparative Example 3 was laminated to broadband infrared reflecting mirror film described in Preparative Example 4 with OCA8171 optically clear adhesive to create a broadband solar mirror film useful for passive radiative cooling of surfaces. Solar reflectivity as measured with a Surface Optics 41 Oi reflectometer was measured to be 0.97. Infrared emissivity as measured with a Surface Optics ET100 was measured to be 0.90.

[00218] Example 7 - Passive Radiative Cooling Film

[00219] UV light reflecting mirror film described in Preparative Example 1 was laminated to UV- Visible light reflecting mirror film described in Preparative Example 3 and also laminated to broadband infrared reflecting mirror film described in Preparative Example 4 with OCA8171 optically clear adhesive to create a broadband solar mirror film useful for passive radiative cooling of surfaces. Solar reflectivity as measured with a Surface Optics 41 Oi reflectometer was measured to be 0.98. Infrared emissivity as measured with a Surface Optics ET100 was measured to be 0.93.

[00220] Prophetic Examples - Modeled

[00221] The 4x4 matrix method using the Berreman algorithm was used for modeling the spectra of constructive and destructive interference generated from layer interfaces of materials having different refractive indices. The Berreman 4x4 matrix methodology is described in the Journal of the Optical Society of America (Volume 62, Number 4, April 1972) and the Journal of Applied Physics (Volume 85, Number 6, March 1999), the disclosures of which are incorporated herein by reference. Input parameters for this optical model were individual layer refractive indices, layer thicknesses, number of layers, and reflection bandwidth including a left band edge and a right band edge. The Berreman methodology calculates the percent light reflected at each layer interface and the percent light transmitted at each layer interface and outputs a reflection spectra and transmission spectra.

[00222] Modeled Example 8 - UV Mirror Protected PEN-Based Broadband Mirror (0.75 F-Ratio)

[00223] A multilayer optical film was designed and modeled as illustrated in FIG. 9. In this figure, “BF” represents the block factor, which is the ratio of thickest layer in the packet divided by the thinnest layer in the packet. The resulting reflection band (i.e., Composite Stack) is shown in FIG. 10. Also shown is “Normalized AMI.5 Global”, which is a representation of solar energy to be reflected, where more reflected energy is correlated to better cooling performance. “AM” is an abbreviation of “air mass”, which is the amount of air mass the sun’s energy must pass through before reaching the earth’s surface. “AM 1.0” represents the sun directly overhead, where sunlight passes through less air in the earth’s atmosphere. This is used to characterize solar energy at sea level near the equator. “AMI .5”, used herein, represents the solar energy close to 45-degrees latitude, where the sunlight passes through more of the atmosphere. “Global” takes into account that sunlight reflects off other objects on the earth (as opposed to only direct energy from the sun). The AMI.5 curve was normalized by maximum energy to be scaled between 0% and 100% energy. The data for the AMI.5 curve are from the ASTM G-173-03 standard.

[00224] The stack consisted of three packets of alternating low and high-index polymer layers. The first packet used 112 optical repeat units (ORU), in which an ORU consists of one low refractive index material and one high refractive index material. The low-index material was represented by the dispersion profile with respect to wavelength of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride (THV). The high-index material was represented by the dispersion profile of polymethyl methacrylate (PMMA). The layer profile for this packet started at 57.6 nm and ended at 74.9 nm with the ORUs equally distributed across this range. The individual layer thickness was quantified by the average physical thickness of the two layers within the ORU. To maximize reflectivity in this packet an F-Ratio of 0.5 was used, meaning the physical thickness weighted by the refractive index of the material should be equal for the high- index and low-index material. It was assumed to have a 1 micrometer thick “boundary layer” of PMMA dispersed on both sides of the stack (as part of the multilayer optical film), since this arrangement is common with extruded polymeric multilayer stacks.

[00225] The second packet used 112 optical repeat units (ORU), in which an ORU consists of one low refractive index material and one high refractive index material. The low-index material was represented by the dispersion profile with respect to wavelength of a 50:50 blend by weight of polymethyl methacrylate (PMMA) and poly vinylidene fluoride (PVDF). The high-index material was represented by the dispersion profile of polyester (PET). The layer profile for this packet started at 68.6 nm and ended at 96.1 nm with the ORUs equally distributed across this range. The individual layer thickness was quantified by the average physical thickness of the two layers within the ORU. To maximize reflectivity in this packet an F-Ratio of 0.5 was used, meaning the physical thickness weighted by the refractive index of the material should be equal for the high- index and low-index material. It was assumed to have a 1 micrometer thick “boundary layer” of PET dispersed on both sides of the stack (as part of the multilayer optical film).

[00226] The third packet used 325 optical repeat units (ORU), in which an ORU consists of one low refractive index material and one high refractive index material. The low-index material was represented by the dispersion profile with respect to wavelength of polymethyl methacrylate (PMMA). The high-index material was represented by the dispersion profile of polyethylene naphthalate (PEN). The layer profile for this packet can be described by a 3^rd order polynomial equation. The equation for the polynomial is shown in Equation 2 (Eqn 2) where “d” is the physical layer thickness and “n” is the layer number from 1 to 650. This profile can also be referenced in FIG. 9 for the “PEN/PMMA” packet. To maximize reflectivity in this packet an F- Ratio of 0.75 was used, meaning the high-index material weighted by the refractive index should make up 75% of the total thickness of the ORU. The low-index materials weighted by the refractive index makes up the remaining 25% of the total thickness of the ORU. By using an F- Ratio not equal to 0.5 all even-order harmonics were not fully suppressed. Instead, the higher order harmonics were leveraged to increase reflectivity across a broader wavelength range. It was assumed to have a 1 micrometer thick “boundary layer” of PEN dispersed on both sides of the stack (as part of the multilayer optical film). d = -5.02 ■ 10^-9n³ + 1.536 ■ 10“⁴n² + 0.2184n + 172.12 (Eqn 2)

[00227] The total number of optically active microlayers was 1098 layers. Including the “boundary layers” the total layer count was 1104 layers. Because of the dissimilar material pairs within the individual optical packets, each packet would either be coextruded and oriented separate or in combination with one another. If coextruded separately the packets would be laminated together with an optically clear adhesive. In the final construction the “PMMA/THV” packet will be the closest packet to the sun for UV protection. An air interface was assumed at the outer surface of the entire construction in the model.

[00228] Modeled Example 9 - PET-Based Mirror with UV Absorber Protected PEN-Based Broadband Mirror (0.75 F-Ratio) [00229] A multilayer optical film was designed and modeled as illustrated in FIG. 11. In this figure “BF” represents the block factor, which is the ratio of thickest layer in the packet divided by the thinnest layer in the packet. The resulting reflection band is shown in FIG. 12. The stack consisted of two packets of alternating low and high-index polymer layers. The first packet used 212 optical repeat units (ORU), in which an ORU consists of one low refractive index material and one high refractive index material. The low-index material was represented by the dispersion profile with respect to wavelength of a 50:50 blend by weight of polymethyl methacrylate (PMMA) and poly vinylidene fluoride (PVDF). The high-index material was represented by the dispersion profile of polyester (PET). The layer profile for this packet started at 55.9 nm and ended at 92.2 nm with the ORUs equally distributed across this range. The individual layer thickness was quantified by the average physical thickness of the two layers within the ORU. To maximize reflectivity in this packet an F-Ratio of 0.5 was used, meaning the physical thickness weighted by the refractive index of the material should be equal for the high-index and low-index material. It was assumed to have a 1 micrometer thick “boundary layer” of PET dispersed on both sides of the stack (as part of the multilayer optical film), since this arrangement is common with extruded polymeric multilayer stacks. Because PET degrades when exposed to UV light a UV absorber was modeled in this packet. A combination of Tinuvin 460 and Tinuvin 477 can be used to protect up to 380 nm. This was included in the 1 micrometer “boundary layer” which is the closest layer to the sun.

[00230] The second packet used 325 optical repeat units (ORU), in which an ORU consists of one low refractive index material and one high refractive index material. The low-index material was represented by the dispersion profile with respect to wavelength of polymethyl methacrylate (PMMA). The high-index material was represented by the dispersion profile of polyethylene naphthalate (PEN). The layer profile for this packet can be described by a 3^rd order polynomial equation. The equation for the polynomial is shown in Equation 3 (Eqn 3) where “d” is the physical layer thickness and “n” is the layer number from 1 to 650. This profile can also be referenced in FIG. 11 for the “PEN/PMMA” packet. To maximize reflectivity in this packet an F- Ratio of 0.75 was used, meaning the high-index material weighted by the refractive index should make up 75% of the total thickness of the ORU. The low-index materials weighted by the refractive index makes up the remaining 25% of the total thickness of the ORU. By using an F- Ratio not equal to 0.5 all even-order harmonics were not fully suppressed. Instead, the higher order harmonics were leveraged to increase reflectivity across a broader wavelength range. It was assumed to have a 1 micrometer thick “boundary layer” of PEN dispersed on both sides of the stack (as part of the multilayer optical film). d = -5.02 ■ 10^-9n³ + 1.536 ■ 10“⁴n² + 0.2184n + 172.12 (Eqn 3)

[00231] The total number of optically active microlayers was 1074 layers. Including the “boundary layers” the total layer count was 1080 layers. An air interface was assumed at the outer major surface of each skin layer. Because of the dissimilar material pairs within the individual optical packets, each packet would either be coextruded and oriented separate or in combination with one another. If coextruded separately the packets would be laminated together with an optically clear adhesive. In the final construction the UV absorber will be the closest layer to the sun for UV protection. An air interface was assumed at the outer surface of the entire construction in the model.

[00232] Modeled Example 10 - UV Mirror Protected PEN-Based Broadband Mirror (0.5 F-Ratio)

[00233] A multilayer optical film was designed and modeled as illustrated in FIG. 13. In this figure “BF” represents the block factor, which is the ratio of thickest layer in the packet divided by the thinnest layer in the packet. The resulting reflection band is shown in FIG. 14. The stack consisted of three packets of alternating low and high-index polymer layers. The first packet used 112 optical repeat units (ORU), in which an ORU consists of one low refractive index material and one high refractive index material. The low-index material was represented by the dispersion profile with respect to wavelength of tetrafluoroethylene, hexafluoropropylene and vinylidene fluoride (THV). The high-index material was represented by the dispersion profile of polymethyl methacrylate (PMMA). The layer profile for this packet started at 57.6 nm and ended at 74.9 nm with the ORUs equally distributed across this range. The individual layer thickness was quantified by the average physical thickness of the two layers within the ORU. To maximize reflectivity in this packet an F-Ratio of 0.5 was used, meaning the physical thickness weighted by the refractive index of the material should be equal for the high-index and low-index material. It was assumed to have a 1 micrometer thick “boundary layer” of PMMA dispersed on both sides of the stack (as part of the multilayer optical film), since this arrangement is common with extruded polymeric multilayer stacks.

[00234] The second packet used 112 optical repeat units (ORU), in which an ORU consists of one low refractive index material and one high refractive index material. The low-index material was represented by the dispersion profile with respect to wavelength of a 50:50 blend by weight of polymethyl methacrylate (PMMA) and poly vinylidene fluoride (PVDF). The high-index material was represented by the dispersion profile of polyester (PET). The layer profile for this packet started at 68.6 nm and ended at 96.1 nm with the ORUs equally distributed across this range. The individual layer thickness was quantified by the average physical thickness of the two layers within the ORU. To maximize reflectivity in this packet an F-Ratio of 0.5 was used, meaning the physical thickness weighted by the refractive index of the material should be equal for the high- index and low-index material. It was assumed to have a 1 micrometer thick “boundary layer” of PET dispersed on both sides of the stack (as part of the multilayer optical film).

[00235] The third packet used 325 optical repeat units (ORU), in which an ORU consists of one low refractive index material and one high refractive index material. The low-index material was represented by the dispersion profile with respect to wavelength of polymethyl methacrylate (PMMA). The high-index material was represented by the dispersion profile of polyethylene naphthalate (PEN). The layer profile for this packet can be described by a 3^rd order polynomial equation. The equation for the polynomial is shown in Equation 4 (Eqn 4) where “d” is the physical layer thickness and “n” is the layer number from 1 to 650. This profile can also be referenced in FIG. 13 for the “PEN/PMMA” packet. To maximize reflectivity in this packet an F- Ratio of 0.5 was used, meaning the physical thickness weighted by the refractive index of the material should be equal for the high-index and low-index material. It was assumed to have a 1 micrometer thick “boundary layer” of PEN dispersed on both sides of the stack (as part of the multilayer optical film). d = 2.01 ■ 10^-7n³ + 2.34 ■ 10“⁴n² + 0.0.2258n + 88.35 (Eqn 4)

[00236] The total number of optically active microlayers was 1098 layers. Including the “boundary layers” the total layer count was 1104 layers. Because of the dissimilar material pairs within the individual optical packets, each packet would either be coextruded and oriented separate or in combination with one another. If coextruded separately the packets would be laminated together with an optically clear adhesive. In the final construction the “PMMA/THV” packet will be the closest packet to the sun for UV protection. An air interface was assumed at the outer surface of the entire construction in the model.

[00237] Modeled Example 11 - PET-Based Mirror with UV Absorber Protected PEN-Based Broadband Mirror (0.5 F-Ratio)

[00238] A multilayer optical film was designed and modeled as illustrated in FIG. 15. In this figure “BF” represents the block factor, which is the ratio of thickest layer in the packet divided by the thinnest layer in the packet. The resulting reflection band is shown in FIG. 16. The stack consisted of two packets of alternating low and high-index polymer layers. The first packet used 212 optical repeat units (ORU), in which an ORU consists of one low refractive index material and one high refractive index material. The low-index material was represented by the dispersion profile with respect to wavelength of a 50:50 blend by weight of polymethyl methacrylate (PMMA) and poly vinylidene fluoride (PVDF). The high-index material was represented by the dispersion profile of polyester (PET). The layer profile for this packet started at 55.9 nm and ended at 92.2 nm with the ORUs equally distributed across this range. The individual layer thickness was quantified by the average physical thickness of the two layers within the ORU. To maximize reflectivity in this packet an F-Ratio of 0.5 was used, meaning the physical thickness weighted by the refractive index of the material should be equal for the high-index and low-index material. It was assumed to have a 1 micrometer thick “boundary layer” of PET dispersed on both sides of the stack (as part of the multilayer optical film), since this arrangement is common with extruded polymeric multilayer stacks. Because PET degrades when exposed to UV light a UV absorber was modeled in this packet. A combination of Tinuvin 460 and Tinuvin 477 can be used to protect up to 380 nm. This was included in the 1 micrometer “boundary layer” which is the closest layer to the sun.

[00239] The second packet used 325 optical repeat units (ORU), in which an ORU consists of one low refractive index material and one high refractive index material. The low-index material was represented by the dispersion profile with respect to wavelength of polymethyl methacrylate (PMMA). The high-index material was represented by the dispersion profile of polyethylene naphthalate (PEN). The layer profile for this packet can be described by a 3^rd order polynomial equation. The equation for the polynomial is shown in Equation 5 (Eqn 5) where “d” is the physical layer thickness and “n” is the layer number from 1 to 650. This profile can also be referenced in FIG. 16 for the “PEN/PMMA” packet. To maximize reflectivity in this packet an F- Ratio of 0.5 was used, meaning the physical thickness weighted by the refractive index of the material should be equal for the high-index and low-index material. It was assumed to have a 1 micrometer thick “boundary layer” of PEN dispersed on both sides of the stack (as part of the multilayer optical film). d = 2.01 ■ 10^-7n³ + 2.34 ■ 10^-4n² + 0.0.2258n + 88.35 (Eqn 5)

[00240] The total number of optically active microlayers was 1074 layers. Including the “boundary layers” the total layer count was 1080 layers. An air interface was assumed at the outer major surface of each skin layer. Because of the dissimilar material pairs within the individual optical packets, each packet would either be coextruded and oriented separate or in combination with one another. If coextruded separately the packets would be laminated together with an optically clear adhesive. In the final construction the UV absorber will be the closest layer to the sun for UV protection. An air interface was assumed at the outer surface of the entire construction in the model.

[00241] Prophetic Example 12 - A passive radiative cooling film according to any of Examples 5 through 7 is prepared except using THV221 hot melt adhesive in place of the OCA8171 optically clear adhesive.

[00242] Prophetic Example 13 - A passive radiative cooling film according to any of Examples 5 through 7 is prepared except adding a siloxane hard coat (containing a UVA) that has an absorption band edge below 350 nm. The siloxane hard coat is disposed on top of the UV-Visible light reflecting mirror film (of Example 5 or 6) or the UV light reflecting mirror film (of Example 7). SilFORT AS4700, available from Momentive (Waterford, NY), is a suitable exemplary siloxane hard coat.

[00243] Foreseeable modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention. This invention should not be restricted to the embodiments that are set forth in this application for illustrative purposes.

Claims

What is claimed is:

1. A broadband reflector comprising: a multilayer optical film comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 90 percent of incident light over at least a wavelength range from 400 nanometers (nm) to 2000 nm or from 350 nm to 2500 nm, wherein the broadband reflector is essentially free of metal.

2. The broadband reflector of claim 1, wherein the multilayer optical film comprises: a) an ultraviolet-visible (UV-VIS) reflector comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 350 nanometers (nm) to 400 nm and an average of at least 95 percent of incident light over at least a wavelength range from 400 nm to 800 nm; and b) an infrared (IR) reflector comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 90 percent of incident light over at least a wavelength range from 0.8 micrometers to 2.0 micrometers.

3. The broadband reflector of claim 2, wherein the polymeric optical layers of the UV-VIS reflector comprise alternating layers of a polyethylene terephthalate (PET) and a blend of a poly vinylidene fluoride (PVDF) and a polymethyl methacrylate (PMMA).

4. The broadband reflector of claim 1, wherein the multilayer optical film comprises: a) a UV reflector comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 350 nanometers (nm) to 400 nm; b) a visible reflector comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 400 nm to 800 nm; and c) an infrared (IR) reflector comprised of at least a plurality of alternating first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 90 percent of incident light over at least a wavelength range from 0.8 micrometers to 2.0 micrometers.

5. The broadband reflector of claim 4, wherein the polymeric optical layers of the UV reflector comprise a PMMA or CoPMMA high refractive index first optical layer in the plurality of first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 350 nm to 400 nm.

6. The broadband reflector of claim 4 or claim 5, wherein the polymeric optical layers of the UV reflector comprise alternating layers of a copolymer of ethyl acrylate and methyl methacrylate (CoPMMA) and a copolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride (THV).

7. The broadband reflector of any of claims 4 to 6, wherein the polymeric optical layers of the visible reflector comprise a PET high refractive index first optical layer in a plurality of first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 400 nm to 600 nm.

8. The broadband reflector of any of claims 4 to 7, wherein the polymeric optical layers of the visible reflector comprise alternating layers of a PET and a THV.

9. The broadband reflector of claim 6 or claim 8, wherein the THV comprises a copolymer comprising 24 to 47 mole % of tetrafluoroethylene monomers, 5 to 23 mole % of hexafluoropropylene monomers, and 35 to 70 mole % of vinylidene fluoride monomers, wherein at least a portion of end groups on the copolymer are nonacidic.

10. The broadband reflector of any of claims 6, 8, or 9, wherein the THV further comprises a calcium carbonate additive.

11. The broadband reflector of any of claims 4 to 10, wherein the visible reflector is disposed between the UV reflector and the IR reflector and the polymeric optical layers of the IR reflector comprise a PEN high refractive index first optical layer in a plurality of first and second polymeric optical layers collectively reflecting at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, an average of at least 95 percent of incident light over at least a wavelength range from 600 nm to 2000 nm. The broadband reflector of any of claims 4 to 11, wherein the visible reflector is disposed between the UV reflector and the IR reflector and the polymeric optical layers of the IR reflector comprise alternating layers of PEN and PMMA. The broadband reflector of any of claims 1 to 12, wherein the broadband reflector absorbs an average of at least 60, 70, 80, 90, or 95 percent of incident light over at least a wavelength range from 3.0 micrometers to 20 micrometers or 8 micrometers to 13 micrometers. The broadband reflector of any of claims 2 to 13, further comprising a transparent adhesive layer or a hot melt THV layer attached to at least one of the UV reflector, the visible reflector, the UV-VIS reflector, or the IR reflector. The broadband reflector of any of claims 2 to 14, further comprising a protective layer comprising a fluoropolymer, the protective layer being an outer layer disposed adjacent to the UV reflector or the UV-VIS reflector. The broadband reflector of any of claims 2 to 15, wherein the IR reflector reflects an average of at least 90 percent of incident light over at least a wavelength range from 0.8 micrometers to 2.5 micrometers. The broadband reflector of any of claims 2 to 16, further comprising a polymeric sheet attached to the IR reflector, the polymeric sheet having a thickness of 1 to 10 millimeters. The broadband reflector of any of claims 2 to 17, further comprising a siloxane hard coat disposed adjacent to the UV reflector or the UV-VIS reflector, the hard coat containing a UV absorber having an absorption band edge below 350 nm. The broadband reflector of any of claims 1 to 18, having a nonplanar shape. The broadband reflector of any of claims 1 to 19, wherein the broadband reflector absorbs an average of at least 60, 70, 80, 90, or 95 percent of incident light over at least a wavelength range from 8.0 micrometers to 13 micrometers and is capable of sub-ambient cooling under direct solar irradiation. The broadband reflector of any of claims 1 to 19, wherein the broadband reflector absorbs an average of at least 60, 70, 80, 90, or 95 percent of incident light over at least a wavelength range from 4.0 micrometers to 20 micrometers and is capable of above ambient cooling under direct solar irradiation.

22. The broadband reflector of any of claims 1 to 21, wherein, at an incident light angle of at least one of 0°, 15°, 30°, 45°, 60°, or 75°, the multilayer optical fdm provides a 1^st order reflection band, a 2^nd order reflection band, and optionally a 3^rd order reflection band, wherein the 2^nd order reflection band substantially overlaps at least one of the 1^st and 3^rd order reflection bands to form a single wide reflection band.

23. A composite cooling system comprising the broadband reflector of any of claims 1 to 22 attached to a roof and/or at least one side of a vehicle. 24. A composite cooling system comprising the broadband reflector of any of claims 1 to 22 attached to a modular data center.

25. A composite cooling system comprising the broadband reflector of any of claims 1 to 22 attached to at least one surface of a building or a shelter.